MEDICAL SCHOOL W.T.WENZELL, Ban Francisco, Cal. ELEMENTS OF CHEMISTEY. FOR THE USE OP COLLEGES, ACADEMIES, AND SCHOOLS. BY M. V. KEGNAULT. ILLUSTRARED BY NEARLY SEVEN HUNDRED WOOD-CUTS. TRANSLATED FROM THE FRENCH, BY T. FORREST BETTON, M.D., M.A.N.S. FELLOW OF THE COLLEGE OF PHYSICIANS OP PHILADELPHIA, ETC. AND EDITED WITH NOTES, BY JAMES C. BOOTH, MELTER AND REFINER U. 3. MINT, AND WILLIAM L. FABER, METALLURGIST AND MINING ENGINEER. SECOND EDITION. TO WHICH IS APPENDED A COMPARATIVE TABLE OP PRENCH AND ENGLISH WEIGHTS AND MEASURES. IN TWO VOLUMES. VOL. II. PHILADELPHIA: CLARK & HESSEE. 1853. . ?o!!c0 of Pharmacy Entered according to Act of Congress, in the year 1853, by CLARK & HESSER, in the Clerk's Office of the District Court for the Eastern District of Pennsylvania. w , TABLE OF CONTENTS OF VOL. II. PREPARATION OF ORES 9 Washing 10 Crushing by cylinders 11 Swing-sieve 15 Jigging-machine 16 Stamping ore 17 Deposite-trough 18 Sleeping-table, or irlcking-buddle 19 Percussion-table, or brake-table 20 MANGANESE 23 " oxides of 23 " acids of 25 " salts of 28 " sulphide and chloride of..... 29 " analytic determination of.... 31 IRON, metallic 36 " oxides of 40 " salts of 44 sulphide of. 47 chloride of 49 cyanides of 50 carburet of, cast-iron 53 analytic determination of 54 ores of 59 reduction of its ores, by the Cata- lonian forge 61 Reduction in the blast-furnace 66 " the blast 67 " mixing ores 70 " blowing the furnace 71 " hot-blast 77 waste-heat of blast-furnace 78 remelting pig-metal 80 conversion of cast into bar-iron.... 82 refining on the forge-hearth S3 ". by puddling 87 blooming and rolling 92 Making sheet and tin plate 99 wire-drawing 101 making steel 102 " forge steel 103 " blistered and cast-steel... 104 tempering steel 107 dry assay of iron-ores 108 analysis of cast, and steel Ill IRON, composition of bar and cast-iron, and steel 116 CHROMIUM, oxides of 118 " chromic acid 122 " salts of 123 " chromates 125 " analytic determination of... 128 COBALT, metal and oxides 130 ' salts of 131 ' arsenical ores 132 ' analytic determination of 133 ' smalt and za/re 134 ' Thenard's blue 135 NICKEL, metal and oxides of 136 1 salts of 137 ' German silver 138 < analytic determination of 139 ZINC, distillation of 141 oxide of 142 salts of 143 sulphide and chloride of 144 analytic determination of 144 metallurgy of. 146 " ' in Belgium 147 " in Silesia 150 " in England 151 CADMIUM, compounds of 153 " analytic determination of 154 TIN 156 oxides of 158 salts of 160 sulphides of 161 chlorides of 162 behaviour of salts of 164 metallurgy of. 166 TITANIUM 169 " oxides of 170 " chlorides of 171 COLUMBIUM, NIOBIUM, PELOPIUM, IL- MENIUM 174 LEAD , 174 " oxides of, litharge 175 " red, or minium 173 " salts of 179 " acetates of, sugar of lead 183 3 TABLE OF CONTENTS. LEAD, carbonate of, white-lead 184 " behaviour of salts of 186 " sulphide of. 186 " chloride of l f " analytic determination of 1* " alloys, type-metal, and soft solder 189 " metallurgy of '. 190 " " reduction by iron.... 192 reverberatory pro- cess 196 " " Scotch hearth 198 cupellation 198 " " Pattinson's process.. 202 " making sheet, and pipe 202 " casting shot 203 BISMUTH 204 " oxides of 205 " salts of, pearl-white 206 " alloys of, fusible metal 208 " analytic determination of 208 " metallurgy of 209 ANTIMONY 211 " oxides and acids of 212 salts of 214 " sulphides of, Kermes mineral 215 " chlorides of 217 " behaviour of salts of 218 " analytic determination of 219 " detection of, in poisoning 221 alloys of 221 " metallurgy of 222 URANIUM, and its oxides 224 " salts of. 225 " analytic determination of..... 228 TUNGSTEN, and its oxides 230 " analytic determination of.... 232 MOLYBDENUM, its oxides and salts 233 VANADIUM 235 COPPER 236 " oxides of 237 " salts of 239 " blue vitriol 240 " " mineral and Scheele's green 242 " " verdigris 243 " sulphides of 243 " chlorides of 244 " analytic determination of 245 " metallurgy of . 247 " ' Mansfeld process.. 249 " eliquation of silver 251 English process.... 256 " alloys of, and zinc 263 " " " brass 264 " " tin, bronze 265 " " " cannon-casting 266 tinning copper and brass 269 " analysis of brass and bronze 270 MERCURY 271 " purification of 272 " oxides of 273 " salts of 275 " fulminating 279 amide-base of 279 " sulphides of, cinnabar 281 MERCURY, chlorides of, calomel 282 " corrosive subli- mate 284 " white precipitate 285 iodides of 286 cyanide of. 287 analytic determination of 288 amalgams of, mirrors 289 metallurgy of, in Idria 290 " at Almaden... 291 SILVER 293 oxides of 294 fulminating 295 salts of 296 " lunar caustic 297 sulphides of 300 chlorides of 301 analytic determination of 303 metallurgy of. 304 " Freiberg process... 305 " Mansfeld " 309 " American " 310 alloys of. 311 " coin and plate 312 assay of alloys of, by cupella- tion 313 assay of alloys of, in the wet way 316 assay of ores of 321 GOLD and its compounds 322 " purple of Cassius 325 " analytic determination of 326 " metallurgy of '. 326 " Tyrolese bowls 328 " alloys of 329 " separation of, and silver, by sul- phuric acid 329 " separation of, and silver, by ni- tric acid 331 " gilding and silvering 331 " " " by immer- sion 332 " galvanic gilding 333 " " silvering 334 " galvanoplastics 335 " assay of alloys of, by quartation. 336 " " by the touch- needle 338 PLATINUM 339 " black 340 " flameless lamp 341 " oxides of 342 salts of 343 " chlorides of 345 " ammonia-bases of 346 " analytic determination of 347 " extraction of 349 OSMIUM 350 " compounds of 351 " extraction of 352 IRIDIUM 353 " compounds of. 354 PALLADIUM, and its compounds 356 RHODIUM, and its compounds 358 RUTHENIUM , .. 360 TABLE OF CONTENTS. FOURTH PART. ORGANIC CHEMISTRY. INTRODUCTION 361-445 Organized and organic bodies 362 Proximate analysis of organic sub- stances 363 Ultimate analysis of organic sub- stances 366 Ultimate analysis, determination of carbon and hydrogen 367 Ultimate analysis, desiccation 369 " " combustion 371 " " of non-volatile li- quids 374 " " of volatile sub- stances 375 " " of gaseous organic bodies 375 " " determination of carbonic acid by volume 377 " " determination of nitrogen by vo- lume 380 Ultimate analysis, determination of nitrogen as ammonia 382 Ultimate analysis, determination of sulphur 385 Ultimate analysis, determination of phosphorus 385 Ultimate analysis, determination of chlorine, bromine, iodine, and oxy- gen 386 Construction of a formula for an organic substance 387 " " when it is acid 387 " " from its mine- ral base 393 " " when it is basic 397 " " when neither acid nor basic 399 Determination of density of vapours 406 Simultaneous temperatures in thermo- meters differently constructed 413 Air-thermometer (note) 414 Analysis of gases, apparatus for 422 " " absorbing reagents... 430 " examples of 433 " " oxygen and nitrogen 433 Analysis of gases, oxygen, nitrogen, and hydrogen 435 Analysis of gases, oxygen, nitrogen, and carbonic oxide 436 Analysis of gases, oxygen, carburetted hydrogen, etc 437 Analysis of gases, complex mixtures.... 443 A2 ESSENTIAL PROXIMATE PRINCIPLES OF PLANTS 446 Cellulose 446 Lignin 449 Albuminous Vegetable Substances 451 Albumen 453 Circular polarization (note) 454 Gluten, vegetable fibrin, and casein... 460 Amylaceous Substances 461 Inulin and lichenin 467 Gums, arabin, cerasin, bassorin 468 Sugar 469 Cane-sugar 470 Caramel, saccharic acid 471 Fruit-sugar 474 Grape-s>ugar 475 Glucic acid 476 Determination of sugar by oxide of cop- per 477 Determination of sugar by polarization 478 Gelatinous Principles, pectose 478 Pectin and pectic acid 479 Table of pectic acids 483 Mannite 484 Action of Acids on Lignin, Starch, and Sugar 485 Dextrin 485 British gum 486 Diastase 487 Glucose, manufacture of 487 Ulinin and humin 489 Action of nitric acid, oxysaccharic acid 491 Gun-cotton 491 Collodion 492 Mucic acid 493 Spontaneous Decomposition of Plants... 494 Mineral fuel 494 Varieties of coal 496 Analysis " 497 Tables of composition of coal.... 500, 503 Alcoholic Fermentation 505 Yeast or ferment 507 Alcohol 511 Alcoholometry 513 Sulphovinic acid 515 Ether 516 Olefiant gas 520 Ethionic acid 522 Dutch liquid 523 Chlorinated olefiant gas 524 Oil of wine 528 Ethers and vinic acids 529 Phosphovinic acid 630 TABLE OF CONTENTS. PAGE Nitric ether 530 Nitrous and sulphurous ethers 531 Boracic and silicic ethers 532 Carbonic ethers, urethan 533 Oxalic ethers, oxamic ether 534 Mucic ether 535 Sulphocarbovinic or xanlhic acid 536 Chlorohydric ether 536 Bromo, iodo, and cyanohydric ethers 537 Sulfhydric ethers 538 Mercaptan 539 Oxidation of alcohol and ether 541 Aldehyde 541 Acetic acid 542 Manufacture of vinegar 543 Pyroligneous acid 545 Acetates 546 Acetic ether 548 Acetone , 549 Mesitylen 550 Cacodyl, alcarsin 551 Chlorinated chlorohydric ether 554 Chlorinated ether 558 Chloral 561 Chloracetic acid 563 Chlorinated compound ethers 564 Table of alcoholic compounds by sub- stitution 566 Ethyl theory (note) 568 Lactic and butyric fermentations 569 Lactic acid 573 Butyric acid, butyramide 574 Methy lie alcohol, wood-spirit 575 Methylic ether 576 Methylsulphuric ether 577 Compound me thylic ethers 578 Marsh-gas 582 Formic acid 583 Methylal 585 Chlorinated methylchlorohydric ether 585 Chloroform 586 Bromo, iodo, sulphoform 588 Chlorinated methylic ether 588 Table of methylic compounds by sub- stitution 591 Methyl 593 ACIDS EXISTING IN PLANTS 594 Oxalic acid 594 Malic acid 595 Equisetic and fumaric acids 596 Citric acid 596 Aconitic acid 597 Tartaric acid .'.. 598 Tartar emetic 600 Action of heat on tartaric acid 601 Racemic acid 603 Tannic acid 605 Gallic acid 607 Ellagic or bezoaric acid 609 Meconic acid 609 Chelidonic acid 611 Quinic acid, quinone 611 ORGANIC ALKALOIDS 612 Quinin 613 Cinchonin 614 Morphin 615 Narcotin ... 616 PAG X Codein 617 Strychnin and brucin 617 Caffei'n or them 618 Nicotin 618 Conicin 620 Quinole'in or leucole 620 Anilin or kynnole 621 Ethylammonia 622 Methylammonia 62.3 Amylammonia 624 NEUTRAL SUBSTANCES IN PLANTS 625 Piperin, picrotoxin, cantharidin 626 Asparagin, aspartic acid 627 Phloridzin, glycyrrhizin 628 NITRILS i 629 Cyanogen, products of 630 " oxacids of 631 " fulminic acid 632 " sulphocyanides 633 ESSENTIAL OILS 634 Oil of terpentine or terebenthen 635 Camphilen, terebilen, tereben 637 Oils of lemon, orange, etc 638 Camphor, Japan 639 " Borneo 640 Menthen, cedren, etc 641 Benzoic Series 641 Oil of bitter almonds 642 Benzarnide 643 Benzoic acid 644 " ethers 645 Sulpho-nitrobenzoic acids 646 Benzoin, benzil, benzin 648 Benzone, arnygdalin 650 Emulsin, synaptase 651 Salicin 652 Saligenin 653 Salicylous acid, oil of spirsea 654 Salicylic acid and ether 656 Oil of wintergreen 656 Oil of Cinnamon 658 Cinnamic acid, cinnamen 659 Balsams of Peru and Tolu 660 Coumarin 661 Oil of Aniseed, anisic acid 662 Anisen, toluidin 663 Oil of Cumin, cuminic acid, cynien 664 Oil of Cloves, eugenic acid 665 Amylic Alcohol 665 Amylin 666 Amylic ethers 667 Valerianic acid 669 EnanthicAcid 670 Caoutchouc 671 Gutta-percha 673 Kesins 673 Pimaric acid 674 Oil of Garlic, allyl 675 Oil of mustard 676 Thiosinnamin 676 Myronic acid 677 PRODUCTS OF DRY DISTILLATION 678 Naphthalin 678 Paraffin 681 Phenic or carbolic acid 682 Creasote 683 Naphtha 683 TABLE OF CONTENTS. FATS Glycerin Stearic acid, stearic candles Margaric acid Oleic acid.. Action of sulphuric on the fat acids .. " nitric " " .. Succinic and adipic acids Suberic and sebacic acids Caproic, caprylic, and capric acids ... Palm-oil, castor-oil Spermaceti, ethal Wax, cerin, myricin ORGANIC COLOURING MATTERS Madder Logwood Saffron, Quercitron, etc Euxanthic acid Carotin Chlorophyll Cochineal Lichens Indigo White indigo Isatin ACTION OF PLANTS ON THE ATMOSPHERE ANIMAL CHEMISTRY Bone Teeth, cartilage, horn Hair, skin, muscular tissue Fibrin, creatin Inosic acid Gelatin, glue Ich thy ocolla, gly cocoll Cerebral substance Nutrition Digestion Blood, circulation of the Respiration and animal heat Secretions Blood ' globules PAGE 684 689 690 692 693 694 695 697 698 699 700 701 703 704 705 706 707 708 709 709 710 71,0 712 714 715 716 719 721 722 723 724 725 726 727 728 729 730 732 734 738 738 739 PAGE Blood hematosin 740 " coaguluni 741 " analysis of 742 Lymph 743 Saliva, gastric juice 744 Bile 745 " cholic acid 746 Biliary calculi and cholesterin 747 Pancreatic and intestinal juice 747 Chyle and milk 748 Lactometry 750 Sugar of milk 751 Casein < 752 Making butter 752 Making cheese 753 Excretions 754 Urine 754 Urea 755 Uric acid and derivatives 757 Hippuric acid 760 Urine, analysis of 761 Urinary calculi 762 Sweat 763 Excrements 763 Intestinal gases 763 TECHNICAL ORGANIC CHEMISTRY 763 Manufacture of bread 764 Brewing 766 Cider and perry 768 Wine-making 769 Manufacture of beet-sugar 771 " cane-sugar 773 Sugar-refining 775 Manufacture of bone-black 777 Soap-boiling 778 Principles of dyeing 781 Mordants 785 Calico printing 787 Tanning 788 Charring wood and coal 790 Manufacture of illuminating gas 792 \ ELEMENTS OF CHEMISTRY. THIRD PART. 732. ALTHOUGH the metals described in the second part of this work are never technically employed in the metallic state, they still find very extensive application in the state of various compounds, all of which are manufactured in chemical works by processes similar to those employed for obtaining them in the laboratory on a smaller scale. Among the metals yet remaining for our examination, however, a considerable number are employed in the metallic state, and are extracted from their ores by processes of a particular kind, called metallurgical processes. In every case when they are to be used in the metallic state they must fulfil all the conditions enumerated ( 276) ; which, however, many do not, as some are of rare occur- rence, while the extracting of others presents too great practical difficulties, ancj. still others have as yet found no technical applica- tion, being, therefore, of purely scientific interest. Nevertheless, on account of the great Analogy existing between them in a chemi- cal point of view, the study of those which find a technical appli- cation cannot be separated from that of those which are not so applied. The latter will, therefore, occupy our attention as well as the former, but to a much more limited extent. MECHANICAL PREPARATION OF ORES. 733. Under the general name of ores are comprised such com- binations of metals, occurring in nature, as contain a sufficient proportion of metal to be worked with profit. The proportion varies with the marketable value of the metal, and according to the greater or less facility with which it can be obtained from its combination in the ore : iron ores, for instance, the commercial price of which metal is very low, must therefore be very rich if they are to be profitably worked. The poorest minerals from which iron 9 10 PREPARATION OF ORES. could be extracted must contain at least 25 per cent, of iron ; and the metal must moreover exist in them in a state from which it can be easily reduced, in order to be iron ores. A mineral of frequent occurrence is iron pyrites, a combination of iron with sulphur, which contains about 47 per cent, of the former, but still cannot be considered as an ore, as the treatment to which it must be subjected in order to obtain a good quality of iron would be far too costly. Copper, on the contrary, the commercial value of which is much higher than that of iron, can be extracted with ad- vantage from ores containing only a few per cent, of the metal, even if these be in combination with sulphur ; and ores which con- tain only some thousandths of silver or of gold can be worked to advantage. 734. An ore, of whatever kind it may be, is seldom sufficiently rich to be at once subjected to metallurgical processes, but is, in general, worked with greater advantage after having been sorted, and prepared by various mechanical operations, which tend to separate from them the greater part of the earthy substances, technically termed gangue, with which they were mixed. The larger pieces of the gangue are usually separated from the ore in the mine itself, and used to fill up the excavations already made in the rock ; so that only such fragments are taken out of the mine as can be advantageously prepared for smelting by mechanical operations. 735. The ores of iron employed are always very rich, as those which are not so have not sufficient value to be made richer by costly mechanical processes ; in general, therefore, the argillaceous parts are merely separated by washing (debourbage).* Sometimes the ore is left exposed to the atmosphere for several months, as the clay is thus rendered more friable anfl more easily detached. The washing of iron ores is performed (in France) in the middle of a stream of water, in a series of apparatus called patouillets. It is sometimes considered sufficient to turn and stir the ore in the stream with a spade, by which the argillaceous part's are detached and carried away ; but the shaking up of the ore is more frequently effected by means of a small water-wheel R (fig. 461), set in motion by the stream. The ore, thrown with a spade into the long trough A, where the water running over it frees it from a part of its clay, is thence transferred to the semi-cylindrical box B, which is filled with water, where it is stirred by iron arms attached to the axle of the water-wheel. The muddy water runs off by an outlet at the top of the box, and the washed ore, which is taken out through the orifice o in the lower part of the box, falls into the trough D, * Since hard ores are more abundant than soft in the United States, the poorer clayey ores, instead of being enriched by any mechanical process, are usually sought after to mix with the harder ores and render them more easy of fluxion in the furnace./. C. B. PREPARATION OF ORES. 11 whence the workman removes it when he finds it to be sufficiently washed. Fig. 461. 736. The ores of other metals, when taken from the mine, are generally sorted by the hands of females and children, who separate them into 1st, pieces rich enough to be immediately sent to the smelting-works ; 2dly, fragments composed of ore and gangue, which must be subjected to mechanical preparations; and 3dly, pieces of gangue, which are thrown aside as useless. Let us now examine the mechanical operations to which the second class is subjected. When the metalliferous mineral is so intimately mixed with the gangue that it cannot be separated by the hammer, the pieces are reduced to a small size between cast-iron cylinders or under stampers. Fig. 462 represents an apparatus of crushing- cylinders, and figs. 463 and 464 show the arrangement of the cylinders. Two kinds of hard cast-iron cylinders are employed ; fluted (fig. 464), and smooth ones (fig. 463) ; in the former of which the large fragments are broken, while the smooth cylinders reduce the pieces furnished by them to a still smaller size. Only one of these cylinders, A, receives motion from the water- wheel, the desired velocity being given to it by a system of cogs, while the second cylinder B is moved by the former. The cylin- der A is borne by two fixed uprights K, while the supports L of B are movable on the sliding-boards ab, cd. The cylinder B there- fore moves away from A whenever a piece presents itself which would oppose too much resistance to crushing ; but at other times, it is kept pressed against A by the weight P, suspended to the ex- tremity of a long lever ST. The ore is brought to the crushing machine by cars, moving on a railroad FF'. The workman throws it with a spade into a wooden hopper U placed above the cylinders ; and when it is reduced in size by passing between them, it falls on an inclined jolting-box M, the bottom of which consists of a wire sieve, with very small open- ings at the top, and larger ones at the lower part. The finest 12 PREPARATION OF ORES. Fig. 462. grains pass through the upper sieves ; while those fragments which have passed the under ones roll to the bottom of the box M, and fall into a wheel RR/R", provided with boxes ; which, by a slow rotary movement, brings the pieces of ore up again into the box U, Fig. 463. Fig. 464. PREPARATION OF ORES. 13 whence they again pass between the cylinders with the ore recently supplied from the mine. The ore, when broken by the fluted cylinders, is thus sorted by the sieves in the box M into different sized grains, from the heaps of which the largest pieces are often removed by hand ; then such portions are separated as are fit for immediate smelting, the pieces of gangue are thrown aside, and the mixture of ore and gangue which requires again to be reduced in size is passed through the system of smooth cylinders. In this case the ore is not thrown directly into the box U, but into a box V divided into different parts (fig. 462), the bottom of which consists of a sieve, which, keeping back the too large fragments, allows only those of the proper dimensions to fall on the cylinders. The crushed ore is again received in a box M, the sieves of which are much finer than those which receive the pieces falling from the fluted cylinders. By this operation pieces of 4 or 5 millimetres (about J inch) are obtained, which is a convenient size for the subsequent operations. The forming of smaller pieces and of dust cannot entirely be avoided, although it is sought to diminish their quantity as much as possible. 737. The ore, reduced to more or less fine grains, is submitted to further operations in the jigging machine, (crible a d^pot,) the theoretical principles of which are the following : If bodies differing in shape, size, and specific gravity be let fall into a liquid which is quiet at the time, these bodies will experi- ence different resistances in their fall, and arrive at different times at the bottom of the liquid ; so that a kind of separation is effected, during their fall, by the position the pieces occupy in the deposite formed at the bottom of the vessel. If we suppose these bodies to be similar as to shape and size, but differing in their specific gravity, then they will all experience equal loss in the totality of their movement in the liquid, because the resistance a body meets with in passing through a liquid, de- pends entirely on its form and extent of surface, but not on its density. But the loss will be more sensible as the momentum of the bodies is greater, that is, as their specific gravity is higher ; so that the least dense particles, traversing the central strata of the liquid more slowly than the others, will arrive last at the lower part of the vessel ; and the deposite formed will thus consist of different layers, in which the particles will have arranged themselves ac- cording to their specific gravities, the most dense occupying the lowest place and the lightest ones the top. Supposing, on the other hand, the bodies falling into the liquid to be all of equal density, and, moreover, all to have the same form, for example, to be all cubes or spheres, but differing in size, then will their momentum during their fall be in proportion to their volume. The resistance opposed to the particles by the liquid will VOL. II. B J 14 PREPARATION OF ORES. be proportioned to their surfaces, as we have supposed both their form and relative position while passing through the liquid to be the same. Therefore, since volumes vary as the cubes of homolo- gous dimensions, while surfaces only vary as the squares of such dimensions, the momenta of the bodies will stand in proportion to the cubes d 3 of one of their dimensions, while the resistance offered to them by the liquid will be proportional only to the squares d 2 of the same dimension. If M and m represent the volumes of two bodies of the same density, and D and d their homologous dimen- sions, then will their momenta be proportional to Mg and mg, or to D 3 8g and d 3 8g ; 8 representing the specific gravities of the bodies, and g their absolute weight. The loss of momentum they experi- ence by the resistance of the liquid will be proportional to D 2 and d 3 ; and is a fractional part of the whole momentum, larger for the smaller bodies than for those of a larger size, this fraction being ^ or ^ for the largest, and J^ or ~ for the smallest, where a represents the coefficient of resistance, which is constant in both cases. The largest particle will therefore arrive first at the bottom of the liquid, and the deposite will consist of strata arranged accord- ing to the size of the pieces constituting them, the largest occupy- ing the lowest situation. Lastly, we will suppose the bodies to be equal as regards density and volume, but differing in form, some for instance, being cubes, and others laminated rectangles ; then will the latter, having a greater extent of surface than the cubes, meet with a greater re- sistance while traversing the liquid ; and the cubes, arriving first at the bottom of the vessel, will leave the flattened particles in a layer on the upper surface of the deposite formed. Let us now examine how these principles may be applied to the preparation of ores. We have seen that the sieves placed under the crushing-cylinders divide the material into equal classes, each of which is composed of pieces of a nearly uniform size ; but we will now, to make the reasoning more simple, suppose these frag- ments, consisting of pure ore, or pure gangue, or a mixture of the two, to be exactly equal as to form and volume. Metalliferous ores being in general much heavier than the gangue by which they are accompanied, the fragments of the former will evidently first arrive at the bottom of the vessel, and on them the pieces composed of ore and gangue will deposit, while the fragments of pure gangue will constitute the uppermost layer. The deposite can then be divided into three parts : pure gangue, which lies uppermost, and is rejected ; pure ore, forming the lowest stratum, which is sent to the smelting-works ; and lastly, an intermediate layer, consisting of ore and gangue not sufficiently rich for immediate smelting, which must again be crushed, and undergo the process of washing over again. It is evidently essential for the process of separation to obtain PREPARATION OF ORES. 15 the fragments as equal as possible, regarding both form and size ; but this condition cannot be fulfilled at will. By means of sieves of different fineness equality of size can be attained with more or less accuracy; but by no known process can the pieces be obtained of a similar form, because this latter character depends on the molecular constitution of the minerals to be separated, on their cleavage, etc. It may therefore very well occur that a species of crushed ore may contain lamillar fragments of pure metalliferous ore, and cubic or spherical pieces of gangue, which nevertheless passed through the same sieve ; and that therefore the ore, which by virtue of its greater specific gravity tends to fall faster through the water than the gangue, will still form the upper layer of the deposite, on account of the greater resistance the liquid offers its lamillar fragments compared with that opposed to the cubic pieces of gangue. As all these circumstances present themselves simul- taneously in practice, the separation of ores from their gangue is prevented from being as perfect as it would be if the simple cases just now supposed could be realized. 738. The separation of ores into pieces of an equal size is of such importance, that it is frequently done with the pieces which have already been sorted by hand, or with the larger pieces from the crushing cylinders. Fig. 465 represents the swing-sieve (crible d secousses) employed for this purpose, which consists of two boxes AJBCD, ef, placed one above the other, both of which are kept in motion by the rods tr and uv, connected with a water-wheel. Part of the water led into the first box by means of the canal os passes, 16 PREPARATION OF ORES. by the canal g, into the box underneath ; and the bottom of both boxes consists of a sieve, the meshes of which are larger in the box ABCD than in the other. A part of the ore which is placed in the upper sieve falls through into the sieve ef, where it is again sifted ; and the ore is thus divided into grains of three different sizes. That which is too coarse to pass through the meshes of the sieve in ABCD falls on the platform mn> while the 'grains which remained on the sieve in e/are collected in the box 5R, and lastly, the finest quality, which has escaped through the under- most sieve, is received by a box placed directly underneath the latter. 739. A jigging machine (fig. 466) consists of a cylindrical box C, the bottom of which is a piece of wire-gauze or netting, with meshes of sufficient fineness to retain the fragments of ore. The sieve is suspended by an iron bar A, attached to a horizontal bar qh, and counterbalance^ by the weight P; and is kept in a tub B, which is filled with water. The work- man sets the machine in motion by means of a ver- tical wooden pole E, which is guided by moving in the slider D. Taking the ore to be washed from the table A, he half-fills the sieve C, and then keeps the latter in a lively jolt- ing motion in the water. The sieve receives during its descent a violent con- cussion against the bottom of the tub, when the water, penetrating through the sieve, holds in suspension the ore, which by the shock is for a mo- ment not influenced by its own weight ; and the different pieces which fall back from the centre of the liquid have a tendency to separate, according to the laws developed above. When the height of the fall is small, a numerous repetition of shocks has the same effect in separating the pieces as when they fall from a greater height. The workman then, after some time, finds 1st, at the upper surface of his sieve, a layer of pure gangue, which can be thrown aside, or, at least, very poor ore, which must be stamped to powder in order to separate any parts that might be worth smelting ; 2dly, a central stratum, consisting of fragments of ore and gangue com- 466. PREPARATION OF ORES. 17 bined, which ought to be reduced in size before being again jigged; and 3dly, at the bottom of his sieve, a layer of ore of sufficient purity to be smelted. The central layer is generally set aside, and, when a sufficient quantity has been collected, is subjected to another jigging without being first reduced in size, by which he obtains again a quantity of ore fit for smelting. In well-arranged works the jigging-machines are set in motion by water-power, in which case apparatus of a much larger size may be used, and may, moreover, be superintended by children. By this process very small fragments of ore, of the diameter of 1 millimetre, may be purified ; but the meshes of the wire-gauze in the jigging-machine must then be much finer than those employed for washing larger fragments. 740. Such ores as cannot be sufficiently enriched by the use of sieves are sent to the stamping-mill (fig. 467), which is com- posed of a sys- tem of stampers PP', consisting of pieces of tim- berP',shodatthe lower endby cast- iron pieces P. All the stampers fall into a single trough u, the bot- tom of which con- sists of a strong sheet-iron plate, sustained by a solid foundation of masonry, while its sides are made of iron sieves, or plates of sheet- iron pierced with holes. A water- wheel moves the Fig. 467. axle xy, on the surface of which cams are fixed, which, by lifting the catches m, set the stampers in motion. (In the cut, the lateral walls of the trough are supposed to have been removed from before three of the stampers, in order to show the iron ends P of the lat- ter.) The cams are so arranged on 'the axle xy, that by always lifting but one of the stampers at a time, the strain on the ma- chinery is kept as constant as possible. A current of water constantly flowing through the trough of the stamping-mill, into which ore is thrown with a spade, the parts which are already reduced to a sufficient fineness flow off through u2 2 18 PREPARATION OF ORES. the lateral sieves, being held in suspension by the water, from which they tend to deposit in the canals CD, E extending along the whole length of the battery of stampers. They are thence led in circuitous windings, called a labyrinth, over the floor of the building. The coarser particles are deposited at the heads of the various canals, while the fine grains are carried farther away ; and as the waters, which traverse the channels at a very slow rate, are often still muddy after having passed through the whole sys- tem, they are conducted into large reservoirs, where they deposit even the finest particles they held in suspension. The depositejn the channels is called sludge, (schlich ;) while that in the reservoirs, which resembles a thin mud, is termed mud orfine sludge, (schlamm :) the former differs in size of grain as well as in metallic richness, according to the different parts of the canals from which it is taken, and is thus divided into several classes, each of which is separately subjected to further operations. The sludge is washed in three different kinds of apparatus : the deposit-trough, (caisse a tombeau,) the sleeping-table or nicJcing- buddle, (table dormante,) and the percussion-table or brake-table, (table & secousse.) 741. The physical principles on which the washing of sludge is founded are rather different from those of the washing in sieves, as the latter is applicable only to fragments of a certain size. The ore no longer acts by its weight in a quiet liquid, but is in this case submitted to the action of running water on an inclined plane. The impulse imparted to the different pieces by the water being now proportional to their surfaces, but independent of their volumes and densities, they would, were their surfaces equal, be carried more or less far by the impulse of the liquid, according to their weight ; and, if their form were similar at the same time, those of the least specific gravity would be carried farthest. But if their densities and volumes were equal, those presenting the greatest extent of surface would be deposited farthest off; and lastly, with equal densities and forms, the smaller particles would go farther than the larger ones, because they present the greater relative extent of surface. We see, therefore, that in these new opera- tions, as well as in washing with sieves, the separation of the ore depends not only on the specific gravities, but also on the volumes and forms of the small pieces; for which reason, the ore to be washed must be of as equal a grain as possible. 742. The deposit-trough consists of long wooden troughs BC (fig. 468), the bottoms of which are slightly inclined, and closed at their extremity C by a board pierced with several holes at different heights, which are closed with stoppers during the operation. The sludge to be washed is placed on the benches A at the head of the machine, where it is met by a current of water, which, taking the ore into suspension, falls into the boxes BC, and there deposits it PREPARATION OF ORES. 19 Fig. 468. again at different distances from the bench A, while the finest par- ticles still remain in the water and render it muddy. As soon as the boxes are filled with water, the supplying stream is turned off, and the openings at the extremity C are uncorked ; the muddy water, then running through the canal UU' and a system of troughs into reservoirs, there deposits the particles it carried away. The washing of a fresh quantity of ore is then begun immediately, the sludge and mud of which is again borne by the water to the reser- voirs and there deposited; and so on until the deposit has attained the thickness of a foot or two ; each operation differing from the former only in the manner in which the water is let off through C, as each time a higher opening is unplugged. The deposite of ore in the bottom of the box AB is divided into three parts, which are treated separately in the subsequent opera- tions. The sludge on the highest part of the inclined is often rich enough to be sent to the furnaces at once ; while the deposite on the centre and lowest part, the latter of which is the poorest, are subjected to new washings, either in the machine just described or on the percussion or the sleeping-tables. 743. The sleeping-tables (sometimes, called in the French, tables jumelles, from their being generally arranged in pairs) consist of inclined tables AB (fig. 469), from 20 to 24 feet long, furnished with borders of wood, serving to keep the water running over them in Fig. 469. 20 PREPARATION OF ORES. its place. At the head A of the table, two laths are set at the angle BAG (fig. 470), on a plane which is more inclined than the long plane ; and between which only a small aperture A is left, through which the water with suspended sludge is introduced. Small trian- gular prisms of wood, set up on this inclined plane, equally divide the arriving stream, and cause the water to flow in a uniform layer over the whole surface of the plane. The ore to be washed is thrown into a trough M (fig. 469), into which a thin stream of water is constantly Fig. 470. falling, and where it is constantly kept in motion by a small bucket- wheel, which again is moved by an overshot water-wheel, fed by the canal oo r . The ore is thus put in suspension in the water, which, continually flowing into a canal placed lengthwise at the head of the tables, finds its way on to the sleeping-tables through the openings A (fig. 470) ; and the plane A (fig. 469), on which it first arrives, being too much inclined to allow any ore to deposit, the forming of a deposite first commences on the tables intended for the purpose. Here the richest parts will form the sediment at the higher end of the table, while the poorest grains will only be de- posited at the bottom of the inclined plane, or even carried away into the canal CC', which leads them into other canals and depo- siting reservoirs. As soon as the table is covered with a sufficient quantity of ore, the workman cuts off the further supply of sludge, and, after having swept all the ore lying between A and uv towards A with a broom, allows a current of clear water to flow over the tables, by which the ore is again spread over the latter ; and while the poorer parts collect towards the bottom of the inclined plane, that lying on the higher parts can in general be at once sent to the smelting-works. The table has at uv a transverse opening, which remains closed during the washing by a valve, which should not project above the table; but at the close of the operation, the valve being opened, the workman sweeps the sludge through the opening uv into boxes placed beneath. The sleeping-tables are more or less inclined, according to the nature of the ore to be washed; the finest ores requiring the greatest inclination. 744. The percussion-table serves for washing the same kinds of ore as the sleeping-table, the one or the other being preferred according to the nature of the ore and gangue in each special case. The percussion-table consists of an inclined board BC (fig. 471), resting on beams of wood to give it greater weight and solidity. PREPARATION OF ORES. 21 The whole is suspended in the air by four chains or bars of iron ab, a'b', ft', ft', of which the former two are attached to fixed sup- ports, while the chains ft', tt f are fixed to a long movable lever LI/, which turns by the axis 00', and serves to vary the degree of in- clination of the plank BC, being held in the height desired by means of iron pins entering the horizontal beam xy. Fig. 471. The cams cc on the axle XX', which is turned by a water- wheel, act on a curved wooden lever K, which pushes forward the sus- pended plank BC, and immediately abandons it again, so that the latter, falling forcibly back against the wooden supporting beams, receives a violent shock throughout its whole mass. Above the head B of the suspended plank is a triangular inclined plane A, fortified with small prisms, and similar to that in fig. 470. The ore to be washed is heaped in the box V, which receives a continual stream of water ; from there it spreads over the slope A and the suspended plank BC, where it has a tendency to deposit. But the violent shocks the plank is constantly receiving, causes the particles to be continually detached and taken into suspension by the water ; so that they are then under the most favourable cir- cumstances to be carried off precisely according to the order of their density and size. The inclination of the plank, the violence and frequency of the shocks, and the quantity of water holding the sludge in suspension, are varied according to the nature of the ore to be washed. 745. By these different methods of washing, sludges of greater or less fineness of grain and richness in metal are obtained, and are sorted accordingly. Each of these kinds of sludge is generally subjected to a chemical test, to ascertain their nature and richness in metal. They are then mixed, according to certain proportions which practice has shown to be the most convenient, foreign sub- stances being added if necessary. These mixtures, called charges, are then ready for fusion in the furnaces. 22 PREPARATION OF ORES. The mechanical preparation of ores is one of the most important operations in the extraction of certain metals. Great intelligence is required in the arrangement of such works, as the processes which perfectly succeed in one locality may be quite inefficient in another, where the ore occurs in a different gangue or presents a different state of aggregation. The adjoined plate gives a connected view of the different appa- ratus for mechanical preparation and washing just described, as well as the succession of canals and arrangement of the depositing reservoirs, which are generally placed under the flooring of the building. The canals and basins form a large labyrinth, the cor- responding parts of which, coming from different washing-machines, unite at points where the muddy water contains similar substances in suspension. The whole apparatus is moved by the same water- wheel RR'. 23 MANGANESE. EQUIVALENT = 28 (350 ; = 100.) 746. Manganese* is obtained by reducing one of its oxides by charcoal at a high temperature. A pure and very dense protoxide, obtained by subjecting carbonate of manganese to strong calcina- tion in a closed crucible, is mixed with T \j its weight of charcoal and yV of fused borax, and heated to the highest possible tempera- ture in a forge-fire, in a "brasqued" or charcoal crucible. The borax added facilitates the union of the metallic globules into a button. The carburetted metal thus obtained is to the pure metal as cast- iron is to malleable iron, and may be purified by a second fusion with a small quantity of carbonate of manganese, in a small, well-closed porcelain crucible, luted into an earthen crucible, as shown in fig. 472. The manganese thus obtained possesses a certain degree of ductility; and, although it may be filed, breaks under the blow of a hammer, showing a gray fracture much resembling that of certain kinds of 472 cast-iron. Its specific gravity is about 8.0 ; and it is as difficult of fusion as iron. Manganese has a great affinity for oxygen, as its surface becomes tarnished by exposure to a moist atmosphere, and covered with dark-brown rust. It decomposes water slowly at ordinary temper- atures with the evolution of hydrogen, but effects rapid decom- position at 212. By blowing on a piece of manganese, the same disagreeable odour is perceived which is given off by a carburetted metal dissolving in a weak acid. To preserve the metal, it must be kept from contact with the air, and is therefore generally kept in naptha, like potassium ; but it is better to put the button in a hermetically sealed glass tube. COMBINATIONS OP MANGANESE WITH OXYGEN. 747. Five compounds of manganese with oxygen are known ; the first of which MnO is a strong base ; the second, Mn 3 3 , plays the part of a very weak base ; the third, Mn0 3 , is neither base nor acid ; while the two last, Mn0 3 and Mn 3 7 , are well characterized acids. * Peroxide of manganese has been known for a long time, but it was not until 1774 that Scheele proved it to be a peculiar oxide, from which Gahn obtained the metal several years after. 24 MANGANESE. Protoxide of Manganese MnO. 748. Protoxide of manganese is obtained by reducing one of the higher oxides of the metal with hydrogen, or by calcining the carbonate without the contact of air ; which is effected by placing the carbonate in a glass bulb A (fig. 473), blown on a tube ab, and com- municating with an ap- paratus disengaging dry hydrogen gas. As soon as the air is completely driven out of the appa- _ ratus by the hydrogen, 473. the bulb A is heated with an alcohol-lamp ; when the carbonate, disengaging its carbonic acid, leaves the prot- oxide, the hydrogen preventing the latter from being surrounded by air. The parts b and c of the tube (fig. 474) are then drawn out and closed by means of a lamp. The protoxide of manganese thus prepared, is a clear, delicate green powder, which Fi 474 oxidizes rapidly in the air, unless it has been subjected to a slightly elevated temperature. The protoxide is better aggregated and less change- able when the decomposition of the carbonate has been effected in a porcelain tube strongly heated in a reverberatory furnace. By heating native peroxide of manganese, or a large mass of carbonate, in a " brasqued" crucible in a forge-fire, a well-aggre- gated, fine green mass is obtained, which the air does not affect at ordinary temperatures. The surface of the mass often consists of a thin pellicle of reduced metal ; but a complete reduction is not propagated by cementation, the immediate contact of charcoal being essential. Protoxide of manganese is a powerful base. Caustic potassa precipitates it from its solutions as white hydrated protoxide, which rapidly changes into brown sesquioxide by absorbing oxygen from the atmosphere. Sesquioxide of Manganese Mn 3 3 . 749. Sesquioxide of manganese Mn 3 3 occurs crystallized in nature, both in the anhydrous and hydrated state ; the latter much resembling in its external appearance the peroxide, with which it is often associated. But the two oxides are easily distinguished by the colour of their streak or powder, that of the peroxide being dark gray, while that of the sesquioxide is brown. OXIDES OF MANGANESE. 25 Peroxide of Manganese Mn0 3 . 750. This oxide, the most abundant of all the oxides of man- ganese, is also the most valuable, from its property of giving with chlorohydric acid the greatest quantity of chlorine. It occurs crys- tallized in elongated prisms of a gray colour and metallic lustre. Hydrated peroxide of manganese is obtained as a dark-brown powder by decomposing manganate of potassa with hot water, or by passing chlorine through water containing carbonate of manga- nese in suspension. By calcining peroxide of manganese in an earthenware retort until the evolution of oxygen ceases, a brown powder containing 27.6 per cent, of oxygen is obtained, with the formula Mn 3 4 . It is generally called red oxide of manganese, and, as it behaves as a combination of protoxide with sesquioxide, is often written MnO, Mn 2 3 ; for when it is treated with an acid, protoxide is dissolved and sesquioxide remains. Manganic and Permanganic acids Mn0 3 and Mn 3 7 . 751. The two acid combinations of manganese with oxygen are obtained by treating caustic potassa with peroxide of manga- nese, either with access of air, or with substances possessing high oxidizing properties. By heating equal proportions of finely pow- dered peroxide and caustic potassa without access of air, and dis- solving the substance obtained in cold water, a green solution is formed, and a mixture of hydrated sesquioxide and binoxide re- mains as a reddish-brown powder. The green liquid contains, besides some potassa in excess, manganate of potassa KO,Mn0 3 , a portion of the binoxide Mn0 2 having been reduced to sesquioxide Mn 2 3 , by giving off oxygen to another portion of the binoxide, which was thus oxidized to manganic acid Mn0 3 . A greater pro- portion of manganate of potassa is obtained by making the calcina- tion in the air ; or still better, in an atmosphere of oxygen. Some peroxide of manganese, reduced to an impalpable powder, is well mixed with some caustic potassa dissolved in as little water as pos- sible ; the paste is dried in a porcelain capsule, and introduced in fragments into a glass tube difficult of fusion, communicating with a retort filled with chlorate of potassa. The tube is heated to a dull-red, and at the same time oxygen is disengaged by heat- ing the chlorate ; but, in order to obtain a considerable quantity of manganate, the operation should be continued for some time. The substance gives with cold water an intense emerald-green solution, which, after being filtered through a small plug of asbes- tus placed in the bottom of a glass funnel, is evaporated under the receiver of an air-pump, over a capsule filled with concentrated sulphuric acid, when beautiful green crystals of manganate of VOL. II. C 26 MANGANESE. potassa are obtained, generally mixed with white crystals of hy drated potassa, which may be easily separated by hand. The green crystals are forced from the mother liquid still moistening them, by placing them for a time on a piece of unburned porous clay. The green crystals of manganate of potassa KO,Mn0 3 dissolve without change in a solution of caustic potassa, and are again de- posited on evaporating the liquid ; but on dissolving them in pure water immediate decomposition takes place, the colour of the solu- tion changing to a beautiful red, and a brown precipitate of brown hydrated peroxide being formed. The red solution then contains permanganate of potassa KO,Mn 2 7 . The easy decomposition of manganic acid, even when in combination with as strong a base as potassa, renders it impossible to obtain the acid isolated. By heating peroxide of manganese with soda or baryta in con- tact with oxygen, the manganates of soda and baryta are obtained, the latter of which is a green powder, nearly insoluble in water. When the green mass containing the mixture of manganate of potassa, caustic potassa, and oxide of manganese is dissolved in boiling water, and boiled for several minutes longer, an intense red solution is obtained, which, after being filtered through asbestus and evaporated under the receiver of an air-pump, gives prismatic dark-red crystals of permanganate of potassa. But the most simple process for obtaining this substance in any quantity is the following : One part of peroxide of manganese, reduced to impal- pable powder, is mixed with one part of chlorate of potassa, and one and a quarter parts of caustic potassa, dissolved in the least possible quantity of water, are added : the paste thus formed is dried in a porcelain crucible, during which process a considerable quantity of manganate of potassa already forms. The whole is af- terwards heated slowly to a dull-red in an earthen crucible, then boiled with water in a glass flask, filtered through asbestus, and the liquid concentrated in a porcelain capsule over an alcohol- lamp, when, on cooling, crystals of permanganate of potassa are deposited, which may be purified by recrystallization. Perman- ganate of potassa is not very soluble, as it requires 16 parts of water to dissolve 1 of the salt at 59, while warm water will dis- solve much more. On adding nitrate of silver to a hot solution of permanganate of potassa, fine crystals of permanganate of silver are deposited on cooling, from which other permanganates may be prepared by adding to it an equivalent quantity of a metallic chloride, for the silver combining with the chlorine leaves its permanganic acid to combine with the metal which existed as chloride. After rubbing the two substances with water, the chloride of silver may be sepa- rated by decantation or by filtration through asbestus. Free permanganic acid can be obtained in aqueous solution by decomposing permanganate of baryta with sulphuric acid, added MANGANATES AND PERMANGANATES. 27 by drops ; when insoluble sulphate of baryta is formed, and the decanted liquid contains permanganic acid. The solution is of a fine red colour, but the acid decomposes easily even in the cold. Organic substances rapidly decompose the salts of both manganic and permanganic acid by taking up a part of their oxygen, for which reason their solutions must not be filtered through paper. If a red solution of permanganate of potassa, containing caustic potassa, is filtered through paper, the filtrate is generally green from containing manganate ; but if the solution is very dilute, or the filtration slow, the liquid completely loses its colour, while the paper takes a deep-brown tinge from the hydrated peroxide which fills its pores. Caustic potassa, added to a dilute solution of permanganate of potassa, immediately changes the colour of the solution, first to violet and then to a fine emerald-green, the permangate being reduced to manganate, while another quantity of potassa has en- tered into combination : KO,Mn a 7 +KO=2(KO,Mn0 3 )+0. The oxygen remains in solution in the water, since only a small quantity was disengaged, and the permanganic solution is very dilute. The decomposition is owing to the strong basic properties of the potassa, which tends to saturate as much acid as possible. The changing from red to green does not take place instantane- ously, and, by adding the potassa in small quantities at a time, the liquid passes through all the intermediate shades between red and green, that is, through all the shades of violet. It was stated that the colour of a green solution of manganate of potassa changes to red by boiling, hydrated peroxide of manga- nese being precipitated ; but this takes place only when the solu- tion is not too concentrated. Green manganate is also changed to red permanganate in the cold, without any visible precipitation of peroxide, by adding more and more cold water, the oxygen dis- solved in which effects the oxidation ; the liquid again passing through all the shades produced by a combination of green and red. If it is desirable that the solution should not be very dilute, it is suificient to leave it in contact with the air, or to pass a current of oxygen through it. The name of chameleon mineral has been given to this substance, on account of the phenomena of changing colour. Manganate of potassa is most rapidly converted into permanga- nate by the addition of any acid, even of carbonic ; but an excess of acid completely discolours the liquid, by forming a salt with the reduced protoxide of manganese, while oxygen is given off. Of the oxides of manganese, only the protoxide and sesquioxide are base's. 28 MANGANESE. PROTOSALTS OF MANGANESE. 752. The protosalts of manganese are of an amethyst, or light rose colour, which, however, very soon changes by agitating the liquid in contact with the air, or even by pouring it from one ves- sel into another.* Caustic potassa or soda precipitates white hy- drated protoxide, which soon changes to brown in the air ; while ammonia has the same effect in a smaller degree, a similar phe- nomena taking place to .that mentioned in 589 for the salts of magnesia, viz. that the ammoniacal salt formed combines with the salt of manganese, and gives a double salt which an excess of am- monia will not decompose. A perfect precipitation cannot there- fore be effected, whatever may be the quantity of ammonia added ; for, if the salt of manganese is neutral, the first drops of ammonia precipitate some protoxide, but at the same time a corresponding quantity of ammoniacal salt is formed, which is soon present in suf- ficient quantity to form with the salt of manganese yet in solution a soluble double salt which is not decomposed by ammonia. An excess of ammonia redissolves the hydrated protoxide already precipitated, by entering into combination with it, unless the precipitate has not already changed to brown sesquioxide, which is insoluble in am- monia. By exposing the ammoniacal solution of protoxide to the air, oxygen is absorbed, and the manganese is at last completely precipitated as hydrated sesquioxide. The alkaline carbonates give a dirty white, and ferrocyanide of potassium a rose-coloured precipitate. The alkaline sulfhydrates precipitate the protosalts of manganese with an orange colour, and sulf hydric acid will not throw them down in the presence of a slight excess of acid, sulphide of manganese being easily decomposed by weak acids. Sulphate of Manganese. 753. Sulphate of manganese is obtained by heating native peroxide with concentrated sulphuric acid, while oxygen is given off; but the residues of red oxide, which remain after the calcina- tion of peroxide for obtaining oxygen gas, are also profitably em- ployed for this purpose. The sulphate is also sometimes prepared by heating the protochloride of manganese obtained by the prepa- ration of chlorine with sulphuric acid. The sulphate crystallizes with different quantities of water, and in different forms, according to the temperature at which the crystallization takes place : thus, when the temperature is below 43, the crystals contain 7 equiva- * The pink colour of protosalts of manganese I have found to be mostly, if not always, due to the presence of a minute percentage of cobalt, which is rarely absent from the ores of manganese. I have these ores containing from 0.01 up to 7.0 per cent, of oxide of cobalt. J. C. B. SESQUISALTS OF MANGANESE. 29 lents of water, and are isomorphous with sulphate of iron, FeO, S0 3 +7HO ; while the crystals formed at a temperature between 43 and 68 present the form of sulphate of copper CuO,S0 3 -f 5HO, the sulphate of manganese also containing 5 equivalents of water : lastly, between 68 and 86 the salt crystallizes with 4 equivalents of water, and is isomorphous with the sulphate of iron FeO, S0 3 +4HO, which has also been obtained crystallized. These are important facts for the theory of isomorphism. Carbonate of Manganese. 754. Carbonate of manganese occurs in nature in rhombohe- drons, which present the same form as those of carbonate of lime, and are generally of a rose or violet colour. Carbonate of iron and carbonate of lime frequently replace part of the carbonate of man- ganese in the same crystal, thus offering a new proof of the isomor- phism of the protoxides of iron and manganese. Carbonate of manganese may be obtained as a dirty white powder by adding carbonate of soda to a solution of sulphate or chloride of manga- nese. It is soluble in water containing carbonic acid. Other salts of manganese are easily obtained by dissolving the carbonate in the corresponding acids. SESQUISALTS OF MANGANESE. 755. Although sesquioxide of manganese combines with acids, the salts it forms are not durable. By slightly heating hydrated peroxide of manganese with sulphuric acid, the former dissolves with a beautiful red colour, which solution, mixed with sulphate of potassa or ammonia, yields by evaporation octohedral crystals of a true manganic alum KO,S0 3 +Mn 2 3 ,3S0 3 +24HO, the exist- ence of which proves sesquioxide of manganese to be a particular oxide, and not a combination of protoxide with peroxide. Oxidizable substances instantly change sesquisulphate of manganese to proto- sulphate, the liquid losing its colour ; a property of the sesquisul- phate which is often made use of in the laboratory to ascertain whether an oxide is present in its highest stage of oxidation, for example, to ascertain whether sulphuric acid contains any sulphu- rous acid, or whether nitric be free from nitrous acid. COMBINATION OF MANGANESE WITH SULPHUR. 756. A hydrated protosulphide of manganese is obtained by adding & solution of an alkaline monosulphide to that of a proto- salt of manganese, when a light-red precipitate is formed, which disengages sulf hydric acid on being dissolved in acids. Anhydrous c2 30 MANGANESE. monosulphide is obtained by heating peroxide of manganese with sulphur, when sulphurous acid is set free : Mn0 2 +2S=MnS+S0 2 . The excess of sulphur is driven off by heating to redness, but the monosulphide thus prepared is almost always mixed with pro- toxide, and may be obtained in a state of greater purity by decom- posing oxide of manganese with sulphide of carbon at a red-heat. COMBINATIONS OF MANGANESE WITH CHLORINE. 757. Protochloride of manganese is prepared by heating native peroxide with chlorohydric acid, while chlorine is disengaged ; but as the native peroxide always contains a certain quantity of iron, the solution usually contains some perchloride of iron, to separate which the solution must be completely evaporated to dryness, by which the excess of chlorohydric acid is also driven off. The residue is dissolved in water, and the liquid boiled for some time with a little carbonate of manganese, which effects the precipita- tion of the peroxide of iron, while carbonic acid is disengaged, as protoxide of manganese is a much stronger base than peroxide of iron.* Protochloride of manganese crystallizes with 4 equivalents of water, one-half of which it gives off at 212 ; but when heated still higher, it becomes completely anhydrous and at last fuses. When fused in contact with the air, the oxygen of the latter expels the chlorine, and the protochloride is converted into protoxide. Ex- periments have been made to turn this property to technical use, by regaining part of the chlorine contained in the protochloride of manganese, which is a residue in the manufacture of bleaching- powder; and it was effected by roasting the protochloride in rever- beratories, and leading the gases, which were highly charged with chlorine, into the chambers where chloride of lime is prepared. The roasting, which was done at as low a temperature as possible, converted the protochloride into sesquioxide, which was treated with chlorohydric acid to obtain a new quantity of chlorine. But, as the oxide thus obtained only gives one-half the quantity of chlorine that an equal weight of peroxide would, and as the opera- tions are too costly, they are no longer continued. . 758. Sesquichloride of manganese Mn a Cl 3 , is obtained by treat- ing hydrated sesquioxide with chlorohydric acid, without applica- tion of heat. The red solution obtained develops chlorine by heating, and changes into protochloride. * The same insolubility of the perchloride of iron is effected by heating the mixture, when dry, to full redness. J. C, B. TESTING THE OXIDES OF MANGANESE. 31 DETERMINATION OF MANGANESE, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. 759. The manganese existing in a solution is usually deter- mined by adding carbonate of soda to the boiling liquid, washing the precipitated carbonate of manganese well with boiling water, and calcining it to a high red-heat, by which it is converted into red oxide Mn 3 4 containing 72.11 per cent, of manganese. The carbonate is dried and calcined with its filter in a platinum crucible, which, being covered with its lid, is placed in an earthen crucible and heated to a strong red-heat. When the liquid from which the oxide of manganese is to be precipitated contains any quantity of ammoniacal salt, it must be evaporated with an excess of carbonate of soda and the residue redissolved in water. 760. Manganese is separated from the alkaline metals by means of carbonate of soda, or by sulf hydrate of ammonia, which pre- cipitates it as sulphide, which, after being washed with water con- taining some sulf hydrate, is dissolved in an acid, and reprecipitated by carbonate of soda. It is easily separated from baryta and strontia by adding sul- phate of soda to the liquid, which precipitates the baryta and strontia as sulphates. It is separated from lime and magnesia by sulf hydrate of ammonia, which precipitates only the manganese as sulphide, if the solution is sufficiently dilute. Its separation from alumina and glucina is easily effected by boiling the liquid for some time with an excess of caustic potassa in contact with the air, when the manganese is precipitated as hydrated sesquioxide, while the two earths dissolve in the excess of alkali. TESTING THE OXIDES OF MANGANESE. 761. In works where bleaching-powder is made, considerable quantities of peroxide of manganese are used, the commercial value of which depends on the quantity of chlorine it will develop when treated with chlorohydric acid; but, as the native peroxide is always mixed with more or less gangue and sesquioxide of man- ganese, it is important that the purchaser should be able to deter- mine the quantity of chlorine which a given weight of oxide will develop by a simple process. One litre of dry chlorine is disengaged by 3.98 gm. of perfectly pure binoxide of manganese at 32 and under the pressure of 760 mm. ; and if it be absorbed by a dilute solution of caustic potassa, and water added until the volume of the liquid is 1 litre, a solution is obtained containing precisely its volume of chlorine, and therefore marking 100 chlorometric degrees. But 3.98 gm. of a peroxide of commerce will, when treated in the same manner, give 32 MANGANESE. a solution containing a less volume of chlorine, the quantity of which, when determined by the common chlorometric processes ( 572), expresses the value of the peroxide employed. Supposing the quantity of chlorine found to be 60, the conclusion follows that the oxide in question only gives a quantity of chlorine represented by 60, while the same weight of pure binoxide yields a quantity represented by 100 ; and, to obtain the same quantity of chlorine as one kilog. of pure binoxide would give, ^ = 1.67 kilog. of the other oxide must be employed. 762. An average sample of the peroxide to be examined being first made by picking small quantities from all parts of the mass, it is reduced to a fine powder, of which exactly 3.98 gm. are intro- duced into a small flask A (fig. 475), about 5 centimetres in dia- meter. By means of a well-fitting cork the flask is furnished with a tube, bent as in the figure, to convey the gas into a long-necked flask B, hold- ing about } litre. The latter is placed in an in- Fig. 475. clined position, and filled up to the neck with a weak solution of caustic potassa. The peroxide is introduced into the flask A with a suitable quantity of chlorohydric acid, which is measured in a tube graduated to 25 cubic centimetres ; and after adjusting the cork, the temperature is gradually raised. The chlorine first expels the air from the flask A, and causes it to fill the upper part of the bulb B, while the water it displaces rises in the neck. Toward the end of the operation, the liquid in A is heated to the boiling point, so that the steam generated drives all the chlorine into the alkaline liquid. The flask B is then taken away, while the boiling is continued in A to prevent any absorp- tion, and the chlorine is determined in the alkaline liquid by one of the chlorometric methods. 763. A solution of sulphurous acid, perfectly free from sul- phuric, may be substituted for the alkaline liquid in the flask B, as the chlorine, when led into the former, converts a corresponding quantity of sulphurous acid into sulphuric, the quantity of which is determined by adding chloride of barium, boiling to expel the excess of sulphurous acid, collecting the precipitate on a filter, and weighing it after calcination. The quality of the peroxide is then proportional to the weight of the sulphate of baryta obtained, 3.98 gm. of pure peroxide giving 10.65 gm. of sulphate of baryta. As the sulphurous acid used must be perfectly free from sul- phuric, it is important to test it to this effect before each determi- nation, which is done by adding a few drops of chloride of barium, TESTING THE OXIDES OF MANGANESE. 33 which should give no precipitate. A certain quantity of chloride of barium may at once be added to the liquid, so that sulphate of baryta forms as the sulphurous acid oxidizes by the oxygen of the and when the solution is to be used, the clear liquid, which air of course is free from sulphuric acid, can be decanted off from the precipitate. The best method of conducting the experiment is that repre- sented in fig. 476. Water, freed from air by boiling, and some Fig. 476. chloride of barium, are introduced into the flask A, into which, as soon as the water has cooled, a current of hydrogen is led, supplied by the generator B. As soon as the air is expelled from A by the hydrogen, a current of sulphurous acid gas is introduced, obtained by heating concentrated sulphuric acid with copper or mercury in the flask C, and purifying it by washing with water in the small flask D. Lastly, the 3.98 gm. of peroxide are heated in the flask E with chlorohydric acid, and the chlorine disengaged is led into the flask A, where it oxidizes a corresponding quantity of sulphur- ous acid to sulphuric, which precipitates as sulphate of baryta, while there is no fear that sulphuric acid might form by the contact of sulphurous with the air. Toward the end of the operation the liquid in A is boiled to expel the excess of sulphurous acid, the oxidation of which is still prevented by continuing the stream of hydrogen ; and finally the sulphate of baryta formed is collected on a filter. 764. The finely powdered oxide of manganese may also be heated with a concentrated solution of oxalic acid, which forms protoxalate of manganese, while the oxygen given off by the re- duction of the higher oxides to protoxide converts a corresponding quantity of oxalic into carbonic acid, which may be precipitated as carbonate of baryta by being led into a solution of baryta, or better still, may be conducted into a weighed bulb-apparatus containing a concentrated solution of caustic potassa, the increase of weight of which after the operation corresponds exactly to the carbonic 3 34 MANGANESE. acid. In either case the gas must be dried by being passed through a tube containing concentrated sulphuric acid. 765. For an accurate estimation of the value of an oxide of manganese it is not sufficient merely to determine the quantity of chlorine it will develop, but the quantity of chlorohydric acid required to disengage the chlorine must also be found. If the oxide is pure binoxide, the chlorine of one-half of the acid is neces- sarily disengaged, while pure sesquioxide will only give one-third of the chlorine; for which reason, in the latter case, one and a half times the quantity of acid is required to give the same quantity of chlorine as when pure binoxide is used ; and lastly, if the oxide is mixed with a gangue of lime, baryta, or oxide of iron, these bases will neutralize a part of the acid without disengaging chlorine. To find the quantity of chlorine required, the acidimetric percentage of 25 cubic centimetres of the acid employed is first determined, and 3.98 gm. of the oxide of manganese are treated with other 25 cubic centimetres of the same acid, the flask containing the mixture being kept heated. The chlorine is lost, but the small quantity of chlorohydric acid which might distil over is condensed in a moist flask through which the gas is led. When all the chlorine is dis- engaged, the small quantity of liquid in the moist flask is added to the residue in the flask in which the gas was developed, the liquid is diluted to the volume of half a litre, and the remaining acid is determined by adding a standard alkaline solution until the pre- cipitate of hydrated oxides, which forms on the addition of every drop, is no longer redissolved by shaking the liquid. This experi- ment gives the quantity of acid which has remained free, and shows, when compared with the former experiment, the quantity of acid required by the oxide of manganese.* * The following is a shorter method of testing peroxides of manganese. The chlorine disengaged from a weighed quantity of the oxide is conducted into the solution of a given quantity of a protosalt of iron, an equivalent quantity of which it oxidizes to peroxide ; so that, if the remaining quantity of protoxide of iron which is determined with permanganate of potassa (as will be described in \ 804) be subtracted from the quantity contained in the protosalt employed, the differ- ence will be in proportion to the chlorine disengaged. The protosalt of iron best adapted to the purpose is the protosulphate of iron and ammonia, which is easily obtained by mixing equal volumes of saturated solu- tions of sulphate of iron and sulphate of ammonia, when the liquid on evaporating yields prismatic crystals of the salt, the formula of which is FeO,S0 3 -f-NH 4 0, S0 3 -f6HO. One hundred grammes of the salt are dissolved in 1837 cubic centi- metres of water, so that the solution contains 5.44 per cent, of the salt; or, 544 parts of the salt corresponding to 184 parts of pure protoxide, exactly one per cent, of protoxide of iron : and the standard solution thus obtained, which is best prepared in larger quantities at a time, is used for all chlorometric determina- tions, as well as for that of chrome. Supposing the quantity of oxide subjected to the test to be exactly one gramme, and the substance to be pure peroxide, which gives one equivalent of chlorine ; then will the quantity of chlorine developed be 0.807 gm. ; and supposing the quantity of the standard solution of iron employed to be 200 cubic centimetres, which contain 2 gm. of protoxide, only 1.68 of which are oxidized by the chlorine ; TESTING THE OXIDES OF MANGANESE. 35 then will the 0.37 gm. of protoxide, determined directly by permanganate of po- tassa, and subtracted from the 2 gm. employed, give the quantity of protoxide which was oxidized, viz. 1.63 gm., which correspond to 0.807 gm. of chlorine, as one equivalent of chlorine oxidizes two equivalents of protoxide of iron. W. L. F. Another method of determining the commercial value of peroxide of manganese, better than that described in the text, is to employ dry oxalate of soda, which is easily prepared and preserved, and of which 152^- grains are just sufficient for 100 grs. of pure binoxide, in order that its oxalic acid may be wholly converted into 100 grs. of carbonic acid. 76 grs. of the dry oxalate and 50 grs. of the per- oxide are introduced with about oz. of water into a small flask containing two tubulures, through one of which an S-tube passes, and through the other a small tube connected with a tube of sulphuric-pumice or chloride of calcium. The whole apparatus being weighed at once, together with about 200 grs. of oil of vitriol, the latter is gradually poured through the S-tube into the little flask. The oil of vitriol disengages the oxalic acid, which is oxidized into carbonic acid by the excess of oxygen over that in the protoxide, and since it cannot pass through either escape-tubes without being dried, the loss of weight of the whole apparatus indicates the loss of carbonic acid alone. The number of grains of loss being doubled, gives the percentage of peroxide equivalent to pure binoxide. The dif- ferent methods of arranging the apparatus will be found in the analytical chemis- tries of Rose and Fresenius, and others, and in the Encyclop. of Chem. The best commercial varieties contain from 80 to 98 per cent, of binoxide. J. G. B. 36 IRON. EQUIVALENT = 28.0 (0=100 ; 350.0). 766. On account of its numerous technical applications, iron is the most important of all the metals. It is used in three states : 1. Bar or malleable iron. 2. Steel. 3. Crude or cast-iron. Steel and cast-iron are combinations of iron with small but vari- able quantities of carbon and silicium. The bar-iron of commerce is not chemically pure, as it contains a small quantity of carbon, and often traces of silicium, sulphur, or phosphorus, which latter remarkably affects its quality. The iron used in fine locksmith's work approaches a state of purity ; but the purest iron is found in piano-forte wires, or ordinary wire, because only iron of great purity can be drawn out into very fine threads. In order to obtain iron chemically pure, some wire is cut into pieces of the same length, and tied in bundles ; when their surface is oxidized, by heating them for a few moments exposed to the, air, or better still, in a porcelain tube through which steam is passed. The bundles of oxidized iron are then placed in a small porcelain crucible with a small quantity of powdered glass ; and the crucible being set in a second earthen crucible, luted externally with clay, is heated in a blast-furnace at the highest temperature that can be produced. The small quantities of foreign matter contained in the iron, are burned by the oxygen of the oxide, while the excess of oxide of iron, combining with the glass, forms a slag. If the temperature be sufficiently elevated the purified iron fuses to a single lump. Pure iron is whiter and more malleable than the iron of commerce, but less tenacious. Pure iron may likewise be obtained by the reduction of one of its oxides by hydrogen, which takes place at a dull red-heat, and may be effected in the small apparatus described (fig. 473) for the preparation of the protoxide of manganese. The metallic iron remains in the tube, in the form of a grayish-black powder, which may be preserved by closing hermetically both ends of the tube while it is filled with hydrogen gas ; for very finely divided iron has so great an affinity to oxygen that it is inflamed by contact with the air ; a property which has given to it the name of pyro- phorio iron. If the reduction be made in a porcelain tube at a high temperature, the metal becomes solid, assuming a metallic lustre, and no longer oxidizing in dry air. IRON. 37 Perfectly pure iron may also be procured, by heating protochlo- ride of iron in a glass tube, through which a current of hydrogen gas is passed ; when the iron forms on the sides of the glass a glit- tering, brilliant coating, in which small cubic crystals may often be seen. 767. The texture of commercial iron varies greatly, according to its mode of manufacture. Pure iron which has been forged and rolled equally in all directions, exhibits a texture of very small, brilliant grains ; but, when drawn out into bars, its texture is often decidedly fibrous, the fibres always running in the direction of the bar, which may be readily proved by breaking the latter. The fibrous texture is highly esteemed, because the iron possessing it is much more tenacious than granular iron, and bears a greater weight without breaking. The fibrous texture of iron is generally regarded as an index of its good quality ; however, skilful work- men can impart this quality also to bars of an inferior sort. Iron of fibrous texture does not always remain in that state, but after some time changes into the granular, or even the laminated tex- ture ; which change ensues most rapidly when the bars are sub- jected to vibration, as, for instance, when they support the floor of a suspension-bridge. The tenacity of the metal diminishes at the same time in a remarkable manner, and it frequently breaks with a load which the bar would easily have borne when its tex- ture was fibrous. A change of this kind is frequently observed in the axles of locomotives and railway-cars.* The specific gravity of wrought-iron varies from 7.7 to 7.9. Iron is the most tenacious of all the metals, a cylindrical iron-wire of 2 millimetres in diameter being able to sustain a load of 250 kilogs. 768. The highest temperature that can be produced in a blast- furnace is required for the fusion of iron, which, however, is more easy when it can be combined with carbon. Iron passes from the fluid to the solid, through the doughy state, and therefore belongs to that class of substances which crystallize with difficulty by fusion. However, if large masses of iron, heated to a very high temperature, be allowed to cool very slowly, indications of crystallization of the cubic form are found in the interior of these masses. f Heated to a white-heat, iron becomes sufficiently soft to assume any form under the hammer ; and two bars, when heated to redness, can be readily soldered to each other without the interposition of another metal, when the surfaces to be joined are completely free from oxide. * The fibrous texture of iron is also changed to the granular by heating the metal to redness, and immersing it while hot into cold water. W. L. F. f Some species of cast-iron, as, for example, that made from the manganiferous sparry iron-ore of Muesen in Westphalia, and that made at Easton, in Pennsyl- vania, the latter of which is remarkable for its extreme ductility when converted into bar-iron, show a laminated texture, which is owing to its being an aggregated mass of laminated prismatic crystals, the angles of which are about 112. IF. L. F. VOL. II. D 38 IKON. Now, as it is known that iron heated in the air soon oxidizes, the blacksmith generally throws a small quantity of sand upon the bars he wishes to solder, which, by combining with the oxide of iron, produces a very fusible silicate, which, forming a kind of varnish on the surface of the metal and preventing its further oxi- dization, is afterward, from its extreme fluidity, entirely driven off by the blows of the hammer. 769. Iron, cobalt, and nickel are the only metals which are remarkably magnetic at the ordinary temperature. A piece of pure iron immediately becomes a magnet, either by contact with or at a short distance from a native magnet, its magnetic properties dis- appearing again as soon as the magnet is removed ; but if the iron is combined with a small quantity of carbon, if it is steely, the magnetism is slower of development, but continues longer after the removal of the magnet. A bar of steel, rubbed against a magnet, acquires permanent magnetic properties, and becomes a true mag- net. The magnetic properties of iron diminish rapidly with the temperature, an iron ball heated to a whitish red-heat no longer exerting any influence over the needle, but recovering its magnetic virtue on cooling. 770. Iron remains unchanged for an indefinite time in dry air, and even in dry oxygen, at the ordinary temperature ; but soon alters in moist air, by becoming covered with rust. The rust of iron, which consists of an oxidation of its surface, is most readily formed in the presence of carbonic acid, of which the air always contains a small quantity. Under the influence of the carbonic acid and the oxygen, the surface of the iron is converted into proto- carbonate, which, on absorbing a new portion of oxygen, is trans- formed into hydrated peroxide of iron, while the carbonic acid disengaged favours the oxidation of an additional quantity of metal- lic iron. It has been observed, that when iron has begun to rust at any particular point, it changes very rapidly around this point, which is produced by a galvanic phenomenon accelerating the oxi- dation. The iron and thin layer of oxide which forms on its surface constitute the two elements of a pile in which the iron becomes posi- tive, and thus acquires an affinity for oxygen sufficiently great to decompose water at the ordinary temperature, with the evolution of hydrogen gas. This phenomenon is rendered very evident by allow- ing moist iron-filings to rust in the air, when, after some time, the odour exhaled by hydrogen gas* made from the carburetted metals is easily recognised. Rust almost always contains a small quantity of ammonia, the presence of which may be recognised by heating it with potassa, and is explained as follows : It has been shown (122) * This peculiar odour is not exhaled by hydrogen gas, but is that of a certain substance called ozone, and shown by Bunsen to be a combination of one atom of hydrogen with three of oxygen, which forms under almost all circumstances where a galvanic current is active. W. L. F. IRON. 39 that when hydrogen and nitrogen meet in the nascent state in a liquid, they combine and form ammonia : now, the water which moistens the rust, being in contact with the air, contains nitrogen in solution, and on the other hand, hydrogen is disengaged by the decomposition of the water. The circumstances under which am- monia can form by the direct combination of hydrogen and nitro- gen are therefore realized. The peroxide of iron, which acts with very powerful bases the part of a feeble acid, retains the ammonia and prevents it from being disengaged. It is important to be aware of the presence of ammonia in rust, as it has been long since admitted, that when spots of rust which were found on sidearms or steel weapons, suspected to have been used in the commission of a crime, evolved ammonia by contact with potassa, it was a proof that the rust was formed by contact with animal matter, and these spots of blood were the cause of its pre- sence. This presumption was erroneous ; for as we have just seen, steel-rust formed by the contact of air alone may contain an appre- ciable quantity of ammonia. Rust soon changes in fresh water, but very slightly in water containing a few thousandths of carbonate of soda or potassa. During the last few years, iron has been preserved from rust by covering its surface with a very thin layer of metallic zinc,* and iron thus coated is called galvanized iron. This phenomenon was explained in 305. Iron soon oxidizes by contact with the air when heated to red- ness, becoming covered with a black pellicle of oxide, which falls off under the hammer. To this easy combustion of iron in the air may be attributed the property which it possesses of giving out sparks when struck by a flint, in which case small particles are detached, which, being strongly heated by friction against the flint, become incandescent by combining with the oxygen of the air, and may easily inflame combustible substances, such as tinder. If the steel be struck for some time over a sheet of white paper, the latter will be covered with small black particles, which are attracted by the magnet, and are, in fact, small spherical globules of mag- netic iron. 771. Iron is readily acted on by chlorohydric acid, protochlo- ride of iron being formed, and hydrogen disengaged. Dilute cold sulphuric acid dissolves it with the evolution of hydrogen, while the concentrated acid also attacks it, but disengages sulphurous acid. Concentrated nitric acid attacks it sharply with a copious * A patent lias lately been taken out in Europe (Vienna ?) for preserving iron from rust by a coating of metallic cadmium, which at the same time imparts a silvery lustre to the surface. Silicate of potassa, the German wasserglas, has also been employed. W. L. F. 40 IRON. disengagement with nitrous fumes,* while the ^ dilute acid dissolves it without any apparent evolution of gas, forming at the same time protonitrate of iron and nitrate of ammonia (122). COMPOUNDS OF IRON WITH OXYGEN. 772. Three compounds of iron with oxygen are known : 1. A protoxide FeO, which is a powerful base, isomorphous with the bases of which the formula is RO. 2. A sesquioxide Fe 2 3 , being a very feeble base, analogous to alumina, and isomorphous with the oxides of which the formula is B 3 3 . 3. Lastly, an acid Fe0 3 , analogous to manganic acid. A fourth compound of iron with oxygen, of the formula Fe 3 4 , is also known, and is called magnetic oxide ; but as it behaves like a compound of protoxide and sesquioxide FeO,Fe 3 3 , it is regarded as such. Protoxide of Iron FeO. 773. Protoxide of iron has hitherto not been obtained in a state of purity. When a large bar of iron heated to redness is allowed to cool slowly in the air, its surface oxidizes, and a black pellicle of a metallic lustre is formed, which falls off under the hammer, and is called finery cinder. If a thin piece of cinder be examined with a lens, it is seen to be composed of several layers ; the outer stratum showing nearly the composition of magnetic oxide Fe 3 4 , while the inside layer, or that immediately in contact with the metal, resembles the protoxide very closely. If a solution of caustic potassa be added to a protosalt of iron, a white precipitate of Jiydrated protoxide is obtained, which soon turns green on exposure to the air, by forming hydrated sesqui- oxide by absorption of oxygen. If boiling solutions be used, and the ebullition prolonged for some time, the white precipitate loses its water of hydration and becomes black ; but the oxide has such an affinity for oxygen that it is impossible to collect it unchanged. It even decomposes water at the boiling point, and is ultimately converted into magnetic oxide. French bottle-glass owes its hue to the presence of this oxide ( 684), which imparts a deep green colour to fluxes. * Very concentrated nitric acid will not dissolve pure iron at all, owing to an electrical phenomenon by which the iron is brought to the passive state, and changes its electropositive power. The iron will continue in this state, and not be attacked by the acid, even on diluting the latter to almost any degree ; but on touching the piece of passive iron, lying in the diluted acid, with a piece of common iron, such as a key, the galvanic current produced by the contact of the two pieces, whose electromotive power is yet different, instantly changes the passive iron back to its natural state, and renders it soluble. IF. L. F. OXIDES OF IRON. 41 Sesquioxide of Iron Fe 3 3 . 774. The sesquioxide Fe 3 3 , or peroxide, is a substance abun- dantly met with in nature, occurring either in the anhydrous or the hydrated state. The anhydrous peroxide forms flattened rhombo- hedral crystals, very brilliant and nearly black, while their powder is of a deep red colour. Mineralogists call it specular iron : it is found in veins in the old rocks. In the fissures of volcanic lavas, thin and brilliant laminae of peroxide of iron are often found, having the form of regular hexagons, and also belonging to the class of specular iron. Anhydrous peroxide of iron, which is also found in compact masses, of an intense red colour, is called by mine- ralogists red hematite, and is known in the arts by the name of bloodstone, a substance extensively employed for polishing metals. Peroxide of iron is prepared artificially by calcining protosul- phate of iron, when sulphurous and sulphuric acids are disengaged, and the peroxide remains in the form of a red powder : 2(S0 3 ,FeO)==Fe 3 3 +S0 3 -fS0 3 . Peroxide of iron thus prepared is known by the name of colco- thar, and used for painting, for polishing silver, and for giving the last polish to mirrors. The intensity of colour of peroxide of iron is in proportion to its compactness. Peroxide of iron may be obtained in the form of small crystal- line lamellae, of great lustre and nearly black, by calcining in a crucible 1 part of sulphate of iron with 3 parts of sea-salt. The calcined matter is treated with boiling water, which leaves the per- oxide. 775. Hydrated peroxide of iron is prepared by adding potassa or ammonia to the solution of a sesquisalt of iron, when a copious brown precipitate is formed. When the reaction has been effected by caustic potassa, the precipitate always retains a small quantity of alkali, which is removed with difficulty only by prolonged boil- ing with pure water. The precipitation may be made by a solution of carbonate of potassa or soda, in which case the precipitate is also hydrated peroxide of iron, the carbonic acid being disen- gaged, or combining with the excess of neutral carbonate, which it transforms into bicarbonate. Hydrated peroxide of iron parts readily with its water by the application of heat, but when heated still further, a temperature is soon attained at which the oxide suddenly becomes incandescent from a spontaneous evolution of heat. This incandescence is only momentary, and the temperature of the oxide again falls to that of the vessel in which it is heated ; but its physical and chemical properties have been remarkably modified, as it has become more compact, and dissolves with great difficulty even in highly concen- D2 42 IRON. trated acids. Sesquioxide of iron, heated to a high white-heat, loses a portion of its oxygen, and is converted into magnetic oxide Fe 3 4 . Peroxide of iron colours fluxes of a reddish yellow, but a consi- derable quantity is necessary to produce this effect in glass. The small quantity of protoxide which imparts a deep green hue to a vitreous flux, does not colour it appreciably when converted into peroxide ( 674). Magnetic oxide of iron Fe 3 4 . 776. A native oxide of iron, intermediate between the prot- oxide and peroxide, is often found in very regular, brilliant octa- hedrons, of a fine metallic lustre. At other times it is found in the old rocks in compact masses, often very large, and is worked as an iron ore. Large quantities of it are found at Dannemora, in Sweden, and from this ore the best quality of iron is obtained. This compound has been called magnetic oxide, from its possessing very highly developed magnetic properties. Native loadstone is formed of this oxide of iron. Magnetic oxide of iron is only produced when iron burns at a high temperature in the air, or in oxygen ; for example, by the rapid combustion of iron-wire in pure oxygen ( 64). But the most certain method of obtaining it in the laboratory consists in heating iron-wire in a porcelain tube, in a current of steam, as in the ex- periment described in 68, when the surface of the wire becomes covered with an infinite number of small, very brilliant crystals, which by the aid of a lens are seen to be regular octahedrons, resem- bling those of the native magnetic oxide. This oxide may also be obtained in the hydrated state, by dis- solving the magnetic oxide in chlorohydric acid, and adding a large excess of ammonia, when a deep green precipitate, becoming black by desiccation, is formed. This hydrate is magnetic, like the anhydrous oxide. Hydrated magnetic oxide may likewise be pre- pared by pouring into ammonia a mixture of equal equivalents of persulphate and protosulphate of iron. In order to make this mixture, two equal volumes of the same solution of protosulphate of iron are used, one of which is transformed into persulphate by evaporating it to dryness with nitric and sulphuric acids, and then redissolved in the other volume of protosulphate. The magnetic oxide does not behave like an oxide per se, but rather like a compound of protoxide and peroxide. Its formula is properly FeO,Fe a 3 , analogous to that of red oxide of manganese MnO,Mn 3 ? . The solution of magnetic oxide in an acid possesses the properties of a mixture of a protosalt with a sesquisalt ; and if an alkali is dropped into the liquid, the peroxide is precipitated before the protoxide. In order to precipitate the two oxides in OXIDES OF IRON. 43 combination the proceeding must be inverted, and the solution of the salt of iron be poured into the alkaline liquid. We shall, more- over, soon see several compounds presenting a similar chemical formula, and affecting identical crystalline forms, but in which the peroxide of iron is often replaced by alumina or by oxide of chrome, while magnesia, protoxide of manganese, or oxide of zinc often take the place of the protoxide. Feme acid Fe0 3 . 777. The third compound of iron with oxygen possesses the properties of an acid corresponding with manganic acid, and is formed under the same circumstances. A mixture of iron filings and nitrate of potassa is heated to redness in an iron crucible, when a beautiful red solution of ferrate of potassa is obtained by treating the mass with water, resembling permanganate of potassa in colour. It is also .-procured by passing chlorine through a concentrated solution of caustic potassa, containing hydrated peroxide of iron in suspension. Pieces of caustic potassa are added from time to time, in order constantly to maintain a large excess of alkali in the liquid. Ferrate of potassa, being nearly insoluble in a concentrated solu- tion of potassa, is deposited in the form of a black powder, which may be almost entirely separated from the mother liquid by drying it on unglazed porcelain. Ferrate of potassa is still less fixed than the manganate, and has not yet been obtained in ft crystalline form. Its solution cannot be filtered through paper,, as it immediately decomposes when in contact with organic matter, forming hydra- ted sesquioxide of iron. 778. The following is the composition of the four oxides of iron : Protoxide FeO Iron 77.78 28 Oxygen 22.22 8 100.00 ~36 Sesquioxide Fe 3 3 ... Iron 70.00 56 Oxygen 3C.OO 24 100.00 80 Magnetic oxide FeO,Fe 3 3 Iron 72.42 84 Oxygen 27.58 32 100.00 116 Ferric acid Fe0 3 Iron 53.84 28 Oxygen 46.16 24 100.00 52 The equivalent of iron is 28, or 350 when that of oxygen is as- sumed as 100. 44 SALTS OF PROTOXIDE OF IRON. 779. The hydrated protosalts of iron are of a bright green colour, which they nearly lose by parting with their water ; and their solutions are also of a bright green. Their taste is astringent and metallic. Potassa and soda, poured into the solution of a protosalt of iron, yield a white precipitate, which immediately turns green by contact with the air, and, when left exposed to the atmosphere for an in- definite time, becomes ochrous, and is converted into hydrated ses- quioxide. This property distinguishes the protosalts of iron from those of manganese, the latter yielding with the alkalies a white precipitate, which turns brown in the air, without passing through the intermediate green. Ammonia produces with the protosalts of iron a reaction re- sembling that with the salts of manganese ( 752). An excess of ammonia redissolves the protoxide; but by absorbing 4he oxygen of the air, the liquid soon becomes clouded, and hydrated sesqui- oxide is precipitated. The alkaline carbonates, poured into a very cold solution of a protosalt of iron, throw down a white precipitate of protocar- bonate, which, not being very fixed, soon parts with its carbonic acid. Sulf hydric acid does not precipitate the protosalts of iron, how- ever slightly acid they may be, while the sulfhydrates give black precipitates. Yellow ferro-cyanide of potassium yields a white precipitate, which soon turns blue by absorbing the oxygen of the air. The red ferro-cyanide gives a beautiful deep-blue precipitate. Succinate and benzoate of ammonia do not precipitate the proto- salts of iron. Phosphate of potassa gives a white precipitate, which turns blue by exposure to the atmosphere. Arseniate of potassa yields a white precipitate, which turns green in the air. Tannin forms no precipitate with the protosalts of iron, but the liquid soon blackens in the air. Protosulphate of Iron. 780. The sulphate is the most important of the protosalts of iron, being used in dyeing, under the name of green vitriol, or cop- ras. It is prepared in the laboratory by dissolving metal- iron in dilute sulphuric acid, when hydrogen is disengaged. This process is sometimes adopted in the arts ; but copperas is generally obtained from the native sulphides of iron or pyrites, which are abundantly found in nature, but cannot be used as iron SALTS OF IRON. 45 ores, because the reduction of the metal would be too expensive, and iron of an inferior quality would be obtained ; but as the py- rites frequently contain some hundredths of sulphide of copper, this metal is extracted from them. For this purpose they are roasted, by a process hereafter to be described, when the metals are oxidized, and a great portion of the sulphur is disengaged in the state of sulphurous acid, while another portion is oxidized still higher, and, by combining with the metallic oxides as sulphuric acid, yields sulphates which are removed by washing. In some localities sulphur is obtained from pyrites by calcining them in retorts, when a portion of the sulphur is disengaged, and a disaggregated magnetic sulphide of iron remains in the retort, absorbing rapidly the oxygen of the moist air, and changing into a sulphate. In other localities, schistous rocks filled with small crystals of pyrites are found, which sometimes change rapidly in the air and fall; tha^b to say, soon become reduced to powder. The sul- phide of iron is then changed into a sulphate, while the schist itself is more or less decomposed, and yields sulphate of alumina, when the two sulphates are dissolved in water. The vitriolic liquids are evaporated in leaden boilers, and con- ducted, when suitably concentrated, into a large vat, where they are allowed to settle for some time, and then are run off into large crystallizing-vats. Strings, on which the crystals of sul- phate of iron form, are suspended in the liquid. When the mother liquid yields no more crystals of the sulphate, even after additional concentration, it is used for the preparation of alum. The water contains sulphate of alumina, which crystallizes with difficulty ; but an addition of sulphate of potassa soon effects the deposition of crystals of alum, which are purified by recrystallization. The sulphate of iron of commerce is often covered with a basic persulphate, rendering its surface ochreous, which is removed by dissolving it in water and boiling the solution with iron filings, which reduce the sesquisulphate of iron to protosulphate. Sul- phate of iron crystallizes at the ordinary temperature with 7 equi- valents of water, while the crystals deposited at 176 contain only 4 equivalents. The same salt readily parts with a portion of its water when heated, but a temperature of nearly 572 is requisite to drive off the last particles of it. Dishydrated sulphate of iron forms a white powder, which, if heated still further, is decomposed by disengaging sulphurous and sulphuric acids, while peroxide of iron remains ( 138). 100 parts of water at 59 dissolve 73 of crystallized sulphate, and at 212 more than 300 parts. Protonitrate of Iron. 781. This salt is obtained by dissolving metallic iron in cold dilute nitric acid, when a certain quantity of nitrate of ammonia 46 IKON. is also formed, which combining with the nitrate of iron, produces a double salt, which is deposited in crystals. The formation of nitrate of ammonia is owing to the fact, that while the iron is being oxidized at the same time at the expense of the oxygen of the water and of that of the nitric acid, hydrogen and nitrogen gas are simultaneously disengaged, and combine in the nascent state to form ammonia. The best method of obtaining protoni- trate of iron consists in decomposing a solution of protosulphate of iron by nitrate of baryta. Carbonate of Iron. 782. Carbonate of iron is found in nature as sparry iron, crystallized in rhombohedrons, resembling those of carbonate of lime, and is highly esteemed as an ore. It is found in veins in the old rocks. Carbonate of iron, heated in an earthen retort, yields magnetic oxide of iron as a residue, and disengages a mix- ture of carbonic oxide and acid. Carbonate of iron has not yet been artificially prepared. Sesquisalts of Iron. 783. These salts are prepared by dissolving the hydrated peroxide .in acids, or by subjecting the protosalts to an oxidizing agency in the presence of an excess of acid. Thus, protosulphate of iron is converted into a persulphate by heating it with nitric acid, while reddish vapours are given off, and the substance be- comes brown. This colour is owing to the fact that the deutoxide of nitrogen which is formed dissolves in the undecomposed proto- sulphate, and produces a highly coloured liquid ( 114). But protosulphate of iron FeO,S0 3 can only be converted into neutral persulphate Fe a 3 ,3S0 3 by adding a certain quantity of sulphuric acid. The salts of protoxide of iron are likewise changed into salts of peroxide by treating their solution with chlorine, in the presence of an excess of acid. Reciprocally, it is easy to transform a sesquisalt of iron into a protosalt, by subjecting it to a deoxidizing action: for example, by boiling its solution with iron filings, or treating it with sulf- hydric acid, in which latter case sulphur is deposited, rendering the liquid milky : Fe 3 3 >3S0 3 +HS=2(FeO,SO s )+S0 3 ,HO+S. 784. The salts of peroxide of iron afford yellow precipitates, the colour of which is deeper in proportion as they approach neu- trality. The fixed alkalis and ammonia yield a brown precipitate of hydrated peroxide, insoluble in an excess of ammonia. The alkaline carbonates give the same brown precipitate of hy- drated peroxide. SALTS OF IRON. 47 Sulfhydric acid produces a white precipitate of very finely divided sulphur ( 783), while the sulf hydrates give brown preci- pitates. Yellow prussiate of potash gives a beautiful blue precipitate. Red prussiate does not precipitate the sesquisalts of iron. These two characters signally distinguish the salts of peroxide of iron from those of protoxide. Benzoate and succinate of ammonia give brown precipitates. The sesquisalts of iron rarely exist in the neutral state, as their solutions always contain an excess of acid. A neutral salt is de- composed by treatment with water into a very basic salt which is precipitated, and an acid salt which remains in solution. Persulphate of iron forms alum with the sulphates of potassa and ammonia, the formulae of which correspond to those of ordinary alum, namely, Fe a 8 ,3S0 8 +KO,S0 8 +24HO and Fe 2 3 >S0 3 + NH 4 0,S0 3 +24HO. They crystallize in regular octahedrons of a violet hue, and are obtained by adding sulphate of potassa or of ammonia to a solution of persulphate of iron, prepared by the process indicated ( 776,) and evaporating the liquid at a low temperature. These alums are easily destroyed by heat. COMPOUNDS OF IRON WITH SULPHUR. 785. Several compounds of iron with sulphate are known. Protosulphide of Iron FeS. 786. Protosulphide of iron is obtained by direct combination of iron with sulphur. When an iron bar, heated to whiteness, is plunged into fused sulphur, the combination takes place with great evolution of heat, the bar becomes corroded, and the fused sulphide of iron falls to the bottom of the crucible. A more convenient method of preparing it consists simply in heating a mixture of iron filings and sulphur in a crucible. Protosulphide of iron combines readily with an excess of iron, producing sub-sulphides, which are met with in several metallurgic processes ; and it also combines very easily with a greater proportion of sulphur. In order to obtain pure protosulphide of iron, the product formed in the pre- sence of an excess of sulphur must be fused in a crucible covered with damp charcoal, in a forge-fire ; when the excess of sulphur is disengaged in the state of sulphide of carbon, and protosulphide remains in the form of a lump possessing a metallic lustre. This sulphide is obtained hydrated in the form of a black powder, when a protosalt of iron is precipitated by a solution of an alkaline sulfhydrate. Sulphur and iron combine together in the presence of water, even at the ordinary temperature. If iron filings and flowers of sulphur are intimate mixed in an earthen vessel and moistened with water, the temperature soon rises, while the colour of the 48 IRON. paste becomes deeper, and, in a few hours, the two substances have combined together. This preparation is sometimes made in the laboratory, as the product finds extensive use in the prepara- tion of sulfhydric acid. When the quantity of material acted on is at all considerable, the reaction is sometimes very powerful and the mixture is thrown from the vessel : great care is therefore re- quisite. Formerly chemists supposed even volcanos to be produced by similar reactions, for which reason the name of Lemery's volcano was given to this preparation. Sesquisulphide of Iron Fe 3 S 3 . 787. Sesquisulphide of iron, corresponding to the sesquioxide, is obtained by decomposing hydrated peroxide of iron by sulfhy- dric acid, at a temperature of 212. This compound easily de- composes. Bisulphide of Iron FeS 3 . 788. Bisulphide of iron FeS 2 , which corresponds to no known oxide of iron, is abundantly found in nature, occurring in the form of brilliant cubic crystals, of a brass-yellow colour, and called by mineralogists iron pyrites, or simply pyrites. Pyrites are often sufficiently hard to strike fire with steel. The same product may be obtained in the laboratory, in the form of a yellow powder, by heating very finely dissolved protosulphide of iron with half its weight of sulphur, until the excess of the latter is volatilized. Its density is 4.98. Bisulphide of iron is not attacked by dilute acids, while the protosulphide, under the same circumstances, gives off sulf- hydric acid in abundance. Iron pyrites, subjected to the action of heat, parts with a portion of its sulphur, which distils over, while a sulphide composed of 100 parts of iron and 68 of sulphur remains, which may be considered as a special sulphide. Magnetic Pyrites. 789. Native sulphides of iron, of a bronze colour, are found in crystalline masses, the form of which is a regular hexahedral prism : they contain less sulphur than the bisulphide, or ordinary pyrites, and are called magnetic pyrites, because they affect the needle. Their composition corresponds in general to the formula Fe 7 S = 5FeS+Fe 3 S 3 . COMPOUND OF IKON WITH NITROGEN. 790. When dry ammoniacal gas is passed over fine iron-wire, heated to a dull red-heat in a porcelain tube, the metal becomes very brittle, and increases remarkably in weight, while a nitruret of iron is formed, containing 12 or 13 per cent, of nitrogen. This product is more readily obtained by heating anhydrous protochlo- ride of iron in a glass tube, in a current of dry ammoniacal gas, COMPOUNDS OF IRON. . 49 when nitruret of iron remains in the form of a metallic sponge, of a silvery whiteness. COMPOUND OF IRON WITH PHOPHORUS. 791. A combination of iron and phosphorus is obtained by heating a mixture of phosphate of lime and charcoal in a forge- fire, in a crucible covered with charcoal, when a very hard and brittle gray metallic lump remains, capable of a fine polish. The composition of this substance corresponds to the formula Fe 4 P. A very small quantity of phosphorous changes the qualities of iron in a remarkable manner, and renders it brittle when cold. Phosphuretted ores may do for cast-iron, but never are fit to be rolled into good bar-iron. COMPOUNDS OF IRON WITH ARSENIC. 792. Arsenic readily combines with iron in a great number of proportions, forming in all cases very brittle compounds, several of which are found crystallized in nature. The mineral called mispickel is a compound of iron with arsenic and sulphur, of the formula FeS a -fFeAs a , while its crystalline form is that of a right prism with a rhombic base. COMPOUNDS OF IRON WITH CHLORINE. 793. Two combinations of iron with chlorine, corresponding to the protoxide and sesquioxide, are known. ProtoMoride of Iron FeCl. 794. This compound is obtained when iron filings are heated with chlorine, care being taken that the latter is not in excess, as otherwise sesquichloride would be formed. It is obtained with greater certainty in a state of purity by heating iron in a current of chlorohydric acid gas. Protochloride of iron forms a brown fluid mass, which crystal- lizes on cooling : it is prepared in solution in water, by heating iron filings with chlorohydric acid and evaporating the liquid, when green crystals of the formula FeCl+6HO are obtained. Sesquichloride of Iron Fe a Cl 3 . 795. Sesquichloride or chloride of iron is prepared by heating iron in a current of chlorine, and volatilizing the product in this gas, when beautiful rainbow-like spangles of a brown or deep green colour are obtained. The chloride dissolves in water, yielding a yellow solution, which can be immediately obtained by treating iron with aqua regia. The solutions of sesquichloride of iron in alcohol and in ether lose their colour and precipitate protochloride of iron when exposed to the solar light. Sesquichloride of iron is decomposed by steam at a red-heat, VOL. II. E 4 50 IRON. when chlorohydric acid is disengaged, and on the sides of the tube in which the experiment is made small glittering spangles of ses- quioxide of iron are deposited, resembling the specular oxide found in the fissures of volcanic lavas. This mineral has been supposed to have been formed in a similar manner. COMPOUNDS OF IRON WITH CYANOGEN. 796. Iron forms several compounds with cyanogen, particu- larly remarkable for their multiple combinations. If cyanide of potassium be added to a solution of a protosalt of iron, protocyanide of iron is obtained as a white precipitate, which retains with great energy a portion of the reagent which served to produce it. It is obtained in greater purity by treating Prussian blue with sulfhydric acid, when a white precipitate, which soon changes to blue in the air, is formed. Cyanide of iron combines with a great number of other metallic cyanides, producing double cyanides, which, besides being of great technical importance, are much used in the laboratory as reagents. In these compounds the iron has lost its habitual characteristic properties, being no longer precipitated by the reagents which usually throw it down from its saline solutions or from the chlo- rides. The characteristic properties of the simple cyanides are also modified in such double salts, for which reason these com- pounds have been considered, not as real double cyanides, but as combinations of the metal with a compound electro-negative body, called ferro-cyanogen. Double Cyanide of Iron and Potassium, or Ferrocyanide of Potas- sium FeCy+2KCy. 797. This double cyanide, which is also called prussiate of pot- ash, is the most important of these compounds, and is brought into commerce in the form of beautiful yellow crystals, of the formula FeCy+2KCy+3HO. It contains 12.8 per cent, of water, which it readily loses on a slight elevation of temperature : 100 parts of water dissolve 25 parts of the salt at ordinary temperature, and 50 parts at the boiling point. This double cyanide is very fixed, being neither decomposable by the alkalis nor even the alkaline sulfhydrates ; while the action of heat destroys the salt and evolves nitrogen, when the residue, treated with water, yields a solution of cyanide of potassium and an insoluble black substance, which is a true car- buret of iron, of the formula FeC 3 . This salt is prepared on a large scale by fusing carbonate of potassa with animal charcoal, which must be prepared expressly from animal matter containing but few phosphates. Calcined bone, dried flesh, skins, and principally old shoes are used for its PRUSSIATE OF POTASH. 51 preparation : these substances leave a carbonaceous residue, highly charged with nitrogen, which is afterward heated with about its own weight of carbonate of potassa, in large cast-iron kettles into which the smoky flame of a reverberatory furnace enters. The carbonate of potassa is first fused alone, and then the animal charcoal is added, when a reaction takes place accompanied with effervescence, and the mass is continually stirred with iron rods. Cyanide of potassium and cyanide of iron are formed, the iron being furnished by the sides of the kettle and the rods ; and when the reaction is ended, the matter is removed and treated with boiling water. The hot solution is filtered, and evaporated to crystallization ; while the mother liquid, on being again concen- trated, still yields crystals, which, with the former ones, are puri- fied by dissolving them in boiling water and allowing the liquid to cool slowly. Within a few years, cyanide of potassium has been prepared by the direct combination of carbon with nitrogen, in the presence of carbonate of potassa; and this process is now applied to the manufacture of prussiate of potash on a large scale. Wood char- coal, impregnated with a concentrated solution of carbonate of potassa, is heated to a high temperature in brick vent-holes, in a current of hot air which has been deprived of its oxygen by pass- ing over a long column of burning coke, From time to time the portion of potashed charcoal at the lower part of the holes is with- drawn, and additional charcoal is introduced through the upper opening to keep the supply constant. The alkaline charcoal, in this operation, is exposed for 10 hours to the action of nitrogen, and then is heated in an iron boiler, with water and finely pow- dered sparry iron. The liquid yields when evaporated beautiful crystals of very pure prussiate of potash, while the residue of the charcoal is again soaked in a concentrated solution of carbonate of potassa and the operation recommenced. The solution of prussiate of potash, added to the solutions of a great number of metallic salts, affords precipitates which are often remarkable for their brilliant colours, and serve as distinguish- ing characters of the metals. In these double decompositions, the cyanide of potassium alone is decomposed, by being changed into a cyanide of the metal which exists in the reacting solution, while this new cyanide combines with the cyanide of iron. If prussiate of potash FeCy+2KCy be added to a solution of sulphate of copper CuO,S0 3 , a characteristic reddish-brown precipitate, of the for- mula FeCy+2CuCy, is obtained. The prussiate, poured into a solution of sulphate of zinc ZnO,S0 3 , gives a white precipitate FeCy+2ZnCy. A series of compounds of similar formulae, all of which contain protocyanide of iron, is thus obtained. The formula of the precipitate obtained with a salt of lead is FeCy+2PbCy, which, by treatment with sulfhydric acid, forms an 52 IRON. insoluble sulphide, and an acid liquid which yields white crystals when evaporated under cover near a saucer filled with concentrated sulphuric acid. These crystals are formed by a real hydracid FeCy-f 2HCy, called ferro-hydrocyanic acid, or hydrocyano-ferric acid, or ferro-cyanhydric acid, the solution of which is inodorous and posseses none of the properties of hydrocyanic acid. The double cyanides may therefore be regarded as ferrocyanides. Prussiate of potash yields a white precipitate with protosalts of iron, composed for the greater part of protocyanide of iron, but always retaining a certain quantity of alkaline cyanide. This pre- cipitate soon changes in the air. With the salts of peroxide of iron, prussiate of potash gives a beautiful blue precipitate, called Prussian blue, which is used in dyeing and in oil-painting. The following reaction ensues between perchloride of iron and prussiate of potash : 2Fe 3 Cl 3 +3(FeCy+2KCy)=6KCl-f(3FeCy-f2Fe 3 Cy 3 ). The formula of Prussian blue is 3FeCy-f 2Fe 3 Cy 3 . 798. If a current of chlorine be passed through a solution of prussiate of potash and the liquid boiled, a green precipitate is formed, which, when heated with chlorohydric acid, gives off a cer- tain quantity of mixed oxides of iron, and leaves a green residue, of the formula FeCy+Fe 3 Cy 3 -f4HO. It is a compound resembling magnetic oxide, if the water of combination be overlooked. 799. If the current of chlorine be stopped at the moment when the solution no longer throws down a blue precipitate of sesquisalts of iron, a liquid, yielding beautiful red crystals on evaporation, is obtained. It is important not to prolong the action of the chlorine too much, and to keep the liquid constantly agitated. The solu- tion is frequently tested with a sesquisalt of iron, and the current of chlorine is arrested as soon as a precipitate is no longer formed. It is also well to neutralize the liquid gradually with a little potassa. The red salt, which has been called cyanoferride or ferricyanide of potassium, has the formula 3KCy+Fe 3 Cy 3 ; and contains no water of crystallization. The reaction from which it originates is the following: 2(FeCy+2KCy)-fCl=(3KCy+Fe a Cy 3 )+KCl. The red prussiate is much less soluble than the yellow, 38 parts of cold water being required to dissolve 1 part of it. Protosalts of iron yield with red prussiate of potash a beautiful blue precipi- tate of the formula 3FeCy+Fe 3 Cy 3 , the reaction being as follows : (3KCy-fFe 3 Cy 3 )-f3(FeO,S0 3 )=3(KO,S0 3 ) + (3FeCy+Fe 2 Cy 3 ). Red prussiate of potash yields with salts of lead a precipitate 3PbCy-hFe 3 Cy 3 , which gives, when treated with sulphuric acid, a precipitate of sulphate of lead and a compound 3HCy-f Fe a Cy 3 , CAST-IRON. 53 called hydro-ferricyanic acid, which dissolves with a red colour. The solution, when evaporated, deposits the salt in yellowish- brown crystals. COMPOUNDS OF IRON WITH CARBON. 800. Iron combines with carbon when in presence of this sub- stance, at a very high temperature. It has been shown ( 795) that a carburet of iron FeC 3 is obtained by decomposing prussiate of potash by heat : by the direct combination of iron with carbon, compounds so rich in carbon are never obtained, as the most car- buretted products only contain about 5 per cent, of carbon, their composition resembling the formula Fe 4 C. These carburetted irons are called cast-iron, which is again divided into white cast- iron and gray cast-iron. Iron, heated in blast-furnaces at a very high temperature in contact with charcoal, passes into the state of cast-iron, which, by cooling suddenly on leaving the furnace, forms hard and brittle metallic masses, whiter than the soft iron, and consisting of white cast-iron. If, on the contrary, the iron be cooled slowly, the carbon which was in combination with the iron separates by crys- tallization, forming an infinite number of small black graphitose spangles, which impart a deep gray colour to the mass. The small spangles of carbon are scattered through the iron, the greater part of which is decarburetted, and such iron, which is called gray or soft cast-iron, is much more malleable than the white sort, and can be cut with a file. All kinds of cast-iron do not lose their combined carbon with equal readiness ; when the iron-ore contained phosphorus or sulphur, the metal retains the character of white cast-iron, even after a very slow cooling. Certain kinds of cast-iron, which contain manganese in combination, possess also the property of retaining their com- bined carbon, and present, after cooling, a crystalline fracture, with very large brilliant laminae, which intersect each other at angles of 120 ; hence the crystalline form is inferred to be a regular hexahedral prism. This iron is called lamellar cast-iron, and is obtained from the manganiferous sparry ores ( 782). When white cast-iron is treated with chlorohydric acid or dilute sulphuric acid, the metal dissolves with evolution of hydrogen gas, but at the same time a volatile oil of a nauseous smell is generated, resulting from the combination of the hydrogen with carbon in the nascent state. If, on the contrary, gray cast-iron is dissolved, a certain quantity of this oil is produced, by the combination of hy- drogen with the portion of carbon which was in combination with the iron, while the free carbon remains in the form of small crys- talline spangles. Cast-iron, under certain circumstances, assumes an intermediate E2 54 IRON. state between the gray and white, when, the separation of graphite not taking place throughout the whole mass, but only in some por- tions, the substance presents the appearance of white cast-iron, more or less spotted with gray. This kind is called spotted or mottled cast-iron, (fonte truitee.) COMPOUND OF IRON WITH SILICIUM. 801. A compound of iron with silicium is obtained by heating in a crucible covered with damp charcoal a mixture of iron filings, silicic acid, and charcoal, in a forge-fire, when a fused metallic lump, possessing a certain degree of malleability, is formed. Iron can combine, in this case, with 9 or 10 per cent, of silicium. Cast-iron, particularly that made in blast-furnaces at very high temperatures with coke, generally contains 1 or 2 hundredths of silicium. DETERMINATION OF IRON, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. 802. In chemical analyses iron is nearly always determined in the state of sesquioxide, and when it exists as such in its solutions is precipitated by ammonia or carbonate of ammonia. It is best to make the precipitation in a hot liquid, as the hydrated sesquioxide is then less gelatinous and more easily washed on the filter. When the iron exists in the state of protoxide, it must be converted into sesquioxide by evaporating the liquid with nitric acid, or by passing a current of chlorine through it ; in which latter case the excess of chlorine must be driven off by boiling. Sesquioxide of iron is then precipitated by ammonia. The superoxidation of the iron may also be affected by adding chlorohydric acid, and then a small quantity of chlorate of potassa, to the liquid, when, by boiling, the chlorohydric acid and chlorate of potassa mutually decompose each other, while chlorine is set free, which produces the superoxida- tion of the iron. Frequently it is preferable to precipitate sesqui- oxide of iron by succinate of ammonia, which throws it down more completely than ammonia, as an excess of this last reagent may redissolve a small quantity. The precipitate of sesquisuccinate of iron is decomposed by heat, leaving pure peroxide of iron. In some cases, sesquioxide of iron must be precipitated with caustic potassa in excess ; but the precipitate then retains a small quantity of potassa with great obstinacy, and is freed from it only by boiling several times with distilled water. When the precipi- tate is copious, it is better, after having collected it on the filter and washed it with a small quantity of hot water, to redissolve it in weak chlorohydric acid, saturate the liquid by ammonia, and precipitate again with succinate of ammonia. When the solution contains organic substances, such as sugar, tartaric acid, etc., ammonia no longer precipitates sesquioxide of iron, nor does even carbonate of ammonia; and the iron must then DETERMINATION OF IRON. 55 be precipitated as sulphide by sulf hydrate of ammonia. The pre- cipitate is collected on a filter, and washed with water, to which a small quantity of sulfhydrate of ammonia is added, in order to prevent the sulphide of iron from being converted into sulphate by contact with the air ; after which the precipitate is redissolved in chlorohydric acid, the iron brought to the state of peroxide, either by means of chlorine or by evaporating the solution with a small quantity of nitric acid, and the sesquioxide formed is then precipi- tated by succinate of ammonia. 803. In order to separate the alkaline metals, ammonia or succinate of ammonia is used after the iron has been brought to the state of sesquioxide. It is separated from the alkalino-earthy metals by the same reagents, care being taken at the same time that the ammonia contains no carbonate, or cannot absorb carbonic acid from the air, as the carbonate of ammonia formed would cause the precipitation of the earths. When iron is to be separated from magnesia, a quantity of sal ammoniac sufficient to prevent the magnesia from being precipitated by an excess of ammonia must be added to the liquid ; but the latter, most frequently, already contains free acid enough to produce the quantity of ammoniacal salt necessary during its saturation by ammonia. In order to separate iron from alumina, the iron is first brought to the state of sesquioxide, if it does not already exist in that state, and then an excess of caustic potassa is added ; when, by boiling the liquid for some time, all the alumina dissolves in the potash, leaving only the sesquioxide of iron as a precipitate. The filtered alkaline liquid is then supersaturated with chlorohydric acid, and the alumina precipitated by an excess of carbonate of ammonia. The separation of iron and manganese is easily eifected when the iron exists as sesquioxide, and we have seen that it can always be readily brought to that state. The manganese, moreover, is always present as a protosalt ; for the other salts of manganese, not being very fixed, are soon converted by ebullition into proto- salts. The same process as described for the separation of sesqui- oxide of iron from magnesia is adopted ; that is, a quantity of ammoniacal salt sufficient to prevent the precipitation of the oxide of manganese is added to the liquid : generally, however, the am- monia necessary to saturate the acid liquid is sufficient to produce the ammoniacal salt required. The sesquioxide of iron is then precipitated by ammonia or succinate of ammonia, and the man- ganese is obtained from the filtered liquid by sulfhydrate of am- monia as sulphide. When a solution of a sesquisalt of iron is precipitated by ammo- nia or carbonate of soda, changes of colour are observed, which may guide the operator in the separation of the iron, and allow the iron and other metals which exist in the liquid to be successively pre- cipitated. The sesquisalts of iron, dissolved in an acid liquid, are 56 IRON. of a very pale yellow colour, and when ammonia or carbonate of soda are added by small quantities at a time, the liquid becomes more and more deeply coloured as it approaches saturation, and at last assumes a deep brown colour before any deposit is formed. If it is then subjected to ebullition, the peroxide of iron is com- pletely precipitated : the liquid is bleached, retaining still all the oxides of the formula RO in solution, which are much more power- ful bases than sesquioxide of iron, and, in general, than the oxides of the formula R 3 3 . In order to make the separation properly, the liquid is first heated to boiling, and the ammonia or carbonate of soda then added, stirring it continually, and discontinuing when the liquid has turned brown. It is then boiled for some time, when a brown precipitate of hydrated sesquioxide of iron is generally formed. If the liquid is not discoloured, a few drops of the reagent are added, it is again boiled, and this is continued until discolora- tion takes place. It is then filtered while boiling, and a consider- able quantity of carbonate of soda is added to effect the precipita- tion of the other metallic oxides which exist in the solution. There is, therefore, a considerable interval between the moment of the complete precipitation of the oxides of the formula R S 3 and that of the commencement of the precipitation of the oxides RO. In this way, sesquioxide of iron may be separated with a con- siderable degree of accuracy from all protoxide with which it is mixed in the liquid ; but the admission of air must be avoided as much as possible, as its oxygen would convert a portion of the protoxide into sesquioxide. It is often necessary, in the analysis of mineral substances, to determine the relative proportions of the sesquioxide and protoxide of iron they contain, which can be done exactly when the mineral dissolves readily in non-oxidizing acids, such as chlorohydric. The material is finely powdered, and treated in a small flask with hot concentrated chlorohydric acid, the liquid being continually boiled, in order that the steam disengaged may prevent the admission of air into the flask ; and the boiling is con- tinued until the greater part of the acid in excess is evaporated. It is then treated with boiling water, and the sesquioxide preci- pitated by carbonate of soda, added by drops, avoiding as much as possible the contact of the air. When the liquid is deprived of colour, it is allowed to rest for some time in the flask, which is corked : the clear liquid is decanted, collected rapidly on a filter, and washed with boiling water. The filtrate contains the prot- oxide of iron, which is brought to the state of sesquioxide by means of chlorine, and precipitated by an excess of carbonate of soda. 804. It is, however, difficult to prevent a portion of the prot- oxide of iron from changing into sesquioxide by absorption of the oxygen of the air. Greater exactness is obtained by another process, which may be applied to various other cases. If a solu- DETERMINATION OF IRON. 57 tion of permanganate of potassa be added to a solution of a proto- salt of iron, the permanganate immediately loses its colour, by being decomposed into protoxide of manganese and potassa, which base combines with the acid, and into oxygen, which converts the protoxide of iron into sesquioxide.* The discolouration of the permanganate of potassa takes place as long as any protoxide of iron remains in the liquid ; but as soon as all the protoxide is changed into sesquioxide, the smallest drop of the solution of permanganate of potassa gives the liquid a very decided red tinge. If the solu- tion of permanganate of potassa is of standard quality, it suffices to measure exactly the quantity necessary to produce a permanent red colour, and the quantity of iron which existed in the state of protoxide can thence be directly inferred. The permanganate of potassa used to make the standard solu- tion is prepared by heating, for two hours, in an earthen crucible, a mixture of 2 parts of binoxide of manganese, 3 parts of caustic potassa, and 1 part of chlorate of potassa. f The mass is broken to pieces after cooling, treated with 3 or 4 times its weight of water, and the liquid filtered through asbestus or powdered glass, to sepa- rate the sesquioxide of manganese. Weak nitric acid is then added until the liquid assumes a beautiful violet-red colour. The solution is preserved in a well-corked bottle, as it would be soon changed by the particles of organic dust floating in the air.J In order to determine the standard of the solution, 1 gramme of highly-polished piano-forte wire, exactly weighed, is dissolved in 25 cubic centimetres of chlorohydric acid, and the liquid diluted with water recently boiled, so as to increase its volume to about 1 litre. Again, 100 divisions of the solution of permanganate of * The solution must necessarily contain free acid enough to dissolve the oxide of manganese formed. W. L. F. f Another proportion, given by Gregory, is as follows : 8 parts of peroxide of manganese, 10 parts of caustic potassa, and 3 parts of chlorate of potash. But the best method, as the only one by which permanganate of potassa can be ob- tained in crystals and free from chloric acid, according to Liebig, is by igniting pure peroxide of manganese with a fixed alkali, with access of air. W. L. F. J The use of permanganate of potassa as a means of determining iron in any case has been objected to by many chemists, on the ground that a standard solu- tion would not keep uniform for any length of time. This objection is unfounded ; for a solution made by dissolving crystals of the salt remained perfectly unaltered for a period of six months, during which time it was often tested. The solution must, however, be kept in a bottle with a tight-fitting ground-glass stopper, and the bottle ought always to be kept as full as possible. The manganate should be converted into permanganate, rather by adding a quantity of boiling water to its concentrated solution than by introducing nitric acid. W. L. F. \ As not even piano-forte wires consist of pure iron, it is better to employ a protosalt at once : of these the protosulphate of iron and ammonia is most com- mendable, as being least of all subject to decomposition, and easy to prepare. Of this salt, 6.429 gm., which correspond exactly to 1 gm. of metallic iron, are dis- solved, and the solution having been made acid, the permanganate may be imme- diately added. W. L. F. IRON. potassa are introduced into a graduated alkalimeter (fig. 477), and poured from it into the vessel B (fig. 478), which contains the protochloride of iron, stirring constantly to facilitate the mixture. The solution of the permanganate is added, by small quantities at a time, until the liquid as- sumes a permanent roseate tinge. The number of divi- sions and fractions of a division necessary to produce this result are noted down : supposing this number to be 75.5 div., the conclusion will follow that 75.5 div. of the solution of Fig. 477. permanganate correspond to 1 gramme of protoxide of iron, and consequently that 1 div. of permanganate corresponds to 0.01325 gr. of metallic iron.* This being done, in order to analyze a substance containing protoxide and sesquioxide of iron at the Fig. 478. same time, 1 gramme of it is dissolved in chlorohydric acid, the liquid is diluted with boiled water until it oc- cupies the volume of about 1 litre, and then the standard solution of permanganate of potassa is carefully added until the liquid assumes a roseate tinge. Let us suppose that to produce this effect, 22.0 div. of the solution of the permanganate were required ; the gramme of the substance subjected to analysis will then con- tain 22.0x0.01324 gr., or 0.291 gr. of iron, existing in the state of protoxide, or, lastly, 0.374 gr. of protoxide of iron. The quantity of sesquioxide can readily be determined by the same process : 1 gramme of the substance is again dissolved in concentrated chlorohydric acid, and then 4 grammes of sulphite of soda, dissolved in a small quantity of water, are poured into the solution gradually and by small quantities. The sulphurous acid which is set free by the reaction of the chlorohydric acid on the alkaline sulphite converts the perchloride of iron into protochlo- ride, so that all the iron in the substance then exists in the solu- tion as protochloride. The liquid is boiled to drive off the excess of sulphurous acid, diluted with water to about the volume of 1 litre, and the standard solution of permanganate is added. Sup- posing that it was necessary to add 36.0 div. of the alkalimeter, in order to obtain a permanent rose-colour, the conclusion follows that the substance contains 36.0x0.01324 gr., or 0.477 of metallic iron. Now, as it has been already found to contain 0.291 of iron in the state of protoxide, there are 0.186 gr. present in a more highly oxidized state, corresponding to 0.266 gr. of sesquioxide. * The result will be the more exact the more dilute a solution of permanga- nate of potassa is employed, and the accuracy of the determination may, in fact, be carried to almost any degree. W. L. F. METALLURGY OF IRON. 59 METALLURGY OF IRON. 805. The only ores of iron employed are the oxides and the carbonate ; while the sulphides, although very abundant in nature, are not used for the extraction of iron, as the process would be too expensive, and, besides, a metal of inferior quality would be ob- tained. The principal ores which are worked are 1. The magnetic oxide, found in considerable masses in the old rocks, principally in the micaceous schists,* in which well-defined octahedral crystals are often found scattered, is generally a very rich ore, affording iron of excellent quality : the greater portion of Swedish iron is procured from it. 2. The anhydrous peroxide of iron, which is found in some transition rocks, and in the secondary rocks, in large masses, re- sembling sometimes real strata. The oxide, in this case, is amor- phous, and is called red hematite. It also constitutes veins in the old rocks, as at Framont, in the Vosges. This ore is used in many of the foundries in the north of Germany. Specular iron is generally found in veins, but rarely in suffi- cient quantity for foundry use. It also forms considerable masses in the old rocks, a most remarkable example of which is the de- posit in the island of Elba.f 3. Hydrated peroxide of iron, which is found in the transition rocks, or at the junction of the transition and secondary rocks, in the form of concrete brown masses, when it is called brown hema- tite. In France, the foundries in the Pyrenees use this ore. 4. Hydrated peroxide of iron, which is also found in small con- crete grains, and is called granular iron ore. It forms deposits A (fig. 479) at the time of separa- tion of certain strata of the Jurassic rocks, but more fre- quently in the middle tertiary Fio . 479 ~ rocks, covering the layers of Jurassic limestone and chalk. The size of the grains varies from that of a pea to that of a millet- seed. The majority of the foundries in the middle of France, and in Champagne and Berry, smelt this ore. An ore is also found in certain stages of the Jurassic rocks, con- sisting of small grains of hydrated peroxide of iron, adhering * A mistake has here crept into the text ; magnetic oxide being seldom or never found in micaceous schists, but occurring in abundance in talcose and chloritic schists, and in serpentine ; while the largest masses of it are found in various igneous rocks of a more recent origin, especially in basalt and dolerite. f At the Serra da Piedade and the Pico da Itabira, both in Brazil, specular iron occurs in such quantity as to form a peculiar species of rock, called itabirite, of a dense and slaty character. W. L. F. 60 IRON. firmly to each other, and forming real strata ; and this ore, from its resemblance to the eggs of fish, is called oolithic ore. 5. Sparry iron, or crystallized protocarbonate, sometimes mixed with considerable proportions of carbonate of manganese, which is found in veins in the old and transition rocks. It sometimes also accompanies the brown hematites which are met with at the line of separation of the old and transition rocks. This ore, smelted with charcoal, yields laminated cast-iron, which is used for manufacturing steel. 6. In the argillaceous strata of the coal-fields, flattened nodules of carbonate of iron, mixed with clay, are frequently found, and are sometimes very rich in iron, constituting an ore the more valuable because it is found in the midst of fuel, and is easily ex- tracted. This ore is very abundant in England. 7. Lastly, an iron-ore is found in some low places, immediately beneath the soil, consisting of hydrated peroxide, mixed with phosphate. This ore yields phosphorous cast-iron, the use of which is limited. It is called bog ore. Iron is sometimes found in the native state, forming often very large compact masses, which are never in place, but have fallen from space as aerolites. This iron, which is never pure, being always more or less mixed with nickel, is often scattered through a grayish stone, the surface of which appears to have undergone an incipient fusion. These masses are called meteoric stones, aerolites, or meteor olites. Probably, a great number of such meteors circulate in space, influenced by the same forces which maintain the planets in their orbit, and fall to the surface of the earth when, by virtue of their motion, they approach near enough to this planet to be acted on by the attraction of the lat- ter. Sometimes meteoric iron possesses all the qualities of mal- leable iron, and cutting-instruments even have, for sake of curiosity, been made of it. 806. Iron ores are never subjected to any complicated prelimi- nary operations. The granular ores are generally held together by a clay, very poor in oxide of iron, and easily removed by wash- ing ( 735). Other ores often require a preliminary roasting, which renders their smelting more easy, by driving off the water, and carbonic acid, if the ore is carbonated, and acting especially by disagregat- ing the ore, and rendering it porous and more friable. 807. We have seen ( 766) that the oxides of iron are very easily reduced when heated in a current of hydrogen : their reduc- tion is also effected under the same circumstances by carbonic oxide gas. It may hence be supposed that the reduction of oxide of iron in ores is not very difficult ; but then the metallic iron formed is still intimately mixed with the gangue, which prevents its particles from uniting together. If the gangue were very METALLURGY OF IRON. 61 fusible, it would be sufficient to heat the ore to a degree sufficient to fuse the former, and by then hammering this metallic sponge, the particles of iron would unite together, while the gangue would be pressed out in the form of scoriae. But, if the gangue fuses with difficulty, it would melt only at the temperature at which the iron, in contact with charcoal, is converted into cast-iron, and we should no longer obtain malleable, but cast-iron. Now, the ordi- nary gangue of iron-ore being quartz or clay, which are two nearly infusible substances, two processes are adopted to fuse them. If soft iron is to be obtained immediately from very rich ores, the latter are heated with charcoal, when the gangue, combining with a portion of the unreduced oxide of iron, forms a very fusible double silicate of alumina and protoxide of iron. A very high temperature, therefore, is not required ; the iron does not pass into the state of cast-iron, and it suffices to hammer the spongy metal to unite it together and press out the scoriae. But a quantity of oxide of iron, proportioned to the quantity of gangue in the ore, is necessarily lost, for which reason this process can only be adopted in the case of very rich ores. If, on the contrary, the iron is to be extracted completely from the ore, the silicate of alumina must be made fusible by giving it another base than oxide of iron. The only base which can be economically substituted is lime ; but as the double silicate of alu- mina and lime is much less fusible than that of alumina and iron, a high temperature is required, and the iron passes into the state of cast-iron, which liquifies at the same time with a double silicate, or slag. As may be seen, the results of these two methods are very dif- ferent. The first is used only in a few places, as it requires rich and very pure ores, and consumes an immense quantity of fuel. It is adopted in the Pyrenees, arid known as the Catalan method. TREATMENT OF IRON-ORE BY THE CATALAN METHOD. 808. The Catalan forge consists of a crucible, or hearth^ made by a quadrangular cavity U (figs. 480 and 481), of about 0.7 m. in depth, and supported by one of the walls of the forge. The crucible is built in solid mason-work of dry stones, fastened together with clay. The part of the mason-work occupied by the crucible does not rest immediately on the ground, but on several small arches, which prevent the dampness from penetrating the crucible and deranging the hearth. Above the arches is a layer of scoriae and clay, covered by a granite slab, which forms the bottom, or the floor of the hearth. The four lateral faces of the crucible rise above the bottom stone. VOL. II. F 62 IRON. The front face h is called the chio, or floss- hole. The opposite face i is called the cave. The left one R is called the porges. Lastly, the right face I is called the ore or contrevent. The face of the chio, which presents a ver- tical surface of about 0.65 m., is formed by three pieces of iron placed end to end, the two extreme ones of which are called latai- roles ; that in the middle, the restanque, serves as a point d'appui for the levers, or fire-irons, with which the workmen raise the mass of iron formed during the process. The left face, the porges, is vertical, and composed of pieces of iron t, f, t (fig. 483) laid endwise upon each other. The right face, the ore or contrevent, is composed of pieces of iron s, *, s (fig. 483), which are wedge-shaped, and slightly in- clined, being so arranged that their sur- face forms a curve. The cave z, which consists wholly of ma- son-work, fast- ened with clay, is slightly in- clined outward to 5 or 8. Fig. 481. which conveys the blast into the furnace, rests on the upper piece of the porges, and is made of a conical piece of copper, the edges of which are merely brought together without soldering. The position of the twyer exerts great influence over the operation : its inclination varies from 35 to 40. The wind is conveyed from the bellows into the twyer through a copper nozzle T, fastened to the wind-trunk G of the bellows by a leather tube. METALLURGY OF IRON. 63 The depth of the Catalan furnace is about 0.7m. Its average width, from the chio to the cave 0.6 Its average width, from the porges to the lower part of the contrevent 0.7 Its average width, from the porges to the upper part of the contrevent 1.0 The bellows of the Catalan forges of Aridge is called a trumpet, (trompe,) and is composed of 1st. An upper basin A (fig. 481), fed by spring-water. 2d. Two pipes B, of about 6 metres in height, formed by trees hollowed out, and crossing the bottom of the basin A. 3d. A lower box C, having two openings, one at D below, the other above at E, to which is fitted a tube EF, terminated by the wind-trunk Gr. The upper opening of the tubes B is contracted by the boards a a which are supported by bars. The aperture formed by the lower part of the boards is called the etranguillon, on a level with which the sides of the tubes are pierced with inclined holes c c, called breathing-holes, (aspirateurs.) Lastly, the tubes enter the upper wall of the box C, and open at a small distance above a bench d. The water of the upper basin A, passing through the etranguil- lon into the vertical pipes B, carries with it the external air, which in this way passes through the openings c c. The water breaking over the bench escapes through the lower orifice D, while the air passes out by the nozzle Gr. The position of the boards forming the etranguillon is regulated by wooden wedges g, which, being fixed to the end of a jointed lever, which a man works by a chain at the bottom of the forge, is elevated or depressed in order to obtain the quantity of air necessary for the various stages of the operation. The beetle, or tilt-hammer, used in forging iron, represented in fig. 482, consists of a cast-iron face P, weighing about 600 kilogs., mounted on a helve of beech-wood, and secured by iron bands, while the gudgeons on which the hammer turns are fastened to a cast-iron piece H fixed to the helve. Fig. 482. 64 IRON. The hammer is raised by means of iron cams b, b, b on the water- wheel A. The iron anvil S is fastened by a tenon c to a piece of cast-iron r, which is itself solidly set by means of wooden wedges into a large block of wood, or a piece of granite, B. In order to accelerate the fall of the hammer, which should strike from 100 to 125 blows per minute, a stone on which the heel strikes is placed under the latter. 809. These general arrangements of the forge being understood, let us now examine it in operation. We shall suppose that the mass or stack of the preceding opera- tion has been removed from the furnace to be forged under the hammer ; and that the workmen are therefore occupied in getting up the fire for another smelting. For this purpose they withdraw from the hearth the hot coals which are still there, detach from the bottom and sides the adhering slag, and return the hot coals to the hearth, which is thus filled as high as the twyer. A work- man divides the hearth into two parts, by a shovel which he places vertically and parallel to the porges, so that the division between the shovel and the porges shall be double of that between the former and the contrevent. Other workmen heap charcoal in the division between the shovel and the porges, and ore, broken to the size of a walnut, between the shovel and the contrevent. The shovel is gradually raised, as the space below is filled, and a wall of ore is thus formed rising to about 0.2m. above the contrevent. The ore is spread so as to form a saddle- back dfff (fig. 483), of which the edge / rests on the one side against the cave, and on the other on the bench of the chio. The surface fg is covered by a layer of brasque, (damp char- coal,) well heaped up, while the space M, comprised between the wall of ore and the furnace, is filled with charcoal. The furnacebeing thus charged, the blast is admitted, at first slowly, and then its force is in- creased. The ore is thus gradu- ally reduced ; while the workmen take advantage of this period to forge into bars the stack of the preceding operation, which they have divided into four parts, as we shall presently see. To do this, they heat these masses of iron in the furnace, by placing them in the middle of the burning char- METALLURGY OF IRON. 65 coal in the space M above the twyer. When they are sufficiently heated, they are removed and forged. As the charcoal diminishes, fresh fuel is added, and small ore, called greillade) which is made by the breaking of the ore as it comes from the mine, is thrown in, being slightly moistened with water, to prevent it from falling too easily between the interstices of the charcoal. Influenced by the wind projected through the twyer, the char- coal burns to carbonic acid in the space near the twyer, while farther off the carbonic acid is reduced, by the charcoal in excess, into carbonic oxide gas, the greater part of which, being obliged to pass through the highly heated ore, reduces the oxide of iron to the state of metallic iron. But the whole of the oxide is not re- duced, as a portion, remaining in the state of protoxide, combines with the gangue of the ore, forming a very fusible compound sili- cate, a large portion of which runs off and collects in the bottom of the hearth, whence it is removed by a small opening in the chio. In two hours, the greillade which falls with the fuel has depo- sited a certain quantity of iron at the bottom of the hearth, and the workman then commences the formation of the mass. He increases the draught of air, and, by carefully introducing a bar between the ore and the contrevent, draws that ore which seems more advanced near to the twyer, and adds at the same time an- other charge of charcoal and greillade. Five hours after the commencement of the operation the ore has entirely fallen into the hearth, and the workman endeavours to unite the various fragments of spongy iron. During the last hour of the process, the workmen break the ore under the forge-hammer, and then sift it, in order to separate the pulverulent material constituting the greillade, of which we have spoken. They then remove the mass from the furnace and carry it to the hammer, where the liquid scoriae are pressed out, and the spongy iron is rendered more compact. The mass is then, by means of a long iron wedge, divided into two equal parts, called massoques, which are hammered into long parallelopipedons, and again cut into two equal parts. Four pieces of iron, called massoquettes are thus obtained, which are rolled into bars in the first stage of the suc- ceeding operation. A smelting by the Catalan method generally lasts 6 hours, pro- ducing 140 to 150 kilogs. of merchantable iron, from 470 kilogs. of ore and about 500 kilogs. of charcoal. The direct extraction of iron in the state of ductile metal is now performed only in the Pyrenees, Corsica, and a few provinces of Spain, the greater portion of iron being obtained by means of blast- furnaces, in which the metal is separated from its ores, as perfectly as possible, by using a very high temperature, at which the iron 66 IRON. combines with a certain quantity of carbon, forming a much more fusible compound than ductile iron. TREATMENT OP IRON-ORES IN THE BLAST-FURNACE. 810. The blast-furnace (fig. 484) is composed of two truncated cones C, B, united at their bases. The upper cone C, called the belly, (cuve,) is made of an inner lining ii f of refractory bricks, sur- rounded by a stratum of scoriae, or broken slag, which separates it from a second brick lining II' 9 built against an outer wall pp', qq r of cut stone or common brick, constituting the main part of the blast-furnace. The upper opening G of the belly is called the Fig. 484. tunnel-head, (gueulard,) and is surmounted by a chimney F, having one or several doors, through which the charges are introduced. The lower cone B, called the boshes, (etalages,) is generally made of quartzose stones difficult of fusion, and which must be very METALLURGY OP IRON. 67 carefully selected, as on them the duration of the furnace greatly depends. In some furnaces the boshes are made of refractory bricks. They are sometimes joined to the belly by a cylindrical union or curve A, in order to avoid a re-entering angle. Below the boshes is a prismatic space E, called the top of the hearth, made of refractory stones, (fire-stone.) Three of its sides descend to the bottom of the furnace, or the crucible D, while- the fourth t stops at a few decimetres above the bottom: this side, which is called the tymp-plate, is supported by strong pieces of iron let into the side-walls of the hearth. The bottom of the hearth is formed of a quartzose stone, beneath which are openings to allow the air to circulate freely below the furnace ; and, in order to prevent the accumulation of water, which would cool the hearth, and even give rise to serious accidents, the main body of the blast-furnace is built on arched galleries II. Three of the walls of the crucible are merely prolongations of its sides, while the fourth is formed by a prismatic stone d, called dam-stone, and which is slightly in front of the tymp-plate; so that the anterior part of the hearth has an opening between the dam-stone and the tymp-plate. We shall call that part of the fur- nace on which the dam-stone and tymp-plate rest the anterior part; the opposite will therefore be the posterior part, and the other two the sides. The posterior part and two sides have lateral openings 0, called the tuyeres, or twyers, through which the pipes which convey air enter the furnace : these openings are on the same horizontal plane, a little above the lower edge of the tymp-plate. To assist the workmen, four niches, allowing them to approach the twyers and hearth, are made in the main body of the furnace, while lateral galleries B, permit them to walk more freely around the furnace and to examine the twyers. The arrangement of the twyers and the pipes which con- vey the air from the blast-machine is seen in fig. 485, which repre- sents a horizontal section of the furnace at the height of the twyers. Each wind-trunk has a register or valve, to regulate the quantity of air admitted. The blast-furnace is generally built, when practicable, against a hill (fig. 484), and strengthened by mason-work. A terrace is Fig. 485. made, at the height of the mouth, 68 IRON. on the sides or top of the hill, a bridge aa r communicating between this terrace and the platform pp f of the mouth. The terrace is reached by an inclined plane, to which the ore and fuel are con- veyed by machinery. The material is then transported in wagons on a railway to the platform pp f . The twyers of blast-furnaces are double conical tubes abed of cast-iron, or copper (fig. 486), and as their ends might melt, in con- sequence of the high temperature to which they are exposed, a current of cold water is continually circulated through them, which, being introduced through the small tube , runs off through the tube t f . The openings of the twy- ers advance as far as the inner wall of the hearth. The nozzle of the Fi 486 wind-tube B is disposed in the twyer, and communicates with the cast-iron tubes of the blowing-machine by a flexible leather tube A. The three twyers are on the same horizontal plane, but the axes of the two twyers on the sides of the hearth are not prolongations of each other, being separated by some centimetres, so that the two currents of air may not interfere with each other. 811. The blowing-machine of a blast-furnace consists of a large cast-iron cylinder A (fig. 487), in which works a cast-iron piston P, packed with tow or leather to render it air-tight. The cylinder is closed above and below, and on the upper lid is a stuning-box w, through which the piston passes. The lid has also two side-openings sli g htl J inclined toward the tap-hole g+ so that it acts like the floor of a hearth for the fused metal. The cupola-furnace is fed by a blowing-machine, which impels the air through two twyers, placed sometimes above each other, as in the furnace represented in fig. 490, and sometimes near each other in the same horizontal plane. The bottom of the furnace being first filled with charcoal and lighted wood, coke is thrown on, the air-blast admitted, and when the combustion is in active operation, the fuel and cast-iron are added in successive layers. The fused metal collects at the bot- toni of the furnace, and the smelting must be effected as rapidly as possible, in order that the cast-iron may not be changed in quality in passing before the twyer. When the cupola contains a sufficient quantity of fluid iron, it is tapped ; and if large objects are to be cast, the moulds are arranged near the furnace, the melted metal being run into them by rills communicating with the tap-hole. Sometimes, three or four cupola-furnaces are required to furnish the amount of fluid metal necessary. When small ob- jects are to be cast, the fused iron is received in vessels like that represented in fig. 489, and carried to the moulds in the different parts of the foundry. 82 IRON - As reverberator/ furnaces permit the remelting of a larger quan- tity of iron than cupola-furnaces, and consume less fuel, they are preferred for casting large pieces ; but in the former the cast-iron is subject to more alteration than in the cupola-furnaces, because it meets with a more oxidizing air, which deprives it of a portion of its carbon. It is essential that the air entering these furnaces should pass through a grate, so as to possess as feeble an oxidizing power as possible. Lastly, the fusion must be made rapidly ; for which reason the cast-iron is placed on the floor of the hearth only when the furnace is in full blast. All kinds of cast-iron cannot be moulded after a second fusion : they must be rich in carbon, so as to be able to lose a small quan- tity of it, without becoming too difficult of fusion. OF THE CONVERSION OF CAST-IRON INTO BAR-IRON. 826. In order to convert cast-iron into bar-iron, the carbon and silicium combined with it must be removed, which is effected by subjecting it to an oxidizing action, which changes the carbon into carbonic acid and the silicium into silicic acid, which latter, combining with the bases, principally with the oxide of iron, forms fusible silicates, which separate in the form of slag. When the cast-iron contains small quantities of sulphur and phosphorus, which is sometimes the case, these must also be separated during the refinery, as they injure the quality of bar-iron, and may even render it unfit for use. This separation is very difficult, and oc- casions considerable waste ; the presence of these two metalloids in cast-iron is therefore avoided as much as possible. If sulphur exists in the ores, it is separated almost completely by previous roasting ; but if it is furnished by the fuel, as happens when coke made from pit-coal is used, a large quantity of flux is required in the blast-furnace, in order that the slag may retain the sulphur in the state of sulphide of calcium. Cast-iron containing any con- siderable quantity of sulphur or phosphorus always yields iron of an inferior quality. When a blast-furnace only produces iron intended for refining, the smelting is generally so conducted that a white cast-iron, con- taining but little carbon, is obtained, which is effected by intro- ducing a great deal of ore, and forcing the air so as to cause a rapid descent of the materials ; but this can only be done with very pure ores and fuel, as otherwise an impure cast-iron, yielding iron of inferior quality, would be obtained. If cast-iron be kept, at a high temperature, in contact with the air, its surface becomes covered with oxide of iron, which reacts on the inner layer of the iron : the carbon of the cast-iron reduces the oxide of iron, and is disengaged in the state of carbonic oxide gas, while the silicium effects a similar reduction and produces silicic METALLURGY OF IRON. 83 acid, which, combining with a portion of the undecomposed oxide of iron, forms a fusible silicate, the composition of which varies ac- cording to the proportion of oxide of iron which enters into it ; but generally it assumes the formula 3FeO,Si0 3 . If, in fact, a more basic silicate, such as 6FeO,Si0 3 , be heated in contact with cast- iron, a portion of the oxide of iron is reduced by the carbon of the cast-iron, and the silicate has a tendency to assume the composi- tion 3FeO,Si0 3 . Cast-iron reacts even on this latter silicate, but less readily and at a higher temperature ; so that the silicates which have a tendency to form resemble closely the formula 3FeO,Si0 3 . The conversion of cast into bar iron is founded on this reaction. The silex of the scoriae is furnished not only by the silicium of the cast-iron, or the grains of sand adhering to its surface, and which come from the moulds in which it has been cast, but a great portion is also produced by the ashes of the fuel used for the refinery. Two different processes are used for refining cast-iron : 1. Refinery with charcoal, called refinery in the small furnace. 2. Refinery with pit-coal, called refinery by the English method, or refinery by puddling. Refinery ly the small furnace. 827. The refinery is effected in a small quadrangular furnace U (figs. 491 and 492), made of iron plates, covered with clay, the depth of which is 9 inches, its width varying from 1J to 2 feet. The air is conveyed by a twyer t, which enters the furnace to the distance of about 4 inches, in such a direction that its prolonged axis would cut the opposite face of the hearth at its lower edge. The copper, or baked-clay twyer, which is represented in fig. 493, generally receives the nozzles of two wooden bellows S, S' (figs. 491 and 492), moved by a water-wheel. The bellows are arranged so as to afford a continuous blast ; and while the movable frame of the one descends and impels the air into the furnace, the other ascends and inspires the external air ; the quantity of air being regulated by the flow of water on the wheel. The blowing- machine we have figured is very imperfect ; and double cylindrical machines, resembling that in fig. 487, the blast of which is regu- lated by a register in the air-pipe, are substituted for it in modern forges. In the front of the furnace is a cast-iron plate aba'b', placed at the height of the upper opening of the furnace, and slightly inclined. At the lower part of the hearth is a tap-hole, which opens at the bottom of the hearth, and serves for the escape of the scoriae. The furnace is covered by a basket-funnel C, having a chimney which carries off the gases arising from the combustion, and sheet-iron plates P are fastened to the funnel, to protect the workmen from the heat. 84 Fig. 493. Fig. 492. The furnace, while containing the charcoal kin- dled in a preceding operation, is filled with fresh charcoal and the air admitted. The cast-iron to be refined is either in the form of pigs or plates, and, when melted, drops to the bottom of the hearth, passing the air of the twyer. The smelting lasts from 3 to 3 J hours. The workmen take advantage of the high temperature developed by the combustion of the charcoal which is placed above the cast-iron, to forge bars of refined iron arising from the preceding operation, as we shall presently explain. The surface of the drops of cast- iron, passing through the air of the twyer, becomes oxidized, and a very basic silicate of iron is formed, which reacts on the carbon of the cast-iron, so that the latter, when it has arrived at the bot- tom of the hearth, has lost a great portion of its carbon, and becomes much less fusible. From time to time, the scorise are withdrawn by opening the tap-hole, a sufficient quantity to con- tinue the decarbonizing action always being left. Frequently the workman allows the air of the twyer to blow directly on the cast- iron, to increase its oxidation. METALLURGY OF IRON. 85 When the mass of iron, partly refined, has become consistent, the workman raises it with his bar above the fuel, which he heaps at the bottom of the furnace, when the air then blowing below the mass subjects it to a powerful oxidizing action. Fresh charcoal is added and the force of the blast increased, so as to fuse the metal a second time. After the second fusion, the refining is very far advanced ; and the iron forms spongy masses, which the workman collects together and welds into one single piece; while he some- time^ draws those pieces which do not appear sufficiently refined nearer to the twyer. When the operation is terminated, the scoriae are completely removed, the mass of iron is withdrawn, its sides are beaten with iron bars, and it is then carried to the hammer. The hearth is then cleansed. A portion of the scoriae is left in the furnace, and the remainder withdrawn, but generally preserved for use in the following operation during the smelting of the iron, for which the scraps of iron detached during the forging of the lump are also made use of. When the iron plate forming the bottom of the hearth becomes too hot, it is cooled by a small quantity of water. 828. The process to which the lump is subjected when it leaves the furnace, consists in placing it on an anvil, when it is beaten in all directions by a heavy hammer (fig. 494). The anvil E is gene- Fig. 494. rally of cast-iron, while the hammer is frequently made of wrought- iron, with a steel face. The head P of the hammer weighs from 600 to 1200 pounds, and is mounted on a wooden helve oa, strengthened by bands of iron. The helve is held in a cast-iron ring, provided with two gudgeons 0, on which it revolves, and which rest on cast-iron collars fastened to uprights. To give additional solidity to the anvil, it is placed on a large block of wood, resting on pile-work driven into the floor of the foundry. The hammer is raised by cams of its weight of ashes and a little sea-salt are frequently added. The part played by these two substances in the process of cementation has not been yet explained. In order to charge a cementation-box, a layer of cement to the depth of about 2 inches is first spread in it, and on this a layer of iron bars is arranged edgewise, so as to leave between them a space of somewhat less than a J inch. The bars are not quite so long as the box, so as to allow room for free ex- pansion : a section of them is a rectangle of about 1 J to 2 inches by J to J- inch. Between and above the bars a layer of cement about J inch in thickness is placed, then a second layer of bars, and so on, until the box is filled to within about 6 inches of the top. It is then closed hermetically with refractory bricks, or better still, with a layer of quartzose sand. The two boxes of a furnace contain from 10 to 20 tons of iron, according to their size. Each box has several openings corresponding to working-holes in the wall of the furnace, through which some of the bars can occa- sionally be withdrawn to estimate the progress of the operation by their appearance. The proper temperature, which is nearly that of the fusing point of copper, is attained in 24 hours, and kept up for 7 or 8 days. Cementation advances more rapidly at a higher temperature, but in that case the products are still less homogene- ous. When the cementation is supposed to be completed, the fur- nace is allowed to cool for several days before being emptied, when the surface of the bars is covered with small bubbles, or blisters, from which circumstance the steel has received the name of blistered steel. This steel can be used only after having been made more homogeneous by fagoting or by fusion. About 50 Ibs. of pit-coal are used for 2 cwt. of crude steel. Bar-steel is refined nearly in the same way as bar-iron. Bundles, made of several bars, sorted by placing the hard on the softer bars, are heated in small blast-furnaces fed with pit-coal, and then new bars are made of them, either by hammering or rolling, which are tempered and then broken into several pieces. Other bundles are made of the fragments, and they are again forged. The fagoting is repeated once, or several times, according to the quality of steel to be manufactured, as the steel becomes softer at each fagoting by losing a portion of its carbon. 855. Iron or steel articles, when finished, are sometimes sub- jected to cementation, by an operation called case-hardening, in order to harden their surface. The articles, arranged in layers 106 IRON. with cement, in sheet-iron boxes, are heated to a high temperature in boxes surrounded by hot walls, which are renewed until the pro- cess is judged to be completed, which is known by pieces of iron- wire, penetrating the boxes and removable at pleasure. The ce- mented articles are tempered by immersion in cold water. Steel objects, of which the surface has been softened so that they might be more easily wrought, are often case-hardened. In order to soften the surface of a steel object, it is heated in a heap of iron filings, and then allowed to cool slowly. 856. Steel acquires a perfectly homogeneous character only by fusion, and then takes the name of cast- steel. The fusion is effected in fire-clay crucibles, in a common furnace, consist- ing of a small rectangular chamber A (fig. 514), of 3 feet in depth, and of which a horizontal section is 1 J by 1J- feet. The chamber is lined with an infusible quartzose grit, and communi- cates with the chimney C by a hori- zontal throat B, the draught being re- gulated by a register r in the chimney. The upper part of the furnace is open, to allow the introduction of the cru- cible and the fuel, but the opening is covered by a lid made of refractory grit, or fire-bricks held together in an iron frame. Several of these melting- Fig. 514. furnaces are generally arranged along- side of each other, while their chimneys are united in the same stack. The crucibles ? a vertical section of one of which is seen in fig. 515, are made of very refractory clay. One of the crucibles is placed in the furnace, covered with burning pit-coal, and the furnace is then filled with coke, merely to heat the sides of the furnace, the chimney, and the crucible. Thirty pounds of cemented steel, broken into pieces, are then in- troduced into the crucible, which is covered with its lid A, and the temperature is rapidly elevated. The fusion of the steel generally requires 4 hours, after which the crucible is removed, the lid taken off, and the fused steel poured into cast-iron ingot-moulds. The crucible is immediately re- Fig. 515. p} ace d j n the furnace, and a new charge introduced for a second fusion, which, however, requires only 3 hours. The same crucible may serve for a third melting, but is afterward rejected as useless. A cast-steel of very superior quality, and known by the name Wootz, has long been manufactured in India. It is made in small STEEL. 107 pieces, weighing at most from 2 to 4 Ibs., by heating iron at a very high temperature in contact with certain vegetables which are car- bonized hy heat. Steel remarkable for its great hardness is obtained by fusing ordinary steel with very small proportions of certain metals, such as silver and platinum. 857. Steel, heated to a very high temperature, and then al- lowed to cool slowly, becomes as soft as cast-iron, and can be cut with a file, or turned in a lathe, but on being heated to redness and then suddenly cooled by dipping it into cold water, is rendered very hard and brittle. The steel, which is less dense than annealed steel, is then said to be tempered. By heating it again to redness and allowing it to cool slowly, it regains its original malleability. Steel objects are first made of annealed steel, with the hammer, file, or lathe, and the proper degree of hardness is then given by tempering ; but as they generally become too hard and brittle by this process, they must be again heated to bring them to a proper degree of softness. The great skill of the workman consists in knowing the exact moment of the completion of the annealing, in which he is guided by the often very brilliant colours displayed on the surface of the metal during the annealing, and which corre- spond exactly to certain temperatures. The colours are produced by thin pellicles of oxide reflecting various colours according to their thickness : in a word, the cause of this phenomenon is the same as that which produces the beautiful iridescence of a soap- bubble. Tempered steel, reheated at 220 produces a straw-yellow colour. " ' " 240 " golden-yellow " " " 255 " brown " " " 265 purple " " 285 " bright blue " " " 295 indigo-blue " " " 315 " very deep blue " The reheating is carried to the production of any particular colour, according to the quality of the steel and the nature of the object. Many cutting instruments are made by forging together bars of steel and soft iron, by which proceeding they are rendered less brittle, but also less hard, than those of pure steel. Gun-barrels are usually made in this manner. When the surface of an object made of non-homogeneous steel is attacked by a feeble acid, the heterogeneous structure of the material is evinced, and different agreeable designs result, which vary according to the process adopted. The steel is then said to be damasked. When the steel is combined with small quantities of foreign metals, which are irregularly scattered through its sub- stance, the effect of the figuring becomes very beautiful. 108 IKON. TESTING OF IKON-ORES. 858. The richness of an iron-ore may be ascertained, either by the dry or the humid way. Testing by the dry way is an imita- tion in miniature of the blast-furnace, and yields the same pro- ducts, viz. cast-iron and slag, and has the advantage of allowing the operator to judge, by the small lump obtained in the assay, of the quality of cast-iron which the ore would produce in the blast-furnace. Nevertheless, before making the assay in the dry way, some pre- liminary experiments in the humid way are generally performed, as they more clearly determine the nature of the ore, and show the quantity of flux necessary to be added to obtain a good smelting. We shall divide the ores, which it may be necessary to assay, into four classes : 1st. Those ores which contain iron in the state of hydrated sesquioxide ; 2d. Ores formed by anhydrous sesqui- oxide ; 3d. Ores of magnetic oxide of iron ; 4th. Sparry ores, that is, those formed by protocarbonate of iron. 1. The ores of the first class, which are much the most abun- dant in France, are tested in the following manner : Ten grammes of the ore are first calcined to redness in a plati- num crucible, to disengage water and carbonic acid. Let p be the weight of the calcined substance, then will (10 p) represent the weight of the water and carbonic acid. Ten other grammes of finely powdered ore are then treated with very weak nitric acid, which dissolves only the carbonates of lime and magnesia which may be in the gangue. (If none existed, there would be no effervescence, and the use of the weak nitric acid would be superfluous.) When the effervescence has ceased, even after the addition of a fresh quantity of acid, the residue is col- lected on a small filter, washed with a little water, and calcined in a platinum crucible. If p' be the weight of this residue, (10 p') will represent the weight of the water, carbonic acid, and lime contained in the ore ; and consequently, (pp r ) will be the weight of the lime. Lastly, 10 gm. of powdered ore are attacked with concentrated chlorohydric acid, and the solution boiled until the residue has en- tirely lost its colour. The quartz and clay, which alone remain as a residue, are collected on a filter and weighed after calcination. Their weight being represented by p", we shall have for the compo- sition of the ore, by collecting the results of all these operations : Water and carbonic acid (10 p) Lime (p~p r ) Quartz and clay p" Oxides of iron and manga- nese, (differentially) 10 - (10 -;?)