OUTLINES OF INDUSTRIAL CHEMISTRY A TEXT-BOOK FOE STUDENTS BY FRANK HALL THORP, PH.D. INSTRUCTOR IN INDUSTRIAL CHEMISTRY IN THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., LTD. 1898 All rights reserved COPYRIGHT, 1898, BY THE MACMILLAN COMPANY. J. S. Cashing & Co. Berwick & Smith Norwood Mass. U.S.A. V Eo tfje J$lem0t|j of LEWIS MILLS NORTON DURING NINE YEARS PROFESSOR OF INDUSTRIAL CHEMISTRY IN THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY 3Efjts iSooft is BeUtcatrtJ IN TOKEN OF WARM PERSONAL REGARD FOR THE KINDLY MAN AND GRATEFUL APPRECIATION OF THE HELPFULNESS AND INSPIRATION OF HIS TEACHING THE AUTHOR PREFACE THE object of this book is to furnish an elementary course in Industrial Chemistry, which may serve as the ground work for a more extended course of lectures, if desired. The writer has endeavored to describe briefly, within the limits of one moderate- sized volume, the more important industrial chemical processes, but omitting matters of detail which properly belong in the larger hand- books. Numerous references are made in the text to periodicals and journals, and to the standard hand-books and encyclopaedias and many special works, where details, lacking in this book, may be found. The bibliographical lists following each section are not complete, but only include those works which will usually be found in most chemical libraries ; the references to the journal literature are merely those articles to which the author's attention has been drawn in the preparation of class-room exercises. The diagrams illustrating the text have, in most cases, been drawn as simply as possible, purposely showing only the essential features. In the selection and order of arrangement of the several sub- jects, the author has necessarily been influenced by his work in this Institute and the requirements of his own class, but it is believed that the book as a whole will be found applicable to the work in most institutions of learning where industrial chemistry is taught. The subject of Metallurgy has been entirely omitted, since there are already several excellent brief text-books dealing with it alone, and instruction in it is generally given independently of that relating to technical chemistry. Likewise the important subject of the coal-tar colors has been condensed into the briefest possible outline, because this is nearly always included in courses in organic chemistry, and there are several small manuals treating of it. Analytical processes have also been omitted as foreign to the intended scope and purpose of the book. It is assumed that students taking this course are familiar with the elements of general chemistry, both inorganic and organic, and with the elements of physics. vii v iii PKEFACE In the compilation of this work, free use has been made of many of the standard English, German, and French hand-books and encyclopaedias, particularly of Professor T. E. Thorpe's Dictionary of Applied Chemistry, the works of Professor Lunge on Sulphuric Acid and Alkali, and Coal-tar and Ammonia, Ost's Technischen Cheinie, and Dammer's Handbuch der chemischen Technologic. The following business firms have courteously loaned cuts and drawings for the illustrations : Curtis Davis & Co., Cambridgeport, Mass., slabbing machine and soap kettle ; William Campbell & Sons, Cambridgeport, Mass., rendering tank ; The De La Vergne Eef riger- ating Machine Co., New York, refrigerating machine ; H. L. Dixon, Pittsburg, Pa., tank furnace for glass; United Gas Improvement Co., Philadelphia, water gas plant ; John Johnson & Co., New York, filter press; Semet-Solway Company, Syracuse, N.Y., coke oven; E. D. Wood & Co., Philadelphia, Pa., Taylor gas producer. The writer wishes to acknowledge his indebtedness to the fol- lowing friends for assistance and advice in the revision of those portions of the work treating of their specialties : C. D. Jenkins, State Gas Inspector of Massachusetts, Illuminating Gas ; A. D. Little, Consulting Chemist, Wood Pulp and Paper ; J. W. Loveland, Superintendent Curtis Davis & Co., Soap Manufacturers, Soap, Candles, and Glycerine; F. G. Stantial, Superintendent Cochrane Chemical Co., Sulphuric, Hydrochloric, and Nitric Acids; the fol- lowing members of the instructing staff of the Massachusetts Institute of Technology: Professor A. H. Gill, Fuels and Oils; G. W. Eolfe, Starch, Glucose, and Sugar; S. C. Prescott, Fermen- tation Industries ; J. W. Smith, Textile Industries. Special thanks are due to Dr. W. E. Whitney, of the Institute of Technology, for much assistance in the proof-reading, and also to Dr. B. L. Eobinson, of the Gray Herbarium, Harvard University, for his painstaking revision of the botanical nomenclature. In the labor of preparation of the book, the author has also had much help from his wife, who copied the entire manuscript and has assisted in the reading of all of the proof. FRANK H. THORP. BOSTON, MASS., October, 1898. TABLE OF CONTENTS PART I INORGANIC INDUSTRIES INTRODUCTION. Objects of Industrial Chemistry 1 Lixiviation 2 Levigation 2 Evaporation 3 Spontaneous -8 By direct heat .... 4 By steam heat .... 6 In vacuum 5 Vacuum pans .... 5 Multiple effect systems . 6 Yaryan evaporator . . 6 Distillation 7 Fractional condensation . . 8 Coupler's still 8 French column apparatus . . 9 Coffey still 9 Sublimation 10 Filtration 11 Bag niters 11 Suction filtration .... 12 Pressure filtration, by use of the filter press 12 Centrifugal filtration ... 14 Sand filters 15 Crystallization 15 Calcination 16 Muffle furnace 16 Reverberatory furnace ... 17 Revolving furnace .... 17 Shaft furnace or kiln . . . 18 Refrigeration 18 Compression machines . . 19 Absorption machines ... 20 Chilling by compressed air . 20 Density 21 Hydrometers 21 Pyknometer 23 WestphaPs balance .... 23 FUELS. Solid fuels 24 Wood, peat, lignite or brown coal, bituminous coal, an- thracite, charcoal, coke 24-28 Beehive coke oven ... 28 By-product coke ovens . . 29 Liquid fuels ....... 30 Crude petroleum and oil resi- dues 30 Gaseous fuels .. . . . . . 30 Natural gas ...... 30 Producer gas 30 Siemen's gas producer . . 31 Taylor's gas producer . . 31 Water gas 33 Coal gas -33 WATER. Hard, soft, saline, alkaline . . 35 Purification by chemical precipi- tation 36 Clark's process 36 Other processes .... 36-37 Boiler scale 37 Water for special industries . . 37 SULPHUR. Extraction, from ore Recovered sulphur . 40 42 ix TABLE OF CONTENTS Purification .... Dejardin's apparatus Sulphur derivatives Sulphur dioxide . Sodium bisulphite . Calcium bisulphite . Hyposulphurous acid Sodium hyposulphite Sodium thiosulphate PAGE . 42 . 42 43-45 . 43 . 44 . 44 . 44 . 44 45 SULPHURIC ACID. Theories of the formation of the acid 47 Sulphur burners 48 Pyrites burners 49 Lump ore burner .... 50 " Fines " burners . . 50-52 "^Glover tower 52 Lead chambers 52 ~ Gay-Lussac tower .... 54 Acid egg 55 Air-lift pump for acid ... 56 Glass and platinum stills . . 56 Cast-iron stills 58 Lunge's plate tower .... 59 Barbier's tower system . . 59 Fuming sulphuric acid ... 60 . SALT. Sources of salt 61 Preparation of salt 63 HYDROCHLORIC ACID AND SODIUM SUL- PHATE. Salt-cake furnaces 67 Open roaster 67 Close roaster 68 Mactear's roaster .... 69 Coke tower for absorption . . 70 Hargreaves-Robinson process . 71 Sodium sulphate 72 SODA INDUSTRY. Leblanc process 73 Black-ash or balling furnace . 74 Lixiviation of black-ash . . 76 Carbonation and evaporation of tank liquor . . . . 77 Thelen'span 79 Soda crystals or sal-soda . . 79 Caustic soda 80 Loewig's process .... 81 Tank waste 82 Methods of treating tank waste 83-84 Ammonia soda process . . . 86 < Parnell- Simpson modification of this process 90 Cryolite soda process .... 92 CHLORINE INDUSTRY. Processes using manganese . 96-97 Dunlop's 96 Weldon's 96 Schlossing's 97 Deacon's copper chloride process 98 Nitric acid processes for chlorine 101 Dunlop's process .... 101 Donald's process 101 Sadler- Wilson process . . . 101 Magnesia processes for chlorine 102 Weldon-Pechiney process . 102 Processes for recovering chlorine from ammonia -soda waste liquors .....'... 103 Electrolytic processes for chlo- rine and caustic soda . .104 LeSueur's process .... 105 Carmichael's process . . . 106 Greenwood's process . . . 106 Holland-Richardson process . 106 Hargreaves-Bird process . . 107 Hermite process 107 Castner's 1 process .... 107 Hypochlorites 108 Bleaching materials . . . 109 Chlorates . . . ^ . . . . -Ill Liebig's process Ill Pechiney's process . . . .112 Gall-Montlaur process . . .113 NITRIC ACID. Method of manufacture . . .114 Guttmann's apparatus . . . 116 Hart's apparatus . . .* . 117 Fuming nitric acid 118 Commercial nitrates , 119-124 TABLE OF CONTENTS XI PAGE AMMONIA. Sources of ammonia .... 124 Gas liquor ....... 125 Feldmann's apparatus . . . 125 Griineberg-Blum apparatus . . 126 Ammonium salts . . . 128-129 POTASH INDUSTRY. Sources of potash salts . . . 130 Strassfurt deposit of potash salts ........ 132 Wool washings ..... 131 Potassium compounds . 135-136 FERTILIZERS. Requisites of a fertilizer . . . 137 Waste products as source of fer- tilizer ........ 138 Bones, blood, garbage, etc. . 138 Peruvian and fossil guanos . . 140 Phosphate rocks ..... 140 Apatite ........ 140 Phosphorites ...... 141 Superphosphates ..... 143 Reverted phosphate .... 144 Phosphatic slag ...... 145 Sewage as fertilizer .... 147 Land plaster ....... 147 LIME, CEMENT, AND PLASTER OF PARIS. Lime ......... 148 Properties of lime .... 148 Limekilns ...... 148 Hydraulic lime ..... 150 Mortar ....... . . 151 Cements ........ 152 Manufacture of cements 154-156 Cement kilns . . . 156-158 Hardening of cements . . . 159 Testing of cement .... 160 Plaster of Paris ...... 163 Properties and composition of ... 165 ... 166 168-169 Lime and lead glass Glass furnaces PAGE Glass pots, open and closed . 170 Plate glass 173 Window glass and glass blowing 174 Crown glass 175 Pressed and cut glass .... 175 Tempered glass 175 Compound glass 176 Colored glass 176 Enamel 178 Iridescent glass . . ... .178 s. Mirrors .... .. . . ".. . 178 CERAMIC INDUSTRIES. Kaolin or china clay . . . .180 Fire-clay 180 Pipe or ball clay 180 Empirical and rational analyses of clays 182 Ceramics 182 Non-porous ware . . . .182 Porcelain and stoneware . 182 Kilns 184 Porous ware 185 Faience and common pot- tery 185 Majolica 185 Tiles 185 Vitrified, encaustic, and glazed tiles . . . .185 Glazes 186 Engobe, enamel, and transparent glazes . . 186 Crazing of glaze . . . 187 Terra cotta 187 Bricks 187 PIGMENTS. White pigments . . . . 190-198 White lead 190 Dutch process 190 Chamber process . . . .192 The'nard's process . . . 193 Milner's process .... 194 Kremnitz process . . . .194 Electrolytic process . . .195 White lead substitutes . . .196 Sublimed white lead . . .196 Lead sulphite 196 X-ll TABLE OF CONTENTS PAGE Pattinson's white lead . .196 White zinc 197 Barytes 197 Gypsum, terra alba .... 197 Whiting 198 China clay 198 Blue pigments .... 198-202 Ultramarine 198 Prussian or Berlin blue . . 200 Smalt and cobalt blues . . 201 Copper blues 202 Indigo 202 Green pigments 202 Ultramarine green .... 202 Brunswick green 202 Chrome and Guignet's greens 203 Copper greens 204 Malachite, verdigris . . . 204 Copper-arsenic greens . . . 204 Scheele's and Paris greens . 205 Terra verde 105 Yellow pigments 205 Chrome yellows 205 Yellow ochre and Sienna . . 207 Cadmium yellow 207 Orpiment 207 Litharge 207 Gamboge 208 Indian yellow or purree . . 208 Orange pigments 208 Orange mineral 208 Chrome orange 208 Antimony orange .... 208 Red pigments .... 209-212 Bed lead, chrome red . . . 209 Red ochre, vermilion . . .210 Iron reds, Venetian red, etc. 210 Realgar, antimony red . . . 212 Carmine and "lakes" . . . 212 Brown pigments 213 Umber, Vandyke brown, and sepia 213 Black pigments 213 Lampblack, ivory - black, bone-black, charcoal, graph- ite, manganese blacks, etc. BROMINE. Methods of extraction " Solidified bromine " Bromides . PAGE 215 217 218 IODINE. Extraction from kelp and varec 218 Extraction from the mother- liquors of sodium nitrate .219 Potassium iodide 220 PHOSPHORUS. Preparation from bone-ash . . 221 Preparation from mineral phos- phates 222 Yellow and amorphous phos- phorus 223 Matches . ."..'.... . . . 224 BORIC ACID. Sources and preparation . . . 225 Borax 226 ARSENIC COMPOUNDS. Arsenious acid, white arsenic . 229 Arsenic acid 229 Sodium arsenate 230 Sodium arsenite . . . 230 WATER-GLASS 230 PEROXIDES. Barium, sodium, and hydrogen peroxides 231 OXYGE-N. From potassium chlorate . . . 283 Deville's process 234 Boussingault's process . . . 234 Brin's modification . . . .234 Tessie du Motay's process . . 235 Linde" refrigeration process . . 236 SULPHATES. Ferrous sulphate, green vitriol . 237- Copper sulphate, blue vitriol . 239 Zinc sulphate, white vitriol . . 240 Aluminum sulphate .... 240 From clay and bauxite . . 241 TABLE OF CONTENTS xin Bayer's method for pure alu- mina 242 Aluminum sulphate from cry- olite 243 Alum 244 Preparation from alunite . . 244 Preparation from clay, cryo- lite, or bauxite .... 245 "Neutral alum" . . . .246 Potassium, ammonium, so- dium, iron, and chrome alums. . 246 CYANIDES. Bunsen and Playfair process . 247 Ammonium sulphocyanide . . 248 Gelis' process 248 PAGE Recovery from the spent ox- ides of the illuminating gas purification 248 Potassium ferrocyanide . . . 249 Potassium ferricyanide . . . 250 Barium sulphocyanide . . . 250 Potassium cyanide 251 CARBON BISULPHIDE 253 CARBON TETRACHLORIDE . . . 255 MANGANATES AND PERMANGA- NATES. Sodium and potassium manga- nates 255 Sodium and potassium perman- ganates 255 PART II ORGANIC INDUSTRIES DESTRUCTIVE DISTILLATION OF WOOD. Pyroligneous acid 257 Methyl alcohol 259 Acetone 260 Acetic acid 261 Acetates 262 Wood-tar 263 DESTRUCTIVE DISTILLATION OF BONES. Bone oil 265 Bone-black 265 ILLUMINATING GAS. Carburetted water gas . . . . 266 Coal gas 268 Purification of gas 274 Oil gas 276 Acetylene 277 Air gas 277 COAL TAR. Properties of tar 278 PAGE Distillation of tar 279 First runnings 282 Light oil 282 Naphtha 282 Carbolic oil 283 Creosote oil 283 Naphthalene 284 Anthracene oil 284 Pitch 285 ^MINERAL OILS. Petroleum industry. Distribution and origin of petroleum 285 Oil-well drilling . . . . . 287 Crude petroleum 290 Refining" 290 " Cracking " of crude oil . . 292 Purification of distillates . . 293 Paraffine oils 294 "Neutral" oils. .... 294 Reduced oils 295 Vaseline 295 Russian petroleums .... 295 XIV TABLE OF CONTENTS Oil testing 295 Use of petroleum oils to pre- vent spontaneous combus- tion of animal and vegetable oils 297 Shale oil industry. Distillation of bituminous shale ......... 298 Ozokerite. Purification of mineral wax . 299 Asphalt. Occurrence and uses of min- eral pitch 299 VEGETABLE AND ANIMAL OILS, FATS AND WAXES. Properties of the fatty oils . .301 Hydrolysis of fats 303 Occurrence and extraction of vegetable oils 304 Occurrence and extraction of animal oils . . . ". - . . 305 Testing of fatty oils 306 Classification of oils 307 Vegetable drying oils . . . 308 Vegetable semi-drying oils . 310 Vegetable non-drying oils . . 313 Marine animal oils .... 314 Terrestrial animal oils . . .315 Solid vegetable fats .... 316 Solid animal fats 317 Waxes. Liquid waxes 318 Solid animal waxes .... 319 Solid vegetable wax .... 320 SOAP. Saponification 321 Cold process soap 324 Boiled soaps 324 Yellow (rosin) soaps . . . 325 White soaps . . ' 325 Toilet soaps 327 Milled soaps 328 Kemelted soaps 328 Transparent soap .... 328 Scouring soaps 328 CANDLES. Dipped, poured, and moulded candles 329 Saponification of fats for candle stock 330 GLYCERINE. Van Ruymbeke process for the recovery of glycerine from spent soap lyes . . . . 332 Glycerine from candle stock . . 333 Glatz process for recovery of glycerine from soap lyes . . 333 Properties and uses of glycerine 334 ESSENTIAL OILS. Properties and methods of ex- traction . '. ... . - . . 335 Characteristics of the individual oils 336-340 RESINS AND GUMS. Resins 341-345 Varnishes. Spirit, turpentine, and lin- seed oil varnishes . . . 345 Oleo-resins. Balsams 346 Caoutchouc (India rubber) . . 346 Guttapercha 350 Gum resins. Properties of individual gum resins 350-351 Gums. Properties of the gums . . . 351 STARCH, DEXTRIN, AND GLUCOSE. Occurrence and properties of starch 353 Corn starch 354 Wheat starch 358 Potato starch 359 Rice starch 360 Sago 361 Arrowroot 361 Cassava ...-..". . . 362 Dextrin. Manufacture and properties of dextrin and of British gum 363 TABLE OF CONTENTS xv PAGE Glucose. Dextrose 364 Lsevulose 364 Commercial glucose .... 364 Conversion 364 Neutralization 366 Bone-char filtration . . . 367 CANE SUGAR. Occurrence and properties of cane sugar 370 Raw sugar manufactured from sugar cane 372 Raw sugar manufactured from sugar beets 376 M Sugar refining 378-382 FERMENTATION INDUSTRIES. Fermentation. Organized ferments .... 384 Mould growths 385 Bacteria 385 Yeast plants 386 Wine. Composition of grape juice . 389 Extraction of the must . . .390 Fermentation of the must . . 390 Preservation of wine .... 392 Champagne 393 Other wines 393 Brewing. Malting 394 Steeping, couching, and flooring 395 Pneumatic malting . . . 396 Mashing 398 Infusion method .... 398 Decoction method .... 399 Boiling of the wort .... 400 Hops 400 Cooling the hot wort .... 401 Fermenting 401 Pitching 401 Bottom fermentation . . . 402 Top fermentation .... 403 Extract in beer 403 Bottling or barrelling . . . 403 Brewed liquors 404 Distilled liquors. Alcohol, manufacture . . . 405 Distillation, of the mash . 407 Purification and rectifica- tion of raw spirit . . . 408 Silent spirit 409 Methylated spirit .... 409 Fusel oil 410 Whiskey 410 Gin . . . ... ./> ; . . .411 Brandy . ;. ..>..>. .* ..!. . 411 Rum 411 Liqueurs and arrack . . . .411 Vinegar. Orleans process 412 Quick vinegar process . . . 413 Cider, wine, and malt vine- gars 414 Lactic fermentation 415 Lactic acid . . 416 EXPLOSIVES. Characteristic properties of ex- plosives 417 Gunpowder 418 Pebble and prismatic powders 421 Brown or cocoa powder . . 422 Mining powders 422 Nitrocellulose . . .<.... . .423 Guncotton 423 Pyroxyline 425 Smokeless powders . . 425, 430 Nitroglycerine 425 Preparation and purification . 426 Dynamite 428 Mica powder ...... 429 Forcite 430 Blasting gelatine 430 Gelatine dynamite and cordite 430 Picrates 431 Melinite 431' Fulminates 431 Sprengel explosives 432 Roburite, romite, bellite, and ammonite 432 Lime cartridges 432 XVI TABLE OF CONTENTS TEXTILE INDUSTRIES. Fibres. Vegetable fibres 434 Cotton 434 Linen 435 Hemp 436 Jute 437 China grass (ramie) . . . 437 Esparto 437 Manilla, sisal, and sunn hemp 437 Animal fibres 438 Silk 438 Wool 442 Wool scouring and recov- ery of wool grease . . 444 Bleaching. Cotton bleaching 446 Market, madder, and Tur- key-red bleach .... 448 Mather-Thompson process . 452 Hermite bleaching process . 453 Hydrogen peroxide and po- tassium permanganate as cotton bleaches .... 453 Linen bleaching 453 Irish process 453 Jute bleaching 454 Hemp bleaching 454 Wool bleaching 455 Stretching of yarn .... 455 "Crabbing" of union goods 455 Stoving 456 Hydrogen peroxide . . . 456 Silk bleaching 457 Mordants. Action of mordants .... 457 Metallic mordants . . 458-462 Organic mordants . . . 462-466 Tannins 463 Coloring matters. Natural dyestuffs 466 Indigo 466 Logwood 467 Bed woods 468 Madder 468 Archil . 469 PAGE Litmus, cochineal .... 469 Lac dye, kermes .... 469 Fustic, quercitron .... 470 Persian berries 470 Curcuma, annatto .... 470 Artificial dyestuffs ... .470 Rosaniline dyes 471 Safranines and indulines . 472 Oxazines 472 Thionines ..... . . . . 473 Aniline black 473 Nitro dyes 473 Nitroso dyes 473 Phthaleins 473 Eosins ....... 474 Bosolic acids 474 Amidoazo dyes 474 Amidoazosulphonic acids . 475 Oxyazo dyes 475 Quinoline and acridine dyes 477 Anthracene dyes . . . .477 Artificial indigo .... 479 Dyeing. Properties of dyestuffs . . .479 Theory of dyeing 480 Methods of dyeing . . . .481 Direct dyes 482 Basic dyes 483 Acid dyes 484 Mordant dyes 486 Colors developed on the fibre 489 Indigo 489 Aniline black . . . .491 Azo dyes developed on the fibre 492 Mineral dyes 492 Textile printing. Block printing 494 Machine printing 495 Color mixing 496 Styles 497 Pigment style 497 Steam style 497 Madder or dyeing style . . 498 Oxidation style 498 Discharge style 498 TABLE OF CONTENTS xvii Resist style 499 Wool printing 499 Silk printing 499 PAPER. Materials for paper 501 Wood pulp . . . . . . . 502 Mechanical pulp .... 502 Chemical pulp 502 Soda process 502 Sulphite process .... 503 Sulphate process . . . 506 Rags 508 Esparto 508 Jute 509 Bleaching paper pulp .... 509 Paper making 509 Sizing 510 Hand-made paper . . . .511 Cylinder machine 511 Fourdrinier machine . . . . 511 Printing paper ...... 512 Wrapping paper .... 512 Writing paper 512 Blotting paper 512 Parchment paper . . . .513 Willisden paper .... 513 LEATHER. Structure of skin 514 Classification of pelts . . . .515 Preparation of the skins . . . 516 Depilation processes .... 516 Liming 516 PAGK Sweating 517 Beaming 517 Bating 517 Tanning processes 618 With tannin. . . ... . 618 Sole leather . . . . . .519 Upper leather . . . . . 520 Currying . . . . . .620 Colored leather 520 Split leathers 520 Tawing (mineral tannage) . 521 Combination tannage . . .521 Chrome tannage .... 521 Oil tanning 522 Degras 523 Sod-oil 523 Morocco leather .... 523 Russia leather 523 Patent leather 523 Parchment 524 Artificial leather . . . .524 Theory of tanning .... 524 GLUE. Sources of glue 525 Constituents of glue .... 525 Preparation of glue . . . .525 Hide glue 525 Bone glue 527 Fish glue 527 Liquid glue 527 Gelatine 627 Isinglass 528 GENERAL REFERENCES ON INDUSTRIAL CHEMISTRY Chimie Industrielle. A. Payen. Paris, 1867. Grundriss der chemischen Technologie. H. Post. Abriss der chemischen Technologie. Chr. Heinzerling. Berlin, 1888. (T. Fischer. ) Traite" de Chiinie applique'e a Plndustrie. Adolphe Renard. Paris, 1890. A Dictionary of Applied Chemistry. T. E. Thorpe. 3 Vols. London, 1891- 1893. (Longmans, Green and Co.) Lehrbuch der technischen Chemie. Dr. H. Ost. 3d Ed. Berlin, 1898. (R. Oppenheiiner.) Handbook of Industrial Organic Chemistry. S. P. Sadtler. Philadelphia. 2d Ed. 1895. (J. B. Lippincott.) Handbuch der chemischen Technologie. Dr. O. Dammer. 5 Vols. Vol. I, 1895. Vol. II, 1895. Vol. Ill, 1896. Stuttgart. (F. Enke.) Chemistry for Engineers and Manufacturers. Bertram Blount and A. G. Bloxam. 2 Vols. London, 1896. (Griffin and Co.) Chemical Technology. R. Wagner. Translated by Wm. Crookes. New York, 1897. (D. Appleton and Co.) Encyclopaedisches Handbuch der technischen Chemie. F. Stohmann und Bruno Kerl. Vol. I, 1888. Vol. II, 1889. Vol. Ill, 1891. Vol. IV, 1893. Vol.V, 1896. Braunschweig. (F. Vieweg.) Chemical Technology. Edited by C. E. Groves and William Thorp. Vol. I, Fuel, 1889. Vol. II, Lighting, 1895. V^l. Ill, Gas and Electric Lighting, etc. xix ABBREVIATIONS OF THE NAMES OF JOURNALS, FREQUENTLY OCCURRING IN THE LITERATURE OF INDUSTRIAL CHEMISTRY. A. or Ann. = Annalen der Chemie und Pharmacie, by Liebig and others, 1832-98+. Ann. chim. phys. = Annales de Chimie et de Physique. Paris, 7 series, 1789- 1898 +. Ber. = Berichte der deutschen chemischen Gesellschaf t. Berlin, 1868-98 + . Bull. Soc. Chim. = Bulletin des Seances de la Socie'te' chimique de Paris. 2 series, 1804 + . Chem. Centralb. = Chemisches Centralblatt. 4 series, 1829-98 -f . Chem. Ind. = Zeitschrift fur die chemische Industrie. 1887 +. C. N. or Chem. N = Chemical News. 1860-98 + . C. R. or Compt. rend. = Comptes-rendus hebdomadaires des Seances de 1' Acade- mie des Sciences. Paris, 1835-98 + . Chem. Zeit. = Chemiker-Zeitung. 1877-1898 + . Dingl. J. = Dingler's polytechnisches Journal. 1820-98 +. Eng. Min. Jour. = Engineering and Mining Journal. 1866-98 + . Jahresb. = Jahresbericht tiber die Fortschritt der Chemie, u. s. w. J. Am. Chem. Soc. = Journal of the American Chemical Society. New York, 1879-98 + . J. Chem. Soc. = Journal of the Chemical Society of London. 1849-98 + . J. Soc. Chem. Ind. == Journal of the Society of Chemical Industry. London, 1882-98 + . W. J. = Wagner's Jahresbericht der chemischen Technologic. 1855-98 +. Zeitschr. angew. Chem. = Zeitschrift fur angewandte Chemie. Berlin, 1887- 98+. Zeitschr. anorg. Chem. = Zeitschrift fur anorganische Chemie. 1892-98 +. Zeitschr. Chem. Ind. = Zeitschrift fur die chemische Industrie. 1887 + . OUTLINES OF INDUSTRIAL CHEMISTRY PART I INORGANIC INDUSTRIES INTRODUCTION INDUSTRIAL chemistry deals with the preparation of products from raw materials, through the agency of chemical change. But there is an occasional exception to this definition ; for a few indus- tries, depending on strictly mechanical changes, are classed among the chemical industries. Since a sharp line cannot be drawn between chemical and mechanical technology, a study of the former neces- sarily involves some consideration of the mechanical appliances and apparatus, by means of which the chemical reactions are carried out. The products of chemical industry are exceedingly numerous and varied in character, but comparatively few come into the hands of the mass of the people for direct consumption. Many of them are used only in making other substances, for it is often the case that the finished product, by-product, or waste- from one industry, be- comes the raw material for another, and it rarely happens that one manufacturer, starting with the raw materials found in nature, produces from them articles for popular use. Thus the chemical industries become a network of interlacing processes, and in con- sidering one it is often difficult to separate it from others which have a more or less direct bearing upon it. Furthermore, as com- petition has become very close in many lines, the use which may be made of by-products and waste is so important, that processes are often carried out with the view of obtaining larger yields or better quality of the by-products, which may have become a source of considerable profit. In a few instances, it might be said that B 1 2 OUTLINES OF INDUSTRIAL CHEMISTRY what were originally the by-products are now the chief products and main support of these particular industries. This is especially true in the case of the Leblanc Soda Industry, which would long since have been abandoned were it not for its production of hydro- chloric acid. The utilization of waste materials furnishes an almost inexhaustible subject for investigation by the industrial chemist. The manipulations of most frequent occurrence in the various processes are here defined and explained for the sake of brevity in the text. LIXIVIATION Lixiviation is the process of separating soluble from insoluble substances by dissolving the former in water or some other solvent. The mixture of substances is put into a suitable vessel, the solvent poured over it, and the whole allowed to stand until a strong solu- tion is obtained, which is then drawn off from the residue. This process is repeated as often as necessary, until the desired amount of soluble matter has been removed. Sometimes the mixture is put into baskets, or on gratings, which are suspended in tanks of water. The solution being, denser than the solvent, sinks to the bottom as it forms, and water comparatively free from dissolved material is thus constantly brought into contact with the substance to be lixiviated. The insoluble substance remains on the grating or in the baskets. When desired, the soluble material may be recovered from the solu- tion by evaporation or precipitation. Extraction is the term usually employed when some solvent other than water is used in lixiviating. Thus we speak of extraction by steam, alcohol, carbon disulphide, etc. LEVIGATION Levigation is the process of grinding an insoluble substance to a fine powder, while wet. The material is introduced into the mill together with water, in which the powdered substance remains sus- pended, and flows from the mill as a turbid liquid or thin paste, according to the amount of water employed. There is no loss of material as dust, nor injury or annoyance to the workmen. Further, any soluble impurities in the substance are dissolved, and the prod- uct thereby purified. The greatest advantage of this process is the facility it affords for the subsequent separation of the product into various grades of fineness, because of the slower subsidence of the finer particles from suspension. The turbid liquid, flows into the first of INTRODUCTION 8 a series of tanks, and is allowed to stand for a certain time. The coarsest and heaviest particles quickly subside, leaving the finer material suspended in the water, which is drawn from above the sediment into the next tank. The liquid is passed from tank to tank, remaining in each longer than it remained in the preceding, since the finer and lighter the particles, the more time is necessary for their deposition. In some cases a dozen or more tanks may be used, and the process then becomes exceedingly slow, as very fine slimes or muds may require several weeks for the final settling. But as a rule, from three to five days is sufficient. The term " levigation " is now often applied to mere sedimenta- tion, a substance being simply stirred up in water, without previous wet-grinding, in order to separate the finer from the coarser parti- cles, as above. EVAPORATION Evaporation, in a technical sense, denotes the conversion of a liquid into a vapor for the purpose of separating it from another liquid of higher boiling point, or from a solid which is dissolved in it. In the great majority of cases, the liquid evaporated is water. If the liquid evaporated is to be recovered, the vapors are con- densed, and the process then becomes one of Distillation (see p. 7). There are four general methods of evaporation : 1. Spontaneous evaporation in the open air. 2. Evaporation by application of heat directly from a fire to the vessel containing the liquid. 3. Evaporation by indirect application of heat from the fire, as by means of steam, with or without pressure. 4. Evaporation under reduced pressure. The first method, by spontaneous evaporation in the open air, is comparatively slow, and requires exposure of very large surfaces of liquid. The time necessary depends upon the temperature and humidity of the air, and the completeness with which the vapors are removed from the surface of the liquid; hot, dry weather, es- pecially if a brisk wind is blowing, evaporates water quite rapidly. This process is only used for the manufacture of salt from sea water, or from natural brines. In certain warm countries con- siderable quantities of salt are thus prepared, and in this country some is made from a brine found near Syracuse, N.Y. Sometimes weak brines are allowed to trickle in fine streams over tall piles or " ricks" of brushwood in the open air. The liquid being so exposed in thin layers, to the air and wind, is concentrated to such 4 OUTLINES OF INDUSTRIAL CHEMISTRY a degree that it will pay to complete the evaporation by artificial heat. The second method,* by direct application of heat from a fire, is very largely used in the arts. This may be done in two general ways : (a) The flames, or hot gases from the fire, are generally allowed to play directly on the bottom of the vessel containing the liquid ; or they may pass through flues or pipes, set into the vessel, so that the liquid surrounds them on all sides (Fig. 1). Such FIG. 1. pans are often several yards in length, and may contain one large flue, or several small ones, according to the work desired ; but this form of apparatus is expensive to build, and difficult to keep in repair. (b) The flames and hot gases may be conducted over the surface of the liquid to be evaporated. This mode is only used for coarse and common products, or in the concentration or recovery of waste materials. But it has the advantage, that the bottom of the pan is less liable to be injured by the crusting of a precipitate upon it. Another point often in favor of surface heating, is that the liquid is evaporated in a reducing atmosphere. But as flue dust and ashes are liable to fall into the pans, the product is usually impure. Large shallow pans are used, which are generally arched over with brick, in order that the heat may be better utilized, through radiation from , the brick walls. There are various ways of setting the pans for this process ; a sim- ple method is shown in Fig. 2. A modification of this method is the use of a long cylinder, set at a slight incline, an^ revolving about its longitudinal axis (Fig. 3). The lower end is open for the entrance of the flames and gases from the grate (A), which pass through the cylinder (B), on their way to the chimney (D). The hot gases are often passed through the flues of a boiler (C), to utilize the waste heat. The solution to be evaporated FIG. 2. * To save expense, the waste heat from calcination or furnacing operations is frequently utilized. INTRODUCTION 5 is fed into the cylinder at the upper end in a small stream, and comes in direct contact with the flame. The water is evaporated, and the solid matter is delivered into the pit or wagon (E) at the lower end of the furnace, in a dry and calcined state. Such fur- naces are frequently used for evaporating waste liquors to recover FIG. 3. the salts which they contain ; and for the treatment of sewage and other liquid refuse. The third method of evaporation, by the use of steam heat, is very often employed where there 'is danger of injury to the product by overheating. (a) Jacketed pans or kettles may be used. These are simply double-walled vessels, the steam being admitted between the walls. (b) The steam may be allowed to circulate through coils of pipe, placed inside the vessel, which is sometimes made of wood. The temperature of the liquid depends on the steam pressure ; very often exhaust steam is employed. The fourth method, evaporation in vacuo, is merely a modifica- tion of either the second or third method, but is considered sepa- rately for convenience. The boiling point of a liquid may be very materially lowered by reducing the pressure within the vessel. Hence, solutions containing substances which would be injured by the heat necessary to boil them under the atmospheric pressure, or liquids boiling at very high temperatures, are evaporated in vacuum pans. The different forms of apparatus used for vacuum evaporation vary much in their details, but all depend on the principle of reduced pressure. The essential parts of the plant are the vacuum pan or still, the pump for exhausting the air and steam from the pan and sending them to the condenser, and the heating apparatus. The vacuum pan is usually a globular copper or iron vessel, pro- vided with a manhole, a pressure gauge, and a discharging valve. Very often a piece of heavy plate glass is set in the side to afford a 6 OUTLINES OF INDUSTRIAL CHEMISTRY view of the interior during evaporation. On the top of the pan is a dome or short tower, from which a pipe leads to a receptacle, called the " catch-all/ 7 that retains any liquid which may escape from the pan. A small pipe returns this liquid to the pan, and a larger one connects the " catch-all " with the vacuum pump, which is an ordinary double-cylinder air pump of large size, driven by an engine. An injector pump, which condenses the steam directly, may be used. The pan is generally heated by steam coils within it, or by a steam jacket, or by both. A very efficient method of vacuum evaporation is that obtained by the use of Multiple Effect Systems. In these greater economy of fuel for heating is secured. The apparatus consists usually of three or four simple vacuum pans, so joined together that the steam from the boiling liquid in the first pan is made to pass through the coils and jacket of the second pan, and the steam generated in the second pan goes through the coils and jacket of the third, and so on through the system. The vacuum maintained in each pan of the series is greater than in the one preceding. Hence, notwithstand- ing its increased concentration, the boiling point of the liquid in the second pan is so low, that the steam from the first pan is sufficiently hot to boil it. Similarly the steam from the second pan is made to boil the liquid in the third, in which there is still less pressure, and so on to the fourth pan, in which the highest vacuum is maintained. As a rule only four pans are used, for it is very difficult to sustain the vacuum sufficiently to work another pan in the series. In many plants only three pans (triple effects) are used. An effective modification of this method is the apparatus known as the Yaryan Evaporator (Fig. 4). It is made in triple and quad- ruple effects, and each pan is exactly like its neighbors. It consists of an outside shell of iron, within which is a system of small tubes (A, A), joined together in groups of five or six, each group constitut- ing a section or unit. The tubes in each unit are so connected at the ends as to form one continuous coil. The liquor to be evaporated is run through the several coils thus constructed in each pan. The tubes in the first pan are heated by steam, introduced into the shell directly from a boiler. As the liquid flows through the tubes, it is brought to boiling, and the steam generated mingles with it, convert- ing the whole mass into foam, which runs through the coil and spurts against a baffle plate in the "separator" (B, B), which is an enlarged chamber at the end of the shell. The steam and liquid are separated, the liquid falling to the bottom and running off into the receiver (C), to be passed through the tubes of the next pan. The INTRODUCTION 7 steam rises, passing through the steam dome and "catch-all" (D), and then into the shell of the next " effect," through the coils of which the liquid is passing under still greater vacuum, and so on through the system. The apparatus is very economical in its use of fuel, and as the liquid is exposed in thin layers to the action of the heat, the evaporation is very rapid; hence the liquid is subjected to a high temperature for only a short time. The apparatus is nearly automatic in its action, and needs but little attention. It can be stopped and started very quickly, since it contains only a small quantity of liquid at one time, and it occupies but little floor space when the several " effects " are placed one over the other. The ordinary form of vacuum pan evaporates about 8 \ Ibs. of water per pound of coal, but it is said that the best forms of Yaryan appa- ratus evaporate from 23|- to 25 Ibs. of water per pound of coal in a triple effect, and 30J- Ibs. in a quadruple effect.* DISTILLATION Distillation is the process of vaporizing a liquid and recovering it by condensing the vapors. The liquid formed by this condensation is called the distillate. Distillation is chiefly employed to separate a liquid from non-volatile matter dissolved or suspended in it ; or to separate one liquid from a mixture of liquids of different boiling points ; that one having the lowest boiling point being the first to begin to pass off as vapor. But the separation of two liquids which are miscible with each * J. Soc. Chem. Ind., 1895, 112. 8 OUTLINES OF INDUSTRIAL CHEMISTRY other is never complete by this means, and is less perfect the nearer their boiling points are together. Liquids which are miscible in all proportions, may be separated quite completely, provided there are a few degrees difference in their boiling points, by employing the principle of fractional condensation of the vapors. This consists in passing the mixed vapors through a condenser which is kept at a constant temperature between the boiling points of the liquids. Thus the vapors of the high-boiling liquid being cooled below the boiling point of that liquid are condensed, while the vapors of the low-boiling liquid being still hotter than its boiling point, cannot condense, but pass on to another part of the apparatus, where they are condensed separately. When the high-boiling distillate condenses, it carries with it more or less of the low-boiling liquid, and hence should usu- ally be returned to the boiler and redistilled. In such mixtures as this, there is a gradual rise in the boiling point during the entire distillation. The chief parts of every distilling apparatus are the boiler or still and the condenser. In practical work the appliance for fractional condensation is placed between the still and the condenser. It may be an apparatus, called a " dephlegmator," in which the vapors are forced to bubble through a layer or column of the condensed higher- boiling liquid ; or the mixed vapors may pass through a tower or pipe, kept at a constant temperature, just above the boiling point of the low- boiling liquid. The still is usually iron, copper, or other metal, heated directly by a furnace, a steam jacket, or a coil. In Coupler's still (Fig. 5) a tower (A) is placed on top of the boiler (B); between the tower and the con- denser is a series of bulbs (C, C) surrounded by a water bath, which may be kept at any de- sired temperature. While the mixed vapors are passing through the bulbs, the high-boiling constituents are condensed, and only the vapor of the more volatile liquid passes through (E) to the con- denser (F). From each bulb a pipe (D) leads back to the tower, into which the condensed heavy liquid is delivered, to be redis- tilled or dephlegmated. INTRODUCTION The French column (Fig. 6) is very similar to the Coupler's appa- ratus, but instead of bulbs, a series of U-tubes (C) surrounded by a water bath is used. The column or dephlegmator (B) is divided into chambers by plates, each of which has a central opening covered by a dome; a small overflow pipe passes from each plate to the next. The vapors from the boiler (A) pass up through the central openings and bubble out under the edges of the domes through the layer of liquid on each plate. The liquid thus condensed flows down through the overflow pipes, and returns to the boiler. The Coffey still (Fig. 7) is much used for alcohol and gas liquor dis- tillation. This consists of two towers, one, called the "analyzer" (E), receiving free steam from the boiler, and the other, called the " rectifier " (G), containing a long coil of pipe (C, C), through which FIG. 6. FIG. 7. the liquid to be distilled flows on its way to the analyzer. The analyzer is divided into a series of chambers by horizontal, per- 10 OUTLINES OF INDUSTRIAL CHEMISTRY f orated plates (A) ; from each plate an overflow pipe (F) passes down and dips into a shallow cup (H) on the next plate below and holding liquid enough to form a hydraulic seal at the lower end of each overflow pipe. These pipes project about an inch, or an inch and a half above the plate in which they are set, thus determin- ing the depth of the liquid layer on each plate. The rectifier is also divided into chambers by perforated plates, but it has overflow pipes in its lower half only. In the chambers lie the coils of pipe (C) through which the liquid to be distilled passes on its way to the analyzer. This still works as follows: Steam from the boiler is blown through (K) into the analyzer, and passes from the top of the analyzer through the pipe (L) to the rectifier. The liquid to be dis- tilled is pumped through the pipe (B) and the coil (C) in the recti- fier, and is delivered at the top of the analyzer through the pipe (D). The cold liquid is heated by the steam surrounding the coils, and is delivered hot at the top of the analyzer. Since steam is being forced up through the perforations, the liquid cannot pass down through them, but is forced to spread out over the plate, and run down the overflow pipe (F) to the next plate, and so through the analyzer. The steam, bubbling up through the thin layers of liquid, heats it very hot, and causes the volatile sub- stances to distill off with the steam. This mixture of steam and vola- tile matter passes from the top of the analyzer, through (L), to the bottom of the rectifier. During its passage up the rectifier, the steam is condensed by coming into contact with the cold pipes (C, C), through which the liquid is flowing to the analyzer. Thus only the more volatile matters pass out at the top of the rectifier, and go to the condenser (0). The water condensed in the rectifier contains some volatile matter, so it is pumped to the top of the analyzer and mixes with the fresh liquor to be distilled. From the bottom of the analyzer a waste pipe (J) carries off the spent liquor which has been deprived of its volatile matter. Distillation in vacuum is sometimes employed, and will be de- scribed in connection with the industries in which it is used. SUBLIMATION Sublimation is the process of vaporizing a solid substance and condensing the vapors to again form the solid directly, without passing through an intermediate liquid state. There are very few substances which vaporize without melting, but in all cases of sub- limation, the change from the vapor to the solid state, is direct, and INTRODUCTION 11 without any formation of liquid. The sublimed body is recovered unchanged chemically, but its physical properties are often more or less altered. Sublimation is influenced by the pressure within the vessel, and is generally carried on under atmospheric pressure only. The process is employed as a means of purification of certain substances, which are heated in closed pans or retorts. . In most cases, the temperature does not exceed a low red heat. Dissociation often occurs in the process. FILTRATION Filtration is the process of separating suspended solid matter from a liquid, by causing the latter to pass through the pores of some substance, called a filter. The liquid which has passed through the filter is called the filtrate. The filter may be paper, cloth, cotton-wool, asbestos, slag- or glass-wool, unglazed earthen- ware, sand, or other porous material. Filtration is very frequently employed in chemical technology, and it often presents great difficulties. In most technical opera- tions, cotton cloth is the filtering material, but occasionally woollen or hair cloth is necessary. The cloth may be fastened on a wooden frame in such a way that a shallow bag is formed, into which the turbid liquid is poured. The filtrate, in this case, is cloudy at first, but soon becomes clear, and then the turbid portion is returned to the filter. Filtration is often retarded by the presence of fine, slimy precipitates, or by the formation of crystals in the interstices of the cloth, from the hot solution. Any attempt to hasten filtra- tion, by scraping or stirring the precipitate on the cloth, will always cause the filtrate to run turbid. A better form is the " bag-filter," which is a long, narrow bag of twilled cotton, supported by an outside cover of coarse, strong netting, capable of sustaining a considerable weight and hydrostatic pressure. These bags are often five or six feet long, and eight inches or more in diameter. The open end of the bag is tied tightly around a metallic ring or a nipple, by which the whole is suspended, and through which the liquor to be filtered is introduced. When hot liquids are filtered, the bags are often hung in steam-heated rooms, the temperature being nearly that of the liquid. In pressure filtration, the liquid is forced through the interstices of the filter by direct atmospheric pressure, the air being exhausted from the receiver; or by hydrostatic pressure, obtained either by means of a high column of the liquid, or by a force pump. By the 12 OUTLINES OF INDUSTRIAL CHEMISTRY first method, called suction filtration, the. liquid may be forced downward through the filter into a receiver ; the precipitate collects on the top of the filter and becomes a part of the filtering- layer. This sometimes causes difficulty, for the particles of certain precipi- tates unite to form an impervious layer. Or the filtrate may be drawn upward through the filter, which is suspended in the liquid to be filtered; thus clogging does not occur so easily, as a large part of the precipitate settles to the bottom of the vessel and does not come in contact with the filter until most of the liquid has been drawn off. In technical work, pressure is usually obtained by the filter press (Figs. 8 and 8 a). This is a strong iron frame, in which a number of cast-iron or bronze filter cells are supported. Each cell is made up of two flat metal plates with raised edges, separated by a hollow " dis- tance frame " of the same metal. There is a hole in the centre of each plate, and grooves on each surface leading to an opening at the lower edge of the plate. A filter is made of two pieces of cloth, slightly larger than the plates, sewed together along the margin of a small circular opening cut in the centre of each. One piece of the cloth is passed through the hole in the plate, and then both pieces are spread out smoothly, one on either side of the plate. Another plate is prepared in the same way, and a distance frame having been placed between them, the cell thus formed is set verti- cally in the press frame, where it is supported by lugs on each plate and distance frame. When the desired number of cells are ready, they are tightly clamped together by means of a heavy screw, which passes through one end of the press frame. Thus a INTRODUCTION 13 series of cells, lined with filter cloth and connected by a straight channel through the central holes, is formed. A powerful force pump drives the liquid to be filtered into the cells, where it passes from one to the other until they are all filled. The hydrostatic pressure forces the liquid through the filters into the grooves in the plates, along which it flows, and escapes through the openings at the lower side of the plate. The sediment retained by the cloth collects in the cell and forms a solid cake, which finally fills each FIG. 8 a. cell completely. The process is then stopped, the cells taken apart, and the cake of sediment having been removed, the cells are returned to the press frame, to be again put into operation. The filtrate is caught in a trough. In another form of press, instead of the central opening, there is a hole in the corner of each plate and distance frame in such a position that, when placed in the press, the holes form a continuous channel through the corner of the whole series of cells. A small hole drilled on the inside of each distance frame, at right angles to the direction of the channel, admits the liquid into each cell. The filter is a piece of cloth hung over the distance frame in such a way that both sides of the frame are covered. A frame so covered is put between each pair of grooved plates. Small holes 14 OUTLINES OF INDUSTRIAL CHEMISTRY are cut in the cloth to correspond to the channel in the corners of the cells. The method of nitration is the same as in the central feed machines. The pressure obtained by the force pump may be only a few pounds, or it may rise to several hundred pounds per square inch. The filter press may contain from a dozen to fifty or more cells, and these cells may be as large as four feet in diameter. For many purposes the press is sur- rounded by coils or jackets, through which steam or refrig- erating solutions may be circu- lated, according as hot or cold filtration is desired. The filter press is very rapid in its action and is extensively employed in industrial chemi- c:il work. For use with acid or corrosive liquids, the plates and distance frames are often covered with lead or some alloy which is not easily corroded. The centrifugal machine (Fig. 9) is, to a great extent, replacing the filter press and other filters, especially when crystals are to be removed. This furnishes the most rapid method and leaves the substance almost dry. The centrifugal machine is a cylindrical box or basket (A) of wire gauze or perforated sheet metal, fixed on a vertical shaft (B), which rotates at a very high speed. The contents of the box are driven to the outer wall by the centrifugal force, the solid matter being retained by the gauze or screen. The liquid passes through and is caught in a fixed shell (C), surrounding the rotating basket. These machines are of various sizes from 12 to 60 inches diameter, and 8 to 36 inches, depth of basket. Two general forms are in use : the over-driven type, in which the driving pulley (P) is fixed at the upper end of the shaft, above the basket ; and the under-driven type, in which the basket is placed on the upper end of the shaft, and the pulley below. In the over-driven type it is frequently customary to suspend the shaft in flexible bearings. Thus the basket is enabled to adjust itself to any change in the FIG. 9. INTRODUCTION 15 centre of gravity, caused by unequal loading, and runs without vibration. Sand filters are sometimes used for work on a large scale. These are made as follows : Into a box having a perforated bottom, is put a layer of coarse gravel ; this is covered with finer pebbles ; these by sand, and a jute or canvas cloth covers the whole. A wooden or iron grating is added to protect the filter, when the sediment is shovelled out. The filter is often placed over a receptacle from which the air may be exhausted, thus affording pressure filtration if necessary. CRYSTALLIZATION Crystals are chemically homogeneous bodies, usually having regular polyhedral forms, and whose molecules have arranged them- selves regularly according to definite laws. The tendency to form crystals is common to almost all chemical compounds under certain conditions, the forms of the crystals being characteristic of the substance. Crystals may form from a fusion, or by sublimation; but crys- tallization almost always takes place from solution. In the majority of cases, the solubility of a substance increases as the temperature of the liquid rises, until a point is reached at which no more of the substance will dissolve, even though the solution is boiling. When a liquid has dissolved all of a solid that it can hold in solution at a certain temperature and pressure, it is said to be saturated for that temperature. Any decrease in the temperature results in the separation of a part of the substance, usually as crystals. There are a few instances where the maximum solubility is reached at temperatures much below the boiling point of the solution, the most notable of these salts being sodium car- bonate and sodium sulphate, both reaching the maximum solubility below 35 C. During the formation of the crystal, there is a ten- dency to exclude from it all matter not homogeneous with it; hence this is an excellent method of purifying salts. But if a concentrated solution, which is very impure, is allowed to crystallize, the impuri- ties may become enclosed in or entangled among the crystals as they form, producing an impure product. This can often be pre- vented by stirring the solution while crystallizing, thus causing the formation of very fine crystals or "crystal meal," which may be more readily washed free from mother-liquor and impurities. The liquid from which the crystals have deposited, is called the mother- liquor ; it contains the greater part of the soluble impurities present 16 OUTLINES OF INDUSTRIAL CHEMISTRY in the original solution, and also a considerable quantity of the salt, which has not deposited as crystals. The amount of the latter depends upon the temperature at which the crystallization took place. By further evaporation more crystals may be obtained, but they are less pure than those first separated. Thus the impurities accumulate in the mother-liquor, and in many cases, being valuable salts themselves, are recovered, and add to the profits of the indus- try. On the other hand, the mother-liquors from some processes are the cause of much annoyance and expense to the manufacturer, since from their corrosive, poisonous, or offensive nature, they can- not be run into the streams or sewers, and their disposal in some other way becomes necessary. If a concentrated solution is allowed to stand quietly while crystallizing, especially if there is a considerable quantity of the liquid and the temperature falls very slowly, the crystals formed are usually large and well defined; on the other hand, if it be stirred, the crystals are small and imperfectly developed, constitut- ing the crystal meal above mentioned. Since large crystals are very compact and offer a relatively small surface to the action of water, they dissolve very slowly, unless pulverized. Crystal meal dissolves more readily, and for this reason is becoming more and more popular with manufacturers. CALCINATION Calcination is the process of subjecting a substance to the action of heat, but without fusion, for the purpose of causing some change in its physical or chemical constitution. The objects of calcination are usually: (1) to drive off water, present as absorbed moisture, as " water of crystallization," or as " water of constitution " ; (2) to drive off carbon dioxide, sulphur dioxide, or other volatile constit- uent ; (3) to oxidize a part or the whole of the substance. There are a few other purposes for which calcination is employed in special cases, and these will be mentioned in their proper places. The process is often called " roasting,' 7 " firing," or " burning," by the workmen. It is carried on in furnaces, retorts, or kilns, and very often the material is raked over or stirred, during the process, to secure uniformity in the product. The furnaces used for calcining substances vary much in their construction, but there are three general classes: muffle, reverber- atory, and shaft furnaces or kilns. Muffle furnaces (Fig. 10) are so constructed that neither the fuel nor the fire gases come in direct contact with the material to be INTRODUCTION 17 calcined. A retort (A) of iron, brickwork, or fire-clay, is placed over the fire grate (G). Flues (F, F) are built around the retort, and through these the hot gases from the fire pass on their way to the chimney (E). * G i F U A ItF PT = 140 (for liquids lighter than water. Tempera- "130 + Be. ture 17.5 C.). The pyknometer is not very often used in technical work, but a brief description of it may not be out of place here. It consists of a small bottle, having ground into its neck a capillary tube enlarged at its upper end, to form a reservoir which is closed by a stopper. The tube is removed and the bottle filled with the liquid to be tested; the tube is then inserted tightly, the liquid displaced rising through the capillary to the enlarged part of the tube. The stopper is then loosely inserted and the bottle placed in a bath at the temperature at which the density is to be taken. When the bottle and contents have reached this temperature the stopper is taken out and the liquid in the reservoir removed by means of absorbent paper, until the level of the liquid recedes within the capillary to a mark thereon. The stopper is then tightly inserted and the bottle removed from the bath, and after cleaning and dry- ing its outside, allowed to stand until it reaches the normal tempera- ture of the room. It is then weighed, and the density of the liquid is calculated from its known volume, previously determined by cali- bration of the bottle. (For determining the density of solids by means of the pyknometer, see T. E. Thorpe's Dictionary of Applied Chemistry, Vol. III., p. 528.) Westphal's balance is a special form of balance for determining the density of liquids. A glass plummet of known weight and volume is suspended from the beam by a fine platinum wire, and *C. F. Chandler, Proc. Nat. Acad. Sciences, 1881. t Alkali-makers' Handbook (Lunge and Hurter), p. 175. 24 OUTLINES OF INDUSTRIAL CHP]MISTRY is submerged in the liquid to be tested. The weight which the plummet loses by this submersion is the weight of the volume of liquid it displaces. The characteristic feature of the instrument is the decimal graduation of the beam, with the use of riders of 0.1, 0.01, and 0.001 part of the weight of the water displaced by the plummet. This permits the actual specific gravity to be at once read off on the beam, as soon as the latter has been brought to equilibrium with the plummet suspended in the liquid in question. FUELS. Fuels are substances which, when burned with air, evolve heat with sufficient rapidity and in sufficient quantity to be employed for domestic or industrial purposes. There are three classes of fuel : solid, liquid, and gaseous. In the majority of these the essential constituent is carbon, but in many of them hydrogen is also an important ingredient. In rare cases sul- phur, phosphorus, silicon, or manganese may take part in the com- bustion; but for the purposes for which fuel is ordinarily used these constituents are deleterious. Oxygen is sometimes regarded as advantageous, but not always. Nitrogen may cause a direct loss of calorific power, owing to its dilution of the combustible gases, but in most solid fuels the percentage of nitrogen is so small that its effect is negligible. SOLID FUELS The solid fuels are wood and other matter containing cellulose, peat, lignite or brown coal, bituminous coal, anthracite, charcoal, and coke. Wood consists of cellulose (C 6 H 10 5 ) W , resins, lignine, various inorganic salts, and water. The quantity of water present has great effect on the heating value and ranges from 25 to 50 per cent in green wood, and from 10 to 20 per cent in air-dried wood. Wood cut in the spring and summer contains more water than that cut in the early part of the winter. A cord of hard wood, such as ash or maple, is about equal in heating value to one ton of bitumi- nous coal ; soft woods, such as pine and poplar, have less than half this amount. Wood burns with a long flame and makes compara- tively little smoke; but its calorific intensity is low, averaging from 3000 to 4000 C. per kilo of air-dried wood. It is, however, easily kindled, the fire quickly reaches its maximum intensity, and FUELS 25 a relatively small quantity of ash is formed. Wood is too expensive for industrial use, except in a few special cases, where freedom from dirt and smoke is necessary. Of other cellulose materials, shavings, sawdust, and straw are used for fuel in some places. They are bulky and difficult to handle, while their heat value, which depends on the amount of moisture they contain, is seldom more than from one-third to one-half that of good coal. Such waste matter as spent tan-bark and begasse (crushed sugar cane), and the pulp from sugar beets is sometimes used for fuel for evaporation or for steam, but owing to the large amount of moisture they contain, the heat value is very low. Peat is the product of slow decay of mosses, especially Spliag- nacece, under water. It is of little importance in this country, but is extensively used in parts of Europe where it is found. Since it contains a large amount of water and inorganic matter, its calorific power is not high, averaging from '3000 to 4000 C. per kilo. It is dug from the bogs and dried in the air, sometimes being heavily compressed to reduce its bulk. As thus prepared, it contains from 15 to 20 per cent of moisture and from 8 to 12 per cent ash. It is used considerably as a packing material, owing to its soft and spongy consistency. Lignite or brown coal is intermediary between peat and bitu- minous coal. It was probably formed from swamp plants which decomposed under water, and is geologically of more recent forma- tion than true coal. It is dark brown or black in color, and its texture is fibrous, earthy, or sometimes vitreous. It usually con- tains from 15 to 20 per cent of moisture, a large quantity of ash, and often a considerable amount of sulphur. It burns freely with a long flame, producing much smoke, and its calorific power varies from 4000 to 5500 C. It is extensively used for heating steam boilers and evaporating pans, and for domestic fires. Bituminous coal is the most important of all fuels. There is a great variety in the kinds of coal classed under this name, but they differ chiefly in the amount of volatile matter, which ranges from 20 to 50 per cent. They were all formed from similar sources, the varieties having resulted from pressure and from exposure to heat. The specific gravity varies from 1.25 to 1.75. They are clas- sified according to their behavior when burning, as fat, caking, and non-caking. Fat coals usually have a dull lustre, are very rich in volatile matter, sometimes containing as much as 50 per cent, and burn with a long, smoky flame, sometimes caking in the fire. Non- caking coals are those which burn freely, with little smoke, and do 26 OUTLINES OF INDUSTRIAL CHEMISTRY not cake. The caking coals burn with a smoky flame and fuse or sinter together. The formation of coal is probably due to a slow decomposition of cellulose matter, under fresh water, by which marsh gas (CH 4 ) and carbon dioxide (C0 2 ) were eliminated. The composition of a typi- cal coal, as shown by the analysis of good samples, may be repre- sented by the symbol (CJH.x) 2 ), and assuming this, the change of cellulose may be represented by the equation : 6 (C 6 H 10 5 ) = 3 CH 4 + 7 C0 2 + 14 H 2 O + C^O* Various changes were afterwards brought about by the heat and pressure within the earth's strata, and the character of the coals modified in many cases. Thus, more or less of the volatile constit- uents were removed, and the coal itself compressed to a very hard, compact mass. When this process went to the extreme, nearly the whole of the volatile constituents were expelled, and the resulting product is the hard coal known as anthracite. Anthracite coals are nearly pure carbon, are very hard and dense, have a very high lustre, and contain but little hydrogen or volatile matter. They burn with a slight flame, form no smoke, have no caking properties, and are difficult to ignite. Their specific gravity is high, being nearly 1.75 in good Lehigh coal. They have a calorific value of from 9000 to 9500 C. Between bituminous and anthracite coals are a number of semi- anthracites, which cannot be classed in either variety. Coal deteriorates considerably when stored, owing to the escape of some of its volatile constituents. There is a popular idea that wetting coal before burning increases its heating capacity ; but this is a fallacy, for a loss of heat results. The average composition of various coals is here tabulated for comparison : Brown coal ...... 1.30 20.9 50.9 10.2 18* Bituminous coal (W, Va.) . - 23.96 67.32 8.72 t Steam coal (Cumberland) . 1.33 15.13 74.53 10.34 . t Anthracite (Pa.) .... 1.56 6.89 91.64 1.47 t Anthracite (R.I.) . ,-Vv 1.85 10.50 85.84 3.66 t Charcoal is made by the dry distillation of wood, at a tempera- ture of from 400 to 450 C. This is done in heaps, or in closed * Gas and Fuel Analyses for Engineers, A. H. Gill, p. 43. t Fuels, Mills and Rowan. FUELS 27 retorts. All the volatile matter is driven off, and the residue con- sists of carbon and the inorganic constituents of the wood. Good charcoal is porous, brittle, with conchoidal fracture, and retains the form of the wood, but has only about three-fourths of the volume and usually about 20 per cent of the weight of wood. It burns with but slight flame, without smoke, and is easily ignited. Containing but little sulphur or phosphorus, it is especially useful in making some high grades of iron and steel. Its calorific intensity is about 7000 C. In this country the most of the charcoal is made by burning wood in "charcoal pits." The wood is heaped in a hemispherical pile around a central opening, and covered with earth and sod, leaving only a few small draught holes near the bottom. Then it is ignited at the centre and allowed to burn until the whole pile is on fire. A smoulder- ing combustion takes place, largely at the expense of the oxygen and hydrogen of the wood fibre, forming water, carbon dioxide and volatile hydrocarbons, which escape. The draught holes are then all closed and the pit is kept carefully covered until the fire smothers and the char- coal is cold. By carbonizing in pits nearly all the volatile matter is lost, or at best, only a part of the tar is saved and the yield of charcoal is only 20 per cent by weight of the wood. But if the process is carried on in retorts, a large amount of gas, pyroligneous acid, and tar is col- lected (see p. 257), and about 30 per cent of charcoal is obtained, together with nearly 40 per cent of pyroligneous acid and 4 per cent of tar. Coke is made by the destructive distillation of coal. It has a silvery white lustre, an open, porous structure, and a metallic ring when struck. It contains all the ash-forming materials of the coal, but nearly all volatile matter and sulphur have been eliminated. For metallurgical purposes it must be sufficiently strong to sustain the weight of the charge in the furnace without crushing. The calorific value is from 8000 to 8500 C. It burns without smoke and FIG. 13. OF THK -T TTTT '-r*fc / 28 OUTLINES OF INDUSTRIAL CHEMISTRY with but little flame, and does not cake. It is made in kilns of two general types: The "bee-hive" coke oven (Fig. 13) is made of brick, with a circular opening (A) at the top and a door (B) at the side, through which the coke is drawn. A part of the coal is burned, in order to carbonize the remainder. As a rule, no attempt is made to save the volatile products or the tar. The yield of coke amounts to only 60 or 65 per cent of the weight of the coal. Coking ovens in which the by-products are saved, are much used in Germany, and to a slight extent in this country. There are sev- eral kinds, but the Otto-Hoffmann, the Simon-Carves, and the Semet- Solvay ovens are most used. In these, the ammonia and coal tar are recovered, and a coke suitable for metallurgical purposes is obtained. The waste gas is employed to heat the retorts. i MI nnnnn-nnnnnnnnpnnnnnnnnn n nnnry r ir liliiiS^^ : ^;*?S* .- .,'-.'.'.,-; '-^ FIG. 14. The Otto-Hoffmann oven is shown in Fig. 14. The retorts are narrow chambers (0) about 30 feet long, 5 feet high, and 22 inches wide, having doors at each end, and heated by vertical flues (T, T) in the walls. Coal is charged through (F, F), while the gases and tar pass off through (A, A) to the hydraulic main (V, V). The gas for heating enters from pipe (G), mixes with hot air from the re- generator (R), and burns in the flue (S) under the retorts, the flame passing up through the flues (T, T), and down through (T', T') to (S'), from which the products of combustion pass through the regen- erator (R r ) and heat it. After a time, the flow of gases is reversed, the producer gas enters through (G f ), and air through (R'), burning together in (S'), while the products of combustion escape through (R). The volatile matter given off from the coal, passes through (V) to washers and scrubbers (see Illuminating Gas), which remove tar and ammonia, while the gas is stored in a holder, to be led, later, through (G, G'), and burned under the retorts. FUELS 29 The Simon-Carves oven (Fig. 15) is also a long, narrow retort (A) with doors at each end, but the heating flues (F, F) are set hori- zontally in the retort walls. The volatile matter escapes from the retort through (B), passes to the washer and scrubber, whence the purified gas goes to the holder, from which it is drawn as needed, through (G), and burned with hot air. FIG. 15. The Semet-Solvay oven (Fig. 16) also has horizontal flues, but deeper and narrower retorts than the two just mentioned. Each retort has an independent set of flues which are placed in the retort A - Charging Holes D - Chimney Canal B - Gas uptake p . Heating Flues C - Gas Inlet to Heating Flues R - Wall between Retorts FIG. 16. lining and backed by a heavy brick retaining wall ; this supports the weight of the roof arch, and also holds the heat during the drawing and charging of the retort. Thus the flue walls can be made much thinner than in the ovens previously mentioned, and the oven works more rapidly, giving a larger yield of coke, and will coke coals which are low in volatile matter. The lining can easily be replaced with- out rebuilding the entire oven. The retorts are usually about 30 30 OUTLINES OF INDUSTRIAL CHEMISTRY feet long by 16 inches wide, and 5J feet deep, and hold about 4}- tons of coal at each charge. No regenerative heating is used, the heat being retained in the walls between the retorts. A number of these ovens have been recently introduced into this country and give excellent results. LIQUID FUELS The most important liquid fuels are crude petroleum, and various oily residues obtained in distilling petroleum, shale oil and coal tar. Crude petroleum and the residuum from the manufacture of burn- ing oils and lubricators, are the chief sources in this country. The residuum from Russian petroleum, called " astatki" is very exten- sively used in southern Russia. Crude petroleum is easily regulated so as to burn without smoke or soot, giving a steady heat and requiring no stoking. It is less bulky, and from two to two and a half times as efficient as anthra- cite coal. Its calorific intensity is about 20,000 C., and it evaporates about 16 Ibs. of water to one pound of oil. One pound of coal-tar residue evaporates 13 Ibs. of water. Liquid fuel is coming into more general use every year, espe- cially where long flame and high temperature are desired. It is usually burned as spray, being forced into the furnace by a large atomizer supplied with an air blast or superheated steam. GASEOUS FUELS Gaseous fuels may be divided into four classes : natural gas, producer gas, water gas and coal gas. Natural gas exists already formed in the earth, and is obtained by boring tube wells, similar to petroleum wells. Its essential heat- producing constituents are methane (CH 4 ) and hydrogen. It is the cheapest and most efficient of all fuels, when properly burned ; but it requires a large amount of air for its combustion, and special burners must be used. Producer gas is made by forcing air through a bed of incan- descent coal or coke, in specially constructed furnaces. Its essential heat constituent is carbon monoxide (CO), of which it contains about 28 to 30 per cent. But it also contains about 63 per cent of nitrogen from the air, and some carbon dioxide, which dilute the gas very much, and reduce its calorific intensity greatly. It is extensively used for fuel, because of its cheapness, cleanliness, and the regularity of the temperature obtained. FUELS 31 In converting carbon to carbon monoxide, about one-third of the heat value of the carbon is set free, thus heating the gas very hot. If it is at once led, through short flues, into the combustion chamber and burned with air, a much higher temperature is ob- tained, than if it is permitted to cool before burning. In modern gas producers, this waste of heat is largely avoided by introducing steam into the incandescent coal, together with the air ; the steam dissociates into hydrogen and oxygen, and the latter gas combines with the carbon, forming more carbon monoxide. These gases, mixing with the producer gas, increase its calorific intensity. FIG. 17. FIG. 18. In the Siemens gas producer* (Fig. 17), the coal is introduced at (E), falls upon the step grate (B, B), and is brought to incan- descence by air entering through the openings while steam is injected from the pipe (C), and the gas formed escapes through (A, A). The ashes fall through the grate (G) into the pit, which is kept closed except when cleaning. A more modern producer (Taylor's) is shown in Fig. 18. The coal rests on a bed of ashes (A, A), and air is forced through the blast pipe (F), raising the fuel to incandescence. The gas formed passes out by the pipe (E). The grate (G) is made to revolve by the crank at (B), and the ashes fall over the edge of the grate at (H). The bed of ashes is kept about 3 feet deep on the revolving bottom at all times. Steam from the pipe (D) is intro- * Jour. Soc. Chem. Industry, 1885, 441. 32 OUTLINES OF INDUSTRIAL CHEMISTRY duced with the air through the blast pipe, which is provided with a hood to disseminate them through the fuel. In all producer gas plants, the regenerative heating system is used. The Siemens regenerative furnace is a type of this style of heating. This furnace is represented in its simplest form in Fig. 19. The material to be heated is placed on the hearth of the furnace (A). There are four passages, B, C, D, and E, filled with loosely piled fire-brick called the "checker work." On their way to the chimney, the hot gases from the furnace pass through and heat two checker works, e.g. (B) and (C). When they are sufficiently heated, the flow of furnace gases is turned into (D) and (E), through which they pass to the chimney. Then fuel gas is conducted through the hot passage (B), to the furnace (A), where it mixes FIG. 19. with air which has been heated by passing through (C). The tem- perature of (A) is thus much higher than if the air and gas arrived at (A) cold. While (B) and (C) are being thus cooled, (D) and (E), are being heated by the furnace gases, and after a time, the dampers are turned, and the gas made to pass through (E), and the air through (D), while the combustion products pass through (B) and (C) to the chimney. Hence the process is an alternating one, the checker works on one side being heated, while those on the other are giving up their heat to the gas and air respectively. Since the interstices between the bricks of the checker work frequently become clogged with ashes and soot, the combustion gases are some- times passed through flues containing narrow tubes, through which the gas and air are passing to the furnace, in a direction opposite to that taken by the fire gases. The waste gases from blast furnaces contain over 30 per cent FUELS 33 of carbon monoxide and about 63 per cent of nitrogen. These gases are largely employed near the furnaces for heating purposes. Water gas is sometimes used as a fuel, but oftener as a con- stituent of illuminating gas (p. 266). It is made by blowing steam over incandescent anthracite coal or coke, and is a mixture of about 45 per cent each of carbon monoxide and hydrogen, with small amounts of nitrogen, oxygen, and carbon dioxide. For the best re- sults, the temperature must not fall below 1000 C. ; above this point, the reaction is : C + H 2 = 2 H + CO. But at lower temperatures, the following takes place : C + 2 H 2 = C0 2 + 4 H. Fuel water gas burns with a pale blue or colorless flame, without smoke or soot. Its calorific value is about 3000 C. per cubic meter. One kilo of coke produces about 1.13 cubic meters of water gas, but anthracite gives a better yield. The fuel is brought to incandescence by a blast of air, and during this part of the process the heat generally goes to waste. When it is white hot, the air is cut off, and the steam is turned on ; decomposition occurs, according to the first reaction above. As soon as the temperature falls below 1000 C., the steam is cut off and the air blast turned on till the coal is again white hot. Thus alternate blowings of air and steam are carried on. The generator gas produced by the air blast is sometimes saved and used, but in making illuminating gas it goes to waste. For illuminating gas, this water gas is " enriched " with naphtha (p. 266). Coal gas is made by distilling bituminous coal in retorts (p. 268). It contains hydrogen and marsh gas in large quantities, about 40 per cent of each, besides small amounts of carbon monoxide, carbon dioxide, nitrogen, oxygen, and hydrocarbons of the C n H 2w and C n H 2n _ 2 series, which impart illuminating properties. It has a limited use in domestic stoves and as a source of power in gas engines. The average composition of the various fuel gases is shown in the following table * : H CH 4 CO C 2 H 4 C0 2 N O H 2 S Natural gas (Ohio) ... 2.2 92.6 0.5 0.3 0.3 3.6 0.3 0.2 Coal gas 47.0 40.5 6.0 4.0 0.5 1.5 0.5 Water gas 45.7 2.0 45.8 4.0 2.0 0.5 Producer gas 6.0 3.0 23.5 1.5 65.0 * Gas and Fuel Analysis for Engineers, A. H. Gill. 34 OUTLINES OF INDUSTRIAL CHEMISTRY When burned with 20 per cent excess of air, and assuming that the escaping gases have a temperature of 500 F., 1000 cubic feet of gas will evaporate the following number of pounds of water, at from GOT. to 212 F.:- Natural gas 893 pounds * Coal gas 591 " Water gas 262 " Producer gas 115 " REFERENCES Liquid Futfl. B. H. Thwaite, London, 1887. (Spon.) Chemical Technology. Groves and Thorp. Vol. 1, Fuel, by Mills and Rowan, Phila., 1889. (Blakiston.) Feuerungsanlagen. F. Fischer, Karlsruhe, 1889. Liquid Fuel. E. A. B. Hodgetts, London, 1890. (Spon.) Die Feuerung mit fliissigem Brennmaterialien. I. Lew, 1890. Fuels. H. J. Phillips, London, 1891. Fuels. C. W. Williams and D. K. Clark, London, 1891. Taschenbuch fur Feuerungstechniker. F. Fischer, Stuttgart, 1893. (Enke. ) Contribution a Pe'tude des Combustibles. P. Mahler, Paris, 1893. Die chemische Technologie der Brennstoffe. F. Fischer, Braunschweig, 1896. (Vieweg.) A Treatise on the Manufacture of Coke and the Saving of By-Products. John Fulton, Scranton, Pa., 1895. Mineral Industry, 1895, 215, W. H. Blauvelt. (By-Product Coke Ovens.) Die Chemie der Steinkohle. F. Muck, Leipzig, 1891. (W. Engelmann.) Die Gasfeuerungen fur Metallurgische Zwecke. A. Ledebur, Leipzig, 1891. (Felix.) Grundlagen der Koks-Chemie. Oscar Simmersbach, Berlin, 1895. (J. Springer.) Gas and Fuel Analysis for Engineers, A. H. Gill, New York, 1896. (Wiley & Sons.) WATER The industrially important sources of water may be thus sum- marized : 1. The sea. 2. Eain water. 3. Surface waters, consisting of a. Flowing waters (streams). b. Still waters (ponds, lakes, etc.). 4. Ground waters, furnished by a. Springs. b. Shallow wells (penetrating but one geological stratum). c. Deep wells (passing through more than one such stratum). * Orton, Geology of Ohio, Vol. VI., p. 644, WATER 35 The impurities contained in water depend upon the character of the ground with which it has been in contact ; they may be classed as soluble and insoluble. The more common soluble impurities are calcium chloride, calcium sulphate, calcium bicarbonate, magnesium chloride, magnesium sulphate, magnesium bicarbonate, sodium chlo- ride, sodium sulphate, sodium carbonate, and organic matter. The usual insoluble impurities are sand, clay, and organic matter. In- soluble suspended matter can be removed by allowing the water to stand and drawing off the clear portions from the sediment, or by filtration (p. 11). If the water contains much organic matter, a layer of coke or charcoal dust is sometimes put in when building a sand filter. A water may contain large amounts of soluble im- purities, and yet answer very well for washing and levigating, while for use in condensers and cooling apparatus this scarcely need be considered at all. Soluble matter may be injurious for some pur- poses and beneficial for others, but as a rule water carrying much suspended matter must be purified. The soluble impurities cause the most difficulty in technical work, especially when the water is to be used in steam boilers. According to the nature of these impurities, water is hard, soft, saline, or alkaline. Hard water contains one or more of the salts of calcium, mag- nesium, iron, or aluminum in solution, and is usually defined as one which precipitates soap from solution. Hence it is customary to determine hardness by titration with a standard soap solution. Temporary hardness is caused by the presence of the bicarbonates of calcium or magnesium, while permanent hardness is principally due to the neutral chlorides and sulphates of these metals. The neutral carbonates of calcium and magnesium are insoluble, but if carbon dioxide is present in the water, they dissolve, probably forming the bicarbonates CaH 2 (C0 3 ) 2 and MgH 2 (C0 3 ) 2 . Soft waters contain very little mineral matter. Eain water as it falls is very soft, and if it could be collected uncontaminated would be far the best for most purposes. Natural soft waters usually fall upon ground nearly free from lime or magnesia, and collect in streams or ponds by percolating through the soil. Very often the soil contains peat or other decayed vegetable matter, from which the water may derive organic impurities or coloring substances, which affect its use for many purposes. Peaty waters often contain organic acids or other material which causes them to attack iron or lead. Saline and alkaline waters are those in which large quantities of soluble sulphates, chlorides, or carbonates occur. They frequently 36 OUTLINES OF INDUSTRIAL CHEMISTRY contain bromides and other salts. Sea-water and certain mine waters containing sulphates of copper, iron, or other metals, are the most important of the saline group. Alkaline waters, e.g. the " alkali " waters of the western states, contain considerable quantities of the alkaline carbonates or sulphates. The purification of water for use in the industrial arts often pre- sents considerable difficulty owing to the nature of the impurity or the magnitude of the plant necessary for large works. When pos- sible the quality of the water should be considered in locating the works, so that little or no purification may be necessary. However, in most localities the boiler water needs some treatment. The following are the usual methods of removing temporary hardness : 1. Treating with sodium carbonate or sodium hydroxide. CaH 2 (C0 8 ) 2 + Na 2 C0 3 = CaC0 3 + 2NaHC0 3 ; CaH 2 (C0 3 ) 2 + 2 NaOH = CaC0 3 + Na 2 C0 3 + 2 H 2 0. 2. Treating with calcium hydroxide or " milk of lime." CaH,(C0 3 ) 2 + Ca(OH) 2 = 2 CaC0 3 + 2 H 2 0. If possible, it is best to use only the clear calcium hydroxide solution obtained by allowing the undissolved lime to settle, but this requires much space for precipitating and settling tanks. If the " milk of lime " is used, the proper quantity of quicklime is carefully weighed, slaked in a small amount of water, and the " milk " then thoroughly mixed with the water to be purified. This is Clark's process. The sludge of calcium carbonate is best removed by the filter press (p. 12). 3. Treating with barium hydroxide or with sodium oxalate. CaH 2 (C0 3 ) 2 + Ba(OH) 2 = CaC0 3 + BaCO 8 + 2 H 2 O ; CaH 2 (C0 3 ) 2 + Xa 2 C A = CaC A + 2 NaHC0 3 . These are very effective, but are too expensive for most purposes. 4. Heating the water to boiling, either in the open air or in special heaters. This decomposes the bicarbonates. CaH 2 (C0 3 ) 2 = CaC0 3 + H 2 + C0 2 . The permanent hardness is less easily remedied, for in every case treatment of the water leaves some substance more or less deleterious in solution, as shown in the following reactions : 1) CaS0 4 + Na 2 C0 3 = CaC0 3 +NaJ30 4 ; 2) CaS0 4 + Ba(OH) 2 = BaSO 4 + Ca(OH) 2 ; 3) CaS0 4 + BaCl 2 = CaCl 2 + BaS0 4 ; 4) CaCl 2 + Na 2 C 2 4 = WATER 37 Magnesium and iron salts react like the calcium salts, though the iron precipitates as hydroxide when sodium carbonate is used. When water containing soluble impurities is evaporated in a boiler, a more or less coherent deposit called boiler scale forms on the plates and tubes. This is chiefly composed of carbonate and sulphate of calcium, while in some cases magnesium hydroxide, mag- nesium sulphate, iron hydroxide or oxide, silica, and organic matter are present. Calcium carbonate alone forms a porous and non-adher- ent scale, which is easily removed by "blowing off" the boiler. Calcium sulphate forms a hard, compact scale, which adheres very firmly. Scale formation is detrimental in several ways ; since it is a poor conductor of heat, the fires must be driven harder; it sepa- rates the water from the boiler plates, which are thus overheated and rapidly burned out. Moreover, the tubes and feed pipes become clogged, and their efficiency is much reduced. The decomposition of bicarbonates of calcium and magnesium by heat, which has already been mentioned, may take place in the boiler. Then, too, calcium sulphate is rendered less soluble by the high temperature and pressure within the boiler, and is deposited as scale. If the water carries magnesium sulphate, this deposits as monohydrated salt (MgS0 4 H.,0). Magnesium chloride is very troublesome, for it not only forms a scale, but also attacks the iron of the boiler, the probable decomposition being shown in the follow- ing equation : MgCl 2 + Fe + 2 H,0 = Mg(OH) 2 + FeCL + H 2 . For the removal of "temporary hardness," and to a certain extent, of calcium and magnesium sulphates as well, "feed water heaters" are advantageous. The water is heated in these, and the scale-forming matter deposited, before it is delivered into the boiler. A recent suggestion * is the use of sodium bichromate within the boiler, as a precipitant for both "temporary" and "permanent" hardness. The reactions involved are the following : CaH 2 (C0 3 ) 2 + Na 2 Cr 2 7 = CaCr0 4 + Na 2 Cr0 4 + 2 C0 2 + H 2 ; CaS0 4 + Na 2 Cr 2 7 = CaCrO 4 + Na 2 S0 4 + Cr0 3 ; MgS0 4 + Na 2 Cr 2 7 = MgCr0 4 + Na 2 S0 4 + Cr0 3 . It is claimed that the calcium and magnesium chromates precipi- tate in the boiler as a loose, non-adherent mass, which is removed by "blowing off" daily. It is further claimed that the free chromic acid does not attack the boiler iron. * Wyatt, Eng. Mining Journal, Vol. LX., 220. 38 OUTLINES OF INDUSTRIAL CHEMISTRY Much care is necessary to avoid an excess of the chemical added. As a rule, the water should be treated before it goes into the boiler, but if the scale-forming material does not amount to more than ten grains per gallon, the purification may be done in the boiler itself, followed by a daily "blowing off." A good circulation of water in the boiler tends to keep the precipitated material loose so that it may be easily blown out. Attempts are made to prevent the scale from attaching itself by introducing oil with the water. Kerosene is said to be the best for this purpose ; but animal or vegetable oils may be decomposed by the heat and pressure of the steam, forming glycerine and free fatty acid. This acid may injure the boiler or the pipes and valves of the pumps. Mineral oils do not decompose in this way, but may enter into the scale themselves. A great many proprietary "anti-scale" preparations are sold, many of which are of no particular value. Most of them are to be used inside the boilers. Some are supposed to act chemically on the impurities, and others are mechanical, preventing the adherence of the scale. The former usually contain soda-ash, caustic soda, barium hydroxide, or sodium phosphate or sulphite. Tannin, usually in the form of sodium tannate, is sometimes employed, by which the calcium and magnesium are separated as tannates. Saline and alkaline waters are troublesome in a boiler, causing "priming," i.e. the passage of foam and water through the steam chest with the steam. Sodium carbonate and sulphate are particu- larly liable to induce priming, hence an excess of these salts must neither be added nor formed in the process of purification. One of the worst complications in boiler water is the simultaneous presence of large quantities of alkaline chlorides and sulphates, together with magnesium sulphate. The magnesium sulphate forms a bad scale, and yet its removal, by means of sodium carbonate, makes the water liable to prime. This difficulty is of frequent occurrence in some of the western states, and no satisfactory method of treating such waters has yet been proposed. In the case of locomotives, the usual remedy is to transfer them periodically to other parts of the road, where a soft water can be obtained, which will dissolve part of the scale, and thus loosen it so that it may be blown out. In regard to the character of the water needed for the various manufacturing processes, only a few general remarks can be made here. A soft water is desirable for a soap works or a bleachery, since the insoluble calcium soaps would otherwise be precipitated and cause a loss of soap, or injury to the goods. A hard water will SULPHUR 39 sometimes cause unevenness in the shade of color in dyeing, but for some dyes, e.g. Turkey red on cotton, it is beneficial. Water con- taining calcium sulphate is considered best for use in brewing. Hardness of the water is of little consequence to the paper maker, but suspended matter or deep color is bad. Suspended matter or soluble coloring matter is also injurious for a bleachery, a dye works, a starch factory, or in fact for almost any industry where the water conies in direct contact with the goods or product. REFERENCES A Treatise on Steam Boilers. R. Wilson, London, 1875. (Lockwood.) Die Chemische Technologic des Wassers. F. Fischer, Braunschweig, 1880. (Vieweg.) Die Verhiitung und Beseitigung des Kesselsteins. W. Storck, Halle, 1881. (W. Knapp.) A Treatise on Steam Boiler Incrustations. C. T. Davis, Washington, 1884. (Industrial Publishing Co.) Water Supply. William R. Nichols, 1886. Report on Boiler Waters of the C. B. & Q. R. R. W. L. Brown, Chicago, 1888. (H. O. Shepard & Co.) Die Verunreinigung der Gewasser. Dr. K. W. Jurisch, Berlin, 1890. (R. Gartner.) Das Wasser. F. Fischer, Berlin, 1891. (J. Springer.) Das Reinigen von Speisewasser fur Dampfkessel. Dr. A. Rossel, Winterthur, 1891. (Moritz Kieschke.) L'Eau dans L'Industrie. P. Guichard, Paris, 1894. (Bailliere.) The Purification of Boiler Feed Waters. Dr. F. Wyatt. (Eng. Min. Jour., 1895, 220.) J. Soc. Chem. Ind., 1884, 51. J. H. Porter. J. Soc. Chem. Ind., 1886, 267. Macnab and Beckett. J. Soc. Chem. Ind., 1891, 611. Archbutt and Deeley. SULPHUR Most of the sulphur used in the industries is derived from the native mineral, which is found in many places, but usually in vol- canic regions. It is always impure, being mixed with gypsum, aragonite, clay, or other matter, in the interstices of which the sulphur is deposited. The formation of sulphur beds may have occurred by the reaction of gases, such as hydrogen sulphide and sulphur dioxide, with each other or with oxygen ; or by the decom- position of metallic sulphides through the agency of heat; or by the reduction of sulphates, especially of calcium sulphate. 40 OUTLINES OF INDUSTRIAL CHEMISTRY The first is probably the most frequent mode of deposition, and may be observed at the present time in many volcanic districts where hydrogen sulphide and sulphur dioxide are escaping. The reactions are the following: S0 2 + 2 H 2 S = 2 H 2 O + 3 S ; These gases are always present where volcanic action is in progress. The reduction of sulphates has probably caused the formation of some stratified deposits. By far the largest part of the world's supply of sulphur comes from Sicily, but some is obtained in Japan, Italy, Greece, and in the United States, particularly near Humboldt, Nevada, at Clear Lake, California, and in Louisiana. But the price of the foreign product is too low to allow profitable working of the deposits in this country. In Sicily it is disseminated through the matrix, sometimes in considerable masses of nearly pure sulphur, but usually in fine seams or grains. The methods of obtaining it are very crude and wasteful. The mines are for the most part open pits, ranging from 200 to 500 feet in depth, and the ore is carried to the surface in baskets or sacks by laborers, who ascend by inclined paths on the walls of the pit. In a few of the better mines, however, hoisting machinery is now used, but only after overcoming the determined opposition of the laborers. The ore is generally refined in a very simple manner, the process being carried on in kilns called " cal- ceroni." As usually constructed, these are shallow pits, about 30 feet in diameter, with walls about 10 feet high, made tight with mortar. They are generally built on a hill-side, and the sloping bottom is beaten smooth. The ore is arranged in the calcerone so as to leave a few vertical draught holes from top to bottom of the heap, which is fired by dropping burning brush or straw into these openings. The sulphur, forming from 25 to 40 per cent of the ore, burns freely r and when the heap is well on fire, the draught holes are closed, the calcerone covered with spent ore, and the whole left for several days. The heat given out by the burning of part of the sulphur is sufficient to melt the remainder from the gangue, and it collects in a pool near a tap-hole, made in the wall at the lowest point. At intervals of a few hours, the melted sulphur is drawn off into moulds. If the temperature rises above 180 C., there is a large formation of plastic sulphur, which will not flow from the SULPHUR 41 tap-hole. The time necessary to burn out a calcerone varies from 35 to 80 days, according to its size, the weather, and the nature of the impurities ; e.g. much gypsum retards the process owing to the water it contains. Usually from a quarter to a third of the sulphur is lost as sul- phur dioxide during the burning. As this causes much damage to vegetation in the vicinity, the burning of calceroni is prohibited during the spring and summer months. It has been proposed to separate sulphur by heating with hot air, with steam under pressure or with superheated steam. But this is unprofitable on account of cost of fuel in those regions where sulphur occurs. It may be separated by a solvent, such as carbon disulphide, which may be recovered afterwards, but this necessitates an expensive plant. But treatment with a solution boiling above the melting point of sulphur has proved successful for some ores. The ore is placed in an iron basket or crate and suspended in a boiling solution of calcium chloride,* which boils at 125 C. Since sulphur fuses at 115 to 120 C., it melts and flows away from the matrix of stones, etc. ; passing through the basket meshes, it falls to the bottom of the tank, and is drawn off and cast in moulds. After the sulphur is melted out, the basket of hot stones is lowered into a tank of water, which is thus heated by the hot stones, while it removes the calcium chloride from them. This warm water is then used to replace that lost by evaporation from the boiling calcium chloride solution. This process causes no loss of sulphur as sulphur dioxide, and no nuisance is created, while a fairly pure product is obtained. The calcium chloride used is a waste product of the ammonia soda industry. In this country, extraction with superheated steam f has been tried and yields an excellent quality of sulphur, without any forma- tion of sulphur dioxide. But the cost of fuel in the West is an obstacle to further development. In Louisiana, it is proposed to force steam, under pressure, through driven wells or tubes, into the sulphur deposit. The sulphur, having been liquefied by the heat, is forced to the surface by the steam pressure, through a small pipe inside of the steam pipe. The industrial success of the process is as yet somewhat problematical. Iron pyrites (FeS 2 ), when heated in a closed retort, yields one atom of sulphur per molecule of sulphide, and has been used as a source of sulphur, but the process is not now employed. * Vincent ; Bull. Soc. Chim., 40, 528. Am. Chem. Jour., VI, 63. t J. Soc. Chem. Ind., 1887, 439, 442; 1889, 696.. 42 OUTLINES OF INDUSTRIAL CHEMISTRY A small portion of the sulphur of commerce is that known as recovered sulphur. This is chiefly obtained from the calcium sul- phide waste of the Leblanc soda process (p. 73), although a small quantity comes from the residues from the purification of illuminat- ing gas by means of moist iron oxide. When iron oxide is used to purify gas, the following reactions take place : Fe 2 O 3 3H 2 + 3H 2 S = 2FeS + S + 6 H 2 0. On exposure to the air, this moist ferrous sulphide is oxidized thus : 2 FeS + 3 H 2 + 3 O = Fe 2 O 3 - 3 H.O + 2 S. Hence the iron oxide is "revivified" and may be used again, and on exposure to the air, oxidation of more ferrous sulphide takes FIG. 20. place with further deposition of sulphur in the mass. After repeat- ing this operation a number of times, there is sufficient free sulphur to be profitably distilled by heating in a retort. But the quantity of recovered sulphur is very small in comparison with the total annual demand, and there seems but little prospect of any great advance in the industry. With the exception of recovered sulphur, the above processes yield a crude impure product, which, however, is good enough for a large number of manufacturing operations. But for some pur- poses a further purification is necessary. This is generally done by distillation in a cast-iron retort, or in Dejardin's apparatus (Fig. 20). The crude sulphur is melted in the vessel (C), heated by the waste heat of the fire, and is then run into the retort (B), SULPHUR 43 heated directly by the fire. The vapors pass into the receiving chamber (E), which is usually made of brick. If the temperature of the chamber (E) is not allowed to rise above 110 C., the vapors condense at once to a fine powder, which is sold under the name of "flowers of sulphur.' 7 If the temperature of (E) rises much above 110 C., the vapors condense as a liquid, which is drawn off into moulds, forming the "roll brimstone" of commerce. The chief uses of crude sulphur are : for making sulphuric acid ; as a germicide in combating Phylloxera, a disease of the grape (this disposes of nearly one quarter of the yearly production); and in making ultramarine and carbon disulphide. The principal uses of refined sulphur are: for making gunpowder and matches, and for vulcanizing rubber. Sulphur melts at 115-120 C. ; it is a very poor conductor of heat and electricity, and dissolves easily in carbon disulphide, less readily in chloroform, benzol, turpentine, and other oils. Its specific gravity is 1.98-2.04. Sicily, owing to its favorable situation as a shipping point, the abundance of cheap labor, and the richness of its deposits will prob- ably continue to supply the major part of the sulphur consumed. But Japanese sulphur has become a considerable competitor with the Sicilian, and a deposit recently opened in one of the New Heb- rides islands (Tanna) gives promise of future importance. SULPHUR DERIVATIVES The most important sulphur compound is sulphur dioxide (S0 2 ). This is extensively made for the manufacture of sulphuric acid by roasting iron pyrites (p. 49). Liquid sulphur dioxide is now an article of trade, but the gas is usually made where it is to be used, by burning sulphur with a proper supply of air. It is occasionally made by decomposing sulphuric acid by means of copper or char- coal : 2 H 2 SO 4 + Cu = CuS0 4 + 2 H 2 + S0 2 ; 2 H 2 S0 4 + C = 2 H 2 + C0 2 + 2 S0 2 . Charcoal yields a gas which is not pure, but may be used for some purposes. Processes for the recovery of sulphur dioxide from furnace gases, by passing them through towers filled with coke, over which water trickles, have been proposed, but are not very practicable. Sulphur dioxide is used in making sulphuric acid ; as a bleaching agent for wool, hair, straw, and other tissues ; as a disinfectant and germicide; for use in ice machines; for making the acid sulphite 44 OUTLINES OF INDUSTRIAL CHEMISTRY liquor used in manufacturing wood pulp; for the preparation of sodium bisulphite ; and to a small extent in the leather and glucose industries. Substances such as wool and straw, when bleached by exposure to sulphur dioxide gas, slowly regain their original color on exposure to the light. The coloring matter is not destroyed, but probably unites with the sulphur dioxide to form a colorless compound, which slowly decomposes. Sodium bisulphite (NaHS0 3 ) is formed by saturating sodium, carbo- nate solution with sulphur dioxide : Na^CO, + H 2 O + 2 S0 2 = 2 NaHS0 3 + C0 2 . It forms a strong smelling solution used as an "antichlor" to remove excess of chlorine from the fibres of bleached cotton or linen goods. Its reaction is probably as follows : Ca (CIO), + 2 NaHS0 3 = 2 NaCl + CaS0 4 + H 2 S0 4 ; or, = Na 2 S0 4 + CaS0 4 + 2 HC1 ; 2 Cl + NaHS0 3 + H 2 = NaCl + H 2 S0 4 + HC1 ; or, = NaHS0 4 + 2 HC1. It also finds some use in other industries, such as chrome tannage, brewing, glucose, and starch making. The solution of bisulphite decomposes on evaporation, giving off part of the sulphur dioxide, and forming neutral sulphite of sodium. Calcium bisulphite [CaH 2 (S0 3 ) 2 ] is made by passing sulphur di- oxide into milk of lime. It is probably a solution of neutral sulphite in an excess of aqueous sulphurous acid. It is used in much the same way as the sodium salt. Hyposulphurous acid (H 2 S0 2 ) and hyposulphite of sodium are of some importance as powerful bleaching and reducing agents. The acid is formed in solution by the action of iron or zinc on aqueous sulphurous acid : H 2 S0 3 + Zn = ZnO + H 2 S0 2 . The zinc oxide then combines with another molecule of sulphurous acid, to form zinc sulphite and water. Sodium hyposulphite (NaHS0 2 ) is made when zinc is dissolved in sodium bisulphite : 3 NaHS0 8 + Zn = Na 2 Zn (S0 3 ) 2 + H 2 + NaHS0 2 . The zinc-sodium sulphite crystallizes, leaving the sodium hyposul- phite in solution. The latter salt is very unstable, rapidly absorbing SULPHURIC ACID 45 oxygen from the air, and should be made immediately before needed. It is much used for reducing indigo in the so-called " hydrosulphite vat." It is to be noted here that the salt sold in commerce under the name of " hyposulphite of sodium " is properly the thiosulphate ( Xa 2 S 2 3 5 H 2 0). This is made by digesting sulphur with a solution of neutral sodium sulphite or sodium hydroxide : 6 NaOH + 4 S = Na 2 S 2 O 3 + 2 Na^S + 3 H 2 0. Sodium thiosulphate is also obtained from the waste sulphide liquors of the Leblanc soda process (p. 83). It crystallizes with five mole- cules of crystal water, ISra 2 S 2 3 5 H 2 O, and is largely used in chrome tanning, in paper bleaching, and in photography. REFERENCES Sulphuric Acid and Alkali, Vol. 1, 2d Ed. G. Lunge, London, 1889. Mineral Resources of the United States. (1882-1893.) United States Consular Reports of the Sulphur Industry. Mineral Industry, Vols. 1-5. (1892-1896.) Journal Society Chemical Industry, 1882, 97. Journal Analytical and Applied Chemistry, 1892, 690. (K. F. Stahl.) SULPHURIC ACID Sulphuric acid is probably the most important of all chemicals, because of its extensive use in a very large number of manufactur- ing operations. Of the immense quantities made yearly, the greater part does not come upon the market ; for, being expensive and diffi- cult to ship, consumers of large amounts generally make their own acid. The commercial grades of acid have special names. A moder- ately strong acid (50-55 Be.), such as condenses in the lead cham- bers, is known as "chamber acid. 7 ' It contains from 62 to 70 per cent of H 2 S0 4 , and is strong enough for use in the manufacture of fertilizer, and for other purposes requiring a dilute acid. By con- centrating this chamber acid, an acid of 60 Be. is obtained, contain- ing about 78 per cent of H 2 S0 4 , which is siifficiently strong for most technical uses. Further evaporation in platinum or iron pans yields an acid of 66 Be., containing 93.5 per cent of H 2 S0 4 , and known as oil of vitriol. Faming or Nordhausen acid, which is still more con- centrated, is prepared by special means. It is essentially a solution of sulphuric anhydride (S0 8 ) in sulphuric acid. This is the acid which was prepared by the alchemists in the Middle Ages. 46 OUTLINES OF INDUSTRIAL CHEMISTRY In about the year 1740, Ward, an Englishman, began to make sulphuric acid on a moderately large scale. He burned sulphur and nitre (KN0 3 ) together, and condensed the vapors in glass vessels containing a little water. The dilute acid so formed was then con- centrated in glass alembics or retorts. In this way an acid was produced at a lower price than the fuming acid could be made, and the industry was soon established 011 a commercial scale. The reactions involved in Ward's process are the bases of the method now in use ; this consists in bringing together, under suitable condi- tions, sulphur dioxide, oxygen, and water as steam, in the presence of certain oxides of nitrogen. The latter probably act as carriers of the oxygen, causing it to unite with the sulphur dioxide and water to form the acid. The apparent reaction is : S0 2 + H a O + = H 2 S0 4 . But this does not represent the actual process, which is more complicated than it at first appears. Several theories have been advanced to explain the reactions occurring in the lead chambers, and the part taken by the nitrogen oxides, but the most generally accepted one, that of Lunge, regards nitrous anhydride (N 2 3 ) * as the essential f actor. f According to this view, the principal reac- tions involved are as follows : 1) 2 S0 2 + N 2 3 + O 2 + H 2 = 2 S0 2 (OH) . (ONO) (Nitrosylsul- phuric acid) ; 2) 2 S0 2 - (OH) (ONO) -f H 2 = 2 S0 2 (OH) 2 + N 2 3 ; or, 3) 2 S0 2 (OH)(ONO) + S0 2 + + H 2 = 3 S0 2 (OH) 2 + N 2 O 3 . First there is a union of sulphur dioxide, nitrous anhydride, oxygen, and water, to form nitrosylsulphuric acid, which probably separates as part of the mist or fog seen in the lead chambers. But in the presence of water vapor or of dilute sulphuric acid, this nitrosylsulphuric acid is at once decomposed, according to reac- tion (2), sulphuric acid being formed, and nitrous anhydride regen- erated; or if sulphur dioxide and oxygen are concerned in the process, then reaction (3) occurs. This cycle of reactions repeats an indefinite number of times. But in the first lead chamber, where the temperature is rather high and an excess of water vapor is * Ramsey and Cundall (J. Chem. Soc., 1885, 672) maintain that N 2 O 3 exists only as a liquid, and on heating, it decomposes into NO and NO 2 ; accepting this view, N 2 O 3 as such, cannot be present in the lead chambers, where the temperature is over 60 C. t Hurter (J. Soc. Chem. Ind., 1882, 49 and 83) supports the theory that nitrogen peroxide (NO 2 ) plays an important part in the process. SULPHURIC ACID 47 usually present, the following secondary reactions probably occur to a greater or less extent : 4) 2 S0 2 (OH) (ONO) + S0 2 + 2 H 2 = 3 H 2 S0 4 + 2 NO, this reaction being only momentary. Since there is usually an excess of oxygen present, however, the nitric oxide here formed is at once brought into action again, thus : 5) 2 S0 2 + 2NO + 3 + H 2 = 2 S0 2 - (OH) . (ONO). If there is a deficiency of oxygen, the nitric oxide is not returned to the process, but passes through the several chambers and, since it is not absorbed by the concentrated acid in the Gay-Lussac tower, it escapes into the atmosphere and is lost. The nitrogen oxides are derived from nitric acid, or by the action of sulphuric acid on sodium nitrate in the nitre pots. When nitric acid is used, it must be introduced in the form of vapor, or at least as a very fine spray, whereupon it reacts as follows : 6) 2S0 2 -f2HN0 3 Perhaps this reaction really occurs in two stages, thus : (a) S0 2 + HN0 3 = S0 2 - (OH) . (ONO) ; (b) 2 S0 2 (OH) (ONO) + H 2 = 2 H 2 S0 4 + N 2 3 . The formula assigned to the nitrosylsulphuric acid may perhaps /m be written S0 2 < , and the compound would then be called nitro- \ sulphonic acid. But in either case the existence of the substance is only transitory, it being broken up at once by the steam and sulphur dioxide present when the process is working properly. In case there is a deficiency of water vapor in the chambers, and especially if the temperature falls too low, the nitrosylsulphuric acid may separate as crystals, which deposit at various points on the walls, forming "chamber crystals." This is an undesirable accident, for when steam or water come in contact with them they decompose into sul- phuric acid, nitric acid, and nitrogen peroxide (N 2 4 ) : 4 S0 2 (OH) (ONO) + 2 H 2 = 4 H 2 S0 4 + N 2 4 + 2 NO. Then the nitrogen peroxide unites with some of the water, N 2 4 + H 2 O = HN0 2 + HN0 3 , forming nitrous and nitric acids directly on the walls, corroding the lead at the point where the cluster of crystals was attached. To 48 OUTLINES OF INDUSTRIAL CHEMISTRY prevent this separation of " chamber crystals " and the retention of nitrogen oxides in the sulphuric acid an excess of steam in the lead chambers is preferred, although it dilutes the acid somewhat. The raw materials employed in sulphuric acid making are : 1. Sulphur. (a) Crude brimstone. (6) Metallic sulphides, such as iron pyrites, chalcopyrite (copper pyrites), sphalerite (zinc blende), etc. (c) Hydrogen sulphide (seldom used). 2. Sodium nitrate or nitric acid. 3. Water as steam. 4. Oxygen as air. The acid may be made from brimstone, pyrites, blende, or hydro- gen sulphide, but they are not used together. Since the burners and chambers employed for one source of sul- phur cannot be adapted to that of another without extensive altera- tions, the manufacturer must decide what material he will use, and erect his plant accordingly. Crude sulphur from the calceroni gives a very pure acid free from arsenic, iron, copper, or zinc, and much smaller condensing chambers may be used for a given yield than when pyrites or blende is employed. The sulphur is placed in iron retorts or on trays in brick ovens, and ignited. The combustion is easily controlled by regulating the amount of air admitted to the retort. Usually the hot vapors from the brimstone burners are passed through a narrow flue or passage, into which a regulated supply of air is admitted. This insures complete combustion of any sulphur that may distil owing to too great heat in the retort. To prevent clogging and loss, as much of the sulphur as possible is con- verted to dioxide. Pyrites, or natural disulphide of iron (FeS 2 ), is a dense, hard mineral of crystalline structure and pale yellow color. The largest deposits in the United States are in Virginia, at Mineral City, and at Charlemont in Massachusetts. Of the foreign deposits, those in Spain * are the most important. A pure pyrites contains 53.3 per cent of sulphur, but that commonly used for acid making carries from 43 to 48 per cent. It seldom pays to use an ore with less than 35 per cent of sulphur, for it will not support its own combustion. The first proposal to use pyrites originated with an Englishman named Hill, who took out a patent for the process in 1818. But it was not until 1838, when the Sicilian government sold the monopoly * Spanish pyrites containing copper is much used in England and to some extent in this country, the burned cinder being afterwards treated to recover the copper. SULPHURIC ACID 49 of the sulphur export to a French firm which nearly trebled the price of crude brimstone, that pyrites began to find favor with acid makers. At the present time, because it is cheap and easily obtained, pyrites has almost completely replaced sulphur for acid making. The product from pyrites is usually contaminated with arsenic, and often with zinc, copper, and selenium. By the oxidation of pyrites in a suitable furnace, the sulphur is converted to dioxide, and iron oxide remains. The reaction may be written as follows : 2 FeS 2 + 11 = 4 S0 2 + Fe 2 O 3 . This is not exact, however, as some sulphur remains in the ore and some sulphur trioxide is formed. The proper regulation of the pyrites burners is one of the problems of the manufacturer. If the ore contains over 35 per cent of sulphur, the burning, once started, generates sufficient heat to maintain the combustion, and no fuel is necessary. But zinc sulphide and the " mattes " from metallurgi- cal processes must be heated by fuel. The complete burning of pyrites is difficult. With lump ore there is apt to be a kernel in the centre of the lump, from which the sulphur is not burned out. If the temperature rises too high, the charge fuses together, forming clinkers or "scar," and chok- ing the furnace. If too much air is admitted, the furnace cools below the temperature at which fresh pyrites will ignite, and the gases leaving the burner are so diluted that the desired reactions do not take place in the lead chambers. With " smalls " the tendency to fuse is more marked than with lump ore, and the fine ore packs together so densely that the air will not penetrate it, and unless it is constantly stirred only the surface is burned. (The lump ore is that which has been broken to about the size of a goose egg, the "smalls" constituting what will pass through a half-inch screen.) Pyrites burners are usually built in benches containing from three to thirty furnaces, in order that the supply of gas may not be broken, while charging or cleaning one furnace. A burner for lump ore (Fig. 21) * consists of a brick furnace, con- taining a grate formed of single loose iron bars (B, B) having a square section, and resting in grooves at each end. These bars may be turned parallel with their longitudinal axes, but have no lateral motion. They are so adjusted that their sides are at an angle of 45 to the vertical. After a charge is burned, the bars are given several quarter turns by means of a key, to allow the cinders on * After Ost, Lehrbuch der technischen Chemie. 50 OUTLINES OF INDUSTRIAL CHEMISTRY them to drop through into the ash pit. Air is admitted by dampers beneath the grate. When properly working, the cinders resting on the bars are nearly cold, the hottest part of the fire being eighteen inches above the grate. The furnaces are lined with fire-brick, and to prevent any access of air except through the dampers, the doors (D, D) for charging, cleaning, raking, etc., are make to fit closely, and are generally luted with clay. All the burners in one bench deliver their sulphur dioxide gas into a common, wide flue, or "dust box" (F), where any fine dust carried along by the gases may settle before they enter the Glover tower. This dust consists of unburned pyrites, arsenic, antimony or zinc oxides, iron oxide, etc. In one or more of the burners a cast-iron "nitre pot" (P) may be set, in which nitrous gases are generated by the action of sulphuric FIG. 21. acid on sodium nitrate. Or the pots may be placed in a small chamber built into the flue (F), and heated by the waste heat of the burners. Sometimes, however, the pots are placed in separate furnaces. A lump burner of average size has a grate area of 15 to 25 square feet. The furnace is sometimes made slightly hopper-shaped in- side, so that it is larger at the level of the charging doors than at the grate bars. About 40 pounds of pyrites, containing 48 per cent of sulphur, are burned per square foot of grate area in 24 hours, a larger quantity of such high-grade ore being liable to cause fusion, unless great care is exercised. A larger quantity of poorer ore may be burned daily, without danger of fusion. A number of burners for smalls have been invented, but that most commonly used is the Maletra burner (Fig. 22). This consists of a series of shelves, about 5 by 8 feet in size, arranged in a tall furnace. At the top is a hopper, through which the smalls are introduced, falling on the top shelf, on which they are spread out by rakes, introduced through the door (A). At the front of the shelf is an opening (B), through which they can be made to fall upon the SULPHURIC ACID 51 next shelf, where they are again spread out in a thin layer. After a time they are raked down to the next shelf, and so on, each shelf being hotter than the one preceding. Finally, the spent cinders are raked out at the bottom at (C). For starting the furnace, the shelves are heated by a coal fire on a special grate, but after the temper- ature is sufficiently high to ignite the charge, combustion continues from the heat given out by the burning pyrites, provided the fur- nace is properly regulated and raked, and fresh ore is introduced as needed. Another form of smalls burner is Spence's furnace, in which the fine pyrites is put into a long muffle, heated by a coal fire or by the waste heat from lump burn- Furnaces modelled after the ers. FIG. 22. Spence type are much used for roasting zinc blende and copper mattes, in which the per cent of sulphur is too low to support combustion without external heat. Even from poor ore, muffle furnaces yield a fairly concentrated sulphur dioxide gas. The Perret-Ollivier furnace is a shelf burner, in which the shelves are set above the grate of an ordinary lump burner. The smalls are spread upon the shelves and the hot gases from the lump ore pass over the surface of the fines, heating the latter to the combus- tion point. The several shelf burners above described must be raked at inter- vals, and this is very hard labor if done by hand rakes, besides allow- ing the entrance of an undue amount of air. To remedy these defects, mechanical raking apparatus has been applied, some being very suc- cessful, though expensive to build and keep in repair. The Gerstenhbf er furnace (Fig. 23) is used somewhat in Germany. It consists of a tall tower containing a series of grates made of triangular bars (T, T) of fire-clay set horizontally. The smalls are introduced from a hopper (H) at the top, in a regular stream, and falling from one grate to the next, are exposed to the hot fumes from the burning pyrites on the lower grates. The cinders are raked out at the bottom of the tower. These furnaces are about 17 feet high and 4 by 2 feet inside diameter. Before starting, the burner is heated 52 OUTLINES OF INDUSTRIAL CHEMISTRY FIG. 23. to a white heat by a coal fire on the grate (G), but no more fuel is used after the pyrites is once ignited. A proper regulation of the flow of smalls will maintain the requisite temperature. The Hasenclever-Helbig- burner consists of a lump burner, joined to a smalls furnace, which is a tower containing shelves, set at an incline of 38, the alternate shelves being parallel. The smalls, fed in at the top through a hopper, fall on the first shelf, and then slide down from one shelf to the next. At alternate ends of the shelves are openings for the fumes to pass upwards. The hot gases are thus forced to travel back and forth, under and over each shelf, as they ascend the tower. The rate of the flow of the smalls through the burners is regulated by the rapidity of the discharge of cinders through an automatic discharging wheel at the bottom. The Glover tower is placed next to the burners, and is now used in nearly all sulphuric acid works. Its functions are to set free the /nitrogen oxides from the Gay-Lussac tower acid ; to cool the burner gases to a temperature of from 50 to 60 C. before they enter the lead chambers ; to furnish a large part of the steam necessary in the lead chambers ; and in many works to concentrate the dilute acid from the lead chambers to a density of 1.75 specific gravity. Moreover, it doubtless increases the yield of sulphuric acid from a plant of given lead chamber capacity, for some acid is formed directly in the tower itself in addition to that condensed in the lead chambers. The tower (20 to 30 feet high and about 10 feet across) is made of sheet lead, joined as described on p. 53, and supported on a frame- work of timbers or steel. It is lined with acid-resisting brick or tile, laid without mortar,* and is filled with broken quartz lumps or flint stones. At the top is an apparatus for distributing the acid, which is to run down through the tower, t The burner gases enter at the bottom, and pass up and out at the top, through a pipe leading to the lead chambers. These form the most important part of a sul- * It has been proposed to lay the brick in plastic sulphur as a cementing substance, t The working of the Glover tower is described in connection with the Gay-Lussac tower. SULPHURIC ACID. 53 phuric acid plant, and it is in them that the reactions involved in the formation of the acid take place. They are immense boxes, made by joining sheets of lead, and are supported from a strong timber framework, by means of lugs or strips of lead, attached to the outside of the sheets. The joints cannot be made with solder, but the edges of the sheets are fused together by means of an aero- hydrogen flame, and the process, called " lead burning " is both diffi- cult and slow. At several points, steam may be introduced into the chambers to supply water vapor as needed. Each chamber is sus- pended above a large, flat, lead pan in such a way that the acid collecting in the pan forms a hydraulic seal for the lower edge of the lead chamber. These pans are 6 or 8 inches wider than the chamber, and have sides from 14 to 24 inches high. There is much difference of opinion among acid makers as to the best size and number of the lead chambers. There are usually from 3 to 5, with a capacity of 140,000 to 200,000 cubic feet in the system. As a rule, the first chamber is the largest, and in it the greater part of the acid is formed. The individual chambers vary from 10,000 to 80,000 cubic feet (100 by 40 by 20 feet). In this climate they are enclosed in a building to avoid changes of temperature, which should not vary much from 50 to 65 C. in the first chamber, and 15 above that of the outside air in the last; and they are usually on the second floor, so that the acid may flow from them by gravity to the evaporating pans sometimes placed on top of the pyrites burners ; and also that the bottoms may be better watched for leaks. In order to observe the working of each chamber, small lead dishes are fastened at various points on the inside of the chamber wall, and from these, pipes called " drips " lead to test glasses outside, where the density of the acid may be taken. A better method is to place the dish inside the chamber at a distance from the wall, support- ing it aboye the level of the condensed acid, and connecting it by means of a pipe with a test glass outside. Panes of glass are some- times set at opposite points in the chamber walls, so that the color of the gases may be observed. This is quite important as a means of controlling the process. In the first chamber the color is white and opaque, owing to the copious condensation of acid vapor, but in the succeeding chambers the color becomes more and more red- dish, owing to the excess of nitrogen oxides. If the color becomes pale in the last chamber, there may be a deficiency of nitrous vapors ; or too much or too little steam ; * or the draught may not be properly * The steam is derived from a boiler, or from the evaporation of water from the diluted tower acid in the Glover tower. 54 OUTLINES OF INDUSTRIAL CHEMISTRY regulated, causing too much or too little oxygen to enter the cham- ber. The standard remedy is to use, at once, more sodium nitrate in the nitre pots, and then to locate the difficulty and gradually bring the system to its normal working condition. From the last lead chamber the gases pass to the Gay-Lussac tower, whose purpose is to recover the oxides of nitrogen which would otherwise be lost. The tower is usually about 50 feet high, and 8 feet across. It is built of lead, supported on a timber frame, in much the same way as the Glover tower. (In many small modern plants, earthenware pipe of large diameter [2 or 3 feet] is often used instead of lead.) The tower is filled with metallurgical coke, the hardest and strongest kind. At the top is a distributing apparatus to spread the acid evenly over the coke. Sometimes two towers are used, the gases passing up through one and then to the bottom of the other, and up through this to the chimney. The acid which flows down the Gay-Lussac tower is that which has been con- centrated in the Glover tower to a density of from 150 to 155 Tw. (about 1.750 sp. gr.). Acid of this strength absorbs the nitrous anhydride (N 2 3 ) and the nitrogen tetroxide (N0 2 or N 2 4 ), but does not absorb nitric oxide (NO) or nitrous oxide (N 2 0). Hence, with normal working of the process, only that part of the nitrogen oxides is lost which is reduced to nitrous and nitric oxide. If there is an excess of oxygen present, some of the nitric oxide is converted to nitrous anhydride, and thus saved. The absorption of these nitrogen oxides takes place only when concentrated acid is run through the Gay- Lussac tower; if the acid is of less than 1.50 sp. gr., it will not absorb them ; for best results it should be 1.75 sp. gr. The solution of nitrous gases, in concentrated sulphuric acid, is known in the works as " nitrous vitriol " ; it is sent to the Glover tower, where it is diluted with water, or chamber acid, till its specific gravity is about 1.6. It then passes down the Glover tower, coming in contact with the hot sulphur dioxide from the burners and steam from the lower part of the tower. The high temperature causes the dilute acid to give out its absorbed nitrous gases, which mix with the sulphur dioxide and pass back into the lead chambers. This pro- cess is called denitration of the tower acid. The heat in the lower part of the Glover tower evaporates a considerable portion of the water from the acid, thus concentrating it again to a strength suffi- cient for use in the Gay-Lussac tower, to which the required amount is returned, and the remainder is added to the acid which has been concentrated in the lead pans (p. 56). The hot burner gases are cooled by contact with the tower acid SULPHURIC ACID 55 in the Glover tower to 50 to 60 C. ; the best temperature at which to work the first chamber is 50 to 65 C. If the nitrogen oxides are allowed to go to waste entirely, about 11 to 13 kilos of sodium nitrate must be used with each 100 kilos of sulphur burned. The recovery process by means of the Glover and Gay-Lussac towers reduces this consumption of nitrate to about 4 kilos per 100 kilos of sulphur, while a larger quantity of nitrous oxides is introduced into the chambers, causing the acid to form more rapidly and in greater quantities. Some manufacturers prefer to supply the nitrogen oxides in the form of liquid nitric acid, introduced into the chambers. This is easily regulated, admits no excess of air, and causes no loss of sul- phur dioxide, such as may happen during the introduction of the! " nitre." But much care must be taken that the nitric acid does notl run down the sides of the lead chamber, nor collect in the acid on! the floor, for then the lead is rapidly corroded. Sometimes the nitric acid is introduced into the Glover tower with the tower acid. The cost of making and condensing the nitric acid must be balanced against the advantages gained by its use. When sodium nitrate is decomposed by sulphuric acid in the nitre pots, the nitric acid vapor enters the bottom of the Glover tower with the sulphur dioxide. Tne vapors here coming in contact with steam begin to react at once, probably as follows : 2 S0 2 + 2 HlsrOs + H 2 = 2 H 2 S0 4 + N 2 3 ; or, 3 S0 2 + 2 HN0 3 + 2 H 2 O = 3 H 2 S0 4 + 2 NO. Thus the process of acid making begins in the Glover tower, and is continued in the chambers according to the reactions already given on p. 46. The nitre pots are fixed under a hopper through which the nitre is introduced. The sulphuric acid for decomposing the nitre is run into the pots through a pipe, sufficient being used to form the acid sodium sulphate (NaHS0 4 ). This is liquid at the temperature of the flue, and after the reaction is ended can be easily run out through a pipe attached to the bottom of the pot. On cooling, this acid sulphate solidifies, forming "nitre cake " (p. 115). FlG - 24< Compressed air is employed to force the concentrated acid from the Glover tower to the top of the Gay-Lussac, and the nitrous vitriol from the Gay-Lussac to the top of the Glover tower. The acid collects in a large oval vessel of cast iron called the acid egg 56 OUTLINES OF INDUSTRIAL CHEMISTRY (Fig. 24), and the compressed air from (B) forces it out through, the pipe (A) to the Glover or Gay-Lussac tower. The "air-lift" pump (Fig. 25) is now used to some extent to raise the acid to the top of the towers. A pipe (P) is sunk into the ground to a depth equal to the height to which the acid from (S) is to be raised; the air from (R) is forced in near the bottom of the pipe, the pressure causing a rush of air up the pipe, carrying before it some of the acid, which is thus thrown out into (T) in " slugs," and not in a continuous stream. The manufacture of chamber acid is shown in the diagram in Fig. 26. The acid condensed in the lead chambers varies from 1.5 to 1.62 sp. gr. If more concentrated, it will absorb oxides of ni- trogen present in the chambers, and its action on the lead becomes serious. If the chamber acid is weak, much con- centration is necessary to produce a commercial acid. As a rule, all cham- ber acid is evaporated to a density of 170 sp. gr. (60 Be.) in shallow lead pans placed over and heated by the waste heat from the pyrites burners or platinum stills. Since acid stronger than 1.70 attacks the lead, " oil of vitriol " is concentrated in glass balloons or in platinum stills. Glass stills placed on sand baths and heated by a fire are used somewhat, and yield a very pure, colorless, and strong acid; but owing to breakage there is much loss and some danger. Platinum stills (Fig. 27) are usually shallow platinum dishes (S, S) covered with a lead hood or bell (B), which is kept cool by a water jacket. The vapors condensing in this hood as a dilute acid do not fall back into the still, but collect in a narrow trough around the lower edge of the bell, and are usually returned to the lead pans FIG. 25. SULPHURIC ACID 57 FIG. 27. or concentrated in the Glover tower. When the acid in the still reaches a density of 1.835 sp. gr. (66 Be.), it is drawn off through a platinum or lead cooling apparatus (C), and thence into the car- boys as "oil of vitriol." Sometimes platinum stills having a spiral partition in the pan are used; in these the dilute acid is compelled to flow a considerable distance over the hot still-bottom before it escapes through a tube leading from the central compartment. The rate of flow through the still determines the density of the acid. The platinum stills are set directly over coke or coal fires on the grate (G), and are not allowed to cool except for repairs. If the chamber acid contains any nitrous vitriol, the stills are rapidly destroyed. To prevent this, it is customary to add ammonium sul- phate to the acid during the concentration in the lead pans. This destroys the nitrogen oxides, thus : N 2 8 + (NH 4 ) 2 S0 4 = 3 H 2 + H 2 S0 4 + 4 K Sometimes the platinum is alloyed with iridium to render it more resistant to the action of nitrous vitriol. A still invented by Herseus* consists of platinum lined with a layer of pure gold rolled with the platinum, and not electroplated. This resists the action of the concentrated acid better than the platinum. When chamber acid is concentrated by running through the Glover tower, it is contaminated with iron from the flue dust of the burners. It is better to further concentrate such acid in cast-iron stills, since, when the density reaches 64 or 65 Be., a precipitate of ferric sulphate forms, which may cake upon the platinum and cause it to crack. The acid intended for oil of vitriol is usually drawn from the lead pans, while that which has been through the Glover tower is frequently not further concentrated. In some modern works the method of making very concentrated acid has been radically changed. A strong acid of 1.6 sp. gr. (55 Be.) is made in the lead chambers and passed through the * J. Soc. Chem. Ind., 1891, 470. Ibid., 1803, 122. 58 OUTLINES OF INDUSTRIAL CHEMISTRY Glover tower, where it reaches a density of 1.77 sp. gr. (63 Be.). It is then concentrated in cast-iron stills (Fig. 28) * to a density of 1.835 to 1.842 sp. gr. (66 to 66.3 Be.). The pan acid enters through the pipe (A) in a regulated stream. The concentrated acid passes FIG. 28. out through (B) into the vessel (C), in which any sediment (sul- phates, etc.) deposits. A concentrated acid (98 per cent H 2 S0 4 ) flows from the spout at the top of (C) into the cooling vessels (E, E). The still is heated with gaseous fuel entering through ( F). Acid over 1.75 sp. gr. has very little action on cast iron, and the stills stand from two to six months' constant use. Sometimes instead of pans or stills two Glover towers are used, the acid being denitrated in that next the chambers, and further concentrated to a density of 63 to 66 Be. in that next the burners. Chamber acid is often concentrated in lead pans by allowing the flame from a coal fire or gas producer to pass directly over the surface of the acid. But it may be thus contaminated with soot and its color become dark brown. Open lead tanks containing lead coils, heated by steam under pressure, are sometimes used for acid concentration to 60 Be. This gives a clean product, but is not so economical as evaporation by the waste heat from the burners. To secure the very intimate mixing of the gases essential in the lead chambers, Professor Lunge invented his plate tower. f This is a tall -tower lined with lead, and divided into narrow chambers by transverse stoneware plates (Fig. 29) perforated by small holes, and so placed that the holes are not in line. By this arrangement the gases and liquids are brought into very close contact, and it is claimed that the chamber space for a given yield of acid can be much reduced. It is recommended that such a tower be placed between each pair of adjoining chambers, and that the plates be * Transactions of the American Institute of Mining Engineers, VoL 16, 517. W. H. Adams. t Zeitschrift fur angewandte Chemie, 1889, 385. J. Soc. Chem. Ind., 1889, 774. SULPHURIC ACID 59 used in the Gay-Lussac tower also. They are not practicable for the Glover tower, because the heat is liable to crack them, and the small holes become clogged with dust. It may be noted here that these Lunge-Euhrmann " plate towers" have found some favor for condensing hydrochloric acid, but are said to obstruct the draught in sulphuric acid mak- ing. The "pipe column" 1 * invention of Gilchrist and Hacker carries out the same idea of mixing the gases more thoroughly. It con- sists of towers containing a num- ber of small earthenware or lead pipes set horizontally, and open- to the air at each end. FIG. 29. Another recent innovation in sulphuric acid making is Barbier's tower system,t in which the lead chambers are abolished and a series of towers substituted (Fig. 30). Sulphur dioxide is led through the towers, which are joined by pipes (A, A) leading from the top of one to the bottom of the next. The towers are filled with perforated pottery ves- sels, affording a large surface exposure. Di- lute nitric acid is sup- plied to each tower by a sprinkler at the top. Beneath the towers are pans (B, B) for collect- ing the acid as it forms. These are placed over a flue leading from a grate at the lower end of the series, and so arranged that the overflow from one pan passes into the next. The acid thus flows toward the fire, becoming more concentrated in each pan. The water vapor and nitrous gases from each pan go directly back into the tower above it. The last two or three pans are not * J. Soc. Ctiem. Ind., 1894, 1142. t Bui. Soc. Chim., 11, 726. FIG 60 OUTLINES OF INDUSTRIAL CHEMISTRY under towers, and in these the acid is concentrated to about 60 Be. by direct heat from a fire, the denitration being effected at the same time. The last tower of the series is a Gay-Lussac for saving the nitrous vapors. The chief advantages claimed for this system are : it occupies less ground and is cheaper to build than the lead chambers ; it works at 90 C., hence atmospheric changes have less influence on the process, and it is suitable for use in hot or cold climates ; and that it gives a greater yield of acid per cubic meter of space than does the chamber system. Although some unfavorable results with this method have been reported,* it does seem that great developments in tower systems may be expected in the near future. A substitute for the cumbersome and expensive lead chamber is much to be desired. When zinc blende or copper mattes are roasted, muffle furnaces externally heated, sometimes by generator gas, are used, as the amount of sulphur in the ore is insufficient for the combustion. These furnaces contain shelves, and are a modified form of shelf burner, the shelves being in the muiEe. Sometimes mechanical rakes are used to draw the charge down from shelf to shelf. Very concentrated acid is now made by artificially cooling oil of vitriol of 66.3 Be. considerably below C. Under such condi- tions crystals of sulphuric a"cid (rnonohydrate) separate. These are quickly freed from mother-liquor by means of a centrifugal machine. The crystals melt at 10 C., and yield an acid of 99.5 per cent H 2 S0 4 , containing only a trace of moisture. FUMING SULPHURIC ACID This is prepared by the dry distillation of sulphate of iron. Copperas (FeS0 4 7 H 2 0) is gently heated in the air until the water is all expelled and part of the ferrous sulphate is oxidized to the ferric state. The mixture of sulphates is then put into small iron retorts, which are heated in a furnace. Decomposition, according to the following equation, ensues : Fe 2 (S0 4 ) 3 - 2 FeS0 4 = 2 Fe 2 3 + 4 S0 3 + S0 2 . The vapors of sulphur dioxide and sulphuric anhydride are con- densed in receivers containing oil of vitriol, which dissolves them. The Nordhausen acid thus formed is a brown oily liquid, fuming in the air, owing to the escape of the dissolved sulphur oxides. By cooling to C., crystals of pyrosulphuric acid (H 2 S 2 7 ) separate. Nordhausen acid is now chiefly produced in Bohemia, where a * J. Soc. Chem. Ind., 1895, 698. SALT 61 pyritiferous shale is found, which, when weathered, forms a basic sulphate of iron, that is dried and distilled. REFERENCES J. Soc. Chem. Ind., 1882-1898 +. Progress in the Concentration of Oil of Vitriol. By W. H. Adams, Transactions of the American Institute of Mining Engineers, 1887-1888. Vol. 16, p. 496. Sulphuric Acid and Alkali. Vol. I. 2d. Ed. G. Lunge, London, 1891. Mineral Industry. Vols. I-V, 1892-1896. Schwefelsaurefabrication. Dr. K. W. Jurisch, Stuttgart, 1893. SALT The sources of salt are : 1. Sea-water. 2. Eock salt. 3. Salt brines derived from springs, lakes, or wells. Atlantic sea-water, except near the mouths of large rivers, aver- ages about 3.4 per cent of solid matter, of which about 75' per cent is sodium chloride, the remainder consisting of chlorides, bromides, and sulphates of potassium, magnesium, calcium, lithium, etc., with minute amounts of other salts. The concentration of sea-water for salt is carried on to some ex- tent in warm, dry countries by solar evaporation, the water usually being exposed in shallow tanks or ponds to the full force of the sun's rays. Sea-water is seldom evaporated over fire because of the cost of fuel. In Russia it is allowed to freeze over the surface, and the ice, which contains but little salt, is removed. This is repeated until the brine is sufficiently concentrated to make the evaporation over fire profitable. Salt made from sea-water ("sea-salt") is very coarse and is usually damp, owing to the presence of some magnesium chloride, which, being a deliquescent substance, attracts moisture from the air. It is of less importance in this country than that made from other brines; the greater part of the sea-salt produced here in 1894 was made in California. Rock salt is found in many countries, and often very pure. In Austria, Germany, Spain, and Louisiana it occurs in large deposits, so pure that it is only necessary to grind it for use, but in most cases it is contaminated with iron oxides, clay, sand, and other im- purities, which often necessitate its purification. In this country it is mined in New York, Kansas, California, Utah, and Louisiana. Tl B R A 62 OUTLINES OF INDUSTRIAL CHEMISTRY As it does not dissolve so readily as finely crystallized salt, it is preferred for many purposes, such as curing meat, preserving green hides, and feeding to live stock. The salt of principal interest in this country is derived from natural brines, found chiefly in New York, Michigan, Kansas, and Ohio, while West Virginia, Utah, Texas, and Pennsylvania produce lesser quantities. The New York deposits are near Syracuse and in the neighbor- hood of Warsaw and Batavia. The Onondaga (Syracuse) deposit has been known since the middle of the seventeenth century, and since 1797 has been the property of the state. That at Warsaw, opened in 1883, is now the most important. The Michigan deposits are near Saganaw Bay and Manistee, a strong brine being obtained by boring. Large amounts of brine are evaporated near Salina, Kan- sas. The Ohio and West Virginia deposits are in the valley of the Ohio Eiver, near Pomeroy and Wheeling. In the Onondaga district, the brine is obtained by boring wells, 8 inches in diameter and from 300 to 350 feet deep, and lined with iron casings to exclude surface water. The state owns and operates these wells, furnishing the brine to the salt makers, and collecting a tax of one cent per bushel of the salt made. This plan is not profitable to the state at present, and it is not improbable that the reservation may be sold. The brine is raised by pumps, worked by an endless wire rope, the power being furnished by an engine. As it comes from the pumps the brine has a slightly turbid appearance, due to clay or fine sand raised from the well, together with minute bubbles of carbon dioxide, with which the brine is charged. It also contains some ferrous carbonate, which is held in solution by the carbon dioxide. As the latter escapes, the ferrous salt absorbs oxygen from the air, and hydrated ferric oxide separates as a yellowish red turbidity, which settles after a time, leaving the brine perfectly clear. For the manufacture of "solar salt," of which a considerable quantity is still made at Syracuse, three sets of tanks are used. The first are called " deep rooms " ; here the brine is received from the pump-house, and the ferric hydroxide and sediment deposit. The clear brine is then drawn into the " lime rooms," tanks about 8 inches deep, 18 feet wide, and from 100 to 400 feet long. In these the evaporation by the sun's rays goes on until small crystals of salt appear. The brine contains calcium sulphate and chlorides of cal- cium and magnesium. The calcium sulphate deposits as gypsum (CaS0 4 2 H 2 0), in long slender crystals, usually in clusters ; but a SALT 63 small portion remains in solution with the salt. The concentrated brine is then drawn into the "salt rooms," which are very similar to the lime rooms, but only about 6 inches deep. In these the salt is deposited, more brine being admitted as the water evaporates, until the layer of salt on the vat floor is about 3 inches deep. About three times in a season the salt is " harvested " ; i.e. it is raked together and put into tubs having perforated bottoms, through which the mother-liquor drains off. It is then taken to the store- house, where, according to the New York law, it must drain 14 days before being marketed. All the vats are built of wood and provided with movable covers to keep out rain. During fair weather these are rolled back. The vats are built on piles, so that the " deep rooms " stand higher than the "lime rooms,' 7 and these in turn are higher than the salt vats ; thus the liquor runs by grav- ity from one set to the next. The mother-liquors contain considerable quantities of calcium and magnesium chlo- rides. The large cubical salt crystals are usu- ally not perfect; they are skeleton crystals, with the edges nearly complete, but with cavi- ties in the crystal faces. This makes the salt more bulky than is the case with fine solid crystals. Moreover, the cavities hold small drops of the mother-liquor, even after draining for some days ; con- sequently, calcium and magnesium chlorides remain in the salt, and these being deliquescent, cause it to become moist in damp weather. In some foreign countries, dilute brine is concentrated by flow- ing over brushwood " ricks,' 7 prior to final solar evaporation (p. 3). Where brine is concentrated by the use of fuel, the product is generally called "boiled salt." This is prepared in several ways. By the Kettle Process, Fig. 31,* the brine is evaporated in cast-iron kettles (A, A) about 4 feet in diameter by 2 feet deep. They are set in rows of from 16 to 25, over a flue leading from the fire box (G) to the chimney. The contents of the kettles near the fire boil * After Merrill, Bui. N. Y. State Museum, III, No. 11. FIG. 81. 64 OUTLINES OF INDUSTRIAL CHEMISTRY down rapidly and produce small dense crys- tals, but in those near the chimney, evaporation is slow, and large crystals similar to solar salt are formed. The two products are generally mixed and sold as "common fine salt." The brine coming from the wells must be purified by adding "milk of lime," and stirring well, otherwise the product will be colored by ferric hydroxide. The lime combines with the carbon dioxide and precipitates the iron. After set- tling, the brine is supplied to each kettle by a wooden pipe (P). The first effect of heating and concentrating the brine is the separation of " bittern," consisting of calcium sulphate and a little magnesium, sulphate. This is removed by the bittern pan (B), a shallow wrought-iron dish, somewhat like a frying pan with very sloping sides and a vertical handle near the cen- tre. Its sides fit closely against the walls of the kettle ; as the bittern collects in the pan, the latter is emptied and replaced several times ; but as soon as the salt crystals begin to form, it is removed. Part of the calcium sulphate, together with some salt, deposits as a scale on the sides of the kettle. This incrustation soon becomes so thick that it causes loss of heat, and it is removed by filling the kettle with fresh water, which dissolves the salt, leaving the calcium sulphate so porous that it is easily scraped away. This deposit collects faster in the front kettles than in those nearer the chimney; when the latter become coated, it is customary to shut down the entire system and clean them all. The salt is removed as it separates, and drained for a short time in baskets (D) placed over the kettles ; it is then dumped into the storage bins (E), where it must remain 14 days. The salt block, as the plant is called, is in continuous operation, night . and day, for about 14 days, two " runs " being made each month. A good average "run" at Syracuse produces about 7800 bushels of salt. SALT 65 Sometimes the kettles are heated by steam jackets ; as all have the same steam pressure the temperature is uniform, and only one quality of salt is produced, v, Salt is also made by the "pan process" (Fig. 32),* of direct evaporation over fire. Large wrought-iron pans (H, H), 24 feet wide, 100 feet long, and 12 inches deep are used. These pans are divided into two sections by a loose partition, which allows the brine to flow slowly from the rear to the front section. A second, smaller pan is set behind and slightly above the first, so that its contents may be syphoned into the front pan. Both are heated by flues from grates (G), but the rear one gets only the waste heat, before the gases pass into the chimney. The ends of each pan are made perpendicular to the bottom, but the sides are inclined, and sloping wooden platforms (F, F), called '-'drips," are joined to them ; on these the salt is drained when removed from the pans. The brine is purified with " milk of lime," as in the kettle process. The pan process permits an easy control of the size of the grain. For the preparation of a very fine grained product, called " factory filled salt," it is customary to add a small amount of sodium carbon- ate to the brine ; this decomposes the chlorides of calcium and mag- nesium and any excess of caustic lime from the " liming." Then a small quantity of butter, glue, or soft soap is added, and forms an insoluble calcium soap with the remaining traces of lime, and this is re- moved by skimming. For both the kettle and the pan process, coal dust is used as fuel. In Michigan and in western New York, brine is evaporated in " grainers " (Fig. 33) * ; these are long, shallow vats of wood or iron, containing steam pipes (P, P), through which live or exhaust steam is passed. The pipes are about 4 inches in diameter and are hung about 6 inches above the floor of the " grainer," which is some 20 inches deep. Once a day the salt is raked up and deposited on draining platforms over the grainers. The brine is purified before evaporation, as in the pan process, and is supplied to the grainer in just sufficient quantities to replace the water evaporated. When the mother-liquors become too highly charged with calcium and mag- nesium chlorides, they are drawn into special grainers, and a low grade of salt is made from them. * After Merrill, Bui. N. Y. State Musuem, III, No. 11. 66 OUTLINES OF INDUSTRIAL CHEMISTRY Brine is sometimes evaporated in vacuum pans, and a very finely crystalline product, the best grade of table and dairy salt results. It is separated from adhering mother-liquor by the centrifugal machine. Strong brine boils at 105-109 C., and so cannot be boiled by free steam, although evaporation of very dilute brine can be slowly accom- plished in this way. The heat in the kettle and pan process is suf- ficient to dehydrate any calcium sulphate in the salt ; when dissolved in water, such products cause a slight milkiness which disappears after a time, owing to the hydration of the calcium sulphate and its solution in the water. Sometimes pure water is introduced into rock salt deposits through tube wells ; when saturated with salt, it is pumped to the surface and evaporated. A much stronger brine than is found in nature is secured in this way. In some places, chiefly in West Virginia and in Germany, large quantities of bromine are recovered from the mother-liquors (also called " bittern ") from the salt industry. In Italy, Austria, and China the manufacture and sale of salt is a government monopoly. In France, Germany, and India salt used for seasoning food is subject to tax. When used for technical pur- poses, or in agriculture, the tax is very small. To prevent fraud, all German salt, not intended for table use, must be mixed with cer- tain substances to render it unfit for eating. Some of these adulter- ants are iron oxide, crude petroleum, coal dust, pyrolusite, carbolic acid, mineral acids, sodium sulphate or carbonate, alum, soot, etc. REFERENCES Die Industrie von Stassfurt und Leopoldshall. Dr. G. Krause, Cothen, 1877. Report on Manufacture of Chemical Products and Salt. W. L. Rowland, United States Census, 1880 ; Washington, 1884. Mineral Resources of the United States. (1882-1893.) Chemische Industrie. 1883, 225. G. Lunge. Report of the State Geologist of New York, 1885, pp. 12-47. I. P. Bishop. Journal of the Society of Chemical Industry, 1888, 660. On the Tees Salt Industry. T. W. Stuart. Die Salz Industrie von Stassfurt. Dr. Precht, 1889. (Weicke, Stassfurt.) Bulletin of the New York State Museum, Vol. Ill, No. 11. Salt and Gypsum Industries of New York. F. J. H. Merrill, Albany, 1893. Forty-seventh Report of the State Museum of New York, pp. 205-257. The Livonia Salt Shaft. James Hall, 1894. Journal of the Society of Arts, 1894. Manufacture of Salt. F. Ward. HYDROCHLORIC ACID AND SODIUM SULPHATE 67 HYDROCHLORIC ACID AND SODIUM SULPHATE. Hydrochloric or muriatic acid is generally made by the action of sulphuric acid on common salt. It is a by-product of the Leblanc soda process, and in the early years of the industry was allowed to escape into the air, as the demand for it was small. But the nuisance caused by the acid fumes in the neighborhood of the alkali works became so great, that in England a very stringent law was enacted forbidding the soda makers to allow more than 5 per cent of the gas to escape into the atmosphere. This made it necessary to absorb the acid fumes in water. The provisions of the present " Alkali Act " permit only 0.2 grain of hydrochloric acid per cubic foot of chimney gas to be discharged into the atmosphere. The Leblanc industry has declined in recent years, but there is an increased demand for hydrochloric acid, and at present this is one of the main products desired. Its chief use is for the generation of chlorine for the manufacture of bleaching powder; now nearly all soda makers also produce bleaching powder, and the profits derived from the latter have largely offset the decline in returns from soda-ash. Up to the present, no better method than the above has been devised for making this acid. The process may be represented by the equation : 2 NaCl + H 2 S0 4 = Na 2 S0 4 + 2 HC1. But as actually carried out it takes place in two stages, according to the following reactions : 1) NaCl + H 2 S0 4 = NaHS0 4 + HC1. 2) NaHS0 4 + NaCl = Na 2 S0 4 + HC1. These reactions may be carried out by heating the mixture of salt and sulphuric acid either in an " open roaster," or in a muffle or " close roaster." These are both called "salt-cake furnaces." 3^ v - : The open roaster (Fig. 34) consists of two parts, the cast-iron pan (A) and the reverberatory hearth (C). The salt and sulphuric 68 OUTLINES OF INDUSTRIAL CHEMISTRY acid (60 Be., sp. gr. 1.72) are put into the pan (A), and are moder- ately heated by a coke fire on the grate (E). The first reaction takes place at a comparatively low heat, and the hydrochloric acid vapors escape through the earthenware pipe (B). Then the fused mass of sodium acid sulphate and undecomposed salt is raked up on the reverberatory hearth (C), where it is exposed to the high tem- perature of the flame from (D). This completes the second reaction, and a pasty mass of normal sodium sulphate is formed. The hydro- chloric acid vapors, set free during the reaction, mix with the furnace gases from (D), and escape through the pipe (F) to the absorbing apparatus. The furnace gases dilute the acid vapors so much, that a very concentrated solution of hydrochloric acid cannot be made with the open roaster; however, it yields acid strong enough for use in Weldon's chlorine process (p. 96). More- over, the soot and dust from the furnace at (D) contaminate the acid, and may cause clogging in the passages and pipes of the absorption apparatus. The open roaster has the advantage over the close roaster, that it yields more sodium sulphate with smaller consumption of fuel. The crude sodium sulphate, called " salt- cake," usually contains a little undecomposed salt and a slight excess of sulphuric acid. The muffle or "close roaster ;> is used very generally on the continent of Europe, and yields a stronger and purer acid than FIG. 35. the open roaster. The usual form is shown in Fig. 35, The pan (A) is built very much as in the open roaster, but is heated by the furnace gases from the grate (D). The acid vapors set free in the pan escape by the pipe (C) to the absorption apparatus. The muffle (B) is made of fire-clay or brick, arid is heated by the flames from the grate (D). The mixture of acid sulphate and salt is raked from the pan (A) into the muffle (B), where it is heated to a red heat, and the acid vapor liberated passes through the pipe (E) to the absorption apparatus. In this form of roaster, the soot and dust from, the grate are kept away from the acid vapor. Also, a very concentrated acid vapor is obtained, which favors the formation of HYDROCHLORIC ACID AND SODIUM SULPHATE 69 a concentrated solution of hydrochloric acid in the absorbers. But the muffles are expensive to build, yield a smaller output of salt- cake, and require more fuel than the open roaster. Moreover, they very often crack, thus permitting acid vapors to escape into the flues and chimney > causing loss and creating a nuisance. It is customary to maintain a slight pressure in the flues and chimney, so that if the muffle cracks, the flue gases force their way into it. This may cause a slight contamination of the acid, but no nuisance is created. Cheaper fuel may be used with these furnaces, but repairs are apt to be expensive. The pan (A) in both furnaces is about 10 feet in diameter, 7 inches thick at the centre and 3 inches thick at the sides. After a charge is drawn, the pan is cooled somewhat before introducing another, for cold salt, coining in contact with the hot pan, might crack it. The sulphuric acid is generally heated to 100 or 130 C. for the same reason. During the second reaction, the charge is constantly stirred with a " rabble," a large hoe-shaped tool, to prevent tf crusting " or burn- ing on to the hearth or retort. The stirring is done by workmen, and as the work is very heavy, they are sometimes careless, and allow a crust to form, which may crack the muffle. Consequently, many attempts have been made to construct mechanical stirrers. FIG. Sfi. The Mactear furnace* (Fig. 36) t is the only one of these that has met with much success. This is a reverberatory furnace with a rotating hearth (A); in the centre of the hearth is a shallow pan (B) into which the mixture of salt and sulphuric acid is run in a slow, continuous stream. The mass overflows on to the hearth, where it is subjected to the high heat of the flames from the grate (G) ; at * Chemische Industrie, 1881, 253. t After Lunge. J. Soc. Chera, Ind., 1885, 534. '0 OUTLINES OF INDUSTRIAL CHEMISTRY the same time, it is mixed and pushed towards the edge of the hearth by stirrers (C), against which the charge strikes as the hearth revolves. The speed is so regulated that the salt is all converted to sulphate by the time it reaches the edge of the hearth. There it falls into an annular trough (D, D), which carries the pasty mass out of the furnace. An apron attached to the edge of the hearth dips into this trough, so that the salt-cake forms a lute, and pre- vents the escape of the acid vapor into the space beneath the hearth. This only imperfectly protects the driving mechanism from the flame and acid vapors, and serious difficulties are consequently incurred in running the furnace. More- over, the acid vapors are much diluted with the fire gases, which renders their absorp- tion difficult. Because of these disadvan- tages, some manufacturers who have tried mechanical appliances have abandoned them, and returned to the hand-worked furnace. If a salt-cake free from iron is desired, lead pans instead of cast-iron ones are used. But these are easily overheated or injured. The hydrochloric acid vapor is absorbed in water, either by passing through tall towers (Fig. 37)* filled with coke, over which water trickles; or in large earthen- ware Woulff bottles (bombonnes), provided with safety-tubes for back pressure, and with a coke tower at the end of the series. The purpose of the tower, which is fed by a spray of water, is to absorb any acid vapors which may pass uncondensed through the bombonnes. These are placed en cascade^ and joined by the side tubulatures, so that a stream of water or dilute acid from the tower will flow through them in a direction opposite to that in which the gas is moving. The Lunge-Rohrmann plate tower (p. 58) has been tried with some success as a substitute for the coke tower and bombonnes, for hydrochloric acid absorption. The condensation of hydrochloric acid vapors is not so simple a process as it at first appears. The gases coming from the roasters * After Lunge. t That is, on a series of steps, so that each stands a few inches higher than the one preceding. FIG. 37. HYDROCHLORIC ACID AND SODIUM SULPHATE 71 are very hot, and must be cooled before they can be absorbed to form a strong acid. Moreover, with open roasters, there is a very large amount of inert gas present (nitrogen and carbon dioxide from the fire) which dilutes the acid vapors. Then, too, the vapors are not set free regularly in any roaster, there being a rapid evolution during the progress of the first reaction, and a much slower liberation dur- ing the second. This may cause a temporary rush of vapors through the apparatus, so that they cannot be properly taken up by the water. The ordinary muriatic acid of trade is an aqueous solution of the acid vapor, having a specific gravity of about 1.20 and containing about 40 per cent by weight of dry hydrochloric acid vapor. It is impure, containing sulphuric acid, chlorine, iron chloride, arsenic, and, generally, lead and calcium chlorides. Its yellow color is partly due to organic matter, and sometimes to iron and free chlo- rine. To remove arsenic and sulphuric acid, the acid is diluted to 1.12 sp. gr., and barium sulphide is added ; a pure hydrochloric acid vapor is then driven out by distillation and absorbed in pure water. Or a solution of stannous chloride in concentrated hydrochloric acid is added to the crude acid, which latter must have a strength of at least 1.15 sp. gr. A brown precipitate of arsenic with some tin separates and is removed by decantation.