-(jp -/)-/' *=(/-/'). If the ore contains only a small quantity of manganese, which is TESTING OF IRON-ORES. 109 -Fig. 516. easily recognised by the ochreous colour of its powder, the weight (p'p") will represent pretty exactly the weight of the anhydrous sesquioxide of iron in the ore, and, consequently, ^ (p'p ft ) will be the weight of the metallic iron. It is more easy to make the assay by the dry way, under the most favourable conditions. Experiment has shown that the cast-iron most readily separates, and a well-fused slag, nearly entirely free from oxide of iron, is obtained when the gangue is composed of clay and carbonate of lime, in such proportions that the latter should be two-thirds of the clay. An addition of chalk or kaolin to 10 gm. of powdered ore is then made, until the mixture resembles the composition just indicated ; which, after being well ground in an agate mortar, is introduced into the cavity abc of a crucible covered with damp char- coal* (fig. 516). The ore is inserted in a heap m into the cavity made with a glass rod, and the crucible is filled with damp charcoal. The lid is luted with clay, and the crucible itself, being set on fire-bricks, or pieces of burnt earth, and secured with clay, is heated in an air-furnace, or in a forge. Fi- gure 517 represents the construction of an air-furnace very suitable for test- ing iron-ores ; it resembles the furnace for melting steel ( 856), but is smaller. Four crucibles may be arranged in this furnace, and 4 tests made at once. The fuel used is a mixture of equal parts of charcoal and coke, taking care to raise the temperature gradually, so that the crucibles may dry slowly, while the register r regulates the draught. Dur- ing the last quarter of an hour the temperature is raised as high as pos- sible. The operation lasts in all an hour and a quarter, after which the Flg * 517> crucibles are removed and allowed to * The preparation of a "brasqued" crucible requires some precautions, which it may be worth while to indicate. " Brasque" is composed of charcoal, powdered and sifted, moistened with water so as to give it a certain degree of consistency, and introduced into a crucible of refractory clay, into which it is rammed with a wooden stamper. This requires several additions of the material, as it becomes compressed by pounding. Before adding a new layer, the surface of the preceding must be made rough, as otherwise it would not incorporate itself with the succeed- ing stratum, and the two layers might separate during the heating, causing cracks to form, through which the liquid substances might escape. When the crucible is filled and the charcoal well-heaped in, a part of the "brasque" is removed with a knife, so as to form a rounded cavity abc (fig. 516), the material taken from which is heaped along the sides of the crucible ; and the surfaces are then rubbed smooth with a strong glass rod. VOL. II. K 110 IRON. cool. The fused lump taken from the bottom of the crucible is composed of a button of cast-iron, surmounted by slag, both of which are weighed together. The slag is then broken off and pounded to pieces, to ascertain that it contains no metallic globules, and the button and globules are weighed. It is proper to remark that as the metal weighed is in the state of cast-iron, that is, combined with a certain quantity of carbon, its weight is consequently rather too great ; but at the same time this excess of weight nearly compensates for the small quantity of iron which always remains in the state of oxide in the slag. Instead of the air-furnace of fig. 517, which is found only in laboratories where such tests are made in quantity, an ordinary blacksmith's forge may be used, when a sort of hearth can con- veniently be made with refractory bricks, in the midst of which the crucible is to be placed. Fig. 518 represents a small portable furnace, which may be con- structed without much expense, and is well adapted for testing iron-ores. It is made of two large refractory crucibles ABec?, ABEF, the upper one of which, forming the lid, has a large opening 0, through which the fuel is charged and the air escapes, while the lower crucible has three holes 0, 0', 0", and its bottom rests on a cup U of baked clay, into which the nozzle a of a bellows enters. The small "brasqued" cru- cible is, in order to place it in the middle of the furnace, set on several pieces of brick placed on each other, to the upper one of which it is luted with clay. The fuel Fig. 518. used is charcoal or a mixture of charcoal and coke. 2. When the ore consists of anhydrous peroxide of iron, the proportion of siliceous gangue can no longer be determined by acting on it with chlorohydric acid, because the native peroxide is unaffected by this acid, and the latter therefore dissolves only the carbonate of lime, which may be thus determined : In order to make the assay in the furnace, of its weight of a fusible silicate, white glass, for example, is mixed with the ore, in order to prevent the too siliceous scoriae from retaining oxide of iron. If this should nevertheless take place, which would be known by the deep green colour of the slag, the test must be repeated, but with an increased proportion of carbonate of lime, or with less glass than before. 3. As even the most concentrated acids act with difficulty on native magnetic iron, the proportion of quartzose gangue by which such ores are accompanied cannot be determined by chlorohydric TESTING OP IRON-ORES. Ill acid, and the assay must be made as in the preceding case, that is, the ore must be immediately fused in a forge-fire with an ad- mixture of white glass and carbonate of lime. 4. Although the native protocarbonate of iron is converted by calcination into magnetic oxide, the loss of weight which sparry ores suffer by heat does not exactly represent the weight of the disengaged water and carbonic acid, because the protoxide of iron absorbs a portion of the oxygen of the carbonic acid which it decomposes. By treating the ore with weak nitric acid, the car- bonate of lime is dissolved ; but a certain quantity of iron being dissolved at the same time, the lime cannot be determined as in the first case, and it becomes necessary to act on the ore with con- centrated boiling chlorohydric acid, in order to convert the iron into sesquioxide. The solution is evaporated to dryness at a gentle heat to drive off the excess of acid, and treated with water, which leaves the quartzose and argillaceous gangue undissolved ; after which the sesquioxide of iron, the protoxide of manganese, and the lime are then successively separated in the liquid by the processes described 803. 859. When the oxide of iron readily dissolves in acids, the quantity of iron existing in an ore can be exactly and rapidly determined by boiling 3 grammes of the finely powdered ore with chlorohydric acid, until the solution loses its colour, evaporating to drive off the excess of acid, and treating the residue with water. The latter, which consists of the quartzose and argillaceous gangue, is collected on a filter and weighed. A standard solution of permanganate of potassa is then poured into the liquid, using the precautions indicated ( 804), until the liquid assumes a perma- nent rose-colour, and the quantity of metallic iron existing in the 3 grammes of ore is determined from the quantity of permanganate of potassa used. If the ore be specular iron, or magnetic oxide, it can only be acted on by chlorohydric acid, after being heated to a high red- heat in a platinum crucible, with 3 or 4 times its weight of car- bonate of soda, or bisulphate of potassa. The peroxide of iron, in this way, becomes disaggregated and easier soluble in chlorohydric acid. ANALYSIS OF CAST-IRON AND STEEL. 860. Cast-iron is a compound of carbon with iron, frequently containing, in addition, a certain quantity of silicium, sulphur, phosphorus, and manganese. We shall proceed to describe the mode of successively determining these several elements. 112 IRON. Determination of Carbon. 861. Gray cast-iron can be easily filed, while white cast-iron and fine metal are, on the contrary, very hard, but when the file will not cut them, they can be pounded in a mortar. Fig. 519 represents a small apparatus of cast-steel, in which the pulverization can be easily effected. It is com- posed of a steel receiver abed, to which is fitted a cylinder efyh, exactly filled by a steel piston P. Some pieces of white cast-iron are placed in the cylinder, the piston P is introduced, and resting the base bo on an anvil, the head of the piston is struck with a hammer. After a certain number of blows, the powdered substance is removed, and passed through a silk sieve ; the fragments then remaining on the Fig. 519. sieve being again broken up in the apparatus, and this process repeated until the whole quantity is reduced to fine powder. Five grammes of powdered cast-iron are then mixed with 100 or 120 gm. of chromate of lead, J of the mixture is set aside, and with the remaining f, 5 gm. of chlorate of potassa are inti- mately mixed, when the whole is introduced into a tube closed at one end, resembling those used for the combustion of organic sub- stances with oxide of copper; and on it the mixture containing no chlorate of potassa is placed. The tube is rested on a sheet- iron grate, while a tube containing chloride of calcium, or pumice- stone soaked in concentrated sulphuric acid, to absorb the moisture given off by the materials, is fitted to its extremity, and the whole apparatus is then arranged as represented in fig. 279. The anterior part of the combustion-tube, which does not con- tain chlorate of potassa, is first heated, and the coals are then slowly approached to that part containing the chlorate. The cast- iron burns, partly at the expense of the oxygen of the chromate of lead, and partly by that disengaged by the chlorate, and car- bonic acid is formed and collected in the globe apparatus. Fresh coals are added, until the end of the tube is reached. The excess of oxygen gas arising from the decomposition of the chlorate is at the same time disengaged and driven through the apparatus ; but a little experience soon teaches how to avoid any danger of an explosion. It is well to place a small quantity of a mixture of chromate of lead and chlorate of potassa at the end of the com- bustion-tube, as the oxygen disengaged from this drives the last traces of carbonic acid through the globe apparatus. The increase of weight of the latter gives very exactly the carbonic acid arising from the carbon of the cast-iron, while the sulphur it may contain ANALYSIS OF CAST-IRON. 113 remains in the combustion-tube in the state of sulphate of lead, and does not affect the result of the experiment. It is important to keep the mixture in the combustion-tube so that a free space may remain in the upper part of the tube, as otherwise the chromate of lead, on becoming doughy and expanded, might obstruct the tube and cause an explosion. The same process necessarily applies to the determination of the carbon which exists in steel and in soft iron. The carbon contained in cast-iron and steel may also be exactly determined by causing these substances to react slowly on chloride of silver. To do this, 30 or 40 grammes of chloride of silver are fused in a porcelain capsule, a piece of iron or steel weighing about 5 gm. and exactly weighed is placed on it, and then water containing a few drops of chlorohydric acid is added. The chlo- ride of silver is gradually decomposed, while protochloride of iron is formed and the carbon set free ; but the reaction is very slow, and often requires several weeks for its completion. There re- mains, at last, a spongy mass of carbon and silicic acid, from which the last traces of iron are extracted by boiling with dilute chlorohydric acid. The precipitate is collected on a filter and weighed after being well dried, or better still, after a calcination in a current of hydrogen gas. Its weight is that of the carbon and silicic acid united ; and it is then calcined in a platinum capsule, by which the carbon burns off, when the weight of the silicic acid remaining can be directly determined, and that of the carbon cal- culated by the difference. As a substitute for chloride of silver, chloride of copper may be employed, which acts more rapidly on the cast-iron, but always disengages a small quantity of carburetted gas, so that the weight of the carbon found is rather too small. 862. We have seen that carbon could exist in cast-iron in two states : 1st, in that of combined carbon, as in white cast-iron and steel ; 2dly, in the state of small isolated laminae, as in gray cast- iron. It is of the highest importance to distinguish these two states of carbon, as they exert a remarkable influence over the nature of the cast-iron, and moreover are easily determined by analysis. In fact, when chlorohydric acid is allowed to act on a white cast-iron or steel, the metal dissolves and evolves a very fetid hydrogen gas, containing a considerable quantity of gaseous carburetted hydrogen, and vapours of certain liquid carburetted hydrogens which have been not yet studied. All the carbon of the cast-iron disappears in these hydrogenated products, and the residue is composed only of the silicic acid produced by the silicium of the cast-iron. If, on the contrary, a gray cast-iron be treated with chlorohydric acid, the gas evolved is still fetid, as the carbon which was in intimate combination with the iron is converted into K2 8 114 IRON. gaseous or liquid carburets of hydrogen, but the isolated carbon which existed in it in the state of graphite remains intact with the silicic acid. The residue is collected on a small filter, and, after being well washed, is dried. Some ether is then poured over the filter, to dissolve any oil which may remain, after which it is again dried at a temperature above 212, and the residue weighed : the weight of the graphite and silicic acid united is thus obtained. The substance is heated in a platinum capsule in the open air, or better still, in a current of oxygen, by which the graphite burns, and leaves as a residue only silicic acid, which can be determined by weight. By subtracting from the whole weight of the carbon obtained by the combustion of the cast-iron the weight of graphite first obtained, the weight of the combined carbon is ascertained. Determination of Silicium. 863. The silicium of cast-iron is determined by dissolving the latter in chlorohydric acid, which converts the silicium into gelati- nous silicic acid. The liquid is evaporated to dryness to render the silex insoluble, then treated with water, and the residue collected on a filter. The silex is weighed, after having been cal- cined at a dull red-heat, and the weight of the silicium is deduced from it. Cast-iron frequently contains particles of slag, so that the residue is composed not only of the silicic acid furnished by the silicium of the cast-iron, but also that of the slag, which may have been more or less altered by the chlorohydric acid. The slag of char- coal furnaces generally resists this acid, while that of coke furnaces is more or less completely acted on by it. By treating powdered cast-iron with weak chlorohydric acid, the iron may be entirely dissolved, without sensibly affecting the slag, while the residue consists of gelatinous silex and slag, and is treated by a solution of caustic potassa, which dissolves the silex and leaves the slag. The silicic acid which has been furnished by the silicium of the cast-iron can thus be exactly ascertained. Determination of Sulphur. 864. The cast-iron is acted on by aqua regia, which dissolves the iron as perchloride, and converts the sulphur -into sulphuric acid. The liquid is diluted with water, and the sulphuric acid pre- cipitated by chloride of barium as sulphate of baryta, from which the weight of the sulphur in the cast-iron may be deduced. Determination of Phosphorus. 865. The cast-iron is acted on by aqua regia, evaporated to dry- ness to drive off the excess of acid, and then treated with water. The liquid, containing phosphorus in the state of phosphoric acid, is ANALYSIS OP SLAGS. 115 then allowed to digest at a temperature of about 212, for several hours, with an excess of sulf hydrate of potassium, which precipitates iron and manganese in the state of sulphides. After separating these by filtration, the liquid contains phosphoric acid and alkaline sulphides, which are decomposed by a slight excess of chlorohy- dric acid, after which the liquid is boiled to drive off the sulf hydric acid. One decigramme of piano-forte wire is then weighed very exactly, dissolved in aqua regia, and added to the solution of per- chloride of iron obtained. An excess of ammonia poured into the liquid then completely precipitates the iron added in the state of hydrated sesquioxide, and carries with it all the phosphoric acid which existed in the liquid, precipitated as a basic perphosphate of iron. This precipitate is weighed after calcination in the air ; and if from it 0.143 gm., the weight of the sesquioxide of iron yielded by 0.100 gm. of metallic iron, are subtracted, the weight of the phosphoric acid, whence that of the phosphorous in the cast- iron may be deduced, is obtained. The same determination may be made in the following manner : After having dissolved the cast-iron in chlorohydric acid, the liquid is filtered and an excess of acetate of soda added, the acetic acid of which is set free and chloride of sodium is formed. Now, as sesquioxide of iron forms with phosphoric acid a phosphate Fe 2 3 PhO s insoluble in acetic acid, the phosphoric acid combines with the proper quantity of sesquioxide of iron to form this phosphate, which is precipitated, collected on a filter, washed with boiling water, and weighed after calcination. The precipitate may also be redissolved in chlorohydric acid, the liquid boiled with sulphite of soda to bring the perchloride of iron to the state of protochlo- ride, and the standard solution of permanganate of potassa poured in to determine the quantity of iron it contains. The weight of phosphoric acid is thence easily deduced, and, consequently, that of the phosphorus contained in the cast-iron. Determination of Manganese. 866. The manganese contained in cast-iron is easily ascertained by the processes described 803. ANALYSIS OF SLAGS AND FURNACE SCORIAE. 867. Slag is composed chiefly of silicates of alumina and lime, but often contains, in addition, small quantities of the silicates of iron and manganese. The various scoriae arising from the refining of cast-iron are composed of silicates of iron and manganese, but may also contain small quantities of silicates of alumina, lime, and potassa, arising from the ashes of the fuel used. Forge scoriae are readily acted on by concentrated chlorohydric acid, by which the ma- 116 IRON. jority of slags is, however, not attacked. These products are ana- lyzed by the processes described in the ^ analysis of glass ( 704), except that, in the case of forge scoriae, it is useless to employ car- bonate of soda and fluohydric acid, as the substance is acted on immediately by chlorohydric acid. REMAKES ON THE COMPOSITION OF IRON, STEEL, AND CAST-IRON. 868. By the hardness of wrought-iron is understood the resist- ance it presents when filed, cut, bored, or struck with a hammer while it is cold, which properties vary greatly in the different kinds of iron manufactured in different furnaces. Iron which when cold readily takes the impression of the hammer, is commonly flexible and tough, but, although of an excellent quality, cannot be univer- sally applied, that which is, at the same time, hard and tough being preferred. The best iron is that which is very hard, without being brittle, that is, without breaking easily under the hammer. Iron which breaks or splits easily when heated is said to be short ; a defect which is produced by a small quantity of sulphur : j~ part of sulphur will make iron slightly short. When iron contains 0.5 per cent, of phosphorus, it is brittle when cold, while a smaller quantity only renders the metal harder, still giving iron of good quality. Wrought-iron may contain 0.25 per cent, of carbon, without pos- sessing the property of remarkably hardening by tempering, which is regarded as characteristic of steel ( 857). When the carbon rises to 0.60 per cent, the metal becomes too steely, and strikes fire with a flint after tempering. The quantity of carbon which renders iron steely, varies with the purity of the metal ; for very pure iron, for example, a larger proportion than for that containing smaller quan- tities of sulphur and phosphorus is required. Steel, refined by fagoting, and which is, at the same time, suffi- ciently hard and tough for cutting instruments, contains from 1.0 to 1.5 per cent, of carbon. When the proportion of the latter is greater, the steel becomes harder, but loses in toughness and par- ticularly in the property of being welded. Steel containing 1.75 per cent, of carbon cannot be welded at any temperature. When iron is combined with 2 per cent, of carbon, it cannot be forged under the hammer. This property may be regarded as dis- tinguishing steel from cast-iron, the compounds of iron with a greater proportion of carbon than 1.9, consequently, being no longer steel, but cast-iron. Cast-steel which contains from 1.9 to 2 per cent, of carbon, cannot be forged, but it never parts with its graphite, even by very slow cooling. Graphite separates by slow cooling, only when the iron is combined with at least 2.5 per cent, of carbon. PROPERTIES OF CAST-IRON. 117 The properties of cast-iron do not depend so much on the whole quantity of carbon contained, as on that with which it is intimately combined. Gray cast-iron most frequently contains only 2 or 2.5 per cent, of combined carbon, the rest of this substance being scat- tered through it in the form of graphitous spangles. Gray cast- iron requires a higher temperature for fusion than white cast-iron, and passes almost suddenly from the liquid to the solid state, while white iron passes through an intermediate doughy state ; on which account, probably, white cast-iron is more easily refined than gray iron containing the same quantity of carbon. Therefore, it is always endeavoured to obtain white cast-iron for refining, when the purity of the ore and the fuel will allow it ; for we have already said ( 826) that with impure ores and fuels, the temperature of a blast furnace producing gray cast-iron must be greatly elevated, unless the gray iron be suddenly cooled on leaving the furnace. Gray cast-iron is converted into white cast iron by sudden cool- ing, while the white passes into the gray state at a higher tem- perature, and by slow cooling. 118 CHROMIUM. EQUIVALENT = 26.7; (333.75,0 = 100.) 869. Chromium* is obtained combined with a certain quantity of carbon, by heating, in a "brasqued" crucible, an intimate mix- ture of sesquioxide of chromium and 15 or 20 per cent, of carbon in a forge-fire, when the carburetted metal remains in the form of a porous lump, as the heat was not sufficient to fuse it. This metallic mass is finely powdered in a steel mortar, intimately mixed with a few hundredths of the green oxide of chromium, and the mixture heaped in a porcelain crucible accurately covered by its lid, which is then placed in a second earthen crucible, likewise "brasqued," and heated to the highest temperature of a forge-fire. The carbon of the carburetted chromium is burned by the oxygen of the oxide, and a purer metal is obtained, in the form of a gray agglutinated mass. This metal is brittle, but may be polished, and then displays a brilliant metallic lustre. It is very hard and scratches glass readily, and its specific gravity is about 6.0. It does not oxidize in dry air at the ordinary temperature, but com- bines rapidly with oxygen when heated to a dull red-heat. It dissolves in chlorohydric and dilute sulphuric acid with evolution of hydrogen gas. Pure metallic chromium is obtained, in the form of a dark-gray powder, by decomposing the violet sesquichloride of chromium by potassium. The pulverulent metal has so powerful an affinity for oxygen, that it ignites before it reaches a dull red-heat, and is converted into green oxide of chromium when heated in contact with the air. COMPOUNDS OF CHROMIUM WITH OXYGEN. 870. Chromium forms many compounds with oxygen : 1. The protoxide CrO, isomorphous with protoxide of iron FeO. 2. The sesquioxide Cr 2 3 , isomorphous with alumina and ses- quioxide of iron Fe 3 3 . 3. An oxide Cr 3 4 , intermediate between the first two, and cor- responding to magnetic oxide of iron FeO,Fe 2 3 ; so that its formula should be written CrO,Cr a 3 . 4. Chromic acid Cr0 3 , corresponding to ferric acid Fe0 3 , and manganic acid Mn0 3 . 5. An intermediate oxide Cr0 3 , which should, however, rather Discovered in 1797 by Vauquelin. OXIDES OF CHROME. 119 be considered as a combination of chromic acid with protoxide of chromium : CrO,Cr0 3 . 6. Lastly, a perchromic acid Cr 2 7 , corresponding to permanganic acid Mn a 7 . Protoxide of Chromium, CrO. 8T1. Protoxide of chrome is obtained by adding caustic potassa to a solution of protochloride of chromium, when a deep brown precipitate of hydrated protoxide is formed. But this substance has so great an affinity for oxygen that it decomposes water as soon as it is set free, disengaging hydrogen, and being converted into a tobacco-coloured powder, which is the hydrate of a definite oxide Cr 3 4 , corresponding to magnetic oxide of iron, and which should consequently assume the formula CrO,Cr 3 3 . The trans- formation takes place very rapidly, at the temperature of boiling water. The hydrate of the oxide of chrome CrO,Cr 3 3 , heated in a closed tube, is converted into the green oxide Cr 3 3 , with the evolution of hydrogen gas. The composition of protoxide of chrome has never been directly ascertained, but has been inferred from the analysis of protochlo- ride of chrome. This oxide contains 1 eq. chromium 26.7 or 333.7 78.53 1 " oxygen 8.0 100.0 21.47 1 protoxide 34.0 433.7 100.00 Sesquioxide of Chromium Cr 2 3 . 872. Sesquioxide of chromium is prepared in several ways : 1. By heating protochromate of mercury Hg 3 0,Cr0 3 ; when oxygen is disengaged, the mercury distils, and Sesquioxide of chrome remains in the form of a deep-green powder : 2(Hg,0,CrO.)=Cr j ,0.+4Hg+50. 2. By heating in a crucible a mixture of 1 part of bichromate of potassa, 1J " sal ammoniac, 1 " carbonate of potassa, when chloride of potassium and oxide of chrome are formed, while the oxygen given off by the chromic acid combines with the hy- drogen of the ammonia : KO,2Cr0 3 +KO,C0 3 +2(NH 3 ,HCl) = 2KC1 + Cr 3 3 -f 5HO+N+ NH 3 ,C0 3 . By treating the substance with water, the chloride of potassium is dissolved, leaving the Sesquioxide of chrome in a state of purity. 3. By heating at a suitable temperature, in an earthen crucible 120 CHROMIUM. or in a retort, 2 parts of bichromate of potassa, and 1 part of sulphur; when the sulphur forms, with the oxygen given off by the chromic acid, sulphuric acid, which combines with the potassa : KO,2Cr0 3 +S=Cr 3 3 +KO,S0 3 . But an excess of sulphur is necessary, as a portion of this sub stance is volatilized without reacting on the chromate. By treat ing it with water, the oxide of chrome often remains mixed with a small quantity of sulphur, which may be expelled as sulphurous acid by heating it in contact with the air. 4. By calcining bichromate of potassa in a "brasqued" crucible, when carbonate of potassa, which is removed by water, and sesqui- oxide of chrome are formed : 2(KO,2Cr0 3 )+3C=2(KO,C0 2 )+C0 3 +2Cr 3 3 . 5. By heating bichromate of potassa to a high white-heat, when half of the chromic acid is decomposed into sesquioxide of chrome and oxygen, and a neutral chromate of potassa is formed, which is removed by water : 2(KO,2Cr0 3 )=Cr 3 8 +30+2(KO,Cr0 3 ). In this case the sesquioxide of chrome assumes the form of crys- talline lamellae. 6. By heating chromate of potassa to a red-heat, in a current of chlorine, when chloride of potassium is formed, and the chromic acid is decomposed into sesquioxide of chrome and oxygen : 2(KO,Cr0 3 )+2Cl=2KCl+Cr 3 3 -f30. Sesquioxide of chrome, thus prepared, appears in the form of green crystalline lamellae. T. Lastly, sesquioxide of chrome is obtained, in the form of small rhombohedral crystals, isomorphous with native crystallized alumina or corundum, by passing through a heated tube a red volatile liquid of the formula Cr0 3 Cl, which we shall describe under the name of chlorochromic acid. 2Cr0 3 Cl=Cr 3 3 +2Cl+0. The crystals which are deposited on the sides of the tube are often 1 or 2 millimetres in size, very brilliant, and of so deep a green colour as to appear black. They are as hard as corundum and readily scratch glass. Their specific gravity is 5.21. Sesquioxide of chrome cannot be decomposed by heat. Hydrogen even does not reduce it at the highest temperature of our labora- tory furnaces ; but charcoal decomposes it in a forge-fire, when it is intimately mixed with the oxide. Vapour of sulphur does not act on it at a white-heat, while sulphide of carbon decomposes it at this temperature, and converts it into sulphide of chromium. Sesquioxide of chrome imparts a green colour to fluxes, and we have already seen that this oxide is used for painting on glass and SESQUIOXIDE OF CHROME. 121 porcelain. A red colour, called pink-colour, is also prepared with chrome, and was first used on porcelain by the English. It is obtained by heating to redness an intimate mixture of 100 parts of stannic acid, 34 of chalk, and 3 or 4 of chromate of potassa, and then treating the powdered material with chlorohydric acid until it has acquired a beautiful rosy tinge. The colouring prin- ciple of this substance is probably an oxide of chrome superior to the sesquioxide. Strongly calcined, it combines with the acids, even when they are concentrated, only with great difficulty; the hydrate must therefore be dissolved when salts of the oxide are to be prepared. In order to prepare the hydrated sesquioxide of chrome, a solu- tion of the sesquichloride is precipitated by ammonia, when a gelatinous bluish-gray precipitate is formed, which must be washed with boiling water. The sesquichloride of chrome used in this preparation is obtained by decomposing bichromate of potassa by sulphurous acid, in the presence of an excess of chlorohydric acid. To effect this a current of sulphurous acid gas is passed through a concentrated hot solution of bichromate of potassa, mixed with chlorohydric acid, when the liquid soon changes in colour, be- coming first brown, and subsequently assuming a beautiful emerald green hue. The reaction is terminated when the liquid still exhales a strong smell of sulphurous acid, after having been left to itself for several hours in a well-corked bottle. Hydrated sesquioxide of chrome dissolves readily in acids. Moderately heated, it loses its water, still preserving the property of easily combining with acids ; but if the temperature be further elevated, the substance suddenly becomes incandescent before reaching a red-heat, and, after incandescence, the oxide is nearly insoluble in acids. 873. Sesquioxide of chrome can combine with powerful bases, and one of these compounds, found in nature, acquires great im- portance from being the ordinary chrome ore. It consists of ses- quioxide of chrome and protoxide of iron, combined according to the formula FeO,Cr 3 8 : in mineralogy, it is called chromate of iron, or chromic iron. Chromic iron has sometimes been found crystallized in regular octahedrons, presenting, therefore, the same form as magnetic oxide of iron FeO,Fe a 3 , and spinell MgO,Al 3 3 , which have similar formulae. Most frequently, chromic iron forms considerable masses, of a deep gray colour and a greasy lustre ; and its bearings resemble those of magnetic oxide of iron. The principal mines of chromic iron are in Sweden, the Ural, and near Baltimore in the United States.* It has been found in * The most extensive and important locality by far, is that of Lancaster and Chester counties, Pennsylvania, which now supplies both the United States and Europe. A considerable part of the ore is now obtained by simply washing the sands of brooks. W. L. F. VOL. II. L 122 CHKOMIUM. France, in the department of Var, but the mine appears nearly exhausted. Chromic Acid Cr0 3 . 874. In order to prepare chromic acid, one and a half times its volume of sulphuric acid is added gradually and in small quan- tities to a solution of bichromate of potassa, saturated at a tem- perature of from 130 to 140, -when bisulphate of potassa is formed, which remains in solution, and the liquid deposits on cool- ing long red needles of chromic acid. When the solution is cooled and the acid liquid decanted off, the crystals are allowed to drain in a funnel stopped with asbestus, and are then spread upon un- burnt porcelain, which absorbs the remaining water. In order to purify them, their aqueous solution is treated with a small quantity of chromate of baryta, which combines with the sulphuric acid, and the filtered liquid is evaporated in vacuo. Chromic acid is of a beautiful red colour at the ordinary tem- perature, but becomes almost black when heated. It decomposes before attaining a red-heat into sesquioxide of chrome and oxygen, and is deliquescent and very soluble, with an orange-yellow colour. Chromic acid is a very powerful oxidizing agent : a few drops of absolute alcohol thrown on it, instantly convert it into sesqui- oxide, with so great an evolution of heat that the alcohol some- times ignites. Hot concentrated sulphuric acid decomposes chromic acid, disengaging oxygen and forming sesquisulphate of chrome. Oxygen is sometimes prepared in the laboratory by heating together equal weights of bichromate of potassa and con- centrated sulphuric acid. Chlorohydric acid converts chromic acid into sesquichloride of chrome, with disengagement of chlo- rine : 2Cr0 3 +6HCl=Cr a Cl 3 +6HO+3Cl. 8T5. Chromic acid appears to be able to combine in several proportions with sesquioxide of chromium. If a solution of bichro- mate of potassa be treated with sulphurous acid until it assumes a brown colour, and at that moment ammonia be added to the liquid, an ochreous precipitate is obtained, which hot water, after some time, decomposes into chromic acid which dissolves, and hydrated sesquioxide of chrome which remains. A similar compound is obtained by decomposing nitrate of chrome by a suitable degree of heat, when a brown spongy mass remains, of which the compo- sition is represented by Cr0 2 , but to which the formula Cr 2 3 , Cr0 3 has been assigned. Perchromic Acid. 876. By treating chromic acid with oxygenated water, a beautiful blue solution is obtained, which, when shaken with ether, loses its colour, and imparts the blue compound to the ether. PROTOSALTS OF CHROME. 123 ihis compound, which is not very stable, has not yet been ob- tained in an isolated state, nor has it been combined with the mineral bases. Its formula is supposed to be Cr 2 r SALTS FORMED BY PROTOXIDE OF CHROME. 877. Protoxide of chrome CrO is a powerful base, but never- theless has been combined with only a small number of acids, on account of the difficulty of obtaining it pure, and the ready sus- ceptibility of change of the salts themselves, which rapidly absorb- ing the oxygen of the air, are converted into sesquisalts. The acetate and the double sulphate of protoxide of chrome and potassa only are known ; but in order to ascertain the distinctive charac- ters of the protosalts of chrome, the protochloride must be resort- ed to. These compounds are known by the following reactions : Caustic potassa at first affords a deep brown precipitate of hy- drated protoxide, but which is immediately changed into a clear brown hydrated magnetic oxide, with the evolution of hydrogen gas. Sulfhydric acid does not precipitate them, while sulfhydrates yield a black precipitate. Bichloride of mercury gives a white precipitate of protochloride of mercury. Lastly, oxidizing reagents, such as chlorine, nitric acid, etc., immediately convert the proto- salts of chromium into sesquisalts. SALTS FORMED BY SESQUIOXIDE OF CHROME. 878. Sesquioxide of chrome is a feeble base, analogous to ses- quioxide of iron. The salts formed by this oxide may exist under two different modifications, which are distinguished by their co- lours, the first being violet, while the second is green. Several acids produce both modifications ; but with others only one of the colours has hitherto been obtained. A green and a violet sulphate are known. Ammonia forms in the solutions of these two salts precipitates which are distinguished by their shades of colour ; the precipitate of the green sulphate being bluish gray, and producing a green solution with sulphuric acid, while that furnished by the violet modification is of a greenish gray, but also produces a green solution when treated with sul- phuric acid. Potassa and soda yield bluish-gray or greenish-gray precipi- tates, which dissolve in an excess of alkali, forming a green liquid, which loses its colour by boiling, as the hydrated oxide is again precipitated. The alkaline carbonates give a greenish precipitate, perceptibly soluble in an excess of the reagent. Sulfhydric acid does not precipitate the sesquisalts of chrome, but the sulfhydrates precipitate those of the hydrated sesquioxide. The sesquisalts of chrome produce, like the protosalts, a glass 124 CHROMIUM. of a characteristic green colour when fused ^with borax. Fused with the alkaline carbonates, or better still, with the nitrates, they form alkaline chromates, which are recognised by the yellow solu- tions they produce, and by their great colouring power. Sesquinitrate of Chrome. 879. Hydrated sesquioxide of chrome dissolves immediately in nitric acid, furnishing a green solution which leaves, after eva- poration, a very soluble green salt, readily decomposable by heat. At a moderate temperature, it yields a brown substance, which is regarded as a sesquichromate of chrome Cr 3 B ,Cr0 3 . Sesquisulphates of Chrome. 880. The neutral sesquisulphate of chrome Cr 3 3 ,3S0 3 has been obtained with three different colours, violet, green, and red, which appear to correspond to three modifications of the salt. The violet sulphate is obtained, by leaving for several weeks, in a badly-corked bottle, 8 parts of hydrated sesquioxide of chrome, dried at 212, and 8 or 10 parts of concentrated sulphuric acid. The solution, which is at first green, gradually becomes blue, and, after some time, a greenish-blue crystalline mass is deposited. With an aqueous solution of this substance, alcohol gives a violet- blue crystalline precipitate, which, after having been dissolved in very weak alcohol, is left to itself. After some time, the liquid deposits small regular octohedrons of the formula O 3 3 ,3S0 3 + 15HO. The green sulphate is prepared by dissolving sesquioxide of chrome, at a temperature of 120 to 140, in concentrated sul- phuric acid, or by boiling the solution of the violet sulphate. The liquid, when rapidly evaporated, yields a green crystalline salt, having the same composition as the violet sulphate. The green sulphate readily dissolves in alcohol with a blue colour, while the violet sulphate is insoluble in it. The violet and green sul- phates are also distinguished by several chemical reactions ; thus, the cold solution of the green sulphate is not completely decom- posed by the soluble salts of baryta, and the decomposition is complete only when the liquid is boiled, while all the sulphuric acid of the violet solution may, on the contrary, be precipitated when cold by salts of baryta. If the violet or green sulphate be heated to a temperature of 392, with an excess of sulphuric acid, a clear yellow mass is obtained, which leaves as a residue the red neutral sulphate of chrome, after the evaporation of the excess of acid. This anhy- drous sulphate is insoluble in water, and dissolves with difficulty even in acid liquids. CHROMIC ALUMS. 125 Chromic Alums. 881. Sesquisulphate of chrome is isomorphous with sulphate of alumina, and may take the place of the latter in the alums. The crystallizable chromic alums contain the violet modification of sulphate of chrome. Three of these alums are known, affording beautiful crystals : Potassic alum Cr 3 3 3S0 3 -fKO,S0 3 +24HO. Sodic alum Cr 3 3 ,3S0 3 -f NaO,S0 3 +24HO. Ammoniacal alum Cr a 3 ,3S0 3 -f (NH 3 ,HO)S0 3 +24HO. Potato-chromic alum is prepared by heating slightly a mixture of bichromate of potassa and sulphuric acid dissolved in water, with a reducing substance, such as sugar, alcohol, etc. ; or by passing a current of sulphurous acid through the liquid. The solution depo- sits by spontaneous evaporation, or even on cooling, if it be suffi- ciently concentrated, large regular octahedrons, like those of ordi- nary alum, of a deep violet red. They dissolve readily in water, with a dirty violet colour, but are insoluble in alcohol. Heated to 176, the solution becomes green, and deposits by evaporation red crystals of alum, but leaves as a residue an uncrystallized mass, which is still a double sulphate of potassa and chrome, but which no longer presents any of the characters of potassa-chromic alum. The solutions of the green sulphates of chromium give the same green product when they are evaporated with sulphate of potassa. CHROMATES. 882. Chromic acid combines with nearly all the bases, forming with the alkalies salts which crystallize perfectly, and are isomor- phous with the corresponding sulphates. The chromates of stron- tian, lime, and magnesia are soluble, while the other metallic chro- mates are insoluble, or nearly so. Chromic acid forms with the alkalies two series of salts : neutral chromates and bichromates, the former of which are of a bright yellow colour, while the bichromates are orange-red. The soluble chromates are easily distinguished : first, by their colour, which is very decided, even in very dilute solutions ; and also, by the cha- racteristic colours of the precipitate they yield with various metallic salts. They form a yellow precipitate with the salts of lead and bismuth, a bright red one with those of mercury, and a deep red one with those of silver. The chromates, heated with concen- trated chlorohydric acid, give a green solution of sesquichloride of chrome. Chromates of Potassa. 883. The compounds of chromic acid with potassa are the most important products of chrome, as large quantities of them are used in dyeing and calico-printing. They are obtained directly from L2 126 CHROMIUM. chrome-ore, that is, from chromic iron. The chrome-ore, which even when purified by washing always contains a certain quantity of quartzose and aluminous minerals, is heated, finely powdered, in a reverberatory furnace, with carbonate of potassa, to which some nitrate of potassa is frequently added, and the material is constantly stirred to facilitate its oxidation. Chromate of potassa, but at the same time, a certain quantity of silicate and aluminate of potassa, are formed, to separate which the roasted substance is treated with water, which dissolves the soluble alkaline salts, after which acetic acid is added to the liquid until it assumes an acid reaction, which is a sign that the neutral chromate of potassa is converted into a bichromate and that the silicic acid is deposited. The bichromate, being much less soluble than the neutral salt, is easily separated by crystallization, and purified by recrystallization. Bichromate of potassa forms beautiful red crystals, which fuse without change before attaining a red-heat, but decompose at a higher temperature into neutral chromate, sesquioxide of chrome, and oxygen which is given off. This salt contains no water of crystallization, and is soluble in 10 parts of cold and in a much less quantity of boiling water. Neutral chromate of potassa is obtained by adding chromate of potassa to a solution of the bichromate until the latter assumes a clear yellow colour, and evaporating the liquid, when yellow anhy- drous crystals are obtained, presenting exactly the same form as sulphate of potassa. The neutral chromate is very soluble, as cold water dissolves more than double its weight of it, and hot water still more. The solution of the neutral chromate of potassa turns the red tincture of litmus blue. The neutral chromate of soda is very soluble in water, and, during cooling from a hot saturated solution, forms crystals corresponding to the formula NaO,Cr0 3 +10HO, and is isomorphous with sul- phate of soda NaO,S0 3 +10HO. Bichromate of Chloride of Potassium, or Chlorochromate of Potassa. 884. If a solution of bichromate of potassa be boiled with chlo- rohydric acid until chlorine begins to be evolved, a brown liquid is obtained, which on cooling deposits beautiful orange-coloured crystals of a salt which may be regarded as a bichromate of chlo- ride of potassium KC1,2O0 3 . This substance may also be con- sidered as a bichromate of potassa, in which one of the equivalents of chromic acid is replaced by 1 equiv. of chlorochromic acid, Cr0 3 Cl ; but then its formula should be written, KO(Cr0 3 + Or O a Cl.) Chlorochromic Acid. 885. A chlorochromic acid OO S C1 may be obtained isolated, by fusing in an earthen crucible 10 parts of sea-salt and 17 parts of bichromate of potassa. The liquid matter is run on a sheet-iron COMPOUNDS OF CHROMIUM. 127 plate, and, when cool, broken into fragments, which are introduced into a glass retort with 30 parts of concentrated sulphuric acid. Reaction commences immediately, a gentle heat is subsequently applied, and a blood-red liquid condenses in the receiver, which should be cooled with ice. The density of this liquid is 1.71 ; it boils at 248. By contact with water it is decomposed into chromic and chlorohydric acids: Cr0 2 Cl-f HO = Cr0 3 -f HC1. It should be kept in glass tubes hermetically sealed. X COMPOUND OP CHROMIUM WITH SULPHUR. 886. If sulphide of carbon in vapour be passed through a heated porcelain tube containing sesquioxide of chrome, the latter is con- verted into crystalline spangles of sulphide of chromium Cr 3 S 3 , re- sembling native graphite. COMPOUND OF CHROMIUM WITH NITROGEN. 887. A compound of chromium with nitrogen is obtained by heating sesquichloride of chrome in a current of dry ammoniacal gas. This substance then presents the form of a brown powder, which is unchangeable in the atmosphere at the ordinary tempera- ture, but readily ignites and is converted into sesquioxide when heated in the air. COMPOUNDS OF CHROMIUM WITH CHLORINE. 888. Chromium forms two compounds with chlorine : a proto- chloride CrCl, corresponding to the protoxide CrO ; and a sesqui- chloride Cr 2 Cl 3 , corresponding to the sesquioxide Cr 2 3 , and capable of existing under two different modifications. Protochloride of chrome CrCl is obtained by passing hydrogen gas over anhydrous sesquichloride heated to redness in a porcelain tube. Protochloride of chrome is white, dissolves in water, yield- ing a blue solution, which absorbs rapidly the oxygen of the air, thus converting the protochloride into an oxychloride O 3 C1 3 0. The solution of protochloride of chrome readily absorbs deutoxide of nitrogen, like the protochloride and protosulphate of iron. 889. Anhydrous sesquichloride of chrome is prepared by heat- ing an s intimate mixture of sesquioxide of chrome and charcoal in a current of dry chlorine, the process otherwise exactly resembling that for the preparation of chloride of aluminum ( 604). The sesquichloride is deposited in the anterior part of the tube, in the form of small spangles of a peach-blossom colour. Anhydrous sesquichloride of chrome may be brought in contact with water without being dissolved by it in the slightest degree, but boiling water dissolves it after some time, giving a green solution. If a very small quantity of protochloride of chrome CrCl be added to cold water, sesquichloride immediately dissolves with evolution of heat, and yields a green solution identical with that obtained by 128 CHROMIUM. dissolving hydrated sesquioxide of chrome in chlorohydric acid. The smallest quantity of protochloride of chrome, ^, is sufficient to produce this remarkable effect. By dissolving hydrated sesquioxide of chrome in chlorohydric acid, a green solution is obtained, which yields, on evaporation, a deliquescent green mass, the formula of which, when evaporated in dry air, is CrCl 3 -f-9HO. Heated, it evolves water and chloro- hydric acid, while oxychlorides remain. Some chemists regard this body as resulting from the direct combination of chlorohydric acid with sesquioxide of chromium, as a Morohydrate of sesqui- oxide of chrome, and give it the formula Cr 3 3 ,3HCl-f6HO. If the hydrated sesquichloride be heated in a current of chlorohydric acid gas, it only loses its water, and is converted into a violet anhy- drous sesquichloride. By pouring chloride of barium into a solution of violet sulphate of chrome, sulphate of baryta is precipitated, and there remains in the liquid a violet sesquichloride of chrome, presenting the same composition as the green sesquichloride. These two modifications are observed in several chemical reactions ; thus nitrate of silver only precipitates when cold f of the chlorine of the green chloride, while the violet sesquichloride immediately parts with the whole of it at the boiling point. The violet chloride is rapidly trans- formed into the green chloride. DETERMINATION OP CHROME ; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. 890. Chrome is always determined in the state of green oxide. To do this, the chrome is converted into chloride or sulphate of sesquioxide, and the boiling solution is precipitated by ammonia. The gelatinous precipitate of -the hydrate is collected on a filter, and, after being well washed, is calcined in a closed platinum crucible.* * A much more exact method is the alkalimetrical determination of chrome, which depends on the same principle as that of peroxide of manganese, described in the note to g 765. The chrome must first be converted into chromic acid, unless it be already in that state, by a fusion with caustic potassa and chlorate of potassa. Chlorohydric acid being added to the solution of the chlorate formed, the latter is then reduced by a protosalt of iron according to the formula, 6FeO+2CrO a =3Fe a O,+Cr a 3 - Now, if a certain quantity of a protosalt of iron has been added, and the surplus of this be determined by permanganate of potassa, according to \ 804, the quantity of chromic acid or oxide may be found by the above formula ; as six equivalents of the protoxide of iron found by subtracting the quantity determined from the whole quantity added, correspond exactly to two equivalents of chromic acid, or to one of sesquioxide of chrome. The protosalt of iron employed is the protosulphate of iron and ammonia, of which a standard solution is kept for the determination of peroxide of manganese. The methods of determining chrome by weight are inexact ; as sesquioxide of chrome cannot entirely be freed from a part of the fixed alkali used for its pre- CHROME. 129 When chrome exists in solution as chromic acid, nitrate of mer- cury is added, and the precipitate of chromate of mercury formed is calcined in a platinum crucible, leaving sesquioxide of chrome, which is weighed. Chromic acid may, also, be converted into ses- quichloride of chrome, by heating the liquid with chlorohydric acid, and passing a current of sulphurous acid gas through it, when oxide of chrome may be precipitated by ammonia. When the oxide of chrome exists in the state of a salt mixed with alkaline or alkalmo-earthy salts, it is precipitated when hot by caustic ammonia, which only precipitates the oxide of chrome, and is filtered rapidly, so as to avoid, as much as possible, the con- tact of the air, in order that the carbonic acid of the air may not precipitate the alkaline earths. If the liquid contains manganese, an ammoniacal salt must first be added in sufficient quantity to prevent the magnesia from being precipitated by the ammonia. The oxides of chrome and the alkaline earths may also be precipi- tated by an alkaline carbonate, but the mixture must then be fused in a platinum crucible with carbonate of soda, when chromate of soda is formed which is dissolved in water. The chrome is then precipitated by the processes described. Oxide of chrome is separated from alumina by boiling the hy- drated oxides with caustic potassa, which dissolves only the alumina. Oxide of chrome is separated from oxide of manganese by adding to the liquid containing the two oxides a quantity of ammoniacal salt sufficient to prevent the oxide of manganese from being pre- cipitated by the ammonia. The liquid is then boiled, and an ex- cess of ammonia added, which completely precipitates the oxide of chrome.* In order to separate oxide of chrome from the oxides of iron, the substance must be heated with caustic potassa in a silver crucible, when chromate of potassa is forme'd, which is dissolved in water, leaving the peroxide of iron isolated. cipitation, and ammonia does not precipitate it perfectly ; and the other method, not mentioned in the text, of precipitating chromic acid by acetate of lead, and weighing the chromate of lead formed, has the disadvantage that chromate of lead is not absolutely insoluble in water. W. L. F. * By far the best method of separating chrome from manganese is to precipi- tate the former as sesquioxide by carbonate of baryta, which leaves the manga- nese in solution. W. L. F. 130 COBALT. EQUIVALENT = 29.5 (369.0 ; = 100). 891. Pure metallic cobalt* is obtained by reducing its oxides in a current of hydrogen gas ; but the metal is then in the form of a black powder which is pyrophoric, like oxide of iron under the same circumstances : it becomes incandescent when projected in contact with the air. The metal is obtained in a more aggre- gated and less oxidizable form, by making the reduction by hydro- gen at a higher temperature, in a porcelain tube heated in a rever- beratory furnace. The oxides of cobalt, like those of iron, are easily reduced by cementation in contact with charcoal. If oxide of cobalt be heaped in a "brasqued" crucible, and heated in a forge-fire, precisely as in the assay of iron, a fused metallic lump of carburetted cobalt is obtained, which is gray, possessing a lustre resembling that of cast-iron ; but it has but little malleability, and breaks under the hammer. Pure fused metallic cobalt may be obtained by adopting a process which does not succeed for iron. Oxalate of cobalt is heaped in a porcelain tube closed at one end, so as to introduce as great a quantity as possible ; and this tube, closed with a lid, is placed in an earthen crucible, and the whole is then heated in a strong forge-fire, after the interstices have been filled with clay. The oxalate of cobalt is decomposed with evolu- tion of carbonic acid, according to the reaction, CoO,C 3 3 =Co+2CO a , when the metallic cobalt alone remains, and, if the temperature be sufficiently high, fuses into a button. The cobalt thus obtained is of a steel-gray colour, susceptible of a fine polish, and of the spe- cific gravity 8.5. Cobalt is nearly as magnetic as iron. Cobalt is less affected by damp air than iron, but after some time becomes covered with a brownish-black rust. Heated in the air, it is converted into an oxide. Cobalt dissolves in chlorohydric and dilute sulphuric acids, with disengagement of hydrogen gas ; but the solution is effected more slowly than that of iron or zinc. COMPOUNDS OF COBALT WITH OXYGEN. 892. Cobalt forms two well defined oxides : a protoxide con- taining 21.32 per cent, of oxygen, and a sesquioxide containing for the same quantity of metal one and a-half times more oxygen. * Cobalt was first obtained in the metallic state by Brandt, in 1733. SALTS OF COBALT. 131 The equivalent of cobalt, deduced from the composition of these oxides by giving to the protoxide the formula CoO, is 29.5. Hydrated protoxide of cobalt is obtained by adding caustic po- tassa to the solution of a salt of cobalt, a sulphate or a nitrate for example. The gelatinous precipitate, of a lavender-blue colour, should be well washed with boiling water to remove the last traces of potassa, and calcined protected from the air. The protoxide is also prepared by calcining carbonate of cobalt in a close crucible. Protoxide of cobalt is a powder of a deep ash-gray colour, which, when heated in the air, absorbs oxygen, and appears to be con- verted into an oxide CoO + Co 3 3 , corresponding to magnetic oxide of iron. It is a powerful base, which forms red salts, isomorphous with those yielded by the other metallic oxides of the same formula. Sesquioxide of cobalt is obtained by passing a current of chlorine through water containing hydrated protoxide in suspension ; when the liquid becomes rose-coloured and a black precipitate is formed. Under these circumstances, a portion of the protoxide is changed into a chloride, which dissolves, and parts with its oxygen to an- other portion of the protoxide, which is changed into sesquioxide : 3CoO-fCl=Co 2 3 +CoCL The whole of the protoxide may be converted into sesquioxide by precipitating the dissolved protochloride by potassa, and again passing chlorine through the liquid ; which is the same as imme- diately treating the hydrated protoxide by a solution of an alkaline hypochlorite. SALTS FORMED BY PROTOXIDE OF COBALT. 893. The protosalts of cobalt are generally of a currant-red or peach-blossom colour. Their solutions are of a currant-red ; but some of them, principally that of the protochloride, are red only when diluted, and change to a bright blue when concen- trated, owing to a dehydration of the salt, or to an isomeric modi- fication. It also occurs when the temperature is elevated. Crys- tals of chloride of cobalt, when cold, are rose-coloured, but when slightly heated, assume a beautiful blue, without perceptibly losing any water ; for they return to the rose colour on cooling. Charac- ters written upon paper with a dilute solution of chloride of cobalt, disappear after the evaporation of the water, because the chloride of cobalt is then in its rose-coloured modification ; but if the paper be brought near to the fire, the chloride is transformed by the ele- vation of temperature into its blue modification, by which the characters become apparent, as the colour of this modification is deeper. As the paper cools, the characters disappear again en- tirely, unless the paper has been too highly heated. This property of chloride of cobalt has given it some celebrity as a sympathetic ink. 132 COBALT. The characters only become blue if the chloride of cobalt used is very pure ; but when it contains a small quantity of nickel they turn green : the purity of the liquid may thus be ascertained. Salts of cobalt yield, with potassa and soda, lavender-blue pre- cipitates. Ammonia does not precipitate the solutions containing an excess of acid, as a double ammoniacal salt, not decomposable by an excess of ammonia, is then formed. The alkaline carbonates produce a rose-coloured precipitate of carbonate of cobalt, while the alkaline phosphates and arseniates throw down peach-blossom coloured precipitates readily soluble in an excess of acid. Yellow prussiate of potash gives a dirty-green precipitate. When the salts of cobalt contain an excess of acid they are not precipitated by sulphuric acid. The alkaline sulf- hydrates afford a black hydrated sulphide. Sulphate of cobalt is obtained by dissolving the oxide in sulphu- ric acid, and crystallizes, at the ordinary temperature, with 7 equivs. of water CoO,S0 3 +7HO, in the same form as sulphate of iron. The formula of the crystals formed between 68 and 86 is CoO,S0 3 +6HO, and they are isomorphous with sulphate of magnesia. Nitrate of cobalt is obtained by dissolving the metal, or the oxide, in nitric acid. The nitrate is easily decomposed by heat, and leaves, when subjected to a moderate temperature, the oxide CoO,Co 3 3 as a residue. Oxalate of cobalt is deposited in small rose-coloured crystals, when oxalic acid is added to a solution of sulphate of cobalt. The salt is but slightly soluble in water. The alkaline carbonates produce in solutions of the salts of cobalt a pale rose-coloured precipitate of the hydrocarbonate 2(CoO,C0 2 )+3(CoO,HO.) COMPOUND OF COBALT WITH SULPHUK. 894. Sulphide of cobalt is prepared by heating the oxide with an alkaline polysulphide : if the calcination be carried to a white- heat, a bronze-coloured metallic button is obtained. COMPOUND OF COBALT WITH CHLORINE. 895. Chloride of cobalt is prepared by dissolving the oxide in chlorohydric acid. We have already said that this chloride exists under two modifications, as a rose-coloured, and as a blue com- pound. COMPOUNDS OF COBALT WITH ARSENIC. 896. Two crystallized arseniurets of cobalt are found in nature ; but these minerals generally contain at the same time arseniurets of nickel and iron. Cobalt is also found in combination, at the ANALYTIC DETERMINATION. 133 same time, with arsenic and sulphur, in the state of a sulfarseniuret CoAs 2 -j-CoS a : mineralogists call it gray cobalt. Its most ordinary crystalline form is the cubo-octahedral. The gray cobalt worked at Tunaberg, in Sweden, which is very pure, is mostly used in labo- ratories to obtain the products of cobalt. To effect this, the pow- dered ore is first roasted in the muffle of a cupelling-furnace, with a gentle heat at the commencement, in order to avoid the fusion of the material, when the sulphur burns to sulphurous acid, a large portion of the arsenic is changed into arsenous acid which is disengaged in white fumes, and another portion of the arsenic is transformed into arsenic acid which remains in combination with the oxidized cobalt, forming arseniate of cobalt. When white fumes are no longer disengaged, a small quantity of powdered charcoal is thrown on the material, and the whole is mixed ; after which the door of the muffle is closed, when the charcoal reduces the arseniate to the state of an arseniuret ; and, if air be admitted, the roasting recommences and removes an additional quantity of arsenic. As this substance, however, cannot be entirely separated in this way, the whole must be roasted with carbonate of soda and a small quantity of nitre, and then heated in a crucible, when the last portions of arsenic combine with the soda, forming arseniate of soda, which is removed by treating the material with boiling water. The cobalt remains in the state of an oxide, generally con- taining a small quantity of peroxide of iron, which is separated by dissolving in nitric acid, evaporating to drive off the excess of acid, and then treating with water. A few drops of carbonate of soda added to the liquid precipitate hydrated peroxide of iron. Lastly, the oxide of cobalt is obtained by adding caustic potassa ; or, when metallic cobalt is to be prepared, the oxalate intended for this pur- pose is obtained by an addition of oxalic acid. The powdered ore may also be immediately fused with a mixture of carbonate of soda and sulphur, when a sulfarseniate of sodium and sulphide of cobalt are formed, which collect at the bottom of the crucible in the form of a ball. This sulphide, heated with dilute sulphuric acid, dissolves by disengaging sulfhydric acid, yielding a solution of sulphate of cobalt. DETERMINATION OP COBALT ; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. 897. Cobalt is determined either as protoxide or in the me- tallic state. It is generally precipitated from its solutions by caustic potassa, when the precipitate, being washed with boiling water and calcined at a strong red-heat in a close platinum crucible, leaves protoxide of cobalt ; but it is always to be feared that a por- tion of the cobalt may remain in the state of sesquioxide. It is, therefore, best to place the oxide in a glass bulb A (fig. 520), and heat it in a current of hydrogen gas, thus restoring the oxide to VOL. II. M 134 COBALT. the state of metallic cobalt, which is weighed as such. When the liquid contains ammonia- cal salts, it must be eva- porated to dry ness with excess of potassa to drive off the ammonia, and then treated with water. Co- balt may also be precipi- tated as sulphide by sulf- hydrate of ammonia ; but the sulphide must then be redissolved in nitric acid, and the oxide precipitated by potassa. 898. Cobalt is separated from the alkaline and alkalino-earthy metals by sulf hydrate of ammonia, which precipitates the cobalt alone as sulphide. If the solution contains magnesia, care must be taken to add an ammoniacal salt, to prevent the precipitation of this substance. The separation of the oxides of cobalt and alumina is easily ef- fected by caustic potassa in excess, which dissolves the alumina and precipitates the oxide of cobalt. It is very difficult satisfactorily to separate cobalt from manga- nese. The best method is to heat the two oxides, first in a current of chlorohydric acid gas, which transforms them into chlorides, and then in a current of hydrogen, which restores the chloride of cobalt to the metallic state, but does not decompose the chloride of man- ganese ; when, by treatment with water, the latter chloride only is dissolved. In order to separate cobalt from iron, the iron is brought to the state of peroxide, and enough sal-ammoniac added to prevent the precipitation of the cobalt by an excess of ammonia, which throws down only the sesquioxide of iron : the cobalt is then precipitated in the filtered liquid by sulf hydrate of ammonia. SMALT, AZURE, OR ZAFFRE. 899. Oxide of cobalt readily combines with fusible silicates, producing beautiful blue glasses, which find an extensive use in por- celain-painting, and are highly valued for their property of resist- ing the highest temperatures, provided no deoxidizing substances be present. A blue glass containing oxide of cobalt is technically prepared, which, when finely powdered, is used for colouring wall and writing paper, and for bluing linen. This glass, called smalt, or azure, is manufactured in large quantities, from the native sulfarseniuret of cobalt, in Saxony and other parts of Germany. The ore is roasted in a reverberatory furnace, in which the vapours of arsenious acid condense in the pipes just below the return-chimney. The ore, properly roasted, is mixed with white sand and very pure carbonate. SMALT. 135 of potassa, in determinate proportions, and fused in glass-house pots. A metallic button, which is called speiss, composed chiefly of arseniurets of nickel and iron, is often deposited at the bottom of the pot. The vitreous substance, which has an intense blue colour, is pounded after cooling, and then ground to a fine powder, which is then suspended in water, when the grosser particles are first deposited, and must again be ground. The supernatant muddy waters are decanted after some time, and poured into buckets, where they gradually deposit finer and finer powder. The clearness of the blue colour depends on the fineness of the particles. COBALT-BLUE, OR THENARD'S BLUE. 900. Oxide of cobalt also enters as a colouring principle into another colour used in painting, and called cobalt-blue, or Thenard's blue. This colouring matter is prepared as follows : A solution of sulphate or nitrate of cobalt is precipitated by phosphate of potassa ; and, on the other hand, a solution of alum is treated with carbonate of soda. The two gelatinous precipitates of alumina and phosphate of cobalt are intimately mixed, in the proportion of 3 volumes of phosphate, and from 12 to 15 parts of alumina ; when the mixture, dried and calcined in a crucible, changes into a beautiful blue powder. It is important to prevent the combustible vapours of the furnace from entering the crucible, as they would seriously injure the shade. This inconvenience is avoided with certainty by placing at the bottom of the crucible a small quantity of oxide of mercury, which produces an atmosphere of oxygen gas, and preserves the oxide of cobalt from reduction. 136 NICKEL. EQUIVALENT == 29.6 (370.0 ; = 100.) 901. Metallic nickel* is obtained in precisely the same manner as cobalt. Oxide of nickel, reduced by oxygen at a low tempera- ture, yields a pulverulent metal, which becomes incandescent in the air, and, when reduced in a " brasqued" crucible in a forge-fire, produces a well- fused carburetted metal. Pure melted metallic nickel is obtained by heating oxalate of nickel in a closed vessel in a strong forge-fire. Nickel is a slightly-grayish white metal, which is so much more malleable than cobalt, that it can be hammered and drawn out into fine wire. Its density is about 8.8. It is nearly as magnetic as iron, but loses this property when heated to about 400. Nickel bears pretty well the contact of a damp atmosphere, but by heating in the air is converted into an oxide. It dissolves in chlorohydric and dilute sulphuric acids, with disengagement of hydrogen gas. COMPOUNDS OF NICKEL WITH OXYGEN. 902. Nickel forms two oxides : A protoxide composed of..... Nickel 78.72 Oxygen 21.28 100.00 and a sesquioxide composed of..... Nickel 71.13 Oxygen 28.87 100.00 From this the equivalent of nickel is 29.6, differing by only one decimal from that of cobalt. Protoxide of nickel is obtained in the hydrated state by treating a solution of sulphate of nickel with caustic potassa, when an apple- green precipitate forms, which, when well-washed in boiling water, and then calcined and protected from the air, yields anhydrous oxide as an ash-gray powder. It is 'also obtained by the calcina- tion of the hydrocarbonate. Although calcined nitrate of nickel leaves some oxide, the temperature must be very high to convert it entirely into protoxide. Sesquioxide of nickel is prepared by subjecting hydrated prot- oxide suspended in water to the action of chlorine, or treating it * Recognised as a peculiar metal, in 1751, by Cronstedt and Bergmann. SALTS OF NICKEL. 137 by an alkaline chlorite. This oxide forms a black powder, which dissolves in hydrochloric acid with disengagement of chlorine. SALTS FORMED BY PROTOXIDE OF NICKEL. 903. The hydrated salts of nickel are of a beautiful green colour, the majority of them becoming yellow by losing their water of crystallization, while' their solutions are of a beautiful emerald green. From the salts of nickel the fixed alkalies throw down an apple-green gelatinous precipitate, while ammonia does not preci- pitate highly acid solutions, and gives only a partial precipitation with neutral solutions, as an excess of the reagent redissolves the precipitate, and the liquid turns blue. The carbonates of soda and potassa produce bright-green precipitates of the hydrocarbonate NiO,C0 3 +NiO,HO, while the alkaline phosphates and arseniates throw down pale-green precipitates. Prussiate of potash gives a greenish-white precipitate. The acid solutions of salts of nickel are not affected by sulf hydric acid, but are partially precipitated when neutral, especially if the acid of the salt is feeble ; while the alkaline sulf hydrates give a black precipitate of hydrated sulphide soluble in an excess of the precipitant. 904. Sulphate ofnickelis generally obtained from the nickel-ore, which is the metallic speiss deposited in the bottom of the crucible in the manufacture of smalt. It is principally composed of arseni- urets of nickel and iron, but frequently contains some traces of cobalt ; in which case, the powdered speiss is fused with a small quantity of alkaline glass, to which a little nitre is added, when the oxide of cobalt passes into the vitreous scoriae, and the purified nickel is concentrated in the lump of arseniuret, because cobalt is more oxidizable than nickel, which has, on the contrary, a greater affinity for arsenic. The arseniuret of nickel is then roasted to drive off the arsenic as completely as possible, and the residue of basic arseniate, after being heated in a crucible with a mixture of carbonate of soda and a small quantity of nitre, is treated with hot water, which dissolves the alkaline salts containing all the arsenic acid in the state of arseniate of soda. The oxide of nickel remain- ing is dissolved in sulphuric acid, the small quantity of persulphate of iron which the sulphate thus formed always contains being easily removed by boiling the liquid with carbonate of lime, which preci- pitates only the peroxide of iron, and introduces no foreign salts into the liquid, as sulphate of lime is very slightly soluble. Sulphate of nickel crystallizes at the ordinary temperature with 7 equiv. of water, but may be obtained combined with 6 equiv. by crystallization from a hot solution. Crystals of sulphate of nickel with 7 equiv. of water often attain a very large size, and exhibit a remarkable phenomenon of molecu- lar movement : on leaving a large crystal to itself for some days, especially if exposed to solar light, it preserves its outward form, M2 138 NICKEL. but loses its transparency ; and, if it be then broken, will be found filled with cavities, the walls of which are lined with brilliant crys- tals of quite another form, and in which the molecules are grouped in a completely different manner, while the substance has not be- come liquid. By adding oxalic acid to a solution of sulphate of nickel, no precipitate is immediately formed, while, after some time, a crys- talline powder of oxalate of nickel is deposited, and only a very small quantity of the metal remains in solution. COMPOUND OP NICKEL WITH SULPHUR. 905. Sulphide of nickel is prepared by heating a mixture of oxide of nickel, carbonate of soda, and sulphur, when the sulphide fuses into a bronze-yellow button, if the temperature is sufficiently elevated. COMPOUND OF NICKEL WITH CHLORINE. 906. Chloride of nickel is obtained by dissolving the oxide, or metallic nickel, in concentrated chlorohydric acid, when the solu- tion deposits green crystals, which, when heated in a tube pro- tected from the air, part with their water, and yield a volatile anhydrous chloride, which sublimes on the sides of the tube in the form of gold-coloured spangles. COMPOUNDS OF NICKEL WITH ARSENIC. 907. Nickel is found in nature combined with arsenic, in the state of arseniurets, NiAs and NiAs a and also occurs as a sulf- arseniuret NiS a -f NiAs a . The native arseniurets are sometimes used for the extraction of nickel, but generally the speiss arising from the manufacture of smalt is preferred for that purpose. GERMAN SILVER, ARGENTAN, OR MAILLECHORT. 908. Nickel is technically used for making an alloy capable of a high polish and the lustre of silver. This alloy, which is com- posed of 100 parts of copper, 60 of zinc, and 10 of nickel, is known in commerce by the various names of G-erman silver, maillechort, packfong, argentan. Various ornamental objects are made of it, but it is chiefly used for spurs, for carriage and harness mount- ings, etc.* It has been proposed for kitchen utensils, but this use would be dangerous, as the alloy readily oxidizes, particularly when in contact with acid liquids, and produces very poisonous salts.f * In England. f German silver finds much more extensive use in Great Britain and the United States, being now a substance almost universally employed for the manufacture of all articles for useful and ornamental purposes which are to be electro-plated. At Birmingham alone, hundreds of tons are annually fashioned into plate of every description, and subsequently coated with silver or gold by the galvanic process. W. L. F. ANALYSIS. 139 DETERMINATION OP NICKEL, AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. 909. Nickel is precipitated from its solutions by caustic po- tassa, or by sulf hydrate of ammonia, and is determined in the state of protoxide, like cobalt, after having been highly calcined ; but, as is the case with cobalt, the degree of oxidation of the oxide which remains is uncertain. In exact analyses, it is preferable to reduce the oxide by hydrogen and weigh the nickel in the metallic state. 910. As nickel is separated from the metals previously studied, by the same processes as those described for cobalt, we shall refer the reader to them (898), and proceed to examine only the separa- tion of cobalt and nickel. Nickel and cobalt are frequently found associated, and their separation, which presents some difficulties, becomes necessary. One of the most simple processes consists in pouring oxalic acid into the solution which contains the two oxides, after which the two oxalates, which precipitated together, are redissolved in ammonia, and the ammoniacal liquid is left in an uncorked bottle, when the ammonia is slowly disengaged, and, as its quantity diminishes, the liquid loses more and more its power of dissolving the oxalates. Now, the two salts not being equally soluble in the ammoniacal liquid, a moment arrives at which the latter does not contain enough ammonia to hold the oxalate of nickel in solution, which is the less easily soluble salt, but at which it can still dissolve the oxalate of cobalt : the oxalate of nickel is then deposited, and the liquid as- sumes a deeper red tinge. When a bright currant-colour is attained, the liquid is decanted, and then contains only cobalt. The small quantity of cobalt which the precipitate of oxalate of nickel always contains, is separated by again dissolving the oxalate of ammonia, and allowing the liquid to evaporate. Another process consists in pouring alternately chlorohydric acid and ammonia into the solution which contains the two oxides, until the liquid yields no precipitate with an excess of ammonia, when a sufficient quantity of ammoniacal salt has formed to constitute, with the metallic salts, double salts which are indecomposable by ammo- nia. The liquid is bottled, and caustic potassa added to it, which does not decompose the double ammoniacal salt of cobalt, while that of nickel parts with the oxide of nickel, which is precipitated. The contact of the air must be avoided during this experiment, as otherwise the cobalt would absorb oxygen and be precipitated in the state of hydrated sesquioxide. The cobalt which remains in the liquid is then precipitated by an alkaline sulphide. These metals may also be separated very accurately by dissolv- ing them in an excess of chlorohydric acid, and diluting with a large quantity of water, after which the liquid is saturated with chlorine gas, and carbonate of baryta in excess added. The liquid 140 NICKEL. is then allowed to rest for 18 hours without heing heated, when the whole of the cobalt is precipitated as sesquioxide, while the nickel remains in solution. The precipitate, which consists of sesquioxide of cobalt and the excess of carbonate of baryta, is col- lected on a filter, and, after being well washed with cold water, is dissolved in concentrated chlorohjdric acid, after which the baryta is precipitated by sulphuric acid, and then the oxide of cobalt by potassa.* * Since the author has published the above methods, a still better one has become known, which is the discovery of Liebig and Wohler, and consists in the following operations : The two oxides intended to be separated are dissolved in pure cyanide of potassium, and the red solution obtained is boiled to expel the excess of prussic acid ; when hydrogen is at the same time evolved, and the cyanide of cobalt changes to cobaltidcyanide of potassium Co 2 Cy 3 ,3KCy, while the nickel remains as potasso-cyanide nickel NiCy,2KCy. An addition of pure oxide of mercury, suspended in water, then precipitates all the nickel as a mixture of oxide and cyanide, while the mercury replaces the nickel in the double cyanide ; after which the precipitate, consisting of oxide and cyanide of nickel, and the ex- cess of oxide of mercury added, is washed and calcined, when pure oxide of nickel remains, and is weighed. The cobalt, which still exists in the solution as cobaltid- cyanide of potassium, is then precipitated by protonitrate of mercury, after having neutralized the liquid with nitric acid ; when a heavy white precipitate is formed, containing all the cobalt as cobaltidcyanide of mercury, which, by calcina- tion in the air, is converted into pure oxide of cobalt, which is weighed. W. L. F. 141 ZINC. EQUIVALENT = 32.6 (407.5; = 911. Zinc is now technically employed in a great number of different ways. That found in commerce is not perfectly pure, while the sheet-zinc more nearly approaches perfect purity, be- cause the presence of the smallest quantity of foreign matter con- siderably diminishes the malleability of the metal and renders it unfit for rolling. Zinc fuses at a temperature of about 930, and boils at a white-heat, when it may be purified by distillation ; to effect which, commercial zinc is placed in an earthen retort, which is arranged in a reverberatory furnace, while below the open neck of the retort a vessel containing water is placed to receive the zinc. Another and more suitable apparatus for this distillation consists of a clay crucible A (fig. 521), the bottom of which is perforated, and rests on a clay disk, or cheese (fromage) B, pierced likewise with a hole. A clay pipe a b, the upper end of which reaches the top of the crucible, being hermetically fastened in both apertures, the zinc to be distilled is placed in the crucible, which, after the lid is luted on, is arranged in a furnace so that the pipe may pass through the grate, beneath which is placed a pan C filled with water. "When the temperature rises in the furnace, the zinc first fuses, and then boils, when its vapour, descending through the pipe and there condensing, allows the liquid metal to run into the pan. This process is called distillatio per descensum. The distillation of zinc does not free it entirely from the metals with which it is combined, since the very high temperature at which the distillation takes place, causes a small portion of the other me- tals to be carried over with the vapours of the zinc. Zinc is of a bluish-white colour, and its fresh fracture exhibits large and very brilliant crystalline laminae. While it is brittle at the ordinary temperature, it becomes malleable at a few degrees above 212, and, when heated to 392, again becomes so brittle that it may be pounded in a mortar. Ignorance of these remarkable pro- perties of zinc for a long time prevented its extensive technical use, and formerly it was only employed for making alloys. It is now rolled into thin sheets for roofing houses, and making bathing-tubs and other vessels of great capacity. Zinc vessels must not be used 142 ZINC. for the preparation of food, because the metal readily oxidizes in contact with the air, when in presence of even the weakest acids, and produces poisonous salts. The density of zinc varies from 6.86 to 7.20, according as the metal has been cast, or rolled. 912. Zinc is a very oxidizable metal, as its surface soon tar- nishes by superficial oxidization in a damp atmosphere, while, when heated in contact with the air at a temperature above its melting point, it becomes incandescent and burns with a dazzling white flame, the brilliancy of which is owing to the vapour of zinc, which, by burning in the air, forms oxide of zinc, a perfectly fixed com- pound, of which the particles, heated to whiteness, communicate a bright lustre to the flame. Zinc dissolves readily in chlorohydric and dilute sulphuric acid, and disengages hydrogen ; and the metal, when impure, dissolves more rapidly than perfectly pure zinc. It decomposes aqueous vapour with disengagement of hydrogen, and is converted into an oxide, the reaction commencing at a tempera- ture a little above 212, when the metal exists in a very finely divided state. Zinc also dissolves with disengagement of hydrogen in a boiling so- lution of potassa and soda, and forms soluble alkaline zincates. When an iron blade is at the same time dipped into the alkaline solution, the water is decomposed even when cold, while the zinc alone dis- solves, the iron acting only by producing with the zinc a voltaic current, in which the latter metal becomes the positive element, and thus acquires an affinity for oxygen sufficiently great to de- compose water at the ordinary temperature in the presence of potassa. The decomposition of water in the presence of potassa, is effected very remarkably by plates of galvanized iron, when very brilliant small crystals, consisting of a hydrated ozide of zinc ZnO+HO are deposited on the sides of the vessel. COMPOUND OF ZINC WITH OXYGEN. 913. Only one oxide of zinc, a very powerful base, is known, the salts of which are isomorphous with those of magnesia and with the protosalts of iron, cobalt, and nickel. The oxide is obtained by heating the metal in contact with the air until it ignites, when a white flocculent substance, of which a portion is carried off by the current of air, is deposited on the edges of the crucible. The old chemists called it lana philosophica, or pompliolix.* The oxide thus obtained always contains particles of the metal, which it may be freed from by levigation. When pure oxide of zinc is to be prepared, it is better to decompose by heat either nitrate of zinc or the hy- drocarbonate which is obtained by adding an alkaline carbonate to the solution of a salt of zinc. When caustic potassa is poured into * It also bore the curious name of nihil album, "white nothing." SALTS OF ZINC. 143 a salt of zinc, a white precipitate of hydrated oxide of zinc is obtained, which retains a certain quantity of alkali with great obstinacy. Anhydrous oxide of zinc is white, and assumes a yellow shade on the application of heat, which disappears on cooling. Oxide of zinc is formed of Zinc 81.5 Oxygen 18.5 100.0 whence the equivalent of zinc is 32.6. Oxide of zinc, when mixed with drying oils, produces a white paint, which may be substituted for white-lead, or ceruse, and has been recently manufactured on a large scale.* It has the advan- tage of not being blackened by sulphurous gases, and not exposing the workmen to the same dangerous affections. SALTS FORMED BY OXIDE OF ZINC. 914. The salts of zinc are colourless when the acid is not coloured. Their solutions yield, with potassa, soda, and ammonia, white precipitates which dissolve in an excess of the reagent ; and the alkaline carbonates throw down a white precipitate, which also takes place with prussiate of potash and the alkaline phosphates and arseniates. Sulfhydric acid does not precipitate the salts of zinc when they contain an excess of acid, but the sulf hydrates give white precipitates. Sulphate of Zinc. 915. The sulphate, which is the most important of the salts of zinc, is readily prepared in the laboratory by dissolving metallic zinc in dilute sulphuric acid. It crystallizes at the ordinary tem- perature with 7 equiv. of water, of which 6 are easily driven off by subjecting the salt to a temperature above 212. Crystallized sulphate of zinc dissolves in two or three times its weight of water, at the ordinary temperature, while at 212 its solubility may be said to be infinite, as it melts in its water of crystallization. Sulphate of zinc is prepared on a large scale by roasting blende in heaps, when a portion of the sulphur is disengaged in the state of sulphurous acid, while the greater part of the blende is con- verted into sulphate of zinc, provided the temperature does not rise above a certain point. The roasted matter is treated with water, and the solution evaporated to crystallization ; and in order to render the salt easily transportable, it is generally melted in its water of crystallization, and poured into square moulds of the size * It is extensively manufactured at Vieille Montagne, and also in New Jersey, from the red oxide occurring near Franklin. 144 ZINC. of a common brick. The salt is called in commerce white vitriol, and is used in the manufacture of calico. Carbonate and Hydrocarlonate of Zinc. 916. When an alkaline carbonate is poured into a solution of sulphate of zinc, a precipitate is obtained, which is not a carbonate, but a hydrocarbonate of zinc (2ZnO,CO a +3ZnO,HO). Anhydrous carbonate of zinc is found in nature, constituting a mineral called calamine, which acquires great importance from being the ordinary ore of zinc. Most frequently, calamine exists in compact masses, and more rarely exhibits distinct crystals belonging, like carbonate of lime, to the rhombohedric system. COMPOUND OP ZINC WITH SULPHUR. 917. Zinc in the state of filings is, when heated with flowers of sulphur, converted into a sulphide ; but it is difficult thus to ob- tain a perfect sulphuration. It is better to heat a very intimate mix- ture of oxide of zinc and flowers of sulphur, when sulphurous acid is disengaged, and sulphide of zinc ZnS, in the form of a yellowish- white powder, remains. Sulphide of zinc is found abundantly in nature, forming a brownish-yellow translucid mineral, crystallized in regular octahedrons, or cubo-octahedrons, and called blende. COMPOUND OP ZINC WITH CHLORINE. 918. Zinc is easily acted on by gaseous chlorine, and converted into a white, butyrous, very fusible substance, which distils only at a red-heat. This chloride is obtained in solution in water, by treating zinc with chlorohydric acid, when the solution, on being evaporated and cooled, becomes crystalline. Chloride of zinc is soluble in water and in alcohol to such an extent, that when an aqueous solution of the salt is concentrated by ebullition, the tem- perature rises continually to 482, at which point the chloride becomes anhydrous, but still preserves its liquid state. This pro- perty suggests the use of a solution of chloride of zinc instead of oil, for baths in which substances are to be heated to a high but certain temperature. DETERMINATION OF ZINC, AND ITS SEPARATION PROM THE METALS PREVIOUSLY STUDIED. 919. Zinc is generally precipitated from its solutions by car- bonate of soda, after which the liquid is boiled, and the gelatinous precipitate of hydrocarbonate of zinc washed with boiling water, when it is determined in the state of oxide after calcination. If the liquid contains much ammoniacal salt, it must be evaporated to dryness with an excess of carbonate of soda, and then treated with water. DETERMINATION OF ZINC. 145 Zinc is frequently precipitated as sulphide by sulfhydrate of ammonia ; when the precipitate is washed with water containing a small quantity of the sulfhydrate, in order to prevent the forma- tion of sulphate of zinc by contact with the air. The hydrated sulphide is redissolved in chlorohydric acid, and the zinc precipi- tated by carbonate of soda as carbonate. 920. In general, zinc is separated from the alkalies and alka- line earths by means of sulfhydrate of ammonia, which precipitates the zinc only as sulphide ; but it is more readily separated from baryta by means of sulphuric acid. Lime may also be separated from oxide of zinc by adding to the liquid containing the two bases an excess of ammonia, and some oxalate of ammonia, which precipitates only the lime in the state of oxalate of lime, while the oxide of zinc remains in solution in the excess of ammonia. The separation of oxide of zinc from magnesia is effected by means of sulfhydrate of ammonia, the precaution being used first to add an ammoniacal salt in sufficient quantity to the liquid to prevent the precipitation of the magnesia by ammonia. Oxide of zinc is separated from alumina by ammonia in excess, which dissolves the former and precipitates the alumina, while a perfect separation is, however, difficult, as alumina is slightly so- luble in ammonia. Oxide of zinc is separated from oxide of manganese by caustic potassa, which redissolves the former and leaves the oxide of man- ganese, especially if the liquid is left exposed to the air for some time, so that the protoxide of manganese may be changed into ses- quioxide. The separation is, however, rarely effected perfectly, the oxide of manganese always retaining some oxide of zinc ; and the precipitate must be redissolved in chlorohydric acid and precipi- tated anew by an excess of potassa. In order to separate zinc from iron, the latter metal is first brought to the state of a sesquisalt by means of nitric acid or chlorine, and then ammonia in excess is added, which redissolves the oxide of zinc and precipitates only the hydrated sesquioxide of iron. It is well to redissolve the oxide of iron in an acid and precipitate it a second time by ammonia in excess, as the small quantities of oxide of zinc, which in the first precipitation had been carried down with the sesquioxide of iron, are thus separated. The separation of zinc from cobalt and nickel is more difficult. The best plan consists in precipitating the metals together by car- bonate of soda, and weighing them in the state of oxides after cal- cination. The mixture of oxides is then placed in a glass globe D (fig. 522), terminating in a curved end bed, which descends to the level of a small quantity of water in the bottle E, and a current of dried chlorohydric acid gas is passed through the tube ab, while the globe D is heated by an alcohol-lamp. The oxides are thus changed into chlorides, when the chloride of zinc, being very volatile, distils VOL.II.~N 10 146 ZINC. Fig. 522. over, and condenses in the tube bed and in the water in the bottle. The chlorides of cobalt, or nickel, on the contrary, remain in the globe D. At the close of the operation, the tube bed is detached and thrown into the bottle E, when all the chloride of zinc is dis- solved ; while, on the other hand, the globe D is heated with acidu- lated water. The metals, being thus separately dissolved, are pre- cipitated in the ordinary manner. METALLURGY OF ZINC. 921. Calamine is the principal ore of zinc. Silicate of zinc is frequently mixed with calamine, but, as it yields very little metal- lic zinc, should not be regarded as a true ore. A certain quantity of zinc is extracted from blende. The principal mines of zinc are those of Tarnowitz, in Silesia, Vieille Montagne, near Lige, and several counties in England. The theory of the metallurgic treatment of calamine is very simple : The ore is calcined, by which process its carbonic acid is driven off and it is rendered friable, after which it is powdered in mills with edge-stones, and the powder, mixed with charcoal, is heated in earthen retorts in a furnace to a strong white-heat. The oxide of zinc is reduced by the charcoal, while carbonic oxide gas is disengaged, and the metallic zinc condenses in allonges fitted to the retorts. 922. The ore of Vieille Montagne is a mixture of silicate and carbonate of zinc, being sometimes compact and sometimes crys- tallized. The gangue consists exclusively of clay, in amorphous masses, scattered through the fragments of calamine. The ore is exposed to the air for several months, to allow the clay to rot, after which it is easily separated ; while sometimes it is washed, and the clay in this manner almost entirely removed. Two classes of ore are distinguished, according to their aspect and chemical composition, the white ore and red ore, the latter of which con- tains more iron than the first, and is less rich in zinc, but more METALLURGY OP ZINC. 147 easily worked. The following is the average composition of these two kinds of ore : White ore. Red ore. Oxide of zinc j ^ LC 46.6 vffen.. , 11.7 33.6 8.4 Silex and clay Water and carbonic Sesquioxide of iron. 14.0 acid 22.7 5.0 20.0 20.0 18.0 100.0 100.0 The washed ore is calcined in conical kilns (fig. 523), resembling limekilns, and heated by two lateral fur- naces, covered by an arch, and terminating in a canal which opens into the kiln by 20 working-holes 0,0,0, arranged in 4 or 5 rows, each opening being four inches square. At the lower part of the furnace are two rec- tangular openings A, intended for the re- moval of the roasted ore, while two cast-iron plates /, /, having an inclination of 45, divide the descending column of ore, and Fig. 523. facilitate its escape from the kiln. The Fig. 624. Fig. 525. 148 ZINC. calcination is continuous, and the ore is charged from above, the large and small pieces being so mixed as to allow an easy passage for the flame. The ore loses during the calcination its water and carbonic acid ; the loss being about 25 per cent. The kilns are heated with pit-coal. The calcined ore is finely powdered in edge-stone mills, sifted, and then sent to the reducing furnace. The furnace is composed of four kilns joined together, the shape of each being that of a cylindrical cradle A (figs. 524 and 525), the upper edge of which is about 8.5 feet above the floor. The posterior part of the furnace is made by a wall bd, inclined back- ward, while the anterior part ac is, on the contrary, entirely open. The hearth F is below the floor of the furnace, into which the flame enters by 4 holes 0, 0, and at the top of the wall are two flues U, U, which open into a chimney in the centre of the building. The chimney, which serves for the 4 kilns, is divided into 4 compart- ments, each having its own register T. In each furnace 42 retorts of refractory clay are arranged, consisting of long earthen pipes bd (fig. 526), closed at one end d, 3.4 feet long, with an internal dia- meter of 5.9 inches. Into each tube a conical cast-iron pipe cd (fig. 527) is inserted, which acts as a condenser, and to which is Fig. 526. Fig. 627. Fig. 528. fitted a second conical sheet-iron pipe ef (fig. 528), having at /an opening of only 0.8 inch. The earthen pipes are arranged in the kiln in 8 rows above each other, their closed ends resting on 8 projecting edges built in the back wall bd of the oven (fig. 524). On the front wall ac, which is open, are arranged 8 cast-iron plates, supported by bricks, and intended for the reception of the anterior part of the tubes, which are slightly inclined forward. The kilns are kept burning for 2 months, after which they generally need repairing. In order to start a new furnace, the open face of the kiln is first closed with brickbats and broken tubes, and cemented with mortar, after which it is heated for several days, at first gradually, and, then to a white-heat. After 4 days of preliminary heating, the tubes are introduced by removing the anterior part of the furnace and ar- ranging them after they have been previously heated ; the inter- stices between the tubes and the anterior compartment through which they pass being luted with mortar ; and lastly, the conical allonge being adapted to each tube. When the crucibles are arranged in the furnace, a small quantity of ore and charcoal is first introduced, these charges being succes- sively increased until, after several days, the regular work of the METALLURGY OF ZINC. 149 furnace begins. This period of the operation is that which alone occupy our attention. The ore is brought in a wooden box, where it is mixed with char- coal, and a little water added. The charge of a furnace consists of 10 cwt. of calcined calamine, and 5 cwt. of dried pulverized pit- coal, which substances are intimately mixed with an iron shovel. The residue of the preceding distillation is removed from each tube, which then, with its cast-iron receiver, is cleaned by means of an iron rod. The lower tubes are first charged. The mixture is introduced by means of semi-cylindrical sheet-iron shovels (fig. 529), fastened to an iron handle ; and when the charging is corn- Fig. 529. pleted the fire is blown up. A large quantity of carbonic oxide is soon disengaged, and burns with a blue flame at the openings of the cast-iron receivers, while in a short time this flame becomes more brilliant, of a greenish-white colour, and evolves white fumes, which is a sign that the distillation of the zinc has commenced, and that it is time to fit the sheet-iron allonges to the tubes. Whatever care may be taken to obtain a uniform temperature, the heat is always greater in some parts of the kiln than in others ; for which reason the upper tubes are charged only with the red ore, as being the most easily reduced, while the white is introduced into the lower ones. After 2 hours' firing, the workman detaches the sheet-iron allonges, and shakes them over a sheet-iron receiver, when a dust of zinc and oxide of zinc, called cadmie, falls down, which is added to the ore in the succeeding operations. An assistant then holds a large sheet-iron spoon (fig. 530), called a poelon, near the opening of each cast-iron receiver, while the master workman introduces an iron rake, with which he draws out the distilled zinc, which has ac- cumulated in a liquid state at the bottom of the allonge, and in the same way detaches the drops adhering to its sides. The liquid zinc collected Flg ' ' in the poelons is covered with metallic scum, con- sisting chiefly of oxide of zinc, which is carefully removed, and the zinc run into rectangular moulds, in pieces weighing from 60 to 70 Ibs. The sheet-iron allonges are immediately replaced and the fire continued. In 2 hours a second drawing is made, and so on until 5 o'clock P. M., when the operation is generally terminated. The tubes are then cleaned, and new ones substituted for those destroyed in the preceding operation. Two operations are thus made in 24 hours, producing together about 6 cwt. of zinc and 30 to 50 Ibs. of metallic dust ; so that by this treatment, calamine yields about 31 per cent, of zinc, about 10 per cent, remaining in the residue. The metal contained in the residue existed in the state of silicate of zinc, which is not reduced by the charcoal. N2 150 ZINC. The greater part of manufactured zinc being used in the shape of rolled zinc, it is necessary again to melt the ingots, which is done in a reverberatory furnace with an elliptical floor of refrac- tory clay and slightly inclined backward. At the lowest part of the floor is a hemispherical crucible in which the melted zinc col- lects, and from which it is dipped out and run into moulds of a suitable form for rolling. The plates are being reheated in a second furnace adjoining the first, by means of the hot gases of the former, and, when they have reached a temperature not exceeding 212, are passed between cast-iron rollers. When they are of suitable size, they are cut into rectangular sheets of the dimen- sions required, the clippings being again fused. Formerly, zinc was fused in large cast-iron pots, which, however, soon became perforated, while the zinc lost many of its qualities by being com- bined with a small quantity of iron. 923. The furnaces and distilling apparatus used in Silesia dif- fer essentially from those in Belgium. Fig. 531 gives a view of a Fig. 531. Fig. 532. Silesian furnace, of which fig. 532 is a vertical section. The distilla- tion is effected in muffles of baked clay M (figs. 533 and 534), about 3 feet in length and 1.5 feet in height, the anterior part of which has 2 openings : the lower openn of distillation is withdrawn, is close , through which the residue during the operation by a clay METALLURGY OF ZINC. 151 loor, tightly luted, while into the upper opening a right angled clay tube bed, closed at d, is introduced. The ore is charged with a shovel through a hole c, which is closed during the distillation Fig. 533. Fig. 534. with a baked-clay stopper. Six or ten muffles are arranged in two rows in a kiln, the side walls of which have apertures for their pas- sage, which are closed by sheet-iron doors, preventing too sudden a cooling of the allonges led. The kiln is heated with pit-coal burned on the grate G, and they are charged with a mixture of equal parts of calcined calamine and charcoal cinders, which, having fallen through the grate, are immediately extinguished in water placed beneath. No pulverized pit-coal is used, lest any coal-dust, carried by the current of gas, should obstruct the allonges ; and the calamine itself is reduced to the size of a pea. The zinc runs through the opening d of the allonge, and is collected in the spaces t of the furnace. Although the operation lasts only 24 hours, the muffles are not emptied until after three operations, when a half- fused greenish mass is extracted as a residue. The calamine is roasted in reverberatory furnaces heated by the waste flame of the reducing furnace. Silesia furnishes the greater portion of the zinc which is brought into commerce. 924. In the Belgian and Silesian processes, the distillation of the zinc is effected per ascensum, while the process employed in England furnishes an example of distilla- tion per descensum. The reducing fur- naces, resembling very much the ordi- nary glass-furnace, being circular (fig. 535), and having the hearth F in the middle, at a certain distance below the floor of the furnace. The ore, mixed with charcoal, is charged in the crucibles Cj which are arranged around the hearth, and introduced through several apertures in the arched roof. There is a hole in the bottom of each crucible, into which an iron tube tt, passing through an aper- ture in the floor of the furnace, and open- ing externally, is introduced. The upper opening of the tube is closed, before the charging, with a wooden stopper, which, by becoming carbonized during the operation, is sufficiently porous Fig. 535. 152 ZINC. to allow the gaseous zinc to escape, while the ore is still retained ; and each pot is covered with a lid accurately luted with clay. The distilled zinc condenses in the iron pipe it, and drops into a sheet- iron receptacle beneath, an iron rod being, from time to time, in- troduced to detach the zinc which may have become solid, and might ultimately choke the tubes. 925. A certain quantity of zinc is also extracted from blende, which is found in large quantities in several localities, after roast- ing the blende as perfectly as possible, first in heaps, by which the greater portion of the sulphur is removed and the ore is rendered very friable, and then in a reverberatory furnace, by which the oxidation of the zinc is completed. The roasted ore, which con- sists of oxide and sulphate of zinc, is reduced by charcoal in a dis- tilling apparatus, in the same manner as calamine. 153 CADMIUM. EQUIVALENT = 56 (700; = 100). 926. Cadmium* is a metal still more volatile than zinc : it distils at a red-heat, and the distillation may be effected in glass retorts which are difficult of fusion. In order to obtain pure cad- mium, a mixture of oxide or carbonate of cadmium and charcoal is heated in a retort, when the cadmium sublimes and condenses in drops in the neck of the retort. The small drops often crystallize on solidifying, the crystalline form of the metal belonging to the regular system. Cadmium is a white metal, rather more gray than tin, and pos- sessing a considerable degree of malleability and ductility. Its density is 8.7, and it fuses long before reaching a red-heat. Cad- mium does not oxidize appreciably at the ordinary temperature, but on being heated, its vapour ignites and burns with brilliancy. Chlorohydric and dilute sulphuric acid dissolve it with the evolu- tion of hydrogen gas. COMPOUND OF CADMIUM WITH OXYGEN. 927. The only oxide of cadmium known is obtained either by heating the metal in the air or by treating it with nitric acid, and then decomposing the nitrate by heat. The oxide forms a brown powder, which resists the highest temperature without volatilizing or melting, and which readily combines with acids, forming colour- less salts, unless the acid itself is coloured. Caustic potassa or soda effects a white precipitate with salts of cadmium, consisting of hydrated oxide of cadmium. Oxide of cadmium is composed of Cadmium 87.5 Oxygen 12.5 100.0 whence its equivalent is inferred to be 56. SALTS FORMED BY OXIDE OF CADMIUM. 928. The salts of cadmium, the greater number of which readily crystallize, are colourless. The fixed alkalies precipitate them from their solutions as gelatinous hydrated oxide, which does not redissolve in an excess of the reagent. Ammonia affords the same * Discovered in 1818, by Hermann and Stromeyer. 154 CADMIUM. precipitate, but an excess of ammonia easily redissolves it. The alkaline carbonates yield a white precipitate of neutral carbonate of cadmium CdO,CO a , insoluble in an excess of the reagent. Sulf- hydric acid throws down, even in the presence of a considerable ex- cess of acid, a very beautiful yellow precipitate, while the alkaline sulfhydrates afford the same precipitate, which is insoluble in an excess of sulfhydrate. A blade of zinc, dipped into a solution of a salt of cadmium, precipitates the metal in the form of crystalline spangles. Sulphate of cadmium crystallizes with 4 equiv. of water. COMPOUND OF CADMIUM WITH SULPHUR. 929. Sulphide of cadmium is found crystallized in nature, but is a rare mineral. It is obtained artificially by passing a current of sulf hydric acid gas through a solution of a salt of cadmium. The beautifully yellow precipitate thrown down is used in paint- ing. Sulphide of cadmium is also prepared in the dry way, by heating oxide of cadmium with sulphur. The sulphide is not at- tacked by dilute chlorohydric acid, but dissolves in the concen- trated acid with the evolution of hydrogen gas. COMPOUND OP CADMIUM WITH CHLORINE. 930. Chloride of cadmium is obtained by heating the metal in a current of chlorine, when a white fusible substance is formed, which sublimes when further heated. By dissolving cadmium in chlorohydric acid, or in aqua regia with an excess of chlorohydric acid, a solution of hydrated chloride is obtained, which crystallizes readily, and loses its water by heat, without being decomposed. DETERMINATION OF CADMIUM, AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. 931. Cadmium is determined in the state of calcined oxide of cadmium, and, when it exists in solution, is precipitated by car- bonate of soda at the boiling point. The precipitation is complete, even when the liquid contains ammoniacal salts. Cadmium is easily separated from all the metals we have hither- to studied, by passing a current of sulf hydric acid gas through the solutions, which must be slightly acidulated by a mineral acid. The precipitate of sulphide of cadmium formed is washed with water containing a small quantity of sulfhydric acid, and then re- dissolved in nitric acid, and the hot solution precipitated by car- bonate of soda. EXTRACTION OF CADMIUM. 932. Cadmium occurs in nature as oxide, or carbonate, spar- ingly scattered through calamine, and is most abundantly found in that of Silesia. When zinc is extracted from this ore, the cadmium CADMIUM. 155 is reduced at the same time, and, as it is much more volatile than zinc, is first disengaged, and burns in the air with the first portions of zinc that are liberated, when a more or less brownish dust is formed, composed of oxide of zinc and 5 or 6 per cent, of oxide of cadmium. This oxide is mixed with J of its weight of charcoal, and then heated to redness in iron tubes, when the greater part of the zinc remains in the residue, because the temperature is not suf- ficiently high to volatilize it, while the cadmium distils with a por- tion of the zinc, and condenses in a second sheet-iron tube which acts as a receiver. By subjecting the product to another precisely similar operation, cadmium, containing only a few hundredths of zinc, is obtained. Its purity is ascertained by striking it with a hammer : a very small quantity of zinc deprives it of its mallea- bility. The purification of the metal is completed by dissolving it in chlorohydric acid, and then precipitating it by a blade of zinc. 156 TIN. EQUIVALENT = 58 (725.0 ; = 100). 933. Common commercial tin is never absolutely pure, as it always contains small quantities of arsenic and other foreign me- tals ; but Malacca tin is nearly perfectly pure. In order to obtain chemically pure tin, the metal of commerce is treated with nitric acid, which converts it into an insoluble white powder consisting of stannic acid, and which oxidizes foreign substances. The stannic acid is reduced to the metallic state by heating it in a "brasqued" crucible, after being washed with weak chlorohydric acid to remove more certainly the foreign substances. Tin is a white metal, resembling silver in its appearance and lustre, and possessing a certain characteristic taste and smell, par- ticularly when held for some time between the fingers. It is very malleable, and may be beaten into exceedingly thin sheets, its mal- leability being greater at 212 than at the ordinary temperature ; but its tenacity is very feeble, for a wire of 2 millimetres breaks under a weight of 24 kilogs. On bending a bar of tin a peculiar noise is heard, called the cry of tin, which is owing to the inter- nal crystalline texture of the metal. The crystalline particles rub upon each other when the bar is bended, while the latter be- comes heated at the point of this internal friction ; and if the bending is repeated several times at the same spot, the evolution of heat becomes sensible to the hand. Tin fuses at 442.4, giving off at a white-heat appreciable va- pours of very feeble tension, for the metal suffers but a slight loss at the temperature of a forge-fire. Tin has a great tendency to crys- tallization, and its crystalline texture is easily demonstrated by attacking its surface by an acid which removes the outer pellicle. The surface of the metal then appears to be watered, in conse- quence of the unequal and various reflections of light by the edges of the crystalline laminae exposed by the acid. Tin may be crys- tallized by fusion, by melting several pounds of the metal in a ves- sel, and allowing it to cool slowly over a heated sand-bath. When a solid crust has formed on the surface, it is pierced with a burning coal and the liquid portion evacuated, when quite large crystals of tin, which, however, are rarely well-defined, are often found on the sides of the vessel. By precipitating tin by means of the galvanic current, it may be obtained in long brilliant prismatic crystals, the form of which has not yet been exactly determined. For this purpose a concentrated solution of protochloride of tin is poured into a glass, and above it PROPERTIES OF THE METAL. 157 a stratum of fresh water is carefully placed ; after which a blade of tin, which traverses both strata, is introduced into the glass, when the blade of tin soon becomes covered with very brilliant metallic crystals. The density of tin is 7.29, and is not sensibly increased by the hammering of the metal. Tin is too ^ malleable to be pulverized in a mortar, for which reason tin filings, or the tin-leaf employed to wrap Unions and chocolate, must be taken when the metal is to be used in a finely divided state. Finely divided tin may also be obtained by a pecu- liar process, consisting in beating the metal, when fused in a cap- sule, rapidly with a large brush until it is entirely cool, when it is reduced into very small globules, which may be separated into globules of various sizes by a kind of levigation. Tin does not sensibly change in the air at the ordinary tempera- ture, but at its fusing point becomes quickly covered with a gray pellicle, which is a mixture of protoxide of tin and stannic acid. Oxidation takes place much more rapidly at a higher temperature, and at a white-heat the metal burns with a white flame. Tin de- composes aqueous vapour at a red-heat, and is converted into stan- nic acid. Concentrated chlorohydric acid dissolves tin with the disengage- ment of hydrogen gas. Dilute sulphuric acid also acts on it, when hot, with the evolution of hydrogen, but the metal oxidizes very slowly. Concentrated hot sulphuric acid attacks tin rapidly: sul- phurous acid is disengaged, and the metal is changed into proto- sulphate. Dilute nitric acid oxidizes tin readily and converts it into stannic acid, while the concentrated acid causes a copious evolu- tion of deutoxide of nitrogen. If the acid is very dilute, the tin is converted into stannic acid without disengagement of gas, the water and nitric acid being simultaneously decomposed and nitrate of ammonia formed ( 122) ; but when the acid is at its maximum of concentration, that is, in the state of monohydrate N0 5 H-HO, it does not attack tin at all, and the metal preserves its bril- liancy. But, if a few drops of water be poured into the acid, the reaction takes place with extreme violence, and the liquid is frequently extravasated by the rapid and sudden disengagement of gas. Aqua regia dissolves tin readily, while, if chlorohydric acid pre- dominates in the mixture, a soluble perchloride of tin is formed. Tin decomposes water in the presence of the fixed alkalies, and disengages hydrogen when heated with a concentrated solution of potassa or soda, while an alkaline stannate is formed. COMPOUNDS OF TIN WITH OXYGEN. 934. Two well-defined compounds of tin with oxygen are known : VOL. II. 158 TIN. Protoxide of tin SnO. Binoxide of tin Sn0 2 , or stannic acid. These two oxides can combine with each other and produce seve- ral intermediate compounds. Protoxide of Tin, SnO. 935. Protoxide of tin is prepared by precipitating a solution of the protochloride SnCl by carbonate of ammonia, when car- bonic acid is disengaged, and a white precipitate of hydrated prot- oxide is thrown down. If the liquid be boiled with the precipi- tate, the latter gives off its water of combination, and is converted into a blackish-gray powder, consisting of anhydrous protoxide, which has great affinity for oxygen, as it oxidizes rapidly in the air, and is converted into stannic acid. The oxide is obtained in a state of greater aggregation, and consequently more fixed, by precipitating protochloride of tin by caustic potassa; when the oxide is first separated in the hydrated state, and combines with the excess of potassa to form a true salt, in which it acts the part of an acid. But, by boiling the liquid, this combination is de- stroyed, and the oxide is precipitated in the anhydrous state, in the form of small black crystals, which, after being washed and dried in the air, remain unchanged for any length of time. When this substance is heated in an oil-bath to about 482, it suddenly decrepitates, increases considerably in volume, and is converted into a number of small brown laminoe, which are soft to the touch. The oxide has not changed in weight during the transformation, and has only passed into an isomeric modifica- tion ; so that this phenomenon must be attributed to a molecular movement, caused, probably, by a change in the crystalline sys- tem. The brown modification of protoxide of tin is immediately obtained by precipitating a solution of protochloride of tin by an excess of ammonia, and boiling the liquid, when it is evaporated in vacuo. The solution of the protoxide in potassa deposits black crystals of the first modification of the oxide ; while if, on the con- trary, a solution of the protoxide of tin in potassa be highly con- centrated by rapid boiling, the oxide is decomposed into metallic tin which is separated, and stannic acid which remains combined with the potassa : 2(KO,SnO) = Sn-f KO,Sn0 3 +KO. Lastly, protoxide of tin may be obtained in the form of a red pow- der, by decomposing the protochloride by ammonia, boiling the liquid a few moments, and then evaporating it at a gentle heat ; the prot- oxide of tin is converted into small grains of a beautiful red,colour, under the influence of the sal-ammoniac formed during the reaction. The red oxide is changed into the brown modification by simple friction with a hard body. OXIDES. 159 Protoxide of tin ignites like tinder when heated in contact with the air, and is changed into stannic acid. Protoxide of tin is composed of Tin 87.88 Oxygen 12.12 100.00 The equivalent of tin is therefore 58. Stannic Acid Sn0 3 . 936. Stannic acid may be obtained under two isomeric modifi- cations, which are clearly distinguished from each other by chemi- cal properties. The first modification, called metastannic acid, is the white powder obtained by treating tin by nitric acid ; while the second, to which the name of stannic acid is given, is prepared by decomposing perchloride of tin SnCl 2 , by water, or a soluble stan- nate by an acid. Metastannic acid is found crystallized in nature in some of the old rocks, forming very beautiful, brilliant crystals, generally of a deep brown colour, and yielding a yellowish powder. The same substance is obtained by oxidizing tin by nitric acid, when a white powder, which is a hydrate, is formed, but which changes by calci- nation into anhydrous metastannic acid. Hydrated metastannic acid, such as is formed by the action of nitric acid on metallic tin, has, when dried in the air, the formula Sn0 3 -f 2HO. It loses one-half of its water at 212, and then presents the composition Sn0 3 +H0, while it loses all its water at a higher temperature. Metastannic acid is not decomposed by heat alone, but is readily converted into metallic tin by contact with charcoal and the com- bustible gases. It is insoluble in water and in dilute nitric and sulphuric acid, while concentrated sulphuric acid dissolves it in considerable proportions. The compound formed is not destroyed by adding water to the liquid ; but by boiling, the metastannic acid separates in the state of hydrate Sn0 2 +2HO. Chlorohydric acid dissolves it, and transforms it into perchloride of tin SnCl 3 . Metastannic acid forms crystallizable salts with the alkalies. It dissolves readily, when cold, in a solution of potassa, and, if frag- ments of potassa be added to the liquid, its solvent power is so far weakened as to cause the metastannate of potassa to be deposited in the form of a crystalline crust, which is separated and spread on a plate of unglazed porcelain, when the mother liquid which moist- ens them is thus absorbed. Analysis has proved the formula of this salt to be KO,5Sn0 3 -f 4HO ; and as that of the metastannate of soda is similar, the conclusion follows that the equivalent of stannic acid which combines with 1 equiv. of the base is not Sn0 3 , but rather Sn 5 10 . Metastannate of potassa dissolves in water without change, and the liquid leaves after evaporation a gummy, 160 TIN. uncrystalline residue. Heating to redness destroys the compound, and the metastannic acid becomes anhydrous and insoluble, so that water will only remove pure potassa. An acid, poured into a solu- tion of an alkaline metastannate, precipitates the metastannic acid in the form of a gelatinous substance, which appears to contain more water than the hydrate Sn 5 10 -f 10HO, and which is soluble in am- monia, while the hydrate Sn 5 10 +10HO is not. A slight elevation of temperature, inferior even to that of boiling water, causes the gelatinous acid to pass into the state of the hydrate, which is inso- luble in ammonia. Stannic acid is obtained by decomposing perchloride of tin by ammonia, or a soluble stannate by an acid. It is a white gela- tinous precipitate, insoluble in water, but readily dissolving in dilute nitric and sulphuric acid, while metastannic acid is insoluble under the same circumstances. The formula of stannic acid, dried in vacuo, is Sn0 3 ,HO. A slight elevation of temperature causes it to pass into the metastannic modification, even without losing its water. Stannic acid dissolves readily in alkaline solutions, and the liquid, when evaporated in vacuo, yields beautiful colourless and transpa- rent crystals, of the formula KO,Sn0 3 -f 4HO. It will hence be seen that stannic acid saturates four times as much base as meta- stannic acid. The same salt is obtained by heating metastannic acid with an excess of potassa in a silver crucible, when the meta- stannic is converted into stannic acid. The completeness of the transformation may easily be ascertained by dissolving a small quantity of the substance in water, and adding an excess of nitric acid ; when the stannic acid, which at first is precipitated, is redis- solved in the acid liquid, which would not take place if metastannic acid were still present. Stannate of potassa is not decomposed by heat like the metastannic, but loses its water, while it redissolves in water without change. 937. Several oxides of tin, intermediate between the protoxide and stannic acid, are known. By digesting hydrated metastannic acid with a concentrated solution of protochloride of tin, the liquid becomes strongly acid, and the metastannic acid is converted into a yellowish powder, which may be considered as a compound of metastannic acid and protoxide of tin, having the formula SnO, Sn 5 10 +4HO. Another intermediate oxide of tin is obtained by mixing hydrated sesquioxide of iron with a solution of protochlo- ride of tin, when a yellowish precipitate is formed, which may be considered as a stannate of tin SnO,SnO a . PROTOSALTS OF TIN. 938. Only a small number of salts formed by protoxide of tin is known. The protosulphate is obtained by saturating, when hot, dilute sulphuric acid with recently prepared and moist hy- SULPHIDES. 161 drated protoxide of tin. The oxide is dissolved, and, on cooling small crystalline lamellae of protosulphate of tin SnO,S0 3 are de- posited. This salt readily dissolves without change in cold water, while heat decomposes it in its solution, and precipitates a sub- sulphate. Protosulphate of tin forms with the alkaline sulphates double sulphates, which are more fixed than the simple sulphate of tin, and may be obtained crystallized. Protonitrate of tin is prepared by dissolving hy drated protoxide in weak nitric acid, when the salt remains in solution ; but it is decomposed when the liquid is evaporated, while stannic acid is formed. SALTS FORMED BY STANNIC AND METASTANNIC ACID ACTING THE PART OF A BASE. 939. It has been shown that metastannic acid combines with concentrated acids, and that stannic acid dissolves even in dilute acids. True salts, in which these bodies act the part of bases, are thus formed ; but they have been too little studied to require our further consideration. COMPOUNDS OF TIN WITH SULPHUR. 940. Tin forms two compounds with sulphur : a protosulphide SnS corresponding to the protoxide, and a bisulphide SnS a corre- sponding to stannic acid. Protosulphide of tin is prepared by heating a mixture of tin filings and sulphur to redness in an earthen crucible, pulverizing the product of this first operation and reheating it with an additional quantity of sulphur, when a mass of a deep gray colour, with very brilliant large crystalline lamellae, is obtained. The same sulphide is pre- cipitated as a deep brown, nearly black powder, in a hydrated state, when a current of sulf hydric acid gas is passed through a solution of protochloride of tin. Concentrated chlorohydric acid dissolves protosulphide of tin with the disengagement of sulf hydric acid, while the presence of a small excess of the former, in a dilute solu- tion of tin, does not prevent the salt from being completely preci- pitated by sulfhydric acid. Per chloride of tin SnCl 3 yields with sulfhydric acid a yellow precipitate of hydrated bisulphide of tin SnS 3 . If sulfhydric acid gas and vapour of anhydrous perchloride of tin be passed through a tube heated to a dull red, bisulphide of tin is deposited in the form of very brilliant crystalline lamellae, of a beautiful golden-yellow colour, which substance is technically prepared in the dry way, and is used, under the name of mosaic gold, for bronz- ing wood. This product is obtained as follows : An amalgam of 12 parts of tin and 6 parts of mercury, pulverized in a mortar, is mixed with 7 parts of flowers of sulphur and 6 parts of sal-ammo- niac, and heated in a long-necked matrass in a sand-bath, the tem- o2 ll 162 TIN. perature of which is gradually raised to a dull red. Sulphur, sal- ammoniac, sulphide of mercury, and protochloride of tin condense in the globe and in the neck of the matrass, while mosaic gold remains at the bottom in the form of a very light, gilded mass, formed by the union of a large quantity of small crystalline la- mellae. The theory of this operation is quite complicated : finely divided tin, when heated with sulphur at a low temperature, is changed into an amorphous bisulphide, which does not present the gilded spangles which alone give it a technical value. By being still further heated it parts with one-half of its sulphur, and passes into the state of monosulphide, which the sal-ammoniac added to the mixture prevents, because, by becoming volatile below a dull red-heat, it absorbs a considerable quantity of latent caloric ; but it facilitates at the same time the sublimation, and, consequently, the crystallization of the mosaic gold which is carried over by the vapour. COMPOUNDS OF TIN WITH ARSENIC. 941. Tin and arsenic combine readily, and in all proportions, forming very brittle crystalline compounds. The arseniurets of tin disengage mixtures of pure hydrogen and arseniuretted hydro- gen by treatment with chlorohydric acid. COMPOUNDS OF TIN WITH CHLORINE. 942. Tin forms two compounds with chlorine : a protochloride SnCl, corresponding to the protoxide, and a bichloride SnCl a cor- responding to stannic acid. Protochloride of tin is obtained by dissolving tin in concentrated boiling chlorohydric acid, when hydrogen gas is evolved. This salt is used in dyeing, and is prepared on a large scale by heating curved bars of tin in large retorts with concentrated chlorohydric acid, after which the saturated liquid is decanted, and the protochloride of tin separated by evaporation in the form of hydrated crystals, of the formula SnCl+2HO. Protochloride of tin dissolves without alteration in a small quan- tity of water, while a large quantity of this liquid decomposes it, and precipitates an insoluble oxy chloride SnCl+SnO. Crystallized protochloride of tin can be freed from its water by heating in a retort, while a small quantity of the chloride is always decomposed during this desiccation, and chlorohydric acid is disen- gaged ; but if the temperature be raised to redness, the protochlo- ride distils over unaltered. Protochloride of tin combines readily with the alkaline chlorides, and yields easily crystallizable double chlorides. Protochloride of tin has such an affinity for oxygen that it readily absorbs this gas from the air, and abstracts it from a great number of oxides, which it reduces to an inferior degree of oxidation, or CHLORIDES. 163 even to the metallic jstate. It readily precipitates mercury, gold, and silver from their solutions in the metallic state, and reduces the salts of sesquioxide of iron and protoxide of copper CuO to the minimum of oxidation. 943. Perchloride of tin is readily obtained by treating tin by an excess of chlorine. The affinity of these two bodies is so great that tin filings ignite when thrown into a bottle filled with dry chlorine. In order to prepare any quantity of perchloride, some tin is placed in a tubulated glass retort, furnished with a well- cooled receiver, and a current of chlorine is passed through the tubulure, when the tin immediately combines with the chlorine ; and, if the retort be gently heated, a liquid distils over and con- denses in the receiver. This liquid, which is generally tinged with yellow by the chlorine it contains in solution, is purified by shaking it with tin filings or protochloride of tin and redistilling it. This substance may also be prepared by heating, in a glass retort, a mix- ture of 1 part of tin filings and 5 parts of chloride of mercury or corrosive sublimate. Perchloride of tin forms a colourless liquid of the specific gravity 2.28, and which boils at 248, the density of its vapour being 9.2. It gives off very thick white fumes when in contact with the air, owing to the immediate combination of the vapour of the anhy- drous chloride, the tension of which is very high at the ordinary temperature, with the aqueous vapour contained in the atmosphere, and the resulting formation of a hydrate which has no sensible ten- sion, and is, consequently, precipitated. If a few drops of water be added to the anhydrous perchloride, a noise resembling that produced by plunging a red-hot iron in water is heard, and the perchloride then combines with the water with great evolution of heat, giving rise to a hydrated chloride of the formula SnCl 2 +5HO, which is deposited in beautiful crystals. The same hydrated perchloride of tin may be obtained by dis- solving tin in aqua regia containing an excess of chlorohydric acid, or by passing chlorine through a solution of protochloride of tin. The hydrated perchloride dissolves in a small quantity of water, and in any quantity whatever of this liquid when it is sufficiently acidulated with chlorohydric acid, while an addition of a quantity of fresh water again decomposes it, and causes the precipitation of hydrated stannic acid. Hydrated perchloride of tin is decomposed by heat, when chlo- rohydric acid is disengaged and metastannic acid remains. Heated with anhydrous phosphoric acid, or with concentrated sulphuric acid, it imparts its water to them, and the anhydrous perchloride distils over. The anhydrous perchloride of tin was called by the old chemists the fuming liquid of Libavius. 164 TIN. Perchloride of tin combines with a great number of metallic chlorides, forming readily crystallizable double chlorides, which all consist of 1 equiv. of perchloride of tin and 1 equiv. of the other metallic chloride. The anhydrous perchloride combines with sulf- hydric acid, and also forms with phosphuretted hydrogen gas a compound of the formula PH 3 ,SnCl 2 . DISTINCTIVE CHARACTERS OF THE SOLUBLE COMPOUNDS OF TIN. 944. Tin forms two series of soluble compounds : 1st, those which correspond to the protoxide SnO, such as the protochloride and the soluble salts formed by the protoxide; and 2dly, com- pounds corresponding to stannic acid ; that is, perchloride of tin and the soluble compounds of stannic acid with the acids. These two series present different reactions, which it is necessary to ex- amine separately. Characters of the Protosalts of Tin. 945. The salts of the protoxide of tin are free from colour when the acid is itself colourless, and always strongly redden tinc- ture of litmus. A small quantity of water in most cases dissolves them, while a greater quantity of this liquid decomposes them, forming a white precipitate, which is generally a basic salt. This precipitation is avoided by acidulating the water with a certain quantity of chlorohydric acid. The caustic alkalies throw down a white precipitate, which is soluble in an excess of the reagent, while, by boiling the liquid, an- hydrous protoxide of tin separates in the form of a black powder. Ammonia also throws down a white precipitate, which is, however, insoluble in an excess of ammonia. The alkaline carbonates likewise yield white precipitates, which are insoluble in an excess of the reagent, and become black by boiling the liquid. Sulf hydric acid precipitates them as a deep-brown powder, while the alkaline sulfhydrates throw down a dirty-white precipitate, which dissolves in a great excess of the reagent. Prussiate of potash yield a white precipitate. Salts of mercury are reduced by the protosalts of tin, a gray precipitate of very finely divided metallic mercury being formed, which collects in globules by trituration. Chloride of gold gives a precipitate which is purple when the so- lutions of protoxide of tin are very dilute, and brown when they are more concentrated. A blade of iron or zinc precipitates tin in the form of gray crys- talline spangles, which assume under the burnisher the ordinary colour and lustre of tin. ANALYTIC DETERMINATION. 165 Characters of the Soluble Compounds of Tin, corresponding to Stannic Acid. 946. The characters about to be indicated all refer to the per- chloride, which is the only soluble compound corresponding to stannic acid which has been properly studied. A solution of perchloride of tin always has a strong acid reac- tion, and is decomposed by a large quantity of water, affording a white precipitate of hydrated stannic acid. Potassa, soda, and ammonia yield a white precipitate, which dis- solves in an excess of the reagent ; but the liquid does not throw down a black precipitate on being boiled, as is the case with the compounds of the protoxide. The alkaline carbonates disengage carbonic acid, and give a white precipitate, which is neither soluble in an excess of the re- agent nor turns black by ebullition. Prussiate of potash gives a white precipitate, which does not form until after some time. Sulf hydric acid gives a dirty-yellow precipitate, which also does not appear immediately, and which, when formed by alkaline sulf- hydrates, is soluble in an excess of the reagent. Chloride of gold throws down no precipitate from a solution of perchloride of tin, which reaction clearly distinguishes the per- chloride from the compounds of the protoxide of the metal. Per- chloride of tin does not precipitate mercury from its solutions in the metallic state. Iron and zinc precipitate metallic tin. DETERMINATION OF TIN, AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. 947. Tin is always determined in the state of calcined stannic acid. Sometimes it is precipitated as sulphide, which is converted into stannic acid by roasting in a platinum crucible ; taking care to add a few drops of nitric acid before the calcination, in order to prevent the separation of metallic tin, which would soon attack the crucible. After the roasting, the crucible is allowed to cool, a small quantity of carbonate of ammonia added, and it is again heated to drive off more readily the last traces of sulphuric acid. Tin is easily separated from all the metals which we have hitherto studied, except from cadmium, by means of sulf hydric acid. The substances are dissolved in chlorohydric acid, so that the tin may exist in the state of a protochloride, and a current of sulf hydric acid is passed through the liquid, in which a large excess of chlorohy- dric acid is left. When the liquid contains an excess of sulf hy- dric acid, the bottle is loosely corked, and left to stand for several hours at a temperature of from 120 to 140. The precipitate is 166 . TIN. then collected on a filter, and, if it is composed only of sulphide of tin, is converted into stannic acid by means of nitric acid. If the substance contains tin and cadmium, these metals are pre- cipitated together by sulf hydric acid, and the two sulphurets are treated with nitric acid, which converts the tin into insoluble stan- nic acid, and dissolves the cadmium, which is then precipitated from its solution by the processes indicated in 931. METALLURGY OF TIN. 948. The binoxide, which is the only tin-ore, originally occurs only in the oldest rocks, forming small veins, or irregular threads, in the granitic formations ; but it is sometimes also found in the dis- aggregated sands arising from the destruction of these rocks. The principal localities of tin are in Saxony, Bohemia, in Cornwall in England, and in the East Indies. The sands containing tin found in Brittany are too poor to be worked with advantage. The crushed stanniferous rocks and the stanniferous sands are washed, in order to separate the gangue mechanically, which is an easy operation, as the oxide of tin is much heavier than the gangue, and, as it is very hard, yields but little dust under the stamper. Sands con- taining only J per cent, of tin may yet be advantageously concen- trated by washing. The washed ores, which consist of a mixture of oxide of tin and some very heavy metalliferous minerals, such as the crystallized sulphides, sulfarseniurets, and oxides of iron, etc., are roasted in heaps or in kilns, when the oxide of tin remains unaltered, while the sulphides and sulfarseniurets become partially oxidized and dis- aggregated, so that if the ore be again subjected to the stampers, the roasted substances are pulverized, while the oxide of tin re- mains nearly in its original condition. By another washing the roasted and stamped sand is easily freed from the substances which have been altered by roasting, and a very rich ore is obtained, yielding often more than 50 per cent, of metallic tin. In Saxony, the ore is fused in a cupola-furnace of about 9 feet in height (figs. 536 and 537). The sides of the oven A are made of slabs of granite, while the bottom consists of a single stone D, called the sole-stone, which is properly hewn, and rapidly inclines toward the anterior part of the furnace, called the breast. The fused materials constantly run into an exterior crucible B, made of slabs of granite lined with damp charcoal. At the lower part of this furnace is a hole which opens over a cast-iron pot C. The furnace is charged by alternate layers of ore and charcoal, the combustion being fed by a blowing-machine, the nozzle of which passes through the twyer o. The oxide of tin is reduced by the carbonic oxide which is pro- duced by its contact with the fuel. The gangue itself, being gene- rally very fusible, yields a doughy scoriae, which flows with the tin METALLURGY OF TIN. 167 into the basin B, whence it is removed from time to time. When Fig. 536. the basin B is filled with melted metal, the stopper is removed from the hole, and the metal runs into the cast-iron pot C, where it is stirred with a stick of green wood,* which, by being par- tially carbonized in the hot liquid, causes a bubbling, produced by the disengage- ment of gas, which raises the dross which is scattered through the metal to the surface of the bath, while it, at the same time, reduces the oxide of tin beneath to the metallic state. When the temperature of the metal is only a 1L few degrees above that of its fusion, it is allowed to rest, and is then removed with iron ladles and run into moulds. The upper strata furnish the purest metal, while those at the bottom con- tain the greater portion of foreign sub- stances. As the scoriae do not become per- fectly fluid, they always contain a quan- Fig. 537. fay O f g ra i ns O f tin, for which reason the richest are added to the ore and fused with the next charge, while the poorest are stamped and the metallic grains separated by washing. The greater part of the scoriae is, however, smelted separately in the same furnace, by increasing the blast and quan- tity of fuel, by which more fluid scoriae are obtained, from which the tin separates more readily, but is gained only in inferior quality. 949. In England, the ore of the stanniferous sands is treated nearly in the same manner, the furnaces being only much higher. The tin furnished by the upper strata of the crucible is alone run into bars, while the balance is again melted. The bars of tin are sometimes heated to above 212 and allowed to fall from a certain height, when the metal, which is very brittle at this temperature, breaks into small crystalline fragments, and is then called grain-tin. The ore taken from the veins is much less pure than that of the sands. After the primary stamping and washing, it is roasted in a reverberatory furnace, when sulphates of iron and copper are formed, which are washed out and separated by crystallization. The ore is then again washed, and the sludge arising from it is * This process, which is called poling, is effected in the Cornish tin-works by boiling billets of green wood in the melted tin, where they are kept under the sur- face by means of an iron frame. W. L. F. 168 TIN. heated on the hearth of a reverheratory furnace with powdered charcoal, to which lime is added to hasten the fusion of the gangue. The scoriae are ladled out from time to time, and the tin is run into moulds. The tin obtained by this process is refined by heating the metal slowly on the hearth of a reverberatory furnace, when the pure tin melts first, and runs out of the furnace, as the hearth is inclined toward the tap-hole, leaving on the hearth an alloy of tin with foreign substances. This method of refining is called liquation. Frequently, two successive liquations are necessary in order to ob- tain very pure tin. 950. Tin is used in the manufacture of various articles, such as kitchen utensils, cotton machinery, etc., etc. ; a small quantity of lead being often added to it to render it less brittle. The alloy generally employed contains 18 per cent, of lead. Tin is also made in very thin sheets, called tin foil, and used either for tinning glass or for wrapping bonbons, chocolate, etc. Tin foil is manufactured by beating, only the best tin being used. It is first run into plates, which are hammered until their thickness is reduced to about 1 millimetre, after which 8 or 10 plates are laid on each other, and the hammering continued until they are sufficiently thin, when they are cut in half, and again laid on each other and beaten, which process is repeated until a hundred sheets, of the thickness required, are obtained. One of the most important applications of tin is that of tinning sheet-iron, as was fully described in 847. 169 TITANIUM. EQUIVALENT = 25 (312.5; = 100). ^ 951. Titanium* has been found combined with oxygen in several minerals : rutile is nearly pure titanic acid, and titanic iron is a mixture, or a compound of titanic acid and oxide of iron. Certain iron-ores contain a very small quantity of these titanic minerals ; and metallic titaniumf is often found in the products of the blast- furnaces in which such ores are smelted. It is especially met with in the metallic masses which adhere to the sides of the furnace, toward the close of the blast, when this process is beginning to slacken, and then appears under the form of small, very brilliant cubic crystals of a copper-red colour, scattered through a mass of half-refined metal, slag, and frequently sulphide of iron. These masses are treated with chlorohydric acid, which dissolves the iron and does not attack the titanium ; by which a large portion of the little crystals are detached, while they still remain mixed with par- ticles of slag, from which they are easily separated by levigation, their density being 5.3, while that of the slag is much lower. These crystals are hard enough to scratch quartz, arid are unaffected by concentrated acids, except by aqua regia, which, however, requires a long time to act on them. When titanic acid is heated in a forge-fire in a "brasqued" cru- cible, it is converted into an aggregated black mass, which is an inferior oxide of titanium, while the portions in immediate contact with the charcoal are still more reduced, having passed into the state of metallic titanium, which forms a pellicle of a copper-red colour around the mass. The best method of preparing metallic titanium in the labora- tory consists in decomposing by heat perchloride of titanium, which is a volatile liquid, in a retort of hard glass placed in a furnace, and through which a current of dry ammoniacal gas is passed ; when the ammonia immediately combines with the perchloride of titanium, which is converted into a white powder. The retort is then surrounded by burning coals and the current of ammoniacal gas kept up ; when a large quantity of sal-ammoniac is sublimed and condensed on the globe and in the neck of the retort, the me- tallic titanium remaining at the bottom in the form of very bril- * Discovered in 1791, "by W. Grdgor. f This product is not metallic titanium, as was erroneously supposed, but a combination of nituret and cyanide of titanium, according to the formula Ti,C a N+ 3Ti 3 N. W. L. F. VOL. II. P 170 TITANIUM. liant small spangles of a purple-red colour. The retort is allowed to cool, still maintaining the gaseous current, and the titanium is then removed. The titanium thus prepared is more easily attacked by acids than that of the blast-furnaces, and nitric acid readily converts it into titanic acid. Heated in the air it becomes incandescent, and is changed into a white powder of titanic acid. COMPOUNDS OF TITANIUM WITH OXYGEN. 952. Three compounds of titanium with oxygen are known : A protoxide TiO. A sesquioxide Ti 3 3 . Titanic acid Ti0 3 . Titanic acid, which is the most important compound, occurs in nature in the form of brownish-yellow opake crystals, called rutile by mineralogists. Rutile, which is not pure titanic acid, but gene- rally contains one or two hundredths of oxide of iron, is isomor- phous with native binoxide of tin. Other minerals, formed by sesquioxide of titanium combined with protoxide of iron, and called titanic irons, appear to be analogous to magnetic oxide of iron. Lastly, the mineral, called anatase, which forms crystals of a beau- tiful blue colour, is composed of nearly pure titanic acid. Rutile is attacked neither by acids nor alkaline solutions, but is acted on, at a red-heat, by the alkalies and alkaline carbonates. Titanic acid may be obtained in a gelatinous state, in which it combines with the acids by heating finely powdered rutile with two or three times its weight of chloride of barium in a strong forge-fire. The powdered substance is calcined and treated with hot water, to dis- solve the chloride of barium which has been left unchanged, when the residue is composed of titanate of baryta and oxide of iron. It is heated in a porcelain saucer with concentrated sulphuric acid, and the temperature elevated sufficiently to drive off the greater part of the excess of sulphuric acid ; after which it is again treated with water, when a residue of sulphate of baryta remains, which is separated by filtering. An excess of ammonia added to the liquid, which contains sulphates of titanium and iron dissolved in an ex- cess of sulphuric acid, precipitates the titanic acid and oxide of iron, after which a small quantity of sulfhydric acid is passed through to convert the oxide of iron into a sulphide. When the gelatinous precipitate has become black, a portion of the superna- tant liquid is decanted and replaced by a solution of sulphurous acid, which dissolves the sulphide of iron by transforming it into a hyposulphite. When the precipitate is completely discoloured, it is collected on a filter and washed with boiling water. Gelatinous titanic acid dissolves in the acids, and by boiling its dilute solutions the greater part of the titanic acid is again depo- CHLORIDE OF TITANIUM. 171 sited. When subjected to heat, a moment arrives at which the substance suddenly becomes incandescent, remaining so only for a moment, after which the titanic acid becomes insoluble in acids. Titanic acid forms no crystallized compounds with the acids, while it forms substances which assume a crystalline texture on cooling by fusion with potassa or soda. But these substances are decom- posed by treatment with water, and while an insoluble residue of titanate with a large excess of acid remains, the alkaline liquid contains but little titanic acid. Titanic acid, heated in a forge-fire in a brasqued crucible, is converted into a black substance, which some chemists regard as a protoxide TiO, but the existence of this substance is not sufficiently proved. By heating it to a high temperature in a current of hydrogen gas, the titanic acid is converted into a black powder, the compo- sition of which very nearly approaches that of the oxide Ti 3 3 . The existence of a sesquioxide of titanium is, moreover, placed beyond doubt by that of the sesquichloride Ti 3 Cl 3 , from which it may be obtained. In fact, on adding ammonia to a solution of sesquichloride of titanium, a brown precipitate of hydrated sesqui- oxide is obtained, which, on being left to itself in water, becomes first black, and then blue, and at last is converted into white titanic acid, with the evolution of hydrogen gas. By treating ses- quichloride of titanium with sulphuric acid, a sesquisulphate of titanium, which crystallizes with difficulty, is obtained. COMPOUNDS OF TITANIUM WITH CHLORINE. 953. Two chlorides of titanium are known : a sesquichloride Ti 3 Cl 3 , and a bichloride TiCl 2 , corresponding to titanic acid Ti0 3 . Bichloride of titanium is prepared by decomposing an intimate mixture of titanic acid and charcoal, heated to a strong red-heat, by dry chlorine, for which purpose the apparatus described for the preparation of chloride of silicium ( 245), and represented in fig. 538, is used. A mixture of charcoal and rutile, reduced to an impalpable powder, is made into a consistent paste with a certain quantity of oil, and calcined to redness in an earthen crucible in the shape of small balls. The balls, which preserve their form, and consist of an intimate and porous mixture of titanic acid and charcoal, are intro- duced into an earthen retort C, into the tubulure a of which a por- celain tube ab is introduced, descending to the bottom of the jretort. After placing the retort in a furnace and fitting a condensing ap- paratus to its neck, a current of dry chlorine is passed through the tubulure ab ; and, when the apparatus has become filled with the gas, the retort is heated to a strong red-heat, while the current of chlorine is continued ; when the bichloride of titanium condenses in the refrigerating apparatus, and may be obtained in large quan- 172 TITANIUM. Fig. 538. tities. The bichloride of titanium thus obtained is yellow, from a certain quantity of chlorine it contains in solution, and is also yet impurified by some sesquichloride of iron. It is obtained pure by shaking it with a small quantity of mercury, which combines with the dissolved chlorine, and then distilling in a glass retort to separate it from the sesquichloride of iron. Bichloride of titanium is a colourless liquid, giving off thick white fumes in the air. Its density at 32 is 1.761, and it boils at 276.8, when the density of its vapour is 6.836. It behaves with water like bichloride of tin, which it closely resembles in its physical and chemical properties. It combines with a small quan- tity of water and forms a crystallized compound ; but a large quantity of water decomposes it by forming a white precipitate of titanic acid, while the liquid contains bichloride of titanium dis- solved in a great excess of chlorohydric acid. The precipitate itself dissolves when treated with chlorohydric acid, but again gives off titanic acid by boiling the diluted liquid for some time, when the latter passes into a modification in which it is extremely insoluble in acids. By passing hydrogen, saturated at the temperature of 212 with vapour of bichloride of titanium, through a porcelain tube heated to redness, crystalline spangles of a deep violet colour, consisting of sesquichloride of titanium, are condensed in the cold portions of the reducing tube. This compound is deliquescent, and dissolves readily in water, producing a violet-red solution, which is one of the most powerful reducing agents. It precipitates gold, silver, and mercury in a metallic state from their solutions, and reduces COMPOUNDS OF TITANIUM. 173 the salts of iron and copper to their minimum of oxidation. It even decomposes sulphurous acid, by setting free the sulphur. The equivalent of the metal and the composition of titanic acid have been inferred from the analysis of the bichloride of titanium. COMPOUND OF TITANIUM WITH SULPHUR. 954. A compound of titanium with sulphur is known, corre- sponding to titanic acid, and closely resembling the bisulphide of tin, or mosaic gold. Bisulphide of titanium TiS 3 is obtained by passing a current of sulfhydric acid gas, saturated at 212 with vapour of bichloride of titanium, through a tube heated to redness ; when the inside of the tube becomes covered with a thick coating of bisulphide of titanium, in the form of scales having a metallic lustre and the colour of brass. DISTINCTIVE CHARACTERS OF THE COMPOUNDS OF TITANIUM. 955. The combinations of titanium are recognised by the above indicated properties of titanic acid, and by the following distinctive reaction : Titanic acid affords with borax, in the oxidizing flame of the blowpipe, a colourless glass, which assumes a deep blue colour in the reducing flame. Titanium is also recognised by the properties of its bichloride, and by the red metallic dust which the latter leaves when decomposed by ammonia under the influence of heat. The combinations of titanium may be easily confounded with those of tin, on account of the close resemblance of the salts of these two metals ; while they may readily be distinguished by means of the blowpipe, as stannic acid, when heated with charcoal and some carbonate of soda, yields metallic tin, which can be imme- diately recognised. DETERMINATION OF TITANIUM; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. 956. Titanium is always determined in the state of calcined titanic acid. Its separation from the -metals we have hitherto studied is effected either by the insolubility of calcined titanic acid in acids, or by the volatility of the bichloride. Titanic acid dissolved in an excess of chlorohydric acid is not precipitated by sulfhydric acid, which property allows its separation from the heavy metals, such as cadmium, tin, lead, bismuth, copper, mer- cury, gold, silver, platinum, etc., which, under the same circum- stances, are all precipitated. p2 174 TANTALUM OR COLUMBIUM, NIOBIUM, PELOPIUM, ILMENIUM. 957. These names have been given to four new metals* found some few years since in minerals, called tantalites and yttro-tan- talites ; but their properties are not yet sufficiently known to de- mand description in this work. LEAD. EQUIVALENT = 103.7 (1296.25; = 958. The lead of commerce is often tolerably pure, and then possesses a great degree of flexibility and malleability. Chemically pure lead is obtained by calcining in a brasqued crucible the oxide obtained by calcining the crystallized nitrate of lead. Lead is a bluish-gray metal, possessing a bright metallic lustre when freshly cut. Its density is 11.445. Lead is so soft as to be easily cut with a knife, and leaves me- tallic-gray marks on paper. Being very malleable when cold, it can be beaten into very thin sheets, and drawn out into fine wire, which is so extremely flexible that it can be tied in knots like a hempen string ; but, on the other hand, possesses so little tenacity that a leaden wire of 2 millimetres in diameter breaks under a weight of 9 kilogs. Lead fuses at a temperature of about 335, giving off appreciable vapours at a red-heat, without being, however, sufficiently volatile to be distilled. It may be crystallized by fusion, by the same pro- cess as that indicated for sulphur and bismuth, and the crystals, although rarely well defined, may be seen to be regular octa- hedrons. Lead soon tarnishes in the air at the ordinary temperature, an extremely superficial layer being formed on it, which is supposed to * Tantalum was discovered in 1801, by Hatchett, in an American mineral, for which reason he called it columbium ; while in the following year it was again dis- covered in a Swedish mineral by Ekeberg, who gave to it the name of tantalum. Niobium and pelopium were discovered in 1846, by H. Rose. Ilmenium was recognised as a peculiar metal in 1847, by Hermann. [The ex- istence of ilmenium is yet a matter of dispute, as some chemists, and especially Rose, regard the ilmenic acid found in samarskite as an impure niobic acid. W. L. F.} OXIDES. 175 be the suboxide Pb 2 ; and when maintained in a state of fusion in the $fr oxidizes very rapidly. During the first few moments it is covered with an iridescent pellicle, which soon changes into a yel- k>w pulverulent dust, while at a red-heat oxidation advances rapidly. The oxide PbO then comes into fusion, and must be run off in order that the oxidation should continue. Lead oxidizes in damp air and the vapour of acids, even in that of carbonic. Distilled water, likewise, under these circumstances, acts the part of an acid, in consequence of the affinity of water for the oxide of lead ; and a sheet of lead dipped into distilled water be- comes covered with a pellicle of white hydrated oxide, or hydro- carbonate, which sometimes forms small crystalline spangles, visible with a lens. The water itself contains a quantity of hydrated oxide of lead, sufficient to be detected by being blackened by sulf- hydric acid. The presence of a small quantity of some salts, chiefly sulphate of lime, prevents the oxidation of lead, for which reason the effects described are not observed in common spring or well water. Concentrated boiling chlorohydric acid acts but very feebly on lead, and dilute sulphuric acid attacks it only when the air has access to it ; while hot concentrated sulphuric acid converts it into sulphate with disengagement of sulphurous acid. Nitric acid, which is the best solvent of lead, acts on it at the ordinary temperature with the evolution of reddish vapours, and forms soluble nitrate of lead. COMPOUNDS OF LEAD WITH OXYGEN. 959. Three compounds of lead with oxygen are known : A suboxide Pb 3 0. A protoxide PbO. A binoxide Pb0 3 , or plumbic acid. Again, protoxide of lead and plumbic acid can combine in various proportions, forming several intermediate oxides, called miniums, of which red-lead is the most important. Suboxide of Lead Pb a O. 960. Suboxide of lead is a black powder obtained by heating the oxalate to a temperature of 572 in an oil-bath, until gaseous carbonic acid and oxide are no longer disengaged. The reaction is represented by the following equation : 2(PbO, C 3 3 ) =Pb 2 + 3CO a + CO. The opinion of some chemists, who regarded suboxide of lead as an intimate mixture of metallic lead with protoxide, is shown to be erroneous by the following reactions : When the suboxide is rubbed with mercury, the latter dissolves absolutely nothing; but solution would take place if any metallic lead existed in the mixture. Again, by treating the suboxide with an aqueous solu- 176 LEAD. tion of sugar, no protoxide of lead is dissolved, showing that none exists in the suboxide, as else it would immediately dissolve. But by treating suboxide of lead with strong acids, even when they are dilute, it is converted into protoxide PbO which dissolves, and into metallic lead. A temperature above 750 immediately effects the same decomposition ; when the calcined substance parts with its lead to mercury, and with its protoxide of lead to a solu- tion of sugar in water. Suboxide of lead heated in the air burns like tinder, and is con- verted into protoxide of lead PbO. Protoxide of Lead PbO. 961. Protoxide of lead is obtained by the calcination of nitrate or carbonate of lead in the form of a yellow powder, which fuses at a red-heat, and yields, on cooling, a mass composed of crystalline lamellae, in which state it is called litharge, while the name of mas- sicot is given to the pulverulent oxide. Well-defined rhombohedral crystals of protoxide of lead are sometimes found in the fissures of lead furnaces. Litharge, when fused in an earthen crucible, readily acts on the latter by combining with silicic acid and per- forating the crucible. Hydrated oxide of lead is obtained by adding ammonia to a cold solution of a salt of lead, when a white precipitate forms, which readily dissolves in a solution of potassa, soda, or ammonia. On evaporating the liquid, the oxide of lead is deposited in the anhy- drous state, in the form of brownish-yellow lamellae, resembling those of litharge. Solutions of baryta and caustic lime may be substituted for those of the alkalies. By adding a concentrated solution of a salt of lead to milk of lime, previously heated to ebul- lition, the oxide of lead is precipitated in the form of small and very heavy crystals of a beautiful red colour, which are more easily procured by boiling a concentrated solution of caustic soda with an excess of protoxide of lead and allowing the liquid to cool. The red crystals of protoxide of lead retain their colour when they are slowly cooled after the application of heat, but turn yellow when the cooling is sudden. Thus, protoxide of lead may assume very different colours, all varieties of which are found in the litharge of commerce. Protoxide of lead acts the part of a true acid with powerful bases, and its solution in alkalies should be considered as saline. The compound of oxide of lead with lime has even been obtained crystallized. A solution of oxide of lead in lime is sometimes used for dyeing hair black ; which effect is produced by the oxide of lead reacting on the sulphur contained in the organic matter, when black sulphide of lead is formed. The same solution is also used in the manufacture of artificial tortoise-shell. OXIDES. 177 Protoxide of lead contains Lead 92.83 Oxygen.... 7.17 100.00 The well-ascertained isomorphism of several compounds of lead with the analogous compounds of baryta and lime, leaves no doubt as to the formula of the protoxide, and it is written PbO, whence the equivalent of lead is deduced as 103.7. Binoxide of Lead, or Plumbic Acid Pb'0 2 . 962. Binoxide of lead, often called also puce-coloured oxide of lead on account of its colour, is prepared by treating heated red lead with dilute nitric acid, which dissolves the protoxide and leaves the plumbic acid in the form of a brown powder. The nitric acid must be renewed until no more oxide of lead is dis- solved ; after which the plumbic acid is dried at a temperature below 212. Plumbic acid is also obtained by treating finely di- vided protoxide of lead suspended in water by chlorine in excess ; or by adding a solution of an alkaline hypochlorite to a boiling solu- tion of acetate of lead. A certain quantity of chloride of lead, which in the latter case is precipitated with the plumbic acid, is removed by boiling the precipitate several times with water, in which the chloride is quite soluble. Plumbic acid contains 1 equiv. of lead 103.7 88.47 1 oxygen 16.0 11.53 119.7 100.00 Heat readily decomposes plumbic acid, by driving off half of its oxygen and converting it into protoxide of lead. Plumbic acid does not combine with the acids, but gives off a portion of its oxy- gen to those which are susceptible of superoxidation ; when salts of protoxide of lead are formed. It rapidly absorbs sulphurous acid with an elevation of temperature, and forms protosulphate of lead ; which property of plumbic acid is often applied to the sepa- ration of sulphurous acid gas when mixed with other gases. It also loses one-half of its oxygen when heated with concentrated sul- phuric acid, and is converted into the protosulphate. With chlorohy- dric acid it evolves chlorine and yields protochloride of lead PbCl. Binoxide of lead readily combines with bases forming several crys- tallizable salts, for which reason it has been called plumbic acid. Plumbate of potassa is obtained by heating a mixture of caustic potassa and binoxide of lead entirely freed from protoxide. The binoxide of lead is placed in a silver crucible, and intimately mixed with a highly concentrated solution of caustic potassa ; after which it is slowly and gently heated, while, from time to time, a small 178 quantity of the substance is dissolved in a little water and decom- posed by nitric acid. When a copious deposit of plumbic acid ensues, the combination may be considered as effected. A small quantity of water is then poured into the crucible, and rapidly de- canted while it is still hot ; when the solution deposits, on cooling, colourless and transparent octahedral crystals of plumbate of po- tassa, of the formula KO,PbO a +3HO. The alkaline liquid float- ing above the crystals contains no plumbic acid, because plumbate of potassa is nearly insoluble in cold alkaline solutions. It is de- composed by solution in fresh water. Plumbates of baryta and lime are obtained as insoluble com- pounds by heating in the air a mixture of these bases and minium. Intermediate Oxides of Lead, Miniums. 963. By heating finely powdered protoxide of lead, or mas- sicot, in the air at a properly regulated temperature, it absorbs oxygen and is converted in a beautiful orange-red powder, called minium.* The composition of this substance varies according to the prolongation of the roasting ; and by continuing it until the minium no longer increases in weight, the product is found to pre- sent a composition corresponding to the formula 2PbO,Pb0 3 . It has been accidentally found crystallized in the fissures of a furnace used for the preparation of minium, and presenting the characters of a well-defined compound, the composition of which corresponded to the formula 3PbO,Pb0 3 . Protoxide of lead and plumbic acid may very probably form several definite compounds ; but minium should not be considered as a peculiar oxide of lead, as it behaves in all its chemical reactions like a compound of the two oxides just mentioned. When treated with nitric or acetic acid, the protoxide of lead is dissolved, while the plumbic acid is set free ; which reac- tion is generally employed for the preparation of the latter sub- stance. Minium may be obtained in the humid way, by adding a solu- tion of plumbate of potassa to an alkaline solution of litharge ; when a yellow precipitate of hydrated minium is formed, which is con- verted by desiccation into a red powder of anhydrous minium. A large quantity of minium is used in the manufacture of crys- tal glass ( 686). In order to prepare minium, powdered litharge is oxidized in a reverberatory furnace at a temperature which should not exceed 570, the massicot being generally prepared from very pure lead expressly for the purpose. The furnaces have two stories, in the lower one of which, where the temperature is highest, the lead is converted into massicot, always taking care that the temperature * We distinguish commercially two kinds of minium : orange mineral, the colour of which is indicated by the name ; and red-lead, which presents a fine vermilion hue. TF. L. F. BED-LEAD. 179 does not rise sufficiently high to fuse the oxide of lead, because the converting of litharge which is not in the state of powder into minium by^rpasting is effected only with great difficulty. The massicot arising from this operation is generally subjected to levi- gation, to free it from the particles of metallic lead it may contain ; after which it is placed in the upper furnace, which is heated only by the waste heat of the lower. It is sometimes simply spread in a thin layer over the floor of the second furnace, its surface being renewed from time to time by stirring it with an iron rod ; while, at other times, it is placed in sheet-iron boxes arranged in the fur- nace. In some manufactories, only one furnace is used for the roasting of the lead and the conversion of the massicot into minium. The lead is first oxidized to litharge, which, after being powdered and levigated, is disposed in flat sheet-iron dishes, which are piled up in the hot furnace. The doors are then closed, and, during the slow cooling of the furnace, the greater part of the massicot is con- verted into minium. Red-lead of a good quality is then obtained by repeating the operation. A certain quantity of minium is also prepared by decomposing carbonate of lead, commonly called ceruse or white-lead, in the air ; when a product of a paler colour than that of red-lead, namely, orange mineral, is obtained. SALTS FORMED BY THE PROTOXIDE OF LEAD. 964. The protoxide is the only oxide of lead which acts the part of a base with acids. It is a powerful base, the affinities of which are scarcely inferior to those of baryta and lime. It is dis- tinguished among the metallic bases by its tendency to form basic salts, w r hich often present all the characters of definite compounds, the solutions of which turn the red tincture of litmus blue. The salts of lead are poisonous: in small doses they occasion colic and pains in the intestines. Workers in lead, particularly house painters, are highly exposed to the disease called lead or painter s colic ; the best treatment of which consists in administering drinks con- taining a small quantity of sulphuric acid, or sulphate of soda, in order to convert the oxide of lead into an insoluble sulphate. Sulphate of Lead. 965. Sulphate of lead being insoluble in water, is easily pre- pared by pouring an alkaline sulphate into the solution of a soluble salt of lead. A large quantity of this product is obtained in the drying-sheds where alum is decomposed by acetate of lead in order to obtain acetate of alumina in solution. Although the sulphate is nearly insoluble in fresh water, it readily dissolves in acid liquids, and particularly in an excess of sulphuric acid. Attention must be paid to this solubility in chemical analyses ; in which case the lead remaining in the liquid is separated by a current of sulfhydric 180 LEAD. acid, which precipitates it as sulphide. Concentrated chlorohydric acid decomposes sulphate of lead, especially at the boiling point, and transforms it into crystalline spangles^ of chloride of lead ; which reaction proves that in a liquid containing an excess of hy- drochloric acid, the chloride of lead is more insoluble than the sulphate. Sulphate of lead cannot be decomposed by heat ; being the only sulphate, among those of the . metals of the fourth class which we have now studied which possesses this stability. When heated to a high temperature in an earthen crucible, the sulphate is never- theless decomposed near the sides of the vessel, by forming silicate of lead by contact with the silex of the crucible. Sulphate of lead is easily reduced by charcoal, the products of decomposition vary- ing with the temperature and proportion of charcoal used. If the charcoal be present in excess and heat applied suddenly, the sul- phate is transformed into a protosulphide PbS ; but if, on the con- trary, the temperature be slowly raised, a considerable quantity of sulphurous acid is disengaged, and the subsulphide of lead Pb 3 S is formed. When only the quantity of charcoal absolutely necessary to convert the sulphuric into sulphurous acid and to reduce the oxide of lead is used, perfectly pure metallic lead re- mains ; while with only one-half of this quantity of charcoal, the protoxide PbO is obtained. By heating 1 equiv. of sulphate and 1 equiv. of protosulphide of lead together in an earthen crucible, sulphurous acid is disengaged, and 2 equiv. of metallic lead remain : PbO,S0 3 +PbS=2S0 3 +2Pb. But by heating a mixture of 2 equiv. of sulphate and 1 equiv. of sulphide, the sulphur is again disengaged in the state of sul- phurous acid, but oxide of lead remains with the metallic lead : 2(PbO,S0 3 )+PbS=3S0 3 +2PbO+Pb. These two reactions are applied in the metallurgy of lead. Iron and zinc decompose sulphate of lead by placing the metals in acidulated water containing sulphate of lead in suspension ; when the lead separates in the metallic state. By boiling solutions of the alkaline carbonates, sulphate of lead is decomposed and converted into carbonate. The decomposition is much more easily effected by the dry way. Nitrate of Lead. 966. Nitrate of lead is prepared by dissolving litharge, or white- lead, or also metallic lead, in an excess of nitric acid, taking care in the latter case to keep the acid in excess. The hot solution, when saturated, deposits regular octahedrons of nitrate of lead on cooling, which are sometimes transparent and sometimes opake, SALTS. 181 but in each case anhydrous. Cold water dissolves only about 4 of its weight of nitrate of lead, while it is much more soluble in hot water. Crystals of nitrate of lead decrepitate on hot coals, and feed the combustion, like all the nitrates. Nitrate of lead is de- composed by heat into hyponitric acid which is disengaged, and protoxide of lead which remains. We have seen ( 118) that this decomposition is applied in the laboratory to the preparation of hyponitric acid. By boiling a solution of nitrate of lead with the oxide or car- bonate of lead, a liquid is obtained which deposits, on cooling, large crystals of a basic nitrate 2PbO,N0 5 +HO. A nitrate of lead possessing still higher basic properties is ob- tained by treating the nitrate, or bibasic nitrate, with ammonia, when a white precipitate of the formula 4PbO,N0 5 -f-3HO is formed. A large excess of ammonia decomposes the precipitate and leaves hydrated oxide of lead. Nitrites of Lead. 967. When thin sheets of metallic lead are digested with the application of heat in a solution of nitrate of lead, a great portion of the lead is reduced without any disengagement of gas, and the liquid assumes a yellow colour, and deposits crystals on cooling, which, when treated with an acid, disengage copious nitrous fumes. Several different salts may be obtained by varying the proportions of metallic lead. By digesting, at a temperature of from 140 to 176, 1 equiv. of nitrate of lead dissolved in a large quantity of water with 1 equiv. of metallic lead, until the lead is entirely dis- solved, a yellow solution is obtained, which, on cooling, deposits large yellow crystalline lamellae of the formula 2PbO,N0 1 -f HO. The reaction producing them is expressed by the following equa- tion : PbO,N0 5 +Pb+HO=2PbO,N0 4 -fHO. The crystals are readily decomposed, even when cold, by a solu- tion of carbonate of potassa ; when carbonate of lead is precipi- tated, and the liquid, when allowed to evaporate, deposits succes- sively crystals of nitrate and nitrite of potassa. It is probable from this that the yellow crystals contain no ready formed hypo- nitric acid, for this does not appears to be able to produce true saline compounds, but that they contain at the same time nitrite and nitrate of lead. Their formula may, therefore, be written 2PbO,N0 6 +2PbO,N0 5 +2HO. By digesting 3 equiv. of metallic lead with a solution of 2 equiv. of nitrate of lead, until the former is completely dissolved, a liquid is obtained which deposits small orange-coloured crystals, much less soluble than the yellow lamellae. The formula of these crystals is 7PbO,2N0 4 -f 3HO: they are also decomposed by the alkaline car- VOL. II. Q 182 LEAD. bonates, and the solution which results from the reaction yields, on evaporation, alkaline nitrate and nitrite. By considering this compound as containing nitrate and nitrite of lead, we may write its formula 4PbO,N0 5 +3PbO,N0 3 +3HO. The same compound is obtained by boiling a solution of the yellow salt with oxide of lead. Lastly, by boiling for a long time with an excess of metallic lead, either a solution of nitrate of lead, or of the yellow or orange- coloured salts just described, small rose-coloured crystals of the formula 4PbO,N0 3 +HO are'obtained, which are, consequently, a quadribasic nitrite of lead. The neutral nitrite of lead is easily prepared with the basic salt, by suspending the latter in water and passing through it a current of carbonic acid gas ; when 5 equiv. of oxide of lead are precipitated as carbonate, while the liquid, on being evaporated in vacuo, deposits yellow prismatic crystals of anhydrous neutral nitrite PbO,N0 5 . By means of this neutral nitrite of lead, the soluble neutral nitrites are easily prepared by double decomposition, by adding to its solution that of the car- bonate or sulphate of the base which it is desired to obtain in combination with the nitrous acid. Phosphates of Lead. 968. Several compounds of oxide of lead with phosphoric acid are known, corresponding to the modifications of phosphoric acid described 842. By pouring a solution of ordinary phosphate of soda (2NaO-f HO)P05+24HO, into a solution of nitrate of lead, a white insoluble precipitate is obtained, which, however, dissolves readily in an excess of acid or alkali. The formula of the preci- pitate is (2PbO+HO)P0 5 : it melts rWily before the blowpipe into a yellow globule, assuming crystalline facets on solidifying ; which character is sometimes used as a blowpipe reaction for phosphates. A basic phosphate 3PbO,P0 5 is obtained by treating the pre- ceding salt with ammonia. The other phosphates have been but little studied. A phosphate of lead combined with a certain quantity of chloride of lead, which occurs in nature, and is called phosphate of lead, crystallizes in regular 6-sided prisms, belonging to the rhombohe- dric system. Its colour is a more or less greenish yellow, and its formula is 3(3PbO,P0 5 )+PbCl. Silicates of Lead. 969. Oxide of lead and silicic acid combine in all proportions, and form, after fusion, vitreous substances, which have a yellow tinge when the proportion of oxide of lead is considerable. The silicates of lead enter into the composition of glass, and have been treated of under this head ( 669). ACETATES. 183 Aluminate of Lead. 970. A compound of oxide of lead with alumina occurs in nature, in which the latter substance plays the part of an acid: the formula of the mineral is PbO,2Al a 3 -f 6HO. Ohromates of Lead. 971. The neutral chromate of lead PbO,Cr0 3 is obtained in the form of a beautiful yellow powder by adding a solution of neutral acetate of lead to one of neutral chromate of potassa. The salt is used in oil-painting, under the name of chrome yellow, and also finds application in dyeing. The shade of chromate of lead varies with the more or less perfect neutrality of the salts used in preci- pitation, and according to the greater or less dilution and the tem- perature of the liquids. Neutral chromate of lead is found in nature, forming beautiful red prismatic crystals, which yield a yellow powder. A bibasic chromate of lead 2PbO,Cr0 3 is obtained by fusing neutral chromate of lead with nitrate of potassa; when beautiful red crystals are deposited at the bottom of the crucible. The supernatant nitrate of potassa is decanted, and the crystals of bibasic chromate of lead are washed as quickly as possible. Acetates of Lead. 972. Neutral acetate of lead, which is extensively used in dye- ing, is prepared by treating litharge with acetic acid or vinegar, taking care to have an excess of acid, to prevent the formation of basic acetates. The liquid, evaporated slowly, yields large crystals, of which the formula 'is PbO,C 4 H 3 3 -f 3HO. (The formula of acetic acid, at its maximum of concentration, is C 4 H 3 3 +HO.) The solution of acetate of lead is perfectly neutral, and absorbs a small quantity of carbonic acid from the air ; when the sides of the vessel become covered with a thin deposit of carbonate of lead, while the solution manifests a slight acid reaction. Crystals of neutral acetate of lead part with their water in a dry vacuum, and when heated. After melting in their water of crystallization, which they lose entirely at a temperature of 212, they undergo the igneous fusion at about 374 ; and, when heated still further, lose a portion of their acetic acid, which is partially decomposed by disengaging carbonic acid, while a basic acetate 3PbO,2C 4 H 3 3 remains, which is itself decomposed at a higher temperature. Acetate of lead has a sweet taste, which becomes astringent and metallic ; and it dissolves in of its weight of cold water. By boiling a solution of neutral acetate of lead with a quantity of litharge equal to one-half of that which the acetate contains, a liquid is obtained which, after evaporation, deposits crystals of a basic acetate of lead of the formula 3PbO,2C 4 H 3 8 +HO. By 184 LEAD. boiling the same solution with a quantity of oxide of lead equal to that which the neutral acetate contains, a liquid results which yields crystals of a still more basic salt, and of which the formula is 3PbO,C 4 H 3 3 +HO. Lastly, by boiling the solution of the last basic salt with an ex- cess of oxide of lead, a very slightly soluble compound is obtained, which is almost entirely deposited on cooling. Its formula is 6PbO,C 4 H 3 3 . In medicine, a solution of basic acetate of lead is employed, under the name of extractum saturni, or liquor plumbi subacetatis, which is obtained by dissolving 2 parts of neutral acetate of lead and 1 part of litharge in 3 \ parts of water, and may, therefore, be considered as containing a mixture of the two sub-acetates 3PbO,2C 4 H 3 3 + HO and 3PbO,C 4 H 3 3 +HO. The solutions of the sub-acetates of lead have a very decided alkaline reaction, and turn blue the red tincture of litmus. Carbonic acid decomposes them, and precipitates carbonate of lead, while the liquid contains neutral acetate mixed with a certain quantity of free acetic acid. Carbonate of Lead. 973. Carbonate of lead is found crystallized in nature, form- ing beautiful and highly refracting transparent crystals, belonging to the fourth system of crystallization, and isomorphous with arra- gonite. The salt is prepared by double decomposition by pouring an alkaline carbonate into the solution of a soluble salt of lead, when a white precipitate is formed, which is the anhydrous neutral carbonate, nearly insoluble in water. Carbonate of lead is used in oil-painting, under the name of white-lead, or ceruse. It is prepared by several processes appa- rently very different from each other, but all consisting in the de- composition of sub-acetate of lead, produced by various reactions, by carbonic acid. One of these processes, called the process of Qlichy, from its having been first employed at Clichy, near Paris, consists in dis- solving litharge in acetic acid so as to obtain a solution of a basic acetate containing a large quantity of oxide of lead, and decom- posing it by the carbonic acid produced by combustion in the furnace which serves to heat the kettles in which acetic acid is saturated with the oxide of lead. To effect this, the air driven across the grate of the furnace by a blowing-machine, is conveyed by pipes into the solution of sub-acetate of lead to be decomposed. In some localities the carbonic acid arising from the earth is used ( 253). Nearly the whole of the oxide of lead is precipitated in the state of carbonate, while the liquid contains all the acetic acid, which is used to dissolve an additional quantity of oxide of lead, and the fresh solution is again subjected to the action of carbonic acid. The same acid may thus serve for the transformation of an WHITE-LEAD. 185 indefinite quantity of oxide of lead into white-lead ; but, a certain quantity of it being invariably wasted in the various manipulations, a small quantity must be added each time. In England, litharge moistened with acetic acid, or with a solu- tion of neutral acetate of lead, is exposed to a current of carbonic acid gas, produced by the combustion of charcoal ; by which means the litharge is in a short time converted into the carbonate of lead. The greater part of the white-lead used in France is prepared in the Department of the North, by a process first adopted in Hol- land, and called, for this reason, the Dutch process. Sheets of lead, of from 0.12 m. to 0.15 m. wide, and from 0.6 m. to 1.0 m. long, coiled up into a cylinder Z (fig. 539), are placed each in a glazed earthen pot, having two little projections 5,6, on which the roll of lead rests. Each pot contains at the bottom a small quantity of common vinegar, made from fermented beer, and is covered with a leaden plate mn which closes it imperfectly. A large num- ber of pots being arranged in several rows on a layer of stable manure, are covered with straw, and a second Fig. 539. row j g p] ace( j on them, with another layer of manure ; which process is continued until 5 or 6 rows of pots are thus ar- ranged. Lastly, the whole is covered with manure, held together by means of boards, so as to allow the air to permeate slowly the whole mass. The vinegar in the pots yields vapour of water and acetic acid, which, by their contact, rapidly oxidize the metal and cover its surface with sub-acetate of lead. On the other hand, by the fer- menting action of the manure, carbonic acid is disengaged and the temperature elevated internally, so that the acid vapours are more and more copiously evolved. The carbonic acid then decom- poses the sub-acetate of lead and transforms it into carbonate, while the acetic acid set free effects the formation of a fresh quan- tity of sub-acetate, which, in its turn, is converted into a carbonate, and so on. In 15 days the operation is terminated, and the disks of lead covering the pots are nearly entirely converted into car- bonate. The leaden rolls, which are more or less deeply corroded, are unrolled, beaten to detach the carbonate, and then placed in other pots until they have completely disappeared. The white- lead is finely powdered, purified by levigation, and placed to dry in porous earthen pots. A certain quantity of sulphate of baryta, or chalk, is often mixed with white-lead, to discover the presence of which the mixture is treated with nitric acid, which dissolves the carbonate of lead and lime and leaves the sulphate of baryta. On evaporating the solu- tion of the nitrates and treating with alcohol, the nitrate of lime is dissolved, while the nitrate of lead remains as a residue. Q2 * 186 LEAD. DISTINCTIVE CHARACTERS OF THE SALTS OF LEAD. 974. The neutral salts formed by the protoxide of lead are co- lourless when the acid is free from colour, while the basic salts, on the contrary, are frequently yellow. The soluble salts have a sweet taste. Caustic potassa and soda yield, when cold, white precipitates of hydrated protoxide of lead, which dissolves in an excess of the re- agent. The alkaline carbonates throw down a white precipitate of car- bonate of lead, insoluble in an excess of the reagent. Sulf hydric acid and the alkaline sulf hydrates produce a black precipitate of sulphide of lead, even when the liquid does not con- tain a great excess of acid, which does not dissolve in an excess of alkaline sulf hydrates. Solutions of lead yield with the soluble sulphates a white preci- pitate, insoluble in water, which at first might be confounded with sulphate of baryta, but which is easily distinguished from the latter by being blackened by sulf hydric acid. Prussiate of potash throws down a white precipitate with salts of lead. By adding chlorohydric acid, or a soluble chloride, to a slightly concentrated and hot solution of a salt of lead, a white precipitate of chloride of lead is obtained, which changes, on cooling, into small crystalline lamellae of a peculiar aspect. If an iodide be substituted for the chloride, gold-coloured yellow spangles, which are equally characteristic, are obtained. Iron, zinc, and tin precipitate lead from its solutions in the me- tallic state. Lastly, the salts of lead are easily recognised in the blowpipe, because, when heated with carbonate of soda on charcoal, in the reducing flame, they yield a globule of metallic lead, easily recog- nised as such by its physical and chemical properties. COMPOUNDS OF LEAD WITH SULPHUR. 975. The sulphide of lead PbS corresponding to the protoxide PbO, found in nature in the form of beautiful bluish-gray and bril- liant crystals, which mineralogists call galena. It is the most com- mon ore of lead, and also the most important, as it furnishes nearly all the lead of commerce. The sulphide is obtained directly by fusing grain lead with sulphur, when the combination takes place with incandescence ; but to obtain a pure sulphide, the substance must be pulverized and heated a second time with sulphur. The black precipitate effected by a current of sulf hydric acid in a solu- tion of a salt of lead is very finely divided protosulphide. Sulphide of lead fuses at a red-heat, and, if allowed to cool very slowly, the mass presents after its solidification a crystalline texture, in which the cubic cleavage is easily distinguished. Sulphide of SULPHIDE. 187 lead is slightly volatile, and may be sublimed in a porcelain tube in a current of gas ; when the colder parts of the tube become coated with small, but extremely brilliant cubic crystals of sulphide. ^ Sulphide of lead reacts readily in the air, the products varying with the temperature and manner of conducting the operation ; and while a great deal of sulphate and oxide of lead is generally formed, a large quantity of metallic lead may also be obtained. We have seen ( 965) that by heating 1 equiv. of sulphate with 1 equiv. of sulphide of lead, 2 equiv. of metallic lead are obtained with disen- gagement of sulphurous acid ; and again, by heating 1 equiv. of sul- phide with 2 equiv. of protoxide, sulphurous acid is disengaged, and 3 equiv. of metallic lead remain : PbS+2PbO=3Pb+S0 2 . As will easily be conceived, these various reactions may occur during the roasting of sulphide of lead ; and we shall, in fact, meet with examples of this in the metallurgy of lead. Sulphide of lead is not appreciably acted on by chlorohydric or by dilute sulphuric acid ; but concentrated boiling sulphuric acid converts it into sulphate with disengagement of sulphurous acid. Nitric acid, even when diluted, acts readily on galena ; and, when the acid is mixed with a sufficient quantity of water, the sulphur is set free, while the lead dissolves in the state of nitrate. Fuming nitric acid converts the sulphide into sulphate ; and lastly, nitric acid in a state of medium concentration, transforms a great portion of the sulphide into sulphate, while the remaining sulphide yields free sulphur and lead which dissolves in the state of nitrate. By heating 1 equiv. of sulphide of lead with 1 equiv. of metallic lead, a subsulphide of lead Pb a S is obtained, which is constantly met with in the metallurgy of lead, where it forms what are called leaden matts. Sulphide of lead appears to possess the property of combining with larger quantities of lead. COMPOUND OF LEAD WITH SELENIUM. Selenide of lead has been found in some mines of galena, chiefly in the Hartz mountains, forming crystalline masses, with cubic cleavage, closely resembling galena. Selenium is extracted from this mineral, by heating in a crucible an intimate mixture of powdered selenide of lead, nitrate, and carbonate of soda, and treat- ing the fused mass with boiling water ; when a solution is obtained containing seleniate of soda, which is separated by crystallization. The seleniate is then boiled with an excess of chlorohydric acid, which converts the selenic into selenious acid ; and, lastly, the sele- nium is precipitated by sulphurous acid. COMPOUNDS OF LEAD WITH ARSENIC. 9T6. Lead and arsenic combine readily, and produce very brittle crystalline compounds. 188 LEAD. COMPOUND OF LEAD WITH CHLORINE. 977. Lead is easily acted on by chlorine, yielding but one com- pound, the protochloride of lead PbCl. Chloride of lead is readily prepared by heating litharge with chlorohydric acid, by which the oxide is transformed into a white crystalline powder, formed of small acicular crystals, or small spangles. The chloride is but slightly soluble, especially in cold water ; and is deposited from a hot satu- rated solution, on cooling, in the form of small crystals, only a small proportion remaining in the mother liquid. Chloride of lead fuses without decomposition before attaining a red-heat, and congeals into a substance resembling horn, and divisible by a knife ; while, at a higher temperature, it gives off copious fumes. It may be prepared by double decomposition, by pouring a solution of sea-salt into a concentrated solution of a salt of lead. Chloride and oxide of lead combine in several proportions, pro- ducing oxychlorides, which crystallize readily by fusion, and, on account of their beautiful yellow colour, are used in painting, under the names of mineral yellow, Cassel yellow, Turner s yellow. Cas- sel yellow, which is prepared by fusing together 10 parts of red- lead and 1 part of sal-ammoniac, consists of large crystalline lamel- lae, of the formula PbCl+7PbO. Turner's yellow is obtained by allowing a paste made with 7 parts of litharge, 1 part of sea-salt, and a certain quantity of water, to rest for several days, and sub- sequently removing the soda by treatment with water, and fusing the residue in a crucible. COMPOUND OF LEAD WITH IODINE. 978. On adding a solution of iodide of potassium to a hot and sufficiently dilute solution of a salt of lead, the liquid deposits, on cooling, yellow crystalline spangles of iodide of lead Pbl, having the lustre of gold. DETERMINATION OF LEAD, AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. 979. Lead is determined in the state of anhydrous protoxide, or as sulphate. It is frequently precipitated from its solutions in the state of carbonate, and converted into protoxide by calcining to redness ; but it is important not to calcine the substance with the filter, as a portion of the lead would then be reduced to the metal- lic state, and attack the platinum crucible, if the experiment were made in a vessel of this metal. Care must therefore be taken to separate the substance from the filter, and drop it into the crucible, after which the filter is burned at the end of a platinum wire held over the crucible, so that the calcined matter may fall into it. The crucible is then heated to redness over an alcohol lamp ; while, for the sake of greater certainty, the substance is moistened with a few ALLOYS OF LEAD. 189 drops of nitric acid, and again calcined. Analogous precautions must be observed during the calcination of sulphate of lead, the sulphate being reduced to sulphide by contact with organic matter. Lead is separated from the alkaline metals by many of the solu- ble carbonates and sulphates, or by sulf hydric acid, all of which reagents precipitate only the lead. It is separated from magnesia, alumina, the oxides of manganese, iron, chrome, cobalt, nickel, zinc, etc., by the alkaline sulphates or sulf hydric acid ; and from cad- mium by the alkaline sulphates, which precipitate only the lead. It is separated from titanium by a current of sulf hydric acid passed through the strongly acid liquid, by which the lead alone is precipi- tated. In order to separate lead from tin, both metals are precipi- tated together by an alkaline carbonate, and afterward by calcin- ing the precipitate and treating it with nitric acid, the tin is con- verted into stannic acid, and the oxide of lead into nitrate of lead ; the latter alone is dissolved by treating again with water. TESTING OF LEAD ORES BY THE DRY WAY. 980. Galena, which is the principal ore of lead, is tested by heating to a strong red-heat in an earthen crucible a mixture of 20 gr. of pulverized galena with 30 gr. of black flux and 5 or 6 gr. of small iron nails, called Paris tacks ; when the galena is decom- posed, its sulphur combining partly with the iron and partly with the alkaline matter of the black flux, and the lead separates and forms a button at the bottom of the crucible. After cooling, the leaden ball is extracted by breaking the crucible, and flattened under a hammer, to see that it contains no iron nails, and then weighed. The small quantity of lead remaining in the slag is of no importance in ordinary testing. ALLOYS. 981. Lead forms several alloys used in the arts, the principal of which are, type-metal, composed of antimony and lead, and the alloys of lead and tin used for soldering and in the manufacture of tin utensils. The alloy used for type-metal corresponds nearly to the formula Pb a Sb, and is composed of Lead 76.2 Antimony 23.8 "mo A small quantity of bismuth is sometimes added. This alloy is analyzed by means of nitric acid, which dissolves the lead in the state of nitrate, and converts the antimony into antimonic acid. It is evaporated to dryness to drive off the excess of acid, after which water dissolves the nitrate of lead, and leaves the insoluble antimony. As it is difficult to convert the whole oi 190 LEAD. the antimony into antimonic acid by means of nitric acid, it is pre- ferabie to reduce the residue to the state of metallic antimony, by heating it in a glass tube in a current of hydrogen gas. The lead is then determined either differentially, or as sulphate by precipi- tating the solution containing it by an alkaline sulphate. If the alloy contained bismuth, the residue obtained by evaporating the nitric solution to dryness must again be treated with water acidu- lated with nitric acid, in order to dissolve the lead and bismuth ; after which the liquid is carefully saturated with ammonia, which would precipitate the bismuth without precipitating the lead, unless a great excess were added. The perfect separation of lead and bis- muth is difficult. Lead and tin combine readily in all proportions ; and the fusi- bility of the alloys formed greatly varies according to the propor- tions of the two metals. Pure lead fuses at 635.0 The alloy Pb 3 Sn " 552.2 PbSn " 465.8 " PbSn a " 384.8 PbSn 3 366.8 " PbSn 4 " 372.2 PbSn 5 " 381.2 Pure tin " 437.0 Thus the most fusible alloy corresponds to the formula PbSn 3 , and fuses at a temperature lower than that of the most fusible me- tal which enters into its composition. These alloys are easily destroyed by eliquation ( 315). For tin-ware, tin is alloyed with 12 or 18 per cent, of lead, by which the metal is rendered harder and more easy to be worked in a lathe. Plumber's solder is composed of Tin 1 part. Lead 2 " This solder fuses at about 527. Tin-worker's solder contains Tin 1 part. Lead 1 The alloys of tin and lead are easily analyzed. It suffices to attack the alloy with nitric acid, which dissolves the lead and con- verts the tin into insoluble stannic acid ; when the tin is determined in the state of calcined stannic acid, and the lead differentially. METALLURGY OF LEAD. 982. A great number of minerals containing lead are found in nature, the principal of which are sulphide of lead or galena, the selenide, carbonate, chlorophosphate, and chromate. The sulphide METALLURGY OF LEAD. 191 and carbonate of lead are the only minerals sufficiently rich to be worked to advantage. Galena is generally found in veins traversing the primitive and transition rocks, and also often forms pipe-veins of greater or less size in the transition rocks and the lower stage of the secondary rocks. Lastly, certain sandstones, belonging to the variegated sandstone (hunter sandstein) formation, are impregnated with small grains of galena, which are easily separated mechanically, when the sandstone is not too hard. Galena always undergoes a mechanical preparation. The ore is first sorted by hand, and the pieces sufficiently rich are smelted im- mediately, while the remainder is crushed between cylinders and sifted. A fresh quantity of ore fit for melting is thus obtained, besides an ore closely mixed with gangue, which is stamped, and then washed in boxes or on tables. These preparations yield a sludge of greater or less fineness of grain, which is sent to the smelting-house. Galena often contains enough silver to allow it to be extracted with advantage ; and its metallurgic treatment is then directed to the extraction of both the lead and silver. Some galenas are mixed with copper pyrites, and then yield a sufficient quantity of copper to make them valuable for the extraction of that metal. Carbonate of lead forms small pipe-veins in the secondary rocks, and exists most frequently in the vicinity of the galena-mines. Its metallurgic treatment is very simple : it is fused, in contact with charcoal, in small blast-furnaces, called elbow-furnaces ; when the lead is reduced and easily separated from the slag. The most common gangue of lead-ore is quartz, carbonate of lime, sulphate of baryta, and fluor-spar. Care must be taken that the melting-bed contains substances essential to an easy fusion of the slag ; for which reason it is often necessary to add foreign substances, in order to obtain more fusible scoriae. 983. The metallurgic processes by means of which lead is ex- tracted from galena are divided into two classes : In the first, the ore is smelted with metallic iron, which separates the sulphur from the lead and forms a fusible sulphide of iron, while the lead is set free. Theoretically, the mixture for smelting should be: 1 equiv. of sulphide of lead ....................... 109.7 1 iron ....................... 28.0 147.7 From which are obtained 1 equiv. of lead 1 sulphide of iron ....................... 44 - 147.7 192 LEAD. The second method is founded on the reactions already men- tioned ( 965). By fusing together 1 equiv. of sulphide of lead and 2 equiv. of oxide of lead, 3 equiv. of metallic lead are obtained, while 1 equiv. of sulphurous acid is disengaged : PbS+2PbO=3Pb-fS0 3 . By melting together 1 equiv. of sulphide and 1 equiv. of sulphate of lead, 2 equiv. of sulphurous, acid are disengaged, while 2 equiv. of metallic lead are obtained. The process founded on the reactions, and called the process by reaction, consists in roasting the galena in a reverberatory furnace until a certain quantity of oxide and sulphate is formed, and then giving a blast, after having intimately mixed the material and closed all the doors of the furnace. During this second period of the operation, the reaction between the sulphate and sulphide takes place, and the lead is separated. 984. The reduction of galena by iron is used especially in the case of ores which are accompanied by a very siliceous gangue, and which are not very amenable to the process by reaction, because a grea't part of the oxide of lead combines with the silex and no longer reacts on the sulphide. The process by iron is employed to a great extent on the Hartz Mountains ; and the following is the plan adopted in the smelting works of Clausthal : A melting-bed is made of sorted ores and sludges, which are mixed with granular cast-iron, and with various secondary products of the further treatment of the ores, the origin of which we shall successively explain. The charge is generally composed of 34 cwt. of sorted ore and sludge, containing 24 cwt. of pure galena. 4 to 5 " of the debris of the cupelling furnaces, which is strongly impregnated with litharge. 1 " of scrapings (abstricJi) of cupellation. 39 " of slag arising from a first fusion of the ore, or yielded by the fusion of the leaden stones, or matts, the ob- ject of which addition is to assist the fusion of the gangues. 1J- " f granular cast-iron. The fusion is effected in a blast-furnace (figs. 540, 541, 542, and 543), about 18 or 20 feet high, and measuring 3 feet at its greatest width. At the bottom of the hearth is a crucible which partly pro- jects from the furnace, the base of which is formed of two blocks of sandstone, making a gutter, on which a mixture of clay and char- coal* is heaped, so as to form a cavity which extends beyond the * Two different mixtures of clay and charcoal are employed in various opera- tions occurring in the German methods of smelting: one consisting of 2 parts of METALLURGY OF LEAD. furnace. A tap-hole opening at the lower part of the crucible per- mits the escape of the liquid products which have there accumulated ; and they are led into a second crucible E, which is wholly external. The furnace receives the blast of two tuyers arranged on the oppo- site side of the tymp. Fig. 540. Fig. 541. Fig. 542. The ore is charged on the side of the tuyers, and the fuel on that of the centre-vent. As slag suddenly cooled by the cold air always adheres around the tuyers, the workman arranges them so as to form a canal which projects for about 6 inches into the furnace, and thus makes a prolongation of the tuyer, which he calls the nose clay and 1 of charcoal, called schweres yestuebbe; and one containing^! of clay and 2 of charcoal, called leichtes gestuebbe. The first I shall, in the following, translate by heavy brasque, and the second by light brasque, To the "leaden stones" (bleistein] I shall give the French name of matt. VOL. II. R 13 W. L. F. 194 LEAD. of the tuyer. The object of the nose is to convey the air imme- diately upon the fuel, and prevent it from first passing through the ore, which would be thus exposed to an oxidizing action, and part with a great deal of oxide of lead to the scoriae. The smelter must also be careful to give a proper shape to the nose of the tuyer, and to modify it according to the blast of the furnace. The temperature must not be very high in the upper part of the furnace, as otherwise a large proportion of galena would be vola- tilized. In all cases, the gases pass, on leaving the throat G, and before reaching the chimney T, several condensing-chambers ar- ranged above the smelting-furnace ; where a plumbiferous dust is copiously deposited, which is carefully collected and thrown into the melting-beds. During the smelting, the scoriae flow off continually, an assistant detaching those which have become solid, and drawing them out with a hook. When the inner basin is full of metallic products, the canal communicating with the basins D and E is opened ; when the substance flows into the external crucible E, and there divides into two layers ; the infe- rior layer being metallic lead, and the upper stratum consisting of subsulphide of lead Pb 3 S, mixed with other metallic sulphides which existed in the ore, and with that of iron arising from the reaction of the metallic iron on the galena. This substance, which is called the first leaden matt, soon solidifies, and is then withdrawn with a hook and set aside. The workman then removes the lead with a ladle, and runs it into moulds which give it the shape of lenticular disks. The poorest scoriae, that is, those least rich in lead, are rejected, while those which float on the Fig. 543. matt - n tne p 0t ^ an( j w } 1 i c } 1 al wa y S contain some grains of lead, are set aside to be added to a subsequent charge ; though poor scoriae are sometimes used for this purpose when rich scoriae are wanting. The charges, or smelting-beds, the composi- tion of which we have just indicated, yield 19 cwt. of lead, and 7 or 8 cwt. of the first leaden matt, containing from 2 to 2J cwt. of lead. 985. The first matts are collected in the foundry, and when there is sufficient quantity of them to be worked up, they are roasted in heaps on a layer of fuel ; when a large portion of the sulphur is disengaged in the state of sulphurous acid. The roasting lasts for 3 or 4 weeks ; after which the material is sorted, and, while the pieces sufficiently roasted are considered as ready for smelting, the others are again roasted. Four successive roastings are necessary for the proper preparation of the material. METALLURGY OF LEAD. 195 A charge of matt is composed of 32 cwt. of roasted matt. 32 4 or 5 2 2 1 of rich scoriae, arising from the smelting of the ores. of debris of cupellation. of scrapings, (abstrich.) of scoriae arising from the reduction of litharge. of granular cast-iron. The roasted matts are smelted in an elbow-furnace, which is a small blast-furnace (figs. 544, 545, and 546), about 4.5 feet in height, widened at its upper part C. Fig. 546 represents a horizontal sec- tion of it made at the height of the tuyer, while fig. 545 shows a vertical section through the line XY of the plane (fig. 546) ; and lastly, fig. 544 gives an anterior view. The furnace is fed by a Fig. 544. Fig. 545. single tuyer T, at the extremity of which a nose of 4 inches in length is allowed to form. At the bottom of the furnace is a brasqued crucible E, projecting partly from the furnace, and com- municating, by means of a canal, with an external crucible F, placed on a lower level. Coke is the fuel used. 196 By the roasting of the matt, a large portion of the sulphide of iron has passed into the state of oxide, which, during the fusion in the elbow-furnace, combines with the silicates of the scoriae and with the ashes of the fuel, forming very fusible scoriae, which flow constantly from the furnace. The sulphide of lead is reduced by the metallic iron, and a fresh quantity of lead and a second matt analogous to the first are formed. When the matt is solidified it is removed and set aside to be again worked, while the metallic lead is run into disks. A smelting-bed of first matt, composed as we have indicated, yields 12 cwt. of lead and 8 cwt. of second matt. The second matts are subjected to a similar treatment, being sub- jected to 3 or 4 successive roastings, and then passed through the elbow-furnace, with additions similar to those of the first. A cer- tain quantity of metallic lead is thus obtained, and a third matt, which is roasted in its turn and melted in the elbow-furnace, yield- ing an additional quantity of lead and a fourth matt. The affinity of the copper existing in the original ore for sul- phur being greater than that of the lead, the former passes indefi- nitely into the matts ; so that the metal, which is found in a very small quantity in the original ore, is concentrated in the fourth matt in sufficient quantity to make it a very rich ore of copper, and capable of being advantageously worked. It is called the copper matt. 986. When the gangue of the galena is but slightly siliceous, the process by reaction is preferred. It is adopted in England, in Carinthia, and the majority of the lead-foundries in France, par- ticularly at Poullauen in Brittany, and Pont-Gibaud in Auvergne. The ore is deposited in the state of sludge on the floor of a rever- beratory furnace (figs. 547 and 548) of about 9 or 12 feet in length, Fig. 547. and nearly the same width, formed either of pulverized scoriae or of a slightly siliceous clay. In the centre there is an excavation B, METALLURGY OF LEAD. 197 in which the fused lead collects, and whence it flows through a small canal into cast-iron pots G. The charge is inserted through an Fig. 548. upper aperture T, furnished with a hopper. Three lateral open- ings 0, o, o are made in both of the opposite faces of the furnace, and serve as working-holes. Pit-coal is burned on the grate F ; and the flame and current of hot air, after having passed through the furnace, traverse long condensing chambers, in which they deposit the substances carried over mechanically or by volati- lization. The quantity of ore treated in the furnace at a time varies in different foundries : 20 or 25 cwt. are used in England. The ore is spread evenly over the floor, and roasted from 2 to 4 hours at a dull red-heat ; when sulphurous acid is disengaged, while a large quan- tity of oxide and sulphate of lead is formed. The workman stirs it frequently, in order to hasten the roasting, at the end of which operation the working-doors are closed and a blast of air is ad- mitted. The unaltered sulphide of lead then reacts on the oxide and on the sulphate ; metallic lead and also the subsulphide Pb a S, which forms a very fusible plumbeous matt, are separated. The fused substances collecting in the inner excavation are allowed to run out after some time, after which the material remaining on the floor is again roasted by opening the working-doors, and stirring the mass with iron rods, while the temperature of the furnace is at the same time allowed to fall. The doors are then again closed, and, another blast of air being admitted, an additional quantity of metallic lead is reduced. These alternate operations are several times repeated. In some works small quantities of lime are from time to time thrown on the floor, in order to lessen the fusibility of the slag ; while in others powdered charcoal is added at a certain period, in order to decompose the oxysulphides of lead which form, and retard the roasting when it progresses too rapidly. Toward the close ot the operation, when the greater part of the lead has run off, there remains on the hearth a scorified slag, impregnated with metallic B2 198 LEAD. lead ; a large portion of which is separated by admitting a blast, and allowing the furnace to cool slowly. This last stage of the ope- ration is called the sweating. The whole operation requires 7 or 8 hours in England, and 12 or 16 in France. The matts arising from the reverberatory furnace are added, in the English works, to the roasting of a fresh quantity of ore ; while in most of the continental works they are passed through an elbow- furnace. The matts are frequently roasted in a heap, and then smelted, after a pro- per addition of scoriae, in a very low "ii elbow-furnace, called a Scotch hearth, in which a reaction takes place between the sulphate, the oxide, and sulphide of lead, while metallic lead, a matt, and scoriae are obtained. Fig. 550 repre- sents a horizontal section of a Scotch furnace ; and fig. 549 shows a vertical cut through the line AB in fig. 550. The furnace is only 3 feet in height ; and the blast is furnished by a single tuyer T. The metallic lead and matt are collected in a cast- iron pot M. The workman removes, from time to time, the slag which accumulates at the bottom of the fur- nace, and as it contains of lead, he throws it back into the Fig. 549. Fig. 550. quantity a considerable furnace. 987. The lead arising from these different processes often con- tains enough silver to allow the extraction of the latter to be made to advantage, and is then called pig-lead, (werkblei.) The silver is separated by the process of cupellation, which is founded on the property of lead to oxidize when heated in contact with the air, while the silver, which remains unaltered, concentrates indefinitely in the lead which remains in the metallic state, and is left isolated at the end of the operation, when all the lead is oxidized. In order to accelerate the oxidation of the lead, the litharge formed must be removed as fast as it is produced, for which purpose the tempera- ture is kept sufficiently elevated to fuse the oxide of lead. As the melted metal forms a convex surface, the litharge flows constantly into the space between the metal and the side of the vessel, and the litharge runs off as it is formed, without the loss of any metal- lic lead, through little gutters cut into the side of the vessel, which are made deeper as the level of the metal sinks. METALLURGY OF LEAD. 199 Figs. 551, 552, and 553 represent a cu- pelling-furnace, used at Clausthal in the Hartz. Fig. 552 gives a horizontal section, made at the height of Ythe line XYof fig. 551; and fig. 551 represents a vertical section made throughthe plane pass- ing through the line ED of fig. 552. Lastly, fig. 553 furnishes an interior view of the furnace. The cupelling- furnace is a kind of reverberatory, consisting of a lateral hearth F. and a circular one A, the floor of which, having the shape of a spherical cap, is composed of bricks zz, placed edgewise on a base uu of scoriae. It is lined internally with a layer of marl mm, which is carefully heaped, and renewed at each operation, and which constitutes the cupel properly so called. The arch of the oven is formed of a riveted sheet-iron cover C, lined with clay, and suspended, by means of chains, to a crane GG'G", by which it can be easily raised and replaced. The furnace has four openings : that by which the flame from the hearth is introduced ; two openings a, a, which receive the nozzles of two bellows which constantly drive air over the surface of the bath, and assist the oxidation, while, at the same time, they remove the litharge from the surface; the aperture P, serving for the in- troduction of the disks of lead; and lastly, the opening 0, which is Fig. 552. the tap-hole for the litharge. At the commencement of the operation, this last open- ing is closed by the cupel, but the latter is gradually notched, so as to keep the spout on a level with the bath of metal. The litharge flowing from the hole o accumulates at L on the floor of the foun- dry, where it solidifies. The cupel must be arranged before commencing the process, for which purpose the cover is removed, and the old cupel, being strongly impregnated with litharge, broken into pieces, which are added to the charges of the ores and matts, as stated m 984 200 LEAD. and 985. The brick floor ii is moistened with water, and succes- sive layers of marl are beaten down upon it with a stamper.* The cover then being replaced, all the joints are accurately luted with clay. Fig. 553. One hundred 'and sixty cwt. of lead being introduced into the furnace, and heat applied, the metal soon comes into fusion ; and the bellows then being gently worked, the oxidation commences, and the surface of the bath becomes covered with a black dust of oxide of lead, mixed with foreign substances. The dust, which is infu- sible at the temperature applied, constitutes the scrapings, (ab- strichs.) The workman throws from time to time a small quantity of powdered charcoal on the bath, and, by means of a billet of wood placed crosswise at the end of an iron rod, removes the abstrichs from the furnace. After some time, the fused litharge begins to appear; and after the first portions, which, being impure, are allowed to flow off, and are set aside, comes the pure litharge, called merchantable litharge, which can be sold in this state, when it is not mixed with the former. The cupellation is continued, the blast being gradually increased to accelerate the oxidation, until all the lead is converted into litharge, and the silver remains isolated in the shape of a disk. At the moment when the oxidation is arrested, and consequently when the cupellation is finished, a peculiar phenomenon is mani- * A layer of marl about an inch in thickness being stamped down, its surface is again loosened by means of an iron rake, to the depth of about half an inch, before the next layer is heaped on ; as without this precaution the layers would form successive strata by the heat of the furnace, and not a consolidated mass. W. L. F. METALLURGY OF LEAD. 201 fested, called the brightning. During the whole period of oxida- tion, the metallic bath appears to be more brilliant than the sides of the furnace ; and its temperature is in fact higher, since it shares not only that of the surrounding space, but also takes ad- vantage of all the heat developed by the chemical combination of the lead with oxygen. But when the lead is completely oxidized, the second source of heat disappears, the small disk of metallic sil- ver falls rapidly to the temperature of the oven, and its original brilliancy is replaced by a dull colour. On the other hand, at the moment when the last traces of lead are oxidized, there exists only on the brilliant surface of the metallic bath a pellicle of melted litharge, which rapidly grows thinner, presenting the rapid succes- sion of colours of a soap-bubble, and at last tears like a veil, dis- playing the surface of the metal. The name of brightning, or fulgu- ration, is given to this rapid succession of optical phenomena. As soon as the brightning appears, the workman pours first hot and then cold water on the hearth, and then removes the cake of solid silver. The silver, called cupel silver, which is not pure, but contains about ^ of lead, is afterwards refined, as will be de- scribed when treating of silver. A cupellation generally lasts 30 hours, including the time neces- sary for the arrangement of the cupel. The cupellation of 160 cwt. of pig-lead, arising from the smelting of the schlichs, yields at Clausthal, 56 marcs of silver, (a marc = J pound.) 118 cwt. of litharge. 21 " of debris of cupellation, (German, heerd.) 15 " of scrapings. 6 " of rich litharge. The rich litharge, which is that obtained during the last stage of cupellation, is not mixed with the rest because it contains a consi- derable quantity of silver. 160 cwt. of pig-lead, arising from the smelting of the matts, yield 62 marcs of silver. 112 cwt. of litharge. 21 " of debris of cupellation. 18 " ofabstrich. 9 " of rich litharge. Wood is the fuel used in cupellation. The litharge arising from cupellation is reduced to metallic lead, a small quantity only being sold as litharge. The conversion of litharge into metallic lead, which is called the revival of the litharge, is effected by smelting the litharge in contact with charcoal in an elbow-furnace, furnished with an outer crucible. The scoriae arising from this fusion are added to the charges of ore, and the lead, alter being run into bars, is sent to market. 202 LEAD. 988. Silver can be advantageously extracted from pig-lead by direct cupellation, only when it contains at least ^ part of silver ; but latterly, much poorer lead has been profitably worked, by first subjecting it to a process called refining l>y crystallizaton.* This operation, which separates the lead into very poor lead and into such sufficiently rich for cupellation, is based on the following prin- ciple : By allowing a large quantity of melted argentiferous lead to cool slowly, and frequently stirring the liquid mass with an iron spatula, a crystalline powder of a poor lead is soon formed, which may be skimmed off as fast as it is produced ; and by thus succes- sively separating a portion of the lead in the state of imperfect crys- tals, the greater part of the silver is left in the metal remaining fluid, which thus becomes much richer. By properly repeating these operations, either on the mass which has been removed in the solid state, or on the portion poured off in the liquid state, on the one hand a poorer and poorer lead is obtained, and on the other, lead which is more and more rich in silver. Only that lead which con- tains a proper quantity of silver is subjected to cupellation, the re- mainder being sold. 989. Metallic lead is technically used in the shape of sheet-lead- for roofing houses, lining bathing-tubs, making gutters and spouts for conveying water, etc. etc. In the manufacture of sheet-lead, the melted metal is allowed to run over a marble table into plates, the size of which is regulated by wooden rulers, and which are then passed through rollers. The rolling-machine is composed of two cast-iron cylinders, the lower one of which alone is turned by machinery, while the upper one is carried round simply by adhesion, the pressure it exerts on the sheet of lead being regulated by a counter weight. Return screws, which fasten the upper boxes of the two gudgeons, limit the elevations of the cylinder, and regulate the thickness of the sheet ; and, as the screws work independently of each other, the side on which the plate is least rolled may be tightened, so as to obtain a uniform thickness. On each side of the cylinders are , tables furnished with iron rails, which receive and guide ^ the sheets. Five or six sheets are rolled, and then passed in an opposite direction between the cylinders, their mo- tion being reversed ; which is repeated until the sheets have acquired the requisite thickness. Leaden pipe is made on a iron mandrel between grooved cylinders, after having been run into a cast-iron mould, abed (fig. 554), in the axis of which is an iron mandrel efj of the proposed diameter of the leaden pipe. A thick leaden-tube, of from 2.0 to 2.3 feet in length, is thus Fig. 554. obtained, and is then fastened on an iron mandrel of * Commonly known as Pattinsori's process. W. L. F. LEAD. 203 the same diameter as that ef of the mould, after which the whole is drawn out between cylinders resembling those used for the drawing of iron-wire. The sides of the pipe are thus reduced in thickness until it attains the length required.* MANUFACTURE OF LEAD-SHOT. 990. Lead alloyed with 0.3 to 0.8 per cent, of arsenic is gene- rally used in the manufacture of lead-shot ; the addition of this small quantity of arsenic giving the lead the property of forming perfectly spherical globules. A sheet-iron sieve is used, shaped like a spherical cap, and pierced with holes of the size of the shot to be made. The dross which forms on the fused lead is first pressed into the sieve, so as to completely line its sides, and the melted metal, being then poured in by small quantities with a spoon, filters through the dross and drops from the perforations. The drops, which should be made to fall from a great height, in order to become solid during their descent, are collected in a reservoir of water ; a greater eleva- tion being required according to the size of the shot. The shot, being sorted into sizes by means of sieves, is polished by causing it to revolve in wooden barrels with a small quantity of plumbago. * The new method of making lead-pipe consists of a powerful press, which forces the lead in a heated and soft state out of an opening in an iron reservoir, having a solid and short mandrel of iron in the centre of the opening, of the same diameter as the interior of the tube to be made. The lead is perfectly hard when issuing from the opening, and presents a tubing of a fine glaze interiorly and exteriorly. By this machine also tubes of any length may be manufactured. /. 0. B. BISMUTBL EQUIVALENT = 213 (2662.5 ; = 100). 991. The bismuth* of commerce is neyer absolutely pure ; but, the foreign metals with which it is alloyed are generally more Me than itself, it may be purified by heating the pulverized with T V of its weight of nitre in an earthen crucible. The kture should be gradually raised until the nitrate is decom- posed ; when the foreign metals oxidize and combine with the po- tman as well as a portion of the bismuth, the remainder of the latter being left as a button at the%ottom of the crucible. In order to obtain bismuth chemically pore, a mixture of sub- nitrate of bismuth and black flux must be fused in a crucible. Bismuth is a grayish-white metal, haying at the same time a very decided reddish shade, which is easily seen by placing a piece of bismuth alongside of a specimen of a white metal, such as zinc, an- timony, etc. Its density is 9.9. It presents a crystalline fracture with large glittering l**!!^ has but slight malleability, and crys- talEzes readily by fusion. Beautiful crystals may be obtained by inaneartfcea ripsak some kilogrammes of bismuth of corn- by fusion with nitre, and allowmgto cool very slowrj. To effect this, the capsule is placed on a bath of heated sand, and corered with a sheet-iron plate, on which burning charcoal is placed. In a short time a hole is made in the solid crust which forms on the Bee, and the liquid metal is allowed to run off. The crust being carefully removed, a geode of very beautiful crystals, frequently of several centimetres in diameter, is displayed. These crystals, which are cubes, or rather pyramidal figures resembling those of sea-salt (498), exhibit Terr elegant iridescent colours, produced by the very thin pellicles of oxide which form on the surface of the metal as it is brought, while hot, in contact with the air. The pellicles present the play of thin scales or soap-bobbies. - Bismuth fuses & 507.2; and a thermometer plunged into melted UiamBih marks this temperature during the whole period of its Bofidifieation. Like water, bismuth expands at the moment of soBdifving. and is therefore lighter when solid than when liquid. It is volatile at a very high temperature, but nevertheless ns unchanged in a dry atmosphere, but when ex- to damp air, becomes covered with a very thin pellicle of itvitklexl OXIDES. 20-5 oxide after some time. Heated in the air, it burns with a small bluish flame, giving off yellow fames. Bismuth decomposes water only at a very high temperature, and effects no decomposition of cold water in the presence of powerful acids. Concentrated chloro- hydnc acid acts on it with difficulty, while sulphuric acid attacks it only when concentrated and hot, with disengagement of sulphurous acid. Xitric acid attacks it very energetically, and dissolves it completely. COMPOUNDS OF BISMUTH WITH OXYGEN 5 992. Bismuth forms two compounds with oxv^en : 1. An oxide BiO s ; 2. An oxide Bi0 5 , or bismuthic acid. An intermediate oxide Bi0 4 is known, but should be regarded as a compound of the two preceding. an& its formula should be writ- ten BiO r Bi0 5 . Oxide of Bismuth BiO s . 993. The oxide of bismuth BiO,. which is obtained by roasting the metal in the air, or better still, by decomposing the basic nitrate of bismuth by heat, presents the appearance of a bright-yellow pow- der, fusible at a red-heat, and producing on solidification a deeper yellow glass, which readily perforates earthen crucibles. The oxide of bismuth is fixed, and its density is 8.45. The oxide can be obtained hydrated in the form of a white pow- der, by decomposing the basic nitrate by an alkali, or by ammonia. On boiling the hydrate in a solution of potassa. it parts with its water, and is converted into a yellow crystalline powder, which is the anhydrous oxide. The chemical composition of the oxide is. Bismuth 89.87 Oxygen 10.13 100.00 Some chemists, regarding this oxide as formed of 1 equiv. of the metal and 1 of oxygen, write its formula BiO. and adopt for the equivalent of the metal the number 71. which is given by the proportion : 10.13 : S9.87 : : 8 : z, whence x=71. But as this hypothesis is contrary to all analogy, and is sustained by no example of isomorphism, we shall assign to oxide of bismuth the formula BiO s . and the equivalent of the "metal will be deduced from the proportion : 10.13 : 89.87 : : 24 : x, whence x=213. TOL.IL s 206 BISMUTH. Bismuthic Acid Bi0 5 . 994. Bismuthic acid Bi0 5 is prepared by passing a current of chlorine through a concentrated solution of potassa in which very finely divided oxide of bismuth is suspended ; or by heating for a long time in the air a mixture of potassa and oxide of bismuth ; or better still, by calcining a mixture of oxide of bismuth, caustic po- tassa, and chlorate of potassa. Bismuthic acid prepared by either of these processes is always mixed with a certain quantity of oxide of bismuth, which may be separated by treating the substance with weak nitric acid, which dissolves the oxide of bismuth, and, when cold, does not affect the bismuthic acid. Bismuthic acid is a bright- red powder, which readily parts with a portion of its oxygen at a temperature slightly above 212, and is then converted into an inter- mediate oxide Bi0 4 . Concentrated acids also decompose it, reducing it to the state of oxide Bi0 3 , which combines with the acid. Bismuthic acid can combine with oxide of bismuth, and thus pro- duce saline oxides ; but these compounds have not yet been much studied. They are obtained by heating in the air a mixture of oxide of bismuth Bi0 3 and caustic potassa, or by passing a current of chlorine through a solution of potassa which contains oxide of bismuth in suspension. When these reactions are terminated, bis- muthic acid is obtained, while, if they are prematurely arrested, brown compounds of variable proportions result, which are combi- nations of bismuthic acid Bi0 5 with oxide of bismuth Bi0 3 . SALTS FORMED BY OXIDE OF BISMUTH. 995. Oxide of bismuth is a feeble base, forming with acids seve- ral crystallizable salts, which water decomposes into basic salts which are precipitated, and into very acid salts which remain in the solu- tion. Nitrate of Bismuth. ^ 996. The nitrate, which is the most important of the salts of bismuth, is obtained by dissolving bismuth in nitric acid. The liquid, when evaporated, yields large, colourless, and deliquescent crystals, of the formula Bi0 3 ,3N0 5 +3HO. It dissolves without decomposition in a small quantity of water, particularly when acidu- lated with a few drops of nitric acid, but is decomposed if the quan- tity of water is greater, a white precipitate of a basic nitrate being formed, which is known by the name of pearl powder. This sub- stance is used for whitening the skin, but is liable to the objection of being blackened by sulf hydric acid. Its composition varies ac- cording to the quantity of water used in the precipitation, the tem- perature, and duration of contact of the basic salt with the water. Boiling water ultimately removes all its acid, and leaves only hydrated oxide. BINARY COMPOUNDS. 207 Sulphate of Bismuth. 997. By heating powdered bismuth with concentrated sulphuric acid, sulphurous acid is disengaged, and the metal is converted into a white, insoluble powder of sulphate of bismuth Bi0 3 ,3S0 3 . This salt is decomposed by treatment with water into a very acid salt which remains in solution, and an insoluble bi-basic sulphate Bi0 3 , S0 3 +H0. Carbonate of Bismuth. 998. By adding carbonate of soda to an acid solution of nitrate of bismuth, a white precipitate of a basic carbonate Bi0 3 ,C0 3 is obtained, which is easily destroyed by heat, leaving a residue of oxide. COMPOUND OF BISMUTH WITH SULPHUR. 999. Bismuth combines directly with sulphur when assisted by heat. To effect the combination, it is sufficient to heat together the two substances in the state of fine powder, a certain quantity of metallic bismuth always remaining mixed or dissolved in the sulphide. In order to obtain the latter pure, the product of the first fusion must be reduced to a fine powder, and again fused in a crucible with an additional quantity of sulphur. The sulphide then appears under the form of a gray ball, possessing a metallic lustre, and evincing in its fracture a fibrous texture. The formula of the sulphide is BiS 3 . It has been found crystallized in nature, and appears to be isomorphous with the sulphide of antimony to which the same formula is assigned. Sulphide of bismuth may be obtained by the humid way in the form of a black powder, by passing a current of sulf hydric acid through a solution of a salt of bismuth. COMPOUNDS OF BISMUTH WITH CHLORINE. 1000. Bismuth combines directly with chlorine with disengage- ment of heat, and even of light, when the metal is very finely divided. If a current of chlorine be led over bismuth heated in a tubulated retort, the chloride distils over and condenses in the form of a readily fusible white substance. The same substance is ob- tained by distilling in a small retort a mixture of 1 part of metallic bismuth and 2 parts of bichloride of mercury. Chloride of bismuth rapidly attracts the moisture of the air, and is converted into ^a crystallizable hydrated chloride; which may also be obtained by dissolving metallic bismuth in aqua regia, and evaporating the liquid. Chloride of bismuth BiCl 3 dissolves without change in water acidulated with chlorohydric acid, but is decomposed by fresh water; when a portion of the chloride dissolves by means ot the chlorohydric acid which is set free, while a white precipitate of oxychloride of bismuth BiCl 3 +2(Bi0 3 -f 3HO) remains. 208 BISMUTH. On pouring an acid solution of nitrate of bismuth into a solution of sea-salt, a white precipitate of very fine crystalline spangles is formed, which is an oxy chloride of bismuth of the formula BiCl 3 -f- 2(Bi0 3 +3HO). This substance is used for whitening the skin, and is called pearl-white. ALLOYS JDF BISMUTH. 1000 bis. By alloying bismuth with lead and tin, very fusible alloys are obtained, which are used for taking impressions, making stereotype-plates, etc. The alloy composed of 1 part of lead, 1 part of tin, and 2 of bismuth fuses at 200, while that containing 5 of lead, 3 of tin, and 8 of bismuth fuses at about 208.4. By diminishing the proportion of bismuth, the fusing point of the alloys obtained varies between 212 and 392, and these substances have been used as washers for the safety-valves of the boilers of high- pressure steam-engines. Their composition was such as to fuse at a point slightly above the temperature corresponding to the maxi- mum of tension which the steam should not exceed. When the safety-valves were out of order or overloaded, and the elastic force of the steam surpassed the maximum, the washers, by beginning to fuse, allowed the steam to escape. This means of safety was soon found to be useless, as the alloy, being kept for a long time at a temperature approaching its melting point, underwent a kind of eliquation a more fusible alloy separated from it, and that which remained was much less fusible than the original alloy. For this reason the use of fusible washers has been abandoned. DISTINCTIVE CHAEACTERS OF THE SOLUBLE COMPOUNDS OF BISMUTH. 1001. We have seen that all the compounds of bismuth, being soluble in a very small quantity of water, are decomposed when treated with a larger quantity, and yield white precipitates of basic salts : therefore, one of the distinctive characters of solutions of bismuth is to become cloudy when diluted with a large quantity of water, The caustic alkalies and alkaline carbonates throw down white precipitates, insoluble in an excess of the reagent. Sulf hydric acid and the sulf hydrates afford black precipitates, which do not redissolve in an excess of sulf hydrate. Iron, zinc, and copper precipitate bismuth in the form of a black powder, which fuses readily on charcoal in the reducing flame of the blowpipe into a metallic globule, which becomes very brittle after cooling, and yields a powder of a characteristic rose-colour. DETERMINATION OF BISMUTH; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. 1002. Substances containing bismuth which are to be subjected to chemical analysis are always dissolved in nitric acid, and the METALLURGY OF BISMUTH. 209 boiling liquid is precipitated by an excess of carbonate of ammonia. The precipitate is washed on the filter, and then calcined in a small porcelain capsule, in which it remains in the state of the oxide Bi0 3 . The calcination should not be made in a platinum crucible, because this metal is easily attacked by oxide of bismuth, especially when a small quantity of metallic bismuth can be produced by a reducing action. The filter should be calcined separately, its ashes sprinkled with a few drops of nitric acid, and then recalcined to decompose the nitrate of bismuth which is formed. It is often necessary to precipitate bismuth in the state of sul- phide by means of sulf hydric acid, as, for example, when the metal exists in a liquid with other metals which are precipitated by the alkalies or alkaline carbonates, but not by sulf hydric acid. It is also precipitated as sulphide when the liquid contains chlorohydric acid, because the precipitate formed by the alkaline carbonates would in this case contain chloride of bismuth, which is difficult to decompose by an excess of alkaline carbonate. The bismuth being in the state of sulphide is collected on a filter, dissolved in nitric acid, and then reprecipitated by an excess of carbonate of ammonia. Lastly, bismuth is sometimes precipitated in the metallic state by a blade of iron or zinc, and the metallic powder, being collected on a filter, is calcined in a porcelain capsule ; after which a few drops of nitric acid are added, it is recalcined, and the bismuth deter- mined in the state of oxide. Bismuth is easily separated by sulf hydric acid passed through an acid liquid, from all the metals we have hitherto studied, with the exception of cadmium, tin, and lead. It is separated from tin by treating the sulphides, immediately after their being precipitated, with a solution of sulf hydrate of ammonia, which dissolves only the sulphide of tin. In order to separate bismuth from lead, both metals are dissolved in nitric acid, and evaporated with an excess of sulphuric acid until the vapours of the acid begin to pass over, after which they are treated with water, which dissolves only the sulphate of bismuth by means of the excess of acid. This process does not effect a very accurate separation. No method of sepa- rating bismuth from cadmium is yet known.* METALLURGY OF BISMUTH. 1003. Bismuth has hitherto been found only in a small number of minerals, the only one of which sufficiently abundant and rich to be used as an ore is native bismuth, which constitutes metallic veins * A perfect separation of bismuth from cadmium is effected by adding a solu- tion of cyanide of potassium to the solution of the two oxides, by which the bis- muth is precipitated, while the cadmium remains in solution as a double cyan of cadmium and potassium. Another method might be based on the solubility of oxide of cadmium in monia, in which oxide of bismuth is insoluble. W. L. F. s2 14 210 BISMUTH. in the quartzose rocks of the old formations. All the bismuth used in the arts comes from Saxony, and is extracted by a very simple process : the ore being heated in close vessels, the bismuth fuses, separates from the gangue, and falls to the bottom of the vessel. The fusion is effected in sheet-iron or cast-iron tubes bd (fig. 555), arranged in a furnace, and inclining down- ward. The ore being intro- duced through the opening d, the latter is closed, while the other end b is closed by a plate having a hole 0, through which the metal escapes. It is received in earthen cups , a, heated by Fig. 555. charcoal placed in the space K beneath, in order to keep the metal fluid. It is then scooped out and run into moulds. The metal thus obtained, which always contains, besides metallic sulphides and arseniurets, some foreign metals, is purified by fusion with T V of its weight of saltpetre. 211 ANTIMONY. EQUIVALENT = 129 (1612.5; = 100). 1004. The antimony* of commerce, which is rarely pure, con- taining most frequently a small admixture of iron, lead, arsenic, and sulphur, is purified in the laboratory by mixing it intimately with T J o of its weight of nitre, and fusing the mixture in an earthen cru- cible ; when the antimony appears in the form of a metallic button, composed of very small crystalline lamellae. The fineness of the grain of antimony is an index of its purity. Antimony is a metal of a slightly bluish, very brilliant, silvery white colour. It fuses at 842, and at a white-heat gives off appre- ciable vapours, at which temperature it may be distilled in a current of hydrogen gas ; but the tension of its vapour being still very feeble, the distillation is slow. Antimony crystallizes readily from fusion, and its fracture presents very brilliant surfaces of cleavage, the disposition of which leads to the rhombohedron, and which are fre- quently of great extent. The tendency of the metal to crystallize may be well seen in the cakes of commercial antimony, their upper surfaces often exhibiting a beautiful star, the rays of which resemble the fern-leaf. It is a very brittle metal and easily reduced to pow- der in a mortar. Antimony does not sensibly alter in the air at the ordinary tem- perature, while it readily oxidizes when kept in a fused state in contact with the air. Heated to a high temperature, it burns with a white flame and gives off copious fumes. If the fused metal, heated to redness, be thrown from a certain height on the floor, a very brilliant phenomenon of combustion is observed, accompanied by thick white fumes. Finely powdered antimony dissolves in boiling concentrated chlo- rohydric acid, with disengagement of hydrogen gas, but does not decompose water in the presence of sulphuric acid, which will not oxidize it except when concentrated and hot, when sulphurous acid is disengaged. Nitric acid, even when dilute, readily attacks it, converting the metal into an insoluble white precipitate. Aqua regia transforms antimony into a chloride which dissolves without change in an excess of chlorohydric acid. COMPOUNDS OF ANTIMONY WITH OXYGEN. 1005. Two well-defined compounds of antimony with oxygen are known, the quantities of oxygen contained in which are as 3 to 5. * Although the ores of antimony were known to the ancients, Basil Valentine was the first who made mention of metallic antimony. 212 ANTIMONY. The most oxygenated compound, of which the formula is Sb0 5 , and which plays the part of an acid, is antimonic acid ; while that con- taining the least amount of oxygen, and is expressed by the formula Sb0 3 , acts as a feeble base. We shall call it sesquioxide of anti- mony, or simply oxide of antimony. A third oxide Sb0 4 , which by some chemists is regarded as an oxide per se, and called antimonious acid, should rather be consi- dered as an antimoniate of oxide of antimony, Sb0 3 .Sb0 5 . Oxide of Antimony Sb0 3 . 1006. Oxide of antimony is formed when antimony is heated in an imperfectly closed crucible, when small elongated and very bril- liant prismatic crystals, which have been called argentine flowers of antimony, are deposited on the sides of the crucible at a little distance above the fused metal. But as it is difficult to prevent the oxide prepared in this way from containing some antimoniate of oxide of antimony, a better method of obtaining the oxide in a state of purity consists in pouring, by small quantities at a time, a solu- tion of chloride of antimony SbCl 3 into a boiling solution of carbo- nate of soda ; when the oxide of antimony separates in the form of small crystals. Oxide of antimony, the colour of which is a grayish white, fuses at a red-heat, and sublimes at a higher temperature. It readily absorbs oxygen when heated in the air, and is converted into anti- moniate of oxide of antimony, while it is indecomposable by heat alone, but is easily reduced by hydrogen or by charcoal. The oxide of antimony, precipitated when cold from the solution of the chloride by carbonate of soda, which is hydrated, and has the formula Sb0 3 -f-HO, dissolves readily in alkaline liquids, form- ing true salts in which it acts the part of an acid. Oxide of antimony contains : Antimony 84. 31 Oxygen 15.69 100.00 Its formula is written Sb0 3 ; and consequently the equivalent of antimony is obtained from the proportion : 15.68 : 84.32 : : 24 : x, whence z=129. Antimonic Acid Sb0 5 . 1007. Antimonic acid is obtained by attacking antimony by nitric acid, or better still, by aqua regia containing an excess of nitric acid, when an insoluble white powder of hydrated antimonic acid is formed, which loses its water at a slightly elevated tem- perature, and is converted into anhydrous antimonic acid. The hydrated acid is also obtained by decomposing the perchloride of ANTIMONIC ACID. 213 antimony SbCl, by water ; but the hydrates obtained by these two processes are far from being identical. Their capabilities of satu- ration with bases being different, they in this respect exhibit a phe- nomenon analogous to that observed in stannic acid, and which was treated of ( 479 et seq.) when speaking of phosphoric acid, which presents the same feature. The product obtained by attacking an- timony by nitric acid, and to which the name of antimonic acid has been preserved, only saturates 1 equivalent of a base, producing neutral salts of the general formula RO,Sb0 5 ; while the precipi- tate obtained by decomposing perchloride of antimony by water saturates 2 equiv. of a base, and forms neutral salts of the formula 2 RO,Sb0 5 . It has been called metantimonio acid. Anhydrous antimonic acid is a powder of a yellowish-white co- lour, which is decomposed by a red-heat, producing antimoniate of oxide of antimony Sb0 3 ,Sb0 5 . The neutral antimoniate of potassa is prepared by heating in an earthen crucible 1 part of metallic antimony and 4 parts of nitrate of potassa, and treating the powdered mass with a small quantity of tepid water, which dissolves the potassa in excess and the unde- composed nitrite of potassa. The residue is then boiled with water for several hours, by which the anhydrous antimoniate of potassa,, which is insoluble, is converted into a soluble hydrated antimoniate. An insoluble residue remains, which is the bi-antimoniate of potassa KO,2Sb0 5 ; and the liquid leaves after evaporation a gummy mass which presents no appearance of crystallization, and the formula of which, when desiccated in dry air, is KO,Sb0 5 +5HO. This neu- tral antimoniate KO,Sb0 5 +5HO is converted into a crystalline powder of bi-antimoniate KO,2Sb0 5 by passing a current of car- bonic acid through its solution. By heating in a silver crucible antimonic acid or neutral antimo- niate of potassa with a large excess of potassa, a fused mass which completely dissolves in a small quantity of cold water is obtained ; and the solution, when evaporated in vacuo, deposits small crystals of metantimoniate of potassa 2KO,Sb0 5 . This salt dissolves, without apparent decomposition, in a small quantity of cold water to which a certain quantity of caustic potassa has been added, while it is decomposed by pure water into potassa and acid metaantimo- niate of potassa. KO,Sb0 5 +7HO, which is but slightly soluble in cold water. Water dissolves it more freely at a temperature of 105 or 120, while a prolonged contact with cold water transforms it into neutral antimoniate of potassa; which transformation is rapidly effected by boiling the liquid. The solution of the acid metantimoniate of potassa possesses the property of precipitating the salts of soda, and yielding an acid metantimoniate of soda, which is almost insoluble in water. It is the only reagent as yet known which precipitates soda from its solutions ; but it is necessary to use freshly prepared acid metantimoniate of potassa, as the salt 214 ANTIMONY. is after some time converted into the common antimoniate, which does not precipitate the salts of soda. Antimoniate of Oxide of Antimony Sb0 3 ,Sb0 3 . 1008. By heating antimonic acid until oxygen is no longer given off, a white powder, of which the composition is Sb0 4 , but which should be written Sb0 4 ,Sb0 5 , remains. This product, which is sometimes called antimonious acid, is also formed when antimony is roasted in the open air. A solution of tartaric acid or bi-tartrate of potassa abstracts its oxide of antimony, leaving the antimonic acid, while a solution of caustic potassa dissolves, on the contrary, the antimonic acid, and leaves the oxide of antimony ; which reac- tions render the existence of both oxide of antimony and antimonic acid in this body very probable. Antimoniate of oxide of antimony is infusible. SALTS FORMED BY OXIDE OF ANTIMONY. 1009. Oxide of antimony SbG 3 is a feeble base, which neverthe- less forms several salts with acids. A nitrate of antimony is obtained by treating cold antimony with fuming nitric acid, in the shape of crystalline spangles of the for- mula 2Sb0 3 ,N0 5 . The salt is decomposed by water, and trans- formed into hydrated oxide of antimony. Several compounds of oxide of antimony with sulphuric acid are known, and present the following composition : Sb0 3 ,4S0 3 +HO Sb0 3 ,2S0 3 Sb0 3 , S0 3 2Sb0 3 , S0 3 . We do not find among these salts the compound Sb0 3 ,3S0 3 , which should be regarded as the neutral sulphate of antimony, from the formula Sb0 3 which we have adopted to represent oxide of antimony. The oxy chloride of antimony SbCl 3 ,2Sb0 3 +HO, the prepara- tion of which will be explained hereafter, is converted into the sulphate Sb0 3 ,4S0 3 +HO when it is treated with concentrated sulphuric acid, while the sulphate Sb0 3 ,2S0 3 is obtained by treat- ing oxide of antimony with fuming oil of vitriol, (Nordhausen sul- phuric acid.) Lastly, the sulphate Sb0 3 ,4S0 3 +HO is decomposed by treatment with hot water, leaving a residue of the formula 2Sb0 3 ,S0 3 . COMPOUND OF ANTIMONY WITH HYDROGEN. 1010. Antimony forms a gaseous compound with hydrogen, which resembles in its composition that of arseniuretted hydrogen and phosphuretted hydrogen gas, but which hitherto has not been SULPHIDES. 215 obtained in a state of purity. By introducing a solution of proto- chloride of antimony into a bottle in which hydrogen is being dis- engaged by the reaction of dilute sulphuric acid on zinc, the hydro- gen always contains a certain quantity of antimoniuretted hydrogen gas, which is easily recognised on igniting the gas, when it burns with a yellowish flame which evolves white fumes, and which, on being allowed to play on a cold porcelain capsule, yields glittering spots of metallic antimony. If the gas be passed through a heated tube, a brilliant ring of metallic antimony forms on the sides of the tube, in front of the heated portion. COMPOUNDS OF ANTIMONY WITH SULPHUR. 1011. Two combinations of antimony with sulphur are known ; and while the formula of the first, which we shall call sulphide of an- timony, is SbS 3 corresponding to the oxide Sb0 3 , the second cor- responds to antimonic acid, and its formula being SbS 5 , we shall call it sulf antimonic acid. Sulphide of antimony is found in nature, and is the only ore of antimony. It always occurs crystallized, but the prismatic crys- tals are so dovetailed into each other, that it is often difficult to ascertain their form. It is sometimes found in isolated crystals, which are prisms belonging to the fourth system. Sulphide of anti- mony, which is of a deep gray colour, and a very decided metallic lustre, fuses below a red-heat, and readily crystallizes on cooling from a white-heat. It exhales copious fumes, and may be distilled in a current of nitrogen gas. Its density is 4.62. The sulphide is formed by the direct combination of antimony with sulphur, by several successive fusions, when a purer sulphide than that occur- ring in nature is obtained, which always contains a small quantity of other metallic sulphides. Sulphide of antimony is easily roasted in the air, during which operation no sulphate is formed, but only oxide of antimony, which combines with the undecomposed sulphide, especially under the in- fluence of an elevated temperature. Fusible oxysulphides are thus formed, which, after cooling, yield brown vitreous substances, called in commerce glass of antimony, liver of antimony, or crocus, accord- ing to the proportions of the substances entering into their compo- sition. Glass of antimony, which contains about 8 parts of oxide and 1 of sulphide, is transparent and of a reddish-yellow colour, while crocus, which contains 8 parts of oxide and 2 of sulphide, is opake and reddish yellow. Liver of antimony is opake and of a deep brown colour, and contains nearly 4 parts of sulphide for 8 of oxide. Hydrogen decomposes sulphide of antimony at a red-heat with disengagement of sulf hydric acid, while the antimony remains in the metallic state ; but it is difficult to prevent a small quantity of antimony from being disengaged in the state of antimoniuretted 216 ANTIMONY. hydrogen gas. Charcoal also decomposes sulphide of antimony at a high temperature, while sulphide of carbon is disengaged, and the antimony remains in the metallic state. It is, however, difficult by these methods to obtain antimony entirely free from sulphur. Iron, zinc, and copper decompose sulphide of antimony at a red- heat ; but the metallic antimony thus obtained always contains a certain quantity of these metals. Concentrated chlorohydric acid readily dissolves sulphide of antimony with disengagement of sulf- hydric acid, which reaction is sometimes applied in the laboratory to the preparation of sulf hydric acid ( 149). Boiling concentrated sulphuric acid attacks sulphide of antimony and evolves sulphurous acid. Nitric acid converts it into an insoluble oxide of antimony and sulphuric acid. The alkalies and alkaline carbonates decompose sulphide of anti- mony both in the dry and humid way, sulphide of antimony and a compound of oxide of antimony with potassa being formed. When the sulphide of antimony is in excess, there is formed in addition a compound of sulphide of antimony with monosulphide of potassium, in which combination the sulphide of antimony acts the part of an acid. If the decomposition be effected in a brasqued crucible, a portion of the antimony separates in the metallic state. The sulphide of antimony SbS 3 may be prepared in the humid way, by passing a current of sulf hydric acid gas through a solution of chloride of antimony SbCl 3 in water charged with chlorohydric acid, when an orange-coloured precipitate of hydrated sulphide is formed, which dissolves readily in the alkaline sulphurets, when it plays the part of an acid. Acids precipitate anew the hydrated sulphide from solutions of the sulphosalts. Heat easily drives off the water from the hydrated sulphide, which then is converted into a gray anhydrous sulphide. In medicine the hydrated sulphide is used either mixed or com- bined with oxide of antimony, and often with sulfantimonic acid SbS 5 , and is known by the name of kermes mineral, golden sul- phide of antimony, etc. Kermes is prepared either in the dry or humid way. In the former case, a mixture of 5 parts of native sulphide of an- timony and 3 parts of dried carbonate of soda is fused in an earthen crucible, and the fused substance, after being reduced to powder, is boiled with a large quantity of water. The hot liquid is rapidly filtered, taking care that it does not cool in the filter ; when the liquid, which is nearly colourless, or but slightly yellow, deposits on cooling a copious brown flaky precipitate, which is the kermes. It should be quickly washed, dried at a low temperature, and kept in well-stoppered bottles. It is obtained in the humid way by boiling 1 part of native sul- phide of antimony, finely powdered, with 20 or 25 parts of dried CHLORIDES. 217 carbonate of soda, and 250 parts of water; the liquid, which is almost colourless, depositing the kermes on cooling. By pouring chlorohydric acid into the mother liquid from which the kermes has been deposited, a precipitate of a deeper red colour than the precipitate is obtained, which has been called the golden sulphide. It is a mixture of sulphide of antimony SbS 3 , sulfanti- monic acid SbS 5 , and oxide of antimony Sb0 3 . It is easy to ascertain that the oxide of antimony exists only as an admixture in kermes mineral and in the golden sulphide ; an examination with the microscope shows the oxide of antimony in the form of white points scattered through the mass. Kermes contains, also, a small quantity of sulphide of potassium combined with the oxide, or with a portion of the sulphide of an- timony. Sulfantimonic acid SbS 5 is obtained by passing a current of sulf hydric acid through a solution of perchloride of antimony SbCL in dilute chlorohydric acid, when a yellow precipitate is formed, readily dissolving in the alkaline sulphides, and forming sulphosalts which frequently crystallize with great facility. For medicinal purposes, a sulfantimoniate of sodium is often prepared by mix- ing intimately 18 parts of very finely powdered sulphide of anti- mony, 12 parts of dried carbonate of soda, 13 of lime and 3J of sulphur, and allowing the mixture, after it has been triturated for a long time, to digest for several days in a flask filled with water, the vessel being frequently shaken. The liquid, when evaporated, first by heat, and then under the receiver of an air-pump, yields large crystals of a pale yellow colour, and of which the formula is 3NaS,SbS 5 +18HO. COMPOUNDS OF ANTIMONY WITH CHLORINE. 1012. Antimony forms two compounds with chlorine, SbCl 3 and SbCl 5 , corresponding to the oxide of antimony Sb0 3 and antimonic acid Sb0 5 . The chloride of antimony SbCl 3 is obtained by passing chlorine slowly through a tube containing antimony in excess, while the per- chloride SbCl 5 would be formed if the chlorine be in too great quantity. The chloride is also obtained by distilling in a glass retort an intimate mixture of 1 part of antimony and 2 parts of ^ bi- chloride of mercury ; but the most economical method of preparing it consists in dissolving native sulphide of antimony in chlorohydric acid, and evaporating the liquid with an excess of acid. In the laboratory the residue of the preparation of sulf hydric acid is used for this purpose. Chloride of antimony SbCl 3 is a white, readily fusible substance, which, from its consistence at the ordinary temperature, was for- merly called butter of antimony. It volatilizes at a temperature below a red-heat. VOL. II. T 218 ANTIMONY. The protochloride of antimony is deliquescent in a moist atmo- sphere, and dissolves without change in a small quantity of water, while the addition of chlorohydric acid is necessary for its solution in larger quantities of the same liquid ; as with much pure water de- composition would ensue, a white soluble powder of an oxychloride of antimony SbCl 3 ,2Sb0 3 +HO, called by the old chemists powder of Algaroth, being formed. By treating a chlorohydric solution of chlo- ride of antimony with hot water, the clear liquid deposits, on cool- ing, crystals of another oxychloride of the formula SbCl 3 ,5Sb0 3 . Kepeated washings decompose the oxychlorides of antimony and leave pure oxide. The best method of preventing solutions of chlo- ride of antimony from being clouded by water consists in the addi- tion of a certain quantity of tartaric acid. Anhydrous chloride of antimony combines with dry ammoniacal gas, yielding a compound of which the formula is NH 3 ,SbCl 3 . With the alkaline chlorides and chlorohydrate of ammonia it forms dou- ble crystallizable chlorides. In surgery, chloride of antimony is used to cauterize wounds. Gunsmiths employ it for bronzing gun-barrels, the iron of which, being thus covered with a very thin pellicle of metallic antimony, is preserved from rust. Per chloride of antimony SbCl 5 is prepared by heating antimony in a current of dry chlorine, the same apparatus being used as that employed for the preparation of the perchloride of tin. The liquid collected in the receiver, which always contains some protochloride SbCl 3 in solution, must be completely saturated with chlorine, and then distilled in a small retort. The first portions which pass over contain a considerable quantity of dissolved chlorine, and are co- loured deeply yellow, while the subsequent liquid, being nearly colourless, is collected by itself. Perchloride of antimony never- theless appears to decompose at the temperature of its ebullition under the ordinary pressure of the atmosphere, as it always disen- gages chlorine when subjected to distillation. DISTINCTIVE CHARACTERS OF THE SOLUBLE COMPOUNDS OP ANTIMONY. 1013. The characteristic reactions of solutions of antimony which we are about to indicate refer to the protochloride of anti- mony and to emetic tartar, which is a double tartrate of antimony and potassa. They will serve to distinguish antimony in all cases, because it is always easy to convert its other compounds into these two products. Solutions of antimony produce with potassa and soda white pre- cipitates, which are easily redissolved in an excess of alkali. Ammonia throws down a white precipitate insoluble in an excess of the reagent. The alkaline carbonates yield, carbonic acid being at the same ANALYTIC DETERMINATIONS. 219 time evolved, a white precipitate of the hydrated oxide, which does not dissolve in an excess of carbonate. Sulf hydric acid and sulf hydrate of ammonia yield a characteris- tic orange-coloured precipitate, which dissolves in an excess of sulf- hydrate. A blade of iron or zinc precipitates antimony in the form of a black powder, from which, by fusion on charcoal before, the blow- pipe, metallic antimony is obtained, possessing the characteristic physical properties which distinguish it from tin, this metal being analogous to it in its chemical reactions. DETERMINATION OF ANTIMONY; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. 1014. Antimony can neither be determined as the oxide Sb0 3 nor as antimonic acid Sb0 5 , as the purity of these substances would always be questionable. It is precipitated from its solution by sulf- hydric acid, a sufficient quantity of chlorohydric acid being added to prevent the liquid from being clouded by water, or still better, tartaric acid, when the addition of this substance does not interfere with the determination of the remaining substances. The liquid, after being saturated with sulf hydric acid gas, is exposed to a gentle heat for several hours in an imperfectly closed bottle, in order to allow the greater portion of the sulf hydric acid to be dis- engaged ; when the precipitate of sulphide of antimony is collected on a filter, and, after being well washed, is dried on the filter at a temperature of 212. The filter, with the substance it contains, being weighed, the latter is separated as completely as possible, and dropped into a small flask ; when the weight of the filter, sub- tracted from that of the filter and substance together, gives the weight of the sulphide. The small quantity which always remains in the pores of the filter can be taken into account by incinerating the paper and considering the residue as antimoniate of antimony Sb0 3 ,Sb0 5 . The sulphide of antimony being now treated with hot aqua regia, the antimony dissolves as perchloride, and the sul- phur in the state of sulphuric acid, the oxidation of the sulphur being accelerated by an addition of a small quantity of chlorate of potassa. Chloride of barium is then poured into the liquid pro- perly diluted with water, while a small quantity of tartaric acid is added to prevent the precipitation of oxychloride of antimony; when sulphate of baryta is precipitated and weighed after calcina- tion. By subtracting from the weight of the sulphide of antimony the weight of sulphur corresponding to the sulphate of baryta, the weight of the metallic antimony is obtained.* * The method given in the text may be considerably shortened, by collecting the sulphide of antimony on a weighed filter, which has been previously dried at 212, (a balanced filter;) when the weight of the filter with the precipitate, after being dried at the same temperature, minus the weight of the filter, gives imme- 220 ANTIMONY. The sulphide of antimony may also be heated in a current of hydrogen gas, when metallic antimony remains, sulfhydric acid and vapour of sulphur being disengaged. For this purpose, the sulphide of antimony is placed in a small porcelain crucible, through the lid of which a tube passes conveying dry hydrogen to the bot- tom of the crucible, and, the temperature being gradually raised, the reaction is maintained until the crucible no longer alters in weight. In no case can antimony be weighed in the state of sulphide, its composition always being a matter of uncertainty. 1015. In order to separate antimony from the metals we have previously studied, the insolubility of antimonic acid in nitric acid is sometimes relied on, and sometimes its precipitation by sulfhy- dric acid, and the solubility of sulphide of antimony in alkaline sulfhydrates. Antimonic acid not being absolutely insoluble in nitric acid, it is always necessary to test for antimony in the liquid by means of sulfhydric acid. In order to separate antimony from the alkaline, alkalino-earthy, and earthy metals, chlorohydric acid is added to the liquid to pre- vent the deposit of oxychloride of antimony, and sulfhydric acid gas is passed through it. When the antimony is nearly wholly pre- cipitated, the liquid is diluted with water, because sulphide of anti- mony is slightly soluble in chlorohydric acid, unless the latter is very dilute ; and sulfhydric acid is again passed through it. The precipitate of sulphide of antimony having been separated on a fil- ter, the substances remaining in solution may be determined by the ordinary processes. Antimony is separated from manganese, iron, chrome, cobalt, nickel, and zinc by passing sulfhydric acid through the liquid acidu- lated with chlorohydric acid. The precipitation of oxychloride of antimony is frequently prevented by the addition of tartaric acid, in which case, however, the other metals can no longer be com- pletely separated from their solutions either by ammonia or the alkaline carbonates, because tartaric acid prevents their precipita- tion. The liquid then being saturated with ammonia, the metals are precipitated by sulf hydrate of ammonia. Antimony is separated from cadmium, lead, and bismuth by saturating the chlorohydric solution with ammonia, and adding a large excess of sulf hydrate of ammonia in which a certain quantity of sulphur has been dissolved. The bottle, imperfectly closed, is exposed for several hours to a temperature of from 120 to 140 ; when the antimony dissolves in the state of sulphide, while the sul- phides of the other metals are precipitated. By decomposing the diately the weight of all the antimony as sulphide SbS 3 , -whence that of the me- tallic antimony may be deduced. The antimony having been in the state of proto- chloride SbCl s , is precipitated entirely as protosulphide SbS 8 , in all cases when the antimonial compound has not been dissolved in nitromuriatic acid. W. L. F. ANALYTIC DETERMINATION. 221 filtered liquid by dilute chlorohydric acid, the sulphide of antimony separates, mixed with a large quantity of free sulphur. Antimony cannot be separated from tin by any of the processes just described. The reactions of these metals being very similar, their separation is consequently a matter of some difficulty. Both metals being dissolved in aqua regia, are precipitated together by a blade of zinc, and the metallic precipitate is weighed. It is then dissolved in aqua regia with an excess of chlorohydric acid, and a blade of tin dipped into the liquid when properly diluted, by which the antimony alone is precipitated, and perfectly, if care be taken to keep the liquid gently heated, with a slight excess of chlorohydric acid. DETECTION OF ANTIMONY IN CASES OF POISONING. 1016. As compounds of antimony act as poisons on the animal economy, it occasionally falls to the lot of the medical man to in- vestigate their toxicological effects, the subject of investigation being sometimes food and sometimes portions of the human body. For this purpose, the suspected matter being diluted with water, a certain quantity of pure chlorohydric acid added, and the liquid boiled, 20 gm. of chlorate of potassa for every 100 parts of mat- ter are thrown into it by small quantities at a time, the liquid is filtered while boiling, and concentrated by evaporation. It is then introduced into a Marsh's apparatus, as represented in fig. 260 ; when a glittering ring of metallic antimony forms in the tube / Protoxide of Copper CuO. 1042. On heating metallic copper in the air, its surface first becomes covered with suboxide Cu 3 0, which subsequently changes into the black oxide CuO. Although protoxide of copper is often prepared by roasting copper turnings, or better still, the very finely divided copper which remains after the calcination of the acetate with access of air, it is obtained more readily by decomposing the nitrate by heat, when the oxide remains in the form of a black pow- der, which rapidly condenses the moisture of the atmosphere. When caustic potassa is poured into the solution of a protosalt of copper, a grayish-blue precipitate of hydrated protoxide is formed, the water of which is readily driven off by heat : it suffices to boil the solution in which it has been precipitated to convert it into a black powder of anhydrous oxide. Hydrated protoxide of copper dissolves in ammonia, producing a solution of a slightly purple-blue colour, called celestial water. Deutoxide of Copper. 1043. This oxide is prepared by treating the hydrated prot- oxide of copper with oxygenated water, when the blue matter is changed into a brownish-yellow substance, from which a slight ele- vation of temperature easily abstracts one-half of its oxygen. Cuprio Acid. 1044. An intimate mixture of very finely divided copper, po- tassa, and nitre, heated to redness and then treated with water, yields a blue solution which appears to contain a combination of an oxide of copper containing more oxygen than the preceding with potassa. This compound, however, is so evanescent that, if the liquid be heated, oxygen is disengaged, and the copper is precipi- tated in the state of black oxide CuO. SALTS. 239 SALTS FORMED BY THE SUBOXIDE OF COPPER Cu fl O. 1045. The salts of the suboxide of copper are obtained by dis- solving hydrated suboxide in dilute acids, which, when they are con- centrated, decompose the suboxide into metallic copper which sepa- rates, and protoxide which combines with the acids. A subsulphite of copper Cu a O,S0 3 , is prepared by decomposing a solution of protosulphate of copper CuO,S0 3 by a solution of sul- phite of soda, when an orange precipitate is formed which is con- verted, by boiling, into a red crystalline powder. When acetate of copper is distilled, a small quantity of a white sublimate, consisting of sub-acetate of copper, is found in the upper part of the retort. The soluble subsalts of copper produce colourless solutions, from which alkalies throw down an orange-yellow precipitate. Ammo- nia gives the same reaction, but an excess of the reagent redissolves the precipitate, producing a colourless liquid which soon turns blue in the air. Sulf hydric acid throws down a black precipitate of these salts, for the study of whose reactions the subchloride CuCl is ex- actly suitable. SALTS FORMED BY THE PROTOXIDE OF COPPER CuO. 1046. These salts, which are obtained by dissolving protoxide of copper, or better still, its hydrate or its carbonate, in acids, are blue or green, when they contain water of crystallization, while in the anhydrous state they are of a dirty white, when the acid is colourless, and their solutions are blue or green. They exhibit the following characteristic reactions : Caustic potassa and soda yield a grayish-blue precipitate of hy- drated protoxide, which is converted into a brown precipitate by boiling. The blue precipitate, which is insoluble in weak alkaline liquids, dissolves with a blue colour in the latter when they are con- centrated. Ammonia throws down the same precipitate, while an excess of the reagent dissolves the precipitate and produces a beautiful blue solution, which then contains a double salt of copper and ammonia, from which caustic potassa precipitates oxide of copper. Sulf hydric acid and the sulf hydrates throw down black precipi- tates, which are insoluble in an excess of sulf hydrate. Prussiate of potash forms, with protosalts of copper, a chestnut- brown precipitate, which assumes a purplish shade when the precipi- tate is very weak. The test is a very delicate one, and will detect the presence of the smallest quantities of copper in a solution. Iron and zinc precipitate metallic copper in the form of a brown powder, which, when burnished, assumes the metallic lustre and ordinary appearance of copper. Protoxide of copper turns borax, and in general all vitreous 240 COPPER. fluxes, green. If the glass be heated in the reducing portion of the flame, it acquires a beautiful red colour, produced by the reduc- tion of the protoxide of copper CuO into the suboxide Cu a O. 'Sulphate of Copper. 1047. Sulphate of copper is found in commerce, where it is known by the name of Hue vitriol, in which state it generally con- tains variable quantities of sulphate of iron. It may be obtained in a state of purity by treating copper of the first quality with sul- phuric acid diluted with one-half its weight of water ; when sulphur- ous acid is disengaged, and sulphate of copper is formed which contains only a trace of sulphate of iron. It is evaporated to dry- ness, and, toward the close of the evaporation, a few drops of nitric acid are added, which convert the iron into sesquioxide. By dis- solving it in water the greater portion of the iron remains in the state of an anhydrous basic sesquisulphate ; when, after boiling the liquid with a small quantity of the hydrate or carbonate of the protoxide of copper, which precipitates the least traces of iron, the liquor is crystallized. Sulphate of copper is soluble in 4 parts of cold and 2 parts of boil- ing water, and crystallizes at the ordinary temperature in beautiful blue crystals, which belong to the sixth system, and of which the formula is CuO,S0 3 +5HO. They are isomorphous with those pro- duced by protosulphate of iron when crystallized at a temperature of about 40, and which likewise contain 5 equiv. of water. When these two sulphates are mixed together, and the compound solution is crystallized, crystals are deposited containing the two sulphates in different proportions, according to the respective quantities of the salts in the solution. A crystal of sulphate of copper may even be made to grow at pleasure, in a solution of sulphate of iron. The crystal then increases by the superaddition of layers of sulphate of iron, which are easily distinguished by their colour. The same crystal, suspended in a solution of sulphate of copper, becomes covered with layers of this latter sulphate, without any remarkable change in its external appearance. Sulphate of copper readily parts by heat with 4 equiv. of water, but retains the fifth with more tenacity. It is entirely decomposed at a high temperature, into oxide of copper which remains, and a mixture of sulphurous acid and oxygen which is disengaged. Sulphate of copper is manufactured in various ways ; and a cer- tain quantity of this salt is obtained in copper furnaces. When sulphuretted copper ores or cupreous matts, are roasted, and the roasted matter is sprinkled with water, a certain quantity of the sulphates of iron and copper is dissolved, and separates by crystal- lization. The sulphate of copper thus obtained, always contains a large proportion of sulphate of iron. Large quantities of sulphate of copper are manufactured from the SALTS. 241 copper sheathing of ships which has been rendered useless by the corrosive action of salt water. The copper is heated to a dull red- heat in a reverberatory furnace, and sulphur thrown in, the doors of the furnace being previously closed, when the sulphur attacks the surface of the copper, covering it with sulphide of copper Cu 3 S, after which it is roasted, and air allowed to enter the furnace freely. A portion of the sulphur is then disengaged in the state of sulphur- ous acid, while another portion changes into sulphuric acid, and forms a basic protosulphate of copper. The sulphatized sheets are then placed in large boilers filled with w r ater, to which a certain quantity of sulphuric acid has been added, when neutral protosul- phate of copper dissolves, and is crystallized by evaporation as soon as the liquid contains a sufficient quantity of it. This process is repeated until the sheets of copper have disappeared. Large quantities of sulphate of copper have been obtained in the refining of old silver coin, as we shall mention hereafter. If sulphate of copper be dissolved in a hot solution of ammonia, a beautiful blue solution is obtained, which deposits on cooling deep blue crystals, the composition of which is represented by the formula CuO,S0 8 +2NH 8 +HO. By digesting hydrated oxide of copper with a solution of proto- sulphate of copper, a green powder, consisting of a hydrated basic sulphate of copper CuO,S0 3 -f 2CuO-f 3HO is obtained. Analo- gous basic sulphates are precipitated when solutions of sulphate of copper are incompletely precipitated by the alkalies. Sulphate of copper forms with the alkaline sulphates double salts which are readily crystallizable, and also produces double sulphates, of various proportions, with the sulphate of magnesia, and with those of the protoxides of iron, zinc, nickel, etc., which are all iso- morphous. These double sulphates, crystallized at the ordinary temperature, contain 5 equiv. of water when the sulphate of copper predominates, and 7 equiv. of water, on the contrary, when the other metallic sulphate is prevailing. In both cases, the sulphates are isomorphous whenever they contain the same quantity of water. Nitrate of Copper. 1048. This salt is prepared by .dissolving copper in dilute nitric acid, when the liquid yields on evaporation beautiful blue crystals, which contain 3 or 6 equiv. of water, according to the temperature at which the crystallization has been effected. It is used in dyeing. The influence of heat changes nitrate of copper into the green basic nitrate 4CuO,N0 5 , and subsequently decomposes it at a more elevated temperature, leaving protoxide of copper. The same basic nitrate is obtained by precipitating the neutral nitrate of ammonia. Carbonates of Copper. 1049. By adding a solution of an alkaline carbonate to a solu- VOL. II. V 16 242 COPPER. tion of sulphate of copper, a bright blue gelatinous precipitate is obtained, which, after some time, changes into a green powder, the composition of which is represented by the formula 2CuO,C0 2 +HO ; the blue gelatinous precipitate appearing to differ from it only in containing more water. By boiling the liquid with the precipitate, the latter is converted into a brown powder of anhydrous protoxide of copper. The green carbonate of copper is used in oil-painting, under the name of mineral green. A hydrocarbonate of copper, of the formula CuO,C0 2 -f-CuO,HO, called malachite, is found in nature in the form of green concrete masses, which are often very compact and of considerable size, and are fashioned into ornamental objects, such as vases, shafts of columns, and table and chimney tops, which are of great value. When polished they display veins of different shades of colours, which are produced by the mammillary structure of the material, and impart a very beautiful appearance to the polished surfaces. Malachite is sufficiently abundant in Siberia to be worked as an ore of copper. Another hydrocarbonate of copper, of which the formula is 2CuO,C0 3 +CuO,HO, and which yields fine blue crystals, also occurs in nature, which substance existed in great abundance in the mines of Chessy, near Lyons, where it. was long smelted as an ore of copper. When finely powdered it is of a beautiful blue colour, in which state it is used in the manufacture of coloured wall-paper, and is called mountain Hue, or native blue ashes, (bleu de montagne, or cendres bleues naturelles.) Artificial blue ashes, of a more brilliant shade than the native product, are made in En- gland, by a process which is kept secret. Arsenite of Copper. 1050. Arsenite of copper, which is used in oil-painting, under the name of iScheele's green, is prepared by dissolving 3 kilog. of carbonate of potassa, and 1 kilog. of arsenious acid in 14 litres of water, and pouring the solution, by small quantities at a time, into a boiling solution of 3 kilog. of sulphate of copper in 40 litres of water, the solutions being stirred constantly during the precipita- tion. The shade of colour is modified by varying the proportions of arsenious acid. Silicates of Copper. 1051. By means of fusion the oxide of copper combines in all proportions with silicic acid, forming green vitreous substances. A crystallized silicate of copper, called dioptase by mineralogists, is found in nature, and presents the formula 3CuO,2Si0 3 -f3HO. Acetates of Copper. 1052. By dissolving protoxide of copper in acetic acid, a green liquid is obtained, which, when evaporated at a proper temperature. SULPHIDE. 243 deposits beautiful green crystals of the formula CuO,C 4 H 3 3 -fHO, and which are soluble in 5 parts of boiling water. It is known in commerce by the name of verdigris, and is manufactured by dis- solving the basic acetate of copper in vinegar. When the salt crystallizes at a low temperature, the crystals are blue, and present the formula CuO,C 4 H 3 3 -f 5HO. A basic acetate of copper is prepared in the South of France by allowing sheets of copper, moistened with vinegar or brought into contact with the grape mash which is undergoing the acid fermenta- tion, to oxidize in the air. The copper sheets become covered with a greenish-blue coat, which is scraped off from time to time, and of which the formula is CuO,C 4 H 3 3 +CuO,HO + 5HO. If it be treated with water, insoluble crystalline spangles of the formula 3CuO,C 4 H 3 3 separate, while a mixture of neutral acetate CuO, C 4 H 3 3 and basic acetate 3CuO,2C 4 H 3 3 dissolves. A basic acetate of copper is made at Grenoble, by exposing sheets of copper moistened with vinegar in hot stoves. This sub- stance appears to be a mixture of the two sub-acetates 3 CuO, 2 C 4 H 3 (X and 3CuO,C 4 H 3 3 . A colour which is a compound of acetate and arsenite of copper CuO,C 4 H 3 3 -f 3(2CuO,As0 3 ) is likewise used in oil-painting, under the name of Scliweinfurt green, and is prepared by mixing boiling solutions of equal parts of arsenious acid and acetate of copper, and boiling the mixture for some time. COMPOUNDS OF COPPER WITH SULPHUR. 1053. Copper burns actively in the vapour of sulphur ( 306), while a sulphide of copper Cu 2 S corresponding to the suboxide Cu 3 is formed. This sulphide fuses more easily than metallic copper, and becomes crystalline on cooling : it is sometimes found in copper furnaces, crystallized in regular octahedrons. It is prepared in the laboratory by heating a mixture of 3 parts of sulphur and 8 of cop- per turnings, grinding the substance obtained again to powder, and reheating with sulphur. This sulphide of copper exists in nature, and sometimes forms beautiful crystals, which are sufficiently soft to be cut with a knife. The sulphide of copper CuS corresponding to the protoxide CuO cannot be prepared by the humid way, by decomposing the solution of a protosalt of copper by sulf hydric acid or a sulf hydrate, as the black powder thus obtained soon changes in the air. In analyses, it is necessary to wash it with water containing a small quantity of sulf hydric acid. The sulphide of copper CuS, when heated, parts readily with one-half of its sulphur, and is converted into the sulphide Cu 2 S. Compounds of sulphide of copper Cu ? S and sulphide of iron Fe 3 S 3 in very various proportions are found in nature, constituting mine- rals which are called copper pyrites, pyritous copper, and variegated 244 COPPER. copper, according to their external mineralogical characters, which frequently agree with their chemical composition. These minerals are very important, as they are the most common ores of copper, and furnish the largest proportion of this metal. COMPOUND OF COPPER WITH ARSENIC. 1054. Copper, heated in a vapour of arsenic, combines readily with a small quantity of this substance, becoming white and very brittle ; but hitherto no definite compound of these substances has been obtained. COMPOUND OF COPPER WITH PHOSPHORUS. 1055. A gray and very brittle phosphuret of copper, contain- ing about 20 per cent, of phosphorus, is formed when very finely divided copper is heated in the vapour of phosphorus. A definite compound of copper and phosphorus Cu 3 Ph is obtained by decom- posing neutral phosphate of copper by hydrogen at a low tempera- ture. Phosphurets of copper are also obtained by the humid way, by passing a current of phosphuretted hydrogen gas through a solu- tion of sulphate of copper. COMPOUND OF COPPER WITH NITROGEN. 1056. A nitride of copper of the formula Cu 6 N is obtained by heating, at a temperature of 509, oxide of copper CuO in a cur- rent of dry ammoniacal gas, when the substance is treated with a solution of ammonia, which dissolves the oxide of copper in excess. Nitride of copper is a deep green powder, which is easily decom- posed by heat, with a slight explosion. COMPOUND OF COPPER WITH HYDROGEN. 1057. A compound of copper with hydrogen is obtained by heating, at a temperature of 158, a solution of sulphate of copper with hypophosphorous acid. The hydride of copper thus prepared is hydrated, and forms a bright brown powder, which suddenly de- composes at about 140 into metallic copper and hydrogen gas, which is disengaged. Chlorohydric acid decomposes it, forming protochloride of copper, while the hydrogen is set free. COMPOUNDS OF COPPER WITH CHLORINE. 1058. Two compounds of copper with chlorine are known : the first Cu 3 Cl corresponds to the suboxide, while the second CuCl cor- responds to the protoxide. Subchloride of copper Cu 3 Cl is obtained by boiling a solution of protochloride of copper CuCl with very finely divided metallic cop- per, when the colour of the liquid changes from green to brown, while white crystalline chloride of copper Cu 3 Cl is soon deposited. ANALYTIC DETERMINATION. 245 The chloride is also obtained by decomposing the protochloride CuCl by heat, the latter parting with one-half of its chlorine. The protochloride CuCl may be reduced to the state of subchloride Cu 2 Cl by pouring protochloride of tin into a solution of protochlo- ride of copper, the decomposition taking place in the cold, while chlorohydric acid, which prevents the precipitation of the oxide of tin, is added to the liquid. The chloride Cu 3 Cl may be obtained crystallized in small tetrahedrons by dissolving it, assisted by heat, in chlorohydric acid, when the chloride is deposited during the cool- ing of the liquid. Chloride of copper Cu 3 Cl fuses at a temperature of about 752, and volatilizes at a red-heat. It is very slightly soluble in water, but dissolves more freely in chlorohydric acid, and particularly in ammonia. It soon alters in the air, and is converted into a green powder consisting of a compound of hydrated oxide of copper CuO and protochloride CuCl. In consequence of the affinity of this sub- stance for oxygen, it is frequently used in eudiometric analyses, and generally in the form of solution in ammonia. Subchloride of copper CuCl is obtained by dissolving the prot- oxide CuO in chlorohydric acid, or by dissolving metallic copper in aqua regia. The chloride is very soluble in water, and crystallizes on cooling from a concentrated solution in the form of long bluish- green needles, of which the formula is CuCl-f-2HO. This chloride is prepared in the anhydrous state by slightly heat- ing copper in an excess of chlorine, when a yellowish-brown com- pound is obtained, which evolves chlorine when heated to a dark red-heat, and is converted into the chloride Cu 2 Cl. The chloride dissolves readily in alcohol, and imparts to it the quality of burning with a beautiful green flame. DETERMINATION OF COPPER, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. 1059. Copper is determined either as anhydrous protoxide CuO or in the metallic state. When copper exists alone in a liquid, it is precipitated by caustic potassa, after which the liquid should be boiled, because the hydrated protoxide is then changed into an an- hydrous oxide, which is more easily washed : the oxide is weighed after being calcined in the air. Copper is frequently precipitated by a blade of iron or zinc, and, if it is to be weighed in this state, must be rapidly washed with boiling water and dried excluded from the air, from which it promptly absorbs oxygen. "When copper is precipi- tated from its solutions by sulf hydric acid gas, the precipitate must be washed with water charged with sulf hydric acid, while the filter on which the substance has been collected must be calcined, and the whole dissolved in aqua regia, from which solution the copper is then precipitated by caustic potassa. v2 246 COPPER. Copper is very accurately determined by the following process, used in the analysis of many cupreous substances : The substance being dissolved in an acid, an excess of ammonia is added to it, which redissolves the oxide of copper, forming a blue solution, remarkable for its great colouring power. A standard so- lution of sulphide of sodium is poured into the liquid from an alkali- meter ; when the copper is precipitated in the state of an oxysul- phide of the formula CuO,5CuS. By careful manipulation, the moment at which the copper is entirely precipitated may be exactly ascertained, as the reaction is finished when the liquid has lost its colour. It is then easy to calculate the quantity of copper precipi- tated, from the volume of the standard solution of sulphide of sodium, supposing always that no other substances which are pre- cipitable by the alkaline sulphide exist in the liquid. In order to prepare the standard solution of sulphide of sodium, 1 gm. of pure copper is dissolved in 5 or 6 gm. of nitric acid ; and about 50 gin. of a concentrated solution of ammonia being added, gentle heat is applied to dissolve completely the precipitate. The solution of sulphide of sodium, the initial volume of which has been measured on the division of the alkalimeter containing it, is then poured into the deep-blue liquid ; and when the latter is only of a light blue, the flask is shaken several times, and then allowed to rest for a few moments. The sulphide of sodium is then added, drop by drop, in order to observe exactly the moment at which the liquid loses its colour, at which point the volume of solution added is marked on the division of the alkalimeter. Supposing this vo- lume to be represented by 137.5 div., it will be thence inferred that 137.5 div. of the solution of sulphide of sodium correspond to 1.000 gm. of metallic copper; and consequently, if, in order to remove the colour of an ammoniacal cupreous liquid, 97.5 div. of the solution of sulphide of sodium are required, the conclusion fol- lows that the tested solution contained ^| . 1.000 gm., or 0.709 gm. of metallic copper. The described process may be applied to solutions containing other metals than copper, as experiment has shown that it gave exact results even when the liquid contained iron, zinc, cadmium, tin, and lead or antimony, because the alkaline sulphide only com- mences to act on the metals named after the copper has been com- pletely precipitated in the state of oxysulphide. It is nevertheless indispensable that the iron should be in the state of sesquioxide, since the presence of protoxide would derange the result. It is not necessary to separate by filtering the deposit thrown down by seve- ral of these metals at the moment of adding the excess of ammonia ; although it may be of advantage when the deposit is very copious, because the latter would prevent the colour of the liquid from being distinguished. v The process of determination just described becomes inaccurate METALLURGY OF COPPER. 247 when the liquor contains cobalt, nickel, mercury, or silver. The presence of silver may be easily avoided, as it is sufficient to add a few drops of sulf hydric acid to the nitric solution, when the silver is entirely precipitated as insoluble chloride. 1060. Copper is easily separated from the alkaline, alkalino- earthy, and earthy metals, from manganese, iron, chrome, cobalt, nickel, zinc, titanium, and uranium, by means of sulf hydric acid, passed through the liquid acidulated by chlorohydric acid, when the copper alone is precipitated in the state of sulphide. It is separated from cadmium, bismuth, and lead, when these metals are dissolved in nitric acid, by means of an excess of carbo- nate of ammonia, which does not dissolve the copper ; which same process may be employed to separate copper from alumina and the sesquioxides of iron and chrome ; but the results are less exact than those of precipitation by sulf hydric acid. The best method of se- parating copper from lead is to add sulphuric acid to the nitric solution of the two metals, and evaporate to dryness to drive off the excess of acid, when the residue, after being moistened with a small quantity of nitric acid and treated with water, consists only of sul- phide of lead. Copper is separated from tin by treating the two metals with nitric acid, evaporating to dryness, moistening the residue with a small quantity of nitric acid, and dissolving it in water, when the tin remains in the state of stannic acid. By the same process, copper may be separated from antimony ; but the results are less exact, because a small proportion of antimony is always dissolved. It is therefore better, after having dissolved the metals in aqua regia, to saturate the solution by ammonia, and add an excess of sulf hydrate of ammonia, in which sulphide of antimony is soluble. The same process will serve to separate copper from tin and arsenic. METALLURGY OF COPPER. 1061. Copper is found in nature chiefly in the state of sulphide, which is rarely isolated, being generally combined with sulphide of iron, constituting copper pyrites Cu 2 S+Fe 2 S 3 , and frequently mixed, in greater or less proportions, with iron pyrites FeS 3 . The most common ores of copper are therefore mixtures of sulphide of iron and copper. Besides copper pyrites, the following ores occur: variegated copper 2Cu 3 S+FeS ; fahlerz, or gray copper, which is a double sulphide of antimony and copper ; and bournonite, which is a multiple sulphide of antimony, copper, and lead ; all of which are very important minerals, being generally very rich in silver. All the ores just named are found in veins traversing the old rocks ; while near these primitive veins deposits of copper ores are often seen, evi- dently arising from the alteration of the ore by the action of water. When slow streams of water, which, in their course, pass over beds of copper ore, and thus generally contain sulphate of copper, drop 248 COPPER. into calcareous earths, or remain in the cavities of calcareous rocks, sulphate of lime is formed and carried off by the water, while car- bonate of copper is deposited ; and if the reaction takes place at a high temperature, oxide of copper is deposited instead of the car- bonate. Lastly, if organic substances be present, the sulphate of copper may be reduced either to the metallic state or to that of sulphide of copper. The occurrence of masses of carbonate and oxide of copper, which are frequently found near veins of copper pyrites, is thus explained, as is also the origin of small crystals of sulphide of copper scattered through certain schistose rocks which are impregnated with bitumen and contain many organic remains. In this way, geologists explain the formation of the cupreous pyrites found scattered in small crystals through bituminous schist, and exhibiting impressions of fishes, which form the bottom of a very extensive basin of secondary rocks in Mansfeld, in the north of Germany. More or less considerable masses of suboxide of copper Cu 3 are sometimes found, which yield a very rich copper ore, very valuable mines of which are in Peru and Chili. The principal localities of copper ore in Europe are in the county of Cornwall in England, Mansfeld and Rammelsberg in the north of Germany, in Sweden, Norway, and the Ural and Altai mountains in Russia. There for- merly existed at Chessy and Saint-Bel, near Lyons, a very pro- ductive mine of oxide and carbonate of copper, which is now exhausted.* 1062. The ores of the oxide and carbonate of copper are very easily worked. It is sufficient to smelt them in contact with char- coal, in cupola furnaces, with scoriae more or less silicious, when an impure copper, called black copper, is obtained, which, after refining, yields marketable copper. 1063. The treatment of the sulphuretted ores is much more complicated. They are first subjected to several preliminary roast- ings, in order to convert a certain portion of the sulphides into ox- ides, after which the roasted ores are smelted in blast or in rever- beratory furnaces, with the addition of scoriae or other fluxes, if the ore does not itself contain a sufficient proportion of silicates. Cop- per has a greater affinity for sulphur than iron, while the latter metal, on the contrary, has a greater affinity for oxygen, especially in the presence of silicic acid ; the oxide of copper, which forms during the roasting, therefore passes entirely into the state of sul- phide, by abstracting the sulphur from the sulphide of iron which remained in the roasted material, the products of the operation being a slag, which contains the greater part of the iron of the * The principal locality of copper ores in the United States is that at Kewenaw Point, Lake Superior, where large masses of native copper are found. Other great localities, omitted in the text, are those in Cuba, Siberia, and Burra Burra in Australia, all of which yield principally oxidized ores. W. L. F. METALLURGY OF COPPER. 249 copper pyrites, and a sulphide of iron and copper, and the cupreous matt, containing nearly all the sulphide of copper of the pyrites, and a much smaller proportion of sulphide of iron. The matt is, consequently, a sulphuretted ore of copper, much richer in copper than the original pyrites. It is again roasted, and melted with silicious scoria, and frequently with ores of oxide of copper, when they are at hand, which process produces a new slag, containing a great portion of the iron of the first matt, and a second cupreous matt, still richer in copper than the first. These successive opera- tions are repeated until an impure copper, black copper, a last cupreous matt, and scoriae, are obtained, the matt being then sub- jected to similar processes, or added to the preceding matt, so that the ultimate product is black copper, which is refined. We shall give examples of this metallurgic process as adopted in some of the most important European w r orks. 1064. At Fahlun, in Sweden, the principal ore is copper pyrites, mixed intimately with iron pyrites and accompanied by a quartzose gangue. The pyritous ores are roasted, mixed with silicious ores, in the proportion of 2 parts of pyritous and 1 of silicious ore, and 10 to 30 per cent, of scoriae, arising from a previous smelting, added. This mixture is smelted in a blast-furnace of about 3 metres in height, and a matt composed of sulphide of iron Fe 3 S and sul- phide of copper Cu 3 S, with a slag which should present nearly the composition of bisilicate of iron FeO,2Si0 3 , are removed from it. The matt, which contains 8 to 10 per cent, of copper, is subjected to four successive roastings, which remove nearly all the sulphur and leave the metals in the state of oxide. The roasted matts are smelted in blast-furnaces, resembling those used for the smelting of the roasted ores, quartz and oxidized or sulphuretted silicious ores which have been previously roasted being added. This smelting yields black copper, a small quantity of cupreous matt, and scoriae, which are chiefly simple silicates of iron FeO,Si0 3 . The cupreous matt is then treated like the first matt arising from the smelting of the ores, while the black copper is refined by a process soon to be described. 1065. The copper ores of Mansfeld are argillaceous schists, containing pyrites scattered through in small crystals, their rich- ness in copper being very variable, while they are strongly impreg- nated with bitumen. They are roasted by being heaped on a pile of wood, which is easily done, the consumption of fuel being small, as the fire is kept up by the bitumen. Five to eight per cent, of fluor-spar, scoriae poor in copper, arising from subsequent opera- tions, and frequently small quantities of cupreous schists containing carbonate of lime, are added, and the mixture is smelted in blast- furnaces 5 or 6 metres high, heated by coke. Fig. 558 represents a vertical section of the furnace passing through one of the twyers, while fig. 557 represents a front view. (The breast of the furnace has 250 COPPER. been removed to show the interior.) The lower part of the furnace is built of quartzose sandstone, and the upper part of bricks. The Fig. 557. Fig. 558. furnace has two twyers, either on the same side, as in fig. 559, or on opposite sides. At the base of the breast of the furnace are two openings 0, - 596?) which slides between the grooves MN, MIS 7 , and which is provided with an appendix D, furnished at its upper part with a small sponge &, placed at the height of the lower orifice a of the pipette. The assayer having so placed the support as to bring the sponge in contact with the pi- pette, opens the stopcock r f 7 and allows the liquid to descend slowly to the level , where the sponge absorbs the last drop of liquid, which would adhere to the end of the pipette. The assayer then brings the opening of the bottle under the pipette, and empties it entirely by opening the stopcock r f . As a large number of assays is gene- rally made at once, there are a series of bottles numbered, in each of which are dis- solved 1.116 gm. of alloy of coin. In order to hasten the solution, all the bottles are placed on a stand, (fig. 598,) and after hav- ing introduced into each the alloy and the nitric acid which is to dissolve it, the stand is plunged into hot water. When the metals are dissolved the nitrous vapours are driven off by blowing into the bottles, and the decilitre of normal solution is introduced, after which they are placed on a second stand, (fig. 599,) suspended on a steel Fig. 599. spring, and held below by a spiral spring ab. The bottles having been closed by their ground stoppers, the assayer grasps the handle ef of the stand and shakes it for a few moments, in order to collect the precipitate and render the liquids 320 SILVER. clear. He then carries the bottles to a black table having numbered compartments, each one being placed in the compartment corre- sponding to its number. The decimal solution is contained in a i bottle (fig. 600) provided with a tube, drawn out at its lower extremity and having a mark corresponding to a capacity of 1 cubic centimetre, which dips into the liquid. The as- sayer, applying his finger to the upper aperture of the tube, withdraws the latter, and allows the liquid to flow slowly until it reaches the level of the mark, and then carries the Fig. 600. cu bj c centimetre thus measured off into the first bottle, re- peating the process with the other bottles. He then examines the bottles successively, and makes with chalk a mark on the black table near each bottle in which a precipitate is formed, and then replaces the bottles on the stand of fig. 599, clears the liquids by agitation, deposits the bottles on the table, and adds another cubic centimetre of the decimal solution to all the bottles in which there was pre- viously a precipitate formed, gradually excluding the bottles in which the liquid was not clouded. By counting the number of chalk-marks near each bottle, a number which represents that of the cubic centi- metres of decimal solution which have been efficient, and deducting j- for the last cubic centimetre, which, probably, has not been wholly used, the assayer finds the number of thousandths which must be added for each alloy to the supposed standard of 2* As the standard solution of sea-salt has been prepared for the temperature of 59 degrees, and as it expands by heat, it is evident that its standard must be altered in volume by the changes of tem- perature. It is therefore indispensable, when the temperature of the solution is not 59, to correct all the results by means of tables made for the purpose, the temperature of the saline solution being read off on the thermometer contained in the tube cb, (fig. 596.) But the corrections are always uncertain, and may be avoided by the following device, by means of which, at the same time, any wrong preparation of the normal solution is ascertained. An assay upon 1 gm. of pure silver, made daily, simultaneously with the tests on the coin, gives for each day the exact value of the standard of the normal saline solution, and all assays made simultaneously may be corrected by the difference of the standard thus found with the normal standard. A large quantity of normal solution of salt is generally made at once, by dissolving 500 gm. of common impure salt of commerce in 4 litres of water, filtering the liquid, and adding the quantity of water necessary to obtain the necessary degree of dilution of the normal solution, supposing the salt to be pure ; by which means a solution is obtained of a degree of concentration only approximative to that desired. In order to ascertain its exact concentration, 1 cubic decimetre of the liquid is poured into a solution of 1 gm. of pure silver in nitric acid. The liquid being cleared by agitation, it ASSAYING OF SILVER ORES. 321 is easy, by means of a decimal saline solution or a decimal solution of silver, to determine exactly the number of thousandths of silver, or of salt, which remain free. The additional quantity of water or salt necessary to obtain the proper dilution of the saline solution is thus found, and, after it has been added, a new test is made, and so on, until the normal degree of concentration is attained. In order to prepare the decimal solution, a decilitre of the normal solution is introduced into a bottle which measures 1 litre to a mark traced on its neck, up to which the bottle is then filled with distilled water. The decimal solution of silver is prepared by dissolving 1 gm. of pure silver in 5 or 6 gm. of nitric acid, and diluting with water until the liquid exactly assumes the volume of 1 litre. When silver contains mercury, the results of the assay by the humid way are inaccurate, because the mercury, being precipitated in the state of chloride, decomposes a portion of the chloride of sodium. The presence of any considerable quantity of mercury in an alloy is easily perceived, because the liquid, in that case, is not cleared by shaking, and the first deposite of chloride of silver does not blacken in the light. The exact standard of the alloy may, however, be obtained by the humid way, by recommencing the test on another portion of the substance after having added a certain quantity of acetate of soda to the nitric solution, by which means the precipitation of the mercury is prevented. ASSAYING OF SILVER ORES. 1145. The argentiferous galenas are assayed by cupelling the lead, after having isolated it by the process described 980. The galena is sometimes also fused with 3 or 4 tenths of its weight of nitre, when the sulphur of the galena is converted into sulphuric acid which combines with the potassa, while the greater portion of the lead separates in the metallic state, retaining the whole of the silver. The argentiferous copper-ores are first assayed for their copper, after which the lump of copper is introduced into the cupel, with the addition of 16 times its weight of lead. The assay for copper is made as follows : If the ore be sulphu- retted, it is first roasted in a small earthen capsule, (called tile in England,) the heat being properly regulated in order to prevent the substance from running together, and the temperature being kept elevated until sulphurous acid is no longer disengaged. The tile being then covered with its lid, the temperature is raised to a white-heat, in order to decompose the sulphates ; after which the roasted material is fused in an earthen crucible with 3 or 4 times its weight of black flux, the fusion being effected in a forge-fire or an ordinary calcining furnace, having a strong draught. After cool- ing, the crucible is broken, and a lump of malleable copper and an 322 GOLD. alkaline slag containing merely a trace of copper are found. Oxi- dized copper-ores need not be previously roasted, but can be imme- diately subjected to the fusion with black flux. Oxidized silver-ores are mixed with 8 or 10 times their weight of litharge and double their weight of black flux, and the mixture is fused in an earthen crucible, when a portion of the litharge is con- verted, by the carbon of the black flux, into metallic lead, which carries with it all the silver; the quartzose and earthy gangues being transformed into slag with the litharge and potassa of the black flux. Ores of silver which contain sulphides and arseniurets are also fused with litharge, but it is in this case frequently unne- cessary to add black flux, because the reaction of the sulphides and arseniurets on the litharge furnishes a sufficient quantity of metallic lead to entirely remove the silver. GOLD. EQUIVALENT = 98.5(1231.25; = 100). 1146. The gold in gold coin and jewelry is never pure, being alloyed with a certain quantity of copper and frequently of silver, to give it a greater degree of hardness. In order to obtain pure gold, gold coin is dissolved in aqua regia, and the solution being evapo- rated to dryness, by gentle heat, to drive off the excess of acid, the residue is treated with water, by which means the silver is separated as insoluble chloride. An excess of protosulphate of iron, which pre- cipitates the gold in the metallic state, in the form of brown powder, is then poured into the liquid, the reaction ensuing according to the following equation : Au 3 Cl 3 +6(FeO,S0 3 ) = 2Au+2(Fe a 3 ,3S0 3 )-f-Fe 2 Cl 3 . The precipitate is digested with weak chlorohydric acid, and, after being well washed, is fused in an earthen crucible with a small quantity of borax and saltpetre. The protosulphate of iron may be replaced by sesquichloride of antimony Sb 3 Cl 3 dissolved in an excess of chlorohydric acid ; the sesquichloride of antimony being con- verted into the perchloride Sb a Cl 5 , while the gold is precipitated in the metallic state. Gold has a characteristic yellow colour, and its density is 19.5. It fuses at a strong white-heat, or at about 2200 of the air ther- mometer, giving off sensible vapours at a very high temperature. A gold wire is converted into vapour when traversed by the current of a powerful electric battery ; and if this take place over a sheet PKOPERTIES OF GOLD. 323 of paper placed at a small distance, the paper becomes coloured of a purplish brown, by the very finely divided gold which is precipi- tated on it. A blade of silver substituted for the paper soon becomes gilded. A globule of gold gives off vapour very copiously when held between two pieces of charcoal terminating the conductors of a pow- erful galvanic battery. Gold is the most malleable of all the metals, ( 295,) and when beaten into very thin leaves is transparent, the transmitted light appearing of a beautiful green colour. Gold may be crystallized by fusion, when it assumes the shape of cubes modified by other facets of the regular system. Native gold is sometimes found in well- defined crystals presenting the same form. When precipitated in a metallic state from its solutions, gold forms a brown powder, which by burnishing soon recovers the me- tallic lustre and characteristic colour of malleable gold, and which aggregates by percussion. If the mass be heated to redness before being hammered, a perfectly aggregated metal can be obtained without having heated it to fusion. Gold does not combine directly with oxygen at any temperature. Chlorohydric, nitric, and sulphuric acids do not affect it, while aqua regia, on the contrary, readilj dissolves it in the state of sesqui- chloride, Au 2 Cl 3 . Gold is also dissolved by chlorohydric acid when a substance capable of disengaging chlorine is added, such as per- oxide of manganese, chromic acid, etc. Chlorine and bromine also attack gold, even when cold, while iodine acts on it but feebly. Sulphur does not attack gold at any temperature, nor does the metal decompose sulf hydric acid ; but by fusing it with the alkaline poly sulphides it is powerfully acted on, a double sulphide being formed, in which the sulphide of gold Au 2 S 3 acts the part of a sulph- acid. Arsenic when assisted by heat combines with gold, and forms a very brittle alloy. Gold is attacked neither by the alkalies nor the alkaline carbo- nates or nitrates. COMPOUNDS OF GOLD WITH OXYGEN. 1147. *Two combinations of gold with oxygen are known : 1. A sub oxide Au 2 0, 2. A sesquioxide Au 3 3 , neither of which forms salts with the oxides. The suboxide Au 3 is obtained by decomposing the chloride Au a Cl by a dilute solution of potassa, in the shape of a deep violet- coloured powder, which decomposes at about 77, disengaging oxy- gen. The oxacids exert no action on this substance, while chloro- hydric acid decomposes it, forming sesquichloride of gold Au 2 Cl 3 , while metallic gold is separated. Sesquioxide of gold (often called auric acid on account of its property of combining with bases) is prepared by digesting a hot 324 GOLD. solution of sesquichloride of gold with magnesia, when aurate of magnesia is formed, which remains mixed with the free magnesia. The deposit is boiled with nitric acid, which dissolves the magnesia and leaves hydrated sesquioxide of gold. Auric acid may also be obtained by exactly saturating a solution of sesquichloride of gold by carbonate of soda, and then boiling the liquid, when a large proportion of the gold is precipitated in the state of sesquioxide, while the other portion remains in solution, but may be precipitated by successively adding to the liquid an excess of caustic potassa and acetic acid. Hydrated auric acid is a yellow or brown powder, which loses its water at a low temperature and becomes anhydrous, while at about 482 it decomposes into gold and oxygen, which reaction is also effected by the. solar light. Deoxidizing substances, such, as the organic acids, or boiling alcohol, reduce it to the metallic state ; while chlorohydric acid dissolves it and produces the sesquichloride Au 3 Cl 3 . The most energetic oxacids do not form definite com- pounds with sesquioxide of gold, while the latter dissolves, on the contrary, readily in cold alkaline solutions, producing alkaline aurates which crystallize by evaporation. By adding a small quantity of ammonia to a solution of sesqui- chloride of gold, a fulminating substance is produced, which con- tains, at the same time, oxide of gold, ammonia, and chloride, and which, by digesting with an excess of ammonia, furnishes a bright brown powder of still higher detonating properties than the first, and which is a simple combination of sesquioxide of gold with am- monia Au 3 3 +2NH 3 +HO. COMPOUNDS OF GOLD WITH SULPHUR. 1148. Although sulphur does not combine directly with gold, two sulphides corresponding to the two oxides are obtained by de- composing the sesquioxide of gold by sulf hydric acid, which, on being passed through a cold solution of sesquichloride of gold, yields a brownish-yellow precipitate, which is the sulphide Au 3 S 3 , readily soluble in the alkaline sulphides. If the solution of the chloride is boiling, a sulphide Au 3 S, of a deep brown colour, is precipitated, while sulphuric and chlorohydric acids are formed : 2Au 3 Cl 3 +3HS+3HO = 2Au 2 S+6HCl-f S0 3 . COMPOUNDS OF GOLD WITH CHLORINE. 1149. By dissolving gold in aqua regia a yellow solution of sesquichloride of gold Au a Cl 3 is obtained, which, when allowed to evaporate slowly in dry air, deposits yellow crystals of a compound of sesquichloride of gold and chlorohydric acid. If the solution be evaporated to drive off the excess of acid, the substance assumes a brown colour, and a deliquescent crystalline mass remains, which HALOID COMPOUNDS OF GOLD. 325 dissolves readily in alcohol and in ether. Sesquichloride of gold dissolves even more rapidly in ether than in water ; for, if an aque- ous solution of the chloride be shaken with ether and water, the supernatant ether contains nearly all the chloride of gold in solu- tion. The solution of sesquichloride of gold in ether was formerly used in medicine under the name of aurum potabile. Sesquichloride of gold forms with several other metallic chlorides double crystallizable chlorides, in order to obtain which it is suffi- cient to mix and evaporate the solutions of the two chlorides. The formula of the double chloride of gold and potassium, which is deli- quescent, is KCl-f Au 3 Cl 3 +5HO, while the formula of that of gold and sodium is NaCl+Au 2 Cl 3 -f 4HO, and that of the double chloride of gold and ammonia is NH 3 HCl+Au 3 Cl 3 +2HO. Compounds of chloride of gold with the chlorides of barium, calcium, manganese, iron, zinc, etc., are also known. Subchloride of gold Au a Cl is prepared by heating the sesquichlo- i-ide of gold Au 3 Cl 3 to a temperature of about 400, when chlorine is disengaged, while a greenish insoluble powder remains. COMPOUND OF GOLD WITH CYANOGEN. 1150. By adding a solution of cyanide of potassium to a con- centrated hot solution of perchloride of gold, until the liquid loses its colour, a solution is obtained, which, on cooling, deposits pris- matic crystals of a double cyanide of gold and potassium of the formula KCy+Au 3 Cy 3 . The crystals, which are efflorescent and very soluble, disengage cyanogen when subjected to moderate heat ; and, when treated with water, a solution is obtained, which, on cool- ing, deposits a double cyanide of the formula KCy4-Au 3 Cy. PURPLE OF CASSIUS. 1151. The name of purple of Oassius is given to a precipitate containing gold, tin, and oxygen, which is used by painters on por- celain and glass, ( 730,) and which is prepared in various ways. Its composition not being always uniform, chemists are not yet agreed upon its nature. It is generally obtained by pouring into a sufficiently dilute solution of sesquichloride of gold, a mixture of protochloride and bichloride of tin, the precipitate showing a beau- tiful purple hue when it is of small bulk, while it assumes a brown colour when more copious. A purple of Cassius of uniform composition is prepared by dis- solving 20 gm. of gold in 100 gm. of aqua regia made of 20 parts of nitric and 80 of chlorohydric acid ; driving off the excess of acid by evaporation in a water-bath and dissolving the residue in 7 or 8 decilitres of water. Some pieces of tin being then placed in the liquid, a purple precipitate of the formula Au 3 0,Sn0 3 +SnO,Sn0 3 -f-4HO is formed, but which may also be considered as 2Au+3Sn0 3 +4HO. The substance, on being subjected to heat, evolves water alone and VOL. II. 2 C 326 GOLD. no oxygen, while the calcined residue presents all the characters of a mixture of metallic gold and stannic acid. But as before calcina- tion the substance will not give off gold to mercury, it is evident that the gold did not exist in it in the metallic state. A beautiful purple of Cassius is obtained by heating suboxide of gold Au 2 with a solution of stannate of potassa. Lastly, purple of Cassius is obtained by fusing together in a cru- cible 1 part of gold, J part of tin, and 4 or 5 of silver, forming a ternary alloy, from which nitric acid extracts the silver, while the gold and tin are precipitated in combination with oxygen, and a brilliant purple is formed, the shades of which can be changed by altering the relative proportions of gold and tin. A solution of sesquichloride of gold stains linen of a purple colour, as it also does the skin and the organic tissues generally ; which colouring is probably owing to suboxide of gold, as friction does not restore a metallic lustre to the spots, although they acquire it in a short time when exposed to solar light in a bottle filled with hydrogen gas. DETERMINATION OF GOLD, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. 1152. Gold is always determined in the metallic state, and is precipitated from its solutions by means of protosulphate of iron, after having added chlorohydric acid to the liquid in order to main- tain the sesquioxide of iron which forms during the reaction in so- lution. But it is important, in order to completely precipitate the gold, that the liquid should contain no nitric acid ; in which case it must be previously evaporated with chlorohydric acid. The gold, when collected on a filter, is calcined to redness before being weighed. 1153. In order to separate gold from the metals previously de- scribed, the insolubility of the metal in nitric acid is sometimes relied on, while at other times all the metals 'are dissolved in aqua regia, and the gold is precipitated by protosulphate of iron, or, better still, by heating the solution with a certain quantity of oxalic acid ; which latter method has the advantage of not introducing a new metal into the liquid. Gold is sometimes also separated by precipi- tating it in the state of sulphide, by sulf hydric acid gas, the sul- phide leaving metallic gold after calcination. METALLURGY OF GOLD. 1154. Gold is almost always found in the native state, being sometimes pure, but more generally alloyed with certain quantities of silver. It occurs in three kinds of bearings : 1. In veins, generally quartziferous, which contain other metallic minerals, as ores of copper, lead, silver, and pyrites; the veins usually traversing the primitive rocks. METALLURGY OF GOLD. 327 2. In small veins scattered through rocks situated at the separa- tion of the crystalline and stratified rocks. 3. In disaggregated quartzose sands, often extensively seen in alluvial formations, and owing their presence to the disintegration of auriferous crystalline rocks which exist in the vicinity. The greater specific gravity of the gold prevents its particles from being carried as far as those of the other minerals with which it was mixed, and its resistance to the action of the greater part of chemi- cal agents preserves it in the state of spangles. Alluvious soils containing gold chiefly occur in open valleys between primitive mountains, where gold is frequently found in place. The principal localities of auriferous sands are in California, Australia, Brazil, Mexico, Chili, Africa, the Ural and Altai Mountains in Siberia the quantity of gold annually extracted from all of which amounted, in 1851, to 178 tons, of which California alone produced 110. Gold is generally found in the sands in the form of spangles, or shapeless and rounded grains, which, when they are of any considerable size, are called river or wash gold, (pdpites.) Grains are sometimes found of the size of a hazel-nut, and pieces weighing several kilogs. have been met with : one lump weighing 36 kilogs. was found in the Ural. Gold exists in the drift-sand of all rivers which arise from, or flow over a large extent of, primitive rocks ; and several auriferous alluvise are known in France, such as those of the Ariege in the Pyrenees, of the Gardon in Cevennes, the Garonne, and the Rhine near Strasburg. It is found in too small quantity to be worked to advantage ; but the inhabitants look for it when they would other- wise be idle, and are then called gold-finders. The spangles of gold scattered through the river-sand are generally so excessively small that more than 20 are often required to make a milligramme. In Siberia, sands containing only 0.000001 of gold are not con- sidered worthy of being worked ; and the Rhenish sands contain, on an average, about J of this quantity. Gold exists also, combined with tellurium, in certain mines of Transylvania. An alloy of gold with silver and palladium, in the form of small crystalline grains, occurs in Brazil, and is called auro- powder or auro-dust. Lastly, all pyrites in primitive rocks contain a small quantity of gold, and are often rich enough to be worked to advantage. 1155. "When gold exists in veins which contain other metals, as lead, copper, or silver, those metals in which the gold is concen- trated are first extracted from the ores, and the gold is then sepa- rated by refining, a process presently to be described. The ore is frequently first subjected to amalgamation, as in the case of silver ores, when the gold dissolves in the mercury, and, after the liquid amalgam has been filtered, a more solid amalgam is obtained, from which the gold is separated by distillation. The ore 328 GOLD. is then smelted, so as to obtain a matt from which a certain quantity of gold can still be extracted. 1156. Auriferous sands are washed in the most simple manner, either in wooden tubs, or on inclined planes over which a current of water flows, and they are then treated by amalgamation. In the Ural, the auriferous sand is poured into boxes, the sheet- iron bottom of which is provided with openings of 2 centimetres in diameter, and, while a stream of water flows through the boxes, the workman stirs the sand constantly with a shovel, when the finer portions fall through the holes and are collected on large sleeping tables covered with muslin. The sand is frequently swept toward the head of the table, where the gold remains with the heavier mine- rals ; and the sand, being enriched by this washing, is again more carefully washed on smaller tables. The titanic iron and magnetic oxide of iron being separated by a magnet, the material is fused in large graphite crucibles, at the bottom of which the gold collects, while the upper part is filled by a slag containing a quantity of un- melted grains of gold. The slag being stamped and washed, the rich schlich thus obtained is smelted, yielding an auriferous lead, from which the gold is separated by cupellation. 1157. In Tyrol a certain quantity of gold is extracted from pyrites by amalgamating them in mills resembling that represented in fig. 601, several mills being generally placed above each other. (The figure gives an external view of the upper mill and a section of the lower one.) The pyrites, in the state of an impal- pable powder, is suspended in water, and conveyed into the upper mill by the conduit G, whence it flows into the second mill by the sluice G'. The bed of each mill is made of a cast-iron Fig. 601. vessel cdef, securely fastened on a strong wooden table ; and in the centre of the vessel is a tubulure traversed by an axis of rotation a5, set in motion by the cog-wheel rr r . The runner-stone mm' of each mill is of wood, and resembling the shape of the bed ; but, being about 2 centimetres smaller, is furnished with several sheet-iron teeth projecting about 1 centimetre. The upper surface of the runner-stone is shaped like a funnel, into which is poured the liquid mud, which passes between the stones and flows out by the conduit G'. The stones make about 15 or 20 revolutions per minute ; and 25 SEPARATION OP GOLD AND SILVER. 329 kilogs. of mercury are placed at the bottom of each, making a layer of about 1 centimetre in thickness, against which the teeth of the wheel constantly strike, while at the same time they stir up the ore. The gold is dissolved by the mercury, and, after continuing this process for 4 weeks, it is withdrawn and filtered through a chamois- skin, which retains a solid amalgam containing nearly one-third of its weight of gold, which is then separated from the other metals by cupellation. ALLOYS OF GOLD. 1158. Gold is rarely used in a state of purity, as it is too soft, and its hardness must be increased by the addition of a small quan- tity of silver or copper, forming more fusible alloys than pure gold. The standard of French gold coin is y 9 ^, the law allowing a va- riation of T o 2 M above and y^ below; while medals contain 0.916 per cent, of gold, with the same variation. There are three legal standards for jewelry, the most common of which is T 7 S %, while those f ioo an d IMS are rarely used ; and the legal variation is y^ below the standard, no superior limit being fixed. Gold is soldered with an alloy called re,d gold, of 5 parts of gold, and 1 of copper ; an alloy made of 4 parts of gold, 1 of copper, and 1 of silver also being used. The clear colour of gold is given to jewelry by dissolving the cop- per which exists in the superficial layer ; to effect which the articles are heated to a dull red-heat, and dipped, after cooling, into a weak solution of nitric acid, which dissolves the copper. A thicker coat- ing of pure gold is obtained by allowing them to remain for 15 minutes in a paste formed of saltpetre, common salt, alum, and water ; the chlorine set free by the action of the sulphuric acid on the salt and saltpetre dissolving the copper, silver, and gold, while the latter metal is again deposited on the article. The sur- faces are then burnished. SEPARATION OF GOLD AND SILVER. 1159. The separation of gold and silver, more generally called the refining of the precious metals, is now done by treating the alloy by concentrated hot sulphuric acid, which dissolves the silver only. But, in order that the alloy may be completely acted on, it should neither contain more than 20 per cent, of gold, nor than 10 per cent, of copper, because sulphate of copper is but slightly soluble in concentrated sulphuric acid. The alloys are fused in crucibles, and when they are too rich in gold, a certain quantity of silver is added silver containing a small quantity of gold being preferred. The fused alloy is granulated by being poured into water, and then placed in a large kettle with 2 \ times its weight of concentrated sulphuric acid marking 66 on the areometer, the kettle being co-* vered with a lid furnished with a disengaging tube. The acid, being 2c2 330 GOLD. heated to boiling, is partly decomposed, and sulphates of silver and copper are formed, while sulphurous acid is disengaged, which is sometimes passed into the leaden chambers where sulphuric acid is manufactured, ( 139.) When gold coin is to be refined, it is merely roasted. After 4 hours, when the alloy is completely destroyed, there is introduced into the kettle a certain quantity of sulphuric acid marking 58, and obtained by the concentration of the acid mother liquid of the sulphate of copper obtained in refining, as will pre- sently be explained. After having boiled the liquid for fifteen minutes, the kettle is taken from the fire and allowed to rest, when the greater part of the gold collects at the bottom of the vessel, from which the nearly boiling liquid is decanted off into leaden boilers containing the mother liquid arising from the purification of the sulphate of copper by crystallization. The boilers are heated by steam ; and after the sulphate of copper at first deposited is re- dissolved, the liquid is allowed to rest for some time, when the whole of the gold is deposited. The clear liquid is then drawn off by a siphon, and passed into other boilers heated by steam, and contain- ing blades of copper, which precipitate the silver in the form of small crystalline grains ; the metal being in a short time so per- fectly precipitated that the liquid is not clouded by common salt. The precipitated silver is carefully washed, and then compressed by an hydraulic press into compact prisms, which, after being dried, are melted in earthen crucibles, furnishing a metal which contains only a few thousandths of copper. As the gold arising from the first action of the sulphuric acid still contains a certain quantity of silver, it is heated anew, in a platinum crucible, with concentrated sulphuric acid> which abstracts the balance of the silver ; a third treatment with sulphuric acid being often required. The gold dust, after being well washed and fused, contains 995 thousandths of pure gold. The acid solution of sulphate of copper which arises from the precipitation of the silver by copper is evaporated in leaden kettles until it marks 40 on the areometer ; a large proportion of the sul- phate of copper being deposited in small crystals during the cool- ing. After another evaporation, the mother liquid yields an addi- tional quantity of crystals ; and the last liquid, which refuses to crystallize, is used as a solution of sulphuric acid, and poured into the cast-iron boiler, after this action on the alloy. The sulphate of copper is purified by recrystallization. When the quantity of gold and silver contained in an alloy does not exceed 0.200 or 0.300, the granular material .is first heated in a reverberatory furnace, when a portion of the copper is converted into oxide, which is dissolved by treating the roasted substance with weak sulphuric acid ; and the alloy, being thus brought to the me- GILDING AND SILVERING. 331 dium standard of 0.500 or 0.600, may be refined by the ordinary process.* GILDING AND SILVERING. 1160. Ornamental objects of copper or bronze were formerly gilded by means of an amalgam of gold, which method has now been superseded by galvanic processes. The amalgam used in mercurial gilding is prepared in the following manner : Gold-leaf is heated to a dull red-heat in a crucible, and triturated with eight times its weight of mercury, and, when the gold is dissolved, it is * The process of refining gold pursued at the United States Mint, in Philadel- phia, is similar to the method formerly called quartation, and consists in melting gold with silver, and then extracting the silver with pure nitric acid. The depo- site of grains of native gold is first melted with borax and saltpetre, occasionally with soda to remove quartz, and being cast into a bar, is carefully weighed, accu- rately assayed to 73^3 for gold, and from the assay and weight the value of the deposite calculated. Although a million of dollars may be deposited in a day, upon an arrival from California, yet such is the expedition of the assay-depart- ment, that in a few days the deposites are all paid off. As soon as the gold is as- sayed, each pound of it is melted with 2 pounds of pure silver, and the mixture, after stirring, poured into cold water, by which it is granulated, divided into small irregular fragments, presenting a large surface to the subsequent action of the acid. The granulations are then put into large porcelain jars of 50 gallons each, of which there are about 70 in use, and nitric acid poured in them. The jars being placed in leaden-lined wooden troughs, containing water, are heated by a steam coil in the water, causing the nitric acid to dissolve out the larger propor- tion of silver. A steam-heat is given during several hours, and the liquid allowed to repose until the following morning, when the solution of nitrate of silver is drawn off by a gold siphon, and transferred to a large vat of 1200 gallons, con- taining a saturated solution of common salt. Fresh acid is then added to the gold in the pots, already nearly parted, steam-heat applied again for several hours, and the whole left again to repose. On the following morning the acid liquid of one of the pots being drawn off and the fine gold removed to its filter, fresh granu- lations of gold and silver are introduced, and the acid liquid of the adjoining pot, containing only a small quantity of nitrate of silver poured over it. A fresh charge of granulated metal is thus first worked by the yet strong acid, which acted on the nearly fine gold of the previous charge. A charge of $800,000 or more is easily worked off, refined, in two days, by 4 pounds of parting acid to every pound of gold. The gold is washed thoroughly on a filter by hot water, pressed in a hydraulic press, further dried, melted with copper, and cast into bars, about 2400 ounces Troy constituting a melt. After being assayed, they are then remelted with the calculated quantities of copper or fine gold requisite to bring them to our standard of 900 thousandths fine, and cast into ingots. Upon their proving correct in the assay, usually to within y^ of the standard, they are delivered to be coined. The chloride of silver, accurately precipitated with a slight excess of salt, is filtered and washed thoroughly on large filters, of 3 by 5 feet and 14 inches deep. It is then transferred to lead-lined wooden vats, reduced to metallic silver by granulated zinc, and, the excess of zinc being removed by sulphuric acid, washed, pressed in the hydraulic press, dried by heat, and remelted with a new portion of gold. This method of parting formerly required 3 parts of silver to 1 part of gold, and the latter constituting a fourth part of the alloy, the process was termed quartation. We have, however, found that 2 parts silver to 1 part gold are quite sufficient ; and if the metal be well granulated, the acid will not leave 10 thou- sandths of silver in the gold, which is sufficient to prevent the too darkening effect of copper in the coin. J. G. B. 332 GOLD. thrown into cold water, in order to prevent the formation of crystals by slow cooling. The excess of mercury being removed by pres- sure, a doughy amalgam remains, consisting of 2 parts of gold and 1 of mercury. Bronze objects require several preliminary preparations. They are heated to redness and then dipped into dilute sulphuric acid to dissolve the oxide which forms on the surface, which operation is called the cleaning, (d^rochage,) and they are sometimes dipped for a moment into concentrated nitric acid, in order to obtain a more perfect cleansing, called ravivage. The surface is then amalgamated by means of the scratch-brush, made of fine brass wire, which is first dipped into a solution of nitrate of mercury, and then pressed on the amalgam of gold, part of which adheres. The article, being rubbed with the brush, is placed on an iron grate over coals, in a chimney which must draw well, in order to carry off the mercurial vapours, which would injure the health of the workmen. The arti- cle is then cleaned with a brush dipped in vinegar, and the parts which are to be bright are polished with blood-stone. By substituting an amalgam of silver for one of gold, and ope- rating in the same manner, copper, bronze, and brass can be covered with a coating of silver. The brass scales of barometers and other instruments are silvered by being rubbed with a cork moistened with mixture of 1 part of chloride of silver, 2 of carbonate of potassa, 1 of common salt, and f of a part of chalk. Gilding ly Immersion. 1161. This process, which is chiefly used for gilding copper jewelry, consists in plunging the articles, after being cleanly scraped, into a boiling solution of chloride of gold in an alkaline carbonate, which is prepared by dissolving, on the one hand, 100 grammes of gold-leaf in 250 grammes of nitric acid at 97, 250 gm. of concentrated chlorohydric acid, and 250 of water, and on the other hand, 3 kilogs. of carbonate of potassa in 20 litres of water, heated in a cast-iron kettle. When the gold is entirely dissolved in the aqua regia, the liquid is poured into a porcelain capsule, and 3 kilogs. of bicarbonate of potassa are gradually added, when a lively effervescence ensues, after the termination of which the contents of the capsule are thrown into the kettle. The liquid is boiled for 2 hours, replacing by hot water that which evaporates ; after which the gold-bath is ready for gilding. When the copper articles are prepared for gilding, they are bound together with a brass wire and suspended to a glass hook. At the right of the bath are placed, 1st. A vessel containing a mixture of nitric, sulphuric, and chlorohydric acids ; 2d. Two ves- sels filled with water ; 3d. A vessel containing a solution of nitrate of mercury ; 4th. A vessel containing water ; while at the left of the bath are 2 or 3 pots holding water. The workman first dips GALVANIC GILDING. 388 the articles into the acid liquid, and then, successively, into the two vessels holding water, into that of nitrate of mercury, into the suc- ceeding one of water, and lastly, into the gold-bath. When they have remained in the bath for about 30 seconds they have taken all the gold they can receive, and are then removed, washed in the pots on the left, and dried in heated sawdust. Their colour is then given by means of a mixture of 6 parts of nitre, 2 of sulphate of iron, and 1 of sulphate of zinc, dissolved in a small quantity of boiling water, into which the gilded articles are dipped ; after which they are dried before a bright fire until the saline coating turns brown. They are then washed with water. Galvanic Crilding. 1162. By means of galvanism a perfectly adherent coating of gold, of any desired thickness, may be applied to copper, brass, bronze, silver, platinum, iron, steel, etc. ; and by using corre- sponding solutions, silver, platinum, cobalt, zinc, etc., can also be deposited on copper and its alloys. The solutions used for galvanic processes are those of cyanide of potassium in which a cyanide of the metal to be deposited has been dissolved; and the same liquid may be used ad infinitum if a clean blade of the metal to be precipitated be kept in the solution and placed in communication with the positive pole of the battery. As the metal in solution is deposited on the articles which communicate with the negative pole, an equivalent quantity of the metal fixed to the positive pole dissolves, while the composition of the liquid remains uniform, if the surface of the metallic blade is nearly equal to that of the ob- jects to be covered. The best solution for gilding is made of 100 parts of distilled water, 10 parts of cyanide of potassium, and 1 part of cyanide of gold. The liquid is placed in a large wooden vat CC' (fig. 602) lined with mastic, and tra- versed by two gilded metallic rods tt', vv', which dip into the liquid, the rod tt r communicating with the negative pole, and the rod vv f with the positive pole of the battery, while two large sheets of gold or heavily gilded copper oo f dip into the bath and communicate with the rod vv f . Resting on the rods tt r and vv' are movable rods ab, of gilded brass, to which the objects to be gilded are suspended. The battery is formed of plates of zinc and copper, dipping into a weak solution of sulphuric acid ; each element being commonly 334 GOLD. composed of a wooden vessel, lined with mastic, in which two con- centric cylinders of copper and zinc, kept apart by wooden pegs, are arranged. The zinc cylinder has been first amalgamated with mercury, in order to protect it from too rapid solution. Water acidulated with sulphuric acid, marking 5 degrees on Baume"s areometer, being placed in the vessels, the zinc of each element is made to communicate with the copper of the succeeding one by means of a strong brass wire attached to the upper part of the cylinders, while the free zinc cylinder of one of the two extreme elements is placed in communication with the rod vv f which forms the positive pole, and the copper cylinder of the other extreme ele- ment communicates with the rod tt' which constitutes the negative pole of the battery. The objects to be gilded should be prepared as for gilding by immersion, but the ravivage is unnecessary. The time of immer- sion varies with the thickness of the coat required ; and the tem- perature of the bath should be between 59 and 68. In order to ascertain the quantity of gold deposited, it is sufficient to weigh the object before and after immersion. Although the solution, the composition of which was just ex- plained, is ordinarily used, the same effect can be obtained with different materials ; and either the cyanide of potassium may be replaced by the double cyanide of iron and potassium, or the cyanide of gold by its sesquioxide, or by the double chloride of gold and po- tassium, or, lastly, by sulphide of gold. The same process is adopted for the gilding of iron, steel, or tin ; but a small quantity of copper must previously be deposited on the object by dipping it, for a few moments, in a bath composed of 1 part of cyanide of copper and 10 parts of cyanide of potassium dissolved in 100 parts of water. Gralvanic Silvering. 1163. Galvanic silvering is applied chiefly to objects made of German silver, or other compositions which closely resemble silver- plate. The thickness of the coating of silver may be increased at pleasure. The solution used for silvering is made of 100 parts of distilled water, 10 of cyanide of potassium, and 1 of cyanide of silver ; the process being the same as that for gilding, with the exception that the sheets of gold in the bath (fig. 602) are necessarily replaced by sheets of silver. The silvered pieces, which, on leaving the bath are of a dead-white colour, are polished by the burnisher, and then heated to a dull red-heat in a muffle, after being dipped into a solu- tion of borax. When cooled, they are plunged into a weak solution of sulphuric acid, and then dried. By an analogous process, platinum may be deposited on copper or silver ; but it adheres with difficulty, and, as yet, it has been found impossible to protect articles covered with platinum from the action GALVANOPLASTICS. 335 of nitric acid. Solutions for the deposition of zinc and lead are prepared by dissolving oxide of zinc or oxide of lead in a solution of cyanide of potassium. GALVANOPLASTICS. 1164. By means of a feeble electrical current a uniform and firm coat of copper can be deposited on any given object, and a raised surface thus be reproduced in relief with extreme exactness. The copper plate thus produced can be used as a mould to form, by means of a galvanic current, a second deposit of metallic copper, reproducing faithfully the original object. These processes are applied to the reproduction of medals and copper plates, the battery used being the same as that employed for gilding, while the liquid for coppering consists of a slightly acidulated saturated solution of sulphate of copper, into which the object on which the metallic copper is to be precipitated is dipped, after being brought into com- munication with the negative pole. The positive pole terminates in a plate of copper of about the same size as the object to be cop- pered, and parallel to it at a short distance. In order to reproduce a medal, the first step is to make its mould in relief, either with plaster, ( 560,) or with fusible alloy, ( 316,) or with stearic acid, and afterward render it impervious, by immersing it, for a few mo- ments, in a melted mixture of stearic acid and white wax, after which it is lined with plumbago, uniformly spread over it with a brush. The object of this coating is to render the surface of the mould a conductor of electricity ; which being done, the mould is dipped into the solution of sulphate of copper, after having secured it by a small copper band around its circumference and fastened it to the negative wire of the battery. The copper which is deposited on the mould can be made of any thickness by keeping it for a sufficient length of time in the bath, and it separates very readily from the mould, which can be used for any number of times. The copper thus precipitated by the galvanic current is in crystalline grains, which are the smaller the more feeble the current is. In order to reproduce the medal, it is not necessary to use a separate battery, as the experiment may be so arranged as to produce the galvanic current in the bath itself. Fig. 603 represents a small apparatus generally used for this purpose. A is a glass ^ vessel, filled with a saturated solution ^ of sulphate of copper, to maintain the saturation of which crystals of sulphate Fig. 603. O f copper are placed on the stand m. A glass cylinder B, open at both ends, is held up by the support ?, I', I" in the vessel A; the bottom of the cylinder being made of GOLD. some porous membranes a bladder, for instance. A weak solution of sulphuric acid is poured into the vessel B ; and two metallic rings a, b, terminating in metallic rods united at their upper part, are dipped, the one b into the solution of sulphate of copper, the other a into a solution of sulphuric acid, and are kept separated by the membrane. A plate of amalgamated zinc is placed on, the ring a, while the mould, on which the copper is to be precipitated is set on the ring b ; and the intensity of the electrical current is gauged by passing the upper leg, ^^ / , of the metallic rods which sup- port the rings a and 5, below a movable magnetic ring, the devia- tions of which are in proportion to the activity of the current. ANALYSIS AND ASSAYING OF ALLOYS OF GOLD. 1165. Alloys of gold and copper may be analyzed by cupelling them with lead, and following exactly the same process as described for the cupellation of alloys of silver and copper. If the alloy con- tains no silver, the weight of the lump obtained represents pretty exactly the quantity of pure gold which existed in the alloy ; but if, as more frequently happens, the alloy contains a certain propor- tion of silver, this latter metal remains alloyed with the gold after the cupellation. However, the process of direct cupellation is at- tended with surplusses and losses which sometimes reach 3 thou- sandths : when the temperature of the muffle is very great, there is a small loss arising from the absorption of a small quantity of gold by the cupel ; and when the heat is too low, the gold retains a small quantity of copper and lead ; although gold loses less by volatilizing than silver. In order to determine exactly the quantity of gold existing in a ternary alloy of gold, silver, and copper, it is cupelled at a mode- rate heat with a certain quantity of silver and lead, in order to obtain an alloy of silver and gold, from which the .latter can be perfectly separated by means of an excess of nitric acid, which dissolves the silver and leaves the gold pure. In order, however, to insure exact results, there must be a certain ratio between the quantities of gold and silver ; because, if the proportion of silver be too small, the nitric acid does not dissolve it entirely ; and if, on the contrary, the quantity of silver be too great, the silver and copper are com- pletely dissolved, while the gold separates in the form of powder, which it is difficult to collect without loss. Experience has shown that the most favourable conditions for the assay, commonly called the parting, (depart,) consist in reducing the alloy to J of gold and f of silver, in which case it is completely acted on, while the sepa- rated gold preserves the form of the original alloy, and does not become divided, if the operation be carefully conducted. This operation has received the name of quartation. The proportion of lead to be added, which varies with the standard of the alloy, is indicated in the following table : ASSAYING OP ALLOYS OF GOLD. 337 Standard of gold alloyed Quantity of lead necessary to be added to entirely with copper. remove the copper by cupellation. 1000 thousandths 1 part. 900 " 10 " 800 " 16 700 " 22 " 600 " 24 " 500 " 26 " 400"! 300 I Q 4 a 200 f d4 lOOJ Let us suppose that the standard of a piece of coin is to be determin- ed, the legal standard of which which may be regarded as its approxi- mate standard, is ^o- The quantity of alloy usually operated on being 0.500 gm., containing, according to the legal standard, 0.450 gin. of gold, therefore 1.350 gm. of silver and 5 gm. of lead must be added. But if an alloy is to be assayed the legal standard of which is entirely unknown, the first step is to ascertain the latter by ap- proximation, by means of the assay by the touch-needle, about to be described, after which the process is continued as usual. The lead is first placed in the heated cupel, and when it is in fusion, the mixture of gold and silver is introduced, having been previously weighed and wrapped in a piece of paper. The cupel- lation is allowed to go on as usual, and requires less care than the cupellation of silver, because silver alloyed with gold is not liable to blister ; but the cupel should be removed immediately after the lightning to avoid loss by volatilization. The lump is removed after cooling, flattened under a hammer, annealed for a few moments, and then rolled between cylinders ; after which the sheet thus obtained is rolled into a spiral form, and subjected to the action of nitric acid in a small assayer's flask, (fig. 604,) into which 30 grammes of nitric acid of 22 Baume' are poured, and boiled for 20 minutes. The acid is then decanted and replaced by 30 gm. of pure concentrated nitric acid marking 32, which is boiled v for 10 minutes ; when the acid is decanted, and the gold, v which has preserved the shape of the alloy, washed several Fig. 604. times. The flask being afterward completely filled with water, its mouth is closed with the thumb, and it is inverted, when the spiral sheet of gold falls slowly through the liquid column, and is received in a small earthen crucible, after which the water is poured off, and the crucible heated to redness in the muffle. The acid should not be too concentrated, because the gold might be divided. When the assay has been made with the precautions indicated, the gold remains in the form of a spongy, brown, and very friable mass, of nearly the same volume as the original alloy ; VOL. II. 2 D 22 338 GOLD. but it contracts considerably when heated in the small crucible, becoming harder and assuming the lustre and colour of malleable gold. The calcined gold being exactly weighed, the standard of the alloy is thus obtained within nearly 1 thousandth. Direct assays made on known alloys of gold and silver have shown that the operation, when carefully performed as just de- scribed, can give rise only to the following errors : True standards of the alloy. Standards found. Differences. 900 900.25 +0.25 800 800.50 +0.50 700 700.00 0.00 600 600.00 0.00 500 499.50 -0.50 400 399.50 -0.50 300 299.50 0.50 200 199.50 0.50 100 99.50 -0.50 Assaying ly the touch-needle. 1166. The assay just described cannot be applied to fine jewelry, because the article would be destroyed by the process, and gold jewelry is therefore subjected to a test called the assay by the touch-needle, which does not injure it, and yet enables a skilful assayer to determine its standard within nearly 1 thousandth. The method consists in rubbing the object against a very hard black- stone, on which it leaves marks, from the colour of which, and their behaviour when moistened with a mixture of nitric acid of a density of 1.34 with 2 per cent, of chlorohydric acid, the assayer forms an approximate opinion of the standard of the alloy. The black-stone used, called touch-stone, is a kind of quartz, coloured with bitumen, which formerly was imported from Lydia, but has likewise been found in Bohemia, Saxony, and Silesia. The conditions essential to a good touch-stone are : an intense black colour, incapability of being acted on by acids, hardness, and a sufficient degree of rough- ness to retain some of the gold. The assayer is provided with a series of small blades, called touch- needles^ consisting of alloys of copper and gold, the standard of each of which is exactly known, which enable him to compare the marks they leave on the touch-stone, before and after the action of the acid, with that of the alloys to be assayed. No regard should be paid to the first marks left by the articles on the touch-stone, as they are made by the superficial layer, and always show a higher standard, because the surface consists of pure gold ; and several marks should therefore be made, the last of which only is examined. Alongside of these marks others are made with that touch-needle the composition of which approaches nearest to PROPERTIES OF PLATINUM. 339 that of the article ; when a glass rod, dipped in the acid, is drawn over both, after which the colour of each mark and the manner of action of the acid are examined. PLATINUM. EQUIVALENT = 98.7 (1233.7 ; = 100). 