* Sulphuric acid alone is removed by adding barium chloride and redistilling. To remove chlorine, the crude acid is digested with strips of copper for some hours. This precipitates arsenic, and the chlorine combines with the copper. The acid is then redistilled. Attempts to recover hydrochloric acid from the waste liquors of the ammonia soda process (p. 86) have not proved very successful. The magnesium chloride mother-liquors from the potash salts of Stassfurt (p. 132) may be decomposed by distillation with steam, and a dilute hydrochloric acid obtained. MgCl 2 + H 2 = 2 HC1 + MgO. But this has not proved a commercial success. The Hargreaves and Robinson process for the direct production of hydrochloric acid and sodium sulphate from salt, sulphur diox- ide, water, and oxygen, is of some importance. The damp salt is pressed into blocks and dried ; it is then charged into vertical cast- iron retorts, a number of which are connected in a series. These * 3 SnCl 2 -f 6 HC14- As 2 3 = As 2 + 3 H 2 + 3 SnCl 4 . 2 AsCl 3 + 3 SnCl 2 = As 2 + 3 SnCl 4 . This leaves stannic chloride in the acid. 72 OUTLINES OF INDUSTRIAL CHEMISTRY are heated from without ; the temperature of the reaction is from 400 to 550 C. The sulphur dioxide, steam, and air are made to pass through all the retorts in succession, the hydrochloric acid being carried along with them. A slight excess of sulphur dioxide and steam is used to prevent the mutual reaction between the hydro- chloric acid vapor and the oxygen, by which chlorine is set free. The decomposition being slow, the gases must be kept in contact with the salt for a considerable length of time ; a cylinder contain- ing 40 tons of material requiring from 15 to 20 days' continuous action to secure complete conversion. The process is an uninterrupted one ; for as soon as no more sul- phur dioxide is absorbed in a given cylinder, it is cut out from the series, the sodium sulphate removed, a new charge of salt blocks introduced, and the cylinder made the final one of the series ; so that newly charged salt is exposed to the most nearly exhausted sulphur fumes. The reaction representing the process appears quite simple : 2 NaCl + S0 2 + H 2 O + O = Na 2 S0 4 + 2 HC1. But the mechanical difficulties encountered in working it were very great, and only within a very short time has the process met with any marked success. Sodium sulphate or salt-cake is most largely used in the produc- tion of soda by the Leblanc process. Large quantities are used for glass making, for ultramarine, in dyeing and coloring, and to some extent in medicine. For some kinds of glass the salt-cake must be free from iron, and consequently it is made in lead pans. Or the sulphate may be purified from iron and excess of acid by dissolving it in hot water, adding " milk of lime," and then stirring into it a solution of bleaching powder. The iron is precipitated as hydroxide and settles on standing. By evaporation, crystals of Glauber's salt (Na 2 S0 4 10 H 2 0) are obtained. But generally the purified solution is rapidly evaporated to dryness, and the product is calcined to remove all the water. REFERENCES Berichte iiber die Entwickelung der Chemischen Industrie, u.s. w. A. W." Hofmann, Braunschweig, 1877. (Vieweg.) Darstellung von Chlor und Salzsaure, unabhangig von der Leblanc Soda Indus- trie. Dr. N. Caro, Berlin, 1893. (Oppenheim.) Sulphuric Acid and Alkali. 2d ed. Vol. II. G. Lunge, London, 1895. (Gur- ney and Jackson.) THE SODA INDUSTRIES 73 THE SODA INDUSTRIES THE LEBLANC SODA PROCESS Nearly all the soda of trade was formerly obtained from certain natural deposits of the so-called " sesquicarbonate," or from the ashes of sea plants. But towards the end of the last century, the sup- ply from these sources became insufficient to meet the increasing demands. About 1775 the French Academy of Science offered a large prize for a method of making soda from salt. Among other processes submitted was one by Nicolas Leblanc, which seemed promising, and being granted a patent in 1791, he began manufact- uring on a commercial scale. But in the French Eevolution his factory was seized, the patent declared public property, and no indemnity was paid to him. Having lost all his property, he finally committed suicide. Leblanc's process was so perfect and complete that very slight changes, and those only in minor details, have been made up to the present. It has been in use now for nearly a century, and although very seriously threatened by newer processes, it still produces about half of the world's supply of soda. Owing to the fact that it pro- duces hydrochloric acid and bleaching powder as by-products, it has been able to survive competition, although its condition is becom- ing more desperate every year. Its chief rival is the ammonia or Solvay process. Within a few years many electrolytic methods for caustic soda have appeared, and the successful production of bleach- ing material by any of these processes will sweep away about the only source of profit now left to the Leblanc manufacturer. It is not probable that this change will come immediately, for the electrolytic processes have not yet entirely emerged from the experimental stage ; but the decline of the Leblanc process is generally regarded as inevitable, and inventors have, for the most part, abandoned further attempts to improve it. The reactions of the Leblanc process are generally expressed as follows : 2) Na 2 S0 4 + 2 C = Na 2 S + 2 C0 2 . 3) Na 2 S + CaC0 3 = Na^COs + CaS. 4) 74 OUTLINES OF INDUSTRIAL CHEMISTRY But these equations * do not represent all the reactions which take place during the process, for a number of other substances are formed. The first equation represents the preparation of sodium sulphate and hydrochloric acid (p. 67). The second and third reac- tions are realized in one operation. The fourth has no direct rela- tion to the process, as the formation of carbonic oxide does not become marked until all the salt-cake has been decomposed. This serves to indicate the end of the process, and aids in the formation of a porous product. The salt-cake should be friable and porous, containing very little free sulphuric acid, and no undecomposed chloride. The carbon is supplied in the form of powdered coal, which should contain very little ash-forming impurity. A little pyrite does no harm, but the coal should be as free as possible from nitrogen, in order to prevent the formation of cyanides and cyanates. Calcium carbonate in the form of pure limestone or chalk, crushed to the size of a small pea, is mixed with the crushed salt-cake and coal in order to carry out the third reaction. If the limestone contains magnesia or silica, there is a consequent loss as insoluble residue. Usually 100 pounds of salt-cake, 100 pounds of limestone, and 50 pounds of coal dust form a charge. This is an excess of limestone, the purpose of which is explained below. The reactions are carried out in a " black-ash " or " balling fur- nace/ 7 which may be worked either by hand or mechanically. The ^J L2^$^ FIG. 38. hand-worked furnace is a long reverberatory (Fig. 38), having two platforms on the hearth. The charge is introduced on the back plat- form (A) nearest the flue, where the heat is not very high. When thoroughly dried and well heated, it is raked down onto the front platform (B), which is a few inches lower than (A). Here the tem- * Lunge (Sulph. Acid and Alkali, Vol. II, 460 et seq.) regards the theory of Scheurer-Kestner (Comptes rendus, 57, 1013, and 58, 501) as correct, viz. that the reactions are : 5 Na 2 SO 4 + 10 C = 5 Na 2 S + 10 CO 2 . 5 Na 2 S + 5 CaCOg = 5 Na 2 CO 3 + 5 CaS. 2 CaCO 3 + 2C = 2 CaO + 4 CO. THE SODA INDUSTRIES 75 perature is high, usually about 1000 C., and the surface of the mass soon begins to fuse. It is then raked over, thoroughly exposing it to the direct heat until it becomes a thick, pasty mass, from which carbon dioxide is escaping freely. After the salt-cake is all decom- posed, the charge begins to stiffen, and the evolution of carbon monoxide is shown by the appearance of jets of blue flame, known to the workmen as " candles." The charge is then raked together into a " ball," which is drawn out of the furnace into an iron barrow. The evolution of carbon monoxide continues for a few minutes after the " ball " is removed, and the bubbles escaping from the pasty mass cause it to become porous. The formation of this gas is due to the action between the coal and the excess of limestone according to reaction (4). The caustic lime formed here slakes during the lixi- viation of the black-ash (p. 76), and swells, thus disintegrating the mass. Although the heavy tools are suspended by chains, their opera- tion is still so difficult, and the temperature is so high, that a man cannot handle much more than 300 pounds at one time. In order to work larger charges, without the expensive hand labor, revolving FIG. 8. black-ash furnaces (Fig. 39) are much used. These are similar to the revolving furnaces described on page 17; the flame from the furnace (A) passes through the cylinder (B). The charge is intro- duced through the manhole (P), and the finished product discharged through the same opening, into the wagon, at the end of the opera- tion. The cylinder is about 16 feet long by 10 feet in diameter, and is revolved by a gear (E) connected with an engine. Projections are fixed in the lining to help mix the contents. The charge is usu- ally about two tons of salt-cake, with proportionate amounts of coal and limestone. It is customary to introduce only the limestone and a part of the coal at first, and to rotate the cylinder until some caustic lime is formed; then the remainder of the coal, together with the salt-cake, is introduced, and the rotation continued until the reactions are completed. The speed varies from one revolution 76 OUTLINES OF INDUSTRIAL CHEMISTRY in three or four minutes, at first, to four or five revolutions per minute during the last part of the process. The hot gases from the black-ash furnace, whether hand-worked or mechanical, pass through the dust box (N), and then through the long flue over the pan (J, J) on their way to the chimney (D). In this shallow pan, the liquor obtained by lixiviating the black-ash is evaporatecj. When crystallized, the salts are removed through the small doors (J). Black-ash is a brownish black or dark gray substance of a pumice-like texture, containing about 45 per cent sodium carbonate, 30 per cent calcium sulphide, 10 per cent caustic lime, and from 10 to 12 per cent of other impurities, sulphate, silicate, aluminate, and chloride of sodium, calcium carbonate, coal, and iron oxide, with traces of cyanides and of sulphides of sodium. The next stage in the process is the lixiviation of the black-ash. This presents some difficulties : if the black-ash is put directly into cold water, it often agglomerates in hard lumps, which dissolve exceedingly slowly ; the free lime present forms calcium hydroxide, which reacts with the sodium carbonate solution, forming some caustic soda ; the solution of sodium carbonate, especially if hot and dilute, reacts on any calcium sulphide present, forming some sodium sulphide ; moreover, moist calcium sulphide oxidizes rapidly to sul- phate in the air, and this reacts with the sodium carbonate. Hence the lixiviation must be done as rapidly as possible, at a low tem- perature, and without exposing the wet black-ash to the air. Shank's process gives the most satisfactory results. The lixivia- tion is carried on in a series of tanks, each having a false bottom perforated with small holes. Because of its density, the solution of sodium carbonate sinks, and passing through these perforations, is drawn off by means of a pipe which delivers it at the top of the next tank. There must always be sufficient liquor in each tank .to keep the black-ash entirely submerged. The process is continuous, sufficient fresh water being admitted to the nearly exhausted ash to give an unbroken flow of strong liquor (above 45 Tw.) from the last tank of the series. When the liquor from the last tank falls to 45 Tw., it is turned into a tank which has just been filled with new ash. The exhausted ash is washed until the wash water has a density of only 1 Tw. Then the residue of calcium sulphide and hydroxide, coal, ashes, and other insoluble matter, which constitutes the "tank waste," is sent to the dump. The tank is then refilled with black-ash and made the last of the series, to receive the strong liquors from the preceding tank. THE SODA INDUSTRIES 77 Since the black-ash contains caustic lime, sufficient heat is gen- erated by its slaking during the lixiviation to warm the concen- trated liquor to about 50 C., which is the best temperature for complete extraction. The temperature of the dilute lye from the first tank of the series is not allowed to rise above 38 C., in order to prevent the above-mentioned interaction between the calcium sul- phide and the sodium carbonate. Good tank liquor has approximately the following composition : Na 2 CO 3 (+NaOH) 23.60* NaCl 50 Na-jS 13 Na 2 S 2 O 3 30 Na 2 S0 4 ' . . . .23 NaoSi0 3 NaCN NaCNS FeS (in solution) The lye obtained by the lixiviation has a specific gravity of about 1.25, and is muddy from suspended impurities. It is purified by settling and then pumped to the top of the " carbonating towers," which are filled with pebbles or coke, or have numerous chains or wire ropes suspended from the top and weighted at the lower ends. The tank liquor trickles over the porous material or chains, and comes into intimate contact with a strong current of carbon dioxide f entering at the bottom and passing up through the tower. The carbon dioxide and oxygen which pass through the tower, convert the caustic soda to carbonate, decompose the ferro-sodium sulphide (solution of ferrous sulphide in sodium sulphide), convert- ing the sodium sulphide into bicarbonate, and precipitating the iron, together with any silica and alumina which may be present. The reactions involved were supposed to be the following : 1) 2 NaOH + C0 2 = Na 2 C0 3 + H 2 O. 2) Na 2 S -f C0 2 + H 2 = NaHC0 3 + NaSH. 3) NaHC0 3 + NaSH = Na 2 C0 3 + H 2 S. But Lunge has shown that reactions (2) and (3) may not be fully realized, and hence that the decomposition of sodium sulphide is * Mohr, Analysis of Soda-ash from Stolberg (Lunge, Sulphuric Acid and Alkali, Vol.11). t This is derived from the gases of the black-ash furnace, which also contain some oxygen. Or it is obtained from the gases from lime kilns, which are much richer in carbon dioxide and introduce less flue dust into the product. 78 OUTLINES OF INDUSTRIAL CHEMISTRY very difficult. Some manufacturers complete the purification of the tank liquor by adding zinc hydroxide, which precipitates the sul- phide : Na 2 S -f Zn (OH) 2 - ZnS + 2 NaOH. If air is blown through the tank liquor, the sodium sulphide is con- verted into thiosulphate : Na 2 S + 2 2 + H 2 = 2 NaOH + Na 2 S A- The tank liquor may be better purified according to Fault's process, in which a little " Weldon mud " is added to the liquor, and air and steam blown through it. This oxidizes the sodium sulphide very completely, besides precipitating ferric oxide, silica, and alumina in the sludge. If the "Weldon mud" be regarded as manganese dioxide, for brevity the reactions may be written as follows : 2 Na 2 S + 4 Mn0 2 + 5 H 2 = 2 NaOH + Na 2 S A 4- Mn (OH)* 4 Mn (OH), + 2 2 = 4 Mn0 2 + 4 H 2 0. Since nearly all the manganese oxide is thus recovered, it may be used repeatedly, until it becomes very much contaminated with ferric oxide, silica, alumina, etc. After settling, the purified and carbonated tank liquor is drawn directly into the evaporating pans, which are usually large shallow iron tanks, the liquor being heated by surface contact with the waste gases from the black-ash furnace. Sometimes deep pans, heated from below, are used, since surface evaporation gives a product contaminated with dust from the furnace. The liquor is evaporated directly to dryness, and the " black salt " (chiefly mono- hydrated sodium carbonate, Na 2 C0 3 H 2 0) is calcined by heating it to a red heat. Sometimes sawdust is mixed with the uncarbonated liquor before evaporation, and then on calcining, the soda-ash is carbonated by the carbonaceous matter from the wood; but the charge is very liable to cake in this operation. The caustic soda and sodium sulphide of the tank liquor are thus converted to sodium carbonate, and, after all the sawdust is burned out, the ash becomes white or light brown. Or the liquor is evaporated till a crystalline mass separates ; then the mother-liquor ("red liquor") is drawn off, and the black salt is raked out of the pan. Much care is necessary to prevent the formation of a crust or the burning on of the precipitated carbonate. In most large works, a semicircular evaporating pan is used, provided with mechanical scrapers, to prevent the black salt from adhering to the pan. The best form of this apparatus is Thelen's THE SODA INDUSTRIES 79 pan (Fig. 40). In this, the scrapers (R, R) move the salts towards the end of the pan as they deposit, and a scoop lifts them to the draining apron. The beam (B) carrying the frame from which the scrapers are suspended, is rotated by the gear (J). For a very light colored product, the crude soda-ash is dissolved in water, and a little bleaching powder solution added; the pre- cipitated iron and other impurities settle out, and the clear solu- tion is evaporated until a thick mass of crystals separates, when the mother-liquor is drawn off to remove any soluble impurities. The monohydrated salt remaining is then' calcined without the addition of carbonaceous matter, to remove its crystal water, and the product is called "white alkali" or "refined alkali." A little sodium chlo- ride is formed by the addition of the bleaching powder, so that refined alkali is not quite so strong as soda-ash. It is chiefly used for glass making and other purposes where iron and sulphides would* be detrimental. Good Leblanc soda is nearly white or pale yellow, and should contain but few black specks. It usually con- tains a little caustic soda, a trace of sulphides and sulphites, some chloride and sulphate, and not over 1 per cent of insoluble matter. It should be finely ground before packing. Soda crystals or sal-soda CN"a 2 C0 3 10 H 2 0) is made by dissolving soda-ash in warm water, allowing the hot solution to stand quietly until all sediment deposits, and drawing off the clarified liquor into crystallizing tanks, where it is cooled to the atmospheric tempera- ture. Large crystals of sal-soda, very nearly pure, are deposited. They contain over 60 per cent of water, and are thus very bulky and not economical to ship ; but they are still preferred to soda-ash by some manufacturers. They do not dissolve so readily as soda- ash. They are sometimes used for making sodium bicarbonate, by exposing them on a grating to an atmosphere of carbon dioxide : 10 H 2 + C0 2 = 2 NaHC0 3 + 9 H 2 0. 80 OUTLINES OF INDUSTRIAL CHEMISTRY The water resulting from the reaction drips through, leaving the bicarbonate on the grating. CAUSTIC SODA Caustic soda is made from soda-ash, or from the " tank liquors " directly, by adding calcium hydroxide (milk of lime) to the solu- tion : Na 2 C0 3 + Ca(OH) 2 = CaCO 3 + 2 NaOH. When caustic soda is the ultimate product, it is generally custom- ary to use this lime mud (CaC0 3 ) instead of limestone, in the charge for the black-ash furnace, for the formation of caustic in the tank liquor is then of course not objectionable. The tank liquor must not have a density of over 20 Tw. (1.10 sp. gr.), or it will attack the calcium carbonate formed, and cause a partial reversion of the reaction. Consequently it is diluted with the wash waters from the lime mud of a previous operation. The liquor is then heated to boiling, and run into large iron tanks, where the " milk of lime " is added, and the mixture well stirred. Air or steam is usually blown into the liquor to assist in the mixing. The air, especially when aided by the addition of " Weldon mud" (p. 97), converts the sodium sulphide to sodium thiosulphate and sulphate : 2 Na 2 S + H 2 O + 40 = 2 NaOH + Na 2 S 2 3 . The thiosulphate is afterwards destroyed by oxidizing it to the sulphate. The solution of caustic soda is allowed to settle and is drawn into cast-iron kettles, which are heated by direct fire until the water is evaporated and the caustic soda remains as a fused mass. Some nitre is then added, or air is blown in to complete the oxidation of any thiosulphate to normal sulphate, which remains in the caustic, reducing its strength. To make very strong caustic, zinc oxide is often used to remove the sulphide from the tank liquors : Na^S -f ZnO + H 2 O = 2 NaOH + ZnS. The precipitated zinc sulphide is settled out, before evaporating the caustic liquor. By calcining the zinc sulphide, the zinc is re- converted to oxide. Sometimes the Yaryan system (p. 6) is used to evaporate the dilute caustic soda solution till it reaches a density of 60 Tw., at which point the other salts, such as sodium carbonate, which are dissolved in the caustic liquor, begin to crystallize; the liquor is THE SODA INDUSTRIES 81 then transferred to the open pan and the evaporation continued, the salts being raked out as they separate. The fused caustic soda is run directly into the sheet-iron drums in which it is sold. These are sealed as soon as cold, to prevent the absorption of moisture by the caustic. Loewig's process * for caustic soda depends on the formation of sodium ferrate (Na 2 Fe 2 4 ), which is then decomposed with water. The soda liquors are mixed with ferric oxide, and the mass evapo- rated to dryness and calcined at a bright red heat, usually in a revolving furnace. By the calcination, a reaction between the sodium carbonate and the iron oxide is brought about, carbon dioxide escaping and sodium ferrate remaining in the furnace. The mass is washed with cold water until all soluble matter is removed ; then water at 90 C. is run over the sodium ferrate, by which it is de- composed, caustic soda formed, and iron oxide regenerated; the last is returned to the calcining process. The ferric oxide used is a natural iron ore, very clean and free from silica or other impurities ; that made by calcining a precipitated ferric hydroxide is not well adapted to the process, as it gives a product difficult to lixiviate. The density of the resulting solution of caustic is about 62 Tw. (1.31 sp. gr.), and so less evaporation is necessary than in the lime process, where the density is only 15 or 20 Tw. Moreover, there are no other salts present, such as sulphate, thiosulphate, sulphide, or chloride, and the product is purer than that yielded by the lime process. But Loewig's process is not so well adapted to use with the Leblanc soda-ash, because the tank liquors must be evaporated to dryness before calcining the ferric oxide and sodium carbonate mixture, and the sodium carbonate must be quite pure. The pro- cess may be advantageously used with ammonia soda-ash, since this is obtained directly as a solid and no evaporation is necessary. Caustic soda of better quality can be made by Loewig's method, but it cannot be made so cheaply as by the use of lime with the tank liquor of the Leblanc process, especially in small works where the output is irregular and uncertain. For although there is no expense for lime, and less fuel is used for evaporation in the former method, yet an extensive and somewhat costly plant, designed to reduce labor to the minimum, is required, and considerable fuel is needed for the calcination. For the preparation of caustic soda by electrolysis of brine, see p % 104. * German Patent, No. 1650, Dec. 21, 1877. J. Soc. Chem. Ind., 1887, 438. Konrad W. Jurisch, Die Fabrikation von Schwefelsaurer Thonerde, p. 13. 82 OUTLINES OF INDUSTRIAL CHEMISTRY TREATMENT OP TANK WASTE In the Leblanc process nearly all the sulphur of the salt-cake remains in the " tank waste " or residue from the lixiviation of the black-ash. The average composition of this waste is shown in the following tables : COMPOSITION OF TANK WASTE FRESH * EEVOLVEE HAND FUBNACE HAND FUENACB Water 29.20 29.96 30.40 Na 2 C0 8 . . 3.16 1.97 1.63 CaCOs 21.19 36 92 38 81 Ca(OH) 2 .... Trace 8 85 9 53 CaS. . 56 89 37 90 35 12 CaSgOs 1 07 68 1 49 CaS0 3 Trace CaSO 4 Trace 0.20 CaSi0 8 3 53 1.34 1 21 Coal . 7.20 7.04 6 27 ALOi 1 02 37 13 FeS 1 65 2 44 2 76 Sand 2.82 1.79 2.61 COMPOSITION OF WEATHERED TANK WASTE 60 YEARS OLD t 19 INCHES BELOW THE SFRFACB 5 FEET BELOW THB SURFACE CaCO 3 53 14 52 77 CaS0 4 17.87 11.11 CaS0 3 0.65 3.10 CaS 2 8 0.80 2.89 CaS ... 0.04 Insoluble in HC1 10.10 10.91 A^Os Fe20s etc . . 7.18 11.04 Water 10.26 8.14 * Chance, J. Soc. Chem. Ind., 1882, p. 266. f Lunge, Sulphuric Acid and Alkali, 2d ed., Vol. II, p. 815. THE SODA INDUSTRIES 83 When fresh waste is thrown on the dump, the changes produced by weathering cause great nuisance. The air is contaminated by the hydrogen sulphide and sulphur dioxide liberated, and the soluble polysulphides of calcium and sodium formed are dissolved by rain- water making the objectionable "yellow liquors/' which run into streams and sewers. In fresh waste the sulphur is chiefly in the form of sulphide and thiosulphate of calcium, but in weathered material these have been converted by oxidation into sulphate and sulphite, which in them- selves cause no trouble except by their bulk. The simplest method of disposing of waste is to send it out to sea and dump it, if the works are so situated that this is convenient ; or, if this is impossible, to spread it evenly and beat it down hard to prevent as far as possible the infiltration of rain. But since the sul- phur thus lost every year represents an enormous money value, many attempts have been made to recover it in an available form. Of the numerous processes proposed only three need be considered here. In Mond's process the waste was treated directly in the lixiviat- ing tanks by blowing air or chimney gases through the wet mass. This oxidized the waste according to the following reactions: 1) 2 CaS + 2 H 2 = Ca(SH) 2 + Ca(OH) 2 . 2) Ca(SH) 2 + 40 = CaS 2 3 + H 2 0. But the hydration and oxidation processes were slow, and after a time it was necessary to lixiviate the mass, blow in air, and again lixiviate. By several lixiviations the calcium sulphydrate and thio- sulphate were dissolved, forming " yellow liquors." To recover the sulphur these were treated while still hot with dilute hydrochloric acid, the following reactions * taking place : 3) CaS 2 3 + 2 HC1 = CaCl 2 + H 2 + S0 2 + S. 4) Ca(SH) 2 + 2 HC1 = Ca01 2 + 2 H 2 S. In the presence of the calcium chloride solution the two gases, sulphur dioxide and hydrogen sulphide, react upon each other, form- ing water and free sulphur : 5) 2H 2 S + S0 2 = 2H 2 + 3S. The hydration and oxidation process was so controlled that the proportion of thiosulphate to sulphydrate yielded one molecule of * Mactear proposed to use the same reactions for the treatment of the drainage from old waste heaps, which were creating a nuisance. 84 OUTLINES OF INDUSTRIAL CHEMISTRY sulphur dioxide to two molecules of hydrogen sulphide. When properly worked very little escape of hydrogen sulphide occurred. The precipitated sulphur was filtered from the solution of calcium chloride which went to waste. The sulphur was then refined. This process recovered about 60 per cent of the total sulphur, but it consumed a great deal of hydrochloric acid, which now has con- siderable value, and some sulphur was lost owing to the formation of sulphate and sulphite of calcium, which, being insoluble, were left in the residue after lixiviation. The process is not now in use. Shaffner and Helbig's* process depends upon the reaction be- tween magnesium chloride and calcium sulphide in a boiling solu- tion : 1) CaS + MgCl 2 + H 2 = CaCl 2 + MgO + H 2 S. 2) MgO + CaCl 2 + C0 2 = CaC0 3 -f MgCl 2 . The second reaction was employed to recover the magnesium chloride, but the calcium carbonate formed was too impure for use in the black-ash furnace. The hydrogen sulphide set free was pure, and could be utilized by burning it with air, and conveying the resulting sulphur dioxide into the lead chambers of the sulphuric acid plant ; or the sulphide could be decomposed with sulphur dioxide, accord- ing to the method given on p. 83, reaction (5). Lime-kiln gases were used for the carbon dioxide in reaction (2). This process was not a commercial success. The Chance-Claus process t appears to be the only successful method of recovering sulphur on a large scale, and even this has not fully realized the original expectations of its promoters. The reac- tions of the process were proposed by Gossage in 1837, but although he worked on the idea for thirty years, and spent a large fortune in experimenting, he failed to make it a success. The following are the reactions involved : 2) 3) CaS + H 2 S = Ca(SH) 2 . A pure carbon dioxide containing at least 30 per cent C0 2 is neces- sary ; this can only be cheaply obtained in a carefully regulated special form of lime kiln. The tank waste is diluted with water and put into one of a series of seven cast-iron cylinders, so arranged that one may be emptied and recharged, while the others are in uninter- rupted operation. The freshly filled cylinder is made the last of the * J. Soc. Chem. Ind., 1882, 264. f J. Soc. Chem. Ind., 1888, 162. THE SODA INDUSTRIES 85 series, while the concentrated carbon dioxide from the lime kilns enter the cylinder containing the most nearly decomposed " waste." The hydrogen sulphide liberated is made to pass into the succeeding cylinders, where it reacts with the calcium sulphide to form calcium sulphydrate, according to reaction (3). This sulphydrate is then decomposed by the carbon dioxide, according to reaction (2). During the formation of the sulphydrate, very little else than nitrogen escapes from the last cylinder ; but when the decomposition of the sulphydrate by the carbon dioxide begins in the last two or three cylinders, hydrogen sulphide begins to escape from the apparatus ; when this gas is 30 per cent H 2 S, it is collected in a gasometer; when below 30 per cent, it is turned into the most recently filled cylinder, where reaction (3) takes place. The hydrogen sulphide collected in the gasometer, together with air, is passed through the Glaus sulphur kiln (Fig. 41), in which the reaction takes place. On the grate (A) is a layer of broken fire-brick covered with about 12 inches of ferric oxide. The mixture of hydrogen sul- H 2 SK> FIG. 41. phide and air is led into the kiln at (B), and made to pass through the ferric oxide (previously heated to a dull red) ; this causes the reaction to take place, and at the same time, the heat generated by the reaction is sufficient to keep the iron oxide at the proper tem- perature, after being once well started. Sulphur, nitrogen, and water vapor escape from the kiln. The sulphur vapor condenses in the chamber (D) as liquid sulphur, and in (E) as flowers of sulphur, while the steam and nitrogen, together with a small quantity of sul- phur dioxide, pass on to a condensing tower, where they are brought into contact with water, to retain the last traces of sulphur dioxide. When working well, this process recovers about 85 per cent of the sulphur. According to Lunge, the form of the kiln has been recently 86 OUTLINES OF INDUSTRIAL CHEMISTRY modified, but the principle of the process is unchanged. The water in the storage gasometer is usually covered with a layer of petroleum oil, to prevent the absorption of the hydrogen sulphide by the water. The process is not very lucrative at present, owing to the low price of sulphur, but since it reduces the nuisance created by the alkali waste, a number of English firms employ it. In 1893, over 30 plants were in operation in England, and more than 35,000 tons of sulphur recovered. For the Parnell and Simpson * process for utilizing alkali waste, see p. 90. THE AMMONIA SODA PROCESS The reactions involved in the ammonia soda process were dis- covered by H. G. Dyar and J. Hemming, about 1838, but owing to the mechanical difficulties, its practical success was not thoroughly established until 1873. In 1863, Ernest Solvay, a Belgian, con- structed an apparatus which has led to an enormous development of the industry, by which one-half of the world's supply of soda is now made. Its advantages lie in the strength and purity of its products and the absence of troublesome by-products, such as " tank waste." But it does not yield chlorine nor hydrochloric acid, all the former going to waste as calcium chloride. The ammonia soda process depends upon the fact that sodium bicarbonate is but slightly soluble in a cold ammoniacal solution of common salt. The technical success of the process depends chiefly on the proper regulation of the temperature during the precipitation, and on the capacity of the works to handle large quantities of gases and liquids. As far as possible, manual labor must be avoided, and the products moved and treated in solution or in suspension. The reactions are as follows : 1) Nad + NH 3 + H 2 + C0 2 = NH 4 C1 + NaHC0 3 . 2) 2 NH 4 C1 + Ca(OH) 2 = CaCl 2 + 2 H 2 + 2 NH 3 . The first equation is the chief one ; the second represents the recov- ery of the ammonia, and is essential to the commercial success of the process. The salt is used as a very concentrated brine, which has been purified from iron, silica, magnesia, etc. ; it is then saturated with ammonia gas, obtained from gas liquors, or by the recovery process according to equation (2). The carbon dioxide is obtained partly from lime kilns and partly from the calcination of the bicarbonate * J. Soc. Chem. Ind., 1889, 11. THE SODA INDUSTRIES 87 to form the normal carbonate (p. 89). It must contain at least 30 per cent of C0 2 , and is prepared in special forms of continuous limekilns. The lime resulting is used in the recovery of the ammonia (reaction 2), and for making caustic soda; the limekiln gases are cooled, and the sulphur dioxide removed, by washing in water before they pass into the carbonating towers. (See below.) The brine is contained in a tank, under the perforated bottom of which the ammonia gas is introduced, and rising through the liquor, is rapidly absorbed. The heat evolved by the absorp- tion is taken up by cold water circulating in coils. When saturated, the am- moniacal brine is pumped into a receiving and settling tank, from which it is de- livered to the " carbonating tower" (Fig. 42).* This is from 50 to 65 feet high, built of cast-iron rings or segments (A, A), each about 3.5 feet high and 6 feet in diameter. At the bottom of each segment is a flat plate having a large hole in the centre. Above each plate is a dome-shaped dia- phragm (D) perforated with a great number of small holes. In modern works a system of pipes passes through each segment, as shown at (B, B); in these, cold water is kept flowing, thus counteracting the heat generated by the chemical action. The ammoniacal brine is forced under pressure through the pipe (P), entering a little above the middle of the tower, which is nearly filled with brine. By this arrangement, any free ammonia in the brine, which would be swept away by the stream of gases passing up through the tower, is taken up by the carbon dioxide in the upper part of the tower. The carbon dioxide, having been previously well cooled, is forced through the pipe (C), entering under the lowest dome, and rising in small bubbles through the perforations in each * After Lunge. FIG. 42. 88 OUTLINES OF INDUSTRIAL CHEMISTRY dome, comes into intimate contact with the ammoniacal brine. The bicarbonate of sodium, thus precipitated gradually works its way down through the tower. A thick, milky liquid, containing the bicarbonate in suspension, and ammonium chloride and common salt in solution, is drawn off through (H) at the bottom. After a tower has been in use for some days, the holes in the domes become clogged with a deposit of bicarbonate crystals, which prevent the free passage of the gases. Consequently, every ten days or two weeks the liquid must be drawn out and the crystals dissolved by filling the tower with hot water or steam. The tower must be cooled before starting the process anew. As a rule, several towers are employed, so that one may be cleaned and cooled without interrupting the operation. The gases escaping from the top of the tower, consisting princi- pally of nitrogen, carbon dioxide, and some ammonia, are passed through scrubbers (p. 273), one of which contains brine, which after- wards goes to the ammonia saturating tank ; in the other is dilute sulphuric acid, to absorb the small amount of ammonia which would otherwise be lost. The carbon dioxide and nitrogen are allowed to escape. The towers are run with the view to the utilization of all the ammonia possible, even though there is considerable loss of salt and carbon dioxide ; usually about one-fourth of the salt remains undecomposed. It is now customary to place a smaller carbonating tower in con- nection with the large one ; in the former the brine is first treated with carbon dioxide and the ammonia converted to neutral carbon- ate (NH 4 ) 2 C0 3 ; then the brine is pumped into the large carbonating tower, where it meets more carbon dioxide, and the bicarbonate is formed, causing the precipitation of the sodium bicarbonate. More heat is liberated in the formation of the neutral carbonate of am- monia than in its conversion to the bicarbonate, hence the tempera- ture of the precipitation is more easily controlled when two towers are used, and less free ammonia escapes with the waste gases. A temperature of about 35 C. is most favorable to the formation of a granular or crystalline precipitate of bicarbonate, and also to the most complete utilization of the ammonia. At higher tempera- tures, too much bicarbonate remains dissolved in the liquor; at lower temperatures there is a tendency to the crystallization of ammonium acid carbonate and ammonium chloride, while the bicar- bonate separates as a very fine precipitate, which is difficult to filter from the liquor. The milky liquor from the bottom of the tower, containing the THE SODA INDUSTRIES 89 sodium bicarbonate in suspension, is filtered on sand filters (p. 15) connected with a vacuum pump ; or better, it is run into centrifugal machines (p. 14), which afford more rapid and complete separation of the mother-liquor. The bicarbonate is then washed with water, to remove as much of the sodium and ammonium chlorides as pos- sible. The mother-liquors and wash waters go to the ammonia recovery process. The sodium bicarbonate is then calcined in large covered cast-iron pans or ovens ; this converts the acid salt into soda-ash, and drives out any ammonia or moisture still in the mass. The following is the reaction : 2 KaHC0 3 = Na 2 CO 3 + CO, + H 2 0. The fumes are passed through coolers and scrubbers to remove ammonia; the concentrated carbon dioxide remaining is pumped into the carbonating towers. The ammonia liquors go to the ammonia stills. A modification of the Thelen pan (Fig. 40, p. 79) is sometimes used for this calcining. A gas-tight cover is placed over the pan, and the scrapers pass back and forth over the pan bottom, being moved by a connecting rod and crank. The gases and steam pass off through a pipe set in the cover. In practice, it has been found best to leave the mass in this pan only until all the ammonia and about 75 per cent of the carbon dioxide of the bicarbonate have been expelled; the calcination is completed in a reverberatory furnace. The product of the calcination is called soda-ash ; it is often very pure, containing only a trace of salt and a little bicarbonate, and is free from caustic soda, sulphide, and sulphate. But its density is only 0.8, while that of the Leblanc product is 1.2. This is dis- advantageous, owing to the larger packages needed for a given weight and to the mechanical loss incurred in operations where the soda-ash is exposed to a strong draught of air. In order to increase the density, it is sometimes subjected to a second heating in a rever- beratory (revolving) furnace. The second reaction, on p. 86, is that on which the recovery of the ammonia depends. The liquid in which the bicarbonate of soda was suspended contains undecomposed salt, ammonium chloride, and ammonium carbonate. It is passed through an ammonia still, usu- ally a tall column or dephlegmator (p. 8). Steam is admitted at the bottom of the apparatus, and bubbling up through the liquid, decomposes the ammonium carbonate into ammonia, carbon dioxide, 90 OUTLINES OF INDUSTRIAL CHEMISTRY and water; the ammonium chloride passes down into the lower part of the tower, or the still proper, where it is decomposed by "milk of lime." The ammonia set free is cooled and used to saturate the brine. The calcium chloride formed remains in solu- tion, and together with the excess of salt, goes to waste. (For the various proposals to utilize the waste calcium chloride for the pro- duction of hydrochloric acid and chlorine, see p. 102.) The damp bicarbonate is dried in an atmosphere of carbon dioxide, at a temperature of about 90 C. ; this prevents decomposition of the sodium bicarbonate, while the ammonium bicarbonate is decom- posed, the vapors passing to the scrubbers, where the ammonia is recovered. A considerable quantity of the bicarbonate of soda is sold directly to the manufacturers of baking powder and the poorer grades to the soda-water makers. Caustic soda can be made stronger and purer from ammonia soda- ash than from Leblanc ash, and the process is not essentially differ- ent, except that no treatment to remove sulphur is necessary ; but it cannot be made so cheaply as from the " red liquors " or the " tank liquors " of the Leblanc process. If pure lime is used for causticiz- ing ammonia soda-ash, the product is better than in the case of the Leblanc ash, as it is free from sulphur, alumina, etc. Loewig's process (p. 81) appears especially suited for causticiz- ing ammonia soda-ash, since it requires an ash free from silica. The Parnell and Simpson process* was expected to solve the problem of the Leblanc " alkali waste " ; but while it is interesting, it has not justified the hopes of its promoters. It was proposed to combine to a considerable extent the two leading soda processes. The reactions involved are as follows : 1) (NH 4 ) 2 S + C0 2 + H 2 = NH 4 HC0 3 + NH 4 HS. 2) NH 4 HS + C0 2 -f H a O = NH 4 HC0 3 + H 2 S. 3) NH 4 HC0 3 + NaCl = NaHC0 3 + NH 4 Cl. 4) CaS + 2 NH 4 C1 = (NH 4 ) 2 S + CaCl 2 f A solution containing a mixture of ammonium sulphide and salt is treated with carbon dioxide, as in the ammonia process. Sodium bicarbonate is precipitated and hydrogen sulphide set free ; this is burned with air, and the sulphur dioxide sent to the lead chambers of the sulphuric acid process. Or the sulphur may also be recovered in a Glaus kiln (p. 85). The ammonium sulphide is obtained by * J. Soc. Chem. Ind., 1889, 11. t Equation (4) does not exactly represent the facts, as some polysulphides are present in the tank waste. THE SODA INDUSTRIES boiling the alkali waste of the Leblanc process, with the ammonium chloride liquors of the ammonia process, or those formed in this (Parnell-Simpson) process. Thus the ammonia is recovered and at the same time the troublesome Leblanc waste is disposed of. When the waste is boiled in the ammonium chloride solution, ammonia gas, together with vapors of ammonium sulphide, is lib- erated. These are led directly into the brine solution in the satu- rating tank. The ammoniacal brine is then pumped into the carbonatiug tower, which is very similar to that described on p. 87. Here the first three reactions take place ; * the hydrogen sulphide generated goes to the sulphur recovery, while the ammonium chloride solution, carrying the sodium bicarbonate in suspension, is drawn out and filtered. The conversion of salt into sodium carbonate by any method involves an endothermic reaction in some part of the process. Thus energy must be expended, necessitating the use of fuel. In the case of the Leblanc process, this expenditure of fuel is large, and is chiefly used in carrying out the reactions in the salt-cake and the black-ash furnaces. But much of the expended energy of this pro- cess reappears in the hydrochloric acid, the principal by-product. In the ammonia process the principal reactions are exothermic, but some fuel is consumed by the calcination of the precipitated bicarbonate and in the preparation of the quicklime used in the ammonia recovery and for generating carbon dioxide. Although less fuel is used than in the Leblanc process, the practical economy of the ammonia process is not so great as would at first appear ; for all the chlorine is lost, together with a large part of the original salt used. As a method of producing soda-ash it is far superior to the Leblanc, but until a practical process for the cheap production of chlorine is discovered, the latter will continue to be an extensive industry. * According to Lunge, Sulphuric Acid and Alkali, Vol. Ill, p. 157, the sodium bicarbonate is formed by agitating the brine with crystallized ammonium bicarbon- ate, the latter being obtained by saturating the ammonium sulphide solution with carbon dioxide (equations 1 and 2) . The carbon dioxide, which must be very pure and concentrated, is made by heating ammonium bicarbonate crystals to 74 C., in a retort, CO 2 , steam, and NH 3 passing off. By scrubbing (p. 273), the carbon dioxide is obtained pure. Ammonium bicarbonate is also prepared by passing lime-kiln gases into a solution of ammonia or neutral ammonium carbonate, and then cooling it to crystallize the bicarbonate. 92 OUTLINES OF INDUSTRIAL CHEMISTRY THE CRYOLITE SODA PROCESS Cryolite is a double fluoride of sodium and aluminum, found as a mineral in southern Greenland. As no other important deposit has been found, the supply is limited, and only two or three manu- factories using this process are in operation, one of which is in this country. The reactions involved are as follows : 1) A1F 3 3 NaF + 3 CaC0 3 = NaAlO, + Na 2 O + 3 CaF 2 + 3 C0 2 . 2) NaA10 2 + Na 2 = Na3A10 3 . 3) 2 Na 3 A10 3 + 3 H 2 + 3 CO 2 = 3 Na 2 C0 3 + 2 Al (OH) 3 . The ground cryolite is mixed with powdered limestone, and calcined at a red heat. Carbon dioxide escapes, and a mixture of calcium fluoride, sodium oxide, and sodium aluminate remains. On lixiviat- ing this mixture with water, another sodium aluminate is formed and goes into solution, leaving the calcium fluoride as an insoluble resi- due. The solution of sodium aluminate is then decomposed according to the third reaction, by passing into it purified lime-kiln gases, or the furnace gases of the calcining operation. Hyd rated alumina is precipitated, while sodium carbonate remains in solution. Sal-soda may be made by evaporating the solution, and was formerly the chief source of bicarbonate for culinary and medicinal purposes. If carried to complete dryness and calcined, a high grade of soda-ash is obtained. By causticizing, it yields a very excellent caustic. The by-products aluminum hydroxide and calcium fluoride are used in the alum and glass industries respectively. Many other processes for the manufacture of soda from salt have been proposed, but none of them are now of any commercial impor- tance. A small amount of soda is still made from kelp or varec, which is the ash of seaweeds. A new process for making soda has been proposed, * which is in- teresting and may be developed in the future, but has not as yet been placed on a practical basis. Salt-cake is made from salt by the Hargreaves process (p. 71) ; then in the same cylinder and at the same temperature, it is treated with water gas. This reduces the salt- cake to sodium sulphide, while water, carbon monoxide, and hydro- gen escape. These vapors are cooled, the water condensed, and the mixture of gases burned, the products of combustion, carbon dioxide and water, passing into the cylinders containing the sodium sul- * J. Soc. Chem. Ind., 1895, 933. THE SODA INDUSTRIES 93 phide. Hydrogen sulphide and sodium carbonate are formed, and as the temperature is much above 100 C., no water can combine with the carbonate. The hydrogen sulphide is burned to sulphur dioxide, and the latter returned to the Hargreaves process. The reactions involved are as follows : 1) 2 NaCl + S0 2 + H 2 + O = Na 2 S0 4 4- 2 HC1. 2) Na 2 S0 4 + 5 CO + 5 H 2 = Na 2 S + 4 H 2 + 5 CO + H 2 . 3) CO + H 2 + 2 = C0 2 + H 2 0. 4) Na 2 S + C0 2 + H 2 = Na 2 C0 3 + H 2 S. 5) H 2 S + 3 O = H 2 O + S0 2 . This process seems to offer several advantages of which the following are the chief : 1. Cheap materials. 2. Small outlay for labor, the materials not been handled from the time the salt is charged into the cylinders until the soda-ash is raked out. 3. No waste products nor nuisance. 4. The temperature constantly decreases, being highest when the furnace is charged and lowest when the soda-ash is finished. 5. The process yields hydrochloric acid which can be utilized for making chlorine. For the methods of producing caustic soda and chlorine by electrolysis of brine, see Chlorine, p. 104. REFERENCES Berichte ueber die Entwickelung der chemischen Industrie. A. W. Hoffmann, Vol. I, 418. (1875.). History, Products, and Processes of the Alkali Trade. Charles T. Kingzett, London, 1877. (Longmans.) Manual of Alkali Trade. John Lomas, London, 1880. (Crosby, Lockwood and Co.) J. Soc. Chem. Ind : 1883, 405, Walter Weldon. 1885, 527, Ludwig Mond. 1886, 412, E. K. Muspratt. 1887, 416, Watson Smith. 1888, 162, Alexander Chance. 1889, 11, E. Parnell. Sulphuric Acid and Alkali. G. Lunge, 2d ed., Vols. II, 1895, III, 1896. (Gur- ney and Jackson, London.) 94 OUTLINES OF INDUSTRIAL CHEMISTRY CHLORINE INDUSTRY. Chlorine is extensively used in the arts as a bleaching and oxidizing agent. It is chiefly employed in the form of a solution of " bleaching powder " or " chloride of lime," which contains cal- cium hypochlorite, and as chlorates or hypochlorites of the alkali metals. Liquid chlorine, compressed in steel cylinders, has recently become an article of commerce, and it appears probable that this form of shipment may be extended in the future. Practically, all the chlorine used in the arts must be derived from the chlorides of sodium, potassium, or magnesium, which are found more or less abundantly in nature. A very large part of the hydrochloric acid made from salt (p. 67) is used for making chlorine. Since this acid is the chief by-product of the Leblanc process, a plant for making bleaching powder is always a part of those works. The important methods of making chlorine from the acid may be considered under two heads : those using manganese oxides for decomposing the acid, and those not using manganese for this purpose. The function of manganese is to oxidize the hydrogen of the acid, forming water and liberating the chlorine. At the same time, the manganese is converted into chloride, and being somewhat ex- pensive, its recovery in a form that permits of its return to the process is essential. The oxides of manganese are found in nature as pyrolusite (Mn0 2 ), braunite (Mn 2 3 ), manganite (Mn 2 3 H 2 0), hausmannite (Mn 3 4 ), wad and psilomelane, the last two of indefinite composi- tion. The reactions occurring when manganese oxides are treated with hydrochloric acid are as follows : 1) MnO + 2 HC1 = MnCl 2 + H 2 0. 2) Mn0 2 + 4 HC1 = MnCl 2 + 2 H 2 + 2 Cl. 3) Mn A + 6 HC1 = 2 MnCl 2 + 3 H 2 + 2 Cl. 4) Mn 3 4 + 8 HC1 = 3 MnCl 2 + 4 H 2 O + 2 Cl. Thus it is readily seen that with pyrolusite, less acid is neces- sary for a given yield* of chlorine, and a smaller quantity of man- ganous chloride must be treated to recover the manganese. This ore is purchased according to its content of Mn0 2 , which is estimated by determining the " available " oxygen. The presence of iron oxides, silica, calcium carbonate, etc., is disadvantageous. CHLORINE INDUSTRY 95 FIG. 43. In small works, especially where no at- tempt is made to recover the manganese, the process is carried on in simple stills of earthenware or sandstone. The earthen- ware stills (Fig. 43)* are cheap, but of limited capacity. They are heated by blowing free steam into the wooden casing in which they are set. The pyrolusite is put into the central perforated cylinder, and the acid runs through the pipe (A), chlorine escaping at (B). Sandstone stills (Fig. 44)* are made from single blocks of sandstone, or built up of slabs, the joints being made tight by a rubber packing, or by a lute of clay and lin- seed oil. The pyrolusite rests on a false bottom (A), and the acid is run in through (B), while steam is blown in through the sandstone pipe (C). Chlorine es- capes through (D). These stills are larger than the earthenware ones, but do not utilize the acid so com- pletely. The pipes through which chlorine is conducted are of lead or earthenware. Since valves in these pipes are rapidly corroded, a device shown in Fig. 45* is used to shut off the flow of gas. A U-shaped bend is made in the pipe, and a small flexible tube attached at the lowest point of the U, connecting it with the vessel (A), filled with water. By raising (A), the water flows into and fills the U-pipe to the line (CD), cutting off the flow of gas. By lowering (A) to (A r ), the water runs out of the U, and the flow of gas is uninterrupted. The liquor remaining in the still con- * After Lunge. FIG. 44. 96 OUTLINES OF INDUSTRIAL CHEMISTRY tains much free acid, manganous chloride, ferric chloride, etc. It continues to evolve some chlorine for a long time, and is a very offensive and troublesome material to dispose of, since it pollutes the air, or the streams, into which it passes. Of the many attempts to recover the manganese, the two follow- ing are the most important : By Dunlop's method, the " still liquor " is neutralized cold, with powdered limestone, until all free acid is removed and the iron pre- cipitated. The clear solution of manganous and calcium chlorides is then mixed with a carefully determined quantity of powdered limestone or chalk, and heated under pressure by steam. This precipitates the manganese as carbonate, which is settled, and the solution of calcium chloride drawn off. The manganous carbonate is washed, and then calcined at about 300 C. in a retort, while water spray and a current of air is introduced. This produces a mixture of Mn0 2 , MnO, Mn 2 3 , etc., containing about 70 per cent of the dioxide. The process requires an expensive plant and consumes a large amount of fuel. The Weldon process,* for manganese recovery, is the most successful, and is in general use in all large works, since it furnishes a continu- ous process for chlorine mak- ing and manganese recovery. The " still liquors " are neu- tralized with just sufficient powdered limestone or chalk to remove free acid and pre- cipitate the iron. This is done in the tank (A) (Fig. 46),f provided with a stirrer. The mixture is then pumped into settling tanks (B, B), where the precipitate deposits. The clear solution of manganous and calcium chlorides is then drawn into the " oxidizers " (C), where steam is blown in to heat it to 55 C. Milk of lime is made from pure lime, especially free from magnesia, and is added from (E) until tests FIG. 46. * J. Soc. Chem. Ind., 1885, 525. f After Lunge. CHLORINE INDUSTRY 97 show that the manganese is all precipitated ; meanwhile air is slowly forced into (C). The quantity of "milk" used is noted, and then from one-half to one-quarter more is added, and the air blast turned on at full strength. This addition of an excess of lime is necessary to hasten and complete the conversion of manganous hydroxide into the peroxide, and to prevent the formation of Mn 3 4 (" red batch "). The total quantity of lime used should be such that the precipitate formed during the blowing contains approximately two molecules of manganese peroxide to one of calcium oxide. This is the so-called " acid calcium manganite " (CaO Mn0 2 ) 4- (MnO Mn0 2 ), a mixture of manganites of calcium and manganese. It forms a thin, slimy, black mass, and is called "Weldon mud." By adding a little more neutralized " still liquors " during the " blowing," some of the calcium oxide in the calcium manganite can be replaced by manganese from the manganous chloride of these liquors. The calcium chloride liquor, in which the mud is suspended, is run into settling tanks (D, D), from which the supernatant solu- tion is drawn off as waste. The Weldon mud is then run into the chlorine stills (F, F) as a thin paste; if of good quality, it contains about 80 per cent of its manganese as Mn0 2 , and owing to its fine state of division, is readily decomposed by dilute hydrochloric acid. A small loss of manganese occurs in the precipitate from the first neutralization with marble or chalk dust; this loss is made up by decomposing some pyrolusite with hydrochloric acid in a small still (G), and adding this liquor to that from the stills (F, F). The Weldon process works continuously and almost automatic- ally, the materials being handled by pumps as liquids or slimes. It is also very rapid, producing large amounts of chlorine, with but slight loss (2 to 3 per cent) of manganese oxide. But even at its best, only about one-third of the chlorine of the hydrochloric acid is obtained as gas, the remainder going to waste as calcium chloride in the liquor from the oxidizers. Schlosing's process * for chlorine by the use of nitric and hydro- chloric acids and manganese oxides depends upon the following reactions : 2 HC1 + 2 HN0 3 + Mn0 2 = Mn(N0 3 ) 2 4- 2 H 2 + C1 2 . The reaction is carried out by heating the mixture of acids and manganese peroxide to 125 C., using an excess of nitric acid. By heating the manganous nitrate to 180 to 190 C., it 'is decomposed, * Zeit. angew. Chemie, 1893, 99, Lunge and Pret. Wagner's Jahresbericht, 1862, 235. H 98 OUTLINES OF INDUSTRIAL CHEMISTRY and nitric acid may be regenerated from the vapors by treating them with air and steam, while manganese peroxide is recovered: Mn(N0 3 ) 2 = Mn0 2 + N 2 4 ; Wischin, Just, and Alsberge have each patented modifications of the above process. Alsberge proposes to apply the method to the recovery of chlorine from the ammonium chloride liquors of the ammonia soda process, by employing the following equations: 1) 2NH 4 Cl+MgO+Mn0 2 =MgCl 2 +Mn0 2 4-H 2 0+2NH 3 . 2) MgCl 2 +Mn0 2 +4 HNO 3 =Mg(N0 3 ) 2 +Mn(N0 3 ) 2 +2 H 2 +01* By evaporating to dryness and calcining the residue, the nitrates are decomposed thus : Mg(N0 3 ) 2 + Mn(N0 3 ) 2 = MgO + Mn0 2 + 2 N 2 4 + 0. The peroxide of nitrogen is converted to nitric acid by treatment with steam and air : Deacon's process! seems to be the most successful method of producing chlorine without the use of manganese. It depends on the oxidation of hydrochloric acid gas, by the oxygen of the air. This is done in the presence of certain metallic salts, which may act as " contact " substances, or as carriers of oxygen from the air to the acid, the apparent reaction being : The most satisfactory "contact" or " catalytic" substance for this purpose is copper chloride. When cupric chloride is heated to 400 C., it dissociates into cuprous chloride and free chlorine. Then, on exposing the cuprous chloride to oxygen, cupric oxide is formed and more chlorine set free. But the cupric oxide, reacting with hydrochloric acid gas, forms water and cupric chloride. The following are the reactions involved : 1) 2 CuCl 2 = Cu 2 Cl 2 + C1 2 . 2) Cu 2 Cl 2 + 2 = 2CuO + Cl 2 . 3) 2 CuO -f 4 HC1 = 2 CuCl 2 + 2 H 2 0. Thus the catalytic substance is regenerated and the cycle of changes begins anew. t Chemical News 22 (1870), 157. CHLORINE INDUSTRY 99 Heat to the amount of 32 calories is absorbed during the disso- ciation of cupric chloride, but in the other reactions 60.4 calories is evolved. Since the sum of the reactions represents a positive gain of 28.4 calories, theoretically when the process is once under way no addition of heat is necessary. But, in fact, some heat must be sup- plied ; this is done by heating the mixture of air and hydrochloric acid gas to 400 C. before admitting it to the " decomposers." Theo- retically, too, all the chlorine of the hydrochloric acid should be recovered, but practically the reaction is far from complete. FTG. 4T. The plant for the process (Fig. 47)* is quite extensive. The gases from the salt-cake pan (A),t together with air, are passed through cooling pipes and drying tower ( B) to condense moisture ; then they go through the "superheater" (C), where the temperature is raised to 400 C. The hot gases then pass into the "decomposer" (D), a tall cast-iron cylinder, containing bits of brick or other porous material which have been soaked in a solution of cupric chloride. Here the above reactions take place, and the resuMng mixture of chlorine, hydrochloric acid, nitrogen, steam, and oxygen, passes through a condensing apparatus (E, E) to remove the hydrochloric acid, and then through a coke tower (F, F) sprinkled with concen- trated sulphuric acid to remove all the moisture; finally, the dry chlorine gas (with the nitrogen and oxygen) goes to the chambers where bleaching powder is made (p. 110). The catalytic substance in the decomposer becomes inactive after a time (it seldom lasts more than four months) and must be re- placed by fresh material. To accomplish this without interrupting the process the decomposers are now built in separate compartments, each holding about six tons of broken brick ; every two weeks one compartment is emptied and recharged without discontinuing the * After Lunge. t Roaster gas is too dilute and impure. 100 OUTLINES OF INDUSTRIAL CHEMISTRY flow of gas through the others. This loss of activity in the cata- lytic substance is attributed* to the presence of sulphuric acid in the gases from the salt-cake furnace. To overcome this difficulty, Hasenclever has devised a method! by which an aqueous solution of impure hydrochloric acid, made in the bombonnes and coke towers, is run into hot, concentrated sulphuric acid (1.42 Tw.) while a blast of air is forced through the mixture. The sulphuric acid absorbs the water and generates pure HCl gas, which mixes with the air in proper proportion for use in the decomposer of Deacon's process. By this method, 84 per cent of the hydrochloric acid gas is decomposed according to the reaction : 2HC1+0 = H 2 + 2C1. The diluted sulphuric acid is concentrated and returned to the process. The dilute hydrochloric acid which passes through the apparatus is recovered by washing the chlorine gas, and is mixed with the strong acid from the roasters. Owing to the admixture of nitrogen with the chlorine, the latter is weaker than that furnished by the Weldon process. It is well suited for making chlorates (p. Ill), but for making bleaching powder a special form of absorption chamber must be used. When the hydrochloric acid gas is taken directly from the salt- cake pan or from the muffle furnace, there is apt to be some diffi- culty in working Deacon's process, owing to the variation in the rate of liberation of the gas. Much care in the regulation of the air supply is necessary. The hydrochloric acid gas from the Hargreaves process (p. 71) is too dilute for direct use in the Deacon apparatus. Arsenic in 'the sulphuric acid used in the salt-cake pan, or for drying the chlorine gas, causes a loss, in the first case by rendering the copper salt inactive, and in the second, by forming hydrochloric acid, thus : + 4 Cl + 2 H 2 = As 2 5 + 4 HCl. Part of this hydrochloric acid combines with the As 2 5 to form a solution which condenses in the pipes between the drying tower and the bleaching powder chambers. But some of the acid is left in the chlorine and attacks the bleaching powder, causing it to be " weak." The cost of a Deacon plant is rather more than of a Weldon * Berichte d. chem. Gesellschaft, IX, 1070. t Lunge, Sulphuric Acid and Alkali, If, 417. CHLORINE bttSTRY^VXv \\\ \ ;. 101 plant of the same capacity ; and while it is theoretically a superior process and requires less labor, it is not yet in general use. Several processes for the preparation of chlorine by the use of nitric and sulphuric acids have been proposed. Dunlop's nitric acid-chlorine process depends* upon one or the other of the following equations: 2 NaCl + 2 NaNO 3 + 4 H 2 S0 4 = 4 NaHS0 4 + N 2 O 4 + C1 2 + 2 H 2 ; 4 NaCl + 2 NaN0 3 + 6 H 2 S0 4 = 6 NaHS0 4 + N 2 3 + 2 C1 2 + 3 H 2 0. The mixture of salt, sodium nitrate, and sulphuric acid is heated in an iron cylinder which is surrounded by the flames of the fire. The vapors leaving the retort are passed through concentrated sul- phuric acid which retains the nitrogen oxides, and the chlorine is then washed with water to remove any traces of hydrochloric acid. The nitrous vitriol obtained may be used in the sulphuric acid manufacture. The process was worked on a large scale at St. Kol- lox, England, but has been abandoned. Donald's process t consists in passing the hydrochloric acid vapor from a salt-cake furnace through sulphuric acid to dry it, and then through a mixture of nitric and sulphuric acids kept at C., when the following reactions take place : 2 HC1 + 2 HN0 3 = 2 H 2 + N 2 4 + C1 2 . The gas mixture thus formed is led through dilute nitric acid, when the following takes place : N 2 4 + H 2 = HN0 3 + HNO 2 . By passing through concentrated sulphuric acid, the nitrous acid and nitrogen oxides are absorbed, while the chlorine is sent to the bleaching powder chambers. The S adler- Wilson $ nitric acid-chlorine process consists in re- acting upon hydrochloric acid with nitric acid, in the presence of sulphuric acid; the operation is carried on in a heated " decom- poser " built of flagstones. The hot, dilute sulphuric acid is again concentrated, and the gases from the decomposer are cooled and passed through a Gay Lussac tower to recover the nitrous vapors. The chlorine is washed to remove free hydrochloric acid, dried and led into the bleaching powder chambers. Many attempts have been made to recover the chlorine from the waste liquors of the ammonia soda process, but no one of them has Lunge, Sulphuric Acid and Alkali, III, 566. t Ibid., 572. J J. Soc. Chem. Ind., 1895, 865. 102 OFTLI'NPS OF INDUSTRIAL CHEMISTRY yet proved a commercial success. Several of them are, however, interesting, and deserve a few words. Solvay conducted elaborate experiments in which he tried to realize the reaction: CaCl 2 + Si0 2 + O = CaSiOg + C1 2 . But calcium chloride is very stable, and its decomposition in this way is incomplete, and requires enormous expenditure of heat, besides that used in evaporating the solution of calcium chloride to dryness. Magnesium chloride is more easily decomposed than calcium chloride, and several processes have been devised, based on the use of this salt. It is proposed to use magnesium oxide or hydroxide instead of lime for decomposing the ammonium chloride solution of the ammonia process ; by this, magnesium chloride is formed and the ammonia gas set free. Both Solvay and Weldon, within a few days of each other, patented methods for carrying out this idea. But the reaction between ammonium chloride and magnesia is not complete, and the solution of magnesium chloride obtained is dilute. Viewed as a method for chlorine, more promising results were ob- tained by using the concentrated magnesium chloride mother-liquors from the Stassfurt industries (p. 132), or from other manufacturing operations. The magnesium chloride solution is evaporated to dry- ness at a very low temperature, and the dried chloride is decomposed by passing air or steam over it while heated to a red heat. The reactions are as follows : 2) The hydrochloric acid obtained is used in the Weldon or Deacon process. The Weldon-Pechiney * process was the most successful of the magnesia methods, though none of them can be said to be profitable. In this, magnesium chloride solution (made by dissolving the oxide in hydrochloric acid, or obtained from waste liquors) is concentrated until it contains six molecules of water for each molecule of magne- sium chloride; then 1-J- equivalents of magnesium oxide is stirred into the solution. The pasty mass heats and soon hardens to a solid cake of magnesium oxychloride, which is broken into lumps about the size of a butternut, and screened to remove the dust. The presence of dust causes the mass to cake badly during the subse- J. Soc. Chem. Ind., 1887, 775. CHLORINE INDUSTRY 103 quent drying. The lumps are dried at a temperature not exceeding 300 C., by passing a current of hot air over them while spread in a thin layer on gratings. Too high temperature causes a loss of chlorine as such. If not thoroughly dried, chlorine is lost as hydro- chloric acid. The dried oxychloride is quickly decomposed in a special form of retort, which has been heated by producer gas to a temperature of 1000 C. before the charge is introduced. Air is passed into the retort to assist in the decomposition, which must be rapid, or the yield of chlorine is reduced. Magnesium oxide is left in the retort, while a mixture of chlorine, hydrochloric acid, and nitrogen escapes. The hydrochloric acid is recovered by wash- ing the gases with water, and is used to dissolve part of the oxide from the retort. The chlorine, mixed with nitrogen, is used for bleaching powder, or for chlorate making, preferably the latter. The residue of magnesium oxide from the retorts is returned to the first stage of the process. The yield, including the hydrochloric acid recovered, is about 88 per cent of the whole amount of chlorine in the magnesium chloride. About 40 per cent is obtained as free chlorine, and 48.5 per cent is returned to the process as MgCl 2 and HC1. Of the several methods that have been devised for the direct production of chlorine from the ammonium chloride formed in the ammonia soda industry, Monet's process, 1 * which provides for the re- covery of the ammonia, has been most carefully developed, but its practical success is as yet problematical. It is based on the disso- ciation of ammonium chloride into ammonia and hydrochloric acid, at a temperature of 350-360 C. ; the hydrochloric acid being then combined with some metallic oxide, to form a non-volatile chloride, to be later decomposed with liberation of the chlorine. Oxide of nickel was used at first, but was later abandoned in favor of mag- nesium oxide. The reactions are : 1) MgO + (2 NH 3 + 2 HC1) = MgCl 2 + H 2 + 2 NH 3 . 2) MgCl 2 + = MgO + C1 2 . Since an excess of magnesia is present, it is very probable that considerable magnesium oxychloride is also formed, according to the reaction : 2 MgO + 2 HC1 = MgO - MgCl 2 + H 2 0. Then this is decomposed by the air (reaction 2), thus : MgO 2 MgCl 2 + = 2 MgO + C1 2 . *Chemische Industrie, 1892, 466. J. Soc. Chem. Ind., 1887, 140, 216, 217, 440; 1888, 626, 845. 104 OUTLINES OF INDUSTRIAL CHEMISTRY The liberated ammonia passes from the apparatus to the scrub- bers of the ammonia recovery process. The complete recovery of this ammonia is the first essential to the success of this method. The ammonium chloride is crystallized from the liquors of the Solvay carbonating towers (p. 87), by cooling them to about C. The dry crystals are then vaporized by introducing them into melted zinc chloride, contained in an iron vessel lined with an antimony alloy. The magnesium oxide, mixed with some potassium chloride, china clay, and lime, is made into balls ("pills"), about one-half inch in diameter, and baked. The decomposer is then filled with the "pills' 7 and heated to 360 C., when vapors of ammonium chloride are passed through the apparatus. The reaction between the ammo- nium chloride and magnesia raises the temperature in the decom- poser above 400 C. Next, inert gases, such as those from lime- kilns, heated to 550 C,, are passed into the apparatus to drive out the ammonia and water vapors; these also heat the charge above 500 C. Air, heated to 800 C., is then admitted to break up the magnesium chloride (reaction 2) and regenerate the oxide ; it also sweeps out the chlorine formed. After cooling to 360 C. ammonium chloride vapors are again introduced and the cycle of operations is repeated. To secure uninterrupted working, there are usually four decomposers in each plant. ELECTROLYTIC PROCESSES FOR CHLORINE AND CAUSTIC SODA By passing a current of electricity through a sodium chloride solution the salt is decomposed into chlorine at the anode and sodium at the cathode. But the latter at once decomposes a mole- cule of water of the solution, forming caustic soda and setting free hydrogen. Hence the products of electrolysis are chlorine, caustic soda, and hydrogen, of which the last mentioned is of no practical value at present. There are serious mechanical difficulties encountered in all elec- trolytic processes for decomposing salt. The chlorine set free at the anode must not be permitted to diffuse through the whole solution, since it causes secondary reactions. To prevent this diffusion, vari- ous devices have been proposed, most of them being porous dia- phragms between the anode and cathode. But no material is yet known which, while offering no resistance to the passage of the electrical current, still prevents the diffusion of the sodium hydroxide CHLORINE INDUSTRY 105 and chlorine solutions. Furthermore, very few substances can be used for the diaphragms, because of the destructive action of the chlorine. The nascent chlorine is also very destructive to the anode and practically only platinum, or slabs cut from magnetite (Fe 3 O 4 ), have proved efficient in withstanding its action. These are expen- sive, and magnetite slabs are very fragile. If the hydrogen liberated at the cathode is permitted to escape through the solution, it stirs the liquid, aiding the diffusion of the chlorine, and the consequent formation of chlorates and hypochlorites, thus : 1) Nad = Na + Cl. 2) Na + H 2 O = NaOH + H. 3) 2 NaOH + 2 Cl = NaCIO + NaCl + H 2 O. 4) 3 NaCIO = NaC10 3 + 2 NaCl. 5) NaC10 3 + 6 H = NaCl + 3 H 2 0. Thus reactions 3, 4 and 5 cause a loss, since they regenerate salt from the chlorine set free. LeSueur's process* formerly employed the apparatus described in Lunge's "Sulphuric Acid and Alkali," Vol. Ill, p. 664. The cathode, of iron wire gauze, was placed in a slanting position. On it rested the diaphragm, consisting of two parts, a sheet of parch- ment paper and a double sheet of asbestos cemented together by blood albumin, coagulated and hardened by treatment with potas- sium bichromate. An earthenware bell enclosed the anode, which was made of lead, carrying carbon rods dipping into the salt solu- tion. Caustic soda was formed in the solution outside the bell, and owing to the inclined position of the cathode, the hydrogen was expected to escape readily, thus preventing polarization. But it proved in practice that the earthenware bells were disintegrated by the caustic soda solution, while the hydrogen set free on the lower side of the cathode did not ascend along the sloping dia- phragm and escape, but diffused through it and found its way into the interior of the cell. This resulted in forming a dangerous mixture of hydrogen and chlorine, and it is said that several serious explosions occurred. Consequently the form of the cell has been altered; but no facts regarding the improved cell can be given, owing to the secrecy maintained about its construction and working. The diaphragms are rapidly destroyed, lasting only from 24 to 48 hours. The anodes are consumed more slowly, lasting about six weeks. The process yields a solution of caustic containing 10 per cent NaOH. * J. Soc. Chem. Ind., 1892, 963; 1894, 453. 106 OUTLINES OF INDUSTRIAL CHEMISTRY In Carmichael's apparatus,* an asbestos diaphragm, impregnated with Portland cement, is used. The diaphragm rests horizontally on the cathode at the bottom of the cell ; above it is a bell to collect the hydrogen given off. The anode is a grating of copper rods, covered with hard rubber, through which numerous platinum points project into the brine. This anode is suspended in the top of the cell, and the chlorine set free is thus only momentarily in con- tact with the liquid. The salt solution is fed into the cell at the top, in a rapid stream of drops while the mixture of caustic soda and salt flows continuously from the bottom. The supply of brine is so regulated that the caustic formed at the cathode is drawn off before it has time to diffuse through the liquid. The solution drawn from the cell contains about 20 per cent of caustic soda, and about 75 per cent of the salt is decomposed. The reaction is carried on at a temperature of about 80 C. in the top of the cell near the anode, while the region around the cathode is kept as cool as possible. Being removed from the immediate action of the chlorine, the dia- phragms are very durable. Greenwood's apparatus! consists of an iron vessel, coated with electrolytically deposited copper ; this is made the cathode, and in it is placed a circular anode coated with carbon. Between the anode and the vessel walls is a diaphragm made up of a series of V-shaped circular troughs of glass or porcelain, fitted together, the spaces between them being packed with asbestos. The chlorine from the anode chamber is led away by suitable pipes, and the caustic-salt solution passes into another similar cell, where more of the salt is decomposed. The cells are placed en cascade, the brine flowing from the top one, down through the series. The solution obtained in this process contains about 2.2 per cent NaOH. In the Holland and Richardson process $ the cathode is covered with cupric oxide. The hydrogen liberated here reduces the oxide to metallic copper, and polarization is prevented. If caustic soda is desired, the cathode is placed horizontally at the bottom of the cell. The caustic solution formed, being heavy, remains on the cathode, while the chlorine "escapes from the anode at the top. When " bleaching liquors " or hypochlorites are desired, the anode is put at the bottom of the cell and the cathode at the top. In this case the chlorine rises through the caustic solution and is absorbed : 2 NaOH + 01, = NaOCl + NaCl + H 2 0. * Zeitschr. f. angew. Chemie, 1896, 537. t J. Soc. Chem. Ind., 1891, 642. J Ibid., 1891, 699. CHLORINE INDUSTRY 107 The Hargreaves-Bird process * employs an asbestos diaphragm, impregnated, with Portland cement, or with clay and sodium silicate j it is fastened on a wire gauze and placed in a horizontal position. To avoid the use of a diaphragm, numerous processes have been proposed in which mercury is used as the cathode or is placed between the anode and cathode. The Hermite process t has attracted much attention as a method of making bleaching and disinfecting liquors from magnesium or sodium chloride solutions; but it is not used for the production of free chlorine or caustic. The Castner process $ appears to be the most promising of the methods using mercury between the anode and cathode. The cell (Fig. 48) is divided into three com- partments, the two outside ones containing brine and the carbon anodes (A), while the middle one contains the caustic solution and the iron cathode (C). The sodium set free is taken up by the mercury, forming an amalgam. The cell is made to rock slightly by the cam (E), and the motion carries the mercury and amalgam into the centre compartment, where the amal- gam acts as the anode during the passage of the current to the cathode, the sodium being liberated. A regulated supply of water flows into the centre compartment continuously, while a corre- sponding amount of caustic solution overflows into a collecting tank, the process being thus uninterrupted. Each cell is about 6 feet by 3 feet by 6 inches, and will decompose about 56.5 pounds of salt daily, producing 38.5 pounds of caustic and 34.5 pounds of chlorine per each 3.5 horse-power. The electrodes being near together, there is but little resistance, and the voltage is only about 4, with a current of 550 amperes. The wear and tear is said to be small. The process is claimed to yield a 20 per cent solution of caustic, free from hypochlorites, while the chlorine gas is very pure, containing only a little hydrogen. The mercury seldom con- tains more than 0.02 per cent of sodium, which is removed electro- lytically. No hypochlorites are produced, and the electrical efficiency is claimed to be over 88 per cent. * J. Soc. Chem. Ind., 1895, 1011. t Ibid., 1888, 292. Zeitschr. f. angew. Chem., 1893, 301. | Engineering and Mining Journal, 1894 [58], 270. FIG. 48. 108 OUTLINES OF INDUSTRIAL CHEMISTRY Although electrolytic processes have been much elaborated within the last decade, the difficulties encountered in preventing the forma- tion of hypochlorites and regeneration of the salt, the destructive action of the chlorine and caustic on the diaphragms and other parts of the apparatus, and the large size of plant needed for a compara- tively small output, have deterred most manufacturers from engaging on a large scale in such an uncertain enterprise. Then, too, except in those favored places where water power can be had cheap, the elec- tricity must be generated by means of boiler, engine, and dynamo, a method which consumes much fuel with low efficiency. The electro- motive force needed to decompose sodium chloride is a little over two volts, but the resistance of the bath, together with polarization, increases the tension to from 3.5 to 4 volts. A current of one ampere at 4 volts will yield, theoretically, 0.00292 pounds of chlorine and 0.0033 pounds of caustic soda per hour. Cross and Bevan* calculate that with an efficiency of 80 per cent, caustic soda costs 12 10s. per ton, and bleaching powder 7 10s. per ton, when produced by electrolysis. According to Haussermann,f one ampere, with 80 per cent efficiency, yields 28.56 grams of NaOH and 25.2 grams Cl in 24 hours, the voltage being 3.5. Thus 35 amperes are needed to produce one kilo of NaOH in 24 hours. If a theoretical yield were obtained, the chlorine evolved would make about 100 pounds of bleaching powder for each 40 pounds of caustic soda produced. But the latter, which is in much greater demand than bleaching powder, can be made more cheaply from ammonia soda ; therefore it would seem that if electrolytic methods prove successful in the future their expansion would be limited to supplying bleaching powder and chlorates, and the caustic be regarded as a by-product. Moreover, the caustic liquors produced by electrolysis are dilute, necessitating much evaporation, and the product is contaminated with much chloride and chlorate. HYPOCHLORITES By passing chlorine into a cold solution of sodium or potassium carbonate, a mixture of the chloride and hypochlorite of the alkali metal is formed. But if any excess of chlorine is introduced, the hypochlorite is decomposed into chloride and free hypochlorous acid (HOC1) : 1) K 2 C0 3 + H 2 + 2 Cl = KC1 + KOC1 + H 2 + C0 2 . 2) K 2 C0 3 + H,0 + 4 Cl = 2 KC1 + C0 2 + 2 HOC1. * J. Soc. Chem. Ind., 1892, 963. t Zeitschrift f. Electrochemie, 1895, 21. CHLORINE INDUSTRY 109 This solution of hypochlorous acid is a powerful bleaching and oxidizing agent. It was first made about 1789, and brought into trade in France as a " bleach liquor " under the name of eau de Javelle, or eau de Labarraque. In 1798 or 1799 Charles Tennant took out a patent in England for a " bleach liquor " made by passing chlorine into "milk of lime," by which a solution of calcium chloride and hypochlorite was formed : 2 Ca (OH) 2 + 4 Cl = CaCl 2 + Ca (OC1) 2 + 2 H 2 O. This bleach liquor is cheaper, stronger, and more convenient to use than bleaching powder (see below), but since it is unstable, evolving oxygen even when kept in a closed vessel in the dark, it is usually made only for immediate use. The tanks in which the milk of lime is treated with chlorine are provided with stirring apparatus ; the temperature must not rise much above 30 C., or chlorates are formed (p. 111). A dilute chlorine may be used. The density of the solution obtained is about 8 Tw. Calcium carbonate suspended in water may also be employed for preparing bleach liquor : CaC0 3 + H 2 + 4 Cl = CaCl 2 + C0 2 + 2 HOC1. These liquors are chiefly used for bleaching vegetable fibres and for disinfectants. The absorption of chlorine in milk of lime soon led to trials of dry, slaked lime or calcium hydroxide for the same purpose. A dry bleaching powder, fairly stable and constant in strength, resulted ; but its composition is not the same as that of the bleach liquor made from milk of lime. It was at first supposed that a direct combina- tion took place between the lime and chlorine, and that the powder was simply calcium hypochlorite [Ca(OCl) 2 ], so the name "chloride of lime " was given to it. Other investigations led to the view that it contained a mixture of calcium chloride and hypochlorite. But this was disproved by Lunge * and his students ; Lunge assigns to /Cl it the formula Ca<^ . Hence it is an oxy chloride of calcium. \0-C1 When dissolved in water, this forms hypochlorite and chloride of calcium. *Chemische Industrie, 1881, 289. Dingl. J., 237, 63. Annalen der Chemie, 219, 129. Berichte d. deutch. chem. Gesellschaft, 1887, 1474. Zeit. f . anorg, Chemie, II, 311. 110 OUTLINES OF INDUSTRIAL CHEMISTRY For making bleaching powder, a very pure, fat lime (p. 148) is desirable. It is slaked carefully, so that the resulting hydroxide contains about 24.5 to 25.5 per cent of water. That is, there should be a slight excess of water over that necessary to form calcium hydroxide. The absorption chambers are brick, cast iron, or lead, and are usually 6.5 feet high, and have about 200 square feet of floor area per ton of bleach made per week. Brick chambers are tarred inside to make them gas tight and to protect them from the chlorine; large ones are usually made from lead, much like the vitriol cham- bers (p. 52), and may have a floor area of 30 by 100 feet. The slaked lime is sifted through screens with from 20 to 25 meshes per linear inch, as only the fine powder is suitable. This is spread three or four inches deep on the floor, and is furrowed with a special rake in order to assist the absorption by increasing the surface. The chlorine is introduced at the top of the chamber, and settling to the bottom because of its density, is at first rapidly absorbed by the lime. After a time the process goes on more slowly, and finally the gas enters under some pressure. In modern works there are three or more chambers in a series, the strongest chlorine entering that con- taining the most nearly finished bleach, and passing out through that containing the fresh lime. The degree of absorption of chlorine is judged by the color of the gases seen through the glass " sights " in the chamber walls. The powder is turned over once or twice, and the treatment ("gassing") continued until tests show that it contains from 36 to 37 per cent of "available chlorine." If under strength (" weak "), after the third " gassing," it should be packed and sold for what it will bring, for further exposure will cause the formation of chlorate and chloride with loss of strength. During the absorption considerable heat is generated ; for strong powder the temperature should not exceed 40 46 C. * The chlo- rine should be admitted in a very slow stream, and should be con- centrated, dry, and free from hydrochloric or carbonic acids. When dilute (as from Deacon's apparatus), a large, special chamber pro- vided with numerous shelves, on which the slaked lime is spread to secure a greater absorbing surface, is employed. The yield from 100 pounds of good lime is about 150 pounds. Bleaching powder is a yellowish white substance, which should be perfectly dry and free from lumps. On exposure to the air, it absorbs moisture and carbon dioxide, giving off hypochlorous acid, * Lunge and Schappi, Dingl. J., 237, 63. CHLORINE INDUSTRY HI the evolution of which gives bleach its peculiar odor. Good samples contain about 36 per cent " available chlorine." Its chief use is for bleaching vegetable fibres for the textile and paper industries. In order to liberate the chlorine for bleaching purposes, the powder is usually decomposed by a mineral acid, thus : the fibre having been saturated with the bleaching powder solution, is passed into a dilute acid bath, where the hypochlorite is decomposed and the chlorine set free. The nascent chlorine combines with the hydrogen of the water, liberating nascent oxygen, which, in turn, destroys the organic coloring matter in the fibre. / CHLORATES Potassium and sodium chlorates are usually made by Liebig's process,* in which double decomposition between calcium chlorate and a chloride, sulphate, or carbonate of the alkali metal is accom- plished. If the chlorine is passed into a hot potash or soda solution, and the liquid evaporated, a very small yield of chlorate, with a large quantity of chloride, is obtained : 3 K 2 C0 3 + 6 Cl = 5 KC1 + KC10 3 + 3 CO* There is also difficulty in separating the chloride and chlorate. In Liebig's process chlorine is passed into milk of lime at or above a temperature of 100 C. ; the apparent reaction being : a) 6 Ca (OH) 2 + 6 C1 2 = 5 CaCl 2 + Ca (C10 3 ) 2 + 6 H 2 O. But this may comprise two minor reactions, viz. : 2 Ca (OH), + 2 Cl, = CaCl 2 + Ca (OC1) 2 + 2 H 2 O ; 3 Ca (OC1) 2 = 2 CaCl 2 + Ca (CIO,)* It is possible, however, that the hypochlorite may decompose thus : Ca(OCl) 2 = CaCl 2 -f 2 , causing waste of chlorine. To prevent this, an excess of chlorine must always be present. Theoretically, only one molecule of cal- cium chlorate is obtained from 12 atoms of chlorine. This would yield two molecules of potassium chlorate, according to the re- action : 6) Ca (C10 3 ) 2 + 2 KC1 = CaCl 2 + 2 KC10 3 . But the actual yield is only about 70 per cent of the theoretical, since much of the potassium chlorate is lost in the mother-liquor. * Annalen der Pharmacie, 41 , 307. 112 OUTLINES OF INDUSTRIAL CHEMISTRY The hot milk of lime is saturated with chlorine, in tanks pro- vided with agitators, and when the liquor has a density of 25 to 30 Tw., it is run off and settled. The clear solution is then mixed with the calculated quantity of potassium chloride (which should be purified, since sodium or magnesium chloride is difficult to separate from the product) ; the resulting solution of potassium chlorate is evaporated in wrought iron pans, to a density of 70 Tw. tested in the hot liquor. On cooling, the chlorate crystallizes nearly pure, and the mother-liquor, containing about 20 per cent KC10 3 , goes to waste. The crude chlorate is purified by recrystallizing from water, and the purified crystals are drained and washed carefully in a centrifugal machine, and may be sold as coarse crystals; or they are ground to a fine powder in buhrstone mills, care being taken that no organic matter, dirt, or metal (iron, etc.) gets into the mill, lest an explosion result. No fire should be permitted in the building, and heating should be by steam, and lighting by electricity. The grinding mill should be at a little distance from the main building. Magnesia* is sometimes substituted for lime, in order to increase the yield of potassium chlorate, since the latter is much less soluble in a magnesium chloride solution than in one of calcium chloride. Thus a yield of 90 per cent can be obtained, owing to more com- plete separation when crystallizing. In this process chlorine is passed into a "milk" of powdered magnesia in water, forming a solution of magnesium chloride and chlorate, which is then con- centrated until crystals of magnesium chloride (MgCl 2 6 H 2 0) separate on cooling. These are removed, and the proportion . of chlorate to chloride in the mother-liquor is about 1 Mg(C10 3 ) 2 to 2.8 MgCl 2 . The theoretical quantity of potassium chloride is then added, and potassium chlorate separates, leaving the magnesium chloride in solution. Any excess of potassium chloride must be avoided, since it would combine with the magnesium chloride to form a crystalline precipitate of a double salt (MgCl 2 KC1 6 H 2 artificial carnallite), which would contaminate the product. The mother-liquors might be worked for chlorine, according to the Wel- don-Pechiney process (p. 102). Sodium chlorate is much more soluble than potassium chlorate, and is more difficult to crystallize. Pechiney devised a method for its production by which a solution of calcium chloride and chlorate, made by treating milk of lime with chlorine, is evaporated to a density of 100 Tw. Then, by cooling the solution to exactly 12 C., a part (f) of the calcium chloride crystallizes as CaCl 2 2 H 2 O, leav- * J. Soc. Chem. Ind., 1887, 248. CHLORINE INDUSTRY 113 ing about one molecule of chloride to one of chlorate in the liquor. Sodium sulphate is then added, which precipitates calcium sulphate, and leaves sodium chloride and chlorate in solution. On concen- trating, sodium chloride crystallizes and is "fished" out of the warm liquor, which, on cooling, deposits crystals of sodium chlorate; these are recrystallized. The process depends on the fact* that a saturated solution of the mixed salts at 12 C. contains 24.4 grams NaCl and 50.75 grams NaC10 3 in 100 c.c., but at the boiling point (122 C.) a saturated solution contains only 11.5 grams NaCl, with 249.6 grams N~aC10 3 ; hence, on cooling to 12 C., all the NaCl, and only 58.6 grams of NaC10 3 , remain in solution, the remaining 181 grams NaC10 3 crys- tallizing. This process has been largely used in France. Chlorate is formed by the electrolysis of a potassium chloride solution, when conducted in such a manner that the alkali formed around the cathode comes into contact with the chlorine set free at the anode, the temperature being kept above 50 C. No hypochlorite can exist at this temperature, and if the liquid is concentrated, the chlorate crystallizes. In the Gall and Montlaur process, a 25 per cent solution of potas- sium chloride is decomposed by a current-density of 50 amperes per square decimeter, the tension of each bath being 5 volts. About 45 per cent of the theoretical yield is obtained, the mother-liquor being again saturated with chloride and returned to the process. The reactions are probably as follows : 2 KOH + Cl = KC10 + KC1 + H 2 ; 3 KC10 = KC10 3 + 2 KC1, the hypochlorite being instantly decomposed by the temperature of the bath. The hydrogen set free in the bath may cause part of the loss : KC10 3 + 6 H = KC1 + 3 H 2 O. Sodium chlorate may be formed in the same way, but being more soluble, does not precipitate as crystals, and hence a larger propor- tion of it is destroyed by the reducing action of the hydrogen. REFERENCES Berichte tiber die Entwickelung der chemischen Industrie, Dr. A. W. Hofmann, Vol. I, Braunschweig, 1875. (Vieweg.) Die Fabrication von chlorsaurem Kali und anderen Chloraten. Dr. Conrad W. Jurisch, Berlin, 1888. (R. Gaertner.) * Lunge, Sulphuric Acid and Alkali, Vol. Ill, 547. 114 OUTLINES OF INDUSTRIAL CHEMISTRY Die Darstellung von Chlor u. Salzsaure, unabhangig von der LeBlanc Soda Industrie. Dr. N. Caro, Berlin, 1893. (R. Oppenheimer. ) Sulphuric Acid and Alkali. G. Lunge, 2d ed., Vol. Ill, London, 1896. (Gur- ney and Jackson.) J. Soc. Chem. Ind : 1883, 103, Ferdinand Hurter. 1885, 525, W. Weldon. 1887, 248, C. Longuet Higgins. 1887, 775, James Dewar. 1896, 713, Ludwig Mond. Zeit. f. angew. Chem., 1893, 301. (Hermite and Dubos Process.) Electro-Chemistry. M. Leblanc, translated by W. R. Whitney, Ph.D., New York, 1896. (Macmillan & Co.) Elements of Electro-Chemistry. Lupke. NITRIC ACID The manufacture of nitric acid is very often combined with that of sulphuric, especially in those factories where the former is employed in making the vitriol. Large quantities, however, are produced for general manufacturing purposes. Practically all nitric acid is now made by treating sodium nitrate (p. 119), with sulphuric acid, in cast-iron retorts. The reactions are as follows : H 2 S0 4 = NaHS0 4 + HN0 3 . 2) 2 NaN0 3 + H 2 S0 4 = Na 2 S0 4 + 2 HN0 3 . In practice, the quantities of material iised do not correspond with either of these equations, but the charge is so regulated that a mixture of acid and neutral sulphates of sodium, which remains liquid at the temperature employed, is left in the retort. If reaction (1) were followed, too much sulphuric acid would be used for profit- able working, except in soda works, where the resulting acid sulphate might be used in the salt-cake furnace. If reaction (2) is carried out, the temperature must be very high, the neutral sulphate solidifies in the retort and is difficult to remove, and the resulting nitric acid may be partly decomposed by the heat before it can escape from the retort, thus causing a diminished yield and a product discolored by the oxides of nitrogen produced. The sulphuric acid employed is usually that from the lead pan evaporation (sp. gr. 1.70), but for nitric acid above 1.38 sp. gr., oil of vitriol of 66 Be. is used, although this decomposes part of the nitric acid formed. The sodium nitrate used is the purified Chili saltpetre, NITRIC ACID 115 containing from 98 to 99 per cent of NaN0 3 , when dried. It should be free from sodium chloride to avoid contaminating the nitric acid with hydrochloric acid. The size of the charge depends on the capacity of the plant, but in some more modern factories it amounts to as much as 1200 pounds of nitrate, with somewhat more than an equal weight of sulphuric acid (sp. gr. 1.70). The old style of plant consisted of a horizontal cast-iron cylinder, 5 or 6 feet long, set over a fireplace in such a way that the flames played over the sides and top, heating all parts to a high tempera- ture. Another and better form of plant is shown in Fig. 49, in which the cast-iron retort (A) is entirely surrounded by the flames from the grate. Cast iron is but little attacked by concentrated nitric acid or its vapors, and it is important to keep the retort hot enough in all parts, to prevent condensation of the acid. A more mod- ern retort is shown in Fig. 50. In the lower part of the retort is a pipe, by which the melted residue of "nitre cake" is run off, after the reaction is finished. For condensing the acid vapors which escape from the retort, a series of glass or earthenware Woulfe bottles (bombonnes) (B, B, Fig. 49) are employed. The first two or three of these bottles are generally placed over the flue by which the fire gases pass to the chimney. Being thus warmed, there is less danger of breakage by the high heat of the vapors from the retort. At the end of the series is usually placed a coke tower, fed with water or concentrated sulphuric acid, to condense the fumes escaping from the bombonnes. Usually, no water is ad- mitted to the bombonnes unless a dilute acid is required ; but they are sometimes placed en cascade, to allow the condensed acid to flow 116 OUTLINES OF INDUSTRIAL CHEMISTRY through the series in a direction opposite to the movement of the acid vapors. The most concentrated acid is condensed in the first two or three bombonnes, but is contaminated with sulphuric acid and nitrogen oxides. The last of the series contains dilute acid, which is con- taminated with chlorine. In the middle bottles is a pure acid of moderate strength. Owing to more or less reduction of the nitric acid in the retort, the condensed acid has a yellow or red color, due to the absorbed nitrous vapors. These are undesirable in a commer- cial acid, and must be removed by "bleach- ing " j the acid is heated to about 90 C., and warm air blown in. which carries away the nitrogen oxides, and is then passed through the coke tower for their recovery. Guttmann's apparatus * is more modern. The large cast-iron retort (Fig. 51) is made in three pieces and is entirely surrounded by the flames from the grate. The gases from the retort pass into a system (Fig. 52) of vertical earthenware pipes (AA), having very thin walls and joined at the top by 180 bends, while they open at the bottom into a nearly horizontal collecting FIG. 51. FIG. 52. pipe (BB), which is divided into chambers by diaphragms. These chambers are joined by U -tubes, passing under the diaphragms. The diaphragms force the acid vapors to pass up one pipe and down * J. Soc. Chem. Ind., 1893, 203. NITRIC ACID 117 the next, in order to go through the system. The thin walls (8 mm.) of the vertical pipes allow very efficient cooling by exposure to the air alone, or they may be placed in a tank of cold water, as repre- sented in the figure. By this very rapid cooling, the acid vapors are condensed quickly. Hot air at 80 C. is injected from (F) into the outlet pipe (D), where it converts some of the nitrous vapors to nitric acid, increasing the yield materially. (The uncondensed nitrous vapors pass into the Lunge-Rohrmann plate tower (E) (p. 58), where the nitrogen oxides are absorbed in sulphuric acid or water.) If the vapors remain in the retort too long, part of the acid is decom- posed, and nitrogen peroxide is formed, and absorbed by the con- densed acid, to which it imparts a red color. But since there is a good draught through the apparatus, the vapors are drawn out of the retort very soon after they are evolved, and are at once con- densed. Thus very little peroxide is formed, and a light colored, concentrated acid is obtained directly. It is claimed that acid of 40 Be. (1.38 sp. gr.), requiring no " bleaching/' may be thus made, and that, with water-cooled pipes, 98 per cent of the theoretical yield is obtained as concentrated acid, while 2 per cent con- -M E denses in the Lunge-Eohr- mann tower. Hart's tube condenser (Fig. 53), for nitric acid, is a new form of apparatus. It is made of glass and earthen- ware tubes, and is placed above the brick arch cover- ing the retort, thus occupy- ing but little floor space. The vapor from the retort (A) passes into the pot (B), and thence through the ver- tical earthenware tube (C). From (C) to (D) extend a number of glass tubes, which are slightly inclined towards (C), and which are cooled by jets of water from the perforated pipe (EE). From (D), the uncondensed vapors pass to a Lunge tower or a coke tower. The acid condensed in the glass tubes flows back into (C), and then into ( B), thus coming into contact with the hot vapors from the retort. This heats the acid so hot, that all the FIG. 53. 118 OUTLINES OF INDUSTRIAL CHEMISTRY nitrous vapors are driven out of it. From (B), the acid flows through the U-tube (F) into bottles or carboys. In this apparatus, the acid is condensed very quickly and but little nitrogen peroxide is formed. If frothing occurs in the retort, the overflow is caught in the pot (B), and may be removed without difficulty. The flow of water from (E) can be so regulated that all or nearly all of it is evaporated on the surface of the glass tubes, thus securing the greatest cooling effect, with small consumption of water. Any condenser water not evaporated is caught in the trough (G). The chief repairs are of broken tubes, which are cheaply and easily replaced. The strength of the nitric acid produced in any apparatus depends upon the strength of the sulphuric acid, on the temperature of the retort, and on the purity of the sodium nitrate. With sulphuric acid of 1.71 sp. gr., the nitric acid varies from 1.38 to 1.42 sp. gr. (40to 42 Be.). If the sodium nitrate contains chlorides, some of the nitric acid is decomposed by the hydrochloric acid produced ; thus : HN0 + HC1 = H0 + N"0 + Cl. It is claimed that with Guttmann's apparatus, an acid of 1.5 to 1.52 sp. gr. (50 Be.), containing about 95 per cent HN0 3 , can be made. For chemically pure acid, perfectly pure materials should be used, although formerly the common acid was purified by treating with silver and barium nitrates, and redistilling. But concentrated acid cannot be distilled without some decomposition, and the product must be " bleached " by heating and blowing in pure air. Fuming 1 nitric acid is a solution of nitrogen peroxide in concen- trated nitric acid. It is red in color and has a specific gravity of 1.55 to 1.62. To make this, perfectly dry sodium nitrate and oil of vitriol (1.84 sp. gr.) are used. The reaction is carried so far that neutral sulphate of sodium is formed by the action of the acid sul- phate on the nitrate : 2 NaN0 3 + 2 NaHS0 4 = 2 Na 2 S0 4 + 2 N0 2 + H 2 + 0. The nitrogen peroxide formed dissolves in the nitric acid to form the fuming acid. A little powdered starch is sometimes added to assist in the reduction of the nitric acid. An impure fuming acid is sometimes prepared by distilling a mixture of concentrated nitric and sulphuric acids. Nitric acid is largely used in the manufacture of explosives ; for parting gold and silver j in the manufacture of coal-tar dyes ; as a NITRIC ACID 119 "pickling liquor" for cleaning metal; and in the manufacture of various metallic nitrates. It is a colorless liquid, boiling at 86 C., but with decomposition. (See above.) The pure acid also decom- poses on exposure to strong light and becomes yellow (N0 2 ). When it acts on metals, the hydrogen liberated at once reduces some of the nitric acid itself, setting free various oxides of nitrogen, of which nitric oxide is the most prominent. Ordinary commercial nitric acid (1.42 sp. gr.) distills at 123 C., and contains about 68 to 69 per cent HISTOg, and corresponds nearly to the formula 2 H]ST0 3 +3 H 2 O. The very concentrated acid of 1.50 sp. gr. contains about 94 per cent HN0 3 . The acid sodium sulphate left in the retort after making nitric acid is called " nitre cake," and is often used in the charge for mak- ing sulphate in the Leblanc process. Various other processes for making nitric acid have been sug- gested, but owing to the low price of Chili saltpetre, none of them are now in use. An ingenious proposal to use the " still liquors " from the chlorine manufacture, instead of sulphuric acid for decom- posing sodium nitrate, is based on the following reactions : 1) 10 NaN0 3 + 5 MnCl 2 = 2 MnO + 3 Mn0 2 2) 3) 2 This permits the manganese to be recovered in a form suitable for use in the chlorine stills again. The " still liquor " is evaporated to dryness, the pulverized residue, mixed with dry sodium nitrate, and the mixture heated to about 230 C. in a retort. .Reaction (1) takes place, and the gases, consisting of a mixture of nitrogen per- oxide and oxygen, are led into a tower and condensed with water as per reaction (2). The nitric oxide produced is treated with air and steam and condensed according to reaction (3). NITRATES The most important nitrates are those of sodium and potassium, but ammonium, lead, iron, silver, strontium, and barium nitrates are used to some extent in the arts. Sodium nitrate,* also called Chili saltpetre, is found in natural deposits in desert regions along the west coast of South America, especially near the boundary lines between Peru, Chili, and Bolivia, * J. Soc. Chem. Ind., 1890, 664; 1893, 128. 120 OUTLINES OF INDUSTRIAL CHEMISTRY in latitude 20 to 26 S. The territory is now chiefly owned by Chili. The deposits extend about 220 miles in length, and average about two miles in width. The crude nitrate, called "caliche" varies from yellowish-white to brown or gray, and contains from 20 to 55 per cent NaN0 3 ; it forms beds about 5 feet thick, lying near the surface, but usually covered by a conglomerate of rock debris, cemented together by salt and gypsum. The region is rainless, and water and fuel, being very scarce, are used as economically as possible in refining the crude ore. The caliche is crushed and boiled with water in tanks heated by steam coils, until the liquor reaches a density of 110 T\v., when it is run off to crystallize. The mother-liquor retains most of the chloride, iodide, and iodate of sodium and magnesium, together with about 20 per cent of the nitrate. Hence the liquors are diluted with the wash water from the residue, and used again to lixiviate another portion of caliche. But after two or three repetitions of this process, the mother-liquor is too contaminated for further use. It is then run off and treated for the recovery of the iodine (p. 218), which it contains. The residue from the lixiviation contains some nitrate, and is washed with fresh water, yielding a weak solution, which is used to dilute the mother-liquors before using them for leaching. The sodium nitrate crystals are drained or " centriffed " and dried in the sun. They are then packed and shipped as crude Chili salt- petre, containing from 94 to 98 per cent of NalSTOs. For many pur- poses this is purified by recrystallization. Large deposits of a very high grade of sodium nitrate have been found recently in Upper Egypt and in the trans-Caspian region, but these have not been much developed as yet, and nearly all the world's supply comes from Chili. The formation of these beds is attributed to the decomposition of sea-plants under such conditions of temperature and humidity that the ammonia produced was converted into nitrate by the action of the nitrifying bacillus, an organism found in the soil. The region being rainless, the sodium nitrate was not washed away. Potassium nitrate, or saltpetre, is derived from three sources : 1. Natural nitrate beds, formed by the decomposition of organic matter in warm, damp climates. 2. Artificial nitrate beds, prepared especially for the purpose. 3. The decomposition of sodium nitrate by potassium chloride. In many tropical countries, especially in India, Persia, and Egypt, native deposits of potassium nitrate are found impregnating the earth in the neighborhood of large cities and towns. This NITRIC ACID 121 formation is due to the action of the nitrifying bacteria, and is not strictly an oxidation process. The deposits are continually form- ing, a white efflorescence appearing on the surface of the ground. This is scraped up, lixiviated with water, and the clarified solution evaporated directly, to crystallize the nitre. But all the calcium nitrate in the mother-liquors is thus lost. By adding potash ob- tained from wood ashes the calcium nitrate is decomposed, and a larger yield of nitre is obtained. The artificial production of saltpetre in beds of decaying organic matter is now of slight importance, though formerly largely prac- tised in Sweden, Switzerland, and France when nitre was collected as a part of each farmer's tax. By this process putrefying organic matter is mixed with old mortar, or with porous earth containing calcium carbonate and wood ashes, and the pile allowed to stand for some months, being occasionally moistened with the liquid drainage from stables. The nitrifying organisms soon impregnate the mass with nitrates of calcium, potassium, and magnesium. On leaching, these go into solution; when boiled with wood ashes, the calcium and magnesium are precipitated as carbonates, while the clarified liquor yields potassium nitrate on concentrating. The solution is clarified by adding a little glue, which combines with the impurities, forming a scum, which is removed by skimming. Potassium nitrate, made by double decomposition of sodium nitrate with potassium chloride, is now the most important from a commercial standpoint. The reaction is very simple : NaN0 3 + KC1 = NaCl + KN T 3 . Commercial potassium chloride, containing about 80 per cent KC1, is dissolved in water in cast-iron, copper, or lead lined wood tanks hold- ing 500 to 600 gallons. When the hot solution has a density of about 40 to 42 Tw. (1.20 to 1.21 sp. gr.), sodium nitrate containing 95 per cent NaK0 3 is added, and the boiling mixture well stirred for an hour. On evaporation, the common salt, being less soluble than the nitrate, precipitates, and as much as possible of it is " fished " out, the concentration being continued until the density of the solution is 100 Tw. (1.50 sp. gr.). The liquid is allowed to stand a short time to settle, and then, while still hot, is drawn from the sediment into crystallizing tank?, where it is actively stirred while cooling. This causes the separation of the nitre as " crystal meal" (p. 16), which is washed with a saturated solution of potassium nitrate (or often with cold water) to remove the mother-liquor and remaining sodium chloride. The wash waters and mother-liquors are used to 122 OUTLINES OF INDUSTRIAL CHEMISTRY dissolve the next lot of potassium chloride. One or two recrystal- lizations free the potassium nitrate from all but a trace of chloride. When the potassium chloride contains some magnesium chloride, it is best to precipitate the magnesium by soda-ash before adding the sodium nitrate, since traces of magnesium chloride may other- wise remain in the product. This salt, being deliquescent, may cause the nitrate to become wet on exposure. The chief uses of potassium nitrate are for making gunpowder and explosives, in matches, in pyrotechnics, in assaying, in metal- lurgical and analytical operations, and for curing meat. Ammonium nitrate is now used to a considerable extent in the manufacture of certain "nameless " explosives, and also, in a less de- gree, for making nitrous oxide (" laughing gas "). It is usually made by neutralizing nitric acid with ammonia. Attempts to produce it by double decomposition of sodium nitrate with ammonium salts result in incomplete reactions, and some sodium nitrate remains un- decomposed. Lead nitrate is generally made by dissolving litharge (PbO) in hot dilute nitric acid. After filtering, the solution is concentrated to a density of 100 Tw. (1.50 sp. gr.) and allowed to crystallize. It is used in dyeing and calico printing, for the manufacture of certain orange and yellow pigments (chrome yellows), for some explosives, and in some kinds of matches. It is important in that it furnishes a moderately soluble lead salt. Ferric nitrate (nitrate of iron) is generally made by dissolving scrap iron in nitric acid of 1.30 sp. gr. The reaction is as follows : 2 Fe + 8 HN0 3 = 2 Fe(N0 3 ) 3 + 2 NO + 4 H 2 0. By concentrating the solution, colorless crystals, containing six or nine molecules of crystal water, are obtained. The aqueous solution will dissolve ferric hydroxide, and this basic solution is much used in textile coloring. By using an excess of iron, and permitting the reaction to continue slowly, after all the acid has been acted upon, a precipitate of insoluble basic ferric nitrate ultimately forms. The solution obtained in this way is of a red-brown color and indefinite composition. It is chiefly used for blacks in silk dyeing, and for iron-buff on cotton. Ferrous nitrate is prepared by dissolving iron in cold dilute nitr-ic acid (1.10 sp. gr.). But a considerable amount of ammonium nitrate is also formed in the solution, according to the reaction : 4 Fe + 10 HN0 3 = 4 Fe(N0 3 ) 2 + NH 4 N0 3 + 3 H 2 0. NITRIC ACID 123 This solution is very unstable and decomposes when heated even slightly, forming basic ferric nitrate and liberating nitric oxide. To prepare a pure ferrous nitrate, decomposition of a ferrous sulphate solution by barium or lead nitrate is employed : FeS0 4 + Ba(N0 3 ) 2 = BaS0 4 + Fe(N0 3 ) 2 . The solution is filtered or decanted from the precipitated barium sulphate. There is a preparation sold as "nitrate of iron," (probably so called because some nitric acid is used in making it), which is not a nitrate, but a basic ferric sulphate and sulphate-nitrate solution. A solution of ferrous sulphate (copperas) is oxidized by nitric acid, according to the following equations : 1) 6 FeS0 4 + 2 HN0 3 + 2 H 2 = 3 Fe 2 (S0 4 ) 2 . (OH), + 2 NO. 2) 6 FeS0 4 + 5 HN0 3 - 3 Fe 2 (S0 4 ) 2 . (N0 3 ) (OH) + 2 NO + H 2 0. 3) 6 FeS0 4 + 8 HN0 3 = 3 Fe 2 (S0 4 ) 2 (N0 3 ) 2 + 2 NO + 4 H 2 0. 4) 12 FeS0 4 + 3 H 2 S0 4 + 4 HN0 3 = 3 Fe 4 (S0 4 ) 5 (OH), + 4 NO + 2 H 2 0. Equation 4 gives the best product. The solution of basic ferric sulphate and sulphate-nitrates is a dark brown-red liquid, and is much used in silk dyeing. It is only mentioned here because of the frequent confusion of names in the commercial article. Silver nitrate is made by dissolving the metal in dilute nitric acid : 6 Ag + 8 HN0 3 = 6 AgN0 3 + 4 H 2 + 2 NO. If the silver contains copper, the resulting solution of nitrates is evaporated to dryness and then heated cautiously to about 250 C., at which temperature the copper nitrate is decomposed into copper oxide, nitric oxide, and oxygen, while the silver salt is not altered. By extracting the residue with water, the silver nitrate is dissolved, leaving the copper oxide. The solution is then evaporated to crys- tallize the silver nitrate. The salt fuses unchanged at 225 C., but decomposes if heated nearly to redness ; it is cast in small sticks, and is much used in medicine for a cautery, under the name of lunar caustic. Silver nitrate has a very corrosive action on organic matter. It is largely used in photography, and to a lesser degree in pharmacy, in the manufacture of mirrors, in preparing " indelible inks," and as a chemical reagent. 124 OUTLINES OF INDUSTRIAL CHEMISTRY Barium nitrate is made by dissolving the native carbonate (witherite) in hot, dilute nitric acid; or it may be prepared by decomposing a concentrated solution (32 Be.) of barium chloride, by the addition of sodium nitrate, the less soluble barium nitrate precipitating. The salt is purified by recrystallization. It is chiefly used for producing "green fire" in pyrotechnics and for making barium peroxide (Ba0 2 ) (p. 231). It is also used as an oxidizing material in certain explosives. Strontium nitrate is made by dissolving the native carbonate (strontianite) in hot nitric acid. Its chief use is for " red fire " in pyrotechnics. REFERENCES Berichte iiber die Entwickelung der chemischen Industrie, u. s. w. A. "W. Hofmann, 1877. (Vieweg, Braunschweig.) Sulphuric Acid and Alkali. G. Lunge. Second ed., Vol. I. (Gurney and Jackson, London.) The Manufacture of Explosives. Oscar Guttmann. (Nitric acid and nitre.) Der Chilisalpeter und Zukunft der Salpeterindustrie. H. Polakowsky. Direct- orium der landwirthschaftl. Hauptgenossenschaft zu Berlin. Berlin, 1893. Zeitschrift f. angewandte Chemie. 1893, 37. Oscar Guttmann. Journal American Chemical Society, 1895, 576. Edward Hart. J. Soc. Chem. Ind., 1893, 128. J. Buchanan. (Sodium nitrate in Chile.) 1893, 203. Oscar Guttmann. (Nitric acid.) AMMONIA Whenever organic matter containing nitrogen is submitted to destructive distillation, more or less ammonia is formed. The chief sources of ammonia are : the distillation of coal for gas or coke, of bituminous shales, and of bones and other animal matter; putrid urine ; the residues of the beet sugar industry and those left after the fermentation of molasses for alcohol ; and the waste gases from blast furnaces. Ammonia can be made from the nitrogen of the air. The reac- tions involved are as follows : 1) Ba(OH) 2 + 3C+2N + = Ba(CN) 2 + H 2 + C0 2 . 2) Ba (ON), + 4 H 2 = Ba (OH), + 2 CO + 2 NH 3 . The first reaction is accomplished by passing air over barium hy- droxide or oxide and carbon, heated to a white heat. Then the temperature is lowered to about 450 C., and steam admitted to de- compose the barium cyanide according to (2). The reactions are not quantitative, and the process is not economical and is unimportant. AMMONIA 125 The chief source of ammonia is the "gas liquor" from the hydraulic main and scrubbers of the illuminating gas manufacture (p. 275). The nitrogen contained in coal is largely converted into ammonia and cyanogen compounds by destructive distillation. The principal ammonium salts are the carbonate, sulphide and sulphy- drate, which are volatile with steam, and sulphate, thiosulphate, sulphite, sulphocyanide, and ferrocyanide, which are not volatile with steam. These salts, together with free ammonia, are found in the " gas liquor." Gas liquor is valued according to its percent- age of ammonium salts, as determined by distilling with caustic soda, absorbing the vapors in normal sulphuric acid and titrating the uncombined acid. The liquor is gauged according to the number of ounces' of concentrated oil of vitriol necessary to neutralize one gallon of it ; e.g., an " eight ounce " liquor requires eight ounces of oil of vitriol to combine with the ammonia from one gallon. More or less tar is mixed with the gas liquor, but on standing this settles to the bottom of the tank. The clear liquor is then distilled to separate the ammonia. There are several forms of apparatus for this distillation. In the simplest form the gas liquor is heated in one still until all the volatile salts are expelled, and then it is drawn into another still, where " milk of lime " is added, and heat again applied until the fixed salts are decomposed and the ammonia driven off. The ammonia and volatile salts are condensed in a vessel con- taining sulphuric or hydrochloric acid. Some hydrogen sulphide and other foul-smelling gases pass out of the absorption vessel, and are led into the chimney or are decomposed in a Glaus kiln (p. 85). In England, a large part of the gas liquor is distilled in Coffey stills (p. 9), but since it is inconvenient to use lime in these stills, most of the fixed salts are lost. The gas liquor, having been heated in the rectifier, passes into the analyzer, and there the volatile ammonia salts and free ammonia are driven out and pass through the rectifier, on their way to the absorption vessel. The more modern apparatus of Feldmann and of Grtineberg and Blum, are now much used on the continent of Europe and in America. Feldmann's apparatus (Fig. 54) is most used in this country. The gas liquor is drawn from the settling tank (F) into the economizer (E), which consists of a long, cylindrical shell, con- taining a number of narrow tubes, through which the gas liquor flows. In the absorption vessel (D) is sulphuric acid, to combine with the ammonia vapors passing from the still by the pipe (G). The hydrogen sulphide and carbon dioxide liberated in (D) are collected under the bell. The heat of the reaction between the acid 126 OUTLINES OF INDUSTRIAL CHEMISTRY and the ammonia raises the temperature of these gases to a high degree. They pass through the outlet pipe into the outside jacket or shell surrounding the tubes in the economizer, where they heat the gas liquor which is flowing through the small tubes, so that it is hot when it arrives at the top of the tower (AB) through the pipe (K). In the tower, the free ammonia and its volatile salts are driven out by the steam which is passing up through it. The liquor containing the fixed ammonia salts then passes to the lower part of (AB), where it is mixed with "milk of lime " while steam is blown in. The mixture then overflow^ through the pipe (M) into the smaller still (C), where all the ammonia set free by the lime, is driven out by a steam jet from (S). This ammonia passes through (ON) in- to the first tower, where it mixes with the gas escaping from (AB), and is absorbed in (D). The waste liquors escape through the pipe (P), and the sludge of calcium salts formed in ( B) is drawn off at regular intervals through (R). The still may be run for months without stopping. The Gruneberg-Blum apparatus is rather, more complicated in its details, but involves nearly the same principles as the above. All the stills mentioned here employ the principle of dephlegmation (p. 8). An appliance for distilling gas liquor is sometimes employed in which the vapors, set free by the action of the lime, are made to bubble through fresh gas liquor in a second vessel. Thus the vola- tile ammonia salts are expelled by the heat of these vapors, and pass off with them to the acid absorption tanks, while the gas liquor is drawn into the first vessel and is there treated with lime. This FIG. 54. AMMONIA 127 method was used in the old apparatus of Griineberg and of A. Mallet. The ammonia gas set free in any of the above described stills is generally absorbed in sulphuric acid. If dilute acid (80 to 100 Tw.) is used, there is no separation of ammonium sulphate crystals in the saturator, and the liquor is easily clarified from tar and sus- pended impurities before evaporating to crystallize. This yields the lightest colored product. If more concentrated acid (140 Tw.) is used, a separation of ammonium sulphate crystals takes place in the saturator, and these are "fished out." But they are often dis- colored, since the liquor has had no chance to clarify by settling. As fast as the crystals are removed, fresh acid is introduced in a small stream into the saturator. This is always covered with a lid, or hood, from which a pipe carries off the foul gases, consisting largely of hydrogen sulphide. These are often led to a Glaus kiln (p. 85) and decomposed to recover the sulphur, thus avoiding con- tamination of the atmosphere. A recent patent * involves the burn- ing of this gas in an atmosphere highly impregnated with sulphur dioxide, whereby the following reaction occurs : 2 H.S + S0 2 = 2 H 2 + 3 S. Care is taken that no ammonia passes out with the gases, a slight excess of acid always being present. The ammonia gas is led into the saturator through a pipe perforated with small holes and sub- merged in the acid. Gas liquor is not always distilled. Occasionally it is neutralized directly with mineral acid and evaporated to dryness, but this pro- duces a salt which is contaminated with tar, while the escape of hydrogen sulphide and other foul-smelling gases during the iieu- tralizating is liable to cause nuisance. Moreover, the solutions thus obtained are dilute, and much fuel is consumed in concentrating them. Ammonia has been made in this country by the destructive distil- lation of waste animal matter from slaughter houses and tanneries. Hair, "fleshings" from tanneries, scrap leather, etc., are the raw materials. These are dried and put into an upright iron cylinder, provided with a manhole at the top and at the bottom, and having a large perforated pipe running up through the centre, about three- fourths of the distance to the top. Hot chimney gases are forced by an air compressor through the pipes of a superheater (a furnace containing coils of pipe heated to a bright red heat), and into the * J. Soc. Chem. Ind., 1897, 536 and 980. 128 OUTLINES OF INDUSTRIAL CHEMISTRY bottom of the cylinder, where they escape through the perforated pipe, and come into direct contact with, and char, the animal mai>- ter.* The volatile products of the heating pass out at the top of the retort into a hydraulic main, similar to those used in gas works. The tarry matter settles in the main, and the gases pass through condensers, which are cylinders containing 4-inch tubes. Both the condensed liquors and the gases pass into absorption tanks contain- ing water. The unabsorbed gases pass through a "scrubber," the same as that used for gas liquor, to remove the last traces of ammonia. The washed gases are burned under the retort. The liquor produced in the absorbers and scrubbers is distilled in an ammonia still, Feldmann's being generally used. The coke remaining in the retort is porous, and contains a high percentage of nitrogen. It is generally used for fuel, but may per- haps be utilized for making cyanides. Ammonium sulphate, as found in commerce, has a light gray or yellowish color, or, if carefully made and washed after crystallizing, is nearly white. When prepared by direct saturation the color may be brown or nearly black. Common acid made from pyrites yields a salt which is yellow in color, owing to the iron or arsenic present. The crystals should be washed, and dried in a lead-lined centrifugal machine. It is sometimes sold damp, but is generally dried by warm air. When sold in large quantities it is always valued accord- ing to its content of ammonia or nitrogen. Good samples contain from 23 to 25 per cent NH 3 . It is largely used as a source of nitro- gen in making fertilizers, but for this purpose must be free from sulphocyanide, which is very injurious to vegetation. When made by absorbing the gas in acid, little or no sulphocyanide is present, but by direct neutralization of the gas liquor the cyanide may sepa- rate with the sulphate. The salt is used as a source of other ammo- nium compounds, and to a slight extent in rendering fabrics and other tissues non-inflammable. By distilling with lime it yields a very pure ammonia gas, which may be absorbed directly in water for the " aqua ammonia " of trade ; or the gas may be passed through towers filled with charcoal, to remove any trace of tar, before ab- sorption. Any sulphuretted hydrogen may be removed by passing the gas over oxide of iron. A considerable amount of liquid ammonia is now prepared and sent into the market for use in ice machines (p. 19). This is com- pressed into steel cylinders, usually containing about 100 pounds of the liquid. * It is said that the process did not prove successful in practice and has been given up. AMMONIA 129 Ammonium chloride is made by absorbing ammonia gas in dilute hydrochloric acid, or by neutralizing gas liquor with the acid directly and evaporating the solution. During the evaporation much of the tarry matter separates, and is skimmed off. Some nuisance may result from the gases escaping during the neutralizing. Another method is to mix a saturated solution of ammonium sulphate with a strong solution of salt or potassium chloride. On evaporating somewhat, monohydrated sodium sulphate (Na 2 S0 4 H 2 0) separates from the hot liquor, leaving the ammonium chloride in solution. On cooling, the ammonium chloride crystallizes : (NH 4 ) 2 S0 4 -{- 2 NaCl = Na 2 S0 4 + 2 NH 4 CL The crystallized chloride is more or less discolored by tar, and is purified by sublimation (p. 10) in iron or earthenware pots or retorts. The ammonium chloride collects on the cover of the pot as a thick, fibrous cake, in which form it comes in trade under the name of sal-ammoniac. This generally contains iron as an impurity, It was formerly made by subliming the soot obtained by burning dried camel's dung, but is now nearly all made from gas liquor. The crystallized salt is often sold under the name of " muriate of ammonia,' 7 and is usually less pure than sal-ammoniac. Muriate of ammonia is much used in the arts for charging Leclanche electric batteries ; in the process of " galvanizing " iron ; in soldering liquors ; for making "rust cement" for pipe joints; and in textile coloring. Ammonium carbonate as found in commerce is not a pure salt, but is a mixture of acid ammonium carbonate (NH 4 HC0 3 ) and a salt of carbamic acid (NH 2 C0 2 NH 4 ). The commercial salt is made by heating a mixture of the sulphate and powdered calcium carbonate in iron retorts. The vapors are condensed in lead-lined chambers, and the impure product is generally sublimed in iron pots having lead caps. A little water is put into each pot along with the salt, this causing the sublimed product to be transparent instead of opaque white. The temperature of this second sublimation is not much above 70 C. Ammonium carbonate is transparent when fresh and pure, but on exposure to the air, becomes covered with a white layer of bicarbon- ate, owing to the loss of ammonia. It is entirely volatile when heated, and from this fact is derived its old name of sal-volatile. It is used considerably in wool scouring, in certain baking powders, in medicine, and for the preparation of " smelling salts, 7 ' and to some extent, as an analytical reagent. Ammonium sulphocyanide (thiocyanate), p. 248. 130 OUTLINES OF INDUSTRIAL CHEMISTRY REFERENCES Acetic Acid, Vinegar, Ammonia, and Alum. John Gardner, F.I.C., F.C.S., London, 1885. (J. and A. Churchill.) Chemie des Steinkohlentheers. Dr. Gustav Schultz, 2te Auf., Vol. I, Braun- schweig, 1886. (Vieweg und Sohn.) Das Ammoniak-Wasser. Albert Fehrmann, Brauschweig, 1887. (Vieweg und Sohn.) Coal Tar and Ammonia, G. Lunge, 2d ed., London, 1887. (Gurney and Jackson.) Ammoniak und Ammoniak-Praeparate. Dr. R. Arnold, Berlin, 1889. (S. Fischer.) Traitement des Eaux Arnmoniacales. L. Weill-Goetz et F. Desor, Strasbourg, 1889. (G. Fischbach.) POTASH INDUSTRY Previous to the invention of the Leblanc Soda Process, the most important alkali was potassium carbonate, potash, which was nearly all derived from wood ashes. But with the development of the soda industry, the demand for potash was greatly diminished, and at the present time, soda has replaced it for all except a few special purposes. The chief sources of potassium salts now are : Wood ashes. Beet-sugar molasses and residues. Wool scourings. (Suint.) Stassfurt salts. Land plants take up considerable quantities of potassium com- pounds from the soil. When the plants are burned, about 10 per cent of the weight of the ashes is potassium carbonate,* which may be obtained by lixiviation. Potash from wood ashes is now chiefly made in Eussia, Sweden, and America, the woods most employed being elm, maple, and birch. Sometimes the stumps and small branches only are burned, the trunks being used for timber. The ashes are moistened slightly, put into tanks having false bottoms on which straw is spread, and then lixiviated with warm water. The lye so obtained is evaporated (sometimes by the waste heat from the burning wood) in iron pots until it solidifies on cooling. The dirty brown mass is then calcined in a reverberatory furnace until all the organic matter is destroyed. The product is known as potash or crude pearlash. It is white or gray in color, and contains about * Those plants which contain much silica or phosphoric acid straw and grasses yield hut little potash. POTASH INDUSTRY 131 70 per cent K 2 C0 3 , with some sulphate and chloride and sodium salts. By redissolving the crude potash in water, settling and concentrat- ing the solution until the sulphates and chlorides separate as crystals, a concentrated and pure lye is obtained. When this is evaporated to dryness and the residue calcined, it yields a much purer product, known as " refined pearlash," and containing from 95 to 97 per cent of K 2 C0 3 . It is necessary that a low heat be employed in the cal- cination, since the charge fuses at a moderate temperature. Often, some quicklime is put in the bottom of the tanks before the ashes are introduced. On leaching, the solution of potassium salts reacts with the lime, forming insoluble calcium salts, and yield- ing more or less potassium hydroxide in the lye. The resulting prod- uct is then a mixture of potash and caustic potash. In the manufacture of beet sugar, a very impure molasses re- mains, containing among other things a large amount of soluble potassium salts. This molasses is now generally fermented, in which process the sugary substances are converted into alcohol, which is distilled off, leaving the mineral salts in the liquid resi- due, called vinasse or schlempe. If this is evaporated to dryness and the mass calcined, the organic potassium salts are decomposed, leaving in the cinder about 35 per cent potassium carbonate, and a large amount of chloride and sulphate, together with sodium salts. If the vinasse be evaporated to dryness and the residue destruct- ively distilled in retorts, a distillate is obtained, containing organic compounds of which methyl alcohol CH 3 OH, ammonia, and tri- /CH 3 methylamine, ]ST CH 3 are valuable. The cinder in the retort con- \CH 3 tains potassium salts, which are obtained in solution by lixiviation, and a considerable quantity of potash is thus recovered. Very often, however, the ash is used as a fertilizer, thus returning the potash to the soil. Wool scourings furnish some potash in countries where much wool is washed. Sheep's wool as it comes from the animal contains from 30 to 75 per cent of its weight of impurities, consisting of dirt, sand, dung, etc. ; wool grease or " yolk," a fat-like substance, made up of cholesterine and compounds of it with oleic, stearic, and palmitic acids ; and " suint" which consists chiefly of potassium salts of oleic, stearic, and other organic acids, with small quantities of chlorides and sulphates and nitrogenous matter. The " suint " exudes from the animal in the perspiration, and is deposited on the wool by evaporation. It is soluble in cold water, and is thus removed 132 OUTLINES OF INDUSTRIAL CHEMISTRY in the scouring process. If these wash waters, containing wool grease and suint, are run into the drains or streams, pollution of the water results. The prevention of this nuisance, as well as the value of the potash, has necessitated attempts to dispose of the washings in some economical manner, and they are usually evaporated to dry- ness and calcined. If the calcination is done in closed retorts, a considerable quantity of ammonia is obtained. The cinder is lixiv- iated, and on evaporation, the solution yields, first, chlorides and sulphates of potassium and sodium, and finally a very pure potash, which averages a little less than 4 per cent of the weight of the raw wool scoured. For the recovery and treatment of wool grease, see pp. 320 and 444. This utilization of wool grease and suint is mainly practised in France, Belgium, and Germany, and in these countries this is done chiefly to prevent the pollution of the streams. Cheap fuel is very essential to a successful working of the process. On a small scale it cannot be carried on profitably, and the wash waters are often run onto the fields as fertilizer. For potassium carbonate from potassium chloride, see p. 135. By far the most important source of potassium compounds at the present time is the great natural deposit of potassium salts found at Stassfurt and Leopoldshall, near Magdeburg, Germany. This consists of immense beds of various salts, which have been deposited from sea water. They were discovered in attempting to reach the underlying rock-salt, but because of the large proportion of potas- sium and magnesium chlorides, the material was at first thrown aside as worthless, the name applied to it, " abmumsalze" indi- cating the small value attached to it. But in 1861-4 methods were devised by which potassium chloride and sulphate could be obtained cheaply from the Stassfurt salts, and since these furnish a valu- able source for nearly all other potassium salts, a rapid development of the industry followed. Sea water contains about 3.5 per cent of solids, consisting of : Sodium chloride 76.49 per cent* Magnesium chloride 10.20 Magnesium sulphate 6.51 " Calcium sulphate 3.97 " Potassium chloride 1.98 " Magnesium bromide * ' * 1 85 " Calcium bicarbonate, etc j * Regnault (Thorpe's Dictionary of Applied Chemistry, Vol. Ill, 266). POTASH INDUSTRY 133 By the evaporation of sea water under certain conditions, these salts, together with various doable salts, formed by mutual inter- reactions, crystallize in the order of their relative insolubility. The Stassfurt deposit was undoubtedly formed by the evaporation of sea water, under peculiar conditions. The mode of formation has been studied by many investigators, to whose memoirs the reader is referred for full explanations.* The deposit is nearly 3000 feet thick, and about 16 different salts have been identified in the various strata. The more important salts and their composition, are given below: Gypsum ........ CaSO 4 .2H 2 O Anhydrite ....... CaS0 4 Kainite ........ K 2 S0 4 , MgS0 4 , MgCl 2 -6H 2 Carnallite ....... KC1, MgCl 2 6 H 2 O Kieserite ........ MgS0 4 -H 2 O Polyhalite ....... K 2 SO 4 , MgS0 4 , 2 CaSO 4 2 H 2 Kock-Salt ....... NaCl Sylvine ........ KC1 Tachydrite ....... CaCl 2 , 2 MgCl 2 12 H 2 Boracite ........ 2 (Mg 3 B 8 Oi 5 ) + MgCl 2 Astrakanite ....... MgS0 4 , Na 2 S0 4 4 H 2 O Schoenite ....... K 2 S0 4 , MgS0 4 6 H 2 O The beds are not sharply defined layers of separate salts, the de- posit being generally regarded as containing four principal "regions." The rock-salt or anhydrite region is the lowest of these. This consists of thin layers of very pure rock-salt, separated by narrow strata (one-fourth of an inch thick) of anhydrite. The anhydrite is separated from the salt mechanically, and the latter is then ground for use directly. This bed is nearly 2000 feet thick in places. The polyhalite region, about 200 feet thick, is above the rock- salt region. It is composed of 91 per cent of rock-salt, and 6|- per cent of polyhalite, with smaller quantities of other salts. The kieserite region, lying next above, is about 185 feet thick, and contains 65 per cent rock-salt, 17 per cent of kieserite, 13 per cent carnallite, and 5 per cent of other salts. The carnallite region lies nearest the surface, and is about 140 feet thick. This is the most important and contains : Carnallite ........... . 55-60 per cent Rock-salt ........ ..... 20-25 per cent Kieserite ............. 16 per cent ........... 4 per cent Boracite / * A very good account is given in Thorpe's Dictionary of Applied Chemistry, Vol. Ill, pp. 266-268. Also see Pfeiffer's Handbuch der Kali-Industrie. I Potassium chloride . . . 16.2 per cent Magnesium chloride . . . 24.3 t Sodium chloride .... 18.7 ' Calcium chloride .... 0.2 t Magnesium sulphate . . . 9.7 Calcium sulphate .... 2.1 i Water . . . 28.8 i Insoluble 00.0 , 134 OUTLINES OF INDUSTRIAL CHEMISTRY In parts of this region, changes have taken place through the action of water, by which considerable deposits of kainite and sylvine have been formed. The composition of raw carnallite is about as follows : II > . 15.7 per cent . * 21.3 " . . 21.5 " . . 0.3 " , . 13.0 " . . 00.0 " . . 26.2 " . . 2.0 The crude carnallite is often colored a deep red by the presence of iron compounds. The present commercial supply of potassium chloride, and inci- dentally of other potassium compounds, is obtained from carnallite. The crude material is treated with the hot mother -liquor from a previous lot, in an iron kettle having a stirring apparatus and a false bottom. This mother-liquor contains about 20 per cent MgCl 2 , which prevents the solution of the rock-salt and kieserite, but does not hinder the dissolving of the carnallite. The action of the magnesium chloride solution is continued until the hot liquor reaches a density of 1.32 sp. gr., when it is drawn off from the sludge and allowed to cool slowly. At this density, the greater part of the potassium chloride crystallizes on cooling, leaving the magnesium chloride and some potassium chloride still in solution. This liquor is then further concentrated, until it contains about 30 per cent mag- nesium chloride. On cooling, crystals having the composition KC1, MgCl 2 6 H 2 0, artificial carnallite, separate, leaving only the excess of magnesium chloride in solution. The artificial carnal- lite is decomposed with water, and the potassium chloride crystallized out, leaving the magnesium chloride in solution; a part of this liquor, diluted with the wash water from the sludge, is used to extract the next portion of raw carnallite. The potassium chloride is washed with a small portion of very cold water, to remove the common salt. The residue from the solution of the raw carnallite consists largely of kieserite mud (MgS0 4 H.,0), which is insoluble in water ; but on standing for some time in contact with water, it passes over into the soluble Epsom salts (MgS0 4 7 H 2 0). At an intermediate stage of the hydration, the mud solidifies in a manner similar to POTASH INDUSTRY 135 plaster of Paris when mixed with, water. When this solidification is about to take place, the mud is moulded into blocks, which become very hard, and in which form it is shipped. But after some time they take up moisture from the air, and fall to a powder of Epsom salt. Glauber's salt is made at Stassfurt in the winter time as fol- lows : Solutions of common salt and magnesium sulphate (e.g. from kieserite) when kept below C. will react together, thus : MgS0 4 + 2 NaCl = MgCl 2 + Na 2 S0 4 , and at the low temperature, the sodium sulphate crystallizes to form Na 2 S0 4 10 H 2 0. Kainite (K 2 S0 4 , MgS0 4 , MgCl 2 - 6 H 2 0) is extensively used in the crude state as a fertilizer. Some of it, however, is treated for potassium sulphate, by the method of H. Precht. When heated with water under pressures of four or five atmospheres, kainite decomposes into a double potassium-magnesium sulphate, magne- sium chloride, and potassium chloride, thus : + 2 KC1 + 16 H 2 0. 3 (K 2 S0 4 , MgS0 4 , MgCl 2 . 6 H 2 0) = 2 (K 2 S0 4 , 2 MgS0 4 H 2 0) + 2 MgCl The double potassium-magnesium sulphate separates in crystals, and is freed from chlorides by washing ; during the washing, one molecule of the magnesium sulphate is also removed, and a salt of the composition, K 2 S0 4 , MgS0 4 , remains. This is dried and calcined, and sold as double potassium-magnesium sulphate; or it may be decomposed directly by treating with a solution of potas- sium chloride of 1.142 sp. gr. : K 2 S0 4 , MgS0 4 + 2 KC1 = MgCl 2 + 2 K 2 S0 4 . The potassium sulphate is separated from the magnesium, chlo- ride by crystallization. Potassium sulphate, made from, kainite as above, or by the action of sulphuric acid on potassium chloride, is largely used as a fertilizer and for the manufacture of potassium carbonate. Potassium chloride, chiefly obtained from carnallite, is exten- sively used for preparing other potassium salts, especially the nitrate (p. 121), sulphate, and carbonate. Potassium carbonate or potash is made from potassium chloride by the Leblanc process, in the same way as soda-ash from salt. But the ammonia process cannot be employed, because the acid carbonate 136 OUTLINES OF INDUSTRIAL CHEMISTRY of potassium (KHS0 4 ) is soluble in ammoniacal solutions, and does not precipitate. Potassium carbonate is sold in trade under the name of potash or pearlash, and is used chiefly in the glass industry, for caustic potash and for chromates of potassium. A considerable quantity is bought by soap makers, and causticized, the solution being used for soft soaps (p. 322). Caustic Potash is made in the same way as caustic soda (p. 80). The mother-liquors from the black-ash lixiviation are decomposed directly with slaked lime. Caustic potash is much more deliques- cent than caustic soda, and is generally made where it is to be used. In soap making, it was formerly customary to saponify the fat with caustic potash, and then to add common salt. An interchange between the potassium and sodium took place, and a hard sodium soap resulted. But as soda is now cheaper, and yields a hard soap directly, potash soaps are only used for special purposes. Potassium nitrate. (See p. 120.) Potassium bichromate (K 2 Cr 2 7 ) is made by roasting chromite (a native oxide of chromium and iron) with potash, lixiviating the fused mass with water, and adding enough sulphuric acid to convert the neutral potassium chromate into bichromate. The reactions involved are as follows : Cr 2 3 -f-30==2Cr0 3 ; Cr0 3 + K 2 C0 3 = K 2 Cr0 4 + C0 2 ; 2 K 2 Cr0 4 + H 2 S0 4 = K 2 S0 4 + K 2 Cr 2 7 + H 2 0. The finely powdered chrome ore is mixed with lime and potash, and roasted at a bright red heat, with free access of air and frequent stirring. After several hours the chromic oxide is all oxidized to chromium trioxide (Cr0 3 ), which combines with the lime and pot- ash to form neutral chromates of calcium and potassium. The mass is then treated with a hot solution of potassium sulphate, which forms potassium chromate from the calcium chromate. The solu- tion of neutral potassium chromate, when saturated, is drawn off and settled. It is then decomposed in lead-lined tanks, by the addi- tion of sulphuric acid. Since potassium bichromate is very much less soluble in cold solution than the neutral chromate, about three- fourths of the total amount of bichromate formed precipitates. The remaining liquor, containing potassium sulphate, is used to leach a new portion of cinder. The precipitated bichromate is recrystal- lized from water. FERTILIZERS 137 The addition of lime to the furnace charge is necessary to pre- vent the fusion of the mass, and to keep it porous, so that the oxidation of the chrome is more complete. Potassium bichromate is much used as a source of other chromium compounds; as an oxidizing agent in dyeing and making coal-tar dyes ; as a mordant ; as a bleaching agent for oils and fats ; and for the preparation of leather in the chrome tannage processes. REFERENCES Die Industrie von Stassfurt u. Leopoldshall. G. Krause. Coethen, 1877. Handbuch der Kali Industrie. E. Pfeiffer, 1887. Die Salz Industrie von Stassfurt. Dr. Precht, Stassfurt, 1889. (R. Weicke.) Die Stassfurter Kali-Industrie. G. Lierke, Wien, 1891. (Hilschmann.) J. Soc. Chern. Ind., 1883, 146, C. N. Hake. Chemische Zeitung, 1890, Grief. 1891, Heyer. Dingler's polyteclmisches Jour. Vol. 241. Precht. FERTILIZERS Growing plants are nourished by certain constituents which they absorb from the soil and air. The chief elements drawn from the soil are potassium, calcium, sulphur, phosphorus, and nitrogen; other elements such as silicon, iron, sodium, magnesium, and chlorine are taken up to a less degree. The natural weathering of the min- erals in the ground usually provide the elements necessary to plant life; but the supply of potassium, phosphorus, and nitrogen may be insufficient and become exhausted by frequent repetitions of the same crops on the same land. The soil becomes less productive, and finally the crops are failures. To supply this continued drain on the soil, fertilizers are employed. The natural fertilizers, barn-yard manure, urine, and decomposing vegetable mould or muck, will not be considered here, as they need little or no treatment before use. By artificial fertilizers we understand those manurial substances, prepared from materials which need some special treatment to render them fit for plant food. The chief requisites of a good arti- ficial fertilizer are : 1. It must contain at least one substance fit for plant food, and this substance must be easily convertible, by the action of rain and moisture, to such a form that plants can assimilate it. 2. It must be dry and finely powdered, so that it may be evenly distributed over the surface of the ground. 138 OUTLINES OF INDUSTRIAL CHEMISTRY 3. It must contain nothing injurious to plant life. 4. It must be cheap. A complete fertilizer should supply the three essentials, potas- sium, nitrogen and phosphorus. But the majority of artificial fertilizers afford only one or two of these elements, and are usually sold for certain crops, or for use on particular kinds of soil. Potassium is generally returned to the soil in the form of sul- phate or carbonate (wood ashes), and occasionally as chloride. The preparation and use of these salts have already been considered and also the preparation of ground kainite (p. 135) for this purpose. Nitrogen is frequently supplied as ammonium salts (p. 128), or nitrates, particularly sodium nitrate (p. 119). But many substances used for fertilizers contain nitrogen in organic compounds, which decompose readily in the soil, setting free the nitrogen. Phosphorus is nearly always applied to the soil in some form of calcium phosphate derived from mineral sources or from organic matter. The most important branch of the fertilizer industry is the preparation of phosphates. Fertilizers are largely made from the waste products of slaughter houses, such as blood, bits of waste meat and other refuse, bones, hoofs, horns, and hair. Tainted meat and animals which have died of disease are also sent to the rendering tanks.* Blood is dried at a moderate heat and crushed to powder between rolls. It contains about 10 per cent 1ST, and is very uniform in composition. Bones are very good fertilizing material, supplying both nitrogen and phosphorus when used as raw bone ; i.e. without treatment other .than grinding. But as a rule the bones are extracted with benzine and then boiled, or extracted with steam under pressure to remove the fats and gelatine (p. 527), after which the residue is ground and used directly for fertilizer as bone meal, the fineness of this " meal " having much influence on the rapidity of its decay in the soil. Being more spongy and soft, it yields its phosphoric acid in a much shorter time than the hard " raw bone.' 7 The latter contains about 22 per cent of phosphoric acid and 4 per cent of nitrogen. But steaming reduces the nitrogen to about 1 per cent, while the proportion of phosphoric acid is raised to 27 or 28 per cent. Bones are often subjected to destructive distillation in retorts, by which nearly all the nitrogen is driven out as ammonia, ammo- nium carbonate, pyridine, and other nitrogenous organic compounds, * "Rendering" consists in extracting all the fats, oils, and gelatinous matter from the carcasses by treating with benzine or steam under pressure. The fat extracted is used for soap stock. ' ' FERTILIZERS 139 while the residue left in the retort, known as " bone-char " or " bone- black," contains calcium phosphates and other salts, mixed with carbon. This bone-char is extensively used as a decolorizing agent in the purification of sugar, glucose, oils, and other liquids ; when it can no longer be employed for this purpose (see p. 265) it is burned with free access of air to form "white-ash," which contains a high percentage of phosphorus. This bone-ash may be used directly as a fertilizer, but is usually treated with sulphuric acid to form " super- phosphate" (p. 143), which is more soluble than the tricalcium phosphate of the bone. A process for extracting the mineral phosphate from bones by digesting with hydrochloric acid has been practised to some extent. The solution of phosphoric acid thus obtained is neutralized with milk of lime, by which the calcium phosphate is precipitated, chiefly as dicalcium phosphate (Ca 2 H 2 P 2 8 ). This is sometimes sold as " precipitated phosphate," but the method is more commonly applied to low grades of mineral phosphates (p. 145) than to bones. Garbage containing fatty matter is now collected in many cities and subjected to a rendering process. It is put into steel digesters and subjected to the action of steam at 50 pounds pressure for eight or ten hours, when the mass is reduced to a soft pulp which is put into presses and the oily matter pressed out. The press-cake is broken up and dried in revolving steam-heated drums, after which it is powdered, sifted, and used for " filler " in fertilizers, under the name "tankage." It contains nitrogen, phosphoric acid, and a little potash. On cooling the oily matter forms a soft grease, which is used for soap and candle stock. The water which is pressed out of the tankage with the grease contains a large amount of ammonium salts and some potash ; it is evaporated to dryness and the residue mixed with the tankage, thus increasing the nitrogen and potash in the latter. Other nitrogenous waste from various industries leather scrap, wool waste and dust from shoddy and felt mills are used to some extent; but these, though very rich in nitrogen, are very slow in decomposing, and are so light when powdered that they are easily blown away. The press-cakes from various oil industries (e.g. the manufacture of cotton-seed, rape, and castor oils) are often ground for fertilizer. Sometimes the cake is burned for fuel and the ashes used for fertiliz- ing, but in this case the nitrogen is lost, only the potassium and phosphorus being returned to the soil. In the manufacture of fish oils there is a considerable amount of residue from which the oil has 140 OUTLINES OF INDUSTRIAL CHEMISTRY been pressed. This is known as " fish scrap," and consists of the scales, bones, fins, and meat of the fish. It contains about 7 per cent of nitrogen and nearly 16 per cent of phosphorus pentoxide (P 2 B ). It is dried (usually by exposure to the sun) and then crushed to a rather coarse powder. It is a valuable fertilizer, decaying rapidly in the soil and feeding the plants continually. Peruvian guano was formerly of great importance as a fertilizer, but now the beds are nearly exhausted. It consists of dried excre- ment, feathers, and carcasses of sea fowl, and is rich in nitrogen and phosphoric acid. It is found in certain islands near the coast of Peru and Chili, and also on the mainland at the base of the Andes, near the sodium nitrate beds (p. 119). The region is dry and hot, and the guana has been thus preserved with a high percentage of nitrogen, largely as uric acid and its salts. It needs no preliminary treatment before spreading on the soil. Fresh guano, collected yearly from various islands in the South Pacific, is damp, and contains a large amount of ammonium carbon- ate ; this must be "fixed" by mixing with sulphuric acid, to prevent loss of the nitrogen. Fossil guanos, consisting of fossil excrement and remains of birds and reptiles, are found in the West Indies, Bolivia, Chili, and the South Pacific islands. Since more or less rain falls in these climates, the soluble ammonium salts and nitrates have been washed out, leaving only the calcium phosphate. Some of these guanos have entered into combination with the rocks on which they were de- posited, thus altering their original character considerably ; e.g. some of them contain a large amount of calcium sulphate. Fossil guanos are prepared in the same way as phosphate rock. (See below.) The largest source of phosphoric acid ,is now phosphate rock, especially apatite and phosphorite. These are found in large deposits in Belgium, Germany, France, Spain, Algiers, Canada, South Caro- lina, Florida, and the West Indies. At present the United States deposits are the most important. Apatite [3 Ca 3 P 2 8 + CaF 2 (CaCl 2 )] is a crystalline mineral, occurring in large deposits in Canada and Spain. The former are very extensive, and are found in Ontario, between the St. Lawrence and Ottawa rivers, and in Quebec Province, along the Gatineau and du Lievre rivers. The mineral sometimes occurs in veins and pockets (bonanzas) of nearly pure, massive apatite ; and in other cases as distinct, hexagonal crystals or nodules, disseminated in calcite or pyroxene. The material is sold on a guarantee of 75 or FERTILIZERS 141 80 per cent of calcium phosphate, and to secure this degree of purity, 'cobbing"* and hand-picking must be employed. The ore being exceedingly brittle and the gangue rock very hard, there is much loss in the "fines," from which it is not profitable to separate the phosphate rock. Apatite varies in character from a moderately hard rock, to a soft and friable mass, called "sugar." The color varies much, but is generally blue-green or red-brown. The tricalcium phosphate being quite insoluble, the mineral must be treated with sulphuric acid to form "superphosphate." But since more or less calcium fluoride and chloride is present, considerable acid is uselessly consumed, and a special condensing apparatus is necessary to retain the vapors of hydrofluoric and hydrochloric acids set free, or a nuisance is created. Apatite also requires a rather strong acid (1.78 sp. gr.) for its decom- position, while the calcite and other minerals connected with it being acted upon, cause considerable loss of acid. These objections do not apply to the phosphorites of the United States and Europe, and the cost of mining is not so great. As a result the Canadian mines are now nearly all closed^ and there seems little probability that they will be opened for many years to come. Phosphorites are amorphous rocks of varying composition, but all containing a large percentage of tricalcium phosphate, and some- times iron and aluminum phosphates. The mode of formation of these rocks has been a much-disputed question, but they are now generally regarded as of organic, and probably animal origin. The beds are filled with fossil remains of land and marine animals and fishes. A nodular variety found in England was erroneously sup- posed to be fossil reptilian excrement, and was called " Coprolites." Some phosphorites are compact and hard to grind, as is the Spanish variety, but the American rock is softer and porous. In the United States there are two varieties, " land rock " and " river rock." Land rock occurs in beds averaging from 10 to 12 inches in thick- ness, and from 2 to 40 feet below the surface of the ground. These beds are sometimes composed of loose pebbles or gravel, but fre- quently these have been compacted into solid layers having a lami- nated structure; or they may form great boulders or conglomerate masses. The beds are often continuous over a large area, but "pockets" or isolated beds are frequently found. Good rock will average from 75 to 80 per cent of tricalcium phosphate (Ca 3 P 2 8 ). In some cases the land rock is hard, dense, and nearly pure (hard * Breaking the large lumps with hammers by hand. 142 OUTLINES OF INDUSTRIAL CHEMISTRY phosphate), while in others it is soft, resembling clay in its consist- ency, and usually containing rather a large proportion of iron and aluminum. Land rock is mined by stripping off the overlying earth, and digging out the phosphate rock with pick and shovel. It has been found practical to use steam shovels and dredges for "soft phos- phate " and " pebble " deposits. In compact rock, blasting is neces- sary. The work is done in open pits, tunnelling not having proved successful. The depth of overburden which may be profitably removed, depends upon the thickness and purity of the deposit, but about 20 feet is the limit, except in the case of very thick beds of high grade ore. For ordinary rock, the limit is about 10 or 12 feet. In a few cases hydraulic mining has been employed to wash away the overburden. After mining, the rock is put through a "breaker," and reduced to lumps about 4 inches in diameter. These go to the "washer" which consists of a long, semicircular trough, set at a slight incline, in which there is a revolving shaft, carrying teeth or blades about 9 inches long, and arranged around it in the form of a spiral screw, having a pitch of about 1 in 6. The trough is set in a tank of water, or a large stream of water enters at the upper end. The lumps of rock are fed into the trough at the lower end, and being caught by the teeth, are forced along and up the trough, against the water. The rubbing against each other, and the action of the water, washes away the sand and clay, and at the upper end the clean rock falls on screens, which separate the several sizes of lumps. It is usually dried by piling it on racks of cord wood, which are then fired and allowed to burn out ; or it may be piled over cast- iron pipes having numerous apertures, and through which hot air from a furnace is forced. The rock is then shipped to the makers of " superphosphate." Eiver rock is dredged or dug from the beds of rivers and streams, especially Peace Eiver and its tributaries in Florida, and from the streams near Charleston and Beaufort, S.C. When the deposit is in the form of loose nodules and gravel, steam dredges or cen- trifugal pumps are used to raise it; but when it is compact rock, special forms of grips and dredges are necessary. In most cases, river mining is not carried on in water more than 30 feet deep. River rock is very similar in composition to land rock, but is darker in color, even black, and contains more animal remains and fossils. Jt is preferred by foreign superphosphate makers and is generally shipped abroad. FERTILIZERS 143 " Superphosphate " is the name given to a soluble phosphate, pre- pared by treating insoluble rock or bone * phosphate, with sulphuric acid. By the action of the sulphuric acid, the insoluble tricalcium phosphate is converted into monocalciiim phosphate (CaH 4 P 2 8 ), while in many cases some free phosphoric acid is also formed. The reactions involved are as follows : A+ 2 H 2 S0 4 +6H 2 = (CaH 4 P 2 8 +2 H 2 0) +2(CaS0 4 - 2 H 2 0). 