1167. Platinum, which was imported into Europe only about the middle of the last century, but was long known in America by the Spanish name of plating a diminutive name for silver, was for a long time quite useless, because no one could work it. The pla- tinum of commerce is nearly pure, as it commonly contains only a small quantity of iridium, which increases its hardness, but dimi- nishes its malleability. In order to obtain perfectly pure platinum, the metal of commerce is dissolved in aqua regia, the solution fil- tered, and chloride of potassium is added, which yields a copious yellow precipitate of a double chloride of platinum and potassium, very slightly soluble in water, but generally mixed with a small quantity of the corresponding double chloride of iridium and potas- sium. The precipitate is mixed with carbonate of potassa and heated to redness in an earthen crucible, when the chloride of platinum gives off its chlorine to the potassium of the carbonate of potassa, leaving the platinum isolated, while oxygen and carbonic acid are disengaged. The double chloride of iridium is also decomposed, but the iridium remains in the state of oxide. The calcined mass is treated with hot water, which dissolves the alkaline salts, and the residue is acted on by weak aqua regia, which dis- solves the platinum alone and leaves the oxide of iridium. Sal ammoniac is added to the solution of chloride of pla- tinum, when a yellow crystalline precipitate of double chloride of platinum and ammonia PtCl 3 +NH 3 ,HCl is formed, which, on being calcined to redness after wash- ing, leaves a spongy mass of platinum, called platinum sponge. In order to reduce platinum-sponge to the state of mal- leable platinum, it is introduced into a brass cylinder efgh, (fig. 605,) the bottom of which fits into a steel cup abed, while a steel piston ik moves in the cylinder. When the cylinder is half-filled with platinum-sponge, the piston is I a. introduced and struck with a hammer, at first 'gently, afterward more powerful; by which means a solid disk Fig. 605. of platinum is obtained in a short time, which is heated 340 PLATINUM. to a white-heat in a muffle, and again hammered on a steel anvil. By repeating these operations, a perfectly malleable plate of plati- num is obtained, which can be rolled into sheets in a small rolling- machine. 1168. Platinum resists the highest temperature of a forge-fire without fusing, but it melts before the oxyhydrogen blowpipe, or between the pieces of charcoal terminating the conductors of a pow- erful battery. Platinum possesses the property of being welded and soldered on itself at a white-heat, the application of which property has just been mentioned in the transformation of sponge platinum into the malleable metal. Platinum is of a grayish-white colour, susceptible of a high polish, and possessing great malleability when pure, while the presence of a very small quantity of foreign matter will profoundly affect this quality. Although the tenacity of pure platinum is hardly inferior to that of iron, the platinum of commerce, which always contains small quantities of iridium, is much less tenacious, for a wire of 2 millimetres in diameter frequently breaks under a weight of 125 kilogs. The density of hammered or rolled platinum is 21.5. Platinum does not oxidize in the air at any temperature, and is acted on by only a limited number of acids. Chlorohydric and concentrated sulphuric acid do not affect it, neither does nitric acid attack it, although it is soluble in this acid when alloyed with a sufficient quantity of silver. Aqua regia is the true solvent of platinum. Platinum is acted on at a red-heat by potassa, soda, and particu- larly by lithia, but remains unchanged when exposed to the action of the alkaline carbonates. A mixture of nitrate of potassa and potassa acts on it much more readily than pure potassa. Sheet- platinum is acted on, only after a long time, by sulphur, phosphorus, and arsenic, while platinum-sponge combines readily with these substances, producing fusible and very brittle compounds. A mix- ture of silex and carbon attacks platinum ; in which manner plati- num crucibles are frequently rendered useless. As the surface of a platinum crucible becomes rough from repeated heating, and the metal very brittle, it should never be heated in contact with char- coal, but rather be placed in earthen crucibles, at the bottom of which a small quantity of quicklime or magnesia is deposited. 1169. Metallic platinum may also be obtained in the form of a very finely divided precipitate, called platinum-black, and then pos- sesses remarkable properties, on which we shall dwell for a short time. Platinum-black is obtained by reducing platinum in solution by an easily combustible organic substance ; to which effect a solu- tion of chloride of platinum PtCl 3 is generally boiled with carbonate of soda and sugar, when chloride of sodium is formed, while the plati- num is precipitated in the metallic state and the oxygen given off by the soda decomposes a portion of the sugar into water and carbonic PLATINUM-BLACK. 341 acid. The flask in which the operation is performed must be fre- quently shaken to prevent the precipitated platinum from adhering to its sides. The precipitate is collected on a filter and dried be- tween tissue-paper. Platinum-black is also prepared by dissolving protochloride of platinum PtCl in a concentrated solution of potassa, boiling the liquid, and then adding a small quantity of alcohol ; when a very lively effervescence of carbonic acid ensues, while the platinum is precipitated. Lastly, it is sometimes obtained by decomposing sulphate of platinum by alcohol with the assistance of heat. Finely divided metallic platinum possesses the property of con- densing gases in very large quantities. Thus, platinum-black which is allowed to remain in an atmosphere of oxygen gas will condense several hundred times its volume of the gas and afterward exhibits very intense phenomena of combustion. If, for example, a drop of absolute alcohol be thrown on platinum-black thus charged with oxygen, the whole substance becomes incandescent ; and if a cap- sule containing platinum-black be placed under a bell-glass filled with air, the sides of which are moistened with alcohol, the vapours of the alcohol undergo a slow oxidation, which converts them into acetic acid. This property of platinum-black depends, in a great measure, on the method employed in its preparation; as for ex- ample, that obtained by decomposing sulphate of platinum by alco- hol is the most active. The action may be measured in the following manner : Having passed to the top of a graduated bell-glass filled with mercury, a small quantity of a solution of formic acid, (an organic acid which is readily converted in water and carbonic acid by oxidizing agencies,) a known weight of platinum-black wrapped' in tissue-paper is introduced into the bell-glass ; when the evolution of carbonic acid immediately begins, but ceases again in a few mo- ments. By ascertaining the volume of gas disengaged, the quantity of oxygen condensed by the platinum-black can be measured. The absorbing property of platinum black is also perceptible, though in a less degree, in platinum sponge, and even in sheet pla- tinum. Thus, it has been shown ( 74), that on throwing a piece of platinum-sponge into a bell-glass containing a detonating mix- ture of oxygen and hydrogen, an explosion immediately ensues : so again, if a current of hydrogen gas be projected on platinum- sponge exposed to the air, the jet of hydrogen ignites. Sheet-platinum does not present these properties at the ordinary temperature, but exhibits them when heated to about 390. If a coil of platinum wire (fig. 606) be placed over the wick of an alcohol-lamp, and the lamp lighted so as to heat the wire to redness, the wire remains incan- descent for an indefinite length of time after the flame be- ' neath has been extinguished, because the vapour of alco- hol, disengaged from the wick, burning when it comes into contact 342 PLATINUM. with the wire, develops heat enough to keep it incandescent. The experiment proceeds better by adding a small quantity of ether to the alcohol; and the little apparatus is known by the name of Davy's flameless lamp. In the same way, if a small quantity of ether be placed at the bottom of a wineglass, (fig. 607,) and a coil of platinum wire, which has been previously heated to redness, be fastened to a pasteboard lid which closes partly the mouth of the glass, the wire remains incan- descent for a long time. In these experiments, the vapours of alcohol and ether are only imperfectly burned, yielding, as products of combustion, volatile substances of highly suffocating properties and con- s ' taining an organic acid ; all of which shall hereafter be described. Deutoxide of nitrogen, and ammonia, mixed with oxygen gas, are converted, by contact with platinum-sponge, into nitric acid, while the compounds of nitrogen and oxygen, on the contrary, are changed into ammonia, by contact with the sponge in an atmosphere of hy- drogen. In order to succeed in the experiment, it is better to heat the platinum-sponge to a temperature of 300 or 400, in a glass tube traversed by the gaseous mixture. Platinum-sponge loses its absorbing property after some time, but regains it by being heated for a few moments in nitric acid, and then calcined at a dull red-heat. Platinum-black, which also loses its activity after some time, is restored to its former state by heat- ing it with nitric acid, washing it with water, and drying it by a gentle heat. COMPOUNDS OF PLATINUM WITH OXYGEN. 1170. Platinum does not combine directly with oxygen, except at a red-heat, or when assisted by the caustic alkalies. Two oxides of platinum are known The protoxide PtO, The binoxide PtO, 2 each of which is a feeble base, forming with powerful acids a series of salts which are easily decomposed by heat and leave metallic platinum. Protoxide of platinum PtO is prepared by decomposing the protochloride PtCl by a solution of caustic potassa, when hydrated protoxide remains in the form of a black powder, which dissolves with a brown colour, in a concentrated solution of potassa. When heated, it first gives off its water, and then oxygen. Hydrated protoxide of platinum dissolves in acids and yields solutions of a deep brown colour, which are not precipitated by sal-ammoniac. Binoxide of platinum PtO a is obtained by adding to nitrate of platinum one-half of the potassa which would be necessary to OXIDES OF PLATINUM. 343 completely decompose the salt, when a voluminous brown precipi- tate is formed, consisting of hydrated binoxide of platinum PtO a +2HO. If a larger quantity of alkali were added, the precipitate would contain potassa in combination. But this oxide is more easily prepared by adding to a solution of per chloride P1C1 3 a large excess of caustic potassa, when at first a yellow precipitate of double chloride of platinum and potassium is formed, but again dissolves if the liquid be heated. The platinum then exists in the solution in the state of platinate of potassa ; and the liquid being supersatu- rated by acetic acid, hydrated oxide of platinum is precipitated. The hydrate parts with its water at a moderate heat and turns black, while it loses its oxygen when exposed to higher a temperature. It dissolves in the acids, and yields orange-yellow solutions, while after calcination it is insoluble. The hydrate also dissolves very readily in a concentrated solution of caustic potassa, and the liquid by evapo- ration deposits crystals of platinate of potassa. Insoluble platinate of potassa is also obtained by mixing the double chloride of plati- num and potassium with a concentrated solution of potassa, drying the substance and heating it until the alkali is fused. By treating it with water the alkaline salts are dissolved, and a brown mass of platinate of potassa remains, which, when treated with acetic acid, leaves hydrated binoxide of platinum. By adding ammonia to a solution of sulphate of platinum, a brown precipitate is obtained, which is a double basic salt, and which, on being diluted for some time with a weak solution of caustic soda, yields a substance of detonating properties when heated to about 410. This fulminating compound, which, however, does not de- tonate by percussion, is regarded as a compound of platinum and ammonia. SALTS FORMED BY THE PROTOXIDE OF PLATINUM. 1171. These salts present but little interest, and have hitherto been but little studied. They form brown solutions which do not crystallize, and from which potassa does not precipitate them when sufficiently diluted, while the alkaline carbonates yield a brown pre- cipitate, which remains suspended in the liquid. Sulf hydric acid and the sulf hydrates throw down a black precipitate. The protoxalate, which is the only protosalt of platinum which has hitherto been obtained in a crystalline form, is prepared by heating the hydrated binoxide of platinum with a solution of oxalic acid, when the former is reduced to the state of protoxide, which dissolves in the excess of oxalic acid, while carbonic acid is disen- gaged. The liquid, when evaporated, deposits the protoxalate of platinum in small coppery-red needles. SALTS FORMED OF THE BINOXIDE OF PLATINUM. 1172. The salts of the binoxide of platinum are of an orange- 344 PLATINUM. yellow colour, and caustic potassa throws down from their solutions a brown precipitate of the platinate of potassa, which dissolves in an excess of caustic potassa. Sulf hydric acid and the alkaline sulf- hydrates yield black precipitates which dissolve in a large excess of sulf hydrate. All the salts are decomposed by heat and leave me- tallic platinum ; and iron as well as zinc decomposes their solutions by precipitating metallic platinum in the form of a black powder. Chloride of potassium and chlorohydrate of ammonia throw down, from solutions of salts of the binoxide of platinum double chlorides, PtCl 3 +KCl, PtCLj-fNHgHCl, as yellow crystalline precipitates, which are very slightly soluble in water, and nearly insoluble in a mixture of alcohol and water. The double ammoniacal chloride yields, by calcination, platinum-sponge ; while the double chloride of platinum and potassium is decomposed by heat into metallic pla- tinum and chloride of potassium ; after which the substance, by treatment with water, yields pure platinum. Bichloride of platinum is the solution extensively used in the laboratory, and presents some peculiar reactions which should be here noted. Potassa and ammonia, their carbonates, and, in gene- ral, all the salts of potassa and ammonia, precipitate platinum in the state of double chlorides, while soda and the salts of soda yield no precipitates. Sulphate of Binoxide of Platinum. 1173. The sulphate of binoxide of platinum is most easily pre- pared by treating the sulphide of platinum obtained by precipitating the chloride with sulf hydrate of ammonia, with fuming nitric acid, and evaporating the solution with a few drops of sulphuric acid to drive off the last particles of nitric acid ; when a deep-brown mass remains which dissolves in water with a brown colour. Nitrate of Binoxide of Platinum. 1174. The nitrate of binoxide of platinum is prepared by care- fully pouring nitrate of silver into a solution of bichloride of pla- tinum until a precipitate no longer forms; when the chlorine is precipitated in the state of chloride of silver, while the solution contains nitrate of platinum, which crystallizes with difficulty. The salt may also be obtained by dissolving the hydrated binoxide in nitric acid. COMPOUND OF PLATINUM WITH SULPHUR. 1175. Platinum combines directly with sulphur, when the metal in a very finely divided state is heated to redness in vapour of sulphur ; but a purer product is obtained by heating in a crucible equal parts of ammoniacal chloride of platinum and sulphur until the chlorohy- drate of ammonia and the sulphur in excess are reduced to vapour. COMPOUNDS OF PLATINUM WITH CHLORINE. 345 The sulphide thus obtained corresponds to the protoxide, and ap- pears as a gray and very brittle mass. The sulphide of platinum corresponding to the binoxide can only be prepared by the humid way, and is obtained by passing a current of sulf hydric acid gas through a solution of the double chloride of platinum and sodium. The bisulphide is a sulphacid which enters into combination with the alkaline sulphides. COMPOUNDS OF PLATINUM WITH CHLORINE. 1176. Two compounds of platinum with chlorine are known, corresponding to the two oxides. The protochloride PtCl is ob- tained by heating dried bichloride of platinum PtCl 3 in an oil-bath, gradually raised to 392, and maintained at this temperature as long as any chlorine is disengaged. The bichloride thus parts with half its chlorine and is converted into a deep-green powder, which is the protochloride of platinum. The protochloride can also be obtained in the form of a greenish-gray precipitate, by passing a current of sulphurous acid gas through a solution of bichloride of platinum which does not contain an excess of acid : sulphuric and chlorohydric acids are formed at the same time. The protochloride is insoluble in water, but dissolves in chlorohydric acid ; and if sal- ammoniac or chloride of potassium be added to this solution, no precipitate is formed, while, by evaporating the liquid, beautiful crystals of double chlorides, of which the formulae are PtCl+KCl and PtCl+NH 3 ,HCl, are obtained. The bichloride of platinum is prepared by dissolving platinum in aqua regia, evaporating the liquid at a moderate heat to drive off the excess of acid, and then treating with water. The solution of the bichloride, which is of a slightly-brownish yellow colour, be- comes deeper when it contains a small quantity of protochloride of platinum. Bichloride of platinum does not crystallize, but remains after evaporation in the form of a deliquescent brown mass, readily soluble in alcohol. It combines with a great number of metallic chlorides ; and the double chlorides of platinum with potassium and with ammonia present peculiar interest in chemical analysis, because they are very slightly soluble in water and insoluble in alcohol. These compounds have already been mentioned when speaking of the determination of potassium, ( 527.) If the double chlorides be dissolved in a large quantity of hot water, and the liquid allowed to evaporate spontaneously, they crystallize in well-defined, regular octahedrons of an orange-yellow colour. It has already been men- tioned that their formulae are PtCl a +KCl and PtCl a +NH 8 ,HCl. Chloride of sodium forms an analogous double chloride with chloride of platinum, which is, contrary to the corresponding compounds of potassa and ammonia, very soluble in water, and even in alcohol ; and the solution of which yields, by evaporation, beautiful yellow crystals of the formula PtCl 3 +NaCl+6HO. 346 PLATINUM. If one of these double alkaline chlorides is intimately mixed with 2 or 3 times its weight of alkaline chloride, and heated slowly in a crucible, metallic platinum is separated in the shape of brilliant crystalline lamellae, which are easily isolated by dissolving the alka- line chloride in water. 1177. If a solution of protochloride of platinum, dissolved in an excess of chlorohydric acid, be gradually poured into caustic am- monia, small green needles of the formula PtCl,NH 3 are deposited, forming a substance called ammoniacal protochloride of platinum; the simplest way of preparing which consists in passing a current of sulphurous acid gas through a boiling solution of bichloride of platinum containing an excess of chlorohydric acid, until the liquid no longer gives a precipitate with sal-ammoniac ; by which means the bichloride of platinum is reduced into protochloride. Ammonia is then added, and the solution, on cooling, deposits am- moniacal protochloride of platinum, which is remarkable for its great stability; as it is scarcely acted on by the most powerful acids, and its ammonia can be driven off only by heating it for a long time with these acids. Ammoniacal protochloride of platinum is soluble in a hot solu- tion of sulphate or nitrate of ammonia, and deposits small yellow crystals on cooling, which appear to be an isomeric modification of the original product. The combination is decomposed at a tempera- ture of 570, leaving metallic platinum. 1178. By digesting ammoniacal protochloride of platinum for some time in a concentrated solution of ammonia, there results a yellowish-white compound, which dissolves in the hot liquid, and is subsequently deposited, on cooling, in large prismatic crystals of the formula PtCl,N 3 H 6 +HO. By pouring nitrate of silver into a hot solution of this substance, the liquid after evaporation yields a white crystallized salt, of which the formula is (PtO,N 2 H 8 ),N0 5 ; and if sulphate of silver be substituted for the nitrate, the chlorine is still precipitated in the state of chloride of silver, and the evaporated liquid deposits a second crystallized salt, of which the formula is (PtO,N 3 H 8 ),S0 3 . The compound (PtO,N 3 H 6 ) is, therefore, a true base, which forms crystallizable salts with the acids, and which may also be obtained in an isolated state by adding a solution of hydrate of baryta to the solution of the sulphate (PtO,N 3 H 6 ),S0 3 until a precipitate no longer forms ; when the sulphuric acid is precipitated in the state of sulphate of baryta, while the liquid remaining exerts a powerful alkaline reaction on coloured tests, and when evaporated under the receiver of an air-pump, deposits white crystalline needles of the formula (PtO,N 3 H 6 ),HO. This base, which we shall call binammonia-oxide of platinum, combines directly with acids, even with carbonic, and is powerful enough to expel ammonia from its saline compounds. SALTS OF PLATINUM. 347 The following compounds have been obtained in a crystallized form : Hydrated base (PtO,N 3 H 6 ),HO. Sulphate (PtO,N 8 H 6 ),S0 3 . Nitrate (PtO,N 3 H 6 ),N0 5 . Neutral carbonate (PtO,N 2 H 6 ),C0 3 -f HO. Sesquicarbonate 2(PtO,N 3 H 8 ),3CO fl +HO. Bicarbonate (PtO,N 3 H 6 ),2C0 3 +HO. Chloride (PtCl,N 3 H 6 ). Bromide (PtBr,N 3 H 6 ). Iodide (PtI,N 3 H 6 ). 1179. The base (PtO,N 2 H 6 ) at 110 loses by heat one equiva- lent of water and one of ammonia, being converted into a new com- pound, insoluble in water, of which the formula is (PtO,NH 3 ). This substance, which we shall call protammonia-oxide of platinum, possesses basic properties in a high degree, as it combines directly with the acids, and yields the following series of products : Anhydrous base (PtO,NH 3 ). Nitrate (PtO,NH 3 ),N0 5 . Sulphate (PtO,NH 8 ),SO,+HO. Chloride (isomeric with ammonia- cal protochloride of platinum)... (PtCl,NH 3 ). Iodide (PtI,NH 3 ). Cyanide (PtCy,NH 3 ). Salts of the protammonia-oxide of platinum are readily con- verted into those of the binammonia-oxide of platinum, by dis- solving them in an excess of caustic ammonia, when they take up 1 equiv. of ammonia and reproduce the salts of the binammonia- oxide of platinum. Reciprocally, salts of the binammonia-oxide of platinum are easily converted by heat in those of the protammo- nia-oxide of platinum by losing 1 equiv. of ammonia. 1180. The two series of salts just described are not the only ones which have been obtained by means of the ammoniacal proto- chloride of platinum. If the chloride (PtCl,N 3 H 6 ) of the binammo- nia platinic series be boiled with weak nitric acid, reddish vapours are disengaged, and, on cooling, a substance is deposited of the formula (PtCl,N 3 H 6 )0,N0 5 , which may be regarded as the nitrate of a third base represented by the formula (PtCl,N 3 H 6 )0. If ammoniacal protochloride of platinum be boiled with a large excess of nitric acid a liquid is obtained which deposits successively, by evaporation, two crystallizable compounds, the formula of the first of which is (PtC10 5 ,N,H 13 ),2N0 5 , which forms small brilliant needles, very slightly soluble in water, and deflagrating when 348 PLATINUM. heated. This compound contains a fourth base, of which the very complex formula is (PtC10 5 ,N 4 H 13 ). This base has been obtained in combination with carbonic, oxalic, phosphoric, and chromic acids, forming salts which crystallize readily, because they are very slightly soluble in water. The formula of the second compound, which remains in the mother liquid, is (PtCl 3 4 ,N 4 H 13 ),2N0 5 , and it may be considered as the ni- trate of a fifth base (PtCl 2 4 ,N 4 H 13 ). COMPOUND OF PLATINUM WITH CYANOGEN. 1181. By heating an intimate mixture of finely divided platinum and ferrocyanide of potassium to a dull red-heat in an earthen cru- cible, and then treating the mass, when cooled, with water, a solution is obtained, which first deposits crystals of undecomposed ferrocy- anide of potassium, but which yields, after additional evaporation, a double cyanide of platinum and potassium. This substance, after being purified by a second crystallization, appears in the form oi beautiful crystals of the formula KCy-f PtCy-f-3HO. Its solutions precipitate a great number of metallic salts, in which precipitates the potassium of the preceding compound is replaced by 1 equiv. of the metal, of which the salt effects the precipitation. DETERMINATION OF PLATINUM, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. 1182. Platinum is determined in the metallic state, or in that of dried double ammoniacal chloride. When platinum exists in a liquid in the state of bichloride, the liquid is concentrated by eva- poration, and twice its volume of alcohol is added, after which chlo- rohydrate of ammonia is poured into the solution, to completely precipitate the platinum in the state of double chloride of platinum and ammonia. The precipitate is washed with alcohol, and dried under the receiver of an air-pump ; and the weight of the platinum is subtracted from that of the double chloride, which contains 44.23 per cent, of metallic platinum. The double ammoniacal chloride may also be calcined in a covered crucible, when sal-ammoniac is disengaged, while metallic platinum remains, which is weighed. But the decomposition by heat requires great care, because it is difficult from preventing some particles of platinum from being carried off by the vapours which are disengaged. Platinum may also be precipitated in the state of double chloride of platinum and potassium, by using the same precautions as in the precipitation by sal-ammoniac ; and by decomposing the double potassic chloride by heat, there is less fear of the platinum being carried off by the gases ; but as the platinum remains mixed with chloride of potas- sium, the residue must be washed several times to dissolve the alka- line chloride. 1183. In order to separate platinum from the metals previously EXTRACTION OF PLATINUM. 349 described, either the insolubility of metallic platinum in all acids except aqua regia and acid mixtures which can evolve chlorine, or the precipitation of platinum by sulf hydric acid, even in acid liquids, or, lastly, its complete precipitation by chloride of potassium or chlo- rohydrate of ammonia, is relied on. It is, however, important to observe that platinum, when alloyed with a considerable quantity of metal soluble in nitric acid, is itself dissolved in the acid; so that only isolated platinum can be considered as insoluble in nitric acid. EXTRACTION OF PLATINUM. 1184. Platinum occurs in the native state in alluvial sands, re- sembling those in which gold is found, generally in open valleys or amid serpentine rocks. The principal localities of platinum are in Colombia, Brazil, and the Ural Mountains in Siberia. It generally occurs in small grains, although pieces weighing 10 kilogs. have been met with. The platiniferous sands, by washing, ultimately yield a sand rich in platinum, but of a very complicated composi- tion ; as it contains, in addition to the platinum, the metals which constantly accompany it, namely, osmium, iridium, palladium, rho- dium, and ruthenium ; and, moreover, gold, silver, iron, and copper ; and lastly, many heavy minerals, such as magnetic oxide of iron, titanic iron, chromate of iron, pyrites, etc. When the platiniferous sand contains any considerable quantity of gold, this metal is first extracted by amalgamation ; when the ore, after being purified as much as possible by mechanical means, is acted on, in glass balloons heated in a sand-bath, by aqua regia con- taining an excess of chlorohydric acid, a small quantity of water being added, so that as little iridium as possible, which would render the platinum brittle, may be dissolved. The aqua regia is renewed several times until the platinum is completely dissolved ; and the operation must be effected in a chimney which draws well, in order to carry off the vapours which are disengaged, and which are ren- dered injurious by the presence of osmic acid. The solution of pla- tinum is decanted, after having been allowed to become clear by rest, and a concentrated solution of sal-ammoniac is added, which precipitates the platinum almost entirely in the state of double chlo- ride of platinum and ammonia. As the mother liquid still contains some platinum and some quantity of foreign metals, the latter are precipitated by blades of iron and zinc, while a black deposit is ob- tained, from which a certain quantity of platinum may be extracted. For this purpose, the deposit is first treated with chlorohydric acid, which dissolves the foreign metals, and the residue is then acted on by very weak aqua regia, which readily dissolves the divided plati- num, without sensibly affecting the iridium ; when sal-ammoniac is added, which precipitates the double chloride of platinum and am- monia. VOL. II. 2 E 350 OSMIUM. The double chloride of platinum and ammonia is calcined at a dull red-heat, and the platinum-sponge which is thus obtained is pulverized by hand, and then diluted with water so as to form a homogeneous mud, which is passed over a sieve, the grosser particles remaining on, which are again pulverized. The workman must ob- serve the greatest cleanliness in the various operations, as the pre- sence of dust, or even a single hair in the mud, will give rise to serious defects in the forged platinum. The powdered platinum is, therefore, generally washed several times, in order to remove all the dust. The platinum paste is introduced into an apparatus resembling that of fig. 605, only larger, care being taken that no bubbles of air are inclosed. The substance is first compressed with a wooden pestle, then with a metallic piston ; when the water separates from the platinum, while the latter becomes more solid ; and the process is terminated by compressing it with great force. The platinum disc is then heated to whiteness in an earthen crucible, placed on an anvil and struck with a heavy hammer, after which it is again heated to whiteness before being forged. OSMIUM. EQUIVALENT = 99.6 (1245.9 ; 0=100). 1185. Osmium, prepared by calcining the double chloride of osmium and ammonia, is of a metallic-gray colour, resembling pla- tinum, while, when it has been reduced by the humid way, it often shows a bluish fringe. The metal is sufficiently malleable to allow of its being rolled into plates or sheets, although it is reduced to powder by percussion. Osmium neither fuses nor volatilizes in a forge-fire, and its density is about 10. The metal combines readily with oxygen ; and when it has been reduced by the humid way, it rapidly absorbs the oxygen of the air, especially when assisted by water, and is converted into osmic acid ; and when heated in oxygen at a low temperature, it ignites and is converted into osmic acid, which sublimes. Concentrated nitric acid acts readily on it and disengages copious reddish vapours, producing soluble osmic acid, which product is also obtained by the action of aqua regia on the metal. The caustic alkalies and alkaline nitrates attack it at a red- heat, the osmic acid combining with the alkalies. Powdered osmium, heated on a blade of platinum, in the flame of an alcohol-lamp, dis- engages vapours of osmic acid, the characteristic penetrating odour of which evinces the presence of very small quantities of osmium. COMPOUNDS OF OSMIUM. 351 COMPOUNDS OF OSMIUM WITH OXYGEN. 1186. Osmium forms a large number of compounds with oxygen, five of which are known, and are The protoxide OsO. " sesquioxide Os 2 3 . " binoxide Os0 3 . " osmious acid Os0 3 . " osmic acid Os0 4 . The two acid compounds are the most important, and the best un- derstood. Protoxide of osmium OsO is prepared by pouring potassa into a solution of the double protochloride of osmium and potassium, when a deep-green precipitate is formed, which dissolves with a green colour in acids, and which is easily reduced to the metallic state by deoxidizing agencies. Sesquioxide of osmium Os 3 3 is obtained by maintaining, for some time, at a temperature of 122, a mixture of osmic acid and ammonia, when a precipitate is formed which is a compound of the sesquioxide of osmium and ammonia, and which dissolves in acids, producing yellow solutions which do not crystallize. If chlorine be passed over a mixture of divided osmium and chloride of potassium, gently heated in a glass tube, a double chlo- ride is obtained, of which the formula is Os Cl -f KC1, and which when treated while hot by a solution of carbonate of potassa, yields a black precipitate of binoxide of osmium Os0 2 . Osmic acid Os0 4 is formed in many ways : 1. By the roasting of osmium in the air, or better still, in an atmosphere of oxygen ; 2. By acting on osmium by nitric acid ; 3. By heating to redness metallic osmium with nitrate of potassa, and decomposing the os- miate of potassa by an acid. Osmic acid is a white substance, which crystallizes in brilliant prisms, and exhales a very penetrating odour resembling that of chloride of sulphur ; and as its vapour excites coughing and irri- tates the eyes and skin, the substance should be avoided with great care. Osmic acid liquifies at a temperature below 212, and boils below a red-heat. It is very soluble in water, although the sub- limed acid requires a long time for solution ; and it also dissolves largely in alcohol and in ether, but after some time is reduced by these liquids, especially under the influence of polar light. It is readily decomposed by deoxidizing agencies, and by the majority of organic substances : it stains the skin and linen black. Iron, zinc, tin, copper, &c. precipitate metallic osmium from its solutions. Osmic acid is a weak acid, which does not directly redden the tincture of litmus, and does not decompose the carbonates, but which combines with the alkalies, although the resulting compounds 352 OSMIUM. are not very fixed, as solutions of the alkaline osmiates disengage, when boiled, vapours of osmic acid. Osmious acid Os0 3 only exists in combination with alkaline bases, and by endeavouring to isolate it, it is decomposed into osmic acid and binoxide of osmium. Osmite of potassa is obtained by pouring a few drops of alcohol into a solution of osmiate of potassa, when the salt is deposited as a rose-coloured crystalline powder, in which case the osmic acid im- parts a portion of its oxygen to the alcohol. Large crystals of os- mite of potassa are obtained by allowing a solution which contains, at the same time, osmiate and nitrite of potassa to rest ; when the osmic is slowly decomposed by the nitrous acid, causing beautiful crystals of osmite of potassa to be deposited. Osmite of soda, which is prepared in the same way, and yields rose-coloured solutions, crystallizes with much difficulty, because it is more soluble. No osmite of ammonia is known, and ammonia immediately re- duces the solutions of osmite of potassa and osmite of soda. We shall not treat of the salts formed by the oxides of osmium with acids, as they are, as yet, but little understood. COMPOUNDS OF OSMIUM WITH CHLORINE. 1187. If osmium be heated in a current of chlorine, two chlo- rides are produced : a bichloride OsCl 2 and a protochloride OsCl, the latter, which is the more volatile, condensing in the most re- mote portions of the tube. It is an orange-coloured, very fusible and deliquescent substance, while the protochloride is of a beautiful green, and its solution in water soon decomposes, chlorohydric and osmic acids being formed, while metallic osmium is precipitated. EXTRACTION OF OSMIUM. 1188. Osmium always accompanies platinum-ore, but exists in it chiefly in combination with iridium, forming compounds of very variable proportions, called iridosmiums. Iridosmium is found in small, gray, very dense spangles, sometimes presenting the form of lamellae with six facets of the rhombohedric system. Being acted on with difficulty by aqua regia, it remains in the residue after the treatment of platinum-ores. Osmium and iridium are prepared by heating in an earthen crucible, for an hour, at a strong red-heat, 100 parts of pulverized iridosmium and 300 parts of nitre, when osmiate and iridiate of potassa are formed. The fused material being run on a cold metallic plate, is then broken to pieces, and intro- duced into a tubulated retort, with a large excess of nitric acid, a well-cooled receiver being fitted to the retort as soon as heat is ap- plied. A great proportion of the osmic acid volatilizes, and con- denses on the sides of the receiver, in the form of beautiful white crystals, which are subsequently dissolved in a concentrated solu- IRIDIUM. 353 tion of potassa, from which all the osmium is afterward precipitated by alcohol, in the state of osmite of potassa, which salt is used in preparing metallic osmium and all its products. When the substances heated in the retort no longer disengage osmic acid, water is added, and the insoluble residue being collected on a filter, then contains a certain quantity of oxide of osmium and a large quantity of oxide of iridium. It is boiled with aqua regia, which dissolves the osmium and iridium in the state of chlorides, after which sal-ammoniac is poured into the solution, when the double chloride of osmium and ammonia is precipitated, together with the corresponding compound of iridium and ammonia IrCl 2 +NH 3 HCl. The double chlorides are suspended in water and subjected to the action of a current of sulphurous acid, when the double chloride of iridium IrCl 3 H-NH 3 HCl is transformed into the double chloride IrCl+NH 3 HCl which dissolves, while the double chloride of osmium remains unchanged and is precipitated. The latter yields metallic osmium by calcination, while the solution which contains the double chloride of iridium and ammonia deposits, by evaporation, beautiful brown crystals, which yield iridium when calcined. IRIDIUM. EQUIVALENT = 99.0 (1237.5; = 100). 1189. Iridium prepared by the calcination of the double ammo- niacal chloride ( 1188) presents the appearance of a gray spongy mass, resembling platinum. Iridium is difficult to solder, and hitherto has not been obtained in a malleable state ; while it is still more difficult of fusion than platinum. The metal is obtained in a compact mass, very hard, and capable of a fine polish by mois- tening powdered iridium with water, compressing it, at first slightly between tissue-paper, and then powerfully by means of a press, and calcining it at a strong white-heat in a forge-fire. The metal thus obtained is very porous, and its specific gravity does not exceed 16.0, while the density of compact iridium is probably equal to that of platinum ; as a native alloy of iridium and platinum is found, con- taining 20 per cent, of platinum, and crystallized in regular octohe- drons, the density of which is 22.3. Nitric acid and even aqua regia do not attack iridium when isolated, although aqua regia dis- solves it when alloyed with platinum or other metals. Heated to redness with potassa or nitre, iridium oxidizes, and iridiate of potassa is formed. It is attacked by chlorine at a red-heat and in the presence of chloride of potassium, a double chloride of iridium and potassium being formed. 2E2 23 354 IRIDIUM. COMPOUNDS OF IRIDIUM WITH OXYGEN. 1190. Four compounds of iridium with oxygen are known : The protoxide Ir^O. " sesquioxide Ir 3 3 . " binoxide I r 2 . " trinoxide Ir0 3 . The protoxide of iridium is obtained by precipitating by an alka- line carbonate the double protochloride of iridium and potassium, when a greenish-gray precipitate is formed which dissolves in acids, yielding green solutions. The oxide is undecomposable by heat, but is easily reduced by hydrogen at a red-heat. Sesquioxide of iridium is formed when iridium is attacked by the alkalies or alkaline metals, and appears as a black powder, inso- luble in acids, but combining with the alkalies, producing brown solutions. Heat restores this oxide to the state of protoxide. If the sesquioxide be dissolved in a solution of potassa, and the liquid be afterward saturated by an acid, a precipitate is thrown down, which turns blue by absorbing the oxygen of the air, and at last assumes an indigo colour, when it has passed into the state of hydrated binoxide of iridium Ir0 3 +2HO. The binoxide may also be obtained by pouring potassa into a solution of sesquichloride of iridium, when no precipitate is formed at first, while the liquid, on being exposed to the air, deposits ultimately a deep-blue precipitate. Lastly, when the trichloride of iridium IrCl 3 is precipitated by an alkali, there results a greenish-yellow precipitate of trinoxide of iridium Ir0 3 , which, however, is always combined with a certain quantity of alkali. If an oxide of iridium be digested with a solution of formic acid until carbonic acid is no longer disengaged, a very finely divided black powder of iridium is obtained, which exerts a powerful absorb- ent action on gases, and causes the ignition of an explosive mixture of hydrogen and oxygen. COMPOUNDS OF IRIDIUM WITH CHLORINE. 1191. Four chlorides of iridium, corresponding to the four oxides, are known. Protochloride of iridium, which is obtained by heating to a dull- red very finely divided iridium in a current of chlorine, combines with the alkaline chlorides and with chlorohydrate of ammonia, yielding products which readily crystallize. Iridium is acted on more powerfully by chlorine when previously mixed with chloride of potassium. Sesquichloride of iridium Ir 3 Cl 3 is prepared by dissolving the sesquioxide in chlorohydric acid, and appears as a hard, uncrystal- lizable, and deliquescent substance, which forms soluble double COMPOUNDS OF IRIDIUM. 355 chlorides with the alkaline chlorides and with chlorohydrate of ammonia. When solutions of these double chlorides are boiled, they deposit very slightly soluble double chlorides, which contain bichloride of iridium IrCl 2 , while corresponding double compounds, containing protochloride of iridium IrCl, remain in the liquid. Sul- phurous acid converts them into double chlorides containing the protochloride. Bichloride of iridium is formed when finely divided iridium or its oxides are dissolved in aqua regia and heated to the boiling point, when solutions of a reddish-yellow colour are obtained. If chloride of potassium be poured into the liquid, a double chloride is obtained, the solution of which is red and deposits octohedric crys- tals, which are of such an intense red colour as to be nearly black, and the formula of which is IrCl 3 +KCl+HO. The ammoniacal bichloride of iridium is very slightly soluble in cold water, but forms with boiling water a solution which on cooling deposits octo- hedral crystals of a deep-red colour. The colouring power of this compound is very great, as 1 part will sensibly colour 40,000 parts of water ; and it is a small quantity of this double chloride which often gives a red hue to the double chloride of platinum and am- monia. Sulphurous acid converts these double compounds into soluble double chlorides, containing protochloride of iridium IrCl, and which are much more soluble, ( 1188.) Lastly, if an oxide or chloride of iridium be treated with concen- trated aqua regia not exceeding the temperature of 110 or 120, a deep-brown solution is obtained, which contains trichloride of iri- dium IrCl 3 . This chloride does not crystallize, but also forms double chlorides with the alkaline chlorides. The solutions of iridium and its different oxides are variously co- loured, from which property the name of iridium has been derived. COMPOUNDS OF IRIDIUM WITH SULPHUR. 1192. Iridium combines directly with sulphur when the finely divided metal is heated in a current of vapour of sulphur, but it is difficult to thus obtain a perfect sulphuration of the metal. If sulf- hydric acid gas be passed through solutions of the various chlorides of iridium, brown precipitates are obtained which are sulphides cor- responding to the chlorides. The most sulphuretted compounds act the part of sulphacids with regard to the alkaline sulphides. The affinity of iridium for sulphur is sometimes applied to the prepara- tion of the metal, iridosmium being fused with a mixture of carbon- ate of soda and sulphur, when the material is acted on, and sulph- ides of iridium and osmium are formed, which are separated by means of water. The sulphides are easily attacked by chlorine, and yield chlorides which are isolated by the processes detailed in 1188. 356 PALLADIUM. PALLADIUM. EQUIVALENT = 53.3 (665.2; = 1193. Palladium is a brilliant metal, of the specific gravity 11.8, and of a white colour intermediate between silver and plati- num, and which begins to fuse at the highest temperature of a forge-fire, and melts readily before the flame of the oxyhydrogen blowpipe. It can be soldered and forged at a white-heat, and it is malleable and readily worked into thin sheets and wire. Palladium does not combine directly with oxygen, but it oxidizes when fused with potassa, or better still, with nitrate of potassa. Sulphuric acid does not act upon it, while nitric acid easily dis- solves it when assisted by heat, and aqua regia dissolves it rapidly. It combines directly with chlorine, sulphur, and silver. Palladium has within the last few years been brought into com- merce, being obtained as an accessory product in the treatment of certain gold-ores and the gold-dust of Brazil, ( 1154,) which con- sist chiefly of an alloy of gold and palladium. Palladium alloyed with ^ of silver is used by dentists, and it has been proposed to use it for the construction of the graduated scales of astronomical instru- ments, because, while it is nearly as white as silver, it is not black- ened by sulf hydric acid ; and the divisions on one of the largest instruments in the Paris observatory are drawn on palladium. COMPOUNDS OF PALLADIUM WITH OXYGEN. 1194. Two combinations of palladium with oxygen are known : a protoxide PdO, and a binoxide Pd0 2 . Anhydrous protoxide of palladium is obtained by decomposing nitrate of palladium by gentle heat, when a deep-gray, metallic powder remains, which loses all its oxygen at a higher temperature. By pouring an alkaline carbonate into a solution of protonitrate of palladium, a deep-brown, precipitate of hydrated protoxide results, which readily dissolves in dilute acids. Binoxide of palladium has not yet been obtained in an isolated form, and when caustic potassa or carbonate of potassa is added to a solution of bichloride of palladium, the brown precipitate which forms always contains alkali. Binoxide of palladium readily parts with half its oxygen at a slightly elevated temperature, and is com- pletely reduced at a higher degree of heat. SALTS FORMED BY THE PROTOXIDE OF PALLADIUM. 1195. The protosalts of palladium yield solutions of a reddish- brown colour, from which potassa throws down a brown precipitate HALOID COMPOUNDS OF PALLADIUM. 357 which dissolves in an excess of alkali, while sulf hydric acid and the alkaline sulphides give black precipitates which do not dissolve in an excess of sulfhydrate. Cyanide of mercury yields a white, slightly grayish precipitate of cyanide of palladium ; and iron or zinc precipitate palladium in the form of a black powder, which assumes a metallic lustre when burnished. Nitrate of palladium is obtained by dissolving palladium in nitric acid, but the evaporated liquid does not deposit crystals, although, if ammonia be added, a crystallizable double nitrate is formed. COMPOUNDS OF PALLADIUM WITH CHLORINE. 1196. Two chlorides of palladium, corresponding to the two oxides, are known. Protochloride of palladium PdCl is obtained by dissolving palladium in aqua regia, when a red solution is formed, yielding on evaporation deep-red crystals, which by the action of heat are decomposed and converted into metal. Proto- chloride of palladium forms double chlorides with the alkaline chlo- rides and chlorohydrate of ammonia. The double chlorides of potassium and ammonia are very slightly soluble in water and inso- luble in alcohol ; their formulse are PdCl+KCl, PdCl+NH ? ,HCl, and they form beautiful crystals ; while the double chloride of sodium, on the contrary, is deliquescent and very soluble in water. The colour of these double chlorides in small crystals is of a slightly reddish-yellow. Protochloride of palladium is converted by the action of aqua regia and moderate heat into the bichloride PdCl a , which after eva- poration under an air-pump assumes the form of a brown crystal- line mass. Bichloride of palladium, which is not very fixed, and the solutions of which are readily decomposed by heat, forms with chloride of potassium a double chloride of the formula PdCl a +KCl, which, being very slightly soluble, is precipitated in red crystalline powder, consisting of small regular octohedrons.* COMPOUND OF PALLADIUM WITH CYANOGEN. 1197. Palladium has a great affinity for cyanogen, and a cyanide of palladium is obtained in the form of a slightly-grayish white precipitate, by adding a soluble cyanide to the solution of a protosalt or of protochloride of palladium, the precipitation, how- * The combination of palladium with iodine deserves some notice, as it is of importance in analytical chemistry, being obtained in the determination of iodine. The iodine contained in any soluble iodide may be very exactly determined by precipitating it by means of nitrate or chloride of palladium, when a black fleecy deposit of iodide of palladium is formed, which does not completely settle down until after 24 hours, and which is insoluble in water, alcohol, and ether. It begins to lose its iodine at a temperature of 212, and is entirely freed from it when heated to about 580, when pure palladium remains, from the weight of which the weight of the iodine with which it was combined may be deduced. W. L. F. 358 RHODIUM. ever, being complete only when the liquid does not contain an excess of acid. Cyanide of palladium combines with the alkaline cyanides and with cyanohydrate of ammonia. A hot and saturated solution of the double cyanide of palladium and potassium deposits, on cooling, small crystalline spangles of the formula PdCy+KCy+HO ; while the same solution by slow eva- poration at the ordinary temperature yields larger crystals of the formula PdCy+KCy+3HO. EXTRACTION OF PALLADIUM. 1198. Palladium exists in small quantities in platinum-ore, and remains in the mother liquid which is obtained when a solution of platinum-ore in aqua regia is precipitated. It has already been mentioned ( 1184) that the metals which remain in this mother liquid are generally precipitated by a blade of iron ; they are then redissolved in aqua regia, and the excess of acid being driven off by evaporation, the residue is treated with water and poured into a solution of cyanide of mercury, which produces a solution of cyanide of palladium, which by the application of heat leaves metallic palla- dium. The greater proportion of palladium is obtained from the Brazil gold-dust, which is dissolved in aqua regia saturated with potassa, and then treated with a solution of cyanide of mercury, which precipitates the palladium alone. Palladium-sponge is con- verted into malleable metal by the same process as that described for platinum. RHODIUM. EQUIVALENT == 52.2 (652.5 ; = 100). 1199. Rhodium exists in small quantities in the majority of platinum-ores, and has also been found in America combined with gold. It is extracted from the metallic precipitate which is obtained by decomposing by a blade of iron the mother liquid which remains after the precipitation of the solutions of platinum-ore in aqua regia by sal-ammoniac. These metals being dissolved in aqua regia, the palladium is precipitated by cyanide of mercury, and the liquid is evaporated to dryness, after having added common salt and an excess of chlorohydric acid ; when the excess of cyanide of mercury is converted into chloride of mercury, while double chlorides are formed with the chloride of sodium. The substance, when dried, is treated with alcohol, which dissolves the double chloride of platinum and sodium as well as that of iridium and sodium ; the double chlo- ride of rhodium and sodium, which is insoluble in alcohol, alone COMPOUNDS OF KHODIUM. 359 remaining. This compound, after being purified by crystallization, is heated in a glass tube in a current of hydrogen, when metallic rhodium remains on dissolving the substance in water. Rhodium has been thus called on account of the rose colour of its solutions. It is a gray metal of the specific gravity 10.6, resembling platinum, but more difficult to solder and fuse than this latter metal. Rhodium does not oxidize in the air at the ordinary temperature, but when very finely divided readily combines with oxygen at a red-heat. The most powerful oxidizing acids, even aqua regia, do not act on the metal when pure, but it readily dissolves in aqua regia when alloyed with platinum or other metals. Potassa and nitre act on it at a red-heat, and convert it into the sesquioxide ; and bisulphate of potassa also attacks it at a red-heat, forming a double sulphate of potassa and sesquioxide of rhodium. COMPOUNDS OF KHODIUM WITH OXYGEN. 1200. The existence of two oxides of rhodium, the protoxide RhO and the sesquioxide Rh 3 3 , is admitted. The protoxide RhO is formed when very finely divided rhodium is roasted in the air at a high temperature ; while if the temperature be lower, oxides intermediate between the protoxide and sesquioxide are obtained. The sesquioxide Rh 3 3 is produced when powdered rhodium is attacked by a mixture of nitre and potassa, when, after treating the substance with water and washing the residue with a weak acid, the sesquioxide remains in the form of a black powder. This is the most important oxide of rhodium, as it combines with the acids and forms salts of which the solutions are red when concentrated, and rose-coloured when more diluted. Potassa precipitates the hydrated sesquioxide from its solutions on boiling the liquid, while ammonia throws down, when cold, a yellow precipitate, which is not deposited for some time, and which is a compound of the sesquioxide with am- monia. Sulf hydric acid and sulf hydrate of ammonia give brown precipitates. Hydrogen reduces solutions of rhodium when aided by solar light, and precipitates from them metallic rhodium ; and iron, zinc, and copper precipitate the metal in the form of a black powder. COMPOUNDS OF RHODIUM WITH CHLORINE. 1201. Two chlorides of rhodium corresponding to_ the two oxides are known, and are prepared by treating the mixture of oxides obtained by roasting rhodium in the air with chlorohydric acid, when two chlorides are formed: the protochloride RhCl, which remains in the form of an insoluble reddish powder, and the sesquichloride Rh 2 Cl 3 , which dissolves. The sesquichloride pro- duces brown solutions, and does not crystallize, but forms with 360 KUTHENIUM. the alkaline chlorides crystallizable double chlorides, of a beautiful red colour, the best method of preparing which consists in heating, in a current of chlorine, a mixture of finely divided rhodium and alkaline chloride. The double chloride of rhodium and sodium crystallizes in beau- tiful red crystals, of which the formula is Rh 2 Cl 3 + 3NaCl+18HO. COMPOUND OF RHODIUM WITH SULPHUR. 1202. Rhodium combines directly with sulphur at a red-heat, forming a sulphide which is fusible in a forge-fire. When sulf- hydrate of ammonia is poured into a solution of the double chloride of rhodium and sodium, a brown precipitate of the sulphide Rh 3 S 3 is obtained. RUTHENIUM. EQUIVALENT = 52.2 (652.5 ; = 100). 1203. A new metal, .to which the name of ruthenium has been given, has been recently found in the platiniferous sands, occurring principally in iridosmium, which sometimes contains 5 or 6 per cent, of it. In its chemical properties, ruthenium closely resembles iridium, with which it was for a long time confounded. Ruthenium is extracted from iridosmium by heating to redness in a porcelain tube, traversed by a current of moist chlorine, a mixture of finely powdered iridosmium with one-half its weight of common salt. The mass, when cooled, is dissolved in water, producing a brownish-red solution, into which a few drops of ammonia are poured after hav- ing heated it to about 120, when a brownish-red precipitate of sesquioxide of ruthenium, mixed with oxide of osmium, is formed. The precipitate is heated in a retort with nitric acid, to convert the oxide of osmium into osmic acid, which is driven off by boiling for a short time. The residue is calcined for one hour in a silver crucible, with a mixture of potassa and nitre, when the material is treated with water deprived of air by boiling, and allowed to rest for 12 hours in a bottle closely corked and wholly filled. The liquid, which is of an orange-yellow colour, is then decanted and saturated with nitric acid, when the sesquioxide of ruthenium is precipitated in a black velvetlike powder, which, by calcination in a current of hydrogen gas, yields metallic ruthenium. Ruthenium is a gray metal, of the specific gravity of 8.6, resem- bling iridium ; and it is infusible, does not consolidate at a red-heat, and is acted on with great difficulty by aqua regia. Several oxides and corresponding chlorides of ruthenium have been obtained. FOURTH PART. ORGANIC CHEMISTRY. INTRODUCTION. 1204. IN this fourth part it is intended to give a description of the substances found in organized beings, as well as the combina- tions derived from them by various chemical processes performed in the laboratory. The majority of organic compounds may be com- pared with those comprised under the head of inorganic chemistry, and, like the latter, may be crystallized by fusion, sublimation, or solution ; and can combine either with acids, or with bases, or may be decomposed into acid and into basic elements, their compounds being subject to the laws of definite proportions in the same man- ner as substances belonging to mineral chemistry. In a word, they possess no peculiar character which authorizes, in a methodic classi- fication, their separation from compounds of mineral chemistry, from which they are distinguished by their origin alone ; the sepa- ration being only admitted because it facilitates the study of organic compounds, which are generally of a complex character, and the properties of which are more readily understood after the student has become familiarized with the most frequent and simple reac- tions of mineral chemistry. There exists, however, in organized beings, a certain number of substances, the essential physical properties of which differ greatly from those just mentioned, and which constitute the organs of vege- tables and animals. They are distinguished by their insolubility in solvents, and by the peculiar forms they assume under the influence of vitality. They undergo, in organized beings, a host of trans- formations, frequently without experiencing any remarkable change in their elementary composition, and thus become fitted for the va- rious parts which they are destined to constitute in organic life. They can in no manner be made to assume a crystalline form ; and whenever they are crystallized or included in compounds subjected to the ordinary laws of definite proportions and capable of crystal- lization, it will be found that they have been completely changed, and that the new differ very materially from the original substances, although their elementary composition is frequently identical. Vo?. II. 2 P 361 362 ORGANIC CHEMISTRY. We shall call these compounds organized substances, or organized matter, to distinguish them from other substances found in living beings, and often confounded with them under the general name of organic substances or matter, which should only be considered as indicating their common origin. The latter name, however, should be applied only to substances of the organic kingdom which are not also found in the mineral kingdom. 1205. Some organic substances contain only carbon and hy- drogen ; and, while the majority of substances found in vegetables contain carbon, hydrogen, and oxygen, those forming the organs of animals consist of carbon, hydrogen, oxygen, and nitrogen. Similar quaternary compounds are found in almost all parts of vegetables, principally in the cereals, which, thence derive their property of nourishing animal life. Some organized beings also contain a greater number of simple bodies : thus, some contain sulphur, others phosphorus. Animals provided with a stony case, or shells, contain a large proportion of carbonate of lime, forming nearly the whole of their external envelop ; while the bones of vertebrated animals contain a large quantity of phosphate and a small proportion of carbonate of lime. Lastly, in all animals and vegetables, salts are found, formed by the mineral bases, combined either with mineral or organic acids, and which, in many cases, ap- pear essential to the existence and development of the organized being. The principal mineral bases found in organized beings are potassa, soda, lime, magnesia, alumina, oxides of iron and manga- nese ; while the mineral acids are carbonic, phosphoric, sulphuric', nitric, and silicic acid. In addition to the salts formed by these substances, the chlorides of potassium, sodium, calcium, and magne- sium, and more rarely their bromides and iodides, also occur. These mineral substances, with the exception of nitric acid, are found in the ashes of organized beings after their combustion. Carbon and its compounds with oxygen may be ranked among organic substances, as they are, in most" cases, extracted from them ; and with still greater reason may ammonia be included among them, as it is always prepared from organic matter. We shall not, how- ever, recur to those substances which have been considered in the preceding parts of this work. 1206. The various organic compounds may be divided into 1. Compounds which cannot be separated into several kinds of substances without evidently changing their constitution and nature, which we shall call simple proximate principles ; 2. Compounds formed of one or two proximate principles, united in definite proportions ; 3. Compounds formed by the union, in indefinite proportions, either of proximate principles, or definite compounds of these same principles. We shall give the name of species to compounds of the first two INTRODUCTION. 363 classes, while substances of the third class will be considered as mixtures of several species, which latter it is always possible to separate, either by mechanical means or chemical processes, with- out altering their nature. The name of proximate analysis is given to the mechanical or chemical operations, the objects of which are to separate the species which immediately constitute organized beings ; and elementary analysis is the operation by which the nature and proportions of the simple bodies composing these beings is determined. Element- ary analysis is generally applied to species, because the knowledge of their composition furnishes one of their most distinctive charac- teristics. PROXIMATE ANALYSIS OF' ORGANIC SUBSTANCES. 1207. The proximate analysis of organic substances is one of the most difficult problems of this branch of chemistry, because the great instability of organic matter, the facility with which it is al- tered by chemical agents, and the great diversity of its nature, do not permit the establishing of well-defined rules, such as those applied to the analysis of mineral substances. Mechanical separation by the lens and microscope affords a means of separation which sometimes succeeds ; and in some cases leviga- tion may be used, by suspending the mixture in w T ater, when the various insoluble species composing it are deposited, more or less rapidly, according to their varieties of density and shape. Neutral solvents, that is, those which exert no chemical action on the organic species to be separated, afford the most ordinary means for the isolation of the latter ; and the substances most frequently employed for the purpose are water, alcohol in various degrees of concentration, ether, and wood-spirit. As they are used sometimes cold and sometimes hot, it is important in the latter case to ascer- tain whether some of the organic species are not modified by the temperature at which the operation is being carried on. Soluble and insoluble organic substances constituting a mixture may be separated by means of neutral solvents, and the solutions, when slowly evaporated at a proper temperature, frequently deposit the species successively in the form of crystals, which can thus be iso- lated ; and, although the separation is generally incompletely effected by the first crystallization, by redissolving the crystalline deposits which have successively formed in the same solvent, as before, and recrystallizing them, the species may be separated in a state of purity. By subjecting a mixture of organic species to the successive action of various solvents, they can generally be separated into several parts, each of which is formed of a more simple mixture than the original mixture. By skilfully applying the action of neutral solv- ents, substances which do not even present great differences of solu- 364 ORGANIC CHEMISTRY. bility in the same solvent can be separated, remarkable instances of which will be mentioned when treating of the analysis of fat sub- stances. Solvents which exert a chemical action on the organic species composing the mixture, but without modifying the species so that it cannot be restored to its original state, are frequently used with success ; but their action must be limited, either to the decomposi- tion of a compound species into simple species, or to simple combi- nations of the species with the substance of the solvent ; in which case one or several of the species combine with the substance of the solvent, and form soluble compounds, the simple species of which may be separated without change. Thus, an insoluble salt, formed by an organic acid with a mineral or an organic base, may be de- composed by a solution of potassa or carbonate of potassa, so that the organic acid shall form a soluble compound with the alkalies, from which it may then be separated without change. Acid solvents are also sometimes employed, as, for example, when an insoluble organic base is combined with an organic or mineral acid, forming an insoluble salt : by treating the substance with a weak solution of chlorohydric or sulphuric acid, the base is dissolved, and may be precipitated by supersaturating the liquid by potassa or ammonia. The metallic salts are sometimes employed to effect double de- composition, in solutions obtained by treating organic mixtures by neutral or alkaline solvents, "Thus, a great number of organic acids form insoluble salts with protoxide of lead ; and by adding acetate of lead to their solutions, previously neutralized by potassa or ammonia, an insoluble salt, formed by the oxide of lead with the organic acid, is precipitated ; and the precipitate, after being well washed, is suspended in water, through which a current of sulf hy- dric acid gas is passed, when the lead is converted into insoluble sulphide, while the organic acid separates and generally dissolves in the liquid. Many organic substances, which do not change in the air in the presence of neutral solvents at the ordinary temperature, possess the property of absorbing oxygen rapidly when in contact with an alkaline liquid, in which case they are converted into acids which combine with the alkali ; and it is therefore important, when alkaline solvents are used, to determine by a preliminary experiment whether the phenomenon just mentioned will take place ; which is done by introducing a small quantity of the organic substance and the alka- line solvent into a graduated bell-glass, filled with air over mer- cury, and to observe whether the volume of air is lessened. 1208. Certain organic species are isolated by distillation, which process requires great caution ; and it is necessary to ascertain whether the product of distillation really pre-existed in the mixture, or whether it has resulted from changes effected by heat in the INTRODUCTION. 365 original substances. Distillation or sublimation must, in many cases, be effected at a temperature below that of the boiling point of substances which volatilize under the ordinary pressure of the atmosphere, because the temperature of ebullition is often sufficiently elevated to change the other organic species which exist in the mix- ture. The substances are then heated in a current of steam, when the vapours of the organic volatile species, having considerable ten- sion at the temperature of 212, are continually carried over by the aqueous vapour, and condensed with it. By this process many of the odoriferous essential oils contained in plants are separated. By applying distillation to organic substances, a mixture of seve- ral volatile species is frequently obtained, which are soluble in each other, and cannot be separated by the means of chemical combina- tion. When such species are unequally volatile, a separation may be effected by subjecting them to successive distillations and dividing the products into fractions, if not absolute, at least sufficient for the study of the properties of the species. The difficulties of such a separation increase as the difference between the boiling points is smaller ; and it is often more advantageous, instead of distilling the mixture under the ordinary pressure of the atmosphere, to boil it under a much weaker pressure, because, in that case, the ratio between their elastic forces becomes much less. We will endeavour to explain this by an example. Let us suppose a mixture of alcohol and ether, in nearly equal proportions. Alcohol alone boils at 173.3, and ether isolated at 94.5, under the pressure of 29.922 inches ; and we will admit, although the supposition is not entirely exact, that the mixture of alcohol and ether boils at 94.5. The normal tension of the va- pour of ether at this temperature is 29.922 inches, while that of alcohol is 4.055 inches, and the ratio of the two tensions is there- fore 0.136. It is evident that the first portions which pass over in distillation Avill contain much more ether than alcohol, but that this will contain, nevertheless, a considerable proportion of the latter substance, since the ratio of the two tensions is represented by 0.136. If, on the contrary, the mixture be boiled under a pressure suffi- ciently feeble for the boiling point to sink down to 32, the normal tension of alcohol at this temperature being 0.492 inches, while that of ether is 7.165 inches, the ratio between the two elastic forces is only 0.068, and consequently much more feeble than at the tempe- rature of 94.5. If, therefore, the retort containing the mixture be surrounded with ice, and the distillation effected by rarefying the air by means of an air-pump, the proportion of alcohol which will pass over in distillation at the same time with the ether will scarcely be one-half of that which distilled at the temperature of 94.5 ; and the proportion will be still less if the retort be surrounded by a refrigerating mixture of ice and common salt at 14. In fact, at this temperature, the tension of the vapour of alcohol is 0.251 2*2 366 ORGANIC CHEMISTRY. inches, while that of the vapour of ether is 4.468 inches ; and the ratio of the two elastic forces is only 0.056.* We will not devote too much time to a general indication of the principal processes employed for the analysis of organic mixtures, as in the following a large number of examples will be given, which are better adapted to illustrate the methods. ELEMENTARY ANALYSIS OF ORGANIC SUBSTANCES. 1209. Although, in the preceding parts of this work, the greater part of the processes employed in chemistry, to determine the ele- mentary composition of organic substances, have been already ex- plained, we still think it necessary to add some new details, and indicate the various precautions to be observed, according to the nature and physical properties of the organic substances to be analyzed. It has been mentioned ( 1205) that the majority of substances extracted from the vegetable kingdom were composed only of carbon, hydrogen, and oxygen, while a certain number of vegetable species and the majority of animal substances contain nitrogen in addition ; and lastly, that some organic substances contain sulphur and phos- phorus. But, by subjecting organic substances to the various reac- tions capable of being performed in the laboratory, other substances are obtained, which are not organic substances, properly so called, because they have not been directly extracted from the organic kingdom, but the study of which presents great interest. Such sub- stance, produced by chemical reactions, often contain elements which have not been met with in organic substances, properly so called, as, for example, chlorine, bromine, iodine, arsenic. Again, organic species which act the part of acids may form salts with mineral bases, while basic organic species form salts with the mineral acids. * The apparatus used for distillation under reduced pressure consists in a re- tort A (fig. 608) arranged in a small kettle containing ice or the refrigerating mix- ture. The retort is fitted to an or- dinary tubulated receiver B, the corks of which are covered with 'sealing-wax, and which is arranged in a vessel, so that it may be en- tirely covered by a refrigerating mixture of crystallized chloride of calcium and ice ; the temperature of which mixture must necessarily :.be much lower than that surround- ing the retort. To the second tu- bulure of the receiver a leaden- ig. bUo. pipe, having a stopcock r and communicating with an air-pump, is fitted. A vacuum is made until the liquid in the retort boils, when the stopcock r is closed, and the distillation is effected by means of the difference of temperature in the retort and the receiver. The distillation can be arrested at will, by allowing air to enter the apparatus through the stopcock r. INTRODUCTION. 367 Now, the study of these salts possesses great interest, because they are more easily obtained in a state of purity than the isolated or- ganic species, and their analysis furnishes very valuable elements for the determination of the composition and constitution of the species. From all this it will be seen that the chemist who devotes himself to the investigation of organic substances must frequently examine elements quite different from those which exist naturally in the substances subjected to analysis, and that the presence of such new elements sometimes obliges him to modify his ordinary pro- cesses. DETERMINATION OF CARBON AND HYDROGEN. 1210. The carbon and hydrogen of an organic compound are always determined by completely burning the substance, either in free oxygen, or by means of the oxygen contained in an easily re- ducible metallic oxide ; when the hydrogen is converted into water, which is absorbed by some highly hygroscopic substance, such as chloride of calcium or concentrated sulphuric acid, while the carbon passes into the state of carbonic acid, which combines with a known quantity of caustic potassa ; the increase of weight of the potassa representing the weight of carbonic acid formed. Oxide of copper CuO, which is generally used to effect the com- bustion, may be prepared in several ways, and in each case presents some special properties on which it is proper to dwell. One of the most simple processes consists in roasting copper turnings at a red-heat in the muffle of a cupelling furnace, (fig. 594,) when, the surface of the copper becoming oxidized, the whole is re- moved afteW few hours' roasting, and rubbed in a mortar to detach the oxide, or to pulverize those sheets of copper which are entirely converted into oxide. The substance is passed over a coarse sieve to separate the sheets of metal, which are again roasted. A very coarse-grained oxide is thus obtained, which attracts but slightly the moisture of the air. A finer oxide, the hygrometric power of which is equally feeble, is prepared by substituting for the copper turn- ings, copper precipitated chemically, or produced by decomposing acetate of copper by heat. An oxide of copper in fine powder, and more easily reducible than that prepared by roasting, may be obtained by dissolving the metal in nitric acid, evaporating the solution to dryness, and cal- cining for an hour, at a dull red-heat, the subnitrate of copper which remains after evaporation. The oxide, which, when ground, pre- sents the appearance of a fine, velvet-black powder, is well adapted to the combustion of organic substances, but rapidly attracts the moisture of the air, and, on this account, requires great caution in analysis, if the amount of hydrogen is to be accurately determined. The oxide of copper produced by the decomposition of the car- bonate by heat is also well adapted to the combustion of organic I 368 ORGANIC CHEMISTRY. substances, but is at least as hygrometric as that prepared bj calcining the nitrate ; which property, however, may be lessened by heating it longer and at a higher temperature, when it again becomes more compact, and is reduced with greater difficulty by combustible substances. Chromate of lead PbO,O0 3 is sometimes substituted for oxide of copper, because organic substances burn readily in contact with the salt ; and, as the chromate fuses at quite a low temperature, the heat is raised toward the close of the combustion, so as to cause its fusion ; by which means the last particles of carbon which may remain after the decomposition of the organic matter are forced into contact with the burning substance, and their combustion is necessarily complete. Chromate of lead possesses another advan- tage in being less hygrometric than oxide of copper, so that the determination of hydrogen may be made more accurately. The chromate of lead should be previously fused in an earthen crucible, rolled into a plate on a sheet of copper, reduced to pcfwder, and im- mediately preserved in a well-stoppered bottle. Before using oxide of copper for combustion, it' is always heated^ to redness in an earthen crucible, in order to destroy the organic dust witlf which it may be mixed and drive off its moisture ; an& the crucible, when removed from the fire, is placed under a bell- glass containing some pieces of quicklime, and allowed to cool. It is frequently used before it is entirely cooled, as there is then less fear of its attracting moisture. '1211. As organic matter burns under conditions differing slightly according to the nature of the substance, we^iall pay at- tention to several cases. We will suppose, in the first place, that the organic substance contains only carbon, hydrogen, and oxygen, and will also examine several points, according to the state of the substance and its greater or less volatility, assuming the substance to be solid, non-volatile, and not decomposable below 212. The combustion is effected in a glass tube a>, (fig. 609,) made a c as strong as possible, and of an (i = ^^/ internal diameter of about 15 Fig. 609. millimetres, being \ metre in length, while one of its ends is drawn out to a point c and turned upward. The other end a, which remains open, has its edges slightly rounded, so as not to injure the cork fitted into it ; which latter should be previously dried in a stove at the temperature of 212, to prevent it from giving off moisture. The glass tube intended for analysis, and which we shall call the combustion-tube, should be thoroughly cleaned by wiping it out with tissue-paper, and then heated throughout its whole length, while a tube open at both ends, and fitted to the nozzle of a bellows, is in- troduced into it, when the current of air thus established removes INTRODUCTION. 369 all moisture ; after which the tube must be closed with a cork. As the combustion-tube may still contain some organic dust, a small quantity of hot oxide of copper, recently calcined, is introduced into it, and, after having shaken the tube, the oxide is set aside. The organic matter intended for analysis having been previously finely powdered, the portion to be subjected to combustion, which varies in weight from 8.300 gm. to 0.500 gm., is very accurately weighed. Larger quantities are sometimes taken when the substance contains but little carbon or hydrogen and great exactness is re- quired in the analysis. It is to be weighed in a small glass tube closed at one end ; and if the matter is hygroscopic, the open end of the tube should be closed with a ground-glass stopper. The mixture of the organic matter with oxide, of copper is made in a mortar of glazed porcelain or glass, which has previously been perfectly dried by being heated in a stove ; but it is better to use a metallic mortar, (fig. 610,) not very deep, and highly polished on the inside, because it is more easily heated, and be- cause metal does not attract moisture like glass. The inside of the mortar should be cleaned, before using it, with a small quantity of oxide of copper, Fig. 610. w hich is afterward rejected. The quantity of oxide of copper to be mixed with the organic matter, and which should be such as to occupy a length of 1 or 2 decimetres in the combus- tion-tube, bfcing first placed in the mortar, the organic matter con- tained in the small tube in which it has been weighed is added ; while, in order that none may adhere to its sides, a small quantity of oxide of copper is passed through the small tube several times and then poured into the mortar. The substance is ground rapidly with the pestle, in order to make a uniform mixture, which is immediately introduced into the combustion-tube, at the bottom of which a small column of pure oxide, of 3 or 4 centimetres in length, has been pre- viously deposited ; for which purpose the substance in the -mortar is dipped up with the tube, or first poured on a copper spoon C, (fig. 611,) and thence, by a copper funnel, into the combustion-tube. A small quantity of oxide of cop- Fig. 611. p er k e i n g rubbed in the mortar to remove any par- ticles of the mixture which may adhere, and then dropped into the tube, the latter is then filled with pure oxide of copper.* * As Mitcherlich's old method of filling combustion-tubes, which for a long time was rejected by the majority of chemists, seems now again to be brought into use, it will be well to mention it. The organic substance is contained in a long tube, the external diameter of which is sufficiently small as to allow of its being inserted into the combustion-tube ; and the oxide of copper is used, after being heated to a dull-red, while it is still of a temperature of about 212, at which degree of heat the organic substance is supposed not to decompose. The absorption of moisture by the oxide of copper is thus prevented during the filling, which is done as fol- lows : Supposing the combustion-tube to be 16 inches long, the lower 2 inches would- be filled with coarse oxide, and then a column of fine oxide would be in- 24 * 370 ORGANIC CHEMISTRY. If the oxide of copper employed is very finely powdered, there is danger that the column will not be sufficiently porous to allow an easy disengagement of gas ; and a small canal must therefore be made in the upper part of the tube throughout its whole length, which is easily effected by carefully dropping the tube lengthwise on a smooth table, and perhaps applying a few slight shocks at the ends. As the oxide of copper during this manipulation has almost always attracted an appreciable quantity of moisture, this must be removed if the exact amount of hydrogen in the substance is to be determined; which is effected by placing the combustion-tube in a tin vessel V (fig. 612) filled with hot water, and made to communicate with a small air-pump P, to the second tubulure of which is fit- ted a tube T, filled with pumice-stone soaked in sul- phuric acid. By working the pump se- Fig. 612. Ver , al J in ? eS > and each time allowing the air to enter which was dried by passing through the tube T, the hygroscopic moisture is completely removed ; but the process can only be employed when the organic substance does not give off sensibly any vapour, in vacuo, at a temperature of 212, and when it cannot, under these circumstances, either give off water or decompose. In any other case the process of desiccation just mentioned could not be employed, and recourse must be taken to the use of coarser and more highly calcined oxide of copper, while serted, occupying about 6 inches ; after which the organic substance is introduced, by inserting the tube containing it in the combustion-tube, and allowing the desired quantity to fall out; after which the small tube is corked, and subsequently weighed to ascertain the amount of substance extracted. The combustion-tube is then filled with another column of 6 inches of fine oxide of copper, and the or- ganic substance is mixed up thoroughly, by means of the spirally-twisted end of a long and clean copper wire, with the columns of oxide below and beneath it; which is easily done by successively screwing the wire down to the layer of coarse oxide, and working it backward and forward for about 5 minutes ; the tube being held with a cloth, because the oxide has the temperature of boiling water. Another inch of pure fine oxide is then added, and the tube is corked. There will then be contained in the tube, 1st, two inches of coarse oxide; 2dly, twelve inches of an intimate mixture of fine oxide and the organic substance ; 3dly, one inch of fine oxide ; and, lastly, a free space of one inch, to allow of rendering the whole CO' lumn porous by shaking. -^W. L. F. ' INTRODUCTION. 371 the mixture must be made in the mortar as rapidly as possible, taking care to- hold the breath. The combustion-tube, after being charged, is enveloped with a thin ribbon of brass, previously annealed, and fastened with -^-- jnYmWrrTaTTT copper-wire, as represented in Fi S- 613 - fig. 613, after which the tube, thus protected, may be heated to a very high temperature without danger. The combustion-tube being placed on a long sheet-iron furnace, Fig. 614. (fig. 614,) the appa- ratus in- tended to absorb wa- ter is fitted to it by means of a very well dried cork. The apparatus con- sists of a tube filled with pieces of chloride of calcium, arranged as in fig. 615, while plugs of cotton, placed at a and 5, pre- Fi S- 615 - vent the small particles of chlo- ride from escaping from the tube. The cork a is covered with sealing-wax, in order that its weight may not change by absorbing or exhaling moisture, if any existed in the air. A U-tube, filled with pumice-stone soaked in concentrated sulphuric acid, is some- times substituted for the tube containing chloride of calcium. The carbonic acid formed by combustion condenses in a concen- trated solution of caustic potassa, marking about 45 Baume', and placed in the apparatus B (fig. 614) described on page 324, vol. i., which is fitted, by means of a caoutchouc connecter, to a tube in- tended to condense the water. As it might be feared that the solution of potassa, notwithstanding its concentration, might part with a small quantity of water to the very dry gases which traverse it, a small U-shaped tube C, containing pieces of caustic potassa, which absorb at the same time the vapour of water and the small quantity of carbonic acid which escapes absorption in the apparatus B, is affixed to the latter. Lastly, a bottle V, the cork of which has a stopcock r, is fitted to this apparatus, thus establishing or interrupting at will commu- nication with the outer air. To the bottle is permanently fitted a U-tube filled with sulphuric pumice-stone* intended to prevent the vapour of water from passing from the bottle V into the tube C. (The U-tube is not represented in tile figure.) 372 ORGANIC CHEMISTRY. The drying-tube A and the whole of the apparatus B and C hav- ing been previously exactly weighed, their increase of weight during the experiment gives respectively the quantity of water and of car- bonic acid formed by combustion. When the apparatus is arranged, the anterior portion a F of the combustion-tube, which contains only pure oxide of copper, is sur- rounded by burning coals ; and in order that the heat may not communicate by radiation to the parts of the tube containing the mixture of oxide and organic matter, a double screen F, made of sheet-iron, and represented in fig. 616, is interposed. When the anterior portion of the tube isi heated to redness, the coals are gradually moved toward the part containing the mixture of oxide and organic matter, the rapidity of moving Fig. 616. the coals being guided by the evolution of gas which is ob- served rising in bubbles through the potash apparatus, and which should never follow so rapidly as not to allow the counting the bubbles which traverse the apparatus B. This is continued until the tube is completely surrounded with coals, when the combustion is terminated, and the evolution of the gases ceases, and very soon the potassa ascends into the globe which communicates with the drying-tube, in consequence of the absorption of the carbonic acid contained in this globe. The globe apparatus is then moved from the position of fig. 617 to that of fig. 618, and if the globes are of suitable dimensions, the solution of potassa will certainly ascend to the drying-tube, ( 260,) and very soon, the absorption _ of carbonic acid continuing, bubbles Fig. 617. Fig^^is! ^ a "" re - en ter the apparatus, passing through the solution of potassa. The coals surrounding the end c of the combustion-tube are then re- moved, and, when the latter is sufficiently cooled, its point is broken with a pincers, (fig. 619 ;) when the gas in the apparatus being rarefied, the outer air enters through the broken point and establishes the equilibrium. A tube S, (fig. 620,) containing pieces of caustic potassa, and furnished with a caoutchouc tube, which it is sufficient to press against the combustion-tube to render the opening tight, is then adapted lg ' 6 ' to the point ; after which the stopcock r of the bottle V is closed, and by opening the stopcock r' the water in this bottle is allowed slowly to escape. The atmo- spheric air, freed from moisture and carbonic acid by its passage through *^ e tu ^ e ^' removes the small quan- tities of vapour of water and carbonic Fig. 620. acid w T hich still remained, and con- veys them into the apparatus A, B, C, where they are condensed. INTRODUCTION. 373 When about 1 litre of water has escaped, the apparatus is taken apart, weighed, and the carbonic acid and water formed during com- bustion exactly ascertained, whence the quantity of carbon and hy- drogen contained in the organic matter can be calculated. As we have supposed the substance subjected to analysis to contain only carbon, hydrogen, and oxygen, the oxygen may be obtained differ- entially, that is, by subtracting the weight of hydrogen and carbon united, from that of the substance subjected to analysis. It frequently happens that it is difficult to completely burn or- ganic substances, either because they cannot be intimately mixed with the oxide of copper, or because, by being decomposed by heat, they leave a charcoal of difficult combustion, which is sometimes de- posited in the upper portions of the combustion-tube, out of contact of the oxide of copper. In this case, it becomes necessary to termi- nate the combustion in a current of oxygen ; for which purpose a mixture of 2 or 3 gm. of chlorate of potassa, coarsely powdered, and 15 or 20 gm. of oxide of copper, is introduced into the bottom of the combustion-tube, while upon this is placed a column of 3 or 4 centimetres of pure oxide, then the mixture of oxide of copper and the organic substance, and lastly the tube, is filled with pure oxide. The apparatus is arranged as has been described. When the organic matter has been completely burned, and the hot coals surround the tube, even as far as the extreme portion which contains the chlorate of potassa, some coals are carefully moved toward this end, in order to disengage oxygen. The first portions of the gas are absorbed by the copper reduced by combustion, and it is only after the entire oxi- dation of this metal that free oxygen begins to pass through the tube, and care must be taken that its evolution be not too rapid. The organic matter is necessarily entirely burned in the atmosphere of oxygen, and the carbonic acid produced is carried by the current of oxygen into the absorbing apparatus, which renders the aspirator useless. The chlorate of potassa should have been previously fused, in order to free it from organic substances and moisture. In this method of operating, it may be feared that the chlorate, by contact with the oxide of copper, may give off a small quantity of chlorine which is not completely retained in the combustion-tube ; which difficulty, however, is remedied by using a longer combustion-tube, and placing, in front of the oxide of copper, a length of 8 or 10 centimetres of litharge, which, at a red-heat, retains the whole of the chlorine. Sometimes the oxygen is prepared in a small separate retort, which is made to connect with the small end of the tube, instead of evolving oxygen by means of the chlorate of potassa placed in the combustion-tube itself. Although the majority of organic substances will burn completely by contact with oxide of copper alone, it is always prudent to per- form one, at least, of the combustions with the addition of chlorate VOL. II. 2 G 874 ORGANIC CHEMISTRY. of potassa, in order to ascertain whether the amount of carbon found has not been too small in the preceding analyses. 1212. If the substance to be analyzed is liquid and non-volatile, as, for example, a fixed oil, it is weighed in a small tube, closed at one end, and introduced into the combustion-tube, after having poured into the latter a column of oxide of copper of 4 or 5 centi- metres in height ; after which the tube is inclined so as to spread the oil over a certain extent of its sides, and then entirely filled with oxide of copper. It frequently happens that complete combus- tion is not effected by the oxide of copper alone, and must be ter- minated in a current of oxygen. Greasy and easily fusible substances should not be triturated with the oxide of copper, because some particles might adhere to the mor- tar and pestle ; but a suitable quantity of the material should, in this case, rather be melted in a small glass boat, made of a piece of tube divided longitudinally, and introduced, after being weighed, into the tube, at the bottom of which the oxide of copper is placed. By heating that portion of the tube which contains the boat, the grease melts, and flows over a certain extent of the tube, which is then to be filled with oxide of copper. It is, in this case, equally prudent to terminate the combustion in a current of oxygen. 1213. Volatile liquid substances are weighed in glass bulbs (fig. 621) hermetically sealed, the manner of making which has ^^^ been described, ( 699,) and the manner of ~** s ^=s^~ filling them in 269. It is essential not Fig. 621. ^0 | )r i n g the bubbles in contact with the hot oxide of copper after they have been opened, as vapours affecting the accuracy of the analysis would infallibly be produced. Two tubes of nearly the same capacity are used, and one of them being filled with recently calcined and still hot oxide of copper, is closed, and allowed to cool completely ; while into the second tube, which is to serve as a combustion-tube, a column of 4 or 5 centimetres of oxide of copper is introduced, and afterward the bubbles are inserted, of which one of the points is broken ; and, lastly, the second tube is filled with the oxide of copper which has been allowed to cool in the first, and is, consequently, free from moisture. It is better, in such analyses, to use coarse oxide of copper, mixed with roasted turnings, because this oxide, even when it completely fills the sec- tion of the tube, is sufficiently porous to afford an easy passage for gases and vapours. The absorbing apparatus is arranged as usual, but the operation is conducted as rapidly as possible, in order that the vapours of the volatile substance may only have time to reach the anterior part of the combustion-tube, which is heated to redness, while the part containing the bubbles is protected by several screens. When the oxide of copper is red for a length of several decimetres, some coals are carefully moved toward the part containing the bubbles, while the distillation of the substance is INTRODUCTION. 375 regulated by the position of the coals. The vapours burn while traversing the oxide of copper ; and when combustion ceases, the tube is surrounded with burning coals, and heated throughout its whole length, after which the experiment is terminated as usual. If the substance to be analyzed is very volatile if it boils, for example, at a temperature below 122 under the ordinary pressure of the atmosphere it is difficult to obtain an exact analysis by the process just stated. The vapours of the substance cannot be pre- vented from penetrating the anterior part of the combustion-tube, before this part is heated to redness, and they thus escape combus- tion and render the analysis inaccurate. The experiment is then arranged in the following manner : The combustion-tube is drawn out at its posterior portion, so as to form a tubulure and above it; a Fig> ! 62 8. copper, of five or six cen- timetres in length, after- ward the mixture cd of the organic substance with oxide of copper, and lastly a length de of 0.2 m. of pure oxide of copper. Over the whole is superimposed a column ef of 0.2 m. of metallic copper, prepared from copper turnings previously roasted in the air to oxidize their surface, and then reduced in a current of hydrogen. The tube being arranged on a long sheet-iron furnace, (fig. 629,) a glass tube, which is made to communicate with the tubulure of a small air-pump P, is fitted to its orifice by means of a cork, while to the second tubulure d of the pump a glass tube def is fastened, of which the vertical leg ef is about 0.8 m. in length, and the curved extremity of which dips into the small mercurial bottle E. In the first place, the air must be completely removed from the apparatus, for which purpose as perfect a vacuum as possible is made with the pump, and the stopcock s is closed, leaving open those at r, r f . After a few moments it is ascertained whether the INTRODUCTION. 381 Apparatus remains empty, in which case the column of mercury in the tube ef should remain absolutely stationary. Some coals are Fig. 629. brought near the end of the tube containing the bicarbonate of soda, when the carbonic acid disengaged drives the air from the tube ; and as soon as the gas begins to be evolved under the mer- cury, the anterior part of the tube, which contains the metallic mercury and a length of some centimetres of pure oxide of copper, is surrounded with hot coals, and it is then ascertained whether the gas which is evolved be pure carbonic acid. For this purpose it is sufficient to collect the gas in a small bell-glass filled with mercury, at the top of which a solution of potassa has been placed ; and if the gas formed is pure carbonic acid, its bubbles will be im- mediately dissolved. When this result is obtained, the coals which effected the decomposition of the bicarbonate of soda are removed, and above the orifice of the disengaging-tube def a large bell-glass C is placed, filled with mercury, and to the top of which fifty or sixty cubic centimetres of a concentrated solution of potassa have been passed. The coals are gradually moved toward the part con- taining the organic matter, conducting the operation as in the de- termination of carbon and hydrogen. Carbonic acid, vapour of water, nitrogen and its oxides, are formed; but the oxides of nitrogen are restored to the state of free nitrogen while passing 382 ORGANIC CHEMISTRY. through the portion of the tube which contains metallic copper, so that only a mixture of carbonic acid and nitrogen reaches the bell- glass, in which the carbonic acid is dissolved by the potassa, while the nitrogen remains free. When the combustion is terminated, the column of pure oxide of copper which separates the carbonate of soda from the original mixture of oxide and organic matter is surrounded with coals ; and lastly, by again heating the carbonate, a new evolution of carbonic acid is produced, which completely drives the gaseous products of combustion into the bell-glass C. It now only remains to measure exactly the nitrogen gas col- lected, for which purpose tfye bell-glass is carried over a large vessel filled with water, when, by opening the orifice of the former, the mercury contained in it falls to the bottom of the vessel, and is replaced by water. The gas is poured into a smaller bell-glass, divided into cubic centimetres, and held in a vertical direction by means of a stand, while the water on the inside and outside of the bell-glass is brought to the same level. When the gas has attained an equilibrium of temperature, its volume V, the temperature , and the height H of the barometer are marked, and the weight of nitrogen gas attained is therefore 0.0012562 gm. V L_ . s=L 1 + 0.00367. t 760 It is important to ascertain whether the gas contains no deutoxide of nitrogen ; to which effect a few bubbles of air are introduced into the bell-glass, when the gas instantly turns red if it contains any appreciable quantity of deutoxide. We shall subsequently point out the means of measuring nitrogen more exactly, and of accurately ascertaining its purity. When the nitrous substance is volatile, the length of the column of pure oxide of copper between the mixture of the oxide with the organic matter, and the bicarbonate of soda, must be increased; and before commencing the combustion, both the anterior part of the tube and the column of pure oxide must be heated to redness. Instead of placing at the bottom of the tube the bicarbonate of soda, intended to disengage carbonic acid, this end of the tube may be terminated by a fine tubulure, which is made to communi- cate, by means of caoutchouc, with an apparatus for disengaging carbonic acid, in which case the exhaustion by the air-pump may be omitted, because the evolution of carbonic acid is prolonged until all the air is driven out. When the combustion is terminated, the cur- rent of carbonic acid is re-established, in order to drive all the nitrogen into the bell-glass. 1218, Nitrogen is also dosed by another process, not of so general application as the one just described, because it is not adapted to the nitrates, but which yields, in the majority of cases, exact results. This process is founded on the fact that nitrous substances, with the exception of those containing nitre or nitrous INTRODUCTION. 383 acid, when heated in contact with hydrated alkalies, give off their nitrogen in the state of ammonia, which can be collected in an acid, and determined in the state of double chloride of platinum and ammonium. In order to effect the decomposition of the nitrous substance, a mixture of lime and hydrated caustic soda is used, which is prepared by slaking quicklime in a solution .of caustic soda containing a quantity of soda equal to nearly half of that of the lime employed, after which the substance is successively ground, dried, calcined in an earthen crucible, again pulverized, and then preserved in a close bottle. We shall call it, for the sake of short- ness, soda-lime. An accurately weighed quantity of the organic matter is mixed with a certain quantity of soda lime, and placed at the bottom of a glass tube dbc (fig. 630) resembling the tubes used for the com- bustion of organic substan- ces by the oxide of copper, and tube is then filled with pure soda lime, while the kulb a PP aratus A--) contain- ing concentrated chlorohy- dric acid, is fitted to the orifice of the tube. The tube is gradually surrounded by hot coals, as in the ordinary combustions of organic substances, the ammonia produced being dissolved in the chloro- hydric acid. When the decomposition is effected, the point of the combustion-tube is broken, and, by blowing through the tube e of the bulb apparatus, the ammonia still remaining in the tube is driven into the chlorohydric acid. The apparatus A is then re- moved, the acid it contains poured into a porcelain capsule, and the apparatus washed several times with a mixture of two parts of alcohol and one of ether, which is then added to the capsule, into which an excess of bichloride of platinum is then introduced, to precipitate the ammonia as double chloride of platinum and am- monium. The precipitate is collected on a small filter, washed with a mixture of alcohol and ether, and weighed after drying : one gramme of double chloride of platinum and ammonium contains 0.06349 gm. of nitrogen. This process of decomposition may be modified so as to obtain a more rapid, and yet very exact analysis, by placing in the bulb apparatus ten cubic centimetres of a standard solution of sulphuric acid, obtained by mixing 61.250 gm. of monohydrated sulphuric acid with one litre of water ; so that 100 cubic centimetres of the liquid will saturate 2.12 gm. of ammonia, corresponding to 1.75 gm. of nitrogen. The decomposition of the nitrous substance is effected in the usual way, and the ammonia dissolves in the sulphuric acid and weakens its standard. If, therefore, the new strength of the liquid be ascertained after the operation, and the strength of the original acid subtracted from it, a difference corresponding to the quantity 384 ORGANIC CHEMISTRY. of ammonia absorbed, and from which the latter may be deduced by a very simple calculation, is obtained. The standard of the acid liquid is determined by means of a solution of saccharate of lime, that is, a solution of caustic lime in sugar and water, which dissolves a much larger proportion of lime than pure water ; and the solution may be kept unchanged in well- stoppered bottles. The first step is to ascertain the number of cubic centimetres of the alkaline solution necessary to exactly saturate 10 cubic centimetres of the normal acid solution ; for which pur- pose the 10 cubic centimetres of normal acid solution are poured into a beaker containing a small quantity of tincture of litmus ; and then the solution of saccharate of lime is added by means of an alkalimeter, until the liquid turns blue, marking the number N of divisions added. In order to be very accurate, the solution of lime must be sufficiently diluted for the saturation to require about 100 divisions of the liquid. The 10 cubic centimetres of the acid solu- tion, which have absorbed the ammonia disengaged by the decom- position of the nitrous substance, are acted on exactly in the same manner. Let us suppose that n represents the number of divisions of saccharate of lime which have effected the saturation J ; then will 0.212 gm. represent the quantity of ammonia absorbed, and ; 0.175 gm. the corresponding quantity of nitrogen.* * Bunsen has recently introduced a new method for determining nitrogen, which, on account of its extreme exactness, especially when the substance is very nitrogenous, deserves to be described. About 5 centigrammes of the substance, without being exactly weighed, are inti- mately mixed with about 5 grammes of fine oxide of copper, and a small quantity of reduced copper filings, and introduced into a very strong glass tube, difficult of fusion, of about 5 inches in length and f inches internal diameter, one end of which, having previously been drawn out, is now connected with an air-pump, after the other end has been sealed, and the air is totally exhausted from the tube ; after which the other end is also hermetically sealed, and both points are strengthened in the flame by thickening the glass. The tube thus prepared is packed with plaster in a strong iron box, or coffin, the lid of which is well se- cured, and the whole is then exposed to a strong white-heat for several hours ; when the organic substance in the tube is entirely converted into carbonic acid, water, and free nitrogen. After cooling, the tube is taken out of the iron box and brought under a graduated cylinder filled with mercury, in a mercury- trough, where one end of the tube is broken off, and the gases, consisting only of carbonic acid and nitrogen, are allowed to pass up into the cylinder. The exact volume of the two gases being now ascertained, and reduced to the cor- rected volume at 32 and 30 inches pressure, the carbonic acid is removed by absorbing it with a bullet of caustic potassa, fixed to the end of a platinum wire, and thus introduced into the gases through the column of mecury. After all the carbonic acid is absorbed, which is the case when a diminution of volume no longer ensues, the exact volume is again ascertained and reduced to 32 and 30 inches, when the difference will give the carbonic acid, while the gas remaining in the cylinder, and measured, is pure nitrogen. The ratio of the nitrogen to the carbonic acid, and consequently to the carbon in the organic substance, being thus obtained, and the carbon being previously determined in the usual manner by combustion, the percentage of nitrogen may easily be calculated. W. L. F, INTRODUCTION. 385 DETERMINATION OF SULPHUR. 1219. The determination of the sulphur contained in organic substances is frequently a matter of great difficulty. Some of these substances are destroyed by contact with concentrated and boiling nitric acid, while the sulphur is converted into sulphuric acid, which is precipitated by the chloride of barium ; but as many organic sub- stances resist the action of nitric acid, the sulphur cannot always in this manner be converted into sulphuric acid. When the organic matter is not volatile, it is mixed with 20 or 25 times its weight of a mixture of nitre and carbonate of soda, and the mixture is thrown, by small quantities at a time, into a platinum crucible heated to redness by an alcohol-lamp. The alkaline sub- stance is then dissolved in water, supersaturated by chlorohydric acid, and the sulphuric acid precipitated by chloride of barium. If the organic substance is volatile these processes are inapplicable, and the operation is then conducted as follows, by a method which suits all cases: The organic matter is subjected to combustion with oxide of copper, as in the determination of carbon and hydro- gen, with the exception that the combustion-tube is provided only with the bulb apparatus (fig. 631) containing a solution of caustic potassa. The greater part of the sulphur is converted into sulphuric and sulphurous acid, which dissolve in the potassa, while a portion of the sulphur, nevertheless, remains in the combus- tion-tube in the state of sulphide and sulphate of copper. The tube, after being allowed to cool, is broken, and the pieces of glass and the oxide are thrown into a flask, where they are boiled with a weak solution of caustic potassa, which completely removes the sulphur and sulphuric acid. The liquid is filtered, and the potassa in the bulb apparatus is added to the filtrate, which is then boiled, and treated with a current of chlorine, which transforms all the sulphur into sulphuric acid. The solution is supersaturated by chlorohydric acid, and the sulphuric acid precipitated by chloride of barium. DETERMINATION OF PHOSPHORUS. 1220. When the phosphuretted organic matter is not volatile, it is mixed with 20 or 25 times its weight of a mixture of carbonate of soda and nitre, and the mixture is thrown, by small portions, into a heated platinum crucible, where the phosphorus passes into the phosphate of soda. The alkaline substance is dissolved in water, saturated with chlorohydric acid, and then 1 gramme of pure iron dissolved in aqua regia is added to the solution. Lastly, the ses- quioxide of iron combined with phosphoric acid is precipitated by an excess of ammonia ; and by subtracting from the weight of this precipitate the weight of the sesquioxide of iron produced by 1 gm. VoL.II.-2H 25 386 ORGANIC CHEMISTRY. of pure iron, the weight of the phosphoric acid is obtained, whence that of the phosphorus may be deduced. If the substance is volatile, it is first decomposed by carbonate of soda in a combustion-tube, and then dissolved in water, the analysis being completed as in the preceding case. DETERMINATION OF CHLORINE, BROMINE, AND IODINE. 1221. No organic substances have as yet been found in nature containing chlorine, bromine, or iodine, but a great number of them have been artificially produced in the laboratory. The determina- tion of these elements is very easily made by heating the organic matter in a combustion-tube, in contact with quicklime, obtained by slaking ordinary quicklime, washing it with water to remove chlorides arising from the ashes of the combustible with which the limestone was originally burned, and then heating it to redness in order to expel the water from the hydrated lime. The lime thus prepared is preserved in a ground-stoppered bottle. If the organic substance is solid and not volatile, it is mixed with a certain quantity of quicklime, and the mixture is introduced into the combustion-tube which is to be filled with pure lime ; but if the substance is liquid and volatile, it is weighed in the glass bubbles before mentioned, which are dropped, after breaking their point, to the bottom of the tube, which is afterward filled with lime. The decomposition of the substance by heat should be effected with the same precautions as combustion by the oxide of copper. The chlorine, bromine, or iodine remain in the tube in the state of chlo- ride, bromide, or iodide of calcium. At the close of the operation, the lime, together with the fragments of the tube, is dropped into a flask, where it is treated with weak nitric acid until the lime is en- tirely dissolved. The liquid is then filtered, and precipitated by nitrate of silver ; the process indicated in 1131 being followed in order to collect and wash the chloride of silver. The determination of iodine is, however, rather more difficult, as a portion of this substance often passes into the state of iodic acid, which, however, is destroyed by passing a current of sulphurous acid through the liquid at a moderate temperature, after having added nitrate of silver to it. DETERMINATION OF OXYGEN. 1222. The oxygen contained in organic substances is always determined differentially, as, hitherto, a suitable process of direct determination has not been discovered. It will hence be seen how important it is to ascertain, with the greatest care, the nature of the elements composing the organic substance ; for if a single element escapes the experimenter, the analysis is inaccurate, not only on account of the omission of the element which was overlooked, but INTRODUCTION. 387 also because the weight of the elementary substance neglected is computed as oxygen. ESTABLISHMENT OF THE CHEMICAL FORMULA OF AN ORGANIC SUBSTANCE. 1223. The elementary analysis of an organic substance is not alone sufficient to establish its chemical formula, because it indicates only the ratios which exist between the weight of the elements which compose it ; and as an infinite number of formulae, the multiples of each other, will all satisfy the ratios given by analysis, the question is, which of these formulae to choose. By studying the various com- binations which the organic substance can form with mineral sub- stances, and the new organic compounds to which they give rise when subjected to the various processes of the laboratory, the chemist can generally collect facts from which a formula may be deduced ; and it is only when the substance has been studied under all its aspects, and in the case that it forms a great number of com- pounds, that its formula, and, consequently, its chemical equivalent, presents any degree of certainty. The numerous changes which, in latter years, the formulae of organic compounds have undergone will therefore not appear surprising, being occasioned by the dis- covery of new compounds, or new chemical reactions, which deprive the formulae adopted of the character of probability they had ac- quired from the facts previously known. As it is impossible to advance any general rules for the establish- ment of the formula of an organic compound, we shall only cite a few examples, to show the spirit which governs such researches. We shall distinguish three cases : 1st, that in which the organic substance is acid ; 2dly, that in which it possesses basic properties ; and 3dly, that in which the organic substance is neutral. CASE IN WHICH THE ORGANIC SUBSTANCE IS ACID. 1224. As the first example, we shall take acetic acid, which contains only carbon, hydrogen, and oxygen. At its maximum point of concentration, acetic acid is a colourless and volatile liquid, which, by combustion with oxide of copper, yields the following composition :* Hydrogen 6.67 Carbon 40.00 Oxygen 53.33 100.00 Dividing the weight of each of these elements by its equivalent, the quotients will necessarily be to each other as the equivalent * In order to render our arguments more simple, we shall always suppose that the results of the direct analyses are scrupulously exact. 388 ORGANIC CHEMISTRY. numbers of the simple elements which enter into the compound, and we thus obtain : For hydrogen = 6.67 carbon ^ = 6.6T " oxygen ^ = 6.67 These quotients being equal, we shall conclude that concen- trated acetic acid contains equal numbers of each of the three elements which compose it, and the most simple formula which can represent the acid is therefore CHO ; while it is evident that the formulae C a H 3 2 , C 3 H 3 3 , C 4 H 4 4 , C 5 H 5 5 represent equally the re- sults of the analysis. On the other hand, we have seen that the greater part of the mineral acids, when brought to their maximum of concentration without any essential change in their chemical pro- perties, are compounds of the anhydrous acid with one or several equivalents of water, which can be replaced by a corresponding num- ber of equivalents of a base, and it must therefore be ascertained whether this is the case also with acetic acid. Moreover, we have seen, in the case of the mineral acids, that the knowledge of the composition of a salt formed by the acid and a mineral base of which the chemical equivalent had been previously ascertained, fre- quently gives the equivalent of the acid itself, and is sufficient to establish its formula. However, the example of phosphoric acid has shown that the same base frequently forms several salts with the same acid, and that it is not sufficient, to establish the formula of the acid, to determine the composition of one of these salts, be- cause the formula would vary with the salt selected. It therefore becomes necessary to determine the composition of all the salts, either in the crystallized state, or after having dried them as much as possible, always avoiding such a change in their chemical consti- tution that the dried salt, when redissolved in water, will not pro- duce the original salt by crystallization. The study of these va- rious compounds furnishes a clue as to whether the salt should be regarded as monobasic, bibasic, tribasic, &c., and thus give the ele- ments necessary to establish its formula. The same method must be observed in establishing the formulae of organic acids ; and we thereupon proceed to apply it to acetic acid. Protoxide of silver is distinguished among mineral bases by the property of forming immediately anhydrous salts, which are in most cases easily obtained in a state of purity, being generally inso- luble, or nearly so ; for which reasons salts of silver are very valu- able in ascertaining the composition of organic acids, and, the more so as their analysis can be made with great accuracy. We shall therefore analyze the acetate of silver, for which purpose an accu- rately weighed quantity of the salt is roasted in a platinum cruci- ble, when, the organic matter being destroyed, metallic silver re- INTRODUCTION. 389 mains, which is weighed. The proportion of protoxide of silver to which it corresponds is then calculated, and the result will be that acetate of silver is composed of Oxide of silver 69.45 Acetic acid 30.55 100.00 Admitting that acetic acid is monobasic, that acetate of silver is anhydrous and formed of 1 equivalent of oxide of silver (116.0) and 1 equivalent of acetic acid, the equivalent of acetic acid will be de- duced from the proportion : 69.45 : 30.55 : : 116.0 : x whence x = 51.0. Now, there is only one way of forming the number 51.0 with whole numbers of equivalents of hydrogen, carbon, and oxygen, and that is by giving to anhydrous acetic acid the formula C 4 H.0 3 , and consequently, to concentrated acetic acid, the formula C 4 H 3 3 -f HO, which satisfies the analysis we have given of this acid. We have, in fact, 3 eq. of hydrogen 3.0 4 " carbon 24.0 3 " oxygen 24.0 5LO It is, moreover, easy to ascertain that such is, in reality, the com- position of the acetic acid contained in the acetate of silver. By burning this salt with oxide of copper, it will be found to contain Oxide of silver 69.45 Hydrogen 1.80 Carbon 14.3T Oxygen 14.38 100.00 Now, the formula AgO,C 4 H 3 3 gives 1 eq. of oxide of silver 116.0 69.45 3 " hydrogen 3.0 1.80 4 " carbon 24.0 14.37 3 " oxygen 24.0 14.38 167.0 100.00 But acetic acid might possibly be bibasic, and the salt of silver contain 2 equivalents of oxide of silver ; in which case the formula of the salt would be 2AgO,C 8 H 6 6 , that of the concentrated acetic acid C 8 H 6 +2HO, and the equivalent of anhydrous acetic acid would be 102.0. The acetic acid might be tribasic, and the formula of acetate of silver 3AgO,C 13 H 9 9 , that of the concentrated acetic 2 H 2 390 ORGANIC CHEMISTRY. acid C l3 H 9 O fl +3HO, and the equivalent of the anhydrous acetic acid might be 153.0. Now, when an acid is bibasic, it forms two series of salts with bases : salts which contain 2 equivalents of base 2RO, and salts containing 1 equivalent of base RO, and 1 equivalent of basic water. If, therefore, acetic acid were bibasic, two series of acetates would be obtained : 1st series 2RO,C 8 H 6 6 , 2d series (RO+HO),C 8 H 6 9 ; and the salts of the second series could not lose their equivalent of basic water, without a great change in their properties. If the acetic acid were tribasic, it should form three series of salts : 1st series 3RO,C 12 H 9 9 , 2d (2RO+HO),C 13 H 9 9 , 3d (RO+2HO),C 13 H 9 6 ; and the salts of the two last series again could not part with their water without an important modification of their properties. In order to decide the question, it is therefore necessary to pre- pare a great number of acetates, dry them as much as possible, without affecting their chemical constitution, that is, in such a man- ner that the dried acetate, redissolved in ivater, shall reproduce the original salt ly crystallization; and lastly, subject these acetates to analysis. It will thus be found that several of these crystallized acetates contain water ; but this should be considered as their water of crystallization, as it may be driven off by heat, and the dried salt, dissolved in water, reproduces, by crystallization, the original salt. The dried salts will present the composition given by the formulae RO,C 4 H 3 3 , 2RO,C 8 H 6 6 , 3RO,C 12 H 9 9 , &c. ; and there being consequently no reason for regarding acetic acid as polybasic, it is considered as a monobasic acid, and the formula C 4 H 3 3 has been adopted as that of the anhydrous acid. 1225. For the second example in establishing the formula of an organic acid, we shall choose malic acid, which, when crystallized, is composed as follows : Hydrogen 4.48 Carbon 35.82 Oxygen 59.70 100.00 Dividing the preceding numbers by their respective equivalents, there results : INTRODUCTION. 391 For hydrogen ................................. it 8 = 4.4S carbon .................................... ^ = 5.97 " oxygen .................................... ^9 = 7.46 The quotients follow the ratios of the numbers 3:4:5; and the most simple formula adapted to crystallized malic acid is therefore C 4 H 3 5 , while the true formula may be one of the multiples C 8 H 6 0, , C 13 H 9 15 , C i ,H u O >0 , etc., etc. The analysis of malate of silver shows that this salt contains : Oxide of silver .................................... 66.67 Malic acid .......................................... 33.33 100.00 This salt does not give off water before decomposing, which leads to the supposition that it is anhydrous ; and if it be regarded as formed of 1 equivalent of oxide of silver and 1 equivalent of malic acid, the equivalent of malic acid will therefore be deduced from the proportion : 66.67 : 33.33 : : 116.0 : x, whence z=58 The combustion of the silver salt with oxide of copper gives for its composition : Hydrogen .......................................... 1.15 Carbon ............................................. 13.79 Oxygen ............................................. 18.39 Oxide of silver ................................... . 66.67 100.00 which exactly corresponds to that given by the formula AgO,C 4 H 3 4 , as may be readily seen : 2 eq. of hydrogen ......... 2.0) ............... 1.15 4" carbon ............ 24.0 V 58.0 ......... 13.79 4" oxygen ............ 32.0 J ............... 18.39 1 " oxide of silver. ..116.0 .............. . 66.67 174.0 100.00 The formula of crystallized malic acid will therefore be C 4 H 3 4 +HO ; but it remains to be seen whether the acid is monobasic, in which case the formula of the crystallized acid would be C 4 H 3 4 -f- HO, and that of malate of silver AgO,C 4 H 3 4 ; Or, whether it is bibasic, which would give to malate of silver the formula 2AgO,C R HXX, and to the crystallized acid the formula Or lastly, whether it is tribasic, in which case the formula of malate of silver would be 3AgO,C 13 H 8 12 , and that of the crystal- lized acid C 13 H 6 13 +3HO. 392 OKGANIC CHEMISTRY. In order to decide the question, other salts formed by malic acid must be analyzed. Now, two malates of lime are known : The formula of the first in the crystallized state is " second " " CaO,C 4 H 3 4 . The first salt loses 6 HO by the action of heat, without change ; for, when dissolved in water, it reproduces the original salt by crys- tallization; and the formula of the dried salt is therefore CaO,C a H 5 9 , which may be written CaO,2(C 4 H 3 4 )-fHO, in which case it is considered as a bimalate of lime containing 1 eq. of water of crystallization. But as this water cannot be driven off without injury to the salt, it must be regarded as basic water, and the formulae of the malates of lime must be written, 1st malate ................................... 2CaO,C 8 H 4 8 . 2d malate ........................... (CaO+HO),C 8 H 4 8 . In this case, malic acid is considered as a bibasic acid. An examination of the other malates leads to the same conclusion. Thus, oxide of zinc forms two malates, the composition of which, in the crystallized state, is represented by the following formulae : 1st malate .................................... ZnO,C 4 H 5 7 , 2d malate .................................... ZnO,C 8 H 8 13 , which, when subjected to the action of heat, lose a portion of their water without change, and become, The 1st .................................... ... ZnO,C 4 H 3 4 . The2d ..................................... ... ZnO,C 8 H 5 9 . If they be further heated,, they again lose water, but are altered. The formulae of dried malates of zinc become very simple, and similar to those of malates of lime, if the malic acid be regarded as bibasic, in which case they are, 2ZnO,C 8 H 4 8 . (ZnO+HO),C 8 H 4 8 . Again, a malate of ammonia is known which crystallizes readily in beautiful crystals, and shows the formula (NH 3 ,HO),C 8 H 4 8 -fHO. But as this salt does not lose water by heat before attaining a temperature at which it is completely altered, the water it contains is therefore basic, and its formula should be written (NH S HO+HO) C 8 H 4 8 . All these considerations must lead us to regard malic acid as a bibasic acid, forming two series of salts, of which the formulae are 2RO,C 8 H 4 8 and (RO+HO),C 8 H 4 8 . 1226. An argument of the same nature, founded on the composition of the various series of salts which the organic acid can form with the INTRODUCTION. 393 same base, after the salts have been dried as far as their chemical constitution will permit, will decide if it be proper to regard this acid as a tribasic acid, in which case three series of salts will in general be obtained, which may be represented by the following formulae, the symbol A designating the equivalent of the tribasic acid : 3RO,A, (2RO+HO),A, (RO+2HO),A. The crystallized salts may contain, in addition, water of crystal- lization, which will be recognised by the fact that in most cases it can be driven off by heat, without altering the constitution of the salt. DETERMINATION OF THE PROPORTION OF BASE WHICH EXISTS IN COMBINATION WITH AN ORGANIC ACID. 1227. In order to establish with any degree of certainty the equivalent of an organic acid, it is necessary, as has been shown, to analyze a great number of the salts which it forms with mineral bases ; and it is consequently useful to dwell for a short time on the processes employed by chemists for this purpose. The proportion of base which exists in a salt formed by an organic acid is almost always determined by calcining the salt in the air, when the mineral base remains, either in the metallic state after the decomposition by heat, or in a state of superior oxidation, when it absorbs oxygen from the air ; or lastly, in the state of carbonate, when the salt is not decomposed by the degree of heat at which the incineration took place. If the organic acid contains sulphur or phos- phorus, the base may remain partly in the state of sulphate or phosphate ; and if it contains chlorine, bromine, or iodine, a portion or the whole of the base may be converted into chloride, bromide, or iodide. The salts formed by the organic acids with the alkalies, leave after calcination an alkaline carbonate; but the base is never determined in this state, because alkaline carbonates attract too readily the moisture of the air. They are converted into sulphates by pouring into the crucible in which the incineration has been effected a weak solution of sulphuric acid, taking care that the effervescence produced does not project any of the substance out of the crucible. It is evaporated to dry ness ; and lastly, the crucible is heated to a strong red-heat, in order to decompose the bisulphate which has formed, when the weight of the base is deduced from that of the sulphate. When the organic salt contains baryta or strontia, the base remains in the state of carbonate, and may be weighed as such ; and if it contains lime, the base still remains in the state of carbon- ate, if the incineration has been effected at a low temperature ; but if the calcination has required a red-heat, the greater portion of the base passes into the state of quicklime. The base may still in this 894 ORGANIC CHEMISTRY. case be determined as carbonate, if the precaution is taken to moisten the matter, after roasting, with a solution of carbonate of ammonia, which is then evaporated at a gentle heat. It is better to weigh the lime in the state of sulphate, to which effect the residue is moistened after incineration with sulphuric acid, and, after having driven off the excess of acid by heat, the crucible is heated to red- ness. The determination of magnesia in the state of sulphate should be performed in the same manner. If the base combined with the organic acid be protoxide or ses- quioxide of iron, the salt is roasted in the air ; and in order to be sur^ that the residue is composed only of sesquioxide of iron, it is moistened with nitric acid, and again calcined ; a similar process being applicable to salts of copper, in which case protoxide of cop- per CuO remains. Zinc, combined with an organic acid, is also determined in the state of oxide ZnO ; but the roasting must be commenced at the lowest temperature possible, in order not to pro- duce metallic zinc, a portion of which might be lost in the state of vapour ; and the roasted matter is moistened with a small quantity of nitric acid, and calcined to redness. The determination of manganese combined with an organic acid presents some difficulties, because the composition of the oxide which remains after the calcination is never exactly known. The salt being first calcined in a small platinum boat, in order to destroy the organic matter, the boat is introduced into a porcelain tube heated to redness, and traversed by a current of hydrogen gas, which is maintained until the tube is completely cooled ; when the boat, which then contains non-pyrophoric protoxide of manganese, is removed. As the compounds of the organic acids with cobalt and nickel leave oxides after incineration, the composition of which is always uncertain, it is best to roast the salt in a platinum boat, and then heat it in a porcelain tube in a current of hydrogen, when the pla- tinum contains the reduced metal, which is not pyrophoric if the calcination has been effected at a sufficiently high temperature. The incineration of salts formed by the organic acids with oxides of chrome leaves pure sesquioxide of chrome, which can be imme- diately weighed. By incinerating the salts formed by protoxide of lead with organic acids, the metal frequently remains in the state of protoxide, although a portion of the oxide of lead is also frequently reduced to the metallic state, so that it is better never to make these incine- rations in platinum vessels, because they might be greatly injured. They are performed in porcelain capsules heated by an alcohol- lamp, so as not to attain the point of fusion of oxide of lead, which in the fused state would attack the glazing of the porcelain. After incineration, concentrated nitric acid is poured into the saucer, which disengages reddish vapours if the substance contains metallic INTRODUCTION. 395 lead. The acid is gently evaporated, and the residue, which is composed of pure protoxide of lead, is calcined at a dull red- heat. The capsule may also be weighed after incineration, and acetic acid afterward poured into it, which dissolves the oxide of lead, and separates the metallic lead which remains in the form of small globules. The globules are washed several times, by decant- ation, in the capsule, which is then dried at a gentle heat ; the latter is then weighed a second time, when the difference gives the weight of oxide of lead formed in the roasted matter. By weigh- ing the capsule a third time, and subtracting this weight from that obtained by the second weighing, the quantity of lead reduced is found, which is to be converted into oxide, by calculation. Lastly, the oxide of lead may be determined in the state of sulphate, in which case, the incinerated matter is moistened with nitric acid, which is evaporated, and then with sulphuric acid, which transforms the nitrate into a sulphate. The excess of sulphuric acid being evaporated, the sulphate is calcined to redness. Oxide of bismuth is determined in the state of oxide Bi0 3 , and protoxide of tin in the state of stannic acid Sn0 3 , the operation being conducted as in the case of oxide of lead ; that is, the sub- stance is incinerated in a porcelain capsule, and the residue, after being moistened with nitric acid, is calcined after the evaporation of the acid. The exact determination of oxide of antimony is very difficult. The best method consists in roasting the salt in a porcelain crucible, and, when the organic matter is burned, to cover the crucible with a lid having a hole in the centre, through which is passed the end of a disengaging-tube which conveys dry hydrogen into the crucible ; when by heating the latter to redness, the oxide of antimony is re- duced to the metallic state. The current of hydrogen is maintained until the crucible is completely cooled, after which the metallic an- timony is weighed. The salts formed by the protoxide and sesquioxide of uranium leave, after roasting, an oxide of uranium, the composition of which is uncertain ; but if the residue be calcined, at a strong red-heat, by placing the platinum crucible which contains it in an earthen crucible heated in a charcoal fire, the oxide 2UO,U 3 3 ( 1025) remains, although it is better to restore, by means of hydrogen, the oxide of uranium to the state of protoxide, by operating as was stated for manganese. The quantity of oxide of silver found in combination with an organic acid may be very accurately ascertained by simple incine- ration, which leaves the silver in the metallic state. If the salt of silver is soluble, it may be dissolved in water and the silver precipi- tated in the state of chloride, in which case a standard solution of common salt may also be used, and the process explained in 1144 adopted. ORGANIC CHEMISTRY. Incineration also gives exactly the platinum contained in the salts formed by organic acids, when metallic platinum remains, from which the quantity of oxide may be deduced by calculation. Salts formed by the organic acids with oxides of mercury are analyzed by the general process described HOT. The ammonia combined with an organic acid is generally inferred from the quantity of nitrogen yielded by the ammoniacal salt in its combustion with oxide of copper, ( 1217 and 1218,) although this base may be directly determined in the state of double chloride of pla- tinum and ammonia, as in the case of ammoniacal salts formed by the mineral acids ; for which purpose the ammoniacal salt is dissolved in a small quantity of water, and a slight excess of bichloride of platinum is added, when, after evaporating to dryness at a gentle temperature, and washing the residue with a mixture of alcohol and ether, the double chloride of platinum and ammonia is obtained isolated. Lastly, the ammoniacal salt may be destroyed by sodic lime at a red-heat, the ammonia collected in an acid solution, and the base determined by one of the two methods described in 1217' and 1218. - 1228. The processes just described are applicable with absolute exactness only when the organic acid contains carbon, hydrogen, oxygen, and nitrogen alone, and their results would be frequently inaccurate if the acid contained, in addition, sulphur, phosphorus, or chlorine. If the acid contains sulphur, the processes described may be era- ployed whenever the sulphate of the metallic oxide is easily decom- posed by heat, and the metallic sulphide is quickly changed into oxide by roasting ; but in every other case some of the processes spoken of would give inexact results. When the base of the salt is an alkaline or alkalino-earthy oxide, or oxide of lead, it is sufficient to heat the incinerated substance with sulphuric acid, when the base remains in the state of sulphate, which is weighed. If the oxide forms a sulphate readily decomposable at a red-heat, the residue after roasting is calcined at this temperature, after having been treated with a small quantity of nitric acid, to prevent the presence of a metallic sulphide, which might injure the platinum crucible. In all cases it is prudent to moisten the substance, after calcina- tion, with a small quantity of carbonate of ammonia, evaporate and recalcine it, by which means the last traces of sulphuric acid are more easily driven off. If the organic acid contains phosphorus, all the processes de- scribed are faulty, and, in order to determine the oxide, the processes by the humid way, described under the head of each metal, must be adopted. Lastly, if the organic acid contains chlorine, bromine, or iodine, it is often necessary to modify the ordinary processes. When the base combined with the organic acid is an alkaline or alkalino-earthy INTRODUCTION. 397 oxide, the residue after incineration is moistened with sulphuric acid, which drives off the chlorine, bromine, or iodine, after which the excess of acid is evaporated and the substance calcined, when the base remains in the state of sulphate. This process does not always succeed easily if the base be oxide of lead, in which case it must be several times evaporated with sulphuric acid, or better still, with a small quantity of a concentrated solution of sulphate of ammonia. The majority of the metallic chlorides, bromides, and iodides are so volatile at a red-heat that the calcination, in the air, of the or- ganic salt containing the chlorine should be avoided ; and, in order to determine the oxide, recourse must then be had to the process of determining by the humid way, described under each metal. The presence of the organic acid sometimes, however, prevents the reactions which the metallic oxide presents when combined with mineral acids, in which case the organic acid must be destroyed, either by concentrated nitric acid, when this is possible, or by mix- ing it with 15 or 20 times its weight of a mixture of carbonate of soda and nitre, thrown, by small quantities at a time, into a silver crucible, heated over an alcohol-lamp ; when the metallic oxide is found in the alkaline residue. CASE IN WHICH THE ORGANIC SUBSTANCE POSSESSES BASIC PROPERTIES. 1229. All the basic organic substances, at present known, con- tain nitrogen. In order to ascertain their equivalent, not only the isolated bases, but also a certain number of salts which these bases form with mineral acids, must therefore be analyzed, preferring those which are most readily obtained in the crystallized form, and which can be most accurately analyzed. We shall take strychnine as an example. The elementary analysis of strychnine yields the following results : Hydrogen 6.58 Carbon 75.45 Nitrogen 8.38 Oxygen 9.59 foo.oo Dividing the preceding numbers by the corresponding equivalent of each simple substance, there results : For hydrogen = 6.58 " carbon ^ = 12.57 " nitrogen fg = 0.60 " oxygen 9 ^= 1.20 The most simple ratios which exist between these quotients are as the numbers 11 : 21 : 1 : 2. The most simple formula of strych- VOL. II. 2 1 398 ORGANIC CHEMISTRY. nine is, therefore, C 21 H n N0 3 ; but as the multiple of the formulae C^HagNgO^ C 63 H 33 N 3 6 , etc. etc. satisfy equally the results of the analysis, the salts of strychnine must also be analyzed. The organic alkalies combine either with hydracids, without de- composing them, or with oxacids ; in which latter case they always acquire the elements of 1 equiv. of water, which cannot be driven off without injury to the salt; and, in this respect, the organic bases behave like ammonia, in their compounds with hydracids and oxacids. We shall first analyze the chlorohydrate of strychnine, after hav- ing dried it at 212, in a current of dry air, because the crystallized salt contains water of crystallization. The elementary analysis will yield for its composition : Hydrogen 6.21 Carbon 68.02 Nitrogen 7.56 Oxygen 8.64 Chlorine 9.57 100.00 The determination, for itself, of the chlorine is sufficient to esta- blish the equivalent of strychnine, admitting that the salt is consti- tuted like the chlorohydrate of ammonia ; that is, that its formula is Sty,HCl, the symbol Sty representing the equivalent of strychnine. In fact, 9.57 of chlorine correspond to 9.841 of chlorohydric acid, and, consequently, 100 of chlorohydrate of strychnine contain 9.841 of chlorohydric acid, and 90.159 of strychnine ; whence the equiva- lent of strychnine will be obtained by the proportion, 9.841 : 90.159 : : 36.5 : x, whence z=334. Now this equivalent corresponds to the formula C 42 H 23 N 3 4 , which gives 22 eq. of hydrogen 22.0 42 " carbon 252.0 2 " nitrogen 28.0 4 " oxygen 32.0 334.0 The formula of free strychnine is therefore C^H^N^, and that of the dried chlorohydrate C 42 H 22 N 2 4 ,HC1. The crystallized base is anhydrous. It is easy to ascertain, by calculating the composi- tion of the chlorohydrate of strychnine in hundredths, from the formula just given, that there result, for each element, numbers identical with those above transcribed, and which we have supposed to be obtained by direct analysis. The formula of strychnine may be verified by the analysis of INTRODUCTION. 399 other salts of the base, as, for example, that of the sulphate. The formula of crystallized sulphate of strychnine, dried at 266, is thus found to be (C 42 H 22 N 2 4 ,HO),S0 3 . 1230. The quantity of mineral acid which exists in combina- tion with an organic alkali is determined by the same means as those used to determine the acid in a mineral salt ; but the analysis demands the greatest care, because the smallest error may seriously affect the generally very complicated formula of the organic alkali. In order to determine the quantity of chlorohydric acid which exists in chlorohydrate of strychnine, the chlorohydric acid is first deter- mined by precipitating it in the state of chloride of silver, in the manner stated in 1131. The weight obtained is generally too small. Admitting, for the moment, the weight obtained to be exact, from this weight may be calculated the quantity of pure silver which would exactly precipitate the chlorohydric acid con- tained in 5 grammes of chlorohydrate of strychnine. The silver is dissolved in nitric acid, and the liquid poured into a solution of 5 grammes of chlorohydrate of strychnine ; after which the solu- tion, when clear, is filtered, and, by the assistance of a decimal solution of silver, the quantity of chlorohydric acid which still remains in the liquid is determined, ( 1144.) Salts formed by the other mineral acids can be analyzed by analogous processes. The compounds which the chlorohydrates of organic bases form with bichloride of platinum are frequently subjected to analysis, by being precipitated in the form of small yellow granular crystals. The composition of the double chloride of platinum and strychnine is analogous to that of the double chloride of platinum and am- monia, and its formula is (C 42 H 33 N 3 OJHCl-f PtCl 2 . By roast- ing this and similar compounds in the air, the organic matter is destroyed and the chlorine disengaged, while the platinum remains ; which process is well adapted to the determination of the equiva- lent of the organic base, and is capable of great exactness, on account of the great weight of the equivalent of platinum. CASE IN WHICH THE ORGANIC SUBSTANCE IS NEITHER ACID NOR BASIC. 1231. When the simple organic substance possesses neither acid nor basic properties, there is no general rule for establishing its equivalent and its formula ; and chemists are then guided by the composition of the products of combination, or decomposition, to which the substance gives rise under the influence of various che- mical agents. They choose, among all the equivalent formulae, that which expresses most simply the whole of the reactions, fre- quently giving preference to the formula which establishes an analogy of constitution with other substances presenting similar reactions. We shall be satisfied with two examples, which we shall select from the most simple. 400 ORGANIC CHEMISTRY. The method of preparing bicarburetted hydrogen or olefiant gas has already been shown, ( 266.) The most simple formula which satisfies the direct analysis of this gas is CH, and we will proceed to show why the formula C 4 H 4 has been assigned to it. By mixing in a large bell-glass equal volumes of olefiant gas and chlorine, a liquid substance condenses, of which the most sim- ple formula is C 3 H 2 C1, and which, by treatment with an alcoholic solution of caustic potassa, loses one-half of its chloride, and one- fourth of its hydrogen, in the state of chlorohydric acid, which combines with the potassa (KO+HC1=KC1+HO); while at the same time a very volatile substance is formed, of which the most simple formula is C 4 H 3 C1. It is but natural to regard the chlorine and hydrogen, which were separated in the state of chlorohydric acid, as united in the compound C 3 H 2 C1, differently from the other portions of chlorine and hydrogen which remain, and which enter into the constitution of the compound C 4 H 3 C1 ; but chemists have gone still further in admitting that the chlorine and hydrogen removed by the action of the potassa existed really in the state of chlorohydric acid in the substance C 2 H 2 C1 ; and, in order to avoid fractional numbers of equivalents, they replace the formula C 3 H 3 C1 by the multiple formula C 4 H 4 C1 2 , which they write C 4 H 3 C1,HC1. If the formula C 4 H 4 is assigned to olefiant gas, the reaction of chlorine on this substance is expressed in the most simple manner possible, by the following equation : C 4 H 4 +2C1=C 4 H 3 C1,HC1. Now, if chlorine is made to act on the substance C 4 H 3 C1, or on the compound C 4 H 3 C1,HC1, a new substance is formed, of which the most simple formula is C 4 H 3 C1 3 , which, when treated by an alcoholic solution of potassa, gives off 1 equiv. of hydrogen and 1 equiv. of chlorine. We shall regard these equivalents as existing in the state of chlorohydric acid in the substance C 4 H 3 C1 3 , as we have done for the substance C 4 H 4 C1 2 , and shall write the formula of the new compound C 4 H 3 C1 3 ,HC1. The reactions by which it is derived either from the substance C 4 H 3 C1, or from the compound C 4 H 3 C1,HC1, or lastly, from the olefiant gas C 4 H 4 , are of the most simple cha- racter. C 4 H 3 C1 +2C1=C 4 H 2 C1 2 ,HC1. C 4 H 3 C1,HC1+2C1=C 4 H 2 C1 3 ,HC1+HC1. C 4 H 4 -f4Cl-C 4 H 3 Cl 2 ,HCl+HCl. In the last two cases, 1 equiv. of chlorohydric acid is set free. The product C 4 H 3 C1 2 , or the compound C 4 H 3 CL,HC1, being sub- mitted, in their turn, to the action of chlorine, yields a new pro- duct, of which the most simple formula is C 2 HC1 3 . If we write this formula C 4 H 2 C1 4 , and if we give it the form C 4 HC1 3 ,HC1, the reactions which produce it by the action of chlorine on the various INTRODUCTION. 401 substances C 4 H 3 C1 3 , C 4 H 2 C1 3 ,HC1, C 4 H 3 C1, C 4 H 3 C1,HC1, and C 4 H 4 , are the following : C 4 H 3 C1 3 +2C1=C 4 HC1 3 ,HC1. C 4 H 3 C1 2 ,HC1+2C1=C 4 HC1 3 ,HC1+ HC1. C 4 H 3 C1 +4C1=C 4 HC1 3 ,HC1+ HC1. C 4 H 3 C1, HC1+ 4C1=C 4 HC1 3 ,HC1+2HC1. C 4 H 4 +6Cl==C 4 HCl 3 ,HCl-f2HCl. The compound C 4 HC1 2 ,HC1 is also decomposed by contact with the alcoholic solution of potassa, but the substance C 4 HC1 3 has not yet been obtained in a state of purity, and seems to be altered itself by the alcoholic solution of potassa. It cannot the less be admitted that this substance pre-exists in the compound C 4 H 2 C1 3 , for the very reason that this establishes perfect uniformity in all the derived compounds a uniformity which, moreover, has hither- to been destroyed by no other reaction. Lastly, the substance C 4 HC1 3 HC1, when subjected to the action of chlorine, assisted by solar light, parts with the whole of its hydrogen, which is disengaged in the state of chlorohydric acid, while a crystalline compound, which is a simple chloride of carbon, the most simple formula of which is C 3 C1 3 , is formed. Various chemical reactions show that one of the equivalents of chlorine is not as deeply interested in the compound as the other two. Removing, for example, this equivalent by an alcoholic solu- tion of monosulphide of potassium, a new chloride of carbon, of which the most simple formula is CC1, will separate, to which, for the moment, we will give the formula C 3 Cl a , in which case the first could be written C 3 C1 3 ,C1. But it would be more pro- per to write their formulae C 4 C1 4 and C 4 C1 4 ,C1 3 , because, with these last formulae, the reactions which give rise to the chloride of carbon C 4 C1 4 ,C1 3 , by the action of chlorine on all the successive compounds of which we have previously established the formulae, are of the most simple kind : C 4 H 3 C1 3 ,HC1 + 4Cl==C 4 Cl 4 Cl 3 ,-f 2HC1. C 4 H 3 C1 3 -f 6C1==C 4 C1 4 C1 3 ,+2HC1. C 4 H 3 C1 3 ,HC1 + 6C1==C 4 C1 4 C1 2 ,+3HC1. C 4 H 3 C1 + 8C1==C 4 C1 4 C1 3 ,+3HC1. C 4 H 3 C1,HC1 + 8C1=C 4 C1 4 C1 2 ,4-4HC1. C 4 H 4 +10C1=C 4 C1 4 C1 3 ,+4HC1. We will remark, in addition, that olefiant gas C 4 H 4 , and all the chlorinated products C 4 H 3 C1, C 4 H 3 C1 3 , C 4 HC1 3 , C 4 C1 3 derived from it, present this remarkable property, that they may be regarded as one and a single molecular grouping C 4 H 4 , modified only by the successive substitution of an equal number of equivalents of chlo- rine for its equivalents of hydrogen. This fact is again corrobo- 2i2 26 402 ORGANIC CHEMISTRY. rated by the following : If the substances are operated on at a tern* perature sufficiently high to allow all of them to exist in the gaseous state, the formula C 4 H 4 , C 4 H 3 C1, C 4 H 3 C1 2 , C 4 HC1 3 , C 4 C1 3 would re- present the same volume of these various gases ; each of these for- mulae corresponding, in fact, to 4 volumes of the vapour of the body to which it relates. The comparisons and similarity of composition just pointed out among, all these substances would disappear, if for each of them equivalent formulae more simple than those we have admitted were adopted, although they would still exist if equivalent formulae were admitted, multiples of those just established ; but there is no reason whatever for thus complicating the formulae. 1232. For the second example we shall choose alcohol, which liquid is composed as follows : Hydrogen 13.05 Carbon 52.17 Oxygen 34.78 100.00 Dividing each of these numbers by the equivalent of the sub- stance to which it belongs, the following quotients result : For hydrogen = 13.05 " carbon ^ = 8.69 CL & A f)C- ' oxygen ~al the rod tp slides a piece of bent iron cd \K terminating below by a ring gh, on which the balloon A rests ; while a second ring ef, fastened to an iron rod, slides along the rod cd, and may be fastened to it at any height by a thumbscrew i, serving to hold the balloon in a fixed position. It is suffi- cient to slide the movable part cd of the support along the upright tp to cause the balloon to dip into the kettle V, where it is then secured by the thumbscrew r. When the metallic bath is used, it should be brought to the liquid state before dipping the balloon into it. A second iron rod t f p r , fastened to the ear ', holds the air thermometer B, resembling that which will be described in a note at page 414. The bath is gradually heated, taking care that the temperature shall constantly rise ; and w r hen the liquid contained in the bal- loon has boiled, it begins to distil, and its vapour drives off the air contained in the vessel, which partly escapes by the point a. If the substance be valuable, the greater portion of that which is evolved can be collected, by introducing the point a into a small tube closed at one end. The temperature is then raised until the point at which the examination is to be made is approached, when all the doors of the furnace are closed, and, stirring the bath con- stantly, the moment is awaited when the temperature becomes sta- tionary. The temperature being marked, the flame of an alcohol lamp is passed under that part of the stem of the balloon which projects from the fluid, in order that no condensed drops shall remain ; after which the point a is quickly closed, and the height T' of the barometer noted down. The balloon is then removed from the bath, and detached when it is cooled. The temperature T of the mercurial thermometer requires a cor- rection, which becomes of great importance in high temperatures, and which is owing to the circumstance that a considerable portion of the mercurial column, not being plunged into the bath, remains at a very low temperature. Let t be the temperature indicated by a small thermometer, the bulb of which is kept in contact with the tube of the principal thermometer, at the height of about one-half of the mercurial column which rises above the level of the bath ; INTRODUCTION. 413 and the division of the principal thermometer, at about 2 or 3 centimetres above the level of the bath : it may then be admitted that (T 0) represents the portion of the mercurial column at the average temperature t. Now, this portion would dilate by (T 9) . T ~J if it were heated from t to T ; for which reason the true temperature T' of the bath is obtained by adding to the tem- perature observed T the number of degrees represented by the expression (T 0) . ^- But as the temperature T' is that of the mercurial thermometer, it is necessary to find the temperature T" which corresponds to it on the air thermometer. Mercurial thermometers agree necessarily from 32 to 212, which are the fixed points by which their scales are governed; while they differ at a temperature above 212, because the various kinds of glass of which the bulbs of thermome- ters are made do not obey the same law of expansion. The fol- lowing table shows the simultaneous temperatures indicated, 1st, by a mercurial thermometer, of which the bulb is made of the ordi- nary glass used in Paris for making chemical tubes ; 2dly, by a mer- curial thermometer, of which the bulb is of crystal from Choisy-le- Roi ; and 3dly, by an air thermometer, of which the volume of air is constant and the pressure variable.* Simultaneous Temperatures Of a mercurial thermo- Of a mercurial thermo- Of an air- meter of ordinary glass. meter of crystal. thermometer. 100 centigrade 100 100 109.98 110.05 110 119.95 120.12 120 129.91 .130.20 130 139.85 140.29 140 149.80 150.40 150 159.74 160.52 160 169.68 170.65 170 179.63 180.80 180 189.65 191.01 190 199.70 201.25 200 209.75 211.53 210 219.80 221.82 220 229.85 232.16 230 239.90 242.55 240 250.05 253.00 250 260.20 263.44 260 270.38 273.90 270 280.52 284.48 280 290.80 295.10 290 * This being a merely comparative table, the centigrade divisions have not been corrected to the corresponding temperatures of the Fahrenheit scale. W. L. F. 2K2 414 ORGANIC CHEMISTRY. Of a mercurial therrno- Of a mercurial thermo- Of an air meter of ordinary glass. meter of crystal. thermometer. 301.08 305.72 300 311.45 316.45 310 321.80 327.25 320 332.40 338.22 330 343.00 349.30 340 354.00 360.50 350 When the operation is performed at higher temperatures, above 570 (Fahrenheit) for example, and great exactness is required, it is better to substitute an air for a mercurial thermometer ; which is absolutely necessary when 660 is exceeded, since at this temper- ature mercury boils under the ordinary pressure of the atmosphere ; and the boiling manifests itself even at somewhat lower tempera- tures in thermometers perfectly freed from air, unless the calibre of the tube be so small as to present great resistance to the ascent of the metal. In a note,* at the bottom of this page, we shall explain * The air thermometer used in these experiments consists of a simple cylin- drical glass reservoir, of about 2 centimetres in diameter and 12 or 15 centimetres in length, and terminating by a capillary tube, of which the calibre is 1 or 2 milli- metres, and which is bent to a right angle, and drawn out at its end. The reservoir ab is kept in the bath, alongside of the balloon in which the vapour is to be generated. The first step is to perfectly dry the reservoir ab, by creating a vacuum in it several times, and allowing air to enter which has been dried, by passing through a tube filled with pumice-stone soaked in concentrated sulphuric acid ; after which the bath is heated, and, when the temperature becomes station- ary at the point at which the experiment is to be terminated, the point of the bal- loon and that of the air thermometer are closed simultaneously, by means of a lamp. The air reservoir is then placed on the metallic support represented in fig. 636, the stem passing through a cork which closes a tubulure made in the centre of the disk ah, while the curved point cd enters a small mercurial bath. The extremity of the point being broken with a pincers, the mercury rises in the tube and partly fills the reservoir ab, which is surrounded with pounded ice, in order to reduce the temperature of the air it contains to 32, when the open point is closed with a ball of soft wax. In order to perform this operation easily, without changing the level of the mercury in the vessel A, a small iron spoon u is used, soldered to an iron rod uv, which slides along a hori- zontal bar vs, itself movable along the ver- tical foot st ; the movable rod vs being fixed at such a height that the bowl of the spoon, filled with soft wax, is exactly at the height and in the direction of the point cd. It is therefore suffi- cient, in order to close the point, to slide the end uv along the horizontal rod vs. The mercury in the vessel A is then exactly levelled to the point i of a double-pointed screw H; the ice which sur- rounded the reservoir ab is removed, and, when the mercurial column attains the temperature of the surrounding air, the difference of height be- tween the mercury in the reservoir ab and the upper point k is exactly measured, by means of Fig. 636. INTRODUCTION. 415 the manner of arranging an air thermometer, and deducing the temperature from it. The balloon A having been well wiped and washed with alcohol, a cathetometer ; and by adding to this difference the length of the screw ki, the height h of the column of mercury elevated in the air thermometer is obtained. Let h be this height at 32, H the height of the barometer also at 32, when the point d is closed with wax; then will (H A ) represent the elastic force of the air in the reservoir ab at the temperature of 32. The support is then inverted, the air thermometer removed, after having detached the spoon u, and it is weighed with the mercury contained : let its weight be represented by Q. The thermome- ter is then filled with mercury, which is boiled to drive off the last bubbles of air ; the point cd being kept, during this time, in a small capsule filled with mercury. When the apparatus is cooled, it is surrounded with melting ice, and completely filled with mercury at 32 ; when it is again weighed, giving now the weight Q'. The weight q of the envelope of glass alone being ascertained, after having emptied it of mercury, (Q q) is therefore the weight of the mercury at 32, and (Q q] is the weight of the mercury in the thermometer when it was on the support. (Q' Q) therefore represents the weight of the mercury at 32, which occupies the same volume as the air remaining in the thermometer when it is at 32, and under the pressure (H A .) If we designate by ef the density of the mercury at 32, Q _ q Q _ Q j represents the capacity in cubic centimetres of the thermometer, and ^ the volume which the air occupies in this apparatus at the moment of closing the point c with wax. Now, the capacity of the thermometer, at the temperature T, being -^p? (1+&T), the volume of air-^p* at 32 and under the pressure (H A ), there- fore occupies, when it is raised to the temperature T, and under the pressure H , a volume Q '~ g (l-f&T). The volume assumed by a volume of air Q ~ Q at 32 and under the pressure (H ^ ), when raised to the temperature T and under the pressure H' , may be calculated, by the known laws of the expansion of air, under changes of temperature and pressure ; and is thus found to be, ^=^(1+ 0.00367, T)?^- which leads to the equation, whence Q' Q Ho ftp 1 + 0.00367.T Qf^q ' H' T may be deduced from this equation, but there is no necessity of knowing its value in order to calculate the density of the vapour, which, in fact, is represented by the expression P'-P+J 0.0012932 . V. 1 + 0.00367.T 760 Substituting for 1 A"^^ t fl e value first found, there results for the expres- sion of the density of the vapour, 0.0012932.V. Q '~ Q Ho ~ Q'- V The second member of the equation contains only known quantities, except, indeed, the ratio ~, which is determined in the following manner : The tube abc being detached from the manometer, the tube gh is completely filled with mercury; and then, bringing the stopcock R, into the position of fig. 639, the mercury in the leg gh is allowed to escape until its level reaches the mark <*, while the mercury 27 418 ORGANIC CHEMISTRY. P' (P -p) therefore represents the weight of the volatile sub- stance which remains in the balloon, the point of which being broken under the mercury, the atmospheric pressure causes the which escapes is collected in a small bottle and weighed. Its weight may be con- sidered as representing the volume v. The mercury is allowed to escape from the leg gh, it until its level reaches another mark /g, on the tube ffh, when the quantity thus obtained, being weighed, compounds to a volume v' which should be a notable fraction of the capacity of the thermometer-tube. This being done, and the level of the mercury reaching the mark a. of the manometer, under the pressure of the atmosphere, the air thermometer is fitted to the manometer, the reservoir ab being kept at the temperature of the surrounding medium. As the two columns of mercury are on a level in the manometer, there is a volume of air (V'-j-v) under the exter- nal pressure H. The mercury is allowed to flow from the two legs of the mano- meter, by bringing the stopcock R into the position in the figure, and the level of the mercury is brought to the mark $ ; when the two columns are now no longer on a level, and their difference of height h can be measured. There is, therefore, a volume of air (V-{-v-\-v') under the pressure (H h) ; and agreeably to the law of Mariotte, V'-fu __ H h whence the volume V may be deduced. It now only remains to ascertain the weight of the vapour which filled the re- servoir a'b' at the moment of closing it, and the capacity of the reservoir. It may be admitted that the reservoir a'b' does not contain any air, because there was originally introduced into it a quantity of volatile matter sufficient to expel all the air. The closed end of the tube is, therefore, broken, and the latter weighed filled with air and the substance it contains ; after which its weight is again ascer- tained when the substance has been removed, the difference of weight n represent- ing the weight of the substance. In order to obtain the volume V of the reservoir, the quantity of water which will fill it is weighed; and now all the elements are known which are necessary to calculate the density of the vapour, by means of the formula the value ascertained by the air thermometer being substituted for ]i Mse? fj . It frequently happens that the substance, the density of whose vapour is to be determined, is changed by absorbing oxygen from the air at the high tem- perature at which it volatilizes ; in which case it becomes necessary to fill the tube a'b' with nitrogen gas, and further, in order to prevent the air from entering freely, to fit a pointed tube by means of a cork to the tube c'd'. By means of the process just described, the density of any vapour might be de- termined at very high temperatures, if it were possible to procure glass tubes of sufficient hardness ; but, unfortunately, the strongest glass softens at a red-heat, and, therefore, cannot be used for higher temperatures. Porcelain tubes, how- ever, made of the same shape as the glass tubes, by the process described in 715, might answer the purpose. It is, moreover, unnecessary to hermetically seal the fine point c'd', when the substance boils at a very high temperature, because there is then no fear, at the moment of withdrawing the tubes from the cylinders, that a portion of the vapours which escape from the reservoir might re-enter the latter. But there are volatile substances, the density of the vapour of which it would be very interesting to know, and which, at a high temperature, attack the alka- line silicates ; in which case tubes of glass or porcelain can no longer be used, and resort must be then had to metallic tubes, previously filled with nitrogen gas. The portion of the volatile substance which remains in the reservoir intended to contain the vapour is then determined by chemical processes. INTRODUCTION. 419 liquid to ascend, and completely fill the balloon, if the air has been entirely driven out by the vapour, as we shall suppose to be the case. The balloon is then inverted, when the volatile substance, if it is liquid, ascends in the neck, and may be removed with a pipette. The balloon is filled with mercury, which is afterward measured by being poured into a large bell-glass divided into cubic centimetres ; by which means the capacity V of the balloon, at the ordinary tem- perature t, is exactly found. If k represents the coefficient of the average expansion of glass, between the temperature t and T, the capacity of the balloon will be V (1+&T) at the temperature T. The volume V (l-f&T) of vapour of the volatile substance, at the temperature T and under the pressure H' , therefore weighs (P ; P-f p), while the weight of an equal volume of atmospheric air, under the same circumstances of temperature and pressure, is 0.0012932 gm. V (l+AT) ^^.^. Thus the density of the vapour of the substance is represented by 0.0012932. We have supposed that the vapour had entirely expelled the air from the balloon, and consequently that the latter was entirely filled with mercury ; which, however, is rarely the case, as most fre- quently a bubble of air remains, and sometimes the remaining vo- lume of air amounts to even more than that, when the vapour is very dense, and a large quantity of material has not been origin- ally introduced into the balloon. The experiment does not fail on this account, for it is sufficient to collect this volume v of air in a small graduated bell-glass, and to measure it exactly. This volume v weighs 0.0012988 t" and H ;/ representing the surrounding temperature and pressure of the air at the moment of measuring the volume v. The weight of vapour in the balloon, at the moment of closing it, is therefore (P' P-f-p p r ). The volume v of air occupies in the balloon, at the moment of closing it, at the temperature T, and supposed to be reduced to the pressure H' , a volume ,/ _ . 1-H.00367.T ETo ' The volume occupied by the vapour in the balloon, at the tempera- ture T and under the pressure H' , is therefore only [V (1+&T) v'] ; and as an equal volume of air, under the same circumstances of tem- perature and pressure, weighs 0.001293 gm. [V (1+&T) - v f ] T _ 420 ORGANIC CHEMISTRY. the density of the vapour is therefore 0.0012932 [V(l-fA;T)-2/] In accurate experiments, care must be taken to leave but a very small quantity of air in the balloon, in order as much as possible to avoid corrections, which always possess some degree of uncertainty. The average coefficient k of the expansion of glass, between the temperatures and T, varies with the different kinds of glass ; and varies, moreover, in the same glass, with the temperature T. We subjoin its value, at different intervals of temperature, for the ordi- nary glass of which the balloons used in Parisian laboratories are made: Between and 100 =0.0000276 150 0.0000284 200 0.0000291 250 0.0000298 " 300 0.0000306 350 0.0000313 Organic substances which boil at high temperatures are fre- quently easily altered by the air, at the temperature to which their vapours must be heated in order to obtain constant densities ; in which case, care must be taken to fill the balloon with carbonic acid gas, when it is placed in the kettle, before heating the latter. For this purpose, the point of the balloon is made to communicate with a small air-pump, to the second tubulure of which an apparatus disengaging carbonic acid gas is adapted; and a vacuum being made several times, and carbonic acid gas allowed to enter each time, the rest of the experiment is then conducted as usual. In many cases it may be of advantage to determine the density of a vapour under a pressure below that of the atmosphere, because then the substance boils at a lower temperature, and in general it is not necessary to raise the temperature so high in order to obtain constant densities. This result is particularly advantageous when substances easily altered by heat are operated on, and the boiling point of which is high. In this case, a capillary tube ab, terminat- , ing in a larger one cd, is soldered to the balloon, (fig. 642 ;) and the latter being placed in the bath, the tube cd is made to communicate with a large bottle placed in a water-bath kept at a constant temperature, approach- ing that of the surrounding temperature ; while the second tubulure of the bottle is made to communicate lg ' ' with a mercurial manometer which indicates the inter- nal pressure at every moment, and with an air-pump, by means of which the air in the bottle and balloon is reduced to the desired INTRODUCTION. 421 degree of elasticity. The experiment is then conducted in the same manner as when the operation is performed under the pressure of the atmosphere ; it being sufficient to substitute in the formula the elastic force of the air observed on the manometer, for the baro- metric pressure H' . The second method, which has just been described, to determine the densities of vapours of volatile substances, may furnish very in- accurate results when it is applied to very impure substances, for example, to those containing a small quantity of less volatile mat- ter, the density of whose vapour is very different from that of the substance being examined. The error increases with the quantity of the substance introduced into the balloon, because the less vola- tile matter is necessarily concentrated in it, and the vapour finally filling the balloon contains a much larger proportion of the foreign matter than the substance which was introduced into it. It is necessary, whenever any doubt may be entertained as to the purity of the substance, the density of whose vapour is to be determined by this method, to carefully collect the portion of matter which remains in the balloon, and subject it to analysis, in order to ascer- tain if its composition differs appreciably from that of the original substance. 1237. It still remains to explain the method of comparing the density of vapour afforded by experiment with the theoretical den- sity calculated from the formula, when the latter is determined. We will take alcohol as an example. The experiments detailed ( 1234) assign 1.602 for the density of the vapour of alcohol, within the limits of temperature in which this vapour obeys the laws of permanent gases. The formula which we have adopted for the equivalent of alcohol is C 4 H 6 2 . Now, as the density of hydrogen is known to be 0.0692, and 2 volumes have been adopted as its gaseous equivalent, the 6 equivs. of hydrogen are therefore represented by 12 volumes of this gas, which weigh 12+0.0692=0.8304. The hypothetic density of the vapour of carbon being 0.8290, ( 203,) and its gaseous equivalent being represented by 1 vol., the 4 equivs. of carbon are therefore represented by 4 vols. of vapour of carbon, which weigh 4x0.8290 = 3.3160. The density of oxygen gas is 1.1056, and its equivalent is repre- sented by 1 vol. ; and 2 equivs. of oxygen are therefore represented by 2x1.1056 = 2.2112. The formula C 4 H 6 3 therefore gives 4 eq. of carbon 3.3160 6 " hydrogen 0.8304 2 " oxygen 2.2112 6.35T6 Now, since ^ 8 = 1.5894 differs but little from the number 1.602, VOL. II. 2 L 422 ORGANIC CHEMISTRY. which has been found by direct experiment, the conclusion may be drawn that the equivalent C 4 H 8 3 of alcohol is represented by 4 volumes of vapour. The difference between the theoretical number 1.5894 and the number 1.602 found by experiment, may be partly attributed to slight errors which always occur in determinations of this kind ; and similar, and even greater differences are observed, when the experiments are conducted with the greatest exactness. This is owing to the fact that the laws of elasticity of gases, and their expan- sion by heat, which we have admitted as being strictly the same for all the gases above taken into account, are not really so under the cir- cumstances accessible to our means of observation. The gases which have not yet been liquefied differ from it themselves very widely, at the ordinary temperature ; and it is, therefore, very probable that the differences are greater for the majority of vapours, even under the most favourable circumstances of temperature and pressure. OF THE ANALYSIS OF GASES. 1238. We have frequently had occasion to refer to the analysis of gaseous substances in the first part of this work, either for the sake of determining the composition of definite gases, or the pro- portions in which such gases existed in mixtures. We have described the most simple processes used by chemists, but as the processes do not afford the degree of precision demanded by the subject, we shall now describe other processes by which a precision can be attained, in the analysis of gases, which is not exceeded by any of the most exact manipulations of chemical analysis. We shall, in the first place, suppose that it is required to analyze a mixture of atmo- spheric air and carbonic acid ; and, while applying the processes already described, we shall discuss the causes of error to which they are subject. It will be recollected that a certain volume of this mixture is measured over mercury in a graduated cylinder, and that in order to be more certain of the degree of moisture of the gas, the latter was saturated with moisture by leaving the sides of the cylinder slightly damp. The first difnculty which presents itself is, What is the tempera- ture of the gas, and what its elastic force ? The temperature of the gas is generally assumed as that indicated by a thermometer placed in the vicinity of the cylinder ; but is it always certain that the two temperatures are identical? As to the pressure, it is generally reduced to an equality with that of the atmosphere, by properly sinking the cylinder into the mercury-bath ; a process which pos- sesses but little accuracy ; or, indeed, when the operation is effected more exactly, a certain column of mercury is left upraised, and measured by a graduated scale, or better still, by the process de- scribed in the note to page 414. INTRODUCTION. 423 In order to absorb the carbonic acid, a small quantity of a con- centrated solution of caustic potassa is introduced into the bell-glass, and the latter is shaken ; after which the proportion of carbonic acid is determined by again measuring the gaseous volume. But the second measuring is still more uncertain than the first, for, to the difficulties already pointed out, is added that of ascertaining the degree of. moisture of the gas in the presence of the solution of potassa ; in addition to which, the form of the meniscus of the liquid is now changed from convex to concave ; and the sides of the bell-glass are moistened with a viscous liquid, which diminishes ap- preciably its diameter. These difficulties are overcome by replacing the solution of potassa by a small ball of potassa affixed to a platinum wire, by which it is introduced into the bell-glass through the mercury ; but in this case the carbonic acid is very slowly absorbed, which renders it neces- sary to wait, not only until the absorption of carbonic acid is complete, but also until the potassa has ab- sorbed all the vapour of water which existed in the gas or on the sides of the bell-glass ; be- cause it would otherwise be im- possible to as- certain its state of saturation. In order to be sure that this condition is ful- filled, the gas must be exactly measured after having with- Fig. 643. Fig. 644. drawn the ball of potassa, and the latter must be again introduced and allowed to remain for at least 12 hours ; when the result of a second measurement of the gas should be identical with the first. The proportion of oxygen in the remaining gas is determined, either from the gaseous volume which disappears when this gas is burned with an excess of hydrogen, or by the diminution of a volume of the gas when left for a sufficient length of time in con- 424 ORGANIC CHEMISTRY. tact with a substance which combines with oxygen. The manner of effecting this absorption by phosphorus has already been ex- plained, ( 946;) and in 83 the eudiometer in which the analysis is made by combustion was described ; but the process is always liable, without regard to the method adopted, to some of the causes of error pointed out above. 1239. With the eudiometric apparatus about to* be described these analyses can, on the other hand, be performed very rapidly, and without any danger of the uncer- tainties just mentioned. Fig. 643 represents the geometrical projection of the anterior surface, and fig. 644 gives a vertical section made through a plane perpendicular to this face; while lastly, fig. 645 shows a perspec- tive view of the whole. The apparatus is com- posed of two parts, which may be separated and united at pleasure ; and, while the first, or the measurer, serves to mea- sure the gas under given conditions of temperature and moisture, in the se- cond the gas is subjected to various absorbent re- agents, on which account Fig. 645. we shall call it the absorption-tube. The measurer is composed of a tube ab of 15 to 20 millimetres diameter internally, divided into millimetres, and terminating above by a curved capillary tube bcr f , while the lower end is luted into a cast-iron piece p f q', having two tubulures a, i, and a stopcock R. To the second tubulure i is luted a straight tube ih, open at both ends, of the same diameter as the tube ab, and also divided into millimetres. The stopcock R has three openings, and resembles precisely that of which sections are seen in figs. 624, 625, and 626, in the three principal positions in which the key may be turned. A communication can therefore be established at will between the tubes ab, ih, or one or other of these tubes only may be opened to the external air. The two vertical tubes and the cast-iron piece form a manometric INTRODUCTION. 425 apparatus contained in a glass cylinder pqp'q* filled with water, which is maintained at a constant temperature, marked by the thermometer T, during the whole time of the analysis. The mano- metric apparatus is fixed on a cast-iron stand ZZ' furnished with adjusting screws. The absorption-tube is composed of a bell-glass gf, open at the bottom, and terminated above by a curved capillary tube fe r. The bell-glass dips into a small mercurial bath U, of cast-iron, exactly represented in figs. 646 and 647 ; while the basin U is fixed on a Fig. 646. plate which can be raised at will along the vertical support ZZ', by means of the toothed rack vw, which works with the toothed pinion o set in motion by the crank B. The ratchet r arrests the toothed- racks and consequently keeps the basin U in any given position. A counterpoise affixed to the ratchet facili- tates its working, and, as it is turned to one side or the other, the ratchet is thrown in or out of gear with the pinion. The ends of the capillary tubes which terminate the absorption-tube and measurer are luted to two small steel stopcocks r, r', the ends of which exactly fit Fig. 647. each other, and which have the same shape as those represented in fig. 639, sections of which are seen in figs. 640 and 641. The absorption-tube is maintained in a vertical position by means of pincers u lined with cork, which are easily opened or closed when the tube is to be removed or replaced. The measurer ab is traversed at b by two platinum wires opposite to each other, the ends of which approach to the distance of a few millimetres from the inside of the bell-glass, and of which the other ends are fast- ened with wax to the lower edge of the large cylinder. The elec- tric spark is passed into the bell-glass by means of these wires ; and the water in the cylinder is no obstacle if the spark be furnished by a Leyden jar. 1240. Let us suppose that in this apparatus a mixture of atmo- spheric air and carbonic acid is to be analyzed. Through the tube ill the measure ab is filled with mercury, until the latter escapes through the stopcock r, which is then closed ; and at the same time the absorption-tube gf is filled with mercury ; to effect which the tube gf is detached from the pincers u, and plunged into the bath U, the stopcock r being open; and the operator sucks with a glass tube furnished with a caoutchouc tubulure, the edge of which is applied to the plane part of the tubulure r. When the mercury begins to escape, the stopcock r is closed. The gas to be analyzed, which has been collected under a small bell-glass, is then introduced into the absorption-tube, and the extra- vasation is easily performed in the bath U, on account of the shape 2L2 426 ORGANIC CHEMISTRY. given to the latter. The absorption-tube being then replaced by the pincers u, the two tubulures r, r' are fitted to each other : then, elevating one end of the bath U, and allowing the mercury of the measurer to flow from the other through the cock R, and lastly, opening the stopcocks r, r', the gas is caused to pass from the absorption-tube into the measurer. When the mercury begins to rise in the capillary tube /+2;=m, II. v +- 2w=n, IV. These four equations are not sufficient to determine the four unknown quanti- ties ; and in fact it is easily seen that one of them is a consequence of the other three, on account of a peculiar relation introduced by the data of the problem By adding together III. and IV. there results which becomes, on account of II., ^ -f 2v -f 2w= V+ a n 5 giving rise, in consequence of the chemical composition of the mixed gases, to the equation: ,, . ,, . V-f- a n=m, or, V-f- o=+n, which includes the equation I. in the other three. In order to solve the question, the quantity y of oxygen must be determined directly by absorption, after which we have for the determination of the three other unknown quantities, ~^-2v-\-2w=m, whence z=2(m + 2n 2a 2y), v-{-2w=n, v=6a-4-6y In 2m, |-|-2i;-f3tt>=a-fy, w=w-f 4rc 3a By. Mixture of Oxygen, Oxide of Carbon, Protocarburetted and Bicarburetted Hydrogen. 1 1270. The analysis is conducted as in the preceding cases, and from it are deduced the relations, INTRODUCTION. 443 l+2v + 2w=m, 2-}- v-{- 2w=n, which four equations are not sufficient to determine the unknown quantities, because they are connected together by the condition The quantity y of oxygen must be determined directly by absorption, which furnishes the equations w=a-{-y m, Mixture of Oxygen, Nitrogen, Oxide of Carbon, Protocarburetted and Bicarburetted Hydrogen. % 1271. The analytic operations having been conducted as in the preceding cases, and the oxygen y=b having been determined by absorption, and lastly, the whole quantity a' of oxygen consumed in combustion having been equally ascer- tained, the following relations are established : - -\-2v-\- 2w=m, whence y=b, ' (m+n). Eudiometric analysis furnishes no verification. Mixture of Oxygen, Hydrogen, Oxide of Carbon, Protocarburetted and Bicarburetted Hydrogen. $ 1272. The analysis having been made as in the preceding cases, the oxygen y=b having been determined by absorbent reagents, and lastly the whole quan- tity a' of oxygen consumed having been equally determined, we have the relations x+z + v + w^V i; which four equations are not sufficient to determine the four unknown quanti- ties x, z, v, and w, because the constant quantities are connected together by the relation wi-f =(V b)-\-a', which reduces the four equations to the four really distinct ones. A new relation between the unknown quantities must therefore be sought experimentally ; and one can be obtained by determining exactly the specific gravity D of the mixture. By designating by d x , d y , d z , d v , d w , the respective densities of hydrogen, oxygen, oxide of carbon, protocarburetted and bicarburetted hydrogen, there results the relation D=xd x -\- yd y 4- zd, + vd v -f- wd u ; 444 ORGANIC CHEMISTRY. which new equation, added to the first four, renders the problem algebraically determinate. A given quantity of the gaseous mixture may also be burned with oxide of copper, and the water formed weighed by using the apparatus described in \ 1214. If p be the weight of the water obtained, W the volume of gas formed by the oxide of copper, t and H its temperature and pressure at the moment of being weighed ; then will the weight of the gas burned be W. and the ratio of the weight of water formed to the weight of gas burned will be P W. 0.001293. On the other hand, let U be the constant volume to which the gas has been re- duced by eudiometric analysis, 6 the equally constant temperature of the water in the cylinder, the elastic force of the original gas being V, we have, for the weight of the gas, U. 0.001293. D. +055850' ?!o If TF designate the weight of water yielded by the gas when completely burned we should have, for the ratio between this weight and that of the gas, U.0. 001293. D. r whence the equation, P W . 0.001293 . D . rniTn^T-, U . 0.001293 . D . or simply, W._ -.H U. 1 + 0.00367. t 1 + 0.00367.0 whence T_ TJ 1 + 0.00367. t V P ' w ' 1 + 0.00367 . ' H " Now the weight of the water is equally expressed by i 7T-H U. 0.001293. 0.622 1 + 0.00367.0 760 giving rise to 3a; . , IT. 760(1 + 0.00367.0). T + " W== U.0.001293. 0.622 ' which new relation may be introduced into the calculation. Mixture of Oxygen, Nitrogen, Hydrogen, Oxide of Carbon, Proto and Bicarburetted Hydrogen. 1273. This is the most complex mixture which will fall under our notice. Its eudiometric analysis will be conducted as in the preceding cases : after having determined directly the quantity y=b of oxygen by absorption, and burned a certain quantity of gas by oxide of copper to ascertain its weight of water formed, the carbonic acid formed during this combustion may also be collected and determined, which furnishes no new relation, but only a verification of the INTRODUCTION. 445 quantity of carbonic acid n found in the eudiometric analysis. The relations are the following : z -\-v x _J_ z _l_ u -f v -f ?= V b, 3 , , _T. 760(1 + 0.00367.0) _ . 2 ~" = U. 0.001293. 0.622 = to which may be added, if the density D of the gaseous mixture has been deter- mined, the relation *, + H + zrf z 4- M <* 4- K 4- <=D. The problem is thus algebraically determined. If each of the numerical deter- minations were made with mathematical precision, the values of the unknown quan- tities, reduced by calculation, would be strictly correct. But, however carefully the operation may be conducted, each of these determinations is liable to slight error. Now, it is easy to be certain that by varying, by a very small quantity, each of the experimental data, b, m, n, a', V, A, and D, the value of the unknown quantities vary often by much larger quantities ; and, by marking certain hypo- theses, properly selected, on the composition of the gaseous mixture, it will be seen that by applying to the formulae numerical data which diifer very slightly, the calculated composition of the gaseous mixture ranges often between very extended limits. This observation is particularly applicable to the relation afforded by the density of the gaseous mixture, because the latter is composed of gases of which the individual densities, in general, differ but slightly. This relation must therefore be used with great caution. We have supposed, in the preceding observations, that the nature of the ele- mentary gases composing the mixture was known; but the question becomes much more difficult when this is not the case, and can, most frequently, only be answered by analysis, which must be most carefully conducted, and repeated several times ; and the operator must satisfy himself that the relations which fre- quently exist between the experimental data, and which we have given in each case, are fulfilled. If the experimental data were mathematically exact, the formulae suitable to the most complicated mixture might be applied to them at once, and the calculation would give no values for the gases which do not exist in the mixture. But, as these data are liable to trifling errors, small values for the gases which do not exist will generally be found, which values the operator must then examine with great care, and particularly the equations which often exist between the numerical data, in order to ascertain if these equations would not be rigorously fulfilled by the experimental data, by altering the latter by quan- tities equal to the extent of error to which each one is liable. None of the me- thods of analysis by absorption indicated ( 1244) should be neglected while examining the errors which each may have produced on the gaseous residue, by the solvent action which the reagents exert on the gas composing this residue. Lastly, if the analyst is provided with large quantities of gas, he may, by sub- jecting them to suitably selected chemical reactions, obtain some light on the nature of the component gases.* * The method for analyzing complicated gaseous mixtures is due to Bunsen, who first employed them in his masterly investigation of the gases issuing from blast furnaces. W. L. F. VOL. II. 2 N 446 PROXIMATE PRINCIPLES OP PLANTS. ESSENTIAL IMMEDIATE PRINCIPLES OF PLANTS. 1274. A microscopic examination of the various component parts of plants shows them all to be constituted of cellular tissue, varying in form according to the part of the vegetable subjected to inspection. The cavities of the tissue are filled with very diversified matter ; sometimes, as in the case of wood, the parietes of the cells are covered by a hard and brittle substance, called lignine, or woody fibre, which frequently almost completely fills their interstices; while at other times, as in the grains of the cerealia, potatoes, and other tubers, the cells contain a quantity of small ovoidal globules, varying in size, constituting fecula, or starch ; and lastly, in the case of the young organs of plants, the cells contain only a more or less viscous fluid, holding in solution mineral salts and various organic substances, the principal of which are gums, gelatinous sub- stances, and certain nitrogenous combinations, designated by the general name of albuminous substances. Oils or fat substances are frequently found in the cells, as in the oleaginous grains, some- times in large quantities. We shall begin by the study of these various substances, which are found in all members of the vegetable world, and which are essential to the existence of plants. CELLULAR TISSUE, OR CELLULOSE, C 12 H 10 10 1275. The cellular tissue is particularly evident in the young organs of vegetables. The cell is formed in the liquids which cir- culate through the plant, and grows by successive agglutina- tion with the cells previously formed, which occasions a modi- fication in the original forms of the cells. Sometimes they are rounded, and show a cer- tain regularity, as in the pith of the elder, (fig. 649,) and in the potato, in which case they con- stitute the cellular tissue pro- perly so called. At other times the cells form elongated tubuli, communicating by their con- tracted extremities, as seen in Fig. 649. n nm i i ^ fig. 650, which represents the longitudinal section of a stalk of asparagus, of which a transverse section is seen in fig. 651 ; and in figs. 652 and 653, which exhibit CELLULOSE. 447 (fig. 653) a fibre of flax or hemp, and (fig. 652) a fibre of cot- ton : the tissue is then called a vascular tissue. As the vegetable portions grow old on the living plant, the vascular vessels are filled with woody fibre, which increases gradually in thickness, and leaves only very narrow canals for the cir- culation of the sap. The whole of this mechanism consti- tutes wood. Among all the substances entering into the composi- tion of plants, the cellular tissue is dis- tinguished by its Fig. 650. Fig. 653. great resistance to chemical agents a resistance which allows its separation in a state of purity sufficiently perfect to permit the study of its chemical proper- ties, and to ascertain its ele- mentary composition. It has thus been found to be identi- cal, in Ms respect, not only in all parts of the same plant, but also in all different vege- tables. Chemists have given the name of cellulose to that constant substance which they regard as forming the cellular tissue of all plants. Cellulose is nearly pure in cotton, in which case it consists of the down of the cotton- seed ; and in hemp and flax, that is in the textile fibres extracted from the plants of these names. Cellulose is also nearly pure in paper and old linen, which are made of the substances just men- tioned, and which, during their prepartion and use, have been sub- jected to various chemical reactions, which have gradually effected the entire destruction of the more changeable foreign substances, mixed with the cellular tissue properly so called. Cellulose is extracted from various parts of plants by subjecting them to successive chemical reactions which destroy the more altera- ble woody fibre, the preparation being longer and more difficult in proportion to the quantity of woody fibre. The substance, when obtained in as disaggregated a form as possible, is digested with hot solutions of caustic potassa or soda, and, after washing the residue, is treated with weak chlorohydric acid, and washed with 448 PROXIMATE PRINCIPLES OF PLANTS. water. By a repetition of this process for a certain number of times, the woody fibre may be completely removed ; although the same result may be obtained more quickly by subjecting the sub- stance to more powerful oxidizing reagents, such as a weak solution of chlorine or hypochlorite of lime, and following each of these treatments with an alkaline solution and dilute chlorohydric acid. Although these various reagents attack the cellular tissue itself, the action on it is much less active than on the substances surround- ing it ; so that if the operation be carefully conducted, and reagents diluted with water be alone used, the greater portion of the cellu- lose escapes destruction. It is washed successively with alcohol and ether to dissolve the fatty matter. Pure cellulose, which is white and transparent, is insoluble in water, alcohol, ether, and the fixed or volatile oils. Dilute acid solutions have but little effect upon it, even at the boiling point, which is also true of sufficiently diluted alkaline solutions. The resistance which cellulose presents to these reagents varies with its cohesion ; recently formed cellulose being much more easily changed than that of older date. Concentrated sulphuric and phosphoric acid attack cellulose, and cause it to undergo a remarkable metamorphosis : after converting it into a soluble substance, called dextrine, they change it to a sugary substance, or glucose. Fuming nitric acid combines, when cold, with cellulose, and converts it into an insoluble sub- stance, eminently combustible and explosive, and which will be de- scribed hereafter. At the boiling point, nitric acid dissolves it, and oxalic acid is formed. Acetic acid, even in a concentrated state, has no action on cellulose. Cellulose, as it exists in the untouched cellular tissue of plants, is not coloured by an aqueous solution of iodine ; but when it has commenced to be disaggregated by sulphuric acid, it assumes a beau- tiful blue colour ; which reaction is frequently used in the study of vegetables under the microscope, because it distinguishes the cellu- lar tissue from certain nitrogenous membranes, which do not possess this property. After some time, a solution of chlorine, or a hypochlorite, com- pletely burns cellulose, forming water and carbonic acid; which combustion is rapid in a concentrated and hot solution of hypochlorite. The elemetary composition of cellulose is, Carbon 44.44 Hydrogen 6.18 Oxygen 49.38 100.00 The formula C 12 H 10 Oj is generally assigned to it ; but as there are no means of determining its chemical equivalent, the formula representing its molecular composition may be a multiple of the LIGNIN. 449 above. It will be remarked that hydrogen and oxygen exist in it in the proportions constituting water. Fig. 654. LIGNIN. 1276. It has been mentioned that the sides of the cells become generally incrusted with a substance formed at the expense of the organic substances dissolved in the sap; which constitution of ligneous matter is very well exhibited in fig. 654, representing a transverse section of a piece of oak-wood, as seen through the microscope. The black spaces are the canals which still re- main in the cells; some of which former, as a, are larger, and appear to be principally used for the circula- tion of the sap. As the wood grows by annual concentric layers, easily counted in old trees, the centre layers are older than the external ones, and their cells are also much more incrust- ed with ligneous matter than the latter. The central layers of the trunk of a tree, constituting the heart, are there- fore firmer and harder than the outer layers, forming the sap-wood; and they are also less subject to change, because they contain less sap and albuminous matter, which are the principal causes of the changes and rotting of wood. Although pure ligneous matter is sometimes deposited in the cells, resinous substances, which colour the wood and increase its combus- tibility, are generally precipitated at the same time ; while pellicles of nitrogenous matter are also formed. No way of isolating the ligneous matter in a state of purity being known, it has hitherto remained undecided whether the chemical composition of this substance is always identical; but sensible dif- ferences, which are observable in chemical reactions on the ligneous matter of various parts of vegetables, may possibly be produced by greater or less aggregation of the substance. Sawdust, successively subjected to the action of water, alcohol, and ether, presents a mix- ture of cellulose, lignine, a small quantity of nitrogenous matter, and several insoluble mineral salts ; and by analysis it is found to contain more carbon and hydrogen than pure cellulose : thus, lig- nine contains more carbon than cellulose, and hydrogen exists in it in a proportion larger than that which would form water with oxygen. The following tables exhibit the elementary composition of several kinds of wood, previously dried in vacuo at a temperature of 212 : 2 N 2 29 450 PROXIMATE PRINCIPLES OF PLANTS, Wood from the Trunk of the Tree. Beech. 49.46 Oak. 49.58 Birch. 50.29...... Aspen. 49.26 Willow. 49.93 Hydrogen .... Oxygen Nitrogen Ashes 5.96 42.36 1.22 1.00...... 5.78 41.38 1.23 2.03 6.23 41.02 1.43 1.03 6.18 41.74 0.96 1.86 6.07 39.38 0.95 3.67 100.00 100.00 100.00 100.00 100.00 Wood from the Branches. Beech. Oak. Birch. Aspen. Carbon 50.37 50.08 51.29 49.59.... Hydrogen.... 6.21 6.14 6.17 6.20..., Oxygen 41.14 41.38 40.41 40.23..., Nitrogen 0.78 0.95 0.87 1.00..., Ashes 1.50 1.45 1.26 2.98..., 100.00 100.00 100.00 100.00 100.00 1277. Wood is decomposed after some time, when subjected to the simultaneous influence of air and moisture, by the influence of a species of fermentation owing to the presence of nitrogenous albu- minous substances, and carbonic acid is disengaged, while the wood is converted into a brown or black substance, called humus, or mould; an alteration which is the more rapid when the wood is of recent formation, because its canals, being less incrusted with woody fibre, contain more sap, and, consequently, more albuminous nitrous mat- ter, which is the principal cause of the change. This substance, by its alteration, gives rise to true ferments, and serves as food for various insects which lodge in the wood and ultimately destroy it. If this be the cause of the rotting of wood, it might readily be pre- vented, if, by certain chemical agents, the alteration of the nitro- genous matter could be prevented, thus rendering it unfit for the food of animals. All poisonous substances which prevent the putre- "faction of animal matter produce this effect ; but the difficulty con- sists in making it penetrate all the vessels and cells of the wood. This question has attracted a good deal of attention in latter years, and several processes have been invented for its economical deter- mination on a large scale. The liquid containing the antiseptic substance has been made to penetrate the smallest vessels of the wood, by immersing one end of the trunk of a tree, of 2 to 4 metres in length, in a tub contain- ing the solution, while to the other end is fitted a cast-iron vessel, in which a vacuum is produced by the combustion of tow soaked in alcohol. By repeating this operation 2 or 3 times, the liquid is forced by the pressure of the atmosphere to traverse the whole length of the trunk. ALBUMINOID SUBSTANCES. 451 Advantage may also be taken of the vital circulation to cause the antiseptic fluid to penetrate trees when standing or when re- cently felled. When the tree is standing, it is sufficient to make at its foot two incisions, separated by an interval of a few centime- tres, and wrap around it a bandage of water-tight stuff, which re- ceives from a tub the liquid to be imbibed by the tree. The sap- wood, of which the canals are very open, is soon injected with the liquid, which, however, penetrates with more difficulty into the heart and the parts thickly incrusted with lignine. When the liquid is coloured, this irregular impregnation is manifested by the differences of shade and by veins, which often gives to the boards an appearance rendered very beautiful by polishing. Lastly, a process called displacement is sometimes used success- fully, which consists in placing the recently felled tree in a hori- zontal position and surrounding the trunk near its butt with a water- tight bag, held in place by a band over a pad of clay, and pouring into the bag the antiseptic liquid by means of a tube entering a tub placed somewhere near. The liquid displaces the sap and takes its place. In this way, the delicate woods, such as the pines and firs, may be rapidly and uniformly injected, but it is not so in the case of hard woods ; as, although the sap-wood is soon injected, the liquid penetrates with difficulty and irregularity into the heart of the tree. This process has been greatly improved, for railroad sleepers, in the following manner : A piece of wood, of twice the length of the sleeper, being sawed in the middle to within 3 or 4 centimetres of the opposite side, and the crack opened with a wedge, between the vertical sides of the crack a tarred rope is in- terposed, which, being strongly compressed when the wedge is re- moved, closes the sides hermetically and forms a small narrow re- servoir in the middle of the piece of wood. The antiseptic liquid, being then poured into this reservoir, ultimately penetrates the whole piece of wood. Of the many chemical substances which may be used for this purpose, the pyrolignite of iron or impure acetate of the protoxide of iron is generally preferred, on account of its efficiency and low price. This substance, which is obtained by means of the acid liquid produced by the distillation of wood in close vessels, contains, in addition to the acetate of iron, creasote and tar, whic assist in the preservation of the wood. Wood is frequently covered with tar and a substance called ma- rine glue, made by melting together 1 part of gum shellac and 2 parts of essence of coal-tar. NITROGENOUS OR ALBUMINOUS VEGETABLE SUBSTANCES. 1278. The nitrogenous matter of plants, designated under the general name of albuminoid substances, play an important part in vegetable physiology ; but as they have hitherto been but imper- 452 PROXIMATE PRINCIPLES OF PLANTS. fectly studied, we shall only state what is with certainty known con- cerning them. All these substances are solid ; some being soluble in water, as albumen, vegetable casein, and legumin ; while others are insoluble, as gluten. They are decomposed by heat, and exhale an odour similar to that peculiar to burnt feathers, giving rise to empyreu- matic gases and products, and leaving as an ultimate residue a black and brilliant spongy coal, the separation of which has been preceded by the fusion and swelling of the original matter. These substances may be indefinitely preserved after being perfectly dried; and in the moist state they can be preserved for a long time, if pro- tected from the air ; while, when placed under the simultaneous in- fluence of air and water, they soon decompose, rot, and call into existence a host of microscopic animalculse. All albuminous substances dissolve in caustic potassa and soda, and, on adding an acid to the solution, a nitrogenous substance sepa- rates, in the form of grayish flakes, which contract, on drying, into a hard and brittle mass, while at the same time a decided smell of sulf hydric acid is disengaged, and the liquid contains a certain quantity of phosphoric acid. The name of protein has been given to this nitrogenous substance, which appears to form the essential principle of all albuminous matter. It is not yet known with cer- tainty in what state the sulphur and phosphorus exist in these sub- stances ; but some chemists suppose albuminous substances to be compounds of protein with different proportions of sulphimide NH 2 S, and phosphimide NH 2 Ph. These sulphuretted and phos- phuretted substances are moreover found in very minute quantities in them. In order to separate protein from the alkaline liquid, acetic acid must be used, because the majority of the mineral acids combine with that substance. Protein is tasteless and inodorous ; soluble in water, alcohol, ether, and the essential oils ; soluble with alteration after some time in boiling water ; and its composition is represented by the formula. C 36 H 25 N 4 lo; Protein combines with acids, forming compounds soluble in water, but which are precipitated by the addition of a great excess of acid, and which are decomposed by the alkalies with the precipita- tion of the protein, which is again dissolved if an excess of alkali be added. Chlorohydric acid yields with protein, and, in general, with all albuminous substances, a blue liquid. Weak sulphuric acid destroys protein at the temperature of 212, forming several new products, among which is distinguished a white crystallizable sub- stance, called leucin. Nitric acid acts powerfully on protein, forming a yellow acid, called xanthoproteic, which combines, at the moment of its forma- tion, with a portion of the nitric acid ; but the compound is destroyed by boiling water and the xanthoproteic acid is precipitated. The ALBUMEN- 453 acid, which, when pure, is of an orange-yellow colour, pulverulent, and tasteless, combines with mineral bases and acids, yielding com- pounds of a more or less deep yellow colour. The xanthoproteates of potassa, soda, and ammonia are soluble ; and the other salts, which are all insoluble, are easily obtained by double decomposition. This reaction of nitric acid on protein is frequently applied in the study of vegetable anatomy to detect albuminous substances, since they are the only ones which turn yellow by contact with nitric acid. There is a still more delicate test in the reddish colour as- sumed by albuminous solutions when in contact with a mixture of nitrate and nitrite of mercury, which is easily obtained by dissolv- ing mercury in an equal weight of nitric acid containing 4J equi- valents of water, and then diluting the liquid with twice its volume of water. This liquid reacts, when cold, on albuminoid substances, and the discoloration is more rapid when it is heated to 212. Chlorine attacks protein suspended in water, and converts it into a white flaky substance, regarded as a chlorite of protein, because its composition is represented by the formula C 3G H 2? N 4 10 C10 3 . This substance, treated with an alkaline solution, loses its chlorine, disengages ammonia, and is converted into a soluble substance, called tritoxide of protein, because its composition corresponds to the formula C 36 H S5 N 4 12 HO. Chlorine produces a similar reaction on all albuminous matter ; and the same substance is also formed when water containing albumen in suspension is boiled for several days. Protein also combines with the alkaline earths, forming a pitchy substance, which becomes very hard by drying ; which property is applied to the manufacture of a luting made of white of egg and slaked lime, ( 661.) Albumen. 1279. Albumen is a principle widely disseminated throughout plants, and existing in them either coagulated in their tissues or dissolved in the liquids which circulate through their vessels. It is also largely found in the animal economy : the serum of the blood and the white of the egg are essentially composed of a solution of albumen in water. Animal albumen appears to be identical in com- position and chemical qualities with vegetable albumen, and many physiologists admit that this substance is furnished immediately to animals by the plants on which they feed. Albumen assumes two very distinct forms : soluble albumen, and coagulated or insoluble albumen ; and in both states, its chemical composition is the same. They will be easily understood by com- paring the albumen of a raw egg to that of one when cooked. The albumen of an egg begins to coagulate at about 140, while that of human serum remains unchanged until about 158; and as a gene- ral rule, albumen coagulates with greater difficulty in proportion to 454 PROXIMATE PRINCIPLES OF PLANTS. the quantity of water in which it is dissolved. Coagulated albumen no longer dissolves in water, but merely swells in it ; while the sub- stance obtained by evaporation, at a low temperature, from an al- buminous fluid, dissolves, on the contrary, in cold water, yielding a stringy liquid. Liquid albumen generally presents an alkaline reac- tion, and turns the plane of polarization of luminous rays toward the left ; serum of the blood and all albuminous liquids exhibiting the same property.* * A large number of substances in the organic kingdom exhibit a physical pecu- liarity belonging to their molecular constitution, which appears to be a special effect of organization, as it has hitherto not been observed in any inorganic sub- stance. It consists in the property possessed by their molecules of impressing modifications on polarized light, which are analogous, in many respects, to those it experiences when passing through non-symmetrical crystallized bodies, which faculty has been called the rotatory power, from the character of the effects which it produces. In this note we shall endeavour to explain its mode of manifesta- tion and the method of measuring its principal peculiarities ; and the idea we shall give it will suffice to attach it, from this time, as a specific character, to substances which possess it, as they will be described. We shall subsequently explain one of its practical applications in detail, and show how it may be applied to the exact determination, in a solution, of the proportion of matter in it which exerts the rotatory power. But, in order that these phenomena may be under- stood by persons who have not made a special study of optics, it is necessary to recapitulate a few of the chief laws of this science, on which the theory of these phenomena is based. When a simple, ray of light, emanating directly from a luminous source, falls, at an angle i, on the surface of a transparent medium, a greater or less portion of the ray is reflected ; and, if the medium is perfectly transparent and its sur- face polished, the portion of light not reflected traverses the medium. The plane containing the incident ray is called the plane of incidence, and the reflecting sur- face at the point of incidence is called the normal. The reflected ray remains in the plane of incidence, and its direction makes an angle i with the normal, equal to that which the incident ray makes with the same normal. The laws which the transmitted ray obeys, when the medium traversed is homogeneous in all direc- tions, are the following : If the transmitted ray is simple, it remains in the plane of incidence, and makes, with the normal, an angle r, so that there always exists between the angle of incidence and that of refraction r the relation ^^=??z, m being a constant quantity for the same medium, and called the index of refraction of the medium. The same laws apply to the case in which the ray of light, instead of falling from empty space on the medium, reaches it after having traversed a first medium equally homogeneous ; and the constant quantity m is then the relative index of re- fraction of the two media, and equal to the ratio of the indices of refraction of these media with regard to the space. The light of the sun is composed of an infinity of variously coloured rays, each of which has its own index of refraction ; and if therefore a mass of solar light be passed through a transparent prism, the rays separate and yield a coloured image, the solar spectrum, elongated in the direction of the refraction ; the rays which have the greatest index of refraction being the farthest removed from the direction of the incident ray. The light of burning bodies affords a similar spectrum, which differs from the solar spectrum in the ratio of intensity of the various coloured parts. The portion of light reflected at the surface of separation of two media varies with the angle of incidence, and is smallest when this angle is 0, that is, when the incident ray is normal to the surface ; while it increases with the value of this angle, and is equal to the incident light, when the angle of incidence is equal to 90, in which case the light is wholly reflected. However, when the ray passes ALBUMEN. 455 Many chemical reagents coagulate albumen when cold. Alcohol reduces it immediately to the insoluble state ; and ether produces the same effect, though more slowly. from a first medium into a second, of which the index of refraction is more feeble, in which case the value of m is smaller than 1, the total reflection of the incident ray commences before the rasant ray ; which occurs at all the incidences for which the relation ^^-=m gives values for the sin r greater than 1. Thus, the total reflection begins at the angle I, for which we have sin I=w; that is, the angle of total reflection. By being reflected at the surface of separation of two media, the nature of light is remarkably modified ; which is readily demonstrated by the apparatus, (fig. 655,) ab and cd are two polished transparent mirrors which revolve around horizontal axes o, o', perpendicular to the plane of the figure. The axes are supported by frames om, o'm', mounted on drums ef, e'f, which turn around the hollow cylinder gh, to which any inclination around the horizontal axis^? can be given. A narrow bundle of rays is received on the first mirror ab, at an incidence z, and the whole instrument is arranged so that the reflected ray shall follow the direction of the axis of the cylinder gh. This reflected ray is received on the second mirror cd at the same angle of incidence i; and by turning the drum e'f around the cylinder gh, all possible angles can be made on the second plane of reflection with the plane of reflection on the first mirror, without changing the angle of incidence f. Now, if the light reflected by the first mirror were still na- tural light, it would be always reflected in the same proportion on the second, whatever might be the azimuth of the plane of the second reflection compared with that of the first. But this is not the case, and the intensity of the light re- flected by the second mirror diminishes in proportion as the azimuth of the second plane of reflection increases, and is a minimum when the azimuth is 90; its variations being moreover symmetrical around the azimuths and 90. By vary- ing the common angle of incidence i, it can be ascertained that the variations of intensity of the light reflected on the second mirror in the various azimuths in- crease as we approach nearer the value of i given by the formula tang z=m, m being the index of refraction of the glass. Light which possesses this property is said to be polarized, and the angle at which it must be reflected from a transparent medium to acquire it is called the angle of polarization : it will be seen that this angle depends on the index of refrac- tion of the substance composing the mirror. Polarized light differs therefore from natural light in this, that while the latter is always reflected in the same proportion from a mirror inclined at the angle with the incident ray, for all azi- muths of the plane of reflection, polarized light is reflected in proportions varying with the azimuth of the plane of polarization ; and, if the angle t satisfies the rela- tion tang is=m, there is a position of the plane of reflection in which the reflected ray is null. The plane perpendicular to this particular direction of the plane of reflection is called the plane of polarization. When a ray of light falls on a mirror at the angle of polarization, the portion reflected is polarized in the plane of incidence ; and if the properties of the re- fracted ray be examined by means of a second mirror which receives it at the Fig. 655. 456 PKOXIMATE PRINCIPLES OF PLANTS. Albumen is extracted from flour by rubbing it with ten times its weight of cold water, allowing it to digest for several hours, de- canting off the water, and digesting with an additional quantity of angle of polarization, it is ascertained that the transmitted ray presents the pro- perties of a ray partially polarized, or of a mixture of natural and polarized light; but the plane of polarization of the polarized portion is perpendicular to the plane of polarization of the reflected portion. It may therefore be admitted that when a ray of natural light falls on a mirror at the angle of polarization, a portion of the light traverses the mirror without modification, but that the other portion is divided into two bundles polarized in planes perpendicular to each other ; and while the first bundle, which is polarized in the direction of the plane of incidence, is reflected, the second, polarized perpendicularly to this plane, is refracted. We recognise, moreover, that these two rectangularly polarized bundles are equal to each other, and that their union produces natural light ; which may therefore be regarded as formed by the union of two equal bundles, polarized at right angles. When the bundle of light which has traversed a first mirror at the angle of polarization traverses a second at the same angle, a portion of the natural light is divided into two bundles rectangularly polarized ; and the bundle polarized in the direction of the plane of reflection is reflected, while the bundle polarized perpendicularly to this plane is refracted and joins the portion polarized by the first refraction. After its passage through the second mirror, the bundle con- tains a portion of polarized light much greater than when it left the first. Trans- mission through a third mirror again increases the polarized portion ; so that after passing through a sufficient number of mirrors, at the angle of polarization, the bundle of natural light is entirely separated into light polarized in the direc- tion of the plane of incidence which is reflected, and into light polarized perpen- dicularly to the plane of incidence which traverses the mirrors. Crystallized media which do not belong to the regular system, effect imme- diately the separation of natural light into its two rectangularly polarized bundles. A bundle of natural light which falls on a rhomboid of Iceland spar, is divided in the crystal into two bundles, of equal intensity, polarized rectangularly, and which separate because they obey different laws of refraction. One of these bundles is polarized in the direction of the plane of the principal section of the rhombohe- dron ; while the plane of polarization of the second is perpendicular to the plane of the principal section. The first obeys the ordinary laws of the refraction of light in homogeneous media, and remains in the plane of incidence, the law ^-^=m being satisfied for all incidences ; for which reason it is called the ordinary ray. The second ray obeys very different laws : it remains in the plane of incidence only when this plane coincides or is perpendicular to the plane of the principal section, and it is only in this case that it satisfies a law-=m' similar to that which the ordinary ray obeys. In all other directions of the incident ray the law of the second refracted ray is more complex ; on which account this ray has been called the extraordinary ray. These two rays do not separate sufficiently to form two isolated images, except when the rhomb of spar is very thick; but a great separation may be produced by replacing the rhomb of spar by a prism cut out of this mineral ; so that the edges of the prism shall be perpendicular to the principal section of the rhombo- hedron. When the refracting angle of the prism is only 5 or 10, the two bundles separate sufficiently, but the images are coloured if the incident ray is not simple. This discoloration is avoided by gluing to the prism of spar a glass prism of a proper angle, the refraction of which, acting in a direction contrary to that of the prism of spar, almost entirely destroys the dispersion of colours. This apparatus, which is frequently used in the study of polarized light, is called an achromatic birefracting prism ; and it enables us to examine, with ease, the pro- perties of light polarized by reflection from a mirror: when used for this purpose, it is often called an analyzing prism. If the light is completely polarized in the direction of the plane of reflection, it is evident that when the plane of the prin- cipal section of the birefracting prism coincides with the plane of reflection, all ALBUMEN. 457 flour. After having repeated this operation three or four times, a liquid is obtained containing a certain quantity of albumen, which can be separated by evaporation at a low temperature. the light will traverse the prism in the state of an ordinary ray, and the extra- ordinary ray will be extinguished. When, on the contrary, the plane of the principal section is perpendicular to the plane of polarization of the ray, the light will pass wholly in the extraordinary ray, and the ordinary ray will be null. In all the intermediate azimuths of the principal section of the birefracting prism, there will be an ordinary and an extraordinary image ; and their relative intensities will vary according to the position of the principal section. The law of these varia- tions is very simple : let C be the angle which the plane of the principal section of the birefracting prism makes with the plane of original polarization ; and I the intensity of the polarized ray which falls on this prism : the intensity of the ordi- nary ray is I cos a , and that of the extraordinary ray I sin 2 : in all cases the rays are complements of each other, for we always have I cos *-{-! sin a ^=l. The birefracting prism is very convenient for determining the direction of the plane of polarization of a polarized ray ; as it is sufficient to find the direction to be given to the plane of the principal section of the prism, in order that the extra- ordinary fasciculus furnished by the normal incident ray may become null. In order to understand the modifications experienced by polarized light when it traverses various media, the apparatus represented in fig. 656 is frequently used ; in which ab represents a polished mirror, receiving the luminous rays at the angle of polarization, and reflecting them in the line cd, while at n is an achromatic bi- Fig. 656. refracting prism, mounted on the centre of a movable index mn, which moves on a graduated circle pg perpendicular to the line cd. The plane of polarization of the ray reflected by the mirror being vertical, the extraordinary image afforded by the birefracting prism will vanish when its principal section is in the vertical plane, and the alidade will then correspond to of the division. AB is a support on which various transparent media, which will be traversed by the polarized ray, as, for example, fluids contained in tubes, can be placed. Fig. 657 represents the longitudinal section of one of these tubes ; which is composed of a tube of thick glass, generally enclosed in a metallic tube to which are fitted the two ferrules m, n, which support the glass plates closing the ends of the tubes. If AB, one of those tubes, filled with water, alcohol, or ether, Fig. 657. be placed on the support, so that the ray of polarized light may be obliged to tra- 458 PROXIMATE PRINCIPLES OP PLANTS. In order to extract albumen from potatoes, they are cut into thin slices, which are digested in water containing two per cent, of sul- phuric acid. The water is decanted after twenty-four hours, and verse the liquid before reaching the birefracting prism, it will be seen that the ray has suffered no essential change in its properties by its passage through the fluid ; it is still completely polarized, and its plane of polarization remains ver- tical. But, on substituting for pure water several other liquids, as, for example, a solution of cane-sugar, the properties of the polarized light are completely modified. Thus, before the interposition of the tube containing the solution of sugar, the extraordinary image of the birefracting prism is null when the index marks ; and the image reappears if the tube be interposed. Nevertheless, the light has not been depolarized by its passage through the solution of sugar, and remains completely polarized ; but its plane of polarization is no longer vertical, and it has been deviated by a certain angle toward the right of the observer who looks through the birefracting prism ; and, in fact, if the index be turned to the right by a certain angle a, the extraordinary image disappears entirely. The solution of sugar has, therefore, turned toward the right, by an angle a., the plane of polarization of the light. If tubes of different lengths be filled with the same solution of sugar, it will be found that the angles of deviation are in pro- portion to the lengths of the tubes. On filling a tube of uniform length, successively, with solutions more and more rich in sugar, it is found that the angles of deviation a. are in proportion to the quantities of sugar contained in the same volume of liquid. It may, therefore, be said in general terms that the deviations, or rotations, of the plane of polarization are in proportion to the number of molecules of sugar which the luminous ray meets in its passage. Let * be the deviation impressed by a homogeneous liquid on the plane of polarization of the simple ray, acting on it under the same cir- cumstances, through units of space and with an imaginary density equal to unity. The density becoming $, without any change in the energy of the molecular action, the deviation, through the unity of thickness, will be [at] i: then, the length becoming I for the same density, the total deviation will be [t] 13. If, therefore, a. represent the deviation observed experimentally, we shall have [>]#=*, whence [ CO,)+NH,=0 4 H 5 0,(NH as C,0.)+C 1 H,0,. If a concentrated solution of caustic potassa in anhydrous alcohol be saturated with carbonic acid gas, the liquor at last sets into a mass, in consequence of a copious deposit of carbonate, bicarbonate, and carbovinate of potassa. Ether, which completes the precipita- tion of the carbovinate of potassa, is poured into the flask, and after having decanted the liquor, the deposit is shaken with absolute alcohol, which dissolves only the carbovinate. The alcoholic solu- tion is filtered and dropped into very anhydrous ether, which again precipitates the carbovinate of potassa. The formula of the salt, dried in vacuo, is KO,(C 4 H 5 0,2C0 3 ) ; and it forms white, pearly 2u2 534 TRANSFORMATIONS OF ALCOHOL. spangles, greasy to the touch. Water decomposes it instantly into alcohol and bicarbonate of potassa. Oxychlorocarlonic Ether C 4 H 5 OC 3 3 C1. 1351. On pouring absolute alcohol into a matrass filled with chlo- rocarbonic gas, COC1 (258,) the temperature rises, and the liquid separates into two layers, the lower of which is formed of oxychlo rocarbonic ether. It is purified by digesting it over litharge or chloride of calcium, and then distilling it. This ether is liquid, colourless, having a penetrating odour, which excites to tears ; and its density is 1.133, while it boils at 201.2, and burns with a green flame. Boiling water decomposes it ; and it may be considered as a compound of carbonic ether C 4 H 5 0,C0 3 and chlorocarbonic gas CO 01. Ammonia decomposes it, chlorohydrate and carbonate of ammonia, and carbonic ether, being formed. Oxalic Ether C 4 H 5 0,C 3 3 , and Oxalovinic Acid C 4 H 5 0,2C 3 3 . 1352. The best method of preparing oxalic ether consists in mixing in a tubulated retort 1 part of oxalic acid dried at 212, the formula of which is then C 3 3 ,HO, with 6 parts of absolute alcohol. A thermometer, the bulb of which reaches nearly to the bottom of the retort, is fitted to its tubulure, and the distillation is continued until the thermometer marks 284, when distilled alcohol is intro- duced and the distillation repeated, ceasing only when the thermo- meter marks 320. The liquid remaining in the retort is then poured into water, when oxalic ether separates as a heavy liquid, which, after being washed several times with water, is again distilled over litharge, which seizes upon the free oxalic acid. The product, after being left for some time in contact with fused chloride of cal- cium, is pure oxalic ether. It is colourless, and of an aromatic odour ; and its density is 1.093, while it is very slightly soluble in water, but perfectly so in alcohol. The density of its vapour is 5.078: it boils at 363.2, and its equivalent C 4 H 5 0,C 3 3 corre- sponds to 2 volumes of vapour. Oxalic ether is decomposed by contact with a solution of potassa, into alcohol and oxalic acid, which decomposition is also effected, after a long time, by pure water ; and when left in a badly-stoppered bottle, in contact with moist air, it deposits crystals of hydrated oxalic acid. Ammonia exerts a remarkable action upon it, forming two new products, oxamid and oxamic ether. On dropping oxalic ether into a solution of ammoniacal gas in absolute alcohol, a peculiar substance, first called oxamethan, is formed, which is now regarded as a compound ether, formed by a peculiar acid, called oxamic, C 3 3 NH 2 ,C 3 3 . On evaporating the liquid, the substance separates in the form of lamellated crystals, of a greasy aspect, melting at about 212, and distilling without change at 248. It dissolves readily in water and in alcohol, its ETHERS. 535 aqueous solution being decomposed, by boiling, into binoxalate of ammonia and alcohol. The formula of oxamic ether is C 4 H 5 0, (C 3 3 NH 3 ,C 2 3 ) ; and the reaction from which it arises is expressed by the following equation : It has already been shown that the oxamid C a 3 NH 3 is formed during the distillation of oxalate of ammonia. This substance is more easily prepared by decomposing oxalic ether by an aqueous solution of ammonia. Oxamid is a white crystalline substance, having no action on coloured tests ; and cold water does not sensi- bly dissolve it, while hot water dissolves a small quantity of it, which is again deposited on the cooling of the liquid. Dilute acids and alkalies, when cold, do not affect oxamid ; but at the boiling point, oxamid again takes up two equivalents of water, and yields ammonia NH 3 ,HO and oxalic acid C 3 3 . On adding to oxalic ether dissolved in absolute alcohol a quan- tity of potassa also dissolved in anhydrous alcohol, in such quantity that it shall saturate one-half of the oxalic acid existing in the ether, a salt almost insoluble in absolute alcohol is precipitated in the form of small crystalline lamellae, consisting of oxalovinate of potassa, which dissolves without alteration in water, but subse- quently crystallizes with difficulty. If too great a quantity of potassa be added, oxalate of potassa and alcohol only are obtained. The formula of the salt is KO,(C 4 H.O,2C 2 3 ) ; and when it is pre- cipitated mixed with a certain quantity of oxalate of potassa, it may be separated from it by treating the precipitate with slightly diluted alcohol, which dissolves only the oxalovinate of potassa. By adding sulphuric acid to this solution, the potassa is precipitated in the state of sulphate, and, if the liquid be then saturated with caustic baryta, a solution of oxalovinate of baryta is obtained. The aqueous solution of oxalovinic acid is readily decomposed by evaporation, and crystals of hydrated oxalic acid are obtained. Mucic Mher C 4 H 5 0,C 6 H 8 7 . 1353. Mucic acid does not form a compound ether by its direct action on alcohol, but a mucic ether is obtained by dissolving, with the aid of heat, 1 part of mucic acid in 4 of sulphuric, and then adding to the liquid, when cooled, 4 parts of alcohol. After some time a copious deposit of acicular crystals is formed, which are purified by solution in boiling alcohol, from which they again sepa- rate on cooling. The crystals are mucic ether C 4 H 5 0,C 6 H 8 7 , which melts at about 284, and is decomposed at 338 without dis- tilling. It dissolves in boiling water, from which it again separates almost entirely on cooling ; and boiling alcohol also dissolves it, while after cooling it retains but very feeble traces of it. 536 TRANSFORMATIONS OF ALCOHOL. Compounds of Ether C 4 H 5 with the Metallic Chlorides. 1354. Simple ether forms crystallizable compounds with several metallic chlorides, particularly with the bichlorides of tin and titanium. By introducing into a very dry bottle, containing bichloride of tin or titanium, an open tube containing ether, and allowing the bottle to rest, crystals remarkable for their sharpness, and of which the formula is 2C 4 H.O,SnCl 2 , 2C 4 H 5 0,TiCl 3 , are formed on its sides. The crystals dissolve without change in ether and absolute alcohol, but are decomposed by contact with water, the ether being set free. Compound of Ether with Sulphide of Carbon, Sulphocarlovinic Acid or Xanthic Acid C 4 H 5 0,2CS 2 . 1355. These compounds are obtained by dropping into a solu- tion of potassa in absolute alcohol sulphide of carbon until the liquid has lost its alkaline reaction, when a peculiar salt of potassa is formed, the greater portion of which separates in the form of orange- coloured crystals. The composition of the salt corresponds to the formula KO,(C 4 H 5 0,2CS 2 ), and it may therefore be regarded as a vinic acid in which the ether C 4 H 5 is combined with sulphocar- bonic acid CS 3 : it is also called xanthic acid. The acid is separated by pouring sulphuric or chlorohydric acid into a solution of xanthate of potassa, when the liquid becomes milky, while a colourless oil separates from it, which is several times washed with water. This is xanthic acid, which is not very fixed when isolated. The alkaline xanthates are soluble in water, while the other metallic xanthates are insoluble and are precipitated in the form of yellow powders. Xanthates yield, by distillation, several new products, which, however, have not been hitherto suffi- ciently investigated. SIMPLE ETHERS. 1356. The equivalent of oxygen in ether C 4 H 5 may be re- placed by respectively 1 equivalent of chlorine, bromine, iodine, sulphur, selenium, tellurium, and cyanogen ; and volatile substances may be thus obtained, some of which can form compound ethers and vinic acids. We shall call this class of ethers simple ethers ; and ordinary ether C 4 H 5 necessarily belongs to it. Chlorohydric Ether C 4 H 5 C1. 135T. This substance is directly formed by the reaction of chlorohydric acid on alcohol. Absolute alcohol, made very cold by being surrounded with ice, is completely saturated with chlorohydric acid gas, and the liquid is then distilled, the gas evolved being con- veyed through a washing-bottle containing water and kept at a tem- perature of 77 or 86, and thence into a receiver cooled by a re- ETHERS. 537 frigerating mixture. Chlorohydric ether being gaseous at a tem- perature above 55.4, traverses the water in the washing-bottle, which retains the excess of chlorohydric acid or alcohol ; and con- denses in the receiver. In order to remove all traces of alcohol and water, the chlorohydric ether is distilled with concentrated sul- phuric acid. The reaction from which it arises is expressed by the following equation : C 4 H 6 3 +HC1=C 4 H 5 C1+2HO. Chlorohydric ether may also be prepared by heating in a flask a mixture of alcohol at 0.85 and concentrated chlorohydric acid of commerce ; the gas being first passed through a washing-bottle containing water, and then through a second containing concentrated sulphuric acid ; both bottles being kept at a temperature of 68 or 77. It may also be procured by introducing into the flask 12 parts of sea-salt, and then adding a mixture of 1 part of sulphuric acid and 5 parts of alcohol. If the temperature of the laboratory exceed 59, the ether may be collected in the gaseous state in bell- glasses over mercury. Chlorohydric ether, at a low temperature, is a colourless liquid, of a sharp, slightly alliaceous smell; and its density at 32 is 0.291, while it boils at 54.5 under the ordinary pressure of the atmosphere. It should be preserved in a vessel the neck of which is hermetically sealed. It dissolves in 50 parts of water at 32, and mixes with alcohol in every proportion. The density of its vapour is 2.235, and its equivalent C 4 H 5 C1 corresponds to 4 volumes of vapour. Aqueous alkaline solutions decompose it slowly into alcohol and chlorohydric acid, the decomposition being immediate if the alkali is dissolved in alcohol. Chlorohydric ether combines with several metallic chlorides, and its compounds may be regarded as compound ethers of the simple ether. It is largely soluble in perchloride of tin, and a definite compound in the form of acicular crystals separates from it. Per- chloride of antimony also forms a crystalline compound, but very soon reaction ensues with the formation of protochloride of anti- mony. Chlorohydric ether also combines with sesquichloride of iron; but all these compounds are destroyed by water, and the chlorohydric ether again becomes free. Chlorohydric ether is freely absorbed by anhydrous sulphuric acid ; a liquid, fuming in the air, and readily decomposed by heat, being formed. Bromohydric Ether C 4 H 5 Br. 1358. This ether is prepared by placing in a tubulated retort, furnished with its receiver, 1 part of phosphorus and 40 parts of alcohol at 0.85, and then adding, drop by drop, through the tubu- lure, 7 or 8 parts of bromine. By the reaction of the bromine on 538 TRANSFORMATIONS OF ALCOHOL. the phosphorus, in presence of the water contained in the alcohol, phosphorus and bromohydric acid are formed, which latter converts the alcohol into bromohydric ether C 4 H 6 3 +HBr=C 4 H.Br+2HO. When the reaction is terminated the retort is heated, still keeping the receiver very cold ; and the bromohydric ether is washed with a very weak solution of potassa, and then distilled over chloride of calcium, when it appears as a colourless liquid, having a density of 1.473, at 32, and boiling at 105.8. lodohydric Ether C 4 H 5 I. 1359. It is prepared by heating in a retort 5 parts of iodide of phosphorus with 2 parts of alcohol at 0.85, shaking with alkaline water the liquid collected in the receiver, and then distilling over chloride of calcium. lodohydric ether is a colourless liquid, having a density of 1.97 at 32, and boiling at 158. Light soon turns it brown, announcing the commencement of decomposition. Its for- mula C 4 H 5 I corresponds to 4 volumes of vapour. Qyanohydric Ether C 4 H 5 Cy. 1360. This ether is obtained by distilling a concentrated solu- tion of sulphovinate of baryta with cyanide of potassium, washing the distilled product with water slightly alkaline, and distilling over chloride of calcium. Cyanohydric ether is a colourless liquid having a strongly alliaceous smell, and highly poisonous : its density is 0.787, and it boils at 179.6. Alkalies dissolved in water decom- pose it slowly, while oxide of mercury effects a much more rapid decomposition, resulting in cyanide of mercury, cyanohydric acid, and alcohol. Sulfhydrie Ether C 4 H 5 S and its Compound Ethers. 1361. Sulf hydric ether is prepared by passing chlorohydric ether through an alcoholic solution of monosulphide of potassium, after which the liquid is allowed to rest, for 24 hours, in a well- corked bottle, and then distilled ; when alcohol, sulf hydric ether, and chlorohydric ether condense in the receiver. This mixture is shaken several times with water, which dissolves the alcohol and chlorohydric ether, and the supernatant fluid, being then separated by means of a pipette, is distilled over chloride of calcium. The first portions which pass over in distillation should be rejected, be- cause they may contain chlorohydric ether. Sulf hydric ether is a colourless, very volatile liquid, of a pene- trating alliaceous smell, to which it is dangerous to be long ex- posed; and its density is 0.825, while it boils at 163.4. It is slightly soluble in water, but in all proportions in alcohol. The density of its vapour is 3.138 ; and the equivalent C 4 H 5 S therefore corresponds to 2 vols. of vapour like ordinary ether C 4 H 3 0. 1362. If chlorohydric ether be passed through an alcoholic ETHERS. 539 solution of sulfhydrate of sulphide of potassium KS,HS, and be distilled, a much more volatile liquid is obtained, the composition of which is represented by C 4 H 6 S 3 ; and which is therefore alcohol C 4 H 6 3 with 2 equiv. of sulphur substituted for 2 equiv. of oxygen. It may be called sulfhydric alcohol, and its formula may also be written C 4 H 5 S,HS, regarding it as a compound ether of sulfhydric ether C 4 H 5 S. It has been called mercaptan, on account of its pro- perty of combining with oxide of mercury, (mercurium captans.) This compound is also obtained by distilling in a water-bath a mixture of a solution of sulfhydrate of sulphide of potassium and a concentrated solution of sulphovinate of lime. The receiver should, in all cases, be cooled, because the product is very volatile : KS,HS + CaO,(C 4 H 5 0,2S0 3 )=C 4 H 5 S,HS-}-KO,S0 3 -fCaO,S0 3 . The substance is freed from a small quantity of sulfhydric acid by distilling it over red oxide of mercury. Sulfhydric alcohol is a colourless liquid, of very disagreeable and penetrating alliaceous smell : its density is 0.84 ; it solidifies at about 7.6, and boils at +96.8 ; the density of its vapour being 2.14, so that its equivalent C 4 H.S,HS is represented by 4 volumes, like that of alcohol. Sulfhydric alcohol forms, with the metallic oxides, compounds in which the hydrogen of the sulfhydric acid is replaced by 1 equiv. of metal, and these compounds have been called mercaptides. The most interesting, on account ' of the facility with which it is pro- duced, is the mercaptide of mercury, which may be called sulplw- mercuric alcohol. In order to prepare it, an alcoholic solution of sulfhydric alcohol is gradually poured upon red oxide of mercury, when they combine with elevation of temperature, while a white substance is formed. It is dissolved in boiling alcohol, and, on cooling, separates into white, pearl-like spangles, of which the for- mula is C 4 H 5 S,HgS. This substance melts at about 185, and de- composes above 248. Treated with sulfhydric acid it yields sul- phide of mercury and sulfhydric alcohol. If sulfhydric alcohol be poured into an alcoholic solution of acetate of lead, a yellow crystalline precipitate of sulphoplumbic alcohol C 4 H 5 S,PbS is formed. When sulfhydric alcohol is heated with potassium, hydrogen is disengaged, and a sulphopotassic alcohol C 4 H 5 S,KS is formed : C 4 H 5 S,HS+K=C 4 H 5 S,KS+H. A solution of the product in alcohol yields, on evaporation, a white granular substance ; and the salt, when treated with acids, yields a salt of potassa and sulfhydric alcohol. When mixed with an alcoholic solution of chloride of mercury, sulphomer curie alcohol is formed.* By distilling a concentrated solution of 2 parts of pentasul- * These bodies may be viewed as sulf hydrates conjugate with 2C a H a . /. C. B, 540 TRANSFORMATIONS OF ALCOHOL. phide of potassium KS 5 with 3 parts of sulphovinate of lime, water and a peculiar etherial liquid pass over, by washing which with water, and distilling it over chloride of calcium, a liquid results of a very disagreeable alliaceous odour, boiling at 303.8, and of which the formula is C 4 H 5 S S . On heating an excess of sulfhydric alcohol with dilute nitric acid the liquor becomes red, from the production of a certain quantity of deutoxide of nitrogen which dissolves in it, but it loses its colour when heated, and after some time an oleaginous liquid separates from it. Nitric acid is gradually added, until the sulf- hydric alcohol is entirely decomposed; after which the liquid is diluted with water, and, after having washed the oleaginous sub- stance several times, it is distilled. This new substance is without colour, of an extremely disagreeable odour, of the density 1.24 ; and it boils at about 266, but not without alteration. Its com- position is represented by the formula C 4 H 5 S,S0 3 ; and it would therefore be a compound ether, formed by the combination of sulf hydric ether with sulphurous acid. When the action of dilute nitric acid on sulfhydric alcohol is prolonged until the oxidizing action ceases, an acid compound is obtained, which forms crystallizable salts with bases ; and from the analyses which have been made, the formula of the salt of baryta would be BaO,(C 4 H 5 S a 4 )+HO. 1363. If chlorohydric ether be passed through an alcoholic solution of sulphocarbonate of sulphide of potassium KS,CS 2 , a sulphocarbonic ether C 4 H 5 S,CS 3 which corresponds to carbonic ether C 4 H 5 0,C0 3 is formed. After having allowed the substances to act for some time, the liquor is heated to drive off the excess of chlorohydric ether, and it is treated with water; when a liquid of an alliaceous smell, heavier than water, separates from it, which new substance is sulphocarbonic ether C 4 H 5 S,CS 2 . A sulphocyanohydric ether C 4 H 5 S,C 3 NS is obtained by distil- ling a mixture of equal parts of sulphovinate of lime and sulpho- cyanide of potassium, both in concentrated solution. The product, purified by washing, and then by distillation, is a colourless, very limpid liquid, of the density 1.020, boiling at 294.8. Its equiva- lent is represented by 4 volumes of vapour. Selenohydric Ether C 4 H 5 Se. 1364. It is obtained by distilling selenide of potassium with sulphovinate of potassa ; but its properties are little known. TelluroJiydric Ether CJSLTe. 1365. By projecting telluride of potassium into a hot solution of sulphovinate of baryta, and then distilling, a liquid is obtained of a reddish-yellow colour, heavier than water, very poisonous, and ALDEHYDE. 541 which boils above 212. It is tellurohydric ether; and oxidizes slowly in the air, depositing tellurous acid. PRODUCTS OF THE OXIDATION OF ALCOHOL AND ETHER. 1366. When alcohol and ether are subjected to a very powerful oxidizing action, they are completely consumed, and converted into water and carbonic acid ; while, when the oxidizing action is less powerful, they are converted into acetic acid C 5 H 3 3 ,HO, in which case they lose 2 equiv. of hydrogen, which form water with 2 equiv. of oxygen given off by the oxidizing substance, while the 2 equiv. of hydrogen are replaced by 2 equiv. of oxygen, also given off by the oxidizing reagent. We thus have C 4 H 5 4- 40=C 4 H 3 3 ,HO+HO, or C 4 H/),HO+40=C 4 H 3 3 ,HO+2HO. When the oxidizing action is still more feeble, it is limited to the abstraction of a single equiv. of hydrogen, and to its replacement by 1 equiv. of oxygen, which furnishes aldehyde C 4 H 4 2 , according to the formulae C 4 H 5 0+20=C 4 H 4 2 +HO, and C 4 H 5 0,HO+20=C 4 H 4 3 +2HO. Aldehyde C 4 H 4 3 . 136T. Aldehyde is formed under a number of circumstances, in which alcohol, ether, and the compound ethers are subjected to oxidizing agencies ; while the best method of preparing it consists in distilling in a retort, at a gentle heat, a mixture of 6 parts of con- centrated sulphuric acid, 4 parts of water, 4 parts of alcohol at 0.80, and 6 parts of finely powdered peroxide of manganese. The retort should only be one-third filled, because the mixture swells considerably during the operation; and a cooling apparatus, through which very cold water passes, and a receiver surrounded by a re- frigerating mixture are fitted to the retort. When the reaction appears to be terminated in the retort, the liquid which condensed in the receiver is withdrawn and distilled at two different times over an equal weight of chloride of calcium. The liquid obtained is composed of aldehyde, a small quantity of alcohol and water, and acetic and formic ether. In order to obtain the aldehyde, it is poured into ether saturated with ammoniacal gas; when white crystals, consisting of a combination of aldehyde and ammonia NH 3 ,C 4 H 4 3 are separated. The crystals are dissolved in their own weight of water, and the solution is introduced into a retort furnished with a receiver cooled by a refrigerating mixture, while sulphuric acid diluted with its volume of water is poured through the tubulure. On distilling it over a water-bath, a liquid is ob- tained which, when distilled over melted chloride of calcium, yields pure aldehyde. VOL. II. 2 V 542 TRANSFORMATIONS OF ALCOHOL. Aldehyde is a colourless, very limpid liquid, of a suffocating odour, and its density is 0.790 at 64.4, while it boils at 71.3, the density of its vapour being 1.479, and its equivalent C 4 H 4 3 there- fore corresponding to 2 vol. of vapour. It dissolves, in all propor- tions, in water, alcohol, and ether, burns with a white flame, and exerts no action on vegetable colours. Aldehyde readily absorbs oxygen from the air, particularly in the presence of water, and is converted into acetic acid, which transformation is effected by all oxidizing agents : thus oxide of silver is reduced by a solution of aldehyde, the metallic silver adhering to the sides of the vessel and covering them with a glittering coating ; and nitrate of silver pro- duces the same effect if a small quantity of ammonia be added. Alkalies decompose aldehyde, forming, together with other products, a brown resinous matter, which reaction is often indicated as being characteristic of aldehyde. Pure and anhydrous aldehyde, preserved for some time in a tube hermetically closed, undergoes isomeric modifications, differing ac- cording to the temperature. At 32 it is converted into a crystal- line, colourless, and transparent substance, which melts at 35.6, and boils at 201.2. The density of its vapour being three times greater than that of aldehyde, its formula may be assumed to be C 12 H 13 6 . It has been called elaldeliyde. If, on the contrary, the external temperature range from 59 to 68, elongated prismatic crystals, which finally fill the tube, are developed in the aldehyde, and which volatilize at 248 without melting. This second isome- ric modification of aldehyde has been called metaldehyde, and the density of its vapour is unknown. Aldehyde is also formed whenever alcohol is burned imperfectly in contact with the air ; for example, when that liquid is dropped upon metallic plates heated to 482, or when a wick soaked in alcohol is lighted, and extinguished as soon as the greater portion of the alcohol has evaporated ; when the wick is carbonized, and the small quantity of vapour of alcohol which comes in contact with the ignited portions is imperfectly burned, and yields aldehyde, which is known by its suffocating smell. A large quantity of aldehyde is also produced in the experiment of Davy's flameless lamp,.( 1169.) When chlorine is passed through diluted and cold alcohol, chloro- hydric acid and aldehyde only are formed, the chlorine then exert- ing an oxidizing agency on the alcohol, by decomposing the water and combining with its hydrogen : C 4 H 5 0,HO-f 2Cl+HO=2HCl+ C 4 H 4 O a . Acetic Acid C 4 H 3 3 ,HO. 1368. Alcohol, when pure, or merely diluted with water, does not combine with the oxygen of the air, while the combination is readily effected in the presence of certain substances the chemical elements of which do not interfere, as, for example, very finely di- ACETIC ACID. 543 vided platinum, which metal may cause the oxidation of a large quantity of alcohol at the expen'se of the oxygen of the air. In order to perform the experiment, a capsule a (fig. 678) containing platinum-black is placed on a plate, and the capsule is covered with a large bell-glass hav- ing an opening o at the top, and which rests on three small wooden wedges, to allow the air to enter from beneath; and finally, a funnel b having a long and delicate neck c is introduced into the opening. By pouring alcohol into the funnel, the liquid drops on the platinum con- tained in the capsule, and while a slight eleva- Fig. 678. t - on O f temperature ensues, vapours which con- dense and trickle down the sides of the glass are developed therein. The liquid thus formed on the bottom of the plate is nearly pure acetic acid ; but there is produced at the same time, 1st, a certain quantity of aldehyde, easily recognised by its smell ; 2dly, a peculiar substance called acetal ; and 3dly, a small quantity of acetic ether, arising from the reaction of the acetic acid on the undecomposed alcohol. If the acid liquor be saturated with chalk and distilled, there is obtained in the receiver, water holding in solution aldehyde, acetic ether, and acetal. If this new liquid be digested with its own weight of chloride of calcium, the latter combines with the water and acetic acid, and etherial liquid separates, which is again distilled, the first portions which pass over being rejected, because they contain a large amount of aldehyde, while the last portions are pure acetal. Acetal is a colourless liquid, boiling at 167, of a density of 0.844, and so- luble in water and alcohol. Its composition corresponds to the for- mula C 14 H 4 4 , and it maybe regarded as being formed by the union in a single group of three molecules of ether, one of them having been modified, under the oxidizing influence, by the substitution of 1 equiv. of oxygen in the place of 1 equiv. of hydrogen, 3C 4 H 5 0+20 = C la H 14 4 +HO. 1369. The oxidation of alcohol at the expense of the oxygen of the air is also effected by organic ferments, and in general by all albuminous substances, upon which mysterious action is based the conversion of spirituous liquors into vinegar, that is to say, into acetic acid. Wines of certain vintages, rich in albuminous matter, soon turn sour in the air, and become vinegar ; which change new wines undergo much more rapidly than the old, because the latter are freed from albuminous substances, which coagulate and fall to the bottom of the barrel ; and therefore, in order to make them fer- ment, they must be diluted with a small quantity of water and be exposed to the air. "What has just been said of wines is equally ap- plicable to other alcoholic liquors, and even 10 solutions of sugar mixed with yeast and exposed to the air. During the acid ferment- 544 TRANSFORMATIONS OF ALCOHOL. ation of alcoholic liquors, a mucilaginous substance, which greatly assists this fermentation, is separated, and which, consisting chiefly of albuminous matter, is called the mother of vinegar. In order that acetification may progress rapidly, the alcoholic liquor must be sufficiently diluted with water, and present a large surface to the oxidizing action of the air. These conditions are ful- filled on a large scale by using an alcoholic liquor containing 1 part of alcohol to 8 or 9 parts of water, and adding about -^ m of ferment- able liquor, such as beet-juice, potato-juice, or small beer, when the liquor thus prepared is dropped into barrels (fig. 679) filled with beech shavings. The lower part of the barrel is pierced with seve- ral holes a, and the upper part with other holes 6, 5, while a false bottom cde forms a vat, into which the alcoholic liquor is poured. The false bottom has a great number of holes, through which pass pieces of twine, having a knob on the end to prevent them from slipping through. The alcoholic liquor flows along the twine, and dropping on the shavings, spreads into a thin layer, and pre- sents a large surface to the oxidiz- ing action of the air, oxidation being effected by means of the ferment con- tained in the liquor and the albumi- nous substances in the wood, while the temperature rises and produces a current of air which enters at the lower holes a and escapes through the upper ones b. Oxidation is so rapid that when the liquid reaches the bottom of the barrel, it frequently no longer contains any alcohol, but if, after one pas- sage, the alcohol is not completely converted into acetic acid, it is passed through a second time. The presence of acetic acid itself assists the acetic fermentation, for which reason the fresh shavings to be used are previously left for some time in concentrated vine- gar. The temperature of the barrel also exerts great influence, and, if it be too cool, heated alcoholic liquor must be added to bring the temperature to between 86 and 97. The acid liquors thus obtained, which constitute common table- vinegar, are dilute solutions of acetic acid, containing in addition the non-fermentable principles which exist in alcoholic liquors. Pure acetic acid is obtained from this liquid by distillation, a very weak acid first passing over, while the following portions contain more acid, and the latter are richer, but are generally deteriorated by the products of the decomposition of foreign substances. The richer liquors are saturated with carbonate of soda, and. crystallized acetate of soda is separated by evaporation, and then decomposed ACETIC ACID. 545 by sulphuric acid, more or less dilute, according to the desired strength of the acetic acid. 1370. Acetic acid is now largely obtained from the acid liquors obtained by the distillation of wood, which yields very complicated products : carbonic acid gas, oxide of carbon, protocarburetted hy- drogen, water containing acetic acid in solution, a volatile liquid called spirit of wood, some other soluble substances, and, lastly, a black, pitchy portion. The solution of impure acetic acid is called in the arts pyroligneous acid; and in order to separate acetic acid from it, it is first saturated with chalk, which furnishes a solution of acetate of lime decomposable by sulphate of soda, acetate of soda and sulphate of lime being formed, which latter, being but slightly soluble, is nearly wholly deposited. The solution is eva- porated to dryness, and the residue heated to 400 or 480, a temperature which does not affect the acetate, but decomposes the empyreumatic substances with which it is mixed. Three parts of roasted acetate of soda being then treated in a distilling vessel with 9.7 of sulphuric acid, the first third of the liquid which distils over, consisting of a weaker acetic acid, is set aside, while the other two- thirds, which are composed of very concentrated acid, always con- tain a small quantity of sulphuric acid, in order to free the product from which it is distilled over anhydrous acetate of soda. The acetic acid thus obtained, having not yet reached its greatest degree of concentration, is exposed to a low temperature by surrounding with ice, or better still by a refrigerating mixture, the vessels contain- ing it; when the acid, at its maximum of concentration C 4 H 3 3 ,HO, sets in a crystalline mass, and the more watery acid is decanted. The crystallized acid is remelted and again cooled, when only one- half of the product is congealed, and the liquid portion being de- canted off, the solid acid may be considered as having attained its maximum of concentration. 1371. Acetic acid, monohydrated, or at its maximum of concen- tration C 4 H 3 3 ,HO, is solid at low temperatures, but melts at 60.8. The acid liquid may be cooled often to 32 and below, without crys- tallizing, and the bottle may even be shaken without causing crys- tallization ; but if a small glass point be introduced, a crystal is immediately formed at the end of the point, and the whole mass gradually crystallizes; the temperature rapidly rising to 60.8, and remaining stationary until the solidification is complete. The density of monohydrated liquid acetic acid is 1.063 at 64.4, and its smell is sharp and penetrating, while its taste is highly acid ; but in this state of concentration it exerts a vesicating action and raises blisters on the skin. It boils at 248, the density of its vapour being 2.09; but it is necessary to measure the density at a very high temperature, because the vapour of acetic acid differs considerably from the laws of permanent gases at temperatures which exceed but slightly its boiling point, (1234.) The equivalent 2 v 2 35 546 TRANSFORMATIONS OF ALCOHOL. C 4 H S 3 ,HO is represented by 4 volumes of vapour, like that of alcohol. Acetic acid mixes with water in all proportions ; and for the first quantities of water added, the acid liquor acquires a density greater than that of the monohydrated acid ; the maximum of density which corresponds to the acid C 4 H 3 3 +3HO being 1.079. By adding larger quantities of water the density diminishes, and the hydrometer can, therefore, not be used to ascertain the strength of acetic liquids. Chlorine acts powerfully on acetic acid, forming, when the latter is in the monohydrated state C 4 H 3 3 ,HO a new acid C 4 C1 3 3 ,HO, called Moracetic acid, in which the hydrogen of the anhydrous acid is replaced by an equivalent quantity of chlorine ; while, if the acid is further diluted with water, the chlorine exerts an oxidizing action by decomposing the water, and the acetic acid is converted into oxalic and then into carbonic acid. Ordinary nitric acid acts but feebly on acetic acid, even when assisted by heat. 1372. Acetic acid forms, with bases, a numerous series of salts, several of which are applied in the arts. They are generally solu- ble in water, and some dissolve in alcohol ; and the acid forms fre- quently several salts with the same base. All the acetates are decomposed by heat, but the decomposition takes place at very different temperatures, and its products vary according to the nature of the base. The acetates formed by the easily reducible metallic oxides, such as the oxides of silver and mercury, leave- a metallic residue, and evolve a portion of their acetic acid unchanged, while another portion of the acid is com- pletely consumed by the oxygen given off by the metallic oxide, and yields water and carbonic acid. The acetates formed by the more powerful bases, as the alkaline acetates, leave as a residue an alka- line carbonate, the acetic acid being converted into a neutral vola- tile liquid C 3 H 3 0, called acetone, or pyroacetic spirit; which reaction is expressed by the following equation : NaO,C 4 H 3 3 =NaO,C0 2 +C 3 H 3 0. Acetates formed by bases of medium strength, as oxide of lead, undergo a complicated decomposition : unchanged acetic acid and acetone are both disengaged at once, while the carbonic acid arising from the portion of decomposed acetic acid is disengaged or remains combined with the base, according to the temperature. Lastly, when the metallic oxide of moderate strength is easily reduced, as oxide of copper, a portion of the acetic acid is consumed by the oxygen of the oxide, and yields carbonic acid, while the residue of the distillation is composed of metal, or suboxide. Acetic acid forms two crystallizable salts with potassa : the neutral acetate KO,C 4 H 3 3 and the linacetate KO,C 4 H 3 3 +HO,C 4 H 3 3 ; the former of which is obtained by saturating acetic acid by car- ACETIC ACID. 547 bonate of potassa and evaporating the liquor. The salt crystallizes with difficulty and is soluble in water and alcohol ; and, if it be dis- solved in an excess of acetic acid and evaporated, crystals of the binacetate are obtained, which is deliquescent, melts at 298.4, and at 392 yields monohydrated acetic acid, furnishing the means of preparing very pure acid. Acetate of soda NaO,C 4 H 3 3 +6HO. It has been seen that this salt is prepared on a large scale in the manufacture of wood-vinegar. It crystallizes in large colourless and transparent prisms, which are often remarkable for the great sharpness of their faces. It has a cool and saltish taste, and dissolves in 3 parts of cold water and 5 of alcohol. When heated, it first dissolves in its water of crystalliza- tion, but soon parts with it ; while, if further heated, it undergoes igneous fusion without decomposition, which begins to ensue only at a degree of heat approaching a dull red. Acetate of ammonia (NH 3 ,HO),C 4 H 3 3 , which is obtained by the direct combination of ammonia with acetic acid, is very soluble in water and alcohol, and is used in medicine. When boiled, it loses a portion of its ammonia and is converted into binacetate. Acetate of baryta BaO,C 4 H 3 3 +3HO forms brilliantly white prismatic crystals, which readily part with 2 equiv. of water at a slightly elevated temperature. Acetate of lime produces only confused crystallizations, resem- bling cauliflowers. Acetate of alumina is prepared by pouring a solution of sulphate of alumina into a solution of acetate of baryta or lead, until no precipitate is thrown down; and the solution, which then contains acetate of alumina, is used in dyeing. In order to separate the salt from it, the liquor must be evaporated in vacuo, because, when heated, acetic acid is disengaged; when the acetate of alumina re- mains in the form of a gummy mass, without any appearance of crystallization. The properties of the acetates of lead and copper, which are of important application in the arts, have already been sufficiently de- tailed when treating of those metals. When concentrated acetic acid is poured into a boiling solution of subnitrate of mercury Hg 2 0,N0 5 , anhydrous white crystalline lamellae of subacetate of mercury Hg 3 0,C 4 H 3 3 are deposited on cooling. Red oxide of mercury dissolves readily in acetic acid, and the liquid yields by slow evaporation beautiful colourless crystals of protoacetate of mercury HgO,C 4 H 3 3 , which dissolves without change in cold water, but on boiling deposits perfectly pure red oxide of mercury. Acetate of silver AgO,C 4 H 3 3 is obtained by dissolving carbonate of silver in acetic acid; and as it is but little soluble in cold water, it may also be prepared by double decomposition, by pouring nitrate 548 TRANSFORMATIONS OF ALCOHOL. of silver into a solution of acetate of soda. If the liquors are con- centrated, the acetate of silver is deposited on cooling. Acetic Ether, C 4 H 5 0,C 4 H 3 3 . 1373. Acetic ether is formed by the direct reaction of acetic acid on alcohol, but the combination is effected with difficulty, because it is necessary to use anhydrous alcohol and acetic acid at its maximum of concentration, and pour back again into the retort the liquor which has passed over in distillation; and the formation of acetic ether is much more rapid if 10 or 15 per cent, of sulphuric acid be added. The best method of preparing this ether consists in pouring a mixture of 7 parts of concentrated sulphuric acid with 8 of ab- solute alcohol, or 10 parts of anhydrous acetate of soda, or 20 parts of acetate of lead, into a retort, and distilling as long as any etherial liquor passes over, the product being collected in a well-cooled re- ceiver. The liquor is poured upon dried pulverized carbonate of soda, which abstracts the greater portion of water from the acetic ether, and combines with the free acetic acid which passes over in distillation. The supernatant liquid stratum is decanted, and dis- tilled over chloride of calcium, which takes up the alcohol ; but the complete purification of acetic ether is very difficult, because it com- bines with chloride of calcium, and forms a crystalline compound, which is destroyed only by the addition of water. Acetic ether is a colourless, very mobile liquid, of an agreeable ether-like smell, and of the density 0.907 at 32. It boils at 165.2, and the density of its vapour is 2.920, its equivalent C 4 H 5 0,C 4 H 3 3 being therefore represented by 4 volumes of vapour. It mixes in all proportions with alcohol and ether, and dissolves in 7 parts of water. It is used in medicine. Sulphacetic Acid C 4 H 4 4 ,2S0 3 . 1374. By bringing into contact anhydrous sulphuric acid and monohydrated acetic acid C 4 H 3 0,H0 3 , the two acids combine and form a compound acid. The liquid is diluted with water and satu- rated with carbonate of baryta, when the free sulphuric acid forms insoluble sulphate of baryta, while the sulphacetic acid yields a soluble sulphacetate of baryta. The liquor, when evaporated, affords crystals of the formula 2BaO,(C 4 H 4 4 ,2S0 3 ) + HO, and which part with their water without decomposition. If the baryta be pre- cipitated from sulphacetate of baryta, by sulphuric acid poured in by drops, or if a solution of sulphacetate of lead be decomposed by sulf hydric acid, an acid liquid results, which on evaporation yields deliquescent crystals, melting at 143.6, and solidifying in a crys- talline mass on cooling. At a more elevated temperature the sulphacetic acid is decomposed. Crystallized sulphacetic acid, placed, in vacuo, over anhydrous phosphoric acid, gives off one equivalent of water, and then assumes ACETONE. 549 the formula C 4 H 4 4 ,2S0 3 -f 2HO; the 2 equivalents of water which it retains being basic. Acetone C 3 H 8 0. 1375. It has been said ( 1372) that the alkaline acetates yield acetone when they are decomposed by heat ; but the best method of preparing it consists in heating a mixture of 2 kilog. of acetate of lead with 1 kilog. of finely powdered quicklime, in an earthen retort, or in the iron bottles used for the transportation of mercury ; the temperature being gradually raised to a dull red- heat. The liquor condensed in the receiver is rectified over chloride of calcium, and then allowed to rest for several days on melted chloride of calcium ; after which it is distilled, the first f only of the product being collected, while the other fourth contains, besides a still large quantity of acetone, a considerable quantity of a peculiar substance, boiling at 248, and which has been called dumasin. Acetone is a very mobile, colourless liquid, of a peculiar odour ; and its density is 0.792, while it boils at 132.1, the density of its vapour being 2.022 ; so that its equivalent C 3 H 3 is represented by 2 volumes of vapour. The formula of acetone may be written C 6 H 6 3 or C 6 H 5 0,HO, in which case its equivalent is represented by 4 volumes of vapour like that of alcohol. It burns with a bril- liant flame ; and is soluble in all proportions in water, alcohol, and ether, while chloride of calcium and caustic potassa readily abstract its water. 1376. On mixing acetone with twice its weight of concentrated sulphuric acid, heat is evolved, and the mixture turns brown, while the smell of sulphurous acid is perceived at the same time ; and if the liquor be then diluted with water and saturated with carbonate of baryta, insoluble sulphate of baryta is separated, and a soluble salt of baryta, which crystallizes in pearly lamellae, is obtained. The formula of the salt is 2BaO,(C 6 H 5 0,2S0 3 )+HO; its equivalent of water being removed by drying. If the acid liquor be saturated with carbonate of lime, a salt of lime is obtained : 2CaO,(C 6 H 5 0,2S0 3 )+HO. If a smaller quantity of sulphuric acid be used, for example, by treating two volumes of acetone with 1 volume of sulphuric acid, a soluble salt of baryta is still obtained by saturating with carbonate of baryta, but which contains only one-half of the sulphuric acid of the preceding acid, and only 1 equivalent of base. The formula of this salt is BaO(C 6 H ? 0,S0 3 )+HO. 1377. By distilling 2 volumes of acetone and 1 volume of sul- 550 . TEANSFORMATIONS OF ALCOHOL. phuric acid, two new products result, mesitylen C 6 H 4 and mesitic ether C 6 H 5 0. The mesitylen floats on the surface of the distilled liquid, from which it is separated with a pipette, and shaken several times with pure water, and then distilled over chloride of calcium. Mesitylen is an oleaginous, colourless liquid, of an alliaceous odour, lighter than water, and boiling at 276.8. 1378. Impure mesitic ether is obtained by treating acetone with sulphuric acid ; while it is obtained in a very pure state by decom- posing the chlorohydric ether C 6 H 5 C1 of acetone by an alcoholic solution of potassa. To effect this, the ether is dissolved in alcohol, and, after having heated it, an alcoholic solution of potassa is added until an alkaline reaction is produced ; when, on diluting the liquor with water, an etherized liquid separates, forming the upper stratum, which is drawn off by a pipette, washed several times with water, and distilled over chloride of calcium. It is a colourless liquid, boiling at 248, insoluble in water, but soluble in alcohol, and its formula is C 6 H 5 0. 1379. On passing chlorohydric acid gas through acetone, it dissolves largely in it, and a brown oleaginous liquid results, which is to be digested for some time over litharge to remove the free chlorohydric acid ; after which it is washed several times with water, and dried by means of chloride of calcium. This liquid is the chlorohydric ether of acetone C 6 H 5 C1, but it is difficult to obtain it pure by this method, and it is more easily effected by pouring into 1 part of acetone, cooled by ice, 2 parts of perchloride of phosphorus PG1 5 , added by small quantities at a time. It is then treated with water, which causes the separation of the chlorohydric ether in the form of a yellow oleaginous liquid. It cannot be distilled, because it is destroyed by heat ; and the alkaline liquids decompose it, even water effecting decomposition after some time. Concentrated nitric acid acts powerfully on acetone, forming several products, the nature of which is, however, not yet sufficiently understood. 1380. From the nature of its compounds, acetone will be seen to resemble alcohol, if its formula be written C 6 H 6 2 . But the acid C 6 H.O,2S0 3 , which may be assimilated with sulphovinic acid, differs from it by saturating 2 equivalents of base, while sulphovinic acid saturates only one. Sulphovinic acid, chlorohydric ether, and the compound ethers of alcohol reproduce alcohol when boiled with alkaline liquids ; while the corresponding products of acetone do not yield acetone under the same circumstances. When the vapour of alcohol is passed over hydrated potassa heated to about 500, acetate of potassa is obtained ; but under the same circumstances acetone does not yield an acid corresponding to acetic acid. Lastly, no compound ether has hitherto been obtained with acetone. CACODYL. 551 Cacodyl Series. 1381. By distilling, in a retort furnished with a receiver, a mixture of equal parts of anhydrous acetate of potassa and arsenious acid, a liquid product is obtained, called at first Cadet's liquid, then alcarsin, and lastly oxide of cacodyl ; and which ignites when exposed to the air, and possesses many other remarkable properties. The composition of this substance, supposed to be pure, corresponds to the formula C 4 H 6 AsO. It behaves in its chemical reactions like the oxide of a radical C 4 H 6 As, playing a part analogous to that of cyanogen, and has been called cacodyl. This radical enters into a great number of other compounds, as shall presently be described.* In consequence of the facility with which this substance changes when exposed to the air, and its poisonous action on the animal economy, great caution must be used in preparing it ; and the retort should be hermetically fitted to the receiver, which must be furnished with a tube to conduct the vapours out of the laboratory. At the close of the operation the receiver contains 3 strata of liquid ; the middle one, which is brown and of an oleaginous consistence, consists of impure oxide of cacodyl, and is decanted by means of a siphon filled with water, and conveyed to the bottom of a bottle filled with boiled water. It is shaken several times with the water, which is then poured off and replaced by alcohol, which dissolves the oxide of cacodyl. By pouring the alcoholic solution into boiled water, the oxide of cacodyl is again precipitated in the form of a liquid layer at the bottom of the bottle ; and the supernatant water being rapidly removed, the access of air is prevented by a rapid current of hydrogen which is passed into the bottle. The latter is then closed, after having introduced into it chloride of calcium in- tended to absorb the water and alcohol ; and the liquid is first decanted in a tubulated retort traversed by a current of hydrogen, and to which a receiver is fitted ; and is then distilled, still keeping up the current of hydrogen, when pure oxide of cacodyl is obtained as a colourless, very fluid liquid. It has a strong and very disa- greeable smell, is very poisonous, and its density is 1.46. It soli- difies at 9.4, and boils at about 302, the density of its vapour being 7.8, and 1 volume of the gaseous substance therefore consist- ing of 2 vol. of vapour of carbon 0.552 6 " hydrogen 0.662 J " vapour of arsenic 5.185 J " oxygen 1.688 7.97T and its equivalent C 4 H 6 AsO is represented by 2 volumes of vapour. * The discovery of cacodyl, and the masterly investigation of all the compounds of this radical, is wholly due to Robert Bunsen. W. L. F. 552 TRANSFORMATIONS OF ALCOHOL. The chemical reaction which produces it is represented by the following equation : 2(KO,C 4 H 3 3 )+As0 3 =2(KO,C0 2 )+2C0 3 +C 4 H 6 AsO. Oxide of cacodyl is insoluble in water, but it dissolves largely in alcohol and ether. It dissolves phosphorus and sulphur without any change, while chlorine, bromine, and iodine decompose it rapidly. It combines with anhydrous sulphuric acid and forms a crystalline, deliquescent compound, which dissolves in water, yield- ing an acid liquid. By pouring a dilute solution of corrosive sublimate into an alco- holic solution of oxide of cacodyl a white precipitate is formed, which is a simple combination of oxide of cacodyl with chloride of mercury, according to the formula C 4 H 6 AsO,2HgCl, and which dissolves in boiling water, and again separates from it in crystals on cooling. Bromide of mercury forms an analogous compound. Oxide of cacodyl dissolves in several acids, with which it appears to play the part of a weak base. By adding nitrate of silver to a solution of oxide of cacodyl in nitric acid a white crystalline precipi- tate is formed, of which the formula is 3C 4 H 6 AsO,(AgO,N0 5 ). 1382. Exposed to the air, oxide of cacodyl becomes heated and incandescent, its combustion being complete, while thick vapours of arsenious acid are formed. But if cacodyl covered with a stratum of water be exposed to the air, the oxygen is slowly absorbed, and arsenious acid, a peculiar etherial substance, and a more oxy- genated product of cacodyl, cacodylic acid, are formed. By adding a sufficient quantity of water the cacodylic acid is dissolved ; and by evaporating the solution and treating with boiling alcohol, the alcoholic liquor deposits, on cooling, cacodylic acid in colourless cystals. This substance, which is inodorous and nearly tasteless, does not change in the air, and is poisonous, but less so than arse- nious acid. It is decomposed at 446 without distilling ; its formula is C 4 H 6 As0 4 -f HO; and it combines with bases without yielding crystallizable salts. Protochloride of tin and phosphorous acid abstract its oxygen and restore it to the state of oxide of cacodyl. 1383. By distilling with highly concentrated chlorohydric acid the compound of oxide of cacodyl with chloride of mercury, a chlo- ride of cacodyl C 4 H 6 AsCl is obtained, which should be brought into contact with chloride of calcium and quicklime, and then redistilled. Chloride of cacodyl is a colourless liquid, heavier than water, of a sharp smell, and insoluble in water and ether, but soluble in all pro- portions in alcohol. It resists a temperature of 49 without be- coming solid, and boils at a little above 212, its vapour becoming incandescent in contact with the air. Nitrate of silver wholly abstracts its chlorine and reproduces oxide of cacodyl. When oxide of cacodyl is treated with gaseous chlorohydric acid, chloride of cacodyl is also formed, but a portion is precipitated in combina- CACODYL. 553 tion with the water formed. The density of the vapour of chloride of cacodyl is 4.86 ; and its equivalent corresponds, therefore, to 4 volumes of vapour. A bromide and iodide of cacodyl may be obtained by similar processes. Chloride of cacodyl is partially decomposed by contact with water, a combination of 3 equiv. of oxide of cacodyl with 3 equiv. of chloride of cacodyl being formed, which is volatile, and boils at 228.2, the density of its vapour being 5.35, so that it is formed of 3 vol. of vapour of chloride of cacodyl and 1 vol. of oxide of cacodyl without condensation. The bromide and irfdide of cacodyl yield similar compounds. By adding perchloride of platinum to an alcoholic solution of chloride of cacodyl, a brick-red precipitate is obtained, which is, probably, a simple combination of the two substances ; while, if the liquid be boiled, the precipitate is redissolved, and yields a liquor from which neither the platinum nor the chloride of cacodyl can be precipitated by reagents which commonly produce that effect. This new compound is a true base which forms crystallizable compounds with several acids. 1384. A sulphide of cacodyl C 4 H 6 AsS is obtained by distilling chloride of cacodyl with sulfhydrate of sulphide of barium, when sulfhydric acid is disengaged, while water and the sulphide of cacodyl pass over in distillation, the latter of which is purified by digesting it over chloride of calcium and carbonate of lead, and then distilling it in a current of hydrogen. Sulphide of cacodyl is a colourless liquid, which does not fume in the air, is insoluble in water, but readily soluble in alcohol and ether. It combines di- rectly with sulphur and forms a more sulphuretted compound, which may be obtained crystallized by dissolving it in ether. It rapidly absorbs the oxygen of the air, and then forms several com- pounds, among which cacodylic acid is observed. Chlorohydric acid decomposes sulphide of cacodyl, disengaging sulfhydric acid, while chloride of cacodyl is formed ; sulphuric and phosphoric acids also decompose it, a sulphate and phosphate of oxide of cacodyl being formed. The density of the vapour of sulphide of cacodyl is 8.39, and its formula therefore corresponds to 2 volumes of vapour. 1385. Cyanide of cacodyl C 4 H 6 AsCy is obtained by distilling oxide of cacodyl with cyanide of mercury, when oxide of mercury remains in the retort, while the cyanide of cacodyl distils over and forms, at the bottom of the water in the receiver, an oily stratum, which, on cooling, assumes a crystalline appearance. The crystals are pressed between several folds of tissue-paper, and distilled over baryta. Cyanide of cacodyl melts at 90.5, boils at 284, and is but slightly soluble in water, but largely so in alcohol and ether. It is an excessively poisonous substance, the vapour of which it VOL. II. 2 W 554 TKANSFORMATIONS OP ALCOHOL. is very dangerous to inhale, and it oxidizes rapidly in the air. The density of its vapour is 4.55, and its equivalent is represented by 4 volumes of vapour. 1386. By heating, protected from the air, cleanly scraped zinc with chloride of cacodyl, the metal is attacked without any evolu- tion of hydrogen, and a white crystalline mass is obtained, on treating which with water to dissolve the chloride of zinc, an olea- ginous liquid, heavier than water, separates, which is digested for some time with highly polished zinc, and then distilled after having been allowed to remain for some time over chloride of calcium and quicklime. This substance, which is cacodyl^ the radical of all the compounds just described, consists of a colourless, highly refracting liquid, still more inflammable than the oxide of cacodyl, which it closely resembles : it solidifies at 212, and boils at about 338. Exposed to a feeble current of air, it forms a thick cloud, and is first converted into oxide of cacodyl, and then into cacodylic acid. Sulphur, chlorine, and bromine combine directly with it, and form sulphide, chloride, and bromide of cacodyl. The density of its vapour is 7.28, and its equivalent C 4 H B As cor- responds to 2 volumes of vapour. The products of cacodyl present a double interest, first as organic substances of which arsenic is the chief constituent, and secondly, because they belong to the small number of organic substances in which the existence of a compound radical has been proved, which, when isolated, reproduces, by direct combination, all the substances of the series. PRODUCTS OF THE ACTION OF CHLORINE ON SUBSTANCES OF THE ALCOHOLIC SERIES. Action of Chlorine on Chlorohydric Ether. 1387. In a badly lighted situation, chlorine exerts no action on chlorohydric ether ; while in a bright light, or still better, in the direct rays of the sun, reaction ensues with development of heat, chlorohydric acid being disengaged, while an etherial liquid con- denses. When any considerable quantity of this liquid is to be prepared, the apparatus is arranged as represented in fig. 680. Into the flask A is introduced alcohol saturated with chlorohydric acid gas, or merely a mixture of equal volumes of alcohol and highly fuming chlorohydric acid of commerce. The gas is passed through a first washing-bottle B containing water, then through a second bottle C with concentrated sulphuric acid, and lastly through a third bottle D again containing water. Into another flask I is in- troduced peroxide of manganese and chlorohydric acid to generate the chlorine, which is washed in the water in the bottle H. The two gases are conveyed, by two tubes, the orifices of which are op- posite to each other, into the flask E, having three tubulures, the ACTION OF CHLORINE ON ETHEKS. 555 lower of which passes into the bottle F intended to collect the least volatile portion of the product, while the most volatile portion col- lects in the bottle G, which should be well cooled. The flask E in Fig. 680. which the two gases unite should be exposed to the sun, at least in the commencement of the operation ; for when the reaction is once established, it continues in the shade, and does not cease with the setting of the sun. Care must be taken to keep the chlorohydric ether in excess as regards the chlorine, as otherwise the latter would exert a subsequent action on the first product and produce a second one more chlorinated. It is moreover difficult to avoid, in an ope- ration which lasts for a long time, the formation of a small quantity of this product, unless the operation be continued in the shade ; but, as it is less volatile, nearly the whole of it remains in the first receiving-bottle. The liquid is washed several times with water, and then distilled in a water-bath, over quicklime, in order to en- tirely deprive it of .water and chlorohydric acid. The first drops which pass over in distillation should be rejected, because they often contain a small quantity of unaltered chlorohydric ether, which re- mains in solution ; and the last fourth is also set aside because it may contain a small proportion of more highly chlorinated pro- ducts. The formula of the liquid thus obtained is C 4 H 4 C1 3 ; and it is monochlorinated chlorohydric ether, presenting the same composition as Dutch liquid, the taste and smell of which it exactly resembles. The density of its vapour is also exactly the same, 3.42 ; while its boiling point is very different, for monochlorinated chlorohydric ether boils at 147.2, while Dutch liquid boils at 180.5. These two substances also differ entirely in their chemical reactions : thus, an alcoholic solution of potassa immediately decomposes Dutch liquid when cold, chloride of potassium being formed and monochlo- rinated bicarburetted hydrogen C 4 H 3 C1 disengaged. Nothing simi- 556 TRANSFORMATIONS OF ALCOHOL. lar occurs in monochlorinated chlorohydric ether ; and if this sub- stance be distilled with an alcoholic solution of potassa, a very small fraction only of it is changed, without producing monochlori- nated bicarburetted hydrogen. Dutch liquid is acted on immedi- ately, when cold, by potassium, hydrogen being disengaged, while chloride of potassium and monochlorinated bicarburetted hydrogen are formed ; but in monochlorinated chlorohydric ether, on the con- trary, the potassium preserves its metallic brilliancy. Dutch liquid differs therefore from its isomeric, monochlorinated chlorohydric ether, in the fact that 1 equivalent of hydrogen and 1 equivalent of chlorine exist in the compound in quite different conditions. In the reactions just described, these two elements behave as if they existed, in Dutch liquid, in the state of chlorohydric acid; for which reason some chemists have assigned to Dutch liquid the for- mula C 4 H 3 C1,HC1, and to monochlorinated chlorohydric ether the formula C 4 H 4 C1 2 , which perfectly represents the difference of the chemical reactions. 1388. By causing chlorine to act gradually and with the assistance of solar light on monochlorinated chlorohydric ether, with the precautions described in the preparation of the various degrees of chlorination of Dutch liquid, the following products are obtained : Bichlorinated chlorohydric ether C 4 H 3 C1 3 , isomeric with monochlorinated Dutch liquid ; Terchlorinated chlorohydric ether C 4 H 2 C1 4 , isomeric with bichlorinated Dutch liquid ; Quadrichlorinated chlorohydric ether C 4 HC1 5 , isomeric with terchlorinated Dutch liquid ; Perchlorinated chlorohydric ether C 4 C1 6 , identical with perchlorinated Dutch liquid, or sesquichloride of carbon. The final product of the action of chlorine on chlorohydric ether is therefore the same as that afforded by Dutch liquid : it is crys- tallyzed sesquichloride of carbon, the properties of which have been described, ( 1338.) The three products C 4 H 3 C1 3 , C 4 H 3 C1 4 and C 4 HC1 5 derived from chlorohydric ether, differ entirely in their phy- sical properties from the isomeric products obtained from Dutch liquid ; and, in fact, Bichlorinated chlorohydric ether C 4 H 3 C1 3 boils at... 167.0 Monochlorinated Dutch liquid " " 239.0 Terchlorinated chlorohydric ether... C 4 H 3 C1 4 " 215.6 Bichlorinated Dutch liquid " " 275.0 Quadrichlorinated chlorohydric ether C 4 HC1 5 " 294.8 Terchlorinated Dutch liquid " " 307.4 The last product, the sesquichloride of carbon, which is common to both series, boils at 356. ACTION OF CHLOKINE ON ETHERS. 557 The difference between the boiling points of isomeric chlorinated products of chlorohydric ether and Dutch liquid becomes smaller and smaller, as the quantity of chlorine substituted for the hydro- gen increases ; and lastly, it is reduced to nothing in the perchlo- rinated products, which are identical : thus The difference of ebullition between monochlorinated chloro- hydric ether and Dutch liquid is 71.0 Between bichlorinated chlorohydric ether, and monochlori- nated Dutch liquid, it is 72.0 Between terchlorinated chlorohydric ether and bichlorided Dutch liquid, it is 59.4 Between quadrichlorinated chlorohydric ether and terchlori- nated Dutch liquid, it is 12.6 Lastly, between identical perchlorinated products, it is ne- cessarily 0.0 1389. Bichlorinated and terchlorinated chlorohydric ethers differ very distinctly in their chemical reactions from their isomerics, monochlorinated and bichlorinated Dutch liquid. In fact, the pro- ducts derived from Dutch liquid yield, with an alcholic solution of potassa, the former, bichlorinated bicarburetted hydrogen C 4 H 2 C1 2 , the latter, terchlorinated bicarburetted hydrogen C 4 HC1 3 ; while the isomeric products derived from chlorohydric ether afford no similar results : they resist the action of potassa, and, after a long time, sub- stitutions of oxygen for chlorine alone are formed. The differences exhibited in this chemical reaction by the two isomeric series is therefore perfectly explained by writing the products derived from Dutch liquid C 4 H 2 C1 2 ,HC1 and C 4 HC1 3 ,HC1. Quadrichlorinated chlorohydric ether and its isomeric terchlori- nated Dutch liquid exhibit also remarkable differences in their chemical reactions ; the latter substance being readily acted on by the alcoholic solution of potassa, and yielding perchlorinated bicar- buretted hydrogen C 4 C1 4 or chloride of carbon ; while quadrichlori- nated chlorohydric ether is much more easily acted on by the alcoholic solution of potassa than the products which preceded it, but the reaction is far from being as simple as that exerted on its isomeric. 1390. Chlorohydric ether may be regarded as being derived from a carburetted hydrogen C 4 H 6 , which has hitherto not been obtained, and which, in its constitution, would differ from carburet- ted hydrogen, which we assumed (1339) as the starting point of the series of Dutch liquid, and we should then have the following series : Carburetted hydrogen unknown C 4 H 6 , density " boils at " Chlorohydric ether C 4 H 5 C1 " 0.840 " 54.5 Monochlorinated chlorohydric ether. C 4 H 4 C1 2 " 1.174 " 147.2 Bichlorinated " " C HC1, " 1.372 " 167.0 2 w2 558 TRANSFORMATIONS OF ALCOHOL. Terchlorinated chlorohydric ether C 4 H 2 C1 4 density 1.530 boils at 215.6 Quadrichlorinated chlo. ether.. C 4 HC1 5 " 1.644 " 294.8 Perchlorinated " " C 4 C1 6 " " 356.0 Products of the Action of Chlorine on Ether C 4 H 5 0. 1391. Ether is very violently acted on by chlorine, the temper- ature rising considerably, while the substance turns black and ignites, if the chlorine be in too great quantity, and if the apparatus is exposed to the sun. By operating in a darkened room, and ex- hausting the action of the chlorine by elevating even slightly the temperature toward the close of the operation, a product is obtained which may be regarded as bichlorinated ether , for its formula is C 4 H 3 C1 2 0. It is a colourless, oleaginous liquid, of a smell resem- bling fennel; and its density is 2.5, while it decomposes at about 284 without boiling. Heated with an alcoholic solution of potassa, chloride of potassium and acetate of potassa are formed, from the following equation : C 4 H 3 OC1 2 +3KO=2KC1+KO,C 4 H 3 3 , the 2 equiv. of chlorine are therefore replaced by 2 equiv. of oxygen. By heating bichlorinated ether in a current of sulf hydric acid gas, chlorohydric acid is disengaged, and, if it be sufficiently heated, an oleaginous liquid, the greater portion of which solidifies on cool- ing, passes over in distillation. This substance is removed, pressed between several folds of tissue-paper, and dissolved in boiling alco- hol. On cooling, crystals of the two substances are separated, which are again crystallized, until only the prismatic forms of a single species are obtained. The composition of the substance then cor- responds to the formula C 4 H 3 S 2 0, and is derived from the primitive substance C 4 H 3 C1 2 0, bichlorinated ether, by 2 equiv. of sulphur being substituted for 2 equiv. of chlorine ; and it is therefore ether C 4 H 5 of which 2 equiv. of hydrogen have been replaced by 2 equiv. of sulphur, or bisulphuretted ether. It is insoluble in water, and decomposed at about 248, without distilling. An alcoholic solution of potassa decomposes it, forming sulphide of potassium and acetate of potassa : C 4 H 3 S 2 0+3KO=2KS+KO,C 4 H 3 3 . Alcoholic liquors which have been used in the purification of bisulphuretted ether deposit, after evaporation, yellow aciculse of the formula C 4 H 3 C1SO, which consist of bichlorinated ether, in which a single equivalent of chlorine has been replaced by 1 equiv. of sulphur. 1392. By arresting the action of chlorine on ether at a suitable moment, the liquid contains a large quantity of monochlorinated ether C 4 H 4 C10, which is particularly formed when chlorine and ACTION OF CHLORINE ON ETHEK. 559 vapour of ether in excess are introduced into a flask exposed to dif- fused light, and the liquid obtained is distilled, dividing the pro- ducts into fractions, when the first portions which pass over in dis- tillation contain a large amount of ether and chlorohydric ether, while the monochlorinated ether C 4 H 4 C10 does not distil before about 356. This product is often formed in large quantities in the preparation of Dutch liquid when the bicarburetted hydrogen be- comes loaded with vapours of ether. The preparation of pure chlorinated ethers is often very difficult, and would be almost impossible if carried on in the sun. A large quantity of chlorohydric ether is necessarily formed in this prepara- tion, from the reaction which the chlorohydric acid, arising from the combination of the chlorine with the hydrogen abstracted from the ether, exerts on the unaltered ether C 4 H 5 ; and if the operation be carried on in a darkened place, the chlorohydric ether is disengaged almost entirely, without being ultimately attacked by the chlorine ; which would not be the case in the light of the sun, because the chlorohydric ether would then be attacked by the chlorine, and yield chlorinated chlorohydric ethers, much less volatile, and which would remain dissolved in the chlorinated ethers. 1393. The action of chlorine on ether does not stop at bichlori- nated ether C 4 H 3 C1 2 0, but continues, if the experiment be made in the sun, furnishing liquids richer and richer in chlorine, and corre- spondingly poor in hydrogen. By exhausting the action of the chlorine, by pouring the highly chlorinated liquid into large bottles filled with dry chlorine, and exposed to intense solar light, there are found white crystals, remarkable for their beautiful forms and their size, consisting of perchlorinated ether C 4 C1 5 0, in which all the hydrogen of ether C 4 H 5 has been replaced by chlorine. Perchlo- rinated ether melts at 156.2, and, when heated to 572, it does not boil, but is decomposed into sesquichloride of carbon C 4 C1 6 , and a liquid product of the formula C 4 C1 4 2 , consisting of chlorinated aldehyd. The decomposition is represented by the following equation : 2C 4 C1 S 0=C 4 C1 6 +C 4 C1 4 2 . When perchlorinated ether is heated with an alcoholic solution of monosulphide of potassium, chloride of potassium and a new com- pound of the formula C 4 C1 3 are found, which substance evidently belongs to the series of bicarburetted hydrogen C 4 H 4 ; 3 equiv. of chlorine having replaced 3 of hydrogen, and 1 equiv. of oxygen oc- cupying the place of the last equiv. of hydrogen. Treated with chlorine, in the sun, the substance C 4 C1 3 reproduces perchlorinated ether C 4 C1 5 0. The two substances C 4 C1 5 and C 4 C1 3 present, therefore, relations precisely similar to those existing between the two chlorides of carbon C 4 C1 6 and C 4 C1 4 , the first of which belongs to the series of chlorohydric ether, and the second to that of bicar- buretted hydrogen. 560 TRANSFORMATIONS OF ALCOHOL. It is essential, in order to obtain pure perchlorinated ether, to expose to the action of chlorine in excess, influenced by the solar rays, only ether already completely chlorinated in the shade and freed from ether and chlorohydric ether ; as otherwise large quan- tities of chloride of carbon C 4 C1 6 , which would remain mixed with the chlorided ether, would be inevitably formed. It is equally necessary to operate upon anhydrous ether, and with perfectly dried chlorine, for, if water be present, it is entirely de- composed by the chlorine, and its nascent oxygen exerts an oxidizing action on the ether, ( 1366,) forming aldehyd C 4 H 4 2 , and conse- quently causing the products of the action of chlorine on aldehyd to be mixed with those of the action of chlorine on ether C 4 H 5 0. Action of Chlorine on Sulfhydric Ether, C 4 H 5 S. 1394. Sulfhydric ether is powerfully acted on by chlorine, with disengagement of chlorohydric acid, and it even ignites when pro- jected into a bottle filled with gaseous chlorine. After attacking the sulfhydric ether by chlorine, in a darkened place, and intro- ducing the chlorine slowly, in order to avoid too great an elevation of temperature, the apparatus is exposed to the sun as soon as the action ceases, and chlorine passed through until chlorohydric acid is no longer disengaged. The liquid is exposed in vacuo near a cup filled with a concentrated solution of caustic potassa, which absorbs the chlorine and chlorohydric acid it contains ; and there remains a yellow liquid, of an extremely disagreeable and persistent smell, of the density 1.673, and which decomposes at about 320. Its for- mula is C 4 HC1 S, and it constitutes quadrichlorinated sulfhydric ether : intermediate products probably exist, but they have not yet been discovered. Action of Chlorine on Alcohol C 4 H 8 2 . 1395. Chlorine acts very powerfully on alcohol, and yields very various products, according to the strength of the alcohol. We shall suppose the most simple case, that in which the alcohol is anhydrous, and admit that the chlorine is perfectly dry. Alcohol absorbs a large quantity of chlorine, without any disengagement of chlorohydric acid, if its temperature be kept sufficiently low ; and if, after a certain length of time, water be poured on the product, an oleaginous liquid is separated from it, which falls to the bottom of the vessel, and is a mixture of several chlorinated substances : this substance is called chloralcoholic oil, but the substances com- posing it are unknown. If the action of chlorine on alcohol be indefinitely continued, an oily liquid soon separates, which gradually increases, and finally constitutes the whole mass. This liquid, which is also very complex, is gently heated, in order to disengage the very volatile products, such as chlorohydric ether and its highly chlorinated products, which, if they remained in the mixture, would OHLOKAL. 561 be subsequently transformed into chloride of carbon C 4 C1 6 . The action of the chlorine is continued, the temperature elevated, and it is terminated by the assistance of the solar rays. The liquid obtained should be mixed with 3 or 4 times its volume of sulphuric acid, and the bottle is shaken several times, after which its contents are distilled over sulphuric acid. The product of this distillation is again distilled in a tubulated retort furnished with a thermo- meter, and the first products, containing a large amount of chlo- rohydric acid, are rejected, the product distilling at 201.2 being separately collected, which forms a colourless liquid, of a suffocat- ing odour, and exciting to tears. Its density is 1.502, and its com- position corresponds to the formula C 4 HC1 3 2 : it is called chloral, but is only ter chlorinated aldehyd. Its equivalent corresponds to 4 volumes of vapour. The formation of chloral by the action of chlorine on alcohol, is explained in the following manner : The formula of anhydrous alcohol is C 4 H 8 2 , while, in the majority of its reactions, it behaves like a compound of ether C 4 H.O and water HO ; and the action of chlorine on alcohol yields the same products as if it acted on a mixture of 1 equivalent of ether and 1 equivalent of water : it first exerts an oxidizing action, by decomposing the equivalent of water, and the product of this action is aldehyd C 4 H 4 3 , which is in fact obtained in large quantity during the first periods of the action of chlorine on alcohol, and may be separated by distillation. But if the action of the chlorine continues, as there is no more water, the previous oxidizing action is replaced by a chlorinating action, by which the substance loses hydrogen and gains equivalent quantities of chlorine ; the reaction ceasing, even in the most intense solar heat of our climate, at the moment when the substance still retains 1 equivalent of hydrogen, and is converted into chloral C 4 HC1 3 2 . The reaction is expressed by the following equation : C 4 H 5 0,HO+8C1=C 4 HC1 3 3 +5HC1. Chloral should therefore be considered as terchlorinated aldehyd. It has hitherto been in vain attempted to remove directly by chlorine the equivalent of hydrogen which remains in terchlorinated aldehyd, so as to produce quadrichlorinated or perchlorinated aldehyd C^UOj,, although this substance has been indirectly obtained, it being one of the products of the decomposition of perchlorinated ether C 4 C1 5 0, by heat, ( 1393.) Chloral dissolves largely in water without decomposing, and if the solution be evaporated in vacuo over concentrated sulphuric acid, crystals are formed consisting of a combination of chloral with water, hydrated chloral C 4 HC1 3 3 ,HO, which exhibits the molecular grouping of alcohol C 4 H 5 0,HO. Chloral has so great an affinity for water that it attracts the moisture of the air, and is con- verted into crystals of hydrated chloral. The crystals may be 36 562 TRANSFORMATIONS OF ALCOHOL. sublimed without decomposing, while they give off their water when they are distilled with concentrated sulphuric acid, and allow anhy- drous chloral to pass over in distillation. Chloral is decomposed by an aqueous solution of potassa, two pro- ducts belonging to the series of protocarburetted hydrogen C 2 H 4 being formed, namely, formic acid C 2 H 3 3 and chloroform C 2 HC1 3 ; and the reaction is expressed by the following equation : C 4 HCl 3 O a ,HO+KO=KO,C 2 H0 3 +C a HCl 3 . The molecular grouping of alcohol is therefore doubled in this case, and produces two groups, exhibiting the grouping of protocarburet- ted hydrogen. When anhydrous chloral is left for some time in a tube hermeti- cally closed it becomes cloudy, and a white substance, which in- creases until it has taken the place of the whole of the liquid, is de- posited on the sides of the tube. This is an isomeric modification of chloral, which no longer presents any of the characteristic proper- ties of the latter substance : thus it is inodorous, resembles porcelain in appearance, and no longer dissolves in w r ater, whence it has been called insoluble Moral. It reproduces, when heated, ordinary chloral, which distils over. If the tube in which the chloral is contained be shaped as represented -in fig. 681, the part a, in which the chloral is solidified, , may be heated, and the liquid chloral obtained in the lg * * part by and since the liquid chloral soon solidifies again, the experiment may be indefinitely repeated in the same tube. It is important to remark that liquid chloral C 4 HC1 3 3 does not correspond exactly to aldehyd, for its equivalent is represented by 4 volumes of vapour, while that of aldehyd C 4 H 4 2 is represented by 2 volumes. It must therefore be admitted that in the conversion of aldehyd into terchlorinated aldehyd or chloral, each molecule of aldehyd has afforded 2 molecules of chloral, or rather that the mole- cules, by being charged with chlorine, have separated so as to fill a double space. If the first hypothesis is correct, insoluble chloral may possibly present the molecular grouping of aldehyd ; while insoluble chloral may possibly also correspond to one of the isomeric modifications of aldehyd described 1367 to elaldehyd or metal- dehyd. If the alcohol contained water, or if the chlorine were not per- fectly dry, the reaction might be still more complicated. Supposing the alcohol to contain an equivalent of water, the first stage of oxidation due to the decomposition of the water would not stop at the formation of aldehyd C 4 H 4 2 , but would convert this substance into acetic aid C 4 H 3 3 . C 4 H 5 0,HO+HO+2C1=C 4 H 3 3 +2HC1; and at a later period during the stage of chlorination, products of the action of chlorine on acetic acid would be formed. CHLORACETIC ACID. 563 But again, acetic acid, by dissolving in unaltered alcohol, might produce, particularly under the influence of the chlorohydric acid, which is copiously formed, acetic ether, which at a later period would form, by the action of chlorine, chlorinated acetic ether. It will hence be seen how complicated these products may become, and it would be often impossible to disentangle the reactions, unless guided by theory. Lastly, if the alcohol were very hydrated, the oxidizing stage would continue until the alcohol was wholly converted into water and Carbonic acid. Products of the Action of Chlorine on Aldehyde C 4 H 4 3 . 1396. From what has been just said concerning the action of chlorine on alcohol, there remains but little to add touching the action of chlorine on aldehyde. By causing chlorine to act on alde- hyde C 4 H 4 3 , a large quantity of chloral C 4 HC1 3 3 is obtained, which is mixed with other less volatile products, which have not yet been examined. They are probably the chlorinated aldehydes C 4 H 3 C10 2 and C 4 H a Cl 2 3 , which a more prolonged action of the chlorine would have converted into chloral. Products of the Action of Chlorine on Acetic Acid, C 4 H 3 3 ,HO. 1397. Chlorine acts powerfully on monohydrated acetic acid, and at last, when assisted by the rays of the sun, deprives it wholly of its oxygen, which is replaced by an equivalent quantity of chlo- rine ; a crystallized product C 4 C1 3 3 ,HO, or chlor acetic acid, which is powerfully acid, and possesses the same capacity of saturation as acetic acid, being formed. Intermediate chlorinated compounds probably exist, but they have not yet been examined. In order to prepare chloracetic acid, ground-stoppered bottles, holding 5 or 6 litres, are filled with very dry chlorine, and into each is poured 4 or 5 grammes of monohydrated acetic acid, after which the bottles are exposed to the sun; when their sides soon become covered with crystals, which consist of a mixture of oxalic and chloracetic acid, while the gas in the bottle is formed of chlorohydric acid and chlorocarbonic gas, resulting from a more advanced decomposition, which takes place, perhaps, in consequence of the small quantity of water from which it is difficult to free the chlorine and the sides of the flask. The crystals being dissolved in water, and the solution evaporated in vacuo over concentrated sulphuric acid, the oxalic acid crystallizes first, when the mother liquid is decanted, completely evaporated, and the residue distilled with anhydrous phosphoric acid. The oxalic acid which might remain is decomposed into oxide of carbon and carbonic acid, and the chloracetic acid distils over, but the first product should not be collected, because it may contain a small proportion of acetic acid. 564 , TRANSFORMATIONS OF ALCOHOL. Chloracetic acid crystallizes in rhombohedral lamellae or in colourless aciculse, deliquescent in the air; and it melts at 113 and boils at about 392. It combines with bases and forms a large number of soluble and crystallizable salts. The formula of chloracetate of potassa is KO,C 4 C1 3 3 +2HO. " of chloracetate of ammonia, (NH S ,HO),C 4 C1 S 3 +4HO. " of chloracetate of silver, AgO,C 4 Cl 3 3 . The chloracetates heated with an excess of potassa yield chloro- form and an alkaline carbonate ; and if the action be prolonged, the chloroform is itself converted into formic acid. We have, in fact, KO,C 4 C1 3 3 +KO,HO=C 2 HC1 3 +2(KO,C0 2 ,) KO,C 4 C1 3 3 +5KO=KO,C 2 H0 3 +2(KO,C0 2 )+3KC1. When chloracetic acid is treated with an amalgam formed of 1 part of potassium and 150 parts of mercury, it is converted into ordinary acetic acid, and hydrogen is substituted for the chlorine : C 4 C1 3 3 ,HO+7K+2HO=KO,C 4 H 3 3 +3KC14-3KO. 1398. Chloracetic acid forms a compound ether, chloracetic ether C 4 H 5 0,C 4 C1 3 3 , and a per chlorinated Mor acetic ether C 4 C1 5 0, C 4 C1 3 3 . Chloracetic ether is prepared by distilling chloracetic acid, or a chloracetate, with a mixture of alcohol and sulphuric acid, and diluting the distilled product with water, when the ether sepa- rates in the form of oil. By exposing it to the sun in bottles filled with dry chlorine, it is converted into an oleaginous product, per- chlorinated chloracetic ether, which boils at 473. Action of Chlorine on Compound Ethers. 1399. Chlorine acts on the compound ethers and removes their hydrogen ; the hydrogen removed being, in all cases, replaced by an equivalent quantity of chlorine. The first action of chlorine on acetic ether C 4 H 5 0,C 4 H 3 3 consists in removing 2 equiv. of hydrogen from simple ether C 4 H.O, and replacing them by 2 equiv. of chlorine ; which furnishes a bichlori- nated acetic ether of the formula C 4 H S C1 2 0,C 4 H 3 3 . It is decom- posed by an alcoholic solution of potassa, and yields of acetate of potassa and chloride of potassium C 4 H 3 C1 2 0,C 4 H 3 3 +4KO=2(KO,C 4 H 3 3 )+2KC1. If, on the contrary, the action of the chlorine be exhausted by intense solar radiation, perchlorinated chloracetic ether results, C 4 C1 5 0,C 4 C1 3 3 . By passing chlorine, under the influence of the solar rays, into oxalic ether C 4 H 5 0,C 2 S until chlorohydric acid is no longer disen- gaged, the ether is converted into a crystalline mass, which may be purified by pressing it between tissue-paper. This is perchlorinated oxalic ether C 4 C1 5 0,C 3 3 , which melts at 291.2, and is decomposed at a higher temperature. SUBSTITUTION. 565 Carbonic ether C 4 H 5 0,CO a subjected to the action of chlorine in diffused light yields chlorinated ether C 4 H 3 Cl a O,C0 3 ; and if the action of the chlorine be continued under the influence of the direct rays of the sun, perchlorinated carbonic either C 4 C1 5 0,C0 3 is ob- tained. 1400. By comparing together the numerous compounds derived from alcohol, it will be observed that the greater part of them are formed by means of the molecule of ether C 4 H 5 0, or that of alcohol C 4 H 5 0,HO, in which the hydrogen or oxygen is replaced by equi- valent quantities of other elements: oxygen, sulphur, chlorine, etc. When the hydrogen is replaced by equivalent quantities of chlorine, the equivalent of the derived substance is, in general, represented by the same number of volumes of vapour as the substance from which it is derived, as in the chlorinated products derived from chlorohydric ether. The same is true when oxygen is replaced by sulphur, as in ether C 4 H.O and sulf hydric ether C 4 H 5 S. In these different cases the gaseous volume of the element substituted is the same as that of which it takes the place. But when oxygen, the equivalent of which is 1 vol., is replaced by chlorine, of which the equivalent is 2 vol., the equivalent in volume of the substance de- rived is often different from that of the original substance : thus, the equivalent of ether C 4 H 5 is 2 vol., while that of chlorohydric ether is 4 vol. Many exceptions to these rules nevertheless occur : thus, aldehyde is derived from ether by the replacement of 1 equiv. of hydrogen (2 vol.) by 1 equiv. of oxygen, (1 vol.,) and yet aldehyde C 4 H 4 3 is represented by 2 vol. of vapour, like ether C 4 H.O ; while by replacing 3 equiv. of hydrogen (6 vol.) by 3 equiv. of chlorine (6 vol.) in the molecule of aldehyde, chloral or terchlorinated alde- hyde is obtained, of which the equivalent C 4 HCl 3 O a is represented by 4 vol., while that of aldehyde is represented by 2 vol. When chlorine is substituted for hydrogen, the chemical proper- ties of the compound, as regards its acid, basic, or neutral reactions, do not, in general, appear to be changed ; the most striking example of which is given by chloracetic acid, which is an acid as powerful as acetic, and possesses exactly the same capacity of saturation. The compound chlorinated ethers present additional examples, and others shall subsequently be described which are not less remarkable. But when hydrogen is replaced by oxygen, the basic, acid, or neu- tral properties of the substances change wonderfully. Thus ether C 4 H 5 0, which has a manifest affinity for acids, loses this property when it is converted into aldehyde C 4 H 4 2 , and becomes a powerful acid when changed into acetic acid C 4 H 3 3 . In order to appreciate more readily the relations of composition of the substances belonging to the alcoholic or vinic series, we have collected them in the following table : VOL. II. 2 X 566 TRANSFORMATIONS OF ALCOHOL. TABLE OF THE COMPOUNDS DERIVED FROM ETHER, C 4 H 6 0, OR FROM ALCOHOL, C 4 H 6 0,HO, BY MEAJtfS OF SUBSTITUTION. Carburetted hydrogen unknown C 4 H 6 , which may be regarded as the starting point of the whole series. SIMPLE ETHERS. Ether C 4 H 8 2 vol. of vapour. Sulfhydric ether C 4 H 8 S 2 Hydroselenic " C 4 H s Se " Hydrotelluric " C 4 H s Te " Chlorohydric " C 4 H 8 C1 4 Bromohydric " C 4 H 8 Br 4 lodohydric " C 4 H 8 I 4 Cyanohydric " C 4 H 8 Cy 4 Sulphocyanhydric ether C 4 H s SCy 4 COMPOUND ETHERS. Alcohols. Ordinary alcohol C 4 H 8 0,HO 4 vol. of vapour. Sulfhydric " C 4 H 8 S,HS 4 " " Sulphopotassic alcohol C 4 H S S,KS Sulphoplumbic " C 4 H s S,PbS Sulphomercuric " C 4 H 5 S,Hg a S. Compound Ethers properly so called. General formula (A representing the acid) C 4 H 8 0,A 2 or 4 vol. Boracic ether C 4 H 8 0,2B0 3 1st Silicic ether: 3C 4 H 8 0,Si0 3 2d Silicic ether 3C 4 H 8 0,2Si0 8 . Vinic adds. General formula of vinic acids formed by the monobasic acids A (C 4 H 8 0-f HO),2A Formula of vinic acids produced by the tribasic acids, such as P0 8 ,3HO (C 4 H 8 0-f2HO),P0 5 . PRODUCTS SUCCESSIVELY DERIVED FROM ETHER C 4 H 8 0. 1st. By oxidation. Ether C 4 H S 2 vol. Acetal (2C 4 H 8 0,C 4 H 4 O a ) Aldehyde C 4 H 4 O a 2 " Anhydrous acetic acid C 4 H 3 3 unknown, remains in combination with the water formed, and yields Hydrated acetic acid C 4 H 3 8 ,HO 4vol. but corresponding to alcohol C 4 H 8 0,HO. 2dly. By the action of Chlorine. Ether C 4 H 8 Monochlorinated ether C 4 H 4 C1 Bichlorinated ether C 4 H 8 Cl a O Perchlorinated ether C 4 C1 0. TRANSFORMATIONS OF ALCOHOL. 567 Sdly. By the successive action of Chlorine and Sulphur. Monochlorinated and monosulphuretted ether C 4 H 8 C1SO Bisulphuretted ether C 4 H 3 S a O. PRODUCTS DERIVED FROM SULFHYDRIC ETHER C 4 H 5 S. By the action of Chlorine. Sulfhydric ether CJIJ3 Quadrichlorinated sulf hydric ether C 4 HC1 4 S. PRODUCTS DERIVED FROM CHLOROHYDRIC ETHER, C 4 H,C1. By the action of Chlorine. Chlorohydric ether C 4 H 6 C1 4vol. Monochlorinated chlorohydric ether C 4 H 4 Cl a 4 " Bichlorinated " " C 4 H 3 C1 3 4 " Terchlorinated " " C 4 H a Cl 4 4 " Quadrichlorinated " " C 4 H C1 8 4 " t> Perchlorinated " " C 4 C1 6 4 PRODUCTS DERIVED FROM ALDEHYDE C 4 H 4 3 . 1st. By the action of Oxygen. Aldehyde C 4 H 3 O a Acetic acid C 4 H,0 3 which remains in combination with the water formed. Idly. By the action of Chlorine. Aldehyde C 4 H a O a 2vol. Terchlorinated aldehyde or chloral C 4 HC1 3 4 Perchlorinadte aldehyde C 4 Cl 4 O a . PRODUCTS DERIVED FROM ALCOHOL C 4 H t O,HO. 1st. By the action of Oxygen. Alcohol C 4 H,0,HO 4 vol. Aldehyde C 4 H 4 O a 2 " parts with its equivalent of water, and belongs to the series of ether. Idly. By the action of Chlorine. Alcohol C 4 H,0,HO 4vol. Aldehyde (1st stage of oxidation) C 4 H 4 2 2 " Chloral (2d stage of chlorination) C 4 HCl 3 O a 2 " Aqueous ether C 4 H 4 0-}-HO yields the same products. PRODUCTS DERIVED FROM AQUEOUS ALCOHOL, C 4 H,0,HO-f HO. By the action of Chlorine. By an oxidizing action, acetic acid C 4 H 3 0,,HO. Aqueous ether C 4 H,0-f-2HO yields the same product. PRODUCTS DERIVED FROM ACETIC ACID C 4 H,0 3 ,HO. By the action of Chlorine. Acetic acid C 4 H 3 S ,HO 4vol. Chloracetic acid C 4 C1 3 3 ,HO 4 " 568 TRANSFORMATIONS OF ALCOHOL. PRODUCTS DERIVED FROM COMPOUND ETHERS. By the action of Chlorine. On Carbonic ether C 4 H 0,CO a Bichlorinated carbonic ether C 4 H 3 Cl 3 0,CO a Perchlorinated carbonic ether C 4 Cl 5 0,CO a On Oxalic ether C 4 H } OA0 3 Perchlorinated oxalic ether C 4 Cl 6 0,C a 3 On Acetic ether C 4 H S 0,C 4 H 8 3 Bichlorinated acetic ether C 4 H s Cl a O,C 4 H 3 3 Chloracetic ether C 4 H S 0,C 4 C1 3 3 Perchlorinated chloracetic ether C 4 C1 S 0,C 4 C1 3 3 . 1401. Some chemists regard ether as a hydrate of bicarburetted hydrogen, and give it the formula C 4 H 4 ,HO ; in which case alcohol becomes a bihydrate of bicarburetted hydrogen, and all the products of the vinic series are considered as derived from the same radical, bicarburetted hydrogen C 4 H 4 . In this point of view, chlorohydric ether is a chlorohydrate of bicarburetted hydrogen C 4 H 4 ,HC1, and should be the first of the series of Dutch liquid C 4 H 3 C1,HC1 ( 1338) ; and the action of chlorine upon chlorohydric ether should therefore yield products identical with those composing this series. Now we have seen that the products derived from chlorohydric ether exhibit, in fact, the same composition as those derived from Dutch liquid, but that they differ essentially in their properties ; and it is there- fore evident that ether cannot be regarded as a hydrate of olefiant gas. Other chemists consider ether C 4 H.O as an oxide of carburetted hydrogen C 4 H 5 , to which they have given the name of ethyl, and have supposed it to be the radical of the ethers. All attempts to obtain this hypothetical root in an isolated form, have hitherto failed ; and its supposition being entirely gratuitous, does not assist the explanation of chemical reactions.* * The theory adopted by the author, in which the unknown carburetted hydro- gen C 4 H 6 is assumed as the starting point of the ether or alcohol series, is entirely French, and is in other countries regarded in a similar manner as the author regards the theory which assumes the hydrocarbon ethyl, C 4 H 5 , as the radical of which ether is the oxide ; but since the masterly investigations of Prof. Frankland, who actually succeeded in isolating ethyl, probability inclines very much to the side of the ethyl theory, which requires description in a work like the present. Before treating particularly of ethyl one general feature of the theory, which equally applies to a number of other substances, must be described : the theory of the pairing or conjugation of organic compounds. An organic body is said to be paired with another when the latter, termed the pair ling or conjugate, enters into combination with the former without the former losing its essential pro- perties ; examples of which also occur in inorganic chemistry, when e. g. oxide of platinum combines with ammonia to form a new oxide, the compound oxide of platinum and ammonia, described (g 1178,) the salts of which present the same general character with those of oxide of platinum. The formula of the compound oxide is PtO,N a H 6 , or PtO,2NH 3 , and it may be regarded as the oxide of a new base, consisting of PtNJJ, or Pt,2NH 3 , 1 equiv. of platinum being paired with LACTIC AND BUTYRIC FERMENTATION. 569 LACTIC AND BUTYRIC FERMENTATION. 1402. Under certain conditions, and when assisted by ferments, sugars and their congeners experience decompositions very different from those which take place in alcoholic fermentation ; and they then give rise to peculiar acids, called lactic and butyric, and to other substances, the nature of which is but little known. The concomitant circumstances, or those which produce lactic and butyric fermentations, are still less known than those of the alcoholic fermentation. The various kinds of sugar, dextrin, sugar of milk, yield a large 2 equiv. of ammonia ; in which case the formula of the oxide in order to express the phenomenon of pairing, would be written Pt(N a H)0 or Pt(2NH 8 )0. In organic chemistry the pairing of combinations is of frequent occurrence ; and one of the most beautiful instances of it is the pairing of hydrogen with one or more equivalents of bicarburetted hydrogen or olefiant gas. Hydrogen may, for the moment, be regarded as a radical, or a metal, of which water is the oxide, sulf hydric acid the sulphide, chlorohydric acid the chloride, etc. ; and now, by pairing it with 1 equiv. of olefiant gas, (assumed to be C 2 H 2 ) there results the com- pound H(C 3 H.,) or C a H 8 ; which, if the theory be correct, ought to form compounds with oxygen, sulphur, chlorine, etc. corresponding to the compounds of those ele- ments with hydrogen. This is actually found to be the case, as will be seen in the description of the substance C a H 3 , or methyl, the radical of its oxide mether, of which methylic alcohol, or wood-spirit, is the hydrate, ($ 1406.) Hydrogen paired with 2 equivalents of olefiant gas, forms the compound H(C 4 H 4 ), or C 4 H 5 , which is the formula of ethyl, and forms an oxide H(C 4 H 4 )0, or ether, corresponding to water, of which alcohol is the hydrate. Ethyl, C 4 H S , is an or- ganic radical, corresponding to a metal in inorganic chemistry, because it has its oxide C 4 H 5 0, its chloride C 4 H S C1, its sulphide C 4 H,S, and similar compounds with other metalloids, and because its oxide, ether, forms salts with acids corre- sponding to those of a metallic base RO. Chloride of ethyl, which the author calls chlorohydric ether, undergoes mutual decomposition with hydrate of po- tassa, forming chloride of potassium and hydrated oxide of ethyl, or alcohol ; which behaviour is peculiar to the metals. If the radical be really hydrogen paired with 2 equivalents of olefiant gas, then will the behaviour of ethyl be in all respects analogous to that of hydrogen; and its chloride, sulphide, etc., will have the properties of acids corresponding to chlorohydric, sulf hydric, etc. ; which is, in fact, the case, as chloride of ethyl forms double chlorides with many metallic chlorides, the formulae of which may be written RC1,H(C 4 H 4 )C1; and the mercap- tids, the general formula of which is RS,H(C 4 H 4 )S, are instances of double sul- phides. Nor does the analogy of hydrogen with its paired compounds stop here ; for as hydrogen forms compounds with arsenic, antimony, and phosphorus, so it is probable that methyl H(C a H a ) and ethyl H(C 4 H 4 ) will form similar substances ; and Frankland has actually succeeded in forming several of them. Cacodyl, which has been described (g 1381) is arseniuretted methyl, corresponding to arse- niuretted hydrogen, and even possessing its properties ; a phosphuretted methyl has been obtained, similar to phosphuretted hydrogen ; and combinations of both ethyl and methyl with zinc, according to the formulas H(C 4 H 4 )Zn and H(C a H a )Zn, are already discovered ; the corresponding compound of hydrogen, however, being yet unknown, which would take the formula HZn. ^ If hydrogen be paired with more than 2 equivalents of olefiant gas, other ra- dicals are formed, which shall be duly mentioned in their proper places ; they are butyryl, valyl, amyl, and several others, corresponding to the formula H(C 8 H 6 ), H(C 8 H 8 ), H(C IO H 10 ), etc. Hydrogen, and all radicals formed by its pairing with olefiant gas, will again form a paired compound with oxalic acid C a 3 , constituting a series of acids, 570 LACTIC AND BUTYRIC FERMENTATION. amount of lactic acid when they are mixed with a solution of di- astase, which has been exposed to the air for some time. Sprouted barley, which has been well soaked in water, is left in the air for two or three days, and then bruised, and, after having diluted it with water it is subjected for several days to a temperature of 77 which will be described in the text. It will suffice at present to give a tabular view of the series, since only one of these acids, the acetic, has been already de- scribed in the present work. Hydrogen.. H paired with C a 3 forms formic acid... C a H0 3 or H (C a O s ) Methyl C a H 3 " " C 2 3 " acetic acid. C 4 H 3 3 or C a H 3 (C a 8 ) Ethyl C 4 H S " " C 2 3 " metacetonic acid C 6 H S 3 or C 4 H S (C 3 8 ) Butyryl.... C,H, " " C a O, " butyric acid.... C 8 H,0 3 or C 6 H,(C a 3 ) Valyl C 8 H 9 " C a 8 " valeric acid.... C 10 H 9 3 or C 8 H 9 (C a 3 ) Amyl C IO H U C a 3 " caproic acid... C^H^Oa or C 10 H u (C a O s ) i I II ! I II I I II I I II Margaryl.. C^H^ " " C a 3 " margaric acid C 34 H 33 3 or C 33 H 33 (C a 3 ) The series is nearly complete, and it is probable that the connecting links, up to margaryl, will be discovered ere long. In the foregoing I have endeavoured to present a general view of the theory adopted in Germany and England, in relation to organic radicals, and paired compounds, without entering into details ; and it now remains only to describe the substances which have been discovered since the original was written, and which will be noticed under the chapters where the new compound ought to find its place. Ethyl C 4 H 8 . This, for a long time hypothetic radical, is obtained isolated by decomposing iodohydric ether, C 4 H 5 I, more properly called iodide of ethyl, by means of me- tallic zinc, in an hermetically sealed tube which has been freed from oxygen by exhaustion with an air-pump. The tube contains, after being heated to above 300, ethyl C 4 H 4 , olefiant gas C a H a , and methyl C a H 8 formed by the decomposition of a certain quantity of ethyl, besides iodide of zinc, which with the methyl forms methylide of zinc C a H 3 Zn. The gaseous ethyl, and the olefiant gas are brought into a glass-tube over mercury, and after absorbing the carburetted hydrogen by fuming sulphuric acid, the tube contains pure ethyl, as a colourless and inodorous gas, burning with a brilliant white flame, and condensing at 9.4 to a very mobile fluid. The density of the gas being 2.000, its formula C 4 H t corresponds to 2 volumes. Stibethyl SbC ia H ls . By moistening with iodohydric ether, in a small flask, a mixture of antimoni- uret of potassium with quartzose sand, and distilling as soon as iodohydric ether no longer evaporates, the receiver is found to contain Stibethyl, a compound of an- timony with 3 equivalents of ethyl, corresponding to antimoniuretted hydrogen SbH B , and the formula of which is SbC ia H 15 or rather Sb,3H(C 4 H 4 ). Stibethyl, is a very mobile and highly refracting fluid of a disagreeable alliaceous odour, of the density 1.324, boiling at 317.3, and yielding a vapour of the density of 7.440, so that its equivalent corresponds to 4 volumes. It is soluble in alcohol and ether, and a drop of the solution ignites in the air. A compound Sb,H(C 4 H 4 ) has also been obtained. Bismethyl BiC ia H 18 . It is obtained with bismuth-potassium similarly as Stibethyl is formed with an- LACTIC AND BUTYRIC FERMENTATION. 571 or 86. The starch of the barley is first converted into glucose by the diastase, after which lactic fermentation is developed by the influence of the air, and the liquid becomes very acid by the quan- tity of lactic acid formed, which is then saturated with lime, evapo- rated to the consistence of syrup, and treated with boiling alcohol, which dissolves the lactate of lime. Lactic acid is still more easily obtained by means of milk, which contains at the same time, the fermenting substance, sugar of milk, and an albuminoid matter, casein, which acts as a ferment, or gene- rates it. When it is allowed to sour in the air, or to turn, a coag- ulum, which is a combination of lactic acid with casein, is formed; and if bicarbonate of soda be added to neutralize the acid, lactate of soda is formed, while the casein, thus set free, again acts as a fer- ment on the sugar of milk, and converts an additional quantity of it into lactic acid. A new coagulum of lactate of casein is thus formed, which is also decomposed by bicarbonate of soda ; and the process is continued until no caseous precipitate of lactate of casein is formed, that is, until the sugar of milk is wholly decomposed. At the close of the operation, acetic acid is poured into the liquor, which is then boiled, when the casein is wholly precipitated in the form of acetate of casein. The filtered liquor is evaporated to dry- ness and the residue treated with boiling alcohol, which dissolves the lactate of soda. Instead of the sugar of milk, glucose or even cane-sugar may be added, but the lactic fermentation of the latter kind of sugar is very slow, and in order that it may take place, the cane-sugar must, probably, be previously converted into fruit-sugar, which transformation is very slow, because it is essential to lactic fermentation that the liquid should not contain much acid. Other albuminoid substances may be substituted for casein : the presence of fatty substances apppears to assist the formation of lactic acid, and some chemists even suppose it to be essential. The formula of lactic acid being C 6 H 5 5 +HO, 2 equivalents of the acid, therefore contain all the elements of an equivalent of fruit-sugar C 12 H 12 13 ; whence it may be admitted that, in lactic fermentation, the molecules of sugar merely change their grouping, without the intervention of any new elements in the reaction. 1403. When liquors which have undergone lactic fermentation, timoniuret of potassium, and behaves analogous to stibethyl, from which it differs essentially by decomposing at a certain temperature wifh a powerful explosion. It is a mobile fluid of the density 1.82, and a highly disagreeable odour; in the air it throws out thick fumes, inflames with a slight explosion and diffuses a deep- yellow smoke of oxyd of bismuth. Composition, Bi,3H(C 4 H 4 ). ZincTcethyl ZnC 4 H s . It is formed in the decomposition of iodohydric ether, or iodide of ethyl by zinc, and its formula is Zn,H(C 4 H 4 ). In contact with the air it burns with a bril- liant flame, giving off dense fumes of oxide of zinc. W. L. F. 572 LACTIC AND BUTYRIC FERMENTATION. are left to themselves for a longer time, another fermentation is de- veloped, and a new acid, called butyric is formed. Introduce into a large bottle 1. A solution of glucose, marking 8 or 10 of Baume. 2. A quantity of chalk equal to one-half of the sugar used. 3. A quantity of casein representing, in the dry state, 8 or 10 per cent, of the weight of sugar contained in the solution, for which purpose either cream-cheese, or Brie-cheese is used; freshly pre- pared gluten may also be substituted for the casein. The sugar is first transformed into a viscous substance which has hitherto been but little studied, and then into lactic acid, large quantities of which may by obtained by arresting the operation at the proper moment ; while if it be continued longer, the lactic acid is finally converted into butyric acid, and a mixture of hydrogen and carbonic acid is disengaged. The butyric fermentation is not generally completed until 2 or 3 months, after which the liquid con- tains a mixture of butyrate, lactate, and acetate of lime. The formula of butyric acid being C 8 H 7 3 HO, we have C 13 H 13 13 =C 8 H 7 3 ,HO-f4H+4C0 3 . which equation accounts for the evolution of hydrogen and carbonic acid during the butyric fermentation. In order to prepare large quantities of lactic and butyric acid, 3 killog. of sugar are dissolved in 13 killog. of boiling water, to which 15 gm. of tartaric acid have been added, then rotten cheese is added, diluted in sour milk, and 1500 gm. of powdered chalk, the whole is exposed to a temperature of 86 to 95, and the mass, being shaken from time to time, becomes completely solid in 8 or 10 days. It is then boiled for half an hour with 10 litres of water containing 10 gm. of quick-lime, and after filtering the liquid and evaporating it to the consistence of syrup, it is allowed to crystal- lize. The crystals of lactate of lime being redissolved in 2J times their weight of boiling water, 100 gm. of sulphuric acid diluted with its weight of water, are added, in order to precipitate the lime in the state of sulphate, and isolate the lactic acid ; after which the acid liquor, when filtered, is boiled with carbonate of zinc, which forms sulphate and lactate of zinc, a portion of w T hich latter salt separates in crystalline crusts during the cooling of the liquid, while an additional portion is removed by again concentrating it. The lactate of zinc, purified by a second crystallization, is subjected to the action of sulf hydric acid gas, and yields pure lactic acid. The compact mass which has yielded lactic acid, being again left to itself, at a temperature of 98, becomes liquid and disengages gas ; and in 5 or 6 weeks, the new fermentation is terminated. The liquid is then diluted with its weight of water, and a solution of 4 killog. of carbonate of soda is added, which precipitates the lime in the state of carbonate and forms butyrate of soda. The liquor, LACTIC ACID. 573 when filtered, is evaporated until it occupies only a volume of 4 or 5 litres, when 3 kilog. of sulphuric acid diluted with its volume of water are added. The liquid then separates into two layers, the upper one of which, consisting of butyric acid, is removed and brought into contact with chloride of calcium, and distilled. A single operation may yield as much as 1 kilog. of pure butyric acid. Lactic Acid C 6 H 5 5 ,HO. 1404. Lactic acid, concentrated as much as possible, in vacuo, over sulphuric acid, is a colourless liquid, of a density of 1.22, and soluble in all proportions in water and alcohol. Its composition is represented by the formula C 8 H 5 5 ,HO, the equivalent of water being capable of being replaced by 1 equiv. of base; and when subjected to heat it gives off its equivalent of water at about 266, and is changed into anhydrous lactic acid, C 6 H 5 5 , which is solid, fusible, very slightly soluble in water, but dissolving readily in al- cohol and ether. In contact with water or moist air, it passes slowly into the state of hydrated lactic acid. Anhydrous lactic acid combines with ammoniacal gas, and yields a product of which the formula is NH 3 ,C 6 H 5 5 . When heated to 482 lactic acid is further decomposed; and together with other products, a white crystalline substance of the formula C 6 H 4 4 , is formed, which melts at 224.6, and sublimes without change at about 482. It combines with ammoniacal gas and forms a compound NH 3 ,C 6 H 4 4 lactamid, which dissolves with- out change in water and alcohol. The substance C 6 H 4 4 , which has been improperly called anhydrous lactic acid, combines readily with water and reproduces hydrated lactic acid.* The lactates of potassa, soda, and ammonia, are deliquescent, and crystallize with difficulty. Lactate of lime crystallizes in small radiating acicube of the for- mula CaO,C 6 H 5 5 -f-5HO, and loses its 5 equiv. of water in vacuo, or at a temperature of 212. Lactate of zinc ZnO,C 6 H 5 5 +3HO, dissolves in 58 parts of cold, or 6 of boiling water, and bears a temperature of 410 without de- composition. Protolactate of iron FeO,C 6 H 5 5 +3HO is prepared by mixing solutions of lactate of ammonia and protochloride of iron, and pre- cipitating by alcohol, or by decomposing lactate of baryta by proto- sulphate of iron. After having separated the sulphate of baryta, alcohol is added to precipitate the lactate of iron in the form of small yellow aciculae. The salt is used in medicine. Lactates of copper and silver are obtained by boiling the carbon- ates of these metals with a solution of lactic acid, and their formulae are CuO,C 6 H 5 5 -f 2HO, and AgO,C 6 H 5 5 +2HO. * It is usually called lactide.J. C. B. 574 LACTIC AND BUTYRIC FERMENTATIONS. Lactic ether C 4 H 5 0,C 6 H 5 5 is obtained by distilling 2 parts of dried powdered lactate of lime, with a mixture of 2 parts of anhy- drous alcohol, and 2 parts of concentrated sulphuric acid, the dis- tillation being arrested at the moment the liquid begins to turn brown. The product is rectified over chloride of calcium, and a colourless liquid obtained, having a peculiar odour, a density of 0.866, and boiling at 170 : lactic ether dissolves in water, alcohol, and ether, and is decomposed by the alkalies, yielding alcohol and lactic acid. Butyric Acid C 8 H 7 3 .HO. 1405. Butyric acid is a colourless liquid, of an extremely dis- agreeable odour, and the smell of rancid butter is owing to the pre- sence of a small quantity of this acid. It solidifies at the tempera- ture of solid carbonic acid, and boils at 327.2. It dissolves in all proportions in water, alcohol, and spirit of wood, and its density is 0.963, while that of its vapour is 3.09, its equivalent C 8 H 7 3 ,HO, corresponding to 4 vol. of vapour. Butyric acid is inflammable, and chlorine acts on it, yielding two chlorinated butyric acids, of which the formulse are C 8 H 5 C1 3 3 ,HO and C 8 H 4 C1 3 ,0 S ,HO. Butyrates of potassa, soda, and ammonia, are very soluble in water, and crystallize with difficulty. Butyrate of lime is much less soluble hot than cold, and a solution of the salt, saturated at a low temperature, sets into a mass when heated. The formula of butyrate of baryta, which is deposited from a hot solution, is BaO,C 8 H 7 3 -f 2HO, while that of crystals developed in a cold solution is BaO,C 8 H 7 3 -f4HO, which latter salt melts in its its own water of crystallization. Butyrate of lead is precipitated in the form of an insoluble liquid, which sets after some time. Butyric acid forms a compound ether, which is easily prepared by mixing 100 gm. of butyric acid, 100 gm. of alcohol, and 50 gm. of sulphuric acid, and shaking them for some moments, when a layer of butyric ether forms on the surface of the mixture. It is washed with water, and purified by chloride of calcium. Butyric ether, though but slightly soluble in water, is very soluble in alcohol, and boils at 230, and its formula is C 4 H 5 0,C 8 H 7 3 . Ammonia reacts on butyric ether, and produces butyramid NH, C 8 H 7 2 . C 8 H 7 3 ,HO+NH 3 =NH 2 ,C 8 H 7 2 +2HO ; the butyric ether gradually disappearing, and the aqueous solution, when evaporated, yielding pearly crystals of butyramid, which melts at 239, and sublimes at a higher temperature without decomposition. Butyrate of lime yields, when heated, an odorous, inflammable liquid, boiling at about 284, and called butyrone. Its formula is C 7 H 7 0, and it arises from the following reaction : CaO,C 8 H 7 3 =CaO,CO a +C 7 H 7 0. WOOD SPIRIT. 575 By operating on considerable quantities of butyrate of lime, there is formed, with the butyrone, a more volatile liquid, boiling at 203, of the formula C 8 H 8 3 , and which has been called butyral. Buty- ral C 8 H 8 3 is to butyric acid C 8 H 7 3 ,HO what aldehyde C 4 H 4 2 is to acetic acid C 4 H 3 S ,HO, which comparison is confirmed by the chemical properties of butyral, since it oxidizes in the air, particu- larly when aided by platinum sponge, and is converted into butyric acid. It reduces oxide of silver like aldehyde, the metallic silver forming a coating on the surface of the vessel. SPIRIT OF WOOD, OR METHYLIC ALCOHOL, AND THE PRODUCTS DERIVED FROM IT. 1406. By subjecting wood to distillation, there is obtained, in addition to the gaseous products, an aqueous acid liquor, which con- tains a great number of different substances ; that which imparts to it its acidity being acetic acid, the method of the extraction of which has been described ( 1370). There also exists a volatile, in- flammable liquid, called spirit of wood. The proportion of this liquid varies according to the nature of the wood and the temperature at which the calcination is effected, and it generally reaches 1 per cent, of the whole quantity of fluid. It is mixed with acetone, aldehyde, methylacetic ether, and two volatile substances to which the names of mesite and xylite have been given, and lastly, a pitch-like matter is also found. The liquor is saturated with slaked lime, which attacks the acids and a portion of the tarry substances, after which the clarified liquor is decanted and distilled until the first tenth is collected in the receiver. This first product, which contains nearly the whole of the spirit of wood, is again distilled, with a small quantity of lime to decompose the methyl- acetic ether, and convert it into spirit of wood. The first portions distilled are alone collected, and by continuing these fractioned dis- tillations, highly concentrated spirit of wood is finally obtained, which, when distilled over lime, yields anhydrous spirit of wood. This is sufficient for all purposes of commerce, but in order to separate the pure principle, methylic alcohol, from it, it is treated with twice its weight of melted and powdered chloride of calcium, with which methylic alcohol forms a crystalline compound, resisting a tempera- ture of 212 without decomposition. It is heated in a water-bath, when the greater portion of the foreign products distils over, and the compound of methylic alcohol with chloride of calcium remains. By treating it with water, it is destroyed, and the methylic alcohol is set free, and separated by distillation. The product again dis- tilled over quick lime, yields pure and anhydrous methylic alcohol. 1407. Methylic alcohol is a colourless liquid, of a peculiar t/ 576 METHYLIC ALCOHOL. odour, resembling that of acetic ether, and its density is 0.798, while it boils at 151.7. Its ebullition in a glass vessel is accom- panied by violent agitation, which renders its distillation difficult, which is avoided by placing a stratum of mercury at the bottom of the vessel. It burns in the air with a flame resembling that of alcohol, and forms a series of compounds so closely resembling those of ordinary alcohol, that it is impossible to separate the study of these two substances, although their origin is very different, on ac- count of which analogy spirit of wood has been called methylic al- cohol (from, /*0i>, ivine, and fay, wood.) Its formula is C 2 H 4 2 , and the density of its vapour being 1.041, its equivalent is represented by 4 vol. of vapour like that of alcohol. Methylic alcohol readily dissolves potassa and soda, and forms, with anhydrous baryta, a crystallizable compound BaO,C 2 H 4 O fi , while the formula of its crystalline compound with chloride of cal- cium is 2 (C 2 H 4 0,) 2CaCl. Its solvent properties closely resemble those of alcohol, all substances soluble in the latter liquid being equally so in methylic alcohol. ACTION OF SULPHURIC ACID ON METHYLIC ALCOHOL. 1408. On mixing 2 parts of concentrated sulphuric acid with 1 part of methylic alcohol, a great elevation of temperature ensues, and if the acid liquor be saturated with carbonate of baryta, sulphate of baryta separates, and there remains in solution a salt called sul- phomethylate of baryta, EaO, (C 2 H 3 0,2S0 3 ) which may be obtained in crystals, by evaporating the liquid to the consistence of syrup, and allowing it to rest in a dry vacuum. All the other sulphome- thylates are easily prepared, by double decomposition, from the sulphomethylate of baryta. By carefully decomposing a solution of sulphomethylate of baryta by dilute sulphuric acid, the sulpho- methylic acid is obtained isolated, and its solution exposed for a long time in a dry vacuum, yields small acicular crystals of hydrated sulphomethylic acid. All the sulphomethylates are very soluble in water, and when heated are decomposed into the metallic sulphate which remains, and a compound ether, methylsulphurie ether C 2 H S 0,SO S , which shall presently be described. 1409. By mixing 1 part of methylic alcohol with 4 parts of concentrated sulphuric acid, and distilling the mixture, an inflam- mable gas of the formula C 2 H 3 is disengaged, consisting of methy- lic ether, which is to methylic alcohol C 2 H 4 2 what ordinary ether C 4 H 5 is to alcohol C 4 H 6 2 . The gas thus obtained is, however, always mixed with small quantities of sulphurous and carbonic acids, which are separated by allowing the gas to remain for some time in contact with caustic potassa. Methylic ether is a colourless liquid, of a peculiar etherial smell, and liquid only at a temperature of 22 to 40 ; and its density being 1.61, its formula C 3 H 3 corresponds to 2 vol. of vapour. METHYLIC ETHER. 577 Water dissolves about 37 times its volume of it, and it is still more soluble in ordinary and methylic alcohol. As we have been led by chemical reactions to write the formula of alcohol C 4 H 5 0,HO, so also we shall be induced to write that of methylic alcohol C 3 H 3 0,HO.* 1410. By distilling 1 part of methylic alcohol with 8 or 10 parts of concentrated sulphuric acid, very little methylic ether is obtained, but an oleaginous liquid distills over, which, when washed several times with water, and then distilled over caustic baryta, presents a composition corresponding to the formula C 3 H 3 0,S0 3 . It is methylsulphuric ether, that is, a compound ether, formed by the combination of methylic ether with sulphuric acid. The correspond- ing compound C 4 H 5 0,S0 3 of the alcohol series has recently been obtained. This product is also obtained by the direct combination of methy- lic ether C 3 H 3 with anhydrous sulphuric acid, the combination being accompanied with great evolution of heat. Methylsulphuric ether is a colourless liquid, of the density 1.324, and which boils at 370.4 ; the density of its vapour being 4.37, and its equivalent therefore represented by 2 vol. of vapour. Methylsulphuric ether is slowly decomposed by cold water, but very rapidly by boiling water, the products of decomposition being methylic alcohol C 2 H 3 0,HO, and sulphomethylic acid C 3 H 3 0,2S0 3 . Dry ammoniacal gas, and the aqueous solutions of ammonia, de- compose methylsulphuric ether, forming a white crystallizable sub- stance, which has been called sulphomethylam, and also methylsul- phamidie ether, regarding it as a compound ether, formed by a pe- culiar acid, methyhulphamidic, which has not yet been isolated ; the formula of this substance, in fact, may be written C 3 H 3 0,(NH,SO a ,S0 3 ). 1411. By introducing anhydrous methylic alcohol and anhy- drous sulphuric acid, separately, into two open tubes entering a very dry bottle, which is then corked, their vapours combine slowly, and an acid is formed, yielding, with baryta, a soluble salt having the same formula is the sulphomethylate of baryta, but differing in its properties. It is therefore an isomeric of sulphomethylic acid. 1412. By causing sulphuric acid, under the most varied circum- stances, to act on methylic alcohol, it has hitherto been impossible to obtain a carburetted hydrogen C 3 H 3 which shall be to methylic ether C 2 H 3 0, what olefiant gas C 4 H 4 is to ether C 4 H 5 0. * Methylic ether is with more propriety called mether, and regarded as the oxide of a radical, C a H 3 , or H(C a H a ), which has been isolated, and called methyl. The following series of compounds, called in the text compounds of methylic ether, and methylic acids, should therefore rather be regarded as salts of the oxide of methyl, or mether ; the methylic acids being merely acid salts. The names of methylonitric, methyloxalic ether, etc., would then change to re- spectively, nitrate of mether, etc. W. L. F. VOL. II. 2 Y 37 / 578 METHYLIC ALCOHOL. Ethers compounded of Methylic Ether and MetJiylic Acids. 1413. Compound methylic ethers are formed under the same circumstances as compound alcoholic ethers, and exhibit the same relations of composition. As in the case of alcohol, two species of combinations of methylic ether with acids are known ; neutral com- pounds, which are compound methylic ethers properly so called, and acid compounds, containing a double proportion of acids, and which we shall call methylic acids. Certain acids form both kinds of com- pounds, an example of which has just been shown in sulphuric acid ; while others produce only the neutral, and others again only the acid compound. Methylonitric Ether, C 3 H 3 0,N0 5 . 1414. The preparation of this substance is not so difficult as that of the nitric ether of the vinic series ; since nitric acid of com- merce may be made to react immediately on methylic alcohol, with- out any fear of the tumultuous and complicated reactions which this acid exerts on vinic alcohol. The best method of preparing methylo- nitric ether consists in heating in a retort a mixture of 1 part of methylic alcohol, 1 part of nitrate of potassa, and 2 parts of con- centrated sulphuric acid, when an etherial liquid is obtained which must be rectified several times over litharge and chloride of calcium. Methylonitric ether is a colourless liquid, of the density 1.182, and which boils at 154.4 ; and the density of its vapour being 2.653, its equivalent C 2 H 3 0,N0 5 is represented by 4 vol. Methy- lonitric ether detonates with extreme violence at a temperature slightly above its boiling point, and must therefore be handled with great caution. A methylonitrous ether C 3 H 3 0,N0 3 would probably be obtained by distilling a mixture of concentrated sulphuric acid and methylic alcohol with nitrate of potassa. Methylocarbonic Acid C 2 H 3 0,2CO a HO. 1415. By passing a current of carbonic acid gas through a so- lution of baryta in anhydrous methylic alcohol, a precipitate results in the form of pearl-like spangles, of the formula BaO(C 3 H 3 0,2C0 2 ), which is the carlomethylate of baryta. The salt is insoluble in methylic alcohol, but dissolves readily in water, being soon decom- posed into carbonate of baryta, carbonic acid and methylic alcohol. Methylocarbonic ether C 3 H 3 0,CO a , has not yet been obtained. Methyloxalic Ether C 3 H 3 0,C 3 0. 1416. This product is prepared by distilling a mixture of equal parts of crystallized oxalic acid, concentrated sulphuric acid, and methylic alcohol, when a liquid is obtained which, when allowed to evaporate spontaneously, deposits white crystals of methyloxalic acid. The crystals are dried between tissue paper, and distilled over litharge. METHYLACETIC ETHER. 573 Methyloxalic ether is a solid substance, melting at 123.8, and boiling at 321.8. It dissolves in water, alcohol, ether, and methylic ether ; and water decomposes it slowly at the ordinary temperature, and rapidly at the boiling point, forming free oxalic acid and me- thylic alcohol. This ether is decomposed by dry ammoniacal gas, and converted into a crystalline substance, of which beautiful crys- tals are obtained by redissolving it in alcohol, and which may be considered as a methyloxamic ether , C 2 H 3 0,(NH 2 C 2 2 ,C 2 3 ). If a large quantity of ammonia in solution be used, methylic alcohol and oxamid NH 2 C 2 3 are obtained. Methylacetic Ether C 2 H 3 0,C 4 H 3 3 . 1417. It is obtained by distilling 2 parts of methylic alcohol with 1 part of monohydrated acetic acid and 1 part of concentrated sulphuric acid. The product is poured over powdered anhydrous chloride of calcium, and shaken frequently, when, by allowing the liquid to rest, two layers are formed, the upper one of which, when distilled over quicklime to retain the sulphurous acid, and then over chloride of calcium to retain a small quantity of methylic alco- hol, yields pure methylacetic ether. It is a colourless liquid, hav- ing an odour resembling that of acetic ether of the vinic series, and its density is 0.919, while it boils at 136.4. The density of its vapour being 2.57, its equivalent C 2 H 3 0,C 4 H 3 Q 3 is represented by 4 vol. of vapour. It has been shown ( 1406) that crude spirit of wood always contains a certain quantity of this substance. Boiling water, and the alkaline solutions particularly, decompose it into methylic . alcohol and acetic acid ; and it dissolves in 2 parts of water, and mixes in all proportions with vinic and methylic alco- hol and with ether. Methylochlorocarbonic Ether C 2 H 3 0,C 2 3 C1. 