2) Ca 3 PA+3 H 2 S0 4 +6 H a O=2 H 3 P0 4 +3(CaS0 4 . 2 H 2 0). 3) Ca 3 PA+H 2 S0 4 + 6 H.O^Ca^PA - 4 H 2 0) + (CaS0 4 - 2H,0). Reactions 1 and 2 are the ones desired in fertilizer making, but if too little acid is used, reaction 3 takes place to a greater or less extent, forming some dicalcium phosphate, which is also insoluble. If too much acid is used, reaction 2 takes place to an undesirable extent, and the product contains an excess of free phosphoric acid, which attracts moisture from the air, making the fertilizer moist and lumpy. A small excess of sulphuric acid over the theoretical quantity needed is generally used to prevent "reversion" (p. 144) as far as possible. The proper regulation of the amount of acid is a matter of great care, and must be controlled by analysis of the material. The acid employed is "chamber acid" of 1.54 to 1.60 sp. gr. Concentrated acid is not used, because water is necessary in order that a hydrated calcium sulphate as well as a hydrated monocalciiim phosphate may be formed. The formation of the gypsum (CaS0 4 2 H 2 0) greatly assists in the subsequent drying of the product. Hydrochloric acid is unsuitable for fertilizer making, because of its expense, and the formation of calcium chloride in the product. The raw phosphate should be as free as possible from impurities, such as carbonates, iron oxide and alumina. About 3 per cent of Fe A + A1 2 3 is the limit now allowed. The phosphate rock, powdered to pass an 80-mesh sieve, is put into a lead-lined mixer, provided with effective stirring apparatus, and the required amount of acid is added. The mixing is complete in two or three minutes, and then the liquid charge is at once run into a brick-lined " pit," where the principal reactions take place. The temperature rises very rapidly to 100 or 110 C., and a great quantity of gases (HC1, HF, CO 2 , and SiF 4 ) escape through the draught flue. As the reaction progresses, the mass becomes stiff and finally solidi- fies, forming a single cake, which is broken up, removed from the * Superphosphate made from bones contains some nitrogen as well as phosphoric acid. 144 OUTLINES OF INDUSTRIAL CHEMISTRY pit, and dried by steam heat, at a temperature of 105 C. The mass is then powdered in a "disintegrator mill." Frequently the superphosphate is mixed with nitrogenous or potash materials in the disintegrator, to furnish a " complete " fer- tilizer. It is then packed in bags and is ready for market. If the phosphate rock contains much iron or aluminum oxide, or if the decomposition by acid has been incomplete, a series of sec- ondary reactions ensues, when the superphosphate is stored. By these, a part or all of the monocalcium phosphate (CaH 4 P 2 8 ), and the free phosphoric acid may be converted into the insoluble di- calcium phosphate, or into insoluble phosphates of iron or aluminum. This constitutes what is called " reversion," and the insoluble calcium or iron phosphates so formed are called "reverted phosphate." Since fertilizer is usually valued according to its percentage of soluble phosphate, reversion is a serious matter for manufacturer and buyer. Reverted phosphate is recognized as having a certain value for fertilizer purposes, but much less than superphosphate. When due to incomplete decomposition of the rock, reversion takes place according to the following reaction : CaH 4 P 2 8 + Ca 3 P 2 O 8 = 2 Ca 2 H 2 P 2 8 . When the rock contains iron or alumina, the temperature of the reaction in the pit is kept as low as possible, to prevent combina- tion between these oxides and the free phosphoric acid formed. It is customary in this case to remove the superphosphate from the pit as soon as it solidifies, and to cool it by exposure to the air. A " double superphosphate " is also made, especially in Europe, and contains more soluble phosphoric acid than the ordinary superphosphate. A certain quantity of bones or phosphate rock is decomposed with sufficient dilute sulphuric acid to set free all the phosphoric acid and precipitate all the calcium as hydrated calcium sulphate. The precipitate is then filtered off by means of the filter press (p. 12), and the clear solution of phosphoric acid is concen- trated by surface heating in lead pans, to a density of 45 Be., at which strength the solution contains nearly 45 per cent P 2 5 . Dur- ing this concentration, the iron and aluminum phosphates separate and are removed. The strong solution of phosphoric acid is then treated with ground phosphate rock, in proper quantity to form monocalcium phosphate, which is dried and disintegrated. The reactions involved are as follows : 1) Ca 3 P 2 8 + 3 H 2 S0 4 + 6 H 2 = 3 (CaS0 4 2 H 2 0) + 2 H 3 PO<. 2) Ca 3 P 2 8 + 4 H 3 P0 4 4- 6 H 2 = 3 (CaH 4 P A + 2 H.O). FERTILIZERS 145 By this process, a very concentrated fertilizer, containing no gypsum or other sulphate, is obtained. Moreover, a low-grade phos- phate rock can be used for making the phosphoric acid, which would not furnish a strong fertilizer with sulphuric acid. A small amount of phosphate rock is used directly for fertilizer, without other preparation than fine grinding. But tricalcium phos- phate, being very insoluble, is only slowly assimilated by plants, and its action is not very marked. Several years are necessary for its complete decomposition. Phosphatic slag is now used to a considerable extent as a fertil- izer, especially in Europe. In the process of making Bessemer steel by the Thomas and Gilchrist method, pig iron from ores containing phosphorus is treated with an excess of lime in a Bessemer con- verter, lined with lime, while a blast of air is forced into the liquid mass. At the high temperature of the melted iron, the phosphorus is oxidized to pentoxide, which combines with the lime. The silica, alumina, lime, and magnesia unite to form a slag, into which the calcium phosphate produced also goes. By proper regulation of the charge, a slag containing about 17 per cent of pentoxide (P 2 5 ) is obtained. The phosphate in the slag is supposed to be a tetracalcic phosphate (Ca 4 P 2 9 ), which is insoluble in water, but is much less stable than tricalcium phosphate. When exposed to the weather in the soil, it decomposes, though somewhat slowly, and the phosphorus passes into a form which plants can assimilate. In order that this decomposition may take place, the slag must be ground very fine, so that 90 per cent of it will pass through a sieve with 100 meshes to FIG. 55. the linear inch. The grinding is best done in a ball mill (Fig. 55), which consists of a cast-iron drum (D), and containing numerous chilled iron or steel balls (B) of different sizes. The coarsely ground 146 OUTLINES OF INDUSTRIAL CHEMISTRY slag is powdered by the rubbing and pounding of the balls as the drum rotates. It then passes through the perforated plates (P) and falls on fine brass sieves (S). The coarser particles, which cannot pass through the sieves, return to the interior of the drum, through the openings (C, C), for further grinding. Slag fertilizer needs no further treatment than very fine grind- ing, but it is slow in decomposing, and its full effect is not obtained for two or three years. It decomposes more rapidly than ground phosphate rock, however, and is cheap. There has been considerable controversy among agricultural chemists as to the relative value of soluble and insoluble phos- phates. Some hold that the soluble phosphate is at once converted into the insoluble form when it comes into contact with the lime, alumina and iron in the soil; and that this insoluble phosphate is dissolved or absorbed by the sap in the plant roots, the sap pre- sumably having an acid nature. Other chemists claim that only the soluble phosphate, as such, can be taken up by the plant. It ap- pears from observed facts, however, that both soluble and insoluble phosphates are taken up by the plant, but the nature of the soil is an important factor. On a soil poor in lime, and containing some organic matter, insoluble phosphates produce their best results ; but if the soil contains much lime, then the superphosphate appears to have the advantage. The soluble character of the superphosphate permits its dif- fusion through the soil by rain, so that it is brought immediately to the roots of the plants. But the insoluble phosphate must be turned under the soil, and the roots grow to it ; then, too, when not finely ground, it possesses but little value, owing to the slow decom- position ; but when in a very fine powder it is taken up in some way by the roots of the plant with fair rapidity. The manufacture and sale of artificial fertilizers are, to a certain extent, under legal restriction in nearly all the states. To prevent fraud, manufacturers are required to take out a license, and to- sub- mit samples for analysis by state chemists ; frequently a guarantee of the stated composition is required. The methods of analyses of fertilizers are set forth in detail in the bulletins of the several state agricultural experiment stations and of the United States De- partment of Agriculture.* In general the matter determined by the analysis may be summed up as : (a) Water, both hygroscopic and combined. * Bull. No. 28, U. S. Dept. Agriculture; Division of Chemistry. FERTILIZERS 147 (6) Total phosphoric acid. (c) Soluble phosphoric acid. (d) Reverted phosphoric acid. (e) Total nitrogen. (/) Potash. Another substance frequently sold as fertilizer is pulverized gypsum (CaS0 4 2 H 2 0), which, when crushed to a fine powder, is brought into commerce under the name of "plaster." As a fertil- izer it is of little value, except in soils poor in lime or those contain- ing " black alkali " (sodium carbonate). But it is also claimed to have a beneficial action in retaining nitrogen in the soil. The calcium sulphate is supposed to be decomposed by the ammonia and carbonic acid from the air and rain, forming ammonium sulphate and calcium carbonate. Ammonium sulphate furnishes nitrogen in a form which plants can assimilate. Much attention has been devoted, especially in Germany, to methods of recovering fertilizing material from the sewage of cities. But when closets are flushed with water, the effluent is generally too dilute to be worth recovering. It is, however, used to some extent, in irrigating lands, generally those owned by the municipality. Sewage is often precipitated with lime or other substance, but this generally renders the sludge useless for fertilizing. The contents of dry vaults or cesspools are collected at regular intervals and used for fertilizing. But sewage treatment of any kind is usually practised to pre- vent pollution and unsanitary conditions in the streams and water supplies, rather than for the utilization of the fertilizing materials to be obtained. REFERENCES Lehrbuch der Diingerfabrication. Paul Wagner. Braunschweig, 1877. Report of the Commissioner of Agriculture of South Carolina, for the year 1880. Chas. U. Shepard. Bulletin de la Socie'te' Chimique, 1834, 219. E. Dreyfus. Die kunstlichen Diingermittel. Dr. S. Pick, Leipzig, 1887. (Hartleben.) The Nature and Origin of Deposits of Phosphate of Lime. R. A. F. Penrose, Bull. 46, U.S. Geological Survey, Washington, 1888. A Treatise on Manures. A. B. Griffiths, London, 1889. (Geo. Bell and Sons.) The Phosphates of America. Francis Wyatt, New York, 1891. (Scientific Publishing Co.) Florida, South Carolina, and Canadian Phosphates. C. C. Hoyer Millar, Lon- don, 1892. (Fischer and Co.) Les Phosphates de Chaux naturels. Paul Hubert, Paris, 1893. 148 OUTLINES OF INDUSTRIAL CHEMISTRY The Phosphate Industry of the United States. Carroll D. Wright, Washington, 1893. (Sixth Special Report of the U.S. Commissioner of Labor.) J. Amer. Chem. Soc., 1893, 321. Chas. U. Shepard. 1895, 47. W. E. Gar- rigues. J. Soc. Chem. Ind., 1888, 79. W. T. MacAdam. 1894, 842. Kalmann and Meissels. Agricultural Analysis. F. W. Wiley, Vol. II, Fertilizers, Easton, Penn., 1896. (Chemical Publishing Co.) LIME, CEMENT, AND PLASTER OF PARIS Good lirne is nearly pure calcium oxide ; it is one of the most important substances used in chemical industry, and is prepared in enormous quantities by calcining calcium carbonate at a bright red heat. If the carbonate used (limestone, chalk, or the shells of mol- lusks) contains much silica, iron, alumina, or other impurity, the lime does not slake freely with water, and is said to be " poor " or "lean." If but small quantities of these impurities are present, a fair lime is produced, when properly burned. But such impure carbonates are very difficult to burn, since slight overheating causes semi-fusion of the lumps, and the lime combines with water very slowly and incompletely, and is said to be "burned to death." A pure lime, which combines readily with water to form a fine white powder, free from grit, and which makes a smooth stiff paste with an excess of water, is called a " fat " lime. Calcium carbonate begins to decompose below a red heat into calcium oxide and carbon dioxide, but the decomposition is not complete until a bright red heat (800 or 900 C.) is reached. The temperature should not rise much above 1000 to 1200 C. ; as there is danger of overheating the lime. For successful burning, it is essential that the gases escape freely from the kiln, the draught usually being sufficient to remove them as they form. This escape may be accelerated by blowing steam or air into the kiln during the burning, or even by wetting the carbonate as it is introduced. If the gases are retained, they cause pressure in the kiln and thus hinder the decomposition; and on cooling, the carbonic acid re- combines with the lime. There are two general classes of limekilns, continuous and periodic. (See Calcination, p. 18.) The former are preferred where fuel is expensive, and where a large regular output is desired. They are tall, narrow furnaces (shaft kilns), built of brick or of iron plates, and vary much in size, but are usually from 40 to 45 feet LIME, CEMENT, AND PLASTER OF PARIS 149 high, by 7 feet in diameter. The carbonate is fed in at the top and the linie taken out at the bottom, without interrupting the process. Figure 56 shows a furnace for burning with "long flame." The fuel is burned on the grate (A), and only the flames and combustion gases pass through (B) to come in contact with the charge in the shaft. The ashes fall into the chamber (D), and are thus kept separate from the lime, which is withdrawn through (C) at regular intervals, causing a slow descent of the charge. Thus a clean lime is obtained. In the continuous kilns which use the "short flame," FlG 56 the carbonate and fuel are charged alternately at the top, and the lime, contaminated with ashes, is taken out at the bottom. Less fuel is needed than for "long flame burning." Fuel gas for lime burning has been successfully introduced in many places. This gives a very clean lime, burned at a constant temperature. In this country, long-flame, periodic kilns are generally used. These require much fuel and time, but are probably preferred because of the simplicity and cheapness of building. They are made of brick or of large blocks of limestone. Two or three feet from the ground an arch (A) (Fig. 57), of large blocks of lime- stone, is turned, numerous small openings being left, through which the flames niay pass into the interior of the kiln. The fire is built under the arch, and on top of the latter the limestone is piled, the lumps varying in size from that of a cocoanut, just above the arch, to that of a goose egg at the top of the kiln. When the FIG. 5T. 150 OUTLINES OF INDUSTRIAL CHEMISTRY kiln is full, the fire is started and the temperature very slowly raised during six or eight hours, to prevent the limestone arch from crum- bling ; then the temperature is kept at a full red heat for two days or more, when the fire is allowed to burn out, and the kiln cools. During the time of cooling, discharging, and recharging, the kiln stands idle, and thus much time is lost. Moreover, a large amount of fuel is necessary to heat the walls of the kiln after each re- charging, so that the method is not an economical one. Excepting the limekilns in the ammonia-soda works, no attempt is made in this country, to save the carbonic acid gas which escapes from the top of the kiln. But in Europe the gas is often collected and used for technical purposes. Freshly burned lime is usually called " caustic " lime or " quick- lime," because of its corrosive action on organic matter. When pure, it is white and amorphous, but iron gives it a yellow or brown color. The crystalline limestones and pure marble yield the best lime. Owing to the loss of water, organic matter, and carbon dioxide during the burning, there is great reduction in the weight of the charge, but only a slight decrease in its volume. As a rule, 100 pounds of good limestone yield about 57-59 pounds of lime, but the shrinkage in bulk is not over 10-15 per cent of the original volume of the limestone. Nor is there much change in the hardness, though lime is much more porous than the limestone, and absorbs consider- able water before slaking. Pure lime is infusible at the temperature of the oxy-hydrogen flame (hence its use in the " calcium light "), but if silica, iron, alumina or other substance is present, the lime combines with it to form a fusible substance (glass or slag). Considered chemically, lime is calcium oxide, and is a powerful base. It combines with acids to form calcium salts ; it has great affinity for water, and when wet the lumps expand and fall to a powder of calcium hydroxide (slaked lime), with the evolution of much heat, especially in the case of " fat lime." When exposed to the air lime absorbs carbon dioxide and moisture, and soon falls to a powder called " air slaked lime," consist- ing of a mixture of calcium carbonate and hydroxide. Lime for mor- tar and many other purposes is always slaked immediately before use. If the limestone contains more than from 8 to 10 per cent of sili- cate of aluminum (clay), and is burned at a moderate temperature, " hydraulic lime " is obtained. This does not slake freely, and if kept in contact with water after slaking it soon hardens again. This hardening is due to a secondary reaction between the water and the LIME, CEMENT, AND PLASTER OF PARIS 151 anhydrous silicates and aluminates of calcium, which have been formed in the burning, and which combine with the water to form hydrated compounds, having considerable hardness. Hydraulic limes are chiefly employed in mortar and cement mixtures. Since much heat is liberated in the slaking of lime, the storage and shipment is attended with some danger. If water comes into contact with the lime in presence of combustible material, fire is very apt to ensue. The uses of lime in the arts are too numerous for extended men- tion, but the following are a few of the most important : in mortar and cement mixing ; in bleaching powder ; in the Leblanc soda pro- cess ; for purifying illuminating gas ; in the preparation and purifi- cation of many chemicals, such as acetic, citric, oxalic, and tartaric acids, potassium chlorate, caustic soda and potash, etc. ; for purify- ing sugar solutions ; in bleaching and dyeing cotton ; in tanning ; in glass making ; in metallurgical operations ; for disinfecting, etc. Mortar is an aqueous pasty mixture of slaked lime, sand, and other materials, which dries without excessive shrinkage and be- comes hard on exposure to the air, owing to absorption of carbon dioxide and formation of carbonate of lime. It will not harden while it remains wet, and this is one of the chief differences be- tween mortar and cement. The hardening of the two substances is due, in part at least, to different causes. If a paste of freshly slaked lime is allowed to dry by exposure to the air, it shrinks considerably, and if in thick masses, numerous cracks are formed. The admixture of three or four volumes of sharp sand prevents this shrinkage by separating the lime paste into very thin layers, which fill the spaces between the grains of sand. The sand also gives the mortar a porous structure, which facilitates the penetration of the carbon dioxide during the hardening period. The interlacing crystals of calcium carbonate enclose the sand grains and join them together, thus increasing the hardness and strength of the mortar. This addition of sand also cheapens the mortar by increas- ing the mass obtained from a given amount of lime. "Fat lime" requires a much larger proportion, which is replaced in part by the impurities in " poor " lime. For a good mortar it is very necessary that the lime be thoroughly slaked. The proper quantity of water should be added all at once, or the product is apt to be granular and lumpy. The mass is cov- ered with a layer of sand, or with boards or canvas, to retain the heat and moisture, and should not be stirred while slaking, but should be allowed to swell and fall to powder without disturbance. 152 OUTLINES OF INDUSTRIAL CHEMISTRY Water is then added, and the paste allowed to stand for several days, or even weeks, well protected from the air, before being stirred up with more water for use in mortar. The first change noticeable in a mortar is the " set," which is a solidification of the mass, due to the loss of its water through evapo- ration or absorption by the bricks, etc. But it is not until after the mass becomes dry that the real hardening begins. This is very slow, since it progresses from without towards the interior of the mass ; and the surface layer of calcium carbonate first formed is but slowly penetrated by carbon dioxide from the air. The interior of thick walls will often show an alkaline reaction after the lapse of a century or two, but after twenty-five years the change is very slight under ordinary conditions. After several hundred years there appears to be a certain amount of combination between the silica of the sand and the calcium carbonate to form a hydrated silicate of calcium. This secondary reaction does not increase the hardness of the mor- tar. Hardening is a true chemical change, and should not be too rapid for the best results. In order to hasten the hardening of mortar and plastering in new houses, builders sometimes build coke or charcoal fires in open grates or baskets. But this is liable to cause uneven drying and excessive shrinkage, resulting in cracks or scaled places. In certain mortars hair or other fibrous material is added to increase the toughness, especially while wet. Since mortar does not harden until dry, it should never be used in damp places, such, as foundations and cellars, nor in very thick walls. Sometimes it is mixed with some cement, increasing its strength and usefulness. When thoroughly hardened, good mortar is about as hard as limestone, and adheres firmly to the bricks or stones of the wall. CEMENT Cement consists of certain anhydrous double silicates of calcium and aluminum, which are capable of combining chemically with water, to form a hard mass. It differs from lime mortar in that it hardens while wet, does not require the presence of carbon dioxide for hardening, and is very insoluble in water. It is very well adapted for use in moist places, or even under water, and since its hardening is simultaneous throughout the whole mass, and is quite rapid in most varieties, it finds extensive use in building operations. There are three general classes of cement : 1. Those formed from certain volcanic tufas, or from artificial mixtures resembling these. Such cements generally need the addi- LIME, CEMENT, AND PLASTER OF PARIS 153 tion of lime before they display hydraulic properties, i.e. form insoluble silicates when treated with water. In this group are the natural volcanic tufas, Pozzuolan, trass, and Santorin earth, together with blast furnace slags and certain coal ashes, which are occasion- ally used. 2. Those which contain a large proportion of free lime, having been made by burning natural argillaceous limestones at a tempera- ture sufficiently high to drive off all the carbon dioxide, but not to fuse the product. These include "hydraulic limes' 7 (p. 150) and Roman cements. 3. Those prepared by burning an intimate mixture of clay and powdered calcium carbonate, at a very high temperature, so that incipient fusion takes place in the mass. These constitute the Port- land cements. 9 Pozzuolanic cements are chiefly derived from volcanic tufas, which are found in Italy, near Naples (Pozzuoli), in the islands of the Grecian archipelago, and in Germany near Andernach on the Rhine. These tufas consist of silicates which are easily decom- posed by acids. They have resulted from the action of volcanic fires, and need no further treatment than fine grinding and mix- ing with lime. Such cements are slow in hardening, but have considerable ultimate strength. Pozzuolan has been used since the time of the Romans, who were well acquainted with its prop- erties. Blast furnace slag is now used to some extent for the production of cement. But in order to develop the hydraulic property, the melted slag must be cooled suddenly ; this is usually done by run- ning it into water. The granulated material thus produced is then very finely ground and mixed with lime. Some slags contain a high percentage of lime-alumina silicate, and hence need less addi- tion of lime. Slag cements have not given entire satisfaction up to the present, although they have been greatly improved within a year or two, by increased care in running the furnace charges. These cements are said to harden more slowly, and to have less resistance to the action of frost than the Portland cements. They shrink considerably, and are liable to crack, but this is remedied somewhat by coarse grinding. Slag cements, low in silica, but hav- ing a high percentage of iron, do not harden well. Hydraulic limes have already been mentioned (p. 150). The free lime which they contain is sometimes slaked with just sufficient water to hydrate the quicklime before the material is sold ; but not enough water should be added to set the cement. 154 OUTLINES OF INDUSTRIAL CHEMISTRY Roman cement is made by burning argillaceous limestone in kilns. It was first made in England by J. Parker, who patented a process for preparing it from the septaria nodules, consisting of clay and chalk found in the bed and along the banks of the Thames River. Later, the beds of clay limestones were used, but as there was much irregularity in the composition of these rocks, the product did not give satisfaction. But by careful selection of the material and proper mixing of different kinds of stone, the quality of cement pro- duced has been improved. These rocks are also found in France, Holland, and Germany, and in the United States. There are sev- eral deposits that are very pure, and vary but little in the different parts of the bed. Roman cement was first made in this country in New York state, from a rock found on the banks of Rondout Creek and near the Hudson River, and is called " Rosendale," from the chief town in the district; it still constitutes a large part of the natural cement made in this country. Another important region is on the Ohio River, near Louisville, the cements made there being known by the latter name. Pennsylvania, Illinois, Wisconsin, and Colorado also supply much natural cement. Nearly all these rocks contain a large percentage of mag- nesia, but this does not appear to injure the cement made from them. The rock is broken into lumps about the size of a goose egg, in order to secure evenness in burning. The burning is done in con- tinuous kilns, as a rule, and the temperature must be very carefully regulated, high enough to drive out nearly all of the carbon dioxide, but not to fuse the rock. Then the rock is carefully ground between buhrstones, and sifted. The finer the grinding, the better the product. In order to secure supposed uniformity in the product,. it is often customary to mix rock from several beds, in the same kiln, but this is of doubtful benefit. The color of Roman cement varies greatly, from pale yellow to red brown, and is due chiefly to the amount of iron and manganese oxides present. But there should not be great variations in the color of the products made from the same rock, as this indicates inequality in burning. Roman cement is generally quick setting, and hence is preferred by many engineers for work under water. It weighs from 50 to 56 pounds per cubic foot. Its strength is inferior to Portland cement. LIME, CEMENT, AND PLASTER OF PARIS The following analyses * are of typical cement rocks : 155 N. Y., ULSTER COUNTY, ROSENDALE. ILLINOIS, UTICA. WISCONSIN, MILWAUKEE. PENNSYLVANIA, COPLAT. CaCO 3 .... 45.91 42.25 45.54 67.14 *1 M>CO 3 . . . 26.14 31.98 32.46 2.90 Y Si0 2 . . . 15.37 21.12 17.56 18.34 FesOi }Q 03 A1 2 3 Na^O 11.38 1.12 1.41 7.49 1 K 2 O 1 0.19 H 2 O }1 07 Undetermined . . 1.20 2.46 ~ 3.94 ^ Analyses of natural cements : KOSENDALE. UTICA. LOUISVILLE, KY. LEHIGH VALLEY. Si0 2 22.75 35.43 21.10 18.28 } j F 2 Q 16.70 9.92 7.51 7.43 It CaO 36.70 16.65 33.67 20.98 44.40 7.00 51.53 2.07 K 2 O . . Na 2 0.80 1.50 C0 2 5.00 11.18 16 20 CaS0 4 .... 6.85 H 2 O . . 1 30 1.16 Undetermined . . 2QO .7O Portland cement is entirely an artificial product, but represents the most important branch of the cement industry. The first patent was taken out in England, in 1824, but the process extended in a few years to France and Germany. In the United States the man- ufacture of this cement was begun in 1878, at Coplay, Penn., but the industry has not yet developed sufficiently to supply more than one quarter of the annual consumption in this country. The materials used are very pure calcium carbonate and fine clay, rich in silica. The English manufacturers prefer chalk and clay mud taken from the mouth (estuary) of the Medway River. In Ger- * W. A. Smith, Mineral Industry, Vol. I, 1892. 156 OUTLINES OF INDUSTRIAL CHEMISTRY many, a marl (calcareous clay) is employed. But in any case the proportion of calcium carbonate to clay must be controlled within tolerably narrow limits. A most thorough mixing of the ingredi- ents is very essential. The calcium carbonate and clay are both finely ground, and often levigated, before they are mixed. There are two methods of mixing in general use : the semi-dry and the wet. In the semi-dry method, the materials are mixed in a wash- mill to a thick " slurry," containing about 40 per cent of water, and which is then ground again in buhrstone mills ; then it is run into shallow pits, where much of the water drains away or evaporates. Sometimes it is dried by the waste heat from the kilns. When dry enough to work properly, the mass is made into balls or bricks (usually by machines) and dried, after which they are ready for burn- ing. In the wet method, the clay and chalk are ground together, and the slurry levigated, so that all coarse particles are eliminated. After settling, the water is drawn off, and the slime dried by waste heat and bricked, as in the semi-dry method. The dry bricks are then burned. Several varieties of kilns are in use for burning Portland cement. Periodic, dome-shaped, or shaft kilns are still much used in this coun- try, but are uneconomical as to fuel and output. Coke is used as fuel, and is charged into the kiln in alter- nate layers with the bricks. The coke, amounting to 40 per cent of the weight of the clinker, is burned out, and the kiln cools and is emptied. Continuous kilns are coming into more general use, however. The great difficulty at first encountered with them was the tendency of the charge to stick to the furnace walls, owing to the high temperature. But this is largely avoided now by proper attention to the kiln while burning. The Dietsch two-storied kiln (etageoferi) (Fig. 58) is much used for Portland ce- ment. The bricks and fuel (which may be soft coal) are charged continuously at the top (A), and descend into the horizon- tal chamber (B), from which the charge is raked into the combus- tion chamber (C) by introducing a tool through the door (D). The burned clinker is withdrawn at the bottom opening (E). Air enters LIME, CEMENT, AND PLASTER OF PARIS 157 at (E), and passing through, the hot clinker, arrives in (C) at a very high temperature, where it supports the combustion of the fuel. The hot gases passing off through (B) and (A) serve to heat the charge before it arrives in (C). These kilns now are often worked with forced draught, and produce about 7 tons of clinker per ton of coal. Hoffmann's ring furnace (Fig. 59) is also much used in cement burning. This consists of an elliptical gallery built around a cen- tral chimney (A). The gallery is divided into 15 or 20 compart- ments (B, B), each having a door (C) opening outside, a flue (D) leading to the chimney (A), and a wide opening (E) into the next compartment. Each flue has a damper, by which connection with the chimney (A) may be opened or closed. The openings (E) between the compartments may be closed with a sheet-iron or heavy paper diaphragm, as will be explained be- low. If the door of the compartment on one side of the dia- phragm be opened, and the damper of the flue (D) leading from the compart- ment on the other side of the diaphragm is also opened, while all the other doors and flues are closed, the draught of the chimney (A) will cause air to enter the open door and pass around the entire gallery, through each compartment in succession, and finally out through the open flue (D) to the chimney. In the roof over the gallery are charg- ing holes (G), several being in each compartment, through which fuel is introduced. The furnace is run as follows: Assume that there are 14 compartments, as shown. Twelve compartments con- tain cement bricks, and their doors and chimney flues are closed. Suppose that No. 1 is being emptied, while No. 14 is being filled. The paper diaphragm closes the opening between No. 13 and No. 14, and the flue (D) of No. 13 is open to the chimney. Compart- ment No. 7 is at the height of combustion, while Nos. G, 5, 4, 3, 2 contain bricks which have been burned. In Nos. 8, 9, 10, 11, 12 are bricks to be burned. Cold air is drawn in through the open door of No. 1, and passing in order through Nos. 2, 3, 4, 5, 6 becomes heated by contact with the hot bricks in these compartments until, after passing through No. 6, which is still red hot, it arrives in No. FIG. 59. 158 OUTLINES OF INDUSTRIAL CHEMISTRY 7 at a very high temperature. In No. 7 the fuel is burning at a white heat, and the hot gases pass on through Nos. 8, 9, 10, 11, 12, 13, from which they escape to the chimney. By this passage of the hot gases through the compartments, the unburned bricks are heated, those in No. 8 being nearly red hot ; but as no fuel has been introduced into these chambers, combustion and white heat are con- fined to No. 7. When No. 14 is filled with green bricks, its doors are closed, and also the chimney damper of No. 13, while that of No. 14 is opened, and the diaphragm transferred to the opening between No. 14 and No. 1. Fuel is now introduced into No. 8, which becomes the combustion chamber, and the door of No. 2 is opened. The burned bricks in No. 2, having been cooled by the passage of cold air, are taken out, while No. 1 is being refilled. Thus the cycle of operations goes on, each compartment in turn being charged with fuel and made the combustion chamber. The temperature in that compartment which has just been filled is only high enough to dry the green bricks well. A paper diaphragm is often used between this chamber and the next one, which is to be filled. When the temperature becomes sufficiently high to burn away this paper, the next compartment is ready, and is thrown into the circuit. This furnace is very economical of fuel, one ton of soft coal burning 6|- tons of clinker, but it requires much labor. The bricks must be accurately piled in order that open channels may be left beneath the charging holes for the fuel, which is thus made to burn in a column extending from the floor to the top of the furnace. The fuel must not contain too much ash. Usually one compartment is emptied each day, and consequently the fire is moved forward each day. Revolving furnaces (p. 17) are also used to some extent for cement burning. A furnace used in this country is about 75 feet long, slightly inclined, and lined with fire-brick. The lower end is 6 feet in diameter and the upper end 5 feet. Crude petroleum is used as fuel, and the furnace is continuous acting. The wet slurry runs in at the upper end and, by drying on the rotating surface, forms little balls or gravel-like lumps which are thoroughly burned in the passage through the furnace, requiring two hours or more. The annual increase in output from rotary furnaces indicates that the method is a successful one. Producer gas will probably soon take the place of crude petroleum, should the price of the latter advance much. Much depends on the proper temperature of the burning, during LIME, CEMENT, AND PLASTER OF PARIS 159 which there is considerable shrinkage ; well burned clinker is a semi-vitrified, brown or grayish green mass. If overburned, it may fuse and take on a blue green or black color j such cement will not combine with water. The clinker is then ground very fine, so that nearly the whole of it will pass through a sieve with 2500 meshes to the square inch. Buhrstone or ball-mills are generally used for this purpose. The Griffin mill, which consists of a heavy steel roll revolving about a vertical shaft, and pressing, by centrifugal force, against a steel ring, is proving very effective. Since only the finest dust is of value in cement, great care is necessary to prevent the coarse material from passing through the mill. After grinding it is gen- erally stored, that any free lime it contains may become air-slaked, before the cement goes to market. The composition of Portland cements varies somewhat, but the following are the extremes : Silica 19.80 .... 26.45 Alumina 4.16 .... 9.45 Ferric oxide 2.19 .... 4.47 Lime 58.22 .... 65.59 Magnesia traces .... 2.89 Alkalies ........ 0.19 .... 2.83 Sulphuric acid 0.19 .... 2.19 Loss on ignition 0.26 .... 2.67 Undetermined residue ... 0.12 .... 1.28 The cause of hardening of cements has been investigated by many chemists and has caused much discussion. Le Chatelier's * investigations show that during the burning a tricalcium silicate (Ca 3 Si0 5 ) is formed by the action of the clay on the lime. At the same time a certain amount of calcium aluminate and ferrite are also formed, besides mono- and di-calcium silicates. When treated with water the tricalcium silicate reacts to form a hydrated mono- calcium silicate and calcium hydroxide : 1) 2 C%Si0 5 + 9 H 2 = (CaSi0 3 ) 2 5 H 2 + 4 Ca (OH)* Then a reaction between the calcium hydroxide, water, and calcium aluminate may occur, forming a hydrated basic calcium aluminate: 2) Ca 3 Al A + Ca(OH) 2 + 11 H 2 = Ca 4 Al 2 7 12 H 2 0. The formation of the hydrated basic aluminate (CaO) 4 , A1 2 3 12 H 2 0, probably exerts some influence on the rapidity of the " setting " of * Annales des Mines, 1887, 388. J. Soc. Chem. Ind., 1888, 567, 847. Thonin- dustrie Zeitung, 1892 (16) 1032. Chemiker Zeitung, 1892, Ref. 342. 160 OUTLINES OF INDUSTRIAL CHEMISTRY the cement, but the hardening is undoubtedly due to the first re- action. The " set " of cement, in contrast with that of mortar, is not due to a drying out of water, but is the beginning of the true hardening process. The rapidity of this " setting " is influenced by the presence of other salts ; alkalies hasten it, while it is retarded by calcium sulphate, magnesium sulphate and chloride, and sodium chloride. It is also retarded proportionally as the amount of sand used is increased. The amount of water used in mixing is about one-third the weight of the cement, and its temperature has much to do with the rate of " setting," warm water hastening it. Portland cement is usually slower in setting than Roman, but when the hardening has begun it progresses more rapidly with the former. There is very little increase of hardness after six months. Portland cement is more durable than Roman under most conditions, and is generally stronger. It forms a denser and heavier powder of a greenish gray color, but when hardened has a drab shade resem- bling the color of the stone quarried at Portland, England, and used much for building in that country ; hence the name. As has been said, variations in color of the same brand of cement may show changes in quality ; if underburned, it is generally yellowish. The weight per cubic foot varies from about 70 to 90 pounds ; the finer the grinding, the less the weight. But as a rule heavy cements are preferred by builders, as they are supposed to be more thoroughly burned ; they are, however, slow in setting. The testing of cement is generally the work of the engineer, rather than the chemist. Chemical analysis is of but little use in determining its properties, and the usual tests applied are phy- sical. They are for : (a) Fineness. (6) Expansion ("Blowing"). (c) Shrinkage. (cf) Rate of hardening. (e) Resistance, to tension to compression. A committee of the American Society of Civil Engineers has recommended certain standard requirements for cements.* In Ger- many, an official standard and method of testing have been adopted. In testing the fineness, three sieves should be used, Nos. 50, 74, and 100, the proportion of each sample rejected by each sieve to * Transactions American Society of Civil Engineers, November, 1885. LIME, CEMENT, AND PLASTER OF PARIS 161 be determined by weighing. The residue remaining in the coarse sieves is of little more value than the same quantity of sand. Expansion, or " blowing," is shown by the swelling and cracking of a pat of cement, three inches in diameter, one-half inch thick in the middle, and very thin at the edges. After setting, a pat of this kind is put into water and left several weeks, being examined every day. If fine cracks appear in the edges, or disintegration occurs, the cement is of poor quality. Expansion may be caused by the presence of unslaked lime, magnesia, or gypsum, or the cement may be underburned. Expansion and shrinkage tests are often made by filling glass bottles or lamp chimneys with the freshly mixed cement. After setting, any expansion will crack the glass. Colored water may be poured on top of the cement. If it runs down be- tween the cement and the glass, shrinkage has probably taken place. The rate of hardening, or the time of setting, is very important in determining the suitability of a cement for a given purpose. Quick-setting cements are usually desirable for work under water. The time is determined by the " normal needle/' 7 * Two of these are used. One is a wire about one-twelfth of an inch in diameter, and is loaded with a weight of one quarter of a pound. The other is one twenty-fourth of an inch in diameter, and carries a weight of one pound. After mixing the cement with water, the time is noted until no impression is made upon it by the point of the first wire. This is the beginning of the " setting." When the second wire will no longer penetrate, the " set " is ended. Cement which will set in less than two hours is called "quick setting"; those taking a longer time are " slow setting." The beginning of the set is sometimes noticed within five or ten minutes after mixing, and usually within half an hour. It is important that the work be not disturbed after the " set " is once established, otherwise, tight and strong joints cannot be made. The resistance tests are the most important. In actual use, cements are generally subjected to compression strains; but since compression tests are difficult to make, it is often the practice to make only the tension tests. Both tests should be made if possi- ble from samples taken from the barrel, and from the sifted cement which passes the No. 100 sieve, as well as with these samples when mixed with various weights of standard sand. This sand is made by pulverizing quartz ; it is sifted and the portion used which passes a No. 20 sieve, and is retained by a No. 30. * Transactions American Society of Civil Engineers, 1893 ; The Testing of Port- land Cement, by Max Gary. 162 OUTLINES OF INDUSTRIAL CHEMISTRY For tension tests, the cement is mixed with water and filled into a metal mould, forming a " briquette," shaped like an hour-glass, the narrow portion having a section exactly one inch square. The briquettes must be made very carefully, or the results will not be uniform. The cement is quickly mixed with water at 60 F., filled into the mould, pressed down well and smoothed off evenly. This is done on a slate or glass plate, to prevent absorption of moisture. As soon as set, the briquette is removed and allowed to stand covered with a wet cloth for 24 hours. It is then placed in water, where it remains until the test is made, when it is fixed in the jaws of a machine, which applies a gradually increasing tension. The number of pounds necessary to fracture the briquette is read on a graduated scale beam. The average of five or ten tests is taken as the breaking strength. The briquettes are usually tested at one day, one week, and four weeks after making. Sometimes they are kept for still longer periods. When made from cement without sand, they are called " neat." The proportions of sand, water, and cement recommended are: For Portland briquettes (neat), 25 per cent of water. For natural cement (Rosendale) (neat), 30 per cent water. For 1 part cement, and 1 part sand ; the water used is about 15 per cent of the total weight of the sand and cement. Another proportion is : cement, 1 part ; sand, 3 parts ; and water to about 12 per cent of the total weight of sand and cement. Compression tests are made on small cubes of the cement in question. They should show at least ten times their tension resistance. But, as has already been said, this test is difficult to make, and is very frequently omitted. Chemical analysis of cement is seldom employed, and chiefly to detect the presence of adulterants. Formerly, the most common adulterant was ground blast furnace slag; but clay, ashes, and hydraulic lime have been employed, and are not always easy to detect. The specific gravity of good Portland cement should not be less than 3.1, but adulterants may reduce it. The presence of con- siderable quantities of manganese would also indicate adulteration. Magnesia in Portland cement is claimed to cause expansion, and 3 per cent is the highest allowable. In Roman cement, however, a large amount is sometimes present without apparent injury. Alkalies in considerable quantities are also questionable ingredi- ents ; not more than 2.5 per cent should be present in a good Portland cement. LIME, CEMENT, AND PLASTER OF PARIS 163 PLASTER OF PARIS Plaster of Paris is made by heating the mineral gypsum (CaS0 4 2 H 2 0) until about three-fourths of its water of crystal- lization has been driven off. The process is called burning, and is usually carried on in kilns, muffle furnaces, or retorts. Direct contact with the fuel is not permitted, lest the action of the car- bonaceous matter should cause a reduction of some of the calcium sulphate to sulphide. Neither should the flame come in contact with the gypsum, but only the hot gases. The burning is a very delicate operation, and requires much care. Gypsum contains about 21 per cent of water of crystallization, of which good plaster should retain 4 or 5 per cent. The loss of water begins at about 80 C., but the most favorable temperature for burning is about 125 C. If heated to 200 C., all the crystal water is expelled, and the product will combine with water but very slowly, the property of rapid setting having been destroyed. Thus it will be seen that the limits of heating are very narrow. The gypsum is broken in rather small lumps to secure evenness in burning; for a fine product, it is sometimes powdered and heated on a plate, while constantly stirred. After burning, the lumps are friable and are easily ground. Sometimes wooden rolls, set edge-runner fashion, are used to grind the burned material. When mixed with water, plaster of Paris forms a paste which soon hardens or " sets," owing to a recombination of water with the burned plaster, to form hydrated calcium sulphate. The theory of this setting has been explained by Le Chatelier.* The composition of the plaster is essentially (CaS0 4 ) 2 H^O* a salt which is soluble, and part of which dissolves in the water used in mixing. But as soon as it dissolves, a combination between it and some of the water takes place, forming CaS0 4 2 H 2 ; this, being much less soluble than the monohydrated salt, at once begins to crystallize from the solution, forming a network of crystals. Then more of the plaster dissolves, becomes fully hydrated, and crystallizes out, increasing the solidity of the "set" by the interlacing of new crystals with those already formed. Thus the cycle of reactions goes on until the plaster is fully hydrated. The theoretical quantity of water necessary to set plaster is about 18 per cent of its weight ; but in fact, from 30 to 35 per cent is generally used. Excess of water renders the mass more plastic *Comptes Rendus, Vol. 96, 717, 1668. 164 OUTLINES OF INDUSTRIAL CHEMISTRY and retards the setting. Very great excess may cause disintegration of the plaster, if left in contact with it for some time after setting, owing to the solution of some of the crystallized calcium sulphate. Plaster expands slightly while setting, and for this reason is valuable for making casts and reproductions. It is largely used for interior decorative work and also as a cement for joining glass and metal ware. The surface of plaster after setting is rather soft, and for many purposes it is desirable to increase the hardness. This may be done by mixing alum, borax, or tartaric acid with it, or by adding some alcohol to the water with which the plaster is mixed. However, these substances retard the setting. By painting or dip- ping plaster casts in melted wax, paraffine, or stearin, or in solu- tions of these in petroleum ether, the pores of the plaster mass are filled and the surface is made smooth, so that dirt will not adhere and the articles may be washed. When treated with a solution of barium hydroxide, the surface of the plaster is coated with barium sulphate and rendered insoluble. If plaster is mixed with a solu- tion of glue or size, the material called " stucco " is obtained. REFERENCES Die hydraulische Morter. Michaelis, 1869. A Practical Treatise on Limes, Hydraulic Cement, and Mortars. Q. A. Gilmore, 1874. Transactions of the American Society of Civil Engineers : 1877 (Dec.). W. F. Maclay. 1885 (Nov.)- Report of Committee on Cement Tests. 1885 (Apr.). E. C. Clarke. 1893. Max Gary. Chemisohe Technologic der Mortelmaterialien. G. Feichtinger, 1885. Journal of the Society of Chemical Industry : 1886, 188, 199. W. C. Unwin. 1891, 927. Recherches expe"rimentales sur la Constitution des Mortiers hydrauliques. Le Chatelier, Paris, 1887. Annales des Mines : XI (1887), 388-465. H. Le Chatelier. Fabrication et Controlle des Chaux hydrauliques et des Ciments. H. Bonnami, Paris, 1888. (Gauthier-Villars et Fils.) Zsment und Kalk. Rudolf Tormin, Weimar, 1892. (B. F. Voigt.) A Manual of Lirne and Cement. A. H. Heath, London, 1893. (E. and F. N. Spon.) Journal of American Chemical Society : 1894, 161. Thomas B. Stillman. For a more complete bibliography, see Thorpe's Dictionary of Applied Chemis- try, Vol. I, pp. 488, 489. GLASS GLASS Glass is an amorphous, transparent or translucent mixture of silicates, one of which is always that of an alkali. The usual silicates employed are those of potassium, sodium, calcium, and lead ; the sili- cates of heavy metals occur in the colored glasses. Glass is not readily decomposed by water or acids (excepting HF). Its behavior towards solvents generally, tends to show that it is a mixture of silicates, rather than a definite compound. Most simple silicates and mixtures of them are difficult to fuse, and when cooled after fusion, have a crystalline structure ; but the alkali-lime and alkali-lead silicates fuse easily, and are generally amorphous after fusion. Furthermore, they have no sharp melting point, and consequently, when allowed to cool after fusion, glass first becomes pasty and then rigid. This property of plasticity while hot permits its use for many articles which could not other- wise be made from it; glass-blowing would be impossible, and only cut or cast ware could be made. G-lass is amorphous when cooled rapidly from a state of fusion, but if cooled very slowly and in a large mass, there is sometimes a tendency of the component silicates to crystallize, causing the glass to lose its transparent character, and become white or porcelain-like in appearance. The same effect is produced if it is kept near its melting temperature for a long time. This phenomenon, known as devitrification, is due to a physical change only, i.e. crystallization. The chemical composition of glass varies considerably, even in the same kinds, but the best varieties seem to approach a definite chemical formula; thus, soda-lime glass approaches Na 2 0, CaO, 6 Si0 2 , and lead glass, K 2 0, PbO, 6 Si0 2 : but it may vary so much that the formula becomes 5 K 2 O, 7 PbO, 36 Si0 2 . Of course potash may be substituted for soda, or vice versa, in either kind, while the relative proportion of the several ingredients may vary between quite wide limits. But as a rule, the higher the percentage of silica, the harder, more difficultly fusible, and more brittle the glass. Increase of alkali makes it softer, more fusible, and less capable of resisting atmospheric changes and chemical reagents. Increasing the percentage of lime decreases the fusibility and renders it harder, but not so brittle as in the case of high silica content. If the alkali used be mixed soda and potash, a more fusible glass is obtained than from either alone. Part of the lime or lead may be replaced 166 OUTLINES OF INDUSTRIAL CHEMISTRY by oxides of other metals, e.g. of iron, manganese, cobalt, copper, barium, zinc, tin, arsenic, etc., and this is generally the case to some extent, in common glass, and to a greater degree in colored glass. Aluminum oxide may replace some of the silica ; the former is often present in considerable amounts, and renders the product tough. Certain fluorides, e.g. calcium fluoride, also enter into the composition of some varieties. Besides the above-named oxides, certain borates and phosphates are occasionally used, to replace a part of the silica in glass manufactured for various optical and chemical purposes; these usually contain zinc or barium also. The well-known " optical glass," made in Germany, contains both zinc and boron. Technically, two kinds of glass are recognized: lime glass and lead glass. The alkali used may be soda, or potash, or both. Lime glass is most common and generally useful. It is cheaper, harder, more resistive, and less fusible than lead glass ; the latter has greater lustre and brilliancy, is heavy and expensive and is used chiefly for cut ware and for optical purposes. The essential materials for glass making are silica, an alkali, and lime or lead. Silica was formerly derived from quartz or flint ; but this is now only used for a particularly fine quality. It is heated to a red heat, and dropped into water, and the friable mass so formed is powdered in a mill. Quartz sand and soft quartzites are the usual sources of silica, and numerous deposits are worked in different countries. Sand of great purity is found in Germany, near Aix-la-Chapelle, and at Niviltein ; in France, at Fontaine bleau ; in Belgium ; in England ; and in Australia. In the United States, extensive beds are worked in Berkshire Co., Mass., and in Pennsylvania, along the Juniata Eiver. The Berkshire deposit is a soft white sandstone, which, when crushed, yields sand which is from 99.6 to 99.8 pure Si0 2 . The Juniata stone is slightly yellow in color, a/id the sand is from 98.8 to 99.7 pure Si0 2 . The most troublesome impurity in sand is iron; for white glass, there should never be more than 0.5 per cent Fe 2 3 . Alkali is derived from the carbonate or sulphate of soda or potash, and these also must be free from iron. Carbonate fuses more readily with the sand than does sulphate, but since the latter is cheaper, it is much used. It is essential to mix carbon in some form with the sulphate, to assist in reduction. For better grades of glass, charcoal dust is used, but for common glass, powdered coal is the reducing agent. The exact nature of the reaction with sulphate appears somewhat uncertain : GLASS 2 Na 2 S0 4 + 6 Si0 2 + C = 2 (Na 2 0, 3 Si0 2 ) + 2 S0 2 + C0 2 .* 2 Na 2 S0 4 + 2 Si0 2 + C = 2 Na 2 Si0 3 + 2 S0 2 + C0 2 .t For lead glass, sulphates are not generally used, since some sodium sulphide is formed by the reduction of the sulphate, and this reacts with the lead, forming lead sulphide, which darkens the glass. Attempts to use salt directly in the glass furnace, as a source of alkali, have not as yet proved satisfactory. It is quite volatile at the temperature of the furnace, and the presence of air or steam is necessary for its decomposition by the silica. For potash, crude pearlash is much used ; but in the better grades of glass the refined pearlash is employed. Sulphate of potassium is difficult to reduce, and is not much used. Lime is now derived from chalk or limestone. For very fine glass, pure marble dust, as free as possible from iron, is employed. For common grades, less pure limestone is used. It may contain a high percentage of silica and considerable alumina, but magnesia or iron in large amounts is objectionable. Magnesia makes the glass hard and infusible. In cheap glass, limestone is sometimes replaced in part by felspar, porphyry, or granite. Carbonates of both alkali and lime are advantageous in the glass mixture, since, as the mass fuses, the escaping bubbles of carbon dioxide serve to stir up and mix the ingredients more thoroughly. Lead is added as litharge (PbO), or red lead (Pb 3 4 ). The latter is preferred, since the oxygen liberated from it is thought to assist in decolorizing the glass by oxidizing the iron; it also prevents reduction of metallic lead. It is essential that the litharge and red lead be free from copper. Besides the above requisites, it is customary to employ other ingredients in every glass mixture, to assist in the decolorization or fusion. The commonest decolorizing material added, is pyrolusite (binoxide of manganese, Mn0 2 ). Iron, when in the ferrous condi- tion, imparts a deep green color to glass; but when in the ferric state, it is much less troublesome, since it only gives a pale yellow color. By .the oxidizing action of the pyrolusite, ferrous iron is con- verted to the ferric condition ; moreover, the silicate of manganese has a violet or pink color, and so helps to neutralize the green. Only a very small percentage of pyrolusite should be thus used. The remedy is not a permanent one, however, and if the glass is exposed to the sunlight for a long time, it develops a violet shade, as may often be observed in the window panes of old houses. * Lehrbuch der technischen Chemie, H. Ost, 202. t Chemical Technology, Wagner, 608. 168 OUTLINES OF INDUSTRIAL CHEMISTRY Arsenious acid (As 2 3 ), or nitre (KN0 8 ), is often added to the materials for white glass. The former is reduced to metallic arsenic, which volatilizes. It affords a very clear and lustrous glass. Zinc oxide is often used to decompose any sodium sulphide, which would give a yellow tinge to the product. In common bottle glass and other cheap grades, where color is no objection, a large amount of blast furnace slag is often used. This generally needs the addition of soda, to render it more fusible and plastic. The formulae for glass mixtures vary much in the different fac- tories, not only because of variations in the composition of the glass produced, but also because the materials are of different degrees of purity. In most cases these are empirical recipes, not based on analysis of the raw materials. The fuel for glass making is an important item. A quick burn- ing material, yielding a long flame, without smoke or soot, is desirable. For very fine grades, wood is still employed in some places, but good coal is now the most common. In this country the discovery of natural gas had a great influence on the glass industry, and within a few years most of the larger plants were moved into the gas territory, Pittsburg becoming the centre of the manufacture. With the decline of the natural gas supply, producer gas (see p. 30) or oil has been substituted as fuel. Gas is an ideal fuel for this purpose, since it is clean, easily managed, and gives a regular heat. It is generally employed in regenerative furnaces (Fig. 19, p. 32). Crude petroleum, or the residuum from kerosene distillation, is now much used and is a good fuel. Whatever the mode of heating, only the flame and hot gases should come in contact with the pots or their contents. There are several forms of glass-furnaces. The common pot furnace has the pots placed in a circle around a central opening in its bed, through which the flame and hot gases come up from the grate, which is below the hearth. The furnace is roofed with a rather flat arch, which deflects the flame down upon and around the pots. When open pots are used, it is essential that no soot or smoke enter the furnace, and much care is necessary in firing. In some forms, the fuel is introduced by mechanical means from beneath the grate, so that the fire burns on top of the pile of coal. This prevents the entrance of cold air into the furnace, and also consumes all smoke. The Boetius furnace (Fig. 60) is much used abroad, and is best adapted for closed pots. Coal or coke is charged at (A), and air GLASS 169 enters through (B, B). The flame passes through (C) into the upper compartment (D), containing the pots. The prod- ucts of combustion escape through (E, E). Siemens gas furnace (Fig. 19, p. 32) is much used be- cause of its economy of fuel, both as a pot furnace and as a tank-furnace. The last named is more economical where a large quantity of one kind of glass is to be made. It replaces the expensive and fragile pots by a single large deep hearth or tank, at one end of which the raw materials are continually introduced, while the glass is with- drawn at the other. Figure 61 shows a plan and elevation of a tank- furnace, in which the batch is introduced at (A). The gas-flame issues from (C, C) and plays over the surface of the charge. The FIG. 60. r ff f? fr FIG. 61. batch (B) soon fuses and the liquid mass flows towards the opposite end of the tank. At (F) are elliptical "floaters" of fire-clay, one end of which rests in recesses in the wall, while the free ends meet in the middle of the furnace. The current of melted glass flowing towards (D), constantly presses these floaters together and prevents their separation. The liquid mass thus passes under the floaters and collects in the compartment (D), from which it is withdrawn through 170 OUTLINES OF INDUSTRIAL CHEMISTRY the openings (E, E). At (B) the temperature is very high, and as the glass flows slowly towards (F), the refining takes place. In (D) the temperature is lower and the glass has cooled sufficiently for working. The impurities, rising to the surface during the melting and refining, are retained by the floaters so that the glass in (D) has a clean surface and is free from bubbles. Small rings of fire-clay may be kept floating on the glass near the working doors (E, E) ; by dipping the glass from the centre of these rings, it is obtained free from any impurities which may be on the surface of the melt in (D). A typical furnace of this kind may be about 75 feet long by 16 feet wide and 5 feet deep, to the level of the doors (E, E). Glass-furnaces must be made from very refractory materials. The dome and arches are usually silica, or Dinas bricks, or ganister, but the bed is generally fire-clay, as this is less attacked by the con- tents of a pot when one breaks. The life of a furnace is very uncertain, but may be several years. If allowed to cool, it is generally necessary to reline it before starting again. Pots for glass making are very carefully constructed, only the best material being used. The breaking of a pot in the furnace is a serious matter, often resulting in the loss of the glass and possible extinguishing of the fire; and, in any case, there is more or less loss of time. Glass-pots are of two kinds, open and closed. Open pots (Fig. 62) are circular vessels, about as wide as they are deep, i.e. from 3 to 5 feet, and usually slightly broader at the top than on the bottom. They are preferred for a quick melt, and are generally used for glass which contains no lead. Closed pots (Fig. 63) are usually longer in one direction, and are about 5 feet by 3J feet, by 4 feet high. The neck of the open- ing is built into the wall of the furnace in such a manner that neither flame nor fire gases can come into contact with, and in- Fm ^ jure the glass, and consequently cheaper fuel may be used ; but these pots heat more slowly than do open ones. They are always used for lead glass. FIG. 62. GLASS 171 * Clay rings are sometimes placed in the pots, so that the glass may be withdrawn without contamination from the floating impuri- ties. Sometimes a partition is constructed across the pot (Fig. 64), the raw materials being intro- duced and melted on one side, and the refined glass, free from impurities, having passed under the partition, is worked out on the other side. The material of the pots is fire-clay ; but the necessary degree of plasticity, with the required infusibility, are possessed but by few clays. To avoid excessive shrinkage when the new pot is heated, a large proportion of burned clay from old pots, entirely free from any adhering glass and ground to a coarse powder, is mixed with the new clay. The mass is then moistened and well kneaded by treading, and is then allowed to stand and " age " for a long time, to increase the plasticity. The pots are built up by hand, the bottom being formed first, and the sides constructed on it. The clay is laid on in small lumps, and each lump is carefully pressed into place by the workman before another is added. From three to five inches is usually added to the height of the pot each day. When finished, it is allowed to stand in a room at constant temperature and protected from draughts of air, for several months, to dry thoroughly. In order to prevent too rapid drying, which might cause cracking, it is generally covered with canvas or paper for the first few weeks. Before placing it in the glass-furnace, a new pot is heated very slowly in a special furnace, until it is brought up to the temperature of the former, into which it is then transferred, while still hot, through an opening in the wall. The wall must be taken down, the broken pot removed, and the new one introduced, without allowing the furnace to cool ; hence the operation is difficult, and requires much skill on the part of the workmen. Once introduced, a pot is kept in constant use, and never allowed to cool; for, if it should, it would crack when heated again. Its life is very uncertain, but a good one will sometimes last for months. The first charge in a new pot is broken glass (cullet), which forms a glaze over the surface, and protects it from the solvent action of the melted raw materials. The general process of glass making is as follows : The finely ground raw materials are very thoroughly mixed, sometimes by regrinding the mixture or " batch." The batch is shovelled into the pot, together with a certain amount of broken glass called " cullet " ; this melts at a comparatively low temperature, and thus assists in liquefying the rest of the charge. More of the batch is added, until 172 OUTLINES OF INDUSTRIAL CHEMISTRY the pot is filled to the desired height with the fused mass; then volatile substances, such as arsenious acid, used in decolorizing the glass, are added. During the melting, much gas (C0 2 , S0 2 , and 0) escapes, and the bubbles rise through the melt, stirring it and causing frothing. A considerable amount of the alkali and other constituents volatilize. The reactions involved are variously written by different authorities : (a) 1) Na 2 C0 3 + CaCO 3 + 2 Si0 2 = Na,Ca (Si0 3 ) 2 + C0 2 * 2) 2 Na 2 S0 4 + 2 Si0 2 + C = 2 Na 2 Si0 3 + C0 2 + 2 SO C0 2 * 3) Na 2 Si0 3 + CaC0 3 + Si0 2 - Na 2 Ca (Si0 3 ) 2 (b) 2 Na*S0 4 + 6 Si0 2 + 0=2 (Na 2 0, 3 SiO a ) + 2 S0 2 -f C0 2 .t When the melt has come to a state of quiet fusion, the temper- ature is generally raised somewhat, and the liquid glass allowed to stand for a time. This is called " refining 1 ," and its object is to form a homogeneous mass, free from bubbles and bits of uncombined silica or other matter. The scum which collects is skimmed off ; it is called " glass gall," and consists of undecomposed sulphates and chlorides of lime and alkali, alumina compounds from the pot, and various other impurities. If too little carbon is used in the batch, the melt is covered with a layer of fused sodium sulphate ; this is known to the workmen as " salt water." Samples of the glass are examined during the refining, and these determine the exact time of heating. After refining, the glass is too liquid to blow, or to work to advantage, and is cooled until it becomes pasty. The quantities of materials used in the batch, for some typical glasses, are shown in the following table : SiO 2 Na 2 C0 3 Na 2 S0 4 CaCO 3 CaO Mn0 2 Pb 3 4 K 2 C0 3 Coke Slag French Plate 100 34 14.5 0.25 (Soda-lime) Bohemian 100 18 40 -4-" (Potash-lime) Window 100 5 37.5 35.8 0.4 4 (Soda-lime) Lead flint 100 60 20 Bottle glass 100 25. 34 3 5 (Green glass) * Wagner, Chemical Technology, 608. t Ost, Lehrbuch d. technischen Chemie, 202. GLASS 178 Glass is known under various names in commerce, according to the method of its manufacture or the uses to which it is put; for example, plate, crown, and window glass. Plate glass is cast on a large iron plate or " casting table," made up of thick, narrow segments of cast iron, bolted together and planed on top. These tables were formerly cast in one piece, and, being large and thick, were very expensive. But when put to use, they soon became warped and dished, owing to unequal expansion of the top and bottom ; this caused much loss of time and glass in the subsequent grinding of the plate. The built-up plate is much cheaper and retains its even surface much longer. The melted glass is poured on the table and spreads out in an even layer. But to give the plate a uniform thickness and to smooth down any inequalities of the surface, a heavy iron roller, travelling on adjustable guides at the edge of the table, is passed over it. The height of these guides determines the thickness of the plate. Both the casting table and the roller are heated before use, so that the glass may not be cooled too rapidly. As soon as the plate is rolled, it is transferred to the floor of the annealing furnace, which is directly in front of the casting table, and which has been heated to the temperature of the glass. The annealing oven is then closed tightly and the fire drawn, leaving the plate to cool very slowly for a number of days. All glass must be annealed. This process probably allows the molecules to arrange themselves so that there is no considerable internal stress when the mass is cold. Unannealed glass, which has been suddenly cooled, is always under high internal strain, which makes it exceedingly brittle, and may even cause it to fly to pieces spontaneously, or when slightly scratched. When removed from the annealing furnace, the plate is uneven and rough, and may be somewhat devitrified on the surface. It is fastened on a horizontal table, and heavy cast-iron rubbers are made to slide over its surface with a rotary motion, while coarse sand and water are sprinkled on it. When the glass is smoothed and of a uniform thickness, it is polished by rubbing with buffers, covered with leather or felt, and used with fine emery dust or putty powder. About one-half of the thickness of the plate is cut away during the grinding and polishing. Plate glass is usually a soda-lime glass. The batch is melted and refined as has been described, great care being taken to remove all the " gall," which is skimmed off immediately before the casting. An especially strong pot is used, which will stand the strain of lift- ing from the furnace while full of melted glass. The furnace is 174 OUTLINES OF INDUSTRIAL CHEMISTRY constructed with brick-lined, cast-iron doors, which open to permit the removal of the pot. The melting and annealing furnaces are often joined, so that the latter may be heated with waste heat. Sometimes several plates are annealed at one time. The chief uses of plate glass are for windows and mirrors. A Considerable quantity of " rough plate," unground, as it comes from the annealing furnace, is used for skylights and for flooring. Window glass is always blown. It is usually a soda-lime glass, and the batch is melted and refined in the usual manner, either in pots or in tanks. After the refining, the glass is allowed to become pasty, and then the blower begins his work. His chief tool is the " pipe," a straight piece of iron tubing, four or five feet long, usually provided with a mouthpiece. He dips the pipe into the soft glass, which is called " metal," and gathers a lump on the end. Then, by blowing through the pipe, while whirling it between the palms of his hands, he forms a hollow globe of glass. This is re-heated in a special furnace (" glory-hole ") until soft, rolled on a flat surface, and then swung in a vertical circle, with occasional blowing through the pipe, until the globe has elongated into a hollow cylinder, closed at one end and opening into the pipe at the other. In order to have plenty of room for the vertical swinging, the workman stands on a plank or bridge placed across a rather deep pit. The closed end of the cylinder is re-heated until soft, and then blown out ; the small opening thus made is enlarged by means of the " widening tongs." The pipe is detached by touching its point of attachment with a wet stick, and the edges of the still soft glass are trimmed with shears. A hollow cylinder, open at both ends, is thus formed, and is cut lengthwise with a diamond. It is then put into the flat- tening furnace, in such a position that the cut is on the upper side. The heat being sufficient to soften the glass, the cylinder slowly opens, and spreads out on the floor of the furnace in a flat sheet. It is then transferred to the annealing furnace for blown ware. This consists of a long oven, heated at one end and cool at the other. A system of endless iron bands carries the glass slowly from the hot to the cool end of the oven. Sometimes the glass to be annealed is placed on a large horizontal table, usually built of slabs of stone, and carefully balanced, so as to revolve easily and slowly, by means of a gear, while a segment passes through a narrow opening in the side of the flattening furnace, where it is exposed to the high tem- perature. The glass is thus slowly carried out of the furnace into a cooler compartment, from which it is removed when nearly cold. This table is chiefly used for window glass. GLASS 175 The glass sheets are now cut to marketable size, without any pol- ishing. Since the surface of blown glass is fused and not polished, it is brilliant and hard. Consequently, it is less easily scratched or etched, and is more durable than plate glass when exposed to the weather. Glass-blowing is an exceedingly fatiguing labor, and only men of strong constitution and good lung power can do it. The mass of glass which a good workman will handle at one time averages about 18 pounds, and from it he will form a cylinder over a yard long and a foot in diameter. Crown glass is a form of blown glass, in which the globular bal- loon first blown is flattened by pressing against a flat surface. The end of an iron rod is smeared with a coating of melted glass, and attached to the centre of the flattened surface. The pipe is then detached, leaving a small hole. By re-heating and rotating the rod swiftly about its longitudinal axis, the balloon opens out, forming a circular plate or disk, with the rod at the centre. Disks 4 or 5 feet in diameter are thus made. But they are not of the same thickness at the edge and middle; where the rod was attached, there is a thick rounded mass called the " bull's-eye." This must be cut out, so large window panes cannot be made from crown glass. Thus it is not an economical form of glass-blowing, and the industry is prac- tically abandoned. A little is now made to supply a small demand for the "bull's-eyes" for decorative purposes. Crown glass has a very brilliant surface. A skilful glass-blower can form all kinds of glass utensils by the use of his pipe and other tools. Wine glasses, tumblers, bottles, and lamp chimneys, for example, are often entirely blown. But much glass ware is now blown in moulds, or pressed. In cut-glass ware, the design is cut in the solid glass, which has been given its general form by blowing or pressing. Sometimes the design is formed in the pressed ware, and the surface only is cut and polished. Glass-cutting is done on a soft steel, copper, or sand- stone wheel, the cutting edge of which is fed with sand or emery and water. The polishing is done on similar wheels of wood, fed with rouge or putty powder. Lead glass is nearly always used for cutting, since it is softer and more brilliant than other varieties. Pressed glass is made by the use of a die or mould ; these moulds are quite expensive, but owing to the great number of pieces of the same form and design that are made with slight labor, pressed ware is fairly cheap. " Tough " or " tempered " glass is produced by a special method 176 OUTLINES OF INDUSTRIAL CHEMISTRY of annealing, the articles so treated being capable of withstanding blows and sudden changes of temperature. This tempering is done by plunging the article, while still so hot as to be somewhat soft, into a bath of oil heated to 100-300 C. This sudden " quenching " hardens the surface of the glass, but causes internal stresses. If scratched or cut slightly, toughened glass is very apt to fly to pieces, sometimes with great violence. And even after standing a long time spontaneous fracture often occurs. It is mainly used for lamp chimneys. A process for making hardened glass plates and window lights is employed, in which cold metallic surfaces are applied to the glass plates while the latter are still plastic. The sudden chilling imparts an exceedingly hard surface to the glass, so that it can be used in exposed situations, such as in street lamps. A compound glass is a recent invention to replace the hardened or tempered glass. Articles are formed of two layers of glass, the inner layer having a low coefficient of expansion while the outside layer has a high coefficient. This glass is particularly recommended for lamp chimneys and chemical vessels which must endure sudden changes of temperature. The ratio between the two coefficients must be very carefully maintained. Colored glasses are produced by adding to the ordinary batch cer- tain metallic oxides or salts, or even finely pulverized metal. These dissolve in the glass, and impart a characteristic color. Green glass is produced by the use of ferrous oxide, chromic oxide, or a mixture of cupric and ferric oxides. The color produced by ferrous oxide is a dull green, of no particular beauty. Copperas or iron filings are generally used in the batch of melted glass to form the ferrous silicate necessary for the color. Chromic oxide (Cro0 8 ) imparts a better green. It is usually produced by adding potassium bichromate (K 2 Cr 2 7 ) to the batch. If an excess of chromium oxide is present, the uncombined portion separates as minute crystals, disseminated through the glass, producing chrome aventurine. A. mixture of cupric and ferric oxides produces green glass, owing to the combined effect produced by these oxides individually. Yellow glass is made by adding sulphur or carbonaceous matter to the batch, producing sodium or potassium sulphides, which color the glass. A common method is to introduce wood or charred horn into the melted glass. Cadmium sulphide is sometimes employed. No sulphur compound can be used with lead glass. A rich yellow stain is obtained by the use of metallic silver or silver chloride; this is much used in making church windows, and was known in GLASS 177 the Middle Ages. A peculiar greenish yellow, fluorescent glass is produced with uranium oxide, but it is expensive. Orange glass of various shades is made by adding selenium (as a selenate with a reducing agent), or a mixture of ferric oxide and manganese dioxide. Blue glass is made with cobaltic oxide (Co 2 3 ) or cupric oxide. A very small percentage (0.1) of cobaltic oxide produces a deep blue color. If more than 5 per cent is used, the color is so deep that the glass may be ground for pigment (smalt). Owing to the intensity of its color, cobalt glass is much used for " flashing " on the surface of white glass. To do this, the blower dips his pipe into the pot of colored glass, and, collecting a small lump, dips it into the pot of colorless glass, or vice versa. By blowing he forms a sheet of colorless glass which is coated on one side with a very thin layer of colored glass, both firmly welded together. Both glasses must have the same composition and the same coefficient of expansion. A light blue (sky-blue) is obtained by the use of a small quantity of cupric oxide. Violet is produced by a small amount of pyrolusite, free from iron. An excess of manganese, especially if much iron is present, gives a deep yellow or brown. Red glass is made with metallic copper, cuprous oxide, or metallic gold. Copper gives a deep ruby red, but gold yields a bluish red, which is more brilliant. For copper ruby the form of cuprous oxide (Cu 2 O 2 ), called "hammer-scale," is used. A small quantity of iron filings, or stannous oxide, is often added to reduce any cupric oxide, The glass obtained from the melt for copper ruby is nearly colorless, or a pale green. By a second careful reheating in a muffle, the deep ruby color is slowly developed. It is so intense that the glass is used for " flashing." Gold ruby is produced in much the same way as copper. Usually a small quantity of gold chloride is added to the batch before melt- ing. On cooling, the glass is colorless, or reddish yellow ; the ruby color appears on reheating. Great care is necessary, for if over- heated the color may change to a dull red brown. A very minute quantity of gold is sufficient to color the glass deeply. Gold ruby is also used for flashing. White, "opal," or "milk" glass is made by adding cryolite or fluorite, with felspar, to the batch for common glass. Calcium phosphate, as bone-ash, may also be used. These substances crys- tallize in the glass when the melt is kept near its fusion point for some time, and thus cause the opalescence. Large quantities of tin or zinc oxides produce a translucent milk glass. 178 OUTLINES OF INDUSTRIAL CHEMISTRY Black glass is obtained by using a large excess of pyrolusite, iron, or copper oxides. The so-called "smoked glass," used for optical purposes, contains some nickel. Enamel is an easily fusible glass, usually containing lead and boric acid, or phosphate or stannate of sodium or potassium. It is usually white, blue, or gray, the color being produced by adding proper oxides. It is used for coating metallic (iron) vessels, pottery, (tiles, flower-pots, bricks, etc.), and porcelain. For cooking vessels it must be free from lead, and is composed of sand, borax, soda, and calcium phosphate or white clay (kaolin). Enamel must have a coefficient of expansion about equal to that of the iron on which it is placed, otherwise the glaze is soon de- stroyed by heating and cooling. Iridescent glass is made by exposing the hot glass to the vapors of stannic chloride (SnCl 4 ), or hydrochloric acid. These vapors attack the surface of the glass and alter its composition. It was formerly supposed that the art of making this glass was invented by the Romans, and later was lost. However, the old Roman glass was not originally iridescent, but has become so through expos- ure to dampness and carbon dioxide. The surface has been partly decomposed, the alkali dissolving, thus producing a thin layer of glass having a different composition and physical structure from the main body. This thin film causes interference of the light rays and produces a play of colors when viewed in different positions. Mirrors were formerly coated with an amalgam of tin. Tin foil was covered with mercury, and the glass, carefully cleaned, was laid on the amalgam, excess of mercury being forced out at the sides, and the amalgam adhering firmly to the glass. But the silver mirror is now the only kind made. A coating of metallic silver is deposited on the glass from an ammoniacal solu- tion of silver nitrate by the use of a reducing agent. Ammonium tartrate, or a solution of glucose or milk sugar in caustic soda, is generally used for this purpose; or aldehyde is sometimes used. The glass is carefully cleaned and covered with the silver solution containing the reducing substance, and heated gently on a steam or hot air bath. The thin layer of metallic silver deposited adheres to the glass, and is washed and dried, and covered with a protecting varnish to prevent the hydrogen sulphide in the air from tarnishing the reflecting surface. Plate glass is generally used for the best mirrors. Blown glass, which is used for the cheaper ones, is very apt to contain bubbles and striae, causing distortion of the image. GLASS 179 Tradition assigns the discovery of glass to the Phoenicians. Glass making is a very old industry, and was known to the early Egyptians, since glass beads have been found in mummy cases at least 3000 years old. Glass articles have also been found in the ex- cavations at Nineveh. From Egypt, the industry was transferred to Rome, and on the fall of the Western Empire the art was carried to Byzantium. Byzantine glass attained a high degree of perfection ; but in the middle of the thirteenth century Venice became the cen- tre of the industry, and Venetian glass-blowers were remarkably expert in the production of beautiful and delicate patterns. Finally, Bohemia took the lead in the manufacture of glass, and has retained a front rank ever since. Window glass was made by the Romans to a small extent, and specimens of such glass were taken from the ruins of Pompeii. In England, it first came into use in houses during the reign of Eliza- beth, but previously to this it had been used in cathedrals and churches. From the records of York cathedral, it is shown that during the time of Archbishop Wilfrid (669-709 A.D.) "glass was placed in the windows so that birds could no longer fly in and out and defile the sanctuary." The contract for the glass in the great West Window, given by Archbishop Melton, is dated 1330. The work was finished before 1350, and the price paid was 6 d. per square foot for white, and 1 s. per square foot for colored glass. This window is 54 feet high by 30 wide, and is to-day regarded as one of the finest examples of stained glass in England. The great East Window (77 feet high and 32 feet wide) was glazed by John Thornton in 1405-1408, for which he received 4 s. per week. These examples demonstrate the high degree of perfection to which the glass industry had advanced during the Middle Ages. At the present time, Belgium and England lead in the produc- tion of window and plate glass, while Germany, France, and the United States also manufacture enormous quantities. Austria and Germany are the leading producers of blown ware. REFERENCES Glass Making. Powell, Chance and Harris. 1883. TJ. S. Census, 1880. Report on the Manufacture of Glass. J. D. Weeks. Die Glas-Fabrikation. R. Gerner, Vienna, 1880. (Hartleben.) Handbuch der Glas-Fabrikation. Dr. E. Tscheuschner, Weimar, 1885. (Voigt.) Die Fabrikation und Raffinirung des Glases. Wilhelm Mertens, Vienna, 1889. (Hartleben.) Verre et Verrerie. L. Appert et Jules Henrivaux, Paris, 1894. (Gauthiers- VillarsetFils.) 180 OUTLINES OF INDUSTRIAL CHEMISTRY Journal of the Franklin Institute. 1887. Glass Making. C. H. Henderson. Proceedings of Engineers' Society of Western Pennsylvania. 1895, 119. A Study of Glass. Robert Linton. CERAMIC INDUSTRIES Clay is a natural hydrated silicate of aluminum, formed by the weathering of felspar or felspathic rock, such as granite. When heated, the water of constitution in the hydrated silicates is driven off, and chemical changes are brought about by which the clay becomes stone-like in its hardness ; and, if pulverized again, its plasticity is gone. Clays which have not been transported by natural waters from the place where they were formed are called primary ; secondary clays are those which have been washed from their original beds and deposited elsewhere. Primary clay which has been derived from pure felspar contains but little impurity other than silica, and is called kaolinite, kaolin, or China clay. It is a white, powdery mass, consisting essentially of hydrated silicate of aluminum, nearly all the alkali having been leached out. The decomposition of a felspar may be represented by the following equation : A1 2 3 , K 2 0, 6 Si0 2 + C0 2 + 2"H 2 = A1 2 3 , 2 Si0 2 2 H 2 + K 2 C0 3 + 4 Si0 2 . But since felspars and granites contain mica and quartz in a greater or less quantity, these are generally found in the kaolin ; if the particles are too coarse, they are removed by levigating. Pure kaolin is almost infusible, but the presence of impurities increases its fusibility greatly. Kaolins are generally of a granular or crystalline structure, and do not form a very plastic mass when wet; hence they are called " lean " clays. When burned, they yield a white or nearly white pottery. Fire-clays are almost infusible. They are generally found under- lying coal beds. In composition they are kaolins, containing a con- siderable amount of free silica, as quartz. They may contain a little more iron than good China clay, but are free from alkalies. Secondary clay, even if derived from pure felspar, generally contains some foreign matter, which has been mixed with it during its transference from the place of formation to the point of deposit. Then, too, the sharp edges of the crystalline particles have been worn off by their rubbing against each other during this motion, and the clay acquires the property of plasticity. These secondary plastic CERAMIC INDUSTRIES 181 clays are called pipe- or ball-clays, and are also known as "fat" clays, to distinguish them from the lean or non-plastic. Fat clays absorb much water and have great binding power, so that they are easily shaped by the potter. But on drying, and especially when burned, they shrink very much. This shrinkage is counteracted by mixing with the fat clay a certain amount of " leaning " material, such as silica, pulverized burnt clay, or " grog," the ground, unglazed body of pottery. Fat clays are much more fusible than lean clays. All clays have a peculiar and characteristic odor when breathed upon or wet. The preparation of clay for the potter is quite simple. It is mined, and allowed to weather for several months, which is said to increase its plasticity. Fine clays which are to be used for the better grades of ware are then thoroughly "slipped" with water in a " blunger " (a vat with mechanical stirrers), and thus levigated. The coarse particles of quartz, mica, and undecomposed felspar are thus separated, and only the clay substance, with a very little finely divided quartz, remains in suspension. The fine mud, called " slip," obtained by settling the wash .waters, is put into cloth bags and pressed, or it is run through a filter-press. It is then ready for use. Clays are sold under the names, kaolin, ball- or potter's-clay, and fire-clay. The most important properties of a clay from the potter's stand- point are its plasticity, fusibility, and contraction when burned. The color of the finished product is very important when making white ware. Plasticity is diminished by the presence of rough or sharp particles of silica, felspar, or other material. Fusibility is important as determining its adaptability to the manufacture of certain kinds of pottery and porcelain, which are burned at a very high temperature. If the clay contains much iron oxide, lime, magnesia, or alkali, it is more fusible than if pure. The properties of a clay are dependent on the form of combina- tion of its constituents, and an empirical analysis is not sufficient for the purpose of the potter. He must have a rational analysis ; that is, he must know the proportions of clay substance (hydrated silicate of aluminum), felspar, quartz, lime, etc., present, in order that he may add the proper amount of those ingredients which are lacking to give a mass having the desired properties. The following are complete analyses, with the corresponding rational analyses of certain clays : 182 OUTLINES OF INDUSTRIAL CHEMISTRY CHEMICAL ANALYSES GERMAN * (SENNEWITZ). BOHEMIAN* CZ M- VIRGINIAN t (KAOLIN). Ouiot (.FIRE-CLAY). ENGLISH t (CORNISH STONE). SiO, 46.8 JtflVy. 50 02 74 93 73 57 ALA .... Fe,0 3 .... CaO 23.8 0.8 38.5 1.1 35.18 0.36 12 17.19 0.79 0.29 16.48 0.27 1.17 MO-O 0.5 trac6 07 46 21 Alkalies. . . . H 2 1.4 8.4 1.4 12.9 3.39 10.57 1.61 5.44 5.84 2.45 99.8 100.7 99.71 100.71 99.98 RATIONAL ANALYSES Clay substance . 63.8 96.6 84.12 48.24 33.57 Quartz . . . . 35.5 2.3 6.55 49.72 41.10 Felspar . . 0.7, 1.1 9.04 2.75 25.31 100.0 100.0 99.71 100.71 99.98 From these it will readily be seen that clays having approxi- mately the same empirical composition may differ widely in fusi- bility, expansion, and in the porosity of the burned product. Quartz, in the absence of bases with which it may combine, increases the expansion and decreases the fusibility. Felspar makes the clay more fusible, acting as a flux on the silica and clay substance. It causes vitrification of the mass, on burning ; and, being itself non- plastic, is often used to modify a too plastic clay. Ceramics comprise two general divisions : (a) articles having a non-porous body, and (b) articles having a porous body. Non-porous ware is hard, impervious to liquids and gases, and has a semi-vitrified appearance on the fractured surface. It is burned at a very high temperature, and is chiefly made from kaolin, with just enough plastic material to enable the workman to form the desired article. This division includes porcelain and stoneware. Porous ware is less dense, has an earthy appearance on the fractured surface, and per- mits the passage of gases and liquids through its pores. It is made from plastic clays, and burned at a low or moderate temperature. It comprises bricks, terra cotta, common crockery, and some kinds of stoneware. There are two kinds of porcelain, the hard and the soft, or " fritted." Both are harder than glass, and very resistive to chem- ical action. * Lehrbuch der technischen Chemie. H. Ost, 227. t Chemistry of Pottery. K. Langenbeck, 10, 111, 165. CERAMIC INDUSTRIES 183 Hard porcelain softens only at the highest attainable tempera- ture, and, when burned, forms a perfectly homogeneous mass, which is translucent. The body is composed of kaolin, quartz, and felspar, in definite proportions. It is glazed with pure felspar, or a mixture of quartz and felspar, with sufficient lime to form a difficultly fusible glass. This glaze, which must have the same coefficient of expansion as the body, is very perfectly welded on to the body, by a second burning at a very high temperature ; and no distinct line of demarkation between the body and the glaze can be seen on a fractured surface. Berlin and Meissen ware are examples. Soft porcelain consists of a kaolin body, with ball-clay, bone-ash, and felspathic materials added. This is burned at a high tempera- ture, and glazed with a lead-boric-acid glass, which is fused on to its surface by a second much lower heating. The glaze does not pene- trate so perfectly, but forms a more superficial layer than is the case with hard porcelain. English china, Sevres ware, and Japanese thin ware are soft porcelain. In preparing the clay for porcelains, the powdered materials are thoroughly mixed, wet, and the " slip " kneaded and allowed to age for several months. The articles are formed on the potter's wheel, a horizontal revolving table, driven by foot or machine power. Sometimes the slip is cast in porous moulds of gypsum or burned clay, which absorb the water, leaving the mud on the face of the mould. Or the partly dried mud is pressed in moulds to form one surface of the article, the other being completed on the wheel, as is the case with dishes and plates. The articles are very slowly dried at atmospheric temperature, and then burned at a low red heat, to give them sufficient coherence to permit of glazing. The finely powdered glaze mixture is stirred up with water to form a cream, into which the articles are dipped and at once with- drawn. A layer of the glaze adheres to the surface, and, after dry- ing, the article is ready for the second or glaze burning. In order to protect them from direct contact with the fire in the kiln, they are enclosed in fire-clay boxes, called "saggers." These are piled in the kiln in columns or "bungs," extending from the bottom to the top. In order to allow sufficient freedom for shrinkage, the porcelain is supported on a " cockspur," a small tripod of fire-clay. The contraction of porcelain on burning is nearly 13 per cent of its original volume. After burning, the ware is sorted ; much is lost owing to warping, to bubbles in the glaze, and to discolorations resulting from smoke and from iron oxide in the material. The body of all ware to be glazed is called " biscuit " after the 184 OUTLINES OF INDUSTRIAL CHEMISTRY first firing ; that of soft porcelain which, has been hard fired is called " Parian." Both are used for statuettes, medallions, and reliefs. Stoneware, which is also a non-porous body, is made from re- fractory material, and burned at high temperatures. But the color of the resulting ware may range from white and gray to yellow and brown. It is not attacked by chemicals, and withstands tempera- ture changes fairly well. The finest quality is the well-known " Wedgwood " ware, which comes in various colors, and is usually not glazed. The gray stoneware, decorated with blue, now so much used for drinking-mugs and ornamental vases, is also of this group. Yellow and brown varieties are much used for mineral water-bottles, bombonnes, condenser tubes, and glazed pipes in chemical factories. The clays are less pure than those for porcelain, and the ware is burned without saggers, at a very high temperature. A " salt glaze " is used, to form which common salt is thrown into the kiln, and, vol- atilizing, combines with the silicates of the stoneware to form double silicates of soda and alumina on the surface of the ware; or the articles are " slip glazed " by applying an easily fusible clay as " slip,' 7 before firing. The kilns for potters' use are of several kinds. The most com- mon form is the up-draught kiln, in which the flame enters at the bottom and passes up between the "bungs," and out at the chimney above. A better form is the down-draught kiln, which is usually built in two stories. The lower story is filled with the ware to be fired at the highest temperature, and the upper with that to be burned at a less heat. The flame from the grate passes up through flues in the kiln walls, and enters the lower chamber near the top. It then goes down between the bungs, and, through openings in the floor, into other flues in the walls, around tfre upper chamber, and thence to the chimney. This kiln is economical of fuel, affords very even temperature in the lower chamber, and utilizes the heat which is lost in the up-draught kiln. A special form of Hoffmann's ring furnace (p. 157) is also employed for pottery and brick burning. In a new form of kiln, the bungs are arranged on cars, which travel slowly through a long gallery, towards the firing chamber. The waste heat from the hot chamber enters the gallery at the end next the firing room, and, coming in contact with the pottery, heats it to a temperature corresponding to its distance from the inlet flue. The cars move through the furnace into a second long gallery, where the heat from the saggers warms the air which is passing into the fur- nace, thus perfectly utilizing the waste heat. The firing compart- CERAMIC INDUSTRIES 185 ment is usually large enough to contain two loaded cars; and the grate being at one end of the firing room, the pottery in each car gets a preliminary firing before it reaches the hottest part of the kiln. As soon as one car is fired, it is pushed into the cooling gal- lery, the rear car is moved into the hottest compartment of the kiln, and another is introduced from the preliminary warming gallery. This furnace is very economical of fuel, gives an even temperature, and the time of firing being greatly reduced, there is less loss of saggers and pottery. Porous ware, the second division of ceramics, is manufactured extensively in all countries. The finest grade is " faience." This is made from a white clay, which is washed, levigated, and aged, much as for porcelain. The better grades are burned in saggers at a high temperature, and glazed with a transparent lead glaze at a much lower heat. Majolica also belongs to this group, being a colored porous body, covered with a non-transparent glaze. Between faience and common pottery no sharp line can be drawn. The color ranges through cream, yellow, brown, and red, and the body consists of more or less fusible clay, with a still more fusible lead glaze, which is often colored with metallic oxides. The clays for common pottery are generally " slipped," and strained through fine sieves to remove stones and coarse grains. The articles are fashioned on the potter's wheel and are air dried. They are then dipped in a glaze made of litharge and clay, shaken to a cream with water. Or the dry mixture is powdered over the surface from a pepper box. Or they are given a " salt " glaze as before described. They are burned without saggers, and at a temperature only suffi- cient to fuse the glaze. Tiles are a special form of pottery, consisting of flat, thin plates, much used for floors, panels, and architectural purposes. They are finer ware than common brick, and more care is taken in the prepa- ration of the body and in the burning. There are three classes, vitrified, encaustic, and glazed. Vitrified tiles consist of single pieces, made by one burning at a very high temperature, so that the entire body of the tile is semi- fused. They are not glazed, and are a form of stoneware much used for pavements and floors, because of their hardness. Encaustic tiles are made from two or more clays, generally of different colors. A facing of fine clay may be put on a back of commoner quality. The ornamental design is made by inlaying the face with other clays, which burn to different colors. All the materials must have the same coefficient of expansion, so that no 186 OUTLINES OF INDUSTRIAL CHEMISTRY cracks form between the different parts of the design. These tiles are generally used for ornamental purposes, and are often covered with a transparent glaze, necessitating two burnings. Glazed tiles are made with a body (which may consist of more than one clay) of uniform color, covered with a transparent glaze, colored or not, according to the effect desired. The dry clay, flint, felspar, Cornish stone,* "grog," and other materials in the mixture for the body of the tile, are put into a revolving drum (Alsing mill), along with a number of round flint stones. After five or six hours' grinding, the mixture is complete. The dry powder is then sifted through a fine sieve. There are two methods of forming the tile, the "dust body" and the "wet body" process. In the dust body method the sifted clay mixture is dampened by spreading on a wet plaster of Paris floor. It is shovelled over and allowed to remain on the floor until the particles of clay will just stick together when pressed in the hand. It is then filled into a metallic mould which contains the intaglio for relief designs ; it is then heavily pressed in a screw or hydraulic press. This compacts the clay, and gives sufficient coherence, so that the green tile may be removed. It is exceedingly brittle, and must be handled very care- fully. It is well dried in a room where there is a good circulation of air. To prevent discoloration, tiles are burned in saggers in which they are loosely packed in quartz sand to prevent their twist- ing and bending, since they become very soft at high temperatures. In the wet body process the slip is moulded in plaster of Paris moulds. After standing half an hour, or more, until the water has all been absorbed by the plaster, the clay cast is removed, dried slowly, and burned as in the case of dust body tiles. Glazes, both for hollow ware of all sorts and for tiles, are of three kinds, engobe, enamel, and transparent. The engobe is a fusible clay, felspar, or alkali, applied in a very thin coating. It forms a thin glaze, usually opaque, which is intended to support a second thicker glaze or enamel. Enamels are usually transparent glazes, holding in suspension, opaque substances such as oxide of tin. A mixture of litharge and tin oxide ("ashes of tin") is very often used for enamel. Transparent glazes are practically lead or lime glass. This is sometimes, though rarely, used as "raw glaze," i.e. the materials are ground fine, mixed, and applied to the ware as a cream with * Cornish stone is partly weathered felspar, being thus a mixture of kaolin, felspar, quartz, and mica. It is mined in England, and much used as a flux and fusible ingredient in porcelain and tiles. CERAMIC INDUSTRIES 187 water. This is difficult to do, owing to the great density of the litharge, which settles out of the cream, on standing even a short time. To avoid this separation and loss, and to allow the use of sub- stances soluble in water, e.g. borax, soda-ash, or boric acid, the glaze is generally "fritted" or semi-fused, before making it into a cream with water. The powdered and thoroughly mixed material, together with coloring substances if desired, is heated in a sagger until it forms a coherent mass, but is not completely fused. The frit is then powdered in a ball mill. Fritted glaze is much more uniform than raw, and there is no tendency to segregation of its components. In all kinds of glazed ware, it is very essential that the glaze and body shall have the same coefficient of expansion, or cracking of the glaze is liable to occur. This is called "crazing,' 7 and is caused by the glaze contracting too much in cooling ; the scaling off of glaze and attached body from high points of the tile, called " shivering," is caused by insufficient contraction of the glaze. To prevent these defects the glaze or the body is so modified that the coefficients of expansion are the same. The exact adjustment of this factor is a matter of experience. The usual methods employed are, to render the body less plastic by the addition of lean clay, grog, or quartz, thus increasing the silica, which increases the expan- sion of the body ; or to modify the glaze by the addition of silica or boric acid for greater expansion, or of lime, lead, or alkali, to increase the contraction. Boric acid, lead, and alkali make it more fusible, and the temperature of the intended burning must be kept in mind when adding these ingredients. Boric acid and lead also increase the brilliancy of the glaze. The addition of certain color- ing matter to glazes also increases the tendency to craze. Alumina is essential in a glaze to prevent devitrification during the burning. Terra cotta has a soft porous body, and is not glazed. Its color depends on the character of the clay. Generally a highly ferrugi- nous clay is used, which has a deep red color when burned. It is extensively employed for architectural effects and for tiles. Bricks are probably the most important of the porous ware. They are made from common clay, which usually contains consider- able impurity, lime and iron oxide often being present in large quantities. The preparation of the clay is a simpler process than for pottery. After digging it is usually weathered for several months, and then screened, to remove pebbles of quartz or lime- stone.* It is then " pugged " or " tempered," by mixing thoroughly * Limestone pebbles are very injurious, since the burning converts them into lumps of lime within the brick, and when the latter is wet or exposed to weather the lime is hydrated, and, expanding, disintegrates the brick. 188 OUTLINES OF INDUSTRIAL CHEMISTRY with water and the ingredients to make the desired " body " ; in the case of a fat clay, these are sand, grog, or other clays. This is done in a " pug mill," a tank containing a very effective revolving stirring apparatus, which pushes the mass out at the bottom in proper condi- tion to be used at cnce. The paste is then moulded into bricks, by hand for the finer sort, and by machinery for the common grades. The latter are apt to be uneven and rough. The moulded brick are then dried in the air, usually in the yard, under a light shed. They are turned over frequently during the drying, which must not be too rapid, lest the bricks crack. The firing is done in kilns which may be built of the air-dried brick, numerous channels being left for the passage of flame and hot gases. This mode of burning results in several grades of brick, owing to the unequal distribution of heat. Or closed kilns, such as the Hofmann ring furnace (p. 157), may be used. This gives a more even product than the open kiln. In this country wood and coal are used for fuel, but gas is fre- quently employed abroad. The temperature in the kiln for common brick seldom goes higher than 1000 C. ; but for hard, paving brick it may be raised to 1200 or 1300 C., producing incipient fusing. The heat also affects the color of some bricks; high temperature yields a dark red, gray, or bluish black, according to the amount of ferroso-ferric oxide (Fe 3 4 ) formed. Clays containing much lime yield yellow or cream-colored brick, if iron is also present. Common brick will fuse if exposed to high heat, and are not suitable for lining fireplaces, furnaces, or ovens. Fire-brick are made from fire-clay, with the addition of a large amount of " grog " or silica. These bricks must resist great heat, and not shrink nor warp. The clay is prepared similarly to that for common brick, but more care is taken in the mixing. The bricks are also heavily pressed to give them density. The burning is at the highest temperature possible, so that 110 shrinkage will occur later when the bricks are in use. They are brittle, and must be supported by a backing of common hard brick. Fire-brick are also made of highly basic, or of acid material, in order to better withstand the action of fluxes. REFERENCES Handbuch der gesammten Thonwaarenindustrie. Bruno Kerl, Braunschweig, 1879. (Schwetsche.) Traite des Arts ceramiques ou des Poteries. Alexandra Bronginart. Lemons de ceramique. A. Salvetat. La Faience. Th. Deck, PIGMENTS 189 Report on the clay deposits of Woodbridge, South Amboy, etc. Public Docu- ments of New Jersey. A Practical Treatise on the Manufacture of Bricks. C. T. Davis. Pottery and Porcelain of the United States. E. A. Barber. Die Steingut-Fabrikation. Gustav Steinbrecht, Leipzig, 1891. (Hartleben.) Ziegel-Fabrikation der Gegenwart. Herman Zwick, Leipzig, 1894. (Hartleben.) Seger's gesammelte Schriften. H. Hecht und E. Cramer, Berlin, 1896. The Chemistry of Pottery. Karl Langenbeck, Easton, Perm., 1895. (Chemical Publishing Company.) PIGMENTS Pigments are mineral or organic bodies, usually insoluble in water, oils, and other neutral solvents, and are used to impart color to a body, either by mechanical adhesion to its surface or by ad- mixture with its substance. In most cases there is no chemical combination between the pigment and the body it colors. Pigments form the basis of paint, which consists of a mixture of a pigment with some drying oil, or with water containing gum or size. It is used for decorative and protective purposes ; if used for outside work, the pigment should be insoluble in water. The color of a pigment depends upon the amount and kind of light which it reflects. It is essential that the pigment be opaque, in order that it may have a good " covering power " or " body ; " i.e. it should entirely conceal the surface to which it is applied. Many pigments are prepared by chemical precipitation, but some of the most impor- tant are not. The chief pigments are given in the following table : WHITES. White Lead. Lead Sulphate. Lead Oxychloride. White Zinc. Zinc Sulphide. Barytes. Gypsum. Whiting. BLUES. Ultramarine. Prussian Blues. Smalt. Cobalt Blues. Copper Blues. Indigo. VIOLET. Ultramarine. GREENS. Ultramarine. Brunswick Green. Chrome Green. Guignet's Green. Copper Greens. Copper and Arsenic Greens. YELLOWS. Chrome Yellow. Yellow Ochre. Cadmium Yellow. Orpiment. Litharge. Gamboge. Indian Yellow. ORANGE. Orange Mineral. Chrome Orange. Antimony Orange. REDS. Red Lead. Chrome Red. Red Ochre. Venetian Red. Vermilion. Realgar. Antimony Red. Carmine. BROWNS. Umbers. Vandyke Brown. Sepia. BLACKS. Lampblack. Ivory-black. Bone-black. Graphite. 190 OUTLINES OF INDUSTRIAL CHEMISTRY WHITE PIGMENTS White lead is the most important of all pigments, and is a very old one, the native carbonate, cerussite, having been used by the Romans. But as this mineral is restricted in its distribution the artificial product was in time brought into use. The so-called Dutch process of making white lead is the oldest known, reference being made to it as far back as 1622. With a few modifications, it is still in use, and yields a product which for many purposes is preferred by painters to the lead manufactured by the numerous newer pro- cesses. It usually has more covering power and a better color. White lead is a basic lead carbonate, and analyses of the best samples give as constitutional formula about 2 PbC0 3 , Pb(OH) 2 , in which there are two molecules of PbC0 3 to one of hydroxide. This appears to be the best ratio. But the white lead of trade varies a good deal, according to the method and conditions of making. In some cases it is nearly pure PbC0 3 , and in others the proportion of carbonate to hydroxide is as high as three to one, or more. But some hydroxide is necessary in order that the white lead may have a good covering power. Then, too, the hydroxide is supposed to combine with the oil chemically to form a " lead soap," which per- haps dissolves in the excess of oil to form a kind of varnish. There are three general methods employed in white lead making, besides numerous patent processes. These are : The Dutch, or Stack process. The German, or Chamber process. The French, or Thenard's process. The Dutch process consists in exposing sheet lead to the direct action of moisture, acetic acid vapors, and carbon dioxide. The corrosion is effected in earthenware pots 8 inches in depth by 5 inches in diameter, glazed inside, and made in the form of crucibles, each containing a shelf. On this shelf is a spiral or "buckle" of thin sheet lead, made by rolling up a sheet of lead 2 feet long by 4 inches wide ; or cast buckles of various forms to expose a large surface to the fumes, may be used. In the lower compart- ment is dilute acetic acid, containing from 3 to 5 per cent C 2 H 4 2 . A large number of these pots so charged are packed in a shed or brick building, having an opening on one side reaching from the ground nearly to the roof. A layer of ashes is spread over the floor first, and then a layer 4 or 5 feet thick of spent tan bark which is moist and ready to ferment. This is well packed down, and the pots placed side by side upon it until the whole space is filled, PIGMENTS 191 excepting about 6 inches next the walls, which is solidly filled in with the tan. More lead buckles or lead gratings are placed across the tops of the pots, so as to form a layer of metallic lead about 4 inches deep. Then about 6 inches above this, and supported by timbers or blocks, is a board floor upon which the next layer of tan, about one foot deep, is placed, and the pots upon it as above described. The doorway is boarded up as the filling continues, and the " stack," as the alternate layers of pots and tan are called, is carried to within a few feet of the top of the shed. For a stack 20 by 12 by 18 feet in size, 40 or 50 tons of lead are required, about 3 tons of lead and 200 gallons of acid being used in each layer of pots. Very soon after packing an active fermentation of the tan sets in, the tempera- ture rising to about 55-60 C. This heat is sufficient to vaporize the acetic acid and water, and these vapors attack the metallic lead, forming a basic lead acetate. Great quantities of carbon dioxide are liberated during the fermentation, and this decomposes the lead acetate, forming basic lead carbonate, or white lead. The reactions, aside from those of fermentation, may be represented by the follow- ing: 1) Pb 4- 2 C 2 H 4 2 = H 2 -f Pb(C.,H30 2 ) 2 . (Normal lead acetate.) 2) 3 Pb(C 2 H 3 2 ) 2 4- 2 H 2 = 2 Pb(C 2 H 3 2 ) 2 , Pb(OH) 2 + 2 C 2 H 4 2 . 3) 2 Pb(C 2 H 3 2 ) 2 / Pb(OH) 2 + 2 C0 2 4- 2 H 2 = 2 PbC0 3 , Pb(OH) 2 4- 4 C 2 H 4 2 . Some authorities consider the reactions to be as follows : a) Pb 4- H 2 4- = Pb(OH) 2 . 6) Pb(OH) 2 4- 2 C 2 H 4 2 = Pb(C 2 H 3 2 ) 2 4- 2 H 2 0. c) Pb(C 2 H 3 2 ) 2 4- 2 Pb(OH) 2 = Pb(C 2 H 3 2 ) 2 , 2 Pb(OH) 2 . (Basic lead acetate.) d) 3 ;Pb(C 2 H 3 2 ) 2 , 2 Pb(OH) 2 j 4 4 CO 2 = 3Pb(C 2 H 3 2 ) 2 + 2 >Pb(OH) 2 , 2PbC0 3 ; + 4H 2 0. Thus the acetic acid, or the neutral lead acetate, is regenerated, and attacks more of the metallic lead, and the process repeats itself. But the action is very slow, the time usually allowed for a stack to work being about three months. If horse dung is used instead of the tan bark, as it formerly was, the process is quicker, taking about two months ; but the sulphur compounds formed in this fermenta- tion darken the white lead more or less. Usually the metallic lead is nearly all corroded and converted into white lead, but never completely, and the product is seldom 192 OUTLINES OF INDUSTRIAL CHEMISTRY equally good in all parts of the stack. When well corroded, the buckles retain their shape, although they have become rather more bulky and of a grayish white color, and have a firm, porcelain-like structure. When soft and powdery, the product is not so satis- factory. The coarse bits which fall among the tan are recovered by hand picking and raking, and the finer particles by levigation. The " corrosions " are then taken to the grinding room and put through rolls, which break them up into fine powder ; the uncorroded lead is simply rolled out into plates and scales, which are retained on the sieves when the mass is screened. The white lead only passes through, and is reduced to a fine powder by wet grinding in an edgestone or horizontal mill, and then levigated. The coarser par- ticles from the first settling tanks are returned to the mills and reground. The supernatant water is drawn off from the last settling tank, leaving a heavy white mud, which is dried in unglazed pots or dishes by heating in ovens at about 80 C. During levigation, the neutral acetate mixed with the white lead is dissolved out. The water is used again and again, until it becomes saturated with lead salts, which are precipitated by adding soda-ash, or by carbon dioxide. The white lead comes in trade either dry or mixed with about 9 per cent of raw linseed oil. Sometimes it is slightly yellow, due to stains from the colored liquids in the tan, or to tarry matters in the acetic acid, or to overheating in the drying. A little indigo or Prus- sian blue is sometimes added to neutralize this. One ton of the metallic lead usually yields about 1^ tons of the white lead. But the process is always somewhat uncertain both as to quantity and quality of the product. Sometimes very little corrosion takes place, and this may also vary in different parts of the stack. The process is slow, a large plant is required, and the capital invested lies idle ; hence the price of white lead is somewhat higher than the simplicity of the method would at first glance appear to warrant. To obtain good results by the Dutch method the lead must be very pure. If any silver, copper, or iron is present, the color of the white lead will be damaged. Antimony, arsenic, and zinc are said to retard the conversion very much. The German, or chamber, process is an artificial method of pro- ducing about the same conditions as prevail inside the stack in the Dutch method. The reactions are the same. Lead plates are hung or arranged on shelves in a closed chamber, provided with a door and window for filling and for watching the process. Dishes of acetic acid are placed on the floor, or acetic acid vapor is introduced from PIGMENTS 193 stills outside, the room is heated by steam to about 38 C., and carbon dioxide is introduced. This is much more rapid than the Dutch method, usually requiring about five weeks, but the quality of the product is not so satisfactory. There are difficulties to contend with in the rate of flow of the acid vapors, steam, and carbon dioxide, and in the regulation of the temperature. Too much acetic acid vapor causes loss of lead as neutral acetate; too much carbon dioxide pre- cipitates normal lead carbonate; too little acetic acid or too high a temperature, with excess of water vapor, may form lead oxide, which, being yellow, injures the product. Many modifications of this process have been invented, and some of them are worked more or less successfully. In one form, the chamber is fitted with tracks, on which cars are run, carrying the sheet lead in frames. A car can be run out, and another introduced, without much loss of time or cooling of the chamber. The white lead made by this method is ground and levigated as already described. The French process, or Thenard's method, depends on precipitation cf a basic lead carbonate from a solution of a basic salt by means of carbon dioxide. The solution generally used is a basic lead acetate, prepared by boiling litharge with neutral acetate. The reactions are: 1) 2 PbO + Pb(C 2 H 3 2 ) 2 + 2 H 2 = Pb(C 2 H 3 2 ) 2 , 2 Pb(OH) 2 . 2) 3 { Pb(C 2 H 3 2 ) 2 - 2 Pb(OH) 2 j + 4 C0 2 = 3 Pb(C 2 H 3 2 ) 2 + 252 PbC0 3 , Pb(OH) 2 j + 4 H 2 0. FIG. 65. The reactions are carried out in the apparatus shown in Pig. 65.* The litharge is mixed with the solution of neutral lead acetate in the tank (A), which is heated by a steam pipe. When saturated, * After Hurst, Painter's Colours, Oils and Varnishes. o 194 OUTLINES OF INDUSTRIAL CHEMISTRY the mixture is run into the settling tank ( B), where the undissolved litharge deposits. The clear solution of basic lead acetate is then run into the precipitating vessel (C), where it is treated with carbon dioxide, introduced through the pipes (D, D). The basic lead car- bonate falls as a heavy white precipitate, while a solution of neutral lead acetate remains. After settling, the solution is drawn into the tank (E), from which it is pumped back into (A), where, after add- ing a small amount of acetic acid, it is used again. The white lead is collected in (F), from which it is taken to be filtered and washed. The carbon dioxide used must be pure and concentrated, and is made by heating calcium carbonate with coke, in a special furnace (G). The gas is passed through water in (H) to remove impurities, and then goes to the precipitating vessel. The precipitation requires from 10 to 14 hours or more, vary- ing, as does also the quality of the product, with the quantity and strength of the solution of basic acetate. The white lead separates in a granular or crystalline form, and is washed, ground, and dried, as in the methods already described. It has less covering power than the amorphous powder produced by the Dutch method, since the minute precipitated crystals are very difficult to pulverize, and are less opaque. Milner's process, one of the several patented modifications of this method, consists in forming a basic lead chloride by mixing litharge in a solution of common salt, and agitating for 4 or 5 hours. The reaction proceeds at the ordinary temperature, and produces a thick white paste, which, together with the caustic soda formed, is then decomposed with carbon dioxide in a tank provided with stirring paddles. The resulting products are white lead and common salt. The mixture is tested from time to time, and when no longer alka- line the reaction is ended. The reactions are : 1) 4 PbO + 2 NaCl + 5 H 2 = PbCl 2 , 3 PbO - 4 H 2 + 2 NaOH. 2) 3 JPbCl 2 , 3 PbO 4 H 2 OJ + 6 NaOH + 8 C0 2 = 4 {2 PbCOg, Pb(OH) 2 + 6 NaCl + 11 H 2 0. By the Kremnitz process, so called from the locality where it is employed, a thick paste is made of litharge and acetic acid or lead acetate solution. This is put into chambers filled with carbon diox- ide, and stirred and raked over until, having absorbed sufficient car- bon dioxide to form the basic carbonate, it has become white. The process must be stopped at the right point, or too much normal car- bonate is formed, and the product injured. PIGMENTS 195 A number of patents have been issued for methods depending upon the precipitation of basic lead solutions with sodium carbonate, but these all have the disadvantage of forming a crystalline product. Electrolytic processes have attracted some attention recently. One of these is a modification of the chamber method. The lead is placed on shelves, covered with carbon, or pure tin plates, through which an electric current is passed. The lead is thus charged, and, it is claimed, is consequently more rapidly converted by the carbon dioxide and acetic acid vapors, while the product is granular, instead of crystalline. A new electrolytic process * consists in decomposing a solution of sodium nitrate in a wooden cell, provided with a porous dia- phragm. The anode is made of metallic lead, and the cathode of copper. Nitric acid is set free at the anode and dissolves the lead, forming a solution of lead nitrate. At the cathode, metallic sodium is liberated, which decomposes the water, forming caustic soda. Then the lead nitrate and caustic soda solutions are allowed to react on each other, precipitating lead hydroxide, which is digested with a solution of sodium bicarbonate, to form neutral lead carbonate. At the same time that the lead nitrate is decomposed by the caustic soda, the sodium nitrate is regenerated and returned to the process. The caustic soda solution formed in the last reaction is used to make more sodium bicarbonate by the addition of carbon dioxide. The lead carbonate formed in this way is claimed to be non-crystal- line, and to have as much covering power as the basic carbonate or common white lead. The reactions are as follows : _ I 1) NaN0 3 + H 2 = NaOH -f HN0 3 . 2) 2 HN0 3 + Pb = Pb(N0 3 ) 2 + H 2 . 3) Pb(N0 3 ) 2 -f 2 NaOH = Pb(OH) 2 -f- 2 NaNO 3 . 4) Pb(OH), + NaHC0 3 = PbC0 3 + KaOH + H 2 0. Keactions (1) and (2) are doubtful, and it is more probable that the following occurs : 2 NaN0 3 + 2 H,0 + Pb = (2 NaOH + H 2 ) -f Hydrogen is liberated at the cathode. The process is claimed to be rapid, requiring only a small plant for considerable output ; and it yields a good paint with very little labor. Owing to the high price of white lead, it is frequently adulterated * J. Amer. Chem. Society, 1895, p. 835. R. P. Williams. 196 OUTLINES OF INDUSTRIAL CHEMISTRY with barytes (BaS0 4 ), lead sulphate, lead carbonate, or calcium car- bonate. Barytes is the most common adulterant, being cheap and heavy. A pure white lead should dissolve in dilute C.P. nitric acid, without leaving a residue. (Common nitric acid will not yield a perfect solution, as it contains sulphuric acid.) White lead is very heavy, having a specific gravity of 6.47. A cubic foot of the dry powder weighs about 185 pounds. It has great value as a pigment, owing to its covering power, its perma- nency, and the readiness with which it mixes with other pigments. But it turns dark on contact with hydrogen sulphide, or if mixed with pigments containing sulphur, such as ultramarine, cadmium yellow (CdS), or vermilion (HgS). It is not suitable for painting the interiors of houses where gas or coal is burned. It is nearly insoluble in water, but, if taken into the system, will in time pro- duce very dangerous poisoning; and too much care cannot be taken in the manufacture to prevent the fine dust from flying about. Sponges are worn over the mouth by the workmen, especially in the grinding room. Sometimes they drink water acidulated with sul- phuric acid, as a preventive and antidote. Owing to the cost and poisonous character of white lead, substi- tutes are used to some extent. These are lead sulphate, sulphite, and oxychloride. Lead sulphate is the base of "sublimed white lead," the chief white lead substitute. By heating galena and coke in a blast of hot air, part of the lead is reduced to the metallic state, and part converted to sulphate and oxide, which, together with some metallic lead, sublime as "lead fume." This is collected in cham- bers and subjected to a second heating in a blast of hot air, which finishes the conversion to sulphate. The zinc present in the galena also passes off with the fume, and is converted to zinc white by the hot air blast. The color of the sublimed white lead is sometimes improved by treating with sulphuric acid. It has good covering power and color, and is not readily affected by hydrogen sulphide. It mixes well with other pigments containing sulphur, and is non- poisonous. Lead sulphite is made by precipitating a basic acetate solution with sulphur dioxide gas, or by subliming mixed lead and zinc ores with carbon, with a limited supply of hot air. Pattinson's white lead is an oxychloride of lead (PbClOH), made by precipitating a hot solution of lead chloride with one-half the quantity of milk of lime necessary for its complete decomposi- tion. The pigment has good body and color, but is not now used. . PIGMENTS 197 White zinc, or Chinese white, is zinc oxide (ZnO). It is made by distilling metallic zinc in tire-clay retorts, and leading the vapors into a flue through which air is drawn. On contact with the air, the hofc vapor at once inflames and burns to the oxide, which is collected in a series of settling chambers. Instead of the metal, calcined zinc ores may be mixed with carbon (e.g. coke), and heated in the retorts, the vapors being burned with air as before. But ores containing cadmium cannot be used, because cadmium oxide also sublimes, and being brown, discolors the product. The oxide is also formed by calcining zinc carbonate or hydroxide. The natural car- bonate, Smithsonite, is, however, seldom pure enough, and precipi- tated carbonate must be used. This is too expensive to compete with the combustion process. Zinc white is very permanent, and works well in water and in oil, of which latter it requires a very large amount, usually about 20 per cent of its weight. Zinc sulphide is sometimes substituted for zinc white. This has more body than the oxide. As a rule, pure sulphide is not used, but a mixture of sulphide and barium or strontium sulphate, ob- tained by precipitating a zinc sulphate solution with barium or strontium sulphide. This is calcined to convert part of the sulphide to oxide. If the vapors of zinc and sulphur are brought together, zinc sulphide is formed; it is collected in settling chambers from which the air is excluded. Zinc sulphide whites are permanent, have good body and color, and mix well with oil and with other pigments, excepting those con- taining lead or copper. Barytes, or barium sulphate, occurs native in large quantities. The mineral is finely ground, treated with hydrochloric acid or with sulphuric acid to remove iron, and then levigated. Precipitated barium sulphate (blanc fixe) is obtained as a by-product in some chemical industries, and is used to a considerable extent as a filler and pigment. It has more body than barytes. Barytes is very heavy, is not affected by sulphur nor other chemicals, and may be mixed with all pigments. It has little body, and does not work well in oil, having a streaky appearance when applied, and drying very slowly. Owing to its weight, one of its chief uses is to adulterate white lead. Gypsum, terra alba, or mineral white, is used to some extent as a pigment, especially for wall-paper printing. The mineral is simply ground, and treated with acid to remove the iron. Precipitated cal- cium sulphate is a by-product of many chemical operations, and is 198 OUTLINES OF INDUSTRIAL CHEMISTRY largely used as a filler in paper making, and for weighting cloth, under the names " Crown tiller " and " Pearl hardening." Whiting, or Paris white, is calcium carbonate. It is prepared by grinding and levigating pure chalk, which occurs in large deposits in England, France, and other countries. Precipitated calcium car- bonate is a by-product from many chemical processes. Whiting is much used to modify the shade of other pigments, and as the basis of whitewash. When mixed with from 15 to 18 per cent of linseed oil, it forms putty. Kaolin, or China clay (p. 180), is sometimes used to modify the shade, or to adulterate other pigments. Its chief uses as pigment are in wall-paper printing, and as filler in cloth and paper. BLUB PIGMENTS Ultramarine is the most important blue pigment. It occurs in nature as the mineral lapis lazuli, but in such small quantities, and the cost of preparation is so great, that this is of no importance as the source of the pigment. Ultramarine is probably a double silicate of sodium and alu- minum, together with a sulphide of sodium. But the composition varies in different samples having the same physical properties. The presence of sulphides seems necessary for the color, since, if treated with acid, hydrogen sulphide is evolved, and the color dis- appears. Numerous formulae have been proposed for ultramarine. Soda ultramarine, poor in silica, is 4 (Na 2 Al 2 Si 2 8 ) -f- N"a;>S 4 ; * that high in silica is 2 (Na 2 Al 2 Si 3 10 ) + Na 2 S 4 .* Soon after the introduction of the Leblanc soda process, blue spots, resembling natural ultramarine in color, were noticed in soda furnaces lined with siliceous material. This suggested the possi- bility of artificial ultramarine. In 1828, Guimet in France and Gmelin in Germany succeeded in making it. Guimet kept his method secret, but Gmelin published his. Afterwards, green, vio- let, and yellow ultramarine were discovered. A white ultramarine is supposed to be the basis of all others, and to it is assigned the formula: Na 2 Al 2 Si 2 8 4- NasS.* Green ultramarine is probably not a distinct chemical compound, but a mixture of ultramarines. None of the above ultramarines, excepting blue and green, have any commercial importance. The materials used for making ultramarines are China clay, sodium carbonate or sulphate, carbon, sulphur, and sometimes si- * Annalen der Chemie, 194, 1-22. R. Hoffmann. PIGMENTS 199 liceous matter. The purity of the material is very important as affecting the shade of the color ; iron is especially liable to make it dull. There are two methods of making it, the sulphate of soda, or indirect method, and the soda-ash, or direct method. In the sulphate method, kaolin, anhydrous sodium sulphate, and charcoal, or pure coal, are powdered and thoroughly mixed. The carbon is necessary to reduce the sulphate to sulphide. Some- times rosin is used as a reducing substance. The kaolin should contain 2 Si0 2 to 1 A1 2 3 , and be as finely powdered as possible. The mixture is packed in crucibles * having tight fitting covers, and is heated at a bright red heat for about 8 hours. The furnace is allowed to cool very slowly, care being taken that no air has access to the contents of the crucibles. When cold, the mass is dull green and porous, and when ground and washed constitutes the ultrama- rine green of commerce. It is obtained by this process only. To make the blue ultramarine, the green powder is subjected to a " coloring " process. It is spread in shallow trays in layers about 1 inch deep, and sprinkled with powdered sulphur. On heating, the sulphur ignites, and is allowed to burn itself out with access of air. Sometimes muffles are used, the sulphur being added in small quan- tities at a time, and the charge stirred with mechanical stirrers dur- ing heating. A part of the sodium sulphide is probably changed to the sulphate or other soluble salts, and the crude blue results. It is powdered and washed to remove soluble salts (]S"a 2 S0 4 , Na 2 S0 3 ), and sometimes boiled with a sodium sulphide solution to remove any free sulphur, which is injurious to the copper print rolls in cal- ico printing. It is then ground and levigated, the different grades being used for different purposes. The shade is usually modified to match certain standards, by blending several lots of colors. The soda-ash, or direst method, yields blue ultramarine at one heating, which may be done in muffles or in crucibles. The usual charge is about 2^- tons, and consists of soda-ash, kaolin, charcoal, and sulphur, ground fine and packed firmly on the floor of the muf- fle, forming a layer about 14 inches thick. A layer of tiles, luted together with clay, is placed on top of the charge, and the front of the furnace is bricked up, a loose brick being left so that samples may be taken out to determine the time of heating. The process is very slow, requiring 3 or 4 weeks, of which 10 or 12 days are required for the slow cooling of the muffle ; during all this time great care is * In modern plants, muffle furnaces are replacing the crucibles for making the green ultramarine. But these must be built very carefully to exclude the air; then they need much time for cooling, usually requiring 10 days or more. 200 OUTLINES OF INDUSTRIAL CHEMISTRY necessary to exclude the air. The mass forms two layers, one bright blue, and the bottom greenish blue. These are separated, washed and levigated. By using large crucibles instead of the muffle, the time of heating is reduced somewhat, but the breakage and extra labor more than offset the gain. To make an ultramarine which is less sensitive to acids, and which will withstand the alum used in paper making, a high per- centage of silica in the pigment is necessary. For such a product, it is customary to use the soda process, and to add powdered quartz, sand, or diatom aceous earth to the charge. The first heating is very important in all processes of making ultramarine blue ; about 700 C. is the proper temperature. If over- heated, the mass may fuse. Exclusion of air is necessary to prevent oxidation and loss of sulphur, which causes the product to turn dull green, brown, or gray. Ultramarine blue is much used in wall-paper and calico printing ; for neutralizing the yellow color in paper pulp, crystallized sugar, and cotton and linen goods ; for laundry blue ; for paint; for printers' ink ; and for coloring mottled soaps. It is a very fast color to light, soap, and alkalies, but is quickly destroyed by even weak acids. Ultramarine violet is made by heating the blue, rich in silica, to 175 C., in an atmosphere of chlorine and steam. Some of the sodium is thus converted to salt, and removed by washing. The violet may also be formed by heating the blue to about 200 C., with 2 or 3 per cent ammonium chloride, in the presence of air. It is not much used, as it has little tinctorial power. Ultramarine red is made by heating the blue to not over 145 C., in an atmosphere of dry hydrochloric acid gas, or in the vapors of nitric acid. It is of but little importance. Prussian blue, or Berlin blue, is the ferrocyanide of iron (ferric- ferrocyanide), Fe 4 5Fe(CN) 6 ( 3 . To make it, a dilute solution of cop- peras (FeS0 4 7 H 2 0), acidified with sulphuric acid, is precipitated with potassium ferrocyanide solution. After decanting the liquor the white precipitate of ferrous-ferrocyanide is oxidized with nitric acid, or with bleaching powder and hydrochloric acid. Exposure to the air also causes oxidation, but the color thus obtained is not so good. Chinese blue is a very pure and carefully prepared Prussian blue. In order to lighten the shade, and to make the pigment easier to grind, a certain amount of alum is added to the copperas solution before precipitating. PIGMENTS 201 A blue which is soluble in water results if the iron solution is poured into the ferrocyanide solution in a slow stream, or if Prus- sian blue is boiled in a ferrocyanide solution. In both cases, the ferrocyanide must be in excess. Prussian blue is not affected by acids, and mixes well with oil, but fades a little on exposure to the light. The color is destroyed by alkalies, and consequently it cannot be mixed with any sub- stance having an alkaline reaction. It has great tinctorial power, but is transparent, and lacks body. It is dissolved by oxalic acid, yielding a blue solution, formerly much used for blue ink. TurnbulTs blue, a deep reddish blue precipitate, is obtained by precipitating a ferrous salt with potassium ferricyanide, [K 3 Fe(C]SI") 6 ], instead of the ferrocyanide. This is similar to Prussian blue. Smalt is a potash-cobalt glass, made by fusing pure sand and potash with cobalt oxide (Co 2 3 ), in a furnace similar to a glass fur- nace. The crude cobalt oxide, called " zaffre," is made by carefully roasting smaltite (CoAs 2 ), cobaltite (CoAsS), or cobalt-nickel py- rites [(CoM) 2 S 3 ]. The ore is carefully sorted by hand, and iron pyrites and other impurities removed ; then it is ground and some- times levigated, and roasted in a reverberatory furnace. A large part of the arsenic and sulphur passes off as oxides. The arsenic trioxide (As 2 3 ) is condensed in long flues or chambers, while the sulphur dioxide escapes to the chimney. A small amount of the sulphur and arsenic is left in the zaffre to combine during the fu- sion, with the iron, copper, nickel, and other injurious metals, forming a speiss, which, being heavier than the glass, settles to the bottom of the pot. The blue glass is refined (p. 172) until all the impurities have settled, and is then ladled out into water. This granu- lates it, and the sand so formed is ground under edge-runners and levigated. The medium fine deposit is the best grade, the finest being too light-colored. The coarse and the very fine are usually remelted. Smalt is a very permanent color, fast to light, and not affected by acids nor alkalies. But it does not work well as a paint either in oil or in water, and is expensive; hence it is now largely replaced by ultramarine. Imitation smalt is sometimes made of sand, colored with ultra- marine. A simple test with acid detects this at once. Prussian blue is shown by treating with alkali. The composition of commercial smalt varies much ; it may con- tain from 2 to 16 per cent of cobaltous oxide (CoO), but it is often difficult to get a good test for the cobalt. 202 OUTLINES OF INDUSTRIAL CHEMISTRY Cobalt blue is made as follows: alumina is heated to a red heat in a crucible with basic cobalt phosphate, made by adding sodium phosphate to a cobalt nitrate solution. Alum and sodium carbonate solutions are mixed, and aluminum hydroxide precipitated. These two products are thoroughly washed, and one part cobalt phosphate is mixed with 8 parts aluminum hydroxide, and the mixture heated to a red heat for three-quarters of an hour, or until the blue color develops. The pigment is then ground wet, washed, and dried. This yields a good oil color. Copper blues are not very important. Mountain blue is the ground mineral azurite, a hydrated copper carbonate (2 CuC0 3 , Cu(OH) 2 ). Bremen blue is a copper hydroxide containing some copper car- bonate and oxychloride. A mixture of common salt, copper sul- phate, and metallic copper in small pieces is kept in tubs for several weeks, being well stirred frequently. A paste of green oxychloride is formed, which is washed free from all soluble salts. A small quantity of hydrochloric acid is then added, and left for several hours. Finally, a solution of caustic soda is added, and thoroughly mixed until the paste acquires a blue color. After washing well and drying, it is ready for use. The copper blues are altered somewhat by exposure to the weather. They are readily darkened by hydrogen sulphide or sul- phur fumes, so cannot be mixed with pigments containing sulphur. They dissolve in acids and in ammonia, and become black when heated, owing to the formation of cupric oxide (CuO). They are opaque in water, but become slightly transparent in oil and lose body. They are at best a greenish blue. Indigo is an organic substance (p. 466) somewhat used as a pig- ment in calico printing. GREEN PIGMENTS Ultramarine green is not very largely used as a pigment. Its preparation is described on p. 199. True Brunswick green is the oxychloride of copper, made by allowing metallic copper to stand for a number of weeks in a solu- tion of common salt which contains sulphates. The insoluble pig- ment is washed through a sieve to remove copper chips, and then dried at a low temperature to prevent decomposition. It is a good PIGMENTS 203 pigment, working well with oil, and having a fair coloring power ; but the color is rather pale. The pigment now sold under the name of Brunswick green is generally a mixture of Prussian blue, chrome yellow, and barytes, the proportion of each depending on the shade desired. These greens are prepared by the dry or the wet methods. In the former, the dry ingredients are mixed in a paint- or edgestone-mill. But the shade is inferior to that produced by the wet method. In this, copperas (FeS0 4 7 H 2 0), lead acetate, barytes, and potassium ferrocyanide and bichromate are used. The iron and lead salts are dissolved separately, and mixed while stirring in the barytes ; some lead sulphate is thus precipitated also. Then, while still stirring actively, the mixture of potassium ferrocyanide and bichromate solu- tion is added. After a few moments further stirring, the pigment is allowed to settle, and the liquor is decanted. Then the precipitate is washed by decantation, filtered, and dried carefully. Or the dry ingredients are finely powdered in an edgestone-mill, and then stirred up thoroughly with water in a tank until, on settling, the liquor is nearly colorless. The precipitate is washed as above described. These greens are sometimes sold under the names Victoria, Prus- sian, or chrome green. They work very well in oil, have good cov- ering power, and are fairly permanent ; but they cannot be mixed with pigments containing sulphur or alkaline substances, nor used where exposed to hydrogen sulphide gas. Alkalies act both upon the Prussian blue and the chrome yellow, causing them to turn red or brown. Sulphur darkens the chrome yellow. Chrome greens are valuable pigments, having a light yellowish green color. The basis is chromic oxide (Cr 2 3 ). By precipitat- ing a solution of a chromic salt with soda, chromium hydroxide [Cr(OH) 3 ] is obtained. This is washed, dried, and calcined at a red heat, until the water is expelled, and chromic oxide results. Gnignet's green * is a chrome green made in the dry way. A mixture of 3 parts potassium bichromate with 8 parts boric acid is heated to dull redness in a reverberatory furnace for four hours. The porous mass is then washed, ground, and dried. In composi- tion, this green is a hydrated chromic oxide, containing a very small quantity of boric acid. A chromium borate is formed by the calci- nation, which is decomposed by the water, forming hydrated chro- * Bulletin de la Societe de Paris, 1, 9. Guignet, Fabrication des Couleurs, 149-153. 204 OUTLINES OF INDUSTRIAL CHEMISTRY mic oxide (Cr 2 3 2 H 2 0), or Cr 2 0(OH) 4 , and regenerating boric acid. Guignet's green is permanent, mixes well with oil and with all other colors, and has good covering power. It is one of the most valuable pigments. Chrome greens, consisting of chromium phosphate, are sometimes made by boiling potassium bichromate with sodium phosphate arid a reducing agent. These are not so good as the oxides, and have paler shades. Copper greens containing only copper salts are of little impor- tance. Only two need be considered here. Mountain green, malachite, or mineral green is a basic copper carbonate [CuC0 3 , Cu(OH) 2 ], occurring as the mineral malachite, which is much used for ornamental bric-a-brac and lapidary work. When ground very fine, it is sometimes used as a pigment, and is permanent in the light, mixes well with oil, and has fair covering power. It is blackened by hydrogen sulphide. An inferior imita- tion of the natural product is made by precipitating copper sulphate solution with sodium or potassium carbonate containing a little white arsenic (As 2 3 ). Verdigris is not of constant composition, but is a basic copper acetate, corresponding nearly to the formula [2 Cu(C 2 H 3 2 ) 2 + CuO]. It is sometimes made by covering copper plates in heaps of the residue from wine presses. Fermentation of the mass produces acetic acid, which, together with the moisture, forms a layer of ver- digris on the copper. This is scraped off, washed, and levigated. A better product is obtained by wetting cloths in vinegar or in pyro- ligneous acid, and spreading them between the copper plates. Ver- digris is not a good pigment, being altered by moisture and light. By dissolving copper oxide, or carbonate, in acetic acid, and evaporating the solution, a crystallized salt having the composition Cu(C 2 H 3 2 ) 2 , Cu(OH) 2 - H 2 0, is obtained, which is called "distilled verdigris " in trade. This, however, is not a pigment. Copper and arsenic greens surpass all others in brilliancy and beauty, but, being exceedingly poisonous, cannot be used for many pur- poses. Scheele's green, which is chiefly copper arsenite (HCuAs0 3 ), is made by dissolving arsenious acid in a hot solution of potassium carbonate, and pouring the liquid into a solution of copper sulphate. The precipitate is carefully washed and dried. It is a grass-green pigment, having little coloring power, and now seldom used. PIGMENTS 205 Paris, or emerald green is an acetoarsenite of copper, [Cu(C 2 H 3 2 ) 2 Ci^As 2 0^7 prepared by adding a thin paste of verdigris in water to a boiling solution of arsenious acid in water ; some acetic acid is then added, and the mixture boiled until the precipitate is of the desired shade ; or the color will develop by simply allowing the mixture to stand for some days. By Galloway's process, sufficient sodium carbonate is added to a copper sulphate solution to precipitate one-fourth of the copper. Then acetic acid is added until the precipitate is just redissolved, and the liquid is heated to boiling. A hot solution of sodium arsenite (arsenious acid dissolved in sodium carbonate) is then added, and the mixture well stirred. The green precipitate is filtered, washed, and dried at a low temperature. For the finest pigment, the solutions should be dilute. Paris green has a peculiar light green shade possessed by no other pigment. It is permanent, works well in oil, and has a good covering power. But owing to its poisonous character its use as a pigment is much restricted. Nearly the whole of the present pro- duction is used to exterminate potato beetles and other insects inju- rious to vegetation. Terra verde is an earthy pigment, containing ferrous silicate as its chief ingredient. Green earths are found in numerous places, but the best are from Cyprus and Italy. They are a dull pale green, and are permanent, but have little covering power. YELLOW PIGMENTS The most important yellow pigments are chrome yellows and yellow ochres ; others are used but little. Chrome yellows have as a basis the chromate of lead, zinc, or barium ; are all made by precipitation and each has a shade peculiar to itself. Lead chromate is made from the lead acetate, or nitrate, and potassium bichromate. The reactions are as follows : a) 2 Pb(C 2 H 3 2 ) 2 +K 2 Cr 2 7 +H,0= 2KC 2 H 3 2 +2C 2 H 4 2 +2 PbCr0 4 . 