1418. This ether is formed under circumstances analogous to those in which the corresponding product of the vinic series is pro- duced, that is, by pouring methylic alcohol into a bottle filled with chlorocarbonic gas COC1. By treating it with water, an oily liquid separates, which is distilled, after being well washed with water, first over chloride of calcium, and then over oxide of lead. It is a colourless liquid, of a suffocating odour. Ammonia dissolved in water decomposes it, chlorohydrate of ammonia and a deliquescent crystalline substance called urethylan being formed; which lat- ter, however, may be considered as methylocarbamic ether, for its formula can be written C 2 H 3 0,(NH 2 ,CO,C0 2 ). MethyloUboracic Ether C 3 H 3 0,2B0 3 and Trimethyloboracic Ether 3C 2 H 3 0,B0 3 . 1419. By treating melted and finely powdered boracic acid with methylic alcohol, a combination ensues with elevation of temperature ; 580 METHYLIC ALCOHOL. and, after driving off the excess of methylic alcohol by heat, there remains as residue a soft, transparent substance, which can be drawn out in threads at the ordinary temperature, consisting of methylo- Uboracic ether C 2 H 3 0,2B0 3 . Water decomposes it immediately into hydrated boracic acid and methylic alcohol. By treating methylic alcohol with chloride of boron, a very vola- tile and colourless liquid is obtained, having a penetrating smell, and the formula is 3C 2 H 3 0,B0 3 , while its density is 0.955 at 32, and it boils at 161.6. The density of its vapour is 3.60. These two compounds burn with a beautiful green flame. Methylosulphocarbonic Ether C 2 H 3 0,CS 2 , and Sulphocarbomethylic Acid C 2 H 3 0,2CS 2 . 1420. By pouring sulphide of carbon into caustic potassa, dis- solved in anhydrous amylic alcohol, silky crystals of sulphocarbo- methylate of potassa KO,(C 2 H 3 0,2CS 2 ) are formed ; and a great number of other sulphocarbomethylates are obtained from this salt by double decomposition. ' If iodine be added to a solution of sulphocarbomethylate of potassa in methylic alcohol, the temperature rises, while sulf hydric acid and oxide of carbon are disengaged. In addition, iodide of potassium, crystallized sulphur, and a brown oil, which, after two or three rectifications, yields pure methylosul- phocarbonic ether ', are formed. This is an amber-coloured liquid, having a density of 1.143 at 59, and boiling at about 338 ; and the density of its vapour being 4.266, its equivalent C 2 H 3 0,CS 2 is represented by 2 volumes of vapour. Methylochlorohydric Ether C 2 H 3 C1.* 1421. By heating in a flask 2 parts of sea-salt with a mixture of 1 part of methylic alcohol and 3 parts of concentrated sulphuric acid, a colourless gas is disengaged, which is to be left for some time in contact with water, to effect the absorption of the mixed sulphurous acid and methylic ether. This gas, which does not liquefy at a cold of 0.4, is methylochlorohydric ether. Its density is 1.728, and its equivalent C 2 H S C1 corresponds to 4 volumes of vapour. It burns with a flame edged with green ; and water dis- solves about 3 times its volume of it. Methyliodohydric Ether C 2 H 3 L 1422. It is formed by pouring 8 parts of iodine into 12 or 15 parts of methylic alcohol, and gradually adding 1 part of phosphorus, and then applying heat to distil the liquor. The liquid collected in the receiver is shaken with water, the ether is precipitated, washed * According to the more probable theory, this substance would be chloride of methyl. W. L. F METHYLIC ETHELS. 581 several times with water, and then distilled, first over chloride of calcium, and then over oxide of lead. It is a colourless liquid, boil- ing between 104 and 122 ; while its density is 2.23T at 69.8. Methylofluohydric Ether C 2 H 3 F1. 1423. This simple ether, the corresponding one of which in the vinic series is not yet known, is prepared by heating in a retort, methylosulphuric ether C 2 H 3 0,S0 3 with fluoride of potassium, or also with fluoride of calcium reduced to an impalpable powder; when a colourless gas is disengaged, of an agreeable etherial smell, burning with a bluish flame, and of which the density is 1.186 ; while its equivalent C 2 H 3 F1 corresponds to 4 volumes. Water dis- solves 1 J time its volume of it. Methylocyanohydric Ether C 2 H 3 Cy. 1424. In order to obtain this ether, it is sufficient to distil methylosulphuric ether with cyanide of potassium, or finely pulverized cyanide of mercury ; when it is obtained as a liquid, insoluble in water, and very poisonous. Methylosulfhydric Ether C 2 H 3 S and its Compounds. 1425. Methylosulfhydric ether is prepared by passing a current of methylochlrohydric ether C 2 H 3 C1 through an alcoholic solution of monosulphide of potassium, heating the liquid, and collecting the distilled products in a well-cooled receiver ; after which they are washed with water and distilled over chloride of calcium. Methylosulfhydric ether is a very volatile liquid, of an extremely disagreeable smell, and its density is 0.846 at 69.8, while it boils at 105.8. The density of its vapour is 2.115, and its equivalent C 2 H 3 S corresponds to 2 volumes of vapour, like methylic ether C 2 H 3 0. Methylosulfhydric ether is a simple ether, which forms a great number of compound ethers by combining with electro-negative sulphides ; and the principal of these compound ethers are : 1426. Methylosulfhydric Alcohol C 2 H 3 S,HS, or methylic alco- hol C 2 H 3 0,HO, in which the 2 equivalents of oxygen are replaced by 2 equivalents of sulphur ; which is obtained by passing a current of methylochlorohydric ether through an alcoholic solution of sulf- hydrate of sulphide of potassium, and then distilling the mixture. It is also prepared by distilling a mixture of sulphomethylate of potassa KO,(C 2 H 3 0,2S0 3 ) with a solution of sulf hydrate of sulphide of potassium ; the distilled product being washed with water, and rectified over chloride of calcium. Methylosulfhydric alcohol, also called methylic mercaptan, is a colourless liquid, of an extremely fetid odour, and very volatile, for it boils at 69.8. It is decom- posed by contact with red oxide of mercury, and yields a crystal- lized product, in which the sulf hydric acid is replaced by 1 equi- 2Y2 582 METHYLIC ALCOHOL. valent of sulphide of mercury Hg 3 S; analogous products being obtained with several other metallic sulphides. 1427. Sulphocarbomethylosulfhydric Ether C 2 H 3 S,CS 3 is ob- tained by distilling a concentrated solution of sulphomethylate of lime CaO,(C 3 H 3 0,2S0 3 ) with a solution, also concentrated, of sulphocarbonate of sulphide of potassium KS,CS 2 , and rectifying the liquid over chloride of calcium. It is a yellowish liquid, of a density of 1.159 at 64.4, while it boils at 399.2. The density of its vapour being 4.650, its equivalent C 2 H 3 S,CS 3 is represented by 2 volumes of vapour: it is methylocarbonic ether C 3 H 3 0,CO a , hitherto unknown, the oxygen of which is replaced by equivalent quantities of sulphur. 1428. By replacing, in the preparation of methylosulf hydric ether, the alcoholic solution of monosulphide of potassium, by an alcoholic solution of bisulphide of potassium, a slightly yellowish liquid is obtained, of an extremely disagreeable and persistent alli- aceous odour; while its density is 1.046 at 64.4, and it boils at 240.8. The formula of this substance being C 3 H 3 S ? , it may be considered as methylosulfhydric ether C a H 3 S, combined with 1 equivalent of sulphur : the density of its vapour is 3.310, and its equivalent corresponds to 2 volumes of vapour. Lastly, by substituting pentasulphide for the bisulphide of potas- sium, there results a product still more sulphuretted, of which the formula is C 2 H 3 S 3 . Protocarluretted Hydrogen C 2 H 4 , or Marsh Gf-as. 1429. Protocarburetted hydrogen evidently belongs to the methylic series, and may be considered as the starting point of this series. By causing chlorine to act on this gas, products are obtained which are identical with those afforded by methylochloro- hydric ether C 2 H 3 C1, and it is not to be doubted, although this is not yet proved, that by causing suitable volumes of protocarburetted hydrogen and chlorine to react on each other, methylochlorohydric ether itself will be obtained. Now, methylochlorohydric ether, treated with an alcoholic solution of potassa, yields methylic alco- hol ; and it has been mentioned ( 1390) that the vinic series may also be regarded as derived from a carburetted hydrogen C 4 H 6 , which is as yet unknown. When vapours of monohy drated acetic acid C 4 H 3 3 ,HO are poured through a glass tube containing platinum-sponge, and heated to 750, the acetic acid is decomposed into carbonic acid and protocar- buretted hydrogen, C 4 H 3 3 HO==2C0 3 +C 3 H 4 . A similar decomposition takes place by heating acetic acid in contact with an excess of alkali ; but in that case the carbonic acid remains combined with the alkali, and the protocarburetted hydrogen FORMIC ACID. 583 alone is disengaged. The most economical manner of preparing the gas consists in heating 4 parts of crystallized acetate of soda with 10 parts of an alkaline mixture composed of 2 parts of caustic potassa and 3 parts of quicklime. In order to make the mixture, the 2 parts of potassa are dissolved in a small quantity of water and sprinkled over with the 3 parts of pulverized quicklime ; and the paste is then heated to a dull-red to drive off the excess of water. Protocarburetted hydrogen also arises spontaneously from marsh mud ( 265) and from layers of bituminous coal. It has never been liquefied at any temperature, and its density is 0.559, while its equivalent C 3 H 4 corresponds to 4 vol. of gas, and it burns with a bluish flame, which is much less brilliant than that of bicarburetted hydrogen. PRODUCTS OF THE OXIDATION OF METHYLIC ALCOHOL. Formic Acid C 2 H0 3 HO. 1430. Methylic alcohol oxidizes, at the expense of the oxygen of the air, in the presence of platinum-sponge, and, like alcohol, it exchanges, in this case, 2 equiv. of hydrogen for 2 equiv. of oxy- gen,* producing a peculiar acid C 2 H0 3 ,HO, called formic, a large portion of which is, however, destroyed by contact with the platinum- sponge, and, especially if the temperature be elevated, complete com- bustion and the formation of carbonic acid ensue : C 2 H0 3 ,HO+20=2CO a +2HO. But formic acid is obtained in a great number of chemical reac- tions, in which certain organic substances are subjected to oxidizing agents ; by heating, for example, a mixture of peroxide of manganese and dilute sulphuric acid, with alcohol, sugar, fecula, tartaric acid, etc., a portion of the organic substance being completely converted into water and carbonic acid, while the other is imperfectly oxidized and produces formic acid. When any considerable quantity of formic acid is to be prepared, 2 kilog. of sugar are dissolved in 10 litres of water, and 6 kilog. of sulphuric acid being gradually added, the mixture is poured into the cucurbit of an alembic, at the bottom of which have been placed 6 kilog. of peroxide of manganese. A lively effervescence ensues immediately, owing to the evolution of carbonic acid, and when it lessens, the capital is adjusted and dis- tillation effected, but it is arrested when 5 or 6 litres of liquid are obtained. This liquid, in which the formic acid is concentrated, is * It is more rational to assume, in the case of both acetic and formic acids, that the alcohol takes up 4 equiv. of oxygen and gives off 3 equiv. of water, because the substitution of oxygen for hydrogen in combinations is scarcely admissible. Vinic alcohol C 4 H 6 O a , by taking up 4 , becomes C 4 H 6 6 , and, by losing 3HO, as- sumes the formula of acetic acid C 4 H 3 3 +aq. In like manner, methylic alcohol C a H 4 O a becomes C a H 4 O s by gaining 4 , and is converted into formic acid C a HO,-f-aq. by giving off 3HO. W. L. F. 584 METHYLIC ALCOHOL. saturated with milk of lime and the formiate of lime crystallized by evaporation. The salt thus forms only crystalline crusts ; and by distilling it with more or less concentrated sulphuric acid, formic acid also more or less concentrated is obtained. If formic acid is to be obtained at its maximum of concentration, the formiate of lime must be converted into formiate of lead, by adding acetate of lead to the solution of formiate of lime ; when the formiate of lead, being but slightly soluble in cold water, is almost wholly deposited, and may be purified by dissolving it in boiling water, which deposits it, on cooling, in small prismatic crystals. Formiate of lead, well dried, is introduced into a long glass tube, heated by some coals, and through which a current of sulf hydric acid is passed, when sulphide of lead is formed, while mono- hydrated formic acid condenses in the receiver. It is a colourless liquid, of a penetrating and characteristic odour, and it solidifies at a few degrees below 32, while it boils at 212. Its density is 1.235, and the density of its vapour being 1.556, its equivalent C a H0 3 ,HO is represented by 4 volumes of vapour. Monohydrated formic acid is highly caustic, and produces blisters on the skin. In combining with water, the first portions of water added elevate its boiling point; with the addition of 20.7 of water, that is 1 equiv., it boils at 222.8. An excess of concentrated sul- phuric acid decomposes formic acid into oxide of carbon and water. At the boiling point, formic acid reduces several metallic oxides, particularly the oxides of silver and mercury. Formiate of potassa and soda are very soluble and deliquescent. Formiate of baryta dissolves in 4 parts of water, and crystallizes readily; the formula of its crystals being BaO,C 2 H0 3 . Formiate of lime dissolves in 10 parts of water, and is nearly as soluble in hot as in cold water. Formiate of lead requires 36 to 40 parts of cold water for solu- tion, but dissolves more freely in hot water, and its crystals are anhydrous. By double decomposition, a formiate of silver may be obtained which is destroyed by being boiled with water. 1431. Formic ether C 4 H 5 0,C 2 HO S of the vinic series is obtained by heating a mixture of 7 parts of dry formiate of soda, 10 parts of concentrated sulphuric acid, and 9 parts of alcohol. It is made on a larger scale and cheaply, by mixing, in a large retort, 80 parts of starch, 120 of ordinary alcohol at 0.85, 120 parts of water, 304 of peroxide of manganese, and 240 of concentrated sulphuric acid. Heat is applied gently, and, when the reaction is fully established, the fire is removed, and the sides of the retort cooled with moist cloths, when a stratum of formic ether separates, which is removed and treated with milk of lime to free it from acids, and subse- quently distilled over chloride of calcium. Formic ether is a colourless liquid, of a mild taste, of a density of METHYLAL. 585 0.912, and boiling at 128.1, which dissolves in 10 parts of water, and mixes in all proportions with alcohol. It should be remarked that formic ether C 4 H 5 0,C 2 H0 3 is isomericwith methylacetic ether C 2 H 3 0,C 4 H 3 3 . Formic ether, treated with chlorine in diffused light, forms a chlorinated ether, of the formula C 4 H 3 C1 2 0,C 2 H0 3 , and, by exhausting the action of the chlorine in the sun, a perchlori- nated chloroformic ether C 4 C1 5 0,C 3 C10 3 is obtained. Methyloformic ether C 2 H 3 0,C 2 H0 3 is prepared in the same man- ner as that of the vinic series, except that spirit of wood is substi- tuted for alcohol, and it is an etherial, very mobile liquid, which boils at about 98.6. Methylal C 6 H 8 4 . 1432. It has not yet been found possible to obtain aldehyde of the methylic series, the formula of which would be C 2 H 3 2 . By distilling a mixture of methylic acid and alcohol over peroxide of manganese, there results a mixture of several volatile liquids, in which methyloformic ether and a peculiar liquid, called methylal^ predominate. The latter being dissolved in water, and potassa added, the alkali decomposes the methyloformic ether, while the methylal separates in the form of a liquid layer floating on the sur- face, which is purified by distillation over chloride of calcium. Me- thylal boils at 107.6, and corresponds to acetal. Its formula being C 6 H 5 4 , it may be regarded as resulting from the union of 3 mole- cules of methylic ether, of which one has taken 1 equiv. of oxygen in the place of 1 equiv. of hydrogen.* ACTION OF CHLORINE ON COMPOUNDS OF THE METHYLIC SERIES. Products of the Action of Chlorine on Methylochlorohydric Ether and on Protocarburetted Hydrogen. 1433. Chlorine acts with more difficulty on chlorohydric ether of the methylic series than on that of the vinic series, the reaction ensuing only when assisted by the direct rays of the sun ; and as these products are more volatile, greater care is required in cooling the receivers. The apparatus described ( 1387) and represented by fig. 680 is used. By maintaining the methylochlorohydric ether in excess, the bottle C, (fig. 680), which should be kept in a refrigerating mixture, receives a very volatile liquid, which should be purified by distilla- tion over concentrated sulphuric acid, and then over quicklime, and which is monochlorinated methylochlorohydric ether C 2 H 2 C1 S . The odour of this product resembles that of Dutch liquid, and its density * Here again it is unnecessary to assume the highly improbable substitution of oxygen for hydrogen, since the reaction is very simply explained by allowing 3 equiv. of methylic ether C S H S 3 to gain 2 equiv. of oxygen, forming C S H 8 6 , and then to lose 1 equiv. of water, which gives methylal C 6 H 8 4 . W. L. F. 586 METHYLIC ALCOHOL. is 1.344 at 64.4, while it boils at 86.9. The density of its vapour being 2.94, its equivalent C 2 H 2 C1 2 is represented by 4 volumes of vapour, like that of methylochlorohydric ether C 2 H 3 C1. 1434. The second product of the action of chlorine on methylo- chlorohydric ether is a liquid having a density of 1.491 at 62.6, and boiling at 141.8 ; the composition of which is represented by the formula C 2 HC1 3 , corresponding to 4 vols. of vapour. This is bichlorinated methylochlorohydric ether, more commonly known as chloroform, which name has been given to it because, in contact with an alcoholic solution of potassa, it yields chloride of potassium and formiate of potassa, C 3 HC1 3 +4KO=3KC1+KO,C 2 H0 3 . Chloroform is produced in several other chemical reactions, and particularly when a solution of hypochlorite of lime is made to re- act on alcohol or acetone. This product has been extensively manufactured since the discovery of its power in effecting the insensibility of patients during surgical operations. Chloroform is also obtained by decomposing hydrated chloral C 4 HC1 3 2 ,HO by a solution of potassa, C 4 HC1 3 0,,HO+KO=C 2 HC1 3 +KO,C 2 H0 3 . Lastly, chloroform is produced when the chloracetates are heated in the presence of an excess of hydrated alkali, KO,C 4 C1 3 3 +KO,HO=2(KO,C0 2 )+C 3 HC1 3 . It is readily and economically prepared, by pouring 35 to 40 litres of water into the cucurbit of an alembic, heating the water to 106, and adding first 5 kilog. of quicklime, and subsequently 10 kilog. of hypochlorite of lime of commerce; and lastly, by pouring in \\ litre of alcohol at 0.85, and, after having mixed it well, and adjusted the capital, heating the liquid to boiling. As soon as distillation commences, the fire is slackened and the pro- cess allowed to continue spontaneously, when an aqueous liquid condenses in the receiver, at the bottom of which a heavier liquid, chloroform, is formed. It is separated and purified by distillation over chloride of calcium ; and the process just described yields about 600 gm. of chloroform. 1435. Chloroform, subjected to the action of chlorine, in the light of the sun, until chlorohydric acid is no longer disengaged, loses its last equivalent of hydrogen, while perchlorinated methylo- chlorohydric ether C a Cl 4 , which is a new chloride of carbon, is formed. This compound is liquid at the ordinary temperature, but at 9.4 solidifies into a pearly crystalline mass ; and it boils at 172.4. Its density is 1.599; the density of its vapour being 5.30, its equivalent is likewise represented by 4 volumes of vapour. 1436. By exposing to the rays of the sun a bottle containing a CHLOROFORM. 587 mixture of protocarburetted hydrogen, and chlorine in excess, a liquid condenses on the sides, which is a mixture of the various chlorinated methylochlorohydric ethers just described, comprising principally chloroform C 4 HC1 3 and chloride of carbon C 3 C1 4 . The first chlorinated product, methylochlorohydric ether C 3 H 3 C1, would probably be obtained by introducing the two gases in an ap- fig. retted hydrogen in excess, and then passing the gases through a paratus resembling that of fig. 680, maintaining the protocarbu- tube cooled by solidified carbonic acid, in order to condense the gaseous ether. In all cases, it is proved that, by the action of chlorine and protocarburetted hydrogen C 3 H 4 , the same products are obtained as by the action of chlorine on methylochlorohydric ether C a H 3 Cl, and it is correct to regard this substance as the starting point of the series. Thus, we have Protocarburetted hydrogen .............. C 2 H 4 , a non-liquefiable gas. Methylochlorohydric ether ....... . ....... C 2 H 3 C1, liquefying at a very low temperature. Monochlorinated methylochlorohydric ether ...................................... C 2 H 2 C1 2 , boiling at 86.9. Bichlorinated methylochlorohydric ether, or chloroform .................... C 2 HC^, boiling at 141.8. Perchlorinated methylochlorohydric ether ...................................... C 2 C1 4 , boiling at 172.4. 1437. But again, it is possible, by operating on chloride of carbon C 2 C1 4 , and by proper chemical reactions, to substitute hydrogen for the chlorine, and ascend from chloride of carbon to protocarburetted hydrogen, passing through all the intermediate products : in order to prove which, it is sufficient to introduce into a flat-bottomed flask a solution of chloride of carbon in aqueous al- cohol, and then to add an amalgam of potassium. On communi- cating the flask successively with two U-tubes, the first of which is kept at a temperature of about 86, and the second cooled by a mixture of ice and salt, then with a bulb-apparatus filled with water, and lastly with a conducting-tube which leads the gases into a bell- glass over the water-cistern, and heating the flask, the chloride of carbon is decomposed, chloride of potassium and caustic potassa being formed ; and the chlorine abstracted is replaced by hydrogen arising from the decomposition of the water. Bichlorinated methylochlorohydric ether C 3 HC1 3 condenses chiefly in the first U-tube, and in the second the monochlorinated methylo- chlorohydric ether C 3 H 2 Cl a , while the water in the bulb-apparatus dissolves the methylochlorohydric ether C 3 H 3 C1, which may be sepa- rated by saturating it with chloride of calcium ; and lastly, proto- carburetted hydrogen is collected in the bell-glass. This inverse transformation has not hitherto succeeded on the corresponding series of chlorohydric ether of alcohol ; but would be 588 METHYLIC ALCOHOL. particularly interesting, as it would enable the preparation of the carburetted hydrogen C 4 H 6 which is still wanting in the series. Bromoform, lodoform, and Sulphoform. 1438. By treating alcohol with bromine, a product correspond- ing to chloral is obtained, which is decomposed by alkaline solu- tions, and yields bromoform C s HBr 3 . lodoform C 3 HI 3 is obtained by pouring a solution of caustic po- tassa, or carbonate of potassa, into alcohol saturated with iodine, until the liquid is discoloured ; when, by adding a large quantity of water, the iodoform is precipitated in the form of small crystalline spangles, which are purified by redissolving them in alcohol and evaporating the liquid. By distilling 1 part of iodoform with 3 parts of sulphide of mer- cury, a yellow oleaginous liquid is obtained, constituting sulpho- form C 3 HS 3 . Action of Chlorine on Metliylio Ether C 2 H 3 0. Action oj (Jriiorine on lYLettiytio J^tner u 2 Jt 3 u. 1439. The action of chlorine on methylic ether is excessively violent, even in diffused light ; and the experiment, being dangerous, must be carefully conducted, in order to prevent the apparatus f ~ bursting to pieces. Figure 682 represents the apparatus most from suit- Fig. 682. able to the production of any considerable quantity of the product. Methylic ether is prepared by heating in a flask A (fig. 682) a mix- ture of 1 part of wood-spirit and 4 parts of cencentrated sulphuric ACTION OF CHLORINE ON METHYLIC ETHER. 589 acid ; allowing the gas to traverse a first washing-bottle B contain- ing water, then a second bottle C containing a solution of potassa in order to retain the sulphurous and carbonic acids, and lastly, a long tube filled with chloride of calcium to dry the gas. (This tube is not represented in the figure.) The chlorine is prepared in the flask G by the reaction of chlorohydric acid on peroxide of manganese, and is washed in the water of the bottle F, and dried by passing through concentrated sulphuric acid contained in the bottle E. The two gases, which are brought together in the flask D, escape through a refrigerator H, made very cold by ice, into the atmosphere by the opening o. The liquids which condense in the flask D and in the refrigerator H fall into the bottle I, which should be entirely inde- pendent of the apparatus, so that if the latter should burst, the products already obtained will not be lost. The apparatus should be arranged in a well-lighted place, but pro- tected from the direct rays of the sun ; and, though the reaction is sometimes long in being established, when once commenced, it con- tinues with great energy. The operator should then regulate the evolution of the two gases with great care : they should meet in such proportion as to destroy each other, immediately, on reaching the flask D ; for if one of the gases should flow too freely, as, for example, if the flask were to become coloured by chlorine, which would require a more rapid disengagement of methylic ether, an ex- plosion would inevitably ensue. In order to prevent this accident, the current of chlorine must be lessened by opening one of the washing-bottles E or F, and the ether must be allowed to flow very slowly until the flask D is deprived of colour ; after which the gases would be made to flow. The bottle I is found to contain a very volatile liquid, of a suffo- cating odour and exciting to tears, which exhales acid fumes by being decomposed by the moisture of the air. Its density at 68 is 1.315, while it boils at 221, and cold water decomposes it, though slowly. This liquid is monochlorinated methylic ether C 3 H 3 C10, the formula of which corresponds to 2 volumes of vapour, like that of methylic ether C 2 H 3 0, from which it is derived. This product, subjected to the action of chlorine, exchanges 1 equivalent of hydrogen for 1 equivalent of chlorine, and becomes bichlorinated methylic ether, the density of which is 1.606 at 68, while it boils at about 266 ; its equivalent C 3 HCl a O corresponding likewise to 2 volumes of vapour. Finally, by again exposing this new product to the action of chlorine, in the rays of the sun, its last equivalent of hydrogen is replaced by 1 equivalent of chlorine, forming per chlorinated me- ihylic ether C 2 C1 3 0, which product has not maintained a state of concentration similar to that of the two preceding, and that of me- thylic ether C 2 H 3 0, for its equivalent corresponds to 4 volumes of vapour. There has been either a doubling of the original mole- VOL. II. 2 Z 590 METHYLIC ALCOHOL. cule, or a separation of the molecules, so that the same num- ber of molecular groups now occupy a double space ; which change of molecular arrangement is manifested by an anomaly in the boil- ing point. It has always hitherto been observed that when a mole- cular group is modified merely by the substitution of 1 equivalent of chlorine for 1 equivalent of hydrogen, its boiling point rises ; which circumstance is not true for terchlorinated methylic ether, compared with bichlorinated methylic ether ; the boiling point of the latter being 266, while that of the former is about 212. Action of Chlorine on Methylosulfhydric Ether. 1440. Chlorine readily acts on methylosulfhydric ether, which gradually exchanges its oxygen for equivalent quantities of chlo- rine, and the final product is perchlorinated methylosulfhydric ether C 2 C1 S S. Action of Chlorine on the Compound Methylic Ethers. 1441. A large number of compound ethers of the methylic se- ries can exchange more or less completely their hydrogen for equi- valent quantities of chlorine. Thus methyloxalic ether C 2 H 3 0,C 2 3 furnishes A bichlorinated methyloxalic ether C 2 HC1 2 0, C 2 3 , And a perchlorinated " " C 3 C1 3 0,C 2 3 . Methylacetic ether C 2 H 3 0,C 4 H 3 3 also yields A bichlorinated methylacetic ether C 3 HC1 2 0, C 4 H 3 3 , And a perchlorinated " " .... C 3 C1 3 0,C 4 C1 3 3 . It has been shown that formic ether of the vinic series C 4 H 5 0, C 2 H0 3 presents the same elementary composition as methylacetic ether C 3 H 3 0,C 4 H 3 3 , although the two substances differ materially in their physical and chemical properties ; and the composition of the perchlorinated products of the two ethers should therefore be similar : not only are they so, but they are identical, constitut- ing one and the same substance, and no longer exhibiting the di- versity of their origin. We have already mentioned an analogous case. Dutch liquid C 4 H 3 C1,HC1 is isomeric with monochlorinated chlorohydric ether C 4 H 4 C1 2 , while the two substances differ distinctly in their physical and chemical properties ; but when treated with chlo- rine, they both yield the same final product, chloride of carbon C 4 C] 6 . Methyloformic ether yields with chlorine two chlorinated ethers : Bichlorinated methyloformic ether C 2 HC1 2 0,C 2 H0 3 , And perchlorinated " " C 2 C1 3 0,C 2 C10 3 . This last ether is liquid, boils at about 356, and is isomeric with chlorocarbonic gas COC1; into which it is entirely converted, by passing its vapour into a tube heated to a temperature above 572. METHYLIC SERIES. 591 Action of Chlorine on Formic Acid. 1442. No chlorinated formic acid is known, and when mono- hydrated formic acid C 2 H0 3 HO is treated with chlorine, the equi- valent of water is always decomposed, chlorohydric and carbonic acids being formed : C 2 H0 3 ,HO+2C1==2HC1+2C0 2 . But it has been shown ( 1431 and 1441,) that the formic acid which exists in formic and methyloformic ethers can exchange its hydrogen for chlorine. 1443. It will be seen from the preceding observations that the compounds of the methylic series may be considered as being pro- duced by the same molecule C a H 4 , that of protocarburetted hydro- gen, or marsh gas, in which one or several equivalents of hydrogen are replaced by a corresponding number of other elements, such as oxygen, sulphur, chlorine, etc. etc. In order to render this method of generation evident, we have collected into a single table all the known products of the methylic series. TABLE OF COMPOUNDS DERIVED FROM CARBURETTED HYDRO- GEN C 2 H 4 , OR FROM METHYLIC ETHER C 2 H 3 0. Protocarburetted hydrogen, or C a H 4 2 vols. Marsh Gas, the starting point of the series. SIMPLE ETHERS. Methylic ether C a H 3 2 " Methylosulfhydric ether C 3 H,S 2 " Methylochlorohydric ether C a H 3 Cl 4 " Methylobromohydric ether C a H 8 Br 4 " Methylodohydric ether C a H 3 Io 4 " Methylohydrocyanic ether C a H 3 Cy 4 " Methylosulphohydrocyanic ether C a H 3 SCy 4 " COMPOUND ETHERS. Alcohols. Methylic alcohol, or \vood-spirit C a H 3 0,HO 4 " Methylosulfhydric alcohol C a H 3 S,HS 4 " Methyloplumbic " C a H 3 S,PbS Methylomercuric " C a H 3 S,Hg a S. Compound Ethers, properly so catted. General formula (A representing the acid) C a H 3 0,A 2 or 4 vols. Methylobiboracic ether C a H 3 0,2B0 3 Trimethyloboracic " 3C 3 H 3 O.BO S 4 " Methylic Acids. General formula of methylic acids formed by the monobasic acids A (C a H 3 0-f-HO),2A Formula of the methylic acids produced by the tribasic acids, such as P0..3HO (C 3 TT 3 0+2HO),PO,. 592 METHYLIC SERIES. PRODUCTS DERIVED SUCCESSIVELY FROM METHYLIC ETHER C a H 8 0. 1st. By Oxidation. Methylic ether C a H 3 2 vols. Methyal (2C 3 H 3 0,C a H a O a ) 4 Anhydrous formic acid C a H0 3 unknown. Remains combined with the water formed and yields Hydrated formic acid C a H0 3 ,HO 4 " But corresponding to methylic alcohol C a H 3 0,HO 4 " 2d. By the Action of Chlorine. Methylic ether C 3 H 3 2 " Monochlorinated methylic ether C a II a C10 2 " Bichlorinated " " C a HCl a O 2 " Perchlorinated " " C a Cl s 4 " PRODUCTS DERIVED FROM METHYLOSULFHYDRIC ETHER C a H 3 S. By the Action of Chlorine. Methylosulfhydric ether C 3 H 3 S 2 vols. Perchlorinated methylosulfhydric ether C 3 C1 3 S. PRODUCTS DERIVED FROM PROTOCARBURETTED HYDROGEN C a H 4 , OR FROM METHYLOCHLOROHYDRIC ETHER C a H 3 Cl. By the Action of Clorine. Protocarburetted hydrogen C a H 4 4 vols. Methylochlorohydric ether C a H 3 Cl 4 " Monochlorinated methylochlorohydric ether C a H a Cl a 4 " Bichlorinated do., or chloroform C a HCl 3 4 " Perchlorinated do., " C a Cl 4 4 " PRODUCTS DERIVED FROM METHYLIC ALCOHOL C a H 3 0,HO. 1st. By the Action of Oxygen. Methylic alcohol C a H 8 0,HO 4 vols. Formic acid C a H0 3 ,HO 4 2d. By the Action of Chlorine. Products unknown. PRODUCTS DERIVED FROM AQUEOUS METHYLIC ALCOHOL C a H 3 0,HO+HO. By the Action of Chlorine. Formic acid.... , C a H0 3 ,HO. An excess of chlorine converts the formic acid, by its oxidizing action, into carbonic acid. Aqueous methylic ether C a H 3 0-}-2HO yields the same products. METHYLIC SERIES. 593 PRODUCTS DERIVED FROM COMPOUND METHYLIC ETHERS. By the Action of Chlorine. On Methyloxalic ether C a H 3 0,C a 3 . Bichlorinated methyloxalic ether C a H Cl a O,C a 3 . Perchlorinated " " C a Cl 3 0,C a 3 . On Methylacetic ether C a H 3 0,C 4 H 3 3 . Bichlorinated methylacetic ether C a H Cl a O,C 4 H 3 3 . Perchlorinated " " C a C1 3 0,C 4 H 3 3 . On Methyloformic ether C a H 3 0,C a H 3 . Bichlorinated methyloformic ether C a H Cl a O,C a H 3 . Perchlorinated " " C a Cl 3 0,C a C10 3 . 1444. Chemists have formed, for the methylic series, hypothe- ses analogous to those proposed for the vinic series. Some regard all simple methylic ethers as produced by the combination of the same radical C 3 H 3 , or methylen, with 1 equivalent of oxygen, sul- phur, chlorine, etc. etc., in which case methylic ether becomes a monohydrate of methylen C a H 2 ,HO, and methylic alcohol its bi- hydrate C 2 H 2 ,2HO. This radical is entirely hypothetical, since as yet no carburetted hydrogen of the formula C 3 H 3 is known which yields by direct combination, either with water or with chlorohydric acid, a simple ether of the methylic series ; a condition indispensa- ble, neverthless, to enable it to be considered as the radical of the series. Moreover, the methylic and vinic series are so similar that their formula cannot be written in two different ways, and we have incontestably proved ( 1401) that bicarburetted hydrogen C 4 H 4 could not be considered as pre-existing in the state of a radical in vinic ethers. Other chemists consider methylic ether C 3 H 3 as the oxide of a radical C 3 H 3 , which they call metliyl, and of which methylochloro- hydric ether is then the chloride ; but as methyl is not any better known than is ethyl and methylen, we see no advantage in resorting to hypotheses of these unknown radicals, especially for the methylic series, which may be as easily derived, by means of substitution, from a perfectly well known hydrocarbon, protocarburetted hydro- gen C 3 H 4 . We have shown it, in fact, ( 1436,) to be very probable that, by causing chlorine, in proper proportions, to act upon carbu- retted hydrogen C 3 H 4 , methylochlorohydric ether C 3 H 3 C1 would be obtained : now, the latter is decomposed by contact with alkaline solutions, and yields wood-spirit, whence the whole methylic series may be subsequently derived.* * Referring the reader, on the subject of the radicals of ether and mother, back to the note to \ 1401, (page 568,) it now only remains to describe the radical methyl, the isolation of which renders the correctness of the French theory ex- tremely doubtful. Methyl C a H 3 . Methyl is given off at the positive pole, in decomposing a concentrated solution of acetate of potassa by a powerful galvanic current, while at the negative pole 2z2 38 594 VEGETABLE ACIDS. OF CERTAIN ACIDS WHICH EXIST IN THE JUICES OF VEGETABLES. 1445. We shall describe in this chapter certain acids which are found ready formed in the juices of vegetables, and which have not been included in any group of substances of analogous composition, as chemists have succeeded in doing for acetic, formic acid, etc. etc. OXALIC ACID C a 3 ,HO. 1446. Of these acids, one of the most important is oxalic, of which the properties were described ( 259) when treating of the compounds of carbon with oxygen, among which oxalic acid is ranked on account of the composition it presents in anhydrous salts. Oxalic acid is found in a large number of vegetables, which fre- quently, as in the case of sorrel,* owe their acid taste to its presence. In the Black Forest (Southern Germany) it is obtained from certain species of rumex, by pounding the plant in troughs and expressing its juice ; after which the residue is moistened with water and ex- pressed a second time. The liquid is clarified with clay, decanted and evaporated to crystallization ; when crystals of binoxalate and quadroxalate of potassa, ( 451,) called in commerce salts of sorrel, are separated. In order to extract the oxalic acid, acetate of lead is poured into a solution of salt of sorrel, when oxalate of lead is precipitated, which is decomposed by sulphuric acid ; after which the liquid, on evaporation, yields crystals of oxalic acid C a O s ,HO +2HO. The greater part of the oxalic acid now in use in laboratories is prepared by the reaction of nitric acid on sugar, (259.) appear hydrogen and carbonic acid, resulting from the oxidation of the oxalic acid formed, at the expense of an equivalent of water, whence the hydrogen. Acetic acid is considered as a pairling of oxalic acid C a O s with methyl C a ll s , which view is sustained by the decomposition of the acid, ensuing as follows : KO,C 4 H 3 3 +2HO=KO,HO+C a H 3 +C a 3 -fHO, or =KO,HO+C a H 3 +2CO a +H. Methyl is also formed in the decomposition of iodohydric ether by zinc, in pre- sence of water ; and in the decomposition of cyanohydric ether (cyanide of ethyl) by potassium. It is a colourless and inodorous gas, almost insoluble in water, soluble in alcohol, and does not liquefy at 0.4. Its specific gravity being 1.037, its formula C a H s corresponds to a condensation to 2 volumes. It should be re- garded as H(C a H a ), or hydrogen paired with elayl, or olefiant gas. Combinations of methyl with several metalloids and metals have been discovered, but are not yet fully investigated ; the only one which is well known being a com- pound of arsenic with 2 equivalents of methyl, or cacodyl, already described, (I-1WU) Zincmethyl ZnC a H 3 or Zn,H(C a H a ) and Phosphuretted methyl P,C 6 H 9 or P,[H(C a H a )] 3 , corresponding to phosphuretted hydrogen have been obtained. Zincmethyl resem- bles zincethyl ; and phosphuretted methyl bears a close analogy to phosphuretted hydrogen. W, L. F. * Oxalis acetosella, whence the name. W. L. F. MALIC ACID. 595 MALIC ACID C 8 H 4 8 ,2HO. 1447. Malic acid is most widely diffused through the organic kingdom, being found partly free and partly combined with potassa, lime, magnesia, and some organic bases, and giving rise to the acid taste observed in fruits before maturity. Malic acid is generally obtained from the berries of the mountain ash, which are collected before maturity, crushed, and their juice expressed. The juice is clarified by being boiled for a few moments with white of egg and filtered, when acetate of lead is added, which yields a white crystalline precipitate of malate of lead ; the salt, however, being always mixed with a small quantity of other organic sub- stances, which are precipitated in combination with the oxide of lead. Malate of lead is nearly insoluble in cold, but readily soluble in boiling water, and is purified by boiling with water the crude malate of lead previously filtered, and rapidly filtering the liquor ; when the latter deposits, on cooling, malate of lead in small crys- talline spangles. The mother liquid is again boiled with the residue of the first ebullition, and this is continued until the hot liquor no longer deposits malate of lead on cooling. The foreign plumbic compounds remain in the residue. Crude malate of lead is usually decomposed by sulf hydric acid, / 1207,) and the impure malic acid is thus isolated ; after which the solution of malic acid thus obtained is boiled for a few moments, in order to drive off the sulf hydric acid, and then divided into two equal parts. One part, which has been accurately saturated with ammo- nia, is poured into the second part, which remained in the state of free malic acid, which furnishes a solution of bimalate of ammonia, or rather a neutral malate of ammonia and water (NH 3 ,HO+HO), C 8 H 4 8 , which is crystallized; and as the salt crystallizes very readily, it is purified by successive crystallizations. If the malate of lead contained tartrate and citrate of lead, as frequently happens, the first crystals deposited by the solution of impure bimalate of ammonia would be bitartrate of ammonia, which is very slightly soluble ; after which the bimalate would crystallize, while the citrate would remain in the mother liquid. In this case, the bimalate of ammonia is again converted into malate of lead, and the salt is again decomposed by sulf hydric acid. The solution of malic acid is evaporated to the consistence of syrup, and then left in vacuo, when it deposits colourless crystals of hydrated malic acid, C 8 H 4 8 ,2HO, which are deliquescent, and cannot be freed from their water without decomposition. Malic acid is a powerful acid, forming a great number of salts, and producing in general, with the same base, two salts, the formulae of which, when deprived of their water of crystallization, are 2RO,C 8 H 4 8 , ' (RO+HO),C 8 H 4 8 , and it is therefore a bibasic acid, as we stated in 1225. 596 VEGETABLE ACIDS. Alkaline malates are very soluble and deliquescent, which is equally true of the malate of ammonia 2(NH 3 ,HO),C 8 H 4 8 ; while the malate (NH 3 ,HO + HO),C 8 H 4 8 , on the contrary, crystallizes readily. Malate of lime crystallizes with 6 equivalents of water of crystallization, and presents the formula (CaO+HO),C 8 H 4 8 +6HO. 1448. Crystallized malic acid melts at 181.4, and, if kept for some time at a temperature of 347, is converted into two new acids, called maleic and paramaleic, which are isomeric, and present the formulae C 4 H0 3 ,HO. Water separates from them, without disen- gagement of gas. If the retort be rapidly heated to 392, the maleic Scid distils over, with vet-y small quantities of paramaleic acid, for, at this temperature, but a small quantity of the latter acid is formed. Distilled maleic acid solidifies in large crystals in the neck of the retort and the receiver, and is very soluble in water and alcohol, its solution not being clouded by limewater, while water of baryta throws down a white precipitate in crystalline spangles, and acetate of lead produces a similar precipitate. The maleatea of potassa and soda crystallize readily. The general formula of thft dried maleates is RO,C 4 HO S , showing maleic acid to be monobasic, Maleic acid has been found in several vegetables, particularly in tho horsetail, (equiset um fluviatile), whence it has also been called equi- setic acid. If maleic acid be heated to only 302, and be kept for some time at this temperature, the second acid, or paramaleic, is abundantly formed instead of the first. It is much less fusible than maleic acid, for it melts at only about 390, and sublimes at a higher tempera- ture ; and it is moreover easily distinguished from it by being very slightly soluble in water, 200 parts of water dissolving about 1 part of it. Paramaleic acid produces with oxide of silver, a salt remark- able for its insolubility, and yields, with potassa, soda, and ammonia, easily crystallizable salts. It may be boiled with nitric acid without undergoing any change. The general formula of the paramaleates is RO,C 4 H0 3 , and that of crystallized paramaleic acid is C 4 H0 3 HO. Maleic acid is converted into paramaleic acid when it is kept for a long time at a temperature exceeding 302, while the maleates themselves, heated to 480 or 570, are converted into paramaleates. Paramaleic acid is also found in vegetables, and having been obtained from fumitory, (fumaria officinalis,) has hence been called fumaric acid. It has also been found in Iceland moss. CITRIC ACID C 13 H 4 O n ,3HO+2HO. 1449. Citric acid, which exists in the juice of a large number of acid fruits, particularly in lemons, gooseberries, and currants, is generally extracted from lemons, by allowing their juice to ferment spontaneously for some time, when mucilaginous substances sepa- rate from it ; after which the liquid is saturated with finely pow- dered chalk, gradually added, so as not to be in excess, and it is boiled. Citrate of lime, being insoluble, is precipitated, and is de- CITRIC ACID. 597 composed by a slight excess of sulphuric acid ; and the sulphate of lime being then separated by filtering, the acid liquid is care- fully evaporated, until a crystalline crust begins to form on its sur- face, when it is left to itself. Citric acid crystallizes in large crystals, the presence of a slight excess of sulphuric acid assisting the crystallization. The acid is very soluble in water, for it dis- solves in J of its weight of cold, and } of its weight of boiling water. After a time, its aqueous solutions become mouldy. The formula of citric acid crystallized at the ordinary tempera- ture is C 12 H 5 11 5HO, while that of the acid dried at 212 is C 12 H 5 11 ,3HO, the 3 equivalents of water which remain being basic, and replaceable by equivalent quantities of bases. The formula of citrate of silver is 3AgO,C 12 H 5 11 , and a methylocitric ether is known of the formula 3(C 2 H 3 0),C ia H 5 O n . The alkaline citrates are soluble, while those of the alkaline earths and other metallic oxides are generally insoluble, but dis- solve in an excess of citric acid. About 1 per cent, of crystallized citric acid may be obtained from the juice of common currants, by fermenting it with beer- yeast, when the saccharine matter is converted into alcohol, which is separated by distillation ; and the residue, being saturated with chalk, yields citrate of lime. 1450. Citric acid is decomposed by heat, carbonic acid being first disengaged, with oxide of carbon and acetone ; while at a higher temperature, an oleaginous substance is formed which dis- tils. If the operation be arrested at the moment of the appear- ance of the oleaginous substance, the residue contains only a very small quantity of unaltered citric acid, and consists almost entirely of a peculiar acid, called aconitic, because it was first found in a vegetable, the aconitum napellus. The composition of this acid C 4 H0 3 ,HO is the same as that of maleic acid, and its properties are very analogous, while it appears to differ from it in some of its reactions, and seems therefore to be a second isomeric modification of this acid. Aconitic acid melts at about 284, and distils at 320 ; but the product which passes over is no longer aconitic acid, oleaginous drops, which crystallize on cooling, being formed. The same pro- duct is necessarily obtained by the direct distillation of citric acid. It dissolves in water, and yields an acid liquid depositing crystals on evaporation, which are purified by being redissolved in alcohol or ether. They are formed by a new acid, which has been called pyroaco- nitic and itaconic acid, the formula of which, in the crystallized state, is C 5 H 2 S ,HO, while that of itaconate of silver is AgO,C 5 H 3 3 . If itaconic acid be again distilled, it is soon found to change, for the oily drops which condense no longer crystallize by cooling, being formed by a new acid, called citraconic. The same acid may be obtained by means of the crude product yielded by the imme- 598 VEGETABLE ACIDS. diate distillation of citric acid, for which purpose it suffices to distil it a second time in a retort heated in an oil-bath, and to collect separately the products which distil at a temperature beyond 392. A very fluid, colourless liquid is thus obtained, boiling at 413, and of which the density is 1.247. Its formula being C 5 H S 3 , its com- position is consequently the same as that of anhydrous itaconic acid. Exposed to a moist atmosphere, it slowly absorbs the vapour of water, and is converted into a crystalline compound which melts at about 176, the formula of which is the same as that of crystallized itaconic acid, and their composition is also the same, while itaconic acid melts only at about 320, and the crystallized acid formed by the combination of anhydrous citraconic acid with water melts at 178. The two products are therefore merely isomeric. Hydrated citraconic acid yields, by distillation, anhydrous citraconic acid. TARTARIC ACID C.H 4 10 ,2HO. 1451. Tartaric is one of the most important of the organic acids, and exists in a great number of fruits, such as grapes, pine- apples, mulberries, and other vegetables. On a large scale it is always made from grape-juice, in which it exists in the state of bi- tartrate of potassa and neutral tartrate of lime, the two salts being in solution; for the first is eminently soluble, and the second, although insoluble in water, dissolves in an acid liquid. When grape-juice is fermented in order to be made into wine, the bitar- trate of potassa and tartrate of lime are slowly precipitated, being insoluble in the alcoholic water, and they form a crust which adheres to the sides of the barrel. This crust, called tartar, is red or white according to the colour of the wine which produces it, and is mixed with many foreign substances. In order to purify this crude tartar, or argolj it is powdered, and boiled for several hours with enough water to dissolve it, after which the liquid is then allowed to cool ; when, in the course of a few days, crystals form, which adhere to the sides of the vessel, while the residue is composed chiefly of foreign substances. The crystals, being separated, are redissolved in boil- ing water, while clay and animal black are added, and the boiling liquid is filtered. The latter yields, on cooling, very pure crystals of bitartrate of potassa, which is the cream of tartar of commerce. In order to extract tartaric acid from cream of tartar, it is dis- solved in about 10 times its weight of boiling water, and finely powdered chalk is gradually added, until effervescence ceases, when the lime has formed, with one-half of the tartaric acid, an insoluble tartrate of lime, while the other half of the tartaric acid remains in the liquid in the state of neutral tartrate of potassa. A solution of chloride of calcium is then added, until no more precipitate is thrown down, when the remainder of the tartaric acid is thus sepa- rated in the state of tartrate of lime. The two portions of tartrate of lime are united and decomposed by sulphuric acid diluted with TARTARIC ACID. 599 3 or 4 times its weight of water, 52 parts of concentrated sulphuric acid being usually taken for 100 parts of cream of tartar, which is a little more than is absolutely necessary to decompose the tartrate of lime. The sulphate of lime being separated by filtering, the acid liquid, evaporated to the consistence of syrup, is then left to itself, in a slightly warm situation to prevent it from becoming too viscous ; when it yields beautiful crystals, which are purified by a second crystallization. The acid is largely used in dyeing. Tartaric acid, dissolved in water, exerts rotation to the right, with a specific energy the greater as the proportion of water is larger and the temperature higher. It then divides the planes of polarization of the various simple rays according to the laws pecu- liar to it, and in which it differs from all known substances. These laws are modified, without losing their peculiarity, when it is dis- solved in alcohol or wood-spirit, but disappear completely when it is brought into the presence of alkaline bases or boracic acid, when the phenomena reassume the appearance common to the generality of substances possessing a rotatory power. Tartaric acid is obtained in large and generally well-defined crystals, of the density 1.75. Boiling water dissolves about twice its weight of it, and cold water a little more than its own weight, while alcohol dissolves it more sparingly. The composition of crys- tallized tartaric acid corresponds to the formula C B H 6 0^ which is commonly written C 8 H 4 10 ,2HO. The two equivalents of water cannot be driven off by heat without injury to the acid, and in the anhydrous tartrates they are replaced by 2 equivalents of the base. The same base generally forms two salts with tartaric acid ; the formula of the first, called neutral tartrate, being 2RO,C 8 H 4 10 , while that of the second, or bitartrate, is (RO-f HO),C 8 H 4 10 . These denominations are very erroneous, since the salts, from their constitution, are both neutral, and because, in both cases, the acid is saturated by 2 equivalents of base ; with the difference that in the second case, one of the equivalents of base, water, does not saturate the acid as regards its reaction on vegetable colours. From its composition, tartaric acid may be regarded as formed of 1 equiv. of acetic acid and 2 equiv. of oxalic acid, and we have, in fact, C 8 H 4 105 2HO=C 4 H 3 3 ,HO+2(C 2 3) HO). It is actually decomposed in this manner, when heated with alka- lies in excess, at a temperature of 302. It is a powerful acid, and dissolves several metals with disengage- ment of hydrogen, particularly zinc and iron. It is decomposed by several easily reducible metallic oxides : thus, at the boiling point, peroxide of lead decomposes it into carbonic acid, water, and formic acid ; the liquid, on cooling, depositing very pure crystals of formiate of lead. The soluble neutral tartrates generally become less soluble by 600 VEGETABLE ACIDS. the addition of an excess of acid, while the insoluble neutral tartrates dissolve, on the contrary, in an excess of acid. 1452. Potassa forms 2 tartrates : the neutral, or rather bi- potassic tartrate 2KO,C 8 H 4 10 +2HO, which dissolves in its own weight of water, and loses by heat its equivalents of water of crys- tallization, and the bitartrate, or rather the monopotassio tartrate (KO+HO),C 8 H 4 10 , which is cream of tartar. This salt requires for its solution 18 parts of boiling and more than 200 of cold water, and it is nearly insoluble in alcohol at 0.85. Its crystals, which are hard and opaque, are decomposed by heat, and yield a mixture of carbonate of potassa and charcoal, or black flux, (438.) Bitartrate of potassa forms a compound with boracic acid, called soluble cream of tartar, which is generally prepared by dissolving in boiling water 47J parts of cream of tartar and 15J parts of crys- tallized boracic acid. The liquor, when evaporated, leaves a non- crystalline white mass, insoluble in alcohol, but which dissolves in 1J part of cold water, or in J part of boiling water. The formula of this substance, dried at 212, is KO,(0 8 H 4 10 ,B0 3 ). At 545 it loses 2 equiv. of water, becoming KO(C 8 H 2 8 ,B0 3 ), and the organic compound which it then contains presents no longer the composition which we have assigned to anhydrous tartaric acid, although when redissolved in hot water it reproduces the original substance. Soda also forms two tartrates, 2NaO,C 8 H 4 O l0 +4HO, which readily parts with its water in a dry vacuum, and (NaO+HO),C 8 H 4 10 . Ammonia also yields two tartrates, of which the formulae are 2(NH 3 ,HO),C 8 H 4 10 +HO, slightly soluble in water, and (NH 3 HO+HO),C 8 H 4 10 . Lime forms 2 tartrates: the neutral salt 2CaO,C 8 H 4 10 + 8HO, which is nearly insoluble in cold water, and is frequently found in beautiful crystals in crude tartar, and the acid tartrate (CaO+HO), C 8 H 4 M . By saturating cream of tartar with carbonate of soda and crys- tallizing it, a double tartrate of potassa and soda is obtained (KO-f- NaO),C 8 H 4 10 +8HO, called Rochelle salt, which is used in me- dicine, and is generally prepared by dissolving in boiling water 1 part of crystallized carbonate of soda and 1J part of cream of tar- tar, when the salt is obtained in large prismatic crystals. All the tartrates, when dissolved in water, exert rotation to the right, while tartrate of lime, dissolved in chlorohydric acid, turns the plane of polarization to the left. Tartar Emetic (KO+Sb0 3 ),C 8 H 4 10 +2HO. 1453. Tartar emetic, one of the most valuable medicines used, is a double tartrate of potassa and oxide of antimony, according to the formula (KO-f Sb0 3 ),C 8 H 4 10 +2HO. It is prepared by boil- TARTAKIC ACID. 601 ing in 5 or 6 parts of water equal parts of oxide of antimony and cream of tartar, and then glass of antimony; the oxy chloride or subsulphate may be substituted for the oxide. The hot solution, when filtered, deposits colourless crystals, soluble in 2 parts of boil- ing and 14 of cold water, which, when heated to 212, part with their 2 equiv. of water of crystallization, while, if heated to 442.4, they lose 2 more equiv., and the remaining product (KO-f Sb0 3 ), C 8 H 2 8 no longer presents the formula of the tartrates, although if it be redissolved in water it reproduces, by crystallization, the original salt, tartar emetic. Acids decompose solutions of tartar emetic, bitartrate of potassa and a basic salt of oxide of antimony being separated. Alkalies and the alkaline earths also decompose them, but this precipitate is frequently not formed for some time, as is the case in potassa and soda ; by using an excess of which bases no precipitate is formed, because the oxide of antimony remains dissolved in the alkaline liquid. Ammonia and limewater immediately effect a precipitate. Sulf hydric acid decomposes the solution of tartar emetic, and an orange-coloured precipitate of sulphide of antimony is formed. Tar- tar emetic is decomposed by heat, and, when calcined in a close ves- sel, yields a residue of antimoniuret of potassium, ( 1017,) while in Marsh's apparatus it produces abundantly antimonial deposits, (1016.) By dissolving in boiling water 9 parts of tartar emetic and 4 parts of tartaric acid, evaporating the solution by a gentle heat, and then leaving it to itself, crystals of tartar emetic first separate, and then, by continuing the evaporation, a crystalline compound, efflorescent and very soluble in water, is deposited, the formula of which is (KO + Sb0 3 ),2C 8 H 4 10 +7HO, corresponding to that of a neutral tartrate. Tartar emetic can also combine with 3 equiv. of bitartrate of potassa, which compound is obtained by dissolving together 10 parts of tartar emetic and 15 of cream of tartar. Lastly, by pouring into a solution of tartar emetic nitrate of silver or acetate of lead, precipitates are obtained which are species of tartars emetic, in which the oxides of silver or lead replace the potassa. Their formulae are (AgO + Sb0 3 ),C 8 H 4 10 and (PbO-f- Sb0 3 ),C 8 H 4 10 , etc. etc.; and, like tartar emetic, they lose 2 equiv. of water at a high temperature. Modifications of Tartaric Acid by Heat. 1454. When tartaric acid is rapidly heated in an oil-bath to the temperature of 338, it fuses without losing any water, while its composition is remarkably modified ; for when redissolved in water and combined with the various bases, it yields salts which differ in their forms and solubility from the ordinary tartrates. The name of metatartaric has been given to this modified tartaric acid. The bimetatartrate of ammonia (NH 3 HO-f HO),C 8 H 4 10 is much more VOL. II. 3 A 602 VEGETABLE ACIDS. soluble than the bitartrate, and produces crystals of a totally dif- ferent form, and the former salt does not precipitate a solution of chloride of calcium, while the bitartrate does. Boiling converts metatartrates into bitartrates. By maintaining melted tartaric acid for a long time at a tempera- ture of 338 it undergoes a second isomeric modification, and forms an acid called isotartaric acid, which, while exhibiting the same composition as tartaric acid, appears to differ from it by saturating only 1 equiv. of base. Isotartrate of lime (CaO+HO),C 8 H 4 10 dis- solves readily in cold water, producing a solution behaving perfectly neutral with litmus paper, which, when boiled, becomes acid and deposits crystals of neutral metatartrate of lime. Isotartrate of ammonia is a deliquescent salt, easily converted by heat into the bimetatartrate. By heating tartaric acid rapidly to 356, it first melts, swells up, loses 12 per cent, of water, and finally solidifies again, forming a substance of the formula C 8 H 4 10 , which has become insoluble in water, and may be easily separated by washing from the portions which have not yet undergone the transformation. This substance, which has been called anhydrous tartaric acid because it presents the composition of the acid in the anhydrous tartrates, is equally insoluble in alcohol and ether; while, when in contact with water, it is converted successively into the preceding modifications of tar- taric acid, the transformation being very rapid in contact with boil- ing water and the bases. 1455. By heating tartaric acid to distillation, it undergoes a decomposition which produces two new pyrogenated acids, which have been called pyroracemic and pyrotartaric acid. Pyroracemic acid is chiefly formed when tartaric acid is rapidly distilled at a temperature of 428. The product, subjected to a second distillation, yields a very acid liquid, consisting of a mixture of pyroracemic and acetic acids, which, when saturated with carbonate of lead, forms soluble acetate of lead, while the pyroracemate of lead remains in the shape of an insoluble precipitate. The preci- pitate is rapidly washed in cold water, suspended in water, and de- composed by a current of sulf hydric acid gas, and the acid solution, when evaporated, is reduced to a syrupy condition without crystal- lizing. Pyroracemic acid forms a great number of salts; the pyroracemate of potassa is deliquescent, while that of soda crystal- lizes readily, and the salts of lime and baryta are soluble in water. Pyroracemate of silver is obtained by double decomposition, and separates in small crystalline spangles of the formula AgO,C 6 H 3 5 , showing the formula of anhydrous pyroracemic acid as it exists in dry salts to be C 6 H 3 5 . The name given to this acid is very im- proper, for it seems to indicate that pyroracemic acid is a special pyrogenated product of racemic acid, which is presently to be described. RACEMIC ACID. 603 If tartaric acid be rapidly heated to about 570 the products of its decomposition differ from those just indicated, and the receiver contains a brown liquid, which is subjected to a second distillation. The first products are collected separately, and the receiver changed when the substance in the retort becomes syrupy. The liquid which then distils sets into a crystalline mass under the receiver of an air-pump, and the crystals are pressed between several folds of tissue-paper, in order to free them from adherent empyreumatic matter, redissolved in water, and, after having discoloured the solu- tion by boiling it with a small quantity of animal black, it is again evaporated, and yields crystals of pure pyrotartaric acid. A much larger proportion of pyrotartaric acid is prepared by subjecting to the action of heat an intimate mixture of tartaric acid and platinum- sponge, or even of powered pumice-stone, the latter substance as- sisting the decomposition, which then takes place at a lower temper- ature. Pyrotartaric acid melts at about 212, and distils at 356, while a portion of it is decomposed. It is very soluble in water and alcohol, and its solutions are not precipitated by baryta or lime- water. Pyrotartaric acid is probably a monobasic acid, of which the formula, in anhydrous salts, is C 5 H 3 3 , PARATARTARIC, RACEMIC, OR UVIC ACID C 8 H 4 10 ,2HO-1-HO. 1456. The acid to which these various names have been given, has only been obtained once, accidentally, in making tartaric acid on a large scale, and never has been since produced. We shall re- tain the name of racemic acid alone. The composition of racemic acid, when dried, is exactly the same as that of tartaric acid, and the composition of the salts it forms with the different bases is also identical with those of the corresponding tartrates, the two acids exhibiting one of the most remarkable examples of isomerism, but crystallized racemic acid contains 1 equivalent of water more than tartaric acid, which is easily driven off by heat. Racemic acid dif- fers from tartaric acid in the crystalline form and solubility of its salts, and also in its physical properties, particularly in the absence of all rotatory action on the plane of polarization. But we shall soon see that this neutrality is owing to its being the union, in equal weights, of two acids, one of which is tartaric acid itself, and the other an acid which differs from it only by an opposition of he- mihedrism in crystalline forms, and by an equally identical rotatory power, but in an opposite direction. Nevertheless, for the mo- ment, we shall continue to describe the properties of racemic acid as though it were simple, in order to conform to the language adopted. Racemic is much less soluble in water than tartaric acid, and as it only dissolves in 5.7 parts of cold water, it is easily separated from the latter acid by crystallization. The two acids are also dis- (304 VEGETABLE ACIDS. tinguished by the manner in which they behave with limewaten thus, tartaric acid does not form immediately any precipitate in lime water, and a crystalline deposit is not thrown down until after some time, while racemic acid immediately affords a white precipi- tate. By dissolving separately in weak chlorohydric acid, tartrate and racemate of lime, and carefully saturating the two liquids with ammonia, the racemate of lime is immediately precipitated in an opaque crystalline powder, while the tartrate of lime, on the contrary, is slowly deposited in the form of small transparent crystals. Like tartaric acid, racemic acid is a bibasic acid, and forms two salts with potassa, one (KO-f HO,)C 8 H 4 10 corresponding to cream of tartar, and even less soluble than that tartrate, while the other 2KO,C 8 H 4 10 is very soluble. Ammonia yields two salts: (NH 3 ,HO+HO),C 8 H 4 10 , which only dissolves in 100 parts of water; and 2(NH 3 ,HO),C 8 H 4 10 , which is very soluble, and affords beautiful crystals. The salt of soda (NaO+HO),C 8 H 4 10 -f 2HO dissolves in 12 parts of water, while the salt 2NaO,C 8 H 4 10 is much more soluble. Racemic, like tartaric acid, forms crystallizable double salts, and produces, with potassa and soda, a double racemate, having the same composition as Kochelle salt, but differing from it in its crys- talline form and in its solubility. Subjected to the action of heat, raceimc acid appears to afford the same modifications as tartaric acid, and pyrogenated acids identical with those produced by the latter substance. Dextro-racemic and Levo-racemic Acid. 1457. The solution of the neutral racemates of soda, potassa, or ammonia, and even that of a double racemate of potassa and an- timony, exert no rotatory power, and if they be allowed to evaporate spontaneously, the form and all the other physical properties of the crystals progressively precipitated are identical in each, and they are merely distinguished from each other by their size. Such is not the case with double racemates of soda and ammonia, or of soda and potassa. Their solutions are still deprived of rotatory power, but the crystals deposited by each are of two kinds, distin- guished from each other by hemihedral facets in opposite directions. If they are separated according to this character, and each sort dis- solved by itself, two solutions are obtained possessing equal and inverse rotatory powers, so that if they are mixed together in equal quantity, the resulting rotatory power is null, like that of the ori- ginal solution before the separation. As a single sorting, by hand, is never strictly exact, separation may be effected more perfectly by redissolving each sort of crystal separately, and rejecting the first which are deposited. Those sub- TANNIC ACIDS. 605 sequently obtained are generally formed alone, and of a single sort, thus completing the separation. The acid peculiar to each sort of crystal is extracted from its salts in a similar manner as tartaric acid is extracted from the tar- trates. One of the acids exerts rotation toward the right, like tar- taric acid, and with the same special characters of dispersion ; and while its chemical composition is the same, it also behaves exactly like it in the presence of boracic acid and the alkaline bases, pro- ducing crystals of exactly the same form. In short, nothing dis- tinguishes it from ordinary tartaric acid; but it is nevertheless, called dextro-racemic acid, in order to recall its origin, and to not decide too hastily on its density. The other acid, extracted from crystals of the opposite form, is identical with tartaric acid in its ponderable composition, but ex- actly inverse in its rotatory properties. They are exerted toward the left, as those of tartaric acid toward the right, with the same energy, the same laws of dispersion, and evincing similar reactions in the presence of the same substances. It has been called levo- racemic acid, and it crystallizes in the same form as tartaric acid, except that its crystals have hemihedral facets in opposite direc- tions. Levo-racemic and dextro-racemic acid being dissolved together in equal weights, combine immediately, and reproduce racemic acid, the mixed solution becoming neutral in polarized light, and the crystals deposited by it exhibiting no distinctive characters. The individual dissymmetry of the two compounds has disappeared in their union, and when combined they are identical with racemic acid which has not been decomposed. TANNIC ACIDS. 1458. The name of tannin has been given to several sub- stances, probably of different composition, which possess the property of forming insoluble compounds with albumen, gluten, gelatin, fi- brin, the animal tissues in general, and the epidermis and skin of ani- mals. These compounds will not putrefy, and are unchangeable by water ; on which properties is founded the process of tanning of skins, to be described at the close of this work. Tannins exist in almost all vegetables, in the bark and leaves of trees, and the seeds of fruits ; the oak, chestnut, elm, and willow containing large quantities of it, while it occurs most abundantly in galls, a sort of excrescence which grows on the leaves of the oak when they have been punctured by a certain insect. In order to extract tannin, the galls are finely powdered and introduced into a displacer, (fig. 683,) the neck of which has been previously stopped with a plug of cotton, the powder being heaped upon it, and ordinary ether of commerce poured - 3A2 606 VEGETABLE ACIDS. on. The tube is corked, and adjusted in a flask, as represented in the figure ; when the ether filters slowly through the galls, while the tannin contained in the latter dissolves in the water given off by the ether, a very small portion being dissolved by the ether itself. The liquid which falls into the flask divides into two layers, the inferior stratum, of the consistence of syrup and colour of amber, being a highly concentrated aqueous solution of tannin, while the upper layer is ether, holding in solu- tion a small quantity of tannin and some other substances extracted from the galls. The ether is again poured upon galls, in order to abstract an additional portion of tannin ; and the aqueous solution of tannin is shaken several times Fig. 683. ^k p ure e t ner? an( j then evaporated under the receiver of an air-pump, when a spongy mass, without any appearance of crys- tallization, generally slightly yellowish, remains, consisting of tannin in its greatest state of purity known. It is a spongy, brilliant, very light, generally yellowish substance, but sometimes is obtained of a perfectly white colour. It dissolves freely in water, and gives it a strongly astringent taste ; and as it reddens litmus and decomposes the carbonates, it is often called tannic acid. Tannin combines with bases, and precipitates the majority of the metallic solutions, the colours of the precipitates being frequently characteristic; whence tannin and an infusion of galls are often used as tests to distinguish various metals from each other. The composition of tannin dried at 248 corresponds to the formula C 18 H 8 12 , which should probably be written C 18 H 3 9 ,3HO ; for, on pouring a solu- tion of tannin into a boiling solution of acetate of lead and main- taining ebullition for some time, a yellow precipitate of the formula 3PbO,C 18 H 5 9 is formed. Tannin yields a deep-blue precipitate with sesquisalts of iron, which compound is very important, being the colouring principle of ordinary writing-ink. In order to prepare ink, 1J part of pow- dered galls are boiled for 3 hours with 15 of water, filling up the water as it evaporates ; after which the liquid is filtered, and 2 parts of gum and 1 part of protosulphate of iron are added, besides frequently a small quantity of a solution of copper. The mixture is frequently shaken, and exposed in open vessels, in order that the protoxide of iron may absorb oxygen from the air and be converted into sesquioxide, which causes the colour of the liquid, at first brown, gradually to deepen and become bluish black. Oxidation being arrested at the proper shade, the ink is bottled. This kind of ink contains a large amount of protoxide of iron, at the moment of using it, and the marks which it leaves on paper, being at first pale, turn black when they have absorbed the oxygen necessary for the peroxidation of the iron. Tannin completely precipitates gelatin and albuminous substances GALLIC ACID. 607 from their solutions ; and animal membranes and skins, dipped into a solution of tannin, ultimately abstract all this substance which is incorporated in the membrane, thus rendering it unchangeable and imputrefiable. Tannin combines also with a large number of the mineral acids, and forms ill-defined compounds, soluble in pure water, but very slightly so in an excess of acid. Gallic Acid C 7 H 3 5 ,HO. 1459. Gallic acid is always prepared from tannin or galls, and several processes may be adopted. 1. By causing sulphuric or chlorohydric acid, diluted with 8 or 10 times their weight of water, to act on tannin, and boiling the mixture for about 12 hours, taking care to fill up the water as it evaporates, the tannin is almost wholly converted into gallic acid, the greater portion of' which crystallizes during the cooling of the liquid. 2. By exhausting powdered galls with cold water, concentrating the filtered liquid by evaporation, and saturating it exactly with caustic potassa. Chlorohydric acid is added to the liquid when cooled, when a deposit of brown crystals of impure gallic acid is precipi- tated, which is dissolved in boiling water ; and the hot solution being left for some time in contact with animal black, which removes the colouring matter, the filtered liquid is allowed to cool, when the gallic acid crystallizes in a state of purity. 3. The process usually employed in the preparation of gallic, acid is founded on a peculiar and spontaneous fermentation experienced by galls, and by which its tannin is converted into gallic acid. Moistened and powdered galls are left for several months at a tem- perature of 68 to 86, in an earthen vessel, when the substance becomes covered with small whitish crystals of gallic acid. Toward the close, the substance is allowed to dry, and is treated with boil- ing alcohol, which dissolves the gallic acid alone, and deposits the greater portion of it on cooling. If an extract of galls be substi- tuted for the galls, the transformation of the tannin takes place in the same way, though more slowly ; while if a solution of /pure tannin be used, the transformation does not ensue. We are hence naturally led to infer that galls contain substances which induce the conver- sion of tannin into gallic acid, and which behave like ferments, since the transformation is arrested by all substances which destroy the fermentation of the yeast. The presence of air does not appear to be necessary, because gallic fermentation of extract of galls takes place even in an hermetically closed vessel. Gallic acid crystallizes in long silky aciculse, which are some- times perfectly white, but more frequently slightly yellowish ; and it is deposited in larger prismatic crystals from an alcoholic or etherial solution. It dissolves in 100 parts of cold and in 3 only 608 VEGETABLE ACIDS. of boiling water ; and it neither precipitates gelatin nor attaches itself to animal membranes ; thus furnishing a ready method of separating it from tannin. The formula of crystallized gallic acid is C 7 H 3 5 ,HO, and it loses 1 equivalent of water at 212. The acid forms a large number of salts, the composition of which has not yet been sufficiently studied ; and therefore chemists are not agreed upon the formula for anhy- drous gallic acid. By dropping an alcoholic solution of potassa into an alcoholic solution of gallic acid, until perfect saturation is effected, white flakes of a salt of the formula KO,3(C 7 H 3 5 ) are deposited ; while an excess of potassa decomposes the gallic acid. By exactly saturating a solution of gallic acid with ammonia, a salt is obtained by evaporation, of which the composition corresponds to the formula (NH 3 ,HO),2C 7 H S 05+HO ; while, if only one-half of the ammonia necessary to saturation be added, there results a com- pound, slightly soluble when cold, and corresponding to the formula (NH 3 ,HO),C 7 H0 3 +C 7 H 3 O r The gallate of lead, which is precipitated by pouring a solution of gallic acid into a boiling solution of acetate of lead in excess, forms white flakes, which change, by heat, into yellowish crystalline granules, corresponding to the formula 2PbO,C 7 H0 3 . It therefore frequently occurs in the gallates, that the acid in combination with the base presents the formula C T H0 3 , which would seem to indicate that such is the composition of anhydrous gallic acid, and that crystallized gallic acid should be written C 7 H0 3 ,2HO -I- HO; one of the equivalents of water being water of crystalliza- tion, while the other two are basic. The aqueous solution of gallic acid remains unchanged in well- closed vessels, but soon becomes mouldy in the air. Gallic acid dissolves in concentrated hot sulphuric acid, forming a red liquid, which, when poured into cold water, yields a red crystalline preci- pitate of the formula C r H 2 4 ; which new compound differs from crystallized gallic acid only in the loss of 2 equivalents of water. A solution of gallic acid colours sesquisalts of iron of a deep blue ; and when the liquid is concentrated, a precipitate of the same colour is formed. Gallic acid precipitates several metals from their solu- tions, particularly silver and gold, which reduction is more easily effected in the light of the sun. 1460. By heating gallic acid in a retort over an oil-bath, it first loses 1 equivalent of water, and then melts, and if the temperature be raised to 365, and kept stationary for some time at this point, carbonic acid is disengaged, while a pyrogenated acid, pyrogallio acid C 6 H 3 3 , sublimes in white crystalline spangles, only a small brown residue being left in the retort. The reaction which pro- duces pyrogallic acid is expressed by the following equation : C 7 H 3 3 =CO a +C 6 H 3 3 . ELLAGIC ACID. 609 If, on the contrary, the temperature be suddenly raised to 460 or 480, water and carbonic acid are both disengaged, and a small quantity of pyrogallic acid still sublimes, while the greater portion of the gallic acid is converted into a brown substance, which re- mains in the retort. In its appearance and chemical properties, this acid closely resembles humic and ulmic acids, ( 1307,) being insoluble in water, but dissolving in alkaline liquids and forming brown solutions, from which acids precipitate the original substance unchanged. This substance has been called metagallic acid, and its composition corresponds to the formula C 6 H 2 2 ; the reaction by which it is derived from gallic acid being expressed by the equa- tion, C 7 H 3 5 =C 6 H 2 2 +C0 2 +HO. Pyrogallic acid may be prepared by carefully heating powdered galls, or still better, its evaporated extract, in an earthen vessel covered with a pasteboard cone, when crystals of the acid sublime on the sides of the cone. Pyrogallic acid, which is very soluble in water, alcohol, and ether, melts at 257, sublimes at about 410, and is decomposed at 482 into water and metagallic acid. It turns salts of the protoxide of iron of a deep blue colour, and those of the sesquioxide of an intense red. Ellagic Acid C 14 H 2 7 ,HO. 1461. Extract of galls, exposed for a long time to the air, con- tains, in addition to gallic acid, another acid, insoluble in water, and to which the name of ellayic has been given. This latter acid is extracted from the deposit formed at the bottom of the vessel, by treating it first with boiling water which dissolves the gallic acid, and then with a solution of potassa which dissolves the gallic acid in the state of ellagate of potassa. The alkaline liquid, when eva- porated, deposits the latter salt in the form of small crystalline spangles, insoluble in fresh water, but dissolving readily in an al- kaline liquid. Acids separate ellagic acid in the form of a slightly yellowish powder. Ellagic acid is insoluble in water, alcohol, and ether, and its composition corresponds to the formula C 14 H 5 10 . It loses 2 equi- valents of water at 248, when its formula becomes C 14 H 3 8 . The formula of ellagic acid in combination with bases being C^H^Oy, that of the dried acid is therefore C 14 2 BLHO, and that of the hydrated acid C 14 H 2 7 ,HO+2HO. Ellagic acid also occurs in the animal economy, sometimes form- ing concretions known by the name of bezoars. Meconie Acid C 14 HO n ,3HO. 1462. Meconie acid is extracted from opium. When chloride 610 VEGETABLE ACIDS. of calcium is poured into an infusion of opium, a precipitate of im- pure meconate of lime is formed, which, after being washed succes- sively with water and alcohol, is treated with 20 parts of hot water, to which 3 parts of chlorohydric acid are added, when the filtered liquid deposits, on cooling, acid meconate of lime. The salt is di- gested with the same quantity of hot acidulated water, and, on cool- ing, the meconic acid separates ; but it is generally necessary to re- peat this operation once or twice before obtaining the acid entirely free from lime. The impure meconic acid may also be combined with potassa, and the meconate of potassa decomposed by chloro- hydric acid, after being purified by crystallization. Meconic acid dissolves in 4 parts of boiling water, from which it is almost wholly deposited, on cooling, in the form of crystalline, pearly white spangles. It is decomposed by long boiling with water, particularly in the presence of chlorohydric acid; carbonic acid being disengaged, while a new acid, called comenic, is formed. It is also destroyed by contact with alkaline liquids, yielding compli- cated products. The composition of crystallized meconic acid is represented by C^H^Oso, which formula should be written C 14 H0 115 3HO+6HO, because the 6 equivalents of water of crystallization are driven off at 212, while the 3 equivalents of basic water may be replaced, either wholly or partly, by bases. In fact, the three following meconates of potassa have been obtained : 3KO,C M HO U , (2KO+HO),C ]4 H0 li; (KO+2HO),C U HO U . By pouring nitrate of silver into a solution of meconate of am- monia, a yellow precipitate of the formula 3AgO,C 14 HO n is formed. Meconic acid presents therefore all the characters of a tribasic acid. It produces a beautiful red colour with sesquisalts of iron. 1463. By boiling meconic acid for some time with acidulated water, it is converted into comenic acid, while carbonic acid is dis- engaged. The formula of comenic acid, is C 12 H 3 8 ,2HO, the 2 equi- valents of water being basic, for the formula of comenate of silver is 2AgO,C 12 H 2 8 . Meconic, by being converted into comenic acid, loses only carbonic acid, according to the equation C 14 HO U ,3HO=2C0 2 4-C 12 H 2 8 ,2HO. Comenic acid is also largely formed in the dry distillation of me- conic acid, but it is then mixed with another acid, pyromeconic, into which comenic acid itself is transformed when subjected to another distillation. In order to obtain pure pyromeconic acid, it must be distilled several times ; and the formula of the crystallized acid is C 10 H 3 5 ,HO, while that of pyromeconate of lead is PbO,C 10 H 3 5 . The following equation shows how this acid is derived from comenic acid : C 12 H 2 8 ,2HO=2CO a ,C 10 H 3 4 ,HO. QUINIC ACID. 611 Comenic and pyrocomenic acids turn sesquisalts of iron of a red colour. CHELIDONIC ACID C 14 H a O ia ,2HO. 1464. In celandine, (chelidonium majus,) a plant of the family of the papaveraceae, there is formed a peculiar acid, called chelidonic^ which is there combined with lime ; besides malic and fumaric acids. The juice of the plant is expressed and boiled to coagulate the albu- minous substances, when, after having added a small quantity of nitric acid, acetate of lead is poured in until a precipitate no longer forms. The chelidonate of lead is alone precipitated, the malic and fumaric acids remaining in solution on account of the excess of nitric acid. The chelidonate of lead, which is mixed with chelido- nate of lime, is decomposed by sulf hydric acid, and the acid liquor is saturated with lime ; after which the chelidonate of lime is crys- tallized several times. The salt is subsequently decomposed by carbonate of ammonia, and the chelidonate of ammonia resulting, by chlorohydric acid ; when the chelidonic acid separates in long crystalline aciculse during the cooling of the liquid. The formula of crystallized chelidonic acid is C 14 H 2 10 +5HO, and it loses 3 equivalents of water at 212. From the composition of its salts it should be regarded as a bibasic acid QUINIC ACID C U H U 10 HO. 1465. This acid is found in cinchona bark, in the state of qui- nate of lime. The bark is boiled with water acidulated with chlo- rohydric acid, which is then saturated with lime, in excess ; when the filtered liquid contains quinate of lime which may be crystal- lized by proper evaporation. The salt is purified by animal black and several successive crystallizations ; and in order to separate the quinic acid from it, 6 J- parts of the quinate of lime are heated with 1 of sulphuric acid diluted with 10 of water, when the lime sepa- rates in the state of sulphate of lime ; after which alcohol is added to effect its complete precipitation, and the filtered liquid is evapo- rated to the consistence of syrup, when the quinic acid crystallizes in large prisms. The formula of the crystallized acid is C 14 H 11 11 ,HO ; and that of quinate of silver is AgO,C 14 H n O n . Quinic acid, subjected to heat, yields very complex products : they are benzin, benzoic phenic, and salicylous acids, all of which shall subsequently be described ; besides a peculiar crystallizable substance of the formula C 24 H 12 8 , very soluble in water and alco- hol, and which has been called hydroquinone. Subjected to the action of sulphuric acid and peroxide of manganese, quinic acid yields a volatile product, quinone, of which the formula is C 24 H 8 8 . In order to obtain a small quantity of this product, 100 gm of qui- nic acid are heated gently in a small retort with 400 gm. of per- oxide of manganese and 100 gm. of sulphuric acid previously diluted 612 OBGANTC ALKALIES. with one-half of its weight of water. A great bubbling ensues in the retort, and a mixture of formic acid and quinone is deposited in the receiver. The latter substance crystallizes in beautiful golden- yellow spangles. Quinon is easily sublimed by the same method as camphor, and it has a strong and irritating odour, resembling that of camphor. It dissolves slightly in cold, but more freely in boiling water, while its true solvents are alcohol and ether. Chlorine acts powerfully upon it, and gradually abstracts all its hydrogen, which is replaced by an equivalent quantitity of chlorine ; and two crystallized chlori- nated products have thus been separated : sechlorinated quinone C 34 H 2 C1 6 8 and perchlorinated quinone C^ClgOg. Quinone also gives rise to a great number of interesting products, but their study would lead us too far. 1466. Vegetables contain several other organic acids, named generally after the plant from which they are extracted, but they are as yet only imperfectly known ; and several of them are proba- bly identical with those already described, for which reason we shall not stop to mention them. ORGANIC ALKALIES. 1467. At the present day a large number of organic substances are known which combine with acids after the manner of mineral bases, forming compounds which exhibit all the characters of salts, and to which the name of organic alkalies, or alkaloids, has been given. Some are found already formed in vegetables, while others are produced by the calcination or other appropriate treat- ment of organic matter. The majority of native alkaloids are ex- tremely poisonous, and rank among the most powerful medicines, which character lends them peculiar importance. All the organic alkalies contain nitrogen and hydrogen, and all, with the exception of ammonia, contain carbon ; while the majority, in addition, contain oxygen ; and lastly, sulphur has been found in some. They all present the remarkable peculiarity which has been described (513) in treating of ammonia; that of combining directly and without decomposition, with the hydracids, by forming chlorohy- drates, iodohydrates, etc. etc., and of fixing, in all salts which they form with the oxacids, 1 equiv. of water, necessary to the constitu- tion of the salt, and which cannot be driven off without destroying its nature. The alkaloids, like ammonia, are therefore bases only when they have combined with the elements of 1 equiv. of water. QUINDT. 613 We shall first describe the alkaloids which exist ready formed in vegetables, and then some of the numerous artificial alkaloids ob- tained in modern days, confining ourselves chiefly to general remarks on the method of their preparation and their properties. The native alkaloids may be divided into two classes : alkaloids volatile without decomposition, and non-volatile alkaloids, each class requiring a special method of extraction. In order to extract those of the first class, the liquid containing them is distilled with potassa or lime, which bases unite with the acid until then com- bined with the alkaloid, while the latter passes over in distillation. The majority of non-volatile alkaloids are very slightly soluble in water, and are prepared by boiling the vegetables containing them with water acidulated with chlorohydric acid, when the alkaloid is dissolved in the state of chlorohydrate, after which the liquid is then saturated with an alkali or with lime, in order to precipi- tate the alkaloid. The deposit is then treated with boiling alco- hol to dissolve the alkaloid, which crystallizes on cooling or by evaporation. NON-VOLATILE NATIVE ALKALOIDS. ALKALOIDS OF THE CINCHONAS. 1468. The bark of the cinchonas contains two principal alka- loids, to which they owe their medicinal virtue : these are quinia and cincTionin. Three species of cinchona are known in commerce, the yellow, red, and gray ; and while quinin predominates in yellow bark, cinchonin is principally found in the gray ; and red bark con- tains nearly equal proportions of quinin and cinchonin. Two other less important alkaloids are also found in the barks, chino'idin and cinchovatin, which are present in very small quantities. Quinin C 38 H 24 N 2 4 . 1469. Yellow cinchona is preferred for the manufacture of quinin, to which effect the bark is bruised and boiled with water containing 15 or 20 per cent, of sulphuric or chlorohydric acid, when the liquid is filtered through a cloth, and milk of lime added until an alkaline reaction is produced with litmus. The deposit formed, which contains the quinin, is squeezed in a press, and the cake resulting treated with boiling alcohol, three-fourths of which being separated by distillation, sulphuric acid is added to the re- mainder until a slight persistent acid reaction is obtained. The liquid is discoloured by animal black, and crystallize when the sulphate of quinin crystallizes first, while the sulphate of cinchonin remains in the mother liquid. By decomposing the sulphate of quinin by ammonia, quinin is obtained in the form of a white pow- der, which, by slow evaporation from an alcoholic solution, is depo- sited in small prismatic crystals. VOL. II. 3 B 614 ORGANIC ALKALIES. Quinin has a very bitter taste, requires for its solution 400 parts of cold and 250 of boiling water, and turns litmus blue. Boiling alcohol dissolves one-half of its weight of it, while ether also dis- solves a considerable quantity, and thus furnishes a method of sepa- rating it from cinchonin, which is insoluble in ether. The formula of quinin, crystallized from an aqueous solution, is C 38 H 24 N 2 4 -f 6HO, and it loses the 6 equivalents of water at 248. Quinin, dissolved in alcohol or acidulated water, exerts a rotatory power toward the left, a-t least at the temperature of 71.6, the power de- creasing as the temperature rises. Quinin forms crystallizable salts with nearly all the acids, its most important compound being the neutral sulphate, used in medicine as an anti-intermittent. Two sulphates of quinin are known. 1. The neutral sulphate, crystallizing in fine silky aciculae, and very slightly soluble in cold water, of which it requires 750 parts for solution, while it dissolves in 30 parts of boiling water. Its formulae is (C 38 H 24 N a 4 ,HO),S0 3 +7HO, and it loses its water of crystallization by heat. It exerts rotation toward the left, like the alkali which acts as its base. 2. The acid sulphate, soluble in 10 or 12 parts of cold water, the formula of which is (C 38 H 24 N 2 4 ,HO,)2S0 3 +8HO, the water of crystallization being driven off by heat. Cinchonin C 38 H 24 N 2 2 . 1470. Cinchonin is prepared either from the mother liquid of sulphate of quinin, or by treating gray cinchona in the manner by which quinin is extracted from yellow cinchona. Cinchonin crys- tallizes readily, and without any water of crystallization, its formula being C 38 H 24 N 2 N 2 , which differs from that of anhydrous quinin only by containing 2 equiv. of oxygen less. Cinchonin is still less solu- ble in water and alcohol than quinin, while it is insoluble in ether. Salts of cinchonin crystallize readily, and are generally more solu- ble in water than the corresponding salts of quinin. When chlorine is made to act upon a concentrated and hot solu- tion of chlorohydrate of cinchonin, a slightly soluble salt is depo- sited, which, when redissolved in water, and treated with ammonia, forms a precipitate of bichlorinated cinchonin C 38 H 22 C1 2 N 3 2 . This substance crystallizes in needles, turns tincture of litmus blue, and forms with acids crystallizable salts, which closely resemble the cor- responding salts produced by ordinary cinchonin, and even appear to be isomorphous with them. In the same way bromine converts cin- chonin into bichlorinated cinchonin C 38 H 22 Br 2 N 2 2 . The elementary composition of the bichlorohydrate of bibrominated cinchonin C 38 H 23 Br 2 N 3 2 ,2HCl is the same as that of the bibromohydrate of bichlori- nated cinchonin C 38 H 22 Cl 2 N 3 2 ,2HBr, while the two substances dif- fer essentially from each other, since the former yields with potassa bibrominated cinchonin, and the latter bichlorinated cinchonin. MORPHIN. 615 Cinchonin, dissolved in alcohol or acidulated water, exerts a ro- tatory power toward the right, while that of quinin is toward the left, and the salts of cinchonin also turns to the right, like the al- kali which forms their base, the chlorinated derivatives of the alkali exerting it in the same direction. Chino'idin. 1471. The mother liquid of sulphate of quinin, after having deposited its sulphate of cinchonin, may yield a small quantity of sulphate of chino'idin. Chinoidin is as yet but little known, and from the analyses which have been made of it, it would appear to have the same composition as quinin. Oinchovatin C 46 H 27 N 3 3 . 1472. Cinchovatin is found chiefly in the cinchona from Jain, (cinchona ovata,} from which it is extracted by the same process as quinin. It is a substance insoluble in water, and soluble in alcohol, from which it is deposited in crystals of the formula ALKALOIDS OF OPIUM. 1473. On making incisions into the head of the white poppy, a liquid issues from it, which hardens in the air into a brown horn- like mass, constituting opium, the chief part of which is imported from the East, and principally from Smyrna. The poisonous pro- perties of opium are owing to the existence of several alkaloids, the principal of which are morphin, narcotin, and code'in ; while several others, less important, and only existing in small quantity, are also extracted: theba'ina, narce'in, pseudomorphin, porphyroxin, and a non-nitrogenous crystalline substance, which does not act the part of a base, and has been called meconin. First quality opium contains about 10 per cent, of morphin and 5 per cent, of narcotin. Morphin C^NO,. 1474. In order to obtain morphin, the opium, cut into thin slices, is macerated for some time with water, and the substance, when softened, is crushed with an additional quantity of water, squeezed in bags under a press, and the cake subjected to similar treatment. The liquid yielded by this process, being evaporated to the consist- ence of an extract, is again treated with a small quantity of water, which dissolves the salts of morphin, and leaves the greater portion of the narcotin mixed with a brown substance. By testing a small quantity of the liquid, the quantity of ammonia necessary to wholly precipitate this substance is ascertained, while only ^ of this quan- tity is poured into the whole liquid, when the impure morphin is precipitated, carrying with it nearly all the colouring matter. By * Aricin is not mentioned by Regnault, and in fact much uncertainty exists as to the alkaloids in cinchona bark, except quinine and cinchona. J. C. B. 616 ORGANIC ALKALIES. then adding the balance of the ammonia, nearly pure morphin is precipitated, and is treated with alcohol marking 20 of Baume', which does not sensibly dissolve the morphin, while it removes almost entirely the resinous matter which adulterates it. The residue is then treated with boiling alcohol at 35 Baume*, which dissolves the morphin and deposits the greater part of it on cooling. Three-fourths of the alcohol are deposited by distillation and the residue yields the balance of the morphin. In order to obtain the base perfectly pure, it is best to redissolve it in weak chlorohydric acid, crystallize the chlorohydrate, and again decompose this salt by ammonia. Morphin readily forms crystals of the formula C^H^NOg+SHO, which lose the 2 equiv. of water by an elevation of temperature, and may be heated to 570 without injury. Cold water dissolves about Y^ of morphin, and hot water nearly double of that quantity ; the solution showing an alkaline reaction with litmus. Weak alco- hol at 20 B. dissolves but very little morphin, while boiling alcohol at 35 B. dissolves ^ of its weight, the greater portion of the mor- phin crystallizing on cooling. It is scarcely soluble in ether, but a concentrated solution of caustic potassa dissolves it without change, by which process the base may be separated from narcotin, the latter being insoluble in alkaline lixivise. Morphin dissolved in acidulated water exerts a rotatory power toward the left, like its salts. Morphin forms crystallizable salts with acids, soluble in water and alcohol, but insoluble in ether. Chlorohydrate of morphin, which is most important on account of its use in medicine, crystallizes in silky tufts, and dissolves in 1 part of boiling or in 20 parts of cold water. Its formula is C^H^NO^HCl-f 6HO, while that of crystal- lized sulphate of morphin is (C 34 H 18 N0 6 ,HO),S0 3 +6HO. Narcotin CJH^NC^. ^ 1475. Narcotin is extracted from the residues left after the extraction of morphin from opium by treating them with ether, which dissolves a mixture of narcotin and porphyroxin, the narcotin greatly predominating. Fresh opium may also be treated directly with ether, when the salts of morphin remain in the residue and the ether contains, with the narcotin and porphyroxin, a certain quantity of meconin. The ether being distilled in a water-bath and the residue treated with water, which dissolves the meconin, the narcotin and porphyroxin are finally dissolved in dilute chlorohydric acid. The solution, when evaporated, deposits chlorohydrate of narcotin, while the chlorohydrate of porphyroxin remains in the mother liquid. The chlorohydrate of narcotin, decomposed by am- monia, yields isolated narcotin, which is purified by crystallizing it in alcohol. STRYCHNIN. 617 Narcotin crystallizes in small rhomboidal prisms, melting at 338, decomposing at about 390, insoluble in cold water, and only dis- solving in 500 parts of boiling water. Alcohol, when hot, dissolves about 7^ of its weight, and ether ^. Narcotin is a much more feeble base than the alkaloids we have hitherto described, since its solutions do not turn to blue the reddened tincture of litmus, although it forms crystallizable salts with acids. The formula of narcotin is C^H^ N0 14 , while that of the chlorohydrate is C JB^NO^HCl. Narcotin, dissolved in alcohol or acidulated water, exerts a rotatory power to the right, opposite to that of morphin; the salts of narcotin pos- sessing the same power as the alkali. Oodein C 34 H 19 N0 5 . 1476. Codein remains in the liquid from which morphin has been precipitated by ammonia, and is extracted by concentrating them through evaporation, adding caustic potassa, and then continu- ing the evaporation to dryness. The residue is treated with ether, which dissolves the codein, and yields, by spontaneous evaporation, large crystals of this substance, which are remarkable for the sharp- ness of their configuration. Codein, which is much more soluble than the other alkaloids of opium, since it dissolves in 80 parts of cold and 20 of boiling water, turns the reddened tincture of litmus blue, and is also highly soluble in alcohol and ether. The formula of codein, crystallized in water, is C^HjgNOjH^HO, and heat readily drives off its 2 equiv. of water, while it crystallizes in the anhydrous state from its solutions in ether. Codein has been used for some time in medicine. ALKALOIDS OF STRYCHNOS. Strychnin C^H^N^ and Brucin C^H^Og. 1477. The majority of the genus of strychnos, particularly the bean of St. Ignatius, (strychnos Ignatia,} nux vomica, (stryclmos nux vomica^ viper-wood, (strychnos colubrina,) and the upas tieutd, (strychnos tieute,) contain two alkaloids in various proportions, strychnin and brucin, remarkable for the very poisonous effect they exert on the animal economy. The two bases are generally extracted from nux vomica by boil- ing the powdered nut with water containing its weight of sulphuric acid, expressing the liquid, and precipitating the two bases by hy- drated lime. The deposit is treated with boiling alcohol, which dissolves the strychnin and brucin; and, on cooling, the greater portion of the strychnin crystallizes. The liquid, concentrated by evaporation, yields less pure strychnin, and the brucin crystallizes last. It is necessary to purify these substances by several succes- sive crystallizations. 618 ORGANIC ALKALIES. Strychnin crystallizes readily in octohedrons with rectangular bases, insoluble in water, slightly soluble in alcohol, and presenting the formula C 43 H 33 N a 4 . It forms easily crystallizable salts, and the formula of crystallized chlorohydrate of strychnin is C^EyS^O^ HCl-f 3HO, while that of the crystallized sulphate is (C^H^O,, HO),S0 3 . Strychnin, dissolved in acidulated water, exerts a rota- tory power toward the left, like its salts.* Brucin crystallizes in right prisms with a rhombic base, and its formula is O-B^NjOg-fBHO ; the 8 equiv. of water being given off by heat. Water dissolves a small quantity of it, and it is much more soluble in alcohol than strychnin. Concentrated nitric acid produces an intense red colour with brucin, which property dis- tinguishes it from a majority of the other alkaloids. Brucin dis- solved in alcohol, or in water to which no acid has been added, deviates to the left like strychnin, its salts presenting the same behaviour. ALKALOID OF COFFEE AND TEA. Caffein or Them C 8 H 5 N 3 2 . 1478. Coffee and tea contain the same alkaloid, which is called caffein or them, according as it has been extracted from either of these substances, because it was at first supposed that they were not identical. In order to extract caffein from coffee, the bruised coffee-grains are treated with water, and subacetate of lead is poured into the liquid, after which, the deposit being separated, sulf hydric acid is passed through in order to precipitate the excess of lead. ' The solution being then evaporated, the caffein crystallizes, and is purified by successive crystallizations. Thein is extracted in pre- cisely the same manner. Caffein crystallizes in silky aciculae, taking the formula C 8 H 5 N 2 2 +2HO, while it loses its 2 equivalents of water at 212, melts at about 356, and sublimes above 570. It is soluble in water, alcohol, and ether ; and its basic affinities are very feeble, for although it dis- solves in acids, it generally leaves them when the solution is eva- porated. VOLATILE NATIVE ALKALOIDS. 1479. Two native alkaloids are now known, which volatilize without change : nicotin, or the alkali of tobacco, and conicin, the alkali of cicuta. Nicotin CJE M N r 1480. Certain varieties of tobacco contain 7 or 8 per cent, of nicotin, which is extracted by digesting the tobacco-leaves with * The elementary composition of this most violent poison is, singular enough, identical with that of rye bread, a most wholesome article of food. The natives of Borneo use the juice of the different kinds of strychnos for poisoning their ar- row-heads, the wound of which is generally fatal. W. L. F. NICOTIN. 619 water, evaporating the infusion to the consistence of an extract, and then treating with alcohol, which is, in its turn, concen- trated, after being decanted. The new extract is treated with potassa, and then shaken with ether, which dissolves the nicotin as well as some foreign substances. Finely powdered oxalic acid is added to the etherial solution, which is to be frequently shaken, when oxalate of nicotin is formed, and precipitated in drops, which are washed several times with water. The oxalate of nicotin being decomposed by potassa, free nicotin is separated by ether. The etherial solution is distilled in a retort over a water-bath, when the greater portion of the ether distils rapidly, while the last particles do not pass over at 212 ; and there exists also a small quantity of ammonia and water, which separate only at a higher temperature. The retort must be kept, for a whole day, at a temperature of 284, and a feeble current of hydrogen must be passed through it, after which the receiver is changed, and the temperature raised to 356, in order to distil the nicotin in a current of hydrogen. Nicotin is an oleaginous, limpid, and colourless liquid, smelling slightly of tobacco, and which boils at 473, but begins to decom- pose at this temperature ; so that it is necessary to distil it under feeble pressure, or in a current of hydrogen gas, so as not to be obliged to raise the temperature to a degree at which the elastic force of the vapour is equal to the pressure of the atmosphere. The density of liquid nicotin is 1.048, while the density of its vapour has been found to be 5.607. Nicotin is very soluble in water, which /then reacts powerfully alkaline ; and caustic potassa precipitates it from its solutions in the form of oleaginous drops, while ether takes it from water and dissolves it in all proportions, alcohol also dis- solving a large quantity of it. It is one of the most powerful poi- sons. Nicotin soon changes in the air, by absorbing oxygen, and is converted into a brown substance of a resinous appearance. The salts of nicotin are in general very soluble, and crystallize with difficulty. The formulae of the sulphate and nitrate of nicotin are (C 20 H 14 N 2 ,HO),S0 3 and (CJH^HO^NO,, according to which the formula of free nicotin is C^H^N^ corresponding to 4 volumes of vapour, like that of ammonia. Nicotin exerts an extremely ener- getic rotatory power toward the left, while its chlorohydrate turns the plane of polarization with the same power toward the right. The various species of tobacco contain very different proportions of nicotin, the following quantities having been found in 100 parts of dry tobacco : Foreign Tobacco. Havana 2.0 Maryland 2.3 Virginia 6.9 French Tobacco. Alsace 3.2 Pas-de-Calais 4.9 Nord.. 6.6 Lot 8.0 The tobacco which contains most nicotin is the best for the manu- 620 ORGANIC ALKALIES. facture of snuff, since the property possessed by tobacco of stimu- lating the mucous membrane of the nose, is owing to the pre- sence of nicotin and ammoniacal salts. Conicin C 16 H 15 N 1481. Conicin is extracted from the seeds of the conium, but it is also found in the leaves and stalk of this plant, previous to its flowering. The bruised seeds being distilled with a solution of potassa, conicin passes over with water and ammonia. The liquid is saturated with sulphuric acid, and evaporated to the consistence of syrup ; when, by treating the extract with a mixture of alcohol and ether, the sulphate of conicin is dissolved, while the ammonia- cal sulphate is left. The solution of the sulphate of conicin is then evaporated, and afterward decomposed by caustic potassa; when the conicin arising from this decomposition is decanted, and then left for some time on chloride of calcium, which abstracts its water, after which it is purified by distillation. Conicin is a colourless liquid, having a sharp smell, which imme- diately produces sickness, and its density is 0.89, while it boils at 338. It is one of the most powerful poisons. Conicin is slightly soluble in water, but dissolves in all proportions in alcohol and ether, its solutions showing a strong alkaline reaction. It rapidly absorbs the oxygen of the air, and then assumes various shades of colour. The salts of conicin are in general deliquescent and not crystalline ; and the composition of the alkaloid corresponds to the formula C 16 H J5 N. ARTIFICIAL ALKALOIDS. 1482. Chemists have long since succeeded in preparing a great number of alkaloids, which have not yet been found in vegetables. Almost all these alkaloids are volatile without decomposition, and contain no oxygen ; and while some resemble, in their properties, nicotin and conicin, others are so closely analogous to ammonia, that, in a purely philosophical classification of substances, it would be impossible to separate them from that base. Quinole'in C 18 H 7 N. 1483. Several native organic bases, particularly quinin, cin- chonin, and strychnin, yield, by distillation with potassa, a volatile alkaloid called quinole'in. It is obtained in greatest quantity from cinchonin, by heating in a tubulated retort some fragments of caustic potassa with a small quantity of water, so as to form a pasty solu- tion, and gradually adding powdered cinchonin. It is heated with an alcohol-lamp until the substance appears to be dried, when hydrogen is disengaged, while water passes over, as also an oily substance, which is rectified a second time over potassa. Quinolem is a colourless oil, of a disagreeable odour, distilling at about 446, ANILIN. 621 insoluble in cold, and scarcely soluble in boiling water, while alcohol and ether dissolve it freely. It forms crystallizable salts with chlo- rohydric, sulphuric, and nitric acids, and it contains no oxygen, its formula being C 18 H 7 N. Quinolein is also found among the products of distillation of coal-tar, and was formerly called leucole. ALKALOIDS DERIVED FROM VARIOUS CARBURETTED HYDROGENS. Anilin C 12 H 7 N. 1484. The majority of the carburetted hydrogens yield, when they are boiled with monohydrated nitric acid, or a mixture of this acid and concentrated sulphuric acid, nitrogenous substances, which result from the substitution of 1 equivalent or 2 equivalents of the compound N0 4 in the place of 1 or 2 equivalents of hydrogen. Thus, we shall soon see that benzin C 12 H 6 , treated with mono- hydrated nitric acid, produces two substances, nitrobenzin CJI S (N0 4 ) and binitrobenzin C 13 H 4 (N0 4 ) 2 . These nitrogenous com- pounds yield alkaloids when they are subjected to the action of reducing substances, as e. g. the sulfhydrate of ammonia, or to the action of nascent hydrogen obtained by causing dilute sulphuric acid to act on zinc in contact with the nitrogenous substance. Thus, by the action of the bisulf hydrate of ammonia on nitrobenzin, we obtain an alkaloid, anilin C 12 H 7 N, from the following reaction : C 12 H 5 (N0 4 )+6(NH 3 ,2HSJ=C 12 H 7 N+6S+4HO+6(NH 3 ,HS). By the action of nascent hydrogen, we have C 12 H 5 (N0 4 )+6H=C 12 H 7 N+4HO. When binitrobenzin is subjected to the same treatment, there results a second alkaloid, nitranilin C 12 H 6 (1S[0 4 )N, according to the following reactions : C B H 4 (NOJ.+6(NH S) 2HS)=C U H.(NO,)N+6S+4HO +6(NH 3 ,HS), 6 C 12 H 4 (NOA+6H=C 12 H^N0 4 )N+4HO. We shall describe only anilin and nitranilin ; the properties of the numerous alkaloids obtained by applying the same processes to other carburetted hydrogens, or substances derived from them, being very similar. Anilin is a colourless liquid, of an agreeable vinous smell, boiling at 359.6, and dissolving slightly in water, but in all proportions in alcohol and ether. Anilin possesses no rotatory power. Chlo- rine and bromine convert it into chlorinated or brominated sub- stances, modified merely by substitution, and which often retain the basic properties and capacity of saturation of the original anilin. Monochlorinated anilin C 12 H 6 C1N, the monobrominated C 12 H 8 BrN, and nitranilin C 12 H 8 (N0 4 )N, are bases which form salts as well defined as anilin itself; while the terchlorinated C^B^C^N and terbrominated anilins C 12 H 4 Br 3 N possess no basic properties. ORGANIC ALKALIES. Iodine may also be substituted for hydrogen in anilin, and a moniodinated anilin C 12 H 6 IN has been obtained which combines with acids. Cyanogen gives rise to no phenomena of substitution, but combines directly with anilin with the evolution of heat, and produces a new crystallizable base, cy anilin C 13 H 7 NCy==C 14 H 7 N 2 , which forms, with the majority of acids, well-defined and crystalli- zable salts. ALKALOIDS DERIVED FROM CYANIC AND CYANURIC ETHERS, PRESENTING A CLOSE ANALOGY WITH AMMONIA. 1485. "We shall subsequently describe, together with some other products of cyanogen, two isomeric compounds of this substance with oxygen, cyanic acid CyO=C 3 NO, and cyanuric acid Cy 3 3 = C 6 N S 3 , which are readily converted into each other, as will be shown in its place. These acids combine with bases, forming cya- nates and cyanurates. Ethylammonia C 4 H 5 (NH 3 ). 1486. By distilling cyanate of potassa KO,CyO with a solution of sulphovinate of potassa KO,(C 4 H 5 0,2S0 8 ) there is obtained a mixture of cyanic ether C 4 H 5 0,CyO and cyanuric ether 3C 4 H 5 0, Cy 3 3 , which are easily separated by distillation, the first being very volatile, while the second boils only at a very high tempera- ture. Cyanic ether dissolves in ammonia with disengagement of heat, and the liquid, when evaporated, deposits beautiful prismatic crystals, which are fusible, very soluble in water and alcohol, and of the formula C 6 H 8 N 3 3 : they result therefrom from the simple combination of 1 equivalent of cyanic ether C 4 H 5 0,CyO==C 6 H 5 N0 3 with 1 equivalent of ammonia NH 3 . Cyanic and cyanuric ethers, treated with caustic potassa, yield carbonate of potassa and an al- kaloid C 4 H 7 N : C 4 H 5 0,C 3 NO+2(KO,HO,=2(KO)C0 3 )+C 4 H 7 K We shall call this alkaloid ethylammonia, and its formula C 4 H 7 N may be written C 4 H 4 NH 3 , considering it as resulting from the com* bination of 1 equivalent of ammonia with 1 equivalent of bicarbu- retted hydrogen C 4 H 4 , while it may also be written C 4 H 5 (NH 3 ), and the alkaloid regarded as belonging to the series of simple ethers. One of the equivalents of hydrogen and carburetted hydrogen C 4 H 6 , the generator of the series, having been replaced by 1 equi- valent of amide (NH a ). In order to obtain ethylammonia, cyanic or cyanuric ether is boiled in a distilling apparatus with an excess of potassa, the va- pours being collected in a well-cooled receiver containing a small quantity of water, which takes the ethylammonia in solution, and thus becomes strongly alkaline, with an intense ammoniacal odour, although it does contain a trace of free ammonia. This liquid is saturated with chlorohydric acid and evaporated, when crystals are ** "*METHYLAMMONIA. 623 obtained which dissolve completely in absolute alcohol, and are again deposited, by evaporation, in crystalline lamellae. This compound is chlorohydrate of ethylammonia C 4 H 7 N,HC1, and is distinguished from chlorohydrate of ammonia by its solubility in absolute alcohol. The chlorohydrate of ethylammonia, perfectly dried, is mixed with double its weight of quicklime, and introduced into a long tube closed at one end, so as to fill one-half of it ; and the other half being filled with fragments of caustic potassa, a disengagement- tube, which enters a flask surrounded by a refrigerating mixture, is adapted to it. Gentle heat being applied, the ethylammonia set free distils, and is condensed in the receiver. It is important to remark that this process exactly resembles that used for obtaining ammonia. Ethylammonia is a colourless, very volatile liquid, boiling at 64.4, exhaling a very penetrating ammoniacal odour, turning blue the reddened tincture of litmus, and exhibiting a causticity resem- bling that of potassa. When a glass rod moistened with chlorohy- dric acid is brought near it, extremely thick white fumes are pro- duced ; and each drop of acid poured into it produces a hissing at the moment of its mixing with the base. Ethylammonia ignites when brought near to a substance in combustion, and burns with a bluish flame. It mixes with water in all proportions, becoming very hot, and giving rise to a solution of which the basic properties absolutely resemble those of ammonia. A solution of ethylam- monia precipitates, in fact, the salts of magnesia, alumina, manga- nese, iron, bismuth, chrome, uranium, tin, lead, and mercury. Salts of zinc throw down a white precipitate, which redissolves in a large excess of the reagent. Salts of copper produce a bluish white pre- cipitate, readily soluble in an excess of the reagent, furnishing a deep-blue liquid, analogous to that produced by an excess of am- monia, (1046.) Ethylammonia combines with all the acids, forming crystallizable salts precisely resembling those of ammonia, and it also furnishes compounds analogous to the amides, ( 514.) In fact, by mixing a solution of ethylammonia with oxalic ether, the mixture becomes cloudy, and alcohol is formed, while acicular crystals of a compound C 6 H 6 N0 3 =C 4 H 6 N,C 3 3 corresponding to oxamide $H 3 ,C 3 3 sepa- rate. MetJiylammonia C 2 H 5 N or C 2 H 3 (NH 3 ). 148T. By boiling methylocyanic or methylocyanuric ether with a solution of potassa, and collecting the product in a well-cooled receiver containing water, a stro^ly^alkaline solution is obtained, which exhales a very penetrating ammoniacal odour. It is satu- rated with chlorohydric acid, evaporated to dryness, and again treated with boiling alcohol, which deposits, on cooling, pearl-like 624 ORGANIC ALKALIES. crystalline lamellae of chlorohydrate of metJiylammonia C 2 H 5 N,HC1. This salt heated with quicklime, as in the preparation of ammonia and ethylammonia, yields methylammonia, which may be obtained in the form of a colourless liquid by cooling the receiver with a proper refrigerating mixture. Methylammonia is gaseous at the ordinary temperature, and may be collected in bell-glasses over mercury, when it resembles ammoniacal gas so closely as to require peculiar attention to distinguish it from it. Methylammonia liquefies at about 32, and its odour is strongly ammoniacal, while its density is 1.08, its chemical equivalent C 3 HN. corresponding, like that of ammonia, to 4 volumes of gas. Methyl- ammoniacal gas is the most soluble of all gases known, since, at 53.6, 1 volume of water dissolves 1040 volumes of it, while at 77 water only takes up 906. Like ammoniacal gas, it is instantane- ously absorbed by charcoal, but it is distinguished from the latter gas by igniting by contact with a lighted candle and burning with a yellowish flame. It produces, with metallic solutions, reactions precisely similar to those of ammonia or ethylammonia. Amylammonia C 10 H 13 N or C 10 H U (NH 3 ). 1488. The oil of potato-spirit C 10 H 13 3 exhibits, as shall soon be shown, a perfect analogy with vinic and methylic alcohols, in the products which it forms with chemical agents, for which reason it has been called amylic alcohol. If amylocyanic or amylocyanuric ether be distilled with a solution of potassa, carbonate of potassa is obtained, besides anew base, amylammonia C 10 H 13 N, which formula may be written C^ H 10 NH 3 , because carburetted hydrogen C 10 H 10 is, in the amylic series, the analogue of bicarburetted hydrogen in the vinic series. It may be also written C 10 H 11 (NH 3 ), if it be consi- dered as resulting from the replacing of 1 equivalent of hydrogen, in the amylic molecule C 10 H 13 , by 1 equivalent of amide (NH 9 ). Amyl is found in solution in the water which has passed over in dis- tillation ; by saturating which with chlorohydric acid, white crys- talline lamellae, soluble in water and alcohol, of chlorohydrate of amylammonia C 10 H 13 N,HC1, are obtained after evaporation. This salt, distilled with quicklime, yields amylammonia in the form of a colourless liquid, of a strong ammoniacal odour, and very soluble in water. Amylammonia precipitates all the metallic salts which are precipi- tated by ammonia ; and with solutions of copper, it yields a precipi- tate which dissolves in an excess of the reagent and colours the liquid blue : nevertheless, to efiect perfect solution, a larger propor- tion of amylammonia must be used than of ethylammonia or methyl- ammonia. Chloride of silver also dissolves in it, but less readily than in ammonia. Amylammonia forms with acids a great number of crystallizable acids. BUTYRYLAMMONIA. 625 Butyrylammonia C 8 H U N or C 8 H 9 (NH 2 ). 1489. Butyrylammonia has not yet been prepared by the gene- ral process which has furnished the foregoing volatile alkaloids ; while among the products of distillation of animal substances, several volatile alkaloids have been found, among which one called petinin C 8 H U N is distinguished, presenting exactly the composition of buty- rylammonia. The composition of this substance presents, in fact, with that of butyric acid C 8 H 7 3 ,HO, the relation which exists be- tween ethylammonia C 4 H 7 N and acetic acid C 4 H 3 3 ,HO. It is a colourless liquid, of a penetrating ammoniacal odour, and forming well-defined salts with acids. 1490. The resemblance with ammonia of the last volatile alka- loids which we have described, is as perfect as that observed between potassa and soda ; and their composition presents the remarkable peculiarity, that they may be considered as formed by the union of 1 equivalent of ammonia with a carburetted hydrogen. The other volatile alkalies, either' native or artificial, which we have described, exhibit a similar grouping in their composition, and should probably be included in a single class, which will, certainly, be subsequently greatly extended. Thus we have, Ammonia* NH 3 Methylammonia NH 3 ,C 2 H 2 , Ethylammonia NH 3 ,CJI 4 , Butyrylammonia NH^CgHg, Amylammonia NH 3 ,C 10 H 10 , Nicotin NH 3 ,C 10 H 4 , Anilin NH 3 ,C 12 H 4 , Conicin NH 3 ,G 18 H 19 , Quinolein NH 3 ,C 18 H 4 . OF SOME NEUTRAL SUBSTANCES FOUND IN VEGETABLES. 1491. In the following chapter we shall describe certain sub- stances found in vegetables, exhibiting no well-marked characters of acidity or alkalinity, and which have hitherto not been attached * The first five compounds in the above table may be considered as ammonia paired with respectively 0, 1, 2, 4, and 5 equivalents of the carburetted hydrogen C a H.i, or olefiant gas ; which, according to the theory of pairing, explained in the note to $1401, would fully explain the ammoniacal properties of the paired com- pounds. They may also be regarded, with equal propriety, as ammonias in which 1 equivalent of hydrogen is replaced by 1 equivalent of the radicals methyl, ethyl, butyril, and amyl, respectively ; which view has gained much probability by the recent investigations of Frankland and Kolbe. W. L. F. VOL. II. 3 C 40 626 INDIFFERENT SUBSTANCES. to any of the great series of organic compounds. These substances being very numerous, we shall only mention the most important and those which are best known. Piperin C 34 H 18 N0 6 . 1492. Piperin exists in pepper, and is generally extracted from white pepper, by treating it with alcohol. The alcoholic solution is evaporated, the residue treated with an alkaline lye, which dissolves various substances, and leaves the piperin isolated. It is to be puri- fied by several crystallizations in alcohol. Piperin forms colourless prisms, which melt at about 212, and is slightly soluble in water, but very soluble in alcohol. Acids dissolve it readily, without forming a fixed compound with it, and, if they are volatile, they part with it wholly by evaporation, which operation is even effected at the ordinary temperature in vacuo. The composition of piperin corresponds to the formula C 34 H 18 N0 6 , showing it to be isomeric with morphin. Picrotoxin C 13 H 7 5 . 1493. Picrotoxin is the poisonous principle of the coculus Indi- cuSj and is obtained by exhausting these berries by alcohol, and evaporating the liquor, when a mixture of picrotoxin with fatty matter remains as a residue. The residue is pressed between folds of tissue-paper, and then redissolved in alcohol, after which the liquor is bleached by animal black, and picrotoxin obtained, by evaporation, in small acicular crystals. Picrotoxin dissolves in 25 parts of boiling water, the greater portion of it being again depo- sited on cooling, while it dissolves readily in alcohol. Picrotoxin does not combine with acids, and it contains no nitrogen, its com- position corresponding to the formula C 12 H 7 5 . Oantharidin C 10 H 6 4 . 1494. Cantharidin, the active principle of cantharides, possesses extremely powerful vesicating properties, and if any portion of the body be exposed to its vapours, swelling accompanied by acute pain immediately ensues. It is obtained by treating powdered can- tharides with alcohol, and evaporating the alcohol, when an aqueous liquid remains, on which floats an oily coat, solidifying on cooling. This coat being dissolved in alcohol and discoloured by animal black, crystals of cantharidin are obtained by evaporation. Can- tharidin contains no nitrogen, and its composition corresponds to the formula C 10 H 6 4 ; but its equivalent has not yet been deter- mined, as no definite compound of it is known. Cantharidin is insoluble in water, but dissolves readily in alcohol and ether. Asparagin C 8 H 7 N 3 5 ,HO. 1495. The name of asparagin has been given to a crystallizable substance, first found in the shoots of asparagus, but which also ASPARAGDT. 627 exists in liquorice-root, in marsh-mallow root, comfrey, potatoes, vetches, and several other plants. It is generally prepared by macerating bruised marsh-mallow roots with very clear milk of lime, filtering the liquid, precipitating the dissolved lime by carbonate of ammonia, and evaporating to the consistence of syrup ; when, in the course of a few days, granular crystals of impure asparagin separate, which are purified by recrystallization. Asparagin does not originally exist in the seeds of the vetch, but is developed during germination and vegetation, to again disappear at the flowering period. In order to extract it, the plant is cut at the proper season, and the juice expressed and boiled, when albumin- ous substances coagulate and are separated. The liquid being evaporated to the consistence of syrup, and left to itself, deposits crystals of asparagin, which are purified by being washed with cold water and recrystallized several times. Asparagin forms beautiful colourless prismatic crystals, requiring for solution about 60 parts of water, at the ordinary temperature, but dissolving more freely in boiling water. It is not sensibly solu- ble in absolute alcohol or in ether. Its aqueous solution feebly reddens litmus ; and when it is poured into a hot solution of acetate of copper, a beautifully blue precipitate is formed, consisting of a compound with oxide of copper, of the formula CuO,C 8 H 7 N 3 5 . The formula of asparagin dried at 212 is C 8 H 8 ISr 2 6 , which should be written C 8 H 7 N 2 5 ,HO ; while the formula of crystallized aspara- gin is C 8 H 7 N 2 5 ,HO+2HO. A solution of pure asparagin, left to itself, remains unchanged for an indefinite length of time, which is not the case if it contains some of the principles which accompany it in the vegetable, when it undergoes a kind of fermentation which converts it into succinate of ammonia. If we observe that 1 equivalent of succinate of am- monia is equal, in its elementary composition, to 1 equivalent of asparagin plus 2 equivalents of water and 2 equivalents of hydrogen^ 2(NH 3 +HO),C 8 H 4 6 =C 8 H 8 N 2 6 +2H04-2H, we may admit that asparagin assimilates to itself 2 equivalents of water and 2 equivalents of hydrogen, produced by the putrefaction ensuing in the liquid, which excites a reducing action in nearly all analogous cases. Under the influence of sulphuric and chlorohydric acid, and of nitric free from nitrous acid, asparagin is decomposed into ammonia and anew acid, called aspartio C 8 H 5 N0 6 ,2HO, which is very slightly soluble in water, but readily so in the acids, with which it afterward parts with difficulty by evaporation. It crystallizes in small pearly leaflets; and may also be obtained by boiling asparagin with a solution of potassa, when ammonia is disengaged, and the liquor contains aspartate of potassa, C 8 H 8 N a 6 +2HO=C 8 H 5 N0 8 ,2HO+NH 8 . 628 INDIFFERENT SUBSTANCES. If asparagin be treated with nitric acid containing nitrous acid, a considerable quantity of bimalate of ammonia (NH 3 ,HO+HO), C 8 H 4 8 is formed, nitrogen being disengaged at the same time. Under the influence of the nitric acid, the asparagin is converted into aspartic acid and ammonia, while the ammonia has been con- sumed by the nitrous acid, yielding water and free nitrogen ; and the aspartic acid, having combined with 2 equivalents of water in the nascent state, has been changed into bimalate pf ammonia, according to the equation, C 8 ILN0 6 ,2HO+2HO=(NH S ,HO+HO),C 8 H 4 8 . It is proper to observe that aspartic acid and asparagin may be considered as malic acid, united to 1 or 2 equivalents of ammonia NH 3 ; that is, as two amides of malic acid. This view of the con- stitution of these substances is corroborated by the fact that the other amides, such as oxamide, butyramide, etc., yield, with nitric charged with nitrous acid, decompositions analogous to those produced by as- partic acid and asparagin, and are converted into oxalic, butyric acid, etc., with disengagement of nitrogen. Phloridzin C^H^O^ 1496. Phloridzin exists in the fresh bark of the apple, pear, plum, and cherry tree, and is generally extracted from the bark of the roots of the apple, by digesting it in weak alcohol, when the phloridzin dissolves and separates by evaporation in silky aciculae, which are purified by recrystallization in alcohol. Boiling water dissolves a large quantity of phloridzin, while it scarcely retains Y^J part of it after cooling ; and alcohol dissolves it readily, the solution exerting no reaction on litmus. The solution of phlo- ridzin in alcohol exerts a rotatory power toward the left. It loses water when heated, and is subsequently decomposed at about 392. Dilute mineral acids dissolve phloridzin when cold, while if heat be applied the liquid becomes clouded, and deposits a new substance, phloretin C 12 H 7 5 , which is obtained in crystalline lamellae by solu- lution in alcohol. G-lycyrrhizin C 36 H 22 12 ,2HO. 1497. This name has been given to a sweet substance found in the aqueous extract of liquorice-root, (glycyrrhiza glabra^) from which it is extracted by adding to the concentrated liquid almost any acid, which yields a flaky precipitate collecting into a tarry mass. This substance, when dried, is dissolved in absolute alcohol, which again deposits it, by evaporation, in the form of an amorphous brownish-yellow mass. Glycyrrhizin is but slightly soluble in cold water, and nearly insoluble when the water contains an acid ; while it dissolves freely in absolute alcohol, but is insoluble in ether. Analysis has assigned to it the formula C 36 H 22 12 ,2HO, and its so- lution produces, with acetate of lead, a precipitate of the formula 2PbO,C 36 H aa 13 . NITRILS. 629 NITRILS. 1498. By causing anhydrous phosphoric acid to act on the am- moniacal salts formed by the organic acids, or on the corresponding amides, a new class of substances, called nitrils, is obtained, the com- position of which may be represented by cyanhydrates of carburetted hydrogen, and which regenerate, by the action of the alkalies, the acid of the original ammoniacal salt, by seizing on the water and disengaging ammonia. We shall give some examples of their curi- ous reactions. Acetonitril C 4 H 3 N. 1499. By heating crystallized acetate of ammonia with anhydrous phosphoric acid, a liquid is obtained soluble in water in all proportions. In order to purify it, it is first digested over chloride of calcium, and then distilled successively over chloride of calcium and calcined mag- nesia. The liquid, which is called acetonitril,* boils at 170.6, and its formula C 4 H 3 N corresponds to 4 vol. of vapour. In contact with hydrated potassa, ammonia and acetic acid are regenerated : C 4 H 3 N+4HO=C 4 H 3 3 ,HO+NH 3 . Potassium decomposes it when cold, cyanide of potassium being formed, and a mixture of hydrogen and carburetted hydrogen dis- engaged. Acetonitril appears to be identical with methylocyanohydric ether C 3 H 3 ,C 2 N, but alkalies do not act upon it as upon other compound ethers, since they convert it into acetic acid and ammonia. Acetonitril is also produced when acetamide C 4 H 3 2 ,NH 3 is heated with anhydrous phosphoric acid. Acetamide, which is obtained by treating acetic ether with ammonia, is white, and crystallizes in prismatic aciculse, melting at 172.4, and boiling at about 428. Chloracetate of ammonia (NH 3 , HO), C 4 C1 3 3 and chloracetamide C 4 Cl 3 3 ,NH a furnish, with anhydrous phosphoric acid, per chlori- nated aeetonitril C 4 C] 3 N, which boils at 177.8, and yields chlora- cetic acid, when the corresponding compound forms acetic acid. Butyronitril C 8 H 7 N. 1500. The butyrate of ammonia and butyramide, heated with anhydrous phosphoric acid, yield butyronitril C 8 H 7 N, an oily liquid, boiling at 245.3, and which potassium converts into cy amide of potassium, hydrogen, and a new carburetted hydrogen. Its for* mula CgHjN corresponds to 4 vol. of vapour. Valeronitril, C 10 H 9 N. 1501. Yaleramide, heated with anhydrous phosphoric acid, pro- duces valeronitril C 10 H 9 N,a colourless liquid, boiling at 257, which is decomposed by potassium, when cold, into cyanide, hydrogen, and a new carburetted hydrogen. * It may be termed methyocyanhydric acid. J.C.B. 3c2 630 DERIVATIVES OF CYANOGEN. PKODUCTS OF CYANOGEN. 1502. Cyanogen is always a product of the decomposition by heat, in the presence of alkalies, of nitrogenous organic substances. Its study, and that of its numerous derivatives, should therefore find a place among substances of the organic kingdom ; but its compounds play too considerable a part in chemical processes and are too fre- quently used in the examination of the salts of various metals to allow us to postpone their consideration until the end of the course. These reasons have induced us to describe, in the first part of our course, cyanogen and its compound with hydrogen, cyanohydric acid. We have seen that cyanogen behaves, in its compounds, like the simple metalloid substances, particularly like chlorine, and we have described in detail the principal compounds it forms with the metals, the simple and multiple cyanides, which are very important compounds, both on account of their use in dyeing, and in chemical analysis. It still remains to us to describe the compounds of cya- nogen with several metalloids, chlorine, iodine, oxygen, sulphur, and several more complicated combinations, which present some points of peculiar interest for our chemical theories. COMPOUNDS OF CYANOGEN WITH CHLORINE. 1503. As yet only two compounds of cyanogen with chlorine are known, the elementary composition of which is exactly the same, while their properties are wholly different, one of the compounds being gaseous at the ordinary temperature of our climate, and the other solid and boiling only at about 390. The gaseous chloride of cyanogen CyCl or C 3 NC1 is obtained by causing chlorine to act on moist cyanide of mercury, which reaction is expressed by the fol- lowing equation : HgCy+2Cl=HgCl-fCyCl. It is also prepared by passing a current of chlorine through a concentrated solution of cyanohydric acid, when the gaseous chlo- ride of cyanogen remains in solution, and may be disengaged by gently heating the liquid, the gas being dried by passing it over chloride of calcium. It is a colourless gas, of a strong odour, caus- ing tears, liquefying at about 10.4, and solidifying at 0.4. Thus, this substance passes through three states in a very small change of temperature. Water dissolves about 25 times its vol., and alcohol and ether 50 times its vol. of it. Liquid chloride of cy- anogen soon passes into the solid modification, called solid chloride of cyanogen. If, in fact, it be enclosed in a glass tube hermeti- cally sealed, it undergoes at first no change, and if the tube be broken, it is wholly evolved in the gaseous state, while, in a few days, long prismatic crystals, ultimately occupying the whole mass, will be found to be developed. If the tube be then broken, no gas is CYANURIC ACID. 681 disengaged, and we find only crystals melting at 284, and boiling at 374. Solid chloride of cyanogen is directly formed, when an- hydrous prussic acid is poured into a large bottle filled with dry chlorine and exposed to the sun. The density of the vapour of solid chloride of cyanogen is three times greater than that of the gaseous chloride, for which reason the formula CyCl has been as- signed to the gaseous chloride, and the formula Cy 3 Cl 3 to the solid. The equivalents of these substances are therefore represented by 4 gaseous volumes. The two chlorides of cyanogen combine directly with ammoniacal gas, and form solid compounds, of which the formulae are, For the gaseous chloride 2NH 3 ,CyCl. " solid chloride 3NH 3 ,Cy 3 Cl 3 . The first is soluble in water, and the second is insoluble. Two compounds of cyanogen with bromine and iodine are also known. COMPOUNDS OF CYANOGEN WITH OXYGEN. 1504. Four isomeric compounds of cyanogen and oxygen are known, cyanic acid, cyanuric acid, cyamelide, and fulminic acid, the first two of which appear to present the same relations of constitu- tion as the gaseous and solid chlorides of cyanogen. By digesting solid chloride of cyanogen with water, chlorohydric acid and a solid white substance, cyanuric acid Cy 3 3 , are formed : Cy 3 Cl 3 +3HO=3HCl+Cy 3 O s . The same compound is found under many other circumstances, and particularly when certain substances of animal origin are decom- posed. A solution of the substance in hot water again deposits it, on cooling, in crystals, which are hydrated and present the formula Cy 3 3 , 7HO, while, when dried at 212, the formula becomes Cy 3 3 3HO ; that deposited from a nitric or chlorohydric solution also present- ing the latter composition. The 3 equiv. of water are basic, and may be replaced partially or wholly by an equivalent quantity of base ; and, in fact, three series of cyanides are known, of which the general formulae are (RO+2HO),Cy 3 3 , (2RO+HO),Cy 3 3 , 3RO,Cy 3 3 . Cyanuric is therefore a tribasic acid. Cyanuric acid, heated in a small glass retort, passes over wholly in distillation, but is then deeply changed, for the distilled product forms a very volatile liquid, of an odour resembling concentrated acetic acid, and which reddens litmus and behaves like a powerful acid. Its composition is the same as that of cyanuric acid dried at 212, but it forms only one series of salts, and should be con- sidered as a monobasic acid. The formula CyO,HO has been 632 DERIVATIVES OF CYANOGEN. assigned to this acid, called cyanic, and to its salts the general formula RO,CyO. Cyanic acid is spontaneously converted into an isomeric substance, called cyamelide, while the transformation does not take place so long as the cyanic acid is kept at a very low temperature ; but, at the ordinary temperature, the liquid soon becomes clouded, while at the same time its temperature rises spontaneously, and it is con- verted into a solid mass, resembling porcelain. This is cyamelide, a wholly neutral substance, insoluble in water, alcohol, and ether, and which reproduces the original cyanic acid by distillation. Cyanic acid may also be transformed, directly, into cyanuric acid, by adding a small quantity of nitric or acetic acid to a concentrated solution of cyanate of potassa, which converts the salt into cyanurate. Cyanic acid may be prepared, directly, in several ways : 1. By passing cyanogen gas through a solution of potassa or car- bonate of potassa, cyanate of potassa and cyanide of potassium are formed, the reaction being similar to that of chlorine on alkaline lixiviae, when it converts them into hypochlorites, ( 450) : 2KO+2Cy=KO,CyO+KCy. 2. By heating a mixture of prussiate of potash and nitrate of potassa or peroxide of manganese, when cyanic acid passes over in distillation. The mixture may also be roasted in the air, and then treated with boiling alcohol, which dissolves the cyanate of 3. By fusing yellow prussiate of potash at a red-heat, and throw- ing litharge into the melted mass as long as the former is reduced. Boiling alcohol then dissolves the cyanate of potassa formed. The fourth isomeric modification of cyanic acid, fulminic acid, is formed under quite peculiar conditions. Mercury or silver being treated with a mixture of alcohol and nitric acid, a very powerful reaction ensues, and various products of the oxidation of alcohol pass into the receiver, among which may be distinguished aldehyde, acetic acid, formic acid, and nitrous, acetic, and formic ethers. A crystalline salt, which is the fulminate of mercury or silver, is de- posited in the retort. The composition of fulminic acid is the same as that of cyanic and cyanuric acids, but it is a bibasic acid, the formula of which should be written Cy 2 8 ,2HO, since it forms, in fact, two series of salts, of which the general formulae are (RO+HO),Cy 2 3 and 2RO, Cy 3 a . The formulae of the fulminates of mercury and silver are 2HgO,Cy 3 3 and 2AgO,Cy 3 3 ; and by treating the fulminate of sil- ver with potassa, only one-half of the silver is precipitated, while a double fulminate, of the formula (AgO+KO),Cy 3 3 , is obtained. The dry fulminates detonate with extreme violence, either by percussion or when heated. Fulminate of mercury is used in the manufacture of percussion caps for firearms. SULPHOCYANIDES. 633 They are prepared on a large scale, by dissolving 1 part of mer- cury in 12 of nitric acid of a density of 1.36, adding to the solution 11 parts of alcohol at 0.80, and then gently heating the mixture in a distilling apparatus, in order to condense the disengaged volatile products, which may be used in another operation. The liquid remaining in the retort deposits the fulminate on cooling. Metallic Sulpliocyanides and SulphocyanoJiydric Acid. 1505. By heating to a dull-red an intimate mixture of 2 parts of prussiate of potash and 1 part of sulphur, and then treating it with boiling alcohol, sulphocyanide of potassium KS,CyS is depo- sited in small crystalline aciculae ; and it may be regarded as a cyanate of potassa, in which the oxygen of the acid and the base is replaced by a corresponding quantity of sulphur. A larger quan- tity is obtained by heating 46 parts of prussiate of potash, 17 parts of carbonate of potassa, and 16 of sulphur, and treating the mass with boiling alcohol. If sulphocyanide of potassium be distilled with phosphoric acid, sulplwcyanohydric acid CyS,HS is obtained, a large proportion of which is, however, decomposed. Acetate of lead may also be poured into the solution of the sulphocyanide of potassium, when sulphocyanide of lead PbS,CyS is precipitated, and is decomposed by sulf hydric acid, a colourless acid liquor, reddening litmus, being formed. Free sulphocyanohydric acid, and the alkaline sulphocyanides, yield, with sesquisalts of iron, precipitates of a blood-red colour, which reaction is often used to detect these salts. By pouring into a solution of an alkaline sulphocyanide, 6 or 8 times its volume of concentrated chlorohydric acid, a deposit of small white aciculae is formed, which are to be washed with a small quantity of cold water. It is a new acid, called persulphocyanohy- dricj of the formula CyS 2 ,HS. This acid may be dissolved in boiling water, and is deposited from it, on cooling, in small crystalline aci- culae. It is a feeble acid, which combines directly, without altera- tion, under certain conditions, while under other conditions it is decomposed. Persulphocyanohydric acid, and sulphocyanohydrate of ammonia, yield, when heated, a great number of new substances, as yet but imperfectly known. 634 x ESSENTIAL OILS. ESSENTIAL OILS. 1506. A large number of volatile substances, possessing gene- rally a powerful and frequently an agreeable odour, adapting them for the toilet, are extracted from vegetables ; and the greater por- tion of them are liquid, while some are solid at the ordinary temper- ature. These substances are in general prepared by expressing the juice of the vegetables which contain them, and distilling it with water, when the essential oil passes over with the water, and, as it is generally less volatile than the latter, the proportion which passes over, compared with the quantity of water, is the greater as the difference between the boiling point of water and that of the oil is less. Parts of the vegetables themselves, the flowers for example, are frequently distilled with water, and when the essential oil is lighter than water, the products are collected in a bottle of peculiar shape, (fig. 684,) called &florence receiver. The bottle is conical, and has a lateral tube communicating with the bot- tom, and of which the orifice is at a lower level than the mouth a of the bottle. The water and oil distilled pass into the bottle through the mouth #, the oil forming the upper stratum ; and when the bottle is filled above the level of the orifice c, the water escapes through the lat- ter, and the essential oil floats on its surface, in a layer of a thickness in proportion to the diameter of the neck Fig. 684. O f t ke Bottle, and which is removed from time to time with a pipette. An ordinary alembic is used for distillation, but the vegetables subjected to the operation must not be allowed to reach a temperature above 212, in order to avoid the generation of empyreumatic products, which, distilling at the same time as the essential oil, would injure its flavour. In order to prevent these accidents, the vegetables are placed in bags, or metallic vessels pierced with holes, and kept above the liquid in the cucurbit, in the space traversed by the vapour. As the water which has distilled over with the essential oil gene- rally dissolves a small quantity of it, sufficient to impart to it its odour, it is carefully collected and sold. Thus, while distilling orange-flowers with water, a certain quantity of essence of orange- flower collects at the top of the florence receiver, while a water, possessing a very agreeable smell, and which is sold under the name of orange-flower water, is found under it. The quantity of essential oil which exists in the portions of vege- tables subjected to distillation is frequently so small that no sepa- rate oil can be obtained, but only an odoriferous water. The same TERPENTINE. 635 thing occurs when the boiling point of the essential oil is very high ; and in the latter case, the fresh water in the cucurbit is replaced by water saturated with salt, which boils at 230, and the vessel containing the flowers is suspended in this water ; when the tension of the vapour of the oil is necessarily greater in this hotter space, and a larger quantity of it passes over. Some essential oils would be very easily injured by heat, and at other times the flowers in which they exist contain alterable princi- ples, and the distilled oil is far from possessing the odour of the flower. They are then not distilled, and we are satisfied with sepa- rating the oil by dissolving it in a fixed oil, of itself inodorous, poppy-oil for example ; for which purpose the flowers are spread thinly over woollen cloths soaked in poppy-oil, when the cloths are piled on each other, and the whole placed under a press. Essential oils differ materially from each other, both in their com- position and chemical reactions ; and, if due regard be paid to the nature of the compounds from which they are derived, we are led to divide them among those series most differing from organic bodies. A great number of oils contain only carbon and hydrogen, while others also contain oxygen, and, lastly, some few contain sulphur. We shall therefore divide them into three groups, and include in the first, those oils which are composed of hydrogen and carbon alone ; in the second, those which contain, in addition, oxygen ; and in the third, the sulphuretted essential oils. HYDROCARBURETTED ESSENTIAL OILS. 150T. The composition of the greater number of these oils cor- responds to the formula C S H 4 , and we therefore here find a great number of isomeric substances, the chemical properties of which are so similar that recourse must be had to very delicate characters to prove their non-identity. The mobility of their molecular constitu- tion is such, that by distilling, or forming them into compounds from which they are subsequently separated, their nature is changed. Essential Oil of Terpentine or Te^ebethene C W ~H. 16 . 1508. This is the most important of the essential oils, on ac- count of its application in the arts, being used in the preparation of varnishes, and, in general, as a solvent for certain substances, which it deposits, by spontaneous evaporation, on the surface of bodies coated with the solution. A viscous substance, called terpentine, consisting essentially of a resin, colophony, or common resin dissolved in oil of terpentine, exudes from the trees of the family of the coniferse, chiefly from the pines. By distilling terpentine with water, the greater portion of the essential oil is carried over by the vapour of water, in which state it 'still contains a small quantity of resin, partly formed by the oxida- tion of the oil by contact with the air. In order to purify it, it is again distilled with water, dried by leaving it for some time over 636 ESSENTIAL OILS. chloride of calcium, and again distilled for the last time by itself, avoiding as much as possible the contact of the air. The essential oil extracted from the various terpentines of com- merce is far from being identical, and appears to vary according to the tree which has produced it. French oil of terpentine, produced by the pinus maritima which grows in the south of France, is a colourless, very volatile liquid, of a characteristic smell and an acrid and burning taste. Its density at 32 is 0.875, while the density of its vapour is 4.76 ; and if it be admitted that its equiva- lent is represented by 4 volumes of vapour, like that of the carbu- retted hydrogen hitherto described, its formula should be written C 20 H 16 . Oil of terpentine, which we -shall call, for brevity's sake, terebenthen* boils at about 300, the boiling point being rarely constant. It deviates polarized light to the left, while the various oils differ from each other in the intensity of their rotatory power ; some even producing deviation to the right, as the oil extracted from the pinus tada of Carolina, which is chiefly used in England. Moreover, the same terebenthen does not maintain an identical rotatory power when it is subjected to successive distillations, and its molecular constitution appears to be modified by the simple process of distillation ; these modifications being much more decided when the distillation is effected under high pressure, and, conse- quently, at a more elevated temperature. An oil of terpentine having been kept boiling, for several hours, under a pressure of 8 or 10 atmospheres, more than one-half of it was converted into an isomeric product which did not boil under 464. Terebenthen dissolves but slightly in water, communicating to it, however, its characteristic odour ; and it dissolves freely in alco- hol, ether, and the fixed oils. It dissolves a large proportion of sulphur, phosphorus, and several organic compounds. 1509. Terebenthen, left for a long time in contact with water, deposits colourless crystals, which have been improperly called hy- drate of terebenthen, because their composition corresponds to the formula C 20 H 16 6HO. A much larger quantity of this compound is obtained by leaving a mixture of 8 parts of oil of terpentine, 2 parts of ordinary nitric acid, and 1 part of alcohol at 0.80, to itself for several months, during which time it is frequently shaken ; when a crystalline magma is formed, which is expressed between tissue-paper, and redissolved in boiling water, from which it is de- posited in small prismatic crystals on cooling. By redissolving it in boiling alcohol, it yields large crystals, which melt at 217.4, while, at a more elevated temperature, they lose 2 equivalents of water, and form a new hydrate C 20 H 16 ,4HO, which distils at about 482 without change. The density of its vapour being 6.26, the equivalent C 20 H 16 ,4HO is represented by 2 volumes. * Called Camphine in the U. S., when purified by distillation. J. C. J3. TERPENTINE. 637 1510. Terebenthen combines readily with chlorohydric acid gas, and absorbs large quantities of it, with elevation of tempera- ture, the saturated liquid depositing crystals, on cooling, varying in proportion according to the nature of the oil, and which are purified by recrystallization in boiling alcohol. The crystals melt at 302, the substance boiling at about 338, with partial decomposi- tion ; and its composition corresponds to the formula C^H^HCl, showing it to be a Morohydrate of terebenthen^ which is some^ times called artificial camphor : it deviates the plane of polariza- tion to the left. The liquid which floats on the crystals, in the preparation of artificial camphor, is itself a liquid chlorohydrate of terebenthen^ of the same composition as the solid chlorohydrate, but which does not solidify at any temperature. If solid chlorohydrate of terebenthen be passed over caustic lime heated to redness, a liquid carburetted hydrogen separates from it, having the same composition and boiling point as the ori- ginal terebenthen, but differing from it by exerting no action on polarized light : it has been called camphilen. It also combines with gaseous chlorohydric acid, yielding, at the same time, a solid and a liquid chlorohydrate ; and it is therefore composed of at least two , distinct liquids, like terebenthen itself. By decomposing the liquid chlorohydrate of terebenthen by means of lime, an essen- tial oil is separated having no action on polarized light, and yield- ing only liquid chlorohydrate with chlorohydric acid, which new oil has been called terebilen. Bromohydric and iodohydric acids pro- duce compounds similar to those of chlorohydric acid. 1511. Terebenthen undergoes very curious isomeric modifica- tions by contact with sulphuric acid. By mixing, in a well-cooled flask, oil of terpentine with about ^ of its weight of sulphuric acid, and leaving the mixture to itself during 24 hours, shaking it fre- quently, a red and viscous liquid is obtained ; and after allowing it to rest for some time, the supernatant oil is decanted, when a black residue, saturated with acid, remains in the flask. If the decanted oil be distilled, a small quantity of sulphurous acid first passes over, and then an essential oil, having the same composition, density, and boiling point as terebenthen, but differing from it in exerting no rotatory power on polarized light, and in forming with chlorohy- dric acid gas a compound of the formula 2C 30 H 16 ,HC1, which con- sequently contains one-half less chlorohydric acid than the chlo- rohydrate of terebenthen. This essential oil has been called tereben. The essential oil modified by sulphuric acid is not solely com- posed of tereben, and when it has separated by distillation, and the temperature is raised to 590, a new product is obtained, composed of a viscous oil, which is bleached by being distilled over an alloy of potassium and antimony, ( 1017). This liquid is highly dichroic ; light which passes through it normally being colourless, while that VOL. II. 3 D 638 ESSENTIAL OILS. obliquely refracted by it, particularly at certain angles of incidence, exhibits a beautiful indigo colour. Its density is 0.940 at 48.2, and it has no rotatory power. It absorbs chlorohydric acid , gas, but without forming any fixed compound, for carbonate of lime readily abstracts the chlorohydric acid. The name of colophen has been given to this gas, the composition of which is the same as that of terebenthen ; and large quantities of it are obtained by the direct distillation of resin. Chlorine acts powerfully on terebenthen and its isomeric com- pounds, chlorohydric acid being disengaged, while a viscous, co- lourless liquid is formed, having the smell of camphor, and which is quadrichlorinated terebenthen, its formula being C^H^Cl^ Oil of Lemons, or Citrene C SO H 16 . 1512. Lemon-peel contains an agreeable-smelling essential oil, of an identical composition with terebenthen, and which we shall call citren. It may be extracted by expressing the yellow part of the lemon peel, but it is more generally separated by distilling the peel with water, in which case the smell of the oil is, however, less, grateful. Citren boils at about 338, and its density is 0.847 at 71.6, while the density of its vapour is the same as that of tere- benthen, for which reason it has received the same formula C^Hjg ; but it polarizes to the right. It combines with chlorohydric- gas forming a liquid and a solid chlorohydrate having the same composi- tion. These chlorohydrates of citren contain twice as much chlo- rohydric acid as the chlorohydrate of terebenthen, and their for- mulae is therefore C 20 H 16 ,2HC1. Oil of Oranges, or Oil of Neroli C 20 H 16 . 1513. Orange-peel, like lemon-peel, contains an essential oil, to which it owes its fragrance, and of which the formula C 2p H 16 is the same. It yields, with chlorohydric acid, a solid and a liquid product, of an identical composition with the chlorohydrates of citren ; and it polarizes to the right. In the bergamot, in juniper-berries, in the seeds of parsley, and many other vegetables, essential oils of the composition C 5 H 4 are found, but which are distinguished by certain chemical properties, and by their rotatory powers, from the essential oils just described. Es- sential oils of bergamot, Seville oranges, cedrat, caraway, and limes rotate toward the right. Essential oils of the same composition are obtained in the distillation of several organic substances. Certain kinds of bitumen yield a yellowish liquid, petrolen, which may be made perfectly colourless by distilling it over potassium, and pre- senting the same composition with oil of terpentine. But as it boils at 536, and the density of its vapour is double, its formula should be written C 40 H 33 . CAMPHOR. 639 OXYGENATED ESSENTIAL OILS. 1514. These oils being numerous, and their chemical properties very various, we shall describe only the most important and best known of them. CAMPHORS. 1515. The name of camphors, or stearoptens, has been given to neutral compounds, solid at the ordinary temperature, volatile, hav- ing an odour resembling those of ordinary camphor, and applicable to the same uses. We shall here treat only of the camphor from Japan and that from Borneo. Japan Camphor C^H^O^. 1516. Japan camphor is extracted from the laurus camphora, the wood of which tree contains it so abundantly that small crystals of it are seen in the fissures. The trunk and branches are split into small pieces and distilled with water in iron boilers, covered with an earthen capital filled with straw or small twigs, on which the cam- phor sublimes and crystallizes in the shape of crude camphor. It is distilled with a small quantity of lime and charcoal in flat-bottomed vessels, resembling those used for the sublimation of chlorohydrate of ammonia, ( 516,) when the camphor sublimes at the upper part, and forms crystalline, colourless, and transparent masses, such as are found in commerce. At the ordinary temperature, the tension of the vapour of camphor is very feeble, and, nevertheless, it ex- hales an intense and characteristic odour ; while, when kept in a close-stoppered bottle, the vapour condenses on its sides, and forms small brilliant crystals, remarkable for their sharpness. Camphor melts at 347, and boils at about 410, its density being 0.986, and the density of its vapour 5.32. From its great elasticity it is very difficult to pulverize. Its chemical composition corresponds to the formula C 10 H 8 0, which is generally written C 20 H 16 3 ; its equivalent then corresponding to 4 volumes of vapour. Camphor is slightly soluble in water, but dissolves more freely in alcohol, ether, and concentrated acetic acid, and it burns with a white and smoky flame. Camphor obtained from the family of the laurels, when dissolved in alcohol, rotates toward the right. Chlorine does not act readily on camphor, but when dissolved in chloride of phosphorus PC1 3 , and subjected to the action of chlorine, it yields chlorinated camphor C 20 H 10 C1 6 3 , which is separated from the perchloride of phosphorus by washing it with water and weak solutions of carbonate of potassa. Camphor absorbs chlorohydric acid gas, and yields a colourless liquid of the formula C 20 H 16 2 ,HC1, which is readily destroyed by water, while camphor separates from it. 1517. Alkaline solutions exert no action upon camphor, but if its 640 ESSENTIAL OILS. vapour be passed over potassic lime heated to 750 in a glass tube, an acid called campholic is formed, which combines with the alkaline substance, and which is then separated by dissolving in water and supersaturating with chlorohydric acid. The precipitated cam- phoric acid is dissolved in a mixture of alcohol and ether, from which it separates in crystals, melting at 176, and boiling at 482. It is insoluble in water, but very soluble in alcohol and ether. When crystallized, its formula is C 20 H 18 4 , or more properly C 20 H 17 3 ,HO, which corresponds to 4 volumes of vapour, for the density of the vapour of campholic acid is 5.9. The formula of campholic acid differs from that of camphor only by containing, in addition, the elements of 1 equiv. of water. The formula of campholate of silver is AgO,CH B 0,. Campholate of lime CaO,C 30 H 17 3 is decomposed by heat into carbonate of lime and a peculiar liquid called campholone C 19 H 17 0. CaO,CJI 1J 0,..CaO,CO,+ C I ,H 17 0. Campholic acid, distilled with anhydrous phosphoric acid, gives off water and carbonic acid, while a carburetted hydrogen C 18 H 16 , called campholen, which boils at 275, is formed. 1518. Cold nitric acid dissolves camphor, and parts with it when diluted with water, while, by the application of heat, a peculiar acid, called camphoric, is developed. In order to prepare this acid, camphor is boiled for a long time with 10 times its weight of nitric acid, and as the latter distils over, it is collected and poured back into the retort. At the close of the operation, the excess of nitric acid is driven off by evaporation, when the camphoric acid separates in a crystalline mass, which is purified by dissolving it in carbonate of potassa, and again separating it by means of nitric acid. Cam- phoric acid is moderately soluble in boiling water, the greater por- tion of it separating during cooling, while alcohol and ether dissolve it readily. Its composition corresponds to the formula C^H^O,, ; and the camphor, by being converted into camphoric acid, combines therefore with 6 equiv. of oxygen, which it takes from the nitric acid. The formula of camphoric acid should be written C 20 H 14 6 , 2HO, because it is a bibasic acid, and the general formula of its salts is 2RO,C 20 H 14 6 . When heated it is decomposed into water and a crystallized substance, boiling at 518, which, from its com- position C 20 H 14 6 , may be regarded as anhydrous camphoric acid. Camphoric acid, dissolved in alcohol, rotates toward the right. 1519. A species of camphor is extracted from the labiates, which, in its chemical composition, appears identical with the camphor of the laurels, but which rotates toward the left. Borneo Camphor C 20 H 18 2 . 1520. From the dryabalanops camphora exudes a more or less viscous oil, containing a crystallizable substance, of which the pro- CAMPHORS. 641 perties are analogous to those of Japan camphor. It has been called Borneo camphor, and is often found crystallized in old trunks of the tree of the dryabalanops camphora. The camphor imported from Borneo and Sumatra is in small, crystalline, colourless, and trans- parent fragments, insoluble in water, but dissolving freely in alcohol and ether. It melts at about 383, and boils at about 419. Bor- neo camphor differs from Japan camphor only by containing 2 ad- ditional equiv. of hydrogen, which are consumed by heating it with nitric acid ; the Borneo being converted into Japan camphor. The liquid portion of the essential oil of the dryabalanops camphora is essentially composed of a liquid carburetted hydrogen C^H^, called borneen, boiling at about 320, and isomeric with oil of terpentine, similarly to which it polarizes to the left, its rotatory power being much greater. Nitric acid, after some time, and assisted by gentle heat, converts borneen into Japan camphor, probably by the mere absorption of oxygen. Of some other Stearoptens analogous to Camphor. 1521. Stearoptens, exhibiting properties analogous to the cam- phors, are found in a great number of vegetables ; but we shall only mention them, for as yet they possess but little interest, and are but little known. Peppermint contains a stearopten of the formula C 2Q H^ 2 , called menthen C^Hj , which boils at 325.4. Oil of mint rotates toward the right. Oil of cedar is composed of a crystallizable substance C 32 H 26 3 , and a liquid carburetted hydrogen, cedren C 3 H 24 , which boils at 478.4. Oil of absinth, when purified, boils at 399. 2, and rotates to- ward the right : its formula being C^H^Oj, it is isomeric with Japan camphor. The root of elecampane (inula hellenium] contains a white crys- tallizable substance, helenin, very soluble in alcohol and ether, melt- ing at 161.6, boiling at about 536, and presenting the formula C<.H,O.. An essential oil, composed of a liquid portion and a portion which solidifies at 9.5, is extracted from roses; but the composition of the two substances is not exactly known. Oil of lavender contains a considerable proportion of Japan cam- phor, and a volatile oil, the essential oil properly so called, which has been used in the arts. BENZOIC SERIES. Oil of Bitter Almonds C 14 H 6 2 . 1522. Bitter almonds contain an essential oil, and a non-vola- tile fatty oil, which latter is expressed by subjecting them to pres- sure ; and if the pulp moistened with water be then distilled in an 3D2 41 642 ESSENTIAL OILS. alembic, a volatile oil, which falls to the bottom of the receiver, passes over with the water. This is the oil of bitter almonds, mixed with cyanohydric acid and two new substances, benzolne and ben- zoic acid, which shall soon be described. They are separated by distilling the crude oil with lime and protosulphate of iron, reduced to a paste with water ; the distilled oil being removed with a pipette, and again distilled in a glass retort, collecting separately the first portions, which contain water. Oil of bitter almonds is a colourless, very fluid liquid, having a peculiar odour resembling that of cyanohydric acid ; and its density is 1.043, while it boils at 348.8. Water dissolves about ^ of its weight of it, while it is indefinitely soluble in alcohol and ether. Its formula is C 14 H 6 2 , and it exerts no rotatory power. Oil of bitter almonds rapidly absorbs the oxygen of the air, and is converted into benzoic acid C 14 H 5 3 ,HO, C lt H 3 +20=C 14 H 9 3 ,HO. Anhydrous benzoic acid is therefore derived from the oil of bitter almonds, by the substitution of 1 equivalent of oxygen in the place of 1 equivalent of hydrogen. Benzoic acid is also formed when oil of bitter almonds is boiled with a solution of potassa ; the hydrated potassa converting, at a high temperature, the oil of bitter almonds wholly into benzoic acid, hydrogen being at the same time disen- gaged. Chlorine, in contact with water, effects the transformation in a very short time. 1523. Dry chlorine acts powerfully on oil of bitter almonds, disengaging chlorohydric acid. When the evolution of the gas has ceased, the liquor is heated to drive off the dissolved chlorine, and a liquid of a penetrating and disagreeable odour is obtained, of the density 1.106, and boiling at 383, which is monochlorinated oil of bitter almonds C 14 H 5 C10 2 . Water, particularly when hot, decom- poses it, forming chlorohydric and benzoic acids : C 14 H 5 C10 2 +2HO=C 14 H 5 3 ,HO+HC1. It has not yet been ascertained if the oil of bitter almonds forms still more chlorinated products with chlorine. Bromine converts it into monobrominated oil C 14 H 5 Br0 2 ; and monoiodinated oil C 14 H 5 I0 3 is obtained, crystallized in laminae, by distilling the monochlorinated oil over iodide of potassium. By replacing the iodide of potassium by sulphide of lead, or cyanide of mercury, a mono sulphuretted oil C 14 H 5 S0 2 , or a monocyanuretted oil C 14 H 5 Cy0 2 , is obtained. Some chemists take a different view of the composition of these various bodies, and admit the existence of an hypothetical radical C 14 H 5 ? , called benzoyl, which, combined with hydrogen, constitutes the oil of bitter almonds C 14 H 5 2 ,H, thus forming a hydruret of benzoyl, while benzoic acid is the oxide of benzoyl C 14 H 5 2 ,0. The chlori- nated, brominated, cyanuretted, and sulphuretted oils are chlorides, bromides, sulphides, and cyanides of benzoyl. BENZOIC SERIES. 643 1524. The chlorinated oil of bitter almonds absorbs a large quantity of ammoniacal gas, and is converted into a white crystal- line compound C 14 H 7 N0 3 , or benzamide : C 14 H 5 C10 2 +2NH 3 =NH 3 ,HCH-C 14 H 5 2 ,NH 2 . By treating the solid product of the reaction with water, the am- moniacal salt which formed during the operation is dissolved, while the benzamide alone remains, and may be crystallized from its solu- tion in alcohol. The relation of benzamide C 14 H 5 2 ,NH 3 with the benzoate of ammonia (NH 3 ,HO),C 14 H 5 3 is the same as that of sul- phamide S0 3 ,NH 3 with sulphate of ammonia (NH 3 ,HO),S0 3 . Benzamide dissolves in boiling water, and separates from it, on cooling, in crystals, which melt at 239, and boil without change at a higher temperature. Benzamide, treated with a cold alkaline lye, undergoes no change, while at the boiling point it yields ben- zoate of potassa and ammonia. Sulphuric acid also decomposes it, sulphate of ammonia and benzoic acid being formed. 1525. The oil of bitter almonds, kept for several weeks at a temperature of 100 to 120, with 20 times its volume of an aqueous solution of ammonia, gives rise to a large number of crystals, which are obtained isolated by removing the unaltered oil by ether. They are dissolved in cold alcohol, which, by evaporation, deposits them in a pure state, when their composition is represented by the formula C 42 H 18 N a . It has been called hydrobenzamide, and its formation is represented by the following equation : 3,C 14 H 6 O a +2NH 3 =C 42 H 18 N 2 +6HO. Hydrobenzamide, dissolved in alcohol, is readily converted, by boiling, into ammonia and oil of bitter almonds. If hydrobenzamide be boiled with a solution of caustic potassa, crystalline flakes are formed, which, by recrystallization in alcohol, furnish colourless crystals of the formula C 42 H 18 N 2 , like that of the original hydroben- zamide, but which differ from it widely in its properties. This new sub- stance, called amarin, is a true organic base, which forms crystal- lizable salts with the acids. The formula of chlorohydrate of amarin is C^HJSF^HCl+HO, while that of the nitrate, which is but slightly soluble in water, is 1526. By adding chlorohydric acid to water which has distilled with the oil of bitter almonds in the preparation of the latter sub- stance, and evaporating it to dryness at a gentle heat, the residue is composed of chlorohydrate of ammonia, and a peculiar substance, called formobenzoylic acid, 'which is removed by dissolving it in ether, when it is deposited after evaporation in the form of crystal- line spangles, having the smell of bitter almonds and a strongly acid reaction. This substance dissolves readily in water, alco- hol, and ether, and its composition corresponds to the formula C 18 H 8 6 , or rather C 16 H 7 5 ,IIO, the equivalent of water being 644 ESSENTIAL OILS. replaced, in the salts, by 1 equivalent of base. The formula of the acid may be written C 14 He0 2 ,C 2 H0 1 ,HO, which would represent it as formed by the combination of 1 equivalent of oil of bitter almonds and 1 equivalent of formic acid ; and such, in fact, is the constitu- tion assigned to it by its behaviour in a great number of chemical reactions : thus, with oxidizing reagents, it yields carbonic acid, pro- duced by the combustion of the formic acid and oil of bitter almonds. Benzoic Acid C 14 H 3 3 ,HO. 1527. Oil of bitter almonds rapidly absorbs the oxygen of the air, and is converted into benzoic acid C 14 H 5 3 ,HO, which same transformation is effected by exposing the oil to oxidizing reagents. Benzoic acid is also extracted from a large number of vegetable and animal substances, in which it generally does not exist already formed, being the product of chemical reactions. In the laboratory it is obtained from the resin of benzoin, by various processes, the most simple of which consists in placing in an earthen or cast-iron capsule 1 kilog. of coarsely powdered benzoin, covering the capsule with a sheet of tissue-paper, the edges of which are pasted to the vessel, and then surmounting it with a pasteboard cone. The cap- sule being heated in a sand-bath for 8 or 4 hours, the vapours of benzoic acid condense on the sides of the cone, after having tra- versed the tissue-paper, which retains a small quantity of the empy- reumatic oily substances, which would injure the product. This process yields very pure benzoic acid, in the form of snow-white crystals of an agreeable odour, but furnishes only a small portion of the acid which the benzoin contains ; 1 kilog. of benzoin yielding only 40 gm. of benzoic acid. By the following process, as much as 140 gm. of benzoic acid may be obtained from the same quantity of benzoin. The resin of benzoin, finely powdered, is mixed with J of its weight of carbonate of soda, and a sufficient quantity of water to make a liquid paste, which is gently heated for several hours, stirring it continually to prevent the melting of the resin. It is then heated with a larger quantity of water, to dissolve the benzoate of soda, and the benzoic acid is separated by the addition of a proper quantity of sulphuric acid. The resin of benzoin may also be treated with 3 times its weight of alcohol at 0.75, and the benzoic acid saturated with carbonate of soda dissolved in 8 parts of water ; and 2 parts of alcohol being finally added, the liquid, when decanted, is distilled in order to separate the greater portion of the alcohol. The resin which was dissolved in the alcoholic liquor separates, while the solution only contains the benzoate of soda, which is decomposed by sulphuric acid, when the benzoic acid separates almost wholly from the liquor when cool. By this method, 1 kilog. of benzoin will yield as much as 180 ) gm. of benzoic acid. BENZOIC SERIES. 645 Benzole acid crystallizes in lamellae or in flexible and brilliant silky aciculse ; and it has, of itself, but little odour, while it gene- rally preserves the smell of benzoin, particularly when it has been prepared by simple distillation. It weakly reddens litmus, melts at 248, and boils at 464, exhaling copious vapours already at a tem- perature of 300 or 400. The density of its vapour being 4.27, its equivalent C 14 H 8 3 HO corresponds to 4 volumes of vapour. It re- quires for its solution 25 parts of boiling and 200 parts of cold water, while it dissolves in 2 parts of alcohol, and is also very solu- *e in ether. ^he general formula of the benzoates is RO,C 14 H 5 3 . The ben- ! a ^?f potassa, soda, and ammonia, are very soluble in water, and crys a i^ w ^ Difficulty, rp^ be nzoate of lime is very soluble in Th ^1? Cr ' t 1 ^ 6 co ^ water reta i ns on ly about ^ of its weight of it. ie ^ enzoa A g jj ver j s p re p are d by double decomposition, by pouring a hot so^ i()n of nitrate of silver into a boiling S0 i ut i n of an alkaline benzoa. when the beT170ate of gilver Ag O,C 14 H 5 3 is precipitated, during t, cooli in the form of colom !f ess ^ 4 ee | le 3 s . Chlorine acts on benzc, ^ when asslbwd b the of ^ sun, and produces chlonnai^ benzo i c acid, retail e the principal properties and capacity of satu ation O f f ree benzoic acid the same products being obtained by heati^ be nzoic acid with the alkaline hypochlorites or with mixtures of cij oro hydric acid and chiov ? , te O f potassa. Two chlorinated benzoic aci&s have been obtained in o^ s manner : Monochlorinated benzoic acid, Terchlorinated " " , C 14 H 4 C10 3 ,HO. C 14 H 2 C1 5 3 ,HO. Vinolenzoio Ether C 4 H 5 0,C 14 H 5 0, Fig. 685. 1528. In order to ^epare this ether, 2 parts of alcohol, 1 krt of ben- zoic acid, and 6 parts of coWntrated chlorohydric acid are heated^n a dis- tilling apparatus, the liquid a( distils being returned several fones to the retort ; when the benzoic i^id is thus almost wholly converted ii zoic ether. But it is better to ai the operation as represented in fig. the mixture is placed over a water-1 in a flask A which is made to commi nicate with a refrigerator so arrange^ as to allow the distilled liquid to gra-\ dually fall back again. The liquid is treated, first with water, and then with a weak solution of carbonate of soda to remove the free benzoic 646 ESSENTIAL OILS. acid, after which the benzoic ether is dried by digesting it over chloride of calcium. Benzoic ether is a colourless liquid of an oleaginous consistence, boiling at 410, and of the density 1.054 at 50. The density of its vapour being 5.41, its equivalent corresponds to 4 volumes of vapour, and it is insoluble in water, but soluble in all proportions in alcohol. Methylbenzoic Ether C 2 H 3 0,C 14 H.0 3 . 1529. By replacing, in the preceding operation, vinic by me- thylic alcohol, methylbenzoic ether* is obtained as an oily liqu^ boiling at 226.4. Sulpholenzoic Acid (C 14 H 4 3 ,S 2 5 ),2HO. 1530. If vapour of anhydrous sulphuric acid be r' 1 ' ? 6 / into a dry and well-cooled flask containing benzoic acid * *}& mass is formed, which is afterward treated with w^ *? f lss lv 7 e z the monohydrated sulphuric acid, and a peculiar *% caU , ed i SP* p ^ zoic, while the benzo- acid is separated an an g ed ; ^ a cid liquid is satura^ with carbonate of 3 wh , en sulphobenzoate of baryta ^o ne remains in the li^- B ? adding chlorohydnc acid, crystals of acid sulphob^ zoate f baryta (BaO-f-HO), (C H^A^s) separate, whicfe ** e redissolved in boiling water and a nr0 4 id 4 crystallized by cooliag- Sulphobenzoic acid may be sepa- rated by decomposing a solution of this salt with sulphuric acid added by drops : it is ve r y soluble in water, remains undecomposed even at 300, and nw be obtained in a crystalline form by evapo- ration. Sulphoben/oic aoid forms two series of salts of which the general formulae are 2RO,(C H H 4 3 ,S !! 0) S (RO+HO),(C 14 H 4 3 ,S 2 S ). It is the^fore a bibasic salt. It wi) be seen that when benzoic acid C 14 H 5 3 ,HO is treated with anhydrous sulphuric acid, 2 equivalents of the latter enter into the new expound, but only after having parted with 1 equivalent of oxyg-n, which has formed water with 1 equivalent of hydrogen givei off by the benzoic acid ; according to the equation C 14 H 5 3 ,HO+2S0 3 =(C 14 H 4 3 ,S 2 3 ),2HO. Nitrolenzoic Acid C 14 H 4 (N0 4 )0 3 ,HO. 1531. Dilute nitric acid does not act readily on benzoic acid, * More properly called benzoic metker. W. L. F. BENZOIC SERIES. 647 but if the fuming acid be used, and in great excess, the benzoic acid is dissolved with the disengagement of nitrous vapours, and the liquid deposits, on cooling, crystals of nitrobenzoic acid C 14 H 4 (NOJ0 3 ,HO, which is purified by recrystallizations. Nitrobenzoic acid is but slightly soluble in cold, but much more so in boiling water ; and dissolves freely in alcohol and ether. If crystallized into benzoate of lime, it takes the formula CaO,C 14 H 4 (N0 4 )0 3 +2HO, and that of baryta, BaO,C 14 H 4 (N0 4 )0 3 +4HO. From its composition it may be admitted that the molecule of nitrobenzoic acid C 14 H 4 (N0 4 )0 3 ,HO is merely that of benzoic acid C 14 H 5 3 ,HO in which 1 equivalent of hydrogen has been replaced by the compound (N0 4 ) ; and many cases will subsequently be met with in which the same substitution may be admitted. If a current of chlorohydric acid gas be passed through an alco- holic solution of nitrobenzoic acid, nitrobenzoic ether C 4 H 5 0,C 14 H 4 - (N0 4 )0 3 is formed, which separates in colourless crystals, fusible at 116.6, and boiling at about 570. Binitrobenzoic Acid C 14 H 3 (N0 4 ) 2 3 ,HO. 1532. By digesting at a gentle heat 1 part of benzoic acid with 12 or 15 parts of a mixture, in equal proportions, of Nordhausen sulphuric acid and fuming nitric acid, we effect the substitution, in the molecule of benzoic acid C 14 H 5 3 ,HO, of 2 equivalents of the compound N0 4 for 2 equivalents of hydrogen, and obtain binitro- benzoic acid C 14 H 3 (N0 4 ) 2 3 ,HO. Bromolenzoic Acid C 14 H 5 Br0 4 ,HO. 1533. By introducing into a very dry bottle benzoate of silver, and bromine contained in an open tube, and leaving it to itself after having closed the bottle, the benzoate of silver absorbs the vapours of bromine, bromide of silver being formed, while the ben- zoic acid combines, at the same time, with the equivalent of oxygen given off by the silver and with 1 equivalent of bromine. By treating it with ether, only the new acid C 14 H 5 Br0 4 ,HO, dissolves, which remains in the form of a crystalline mass. It is important to remark that bromobenzoic acid has not preserved the constitution of benzoic acid, but that it is formed by the addition, and not the substitution, of new elements. Benzoate of Oil of Bitter Almonds. 1534. When moist chlorine is passed through oil of bitter almonds, crystals insoluble in water, but very soluble in alcohol, are, after some time, developed in it. The composition of this substance may be represented by the formula (2 C 14 H 6 O a ,C 14 H 5 3 ); 3 mole- cules of the oil being grouped into one, after one of these molecules 648 ESSENTIAL OILS. has been converted into benzole acid, by the oxidizing action of the moist chlorine. Its composition would therefore be analogous to that of acetal ( 1368) and of methylal, ( 1432.) Benzoin C 14 H 6 2 . 1535. If crude oil of bitter almonds be shaken with an alco- holic solution of potassa, the oil sets, in a few minutes, into a crys- talline mass ; the presence of a certain quantity of cyanohydric acid being necessary to the transformation. The new substance is crystallized by purifying it in alcohol. This substance, to which the name of benzoin has been given, presents exactly the same composition as the oil of bitter almonds, melts at 248, and may be distilled without change. Though insoluble in cold, it is slightly soluble in boiling water, and rather freely so in alcohol. Melted with hydrate of potassa, it yields benzoate of potassa. If it be left, for a long time, with an aqueous solution of ammonia, a white powder is formed, nearly insoluble in water, alcohol, and ether, which has been called benzo'inamide, and presents the formula C 43 H 18 N 2 : it may be supposed to be formed by means of 3 equivalents of ben- zoin 3(C 14 H 6 2 ) and 2 of ammonia, from the equation 3C 14 H 6 2 +2NH 3 =0 4J H 1S N 2 +6HO. 1536. Benzoin dissolves when heated with nitric acid, and a new substance of the formula C 14 H 5 3 , separates after cooling, called benzil) which therefore results by the simple abstraction of 1 equivalent of hydrogen from the benzoin. The same compound is obtained when chlorine is caused to act upon benzoin heated to fusion, when the equivalent of hydrogen is disengaged in the state of chlorohydric acid. Benzil is crystallized by purifying it in al- cohol, and is a ^lightly yellowish substance, melting at about 194. Benzil is not changed, even at the boiling point, by an aqueous solution of potassa, while in contact with an alcoholic solution of the same alkali, it abstracts 1 equivalent of water, and is converted into an acid, called benzilic, of the formula CggH^Og, which results from the combination of the elements of 2 equivalents of water with 2 equivalents of benzil : The same acid is formed by heating benzoin with an alcoholic solution of potassa, saturating the hot solution with chlorohydric acid, and allowing it to cool, when benzilic acid is deposited in crys- tals. It melts at 248, and decomposes at a higher temperature, giving off a certain quantity of benzoic acid. Benzine C^Hg 153T. When benzoic acid C 14 H 5 3 ,HO is heated with 3 times its weight of hydrate of lime, carbonate of lime is formed, while a BENZOIC SERIES. 649 colourless, very volatile liquid, of the formula C 13 H 6 , and called benzine, distils over, which is rectified over quicklime. The reaction is expressed by the equation 14 H,O s ,HO-2(CaO,CO,)+0 1 ,H,. Benzine is also formed when benzoic acid in vapour is passed through a tube filled with fragments of pumice-stone and heated to redness ; benzine and carbonic acid alone being formed : C I4 H 5 3 ,HO=C 12 H 6 +2CO,. Benzine is also produced by the decomposition of a great number of organic substances by heat : thus, a considerable proportion of it is found in the volatile oils formed in the manufacture of illuminat- ing gas. Benzine boils at 186.8, and its density is 0.85, while that of its vapour is 2.38, its equivalent corresponding to 4 volumes of vapour. At 32 it sets into a crystalline mass, which melts only at 44.6 ; and it is insoluble in water, but very soluble in alcohol and ether. Benzine is easily acted on by dry chlorine, when exposed to the rays of the sun ; and if it be poured into a large well-dried bottle, filled with chlorine, and the bottle be exposed to the sun, it becomes filled with white vapours, while the sides are covered with white crystals of the formula C 12 H 6 C1 . The behaviour of this substance with an alcoholic solution of potassa leads us to write its formula C 12 H 3 C1 3 ,3HC1 ; the solution, in fact, decomposing it by abstracting 3HC1 ; while, if the liquid be diluted with water, an oily and co- lourless liquid, insoluble in water, and of the formula C 12 H 3 C1 3 , separates, the density of the vapour of which being 6.37, its equiva- lent corresponds to 4 volumes. This is therefore terchlorinated benzine, and the crystalline substance formed by the direct action of chlorine on benzine may be regarded as a terchlorinated trichlo- rohydrate of benzine. This same decomposition of the crystalline compound takes place when it is distilled several times alone, or still better, over lime. Bromine yields with benzine an analogous product C 14 H 3 Br 3 , 3HBr, which, with the alcoholic solution of potassa, also produces terbrominated benzine 14 H 3 Br 3 . 1538. Common nitric acid acts but feebly on benzine, while if it be heated with the fuming acid, it dissolves, and an addition of water precipitates from it a yellowish liquid C 12 H 5 (N0 4 ), nitroben- zine. It may be granted that this substance is formed by the sub- stitution of 1 equivalent of the compound N0 4 for 1 equivalent of hydrogen of the benzine. Nitrobenzine solidifies at 32, and melts only at 37.4, while it boils at 415.4 without change. By causing a large excess of fuming nitric acid to act for a long time on benzine, we can succeed in replacing 2 equivalents of hy- drogen by 2 equivalents of the compound (NOJ, and producing VOL. II. 3 E 650 ESSENTIAL OILS. binitrobenzine C 12 H 4 (N0 4 ) 2 , which, by the addition of water, is precipitated in the form of a crystalline powder. By crystallization in alcohol, it is obtained in large brilliant lamellae. By subjecting nitrobenzine and binitrobenzine to certain re- ducing agents, they are converted into two very remarkable sub- stances : anilin C 13 H 7 N, and nitranilin C 12 H 6 (N0 4 )N, which are true volatile organic bases. Sulphobenzinic ac^C 12 H 5 ,S 2 5 ,HO, and Sulphobenzine C 12 H S ,S0 2 . 1539. Benzine is not appreciably acted on by ordinary sul- phuric acid, while the anhydrous acid dissolves it with elevation of temperature, a viscous liquid being formed, which, when treated with water, deposits a crystalline precipitate, sulphobenzine, and pro- duces a solution containing, with ordinary sulphuric acid, a new acid, called sulphobenzinic. Sulphobenzine should be purified by crystallization in alcohol, after which it is a colourless substance, melting at 212, and boiling at about 750, without change. Its formula is C 14 H 6 ,S0 2 , and the following equation expresses the reaction which produces it : C ia H 6 +2S0 3 =C 12 H 5 ,S0 3 +S0 3 ,HO. By saturating the acid liquid with carbonate of baryta, the free sulphuric acid is precipitated, and a solution of sulphobenzinate of baryta is obtained. By pouring sulphate of copper into the latter, this salt is converted into sulphobenzinate of copper, which crystal- lizes readily according to the formula CuO^C^H^S/),.). When decomposed by sulf hydric acid, it produces isolated sul- phobenzinic acid, a very acid liquid which may by crystallized by evaporation. Benzone C 13 H 5 0. 1540. When benzoate of lime is subjected per se, without any addition of an excess of hydrated lime, to the action of heat, with the benzine, two other products are formed : benzone, and a crystal- line substance of which the nature is not yet known. As these two latter substances boil at much higher temperatures than benzine, they are easily separated from it, by heating the mixture to 428, at which temperature the benzine is wholly volatilized. The residue being cooled to 4, nearly all the solid substance is deposited, and the benzone, which remains fluid, may be decanted. Benzone is an oily liquid of the formula C 13 H 5 0, the reaction from which it arises being expressed by the equation CaO,C 14 H 5 3 =CaO,C0 2 +C 13 H 5 0. AMYGDALIN CJBWSTA,,. 1541. Bitter almonds do not contain the oil of bitter almonds BENZOIC SERIES. 651 I ready formed, but in its stead a very remarkable substance, called amygdalin, which is converted in the oil by the action of a second substance, called emulsin. In order to prepare amygdalin, bitter almonds are subjected to very heavy pressure, when a fatty, colour- less, non-volatile oil exudes, called oil of sweet almonds, because it also exists in this species of almond. The balance of the oil is then removed by treating the crushed cake several times with ether ; after which the pulp is boiled twice with alcohol, to dissolve the amyg- dalin, the greater portion of the alcohol being afterward separated by distillation ; when the residue deposits the amygdalin, on cooling, in crystalline lamellae. Amygdalin dissolves readily in water, and is deposited from it in beautiful crystals, of the formula C 40 H 27 N 3 33 -f6HO ; the 6 equivalents of water being disengaged at 248. It dissolves freely in boiling alcohol, but is nearly insoluble in cold alcohol. Amygdalin rotates toward the left. When heated with a mixture of peroxide of manganese and sul- phuric acid, it is decomposed into ammonia, carbonic acid, formic acid, and oil of bitter almonds, by which process it yields more than one-half of its weight of oil. 1542. By pouring into a solution of amygdalin in 10 parts of water, an emulsion of sweet almonds, cyanohydric acid and oil of bitter almonds, readily known by their smell, are immediately formed. The name of synaptase has been given to the active sub- stance effecting the transformation, which exists both in sweet and in bitter almonds. In order to prepare synaptase, sweet almonds, from which the oil has been previously expressed, are treated with water, and to the solution is added, first, acetate of lead in order to precipitate a gummy matter, then acetic acid to coagulate the albumen, and lastly, a large quantity of alcohol, after having pre- cipitated the excess of lead by sulfhydric acid; when synaptase is deposited in flakes, which change, on cooling, into a brittle, gum- like substance. The action of synaptase on amygdalin may be com- pared to that of yeast on sugars, its analogy with the phenomena of fermentation being perfect, while the products of the reaction are complicated, and a considerable quantity of sugar is formed. One part of synaptase is sufficient to decompose 10 parts of amyg- dalin. Synaptase is soluble in water, but it coagulates at 140, and then loses all its power over amygdalin. In order to produce perfect transformation, the amygdalin must be dissolved in a large quantity of water. From this it will be seen that, in order to prepare the oil of bitter almonds, the pulp must not be immediately distilled with water, but must be digested in the cold, or better still, at a temperature of 86, long enough to allow the amygdalin to be wholly decomposed by the synaptase. The essential oil and the cyanohydric acid are then separated by distillation. 652 ESSENTIAL OILS. ESSENTIAL OIL OF SPIRAEA ULMARIA, AND THE SALICYLIC SERIES. 1543. By distilling the flowers of the meadow-sweet (spiraea ulmaria) with water, an essential oil C 14 H 6 4 is obtained, accompanied by a carburetted hydrogen, isomeric with oil of terpentine, and a crystalline substance analogous to camphor. The oil possesses acid properties, and has hence been called spiroylous acid, and salicylous acid from its correlations with a neutral substance, saticin, which exists in the bark of the willow. Salicin treated with a mixture of sulphuric acid and bichromate of potassa yields, in fact, a large pro- portion of oil of spiraea ; and we shall, therefore, commence with the description of this substance, which it is impossible to separate from the series of salicylic products. Salicin C 26 H 18 14 . 1544. In order to prepare salicin, the bark of the willow is ex- hausted by boiling water, and litharge is added to the concentrated solution until the liquid is deprived of colour. The oxide of lead is then partially precipitated by sulphuric acid, the precipitation being finished by sulphide of barium, added by drops to prevent its being in excess. The filtered liquid is evaporated, and then deposits impure salicin, which is purified by dissolving it in water, discolouring it by animal black and recrystallizing it. Salicin crystallizes in white inodorous aciculae of a bitter taste, and without any reaction on vegetable colours. It loses nothing of its weight at 212, melts at 248, and is decomposed at a higher temperature. 100 parts of water, at the ordinary temperature, dis- solve 5.6 of salicin, while boiling water dissolves it much more freely, and alcohol also dissolves it, but it is insoluble in ether. Salicin polarizes toward the left. Cold concentrated sulphuric acid dissolves salicin, and it becomes of a blood-red colour ; which reaction is a test of salicin in the bark of the willow and poplar tree. Dilute sulphuric and chlorohydric acids decompose salicin at the boiling point into glucose C 13 H 13 13 , and a resinous substance, called saliretin C 14 H 6 2 , according to the equation C 26 H 18 14 = C 12 H 12 12 + C 14 H 6 3 . 1545. Nitric acid forms, with salicin, very various products, ac- cording as it is more or less dilute. If 1 part of salicin be treated with 10 parts of nitric acid at 20 Baumd, and the mixture be left to itself for 1 or 2 days, shaking it frequently to hasten the solu- tion of the salicin, a yellow liquid is obtained, which deposits a white substance, crystallized in small needles, and called helicin. It is very soluble in hot water, but scarcely so in cold, and its formula is CJE ]6 14 -f3HO, the 3 equiv. of water being given off at 212, with- out alteration, while it melts at about 347. A solution of potassa, SALICIC SERIES. 653 baryta, or ammonia decomposes it into glucose and oil of spiraea C 14 H 6 4 : C M H I6 U +2HO= 2 C1,HC1, C 20 H 4 Br 4 ,HBr. ..................... C 20 H 5 C1 3 ,2HC1, C 20 H 4 Br 2 Cl 2 ,Br 4 ..................... C 20 H 2 Br 4 Cl 2 ,2HBr. 1584. Nitric acid reacts readily on naphthalin at the boiling point, converting it rapidly into an oil which solidifies on cooling, and should be purified by several crystallizations in alcohol. Its (380 PRODUCTS OF DRY DISTILLATION. formula being C^H^NC^), it may be considered as naphthalin in which 1 equiv. of hydrogen is replaced by 1 equiv. of the compound NO . By continuing the action of the nitric acid, we obtain suc- cessively BinitrmapWialin ............................ C 20 H 6 (N0 4 ) and Trinitronaphthalin ........................... C 20 H 3 (N0 4 ) 3 . By causing sulf hydrate of ammonia to act on an alcoholic solu- tion of mononitronaphthalin C 20 H 7 (NOJ, an organic base is obtained, naphthalidam C 20 H 9 N: C 20 H 7 (N0 4 )+6(NH 3J 2HS)=C 20 H 9 N-f-4HO+6S+6(NH 3 ,HS). This substance crystallizes in white needles, melting at 86, and boiling at about 570, without alteration, which combine with the acids and form crystallizable salts, the formula of the chlorohydrate being C 20 H 9 N,HC1, and that of the sulphate (C 20 H 9 N,HO),S0 3 . Under the same circumstances, binitronaphthalin C 20 H 6 (N0 4 ) 2 , and the trinitronaphthalin C 20 H 5 (N0 4 ) 3 , yield other alkaloids C 20 H 8 N 2 , ^yj. By causing nitric acid to act on chlorinated naphthalins, there re- sult either substitutions of the compound N0 4 for hydrogen, or pro- ducts of oxidation in which the molecule of naphthalin is modified by the substitution of oxygen in the place of hydrogen ; and in this manner have been obtained Trichlorinated binitronaphthalin ...... C 20 H 3 C1 3 (N0 4 ) 2 , and the products of oxidation: ................. C 20 H 4 C1 2 2 ,0 2 , CI It will be seen that from no carburetted hydrogen are more numerous products derived than from naphthalin ; which probably arises from the fact that no other one has been so carefully examined in this point of view. 1585. Concentrated sulphuric acid acts readily on naphthalin, and yields acid compounds. By heating naphthalin to about 194 with concentrated sulphuric acid, it dissolves in it, and forms a syrupy liquid, generally reddish, which, when exposed to a moist air, sets in a crystalline mass, readily soluble in water, producing an acid liquid which forms, with carbonate of lead, two salts unequally so- luble in alcohol. The acid of which the salt of lead is more soluble in alcohol is by far the more abundant, and has been called sulpho- naphthalic acid; the general formula of its dried salt being HO, (CgoHySijOg.) The other acid has received the name of sulphonaph- thic acid, but its composition is not exactly known. By causing concentrated sulphuric acid to act on trichlorinated PARAFFIN. 681 and on quadrichlorinated naphthalin, there result acids perfectly analogous to sulphonaphthalic acid, forming salts of the general formulas, when dried, RO,(C 20 H 4 C1 3 ,SA), RO,(C 20 H 3 C1 4 ,S 2 5 ). By substituting anhydrous sulphuric for monohydrated sulphuric acid, two neutral crystallizable substances are obtained in addition to the same acid compounds : sulphonaphthalin, of which the formula is C 20 H 8 ,S0 2 , and sulphonaphthalide, the composition of which ap- pears to correspond to the formula C 24 H 10 ,S0 2 . These substances are generally accompanied by a red colouring matter, of which the composition is not yet exactly known. Paraffin. 1586. A small quantity of this substance is found among the products of distillation of bituminous coals, together with a great number of organic substances; and it is concentrated in the sub- stances which volatilize last, when these products are subjected to redistillation. In order to extract it, the substance is heated with concentrated sulphuric acid, which carbonizes the greater portion of the substances mixed with the paraffin, when, if the liquid be allowed to rest, at a temperature of 122 or 140, the pure paraf- fin forms an oily layer on the surface, which solidifies on cooling. The substance is expressed several times between tissue-paper, which absorbs the oily portions, and it is purified by solution in boiling alcohol, or in a mixture of alcohol and ether, whence it is deposited, on cooling, in the form of brilliant spangles of a greasy lustre. A large quantity of paraffin may be obtained by distilling a mix- ture of wax and lime, when the oily product which solidifies on cool- ing, after being expressed between tissue-paper, furnishes pure paraf- fin by crystallization in alcohol or in ether. Paraffin melts at 116.6 and boils at about TOO , while, if it is not carefully heated, a portion of it is decomposed and yields gaseous products. It is distinguished by great stability, since concentrated sulphuric acid, at a temperature not exceeding 212, ordinary nitric acid, and chlorine, exert no action upon it, to which property it owes its name, (from parum affinis.) Paraffin burns in the air with a brilliant flame, and very good candles are made of it. 100 parts of boiling alcohol dissolve about 3.5 of it, nearly all of which is de- posited on cooling. The name of eupione has been given to volatile oils obtained, in greater or less quantity, in the preparation of paraffin, which are mixtures of various carburetted hydrogens, analogous to those con- stituting petroleum. 682 PRODUCTS OF DRY DISTILLATION. PHENIC ACID, PHENOLE, OR CARBOLIC ACID CH S 0,HO. 1587. These various names are given to a product extracted from coal-tar, by distilling the oily part of the tar and collecting separately the portion which passes over between 300 and 400. The liquid distilled between these two degrees is shaken several times with a very concentrated solution of caustic potassa, to which fragments of hydrate of potassa are added, when the oil disengages a disagreeable odour, and sets into a crystalline mass. Water being then added, and the whole heated to boiling, the liquid separates into two layers : a light, oily layer, which is removed, and a heavier, aqueous liquid, which is treated with chlorohydric acid. The oil which is thus separated by rising to the surface is decanted, digested over chloride of calcium, and distilled several times. This oil, which is phenic acid, and becomes solid at a low temperature, is also formed in the distillation of salicylic acid with lime, and in that of benzoin. Phenic acid constitutes, at the ordinary temperature, a white crys- talline compound, melting at about 95.0, and boiling at 370.4 ; of the density 1.065 at 64.4; slightly soluble in water, and dis- solving in all proportions in alcohol and ether. It combines with potassa to a crystalline salt KO,C 12 H 5 0, and forms analogous com- pounds with baryta and lime. It reduces several metallic salts, par- ticularly the salts of silver and mercury. Chlorine acts readily on phenic acid, and the following phenic acids have thus been obtained: Bichlorinated..... ....................... C 12 H 3 C1 2 0,HO, and Trichlorinated Bromine forms analogous products. Nitric acid also acts on phenic acid, and yields successively binitrophenic acid C 12 H 3 (N0 4 ) 2 0,HO, and trinitrophenic acid C 12 H 2 (N0 4 ) 3 0,HO; which two products are generally prepared by at- tacking directly, by nitric acid, the portion of oil of coal-tar which distils between 354 and 374, when a very energetic reaction ensues, furnishing a brown mass, which is washed with cold water and dis- solved in ammoniacal water heated to boiling. The liquid deposits, on cooling, binitrophenate of ammonia, which is to be purified by several crystallizations; and which, by decomposition with chlorohydric acid, yields binitrophenic acid. This acid, which crystallizes in right-angled prisms, with a rectangular base, and of a slightly yel- lowish colour, is suddenly decomposed by heat. It dissolves slightly in boiling water, and is wholly deposited from it on cooling, while alcohol and ether dissolve it largely. Boiling nitric acid acts readily on binitrophenic acid, and con- verts it into trinititophenic acid C 12 H 2 (N0 4 ) 3 0,HO, which has been known for a long time under different names; having been called Welter's bitter, nitrocarbonic acid, picric acid, etc. It is obtained NAPHTHA. 683 by the action of nitric acid on the most diversified organic sub- stances, particularly on nitrogenous substances of animal origin, such as silk, fibrine, and animal tissues. Salicin treated with nitric acid yields a large quantity of trinitrophenic acid, and we shall see that it is also obtained in treating indigo by the same acid. It crystallizes in brilliant yellow prisms, is but slightly soluble in cold, but largely so in hot water, while alcohol and ether dissolve it freely. It forms yellow crystallizable salts with bases which detonate when heated. CREASOTE C M H 16 0,. 1588. A liquid substance, called creasote, and possessing some interest in being used to allay toothache, is extracted from wood-tar and pyroligneous acid, by a long and complicated process. The wood-tar is distilled until a pitchlike mass alone remains, when the distilled liquid separates in the receiver into three layers, the lower of which, containing the creasote, is saturated with carbonate of soda ; after which the supernatant oil is decanted and again dis- tilled ; the first products, which are lighter than water, being rejected, while the heavier oil is collected and again distilled. This oil is then shaken several times with a weak and hot solution of phos- phoric acid, washed until it gives off no more acid, and treated with an alkaline solution of the density 1.12, when the creasote leaves the oil, and dissolves in the alkaline liquid, which is separated and exposed for some time to the air, to oxidize a foreign substance which discolours the liquid. Lastly, the solution, after being satu- rated with phosphoric acid, is distilled, when the creasote volatilizes with the water and separates in the receiver in the form of an oily layer. Creasote is a colourless, oleaginous liquid, of a penetrating and disagreeable odour and an acrid and burning taste ; cauterizing the organic tisues, coagulating albumen, and preventing the putrefaction of meat. It boils, without change, at about 390, and is insoluble in water, but readily so in alcohol and ether. It forms, with potassa and soda, crystalline compounds, from which acids separate it without change ; and its composition corresponds to the formula C 28 H 16 4 . An alcoholic solution of creasote is used in medicine. NAPHTHA, OR PETROLEUM. 1589. In many countries, odoriferous oils exude from the ground, accompanied generally by hot or cold water, and sometimes by combustible gases ; and when such liquids are collected in natural or artificial reservoirs, the oil floats on the surface. The general name of petroleum is given to these oils, the nature of which is evi- dently very diversified, for some of them distil wholly without change, while others leave a considerable residue *of fixed oil, which is decomposed by heat. The most abundant springs of petroleum 684 FATS. . are In the neighbourhood of Baku in Persia, where jets of com- bustible gas, copious enough to enable the inhabitants to use it for cooking their food, issue simultaneously from fissures in the ground ; and some springs of petroleum are also found at Amiano, in the Duchy of Parma. Petroleum is purified by distillation with water, and the product is known in commerce by the name of oil of naphtha, or oil of petroleum. Oil of naphtha, which presents the density of about 0.84, and gives a peculiar odour, contains no oxygen, and appears to be formed by the mixture of several carburetted hydrogens. If it be distilled in a retort furnished with a thermometer, ebullition is found to com- mence when the thermometer marks 250 to 284, while the temper- ature gradually rises, and the last portions do not distil below 570. If the products of distillation be collected separately, the most vola- tile is a liquid boiling at about 194, after which numerous products pass over, boiling at higher and higher temperatures, while it has hitherto been impossible to separate a liquid presenting a constant boiling point, mixtures only having been obtained. The composition of the most volatile products correspond approximately to the formula CH, and they are isomeric with olefiant gas, while the less volatile products contain less hydrogen. The essential oils which form petroleum are remarkable for their resistance to chemical agents, since they are scarcely affected by concentrated sulphuric and nitric acids ; and they are used in the laboratory for the preservation of potassium, ( 426.) THE FATS. 1590. The name of fats is commonly assigned to substances of organic origin, liquid or solid, but melting at a very low tempera- ture, which, when spread in a liquid state on paper, render it trans- lucent, and make permanent stains on it, known by the name of grease- spots ; while the chemist defines fats by certain chemical properties, and, particularly, by their manner of composition, as shall subse- quently be shown. Fatty substances are found both in the vegetable and animal kingdoms, and seem to be identical in both ; which has led some physiologists to the opinion that animals merely assimilate to them- selves those which exist in vegetables, without their undergoing any chemical change. Although we shall reserve for the close of this work the study of the principal substances constituting the animal eco- nomy, we shall not, in this place, separate the fatty substances of the two kingdoms. Vegetable fats are generally fluid at the ordinary temperature, while several of them coagulate and solidify, more or less perfectly, FATS. 685 at a low temperature. They are completely liquid only at a high heat, and at the ordinary temperature possess a certain degree of viscidity, called an oily consistence. The fat of warm-blooded ani- mals is solid, its firmness varying according to the position it occu- pies in the body of the animal ; while that of fishes and cold-blooded animals in general is fluid. In plants, fat is found chiefly in the seeds and pericarp of the fruit, in the form of small drops which fill peculiar cells, and also exists in the shape of a waxlike substance on the surface of the leaves and bark. The proportion existing in seeds is often very considerable : thus, flaxseed contains about 20 per cent, of oil, and rapeseed 35 to 40, while the seed of ricinus communis, which fur- nishes castor-oil, contains as much as 60. The oil is generally ex- tracted merely by expressing the seeds, but in order to render it more fluid they are heated, and then compressed between hot plates. When the proportion of oil is smaller, fermentation is sometimes resorted to for the destruction of a portion of the organic substances and in order to break up the fruit. Lastly, in the laboratory, sol- vents are sometimes used, chiefly ether, which is then driven off by evaporation. Animal fat may be obtained either mechanically or by the action of heat. In order to purify it in the laboratory, it is generally dis- solved in ether ; but it must not be forgotten that this liquid can also dissolve some of the foreign substances mixed with the fat. The melting point of fat varies from 23 to 140, while at temperatures above 480 they yield copious and very acrid fumes, but do not distil without alteration, whence they are called fixed oils. At an intense heat they are wholly decomposed, and produce gases of great illuminating power. 1591. Oils generally absorb oxygen from the air, but in very various proportions ; and while some absorb but small quantities of it without sensibly changing in appearance, merely acquiring a dis- agreeable smell, when they are said to become rancid, others absorb larger proportions of oxygen, become covered with a coating of a resinous appearance, and are finally completely solidified ; and these are called drying-oils, the only ones which can be used in painting. Linseed, nut, hemp, poppy, and castor-oil are drying-oils, while some fish-oils appear to possess the same property. The fat of warm-blooded animals, the oil of almonds, olive-oil, rapeseed-oil, &c. are not drying-oils. The chemical action which produces the solidification of drying- oils is sometimes limited to a simple combination with oxygen ; as in the case with linseed-oil, which absorbs large quantities of oxy- gen without disengaging any gas; but more frequently carbonic acid, and sometimes hydrogen, is evolved. Absorption goes on slowly at first, but subsequently becomes more rapid, especially when the oil is spread over a large surface or on porous bodies. Drying-oils VOL. II. 3 H 686 FATS. dry more quickly when they have been previously boiled with litharge or peroxide of manganese ; in which case they contain a small quantity of these metallic oxides in solution. 1592. The greater part of animal fats is formed of several proximate principles united in indefinite proportions ; and of which chemists have distinguished only three : stearin, margarin, and olein. These principles behave, in chemical reactions, like compounds of the same substance, glycerin, with a fatty acid, peculiar to each of these principles. Stearin and margarin, to which beef and mutton fat owe their solidity, are converted into glycerin, and two fatty acids, which are stearic acid for stearin, and margaric acid for margarin ; while olein, to which fats owe their oleaginous character, is trans- formed into glycerin and oleic acid. In several fatty substances, such as butter, we find, in addition, small quantities of peculiar fatty matters, called butyrin, caprin, and caproin, which may be considered as compounds of glycerin w T ith volatile acids, differing in each of these substances, and which have been called butyric, capric, and caproic acids. We have shown that butyric acid is formed in a peculiar fermentation of sugar ; and it will now soon be seen that the same acid arises, as also capric and caproic acids, from the ac- tion of nitric acid on stearin, margarin, and olein. The fat of the goat contains, in addition to the ordinary immediate principles, a small quantity of a peculiar fat, called hircin, which behaves like a compound of glycerin and a peculiar volatile acid, hircic acid. Lastly, another fatty substance is found in fish-oils, which may be considered as a compound of glycerin and a peculiar acid, called pJiocenic, ap- pearing to be identical with valerianic acid. A peculiar fat substance is extracted from the head of the sperm whale, called spermaceti, the constitution of which is very different from that of other animal fats, since it does not contain glycerin, but in its stead another neutral substance, called ethal; while the fat acid which is combined with the ethal has received the name of ethalic acid. Lastly, the various kinds of wax, which should be classed among the fats, from the definition given of the latter, ( 1590,) differ com- pletely from it in their chemical composition, as shall presently be shown. 1593. Stearic, margaric, and oleic acids are weak acids, which are displaced from their compounds by a majority of the other acids ; and they are insoluble in water, but soluble in alcohol, and very feebly in ether. They are less easily melted than the proxi- mate fatty principles which produced them, and they do not distil without alteration under the ordinary pressure of the atmosphere. They are then decomposed at a temperature above 570, yielding very complicated products ; but they may be distilled in vacuo, be- cause the distillation is then effected at a much lower temperature. 1594. The chemical operations by which natural fat substances FATS. 687 are converted into glycerin and fat acids are known by the general name of saponification. They are various ; and the saponification of fats may be effected either by alkalies or by powerful acids, or by the action of heat alone. If fats be heated to a temperature of 570, in an apparatus tra- versed by a current of steam, under a pressure inferior to that of the atmosphere, the glycerin is converted into several products soluble in water ; while the fat acids, set free, distil without altera- tion ; thus furnishing an example of saponification by heat alone. The action of hot alkaline lixivise decomposes fats and oils into glycerin, which dissolves in the aqueous liquid, and into fat acids, which combine with the alkali and form salts, commonly called soaps, which are insoluble in the alkaline liquor, but readily dissolve in a sufficient quantity of water. This operation, called saponifi- cation by bases, may be effected not only by alkaline bases, such as potassa, soda, and ammonia, but also by other metallic oxides which possess powerful basic properties, such as baryta, strontia, lime, and the protoxides of lead and zinc. The other metallic oxides no longer produce the saponification of fats, that is, their decom- position into glycerin and fat acids ; while they may combine with the isolated fat acids and form insoluble soaps. Water is generated during saponification, for the united weight of the glycerin and fat acids is greater than the weight of the original fat. The neutral alkaline carbonates can also effect the saponification of fats, in which case they part with one-half of their alkali, which produces saponification, while the other half retains all the carbonic acid in the shape of bicarbonate ; carbonic acid being disengaged only if heat is applied, because the bicarbonate is then decomposed. Powerful acids, such as sulphuric, also effect the saponification of fats ; and if the proportion of acid be not very great, the fat acid is isolated, the glycerin combining with the animal acid to form a compound acid. If the weight of the mineral acid exceed the half of that of the fat acid, it often combines with the latter, producing sulphogly eerie, sulphostearie, sulphomargaric, and sulpJioleic acids. Smaller quantities of sulphuric acid are however sometimes used to purify the oils intended for burning in lamps, in which case the acid selects the foreign substances more easily acted on, contained in the oils, dissolving them, and effecting only an insensible saponification. 1595. No fatty substance is soluble in water, which does not even moisten them ; while they are somewhat soluble in absolute alcohol and wood-spirit, ether and the essential oils dissolving them much more freely. The liquid fats are the best solvents of solid fats. We have seen that natural fats are rarely simple, nearly always mixtures or indefinite compounds of various different fatty substances, which are separated only with the greatest difficulty. When the fat is solid, it is sufficient to melt it, and allow it to cool slowly, to observe in it the forming of solid lumps, the nature of 688 FATS. which differs from the liquid part. So again, certain fatty oils, olive-oil, for example, deposits, by slow cooling, more or less copious flocculi, which differ from the liquid portion ; and by expressing these solidified portions between tissue-paper, a large quantity of interstitial liquid oil can be separated, furnishing a mixture of stearin and margarin, adulterated merely with a small quantity of olein. The proportions of stearin and margarin in the substances expressed vary according to the nature of the original fats. When they are yielded by mutton or beef fat, or lard, they are composed almost wholly of stearin ; while, if furnished by human fat or olive- oil, they consist chiefly of margarin. These substances may be more perfectly isolated by a proper use of solvents. The immediate fluid constituent of animal fats, olein, is still more difficult to isolate, the oil which flows from the compression of such fats being olein saturated with stearin or margarin. The most fluid vegetable oils are themselves olein, containing more or less stearin and margarin in solution ; and by cooling them gradually and de- canting the fluid, a large portion of the solid constituent may be separated ; or the oil may also be shaken with alcohol, which dis- solves the olein much more freely than the stearin and margarin, and the alcoholic solution may be evaporated: but all these pro- cesses never effect a perfect separation. It is moreover highly pro- bable that stearin, margarin, and olein are not merely mixed in the majority of fats, and that they are in the state of indefinite com- pounds. Olein does not appear to be identical in the various vegetable oils, since several chemical experiments seem to prove that it differs in the drying and non-drying oils. If, for example, a non-drying oil, such as olive-oil, be agitated with a small quantity of hyponitric acid, or with a solution of subnitrate of mercury, which contains hyponitric acid, the oil becomes completely solid after some time, and is converted into a crystalline substance, elaidin. Drying-oils do not possess this property, which thus furnishes a test, applicable to commercial purposes, of the purity of olive-oil, which is fre- quently adulterated with other vegetable oils, and particularly with poppy-oil. Fat acids which are capable of crystallization may be obtained in a state of purity, and since they at the same time form a great number of definite compounds, their properties and chemical com- position have been more accurately ascertained than those of the fats which furnish them. Nevertheless, uncertainties still exist, on account of the very high value of their chemical equivalents ; the smallest errors in analyses corresponding to 1 or several equivalents of simple elements, and sufficing to change the formulae. We shall examine only the most important and most common fatty substances, commencing with the study of glycerin, which is an essential and constant principle of the majority of these substances. GLYCERIN. 689 G-lycerin C 6 H 7 5 ,HO. 1596. The most simple method of preparing glycerin consists in heating fats with protoxide of lead, in the presence of water, when saponification is soon effected, an insoluble soap of lead being formed, while the glycerin remains dissolved in the water. The aqueous solution is subjected to a current of sulfhydric gas, which precipitates a small quantity of oxide of lead dissolved in it in the state of sulphide ; after which it is concentrated at a gentle heat, and the evaporation completed in vacuo. Glycerin, dried in vacuo at 212, is a syrupy, colourless, inodor- ous liquid, tasting like sugar, from which circumstance it has de- rived its name, (y^vxv^ sweet,) insoluble in water, but soluble in all proportions in alcohol and ether. It is decomposed by heat, yielding very complex products ; among which is remarked an oily, colourless, extremely disagreeable-smelling liquid, called acrolein, and present- ing the formula C 6 H 4 2 . Oxidizing substances, such as ordinary nitric acid, or a mixture of sulphuric acid and peroxide of manga- nese, form with glycerin, oxalic, formic, and carbonic acids. Chlorine and bromine act on glycerin, and form chlorinated and brominated compounds, which can only be expressed in equivalents by doubling the ordinary formula of glycerin, that is, by writing it C 12 H 14 10 ,2HO, which furnishes, Original glycerin C 12 H 14 10 ,2HO, Trichlorinated " C 12 H n Cl 3 10 , Tribrominated " C 12 H n Br 3 10 . But it is difficult to decide the question, owing to the want of means of ascertaining the purity of the chlorinated and brominated sub- stances, inasmuch as they do not crystallize. By mixing 2 parts of concentrated sulphuric acid with 1 part of glycerin, combination ensues, with elevation of temperature; and by leaving the mixture to itself for some time, shaking it frequently, an acid compound, sulphogly eerie acid, is produced, which forms soluble salts with lime and oxide of lead ; the lime-salt being pre- pared by adding water to the mixture, saturating it with chalk, and filtering to separate the sulphate of lime. The liquor, when evaporated, yields sulphoglycerate of lime, of which the formula, when it is dried at 248 in vacuo, is CaO(C 6 H 7 5 ,2S0 3 ), and which dissolves in one-half of its weight in water, but it is insoluble in alcohol and ether. Glycerin also becomes heated when it is mixed with anhydrous or hydrated phosphoric acid; ^phosphogly eerie acid, which dissolves in water, being formed. By saturating the liquid with carbonate of baryta, and lastly by caustic baryta, the free phosphoric acid is precipitated in the state of phosphate of baryta, while the liquid contains pTiosphoglycerate of baryta, which is separated by evapora- 3 H 2 44 690 FATS. tion. The formula of this salt, dried at 284, is 2BaO,(C 6 H 7 6 , Phosphoglyceric acid has been found ready formed in the yolk of eggs. Sulphoglyceric and phosphoglyceric acids yield a large quantity of acrolein when they are decomposed by heat ; which is, in fact, the best method of preparing this substance. Stearin and Stearic Acid. 1597. The most efficient method of isolating stearin consists in melting tallow with oil of terpentine, when the oil, after being de- canted, deposits a solid substance on cooling, which is subjected to pressure between the folds of tissue-paper in a press. After being similarly treated several times, it is dissolved in ether, with the as- sistance of heat, when the greater portion of it is again deposited on cooling. The stearin thus obtained is considered as pure. Chemical analysis, added to the knowledge of its products of sapo- nification, have assigned to stearin the formula C 142 H 140 16 , which is more properly written (C 6 H 7 5 +HO),2C 68 H 66 5 . Stearin is therefore admitted to be an acid compound, analogous to sulphovinic acid (C 4 H 5 0,HO)2S0 3 , and formed by the combination of 2 equiv. of stearic acid C 68 H &6 5 with 1 equiv. of glycerin and 1 equiv. of water. Stearin crystallized in ether forms small white lamellae, of a pearly lustre, melting at from 140 to 144, and setting, on cooling, into a white opake mass, presenting no appearance of crystalliza- tion. It is completely insoluble in water, but dissolves in 8 parts of boiling alcohol, separating from it almost entirely on cooling; while ether dissolves a large proportion of it at the boiling point, but when cooled only retains about 2 fo. 1598. Stearic acid is an important article of commerce, of which candles, called stearic candles, are made. It is prepared by sapo- nifying beef or mutton suet by lime : 500 kilog. of suet and 800 litres of water are placed in a wooden vat, holding 2000 litres, and lined with lead, and heated by steam conveyed directly into the vat by means of a circular tube pierced with holes ; and when the suet is melted, about 600 litres of a solution of lime, containing 60 kilog. of quicklime, is added, and the mixture is continually stirred. After 6 or 7 hours, the saponification is terminated, and the soap of lime has formed a consistent mass, which becomes very hard on cooling. It is reduced to a fine powder, and decomposed by sulphuric acid, diluted with water, in vats similar to the first, and heated by steam, when the fatty acids, set free, form an oily layer on the surface of the acid liquids. The melted fat is decanted, and washed several times, while hot, with water charged with sulphuric acid, and then with fresh water ; and it is finally run into tin moulds, forming cakes of 3 or 4 kilogs. STEARIC ACIDS. 691 in weight. This mass, which is still a mixture of stearic, margaric, and oleic acids, is first powerfully compressed when cold, in order to express the greater part of the oleic acid, and then at a tempera- ture of 90 or 100, to drive out the remainder. The oleic acid thus expressed is of a deep brown colour, and contains nearly all the margaric, besides a certain quantity of stearic acid. The cakes remaining after this compression are again melted, in contact with a dilute solution of sulphuric acid, which removes the last traces of lime from the fatty substance ; after which it is freed from the ad- hering acid by washing it in boiling water. It is then poured into moulds, where it becomes solid, and is thus brought into commerce as refined stearic acid, used for the manufacture of candles. 1599. Large quantities of solid fat acids are now prepared for the manufacture of stearic candles by a very ingenious process, in which saponification by sulphuric acid is combined with distillation of the fat acids, in intensely heated steam, having but little tension. This process enables the use of fats of all kinds, and of the most inferior qualities. The fats, placed in boilers heated by steam, are first treated with a quantity of concentrated sulphuric acid, which varies from 6 to 15 per cent., according to the nature of the fat. The temperature being raised to 212, and kept at that point for 15 or 20 hours, under constant stirring, the fat acids are set free, and the glycerin is almost wholly converted into sulphoglyceric acid ; while the greater portion of the foreign substances are destroyed by the sulphuric acid, yielding carbonaceous residues and products soluble in water. The fat acids are washed with water, and then placed in a distilling apparatus, through which steam heated to about 600 is passed, with an elastic force inferior to that of the atmosphere, when the fat acids distil with the water, and by pressure can be brought into a state fitted for the manufacture of candles. 1600. Very pure stearic acid may be obtained, for laboratory purposes, by crystallizing the stearic acid of commerce several times in boiling alcohol. Stearic acid yields, by slow cooling, beautiful and pearly crystals, melting at 158, and at a temperature of 570 giving off vapour without alteration. It may be distilled in vacuo, and is completely insoluble in water, but very soluble in boiling alcohol and ether. The formula of crystallized stearic acid is C 68 H 68 7 , which should be written C 68 H 66 5 ,2HO, since 2 equiv. of a base may be substituted for 2 equiv. of water ; showing it, therefore, to be a bibasic acid. The acid forms two salts with potassa : bipotassic stearate 2KO, CggHeA' and . mono P ota * s stearate (KO+HO),C 68 H 66 5 .* The former is obtained by treating stearic acid with an equal weight of * These salts would with more propriety be called basic and neutral stearates of potassa. W. L. F. 692 FATS. hydrate of potassa, dissolved in 20 parts of water, when the salt remains in the form of clots, which are compressed between tissue- paper. It is then redissolved in 15 or 20 parts of boiling alcohol, and the liquid allowed to cool, when the bipotassic stearate is de- posited in white crystalline lamellae. It dissolves without . change in 10 times its weight of water, but, when cold, produces only a mucilaginous liquid, which does not become perfectly fluid and limpid unless it be heated to boiling. When a larger quantity of water is poured into this solution, a clouded, opalizing liquid is obtained, in which a large number of small crystalline spangles of extreme de- licacy swim, and which settle to the bottom of the vessel, if it be allowed to rest. These small crystals constitute monopotassic stea- rate, of which the formula is (KO+HO),C 68 H 66 5 . Alcohol does not effect this decomposition in the bipotassic stearate. Soda forms two stearates analogous to those of potassa : stearates of baryta, strontian, and lime, which present the formula 2RO, CggHggOg, are prepared by double decomposition from the bipo- tassic stearate, and are completely insoluble in water. The lead- salt is obtained in the same way, but the stearate of lead used in pharmacy for the making of plasters is prepared by directly sapo- nifying fats by litharge in the presence of water. Spring-water is generally hard, and is then unsuitable for washing, owing to the presence of calcareous salts, which decompose the alkaline soaps as they form, and make insoluble soaps ; and alkaline soap can only dissolve when the calcareous salts are completely decomposed. Water is rendered fit for washing by adding a small quantity of carbonate of soda, which decomposes the salts of lime. Stearic acid forms vinostearic and methylostearic ethers, which are obtained by dissolving stearic acid in absolute alcohol or wood- spirit, and passing through it a current of chlorohydric acid gas ; when the ethers, after being precipitated by water and crystallized in alcohol, form white substances of a greasy lustre, and melting at from 86 to 95. Margario Acid C 68 H 66 6 ,2HO. 1601. By decomposing with acids a soap made of human fat, a mixture of fatty acids is obtained, melting at about 135, and which is considered as composed solely of margaric and oleic acids. Mar- garic acid is supposed to be produced by the saponification of a sim- ple fat, margarin, but which probably exists in combination with olein. Margaric acid is also formed in the distillation of stearic acid and the fats in general, as well as when the latter are subjected to the action of oxidizing reagents. Chemists are not agreed upon the formula of margaric acid ; and while some write it C 68 H 66 6 , 2HO, a formula which differs from that of stearic acid by 1 equiva- lent of oxygen, others assert that its composition is identical with that of stearic acid. OLEIC ACID. 693 The best method of preparing margaric acid consists in saponify- ing human fat or olive-oil by potassa, and pouring acetate of lead into the solution, which yields a precipitate of margarate and oleate of lead. The precipitate being treated several times with ether, which completely dissolves the oleate of lead, and a much smaller proportion of margarate, the remaining margarate of lead is decom- posed by dilute nitric acid, and the margaric acid arising from it is purified by crystallization in alcohol. In its physical properties, margaric closely resembles stearic acid, but it melts at a lower temperature, viz. at 140. It forms two salts with potassa : the bipotassic margarate 2KO,C 68 H 66 6 , and the monopotassic marga- rate (KO+HO),C 68 H 66 6 ; which are formed under the same circum- stances as the corresponding stearates, and nearly resemble them. Okie Acid C^H^ 1602. In order to separate this acid, oils very rich in olein, such as olive-oil and oil of almonds, are saponified by potassa ; when the soap is decomposed by tartaric acid, and the fatty acids which sepa- rate are decanted. The latter are digested in a water-bath with one-half of their weight of finely-powdered oxide of lead, thus form- ing a soap of lead, consisting of both the oleate and the margarate. This soap is digested for 24 hours with twice its volume of ether, which dissolves the oleate, and the etherial liquor being evapo- rated, the oleate of lead is decomposed by chlorohydric acid. The oleic acid thus obtained is, however, not pure, and must be redis- solved in ammonia, precipitated by chloride of barium, and the oleate of baryta must be purified by several crystallizations in boiling alco- hol. Lastly, the oleate of baryta is decomposed by tartaric acid, operating in a bottle perfectly fitted and well corked, to prevent the oleic acid from absorbing the oxygen of the air. Oleic acid is a colourless liquid, solidifying below 53.6, and insoluble in water, but very soluble in alcohol, ether, and the essen- tial oils. It does not redden litmus, even when dissolved in alcohol ; and it readily absorbs oxygen from the air. The formula C 36 H 3 3 , HO, which has generally been assigned to this acid, should probably be doubled and written C 72 H 66 6 ,2HO, in which latter case the acid would be considered as bibasic. Oleic acid is decomposed by heat, but may nevertheless be distilled in vacuo. The products of its decomposition are very various ; and a fatty acid, called sebacic, which characterizes oleic acid under these circumstances, is remarked among them. Treated with nitrous acid, oleic acid is easily trans- formed into an isomeric modification, elaidic acid, which sets into a crystalline mass, and which shows a very strong acid reaction. It dissolves in boiling alcohol, and separates partly from it, on cooling, in large crystalline lamellae, which melt only at 111.2. ^ of ni- trous acid will effect the transformation of oleic acid, but it rapidly increases with the quantity of nitrous acid used. Elaidic acid 694 FATS. oxidizes rapidly in the air, particularly if it be heated to 140 or 160. The alkaline oleates are readily formed by dissolving oleic acid in alkaline lixivise, or by treating the alkaline carbonates by an alcoholic solution of oleic acid ; other metallic oleates being prepared by double decomposition. The formula of oleate of baryta is BaO, CggH^Og. A large quantity of water decomposes the alkaline oleates, salts containing a smaller proportion of base being deposited ; which decomposition is however less readily effected than in the stearates and margarates. ACTION OF SULPHURIC ACID ON THE NATURAL FATS. 1603. When sulphuric acid is made to act on stearin, the latter is decomposed in the same manner as when in contact with the hydrated alkalies ; stearic acid being set free, and the glycerin combining with the sulphuric acid to form sulphoglyceric acid. It is as yet unknown what reaction sulphuric acid exerts on margarin or on olein when isolated ; the reaction on the natural fats, which are mixtures or compounds of these two substances, and particularly on olive-oil, having hitherto only been studied. When olive-oil is treated with one-half of its weight of concen- trated sulphuric acid, by placing the bottle containing the two sub- stances in a refrigerating mixture, in order to prevent an elevation of temperature, a homogeneous liquid of a viscous consistence is formed, composed of sulphoglyceric acid and two new compound acids, called sulpfiomargaric and sulpholeic. By adding a great excess of cold sulphuric acid, the sulphomargaric and sulpholeic acids are separated from the sulphoglyceric acid, which remains in solution, while they form an oily coating on the surface, which is removed and washed with a small quantity of water, to free it from the sulphuric acid. These acids dissolve readily in water and alco- hol, and form well-defined salts. Their aqueous solution decom- poses spontaneously in the cold, and more rapidly at the boiling point, into sulphuric acid, and new fat acids, which appear to differ from margaric and oleic acids only by the addition of 1 or more equivalents of water. Margarin yields the three acids, metamar- garic, hydromargaric, and hydromargaritic ; while oleic acid fur- nishes but two, metoleie and hydroleic acids. The three acids derived from margarin are solid at the ordinary temperature, rneta- margaric acid melting at 122, hydromargaric at 140, and hydro- margaritic at 154; while metoleie and hydroleic acids are oily liquids. All the new fat acids, being insoluble in water, are readily soluble in alcohol and ether. Metoleie and hydroleic acids, carefully heated in a retort, are decomposed, and disengage pure carbonic acid, while, together with some empyreumatic substances, an oily liquid, composed of two iso- meric carburetted hydrogens, presenting the composition of olefiant DECOMPOSITION OF FAT ACIDS. 695 gas, condense in the receiver, and may be separated by distillation at different temperatures. The first, oleen, boils at 131, has a disagreeable and penetrating odour, and the density of its vapour has been found to be 2.87, while its formula is C 12 H 12 , which is represented by 4 volumes of vapour. The second compound, elaen, the formula of which appears to be C 18 H 18 , boils at 230. ACTION OF NITRIC ACID ON STEAKIC, MARGARIC, AND OLEIC ACIDS. 1604. Nitric acid reacts energetically on the fat acids, forming with them very complicated products, among which are some new and highly interesting acids. Since during the first periods of the reaction of nitric on stearic acid the latter is converted into margaric acid, the products afforded by margaric and oleic acids only remain to be described. The ultimate products of the reaction are very complicated, and may be divided into two classes : the volatile acids which condense in the receiver, and the fixed or slightly volatile acids which remain in the retort. We shall here enumerate them with their formula, in order that the curious relation between them may be more easily seen. The fourth column contains the carbu- retted hydrogens from which they may be supposed to be derived by substitution. Volatile Acids. Formic acid C 2 H 2 4 or C 2 H 3 ,HO C 2 H 4 Acetic " C 4 H 4 4 C 4 H 3 3 ,HO C 4 H 6 Acetonic C 6 H 6 4 C 6 H 5 3 ,HO C 6 H 8 Butyric C 8 H 8 4 C 8 H 7 3 ,HO C 8 H 10 Valerianic C 10 H 10 4 C 10 H 9 3 ,HO C 10 H 12 Caproic " C 12 H 12 4 C 12 H n 3 ,HO C 12 H 14 (Enanthylic C 14 H 14 4 C 14 H 13 3 ,HO C 14 H 16 Caprylic C 16 H 16 4 C 16 H 15 3 ,HO C 16 H 18 Pelargonic " C 18 H 18 4 C 18 H 17 3 ,HO C^H^ Capric C 20 H 20 4 C 20 H 19 3 ,HO C 20 H 22 . It will be seen that if the equivalent of basic water be not sepa- rated in the formula, all these acids may be regarded as compounds of 4 equivalents of oxygen with carburetted hydrogen isomeric with olefiant gas. If, on the contrary, the basic water be isolated, they may be regarded as resulting from the substitution of 3 equivalents of oxygen for 3 equivalents of hydrogen in carburetted hydrogens of which the general formula is C 2w H 2n+2 (n being a whole number :) but only one of these carburetted hydrogens, the protocarbu- retted C 2 H 4 , is as yet known with certainty.* * This theory has already been noticed in the note to $ 1401, where it is also shown that the acids in the above table may more properly be considered as oxalic acid paired with one equiv. of a carburetted hydrogen of the general 696 FATS. The slightly volatile acids which remain in the retort are Succinic acid C 8 H 6 8 or C 8 H 4 6 ,2HO Adipic " C 12 H 10 8 C 12 H 8 6 ,2HO Pimelic C 14 H 12 8 C 14 H 10 6 ,2HO Suberic C 16 H 14 8 C 16 H 12 C ,2HO Sebacic C 20 H 18 8 C 20 H 16 6 ,2HO If we omit the basic water contained in the formula, we shall find all these acids to result from the combination of 8 equivalents of oxygen with the carburetted hydrogens of which the general formula is C 2n H 2(n _ 1) . 1605. In order to obtain these various products, it is necessary to operate on a somewhat considerable quantity of oleic acid. The nitric acid should be first introduced by itself into a tubulated retort, and heated to 120 or 140, the oleic acid being added by small quantities at a time. Violent reaction ensues at each addition ; and when all the oleic acid has been poured into the retort, the heat is continued until reaction ceases. The liquid collected in the receiver consists of water containing the most soluble of the volatile acids, such as formic, acetic, acetonic, and butyric acids, covered by an oily layer which contains the valerianic and other acids. The latter is de- canted, saturated with water of baryta, and the various salts of baryta formed are separated by successive crystallizations. The caproate of baryta crystallizes first, and then successively the oenanthylate, the caprylate, the pelargonate, the caprate, and lastly the valerianate of baryta. The more volatile acids, when dissolved in water, are saturated by carbonate of soda, and the solution evaporated; when the first crystals deposited from the cold solution are acetate of soda ; while if sulphuric acid be then poured into the mother liquid, an oily layer, composed of butyric and metacetonic acids, is separated. When the slightly volatile acids which remain in the retort are chiefly sought to be obtained, the action of the nitric acid must not be too much prolonged, since a portion of them would then be de- stroyed. The oleic acid is then acted on by double its weight of nitric acid, and the action is continued until no more reddish vapours are disengaged, when a portion of the oleic acid has dis- appeared, being converted into products which dissolve in the aqueous liquid. The supernatant oil is decanted, and again acted on by nitric acid ; this process being continued until it has nearly disappeared, when the slightly volatile acids are found in the watery liquids arising from this treatment. sible; and while of the hydrocarbons assumed in the text as the radicals only one is known, several of the formula just mentioned have been isolated, such as methyl C a H g , ethyl C 4 H S , valyl C 8 H 9 , and amyl C 10 H tl . W. L .F. SUCCINIC ACID. 697 Succinic Acid C 8 H 4 6 ,2HO. 1606. Succinic acid is produced not only by the action of nitric acid on fatty acids, but is also found under other remarkable cir- cumstances. It is generally prepared by distilling amber, a sub- stance of organic origin, sometimes found in strata of lignite, and occurring in large quantities in the alluvial sands of the Baltic. Amber distilled in a glass retort yields an acid water, and empy- reumatic oils, which remain in the paper through which the acid liquid is filtered. The latter being saturated with chlorine in order to destroy some foreign substances, and then evaporated, the suc- cinic acid is deposited in crystals. An aqueous solution of impure asparagin left to itself for some time is converted by a species of fermentation into succinate of ammonia. Impure neutral malate of lime, such as is directly obtained from the berries of the service-tree, left for several months, under a layer of water, in a vessel covered merely by a sheet of paper, undergoes an analogous fermentation, the liquor becoming covered with mucilage, while crystals of hydrated carbonate of lime are deposited on the sides of the vessel, and acicular crystals of succinic acid are developed on the deposit of malate of lime. Succinic acid melts at 365, boils without alteration at 473, and may be sublimed at much lower temperatures. Cold water dissolves about I of its weight of it, and boiling water about J; and it also dissolves in considerable quantity in alcohol, but very slightly in ether. The formula of succinic acid, crystallized in water, is C 8 H 6 8 , which is generally written C 8 H 4 6 ,2HO, since 2 equiv. of base may be substitued for 2 equiv. of water. At 284 it loses 1 equiv. of water, and after several distillations becomes perfectly anhydrous; its composition then corresponding to the formula C 8 H 4 6 . Nitric acid and chlorine do not sensibly act on succinic acid, while anhydrous sulphuric acid forms a compound acid with it, called sulplwsuccinic. Adipic Acid C 12 H 8 65 2HO. 1607. This acid is formed by the reaction of nitric on oleic acid, being deposited after the suberic and pimelic acids, which are less soluble. The best method of preparing it consists in boiling, in a large retort furnished with its receiver, tallow with nitric acid of commerce, renewed until the fatty substance has entirely disappeared. The distilled portions are returned to the retort, and the reaction of the nitric acid is continued until crystals appear in the receiver, after which the liquid is concentrated in a water-bath, when it c:agulates into a crystalline mass. It is washed, first with concen- trated nitric acid, then with the same acid more diluted, and lastly with fresh water. Treated again with boiling water, it dissolves and deposits, on cooling, very pure crystals of adipic acid. VOL. II. 3 I 698 FATS. This acid melts at 266, may be distilled without alteration, and forms well-marked salts, of which the general formula is 2RO, C 12 H 8 6 . When an alcoholic solution of adipic acid is saturated with chlorohydric acid gas, an oil .is obtained having the smell of pippin apples, and known by the name of adipic ether 2C 4 H 3 0,C 12 H 8 6 . Suberic Acid C 16 H 12 6 ,2HO. 1608. Suberic acid is formed by the action of nitric acid on fats, being the first deposited when the liquid is crystallized ; while it has also been directly obtained by causing the same acid to act on cork, which is the most convenient method of preparing it. The rasped cork being boiled with nitric acid of commerce, the acid liquid is con- centrated by distillation, and allowed to cool, when suberic acid is deposited, and may be purified by solution in boiling water and recrystallization. Suberic acid forms small, hard, granular crystals, soluble in about 2 parts of boiling water, which scarcely retains T ^ after cooling, while it is very soluble in alcohol and ether, especially at the boiling point. The alkaline suberates are soluble in water, and nitrate of silver effects in their solution a precipitate of suberate of silver, of the formula 2AgO,C 16 H 12 6 . By saturating an alcoholic solution of suberic acid with chlorohydric acid gas, vinosuberic ether 2C 4 H 5 0,C 16 H 12 6 is obtained, as an olea- ginous, colourless liquid, which boils at about 500. Sebacic Acid C 20 H 16 6 ,2HO. 1609. It has been mentioned ( 1602) that sebacic acid is con- stantly formed in the distillation of substances containing olein or oleic acid, and that it is regarded as characteristic of these sub- stances : it is separated by treating the distilled products several times with boiling water. Acetate of lead is poured into the solu- tion, and the salt of lead precipitated is decomposed by sulphuric acid, when the sebacic acid is deposited from the boiling aqueous solution in the form of crystalline, pearly lamellae. This acid melts at 260.6, distils without alteration, and is slightly soluble in cold, but much more freely in boiling water, while alcohol and ether dis- solve it readily. It forms crystallizable salts with the alkalies of the general formula 2RO,C 20 H 16 6 . It produces a compound ether 2C 4 H 5 0,C 20 H 16 6 under the same circumstances as the preceding acids.* * The admirable examination of the fats and fat acids by Chevreul was the first investigation which gave an insight into the chemistry of organic compounds. But more recent investigations have developed the singular transformations to which they are subject; such as, the action of sulphuric acid, their oxidation into other acids, &c. W. L. F. CAPROIC ACID. 699 OF SOME VOLATILE ACIDS EXTRACTED FROM NATURAL FATS. Hircio Acid. 1610. Hircic acid is obtained by saponifying the fat of the goat by an alkali, and decomposing the soap resulting by tartaric acid ; after which the aqueous liquid is separated and distilled, when the hircic acid, being volatile, passes into the receiver. It is saturated with water of baryta, and the hircate of baryta, which is obtained by evaporation, is decomposed by distilling it with sulphuric acid diluted with its weight of water, when the hircic acid forms an oily stratum on the surface of the water which condenses in the receiver. It has a decided goatlike smell, is slightly soluble in water, but easily so in alcohol or ether, and its composition is un- known. Phocenic Acid. 1611. The oil of the sperm whale and dolphin yields, by saponi- fication, in addition to the ordinary fat acids, a peculiar volatile acid, called phocenic, which appears to be identical with valerianic acid. Caproic, Capric, and Caprylic Acids. 1612. These three acids are found among the products of the oxidation of oleic by nitric acid, and are also obtained mixed with butyric acid when butter is saponified by the alkalies. It is admitted that butyric, capric, caproic, and caprylic acid in butter are com- bined with glycerin, and form peculiar substances : butyrin, caprin, caproin, and caprylin. In order to prepare these substances, butter is kept for a long time at a temperature approaching its melting point, when a liquid por- tion separates, in which the butyrin, caprin, caproin, and caprylin are principally concentrated. This oily portion is treated, after being decanted, with an equal part of anhydrous alcohol, and shaken frequently; the alcoholic solution leaving by evaporation an oil formed of a mixture of butyrin, caprin, caproin, and caprylin. If, on the contrary, the butyric, capric, and caproic acids are to be isolated, the butter is saponified with an alkali, and the soap decomposed by an aqueous solution of tartaric acid, when the acids sought remain in the watery liquid ; which is separated and distilled. The acids, being volatile, pass over, and are then saturated with caustic baryta, and evaporated, which furnishes a mixture of buty- rate, caprate, caprylate, and caproate of baryta. The salts are separated by crystallization, the caprate of baryta being first de- posited, then the caprylate, the caproate, and lastly the butyrate. The acid of each of these salts may be easily separated by distil- ling them with a small excess of sulphuric acid diluted with its 700 FATS. weight of water, when the acid passes into the receiver with the water, and forms an oily coating on its surface. Oapric acid is liquid above 62.6, but solidifies into crystalline aciculse when the temperature is lower ; and it is very slightly solu- ble in water, but readily so in alcohol. The formula of free capric acid is C 20 H 19 3 ,HO, that of the caprates being RO,C 20 H 19 3 . Oaprylic acid is solid below 57.2, and boils at about 464. Water dissolves only a very small quantity of it, even at the boiling point, while it is very soluble in alcohol and ether ; and the general formula of the caprylates is RO,C 16 H 15 3 . Caproic acid is an oily liquid at the ordinary temperature, and does not solidify even at 14, while it boils at about 410, and dis- solves in 75 parts of water and in all proportions in alcohol. The general formula of its salts is RO,C 12 H n 3 . These various acids form compound vinic and methylic ethers, which may be obtained by passing chlorohydric acid gas through alcohol or wood-spirit holding the acids in solution. PALM-OIL. 1613. This oil, which is imported chiefly from Guinea, has, of late years, become an object of great commercial importance. It is gene- rally of a reddish-yellow colour, and melts at a temperature varying from 80 to 86. It is supposed to be formed of olein, margarin, and a new fatty substance, called palmitin, which is extracted by express- ing the oil and washing the residue several times with alcohol, when the palmitin is isolated and purified by being washed in ether. Palmitin forms crystalline aciculse, melting at 118.4, but decom- posing at a high temperature ; and it is nearly insoluble in alcohol, even at the boiling point, but dissolves largely in ether. Alkalies convert it into glycerin, and into a new acid called palmitic. Its composition corresponds to the formula C 70 H 66 8 , which is written C 6 H 4 2 ,C 64 H 62 6 ; the formula of free palmitic acid being C 64 H C2 6 , 2HO. CASTOR-OIL. 1614. Castor-oil is extracted from the ricinus communis, and forms a white or somewhat yellowish oil, slightly fluid, which soon becomes rancid in the air. When saponified, it yields glycerin, and three new fatty acids : stearoricinic, called also margaritic, ricinic, and oleoricinic or elalodic acids. By decomposing, by an acid, soap made with castor-oil, an oil separates, which partially coagulates at the ordinary temperature. The solid part being separated and ex- pressed between bibulous paper, the residue is dissolved in boiling alcohol, when, on cooling, pearly crystalline lamellae of stearoricinic acid separate, which melt only at 266. The greater portion of the oil which has been separated by expression from the stearori- cinic acid coagulates at 28.4, and is also separated, by expression SPERMACETI. 701 between tissue-paper, from the portion which remains liquid, when it constitutes ricinic acid, which melts at 71.6, and may be distilled without alteration. Lastly, the name of oleoricinic acid has been given to the portion of the acid oil which did not become solid at 28.4. SPERMACETI. 1615. A peculiar fat oil, which, by exposure to the air for a few days, deposits a crystalline substance called spermaceti, is extracted from the brain of the sperm whale. The crystalline mass is ex- pressed to separate the part which remains liquid, and digested in a hot lye of potassa, while the oily fluid is washed several times with boiling water, and poured into crystallizing vessels, in which it solidifies into crystalline masses, constituting the cakes of spermaceti found in commerce. In order to obtain it in a state of purity, it is necessary to crystallize it several times in alcohol, when it takes the name of cetin. Cetin is a white substance of a crystalline texture, almost inodor- ous, melting at 120.2, and solidifying, by slow cooling, into a mass composed of large crystalline lamellae. It is insoluble in water, and 100 parts of boiling alcohol dissolve 16 parts of it, but retain only 3 after cooling ; while ether and the essential oils dissolve it freely. Its composition corresponds to the formula C 32 H 32 2 . Spermaceti is saponified by potassa, but it differs from all fat substances we have hitherto described by yielding no glycerin, but in its place another very remarkable neutral substance, called ethal, while the fat acid which combines with the alkali has received the name of etJialic acid. The saponification of spermaceti is much more difficult than that of the other fats, since it can only be effected by a concentrated solu- tion of potassa, assisted by heat, and continued for several days ; or better, by melting 2 parts of spermaceti in a capsule and adding 1 part of caustic potassa broken into small pieces, and stirring it con- stantly. After some time, as soon as the substance has become com- pletely solid, it is treated with boiling water and chlorohydric acid, when the ethalic acid separates and forms an oily layer on the sur- face of the liquid. The oil being decanted, and treated in the same manner by potassa, is again saturated with chlorohydric acid, and the oil obtained is heated with hydrated lime, when the ethalic acid alone combines with the lime, leaving the ethal isolated. The latter is removed by boiling alcohol, which is then driven off by distilla- tion, and it is finally crystallized by dissolving it in ether. Ethal melts at 118.4, crystallizing readily, on cooling, in brilliant lamellae, and it is insoluble in water, but dissolves in all proportions in alcohol and ether. It may be distilled without alteration. Its composition corresponds to the formula C 32 H 34 2 , and exhibits seve- ral reactions which assimilate it to alcohol and wood-spirit, on which account it has even been called ethalic alcohol. 3i2 702 FATS. 1616. If a mixture of ethal and concentrated sulphuric acid be heated, stirring it frequently, an acid product is obtained consist- ing of a mixture of pure sulphuric acid and a compound acid, sulph- ethalic acid (C 32 H 33 0+HO),2S0 3 , which is to ethal C 32 H 34 2 what sulphovinic acid (C 4 H 5 0-f HO),2S0 3 is to alcohol C 4 H 6 2 . The acid mass being dissolved in alcohol and saturated with potassa, sulphate of potassa is precipitated, while the sulphethalate of po- tassa (C 32 H 33 0+HO),2S0 3 remains in solution, and crystallizes by evaporating the liquid. By heating in a retort equal volumes of ethal and perchloride of phosphorus, chlorohydric acid is disengaged, and protochloride of phosphorus first distils, then the perchloride, and lastly an oily pro- duct of the composition C 32 H 33 C1, which may be regarded as the cJilorohydric ether of ethalic alcohol C 32 H 34 2 . In order to obtain it pure, it should be distilled a second time with perchloride of phosphorus, washed with water, and distilled over a small quantity of quicklime. By heating ethal with 5 or 6 times its weight of potassic lime to a temperature of 410 to 430, pure hydrogen is disengaged, and ethalic acid C 32 H 31 3 ,HO is formed, which is to ethalic alcohol C 32 H 34 2 what acetic acid C 4 H 3 3 ,HO is to vinic alcohol C 4 H 6 2 . In order to separate this acid, the alkaline mass is diluted with water and saturated with chlorohydric acid, when the ethalic acid separates in the form of flocculi, but always mixed with unaltered ethal. In order to purify it, it is heated with a solution of caustic baryta, which combines with the ethalic acid, after which it is eva- porated to dryness, and the residue treated with alcohol to dissolve the ethal. The residue, which is composed only of ethalate of ba- ryta, is decomposed by chlorohydric acid, while the ethalic acid, set free, is purified by solution in ether. 1617. We have shown (1615) that spermaceti is converted by saponification into ethal and ethalic acid ; and a large quantity of the latter acid may also be obtained by decomposing spermaceti soaps by acids. Ethalic acid melts at about 140, crystallizing, on cooling, in brilliant aciculse ; and it is insoluble in water, but very soluble in alcohol and ether. The general formula of its salts is RO,(C 32 H 31 3 ). As ethalic acid exists in palm-oil, either isolated or combined with glycerin, it has also received the name of palmitic acid. By distilling ethal several times with anhydrous phosphoric acid, a volatile liquid of the formula C 32 H 32 is obtained, which has been called ceten, and forms in the series of ethalic alcohol the analogue of olefiant gas in the vinic series. This liquid boils at about 527 without alteration, and its formula corresponds to 4 volumes of vapour. WAX. 703 WAX. 1618. Chemists give the name of wax to substances arising from various sources, the type of which, heeswax, will alone occupy our attention, because it is best known ; and we shall omit the other substances produced by vegetables, which frequently resemble ordi- nary wax only in appearance or in physical properties. Wax forms the solid portions of the honeycomb ; and when the honey has been removed by expression, the wax is melted with hot water, and washed several times with water, when a yellow substance remains, the smell of which resembles that of honey. By exposing it in large sheets on the grass to the action of moist air and the rays of the sun, the odoriferous and colouring substances are de- stroyed, and white wax remains ; the bleaching being more promptly effected by chlorine or the alkaline hypochlorites, and by oxidizing reagents in general. White wax contains less carbon and more oxygen than yellow wax. Bleached wax is translucent to a certain degree, shows a density varying from 0.960 to 0.996, is hard and brittle at 32, but very malleable at 86, and melts at about 149. Boiling alcohol sepa- rates it into, (1) myricin) almost insoluble in boiling alcohol ; (2) cerin^ also called cerotic acid, soluble in boiling alcohol, but de- posited from it, on cooling, in small crystalline aciculse ; and (3) into cerolein, which remains in solution in the alcohol when cooled. The proportions of these substances vary. Wax yields, by distillation, a small quantity of acid water, com- bustible gases, and liquid oils, isomeric with olefiant gas, besides a solid substance, composed essentially of margaric acid and a crys- tallizable substance very analogous to paraffin. By distilling it with lime, yellow oils of complex composition are first obtained, and then a large quantity of the crystalline substance about to be de- scribed. Oerin or Cerotic Acid C 54 H 54 4 ==C 54 H 53 3 ,HO. 1619. When wax is boiled for some time with alcohol, and the liquor allowed to cool, the deposit which is formed is composed chiefly of cerin and myricin, which must be again dissolved in boiling alcohol, until the substance deposited during the cooling of the liquid melts only at 158. It is redissolved in boiling alcohol, and acetate of lead is added, the precipitate of cerotate of lead being washed, when hot, with alcohol and ether, and then decomposed by acetic acid. The cerotic acid is crystallized by dissolving it in boiling alcohol ; and the pure acid, which melts at 172.4, is insoluble in water. Myricin. 1620. Myricin is very slightly soluble in alcohol, 200 parts of boiling alcohol being required to dissolve 1 of it, which is again 704 ORGANIC COLOURING MATTERS. deposited, during the cooling, in white flakes; while it requires about 100 parts of cold ether for solution. It melts at 161.6, and partly sublimes without change at a higher temperature. Its ele- mentary composition corresponds to the formula 032119204; and when heated for a long time with a concentrated solution of caustic potassa, it is converted into palmitic acid C 92 H 31 3 ,HO, which re- mains combined with the potassa, and a neutral substance, melissin C 60 H 62 2 , which in its chemical reactions resembles ethal. Cerolein. 1621. Cerolein, which remains in solution in the cold alcoholic liquor with which wax has been treated, is separated by evaporation from alcohol, and appears as a soft substance, fusible at 84.2, very soluble in alcohol and cold ether, and reddening litmus. It contains more oxygen than cerin and myricin. ORGANIC COLOURING MATTERS. 1622. While vegetables contain very various colouring matters, unequally distributed through their various parts, they also fre- quently enclose substances which are colourless, or nearly so, con- stituting a part of the living vegetable, but which acquire very beautiful colours by contact with atmospheric air or the reaction of various chemical agents. Nearly all organic colouring matters change in the air, especially when exposed to the sun, and undergo partial combustion, being converted into colourless substances ; and the quality of the colour- ing matter depends upon the time in which this change is effected. Chemical agents generally modify the shade of organic colouring matters, forming compounds with them or converting them into other substances equally coloured, which properties are frequently applied in dyeing. The metallic oxides especially combine with a grea-t number of colouring matters possessing acid properties ; and the majority of the oxides, such as that of alumina, tin, etc., thus form insoluble compounds, exhibiting often very beautiful colours, and which are used, under the name of lakes, for painting in oil and in water-colours. Very porous charcoal, particularly animal black, absorbs the majority of organic colouring matters dissolved in water, without alteration, and again deposits them if a small quantity of alkali be added to the water ; woody and animal fibre possessing the same property. Moist chlorine destroys all organic colouring matters, by exerting on them a powerful oxidizing action, owing to the de- composition of water; and sulphurous acid also bleaches them, MADDER. 705 either by removing their oxygen, or by combining with the substance without altering it, and thus forming colourless compounds. A large number of reducing substances, such as nascent hydro- gen, sulf hydric acid, the alkaline sulphides, the hydrated protoxides of iron and manganese, etc., bleach colouring matters by abstract- ing their oxygen. We shall here treat only of the organic colouring matters used in dyeing. COLOURING MATTERS OF MADDER. 1623. Madder, (rubia tinctorum,) also known by the name of alizari, is one of the most important dyestuffs, which is extensively cultivated in the Levant and the East Indies, as well as in France, particularly in Alsace and the county of Avignon. Madder con- tains several colouring matters, the majority of which are as yet but imperfectly known ; and the plant, w r hile growing, contains only a yellow sap, without any red-colouring principle, the same being true of the root ; while, when the latter has been separated from the plant and dried in the air, a red substance is developed which imparts its colour to all the ligneous portions. In dyeing, sometimes crude madder is used, and sometimes that which has undergone several preparations, of which the intention is to reduce the colouring matter to a smaller volume, or to destroy some of the colouring principles, the presence of which affect the shade of the red colour. When ground madder is exhausted by cold water, a yellow colouring matter, or xanthin, very soluble in water, is extracted from it ; and if the residue be treated with one-half of its weight of concentrated sulphuric acid heated to 212, a large portion of the ligneous matter is altered, becoming soluble in water, and, after several washings, yielding a brown substance, easily pulverized after desiccation, and constituting the article known in commerce by the name of garancin or madder-red. Madder-red contains another colouring matter of a beautiful red hue, called alizarin, mixed with some other colouring principles. When treated with boiling alco- hol, it furnishes a beautifully red solution, which deposits, on eva- poration, a substance of an ochrous yellow colour, and named colorin. Colorin is chiefly formed of alizarin, fatty matters, and a small quan- tity of other colouring matters ; and if it be carefully heated, it emits yellow vapours, which condense in the form of bright-red needles, constituting alizarin, mixed merely with a small quantity of empyreumatic oil, from which it may easily be freed by crystal- lizing it in weak alcohol. Alizarin presents all the characters of a definite compound, and its analysis has led to the formula C 30 H 8 4 . It forms very fine aciculse of an orange-yellow colour, nearly insoluble in cold water, slightly soluble in boiling water, but very soluble in alcohol. It 45 706 ORGANIC COLOURING MATTERS. dissolves readily in alkaline lixiviae and ammonia, furnishing solu- tions of a violet colour, and yielding bluish precipitates with solu- tions of baryta, strontian, and lime : concentrated sulphuric acid also dissolves it, forming a brown liquid, from which the alizarin is precipitated unchanged upon the addition of water. 1 624. Very variously coloured products have been obtained by different methods of treating madder-root, which, however, do not exhibit the characters of definite substances, and are probably only mixtures. When madder-root, previously washed, is boiled with a concentrated solution of alum, a red liquid is obtained, depositing, on cooling, a brownish-red substance, which is separated, while the filtered liquid is of a pure red, and by the addition of sulphuric acid gradually deposits the colouring matter, a mere trace of it remain- ing in the solution after 24 hours. The precipitate, after being washed, first with weak boiling chlorohydric acid, and then with cold water, is redissolved in alcohol, which solution is evaporated, and the residue treated several times with ether, when a colouring matter dissolves, called purpurin or madder-purple, which remains after the evaporation of the ether, in the form of a bright-red pow- der. This substance is insoluble in cold water, but very soluble in boiling water, alcohol,' and ether ; and its analysis has led to the formula C^H^O^ : but as it has not been obtained in a crystallized form, it is difficult to assert that it is a simple substance. The name of madder-red is given to a colouring matter found in the brown precipitate deposited by a hot decoction of madder, on cooling ; which substance sublimes at about 437, forming crystals of a yellowish red colour, and of a composition corresponding to the formula C 20 H 10 15 . By dissolving the colouring matters of madder in a solution of alum, and then adding carbonate of soda, pecipitates of very beau- tiful colour and great stability are obtained, consisting of compounds of alumina with the colouring matters, and called madder-lakes, which are used in painting. COLOURING MATTERS OF LOGWOOD. 1625. The name of hematin has been given to the substance to which logwood owes its value as a dyestuff. It is readily ob- tained by making a decoction of powdered logwood, evaporating it to dryness, and treating the residue with alcohol, when hematin is deposited in crystals, varying in depth of colour according to their size, but producing a yellow powder. The aqueous solution of hematin is colourless in the air, but if ammonia be added, it assumes an intense red hue ; the substance produced by this reaction being named hematein, which is granular and crystalline, showing a violet- black colour and metallic lustre. It dissolves in water, and turns it of a deep purple colour. Hematein appears to differ from hema- tin by containing 1 equiv. less of water, the formula of dried QUERCITRON. 707 hematin being C 16 H 7 6 ,HO, and that of hematein C 16 H 6 6 ; while the formula of hematin crystallized from an aqueous solution is C 16 H 7 6 ,HO+2HO. Hematin possesses the properties of a feeble acid, its aqueous solution being precipitated by baryta and acetate of lead. Hema- tate of lead, decomposed by aqueous sulf hydric acid, forms a liquid which deposits nearly colourless crystals of hematin on evaporation. COLOURING MATTERS OF SAFFLOWER. 1626. The safflower is used in dyeing, and produces colours which vary from a delicate rose to a deep poppy hue. Several colour- ing matters exist in the flowers ; and when they are exhausted by water, they yield a yellow colouring matter, useless in dyeing, which combines with bases ; the formula of its compound with oxide of lead being 3PbO,C 16 H 10 I( , If safflower, exhausted by cold water, be treated with a solution of carbonate of soda, a red solution is obtained, by accurately neu- tralizing which with acetic acid, and dipping cotton into it, the* red colouring matter, or carthamin, is precipitated. As soon as the liquid is nearly bleached, the cotton is removed, and treated with water containing ^ of carbonate of soda, when the carthamin dis- solves, and, if citric acid be added to the liquid, is again precipitated in the form of crimson flakes. The precipitate being redissolved in alcohol and evaporated, a deep-green substance is obtained, which changes colour when seen in different lights. The formula C U H 8 7 has been assigned to carthamin. BRAZIL OR PERNAMBUCO WOOD. 1627. Decoctions of Brazil or Pernambuco wood are used in dyeing, and produce red colours which are not very permanent. The colouring principle of this wood, called brazilin, has been ob- tained in small orange-coloured crystalline aciculse, soluble in water, alcohol, and ether, but of unknown composition. Brazilin assumes a purple hue on contact with the alkalies, while the action of acid and of ammonia converts it into a new substance, brazilem, which is of a deep purple/ WELD. 1628. Weld (reseda luteola] contains a colouring principle of a beautiful yellow colour, called luteolin, which is extracted by boiling water, and appears as a yellow substance, soluble without decompo- sition, and subliming in small aciculse. It is very slightly soluble in water, and yet the small quantity which dissolves in it is suffi- cient to afford beautiful dyes, remarkable for their stability. QUERCITRON. 1629. The name of quercitrin has been given to a colouring principle found in the bark of a certain species of oak, the quercus 708 VEGETABLE COLOURING MATTERS. nigra, from which it is extracted by treating the powdered bark with alcohol, precipitating the tannin by gelatin, evaporating the liquid, and dissolving the residue in alcohol and then in water. Quercitrin is a yellow crystalline substance, of the formula C 16 H 9 10 , which dissolves in 100 parts of cold water, and in 4 or 5 of absolute alcohol. ARNOTTO. 1630. This is the name of a reddish-yellow substance, arising from the fermentation of the bixia orellana, and imported from Brazil, Guiana, and the East Indies. Arnotto contains two dis- tinct colouring matters, one of which is yellow, and soluble in water and alcohol, but very slightly soluble in ether ; while the other, which is red, is slightly soluble in water, but highly so in alcohol and ether. RED SANDERS. 1631. The name of santalin has been given to the collection of colouring matters of the wood of the pterocarpus santalinus, and it is extracted by treating this wood, ground to powder, by alcohol, when the solution is of a reddish-yellow colour, and leaves, after evaporation, a resinous substance of the same colour. It dissolves in the alkaline lixiviae, and turns them of a violet colour. INDIAN-YELLOW. 1632. A substance used in dyeing, and known by the names of purree and Indian yellow, is imported from China and the Indies, but its origin is unknown. It dissolves in water acidulated with chlorohydric acid, while a crystalline substance separates, called euxanthic acid, which forms nearly one-half of the weight of Indian yellow ; some foreign substances being precipitated at the same time. In order to prepare pure euxanthic acid, Indian yellow is treated with acetic acid, and acetate of lead is added to the liquid, when euxanthate of lead is precipitated, and may be decomposed by sulf- hydric acid. By boiling the liquid, the euxanthic acid is dissolved, and crystallizes, on cooling, in long, yellow, silky needles, which are readily soluble in alcohol and in ether. Its formula, when dried at 212, is C 42 H 18 22 ; while, if it be heated still further, the euxan- thic acid melts and evolves vapours which solidify in small crystals, constituting a new substance, euxanthone C 42 H 12 I2 , which is also ob- tained either by the distillation of euxanthate of lead or by causing concentrated sulphuric or chlorohydric acid to act on euxanthic acid. We have, moreover, C 42 H 18 22 =C 40 H 12 12 +2C0 2 +6HO. Euxanthone possesses no acid properties. With chlorine, bromine, or nitric acid, euxanthic acid yields products by substitution, with the formulse C^H^CIA,, CJI 16 Br 2 22 , CJH^NOJO^. The chlo- CHLOROPHYLL. 709 rinated and brominated euxanthic acids dissolved in concentrated sulphuric acid, and precipitated by water, yield chlorinated euxan- thone C 40 H 10 C1 2 12 or brominated C 40 H 10 Br 2 12 . CAROTIN. 1633. Carotin, the red-colouring matter of carrots, is extracted by diluting carrot-juice with 4 or 5 times its volume of water, and then adding sulphuric acid, which precipitates the colouring matter with the albumen and fatty substances. The latter are separated by boiling the precipitate for some time with a solution of caustic potassa, which dissolves them ; and the carotin is purified by boiling it with dilute sulphuric acid, and digesting it, first with ordinary, and then with absolute alcohol. The substance, when dried, is treated with sulphide of carbon, which dissolves the carotin, after which f of the liquid are separated by distillation, anhydrous alco- hol is added to the residue, and the liquid is exposed to the air, when, after some time, small copper-coloured crystals of pure caro- tin are deposited. Carotin melts at about 338, but is decomposed at a higher temperature, and it is nearly insoluble in water, alcohol, and ether. Its elementary composition is the same as that of oil of terpentine, but no means of ascertaining its equivalent are known. GREEN AND YELLOW COLOURING MATTER OF LEAVES. 1634. The green-colouring matter of leaves, or chlorophyll, exists in them but in a very small quantity, and is exceedingly dif- ficult to extract in a state of purity. The best method known con- sists in digesting the leaves for several days with ether ; after which the liquid is filtered and evaporated to dryness, when the greater portion of the residue is composed of a substance analogous to wax and of chlorophyll. It is dissolved in boiling alcohol, which deposits, on cooling, the greater part of the wax ; and the alcohol being again evaporated, and the residue treated with a smaller proportion of boil- ing alcohol, wax still separates on cooling. The solution is finally evaporated, and the residue treated with concentrated chlorohydric acid, which yields a beautiful green solution. The liquid is satu- rated and filtered, after having introduced some pieces of marble into it, when the chlorophyll, which is rendered insoluble, being precipitated, is washed with weak chlorohydric acid, and then with fresh water. Chlorophyll is insoluble in water, but readily soluble in alcohol and ether, and sulphuric and chlorohydric acids dissolve it without change ; a large quantity of water precipitating it again. From an analysis made of it, the composition of chlorophyll, dried at 266, would correspond to the formula C 18 H 9 N0 8 . The name of xanthophyll has been given to the yellow-colouring matter of autumnal leaves ; but nothing is with certainty known as to its nature. VOL. II. 3 K 710 VEGETABLE COLOURING MATTERS. COCHINEAL. 1635. The cochineal (coccus cacti) is a small insect found on the nopal, (opuntia coccinillifera,) and furnishing the most brilliant red colours for dyeing ; those found in commerce being composed only of the dried insects. When these are boiled with water, a red liquid is produced, which is clouded by the addition of alum or bitartrate of potassa ; a precipitate being formed which remains a long time in suspension, and which consists of the colouring matter and vari- ous fatty and albuminous substances, constituting the carmine of commerce. If cochineal be boiled with a weak solution of carbonate of soda, and alum be added to the liquid, red precipitates of alumina, combined with the colouring matter, are formed, known by the name of carmine lake. The name of carmin has been given to the colouring matter of cochineal, but it is doubtful whether it has been obtained in a state of purity. The powdered cochineal is treated with ether to dissolve the fatty matters, and then with boiling alcohol to dissolve the carmin, which is deposited during the cooling of the liquid. In order to purify it, it is dissolved in alcohol to which an equal volume of ether has been added, when the carmin is slowly deposited in the form of small purplish-red grains. The substance thus obtained melts at 104, and is soluble in water and alcohol, but insoluble in ether. Acids heighten its red colour, while alkalies turn it of a violet hue. ARCHIL AND LITMUS. 1636. The name of archil is given in commerce to some very com- plex colouring substances extracted from various species of lichens, among which may be distinguished the lecanora parella, the vario- laria dealbata, the roccella tinctoria, etc. In order to obtain the archil, the lichens are mashed, and macerated in wooden troughs with a mixture of urine and ammonia, or urine and lime, when the substance ferments after some time, and is frequently stirred and kept at a temperature of 77 or 86. After several months the archil is ready for commerce, and is put into barrels. The litmus used in the laboratory is prepared from the same lichens, and by a similar fermentation. The colouring principles of archil and litmus have hitherto not been isolated with certainty, although several red, non-crystalline substances have been separated, to which various names have been given, but which exhibit none of the characters from which they might be supposed to be definite compounds. But by operating directly on the lichens, perfectly well-defined crystallizable sub- stances have been extracted, from which the colouring matters of archil and litmus probably originate during the fermentation of the plant. LICHENS. 711 By exhausting the roccella tinctoria or the leca/iora parella by ether, and concentrating the etherial solution by distillation, greenish crystals of an acid substance, termed lecanorie acid, are separated, which are purified by washing them with a small quantity of ether and crystallizing them several times in alcohol. Pure lecanorie acid is colourless, and requires for solution 250 parts of boiling water, being still less soluble in cold water; while it dissolves in 15 parts of alcohol and in 80 of ether. It reddens litmus and decomposes the carbonates, and the general formula of its salts is RO,C 18 H 8 8 . If lecanorie acid be boiled for a long time with absolute alcohol, lecanorie ether C 4 H 5 0,C 18 H 8 8 is formed, which is separated by evaporating to dryness and again treating with boiling water, which, on cooling, deposits it in the form of small crystals, which may be sublimed without alteration. A methyllecanoric ether C 2 H 3 0,C 18 H 8 8 is pre- pared in the same manner. 1637. Lecanorie acid is decomposed by heat into carbonic acid and a new substance, orcin, which volatilizes. It undergoes the same decomposition when heated with the alkalies, or treated even with cold sulphuric acid. The best method of preparing orcin consists in boiling lecanorie acid with an excess of water of baryta, precipi- tating the baryta by carbonic acid, and filtering the boiling liquid, which, after evaporation, furnishes crystals of impure orcin. These being redissolved in water, the liquid is boiled for some time with alumina or recently precipitated sesquioxide of iron; when the filtered liquor deposits, on evaporation, pure orcin, in long, slightly yellowish prismatic crystals, which first part with water by heat, and then sublime without alteration. Orcin dissolves readily in alcohol. The formula of its hydrated crystals is C 16 H 8 4 ,3HO, and it is precipitated by acetate of lead, furnishing a compound of the formula 5PbO,C 16 H 8 4 . Ammonia, oxygen, and water convert orcin into a colouring substance, orcein, which appears to be one of the colouring prin- ciples of archil. The reaction is arrested when the substance communicates a beautiful violet colour to the water ; for if it were prolonged, new substances would be formed, which would turn the water to a brown colour. According to an analysis, the formula of orcein would be C 16 HgN0 7 ; and it produces, with potassa and soda, violet-red solu- tions, and with ammonia a beautiful violet colour. 1638. By exhausting the lecanora parella, divided into small pieces, by boiling water, a yellowish-brown liquid is obtained, which deposits, on cooling, crystalline flocculi of an acid substance, called erythric acid, while the mother liquid contains another substance, pieroerythrin, which is a product of the alteration of erythric acid by boiling water. Erythric acid is purified by dissolving it in alcohol, and constitutes a white crystalline substance, requiring more than 200 times its weight of boiling water for solution, the greater por- 712 VEGETABLE COLOURING MATTERS. tion of it being deposited on cooling. It is more soluble in alcohol and in ether, and its solutions redden litmus. Its composition cor- responds to the formula C 34 H 19 Oi 5 ,4HO ; and when heated, it first melts, and is then decomposed, giving rise to orcin, which sublimes. The cold alkalies dissolve it without change, while if it be heated to the boiling point, orcin and carbonic acid are formed. A solu- tion of erythrate of ammonia, exposed to the air, soon produces a liquid of a deep purple colour. If erythric acid be boiled with absolute alcohol, a compound, erythric ether (C 4 H 5 0+3HO),C 34 H 15 O n , formerly called pseudoery- thrin, is formed, which is soluble in boiling water, and separates from it, on cooling, in crystalline aciculse, or in oily drops which soon become solid. The picroerythrin remaining in the mother liquid which has de- posited the erythric acid, and which is formed directly by boiling erythric acid for a long time with water, differs in its composition from the latter acid only by containing 5 additional equivalents of water, its formula being C 34 H 24 20 . The picroerythrin remains, after evaporation, in the form of a white crystalline mass, which is converted into orcin and carbonic acid, either by heat alone or by boiling it with alkalies. By exposing erythric acid dissolved in hot water to the air for several days, the liquor turns brown, and then contains two new crystallizable substances, called amarythrin and telerythrin, the first of which is very soluble in water and alcohol, while the second is insoluble in cold alcohol, thus furnishing an easy means of sepa- rating it from the first. The composition of these substances is unknown. INDIGO. 1639. Indigo is found in a great number of vegetables, particu- larly in plants of the genus indigofera, in the polygonum tinctorium, and in woad; being chiefly obtained from the indigoferous plants. After the flowering of the plant, the leaves which contain the greater proportion of indigo are removed, and dried in the sun ; and then they are, after being crushed, infused for 2 or 3 hours with 3 times their volume of cold water. The solution, after being strained through a cloth, is stirred in the air for some time ; after which 5 litres of limewater for every 10 kilog. of dried leaves are added, when the liquid soon turns blue and deposits indigo. The deposit is separated, washed with a small quantity of boiling water, and, after being drained on a cloth, is subjected to heavy pressure. This substance, after being dried in the air and cut in pieces, constitutes the indigo of commerce, which is, however, very impure, and con- tains only about 45 per cent, of real indigo or indigotin^ the balance consisting of resinous substances, fecula, carbonate of lime, and a large number of other saline substances. In order to remove the INDIGO. 713 greater portion of these foreign substances, the powdered indigo is washed successively with boiling water, alcohol, and weak solutions of chlorohydric acid. Pure indigotin is obtained by heating indigo in a glass tube in a current of hydrogen, until crystals begin to sublime in the anterior part of the tube, the temperature being kept as low as possible ; when the indigotin volatilizes with a violet vapour, as deep coloured as that of iodine, and is deposited in the form of beautiful crystal- line needles of a purplish violet colour. The same vapours are evolved when indigo is thrown on a hot body, but the greater por- tion of the indigotin is then decomposed. Indigotin is wholly insoluble in water, and nearly so in alcohol and ether ; and its composition corresponds to the formula C 16 H 5 N0 2 . 1640. Dilute acids do not act on indigotin, while concentrated and particularly Nordhausen sulphuric acid dissolve it readily, and produce a beautiful blue liquid ; the reaction being not owing to solution, but rather to an actual combination of the indigotin with sulphuric acid. When indigo is digested with about 5 parts of monohydrated sul- phuric acid, raising the temperature to about 122, the indigo dis- solves, and forms a liquid of a very intense purple, depositing a blue precipitate when diluted with water, which is collected on a filter, and washed with water acidulated with chlorohydric acid until the washings contain no more sulphuric acid, when it is dried by heat- ing it to 248 in vacuo. This compound, called indigo-purple, or sulphopurpurio acid, has the formula C 16 H 5 N0 2 ,S0 3 , and dissolves in pure, but is insoluble in acidulated water. It forms, with the alkalies, purple compounds which are precipitated in flocculi. By treating, on the contrary, 1 part of indigo with 15 or 20 parts of monohydrated sulphuric acid, or 8 or 10 parts of Nordhausen acid, and keeping the mixture for some time at a temperature of 122 or 140, a beautifully blue liquid is obtained, which contains another compound of indigotin with sulphuric acid, sulphindigotic acid. By adding to this liquid 40 or 50 times its volume of water, a small quantity of indigo-purple, which is collected on a filter, sometimes separates. The liquid being saturated with carbonate of potassa, a precipitate of sulphindigotate of potassa is formed, which is soluble in fresh water, but insoluble in water highly charged with sulphate of potassa. It is washed with a solution of acetate of po- tassa, which not only dissolves the sulphindigotate, but also removes the sulphate of potassa ; and lastly, it is treated several times with alcohol, which removes the acetate of potassa without dissolving the sulphindigotate. The formula of sulphindigotate of potassa is KO,(C 16 H 4 N0 2 , S 2 5 ), showing the indigo to have lost 1 equiv. of hydrogen, which combined with 1 equiv. of oxygen given off by the sulphuric acid, and which separates in the state of water when sulphindigotic acid 3K2 714 VEGETABLE COLOURING MATTERS. is combined with bases. Several other sulphindigotates may be obtained from the potassa salt by double decomposition. Lastly, by causing a larger quantity of fuming sulphuric acid to act on indigo, a new acid is formed, together with the sulphindigotic acid, forming, with the alkalies, more soluble salts than the sulphin- digotates. This acid, the composition of which is unknown, has received the name of hyposulphindigotic acid. White Indigo. 1641. When blue indigo is subjected to reducing agents, it com- bines with the hydrogen set free, and is converted into a colourless substance, called white indigo, or colourless indigotin, which by expo- sure o the air again passes into the state of blue indigo. It is prepared by placing in a barrel holding 1 hectolitre, a J kilog. of indigo of commerce, 1 kilog. of sulphate of the protoxide of iron, and 1 J kilog. of lime ; after which the barrel is filled with tepid water, shaken actively, and hermetically closed. After two days, the clear supernatant liquid is drawn off by a siphon, and conveyed into large bottles filled with carbonic acid, at the bottom of which acetic or chlorohydric acid, charged with sulphuric acid in sufficient quantity to saturate the lime, has been placed. The liquid imme- diately becomes clouded, grayish-white flakes being precipitated, which are collected on a filter and rapidly washed, first with water charged with sulphurous acid, and then with recently boiled fresh water. The filter is expressed between tissue-paper and the sub- stance dried in vacuo. This substance is white indigo, but it is very difficult to prevent it from absorbing a small quantity of oxygen from the air, and it should be kept in bottles filled with carbonic acid. It is insoluble in water, soluble in alcohol and ether, does not act on litmus, and is decomposed by heat. It rapidly turns blue in water containing air, and does not combine directly with the weak acids ; although during the reduction of sulphindigotic acid by sulf hydric acid a colourless substance is obtained, which is probably a compound of colourless indigo with sulphuric acid. Nordhausen acid dissolves it, but the liquid is of a beautiful purple colour ; and all oxidizing agents convert it instantly into indigo-blue. White indigo readily combines with bases, furnishing several soluble compounds ; which is the case with the alkalies, ammonia, lime, baryta, and magnesia ; the solutions being yellowish, but soon turning blue in the air. The other metallic oxides form insoluble compounds, which are easily obtained by double decomposition. The composition of white indi- go corresponds to the formula C 16 H 6 N0 2 , and differs from that of blue indigo C 16 H 4 N0 2 only by containing 2 additional equivalents of hydrogen. INDIGO. 715 Products of the Action of Nitric Acid on Indigo. 1642. The action of nitric acid on indigo produces isatin C 16 H 5 lSr0 4 , remarkable for the numerous substances which have been derived from it. A liquid paste is made with 1 kilog. of indigo of commerce and water, which is carefully heated in a porcelain cap- sule, nitric acid being gradually introduced with constant stirring, until 600 or 700 gm. of acid are added. The indigo has then dis- appeared, and the liquid, which is more or less brown-coloured, contains the isatin, mixed with several other substances, which have not yet been examined. The liquid, being diluted with a large quantity of water, is heated to boiling, and the boiling liquid rapidly filtered, when the isatin is deposited, on cooling, in reddish mamil- lary crystals. The deposit remaining is heated with the mother liquid which has deposited the first crystallization of isatin, which furnishes an additional quantity ; and this process is repeated until no more isatin is deposited. Isatin may also be obtained by heating indigo with a mixture of bichromate of potassa and sulphuric acid, dissolved in 20 or 30 parts of water. Isatin is slightly soluble in cold water, but largely so in boiling water, and still more freely in boiling alcohol ; and its solutions do not act upon litmus. When heated, it first melts, and then gives off vapours of unaltered isatin, the greater portion of the substance being nevertheless decomposed, and leaving a copious carbonaceous residue. Concentrated nitric acid, when cold, readily dissolves isatin, forming a brownish-red liquid, which deposits unaltered isa- tin ; while if the liquid be boiled, lively reaction ensues, and oxalic acid is formed. Isatin is easily acted on by chlorine, and yields products derived by substitution. The isatin must be diluted with water, and a current of chlorine passed through, when monochlorinated isatin C 16 H 4 C1N0 4 is first formed ; while if the action of the chlorine be prolonged, bichlorinated isatin C 16 H 3 C1 2 N0 4 is produced ; the same compounds being obtained by causing chlorine to act on indigo. Bichlorinated isatin is more soluble in water and in alcohol than monochlorinated isatin. Isatin and indigo, in contact with melted hydrate of potassa, evolve hydrogen, and anilin is formed, ( 1684 ;) while, under similar circumstances, monochlorinated isatin produces monochlorinated anilin, and bichlorinated isatin bichlorinated anilin. When a concentrated solution of potassa is poured over isatin, there results first a violet-coloured liquid, which by boiling, and after being diluted with water, is converted into a yellowish solu- tion, depositing crystals on evaporation. Here isatin has seized upon the elements of 1 equiv. of water, and been converted into a new acid, called isatic, the formula of isatate of potassa being KO, C 16 H 6 N0 5 . 716 VEGETABLE PHYSIOLOGY. With ammonia, isatin and isatic acid form numerous compounds, which will not occupy our attention. By subjecting isatin to the action of reducing agents, it is changed into isathyd C 16 H 6 N0 4 , by a reaction precisely similar to that which converts blue into white indigo. Sulf hydrate of ammonia being poured into a hot alcoholic solution of isatin, and the mixture al- lowed to rest for some days in a well-corked bottle, sulphur is depo- sited, at the same time with laminated crystals of isathyd, which are colourless or slightly grayish. They are insoluble in water, but slightly soluble in boiling alcohol, from which they are depo- sited on cooling ; and they are decomposed by heat. By treating monochlorinated and bichlorinated isatin in the same manner, there results monochlorinated isathyd C 16 H 5 C1N0 4 and bichlorinated isa- thyd C 16 H 4 C1 2 N0 4 . If sulf hydric acid be substituted for sulf hydrate of ammonia, the isatin is not satisfied with 1 equiv. of hydrogen, but also exchanges 2 equiv. of oxygen for 2 equiv. of sulphur, and furnishes a new sub- stance, lisulphisathyd C 46 H 6 N0 2 S 2 , which, when treated with an alcoholic solution of potassa, forms a red liquid, depositing colour- less crystals of sulphisathyd C 16 H 6 N0 3 S. If, on the contrary, the bisulphisathyd be heated with a highly concentrated solution of potassa, the 2 equiv. of sulphur are removed, and a rose-coloured liquid is obtained, holding a rose-coloured sub- stance in solution, of the same elementary composition with white indigo, and which has received the name of indin. ACTION OF VEGETABLES ON THE ATMOSPHERE. 1643. Vegetables derive the materials necessary for their growth, principally from the atmosphere ; but as the various cir- cumstances of this phenomenon are not well understood, we shall only mention what is most accurately known on the subject. All vegetables spring from a seed which is the product of a simi- lar vegetable, and if properly dried and preserved from moisture and the attacks of insects, appears to be able to retain its germinating principle for an indefinite length of time. But if it come into contact with water, and the temperature be not too low, it soon swells, while its woody envelope cracks, and filaments, or radicles, which endeavour to penetrate the earth, start from one side, and from the other rises a small stem, the germ, in an opposite direc- tion, into the air. These primary developments of vegetable life take place at the expense of the amylaceous matter of the seed, in which is formed a nitrogenous principle, called diastase in the ce- realia, the special office of which is to convert rapidly the starch into dextrin and sugar, that is, into soluble principles, which, by means of agencies as yet unknown, are again organized, and transformed into cellulose, in its turn serving for the formation of the primary VEGETABLE PHYSIOLOGY. 717 cellular tissues of the germ and radicles. During this first epoch of vegetable life, carbonic acid is disengaged, and the presence of oxy- gen appears essential, for moistened seeds will not germinate in an atmosphere deprived of this gas. The portions of the seed which furnish the amylaceous substance, the cotyledon^ have then lost their consistence, and wither. When it reaches the air, the germ assumes a green colour, and throws out the primary leaves. The phenomena of assimilation are then wholly changed, and the new vegetable seeks the elements ne- cessary to its growth, principally in the atmosphere ; and its green portions, the leaves chiefly, under the influence of solar light, ab- sorbing the carbonic acid of the air, assimilate to themselves the carbon, and give out oxygen into the atmosphere ; while they also possess themselves of a certain quantity of nitrogen, which serves for the formation of the nitrogenous principles essential to them. The hydrogen is evidently furnished by the water which arises both from "the vapour disseminated in the atmosphere and the moisture of the soil. The greater portion of the water remains as such in the vegetable, and forms the sap, which serves to transport, through the various parts of the plant, the nutrient principles, rendered solu- ble by actions at present unknown ; while another part of jthe water is probably decomposed, by the action of the vegetative forces, into hydrogen which is assimilated, and into oxygen which is disengaged with that arising from the more or less complete decomposition of the carbonic acid. 1644. In this theory of vegetable growth, we have supposed the earth to play but an unimportant part, and to serve merely as a base on which the plant is erected, and whence, by means of its roots, it can procure the greater portion of water necessary for sap ; but the daily experience of the farmer proves that its part is less passive. When the soil is deprived of organic substances in decom- position, it is known to have lost its fertility, and to give birth to a small number of dwarfish plants, which struggle with difficulty- through the various phases of an ephemeral existence ; and in order to restore its fertility, it must be supplied with organic detritus, principally animal substances, known by the name of manures. Manures supply the roots with organic, chiefly nitrogenous sub- stances, which the vegetable assimilates to itself; while they also furnish mineral principles, either already soluble or rendered so by the chemical agencies developed in the earth. These constituents, which are found again in the ashes of the vegetable, are necessary to its well-being ; and when they are wanting in the soil, or do not exist in sufficient quantity, the plants wither, and are unable to con- struct the mineral framework which appears to be essential to some of them. 1645. The following are some experiments in support of this theory : 718 VEGETABLE PHYSIOLOGY. The decomposition of carbonic acid by the green portions of vegetables can be very easily demonstrated. By placing fresh leaves in a bell-glass, partly filled with water, and partly with car- bonic acid gas, and exposing the glass to the sun, the carbonic acid disappears, and after some time is replaced by a rather smaller quantity of oxygen ; and as carbonic acid contains a volume of oxygen equal to its own, we may conclude from this experiment that all the oxygen of the carbonic acid is not set free. The car- bonic acid, very probably, is only partially decomposed by the vegetable, being, for example, reduced to the state of carbonic oxide, which enters into the constitution of new organic substances, the remainder of the oxygen arising from the decomposition of the water. If part of a branch of a tree be placed in a bell-glass ex- posed to the sun, and into which has been introduced a mixture in known proportions of atmospheric air and carbonic acid, it will be easy to ascertain that the gas which escapes from the bell-glass is almost wholly deprived of its carbonic acid, and that the lat'ter is replaced by oxygen. This decomposition of carbonic acid by the leaves takes place only under the influence of the solar rays and the diffuse light of day; while in the dark, or when exposed to artificial light, an inverse action ensues. Experiment shows that in this case, they evolve carbonic acid and absorb oxygen, while if the effects of the day be compared with those of the night, the former will be found to exceed the latter greatly, and consequently the action resulting is that which takes place under the influence of the solar rays. Those parts of the vegetable which are unprovided with the green parenchyma, the roots, chiefly behave with regard to the atmo- spheric air, even in the sun, like the green parts in the dark, since they absorb oxygen and evolve carbonic acid. The absorption of oxygen appears to be essential to them, for a vegetable soon perishes when its roots are in an atmosphere deprived of this gas. The following experiment proves very conclusively the manner in which a plant grows at the expense of the elements of atmospheric air : A known weight of seed is sown in a soil formed of pounded bricks or quartzose sand previously calcined and washed, this artificial soil being placed under a bell-glass so arranged as to be kept properly moist, and exposed to the sun, while a current of air, to which 1 or 2 hundredths of carbonic acid gas are added to assist the development of the vegetable, is passed through the bell-glass. The seeds soon germinate, the plants grow, and pass through the various phases of vegetable life, without, however, ever attaining the development and strength they would have acquired in a fertile soil. They are then removed, and the absolute quantities of carbon, hydrogen, oxygen, and nitrogen which they contain are ascertained by chemical experiment. It is evident that the soil could afford them nothing, as it is unchangeable, and at all events contains neither ANIMAL CHEMISTRY. 719 carbon nor nitrogen ; and therefore, if they have not borrowed their carbon and nitrogen from the air, they can contain only the carbon and nitrogen which existed in the seeds. Now, it is easy to analyze a sample of seed identical with that which has germinated, and determine by calculation the carbon and nitrogen contained in the seeds which have vegetated ; and by comparing this quantity of carbon and nitrogen with that found in the plants, the latter will be found to be much larger. It must therefore be admitted that the plant has absorbed carbon and nitrogen from the atmosphere. 1646. We have shown (95) that atmospheric air contains only from 4 to 6 ten-thousandths of carbonic acid, which very small proportion is still sufficient to furnish the carbon which accumulates in the vegetables covering the earth. But the carbonic acid of the air, which thus disappears, is constantly reproduced and restored to the atmosphere by the respiration of animals, the decomposition of vegetables, and the chemical reactions taking place in the interior of the globe. Moreover, the terrestrial atmosphere is of con- siderable extent, and the total amount of carbonic acid which it contains includes a quantity of carbon greater than the whole vegetable kingdom ; and the continual agitation of the atmosphere mixes all its component parts, and assists the absorption of carbonic acid by plants by constantly renewing the air which surrounds them. ANIMAL CHEMISTRY. 1647. The body of every animated being may be considered as a laboratory in which extremely numerous chemical reactions are performed, the majority of which are very complicated and as yet but little understood; as well upon the substances which al- ready constitute the being, as on the new substances taken in as food. In the present state of science, it is impossible to decide whether all these reactions are owing, solely, to forces of the same nature as those which determine the chemical metamorphoses witnessed in the laboratory, or the unknown and undefinable cause, which is called life or vitality, introduces into it some special forces.* Even admitting that we can explain, without resorting to other agents than the ordinary chemical forces, all the chemical modifications of substances in the vegetable or animal economy, we should still be obliged to admit the existence of special, and so to say, intelligent actions, in order to explain the varied, and yet so clearly marked forms which solid matter assumes in the composition of the various * We use here the -word forces, because it is generally used in this sense ; but it must not be forgotten that it in no wise satisfies the definition of it given in me- chanics. It merely expresses the efficient and unknown cause of complicated effects, the exact analysis of which is at the present day as yet impossible. 720 ANIMAL CHEMISTRY. organic forms, so different from those assumed by matter when it simply obeys the laws of molecular attraction, without regard to the organism. A single substance, modified by the vital forces, may assume the most varied organic forms, and different states of aggregation, which frequently alter its apparent properties so greatly as to lead us, at first sight, to consider them as different substances. The progress of substances in the economy is governed by laws and directed by mechanical arrangements, generally of difficult explanation, and acting by instinct, which impel these sub- stances successively into the vessels in which they are elaborated and fitted for the special functions assigned to them in the organism. The study of the modification of matter in the vegetable and animal economy, therefore, presents difficulties much greater than those of the chemical phenomena observed in the laboratory. They occur between substances generally of very complex composition, of extreme mobility, and difficult definition by the characters we have adopted for mineral substances. At each step we meet with those mysterious agencies, by which very small quantities of certain substances of a nature still problematical, execute, without any ap- parent intervention of their chemical elements, reactions between incomparably larger quantities of other substances : phenomena of which many examples have already been mentioned in the pre- sent work, and from the explanation of which chemists generally extricate themselves by calling them phenomena of contact, or fermentations. Again, other circumstances increase the difficulty of this study. Substances are modified in the animal and vegetable economy, suc- cessively, and in special organs which it is impossible to detach from the organized being in order to study the reactions which take place in each of them, without altering completely the con- ditions which would have existed in the animated being. Lastly, in the laboratory, chemical reactions are studied in unassailable vessels which play no part in the phenomena, which is altogether different in organized beings, chemical reactions being there effected in vessels the substance of which, for the most part, shares in the reaction, and thus immeasurably complicates the phenomena. We have been satisfied with describing the substances of vegetables, uninfluenced by vegetative life, and have not touched upon their modifications in the plant, since we could have advanced but a few vague and uncertain notions. Our knowledge of the modifications of substances in the animal economy are not much more accurate ; and to avoid the danger of stating any rash opinions, we should observe the same caution, and only describe the property of those substances when they are no longer influenced by vitality. But here the question becomes much more important, on account of its intimate connection with the medical sciences, in which our acquaint- BONE. 721 ance with the chemical reactions ensuing in the human body in health or in disease is of the highest importance, inasmuch as it may furnish valuable means of diagnosis, or may discover the treatment applicable to various pathological conditions. We shall describe the most important and best-known animal substances, with their properties, when they are uninfluenced by vitality ; and then endeavour to give a general idea of the opinions on the chemical phenomena which take place in the economy. SOLID ANIMAL SUBSTANCES. 1648. We shall begin with the study of the solids which form the various organs of animals, and constitute, as it were, the labora- tory and apparatus in which are performed the great phenomena of life. We shall divide them into the bones, teeth, cartilages, the corneous tissue, the skin, and the various membranes, muscular flesh, fatty substances, and the cerebral substance. 1649. BONES. Bones form the framework, or what is called the skeleton of vertebrated animals. They are composed of an organic portion, the cartilaginous substance, and of earthy matter, consist- ing chiefly of carbonate and phosphate of lime, and constituting in the mammiferse about f of the weight of the bone. The bones are covered externally with a fibrous membrane, the periosteum, which contains the external blood-vessels distributed to the bones, and supplies them with matter for increment. Internally is found an- other membrane, the medullary, which also receives blood-vessels. When a bone is suspended for several days in a weak solution of chlorohydric acid, the earthy salts are dissolved, and there remains only the cartilage, retaining exactly the shape of the bone, but re- duced to a soft and translucent substance. It is necessary to renew the liquid several times, and lastly to wash the cartilage with fresh water until no traces of acid remain. When dried, the cartilaginous substance partly loses its translucency and becomes brittle. Ether separates a small quantity of fatty matter from it. Cartilage is insoluble in cold water, but ultimately dissolves wholly in boiling water, being converted into a substance commonly called gelatin. We subjoin the average composition of the bones of an adult man and that of an ox, in a state of health : Man. Ox. Organic matter 33.30 33.30 Basic phosphate of lime with a small quantity of fluoride of calcium 53.04 57.35 Carbonate of lime 11.30 3.85 Phosphate of magnesia 1.16 2.05 Soda and chloride of sodium 1.20 3.45 100.00 100.00 The composition of the bones of the other mammalia and of birds is analogous, while in fishes the proportion of the organic and earthy VOL. II. 3 L 46 722 ANIMAL CHEMISTRY. matters varies considerably, and they may be divided into bony fishes, whose bones contain large quantities of calcareous salts, and cartilaginous fishes, whose bones are nearly destitute of these salts. The proportion of cartilaginous matter being always greater in the bones of fishes than in those of other vertebrated animals, the former are the more flexible. 1650. TEETH. The composition of the teeth of the mammalia does not differ much from that of their bones, as will be seen from the following analysis : Man. Ox. Cartilaginous matter 28.0 31.0 Phosphate of lime, with fluoride of calcium 64.3 63.1 Carbonate of lime 5.3 1.4 Phosphate of magnesia 1.0 2.1 Soda with a small quantity of chloride of sodium ... 1.4 2.4 100.0 100.0 The part of the tooth beyond the gum is covered with a white, very hard enamel, almost wholly composed of phosphate of lime, carbonate of lime, and a small quantity of fluoride of calcium. The enamel of human teeth has been found to contain about 90.0 of cal- careous and magnesian phosphates, and 8.0 of carbonate of lime. 1651. CARTILAGES. The name cartilage has been given to a dry, elastic tissue, containing only a few hundredths of earthy salts, and very widely distributed in the animal economy, sometimes serv- ing to connect the ends of bones which move on each other, and some- times being prolongations of the bones, as in the ribs, for example, and furnishing them an elasticity suitable to their functions; while it finally sometimes forms the solid part of certain organs, as the nose, ear, the trachea, etc. The chemical nature of all cartilages does not appear to be the same, for while some seem to be identical with the cartilage of the bones, and are converted, by boiling water, into gelatin, others, such as the cartilages of the nose and ear, do not undergo this transformation. Cartilages are characterized by corpuscles of peculiar form, called cartilaginous corpuscles. 1652. CORNEOUS, OR HORNY MATTER. The horns, nails, claws, and hoofs of animals are formed of substances possessing very similar properties, and which hitherto have been regarded as identical : they are designated by the general name of horny matter. They are insoluble in water, and soften in boiling water, and their composi- tion is as follows : Cow Horns. Buffalo Horns. Human Nails. Carbon 50.8 51.4 51.1 Hydrogen 6.8 6.8 6.8 Ox yg en 23.5 1 24 . 2 . Sulphur 2.6 / Z4A *" Nitrogen 16.3 17.4 16.9 100.0 100.0 100.0 HAIR. 728 1653. HAIR, FEATHERS, SCALES. Human hair, as well as that of animals, is composed of an organic matter which does not appear to differ essentially from horn in its chemical composition and its behaviour with reagents. They contain several fatty substances, generally coloured, from which their hue is ordinarily derived. The feathers of birds closely resemble horn ; the same being true of the scales of reptiles. For want of accurate experiments, the identity of all these substances is admitted. The composition of fish-scales, on the contrary, resembles that of bone, since they contain 40 to 50 per cent, of phosphate of lime, from 3 to 10 per cent, of carbonate of lime, and from 40 to 55 per cent, of organic matter. 1654. SKIN AND MEMBRANES. The skin of animals is divided into three principal parts: 1st, the skin, properly so called, or derma, which envelops immediately the muscles and bones ; 2dly, the papillary tissue, formed by a delicate, extremely sensible tissue, traversed by small blood-vessels and nerves, and containing the pig- ment which colours the skin so variously in the different races of men throughout the globe ; and, 3dly, the outer covering, or epider- mis, a simple pellicle, very thin, but very resisting, pierced by numerous small orifices, through some of which the hairs pass, while others give exit to the fluids of perspiration ; and still others allow certain fatty substances to exude. The skin, which is soft and flexible w r hen washed in water, becomes hard and coriaceous by drying. When dipped in a solution of tannin, it combines with it without falling to pieces, and becomes imputrescible, which con- stitutes the process of tanning. When boiled with water it dissolves entirely into a gelatinous substance, commonly called glue ; but the transformation does not take place in the mucous membranes, which appear to consist of substances differing from those of the skin. 1655. MUSCULAR TISSUE. Meat, or flesh, is the collection of several organs, called muscles, each of which is formed by an assem- blage of fibres united in bundles. A multitude of nerves and canals, through which various fluids circulate, traverse this tissue in all directions ; thus rendering muscular flesh a very complicated assem- blage. The substance which constitutes the muscular network is called fibrin, which of itself is colourless ; flesh owing its red colour to the blood which fills an infinity of small capillary vessels distri- buted throughout it. One hundred parts of beef are reduced, by desiccation, to 25 parts, and, after incineration, there remains about 1J part of salts, composed chiefly of phosphates of potassa, soda, and lime, and a small quantity of alkaline chlorides. By exhausting finely chopped beef by cold water, about 6 hun- dredths of it are dissolved, one-half of which is composed of albu- men, and other materials of the blood coagulable by heat. If therefore the liquid be boiled, there remains in solution only 3 hun- 724 ANIMAL CHEMISTRY. dredths of matter, composed of soluble alkaline salts, -a crystallizable nitrogenous substance, called creatin, (from xpw, flesh,) and salts formed by a peculiar organic acid, called inosic. If, on the con- trary., flesh be treated with hot water, the albuminous substances coagulate immediately, and the same substances dissolve as in cold water ; while, if the ebullition be prolonged, a small quantity of gelatin is dissolved in addition, as is the case in making soup. A portion of the fat is also forced from its cells, and floats on the surface of the liquid. Muscular flesh yields leucin ( 1278) by being boiled with dilute sulphuric acid. 1656. Fibrin. It is difficult to separate fibrin from muscular flesh, because it is intimately mixed with other substances which behave in a very analogous manner toward chemical agents. It is generally extracted from freshly drawn blood by beating it with rods, to which the fibrin adheres in the form of long colour- less filaments. They are washed with much water, to detach the other soluble or insoluble principles of the blood ; and then, after being dried, they are treated with alcohol and ether, which remove the fatty matters. The fibrin is then washed with a very dilute solution of chlorohydric acid, and, lastly, with distilled water. Fibrin is a white, tasteless, and inodorous substance, completely insoluble in water, alcohol, and ether, and, by drying, assuming a horny consistence. Prepared in the method just stated, it leaves 2 or 3 per cent, of ashes, composed chiefly of calcareous and mag nesian phosphates. A long boiling with water alters it and dis- solves a portion of it ; and when left in water and exposed to the air it soon putrefies, but may be preserved for an indefinite length of time in alcohol. Acids convert it into a gelatinous mass, insoluble in acid liquids, but soluble in fresh water, while it dissolves readily in alkaline lyes, even when they are diluted ; and if the solution be saturated with an acid, a precipitate is formed, which, however, cannot be considered as the original fibrin. According to the most reliable analyses of fibrin, it contains Carbon 62.78 Hydrogen 6.96 Nitrogen 16.78 Oxygen ..13.48 100.00 1657. Albuminous Substances. We shall not here again refer to the albuminous substances, which have been sufficiently de- scribed, ( 1279.) Their identity in the two kingdoms, though far from being demonstrated, is generally admitted. 1658. Oreatin C 8 H 9 N 3 4 . In order to obtain creatin, finely chopped meat is treated with an equal weight of cold water ; and after having stirred the mixture for some time, it is expressed in a CREATIN. 725 canvas bag, the filtered liquid being used in treating an additional quantity of meat. The liquid, being then heated to 212 in a water- bath, in order to coagulate the albuminous substances, is evapo- rated after being filtered, and the new deposits which form are sepa- rated. When the liquid is reduced by evaporation to I of its vo- lume, water of baryta is added, furnishing a precipitate of various phosphates and sulphates, which are to be separated. The evapo- ration is continued until the liquid is reduced to -fa of its original volume, and it is then allowed to evaporate spontaneously in a warm place, when crystalline aciculae of creatin are formed, which are to be washed in cold water and alcohol, and redissolved in boiling water, which, on cooling, deposits them in a state of purity. Lean meat is best adapted to this purpose, that of fowls and the weasel yielding the largest proportion of creatin : 100 kilog. of beef yield 62 gm., and 100 kilog. of horseflesh have furnished 72 gm. Creatin is a neutral, inodorous, and colourless substance, soluble in 75 parts of cold and in a much smaller quantity of boiling water ; and separating, on cooling, from its saturated aqueous solution, in the form of prismatic crystals, which lose 18 per cent, of water when dried at 212. It dissolves in 90 parts of absolute alcohol ; and the formula of crystallized creatin is C 8 H 9 N 3 4 +2HO. Creatin it not affected by very dilute acids, while concentrated acids abstract 4 equiv. of water from it, and convert it into a sub- stance C 8 H 7 N 3 2 , or creatinin, which is a true organic alkali, pos- sessing a very strong alkaline reaction comparable with that of ammonia, and forming crystallizable salts with all the bases. Creatin also dissolves without alteration in very dilute alkaline lyes, while the concentrated alkalies decompose it, ammonia being evolved, besides carbonic acid which combines with the alkali, and a new organic base, sarcosin C 6 H 7 N0 4 . The decomposition is gene- rally effected by boiling creatin with a concentrated solution of baryta, the reaction being expressed by the following equation: C 8 H n N 3 6 +2Ba04-2HO=C 6 H 7 N0 4 +2NH 3 +2(BaO,C0 2 ). Sarcosin crystallizes in right prisms, with a rhombic base ; exerts no reaction upon coloured reagents ; but forms crystallizable salts with several of the acids. It is insoluble in alcohol and ether. 1659. Inosic Acid C 10 H G N 2 10 ,HO. This acid remains in the mother liquid which has deposited creatin, and is extremely soluble in water ; while, if alcohol be added, the liquid becomes milky, and in the course of a few days small yellowish crystals of inosate of potassa, or baryta, if the latter base has been used in the prepara- tion of the creatin, are developed. The crystals being redissolved in boiling water, and chloride of barium added, crystals of inosate of baryta are deposited, on cooling, which may be purified by several crystallizations, and then take the formula BaO,C 10 H 6 N 2 10 -f7HO -3L2 726 ANIMAL CHEMISTRY. By decomposing it by sulphuric acid, free inosic acid is obtained, which does not crystallize in an aqueous solution unless alcohol be added. The formula of inosate of silver is AgO,C 10 H 6 N 2 10 . 1660. G-elatinous Substances. We have mentioned that the skin, the cartilaginous substance of the bones, and the cartilages properly so called, when boiled with water, ultimately dissolve wholly, and form a viscous liquid, which becomes gelatinous on cooling. For a long time it was supposed that all the substances formed un- der these circumstances were identical, and the general name of gela- tin was assigned to them ; but it is now admitted that there are two : one being afforded by the skin, intestinal membranes, and tendons, which has retained the name of gelatin, while the other, called chondrin, is furnished by the cartilaginous substance. The chemical reactions and composition of these two substances differ from each other, since solutions of chondrin are precipitated by sulphate of alumina, alum, and sulphate of iron, which do not affect solutions of gelatin. The formula C 32 H 26 N 4 14 has been given to chondrin, and that of C 13 H 10 N 2 5 to gelatin ; but these formulae are very uncertain, because there are no means of ascertaining the purity of the substances and of determining their equivalents, no definite compound with them being known with certainty. In the applications of the two substances no distinction is made, and they are generally indiscriminately called gelatin and glue. Pure gelatin is colourless and transparent, as is the case in the fish-glue, or ichthyocolla, found in commerce. When heated it melts, and congeals on cooling into a remarkably coherent mass. Cold water merely softens and swells, without dissolving it, while boiling water dissolves it, and forms a viscid liquid, which coagulates into a more or less consistent jelly on cooling. Alcohol precipitates gelatin from its aqueous solution. Prolonged ebullition with water destroys gelatin, and it afterward no longer coagulates. We have already said ( 1458) that tannin completely precipitates gelatin from its solutions. 1661. Glue is manufactured from leather scraps, tendons, horns, and hoofs of animals. As animal substances putrefy readily, they are soaked, if they cannot be immediately used, for 15 or 20 days in milk of lime, and then dried in the air, which prevents their fer- mentation. When required for use they are digested for some time in water, which causes them to swell and removes the lime. Animal substances intended for the manufacture of glue are placed in boilers with water, rapidly heated to boiling, which is stirred, from time to time, the operation being continued until a portion of the liquid taken from the kettle congeals on cooling. The liquid is then decanted into a second kettle, kept at a tempera- ture of nearly 212, in order that the liquid may not become too viscid before depositing the substances it holds in suspension ; and after some hours, it is run into moulds made of pine-wood, and GLUE. 727 allowed to cool. When the glue sets, which generally takes place in 15 or 18 hours, the moulds are carried to a well-ventilated and cool drying-room, where the glue is separated by a flexible and wetted knife, and spread upon a table likewise wetted. It is imme- diately cut into small sheets by means of a brass wire, and spread on nets to dry, whence commercial glue usually shows the prints of the threads of the net. The residue in the boiler, treated with a fresh quantity of boiling water, may afford more glue. 1662. Gelatin is extracted from bones by two different pro- cesses. In the first, the bones are subjected to the action of steam, under high pressure, in a Papin's digester, when the greater part of the gelatin dissolves in the water, while the bones still retain a sufficient quantity to allow of their being used in the manufacture of animal black. If it be desired to prepare gelatin for alimentary purposes, the temperature should not be raised above 223 or 226, and beef-bones only should be used, because the bones of sheep or hogs would give the gelatin a disagreeable taste and smell. By the second process, which yields more gelatin than the pre- ceding, the bones are crushed between rollers and boiled for some time with water, in order to extract the grease which is separated. They are then digested for 24 hours with a dilute solution of chloro- hydric acid, which dissolves the calcareous salts ; for which purpose a weight of chlorohydric acid, at 22 Baume, equal to that of the bones, is used, but it serves for several times. The bones, deprived of their calcareous salts, are washed until the water is free from acidity ; after which they are boiled with water in a cast-iron kettle. Not more than the quantity of water necessary to obtain a solution of gelatin which will set on cooling should be used, and added at 3 different times, because the solution of gelatin is injured by too long boiling. Fish-glue, or ichthyocolla, is prepared from the swimming-bladder of the sturgeon by merely drying it ; and is chiefly used in refining wines ; but pure gelatin, obtained from bones, will answer the same purpose. Fish-glue softens in cold water, and readily dissolves when the temperature is raised. When poured into a slightly acidulated liquid the solution coagulates, and its filaments carry down, as in a net, the mucilaginous substances in the liquid. Mouth-glue is made of a concentrated solution of gelatin, with the addition of a small quantity of sugar and gum-arabic ; the solution being boiled in order to dissolve the gelatin completely, and the liquid poured into moulds made of oiled paper, where it becomes solid. 1663. Sugar of gelatin, or glycocoll, C 4 H 5 N0 4 . Sulphuric acid effects a very remarkable change in gelatin, and converts it into a crystallizable substance of a sweet taste, acting the part of a feeble alkali, and called glycocoll, or, more improperly, sugar of gelatin. In order to prepare it, 1 part of gelatin is digested 728 ANIMAL CHEMISTRY. for 24 hours with 2 parts of concentrated sulphuric acid, and 10 parts of water being added, it is boiled for 5 hours. The liquid, saturated with chalk, and then evaporated to the consistence of syrup, deposits, after some time, crystals of gtycpcoll; their forma- tion taking place very slowly, sometimes requiring a whole month for completion. Boiling alkaline solutions effect the same change in gelatin, in which case ammonia is disengaged. But the best method of preparing pure glycocoll consists in boil- ing, with 4 times its weight of concentrated sulphuric acid, a peculiar acid found in the urine of herbivorous animals, which we shall soon describe under the name of hippuric. Hippuric acid C 18 H 8 N0 5 ,HO then separates into benzoic acid C 14 H 5 3 ,HO, which is almost wholly deposited on the cooling of the liquid, and into glycocoll C 4 H 5 N0 4 , which remains in solution in combination with the chlorohydric acid. The chlorohydrate of glycocoll is evaporated to dryness in a water- bath, and purified by several crystallizations in water, after which it is supersaturated with ammonia, and again treated with highly concentrated alcohol, which precipitates the glycocoll in the form of small crystals. The reaction is expressed by the following equation : C 18 H 8 N0 5 ,HO+2HO=C 14 H 5 3) HO+C 4 H 5 N0 4 . Glycocoll is a white substance, having a sweet taste, but which does not ferment. It is soluble in water, nearly insoluble in alcohol and ether, and forms crystallizable compounds with the majority of the acids, without exerting any action on red litmus. It also com- bines with potassa and several metallic oxides. 1664. FATTY SUBSTANCES. We shall not again refer to the fatty substances which are found in animals, since they are identical with those existing in vegetables, and which have been minutely described ( 1590 et seq.) 1665. CEREBRAL SUBSTANCE. The cerebral substance is com- posed essentially of, 1st. A solid fat acid, containing phosphorus, and called cerelric acid ; 2d. A liquid fat acid, also containing phosphorus, called oleophos- pJioric acid; 3d. A peculiar fatty matter, or cholesterin, which shall be de- scribed when treating of bile ; 4th. Small quantities of ordinary fatty substances, such as stearin, margarin, and olein. Cerebric acid is a white substance, which may be obtained in crystalline granules, dissolving readily in alcohol and boiling ether, while cold ether retains but a small quantity of it. It melts when heated, and is very easily decomposed. It combines with bases without forming crystallizable salts, and its analysis exhibits NUTRITION. 729 Carbon 66.7 Hydrogen 10.6 Nitrogen 2.3 Phosphorus 0.9 Oxygen .' 19.5 100.0 But it is difficult to decide whether the matter subjected to analysis was a simple substance. Oleophosphoric acid is a yellowish oil, insoluble in water and cold alcohol, but very soluble in boiling alcohol and ether. It combines with bases, but forms no crystallizable salts. By contact with water, it is spontaneously decomposed into phosphoric acid, which dis- solves, and an oily substance analogous to and perhaps identical with olein. OF CERTAIN CHEMICAL PHENOMENA WHICH OCCUR IN THE ANIMAL ECONOMY. 1666. The substances we have just enumerated form the labora- tory and apparatus in which all the chemical reactions of the economy take place ; but it is important to remark that these sub- stances do not act an inert or merely formal part ; influenced by the nervous system, they not only assume the shapes and movements necessary for the circulation of the fluids, but also intervene in the chemical reactions by being constantly dissolved and renewed. We shall give the general name of nutrition to the collection of chemical phenomena which occur successively in alimentary substances, from the moment they are taken into the mouth, until, after having tra- versed the whole of the general circulation, they are rejected in the gaseous state, with the air expired, or in the state of solids and liquids, in the urine or excrements. The phenomena of nutrition, starting from the ingestion of food, follow and succeed each other in this order : 1st. Digestion, 2d. Respiration, 3d. Circulation, 4th. Excretion. 1667. We shall give an idea of the various apparatus in which these phenomena are produced, by describing the liquids arising from the decomposition of the alimentary substances, and to which physiologists attribute the chief modifications of these substances in the economy. In order to render our explanation more clear, we have figured (fig. 686) the various organs and circulatory apparatus in which the chemical phenomena take place in man, and have en- deavoured to preserve, as far as possible, their actual form ; but we have been unable to represent the relative positions they occupy in the body, where they are dovetailed into and cover each other. 730 ANIMAL CHEMISTRY. Fig. 686. DIGESTION. 1668. The object of digestion is to modify, disaggregate, and dissolve alimentary substances, in order to enable them to pass sub- sequently into the general circulation. The various acts of the function of digestion are as follows : From the mouth, where the food is chewed by the teeth and moistened with saliva, it is conveyed into the stomach A, passing through the ossophagus 0. The function of the saliva is chiefly DIGESTION. 731 physical, and assists the mastication and deglutition of food. The saliva may, however, act chemically, by effecting the transformation of the starch into dextrin and glucose ; the latter action being pro- bably very limited, because at a later period the food comes into contact with several other juices which effect the same transformation. Having reached the stomach A, the food is subjected to the action of a special juice, called gastric, secreted by the parietes of the stomach, and furnished by peculiar vessels belonging to the sanguine circulation. The gastric juice modifies, dissolves, or digests only the nitrogenous alimentary principles, such as the albumen, fibrin, casein, without in any way altering the fatty substances, and merely producing the hydration of the amylaceous matter. When the food has remained for some time in the stomach A, it leaves it, impregnated with gastric juice, and passes into the duode- num a, where it first meets with the bile, brought from the gall- bladder B and liver F, by the duct cd, called ductus choledochus. The action of the bile on food is not well known, and some physio- logists even believe it to act no part in the phenomena of digestion, and consider it as merely an excrementary fluid. 1669. In the duodenum the food is moistened, not only by the bile, but also by the pancreatic juice, supplied to the duodenum by the pancreatic duct, e, which juice is produced in a peculiar organ, the pancreas C, where it is extracted from the fluids carried into the latter by the circulation. The pancreatic juice acts, instanta- neously, on the non-nitrogenous alimentary substances, converting the fecula into glucose, and the fatty matters into an emulsion, which renders them fit for absorption. 1670. The alimentary substances, modified by the successive influence of the gastric juice, bile, and pancreatic juice, pass from the duodenum a into the small intestine D,D, . . . a tube of considerable size, extending from the duodenum to the coecum E, which itself communicates with the large intestine EE'E^E' 7 '. The extremely long parietes of the small intestine chiefly effect the absorption of the digested food and its passage into the circulation. The ali- mentary substances which reach the intestine in a condition to be absorbed, are of two kinds : 1st. Nitrogenous substances, dissolved by the gastric juice, and amylaceous substances, converted into dextrin and sugar by the action of the saliva and the pancreatic juice ; and, 2d. The fatty substances which have been made into an emulsion, by the pancreatic juice, without being dissolved. A special system of absorbent vessels, terminating in the small intestine, is contrived for each of these peculiar conditions of the absorbable alimentary substances : 1st. The system of the venaporta fff'i which absorbs the nitrogenous and saccharine matters, and conveys them, with the venous blood of the intestines and the spleen R, into the liver F, where they undergo peculiar modifica- tions, to pass thence in the right auricle Gr of the heart; and, 732 ANIMAL CHEMISTRY. 2d. The system of cJiyliferous vessels g, g, g, which absorbs only the fatty substances, and conducts them into the left subclavian vein i, i, to pass thence directly into the right auricle G of the heart, without traversing the liver. In the small intestine is effected the division between the digested alimentary substances, which are to be absorbed by the organism, and are called, on that account, accrementitions substances, and those which, remaining untouched, or having been insufficiently modified by the digestive fluids, are rejected externally, and consist of the excrementitious substances or fseces. 1671. The dimensions and developments of the who*le digestive apparatus, stomach, duodenum, and small intestine, vary greatly in different classes of animals : in the carnivorous, the food of which is much more easily dissolved by the gastric and pancreatic juices, they are relatively much less developed than in the herbivorous ani- mals, of which the food, being highly charged with ligneous matter, dissolves with much greater difficulty. 1672. The residue of the alimentary matter passes from the small into the large intestine EE'E^E'", where it remains a greater or less length of time, and probably experiences new modi- fications and peculiar absorptions. It there acquires a disagree- able and peculiar odour, the cause of which is unknown, and is finally rejected, in the state of excrement, by the anus H. CIRCULATION OF THE BLOOD. 1673. We have followed the course of the alimentary matters through the primse vise, from their entrance at the mouth to the absorption of the digested portion into the general circulation, and the rejection of the residue by the anus. In following the new route of the digested portion, we shall find it ministering to the growth and renovation of the organs, to the production of juices essential to the chemical operations we have enumerated, and to the develop- ment of heat necessary to the animal, to be excreted, finally, either in gaseous compounds, with the gases of respiration, or in solution in the urine or sweat, or in forming peculiar fluids, such as milk, semen, etc. After their absorption by the vena porta fff, or by the chyli- ferous vessels g, g, g, the digested alimentary principles reach, by various routes, the general circulation, that is, the right ventricle I of the heart, where they are mixed with the venous blood, which arrives from all parts of the body through the upper vena cava mm' and the lower nn'n", after having effected alimentation, and been subjected to the phenomena of respiration, etc., which shall pre- sently be described. The instinctive contractions of the ventricle I drive all this mixture through the pulmonary artery ll'l" into the lungs P, P, where it meets with air, and produces the phenomena of respiration. The blood, before reaching the lungs, has a deep brown colour, and is venous Hood ; while as soon as it comes into DIGESTION. 733 contact with the air in the lungs, it turns of a bright red, and gives off the greater portion of the carbonic acid it contained, which is an essential product of the chemical reactions it experienced in its nu- trient functions, replacing it with a certain quantity of oxygen, and thus constituting arterial blood, which returns to the left ventricle J of the heart through the pulmonary veins 0, o. The heart impels it into the aortic or arterial system K, K, K, . . . to be distributed to all the organs of the body. The principal forces which effect this circulation appear to be the contractions of the left ventricle J, as well as the contractive forces of the arterial coats. If the arterial blood experiences chemical changes between leaving the heart and entering the organs, they are as yet unknown. The arterial blood, after reaching the tissues of each organ, that is, 4 after having entered the capillary circulation, experiences che- mical modifications, differing in each organ. The oxygen which it had absorbed by contact with the air in the lungs, and which had effected its red colour, gradually disappears, producing the pheno- mena of oxidation, while it is replaced more or less completely by carbonic acid, which is one of the products of oxidation ; the blood then receiving its brown colour, and becoming venous. Arterial blood may be considered as of the same composition at the moment of entering each organ, which is not true of venous blood, the latter certainly undergoing special modifications in the various organs through which it passes, and which it nourishes. It is this blood, modified by the various functions it has fulfilled in the organs, which separates into two different liquids, venous blood properly so called, and lymph, both of which return to the right heart GI by special muscular systems, and are there mixed with the new liquids arising from digestion, to form a new blood, possessing all the necessary nutritive powers, and which again resumes the round of the circulation. The course of the blood from the right heart GI, to the left heart JL, passing through the capillary system of the lungs, is called the lesser circulation, while its return from the left heart to the right, passing through the capillary tissue of the organs of the body, is the greater circulation. 1674. We have said that the arterial blood, passing through the capillary tissue of the organs, is chemically modified and con- verted into venous blood and lymph: now, it happens that while traversing certain capillary tissues, the blood gives out certain liquid or gaseous products. When the products, thus separated, are to be used for special purposes, they are called secretions ; but when, on the contrary, they are to be rejected, they are termed ex- cretions. The principal secretions are, 1st. The gastric juice, secreted by the stomach. 2d. The pancreatic juice, formed in the pancreas, whence it passes into the duodenum. VOL. II. 3 M 736 ANIMAL CHEMISTRY. oxygen consumed, depends greatly on the nature of the food, and varies very little in animals living on the same aliments, though they may belong to very different species. The greatest absorp- tion of oxygen in the state of non-gaseous compounds takes place when animals are fed on meat ; the ratio between the weight of oxygen contained in the carbonic acid and the whole oxygen con- sumed, being then comprised between 0.67 and 0.74. This ratio is greater when animals are fed on vegetables ; and in rabbits sub- jected to this regimen, it has varied from 0.85 to 0.95. It is still greater when animals are fed on bread or grain ; for it may equal, and sometimes even exceed unity, so that the animal then evolves in the state of carbonic acid, a quantity of oxygen greater than that which it has taken from the atmospheric air, the excess of oxygen necessarily proceeding from the food. In a rabbit fed temporarily on bread and bran, the ratio between the oxygen contained in the carbonic acid exhaled and the whole quantity of oxygen consumed was 0.997; while in chickens fed on grain it varied from 0.90 to 1.03 ; and lastly, in animals absolutely dieted, the ratio was nearly the same as when they are fed on meat. In fact, the carbon fur- nished for respiration can, in this case, only arise from themselves, that act being then accomplished in the"m, as if they were car- niverous, even though they were birds which naturally feed on grain. 1679. In the mammiferae and in birds, the quantity of carbonic acid formed by contact with the body, and which is disengaged by the intestinal canal, is always very small, since it rarely reaches -^ of that furnished by the pulmonary respiration. Small quantities of hydrogen and protocarburetted hydrogens traces of ammonia, and excessively small quantities of sulphuretted gases, are disengaged through the same passages. To recapitulate, in warm-blooded animals, the pulmonary respiration predominates so greatly over the secondary causes of exhalation and absorption which accompany it, that all the peculiarities which characterize it may be inferred from observations made on the whole respiration, as though it alone were active. On the contrary, in cold-blooded animals, the cu- taneous respiration predominates to so great a degree that frogs have continued to breathe for several days when deprived of their lungs, nearly with the same energy, absorbing and evolving the same gases, in nearly the same proportion, as well as in nearly the same absolute quantities. 1680. Hibernating animals, as the marmot, during their wak- ing life, breathe precisely in the same manner as other animals, while the phenomenon is wholly changed during their sleep, their temperature then exceeding that of the surrounding medium only by a few degrees, and the consumption of oxygen being excessively- feeble, and generally less than ^ of that required by the same ani- mals when awake. Rather less than one-half of this oxygen only RESPIRATION. k 737 is found in the carbonic acid exhaled, the balance being assimilated internally in the shape of non-gaseous compounds, and being pro- bably partly used to form water, a small portion of which is lost by perspiration, on account of the low temperature of the animal. It hence follows that the weight of the carbonic acid exhaled is less than that of the oxygen absorbed, and the animal increases in weight by perspiration. This increase, however, does not take place continuously, for, every few days, the animal generally par- tially awakens and expels his urine. When the marmot fully awakes, his respiration becomes extremely active, much more so than when he has been awake for some time ; and his temperature rises rapidly, while his limbs gradually lose their numbness, and the animal is seized with a violent shivering, caused by the sensa- tion of cold, which he did not feel during sleep. The conditions of existence are no longer the same in the two states of the same ani- mal. The waking marmot becomes asphyxiated, like the other mammiferse, in an atmosphere poor in oxygen, while in the torpid state he would be unaffected by it. He cannot, however, bring himself voluntarily to this state, in order to continue to live in an atmosphere which his instinct tells him must prove fatal to him. 1681. The respiration of animals does not appear to be changed in an atmosphere richer in oxygen than ordinary atmospheric air, nor even in pure oxygen; the same being true of an atmosphere containing a large proportion of carbonic acid, provided it contain also a sufficient quantity of oxygen. Lastly, if the nitrogen of our ordinary atmosphere be replaced by an equal volume of hydrogen, the animal breathes as usual, without any injurious effects. 1682. The internal combustion of the carbon which serves to form carbonic acid is certainly one of the sources of animal heat. This fact is evident, not only as being a necessary consequence of the evolution of heat which always ensues on the combustion of carbon, either by active burning or in solutions, as in alcoholic fer- mentation, but is also manifested in the variations of respiration, according to circumstances, in maintaining the constancy of tem- perature. Thus, the quantity of oxygen consumed by the same animal, and the quantity of carbonic acid exhaled in equal periods, are the greater in proportion to the depression of the surrounding temperature ; and it is also greater when the nitrogen of its artificial atmosphere is replaced by hydrogen, the relative refrigerating power of which is much greater. On this account, animals of the same class consume, in a given time, a quantity of oxygen in inverse ratio to their size ; the loss of heat from the surface being proportionally much greater in the smaller than in the larger animal. For example, the consumption of oxygen for 100 gm. of substance is 10 times greater in sparrows than in fowls. It has long since been admitted that the heat evolved by an animal in a given time is precisely equal to that which, by a vivid combustion 3 H 2 47 738 ANIMAL CHEMISTRY. in oxygen, the carbon contained in the carbonic acid produced would afford, and the hydrogen which would form water with that portion of oxygen consumed, which is not found in the carbonic acid. It is highly probable that animal heat is wholly produced by chemi- cal reactions ensuing in the economy; but the phenomenon is too complex to allow of its calculation from the quantity of oxygen con- sumed. The substances consumed by respiration generally consist of carbon, hydrogen, nitrogen, and oxygen, often in considerable proportion ; and when they are completely destroyed by respiration, the oxygen they contain contributes to the formation of water and carbonic acid, and the heat evolved is necessarily very different from that which carbon and hydrogen, supposed to be free, would give off in burning. These substances, moreover, are never completely consumed ; a portion being converted into other substances, which play special parts in the animal economy, or which escape in the excretions, in the state of highly oxidized matters, (urea, uric acid.) Now, in all these transformations and assimilations of substances in the organs, heat is evolved or absorbed; but the phenomena are evidently so complicated that we shall probably never be able to make them the subject of calculation. 1683. We shall now describe more in detail the principal pro- perties and chemical composition of the liquids which are found in the animal economy. BLOOD. 1684. The blood is a liquid which circulates in the various parts of the animal economy, and furnishes the organs with the materials necessary for their life and growth. In vertebrated animals, such as man, the mammifera, birds, reptiles, and fishes, the blood is of a bright red colour ; while in the invertebrata, as in insects, the crus- tacese, mollusks, and zoophytes, it is much more fluid and colourless, or merely tinged of a yellow, green, rose, or lilac hue. The blood is much denser and thicker in man and the warm-blooded animals, such as the mammiferse and birds, than in cold-blooded animals; its density and viscidity varying according to the food and the more or less recent loss of blood which the animal may have sustained. In an adult man, the average density of the blood is 1.054 at 59 ; being somewhat less in females, particularly during pregnancy, when it falls to 1.045. Two kinds of blood are distinguished in man and warm-blooded animals : arterial blood, which is of a vermilion red, and venous blood, the colour of which is darker and of a brownish red, which peculiar colour is produced, as we have shown, ( 1673,) by the action of the atmospheric oxygen on the blood; and it therefore exists only in animals which breathe in the air, and is not observed during intra- BLOOD. 