6) 2 Pb(N0 3 ) 2 + K 2 O 2 7 + H 2 = 2 KN0 3 + 2 HN0 3 + 2 PbCr0 4 . In order to modify the shade, lead, barium, or calcium sulphate is mixed with the chromate in the grinding-mill. Or a portion of the lead is precipitated as sulphate or carbonate along with the chro- mate j this is done by mixing sodium carbonate or sulphate with the 206 OUTLINES OF INDUSTRIAL CHEMISTRY potassium bichromate. Chrome yellows are called "pure" when lead sulphate has been used to modify the shade. The precipitate is well washed by decantation, and the pulp freed from water in the filter press, or in a centrifugal machine, or by pressing in cloth bags. It should be dried at a low temperature, and well ground either dry or in oil. For the best color, the lead nitrate should be used in slight excess. When lead nitrate is used in making the chromate, it is customary to recover the potassium nitrate from the liquor and first wash-waters, the free nitric acid being neutralized with pearlash before evaporating. The excess of lead salt is precipitated from the waste liquors on the addition of .the pearlash. Chrome yellow is sometimes made by digesting lead sulphate with a hot solution of potassium bichromate until the desired shade is developed. Lead chromate is a brilliant yellow, mixes well with oil, and has great covering power. It is blackened by hydrogen sulphide, and should not be mixed with pigments which contain sulphur, or are strongly alkaline. When treated with a caustic alkali, lead chro- mate is converted into a basic salt, having a red or orange color. These basic chromates are prepared for pigments, and sold under the name of chrome orange and chrome red. They are made by boil- ing chrome yellow with calcium or sodium hydroxide. The follow- ing is the reaction involved : 2 PbCr0 4 + 2 NaOH = Na 2 Cr0 4 + PbCr0 4 , PbO - H 2 0. Quicklime gives a paler color than caustic soda. Chrome red is also made by digesting white lead with potassium bichromate and caustic soda. Zinc chromate is made from zinc sulphate and neutral potassium chromate. Bichromate cannot be used because of the ready solubil- ity of the zinc chromate in free acids. But if the solution is alka- line, zinc hydroxide is precipitated also, hence the method needs much care. Zinc chromate is also made by boiling zinc oxide with potassium bichromate. The pigment has a light lemon color, and is permanent. It is not affected by sulphur, and can be mixed with other pigments. It is very soluble in mineral acids, and is decom- posed by caustic alkalies. Barium chromate is much like the zinc salt, but is a greenish yellow color. It is made in the same way as is the zinc chromate, but from barium chloride. It is not used to any extent. PIGMENTS 207 Yellow ochres and Siennas are natural mineral products, varying from bright yellow to brown. The color is due to hydrated oxide of iron, and in Sienna there is a little manganese oxide. The pigments contain sand and clay in large quantities, and are decomposition products from iron-bearing minerals. The Siennas are usually finer grained and contain less gangue mineral than the ochres. They occur in beds in the earth, and the only preparation necessary is grinding and levigating. They are very permanent, mix well with oil and with other pigments, have good covering power, and are cheap. If ochres and Siennas are calcined, the water of hydration is removed from the ferric hydroxide, and the color becomes orange or red. Burnt Sienna, made by heating raw Sienna to a low red heat, is reddish orange in color. Cadmium yellow is cadmium sulphide (CdS), and is made by precipitating a cadmium solution with hydrogen sulphide. If the solution is strongly acid, the color becomes more nearly orange. It is a brilliant yellow, very permanent, and mixing well with oil and with other pigments, excepting lead and copper compounds. It is chiefly used as an artist's color. Sometimes cadmium yellow is made by using ammonium sulphides instead of hydrogen sulphide to precipitate the pigment ; but in this case free sulphur is present in the precipitate, and causes changes in the color when mixed for use. Orpiment is arsenic trisulphide (As 2 S 3 ). It is found native as a mineral, which is simply ground for pigment. It is also extensively made by precipitating a dilute solution of arsenious acid in hydro- chloric acid with hydrogen sulphide ; or by subliming a mixture of arsenious acid and sulphur from a retort. The pigment obtained by either method is finely ground. Orpiment is a very bright yellow, mixes well with oil, and has good covering power ; but it is not permanent on exposure to light, and cannot be mixed with many other colors. It is also very poison- ous. It is sold under the name of royal yellow, or king's yellow. Litharge is lead monoxide (PbO), and is made by oxidizing metal- lic lead at a temperature so high that the oxide formed is melted. This is collected in pots, and cooled slowly. Part of the product separates as a flaky mass, and the remainder forms a hard cake, which is ground and levigated, and forms a buff-colored powder. It is not so important as a pigment as for the preparation of 208 OUTLINES OF INDUSTRIAL CHEMISTRY "boiled linseed oil," p. 308. It is also extensively used in mak- ing lead glass and pottery glazes. Another variety of lead monoxide, having a lighter yellow shade, is " massicot," which is formed by oxidizing lead at so low a temper- ature that no fusion of the product takes place. It is chiefly pre- pared for the manufacture of red lead (p. 209). Yellow lead oxide is also made by heating white lead. Gamboge is a gum-resin obtained from a tree (Gardnia Morella, Desr.) of Siam. Incisions are made in the bark of the tree, and the sap is collected in bamboo receivers, in which the yellow resin is left on evaporation. Gamboge emulsifies with water, and is used as a water-color paint. It cannot be used as an oil paint except when mixed with alumina. Indian yellow, or purree, is made by heating the urine of cattle that have been fed with leaves of the mango tree, the color being produced by an excessive secretion of bile, which has passed into the urine. The pigment precipitates, and is pressed and dried ; it consists of salts of euxanthic acid, an organic body. It is a bright yellow, but not permanent in the light, and is very expensive. ORANGE PIGMENTS Orange mineral is lead tetroxide (Pb 3 4 ), prepared by heating white lead in the presence of air. It is usually made from the scum which collects on the surface of wash-waters used in levigating white lead. 2 PbC0 3 , Pb(OH) 2 + = Pb 3 4 + 2 C0 2 + H 2 0. In composition and properties it is similar to red lead (p. 209), but has a slightly lower specific gravity (6.95). Chrome orange has been described in connection with chrome yellow, p. 206. Antimony orange is antimony trisulphide, made by precipitating a moderately concentrated solution of antimony chloride with hydro- gen sulphide. The precipitate is washed in dilute hydrochloric acid, and then levigated. It must be dried at a low temperature. It has a bright orange color in oil or water, is permanent and of good body, but is decomposed by alkalies. It is chiefly used for vulcanizing rubber, producing the red " antimony rubber " of com- merce. PIGMENTS 209 RED PIGMENTS Bed pigments form a numerous and important group, containing some of the brightest and most permanent colors. Red lead is lead tetroxide (Pb 3 4 ), having the same chemical composition as orange mineral (p. 208), but differing in its physical properties. It is made by the direct oxidation of metallic lead. The process is carried on in two stages. In the first or " dressing " operation the lead is converted into massicot by heating with free access of air in a reverberatory furnace to a temperature just above that of melted lead (340 C.). The temperature must be very care- fully regulated, for if the massicot melts it passes into ordinary litharge, from which red lead cannot be made. As fast as a layer of oxide forms it is pushed to the back of the hearth with a " rabble " ; finally, the unoxidized lead is allowed to run off, and the massicot is raked out and cooled. It is pale yellow, of granular texture, and contains pellets of unoxidized lead. It is finely ground and levi- gated, and then transferred to the second or " coloring process " ; it is heated to a dull red heat in a muffle or reverberatory furnace with access of air. The mass is stirred frequently to assist the absorp- tion of oxygen, and to develop the color. Samples are taken at inter- vals, until the desired shade is obtained, which usually takes from 40 to 48 hours ; then the furnace is allowed to cool. The product is usually ground before packing for market. Red lead is somewhat variable in color, but is a good pigment of great covering power and brilliancy. It has a specific gravity of 8.5. Chemically, it is regarded as a mixture of lead monoxide and peroxide (2 PbO -f Pb0 2 ), but commercial samples vary some from this formula. When treated with dilute nitric acid, the monoxide dissolves, leaving the peroxide as a brown powder ; this constitutes a test for red lead, since no other red pigment turns brown with nitric acid. The chief use of red lead is for glass making, for which a very pure grade is necessary. Owing to its oxidizing effect with linseed oil, it is extensively used, mixed with this oil, as a lute in plumbing and gas fitting. It is also valuable as a painter's color. Chrome red is a basic lead chromate (PbCr0 4 , PbO H 2 0), made by boiling chrome yellow with caustic soda or with lime, as described on p. 206. It is also made by boiling white lead with a solution of neutral potassium chromate. When the desired shade is developed, the pigment is washed, ground, and levigated. 210 OUTLINES OF INDUSTRIAL CHEMISTRY It is a fairly bright red, of good body, working well in oil. Like all lead pigments, it is darkened by sulphur and hydrogen sul- phide. It is sold as Chinese red, American vermilion, and Victoria red. An imitation of chrome red is made by coloring white lead with some of the coal-tar dyes, especially with eosins. Red ochre is made by calcining ordinary ochre at a low red heat until more or less of the water of hydration is driven off. The shade depends on the time of heating, the longer the calcination the more purple the product. Red ochres are essentially ferric oxide with alumina, silica, and lime. The native oxides, hematite and limonite, are seldom used for pigment, being hard to grind. But in a few places soft deposits of hematite are found, which yield a pale red pigment without further treatment than grinding. These ochres are sold as Indian red, light red, Venetian red, etc. Iron reds are now being prepared in large quantities, chiefly as by-products from other manufactures. These are sold as rouge, colcothar, Venetian red, etc., and all contain ferric oxide as the col- oring matter. When fuming sulphuric acid is made by the dry distillation of copperas (p. 60), a residue of ferric oxide remains in the retort. This is ground, levigated, and sold as colcothar. It is nearly pure Fe 2 3 . In the manufacture of galvanized iron or tinned ware, the rolled sheet iron is dipped into a bath of acid to dissolve any oxide from its surface before putting it into the bath of melted zinc or tin. These acid " dipping liquors " contain much iron, which is precipi- tated by adding soda-ash or lime, and used as pigment. If sulphuric acid is used in the dipping liquors, and is neutralized with lime, the precipitate consists of ferric hydroxide, with more or less calcium sulphate. By calcining, a light red pigment, called Venetian red, is formed. Many metallurgical operations yield liquors containing much iron, which is precipitated with lime, forming Venetian red. These iron reds are very permanent, and valuable pigments. They work well in oil, mix with all other pigments, have very good body, and are cheap, but the color is not so bright as in some pigments. Vermilion is mercuric sulphide (HgS). It occurs in nature as the mineral cinnabar, but the pigment is now all made artificially. PIGMENTS 211 It is one of the brightest reds, and has been known for a long time. It is made in two ways, by the wet and by the dry process. In the wet process, 100 parts of mercury are ground with 38 parts of flowers of sulphur until thoroughly incorporated ; then the mass is digested at about 45 C., with a solution of 25 parts caustic potash in 150 parts water. The mixture is stirred frequently, and any water lost by evaporation is replaced. After 2 or 3 hours the mass be- comes brown, and then gradually turns red. When the desired color is acquired, which usually takes about 8 hours, the pigment is at once washed by decantation, since further action of the potash dulls the color. The pigment is ground, and dried carefully. The temperature must be kept between 40 and 45 C., for if over-heated it becomes brown. Solution of potassium or sodium polysulphide may be used instead of the potash. The brilliancy of the color may be increased by treating with hydrochloric or nitric acid. The dry methods yield the best product. The Dutch process con- sists in heating mercury and sulphur together in shallow iron pans until they combine to form a black mercuric sulphide (HgS, ethiops mineral). This is pulverized, and introduced into earthenware re- torts in small amounts at a time. The larger part of the black sul- phide sublimes into the upper part of the retort as a bright red powder. This is ground, washed, treated with acid, and levigated. Chinese vermilion is the finest quality, and its manufacture was long kept a secret. Now it is known to be made by a process simi- lar to the Dutch method, but owing to the patience and care exer- cised by the Chinamen a very fine product is obtained. Vermilion is a very heavy, opaque, and brilliant pigment. Owing to its weight, it settles out of the oil when used for paint, causing difficulty in applying it evenly. It is permanent, and not readily affected by acids and alkalies. When heated in a closed tube it turns black, and finally sublimes unchanged, thus furnishing a good test for its purity. It is sometimes adulterated with red lead, iron reds, or carmine lakes, but these leave a brown or black residue when heated. Vermilion is very expensive. Vermilionettes are brilliant red pigments, produced by coloring neutral white bodies, such as barium sulphate, lead sulphate, or white lead with coal-tar dyes of the eosin class. The white base is stirred up with a solution of the dye, and lead acetate or alum is added, which precipitates the color upon the white base. Orange mineral is sometimes mixed with vermilionettes to brighten the color. These work well in oil, have good body, and are brilliant, but fade on exposure to the light. 212 OUTLINES OF INDUSTRIAL CHEMISTRY Realgar, the disulphide of arsenic (As 2 S 2 ), occurs in nature in small quantities as a brilliant red mineral which, when ground, fur- nishes a fine pigment. But the chief supply is obtained artificially by fusing together white arsenic (As 2 3 ) and sulphur in the proper proportions, or by distilling arsenical ores with sulphur. The crude product is remelted, and arsenic or sulphur added, as need be, to give the desired shade. As a pigment, realgar is subject to the same disadvantages as orpiment (p. 207). It is much used, however, in preparing " Bengal lights/' and for unhairing hides for tanning. Antimony red, or antimony vermilion, is an oxysulphide of antimony, made by precipitating an antimony chloride solution with thiosulphate of soda. On heating the solution to 55 C., a red precipitate separates. This is washed and dried at about 50 C. It is also prepared by dissolving tartar emetic in tartaric acid solu- tion, mixing with sodium thiosulphate, and heating to 90 C. Antimony red is used for oil and water colors, and to some ex- tent in calico printing. It has good body, and is permanent if not mixed with alkalies or with alkaline vehicles. Carmine pigment belongs to the class of pigments called " lakes," which are metallic salts of organic color acids. The coloring matter in carmine is the organic substance carminic acid (C 17 H 18 10 ), ob- tained from the bodies of the cochineal insect. The lake is pre- pared by extracting the crushed insects with hot water, filtering, and adding a solution of alum or tin chloride, and cream of tartar. After standing, the pigment precipitates. Or the lake may be pre- cipitated at once by adding sodium carbonate to the mixed solutions. The extraction is done in tinned copper vessels, and hard water is said to improve the color of the pigment. Carmine is a very bright scarlet, the tin salt being brighter than the aluminum. It works well in oil and as a water color, but fades on exposure to sunlight. It is soluble in strong caustic alkalies. Cochineal lake, crimson lake, Florentine lake, and others, are car- mine lakes, containing a larger proportion of alumina or metallic base than does carmine. Madder lakes and Brazil-wood lakes are prepared by precipitat- ing extracts of these substances with alum and tin, by adding so- dium carbonate. They furnish red pigments of various shades, but lacking in coloring power. PIGMENTS 213 Yellow lakes are made from fustic, Persian berries, or quercitron bark extracts, in the same way as the madder lakes are made. Many of the coal-tar dyes may be precipitated as lakes, and a great number of pigments are thus prepared. But many of them are deficient in covering power, and lack permanency on exposure to the light. BROWN PIGMENTS Umbers are ochres containing more manganese than Sienna con- tains. They are complex mixtures of silica, alumina, iron, man- ganese, lime, and other matter. There are two varieties, raw and burnt. Eaw umber has received no f urthur treatment than grinding and levigating. Burnt umber has been calcined at a low, red heat, whereby more or less of the water of hydration of the iron oxide has been driven out, giving a darker shade to the product. The best umber comes from Cyprus, but many other localities furnish it in various shades. It is very permanent, has good covering power, and mixes well with all other pigments. It is not affected by acids nor alkalies, and is very cheap. Vandyke browns are indefinite mixtures of iron oxides and or- ganic matter. They are obtained from certain bog-earth or peat deposits, or from ochres containing bituminous matter. They are also made artificially from charred organic substances, such as bark, cork cuttings, or bone dust. Mixtures of lampblack, yellow ochre, and iron oxide are also sold as Vandyke browns. These pigments are permanent, mix well with all other colors, and have good body. Sepia is an organic pigment obtained from the cuttle-fish (Sepia officincdis), that secretes it as a dark liquid, to be discharged in the water to hide his movements when disturbed. It is contained in a small sac, which is removed and dried. To purify the pigment, it is dissolved in caustic soda, and the decanted solution is acidified with hydrochloric acid. The pigment thus precipitated is washed and dried. Sepia is a dark brown, fine grained pigment, very permanent and capable of mixing with all other colors. It is chiefly used as a water color by artists. BLACK FIGMENTS Black pigments nearly all contain carbon as the base. The most important is lampblack, which is the soot produced by the incom- 214 OUTLINES OF INDUSTRIAL CHEMISTRY plete combustion of organic substances, for the most part, of an oily or resinous nature. The knots and other refuse from pitch pine and hemlock, the crude mineral oils, residues from petroleum refin- ing, and the " dead oils " from coal-tar distillation furnish most of the lampblack. The burning is conducted at so low a temperature, and with such a limited supply of air, that only the hydrogen of the hydrocarbons is consumed, the carbon depositing as soot in a series of chambers, through which the combustion products are led. Some oil is apt to distill into the first chamber, mixing with the lampblack, which is then not good for paint, as it dries very slowly ? and is dangerous to store on account of its liability to spontaneous combustion. Sometimes natural gas flame is directed against cold iron plates, the sudden reduction of temperature causing a separation of carbon, which deposits on the plates. Lampblack is a very fine grained pigment, permanent, and of great covering power. It is difficult to mix with oil or with water, and dries very slowly. It is largely used for printing-ink. Ivory-black is made by heating the refuse from ivory working in closed retorts until all organic constituents are decomposed. The retorts must not be opened until quite cold. The charred mass is ground very fine, and yields the finest quality of black pigment. It is an intense black, but since it acts like bone-char on organic coloring matter, it cannot be mixed with most pigments of an organic nature. Bone-black is an inferior black, made from bones charred in a retort. When coarsely pulverized, it is extensively used for decol- orizing syrups and oils. It is finely powdered for pigment, and is much used in making leather blacking, where the calcium phosphate and carbonate in it are also of importance. Charcoal from soft wood, ground very fine, is sometimes used as a pigment, and to mix with other blacks. It is not so soft and fine as lampblack. Graphite is employed as a pigment in pencils, crayons, and in stove-blacking. It also forms the basis of a protective paint for metal. It is a dull black, very inert and permanent. Manganese ores, such as pyrolusite (Mn0 2 ) and hausmannite (Mn 3 4 ), are sometimes powdered for pigments. But they act as " dryers " when used with oil, and are rarely used in paint. Black lake, made from logwood decoction and potassium bichro- mate with copper sulphate, is a blue black, but not permanent. Tannate of iron blacks, derived from tannin liquors, copperas, and alum, also fade on exposure to the light. BROMINE 215 REFERENCES Lehrbuch der Farbenfabrikation. I. G. Gentele, Braunschweig, 1880. (Vie- weg u. Sohn.) Die Erd- Mineral- und Lackfarben. Dr. Mierzinski, Weimar, 1881. (Voigt.) Chemistry of Pigments. J. M. Thomson. Lecture before the Society for the Encouragement of Arts, Manufactures, and Commerce. London, 1885. (W. Trounce.) Fabrication des Couleurs. Ch. Er. Guignet, Paris, 1888. Oel und Buchdruckfarben. Louis E. Andes, Leipzig, 1889. (Hartleben.) Die Fabrikation des Ruses und der Schwaerze. Dr. H. Koehler, Braunschweig, 1889, ( Vie wegu. Sohn.) The Chemistry of Paints and Painting. A. H. Church, London, 1890. (See- ley.) Painters' Oils, Colours, and Varnishes. George H. Hurst, London, 1$92. (Griffin and Co.) Pigments, Paints, and Painting. George Terry, London, 1893. (Spon.) Die Fabrikation der Mineral- und Lackfarben. Dr. Josef Bersch, Leipzig, 1893. (Hartleben.) Die Fabrikation der Erdfarben. Dr. Josef Bersch, Leipzig, 1893. (Hartleben.) Handbuch der Farben-Fabrikation. Dr. S. Mierzinski, Leipzig, 1898. (Hartle- ben.) Das Ultramarine. C. Furstenau, Wien, 1880. (Hartleben.) Journal of the Society of Chemical Industry. 1887, 719. Rawlins. (Ultramarine.) 1890, 1137. Wunder. (Ultramarine.) 1891, 709. C. O. Weber. (Chromium Pigments.) Journal of American Chemical Society, 1880, 381. H. Endemann. BROMINE Bromine is widely distributed in nature as bromides, usually accompanying common salt and magnesium chloride. The world's supply is obtained from "bittern," the mother-liquor of the salt industry. Stassfurt furnishes about two-thirds of the supply, and nearly all the remainder is extracted from the brines found in Ohio, West Virginia, and Kentucky, along the Kanawha and Ohio rivers. The American product in 1893 was about 348,000 pounds. Small quantities are obtained from the mother-liquors of the Chili salt- petre industry, and in Europe from kelp. Bromine is present in the bittern as magnesium bromide, and to a lesser extent as sodium bromide. Associated with these are large quantities of magnesium and sodium chlorides. There are two gen- eral methods of extracting bromine from bittern, the continuous process, chiefly used at Stassfurt ; and the periodic process, generally used in this country. 216 . OUTLINES OF INDUSTRIAL CHEMISTRY The continuous process depends on the decomposition of the magnesium bromide by chlorine gas. A sandstone or earthenware tower is filled with broken brick or burned clay balls ; chlorine gas and steam are introduced at the bottom of the tower, and rising between the balls, meet descending streams of hot bittern. By reac- tion between the chlorine and the magnesium bromide, the bromine is set free. The chlorine stream must be regular, and so controlled that no excess is used j otherwise some bromine chloride is formed. Part of the bromine dissolves in the liquor as soon as set free, and this liquor flows into a special receiver, heated by steam ; here it is boiled to drive out the bromine, which, together with water vapor, passes bac^: into the tower, entering at the bottom, and mixing with the chlorine. At the top of the tower, the bromine vapor passes out into an earthenware worm-condenser, which empties into a closed vessel. An outlet pipe from the top of this receiver passes into a small tower, filled with moist iron turnings or scrap iron. Any uncondensed vapors of bromine, passing out of the receiver, combine with the iron to form ferrous bromide, which is used for making potassium bromide. In this process, any bromine chloride formed in the tower is decomposed before it can pass into the condensing worm, by the fresh bittern entering at the top of the tower. Bromine chloride is a very volatile liquid, and would contaminate the bromine. The exhausted bittern from the heating-vessel goes to waste. The chlo- rine gas necessary is made in special stills from manganese binoxide and hydrochloric acid. The periodic process depends on the following reaction : MgBr 2 + 2 H 2 S0 4 + Mn0 2 = MgS0 4 + MnS0 4 + 2 H 2 O + 2 Br. This is carried on in sandstone stills, heated by steam. A charge of pyrolusite, sufficient for several days, is put into the still, and the bittern, heated to 60 C., is run in. The quantity of sulphuric acid to be added is very carefully gauged with each charge of bittern in order that none of the magnesium chloride shall be decomposed. Usually, a little of the magnesium bromide is left in the bittern, since the high temperature necessary to decompose the last traces would also decompose some of the chloride, which would form bro- mine chloride, and contaminate the product. The bromine distills over into a condensing worm, as above described. The exhausted bittern is drawn off after each charge, and goes to waste. At the present time, considerable potassium chlorate is used instead of pyrolusite for the oxidizing agent. This is especially advantageous BROMINE 217 if the bittern contains much calcium chloride, since only one-half as much sulphuric acid is necessary, and there is, consequently, less difficulty from calcium sulphate: Neither the stills nor the tower should be lined with pitch or tar, since these substances absorb much bromine. The crude bromine obtained by either process contains some bro- mine chloride, lead bromide from the pipe-joints and connections, and some organic matter. It is purified by shaking with ferrous, sodium, or potassium bromide, and re-distilling from glass retorts. The bromine chloride is thus decomposed, and the salts of the heavy metals remain in the still. Very pure bromine is obtained by neu- tralizing with barium hydroxide solution, evaporating to dryness, and calcining at a red heat. The barium bromate and chlorate formed in the neutralizing are decomposed to form barium bromide and chlo- ride. By extracting the mass with alcohol, the bromide is dissolved. The barium bromide obtained by evaporation of the alcohol is de- composed with pyrolusite and sulphuric acid, the pure bromine passing to the condenser as vapor. Operations with liquid bromine must be carried on in the open air, or in a strong draught. If inhaled, the vapors are suffocating, and cause great irritation of the air passages. The liquid attacks the skin, and causes sores which heal very slowly. Bromine is largely used in making certain coal-tar dyes, such as the eosins ; for sodium and potassium bromides ; and to some extent as a chemical reagent, and for making organic bromides. It is considered dangerous freight by transportation companies, and so only its salts, especially potassium bromide, are usually shipped. " Solidified bromine " is a convenient form for laboratory work. This consists of sticks of diatomaceous earth, pressed with size or molasses, burned till coherent, and soaked in liquid bromine. The porous material absorbs from 50 to 75 per cent of its weight of the liquid. Potassium bromide is made by decomposing iron bromide with potassium carbonate. The ferroso-ferric bromide (Fe 8 Br 8 ), made by adding more bromine to ferrous bromide, is usually employed. Fe -f Br 2 = FeBr 2 . 3 FeBr 2 + 2 Br = Fe 3 Br 8 . Fe 3 Br 8 + 4 K 2 C0 3 + 4 H 2 = Fe 8 (OH) 8 + 8 KBr + 4 C0 2 . The solution is filtered and evaporated, yielding cubical crystals of the salt, free from bromate, which is always formed when bromine is neutralized directly with alkali. 218 OUTLINES OF INDUSTRIAL CHEMISTRY Potassium bromide is used in medicine and in photography, espe- cially in the preparation of silver bromide plates and films. Sodium bromide is similar to the potassium salt, is used for the same purposes, and is made in the same way ; but it does not crystal- lize so well. REFERENCES Berichte iiber die Entwickelung der chemischen Industrie. A. W. Hofmann, 1875, 129. Moniteur scientifique, 1879, 905. H. S. Welcome. Handbuch der Kali-Industrie, E. Pfeiffer, 321. Braunschweig, 1887. (Vieweg.) IODINE Iodine is obtained from the ashes of seaweed, and from the mother-liquors of the Chili saltpetre industry. Along the coasts of France, Scotland, and Norway, seaweed is collected and burned* at as low a temperature as possible. The ash, called kelp, or varec, contains from 0.5 to 1.5 per cent of its weight of iodides of sodium and potassium. It is lixiviated, and the filtered solution is systematically evaporated. First, sodium sulphate, and then common salt, crystallizes. By further evaporation, sodium carbonate, together with more salt and potassium chloride, sepa- rates. The mother-liquor is then treated with sulphuric acid to decompose the alkali sulphides and sulphites formed by reduction of the sulphates during incineration. This precipitates sulphur, and the sodium sulphate formed crystallizes. The mother-liquor, still holding the iodides in solution, is then heated to 60 C. in iron retorts with lead covers, and having pipes leading to condensers. f Small quantities of pyrolusite are introduced into the retort period- ically, when the following reaction takes place : 2 Nal + 3 H 2 S0 4 + Mn0 2 = MnS0 4 + 2 NaHS0 4 + 2 H 2 + I 2 . Pyrolusite is added as long as iodine distills off; but excess must be avoided, lest bromine and chlorine be set free from the salts * By burning the seaweed in closed retorts, the loss of iodine by volatilization is reduced. t The condensers, called udells, are bottle-shaped vessels of earthenware, arranged horizontally, 5 or 6 in a series, the neck of one entering the bottom of the next. In the lower side of each is a small hole, through which the condensed water drains off. Each still has two sets of udells, which are left in position during repeated charges of the still, until they are filled with solidified iodine. Recently the condensers have been made of seven or eight lengths of plain earthenware pipe, each length 3 feet long by 1 feet in diameter, and the joints luted with clay. IODINE 219 still present in the liquor, and combine with the iodine to form tribrom- or trichlor-iodine (IC1 3 ). Sometimes the iodine liquor is decomposed by leading chlorine gas into it, the same as in making bromine (p. 216). The crude iodine precipitates as a paste, and is washed and then dried on porous plates. Much care is necessary to avoid an excess of chlo- rine, since this forms volatile iodine trichloride (IC1 3 ), and causes loss. By heating the acidified iodine solution with ferric chloride or potassium chlorate, the iodine is liberated and distills off, with some water, and no trichloride is formed, thus : a) 2 Nal + 2 FeCl 3 = 2 FeCL, + 2 NaCl + I 2 . 6) 6 Nal + KC10 3 + 3 H 2 O = 6 NaOH + KC1 + 61. Another method is to mix the kelp with a little water and sul- phuric acid, and to add potassium bichromate. 6 NaI+10 H 2 S0 4 +K 2 Cr 2 7 = 6 NaHS0 4 +K 2 Cr 2 (S0 4 ) 4 +7 H 2 0+6 1. The precipitated iodine is washed, dried, and sublimed. It has been proposed to heat the kelp directly with powdered bichromate, decomposition taking place at a red heat, and the iodine subliming : 6 KI + K 2 O 2 7 = 4 K 2 + O 2 3 + 61. Numerous other processes have been devised for obtaining iodine from kelp, some of which are in use. The recovery of iodine from the mother-liquors of Chili saltpetre is now most important. The iodine is chiefly in the form of sodium iodate (NaI0 8 ), and the process depends on the following reaction : 2 NaI0 3 + 5 S0 2 + 4 H 2 = Na 2 S0 4 + 4 H 2 SO 4 + I 2 . In practice, the sulphur dioxide is used in the form of sodium bisulphite solution, containing some neutral sulphite. This is made immediately before use by leading sulphur dioxide gas into sodium carbonate solution until the liquid contains one part of neutral sul- phite to two of acid sulphite. The requisite quantity of this acid sulphite liquor is added to the mother-liquor, and thoroughly agi- tated ; the precipitated iodine is collected on filters made of coarse bagging or canvas, and after washing is pressed heavily to remove excess of water. The reaction is probably as follows : 2 NaI0 3 + 3 Na 2 S0 3 + 2 NaHS0 3 = 5 Na a S0 4 + I, + H 2 0. 220 OUTLINES OF INDUSTRIAL CHEMISTRY But since some sodium iodide is also present, the excess of bisulphate employed decomposes it according to the reaction : NaI0 3 + Nal + 2 NaHS0 3 = 2 NajS0 4 + I 2 + H 2 0. Sometimes the iodine is precipitated as cuprous iodide (Cu 2 I 2 ) by adding copper sulphate and sodium bisulphite to the mother-liquors, but this is now less frequently done than formerly. The cuprous iodide was shipped to Europe, and used to make potassium iodide by treating with potassium carbonate. The liquors from which the iodine has been separated are re- turned to the lixiviation tanks for the treatment of the crude "caliche" (p. 120). The crude iodine obtained by any of the above processes is puri- fied by re-subliming in iron retorts, the vapors being condensed in earthenware receivers. The temperature of the retorts must be very low in order to form large crystals, and the condensers must not be so cool as to cause sudden condensation of the vapors. The chief uses of iodine are in the manufacture of coal-tar dyes and organic compounds, and in medicinal preparations. The most important iodine derivative is potassium iodide (KI). This is made in several ways : (a) Iodine may be dissolved in a caustic potash or carbonate solution, the solution evaporated to dryness, and the mixture of iodide and iodate so obtained calcined with powdered charcoal at a low red heat, to decompose the latter salt. 61 + 6 KOH = 5 KI + KI0 3 + 3 H 2 0. The calcined mass is lixiviated, filtered, and crystallized. Very pure materials are needed in this process. (6) A better method is to form ferroso-ferric iodide, and decom- pose this with pure potassium carbonate. Metallic iron is dissolved by digesting with iodine and water, forming ferrous iodide, which is then treated with sufficient iodine to form the ferroso-ferric salt : Fe + 2 1 = FeI 2 . 3FeI 2 + 2I = Fe 3 I 8 . Fe 3 I 8 -{- 4 K 2 C0 3 + 4 H 2 = Fe 3 (OH) 8 + 8 KI + 4 C0 2 . This method, if carefully worked, yields a very pure salt, entirely free from potassium iodate. The precipitated ferroso-ferric hy- droxide is granular, and more easily washed than is ferrous hydroxide, PHOSPHORUS 221 (c) Barium iodide is made by agitating barium sulphide solution with iodine. The clear solution is then boiled with potassium sul- phate solution, the precipitated barium sulphate filtered off, and the filtrate evaporated until the potassium iodide crystallizes : BaS + I 2 = BaI 2 + S. BaI 2 + K 2 S0 4 = BaS0 4 + 2 KL Potassium iodide is chiefly used in medicine as an alterative and diuretic. A small quantity is used in photography. Lead, mercury, and ferrous iodides are used to a small extent in medicine, but these are not important. REFERENCES Wagner's Jahresbericht iiber die Leistungen der chemischen Technologic : 1879, 337. G. Langbein. (Jod-Gewinnung in Chili.) 1879, 334. E. Sobering. (Jodkalium.) Journal of the Society of Chemical Industry : 1893, 128. J. Buchanan. (Extraction of Iodine in Chili.) PHOSPHORUS The discovery of phosphorus, about 1675, is attributed to an alchemist, Brand, at Hamburg. Urine which had been evaporated to a thick syrup, was heated in an earthenware retort with sand, the phosphorus distilling off. It was known only as a chemical curios- ity until Scheele, in 1775, made it from bone-ash; soon after it assumed some commercial importance. Bone-ash is still a leading source, but recently the mineral phosphates, being cheaper, have been employed. Ground bone-ash is treated with sulphuric acid, forming calcium sulphate and mono-calcium phosphate (p. 143) ; the latter is leached out of the sulphate with hot water. The solution is decanted, and evaporated to a thick syrup in lead pans, pulverized charcoal or coke is stirred in, and, after drying in iron pans over direct fire, the mass is put into small earthenware retorts, several of which are placed in a furnace at one time. These are heated moderately at first, and the mono-calcium phosphate decomposes, forming calcium metaphosphate [Ca(P0 3 ) 2 ]. The temperature is then raised, and the carbon decom- poses the metaphosphate, forming tricalcium phosphate, phosphorus, and carbon monoxide. The reactions involved are as follows : 1) Ca 3 (P0 4 ) 2 + 2 H 2 S0 4 = CaH 4 (P0 4 ) 2 + 2 CaS0 4 . 2) CaH 4 (P0 4 ) 2 = 2 H 2 + Ca(P0 3 ) 2 . 3) 3 Ca(P0 3 ) 2 + 10 C = Ca 3 (P0 4 ) 2 + P 4 + 10 CO. 222 OUTLINES OF INDUSTRIAL CHEMISTRY Thus only two-thirds of the phosphorus is obtained free. But by adding silica to the mixture complete decomposition results : 4) 2 Ca(P0 3 ) 2 + 10 C + 2 Si0 2 = 2 CaSi0 3 + P 4 + 10 CO. The distillation is very slow, requiring 4 or 5 days. The phospho- rus vapor is condensed in closed vessels, and collects under hot water as a thick liquid ; it is purified as described below. A more direct process, 1 * now largely employed, consists in decom- posing mineral or bone phosphates with sufficient acid to convert all of the calcium to sulphate, and a solution of free phosphoric acid is formed. This solution is filtered through a bed of ashes supported on a grating in a lead-lined wooden tank, and the sulphate washed with water. The solution of phosphoric acid is concentrated to a density of from 65 to 100 Tw. in lead-lined tanks, heated by high- pressure steam coils. An effective stirrer is used to prevent the calcium sulphate, which separates, from depositing on the coils. The solution is drawn into cooling tanks, where nearly all the sulphate separates. The concentrated phosphoric acid is mixed with sawdust, charcoal, or coke powder, and dried in an iron pot or muffle. Sawdust is used when the solution is concentrated to 65 Tw., but for charcoal or coke a thick syrup is necessary. The dried mass is filled into earthenware retorts, each holding about 25 pounds ; 24 of these retorts are heated in one furnace. From each retort, a pipe leads to a trough containing water, and dips just below the surface of the water. The temperature is raised to a white heat. The distillation requires about 16 hours, the melted phosphorus col- lecting in the troughs under the water. The reactions involved are as follows : 1) Ca 3 (P0 4 ) 2 + 3 H 2 S0 4 = 3 CaS0 4 + 2 H 3 P0 4 . 2) 2 H 3 P0 4 = 2 HP0 3 + 2 H 2 0. 3) 4 HP0 3 + 12 C = 12 CO + 2 H 2 + P 4 . A continuous process for the direct production of phosphorus from calcium phosphates by means of the electric furnace has been devised by Eeadman, Parker, and Robinson.f An intimate mixture of carbon, phosphate, and flux is heated in a tightly covered electric furnace, having an outlet pipe leading to a condenser, into which the phosphorus and gas pass. The residue fuses to a slag in the fur- nace, and is tapped off at intervals, fresh charges being introduced without interrupting the electric current. This method avoids the * J. B. Readman, Thorpe's Dictionary of Applied Chemistry, Vol. Ill, 185. t J. B. Readman, I.e. PHOSPHORUS 223 use of sulphuric acid, the concentration and handling of phosphoric acid, uses no earthenware retorts, and saves time ; it is further claimed that less coal is used. The crude phosphorus made by any of the above processes con- tains sand, carbon, clay, and other impurities. It is purified by melting under warm water, and straining through canvas bags; formerly chamois leather was used. Or it is redistilled from iron retorts. Sometimes it is treated with a 3 per cent solution of potas- sium bichromate and its equivalent of sulphuric acid, in a lead-lined agitator which is heated by steam coils. After a couple of hours agitation, the phosphorus is nearly transparent, and of a light yel- low color. It is washed with hot water, filtered through canvas bags, and moulded into " sticks " by pouring into glass or tin tubes placed in cold water. For shipment, phosphorus is packed in water in tin boxes, the lids of which are tightly soldered. Yellow or ordinary phosphorus is a pale yellow, translucent, wax- like mass of 1.82 specific gravity, very inflammable, and combining directly with oxygen, sulphur, and the halogens. It melts at 43.3 C. under water, and at 30 C. when dry ; it distills at 269.* It is very soluble in carbon disulphide, sulphur chloride, and phosphorus trichloride, slightly so in caustic soda solution, but insoluble in water. It is exceedingly poisonous, less than 0.15 gram being a fatal dose. Persons working continuously with yellow phosphorus are subject to necrosis, usually appearing first in the jawbones. The chief uses of yellow phosphorus are in making matches and phosphor-bronze, and for rat poison. Amorphous or red phosphorus is made by heating the yellow variety for several hours in closed retorts at 250 C. If an auto- clave be employed, and the temperature raised to 300 C., the press- ure inside the vessel makes the process much more rapid. The hard mass thus produced is ground under water, and the powder boiled with caustic soda solution to remove any unchanged yellow phosphorus. Carbon disulphide is sometimes used instead of caus- tic soda, but this is expensive and easily inflamed. After boiling in water, filtering, and drying by steam heat, the amorphous phospho- rus is packed dry. Eed phosphorus is a reddish brown, opaque substance, having a specific gravity of 2.25. It is not affected by heating in the air until the temperature reaches 260 C., at which point it inflames. By heating in an atmosphere of nitrogen or car- bon dioxide, it distills, returning to the yellow variety. It is insol- uble in carbon disulphide, caustic soda, and in water, and is not * J. B. Readman, I.e. 224 OUTLINES OF INDUSTRIAL CHEMISTRY poisonous. The chief use of red phosphorus is in the manufacture of " safety matches." MATCHES In about 1812, the so-called " chemical matches " were invented. Sticks were dipped in melted sulphur, and the " head " coated with a mixture of sugar and potassium chlorate. It was fired by dipping into a bottle containing asbestos moistened with sulphuric acid. Friction, or lucifer, matches were invented in 1827, in England. The heads were a mixture of antimony trisulphide and potassium chlorate, made into a stiff paste with water and gum. They were ignited by rubbing on sand or emery paper. The antimony trisul- phide was soon replaced by phosphorus, and the potassium chlorate by nitre. At the present time, lead peroxide, red lead, or man- ganese dioxide are used instead of nitre as the oxidizing substance. Chlorates are used, but sparingly, since they form explosive mixtures. Soft wood, generally pine or spruce, is cut by machines to form the sticks, which are thoroughly kiln-dried. They are then fixed in a frame so that each stick stands alone, and the end of each stick is well soaked in melted sulphur, paraifine, or stearic acid. The igniting mixture is made by slowly stirring phosphorus into a warm solution of dextrine or glue ; the oxidizing materials are then added, and the paste stirred until cold. It is frequently colored with ultramarine, lead chromate, chalk, or lampblack. It is then spread evenly in a thin layer on a table, and the prepared sticks dipped into it once or twice. .After drying, the heads are sometimes dipped in thin shel- lac or other varnish, to protect them from the moisture in the air. Safety matches are made without yellow phosphorus. The match head is generally sulphur, or antimony trisulphide, with potassium chlorate, or bichromate, as the oxidizing material. Sometimes red lead, lead peroxide, or manganese dioxide is used as a part of the oxidizing material. The surface upon which the match must be lighted is coated with a mixture of red phosphorus, antimony trisul- phide, and dextrine, or glue. Powdered glass or emery is used to increase the friction. The compositions used on matches are carefully guarded as trade- secrets, and are different in different factories. One is given as follows : HEAD COMPOSITION KC10 3 5 parts K 2 Cr 2 7 2 parts Glass Powder 3 parts Gum 2 parts EUBBING SURFACE Sb 2 S 3 5 parts Red Phosphorus ... .3 parts Mn0 2 Imparts Glue 4 parts BORIC ACID 225 The friction of the match head on the prepared snrface develops sufficient heat to convert a little of the red phosphorus to the yellow variety, which at once combines with some of the potassium chlorate and antimony sulphide, evolving enough heat to inflame the mixt- ure on the head. To prevent the burned stems from smouldering, the sticks are sometimes soaked in a solution of magnesium sulphate, alum, or sodium phosphate before making the head. In some countries, notably Switzerland, the manufacture and sale of matches containing yellow phosphorus is prohibited. REFERENCES Chemical News, 1879, 147. J. B. Readman. (Manufacture of Phosphorus.) Chemiker-Zeitung, 1881, 196. A. Rossel. (Matches without Phosphorus.) Journal of the Society of Chemical Industry : 1890, 163, 473. J. B. Readman. (Manufacture of Phosphorus.) 1891, 445. J. B. Readman. (Manufacture of Phosphorus. ) BORIC ACID Boric acid, B(OH) 3 , occurs in volcanic regions, especially in Tus- cany, as a constituent of the vapors, called soffioni, which escape from hot springs and from openings in the ground, called fumeroles. In some places the water has evaporated from the fumeroles, and the boric acid has crystallized, forming the mineral sassolite. Combina- tions of boric acid with sodium, magnesium, and calcium are found in various places : as, tinkal (native borax), Na 2 B 4 7 10 H 2 ; bora- cite, 2 (Mg 3 B 8 15 ), MgCl 2 ; borocalcite, CaB 4 7 - 6 H 2 ; and borona- trocalcite (ulexite), ]STa 2 B 4 7 , (2 CaB 4 7 ), 18 H 2 0. In Tuscany, natural or artificial ponds (lagoons) are formed around the fumeroles, or a series of masonry basins or tanks are constructed over them, and the soffioni made to bubble through water in these, thus washing most of the boric acid from the vapors. These tanks are so arranged that the water from one flows into another at a lower level ; in the final basin, a solution containing about 2 per cent boric acid is obtained. The solution is evaporated, either in lead-lined vessels, heated by the steam from the fumeroles, or in cement-lined tanks, having coils through which the steam passes. Calcium sulphate deposits freely during the evaporation of the solution, which is concentrated to 1.08 specific gravity. It is then crystallized in lead-lined wooden vats. The crystals are drained for some hours, and dried on a floor also heated by steam from the Q 226 OUTLINES OF INDUSTRIAL CHEMISTRY fumeroles. The crude boric acid thus formed is purified by re- crystallization. In many places in Tuscany, bored wells have been sunk from 200 to 300 feet, and the vapors escape from these as from the natural fumeroles. Considerable boric acid is made in California and Nevada by decomposing the borax found there, with hydrochloric or with sul- phuric acid. The borocalcite, found in Chili, is decomposed in the same way. Much boric acid is made from the boracite in the Stassfurt salts. The mineral is crushed, and treated with just enough hydrochloric acid to decompose it. A rather vigorous reaction takes place, and the mass becomes pasty. It is dissolved in boiling water, and care- fully tested for free hydrochloric acid ; if none is present, the solu- tion of boric acid is decanted from the sediment of clay and sand, or filtered through linen bags, and is crystallized in lead-lined or iron tanks.* Sulphuric acid is also used to decompose the boracite, in which case the mother-liquors from the boric acid contain magne- sium sulphate; this is recovered as Epsom salt. The following reactions are involved : 1) (2 Mg 3 B 8 15 ), MgCl 2 + 12 HC1 + 18 H 2 O = 7 MgCl 2 + 16 B(OH) 3 . 2) (2 Mg 3 B 8 15 ), MgCl 2 + 7 H 2 S0 4 + 18 H 2 = 7 MgS0 4 + 2 HC1 + 16 B(OH) 3 . The actual quantity of acid used is determined for each lot of salt. Boric acid forms pearly wnite, laminated crystals, very slightly soluble in cold water, but dissolving readily in hot water. It has but little taste. When heated, it loses water, and at 140 C. forms pyroboric acid, H 2 B 4 7 . At a red heat, all the water is expelled, and boric anhydride (B 2 3 ) results ; this is stable and non-volatile, even at high temperatures. Consequently, it will decompose nearly all metallic sulphates, carbonates, and nitrates when fused with them, forming metallic borates. Hence it is used as a flux. Boric acid is chiefly used in the preparation of borax ; in enamels and glazes for pottery ; in making Guignet's green ; as an antiseptic in medicine and surgery ; and for preserving fish, meat, and milk. Borax, sodium biborate, Na 2 B 4 7 , is the only important salt de- rived from boric acid. It is found native in Thibet, Ceylon, and California. But little is known of the method of preparing borax *F. Wittig (Zeit. angew. Chem., 1888, 483), recommends iron crystallizing tanks, because lead-lined vessels buckle and leak, owing to the changes of tempera- ture. The iron soon becomes polished, and yields perfectly clean crystals. BORIC ACID 227 in Thibet. It conies from that country as tinJcal, an impure, crys- tallized borax, containing lime, magnesia, sulphates, and chlorides, and a greasy substance added presumably to protect the crystal from efflorescence and breakage. The tinkal is purified by dissolv- ing in hot water, and adding lime-water and calcium chloride, to precipitate the grease as lime soap. After filtering, the borax is crystallized by concentrating the solution. A large quantity of borax is obtained from the water of Borax Lake, in California ; and from certain marshes in California and in Nevada, where borax, together with sodium carbonate, sulphate, and chloride, forms an efflorescence or crust on the surface of the marsh, owing to the evaporation of water. The mud of these marshes often contains crystals of borax and soda, which are picked out by hand ; it is leached with water to dissolve the finer crystals. In San Bernardino County, California, there is a vein of mineral, consisting chiefly of calcium borate and carbonate, which is exten- sively worked for boric acid and borax. A similar deposit is found in Oregon. The calcium borate is washed to remove soluble sul- phates and chlorides, and then boiled with a slight excess of sodium carbonate. The clarified liquid is allowed to crystallize, and a crude borax, containing Glauber salt, is obtained. This is redissolved to form a solution of 30 Be., measured hot, a little sodium hypochlorite is added, and the liquid is run into closed crystallizing tanks, where it cools very slowly. When the temperature falls to 33 C., the mother-liquor is drawn off to prevent contaminating the borax crystals with the Glauber's salt, which separates below that tem- perature, and for which the mother-liquor is then worked. A deposit of borocalcite called pandermite is found in Asia Minor, and is worked in a similar manner. The crude borax is purified by recrystallization in lead-lined tanks. In order to form good crystals, the solution must cool very slowly, and the tank should be tightly closed to prevent the forma- tion of a surface crust. In crystallizing borax, a small excess 'of sodium carbonate (5 per cent.), in the solution is advantageous ; but more than this results in the formation of neutral sodium borate, NaB0 2 , 4 H 2 0, according to the reaction : Na 2 B 4 O 7 -|- Na 2 C0 3 = 4 NaB0 2 + C0 2 . Much of the boric acid produced in Italy is converted to borax, by dissolving it in a boiling solution of sodium carbonate. The solution is then concentrated to 22 B&, at 104 C., and after settling, is run into the crystallizing tanks, which are shallow and open, so 228 OUTLINES OF INDUSTRIAL CHEMISTRY that the borax deposits within three days ; but for recrystallization, deep tanks, tightly covered, and lagged to prevent radiation of the heat, are used. The crystallization requires from 16 to 18 days, and the crystals formed are usually large. Borax comes in trade in two forms ; common or prismatic borax, Na 2 B 4 7 - 10 H 2 O, and octahedral borax, Na 2 B 4 7 5 H 2 O. The for- mer is produced by crystallizing from a solution of 22 Be., which is permitted to cool to 27 C. ; the latter is obtained when a solution of common borax is concentrated to 30 Be., and cooled only to 56 C. Prismatic borax forms large, monoclinic crystals, and effloresces in the air j it melts in its water of crystallization when heated, after- wards swelling greatly, forming a spongy mass, but at a red heat fusing and becoming transparent and glassy. Octahedral borax forms regular octahedrons, permanent in dry air, but absorbing moisture on exposure, and passing into the pris- matic variety. It fuses readily without intumescence, and is there- fore preferred as a flux and for brazing and soldering. Borax is used as a flux in welding and brazing metals ; in enamel and glazes for metal ware and pottery ; in laundry work, and in starch to increase the gloss ; in soaps, especially those intended for use in hard water ; for the preservation of meat ; as a mordant in dyeing ; for the ungumming of raw silk ; in medicine, and in phar- macy ; and with casein for the preparation of paste. REFERENCES Hofmann's Bericht iiber die Entwickelung der Chemischen Industrie. 1875, 324, 343. Handbuch der Kali-Industrie. E. Pfeiffer, Braunschweig, 1887. (Boracit.) Chemiker-Zeitung : 1879, 46. F. Filsinger. (Boric Acid from Boracite.) 1887, 605. L. Darapsky. (Borax in Chili. ) Third Annual Report of the California State Mineralogist, 1883. Zeitschrift f iir angewandte Chemie : 1888, 483. F. Witting. (Borax from Boronatrocalcite.) 1891, 367. 1892, 241. Dr. Scheuer. (Boric Acid and Borax Industry.) Journal of the Society of Chemical Industry : 1889, 857. C. N. Hake. (Borax Lake in California.) 1892, 683. Dr. Scheuer. Engineering and Mining Journal : 53, 8. J. F. Kemp. (Borax.) 54, 247. Die Stassfurter Kali-Industrie. G. Lierke, Wien, 1891. ARSENIC COMPOUNDS 229 ARSENIC COMPOUNDS Arsenious acid, white arsenic, or arsenic trioxide (As 2 3 ), is the most important arsenic derivative. It is made by roasting arsenical pyrites (mispickel), FeAsS ; or as a by-product in the preparation of zaffre from cobaltite (CoAsS), or smaltite (CoAs 2 ), and in roasting certain arsenical tin ores before smelting. The roasting is done in reverberatory furnaces, and the vapors of white arsenic sublime off, and are condensed as a powder in long horizontal canals, or in chambers. The crude product is purified in a small reverberatory furnace, fired with coke, or in cast-iron pots, a number of which are set in a furnace, all being connected with a single condensing chamber or canal. Directly over the pot an iron drum or cylinder is often placed, from the top of which a short pipe leads to the condensing chamber. After resubliming, the oxide is a white granular powder, which is usually ground before packing for market ; or, by a second subli- mation under slight pressure in an atmosphere of arsenious acid, it is obtained in an amorphous or vitreous state. For this the pot is heated red-hot, and the " arsenic meal " introduced through an open- ing in the cap of the drum, which is then closed. The arsenic vapor rises into the drum, and condenses on its walls as a transparent layer of " arsenic glass." White arsenic, or, as it is commonly called, arsenic, comes in commerce as a powder, and as a' "glass." On standing, the latter changes to a crystalline state, and becomes white, opaque, and porce- lain-like in structure. It has no odor, and a very slight metallic taste, is difficultly soluble in water, and vaporizes without melting when heated in the open air. It is used in glass-making ; when dis- solved in glycerine, as a mordant in calico printing; in making various pigments ; for preparing fly and rat poisons ; as a preserv- ative for green hides; for the manufacture of arsenic salts and preparations ; in medicine ; and formerly, to a great extent, in the preparation of aniline from nitrobenzene. Arsenic acid, H 3 As0 4 , is prepared by heating 4 parts arsenic tri- oxide with 3 parts concentrated nitric acid (1.35 sp. gr.), and evapo- rating the solution to a thick syrup, in which form it is usually sent to market. By evaporating it to dryness, and igniting at a red heat, arsenic pentoxide, As 2 5 , a hygroscopic body, is formed. Arsenic acid attacks the skin, producing blisters, but is less poi- !- O A ..T 230 OUTLINES OF INDUSTRIAL CHEMISTRY sonous than arsenious acid. It is chiefly used in calico printing, but was formerly much employed as an oxidizing agent in making certain coal-tar dyes (rosanilines). Sodium arsenate, Na 2 HAs0 4 , is made by heating white arsenic with sodium nitrate, or by dissolving white arsenic in sodium car- bonate solution, adding some sodium nitrate, evaporating to dryness, and calcining the mass. By dissolving in water, and crystallizing, the salt Na 2 HAs0 4 12 H 2 O, is obtained. This usually contains some NaH 2 As0 4 H 2 O (binarsenate). It is used as a substitute for the "dung-bath" in dyeing ali- zarines, and in calico printing, to prevent discoloration of the white parts of the pattern by rendering the excess of mordant insoluble, so that it does not " bleed," i.e. diffuse into the white portions of the cloth. Sodium arsenite, NaAs0 2 (meta-arsenite), is prepared by neutral- izing arsenious acid with sodium carbonate, or hydroxide solution, and boiling for some time. The salt has been used instead of the " dung-bath " in dyeing. . Orpiment and Realgar have been described on pp. 207 and 212. WATER-GLASS The substances sold under this name are silicates of sodium, or potassium, or of both. They are soluble in water, and are generally sold as thick, sirupy liquids. Commercial water-glass is not of definite composition, but is approximately Na 2 Si 4 9 . It is prepared by fusing powdered quartz, or infusorial earth, with caustic soda or with sodium carbonate. A small quantity of charcoal is also added, to assist in the complete reduction of the carbonate. Sodium sulphate may be used instead of the carbonate. The fusion is done in a reverberatory furnace, and requires 8 or 10 hours. Sometimes ordinary glass-pots and furnaces, p. 168, are used. The product is a translucent or transparent glass, slightly green, from traces of iron. It is powdered, and boiled in water, best in a digester under pressure, until the liquor is nearly neutral. A small quantity of copper or lead oxide is added, to decompose any sodium sulphide formed during the reduction. After 10 or 12 hours the solution is drawn from the boiler, filtered on cloth, and allowed to settle. It is then concentrated to 140 Tw. (1.7 sp. gr.). The material used must be pure, and especially be free from lime, alumina, etc. PEROXIDES 231 Water-glass is also made by boiling silica in a digester with a solution of caustic soda for a long time at 60 pounds pressure. This yields a solution of the silicate directly, which needs only a little concentrating. Sometimes gelatinous precipitated silica is dissolved in caustic soda, and the solution is evaporated. By using a mixture of equivalent weights of sodium and potassium carbonates, a more soluble glass is produced, which is sometimes called " double soluble glass." Potassium silicate, which forms a more soluble glass than sodium silicate does, is made in the same way. Water-glass is readily decomposed by acids, even carbon dioxide setting free silica, and forming a salt of the alkali. It is used extensively as an addition to yellow or laundry soaps ; as a fixative for pigments in calico printing ; as a vehicle for pigments in fresco painting ; for rendering cloth and paper draperies non-inflammable ; as a preservative for timber and porous stone ; in the manufacture of artificial stone ; and in cement mixtures for glass, pottery, wood, and leather. PEROXIDES Barium peroxide,* Ba0 2 , is made by calcining barium nitrate, and heating the oxide thus obtained in an atmosphere of dry, pure air. The nitrate is packed in crucibles, and heated in a furnace at 880 C. for several hours. The mass fuses, and for the first 3 or 4 hours continues to evolve nitrous gases, but finally becomes solid, though of a spongy, porous character. This is barium monoxide, and must be carefully protected from moisture and carbon dioxide. It is broken up into small lumps, and put into flat iron trays, which are set in wide, cast-iron pipes, through which a current of air can be passed. The air is dried thoroughly, and freed from carbon dioxide before it enters the pipes, by passing it through a drying tower, or drum, filled with caustic soda or quicklime. The pipes are heate.d to a low red heat (750 C.), and the air passes through them. The barium oxide takes up an atom of oxygen, forming the peroxide, while nitrogen escapes from the pipe. The product is cooled away from contact with air. By adding an excess of barium hydroxide solution to a solution of hydrogen peroxide, a precipitate of hydrated barium peroxide, Ba0 2 8 H 2 is obtained, which is stable. By drying this at 130 C., all the water is expelled, and the pure peroxide remains. * J. Soc. Chem. Ind., 1890, 246. L. T. Thome. Chemiker-Zeitung, 1894, 68, 232 OUTLINES OF INDUSTRIAL CHEMISTRY Barium peroxide is a gray or white powder, insoluble in water, but combining with it to form a hydrated compound. It is easily decomposed by dilute acids, and even takes up carbon dioxide from the air. Heated to a bright red heat (1000 C.), it decomposes into monoxide and free oxygen. Its chief uses are for making hydrogen peroxide, and in the preparation of oxygen gas. Hydrogen peroxide,* H 2 2 , is made by decomposing barium perox- ide with dilute mineral acids. The powdered barium peroxide is "hydrated" by pouring it into water, and stirring for about 3 hours, until a smooth white paste is formed. This is added, a little at a time, with active stirring, to the dilute acid, contained in a lead- lined vessel. The temperature during decomposition must not rise above 15 C., and the vessel is cooled with ice-water. The precipi- tated barium salt is allowed to settle, and the clear solution of hydrogen peroxide is decanted, and sometimes filtered rapidly on cotton cloth. If an excess of barium peroxide is used, the liquor is alkaline, and will not keep. In this case, a little more acid is added, and prevents decomposition. The commercial strength is known as a 10- volume solution, i.e. 3 per cent H 2 2 . By using hydrofluoric acid, the precipitate of barium fluoride may be readily employed to generate more of the acid ; if nitric acid is used, a considerable part of the barium is recovered as barium nitrate, with which more barium peroxide can be made. Hydrogen peroxide is a powerful oxidizing agent towards sub- stances capable of oxidation, but with bodies which give off oxygen readily it acts as a reducing agent, giving up one atom of oxygen to unite with the oxygen from the body in question, forming a molecule of the free gas. It is used extensively as a bleaching agent, espe- cially for animal fibres and tissues, such as silk, wool, hair, feathers, bone, and ivory. It has long been used as a hair bleach for toilet use. As a disinfectant and antiseptic, it finds use in surgery ; for restoring the colors of oil paintings which have darkened with age, it is very effective, if the paint contains lead ; the lead sulphide is oxidized to the sulphate by the peroxide, the black color of the for- mer being destroyed. Hydrogen peroxide has also been proposed as a substitute for sodium bisulphite and thiosulphate, as the reducing material for chrome tannage processes ; also as an antichlor, for use after chlorine bleaching ; and as a general antiseptic, for use in the * Zeitschr. f . angew. Chem., 1890, 3. G. Lunge. J. Am. Chem. Soc., 12, 64 A. Bourgougnon. J. Soc. Chem. Ind., 1890. Kingzett, OXYGEN 233 fermentation industries, and as a preservative for milk, beer, wine, and other fermentable liquids. Sodium peroxide,* Na 2 2 , has recently appeared in commerce as a bleaching material. The technical production depends upon the oxi- dation of fused metallic sodium, by exposing it to a current of pure dry air or oxygen. The sodium is contained in aluminum trays, which are put on cars, and pushed slowly through a wide iron pipe, externally heated to 300 C., while air, purified as described on p. 231, passes through the pipe in the opposite direction. The tem- perature must not rise above 300 C., and the oxidation must be slow. Sodium peroxide is a yellowish white,, very hygroscopic powder, which is chiefly used as a powerful bleaching agent. It gives off 20 per cent of its weight as active oxygen, t It dissolves in dilute acids without evolving oxygen, if the vessel be kept cool, yielding a strong solution of hydrogen peroxide. It dissolves in water with the loss of some oxygen, and a great evolution of heat, which may be suffi- cient to set fire to inflammable bodies. It is too strongly alkaline for silk or wool bleaching, and should be converted into magnesium peroxide for this purpose. This is easily done by adding magnesium sulphate solution : Na 2 2 + MgS0 4 = Na 2 S0 4 + Mg0 2 . The solution of sodium peroxide attacks cellulose, and produces an effect similar to that obtained by "mercerizing" with caustic soda. OXYGEN Numerous processes have been devised for the technical produc- tion of oxygen, but most of them are so expensive, or require such complicated plants, that only two or three are in actual operation on a large scale at the present time. The decomposition of potassium chlorate by heating, with the addition of manganese dioxide, has been much employed, and is still the favorite laboratory method of obtaining a pure gas. The addi- * J. Soc. Chem. Ind., 1892, 1004 (Patent to H. Y. Castner) ; 1893, 603. Chemical Trade Journal, 11, 208. t Barium peroxide liberates 8 per cent of its weight of active oxygen, while a 12-volume solution of hydrogen peroxide liberates only l per cent of its weight of active oxygen. 234 OUTLINES OF INDUSTRIAL CHEMISTRY tion of pyrolusite lowers the temperature of the decomposition, and reduces the liability of explosion. It is highly important that the potassium chlorate and pyrolusite be free from carbonaceous matter. Deville's process. By allowing sulphuric acid to drop ;n fine streams on red-hot surfaces, it breaks up according to the reaction: 2 H 2 S0 4 = 2 S0 2 + 2 H 2 + 2 . In order to separate them, the gases evolved are passed though cool- ing coils to condense the water, and then through scrubbers contain- ing water, to remove the sulphur dioxide. The retort is usually filled with broken brick, pumice, or other porous, acid-resisting material. The process has no significance as a method of prepar- ing oxygen alone, but has been used for making sulphuric anhydride, SO 3 , the water being first^ condensed, and the sulphur dioxide and oxygen uniting to form the trioxide. About 114 litres of oxygen are obtained from 1 kilo of sulphuric acid by this method. Boussingault's process, as modified by Brin brothers, is now worked on a large scale, and is often called Erin's process.* Bous- singault discovered that barium peroxide (Ba0 2 ), when heated to a high temperature, decomposes into the monoxide and oxygen, the latter passing off. Then by heating the barium oxide to a low red heat in a current of air, the peroxide can be regenerated. But his attempts to utilize the process were unsuccessful, because the monox- ide soon became inert, and would not absorb oxygen from the air. This was due to the fact that the moisture and carbon dioxide in the air converted the barium oxide to hydroxide and carbonate, which are very stable bodies, even at high temperatures, consequently the regeneration of peroxide rapidly decreased. As modified by Brin brothers, the temperature of the retort remains constant, while all moisture and impurities are removed from the air. Barium oxide is made from barium nitrate, as de- scribed on p. 231 , and put into vertical retorts, or long narrow pipes, suspended in a furnace heated by producer gas. When the tempera- ture reaches 700 C., purified air is forced into the retorts under a pressure of 15 pounds per square inch, and the monoxide takes up an atom of oxygen, and forms the peroxide. The air supply is then cut off, and the pump reversed, so as to form a vacuum in the retort, reducing the pressure to about 26 to 28 inches of mercury. Under these conditions, the barium peroxide gives off an atom of oxygen, and is reduced to the monoxide. The gas is pumped into the gas- ometer, and when it ceases to be evolved the pump is reversed again, * J. Soc. Chem. Ind., 1890, 246. L. T. Thome. 1889, 82 and 517. OXYGEN and air forced into the retort, to oxidize the monoxide to peroxide again. The air is passed through purifiers, one filled with quicklime, and the other with caustic soda ; these remove the water and carbon di- oxide. By the alternate use of pressure and vacuum, the temperature may be kept constant at 700 C. The oxygen obtained is about 96 per cent pure. The baryta is removed once in six or eight months, and broken up to prevent caking, after which it is returned to the retort. The yield of oxygen gas at each operation is said to be about 10 litres per kilo of barium oxide employed. The cost of the gas in England is from 3s. to 7s. per 1000 cubic feet. Tessie du Motay process.* This depends on the following reac- tions : 1) 2 Na 2 Mn0 4 + 2 H 2 = Mn 2 3 + 4 NaOH + 3 O. 2) Mn 2 3 + 4 NaOH + 30 (air) = 2 Na 2 Mn0 4 + 2 H 2 0. First, sodium manganate is prepared by mixing a manganese oxide with caustic soda, and heating with free access of air. The following reaction takes place : 2 Mn0 2 + 4 NaOH + O 2 (air) = 2 Na 2 Mn0 4 + 2 H 2 0. The sodium manganate thus made is crushed, and mixed to a paste with caustic soda solution, containing from 5 to 10 per cent NaOH. This is dried slowly and completely in shallow pans, and then ignited in a crucible at a white heat, to render it spongy. But it must not fuse. This yields a porous manganate, containing an excess of caustic soda, which is filled into long clay, or cast-iron retorts of peculiar construction,! set at an incline in the furnace, and heated to a regular temperature of 400^50 0. Superheated steam is then admitted to the retort, where it deoxidizes the man- ganate, regenerating the manganic oxide and caustic soda, while oxygen is liberated, and is cooled and collected in a gasometer. Then the process is reversed, and purified air, which has passed through a heating pipe, set in the furnace, is admitted to the retort, where it oxidizes the material, regenerating the sodium manganate, while pure nitrogen escapes. The cycle of operations is repeated indefinitely. In order that the supply of oxygen may be continuous, the plant is usually built in duplicate, so that the contents of one set of retorts is being oxidized with air, while that of the other is being deoxidized with steam. * J. Soc. Chem. Ind., 1892, 312. F. Fanta. t For details, see J. Soc. Chem. Ind., 1892, 315. 236 OUTLINES OF INDUSTRIAL CHEMISTRY It is essential that the sodium manganate be granular, and that it do not fuse in the retort j also, that both the air and the steam introduced be dry, and at least as hot as the contents of the retort. An excess of caustic soda seems to be necessary, to render the manganate spongy and granular. This process is complicated in it's working and apparatus, and is apparently not so economical as in the Brin method. Linde refrigeration process.* Refrigerating machines, depend- ing upon the expansion of compressed air, have recently been brought to a high state of perfection, and it is claimed that a temperature of 200 C. can be secured on an industrial basis. This being below the critical temperature of air, the latter is liquified. By allowing this liquid air to evaporate at the ordinary atmospheric pressure, the nitrogen escapes more rapidly than the oxygen, and a residual gas is thus obtained, containing over 70 per cent 0. This is concen- trated enough for many purposes, and the process, which is entirely mechanical, may have some future development. Methods for the production of oxygen by the electrolysis of water are far too slow and expensive for industrial use. The same is probably true of the methods depending on the formation of cal- cium plumbate (Ca 2 Pb0 4 ), and its decomposition into calcium car- bonate and lead peroxide (Pb0 2 ), from which oxygen may be obtained : 1) 2 CaC0 3 + PbO + (air) = Ca 2 Pb0 4 + 2 C0 2 . 2) Ca 2 Pb0 4 + 2 Na 2 C0 3 + 2 H 2 = 4 NaOH + 2 CaC0 3 + Pb0 2 . 3) 2 CaC0 3 + Pb0 2 = 2 CaC0 3 + PbO + O. The uses of pure oxygen in the arts are not very numerous, since, for most oxidizing purposes, air, even though diluted with nitrogen, may be used. It is, however, employed for the oxy-hydrogen flame in melting platinum and other refractory metals, and for soldering and brazing ; in the calcium or Drummond light ; for the purifica- tion of illuminating gas; for the destruction of fusel oil in high wines ; and, to a small extent, in medicine, and in the manufacture of sulphuric anhydride. Its use has been proposed to hasten the melting and refining of glass ; as a partial substitute for air in blast furnace running ; for the oxidation of drying oils in varnish making ; and to assist the action of bleaching powder in textile bleaching. * J. Soc. Chem. Ind., 1895, 984. M. Schroeter. U. S. Consular Reports, 54, 64. Chas. de Kay. SULPHATES 237 REFERENCES Chemical Trade Journal, 1887, 145. Journal of the Society of Chemical Industry : 1885, 568. W. Smith. 1889, 82, 517. 1890, 246. L. T. Thome. 1892, 312. F. Fanta. 1895, 984. M. Schroeter. Chemische Industrie, 1890, 104, 120 ; 1891, 71. G. Kassner. SULPHATES / The sulphates of ammonium, magnesium, potassium, and sodium have already been discussed in connection with the industries with which they are most nearly related. Ferrous sulphate, green vitriol, or copperas, FeS0 4 - 7 H 2 0, is a by-product of many industries. When pyrites is distilled for sul- phur, the residue, consisting of ferrous sulphide, is piled upon inclined tables in the open air, and allowed to weather, water being poured over the heap if there is not sufficient rain. Oxidation takes place, and both ferrous and ferric sulphates are formed in the mass. These dissolve in the water, and the solution of mixed sulphates flows into a tank, containing some sulphuric acid and scrap iron. The reaction between the acid and the iron reduces the ferric salt, and a solution of ferrous sulphate is obtained. This is decanted from the sediment, and evaporated until saturated in lead or iron pans, containing scrap iron. It is then allowed to settle, and the clear green solution of copperas is decanted from the basic ferric salt, which deposits as a yellow mud. The solution is cooled, and light green crystals of ferrous sulphate (FeS0 4 7 H 2 0) separate, and are drained, or freed from mother-liquor in centrifugal machines. The mother-liquor goes back to the neutralizing tanks, and is mixed with fresh liquor. Sometimes pyrites is weathered directly for copperas. The pro- cess is carried on as above described, except that the free sulphuric acid formed makes the addition of acid to the liquor unnecessary. The receiving tank at the lower end of the oxidizing tables contains the acid liquor, to which scrap iron is added to reduce the ferric salt. FeS 2 + H 2 + 7 = FeS0 4 + H 2 S0 4 . A large amount of green vitriol is obtained as a by-product in the manufacture of aluminum sulphate from shale containing pyrites 238 OUTLINES OF INDUSTRIAL CHEMISTRY (p. 245). The basic ferric sulphate separated is reduced by treat- ment with acid and scrap iron. Wet metallurgical processes for the production of cement copper also furnish a very considerable amount of copperas. Copper sul- phide ores, low in copper, are exposed in heaps to the weather for several months, being frequently moistened with water. By oxida- tion of the sulphides, copper and iron sulphates are formed, and are leached out by the water. These liquors are run into tanks contain- ing scrap iron, which precipitates the copper, and also reduces the ferric sulphate to the ferrous state. The solution of copperas is clarified, and evaporated to crystallize. In this country, the " sludge acid " of petroleum refining is often diluted, and used to make ferrous sulphate, by dissolving scrap iron in it. The acid "pickling liquors," used in foundries and wire mills for cleaning the surfaces of castings and wire, are treated with scrap iron to neutralize free acid, and the solution then evaporated for copperas. All processes for making ferrous sulphate yield dilute solutions, which are best evaporated by direct application of heat to the sur- face of the liquid (see &, p. 4), thus preventing oxidation. After clarification, the liquid is put into large lead-lined tanks, in which strings or wooden rods are suspended; on these the large bluish green crystals of ferrous sulphate form. The crystals contain 7 molecules of crystal water ; when heated to 140 C., 6 molecules of water are expelled, but the last molecule is not removed until the temperature reaches 260 C. ; at this temper- ature, some of the acid begins to escape, and the formation of the basic salt begins. At a red heat, sulphuric anhydride is given off, and ferric oxide is left. The crystals of ferrous sulphate effloresce quickly when exposed to the air, their surfaces becoming coated with a brownish white powder of basic ferric sulphate, formed by oxidation. Ultimately, the entire crystal is converted to this basic salt. By adding alcohol to a ferrous sulphate solution, the salt is precipitated in fine crys- tals, which are much more stable in the air than are the ordinary kind. Copperas solution oxidizes quickly in the air, and a yellow pre- cipitate of basic ferric sulphate separates. Commercial green vitriol very often contains copper sulphate, and sometimes nickel sulphate. When very large quantities of these impurities are present, the color is very dark, and the salt is called " black vitriol." Ferrous sulphate is largely used as a mordant in dyeing ; in the SULPHATES 239 preparation of fuming sulphuric acid ; for disinfecting purposes ; in the manufacture of ink, Prussian blue, and various pigments ; and for precipitating gold from solution in metallurgical processes. Copper sulphate, blue vitriol, or "bluestone." CuS0 4 - 5 H 2 0, is now largely obtained as a by-product in the " parting " of gold and silver with sulphuric acid. The gold and silver alloy is boiled with concentrated sulphuric acid in cast-iron pans; the silver is dissolved, the solution separated from the residue of gold, and the silver sul- phate decomposed with metallic copper. Metallic silver precipi- tates, and copper sulphate remains in solution. Copper sulphate is also prepared by allowing sulphuric acid to drip on scrap copper with free access of air, the copper being slowly oxidized and dissolved. Or metallic copper, contained in lead-lined tanks, may be treated with hot acid. Scrap copper is often heated red-hot in a furnace, and then sulphur is thrown in, and the door tightly closed. Cuprous sulphide is formed, which is then oxidized at a red heat by admitting air into the furnace. A mixture of cop- per sulphate and oxide is thus produced, which is treated with hot dilute sulphuric acid, and the solution so obtained is evaporated. 1) 2Cu + S = Cu 2 S. 2) Cu 2 S + 5 O = CuS0 4 + CuO. 3) (CuS0 4 + CuO) + H 2 S0 4 = 2 CuS0 4 + H 2 0. Copper sulphide ores, chalcopyrite, and chalcocite, and artificial copper mattes, are sometimes converted into blue vitriol; but the ferrous sulphate formed crystallizes with the copper, sulphate. Such blue vitriol is much used where iron is not injurious. The iron may be removed by roasting the salt until the ferrous sulphate is decom- posed into oxide, and then dissolving in water and recrystallizing. Or the solution may be boiled with a little nitric acid, or lead perox- ide, until the iron is converted to the ferric state, when, by adding copper carbonate, or oxide, or barium carbonate, and boiling again, the iron precipitates. Some copper ores contain zinc, and yield a bluestone, contami- nated with zinc sulphate. The acid " dipping liquors " from copper and brass works are also used for blue vitriol, but these are gener- ally contaminated with zinc. The hammer-scales (copper oxide) pro- duced in rolling and working sheet copper, are often dissolved in dilute acid to form blue vitriol. Copper sulphate forms deep blue crystals, containing 5 molecules of water. In dry air, the crystals effloresce, and fall to a white 240 OUTLINES OF INDUSTRIAL CHEMISTRY powder, but all the water does not escape until the mass is heated to 240 C. The anhydrous salt is a white powder, and will abstract water from alcohol or organic liquids. Bluestone is largely used as a mordant in calico printing, and in dyeing; for preparing other copper salts and pigments; in the preparation of germicides and insecticides (Bordeaux mixture, etc.), for batteries, and electrolytic baths ; in metallurgy, and in most operations where a soluble copper salt is desired. Zinc sulphate or white vitriol, ZnS0 4 7 H 2 0, is not of very great importance. It is made by roasting zinc blende (sphalerite), or zinc-lead ores,* and leaching the mass with water or dilute sulphuric acid. Or scrap zinc is dissolved in dilute acid. The solution may be purified from copper by introducing a plate of metallic zinc, upon which the copper deposits. Iron is removed by heating the solu- tion in the air for a considerable time, while stirring well, and then adding a small amount of zinc carbonate or oxide, to precipitate the ferric oxide. Zinc sulphate forms colorless crystals containing 7 molecules of water, which effloresce in the air. It is very soluble in water. When heated, the crystals melt in their water of crystallization, and at 100 C., 6 molecules of water are expelled. The final molecule is driven off at 300 C., while at a red heat, the anhydrous salt decom- poses, leaving a residue of zinc oxide. Zinc sulphate is used somewhat in dyeing and printing; as a disinfectant ; for preserving and clarifying glue solutions ; in medi- cine as an astringent, and in lotions ; in the preparation of dryers for " boiled oils " ; and to some extent, as a preservative for hides and timber. Aluminum sulphate, Al 2 (S0 4 )g, 18H 2 0, is now, extensively em- ployed in the arts, under the name "concentrated alum." It is usually prepared from pure kaolin, or from bauxite [A1 2 0(OH) 4 , or A1 2 3 '2H 2 0], or from the hydrated alumina obtained in the cryolite soda process (p. 92). Aluminum hydroxide, prepared from bauxite or cryolite, is almost entirely free from iron, since it is precipitated from an alkaline solution of sodium aluminate, in which the iron of the mineral is not soluble. When this hydroxide is dissolved in pure sulphuric acid, a very pure aluminum sulphate is formed. * Bruno Kerl, Mineral Industry, 1895, 83. SULPHATES 241 (a). Aluminum sulphate from clay : China clay, free from cal- cium carbonate, is calcined at a moderate heat, until nearly all of its water is expelled ; then it is powdered and sifted through very fine sieves, and mixed with a little less than the theoretical quantity of sulphuric acid of 1.45 to 1.50 sp. gr., and heated with free steam to start the reaction, which soon becomes very violent. The mass swells, and quantities of steam escape, but when the reaction ceases, the swelling subsides. If it is now allowed to cool, a stone-like substance is obtained, which is much employed in the arts as " alum cake." It contains all the silica and iron impurities of the clay, and usually from 2 to 3 per cent of free acid. But if the thick pasty mass is diluted with warm water while still hot, and decanted or filtered from the insoluble impurity, a solution of the sulphate is obtained, which on evaporation yields a salt containing about 0.2 per cent iron, and a trace of free acid. It is often customary to convert this solution directly into alum (p. 244), by adding the necessary alkaline sulphate. (b). Aluminum sulphate from bauxite : Bauxite is more easily decomposed by acid than is clay, but if dissolved directly, the prod- uct contains a large amount of iron. However, considerable bauxite is decomposed with acid to form a hard cake which is known in trade as " alumino-ferric cake," and is used for many purposes where iron and free acid do no harm, and a cheap source of soluble alumina is desired; e.g. in precipitating sewage and waste liquors from dyeworks. But a pure sulphate is obtained by the following processes : The bauxite is roasted and powdered very fine, and is mixed with calcined and very finely powdered soda-ash, in the proportion of 1 molecule of A1 2 3 to 1.1 molecules of Na 2 O. If the bauxite contains much silica, more soda may be used, but the amount should not be sufficient to leave free carbonate in the product after calcination, otherwise the mass may fuse, and the solution of sodium aluminate obtained by lixiviating will be unstable. The mixture is calcined at a white heat, until all carbon dioxide and water are expelled; this requires 3 or 4 hours. The product is a porous, pale green or blue mass, which is ground and lixiviated with hot water, in a wooden tank, while stirring actively. A little caustic soda is added to the water, to prevent precipitation of alumina. (See Bayer's process, below.) The lixiviation must be rapid, not occupying more than 10 minutes, after which the solution of aluminate is decanted. According to Jurisch,* the liquor should be at least 35 Be. density, * Fabrikation von Schwefelsaure Thonerde, 52. 242 OUTLINES OF INDUSTRIAL CHEMISTRY and contain 170 grams A1 2 3 , and 182 grams JSTa 2 0, per litre. Weaker solutions are said to yield a slimy precipitate of alumina, when decomposed in the next stage of the process. The liquor is quickly filtered (a filter press is recommended), heated to 90 C., and de- composed by passing carbon dioxide into it, by which hydrated alumina is precipitated in a granular form, which is readily washed free from soda. The silica and iron remain dissolved in the mother- liquor. The carbon dioxide may be derived from limekiln gases, or from the calcination of sodium bicarbonate. The pure aluminum hydroxide thus prepared is added slowly to hot, pure, concentrated sulphuric acid, until the frothing ceases ; the solution is run into flat lead pans to cool, when it forms a crys- talline mass. If an excess of alumina is used in neutralizing the acid, basic salts result. The sulphate made in this way is nearly free from iron and silica, but sometimes contains small quantities of soda. It is now much used in the arts under the name of "concentrated alum." From analysis, the formula appears to be, A1 2 (S0 4 ) 3 20 H 2 0, but the slight excess of water may be hygroscopic, and not combined. According to the patented process of K. J. Bayer,* a solution of sodium aluininate is prepared, containing 1 A1 2 3 to 1.8 Na 2 ; by stirring more powdered alumina into this, a crystalline precipitate of aluminum hydroxide separates, until the solution contains the molecular proportions, 1 A1 2 3 to 6 Na 2 O, silica and other impurities remaining in solution. When evaporated to a density of 40 Be., and digested with finely powdered bauxite, at 170 C., under pressure of 4 atmospheres, while stirring actively, the solution dissolves more alumina out of the bauxite, to again form sodium aluminate liquor, having the molecular proportion of about 1 A1 2 3 to 1.8 Na 2 0. This solution is decomposed as above, and the cycle of operations re- peated. The silica dissolved in the aluminate solution is precipi- tated during the digestion as an insoluble double silicate of sodium and aluminum (Na 2 Al 2 Si 3 10 + 9 H 2 0), and remains with the resi- due, together with the iron. The hydrated alumina precipitated is washed free from sodium salts, and dissolved in acid as already described. Another process for sulphate consists in dissolving bauxite in dilute acid, at a temperature of 90 C., with the addition of a little sodium nitrate to oxidize all the iron to the ferric state ; then more bauxite, together with a little potash alum, is added. After stirring * Jurisch, Fabrikation von Schwefelsaure Thonerde, 17-18. German patents, 43,977 (1887) and 65,604 (1892). J. Soc. of Cliem. Ind., 1888, 625. SULPHATES 243 thoroughly, the whole is left for several weeks. The iron combines with some of the alumina to form a precipitate, 2Al 2 (S0 4 ) 3 + 2Fe(OH) 3 . (c). Sulphate from cryolite : The hydrated alumina obtained in the cryolite soda process (p. 92) may be dissolved to make aluminum sulphate in the usual way. The product may contain some soda. Another method of utilizing cryolite depends on the following reactions : 1) 6 NaF, 2 A1F 3 + 6 Ca(OH) 2 = 6 CaF 2 + 2 Al(NaO) 3 + 6 H 2 O. 2) 2 Al(NaO) 3 + 6 NaF, 2 A1F 3 = 2 A1 2 3 + 12 NaF. 3) Al A + 3 H 2 S0 4 = A1 2 (S0 4 ) 3 + 3H 2 0. Powdered cryolite is boiled with milk of lime, and the solution of sodium aluminate decanted. By boiling the aluminate liquor for a long time, with more powdered cryolite, while stirring thoroughly, the second reaction takes place ; the residue is chiefly hydrated aluminum oxide, while sodium fluoride goes into solution. By boil- ing the latter with milk of lime, caustic soda may be obtained as a by-product. 2 NaF + Ca(OH) 2 = CaF 2 + 2 NaOH. By evaporating an aluminum sulphate solution until very con- centrated, and then cooling, a solid cake of the salt having a crystal- line structure is obtained ; its composition corresponds to A1 2 (S0 4 ) 3 .20H 2 0. It is difficult to obtain single crystals, but the usual formula assigned to them is A1 2 (S0 4 ) 3 18 H 2 0. The commercial product, however, never corresponds exactly to this formula. As now prepared, it contains but little free acid, or excess of alumina (basic salt), and only a minute trace of iron. It should contain 14 to 14.5 per cent A1 2 3 , and dissolve readily in water to form a clear solution; i.e. no basic salt should be present. About 0.5 per cent free acid, and 0.01 to 0.1 per cent Fe 2 3 , are the average content of commercial sam- ples. Since it may now be had of great purity, aluminum sulphate has largely replaced alum in the arts. It is extensively used as a mordant in dyeing ; in preparing size for paper ; for making alum and aluminum salts (red liquor, etc.) ; in tawing skins ; for pre- cipitating sewage or coloring matter from water; and, in general, for all purposes where alum was formerly used. 244 OUTLINES OF INDUSTRIAL CHEMISTRY ALUM An alum is a double sulphate of a univalent alkali metal and a hexad metallic radical of the form (E 2 )=, crystallized with 24 mole- cules of water. The general formula is therefore M 2 S0 4 ',R 2 (S0 4 ) 3 .24H 2 0, or, as it is more frequently written, MR(S0 4 ) 4 12 H 2 0. The alkali metal may be sodium, potassium, ammonium, lithium, caesium, or rubidium. The hexad radical contains aluminum, chromium, iron, or manganese. In the vast majority of alums, the essential part is alu- minum sulphate, but since this does not crystallize well alone, it has, until recently, been difficult to obtain it pure enough for most pur- poses. But the addition of an alkali sulphate forms alum, which crystallizes beautifully and is very pure, while the alkali sulphate itself has no injurious action in most cases where aluminum sul- phate is used. But since "concentrated alum' 7 (p. 240) can now be had very pure, it is generally preferred, because of its greater strength and solubility. All alums crystallize, with the same number of molecules of water, in the regular system, either as octahedrons, or as cubes. They are all isomorphous, and a crystal of one kind of alum will continue to grow by accretion, if placed in a solution of another alum. Alum crystallizes from solution very perfectly, and forms exceedingly pure crystals, even from impure solutions ; it is because of this property that it finds such extended use in the arts. Alum occurs in nature in small quantities, produced by the action of volcanic gases on rocks consisting of potash-aluminum silicates; also in combination with iron and aluminum hydroxides in the mineral alunite, or alum stone, K 2 S0 4 , A1 2 (S0 4 ) 3 , 4 A1(OH) 3 , also formed by volcanic action. Other sources are alum slates and shales, clay, bauxite, and cryolite. Alunite, or alum stone, is insoluble in water. It is calcined in heaps, or in small shaft kilns, at about 500 C., and the mass is then exposed to the weather for several months, being moistened from time to time. The calcination converts the iron and aluminum hydroxide into insoluble oxides, and the weathering forms alum in the mass, which is dissolved by lixiviation, and recrystallized. The alum thus obtained is basic, and crystallizes in cubes ; owing to imperfect settling of the liquors before crystallization, some iron oxide is inclosed, giving the crystals a red color. This iron is, how- ever, quite insoluble, and, no free acid being present, the alum yields ALUM 245 a very pure, neutral solution, and is especially desired for many purposes. It is most extensively made at Tolfa, near Rome, and so is called Roman alum. An imitation is made by coloring alum crystals derived in other ways, with, brick dust, or with iron oxide (Venetian red). Alum slates or shales are mixtures of iron pyrites, aluminum silicates, and bituminous matter. By exposure to the weather, the pyrites is oxidized to ferrous sulphate and sulphuric acid, and these react with the aluminum silicate to form aluminum sulphate. Basic ferric sulphate is also formed. The oxidation can be greatly has- tened by roasting the shale before weathering it, but the temperature must not be high enough to drive off the sulphur. After weathering, the mass is systematically lixiviated, and a solution of aluminum sulphate, having a specific gravity of about 1.16, and containing some calcium and iron sulphates, comes from the leach tanks. This is clarified by settling, and some of the calcium and basic ferric sul- phates deposit. The solution is evaporated in lead or iron pans by surface heating with direct flame, until ferrous sulphate crystallizes on cooling, and then the mother-liquor containing the aluminum sul- phate is further concentrated to 1.40 sp. gr. During this evapora- tion, more calcium sulphate and a basic ferric sulphate separate. Scrap iron is generally placed in the vessel during concentration, to convert the ferric sulphate into the basic salt, and to reduce the destructive action on the pan. The hot solution is decanted from the sediment, and mixed with potassium or ammonium sulphate in exact amount to form the alum. By agitating the liquid during the cooling, very fine crystals of alum, called " alum meal," separate. If the aluminum sulphate solution contains much iron, as is gen- erally the case when working on a large scale, it is often the prac- tice to add potassium chloride to form the alum. By decomposing the iron sulphates, this forms potassium sulphate in the solution, and, at the same time, converts the iron into the very soluble ferric and ferrous chlorides, which remain in the solution when the alum separates. But with a pure solution of aluminum sulphate, this causes loss by converting part of the aluminum into the very soluble aluminum chloride : 4 A1 2 (S0 4 ) 3 + 6 KC1 = 3 SK 2 S0 4 , A1 2 (S0 4 ) 3 | + 2 A1C1 3 . The alum meal is washed with cold water in a centrifugal machine, and recrystallized. It is sold both in the crystallized and in the powdered form. The manufacture of alum from clay, bauxite, or cryolite in- 246 OUTLINES OF INDUSTRIAL CHEMISTRY volves the preparation of a pure solution of aluminum sulphate by methods already given, and the addition of the exact quantity of alkali sulphate to form the alum. Blast furnace slag has been proposed as a source of alum. It is decomposed with hydrochloric acid, and the aluminum chloride solu- tion is decomposed with calcium carbonate ; the aluminum hydroxide so obtained is dissolved in sulphuric acid. The process is not suc- cessful, however. "Neutral alum" is made by adding sodium or potassium carbon- ate, or caustic soda to an alum solution, until a slight precipitate remains, even after vigorous agitation. After filtering, cubical crys- tals of the neutral alum can be obtained, but, as a rule, the neutral solution is made by the user, and is not crystallized. Neutral alum is much used in mordanting, because of the great readiness with which it deposits alumina on the fibre. The most important alums of commerce are potassium alum, K 2 S0 4 A1 2 (S0 4 ) 3 24 H 2 0, and ammonium alum, (NH 4 ) 2 S0 4 - A1 2 (S0 4 ) 3 . 24 H 2 0. The latter is less soluble than the potash salt, but in all other re- spects they are quite similar. Both are stable in the air. Sodium alum, Na 2 S0 4 - A1 2 (S0 4 ) 3 24 H 2 0, is very soluble in water, and difficult to purify. Moreover, the crystals effloresce on exposure to the air; in this condition, they are sometimes sold as "porous alum." When heated, alum loses water and some sulphuric acid, and falls to a white powder, " burnt alum," which is difficultly soluble in water. This is used occasionally as a caustic in medicine. The chief uses of common alum are as a mordant in dyeing; m preparing size for paper-making ; in tawing skms ; in making pig- ment lakes ; for clarifying turbid liquids, and precipitating sewage ; and for hardening plaster of Paris casts, and other articles. Besides the common alums of trade, containing aluminum sul- phate as a basis, two others, iron alum and chrome alum, are also employed in the arts to some extent. Iron alum, which may be either (NH 4 ) 2 S0 4 , Fe 2 (S0 4 ) 3 24 H 2 0, or K 2 S0 4 , Fe 2 (S0 4 ) 3 24 H 2 0, is made by oxidizing a copperas solution to form ferric sulphate, adding the proper quantity of alkali sul- phate, and cooling below 10 C. It forms pale violet crystals, which are rather unstable, efflorescing and oxidizing in the air, forming basic ferric salt. Iron alum is chiefly used as a mordant. Chrome alum, K^SO^ Cr 2 (S0 4 ) 3 24 H 2 0, is largely produced as a CYANIDES 247 by-product in the manufacture of alizarine. A mixture of potassium bichromate and sulphuric acid is employed to oxidize anthracene (Ci 4 H 10 ) to anthraquinone (C 14 H 8 2 ), from which the alizarine is pro- duced. The effect of the reducing action of the organic body on the bichromate mixture is to form potassium and chromium sulphates in the solution in proper proportion to unite in chrome alum : C 14 H 10 + K 2 Cr 2 7 + 4 H 2 S0 4 = C 14 H 8 O 2 + KJSO* Cr 2 (SO 4 ) 3 + 5 H 2 0. Chrome alum forms deep violet crystals, which effloresce on exposure to the air. It is used as a mordant ; and in tawing skins, especially in certain chrome tannage processes. REFERENCES Die Fabrikation des Alauns, des Bleiweisses und des Bleizuckers. Dr. F. Jiine- mann, Leipzig, 1882. (Hartleben.) Die Fabrikation von schwefelsaurer Thonerde. K. W. Jurisch, Berlin, 1894. (Fischer. ) Journal of the Society of Chemical Industry : 1882, 124. B. E. R. Newlands. 1883, 482. J. W. Kynaston. 1886, 16. J. W. Beveridge. 1888, 625. (Bayer's Patent for Alumina Hydrate.) 1892, 4 and 321. Chemical News, 42, 191 and 202. CYANIDES Cyanides are now produced from the spent iron oxide from gas purification, and from fusions of alkaline carbonates with nitroge- nous organic matter and iron borings. A small quantity of ammo- nium sulphocyanide (thiocyanate) is made synthetically, but the manufacture of cyanides directly from the nitrogen of the air has not yet been put on a commercial basis. Bunsen and Playfair's process for making cyanides, by heating barium carbonate with powdered charcoal in an atmosphere of dry nitrogen, cannot be worked successfully on a large scale. It depends on the following reaction : BaC0 3 + 4 C + 2 N = Ba(CISr) 2 + 3 CO. A large amount of cyanogen compounds are present in the gases from iron blast furnaces, and much ingenuity has been expended on methods for recovering these salts, but as yet with little success. Practically, all cyanogen derivatives are now made from either ammonium sulphocyanide or alkali ferrocyanides. 248 OUTLINES OF INDUSTRIAL CHEMISTRY Ammonium sulphocyanide (thiocyanate), NH 4 SCN, is sometimes prepared by Tscherniak and Giinzburg's modification of Gelis' pro- cess.* This depends on the following reactions : 1) CS 2 4-2NH 3 = NH 4 S 2 CNH 2 . (Ammonium dithiocarbamate.) 2) NH 4 S 2 CNH 2 = NH 4 SCN + H 2 S. Carbon disulphide and ammonium hydroxide (0.91 sp. gr.), in proper proportion for reaction (1), are heated in an autoclave to 125 C., while stirring actively. The steam is then cut off, but the stirring continued until the pressure rises to 15 atmospheres. This completes the first reaction, and the contents of the autoclave are blown off into a still, which is heated to 110 C., at which point the ammonium dithiocarbamate is decomposed. The products of distil- lation are passed through condensers and scrubbers to collect vola- tile ammonium salts and carbon disulphide, while the hydrogen sulphide is conducted into a gasometer. The liquid in the still contains ammonium sulphocyanide, and is evaporated in tin vessels, and crystallized. Sometimes lime and manganese peroxide are added to assist the reaction in the autoclave, in which case calcium sulphocyanide is formed : 2 CS 2 + 2 NH 3 -f Mn0 2 + CaO = Ca(SCN) 2 + MnS + S + 3 H 2 0. Ammonium sulphocyanide and potassium ferrocyanide are now largely obtained from the spent iron oxide from the purification of illuminating gas. The spent oxide is first lixiviated with warm water (60 C.), until the liquor has a density of from 1.07 to 1.085. The solution, containing ammonium sulphocyanide and other am- monium salts, is evaporated to 1.2 sp. gr., and cooled, when the associated salts (ammonium sulphate, etc.) crystallize. The mother- liquor is further concentrated, and impure crystals of the sulpho- cyanide separate, which are purified by recrystallization. Ammo- nium sulphocyanide is also obtained from gas-liquor by treating the non-volatile residue from the steam distillation (see Ammonia) with copper and iron sulphates, whereby cuprous sulphocyanide is formed. This is washed, and treated with ammonium sulphide, forming cuprous sulphide and ammonium sulphocyanide. The latter is then extracted with water. Ammonium sulphocyanide is very soluble in water and in alcohol. It is used as a source of other sulphocyanides, and in dyeing, to pre- vent the injurious action of iron on the color. * Dingler's Polytechnisches Journal, 245, 214. CYANIDES 249 The residue from the lixiviation is mixed with quicklime (which is slaked by the moisture in the damp mass), and heated by steam in closed vessels to 100 C. The lime decomposes the ferric ferrocy- anide and the double iron-ammonium cyanides, setting free ammonia gas, which is absorbed in scrubbers, and forming calcium ferro- cyanide, which is obtained by lixiviating the mass. The solution of calcium ferrocyanide is evaporated, and treated with the calculated amount of potassium chloride to form the difficultly soluble calcium- potassium ferrocyanide, CaK 2 Fe(CN) 6 . This is separated from the mother-liquor, washed, and decomposed with potassium carbonate to form potassium ferrocyanide. The reactions are : 1) Fe 4 SFe(CN) 6 | 3 + 6 Ca(OH) 2 = 3 Ca 2 Fe(CN) 6 + 4 Fe(OH) 2 . 2) (NH 4 ) 3 Fe 3 SFe(CN) 6 S3 + 6Ca(OH) 2 = 3 Ca 2 Fe(CN) 6 + 3 Fe(OH) 3 + 3 ISTH, + 3 H 2 0. 3) Ca 2 Fe(CN) 6 + 2 KC1 = CaK 2 Fe(CN) 6 + CaCl 8 . 4) CaK 2 Fe(CN) 6 + K 2 C0 3 = K 4 Fe(CN) 6 + CaC0 3 . Potassium ferrocyanide, K 4 Fe(CN") 6 3 H 2 0, also called yellow prussiate of potash, is also made by fusing together potassium car- bonate, iron borings, and nitrogenous organic matter of any kind (horn, hair, blood, wool waste, and leather scraps).* The potash is fused in a shallow cast-iron pan, set in a reverberatory furnace, and the organic matter, mixed with from 6 to 8 per cent of iron borings, is stirred in, in small portions at a time, until about 1^ parts of the mixture for each part of potash have been added. The temperature must be kept high enough to keep the mass perfectly liquid, but not hot enough to volatilize the cyanogen salts. The reaction is violent at first, and when the liquid remains in quiet fusion the process is ended, and the melt is ladled into iron pans to cool. The mass, containing a number of substances (KCN, K 2 C0 3 , K 2 S, FeS, metallic iron, carbon, etc.), is broken up into lumps the size of an egg, and digested with water at 85 C. for several hours. During this process, reactions take place between the potassium cyanide and iron sulphide, by which the ferrocyanide is formed : 6 KCN + FeS = K 2 S + K 4 Fe(CN) 6 . Liebig explains the reactions during the fusions as follows: part of the carbon and nitrogen of the organic matter combine to * The organic refuse is sometimes partially charred in retorts, by which much ammonia is driven off and saved. But the yield of ferrocyanide is then less, since the nitrogen content of the char is small. 250 OUTLINES OF INDUSTRIAL CHEMISTRY form cyanogen (CN) 2 , while some of the potash is reduced by the excess of carbon to metallic potassium, which at once unites with the cyanogen to form potassium cyanide. The sulphur in the organic matter combines with the iron, forming ferrous sulphide. Finally, on lixiviating, the formation of the ferrocyanide takes place. The solution is evaporated in iron pans by the waste heat of the furnace, and clarified while hot; on cooling, the crude ferro- cyanide crystallizes, and is purified by recrystallization. The mother-liquors yield more impure salt on further evaporation. Potassium ferrocyanide forms splendid large lemon-yellow crys- tals, having 3 molecules of crystal water, which it gives off at 100 C., and is converted to a white powder. It is not poisonous. It is largely used for making Prussian blue ; in calico printing, and in in dyeing; for case-hardening iron; for making potassium cyanide and ferricyanide ; and to a small extent in explosives, and as a chemical reagent. Barium sulpho cyanide, Ba(SCN)^, is made by heating ammonium sulphocyariide with barium hydroxide solution, under slight pressure. Ammonia distills off, and the liquid is evaporated to yield the barium salt, Ba(SCN) 2 2 H,O. This is generally used for making potassium and aluminum sul- phocyanides, KSCN and A1(SCN) 3 , which are used in textile dyeing and printing. Potassium ferricyanide, red prussiate of potash, K 3 Ee(ClST) 6 , is usually made by passing chlorine gas into a solution of the ferro- cyanide, until ferric chloride no longer forms a precipitate, only pro- ducing a brown color in the liquid. It may also be made by exposing the dry powdered ferrocyanide to chlorine until a test portion, dis- solved in water, gives nothing but a brown color with ferric chloride. 2 K 4 Fe(CN) 6 + 2 01 = 2 KC1 + 2K 3 Fe(CN) 6 . Excess of chlorine must be avoided, since this forms a dirty green precipitate (Berlin green) in the solution, which cannot be removed by filtering. Lunge * recommends boiling the solution of ferrocyanide with lead peroxide, while passing a stream of carbon dioxide through the liquor : 2 K 4 Fe(CN)e -f H 2 + = 2 K 3 Fe(CN) 6 + 2 KOH ; but the final reaction may be written : 2 K 4 Fe(CN) 6 + Pb0 2 + 2 C0 2 = 2 K 3 Fe(CN) 6 + PbC0 3 + K 2 C0 3 . * Dingler's Polytecbnisches Journal, 238, 75. CYANIDES 251 An excess of carbon dioxide is necessary to prevent decomposi- tion of the ferricyanide by the lead oxide and alkali. A very good product is obtained by the action of potassium per- manganate on a mixture of calcium and potassium ferrocyanide solu- tions : 3 Ca 2 Fe(CN) 6 + 7 K 4 Fe(CN) 6 + 2 KMn0 4 = 10 K 3 Fe(CN) 6 + 6 CaO + 2 MnO. The calcium and manganese hydroxides formed are but slightly soluble, and are easily removed from the solution by carbon dioxide, and the ferricyanide purified by crystallization. Potassium ferricyanide crystallizes in blood-red prisms, without crystal water, and is very soluble, forming a solution of an intense yellow color. With ferrous salts, it gives the blue pigment, Turn- bull's blue. With ferric salt, it gives a brown coloration, but no pre- cipitate. Its solution, with caustic potash, is a powerful oxidizing liquid, and as such is used in calico printing for a " discharge " on indigo and other dyes. It also forms part of the sensitive coating for "blue print" papers. It has been recommended for use with the potassium cyanide solution in gold extraction. Potassium cyanide, KCN, is generally made by fusing the ferro- cyanide with potassium carbonate, until the evolution of gas ceases. The following is the reaction : - K 4 Fe(CN) 6 + K 2 C0 3 = 5 KCK -f KCNO + C0 2 + Fe. The metallic iron separated sinks to the bottom of the crucible, and the fused mixture of cyanide and cyanate is run off. The addition of powdered charcoal reduces part of the cyanate to cyanide. The product is pure enough for many purposes. The cyanate, which is sometimes injurious, may be reduced by the action of metallic zinc or sodium, or the cyanide may be extracted with alcohol, acetone, or carbon di sulphide. By fusing the ferrocyanide with sodium carbonate, a mixture of sodium and potassium cyanides is obtained, which is extensively employed in the arts under the name of "cyan-salt." This is cheaper than the pure potassium salt. Potassium cyanide is also made by fusing the dry ferrocyanide in closed crucibles, until nitrogen ceases to be given off. Carbide of iron is formed, and sinks to the bottom of the crucible, if the fusion is allowed to stand for a considerable time. But the separation is imperfect, and the product is usually dissolved in alcohol or acetone, and the clarified solution heated in a still to recover the solvent. 252 OUTLINES OF INDUSTRIAL CHEMISTRY The product is then heated until it fuses, and when cold, it forms a white, transparent mass. Air must be carefully excluded during the whole process, to prevent the formation of cyanate. The re- action is : K 4 Fe(CN) 6 = 4 KCN + FeC 2 + N 2 . But the product is not entirely free from potassium carbonate, since it is practically impossible to evaporate a cyanide solution without some decomposition and escape of hydrocyanic acid. The caustic potash thus formed then combines with carbon dioxide from the air. Water cannot be used to leach the iron carbide residue, since the potassium cyanide in solution at once recombines with the iron to form ferrocyanide again. Potassium cyanide is made from the sulphocyanide, by extract- ing the sulphur with zinc or lead.* The zinc is melted in a graphite vessel, and charcoal powder is spread over its surface. The sulpho- cyanide is stirred into the fused metal until the mass becomes a thick paste, when it is allowed to cool. It is then systematically lixiviated in tanks similar to Shank's apparatus (p. 76). Any alkali sulphide is precipitated by adding lead cyanide. The solu- tion is evaporated in vacuum, and yields an impure product, con- taining cyanate and double zinc-potassium cyanide. Cyanides are also produced by conducting ammonia gas through vertical retorts, containing charcoal and alkali carbonate, and heated to a red heat. The mass is then withdrawn from the retort, lixivi- ated, and the solution concentrated to 1.4 sp. gr. Potassium car- bonate is added to the cold solution, precipitating the potassium cyanide, which is freed from mother-liquor in centrifugal machines, and recrystallized : K 2 C0 3 + C + 2 NH 3 = 2 KCN + 3 H 2 0. Castner proposes to run metallic sodium through a retort filled with coke, while passing ammonia gas into it. The reaction is said to work at a lower temperature than in other processes. Many other patents for the production of cyanides have been taken out, but at present nearly the whole supply of alkali cyan- ides is derived from potassium ferrocyanide. Potassium cyanide comes in commerce as white lumps or powder, very soluble in water and having alkaline reaction. It smells some- what like bitter almond oil, owing to the prussic acid liberated from it by the action of carbon dioxide and moisture in the air. On stand- * J. Soc. Chem. Ind., 1892, 14. CARBON DISULPHIDE 253 ing, or when warmed, its aqueous solution decomposes, forming ammonia and potassium formate : KCN + 2 H 2 = NH 3 + HCOOK. The commercial salt always contains cyanate and carbonate, and is sold in various grades for particular purposes. The best quality is about 98 to 99 per cent KCN, but ordinary grades contain but 65 or 70 per cent. It is a very powerful reducing material when heated with reducible substances, and hence its use as a flux. It is extremely poisonous, both when taken internally and when intro- duced directly into the blood. It is extensively employed in elec- troplating as the solvent in the bath, -as it forms soluble double cyanides with gold, silver, copper, and other metals ; it is also used as a flux in assaying and metallurgy ; its greatest use at the present time is for the recovery of gold from low grade ores and tailings of other reduction processes. A weak solution is used to dissolve the gold, forming aurous potassium cyanide, AuCN, KCN. It was for- merly much used in photography for " fixing " the image, but for this purpose it has been largely replaced by sodium thiosulphate. CARBON DISULPHIDE Carbon disulphide, CS 2 , is extensively employed as a solvent, especially for grease and oils. It is made by passing sulphur vapor over coke or charcoal, which has been heated to a " cherry red " in a vertical retort of cast iron or glazed earthenware. From the top of the retort, a w r ide pipe leads to a vessel in which uncombined sul- phur vapor, passing out with the carbon disulphide, is condensed. The carbon disulphide passes on, and, condensing in a Liebig's con- denser, collects under water in a receiver, and is drawn into tanks, from which it is forced by compressed air into storage tanks placed on a higher level. The uncondensable gases, chiefly hydrogen sul- phide, are led from the receiver into a tower containing plates or shallow trays, over which vegetable oil trickles, to absorb any trace of disulphide vapor ; then they go into a second tower, containing layers of lime, or iron oxide, which absorb the hydrogen sulphide. When sufficiently charged, the oil is heated, and the disulphide dis- tills off ; the oil is then returned to the tower. Of the various forms of apparatus devised for making carbon disulphide, that of I. Singer * is one of the best. The crude disul- * J. Soc. Chem. Ind., 1889, 93. 254 OUTLINES OF INDUSTRIAL CHEMISTRY phide attacks nearly all metals, and the receiver, tank, and pipes should be lined with lead. Eetorts of cast iron are made very heavy, but are rapidly destroyed by the action of the sulphur. Very pure coke or charcoal is necessary, and it should be heated immediately before charging into the retort, to expel any absorbed oxygen or moisture, since these combine with some of the sulphur vapor, and form impurities in the product. The temperature should be kept as constant as possible, at a red heat. The sulphur is sometimes intro- duced in a solid state, through an opening near the bottom of the retort, but it is better to melt it in a separate vessel, and allow it to flow in a small stream, entering the retort at the bottom. It has recently been proposed to vaporize the sulphur before it enters the retort, the chief difficulty then being to prevent its passing through the retort uncombined. The crude carbon disulphide is impure, and has a very offensive odor. It is purified by forcing lime-water in a fine spray, from a perforated lead coil, through the carbon disulphide liquor, until the water running out of the tank is clear. This removes the hydrogen sulphide, and the washed carbon disulphide is then mixed with a little colorless oil; some water, containing a little lead acetate, is added to remove the remaining sulphur impurities, and the mixture is distilled on a steam bath. Sometimes the crude product is puri- fied by distilling in a large boiler with some caustic soda, or milk of lime, or by shaking with anhydrous copper sulphate, and then re- distilling by steam heat. Carbon disulphide is a pale yellow, or colorless, heavy, mobile liquid, having a fetid odor when impure, boiling at 46 C., and extremely volatile at ordinary temperatures. Its vapors inflame at 149 C., are very heavy, and are poisonous when breathed. It is sent to market in sheet iron cans, or drums, and is regarded as dan- gerous freight because of its extreme volatility, and the explosive nature of its vapor when mixed with air. When burned, it produces large quantities of suffocating gases (C0 2 , S0 2 ). It is very slightly soluble in water, but mixes well in all proportions with ether, ben- zene, alcohol, and many oils. It dissolves sulphur, phosphorus, iodine, camphor, wax, tar, resins, rubber, and nearly all oils and fats. Hence its use as a solvent and extractive agent is very exten- sive. It is also used as a disinfectant ; as a germicide and insecti- cide in agriculture, and in museums and herbariums ; in refrigerating machines ; for exterminating moles, rats, woodchucks, and other bur- rowing animals; in the manufacture of rubber cement; in making cyanides and carbon tetrachloride ; and in organic preparation work. MANGANATES AND PERMANGANATES 255 CARBON TETRACHLORIDE Carbon tetrachloride is made by passing a mixture of carbon disulphide vapor and chlorine through a red-hot porcelain tube.* A mixture of sulphur chloride, S 2 C1 2 , and carbon tetrachloride results, which is treated with milk of lime, and digested with potash, and the tetrachloride distilled. Or dry chlorine may be led into carbon disulphide containing a little iodine in solution, f The tetrachloride is distilled off, and washed with alkali, to remove iodine and sulphur chloride. CS 2 + 6 01 = C01 4 + S 2 C1 2 . Carbon tetrachloride is a heavjr, colorless liquid, boiling at 76 C. It is a good solvent for many substances, and may be used instead of chloroform or carbon disulphide for extractions. It is not inflamma- ble, and is less poisonous than the latter. MANGANATES AND PERMANGANATES Sodium manganate, Na 2 Mn0 4 , is made by mixing sodium nitrate or caustic soda solution, with powdered pyrolusite, or manganese oxides, evaporating to dryness, and calcining the mass at a red heat, with access of air, in shallow vessels. The following is the reaction involved: Mn0 2 + 2 NaOH -f O = Na 2 Mn0 4 + H 2 0. The product of the fusion is a dull green, porous mass, which, if lixiviated, yields a green solution of the manganate. But this is unstable, and if exposed to the air, or treated with an acid, or boiled, the manganate is converted into permanganate : 3 Na a Mn0 4 + 2 H 2 O = 2 NaMnO 4 + 4 NaOH + Mn0 2 . In alkaline solution, however, the manganate is more stable. Sodium manganate is a powerful oxidizing agent, and is used as a disinfectant. It is also converted to the permanganate, and sold in solution as " Condy's liquid " for disinfecting purposes. Sodium permanganate does not crystallize well. Potassium manganate, K 2 Mn0 4 , is very similar to the sodium salt, and is made in the same way. It is chiefly used in preparing the permanganate, KMn0 4 , which crystallizes very well. This, being * Kolbe, Annalen der Chemie und Pharmacie, 45, 41 ; 54, 145. t Lever and Scott, English Patent No. 18,990, 1889. 256 OUTLINES OF INDUSTRIAL CHEMISTRY easily purified, and stable when crystallized, is the most important permanganate of commerce. It is generally made by decomposing potassium manganate with sulphuric acid, carbon dioxide, or with chlorine, and is purified by recrystallizing. 3 K 2 Mn0 4 + 2 H 2 S0 4 = 2 KMnO 4 + 2 K 2 S0 4 + Mn0 2 + 2 H 2 0. 3 K 2 Mn0 4 + 2 C0 2 = 2 KMn0 4 + 2 K 2 C0 3 + Mn0 2 . 2 K 2 Mn0 4 + C1 2 - 2 KMn0 4 + 2 KC1. Potassium permanganate forms deep purple, prismatic crystals, which dissolve in 16 parts of cold water. The solution has a power- ful oxidizing action, and can only be filtered on glass-wool or asbes- tos. When mixed with organic matter, the dry powder is subject to spontaneous combustion, and forms explosive mixtures with easily oxidizable substances. It is used as a disinfectant ; in bleaching and dyeing ; for coloring wood a deep brown ; for purifying ammonia and carbon dioxide gases ; and in medicine. PART II ORGANIC INDUSTRIES DESTKUCTIYE DISTILLATION OF WOOD THE properties of wood have been considered on page 24. It consists mainly of cellulose (C 6 H 10 5 ) n , with its incrusting layer of lignin, and of sap, containing water, resins, tannins, coloring matter, and mineral salts. Air-dried wood contains from 15 to 20 per cent of moisture. When heated in closed retorts away from the air, the cellulose and ligneous matter decompose after the moisture is ex- pelled, and a large number of substances result, only a few of which are of commercial value. These crude products are gases, thin liquids, viscous liquids or tar, and charcoal. When wood is car- bonized in pits (p. 27). the volatile products go to waste. But by the use of retorts, which is rapidly extending to all countries, the valuable by-products, liquid distillates and tar, are saved ; the gases evolved are mainly hydrogen, methane, ethane, ethylene, carbon monoxide, and carbon dioxide ; they have no value for illuminating, and are generally burned under the retorts, thus economizing fuel. When wood is heated in retorts, the moisture is driven out, but no decomposition occurs until the temperature approaches 160 C. Between 160 and 275 C., a thin, watery distillate, known as " pyroligneous acid," is chiefly formed; above 275 C. the yield of gaseous products becomes marked, and between 350 and 450 C. liquid and solid hydrocarbons are most extensively formed. Above this last temperature, little change occurs, and charcoal, containing the mineral ash, remains in the retort. The pyroligneous acid contains the important liquid distillates, methyl alcohol and acetic acid, together with acetone, methyl acetate, allyl alcohol, phenols, and a great many other substances. The tar contains aromatic hydrocarbons and paraffines. Its most valuable constituent is the creosote oil, containing guaiacol, creosol, and other s 257 258 OUTLINES OF INDUSTRIAL CHEMISTRY phenols of high molecular weight. A comparatively small amount of phenol or carbolic acid is present, however. The proportion of gaseous products to liquid distillate and char- coal is largely dependent upon the method of heating the retort; by rapid heating to a high temperature, the quantity of gas is much increased ; by distillation at a low temperature, the yield of pyro- ligneous acid, tar, and charcoal is greater. The variety of wood used, affects the amount of acid |D and tar ; deciduous trees, espe- cially birch, oak, and beech, are preferred ; coniferous woods yield less acid, but afford a tar (Stockholm tar) containing much resin and turpentine. Since the yield of acid and tar is increased by the rapid removal of the vapors from the retort, in modern plants exhausters are used. The retorts employed are wrought-iron cylinders set in pairs, in brick furnaces, so that the flame does not strike directly upon them. They may be hori- zontal or vertical. The horizontal retort (A), Fig. 66*, has a door at the front, while from the back a pipe (B) conducts the vapors to the condenser (C), from which the uncondensed gases pass through the pipe (D) to the grate and are burned. The condenser is made of coils of copper pipe, surrounded by a water jacket or tank, but having the elbows outside the tank, for easy removal for cleaning. The wood is piled by hand lengthwise, in the hot retort, after the charcoal from the previous charge has been drawn into a closed vessel to cool. When distilling conif- erous woods, which yield much tar, a tar separator is put between the retort and the condenser. The pyroligneous acid is col- lected in wood tanks, where tarry matters deposit on standing. Vertical retorts, Fig. 67*, are made in duplicate, and so arranged that when a charge has been carbonized, the retort (A) is lifted out of the furnace by means of a crane and allowed to cool unopened, and another, charged with fresh wood, is at once put into its place. * J. Soc. Chem. Ind., 1897, 667 and 722 (M. Klar). DESTRUCTIVE DISTILLATION OF WOOD 259 This economizes time and heat, and no cooling vessel is needed ; but two sets of retorts are required, and the wear from frequent moving is considerable. The condenser is similar to that described above. Kilns built of brick, similar to the beehive coke oven (p. 28), but provided with an exit pipe for the volatile products, are occa- sionally used, but less successfully than the iron retorts. In the collecting tanks, the pyroligneous acid separates from the tar, which settles to the bottom. The yield of acid is about 30 per cent, and of tar about 10 per cent of the weight of the dry wood. The acid averages about 10 per cent acetic acid, 1 per cent methyl alcohol, and 0.1 per cent acetone. It is a dark red-brown liquid, having a strong ac;d reaction and a peculiar empyreumatic odor. Its density varies according to the nature of the wood distilled, but usually falls between 1.020 and 1.050 sp. gr. It finds limited use in the manufacture of an impure acetate of iron, known as " black iron liquor " or " pyrolignite of iron." But for most purposes it is puri- fied, to separate the methyl alcohol, acetone, and acetic acid. The boiling point of methyl alcohol is 66 C., while that of acetic acid varies from 100 to 120 C., according to the amount of water present. Hence if the pyroligneous acid is distilled, and the receiver changed when the temperature approaches 100 C., the greater part of the methyl alcohol, together with acetone, methyl acetate, allyl alcohol, etc., is separated from the acetic acid and its homologues. But usually the vapors from the distillation are passed through milk of lime, which combines with the acetic acid to form calcium acetate, while the alcohol vapors pass on and are condensed. Most of the tarry matter remains in the still. If the solution of calcium acetate thus formed is filtered and evaporated to dryness, the salt is ob- tained in a commercial form, known as "gray acetate of lime." During the evaporation much of the tar and oily impurities rise to the surface and are removed by skimming. The tarry matters remaining in the acetate decompose during the drying process. If the pyroligneous acid is neutralized with lime before distilling off the methyl alcohol, the resulting calcium acetate is contaminated with much tar, and when evaporated to dryness forms the commer- cial " brown acetate of lime." The crude methyl alcohol, wood naphtha, or wood spirit, is purified by diluting with water until it becomes milky, owing to the separa- tion of oily impurities (ketones and hydrocarbon oils), which collect in a separate layer on standing, and are removed. The liquid is then redistilled over lime in a rectifying still (p. 9). The lime fixes the traces of acid and decomposes methyl acetate. The recti- 260 OUTLINES OF INDUSTRIAL CHEMISTRY fied spirit is usually filtered through a tower containing charcoal, to remove the coloring matter and unpleasant odor as much as pos- sible. By distilling again, over lime, methyl alcohol of 99 per cent is obtained. Acetone boils at 56.3 C., and is not removed from the methyl alcohol by distillation or treatment with lime. Hence the alcohol is treated with chlorine, which combines with the acetone, forming chlor-acetones, having high boiling points, and from which the alcohol is separated by distillation. Or iodine and caustic soda may be added ; these react with the acetone to form iodof orm, which precipitates. If calcium chloride is added, it combines with the alcohol to form a crystallized solid which is stable at 100 C. This is gently heated until the acetone is driven out, and is then treated with hot water under pressure ; the calcium chloride compound is decomposed and the methyl alcohol distills off. Commercial methyl alcohol is often slightly yellowish in color and generally has a disagreeable odor. It is largely used as a solv- ent in varnish making, for which purpose the presence of acetone is desirable, and in the coal-tar dye manufacture, where a pure alco- hol, free from acetone, is required. In European countries crude wood spirit is much used for mixing with ethyl alcohol, to prepare "methylated spirit," or "denaturated ethyl alcohol" (p. 409). Acetone, when recovered from wood spirit, is generally distilled from the calcium chloride compound with the methyl alcohol. It is, however, generally prepared by the dry distillation of calcium ace- tate : (C 2 H 3 2 ) 2 Ca = CaC0 3 + CH 3 - CO - CH 3 . The product obtained by either of the above methods is crude ; sodium bisulphite is added, and combines with the acetone to form a double salt, which is readily purified by crystallization from aque- ous solution. This is then decomposed by heating with sodium car- bonate solution, setting free the acetone, which is distilled off in a very pure state. A commercial method for the production of acetone, devised by Dr. E. B. Squibb,* consists in passing acetic acid vapor through a rotating iron cylinder, heated to about 500- 600 C., and containing pumice stone with precipitated barium carbonate. On leaving the still the vapors pass through a fractional condensation apparatus, to remove water and acetic acid ; the dilute acetone condenses in a second condenser. This is a good solvent for many substances, and may be used for making chloroform. The reaction is : 2 C 2 H 4 2 = H 2 + CH 3 - CO - CH 3 + C0 2 . * J. Am. Chem. Soc., 17, 187. DESTRUCTIVE DISTILLATION OF WOOD 261 The barium carbonate acts merely as a contact body, since the tem- perature is always above that at which barium acetate decomposes. Acetone is a colorless mobile liquid, having a peculiar odor and unpleasant taste. It boils at 56.3 C., and mixes with water in all proportions. It is an excellent solvent for many resins, gums, and other organic substances. It is much used for preparing chloroform, iodoform, and the medicinal preparation, sulphonaL In Europe it is also used in the denaturation of ethyl alcohol. Commercial acetic acid is prepared from gray or brown acetate of lime* (p. 259) by distilling with concentrated hydrochloric acid, in copper stills, care being taken to have an excess of lime salt in the retort. Thus the calcium acetate is decomposed, and acetic acid, with calcium chloride, results. The acid is a slightly colored liquid, containing about 50 per cent anhydrous acid. It may be further purified by distilling again, over a little potassium bichromate, and filtering through freshly burned charcoal. If the hydrochloric acid is diluted before heating it with the calcium acetate, the distillate contains only 30 per cent C 2 H 4 2 , and is much purer, usually requir- ing no second distillation for technical uses. Stronger acid may be made by neutralizing the 50 per cent acid with lime, evaporating to dryness, and again decomposing with concentrated hydrochloric acid. When pyroligneous acid is distilled without neutralizing with lime, the distillate collected between 100 and 120 C. is a dilute and highly colored liquid, known as "wood vinegar." This contains a little tar and empyreumatic matter, and is used for some technical purposes, but is generally purified by converting it to the calcium salt and distilling with mineral acid, as above. Sulphuric acid is not generally used to decompose calcium acetate, because the calcium sulphate is difficult to remove from the still. Also, the impurities present frequently cause reduction of sulphuric acid, contaminating the product with sulphurous acid. Since soda-ash is now cheap, it is generally used, instead of lime, for the neutralizing. Sodium acetate may be purified by crystalliz- ing, or it may be fused without decomposing, to destroy the tarry matters. It may be decomposed with sulphuric acid, since sodium sulphate is readily removed from the still. Fused sodium acetate may be decomposed by distilling with con- centrated sulphuric acid at 120 C. ; the sulphuric acid absorbs any moisture, and the very concentrated, nearly anhydrous glacial acetic * Brown acetate of lime is calcined at 230 C., to destroy tarry matters before de- composing with the hydrochloric acid. 262 OUTLINES OF INDUSTRIAL CHEMISTRY acid, which crystallizes if cooled to 16.5 C., is obtained. This is also made from calcium acetate, by decomposing the latter in solution with sodium sulphate, filtering off the calcium sulphate, evaporating the sodium acetate solution to dryness, and fusing. The fused salt is distilled with oil of vitriol as above described, and the sodium sulphate so formed is used to decompose more lime salt. Common acetic acid of commerce is a slightly colored liquid of about 1.040 sp. gr. (8 Tw.), and containing approximately 30 per cent anhydrous acid. It is used in the preparation of acetates, in the manufacture of white lead, and in pharmacy. Stronger acid is used in coal-tar color making and for preparing ethyl acetate for a solvent of nitrocellulose in manufacturing explosives. Some pure acetic acid from wood distillate is used for vinegar, but lacks the characteristic salts and flavoring substances present in true fermen- tation vinegar (p. 415). Acetates. Aluminum acetate in the pure state is not known, but a solution of it in acetic acid, called " red liquor," is largely used in dyeing and in calico printing. It is made by dissolving aluminum hydroxide in acetic acid, or by decomposing lead or calcium acetates with aluminum sulphate or alum : A1 2 (S0 4 ) 3 + 3 Pb (C 2 H 3 2 ) 2 = 2 Al (C 2 H 3 2 ) 3 + 3 PbS0 4 . Calcium acetate yields the best red liquor ; that made from lead acetate is not entirely free from lead, which dulls the shade of deli- cate colors ; when made from alum it contains sulphate of the alkali metal, and decomposes more readily than when made from aluminum sulphate. Several basic aluminum acetates are made by adding sodium carbonate to the normal acetate solution. These deposit alumina on the fibre very readily. Chromium acetate finds some use as a mordant in calico printing. It is usually made by dissolving chromium hydroxide in acetic acid, or by decomposing a solution of chromium sulphate or chrome alum with lead or calcium acetate. The solution is violet, but becomes green if heated. It may be evaporated to dryness without rendering the salt insoluble, and the solution does not dissociate. Alkalies and alkaline carbonates yield no precipitate in the cold solution, but when heated, a precipitate of chromium hydroxide forms. Basic acetates are prepared by adding lead or calcium acetate to basic chromium sulphate solution. Sulphate-acetates are also made and used as mordants. Calcium acetate has been mentioned as brown or gray acetate of lime (p. 259). The pure salt, occasionally used as a mordant, is DESTRUCTIVE DISTILLATION OF WOOD 263 made by neutralizing acetic acid with the theoretical quantity of lime. Litmus does not show the point of neutrality. The crystal- lized salt, Ca (C 2 H 3 2 )2 H 2 O, is very soluble in water. Cupric acetate, Cu (C 2 H 3 2 )2 H 2 0, is best made by adding lead acetate to copper sulphate solution : CuS0 4 + Pb (C 2 H 3 2 ) 2 = Cu (C 2 H 3 2 ) 2 + PbS0 4 . It may be made by dissolving verdigris, or copper carbonate or oxide, in acetic acid. For basic acetates see p. 204. Ferrous acetate, Fe (C 2 H 3 2 ) 2 4 H 2 0, may be prepared from cop- peras and lead or calcium acetate ; or by dissolving scrap iron in acetic acid. It is quickly oxidized in the air to basic ferric acetate. " Pyrolignite of iron," black liquor, or iron liquor, is made by dissolv- ing scrap iron in pyroligneous acid. It is sold as a dirty olive-brown or black liquid, having a density of about 25 Tw., and consists mainly of ferrous acetate, with some ferric acetate and tarry matter. It is used as a mordant in dyeing black silks and cottons, and in calico printing. Ferric acetate, Fe 2 (C 2 H 3 2 ) 6 , made by adding lead acetate to fer- ric sulphate, is stable in cold solution. It forms basic salts when treated with caustic soda. It was formerly used in black silk dyeing. Sodium acetate, NaC 2 H 3 2 3 H 2 0, forms needle-like crystals which melt in their crystal water when heated ; when anhydrous it fuses without decomposition. It is chiefly used for making pure concentrated acetic acid, in making certain diazo bodies, and as a developer for the azo-dyes, in which the color is made on the fibre. Lead acetate, Pb (C 2 H 3 2 ) 2 3 H,0, "sugar of lead," is made by dissolving litharge in acetic acid. If wood vinegar is used, the product is "brown sugar of lead." With an excess of litharge, basic acetates are formed. The normal salt is very soluble in water, and is used for making other mordants and for chrome yellows. The salts are poisonous, and are affected by the carbon dioxide and hydrogen sulphide in the air. Wood-tar varies somewhat in character with the kind of wood carbonized. It is washed with hot water, or treated with milk of lime, to remove acetic acid, and then washed with very dilute sul- phuric acid. Excess of water is evaporated by warming in steam- jacketed vessels. The tar is then distilled in iron stills, provided with stirring apparatus, the temperature being raised very slowly. 264 OUTLINES OF INDUSTRIAL CHEMISTRY The distillate collected below 150 C. is called "light oil," and is chiefly used as a substitute for oil of turpentine in varnish and paints. Between 150 and 250 C. the " heavy oil " is collected, con- taining creosote, toluene and paraffine bodies. By stopping the dis- tillation at 250 C., a thick, brownish liquid is obtained, which is used in making axle grease, shoemakers' wax, for lampblack, and for coating the interior of casks and barrels to render them impervi- ous to liquids. The creosote oil is washed with caustic soda, and boiled in the air to oxidize various substances which it contains. The alkaline solu- tion is then acidified with sulphuric acid, to precipitate the creosote, which is treated with alkali and acid as before. It is then distilled again, and the distillate, collected between 200 and 220 C., is the commercial wood-tar creosote. It has a strong, smoky odor, is a good antiseptic, and is not poisonous. Stockholm tar and pine tar are obtained by a crude distillation of pitch-pine or other coniferous wood, in heaps, covered with turf. These are of different composition from retort tar, and are mainly used for tarred ropes, with oakum for ship calking, and for pre- serving timber. REFERENCES Das Holz und seine Distillations-Producte. Dr. G. Thenius, Leipzig, 1880. (Hartleben.) Die Meiler und Retorten Verkohlung. Dr. G. Thenius. Das Chemische Technologic der Brennstoffe. F. Fischer, Braunschweig, 1880. (Vieweg u. Sohn. ) Die Verwerthung des Holzes auf chemischen Wege. Joseph Bersch, Leipzig, 1883. (Hartleben.) Destructive Distillation. E. J. Mills, London, 1892. (Gurney and Jackson.) Handbuch der Organ ischen Chemie. Victor Meyer and Paul Jacobson. Vol. I. Articles " Essigsaure " and " Methylalkohol. " Leipzig, 1893. (Viet u. Cie.) Handbuch der Organischen Chemie. F. Beilstein. Vol. 1. 3d Ed. Purifica- tion of Wood Spirit. Leipzig, 1894. (L. Voss.) Jahres-Bericht liber die Leistungen der technischen Chemie : 1892. F. W. Lefelmann. (Distillation of Wood.) 1893, 14. J. Sartig. (Distillation of Wood.) Journal of the Society of Chemical Industry : 1892, 395 and 872. John Chorley and Wm. Kamsay. 1897, 667, 722. M. Klar. (Modern Distillation of Wood.) ILLUMINATING GAS 265 DESTRUCTIVE DISTILLATION OF BONES Bones are usually extracted with benzine or with carbon disul- phide, and the fatty matter used for soap stock. They still contain nitrogenous organic substances, and are distilled in iron or clay retorts, similar to those used in coal-gas making (p. 268), yielding volatile products, consisting of gases, ammonium salts, and bone oil ; these pass through condensers, where the water and bone oil con- dense; the gases pass into a receiver containing sulphuric acid, which takes up the ammonia and its volatile compounds; the in- flammable gases are burned under the retort. The bone oil (" Dippel's oil ") and aqueous liquor collected under the condensers are separated by gravity. The liquor contains am- monium carbonate, cyanide, sulphocyanide, and sulphide, and is treated in the same way as gas liquor (p. 125) for the recovery of the ammonia. The crude bone oil is a dark-colored, foul-smelling liquid, lighter than water. It is redistilled and divided into numerous fractions. At high temperatures it also yields ammonium carbonate and cyanide; the thick tar remaining in the still is the basis of commercial Brunswick black. The constituents of bone oil are exceedingly numerous, but the most important are pyrrol, C 4 H 4 NH; pyridine, C 5 H 5 N ; picoline, C 5 H 4 (CH 3 )N; lutidine (dimethylpyridine) ; collidine, C 5 H 2 (CH3) 3 ]Sr ; and quinoline, C 6 H 4 C 3 H 3 K These have but little technical use, but are employed in Europe for denaturating alcohol, and in the prepara- tion of certain antiseptics. They are closely related to some of the alkaloids, but are not as yet used to prepare them. The residue from the bone distillation is the bone-black or bone- char of commerce. It forms about 65 per cent of the original weight of the bones and consists largely of calcium phosphate and carbonate, impregnated with free carbon. While still hot, it is drawn from the retort into closed vessels and cooled out of contact with the air. It is largely used in decolorizing sugar solutions, glucose, glycerine, oils, paraffine, vaseline, etc. It loses its effec- tiveness after a time, and is then "revivified" (p. 369). When it becomes too finely powdered for successful filtration, it is used as a fertilizer (p. 139). ILLUMINATING GAS Illuminating gas may be made by enriching water gas with oil gas, or by the destructive distillation of coal, wood, or petroleum. 266 OUTLINES OF INDUSTRIAL CHEMISTRY Coal gas, such as is generally used at the present timp, was first employed for house illuminating by William Murdock, in London, in 1792. It was introduced for street lighting in -London in 1812, and in Paris in 1815. In this country, the so-called water gas, enriched with naphtha, has largely replaced coal gas in many of the large cities. This has greater illuminating power, requires a smaller plant and less labor, and ensures greater economy of working. Water gas is produced by the action of steam on incandescent carbon, according to the reactions : C + C0 2 = 2 CO. It is composed chiefly of hydrogen and carbon monoxide, is non- luminous, and has a high heat value. Luminosity depends on the presence of hydrocarbons, such as ethane, C 2 H 6 , ethylene (ethene), C 2 H 4 , acetylene C 2 H 2 , and benzene, C 6 H 6 , and their homologues, the most important of these "illu- minants " being ethylene and benzene. In order to render the water gas luminous, it is carburetted with gases derived from oil, which are rich in illuminants. Illuminating water gas is now made by two general methods: (a) the carburetted gas is made in. one operation; (6) non-luminous gas is prepared, and then carburetted by a second process. The first method is most successfully carried out by the Lowe process. The generator (Fig. 68) is filled with anthracite coal or coke, which is brought to incandescence by a blast of air. The gases from the generator, at this time consisting mainly of carbon monoxide and nitrogen, enter at the top of the carburettor, a circular chamber lined with firebrick, and containing a " checker-work " of the same material ; while passing down through this, the producer gas (p. 30) is partly burned by an air blast which enters the apparatus near the top, and the checker-work is heated white hot. The gases pass on to the " superheater," a taller chamber, also filled with checker- work. At the bottom of this an air blast is introduced to complete the burning of the producer gas and to raise the temperature of the checker-work to a very bright red heat. From the top of the super- heater, the waste gases escape into a hood leading into the open air. When both the carburettor and superheater have reached the desired temperature, the air blasts are cut off, and steam is introduced into the generator, where it is decomposed by the incandescent fuel, according to the reactions. The water gas thus formed passes into the carburettor, while a small stream of oil is being introduced ILLUMINATING GAS 267 through a pipe at the top. The oil is decomposed by contact with the hot checker-work, forming illuminating gases which mix with the water gas, and passing into the superheater, are completely fixed as non-condensable gases. FIG. 68. It is customary to run the air blast for some eight minutes, when the fuel reaches a temperature of about 1100 C. The steam, super- heated before entering the generator, is run about six minutes, until the temperature of the generator and carburettor has fallen below the point at which decomposition occurs. In order to economize heat, the hot carburetted gas is passed through a pipe surrounded by a jacket, within which the oil is circulating, thus heating it be- fore it enters the carburettor. The lower end of the pipe leading from the superheater is closed by a water seal, to prevent any back- ward rush of the gas during the operation of the air blast. It is cus- tomary to lead the gas from the superheater into a storage holder, from which it is drawn through the purifying apparatus. In this process, the blowing of air and of steam are intermittent, but the actual formation of gas is accomplished in one operation. 268 OUTLINES OF INDUSTRIAL CHEMISTRY The second method of preparing illuminating water gas is the Wilkinson process. Water gas is made by blowing steam into the hot coal in the generator, and is stored in the holder. A measured quantity of gas is then introduced into the carburettor, a closed iron box, containing slightly inclined plates, over which the exact amount of oil necessary to carburet the gas, is flowing in very thin layers. The carburettor is also provided with a steam jacket and coils to keep the temperature high enough to vaporize the oil. These vapors mix with the gas and pass at once into the fixing apparatus, which is a long, narrow, fire-clay retort, kept at a white heat by external fire. Here the oil vapors are " cracked " into hydrocarbons, which are non-condensable gases, and being mixed with water gas, render it luminous when burned. The mixed gases then go directly to the scrubbers and purifiers. For 1000 cubic feet of gas, about 50 pounds of anthracite and 4.2 to 5 gallons of naphtha are consumed. The impurities in the water gas are essentially the same as those in coal gas, and the method of washing and purifying are the same. The illuminating value of coal gas is frequently raised by mixing it with carburetted water gas. Owing to its high percentage of car- bon monoxide, water gas is exceedingly poisonous when inhaled, and much care is necessary to prevent leakage into inhabited rooms (see table, p. 278). Coal gas, prepared by the destructive distillation of bituminous coal, is generally made by the smaller gas companies in this country. In Europe scarcely any water gas is made for illuminating purposes. The composition and yield of coal gas depends upon the kind of coal used and the manner of distillation. A " fat " coal, moderately low in sulphur and caking on distillation to a good coke (e. g. the Penn- sylvania gas coals), is most desirable for illuminating gas. The temperature of the retort is a very important factor in the character of the distillation products. When it is low, the quantity of gas formed is small, but it contains a large percentage of illuminants, and hence is of a high candle power. When the temperature in the retort is high the effects are as follows : (a) the yield of gas is much increased, but the percentage of methane, ethane, and hydrogen is much greater, and since these have very little illuminating value, the gas is of low candle power ; (6) the yield of tar is increased ; (c) the vapors of the heavy hydrocarbons which constitute some of the tar are decomposed on coming in contact with the hot retort, form- ing gases of lower carbon content, and depositing free carbon on its ILLUMINATING GAS 263 walls. This " gas carbon " * adheres very firmly and if allowed to become thick causes much loss of heat. It is especially liable to deposit if there is undue pressure in the retort, which may be the case if the exhausters are not working properly ; (d) there is a larger yield of organic bodies having ring nuclei in their composition, such as benzene, naphthalene, phenols, anthracene, etc. These not only cause loss, but also cause clogging in the service pipes and burners. The products of the distillation are gas, ammoniacal liquor, tar, and coke. When coal is distilled for coke (p. 27), the ammoniacal liquor and tar are sometimes saved by the use of by-product ovens, but the gases are burned for fuel or go to waste. When distilled for illuminating gas, the process is carried on with a view to the best yield of high quality gas, but the ammoniacal liquor, tar, and coke are valuable by-products. The coke is too soft for metallurgical purposes, and is chiefly used to heat the retorts or sold for domestic fuel. FIG. 69. A diagram of a complete plant for coal gas making is shown in Fig. 69. The retorts, (A), are Q-shaped, fire-clay vessels, about 8 feet long, 18 inches wide, and 15 inches high ; they are set six or eight together in a furnace, the whole constituting what is called a *Gas carbon is much used for electric light carbons, battery plates, and other electrical appliances. It is denser and purer than most other forms of carbon. 270 OUTLINES OF INDUSTRIAL CHEMISTRY "bench." Each retort has a cast-iron mouthpiece projecting out of the furnace, and carrying the door, closed by a screw clamp. Ke- torts may be " single," i.e. closed at one end and having but one door for charging and discharging ; or they are " through " retorts, about 18 feet long, having a door at each end, so that they may be charged or emptied from either side of the furnace. A modified form of the latter is the " inclined " retort, set at an incline of about 32, the coal being run in at the upper end, and the coke discharged by gravity, by opening the door at the lower end. Each bench is heated to 1000 or 1200 C. by a coke fire on a grate below the re- torts, or, in more modern plants, by generator gas. A number of benches are built together, and constitute a " stack." From the front of each retort a vertical cast-iron pipe (B) about 6 inches in diameter, and called the " stand-pipe," ascends to the top of the bench, where it joins the "bridge-" and "dip-pipes," which conduct the volatile products from the retort to the hydraulic main (C). This is a long covered trough, extending the entire length of the stack, and receiving the gas and distillate from each retort. In it the greater part of the tar and oily products condense and collect under the water which is kept in the main to act as a seal to the ends of the dip-pipes, to prevent the gas from passing back into the retort when the latter is opened. Ammonium salts, such as sulphate, sulphide, and carbonate, are washed from the gas as it bubbles through the water, and are afterwards recovered (p. 125). The ends of the dip-pipes must not extend more than 2 inches into the water ; otherwise, there is pressure in the retort and con- sequent loss from leakage and from deposition of carbon in the retort and stand-pipe. If the gas is allowed to cool in contact with the tar, the latter absorbs some of the illuminants, thus reduc- ing the candle power (p. 276). If the stand-pipes are too hot, the volatile constituents of the tar are driven out, and a very thick mass deposits, causing clogging. From the hydraulic main a pipe (not shown) leads to the con- denser (D), which consists of a series of vertical cast-iron pipes, connected by bends at the top, and opening at the bottom into an iron box. This box is divided by transverse partitions which do not extend to the bottom, merely dipping into the ammoniacal liquor and tar contained in it. The liquor forms a seal, thus forcing the gas to pass through the pipes, while the condensed products flow along the bottom of the box to the tar well. These condensers are simply air cooled, but certain forms are constructed with water coolers. In those most frequently in use in this country the pipes are laid at a very slight incline to the horizontal. ILLUMINATING GAS 271 The annular condenser consists of a series of vertical pipes con- nected by diagonal pipes leading from the bottom of one to the top of the next. Through each of these vertical pipes a smaller tube passes parallel to the length of the pipe and opening to the air at both ends, thus forming an annular space in each pipe, through which the gas passes dowmvard, and then through the diagonal pipe to the top of the next. In this way a very large air-cooled surface is obtained. At the bottom of each cooling pipe a small pipe car- ries away the condensed tar and liquor. The tubular condenser consists of a rectangular box about 2 feet wide and 20 feet high, divided into narrow sections by partitions extending alternately to within a few inches of the top and of the bottom. Through each section, a number of narrow horizontal tubes, open to the air at each end, extend from one side of the box to the other. In this way the gas passing through the sections is exposed to a very large cooling surface. Water condensers consist essentially of pipes surrounded by flow- ing water. Through these the gas is made to pass in a direction opposite to that in which the water flows. By regulating the supply of water, the temperature is easily controlled. The object of the condenser is to cool the gas slowly to the tem- perature of the atmosphere, provided this is not under 50 C. Cool- ing below this causes condensation of somo of the illuminants, with corresponding loss. If the cooling is very rapid, the tarry matter separates quickly, and drags some of the lighter hydrocarbons down with it. The exhauster (E, Fig. 69) is to draw the gas from the retort, through the hydraulic main and condenser, and to act as a pump to force it through the remaining parts of the plant. By drawing the gas out of the retort quickly there is less decomposition of the gas itself, and hence less carbon is deposited in the retort; a larger yield results and less fuel is necessary, while the retort lasts longer. Another form of exhauster is a direct-acting pump, which draws the gas from the retort and condenser, and forces it to the purifiers. Root's rotary exhauster is frequently employed, but BeaPs (Fig. 70) is more generally used. This consists of an outer circular casing having inlet and outlet pipes, and an inner revolving drum (B), which turns on an eccentric axis in such a way that the drum just touches the lowest point of the inner surface of the casing. Through slots cut in the drum, two blades or diaphragms (D) slide freely over one another, to form a double diaphragm, variable in width, according to the relative position of the blades to each other. 272 OUTLINES OF INDUSTRIAL CHEMISTRY In the outer end of each blade is a pin, which travels in a circular groove sunk in the ends of the casing. Thus as the drum revolves about its axis, the pins, travelling in the fixed groove, draw the blades in and out, across the axis of the drum. The outer ends of the blades are thus always kept in contact with the walls of the casing. The exhauster is driven by an engine, and the rotary blades and drum catch the gas which enters through the inlet, and force it out through the other pipe. FIG. 70. FIG. 71. The steam jet exhauster (Fig. 71*) is very effective, but heats the gas, which is afterwards cooled in the washer. A jet of steam is blown through conical openings into a wide pipe, drawing the gas along with it into the cones. The tar extractor (F, Fig. 69) is a short tower filled with nu- merous horizontal perforated plates. The friction of the gas in pass- ing through the small holes in these plates removes the last traces of tar and prevents clogging in the scrubber. In Europe the apparatus of Pelouze and Audouin is much employed. This is a bell made up of three layers of wire netting, or of perforated plates, which is sus- pended in a water seal. The gas enters under the bell and passes through the meshes or perforations of the bell walls, to which the tar particles attach themselves and finally drop to the bottom and run off by a special pipe. The scrubber and washer are intended to remove the ammonia and part of the carbon dioxide and hydrogen sulphide. In the former the gas is brought into contact with thin films or layers of ammoniacal liquor from the hydraulic main or condensers, which trickles over coke, twigs, wooden slats, or pebbles, in a tower. This liquor absorbs some of the carbon dioxide and hydrogen sulphide, which combine with the ammonia. In tlie washer the gas is brought * After Ost, Lehrbuch d. tech. Chemie. ILLUMINATING GAS 273 in contact with pure water, trickling over twigs, coke, etc., and which removes the ammonia from the gas. Tower scrubbers are tall cast-iron vessels built in segments, each of which has a " grid " or grating, upon which the filling material is supported. Two towers are always used in conjunction, the first fed with arnmoniacal liquor and the second with water. The amount of liquor and water is very carefully regulated, and the gas entering at the bottom of the first tower passes up and then to the bottom of the second, and is thus first brought into contact with the strongest liquor and finally with pure water. These tower scrubbers are now only used in old plants ; in all modern establishments they have been replaced by scrubber-washer machines. The Standard scrubber-washer machine (G, Fig. 69) is a Q-shaped iron vessel, divided into a series of narrow chambers by transverse partitions. In the upper half of the apparatus is a revolving shaft carrying a number of thin wooden grids, bolted together in parallel segments, with blocks making a space of about one-eighth of an inch between each pair of grids. A group of these slats revolve in each chamber. Water at about 60 F. is admitted to the last chamber of the series, at the rate of about one gallon for each 1000 cubic feet of gas, and, automatically regulated, flows from chamber to chamber in a direction opposite to that in which the gas is passed. Thus the fresh water comes in contact with the most nearly purified gas. The level of the water is lower in each succeeding chamber, until in the first chamber, where the gas enters the apparatus, the strong ammo- niacal liquor is only a few inches deep. By the revolution of the shaft, the grids are submerged in the liquor, and freshly wetted surfaces are brought into the upper part of the apparatus. By a suitable arrangement of baffle plates, the gas is made to enter each chamber at the centre, and find its way to the circumference by passing through the narrow spaces between the grids. The water, forming a thin film on them, absorbs the ammo- nia, carbon dioxide, etc. ; and as the shaft revolves from 12 to 15 times per minute, the solution formed is at once mixed with the liquor in the bottom of the chamber. The machine does its work very effectively, and in this country is rapidly replacing the tower scrubbers. From the scrubbers the gas passes to the purifiers (H, Fig. 69), whose chief purpose is to remove sulphur compounds. They are shallow rectangular iron boxes, each having a false bottom, upon which the purifying material rests. The gas enters under this grating and leaves by a pipe opening just under the cover, which 274 OUTLINES OF INDUSTRIAL CHEMISTRY rests in a hydraulic seal, and is lifted by a travelling crane. Usually four purifiers are plaeed in a series, one of which is emptied and recharged at a time, without interrupting the purification process. The foul gas enters the most nearly exhausted purifier, and, passing through the others, leaves the apparatus through that most recently charged, connection being made between the purifiers by means of a complicated piece of apparatus (L and 0, Fig. 69) called the centre seal. The purifying materials may be slaked lime or hydrated ferric oxide. Lime is the oldest material used and is also the best, since it removes both the carbon dioxide and carbon disulphide. But it is expensive, and the spent lime, having a most offensive odor and con- siderable bulk, is difficult to dispose of. The lime should be thor- oughly slaked several days before use, and should contain as much water as it will hold without becoming pasty or liquid. It is placed in the purifiers in layers about six inches deep. The reactions occur- ring with lime are : 1) Ca(OH) 2 + 2 H 2 S = Ca(SH) 2 + 2 H 2 0. 2) Ca(OH) 2 + H 2 S = CaS + 2H 2 0. 3) CaS + CS 2 = CaCS 3 , (calcium thiocarbonate). 