739 uterine life. The colour of foetal blood is intermediate between that of the venous and arterial blood of adult age. 1685. When fresh blood of a vertebrated animal is examined under the microscope, it is seen to be formed of a colourless, or nearly colourless liquid, in which red bodies, similar in form, and called blood-globules, are disseminated, which are characteristic of each genus of animals. They form in man and the greater part of the other mammiferse small, circular, flattened disks ; while in birds, reptiles, and fishes, they are elliptical. Their diameter in man is about ^ of a millimetre, being smaller in the majority of other mammiferae, and in the goat attaining only about $s. In birds, these globules are larger than in the mammiferse ; while they attain their greatest size in the family of the batrachians and reptiles : thus, in the blood of the frog, they are nearly ^ of a millimetre in length and ^ in breadth. Lastly, in fishes, the globules are intermediate in size, between those of birds and those of reptiles. Fig. 687 represents the blood-globules of the frog, consisting of flattened elliptical disks, of which the central part, less coloured and protruding, is surrounded by a kind of deep-coloured border. Their anatomical study by the microscope and powerful chemical reagents shows them to be com- posed of two entirely distinct parts, a central nucleus and an envelope resembling a small bladder, con- taining a coloured gelatinous and very elastic substance. When any part of a frog, sufficiently thin to be translucent, such as the web of Fi S- 687 - the foot or the tongue, is examined under the microscope, the globlues will be seen to be rapidly carried through the capillaries with the watery fluid, and to be momentarily compressed in order to pass through the smallest tubes. Blood- globules may be preserved for a long time in their natural liquid ; while, when water is added, they swell, probably in consequence of endosmose, and tend toward a spherical shape. The central nucleus does not appear to undergo any change. Certain acids, such as phosphoric, oxalic, citric, and acetic, rapidly dissolve the external envelope and expose the nucleus ; while alkaline liquids dissolve the whole globule. The globules remain unchanged, and without any appreciable alteration of form, in a solution of sugar or gum, and in several saline solutions, such as those of nitrate of potassa or soda, and chloride of potassium and of sodium. Fig. 688 represents the globules of human blood, in which, as in the blood-globules of the other mammiferae, the central portion is less projecting than the 740 ANIMAL CHEMISTRY. border, while the nucleus is not dis- tinct, although we are led to admit the existence of one by analogy, and by the manner in which the globules are decomposed by chemi- cal agents. In fig. 688 a is a front view of the globules, and b a profile view of the same. In addition to the red globules which give colour to the blood, the microscope detects a very few co- lourless globules, of spherical form, closely resembling those seen in chyle, and some of which appear to be composed of fat alone. The white or scarcely coloured globules in the blood of the in- vertebrata differ greatly from those of vertebrated animals, and their size varies in the same individual, while their form is generally spherical, and their surface is covered with asperities. No central nucleus can be distinguished. 1686. The liquid surrounding the blood-globules of vertebrated animals is water, containing in solution a great number of different substances. The presence of albumen, fibrin, various fatty substances, some of which contain sulphur and phosphorus, a great number of salts, such as the chlorides of potassium and sodium, chlorohydrate of ammonia, the sulphates of soda and potassa, the phosphates of soda, lime, and magnesia, the carbonates of soda, lime, and magnesia, and of alkaline salts, formed by fatty acids and by lactic acid, have been detected in blood. This fluid contains also several gases in solution : oxygen, carbonic acid, and nitrogen, which arise from the action of the air in the lungs. It has a peculiar mawkish taste, charac- teristic in some animals, and always exerts a well-marked alkaline reaction, which appears to be an essential of its nature, for animal life ceases when, by direct injections, the blood can be made acid. In a healthy man, 100 parts of blood contain, on an average, 79 parts of water, 1 part of mineral salts, 19 of albuminous substances, and some thousandths of fibrin, besides the red colouring matter known by the name of hematosin; which proportions vary greatly with the state of health. In the blood of birds, the relative quan- tity of water is generally somewhat smaller than in man, while it is greater in that of the batrachian reptiles and fishes. As much as 98 per cent, of water has been found in the blood of a frog. 1687. Blood drawn from a vein soon loses its fluidity and coa- gulates; which generally commences in 5 or 10 minutes after its extraction, but is not complete until the lapse of 8 or 10 hours. A gelatinous matter forms, which thickens more and more, until, after a certain length of time, the blood separates into two portions: one, BLOOD. 741 fluid, yellowish and transparent, called the serum; and the other, gelatinous and elastic, of a deep red colour, and called the clot, co- agulum, or crassamentum of the blood. The coagulation of blood is produced by the fibrin, which remains in solution so long as the blood is under the influence of vitality, but separates from it when it is removed from the animal economy, carrying with it the blood- f lobules, in the same way that soluble albumen, used for the clari- cation of a muddy liquor, carries down the corpuscles which exist in it, as soon as it is coagulated by heat. If, instead of allowing the blood to rest, it is beaten with rods, the fibrin still coagulates, and forms whitish and elastic filaments, which adhere to the rods, the blood-globules not being included, because they are detached by the agitation of the fluid. Defibrinated blood no longer coagu- lates. It is easy to demonstrate, on the blood of frogs, the globules of which are too large to pass through filtering-paper, that fibrin is really in solution in the serous liquid, and does not constitute any part of the globules, as was long supposed. It is sufficient to pour upon a filter, previously moistened, the blood of a frog, at the mo- ment of its extraction, to show that a portion of the liquid passes through the filter before the commencement of coagulation ; and after collecting this portion in a watch-glass, the microscope will exhibit in it, after a short time, a colourless clot, which may be made visible by collecting it on a needle. This experiment does not succeed in human blood, nor in that of other mammiferse, be- cause the fluid is more viscid and the globules are sufficiently small to pass through the paper. The blood-globules are not uniformly distributed throughout the coagulum, but fall toward the lower part, while the upper strata generally contain but very few of them ; in which case they contract still further, and form a sort of pellicle, called the buffi/ coat of the blood. By forcibly compressing the clot, the greater part of the liquid serum may be expressed from it. Serum is a yellow, slightly viscid fluid, of a density ranging from 1.027 to 1.029 : it has a slightly saline taste, and coagulates at about 168.8, which property it owes to the albumen. Several saline substances prevent the coagulation of the blood : as, for example, sulphate of soda, the chlorides of sodium and potas- sium, nitrate of potassa, borax, etc. ; and the proportion of these salts must be about ^ of the weight of the blood. The dilute mine- ral acids also prevent the coagulation of blood, but impart to it an oily consistence. A temperature of 86 or 104 appears to be the most favourable for coagulation, while cold retards it considerably. Healthy human venous blood yields Coagulum 13.0 Serum .87.0 100.0 742 ANIMAL CHEMISTRY. (Fibrin 0.30) CoagulumX m v i f Hematosin 0.20 V13.00 | lobules | Albuminous matter 12 .50 j (Water 79.00 J Albumen T.OO "*] Fatty substances 0.06 (^Various salts with mineral bases 0.94 100.00 1688. Hematosin, or the red colouring matter of blood, has probably not yet been extracted in a state of purity, and has not been obtained crystallized. In order to obtain it, sulphuric acid is added, by small portions at a time, to blood previously defibrinated by beating; until, by the coagulation of the albuminous substances, the liquid becomes like a thick broth of a brown colour. This mass being diluted in a small quantity of alcohol, filtered through mus- lin, and compressed, the residue is treated several times with alco- hol acidulated with a small quantity of sulphuric acid, until the liquid has lost its colour, and the albuminous matter is thus almost completely bleached. The alcoholic liquor is supersaturated by ammonia, and then evaporated to dryness ; when the residue, which is composed of hematosin, mixed with some fatty and some alkaline substances, is treated successively by ether, alcohol, and water, which dissolve the foreign substances and leave the colouring mat- ter. It is then purified by dissolving it in ammoniacal alcohol, and again separating it by evaporation ; the hematosin remains in the form of a blackish-red amorphous mass, which is tasteless and ino- dorous, and insoluble, when cold, in alcohol, water, or ether ; while it dissolves readily in alcoholic solutions of potassa, soda, and ammo- nia, which it colours intensely red. This substance contains as much as 10 per cent, of sesquioxide of iron, which appears essential to the existence of the globules. 1689. The quantitative analysis of blood is very difficult, and no very accurate process is yet known; the following being that most generally adopted by physiologists : The blood is first beaten with a brush, until the fibrin is separated as perfectly as possible, in whitish filaments, which are carefully collected, and weighed, after being washed, on a cloth, with water, and then dried at 212 until the weight remains constant. Three or four times its volume of a saturated solution of sulphate of soda being added to the defibrinated liquid, in order to prevent the alter- ation of the globules, it is rapidly filtered, causing bubbles of air to pass constantly through the liquid in the filter, to prevent the globules from adhering to each other. In this particular case, the blood-globules do not pass through the filter, and the sulphate of soda prevents the coagulation of the small quantity of fibrin which may still remain in the liquid. The globules are washed with a LYMPH. 743 solution of sulphate of soda, dried in vacuo, and then treated suc- cessively with ether which dissolves the fatty matter, with alcohol which dissolves a small quantity of foreign organic matter, and with water which removes the sulphate of soda. The dried globules are insoluble in these various liquids, and undergo no change ; and after being again dried, they are weighed. This being done, another portion of the same blood is allowed to coagulate spontaneously, and the crassamentum being separated as completely as possible from the serum, they are weighed sepa- rately. The serum is then evaporated in a water-bath, and the residue dried at 212 or in vacuo, by which means is ascertained the proportion of dry substances and of water constituting the fluid. On the other hand, the crassamentum is perfectly dried at 212, and its loss of weight is supposed to represent the water of the serum which was contained in the coagulum; when, by a proportion founded on the knowledge of the composition of the serum, above given, the weight of the serum contained and the weight of the solid parts of the serum which remained in the dried coagulum is ascertained. The latter weight, subtracted from that of the dried coagulum, represents the united weight of the fibrin and globules, which should be equal to the sum of the weights of the fibrin and globules obtained separately in the first analysis. The fatty sub- stances are separated from the dried coagulum and from the residue of the evaporation of the serum by treating them with ether. Lastly, the mineral salts are obtained by incinerating separately the coagulum and dried serum, and ascertaining the weight of the ashes, which may be then subjected to a special analysis, if a suffi- cient quantity of blood has been operated on. By subtracting the weight of the ashes and that of the fatty matter found in the serum from the weight of the dried serum, and taking into account the serum interposed in the coagulum, the weight of the albuminoid substances is obtained, added to a small quantity of other organic substances. LYMPH. 1690. Lymph is a liquid brought from all the organs of the body, by a system of vessels called lymphatic. It is a limpid, slightly viscid fluid, having an alkaline reaction, and coagulating spontaneously like blood. Its composition resembles that of fluid blood, with the exception of the coloured corpuscles; while fibrin, albumen, and the saline substances peculiar to blood are also found in lymph. The lymphatic vessels which convey the lymph from the intes- tines, perform, during digestion, the function of absorbing the fatty matters ; in consequence of which the lymph at this time acquires an opaline and whitish tinge, resembling milk. The name of chyle is given to this mixture of intestinal lymph with the fatty matter, 744 ANIMAL CHEMISTRY. and the lymphatics of the intestine have received the name of chy- Uferous or lacteal vessels, from their function of conveying the white chyle. LIQUIDS WHICH APPEAR TO PLAY A PART IN DIGESTION. 1691. Various liquids occur in the intestinal canal of animals, secreted by special organs enumerated 1667 et seq., and the prin- cipal duty of which appears to be to effect the solution of aliment- ary substances and their passage into the blood. Physiologists divide them into 1st. Saliva. 2d. Gastric juice. 3d. Bile. 4th. Pancreatic juice. 5th. Intestinal juice. As the chemical nature of these various fluids is far from being precisely ascertained, we shall confine ourselves to the most general information on the subject. SALIVA. 1692. Saliva, the liquid which moistens the mouth, is secreted by peculiar glands, called salivary, in various quantities, according to the wants of the animal ; the fluid being introduced most abun- dantly into the mouth during mastication, while its chief function appears to be to assist deglutition. The saliva, as it exudes from the mouth, is a ropy and opaline fluid, which, when allowed to rest, separates into an upper clear and fluid portion, and a lower more viscid portion, in which swim filaments of mucus and remains of organic substances. The density of saliva is but little greater than that of water, since it rarely exceeds 1.008, and its reaction is gene- rally slightly alkaline. It precipitates several metallic solutions, and deposits, at the boiling point, some coagulated principles. Ab- solute alcohol precipitates from saliva a peculiar matter, called pty- alin, to which physiologists attribute a special function, because it converts starch into dextrin in a pretty short space of time, and subsequently into glucose ; but this property is known to belong to all albuminous substances. To the saliva is attributed the forma- tion of the deposits which adhere to the teeth, commonly called dental tartar, but which consist of earthy phosphates and carbon- ates, mixed with mucus and other organic substances which are as yet unknown. GASTRIC JUICE. 1693. The gastric juice is secreted by the parietes of the stomach, varying in quantity with that of the food to be digested ; and its duty is to effect the solution of nitrogenous organic sub- BILE. 745 stances, for it appears to exert no action on fecula or fatty matters, since the latter leave the stomach without any remarkable change, and meet in the intestine only the fluids which, by affecting their solution or disaggregation, enable them to be absorbed. When freed by filtration from certain mucilaginous substances and organic remains, gastric juice is a colourless and limpid fluid, having a saline taste, and a feeble but peculiar odour, which varies in different animals ; and it always exerts a decided acid reaction on litmus. It may be preserved unchanged for an indefinite length of time in the air, and without losing the property of effecting the solution of nitrogenous alimentary substances. The essential con- stituents of gastric juice are alkaline salts, certain organic sub- stances, and a free acid ; the whole being dissolved in a large quan- tity of water, which forms 98 or 99 per cent, of the juice. The salts of gastric juice are chiefly alkaline chlorides and sulphates, in which soda predominates, the phosphates being found only in a very small proportion. In addition, small quantities of sulphate, carbonate, and phosphate of lime are also met with. Gastric juice is divided into two organic compounds : a mucilagi- nous substance, the nature and functions of which are not deter- mined, and a special nitrogenous substance, to which the greatest share in the phenomenon of digestion is attributed, known by the names of cJiymosin, pepsin, and gasterase. It may be precipitated from gastric juice by alcohol and acetate of lead, or may be sepa- rated by evaporation, it being in both cases obtained in an amor- phous form, from which it is impossible to decide whether it is a simple and definite substance. The acidity of gastric juice appears to be always due to the pre- sence of a small quantity of free lactic acid. When meat, cut into thin slices, is dipped into gastric juice, it is seen, at first, to swell and become translucent, after which it gra- dually disaggregates, and finally is wholly dissolved. From this powerful action we might be led to suppose that gastric juice would act on the coats of the stomach ; but they are covered by a mucus, which is constantly renewed, and preserves them from contact with the juice; while, after death, this mucus becomes putrid, and the gastric juice then attacks the coats of the stomach. BILE. 1694. Bile is a liquid secreted by the liver, and collected in a special receptacle, the gall-bladder ', placed immediately below the secreting organ. Bile is a ropy fluid, in man of a yellowish-green colour, of a brownish-green in the ox, and of an emerald-green in birds, amphi- bious animals, and fishes. It has a peculiar nauseous smell and a bitter taste. When poured into water, it first falls to the bottom of the fluid, but dissolves, on stirring, almost wholly, forming a VOL. II. 3 N 746 ANIMAL CHEMISTRY. frothy liquor. The reaction exerted by bile on organic colouring matters is not constant : it is frequently alkaline, sometimes neutral, and sometimes sensibly acid. Bile soon undergoes a change in the air, and putrefies, emitting a very disagreeable odour ; and it coa- gulates by boiling. Acids effect a copious precipitate in it. Although bile has been studied by a great number of chemists, they are not yet determined as to its nature, owing to the great mobility of its constituent principles in the presence of chemical agents. Bile may be considered as a soap, with soda for its base, and formed by two acids, called cholic and choleic, and containing, in addi- tion, small quantities of a crystallizable fatty substance, or cholesterin, fatty acids, and various salts, of which potassa, soda, ammonia, and magnesia, form the bases. The formula of cholic acid, which con- stitutes the greater portion of bile, is C^H^O^ ; and by being boiled with caustic potassa, it is converted into glycocoll C 4 H 5 N0 4 , and a new acid, called cholalic, C 48 H 36 6 ,HO : C 52 H J3 NO I2 =C 4 H 5 N0 4 +C 18 H 36 6 ,HO+HO. But if the boiling be prolonged for some time, the cholalic acid is itself converted into a substance of a resinous appearance, dyslysin, to which the formula C 48 H 36 6 ,2HO has been assigned. The fol- lowing equation represents the final reaction: C 52 H 43 N0 12 =0 4 H 5 N0 4 +C 48 H 36 6 ,2HO. Cholalic acid crystallizes readily in alcohol or in ether, the for- mula of its crystals being C 48 H 36 6 ,HO+5HO. They are scarcely soluble in cold water, while they dissolve readily in solutions of the caustic alkalies and alkaline carbonates, but the salts thus formed do not crystallize by evaporation. If, on the contrary, an alcoholic solution of cholalic acid be neutralized by potassa, and ether added to it, colourless needles of cholalate of potassa KO,C 48 H 36 6 are de- posited. At a temperature of 392, crystallized cholalic acid C^HggOgjHO-j-SHO is converted into a new acid, choloidio CJHgeOgjSHO ; and if it be heated to 570, it is changed into dysly- sin C 48 H 36 6 ,2HO ; water only being parted with during these suc- cessive changes. The second acid of bile, or clioleic acid, which contains a large amount of sulphur, has hitherto not been obtained in a state of purity. Boiling alkaline solutions convert it into cholalic acid and a neutral sulphuretted substance, taurin C 4 H 7 NS 2 6 , remarkable for its beautiful crystalline Torms. Taurin is also formed by boil- ing bile with chlorohydric acid. It is a substance very soluble in boiling water, but nearly insoluble in absolute alcohol, and exerting no action on coloured reagents. PANCREATIC JUICE. 747 Biliary Calculi, and Cholesterin 1695. Concretions of diversified forms and size, called biliary calculi, are frequently developed in the gall-bladder and biliary ducts. They are essentially composed of a fatty, crystallizable substance, cholesterin, mixed with substances of a resinous appear- ance and mucus. When the powdered calculi are treated with boiling alcohol, and the liquid is bleached by animal black, beautiful crystalline, brilliant, and colourless lamellae of cholesterin separate on cooling. It is a neutral, insipid, and inodorous substance, slightly soluble in cold, and very soluble in boiling alcohol. It melts at 278.6, being decomposed only at a very high temperature, and it resists the action of alkaline lixivise. Cholesterin is deposited from its alcoholic solutions in the state of hydrated cholesterin, which loses all its water at 212. The composition of dried cholesterin corresponds to C 26 H 22 0, but its true formula cannot be exactly determined, for no definite compound of it is known. Chlorine forms products of substitution with it, its action stopping at quadrichlorinated cholesterin C^H^Cl^O. PANCREATIC JUICE. 1696. The functions of the pancreatic juice appear to be to effect the disaggregation of fatty substances, and to enable them to pass into the circulation, ( 1669.) In fact, by mixing, at the tem- perature of 100 or 104, (which is that of warm-blooded animals,) pancreatic juice with oil, butter, or fat, these substances are rapidly converted into an emulsion, and yield a whitish and creamy fluid ; being, moreover, chemically altered and separated into fatty acids and glycerin. Of all the various fluids in the animal economy, pan- creatic juice is the only one which exerts this remarkable action on fats. Pancreatic juice is a colourless, adhesive fluid, which becomes frothy by shaking, and constantly displays an alkaline reaction. Heat coagulates it completely into a single mass, in which respect it closely resembles white of egg, but differs from it in many special properties. If alcohol be poured into pancreatic juice, the active coagulated principle is precipitated, but is wholly redissolved in cold water, even after desiccation, while the white of egg, when coagulated by alcohol, is insoluble in water. In addition to the organic sub- stances, pancreatic juice contains alkaline carbonates and chlorides, and some few phosphates ; the predominating base being soda. INTESTINAL JUICE. 1697. The name of intestinal juice is given to a fluid secreted by the intestinal canal, and to which the liquefaction of amylaceous and ligneous substances is partly attributed ; but the juice has hitherto not been obtained separately, being always mixed with other diges- 748 ANIMAL CHEMISTRY. tive juices. The mixture exhibits sometimes an alkaline, sometimes an acid reaction, according to the nature of the food ; but nothing accurate is known concerning its composition. CHYLE. 1698. Chyle is the fluid contained in the chyliferous vessels. When taken from the thoracic duct, which is the common trunk of these vessels, it is generally clouded and milky ; its reaction being always alkaline. Its opacity is owing to the fatty matter which exists in it as an emulsion ; and the microscope detects in it two kinds of colourless globules, some of which are fatty, while others constitute a peculiar substance, called chyle-globules, the shape of which is irregular. When exposed to the air, chyle soon coagulates and divides into two portions: a colourless, or slightly reddish coagulum, and a colourless liquid, termed serum of the chyle ; the fatty matter origin- ally in suspension collecting on the surface of the serum. The coagulation of chyle, like that of the blood, is owing to the separa- tion of the fibrin, which becomes insoluble, and carries with it other substances ; while the serum chiefly contains albumen, which coagu- lates when the fluid is boiled. The relative proportions of the coagulum and serum are very variable, according to the species of animal, and, above all, according to the food. The chyle of a horse yields from 1.1 to 5.6 per cent, of fresh and from 0.2 to 1.7 of dried coagulum; while that of the dog yields from 1.3 to 5.7 of the same substance when moist, and from 0.2 to 0.6 when dried. MILK. 1699. Milk is a liquid secreted by special glands, called mam- mary, in the females of animals, after delivery. It is white and opake, and serves as a type of all fluids of analogous appearance, which are then said to be milky. The opacity of milk is owing to a multitude of small fatty globules, of from 1 to 3 hundredths of a milli- metre in diameter, which are sus- pended in it in a state of emulsion. These globules are easily seen by examining a thin film of milk with a microscope, when they present the appearance represented in fig. 689. When milk is allowed to rest, the fatty globules, by virtue of their low specific gravity, rise to the surface, and form a coat of Fig. 689. cream. Ether does not remove the fatty gloubles by simply being shaken MILK. 749 with milk ; while, if a few drops of acetic acid be added to it, and the liquid be then boiled, the globules unite, and may be dissolved by ether. If a concentrated solution of sulphate of soda or sea-salt be stirred in milk, and the whole then filtered, the globules are arrested, and the fluid which passes through is nearly transparent. Milk contains, in addition to the fatty substance, a nitrogenous substance, which we shall describe under the name of casein, and to which it owes its principal nutrient qualities, a peculiar sugar, sugar of milk, albuminous substances, and mineral salts, all of which exist in it in different proportions, not only in the different species of animals, but even in the same individual. They depend greatly on the food, the greatest variations being found in the fatty matter, which does not exist in the same quantity at the beginning and end of the milking. The transparent part of milk, or whey, is much more constant, and is appreciably the same in the different periods of the same milking. The fatty globules, collected together, form butter. Milk is habitually alkaline, but it soon sours in the air, particu- larly in warm or stormy weather, lactic acid being developed, which causes the coagulation of the casein. The caseous matter separates in clots, carrying with it the fatty globules ; and the milk is then said to be turned. This change is avoided, without injuring the quality of the milk, by the addition of 2 or 3 thousandths of bicar- bonate of soda; while the addition of a few drops of any acid will turn it. Fresh milk does not coagulate by boiling, but its surface becomes covered with white pellicles of an albuminous substance, which contains the fatty globules ; and when the milk boils, these pellicles prevent the escape of the steam, causing the liquid to boil over if the vessel be not removed from the fire. 1700. An accurate analysis of milk is a delicate operation, requiring a considerable length of time. The milk being evaporated to dryness in a procelain capsule heated in a water-bath, the residue is dried at 248, and weighed; the weight of the residue reaching 11 or 12 hundredths in cow's milk of good quality. It is treated with a mixture of alcohol and ether, which dissolves only the fatty matter; after which the latter, being separated, is evaporated and weighed. The casein, sugar of milk, and the salts remain in the residue after the treatment by alcohol and ether, and are weighed together after being dried, when the residue is incinerated, and yields the mineral salts, by subtracting the weight of which from that of the residue, the casein and sugar of milk are determined. The sugar is more accurately determined by optical experiments, for it possesses considerable rotatory power on the plane of polarization. For this purpose the rotatory power a of a certain weight p of sugar of milk, dissolved in 100 cubic centimetres of water, and observed in a tube 0.3 m. in length, being first ascertained, a certain quantity of fresh milk is heated to 105 or 120, and treated with a few cubic 750 ANIMAL CHEMISTRY. centimetres of acetic acid, which coagulates the casein and fatty matter. It is filtered, and some cubic centimetres of a solution of acetate of lead is added, which precipitates the albuminous sub- stances, thus furnishing a perfectly limpid liquid after filtering. The rotatory power a' of this liquid in the tube of 0.3 m. in length being ascertained, the proportion x of sugar contained in it is then given by the proportion a: a': :p:x; in which x does not represent exactly the proportion of sugar exist- ing in 100 cubic centimetres of milk, because, before subjecting the liquor to optical examination, several liquids were added to the milk, while, if the quantity of the liquids added be exactly known, a cor- rection can be made which furnishes the exact proportion of sugar in the milk subjected to analysis. The casein is ascertained differentially. 1701. The richness of various kinds of milk in fatty matters may be ascertained by a very simple experiment with a small in- strument called a lactoscope; the experiment being founded on the fact that the degree of opacity of various kinds of milk, reduced to the same density, is very nearly in proportion to the quantity of fatty matter they contain in suspension. The lactoscope is a species of small opera-glass, formed by two plane glasses, which may bo Gradually brought into contact and separated by means of a very ne screw, the separation of the glasses being shown by a circular graduation marked on their rims. A small funnel at the upper part serves for the introduction of the milk between the glasses, while on the other side is the handle of the apparatus. When the glasses are in contact and the division marks 0, the milk is poured into the funnel, the glasses being separated by turning the movable mounting, while the milk falls between the glasses. The experi- menter then stands before a candle at the distance of about 1 metre, and having brought the glasses together until the flame becomes distinctly visible, he gradually separates them until the exact moment at which the flame ceases to be visible. The relative richness in fatty matters of various samples of milk is given with sufficient accuracy by the degrees of separation of the glasses at the moment of the disappearance of the flame. The mineral salts contained in 1000 parts of cow's milk have been found to consist of Phosphate of lime 1.805 " magnesia 0.170 " iron 0.032 " soda 0.225 Chloride of sodium 1.350 Carbonate of soda 0.115 3.697 LACTIN. 751 Ass. 90.5 1.4 Goat. 82.0 4.5 Mare. 89.6 trace Bitch. 66.3 14.8 Human 88.6 2.6 6 .4 4. 5 8.7 2 .9 4 .9 1 .7 9. 1.7 16 .0 3 100 .9 XJ" 100 .0 100. 100.0 100 .0 The analyses made of various kinds of milk have furnished, as an average, the following compositions : Cow. Water 87.4 Butter 4.0 Sugar of milk and soluble salts 5.0 Casein, albumen, and insoluble salts... 3.6 1702. The first milk furnished by the mammae after delivery is called colostrum, and differs greatly in appearance from the milk which flows some days subsequently, being less fluid, exhibiting the consistence of serum, and showing a yellowish colour, while the microscope detects in it globules of fat, mucus, and irregularly shaped granules. To the colostrum are attributed purgative pro- perties, which free the child from the meconium collected in its in- testines. Sugar of Milk C 24 H 24 24 . 1703. Sugar of milk, or lactin, is extracted by pouring into milk an acid which causes the coagulation of the casein, and then filtering and evaporating the liquid to the proper degree of concen- tration, when the latter gradually deposits sugar of milk, which forms semi-transparent and very hard crusts on the sides of the vessel. Sugar of milk is chiefly prepared in Switzerland, where the fluids which remain after the separation of the butter and casein are likewise used in making Gruy^re cheese. The taste of sugar of milk is sweet and agreeable, and milk owes its sweetness to it. It rotates toward the right. Heated to 248, it loses 2 equiv. of water without melting, while at 300 it loses 3 equiv., and its composition is then represented by the formula C 2i H 19 19 , which is also the case when it is combined with oxide of lead. Sugar of milk dissolves in 6 parts of cold, and 2 parts of boiling water, but is insoluble in alcohol and ether. Dilute acids convert it into glucose ; while nitric acid, when heated with it, yields oxalic and mucic acids, the production of which latter distinguishes sugar of milk from the other sugars we have described. Sugar of milk undergoes alcoholic, lactic, or butyric fermentation, according to the nature of the ferment and the circumstances in which it is placed; the casein and albuminous substances producing these various fermentations. If fresh milk be maintained at a tempera- ture of 104, sugar of milk undergoes alcoholic fermentation, while if the milk be previously exposed to the air for some time, the casein is changed and produces lactic fermentation. It should be re- 752 ANIMAL CHEMISTRY. marked that the elementary composition of lactic acid C 6 H 5 5 ,HO is the same as that of sugar of milk ; and it may therefore be sup- posed, that in lactic fermentation the latter merely experiences ai) isomeric modification. Casein, or Oaseum. 1704. In order to separate casein from milk, a certain quantity of sulphuric acid is added, which forms an insoluble compound with casein, precipitated in clots, and carrying with it the greater portion of the butyrous matter. The precipitate is collected on a filter and washed with distilled water, and then treated with a solution of car- bonate of soda, which dissolves the caseous matter, forming a syrupy and cloudy liquor. If this be kept for some time at a temperature of 68 or 77, the fatty substance forms a coat on the surface. The inferior aqueous liquid being drawn off by a siphon, and sulphuric acid added which again precipitates the casein, the latter is boiled with water to remove the sulphuric acid, when a portion of the casein is dissolved, which must be precipitated anew by carefully saturating the acid liquid with carbonate of soda. The casein is collected on a filter, washed with distilled water, and then, after being dried, with alcohol and ether, which dissolve the balance of the fatty substances. The casein is then considered as pure, although it possesses no cha- racter by which it may be ascertained to be a simple substance. Casein is a white substance, resembling in appearance coagulated but pulverulent albumen. It is inodorous, tasteless, insoluble in water, alcohol, and ether, and always reddens litmus, although it is difficult to decide if this reaction be peculiar to it. It dissolves in alkaline liquids, from which acids precipitate it ; and nearly all the acids precipitate it from milk, while the precipitate, which is a com- pound of casein with the acid, is redissolved in an excess of the latter acid. The sulphuric and chlorohydric compounds are less soluble, and when they are decomposed by the alkaline carbonates, or by that of lime or baryta, the casein dissolves and combines with a portion of the base. Manufacture of Butter. 1705. Butter which is merely the aggregation of the fatty globules of milk, is obtained from the cream which forms on the surface of this fluid when it is allowed to rest. The cream is poured into machines called churns, the forms of which vary in different countries ; one of the best being a small barrel, having internally a dasher revolving on an axis. The dasher is rapidly turned, when the small fatty globules of the milk adhere to each other, and form, after some time, grains of butter, which separate from the watery fluid, or buttermilk, containing the casein, sugar of milk, and other soluble principles. The churn is then stopped, the CASEIN. 753 lid removed, and replaced by a covering of thin muslin stretched over wire-gauze. After churning slowly for a short time, nearly all the buttermilk flows out, and fresh water being substituted for it, the churn is again set in motion ; which washings are repeated until the water comes out perfectly clear, when the butter is removed from the churn. Pure butter may be considered as a mixture of margarin, olein, and small quantities of butyrin, caprin, and caproin. The excellence of butter depends not only on the quality of the milk, but also on its manufacture, since it is essential to use fresh cream, which can only be done on large farms, for in small ones it is necessary to save the cream of several days to have enough for a churning. Butter will keep longer when well freed from butter- milk, since the caseous and albuminous principles of the latter change first, and produce acid fermentations, which separate the butyric acid and other volatile acids, imparting to the butter a disa- greeable, rancid taste. The decomposition of these substances is prevented by the addition of chloride of sodium, or by salting the butter. Manufacture of Cheese. 1706. Cheese is a mixture, in different proportions, of coagu- lated caseous matter and butter, and is generally prepared from skimmed milk, which has consequently lost the greater part of its fatty substances. When sufficiently compressed it is hard, trans- lucent, yellowish, and possessing a greasy lustre, due to the butter it contains, and which may be easily separated from it by ether. The caseous matter separates in the form of cheese, when milk is left for some time, and at a slightly elevated temperature, in contact with the mucous membrane of the stomach of young calves, called rennet. The active principle of the rennet is called chymosin, but it has not yet been isolated with certainty, and nothing accurate is known concerning its manner of action. By maintaining the tem- perature at 77 or 86, the caseous matter sets into mass, which is constantly agitated for some time until it becomes sufficiently solid ; after which it is placed on a cloth, in a mould, and allowed to drain. If a hard cheese, and one that will keep for a long time is desired, the substance is pressed in the mould, so as to drive out the greater portion of the liquid. The cheeses are then laid on boards in a room, and left there for some time, their surface being frequently sprinkled with common salt. The various kinds of cheese depend on the nature of the milk used in their manufacture, the proportion of cream left in it, and lastly, on the method employed for its manufacture. 48 754 ANIMAL CHEMISTRY. EXCKETIONS OF THE ANIMAL ECONOMY. 170T. A great number of products, which have escaped assimi- lation, are rejected from the body of the animal. The water which existed in the food or drink, or that which was formed by the che- mical reactions which take place in the animal economy, are ex- pelled, either in the urine, or in the excrement or fceces of the intestinal canal, or by perspiration, or lastly, in the state of vapour, with the heated gases which escape from the air-passages in the act of respiration. The urine contains solid substances in solution, which arise from the various chemical reactions effected by vital action ; while the excrements of the intestinal canal are composed of insoluble substances and substances in solution in water. Lastly, gases, called intestinal, frequently escape from the intestinal canal, which are formed in the chemical reactions ensuing in the stomach and intestines. We shall successively describe, 1st. The urine of animals. 2d. The excrements, or faeces. 3d. The intestinal gases. 4th. The sweat. 5th. The gaseous products formed by the act of respiration. The latter products having already been described, the first four only will occupy our attention. URINE. 1708. The urine is formed from the blood, by an analysis of this fluid in the kidneys ; and its composition varies in different animals, the difference depending chiefly on the food. In the car- nivorous mammiferse, the urine contains, in addition to mineral salts, albuminous and mucilaginous matter, and two substances of which we have not yet spoken, urea and uric acid. Urea often constitutes, of itself alone, more than one-half of the solid sub- stances. The urine of herbivorous animals contains much less urea, while its place is occupied by a considerable quantity of a peculiar acid, called hippuric. The urine of all the mammiferse in a state of inanition is similar, and resembles that of animals fed on meat, which might be expected, since the life of an animal in a state of inanition is supported at the expense of its own substance. Birds and fishes have no particular apparatus for the escape of the urine, which is voided with their excrement. The urine of the batrachians, of frogs for example, is very liquid, and contains only a trace of urea, while that of reptiles is nearly solid, and is chiefly composed of uric acid. The quantity of urine voided by the same mammiferous animal varies with its food, and even changes with the same food, accord- ing to the surrounding temperature, a condition of repose or mo- UREA. 755 tion, and the pathological state of the subject. The volume of urine evacuated is in inverse proportion to the perspiration: thus, all other things being equal, the urine is more copious in winter than in summer, and in cold more so than in hot climates. The chemi- cal composition of urine is not less variable in the same individual, that formed during digestion being always more rich in urea. On an average, an adult man forms, in 24 hours, 30 to 40 gm. of urea, which are evacuated with the urine. We shall describe, with some minuteness, the principal organic substances found in the urine of animals, these substances being interesting, not only to the physiologist, but also to the chemist, since they assist in the production of many curious metamorphoses. Urea C 2 H 4 N 2 2 - 1709. Urea is obtained by evaporating fresh urine until it is reduced to ^ of its volume, allowing it to cool, and gradually adding nitric entirely free from nitrous acid, until no more precipitate is ef- ected ; when the urea thus forms a compound with the acid, nitrate of urea, which is very slightly soluble when cold, and is deposited in small coloured crystals. They are collected on a filter, washed with a small quantity of cold water, and, after being expressed between blotting-paper, are redissolved in boiling water, and the liquid boiled, for a few moments, with animal charcoal, deprived of its calcareous salts by chlorohydric acid ; when the salt is again al- lowed to crystallize, by cooling. The nitrate of urea is obtained perfectly pure after several crystallizations, and is then decomposed by carbonate of baryta, which sets the urea free, and with the nitrate of baryta first formed remains in the liquid. The latter is evapo- rated to dryness, and the residue treated with boiling alcohol, which dissolves the urea alone, depositing it again on cooling, or by eva- poration, in long prismatic crystals. Urea may also be artificially produced by combining cyanic acid C 2 NO,HO with ammonia NH 3 ; the composition of cyanate of am- monia (NH 3 ,HO),C 2 NO being identical with that of urea C 2 H 4 N 2 2 , and being, when left in water, immediately converted into its iso- meric substance, urea. The following process, founded on the above, furnishes the means of obtaining large quantities of very pure urea : Cyanate of potassa is first formed, by heating to a nascent red-heat, in a retort, a mixture of 28 parts of dried prussiate of potash and 14 of binoxide of manganese, ( 1504 ;) after which it is dissolved in water, treated with sulphate of ammonia, evaporated to dryness, and again treated with alcohol, which dissolves the cyanate of am- monia converted into urea, and leaves sulphate of potassa. The alcoholic liquor, when evaporated, yields beautiful crystals of urea. Urea is a colourless, inodorous substance, of a fresh taste, very soluble in water, less so in alcohol, and almost insoluble in ether. Its solutions do not act upon litmus, although it combines with a 756 ANIMAL CHEMISTRY. great number of acids, and forms crystallizable salts which exhibit the same rules of composition as the organic alkalies. There is, however, this difference between urea and the alkaloids, that it does not combine indiscriminately with all the acids : thus, it forms no compound with lactic acid, the acid properties of which are, never- theless, well marked. It melts at 248 without change, being at a higher temperature decomposed into ammonia, which is disengaged, and into cyanuric acid, which remains-in the retort; and if it be further heated, the cyanuric acid is converted into its isorneric mo- dification, cyanic acid, which passes over in distillation. The urea is in this way separated into ammonia NH 3 , and into cyanic acid C 2 NO,HO; and if these products are united in water, they again form urea. A certain quantity of urea is always formed in the neck of the retort, because the cyanic acid, at the moment of distil- lation, meets with the ammonia evolved during the first period of its decomposition. Urea combines with several metallic oxides, particularly with the oxide of lead, which it dissolves ; and it also forms definite and crystal- lizable compounds with chloride of sodium, chlorohydrate of ammo- nia, corrosive sublimate, nitrate of silver, and other substances. Hyponitric acid soon destroys urea, by decomposing it into carbonic acid and nitrogen, and moist chlorine produces the same effect. Nitrate of mercury dissolved in nitric acid likewise decomposes urea, at the boiling point, into carbonic acid and nitrogen ; and as the other components of urine do not disengage carbonic acid under the same circumstances, this reaction may be used for ascertaining very exactly the quantity of urea in a sample of urine, by collecting the carbonic acid in a weighed bulb-apparatus containing a concen- trated solution of caustic potassa; the increase of weight of the apparatus, multiplied by the number 1.371, giving the weight of the urea. A solution of urea, heated to 284 in a glass tube hermetically closed, is converted into carbonate of ammonia, by taking up the elements of 4 equiv. of water : C 2 H 4 N 2 2 +4HO=2[(NH 3 ,HO),C0 2 ]. A prolonged ebullition with the caustic alkalies or mineral acids effects the same decomposition, which also ensues in urea dissolved in urine, when the latter is left to rest for several days; the albu- minous substances contained in it exerting a special kind of fer- mentation on the urea. In consequence of this decomposition, pu- trefied urine is highly ammoniacal. ^ Nitrate of urea is formed by the direct combination of urea with nitric acid, and we have mentioned that it is precipitated in the form of small crystals when nitric acid is poured into a concentrated solution of urea. If heat be applied, the nitrate of urea crystallizes URIC ACID. 757 on cooling in beautiful crystals, of the formula (C 2 H 4 N 2 2 ,HO),N0 5 , and which dissolve in 10 times their weight of cold water. Oxalate of urea is still less soluble in cold water than the nitrate, and its formula is (C 2 H 4 N 2 2 ,HO),C 2 3 . Urea absorbs immediately chlorohydric acid gas, and is converted into the chlorohydrate C 2 H 4 N 2 2 ,HC1, which is very soluble in water. Uric Acid C 10 H 4 N 4 6 . 1710. Healthy human urine generally contains 1 part of uric acid for every 30 parts of urea ; which quantity may vary according to the food. Uric acid being very slightly soluble in water, is often de- posited during the cooling of urine, in the form of small granular crys- tals, generally of a red colour. The excrement of birds and serpents contains very considerable quantities of it; and guano,* which has been used during the last few years as a manure, and is merely the excrement of sea-birds, contains a large proportion of uric acid. In the laboratory, uric acid is generally obtained from the excre- ment of the boa serpent. The powdered excrement being heated with a solution of potassa, which dissolves the uric acid and some other substances, the liquid is filtered and an excess of chlorohydric acid added, when the uric acid is almost wholly precipitated, since it requires about 1000 parts of water for solution. The acid is purified by dissolving it several times in alkalies and precipitating it by chlorohydric acid. Pure uric acid forms small crystalline lamellae, white, soft to the touch, inodorous, and tasteless : it feebly reddens litmus, and com- bines with all bases, the alkaline urates alone being soluble. The acid is insoluble in alcohol and ether. 1711. Oxidizing reagents decompose uric acid in a very remark- able manner, producing many new substances, of which we can here only give a superficial description. By heating water containing uric acid in suspension with bin- oxide of lead, the uric acid dissolves with a copious evolution of car- * Bunzen gives the following as the average composition of the finer qualities of guano : Urate of ammonia 9.0 Oxalate of ammonia 10.6 Oxalate of lime 7.0 Phosphate of ammonia 6.0 Double phosphate of magnesia and ammonia 2.6 Sulphate of potassa 5.5 Sulphate of soda 3.8 Chlorohydrate of ammonia 4.2 Phosphate of lime 14.3 Clay and sand 1.7 Water and undeterminable organic substances 35.3 100.0 The result is calculated from numerous analyses of different kinds of guano, made by various chemists. W. L. F. VOL. II. 3 758 ANIMAL CHEMISTRY. bonic acid, and the liquid deposits, on cooling, a neutral substance C 4 H 3 N 2 3 , which has already been found in the liquor amnii of the cow, and named allanto'in. It crystallizes in white prisms, much more soluble in boiling than in cold water, and, when heated with nitric acid, it yields a considerable quantity of nitrate of urea ; while it forms chlorohydrate of urea with chlorohydric acid ; a peculiar acid C 10 H 7 N 4 9 , called allanturic, being formed simultaneously in both cases, which is also produced when uric acid or allantoin is boiled with water and binoxide of lead. If uric acid be heated with 4 times its weight of nitric acid of the density 1.4, the former dissolves with effervescence, and the liquid deposits, on cooling, a crystallized substance, alloxan C 8 H 4 N 2 10 , which reddens litmus. This substance, treated when cold by alkalies, is converted into an acid C 4 HN0 4 , called alloxanic, which crystal- lizes in aciculse, and forms perfectly well-defined salts. The allox- anate of baryta, which may be directly prepared by heating to 140 a mixture of alloxan and an excess of baryta, is decomposed at the boiling point into carbonate of baryta and a new salt of baryta, mesoxalate of baryta 2BaO,C 3 4 , from which the mesoxalic acid may be separated by sulphuric acid. The formula of crystallized mesoxalic acid is C 3 4 ,2HO ; its 2 equivalents of water being basic, and the anhydrous acid, as it exists in the salts, containing only carbon and oxygen. Alloxanic acid alone, when boiled for some time with water, gives off carbonic acid, and is separated into two substances : leucoturic acid C 6 H 3 N 2 6 , which is almost wholly precipitated in small granular crystals during the cooling of the liquid ; and diffluan C 6 H 4 N 2 5 , a neutral substance, highly soluble in water, but insoluble in absolute alcohol, and yielding alloxan when treated with nitric acid. Lastly, when a solution of alloxan is boiled with an excess of ammonia, a yellow nitrogenous acid is formed, called mycomelinic acid C 16 H 10 N 8 10 , almost insoluble in cold and very slightly soluble in boiling water. It forms yellow salts with bases. We have shown that by heating uric acid with 4 times its weight of nitric ^acid, alloxan C 8 H 4 N 2 10 is obtained; and if the quantity of nitric acid be doubled, and the action prolonged, or if the alloxan be heated with this acid, a new substance, parabanic acid C 6 N 2 4 ,2HO is formed, which remains in solution, but is deposited by evaporation in colourless crystalline lamellae. Parabanic acid heated with an excess of ammonia is ^ converted into oxaluric acid C 6 N 2 H 3 7 ,HO which is itself, by continued boiling with water, separated into oxalic acid and oxalate of urea. By causing sulphurous acid and ammonia to act successively on alloxan, a new acid of a very complicated composition is produced, called thionuric acid C 8 H 2 N 3 14 S 2 . For this purpose, cold sulphurous acid is added to a concentrated aqueous solution of alloxan, until the latter smells of the acid ; after which it is saturated with carbonate URIC ACID. 759 of ammonia, caustic ammonia is added, and the whole boiled, when the thionurate of ammonia crystallizes on cooling. By pouring acetate of lead into a solution of this salt, thionurate of lead is pre- cipitated, which, when decomposed by sulf hydric acid, yields free thionuric acid, crystallizing in small aciculse which redden litmus. If chlorohydric acid be added to a boiling solution of thionurate of ammonia, very fine silky needles of a new substance, uramil C 8 H 6 N 3 6 , are deposited, which, though very slightly soluble in hot water, and almost insoluble in cold water, dissolve readily in am- monia. The ammoniacal solution turns of a reddish-purple colour in the air, and then deposits green crystalline aciculse of a metallic lustre. Nitric acid converts it into alloxan. By adding sulphuric acid to a solution of thionurate of ammonia, we do not obtain uramil, but uramilic acid C 16 H 10 N S 15 , which is deposited by evaporation in a water-bath in the form of prismatic crystals or silky aciculae, much more soluble in hot than in cold water. Uramilic acid forms crystallizable salts with bases. By treating uric acid with an aqueous solution of chlorine, or boiling it with 32 parts of water, and adding nitric acid by drops until the uric acid is dissolved, it is converted into a neutral sub- stance, alloxantin C 8 H 5 N 2 10 , which is deposited by evaporation of the liquid in colourless or slightly yellowish crystals, turning red by contact with the air and in the presence of ammonia, and assuming a metallic lustre. Oxidizing reagents convert alloxantin into alloxan, and the former is also obtained by treating alloxan with reducing substances, particularly with sulf hydric acid, protochloride of tin, or by zinc in the presence of chlorohydric acid. When alloxan is converted into alloxantin by sulf hydric acid, the liquid, by being boiled, still maintaining the current of sulf hydric gas, furnishes a new acid, dialuric acid C 8 H 4 N 2 8 , which is deposited in crystals on cooling, and possesses active acid properties. The majority of the products derived from uric acid produce, in the presence of ammonia, a neutral substance, murexid C 12 H 6 N 5 6 , remarkable for its beautiful rose colour. In order to prepare it readily, 1 part of alloxan and 27 parts of alloxantin are dissolved in boiling water, and when the liquid has cooled to 158, carbonate of ammonia is added, but not in excess. The liquid then deposits crystals of murexid, which is but slightly soluble in water, while it turns it of an intense purple colour. Its crystals are red and dis- play the greenish reflection of the wings of the Spanish fly; it is insoluble in alcohol and ether. Murexid is decomposed by the alkalies and acids into several products, among which may be distinguished alloxan, alloxantin, and a new crystalline substance, murexan C 6 H 4 N 2 5 , crystallizing in small silky, colourless spangles, and nearly insoluble in water. When exposed to the air and ammoniacal vapours, it assumes a beautiful red colour, and is converted into murexid ; exhibiting a phenomenon 760 ANIMAL CHEMISTRY. analogous to that of colourless orcin, which under the same circum- stances is converted into coloured orcein. On evaporating rapidly by boiling a solution of alloxantin in chlorohydric acid, and allowing it to cool, the liquid deposits crys- tals of a new acid, called allituric acid C 6 H 2 N 2 3 ,HO. If dilute nitric be substituted for the chlorohydric acid, and the liquid be treated with sulf hydric acid as soon as the alloxantin is dissolved, alloxan is deposited ; and when the liquid is decanted and mixed with nitric acid it deposits an ammoniacal salt, formed by a new acid, called dilituric, the composition of which is as yet unknown. 1712. The rapid enumeration of the numerous products derived, thus far, from uric acid, proves very clearly the extreme mobility of certain organic molecular groupings. Hippuric Acid C 18 H 8 N0 5 ,HO. 1713. Hippuric acid exists in the urine of herbivorous animals and of young children. It is prepared by evaporating the fresh urine of a horse to J of its volume, and adding chlorohydric acid ; when the liquid, on being left to itself, deposits coloured crystals of impure hippuric acid. They are redissolved in boiling water, when the liquid, after being bleached by animal charcoal, deposits white prismatic crystals of very pure hippuric acid, on cooling. Hippuric acid is much more soluble in hot than in cold water, and dissolves freely in alcohol, but is almost insoluble in ether ; and it forms, with bases, salts remarkable for their beautiful crystalline forms. Under many circumstances, hippuric yields benzoic acid. When heated, it first melts, and is then decomposed, giving rise to cyano- hydric acid, and a copious sublimation of benzoic acid, besides se- veral other substances, the nature of which is not yet known. If a solution of hippuric acid be boiled with powerful acids, the hippuric acid undergoes a very remarkable decomposition, already mentioned, (1663,) being separated into glycocoll and benzoic acid: C 18 H 8 N0 5 ,HO+2HO=C 14 H 5 3 ,HO+C 4 H 4 N0 3 ,HO. Hippuric acid also furnishes benzoic acid when it is treated with oxidizing reagents, as, for example, by boiling its aqueous solution with brown oxide of lead, or with sulphuric acid and peroxide of manganese; carbonic acid being disengaged at the same time. Benzoic acid is also formed when it is heated with sulphuric acid at a temperature exceeding 248. Lastly, under the influence of certain ferments, hippuric acid is decomposed, and yields benzoic acid. These ferments naturally exist in the urine of herbivorous animals; and if the urine of a horse be allowed to become putrid, and be then concentrated by evaporation, a copious crystallization of benzoic acid is separated. This furnishes an economical method of preparing this acid, which URINE. 761 is also frequently found, ready formed, though in small quantities, in the urine of the herbivorae. Reciprocally, benzoic acid is readily converted, in the animal economy, into hippuric acid ; and, after eating a small quantity of benzoic acid mixed with our food, we shall find a considerable quan- tity of hippuric acid in the urine arising from the digestion of this food. Healthy human urine almost always contains a very small quantity of hippuric acid. ANALYSIS OF UKINE. 1714. The substances generally looked for in human urine are urea, uric acid, and the salts ; the other principles, such as creatin, hippuric acid, and albuminous substances, generally existing in a quantity too small to allow of their accurate quantitative determi- nation. In order to obtain the urea, the urine is evaporated at a low tem- perature, and treated with alcohol, which dissolves the urea, to- gether with a small quantity of unknown matter, while the uric acid, urates, and mineral salts remain in the residue. It is evapo- rated to dryness at a very gentle heat, and treated with a small quantity of dilute nitric acid, and again evaporated, when nitrate of urea remains and is weighed. It is, however, always to be feared that some of the urea may be destroyed during the evaporation, because a small quantity of nitrous acid may be formed by the reac- tion of foreign organic matters on nitric acid, and we have shown ( 1709) that nitrous acid readily destroys urea. It is therefore much more exact to determine the urea by the quantity of carbonic acid which is evolved when a known weight of urine is decomposed by a mixed solution of nitrate and nitrite of mercury. ( 1709.) The uric acid is separated by pouring chlorohydric acid on the residue of urine which did not dissolve in the alcohol, and treating it with a sufficient quantity of weak alcohol, when the mineral salts are wholly dissolved, while the uric acid alone remains, and is weighed after desiccation. The mineral salts are obtained by evaporating another portion of urine and incinerating the residue. The alteration which the original salts may have undergone by roasting must necessarily be taken into account. We have said that urea forms more than one-half of the residue after the evaporation of the urine ; and as this substance contains about one-third of its weight of nitrogen, the greater portion of the nitrogen of the food will be included in it. The proportion of urea and uric acid is much greater when animal food is used than when the subject feeds on vegetables. 1715. In various diseases the urine is greatly changed, and ren- ders the physician valuable assistance in the diagnosis of altera- tions which have taken place in the economy. In a peculiar disease 3o2 762 ANIMAL CHEMISTRY. called diabetes mellitus, the urine is loaded with a considerable quan- tity of fermentable sugar, called diabetic sugar, which appears to be identical with glucose. Persons affected with this disease suffer constantly from thirst, drink largely, and pass considerable quanti- ties of urine. The sugar is separated by evaporating the urine in a water-bath, and treating the residue with weak alcohol, which dis- solves the saccharine matter. The liquid is bleached by animal charcoal, concentrated by evaporation to the consistence of syrup, and kept for a long time at a low temperature ; when the sugar is deposited in the shape of little pyramids, which are washed with absolute alcohol, and purified by recrystallization. The proportion of sugar in diabetic urine may be ascertained very exactly by optical experiments. (See note to page 478.) * CALCULI OP THE BLADDER. 1716. Concretions, which sometimes attain a considerable size, are frequently found in the bladder, and are called urinary or vesi- cal calculi. They are formed of very various substances, and are divided into, 1st. Calculi of uric acid, which are the most common, and are known by the physical and chemical properties of uric acid, particu- larly by that of dissolving in nitric acid, and producing a rose colour when the solution is evaporated in the presence of ammonia. 2d. Calculi of urate of ammonia, which exhibit, with nitric acid, the same phenomena as calculi of free uric acid, but which evolve, in addition, ammonia when they are heated with potassa. 3d. Calculi of phosphate of lime, which dissolve readily and with- out effervescence in dilute chlorohydric acid. By an excess of sesqui oxide of iron added to the liquid, and then supersaturating it with perfectly caustic ammonia, the phosphoric acid is completely pre- cipitated, in combination with the sesquioxide of iron, ( 865,) while the lime remaining in solution may be precipitated by oxalate of ammonia. 4th. Calculi of a compound phosphate of magnesia and ammonia, which also dissolves readily in dilute chlorohydric acid. After having precipitated the phosphoric acid in combination with the sesquioxide of iron, as in the preceding calculi, carbonate or oxalate of ammonia is added, which precipitates the lime, if any be present, while the magnesia remains in solution, and may be separated by the processes indicated, ( 592.) The ammonia is separated by heat- ing another portion of the calculus with hydrated potassa. The majority of urinary calculi are complicated, being composed of a nucleus of uric acid of greater or less size, around which are formed concentric concretions of phosphate of lime and phosphate of mag- nesia and ammonia. 5th. Calculi of oxalate of lime, called also mulberry calculi, be- cause their rugose and mamillated surface resembles that fruit. EXCREMENT. 763 They dissolve with difficulty in chlorohydric acid, but readily in concentrated nitric acid, which converts the oxalic into carbonic acid. The lime is separated by the processes indicated 594. By heating these calculi with concentrated sulphuric acid, a gaseous, inflammable mixture of carbonic acid and oxide of carbon is disen- gaged. 6th. Calculi of cystin. These calculi are very rare, and are formed by a sulphuretted organic matter, easily recognised by its chemical properties. Cystin is obtained in a state of purity by dissolving powdered cystic calculi in ammonia, filtering the solution, and then evaporat- ing, when the cystin separates in small crystals, which do not retain the ammonia. The composition of cystin corresponds to the formula C 6 H 6 N0 4 S 2 , and it is a colourless, crystalline, inodorous substance, insoluble in water and in alcohol, but dissolving readily in ammonia. With the acids it plays the part of a weak base, readily dissolving in them, without forming fixed compounds. SWEAT. 1717. Sweat is a liquid of acid reaction, which exudes from particular openings in the skin. It contains some unknown animal substances, and some mineral salts, among which have been found chloride of sodium, chlorohydrate of ammonia, the sulphates and phosphates of potassa and soda, phosphate of lime, and traces of oxide of iron. EXCREMENTS. 1718. The excrements of mammiferous animals are composed chiefly of animal substances which have escaped liquefaction during their passage through the stomach and intestines, and contain, in addition, fatty matters, and several soluble and insoluble substances, the nature of which is unknown. In the newly-born infant, the intestinal canal contains a brown substance, called meconium, which the child voids during the few first days of extra-uterine life, the excrements soon changing when it is fed on milk. Meconium con- tains a considerable quantity of cholesterin, and a substance analo- gous to casein of milk. Birds void their excrement and urine through the same canal, and they contain a large quantity of uric acid, besides some un- known substances. INTESTINAL GASES. 1719. Gases are always evolved during digestion, their quantity varying with the food and the peculiar constitution of the individual. These gases are essentially composed of nitrogen, carbonic acid, hy- drogen, carburetted hydrogen, and frequently of a small quantity of sulf hydric acid. The proportions of the gases range between widely extended limits. 764 OF THE MANUFACTURE OF THE PRINCIPAL PRODUCTS OF ORGANIC ORIGIN, USED IN THE ARTS, OR IN DOMES- TIC ECONOMY. 1720. We shall close the present work by a brief account of the manufacture of the principal products, of organic origin, which are used in the arts, or in domestic economy. We shall, in this de- scription, dwell only on the general chemical principles of these several manufactures, without touching upon the mechanical part, which is foreign to our subject, and would require details, the de- scription of which would exceed our limits. MANUFACTURE OF BREAD. 1721. Bread is made from the flour of the cerealia, that is, from the product of the grinding of the grain, freed, by sifting or bolting, from the cortical portions, called bran. Bran still contains a con- siderable quantity of starch and nutritious matter, while the woody substance which constitutes the envelope of the grain, and which is of difficult digestion, exists in the proportion of about 8 hundredths ; this proportion varying with the method of bolting. Wheat-flour, which is the richest in gluten, is generally used in making bread, although, in countries where wheat cannot be grown, the inhabitants use barley or rye-flour, or mixtures of these cerealia, called meslin, (me'teil,) which is obtained by sowing them together. A small quantity of rye-flour is often added to wheat-flour, in order to give the bread more flavour. The following is the average composition of the principal wheat- flours consumed in France : Unbolted flour of Flour of hard i Flour of soft native wheat. wheat from Odessa. wheat from Odessa. Water ..10.0. 12.0. 10.0 Dry gluten ..11.0. 14.6. 12.0 Starch ..71.0. 57.6. 63.3 Glucose .. 4.7. 8.5. 7.4 Dextrin .. 3.3. . + 5.0. 5.8 Bran 0.0 2.3 1.5 100.0 100.0 100.0 1722. The various processes in bread-making are mixing the flour with water, kneading, fermentation or rising, moulding it into loaves, and baking. By the first, the starch and gluten are moist- ened with water, and the soluble principles, such as dextrin, glu- cose, and the albuminous principles, dissolved; but as the paste, kneaded merely with water, would produce a hard bread, difficult of digestion, the light and puffy consistence seen in well-made bread MAKING BREAD. 765 is imparted to the crumb through a ferment added to the paste, which acts on the dextrin and glucose, by effecting alcoholic fer- mentation. The gases which are disengaged during fermentation swell the paste, to which the gluten gives elasticity; and, if it be well made, all the small gaseous bubbles remain in the bread. The ferment is generally made by taking, at the close of each opera- tion, a portion of the paste, and setting it aside for some time ; when it is called leaven or rising. In large cities, or wherever breweries are found, a small quantity of beer-yeast is added to the rising to give it more activity ; but the quantity must be carefully regulated, as too much would give a disagreeable flavour to the bread. The following is the process adopted in the Paris bakeries : The leaven being left, for 7 or 8 hours, in a gentle and uniform tem- perature, swells visibly and disengages an alcoholic odour, when it constitutes what is called head-yeast, (levain de chef.) It is kneaded with a quantity of water and flour sufficient to double its volume, still retaining the consistence of a firm paste, and is again allowed to rest for 6 hours. After this time, when the paste has become levain de premiere, an additional quantity of water and flour is added, and it is again mixed, the proportion of water being greater than in the previous operation; which process yields levain de seconde. Lastly, a similar addition is made to the levain de seconde as was made to the levain de premiere, the paste being carefully worked, and a levain de tons points obtained, the volume of which should be, in winter, nearly one-half of that of the dough intended for baking, and in summer only one-third. A certain quantity of salt is generally added, to heighten the flavour of the bread ; J kilog. of salt being used for every 150 kilog. of flour, in the Paris bakeries. The dough is then kneaded. The quantity of water necessary for the formation of the paste being first added to the rising, it is mixed for a long time, in order to obtain a perfectly homogeneous, fluid paste, to which the flour is gradually added, and which is then called the sponge. When the dough has been sufficiently worked, it is collected into a single mass, then again thoroughly worked by turning it in all directions, and finally let fall into the trough with its whole weight. The kneading being terminated, the dough is divided into loaves, which are weighed to ascertain if they reach the legal standard, ac- cording to which 115 or 117 of dough should give 100 of baked bread. They are then dusted with flour or Indian corn meal, and placed on tables in front of the oven, to keep them at the proper temperature ; when more active fermentation ensues, while the loaves gradually swell, until they have attained the proper size to be placed in the oven. The fermentation must not be too much prolonged, because it might degenerate into acetic fermentation, which would liquefy a portion of the gluten, and thus diminish the consistency of the dough. 766 TECHNICAL ORGANIC CHEMISTRY. The oven is generally of an elliptical form, and heated by wood or fagots of little value. The fuel should be properly distributed, in order to obtain a nearly uniform temperature ; and bakers remove about 30 to 35 per cent, of the fuel in the state of hot coals. The proper temperature for baking bread is about 570. The largest loaves are first introduced, and then the smallest, which are placed in the front part, because they are to be first withdrawn ; and the door is then closed. The heat dilates the gases, arrests the fermentation, vaporizes a portion of the water, and gives consist- ency to the gluten and amylaceous matter, which retain the shape they have assumed. The inside of the loaf, or crumb, does not attain a temperature above 212, on account of the continual evolu- tion of steam, while the outer portion, or crust, is completely dried, and has become torrefied by having reached a temperature of about 400. Round loaves weighing 8 pounds remain about 60 minutes in the oven, and split loaves of 4 pounds from 36 to 40 minutes. When removed from the oven, they are laid upright, in order that they may not break before having acquired all their consistency, and at some distance from each other, that the vapours may pass off more easily. The manufacture of bread has of late years been much assisted by the introduction of mechanical kneading and aerothermal ovens, which effect a more uniform baking. BREWING. 1723. Beer is an alcoholic beverage, made from the amylaceous substance of the cerealia, chiefly from barley, the price of which is lowest. The process of brewing may be divided into four distinct stages: 1. The malting, of which the object is to produce in the barley the principle which effects the conversion of starch into dex- trin and glucose, and which essentially consists in causing the barley to sprout under the influence of a proper temperature and degree of moisture, diastase being formed at the origin of the sprouts, and in the succeeding operation converting the starch into soluble dex- trin ^and glucose. 2. The preparation of the wort, (mout,) or sac- charification of the malt, which consists in treating the ground malt with water at a suitable temperature, in order to cause the diastase to act on the starch and dissolve the dextrin and glucose which result from this action. 3. The boiling with hops, which consists in heating the wort with hops in order to give it a peculiar taste and aroma. 4. Fermentation, which consists in mixing the cooled wort with a ferment, in order to effect the conversion of glucose into alcohol. ^ The barley is first placed in large vats of mason-work, with 4 times its volume of water, being stirred frequently to expel the bubbles of air between the grains, while those which arise on the surface, being generally defective, are skimmed off. The object of BREWING. 767 tliis process is chiefly to swell the grains, in order that they may sprout more easily; and it lasts 24 or 36 hours in winter, during which time the water is renewed 3 times ; while in summer it re- quires only 10 or 12 hours, but the water must be renewed 4 or 5 times. The barley thus swollen is carried to the malt-house, a kind of cave or cellar, the floor of which must be kept scrupulously clean to avoid all injurious fermentations. Germination requires the assist- ance of moisture, air, and a temperature of from 59 to 62, which conditions are most readily realized in spring or autumn ; whence the name of March leer is given to that made in the spring, and is considered superior to that made in any other season. In the malt- house the barley is spread in a layer of about 1 J feet in depth, and thus left until it becomes heated; but when it begins to sprout, the thickness of the layer is reduced to 1 foot, and then to 3 inches when the germination approaches the proper point. It is also fre- quently stirred in order to renew the air in the interior of the layer. In the hot season, the germination is terminated in 10 or 12 days ; while it requires 15 or 20 days toward the close of autumn, the sprout having then become -f as long as the grain. When the barley has properly sprouted, it is dried rapidly, in order to arrest the loss of the amylaceous matter which would ensue from a longer growth of the sprout and radicles. The drying is first made in the open air, by spreading the grain over the floor of a well-aired granary, and then in a stove traversed by a current of hot air, and called a malt-kiln. Desiccation renders the radicles of the barley very brittle, but they are easily removed by sifting them in a winnowing-macJiine or fan. The sprouted barley thus freed from the radicles is exposed for some time to the air, when it imbibes a small quantity of moisture, which facilitates its grinding. This operation is effected between horizontal stones, kept at such a dis- tance from each other that the grain is broken and torn without being reduced to flour. The product is malt, which is stowed away for future use. 1724. The saccharification of the malt is effected in large wooden vats, having a double bottom pierced with holes, intended to support the barley and facilitate the introduction and escape of the liquid. In the space between the two bottoms are the discharging-tube and one which conveys hot water. When the malt is placed in the vat, water at 140, and equal in weight to 1J times that of the malt, is poured in, the mixture being actively stirred with a kind of fork. It is then allowed to rest for J an hour, until the malt is thoroughly moistened, when water at 196 is added until the temperature of the mixture attains 167, which is the most favourable for saccha- rification ; after which it is again stirred, the vat covered, and the reaction allowed to continue for 3 hours. The saccharine fluid, or 768 TECHNICAL ORGANIC CHEMISTRY. wort, is then conveyed into a reservoir, and thence into the boilers intended for the decoction of hops. As the first digestion with water only abstracts from the malt 0.6 of the saccharine matter it can furnish, an additional quantity of water at 176 is added, equal to one-half of that used in the first operation, and is allowed to act for 1 hour, the liquid produced being added to the first. Lastly, the malt is exhausted by water at 212, and a liquid obtained which is used in making small-beer. The exhausted malt* is used as food for animals. The wort is heated to ebullition with hops in boilers, which must be kept covered to prevent the escape of the essential oil to which beer owes its aroma, and are furnished with an apparatus which constantly stirs the mixture. The strength of the wort is sometimes increased by the addition of glucose, ( 1306,) molasses, or raw sugar. The wort thus hopped is conveyed into reservoirs, where it is clari- fied by rest, and then run off into other reservoirs, where it is cooled as rapidly as possible, by allowing the liquid layer only a thickness of 4 or 5 inches ; the cooling vats being placed in large rooms sur- rounded by Venetian blinds, in order to afford a free circulation of air. The proportion of hops is about 1 kilog. for every hectolitre of table-beer, and 2 kilog. for every hectolitre of strong-beer. When the wort is cooled, it is poured into a fermenting vat or tun, and a quantity of yeast added, varying, according to the season and strength of the wort, from 2 to 4 kilog. for every 1000 litres, and maintained at a temperature of about 68. The fermenting- house should be well aired, in order to allow the carbonic acid to pass off rapidly. The fermentation lasts from 24 to 48 hours, pro- ducing a large quantity of froth, which falls from the tun into spouts arranged for the purpose, and which, when collected and expressed in bags, constitutes beer-yeast. The tuns are always kept full by adding the liquid separated from the froth. The fermentation of table-beer is completed in small casks filled to the bung, and placed on a scaffolding over a spout which carries off the froth still arising from the liquor ; and when the fer- mentation is finished the kegs are plugged, and the beer only requires a clarification with fish-glue. Strong-beer is allowed to ferment slowly for several weeks after the fermentation in the tun, in large vats, holding as much as 2600 gallons. CIDER AND PERRY. 1725. An alcoholic liquor, called cider, is prepared from apples, and constitutes almost the sole drink in Normandy and Picardy ; while pears yield a similar beverage, called perry. In the making of cider, a certain quantity of pears is often added to the apples, to give the liquor a higher flavour. * * Called, in this country, grains. TRANS. WINE-MAKING. 769 In order to make cider, the apples are crushed in a vertical mill, turning in a stone trough, with a pressure not great enough to mash the seeds, which would injure the flavour of the cider. About 10 or 15 per cent, of water is generally added. The mashed apples being put into heaps, and left for 24 hours, the cellular-tissue begins to separate, and fermentation develops a peculiar colouring matter, which gives cider its yellow tinge. After this maceration, the pulp is pressed, and 500 kilog. of juice are generally extracted from 1000 kilog. of apples. The apple-mash is again ground, after the addi- tion of about 250 litres of water, and expressed; the liquid thus obtained yields cider of an inferior quality. The apple-juice is allowed to ferment in vats or barrels, where it is freed from various substances, which are either deposited or float on the surface in the shape of froth. It is drawn off into large hogsheads, which are but loosely corked, in order to give exit to the carbonic acid generated during fermentation. During this second stage of fermentation, the cider retains a sweet taste, much admired by some persons ; but in countries where cider is the general beverage, fermentation is allowed to continue to its completion, by which the liquor acquires an acid and slightly bitter taste. WINE-MAKING. 1726. Grapes contain extremely numerous proximate principles: cellulose, pectin and its congeners, ( 1296,) grape-sugar, tannin, albuminous substances, yellow, blue, and red colouring matters, fatty substances, tartrates of potassa and lime, silica, oxide of iron, etc. etc. Wine derives its alcohol from glucose; while the colouring matters and tannin, which exist chiefly in the skin of the fruit and the grape-stems or stalk, impart different shades to the various wines, according as one or other of the colouring principles predominates. These principles are not all equally fixed; the blue colour changing first, while violet-coloured wines become more red with age, and acquire a yellowish tinge when they are very old, because the red principle is destroyed before the yellow. In wine-making, the grapes are, in the first place, pressed, most frequently by the feet of men, who walk about in the vat. In the manufacture of white wine, the pulp alone is pressed ; while, if red wine is to be made, the pulp is left for several days to itself, to allow fermentation to take place, and the liquor to dissolve the colouring matters and tannin of the skins of the fruit and of the stalks. The pressing is frequently repeated, when the tissues are party broken up by fermentation ; but this is an operation requiring caution, as the carbonic acid, which is copiously evolved, might asphyxiate the workmen. For wines of superior quality, a partial picking is often performed, that is to say, a portion of the stalks are removed, when the latter are too abundant, as is the case in years when grapes are not very plenty. The vats in which the first fermentation is VOL. II. 3 P 49 770 TECHNICAL ORGANIC CHEMISTRY. effected are left open, though it would probably be better to keep them closed, in order to avoid the contact of air, which often pro- duces acetic fermentation in the scum collected on the surface. The duration of the fermentation varies with the temperature and nature of the grape, and is known to be terminated by the almost complete cessation of the evolution of gas, and the colour of the wine, which contains a sufficient quantity of the colouring matter. For ordinary wines, it lasts from 3 to 8 days ; while in some localities it is con- tinued for a month or six weeks, the vats being then closed after the eighth day. When fermentation has ceased, the clear liquid is drawn off by a stopcock, and the must is expressed; the latter being generally diluted with a small quantity of water, and again subjected to pres- sure, yielding a very weak wine, called piquette, which soon turns sour. The wine which flows spontaneously and that separated by compression of the pulp are generally mixed together, but are kept separate in the making of wines of superior quality, because that yielded by expression always contains some acid principles fur- nished by the stalks and seeds. The wine is received into hogsheads, which are generally not closed, because fermentation goes on slowly, and carbonic acid is for a long time evolved. When this ceases, the wine is again drawn off, and, about the month of March or April, the fining is com- menced. Red wines are commonly fined with white of eggs, bullock's blood, or gelatin, which substances combine with the tannin and a portion of the colouring principle, and carry down, by coagulating, the substances in suspension which muddied the wine. To fine white wines, which contain but little tannin, it is necessary to use fish-glue, because it coagulates much more rapidly. In bad years, when the grapes do not ripen perfectly, the quality of the wines is greatly improved by adding a certain quantity of glucose to the fermenting- vat. Sparkling wines, such as champagne, are prepared from a black grape, the juice of which generally contains more sugar than the white grape ; but in order to avoid colouring the juice, great care is taken not to rupture the husk of the grape or of the stalks. The grapes, gathered in warm weather, are carried with great care to the press, when, by a first and gentle pressure, the juice which is to make wine of first quality is obtained, while the must, being again stamped, and more powerfully expressed, furnishes a juice from which pink champagne is made. A third and fourth pressing is sometimes made, but the products are added to the ordinary red wines. The white or pink juice is allowed to ferment in large hogsheads, where it is freed from the greater portion of its yeast, which floats on the surface with the scum. In 24 hours the juice is drawn off into other hogsheads, which are kept nearly filled, and MANUFACTURE OF BEET-SUGAR. 771 imperfectly closed, so as to allow the disengagement of carbonic acid. In a month it is drawn off and fined for the first time, a second fining being applied after the following month, after having drawn it off, and a third one in the month of April, when it is bottled. Three to five per cent, of its weight of sugar-candy, dis- solved in an equal weight of water, is then added to the wine. The bottles are very carefully closed with corks, held down by iron wire, and surmounted by a metallic cap ; and they are laid upon their side, a lath of wood being placed between each two bottles. A por- tion of the sugar added undergoes alcoholic fermentation, under the influence of the yeast which still exists in the wine, but the carbonic acid, finding no escape, remains in solution in the liquor, which also retains a sweet taste, produced by the portion of the sugar which has not fermented. MANUFACTURE OF BEET-SUGAR. 1727. The sugar-beet cultivated in France for the production of beet-sugar, is the species called the white Siberian sugar-beet, and shows the following average composition : Water 83.5 Sugar 10.5 Cellulose 0.8 Albuminous substances 1.5 Various organic substances, and mineral salts 3.7 9 100.0 The beets are taken out of the ground when they have acquired their full growth, and carefully separated from those which have been injured by the operation, since the latter do not keep, and should be used immediately. The beets are made into heaps in the field, and covered with leaves, until there is danger of frost, when they must be housed, or buried in pits. The upper part of the root, at the starting-point of the stalk, is cut off, because this por- tion is harder and contains but little sugar. The beets, after being cleansed and washed, are thrown into a machine which reduces them to as fine a pulp as possible and breaks up the cells. The pulp is placed in woollen bags, laid on each other, and between which metallic plates are introduced ; after which the mass is compressed by a screw-press, and the juice which flows out, and which constitutes about 0.4 of the juice contained, collected. The bags and plates are then placed under the platform of an hydraulic press, which is unscrewed after having maintained the pressure for about 10 minutes, when the bags are placed two by two between two plates, and again still more powerfully com- pressed. In this manner, 75 to 80 per cent, of beet-root juice may be extracted, only about 15 parts being left in the pulp. 772 TECHNICAL ORGANIC CHEMISTRY. 1728. As the juice soon changes, it is essential to raise it, as quickly as possible, to a high temperature, in order to destroy the ferments ; and to saturate with lime the free acids, which would soon convert a portion of the sugar into sugar turning to the left. For this purpose, the juice, on leaving the press, is conveyed into a double-bottomed boiler, heated by steam, and the temperature is rapidly raised to 140 or 158, after which it is conveyed into another boiler, also heated by steam, where the defecation, or treat- ment with lime, is effected. Hydrated lime is usually made by pouring on quicklime 10 times its weight of boiling water, and, when the lime is entirely slacked, passing it over a metallic sieve, which arrests the grains of sand and the non-decarbonated portions. The juice is first heated to 167 in the defecating boiler, the milk of lime is then added, and the whole is stirred, to render the mixture homogeneous; when the temperature is raised to 212, the supply of steam being cut off when ebullition commences. The lime combines with the free acids, the albuminous substances, the fatty and colouring matters, and produces insoluble compounds, effecting at the same time a kind of clarification, by carrying down, with the insoluble compounds, organic remains which were suspended in the juice. A thick scum having formed on the surface of the liquid, the latter is kept from boiling, in order to prevent its rupture by the bubbles of steam. The proportion of lime added varies with the nature of the beets and with their freshness ; only 3 Ibs. for 1000 pints of juice being used in the beginning of the season and with fresh beets, which quantity is gradually increased, and frequently reaches 10 Ibs., before the close of the season. * An excess of lime remains in the liquor, and forms a deliquescent com- pound with a portion of the sugar, which must be lessened as much as possible, because it causes a loss of sugar. In some factories, it has been endeavoured to saturate it with a proper quantity of acid. 1729. When the defecation is terminated, the liquor is drawn off and filtered through animal charcoal, the filters used for this pur- pose being large sheet-iron cylinders, having a false bottom, pierced with holes, like a cullender. A cloth is extended over the bottom, on which is spread very coarsely powdered animal charcoal, added in successive layers, until it fills the cylinders to l foot from the top, when another cloth is laid upon it, and is covered by another me- tallic plate pierced with holes ; each filter receiving 6000 to 8000 Ibs. of charcoal. The filters should be kept constantly filled with fluid, which is easily done by means of a stopcock. After this process^ by which the juice loses a portion of its colouring matter, and the lime in excess, which adhere to the charcoal, it is conveyed as rapidly as possible into the concentrating boilers, which are generally shallow, and are heated by the circulation of high-pressure steam through copper tubes arranged over their bottoms. The juice is raised to a temperature of 70 in 10 or 12 minutes. The workman judges, MANUFACTURE OF CANE-SUGAR. 773 by signs learned by experience alone, if it is properly concentrated, or if the boiling is completed. During the ebullition, which termi- mates at a temperature of 266 to 275, a considerable portion of the sugar is altered, and, to dimmish the loss, the evaporation must be effected as rapidly as possible. This operation has been greatly improved by boiling in vacuo, that is in close boilers, heated by steam, and brought into communication with worms and receivers in which a vacuum is made ; when ebullition takes place at a lower tempera- ture, the quantity of sugar changed is much smaller. 1730. When the syrup is properly boiled, it is collected in a cooler, which usually receives the products of 5 or 6 boilings ; and its temperature then falls to about 176. Crystallization then com- mences, but as soon as any crystals form, they are detached from the sides, and the syrup stirred to bring them again into suspen- sion. When the temperature has fallen to 130 or 122, the syrup is poured into large conical moulds of metal or baked clay, resting on the point, which is furnished with a hole previously stopped with a plug of wet muslin. The moulds are ranged on long benches, with openings through which the escaping fluids fall into zinc gut- ters, whence they flow into reservoirs. The temperature of the room containing the moulds should be about 86. Crystallization is completed in 24 or 36 hours, when the plug is removed from the opening in the mould, and the point of the loaf pierced with an awl, so as to draw off the molasses, which is again concentrated, even further than the original syrup, and crystallized in moulds. When the molasses is too highly coloured, as happens sometimes, it is diluted with a sufficient quantity of water, filtered through animal charcoal, concentrated and recrystallized. The syrup which drains from the second sugar is frequently subjected to the same process for a third time, but the crystallization then requires a great length of time. When the sugar has drained sufficiently, the loaves are loosened, that is, the moulds are inverted, and the loaves detached by gentle blows ; after which they are placed in the wareroom, protected from dampness. This is raw beet-sugar, which requires refining before being fitted for consumption. MANUFACTURE OF CANE-SUGAR. 1731. Of all sacchariferous plants, sugar-cane is the most rich in sugar, since it yields 0.90 of juice, containing from 0.17 to 0.22 of crystallizable sugar; but in the majority of the colonies its ma- nufacture is still so rude that nearly one-half of the sugar contained in the cane is lost. The richest variety of sugar-cane is the ribbon- cane, or Otaheite cane, containing, on an average, Water 72.1 Sugar 18.0 Woody tissue 9.9 10OO 3p2 774 TECHNICAL ORGANIC CHEMISTRY. It leaves about 0.4 of ash containing a considerable quantity of silex, like that of all the graminese ; and the ash consists of Silex 68 Potassa 22 Lime .10 100 1732. When the canes are cut, they soon become damaged by fermentation, and should therefore be carried immediately to the mill. The latter is composed of large stone or cast-iron cylinders, between which the canes are crushed ; the best being provided with five crushing-cylinders, so that the cane is compressed four times. They are turned by a water-wheel or by steam ; and in the major- ity of sugar-works only about 50 kilog. of juice are extracted from 100 kilog. of cane, while in the best mills about 65 are obtained ; 40 kilog. of juice being in the former case left in the cane-trashy and 25 in the latter. The woody fibre of the cane renders it very difficult to extract the juice completely, which would require greater power; and in the colonies the trash is, generally speaking, the only fuel used. The rapid and perfect extraction of the juice is the most important part of the process, and that which produces the greatest loss of sugar when not well performed. The fresh cane-juice, which, in addition to the sugar, contains merely very small quantities of albuminous substances, is allowed to remain for an hour in a reservoir to become clear, and is thence conveyed into the boilers, five of which generally make a set. The first, which is the most remote from the furnace, is used for defecation, (or temper- ing ;) in which case only ^ O f the quantity of lime necessary for the defecation of beet-sugar is used ; about 0.2 or 0.3 for 1000 of juice. It is then heated to boiling, and rapidly skimmed. The defecated juice is thence conveyed into the second boiler, where evaporation commences; the skimmings from this boiler being removed and thrown back into the first. The liquor then passes into the third boiler, where the evaporation is continued ; and during its sojourn in this boiler, the workman ascertains if it has been properly defe- cated, or if it requires the addition of a small quantity of lime. He then transfers the liquid into the fourth boiler, where it is concen- trated to the consistence of syrup ; and lastly into the fifth, where it is concentrated to the consistence suitable for crystallization. In the best establishments the boilers rest on pivots in their cen- tral line, and are placed below each other, which arrangement greatly facilitates and accelerates the working. The boiling is then run off into large flat reservoirs, where it is allowed to cool and crystallize for 24 hours, when the granular mass is poured into moulds, in which the crystallization is completed, and is finally drained. SUGAR-REFINING. 775 The operation generally yields in most of the works, Brown sugar 55 to 66 Sugar which remains in the molasses, for the greater part uncrystallizable 25 to 20 Sugar left in the trash 80 to 75 160 to 160 In several important sugar-works, an apparatus for evaporating in vacuo has been tried, which considerably diminishes the loss of sugar in the molasses, and also furnishes a better article ; but the primitive cost of such apparatus, combined with the want of fuel, will for some time prevent this more perfect process from being generally introduced. Molasses is used in the manufacture of several alcoholic liquors, such as rum, ratafia, etc. SUGAR-REFINING. 1733. A large quantity of cane-sugar is consumed in the state of brown sugar, while the greater portion of it is refined ; and raw beet-sugar must also be refined, as otherwise the flavour and smell of the beets would render it unfit for use. The refiner generally mixes cane and beet-sugar in proportions which facilitate the pro- cess. Cane-sugar, during its voyage from the colonies, has gene- rally undergone some change, and contains a small quantity of acid, while beet-sugar, on the contrary, contains a small quantity of sac- charate of lime ; and by mixing them in proper proportions, the acid of the cane-sugar is saturated by the lime of the beet-sugar. The raw sugars being mixed on a table made of flag-stones, and passed through a sieve, the mixture is dissolved in 30 per cent, of its weight of water. The solution is effected in boilers heated by steam, and placed sufficiently high to allow the syrup to fall directly into charcoal filters, after which the clarifying is commenced. This operation consists in adding to the syrup 5 per cent, of its weight of finely powdered animal charcoal, (bone-black,) and 1 or 2 of an albuminous substance coagulable by heat ; bullock's blood, defibrin- ated by beating, and diluted with 4 times its weight of water, being generally used. The liquid is stirred, and allowed to boil, when the syrup is run into peculiarly shaped filters, which arrest the sub- stances in suspension and the scum. The best filters are those made of an upright wooden case, containing a great number of bags, made of cotton or woollen drugget, the mouth of which is above the top of the case, while the lower part passes through the bottom and opens below. The muddy liquor being poured into the case, filters from without into the bags, which are kept from col- lapsing by hoops of wood or iron, by which means filtration ensues over a large porous surface, and the filters are moreover easily washed. The residue in the case is washed with fresh water, which 776 TECHNICAL ORGANIC CHEMISTRY. furnishes a weak solution of sugar, used to dissolve the new sugars ; and is then sold as manure, under the name of refinery -black. The clarified syrup is immediately filtered through charcoal, in an apparatus resembling that used for the bleaching of tempered sugar-beet juice, ( 1729,) and is then conveyed into the boilers. In almost all the large refineries, it is now boiled in an apparatus calculated to evaporate in vacuo. The concentrated syrup is col- lected in kettles in which the temperature is raised to 176, in order to retard crystallization, and redissolve the crystals which had be- gun to form in the evaporating kettles, where the boiling point is not very high. Crystallization soon commences in this kettle, while the temperature falls, and the liquid is frequently stirred, and the mixture of syrup and crystals poured into moulds, which are placed in a room contiguous to the boilers. The moulds are generally of baked clay, and are 50 centimetres in height, and from 15 to 22 wide at the base. Before using new moulds, they are kept filled for several days with a thin pap of clay, which closes the pores of the earthenware, and prevents the absorption of the syrup and the adhesion of the loaves. The moulds are perforated at the lower part, the holes being closed with a plug of wet muslin ; and the moulds are arranged on a double bench, furnished with openings, and of which the lower part, made of zinc, conveys the drippings into a canal communicating with a reservoir kept for the purpose. When the moulds are filled to about 1 centimetre below the top, they are allowed to rest for some time ; when there forms on the surface of the syrup a crystalline crust, which is broken, and the broken crystals are thrown to the bottom, the syrup being stirred at the same time in order to equalise the temperature, which always falls most rapidly toward the apex of the cone. The crystallizing- room is kept at a temperature of about 95. After remaining 8 or 12 hours in this room, the moulds are carried into low apartments with brick floors, and heated by steam conveyed in pipes on the floor or around the walls. The plug is then removed from the hole in the moulds, and the loaf pierced with an awl ; when it is allowed to drain, and in 12 hours the base of the loaf is nearly white and dry. The sugar, which now is called drained green or raw sugar, is then left in the moulds for 6 or 7 days to complete the draining, after which the workman smooths the base of the loaf with a plane, and adds to it a layer of purely white sugar, for which he generally uses scrapings of refined sugar, in order to make the base of the loaf perfectly level, as it would otherwise be disfigured by a depres- sion in the centre. The claying is then commenced, which consists in pouring into each mould a paste of clay diluted with water to the thickness of 2 or 3 centimetres. The water from the clay, filtering slowly through the loaf, becomes saturated with nearly pure sugar in the upper strata, which are nearly bleached by draining, and d'r > places in the lower parts the coloured molasses which moisten the BONE-BLACK. 777 porous crystalline mass. After 7 or 8 days of claying, the clay forms a firm coating on the surface of the loaf, which is removed by a spatula. The base of the loaf is again smoothed, and it is sub- jected to another claying resembling the first. These two processes generally produce refined sugar, although a third claying is some- times necessary. After the last claying, the loaves are laid on their sides, and the bases being again smoothed, the moulds are slightly tapped, in order to detach the loaves from their surfaces, and thus allow the last portions of syrup to pass through more easily. The moulds are then placed in their former position, to collect the syrup in the apex and cause it to flow out as completely as possible ; after which they are set on their bases, and thus left for 24 hours, in order to spread the syrup yet contained in the apex, which would sensibly colour the latter, throughout the whole loaf. These alternate positions are repeated several times, until the whole mass has acquired a uniform colour ; after which the loaves extracted from the moulds are exposed to the air for 24 hours, and then dried in ovens at a temperature not exceeding 113. In some manufactories, decolouring is substituted for claying. This operation consists in pouring upon each loaf, in the mould, a certain quantity of a syrup saturated with sugar, and purer than that which moistens the loaf, when the latter syrup is displaced by the syrup added, and escapes through the apex of the mould. The first "clairce" is replaced by a second, composed of a syrup still purer than the first, and so on, until the last clairce consists of per- fectly refined sugar. This process is much more expeditious than that of claying. The name of lumps, or bastards, is given to sugars of inferior quality, for the making of which the coarsest raw sugar, the green syrups, and residues are used. They are clarified and boiled as are sugars of superior quality, but are crystallized in larger moulds, and the loaves are decoloured or clayed once oftener than sugars of first quality. The apex of the loaf is generally coloured, and must be removed. A kind of white loaf-sugar, called dried sugar, has been for a long time manufactured at Marseilles, (sucre tape.) It is prepared by rasping the best quality of lumps without allowing them to dry, passing the substance through a coarse sieve, and introducing it into small moulds, previously moistened, into which it is pressed with a flat pestle. After some time the loaves are taken out and placed in a stove. BONE-BLACK. 1734. Animal charcoal, or bone-black, used for bleaching sugar, is generally made in the vicinity of large cities, because bones are there cheaper and more easily procured. The bones form about J 778 TECHNICAL ORGANIC CHEMISTRY. of the -weight of the recently slaughtered animal; and those which are of sufficient size and thickness are set apart for the use of turners. The fat, used in the manufacture of stearin candles, is first extracted from the bones intended for making bone-black, by breaking them into pieces and heating them with water in large boilers, in which they are frequently stirred, when the fat separates and floats on the surface. The bones are removed from time to time with a strainer, and fresh ones added. A portion of the bones, before being car- bonized, is used for the preparation of gelatin, ( 1662.) The bones, after being deprived of their fat, are drained and dried in the air, and then carbonized in cylinders, or in large cast-iron or earthen pots, generally about 1 foot in diameter, and 1J foot in height, which are piled on each other or ranged in rows in large furnaces heated to redness with bituminous coal, which temperature having been kept up for 6 or 8 hours, the pots are removed. When they are perfectly cold the bone-black is removed and ground between cylinders ; all dust being avoided as much as possible, because enough is always formed for the clarifying of sugar, (1733.) The dust and variously sized grains are separated by bolting and sifting in sieves with meshes of suitable size. Bone-black which no longer exerts any bleaching power on juices and syrups, may have this power restored, and be made useful in future operations, by removing the soluble substances in them by washing, and recalcining them, which carbonizes the adhering organic matters and exposes the carbonized portions. Their surface, how- ever, being still covered with a pellicle of vegetable charcoal, which diminishes sensibly their activity ; the former is removed by rubbing them slightly between horizontal grindstones which do not exert sufficient pressure to crush them, and by separating the dust formed by bolting. By this reviving, bone-black loses 4 to 5 per cent, of its weight ; but the operation may be repeated 20 or 25 times on the same charcoal. MANUFACTURE OF SOAPS. 1735. We have mentioned ( 1594) that the salts formed by fatty acids with the metallic oxides are called soaps. Soaps of which the base is potassa, soda, or ammonia, are the only ones soluble in water; and soaps of potassa and soda alone are used for washing and for the toilet. In commerce, soaps are divided into hard soap, of which the base is soda, and soft soap, of which the base is potassa ; the latter being more generally used in northern countries, while in France the hard soap is preferred. Soaps formed by the same base are harder in proportion to the melting point of the fatty substances used in saponification. Soaps are made by boiling fatty substances with more or less con- centrated lyes of caustic potassa or soda; which are obtained by decomposing the alkaline carbonates, when cold, by hydrated lime. MANUFACTURE OF SOAPS. 779 False-bottomed vats are generally used, and on the upper bottom, which is covered with straw, the slaked lime is placed, mixed with the powdered alkaline carbonate, and it is then covered with water to the depth of about 5 inches. In a few hours the liquid has fil- tered through the solid matters, and collected on the lower bottom, whence it is then drawn off into a separate vat, to be pumped back into the first vat, and once more to filter through the lime ; this process being continued until the alkali is completely deprived of its carbonic acid. By washing the remaining lime with water, alkaline lyes are obtained, which are generally used in the first stage of saponifica- tion of fatty substances. Saponification is effected in large boilers, which are first filled to one-fourth with weak lye, and into which the fatty substance is gradually poured, taking care to constantly stir the mixture; weak lye and fat being then added successively until the boiler is sufficiently filled. An emulsion of soap, with an excess of fat, is first formed in a liquor which contains but little free alkali, and which must be kept uniform by continual stirring, when a stronger lye is introduced, which converts the soap having an excess of fatty acids into a more basic and soluble soap. This more highly charged lye is added by different portions at a time, and, in the last place, it is mixed with common salt, or other alkaline salts, which entirely precipitate the soap and separate it from the lye. It is allowed to cool, and the aqueous liquid containing the glycerin, the alkaline salts which have effected the separation of the soap, and the excess of alkali, is drawn off. A last concentrated lye being then added, the whole is heated to ebullition, which temperature is maintained until the lye has attained a density of 1.15 to 1.20, when the supernatant soap is removed and run into moulds, and, after it has become sufficiently solid, is divided in parallelopipedons of proper dimensions by means of a wire. 1736. Marseilles soap is that most esteemed, and is made from caustic soda and inferior quality olive-oil yielded by the hot ex- pression of the olive-must from which first quality olive-oil has been already obtained. Two kinds of artificial soda are used for these soaps, one called sweet soda, which should be as pure as possible, since it affects the saponification, and the other highly charged with sea-salt, and called salt soda, which is used for furnishing to the first soap, having an excess of fatty acid, the quantity of base necessary to entirely precipitate it from the liquid. The sweet soda, broken up, is mixed with J- of its weight of caus- tic lime, previously slaked and placed in vats of mason-work, called barquieux, where the mixture is lixiviated several times, furnishing liquids of decreasing strength. Saponification is effected in large kettles with sloping sides, made of bricks, and with a copper bottom : a lye marking 12 Baume' being first introduced and boiled, the oil is gradually added, and the whole is constantly stirred. After some time a lye marking 15, and at a later period a lye marking 20, 780 TECHNICAL ORGANIC CHEMISTRY. is introduced. The whole operation, called emptitage, ksts about 24 hours, and produces a soap with an excess of fatty acid ; it being important that the soda should be as free as possible from sea- salt. Having reached this point, the relargage is commenced, the ob- ject of which is to make the soap more alkaline and separate it from the lyes; to which effect a workman throws in gradually, on the surface of the kettle, a salt lye, marking from 20 to 25, while another stirs the whole continually, when the paste, hitherto homo- geneous and viscid, is converted into clots, which separate from the aqueous liquid. It is allowed to rest for 2 or 3 hours, when the lye is drawn off. After this operation, which is called epinage^ it is again treated twice with fresh salt-lye, in order to give the proper consistency to the soap ; and then, after having drawn off the last water, the paste is worked with shovels to render it homogeneous, small quantities of weak lyes or fresh water being frequently added, according to the nature of the soap to be made; after which it is run into moulds, and cut into small pieces after cooling. 1737. Two kinds of soap are found in commerce ; the white and marbled soap. The bluish veins observed in the latter are pro- duced by a small quantity of soap having a base of alumina and protoxide of iron, and by sulphide of iron yielded by a small quan- tity of sulphide of sodium which always exists in the lye. Of them- selves, these foreign substances are of no use, and may even in some cases be injurious ; but as their presence is a certain index that the soap does not contain more than 30 per cent, of water, marbled soap is highly valued on that account. When the paste contains more water, it is more fluid and light, and metallic compounds are easily deposited in it, and cannot be distributed through the soap in veins. White soap is made by diluting the paste at a moderate temper- ature, in weak lyes, and allowing it to rest in tight kettles ; when the soaps of alumina and iron falling to the bottom, the supernatant white soap is removed and carried to the moulds. In order to pre- pare marbled soap, less lye is added, and the soaps of alumina and iron are not so completely deposited, and separate in veins through- out the mass. Cakes of marbled soap generally lose their colour in the air, because the protoxide and sulphide of iron are converted into sesquioxide ; but the marbling is always seen in freshly cut soap. Marbled soaps generally contain 30 per cent, of water, and white soaps not less than 40 or 50. Resins form, with the alkalies, salts which exhibit characters re- sembling those of the soaps ; and yellow soaps are now made, the fatty acids of which are partly replaced by colophony. 1738. Soft soaps are made with hempseed, linseed, colza, and other oils, the base being potassa. Their natural colour is of a brownish-yellow, while a greenish tinge is generally given to them by the addition of a small quantity of indigo. The process is nearly DYEING. 781 tne same as that of making hard soaps, except that lyes of potassa are substituted for those of soda ; and when saponification is com- pleted, and the soap has become transparent, it is evaporated to the proper consistency, and run into hogsheads. This soap is always more alkaline than soda-soap, and dissolves more easily in water. Toilet-soaps are made with soda, and are generally highly hy- drated, being prepared either from olive-oil or tallow, and their agreeable odour is owing to essential oils mixed with them in the moulds. Colourless or coloured transparent soaps are made by dis- solving in alcohol well-dried soap made of beef-suet, concentrating it properly by distillation, and pouring the limpid and transparent fluid into moulds, where it becomes solid. Various organic colouring matters may be incorporated with it. CHEMICAL PRINCIPLES OF THE ART OF DYEING. 1739. The art of dyeing has been of late so scientifically culti- vated, that it would require much greater space than the limits of an elementary course can afford, to give a complete idea of it ; and we shall therefore be obliged to confine ourselves to the explanation of the chemical principles on which is based the preliminary prepa- ration of the textile fibres to render them fitted for the manufacture of tissues, and those on which is founded the art of fastening colour- ing matters. Preliminary Preparation of the Textile Fibres. 1740. The textile fibres used in manufactures are either of vegetable or animal origin ; the first being chiefly hemp, flax, and cotton, and the second wool, hair of animals, and silk spun by the silkworm. Cotton is nearly pure lignin, while hemp and flax are composed of lignin in long filaments, which, when dry, adhere to each other by means of a gelatinous substance, called pectin, although it differs probably from that found in fruits, and which must be removed to render them fit for spinning and weaving. For this purpose, they are rotted, which operation consists in plunging them, tied in bun- dles, into water, where they are left until fermentation commences, which is manifested, in stagnant waters, by a very disagreeable odour. The bundles are then withdrawn from the rotting-pond, and, after having been dried in the air, are subjected to mechanical operations, of which the object is to detach the foreign substances, which have become friable by the desiccation ensuing on the rotting, and to isolate the fibres. Hemp and flax thus prepared are fit to be converted by spinning into unbleached thread, which may be im- mediately used for weaving. Cotton undergoes no preliminary pre- paration, and may be immediately spun and woven. 1741. Wool, as it is found on the living animal, is impregnated VOL. II. 3 Q 782 TECHNICAL ORGANIC CHEMISTRY. with a considerable quantity of foreign substances, commonly called grease* (suint,) and which consist essentially of substances soluble in water, and fatty substances insoluble in that^ fluid. Sheep are usually washed before being shorn, and then yield what is called ivashed wool, which has thus lost a large portion of its soluble mat- ters, and a portion of the fatty matters, which separated in the state of an emulsion. Wool which has not undergone this operation is called unwashed wool; and the process by which the grease is removed from wool is known by the name of scouring. Unwashed is scoured with washed wool, in a bath of 300 litres of water and 72 to 78 of putrid urine, the whole being heated to 122 or 140 for soft wool, and to 158 or 167 for harsh wool. After dipping 3 or 4 kilog. of unwashed wool into the bath, and stirring it with a stick for 10 minutes, they are removed, and allowed to drain over the kettle ; the same being done with another lot of 3 or 4 kilog., until about 40 kilog. in all have been thus treated. 6 or 7 kilog. of putrid urine are then added, and 50 kilog. of washed wool passed through it, which is scoured, both by the carbonate of ammonia of the putrefied urine and the alkaline substances yielded by the unwashed wool. The same operation is repeated on a new lot of 40 kilog. of washed wool ; after which a new dose of 6 or 7 litres of putrid urine is added, and 20 kilog. of unwashed wool washed in it. This alternate scouring of washed and unwashed wool is continued during the w^hole day, adding urine at each fresh quantity of unwashed wool. After this operation, the unwashed should be considered as washed wool, and treated accordingly. When the wool-scourer has no unwashed wool, he makes his bath of 650 litres of water and 300 litres of urine, heats it to 120 or 140, and passes through it 30 kilog. of wool in 5 lots, each of which he leaves in the bath for 12 or 15 minutes, after which he adds 1 litre of water and 2 of urine, and then scours an additional portion of 30 kilog., and so on. Some scourers add marly clay to their bath. Washed wool contains less than 15 per cent, of grease, while un- washed contains much more ; and, by washing, scouring, and drying, loses as much as 60 or 70 per cent, of its weight. When the washed wools contain less than 5 per cent, of grease, they are scoured with soap or carbonate of soda. The nature of the fatty matters of the grease is peculiar, and they have been called stearerin and elaierin; the first of which is souble but uncrystallizable, while the second is oleaginous. These fats are not saponified by weak alkaline lyes, but, when they are boiled for a long time with a solution of caustic potassa, the liquid is found to contain two salts of potassa, formed by peculiar fat acids, which have been called steareric and elaieric acids; while nothing analo- * In England it is called the yolk. TRANS. DYEING. 783 gous to glycerin has yet been found. The oxygen of the air may possibly have some share in the formation of these fat acids. After scouring, the wool is washed in river- water in willow baskets. When it is intended to be perfectly white, it is exposed for some time in a moist state in rooms in which sulphur is burned, when the sulphurous acid finishes the bleaching, ( 131,) and the excess of it is removed by fresh washings. It is important not to prolong too much the action of the sulphurous acid, because it exerts a decom- posing agency on the nitrogenous substance of the wool. Wool contains, in addition, a proximate sulphuretted principle, which may be separated by successive immersions in limewater. Wool which has been heated with a weak alkaline solution disen- gages sulf hydric acid when it is again heated with acidulated water, and is blackened when boiled with a solution of a salt of lead or protoxide of tin. 1742. Kaw silk, as it is obtained from the cocoons, is impregnated with a gelatinous substance, which makes it very stiff, and generally gives it a golden-yellow tinge. This substance, which forms about J of the weight of raw silk, dissolves readily in alkaline liquids ; but as the caustic alkalies attack the silk itself, soap is almost always used, and sometimes, though rarely, carbonate of soda. This operation, which is called scouring (d^creusage) the silk, is divided into three stages : the ungumming, (de^gommage,) boiling, and bleaching. The ungumming is done in a tinned boiler, containing, for every 100 parts of silk, 1800 or 2500 parts of water and 30 of soap. It is first boiled to dissolve the soap, and then cold water is added, so as to lower the temperature to about 200, when the silk is dipped into it in skeins, supported by sticks, called lisoirs, being there left until all the gelatinous matter is dissolved, and afterward wound on a bobbin. This operation lasts from f to 1J hour. Seve- ral skeins are then united, forming a hank, which is boiled for 1J hours in a bath containing 20 or 30 parts of soap for 2000 of water, which constitutes the boiling, (cuite.) The hanks are undone, twisted into skeins, wound on a bobbin, and then washed in a weak solution of carbonate of soda and in river-water. The bleaching consists in dipping the silk held by the lisoirs into a bath heated to 203, and composed of 300 litres of water and from 500 to 750 grammes of white Marseilles soap. Silks which are intended to be brilliantly white are exposed, in addition, to sulphurous acid. PRELIMINARY PREPARATION OP STUFFS. 1743. Before being printed, cotton stuffs are singed or shorn, with the intention of removing the filaments which project from the tissue. The shearing is performed by machines, called shearing- machines, composed of two revolving cylinders, one of which, fur- nished with brushes, raises the nap, while the other, provided with knives arranged spirally, shears it. In singing, the stuff is passed 784 TECHNICAL ORGANIC CHEMISTRY. rapidly over a metallic cylinder, heated to nearly a white-heat, which burns off the down. 1744. Cotton stuffs which, are intended to be perfectly white are previously bleached, which operation is also more or less com- pletely performed on goods which are to be printed. Linen and cotton goods are bleached by two different processes : 1. By washing them in alkaline lyes, and exposing them on the grass; 2. By chlorine or the alkaline hypochlorites. The first is the oldest, and was used particularly for bleaching flax and hempen goods. It is divided into the following opera- tions : 1. Scouring, which consists in dipping the stuffs for 24 hours in a weak solution of caustic potassa, heated to about 99, wash- ing, and then boiling them for 20 minutes in the same alkaline lye. 2. The boiling, which consists in boiling (as was stated 1743) the scoured stuffs, after having washed them in water, and compressed them between cylinders. 8. Bleaching, which consists in boiling them for 6 hours with an alkaline iye, containing 1 part of caustic potassa for 16 parts of stuff, washing them, and exposing them for 5 or 6 hours on the grass ; the alkaline washings and exposure on the grass being renewed until the stuffs are perfectly bleached. During the exposure on the grass, the colouring matters are bleached by the influence of the solar rays and moisture; the absorption of oxygen converting them into new substances more readily soluble in the alkaline liquors. Lastly, the stuffs are passed through water heated to 105 or 120, containing about ^ of sulphuric acid, which dissolves the metallic oxides; after which they are washed and calendered. This process requires a great length of time, and bleaching by chlorine or the hypochlorites is more expeditious. The chlorine acting on the colouring matters, in the presence of water, decomposes the water into hydrogen, which combines with the chlorine to form chlorohydric acid ; while the oxygen in the nascent state oxidizes the resinous and colouring matters, and renders them soluble in alkaline lixivioe. The hypochlorites are reduced to the state of me- tallic chlorides, and act at the same time by means of the nascent oxygen given off by the hypochlorous acid and the base ; while the concurrence of an acid effecting the decomposition of the hypochlo- rites hasten the bleaching. Thus in both processes it is in the end always an oxidizing action which effects the bleaching and destruc- tion of the foreign substances. Hypochlorite of lime, dissolved in water, is now solely used in bleaching ; and^ it is preferable to all dilute solutions, because it is less liable to injure the ligneous fibre of the tissue ; although the bleaching then requires more time. ^ The stuffs, after being passed over the heated cylinder to be singed, are immediately dipped into a vat filled with water to cool them, where they then remain for 24 hours, and lose a considerable DYEING. 785 portion of their soluble principles. They are then to be perfectly dried, either by being beaten or compressed between cylinders, and then kept for 12 hours in a vat filled with water heated by steam, where they are arranged in alternate layers with slaked lime. After being again beaten, they are left for 12 hours in a lye of caustic soda, consisting, for 300 parts of stuffs, of 10 parts of caus- tic soda for 1500 of water. This lye is replaced by another con- taining only 7.5 of soda, which is also allowed to act for 12 hours ; after which the stuffs, pressed dry, are passed through the hypochlo- rite of lime, and then through sulphuric acid. The bath of hypo- chlorite generally contains 0.15 litre of chlorine in a litre of water; and the stuffs, after being immersed in it, are passed between two wooden cylinders, descending thence immediately into a bath acidu- lated with sulphuric or chlorohydric acid, which hastens the bleaching by isolating the hypochlorous acid. After being washed in fresh water, they are for a second time subjected to the action of alkaline lyes, hypochlorite of lime, and the acid bath ; and lastly, after an- other washing in fresh water, they are dried in drying-machines, and more body is given to them by dressing them with starch. Mordants. 1745. The tissues of muslin or linen stuffs have, for a great number of colouring substances, an affinity sufficiently powerful to fasten them on their surface, and to acquire a deep colour; w r hile the combination is rarely strong enough to enable them to resist washing, particularly with alkaline soaps. They are made fast, and at the same time the colour is heightened, by previously depositing on the tissues certain substances which have a greater affinity for these tissues than the colouring matters, and which possess, at the same time, the property of forming with the colouring matters com- pounds sufficiently fixed to resist washing in fresh water and in soap- suds. These substances, which thus play an intermediate part between the woven fabric and the colouring matters, are called mordants. The affinities by virtue of which they are fastened on the fabric exhibit this essential difference from those observed in ordinary chemical operations, that, in the latter, combination generally ensues only between disaggregated substances, and if one of the substances is originally aggregated, it becomes disaggregated by the simple fact of combination ; while, in dyeing, the woven fabric retains its form and consistence without being in the slightest degree disaggre- gated by the mordants and colouring matters. Certain mordants do not change the shade of the colouring matters, such, for example, as the salts of alumina and chlorides of tin ; while others, on the contrary, alter the colour, as the salts of iron, manganese, and copper. The salts of alumina used as mor- dants are the sulphate, and acetate of alumina, and alum ; the fast- ening of colours with alum being also called aluming. 3, Q 2 50 786 TECHNICAL ORGANIC CHEMISTRY. In order to alum cotton, flax, or hempen stuffs, they are left for 24 hours in a tepid bath containing 1 part of alum for 6 parts of fabric, when a portion of the alum adhering to the stuff renders the latter 'fit for dyeing. For dark colours, the ordinary alum of com- merce is used ; Roman, or purified alum, ( 600,) being preferred for bright colours, because common alum always contains a small quantity of sulphate of iron, which would modify the shade. Wool is alumed by being first boiled in bran-water for an hour and washed in fresh water, and then kept for 2 hours in a boiling solution which contains 10 to 15 per cent, of alum, a small quantity of cream of tartar being generally added, which facilitates the de- posit of the alumina on the tissue, perhaps by converting a portion of the sulphate of alumina into a tartrate of more easy decomposi- tion. When the wool is alumed, it is left to rest for 2 days, before dyeing, in order to render the combination of the mordant with the fibres more intimate. Silk is alumed when cold, by keeping it for 15 or 16 hours in a bath containing ^ of alum ; after which it is removed and washed. Acetate of alumina, which is often used as a mordant for ligneous stuffs, and for certain colours, is prepared by decomposing alum by acetate of lead ; the solution of acetate of alumina thus obtained being generally thickened with starch or gum. Stuffs of lignin mordanted with alum, are again subjected, before being dyed, to another operation, the effect of which is not well un- derstood : they are immersed, for some time, in two baths of water, containing 6 or 8 per cent, of cow-dung. To the first of these baths a certain quantity of chalk is added, the intention of which appears to be to saturate the acid partly adhering to the tissue with the mordant ; while the second contains only water and dung. The temperature of these two baths varies according to the nature of the stuffs and that of the mordants. The cow-dung appears to act by means of the phosphates it contains, for a mixture of phosphate of soda and lime can be substituted for it. Protochloride of tin is chiefly used for obtaining the oxide of tin as a^mordant, which adheres very firmly to the tissues. Bichloride of tin is often used for freshening colours, particularly those of cochineal and madder. The mordant of oxide of iron is furnished by the protacetate of iron, prepared by the reaction of pyroligneous acid on old iron. Dyeing. 1746. After the stuffs are mordanted, they are immersed, in order to be dyed, in solutions of colouring matter, of various temperatures, and then left for a longer or shorter time, according to the nature of the stuff and the tint of colour to be obtained. It is essential that all parts of the fabric should remain the same length of time in the dye ; to which effect it is rolled around a wooden roller suspended CALICO PRINTING, ETC. 787 over the dye-tub, and is unrolled through the tub ; this process being continued until the colour has obtained the shade required. In order to obtain a uniform shade, it is better to use several successive baths of different strength, commencing with the weakest. The baths are sometimes composed of a single colouring matter, and sometimes of a mixture of several, while at other times the stuff is passed successively through two baths containing different colours, and thus an intermediate shade is obtained. The colours are fast- ened by washing in soapsuds or in other solutions. It would lead us too far to give a description of the methods of preparing the different solutions for dyeing, and the manipulations of the process. Calico and other printing. 1747. Designs of various colours are printed on smooth goods ; the impression being effected either by an actual printing off of the colouring matter by means of wooden blocks carved in relief, or engraved rollers of copper ; or by the sole application of mordants followed by dyeing in the tub. In the latter case, the colouring matter adheres only to the mordanted designs, the latter retaining the shade desired, and the ground of the stuff preserving its original colour after being washed. Colouring matters printed directly on stuffs should be thickened, so that they will not run, and that the designs may retain their sharpness. The thickening substances used are starch, gum-sene- gal, and gum-tragacanth, to which a certain quantity of pipe-clay, and sometimes of gelatin, is often added. The stuffs should be pre- viously mordanted, or the mordant incorporated with the colour. 1748. In order to explain how designs are produced by dyeing, we shall give some examples. Let us suppose that a red design is to be produced on a white ground : the design is then printed on the stuff with a thickened mordant of alum, and the stuff passed through the madder-tub ; when the colouring matter adheres firmly only to the mordanted design, which alone will remain red after washing. If, on the contrary, a white picture is to be produced on a red ground, the picture is first printed with a properly thickened oleaginous substance, and passed through the mordant, by which means the picture is reserved, and when the stuff is passed through the madder-tub the ground alone will be dyed red. Another method still may be employed by dyeing the stuff of a uniform red colour, and printing the design with a non-volatile vegetable acid, such as, for example, citric or tartaric, sufficiently thickened ; after which it is passed through a bath of hypochlorite of lime, which imme- diately destroys the picture, without attacking the ground. This process is called discharging the colour. In order to obtain a violet design on a more or less deep red ground, the stuff is mordanted with alum, and the design printed 788 TECHNICAL ORGANIC CHEMISTRY. with a thickened mordant of iron, and then passed through the madder-tub; when the ground will become red, and the design violet. If, on the contrary, a red design on a violet ground is de- sired, the stuff is passed through a mordant of alumina, and the design printed with an oily substance ; and after being mordanted with acetate of iron, the oily reserve is removed by alkaline lyes, and the stuff is passed through the madder-tub. Designs of more than two colours are obtained by machines com- posed of several cylinders, each of which prints a peculiar mordant, or reserve, or acid on the stuff, which then passes into the dif- ferent dye-vats. Although the processes described are far from being the only ones used in dyeing, they will serve to give a general idea of the art. Fixing of Colours by Steam. 1749. Many colours are more firmly fastened and afford more beautiful shades when the dyestuffs are exposed to the action of steam. Under the influence of heat, the woven fabric and colouring matters become more closely combined, and the shades are often modified in a peculiar manner* TANNING. 1750. Skins of animals soon become putrid in moist air ; and although they will preserve for a long time in dry air, they become hard and brittle. The intention of tanning is to combine the ani- mal substance with a certain quantity of tannin, which renders them imputrescible, and gives them softness and impermeability; while the latter properties are still further increased by the process of currying. A tanned hide is called leather. Three kinds of skins are used in tanning : green hides, or the fresh skins brought to the tanner soon after the death of the animal ; and dry and salt hides, which come from foreign countries, chiefly from South Ame- rica. Hides are divided into two kinds : soft hides, which retain their suppleness after tanning, and hard hides, which, on the con- trary, are to be very hard, and as impervious as possible. Soft hides are made from the skins of cows, calves, horses, etc. ; while those of the ox and buffalo are reserved for hard hides. Yery thin and soft hides are prepared from the skins of sheep and goats, which are used for making gloves or in the manufacture of mo- rocco. Skins intended for soft hides are subjected to a previous washing in running water, in order to soften and soak them, and remove all their soluble principles ; which operation lasts only for 2 or 3 days for green skins, but for a much longer time for dry or salt skins, because the latter must be submitted to several washings, treadings, and stretchings, before they acquire the necessary pliancy. After being soaked, the skins are carried to the scalding-vats, TANNING. 789 consisting generally of five vessels filled with milk of lime, of greater or less strength. The skins pass successively through them, com- mencing with the weakest. Each vat contains from 200 to 300 skins ; the whole operation lasting 3 or 4 weeks. This being done, the hair is removed, by scraping the skins from above downward, with a dull knife ; after which they are washed and worked on the horse-beam : 1st. In order to remove any scraps of flesh which might adhere to them ; 2dly. To remove the useless portions, and the edges, which are always thicker than the other parts ; 3dly. To smooth the asperities which cover the skin on the hairy side, which is done with a piece of well-cemented, hard sand- stone ; 4thly. To completely cleanse both sides of the skin, which is done with a circular knife, wetting the skin frequently. After these various operations, the skins are raised; that is, they are left for several days in weak acids, for which purpose the ooze, (jusde,) or infusion of tan, is generally used, consisting of the tan exhausted by the tanning of skins in the vats, and which, after having become acid in the air, contains a certain quantity of lactic acid. During the first four days, the skins are removed every day, fresh ooze being added each time ; after which they are allowed to remain for 3 or 4 days in the ooze, and are then carried to a weak infusion of new tan, where they remain for 15 days, increasing the strength of the liquid from time to time. They thus undergo a kind of preli- minary tanning, and are prepared for the ultimate tanning, in the vats. The latter, which are of mason-work, are first charged with a layer of old tan, about 0.15 m. in thickness, then with a layer of fresh tan, only a few centimetres thick ; after which the skins are laid upon each other, being separated by layers of tan ; and lastly, above the last coat of tan a layer of old tan is placed, 0.3 m. in thickness; when the whole is covered with boards, kept down by heavy stones. Enough water is then let in to moisten the whole mass, dissolve the tannin, and bring it successively in contact with the skins. The vats thus filled, and containing 600 or 700 skins, are left for 5 or 8 months, during which time the skins are only once taken out, in order to renew the tan between them. 1751. In making coarse leather, the scalding, which here is not sufficiently efficient, is replaced by a slight putrid fermentation of the skins, in rooms warmed by steam. The hair is then removed in the ordinary way, and they are placed in the ooze, the raising being accelerated by the addition of a small quantity of sulphuric acid from time to time ; after which they are buried with the tan in the vats, where they are left for 18 months or two years. Hides may be tanned much more rapidly, by keeping the swollen skins for 2 or 3 weeks in infusions of tan, which are frequently re- placed by stronger ones. The leather thus made is not so strong, and has a deep colour, which keeps down its price. 1752. After being tanned, the hides are cleaned on tables, with 790 * TECHNICAL ORGANIC CHEMISTRY. brushes, and then dried in the air, when they are hammered or rolled, so as to give them the proper consistence ; after which they are sold to the currier, when they undergo various mechanical ope- rations, and are impregnated with fatty substances, according to the uses to which they are destined. Leather is generally coloured black with acetate of iron, made by dissolving scraps of old iron in sour beer ; several coats of this salt being passed over the surface of the leather ; when the tannin combines with the protoxide of iron, which, by the action of the air, passes into the state of sesqui- oxide, and produces a very intense black. 1753. The sheep and kid skins used for glove making are cleaned by smearing the fleshy side with a mixture of lime and orpiment, when in 24 hours the hair comes off with the greatest ease. The skins are then worked into various shapes on the beam, and are then immersed for 3 weeks in winter, and only 2 or 3 days in sum- mer, in a bran-bath, which, by fermentation, produces lactic acid, and effects the raising of the skins. The latter are then made im- putrescible, not by tannin, but by chloride of aluminum, for which purpose they are dipped into a hot solution, containing, for each skin, 600 to 900 gm. of alum, and 150 to 200 gm. of sea-salt. They are then bleached, by immersion for 12 hours in a bath composed, for each skin, of 600 or 700 gm. of flour, and the half of the yolk of an egg, which is beaten to the consistence of honey, adding the tepid liquor which was used for aluming. The skins are then dried, and subjected to various mechanical operations. 1754. Morocco is chiefly made from goat-skins, which, after being fleshed, and deprived of their hair by lime, are washed for a long time with the greatest care, in order to entirely remove the lime, which would injure their quality ; and to effect this more per- fectly, they are left for 24 hours in a bath of sour bran. Skins intended to be dyed red are sewn together by twos, the fleshy side within, so as to form a bag which will hold air ; after which they are dipped into a bath of chloride of tin, which acts as a mordant, and subsequently into one of cochineal, to dye them. After being rinsed, one side of the bag is ripped open, and the tanning matter introduced, the latter in this case consisting of sumac, which is much richer in tannin than tan is ; and they are then stirred for 4 hours in a weak solution of sumac, where they are left for two days. Morocco which is to be dyed of any other colour than red is tanned before being dyed ; and in all cases the skins are subjected to nu- merous mechanical operations before being fit for sale. CARBONIZATION OF WOOD AND BITUMINOUS COAL. 1755. The greater portion of charcoal used is made in the woods, by carbonizing wood in pits.* On a very hard hearth, three or four *The American technical term "pits," for the heaps of wood to be carbonized, MANUFACTURE OF CHARCOAL, ETC. . 791 large sticks, forming a chimney of from 0.25 m. to 0.30 m. in length, are arranged vertically ; and around this chimney the wood is set upright, in three different stories, the diameters of which diminish successively, so as to form the trunk of a cone resting on its larger base. The largest sticks are placed nearest the axis of the kiln, and the smallest, with the branches, near the surface ; after which the pit-kiln is covered with earth, leaves, and coal-dust aris- ing from preceding operations. Holes pierced through the base of the pit allow of the introduction of the air necessary to combustion. When the pit is built, a fire of pine-wood is made in the chim- ney, and kept up for 2 or 3 hours, at the end of which time it has communicated to the neighbouring logs, and the chimney is almost wholly filled with small charcoal : it is then covered, and holes, which act as chimneys and draw combustion to the parts they penetrate, are made around the upper part of the pit. Thick, white smoke at first escapes, but it soon becomes transparent and bluish, which is a sign that combustion is progressing in the upper part of the kiln. The upper holes are then closed, and others made somewhat lower down, which are again closed when the same smoke again appears, others being made, and so on, until the bottom of the pit is reached. Carbonization thus extends from above down- ward ; and the surface of separation of the carbonized wood and that yet untouched by the fire, is an inverted cone, having the same axis with that of the pit, and spreading more and more as carboni- zation advances, to be at last lost in the base of the pit. The wood diminishes considerably in volume by carbonization, and the pit be- comes smaller. When carbonization is terminated, the openings are closed, and the fire is allowed to go out, after which the heap is overturned, and the imperfectly carbonized pieces are picked out, which would smoke in the fire. The gases evolved during combustion are composed of nitrogen, which proceeded from the air used in combustion ; carbonic acid and oxide, produced partly by active combustion of the wood, and partly by its calcination ; hydrogen ; vapour of water ; and several organic substances furnished by the distillation of the wood, among which may be distinguished acetic acid, wood-spirit, and tarry sub- stances. The relative proportion of all these products varies at the different stages of the process. Wood yields, by carbonization in pits, about 15 per cent, of char- coal, and 25 to 30 by distillation in close vessels; but the latter process is one adopted with advantage only in the making of pyro- ligneous acid and tar, the charcoal thus obtained being not much valued on account of its lightness. 1756. Bituminous coal is often carbonized in pits in the vicinity must not be confounded with the usual meaning of the word. The German name metier is used in England. W. L. F. 792 TECHNICAL ORGANIC CHEMISTRY. of the mines. The pits generally receive an elongated prismatic shape, and contain horizontal, longitudinal, and transverse canals, beside's vertical chimneys, for the circulation of air. The largest lumps of coal are placed on the inside and the smallest on the out- side ; while the covering is made of coal-dust and coke, moistened to gi've it more consistence. The process closely resembles that of making wood-charcoal. Coke is also made by subjecting the bituminous coal to imperfect combustion in furnaces, where the ingress of air is so regulated as to consume the least possible quantity of carbon. Lastly, coke is obtained by the distillation of bituminous coal in retorts, the principal product being illuminating gas, while the coke is only an accessory product ; and as it is very light, it is used only for domestic purposes. ILLUMINATING GAS. 1757. Illuminating gas is generally obtained from the calcina- tion of bituminous coal ; but all kinds are not equally adapted to the purpose, the best being those designated ( 1315) under the name of bituminous coal burning with a long flame. The coals of Mons and Commentry, which are generally used in Paris, yield on an average 23 cubic metres of gas for 100 kilog. Distillation is effected in large cylindrical cast-iron retorts, ranged parallel to each other, to the number of 2, 3, or 5, over the same furnace ; each retort being pro- vided with a vertical tube, through which the coal is introduced, and to which is fastened the pipe for the discharge of the gas. The temperature of the furnace should be kept at a bright cherry red, because, if it is greater, the gas does not give much light, for the bicarburetted hydrogen gas, and the very volatile oils, to which the brilliancy of the flame is chiefly owing, deposit carbon, and are con- verted into protocarburetted hydrogen, the combustion of which gives but little light ; and if, on the contrary, the temperature is too low, a large quantity of essential oil is formed, which cannot remain in suspension in the gas, but is deposited in the refrigerators. The duration of distillation varies according to the quality of the coal, its hygrometric state, and the arrangment of the apparatus ; and the residue consists of a light coke, much used for domestic purposes. The gas produced by the distillation of bituminous coal is com- posed chiefly of protocarburetted hydrogen, mixed with various quantities of bicarburetted hydrogen, hydrogen, oxide of carbon, carbonic acid, nitrogen, oleaginous matters more or less easily con- densed, ammoniacal and sulphuretted compounds, and tarry sub- stances. ^ As in this state it exhales a very fetid smell, and the pro- ducts of its combustion are themselves odoriferous, it is necessary to purify it, especially for domestic use ; to which effect it is con- veyed from the retort into a small barrel, partly filled with water, through a pipe entering the liquid to the depth of 2 or 3 centime- tres, so as to intercept the communication of the retort with the ILLUMINATING GAS. 793 apparatus in which the gas is collected. The greater part of the water and tar condenses in the barrel, which is furnished with a discharging-pipe to maintain a constant level in the barrel, and to allow the excess of the condensed products to escape. The gas on leaving the barrel traverses a series of pipes more or less cooled, in which the condensation of the water and tar is completed, is then conducted through boxes containing metallic salts, chiefly chloride of manganese and sulphate of iron, which decompose the ammoniacal salts, and isolate the sulf hydric acid ; and finally passes through other boxes containing hydrated lime, which absorbs the sulf hydric gas, the carbon acid, and the other acid vapours. But these purifications must not be pushed too far, because the gas would be deprived of too much of its oily vapours, and its illuminating power would be sensibly decreased. The gas is collected in gasometers, resembling immense bells, made of sheet-iron, and inverted in cisterns of corresponding size, built of hydraulic mason- work, and filled with water. The weight of the gasometer is partially balanced by counterpoises, which should leave it only the weight necessary to the pressure required for the distribution of the gas to the various jets it is to feed. The pressure is composed of, 1st. The resistance which the gas meets in circulating through pipes ordinarily of great extent; 2dly. The excess of elastic force which it must retain in order to feed the jets ; 3dly. The pressure necessary to drive it to the highest points, the level of which is often higher than that of the gasometer. The last pressure may be easily calculated after ascertaining the difference h of the level of the' gasometer and the highest jet, and the density d of the gas as com- pared to that of the air, when it is equal to the weight of a column of water, the height of which is represented by 0.001293 hd.* * A more economical process of manufacturing gas has recently been put in operation in Manchester, England. Three or five retorts are used, the central one of which is charged with metallic iron and coke, or with coke alone, and traversed by a current of steam, which thus is decomposed into hydrogen and oxygen. These gases are led through the other retorts, in which coal is being distilled, when the free hydrogen combines with the nascent carbon resulting from the decomposition of different hydrocarbons, and forms olefiant gas, which imparts a great brilliancy to the flame. The gas thus manufactured is called hydrocarbon gas ; and I had opportunity to assure myself that its illuminating power is double that of ordinary gas under the same circumstances, while the cost of producing it is at least not higher. W. L. F, VOL. II. 3 R GENERAL INDEX. Acetates, ii. 546. Acetic acid, ii. 542. Acetone, ii. 549. Acids, vegetable, ii. 594. Aconitic acid, ii. 597. Acumination of crystals, i. 18. Adipic acid, ii. 697. Air, analysis of, by the eudiometer, i. 129. Air, atmospheric,!. 119. Air, only a mixture, i. 131. Air-thermometer, (note,) ii. 414. Albumen, ii. 453.' Albuminous vegetable substances, ii.451. Alcarsin, ii. 551. Alcohol, ii. 511. Alcoholic fermentation, ii. 505. Alcoholometry, ii. 513. Alcohol and ether, oxidation of, ii. 541. Aldehyde, ii. 541. Alkalimetry, i. 448. Alkaline earths, their separation and determination, i. 564. Alkaline metals, i. 434. ^ Alkalino-earthy metals, i. 528. Alkaloids, ii. 612. Alloys, i. 377. Allyl, ii. 675. Almaden, extraction of mercury at, ii. 291. Aluminum, i. 567. Alumina, salts of, 570. Alumina, characters of the salts of, i. 578. Alumina, silicates of, i. 575. " sulphates of, i. 570. Alums, manufacture of, i. 571. Amalgams, ii. 289. Ammonia and alkalies, determination of, i. 572. Ammonia, behaviour of potassium and sodium to, i. 520. Ammonia, carbonates of, i. 520. Ammonia, chlorohydrate of, i. 516. " compounds of, i. 514. " phosphates of, i. 519. " sulf hydrate of, i. 518. Ammoniacal salts, distinctive character of, i. 521. Ammoniacal solution, action of the bat- tery on an, i. 521. Amygdalin, ii. 650. Amylaceous substances, ii. 461. Amylammonia, ii. 624. Amylic alcohol, ii. 665. Amylic ethers, ii. 669. Analysis, i. 138. " of gases, ii. 422. " proximate, of organic sub- stances, ii. 363. " ultimate, of organic sub- stances, ii. 366, 386. Anilin, ii. 621. Animal chemistry, ii. 719. " heat, ii. 734. Anisic acid, ii. 662. Antimony, ii. 211. " alloys of, ii. 221. Antimony, analytic determination of, ii. 219. Antimony, behaviour of salts of, ii. 213. " chlorides of, ii. 217. Antimony, detection of in poisoning, ii. 221. Antimony, metallurgy of, ii. 222. " oxides and acids of, ii. 212. salts of, ii. 214. sulphides of, ii. 215. Arabin, ii. 468. Arseniates and arsenites, determination of, i. 429. Arsenic acid, i. 282. " " antidotes to poisoning by, i. 285. " " its preparation, i. 280. 795 796 GENERAL INDEX. Arsenic acid, its properties, i. 279. Arsenic acid, researches in poisoning by, i. 285. Arsenious acid, analysis of, i. 281. " " properties of, i. 281. Arsenious acid, detection of, in animal matter, i. 289. Asparagin, ii. 627. Atmosphere, action of plants on the, ii. 716. Atmospheric air, i. 119. B. Balsams, ii. 660. Bar-iron, composition of, ii. 116. " from cast-iron, ii. 82. Bassorin, ii. 468. Barium, and its oxides, i. 528. " chloride of, i. 533. " sulphide of, i. 533. Baryta, salts of, i. 532. Baryta, distinctive character of the salts of, i. 534. Beet-sugar, manufacture of, ii. 771. Belgium, reduction of zinc in, ii. 147. Benzamide, ii. 643. Benzil, ii. 648. Benzin, ii. 648. Benzoic acid, ii. 644. " ethers, ii. 645. Bezoaric acid, ii. 609. Bile, ii. 746. Biliary calculi, ii. 747. Bismuth, ii. 204. " alloys of, ii. 208. Bismuth, analytic determination of, ii. 208. Bismuth, metallurgy of, ii. 209. " oxides of, ii. 205. " salts of, ii. 206. Bitter almonds, oil of, ii. 642. Blast-furnace, ii. 66. Bleaching by chlorine, i. 218. " by sulphurous acid, i. 177. " salt, manufacture of, i. 551. Blistered steel, ii. 104. Blood, analysis of, ii. 742. " coagulum, ii. 740. " circulation of the, ii. 732. " globules, ii. 739. Blooming iron, ii. 92. Blowpipe, hydroxygen, i. 92. " with atmospheric air, i. 87. Blue vitriol, ii. 240. Bodies, simple and compound, i. 10. " states of, i. 11. Bodies, external characters used to dis- tinguish, i. 13. Bohemian glass, i. 627. Boiling-points of saline solutions, i. 410. Bone, ii. 721. Bone-black, decoloring power of, i. 307 " manufacture of, ii. 777. Boracic acid, i. 292. " " analysis of, i. 295. Boracic ether, ii. 532. Borates, determination of, i. 430. Borax, manufacture of, i. 491. " test, i. 493. ;' . ... Borneo camphor, ii. 640. Boron, i. 292. " action of the metals on, i. 377. " equivalent .of,, i. 295. " fluoride of, i. 296. Brake-table, ii. 20. Brass, ii. 264. ^ " analysis of, ii. 270. Brass and copper turning, ii. 269. Bread, making, ii. 764. Brewing, ii. 766. British gum, ii. 486. Bromates, determination of, i. 426. Bromic acid, i. 241. Bromides, i. 423. " properties of metallic, i. 387. Bromine in organic bodies determined ii. 386. Bromine, preparation and properties of, i. 240. Bromohydric acid, i. 242. Brucin, ii. 617. Butter, making, ii. 752. Butyric acid, ii. 574. fermentation, ii. 569. Butyfamide, ii. 574. c. Cacodyl, ii. 551. Cadmium and its compounds, ii. 153. Cafei'n, ii. 618. Calcium, determination of the equiva- lent of, i. 538. Calcium, distinctive character of the salts of, i. 557. Calcium, oxides of, i. 537. Calcium, sulphide, chloride, and fluoride of, i. 556. Calculi, urinary, ii. 762. Calico printing, ii. 787. Calomel, ii. J282. Camphilen, ii. 637. Camphor, ii. 639. Candles, stearic acid, ii. 690. Cane-sugar, ii. 470. rnanufature of, ii. 773. Cannon casting, iuz6'6. Cantharidin, ii. 626. Caoutchouc, ii. 671. Capric acid, ii. 699. Caproic acid, ii. 699. Caprylic acid, ii. 699. GENERAL INDEX. 797 Caramel, ii. 471. Carbolic acid, ii. 682. Carbonated waters, i. 311. Carbonates, determination of, i. 430. Carbon, action of on metals, i. 377. Carbon, hydrogen, and oxygen, analysis of compounds of, i. 323. Carbon, nitrogen, compounds of, i. 337. " oxygen, compounds of, i. 309. " sulphur, compounds of, i. 333.. " -different forms of, i. 304. " organic determination of, ii. 367. Carbonic acid, analysis of gaseous, i. 316. " liquid and solid, i. 313. Carbonic acid", "preparation and proper- ties -of, i. 309. Carbonic ethers, ii. 533. Carbonic oxide, eudiometric analysis of, i. 321. Carbonic oxide, preparation of, i. 319. Carburet of iron, ii. 53. Carotin, ii. 709. Cartilage, ii. 722 Casein, ii. 748. " vegetable, ii. 460. Cassius's purple, ii. 325. Cast-iron, ii. 53. " analysis of, ii. 111. " composition of, ii. 116. " reduced to bar, ii. 82. Castor-oil, ii. 700. Cast-steel, ii. 104. Catalonian forge, ii. 61. Caustic, lunar, ii. 297. Cedrin, ii. 641. Cellulose, ii. 446. Cementing apparatus, i. 622. Cement, manufacture of hydraulic, i. 616. Cerasin, ii. 468. Cerebral substance, ii. 728. Cerin, ii. 703. Cerium, i. 583. Charcoal, i. 592. Charcoal, power of to condense gases, i. 307. Charring wood, ii. 790. Cheese, ii. 753. Chemical affinity, i. 12. Chemical and physical phenomena, dif- ference between, i. 9. Chemical nomenclature, i. 93. Chemical notation and formulas, i. 73. Chemistry, definition of, i. 10. Chelidonic acid, ii. 611. Chloral, ii. 561. Chlorates, i. 425. Chloric acid, i. 219. Chlorides, determination of, i. 423. Chlorides, metallic, preparation and pro- perties of, i. 386. Chlorometry, i. 552. 3K2 Chlorine and hydrogen, compounds of, i. 230. Chlorine and nitrogen, compounds of, i. 227. Chlorine and oxygen, compounds of, i. 21 9 Chlorine, behaviour of to metallic oxides, i. 385. Chlorine, bleaching by, i. 218. " equivalent of, i. 228. " preparation of, i. 215. " organic determination, ii. 336. Chloroform, ii. 586. Chlorohydric acid and its compound, i. 230. Chlorohydric ether, ii. 536. Chlorophyll, ii. 709. Chlorous acid, i. 225. Chloroxycarbonic gas, i. 321. Cholesterin, ii. 647. Cholic acid, ii. 746. Chromates, ii. 125. Chronic acid, ii. 122. Chromium, analytic determination of, ii. 128. Chromium, oxides of, ii. 118. " salts of, ii. 123. Chyle, ii. 748. Cider, ii. 768. Cinnabar, ii. 281. Cinnamic acid, ii. 659. Cinnamon, oil of, ii. 658. Cinchonin, ii. 614. Citric acid, ii. 596. Circular polarization, (note,) ii. 454. Clay, i. 652. Cleavage of crystals, i. 15. Cloves, oil of, ii. 665. Coal, table of composition of, ii. 500. " varieties of, ii. 496. Cobalt, analytic determination of, ii. 133. " oxides of, ii. 130. " salts of, ii. 131. Cochineal, ii. 710. Codein, ii. 617. Cohesion, i. 12. Coin, ii. 312. Coking coal, ii. 790. Collodion, ii. 492. Colouring matters, organic, ii. 704. Columbium, ii. 174. Concrete, manufacture of, i. 618. Conicin, ii. 620, Coumarin, ii. 661. Copper, ii. 236. alloys of, and zinc, ii. 263. tin, ii. 265. analytic determination of, ii. 245, and brass, tinning, ii. 269. chlorides of, ii. 244. Copper, English process of smelting, ii. 256. 798 GENERAL INDEX. Copper, Mansfeld process of smelting, ii. 249. Copper, metallurgy of, ii. 247. oxides of, ii. 237. salts of, ii. 239. sulphides, ii. 243. Creatin, ii. 724. Creasote, ii. 683. Crucibles, i. 667. Crystalline forms, six systems of, i. 20. 1. Regular system, i. 21. 2. Dimetric, i. 25. 3. Hexagonal, i. 30. 4. Trimetric, i._36. 5. Monoclinic, i. 40. 6. Triclinic, i. 42. Crystallization of the metals, i. 367. water of, i. 398. Crystallography, i. 14. Crystals, axes of, i. 19. " cleavage of, i. 15. " fundamental forms of, i. 15. " imperfections of, i. 55. Cumin, cuminic acid, ii. 664. Cupellation, ii. 198, 313. Cyanides, i. 424. Cyanhydric or prussic acid, i. 342. Cyanhydric or prussic acid, analysis of, i. 344. Cyanogen, analysis of, i. 339. Cyanogen, origin and preparation of, i. 338. Cyanogen, products of, ii. 630. D. Decoloring power of bone black, i. 307. Deliquescence and efflorescence, i. 98. Density of vapours, ii. 406. Deposit-trough for ores, ii. 18. Deutoxide of nitrogen, i. 145. Dextrin, ii. 485. Diastase, ii. 487. Didymium, i. 583. Digestion, ii. 730. Dimorphism and polymorphism, i. 60. Distillation of oil of vitriol, i. 179. " phosphorus, i. 256. Dry distillation of organic bodies, ii. 678. Ductility of metals, i. 368. Dutch liquid, ii. 523. Dyeing, principles of, ii. 781. E. Earthenware, various kinds, i. 664, 667. glaze for, i. 666. " analysis of, i. 671. Earths, analytic determination of, i. 594. Earthy metals, i. 569. Ellagic acid, ii. 609. Elements, classification of, i. 76. " tabular view of, i. 64. Emulsin, ii. 651. Enanthic acid, ii. 670. Engraving by fluohydric acid, i. 251. Equisetic acid, ii. 596. Erbium, i. 583. Essential oils, ii. 634. Ethal, ii. 701. Ether, ii. 516. Ethers, compound, ii. 529. Ethionic acid, ii. 522. Ethyl theory, (note,) ii. 568. Ethylammonia, ii. 622. Eudiometer, i. 104. Eudiometer, analysis by the, i. 129, 145 321. Eugenic acid, ii. 665. Euxanthic acid, ii. 708. Evaporation, i. 100. " of salines, i. 500. Excrements, ii. 763. Excretions, ii. 754. F. Fats, ii. 684. Ferment, ii. 507. Fermentation, alcoholic, ii. 505. " butyric and lactic, ii. 569. Fibrin, ii. 724. " vegetable, ii. 460. Fire-brick, i. 667. Flame, the nature of, 487. Flameless lamp, ii. 341. Fluohydric acid, analysis of, i. 251. " " engraving by, i. 251. " " preparation of, i. 250. Fluorides, analytic determination of, i. 424. Fluorine, i. 424. Fluor-spar, i. 556. Fluosilicic acid, i. 301. Forge-hearth, ii. 83. Forge-steel, ii. 103. Formic acid, ii. 583. Formula, construction of organic, ii. 387 Freiberg, extraction of silver at, ii. 305. Frigorific mixtures, i. 412. Fruit-sugar, ii. 474. Fuel, mineral, ii. 494. Fulminating mercury, ii. 279. silver, ii. 295. Fulminic acid, ii. 632. Fumaric acid, ii. 596. Fuming sulphuric acid, i. 185. Fusible metal, ii. 208. G. Gallic acid, ii. 607. Galvanic gilding and silvering, ii. 333. GENERAL INDEX. 799 Galvanoplastics, ii. 335. Garlic, oil of, ii. 675. Gases, analysis of, ii. 422. " collection of, over mercury, i. 94. Gases, condensation of, by charcoal, i. 307. Gases, solubility of, in water, i. 101. Gasometer, i. 82. Gastric juice, ii. 744. Gelatin, ii. 726. Gelatinous principles in plants, ii. 478. Geology, i. 351. Geological division of the formations, i. 361. German silver, ii. 138. Gilding, ii. 331. " galvanic, ii. 333. Glass, analysis of, i. 648. blowing on the table, i. 642. composition of, i. 623. kinds of, i. 626. manufacture of, i. 627-640. properties of, i. 641. Glaze, i. 659. Glucic acid, ii. 476. Glucinum and its compounds, i. 579. Glucose, manufacture of, ii. 487. Glue, ii. 726. Gluten, ii. 460. Glycerin, ii. 689. Glycocoll, ii. 727. Glycyrrhizin, ii. 628. Gold and its compounds, ii. 322. " analytic determination of, ii. 326. " alloys of, ii. 329. assay of, ii. 366. " parting by acids, ii. 331. Goniometer, i. 51. Graduating glasses, i. 103. Grape-sugar, ii. 475. Gums, ii. 468. Gun-cotton, ii. 491. Gunpowder, analysis of, i. 608. " composition of, 589. " manufacture of, i. 595. Gunpowder, testing the strength of, i. 606. Gunpowder, theory of its effects, i. 587. Gutta-percha, i. 673. H. Hair, ii. 723. Haloid salts, i. 397. Hematosin, ii. 740. Hemitrope crystals, i. 59. Hexagonal system of crystals, i. 30. Hippuric acid, ii. 760. Horn, ii. 722. Hot-blast, ii. 77. Humin, ii. 489. Hydraulic lime, i. 614. Hydrogen, behaviour of to oxides, i. 383. " equivalent of, i. 11. Hydrogen, organic determination of, ii. 367. Hydrogen, preparation of, i. 89. and arsenic, i. 282. and chlorine, i. 230. and iodine, i. 247. and nitrogen, i. 162. and oxygen, i. 96. and phosphorus, i. 270. and sulphur, i. 201. Hydroxygen blowpipe, i. 92. Hypochlorates, analysis of, i. 425. Hypochloric acid, i. 227. Hypochlorites, i. 467. Hypochlorite of lime, i. 550. Hypochlorous acid, i. 223. Hyponitric acid, i. 155. Hypophosphites, i. 428. Hypophosphorous acid, i. 266. Hyposulphates, i. 427. Hyposulphite of soda, i. 494. Hyposulphites, i. 428. Hyposulphuric acid, i. 197. " sulphuretted, i. 197. Hyposulphurous acid, i. 196. I. Ichthyocolla, ii. 727. Idria, extraction of mercury in, ii. 290. Illuminating gas, ii. 792. Ilmenium, ii. 174. Indigo, ii. 714. Inosic acid, ii. 725. Intestinal gases, ii. 768. " juice, ii. 747. Introduction to general chemistry, i. 9. Introduction to organic chemistry, ii. 361-445. Inulin, ii. 467. lodates, i. 426. Iodides, metallic, i. 387. Iodides, analytic determination of, i. 424. Iodine, action of on the metals, i. 377. " organic determination of, ii. 386. Iodine, properties and preparation of, i. 244. Iridium, ii. 353. Iron, analytic determination of, ii. 54. " analysis of cast, and steel, ii. 111. " and its oxides, ii. 36. " cast, converted into bar-iron, ii. 82. Iron, composition of bar, cast, and steel, ii. 116. Iron, dry assay of ores of, ii. 108. " making steel, ii. 102. " ores of, ii. 59. 800 GENERAL INDEX. Iron, reduction of the ores of, ii. 61. " salts of, ii. 44. " sheet, and tin-plate, ii. 98. " wire-drawing, ii. 101. Isatin, ii. 715. Isomorphism, i. 61. J. Japan camphor, ii. 639. Jigging machine, ii. 16. K. Kermes mineral, ii. 218. Kyanole, ii. 621. Lactic acid, ii. 573. " fermentation, ii. 569. Lactometry, ii. 750. Lanthanum, i. 583. Law of multiple proportions, i. 12. Laws of combination of gases, i. 158. " constitution of salts, i. 391. Lead, alloys of, ii. 189. " analytic determination of, ii. 188. " and its oxides, ii. 174. " casting shot, ii. 203. " cupellation of, ii. 198. Lead, desilverized by crystallization, ii. 202. Lead, metallurgy of, ii. 190. " red, or minium, ii. 178. " salts of, ii. 179. " " acetates, ii. 183. " " carbonates, ii. 184. " behaviour of, ii. 186. " sheet, and pipe, ii. 202. " glass, i. 673. Lemons, oil of, ii. 638. Leucole, ii. 620. Lichenin, ii. 467. Lichens, ii. 710. Lignin, ii. 449. Lime, i. 537. " for mortar, i. 611. " hydraulic, i. 614. " hypochlorite of, i. 550. " kiln, i. 539. " native carbonates of, i. 547. " phosphates of, i. 549. " salts of, i. 542. Limestones, composition of, i. 615. " analysis of, i. 618. Litharge, ii. 175. Lixiviation of nitre-beds, i. 456. Logwood, ii. 706. Lunar caustic, ii. 297. Lustre, metallic, i. 365. Lymph, ii. 743. M. Madder, ii. 705. Magnesia, i. 558.. " salts of, i. 559. " phosphates of, i. 561. " behaviour of salts of, i. 563. Magnesium, i. 558. Malic acid, ii. 595. Manganese, and its oxides, ii. 23. Manganese, analytic determination of, ii. 31. Manganese, acids of, ii. 25. " salts of, ii. 28. Mannite, ii. 484. Mansfeld, extraction of silver in, ii. 309. " " copper in, ii. 249. Margaric acid, ii. 692. Marsh gas, i. 330, and ii. 582. Marsh's apparatus for arsenic, i. 286. Matches, phosphoric, i. 259. Meconic acid, ii. 609. Menthen, ii. 641. Mercaptan, ii. 589. Mercurial cistern, i. 94. Mercury, ii. 271. " amalgams, ii. 289. Mercury, analytic determination of, ii. 288. Mercury, chlorides of, ii. 282. " metallurgy of, in Idria, ii.290. Mercury, metallurgy of, at Almaden, ii. 291. i Mercury, oxides of, ii. 273. " salts of, ii. 275. " sulphides of, ii. 281. Mesitylen, ii. 550. Metallic veins, i. 363. Metals, i. 349. " action of oxygen on, i. 374. Metals, action of sulphur and chlorine on, i. 376. Metals, action of other metalloids on, i. 377. Metals, alkaline, i. 434. " alkalino-earthy, i. 528. " chemical properties of, i. 371. " classification of, i. 372. " crystallization of, i. 367. Metals, malleability and ductility of, i. 368. Metals, opacity, lustre, and colour of, i. 368. Metals, physical properties of, i. 365. " properties of oxides of, i. 380. " " chlorides of, i. 386. " relations of, to heat, i. 371. Metalloids, i. 79: " equivalents of the, i. 345. Methylal, ii. 585. GENERAL INDEX. 801 Methylic alcohol, ii. 575. " compounds, table of, ii. 591. Methylic ethers, ii. 548. Methylammonia, ii. 623. Milk, ii. 748. " sugar of, ii. 751. Minium, ii. 178. Mineral fuel, ii. 494. " green, ii. 242. Mirrors, ii. 289. Molecular decrements, i. 44. Molybdenum, ii. 233. Monobasic and polybasic salts, i. 395. Monoclinic system, i. 40. Monometric " i. 21. Mordant, ii. 785. Morphin, ii. 615. Mortar, i. 611. Mucic acid, ii. 493. " ether, ii. 536. Multiple proportions, law of, i. 12. Muscular tissue, ii. 723. Mustard, oil of, ii. 676. Myricin, ii. 703. Myronic acid, ii. 677. N. Naphtha, ii. 683. Naphthalin, ii. 678. Narcotin, ii. 616. Nickel, analytic determination of, ii. 139. Nickel, in German silver, ii. 138. " oxides of, ii. 136. " salts of, ii. 137. Nicking-buddle, ii. 19. Nicotin, ii. 618. Niobium, ii. 174. Nitrates and nitrites, determination of, i. 424. Nitre-beds, i. 454. Nitric acid, i. 133. " analysis of, i. 138. Nitric acid, formation and preparation of, i. 135. Nitric acid, manufacture of, i. 137. " ether, ii. 530. " oxide, analysis of, i. 150. Nitrils, ii. 629. Nitrogen, i. 117. Nitrogen and carbon, compounds of, i. 337. Nitrogen and chlorine, compounds of, i. 227. Nitrogen and hydrogen, compounds of, i. 162. Nitrogen and iodine, compounds of, i. 248. Nitrogen and oxygen, compounds of, i. 132. Nitrogen and phosporus, compounds of, i. 275. Nitrogen, chemical and physical proper- ties of, i. 119. Nitrogen, deutoxide of, or nitric oxide, i. 145. Nitrogen, equivalent of, i. 159. Nitrogen, organic determination of, i. 380. Nitrogen, preparation of, i. 119. ' ; protoxide of, i. 142. X T itrous acid, analysis of, i. 154. Sitrous acid, preparation and properties of, i. 153. Sitrous matters, lixiviation of, i. 456. Nutrition, ii. 729. 0. Oil of aniseed, ii. 662. ;< bitter-almonds, ii. 642. : < cinnamon, ii. 658. ;< garlic, ii. 675. ;< mustard, ii. 676. ;< spiraea, ii. 654. " wine, ii. 528. Oils, essential, ii. 634. Olefiant gas, ii. 520. Oleic acid, ii. 693. Opacity of the metals, i. 365. Optical glass, ii. 639. Ores, crushing, ii. 11. " preparation of, ii. 9. " stamping, ii. 17. " washing, ii. 10. Ornaments and painting of earthenware, i. 667. Osmium, ii. 350. " extraction of, ii. 352. Oxalates of potassa, i. 467. Oxalic acid, i. 322, ii. 594. " ethers, ii. 534. Oxides, preparation of, i. 381. " determination of, i. 422. Oxygen and arsenic, compounds of, i. 280. Oxygen and carbon, compounds of, i. 309. Oxygen and chlorine, compounds of, i. 219. Oxygen and hydrogen, compounds ot, i. 96. Oxygen and nitrogen, compounds or, i. 132. Oxygen and phosphorus, compounds ot, i. 266. Oxygen, preparation of, i. *9. " properties of, i. 85. Oxysaccharic acid, ii. 491. 51 802 GENERAL INDEX. P. Palladium, ii. 356. Palm-oil, ii. 700. Pancreatic juice, ii. 747. Paraffin, ii. 681. Parting of gold and silver, ii. 329. Pearl-white, ii. 206. Pectic acids, table of, ii. 483. Pectose, ii. 478. Pelopium, ii. 174. Perchloric acid, i. 222. Percussion-table, ii. 20. Perry, ii. 768. Peru, balsam of, ii. 660. Phenic acid, ii. 682. Phloridzin, ii. 628. Phosphates, determination of, i. 428 Phosphoric acid, preparation of, i. 260. " analysis of, i. 263. matches, i. 259. Phosphorous acid, i. 264. Phosphorus, properties of, i. 254. " preparation of, i. 257. " equivalent of, i. 268. " and hydrogen, i. 270. " and oxygen, i. 260. Phosphorus, organic determination of, ii. 385. Phosphovinic acid, ii. 530. Phosphurets, i. 389. " determination of, i. 423. Physical and chemical phenomena, i. 9. Physical properties of the metals, i. 365. Picrotoxin, ii. 626. Pig-metal, ii. 80. Pimaric acid, ii. 674. Piperin, ii. 626. Plants, proximate principles of, ii. 446. " decomposition of, ii. 494. Plate, silver, ii. 312. Platinum, ii. 339. " ammonia-bases of, ii. 346. Platinum, analytic determination of, ii. 348. Platinum black, ii. 340. " extraction of, ii. 349. " oxides and salts of, ii. 342. Polarization, circular, (note,) ii. 454. Porcelain, materials for, i. 652. " ware, making, i. 655. " glazing and burning, i. 659. Potassa, i. 441. " salts of, i. 446, 471. Potassiam, compounds of, i. 368. " equivalent of, i. 445. Pottery, i. 651. " porous, i. 664. Proximate analysis of organic bodies, ii, 362. Proximate principles of plants, ii. 446. Prussic acid, i. 842. Puddling-furnace, ii. 87. Purple of Cassius, ii. 325. Pyroligneous acid, ii. 545. Q. Quartation, assay by, ii. 336. Quercitron, ii. 707. Quinic acid, ii. 611. Quinin, ii. 613. Quinolein, ii. 620. R. Racemic acid, ii. 603. Red-lead, ii. 178. Resins, ii. 673. Respiration, ii. 734. Rhodium, -ii. 358. Rhombic system, i. 36. Rocks, principal kinds of, i. 358. Rocks, stratified and non-stratified, ii. 352. Rocks, metallic veins in, ii. 363. Rupert's drops, ii. 641. Ruthenium, ii. 360. s. Safety-tubes, i. 148. Saffron, ii. 707. Salicin, ii. 652. Salicylic acid, ii. 656. Saliva, ii. 652. Salines, i. 500. Saline solutions, boiling points of, i. 410. Salt, determination of the electronega- tive body of a, i. 421. Salt, extraction of rock, i. 496. Saltpeter and sulphur, pulverization of, i. 591. Saltpeter, refining, i. 459. " testing, i. 461. Salts, i. 389. Salts, coloured tests of the neutrality of, i. 390. Salts, decomposition of, by acids, i. 413. " " by bases, i. 416. Salts, determination of the solubility of, i. 404. , Salts, determination of the curves of so- lubility of, i. 406. Salts, haloid, i. 397. " law of the constitution of, i. 291. Salts, laws of the decompositions of, i. 414. Salts, monobasic and polybasic, i. 395. Salts, mutual action of, in the dry way, i. 418. Salts, mutual action of, in the wet way, i. 418. Salts, neutral, acid, and basic, L 389. Salts, reciprocal action of, on salts, i. 417. GENERAL INDEX. 803 Salts, solubility of, i. 402. Salt-works, working up residues of, i. 506.* Scheele's green, ii. 242. Scotch hearth, ii. 198. Sea-salt, extraction of, i. 503. Sebacic acid, ii. 698. Secretions, ii. 738. Selenic and selenious acids, i. 209. Selenium, i. 208. Sheet-iron, ii. 98. " lead, ii. 202. Shot-casting, ii. 203. Silica, preparation of, i. 298. Silicic ethers, ii. 532. Silicium, i. 298. " fluoride of, i. 301. Silicofluohydric acid, i. 302. Silesian extraction of zinc, ii. 150. Silver, ii. 293. " alloys of, ii. 311. " " assay of, ii. 313. " analytic determination of, ii. 303. " assay of ores of, ii. 321. " chloride of, 301. " extraction from copper, ii. 251. " " " lead, ii. 198. " fulminating, ii. 295. " metallurgy of, ii. 304. " oxides of, ii. 294. " parted from gold, ii. 329. " salts of, ii. 296. Silvering, ii. 331. " galvanic, ii. 334. Simple and compound bodies, i. 10. " " crystals, i. 16. Sinaptas, ii. 657. Skin, ii. 723. Sleeping-table, ii. 19. Smalt, ii. 134. Soap, manufacture of, ii. 778. Soda, borates of, i. 486. " carbonates of, 477. " caustic, i. 474. " hyposulphite of, i. 494. " phosphates of, i. 480. Soda, distinctive character of the salts of, i. 610. Soda-ash, manufacture of, i. 477. Sodas, test of commercial, i. 480. Sodium, i. 473. " chloride of, i. 495. Soft solder, ii. 189. Solubility of gases in water, i. 101. Spermaceti, i. 701. Stamping ores, i. 17. Steam-colours, i. 788. Stearic acid, i. 690. Steel, analysis of, ii. 111. " composition of, ii. 116. " manufacture of, ii. 102. " tempering of, ii. 107. Stoneware, i. 664. Strontia, its salts, i. 535. Strontium, i. 535. Strychnin, ii. 617. Suberic acid, ii. 698. Succinic acid, ii. 697. Sugar, ii. 469. " extraction of, ii. 771. " refining of, ii. 785. " of milk, ii. 751. " of lead, ii. 183. Sulfhydric ethers, ii. 538. Sulphates, analysis of, i. 426. Sulphides, analysis of, i. 422. " properties of metallic, i. 387. Sulphocarbonic acid, i. 335. Sulphocyanides, ii. 633. Sulphosalts, analysis of, i. 431. Sulphovinic acid, ii. 515. Sulphur, i. 169. action of, on the metals, i. 376. and chlorine, i. 234. and hydrogen, i. 201. and oxygen, i. 173. equivalent of, i. 198. organic determination of, ii.385. Sulphuretted hydrogen, i. 201. Sulphuric acid, i. 178. " analysis of, i. 180. " " fuming, i. 185. " ether, ii. 516. Sulphurous acid, preparation and pro- perties of, i. 174. Sulphurous acid, bleaching by, i. 177. Sweat, ii. 763. Swing-sieve for ores, ii. 15. Synthetic composition of water, i. 103. T. Tannic acid, ii. 605. Tanning, ii. 788. Tartaric acid, ii. 598. Tartar emetic, ii. 600. Teeth, ii. 722. Tenacity of metals, i. 370. Terbium, i. 583. Terebilen, ii. 637. Terpentine, oil of, ii. 635. Textile fabrics, colouring, ii. 781. Them, ii. 618. Thenard's blue, ii. 135. Thermometers, temperatures in differ- ent, ii. 413. Thermometers, air, (note,) ii. 414. Thiosinnamin, ii. 676. Thorinum, i. 583. Tiles, i. 666. Tin and its oxides, ii. 156. " alloys of copper and, i^ " behaviour of salts " chlorides of, ii. " metallurgy of, ii 804 GENERAL INDEX. Tin, salts of, ii. 160. Tin-plate, ii. 98. Tinning copper and brass, ii. 269. Titanium, ii. 169. Toluidin, ii. 663. Truncation of crystals, i. 17. Tungsten, ii. 230. Type-metal, ii. 189. Tyrolese bowls, ii. 328. u. Uranium, ii. 224. Urea, ii. 754. Uric acid and its derivatives, 11. / 55. Urinary calculi, ii. 762. Urine, analysis of, ii. 761. V. Valerianic acid, ii. 667. Vanadium, ii. 235. Vapours, density of, 406. Verdigris, ii. 243. Vitriol, blue, ii. 240. w. Washing gelatinous precipitates, i. 584. Water, i. 96. " analysis of, by galvanism, i. 110. Water and carbonic acid, determination of, i. 121. Water, evaporation of, i. 100. " of crystallization, i. 398. " solubility of gases in, i. 101. " synthetic composition of, i. 103. Waters, carbonated, i. 311. Wax, ii. 703. White precipitate, ii. 285. Wine-making, ii. 796. Winter-green, oil of, ii. 656. Wire-drawing, ii. 101. Wood, charring, ii. 790. " spirit, ii. 575. Woolf s bottles, theory of, i* 147. X. Xanthic acid, ii. 536. Yeast, ii. 507. Yttrium, i. 583. y. z. Zaffre, ii. 134. Zinc and its oxide, ii. 141. " salts of, ii. 143. " analytic determination of, ii 144. " metallurgy of, ii. 146. Zirconium, ii. 582. THE END. Proxima 362. 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