4) Ca(OH) 2 +'C0 2 = CaC0 3 + H 2 0. Since carbon dioxide will decompose calcium sulphide, sulphy- drate, or thiocarbonate, if gas containing it is passed through a foul purifier, the following is liable to take place : CaS + C0 2 + H 2 = CaC0 3 +H 2 S. CaCS 3 + C0 2 + H 2 = CaC0 3 + CS 2 + H 2 S. The volatile sulphides thus liberated must be removed in a second purifier, into which no carbon dioxide enters. Carbon dioxide has a very deleterious effect on the illuminating power of the gas. When iron oxide is used, only the hydrogen sulphide is removed from the gas : 2) Fe 2 3 3 H 2 + 3 H 2 + 3 H 2 S = Fe 2 S 3 + 6 H 2 0. The oxide is a natural bog iron ore, Fe 2 3 3 H 2 O. When fresh it contains about 50 per cent, water and a large amount of vegetable matter, but before use it is dried until about one-half of the moisture is expelled, and is then mixed with an equal bulk of sawdust to ren- ILLUMINATING GAS 275 der it more porous. When it becomes inactive through absorption of sulphur, it is "revivified" by removing it from the purifier and spreading it in a layer a foot or more in depth, where the air can act upon it. Considerable heat is evolved by the action of the oxy- gen of the air on the iron sulphides : Fe a S 3 + 30 = Fe A + 3 S. Thus free sulphur is deposited in the oxide. The ore may be revivi- fied repeatedly until the free sulphur accumulates in it to the amount of 50 or 55 per cent, when the proper action in the purifiers is hin- dered, and fresh oxide must be used. If some air is admitted along with the gas, the iron oxide is revivified in the purifiers, and need not be removed so often ; but this dilutes the gas slightly with nitro- gen. One ton of good iron oxide will purify about one and a quarter million cubic feet of gas. Sometimes lime is used before the iron oxide, in order to remove carbon dioxide. Any sulphur compounds of the lime which may be formed are decomposed by the carbon dioxide in the foul gas (see above). A considerable amount of carbon dioxide is present in un- purified water gas, and is generally thus removed before the gas enters the iron oxide purifiers. The purified gas passes through the station meter (I, Fig. 69) and then to the holder (J), from which it is delivered to the street mains. The usual impurities found in gas are ammonia, hydrogen sul- phide, and carbon dioxide. Ammonia is detected by holding a strip of wet turmeric or litmus paper in a stream of the gas ; the former becomes brown or red, and the latter blue. For hydrogen sul- phide, paper wet in lead acetate or silver nitrate is used. Carbon dioxide is detected by shaking a small bottle of the gas, freed from hydrogen sulphide, with lime or baryta water. The yield from one ton of good gas coal is approximately : 10,000 cu. ft. 16 candle power gas. 1400 pounds coke. 120 pounds tar. 20 gallons ammoniacal liquor (10 to 12 oz.). When the ammoniacal liquors from the hydraulic main, con- densers and scrubbers are mixed, the "gas liquor" thus formed is of approximately "10 ounce" strength, i.e. the ammonia gas which can be liberated from one gallon of the liquor will completely 276 OUTLINES OF INDUSTRIAL CHEMISTRY neutralize 10 ounces by weight of real sulphuric acid. It is used for the production of ammonia (p. 124). The tar is pumped from the tar well into barrels or tanks for shipment to the tar distiller (p. 279). The illuminating power of gas is expressed in "candles," by which is meant the ratio of its illuminating power to that of a "standard candle," as measured by a photometer. The English standard is the light of a sperm candle, weighing one-sixth of a pound, when burning 120 grains per hour. But this is subject to variation, and much ingenuity has been expended in devising a better standard. A burner designed for use with a mixture of air and pentane, C 5 H 12 , has found some favor in Europe. In Germany the light of a lamp burning amyl acetate, with a specified height of flame and size of wick, is the official standard. In this country standard candles are used. When testing gas, it is customary to burn it at the rate of 5 cu. ft. per hour, in a burner of the argand type. Ordinary coal gas is generally about 16 candle power, but it is now frequently the practice to "enrich" it by putting into the retort, along with each charge of coal, an iron cylinder containing petroleum oil. This is closed with a cork, which soon burns out, and the oil escapes and is decomposed, the vapors mixing with the coal gas, thus increasing its illuminating power. A recent improvement in gas lighting is the introduction of incandescent burners, in which the non-luminous flame of a Bunsen burner is made to heat a mantle or gauze composed of the oxides of various rare earths, especially thorium and cerium. The mantle being raised to incandescence, glows with a powerful light, while very little heat is given out. The consumption of gas in these burners is usually about three and one-half feet per hour, and their efficiency is about four times that of an ordinary argand burner. They are advantageous to use with a gas of low illuminating power, provided it has considerable heating value. Oil gas is now largely made by " cracking " certain petroleum, tar, or shale oils in retorts. In Pintsch's process the retort is divided by a transverse partition into an upper and a lower chamber. The oil is cracked and vaporized in the upper chamber, and the vapors pass into the lower compartment, whic.h is heated to nearly 1000 C., where the vapors are "fixed" and form permanent gases. In Peebles' process the retorts are not heated so hot, and the oil is partly cracked and partly distilled and fractionated, so that only very volatile hydrocarbons leave the apparatus ; the heavier oils are condensed and returned to the retort. The gas is then purified and ILLUMINATING GAS 277 used to enrich other gases, or is burned alone, or with air. Oil gas has a very high candle power, usually over 50. That made by the Pintsch process is extensively used in the pure state for lighting railroad cars. It is compressed into cylinders for carriage, but the pressure must be low ; otherwise great loss of illuminating power occurs, owing to the condensation of the heavy illurainants. It can only be burned in special forms of burners, otherwise it is very liable to smoke or deposit soot. It is rich in benzene and olefine hydrocarbons. By mixing with a certain amount of pure oxygen the combustion and illuminating power can be greatly improved. Acetylene has recently become prominent as a possible future illuiniiiant. By heating a mixture of coke powder and lime in an electric furnace, calcium carbide is produced. When treated with water this is decomposed, with formation of acetylene : CaC 2 + 2 H 2 = Ca(OH) 2 + C 2 H 2 . It burns readily with separation of carbon, which is heated to incan- descence in the flame, and gives the gas a high illuminating value. But it cannot be used successfully to enrich coal or water gas, since its candle power is very much lowered by mixing with other gases. When burned in a special form of burner, under high pressure, it yields a very brilliant light. It has some action on copper and brass, and under certain conditions might attack the brass valves and stop-cocks employed in gas fitting, and form a highly explosive body. One ton of calcium carbide of 80 per cent purity will produce about 1000 cu. ft. of acetylene gas, and it has been proposed to employ it in small generators for illuminating purposes. But the present cost of calcium carbide is prohibitory to any extended use of acetylene. Air gas, so called, is produced by causing air to pass through layers of the very volatile petroleum distillates, having densities from 80 to 90 Be. The air, together with sufficient vapor to form a combustible mixture, is led directly into the burner, since it cannot be piped any considerable distance without condensation of the illuminants. The rate of flow of air through the apparatus must be very exactly regulated. Air gas is much used when other gas is not available. In some parts of Europe, where coal is very expensive, gas is made by distilling artificially dried peat. The gas contains more carbon dioxide than coal gas, and more lime is needed for purifica- tion. It is about 18 candle power, and considerable tar and ammo- niacal liquor is also obtained. 278 OUTLINES OF INDUSTRIAL CHEMISTRY The average composition of different varieties of gas is shown in the following table : * ANALYSES. COAL. WATER (CARBUEETTED). WATER (FUEL). OIL. Candle power . . 17.5 25.0 65.0 Ilium inants . . 5.0 16.6 45.0 Marsh Gas . . . 34.5 19.8 1.0 38.8 Hydrogen . . . 49.0 32.1 52.0 14.6 Ethane Carbonic Oxide . 7.2 26.1 38.0 Nitrogen . . . 3.2 2.4 3.0 1.1 Oxygen .... . Carbonic Acid 1.1 3.0 6.0 REFERENCES Practical Treatise on the Manufacture and Distribution of Coal Gas. Samuel Clegg, London, 1859. Traits' theoretique et pratique de la Fabrication du Gaz. E. Borias, Paris, 1890. Manufacture of Gas from Tar, Oil, etc. W. Burns, New York, 1887. Practical Treatise on the Manufacture of Coal Gas. W. Richards, London. Fabrikation der Leuchtgase. G. Thenius, Leipzig, 1891. The Chemistry of Illuminating Gas. N. H. Humphreys, London, 1891. (King.) The Chemistry of Gas Manufacture. W. J. A. Butterfield, London, 1896. (Griffin and Co.) A Textbook of Gas Manufacture. John Hornby, London, 1896. (Bell and Sons.) A Treatise on Gas Manufacture. W. King. (King.) Gas Engineer's Handbook. T. Newbiggin, London, 1889. (King.) Handbuch ftir Gas-Beleuchtung. E. Schilling, 1892. Journal of Gas Lighting. London. Vols. 59, 60, 61, 62, and others. (Coal Gas.) COAL-TAR The tar collected from the hydraulic main and condensers of the gas works is a black, oily, foul-smelling liquid averaging 1.15 sp. gr. Its composition is exceedingly complex, and it is always mixed with some of the gas liquor, while it retains in solution several of the constituents of the illuminating gas. In the early days of "gas making, the tar accumulated in large * C. D. Jenkins. Reports of the Mass. State Gas Inspectors. COAL-TAR 279 quantities, and no use being known for it, became a great nuisance. But the discovery of several important substances in distillates from it has given rise to great industries. Coal-tar is used to some extent without treatment for preserving timber, making " tar paper," as a protective paint and cement for acid pipes and condensing vessels, and in forming certain furnace linings. But nearly all the tar now produced is subjected to frac- tional distillation for the separation of the more important constitu- ents. These may be considered in three general classes : (a), the hydrocarbons, the most valuable, are bodies of a neutral character, not affected by dilute acids nor alkali ; (6), the phenols, bodies of a weak acid character, and containing oxygen ; (c), the bases, which contain nitrogen, and are generally present in such small amounts that they are not recovered. The method of distillation varies con- siderably as the market price of the distillates fluctuates, and accord- ing to the composition of the tar received from different gas works. If benzenes are low in price, the light oils are collected together. As a rule, the phenols are not all separated, since the demand for them is not very great. Some tars are distilled only until the light oils are removed, and the residue employed for asphalt. But when anthracene is present, the distillation is carried on until the heavy oils are removed, and the residue is sold as pitch. When received from the gas works, the tar is run into a tank above the level of the still, or into a brick-lined cistern sunk in the ground, and is allowed to stand until the ammoniacal liquor mixed with it has separated by gravity. To facilitate this the tar is some- times warmed by a steam coil in the tank, especially in cold weather. Since the gas liquor causes frothing in the still, it is removed as completely as possible, and sent to the ammonia distiller. In the early days of the industry old boilers were frequently employed as stills, but in modern works the stills are especially con- structed for the purpose. They are sometimes horizontal cylindri- cal vessels, having a capacity of from 15 to 25 tons, and, in some cases provided with two or more still-heads. But a better form is a vertical cylinder made of wrought-iron or steel plates from three- eighths to one-half of an inch thick; the diameter is equal to the height, and the bottom is concave. The top is a cast-iron dome, pro- vided with a manhole, an inlet pipe for the tar, a broad, curved out- let pipe ("goose-neck") for the vapors, and a small overflow pipe ("tell-tale"). Sometimes there is a safety-valve and thermometer tube ; if the former is omitted, the manhole cover is not screwed down, but closes the opening by its own weight ; should excessive 280 OUTLINES OF INDUSTRIAL CHEMISTRY pressure develop within the still, the cover is lifted and the vapors escape. The arched bottom rises to a considerable height, thus dis- tributing t?ie heat into the interior of the mass of tar, and the outlet pipe being placed at the lowest point, it is also of assistance in emptying the still. The bottom is sometimes protected from direct contact with the flame by a brick arch (curtain arch). There is usually a coil in the still, through which superheated steam is blown, towards the end of the process, to assist in the distillation of the heavy oils. These upright stills are set in furnaces so that the flames play under the bottoms, and about half way up the height, through side flues in the brick setting. They vary much in size ; in England they are from 10 to 20 tons capacity; in Germany larger ones are used. The condenser consists of a cast- or wrought-iron or lead worm, placed in a tank of water. A steam pipe is arranged to warm the water, if necessary. While the still is yet hot from the previous distillation, the tar is run in. Since the large mass of cold tar requires some time for heating, the fire is started when the still is half full. When the tar runs from the tell-tale pipe, the manhole and valves are closed, and the heat raised until the contents begin to froth. The overflow pipe is then opened, and any ammoniacal liquor which has separated is drawn off. The heating is continued carefully until the still-head gets warm, and puffs of vapor, and finally drops of liquid, begin to come from the condenser. The fire is then moderated, in order to prevent boiling over. A closed receiver is placed at the end of the condenser, and the distillation is continued very slowly, until the temperature reaches 105 C., when, as a rule, the first receiver is changed. The distillate is commonly separated as follows : First runnings, or "first light oil," to 105 C. Light oil, to 210 C. Carbolic oil, to 230 C. Creosote oil, to 270 C. Anthracene oil, " green oil," above 270 C. Sometimes the first runnings and light oil are collected together until the temperature reaches 170 C. ; and the distillate between 170 C. and 230 C. is taken as carbolic oil. The temperature at which the distillation is stopped depends upon the quantity of anthracene in the distillate and upon whether it is desired to pro- duce hard or soft pitch. The first runnings, or first light oil, contain water, ammonium COAL-TAR 281 salts, the very volatile oils, and a small quantity of heavier oils car- ried over mechanically. After this distillate has run for some time, it nearly ceases, although the fire is now increased. This is known as the "break," and is the point where the receiver is generally changed. During the interval a peculiar sputtering noise ("rattles") is heard in the still, caused by drops of condensed water falling into the tar, which is now considerably above 110 C. When the liquid begins to run from the condenser again, the "second light oil" is collected until the temperature of the tar reaches 210 C., or until the distillate equals 1.000 sp. gr. This is shown by catching some of it in a glass of water; if it forms spheri- cal drops which neither sink nor rise in the water, but float at what- ever point they happen to fall, the receiver should be changed. During this period very little cooling water is admitted to the con- denser, so that it is warmed to 40-50 C. ; the water is then cut off entirely. The carbolic oil is distilled until the temperature of the tar reaches 240 C., or until a few drops of the distillate cooled on an iron plate show crystals, of naphthalene. This oil contains phenols, and as the naphthalene is less soluble in the heavy oils than in the phenols, its crystallization indicates that all the latter have distilled off. The warm water in the condenser prevents crystallization in the worm ; towards the end of this period it is sometimes necessary to heat the water by a steam coil. The receiver is again changed, and the " creosote oil " collected until the temperature reaches 270 C. The first runnings of this contain much naphthalene, but later the quantity present is small, and remains dissolved in the heavy oil. This distillate is the least valuable and is often not purified further. The anthracene oil, or "green oil," collected over 270 C., con- tains anthracene, the most valuable constituent of the tar. The water in the condenser is now brought to the boiling point. Super- heated steam is injected into the hot tar in the still to aid in carry- ing over the heavy vapors. The process is generally stopped when the distillate becomes " gummy " ; on cooling it has about the con- sistency of butter. The pitch left in the still is a thick, viscous mass while hot, and if run out immediately will take fire in the air. After cooling a few hours, it is run out through the pitch cock, and, when cold, hardens and is sold as " hard pitch." But the still must be emptied while the pitch is warm enough to drain out completely, for if any is left in the still the heat radiating from the brickwork will con- 282 OUTLINES OF INDUSTRIAL CHEMISTRY vert it into coke, which fastens very firmly to the still bottom and does not dissolve when a fresh charge of tar is run in. To facilitate emptying, and also to supply a demand for " soft pitch," it is often the practice, after the anthracene oil is distilled, to pump into the still a certain amount of creosote or carbolic oil, or the " dead oils " from which the anthracene has been extracted. This mixes with the hot tar and produces a pitch of any desired consistency, according to the quantity of oil used. Stills are sometimes provided with mechanical stirring apparatus to prevent the pitch from burning on the bottom, and to assist in mixing it with the oils used for softening it. The crude distillates obtained directly from the tar are further purified and separated into commercial products. The first runnings contain ammoniacal liquor and naphtha, which are usually separated by gravity. The former is put with the gas liquor from the tar ; the latter is usually refined with the light oil distillate. The light oil contains benzene, toluene, and xylene, with some thiophene, phenols, pyridine bases, and heavy oils. It is distilled in stills much like those used for tar, but smaller. Two fractions are made, naphtha, which distills under 170 C., being further purified ; and the last runnings, which are put with the carbolic oil. The naphtha is put into a lead-lined vessel provided with an agi- tator, and thoroughly mixed with dilute caustic soda solution. This combines with the phenols, which are thus removed when the soda solution is drawn oft'. After washing the oil with water, about 5 per cent of sulphuric acid (sp. gr. 1.83) is added and agitated with the oil, the temperature being kept low. This dissolves thiophene, un- saturated hydrocarbons and pyridines, and chars and destroys other matter. The acid tar thus formed is drawn off and the oil washed several times with water, and finally with caustic soda to remove all the acid. The washed oil is then redistilled. When collected up to 110 C., the distillate is called "90 per cent benzol," since that amount by volume distills below 100 C. It contains about 70 per cent pure benzene, 24 per cent toluene, and some xylene. If col- lected up to 140 C., the distillate is known as " 50 per cent benzol," and contains about 46 per cent pure benzene. Between 140 C. and 170 C. a distillate called "solvent naphtha" or "benzine" is ob- tained. This consists mainly of xylenes, cumenes, etc., and is used as a solvent for resins and rubber, and to wash the crude anthracene obtained from the anthracene oil. It is also employed to enrich illuminating gas, and as a cleansing agent for grease-stained fabrics. COAL-TAR 283 It must not be confused with petroleum benzine (p. 292), which is of different composition. The crude 50 or 90 per cent benzol is chiefly employed in the coal-tar dye industry. By careful distillation in a rectifying still, such as Coupier's or Sevalle's (pp. 8, 9), it yields pure benzene, boiling at 80-82 C., toluene at 110-112 C., and xylene, 137-143 C. The carbolic oil contains phenols and naphthalene ; after cooling, the oil is pressed or filtered out of the magma of crude naphthalene crystals, which are purified by treating with sulphuric acid and heating to destroy the phenol left in them. After separating the acid tar and washing, the naphthalene is distilled or sublimed (p. 10). The oil pressed from the naphthalene crystals may be treated by either of the following processes to recover the phenols: (a) The oil is agitated with dilute caustic soda, which dissolves the phenols, forming a solution of " sodium carbolate." This separates by gravity from the undissolved neutral oils and is drawn off and decomposed with sulphuric acid, whereby crude carbolic acid (phenol), separates as an oily liquid, (b) The oil may be heated with a mixture of lime and sodium sulphate, sodium carbolate being formed and calcium sulphate precipitating. After the impurities have settled, the solu- tion of phenols (tar acids) is decanted and sold as crude carbolic acid. This is purified by repeated distillation in a column apparatus of iron or copper, with zinc condensers. Sometimes potassium bichro- mate and sulphuric acid are put into the still to oxidize the impuri- ties. Crystals of phenol separate from the distillate on cooling, while the cresols remain liquid. The phenol is separated from all liquid matter by a centrifugal machine. By treating the alkaline solution of phenols with an insufficient quantity of acid, the cresols are precipitated first and may be separated, the phenol being sepa- rated afterwards with more acid. Crystallized phenol, C 6 H 6 OH, melts at 42 C., but the presence of a very little water causes the whole mass to liquify. It boils at 184 C., and can be distilled unchanged. Carbolic acid is a violent poison and has a very penetrating odor. It is a powerful antiseptic, germicide, and disinfectant. It is the source from which many dyes, explosives, and medicinal chemicals are prepared. When dissolved in soap, the crude tar acids are often used as antiseptics under the names lysol and kreolin ; these are soluble in water or emulsify with it. The creosote oil also furnishes naphthalene, which crystallizes on cooling. It is filtered, or pressed in presses which have steam-heated 284 OUTLINES OF INDUSTRIAL CHEMISTRY plates; the crude naphllial en e is washed with caustic soda solution and with concentrated acid, and is distilled or sublimed. The oil contains cresols and higher phenols, naphthol, and liquid paraffine, which have but little value and are not separated. It is chiefly used for preserving ("pickling") timber and railroad sleepers. The timber is thoroughly dried, placed in tanks from which the air is exhausted, and the hot creosote oil pumped in under heavy pres- sure. A small amount is used for lubricant, and as an illuminant for outdoor work where smoke is of no consequence. It is also used as fuel, and extensively in the preparation of " sheep dips," liquids used for destroying ticks and vermin on sheep and cattle. Naphthalene is one of the most important constituents of coal-tar, forming over 5 per cent of it. It forms shining white plate-like crystals, which melt at 79 C., and boil at 218 C. It has a peculiar penetrating odor, and is much used instead of camphor to protect woollen goods and furs from moths ; it is also used to prepare naphthols, naphtylamines, and phthalic acids for the manufacture of dyes. Nitron aphthalene is employed to remove the "bloom" from mineral oils (p. 294). The anthracene oil, or "green oil," contains about 10 per cent anthracene, C 14 H 10 , together with other solid hydrocarbons, such as phe- nanthrene, chrysen, carbazol, paraffine, and liquid oils of high boiling points. The mass is cooled until the solid matter has crystallized, when the liquid oils are removed by bag filtering or by a filter press or centrifugal machine. The crystalline mass so obtained is pressed in canvas bags in a hydraulic press at a temperature of 40 C. The oils expressed are then again chilled to a low temperature and pressed, or are redistilled to recover more anthracene; then they are mixed with the creosote oil or run back into the tar still to soften the pitch. The crude 30 per cent anthracene from the press is pulverized and washed with creosote oil or with solvent naphtha from the light oils, which dissolves much of the contaminating substances, but does not remove carbazol. The magma is again " centriffed " or pressed, and the liquid separated is distilled to recover the naphtha, while the residue of .phenanthrene, which has no special value, is usually burned for lampblack. By these washings, the anthracene is raised to about 50 per cent, when it is sold to the alizarine manufacturer. For further purifica- tion, it is washed with caustic potash to remove carbazol, and then it is sublimed in an atmosphere of superheated steam. It forms white plates of pearly lustre, melting at 213 C. and boiling at MINERAL OILS 285 ;>60C. It is employed entirely in the preparation of artificial alizarine. The pitch left in the still after the distillation is either hard or soft, as described on page 281. If so soft that it remains liquid when cold, it is often used as a black varnish for painting metal work and wood, or for making tarred paper or roofing paper. Medium soft pitch is used as a cement in preparing " briquettes " from coal dust for fuel. Pitch is also mixed with asphalt for making sidewalks and pavements. Soft pitch softens at about 38-40 C. and melts at 60 C. When a small piece is chewed, it coheres together like gum. Hard pitch softens at 75-SOC., and melts above 120 C. When chewed, it pulverizes into a non-cohesive powder in the mouth. REFERENCES Coal-Tar and Ammonia. Geo. Lunge, London, 1887. (Gurney and Jackson.) Die Chemie des Steinkohlentheers. Gustav Schultz, Braunschweig, 1890. (Vie\veg.) Die Technische Verwerthung des Steinkohlentheers. G. Thenius, Vienna, 1887. Das Anthracene und seine Derivate. G. Auerbach, Braunschweig, 1880. MINERAL OILS THE PETROLEUM INDUSTRY Petroleum is widely distributed, being found in many places in sufficient quantities for profitable working. The principal deposits in America are located in Pennsylvania, New York, Ohio, West Virginia, California, Colorado, and Canada; some oil comes from Indiana, Kansas, Kentucky, and Texas. The next in importance to the American oil fields are the Russian, in the Baku district around the Caspian Sea, in the Caucasus mountains, and along the northeast coast of the Black Sea. Less important deposits occur in Persia, Burmah, China, Galicia, and Romnania. Small deposits are worked in Germany, Hungary, Algiers, Japan, Venezuela, New Zealand, and in some of the islands of the Pacific. Petroleum occurs in all geological formations from the Silurian to the Tertiary, the New York and Pennsylvania deposits being in the Devonian a,nd Upper Silurian, the Colorado fields in the Creta- ceous, and those in California in the Miocene epoch or Middle Ter- tiary. The Russian, Galician, and Indian oils are chiefly in the Tertiary. In all cases, the strata in which it is found are horizontal 286 OUTLINES OF INDUSTRIAL CHEMISTRY or but slightly inclined, usually not over 30. It is generally found in sandstones or conglomerates, called " oil sands," overlaid with an impervious shale or slate. Frequently several layers of sandstone are struck, lying between beds of the shale. The origin of petroleum has been the subject of much study by many eminent chemists. Berthelot regarded it as the product of the action of steam and carbon dioxide on the alkali metals. Men- deleeff supposed it resulted from the decomposition of metallic car- bides by water. This necessitates the acceptance of La Place's theory of the formation of the earth, and the assumption that heavy metals, such as iron, were among the first substances to condense into the liquid and solid state, thus forming the central portion of the earth ; and that these metals then combined with the carbon from the surrounding atmosphere to form carbides, which were after- wards decomposed by water, from the cooled surface, which perco- lated down through cracks and fissures caused by the cooling and shrinkage of the earth's crust. Thus hydrocarbons were formed and metallic oxides left in the earth. This theory requires that all petroleums have approximately the same composition, in whatever formation they are found, but this is not the case. Another hypothesis supposes petroleum to be of organic origin. Here again are several theories as to the formation of the oil from the vegetable or animal remains. One is that the organic matter, probably consisting of vegetable matter and mollusks, decomposed under salt water with exclusion of oxygen and at a rather low tem- perature.* Another, that only animal matter is the basis of the oil and that the nitrogen of the animal tissues escaped as ammonia or other nitrogen compounds, and that the remaining fat was subjected to a species of dry distillation under great pressure, yielding crude petroleum. There is reason to believe that the New York, Pennsyl- vania, and Ohio petroleums are of vegetable origin,f but those of California, $ Texas and some others contain nitrogen and are found in rocks filled with animal remains. The crude oil usually consists of hydrocarbons, present in homol- ogous series, though oils from different localities show differences in these series. The Pennsylvania oils contain members of the marsh gas series with the general formula, C n H 2n + 2 ; all of these, from methane, CH 4 , up to solid paraffines with C^H 58 , have been iso- * Phillips. Am. Chem. Jour., 16, 409-429. t Orton. Report on Occurrence of Petroleum, Natural Gas, and Asphalt in West- ern Kentucky. 1891. 1 Peckham. Am. Jour. Science, 48. (1894.) MINERAL OILS 287 lated from these oils. Also, small amounts of the olefine series, C n H 2n , and the benzine series, C n H 2n _<;, and in some oils, some sulphur and nitrogen have been found. The Russian oils, however, consist largely of the naphthene series, having the general formula C n H 2n , isomeric with the olefines, but differing from them in their proper- ties. Consequently, the refining of the Russian oil is not quite the same as that of the American oils. In many places crude oil comes to the surface in small quantities, mixed with the water from springs, the first discoveries having been reported as "oil springs." The explorers in central New York, as early as 1630, mentioned an Indian remedy containing petroleum. Later it was sold as " Seneca oil," by the Seneca Indians. Their method of collecting it was to spread blankets on the surface of the water on which the oil was floating, wringing it out when the blanket became saturated. If the layer of oil was thick enough, it was skimmed off with a flat board. About the middle of this century, petroleum from various parts of the world had begun to attract some attention, and crude methods of refining it had been devised ; in some few instances this purified oil was being used for illuminating. But none of these efforts had been very successful, and it was not until 1859, when Mr. Drake drilled the first productive oil well near Titusville, Pa., that the real development of the petroleum industry began. 5 * The Russian, Indian, and Galician oils were mentioned by explorers during and before the Middle Ages, but the industries have never been de- veloped to any great extent, until within the last twenty years, when the Russian fields have become very important. The crude oil is obtained by boring tube wells through the shale into the sand rock. There is no certainty beforehand that a well will yield oil, and, indeed, about one-fifth of those bored in this country produced none; these are called "dry holes." The machinery used in oil-well drilling is very ingen- ious, and a great number of special devices have been invented to overcome the numerous obstacles encountered. Only the principal tools can be mentioned here. The chief one is the "centre-bit" (Fig. 72), a chisel-shaped piece of steel 4 feet long and weighing about 300 Ibs., the cutting edge of which is nearly as wide as the diameter of the well. Above the centre-bit is the * A period of wild excitement and speculation followed, the description of which by Peckham, Crew, and others, is very interesting reading. 288 OUTLINES OF INDUSTRIAL CHEMISTRY " auger-stem," a rigid bar from 12 to 45 feet long, to which the bit is screwed. Its chief purpose is to guide the bit and keep the hole straight; it also adds weight to the drill. Next above the auger- stem is a peculiar piece of apparatus called the "jars" (Fig. 73). It consists of two links of steel which have a sliding motion, one within the other, of from 20 to 24 inches. The object of this is as follows : the centre-bit frequently becomes fastened in the hole, either by fragments of broken rock acting as wedges between it and the sides of the well, or through sinking into a seam in the rock. Any attempt to loosen it by a steady upward pull would break the rope, but a sudden upward shock is generally sufficient to loosen it. This is obtained by the movable links of the jars. But they are not allowed to close completely, and so give a downward stroke, unless the tools become fast in the well. Above the jars is a long, heavy steel bar called the " sinker-bar." Through its momentum this gives greater effect to the action of the jars. To the top of the sinker-bar the rope is attached, by which the entire mass is lifted and dropped, just as a pile-driver is operated. The drop allowed for each stroke of the bit is about two feet. The rope is fastened to the "temper-screw," which lowers the tools slightly as the rock is cut away by each blow of the bit, and turns them in the hole so that the next cut shall be at a slight angle to the last one. When all screwed together, the drilling tools form a rod about 60 feet long and weighing about a ton. Over the spot where the well is to be drilled a heavy timber structure is built, called the " derrick " ; this is from 35 to 80 feet high, and from 12 to 15 feet square at the bottom, tapering to about 5 feet square at the top. On the floor of the derrick is the windlass for handling the drilling tools, the rope passing over a small wheel at the top. During the drilling the rope passes through a clutch at the end of a large walking-beam, driven by the engine, imparting a rapid up and down motion to the tools. An iron "drive-pipe" is sunk through the drift and clay to the solid bed-rock. If the latter is within 15 or 20 feet of the surface, a shaft 6 or 8 feet square is sometimes dug down to it. Then the drilling of the well proper begins, which is usually 7-J inches in diameter to the bottom of the water-bearing strata. Then the hole is decreased to 5| inches diameter, and a tube, called the "casing," is put down ; this is provided with a rubber or leather collar to fit closely against the shoulder formed where the diameter of the well MINERAL OILS 289 decreases, making a water-tight joint. Then the hole is continued to the oil-bearing strata, by means of a 5J-inch bit. At frequent intervals it is necessary to remove the mud and splinters of rock. This is done by the "sand-pump," or "bailer," which is a long metal tube, having a valve in the bottom. It is low- ered until a pin on the under side of the valve strikes the bottom of the well. The water, which is always present, rushes into the bailer, drawing with it the debris ; then the tool is at once raised and the valve closes. It is customary to drill some distance into the oil-bearing stratum, and sometimes a cavity filled with gas, oil, and water is struck. The pressure is occasionally so great as to drive the oil to the surface, sometimes with great force. Such wells are called " gushers." They seldom continue to flow for more than a few days or weeks, when pumping must be employed. Some of these gushers have produced enormous quantities of oil, as much as 3000 barrels a day when at their height. But most wells do not gush, and it is now quite customary to re- sort to "torpedoing," in order to increase the yield of oil. A tin shell, from 3 to 5 inches in diameter and from 5 to 20 feet long, is filled with nitroglycerine and lowered to the bottom of the well. On top of the can is a percussion cap, which is fired by dropping a piece of iron, called a "go-devil," weighing several pounds, into the well. The resulting explosion cracks and shivers the rock, giving the oil a better opportunity to flow into the well. Very often a well gushes after torpedoing, and measures are usually taken beforehand to dispose of the first heavy rush of oil and water. The finished well is prepared for pumping by lowering a 2-inch pipe, at the bottom of which is the oil pump, worked by a wooden rod inside the pipe. Fig. 74 shows sections through a pumping and through a flowing well. In a flowing well no pump rod is introduced, but the space between the casing and tubing is tightly closed at the top, in order to force both gas and oil through the tubing. The wells range in depth from 50 to 4000 feet, the average in ]N~ew York and Pennsylvania being from 1200 to 1800 feet. The cost varies, but from 3000 to 4000 dollars is about the average. The ordinary produc- tion varies from one to several hundred barrels per day. The crude oil is now generally carried from the wells to the 290 OUTLINES OF INDUSTRIAL CHEMISTRY refineries by pipe-lines, six- or eight-inch pipe, through which the oil is pumped. At frequent intervals along the pipe-lines are tanks of from 30,000 to 40,000 barrels capacity, in which the oil is stored until wanted for refining. Of course this system mixes all varieties of oils ; hence, if a special kind is required, it must be transported in tank cars or in barrels. Crude petroleum is a thick, sirupy liquid varying in color from greenish brown to nearly black; some varieties are reddish brown or orange when viewed by transmitted light. Nearly all show some fluorescence, and have a rather unpleasant odor. The specific gravity varies from 0.782 to above 0.850, in oils from different localities. As it comes from the well, more or less gas is dissolved in it, consisting chiefly of marsh gas, CH 4 ; ethane, C 2 H 6 ; propane, C 3 H 8 ; and butane, C 4 H 10 . A very small amount of phosphorus is often present, but seldom more than 0.05 per cent. The oils from Ohio and Canada have a very unpleasant odor, because they contain some sulphur compounds. Sand and water are also mixed with the crude oil, but these settle on standing in the storage tanks. In order to separate the various products from the crude oil, it is subjected to fractional distillation. The higher the percentage of the illuminating oils, the more profitable for the refiner ; but many crude oils are distilled only for the lubricating oils. A few may be used as lubricants without distilling. Considerable petroleum was used for fuel, but this is being replaced by the residuum from which the more valuable illuminating oils have been separated. Refining consists in the separation and purification of the market- able products of the crude oil, which is usually separated into FIG. 75. about five portions. These are naphthas, illuminating oils, lubri- cating oils, parafnnes, and coke. The process is usually worked in two stages : the distillation and refining first of the light oils, and then of the heavy oils. It is only in the large refineries that both processes are carried out ; usually one refiner produces the naphthas, MINERAL OILS 291 burning oils, and "residuum," and another starts with the residuum and finishes the process. For distilling the light oils, two forms of still are in use. The cylindrical or horizontal still (Fig. 75) is about 30 feet long by 10 or 12 feet in diameter, and is set in a brick furnace, with the upper half of the still exposed to the air. It holds about 600 barrels, and is provided with steam coils and arrangements for blowing in free steam during the distillation, which assists in the process by mechan- FIG. 76. ically helping to carry over the oil vapors. The upright or "cheese- box " still (Fig. 76) holds 1000 barrels or more, is set directly over the furnaces (B, B), and is exposed to the air. It is 30 feet in diam- eter and about 10 feet high, and has steam coils and pipes for free steam as above described. The bottom is double-curved to permit of some expansion. The condensers are long straight pipes set in troughs through which water flows, or they are coils set in tanks of cold water. They are so arranged that the distillates are delivered at some dis- tance from the still, to diminish the fire risk. Each pipe is usually provided with a trap by which the gases (passing over with the oil vapors) are collected and then led under the still -and burned, thus economizing fuel. Sometimes the very light oils are burned with the gases, but they are usually condensed, forming the "benzine distillate," or crude naphtha. This is stopped when the gravity reaches 62 Be. (sp. gr. 0.729). Then comes the kerosene, or burning oil distillate, until the gravity equals 0.790, or for very heavy illu- minating oils, 0.820. Here the distillation is stopped and the resid- uum drawn off, to be distilled for lubricating oils, in the " tar stills." Since the illuminating oils are the most valuable, a process 292 OUTLINES OF INDUSTRIAL CHEMISTRY known as "cracking," * by which the yield of these is increased, has come into general use in recent years. As has already been shown, the upper part of the still is exposed to the air and thus cooled. When the heavy oils begin to distill, the fire is so modified that only the bottom of the still is heated very hot, while the top and sides cool somewhat. Thus the heavy-oil vapors are condensed within the still itself, and drop back into the residuum, which, being much hotter than the boiling point of the oil, causes a breaking up of the oils of high molecular weight into lighter oils of less molecular weight and lower boiling points, while some carbon separates, form- ing a coke on the bottom of the still. This deposit of carbon must be removed at frequent intervals. The reactions which occur in "cracking" are probably complex. The heavy oils are decomposed into parafiines and olefines of lower boiling points, and very probably hydrocarbons of the aromatic and methylene series are also produced. The number of products is doubtless quite large. As examples of what may, perhaps, take place, the following may be assumed : the hydrocarbon, C^Hgg (octadecane), boiling at 317 C., might decompose into C 10 H 22 (decane), boiling at 173, and C 7 H 16 (heptane), boiling at 98 C., and carbon. Or it might form a paraffine and an olefine, e.g. C 8 H 18 (octane), boiling at 125 C., and C 10 H 20 (decylene), boiling at 172 C. The lower boiling product would be put with the naphtha distillate, and the higher boiling would form a part of the burning oil. The several distillates obtained from the crude oil are redistilled and divided into further subdivisions. The benzine distillate yields t ' Cymogene, B. P. = 32 F. Sp. Gr. = 0.590 - 0.610 ] Rhigolene, B. P. = 60 F. Sp. Gr. = 0.625 - 0.631 \ Gasoline, B. P. = 115 F. Sp. Gr. = 0.635 - 0.666 j C Naphtha (Benzine) B. P. = 122 - 140 F. Sp. Gr. = 0.678 - 0.700 B Naphtha, Sp. Gr. = 0.714 - 0.718 A Naphtha (Petroleum naphtha), Sp. Gr. = 0.741-0.745 The burning oil distillate yields : 110 fire test burning oil (" Standard white "). ) F _, 120 fire test burning oil (" Prime white"). ( 150 fire test burning oil (" Water white"). * The history of the discovery of this process is given in chap, iii of Petroleum Distillation, by A. N. Leet, New York, 1884. fBoverton Redwood Groves and Thorp's Chemical Technology, Vol. II. MINERAL OILS 293 The residuum from the above distillation is transferred to the tar still, or if the distillation has been carried on under vacuum, it is known as "reduced oil," and is used to make fine lubricating oils or vaseline. The tar stills are cylindrical, and are set in much the same way as those already described, but are encased in brickwork almost to the top. They are provided with pipes for introducing superheated steam, and are much smaller than the crude oil stills. The first distillate is collected until the gravity is about 38 Be. (0. 834 sp. gr.), and is mixed with the next charge of crude oil, or washed with acid and soda and refined for burning oil. Then follow several distillates of increasing color and density, which are purified as described below, and treated to separate the paraffine wax and lubricating oils. The distillation is carried on until the still bottom is red-hot, when a gummy yellow distillate, called "yellow wax," is collected. This contains anthracene and other hydrocarbons of high molecular weight. The residue of coke is highly valued for electric light carbons and other electrical purposes. The fractions collected from the burning oil distillate are more or less yellow, colored by tarry matters, which would collect in the lamp-wick and soon choke it. To remove these impurities, the oil is put into an " agitator," a large, lead-lined, iron tank, where it is mixed with from 1 to 2 per cent of concentrated sulphuric acid, and the mixture stirred by blowing in air at the bottom. The acid unites with the tarry matters, and when the blast is stopped, sinks to the bottom and is drawn off as "sludge acid." Water is added, and after the mixture is agitated, is drawn off. Next a solution of caus- tic soda is introduced (about 1 per cent), and the contents of the tank again agitated. Then the oil is again washed with water and drawn into the settling tanks, where the suspended water settles out, leaving a bright, clear oil. These tanks are very shallow, usually only about 1 foot or 15 inches deep, but may cover an area of 20 by 30 feet. They are exposed to the light and air, and usually contain steam coils for warming the oil in winter. If the oil is now found to have too low a flash point (p. 295), it is run through a "sprayer," an upright pipe with cross-arms of small perforated pipe, through which the oil is forced into the air in fine jets or spray; after falling some distance, it is collected in tanks. By this exposure to air, any light oils, such as benzine or naphtha, are volatilized, and the flash point thus raised. But spraying is less frequently necessary now, since more care is taken in the original distilling. 294 OUTLINES OF INDUSTRIAL CHEMISTRY Instead of washing, some kerosenes are redistilled, but this generally fails to remove all the yellow color, though, when burned, they do not form a crust on the wick, due to traces of caustic soda or sodium sulphate. A small amount of burning oil of very high fire test (about 300 F.) is made by treating a crude oil distillate (0.823 to 0.846 sp. gr.) with a very large proportion (5 to 7 per cent) of sulphuric acid, washing with caustic soda, and redistilling with caustic soda lye in the still. This oil is sold as mineral colza, mineral seal, and mineral sperm oil. The paraffine oils are treated with acid in agitators which may be heated by steam pipes ; they are washed and then chilled and left several hours until the paraffine crystallizes. The soft mass is then put into canvas bags and pressed at 40 F. in hydraulic presses. The crude paraffine cake is again melted, crystallized, and pressed. It is then washed with a little benzine and pressed once more. It is finally melted and filtered hot through bone-char, and on cooling, forms the white commercial paraffine. The oils expressed are lubri- cating oils of various grades. After the paraffine is removed, some of the lighter lubricating oils are converted into "neutral oils" by bone-char filtration and exposure to sunlight and air, to remove the " bloom," so that they may be used to adulterate certain animal and vegetable oils. It may also be removed chemically by adding about 1 per cent of nitro- naphthalene, or dinitrobenzol, or nitric acid. Bloom has no injurious effect upon the oil or machinery. Crude petroleums containing sulphur (e.g. those from Ohio and' Canada) are more difficult to refine, and consequently were formerly only used for fuel. Successful methods for refining them are, how- ever, now in use. The common process is to pass the vapors from the crude oil distillation over copper oxide ; or to collect the distil- lates from the crude oil separately and redistill them with a large excess of copper oxide, or a mixture of lead and copper oxides in a still, which is provided with an agitator. The residue consists of a mixture of tar, copper sulphide, and oxide. This is pressed and calcined at a low temperature, the combustion of sulphur and tar furnishing sufficient heat. The final product is copper oxide which is returned to the process. A solution of litharge in caustic soda is sometimes used in the agitator after the usual acid and alkali treats ment, to remove the sulphur, but this is not always a success; though it destroys the offensive odor, traces of sulphur sometimes remain and become noticeable on burning. MINERAL OILS 295 The lighter lubricating oils are called "spindle oils" and are used on rapid running bearings. " Machinery oils " form the middle grades, and " cylinder oils " are the heaviest. Paraffine in lubricat- ing oils is said to reduce its viscosity and cause it to become gummy when in use. " Reduced oils " are made from the residuum left after distilling the burning oils from some crude petroleums by the aid of vacuum (p. 5); or by simply exposing certain crude oils to the sun and air in shallow tanks which may be gently heated by steam-coils in winter. The very light oils soon evaporate and the suspended im- purities settle. Another process is to let the crude oil flow in thin films over woollen blankets suspended in warm rooms; the very volatile oils evaporate and much of the suspended matter is retained by the cloth. By these methods, oils are obtained which are entirely free from any decomposition products due to heating, and from any chemicals such as are used in washing and bleaching ordinary lubri- cating oils. Crude oils of high gravity (below 32 Be.) are usually selected for this purpose. Reduced oils are valuable lubricators and command a good price. Sometimes they are char-filtered to improve their color and quality." Vaseline or petrolatum is made from the residuum of vacuum dis- tilled crude oils. It is treated with acid and soda, washed and char- filtered, and sometimes redistilled in vacuum. The Russian petroleums are distilled in much the same way aa the American, but less acid is used, as the naphthenes are somewhat soluble in it. It is found practicable to use continuous stills as the residuum is more fluid than in the case of American oils. The stills are heated by separate furnaces and connected in such a manner that the overflow pipe from one is the supply pipe for the next, the resid- uum from the last passing through coils placed in the supply tank, so that the crude oil is warm when it enters the first still. By care- ful regulation of the heat and the flow of oil, each still can be made to yield a distillate of constant gravity. Russian petroleum yields about 38 per cent illuminating oils, which is lower than the Pennsylvania oils. Since fuel is scarce, the residuum, called astatki, is burned in special burners and furnaces. The yield of lubricating oils is large, being nearly 36 per cent. They are said to be superior to American lubricators for use in cold countries. Oil-testing. The usual test for kerosene is the flame test, i.e., the determination of the temperature at which the vapors take fire when mixed with air. The point usually taken is the " flash point," 296 OUTLINES OF INDUSTRIAL CHEMISTRY the temperature at which the oil gives off sufficient vapor to form a momentary flash when a small flame is brought near its surface. The "fire test" determines the temperature at which the oil gives off enough vapor to maintain a continuous flame if ignited; in other words, it shows the temperature at which the oil burns in the air, and is about 20 F. higher than the flash point. Both the flash point and the burning point are lower than the boiling point. The flash point is determined in a special appa- ratus, and in many states and countries the par- ticular instrument and its dimensions are specified by law. In this country, " open testers " are largely used, but recently Abel's "closed tester" has be- come very popular, and is now the legal instrument in England and Germany. There are many forms of apparatus for oil testing, but the two above men- tioned cover the general principles involved in all. Open testers do not represent the conditions pre- vailing in an ordinary lamp ; the closed tester more nearly approaches these, and its indication is usually about 20 F. lower than that shown by the open tester. Tagliabue's open tester (Fig. 77) is very simple. A copper water bath (A), heated by the small lamp (B), contains the glass dish in which the oil to be tested is placed. A delicate thermometer (E) is hung to dip into the oil. Some- times a stirring apparatus is provided for both the water bath and the oil. The water bath is slowly heated, and at regular intervals of temperature a lighted match or small gas flame is passed half an inch above the surface of the oil. The tempera- ture at which a flame passes completely over the surface is noted as the flash point. The heating is usually continued until the oil catches fire on applying the light, when the temperature is taken as the burning point. The apparatus is rather crude and is open to errors. Abel's closed tester (Fig. 78) is more compli- cated, but obviates some of the errors of the open cup. It consists of a copper cylinder (K, K) in which is the water bath (F). In the upper part of the water bath is an air chamber (B) in which FIG. Fiu. 76. MINERAL OILS 297 is suspended the copper vessel (A) carrying the oil. All these vessels are provided with close fitting covers. The cover of (A) has three openings which may be opened or closed by a small lever. The cover also carries the thermometer (D), dipping into the oil, and a small lamp or gas flame set on an axis at (C), so that the flame may be brought directly over the middle opening in the cover. Usually the lever which moves the cover of the opening, simultaneously turns the flame down to it. The ther- mometer (E) dips into the water bath, which is heated to 54 G. before the oil is introduced into (A). When the thermometer (D) registers 18-19 C. the testing is begun, and repeated with each rise of a degree, until the flash is seen. This instrument is officially used in Germany, the lever being run by clock-work. It is also used in England, the law requiring a flash test of 73 F., which is rather low for safety ; it should not be under 100 F. In this country, each state has its own standard. Some require 150 F. fire test in open cups, and others 110 F. Most states fix 110 F. flash test. Lubricating oils are usually tested for viscosity, gravity, flash, and burning points, congealing point and color. The gravity is usually determined with the hydrometer or Westphal balance. In this country, the Baume instrument is almost always used. Viscosity is determined by relative tests, e.g., the rate of flow of the oil through a capillary tube or narrow opening, as compared with the rate of flow of pure sperm oil through the same tube or opening. Temperature is here a very important factor. The congealing point, or " cold test,' 7 determines the temperature at which the oil becomes pasty or solid through the crystallization of dissolved paraffine or other matter. This test is of great moment if the lubricators are to be used in cold climates. Color tests are chiefly made on oils intended for export, by com- paring a tube full of the oil with standard glass plates of various tints, in a colorimeter. For burning oils the colors range from pale yellow or straw to water white. Certain animal and vegetable oils, when soaked up in waste, will take fire on standing. This is especially true of linseed, cotton-seed, corn, lard, and neatsfoot oils, and is caused by the rise in temperature due to the oxidation of the oil. If from 40 to 50 per cent of mineral oil be added to these oils, this spontaneous combustion is prevented to a great extent. This is one of the uses of the neutral oils (p. 294). 298 OUTLINES OF INDUSTRIAL CHEMISTRY SHALE OIL INDUSTRY In Scotland, Germany, and a few other countries, mineral oils are produced by the destructive distillation of certain bituminous shales. These are soft, light brown, or gray rocks, which do not contain oil as such, but are permeated with bitumen, a very complex organic substance similar to pitch. When heated in retorts this decomposes into gas, oily products, ammonia, and tar, leaving a carbonaceous residue. The temperature of the distillation greatly influences the character of the products, a low temperature affording an increased yield of oil. The shale is broken to small size and heated to a low red heat in vertical retorts into which steam is injected to assist in the distilla- tion. Both continuous and intermittent systems of distillation are in use, the former being generally employed in Scotland. The shale is charged at the top of the retort and when "spent" is drawn while still hot upon a grate beneath the retort, where its carbona- ceous matter (amounting to 10-15 per cent) is burned, thus econo- mizing fuel. The products of the distillation pass through a series of pipes similar to the hydraulic main and condensers of the coal-gas manu- facture. The light naphtha vapors and gas pass into a coke tower through which heavy paraffine oil trickles ; this absorbs the naphtha, while the gas passes on and is burned under the retorts. In the hydraulic main and condensers the other distillates condense in two layers, the ammoniacal liquor below and the tar and oil above. These are separated by gravity. The ammonia liquor is treated in the same way as that from coal gas (p. 125). The oily tar (0.865 sp. gr.) is distilled in much the same way as crude petroleum until only solid coke remains in the still. The distillates are collected together as " once run oil " and washed in agitators with sulphuric acid and caustic soda, and then fractionally distilled. These dis- tillates are each purified, yielding commercial naphtha, burning oils, lubricator oils, and solid paraffine. The acid tar from the washing yields some ammonium sulphate, and tarry matter which is used for fuel. The soda tar is treated with carbon dioxide, which liberates the creosote, used for the same purpose as that from coal-tar. The carbonate of soda solution is causticized and used again. OZOKERITE Ozokerite is a natural, paraffine-like substance containing a small quantity of oily matter. It was probably formed by the evaporation MINERAL OILS 299 of petroleum until the more volatile oils had escaped. It occurs in irregular seams and masses in the earth in Galicia, in the Caucasus, and in Colorado. In Galicia it is mined by sinking shafts and drift- ing, following the seams. The wax is separated from the earthy impurities by hand picking and by washing, the wax being lighter than water and rising to the surface. The residue is boiled with water to melt out the remaining wax, which is skimmed from the surface. Extraction with benzene is also employed. The wax is sometimes distilled, by which light oils, illuminating oils, heavy oil, and paraffine are obtained. Or it is refined by treat- ing with sulphuric acid and caustic soda, followed by a charcoal or bone-black filtration. The product, called ceresine, melts at 61 to 78 C.* and is similar to beeswax. It appears to belong among the olefmes, having the general formula C n H 2n . Its color ranges from pale yellow to white, according to the degree of refining. It is used as candle stock ; for preparing insulating compounds for electrical work ; in making a black dressing for shoes and har- ness leather, and to adulterate beeswax. ASPHALT Asphalt or mineral pitch is probably an oxidized residue from the evaporation of petroleum. This name is usually applied only to the solid bitumens, the semi-solid or liquid bitumen being called maltha, or mineral tar. Asphalt generally contains sulphur and nitrogenous bodies, but is chiefly composed of hydrocarbons. The crude mate- rial consists of two chief ingredients, that soluble in petroleum spirit, called petrolene, and an insoluble black substance called asphaltene. Asphalt occurs in large quantities in and near the " pitch lake " on the island of Trinidad ; also in Cuba, Venezuelar, California, Utah, Texas, Canada, and in many European countries. The Utah deposit is particularly pure (gilsonite) and is much used for black varnish and for insulating material. It is also much used as a protective paint for the interior of chlorine stills, bleaching powder chambers, acid tanks, and for waterproofing purposes. Its chief use is for sidewalks and pavements, for which it is mixed with pulverized limestone or with the natural asphalt rock. The latter falls to a loose granular mass when heated until the asphalt softens, and is then rolled and stamped into place with hot irons. A certain proportion of purer asphalt, or of the heavy petroleum oils, is oftn added to the mixture to render it more plastic. * Redwood. 300 OUTLINES OF INDUSTRIAL CHEMISTRY Crude asphalt contains much moisture and mineral matter. It is refined by heating until melted, whereby the moisture is expelled and some of the mineral matter separates by subsidence. Two varieties of Trinidad asphalt are in commerce, " lake pitch " and "land pitch." The latter is harder, and has the higher melting point. Asphalt is soluble in carbon disulphide, acetone, and ben- zene, but not in alcohol nor water. When heated it softens at from 80 to 100 C. REFERENCES Petroleum Distillation. A. N. Leet, New York, 1884. Report on Petroleum ; IT. S. Census, 1880. S. F. Peckham, Washington, 1885. Das Erdb'l von Baku. C. Engler, Stuttgart, 1887. (Enke.) A Practical Treatise on Petroleum. Benj. J. Crew, Philadelphia, 1887. (Baird &Co.) Die Deutsche Erdole. C. Engler, Stuttgart, 1888. (Enke.) Le Petrole. Henry Deutsch, Paris. Das Erdb'l und seine Verarbeitung. A. Veith, Braunschweig, 1892. (Vieweg.) Petroleum; Its History, Origin, etc. William T. Brannt, Philadelphia, 1895. (Baird & Co.) Die Fabrikation der Mineralble. W. Scheithauer, Braunschweig, 1895. (Vieweg.) Treatise on Petroleum, 2 vols. Boverton Redwood and G. T. Holloway, London, 1896. (Griffin & Co.) U. S. Geological Survey, 8th report. (Formation of Petroleum.) American Chemical Journal, 16, 406. The Origin of Petroleum and of Natural Gas. F. C. Phillips. Proceedings of the American Academy of Arts and Sciences, Vol. 32. Investi- gations on American Petroleum. Charles F. Mabery. Proceedings of the American Philosophical Society, Vol. 36, No. 154. Origin and Chemical Composition of Petroleum. S. P. Sadtler. Journal of the Society of Chemical Industry : 1890, 359. The Oil Fields of India, Burmah, etc. B. Redwood. 1894, 719, Removal of Sulphur from Petroleum. 1894, 790, Origin of Petroleum. F. C. Phillips. 1894, 794, Present State of the Petroleum Industry. 1894, 872, American and Russian Petroleums. Journal of the Association of Engineering Societies : 1894, On the Composition of the Ohio and Canadian Sulphur Pe- troleum. C. F. Mabery. Mineral Resources of the United States, 1882-1893. Report of Experts on Asphalt Paving. Department of Public Works, Philadel- phia, 1894. L'Asphalte. Leon Malo, Paris, 1888. (Baudry et Cie.) Mineral Oils and their By-Products. I. I. Redwood, London, 1897. (E. & F. N. Spon.) VEGETABLE AND ANIMAL OILS 301 VEGETABLE AND ANIMAL OILS, FATS AND WAXES These oils are usually called " fatty " oils, to distinguish them from the mineral and essential oils. They are very widely dissemi- nated in nature, both in plants and in animals, and often form a large percentage of the weight of the substance in which they are found. They differ from the mineral oils in their chemical composi- tion, being compounds of organic acids, with bodies belonging to the group called alcohols; i.e. they are esters or compound ethers of the organic acids. In the majority of cases, the alcohol from which these esters are derived is glycerine, or glycerol, C 3 H 5 (OH) 3 , a tri- atomic alcohol; but occasionally, e.g. in the waxes, a mouatomic alcohol is the base. The ethers formed from glycerine with the fatty acids are called glycerides, a name which is sometimes applied to the oils also. The glycerine radical C 3 H 5 is called glyceryl. The acids most commonly found in these glycerides are shown in the following tables : SATURATED ACIDS. (ACETIC SERIES.) ACID. FORMULA. MELTING POINT. BOILING POINT. SPECIFIC GRAVITY. Butyric . . C 4 H 8 2 - 3 163 C. 0.958 Caproic . . C 6 H 12 2 - 1.5 205 0.929 Caprylic . . C 8 H 16 2 + 15 236 0.935 Capric . . CioH 2 oO 2 + 30 269 0.930 Laurie . . Ci2H 2 4O2 + 43.5 225 at 100 mm. pressure. Myristic . Ci4H 28 O 2 + 54 250 at 100 mm. pressure. Palmitic . . CieH 32 2 + 62 271.5 at 100 mm. pressure. Stearic . . Ci 8 H3eO 2 + 70.9 291 at 100 mm. pressure. - Arachidic C 2 oH4o0 2 + 75 Carnabuic C24H 48 2 + 72.5 Cerotic . . C 2 ?H540 2 + 78 302 OUTLINES OF INDUSTRIAL CHEMISTRY UNSATURATED ACIDS. (ACRYLIC SERIES.) ACID. FORMULA. MELTING POINT. BOILING POINT. C 3 H402 8C 140 C Crotonic C 4 H 6 Oa 72 180 Hypogaeic / . . . . Physetoleic f . . . . Oleic . C 16 H 30 2 ClsH (33 (30 14 Emcic / 134 \.>22ni4t>\J% J /60 UNSATURATED ACIDS. (PROP10LIC SERIES.) ACID. FORMULA. MELTING POINT. SPECIFIC GRAVITY. Linoleic Liquid at 18 C Linolenic Ricinoleic . . . . CisH3o02 CisHs^Og - 10 C. 0.940 The acids containing ten or fewer carbon atoms in the molecule may be distilled under ordinary atmospheric pressure without de- composition ; they are called volatile fatty acids. The others given in the tables are called non-volatile acids; some of them may be distilled uiidecomposed under reduced pressure or by superheated steam. With the exception of a few of the less common oils and waxes, only acids having an even number of carbon atoms in the molecule occur in the fatty oils. The glycerides composing the greater part of the important commercial fats are those of butyric, lauric, pal- mitic, stearic, oleic, linoleic and ricinoleic acids ; to a less extent occur the esters of caproic, caprylic, crotonic, and myristic acids. The fats are always mixtures of several glycerides, and the propor- tion in which these are present determines the nature of the fat, whether hard, soft, or liquid ; while certain peculiar properties of some fats are due to the presence of one or two particular gly- cerides. The glycerides of palmitic and stearic acids are white crystalline solids, melting at 61 and 72 C. respectively ; that of oleic acid is liquid at ordinary temperature. VEGETABLE AND ANIMAL OILS 303 The fatty acids are monobasic, and glycerine being a triatomic alcohol, the glycerides are composed of three acid radicals combined with one alcohol rest; thus the glyceride of palmitic acid has the formula (C 16 H 31 2 ) 3 =C 3 H 5 , and is called tripalmitin, or, more often, simply palmitin. The glyceride of stearic acid is (C 18 H. K 2 ) 5 =C 3 ~K S , called tristearin or stearin. That of oleic acid is (CigH^j^CjHa called triolein or olein. The fats and oils are lighter than water. They cannot be boiled or distilled, even under reduced pressure, for when heated much above their melting point they decompose. Among other products of decomposition is a substance called acrolein, CH 2 =CH CHO. This is a low boiling liquid, having a very disagreeable odor, and whose vapors are very irritating to the eyes. Fresh fats are nearly odorless and of neutral reaction, but when exposed to the air for some time many of them undergo a change by which the glycerides are decomposed and the fatty acids set free, while glycerine is formed and usually further decomposed at once. This breaking up of an organic ester into free acid and an alcohol is called hydrolysis, since the elements of water are taken up by the acid and alcohol. Thus if E. represent the acid radical, hydrolysis of a fat may be represented by the general equation : CH 2 OR CH 2 OH. I I CHOR + 3 H-OH = CHOH + 3 H-OR. I i CH 2 OR CH 2 OH. s This change is often brought about by the fermentation or putre- faction of other substances of a gelatinous or albuminous character present in the oil, and is accompanied by numerous secondary re- actions, which produce bodies of a very disagreeable odor and taste. The oil is then said to be " rancid." Hydrolysis may be readily brought about by chemical means, and is then called " saponification " ; in this case the reaction is much more complete, and these secondary reactions do not occur. The process is employed in soap and glycerine manufacture, as will appear later. Certain oils are oxidized when exposed to the air, and are con- verted into thick gummy or resinous masses, or in thin layers form dry, hard, transparent or translucent films. This change is called " drying," and is most noticeable in oils containing the glycerides of 304 OUTLINES OF INDUSTRIAL CHEMISTRY linoleic, linolenic, and ricinoleic acids, which, being unsaturated, oxidize very readily. Oils and fats are found in every part of plants and animals, certain parts being richer than others. In plants, the seeds or fruit generally contain the most oil, but the quantity varies, even in the same variety of plant, according to the soil, cultivation, climate, and the maturity of the fruit. Usually it is in inverse ratio to the amount of sugar and starch present. In animals, most of the fat is found in the abdominal cavity, surrounding the kidneys, or in a layer just beneath the skin. The latter is especially true in the case of marine animals (whales, etc.) and those living in cold climates. The vegetable oils are obtained by crushing or grinding that part of the plant richest in oil, and then pressing the crushed material, or extracting it with some solvent, such as benzine or carbon disul- phide. Mills for crushing olives are of great antiquity, the oldest form being light edge-runners of wood or stone, that did not break the kernels. Heavy edge-runners of stone or iron (Fig. 79) are used at the present time, but steel rolls and buhr-stone mills are more gen- erally employed. The edge-runner consists of two heavy rollers (A, A), fixed on a common axle (B), and travelling in a circle around a verti- cal shaft (C). The rollers rest on a solid stone or metal bed (D), on which the material to be ground is spread. Scrapers (E) are fixed on the shaft so that they bring the material directly into the path of the rollers. The ground pulp is pressed in strong canvas or horsehair bags. Sometimes part of the oil is expressed cold, and the meal is then heated and pressed a second time while hot. Cold-pressed oils are lighter color and of better quality, but hot pressing gives a larger yield. Wedge-presses and screw-presses were used in ancient times, but the invention of the hydraulic press by Bramah in 1795 revo- lutionized oil pressing. Knuckle-joint and eccentric presses are later inventions, but are not so extensively used. The hydraulic press (Fig. 80) consists of a large piston or ram FIG. 79. VEGETABLE AND ANIMAL OILS 305 FIG. 80. (R), which is forced out of its cylinder (C) by the hydrostatic pros- sure of a liquid pumped into the cylinder in. a small stream. The bags of pulp (B) are placed between the ram and a fixed top plate (P), and the oil expressed is caught in troughs placed around the ram head. In 1850 Jesse Fisher of Birming- ham, England, invented the extrac- tion process, using a volatile solvent such as carbon disulphide, or better, petroleum naphtha. The solvent is pumped into a closed vessel contain- ing the pulp. After extraction, the solution of oil in the solvent is drawn off and the latter recovered by dis- tilling it off from the oil. This method gives a larger yield of oil, comparatively free from gelatinous matter, but some resins and coloring matter may be dissolved, thus con- taminating it. A very complicated and expensive recovery plant which is also costly to operate is required. Moreover, if the extraction is carried too far, the residue of crushed seed pulp has no value as animal food and can only be used as fertilizer or fuel. Pressing involves less fire risk and yields a lighter colored oil, especially if done cold, while the press-cake from many vegetable oils has a high value as cattle food, owing to the oil remaining in it. Animal oils are contained in cells composed of membraneous tissue which putrefies soon after the animal is killed, causing the fat to become rancid and have a bad odor. Consequently it must be rendered immediately. These oils are obtained by: (a) melting, " trying out " or rendering in open kettles. The fat is chopped into small bits and heated over a fire with a very little water. The tissue shrivels together forming " cracklings," which float on the oil and are removed by straining and are pressed to obtain all the oil. Much care is required to prevent overheating, and this process has been generally abandoned in favor of steam rendering (see below) ; (6) by boiling with water to which sulphuric acjd is sometimes added to decompose the cell walls, thus liberating the oil ; (c) by heating with direct steam under pressure in large digesters or auto- claves (Fig. 81), breaking down the cell walls. The fat is intro- 306 OUTLINES OF INDUSTRIAL CHEMISTRY duced through the manhole (B) which is closed when the digester is nearly filled to the top, and steam at about 50 pounds pressure is admitted by the pipe (C) entering near the bottom. Before closing the di- gester, the fat is sometimes washed by flushing with water which runs off by the cocks (D) and (E). The foul- smelling gases given off during the rendering are conducted away by the pipe (H), and after cooling to con- dense steam they are discharged into the chimney or into a closed sewer. After several hours heating, the steam is cut off, the pressure relieved, and the digester allowed to remain quiet until the oil has risen to the top, leav- ing the cracklings and condensed water in the bottom of the tank. The prog- ress of the separation may be followed by trials at the test-cocks (F, F). The water is then drawn off through (E), until the oil reaches the level of (G), through which it is then drawn off. The cracklings are discharged by dropping the lower manhole cover (J). In testing fatty oils, certain distinguishing properties and reac- tions are sought. The specific gravity is an important indication as to the purity of the sample. It is determined by the Westphal bal- ance, Sprengel tube, or specific gravity bottle. The saponification value * represents the number of milligrams of potassium hydroxide needed to saponify one gram of the oil. It is determined by saponifying one or two grams of the oil with 25 cubic T^ centimeters of alcoholic potassium hydroxide and titrating the ex- LI N cess alkali with hydrochloric acid, using phenolphthalein as indi- cator. The iodine (or bromine) value* represents the percentage of iodine (or bromine) absorbed by the oil, forming addition, or to a smaller extent, substitution products. The saturated, fatty acids and their glycerides do not combine with the halogens to any appre- Fio. 81. * Oils, Fats, and Waxes. Benedikt-Lewkowitsch. VEGETABLE AND ANIMAL OILS 307 uiable extent ; but those of the oleic or ricinoleic series combine with two atoms of iodine (or bromine) ; those of the linoleic unite with four, and of the linolenic with six, atoms of the halogen. Thus the determination of this value affords a method of determining the per- centage of unsatarated fatty acids (or glycerides) present in the oil. The weighed amount of oil (0.2 gram) dissolved in chloroform is mixed with a standard solution of iodine in mercuric chloride and shaken gently. After standing in the dark for four hours, the ex- N cess of iodine is titrated with sodium thiosulphate.* The number of cubic centimeters of thiosulphate used, multiplied by its value in terms of iodine, gives the number of grams of iodine absorbed by the oil ; this divided by the weight of oil used and multiplied by 100 gives the iodine value. The Maumene test f shows the amount of heat developed when oil is mixed with sulphuric acid. Fifty grams of the oil are treated with ten cubic centimeters of strong acid under exact conditions, and the " rise in temperature " observed. The elaidin test depends upon the fact that nitrous anhydride (N" 2 8 ), when brought into contact with olein, converts it into the isomeric solid elaidin, but the glycerides oi linoleic, linolenic, and isolinolenic acids are not affected by this treatment. Thus the non- drying oils become solid, while the semi-drying and drying oils re- main liquid, or at most, become buttery. Five grams of oil are mixed with seven grams of nitric acid (1.34 sp. gr.), about one gram of copper wire added, and the glass placed in cold water (15 C.) and the oil well stirred. After standing two or three hours the solidity of the elaidin cake is examined. For convenience in study, the fatty oils are generally classified according to certain similarities in their properties and sources. A convenient classification is as follows $ : A. Oils and Fats. Glycerides. I. OILS OR LIQUID FATS. 1. Vegetable Oils. 1. Drying Oils. 2. Semi-Drying Oils. 3. Non-Drying Oils. * Oil Analysis. A. H. Gill. t Corapt.-Rend., 35 (1852), 572 t Oils, Fats, and Waxes. Benedikt-Lewkowitsch. 308 OUTLINES OF INDUSTRIAL CHEMISTRY 2. Animal Oils. 1. Marine Animal Oils. (a.) Fish Oils. (6.) Liver Oils. (c.) Blubber Oils. 2. Terrestrial Animal Oils. II. SOLID FATS. 1. Vegetable Fats. 2. Animal Fats. B. Waxes. Non-Glycerides. I. LIQUID WAXES. II. SOLID WAXES. 1. Animal Waxes. 2. Vegetable Waxes. A. OILS AND FATS VEGETABLE DRYING OILS Linseed oil is derived from the seeds of the flax plant Linum usitatissimum, L., which is extensively cultivated in Northern Europe, Italy, Turkey (near the Black Sea), India, Argentina, and in the United States. When the plants are raised for their fibre (p. 435), they are pulled up before the seeds are ripe ; such seed must be aged several months before pressing, but the best oil is obtained from ripe seed. The yield is from 25 to 32 per cent, ac- cording as the seeds are pressed or extracted. The cold-pressed cake is often heated and pressed again. Cold-pressed oil is a clear, golden yellow, while the hot-pressed product is amber or brown. The latter may be "bleached" by treating with a solution of ferrous or zinc sulphate and exposing it to the sunlight. The crude oil is puri- fied by agitation with sulphuric acid, followed by washing with water; it is then called "raw oil." Linseed oil is the most important of the drying oils. It contains* about 65 per cent of the glycerides of isolinolenic acid, C 18 H 30 2 , and 15 per cent each of the glycerides of linoleic, C 18 H 32 2 , and lino- lenic, C 18 H 30 2 , acids and 5 per cent of olein. These glycerides absorb oxygen, and are probably converted into anhydrides, which are quite insoluble. This causes the oil to become thick and darker colored, and, when in thin films, to form a dry, hard varnish. This drying * K. Hazura. Zeit. fur Angew. Chem., 1888, 312. VEGETABLE AND ANIMAL OILS 309 .may be hastened by the so-called " boiling" of the raw oil. The lat- ter is heated with certain salts (such as litharge, lead acetate, or the peroxide or borate of manganese), called "driers," which probably act as carriers of the oxygen. A part of the glycerides is decomposed and the insoluble gummy anhydrides are formed, while some acrolein is set free. The boiling is carried on in open kettles heated by direct fire or by high pressure steam, and is sometimes aided by blowing air into the hot oil. When the latter has lost from 8 to 10 per cent of its weight, the process is stopped. The temperature em- ployed varies with the kind of drier used, being highest (250 C.) with litharge; but this gives a dark-colored product. The lower the temperature the lighter colored the product, and the longer the oil must be heated. By heating the oil for several days with borate of man- ganese at 60 C. to 125 C., a very light-colored boiled oil is produced. All boiled oil should stand several months, or even a year, before use, in order that the impurities may settle. Very little of the drier is dissolved by the oil, and the clarified boiled oil is decanted from the residue. It dries very readily, and is much used for paint mix- ing. If the boiling is continued for ten or twelve hours, at a high temperature, the oil becomes a thick, sticky, viscid mass, used as the basis of printers' ink. It will be noted that this boiling is really a decomposition, or, perhaps, a polymerization process. Several grades of linseed oil are in the market, the Calcutta being considered the best in this country, while the Western and La Plata oils are often of poorer quality. In Europe the Baltic oil| is held in high esteem, while the Indian oils are regarded as low grade. Lin- seed oil is frequently adulterated with mineral oil, or with rosin, corn, menhaden, or cotton-seed oil. Eaw linseed oil has a specific gravity of 0.930 to 0.939; a saponi- fication value of 189 to 195, and an iodine value of 170 to 188. (Boiling lowers the iodine number.) It does not yield solid elaidin. It is used as a soap stock for soft soap, in some kinds of paint, for varnish making, and for rubber substitute. Boiled oil is used for paint, for printing inks, for oilcloth making, and in the preparation of linoleum. For this last, the partially boiled oil is exposed to the air at a moderate temperature (20 to 22 C.), until oxidized to a translucent jelly. It is then thoroughly incorporated with ground cork, and is rolled into sheets and dried. Press-cake from raw oil, is one of the most valuable cattle foods. t Lewkowitsch, Oils, Fats, and Waxes. Allen, Commercial Organic Analysis, Vol. IL 310 OUTLINES OF INDUSTRIAL CHEMISTRY By the oxidation of certain oils, as in "drying," considerable heat is generated, and if they are exposed in thin layers, on porous, in- flammable material (e.g. when absorbed in cotton rags or waste), spontaneous combustion frequently takes place. This is particularly liable to occur with linseed oil; it may be prevented by the addition of mineral oils. Hemp oil is obtained from the seeds of the common hemp, Can- nabis sativa, L. The yield is about 30 per cent. It is a greenish yellow oil of 0.925 to 0.930 sp. gr. Its saponification value is 190 to 191.1, and its iodine value 143 to 148. It is a poor drying oil, but is used in paint and as an adulterant for linseed oil ; also as stock for soft soap. The press-cake contains sharp bits of the shell, which render it unfit for cattle food. Poppy oil is a good drying oil, obtained from the seeds of the poppy, Papaver somniferum, L. The yield is about 45 per cent of a thin, yeilow, odorless oil of 0.924 to 0.927 sp. gr. ; its saponification value is 190.1 and iodine value, 134 to 137. It is used as a salad oil and to adulterate olive oil; but mainly in the preparation of fine col- ors for artists' use. Sunflower oil is a colorless or pale yellow, palatable, nearly odor- less oil, obtained from the seeds of the common sunflower, Heliantlms annuus, L. The yield is about 30 per cent, and the press-cake is a valuable cattle food. The oil contains the glycerides of oleic, palmitic, arachidic, and linoleic acids. Its specific gravity is 0.924 to 0.926; saponification value, 193 to 194; iodine value, 120 to 133. It is used as a soap stock, for wool oiling, and to adulterate olive oil. VEGETABLE SEMI-DRYING OILS These oils have an intermediate position between the true drying and the non-drying oils, some of them showing distinct drying proper- ties, while others do not. This is also indicated in their iodine values. Corn oil or maize oil is derived from the germ of the common corn, Zea Mays, L. The germ is removed from the grain (which is used for making starch or alcohol), and when pressed, yields a yellow, fluid oil of 0.920 to 0.925 sp. gr. Its saponification value is 188 to 193; its iodine value 111 to 123; Maumene test, 56 to 60 C. It is used in making soap and lubricants, and the press-cake is an excellent cattle food. Cotton-seed oil is derived from the seeds of the cotton plant, Qossypium herbaceum, L. After the husks are removed in cylinders containing rotary knives, the seeds are crushed in a roller mill. VEGETABLE AND ANIMAL OILS 311 The meal is heated in iron kettles at 75 to 90 C., and pressed in horsehair bags. The yield is about 18 per cent. If the seeds are hulled, the press-cake is a valuable cattle food ; otherwise, the sharp husks render it unfit for anything but fuel or fertilizer. The crude oil is reddish-brown to black in color, and must be refined for most purposes. It is settled until a slimy precipitate has deposited, then agitated with a caustic soda solution of 1.060 to 1.090 sp. gr., and again allowed to settle. The sediment, called " foots," is used for soap stock. If the oil is clarified with fullers' earth and chilled below 12 C., the palmitin and stearin crystallize and are removed by cold pressing. This solid fat, called " cotton- seed stearin," is used in making oleomargarine. The oil expressed is clear and light-colored, and is extensively used as a salad oil and to adulterate olive oil. It is also used in the manufacture of " com- pound lard," " cottolene," etc., for which it is mixed with about one and one-half times its weight of beef stearin ; and in btitterine and oleomargarine, to soften them in cold weather. Refined cotton-seed oil has a pale straw color and a specific gravity of 0.922 to 0.930. Its saponification value is 191 to 196; iodine value, 101 to 116 ; the elaidin test gives a soft buttery mass ; Maumene test, 70 to 90 C. It is usually free from acids and has a pleasant taste. The poorer grades are used for soap making. It is not often adulterated, but occasionally linseed oil is mixed with it. Sesame or Gingili oil is obtained from the seeds of an East Indian plant, Sesamum Indicum, L., which is also grown largely in Egypt and Asia Minor. The crushed seeds are first pressed cold and then hot. The yield is 30 to 50 per cent of thin, yellow, odorless oil of pleasant taste, which does not become rancid on exposure. It consists of 76 per cent olein, the remainder being glycerides of palmitic, stearic, and myristic acids. Its specific gravity is 0.921 to 0.924; saponification value, 190 to 194; it yields a soft elaidin ; the iodine number is 103 to 110 ; and the Maumene test, 65 to 68 C. The best quality is used as a table oil or to adulterate olive oil ; the common grades are good burning oils or soap stock. Rape-seed or colza oil is obtained from the seeds of several varieties of Brassica campestris, L. The seeds are crushed and heated by steam before pressing j this coagulates the albumin and improves the quality of the oil. The yield is about 36 per cent of crude oil which is refined by agitation with one per cent sulphuric acid and washing with alkali ; this removes traces of sulphuric acid and the free fatty acids formed by its action. The lighter colored 312 OUTLINES OF INDUSTRIAL CHEMISTRY and best grades are generally called colza oil, rape oil being applied to the commoner grades. Both contain the glycerides of oleic, stearic, and erucic or brassic acids. The specific gravity ranges from 0.913 to 0.916 at 15.5 C. ; the iodine value is 97 to 106; saponifi- cation value, 171 to 178; by the elaidin test, solidification takes place very slowly, frequently requiring 50 to 60 hours, and the elaidin is very soft; Maumene test, 50 to 62 C. The purified colza oil is a pale yellow and is odorless ; it is chiefly used as a condiment and as a burning oil. It is often adul- terated with hemp, cotton-seed or fish oils or with rosin oil. Common rape oil is used as a lubricant, and being very viscid, is frequently employed as a standard for measuring viscosity. When exposed to the air, it becomes thick and gummy, but does not really " dry." Castor oil is obtained from the seeds of Ricinus communis, L. They are cold pressed for the first grade of medicinal oil, and hot pressed for the common qualities, about 40 per cent of oil being obtained. It is very viscid, of 0.960 to 0.970 sp. gr., and contains the glycerides of stearic and ricinoleic acids. Its saponification value is 178 ; iodine value, 85 ; and Maumene test, 47 C. It is very apt to become rancid, and is soluble in alcohol and glacial acetic acid, and insoluble in petroleum spirit. Its purgative action is probably due to an alkaloid present in it. Large quantities are used in making " Turkey-red oil," which is prepared by treating the castor oil with sulphuric acid at less than 40 C., and washing with a strong brine to remove the excess of acid. The oil is decanted from the brine and carefully neutralized with ammonia or soda, by which Turkey-red oil, the alkali salt of ricinoleo-sulphuric acid C 18 H33(HS0 3 )03, is formed. Oil thus prepared has largely replaced that made from olive oil for use in dyeing cotton with alizarine. Its exact composition is as yet uncertain, various views having been advanced.* Castor oil is also used for making transparent soaps and common soap ; its viscosity being greater than that of any other oil at the ordi- nary temperature, it is largely used as a lubricant for heavy machinery. By blowing air through hot cotton-seed, linseed, lard, or rape oil, it is partially oxidized and converted into a thick viscous oil of very high gravity (0.942 to 0.970). Mixed with mineral lubricating oils, these " blown oils " are used as substitutes for castor oil for heavy machinery. * J. Soc. Chem. Ind., 1883, 537. Liechti and Suida. J. Soc. Chem. Ind., 1884, 412. Mueller and Jacobs. Dingler's polytechnisches Jour., 254, 346. Schmid. J. Soc. Dyers and Colorists, 1891, 69. Scheurer-Kestner. VEGETABLE AND ANIMAL OILS 313 VEGETABLE NON-DRYING OILS These usually contain a high percentage of olein, absorb little or no oxygen and do not dry in the air, yield solid elaidin, and have lower iodine values than the drying oils. Peanut or earthnut oil is obtained from the fruit of Arachis hypogcea, L. The oil is a light greenish yellow, with a peculiar odor and taste, but when refined and bleached is colorless and without taste. It contains glycerides of arachidic and hypogseic acids, besides olein, palmitin, and others. Its specific gravity is 0.916 to 0.922 ; saponification value, 190 to 196 ; and iodine value, 85 to 105 ; Maumene test, 44 to 67 C. It is employed as an adul- terant for olive and lard oils, as a salad oil, and for soap making. Olive oil is obtained from the fruit of the olive tree, Olea Europwa, L. Both the fruit pulp and the kernel contain oil, but the former yields the better quality. The fruit is crushed in mor- tars or edge-runners (care being taken not to break the kernels) and cold pressed. A small quantity of "virgin oil" is thus obtained, which is used as a condiment. The residue is stirred up with hot water and pressed harder than before ; then it is ground a second time, crushing the seeds, stirred up with hot water, and pressed as hard as possible. The final press-cake is extracted with carbon disulphide, or is put into pits with water and allowed to ferment for some weeks. The oil rises to the top and is skimmed off. The several grades of oil obtained are purified by heating to coagulate the albuminous matter, and settling. A dark-colored, mucilaginous substance, called " foots," deposits, and is used for soap stock. The lighter colored oils are used for the table and the others for lubricators, illuminants, and soap stock. Considerable of the grade called " Gallipoli " is used for making " Turkey-red oil " and for oiling wool after scouring. Olive oils vary in color from pale yellow with a greenish tinge (due to traces of chlorophyl) to greenish or brownish yellow in the poorer qualities. First-grade oils are odorless and palatable, but the lower grades are strong smelling and usually have a disagree- able taste. On exposure to the air olive oil is very apt to become rancid. The specific gravity varies from 0.914 to 0.918 ; its saponi- fication value is 185 to 196 ; iodine value, 77 to 88 ; the elaidin test shows a solid mass within two hours, which is not displaced by inverting the vessel ; Maumene test, 41 to 45 C. The oil contains about 72 per cent of olein and linolein, and about 28 per cent mixed palmitin and stearin. Being very expensive, it is frequently adul- 314 OUTLINES OF INDUSTRIAL CHEMISTRY terated with cotton-seed, sesame, or rape-seed oil, while poppy, lard, and peanut oils are less commonly used. MARINE ANIMAL OILS These oils absorb oxygen, do not yield solid elaidin, and have high iodine values. They are glycerides, and are liquid at ordinary temperatures. It should be noted that the varieties of sperm oil do not belong with this group, since they are liquid waxes, although obtained from blubber. FISH OILS These are obtained by boiling the entire body of the fish. Menhaden or pogy oil is derived from a small fish, Alosa Men- haden. It is of a brownish color, has a fishy odor, and dries in the air. Its specific gravity is 0.927 to 0.933 ; saponification value, 189 to 192 ; iodine value, 148 to 160 ; Maumene test, 123 to 128 C. It is extensively used in currying (p. 520), to adulterate linseed oil and as a substitute for it, and for adulterating whale oils, etc. It is itself often adulterated with mineral oils. LIVER OILS These oils contain cholesterol and other biliary ingredients which are unsaponifiable. Cod-liver oil is obtained from the liver of the codfish, Gadus morrhua. The livers are rendered by steam heat, and the oil, sepa- rated, is chilled until the stearin solidifies, when it is pressed and the clear oil collected. Several grades are made, pale, light brown, and dark brown. The pale oil is a limpid light yellow, having little taste or smell, and is used in medicine ; its chief value in this is probably due to the presence of traces of biliary compounds, rendering it very readily digested and assimilated. The darker, less pure grades are used for leather dressing. Cod- liver oil contains glycerides of oleic, myristic, palmitic, and stearic acids, some volatile fatty acids, and cholesterine ; also traces of iodine and phosphorus. The specific gravity is 0.922 to 0.930 at 15 C. ; the saponification value, 182 to 189 ; iodine value, 141 to 159; Maumene test, 102 to 113 C. It is frequently adulterated with shark-liver oil, seal oil, and other fish oils. Shark-liver oil is chiefly obtained from the livers of the sunfish, Squalus maximus. Its specific gravity is 0.911 to 0.928. It is a clear yellow oil, containing a large amount of cholesterine, and is chiefly used for adulterating cod-liver oil and in dressing leather. VEGETABLE AND ANIMAL OILS 315 BLUBBER OILS Whale oil or train oil is obtained from the blubber of the Green- land or "right" whale, Balcena mysticetus, and other animals of the whale tribe. By boiling the blubber in water, the oil rises to the surface and is skimmed off. It is yellowish brown in color and has a strong fishy odor. Its composition is variable and but little is known about it; glycerides of some of the lower members of the acetic series are often present. The glyceride of valeric acid, C 5 H 10 2 , is characteristic of some whale oils. The specific gravity is 0.925 to 0.930; saponification value, 188 to 193; iodine value, 120 ; Maumene test, 85 to 91 C. Some varieties dry on exposure to the air. Whale oil is used for leather dressing, in tempering steel, and as an illuminating oil. Porpoise oil, derived from the porpoise, Phoccena brachyciitm, is very similar to whale oil, and is obtained in the same way. Its density is 0.920 to 0.930 ; saponification value, 216 ; it yields a small amount of elaidin. The best grades (jaw oil) are used for lubricating clocks and watches, the commoner qualities for soap stock, for leather dressing, and as illuminating oil. Blackfish oil is obtained from the blubber of the blackfish, Globicephalus melas. It is a pale yellow oil, which separates spermaceti (cetyl palmitate) 011 standing. That from the head and jaw is the finest quality, and is used for lubricating clocks and fine machinery. TEKRESTRIAL ANIMAL OILS These oils have low iodine value and yield solid elaidin. They are derived from the feet of cattle, horses, and sheep, or are ex- pressed from lard and tallow. Neat's-foot oil is made by boiling the feet and shin bones of cattle in water. It is a pale yellow, limpid oil of 0.916 sp. gr. at 15 C., is nearly odorless, and deposits stearin on stand- ing. Its saponification value is 194 ; iodine value, 70 ; it yields a solid or semi-solid elaidin; Maumene test, 47 to 48.5 C. It is nearly pure olein, and does not readily become rancid nor gummy when used on machinery. It is used for a fine lubricator and for leather dressing. It is often adulterated with fish, rape, cotton-seed, and mineral oils, and other hoof oils. Lard oil is prepared by cold pressing lard (p. 317). The best quality is limpid and colorless, and consists of olein, with some 316 OUTLINES OF INDUSTRIAL CHEMISTRY palmitin and stearin, the quantity of these latter depending upon the temperature of the pressing ; poor grades have a brown color and offensive odor. It has a specific gravity of 0.915 at 15.5 C. ; a saponification value of 195 to 196; iodine value, 56 to 74; it yields solid elaidin. It is used as an illuminant, as a lubricant, and for oiling wool. It is frequently adulterated with cotton-seed oil, cocoanut olein, " neutral mineral oil," or rape oil. Tallow oil consists mainly of olein, and is obtained by pressing tallow (p. 317). It is chiefly mixed with mineral oil for use as a lubricant. If selected, fresh tallow is rendered at 65 C., and the clear oil kept for twenty-four hours in a graining vat, the stearin and part of the palmitin crystallize. By pressing, the liquid olein and some palmitin is obtained as " oleo oil," which is used for arti- ficial butter making. Low grades of tallow oil are not white, and are called " red oil " in trade ; these must not be confounded with the red oil which consists of oleic acid (p. 330). The press-cake (chiefly stearin) is used as a soap or candle stock. SOLID VEGETABLE FATS Palm oil is obtained from the fruit of several varieties of palm, Elceis Guineensis, Jacq., native to the west coast of Africa. It is a mixture of palmitic acid, palmitin, and olein, and is semi-solid in this climate. When fresh it is red or orange yellow, but on stand- ing, especially if exposed to the sunlight, it becomes brownish yel- low or drab. It may be bleached by heating and blowing in air ; or by treating with potassium bichromate and hydrochloric acid. Fresh oil has a pleasant odor, but is very liable to become rancid, when it contains a large percentage of fatty acids and has a disagree- able odor. Its specific gravity is 0.920 to 0.946 ; the saponification value is 196 to 202 ; iodine value, 50.4 to 52.3. It is used as a candle and soap stock, and in making lubricants. Palm kernel, or palm nut oil is derived from the kernels of the fruit of Elceis Guineensis, Jacq. It is similar to and used in the same way as cocoanut oil. Cocoanut oil is derived from the cocoanut, Cocos nucifera, L. (or butyracea, L. f.), the chief commercial supply coming from India, Ceylon, and the South Sea Islands. The dried meat (" copra ") of the nut is pressed or boiled in water. The oil, which is a solid fat in this climate, contains the glycerides of myristic, palmitic, stearic, lauric, capric, caprylic, and caproic acids. It melts at 20 to 28 C. ; its saponification value is 250 to 268 ; its iodine value, 8.9. VEGETABLE AND ANIMAL OILS 317 It is very liable to become rancid. It is much used for soap stock, especially for the " cold process " soaps, and since it is not readily precipitated by salt, for marine soaps ; but it needs a strong lye for its saponification. It is also said to be used for artificial butter. By cold pressing, a solid stearin is obtained which is used in mak- ing candles. Cacao-butter is obtained from the cacao bean, the seeds of Tliebroma Cacao, L., and is a solid fat having a pleasant odor and the flavor of chocolate. It consists of the glycerides of palmitic, stearic, and lauric acids, with traces of linoleic and arachidic acids. It is used for ointments and salves in pharmacy, and in the manu- facture of "chocolate creams," and for toilet soaps. It is often adulterated with tallow, vegetable oils, beeswax, or paraffine wax. Its specific gravity is 0.890 to 0.900 at 15 C. ; saponification value, 192 to 202 ; iodine value, 32 to 37.7. Japan wax is obtained from a species of Rlius by boiling the fruit in water. It is a pale yellow or white, has a greasy feel, and can be kneaded in the fingers. It consists of palmitin, C 3 H 5 (C 16 H 31 2 ) 3 , with some stearin, and is easily saponified. It is not a true wax. It melts at 53 to 54 C., and its specific gravity is 0.970 to 0.980 at 15 C. It is soluble in benzene, petroleum spirit, and in boiling 97 per cent alcohol. It is used for candles, for wax matches, as a fur- niture polish, and for adulterating beeswax. SOLID ANIMAL FATS Lard is prepared from the fat of the hog. It is rendered at a low temperature, and is a softer grease than tallow. It is a mixture of palmitin, stearin, and olein. It melts at 28 to 45 C., forming a clear liquid. Its specific gravity is about 0.932; saponification value, 195 to 196; iodine value, 59; Maumene test, 24*to 27 C. When pure, it is white, nearly odorless and tasteless. By pressing it yields lard oil (p. 315). It is often adulterated with water, 25 per cent or even more being worked into it ; or with cotton-seed oil and stearin ; or with beef fat and cocoanut oil. The chief uses of lard are for culinary purposes, for soap stock, for butterine, and in ointments and salves. " Compound lard " is a mixture of beef stearin and cotton-seed oil. Tallow is the solid fat of the sheep or ox. Before rendering, it is customary to break up the tissues by grinding with hollow rolls having a rough surface and heated by steam. The rendered tallow solidifies at about 34 to 45 C., and is graded according to its ap- 818 OUTLINES OF INDUSTRIAL CHEMISTRY pearance, hardness, odor, and rancidity. It consists of abont two- tliirds palmitin and stearin, and one-third olein. Its density at 99 C. is 0.860 to 0.862 ; saponification value, 195 to 198 ; iodine value, 40. It is extensively used for soap and candle stock, for lubricating, and as a leather dressing. Bone tallow is a soft grease obtained by boiling fresh bones in water to extract the marrow and fat. It is dark-colored and foul- smelling and usually contains calcium phosphate. It is mainly used for cheap colored soaps. Butter fat is derived from cows' milk. It is very complex, containing glycerides of a number of acids ^of which oleic (60 per cent), palmitic, stearic, and butyric (5 per cent) are the most im- portant; small quantities of the glycerides of capric and caproic acids are also present. Butter fat has a specific gravity of 0.870 at 99 C. ; its saponification value is 221 to 227 ; iodine value, 26 to 35. It is the basis of butter, of which it forms about 90 per cent, the re- mainder being water, salt, curds, and coloring matter. It is made by churning cream to cause the agglomeration of the fat globules into a solid mass. Sour cream churns more easily than sweet cream. The latter is removed from the milk by a separator * or by skim- ming before the milk sours. Butter from sour cream will not keep unless well salted, since it contains sufficient casein to increase its liability to become rancid, by which a considerable amount of butyric acid is formed. Butter is usually colored with carrot juice, saifron, turmeric, or annato ; or sometimes with certain coal-tar colors. Butterine, oleomargarine, and margarine are butter substitutes made from mixtures of animal and vegetable oils, flavored with some butter, and colored to imitate it. Oleo oil from tallow, and neutral lard are much used. These are mixed with cotton-seed oil in cold weather (or with peanut or sesame oil abroad) to increase the per- centage of olein. . B. WAXES I. LIQUID WAXES Sperm oil is obtained from the blubber and head cavity (" case ") of the cachalot, or sperm whale, Physeter macrocephalus, the case alone sometimes yielding several barrels of free oil. The composition * Before churning, sweet cream is always allowed to "ripen"; i.e. to stand a few hours undisturbed after separating. Usually a " starter" is added to set up lactic fermentation ; by using pure cultures of acid-forming bacteria, the quality and flavor of the butter can be much better controlled than when the ripening is spon- taneous. WAXES 319 of sperm oil is not definitely known, but it differs materially from most oils. It contains no glycerides, consisting mainly of esters of monatomic alcohols. Some authorities hold that dodecatyl alcohol C^HasOH, and its allied homologues, such as cetyl alcohol, C^H^ OH, are present, but this is denied by Lewkowitsch. The oil holds in solution a considerable amount of spermaceti (below), which is usually filtered out of the cold oil before it is sold. Sperm oil is a limpid, golden yellow liquid, having a slight fishy odor; its specific gravity is 0.875 to 0.884 at 15.5 C. ; saponification value 123 to 147 ; iodine value 81.3 to 85 ; it yields a solid elaidin ; Maumene test 45 to 47 C. It is a very valuable lubricator, especially for rapid running machin- ery, since its viscosity is very great considering its low density, and varies but little with changes of temperature ; and because it does not become gummy nor rancid. It is also used for illuminating, for leather dressing, and in tempering steel. Because of its high price, it is often adulterated with mineral oils or with other fish oils. The related Doegling or Bottlenose oil is also a liquid wax. II. SOLID ANIMAL WAXES Spermaceti is a crystalline wax found in the head of the sperm whale and which separates from sperm oil when chilled ; it is ob- tained by expressing the oil. The brown or yellow scales of crude spermaceti are treated with a little caustic potash to remove adher- ing oil, and are thus rendered white and translucent while they re- tain their crystalline structure. Spermaceti consists mainly of cetyl palmitate, C^H^O C 16 H 31 0. It is odorless and tasteless and melts at about 45 C. Its specific gravity is 0.943 at 15 C. ; saponification value 108 to 128 ; it burns with a large clear flame. Its chief uses are in candle making, in confectionery, and in pharmacy. Beeswax is obtained from the honey-comb of bees by melting it in hot water ; the floating layer of tough brown or yellow wax is drawn off into moulds. It may be bleached by exposure in thin films to the sun and moist air, or by the moderate action of chromic or nitric acid, or hydrogen peroxide. Bleached wax is white, and has neither taste nor smell. It consists mainly of myricyl palmitate, C3oH 61 C ]6 H 31 0, and some cerotic acid, C^R 54 2 . It melts at 63 to 64 C., and has a specific gravity of 0.965 to 0.969 at 15 C. It is often adulterated with water or white mineral powders to increase its weight. Stearin, paraffine, cerasin, tallow, and vegetable wax are often added as adulterants. It is used in candle making, in phar- macy, and for many other purposes in the arts. OUTLINES OF INDUSTRIAL CHEMISTRY Chinese wax, or insect wax, is secreted by an insect, Coccus ceri- ferus, Fabr. The wax is deposited on the branches of certain trees, which are cnt off and the wax removed by hand. It is melted in boiling water to separate the dirt, bark, etc. It is white, crystalline, and very hard, without taste or smell. It is soluble in benzine, and slightly so in alcohol and ether. It consists of ceryl cerotate, C^H^O-C^HsA Its specific gravity is 0.970 at 15 C., and it melts at 82 to 83 C. It is used for fine candles, in medicine, as size for paper, and as a furniture polish. Wool grease is the greasy substance exuding with the perspi- ration from sheep ; it is precipitated by sulphuric acid from the alkaline waters in which the raw wool has been washed ; it is also largely obtained by extracting raw wool with gasoline. It is yellow or dark brown, has an unpleasant odor, and forms an emulsion with water. It is very complex in composition, containing several gly- cerides, in addition to the stearic and palmitic ethers of choles- terin and isocholesterin, and potassium salts of several fatty acids. A large amount of unsaponifiable matter is also present. Purified wool grease has a specific gravity of 0.973 at 15 C. ; saponification value 98 to 102.4 ; iodine value 25 to 28. Lanolin is made by washing wool grease with water until all the soluble matter is removed, melting by heating in water, skimming and allowing it to cool and solidify. Lanolin is much used in phar- macy as a basis for salves, ointments, and emulsions. It contains about 25 per cent of water, and forms a very soft ointment. SOLID VEGETABLE WAX Carnauba wax is derived from a species of palm, Copernicia ceri- fera, Mart., native in Brazil. It forms a coating on the leaves, and is removed by shaking or pounding. The raw wax is of a grayish or greenish yellow and is very hard, though readily powdered. When purified, it has no odor nor taste, melts at 83 to 88 C., and has a specific gravity of 0.990 to 0.999 at 15 C. Its constitution is complex, but it contains myricyl cerotate CgoH^O C^H^O, myricyl alcohol C 30 H 61 OH, cerotic acid C 27 H S4 2 , and other bodies. It is used for candle making and for adulterating beeswax, and in varnish. REFERENCES Die Chemie der Austrocknenden Oele. G. J. Mulder, Berlin, 1867. Die Fettwaaren und fetten Oele. C. Lichtenberg, Weimar, 1880. Die Trocknenden Oelen. L. E. Andes, Braunschweig, 1882. (Vieweg.) Technologic der Fette und Oele. C. Schaedler, Berlin, 1883. SOAP 321 Oils and Varnishes. J. Cameron, London, 1886. (J. and A. Churchill.) Commercial Organic Analysis. A. H. Allen. Vol. II. London, 1886. Das Wachs und seine technische Verwendung. S. Sedna, Wein, 1886. Animal and Vegetable Fats and Oils. W. T. Brannt, Philadelphia, 1888. Die Fetten Oele des Pflanzen und Thierreiches. G. Bornemann, Weimar, 1889. Die Untersuchung der Fette, Oele, Wachsarten, u. s. w. C. Schaedler, Leipzig, 1890. Les Corps Gras. A. M. Villon, Paris, 1890. Les Matieres Grasses. G. Beauvisage, Paris, 1891. Painters' Colours, Oils, and Varnishes. G. H. Hurst, London, 1892. (Griffin & Co.) Die Sclimiermittel. J. Grossmann, Wiesbaden, 1894. Oils, Fats, and Waxes. C. R. Alder Wright, London, 1894. (Griffin & Co.) Chemical Analysis of Oils, Fats, and Waxes. R. Benedikt. Translated by J. Lewkowitsch. London, 1895. Chemical Technology. C. E. Groves and Wm. Thorp. Vol. II. Lighting. Philadelphia, 1895. (P. Blakeston, Son & Co.) Analyse der Fette und Wachsarten. R. Benedikt und F. Ulzer, 3 te Auf. Berlin, 1897. (J. Springer.) A Short Handbook of Oil Analysis. A. H. Gill, Philadelphia, 1897. (Lip- pincott Co.) SOAP Soaps are metallic salts of certain non-volatile fatty acids, the commercial article usually containing a mixture of several of these salts. Soaps intended for washing purposes should contain only soluble salts of the acids ; i.e. those of sodium, potassium or ammo- nium ; the calcium, magnesium, lead, and other heavy metal soaps are insoluble in water. As already explained, the common fats and oils contain the fatty acids in combination with glycerine, forming glycerides, an* it is from these that soaps are generally made. The process of decom- posing the glycerides and forming soap is called saporiification, although this term is generally used to denote the decomposition of any organic ester into its basic alcohol and free acid. Saponification is effected in several ways : (1) By the action of water or steam at high temperature or pres- sure : C 3 H 5 (C M HaA), 4- 3 H 2 = C 3 H 5 (OH), + 3 C^HgA . This hydrolysis may be accomplished at a much lower- tempera- ture if the water is acidulated with a dilute mineral acid,, which seems to assist the action of the water in some way, without enter- ing directly into the reaction. The amount needed is small, and it is all found unchanged, mixed with the products, of the- reaction. 322 OUTLINES OF INDUSTRIAL CHEMISTRY This method is chiefly employed for the preparation of glycerine and to obtain the free fatty acid. (2) By the action of caustic alkalies : C 3 H 5 (C 18 H3A) 3 + 3 NaOH = C 3 H 5 (OH) 8 + 3 C 18 H 35 2 Na. This is the reaction employed in ordinary soap making, the caustic uniting with the fatty acid radical to form the soap, i.e. an alkali salt of the acid. The glycerine formed is a by-product, and is often not recovered from the lye; but the more progressive soap makers have now added a glycerine recovery plant to their works. The chemistry of saponification was first explained by Chevreul, who attributed the cleansing action of soap to free alkali formed by the decomposition of the soap when brought into solution. Krafft and Stern 1 * confirm this, and hold that in the hot dilute soap solu- tion, part of the soap is dissociated into free acid and free alkali, but on cooling, the free acid unites with some of the undissociated neu- tral soap, to form insoluble bi-palmate, bi-stearate, or other bi-salt, leaving the free alkali in solution. The turbid appearance of the solution may be due to oily drops of the free fat acid. The alkalies commonly used for soap making are caustic potash and soda. The former yields a " soft soap," which is liquid under ordinary conditions, because of the lower melting point, greater solu- bility, and possible deliquescence of potassium soaps. The glycerine formed remains mixed in the soft soap. Previous to Leblanc's invention of the soda process, soap was made with caustic potash derived from wood ashes and lime. Com- mon salt was added after the saponification of the fat was complete, forming hard sodium soap, according to the reaction : KCwHjA + NaCl = KC1 + NaC M H0 2 . But now most soft soaps are made from soda soaps by adding a large quantity of water. The fatty material (soap stock) varies according to the kind of soap desired and the facility with which certain stocks may be ob- tained. For white soaps, the best grades of tallow, lard, palm oil, or cocoanut oil are chiefly used in this country. Cotton-seed oil is very liable to become rancid and to cause yellow or brown spots in the product, besides giving it a bad odor and a greasy appearance. Corn oil is also subject to rancidity. In Europe, Castile soap is made from second quality olive oil, to which some cocoanut oil is generally added. * Berichte d. deutschen chemischen Gesellschaft, 27, 1747. SOAP 323 Laundry soaps are made from tallow, bone grease, and house grease, and often palm and cotton- seed oils. Yellow soaps are made from these materials, with the addition of a certain proportion of rosin. The latter combines readily with alkali, but forms a rather soft soap, with good lathering properties ; rosin is cheaper than most of the fats, and when used in proper quantities, adds certain valuable properties to the soap, and is not an adulterant. The non-drying oils, with caustic soda, generally yield the hard- est soaps, while the semi-drying and drying oils form products of butter-like consistency. Cocoanut oil saponifies readily with strong lye, without boiling ; hence is used for "cold process" soaps. "German mottled," or "olein soaps," are made from crude oleic acid ("red oil"), obtained in the candle industry (p. 330). The spent lyes from white or yel- low soaps are often used in making red-oil soap, in order to save all the alkali, since the oil will combine with the carbonate as well as with the caustic. Toilet soaps should be made from the best material, but many cheap grades are made from poorer stock than laundry soap, and the defects covered by high color and perfume. Some toilet soaps are made by melting together two or more kinds of soap. Good soap cannot be made from poor material. The lye must be a caustic liquor, free from other salts, sulphides and sulphites being especially injurious, since they cause discoloration of the soap. In many large works the lye is prepared by causticizing soda-ash with lime. When caustic is purchased, it is simply dissolved to form a solution of the desired strength, varying from 18 to 30 Be. Fio. 82. Soap kettles are square or round, and vary in size from 10 feet in diameter by 15 feet deep, to 25 by 35 feet, and capable of holding 300,000 pounds of soap. In modern factories they are always heated by steam ; very small ones, used for remelting toilet soaps, etc., being 324 OUTLINES OF INDUSTRIAL CHEMISTRY steam-jacketed, and the larger ones having both open and closed coils. A modern form (Fig. 82) has a conical bottom, in which the steam coils (A, B) are arranged. Such a kettle, calculated to hold 100,000 pounds of soap, is about 15 feet in diameter and 21 feet high, the cone bottom being about 5 feet deep, and the cylindrical walls about 16 feet high. It is made of f-inch boiler plate, and is sheathed with 2-inch pine staves. It rests on stone pillars and foundations, and has large draw-off cocks in the cone, for running off waste lyes while the soap is pumped away through a pipe (D) passing through the side of the kettle- Soaps are made by various processes, but the most common are the following : (1) The fat is treated with the exact amount of caustic alkali needed to saponify it, leaving the glycerine in the soap. The so-called "cold process" soap is the most common example of this method. (2) The fat is boiled with solutions of caustic alkali until saponi- fication is complete, or until the soap attains certain desired proper- ties. The glycerine remains mixed with the product, as in the case of soft and " marine" soaps; or it is excluded, as in the case of yel- low, laundry, mottled, and curd soaps. (3) A free fatty acid is neutralized by treatment with an alka- line hydroxide or carbonate, as in the case of oleic acid. The cold process is the simplest of soap-making methods, but requires carefully calculated quantities of caustic and fat, and the latter must be well refined. Since it is difficult to calculate the exact amount of alkali, such soaps usually contain free fat or free alkali, or both. Cocoanut oil and tallow are chiefly used, and are melted and run into a mixing tank heated by steam, or into a crutcher (p. 325). Then a definite quantity of strong caustic soda lye, 32 to 36 Be., is added, and the mixture well stirred for a few minutes. The heat of the reaction is sufficient to carry it on when once started. After saponification is well under way, the stirring is stopped and the mixture is run into " frames" (p. 326), where it stands several days, to complete the reaction and to cool. This leaves all the glycerine and any excess lye in the soap. The product looks well when fresh, but is very apt to turn yellow and become rancid. Most soaps are boiled. The process is usually divided into several stages. The melted fat and lye of about 15 Be. (1.115 sp. gr.) are run into the soap kettle together, while free steam is blown in to mix them, and to form an emulsion of the oil and lye, which is essential to the beginning of saponification, or, as the soap-boiler SOAP 325 terms it, "to kill the stock." When the emulsion forms, the lye has " caught the stock." If the lye is too strong at first, it does not " catch," and water is added and the heating continued until the emulsion forms. Strong lye is then carefully added in small por- tions at a time, and boiling is continued to complete the saponifica- tion. If a wooden stirring paddle be pushed into the mass at this time the soap adheres to it when drawn out, and long strings of soap hang down from it. There is no separation of the lye. When the process is finished, as is shown by the soap having a dry, firm feel between the fingers, the soap is " grained" or "salted out," by adding common salt. This causes a separation of the soap from the lye and glycerine, which is shown by the soap sticking to the paddle while the lye runs off. When properly salted, the soap boils in broad, smooth patches, and is hard, and not sticky, when cold. The steam is then cut off and the soap allowed to stand for several hours, when it rises to the top. The salt lye, which contains most of the glycerine, is drawn off, leaving the soap in the kettle. Strong lye, 25 Be. (1.205 sp. gr.) is now added, and for yellow soaps, rosin is introduced ; for white soap, tallow or cocoanut oil are used instead of the rosin. The boiling is continued for two or three days, until the soap becomes clear and semi-transparent. This second boiling is called the " rosin change " or the " strong change " ; during this time, the soap rises fully one-third the depth of the kettle, and often stands higher than its sides. For this reason, the kettle is not filled more than two-thirds full at first. When the rosin or cocoanut oil is saponified, the kettle is allowed to stand quietly for a number of hours, when the lye is drawn off. The next step is called " finish- ing," "settling," "pitching," or "fitting." Water is added to the boiling soap until it loses its granular appearance, after which it is allowed to settle for several days. This removes excess caustic and any insoluble impurities. The contents of the kettle separate into three layers, the soap on top, and the lye at the bottom, and between them a dark-colored layer, called "nigre," containing caustic lye, soap, water, and various organic impurities. The lye and nigre are drawn off into separate tanks, and the soap is pumped into the crutcher, which is a very^ efficient mixing ma- chine. One form (Fig. 83) consists of a broad, vertical screw, work- ing within a cylinder, which is placed in a larger tank. The action of the screw draws the liquid soap in at the bottom and discharges it over the top of the cylinder, to again pass through the apparatus. A very thorough mixing is thus secured. The perfume, and any filling material, such as silicate of sodium, 326 OUTLINES OF INDUSTRIAL CHEMISTRY sodium carbonate, borax, talc, etc., are added in the crutcher. These ingredients are well mixed with the soap, which becomes lighter colored, and then stiff and thick. After crutching for from 3 to 15 minutes, the soap is run into " frames " (Fig. 84), which are large sheet-iron boxes, mounted on wheels, and having removable sides. PIG. 88. FIG. 84. Each frame holds from 1000 to 1700 pounds, or one crutcher full. When it has solidified, after 24 to 36 hours, the sides are removed, and the block of soap stands several days in the air to cool thor- oughly. Then it goes to the "slabber" (Fig. 85), a machine contain- ing a number of tightly stretched steel wires, which are pushed against the block of soap, cutting it into slabs of the desired thick- ness. These then pass through a " cutter," a similar machine, which forms them into rough bars, which are put into the dry room, kept at a temperature of about 90 F., for 12 to 15 hours. They are then run through the press which forms the commercial bar and stamps on it the trade mark, name, or other design. They finally pass on an endless belt to the wrappers, who enclose them in separate papers and pack them in boxes, which are immediately nailed up for market. " Boiled-down soap " is made by treating the soap, after the lye has been drawn off, with strong brine, and then boiling it down. Sometimes the soap is settled and the nigre and lye separated before boiling down. This reduces the percentage of water in the soap, leaving it dry and hard. If soaps in which no rosin is used are SOAP 327 boiled down on the lye until the latter becomes concentrated enough to precipitate the soap, and then run into frames and cooled very slowly, the small quantity of lye and other impurities mechanically enclosed segregate during the cooling into those parts of the mass which are the last to solidify, and cause the appearance called FIG. 85. "mottling." By adding a small amount of copperas, ultramarine, lampblack, or other pigment, the mottling becomes more promi- nent. Castile or Marseilles soaps have a green mottle, changing to red on exposure to the air. This is due to the presence of cop- peras, which precipitates the ferrous hydroxide with the lye in the soap; on contact with the air, the green hydroxide is changed to the red ferric salt. Rosin produces a more uniform soap, without mottle. Toilet soaps are made in the same general way as the yellow soap, but from finer stock and with greater care to secure the com- plete removal of free alkali. A little unsaponified fat is better than excess alkali. 328 OUTLINES OF INDUSTRIAL CHEMISTRY Three classes of toilet soaps are made, milled, remelted, and transparent. Milled soaps are made by shaving very thoroughly dried bars of good soap to fine chips, and drying again until only about 10 per cent water remains. The dried soap is then ground in an edge-runner mill, and the perfume and any ether ingredients desired are added at the same time. After thorough incorporation, the soap is forced through a die plate by heavy pressure, forming a long bar, which is cut into cakes; these are stamped and pressed into the desired shape. This process allows the use of very delicate perfumes and other ingredients which would be destroyed by heat. It also furnishes a hard cake which does not wear away so rapidly when in use. Remelted soaps, chiefly made in England, are prepared by re- melting one or more kinds of soap, together with the perfumes and other ingredients, in a steam-jacketed kettle. By rapid agitation of the melted mass with paddles, air bubbles can be disseminated through the soap, which gives the cake sufficient buoyancy to float on water after stamping. Transparent soaps may be made in two ways : (a) A common soap is dissolved in alcohol, the solution decanted from insoluble impurities, and the alcohol distilled off, leaving the soap as a trans- parent jelly, which is carefully dried in moulds to form the cake. (6) A cold-process soap is made by letting the fatty material stand with the lye until saponified, the coloring matter, perfumes, etc., having also been stirred in. The glycerine formed, remaining in the soap, causes the latter to have a translucent appearance. By adding more glycerine, with a little alcohol, or a solution of cane sugar, the transparency is increased. Special scouring soaps for cleaning metal and unpainted wood- work are made by adding powdered sand, glass, or pumice-stone to a yellow soap. Strongly alkaline soaps often contain ground soda- ash, borax, and sodium silicate as "fillers," or frequently as in- tentional adulterants. Sodium silicate is very generally added to yellow soaps, as it hardens them somewhat and also possesses de- tergent properties itself. A few insoluble soaps of the heavy metals are prepared for use in pharmacy, the most important being lead soap or "lead plaster," which is made by decomposing a neutral soap with a soluble lead salt, or by heating olive oil with a paste of lead oxide in water. CANDLES 329 CANDLES The materials used for candles are : free fatty acids, especially palmitic and stearic ; hydrocarbons, such as paraffine and ozokerite ; and certain esters of the fatty acids, especially tallow and waxes. The requisites for candle stock are, that it shall burn freely without smoke or smell ; that it shall not soften at so low a temperature that it loses its form from the heat of its own flame ; and that when melted it shall be a fluid capable of being drawn into the wick by capillarity. Some glycerides, such as tallow, burn with a foul- smelling, smoky flame, and hence are only used in the cheapest candles. Also, they soften at too low a temperature, and the can- dle readily bends and gutters. Both these objections also apply to paraffine and to some of the solid fatty acids. Candles are made by dipping, pouring, and moulding. For dipped candles, the wick is repeatedly introduced into the melted stock, each layer of fat being allowed to solidify before the next dip. Tallow dips, the poorest candle made, are prepared in this way. Poured candles are made by pouring the melted stock in a slow stream over the wick, which is stretched in a frame. This method is used for wax candles, since the wax contracts too much on cooling to allow casting. While still plastic, they are rolled on a flat table under a board, to give them a uniform diameter. Most candles are now moulded in a cylindrical metal form through which the wick is drawn in the line of its axis. The mould can be surrounded .with hot or cold water to facilitate the casting and removal of the candles. Wicks are of plaited or twisted cotton yarn, usually flat, except for tallow dips, when they are round. They are so prepared that the end curls over and burns off as the candle is consumed, thus making snuffing unnecessary ; * also, they are often treated with ammonium phosphate or borate to prevent their smouldering and emitting bad odors when the candle is extinguished. Paraffine, ozokerite, and sperm candles (from spermaceti) are moulded. In order to prevent softening at too low a temperature, and to render them less brittle when handled, a little stearic acid is usually added. * This is accomplished in several ways ; one side of the wick may be dipped in size, or one thread be drawn a little tighter than the rest. 330 OUTLINES OF INDUSTRIAL CHEMISTRY The most important candle stocks are palmitic and stearic acids and paraffine wax. Palmitic and stearic acids are usually made from tallow or palm oil by saponifying with lime, or water, the hydrolysis with the latter being often assisted by the addition of a little acid. Saponincation with lime is carried on in two ways : (a) by boiling in open vessels with about 16 per cent of lime. The resulting insoluble lime soap consists of calcium oleate, palmitate, and stearate. It is separated from the lye and free glycerine which is also formed, and is decom- posed by treatment with sulphuric acid and steam, setting free the fatty acid, (b) Or the fat may be saponified by Milly's process ; i.e., boiled in closed vessels called autoclaves, under pressure of from 8 to 10 atmospheres, with from 2 to 4 per cent of lime. The latter probably merely starts the hydrolysis, which is finished by the steam and water present. The products of the reaction are lime soap, free fatty acid, and glycerine. The turbid mixture is treated hot with just sufficient sulphuric acid to decompose the lime soap. The calcium precipitates as sulphate, while on top of the water (which contains the glycerine) is a layer of fatty acid. This is skimmed off and treated with water acidulated with sulphuric acid to insure complete decomposition of the lime soap. The melted fatty acids obtained by either of these processes are run into shallow pans and allowed to stand a few days at a tem- perature of about 30 C., when the palmitic and stearic acids crys- tallize. The magma is first pressed cold, and then at 40 C., in bags in a hydraulic press ; the liquid oleic acid separated forms the com- mercial "red oil" or "olein" employed for soap stock; the solid fatty acids compose the candle stock which is called " stearin." * It melts at 52 to 55 C. The yield from tallow or palm oil is 44 to 48 per cent stearin. Saponification by water alone is accomplished by heating the fat in an autoclave with water to about 200 C. under pressure of about 15 atmospheres. A current of superheated steam is introduced, thus thoroughly mixing the contents of the vessel. The free fatty acid and the glycerine both distill over with the steam, the former condensing in the first receiver, while the latter passes on to another. This process needs much care in the regulation of the heat and to secure the complete decomposition of the glycerides, but, when properly worked, yields very pure products. The fatty acids are chilled and pressed as above described, to separate the olein. *Not to be confounded with the glyceride of stearic acid, p. 303. CANDLES 331 The yield of stearin is about 50 per cent from tallow or palm oil. Slightly rancid stock is more easily decomposed than neutral fat. By adding from 4 to 5 per cent of strong sulphuric acid to the water in the autoclave, the hydrolysis is accomplished at 120 to 150 C. A part of the glycerine is converted into glyceryl-sulphuric /OH acid, S(X , while some of the oleic acid, which is an "\0 - C 3 H 5 (OH) 2 /COOH unsaturated body, forms sulpho-stearic acid, C 17 H3/ . By \0 - S0 3 H the action of the water, this is converted into hydroxystearic acid, /COOH C^HS/ , while sulphuric acid is regenerated. The hydroxy- \OH stearic acid separates as a solid with the free stearic and palmitic acids, and in the subsequent purification of these by distillation with superheated steam, it is decomposed, separating more water and the residue polymerizing to form iso-oleic acid (C^H^O*,), a solid, melting at 45 C. Thus the yield of solid fat acids is slightly increased, being about 55 per cent from tallow. Another method of acid saponification consists in heating the fat with concentrated sulphuric acid for a few minutes only, until the cell walls of the fat are destroyed and the hydrolysis is begun. The saponification is completed by boiling with water. The mixed palmitic, stearic, and oleic acids are chilled and pressed as already described. Saponification with acid gives a discolored product, which is usually purified by redistilling with superheated steam. The liquid " olein " separated from the fatty acids by any saponi- fication method, is of less value than the solid acids. A process for producing palmitic acid from this oleic acid is based on the fol- lowing reaction : CigHgA + 2 NaOH = C 16 H 31 O 2 - Na + C 2 H 3 2 Na + H 2 . Caustic soda solution and oleic acid are heated together in an iron vessel provided with an agitator, until all the water is evaporated. The heat is then raised to a little over 300 C., when the evolution of hydrogen becomes active. When the hydrogen ceases to escape, the product is treated with water, which dissolves the sodium ace- tate and any undecom posed caustic, leaving sodium palmitate undis- solved. This is decomposed with sulphuric acid to obtain the free 332 OUTLINES OF INDUSTRIAL CHEMISTRY fatty acid. But the product is too soft and is an unsatisfactory candle stock, hence the method is not now in use.* After purification, the free fatty acids, obtained by any of the processes above described, are employed for candle stock. The aqueous solutions of glycerine (" sweet waters "), resulting from the saponification, are used in the manufacture of pure glycerine. GLYCERINE There are two kinds of refined glycerine, C 8 H 5 (OH) 3 , on the market, dynamite glycerine and chemically pure glycerine. These differ only in color and in the content of pure glycerine. It is largely recovered from the spent lyes from soap making and from the " sweet waters " from the digesters where fats have been saponi- fied with lime or with water under pressure.! Much crude candle glycerine is imported into this country from Europe, that from France, Italy, and Spain being derived from olive oil. Spent soap lyes are very dilute solutions of glycerine and con- tain much impurity. The successful recovery of glycerine from them is one of the recent triumphs of chemical industry. The Van Ruymbeke process is the latest and best. In this the lye is settled and drawn off from the sludge. It is then treated with a special chemical called " persulphate of iron," the exact composi- tion of which is not disclosed, but which contains about 50 per cent of sulphuric acid. It is possibly a mixture of ferrous and ferric sulphates. This forms a copious precipitate, consisting of ferric hydroxide and iron soaps, which drags down all other insoluble impurities. This precipitate is removed by filter pressing and the clear liquid tested for any excess of iron sulphate. If any is pres- ent, it is exactly neutralized with caustic soda and the precipitate filtered off. This leaves the lye almost water white and ready for the evaporation, which is done under high vacuum (27 to 28 inches), in a still, across the middle of which is a steam chest having small vertical tubes. Fresh lye is introduced, as the evaporation pro- gresses, to maintain the level of the liquid. A salt-catch is placed below the steam chest in the evaporator, and in this the salt and sodium sulphate which separate, collect, and at the end of the opera- tion are removed through a door in the front. The salt thus recovered is sent to the soap maker, to be used again in salting out soap. * J. Soc. Chem. Ind., 1897, 391. t Saponification with acid destroys much of the glycerine. GLYCERINE 333 The vapors from the evaporator pass through a series of " catch- alls " to retain any lye, and then go to a wet vacuum pump, which is provided with a jet condenser. The evaporation is usually carried on in two or more stages ; sometimes it is continued to a point at which sodium sulphate will crystallize, which is thus removed; by further evaporation in vacuum, the common salt is crystallized. When the lye attains a density of 32 Be. (1.295 sp. gr.), it con- tains about 80 per cent of glycerine, and is called crude glycerine. This is then distilled under a very high vacuum (28 to 29 inches) in a still consisting of a cylindrical iron shell containing a closed steam coil and a perforated pipe, through which superheated steam is introduced. The glycerine in the crude liquid passes over with the steam into coolers, which are simply cast-iron drums, cooled by the outside air. Most of the glycerine condenses here, while the uncon- densed steam and some glycerine passes on to a surface condenser. The vacuum is maintained by a dry vacuum pump. The glycerine collected in the cooling drums is concentrated in vacuum pans until its specific gravity reaches 1.262. It is then passed through a filter press, which removes any suspended dirt, and gives a clear, bright product. As a rule, the glycerine recovered from soap lye is not bleached, and is generally sold as dynamite glycerine. Chemically pure glycerine is made from candle crude glycerine by the Van Ruymbeke process. The crude liquid, having a density of 28 Be., is diluted, and treated with milk of lime to neutralize any acid. It is then treated with a bleaching material known as " black," the composition of which is kept secret. After filter pressing, the glycerine is concentrated to a density of about 31 Be., in an appa- ratus similar to that used for dynamite glycerine. It is then distilled, as in the case of the latter, and the product condensing in the cool- ers is thoroughly bleached by treatment with more " black," and is then filter pressed. The density of chemically pure glycerine is not required to be so high as that of dynamite glycerine, hence no final concentration is necessary. A very fine grade of chemically pure glycerine is sometimes prepared from dynamite glycerine by subject- ing it to the same process employed for candle crude glycerine. Of the other methods for recovering glycerine, only the Glatz pro- cess needs consideration here. In this the lye is treated with a small amount of milk of lime, and then all alkali neutralized with hydrochloric acid, and the liquid filter-pressed to remove the precipi- tated matter. By evaporating the filtrate under a vacuum, crude glycerine is obtained, which is distilled under low vacuum with superheated steam, the still being heated by direct fire. The prod- 334 OUTLINES OF INDUSTRIAL CHEMISTRY uct is then concentrated in a Yaryan or similar evaporator, until heavy enough for market. The yield of glycerine is always calculated on the amount of fat saponified. By careful work, 6.75 per cent of marketable glycerine can be obtained by the Van Ruymbeke process. Glycerine is a thick, viscid liquid, having a sweet taste and unc- tuous properties. It is soluble in water and in alcohol. High grade dynamite glycerine is of a very pale, yellow color, odorless, and free from acids. It contains no iron, lead, or calcuim salts, and only a trace (0.006 per cent, at most) of chlorides. The ash is not over 0.01 per cent. The specific gravity should not be less than 1.262 at 15 C. It is chiefly used in making nitroglycerine ; also to some extent as a solvent; in the preparation of printers' ink-rolls, and for increasing the body or viscosity of other liquids. Chemically pure glycerine is colorless, containing less than 0.009 per cent car- bonaceous residue, no chlorides, and leaves no ash. Its density is about 1.260 sp. gr. It is largely used as a preservative for tobacco; for confectionery ; in pharmacy ; in the preparation of cosmetics ; as a sweetening agent in fermented drinks, and in preserves; and owing to its non-volatile and non-drying character, as an addition to inks intended for rubber stamps. REFERENCES Technology of Soap and Candles. K. S. Christian!, Philadelphia, 1881. (Baird &Co.) Das Glycerine. S. W. Koppe, Wien, 1883. (Hartleben.) Soaps, Candles, Lubricators, and Glycerine. W. L. Carpenter, London, 1885. The Art of Soap Making. A. Watt, London, 1887. Handbuch der Seifenfabrikation. C. Diete, Berlin, 1887. Guide pratique du Fabricant de Savons. G. Calmels and E. Saulnier, Paris, 1887. Traite" pratique de Savonnerie. E. Morride, Paris, 1888. Soaps and Candles. J. Cameron, London, 1888. (Churchill.) Manufacture of Soaps and Candles. W. T. Brannt, Philadelphia, 1888. (Baird &Co.) Seifenfabrikation. (2 Bander.) A. Englehardt, Wien, 1888. Der praktische Seifensieder. H. Fischer, Weimar, 1889. (Voigt.) Die Seifen-Fabrikation. F. Wiltner, Wien, 1891. (Hartleben.) A Handbook of Modern Explosives. (Glycerine.) M. Eissler, New York, 1890. Soap Manufacture. W. L. Gadd, London, 1893. (Bell & Sons.) Savons et Bougies. J. Lefevre, Paris, 1894. Manufacture of Explosives. (Glycerine.) O. Guttmann, London, 1896. Journal of the Society of Chemical Industry, 1839, 4. O. Hehner. American Chemical Journal : 17, 59. Evans and Beach ESSENTIAL OILS 335 Journal of Analytical and Applied Chemistry : IV, 147. J. F. Schnaible. V, 379. E. Twitchel. VI, 423. W. H. Low. Railroad and Engineering Journal : 65, 495 and 551. C. B. Dudley. 67, 199 and 251. C. B. Dudley. ESSENTIAL OILS The essential or volatile oils are liquids which give the peculiar odors to plants. They occur already formed in the plants, or are produced by the combination of substances in the plant, which react when brought into the presence of water. They have strong and characteristic odors and pungent taste, and are generally volatile without decomposition. There are three general classes of these oils : (a) those containing carbon and hydrogen only, and which consist of terpenes of the general formula (C 10 H 16 )^; (6) those containing carbon, hydrogen, and oxygen, and mainly composed of ethers, aldehydes, ketones, or phenols; (c) those containing sulphur or nitrogen. The oils are frequently mixed with solid, oxygenated bodies, called resins, which have an acid or anhydride character. These mixtures are gener- ally called oleo-resins, or balsams. The volatile oils are liquid at ordinary temperatures, and are usually nearly colorless when fresh, but become darker and thick on exposure. Many of them are optically active. They are nearly insoluble in water, though imparting their peculiar odor or taste to it. They dissolve in alcohol, carbon disulphide, petroleum ether, and in fatty oils. Excepting those containing organic ethers, they are not saponifiable. Some of the essential oils can be prepared synthetically, but most of them are obtained by distilling the plant with water ; by extracting it with solvents ; by pressing ; by maceration in fat ; or by erifleurage, or absorption in fat. By far the greater number of commercially important essential oils are obtained by distillation with water or steam or by pressing. In the distillation process, the oil-bearing material is put into a still with a considerable quantity of water, which is then brought to boiling. The steam carries the oil into the condenser mechanically, where a mixture of oil and water is obtained, which is usually milky at first. On standing, it separates into two distinct layers, the oil 336 OUTLINES OF INDUSTRIAL CHEMISTRY usually, but not always, on top. The water is drawn off, and re- turned to the still with the new charge; or the receiver is so ar- ranged that the water returns continuously to the still through a siphon. When extraction is employed, alcohol, carbon disulphide, ether, or petroleum naphtha, may be used. The solvent is evaporated from the oil, and recovered. Some oils, especially those of lemon and orange, are obtained by the use of hydraulic or screw presses. The product is fragrant, but rather deeply colored. Maceration in fat is employed for some essences which are injured by high temperatures. The fat used is a perfectly pure and sweet lard, tallow, or heavy paraffine oil which is melted in a water bath. The flowers or leaves are stirred in and digested until ex- hausted. The fat takes up the essential oil and is treated with alco- hol, which extracts part of the essence. These alcoholic solutions are much used in perfumery ; the fat, still containing some of the essential oil, is used for pomades and similar purposes. Enfleurage is employed for those very delicate oils whose odors are destroyed by even moderate heat. The flowers to be extracted are laid in a wooden frame on the glass bottom of which a thin layer of perfectly neutral fat is spread. A number of frames are placed in a pile and allowed to stand for some hours, when the flowers are replaced by fresh ones. This is repeated until the fat has become strongly charged with the perfume. Oil of turpentine or spirits of turpentine is derived from conifer- ous trees, especially from the pine, Pinus palustris, Mill., and P. tceda, L., and from the Scotch fir, P. sylvestris, L. The trees are " boxed," i.e. a cavity is cut near the root, and the bark channelled with shallow cuts which lead down to the box. The crude turpen- tine (an oleo-resin) flows from the cuts and collects in the box, from which it is dipped out at intervals. It forms an exceedingly sticky, viscid liquid balsam which is distilled with steam. The volatile oil of turpentine (about 17 per cent) passes over with the steam, while a residue of resin (rosin or colophony) remains in the still. . The oils obtained from different varieties of coniferce differ some- what in their properties. Three commercial grades are important : (a) French turpentine consisting chiefly of a terpene, C 10 H 16 , and called terebenthene or Imvopinene, which has a laevo-rotary action on polarized light rays ; (6) American or English turpentine consisting of a terpene, C 10 H 16 , called australene, which has the same specific gravity, boiling point, and chemical properties as terebenthene, but ESSENTIAL OILS 337 is dextro-rotary ; (c) Russian turpentine which contains the terpene, sylvestrine, and some of a pinene, resembling australene but differing in its rotary power. The oil of turpentine first distilled is usually washed with caustic soda solution to saponify any rosin acids, and is then redistilled, forming the " rectified spirits of turpentine." Commercial oil of turpentine is a water-white, mobile, light re- fracting liquid of 0.640 to 0.872 sp. gr., and distilling between 156 and 170 C. It is insoluble in water and in glycerine, but very soluble in ether, absolute alcohol, carbon disulphide, chloro- form, benzene, fatty oils, and other essential oils. It dissolves resins, caoutchouc, wax, phosphorus, and sulphur. On exposure to the air, it absorbs oxygen and becomes resinous. It is inflammable and burns with much smoke. It reacts readily with many chemical reagents, producing substances used in medicine and the arts. Oil of turpentine or " turps " is extensively used as a solvent for resins and oils in making varnishes and paints. According to Kingzett, the oxidation of turpentine produces cam- phoric peroxide, C 10 H 14 4 , which, when treated with water, forms camphoric acid and hydrogen peroxide. By exposing Russian tur- pentine to a current of air in the presence of warm water, the disin- fectant " sanitas " is made. Camphor,* C 10 H 16 0, is one of the oxygenated essential bodies (probably a ketone) occurring in many crude volatile oils. The commercial article is obtained from the wood of the camphor laurel, Cinnamomum Camphora, Nees & Eberm. The tree is native in Japan and Borneo. The trunk and branches of the tree are roughly distilled with water, and the crude camphor purified by sublimation. Camphor is a white, translucent, fibrous body having a peculiar, penetrating odor and pungent taste. It melts at 175 C., and boils at 204 C., and is volatile at ordinary temperatures. Its density is 0.986 to 0.996. It burns with a very luminous flame, but emits much smoke. It is very slightly soluble in water, but dissolves easily in alcohol, ether, chloroform, carbon disulphide, acetone, and essential oils. It is largely used in medicine and pharmacy, and as a protective against the ravages of insects. Thymol, C 10 TI 13 OH, is a phenol occurring in the oil of thyme and in some other volatile oils. It is similar to carbolic acid in its character, and it is obtained by washing the crude oil with caustic soda, the alkaline solution of thymol being separated and decom- * J. Soc. Chem. Ind., 1884 (3), 353. 338 OUTLINES OF INDUSTRIAL CHEMISTRY posed with mineral acid ; or the oil is chilled and the thymol crys- tallizes and may be filtered out. It is a colorless crystalline body, having a specific gravity of 1.028, and melting at 44 C. It is very slightly soluble in water, but readily so in alcohol, glacial acetic acid, ether, etc. It is a pow- erful antiseptic, and is much used in medicine and in pharmacy. Menthol, C 10 H 19 OH, is an alcohol occurring in oil of pepper- mint, and which crystallizes when the oil is chilled. It is a white solid, very sparingly soluble in water, but readily so in ether, alco- hol, and fixed and volatile oils. It does not combine with caustic alkalies. It melts at 41 to 43 C. It is much used as a remedy for neuralgic pains and headache. The essential oil of almonds is produced by the action of emulsin, a nitrogenous ferment upon amygdalin, a glucoside. To obtain it, the marc of almond kernels left after pressing for the fixed oil, is distilled with water. It contains benzaldehyde, with some hydro- cyanic acid and other nitrils. It is purified by redistillation over a mixture of lime and ferrous sulphate. It is readily oxidized on ex- posure to the air, forming benzoic acid. Artificial almond essence is made by boiling benzal chloride with lead nitrate or calcium car- bonate and water. This oil is used in making dyes and as a flavor- ing extract. Nitrobenzene is used under the name " rnirbane," as a substitute for almond essence for scenting soaps. Oil of bergamot is prepared from the fruit of a species of orange, Citrus Bergamia, Kisso, by hand pressing or distillation with water. It is a light green, pleasant smelling oil, containing a large amount of a terpene, citrene, C 10 H 16 , boiling at 175 to 177 C. It is chiefly used in perfumery. Oil of Cajaput, prepared from the leaves of Melaleuca Leucaden- dron, L., is a green liquid of peculiar odor, distilling at 170 to 180 C. Cedar oil is obtained by distilling the wood of red cedar, Juni- perus Virginiana, L., with water. It contains a mixture of cedrene, C 15 H 2 4, and a camphor-like body, C )5 H 26 0. Chamomile oil, distilled from Anthemis nobilis, L., consists of isobutyl and amyl esters of angelica and tiglic acids. Cinnamon oil or oil of cassia is distilled from the inner bark of Cinnamomum Zeylanicum, Nees. It is a yellow oil, consisting mainly of cinnamic aldehyde, with a little cinnamic acid. It is slightly heavier than water. Oil of cloves is obtained by distilling cloves (the flower buds of Eugenia caryophyllata, Thunb.) with water. It is a mixture of a ter- ESSENTIAL OILS 339 pene, C 15 H 24 (boiling at 251 C.), and eugenol, C 10 H 12 2 . It is yellow, of a penetrating odor and heavier than water. Eucalyptus oil, distilled from the leaves of several Australian trees, Eucalyptus Globulus, Labill., and others, is used in perfumery, in medicine, and in scenting soaps. It contains terpenes (especially pinene, C 10 H 16 ), cymene, and eucalyptol or cineol, C 10 H 18 0. Geranium oil is distilled from the leaves of Pelargonium Radula, L'Herit. Its odor resembles that of rose oil, which it is chiefly used to adulterate. Lavender oil is distilled from the flowers of Lavandula vera, D. C. It has little odor when first prepared, the perfume being developed by exposure to the air. Oil of spike is obtained from L. Spica, Cav. It is similar to lavender oil and is used in porce- lain painting. Oil of lemon is expressed from the rind of the fruit of Citrus Limonum, Risso. Poor grades are made by distilling the rind. The oil contains a terpene (limonene), C 10 H 16 , boiling at 176 C. It is chiefly used in perfumery, and as a flavoring essence in confectionery. Mustard oil is distilled from the seeds of Brassica nigra, Koch., after the fixed oil has been removed by pressing. It contains nitro- gen and sulphur, and its essential principle is allyl thiocarbamide, C 3 H 5 N:CS. It is a pale yellow oil of 1.015 to 1.025 sp. gr., boiling at 148 C., and having a pungent, disagreeable odor. It is a powerful irritant and produces blisters on the skin. It is not pres- ent in dry seeds, but is formed by the action of a ferment, myrosin, upon a glucoside, potassium myronate, in the presence of water. Artificial mustard oil is prepared by distilling allyl iodide with potassium thiocyanate : C 3 H 5 I + KSNC = KI + C 3 H 5 . N : CS. Oil of peppermint, obtained by distilling the herb Mentha piperita, L., is a colorless or greenish-yellow liquid, of strong pungent taste and odor, having a specific gravity of 0.900 to 0.920. It is a mixt- ure of menthol, C 10 H 19 OH, with several terpenes. It is much used in medicine and as a flavoring essence. Attar of roses is obtained by distilling the flowers of various species of rose. It is a pale yellowish liquid, somewhat lighter than water, having a very delicate, rich odor. It crystallizes at ordinary temperatures and deposits an inodorous body resembling paraffine. The constitution of the oil is not known. Owing to its high price, it is always adulterated with geranium oil, which resem- bles it somewhat in odor. 340 OUTLINES OF INDUSTRIAL CHEMISTRY Oil of rue is distilled from the herb Rata graveolens, L. It con- sists mainly of methyl nonylketone, C 9 H 19 * CO CH 3 . Oil of sassafras is distilled from the root of Sassafras officinale, Nees & Eberm. It contains safrol, C 10 H 10 2 , and some pinene, C 10 H J6 . Safrol melts at 8 C. and boils at 228 to 235 C. Sassafras oil is much used for flavoring. Oil of thyme or origanum is derived from the leaves and flowers of Thymus vulgaris, L. It is yellowish red, has a pungent taste, and a specific gravity of 0.900 to 0.930. It contains a laevo-pinene, C 10 H 16 , boiling at 160 C. ; thymol, C 10 H 14 0, and cymene, CioH^, boil- ing at 175 C. Oil of wormwood is distilled from the herb Artemisia Absin- thium, L. Oil of wintergreen is distilled from the leaves of Gaultheria pro- cumbens, L. It contains methyl salicylate, C 6 H 4 (OH) COO CH 3 , with a little terpene. It is a liquid of pleasant smell and taste, boiling at 218 C., and having a specific gravity of 1.175 to 1.185 at 15 C. It rotates the plan of polarization to the left. It is much used as a flavoring essence. An artificial oil is made by heating salicylic acid with oil of vitriol and methyl alcohol. REFERENCES Treatise on the Manufacture of Perfumes. J. H. Snively, New York, 1890. Die fliichtigen Oele des Pflanzenreiches. G. Bornemann, Weimar, 1891. Handbuch der Parfumerie- und Toilettenseifen-fabrication. ' C. Deite, Berlin, 1891. (J. Springer.) The Art of Perfumery. C. H. Piesse, London, 1891. 5 Ed. Practical Treatise on the Manufacture of Perfumery. W. T. Brannt, Phila- delphia, 1892. Odorographia; a Natural History of Raw Materials and Drugs used in the Perfume Industry. J. Ch. Sawer, London, 1892, Part I. 1894, Part II. (Gurney and Jackson.) Perfumes and their Preparation. G. W. Askinson. Trans, by J. Furst, Lon- don and New York, 1892. Fabrication des Essences, et des Parfums. P. Durvelle, Paris, 1893. Descriptive Catalogue of Essential Oils and Organic Chemical Preparations. F. B. Power, New York, 1894. (Fritsche Bros.) Die Riechstoffe u. Ihre Verwendung. Dr. St. Mierzinski, Weimar, 1894. (F. Voigt.) Aether und Grundessenzen. Theodor Horatius, Leipzig, 1895. (Hartleben.) Semi- Annual Reports. 1892 +. Schimmel and Co. (Fritsche Bros.), Leipzig and New York. RESINS AND GUMS 341 RESINS AND GUMS Resins are oxygenated bodies, generally produced by the oxida- tion of terpenes or related hydrocarbons in plants or in essential oils. They are found as natural or induced exudations from plants, often mixed with the essential oil, forming oleo-resin or balsam, or with mucilaginous matter, forming gum-resin. True resins are com- pact masses, insoluble in water, devoid of marked taste or odor, and usually composed of substances of an anhydric or acid nature. They are nearly all soluble in alcohol, ether, benzene, and in most volatile oils, and may usually be saponified with caustic alkali. When heated, they soften below their melting points, but cannot be dis- tilled undecomposed. The chief uses of resins are : in making var- nish ; for soap ; as a constituent of sealing wax ; in medicine, and in sizing paper and cloth. Common rosin, or colophony, is a resin obtained by the distilla- tion of turpentine oil from crude turpentine (p. 336). Three grades of rosin are in the market, " virgin," yellow dip, and hard. Virgin rosin is made from the first turpentine that exudes after the tree is "boxed." It is of a very light yellow or amber color. The greater part of the crude turpentine furnishes yellow dip. The hard is made from the scrapings from the tree after the turpentine has be- come too thick to run into the box ; it is very dark, being nearly black. " White rosin " contains some water, which renders it opaque ; but as soon as the water evaporates, the whiteness disappears. Rosin is very brittle, melts at 100 to 140 C., and has a specific gravity of about 1.08. It contains a large amount of abietic anhy- dride, CuH 62 4 , which is readily converted into abietic acid, C^H^Og. Rosin is converted by alkalies into " rosin soap " (p. 323), which is deliquescent and very soluble in water. Rosin is used as a constitu- ent of laundry soaps ; as an addition to cheap varnishes ; and as a flux in soldering and brazing rnetals ; in pharmacy ; in ship calking ; and as an adulterant of fats, waxes, and mineral oils. Rosin must not be confounded with wood-tar, or pitch, obtained by the destructive distillation of wood. Rosin may be distilled in vacua, or by the aid of superheated steam, with very little decomposition ; but when heated in a retort, it yields decomposition products consisting of gases, liquids, and pitch. The liquid distillate is composed mainly of " rosin spirit," * a * Renard. J. Chem. Soc., 46, 843. 342 OUTLINES OF INDUSTRIAL CHEMISTRY very complex body, boiling below 360 C., resembling oil of turpen- tine, for which it is sometimes substituted, and " rosin oil," * a heav- ier liquid, boiling above 360 C. The rosin oil is purified by treatment with a little sulphuric acid, followed by lime water, and then redistilled, sometimes with caustic soda in the still. It has a specific gravity of 0.980 to 1.100 ; is water white to brown in color, and is very slightly soluble in alcohol, but easily dissolved in fatty oils, ether, chloroform, etc. It is nearly odorless, and has a strong, peculiar taste. It is not subject to true saponification, although when treated with milk of lime, a combina- tion between the terpenes of the oil and the calcium hydroxide takes place, forming a solid mass. This is stirred up with more rosin oil, to form a soft mixture of about the proportions, 13 C 10 H 16 Ca (OH) 2 , which is the commercial "rosin grease," used as a lubricant on iron bearings. Rosin oil is largely used in making such lubricants, and as an adulterant for olive and boiled linseed oils. Burgundy pitch is a resin resembling common rosin, but obtained from the Norway spruce, Picea excelsa, Link. The trees are scari- fied, and the resin allowed to harden, when it is collected and treated with boiling water, to remove the volatile oils. Its chief constituent is abietic anhydride. When stirred up with fats and water, melted rosin forms a mass resembling Burgundy pitch, in its opacity and other properties. Mastic and Sandarac are somewhat similar resins, obtained from evergreen shrubs which grow along the shores of the Mediterranean Sea, especially on the island of Chios, and in northern Africa. The former, derived from Pistada Lentiscus, L., occurs in commerce as small translucent grains, or "tears," which soften when masticated and have a slightly bitter, aromatic taste. It is soluble in acetone alcohol, and turpentine oil, and is used in varnish making and in pharmacy. Sandarac, also called "gum juniper," is obtained from CaUitris quadrivalvis, Vent., an evergreen growing in northern Africa. It is used in varnishes. Amber is a fossil resin found along the coast of the Baltic Sea, in Germany. It is the hardest and heaviest of all resins, is capable of taking a high polish, and is insoluble in most of the ordinary sol- vents. Its color varies from very light yellow to deep brownish red. It often contains perfect specimens of fossil insects. When heated above its melting point, it is partly decomposed, and then becomes soluble in alcohol and in oil of turpentine. * Kenard. J. Chem. Soc., 24, 304, 1175. RESINS AND GUMS 343 Transparent pieces of amber are much prized for jewelry, fancy articles, mouth-pieces for pipes and cigar holders, and for other orna- mental purposes. It is also used in preparing a fine transparent varnish for use on negatives in photography. When subjected to destructive distillation, amber yields a gas, an organic acid (succinic acid), and an oil called "oil of amber." This oil and the acid are used somewhat in pharmacy. By treating oil of amber with fuming nitric acid, a substance resembling musk in odor, and other properties is obtained. But the artificial musk* of com- merce is now made from butyl toluene, by the action of nitric and sulphuric acids. Copal is a very valuable resin. Soft copal, soluble in ether, is obtained from living trees in Java, Sumatra, the Philippine Islands, and New Zealand. The better quality, hard copal, is a fossil gum, found in irregular lumps, buried in the earth, in the East Indies, Madagascar, West Africa, and South America, the last variety being called gum animi. Hard copal varies in color from pale yellow to brown. Its specific gravity is usually 1.059 to 1.072. It has a higher melting point than soft copal, and is insoluble in ether or volatile oils. But by heating above its melting point, a partial decomposition takes place, and the resin is rendered more soluble in these solvents. Hard copal is the hardest of all resins, except amber, and is most valuable for varnish making. For this it must first be melted, or " run," and while in the liquid state, hot oil of turpentine is slowly added and mixed with it. Dammar is obtained from a coniferous tree, Agathis loranthifolia, Salisb., in the Moluccas. The resin exudes from the tree in drops, and is collected after it dries. It is soluble in essential and in fixed oils, in crude benzene, and partially so in alcohol and ether. It is very light colored, and makes a very transparent varnish. Kauri, or Australian dammar, is obtained from a New Zealand tree, Agathis australis, Stend. Much of the kauri of trade is a fossil resin, and is somewhat darker colored than the true dammar and copal. It is extensively used for varnish making, being cheaper than copal. Dragon's blood is a deep crimson red resin, which exudes from the fruit of a palm tree, Dcemonorops Draco, Blume., indigenous in the East Indies. It is collected by the natives and made into irregu- lar lumps, or cast into long sticks in moulds made by rolling palm leaves into cylinders and closing one end. It is freely soluble in nearly all of the ordinary solvents, except petroleum ether, oil of * Bauer. Berichte der deutschen chemischen Gesellschaft, 24, 2832. 344 OUTLINES OF INDUSTRIAL CHEMISTRY turpentine, and ether. It is slightly soluble in the two latter. It is used in pharmacy, and in certain colored varnishes. Guaiacum is a resin derived from certain West Indian trees, especially Guaiacum sanctum, L., and G. officinale, L. It exudes from the trees through incisions, and forms " tears " or lumps which are sent to market. It is soluble in ether, alcohol, chloroform, acetone, and caustic soda. Its alcoholic solution is employed as a reagent for oxidizing substances, with which it shows a blue color, which is destroyed by reducing agents, but reappears when again oxidized. Hydrogen peroxide, however, does not change the color to blue unless in the presence of blood. Hence guaiacum in alcohol, with hydrogen peroxide, is used as a reagent for detecting blood stains. Guaiacum is also used in medicine in treating rheumatism and gout. Lac is a resin produced by the bite or sting of certain insects, Coccus lacca, Kerr, on the small twigs of several species of East Indian trees, of which Picas Indica, L., and F. religiosa, L., are the chief. The resin appears to be formed from the plant sap by the female insect, from whose body it exudes, ultimately burying the insect and her eggs, and forming a thick excrescence on the twigs. It is collected, together with the twigs which it envelopes, and is brought into commerce as "stick lac." The insect also secretes a brilliant red dye which is extracted by macerating the crude lac in warm water. The aqueous solution is evaporated to dryness, and the residue sold as lac-dye. After the dye is extracted, the resin is known as "seed lac." This is refined by carefully melting and straining through muslin bags to remove foreign matter. The melted lac is then poured in thin films over cold porcelain, copper, or wood cylinders, or plates, and allowed to cool, when it hardens and scales off in thin flakes, and is called " shellac." Or it is poured into moulds to form " button," or " garnet lac." The shellac is the better quality, and is of a pale orange, or red color, and is nearly transparent. It is used for spirit varnish. Lac is partially soluble in strong alcohol, forming a turbid, gummy liquid much used as a varnish and wood filler. It is partly soluble in ether, chloroform, and turpentine, but is completely dissolved by caustic alkalies and borax solutions. Such solutions are used as water varnishes. Lac is also used as the basis of the better grades of sealing wax. Bleached shellac is made by passing a stream of chlorine gas into an alkaline solution of lac ; the precipitated lac is melted under water and "pulled" to make it white and fibrous. It is used for white varnishes. RESINS AND GUMS 345 Elemi is a resin obtained from certain trees, Canarium commune, L., in the Philippine Islands, Canarium Mauritianum, Blnme., in Mauritius, Amyris elemifera in Mexico, and from several varieties of Idea in Brazil. The resin varies from white to gray in color, and is soft and tough. It softens at 75 C., and melts completely at 120 C. It is soluble in alcohol and other solvents, and is used chiefly to give toughness to varnishes made from harder resins. VARNISHES The resins are chiefly important as furnishing the material for varnish making. A varnish is a solution of a resin, or of a drying oil, which, when exposed to the air, becomes hard and impervious to air and moisture, through evaporation of the solvent or oxidation of the oil. Three classes of varnishes are important : (1) Spirit var- nishes, consisting of resin dissolved in alcohol, petroleum spirit, acetone, or in any other volatile solvent ; (2) turpentine varnishes, in which the resin is dissolved in oil of turpentine ; and (3) linseed oil varnishes, which may consist of linseed oil alone, or with the addition of resin and turpentine oil. Spirit varnish dries rapidly, leaving the resin as a thin and brilliant film on the surface to which it is applied. This film is very brittle, and liable to crack and scale off. The addition of turpentine overcomes this difficulty to some extent. Spirit varnishes are very often colored with dyes soluble in alcohol, or with dragon's blood, gamboge, or cochineal. The most important spirit varnishes are made with shellac, though mastic, sandarac, and dammar are used. Turpentine varnish is tough and flexible, but much slower in drying than the spirit varnishes. The resin is simply dissolved in the hot oil, and after cooling is ready for use. Linseed oil varnishes are the most important. If well boiled oil (p. 308) is applied to a surface it dries to a hard film, but without much brilliancy of surface. By dissolving a resin in the boiled oil and thinning to the proper consistency with turpentine, a varnish is obtained which dries with a very hard, glossy surface, impervious to air and moisture. The resins used are mainly amber, copal, anime, kauri, and dammar, for transparent varnish. The hard resins are not directly soluble in the oil, but must first be partly decomposed, or " run," by heating above their melting points. There is consider- able evolution of irritating gases during this fusion, and an oily distillate is often collected. The residue in the pot is then soluble in the hot boiled oil, which is run direct from the boiling kettle into 846 OUTLINES OF INDUSTRIAL CHEMISTRY the resin melting kettle. After thorough, stirring the mixture is usually heated some time longer to secure homogeneous solution. It is then cooled to about 130 or 140 C., and thinned to the desired consistency with oil of turpentine. The varnish is allowed to stand in storage tanks for several months, or even for a year or two, until thoroughly clarified. The boiling of the oil and of the varnish involves considerable risk from fire. The oil froths very much, and the vapors given off are inflammable, hence it is usually the custom to build the furnace with the fire-door opening through a partition into another room. The vapors should be led into a flue having a good draught. OLEO-RESINS Oleo-resins are mixtures of the resin and the essential oil of the plant from which they exude. Among them is a group of substances which have peculiar odor and pungent taste, and which are called balsams. They are the exudations from tropical trees belonging to the genera Myroxylon and Styrax. The most important are Benzoin, Peru, Tolu, and Storax balsams. They contain free benzoic or cin- namic acids, or compounds of them, to which their peculiar properties are due. The balsams are chiefly used in medicine and pharmacy, and for incense and perfumes. The so-called Canada balsam is an oleo-resin containing turpen- tine, and is not a true balsam. CAOUTCHOUC OR INDIA RUBBER Belated to the resins and essential oils is caoutchouc or India rubber. This is suspended in minute globules in the juice or latex of certain plants belonging to the orders Euphorbiacece, Apocynacem, and Artocarpacece, native in nearly all tropical countries. There are some 60 species grouped in the 5 genera, Havea, Maniliot, Vahea, Landolphia, and Castilloa. The finest grades come from South Amer- ica (Para), and Madagascar. In Brazil the trees are from 12 to 15 years old when tapped, and yield about 10 pounds of milky juice, or over 3 pounds of gum daily. Medium and low grades are obtained from Central America, East India, Java, Borneo, and the west coast of Africa. The plants in Africa are generally vines ; the bark is partly stripped off, and the juice coagulates on the vine by the evaporation of its very volatile constituents. The juice, which is quite distinct from the sap of the rubber plant, and some of whose constituents are probably waste products as far as the vital processes of the plant are concerned, is collected RESINS AND GUMS 347 in July, August, October, and November. It is coagulated by heating and exposing in thin layers to the smoke of burning palm nuts, as in Brazil ; or it is boiled with water ; or dilute acid, salt water, wood- ash lye, or alum is added, in which case the crude rubber is usually wet and porous. Caoutchouc has the composition (C 10 H 16 ) n , and is therefore a polymer of terpene. Commercial caoutchouc appears to contain two modifications, one soft and viscous, and the other hard and fibrous. These have the same properties in general, but differ in solubility in cold benzene or naphtha; the hard variety swells and softens, while the viscous caoutchouc dissolves to form a true solution. Fresh samples are nearly white, but darken on exposure. Commercial grades are nearly black, owing to discoloration by smoke and exposure to the air, and often have a very foul odor due to fermentation. When soaked, the crude gum absorbs from 10 to 25 per cent of water. It is sticky, and freshly cut surfaces unite very firmly. Dilute acids and alkalies have no action on it, but strong acids and free chlorine or bromine destroy it. Oils and grease also cause it to become hard and brittle after a time. It is soft and elastic at ordinary temperatures, and if heated becomes very sticky and loses its elasticity at about 120 C., and melts at 150 C. It is soluble in carbon disulphide and chloroform and partially so in ether, oil of turpentine, benzene, and naphtha. Its specific gravity is 0.915. The crude gum contains much dirt, sand, gravel, bark, etc., which is removed by a washing process. It is boiled in water until softened, and is then ground between corrugated rolls, which flatten the lumps into thin sheets while a stream of water plays over the mass, washing away the impurities. Good Para rubber loses about 15 per cent of its weight during this washing, while low grades shrink from 30 to 40 per cent. Following the washing, the rubber is very thoroughly dried, hanging for several weeks in well ventilated lofts heated to 90 F. This leaves it very pure. But for most manufacturing purposes, a pure gum is neither necessary nor desirable, and in order to impart to it certain properties, it is mixed or " compounded " with various materials. This is done in a " mixing mill," which consists of a pair of heavy, smooth, hollow, iron rollers, one of which is heated by steam to about 80 C. The materials added are vulcanizing agents such as sulphur, metallic sulphides and oxides, coloring pigments, fillers, or inert "make weights," such as whiting, barytes, plaster of Paris, etc., rubber substitutes, or cheap gums. These are thoroughly ground with the 348 OUTLINES OF INDUSTRIAL CHEMISTRY gum to produce a homogeneous mass, which can then be fashioned into any desired form and finally vulcanized. The clean surfaces of unvulcanized rubber will unite if brought in contact with each other. It is on this property that the manu- facture of soft rubber goods chiefly depends. In order to prevent accidental adhesion, fresh surfaces are dusted with talc, starch, or flour, or pieces of plain cotton sheeting are interposed. Vulcanization or curing is a chemical change, whose nature is not understood, which is produced in the rubber by heating it with sulphur, metallic sulphides or oxides. It can be carried 011 by dry heat at 125 C., if some metallic oxide, such as litharge or zinc oxide is present in the compound. The goods are placed in a closed chamber heated by steam ; the latter, however, does not come into contact with the rubber, as it does when curing with wet heat. Metallic oxides are much used for this form of vulcanizing. A cold process of vulcanizing was discovered by Alexander Parkes. This consists in soaking the rubber article in a solution of sulphur chloride in carbon disulphide. It can only be used for small articles having thin layers of caoutchouc, since the action of the solution is merely superficial. For soft rubber goods, about 10 per cent of sulphur is added in the compounding mill, but only a part of this sulphur is chemically combined in curing, the remainder being mechanically mixed with the product. Vulcanizing destroys the adhesive property of rubber and ren- ders it more elastic,* less soluble, and less susceptible to temperature changes, it neither becomes sticky when moderately heated, nor brittle when cold. If antimony sulphide, Sb 2 S 5 , is used when vul- canizing, the color of the product is red, owing to the formation of the trisulphide, Sb 2 S 3 , the remainder of the sulphur combining with the rubber. Rubber substitutes are extensively used in the so-called mechanical goods, such as bicycle pedals, door-mats, solid cushions, and springs. The best of these is balata, obtained from the juice of Mimusops KauJci, L., a tree native in Guiana. This is an intermediate sub- stance between gutta-percha and caoutchouc. By mixing powdered sulphur with raw linseed oil f and heating in a vulcanizer, a substance resembling rubber is obtained. Or by treating the oil with sulphur chloride, a gummy mass of light color * When unvulcanized rubber is stretched, it regains its original form only very slowly. t Rape seed and castor oils are much used abroad for these rubber substitutes. RESINS AND GUMS 349 is produced. These " sulphurized oils " are largely mixed with low grade rubber and with coal-tar or resins, for cheap goods. Some- times they are used without the addition of any rubber whatever. "Reclaimed" or " devulcanized " rubber is made by grinding old rubber stock and scraps to a powder and sifting out the cloth or other fibre present; then the powder is agglomerated by heating with steam at 100 pounds pressure, and then dried. Sometimes the fibres are destroyed by boiling with dilute sulphuric acid; after washing, the mass is steamed as above. Or the old rubber is boiled in an 8 per cent caustic soda solution, and, after washing and drying, is dissolved in carbon disulphide or benzene. The solvent is distilled off to obtain the rubber. Reclaimed rubber has very little strength, and is usually incor- porated with fresh gum. Vulcanized rubber deteriorates by keeping, and ultimately be- comes hard and brittle. This apparently occurs through oxidation, and is largely influenced by the nature of the compound, oxidizing substances such as lampblack being especially liable to spoil the rubber. Rubber cement is made by dissolving a pure rubber in cold naphtha. A little powdered chalk is usually added. The uses of rubber are exceedingly numerous, but the largest quantities are used for overshoes, boots, rubber clothing, bicycle tires, and hose. It may be moulded, as for boot heels, solid rubber hose, etc., or made into rubber fabric. This latter is done by spread- ing a thin layer of the unvulcanized rubber compound on a backing of cotton or woollen cloth. The rubber may be calendered in such a way that it penetrates between the fibres ("friction coating"), or it may be simply applied to the surface of the cloth ("even motion coating"). Rubber shoes and clothing, and other fabric articles are entirely put together before vulcanizing, the seams being joined by rolling the edges into contact, when they adhere. Such goods are usually vulcanized by heating at 260 E. for about six hours. Hard rubber, vulcanite, or ebonite is usually made from the cheaper grades of rubber, especially that from Borneo and Java, and contains a large amount of filling material. From 25 to 50 per cent of sulphur is added, and the mass heated to 140 to 150 C., in vulcanizing. It is often shaped in the form desired after it has been vulcanized. 350 OUTLINES OF INDUSTRIAL CHEMISTRY GUTTA-PERCHA Gutta-percha* is obtained from the juice of Dichopsis Gtitta, Benth. & Hook., a tree native in the East Indies. The tree is tapped in much the same way as for caoutchouc. The crude material is purified by grinding in hot water, by which the chips, bark, sand, etc., are removed. The plastic mass is then rolled into sheets or formed into threads and rolled into balls and pressed. In composition it is a terpene (C 10 H 16 ) U , but it also contains some oxygenated resinous bodies. Its texture is fibrous, its color varies from white to brown, and when free from air its specific gravity is slightly greater than 1.000. It is tough and inelastic when cold, but becomes very plastic at 50 C., and melts at 120 C. It is solu- ble in carbon disulphide, chloroform, and warm benzene. Alkalies and dilute acids have no action on it, but strong nitric and sulphuric acids destroy it. By vulcanizing with sulphur, it is rendered harder and less plastic when heated. It is very easily oxidized in the air and becomes brittle. It is a very poor conductor of electricity and is better than rubber for insulating purposes, for which it finds its chief use. GUM RESINS Gum resins are exudations from plants ; they are the inspissated juice, and contain both gum and resin. They form emulsions with water, a portion of the gum dissolving. Ammoniacum is derived from a Persian plant, Dorema Ammonia- cum, Don. It forms drops, yellow on the surface and milky within. It is partly soluble in water, and has a peculiar odor and bitter taste. It is employed in medicine. Asafoetida is obtained from the roots of two plants, Ferula Nar- thex, Boiss., and-.F. foetida, Eegel, native in Thibet and Turkistan. It forms tears and nodules, frequently contaminated with earthy impurities. It has a powerful garlic odor and bitter taste. It is mainly used in medicine as a stimulant. Euphorbium is derived from a species of cactus, Euphorbia resini- fera, Berg., native in Morocco. It has a very pungent taste, an aro- matic odor, and the powdered gum irritates the throat and nose. It is a violent emetic and purgative, and is chiefly used in veteri- nary medicine. Galbanum is obtained from Persian plants, probably Ferula g^l- baniflua, Boiss. & Buhse. It forms tears, or irregular lumps, of * J. Soc. Chem. Ind., 1897, 815. RESINS AND GUMS 351 brownish yellow color, aromatic odor, and bitter taste. The several varieties found in commerce are used in medicine, and as con- stituents of incense. Gamboge (p. 208) is an orange-red substance, derived from a tree, Garcinia Hanburyi, Hook., or G. Morella, Desr., native in Cochin China, and Siam. It is soluble in alcohol, has an acrid taste, and is a powerful purgative. Its chief uses are in medicine, and as a pigment. Myrrh is obtained from a shrub, Commiphora Myrrha, EngL, growing on the coast of Arabia. It comes in commerce as red- brown, dusty lumps, breaking with an oily appearing fracture. It has a fragrant odor and bitter taste, and emulsifies with water. It is used as a tonic in medicine, and in preparing incense. Olibanum or frankincense is derived from several species of Bos- wellia, the trees being native in Africa and Arabia. It forms tears of a yellow brown color and milky appearance. It has a slight turpentine-like taste, and an aromatic odor. It forms an emulsion with water, and was formerly much used in medicine. It is now chiefly employed in preparing incense. GUMS Gums are amorphous bodies of complex constitution, nearly all of vegetable origin, and soluble in, or, at least, gelatinizing with water, but insoluble in alcohol. When boiled with dilute acid they yield sugars, and when oxidized are converted into oxalic or mucic acids. Acacia, Gum Arabic, or Gum Senegal, is derived from numerous plants of the Acacia family, mostly native in Africa. It forms lumps of various sizes, ranging in color from transparent white to red-brown. Its chief constituent is arabic acid, or arabin, C^H^On, as calcium salt. It dissolves in cold or hot water with equal readi- ness, and is much used in pharmacy in preparing emulsions. Low grades are used for mucilage, in calico printing, in thickening ink and water colors, and as stiffening in cloth. Tragacanth is an exudation from Astragalus gummtfer, Labill., growing in the Levant. It forms dull white, translucent plates, which swell in water and partly dissolve, forming a thick mucilage. Its uses are similar to those of gum Arabic. Agar-agar or Bengal isinglass is a dried seaweed, Gracilaria liche- noides and Eucheuma spinosum, collected in China. It forms a jelly with water. Iceland moss, Cetraria islandica, yields a jelly containing two 352 OUTLINES OF INDUSTRIAL CHEMISTRY gums, liehenine, C 6 H 10 5 , and isolichenine. The former is not col- ored blue by iodine, while the latter is. Irish moss, Chondrus crispus, yields a soluble gum, which is not colored blue by iodine. REFERENCES Report on the Gums, Resins, Oleo-resins, and Resinous Products of India. M. C. Cooke, London, 1874. Manufacture of India Rubber and Gutta-percha. Cantor Lectures Soc. of Arts. Thos. Bolas, London, 1880. Varnishes, Lacquers, Siccatives, and Sealing Waxes. E. Andres. Translated by Wm. T. Brannt, Philadelphia, 1882. (H. C. Baird & Son.) Practical Treatise on Caoutchouc and Gutta-percha. R. Hoffer. Translated by Wm. Brannt, Philadelphia, 1883. (Baird & Co.) Die Fabrikation der Kautschuk- und Gutta-perchawaaren. C. Heinzerling, Braunschweig, 1883. (Vieweg.) Oils and Varnishes. James Cameron, Philadelphia, 1886. (Blakiston, Son & Co.) Practical Treatise on the Raw Material and Manufacture of Rubber. G. N. Nesienson, New York, 1890. Der Fabrikation der Lacke, und Firnisse. Paul Lohmann, Berlin, 1890. Fossil Resins. C. Lawn and H. Booth, New York, 1891. Die Fabrikation der Lacke Firnisse, u. s. w. E. Andres. 4 te Auf. Wien, 1891. (Hartleben.) India Rubber. Special Consular Reports, Washington, 1892. (Government Printing Office.) Notes on Varnish and Fossil Resins. R. I. Clark, London, 1892 (?). Le Caoutchouc et la Gutta Percha. E. Chapel, Paris, 1892. Painters' Colours, Oils, and Varnishes. G. H. Hurst, London, 1892. (Griffin & Co.) The Chemistry of Paints and Painting. A. H. Church. 2d Ed. London, 1892. (Seeley & Co.) Le Caoutchouc et la Gutta-percha a L' Exposition Universelle, de 1889. Ren6 Bobet, Paris, 1893. Pigments, Paints, and Painting. G. Terry, London, 1893. (Spon & Co.) Fabrication des Vernis. L. Naudin, Paris, 1893. Journal of the Society of Chemical Industry. 1894. C. 0. Webber. Die Fabrikation der Copal-, Turpentinol- und Spiritus-Lacke. L. E. Andes. 2 te Auf. Wien, 1895. (Hartleben.) Couleurset Vernis. G. Halphen, Paris, 1895. Die Harze und ihre Producte. G. Thenius, Wien, 1895. (Hartleben.) Gummi arabicum u. dessen Surrogate in festem u. fliissigem Zustande. L. E. Andes, Wien, 1896. (Hartleben.) STARCH, DEXTRIN, AND GLUCOSE 353 STARCH, DEXTRIN, AND GLUCOSE Starch is widely and abundantly distributed in the vegetable kingdom, occurring in nearly all plants in a greater or less quantity. It forms rounded grains of characteristic appearance in the several varieties, and is most abundant in the fruit, tubers, seeds, and stems of the plants from which it is industrially obtained. It is a typical carbohydrate, and on analysis corresponds to the formula C 6 H 10 5 ; but it is probable that the true symbol is some multiple of this, and that the formula should be written (C 6 H 10 O 5 ) W where n is 4 or more. Starch has not yet been prepared synthetically, and even its for- mation in plants is not fully understood ; but it appears that the chlorophyl (the green coloring matter in plants) enters into the reaction in some way, perhaps as a "contact" substance. The carbon dioxide of the air is reduced by the joint action of the chlorophyl and sunlight, the carbon being assimilated, and part of the oxygen, at least, being set free. The formation of starch might be represented thus : 6 C0 2 + 5 H 2 = C 6 H 10 5 +.6 O 2 . It is, however, probably not formed directly, but may be an alter- ation product of the sugar which is so formed. As hypothetical reactions, the following will serve to show the outline of the process, but it is by no means certain that these truly represent the exact changes which occur : 6 C0 2 + 6 H 2 = C 6 H 12 6 + 6 O* CeHjA = C 6 H ]0 5 + H 2 0. It appears somewhat improbable that substances of such high molecular weight as glucose, C 6 H li5 6 , or starch, should be formed directly from the reduction of carbon dioxide. According to Baeyer,* it is more probable that formaldehyde, CH 2 O, is first produced, and then by a polymerization process, the glucose is formed, from which starch is derived : 6C0 2 + 6H 2 = 6CH 2 + 60 2 . 6CH 2 O = C 6 H 12 6 . The starch is formed in the leaves and green parts of the plant, being then transported in soluble form to the other parts, where it is at once applied to the building up of the tissues, or is deposited as * Berichte der deutchen chemischen Gesellschaft, 3, 67. 2A 354 OUTLINES OF INDUSTRIAL CHEMISTRY reserve material for the future nourishment of the plant, or of a new individual ; the greatest deposits are generally found in the roots, tubers, or seeds. As seen under the microscope, a starch granule is made up of different layers, arranged around a nucleus, a dark interior portion, generally at one side of the granule. Each granule consists of an interior substance called " granulose," and an exterior transparent covering, inert and insoluble, and resembling cellulose in structure. But recent investigations tend to prove that the " starch cellulose " is not present as such in the granule, but is formed from the starch substance by the action of acids or by fermentation. Starch is entirely insoluble in cold water, but when heated to 70 or 80 0., the granules swell and finally burst, and the starch substance "granulose," combines with the water to form paste. When this is boiled in an excess of water, it goes into solution and may be filtered. The solution yields an intense blue color with iodine, hence its use as an " indicator " ; it is optically active and rotates the plane of polarization to the left. By exposing starch to the action of cold dilute mineral acid for several days, it is converted into a soluble modification called amylodextrin, which dissolves in warm water without forming a paste. When heated dry to 200 C., starch is converted into dex- trine or British gum. The chief industrial sources of starch are potatoes, wheat, corn, rice, arrowroot, and certain varieties of palm trees (sago). In Europe, potatoes, rice, and wheat are used, while in this country corn and wheat are mainly employed. The separation of the starch, which is mixed with various nitrogenous and fatty matters and some mineral impurities, is essentially a mechanical process; but much care is needed to prevent changes which would spoil the product. Corn starch* is usually made by the alkaline or " sweet" process ; sometimes by an acid or fermentation method similar to that em- ployed for wheat starch. In the alkaline process the grain is run through a fanning mill to blow away dust, husks, etc., and is then steeped in water at from 70 to 140 F. for from three to ten days, when the softened grains are crushed between rolls. This steeping removes much of the oil and swells the gluten and albuminous matter so that it is readily attacked by the alkali. After a time putrefactive fermentation sets in and hydrogen sulphide is evolved. Since this causes a nuisance, the method has been replaced in some factories * J. Soc. Chem. Ind. 1887, 80. Geo. Atchbold. STARCH, DEXTRIN, AND GLUCOSE 355 by the Durgen system, in which a continuous stream of water at 130 to 140 F. flows slowly through the steeping tanks. After three days the grain is soft, while a large quantity of extractive matter has been washed away. The grain is. then ground in buhr- stone and roller mills through which water is flowing ; the starchy magma goes to revolving sieves of brass wire for the coarser strain- ing, and then to cylindrical reels covered with bolting cloth. The mass which passes over the sieves is reground and again sifted. The waste glutinous matter is pressed and dried for cattle feeding, or is sold wet as " swill " for hogs.,2? <^s The milky liquor from the sieves is settled and drawn off from the crude starch, which is washed twice with fresh water and then pumped into vats having good stirring apparatus, and provided with holes in the sides, closed by plugs and used for decanting the liquor. A dilute caustic soda solution of 7 or 8 Be. is stirred into the starch until the liquid becomes greenish-yellow ; then the whole is stirred for several hours. When a test shows that the suspended matter settles in two layers, the starch on top, sedimentation is allowed to take place and the supernatent liquor, containing much oil and nitrogenous matter in solution, is drawn off. The sediment is stirred up with water, allowed to stand until the gluten has de- posited, and then, by pulling the plugs in succession, the starch in suspension is "siphoned off" into tanks. By several repetitions of this process the starch is nearly all removed from the gluten and at the same time is separated into several grades. The residue then flows onto a long, slightly inclined table, or " run," from 60 to 120 feet long and having a fall of 3 or 4 inches. A stream of water flows slowly over it and washes away the gluten and fibrous matter, while the starch deposits on the table. The starch collected in the several tanks is washed with water and sometimes again siphoned, and is then run through bolting cloth to the settling tanks, where it deposits in a dense compact layer from which the water can be drawn off very completely. The wet starch is then shovelled into frames lined with cloth and having perforated bottoms, through which the water drains. The cake of damp starch is cut into smaller blocks and placed on porous floors of plaster of Paris or brick, which absorb the adhering water. * The starch is removed to the dry room and kept at a temperature of 125 F. for several days. While it is drying, the impurities still remaining in it find their way to the surface, where they form a * These floors may be subsequently dried by passing hot air through flues ar- ranged in them. 356 OUTLINES OF INDUSTRIAL CHEMISTRY yellowish deposit which is cut away when the starch is nearly dry. The block is then wrapped in paper and further dried at 150 to 170 F. for several days. During this time the mass contracts and cracks into a number of irregularly shaped prismatic rods, called "crystals," though they are not true crystals. The entire drying process requires several weeks, and the product as sent to market contains about 10 to 12 per cent of water. In recent working the process is so modified that the corn oil can be saved. After careful steeping, the grain is coarsely ground and the meal is agitated with water in long troughs; the husks and germ, being lighter than the starchy portions, are floated off. These contain the most of the oils, nitrogenous matter (gluten), and albu- minoids of the grain, and are treated to extract the corn oil (p. 310), or dried for cattle food. Sometimes sulphurous acid is added to the water used for steep- ing, in order to prevent putrefactive fermentation, and also to bleach the starch. The settling tanks may be replaced by two or three long tables set at a very slight incline. The milky fluid passes down one table, depositing a large part of its starch, while most of the fibrous and albuminous matter remains in suspension and passes to another table, where a poorer grade of starch is deposited. Centrifugal machines have recently come into use for separating the starch from the wash water. These machines are of two kinds, those having a perforated basket, and those in which the basket is of unperforated sheet metal. In the latter, the starch is thrown against the cylinder wall and packed so firmly that it remains as a thick layer, while the water collects in the middle of the drum and can be drawn off very completely, carrying with it much of the glutinous and fibrous matter. In a perforated drum the water passes through, leaving the solid matter behind. The starch, being heavier than the cellulose, forms a layer directly on the basket walls, while inside of this is a layer of gray starch containing the impurities ; this latter is scraped off and washed again. The starchy liquid running into the basket must not be too thick, otherwise the load does not distribute itself evenly in the basket. Corn contains about 54 per cent of starch, and the actual yield obtained in technical work is about 50 per cent, or 28 pounds of starch from a bushel (56 pounds) of corn. About 13 pounds of gluten suitable for cattle food is also recovered per bushel of corn. The best grade of corn starch is largely consumed for food, but its principal use is in laundry work. Lower grades are chiefly employed in manufacturing and in textile industries. In many STARCH, DEXTRIN, AND GLUCOSE 357 technical operations the so-called " green starch " is used. This is the product obtained directly from the centrifugal machine, inclined table, or settling tanks after a partial drying. It contains some impurities and is generally damp, often containing 40 per cent of water. It is mainly employed for glucose making, for stiffening and size, in color mixing for calico printing, and in the manufacture of paper boxes. OUTLINE OF THE PROCESS FOR CORN STARCH Corn v ^/^ *j* &**& | ) Husks. h Carries starch and gluten Reground (steel rolls) Agitated in tank "Slop" passed through slop (Qx^-voJ j machine, a wringer to re- Fed to "runs" or tables move residual starch water (120 ft. by 2 ft., with gentle incline) Starch water Wet feed T ) 1 Consists of husk and bits of germ Passed to dry room Dry Feed Gluten Settled | returned to (Z Starch Liquor Rejected 1 Gluten .' Filter-pressed Cake ground and passed through driers Process generally repeated Cooled 358 OUTLINES OF INDUSTRIAL CHEMISTRY Wheat starch is made by the fermentation or " sour " process, or by Martin's process without fermentation. By the sour process, all the gluten, of which wheat contains a large amount, is destroyed, consequently there is considerable loss. The grain is soaked in water until soft, and then crushed between rolls or pressed in bags. The starch is washed out of the crushed pulp with water, and the milky liquid is run into tanks and allowed to ferment. In order to hasten this, some of the sour liquor from .a previous fermentation is added. The temperature is kept at about 20 C., and the contents of the cistern well stirred frequently. The fermentation lasts from 1.0 to 14 days; the sugar, albumin, and gummy matters of the wheat undergo an alcoholic fermentation, followed by the development of acetic, lactic, and butyric acids. These acids then attack the gluten, dissolving it in part, and de- stroy its tough and sticky properties, so that it is easily washed free from the starch. The washing is done in revolving sieves, in which the swollen gluten, cellulose, etc., remain. The starch is re- peatedly washed and sieved, or levigated, until sufficiently pure and white, when it is dried as already described under corn starch ; but more care is necessary, because of the tendency of the mass to cake together, owing to the presence of a trace of gluten. The process must be carefully watched lest the fermentation go too far and putrefaction set in, thus causing a loss of starch. The acid waste liquors are difficult to dispose of, and cause considerable nuisance in the neighborhood. Usually about 59 pounds of starch and 11 pounds of bran are obtained from 100 pounds of wheat. But only a small quantity of sour gluten is recovered. By Martin's process part of the nitrogenous matter (gluten) is recovered. Ordinary wheat flour from which the bran has been removed is used instead of the whole grain. The flour is kneaded with 40 per cent of water to form a stiff dough, which is then washed in small portions at a time in a fine sieve, while small jets of water continually play upon the mass, carrying away the starch.. By treating the partly washed starch with a solution of caustic soda (sp. gr. 1.013) and allowing it to stand a few hours, the remain- ing gluten is swollen and may be removed by sieving on bolting cloth. The pasty mass of gluten left in the sieves is utilized in the manufacture of macaroni, noodles, and gluten bread, but more espe- cially for paste and for cement for leather, and as a thickening material instead of casein or albumin in textile working. Fesca's modification of Martin's process consists in stirring wheat flour into water to form a thin " milk," which is then run into cen- STARCH, DEXTRIN, AND GLUCOSE 359 trifugal machines. The starch, being heavier than the gluten, col- lects next the revolving sieve. The interior layer, consisting of a mixture of starch and gluten, is removed, washed with water, and again " centriffed." But much starch remains in the gluten. The yield by Martin's method is about 55 pounds of starch and 12 pounds of gluten from 100 pounds of wheat. By Fesca's process, only 40 to 45 pounds of starch are obtained from 100 pounds of wheat. Potato starch is very important in Europe. The tubers contain an average of about 20 per cent of starch and 75 per cent water. The skin contains some fats and coloring matter, but no starch. The adhering dirt and sand are carefully removed by washing in a revolving drum made of wood or iron slats with narrow openings between them for the escape of the dirt, etc. Inside the drum are revolving arms which rub the potatoes together, or revolving wire or bristle brushes which scrub them as the drum turns. The wash- ing must be very thorough or the quality of the starch suffers. The tubers are next rasped or ground in a machine consisting of a revolving cylinder or roll, around whose outer surface are set a large number of narrow knife-edges or saw-blades, which project about one-fifth of an inch. These knife-edges rotate very close to fixed wooden bars which catch and hold the potato while it is scraped into soft pulp. Another kind of rasper consists of a fixed hollow cylinder, having saw-blades set on its inner surface, against which a revolving fork rubs the potatoes. The starch in the potato is enclosed in little cells or bags of cellulose, a number of granules being in each cell. Since the starch can only be washed away from the ruptured cells, the finer the pulp the larger the yield of starch. But even with the best raspers many cells escape unbroken, and usually about 15 per cent of the starch is lost. Sometimes the pulp is reground after it has been washed, which increases the yield of starch slightly. The pulp, consisting of starch and cellulose fibre and tissue, passes into a series of shaking sieves, where . the starch is washed away with a limited amount of water. A better apparatus consists of a series of revolving wire gauze cylinders (30 to 35 meshes to the inch), containing brushes which revolve in a direction opposite to the motion of the cylinder. Fine jets of water play upon the pulp and wash out the starch. The milky liquor passes to a revolving sieve with 50 meshes per inch, which retains any fibre that passes through the coarser screens. Long semicylindrical sieves contain- ing brushes set in the form of an Archimedian screw around a 360 OUTLINES OF INDUSTRIAL CHEMISTRY revolving shaft are sometimes used. The brushes push the pulp along from one end to the other, at the same time thoroughly work- ing it over, while the starch is washed out by jets of water. The waste pulp passing over the sieves is treated by Buttner and Meyer's process ; it is pressed and dried rapidly until the moisture is about 12 per cent. It is sold as a low grade cattle food. The starch suspended in the wash water is run over inclined tables similar to those already described. The crude product is stirred up with water in a tank, and after the sand and heavy dirt has settled, the starch in suspension is rapidly " siphoned " off through holes in the side of the tank. By levigation, the starch is obtained in several grades of purity. Centrifugal machines are also employed to separate the starch and wash water, but with less success than in the case of corn, wheat, or rice starch. The crude starch obtained by any of these methods is purified by repeated washings and levigation, with an occasional passing through sieves or bolting cloth to remove fibre. The purified starch is dried in much the same way as is corn starch. Potato starch is also made by the " rotting " process, in which the moist, sliced material is heaped in a warm room. Fermentation and ultimate decomposition of the cell walls takes place, so that the starch can be washed out of the pulp. Much care is necessary that the fermentation does not attack the starch itself. The mass must be turned over frequently during decomposition. The wash waters from potato starch contain much potash, phos- phoric acid, albumin, and nitrogenous matter, which soon ferment and become very offensive. If possible, they should be used at once to irrigate land. Much ingenuity has been expended to devise means of making them less offensive, but without much success. The yield from 100 pounds of potatoes is about 15 or 16 pounds of dry starch. The product is chiefly used in the textile industries, for laundry purposes, and in glucose and dextrine making ; for the two last mentioned it is customary to use the " green starch," con- taining from 30 to 40 per cent water. Rice starch* is chiefly produced in Europe, only the broken grains separated with the husks in the cleansing mills being used. Bice contains nearly 80 per cent of starch, but its separation is very difficult, since the cells of the grain are composed of very dense glu- tinous material and the starch granules are cemented together very solidly by albuminous and gummy matter. In order to soften the * J. Berger, Chem. Zeitung, 14, 1440 and 1571 ; 15, 843. STARCH, DEXTRIN, AND GLUCOSE 361 gluten, the rice is macerated in very dilute caustic soda (sp. gr. 1.007) containing about 0.5 per cent caustic. After soaking about 18 hours with frequent stirring, the liquor is drawn off and a fresh caustic solution is added. When the grain is soft it is crushed in mills while a stream of dilute caustic plays over the mass, dissolving a part of the glutinous matter, and swelling the remainder so that it, together with the fibrous matter, may be removed by sieving. The starch is then separated from the liquor by centrifugal machines, and further purified by washing it with water, running it through centrifugal machines or settling tanks, and finally filter-pressing and drying in much the same way as for corn starch. The yield is about 85 per cent of the total starch in the rice. The fibrous matter and gluten passing over the sieves are used as cattle food, or if care- fully dried and pulverized, are sometimes sold as "rice meal." The caustic solutions contain gluten which is precipitated by acidi- fying them. Much care is necessary to prevent any fermentation of the liquors or of the wet starch, if the drying be too slow. In order to correct the slight yellow tinge, due to traces of impurity in the starch, a little ultramarine is generally added in the settling tanks or centrifugals. Prussian blue or alkaline blues which are not fast against alkali should not be used. Sago is a starch prepared from the pith of several varieties of palm trees (genera Metroxylon, Arenga, and Borassus), indigenous in the East Indies. The trees are cut down and the pith, sometimes amounting to 700 pounds from one tree, is removed from the trunks. It is a mixture of starch and woody fibre and is pounded fine in wooden mortars ; the starch is washed out with water and purified by sieving and washing as in other cases. This furnishes the sago flour of commerce. Pearl sago is made by kneading the sago flour to a dough with water, and then working the dough through a sieve into a hot pan, greased with oil, and kept shaking constantly ; a por- tion of the starch is converted into paste by the heat, and coats the outside of the granules, which then stick together and form little translucent globules. Imitation sago is now made from potato or other starch. Sago is chiefly used as food and swells in hot water without destroying the globular form. Arrowroot * starch is obtained from the roots of several varieties of plants belonging to the genus Maranta. The long slender roots are soaked in water until the coarse outer skin softens, when it is stripped off. After washing, the roots are rasped to a pulp, from which the starch is washed with water, sieved, and settled to remove * J. Soc. Chem. Ind., 1887, 334. 362 OUTLINES OF INDUSTRIAL CHEMISTRY fibrous matter and soluble impurities. Owing to the large amount of fibre present, fine grinding is difficult, and considerable starch is lost in the waste pulp. Also, there is much trouble in sieving; hand sieves are used, since mechanical ones soon become choked by the fibres. The- starch is dried in the open air on wire screens until no more than 14 to 17 per cent of water remains. The drying house is a light shed, open on all sides for the free circulation of air. In damp weather much care is necessary to keep the wet starch from souring, especially if any impurity is present. Arrowroot starch is much used for food, but is also desirable for laundry and sizing pur- poses. It forms a stiff er jelly than do most other starches. Cassava starch is similar to arrowroot and is obtained from the roots of several species of Maniliot, which are indigenous in Brazil, but which are now cultivated in other tropical countries. The starch is also called Brazilian arrowroot and is prepared similarly to the true arrowroot. By heating the damp starch in shallow pans while stirring actively, the granules burst and adhere together, form- ing the mass into small, irregularly shaped translucent kernels, known as tapioca. This is somewhat soluble in cold water, and is very easily swelled by boiling water to form a transparent jelly. There are several other starches similar to sago and cassava which are used as food, the most important of these being curcuma, tous- les-mois and arum. Some starch is prepared from the nuts of the horse-chestnut tree, JEsculus Hippocastanum, L., which contains about 25 per cent of starch. But since it is nearly impossible to remove the bitter principles, the starch is only used for stiffening and sizing purposes. The chief uses of starch are : for stiffening purposes in laundry work and finishing cotton cloth rice starch is best for this and the addition of a little parafnne or stearin increases the gloss ; for thickening material in calico printing ; as paste for adhesive pur- poses for which wheat starch is best ; in sizing paper ; for glucose making, in which corn or potato starch is generally used ; as a food ; and as a toilet powder, for which rice starch is generally pre- ferred. Starch is readily detected by the microscope or by use of a solu- tion of iodine. There are several methods for determining the amount of starch in a given substance, but nearly all of them de- pend upon the direct isolation of the starch, or its conversion into sugar, which is then determined by means of Fehling's solution. STARCH, DEXTRIN, AND GLUCOSE 363 DEXTRIN Dextrin corresponds to the formula (C^H^Ou^ and is some- times considered an intermediate product between starch and dextrose. The commercial product, called dextrine, or British gum is made by heating dry starch to a temperature of 200 to 250 C. in a revolving iron cylinder over free flame, or in an oil bath, or by a steam jacket; or the starch may be moistened with nitric or hydrochloric acid, dried at 50 C. and then heated to 140 to 170 C. ; this gives a lighter colored product, but since it contains some sugar, its adhesive power is less than if made without acid. After roasting, the dextrine is cooled quickly to stop the conversion, and is powdered in a mill and sieved on bolting cloth. The product is an indefinite mixture of several dextrins with unchanged starch. The dextrins are soluble in cold water and form a thick viscous syrup which has strong adhesive properties and is therefore much used as a substitute for gum Arabic in pre- paring mucilage and for thickening colors in calico printing. By acting upon starch paste with diastase, a syrupy liquid con- taining dextrin and sugar (maltose) is obtained; starch is mixed with water at 50 C., and then heated to 65 C., when the necessary amount of malt (carrying the diastase) is added, and the temperature raised to 73 C., until iodine gives a reddish violet, instead of a blue color. The solution is then boiled to destroy any remaining diastase, cooled, filtered, and concentrated in vacuo to the desired density. It is established that there are several dextrins produced simul- taneously with the formation of the sugar by this action. Dextrin syrups are used in brewing, for thickening tanning extracts, and in confectionery. The products obtained by these various methods vary somewhat in their properties, and have been assigned distinguishing names, erythrodextrin, achroodextrin, and maltodextrin. They are all soluble in water, insoluble in alcohol, strongly dextro-rotary, and yield dextrose by hydrolysis. Erythrodextrin yields a red color with iodine, while the others yield no color. GLUCOSE Under the name " glucose " are grouped not only substances de- rived from starch by hydrolysis, such as dextrose, maltose, dextrins, etc., but also those resulting from, the inversion of sugar, such as laevulose. 364 OUTLINES OF INDUSTRIAL CHEMISTRY Dextrose, C 6 H 12 6 , and the isomeric laevulose occur in the juice of many fruits, such as grapes, cherries, bananas, pears, etc., but in quantities varying even in the same fruit, according to the season and their degree of ripeness. But these sugars are very seldom pre- pared from fruit juice, being more easily obtained from starch, from which the most of the so-called " fruit sugar " and " grape sugar " of commerce are made. Common honey is a mixture of dextrose, Isevulose, dextrin, and saccharose (cane sugar), extracted already formed, from the plant by the bee. Dextrose is less soluble in water than is cane sugar, but does not crystallize readily from solution. When crystallized at moderate temperatures, it contains one molecule of crystal water ; but from hot water or from alcohol it separates in the anhydrous state. It is a little more than half as sweet as sugar, and yields an anhydride, C 6 H 10 5 (glycosan), which is tasteless. Dextrose rotates the plane of polarization to the right 52.5. It is readily fermentable, and reduces alkaline copper solutions (Fehling's solution). It occurs in nature in combination with other organic substances, forming the "glucosides." Laevulose is very soluble in water, but crystallizes from alcohol without crystal water. It rotates the plane of polarization of the light ray very strongly to the left (about 92), but the rotation is variable with the concentration and temperature. It has a very sweet taste, and is very easily fermented by yeast. It also reduces alkaline copper solution. Maltose, see p. 398. Commercial glucose is always prepared from starch as the cheap- est and most convenient raw material. By boiling -starch paste with mineral acids, it is converted into dextrin, maltose, and dextrose, the amount of the last depending upon the time of the boiling. The acid does not appear to enter into the reaction, but merely assists the combination between the starch and water, by which the glucose is formed. This is a process of " hydrolysis." It might be repre- sented by an equation : (C 6 H 10 5 ) n + nH 2 = n (C 6 H 12 6 ), but this does not represent the changes which actually occur, for a f number of intermediate products . are formed ; of these, the dex- trin is never entirely converted into sugar, some remaining un- changed in the commercial glucose. The yield of dextrose is seldom more than 85 or 90 per cent of the theoretical, as calculated from the STARCH, DEXTRIN, AND GLUCOSE 365 above equation. The best conversion is obtained with hydrochloric acid, which is generally used in this country, but in Germany sul- phuric acid is used, as it is more readily separated from the product. In Europe potato, rice, and sago starch are chiefly used for glucose making, but in this country corn starch is exclusively employed. It is used " green," and is prepared on the premises. The corn is steeped from 3 to 5 days in water at 150 F., with the addition of 250 gallons of sodium bisulphite liquor of 8 Be. to each 2000 bushels of corn ; the starch is then prepared as described on p. 356. The process of making glucose varies slightly, according as syrup or solid grape sugar is to be the final product. For syrup, less acid is used, and the boiling is stopped as soon as a test with iodine gives a port- wine color. This may leave a large amount of dextrin in the product. For solid dextrose, the boiling is continued until alcohol* causes no precipitate to form in a test portion of the liquid. For the conversion, the starch is stirred with water in a tub, to form a " milk " of about 20 Be. Sometimes a part of the acid is added to this milk, and the mixture warmed to about 38 C. It is then pumped in a small stream into the boiling dilute acid (1 to 3 per cent acid) contained in the converter, the rate of inflow being so regulated that the boiling of the acid liquid is not interrupted. The converter may be an open vat of wood, lined with lead, and provided with stirring apparatus and steam coils. But open con- FIG. 86. verters are now abandoned nearly everywhere in favor of closed converters (Fig. 86). These are usually made of cast iron, cop- per, or wood, strong enough to withstand a pressure of 5 or 6 atmospheres. Steam at 25 to 30 pounds pressure is admitted * Starch and dextrin are precipitated by alcohol, but dextrose is not. 366 OUTLINES OF INDUSTRIAL CHEMISTRY through the perforated copper pipe (A). The starch milk is pumped in through the copper pipe (B) [the dilute acid having been pre- viously introduced through (D)], the air vent (V) being opened at this time, while the pressure is kept at 25 pounds. As soon as the converter is full, the air vent is closed, and the pressure is raised to 30 pounds for about 40 minutes, or until the iodine test shows that the conversion is complete. For syrup, the average time elapsing from the beginning of the starch introduction to the discharge of the converter is about 1 hour and 10 minutes, and the density of the liquid about 16 Be. ; for grape sugar, about an hour and a half is necessary, with the above pressure and amount of acid. The liquid is now cloudy, and cannot be clarified by filtration. The FIG. 8T. valve (0) is opened, and the liquid is blown through the pipe (C) into the neutralize?. The converter is provided with a waste pipe (F) for cleaning purposes. The neutralizer is a tank (Fig. 87) provided with an effective stirring apparatus (A, A). Immediately after the converter liquid has been received into the neutralizer it is treated with sodium carbonate solution,* introduced through the sprinkler (B), to remove the excess of acid. It is left very slightly acid to litmus, a pinkish lilac color being about right. If made alkaline, the syrup becomes colored in the char filtration, and if too acid, it has a turbid appearance. Much of the dissolved gluten is precipitated during the neutralizing, and forms a greenish drab scum. The liquid, called "light liquor," is then run through bag filters to remove suspended impurities, and the clear, amber-colored liquid is then run through bone-char filters, displacing the "heavy liquor" * In Europe powdered chalk is often used to neutralize the sulphuric acid, the precipitate of calcium sulphate being separated from the liquor by filter-pressing. STARCH, DEXTRIN, AND GLUCOSE 367 for which the filters have previously been used. About 8000 gallons of "light liquor" is run through 16 tons of bone-char, which has been used to clarify about 3500 gallons of "heavy liquor.' 7 The filtrate is colorless, or faintly amber-colored, and has a slightly acid reaction. It is now concentrated in the Yaryan triple effect evapo- rator to a density of 27 to 28 Be., when it forms the "heavy liquor" above mentioned. The bone-char in the filter is freshly calcined, dusted, and "tempered" with acid, and washed with water. The wash water is removed by compressed air, and the filter is filled with the heavy liquor. After standing about an hour, the outlet pipe is opened, and the filtrate runs out in a slow stream, while more unfil- te.red liquid enters. The flow is secured by the hydrostatic pressure of the liquid entering the filter from a tank elevated above it. The filtrate is practically colorless, and has a very faint odor. It is con- centrated in a vacuum pan to a gravity of 40 to 44 Be. (1.375 to 1.43 sp. gr.). During this evaporation a small amount of a solution of sodium bisulphite (8 Be.) is added to the syrup to bleach it, and to prevent any tendency to fermentation, or to become brown when heated. The syrup, composed of maltose, dextrose, and dextrin, is known in commerce as " glucose " ; the name " grape sugar " is applied to the solid product obtained by carrying the conversion further. Grape sugar forms a compact mass of waxy texture, but containing no separate crystals of dextrose. A method for the production of crystallized glucose (dextrose) has been devised by Behr, in which a concentrated glucose solution is allowed to stand at about 35 C. in contact with some crystals of pure anhydrous dextrose, until a large part of the dextrose separates as a mass of crystals. By running through a centrifugal machine, the uncrystallized syrup is thrown off, leaving the pure crystals. If glucose is dissolved in hot concentrated methyl alcohol, on standing the solution deposits crystals of pure anhydrous dextrose. The bone-char niters* used for glucose are cast-iron cylinders, built up in segments. As commonly constructed (Fig. 88) one holds about 16 tons of bone black. In the bottom is a perforated grating (A), covered with burlap, on which the char rests. Beneath this grating is the outlet pipe (B), which is carried up outside the filter to the level of the top of the char when the filter is full. By this r arrangement no liquor flows from the filter until the char is entirely covered, the liquor filters slowly and with less tendency to form channels, and the char does not pack nor become clogged. On one * Similar filters are used for filtering sugar, oils, etc. In large sugar refineries they hold from 30 to 40 tons of bone-black. 368 OUTLINES OF INDUSTRIAL CHEMISTRY side, near the bottom, is a manhole through which the exhausted char is removed. In the top is another manhole for introducing the char, and also an inlet pipe (C) for (f If 1 the liquid to be filtered, another (D) for steam, and an air vent (E). A pipe (G) serves for the introduction of compressed air, to assist in forc- ing the liquor or wash waters through the char when emptying the filter, and for running off the overflow of wash waters when boil- ing out the char. A branch (F), placed in the outlet pipe directly below the filter, permits connection with steam through (H), or with a hot water pipe (J), to be used in washing the char; it also connects with a waste pipe (L), through which the waste liquors can be run off. The inlet pipe (C) is so ar- ranged that it may be connected by means of a rubber hose with the pipes supplying the "light liquors" (N), "heavy liquors" (P), wash waters (S), or tempering acid (T). The outlet pipe (B) is also connected in the same way with pipes leading to the storage tanks for the filtered syrups and "sweet water." Below the lower manhole runs an endless belt which receives the spent char and conveys it to the revivifying kilns. The bone-black is made by charring bones in retorts, and then crushing to grains about 2 or 3 mm. in diameter. When new it has a velvety black or brownish color, and often contains traces of tar and other impurities. After it has been used a few times, the grains become rounded, and many of the impurities are washed away. The syrup first run through the filter is completely decolorized by the action of the char; but after a time its decolorizing power is impaired, and the filtrate begins to show a faint yellow color. Finally it runs so deeply colored that no advantage is gained by filtration. Then the light liquor remaining in the filter is displaced by water (usually condensed water) ; when the gravity of this wash water falls below 10 Be., it is collected in a special tank as " sweet water," * until the gravity falls to 1 or 2 Be. Then boiling water is * The " sweet water " is used to wash the bag filters, or it is added to the " light liquors." STARCH, DEXTRIN, AND GLUCOSE 369 introduced through (F) at the bottom of the filter, and run out through (G) at the top, and then to the sewer, as long as any matter can be washed out of the char. The washed char is drained, and then "steamed down" by steam from (D) to displace the wash waters. It is then shovelled out through the lower manhole onto the conveyer, and carried to the kilns where it is revivified, i.e. its decolorizing power is restored. It is dried by passing over tubes heated by waste gases from the fur- nace. The dry char passes automatically into narrow vertical retorts of cast iron kept at a full red heat. The lower ends of these retorts project below the furnace, and end in sheet iron tubes into which the hot char passes, and is cooled before it is exposed to the air. At the bottom of each tube is a valve which automatically discharges a certain quantity of the char at regular intervals onto a belt conveyer running below the kiln, and which carries the revivi- fied char to revolving reels, where it is sieved to remove the fine particles before returning it to the filter. The fine char ("spent black ") falling through the sieve is of no further use, and is sold to the fertilizer maker. In order to replace this constant waste as fine dust, about 200 pounds of new char is run into the filter with each charge. Much new char at a time is undesirable, since the tarry matters in it tend to color the syrup. After revivifying, the char is boiled one-half an hour in the filter with hydrochloric acid ; then it is drained through (F), and the acid washed away with condensed water. The char is now ready for use. The life of the char in glucose making is about 3 months of continuous service, and during that time it is revivified about once in every 3 or 4 days. Glucose is not so freely soluble in cold water as is cane sugar, nor is it so sweet. When the glucose is to be used for syrup, some manufacturers have tried to increase its sweetening power by add- ing a small quantity of saccharine, an intensely sweet organic sub- stance. But this is probably not practised to any great extent. Considerable discussion relative to the healthfulness of glucose as a food has been aroused at times ; but when properly made, it is improbable that it is in any way injurious to health. Dextrose belongs to that class of sugars which are capable of fermentation, with the formation of alcohol, water, and carbon dioxide. Because of this, glucose is often added to wine and beer wort before fermenting, in order to increase the percentage of alcohol in the beverage. In alkaline solution, glucose has a very strong reducing action, and finds some use in the arts for this pur- pose ; i.e. for the reduction of indigo to the soluble form known as 2B 370 OUTLINES OF INDUSTRIAL CHEMISTRY " indigo white," in the dye vat. It is also extensively used in the manufacture of confectionery, jellies, preserves, medicines, and table syrups. Being a thick, heavy liquid, glucose syrup is much used as a thickening agent in many industries and to give body to many extracts and decoctions in pharmacy. Since it is a neutral sub- stance, odorless and colorless, it is a favorite adulterant for thick liquids, such as extracts of logwood, tannins, and natural dyewoods. Dextrose can be made from cellulose (C 6 H 10 5 ) rt , the conversion being effected in the same way as when starch is used; but it is more difficult and less complete with dilute acid. It is thus possible to make sugar from sawdust or old cotton rags ; but it is not now, and probably never will be a profitable process. REFERENCES Die Chemie der Kohlenhydrate. R. Sachsse, Leipzig, 1877. Die Starkefabrikation. F. Stohmann, Berlin, 1879. Starch, Glucose, and Dextrin. Frankel and Hutter, Philadelphia, 1881. Report on Glucose by the National Academy of Sciences to Commissioner of Internal Revenue. Washington, 1884. (Government Printing Office.) Die Starkefabrikation, Dextrin- und Traubenzucker-fabrikation. L. von Wag- ner. 2 te Auf. Braunschweig, 1886. (Vieweg.) Die Fabrikation der Starke, des Dextrins u.s.w. K. Birnbaum, Braunschweig, 1887. (Vieweg.) Handbuch der Kohlenhydrate. B. Tollens, Breslau, 1888. Manual of Sugar Chemistry. J. H. Tucker. 3d Ed. New York, 1890. Fabrication de la Fecule et de L'Amidon. J. Fritsch, Paris, 1892 (?). Die Starke-Fabrikation. B. von Posanner, Wien, 1894. (Hartleben.) Die Starke-Fabrikation u. die Fabrikation des Traubenzuckers. F. Rehwald. 3 te Auf. Wien, 1895. (Hartleben.) Zucker- und Starke-fabrikation. Otto. Essai des Farines. Cauvert. Die Fabrikation der Kartoffelstarke. O. Saare, Berlin, 1897. (Springer.) CANE SUGAR Sucrose or cane sugar, C^H^On, is found in many plants, but usually in association with other substances which render its ex- traction difficult and unprofitable. The presence of dextrin, glu- cose, "invert sugars " (dextrose and Isevulose), and dissolved mineral salts in any considerable quantity, prevents the crystallization of much of the sucrose. The commercially important sources of sugar are sugar cane, Saccharum officinarum, L., sugar beet, Beta vulgar is, L., sugar maple, Acer saccharinum, Wang., and the date palm, Phoenix dactylifera. The sorghum plant, Sorghum vulgare, Pers., CANE SUGAR 371 contains considerable sugar, and although much experimenting has been done, owing to its varying content of sugar and its large per- centage of gums and dextrin, it does not afford a satisfactorily crystallized product. Maple sugar is only of special value for its peculiar flavor as a crude sugar. If refined, it loses this character- istic taste and is not distinguishable from ordinary cane sugar. Date palm sugar is produced in India as a low grade crude sugar ; it is known as "jaggary " and is shipped for refining. The popular term " sugar " was originally used to include all substances having a sweet taste ; hence the names, cane sugar, fruit sugar, sugar of lead, etc. But now the name is restricted to sucrose as obtained from cane or beets. The chemical term " sugar " includes a large class of bodies belonging to the carbohydrates. Sucrose is a crystallized body, soluble in one-half its weight of cold water, and in much less hot water. Its specific gravity is 1.593. It forms salts called sucrates, with certain metallic bases, such as potassium, calcium, barium, and strontium, and on this fact depends the use of lime, baryta, and strontia for recovering sugar from molasses. The sucrose derived from the various sources is identical in all cases, though the raw sugars differ somewhat in flavor and color, owing to the nature of the impurities they contain. The sugar cane and sugar beet supply nearly all the sucrose of commerce. The former grows only in those climates which are warm and moist, with intervals of .hot, dry weather; the most of the supply comes from the West Indies, the Philippines, Java, the Sand- wich Islands, Brazil, and Louisiana. Sugar beets thrive best in a temperate climate and are extensively raised in Germany and France. Extensive experiments in raising them have been made in this country, and there seems to be 110 obstacle in the way of climate or soil to their cultivation ; but it appears that under the present conditions of the sugar industry there is more profit for the farmer in other crops. In the growing plant, the only sugar present is glucose, the sucrose not being secreted until the plant reaches maturity. Anal- ysis of the ripe cane gives the following average : Sugar 18.% Fibre 9.5 Water 71. Analysis of the ripe cane juice shows : Water 80.% Sucrose 18. Glucose 0.30 Gums (Albuminoids) 1.40 Mineral Salts . . 0.30 372 OUTLINES OF INDUSTRIAL CHEMISTRY But, owing to the imperfect extraction of the juice, and to losses during its evaporation and clarification, the actual yield of sugar is much less than the analysis would indicate. Usually from 16 to 20 per cent of the juice is left in the " begasse" i.e. the waste cane pulp. The preparation of raw sugar from sugar cane may be con- sidered under four heads : (a) extraction of the juice; (6) clarifica- tion ; (c) evaporation ; and (d) separation of the crystals. (a) Extraction. The cane is stripped of its leaves in the field and taken to the mill, where it is crushed and as much as possible ifh ifh of the juice is expressed. This must be done very soon after cut- ting, or fermentation begins and much sugar is lost. The mills (see Fig. 89) consist of two or three horizontal rolls from 30 to 60 inches in diameter, so set that their axes are parallel, and either at the vertices of an isosceles triangle (as in the figure), or in the same perpendicular. The rolls are set in adjustable bearings. When there are three rolls, the cane passes between the top roll (T) and first bottom roll (B), and then between the top and the second bottom roll (D), which are set closer together, so that it is crushed twice. It is usually passed through two or three mills, and about 60 or 70 per cent of the juice extracted. It is customary in Louisiana to use shredder machines. These consist of toothed wheels, revolving at different speeds, which cut and break the cane into a soft, pulpy mass before it goes to the mills. This increases the yield of juice to a little over 75 per cent of the total content of the canes. The crushed cane, coming from the extraction mills, is generally macerated in about 10 or 12 per cent of cold or hot water, to which a little milk of lime has been added, and is then again passed through the mill. This gives an additional increase of 2 or CAXE SUGAR 373 3 per cent in the yield of juice. The expressed juice is caught in a trough under the mill and is run off ; the begasse or " trash " is burned under the boilers. The furnace must be large and a forced draught is used to keep them white hot. Diffusion methods for extracting cane juice, similar to those used for sugar beets (p. 376), but at a temperature of 90 C., have been tried, but, excepting on a few plantations in Louisiana, with no great success, since the refuse needs much handling and drying before it can be burned, and an abundant supply of water is necessary. (6) The bits of cane floating in the juice when it comes from the mills are removed by straining through wire screens. The juice also contains organic acids, nitrogenous bodies, and invert sugar in solution, which are very susceptible to fermentation. To remove these, the juice is defecated. It is passed through a heater, placed in the vapor pipe of the vacuum pan, and then into the defecator tanks, which are heated by a steam coil. Here milk of lime is added in such proportions that the acids are almost neutralized and the juice left very slightly acid to litmus. The lime, aided by the heat, coagulates the albumin and part of the gummy matters. The liquid is rapidly heated to boiling, which causes the coagulum to rise as a scum, usually about 2 inches thick and consisting of lime salts, holding all the suspended impurities mechanically entangled in it. After standing one-half an hour or an hour, the scum begins to crack and is skimmed off; or the juice is drawn off from beneath it. The scum is run into scum tanks, where it is mixed with more lime and with sawdust to assist in the subsequent filter-pressing by making the cake more porous. The filtrate is mixed with the juice from which the scum is decanted, and the whole is then ready for evaporation. Calcium acid phosphate is sometimes used instead of lime for defecation, but not generally. The juice contains gummy matter and other impurities, which interfere with the crystallization of the sugar, somewhat, but they cannot be removed entirely, since no cheap, non-poisonous material is known that will coagulate all the gums. Defecation is probably the most important step in sugar- making, since on its successful working depends in a great measure the amount and quality of the sugar produced. (c) The process of evaporation of the juice has been greatly improved in recent years in the larger sugar houses. By the old method it is boiled down in open pans until the mass begins to "grain," i.e. to crystallize, and then it is emptied into shallow tanks where it is stirred while cooling. The mixture of crystallized 374 OUTLINES OF INDUSTRIAL CHEMISTRY sugar and ^ molasses is then filled into hogsheads; holes are bored through the ends of the casks, which are then placed on end, in a rack, for several weeks, and the molasses allowed to drain out into a receptacle underneath. The holes are then plugged and the hogs- head of sugar is sent to market. The best grades of sugar made in this way are called muscovado; they are light brown in color and contain from 87 to 91 per cent of sucrose. This process is now but little used, and only in the less progressive countries. Probably no planter can derive any profit from muscovado sugars in the present state of the industry ; there is too much invert sugar produced, together with coloring matter formed during the boiling. Low grade sugars are produced in this way, especially the jaggary sugars. The molasses from muscovado sugar was formerly used as table syrup, and some is still so used. Concrete sugars are made by evaporating the juice directly to a hard mass in a special pan called a " concretor," no attempt being made to separate the crystals from the molasses. In all the more modern sugar houses, the juice is evaporated in vacuum pans. It is generally concentrated in a triple effect apparatus, until the solution contains about 50 per cent solids, and the separation of crystals is about to begin. It is then trans- ferred to a simple vacuum pan, called the " strike pan," where the evaporation is continued slowly under high vacuum ; the object is to build up the crystals on the crystal points. (d) When the grain has reached the desired size, the mixture of crystals and syrup, which is called " masse-cuite" is emptied into storage tanks, where it cools somewhat. It is then run into cen- trifugal machines which separate the molasses from the sugar. The latter is called the " first sugar " and is at once packed for market. When of good quality, these centrifugal sugars are light colored and contain 95 to 97 per cent 'pure sugar. Sometimes the juice is treated with sulphur dioxide in the defecators, and the sugar, which is then nearly white, is called " plantation granulated." The molasses separated from the first sugar is called first molasses and contains 45 to 50 per cent of sucrose. It is diluted and defecated with lime or with calcium acid phosphate, and the clarified syrup is reboiled in the vacuum pans to obtain a " second sugar." This is slow to crystallize, and the concentrated syrup is allowed to stand from 3 to 7 days in a room kept at a temperature of 60 C., until the crystallization is complete. The mass is then " centriffed," yielding a "second" or "molasses" sugar, and 'second" molasses. This sugar is of variable quality, and may be sent to market for what it will bring, or it may be dissolved CANE SUGAR 375 in water and the syrup added to the juice going to the vacuum pan. The second molasses contains about 40 per cent sugar, which it does not pay to recover. It is sometimes fermented for making rum or alcohol ; or, since it contains a high percentage of carbona- ceous matter, it is often injected into the furnace in a fine stream, where it has a certain fuel value. A small amount is used for feed- ing cattle. It is not suitable for use as a table syrup or for culinary purposes ; but a small amount of the first molasses is used in this way. SYNOPSIS OF RAW SUGAR MAKING FROM SUGAR CANE Cutting and Stripping in Cane field (Shredders) Mills 36 to 40 per cent Begasse Furnaces i 60 to 70 per cent Juice. 1 Defectors 1 1 -I Bag Filters or Scum Filter-presses | Filter-press Press Liquor Press Cake Multiple Effect " Strike " Vacuum Pan Centrifugals First Molasses (Defecators) Vacuum Pans First Sugar If iled blank " If " boiled to grain Wagons to " Hot Room " (3 to 7 days) Centrifugals Second Molasses | (Rum Used for \ Feeding Cattle [Fuel Second Sugar 376 OUTLINES OF INDUSTRIAL CHEMISTRY The preparation of raw sugar from beets is an extensive indus- try in Europe. It consists in the following operations : (a) wash- ing and slicing the beets ; (b) extracting the juice ; (c) clarifying it ; (d) evaporating it ; (e) separating the crystals ; (/) treating the molasses. (a) The beets are washed in long troughs, each containing a revolving shaft which carries pins set in the form of a screw. These push the beets along against a stream of water flowing through the trough, and by rubbing them against each other, loosens the sand and loam, which are carried away by the water. The beets are then cut into slices, from 0.5 to 1 mm. thick, by a machine con- taining revolving knives. (b) The juice is now usually extracted from the sliced beets by the diffusion process. The chips are put into vertical iron cylinders, and systematically digested with water at a temperature of 60 C. The digesters are arranged in batteries of ten, and between each two is a " juice warmer " or " calorisator," to maintain the tempera- ture of the apparatus. These are similar in construction to the economizer of a Feldmann's apparatus, and consist of narrow brass pipes surrounded by a steam jacket. When the chips are exhausted, they are removed, the digester refilled and made the last of the series. Fresh water is admitted to the tank containing the most nearly exhausted chips, and passes into the others in succession, finally leaving that most recently filled, as a sugar solution contain- ing nearly as much sucrose as does the original beet sap ; all but 0.5 per cent of the sugar is extracted. About 150 parts sugar solu- tion are obtained for every 100 parts, by weight, of beets. The spent chips are rich in nitrogenous matter and are often pressed and dried for cattle food ; or they are returned to the field for fertilizing. The process of diffusion depends upon osmosis. When the vege- table cell is surrounded by water, or by a sugar solution of less density than is the sap, the sugar and other crystallizable substances are displaced by the water and pass through the cell walls, while the colloid bodies (gums, albuminoids, etc.) are, for the most part, re- tained by the membrane. Thus the juice obtained by diffusion is much purer than that obtained by other means. Sometimes the beets are rasped to a soft pulp in machines simi- lar to those used in making starch from potatoes. The juice isjhen expressed in hydraulic presses or between rolls. In the maceration process the rasped pulp is systematically lixiv- iated with water, while in other methods centrifugal machines are used to extract the juice. CANE SUGAR 377 (c) The juice is clarified in much the same way as is that from sugar cane. After passing through a sieve to remove coarse sus- pended impurities, the juice is defecated with lime to neutralize the organic acids and to coagulate the albumin and mucus. Any excess of lime is removed by forcing carbon dioxide into the liquid after the neutralizing. The precipitate of calcium carbonate with coagu- lated albumin, etc., is removed by filter-pressing. The clarified juice is then treated with sulphur dioxide to bleach any coloring matter. Care is necessary, in both these saturation processes, to leave the juice very slightly alkaline, otherwise inversion of the sucrose may be caused. (d) The evaporation of the clarified juice is carried on in two stages, by the use of triple effects and a strike pan, much in the same way as is that from sugar cane. The syrup may be " boiled to grain," in which case sugar crystals are formed in the strike pan ; or it is " boiled blank," by which a clear, thick liquid is obtained, which deposits sugar crystals on cooling. The first method is gen- erally employed and gives the largest yield of sugar; but a very pure syrup is required. If the syrup froths badly during evaporation, a small amount of butter or other fat is introduced. (e) The mixture of molasses and sugar is separated in centrifugal machines as described on p. 374. The raw sugar so obtained is very similar to the first sugar from cane. (/) The molasses is boiled down for a second sugar and second molasses as already described. The latter contains over 40 per cent of sugar which cannot be crystallized. This is now generally re- covered by treating the molasses with quicklime or strontium hy- droxide in excess. A tricalciumsucrate, C 12 H 2 20 n 3 CaO, is formed, which may be washed with alcohol to remove the non-sugar sub- stances ; or it may be separated from the diluted syrup as a precipi- tate, and filter-pressed, leaving the impurities in solution. It is then powdered and mixed with water to form a paste ; this is either used instead of lime for defecating the fresh juice, or it is decomposed by passing carbon dioxide into it. In either case, the calcium precipi- tates, leaving the sucrose in solution. In the strontium process, a hot, concentrated solution of strontium hydroxide is added to the molasses ; on cooling, crystals of the diffi- cultly soluble mono- or di-strontium sucrate are deposited. These are separated by filter-pressing and used to defecate fresh beet juice ; or they may be decomposed with carbon dioxide to remove the stron- tium and set the sugar free. 378 OUTLINES OF INDUSTRIAL CHEMISTRY Beet sugar molasses contains a large amount of potassium salts, especially sulphate, which prevent the crystallization of a part of the sugar content. These are sometimes removed by adding aluminum sulphate, thus forming an alum with the potash salt. The alum is then eliminated by subjecting the molasses to dialysis, the potash salts passing through the membrane and the sugar remaining. Beet sugar molasses also contains certain nitrogenous bodies (amines?) which impart a very unpleasant odor and taste, rendering it unfit for table use. But it is nearly free from invert sugar and glucose, and so large amounts of lime may be used in defecating, without injury to the sugar. When heated with glucose, lime colors the product quite deeply. In this country, the tariff on raw sugar is adjusted according to its color, without regard to the actual amount of sucrose. Since some of the better grades of centrifugal sugars are nearly as white as the refined article, the law is sometimes evaded by mixing in a small quantity of the deeply colored second molasses. The color is merely on the surface of the grain, and a simple washing with water or dilute syrup in a centrifugal machine is sufficient to remove a large part of it. SUGAR REFINING Raw sugar derived from any source is more or less deeply colored and impure, and must be refined to yield the pure white sugar for consumption. It would seem that, on economical grounds, the refin- ing should be done at or near the place where the sugar is produced. But at present the refineries are not in the same countries that pro- duce the raw sugar ; indeed, they exist solely to remedy the errors and careless work of the raw sugar maker, or to circumvent unfavor- able import duties levied on the refined sugar. Sugar refining is, in theory, a simpler process than the prepara- tion of the raw sugar, but it requires great care and attention to de- tail, as well as much expensive machinery. It consists in dissolving the crude material, separating the impurities, and recrystallizing the sugar. A refinery needs a frontage on navigable water and ample dock and storage sheds. An abundant water supply for condensers, for washing purposes, for melting the sugar and for boiler use, is absolutely necessary. A large refinery, capable of treating 900 tons of sugar per day, will use about 1,700,000 gallons of water daily ; of this, about 1,000,000 gallons is used in the condensers of the vacuum pans. The next largest consumption is in washing the char filters. On the ground floor of the refinery are the melting tanks, in each CANE SUGAR 379 of which usually 16,000 pounds of sugar can be dissolved, to form a syrup of 1.25 sp. gr. and containing 55 per cent solids. If a centrifugal * or artificially colored raw sugar is to be used, it is first dumped into elevators which carry it to the washing plant. There it is mixed with a syrup and some cold water, and the thick magma passed into centrifugal machines, where the syrup, carrying most of the superficial coloring matter and some of the glucose, gums, and dirt, is thrown off. This leaves the raw sugar about 99 or 99J per cent pure ; it is then sent to the melter. The syrup goes to the melter later, and is mixed with a lower grade of sugar. The melter is heated by closed steam coils, contains an effi- cient stirring apparatus, or mixer, and has a false bottom, to retain coarse impurities, such as straw, bits of cane, leaves, sticks, and stones. In starting the day's work, it is customary to begin with the purest sugar, e.g. the centrifugal, and after a certain amount of this has been dissolved and pumped away, to melt a less pure sugar, e.g. the muscovado; then the temperature is raised, and molasses and poor concrete sugars are put into the melter ; next come the syrups from washing the raw sugar, together with various syrups from the refining process ; these are followed by the various scums and " sweet waters " (wash waters) of the refining. The melter is filled about one-third full of water at 170 F., the stirrer put in motion, and the first charge of sugar dumped in ; after 15 minutes it is dissolved, and the liquor, varying in color from a light straw color to dark brown, is pumped directly to the " blow- ups." The blow-ups are defecators, capable of holding one melt (16,000 pounds of sugar). They are heated by closed steam coils, and each has a perforated coil, through which air is forced to agitate the liquor. The temperature is kept at 160 F. for centrifugal sugars, but lower grades must have more heat. This defecation is intended to remove the gums, organic acids and impurities (amines, etc.), and any fine suspended dirt. The materials used are lime, alum, clay, blood, or other form of albumin, soluble phosphates, and often fine bone-char. Sugars which contain but little glucose will bear a large quantity of lime, without risk of darkening the color. Liquid blood is often used, about 4 gallons being necessary for each blow-up. The coagulated blood rises to the top as a scum, entangling the impurities, which are thus separated from the liquor. Soluble cal- cium phosphate (acid phosphate) is now much used instead of blood, * Centrifugal sugars, as distinguished from concrete or muscovado sugars, are those from which the molasses has been separated by the use of centrifugal machines. 380 OUTLINES OF INDUSTRIAL CHEMISTRY the amount being about one-half of one per cent of the weight of the sugar. The mixture is agitated for about 20 minutes, and then exactly neutralized with lime, when a flocculent precipitate separates, carrying with it the gums and suspended matter. After the defecating material has been added, the temperature is raised to 212 F., and the air blast turned on for about 20 to 30 minutes. When a number of deep cracks appear in the scum, the reaction is ended, and the liquor is drawn off. From the blow-ups the defecated liquor passes into bag niters, from which the iiltrate must run perfectly clear, or the sugar will not be white. The bags are similar to those described on page 11. They are suspended in a closed room, about 12 by 6 by 8 feet, fitted with an open steam coil, by which the bags are heated to 180 F. be- fore the liquor is allowed to run into them. The first runnings are muddy, and are refiltered. When it runs clear, the liquor is col- lected in tanks placed above the char-filters. The bags finally become clogged with mud, which is very slimy, and the filtration is very slow, but is usually allowed to continue for about twenty hours. Then the bags are flushed with " sweet water," which is drawn out by a suction pipe, and returned to the defecators. The bags are then flushed with hot water, until the liquor draining from them contains only 2 per cent of solids. They are then turned inside out, in a tank of hot water, to wash off the soft mud, and are finally thoroughly washed with clean water and dried. The mud washed from the bags contains about 20 per cent sugar, and is sent to special tanks, where, after further dilution with water, lime is added until the liquor is strongly alkaline, when it is filter- pressed. The clear syrup from the filter-press is used to flush the bag filters and to mix with the melting water for raw sugar. The mud in the filter-press is washed with hot water, the wash waters, constituting the " sweet waters," being used for diluting and flush- ing. The mud, still containing about 2 per cent of sugar, which it does not pay to recover, is thrown away. The clear, straw-colored syrup from the bag filter is now run into the char filter. These are very similar to those used for glucose (Fig. 88, p. 368), but are larger, being 16 feet deep and 10 feet in diameter. The bone-char is in grains, which pass a No. 16 sieve, but remain on a No. 30 sieve. Finer grains clog the filter, and coarser ones have less action on the coloring matter in the syrup. The char is washed with hot water before the syrup is run in, but it is not "tempered" with acid, as is the case in glucose filtering. About 1 pound of char is used for each pound of sugar melted, and it takes 6 hours to fill CANE SUGAR 381 the filter before the filtrate begins to run. After revivifying, the char enters the filter at about 150 F., and the liquor is filtered at the same temperature. After some time the filter becomes clogged, and it is often necessary to use compressed air to force the liquor through the char. At first the syrup is water white, but later it becomes col- ored, and finally the char is "spent," and must be revivified. The char is washed with hot water, and the wash waters are saved until they contain only 2 per cent of solids ; below this they are thrown away. This cleansing of the char requires about 20 hours. It is then revivified, as described on page 369. The filtered syrup then goes to the vacuum pans, which are of copper, about 12 feet high and 10 feet in diameter, a "goose-neck" connecting each pan with the condenser. A pan full of syrup is called a "skipping." For granulated sugar, the syrup is run in until the steam coil is covered, and the boiling is carried on at 160 F., until grains appear; then more syrup is added, slowly, and the grains grow until the desired size is reached. Tests are taken from time to time, by means of the "proof stick," a solid brass rod pass- ing through a stuffing box and projecting into the interior of the pan. In one side of the rod, near the inner end, is a small cavity, about one-half inch deep. When the rod is pulled out until this cavity is outside the stuffing box, 2 or 3 cubic centimeters of syrup mixed with crystals is obtained. Thus small samples are readily obtained at any time, without interrupting the vacuum ; and from the appearance of these samples, the sugar-boiler judges of the prog- ress of the evaporation. The time required to complete the process is from 2 to 3 hours. When the grain is large enough, the vacuum pumps are stopped* and air is slowly admitted to the pan. The bottom valve is then opened, and the magma of sugar and syrup drops into coolers, or mixers, directly beneath, and is stirred while cooling, to prevent the grains agglomerating. The sugar and syrup are separated in cen- trifugal machines. The former is washed in the centrifugal, to remove adhering syrup, and is then dropped into a storage bin, from which it is carried by a belt conveyer to the granulator. This is a long, rotating cylinder of iron, set at a slight incline, and heated by steam. By passing through this hot tube, the sugar is thoroughly dried, while the rotation prevents the grains sticking together. It then passes through a series of sieve reels, which usually separate the grains into three or four sizes, the commercial sizes being packed in barrels for market. The syrup from the centrifugals is reboiled with more fresh 382 OUTLINES OF INDUSTRIAL CHEMISTRY syrup, or, if its color is too deep for this, it is sent back to the char filter, after which it is boiled to grain for soft sugars, the tempera- ture in the vacuum pan being 110 to 125 F. These soft sugars are "centriffed," but not put through the granulator, and are boiled to a finer grain than is the granulated. In many cases they are redis- solved and converted into granulated sugars. The syrup from them is amber colored or brown, and is barrelled for table syrup or for manufacturing purposes. SUGAR REFINING Raw Sugar Warehouse Elevators Mixers Centrifugals Sugar Raw s 1 Bins yrup Mel ters Blow Bagf -ups liters Scums ("Mud") Washing free from sugar liquor Removing mud from bags Syrup Heating tanks Bone-black ("Char") Filters shii Mud blow-ups Washing bags for | next day's use Filter-press I Dry mud Thin liquor, put to various uses. Washing liquors Vacuum pans from Char | j Mixers Thin liquor Char to Kilns Triple effect Centr fugals Hea\ 1 ugar | ry liquor Syrup S 1 Returned to Reboiled Bins Char filter for sugar Centrifugal Granulator l' : Dryer Barrel syrup Soft I sugar Barrels CANE SUGAR 383 The loaf sugar of commerce is made by running the magma of syrup and fine crystals from the vacuum pan into conical moulds where it is allowed to stand for some time. A further crystalliza- tion of sugar takes place which cements the grains together, while the uncrystallized syrup drains off through a small hole opened in the point of the cone. A little water is poured on the surface of the sugar, and, percolating down through the mass, displaces any syrup remaining. This draining is slow, and it is now customary to place several of the cones in a centrifugal machine, with their points towards the outside of the drum. The syrup and wash waters are forced through the mass, which is left as a dry, hard conical lump, the " sugar loaf " of trade. AVERAGE ANALYSES OF SUGARS RAW SUGAR. CANE SUGAR. GLUCOSE.* WATER. ORGANIC MATTER. ASH. Good centrifugal . . 96.5 0.75 1.50 0.85 0.40 Poor centrifugal . . 92.0 2.50 3.00 1.75 0.75 Good muscovado . . 91.0 2.25 5.00 1.10 0.65 Poor muscovado . 82.0 7.00 6.00 3.50 1.50 Molasses sugar . . 85.0 3.00 5.00 5.00 2.00 Jaggary sugar . . . 75.0 11.00 8.00 4.00 2.00 Manilla sugar . . . 87.0 5.50 4.00 2.25 1.25 Beet sugar, 1st . . 95.0 0.00 2.00 1.75 1.25 Beet sugar, 2d . . . 91.0 0.25 3.00 3.25 2.50 REFINED SUGAR. Granulated sugar . . 99.8 0.20 0.00 0.00 0.00 White coffee sugar . 91.0 2.40 5.50 0.80 0.30 Yellow X C sugar 87.0 4.50 6.00 1.50 1.00 Yellow sugar . . . 82.0 7.50 6.00 2.50 2.00 Barrel syrup . . . 40.0 25.00 20.00 10.00 5.00 REFERENCES A Treatise on the Manufacture of Sugar from the Sugar Cane. Peter Soames, London, 1872. (Spon & Co.) Guide pratique du Fabricant de Sucre. N. Basset, 3 vols., Paris, 1875. Manuel pratique de Diffusion. Elie Fleury et Ernst Lemaire, Paris, 1880. The Sugar Beet. L. S. Ware, Philadelphia, 1880. (Baird & Co.) Manual of Sugar Chemistry. J. H. Tucker, New York, 1881. Die Zuckerarten und ihre Derivate. E. von Lippmann, Braunschweig, 1882. *The term "glucose" includes sugars which reduce Fehling's solution, but are not necessarily optically active. 384 OUTLINES OF INDUSTRIAL CHEMISTRY Trait^ theorique et pratique de la Fabrication du Sucre. Paul Horsin-De'on, Paris, 1882. (Bernard et Cie.) Report on Sorghum Sugar by a Committee of the National Academy of Science, Washington, 1883. Lehrbuch der Zuckerfabrikation. K. Stammer. 2 te Auf. Braunschweig, 1887. (Vieweg u. Sohn.) Handbuch der Kohlenhydrate. B. Tollens, Breslau, 1888. Sugar. A Handbook for Planters and Refiners. C. G. W. Lock and B. E. R. Newlands and J. A. R. Newlands, London, 1888. (Spon.) Die Zuckerriibe. H. Briem, Wien, 1889. Manuel Pratique du Fabricant de Sucre. P. Boulin, Paris, 1889. A Guide to the Literature of Sugar. H. L. Roth, London, 1890. Handbuch der Zuckerfabrikation. 3 te Auf. F. Stohmann, Berlin, 1893. (Paul Parey.) Introductory Manual for Sugar Growers. F. Watts, London, 1893. (Long- mans, Green & Co.) Die Zuckerfabrikation. B. von Posanner, Wien, 1894. La Sucre et 1'Industrie sucriere. Paul Horsm-De"on, Paris, 1894. (Bailliere et Fils.) Handbook for Sugar Manufacturers and their Chemists. G. L. Spencer. 3d Ed. New York, 1897. (Wiley & Sons.) Handbook for Chemists of Beet-sugar houses and Seed-culture Farms. G. L. Spencer, New York, 1897. (Wiley & Sons.) FERMENTATION INDUSTRIES Fermentation is a general term applied to various chemical changes caused by the action of certain substances called ferments. These are of two classes: (a) Unorganized chemical substances, sometimes called enzymes, and including such bodies as diastase, invertase, pepsin, ptyalin, emulsin, etc. Their function is generally to assist in the assimilation of nutritive material by the animal or plant in which they occur, the changes which they cause being some- times of the nature of hydrolysis. (6) Organized bodies or living organisms, which produce very complex changes in the substance upon which they act, probably caused in part by the enzymes secreted by them. The product formed varies according to the kind of organism predominating in the liquid, and the fermentation is distinguished as alcoholic, acetic, lactic, butyric, etc. Of these, the first three are the most important. Organized vegetable ferments may be divided into three classes : (1) Mould growths. (2) Yeast plants, or Saccharomycetes. (3) Bacteria, or Scliizomycetes. These are all capable of growth and reproduction, and associated with the former are the chemical changes called fermentation and FERMENTATION INDUSTRIES 385 putrefaction. It is generally true that alcoholic fermentation is caused by the yeasts, while putrefactive fermentation is due to bacteria; but there are some exceptions. Organized ferments may be reproduced by microscopic spores, which propagate when introduced even in small quantities into a fermentable liquid, and cause the chemical change of a large part of it. Consequently these spores, floating in the dust in the air, find their way into fermenting liquids which, when freely exposed to the air, may, therefore, contain many kinds of ferments. The moulds are thread-like plants, devoid of chlorophyl, and forming a somewhat felted mass called the mycelium. They grow readily upon fruit, damp wood, wet grain, or on the walls of damp cellars and similar places, forming greenish, bluish, or gray vegeta- tions, which emit a characteristic musty odor. They exert an oxidizing action upon organic matter and hydrolyze starch. Since they develop musty or sour odors and taste in the nutrient medium, destroy sugars, and often form coloring matter, they are injurious in fermenting processes. But their presence is mainly due to negli- gence and lack of cleanliness and proper ventilation. The bacteria, splitting ferments, Schizomycetes, are microscopic plants of the lowest order, forming rods, or spiral, thread-like, or rounded cells. These propagate by fission with astounding rapidity, if the conditions are favorable ; if not, some forms develop spores, which may be exposed to extreme cold or to moderately high tem- perature without losing their power of germinating when brought into a proper medium. These spores are scattered everywhere, in the soil, the air, and water; being very minute, they are transported by every puff of wind, and thus readily find access to liquids and moist substances exposed to the air. For their nutriment and propagation they need about the same substances and condition of temperature as the yeasts (see below). They cause oxidation and decomposition, and often putrefaction, in many bodies containing albuminous and nitrogenous material, and the products of these reactions are some- times extremely poisonous. Some of them cause acute diseases in man and in animals. Many of the " diseases " of wine and beer, as well as acetic, lactic, butyric, and other fermentations, are caused by them. Also the production of nitrates and nitric acid in the soil (p. 121) is attributed to the action of bacteria. Bacteria are much more susceptible to the action of antiseptic substances than are the yeasts, but heat and cold affect them less. Thus the process of Pasteurization (p. 392) is not a sure protection against their action. 2c 386 OUTLINES OF INDUSTRIAL CHEMISTRY The yeasts, Saccharomycetes, have great technical importance, owing to the part they take in alcoholic fermentations. Several species are recognized, each playing some particular role in the fer- mentation. Thus Saccliaromyces cerevisice is the particular ferment for beer; /S. ellipsoideus is the chief organism present in fermenting wine, and in any spontaneous fermentation. Yeast consists of an aggregation of plant cells, forming a slimy, yellow mass of peculiar odor, and having an acid reaction. Under proper conditions, these propagate with great rapidity. The tem- perature must be constant at from 20 to 30 C.,* and substances necessary for the growing plant must be present ; these are a fer- mentable sugar, nitrogenous matter, and certain mineral salts such as phosphates and sulphates of calcium, potassium, or magnesium. Air (oxygen) is necessary, especially at first; later it is often ex- cluded to prevent secondary fermentations, by which the alcohol formed is converted into acetic, butyric, or lactic acid. Through alcoholic fermentation the fermentable substance in the liquor is converted into alcohol and carbon dioxide: C 6 H 12 6 = 2 C 2 H 5 OH + 2 CO 2 . But this does not express the true decomposition, for a large num- ber of other substances are formed at the same time, the more im- portant being glycerine, succinic acid, butyl, isobutyl, and amyl alcohols (fusel oil), and various organic ethers. Owing to these sec- ondary reactions, the yield of alcohol is somewhat reduced. When the amount of alcohol formed in the liquid equals 14 to 15 per cent, the yeast can no longer propagate itself, and the fermenta- tion ceases. The presence of certain mineral salts such as borax, mercuric chloride, sulphurous acid, and free caustic alkalies, often retards or prevents fermentation. The fermentable substance in the liquid to be fermented with yeast is generally a sugar, dextrose being the most readily converted ; and it is quite possible that other sugars are first changed to glucose before the real fermentation begins. For example, cane sugar is not in itself readily fermented, but by the action of the invertase secreted by the yeast, it is converted (hydrolyzed) into dextrose and laevulose, which are readily fermented. The invertase is not destroyed in this hydrolysis, and hence there is scarcely any limit to the amount of cane sugar which may be hydrolyzed by a small quantity of inver- tase. Maltose, C^H^On, is also readily converted, by yeast, into fermentable dextrose, and thence into alcohol and carbon dioxide; * A higher temperature is conducive to the formation of fusel oil. FERMENTATION INDUSTRIES 387 or, perhaps the maltose is fermented directly, without the interme- diate formation of dextrose. Starch is not capable of direct alcoholic fermentation, but must first be converted into fermentable sugar. This conversion is easily accomplished by the action of diastase, which changes the starch into maltose. Yeasts are also grouped in two general classes, viz. : top yeasts and bottom yeasts. The former require rather high temperature (15 to 30 C.) for the fermentation, which is very active, the rapid evo- lution of carbon dioxide causing the liquid to bubble violently, and carrying the yeast to the surface. This yeast is used for heavy ales and beer, for alcohol and high wines, and for some wine. Bottom yeast acts at a lower temperature (4 to 10 C.), and the fermentation is slow; the evolution of carbon dioxide is gradual, and the yeast remains on the bottom of the vat. The researches of Pasteur, Reess, Hansen, and others, have thrown much light on the nature and properties of the yeasts. Hansen divides the Saccharomyces into six typical species, as follows : Saccharomyces cerevisice, the beer ferment most commonly em^ ployed in breweries. It may be a top yeast, i.e. floating on the sur- face of the fermenting liquid, or a bottom yeast, according to the conditions existing during the fermentation. Saccharomyces Pastorianus I., a beer ferment which causes an unpleasant bitter taste in beer. It is a bottom yeast, remaining on the bottom of the vat during the fermentation. Saccharomyces Pastorianus II., a top yeast found in beer, but which appears to have no action upon it. Saccharomyces Pastorianus III., a beer ferment causing cloudi- ness and disease in the beer.. It is a top yeast, resembling the last two. Saccharomyces ellipsoideus /., a bottom yeast, the true wine fer- ment. It occurs on the grapes. Saccharomyces ellipsoideus II., a yeast causing the cloudiness in turbid beer. It is a bottom yeast, and resembles the last mentioned above. In addition to the above, Hansen also isolated from a brewer's yeast two varieties, known as Carlsberg Nos. 1 and 2, and closely resembling S. cerevisice. No. 1 yields a beer with less carbon diox- ide than No. 2, and is mainly employed for bottle beers ; No. 2 is used for export beers. All these yeasts ferment glucose, sucrose after inversion, and maltose, but not lactose. Other yeasts are known which ferment sucrose, but not maltose, and still others which contain no invertase, and will not ferment sucrose. 388 OUTLINES OF INDUSTRIAL CHEMISTRY For technical purposes, it has long been the custom to use culti- vated yeasts for alcoholic fermentation; but Pasteur showed that these contain many "wild yeasts," i.e. plants whose nature and ac- tions were either unknown, or are detrimental to the product. Han- sen reasoned from his observations on the effect produced by the eight above described yeasts, that for a uniform quality of product there must be exactly the same kind, or kinds, of yeast employed in each brew. Hence he devised his system of pure yeast cultures, obtained in sterilized nutrient material by propagation from a single plant. Thus a single variety of yeast is obtained, by the use of which the fermentation is more easily controlled. In fermentations at a high temperature, where the amount of alcohol formed is near the maximum, the yeast plant generally dies ; but by low temperature fermentation the propagation of the plant is so rapid that a large excess is formed over the amount needed for the next lot of liquor to be fermented. Hence the brewer has yeast to sell, and at the same time is enabled to preserve the variety un- changed through a considerable period of time. There are three purposes for which the alcoholic fermentation is carried on technically : (a) for the manufacture of the yeast ; (6) for the carbon dioxide formed ; (c) for the alcohol. The first of these is usually associated with the third, and con- sists in growing a pure yeast free from wild yeast and other fer- ments. The process of growth is carefully watched by the aid of the microscope, and the appearance of any injurious variety con- demns the whole lot. Those most generally cultivated are the S. cerevisice and S. ellip- soideus. The cells are filtered out of the liquid in which they are grown, by fine sieves, usually of bolting cloth, and are washed with cold water, filter-pressed, and the cake heavily pressed. It is then mixed with from 25 to 50 per cent of starch or flour and brought into market as " compressed yeast." By drying at a low tempera- ture the plant retains its vitality for the most part, and will grow when put into a fermentable solution. The liquid from which the yeast cells have been filtered is some- times allowed to ferment further until the action ceases ; it is then distilled for alcohol. The yeasts are grown in a filtered extract of malt, and since they require free access of oxygen for their greatest development, it is now customary to force a blast of sterilized air through the fermenting liquid. This hastens the process and in- creases the yield of yeast, but decreases the formation of alcohol so that its recovery is unprofitable. FERMENTATION INDUSTRIES 389 At a low temperature, compressed yeast will keep for a long time ; but in warm, moist air it rapidly decomposes or develops mould growths. Dried yeast is less active than the compressed, but will bear exposure to the air and can be kept for a longer period. The chief use of commercial yeast is for bread making. Fermentation for the carbon dioxide is practically confined to the manufacture of bread. In this a mixture of flour and water is allowed to ferment. The nitrogenous matter in the flour furnishes nutriment, and the starch is partly converted into fermentable sugar by the ferments always present in the flour and yeast. A vigorous alcoholic fermentation begins, liberating a considerable volume of carbon dioxide, which, being retained by the pasty dough, causes the whole mass to swell and become porous. When bread dough is baked, the heat kills the yeast, stopping all fermentation, and at the same time evaporates off the alcohol, and finally it hardens the gluten, dextrin, and starch paste, retaining the porous structure in the mass. Fermentation for the alcohol is a very extensive industry. This may take place without the addition of prepared yeast, as in the case of most wines ; but the germs of the ferment are then derived from the air or are present upon the skins of the fruit, and so when the latter is crushed they are mixed with the juice. In all cases, how- ever, where starch is to be converted into alcohol, malt and yeast are employed. "WINE Wine is fruit juice which has undergone an alcoholic fermenta- tion ; it is most commonly made from grapes. The fermentation is spontaneous and progresses without special attention until the sugar has been converted to alcohol. The fermentable sugars in grape juice are dextrose, Isevulose, and some inosite ; when fully ripe it contains on an average 18 per cent of fruit sugar, in addition to tartaric acid (as potassium bitartrate), malic acid, a little butyric acid, albuminoids, non-nitrogenous matter, and ash. All these vary in quantity according to the kind of grape and the nature of the soil and climate. The grape skins contain tannin (C 14 H 10 9 ), oils, and (except in white grapes) coloring matter (oenocyanin). These all pass into the juice when the grape is pressed. The character of the soil in which the vine grows influences the fruit very materially. It must be light and porous, and contain salts of potassium, lime, magnesium, iron, and sodium, especially sul- phates, phosphates, chlorides, and silicates. Decomposed volcanic 390 OUTLINES OF INDUSTRIAL CHEMISTRY rock, such as granite and lava, appear to furnish the best soil. A warm summer with only a moderate amount of rain is essential for a high percentage of sugar in the juice, and the highest percentage is usually obtained in October in latitude near 40. If the grapes are allowed to hang until overripe, the amount of sugar decreases somewhat, but the wine sometimes has a peculiar bouquet which is much prized. When ripe, the grapes are carefully picked and sometimes sorted into several grades. For the finest wines they are removed from the stems, since these contain an excess of tannin and tartaric acid. They are crushed between wooden rolls or by pounding in mortars, or by treading with the bare feet. The juice is extracted by press- ing, or better in centrifugal machines. It is called " must " and con- tains the soluble matter of the grape. The quality of the wine de- pends in a great measure on the ratio of the sugar to the free acids (tartaric and malic). The most favorable ratio is 1 part of acid to 29 parts of sugar, but the average is about 1 to 16. For red wines it is customary to allow a partial fermentation of the mash before pressing out the juice. The alcohol thus formed extracts the coloring, matter from the skins more thoroughly than it can be directly expressed. White wine is made from white grapes. Through the action of the wine ferment, Saccharomyces ellipsoideus, present on the grape and in the air of grape-producing regions, fer- mentation begins in the must at once. It takes place in two stages : the active fermentation, which lasts from one to three weeks ; and the still fermentation, continuing for several months. The former takes place in open vats or tubs at a moderate temperature (10 to 30 C.). It may be a " bottom fermentation," where the temperature is from 10 to 15 C., or a " top fermentation " at 20 C. or above. The former is generally practised in Northern Europe and produces wines low in alcohol but having a fine aroma or "bouquet." Top fermentation, which is more rapid, seldom lasting more than a week, is carried on in Southern Europe, and yields wine high in alcohol but lacking bouquet. In a few hours after being put into the fermenting vats the clear must becomes turbid and acquires a sour taste and smell ; soon a rapid evolution of carbon dioxide begins and a froth forms on the surface. Some manufacturers expose the must freely to the air and stir it frequently to aerate it, but others exclude the air as much as possible. A moderate amount of aeration, especially at first, is doubtless beneficial ; but towards the end of the active fermentation too much air admission may introduce the acetic ferment, Bacterium FERMENTATION INDUSTRIES 391 aceti. During this fermentation the albuminoids are largely con- sumed by the growing yeast. Finally the active fermentation be- comes slow and the must is now known as " new wine." It is drawn into closed tubs or casks which are filled quite full and the opening loosely closed to prevent the access of the acetic ferment. Here the still fermentation takes place, the time depending largely upon the temperature of the fermenting cellar; the lower the temperature, the less rapid the fermentation. The yeast settles, and as the alco- hol content increases, a crystallization of acid potassium tartrate, together with some calcium salts and coloring matter, takes place, forming as a deposit called argol ; this is the source of the " cream of tartar " of'commerce. When it has become clear, and nearly the whole of its sugar con- tent has been converted into alcohol, the wine is drawn off into large casks. The bungs are closed and the wine allowed to " ripen " for perhaps two or three years. During this process, which is essentially an oxidation, the albuminoids and tannins are largely precipitated, together with some of the coloring matters and other impurities. At the same time the higher alcohols or fusel oil formed during the fermentation combine with the free acids present to form organic ethers which impart the peculiar flavors to wines. In order to hasten the ripening process, the wine is frequently drawn off from the casks and a little gelatine, isinglass, milk, blood, or albumin added each time. This forms a precipitate which drags down the fine suspended matter. Gelatinous silicic acid, kaolin, gypsum, or plaster of Paris are also used for this clarifying. The last two, how- ever, react with the tartrate of potassium always present in the wine, forming potassium sulphate and precipitating calcium tartrate. The former remains in the wine, and since it has an injurious action on the human system, the use of plaster and gypsum is prohibited in some countries. When the ripening process is complete, the wine is bottled and is ready for consumption. The use of pure cultures of yeast for the fermentation of wine has recently been introduced with good results, yielding products which ripen more readily and have good keeping qualities. Wine is subject to various " diseases " due to bacteria and other ferments. Sourness is caused by an acetic fermentation due to too much exposure to the air. Kopiness is the result of mucus fermen- tation. Stale or flat taste and bitterness are produced by a peculiar fungus or plant growth. These troubles may be prevented by care in handling the wine, attention to cleanliness, and by always keep- ing the casks full to prevent the entrance of air. Any shrinkage 392 OUTLINES OF INDUSTRIAL CHEMISTRY through, evaporation or leakage should be replaced with more wine at once. Those diseases which are caused by ferments can usually be remedied in the early stages by heating the wine to about 70 C., which kills most of the injurious germs and renders the wine capa- ble of long keeping and transportation. This process, called Pasteur- izing, does not injure the aroma and other qualities. It is carried out by immersing the bottled wine in hot water, or by running the wine from the cask through long pipes placed in tanks of hot water. Other methods of improving the keeping qualities of wine are the addition of salicylic or boric acid, but these are considered injurious to health and are prohibited in some European countries. A very general practice is to fume the casks with sulphur dioxide and to wash them with sodium bisulphite solution before filling with wine. Sometimes sulphurous acid is added to the wine to act as a preserv- ative. Wine made from grape juice as it is expressed from the fruit is rarely found in market. The juice varies from year to year accord- ing to the amount of rain, sunshine, average temperature, fertiliza- tion and other causes ; thus the proportion of sugar, tannin, acid, etc., changes, and the wines vary somewhat on fermentation. For this reason, must or new wine is " improved." A common method is to mix in the juice of other kinds of grapes or to add new wine of different character. If the must is too high in sugar and low in acid, a sour wine is added until the desired ratio is obtained. If already too sour, it is " Gallized " by adding water and sugar, or " Chaptalized " by neutralizing the excess of acid with marble dust or precipitated calcium carbonate. To make a sweet wine, a con- siderable amount of cane sugar is added. These modifications are restricted by legal enactment in most European countries, and the addition of large quantities of alcohol, glucose, and glycerine (Seheeleizing) is generally prohibited. But in the case of certain heavy Spanish and Portuguese wines, such as Port and Madeira, the addition of rectified alcohol is recognized as legitimate. But such substances as logwood, cochineal, kermes, or other natural or coal-tar coloring matters, are always considered adulterants. Much inferior wine is made by leaching the pulp (" marc ") from the wine-press with water, adding sugar, and fermenting the ex- tract. This gives a cheap wine, much used by the poorer people of France and other European countries. But it must not be sold as a natural wine. Considerable artificial wine is made by mixing water, alcohol, FERMENTATION INDUSTRIES 393 sugar, glycerine, tartaric acid, tannin, fruit essences, etc., to produce a liquor resembling the natural product. Within a few years an industry has been established in France for the manufacture of wine from raisins and prunes. These are macerated in a mixture of water, brandy, sugar, tartaric and tannic acids, and the whole fermented with yeast. The product is colored if desired. Champagne is made from certain sweet white wines. The must is pressed from the grape as soon as possible after picking, and then fermented. The new wine is clarified with isinglass and "im- proved" very carefully by mixing with other wines. A certain amount of cane sugar, mixed with Cognac is then added and the wine bottled (the best corks, which have been soaked in wine, are used) and placed in a room warmed to 24 C. A fermentation takes place in the bottle and the wine becomes highly charged with car- bon dioxide. The amount of sugar added is calculated to liberate enough of this gas to cause a pressure of about five atmospheres in the bottle.* The bottles are placed on the side and left for some months; then they are turned with the cork down, until the sedi- ment collects just above it. The cork is then carefully removed for an instant, until the sediment has blown out. The loss is replaced with liqueur (a solution of cane sugar and aromatic essences in the best Cognac), the cork is replaced and wired in, and the label put on the bottle. It is then ready for market. An imitation champagne is now largely made by forcing carbon dioxide into a sweet, white wine, *to which some liqueur has been added. Besides grape wines, other fermented fruit juices are used as beverages. Of these, the commonest in this country are hard cider and currant wine. These do not keep well unless sugar has been added before fermenting. Palm wine is made in tropical countries from the sap of the palm. Pulke is a drink prepared in Mexico from the juice of certain cactus plants. Kumis is a wine-like drink made from the fermented milk of cows, mares, or goats. The milk sugar is converted into lactic acid, alcohol, and carbon dioxide. It is chiefly made by the inhabitants of the Russian steppes. * From 5 to 8 per cent of the bottles burst. 394 OUTLINES OF INDUSTRIAL CHEMISTRY BREWING Brewing involves alcoholic fermentation, but it differs from wine making in that it is always started by the addition of yeast to the liquid to be fermented. Spontaneous fermentation is not desired, and precautions are taken to prevent it. Beer is a fermented alcoholic drink intended for consumption during the after fermentation, while still charged with carbon dioxide. It is made from sprouted grain (malt), starchy materials, and hops. The malt is generally barley, as this yields the largest percentage of diastase and affords the richest, best flavored beer.* The starchy material is derived from unmalted corn, rice, or other grain. The quality of the water used for brewing is very important as affecting the product. In general, the water should be moderately hard and the salts desired in it are calcium and magnesium sul- phates and sodium chloride. If very much iron is present, the water should be purified ; very soft water is improved by the addi- tion of gypsum. Water containing much organic matter in solution, or an unduly large number of bacteria, should not be used. The processs of brewing may be divided into malting, mashing (including the boiling and cooling of the wort), fermentation, and bottling or barrelling. Malting is now very generally done by separate concerns, except in only the largest breweries. * The process consists in cleaning, softening, sprouting, and drying the grain. During the sprouting, two ferments, diastase and peptase are formed, while the cell walls enclosing the starch are softened and disintegrated so that the inte- rior of the kernel becomes " mealy," thus facilitating the transforma- tion of the starch into sugar. The production of diastase is the chief aim of the maltster. The secretion of this ferment increases as the germination proceeds, until it reaches a maximum, after which it decreases if the germination is not stopped. The amount of diastase is estimated by the length of the sprout or acrospire, and is greatest when this has extended about three-fourths of the length of the grain. The appearance and length of the rootlets also serves as a guide to the experienced maltster. The mode of the formation of the diastase is not yet known, It is a nitrogenous body, easily soluble in cold water and possessing the power to convert very large quantities of starch into maltose, * Wheat, corn, and other grains are occasionally malted for certain kinds of beer. FERMENTATION INDUSTRIES 395 C^HaOu, and dextrin. Since good malt contains a great excess of diastase over the amount needed to convert its own starch into sugar, mixtures of raw grain and malt are allowed to react until the starch of the former is converted into sugar, and then the whole is fermented. The dust, dirt, dead and broken kernels, and foreign seeds are first removed by careful sieving in revolving sieves, the dust and chaff being blown away by a strong blast of air. The grain is then " steeped " by soaking it for two or three days in water at 12 C., in wood-lined tanks or cemented cisterns. It is stirred frequently, and the dead kernels float and are removed. The water extracts much soluble matter, oil, etc., from the grain, and is changed as it becomes colored. The grain increases about 20 or 25 per cent in volume and about 50 per cent in weight, and when a test of a few kernels shows that they are so soft that the skin may be readily removed, the grain is couched by piling in a nicely levelled heap about 20 to 24 inches deep, on the malting floor, which is made of cement and is kept very clean. The room is usually only moderately lighted, and the air is kept moist by frequently sprinkling the grain and floor with water ; a good circulation of air in the room to supply plenty of oxygen to the grain is a prime essential. Great care is taken to keep the tem- perature even, at about 15 to 16 C. Higher temperature tends to cause mould growth and excessive root development. After a few hours the temperature begins to rise within the couch, and, as the grain heats, it becomes moist on the surface ("sweats ") and evolves an agreeable odor. The germination has begun, and very soon the rootlets appear. The time of couching is from 20 to 30 hours, accord- ing to the temperature and time of steeping. The grain is then floored by spreading it with wooden shovels on the floor, in an even layer about 10 inches deep. To prevent its heating too rapidly, it is turned over every 5 or 6 hours, thus bring- ing new grain to the top ; each succeeding day the layer is spread thinner, until it is finally only 4 inches deep ; the grain is sprinkled from time to time to keep it moist. The germination is rapid and must be carefully watched; after from 6 to 12 days, when the acrospire has reached the desired length, the growth is stopped by spreading it in thinner layers ; the moisture evaporates and the germ withers. The " green malt" is then transferred to the drying room, which usually has two floors, made of wire gauze or perforated iron plates. The malt is spread on the upper floor and dried at a temperature of 38 to 50 C. To produce kiln-dried malt, 396 OUTLINES OF INDUSTRIAL CHEMISTRY it is transferred to the lower floor, where it is much hotter, and is dried at 100 C. ; sometimes it is even partially charred. The air in the drying room may be heated by fire gases passing through pipes under the gratings, or by an open fire in the lower part of the room; in this latter case the products of combustion pass through the malt, imparting -a darker color and a peculiar taste to it and to the beer made from it. The character and color of the beer are much influenced by the mode of drying the malt. The higher the temperature, the more diastase is destroyed and the less soluble the protein is rendered. After drying, the rootlets are brittle and are easily removed by passing the malt through cylindrical sieves con- taining rotary brushes. The production of a malt uniform in its properties throughout by the above method is very difficult, while different lots are sure to vary a good deal, according to the temperature and humidity of the air. Consequently, at certain seasons of the year, it was customary to suspend operations. Pneumatic malting has been recently intro- duced, and as it remedies the above difficulties, prevents mould and acidity, is easily controlled, and requires less labor and less floor space, it has replaced the old system in all large malt houses. Two forms of pneumatic malting have been devised. The Galland process consists in placing the softened grain in a rotating drum (Fig. 90), containing along its inner circumference several channels (A, A), covered with wire gauze and opening into the chamber (C) at the end of the drum. A tube (B) of wire gauze extends along the centre of the drum and connects with an outlet pipe (E). Into the chamber (C) a pipe (D) opens, which contains a valve that makes connection with the flue (F), or with the pipe (G), as desired. Air is drawn through coke towers, kept at a constant temperature of about 14 C., and through which water trickles. The air then passes down the flue (H), where it is in contact with a fine spray of water escaping under pressure from the supply pipe (J). It is thus cooled, or warmed, as necessary to the constant temperature of 14 C., and, laden with moisture> passes through (F) and (D) into the chamber (C), and thence into the drum, through the channels (A, A). The drum is filled about two-thirds full with the swollen grain ; and as it rotates about once in 40 to 50 minutes, there is a slow turning over of the whole mass of the grain. The air, entering through (A, A), passes through the mass, and enters the inner tube (B), from which it passes to (E), and thence to the exhauster, which drives it out of the building. Thus the grain is kept at a constant temperature in a moist atmosphere, with a very effective circulation FERMENTATION INDUSTRIES 397 of air, and a constant change of surface of the kernels, which pre- vents undue heating. The grain sprouts as on the malting floor, but there is no handling and consequent breaking and crushing of the kernel, and no opportunity for the development of mould ; since the air is filtered, very few germs are introduced. When the germina- tion has gone as far as is desired, the valve in (D) is changed to cut off the moist air, and connection is made with (G), from which warm, dry air is drawn into the drum, rapidly drying the acros-pire and rootlets. The drums hold from 1J to 5 tons of barley at a charge, and the time necessary for the process is about 8 days. FIG. 90. By the Saladin system, the softened barley is placed in a long tank, having a false bottom of gauze, and provided with a mechan- ical stirring apparatus, travelling from one end of the tank to the other on a movable carriage. This stirrer hangs down into the grain, and mixes it effectively without crushing any kernels. Moist air enters under the false bottom, and passing through the wet grain, escapes into the room, and is drawn away by an exhauster. When the sprouting is ended, warm, dry air is drawn through the malt y as above described. Mashing consists in converting the starch in the mixture of grain and malt into maltose and dextrin, through the action of the dias- tase in the malt, and at the same time extracting, the soluble carbo- 398 OUTLINES OF INDUSTRIAL CHEMISTRY hydrates and nitrogenous bodies. The peptase, going into solution, is supposed to convert part of the albuminoids into peptones and amides, which are readily soluble in water, and constitute a part of the " extract " present in the finished beer. Some of these bodies, however, if present in a large amount, may cause cloudiness in the product, as they are precipitated from cold solution by alcohol. It is generally supposed that by drying the malt at a high temperature these protein substances are rendered less soluble in the mash liquor, and being thus filtered out, the beer is clear and bright. The use of unmalted grain, especially corn or rice, in mashing, is also advocated, * on the ground that it contains no protein matter to cloud the beer. But the real nature and value of peptones in the mash liquor is not yet definitely settled. The most favorable temperature for the action of the diastase is from 60 to 65 C., at which point it rapidly hydrolyzes the starch, and converts it into maltose and numerous dextrins, amylodex- trin, erythrodextrin, and archodextrin probably being intermediate products. About one-fourth of the starch is usually left in the form of dextrin. According to Ost, the large starch molecule decomposes into sev- eral smaller dextrin molecules : mn (C^HaoOio) = n (mC 12 H2o0 10 ). Of these dextrins, some combine with water to form maltodextrin, an intermediate product between dextrin and maltose, which fer- ments very quickly with top yeast. These dextrins are further converted into maltose by the diastase : mCuHaAo + mH 2 = m (C 12 H 22 0,i). A complete conversion of the starch into maltose is not desired for beer, since the presence of the unfermentable dextrin imparts fulness of body and nutritive properties, which are increased by the albuminoids, peptones, and amides. These also keep up a slow fer- mentation after the beer has been drawn into casks or bottles. It is often customary, therefore, to limit the diastatic action by kiln-dry- ing the malt at a high temperature, or by mashing with very hot water at first, or by rapidly heating a part of the mash to boiling. There are two general processes of mashing : the infusion method, generally practised in the United States and in England ; and the decoction method, usually employed in Europe. By the former pro- cess the dry malt is crushed between rolls so that the hull bursts, but * Robert Wahl, Indian Corn in the Manufacture of Beer, U. S. Dep't Agricul- ture, Washington, 1893. FERMENTATION INDUSTRIES 399 it is not ground. It then passes into a large " mash-tub," provided with a cover and an effective stirring apparatus. English brewers mix the malt directly with hot water at 75 C., as it saves time and labor, and the extraction of the malt seeing to be more complete. But this hot water destroys much of the/diastase, and prevents the complete action of the peptase on tire albuminoids, thus leaving them in the beer, where they sometimes cause cloudiness. American brewers usually mix the malt with a little water at 50 to 60 C., and the temperature is kept there for some time, as this is the most favorable temperature for the diastase and peptones to do their work. Then the mash is slowly heated to 70 C., by running in boiling water or free steam. By this slow heating the starch is all converted by the diastase before it is hot enough to form a paste. Some brewers prefer to start with cold water in the mash-tub, and heat slowly to 70. The raw cereal used in the mash is generally ground and mixed with a small quantity of the malt in a special tub; then water at about 38 C. is run in, and after about 30 minutes the temperature is raised to 60 C., where it remains another half-hour, the stirrer being in constant operation. Then the mixture is heated to boiling for an hour, and finally the softened raw grain is run into the mash- tub, where the rest of the malt has been wet with water at 38 C., and the mashing process proceeds as above. Mashing usually takes an hour or more, and the stirrer is kept in constant operation. The product is a liquid called " wort," contain- ing maltose, isomaltose, dextrins, peptones, and amides. The decoction process yields a more concentrated wort, and is generally used where fuel is expensive, and when a full bodied, highly extractive beer is desired. The crushed malt is mixed with twice its volume of cold water in the mash-tub, and then the full amount of water desired is made up by adding boiling water, thus raising the temperature of the mash to 38 C. About one-third of the whole mash is then pumped into the decoction pan (a boiler heated either by free fire or by steam, and having a good stirrer), where it is rapidly heated to boiling, and at once run back into the mash-tub, where the stirrer is working actively. This raises the temperature of the mash to about 50 C. Again one-third of the contents of the mash-tub is heated to boiling in the decoction pan, and run back, heating the mash to 62 C. Another repetition of this process raises the temperature to 70 to 72 C., when the mash is allowed to stand quietly for 30 minutes. The wort obtained by either process is filtered from the husks of 400 OUTLINES OF INDUSTRIAL CHEMISTRY the malt, and other solid residue. When the infusion process is used, the mash-tub generally has a false bottom of perforated copper plate, the holes being sufficiently fine to retain the residue. When the stirrer is stopped, this insoluble matter settles to the bottom, and collecting on the grating, forms a filtering layer which retains the suspended matter, while the wort is drawn off below the false bottom. The first runnings are turbid, and are refiltered. In the decoction process, it is customary to run the mash into a special tub for this filtration. In order to remove all the wort from the residue, a washer called a " sparger" is used. This is merely a large Barker's mill with arms extending to within half an inch of the sides of the mash-tub, and with a row of holes one-twentieth of an inch in diameter, and two inches apart, extending along the back of each arm. The flow of water causes the arms to rotate, and it is evenly distributed. The process is continued with hot water (75 C.) until the washings reach a density of 1 Tw. The filtered wort is next run into the brewing kettle or copper, where it is boiled for some time. This has several objects : (a) It concentrates the wort, which, by the infusion process especially, is very dilute, and about one-fourth of the water must be evaporated. (6) It destroys the diastase, peptase, and any other ferment which may be present, and thoroughly sterilizes the wort. (c) It coagulates and precipitates most of the albuminous matter remaining in the wort. (d) It affords an opportunity of adding the hops, which are boiled with the wort from one-half an hour to an hour. Hops are the female flowers (catkins) of Humulus Lupulus, L. The leaflets contain tannin, while the yellow powder (lupulin, hop meal, or hop flour), attached to the surface of the catkin, contains hop oil, certain alkaloids or bitter principles, and resins. The oil is volatile, and is present to the extent of 0.25 to 0.30 per cent. It imparts the bitter flavor to the beer. If boiled too long, part of this oil is lost. The alkaloids are supposed to give the narcotic char- acter to hops. The resins contain most of the antiseptic principles, which are protective against the lactic ferment, and, to a less degree, against the acetic ferment ; hence more hops are added to lager beer which is stored several months before going to market, than to that intended for immediate consumption. About one pound of hops to 100 gallons of wort is the lowest limit, while as much as 12 pounds per 100 gallons are used for some of the heavy English ales and porters. FERMENTATION INDUSTRIES 401 The best varieties of hops are raised in Bohemia and Bavaria, but they are also largely cultivated in other parts of Germany, in France, and in the United States. After boiling the wort from one to six hours, according to the character of the wort, and of the beer desired, the hop catkins are removed by straining the wort through sieves in a vessel called the " hop-back.' 7 They are then washed, and sometimes pressed, to obtain all the extractive matter. The hot wort is then pumped through a rose or sprayer into a receiving tank placed in a well-ventilated room. It falls for some distance as a fine mist, and is aerated and cooled some 25 to 30. It stands in this tank until a sediment deposits. The wort is still hot, and is drawn off and rapidly cooled* to the temperature of fermentation by running over the Baudelot cooler, or " beer-fall." t This consists of a series of horizontal copper pipes, about two and one-half inches in diameter, placed, one above the other, to a height of ten or twelve feet, and through which cold water or ammonia circulates ; the wort, running over the surface of the pipes in thin films, is quickly cooled to the temperature of the water. Sometimes the flow of wort is inside the pipes, and the water passes over the outside of the beer-fall. From the cooler, the wort passes to a tank, where it is allowed to settle, and the clear liquid is then drawn into the fermentation butts. These are made of oak, and lined with pitch or asphaltum, and hold from 1500 to 3000 gallons. They are set in underground cellars or, more commonly now, in rooms cooled to a constant tem- perature by refrigerating machines; or water, cooled to the tem- perature of fermentation, flows through a coil of copper pipe placed in the butt. A certain amount of pure yeast is added to each tub, the process being called "pitching," and within a few hours the active fermentation begins. In some breweries it is now the practice to add the yeast in the settling tanks ; after a few hours the wort is drawn from above the sediment (consisting of coagulated albuminous matter, dead yeast cells, hops, and other solid impurities), and passes into the fermentation butts, carrying with it enough young yeast cells to cause active fermentation. According as the temperature of the * Lactic or acetic fermentation, which would sour the beer, is apt to take place during the cooling. To prevent infection of the wort by bacteria and wild yeasts, systems for ventilating the cooling rooms with filtered or sterilized air are often used. t This apparatus has generally replaced the old style, shallow cooling pans in which the wort was exposed to the air in a broad layer only a few inches deep. 2D 402 OUTLINES OF INDUSTRIAL CHEMISTRY wort is low (5 to 8 C.) or high (15 to 18 C.) there is a " bottom " or a "top fermentation." The former is used for lager beers, and the latter for ale, porter, and stout. In the bottom fermentation the active fermentation does not begin for 12 to 18 hours after pitching. Then a scum appears on the wort, and is blown into a foam by the escaping carbon dioxide. After three or four days this foam rises to the top. or even several inches above the top of the butt, while its surface is broken by deep cracks. The carbon dioxide escapes over the sides of the butt, and falling to the floor is usually carried away by an artificial draught.* Finally the surface of the foam shows a brown color, and in six or seven days the active fermentation diminishes, the temperature falls, and the yeast settles to the bottom. After ten days the active fermentation ceases entirely, and the new beer is drawn into storage vats, carrying with it some yeast, which sets up an after fermenta- tion; the maltose remaining is slowly decomposed, and substances are formed which improve the flavor. These casks are of oak, coated with pitch inside, and usually holding about 1500 gallons. The temperature during this period is kept low, and air is given free access to the liquor. The yeast grows thriftily, and consumes more of the albumins, so that lager beers are lower in these, and are more stable than top fermentation beers. The time of this storage varies from three to six months. To assist in clarifying it, the beer is usually drawn into " chip casks," in which are shavings of beech wood which have been well cleaned by boiling with sodium carbon- ate. For the same purpose, isinglass dissolved in pyroligneous or sulphurous acid is usually added in the chip casks, together with * The amount of carbon dioxide formed is said to be about equal to the weight of the alcohol. Methods have recently been devised to save this gas for use in refrigerating machines, or for carbonating the finished beer. It is evolved rapidly and regularly for some time, and is collected in a hood let down over the fermenta- tion vat to within a few inches of the surface of the liquid. The level of the gas is gauged by means of a toy rubber balloon, filled with air, which floats on the surface of the gas. The carbon dioxide is carefully pumped from the hood so that no air is drawn with it. It is then purified by passing through water, and then through a solution of potassium permanganate, and finally through concentrated sulphuric acid. It is compressed at about 60 atmospheres, and then passed through cooling coils for condensation. The compressed gas is said to be about 99 per cent pure, and is used to some extent to force the beer through the various pipes from the storage cellar to the place where it is drawn into casks or bottles, thus replacing pumps with their contaminations. It is also used in the cooling machines, being circulated through the coils instead of brine or water. It is very satisfactory for this purpose, since the escaping gas does no harm in case there is a leak. About 2200 pounds of liquid carbon dioxide are said to be obtained from 600 barrels of wort. A. Marcet, J. Soc. Chem. Ind., 1894, 825. FERMENTATION INDUSTRIES 403 some actively fermenting young beer. The yeast cells attach them- selves to the shavings, and the beer is left clear. Top fermentation is usually employed in England, and largely in this country for ales, etc. The fermentation is very active, usually ending in from three to five days, and the yeast is partly carried to the surface of the wort by the rapid evolution of the carbon dioxide. A certain amount of bottom yeast is also formed. The top yeast is removed by skimming, and the beer is drawn into small casks hold- ing from two to four barrels each for the after fermentation. These casks are placed in a cold room, and the process goes on until most of the yeast has been forced out of the bung-hole. The cask is then bunged and allowed to stand until the sediment has deposited, when the clear beer is drawn off into barrels for market. Isinglass or gelatine is often added to assist in settling the sediment. Top fermentation is favorable to the development of other fer- ments, and a high percentage of alcohol is often depended upon to prevent these growths. In order to increase the alcohol and dextrin without increasing the quantity of malt, it is* frequently customary to add sugar or glucose to the wort in the brewing kettle. During the fermentation the contents of the tub are stirred occa- sionally to aerate the wort. The progress of the fermentation is judged by the readings of a hydrometer, and as the density of the wort decreases as the fermentation advances, the process is called "attenuation." The temperature is carefully watched, and not allowed to rise above 18 C. Besides alcohol and carbon dioxide, beer contains glycerine, suc- cinic acid, amides, peptones, and dextrins. Phosphoric, acetic, and lactic acids are also present in a small quantity. All the soluble constituents of the beer, except the alcohol and carbon dioxide, and which give it its nutritive qualities, are grouped together under the name of " extract." English ales, porters, and stouts are rich in extract, but most German and American beers contain only a moder- ate amount of it. Sometimes beer is flavored with bitter substances, such as quas- sia and gentian root ; or ginger or coriander may be added for pun- gency, but this is prohibited in many countries. Bottling or Barrelling. Much of the success with which certain beers meet in commerce is due to the care exercised on this point. The barrels are coated on the inside with brewers' pitch, a mixture of rosin and rosin oil which softens at 50 to 60 C. This prevents the beer from soaking into the staves and extracting color or flavor 404 OUTLINES OF INDUSTRIAL CHEMISTRY from the wood. All barrels, and especially old ones which are re- turned for refilling, should be thoroughly scalded and washed out. If this is not done the beer is liable to sour before it reaches the con- sumer. It is frequently customary to fume the barrels with sulphur dioxide or to wash them with sulphurous acid or bisulphite solution. The practice of adding a certain proportion of calcium or potassium bisulphite to each barrel of beer before shipment is nearly univer- sal. This prevents the development of injurious ferments. Sali- cylic acid is often added to improve the keeping qualities, but with doubtful benefit to the consumer. Bottles must be clean and only the best quality of corks should be used. Bottled beer is usually " Pasteurized " at 60 C. for about an hour. It is very essential that both barrels and bottles should be entirely full, for if an air space is left the beer becomes flat and stale. The quality of beer depends mainly on the purity of the water and yeast employed, and upon the care taken to keep all parts of the brewery exceedingly clean. All vats, tubs, coolers, and pans must be thoroughly washed and scalded immediately after use, and the floors and walls of the brewery must be perfectly clean. Various kinds of beers are recognized in commerce, according to the appearance, mode of preparation, flavor, strength of alcohol and of extract, etc. Ale is a light-colored beer, often rather strong in alcohol, and made by top fermentation with the use of a large amount of hops. Porter is a dark-colored beer, containing much sugary matter and extract. For this, the malt is kiln-dried at such a high temperature that it is partially charred, forming caramel which colors and flavors the beer. Stout is similar to porter, but contains more alcohol and extract. Lager beer is made by bottom fermentation, is rather low in alcohol, and contains a moderate amount of extract. Export lagers are made from stronger worts and contain more alcohol and extract. A special brew made in the spring from very concentrated wort and but little hops is called bock beer or Salvator beer. It contains much unfermented sugar and will not keep long. Berlin weiss-bier is made from a mixture of three parts malted wheat to one of barley malt. It is fermented by top fermentation, and is usually bottled before the after fermentation is ended. Thus it contains much carbon dioxide and foams excessively. It is very light-colored and contains lactic acid. FERMENTATION INDUSTRIES 405 The following table shows the average composition of beers ac- cording to various authors : SP. GR. (17.5 C.) ALCOHOL. EXTRACT. ACIDS. (Acetic, Lactic, etc.) ASH. Vienna lager * .... 1.017 3.70 5.71 0.008 Pilsner lager * .... 1.016 3.43 5.45 0.008 Munich export * .... 1.020 3.94 6.72 0.010 Munich Salvator * ... 4.78 10.67 Berlin Weiss-bier* . . . 1.012 2.82 4.21 Burton pale ale I ... 5.37 5.13 0.16 0.55 Dublin stout XXX t . . 6.78 9.52 0.29 1.40 Milwaukee lager J . . . 1.010 4.28 4.18 0.057 0.196 Milwaukee Bavarian J . . 1.0187 5.06 6.26 0.074 0.346 St. Louis export J . 1.0178 4.40 6.15 0.067 0.312 Philadelphia lager t . . 1.0147 4.29 5.22 0.086 0.241 * Ost, Technischen Chemie, p. 455. t Allen, Commercial Organic Analysis, Vol. II, 2d Ed., p. 92. J Crampton, U. S. Dep't Agriculture, Bulletin No. 13, part 3, p. 282. DISTILLED LIQUORS Distilled liquors are obtained by distilling alcoholic liquids pre- pared by fermentation. They are essentially mixtures of ethyl alcohol and water in varying proportions with minute quantities of organic ethers and higher alcohols. Pure ethyl alcohol may be con- sidered the representative and chief constituent of these liquors. When first distilled they contain neither extractive nor mineral matter, and are much stronger in alcohol than fermented liquors. Alcohol is always prepared on a technical scale by fermenting sugar, which in most cases is derived from starch by conversion with diastase, or from the molasses of the sugar industry. In the United States the materials employed are corn, rye, and barley ; in England, barley, rice, corn, and rye are used ; while in Germany, the potato and molasses are the principal sources. The products obtained from these several raw materials vary somewhat in their character, flavor, and strength. Since the largest possible yield of alcohol is desired from a given amount of starchy material, the latter is so treated that the most complete conversion into maltose is obtained with as little dextrin as may be. This is accomplished by treating the starchy material with malt prepared with the view of obtaining all the diastase pos- sible. For this purpose, the germination is stopped earlier and the 406 OUTLINES OF INDUSTRIAL CHEMISTRY drying temperature kept lower than in the case of malt for brew- ing. The preparation of pure alcohol from corn is carried on abont as follows: The corn, usually degerminated, is ground to a coarse meal between rolls, and a weighed amount of this meal is run into a closed iron digester (called a " cooker ") provided with a stir- ring apparatus. Here it is mixed with water and heated by steam under pressure of two or three atmospheres for an hour or two. It is then blown out into another vessel ; or it may be cooled in the cooker. (The cooling is sometimes hastened by exhausting the air from the vessel by a pump.) As soon as the temperature reaches 63 C., the required amount of ground malt, mixed with a little water, is added and the mass thoroughly stirred. The temperature must not be allowed to go above 63 C., in order that the least pos- sible amount of dextrin may be formed. The resulting wort is drawn off through a sieve to remove the husks of the grain, which are washed with hot water and the washings added to the wort. The latter is then rapidly cooled (to prevent the development of acetic fermentation) and drawn into the fermenting vats. These are very large cylindrical wooden tubs, sometimes 25 feet deep and 20 feet in diameter. A distillery usually has 6 of these tubs, one being emptied and recharged every day. The fermentation of the wort is started by adding yeast, as in the case of brewing ; but for alcohol, the quantity of yeast and the temperature of fermentation are regulated with the view of converting all the sugar into alcohol as rapidly and completely as possible. The legal limit of the time for fermentation is 72 hours, hence the distiller must force the process to convert all the sugar of his wort. Moreover, too slow fermentation is favorable to the development of the acetic and lactic fermentations, with consequent loss of alcohol. The tempera- ture is therefore high, being 20 to 25 C., and a very active top fer- mentation is carried on. But these conditions produce an increased amount of fusel oil. If the temperature rises much above 25 C., a notable loss of alcohol through evaporation occurs. During the final part of the fermentation, a portion of the dextrin in the mash is converted into maltose by the diastase still remaining, and this sugar is then fermented by the yeast. The malt liquor boils and sputters in the tub, but any undue amount of frothing is combatted by sprinkling oil on the surface. To prevent the development of bacteria and wild yeasts, it is now often customary to add a little hydrofluoric acid or alkali fluoride to the mash, after the conversion of the starch by the diastase. It increases the yield of alcohol by preventing these secondary fer- FERMENTATION INDUSTRIES 407 mentations, and tends to reduce frothing. It is also recommended as a disinfectant and germicide for general cleaning purposes in the vats and tubs. When the fermentation ceases, the mash consists of a mixture of slimy, solid matter, with water, alcohol, fusel oil, acids, etc. The amount of alcohol varies from 10 to 13 per cent by volume, and is separated from the other constituents by distillation. This was formerly carried on in simple stills,* heated by direct firing, and connected with a condensing worm. They were intermittent in action and yielded a very dilute distillate, which had to be re- peatedly redistilled to obtain a strong alcohcl; thus, e.g., from a mash containing 10 per cent alcohol, the first distillate contains about 28 per cent alcohol ; by redistilling this distillate, the alcohol percentage is raised to 50 per cent ; by another redistillation it is raised to 70 per cent, and this in turn, yields an 80 per cent alcohol. By many redistillations, an alcohol of 95 per cent may be obtained, but above this redistillation yields no further separation. But the principle of fractional condensation is now employed, and improved stills, with dephlegmation and rectifying apparatus, make it possible to obtain concentrated alcohol by two distillations. And further, the old interrupted working has now given way to continuous processes, by which the inflow of mash and the outflow of exhausted mash (slops) are unbroken. For distilling potato mashes, which are thick and slimy, no continuous acting still has proved successful, and the intermittent Pistorius apparatus, consisting of two connected stills and a de- phi egmator is much used. For distilling wines for brandy, the Savalle apparatus is generally employed. The Coffey still in various modified forms is largely used for grain mashes; the mash| enters the analyzer hot after having passed through the rectifier. From the top plates of the rectifier, the alcohol vapor passes into a copper condensing worm, which empties into a small box with glass sides, through which the density of the liquid may be observed by means of an hydrometer floating in it. The box is locked and sealed by the revenue officer stationed in the distillery, and the distiller has no access to the liquor. It overflows into tanks * The old pot stills are now used for the distillation of certain drinkable spirits (especially whiskey), but they are uneconomical of fuel and time. t By its passage through the still, the mash is entirely deprived of its alcohol, but the non-volatile matter, consisting of fats, protein, undecomposed starch, and other non-nitrogenous bodies, flows continuously from the waste pipe of the si ill. This residue usually contains over 90 per cent water, and is often fed as " slop " to cattle. 408 OUTLINES OF INDUSTRIAL CHEMISTRY where it is gauged by the revenue officer as crude or raw spirits. It contains some aldehyde and fusel oil ; the latter, constituting the greater part of the impurities present, imparts a nauseous odor and taste, and is removed by further purification. The raw spirit is diluted with water and run through a wood-charcoal filter similar in form to the bone-char filter used for glucose ; the charcoal absorbs the fusel oil. Another method (that of Bang and Ruffin) is to treat the alcohol with caustic soda and then with dilute sulphuric acid to destroy the aldehydes ; the diluted alcohol is then agitated with petroleum distillates boiling slightly above 100 C. The petroleum oil probably absorbs the fusel oil. The dilute purified alcohol is then rectified in a still provided with a column or dephlegmator tower, similar to the Coupier still or French column apparatus, Figs. 5 and 6. Savalle's apparatus is largely used abroad. Rectification is an intermittent process, the still being entirely emptied and cleaned before a new charge is introduced. The boilers are very large and are usually made of iron. The products of the distillation are divided according to their character and percentage of alcohol, into : (a) First runnings, consisting of some alcohol, with aldehyde and ethers. (b) Cologne spirit, a very pure distillate, with about 96 per cent of alcohol. (c) Common alcohol, containing about 80 to 95 per cent alcohol. (d) Alcohol No. 2, a weak distillate. (e) Fusel oil. These distillates are separated by the revenue officer, who turns the flow from one receiver into the next, according to the densities shown by the hydrometer floating in a glass box similar to that de- scribed on p. 407, and through which the distillates pass. First runnings are usually sold to chemical works, as are also fusel oils. Cologne spirit and No. 1 alcohol, which generally constitute by far the largest part of the distillate, are sold as such to the dealer. Alcohol No. 2 may be redistilled, but is usually diluted with water to bring the alcohol to about 50 per cent, and is then stored in oak barrels to " age," after which it is usually sold as " whiskey." During the aging the fusel oil in the liquor is broken up or formed into ethers, thus removing the nauseous odor and taste of the raw spirit. The longer the aging, the more complete the removal of the fusel oil and the richer the flavor of the liquor becomes. It also extracts some coloring matter from the wood of the barrel, and thus in time FERMENTATION INDUSTRIES 409 acquires the light reddish-brown shade of the commercial whiskey. But this color is now very generally imitated by adding some caramel. The Coffey still and others on the same principle are well adapted to the production of pure alcohol, or, as it is generally called in England, " silent spirit," since it has no special odor nor flavor to distinguish its origin, as is the case when pot stills are used. In all countries, the manufacture of strongly alcoholic liquors is made a means of raising revenue by the government. Consequently these industries are subject to constant, and often annoying, inter- ferences by the revenue officials, and many burdensome laws are enacted, presumably to prevent fraud. In this country, both the malt and the grain used in the mash are weighed by the revenue officer, the time of fermentation is limited to three days, and the entire process of distillation is conducted under the direct super- vision of the inspector. The amount of crude spirit produced is gauged by the officer, and also the quantities of the several grades of rectified alcohol produced, and these are run directly from the still into storage tanks in the government storehouse. From these tanks it is soon drawn into barrels (which must be new), and each cask is at once gauged by the officers, and the number of gallons of absolute alcohol contained in the liquor, and upon which the tax must be paid, is determined. The cask is then put into the bonded warehouse, where it may remain eight years by the present law, but at the end of four years the tax must be paid. The present tax is $1.10 per proof gallon of 50 per cent alcohol (by volume), or $2.07 per standard gallon (231 cubic inches), of 94 per cent alcohol. The cost of making a gallon of cologne spirit is less than 20 cents. This tax is a heavy burden on many industries which use alcohol for manufacturing purposes, especially in varnish-making and the coal- tar dye industries. The law permitting untaxed alcohol to be used in the arts has not yet been put into operation. In England the revenue tax is much higher than in this country, being 10s. 6d. per gallon of proof spirit.* But the law permits the preparation of "methylated spirit," consisting of 90 per cent alco- hol, to which 10 per cent of crude methyl alcohol (wood spirits, p. 259) has been added. This is free of tax, since the liquor is pre- sumed to be undrinkable, bat serves very well for many technical * Proof spirit is alcohol of such strength that 13 gallons of the spirit have the same weight as 12 gallons of distilled water at 10 C. Proof spirit contains 49.24 per cent of absolute alcohol, by weight. 410 OUTLINES OF INDUSTRIAL CHEMISTRY purposes, and for burning in alcohol lamps. In Germany a similar provision exists, but in addition to wood spirits, a certain amount of pyridine (bone oil) must also be added. This gives the "denat- urated" alcohol a very offensive odor, bat does not injure it for many uses. The fusel oil consists mainly of amyl alcohol, with some butyl, propyl and allyl alcohols. It is always present in crude spirits, and, to a small extent, in the rectified alcohol and liquors. It is gen- erally supposed to have a very destructive action on the health, and its complete removal from liquors has always been insisted upon. But recent experiments* tend to show that, aside from the nauseous odor and flavor which it imparts to the liquor, it has very little, if any, injurious effect on the system. The results ascribed to it are probably due to common alcohol. Fusel oil (amyl alcohol) is used largely in the preparation of the so-called " fruit essences," which are organic ethers, and which are used in ice cream, soda water, sherbets, etc. Alcohol is extensively used in the arts as a solvent ; in per- fumery; for making various essences, tinctures, and extracts in pharmacy ; for vinegar-making ; and in chemical manufacturing for preparing ether, chloral, chloroform, ethyl nitrite, and various ethyl derivatives, especially for use in the coal-tar dye industry. A con- siderable amount is used in museums for preserving anatomical and other specimens. Whiskey is a distilled liquor made from fermented grain mash. The malt having been dried over an open fire, retains an empy- reumatic flavor, which reappears in the product. The mash is prepared as already described for alcohol ; after fermentation it is distilled from a pot still or copper, and the distillate condensed in a worm, without any attempt at dephlegmation. A little soap is often put into the still to prevent frothing. The first product, called " low-wines," is redistilled, and yields foreshots, clean spirit (whiskey), and feints, while spent lees are left in the still. The foreshots and feints are redistilled with the next charge, while the clean spirit is dilated with water to about 50 to 60 per cent of alco- hol, and then put in bond to age until the fusel oil flavor disappears. As a rule whiskeys are now mixed with some silent spirit made with a Coffey still. When first distilled, whiskey is colorless ; but it takes coloring matter from the wood of the casks while aging. Much artificial whiskey is made in this country by " compound- * J. Soc. Chem. Ind., 1891, 312. A. H. Allen. FERMENTATION INDUSTRIES 411 ing." Strong alcohol is diluted with water to a strength of 50 to 55 per cent by volume, colored with caramel, and a very small quantity of essential oils or flavoring substances is added to imitate the odor and taste of the natural whiskey. The empyreumatic flavor is obtained by adding a few drops of creosote to each barrel. Gin contains about 40 per cent of alcohol, and is made from a fermented grain mash in much the same way as alcohol, but the distilled liquor is left colorless, and is flavored by distilling in pot stills with juniper berries, anise seed, coriander, cardamon seeds, calamus root, or fennel. The best gin is made in Holland, at Schie- dam, from rye mash, and is distilled only in pot stills, with juniper berries. Brandy is made by distilling wine, or the fermented juice of other fruit, such as apples, peaches, cherries, blackberries, etc. The best brandy (Cognac) is made by distilling a good quality of white wine, but much inferior stuff is made by distilling low grades of red wine. It is customary to leech the solid residues from wine-pressing with water, and to ferment the liquid so obtained ; this is then distilled for inferior brandy. Cheap brandies are distilled directly from the wine, but fine grades are rectified once or twice. The distillate is colorless, but takes color from the casks. It is also customary to add caramel. Brandy contains from 47 to 54 per cent of alcohol, by volume, and owes its peculiar flavor to oenanthic ether. Pot stills are always used in order to preserve the flavors. Cherry brandy is extensively made in southern Germany, where it is called Kirsch- wasser. Some of the pits are crushed and added to the fermented juice, thus flavoring the product with bitter almond and prussic acid. Imitation brandy is made from grain alcohol by diluting and adding various flavoring matters (oenanthic ether, bitter almonds, catechu, etc.), and coloring with caramel. Rum is made from fermented molasses or megass (macerated crushed sugar cane). It is twice distilled, and the new rum is color- less and has a disagreeable odor, which is removed by treating with charcoal and storing for a long time. It is often colored with burnt sugar. It contains about 55 per cent of alcohol, and its flavor is due to ethyl acetate and butrate. Jamaica rum is said to be flavored by putting sugar cane leaves in the still. Ethyl butrate is made on a large scale, and sold as " rum essence," to be used in making imi- tation rum from grain spirit. Liqueurs and cordials are usually strong alcoholic beverages com- pounded from grain alcohol, with various flavoring essences. They are usually flavored with cane sugar. 412 OUTLINES OF INDUSTRIAL CHEMISTRY Arrack is made by distilling the fermented juice of the cocoanut palrn. It is sometimes flavored with poppy or hemp leaves, or stra- monium juice. A distilled liquor made from malted rice is often sold as arrack. Absinthe is made in much the same way as gin, but is flavored with wormwood. VINEGAR Next to the alcoholic fermentation in technical importance is the acetic fermentation, which is caused by a group of bacteria. These micro-organisms cause the oxidation of the alcohol, probably into aldehyde, and ultimately into acetic acid, thus : 2 C 2 H 5 OH + 2 = 2 C 2 H 4 + 2 H 2 0. 2C 2 H 4 + 2 = 2C 2 H 4 2 - The specific acetic ferment is Bacterium aceti, but the related species, B. Pasteur ianum, B. xylinum, and B. Kutzingianum,, doubtless cause more or less oxidation of the alcohol. For this oxidation the liquid must not contain more than 10 per cent of alcohol, and certain nitrogenous matters suitable for the nourishment of the ferment must be present. The materials used for fermented vinegar are cider, wines, decoc- tions made from malt, beer which has not been boiled with hops, beet sugar solutions, diluted alcohol mixed with malt infusion, and occasionally glucose or molasses. The acetic ferment propagates very rapidly in a liquid containing from 2 to 3 per cent of alcohol, nitrogenous matter, and phosphate of potassium, calcium, or ammo- nium, if the temperature is kept between 20 and 35 C. A thick film, or skin, forms on the surface of the liquid, and finally sinks, owing to its increasing weight, forming the "vinegar mother"; then the formation of acid ceases. If the fermentation is very active after the alcohol is all converted, the resulting acetic acid may itself be attacked and decomposed into water and carbon dioxide. This, however, does not take place if a fresh supply of alcoholic liquor is added. Under the most favorable conditions the ferment cannot live in a liquid containing much more than 13 per cent of acetic acid. In the Orleans process of making vinegar from wine, oak casks of about 300 litres capacity are used. The cask is filled about one-third full of strong vinegar containing some ferment, and about 10 litres of wine (previously filtered through beechwood shavings until clear) are added, and the whole allowed to stand at a temperature of from 25 to 30 C. After about eight days the wine has soured, and another portion of 10 litres of wine is added. This process is repeated until FERMENTATION INDUSTRIES the cask is about half full, when about one-third of the vinegar is drawn off, and the process of adding fresh wine is resumed. This goes on, under favorable circumstances, for several years, until the cask becomes too full of sediment ; then it is emptied, and .thoroughly cleaned by washing and scalding with hot vinegar. The casks have openings at the top for the admission of air, and the fermentation is largely spontaneous. The action of the ferment may be checked if the temperature falls too low ; or if the wine added is very low in alcohol, it may not support the ferment, and the vinegar is decomposed into water and carbon dioxide. The ferment may also be weakened or destroyed by the presence of vinegar eels, Angaittida aceti, a species of micro- scopic worm, which deprives the ferment of the oxygen needed for its propagation. The Orleans process is slow, but the resulting vinegar has a fine flavor and aroma. Pasteur suggested a modification of the above process, in which the ferment is cultivated in a suitable liquid, and the alcoholic liquid is added regularly when the "mother" is well started. When the acid formation becomes slow, the "mother" is collected and washed, and used to start a new fermentation. The " quick vinegar process " is now generally practised for fer- menting malt decoctions, diluted alcohol, or the extract from any fermented mash. The liquid should be clear, and free from any sediment or slime. The fermentation is carried on in tall vats, or casks, about 12 feet high by 5 feet in diameter. These have perfo- rated false bottoms, on which rests the filling of beech wood shavings, reaching nearly to the top of each cask. Over the shavings, a few inches below the cover of the cask, is a perforated wooden plate, through the holes of which short pieces of twine are drawn; 4 or 5 glass tubes are set in this plate, to permit the upward passage of the air. The beech shavings are boiled in water, and then soaked in strong vinegar, before filling into the vat. Their purpose is to spread the liquid into very thin films, so that the oxidation may be rapid. They also serve as points of attachment for the ferment; The liquid to be fermented, a mixture of dilute alcohol and vinegar, is fed in a slow stream on to the top of the cover, through which it percolates, dripping from the ends of the twine, upon the shavings. It comes in contact with the ferment on the shavings, and with the current of air passing up through the mass, and the alcohol is rapidly oxidized into acetic acid. The temperature within the vat rises, causing the air to rise and escape through the openings in the top, 414 OUTLINES OF INDUSTRIAL CHEMISTRY while fresh air enters through holes in the sides of the vat, just on a level with the false bottom, thus causing a continual circulation of fresh air within the vessel. The temperature is shown by a ther- mometer, and is kept as near 30 C. as. possible, by regulating the temperature of the air admitted into the cask. If allowed to go too high, much alcohol is lost by evaporation, and the vinegar is weak. Too rapid an air current also evaporates much alcohol. The vinegar formed collects under the false bottom, and flows out through a siphon. If the liquor does not contain more than 4 per cent of alcohol, it may all be converted by one passage through the vat, but the result- ing vinegar is weak. Hence it is customary to add more alcohol, and run the liquor through the cask again. Or, as is often done, it flows through a series of vats. A very exact regulation of the strength and flow of alcoholic liquid, and of the amount of air admitted, is essential to successful working. Pure air and good ventilation of the room are also neces- sary. Considerable alcohol is lost by evaporation, amounting, even in good work, to about 15 to 20 per cent of that in the original liquid. The air leaving the converters is often washed with water to recover the vaporized alcohol and acetic acid. On an average, the vinegar produced contains about 6 per cent acetic acid, which may be increased to 10 or 12 per cent by proper regulation of the process ; there is, however, a consequent diminished yield of vinegar. The time required to produce finished vinegar is from 8 to 12 days. The amount of alcohol added must be so regulated that the liquid leaves the vat, still containing a very small percentage of unchanged alcohol, for, if it is all converted, the oxidation extends to the acetic acid, and some may be lost through decomposition into water and carbon dioxide. Many accidents cause the process to go wrong, and much care is necessary to secure regularity of product and yield. If vinegar eels appear, it is customary to kill them by adding hot vinegar until the temperature of the vinegar running out of the cask has risen to 50 C. The vinegars made from different sources vary in color, taste, specific gravity, and other properties. Cider vinegar is usually made by spontaneous fermentation of cider in barrels with open bungs. Sometimes "mother" is added to hasten the action. It is yellow or brown in color, has an odor resembling apples, and contains malic acid. Wine vinegar is light yellow or red, according as it is made from white or red wine, that made from the former being considered the FERMENTATION INDUSTRIES 415 better. It contains tartaric acid, and some acid potassium tartrate, with other matters derived from the wine, some of which influence the flavor of the product. It has a particularly agreeable aroma and taste, and is considered the finest for table use. Malt and beer vinegars are brown in color, and contain dextrin and protein, and other extractive matters, together with acetic ether, which impart peculiar odors and flavor to them. They also contain phosphates and other mineral matter. Spirit vinegars, made from diluted alcohol, are nearly colorless, and since they contain little or none of the extractive matter present in fruit or malt vinegars, they lack much of the flavor and odor of these. Sometimes they are colored with caramel, and are often flavored with one or more of the characteristic ingredients of cider, wine, or malt vinegars, and sold under these names. Very weak vinegar will not bear much agitation nor handling without decomposition; it is often the practice to add a certain amount of sulphuric acid, under the pretence of preserving the vinegar when shipped. Good vinegar, however, is never treated in this way by reputable makers. Imitation vinegar is often made from dilute acetic acid derived from wood distillation. This is colored with caramel, and gen- erally flavored with acetic ether ; ' but usually contains no phos- phates, tartrates, nor other substances characteristic of true vinegar. Traces of empyreumatic matter are often present, which may give it a disagreeable flavor. Vinegar is chiefly consumed as a condiment, or used for making pickles. LACTIC ACID A fermentation of some technical importance is that produced by certain bacteria, especially Bacterium acidi lactici, by which sugars are converted into lactic acid : C 6 H 12 O 6 = 2 C 2 H 4 (OH)COOH. These ferments are generally distributed on the surface of grains, fruits, and malt, thus finding access to mashes and worts ; under favor- able circumstances they grow exceedingly rapidly, and cause souring of the liquid. But since they cease to propagate after the liquid contains about 1 per cent of lactic acid, and as this acid is a good protection against the development of other bacteria, while it has but little effect upon yeast, it is often customary to allow the lactic fermentation to take place in connection with the alcoholic, especially in grain mashes for alcohol. 416 OUTLINES OF INDUSTRIAL CHEMISTRY Lactic acid, CH 3 CH(OH) - COOH, is prepared by fermenting a sugar solution, and neutralizing the acid as soon as formed, with calcium carbonate. The solution of calcium lactate is concentrated, and the salt decomposed with sulphuric acid. Lactic acid forms a syrupy liquid which is now used in dyeing and calico printing as a substitute for tartaric and citric acids. An- timony lactate is used in place of tartar emetic in mordanting. REFERENCES The Chemistry of Wine. G. J. Mulder. Translated by H. Bence Jones. Lon- don, 1857. (Churchill.) Lehrbuch der Gahrungs Cheraie. Adolf Mayer, Heidelberg, 1874. (Winter.) On Fermentation. P. Schutzenberger, New York, 1876. (Appleton & Co.) Traite" general des Vins et de leurs Falsifications. Emile Viard, Paris, 1884. (Savy.) Die Bereitung, Pflege und Untersuchung des Weins. J. Nessler, Stuttgart, 1889. The Micro-organisms of Fermentation. A. Jorgenson. Translated by H. T. Brown. London, 1889. Traite" pratique de 1'Art de Faire le Vin. Frederic Cazalis, Paris, 1890. (G. Masson. ) L 1 Art de Faire le Vin avec les Raisins sees. J. F. Audibert, Paris, 1891. Etudes sur la Biere. M. L. Pasteur, Paris, 1876. (Gauthier-Villars. ) Lehrbuch der Bierbrauerei. Carl Lintner, Braunschweig, 1878. (Vieweg.) Gahrungs-Chemie fur Praktiker. Josef Bersch, Berlin. (Wiegandt, Hempel, und Parey.) Vol. I. Die Hefe und die Gahrungs Erscheinungen. 1879. Vol. II. Fabrikation von Malz, Malzextract und Dextrin. 1880. Vol. III. Die Bierbrauerei. 1881. The Brewer, Distiller, and Wine Manufacturer. John Gardner, Philadelphia, 1883. (Blakiston, Son & Co.) The Theory and Practice of Modern Brewing. Frank Faulkner. 3rd Ed. London, 1888. (F. W. Lyon.) Handbuch der Bierbrauerei. Conrad Schneider u. Gottlieb Behrend, Halle a. S., 1891. (W. Knapp.^ Chemistry in the Brewing Room. Chas. H. Piesse, London, 1891. Manual of Brewing. E. G. Hooper. 4th Ed. London, 1891. (Sheppard & St. John.) A Textbook of the Science of Brewing. E. R. Moritz and G. H. Morris, Lon- don, 1891. (E. & F. N. Spon.) La Biere. L. Lindet, Paris, 1892 (?). Les Distilleries. M. Desire" Savalle, Paris, 1881. (G. Masson.) A Practical Treatise on the Raw Materials and the Distillation and Rectification of Alcohol. Wm. T. Brannt, Philadelphia, 1885, (H. C. Baird & Co.) L'Alcool. Albert Larbaletrier, Paris, 1888. (Bailliere et Fils.) A Treatise on Alcohol, with Tables of Spirit-Gravities. Thomas Stevenson, London, 1888. (Gurney & Jackson.) Traite" de la Distillation. J. Fritsch et E. Guillemin, Paris, 1890. (G. Masson.) EXPLOSIVES 417 La Fabrication des Liqueurs et des Conserves. M. Ch. Girard, Paris, 1890. (J. B. Bailliere.) Nouveau Manuel complet de la Distillation des Grains et des M Classes. Albert Larbaletrier et M. F. Malepeyre, Paris, 1890. Les Appareils de Distillation et de Rectification. Emile Barbet, Paris, 1890. (G. Masson.) Traite" de la Fabrication des Liqueurs et de la Distillation des Alcools. P. Duplais, 2 vols., Paris, 1891. (Gauthier-Villars.) Das Flussaureverfahren in der Spiritusfabrikation. M. Maercker, Berlin, 1891. (P. Pavey.) La Rectification de PAlcool. E. Sorel, Paris, 1894 (?). (G. Masson.) Cheinie du Distillateur. M. P. Guichard, Paris, 1895. (Bailliere.) Industrie de la Distillation, Levures et Alcools. M. P. Guichard, Paris, 1897. (Bailliere.) Etudes sur le Vinaigre. M. Pasteur, Paris, 1868. Acetic Acid and Vinegar, etc. John Gardner, London, 1885. (Churchill.) Vinegar : A Treatise on the Manufacture of Vinegar. Win. T. Brannt, Phila- delphia, 1890. (Baird & Co.) Die Essigfabrikation. J. Bersch. 4 te Auf. Wien, 1895. EXPLOSIVES Explosives are chemical compounds or mechanical mixtures which are capable of very rapid decomposition or combustion, upon the application of a shock, or of a small amount of heat. Through the agency of chemical action they suddenly generate large volumes of gas, which is heated to a high temperature at the moment of liberation. Explosives comprise gases, liquids, and solids. Explo- sive gas mixtures will not be considered here, since they have no technical application, though often introducing very dangerous com- plications in certain technical processes. Liquid explosives, except- ing only nitroglycerine, which is seldom used in the liquid condition, have little or no industrial importance, since, being extremely sensi- tive to shocks and heat, they are too dangerous to handle or transport; for the same reasons many endothermic bodies, such as the halogen compounds of nitrogen, and the diazo-bodies are not employed. When the combustion takes place under such conditions that the gases formed cannot readily escape, a very high pressure is suddenly developed, liberating such a great amount of heat that the entire mass is instantly decomposed with explosive violence. In the same way if an explosive is subjected to a sudden and extremely high pressure the entire mass instantly explodes. This latter form of decomposition is called "detonation," and is usually caused by ex- 2E 418 OUTLINES OF INDUSTRIAL CHEMISTRY ploding a small quantity of some violent explosive, such as fulminate of mercury, or silver, in contact with the substance to be detonated. The energy of an explosive is mainly determined by the amount of gaseous products formed by its decomposition, the rapidity of their evolution, and the temperature to \vhich these gases are heated. It has been calculated that the explosion of one cubic kilogram of dynamite, measuring 9 cm. on the side of the cube, occupies ^^QU" ^ a second, while the same weight of ordinary black powder requires y-J-^ of a second. But the volume of gas set free by the dynamite is about 530 litres when reduced to C. and at 760 mm. pressure ; while the gas from gunpowder, under the same conditions of tem- perature and pressure, amounts to about 270 litres. Moreover, the temperature of the gas from the dynamite is very much higher than is that from gunpowder. Nearly all explosions caused by chemical action are merely rapid oxidations of substances containing carbon, hydrogen, or nitrogen. The slower the oxidation the weaker the explosion, while for the most energetic action the combustion must be practically instanta- neous. The speed of the oxidation depends largely on the size of the particles of the explosives, and also upon their composition. Chemically homogeneous substances are usually more powerful ex- plosives than the most carefully prepared mixtures, since in the former the combustion is propagated from molecule to molecule more rapidly. Explosives which decompose suddenly cause a very different result than those which are slow burning. The former, even when exploded in the open air, have a shattering action upon any sub- stance with which they are in contact. They are used in hard rock blasting, especially where large pieces of the stone are not desired, or when the rock is full of cracks or seams ; fewer drill holes are needed, and the rock is shattered for some distance away from the blast. But for military purposes, for quarrying and blasting in soft rock or coal, slow burning powder is preferable to the more powerful dynamite. Gunpowder is a mechanical mixture, and is the oldest and a very important explosive. Tradition assigns its discovery to Berthold Schwartz, a monk at Frieburg, Germany, in the fourteenth century, and it was used at the battle of Crecy in 1346, and again at Augsburg in 1353. It was probably derived from the formula of the " Greek fire " of the Orient. Its constituents are potassium nitrate, sulphur, and charcoal. Since these must be very pure, the manufacturer generally purifies them. Only roll brimstone is used, and this is EXPLOSIVES 419 sublimed in Dejardin's, or other similar apparatus. The flowers of sulphur, which first distill over, are contaminated with sulphur dioxide, and are redistilled with a new portion of sulphur. The purified brimstone is finely ground in ball-mills, disintegrators, or under edge-runners, sometimes with the addition of a part of the charcoal. Bronze balls are used in the mill ; the dust is carefully sifted. The nitre is purified from chloride, or sodium nitrate, by several recrystallizations from pure water, the solution being stirred while cooling in order to separate fine crystals. These are washed with water while in the centrifugal machine, or on a draining platform. They are not usually dried before mixing. Carbon for gunpowder is best obtained from charcoal prepared from light, soft woods, such as willow, poplar, alder, or blackthorn. Young trees cut in the spring when full of sap are preferred. The bark is removed, and the wood stored for about two years until thoroughly dried. It is then carbonized in sheet-iron cases, which are heated in retorts, from which the products of distillation may be collected or not, as desired. The temperature of the carbonization depends upon the kind of powder to be made. For black powder it ranges from 350 to 500 C. ; for brown powder it does not exceed 280 C. When the carbonization is ended, the cases are removed and allowed to cool before they are opened. The charcoal is then sorted to secure uniformity in the product, and is stored for some time before grinding, to allow it to absorb all the oxygen possible ; other- wise spontaneous combustion of the powdered charcoal is liable to occur. Charcoal for black powder contains about 80 to 90 per cent car- bon, 5 to 7,5 per cent of oxygen, and 2 to 3 per cent hydrogen. That for brown powder contains about 70 to 75 per cent of carbon, 20 to 25 per cent oxygen, and 4.5 to 5 per cent of hydrogen. The residue, in each case, is ash. The ground materials are weighed, due allowance being ma$e for the moisture in the nitre, and then put into the mixing machine; this consists of a gun-metal cylinder revolving around a horizontal shaft, which turns in a direction opposite to that of the cylinder, and carries arms which stir up the mass as they revolve. After mixing, the "green charge" is sifted again, moistened with from 5 to 6 per cent of water, and spread on the bed of the incorporating mill. This is an edge-runner, having steel rolls, which travel on a bed of bronze or stone. The rollers are usually about 15 inches wide, and weigh 3 tons each. They make 7 or 8 revolutions per minute, and the 420 OUTLINES OF INDUSTRIAL CHEMISTRY usual time of grinding a charge is from 3 to 6 hours. Travelling wooden scrapers push the charge from the sides of the bed into the path of the rollers. The charge is kept moist during the incorpo- rating, but explosions, the causes of which are not easy to discover, occur frequently. Consequently, the mill is arranged to run as nearly automatically as possible, and the workmen leave the build- ing during this process. The "mill-cake" coming from the incorporating mill is lumpy, and is reduced to tine powder by passing through the "breaking down machine." This consists of two sets of gun-metal rolls, placed one over the other, the upper set being corrugated and the lower pair smooth. These rolls are set in movable bearings, which allow them to separate slightly, in case of any excessive pressure. The mill- cake is thus reduced to a fine meal, containing from 1 to 4 per cent of moisture. This is put into wood-lined metal fiames, or simply spread between ebonite plates, and pressed in an hydraulic press to the desired density, usually 300 to 450 pounds pressure per square inch being applied. The press-cake so formed may be as thick as desired, for special purposes, but is usually about one-half an inch thick. For common powder, this compact, dense press-cake is put through the granulator, which consists of two or three pairs of grooved or toothed rolls of gun-metal; between them are inclined oscillating sieves, which sift the material from one pair of rolls and deliver the coarse particles to the next pair, where they are again crushed. Under the whole series of rolls are two sieves, the upper having a No. 10 mesh and the lower having a No. 20 mesh. These remove the coarse particles, and the fine grains are run over several finer meshed sieves, to obtain various grades of sporting powder, and dust. The grains thus separated are glazed; i.e. the powder is placed in revolving wooden drums, in which, by rubbing against each other, the sharp corners and edges are worn off. Powder which has been heavily pressed is hard and dense, and takes considerable polish. For common grades, it is customary to add about one ounce of graph- ite to every 100 pounds of powder in the glazing drum. This coats the grains and fills the pores, thus protecting them from moisture and atmospheric influences. After glazing, the dust is removed by sifting, and the powder is dried. It is spread in wooden frames having cloth bottoms, and these are placed in racks in a room through which a current of warm air is circulating, and which is kept at a constant temperature of 35 to 60 C., according to the nature of the powder. The temperature is raised slowly, and, after drying, the powder is cooled slowly, the en- EXPLOSIVES 421 tire process requiring about 24 hours. Sometimes the powvler is dried in a stream of cold air which has been passed over calcium chloride, sulphuric acid, or quicklime, to dry it before it enters the dry-room. Many schemes have been devised for drying powder in vacuum, but they have not proved practical. After drying, the powder is given a final glazing, and is sifted to remove the dust, and is then ready for use. Special forms of powder are used for particular purposes. The coarse grains are used for blasting, the fine grains for small arms, while the fine dust is not desirable for any purpose, except in fire- works. Pebble and prismatic powders are chiefly used for ordnance. The press-cakes of the " green charge " are cut into pebbles, which are glazed and dried like common powder, but the drying must be slow. For the prismatic powder, the green charge is pressed in hexagonal moulds to form short prisms, from f to If inches in diame- ter. With the solid prism the burning surface continually dimin- ishes as the combustion progresses, thus decreasing the rapidity of the gas evolution. For use in heavy ordnance, it is best that the evolution of gas (t. e. the combustion), shall be slow at first, until the inertia of the projectile is overcome, and then an increasing evolu- tion of gas is desired. By perforating the prism with one or more holes the combustion extends along the perforations into the interior, hollowing out the grain and continually increasing the burning sur- face, with consequent increased evolution of gas. Thus less strain is exerted on the gun, and greater velocity imparted to the ball. Fine grain powders burn much more rapidly than do coarse grain, and the strain on the gun is proportionately greater. The United States army standard black powder is composed of: Potassium nitrate, 75 per cent by weight. Carbon (as charcoal), 15 per cent by weight. Sulphur,- 10 per cent by weight. The combustion of this powder in an unconfined state may be represented as follows : 2 KN0 3 + 3 C + S = 3 C0 2 + N 2 + K 2 S .* But when exploded in a confined space under pressure, the reac- tion becomes very complex, and many other substances are formed. According to Debus, t it is represented by the following equa- tion : 8 KN0 3 + 9C + 3S = 2 K 2 C0 3 + K 2 S0 4 + K 2 S 2 + 7 C0 2 + 4 N 2 * C. E. Munroe, Rec. U. S. Naval Institute, 4, 21. t Annalen der Chemie und Pharmacie, 265, 312. 422 OUTLINES OF INDUSTRIAL CHEMISTRY According to Guttmann,* some fifteen products are formed by the free burning of jpowder, of which the chief are potassium sul- phate, potassium carbonate, carbon dioxide, nitrogen, and carbon monoxide. The products of the combustion consist of about 57 per cent solids and 43 per cent gases, by weight. The pressure exerted by the explosion of powder entirely filling a closed space is about 44 tons, or nearly 6,400 atmospheres per square inch. Brown or cocoa powder is much used for military purposes, espe- cially for heavy guns. Its combustion is slower and smoke less dense than with black powder. It contains about the following in- gredients : Potassium nitrate 79 percent. Sulphur 2 to 3 " Carbonaceous matter 18 " " Moisture to 1 " The carbonaceous matter is partially charred rye straw, which, it is supposed, is carbonized by exposing it to superheated steam until it takes on a light brown (chocolate) color. Owing to incom- plete carbonization of the straw, the charcoal is readily combustible, and can be used with a very small proportion of sulphur. Mining powders of several grades are made by varying the pro- portion of nitre, sulphur, and charcoal, according as a quick or slow burning explosive is desired. These are generally coarse-grained, and are cheaper than the finer, rifle powders. Sometimes they are made with sodium nitrate instead of with potassium nitrate, but this salt is somewhat hygroscopic and may absorb sufficient moisture to damage the powder. Potassium chlorate has been used instead of nitre, but it is more expensive and more dangerous in mixing and handling, owing to its sensitiveness to shocks. A white gunpowder was formerly made from potassium chlorate, potassium ferrocyanide, and sugar. It possessed no special advantages over common black powder. The nitrates of barium and ammonium have been used to replace the potassium salt, but find no general use, owing to their greater cost. A so-called "amide powder" is made in Germany, which contains a large amount of ammonium nitrate mixed with potassium nitre. It is claimed to form very little smoke. Gunpowder ignites at about 300 C., and the rapidity of combus- tion increases with the increase of pressure. Hence the importance of a tamping " in blasting. * Industrie der Explosivstoffe, p. 309. EXPLOSIVES 423 Nitrocellulose or gun-cotton is cellulose hexanitrate, C 12 H 14 4 (N0 3 ) 6 , when pure (assuming the simplest possible formula for cellulose, n(C 6 H 10 O 5 ), where n = 2), but the commercial grades contain some lower nitrates. It is a true chemical compound, but is very unstable. It is easily made by dipping clean cotton fibre into a mixture of concentrated nitric and concentrated sulphuric acids : (C 6 H 10 5 ) 2 + 6 HN0 3 - C 12 H U 4 (NO,). + 6 H 2 * It was formerly considered a true nitro-body with the formula C 6 H 7 5 (N0 2 ) 3 , but it is now regarded as a. nitrate of cellulose. Its decomposition on explosion is represented by the following equa- tion : C 12 H 14 4 - (N0 3 ) 6 = 7C0 2 + 5CO + 6]Sr + 8H+3 H 2 O. The amount of gas set free by the explosion of one kilogram of gun-cotton, reduced to C. and 760 mm., calculating the water as vapor, is 859 litres, which is a greater volume than that from any other explosive. Since the amount of heat liberated by its decom- position is 1074 calories, f the products of combustion are entirely gaseous and enormously expanded. Gun-cotton was discovered by Schoenbein in 1846, and attempts were made in several countries to use it for military purposes. But several spontaneous explosions of magazines occurred, which soon caused it to be given up. In 1865 Abel showed that these explo- sions were caused by the presence of acid within the fibre. Cotton fibre is a long, hollow tube, much twisted and shrunken, into which the acid penetrates and is only removed with great difficulty, if the fibre is not cut and ground to a fine pulp. Abel improved the pro- cess of manufacture, and now gun-cotton, when properly made, is considered one of the safest of explosives. Owing to the cost and difficulty of its preparation, its use is mainly confined to military purposes and the production of high grade " smokeless powder." The cotton used is " waste " from cotton spinning, and contains dirt and grease, besides natural gums and oil. To clean it, it is first given a " soda boil." About 200 pounds of cotton are boiled for eight hours in a solution of 35 pounds of caustic soda in 250 gallons of water. The lye is drawn off and the cotton boiled for eight hours in clean water, after which it is washed in a centrifugal machine with hot water, until free from alkali. It is then spread on wire netting and dried in a room kept at 180 F. To remove the knots and to loosen up the fibre, it is run through a " picker ma- * Guttmann, Industrie der Explosivstoffe, 318. t Berthelot. 424 OUTLINES OF INDUSTRIAL CHEMISTRY chine," after which it is again dried for eight hours at 225 F., while a strong draught is maintained through the dry-room. The cotton is then nitrated in the " dipping room " in cast-iron tanks, each about one foot deep by 10 by 16 inches at the top, and surrounded by a water-jacket, through which cold water flows. The great volume of fume liberated during the nitrating is carried away through a hood above each dipping tank. The acid used is a mixture of one part concentrated nitric (sp. gr. 1.50), with. three parts of concentrated sulphuric (sp. gr. 1.85). The dry cotton is weighed out in one pound bunches and about one-third of a pound is thrown into the dipping tank at one time, and quickly submerged in the acid by means of a steel fork. When the whole pound has been added, the mass is allowed to stand quietly while the other tanks are similarly charged. In about ten minutes the cotton is raked out of the acid, and placed on an iron grating, against which it is pressed by means of a lever carrying a cast-iron plate, the excess of acid flowing back into the tank. The cotton, still retaining about 11 times its weight of acid, is then placed in an earthenware crock, which, is covered and set in a trough of cold water for 24 hours. During this period of digestion, the acid completes the conversion of the cotton into cellulose nitrate. The acid in the dipping trough is replenished and a new charge of cotton is introduced. The gun-cotton is transferred from the crock to a centrifugal machine, where as much as possible of the spent acid is thrown off, and is generally returned to the acid makers. The gun-cotton is then quickly plunged, in small quantities at a time, into a large vat full of cold water. The contact of the strong acid still in the cotton, with the water, is liable to generate much heat, and to avoid danger only small quantities of cotton are introduced at a time, and thor- oughly stirred by a paddle wheel, to dissipate the acid through the large volume of cold, water and thus keep down the temperature. After washing in the vat, the gun-cotton is again placed in the cen- trifugal machine and washed with fresh water. Then it is boiled with dilute sodium carbonate solution for eight hours; or sometimes it is boiled with water only, for two or three days. The boiling is done with steam coils, which are surrounded with very fine wire gauze, at a distance of two or three inches, to prevent the gun-cotton coming in contact with the hot pipes. The gun-cotton is again washed in the centrifugal machine and then boiled in clear water for eight hours, and the centrifugal washing repeated. It may then be dried at a temperature not exceeding 40 C., if it is to be used in ^v EXPLOSIVES loose form. For military use and for smokeless powder, it is not dried, but is put into a pulping machine or " hollander," similar to those used for paper pulp, p. 506, in which it is cut and torn, under water, into short, loose fibres. The pulp is then transferred to the washing machine, or "poacher," which contains a paddle wheel; here it is washed with pure water until it is free from all traces of acid. It is then tested with a mixture of ether and alcohol, for soluble cellulose nitrates, which must not be present. The contents of the poacher are then mixed with lime-water, precipitated calcium carbonate, and caustic soda in small quantities, and is then drawn directly into the moulding presses, where the excess water is pressed out, and the gun-cotton formed into cakes sufficiently hard to bear handling. These are then pressed heavily in a hydraulic press to form very compact cakes of the size and shape desired. For most military purposes, the press-cakes contain from 16 to 30 per cent of moisture ; these will explode with the same energy as when dry, and are considered much safer to transport and handle. They are exploded by detonation with a fulminate of mercury cap. Cellulose hexanitrate is insoluble in water, alcohol, ether, and chloroform. It is somewhat soluble in acetone and in ethyl acetate, and swells to form a jelly-like mass with nitrobenzene. It resembles the original cotton in appearance, but is slightly harsher to the touch. It is not exploded readily by shocks, but explodes with great violence when detonated. When unconfined, it burns rapidly with a large flame. When not washed entirely free from acid, it is liable to spontaneous decomposition and explosion. Lower cellulose nitrates are prepared for making collodion, cellu- loid, and smokeless powder. These nitrates are called pyroxyline, and consist of the di-, tri-, tetra-, and penta-nitrates. They are solu- ble with greater or less readiness in ether and mixtures of alcohol and ether. The degree of solubility depends upon the strength of the acid used, and the temperature and time of the nitrating. Some- times nitre, instead of nitric acid, is mixed with the sulphuric acid in making pyroxyline. Nitroglycerine, C 3 H 5 (N0 3 ) 3 , was discovered in 1847, but no at- tempt to make practical use of it was made until about 1864, when Nobel established a factory and began its production on a large scale. But very soon a number of explosions occurred when handling and transporting the liquid, and means were at once sought to render it less dangerous. In 1866 Nobel invented dynamite, by absorbing the liquid nitroglycerine in diatomaceous earth, and this is now the form in which most nitroglycerine is utilized. 426 OUTLINES OF INDUSTRIAL CHEMISTRY The name nitroglycerine is a misnomer which was given under the erroneous supposition that it contained the nitro group N0 2 , but its true constitution was later shown to be glyceryl trinitrate. It is easily made by the action of concentrated nitric acid on glycerine : C 3 H 5 (OH) 3 + 3 HN0 8 = 3 H 2 + C 3 H 5 (N0 8 )3. Since the nitric acid must be very concentrated for this reaction, it is customary to mix it with concentrated sulphuric acid ; this ab- sorbs the water which is formed during the nitration and which would otherwise dilute the acid too much. The glycerine used is the very concentrated dynamite glyc- erine (p. 333) of at least 1.262 sp. gr. The proportions of acid used are about 3 parts of nitric acid (93 to 95 per cent HN0 3 ) and 5 parts .of sulphuric acid (96 per cent Hj,S0 4 ), the mixture being well cooled before use. The glycerine must be run into the acid, in order that it may be nitrated rapidly. It would be difficult to thoroughly mix the acid into the glycerine, owing to the viscosity of the latter, especially when cold. Mowbray, who prepared the nitroglycerine for the Hoosac tun- nel in 1868, was the first to use cold compressed air to stir the mixture. His apparatus (Fig. 91) con- sists of a circular wooden trough full of cold water, in which are earthenware pitchers, each containing 17 pounds of mixed acid. Glycerine was dropped into the acid from jars placed on the shelf above, while a blast of cold air was introduced by means of a glass tube dipping into the pitcher. Above the trough was a hood to carry off the fumes. Much heat was set free during the nitrat- ing, and was carried away by the cold water in the trough, and by the cold air-blast. The best temperature is about 20 C. ; if it goes much above 20 C., much fume of nitrogen peroxide is set free ; above 30 C. the reaction becomes dangerous, and the pitcher was at once overturned and the contents " drowned " in the large quantity of cold water in the trough. About 2 pounds of glycerine was ni- trated in each pitcher at one charge, and this required one and a half hours for its introduction into the acid. When nitrated, the contents of the pitcher was poured into a large vat of cold water ; the nitroglycerine sunk to the bottom and the acid water was drawn FIG. 91. EXPLOSIVES 427 off. After several washings with water, and finally with a sodium carbonate solution, the explosive was ready for use. By more recent methods, the entire amount of acid is mixed and placed in one vat, and several hundred pounds of the glycerine is introduced in numerous fine streams from a perforated pipe, or as a fine spray by means of an injector with a blast of air. A coil for' the circulation of cold water is placed in the vat, and several air pipes are provided, through which cold compressed air is forced into the mixture. The vat is covered and a pipe carries the fumes to the chimney. The temperature of the reaction is determined by a ther- mometer, and is regulated by the rate of inflow of the acid and by the use of the compressed air agitators. After the reaction is over, the entire mass is drawn into the separator tank ; in about 30 minutes the nitroglycerine has risen to the top, if pure materials have been used, and is drawn off by a special cock above the acid, and is run at once into a tank containing water at 15 C. ; colder water might cause it to freeze. The temperature is watched care- fully, and must not rise above 30 C. The product is washed several times in water and then with a sodium carbonate solution, to remove all traces of acid. In order to have a better control of the nitration, Boutmy and Faucher proposed to mix the glycerine with part of the sulphuric acid, and to cool the resulting sulphoglyceric acid, C 3 H 5 (OH) 2 (HS0 4 ), or C a H 5 (HS0 4 ) 3 . Then to mix the nitric with the remainder of the sulphuric acid, cool, and to add the sulphoglyceric acid ; it is thus nitrated to form the nitroglycerine, but much less heat is evolved than when nitrating the glycerine directly. But on trial of the process, several serious explosions occurred which were not clearly explained, and it has been generally abandoned. On explosion, the nitroglycerine decomposes about as follows : 2 C 3 H 5 (N0 3 ) 3 = 6 CO, + 6 N + 5 H,0 + 0. The volume of gas at 100 C. thus produced is about six times as great as from gunpowder, and the actual temperature of the explo- sion is much higher than that of gunpowder,- being about 3000 C. as calculated by Wuic (quoted by Guttmann). The volume of gas pro- duced by one litre of nitroglycerine is about 1135 litres. According to Ost,* the temperature of the explosion, as calculated from the observed heat of the explosion and the specific heat of the products of the combustion, is 6980 C. The volume of gas reduced to and 760 mm. from one kilo of nitroglycerine is 713 litres, but at 6980 C. * Lehrbuch der technischen Chemie, 158. 428 OUTLINES OF INDUSTRIAL CHEMISTRY the volume is 18,966 litres [713 x (1 -f -^W)] and tlie pressure is about 31,367 kilograms per square centimeter. Nitroglycerine is a heavy oily liquid of a pale yellow color and sweet taste. Its specific gravity is 1.60. It is insoluble in water, but dissolves in ether, benzene, methyl alcohol, and chloroform. It freezes at about 8 C. and thaws at about 12 C , though there is some varia- tion in these points in different samples, according to their purity. It explodes when heated to 180 C., but burns in the open air without explosion, if in small quantities. It is very sensitive to shocks and may readily be detonated by a sharp blow. "When pure, it keeps indefinitely in a dark place, but exposure to sunlight increases its sensitiveness and may cause spontaneous explosion. Taken inter- nally, it is very poisonous and is a powerful medicinal agent, some- what resembling strychnine in its physiological effects ; ten grains are said to be a fatal dose, while smaller quantities cause headache and vertigo ; even when only in contact with the skin, it is said to cause violent headache. It is used as a remedy in angina pectoris, and is injected into the blood in cases of poisoning by carbon monox- ide, or water-gas. As an explosive, it is only used in the liquid state for " torpe- doing" oil and gas wells (p. 289). When frozen, it is much less sensitive to shocks, and may be transported and handled with safety. But before use, it should be thawed by standing in a room warmed to about 20 C. It is one of the ingredients of a large number of high explosives which, although not so powerful as the nitro- glycerine itself, are much safer and more convenient to handle. These explosives may be divided into two classes: (a) those in which the nitroglycerine is absorbed in some inert, non-explosive material, and (ft) those in which it is mixed or combined with sub- stances which are in themselves explosive. The most important example of the first class is dynamite ; in this the nitroglycerine is absorbed in infusorial earth, white clay, pulverized mica, sawdust, or powdered charcoal. The chief requisite of a good absorbent or " dope " is that it shall hold the nitroglycerine without any oozing or dripping, otherwise the liquid spreads in thin films over the out- side of the package, and becomes extremely sensitive to shocks, and very dangerous. Infusorial earth, often known by its German name, Kieselguhr. is generally used as an absorbent. This consists of a white clay, containing a large amount of the frustrates of diatom es, which are chiefly minute tubes, into which the nitro- glycerine is drawn by capillary attraction, and permanently held. The kieselguhr is calcined to dry it, and to destroy organic matter, EXPLOSIVES 429 and is then mixed by hand with the requisite amount of nitro- glycerine and a little calcined soda, to destroy any acidity. With three parts of nitroglycerine to one of kieselguhr, the dynamite is plastic, and contains 75 per cent of its weight of nitroglycerine. This is usually called dynamite No. 1, or giant powder. It is packed into tubes of paraffined paper, and compressed by hand to form car- tridges of the desired weight. It is not very sensitive to shocks, but is readily detonated by an explosive cap. In cold weather the nitro- glycerine congeals, and such frozen dynamite does not yield good results. It is best thawed by placing in a warm room for some time before use. It should never be placed near a stove or fire, since it is almost certain to explode if heated to 180 C. Dynamite is also made with 50, 30, or even 10 per cent of nitroglycerine, and used where the No. 1 grade would cause too much shattering. Mica powder consists of powdered mica, in which about 50 per cent of nitroglycerine is absorbed. The other explosives with inert dope are not now important. A great number of explosives with an active dope are on the market. Most of them consist of mixtures of sulphur, sodium or potassium nitrate, powdered charcoal, wood fibre or other carbo- naceous matter, impregnated with nitroglycerine. These are sold under various fancy names, such as Vulcan, Hercules, Judson, Atlas, and Hecla powders, and lithofracteur carbonite, stonite, vigorite, etc. As typical examples of these explosives, the following will serve : ATLAS POWDER GRADE A. GRADE B. Sodium nitrate 2 34 Wood fibre 21 14 Magnesium carbonate ..... 2 2 Nitroglycerine 75 50 JUDSON POWDER Sodium nitrate 64 Sulphur 16 Cannel coal 15 Nitroglycerine 5 FORCITE Potassium nitrate 18 Gelatinized cotton 7 Nitroglycerine 75 430 OUTLINES OF INDUSTRIAL CHEMISTRY Forcite is a plastic mass, resembling rubber, impervious to water, and safe to handle. It is made by treating finely pulped cotton with high pressure steam until the whole mass is converted into a jelly, which is then mixed with nitroglycerine at a temperature of 40 C., and powdered nitre is then added. Nitrogelatine or blasting gelatine is made by dissolving soluble nitrated cellulose (collodion) in nitroglycerine. The latter is warmed to about 35 C., and the collodion slowly stirred in, until 7 or 8 per cent has been added. After a time the mass becomes viscous, and is formed into cartridges. It is not very sensitive to shocks, and may be made less so by adding 3 or 4 per cent of camphor. It is not affected by water and hence may be used for submarine work. It keeps well when stored, and is a more powerful explosive than dynamite. Gelatine dynamite consists of blasting gelatine, mixed with wood pulp (4-J- per cent) and potassium nitrate (26 per cent), together with a little sodium. carbonate. An explosive somewhat similar to blasting gelatine is cordite, a "smokeless powder," which has been adopted by the English gov- ernment as a military explosive. This was patented by Abel and Dewar, and consists of: Nitroglycerine 58 parts. Gun-cotton 37 " Vaseline 5 " Acetone 19.2 The nitroglycerine and gun-cotton are mixed by hand, the acetone is added, and the paste worked in a kneading machine for 3^- hours. The vaseline is then added, and the whole kneaded for 3 hours more. The paste is then forced through a spaghetti machine to form threads, which are wound on drums and dried at 40 C. for several days to evaporate off the acetone. The threads are then cut into convenient lengths for use in cartridges. Smokeless powders are now very important for military and sporting purposes. They are probably too expensive for blasting and mining. The base of these powders is nitrated cellulose, which has been treated in various ways to render it slower in burning than gun-cotton, and also less sensitive to heat and shocks. As a rule, they are less inflammable than gun-cotton, and require stronger deto- nators. Since metallic salts cause smoke, they are not used in these powders. There are three general classes of smokeless powders now in use : (a) Those consisting of mixtures of nitroglycerine and EXPLOSIVES 431 nitrated cellulose, which have been converted into a hard, horn-like mass, either with or without the aid of a solvent. To this group belongs ballistite, containing 50 per cent nitroglycerine, 49 per cent nitrated cellulose (collodion), and 1 per cent diphenylamine ; also, cordite (see above), Leonard's powder and amberite. This last con- tains 40 parts nitroglycerine and 56 parts nitrated cellulose. (6) Those consisting mainly of nitrated cellulose of any kind, which has been rendered hard and horny by treatment with some solvent, which is afterwards evaporated. These are prepared by treating nitrated cellulose with ether or benzene, which dissolves the collodion, and when evaporated leaves a hard film of collodion on the surface of each grain. Sometimes a little camphor is added to the solvent, and, remaining in the powder, greatly retards its combustion, (c) Those consisting of nitro-derivatives of the aromatic hydrocarbons, either with or without the admixture of nitrated cellulose ; to this group belong Dupont's powder, consisting of nitrated cellulose dissolved in nitrobenzene ; indurite, consisting of cellulose hexanitrate (freed from collodion by extraction with methyl alcohol) made into a paste with nitrobenzene, and hardened by treatment with steam until the excess of nitrobenzene is removed ; and plastomenite, consisting of dinitro- toluene and nitrated wood pulp. Another class of explosives which are not, however, employed to any extent, are the picrates and picric acid. By treating phenol, C,jH 5 OH, with concentrated nitric acid, tri-nitrophenol or picric acid, C 6 H 2 (OH) - (N0,) 3 , is formed. The alkaline salts of this body (called picrates) are powerful explosives. Ammonium picrate mixed with potassium nitrate has been proposed as a military explosive. Melinite is a mixture of picric acid with collodion, or in one form is supposed to be fused picric acid alone, which has been melted in a carefully regulated oil-bath. It was tested in France for a military explosive for shells, but was found to attack the metal of the shell. The salts of fulminic acid, C 2 H 2 2 N2, called fulminates, are ex- ceedingly dangerous, being very easily exploded by shocks or blows. The silver and mercury fulminates are the most important. The former is too dangerous for general use, but the latter is largely used as the " primer " in percussion caps. It is made by mixing a solution of mercuric nitrate and nitric acid with alcohol. It is a very dangerous explosive when dry. In order to avoid danger in shipping and handling, a class of explosives has come into use in which the ingredients, in themselves non-explosive, are mixed immediately before use. These are called 432 OUTLINES OF INDUSTRIAL CHEMISTRY Sprengel explosives, from the name of the inventor ; they are very powerful in many cases, and some of them are extensively used. Roburite consists of dinitrochlorbenzene, cr possibly dinitrobenzene alone, mixed with ammonium nitrate. It does not explode by fric- tion or shock, but is readily detonated. It yields hydrochloric acid in the combustion gases, and hence is disadvantageous in mining. Bellite and securite are somewhat similar to roburite. Romite con- tains nitronaphthalene, paraffine, potassium chlorate, and ammonium nitrate, in various proportions. Ammonite contains nitronaphthalenes and ammonium nitrate. Rack-a-rock is made from potassium chlo- rate soaked in nitro benzene, or in the " dead oil " from tar. It is very powerful, and moderate in price. It was largely used in the removal of Hell Gate in New York Harbor. Panclastite is a liquid consisting of carbon disulphide with liquid nitrogen peroxide. Hellhoffite consists of nitro- and dinitro-benzenes dissolved in nitric acid. In coal mines, especially where "fire damp" is prevalent, lime cartridges are sometimes used. These are made by compressing quicklime into cylinders, leaving a small hole down the middle. They are put into drill holes, and tamped with sand. Water is poured into the hole, and, passing into the perforated cylinder, wets the lime, which swells greatly on slaking, and exerts great pressure. The coal is broken down without any flame or concussion, and hence there is no danger from the gas. REFERENCES Tri-Nitroglycerine as applied in the Hoosac Tunnel. Geo. M. Mowbray, New York, 1874. (Van Nostrand.) Notes on Certain Explosive Agents. Walter N. Hill, Boston, 1875. Researches in Explosives. Captain Noble and E. A. Abel. Part I. Fired Gunpowder. London, 1875. Part II. Fired Gunpowder. London, 1880. Dynamite, ihre okonomische Bedeutung und ihre Gefahrlichkeit. Isador Trauzl, Wien, 1876. Coton-poudre, nitroglycerine et dynamites. M. Pellet, Paris, 1881. Zur la Force des Matieres explosives d'apres la Thermochimie. M. Berthelot. 2 Vols. Paris, 1883. Die neuen Sprengstoffe. Isador Trauzl, Wien, 1885. Les Explosifs modern es. Paul F. Chalons, Paris, 1886. Manuel du Dynamiteur. La Dynamite de Guerre et le Coton-poudre. M. Dumas-Giulin, Paris, 1887. A Dictionary of Explosives. J. P. Cundill, London, 1889. TEXTILE INDUSTRIES 433 A Handbook on Modern Explosives. M. Eissler, London, 1890. (Crosby, Lockwood, & Son.) Die gepresste Schiesswolle. Franz Plach, Pola, 1891. (E. Scharff.) Explosives and Ordnance Material, etc. Stephen H. Emmons. Keprint from. Vol. 17, Proc. U. S. Naval Institute, Baltimore, 1891. The Dangers in the Manufacture of Explosives. Oscar Guttmann, London, 1892. Blasting. Oscar Guttinan, London, 1892. Les Explosifs industriels. J. Daniel, Paris, 1^93. (Bernard et Cie.) Index to the Literature of Explosives. Chas. E. Munroe, Baltimore, 1893. Die Industrie der Explosivstoffe. Oscar Guttmann, Braunschweig, 1895. (Vie- weg u. Sohn.) Die Explosiven Stoffe. Franz Boeckmann. 2" Auf. Wien, 1895. (Hartleben.) Journal of the Society of Chemical Industry : 1890, 265. Geo. McRoberts. Blasting Gelatine. 1890, 476. Geo. McRoberts. Blasting Gelatine. TEXTILE INDUSTRIES FIBRES Textile fibres are divided, according to their source, into vege- table, animal, and mineral. Of these only the first two will be considered here, since mineral fibres, consisting of asbestos, slag- wool, glass-wool, metallic wires, etc., are never subjected to any of the processes of bleaching, dyeing, or chemical treatment which come within the scope of this book, though they are sometimes used for packing, lagging, or filtering purposes in chemical works. Vegetable fibres are plant cells of rather simple structure, usually forming a part of the plant itself. They are capable of withstanding high heat, and are not readily attacked by dilute alkalies to cause disintegration or weakening. They consist essentially of cellulose (C 6 H 10 5 ) /; , which may be very pure, or mixed with its alteration products ; in a few instances, the fibre as actually employed consists entirely of cellulose derivatives obtained by chemical means. Con- centrated caustic alkalies form alteration products with vegetable fibre ; free sulphuric, or hydrochloric acid, if strong, quickly destroys the fibre, but nitric acid forms nitrates, or oxidized derivatives. Animal fibres are essentially nitrogenous substances (protein matter) often containing sulphur. They may consist of complex cell structures, or bundles of cells enclosed in a single envelope, or they are solid filaments formed from a liquid secreted by caterpillars, spiders, or certain mollusks. They are readily destroyed by hot alka- lies, but withstand the action of mineral acids very well. They are much more easily injured by dry heat than are the vegetable fibres. 2F 434 OUTLINES OF INDUSTRIAL CHEMISTRY VEGETABLE FIBRES Vegetable fibres are divided into two groups, seed hairs, con- sisting of single cells, and bast fibres, consisting of bundles of fibre- cells joined together to form filaments of greater or less length. The most important vegetable fibres are cotton, flax (linen), hemp, jute, China grass, and esparto. Cotton fibre consists of the seed hairs of several species of Gos- sypium, plants belonging to the Malvacece, or mallow family. The most important commercial varieties are Gossypium barbadense, L. (Sea Island cotton), G. herbaceum, L., or G. hirsutum, L. (upland cotton of the southern states), G. arboreum, L. (Indian and Egyptian), and G. Peruvianum, Cav. (Brazil, Peru, and neighboring countries). The varieties are distinguished by difference in the length and fine- ness of the fibre or staple. The following table * shows the average length and diameter in inches of the principal commercial grades : Sea Island LENGTH OF STAPLK. DIAMETER OF STAPLE. Max. Min. Average. 1.80 1.60 1.06 1.52 1.31 1.02 1.41 .88 .81 1.30 1.03 .77 1.61 1.02 .93 1.41 1.17 .89 .000640 .000775 .000763 .000655 .000790 .000844 Upland. Egyptian Indian Thus it will be seen that the longest fibres have the least diam- eter ; they are also silkier, and can be spun into the finest threads. The fibres are attached thickly to the surface of the seed, and as they develop a mass of lint is formed which ultimately bursts the enclosing pod or boll. Each fibre consists of a single long cell ; but as it grows the cell walls become thinner, and finally collapse to form arfl'at tube. After the boll bursts the liquid cell content solidi- fies by exposure to the sun and air, the dissolved matters are depos- ited somewhat irregularly on the different parts of the cell wall, and, consequently, the fibre twists into a spiral shape. Thus, as seen under the microscope, cotton fibre appears as an irregular, twisted, and flattened tube, tapering to a point at one end. The unripe fibres are comparatively straight, but if made into yarn they twist and * Walter H. Evans, Bulletin No. 33, U. S. Dept. of Agriculture, p. 77. TEXTILE INDUSTRIES 435 curl, and are of little value ; being difficult to dye, they cause specks in the dyed goods. Cotton fibre consists essentially of cellulose enclosed in a film or outside skin of modified cellulose. On the surface is a deposit of wax and oily matter which protect it from the action of moisture, .and which is removed in the bleaching process before dyeing or printing the cotton goods. The cellulose of the fibre is scarcely affected by cold dilute mineral acids, but if allowed to dry on the fibre the acid quickly attacks it. Concentrated sulphuric acid con- verts cotton into a gelatinous mass, from which water precipitates a starch-like body called amyloid.* By longer action of the strong acid, cotton is converted into a soluble compound (cellulose sulphuric acid), then into dextrin, and finally into dextrose. Boiling in dilute alkalies has no injurious action on cotton if the air is excluded; otherwise there may be more or less formation of oxycellulose which may weaken the fibre. When treated with caustic soda solution at 50 T\v., the fibre becomes rounded, swollen, and semi-transparent, and the interior cavity almost disappears, while a marked shrinkage in length takes place. It gains in weight and in strength, while its affinity for coloring matter is much increased. The fibre probably enters into combination with the alkali to form a compound of the formula C^H^O^ N%O, which decomposes with water to form hydrocellulose, C^H^O^ H 2 0. This action was dis- covered by John Mercer, hence the name "mercerized cotton" applied to fibre which has been so treated. f Flax or linen is the bast fibre of the flax plant, Linum usitatissi- mum, L. The individual fibres are long cylindrical cells, pointed at the ends, and having thick walls with a narrow central cavity. Each fibre is marked with transverse bands, and has a glistening surface. The average length is from 2 to 4 cm. ; the individual cells are united in bundles, firmly glued together, consequently linen is much less elastic than cotton fibre, next to which it ranks in importance among vegetable fibres. In warm countries flax is raised chiefly for the seed. (See Linseed Oil, p. 308.) That grown in temperate cli- mates has much the better fibre. It is pulled up by the roots before * Parchment paper is produced by the short action of strong acid on paper whereby a layer of amyloid is formed on the surface. t The process has recently been further developed for the production of a silky lustre on cotton goods. The yarn is mercerized while tightly stretched on a frame, and is washed and dried in this state of tension. This prevents, to a great measure, the shrinkage which would otherwise occur, and gives a high lustre to the fibre, especially noticeable in the dyed goods. Such mercerized cottons are now made to imitate silks. 436 OUTLINES OF INDUSTRIAL CHEMISTRY the seeds ripen, and is immediately subjected to the process of "rippling," i.e. it is drawn through the teeth of a coarse comb to detach the seeds. To separate the bast fibre from the rind, woody tissue, and pith, the flax is "retted." This may be done in five different ways : (a) Eetting in stagnant water is practised in Ireland and to some extent in Russia. The flax is put into pools of soft water and left until fermentation sets in; this softens and partly destroys the gummy and resinous matter cementing the fibres to the ligneous tissue. Great care is necessary that the bast fibres themselves are not attacked. The fermentation is often very offensive. When it has gone far enough, the flax is exposed to the action of the air and sunlight for several days ("grassed"). (b) Ketting in running water is extensively practised in France and Belgium. The flax is put into crates and submerged in streams. The fermentation takes place as above, but requires a longer time. The coloring matter is washed away, and a lighter colored product is obtained. (c) Dew retting consists in exposing the damp flax to the weather for several weeks. The fermentation takes place much as above. (d) Eetting in water at 30 to 35 C. hastens the fermentation greatly, so that it is generally complete in about three days. The flax is often passed between squeeze rolls, to assist in detaching the woody fibre. By treating the flax with water and steam under pressure, it is rapidly retted, and the fibre has a silky lustre. (e) Mineral acids are sometimes used in stagnant water retting, to prevent the offensive odor. By digesting the flax in very dilute hydrochloric acid, followed by a weak alkali bath, the retting is quickly finished. Various mechanical processes are employed to detach the ligneous matter from the fibre after retting. Breaking consists in crushing the flax with grooved rolls; after this it is "scutched," i.e. the crushed mass is pounded by hand in a machine, to remove the loos- ened matter. Heckling is a combing process to draw the fibres parallel and make them suitable for spinning. Linen fibre is not so pure cellulose as cotton, but, in general, acts like the latter. It is stronger, has more natural lustre, is more diffi- cult to bleach and dye, and, being a better conductor of heat, feels cold to the touch. Hemp is the bast fibre of Cannabis sativa, L., which is largely cultivated in Eussia and Italy. The fibres are separated from the TEXTILE INDUSTRIES 437 wood and pith of the stalks in the same general way as flax. They are stronger and coarser than flax, and, being more deeply colored, are mainly used for rope, coarse canvas, and bagging. Jute is the bast fibre of several species of Corchorus, of which C. capsularis, L., is the most important. The plants are indigenous to India, and their cultivation is mainly confined to India and Cey- lon, though some has been raised in Louisiana and Mississippi. The fibre is obtained very pure by simple retting in water. It is very long, sometimes reaching two meters, but the fibre cells are very short, and the filaments are not so strong as those of flax or hemp. The fibre is light yellow, and has, a high lustre. It is quite suscepti- ble to the action of acids and alkalies, and is easily/destroyed by min- eral acids. It cannot be bleached with bleaching powder, since the chlorine combines with the jute. Sodium hypochlorite in weak solu- tion, or potassium permanganate, followed by sulphurous acid, may be used to bleach it. It differs in its chemical composition from cotton and flax. Its cellulose is all combined with lignified tissue, forming bastose. Jute resembles cotton which has been mordanted with tannin, and can be dyed directly with basic dyes. China grass, or ramie, is a bast fibre derived from Boehmeria nivea, Gaud., a species of nettle cultivated in China and Eastern Asia. The fibre is difficult to detach from the ligneous matter ; ret- ting usually divides it into its component cells, which cannot then be separated from the stem and bark. It is customary to separate the fibres by crushing the green stalk and washing away the woody matter with running water, but this method is expensive. The fibre has a brilliant lustre (which dyeing is liable to injure), and is easily bleached. It is very strong, and is nearly pure cellulose. Esparto is a grass with tough fibre, cultivated in Spain, and chiefly used for cordage and paper making. Manilla hemp and sisal are used as substitutes for hemp. The former is obtained in the Philippine Islands, from the leaves of a wild plantain, Musa textilis, Nee., and, being tough and light, is much used for cordage and ropes. Sisal is obtained from an agave plant, Agave rigida, Mill., and A. Americana, L., in Central America and the West Indies. It is chiefly used for burlap as a substitute for jute. Other vegetable fibres of small importance are eocoanut fibre, from the husk of the eocoanut, used for brushes, mats, and cordage; New Zealand flax, a long fibre prepared from a New Zealand plant, Phor- mium tenax, Forst., and chiefly used for ropes; Sunn hemp, an Indian plant, furnishes a fibre suitable for ropes and cordage. 438 OUTLINES OF INDUSTRIAL CHEMISTRY ANIMAL FIBRES Of animal fibres, only silk and wool are of much technical im- portance. Silk fibre forms the cocoon of the silkworm, Bombyx mori. The worm has two glands, situated on either side of its body, each connected by a duct with a capillary opening (spinneret) in the worm's head. These glands each appear to secrete two transparent liquids ; the one, fibroine, C 15 H 23 N 5 6 , constituting from one-half to two-thirds of the whole secretion, forms the interior and larger part of the silk fibre; the other, sericine, C^H^lS^Os, also called silk glue, is yellowish in color and is readily dissolved in boiling water, hot soap solutions, or by alkalies. It forms the outer coating of the fibre. As soon as discharged into the air, the fluids from the spinnerets solidify, and coming in contact with each other at the moment of discharge, are firmly cemented together by the sericine ; hence, under the microscope the fibre shows two separate structureless filaments. The cocoon is made up of one continuous fibre, from 350 to 1200 meters long, with an average diameter of .018 mm. Silkworms are raised from eggs kept in an incubator from twelve to eighteen days, while the temperature is very slowly raised from 18 to 25 C. The caterpillars have a prodigious appetite, and are fed regularly on mulberry leaves (Morus alba, L.,) for about thirty days, during which time they grow rapidly, casting their skins every five or six days, and attaining a length of about 8 cm. Then they cease to eat, and crawl upon twigs, where they spin their cocoons. This spinning requires about three days, when the worms are killed by heating the cocoons in an oven at 60 to 70 C. for three hours, or by steaming them for 10 or 15 minutes. After sorting, the cocoons are reeled. This is an entirely mechanical process requiring much skill. The cocoons are soaked in water at 60 C., until the silk glue is softened. Then the operator catches the loose ends of several fibres on a small brush, and passes them through the agate or porce- lain guides of the reel, where they are twisted to form threads of sufficient size for weaving. Two threads are formed simultaneously on each reel, and are made to cross and rub against each other to remove kinks and to straighten them, and also to rub the softened- silk-glue coverings together, so that the fibres adhere and form solid, uniform threads, raw silk. There is considerable waste, con- sisting of short and tangled fibre from the exterior of the cocoons, and from those which have been opened by the moth in escaping. This is worked up as floss, and for making spun silk. Raw silk is exceedingly hygroscopic, and, under favorable cir- TEXTILE INDUSTRIES 439 cum stances, will absorb as much as 30 per cent of its weight of moisture, and still seem quite dry. It is, therefore, customary to determine the moisture in each lot at the time of sale. This is called "conditioning," and must be done with great care, usually in official laboratories. A sample is taken from each bale, and, after careful weighing, is dried in a current of air in a special apparatus, at a temperature of 110 C., until the weight becomes constant. From the average of several tests the absolute amount of dry silk is determined, to which the legal amount of moisture permissible (11 per cent) is added, and the result taken as the weight of the raw silk. Raw silk consists of about 25 per cent sericine, the remainder being pure fibroine, and has a very harsh feel and is stiff and coarse. Before it is made into yarn or cloth, it is usually subjected to vari- ous treatments to make it soft and glossy. The first process is called discharging, stripping, or ungumming, and its purpose is to remove more or less of the silk glue (sericine) from the fibre, ac- cording to the kind of goods desired. The hanks of silk are sus- pended on wooden sticks in a vat filled with soap solution at 95 C. This is made by dissolving Marseilles, or olein soap to the amount of 30 per cent of the weight of the silk, in soft water, entirely free from lime. The hanks are turned several times by hand in this liquor, during a period of from one to one and a half hours ; the fibres swell, become sticky, and finally the sericine dissolves, leaving the silk glossy and soft. The soap bath is not boiled, as that would tangle the fibres and cause the yellow color often present in the sericine to become fixed on them ; also long boiling weakens silk. For very fine work, two or three soap baths are employed, the raw silk being first put into that which has been longest in nse and which is therefore strongly charged with dissolved sericine ; * there the glue is softened and partly removed ; the hanks are transferred to the succeeding baths in order, finally leaving the one. most recently prepared. This yields very soft, white silk, which is rinsed in a warm dilute sodium carbonate solution and then wrung. That which is to be sold as white silk or dyed a very light shade is then subjected to a second discharging process, in which the hanks are tied in several places with tape, enclosed in linen bags, and boiled in a 15 per cent soap solution from one-half to three hours, to remove all the glue. This product, called " boiled-off silk," has lost from 20 * The soap liquor finally becomes heavily charged with sericine and is drawn from the tank as " boiled-off liquor." It is used in making up the dye bath for silk dyeing, pp. 481, 486, and 489. 440 OUTLINES OF INDUSTRIAL CHEMISTRY to 30 per cent of its original weight, in order to reduce this loss of weight, raw silk is often treated in a weak soap bath until the waxy matters have been partly removed, and is then washed and some- times bleached by exposure to sulphur dioxide vapors. The product, called " ecru silk," is harsh to the touch, but has lost only about from 2 to 4 per cent of its original weight ; it is chiefly used in the warp of black silk and for the back of velvet. Another process * of treating raw silk for dyeing, while leaving a large part of the sericine on the fibre, is employed for producing souple silk. The hanks are first scoured in a 10 per cent soap solu- tion for an hour or two at 25 to 35 C. to soften and swell the fibres. They are then bleached by working for 10 or 15 minutes in very di- lute aqua regia or in a dilute solution of nitrous acid in concentrated sulphuric acid. The bleached silk is then exposed to sulphur fumes for several hours, until sufficiently white. It is then soupled, i.e. worked for an hour and a half in a solution of cream of tartar or magnesium sulphate, 3 or 4 grams to the liter. This swells and softens the fibre, which was left harsh by the bleaching process. Soupled silk has lost only 6 or 8 per cent of its original weight, but is weaker than boiled-off silk. Concentrated mineral acids, especially hydrochloric, dissolve silk completely. Very dilute acids are absorbed by it, thus increasing the lustre and imparting a peculiar feel to the fibre, which when compressed emits a curious rasping sound called "scroop." The property of scroop may be given by treating the silk in a bath of di- lute sulphuric, acetic, or better, tartaric acid, and drying without washing. Caustic alkalies in strong solution rapidly destroy silk if heated ; but in cold solution, caustic soda of 50 Tw. has very little action on the fibre and may be used to produce the crinkled appear- ance on mixed cotton and silk goods similar to seersuckers. Ammo- nia has little or no action on the fibroine but dissolves the sericine. Alkaline carbonates are less destructive than caustic, but attack the fibre slowly. Borax dissolves sericine without material injury to the fibroine, but is not so good as soap for ungumming raw silk. Lime water swells the fibre, makes it brittle, and dulls the lustre. Chlo- rine destroys silk as do other oxidizing agents unless used very dilute and with much care. When soaked in solutions containing metallic salts, especially iron, aluminum, tin, lead, or copper, silk absorbs some of the salt and a precipitation of basic salt within and upon the fibre occurs. On this fact depends the weighting of silks (p. 461). Besides the cultivated silks, certain kinds of wild silks are of * Chemische Technologie, Wagner. TEXTILE INDUSTRIES 441 some commercial importance. The most important is tussur silk, obtained from the cocoons of Indian and Chinese moths, Antliercea mylitta and A. pernyi. The fibre is double and somewhat flat, each filament being composed of a number of fibrillse. It is brown in color, is stift'er and coarser than ordinary silk, and differs in its chemi- cal composition, containing less carbon and nitrogen and more oxy- gen. It is more resistant to the action of alkalies and acids and to bleaching agents. It is difficult to bleach and dye, and is chiefly em- ployed in making pile fabrics, such as velvets, plush, and imitation sealskin. Other wild silks are nmga silk from Anther cea Assama, and eria silk from Attacus ricini, both found in India : yamamai silk, from Anthercea yamamai of Japan ; sea-silk or byssus, produced by a mollusk, Pinna nobilis, found in the Mediterranean Sea. The fibre of sea-silk is brown and very soft, and is not easily affected by acids or alkalies. The following analyses from HummePs Dyeing of Textile Fab- rics, are of interest. Composition of the cocoons : Moisture 68.2 Silk 14.3 Floss 0.7 Chrysalis 16.8 Composition of raw silk : YELLOW ITALIAN SILK. WHITE LEVANT SILK. Fibroine 53.37 54.04 Gelatine 20.66 19.08 Albumin 24.43 25.47 Wax 1.39 ..... 1.11 Coloring matter .... 0.05 0.00 Resinous and fatty matter . 0.10 0.30 100.00 100.00 The ultimate analysis of silk fibroine is shown in the following table:* Tcsstra FIBROINB. MULBERRY FIBROINE. (Calculated for Cu^n^M Carbon .... 47.18 47.78 Hydrogen . . . 6.30 6.23 Nitrogen . . . 16.85 18.90 Oxygen .... 29.67 26.04 100.00 98.95 * Manual of Dyeing, Knecht, Rawson, and Loewenthal, p, 56. 442 OUTLINES OF INDUSTRIAL CHEMISTRY Artificial silk is made from certain soluble cellulose nitrates by Lehner's process. Ordinary collodion, containing from 10 to 12 per cent pyroxyline in solution, is treated with dilute sulphuric acid, which causes a molecular change, making the substance more fluid. The solution is filtered and made to flow through very fine glass tubes, into water, which at once coagulates the collodion. The transparent filament formed closely resembles the natural silk fibre in appear- ance, and several of them are twisted together into a thread of the desired size, which is wound on a reel. By dehydrating, the thread becomes white and highly lustrous, like "boiled-off" silk. It is still very inflammable, and is next " denitrated " by treating it with a cold solution of ammonium sulphide, which destroys the cellulose nitrate and leaves the pure cellulose with a high silky lustre, but 110 more inflammable than ordinary cotton. Wool is the hair of the sheep, but that of certain goats, such as the alpaca, cashmere, and mohair, as well as that of the camel, are also classed with wools. Wool differs from true hair only in its physical structure, being covered with minute overlapping scales and having a twisted or curled fibre. The character of wool varies with the breed, food, and care of the sheep, and the climate and nature of the soil on which the food is grown. The fibre varies from short, fine, and wavy, to long, coarse, and straight in different breeds. The length ranges from 1 inch to 10 inches in different varieties, even reaching 16 inches in the case of certain cashmeres and mohairs. The wool cut from one animal is called a fleece, and the different grades in each fleece are separated by hand, that from the neck, back, and shoulders being the longest and best quality. The long staple wools have a silky appearance and are often called lustre wools. They are generally used for worsted goods, while the short, fine wools are made into woollen goods. Mohair, obtained from the Angora goat, has a very high lustre and is soft and fine, as are also the al- paca, vicuna, and llama wools derived from South American goats. Sheep pelts are often soaked in " milk of lime," or sodium sul- phide to loosen the wool before making leather from the skin. Such wool is known as "pulled wool," and is of poor quality. Wool is very hygroscopic, and may contain from 8 to 12 per cent of moisture in hot, dry weather, up to 50 per cent in very damp air. On an average, it contains about 18.25 per cent, and this is the legal limit in most European countries, and is generally determined in " conditioning laboratories," as in the case of silk. The temperature of drying is kept between 105 and 110 C., since above this temper- TEXTILE INDUSTRIES 443 ature there is danger of injuring the fibre. At 100 C. wool becomes plastic, and after cooling retains the shape into which it may have been formed while hot. Each wool fibre is covered with a layer of broad scales, projecting in the same direction and overlapping much like shingles on a roof, the outer edges being more or less free. When the approximately parallel fibres are moved upon each other by rubbing or " milling," the scales interlock and cause "felting." The interior substance of the fibre is composed of narrow cells tapering towards each end. Some wools also have a central or medullary part, made up of cells of different shape, and which usually contain the coloring matter of the fibre. Such wools are stiff and brittle, and resemble hair in their properties ; the best wools are free from such medullary cells. The internal cells appear to have more attraction for dyes than do the outer horny scales, and much of the effect of acids and other additions to the dye-bath is supposed to be due to the raising of these scales by their action, thus permitting the access of the dye to the interior substance. Diseased and dead fibres, known as "kemp," do not color well, since they have a very impenetrable layer of these scales ; moreover, they do not felt properly, and are dull in lustre. Pure wool fibre, consisting for the most part of keratine, the characteristic constituent of horn, feathers, etc., is not of constant chemical composition, varying in different qualities and kinds. The approximate composition of keratine from wool is : Carbon . 49.25* Nitrogen 15.86 Hydrogen 7.57 Sulphur 3.66 Oxygen 23.66 The presence of sulphur is characteristic of wool, and often causes difficulties in mordanting and dyeing. The ash of the fibre averages less than 1 per cent of the weight of the wool. When heated to 130 C., with water under pressure, and dried, wool is rendered very brittle. Dilute acids have no apparent action on it, but a small percentage is absorbed and cannot be readily removed by washing ; very concentrated mineral acids destroy the fibre. By treating mixed cotton and wool goods with a dilute sulphuric or hydrochloric acid, and drying at 110 C., the cotton is " carbonized " (p. 435), and when heated crumbles to dust and falls away from the unchanged wool. The same result is obtained by treating the goods * Hummel, Dyeing of Textile Fabrics. 444 OUTLINES OF INDUSTRIAL CHEMISTRY with hot, dry hydrochloric acid gas. Alkalies attack wool energeti- cally, the caustic alkalies and lime being most destructive, especially in boiling solution, by which the fibre is completely destroyed. Alkaline carbonates are much less injurious, and are used in dilute solution for scouring wool. Ammonia and ammonium carbonate have very little tendering effect on it, and are best for washing, for which soap, borax, and sodium phosphate are also used. When strong and allowed to act for some time, oxidizing agents cause the fibre to become tender. Very dilute solution of potassium bichro- mate is largely used in mordanting wool, but care is necessary to prevent "over chroming." When moist, chlorine is taken up by wool, and the fibre made very tender, but a very slight treatment with it makes the wool more susceptible to certain dyes ; dry chlo- rine is said to have no action. Wool is colored yellow by hypo- chlorous acid, hence bleaching powder is not used to bleach the fibre. When boiled in solutions of various metallic salts, it absorbs a considerable amount of them, and it is often so treated when mor- danting before dyeing. The nature of the reactions occurring is not clear, but apparently there is a direct union between the fibre or some of its constituents and the salt. Wool has great affinity for many dyes, and the colors produced are generally faster than when dyed on cotton or silk. Before it can be subjected to any manufacturing process, raw wool must be washed and scoured to remove impurities, which are present to the extent of from 30 to 80 per cent of the total weight, These consist of: (a) yolk or wool grease, and (6) suint, which exude from the body of the animal with the perspiration ; and (c) dirt mechanically mixed with them or entangled among the fibres. The wool grease is soluble in ether, benzene, or carbon disulphide, and is made up of fatty or wax-like bodies, consisting largely of solid alcohols, especially cholesterine and isocholesterine, together with the oleic, palmitic, and stearic acid esters of those alcohols. These substances are not easily saponified with alkali, but can be emulsified with soap solution, and thus easily removed from the fibre. Suint is soluble in water, and consists mainly of potassium salts of oleic, stearic, valeric, and acetic acids, together with sulphates, chlorides, and phosphates, and nitrogenous bodies. These are generally removed by washing in a solution of soap. A soft soap, made from Gallipoli oil (p. 313), is preferred for the best qualities of wool, but usually a cheaper soap, containing some sodium carbonate, is employed. The washing is done in machines, TEXTILE INDUSTRIES 445 and care is taken not to entangle the fibre any more than need be. There are usually three tanks, placed en cascade, and so arranged that the wool may be automatically passed -from one to the next, while the liquor is drawn from one to the other in a direction oppo- site to the movement of the wool. The raw wool is introduced into the soap liquor containing more or less impurity from its previous use in the other tanks. The temperature should be from 35 to 40 C., but is generally higher. The wool is submerged and pushed forward a short distance by prongs or gratings which work auto- matically. At each stroke, a portion of the wool is caught and pushed between squeeze-rolls, which expel the liquor ; it then passes into the next tank, where it is washed in the same way with cleaner soap liquor, and then goes through squeeze-rolls into the last tank, containing clear water or fresh soap liquor. The wash liquor, aided by the free alkali added and the potassium oleate, etc., in the suint, emulsifies and dissolves the wool grease and suint,. loosening the mechanical impurities, which sink to the bottom. After wash- ing in clean water, the wool is dried on wire netting by a current of warm air. The foul-smelling, dirty brown liquor from the first tank is drawn off, and may be evaporated directly and calcined to recover the potash, which amounts to from 1 to 8 per cent of the weight of the wool. Or it may be treated to recover the wool grease, sometimes called Yorkshire grease; it is settled to remove coarse dirt, and then sulphuric acid is added in slight excess, to decompose the soaps and set free the fatty acids, which rise to the surface, carrying the wool grease with them. The water is drawn off from the magma, which is pressed, hot, in canvas bags. The grease is kept in a liquid condition until all sediment deposits, when it is drawn into casks, where it solidifies on cooling. It is used as a lubricator, and in leather dressing. By passing the clarified wash liquor through a machine similar to a cream separator, the grease is very neatly separated from it. For the preparation of lanolin from this grease, see p. 320. Wool is often treated by methods intended to recover the yolk and suint separately. This is usually done by extracting first with a volatile solvent (carbon disulphide or petroleum spirit) to remove the wool grease, and then washing the wool in water to remove the suint. The washed wool is harsh and brittle, and before being manu- factured must be softened by oiling. Pure olive oil is best for this, but lard, colza, hemp and mineral oils, and sometimes "red oil" (oleic acid) are also used. This in turn must be removed by scour- ing before dyeing. 446 OUTLINES OF INDUSTRIAL CHEMISTRY Wool was formerly scoured by treatment with stale urine, called "lant," its efficiency being due to the ammonium carbonate in it. But this method has been generally abandoned in favor of soap-scouring. The addition of a little ammonium carbonate to the soap bath would improve its action, but the salt is too expensive for general use. BLEACHING Natural fibres, whether vegetable or animal, always contain cer- tain coloring matters, which, even though present in very small quan- tities, impair the purity of the white, desirable in most uncolored fabrics. Moreover, there are always certain gums, waxes, resins, and oily matters on the fibre, either natural to it, or added to facili- tate the spinning and weaving operations. In woven goods there is more or less sizing material, consisting of starch, china clay, metallic salts, and oxides, etc., put upon the fibre to assist in the weaving or to improve the appearance or weight of the cloth. If left upon the goods, these substances will prevent the proper action of mordants and dyes, while some of them detract from the appear- ance of those fabrics which are to be sold uncolored. It is the work of the bleacher to remove all these foreign substances and decolorize the fibre. In general, the bleaching process is divided into two stages, the washing or scouring, and the bleaching proper or chemical treatment. The method of treatment and the material used vary with the different kinds of fibre. COTTON BLEACHING Cotton is commonly bleached in the yarn or woven piece, since there is no special demand for bleached cotton-wool. Yarn bleaching. If the cotton is to be dyed in dark colors, it is customary to give it a thorough boiling in water alone, or with the addition of some soda-ash, to remove the grease, wax, and resinous matters. After washing, it is at once dyed. But for white yarn, or that to be dyed any light shade, the bleaching process is more complicated. The hanks of yarn are linked together to form a chain, and then loosely packed into a closed iron vessel, called a " kier," where they are boiled for several hours with caustic soda or soda-ash, under a low pressure (5 pounds per square inch), or even in open vessels. The kier has a false bottom, upon which the yarn rests. A vertical pipe passes up through the centre of the kier, to TEXTILE INDUSTRIES 447 within a few inches of the top. Across the upper end of this pipe is a dome-shaped bonnet, and at the lower end is a steam injector which forces the liquor collected under the false bottom up through the pipe against the bonnet, which distributes it over the yarn, through which it percolates, collecting under the false bottom. Thus a constant circulation of the liquor is maintained in the kier. On an average about 4 per cent (of the weight of the goods) of soda- ash is used in the lye. The yarn is then washed with clean water and is treated with a cold dilute bleaching powder solution, called the " chemick." This is about 2 Tw., and is pumped over the yarn as it lies in a wooden tank having a false bottom. After 5 or 6 hours the yarn is re- moved, squeezed, and washed in water for a few minutes. It is then " soured " by plunging into a tank containing a dilute sulphuric or hydrochloric acid of about 1 Tw. Chlorine is thus liberated from the bleach absorbed in the fibre, and sets free oxygen from the water, which at once attacks and destroys the coloring matters, the yarn becoming pure white. This process requires about 15 to 20 minutes ; then the yarn is thoroughly washed in water and passed into a hot soap solution, to which a little bluing (ultramarine) has been added, if the yarn is to be sold uncolored. The soap is worked into the yarn by squeeze-rolls, until the fibres are uniformly blued ; then the excess of soapy water is removed in a centrifugal machine, and the yarn is dried. One of the best machines for yarn washing is the Haubold ma- chine. This consists of a circular tub containing a rotating central shaft from which square bobbins radiate. OH these the hanks are hung, and as they are carried slowly forward, a suitable gearing imparts to the bobbins an intermittent forward and backward rota- tion on their own axes. The tank is divided by a radial partition, on one side of which fresh water enters, while on the other the dirty water flows out. The hanks are moved against the current of water, and are taken out when they come to the partition on the side where the clean water enters. In other washing machines, the yarn is pounded by heavy wooden hammers driven by power. Or, as shown in Fig. 92, the hanks tied together to form a chain are washed by passing through squeeze-rolls (A, A) and under a stretching roller (B), placed in the bottom of the wash tank. The yarn thus passes down and up under the rollers and between the squeeze-rolls several times. Improved apparatus is now employed, in which the lye-boiling, chemicking, souring, and washing are all carried on in one wooden 448 OUTLINES OF INDUSTRIAL CHEMISTRY vessel. The yarn is not moved during the process, and the various liquors are pumped through the apparatus in their order, and the labor is thus much reduced. The most important branch of cotton bleaching is the bleaching of cloth. It is done by one of three methods : the market bleach for goods to be sold as white muslin; the Turkey-red bleach, for goods to be dyed red with alizarin ; the madder bleach designed for cloth which is to be printed with various mordants and then dyed in a bath of madder or alizarin. It is the most thorough, and leaves the cotton white and almost pure cellulose. It is necessary to re- move every impurity which can attract the dye or prevent its taking FIG. 92. the fibre. If the cotton is not chemically clean before printing, the pattern will not be clear and sharp, nor the background a pure white. The madder bleach is carried out as follows : The separate pieces of goods are marked on the ends for future identification, and then stitched together, end to end, to form a continuous web, which is first "singed" to remove the lint, floss, and loose hairs, as these would prevent the printing of sharp designs. This may be done by passing the cloth, opened to its full width, over one or two red-hot copper plates, slightly curved and set in the roof of a fur- nace ; it is difficult to keep these evenly heated, owing to the cooling effect of the rapidly moving cloth, and the singeing is liable to be imperfect in places. Consequently a revolving hollow roll is some- times used, which is kept red hot by passing the flames of the fur- nace through it on their way to the chimney. Or the cloth may be passed over a row of Bunsen gas flames. Directly over these is a TEXTILE INDUSTRIES 449 small roller, under which the cloth passes at sufficient tension to cause the "nap" to stand out well as it comes into the flame. As soon as the cloth passes the hot plate or flame it is plunged into a trough of water, to extinguish any sparks. The goods are then thoroughly wet in water (the "gray-wash"), and much of the sizing and dirt is removed. The cloth is then usually piled in a heap and left over night, to thoroughly soften the gums and starchy matters left in it. It is then given the " lime- boil," with milk of lime under pressure preferably in the injector kier. The cloth is passed through a trough of milk of lime, of which it absorbs about 4 or 5 per cent of its own weight. Without wringing, it is passed into the kier, which is filled nearly full, and packed by boys, who tread the cloth down evenly, so that the liquor will be forced to pass through it, and not through channels between the folds. Water is introduced, and then steam is blown in until the air is expelled and the kier is hot, when the cover is screwed down and the boiling con- tinued under from 10 to 70 pounds pressure, for several hours. The kier (Fig. 93 *) is made of boiler plate, and is from 6 to 10 feet high by 4 to 6 feet in diameter; it will hold from 600 to 3500 pounds of cloth. Steam is admitted through (A), and passing the injector (G), draws the lime water through (B) and delivers it through (C) to the nozzle (N), which sprays it over the goods. The pressure in the upper part of the kier forces the liquor through the goods, and it collects among quartz pebbles in the bottom, whence it is drawn through (B) to the top of the kier. If needed, water is admitted through (D) and milk of lime through (E). At the end of the operation the waste liquor is drawn off through (F). The object of this lime-boil, or "lime-bowk," as it is sometimes called, is to convert the fatty matters into lime soap, to dissolve the remaining starch and other soluble substances, and to so change the natural impurities chemically, that they, together with the lime soap formed, are readily removed in succeeding operations. The cloth is usually darker after this treatment than before. It * After, Knecht, Rawson and Loewenthal, Manual of Dyeing. 2G 450 OUTLINES OF INDUSTRIAL CHEMISTRY is next washed in machines similar to that shown in Fig. 92, to re- move excess lime, soluble matters, and loose dirt. The rope of cloth is thus passed through the water and between the rolls (A, A) several times, while it is sprayed by a heavy stream of water from the pipe (C) as it comes up to the squeeze-rolls. It now passes to the first-sour, or gray-sour, where it is treated with dilute sulphuric or hydrochloric acid at 1 or 2Tw.; this de- composes the lime soap, and removes any iron stains and other metallic oxides. The goods are then passed through squeeze-rolls, to remove the excess of acid, and are thoroughly washed to prevent the acid from rotting the fibre, as it would on long exposure to the air. The lye-boils, of which there are two or three, are also carried on in the injector kier. In the first boiling the goods are treated with 1 per cent soda-ash* for about 3 hours; in the second about 3.6 per cent soda-ash, 0.8 per cent caustic soda, and 1.6 per cent of rosin are used, and the whole boiled for 12 hours ; the third lye-boil is with soda-ash alone, and continues for 3 hours. These boilings remove the remaining fats and oils from the lime soaps, and extract much of the brown coloring matter. The addition of rosin is a character- istic of the madder bleach, and is supposed to remove certain sub- stances from the cotton which readily attract the dye. After a thorough washing, the next process is the " chemicking," or treatment with bleaching powder, which is done in a machine similar to the squeeze-rolls used in the souring. The cloth while still wet is passed through a clear, cold solution of bleaching powder at y to 2 Tw. It is then piled in a heap and left for some hours. The bleach is partly decomposed by the carbon dioxide of the air, and hypochlorous acid is set free ; this decomposes in the presence of organic coloring matter, liberating oxygen, which destroys the color. If the bleach liquor is too strong the cotton is attacked and oxy cellulose formed, which is objectionable. After the chemick, the cloth is piled for a few hours ; then it is next subjected to the " white-sour." It is treated with dilute min- eral acid, to complete the liberation of chlorine from the bleach remaining in the fibre. Hydrochloric acid is the best for this, since it renders the lime more soluble. The cotton is completely decolor- ized, and after about three hours is thoroughly washed. It is passed through squeeze-rolls, and then opened out smooth and passed over large copper drums, heated by steam, to dry it thoroughly. The whole time necessary for the madder bleach is about five days. * These percentages are calculated on the weight of the goods. TEXTILE INDUSTRIES 451 For 24,000 kilos of cloth the following scheme is given by Hum- mel : * 1. Wash after singeing. 2. Lime-boil: 1000 kilos lime ; boil 12 hours; wash. 3. Lime-sour : hydrochloric acid, 2 Tw. ; wash. 4. Lye-boils : 1st : 340 kilos soda-ash (li per cent ash) : boil 3 hours. 2d: 860 kilos soda-ash ( = 3.6 per cent). 380 kilos rosin (= 1.6 per cent). 190 kilos solid caustic soda (= 0.8 percent). Boil 12 hours. 3d: 380 kilos soda-ash (=1.6 per cent); boil 3 hours; wash. 5. Chemicking : bleaching powder solution, y to y Tw. ; wash. 6. White-sour : hydrochloric acid, 2 Tw. ; pile 1 to 3 hours. 7. Wash, squeeze, and dry. The Turkey-red bleach is employed for cotton which is to be dyed a full color with alizarin red. It is essential that the fibre shall not be singed nor exposed to chlorine,f since the development of a brilliant red would be thus prevented. The process is there- fore simpler, the outline for 2000 kilos of cloth being as follows : $ 1. Wash. 2. Boil 2 hours in water ; wash. 3. Lye-boils : 1st: 90 liters of caustic soda solution, 70 Tw. (= 4-j- per cent of weight of goods) ; boil 10 hours ; wash. 2d: 70 liters of caustic soda solution, 70 Tw. (= 3J per cent of weight of goods) ; boil 10 hours ; wash. 4. Sour : sulphuric acid, 2 Tw. ; steep 2 hours. 5. Wash well, and dry. The market bleach differs from the madder bleach chiefly in that the singeing and rosin-boil are omitted and the cloth is starched and blued slightly before drying. An outline of the process is about as follows : 1. Gray-wash. 2. Lime-boil : 8 to 12 hours ; wash. * Dyeing of Textile Fabrics, p. 77. t The injurious action of the chlorine is supposed to be due to the formation of oxycellulose. J. Soc. Dyers and Colorists, 1886, 29. J Hummel, Dyeing of Textile Fabrics, p. 85. 452 OUTLINES OF INDUSTRIAL CHEMISTRY 3. Lime-sour: hydrochloric acid, 2 Tw. ; steep 2 to 4 hours; wasli well. 4. Lye-boils : 1st. 1^- to 3 per cent soda-ash ; boil 3 to 12 hours. 2d. 1 ^ to 3 per cent soda-ash ; boil 3 to 12 hours ; wash well. 5. Chemick : bleaching powder solution, -J- to -J- Tw. ; pile 6 to 12 hours. 6. White-sour : hydrochloric acid, 2 Tw. ; pile 3 hours ; wash. 7. Starched and blued. 8. Calendered. 9. Tentered and folded. Much care is taken in the finishing operations. The bluing is generally mixed with the boiled starch, and after passing through squeeze-rolls, the lightly starched cloth goes to the calender ma- chine. Here it is heavily pressed between hot, polished steel rolls to give it a smooth and glossy surface. Next it goes to the tenter- ing machine, which consists of a travelling frame with parallel sides, carrying clips or hooks, to which the cloth is fastened by the selvedges. The side rods of the frame have an intermittent back- ward and forward movement which stretches and draws the cloth in the direction of its width. Beneath are a number of flat steam- boxes, the heat from which rapidly dries the cloth. Finally, it goes to a folding machine, by which the cloth is laid in folds one yard in lengbh ; the number of yards required for a bolt is then cut off. Various modified bleaching processes have been devised, chiefly with the view of saving time, labor, and wear on the goods. That of Horace Koechlin has been introduced in some works. The lime- boil is abolished, and a single caustic soda and rosin-boil is substi- tuted for the lye-boils. A special horizontal kier is used, into which cars packed with the cloth can be run. The boiling here is not essentially different from that in the ordinary form, but the cars are run out and others immediately run in, without material cooling of the kier ; thus much time is saved. The chemicking, souring, and washing are carried on in the usual way. In the Mather-Thompson process* the same kier is used as in the Koechlin process, but a special apparatus is employed for the subsequent chemicking, followed by a soda-boil and a second chem- icking. After passing through the bleaching powder solution the * For details of this process, see Thorpe's Dictionary of Applied Chemistry, Vol. I, 321. TEXTILE INDUSTRIES cloth is exposed to the action of carbon dioxide gas to set free the hypochlorous acid ; this hastens the bleaching. The Hermite bleaching process* depends upon the electrolytic decomposition of magnesium or aluminum chloride, to form bleach liquors consisting of hypochlorites of these metals ; the liquors are employed instead of bleaching powder for chemicking. Peroxide of hydrogen used in conjunction with soap, magnesia, and caustic soda in a boiling bath gives an excellent bleach on cotton. But its cost is yet too great to allow of its general use for this purpose. Permanganate of potassium, in slightly acid solution, gives a very good bleach on cotton which has been boiled in caustic soda to remove gums and oily matters. Alkaline permanganate must be avoided, as it forms oxy cellulose. When removed from the perman- ganate bath, the goods are colored a deep brown, but a pure white is produced by passing them into a bath of sodium bisulphite or sulphurous acid. The process is worked cold and the goods must be thoroughly washed after bleaching. LINEN BLEACHING Linen contains more than 25 per cent coloring matter and other impurities (chiefly pectic acid, so-called), and the bleaching process is more, difficult and tedious, although essentially similar to that used for cotton. Linen is more readily attacked by alkalies, acids, or chlorine, and more care and time (from 3 to 6 weeks) are needed to prevent injury to the fibre. The liquors are much weaker and the processes are usually repeated several times. It is also cus- tomary to " grass " linen for a week ; i.e. to expose it to the sun and dew by spreading it on the grass. It is frequently moistened to assist in the bleaching. It is supposed that the ozone in the air is here the active agent. Linen is bleached in the form of thread, yarn, or cloth. Accord- ing to the degree of whiteness, it is said to be quarter, half, or three- quarters bleached, but the strength of the fibre diminishes as the purity of the white increases. The following outline of the Irish process for yarn bleaching is according to Hummel | : 1. Lye-boil : 10 per cent soda-ash in solution, boil 3 to 4 hours, wash and squeeze. 2. Chemick: reel one hour in bleaching powder solution at i Tw. ; wash. * Hurter, J. Soc. Chem. Ind., 1887, 337. t Hummel, Dyeing of Textile Fabrics, p. 88. 454 OUTLINES OF INDUSTRIAL CHEMISTRY 3. Sour : steep one hour in sulphuric acid at 1 Tw. ; wash. 4. Lye-boil (scald.) : boil one hour with 2 to 5 per cent soda-ash in solution ; wash. 5. Chemick : reel again as in (2) ; wash. 6. Sour, as in (3) ; wash well and dry. This gives a half bleach ; for three-quarters bleach, repeat Nos. 4, 5, and 6, but after the lye-boil (4), grass for a week; and in (5), instead of reeling the yarn, allow it to steep in the bleach liquor for 10 to 12 hours. Linen piece goods * are bleached similarly to cotton cloth, but the details vary. There are the same lime-boil, sour, and several lye-boils with caustic soda, then a grassing for several days, followed by a chemick, sour, and third soda-boil, another grassing, and a second chemick. If not white, the goods are rubbed between rub- bing boards with a strong soap solution, to remove mechanically the fine black specks called "sprits' 7 adhering to the fibre. This is followed by a third grassing, chemick, sour, and washing. Potassium permanganate has been recommended for linen bleach- ing in conjunction with sulphurous acid or hydrogen peroxide. These substances are said to act rapidly and to reduce the time of bleaching to a few days. Jute is bleached by simple treatment with bleaching powder solution, followed by a sour and a thorough washing. The bleach liquor is very strong, and the temperature rather high, 37 to 48 C. For a full bleach, three baths of bleach liquor are used, varying in strength from 20 per cent down to 5 per cent of bleaching powder, the yarn being hung in each tank for about three-quarters of an hour. Unless this is carefully done, the fibre is weakened. The use of weak hypochlorite of sodium is advocated in place of bleaching powder, the soda, it is claimed, preventing the formation of chlo- rinated derivatives of the jute. (In the presence of water, chlorine combines with the jute, forming yellow chlorination products.) Hemp is not often bleached, since its chief use is for cordage and twine, where the color is of no consequence. It is sometimes par- tially bleached by boiling in sodium silicate, washing and treating with bleaching powder solution for some hours, then souring in dilute acid and washing thoroughly. * Herzfeld, Handbuch der Farberei, p. 376. Also see Hummel. TEXTILE INDUSTRIES 455 'WOOL BLEACHING The preliminary operations of washing and scouring the loose wool have already been described on p. 444. After spinning, the yarn is left greasy, and a second scouring is necessary before bleach- ing or dyeing. Wool yarn, especially when tightly twisted, shows a decided ten- dency to curl and shrink when wet in warm water. As this would cause tangles and felting in the scouring and dyeing, the yarn is stretched on a strong frame carrying a number of projecting arms. A hank of yarn is hung over two of these arms, and is stretched tight by means of screws which separate the arms. When filled, the frame is submerged in boiling water for half an hour. It is then taken out, and the yarn allowed to cool while stretched. The hanks are then shifted so that the portion that was in contact with the arms now comes between them, and the entire process repeated. This removes all the " curl," and the yarn is ready for scouring, which may be done by hand or in machines. In the first method, the hanks are suspended from wooden rods in the tank containing the hot scouring liquor (soap solution), and are swung to and fro, with frequent turning of the rod, to wet all parts of the hank. They are then washed by swinging them in a tank of water. An effective scouring machine for yarn consists of a pair of squeeze-rolls placed over a tank filled with soap liquor, and containing several rollers, under and over which the hanks, tied together in a chain, are passed. Woollen cloth may be scoured in a scouring machine called a " dolly " ; the cloth is passed as a rope, through the soap liquor, and then between squeeze-rolls. But "goods which are liable to crease must be scoured in the open-width scouring machine. The cloth is then sprayed with clean water, returned to the soap bath, and again put through the squeeze-rolls. The dirty soap liquor expressed is caught in a special trough, and is run off. The cloth is finally washed with water to remove all the soap. Mixed goods, called " unions," composed of cotton warp and wool weft, or goods made of two kinds of wool, will " cockle " or wrinkle when wet, owing to unequal shrinkage. They are consequently " crabbed," to take the stretch out of the fibre. The cloth is passed through a bath of boiling water, and at once rolled tight and smooth on a roller or beam. After cooling on the roll, it is again passed through hot water, and rewound on a second beam. The process is repeated a third time, using cold water, and rolling the cloth under heavy pressure, obtained by a weighted roller resting on top of the 456 OUTLINES OF INDUSTRIAL CHEMISTRY beam. In order to stretch the goods under higher temperatures than they will be subjected to in the subsequent dyeing, they are next steamed by rolling them on a perforated iron cylinder, into which steam at 40 pounds pressure is admitted and forced through the whole thickness of the cloth. After cooling, it is rewound on another perforated roll, and steamed again. This rewinding brings those portions of the cloth which were on the outside of the roll, into the centre and nearer the steam entrance, so that the effect of the high temperature is made more even throughout the piece. The goods may now be scoured and dyed without shrinkage, provided that the temperature in these processes does not exceed that obtained in the crabbing and steaming. Wool cannot be bleached by any process similar to that used for vegetable fibre, since it would be dissolved by the lye-boils, while chlorine would combine with the fibre without destroying the natural yellow color. The bleaching agent most generally used is sulphur dioxide, or its solution in water as sulphurous acid. It is almost always used as gas, and the operation is called " stoving," sulphur- ing, or gas bleaching. It is carried on in a closed brick chamber, or " stove," about 6x10x6 feet, the wooden lining of which is made fast by wooden pegs, so that all metal (especially iron) is excluded. The washed and scoured hanks are hung on wooden rods, for 6 or 8 hours, in contact with the sulphur fumes produced by burning sulphur in a pot in the bottom of the stove. Thin cloth is stoved by passing it, in the open width, in a zigzag course up and down many times over rollers at the top and bottom of the chamber, which it finally leaves through the same narrow slit at which it enters. It may be pass 3d through the chamber several times, until sufficiently bleached. Sometimes the goods are soaked for 24 hours in a solution of sulphurous acid, or sodium bisulphite with mineral acid, and then wrung and washed. The action of sulphur compounds in bleaching wool is not entirely clear. By some authorities, the sulphur is supposed to decompose the water present, liberating hydrogen, which, in turn, unites with the color to form a colorless body. By others it is thought that the sulphur enters into combination with the coloring matter to form a colorless sulphite compound. But whatever the actual reaction, the bleach is not permanent, and after some time the yellow color gradually returns, especially if the goods are washed with soap or alkalies. Hydrogen peroxide is an effective but expensive bleaching agent TEXTILE INDUSTRIES 457 for wool. Since it affords a permanent bleach, the coloring matter is probably oxidized and destroyed. The goods are soaked at 15 C. for 24 hours in a 3 per cent solution of hydrogen peroxide, contain- ing 2 per cent of ammonia (sp. gr. 0.910). Increasing the temper- ature hastens the process. Hydrogen peroxide is also used for bleaching hair, furs, and feathers. SILK BLEACHING The boiling off and discharging of raw silk has already been considered (p. 439). It is often subjected to various mechanical treatments to increase its lustre, e.g. " stretching," in which the hanks are given a series of violent jerks while suspended from a fixed peg ; " glossing," in which they are twisted very tight ; or "lustring," by steaming them while in a state of great tension. Silk is bleached with sulphur dioxide, or with hydrogen peroxide, or with potassium permanganate and sulphurous acid. The stoving process, similar to that used for wool bleaching, is repeated several times, the silk being washed between each operation. It is then tinted with a trace of some blue or other coal-tar dye to make it appear a clearer white. Tussur silk is hard to bleach, and cannot be decolorized by stov- ing. A bath of barium peroxide in water, followed by dilute hydro- chloric acid, is recommended by Tessie du Motay. Ammoniacal hydrogen peroxide may also act on silk as on wool. But at best, tussur silk can only be bleached a light cream color. MORDANTS A mordant is a substance used in textile dyeing and printing, either to fix or to develop the color on the fibre. In the first case, it combines with the fibre, and forms a body having affinity for color- ing matter ; in the second, it becomes an essential constituent of the color when deposited on the fibre. Metallic mordants are abstracted from aqueous solution, wholly or in part, by the fibre, upon which they generally deposit metallic hydroxides or basic salts, which form color lakes in the dyeing process. Mordants are either of mineral or of organic origin. The former comprise the common mineral acids, and salts of aluminum, chro- mium, iron, copper, antimony, and tin, and to a lesser degree those of manganese, cobalt, nickel, uranium, vanadium, and tungsten. The organic mordants are certain organic acids, especially acetic, oxalic, tartaric, citric, lactic, the sulphated ricinoleic and oleic acids forming 458 OUTLINES OF INDUSTRIAL CHEMISTRY Turkey-red oil, and tannin substances, mainly derivatives of gallic or protocatechuic acids. Only the most important of these mordants can be mentioned here. Aluminum mordants are chiefly the acetate or "red liquor" (p. 262), sulphate (p. 240), and the alums (p. 244). The chlorides and nitrates are rarely used. Aluminum salts are used for mor- danting cotton, linen, and wool, but very seldom for silk. Alum and normal sulphate do not readily yield alumina to cotton. Basic sulphates are generally used, and deposit over 50 per cent of their alumina on the fibre, when it is steeped in them, and then dried and aged in a warm atmosphere. Sometimes the fibre is first soaked in some such substance as tannic acid, Turkey-red oil, or stannate of soda, which forms insoluble compounds with the alumina of the basic sulphate, or precipitates it as such in an insoluble form. The acetate is only used for Turkey-red, and the alumina is fixed by the evapora- tion of acetic acid during the aging. Alum and neutral sulphate are much used for wool, the fibre decomposing these solutions when boiled in them, and retaining the alumina in an insoluble form. The wool fibre is both acid and basic in character, dissociating these salts, and combining with both the acid and the base of the salt. This reaction is most complete at a boiling temperature ; but for the best results the salts must not be decomposed until they have had time to penetrate into the fibre. Decomposition is retarded by using tartrates or oxalates in con- junction w r ith the aluminum sulphate; these probably form alu- minum tartrate or oxalate by double decomposition, and the aluminum is slowly given up to the fibre. Acid potassium tartrate (cream of tartar) has the best effect, but free sulphuric, hydrochloric, or oxalic acids also retard the decomposition. Silk is very seldom mordanted in this way, as the lustre would be injured. Chromium salts, which react similarly to the aluminum salts, are used for cotton, linen, and wool. With these are included the chromates and bichromates, but in all cases chromic oxide, Cr 2 O 3 , is fixed on the fibre. Chromic acid and its salts act here as oxidiz- ing agents, and are themselves reduced to chromic oxide before deposition. Cotton and linen are difficult to impregnate with chromium salts. The sulphates, nitrates, and acetates are much used in calico print- ing, while bichromates and alkaline solutions of chromium hydroxide are used in dyeing and printing. The most successful method of mor- danting cotton with chromium salts is that proposed by H. Koechlin. TEXTILE INDUSTRIES 459 The cotton is soaked in the solution of chromium salt (preferably basic salt), dried and passed through boiling soda solution ; the pro- cess is repeated until the goods are sufficiently mordanted. Another process is to prepare the goods with tannin, or with Turkey-red oil, and then soak them in the chromium solution ; the fixing is done in cold lime-water. A solution of basic chromium acetate is used for cotton; after steeping some hours, it is dried and steamed in a closed chamber, to fix the chromium oxide on the fibre. Wool is mordanted with chromium fluoride, chrome alum, or bichromate (chromic acid). Chrome alum yields the largest quan- tity of chromium to the fibre, but in dyeing, the result is less satis- factory than with bichromates. The addition of cream of tartar to chrome alum is an improvement. Chromium fluoride mordants wool very well, being easily but slowly decomposed, without the use of tartrates. A little oxalic acid is generally added. The chromic acid thus deposited on the fibre does not effect the feel or spinning quali- ties of the wool, while the hydrofluoric acid set free appears to have no injurious action on the dye or goods. Potassium bichromate is the most generally useful mordant for wool, yielding fast and brilliant colors on dyeing. The mordant bath contains potassium bichromate to the amount of 2 to 4 per cent of the weight of the wool, dissolved in water equal to 50 to 100 times the weight of the wool. The goods are boiled in this for one or one and a half hours, and washed, and are then ready for dyeing. Sulphuric acid is sometimes added to the mordant bath in small amounts, but better results are obtained with oxalic acid or cream of tartar, which reduce part of the bichromate to chromium hydroxide on the fibre ; by treating the chromed wool in a bath of sodium bisulphite the reduction is more complete. An excess of chromic acid in the fibre oxidizes the color, deadening it when dyed, and also weakens the fibre. Such "overchromed" wool is said to be greatly improved by reduction of the bichromate in the fibre before dyeing. The nature of the changes which take place in mordanting wool with bichromate has been much studied, but is not yet clearly proved. The work of Knecht,* and of Kay and Bastow, t indicate that the potassium bichromate is partly dissociated into neutral chromate and chromic acid: K 2 Cr 2 O 7 = K 2 Cr0 4 + Cr0 3 , * Journal of the Society of Dyers and Colorists, 1888, 104; and 1889, 186. Mbid., 1887, 118. 460 OUTLINES OF INDUSTRIAL CHEMISTRY the latter being absorbed by the fibre, while the neutral chromate remains in the bath. This chromic acid is subsequently reduced during the dyeing. Silk is sometimes mordanted with basic chromium salts, and potassium bichromate is occasionally used as an oxidizing agent in dyeing catechu browns and logwood blacks. Iron salts are largely used, both in dyeing and printing, and on all fibres. Both ferrous and ferric salts are employed, the most im- portant being sulphates, basic sulphates (nitrate of iron), acetates, and nitrates. They are not only applied as mordants, but also as oxidizing and weighting materials to modify the shades of color, or to increase the stiffness and density of the goods. With most dyes, iron salts tend to " sadden " or darken the shade, and are therefore chiefly used for dark colors, especially browns and blacks. In mordanting, the iron is usually fixed on the fibre as hydroxide or tannate. Cotton is treated with ferrous sulphate (copperas, p. 237), after having been previously steeped in tannin, thus precipitating tan- nate of iron on the fibre. Ferrous acetate (pyrolignite of iron, p. 263) is used by impregnating the fibre with the solution, drying, and aging, or the goods may be passed through lime-water. It is also used with tannin-prepared cotton. Nitrate of iron (basic sul- phate, p. 123) is generally used for cotton, which is merely saturated in the solution, and then passed into lime-water or sodium carbonate solution, the process being repeated until sufficient hydroxide has been deposited on the fibre. Iron buff is produced in this way. Sometimes the goods are prepared with tannin, passed through the lime-water to form calcium tannate, and then into the iron solution. This produces ferric tannate, varying in color from brown to black. Wool is sometimes mordanted by boiling with oxalic acid and copperas, the latter chiefly to sadden the color ; but other iron salts are not used. Silks are extensively treated with iron salts in dyeing blacks. The pyrolignite of iron is chiefly used on raw silks which have been previously prepared with tannin, preferably chestnut extract. The silk is worked in a warm (60 C.) pyrolignite of iron solution, ex- posed to the air for a short time, and then washed. By sufficient repetition of this treatment the weight can be increased from 200 to 300 per cent of the original weight of the silk. Hard water greatly assists this process. The color produced is a bluish black ; the lus- tre is dulled, but is restored by a bath of very dilute hydrochloric acid, to which a little olive oil has been added. Boiled-off silk is weighted and dyed by the use of nitrate of iron, TEXTILE INDUSTRIES 461 the silk being worked in the iron liquor, washed, and put into a boil- ing soap solution composed of "boiled-off liquor" (p. 439), olein soap, and a little soda crystals. This precipitates the ferric hydrox- ide. The silk is then washed with hard water (which helps fix the iron), and the whole process repeated until sufficient iron has been deposited on the fibre. With each operation, the weight of the silk is increased about 4 per cent, and the color becomes dark brown, though the lustre is preserved. This weighted and mordanted silk is then dyed black. Eaw silk is also weighted with nitrate of iron and has greater affinity for the iron salt than has boiled-off silk. Copper salts are chiefly used as oxidizing materials in mordant- ing, acting as carriers of oxygen. Copper sulphate (blue vitriol, p. 239) and acetate (verdigris, p. 204) are most used. Copper sulphate is used in producing logwood blacks and cutch browns on cotton. On wool, it is used together with aluminum sul- phate and copperas for logwood blues and blacks, and also with potassium bichromate. Copper salts act as saddeners for logwood blacks on silk. Antimony salts used as mordants are tartar emetic (potassium antimony tartrate), double oxalates of potassium and antimony, and fluorides of antimony and sodium. They are always used after tan- nin mordanting on vegetable fibre, where they form antimony tannates. They are not used for silk or wool. Tartar emetic is generally employed, and its application is very simple ; the tannin- mordanted cotton is passed at once into a cold bath of the salt, and then thoroughly washed before drying. Tin salts are valuable mordants, yielding especially brilliant shades. The salts chiefly used are stannous chloride (tin crystals, SnCl 2 2 H 2 0), stannic chloride, SnCl 4 , sodium stannate (" preparing salt," Na^SnOg), and stannous nitrate, Sn(N0 3 ) 2 (known only in solu- tion). " Tin sjjirits " is a general name for a number of tin solutions of various composition, made with nitric, sulphuric, or oxalic acid. By dissolving granulated tin in concentrated hydrochloric acid, a so- lution of stannous chloride is formed, which is sold as "muriate of tin" ; or tin crystals are separated from it, and the mother-liquors, containing a large amount of tin chloride, are often sold as muriate of tin, single or double, according to the strength. "Pink salt" is a double stannic-ammonium chloride, SnCl 4 -f 2 NH 4 C1, formerly much used as a mordant. Various solutions of stannic salts were much used under such names as Cotton Spirits, Pink Cutting Liquor, Oxy- muriate of Tin, Solution of Tin, etc. '\ B R A 462 OUTLINES OF INDUSTRIAL CHEMISTRY Cotton and linen are not often mordanted with stannous salts, but being powerful reducing agents, they (especially tin crystals) are used by the calico printer in " discharges," or " resists." Stannous chloride reduces iron salts and is used to neutralize the effect of iron impurities in calico printing. Stannic salts are much used as mor- dants on cotton and linen, when these are dyed with natural dye- stuffs, such as camwood, barwood, fustic, etc., and for some of the aniline dyes. Tannic acid is used before the tin, and stannic oxide or stannic tannate is fixed on the fibre. Stannate of soda is also used to mordant cotton and to prepare it for printing ; the goods are steeped in the solution and then passed into a bath of dilate mineral acid or aluminum sulphate, which precipitates stannic hydroxide on the fibre. Wool is often mordanted with stannous chloride by entering it in a cold bath of about 4 per cent tin crystals (calculated on the weight of the wool) and 2 per cent oxalic acid or cream of tartar. This is then slowly heated to boiling. Too much tin salt makes the wool harsh and prevents proper felting in the milling process. Stannic chloride is not a suitable mordant for wool, but impure mixtures of stannic and stannous salts are often used as mordants for cochineal scarlets on wool. Wool is sometimes prepared with sodium stannate for printing, followed by treatment with dilute sulphuric acid. Black silks are weighted with stannous chloride together with catechu, on fibre which has already been weighted with iron. For weighting light-colored silks, stannic chloride (tin spirits) is often used. The raw fibre is steeped in a solution of tin salt until im- pregnated, and the tin hydroxide is fixed by treatment with cold di- lute soda solution, or by merely washing in water. The silk is then " boiled-off " in soap liquor to remove the harsh feel. The weight is increased about 25 per cent by this process. But stannic chloride has an injurious action on the fibre if too strong (over 50 Tw.) and shrinks it very much, besides destroying certain dyes which may be afterwards used. Acetic acid (p. 261) is largely used in dyeing and printing, but more as an assistant than a mordant. It neutralizes many bases without affecting the dyeing process, and it does not attack vegeta- ble fibre under any conditions. Crude pyroligneous acid contains reducing substances, and because of this is used where oxidation is to be prevented. Oxalic acid, H 2 C 2 4 2 H 2 0, forms crystals readily soluble in water. It is largely used in dyeing, mainly as an addition to the dye-bath to retard the deposition of the color, and for a fixing agent TEXTILE INDUSTRIES 463 in mordanting wool with bichromate, aluminum sulphate, or cop- peras. Tartaric acid, C 2 H 2 (OH) 2 (COOH)2, is often used as an addition to the mordant bath for wool, and to the d}^e-bath to retard the dyeing, and in clearing and brightening the color on silk after dyeing ; also as a " resist " and " discharge " in calico printing. The most im- portant tartrates are cream of tartar, C 4 H 4 4 (OH) (OK), and tartar emetic, C 4 H 4 6 K - (SbO) + H 2 0. Citric acid, C 3 H 4 (OH)(COOH) 3 , and lactic acid, C 2 H 4 (OH)COOH, (p. 415), are used somewhat in place of tartaric acid, but more especially as resists, etc., in calico printing. Turkey-red oil (p. 312), or soluble oil, is used as a mordant on cotton for dyeing with basic dyes and Turkey-reds, and for preparing cloth for calico printing. TANNINS Tannins, many of which are used in tanning, are also very impor- tant mordants, their value here depending upon the fact that they are readily absorbed by cotton, linen, and silk, while they retain their property of precipitating insoluble metallic compounds in the fibre, and also of uniting with the basic dyes. They may be divided into two classes : (a), those related to gallic acid (trioxyberizoic acid), and (6), those related to protocatechuic acid (dioxybenzoic acid). When heated, the former yield pyrogallol, and the latter, pyrocate- chin (orthodioxy benzene). Tannic acid is the most important of the tannins. It is a digallic acid, C 6 H 2 (OH), CO 2 - C 6 H 2 (OH) 3 . C0 2 H. It is soluble in six parts cold water, and is obtained by extracting powdered gall-nuts with water, alcohol, and ether. On evaporation the aqueous solution yields the tannin as a colorless, or light yellow, amorphous, scaly, or vitreous mass. Tannic acid is precipitated from aqueous solution by dilute sulphuric, or hydrochloric acid, by alka- lies, chlorides, etc., but not by nitric acid, or Glauber's salt. Gela- tine or untanned hide removes it completely from solution. It is a weak acid, but will decompose alkali carbonates. It is easily oxid- ized, and reduces many metallic salts, Fehling's solution, and per- manganates. It forms a blue-black precipitate with ferric salts, and belongs to group (a), above mentioned. The tannins occur in numerous plants, being found in the roots, bark, wood, leaves, flowers, fruit, seed-pods, or in excrescences on the plant. The chief commercial sources are gall-nuts, sumach, oak and hemlock bark, mimosa bark, chestnut wood, cutch (catechu), gambier, myrabolans, valonia, divi-divi, kino, quebracho, and canaigre. 464 OUTLINES OF INDUSTRIAL CHEMISTRY Galls, or nut-galls, are excrescences on various kinds of oak trees, produced by the sting of the female gall wasp, Cynips gallon tinctorice, Oliv., and in which the eggs are deposited. Young nut-galls, from which the insect has not yet escaped, are greenish or bluish in color, and are very rich in tannin; afterwards they become yellow, and the percentage of tannin is very much decreased. The best qualities come from Persia, but the Levant galls, from Smyrna and Tripoli, contain from 55 to 60 per cent tannic acid and some gallic acid. Poorer grades come from Italy, France, Germany, and Austria. Japanese and Chinese galls are caused by the sting of an insect (plant louse) on the leaves of plants (Rlius semialata, Murr.) of the sumach family. These galls are very irregular in shape, and are light and hollow, but contain 70 per cent tannin, or even more. Sumach of commerce consists of the leaves and young twigs from various plants of the Hhus family, especially Rlius Coriaria, L. ; poorer grades are derived from R. Cotinus, L. These shrubs are found in many countries, but Italy, Spain, Greece, and Virginia fur- nish the better grades. Sumach is largely used in mordanting, since it contains very little coloring matter to stain the goods. Good sam- ples contain from 15 to 20 per cent of tannin, and are sold as a fine powder, or as leaves, mixed with twigs and stems. Much is now sold as " extract," a thick brown liquid obtained by evaporating the aque- ous solution, usually in vacuum. Catechu, or cutch (terra japonica), is obtained from the wood and pods of Acacia Catechu, Willd., and from the betel nut, the fruit of the Areca Catechu, L., a species of palm-tree. Both plants are natives of India. Cutch appears in commerce as dark brown, irregu- lar lumps, which dissolve in water, forming a dark brown solution. It contains a tannin called catechu-tannic acid, and another body, catechin. It is extensively used as a brown dye on cotton, for calico printing, and also in the weighting of black silks. It is a good mor- dant for certain basic coal-tar dyes, when employed in dyeing com- pound shades. On cotton, copper salts should always be used in conjunction with cutch. Gambler is extracted from the leaves of an Indian shrub, Uncaria dasyoneura, Korth. It has a yellow color, and is used somewhat as a pigment and as a yellow dye. It is slightly soluble in cold water, and very readily so in hot water. In commerce it appears as small cubical blocks, containing about 40 per cent tannin, chiefly as cate- chu-tannic acid. Gambier is used in silk and cotton dyeing, much in the same way as catechu. It is extensively used in tanning Mo- rocco leather. TEXTILE INDUSTRIES 465 Myrabolans are the dried fruit of certain Indian and Chinese trees, Myrobolanus Chebula, Gsert. They appear in commerce as dried and shrivelled nuts about an inch long, containing about 30 per cent tannin (ellagitannic acid), and also a brownish coloring matter. They are used in place of tannic acid, for some purposes in mordanting cloth, and also in weighting black silks. Valonia is the acorn cups of an oak, Quercus ^Egilops, L., native of Greece, Asia Minor, and France. The cups are very large, and cov- ered with coarse hair, or " beard," which is especially rich in tannin. They are drab in color, and contain a yellow coloring matter. Good valonia contains about 30 per cent of true tannic acid. Divi-divi is the fruit of a West Indian tree, Ccesalpinia coriaria, "Willd. It forms very thin pods about three inches long, and often folded and twisted, and containing about 30 per cent of ellagitannic acid, with some gallic acid. The color of the pods varies from light brown to black, and considerable coloring matter is present, which stains the goods. It is used for mordanting blacks on cotton and silk. Chestnut, Castanea saliva, Mill., furnishes a tannin extract, the composition of whose tannin is unknown. The extract is a black solid, or a brown syrup, forming turbid solutions with water. It is very extensively used in weighting black silk. Kino is the dried sap of certain trees, Pterocarpus Marsupiurrij Roxb., Butea frondosa, Roxb., and Eucalyptus rostrata, Schlecht. It forms small garnet-red angular grains, slightly soluble in water, and contains a large quantity of kinotannic acid, a substance of unknown composition. The chief supplies come from India, Africa, and Australia. It is chiefly used in medicine, and resembles catechu. Oak and hemlock bark are rich in tannins, containing about 15 per cent, but they are contaminated with certain anhydride substances which are slightly soluble in water, and color the goods a deep brown or red, and hence are unsuitable for mordants. These anhydrides are called phlobaphenes, and are much like the tannins in their action, combining with fibre and precipitating gelatine, ferric salts, etc. These barks are extensively used for making leather, especially the heavy and strong kinds. Mimosa bark is obtained from several species of Acacia in Aus- tralia. It contains about 24 per cent tannins, which are derivatives of protocatechuic acid. Quebracho is an extract made from hardwood trees, Aspidosperma Quebracho, Schlecht, and Quebrachia Lorentzii, Griseb., natives of South America. It contains about 25 per cent of tannins, contami- nated with red coloring matter. 466 OUTLINES OF INDUSTRIAL CHEMISTRY Canaigre is obtained from the roots of a species of dock, Mumex hymenosepjtlus, Torr., a native of Arizona and New Mexico. It is now extensively cultivated in the southwestern part of the United States. It contains about 30 per cent of tannin, together with a bright yellow coloring matter, much resembling gambier. It is always sold as extract. Extracts are now prepared from nearly all of the above tannin substances, by treating them with water and evaporating the tannin solution to a thick syrup, or even to dryness, generally by the aid of vacuum. These extracts are much more economical to ship, and more convenient to use, but are frequently adulterated with glucose or other matter. COLORING MATTERS NATURAL DYESTUFFS Natural dyestuffs have been employed for textile coloring since prehistoric times. They are soluble in water and have more or less tendency to combine directly with the fibres. Many of them are not in themselves dyes, but form color lakes by combination with mordants. In recent years they have been very generally replaced by the more brilliant and readily applied artificial colors. Indigo is one of the oldest known dyes, and probably originated in India. It exists in the indigo plant, Indigofera tinctoria, L., and in woad, Isatis tinctoria., L., in the form of a glucoside, indican, C 26 H S1 N0 17 , which is decomposed by acids to form the coloring prin- ciple indigotine, C 16 H 10 N 2 2 , and a sugar. To isolate the coloring matter, the stems and leaves of the plant are put into a cemented cistern and covered with water. A fermentation soon begins, caus- ing a rise in the temperature, while the indican is decomposed and the sugary matter destroyed ; at the same time, the indigo is reduced to indigo white, C 16 H 12 N 2 2 . This dissolves to form a greenish- yellow liquid, which is drawn off into vats and violently stirred and splashed by the workmen for several hours, in order to thoroughly aerate and oxidize the indigo white. The blue pigment precipitates, and after settling, the liquor is drained off. The magma is re- peatedly washed and finally boiled, to prevent any further fermenta- tion, and is filtered, drained in cloth-lined frames, and finally pressed into cakes ; these are carefully dried, away from the sunlight. The yield is about 0.2 to 0.3 per cent of the weight of the plant. The indigo of commerce forms dark blue cubical cakes having a matt, earthy appearance on the fractured surface. Its content TEXTILE INDUSTRIES 407 of pure indigo varies from 20 to 90 per cent and averages about 45 per cent. It contains indigo red and indigo brown, which affect the shade of the blue; also moisture and mineral and glutinous substances. Indigo is tasteless, odorless, insoluble in water, alcohol, ether, dilute acids or alkalies. By careful heating it sublimes. If very finely powdered, concentrated and fuming sulphuric acid dissolve it to form mono- and disulphonic acids, the latter being soluble in water. The sodium salts of these indigo sulphonic acids constitute the indigo extract, soluble indigo, or indigo carmine of commerce.* These are obtained by neutralizing the sulphuric acid solution of indigo with sodium carbonate, and precipitating the indigo carmine by adding common salt. True indigo carmine is the sodium salt of the disulphonic acid, and is dyed on animal fibres as an acid dye, p. 484; when sold as a dry powder it is called "indigotine." For methods of indigo dyeing, see p. 489. Logwood is the heart wood of a tropical tree, Hcematoxylon Campecliianum, L., native in Central America. It is brought in commerce in the form of logs, chips, and extract. The chromogen (p. 479) in the wood is hcematoxylin, C 16 H 14 6 , which forms nearly colorless crystals when pure; it exists in the wood as a glucoside and partly in the free state. It is readily oxidized, especially in the presence of an alkali, to form haematein, C 16 H 12 6 , which is the real dyestuff. This forms colored lakes with metallic bases, yielding violets, blues, and blacks with the various mordants. The logs are chipped or rasped to form a coarse powder, which does not contain much haematein when fresh, the dyestuff being formed by "curing" or oxidizing. The rasped wood is fermented by moistening with water and exposing in heaps to the air. To control the temperature and give better exposure, the heap is shovelled over and sprinkled with water at frequent intervals, until the chips assume a deep, reddish-brown color, or even develop a bronze shade. Alkalies, potassium nitrate, chalk, or ammonium chlorate are sometimes added to hasten the process. The cured chips yield a decoction which is rapidly taken up by the fibre in dyeing operations. The amount of water in cured ,chips is nearly double that contained in the fresh wood. Most " extract " of logwood is now made from chips which are not cured. They are put into an extractor, an iron vessel provided * Artificial indigo is made from orthonitrophenylpropiolic acid, by heating with caustic soda solution in the presence of a reducing substance, such as glucose. This method is only used in certain forms of calico printing, the blue being thus developed directly on the fibre. But the cost of natural indigo is still less than that of the artificial product. 468 OUTLINES OF INDUSTRIAL CHEMISTRY with a false bottom and a perforated steam coil. The extractors are often set in batteries, so arranged that the liquor from one flows into the next more recently filled vessel, finally leaving that con- taining the freshest wood. Pressure extraction is often used, but an increase of over 15 pounds is liable to cause decrease in the coloring power of the product. After settling to separate wood fibre and resin, the liquid from the extractors is evaporated in. vacuum pans, the Yaryan being often used for the dilute liquors. When it becomes thick, the evaporation is continued in a common vacuum pan (strike pan) until a density of about 50 Tw. is reached for liquid extract ; or it may be continued until a solid extract is obtained 011 cooling. Throughout the process, precautions are taken to prevent access of air and consequent oxidation of the product. The use of chemicals to develop the color in the extract itself is of doubtful value, as this development should only take place in the dye-bath. The yield of solid extract is about 20 per cent with pressure, and without pressure about 16 per cent. Logwood extract is frequently adulterated with glucose, molasses, and chestnut, hemlock, and quercitron extracts. Logwood is chiefly used with a chrome or iron mordant for blacks on wool and cotton. Red woods of commerce are Brazil wood, Ccesalpmia Bmsiliensis, L., and Pernambuco wood (C. Crista, L.), from Brazil, West Indies, and Bahama ; sappan wood, C, Sappan, L., from China, Japan, and Siam; Lima wood, C. bijuga, Sw., from Central America; and peach wood, (7. ecliinata, Lam. These contain the chromogen bmsilin, C 16 H 14 O 5 , which is chemically related to hsematoxylin. Brasilin is colorless, but dissolves in alkalies, forming a red solution which oxidizes on exposure to the air, forming brasilein, CwH^Oa; this combines with alumina to form red lake similar to alizarin red, but more fugitive. Another class of red woods contains santalin (C 15 H 14 5 ). These resemble Brazil woods in color, but are heavier and of harder text- ure. The more common ones are sandal wood, Pterocarpus santa- linus, L., from Madagascar and the East Indies ; bar wood, Baphia nitida, Lodd., and camwood. Madder is the pulverized root of Rubia tinctorum, L., a plant formerly largely cultivated in Europe and Asia Minor. It contains glucosides which are decomposed by fermentation, forming alizarin, C 14 H 6 2 (OH) 2 , and purpurin, C 14 H 5 2 (OH) 3 , which are identical with di- and trioxyanthrachinon. Madder extract is prepared by fer- mentation and evaporation of the filtered solution, yielding "gar- ancine " and " madder flowers." TEXTILE INDUSTRIES 469 Madder has been used for ages in dyeing Turkey-red on cotton, affording one of the brightest and fastest colors. But in 1868, Grsebe and Liebermann made artificial alizarin from anthracene derived from coal-tar. In consequence of this discovery, the madder industry has nearly disappeared. Archil or orseille (cudbear) is an important dyestuff derived from certain lichens, Roccella tinctoria, D. C., E. fuciformis (L.) D. C., indigenous in Madagascar, Zanzibar, Azores, Ceylon, and France, and Lecanora tartarea, Achar., from Sweden. They contain mixtures of phenols and phenol acids, which, when treated with ammonia and exposed to the air, yield orcein, a violet powder sold as "cudbear." It is either a paste or powder prepared by evaporating the aqueous extract to dryness in vacuum. The powder dissolves in alkalies and forms colored lakes with heavy metals and lime. It was for- merly much used in wool dyeing, yielding violet and red shades. Litmus is obtained by treating the above mentioned lichens with ammonia and potash, and fermenting the mass. The dyestuff forms a red color-acid, whose alkali salts are blue. The commercial article consists of calcium carbonate, or sulphate, which is mixed with the coloring matter and formed into small cubes. It is not used as a dye, but is interesting because of its use as an indicator. Cochineal consists of the dried bodies of the female insects, Coccus cacti. These insects live on certain cactus plants in Mexico, Central America, Algeria, and the East Indies ; they are collected, and killed by placing them in ovens or in hot water, or by steaming them. When killed by dry heat, the cochineal is coated with a silvery gray powder, consisting of a wax, coccerin; but if boiled or steamed, the cochineal is " black," and of less tinctorial power. The silver gray is often imitated by dusting the black cochineal with powdered stearic acid or talc. The coloring principle is carminic acid, C 17 H 18 IO , a glucoside, soluble with a deep red color in water, and forming scarlet lakes with alumina and tin salts. Cochineal contains about 10 per cent carminic acid. The dye is chiefly used on wool. Cochineal yields the pigment carmine (p. 212). Lac dye is also obtained from an insect, Coccus lacca, which exudes the lac resin (p. 344). The collection and preparation of the resin involves the preparation of the dye. The latter is very similar to carminic acid, and is prepared by extracting the gum with sodium ' carbonate. Kermes is similar to cochineal, and consists of dried insects, Coccus ilicis, from northern Africa and Spain. It is seldom used in dyeing at the present time. 470 OUTLINES OF INDUSTRIAL CHEMISTRY Fustic is the heart wood of Chlorophora tinctoria, Gaud., or Madura tinctoria native in West Indies and tropical South America. It yields a coloring principle, morin, C 12 H 8 5 , which forms lemon yellow lakes with alumina. It is sold as chips, and as an extract, and is chiefly used for wool dyeing, especially for modifying the shade of logwood, and other dyes. Young fustic is the heart wood of a sumach, Rlius CQtinus, L., native in Spain, Italy, Hungary, and the Levant. It yields an orange-colored lake with alumina and tin. The color principle is a glucoside, fustin. Quercitron is the powdered bark of the North American tree, Quercus coccinea, var. tinctoria, Gray. It contains a dyestutf, quer- citrin, C^M^Oso, which is converted by dilute acid into quercetin, C^H^On, and isodulcit, C 6 H 14 6 . Quercetin dissolves in alkali with a yellow color, and forms yellow lakes with alumina and tin. By extracting the bark with alkali, and neutralizing the extract with sulphuric acid, a mixture of quercitrin, quercitin and isodulcit is obtained, which appears in commerce as "flavine." Both the bark and the extract are used in wool dyeing and calico printing. Persian berries are the dried fruit (berries) of certain buckthorn (Rhamnus) species, growing throughout southern Europe. The col- oring principle is a glucoside, which is decomposed by acids into isodulcit and rhamnetin, Ci 2 H 10 5 , the latter being the dyestuif . It forms yellow and orange shades with alumina and tin, arid is mainly used in calico printing. Curcuma, or turmeric, is the dried root of various species of Curcuma of Central Asia. The dyestuif is curcumin, C 14 H 14 4 , which yields a tolerably fast yellow on cotton. It is also used to color oils, and wax. Annatto (arnotto) is obtained from the fruit of the West Indian and South American trees, Bixa Orellana, L. It contains the orange dye, bixin, C 2 8H 34 5 , and comes in commerce as a thick paste, or dry cakes. It is mainly used for coloring butter and cheese. dutch is described on p. 464. ARTIFICIAL DYESTUFFS The artificial organic dyestuff industry originated in England with the discovery of the lilac color, mauve, by Perk in, in 1856. This was obtained by direct oxidation of aniline containing toluidine. In 1859 Verguin made magenta, or fuchsine, and each following year other colors were discovered, until at the present time there are several thousand dyes on the market, and a stupendous industry has TEXTILE INDUSTRIES 471 arisen in their manufacture. Because the first dyes were prepared from aniline, the colors were known as "aniline dyes/' a name still applied to them as a class, but they are more generally called "coal-tar dyestuifs." They are derived from various substances, most of which are derivatives of aromatic bodies, especially those of benzene, naphthalene, and certain pyridine bases, particularly quinoline. The limits of this book will not permit a full consideration of the individual dyestuffs, and recourse must be had to the numerous handbooks mentioned in the references. The coal-tar colors may be divided into the following groups * : I. Aniline, or Amine dyes. (a) Eosaniline derivatives. (6) Safranines and Indulines. (c) Oxazines. (d) Thionines (sulphur compounds). (e) Aniline black. II. Phenol dyes. (a) Nitro bodies. (6) Nitroso bodies. (c) Phthaleins and Indophenols. (d) Rosolic acid. III. Azo dyes. IV. Quinoline and acridine derivatives. V. Anthracene dyes. VI. Artificial Indigo. I. The aniline or amine dyes include all those which contain derivatives of nitrogenous bases, excepting only the azo colors. (a) The rosaniline group contains derivatives of amido-triphenyl methane, in which three benzene rings are attached to the same car- bon atom. The hydrogen of the amido groups may be replaced by other radicals, and thus the structure of the individual dyes becomes very complex. These substances are made from aniline or its homo- logues. The most important dyes of this group are the following : Magenta, or fuclisine, consists of rosaniline and para-rosaniline hydrochlorides, and is made by oxidizing aniline containing toluidine with nitrobenzene ; formerly arsenic acid or mercuric chloride was used as the oxidizing agent. * After Beuedikt-Knecht, Chemistry of Coal-Tar Colors. 472 OUTLINES OF INDUSTRIAL CHEMISTRY Add magenta, or fachsine S, is an alkali salt of tlie trisulphonic acid of ordinary magenta. Methyl violet, or Paris violet, is a salt of pentamethyl-para-rosani- line, made by oxidizing dimethyl-aniline with copper chloride. Methyl green is formed from methyl violet by the action of methyl chloride. Alkali blue, or Nicholson's blue, is the sodium salt of the mono- sulphonic acid of triphenyl-rosaniline blue, which latter is formed by the action of aniline upon para-rosaniline, in the presence of oxalic or benzoic acids. Benzaldehyde green, or malachite green, is made by heating dimethyl- aniline with benzaldehyde in the presence of fused zinc chloride. Acid green, or Helvetia green, is the sodium salt of the monosul- phonic acid of benzaldehyde green. Auramine is a yellow dye made by treating dimethyl-aniline with phosgene (COC1 2 ), and heating the product to 150 C. with ammonium chloride and zinc chloride. (6) The safranines, indulines, and nigrosines are basic dyes which are not of similar composition, but are derived from the same sub- stances. Safranine is made by oxidizing a mixture of one molecule of a diarnine (e.g. para-phenylenediamine, C 6 H 4 (NH 2 ) 2 ) and two molecules / / 3 x of a monamine ( e.g. toluidine, C 6 H 4 ^ . The dye comes in NNH,' commerce as the chlorhydrate of the color base. Magdala red (naphthalene red) is made by heating amidoazonaph- C 10 H 7 N thalene, II , with the hydrochloride of a-naphthylamiue, C 10 H 7 NH 2 HC1. It is chiefly used in silk dyeing. Mauvein (mauve) is made by oxidizing aniline containing tolui- dine, with chromic acid. It is the first aniline color that was made. Induline (indigo substitute, fast blue) is made by heating amido- azobenzene with aniline. The product is rendered soluble by con- version into a sulphonate. Nigrosine is a bluish-gray dye made by heating aniline-chlor- hydrate with nitrophenol. (c) Oxazines are represented by cotton blue, prepared by treating /?-naphthol with nitrosodimethyl-aniline hydrochloride ; gallocyanine, made by treating gallic or tannic acid with nitrosodimethyl-aniline hydrochloride; Nile blue, made by the action of nitrosodimethyl- meta-amidophenol on a-naphthylamine. TEXTILE INDUSTRIES 473 (d) Thionines are dyes containing sulphur, and are made from para-ainido bodies. The most important dye of this class is methylene blue, tetramethyl-thionine chloride, made by treating nitrosodimethyl- aniline with hydrogen sulphide, and oxidizing with ferric chloride. (e) Aniline black is of unknown composition. It is always pro- duced directly upon the fibre by methods given on p. 491. II. The phenol dyes contain hydroxyl groups, imparting acid properties to the dyestuff. (a) Nitro dyes are, for the most part, yellow dyes having a strong acid character. By reduction in acid solution, they yield colorless amido compounds. Picric acid is trinitrophenol made by nitrating either pure car- bolic acid or phenyl-sulphonic acid. It forms yellow, scaly crystals, and is used in silk and wool dyeing. Its alkali salts are explosive. Victoria yellow is made by treating para-toluidine, C 6 H 4 CH 3 NH 2 , or para-cresol, C 6 H 4 CH 3 OH, with nitric acid. Naphthol yellow (Martins yellow) is the sodium, potassium, or lime salt of dinitro-tt-naphthol. It yields a gold yellow on silk and wool, but is volatile when slightly heated. Naphthol yellow S is made by nitrating a-naphthol trisulphonic acid, C 10 H 4 (S0 3 H) 3 OH by which two of the sulphonic acid radicals are replaced by nitro groups. It is much faster than the preceding dye. Aurantia is made by nitrating diphenylamine or methyl-diphenyl- aniine, CH 3 N(C 6 H 5 ) 2 . The commercial dye is the ammonium salt. (6) Nitroso bodies produced by the action of nitrous acid on phenols yield coloring matters; only those derived from resorcin are important. Resorcin blue is the ammonium salt of tetrabromresorufin. Ee- sorcin is treated with nitrous acid to form nitrosoresorcin, which combines with more resorcin in the presence of sulphuric acid to form resorunn. This is then treated with bromine. (c) Phthaleins are produced from phthalic acid or its anhydride by combining with phenols. The products are derivatives of tri- phenyl-methane, and a number of very important dyes are found in this group. Phenol-phthale'in is produced by the moderate heating of two molecules of phenol with one molecule of phthalic anhydride. It is only used as an indicator in alkalimetry. Fluorescein, derived from resorcin and phthalic anhydride, is the base of the important eosins. The sodium salt of fluorescein is the 474 OUTLINES OF INDUSTRIAL CHEMISTRY dyestuff uranin. Eosins are the halogen derivatives of fluoresce'in ; the eosin yellow shade, or eosin G, is the sodium salt of tetrabrom- fluorescei'n ; eosin B, or erythrosin, is the alkali salt of tetraiodofluo- rescei'n ; rose Bengale is the tetraiododichlorfluorescei'n ; $)liloxin is the tetrabromdichlorfluorescein These dye brilliant pinks having a yellow fluorescence, on silks and wools. Rhodamine is made by heating phthalic anhydride with diethyl- I, CH/ X OH 2 H 5 ) 2 meta-amidophenol, C 6 H 4 < . It dyes a brilliant pink on X OH wool and silk, and is comparatively fast to light, a property lacking in the eosins. Oalle'in is the phthale'in of pyrogallol, and when heated with strong sulphuric acid forms the olive green dye called coerulein, belonging to the azo dyes. It is very fast when used with a chro- mium mordant. Indophenol is made by oxidizing a phenol and a para-diamine, particularly a-naphthol and dimethyl-para-phenylenediamine. It yields shades resembling indigo on cotton and wool, and may be reduced by glucose and caustic soda to a colorless indophenol white, which oxidizes in the air to again form the blue ; hence it is much used in indigo vats to brighten and cheapen the vat indigo colors. (d) Rosolic acids are made from rosaniline or para-rosaniline by treating with sodium nitrite, and then boiling with sulphuric acid. This forms rosolic acid, or aurin, which are red dyes of unstable character. III. Azo dyes. These contain the chromophor N : N . They are all prepared by treating diazo compounds with amines or phenols of the aromatic series. The dyes are amido or hydroxyl compounds of the azo bodies, and three groups are distinguished : the amidoazo dyes, amidoazosulphonic acids, and the oxyazo dyes. (a) Amidoazo dyes. Chrysoidine is diamidoazobenzene hydrochloride, C 6 H 5 N:N.C 6 H 8 (]SrH 2 ) 2 .HCl, and is made by adding a solution of meta-phenylenediamine to "a solution of diazobenzene chloride. It yields a brownish-orange color on silk, wool, and tannin-mordanted cotton. Bismarck brown, or phenylene brown, is triamidoazobenzene hydrochloride, and is made by the action of nitrous acid on meta- phenylenediamine. It is much used for leather dyeing, and for TEXTILE INDUSTRIES 475 wool, and cotton mordanted with tannin, yielding a full brown shade. (6) Amidoazosulphonic acids. Fast yellow, acid yellow, is the sodium salt of amidoazobenzene, disulphonic acid. It is much used for dyeing compound shades in acid baths with acid magenta, indigo extract, etc., and for making other diazo colors. Methyl orange, helianthin, orange III, is made by the action of dimethyl-aniline on diazobenzene-sulphonic acid. Its formula is (CH 3 ) 2 K C 6 H 4 - N : N - C 6 H 4 . S0 3 Na. It is used in acid bath for dyeing silk and wool, and as an indicator in volumetric work. Tropceolin 00, diphenylamine orange, is made by treating diazo- benzene-sulphonic acid with diphenylamine, and is used to dye silk and wool a golden yellow. Metanil yellow is made by the action of diphenylamine upon meta- amido-benzene-sulphonic acid. (c) Oxyazo dyes. The primary aromatic amines, when diazotized, will combine with phenols and phenol derivatives, forming azo dyes. The number in this group is therefore very large, many shades of yellow, orange, red, and brown being known. When amidoazo compounds are di- azotized, secondary azo bodies are formed ; they contain two of the chromophor groups N : N , and form one class of the tetrazo group. Orange G is the sodium salt of diazobenzene-/3-naphthol-disul- phonic acid. Azococcin 2 R is made by treating diazoxylene hydrochloride with tt-naphthol-monosulphonic acid. It is a red color used in silk dyeing. Wool scarlet R is -made by treating diazoxylene hydrochloride with tt-naphthol-disulphonic acid. Scarlet 2 R, Ponceau 2 R, xylidine red t is made by the action of /?-naphthol-disulphonic acid upon diazo-meta-xylene hydrochloride. It is much used in the place of cochineal. Scarlet 3 R, Ponceau 3 R, cumidine red, is made by treating diazo- meta-cumene with /3-naphthol-disulphonic acid. Fast red A, Roccelline is made by treating /3-naphthol with a-diazo- naphthalene sulphonic acid. It is much used instead of orchil or barwood. Fast red B, Bordeaux B, is obtained from diazonaphthalene hy- drochloride and /3-naphthol-disulphonic acid. 476 OUTLINES OF INDUSTRIAL CHEMISTRY Of the secondary diazo colors (tretrazo dyes) the following are important. Cloth red G is made by treating diazotized amido-azotoluene with /?-naphthol-sulphonic acid. It is used to replace red woods in dyeing and is fast to light and milling when dyed on a chromium mordant. Crocein scarlet 3 B, Ponceau 4RB, is formed by the action of diazotized amidoazobenzene-monosulphonic acid upon /J-naphthol- sulphonic acid. It is much used for wool dyeing. Brilliant crocein, cotton scarlet, is made by treating diazotized amido-azobenzene with /?-naphthol-y-disulphonic acid. It is the purest and brightest of the scarlets and is used on cotton, wool, and silk. It is fast to light and milling. Biebrich scarlet, Ponceau 3 R B, is made from diazotized amidoazo- benzene-sulphonic acid and /8-naphthol. It is an acid dye used on silk and wool for shades similar to cochineal. Wool black is formed by the action of diazotized amidoazoben- zene-disul phonic acid on para-tolyl-/?-naphthylamine. It dyes a deep blue black which is fairly stable. Naphthol black B, brilliant black, is prepared from amidoazo- naphthalene-disulphonic acid and /J-naphthol-disulphonic acid. Naphthol blacks 8 B and 6 B are similar. They are chiefly used in wool dyeing. The class of tetrazo dyes derived from benzidine, tolidine, and stilbene has become very important, since they color unmordanted vegetable fibres ; also, many of them act as mordants for other coal- tar dyes. Congo red, first made in 1884, was the first of these dyes to appear. It is made by treating diazotized benzidine with two mole- cules of a-naphthylamine-sulphonic acid ; its formula is C 6 H 4 - N : N - C 10 H 5 (NH 2 ) S0 3 Na. C 6 H 4 - N : N - C 10 H 5 (NH 2 ) . S0 3 Xa. It dyes Turkey-red shade on cotton, which is fast to washing, but the slightest trace of acid changes it to blue, Benzopurpnrin 4B is made from diazotized ortho-toluidine and /3-naphthylamine-sulphonic acid. Benzopurpurin 6 B, deltapurpu- rin, and rosazurin B are similar dyes. These all yield red shades on cotton and wool. Benzoazurin is made from diazotized dianisidine and a-naphthol- sulphonic acid. It dyes a blue shade, and may be used with other dyes for mixed shades and in dyeing mixed goods. TEXTILE INDUSTRIES 477 Chrysamine is a yellow dye produced from tetrazo-diphenyl, or ditolyl, chlorides and salicylate of soda. Its formula is : C 6 H 3 (CH 3 ) - N : N - C 6 H 3 (OH) . COONa. C 6 H 3 (CH 3 ) - N : N - C 6 H 3 (OH) . COONa. It is used for cotton dyeing and also for mixed goods ("unions "). Azo-blue is produced by the action of tetrazo-ditolyl chloride on /J-naphthol-sulphonate of soda. It is not fast to light. Hessian purples are produced by the action of diazotized diamido- stilbene-disulphouic acid upon various aromatic amines and phenols. These resemble the benzidine dyes, and are applied 011 cotton in a soap biith or with salt and acetic acid. Mikado dyes are made by treating glycerine or other oxidizable substances in alkaline solution, with para-nitrotoluene-sulphonic acid. Primuline is a yellow dye made by the action of sulphur on para- toluidine and sulphonating the product. By treating cotton, dyed with primuline in a diazotizing bath, and then passing into an alka- line solution of phenols, various yellow, red, or brown shades are formed on the fibre (" ingrain colors "). IV. Quinoline and acridine derivatives furnish several important dyes. Quinoline yellow is made by heating quinaldine, C 10 H 9 N, with phthalic anhydride and zinc chloride, and then sulphonating the product. It yields pure yellow shades on wool and silk in acid baths. Flavaniline is made by heating acetanilide with zinc chloride to 250 to 270 C. for several hours. The color is converted into the hydrochloride, which is a basic dye applied to cotton (mordanted) and wool or silk. The shade is a greenish yellow. Photphine or chrysaniline is produced as a by-product in making magenta by the arsenic acid process. The commercial dye is the nitrate of diamidophenylacridine, and is chiefly used in silk dyeing and for leather coloring. V. The anthracene colors, although not very numerous, are all mordant dyes, the alizarins being distinguished by their fastness to soap, acids, chlorine, and light, surpassing in this respect nearly all the other natural or artificial dyes. They all contain free hydroxyl groups, are insoluble in water, but dissolve in caustic alkalies. 478 OUTLINES OF INDUSTRIAL CHEMISTRY Alizarin is dioxany thraquinone, C 6 H 4 < >C 6 Hjj(OH) 2 , and is the X CO X coloring principle of madder (p. 468). It is made artificially by /CHv oxidizing anthracene, C 6 H 4 \ /C 6 H 4 to form anthraquinone, the XX sulphonic acid of which is then fused with caustic soda and potas- sium chlorate. If anthraquinone monosulphonic acid is employed, alizarin (blue shade) is obtained ; with a-disulphonic acid, Jlavopur- purin, and with /3-acid, anthrapurpurin is formed, each of these being a trioxyanthraquinone. Alizarin is brought into commerce usually as a paste with water, containing 20 per cent of the dyestuff. Its color principles have been described in connection with madder (p. 468). It sublimes, and forms orange-red crystals. Anthrapurpurin (isopurpurin) is isomeric with the pur pur in of madder. Flavopurpurin forms yellow needles melting above 330 C. Commercial alizarin is a mixture of alizarin, anthrapurpurin, and flavopurpurin, a large percentage of the last two yielding the alizarin, yellow shade, or alizarin G. By treating the ordinary alizarin with fuming sulphuric acid, it is converted into a monosulphonic acid, whose sodium salt constitutes the alizarin S of commerce. It is soluble in water, and is used for wool dyeing only. Its shades are similar to those produced by ordinary alizarin. Anthracene brown, or anthragallol, is made by heating gallic acid with phthalic anhydride and zinc chloride," or with benzoic acid and concentrated sulphuric acid. It is isomeric with anthrapurpurin, etc., and yields various shades of brown with metallic mordants. The color is fast to light and milling. Alizarin orange is /?-nitroalizarin, made by acting on alizarin, blue shade, with nitrous acid. It yields orange shades with alumina, and red-violet with iron. It is mainly used as a steam color in calico printing. Alizarin blue is made by heating /3-nitroalizarin with glycerine and sulphuric acid. It is sold as a paste, and is mainly used as a steam color in calico printing. It may be- reduced and rendered soluble, and used as a vat dye similar to indigo. By mixing the paste with sodium bisulphite solution, and allowing it to stand some days, a water soluble color, alizarin blue S, is formed, which is very fast to light, and has generally replaced the insoluble blue. Alizarin green S is produced by treating alizarin blue with fuming TEXTILE INDUSTRIES 479 sulphuric acid. It produces green shades of blue on wool, which are fast to milling. Alizarin black S is the sodium bisulphite compound of dioxynaph- thoquinone. It is made by treating a-dinitronaphthalene with zinc and concentrated sulphuric acid, and then combining the product with sodium bisulphite. It is used on wool, mordanted with potassium bichromate, for various shades of slate and black. The colors are fast to light. VI. Artificial indigo (see p. 467). A dyestuff sold as "im salt" is a sodium bisulphite compound of orthonitrophenyl-lacto- methylketone, which is soluble in water. When applied to cotton, and the goods then passed through caustic soda liquor, a deep indigo blue is developed. DYEING Dyeing is the process of precipitating coloring matter upon or within the substance of a body by chemical action. Dyestuffs are distinguished from pigments by the fact that they are soluble in water, or in the liquid of the dye-bath, from which solution they are abstracted by the material to be dyed. In the vast majority of cases dyes are applied to textile fibres or fabrics, but occasionally natural products, such as straw, feathers, horn, leather, ivory, bone, or wood, may be dyed. The substance is immersed in a hot or cold aqueous solution of the dyestuff, except in a few rare cases, where other solv- ents than water may be used, or the solution applied as a spray. The solution may be neutral, acid, or alkaline, according to the nature of the material and of the dyestuff ; thus alkaline or neutral baths are generally used for cotton and vegetable fibres, neutral or acid baths for wool, and acid or alkaline baths for silk. Dyestuffs are sometimes spoken of as substantive and adjective ; the former will color fibres directly, the latter will only color, with any permanence, when used in conjunction with a mordant. Nietzki designates the two classes as direct dyes and mordant dyes. Hum- mel * divides coloring matters into monogenetic, or those which pro- duce only one color under any condition ; polygenetic, those which produce several colors, according to the mordant used. The artificial coal-tar dyes have been very carefully studied, and the theory of the relation of color to constitution proposed by Witt is generally accepted. He shows that by the introduction of certain groups (called ehromophores) into colorless aromatic hydrocarbons, * Dyeing of Textile Fabrics, p. 147. 480 OUTLINES OF INDUSTRIAL CHEMISTRY colored substances (called chromogens) are produced. These chro- mogens possess very slight coloring powers in themselves, but are converted into dyestuffs by the addition of certain salt-forming ("auxochrornous") groups, such as hydroxyl (OH), or the aniido group (NH 2 ). The salts formed are of a deeper color than the free dyestuif. Thus, benzene is colorless, but the introduction of chro- mophorous groups, such as the nitro group (N0 2 ), or the azo group ( N = N ), forms the feebly colored chrornogens, mono-, di-, and tri-nitrobenzene and azobenzene. The chromogens, in turn, may take up the auxochromous groups (OH) or (NH 2 ), and form dye- stuffs such as picric acid, C 6 H 2 (N0 2 ) 3 (OH), or amidoazobenzeiie, C 6 H 5 N=NC 6 H 4 NH 2 . If the auxochromous groups are converted into salts the color is much intensified; thus sodium picrate is a much darker, deeper yellow than picric acid. But the sulpho-group, S0 3 H, and the carboxyl group, C0 2 H, are not auxochromous, not- withstanding that they form salts, since they impart very little tinctorial power to the chromogens. From this Witt drew the fol- lowing conclusions : 1. The simultaneous occurrence of a chromophor and an auxo- chromous group is essential to the development of tinctorial proper- ties in an aromatic substance. 2. The chromophor exerts a greater color-generating influence in the salt-like derivatives of the dyestuff than in the free compounds. 3. In the case of dyes of similar constitution, the one having the more stable salts is the better. The theory of dyeing has not yet been clearly elucidated. The mechanical theory assumes the coloring to be due to a mechanical absorption of particles of coloring matter into the pores of the fibre ; the chemical theory supposes a chemical combination to take place between the coloring matter and some, or all, of the constituents of the fibre. By the former theory, the cause of the inability of many dyes to color all fibres equally well is ascribed to the difference in the size of the dye molecules, or of the pores of the various fibres. Further, the pores are supposed to expand by heat, or by the action of certain chemicals, and to contract by cold or by astringent sub- stances. The chemical theory is supported by the facts that textile fibres are either acid, or acid and basic in character, and have the power of absorbing and retaining alkalies, acids, and some salts ; and further, that all coloring matters have either an acid or basic charac- ter. Between these two theories is Witt's solid solution theory; this supposes that fibres extract coloring matters from aqueous solu- tion in much the same way that ether withdraws certain bodies from TEXTILE INDUSTRIES 481 their aqueous solutions, the fibres thus acting as solid solvents for the dyes. However, it seems probable that with wool and silk the process is truly chemical ; but with cotton and other vegetable fibres, which have a totally different composition from the animal fibres, the question is not, as yet, definitely decided. The methods of dyeing and composition of the dye-bath depend essentially upon the nature of the fibre and of the dye. As a rule silk and wool are dyed directly, although mordants are used in some cases. Cotton and linen have much less affinity for coloring mat- ters ; and, with the exception of certain coal-tar dyestuffs of the ben- zidine class and the related primuline derivatives (ingrain colors), a mordant is always used. The character of the water is of much importance in dyeing. The most injurious impurity is iron, since this dulls (saddens) the shade of most colors. A hard water, containing lime or magnesium salts, should generally be purified before use, though in a few cases, notably in Turkey-reds and in dyeing with logwood, the presence of lime is necessary. Suspended matter must be removed. Stone dye-vats were formerly much used, but these are now largely replaced by iron tanks. Or, for certain delicate colors, especially on silk, the tanks are made of wood, so put together that no iron shall come in contact with the dye liquors, and copper steam pipes are used for heating. Hanks to be dyed are suspended from sticks laid across plain, open tanks, provided with false bottoms, under which steam is introduced. Since this involves much hand labor in turning the hanks, many machines have been devised, in which the hanks are usually weighted at the lower end by rollers to keep them -straight, and are suspended on rollers of wood or porcelain, which are rotated by suitable driving-gear. Or they are fixed on sticks on the periphery of a rotating drum, which is partly submerged in the dye-bath; the apparatus is enclosed in a wooden case to confine the steam and heat, and to prevent too much cooling of the yarn while not submerged. Sometimes yarn is dyed in warps and in the " cops " formed on the spinning-frames, but the machines for such dyeing are too complicated for description here. A large part of dyeing operations are done on piece goods, for which machines are generally used. A simple vat, with a winch placed above it, is very often used. The pieces (previously sewed together to form an endless band) are made to pass continuously through the liquor, a certain amount of slack being allowed, to increase the time of exposure to the dye. The goods pass through 2i 482 OUTLINES OF INDUSTRIAL CHEMISTRY the bath several times, until the desired shade is obtained. The most common machine for cotton goods is the "jigger." In this two rolls are placed in the bottom of the vat, and three guide rolls at the top. The cloth, unwinding from a beam above the machine, passes in the open width over the first top roll, into the dye liquor and under the first submerged roll ; it then ascends to the middle roll at the top of the vat and again passes down under the second submerged roll, from which it goes out of the dye, over the third guide roll, and is wound on a second beam. The machine is then reversed and the cloth run back, over and under the rolls to the first beam. When dyed, the goods are drawn on to the " batch roll," from which they are soon run through the washing machine. For mordanting and dyeing cotton cloth in the piece, "padding machines" are much used. This consists of a small vat or tank, above which are squeeze-rolls to remove the excess of liquor, and the goods are consequently less likely to become uneven in color by further action of the absorbed dye liquor while on the " batch roll." Padding machines with large rolls have, to a great extent, replaced jiggers for cotton dyeing. Dyes may be grouped, according to the method of application, into five classes : 1. Direct dyes, which yield full colors, without the assistance of mordants. 2. Basic dyes, which form insoluble tannates and require mor- dants on vegetable fibres, but dye animal fibres without mordants. 3. Acid dyes, which require no mordant on animal fibres, but which find only a limited use for vegetable fibres. 4. Mordant dyes, which require a metallic mordant on both animal and vegetable fibres. 5. Special dyes, which can only be applied to or developed in the fibre by special processes. 1. The direct dyes comprise the beuzidine dyes (Congo, diamine, Hessian, and benzo colors), and certain ingrain colors derived from primuline and from some of the benzidine dyes, by diazotizing the amido groups after dyeing on the fibre, and then " developing " the color by treating with phenols, naphthols, or amines. Being very soluble, they are prone to " bleed " when the goods are washed, but owing to this same fact they are very easy to dye evenly (" level ") on the goods. They are applied to all fibres without mordants, generally in neutral or alkaline baths ; the addition of a little acetic acid renders them fast to milling on wool. Some substance called TEXTILE INDUSTRIES an " assistant " is usually added to the dye-bath to accelerate, retard, or modify the deposition of the color ; but this does not enter into combination with the color (or with the mordant when used with basic, acid, or other dyes). The assistants used for direct dyes are common salt, Glauber's salt, sodium phosphate, borax, soda, or soap; these are added in amounts varying from 5 to 20 per cent. They render the dye less soluble and cause a more complete precipitation on the goods, or retard the deposition by increasing the solubility. Cotton is dyed with the direct dyes in a boiling bath, usually with from 10 to 15 per cent common salt or Glauber's salt. The ingrain colors are obtained by dyeing in the usual way, diazotizing in a cold bath of sodium nitrite acidulated with hydrochloric acid, and "developing" in a suitable developer to produce the desired color. Wool is dyed from baths containing salt or Glauber's salt, with the addition of a little acetic acid to render the color fast to milling. The shades are generally faster and deeper than on cotton. Mixed wool and cotton goods (" unions ") are often colored with such direct dyes as have equal affinity for the two fibres, in order that the shades may match. The evenness of the shade in these goods can often be improved by varying the amount of assistant employed in the bath. Silk takes the direct dyes very well, fast and brilliant shades being obtained. The assistant used is sodium phosphate or soap. Mixed silk and cotton goods are also dyed with these colors ; since some of them color cotton but not silk in a soap bath, it is often possible to dye two shades on such mixed goods, producing varieties of " changeable " or u shot " effects. For example, the cotton may be dyed in a soap bath and the silk dyed in a second bath of an azo or acid color, which has no affinity for cotton. 2. Basic dyes are the salts of colorless bases which contain chromophorous groups. The color does not appear until the forma- tion of the salt. The dyestuffs decompose in the dye-bath, setting free the acid, while the base combines with an acid constituent of the animal fibre, or with the acid mordant in the case of vegetable fibre. These dyes are monogenetic, but they vary t much in their constitution, fastness, and brilliancy of shade. They have great tinctorial power, but are generally fugitive, being rapidly faded by light, soap, and milling. The commercial dyestuffs are usually salts of acetic, oxalic, nitric, sulphuric, or hydrochloric acid, and most of them are soluble in water. They are used in neutral or slightly 484 OUTLINES OF INDUSTRIAL CHEMISTRY alkaline or acid baths. Excess of acid or alkali must be avoided, as it prevents complete exhaustion of the dye-bath. Calcareous water is especially bad for these colors, since it precipitates the color bases as a white, curdy mass which adheres to the fibre, weakening the color and causing spots and uneyenness. Basic dyes can be mixed in the same bath to form compound shades. Cotton is generally mordanted with tannin, Turkey-red oil, or soap, before dyeing with basic dyes. The mordanted cotton is dyed in a separate bath, to which the color is added in small portions at a time during the dyeing, to prevent unevenness in the shade. The temperature is raised slowly to 60 C., but no higher, lest the brill- iancy be injured. The goods are wrung, or hydro-extracted, but not washed, after dyeing. Wool is dyed directly by the basic dyes, but a little acetic, sul- phuric, or hydrochloric acid, or alum or sodium acid phosphate is added, to moderate the absorption and afford level dyeing. The wool fibre has an acid character, decomposing the dye, and combining with the color base to form a lake. But certain basic dyes, especially methyl and benzaldehyde greens, will not dye wool until it has been mordanted with sulphur by treating with sodium thiosulphate, alum, and sulphuric acid. The mordant is then fixed in very dilute ammonia. The dyeing is usually done in a boiling bath, the tem- perature being afterwards lowered to 60 C., or even to 40 C., while the wool remains in the bath. Silk has greater affinity for basic dyes than has wool. The dye- ing is done in a neutral, alkaline, or slightly acid bath ; usually an alkaline bath with soap or "boiled-off liquor" is employed. The temperature is between 80 C. and boiling. For the acid bath, acetic, tartaric, or sulphuric acid is generally used. After dyeing and washing the silk is generally " brightened " by passing through a dilute acid, and after hydro-extracting, is dried. Union goods are dyed in a neutral or acid bath, the cotton having been previously mordanted cold, with tannin and antimony, which do not unite with wool. Silk and cotton mixed goods are first dyed so that the silk is colored, and are then passed through cold tannic acid to mordant the cotton, and dyed a second time. 3. Acid dyes are dyed in acid baths, and may be mixed in the same bath for compound shades. But some of them act like direct dyes when used on cotton, while others are dyed on mordanted wool. The classification is somewhat arbitrary, but an acid bath is always used for animal fibres. The commercial dyestuffs consist of the alkali or lime salts of the color acid, excepting only picric acid, TEXTILE INDUSTRIES 485 which is used in the free state, its salts being explosive. The acid dyes are grouped, according to their constitution, into : (1) Nitro compounds. (2) Sulphonated basic dyes. (3) Azo colors. Sometimes the eosins are classed with the acid dyes, since they are also dyed from a very weak acid (dilute acetic) bath. The nitro dyes owe their acid nature and coloring properties to the chromophorous nitro groups which they contain. Besides these, there are usually auxochromous radicals, such as hydroxyl or the imido group (NH) present. The sulphonated basic dyes are derived from bases which are coloring matters, by introducing the sulpho group (SO ;{ H). This group causes no material change in the shade of the basic dye, but the coloring power is reduced, and the dye can no longer combine with tannin mordants; the fastness to light is much increased. The azo colors contain the azo group ( N = N ) as chromophor, and as auxochromous group, either hydroxyl or amido groups, NH 2 . These are the most numerous and important of the acid dyes, and are most extensively used on wool. Some of the azo colors may be dyed without a mordant, while others are dyed upon a metallic mordant, such as alum, chromium fluoride, or potas- sium bichromate. The colors are fast upon wool, and fairly so on silk, and are chiefly used for these fibres. They are fast to light and acids, but since they are not fast to washing, their use on vege- table fibres is limited. Cotton is dyed in a very concentrated bath, to which common salt, alum, and acetic acid are added; or a mordant bath of alum and soda (basic alum), or of stannic chloride, followed by basic alum, is used before dyeing. Tannin treatment before the alum mordanting renders the color faster to washing. (The shades on unmordanted cotton are not fast to washing.) After mordanting, the goods are wrung and dyed without washing. After dyeing, they are dried without washing. Mordanted cotton is dyed at about 50 C. ; but for unmordanted goods the temperature is slowly raised to boiling. Linen is rarely dyed with acid colors, since the shades are not fast enough to warrant it. Wool is dyed with acid colors in a boiling bath of the dyestuff, to which a restraining assistant (Glauber's salt) may or may not be added. To develop the color, sulphuric acid is added, a little at a time, during the boiling, thus freeing the color-acid very gradually, and affording level shades. Sometimes ammonium acetate, or sul- phate, is used in the dye-bath, which, decomposing slowly in the 486 OUTLINES OF INDUSTRIAL CHEMISTRY boiling liquor, sets free its acid, while ammonia escapes. The free acid then decomposes the dyestuff, and the color-acid is deposited on the fibre. In the case of the alkali blues, the color-acid is insoluble in water, but its alkali salt dissolves readily, yielding colorless solu- tions. To dye these, the goods are boiled in a bath of borax or soda, to which the dyestuff is added; when impregnated with the alkaline solution, the wool, still uncolored, is dipped in an acid bath. This decomposes the alkali salt, and the free color-acid develops on the fibre as a deep blue color. The acid colors, especially the sul- phonated basic dyes, when dyed on the fibre, are destroyed by alka- lies. Some are very fugitive to light. Silk is usually dyed in a slightly acid bath containing 10 per cent "boiled-off liquor." The dye solution is sometimes added to 'the bath all at once; in other cases it is added gradually, the tem- perature being kept near boiling. After dyeing, silk is washed and passed into a dilute acid solution to brighten the color, and is dried without further washing. 4. The mordant dyes yield colors which are generally fast to washing, soaping, milling, and light. They comprise a great variety of coloring matters, both of natural and artificial origin, which are dyed on all fibres by the aid of metallic mordants. Many of these dyes are polygenetic, and they all possess the property of forming insoluble color lakes with metallic oxides. The mordanted goods are passed into a dye-bath, which usually contains nothing but the color ; but in the case of certain natural dyewoods, the mordant and dye may be applied in the same bath, while in others the goods are first impregnated with the dye, and the color fixed on the fibre by subsequent treatment in the mordant bath. This last process is generally known as " stuffing and saddening." The mordant oxides chiefly employed are those of aluminum, chromium, iron, and tin. Mordant colors may be mixed in the same dye-bath, provided the same mordant is used for each. Many of the artificial mordant colors are nearly insoluble in water, and if once dried, are difficult to again dissolve in the dye-bath. Hence they are often sold as "pastes," containing from 60 to 80 per cent of water. The mordant colors themselves frequently serve as mordants for fixing basic dyes, hence the latter are often used to brighten the shade of the former. Cotton is always mordanted in separate baths before dyeing with these colors. Until recently, mordanting with chromium on cotton has been difficult, and the results of the dyeing unsatisfactory, especially on yarn. But the application of certain basic chromium TEXTILE INDUSTRIES 487 acetates, chlorides, etc., especially by Koechlin's method (p. 458), has made it possible to dye new shades on cotton. Sometimes the cotton is prepared with Turkey-red oil before mordanting with chromium. Aluminum mordants are largely used on cotton for mor- dant colors, but iron and tin less frequently. Turkey-reds, alizarin red, ccerulei'n, and other alizarin colors, and logwood blacks, are the chief mordant colors on cotton. For centuries Turkey-reds have been produced on cotton by the aid of madder, oil, and aluminum salts, This gives a most brilliant red, and one of the fastest colors to light, washing, or friction, as well as to chemical reagents. By the old process, much time, usually about four weeks, was consumed in the dyeing, but now it has been shortened to about three days. Madder has been completely replaced by the artificial alizarin, produced from coal-tar (anthracene, p. 284). The process of dyeing Turkey-reds on cotton is complicated, and a special mordanting of the goods is necessary. The outline of the process is as follows : The bleached cotton (p. 451) is first oiled with olive, castor, or Turkey-red oil, (p. 312) the goods being steeped in an emulsion of the oil in sodium carbonate solution, or padded in a 10 or 15 per cent solution of neutralized Turkey-red oil in water. The excess of oil is squeezed out and the goods " aged," or steamed, at about 5 pounds pressure, to render the oil insoluble and to fix it on the fibre. An oxidation and probable polymerization of the oleic acid and other constituents of the oil occurs, and substances are fixed in the fibre which combine with and assist in the fixing of the metallic mordants, and also, per- haps, form a varnish coat over the color lake, protecting it from air and chemicals, thus increasing the fastness and lustre of the dyed fabric. The oiled cotton is then sometimes steeped in a decoction of sumach, but this is not essential, and is very generally omitted. The mordanting is done by working the goods in a tepid solution of aluminum acetate (red liquor), or basic aluminum sulphate, the oxide being fixed by aging, or by treatment in a bath of powdered chalk and water, or sodium phosphate, which also removes the excess of oil from the fibre. Formerly sodium arsenate was used for this " dung-bath," and afforded very light shades. The dyeing is accom- plished by entering the mordanted cotton in a cold bath of alizarin suspended in water, containing some lime, calcium being essential to the formation of the colored lake ; hard water, free from iron, is preferred for this bath, but if not available, powdered chalk or calcium acetate is added. The temperature is very slowly raised to 70 C., where it is kept until the dye-bath is exhausted. The cotton is then wrung and dried. The color at this time is a dull red, and, 488 OUTLINES OF INDUSTRIAL CHEMISTRY to develop the brilliant shade, the goods are steamed at about 15 pounds pressure for an hour. Sometimes they are oiled a second time before steaming. They are then thoroughly washed with soap, two or three soapings being usually given. Stannous chloride is sometimes added to the soap bath to increase the brilliancy ; also it is very essential in Turkey-red dyeing that neither the mordants nor the dye-bath shall be contaminated with the slightest trace of iron in any form. Turkey-reds are dyed by several other processes, which cannot be considered here.* Various shades of violet, lilac, and purple are dyed on cotton with alizarin by mordanting with ferrous acetate (pyrolignite of iron, p. 263) instead of red liquor, and usually omitting the oiling. A tannin-iron mordant affords purple blacks, while mixtures of iron and aluminum mordants give various shades from claret red to chocolate. Linen is dyed with alizarin in the same way as cotton. The fastness of Turkey-red to washing and soap makes it especially valuable for dyeing linen yarn, which is then woven into figured wash goods. Other alizarin colors are dyed on cotton and linen with the various aluminum, chromium, and iron mordants. The methods vary somewhat with each dye, and must be sought for in special works on dyeing. Logwood yields blacks and grays on cotton mordanted with tan- nin and iron, or with iron salts alone. "Nitrate" and acetate of iron give the best shades, but copperas is much used for cheap blacks. Stannous chloride yields purple shades, while blues are obtained with copper sulphate or acetate. Wool is largely dyed with mordant colors, both natural, such as logwood, fustic, quercitron, and cochineal, and with artificial aliza- rins and azo colors. The alizarin colors are generally faster to light, chemicals, milling, and washing than the natural coloring matters. It is very essential in dyeing wool with the mordant colors that the fibre shall be thoroughly scoured, and entirely free from oil or grease, as these would form soaps with the metallic mor- dants, and cause spots on the goods while making the color less fast to milling and friction. The mordants for wool are generally the same as those for cotton; aluminum salts are employed for aliza- rin, but chromium is the usual mordant for these dyes. The wool is boiled with about 3 per cent (of the weight of the goods) of potas- sium bichromate, often with the addition of 1 per cent sulphuric * See Dyeing of Textile Fabrics, J. J. Hummel, p. 427 et seq. TEXTILE INDUSTRIES 489 acid. Cream of tartar is sometimes used with bichromate for the finest work. About 3 per cent of chromium fluoride, with half its weight of oxalic acid, has been much used of late years. After the oxide is fixed by aging several hours in a dark place, the wool is washed, and is ready for dyeing. The dye-bath is generally pre- pared with pure water and the dye alone, but for some of the aliza- rin colors a very little acetic acid is added. The goods are entered when the bath is about 30 to 40 C., and the temperature is raised slowly so that it reaches the boiling point in an hour; the boiling is continued for another hour or more. If these precautions are not observed, the dyeing is apt to be uneven. Some of the alizarin colors may be mordanted and dyed in one bath ; potassium bichromate or chromium fluoride are used in this way, the goods being entered into the cold bath, which is slowly raised to boiling. The dyes must be able to withstand the oxidizing action of chromic acid. This " single bath " process is very apt to waste color, and the shades produced are less fast, especially to milling. Silk is not commonly dyed with mordant colors, since the shades are less brilliant than those obtained with the substantive dyes, and the latter are cheaper and sufficiently fast for most purposes on silk. When mordant dyes are used, the silk is first mordanted by steeping in basic aluminum sulphate or acetate for some hours, and fixing in cold silicate of soda solution at J Tw. It is then dyed without dry- ing. For chrome mordanting, a solution of chromium chloride is used. The dye-bath is prepared with " boiled-off liquor," which is neutralized or slightly acidified with acetic acid. The silk is worked in the cold bath for 15 minutes, and then the temperature is slowly raised to boiling, and kept there for an hour. After washing in water, the silk is passed into boiling soap liquor, and finally bright- ened by very dilute acetic acid at 30 to 40 C. ' 5. The special dyes include those colors which are prepared or developed directly on the fibre by peculiar processes. They include indigo, aniline black, certain azo colors developed on the fibre, and the mineral colors used in dyeing. Indigo, p. 466, is chiefly dyed on cotton and wool. It is insoluble in water, but by reducing agents is converted into indigo white, which is soluble in alkaline liquors. This reduction is performed in the vat in which the dyeing is to be done. Cotton is dyed with indigo in the " hyposulphite," or " hydro- sulphite " vat, the copperas vat, or the zinc vat. The hydrosul- phite vat is prepared by reducing indigo with sodium hyposulphite, NaHS0 2 , p. 44. The indigo is mixed with milk of lime, and the hyposulphite liquor added and heated to CO C., until the liquor 490 OUTLINES OF INDUSTRIAL CHEMISTRY becomes yellow. After cooling, the bronze colored scum is removed, and the cotton is at once immersed in the reduced indigo solution. When the fibre is impregnated with the liquor, it is passed through squeeze-rolls, and exposed to the air until the indigo white becomes oxidized, forming indigo blue, the color being developed in the inte- rior of the fibre. The copperas vat is made by adding indigo to a copperas solution, and then slowly running in milk of lime. The reactions occuring are probably as follows : 1) FeS0 4 + Ca(OH) 2 = Fe(OH) 2 + CaS0 4 . 2) 2 Fe(OH) 2 + 2 H 2 O = 2 Fe(OH) 3 + H 2 . 3) deHjoN A + H 2 = CuHuN A- The hydrogen is not set free as gas, but immediately combines with the indigo to form indigo white, which is dissolved by the excess milk of lime. The copperas must be free from copper, or ferric and aluminum sulphates to prevent loss, and the indigo must be ground very fine. (The sediment is quite bulky in this vat.) The cotton is treated the same as in the hydrosulphite vat. The zinc vat is prepared by adding zinc dust to a mixture of indigo and milk of lime. The zinc decomposes water in the presence of lime, and forms zinc oxide, while the hydrogen reduces the indigo to indigo white, which dissolves. The amount of sludge formed in this vat is small, and the process is easily managed. By feeding the vat with more indigo, lime, or zinc, as required, it can be kept in good order for months. Excess of zinc causes frothing. The dye- ing process is similar to those above described. Loose wool or yarn is dyed with indigo in the hydrosulphite vat, prepared as for cotton. The woad vat is used for woollen cloth ; a mixture of woad with water is allowed to stand for some hours at 70 C., and then bran, indigo, madder, and lime are added. A butyric fermentation sets in, and when this is well established more lime is added; hydrogen is set free, and reduces the indigo. In about three days the vat is ready for dyeing. After use, more lime and bran are added as required to control the fermentation, and every day or two more indigo is put into the vat. The wool, wet in warm water, and wrung, is submerged in the vat, where it is worked from twenty minutes to two hours. It is then wrung to recover as much of the indigo solution as possible, and at once exposed to the air to oxidize the indigo white. For clear, fast blues, the goods are returned to the vat two or three times. For the best and fastest color, the wool should be dyed before weaving, and sometimes dyed again after milling. After dyeing, the goods are very thoroughly washed TEXTILE INDUSTRIES 491 with water in a "dolly," and then scoured with soap and fuller's earth to remove all the loosely adhering indigo, which would other- wise cause the goods to " crock." It is often customary to dye woollens with red woods before the indigo dyeing, in order to give "bloom" to the finished goods. The soda vat is used quite extensively in Europe. In this, molasses, bran, lime, and sodium carbonate are mixed with indigo ; a butyric fermentation results, and the indigo is reduced. The colors obtained are brighter than in the woad vat, but not so full. Indigo was formerly reduced in a vat containing putrid urine, salt, and madder. The ammonium carbonate formed by the putre- faction dissolves the reduced indigo. The process has been generally given up. Silk is not dyed with indigo to any extent. Aniline black is a dye of unknown constitution, produced on the fibre by oxidation of aniline. It is insoluble in all solvents except strong sulphuric acid. It is extensively produced on cotton, but is not suitable for animal fibres, since it injures the strength, lustre, and feel of the goods. Unless great care is exercised, even cotton fibre is weakened. The oxidizing agent generally employed in coloring yarn is potassium bichromate in acid solution, but for piece goods sodium or potassium chlorate is preferred. The direct oxidation of aniline is difficult, unless certain easily decomposed metallic salts are present to act as carriers of oxygen. Of these, cupric chloride, sulphate, or sulphide, or cuprous sulphocyanide are generally used ; vanadium chloride in minute quantities produces a rapid and suc- cessful oxidation of the aniline. Potassium ferrocyanide is also ef- fective. For calico printing, the soluble copper salts are not used, since they injure the printing rolls and "doctors " of the machine. To produce level dyeing and for the most complete utilization of the materials of the bath, the process is carried on at a moderate tem- perature (50 to 60 C.) in many cases. But such blacks are usually incompletely oxidized and are very apt to develop a green shade after a time, or if exposed to the action of acids. This greening may be prevented by dyeing at a temperature of 75 C., but in this case the reactions between the constituents of the bath take place very rapidly, and the color is loosely deposited upon and not within the fibre, and the goods " crock " badly ; at the same time, much black is precipitated in the dye-bath and thus lost. Many different receipts for dyeing aniline blacks have been 492 OUTLINES OF INDUSTRIAL CHEMISTRY devised, but the following, proposed by Evans* will furnish an example : 10 parts ammonium chloride. 10 parts sodium chlorate. 10 parts copper sulphate. 35 parts aniline hydrochloride (crystals). X parts aniline oil. 200 parts water. The ammonium chloride and sodium chlorate are dissolved together in 65 parts water; the copper sulphate is dissolved in 55 parts water ; the aniline hydrochloride is dissolved in a little hot water and neutralized with sufficient (X parts) aniline oil. All solutions are thoroughly cooled and then the aniline hydrochloride is added to the sodium chlorate ; next the copper solution is stirred in and water sufficient to make the density of the mixture 14 Tw., is added. The cotton is padded two or three times in this liquor and all excess is removed in a centrifugal machine. The goods are then " aged " by exposure for 14 hours in an atmosphere near 30 C. They are then treated at 80 C. in a bath of potassium bichromate (10 parts), soda (5 parts), common salt (5 parts), and water (1000 parts). They are then washed in slightly warm water and steamed at 15 pounds to develop the color fully. Aniline blacks are often " topped " with methyl violet or logwood to prevent " greening " and crocking. Cotton and linen are now often dyed with insoluble azo dyes, de- veloped on the fibre. These are fast to acids, alkalies, and washing, but fade in the light and will often " crock." They are produced by impregnating the fibre with a phenol (naphthol) and developing the color by treating the saturated fibre in a cold bath of the-diazotized base. After washing in water, the goods are soaped at 60 C. and again washed to make the color as fast as possible to rubbing. The diazo compound is prepared by treating an amido body with sodium nitrite and hydrochloric acid at a low temperature. The amido bodies used are such substances as para-nitraniline, yielding a scar- let, methyl-amido-phenol (anisidine), yielding a blue, and some others. Certain so-called mineral dyes are produced on the fibre by satu- rating it with a solution of metallic salt, and passing it into a second solution which decomposes the first salt, forming a colored precipi- * J. Soc. Dyers and Colorists, 1891, p. 20. TEXTILE INDUSTRIES 493 tate on the fibre. The most important mineral colors are chrome yellow and orange, iron buff, Prussian blue, and manganese brown. Chrome yellow is dyed on cotton as follows : The fibre is soaked in a solution of lime-water ; after wringing, it is soaked in a solution of lead acetate or nitrate, a basic salt being preferable since it de- posits a larger amount of lead on the fibre. The cotton is then re- turned to the lime-water bath, and, after wringing, is passed into a solution of sodium or potassium bichromate, to develop the color. After passing through a bath of very dilute hydrochloric acid, the cotton is washed and dried. By adding zinc sulphate to the chrome bath, the shade of yellow may be lightened. Chrome orange is produced by treating the fibre in a bath of lime- water or alkali, after dyeing with chrome yellow ; this produces basic lead chromate (p. 206). Chrome green is not important since it is very pale and of no par- ticular beauty. It is produced on cotton by the processes used for mordanting with chromium salts (p. 458). On wool it may be formed by digesting the fibre in a strong solution of bichromate, and then passing it through a sodium bisulphite solution. Iron buff, or nankin yellow, consists of ferric hydroxide, precipi- tated on the fibre. It is only dyed on cotton, the fibre being satu- rated with a solution of iron salt and the color developed by treatment with caustic soda, soda-ash, or calcium hydroxide solution, in the same way as when mordanting with iron salts (p. 460). By repeating the operation, greater depth of color may be obtained. When ferrous salts are used, they are oxidized by treating the fibre in a bath of bleaching powder solution, after precipitating the hy- droxide. The iron salts generally used are the basic ferric sulphate (nitrate of iron) and ferric nitrate. Pyrolignite of iron is unsuitable because the tarry impurities prevent the development of pure shades. Prussian blue is produced on the fibre by two methods. For cotton it is customary to first dye an iron buff and then digest it in a solution of potassium ferrocyanide, acidulated with hydrochloric acid. Deeper shades are produced by repeating the process for buff, and again developing the blue. Wool is sometimes dyed with Prussian blue but without previous mordanting with iron. The wool is introduced into the cold bath of potassium ferrocyanide, strongly acidulated with sulphuric or nitric acid. The temperature is slowly raised to boiling, whereby the yellow prussiate is decomposed and the blue pigment deposited in the fibre. The color is brightened by the addition of a little stannous chloride or " muriate of tin " to the bath during the last half -hour of boiling. 494 OUTLINES OF INDUSTRIAL CHEMISTRY Silk is dyed with Prussian blue in the process of weighting (p. 460) for black dyeing, the mordant in this case being basic ferric sulphate. If the blue color is to remain as the final dye, the goods are softened after dyeing, by working in a bath containing a little olive oil and sulphuric acid. Manganese brown consists of the hydroxide, or oxide, of man- ganese, and is only dyed on cotton. The goods are steeped in manganous chloride solution, free from acid, and the color is de- veloped in a mixed solution of caustic soda and bleaching powder. Or a deep brown is developed by passing the goods through a bath containing potassium permanganate and sodium carbonate solutions. This color is fast to light, soap, and dilute acids and alkalies, and may also serve as a base on which to dye aniline blacks ; in this case the oxide on the fibre assists in the oxidation of the aniline. TEXTILE FEINTING Textile printing may involve the application of a single coloring matter to one side of the fabric, or the forming of intricate designs in as many as 18 or 20 different colors, by one passage of the cloth through the printing machine. The pattern is usually produced on one side only of the cloth, but sometimes the same or a different design appears on each side. There may be a colored figure on a white or colored background, or a colorless design may be produced on a colored background. Textile printing is sometimes called topical coloring. The earliest attempts at this form of decoration, made by pre- historic races, were doubtless carried out by mixing pigments with water or with a gum solution, and painting the design on the fabric. Later, the art was developed to painting the mordants in the form of the design, and then dyeing the fabric in some natural dyestuffs. Stencilling was also invented early, but the first great advances were made with the invention of block printing, which was followed by roller printing. For block printing the design is made in relief on blocks of hard wood. The cloth is spread evenly on a firm table, and the printer, having daubed the relief with color, applies the block to the cloth and strikes it with a hammer to drive the color into the fabric. In order that the lines of the figure may not overlap, or spaces be left imprinted which should be colored, exact placing or " registering " of the block is very important. This is gauged by pin points set in the corners of the block, which mark the exact spot where it is TEXTILE INDUSTRIES 495 to be applied for the next impression. Much experience is neces- sary for this and also for judging of the amount of color taken from the daubing pad by the block. At the present time, block printing is generally used only for very large designs; those containing a great variety of colors may be printed thus, but a separate block is necessary for each color used ; and since one block usually serves only for a part of the whole design, several blocks may be needed for each color. Thus the process is very slow and laborious, making it expensive. Roller or machine printing has now generally replaced all other processes. One engraved copper roll is employed for each color in the design, except in a few cases where a color is produced by print- ing one over another, as a yellow over a blue to make green. The design, drawn by the artist, is enlarged several times and engraved on a zinc plate. The copper roll is turned perfectly true in a lathe, and then polished. Its surface is coated with wax or a special varnish, through which the design is scratched by a stylus of a pantagraph machine, following the pattern on the zinc plate ; this reproduces the design and at the same time reduces it to the required size. The roll is then etched with nitric acid, until the figures have the necessary depth. After washing off the acid, the wax is re- moved, and the hollow roll is slipped on a mandrel for use in the machine. The color is fed to the print roll from the color box by a revolving cylindrical brush called the " furnisher," which dips into the color paste. This covers the entire surface of the roll with the color and fills the depressions of the design. A sharp steel blade, called the "doctor,"* rubs against the surface of the roll as the latter revolves, and scrapes off all excess of color, leaving only that contained in the depressions of the pattern. Beneath the cloth a similar blade rubs the roll, removing from it any bits of dirt or lint which may adhere after the cloth has been printed. The print rolls are all set around one central drum called the "bowl," against which they press, and which is covered with several thicknesses of strong linen and woollen cloth called "lap- ping," which will withstand the repeated pressure without breaking. This lapping must be very evenly placed, or streaks will appear on the printed goods. The cloth to be printed passes between the rolls and the bowl, considerable pressure being brought to bear upon it, so that it is forced into the engraving on the roll and takes out all the color. Between the lapping and the cloth to be printed, an * In order that irregularities may not be worn in the edge of the doctor or on the print roll, the former is given a slight sidewise movement by a suitable gearing. 496 OUTLINES OF INDUSTRIAL CHEMISTRY endless band or " blanket " of thick woollen cloth passes. This adds to the elasticity of the lapping, affording a better impression of the engraving, and protecting the lapping from color and moisture. The blanket is often 40 to 50 yards long, and goes over drying drums before it passes around the bowl. In order to keep the blanket free from color stains, a piece of unbleached cotton cloth, called " gray cloth " or " back cloth," is interposed between it and the print cloth. This gray cloth is sometimes used once or twice for this purpose and then sent to the singeing and bleaching process, after which it is itself printed, usually with a dark color. Thus three long webs of cloth pass between the rolls and the bowl at once, the blanket, back cloth, and print cloth. The printing colors may be soluble dyestuffs or insoluble pig- ments made into a paste with water, oil, or other medium ; in many cases mordants alone are printed on the fabric. It is also essential that the color pastes shall contain some material by which the pig- ments may be fixed on the fibre so that they will not rub off in the finishing operations. In order that the printing colors may adhere to the rolls and not run when applied to the cloth, thickening agents are employed. The most important of these are British gum, starch, flour, gum arabic, Senegal, or tragacanth, and blood or egg albumin. It is necessary that these shall not form any chemical combination with the color or the mordants. Some thickeners are insoluble in cold water, while others are more or less soluble, and the printer must select that best adapted to his purpose and the color he wishes to use. The preparation of color pastes is called " color mixing " and requires much care. The ingredients are mixed in special ves- sels called " color pans," these being jacketed copper kettles which may be heated by steam or cooled by water, as required. If starch or flour is used, it must be very well boiled to a smooth paste before the color is stirred in. British gum and Senegal are dissolved in hot water with constant stirring, while tragacanth is boiled for several hours. Albumin is dissolved in water at less than 50 C., while stirring constantly. After mixing, the color paste must be strained to remove any lumps, dirt, or grit, and to form a smooth paste of homogeneous character. For large lots, this is sometimes done by machinery, but in most cases the straining cloth is folded over the paste like a bag, and then twisted by hand by the work- men, thus forcing the paste through the cloth. It is now ready to put into the color boxes of the machine, from which the furnisher roll feeds it to the print roll. But the color is not always printed on the goods. Sometimes TEXTILE INDUSTRIES 497 only the mordants, mixed in the thickener, are printed, the goods being afterwards immersed in the dye-bath, and taking the color only where mordanted. Or a substance called a " resist " is printed to prevent the dye from taking the fibre in the printed portions ; thus white spots or figures are left on a colored background. Or " discharges " may be printed on dyed material, destroying or bleaching the color where they touch. After printing, the cloth is dried by passing above a series of steam boxes, or hot pipes, but generally not close enough to touch them, lest some of the colors should be changed by the heat. With many colors, however, the drying is done more quickly by passing the print over a steam-heated roll or " drying-can." For pigments in albumin thickening, this direct drying is sufficient to fix the color on the fibre, and the goods may be finished at once. The method of producing the colored design in calico printing is called a " style." The following are the most important : pigment style, steam style, madder or dyeing style, oxidation style, discharge style, and resist style. The pigment style is now of less importance than it formerly was. Insoluble pigments, such as ultramarine, Guignet's green, chrome yellow, vermilion, etc., are mixed with the thickening paste, printed directly, and the print dried by passing over a hot roll. If the thickening employed is gum, starch, or dex- trine, the resulting print is not fast to washing, and is known as " loose pigment style." But if blood or egg albumin is used, and the print dried at a high temperature, or steamed to coagulate the al- bumin, the color is fixed on the fibre, and is fast to ordinary wash- ing and soaping. The steam style, formerly called the extract style, is used for those colors in which the mordant, dyestuff, and thickening can be mixed cold or at. moderate temperatures without the formation of the color lake. Very often acetic acid is added to retard the action between the dyestuff and mordant. Tannic acid is much used as a mordant in steam colors. The cloth is generally prepared by oiling it slightly with Turkey-red oil, or "oleine," before printing. The printed cloth is usually arranged on racks on a car which can be run directly into the steamer, or the goods are made to pass through a continuous steamer, consisting of a large closed vessel containing numerous rollers at the top and bottom, over which the cloth passes up and down many times. The steam is under 3 to 10 pounds pressure, whereby the acetic acid vaporizes, the reaction between the mordant and dyestuff is brought about, and the color developed 2K 498 OUTLINES OF INDUSTRIAL CHEMISTRY on the fibre. The print is now washed in a soap bath to remove the thickening. When basic dyes and tannic acid are used, the printed and steamed goods are passed through a bath of tartar emetic or other antimony salt, to fix the color on the fibre. Steam style is now very generally used, and with many dye-stuffs. In the madder or dyeing style, only the mordant is printed, and fixed on the fibre by drying, steaming, or aging. The goods are usually "dunged" in a bath of cow-dung and chalk, to remove excess of mordant from the surface of the fibre, and thus prevent its spreading to the unprinted portions of the cloth and blending the figures. Arsenate of soda was formerly used for this purpose, but recently phosphate of soda has been largely substituted. After dunging, the goods are thoroughly washed, and at once dyed in an alizarin or madder bath. With different mordants these give dif- ferent shades ; thus alumina yields reds and pinks ; tin gives scarlet ; chromium, maroon ; and iron, chocolate or brown. But the number of colors obtained in this way is limited, and the process is largely given up in favor of the more convenient steam style. The oxidation style is chiefly used for aniline blacks. The goods are printed with a paste containing aniline salt, sodium or potassium chlorate, and usually a trace of vanadium salt, all worked into a suitable thickening. After printing, the goods are "aged" for two days, or for a short time in a steam " ager," and are passed through a potassium bichromate solution at 70 C. ; they are then washed in a hot soap solution. Manganese browns for backgrounds are some- times printed by padding the surface of the cloth with manganous chloride or sulphate, and, after drying, padding again with caustic soda. The cloth is then washed and passed into a solution of bleaching powder, whereby a hydrated peroxide of manganese is formed on the fibre as a uniform brown color. This is then printed again by the discharge style to produce a figured pattern. In the discharge style, the dyed cloth is printed Avith a discharge paste, leaving a white figure on a colored ground. Or it is often cus- tomary to add some color to the paste which is not affected by the discharge, and which remains on the goods where printed ; e.g. certain pigments, such as chrome yellow, Guignet's green, and vermilion. Thus colored figures are obtained on a ground of different color. Common discharges are stannous chloride, zinc dust and sodium bisulphite, or sodium bichromate, the last being used in connection with a sulphuric acid bath. Tartaric, citric, and oxalic acids are also used as discharges, acting on the mordants to render them soluble in TEXTILE INDUSTRIES 499 the printed portions, whence they are removed by washing, so that, in subsequent dyeing, the color does not take the fibre in these spots. Alkaline discharges, made with caustic soda and potassium ferri- cyanide, or potassium bichromate and caustic soda, are used with indigo. In the resist style, substances are printed on the cloth which prevent the fixing of the mordant or color in the printed portions. Thus, when dyed, the printed pattern appears white on a colored ground. Resists may act mechanically or chemically. Those of the first kind are generally oils or resins with china clay, which are insoluble and prevent access of the dyestuff to the fibre. Chemical resists are generally citrate of sodium, or acetate of calcium, the former being preferred for preventing the fixing of alumina or iron mordants, and the latter to hinder the development of aniline blacks. After printing, the cloth is dunged, washed, and dyed. For resists on indigo dyed goods, the cloth is printed with zinc sulphate or copper sulphate. In all styles where the cloth is dyed after printing, the white parts of the figure are usually discolored by the dye, and it becomes necessary to " clear " them, generally by " chemicking " in a solution of bleaching powder so dilute as not to affect the color in the mor- danted parts of the goods. This is followed by a thorough soaping and washing. The printed calico is usually finished by starching, bluing slightly to improve the appearance of the white, tendering, and finally calendering between hot rolls. Wool is extensively printed for delaines and challis, the steam and discharge styles being most commonly employed. It is usually prepared for printing by passing through bleaching powder liquor, and then through an acid bath, the chlorine imparting to the wool a greater affinity for the acid colors. The color is prepared with thickening, much as for cotton, and after printing the cloth is usually steamed and washed. Direct and basic colors are printed without further addition to the paste; acid colors require a little oxalic or tartaric acid ; for mordant colors, acetate of chromium or of aluminum is employed, while for discharge styles stannous salts are used as reducing agents in the paste. Silk is printed in much the same way as wooL It is usually mordanted with tin, and sometimes with an acid. 500 OUTLINES OF INDUSTRIAL CHEMISTRY REFERENCES Die Rohstuffe des Pflanzenreiches. J. Wiesner, Wien, 1873. Dyeing and Calico Printing. F. Crace-Calvert, Manchester, 1876. (Palmer & Howe.) Etudes sur les Fibres ve"getales textiles. M. Ve'tillard, Paris, 1876. Le Conditionneraent de la Soie. Jules Persoz, Paris, 1878. Calico Printing, Bleaching, r.nd Dyeing. C. O'Neill, London, 1878. Bleicherei, Farberei und Appretur. C. Romen, Berlin, 1879. Die Gewinnung der Gespinnstfasern. H. Richard, Braunschweig, 1881. The Wild Silks of India. Thomas Wardle, London, 1881. Die Technologic der Gespinnstfasern. 2 Bde. H. Grothe, Berlin, 1882. Die Wascherei, Bleicherei und Farberei von Wollengarnen. R. Sachse, Leip- zig, 1882. Dyeing and Tissue Printing. W. Crookes, London, 1882. (Bell & Sons.) Structure of the Cotton Fibre. F. Bowman, Manchester, 1882. Ramie, Rhea, Chinagras und Nesselfaser. Bouche" u. Grothe, Berlin, 1882. Trait^ pratique du De"graissage, etc. A. Gillet, Paris, 1883. Ueber pflanzliche Faserstoffe. F. von Hohnel, Wien, 1884. Bleaching, Dyeing, and Calico Printing. J. Gardner, London, 1884. The Dyeing of Textile Fabrics. J. J. Hummel, London, 1885. (Cassell & Co.) The Structure of Wool Fibre. F. J. Bowman. 2d Ed. Manchester, 1885. (Palmer & Howe.) Les Soies. N. Rondot, Paris, 1885. The Printing of Cotton Fabrics. A. Sansone, Manchester, 1887. (Heywood & Son.) Report on Indian Fibres and Fibrous Substances. C. F. Cross, E. J. Bevan, C. M. King, and E. Joynson, London, 1887. Microscopic der Faserstoffe. F. von Hohnel, Wien, 1887. Dyeing. A. Sansone, Manchester, 1888. (Heywood & Son.) Das Fa'rben und Bleichen von Baumwolle, Wolle, Seide, Jute, u.s.w. J. Kerz- feld, Berlin, 1889. Die Echtfarberei der losen Wolle in ihrem ganzen Uinfange. Alfred Delmart. 3 Bde, 1887-1891. Reichenberg i. B. Die Jute und ihre Verarbeitung. E. Pfuhl. 3 Bde. Berlin, 1888-1891. (J. Springer.) Handbuch der Farberei. A. Ganswindt, Weimar, 1889. L'Industrie de la Teinture. C. L. Tassart, Paris, 1890. (Bailliere et Fils.) The Cotton Fibre, Its Structure, etc. Hugh Monie, Manchester, 1890. Report on Flax, Hemp. Ramie, etc. U. S. Dep't Agriculture, Washington, 1890. Le Soie. L. Vignon, Paris, 1890. Industrie de la Soie. F. Debaitre, Paris, 1890. Traite de Teinture sur laine et sur etoffes de laine. P. F. Levaux, Liege, 1890. (J. GoJenne.) Traite' Pratique de Teinture et Impression. M. de Vinant. 2d Ed. Paris, 1891. Die chemische Technologic der Gespinnstfasern. O. N. Witt, Berlin, 1891. Tintura della Seta. Teodoro Pascal, Milano, 1892. (U. Hoepli,) Traite' de la Teinture et de 1'Impression. J. Depierre, Paris, 1891-1892. 2 Tomes. (Baudry et Cie.) PAPER 501 Die Praxis der Farberei von Baumwolle u.s.w. J. Herzfeld, Berlin, 1892. Silk Dyeing, Printing, and Finishing. J. H. Hurst, London, 1892. (George Bell & Sons.) Textiles Ve>etaux. E. Lecornpte, Paris, 1893. Manuel of Dyeing. E. Knecht, C. Rawson, and R. Loewenthal. 3 Vols. London, 1893. (Griffin & Co.) La Pratique du Teinturier. Jules Jaron, Paris, 1894. 2 Toines. (Gauthier- VillarsetFils.) Cellulose. Cross & Bevan, London, 1895. Bleichen u. Farben der Seide u. Halbseide. C. H. Steinbeck, Berlin, 1895. (J. Springer.) Bleaching and Calico Printing. Geo. Duerr and Wm. Turnbull, London, 1896. (Griffin & Co.) The Cotton Plant. Bulletin No. 33, U. S. Dep't of Agriculture, Washington, D.C., 1896. Das Anthracene und seine Derivate. G. Auerbach. 2 te Auf. Braunschweig, 1880. Die Industrie der Theerfarbstoffe. C. Haussermann, Stuttgart, 1881. Die Chemie des Steinkohlentheers. G. Schultz. 2 te Auf. 2 Bde. Braun- schweig, 1886. Die kiinstlichen organischen Farbstoffe. P. Julius, Berlin, 1887. The Chemistry of the Coal-Tar Colours. R. Benedikt, translated by E. Knecht. 2d ed. London, 1889. (Bell & Sons.) Organische Farbstoffe, welche in der Textilindustrie Verwendung finden. R. Mohlau, Dresden, 1890. (Julius Bloem.) Les Matieries colorantes, etc. C. L. Tassart, Paris, 1890. Tabellarische Uebersicht der kiinstlichen organischen Farbstoffe. Schultz & Julius. 2 te Auf. Berlin, 1891. Chemistry of the Organic Dyestuffs. R. Nietzki, translated by Collin & Rich- ardson, London, 1892. Cheinie der organischen Farbstoffe. R. Nietzki. 2 te Auf. Berlin, 1894. Tabellarischen Uebersicht der kiinstlichen organischen Farbstoffe. A. Lehne, Berlin, 1894. PAPER Paper consists of cellulose fibres matted or felted into a coherent sheet. Usually a certain amount of mineral matter, or " loading " is incorporated with the paper to increase the weight and render it smooth and less porous. The raw materials furnishing the fibre are wood pulp, cotton or linen rags, esparto, straw, hemp, flax, jute, etc. Old paper and the trimmings and waste from paper mills are also reworked. The common loading materials are clay (kaolin), ground talc or steatite, gypsum, or precipitated calcium sulphate (pearl hardening, crown filler, etc.), and barium sulphate (blanc fixe). In nearly every case the cellulose fibres must be freed from in- 502 OUTLINES OF INDUSTRIAL CHEMISTRY crusting matter and treated in such, a way as to reduce the substance to a state of minute subdivision and to isolate more or less com- pletely the individual fibres. It is largely in this isolation that chemical processes are involved in the industry. Wood pulp is made from poplar (Populus grandidentata, Michx.), spruce (Picea rubra, Link.), hemlock (Tsuga Canadensis, Carr.), pine (Pinus Strobus, L.), cotton wood (Populus monilifera, Ait.), basswood (Tilia Americana, L.), white birch (Betula papyrifera), and maple (Acer dasycarpum, Ehrh.). Wood pulp is of two kinds, mechanical and chemical. Mechani- cal pulp is made by forcing a large stick of wood against a revolving sandstone, or emery wheel, over which a jet of water plays continu- ously. The resulting pulp is washed away by the water and passes several screens to remove insufficiently disintegrated particles. The mixture of pulp and water then flows into a tank in which a cylin- der covered with wire gauze is revolving. The water passes through and a layer of pulp adheres to the cylinder and is delivered onto an endless blanket ; this carries it to a pair of squeeze-rolls where it is compacted. It is then cut into sheets of convenient size, several of which are pressed into one thick " board " for transportation. Me- chanical pulp is contaminated with lignin and resinous matters, which turn brown on exposure to light. The fibres are short and do not mat together well, so the paper made from it is not strong ; such pulp is only used for cheap paper (e.g. newspaper) and generally in conjunction with other fibres and chemical pulp. By dipping a strip of paper into a solution of phloroglucin in hydrochloric acid, the presence of ground pulp may be detected by the appearance of a magenta red color ; an aqueous solution of aniline sulphate will yield a yellow color. Chemical pulp is prepared by the soda process, the sulphite process, or by the sulphate process. The soda process is largely used for soft woods, especially poplar, cotton wood, and basswood. The bark is re- moved by hand shaves, but the knots and rotten wood are generally disregarded. The wood is put through a chipping machine which cuts it across the grain and reduces it to fragments about three-eighths of .an inch thick. After the chips are dusted by blowing them against a screen, they are filled into the digesters. These consist of rotary horizontal cylinders holding about 3 cords of wood, or rotary globular boilers, holding about 5 cords. Recently, upright fixed digesters heated by live steam have come into general use. The digester is nearly filled with chips, which are then covered with a caustic soda liquor of about 11 Be. They are boiled for from 8 to 10 hours at a PAPER 503 pressure of from 90 to 110 pounds. The effect of this " cooking " is to reduce the wood to a soft mass of grayish brown color, while the liquor has become dark brown and has a density of lli Be. The non-cellulose matters of the wood (lignin, resins, etc.) which consist largely of organic acids, are decomposed by or combine with the soda, and consequently the alkali is nearly all neutralized during the pro- cess. The pulp and "black liquor" are blown out into a tank having a sloping bottom and covered with a closely fitting lid. Here the pulp is systematically washed and the wash-waters are saved until their density falls below 8 or 9 Be. The liquor is pumped into a mul- tiple effect evaporator and evaporated to 38 Be., when it is sent directly to a revolving calcination furnace (p. 4) from which a dry soda-ash is recovered ; this is recausticized for use in the digesters. From 85 to 90 per cent of the original soda is thus recovered. The caustic soda has a direct action on the cellulose itself, espe- cially when the pressure is high ; hence some of the fibre is dissolved or destroyed, while all of it is weakened somewhat. The pulp pro- duced is very soft, and though of a dark color, is easily bleached. The yield from poplar is about 40 per cent of the weight of the wood. In the sulphite process, the wood (generally coniferous wood) is boiled under pressure with sulphurous acid or, more commonly, with acid sulphite of calcium and magnesium. The action of the sulphur- ous acid under pressure and at a high temperature upon the lignin and other incrusting matters of the wood fibre is probably a hydrol- ysis ; by this, these complex molecules are broken down, the result- ing products being largely organic acids and aldehydes, soluble in the liquor. But, owing to secondary reactions among themselves, certain acids and insoluble tar-like substances are also formed, which the reducing nature of the sulphurous acid does not appear to entirely prevent. The acid sulphites react much like sulphurous acid, but the bisulphites combine with the aldehydes formed in the first stage of the decomposition, producing stable and soluble double salts. The organic acids which are also formed decompose the bisulphites and form soluble calcium and magnesium salts, while sulphurous acid gas is set free, causing a constant increase in the pressure within the digester. The acid sulphites also tend to bleach the coloring matter of the fibres by forming colorless compounds with them, but this is a very unstable bleach and the original color soon returns when the pulp is made into paper. Hence for perma- nent whiteness the pulp is further bleached with chlorine. Bisul- phite of calcium is unstable and decomposes readily into neutral 504 OUTLINES OF INDUSTRIAL CHEMISTRY sulphite, setting free sulphurous acid. This results in the precipi- tation of the neutral sulphite on the fibre, which is left harsh, even after long washing. Magnesium bisulphite is more stable, and, although less corrosive to the fibre, it dissolves the non-cellulose matter even more completely than does the lime salt ; further, any sulphate or neutral sulphite which may be formed is easily washed off and the pulp is left soft and white. Sodium bisulp'hite gives a better product than either of the above, and strong liquors can be made from it ; but it is too expensive for general use. Bisulphite liquors are made by passing sulphur dioxide through towers packed with dolomite, over which water is trickling ; or by leading sulphur dioxide into closed vessels about half full of milk of lime (prepared from dolomite). Within the vessel is a system of revolving paddles, half submerged in the liquor, and thus presenting large surfaces, wet with the liquor, to the action of the gas ; they also splash the spray into the atmosphere of gas, thus securing rapid and complete absorption. Usually a series of three of these tanks are used, the strong gas entering the most concentrated liquor, which is thus brought up to a gravity of about 1.045 to 1.060 (6 to 8 Be.), and containing 3^ to 4^ per cent S0 2 . The sulphur dioxide is pre- pared by burning brimstone in an iron retort. Much care is neces- sary in regulating the air supply to the burner; too much air forms S0 3 , which produces sulphates in the liquor; it also causes over- heating of the furnace, and consequent sublimation of sulphur into the cooling pipes and absorption tanks, where polythionic acids (thiosulphates) are formed. These precipitate sulphur in the pulp in the digester, and cause trouble in the paper making. Too little air supplied to the burner also causes sublimation of sulphur. The hot gases from the burner are cooled to 10 or 15 C. by passing through water-cooled lead pipes. For the strongest liquor, the tem- perature in the absorption tanks must be kept as low as possible. The tanks for storing the sulphite liquors are sometimes lined with lead, though unlined tanks of hard pine are often used. Large quantities of liquor may be kept without much loss of strength, either through oxidation to sulphate, or evolution of gas and precipitation of sulphite. Bronze rotary pumps or lead-lined acid eggs are used for pumping the liquor. Sulphite, digesters are usually made of steel and lined with 3 to 4 inches of neat Portland cement, or with a mixture of Portland cement and sand, faced with a layer of hard-burned, acid-resisting brick. The acid liquors have a very corrosive action on iron, and much experimenting has been done to find a metal lining suitable PAPER 505 for this use. Lead resists the action very well, but when used as a lining it soon cracks or warps. It also gives much trouble through its tendency to " crawl," and has been abandoned in favor of cem- ent. By filling the digester entirely full of liquor and heating, a layer of calcium sulphite may be deposited as scale on the walls, and afford much protection to the iron. Bronze digesters have also been tried, but are too expensive, do not resist the liquor, and are lacking in strength, several having exploded. Two types of digester are now in use, the rotary and the upright. The former are usually large, globular vessels, heated by free steam, introduced through the hollow trunnions. Live steam must be as dry as possible, to avoid diluting the liquor too much. The digesters have manholes, and also suitable blow-off valves for the escape of gas, if the pressure be- comes too high. For making sulphite pulp, all bark, knots, and dead wood are cut out of the sticks, which are then chipped across the grain, as for soda pulp. The boiling is carried on by the " quick-cook" or the " slow-cook " method. In the quick-cook system the digester is com- pletely filled with chips, and all the liquor (about 1200 gallons per cord of chips) is run in as rapidly as possible, through a large pipe. As a rule the liquor is about 10 Tw. (7 Be.), with 31- per cent S0 2 . At first the pressure is raised slowly, in order to avoid the hammer effect of the live steam coming in contact with the cold digester con- tent, and also to avoid too high a temperature before the liquor has penetrated into the interior of the chips ; otherwise the wood may be burned, and rendered brown or red. The temperature (which is the most important factor in the process) should not exceed 300 to 312 F. (149 to 156 C.). It should be regulated by a thermometer, since no dependence can be placed on the pressure indications as a means of determining the conditions within the digester. During the 12 or 18 hours' boiling, considerable gas is evolved, and there is a steady increase in the pressure, which reaches 75 to 85 pounds. In the slow-cook process a very large digester (14 by 45 feet), heated by lead coils in the lower part, is used. The chips are packed evenly in the digester, and wet steam at 100 C. is introduced for 12 hours, until all the air is expelled and the charge heated to 100 C. No pressure is used, and the condensed water is allowed to flow out freely. Then the manhole and outlet cocks are closed, and the cold liquor of 1.042 sp. gr. is run in. This causes a partial vac- uum, and a better penetration of the liquor into the chips is secured. When the digester is almost full of liquor, the heating is begun, and raised to 110 as rapidly as possible, though it usually requires 12 506 OUTLINES OF INDUSTRIAL CHEMISTRY hours. The steam is so regulated that this temperature is main- tained for about 12 hours, when it is slowly raised to 120 C., and a maximum pressure of about 50 pounds is secured. The total time of boiling is about 36 hours. Usually the pulp is blown out of the digester into a draining tank, where it is washed with pure water. When washed in the digester, as is sometimes done, cold water must be run in at once after the liquor is drawn off, to prevent burning the pulp by the heat radiated from the digester walls. Pulp which is to be bleached must be very thoroughly washed, since any bisul- phite left in the fibre acts as an " antichlor," and destroys the bleach liquor. The undecomposed shives must be removed by screening the pulp before bleaching. Sulphite pulp has longer and stronger fibre than soda pulp, and is lighter colored, some samples being nearly as white as the bleached pulp. It is often used unbleached, but contains some dirt and has a harsh feel. If the chips have not been entirely covered by the liquor, or if the latter has been weakened by too much gas blown off during the boiling, the pulp may be burned, and black, charcoal-like specks appear in it. The waste sulphite liquors are light brown color, and contain much extractive matter from the wood ; their dis- posal is often a serious matter, and it has been suggested * that they may furnish material for oxalic or pyroligneous acid, or alcohol. The sulphate process consists in boiling wood chips in an iron vessel at from 75 to 150 pounds pressure, for 35 hours, in a solution of sodium sulphate at 12 to 15 Be., and containing some caustic soda and carbonate. During the boiling the sodium sulphide formed by reduction of the sulphate prevents oxidation of the fibre, hence a good yield of strong fibre is obtained. The waste liquor is evapo- rated, and the residue is calcined (forming some sodium sulphide) and leached ; the solution is heated with milk of lime until partially causticized, and is then returned to the boiler. The gases and liquors formed have a very offensive odor. The pulp is soft and strong, and is mainly prepared from spruce and fir. The pulp made by any of the above processes is now sent to the " Hollander," or " beating engine " (Fig. 94). This is an oval tub 15 to 20 feet long by 3| feet deep, and having a vertical par- tition called the " mid-feather " extending along the middle, about two-thirds of its length. On one side of this and extending across one-half of the width of the tub is a large roll (A), carrying on its circumference a number of knives (C). The floor is curved up- ward behind the roll (A), conforming closely with its curvature, but * Griffin and Little, Chemistry of Paper Making, p. 271. PAPER 507 extending only about half its height, as shown at (B). From this highest point the floor falls away to the level of the rest of the tub bottom. Under the roll is the " bed-plate " (D), fitted with knives similar to those on (A). (A) is revolved in the direction shown by the arrow, and the pulp is drawn in between the roll (A) and the curved bottom (D), and the fibres are torn apart. It then passes over the back-fall (B) and thence around through the passage on the other side of the mid-feather to the front of the roll and again passes between the knives. (A) is suspended upon adjustable bear- ings so that the distance between the two sets of knives may be regulated. They are not set very close for breaking and disintegrat- . 94. ing the washed pulp, as it is not desired to break the knots and un- decomposed wood, which would cause dirt and shive in the pulp. In order to complete the washing of the pulp during its disinte- gration one or two drum- washers (E) are usually placed in each hoi- lander. These are rotating cylinders covered with fine wire gauze and divided into compartments by curved partitions. A conical tube passes through the centre of the drum, the narrow end being towards the mid-feather. The partitions radiate from this cone to the wire gauze periphery of the drum. The outer end of the drum is solid, but that next the mid-feather has a central opening (F), through which each compartment discharges its content of water into the trough attached to the mid-feather. The drum, supported in adjusta- ble bearings, is partly submerged, and the water, passing through the gauze, is caught in the compartments as the drum rotates and dis- charged through (F). It flows into the trough and out through the 508 OUTLINES OF INDUSTRIAL CHEMISTRY pipe (G). The gauze holds back the pulp which again passes around the mid-feather to the roll (A). Another form of hollander, requiring less floor space, is shown in Fig. 95. In this the pulp passes below the floor and back-fall on its return to the front of the roll. The machine is but little wider than the length of the roll (A), the washing drum (E) being directly be- hind the roll. After breaking, the pulp is carried by a strong stream of water onto a sluice or inclined way having a number of transverse slats across the bottom. The knots and lumps lodge against these ob- structions, while the fine pulp flows on with the water to the bleach- ing tanks. Fm. 95. Rags, both cotton and linen, are largely used in paper making. These are collected in all countries, and arrive at the mill in various conditions of filth. They are first sorted by hand, the seams cut open, and all buttons, metallic hooks, etc., removed. The dust is then beaten out in machines having rapidly revolving arms, and then the rags are cut into small pieces and boiled for 12 hours or longer, under a pressure of 60 or 70 pounds, in rotary horizontal cylinders, or in horizontal kiers (p. 452), with 5 to 18 per cent of milk of lime. Sometimes a little soda-ash is added to the liquor for colored rags. After boiling they are dumped in heaps to drain and soften for a day or two. After washing with hot water, they are sent to the pulping machine. Esparto, or Spanish grass, is derived from Lygeum Spartum, Loefl. and Stipa tenacissima, L. The bast fibres are similar to those of straw, bat give a stronger paper. It is chiefly used in Europe, being too expensive to compete with wood pulp in this country. Esparto and straw are boiled with caustic soda in upright digesters. In PAPER 509 rotary boilers the fibre forms little balls ("fish eggs "), which cause little spots or lumps in the paper. The pressure and time of boil- ing vary. The waste liquor is evaporated, and the alkali recovered (p. 503). After washing, the pulp bleaches well with bleaching liquor. In this country, straw is generally boiled with lime to prepare a pulp for strawboard. Jute has very short fibre, so the fibre bundles are not separated, and only the lime-boil is employed. The bleaching of paper pulp is done by agitation with a weak calcium hypochlorite solution. If the liquor is heated to 90 or 100 F., or a little acid added, the process is hastened. Alum forms aluminum hypochlorite with bleaching powder solutions, which is very effective ; a slightly acid alum or " bleaching " alum is com- monly used. The bleaching is carried on in special vessels ("chests "), or in the beating engines or hoi landers, the latter giving the best results. Only a clear solution of bleaching powder should be used, so that no dirt be introduced in the insoluble residue, as it would cause spots in the paper. Rags require the least bleaching (2 to 5 pounds bleaching powder to 100 pounds of stock), and spruce pulp the most (about 18 to 25 pounds per 100 pounds for sulphite spruce pulp). As soon as bleached, the process should be stopped, espe- cially if the liquor has been heated ; otherwise the fibre is liable to be chlorinated, and color again taken up. The excess of hypo- chlorite in the pulp is washed out with water, or is destroyed by adding an antichlor, such as sodium thiosulphate (p. 45), in the beating engine. Neutral calcium sulphite is also recommended, but its action is slow : - Ca(C10) 2 -}- 2 CaS0 3 = 2 CaS0 4 + 2 CaCl 2 . The pulp must be thoroughly washed after bleaching, even when antichlors are used, since injurious substances may be left in the pulp. The action of the antichlor is as follows : 2 Ca(C10) 2 + NaA0 8 + H 2 = 2 KaCl + 2 CaS0 4 + 2 HC1 ; or, in dilute solutions : Ca(C10) 2 + 4 Na 2 S 2 3 + H 2 = 2 Na 2 S 4 6 + 2 NaOH + CaO + 2 NaCl. Other materials than bleaching powder, such as ozone, hydrogen peroxide, sulphurous acid, or liquid chlorine, have been suggested for bleaching, but as yet these are of much less importance than the hypochlorites. 510 OUTLINES OF INDUSTRIAL CHEMISTRY The paper-making process is chiefly mechanical. It is essential that the water used be clear and colorless, since color or suspended matter will be taken up by the pulp. The first operation is " fur- nishing" or charging the hollander with the stock; the kinds and quantity of material employed depend on the quality of the paper to be produced. Rag stock is only used for the best grades, especially writing papers. New linen rags and waste are used for bond paper, but the softer writing papers are made from old rags. The quality of paper depends largely on the thorough separation of the fibres and mixing of the ingredients in the hollander. In order to give the paper body, weight, and greater smoothness, mineral filler or "loading" material is employed. This must be exceedingly fine, and not have too high a specific gravity or solubility in water, as its retention in the mat of the fibre would be thus reduced. It must be free from dirt, grit, and mica, since these cause scratches on the polishing rolls or spots on the paper. The loading is done in the hollander after the fibre has been well beaten with water. The filler is thoroughly mixed with the pulp, and then, for engine sized paper, the sizing materials are added, and the whole beaten until a perfect mixture of all the materials is obtained. Papers intended for printing or writing must be sized or coated on the surface with some substance which will prevent the absorp- tion and consequent spreading of the ink. For liquid writing inks, the sizing must be more perfect than for the viscid printing inks. Almost the only sizing materials now used are gelatine " animal size," (used on the better grades of paper) rosin, and casein. These are applied in several ways. Animal size is applied to hand-made papers by dipping each sheet separately into a tub of the glue solution, and allowing it to dry slowly. The operation is called "tub sizing." Machine-made writing paper is passed in continuous web through a trough filled with the glue solution. It is then cut into sheets, and dried very slowly by hanging it in a loft kept at an even tempera- ture ; or, in cheaper grades, after leaving the size trough, the web passes over a series of skeleton driers, within which fans keep up a rapid circulation of air. Slow drying is essential to animal size, in order to bring it to the surface. Printing papers (except some kinds of newspaper) made at the present time are "engine sized"; i.e. a rosin soap (prepared by boiling rosin with soda-ash) is added in the hollander, and, after beating, a solution of aluminum sulphate is intro- duced. The alum decomposes the rosin soap, forming a precipitate of free rosin, and perhaps some alumina which become entangled in the openings between the fibres. When the paper passes between PAPER 511 the hot calender rolls in finishing, this rosin is fused and forms a varnish-like layer on the surface. The aluminum sulphate should be neutral or basic, since free acid decomposes the size and injures the color and strength of the paper. For good results, an excess of alum over the amount needed to decompose the rosin soap must be used ; and the precipitated alumina helps to hold the finer parts of the fibre and filler in the pulp while forming the sheet. Paper is usually colored by adding pigments or dyes to the pulp in the hollander. For white paper, the slight yellow tinge of bleached fibre is neutralized with a trace of blue or pink, ultra- marine or coal-tar dyes being used. Some pigments are precipitated on the fibre by adding solutions in the hollander ; e.g. potassium bi- chromate and lead acetate. The sheet is formed in three different ways : by the hand frame, by the cylinder machine, and by the Fourdrinier machine. The hand frame, used for hand-made paper, is simply a rectangular frame, covered with wire gauze, and having a slight, removable ledge around the sides. This frame is submerged in the pulp, mixed to a thin cream with water ; when raised, the ledge retains some of the pulp on the gauze, while the water drains through ; at the same time the workman shakes the frame slightly from side to side, causing the fibres to " felt," and forming a mat of pulp on the gauze. The frame is then inverted over a woollen felt blanket, on which the sheet of pulp drops. A number of these pieces of felt, each carrying a sheet of pulp, are piled one above the other, and heavily pressed until the water is expelled. The sheets are then " tub-sized," as above described. The final finish is given by calendering between hot rolls. The cylinder machine is essentially the same as that described for mechanical pulp, on p. 502. The web of paper pulp is carried on an endless blanket over a large drying cylinder, and then lifted and passed between heated rolls. The paper thus made is weak, since the fibres are not well felted. They are used for tissue and blotting papers, and are not sized. The Fourdrinier machine is very complicated. Essentially, it is as follows : An endless web of wire gauze is supported horizon- tally on a number of rollers, and travels continually in one direction. The paper pulp flows onto this from a storage tank called the " stuff chest," the thickness of the sheet being regulated by the supply of pulp. The wire gauze is given a continuous sidewise shaking motion which felts the pulp, while the water drains away. The water is drawn away by the action of " suction boxes " from which the air can be partially exhausted, and over which the gauze travels. The 512 OUTLINES OF INDUSTRIAL CHEMISTRY web is next transferred to an endless blanket which carries it between squeeze-rolls, and then onto a second felt, where it is again passed between rolls. It finally passes a series of "couch rolls," " press rolls," drying cylinders, and calender rolls to compact, dry, and polish the paper. By fixing a slightly raised design on the wire gauze of the hand frame the paper is made slightly thinner along the lines of the pat- tern, and so-called "water marks" are made. The same effect is obtained on paper made on the Fourdrinier machine by placing a light roller ("dandy roll") carrying the design in relief, between the first and second suction boxes, so that an impression is made on the soft pulp. If the roll is covered with wire gauze the impression of the weave of the gauze is obtained, producing the " wove " papers. A smooth roll carrying ridges forms the parallel lines on "laid" paper. By using a roll with a depressed or engraved design the paper is made thicker in the lines of the pattern. Imitation water marks are often made by pressing the finished paper with plates carrying the design in relief, or by slightly parchmentizing the sur- face by printing with certain chemicals, such as zinc chloride or sulphuric acid. The finishing of smooth and highly sized paper is done by calen- dering, or passing the web between polished rolls of chilled iron, under heavy pressure. A higher gloss is obtained by using calen- ders with rolls made of heavily pressed paper, alternating with polished iron rolls. Friction calendering consists in passing the paper between a pressed paper roll running at high speed, and an iron roll running slowly. For very high gloss the paper is " plated " ; i.e. passed through heavy rolls while the sheets lie between polished zinc plates. Printing papers are usually white, and often contain a large amount of loading material. In this country they are chiefly made from wood pulp. Some kinds are heavily calendered to secure a smooth surface. Cheap newspaper is largely made of mechanical pulp. Wrapping papers are made from straw, jute, manilla hemp, old rope, and colored rags. The stock is seldom bleached, and hence is very often deeply colored. Wrapping papers are frequently calendered, and always sized. Writing papers are made from the best materials, and are highly sized and carefully calendered. Blotting and tissue papers are unsized and unfilled, the former being loosely felted and thick ; the latter is made from long fibres, especially hemp and cotton, and is the thinnest paper made. PAPER 513 Parchment paper is made by dipping unsized paper into sulphuric acid, diluted with one-fourth its volume of water, to which a little glycerine is added. It is quickly removed and washed with water, then with dilute ammonia, and again with water. The acid converts the exterior cellulose of the fibres into amyloid, which coats the fibres and cements them together, forming a translucent parchment- like material of great toughness. The action of strong zinc chloride solution (sp. gr. 1.82) is also to parchmentize the paper. After washing, the paper is pressed between rolls, dried, and sometimes calendered. Willisden paper is made by passing the web through a strong solu- tion of Schweitzer's reagent (copper hydroxide dissolved in strong ammonia water), and pressing together several sheets so prepared without washing. The surface of the cellulose is softened and made- sticky, and the sheets are compacted into a single thick one. The evaporation of the ammonia leaves the cupro-cellulose in the fibres, which are thus coated with a green varnish-like substance, and ren- dered waterproof. The testing of paper should be both microscopical and chemical ; considerable attention is given to this on the continent of Europe, but in this country it is seldom employed. The methods and details may be found fully described in Griffin and Little's Chemistry of Paper-Making, Chap. IX., and in the works 'of Wiesner and of Herzberg. REFERENCES Die Fabrikation des Papiers. L. Miiller, Berlin, 1877. The Manufacture of Paper. C. T. Davis, Philadelphia, 1882. Guide pratique de la Fabrication du Papier. A. Proteaux, Paris, 1884. Handbuch der Papierfabrikation. S. Mierzinski, Wien, 1886. Die Microscopische Untersuchung des Papiers. J. Wiesner, Leipzig, 1887. Die Fabrikation des Papiers. E. Hoyer, Braunschweig, 1887. (Vieweg o. Sohn. ) Die Bestimmung des Holzschliffes im Papier. A. Mtiller, Berlin, 1887. (J. Springer.) The Practical Paper Maker. J. Dunbar. 3d Ed. London, 1887. (E. and F. N. Spon.) Papier Priifung. W. Herzberg, Berlin, 1888. (J. Springer.) A Textbook of Paper Making. C. F. Cross and E. J. Bevan, London, 1888. (E. and F. N. Spon.) Le Papier. P. Charpentier, Paris, 1890. (Tome X., Encyclopedic Chimique, par M. FrSmy.) The Art of Paper Making. A. Watt, London, 1890. Technologie der Papier Fabrikation. Wurtemberg, 1893. (Guntler-Straib.) The Chemistry of Paper-Making. R. B. Griffin and A. D. Little, New York, 1894. (Lockwood & Co.) 2L 514 OUTLINES OF INDUSTRIAL CHEMISTRY A Treatise on Paper-Making. Carl Hoffman, New York, 1895. (Lockwood &Co.) Paper Trade Journal, New York, 1893, June 24, et seq. : Evolution of the Sulphite Digester. H. A. Rademacher. Journal of the Society of Chemical Industry : 1890, Chemistry of Hypochlorite Bleaching. C. F. Cross and E. J. Sevan. 1890, 9, 241, Paper Testing. H. Schlichter. United States Consular Reports, 1894. Parchment Paper. LEATHER The skin, when removed from the animal, very soon becomes putrid if kept moist, and is hard and horny when dried ; in either case, boiling water converts it into soluble glue. Leather is skin so treated that it remains more or less soft and pliable, does not putrefy, and is not readily changed into glue. Animal skins are made up of three layers, the epidermis, the fatty tissues, and between them the corium, cutis, or skin proper. The epidermis is thin and the roots of the hair are attached to it. It consists of individual cells, which become dead and dry on the outer surface, and are easily detached by friction or abrasion. These cells are largely composed of keratin, a substance rich in sulphur, and very little affected by cold water ; even hot water does not produce gelatine from it. But the young, interior cells are somewhat attacked by lime-water. The hair and keratin substances seem to be dissolved by concentrated alkali or alkaline sulphide solutions. The fatty tissues form the innermost layer of the skin, and consist of a loose network of con- nective tissue, containing fat cells, blood vessels, sudorific glands, and muscular fibres. The ducts of the sweat glands pass through the corium and epidermis. The corium or dermis is the only part of the skin of value for leather; it consists of connective tissue composed of bundles of fibres which interlace somewhat loosely on the under side of the skin, but are closely matted on the epidermal side. This fibrous substance consists chiefly of collagen, which appears to be altered by the action of boiling water and converted into soluble gelatine or glue. Some authorities hold that an intercellular substance, coriin, comparable to sericine or silk glue, p. 438, fills the spaces between the bundles of fibres, and cements them together when the skin dries, making the skin hard and stiff. Other writers regard the coriin as merely an alteration or decomposition product of collagen. Both collagen and coriin are bodies of an albuminoid LEATHER 515 character, and little is known of their exact chemical composition. They are soluble in alkalies, but only slowly so in lime-water, the coriin being the more readily dissolved; the coriin also dissolves in solutions of chlorides of the alkalies and alkaline earths. Pelts are divided by the tanner, according to their size, into three general classes: (a) hides, comprising the skins from large and fully grown animals, such as the cow, ox, horse, buffalo, walrus, etc. ; these form thick heavy leather, used for shoe soles, large machinery belting, trunks, and other purposes where stiffness and strength, combined with great wearing properties, are essential ; (6) kips, the skins from undersized animals or yearlings of the above species; (c) skins obtained from small animals, such as calves, sheep, goats, dogs, etc. These yield lighter leather suitable for a great variety of purposes. The thickest and heaviest hides come from rough, sparsely settled countries. The same hide varies in thickness and texture in different parts, being thicker on the neck and butt than on the flank and belly. They frequently show injury, such as cuts, brand marks, and holes or thin places caused by the bot-fly or warble. Diseased hides are often sold, which, besides yielding a poor leather, are a source of danger to the workmen, owing to the contagious nature of some of the diseases (especially anthrax); hence disinfectants should be freely used in the tannery. Pelts come to the tanner " green " (fresh from the animal), salted (where the salt has been thickly rubbed on the flesh side), or dried. Green pelts are usually washed in clear water to free them from blood and dirt; salted pelts, if not dried, are merely washed in several changes of water. It is essential to remove all the salt before beginning the unhairing process, as it retards the action of the lime and interferes with the "plumping" of the skin. It is also liable to cause an efflorescence ("spueing") on the finished leather. Dried hides must be softened by soaking them in luke- warm water or in the liquor drawn from the soaking of a previous lot. The water dissolves part of the hide substance and putrefac- tion soon begins in the liquor, developing an alkaline reaction owing to the formation of amines and ammonia, and giving it a much more rapid softening action on the skin ; but great care is necessary in using this "putrid soak," lest the decomposition attack the hide fibre itself. Any injurious action may be lessened by "handling," i.e. drawing the skins from the lower part of the pit and throwing them back on top of the heap. Sometimes careful soaking in a warm, very dilute sodium sulphide solution is substituted for the 516 OUTLINES OF INDUSTRIAL CHEMISTRY putrid soak. The time of soaking varies from two or three days to as many weeks, depending upon the thickness and dryness of the hide and the age and temperature of the " soak " liquors. When the -hide is soft enough to bend in a short turn without cracking, it is put into the " stocks," where it is pounded and rolled under heavy wooden mallets and rolls. The character of the water used in the tannery is important. Soft water makes the skins thin and slim, which is desirable in light leather. Water containing calcium or magnesium sulphate " plumps " or swells the hide, thus exposing a larger surface to the action of the tan liquors, which is desirable for heavy hides. Chlorides cause the hides to " fall," i.e. to become thin and flabby. This may be due to the greater solubility of the coriin in saline liquors. If used for washing after the liming, water having tempo- rary hardness tends to fix the lime among the fibres in an insoluble form, thus causing the leather to be harsh on the grain and produc- ing colored spots because of unequal deposits of tannin and coloring matters in the tan pits. Hard water also causes waste of tannin matters through the formation of insoluble compounds with lime and magnesia. If the water contains organic impurities, it may have an acid nature and cause the hides to "fall" after liming, or it may engender putrefactive changes in the skin. When thoroughly cleaned and softened, the hides undergo the depilation or imhairing- process. This removes the hair and epi- dermis, and also the fatty tissues from the under side of the skin. It is done in several ways : by treatment with an alkaline solu- tion which attacks and softens the inner layers of epidermal cells, loosening the outer layer and hair, so that they may be scraped away ; or by " sweating," in which the young epidermal cells are softened by putrefaction until the outer layers are loosened. Lime is the most common unhairing material, sometimes aided by the addition of sodium sulphide, arsenic compounds, or calcium hydro- sulphide. Liming. The skins are laid in a vat or pit with milk of lime, which loosens the epidermis and forms a soap with the fatty matter. It also dissolves the coriin, loosening the fibres, which swell and " plump " the hides. It is used in excess in amounts varying from one-half pound for a small light skin to 4 pounds for a heavy one. The vats or pits when prepared to receive the skins, are called "limes." The skins are frequently turned over and worked about ("handled") ; for heavy hides which are to form stiff, hard leather, the liming only lasts a few days ; but for a soft, elastic, pliable product, the LEATHER 517 process continues for 15 or 20 days, or longer. Warming the limes to 85 or 90 F. hastens the action very much, but causes the skins to "fall." The addition of sodium sulphide to a thick cream of lime yields a paste which may be spread on the hair side of the skin, and, after being folded together for a few hours, the hair is easily detached. Arsenic sulphides, realgar and orpiment (about 10 per cent of the weight of the lime), are frequently added to the limes, forming calcium sulph-arsenite (HCaAsS 3 ), which is a very rapid depilatory. " Sweating " is much used for hides which are to be made into sole or other stiff leather. The hides are hung in a room kept at a constant temperature of 18 to 21 C., the atmosphere being saturated with moisture. Putrefaction attacks the inner layer of the epider- mis, and in a few days the hair is loosened. Before treating with tannin, sweated hides must be " plumped " by immersion in dilute acid. After the hair has been loosened, the skin is laid across a sloping " beam " of wood, and the hair and epidermis are scraped away with a blunt knife. The fatty tissues are removed in the same way, but a sharper knife is used. These operations are known as " beaming." After trimming off the waste parts of the skin, it is thoroughly washed, and is usually again scraped on the "beam" (scudded) to remove as much of the lime as possible. All these operations described above are carried on in the " beam house " of the tannery. If soft, pliable leather is to be made, the skins are next subjected to the " bating," or " puering," process to destroy the " plumping " produced by the lime, and also to cause other changes, the nature of which is rather obscure. Some authorities claim that the bate merely removes the lime from the pores of the hide, while others assert that it also takes away some of the coriin, thus leaving the fibres looser, and allowing more perfect action of the tan liquors. The latter view seems quite probable, and there is little doubt that the bacteria in the bate do feed upon the hide substance. Further, the ferments, tripepsin, pancreatin, etc., present, undoubtedly exer- cise some function, for when used alone they will cause a "plumped" skin to fall. The ammonium salts formed doubtless also assist in the solution of the lime in the skin. Bating consists in soaking the hides in a mixture of dog or bird dung in warm water. This quickly becomes putrid, and evolves hydrogen sulphide, while the liquor acauires an alkaline reaction. The process lasts from 2 to 4 days, according to the thickness of the skin and the temperature. It is largely dependent upon the atmospheric conditions; in the 518 OUTLINES OF INDUSTRIAL CHEMISTRY warm, sultry weather, such, as usually precedes a thunder-storm in this climate, the action becomes extremely rapid, and a few hours is often sufficient to injure the skin. Great care must be exercised at all times, and the skins stirred about frequently to prevent too great local action, resulting in thin places or in holes in the leather. Many proposals have been made to replace the offensive bate with pure solutions of weak mineral and organic acids ; but these have not generally found favor with tanners, the common objection being that the leather is made harsh, and has a bad grain. After bating, the fibres have become soft and pliable, and the whole skin has a smooth, slippery feel. As these qualities are not desirable in sole leather, heavy hides are not bated. In order to complete the removal of the lime, it is customary to next pass the skins into the "bran drench," consisting of an infusion of bran and water at a temperature of about 32 C. On standing, this soon develops a fermentation, in which butyric and acetic acids are formed, dissolving the lime. The skins are now ready for actual conversion into leather, or the tanning process. This is done in three ways : - (1) With tannin in any form (vegetable tannage). (2) With metallic salts (mineral tannage). (3) With oils or fats (oil tannage). 1. The sources of vegetable tannins have been considered on p. 463. For leather, it has been found essential that the tannin material shall yield other extractive matters than tannic acid when treated with water. These non-tannins are mainly sugars, gums, resins, and coloring matters.* They assist in the tanning in several ways, some of them are directly absorbed by the skin, increasing its weight and solidity ; others set up fermentations in the tan pit, producing organic acids which assist in the formation of a leather of a good body and weight. The tan liquors are prepared by system- atic lixiviation of the ground tan-stuffs in pits, the strongest liquors coining in contact with the freshly ground material. The tempera- ture is important, warm water being generally best for complete extraction, although gambier requires cold water. The spent tan is usually burned for fuel. Extracts, alone or in conjunction with tan liquors, are becoming more generally used. They are simply dissolved in water, and may be added as needed ; but they are often * The tannins derived from gallic acid cause a white efflorescence (ellagic acid) on the leather, while those of the protocatechuic acid group deposit red coloring mat- ters (phlobaphenes) in it. LEATHER 519 adulterated with glucose or molasses, consequently tests with the barkometer* are of no value unless the material is known to be pure. Vegetable tanning is used for sole leather, upper leathers, and colored leathers (morocco). Sole leather is heavy, solid, and stiff, but may be bent without cracking. For this, tanning materials such as oak or hemlock bark, mimosa, chestnut wood, quebracho, valonia, and myrabolans are used. The hides ("butts") are first hung from frames in pits (suspenders), containing weak or nearly spent tan liquors from a previous lot. Here they are mechanically agitated, so that they take up the tannin evenly. Strong liquors would so harden the surface as to prevent thorough penetration into the interior of the hides. This partial tanning gives the skins suffi- cient strength to withstand the rough usage which they receive when transferred to the handlers. These are pits in which the hides lie flat in a pile, which is worked over, or " handled," once or twice a day for a month or six weeks. There are several of these pits, and the hides are treated systematically, first with weak and then with stronger liquors, usually strengthened with extracts. They are then put into the "layers." These are pits filled with alternate layers of hides and ground bark, valonia, etc. ; strong liquor (ooze) of 35 barkometer is run in until the hides are sub- merged, and the pit well is covered with ground bark to exclude the air. After 8 or 10 days, the hides are taken out, rubbed clean, and " laid away " again in fresh tan and stronger liquor, in which they remain a longer time. This process is repeated as often as necessary, the whole time consumed being, on an average, from 8 to 10 months. It may be hastened by keeping the liquor in the tan pit in constant circulation; or by using pressure to force the liquor into the skins; or by using very strong extracts, and continually moving the skins. Various electrical tannage processes have been devised, in which the hides are suspended in strong liquors, and kept in motion while a current of various densities and voltage, depending upon the liquor, is passed through the solution. This is claimed to hasten the pro- cess, but the product has been criticised as lacking substance ("hun- gry "), or being brittle. This is true of most rapid tannages.' Sole leather is usually finished by brushing and washing, followed by slow drying ; the drying is retarded by oiling the leather several times on the grain. When partly dry, it is " sammed " by piling in a heap and covering until heating is induced. It is then " struck * A special form of hydrometer for determining the strength of tan liquors. 520 OUTLINES OF INDUSTRIAL CHEMISTRY out/ 7 i.e. stretched by working with a triangular tool having blunt edges, or by rolling with a heavy roller under pressure in a machine. The weight of the leather is sometimes increased by impregnating it with glucose, or with barytes or other mineral salts. Dry hides yield about 150 per cent of their weight in leather, while green hides make only about 55 per cent. Upper or dressed leather is made from kips and large calf skins. After bating, the skin is usually shaved on the flesh side to make it of uniform thickness. It is then tanned and the grain hardened by handling or tumbling in revolving boxes or drums, in a rather strong solution of tan liquor, usually prepared from gambier. The tannage is completed with mimosa, myrabolans, valonia, or bark, the liquors sometimes being heated to 50 or 60 C. After a final tumbling in sumach liquor, the leather is finished by currying. That is, it is first scoured with brushes and then rubbed with a " sleeker," a smooth stone or piece of glass which removes the creases and wrinkles and stretches the leather. It is then "stuffed" with a mixture of oil, soap, and tallow which is worked into it by rolling or tumbling in a drum. Olive, neat's-foot, sperm, and fish oils are much used for this, as is also degras (p. 523). Upper leathers are usually blacked by rubbing with a mixture of lampblack and oil or tallow ; or they may be painted with a solution of copperas and log- wood. Colored leather is made chiefly from goat, sheep, and calf skins. These are limed, unhaired, bated, and drenched as above described, and are tanned with gambier or sumach liquors, in tumblers or drums, or in tubs, or handlers where they are kept in motion. Colored leathers are usually dyed with basic dyestuffs or with natural dyewood extracts, particularly logwood. After tanning, they are passed into a bath of tartar emetic to fix the tannin before dyeing. The dyeing is done in slightly warm baths, as hot liquors are injurious. The skin is folded down the middle with the grain side out, and is then laid in a slightly warm solution of the dye in a shallow tray ; or the skin may be sponged with the dye on the grain side while spread on a table. If it is to be dyed through, it is worked with the dye solution in a tumbler or paddle-wheel. After bating or when partially tanned, the skins are usually split into two or three layers, by a sharp knife driven by machinery. The grain side is finished to form " skivers," while the flesh side is made into patent leather, wash leather (chamois), or into cheap leather with an artificial grain. The very thin grain splits from sheep and calf leather are used for book bindings. The flesh splits c LEATHER 521 are often given an artificial grain ("pebbled"), by rolling with an engraved roll, or with a die under heavy pressure. This imitation may be carried so far as to make small punctures in the leather with fine pin points to resemble the pores and hair sheaths of the natural grain. Or an electrotype may be made from a piece of natural leather, and this copy fixed on the die. 2. Tanning with metallic salts or tawing is employed for small skins and light leathers, and has recently become very important in this country; the salts used are certain aluminum, chromium, and iron compounds, especially sulphates, chlorides, and bichromates. Alum (or aluminum sulphate) is much employed (always in conjunc- tion with common salt) for white and kid leathers. After liming, usually with the addition of arsenic, for three or four weeks, and unhairing and fleshing, the skins are very thoroughly bated, drenched, and scudded. For white leather, the split skins are tumbled in a drum with a solution of alum and salt, and after lying folded several hours are dried without washing. The hard skin is then softened by pounding, rolling, and stretching. Kid leather for gloves, and calf kid are made by tumbling or treading the split skins in a mixt- ure of alum, salt, flour, egg-yolk, and olive oil, until they are thor- oughly impregnated, and then drying. The leather is colored with natural or coal-tar dyes, and is usually again tumbled in the salt and egg-yolk emulsion. It is softened by " staking," i.e. pulling across the edge of a blunt knife fixed in a vertical position in a post. The flesh side is shaved, and the grain glazed or polished carefully by rubbing with a sleeker, or in a glazing machine. Very excellent leather is produced by combining the alum tan- ning process with tannage in gambier liquor, the method being known as the combination tannage, or dongola process. This is much used for making leather resembling kid, but stronger and cheaper, which is largely used for ladies' shoes. The prepared skins are tawed in alum and salt and then laid in gambier liquor for several days or a week. Chrome tannage, or tawing with chromium salts, has been chiefly developed in this country and is now in general use here. The prin- ciple of the process consists in precipitating an insoluble chromium hydroxide or oxide on the fibres of a skin which has been impreg- nated with a soluble chromium salt, usually potassium bichromate; basic chromium chloride, chromium chromate, and chrome alum are also used. The skins, having been limed, unhaired, fleshed, bated, drenched, and scudded, are worked in a solution of potassium bi- 522 OUTLINES OF INDUSTRIAL CHEMISTRY chromate to which some common salt has been added, together with one-fourth to three-fourths of the theoretical amount of hydrochloric or sulphuric acid necessary to liberate all the chromic acid (Cr0 8 ). After several hours, when the skin shows a uniform yellow color when cut through the thickest part, it is removed, the excess of water pressed out or drained away, and the skin worked in a bath of sodium bisulphite (NaHS0 3 ), or thiosulphate, to which has been added some mineral acid to liberate the sulphur dioxide : 1) K 2 2 7 + 2 HC1 = 2 KC1 + H 2 + 2 Cr0 3 . 2) Na 2 S 2 3 + 2 HC1 = 2 NaCl + H 2 + S + S0 2 . 3) 2 Cr0 3 + 3 S0 2 + 3 H 2 = 3 H 2 S0 4 + Cr 2 3 . The chromic acid is absorbed by the fibre and is later reduced in situ by the sulphurous acid. It is necessary to use a strong solution of the reducing agent, so that the reduction may be fully accomplished before the chromic acid has time to "bleed" from the skin. The strength of solutions recommended vary somewhat in the various processes, but are usually made from 10 to 30 grams per litre- for the bichromate, and 30 to 50 grams for sodium thiosulphate. Calculated on the weight of the skin, from 4 to 9 per cent of bichromate, and about 15 per cent thiosulphate are usually employed. The amount of chromic acid fixed on the fibre is about 4 to 6 per cent, calculated as bichromate, K 2 O 2 7 . Chrome leather is tough and resists moisture very thoroughly. On this latter account, skins which are to be dyed should be intro- duced into the dye at once after reducing and washing, for if allowed to dry, the dyeing is incomplete. The leather may be heated to 80 C. or more without injury, and hence can be dyed with some of the alizarin colors. It is a very rapid process, the time of steeping in the chrome bath being only a few hours and even less in the re- ducing bath. It is a very light tannage, and on thick skins has con- siderable tendency to contract the fibre, and so is not used for sole or upper leathers. It is chiefly employed for glazed kid, calf kid, and glove leathers. The tanned or colored skins are oiled and stuffed before drying. Chrome processes have been covered with patents, and consider- able litigation is now going on in this country concerning them. Tawing with iron salts has been the subject of several patents, but these processes are little used. 3. Tanning with oils consists in saturating the flesh side of split skins with oils (whale or cod liver), and allowing- them to lie in . LEATHER 523 heaps until an oxidation or fermentation of the oil ensues. The mass heats, and a soft spongy leather, such as chamois and buff leather, is formed. The skin being Mmed, bated, and drenched, excess of water is removed by pressing, and the skin is worked in the stocks with oil. After partial drying it is again stocked with oil; this is continued until all the moisture in the skin has been replaced by oil. After partial oxidation the excess grease is removed by pressing, or in the centrifugal machine. The thick, greasy mass expressed, called "degras," consists of semioxidized oil, and is a valuable currying agent. The skins are now washed in a bath of soda or potash to remove the rest of the grease. These alkaline wash- waters are treated with mineral acid, decomposing the soaps, and setting free the fatty acids which rise, and are skimmed off as " sod-oil," also used in currying. These oils have undergone a pecul- iar change in which oxy-acids are formed which unite with the hide fibre, similarly to the combination of tannic acid, and washing with soap or alkali is not sufficient to remove the combined fat; but the uncombined fat is washed away completely. The oil-tanned skins are finally stretched, scraped, and bleached in the sun, or in sulphur dioxide. Chamois leather is often further softened by freezing while wet. Morocco leather is made from goat skins tanned with sumach, which gives a very light-colored product. The prepared skins are tanned by paddling in sumach liquor ; or they are sewed up to form bags which are filled with the liquor, and then piled in a tank where the pressure of one bag upon the other forces the liquor through the skins. The so-called French morocco is made from sheep skins, either whole ("roans"), or split ("skivers"). These leathers are usually dyed in colors, two skins being placed with their flesh sides together, and brushed over with the color, or immersed in a tray or drum filled with the dye liquor. To imitate the grain of goat skin, French calf is usually "grained" by rolling under a cork-surfaced board. Russia leather was formerly tanned with willow bark, but oak bark is now much used, especially for imitations. The peculiar odor is due to an oil obtained by distilling birch bark, and used for curry- ing the leather. The dull red color is produced by dyeing with red wood (Brazil or saunders-wood). Patent leather is made by coating a tightly stretched split skin, or " skiver," with a varnish of linseed oil, containing lampblack, Prus- sian blue, or other pigment. While the leather is still stretched the 524 OUTLINES OF INDUSTRIAL .CHEMISTRY varnish is dried at 70 C., and the surface is smoothed with fine pumice, and other coats of varnish laid on and dried. The final coat is polished with tripoli, or rotten stone Parchment and vellum are made from untanned split skins. The former is made by stretching wet sheep skin, after liming and flesh- ing, 011 a frame, and drawing it smooth and free from wrinkles. Powdered chalk is dusted over it, or mixed with water and painted on the skin to absorb the grease, and the surface is then smoothed by rubbing with pumice. After scraping with a steel blade and a final smoothing, the skin is slowly dried in a shady place. Vellum is made from calfskin, only those of uniform color being used. The liming lasts for three or four weeks, and the washing is very thor- ough. The skin is then split and stretched on a frame, and dried with scraping and pumicing as in the case of parchment. Artificial leather is made from paper and certain cellulose deriva- tives (" viscoid "). or from various kinds of fibrous materials coated with gelatine and heavily compressed. Sometimes leather scraps and trimmings are ground to shreds and soaked in gum or gelatine, and formed into boards by heavy pressure. These leatherettes are chiefly used for embossed trimmings in book binding, and in places where pliability is not essential. Degras is now so important as a currying agent that it is manu- factured on an extensive scale. The wash leather produced is again saturated with oil, and the oxidized oil pressed out ; the process is repeated an indefinite number of times, as long as the skin holds together. The exact nature of tanning is not understood, but two theories are advanced by authorities. The physical theory admits no chemi- cal combination between the tan-stuff and the hide fibre, holding that the latter is merely coated with the tan-stuff, and the individual fibres being thus prevented from adhering to each other on drying the leather remains soft and pliable. The chemical theory assumes a true chemical combination to exist between the tan-stuff and the hide substance. With tannic acid and tannins, at least, there does appear to be a chemical union, and this may also be true of chromium salts. But with alum, which may be entirely removed from the leather by hot water, the combination certainly does not seem to be complete. With oil tannage the grease appears to decompose within the hide substance and become fixed on the fibre by oxidation, but without true combination, the process being analogous to the dyeing with reduced indigo, p. 490. GLUE 525 REFERENCES Grundziige der Lederbereitung. C. Heinzerling, Braunschweig, 1882. (Vieweg.) The Manufacture of Leather. C. T. Davis, Philadelphia, 1885. (Baird & Co.) Text-book of Tanning. H. R. Proctor, London, 1885. (E. and F. N. Spon.) Traite" pratique de la Fabrication des Cuirs, etc. A. M. Villon, Paris, 1889. (Baudry et Cie.) The Art of Leather Manufacture. A. Watt. 3d Ed. London, 1890. (Lock- wood.) Die Lohgerberei. F. Wiener. 2 te Auf. Leipzig, 1890. Leather Manufacture. J. W. Stevens, London, 1891. Praktisches Lehrbuch der Lohgerberei. S. Kas, Weimar, 1891. (Voigt.) Industrie des Cuirs et des Peaux. T. Jean, Paris, 1892. Cuirs et Peaux. H. Voinesson de Lavelines, Paris, 1894. (Balliere et Fils.) Die Herstellung der lohgaren Leder. L. Hoffmanns, Weimar, 1893. (Voigt.) GLUE Glue is a decomposition product from animal connective and elastic tissues.* When heated with water, these tissues lose their peculiar structure, swell, and finally dissolve, forming a non-adhesive solution. On cooling, this jellies and dries into a horny, translucent mass, which is the glue. When redissolved in hot water, this forms a thick solution having strong adhesive properties. Gelatine is made more carefully, from better stock, but chemically there is no differ- ence between it and glue. Both swell with cold water, but do not go into solution until the water is heated. Commercial glue from any source contains two essential constitu- ents, glutin, an amorphous, odorless, tasteless protein substance, soluble in hot water, having great adhesive strength, and precipitated from solution by tannin or alcohol ; and chondrin, similar to glutin, but mainly derived from the cartilaginous and young bone tissues, and having less adhesive strength. There are three general classes, hide glue, bone glue, and fish glue. Hide glue is made from glue stock, i.e. waste bits of hide trimmings, skivings, fleshings, and other untanned refuse from the beam house ; slaughter-house waste, such as the ear-laps and heads (petes), sinews, feet, and tails of cattle and sheep ; and the skins of rabbits, hares, and dogs, and scraps of alum tawed leather. Tanned skins are of no use for glue-making. The stock, wet, or dried and salted, is washed, and then limed for from' six weeks to several months, during which time it is thoroughly and frequently stirred. It swells, and the fats are converted into * Ost, Lehrbuch der technischen Chemie, p. 591. 526 OUTLINES OF INDUSTRIAL CHEMISTRY lime soap, while blood, flesh, and coriin are partly dissolved. The stock is then thoroughly washed in tubs, with mechanical stirrers, or rollers, to remove the lime, lime soap, and dirt; the last trace of lime is removed by treating with dilute hydrochloric acid, or, better, with sulphurous acid, which both plumps and bleaches the stock. The excess acid is washed away, and the stock is ready for " cooking " or " boiling," to convert the collagen into glue. The temperature of heating is from 65 to 100 C., although actual boiling of the liquor is avoided. The kettles are open wooden vats,* heated by closed steam coils, above which is a perforated false bottom ; above this is a grating, then a layer of excelsior or straw, and finally an iron grating, upon which the glue stock rests. Water is added, and the contents of the kettle is heated until the stock dissolves, forming a solution thick enough to jelly on cooling. Long cooking of the solution must be avoided, or considerable decomposition occurs, and the strength of the product is decreased. The grease and lime soaps rise, and are skimmed off; the solid matter, consisting of hair, etc., sinks, and, together with the excelsior, forms a filter through which the liquor is slowly drawn off from under the false bottom, and a clear solution is obtained ; or the liquor may be fil- tered on felt or in bag filters. The stock is not all dissolved in the first liquor, and usually from three to five boilings with fresh water are necessary to extract all the glue ; these later solutions are thicker and stronger, consequently all the liquors are usually mixed together, except the first, which yields the finest product. Preservative agents, such as zinc sulphate (p. 240), alum, borax, salicylic acid, formalin, etc., are added to the liquor. Alum is said to injure the adhesive strength. Sometimes the stock is treated in closed kettles with direct steam under pressure, thus causing rapid melting. If the liquor is too thin to jelly, it is concentrated in a vacuum pan; or it maybe boiled down in an open kettle, coagulating the albuminous matter, which is removed by skimming; a clear glue is thus obtained, but its strength is lessened. The solution is then run into coolers, which differ in size and shape. A good form is a gal- vanized iron pan 13 inches long by 11 inches wide by 9 inches de_ep, and having slightly flaring sides. This is cooled by standing in cold water, or by the use of refrigerating machines. In from 12 to 24 hours the solution jellies, forming a mass containing about 85 per cent water. This is turned out on a table and cut into plates from one-eighth to one-fourth of an inch thick, * Tinned metal kettles are sometimes used instead of wooden vats. GLUE 527 by means of wires stretched tightly across a frame. These slices must be carefully dried at once ; they are put in single layers on wire frames and passed into the dry-room, a long, narrow room from which sunlight is excluded, and which is heated by hot air, blown in at the end farthest from where the glue enters. The jelly is very apt to develop mould or to liquefy through the action of bacteria, while if the temperature rises over 35 to 40 C., it is liable to melt, forming a "daub." But in clear, cold weather, the temperature may rise to 43 C. In summer it is nearly impossible to dry the films properly and no glue is made. If the wet film is frozen, the glue is very spongy and porous when dry. The glue should dry in about 24 hours, when the trays are removed from the hot end of the dry- ing-room and the films broken or ground in a disintegrator mill and packed for shipment. The dry glue contains about 15 per cent water. Bone glue is not essentially different from hide glue, and is made from green bones which, for the better qualities, must be quite fresh. They are boiled with water, and the oily matter skimmed off as it rises ; or better, the bones are extracted with benzine or other solvent, in a " rendering tank," p. 306. The extracted bones are crushed and treated with dilute hydrochloric acid (sp. gr. 1.05) until the calcium phosphate and other salts are dissolved. The cartilaginous residue is then treated with lime-water to remove any acid. After washing, the mass is boiled with water or steamed in a digester until dissolved. Any grease is skimmed or filtered off and the gelatine is chilled and dried as already described. Benzine extracted bones are often crushed and boiled directly or steamed for glue. The glue solution is then strained through a cloth, bleached by treatment with sulphurous acid, and evaporated at about 60 C. in vacuo, or in open troughs with a rotary steam-coil half sub- merged in the liquid. The thick solution is then chilled, jellied, and dried as above. Fish glue is made by boiling the heads, fins, and tails of fish at 110 C. It has very weak jellying properties and is generally made into liquid glue, the disagreeable odor being destroyed by adding creosote, oil of sassafras, or other strong-smelling substance. Liquid glue is made by treating fish or common glue with acetic, nitric, or hydrochloric acid, whereby the property of gelatinizing when cold is lost. But the adhesiveness is not materially changed ; and since such glues do not require to be heated or applied to hot surfaces, they are extensively used. Gelatine is prepared from calf or sheep skin and from sturgeon 528 OUTLINES OF INDUSTRIAL CHEMISTRY and other fish skin. The first liquors formed in the boiling or steaming yield a colorless gelatine which is used for food and in the preparation of photographic emulsions. The solution is often filtered on bone-black or bleached with sulphur dioxide before jelly- ing. Much is used in clarifying liquors containing tannins, espe- cially wines, etc. Isinglass is a pure white, odorless, tasteless gelatine, prepared from the inner skins of the swimming bladders of fish. It is almost entirely soluble in water at about 50 C., and forms a transparent jelly on cooling. Owing to its high price and slight, adhesive strength, it is used only for food and in clarifying liquors, such as wine, beer, coffee, etc. A vegetable gelatine derived from a species of algae or seaweed forms the agar-agar, p. 351, or Bengal isinglass of commerce. Satisfactory methods for glue testing have not yet been devised. The usual tests are determinations of the viscosity and firmness of the jelly formed, but the adhesiveness does not depend upon the quality of the jelly. Glue is usually sold according to its color and physical properties, and should be free from grease. REFERENCES Die Fabrikation chemischen Products aus thierischen Abfallen. H. Fleck, Braunschweig, 1878. Die Leim und Gelatin Fabrikation. 2" Auf. F. Dawidowsky, Wien, 1879. Glue and Gelatine. Dawidowsky-Brannt, Philadelphia, 1884. (Baird & Co.) Cements, Pastes, Glues, and Gums. H. C. Standage, London, 1893. INDEX Abraumsalze, 132. Absinthe, 412. Absorption machines for refrigeration, 20. Acetate of aluminum, 262. of calcium, 262. of calcium, brown and gray, 259. of chromium, 262. of copper, 263. of iron, 263. of lead, 263. of sodium, 263. Acetone, 260. Acetylene gas, 277. Acid, acetic, 261, 462. acetic, glacial, 261. " chamber," 45. citric, 463. hydrochloric, 67. hyposulphurous, 44. lactic, 415, 463. muriatic, 67. nitric, 114. nitrosylsulphuric, 46, 47. oleic, 330. oxalic, as assistant in dyeing, 462. palmitic, 330. pyroligneous, 257. stearic, 330. sulphuric, 45. sulphuric, fuming, 45. tannic, 463. tartaric, as assistant in dyeing, 463. Acid dyes, 484. "Acid egg," 55. Acridine dyes, 477, Acrolein, 303. Agar agar, 351, 528. Agitator for petroleum refining, 293. Air gas, 277. Air-lift pump, 56. Alcohol, 405. methyl, 259. Ale, 404. 2M Alizarin, 468, 478. Alkaline process for corn starch, 354. Alkaline water, 35. Alum, 244. " Alum meal," 245. Alum shales as source of alum, 245. " Alumino-ferric cake," 241. Aluminum acetate, 262. sulphate, 240. sulphate from bauxite, 241. sulphate from clay, 241. sulphate from cryolite, 243. Aluminum mordants, 458. Al unite as source of alum, 244. Amber, 342. Amberite, 431. American vermilion, 210. Amide powder, 422. Amidoazo dyes, 474. sulphonic acids, 475. Ammonia, 124. soda process, 86. Ammoniacum, 350. Ammonite, 432. Ammonium jdum, 246. carbonate, 129. chloride, 129. nitrate, 122. sulphate, 128. sulphocyanide, 248. Amorphous phosphorus, 223. Amylodextrin, 354. Amyloid, 435. Analyzer, 9. Aniline black, 473, 491. dyes, 471. Annatto, 470. Annealing furnace for glass, 173. Anthracene colors, 477. oil, 284. Anthracite, 26. Antimony orange, 208. red, 212. salts as mordants, 461. "Anti-scale" preparations, 38. Apatite, 140. 529 530 INDEX Archil, 469. Argol, 391. Arrack, 411. Arrowroot, 361. Arsenic acid, 229. compounds, 229. Arsenious acid, 229. Artificial dyestuffs, 470. leather, 524. silk, 442. Arum, 362. Asafoetida, 350. Asphalt, 299. Asphaltene, 299. " Assistant" in dyeing, 482. Astatki as fuel, 30, 295. Attar of roses, 339. Auxochromous groups, 480. Azo dyes, 474. Bag filter, 11. filter for sugar, 380. Balance, Westphal's, 23. Balata (rubber gum), 348. Ball clay, 181. mill, 145. Balling furnace, 74. Balsams, 346. Balsam of Peru, 346. of Tolu, 346. Storax, 346. Barbier's tower system for acid, 59. Barium chromate, 206. nitrate, 124. peroxide, 231. sulphocyanide, 250. Barkometer, 519. Barytes, 197. Basic dyes, 483. " Bating " of skins, 517. Baudelot cooler for beer, 401. Baume hydrometer, 22. Bayer's process for pure alumina, 242. Beating engine for paper-pulp, 506. Bee-hive coke oven, 28. Beer, 394. Beer-fall, 401. Beet sugar, 376. Begasse as fuel, 25, 372. Bengal isinglass, 351, 528. Benzine distillate from petroleum, 291. Benzoin, 346. Berlin blue, 200. Biscuit ware (ceramics) , 183. "Bittern," 66. Bituminous coal, 25. Black-ash, 76. furnace, 74. Black glass, 178. "Black iron liquor," 259, 263. Black lake, 214. pigments, 213. Blanket (on printing machines) , 495. Bleaching powder, 94, 109. "Bleach liquor," 109. Bleaching, 446. of cotton, 446. of hemp, 454. of jute, 454. of silk, 456. of wool, 455. Block printing, 494. Blood as fertilizer, 138. " Bloom " in mineral oils, 294. Blotting paper, 512. "Blown oils," 312. " Blow-ups " for sugar refining, 379. Blue glass, 177. pigments, 198. "Bluestone," 239. Blue vitriol, 239. Bock beer, 404. Boetius furnace for glass, 168. Boiled salt, 63. " Boiled oil," 308. " Boiled-off liquor," 439. "Boiled -off" silk, 439. Boiler scale, 37. JBombonnes, 70, 115. Bone-ash as source of phosphorus, 221. Bone-black, 139, 214, 265, 368. Bone-char, 139, 265, 368. Bone-char filter, 367. Bone glue, 527. Bone-meal, 138. Bone oil, 265. Boracite as source of boric acid, 226. Borax, 226. Boric acid, 225. Boussingault's process for oxygen, 234. Bowl (for printing machine), 495. Brandy, 411. Bran drench, 518. Brazil wood, 468. lakes, 212. Bremen blue, 202. Brewing, 394. Brewing kettle, 400. Bricks, 187. Brimstone, roll, 43. Erin's process for oxygen, 234. British gum, 363. Bromine, 215. Brown coal, 25. pigments, 213. powder, 422. Brunswick green, 202. INDEX 531 Burgundy pitch, 342. "Burning" (calcining), 16. Butter fat, 318. Butteriue, 318. Cacao-butter, 316. Cadmium yellow, 207. Calceroni, 40. Calcination, 16. Caliche, 120. " Calorisator " for beet juice, 376. Camphor, 337. Camwood, 468. Canaigre, 466. Candles, 329. Cane sugar, 370. Caoutchouc, 346. Carbolic oil, 281, 283. Carbon disulphide, 253. tetrachloride, 255. Carbonating tower, 87. Carburettor for water gas, 266. Carmichaei's electrolytic apparatus, 106. Carmine, 212. Carnallite, 134. Cast-iron still for sulphuric acid, 58. Castner's electrolytic apparatus, 107. "Catch-all," 6, 7. Catechu, 464. Caustic potash, 136. soda, 80, 90. Cement, 148, 152. Centre-bit, 287. Centrifugal machine, 14. sugars, 374. Ceramic industries, 180. Ceresine, 299. Chamber acid, 45. " Chamber crystals," 47. Chamber process for white lead, 192. Chamois leather, 520. Champagne, 393. Chance-Glaus process for the treatment of tank waste, 84. " Chaptalized " wine, 392. Charcoal, 26. as pigment, 214. " Cheese-box " still for petroleum, 391. Chemical pulp, 502. Chemical theory of dyeing, 480. of tanning, 524. " Chemick," 447. Chestnut extract, 465. Chili saltpetre, 119. China clay, 180. as pigment, 198. China grass, 437. Chinese blue, 200. Chinese red, 210. vermilion, 211. wax, 320. white, 197. Chip casks, 402. Chlorates, 111. "Chloride of lime, "94. Chlorine industry, 94. still, earthenware, 95. still, sandstone, 95. Chondrin, in glue, 525. Chrome alum, 146. green, 203, 493. orange, 206, 208, 493. red, 206, 209. tannage, 521. yellow, 205. yellow as dye, 493. Chromium salts as mordants, 458. Chromogens, 479. Chromophores, 479. Cider, 393. vinegar, 414. Clark's process of water purification, 36. Glaus kiln, 85. Close roaster, 68. Closed pots for glass, 170. Coal gas, 268. Coal-tar, 278. distillation, 280. dyestuffs, 471. Cobalt blue, 202. Cochineal, 469. lake, 212. Cocoa powder, 422. Cocoanut fibre, 437. Coffey still, 9. Coke, 27. Coke tower, 70. Colcothar, 210. "Cold test" for oils, 297. Collagen, in skins, 514. Cologne spirit, 408. Colophony, 341. Color mixing, 496. pans, 496. Colored glass, 176. leather, 520. Combination tannage, 521. Compound glass, 176. "Compound lard," 317. Compression machines (refrigeration), 20. " Concentrated " alum, 242. Concrete sugars, 374. Condenser for gas-making, 270. " Conditioning " of silk, 439. of wool, 443. " Condy's liquid," 255. Copal, 343. 532 INDEX Copperas, 237. Copper greens, 204. salts as mordants, 461. sulphate, 239. Cordite, 430, 431. Coriin, in skin, 514. Cornish stone, 186. Cotton, 434. bleaching, 446. dyeing, with acid dyes, 485. dyeing, with aniline black, 491. dyeing, with basic dyes, 484. dyeing, with direct dyes, 483. dyeing, with indigo, 489. dyeing, with ingrain azo dyes, 492. dyeing, with mordant dyes, 486. "mercerized," 435. Cotton-seed oil, 310. stearin, 311. .Coupler's still, 8. " Crabbing " of mixed wool goods, 455. " Cracking " of crude petroleum, 292. " Crazing " of pottery, 187. Cream of tartar, 391. Creosote oil, from wood-tar, 264. from coal-tar, 283, 281. " Crown filler," 198. Crown glass, 175. Crude petroleum as fuel, 30. Crutcher, for soap, 325. Crystals, 15. Crystal meal, 15. Crystallization, 15. Cryolite soda process, 92. Cudbear, 469. Curcuma, 362, 470. Currying, 520. Cut glass, 175. Cutch, 464. Cyanides, 247. "Cyan-salt," 251. Cylinder machine for paper, 511. Cylinder oil, 295. Dammar, 343. Date palm sugar, 371. Deacon process for chlorine, 98. Decoction method of mashing, 399. Deep rooms (for salt making), 62. Defecation of sugar beet juice, 373. of sugar cane juice, 377. Degras, 523, 524. Dejardin's sulphur apparatus, 42. Density, 21. Dephlegmator, 8. Depilation process (in tanning), 516. Destructive distillation of bones, 265. of wood, 257. Detonation, 417. Deville's process for oxygen, 234. Devitrification of glass, 165. Devulcanizatiou of rubber, 349. Dextrin, 363. Dextrine, 363. Dextrose, 364, 369. Dietsch cement kiln, 156. Diffusion process for sugar beets, 376. for sugar cane, 373. Digesters for sulphite pulp, 504. " Dippel's oil," 265. Direct dyes, 482. Direct specific gravity hydrometer, 21. "Discharge" (in textile printing), 497. Discharge style (in textile printing) , 498. Discharging of silk, 439. Distance frame (of filter press), 12. Dolly, for cloth scouring, 455. Donald's process for chlorine, 101. Dongola process for leather, 521. Down-draught kilns, 184. Dragon's blood, 343. Dressed leather, 520. "Driers " for boiled oil, 309. " Drips," for sulphuric acid, 53. Drying of oils, 303. Dunlop's method for the recovery of manganese oxides, 96. Dunlop's nitric acid-chlorine process, 101. Durgen system of preparing corn starch, 355. Dutch process for vermilion, 211. for white lead, 190. Dyeing, 497. Dyeing style (textile printing), 498. Dynamite, 428. Eau de Javelle, 109. Eau de Labarraque, 109. Ebonite, 349. Edge-runner, 304. Elaidin test of oils, 307. Electrolysis of brine, 104. Electrolytic processes for white lead, 195. Elemi, 345. Emerald green (pigment), 205. Enamel, 178, 186. Encaustic tiles, 185. Enfleurage, 335, 336. Engobe (glaze), 186. Enzymes, 384. Eosins, 473. Epsom salts, 134. Esparto, 437, -508. Essential oils, 335. Etageofen, 156. Ethiops mineral, 211. Euphorbium, 350. INDEX 533 Evaporation, 3. "Even motion coating" (rubber cloth), 349. Exhauster for gas, Beale's, 271. steam-jet, 272. Explosives, 417. " Extract " in beer, 403. Extraction, 2. Extraction process for oils, 305. Extracts (tannin), 466. Faience, 185. " Fat clay," 181. " Fat lime," 148. Fatty oils, 301. Feldmann's ammonia apparatus, 125. Fermentation, 384. bottom, 31)0, 402. top, 390, 403. Fermentation industries, 384. Ferments, 384. Ferric nitrate, 122. Ferrous nitrate, 122. sulphate, 237. Fertilizers, 137. Fibres, 433. animal, 438. vegetable, 434. Fibroine of silk, 438. Filter press, 12. Filtration, 11. Fire-brick, 188. Fire-clay, 180. " Fire-test " for oils, 296. '' Firing " (calcining), 16. " First sugar," 374. Fish glue, 527. scrap, 140. Flash point of oils, 295. Flax, 435. " Floaters " in glass furnace, 169. Flowers of sulphur, 43. Forcite, 430. Fourdrinier machine, 511. Fractional condensation, 8. Frankincense, 351. French column apparatus for distilla- tion, 9. French process for white lead, 193. "Friction coating" (rubber cloth), 349. Fuels, 24. gaseous, 30. liquid, 30. solid, 24. Fulminates, 431. Fumeroles, 225. Fuming acid, nitric, 118. sulphuric, 45, 60. Furnace, annealing, 173. "balling" (black-ash), 74. flattening, 174. glass, 168. muffle, 16. reverberatory, 17. revolving, 17, 75. shaft, 18. tank, 169. " Furnisher," 495. Fusel oil, 408, 410. Fustic, 470. Galbanum, 350. Gall and Montlaur process for chlo- rates, 113. Gal land process for malt, 396. "Gallized" wine, 392. Gall-nuts, 464. Galls, 464. Gambier, 464. Gamboge, 208, 351. Garbage as fertilizer, 139. Gas, analyses of, 278. coal, as fuel, 30. fuel, 30. illuminating, 265. natural, 30. producer, 30. water, as fuel, 33. water, as illuminant, 266. Gas producer, Siemens', 31. Taylor's, 31. Gay-Lussac tower, 54. Gelatine, 525, 527. dynamite, 430. Gelis' process for ammonium sulpho- cyanide, 248. German (chamber) process for white lead, 192. Gerstenhofer furnace (pyrites), 51. Giant powder, 429. Gin, 411. Glass. 165. gall, 172. stills for sulphuric acid, 56. Glass-making process, 171. Glatz process for glycerine, 333. Glauber's salt, 72, 135. Glazes, 186. Glazed tiles, 186. Glover tower, 52. Glucose, 363, 364, 369. converter, 365. Glucosides, 364. Glue, 525. Glutin, 525. Glycerides in oils, 301. 534 INDEX Glycerine, 332. chemically pure, 333. crude, 333. dynamite, 332. from soap lyes, 332. Grainers for salt, 65. " Graining " of morocco leather, 523. Granulator for sugar, 381. Grape sugar, 364, 367. Graphite as pigment, 214. Green glass, 176. " Green oil," 281, 284. Green pigments, 202. " Green starch," 357. Green malt, 395. vitriol, 237. Greenwood's electrolytic apparatus, 106. Griffin mill, 159. "Grog, "181. Griineberg-Blum ammonia still, 126. Guaiacum, 344. Guano, 140. Guignet's green, 203. Gum, acacia, 351. animi, 343. Arabic, 351. juniper, 342. Senegal, 351. tragacanth, 351. Gum-resins, 350. Gun-cotton, 423. Gunpowder, 418. Gutta-percha, 350. Guttmann's nitric acid apparatus, 116. Gypsum, 197. Hand frame for paper making, 511. "Handling" of hides in the "soaks," 515. Handlers for hides while tanning, 519. Hard porcelain, 183. rubber, 349. water, 35. Hardness, temporary (of water), 35. permanent (of water), 35. Hargreaves process, 71. Hargreaves-Bird electrolytic process, 107. Hart's nitric acid apparatus, 117. Hasenclever-Helbig pyrites burner, 52. Hemlock bark, 465. Hemp, 436. bleaching, 454. Herseus' gold-lined acid still, 57. Hermite electrolytic process, 107. bleaching process, 453. Hide glue, 525. Hides, 515. Hoffmann's cement furnace, 157, 184. Holland-Richardson electrolytic process, 106. " Hollander " (pulp machine) , 506. Hop-back, 401. Hops, 400. Horizontal still fcr petroleum distilla- tion, 291. Hydraulic lime, 150, 153. main, 270. press, 305. Hydrochloric acid, 67. Hydrogen peroxide, 232, 453, 456. Hydrolysis of oils, 303. Hydrometer, Baume's, 22. direct specific gravity, 21. Twaddell's, 22. Hypochlorites, 108. Hyposulphurous acid, 44. Iceland moss, 351. Illuminating gas, 265. Indian red, 210. yellow, 208. Indigo, 202, 466. carmine, 467. "Indigo salt," 479. " Indigotine," 467. Indulines, 472. Indurite, 431. Infusion method of mashing, " Ingrain colors," 477. Iodine, 218. value of oils, 306. Iridescent glass, 178. Irish moss, 352. Iron alum, 246. buff, 460, 493. salts as mordants, 460. Isinglass, 528. Ivory black, 214. " Jaggary " sugar, 371. Japan wax, 317. "Jars," 288. " Jigger," 482. Jute, 437, 509. bleaching, 454. Kainite, 135. Kaolin (kaolinite), 180. as pigment, 198. Kauri, 343. Kemp, 443. Keratine, 443. Kermes, 469. Kerosene, distillate from petroleum, 291. INDEX 535 Kettle process for salt, 63. Kier for cotton bleaching, 449. Kilns, 18, 148, 149. Kino, 465. Kips, 515. Koechlin's bleaching process, 452. Krenmitz process for white lead, 194. Kumis, 393. Lac, 344. Lac-dye, 344, 469. Lactic acid, 415. Laevulose, 364. Lager beer, 404. "Laid" paper, 512. "Lakes, "212. Lanolin, 320. Lant for wool scouring, 446. Lard, 317. oil, 315. " Layers " for tanning hides, 519. Lead acetate, 263. chromate, 205. nitrate, 122. . "Lead plaster," 328. Lead sulphite, 196. burning, 53. chambers, 52. glass, 166. pans, 56. Leather, 514. Leblanc soda process, 73. Le Sueur's electrolytic process, 105. Levigation, 2. Liebig's chlorate process, 111. Light oil from wood-tar, 264. from coal-tar, 282. Lignite, 25. Lima wood, 468. Lime, 148. boil in bleaching, 449. cartridges, 432. glass, 166. Limekilns, 148. "Lime rooms," 63. Liming of skins, 516. Linde refrigeration process for oxygen, 236. Linen bleaching, 453. Linseed oil varnish, 345. Liqueur, 393, 411. Liquid fuels, 30. glue, 527. Litharge, 207. Litmus, 469. Lixiviation, 2. Loaf sugar, 383. Loewig's process for caustic soda, 81. Logwood, 467. "Long flame burning," 18. "Low wines," 410. Lucifer matches, 224. Lunge plate, 58, 70. Lye-boils in bleaching, 450. M Machine printing, 495. Mactear's furnace, 69. Madder, 468. bleach for cotton, 448. lake, 212. style (textile printing) , 498. Majolica, 185. Malachite green (pigment) , 204. Maletra pyrites burner, 50. Maltha, 299. Malting, 394. Manganates, 255. Manganese brown, 494. Manilla hemp, 437. Maple sugar, 371. Market bleach, 451. Martin's process for wheat starch, 358. Mashing, 397. Masse-cuite, 374. Massicot, 208, 209. Mastic, 342. Matches, 224. Mather-Thompson bleaching process, 452. Maumene test of oils, 307. Mechanical theory of dyeing, 480. of tanning, 524. Mechanical wood pulp, 502. Melinite, 431. Melter for sugar refining, 379. Menthol, 338. Methyl alcohol, 259. Methylated spirit, 409. Mica powder, 429. Milk glass, 177. Milner's process for white lead, 194. Mimosa bark, 465. Mineral dyes, 492. green, 204. oils, 285. phosphates as source of phosphorus, 222. white, 197. Mirrors, 178. Mond's process for chlorine, 103. for treating tank waste, 83. Mordants, 457. Mordant dyes, 486. Morocco leather, 523. Mortar, 151. Mother-liquor, 15. Moulds, 385. 536 INDEX Mountain blue, 202. green, 204. Muffle furnace, 16. roaster, 68. Muga silk, 441. Multiple effect system of evaporation, 6. Muriatic acid, 67. Muriate of tin, 461. Muscovado sugar, 374. Musk, artificial, 343. Must, 390. Myrabolans, 465. Myrrh, 351. N Naphthalene, 284. Natural dyestuffs, 466. gas, 30. Neutral alum, 246. " Neutral oils," 294. Neutralizer for glucose, 366. New wine, 391. "Nigre" of soap, 325. Nigrosines, 472. Nitrates, 119. Nitrate of iron, 123, 460. Nitre cake, 55. pot, 50. Nitric acid, 114. Nitric acid-chlorine processes, 101. Nitrocellulose, 423. Nitro dyes, 473. Nitrogelatine, 430. Nitroglycerine, 425. Nitrogenous waste as fertilizer, 139. Nitroso dyes, 473. Nitrosulphonic acid, 47. "Nitrous vitriol," 54. Nitrosylsulphuric acid, 46, 47. Non-porous ware (in ceramics), 182. Nordhausen sulphuric acid, 45. Normal needle for cement tests, 161. Nut-galls, 464. Oak bark, 465. Oil, almond (essential), bergamot, 338. blackfish, 315. blubber, 315. cajaput, 338. cassia, 338. castor, 312. cedar, 338. chamomile, 338. cinnamon, 338. clove, 338. cocoanut, 316. cod-liver, 314. Oil, colza, 311. corn, 310. cotton-seed, 310. earthnut, 313. eucalyptus, 339. fish, 314. geranium, 339. Gingili, 311. hemp, 310. lard, 315. lavender, 339. lemon, 339. linseed, 308. liver, 314. menhaden, 314. mustard, 339. neat's-foot, 315. "oleo,"316. olive, 313. origanum, 340. palm, 316. palm-nut, 316. peanut, 313. peppermint, 339. pogy, 314. poppy, 310. porpoise, 315. rape-seed, 311. rose, 339. rue, 340. sassafras, 340. sesame, 311. shark-liver, 314. sperm, 318. sunflower, 310. tallow, 316. thyme, 340. train, 315. turpentine, 336. whale, 315. wintergreen, 340. wormwood, 340. Oil gas, 276. Oil of vitriol, 45, 57. Oil tannage, 522. Oil tester, closed (Abel's), 296. open, 296. Oil well drilling, 287. torpedoing, 289. Oils, drying, 308. non-drying, 313. marine animal, 314. semi-drying, 310. terrestrial animal, 315. Olein, 303, 330, 331. Oleo-resins, 346. Olibanum, 351. Opal glass, 177. Open pots for glass, 170. roaster, 67. INDEX 537 Orange glass, 177. mineral, 208. pigments, 208. Origanum, 340. Orleans process for vinegar, 412. Orpiment, 201. Orseille, 469. Otto-Hoffmann coke oven, 28. " Overchromed " wool, 459. Oxidation style (textile printing), 498. Oxazines, 472. Oxyazo dyes, 475. Oxygen, 233. Ozokerite, 298. Padding machine, 482. Palmitin, 303. Panclastite, 432. Pan process for salt, 65. Paper, 501. Paper-making process, 509. Paraffine oils, 294. Parchment, 524. paper, 513. Paris green, 205. white, 198. Parke's process of vulcanizing, 348. Parnell-Simpson process for utilizing tank waste, 90. " Pasteurizing" of wine, 392. Patent leather, 520, 523. Pattinson's white lead, 196. Pauli's process for purifying tank liquor, 78. Peach wood, 468. Pearlash, 130. " Pearl hardening," 198. Pearl sago, 361. Peat, 25. Pebble powder, 421. Permanent hardness in water, 35. Permanganates, 255. Pernambuco wood, 468. Peroxides, 231. Perret-Ollivier burner, 51. Persian berries, 470. Petrolene in asphalt, 299. Petroleum, crude, 290. industry, 285. refining, 290. refining of sulphur bearing, 294. Phenol (carbolic acid), 283. dyes, 473. Phosphate rock, 140. Phosphatic slag, 145. Phosphorites, 141. Phosphorus. 221. Phthale'ins, 473. Physical theory of tanning, 524. Picrates, 431. Pigments, 189. Pigment style (textile printing), 497. Pipe clay, 181. Pipe-column, 59. Pitch from coal-tar, 285. " Pitching " of wort, 401. Plaster of Paris, 163. Plate glass, 173. tower (Lunge's), 58, 70. Platinum stills, 56. " Plumping " of hide, 516, 517. Pneumatic malting, 396. Porcelain, 182. Porous ware (in ceramics) , 182, 185. Porter, 404. Portland cement, 155. Potash industry, 130. Pot furnace for glass, 168. Pots for glass, 170. Potassium alum, 246. bichromate, 136. bromide, 217. carbonate, 135. chlorate, 111. cyanide, 251. ferricyanide, 250. f^rrocyanide, 249. manganate, 255. nitrate, 120. permanganate, 255. silicate, 231. sulphate, 135. Potato starch, 359. Pozzuolanic cements, 153. Press-cakes from oil industry as fertil- izer, 139. Pressed glass, 175. Prismatic powder, 421. Producer gas, 30. Proof stick, 381. Prussian blue, 200. as dye, 493. " Puering " of skins, 517. Pulk6, 393. " Pulled wool," 442. Purifiers for gas, 273. Purification of water, 36. Purpurin, 468. Purree, 208. " Putrid soak " (for dried hides), 515. Pyknometer, 23. Pyrites, 48. burners, 49. " smalls," 49. Pyroligneous acid, 257. Pyrolignite of iron, 259, 263. Pyroxyline, 425. 538 INDEX Q Quebracho, 465. Quercitron, 470. Quick-cook sulphite process, 505. Quick vinegar process, 413. Quinoline, derivatives, 477. Rabble, 69. Rack-a-rock, 432. Rags as paper stock, 508. Ramie, 437. Rational analyses of clays, 182. Realgar, 212. " Reclaimed " rubber, 349. Rectifier, 9. Red glass, 177. lead, 209. ochre, 210: pigments, 209. phosphorus, 223. prussiate of potash, 250. woods, 468. "Red oil, "330. " Reduced oil," 293, 295. Refined pearlash, 131. Refining of glass, 172. Refrigeration, 18. Regenerative furnace (Siemens'), 32. Rendering of fats by steam, 305. Rendering tank, 306. Resins, 341. "Resist," 497. Resist style (textile printing) , 499. Retorts for wood distillation, 258. Retting of flax, 436. Reversion of superphosphates, 144. Revivifying of bone-char, 369. " Ricks " for brine evaporation, 3. "Roasting" (calcination), 16. Roburite, 432.- Rock salt, 61. Roller printing, 495. Roman alum, 245. cements, 154. Romite, 432. Rosaniline dyes, 471. Rosendale cement, 154. Rosin, 341. Rosin change in soap boiling, 325. grease, 342. oil, 342. soap, 323. spirit, 341. Rosolic acids, 474. Rotary furnaces, 4, 17, 158. "Rotting process" for potato starch, 360. Rouge, 210. Rubber, 346. cements, 349. compounding, 347. substitutes, 348. Rum, 411. Russian leather, 523. Russian petroleum, 295. S Sadler- Wilson chlorine process, 101. Safety matches, 224. Safranines, 472. Sago, 361. Sago flour, 361. Saladin system of malting, 397. Sal-soda, 79. Salt, 61. Salt-cake, 72. furnace, 67. " Salt water " in glass furnace, 172. Saltpetre, 120. Sandalwood, 468. Sandarac, 342. Sand filter, 15. " Sanitas," 337. Saponification, 303, 321. by heating with water, 330. by lime, 330. by Milly's process, 330. by sulphuric acid, 331. value, 306. Sappan wood, 468. Schaffner-Helbig process for treating tank waste, 84. " Scheelizing " of wine, 392. Scheele's green, 204. Schlempe, 131. Schlossing process for chlorine, 97. Scrubber, 272. Scrubber-washer, 273. Sea-salt, 61. Sea-silk, 441. " Second light oil," 281. " Second sugar," 374. Semet-Solvay coke oven, 29. "Seneca oil," 287. Separator, 6. Sepia, 213. Sericine, 438. Sewage as fertilizer, 147. Shaft furnaces, 18. Shale oil industry, 298. Shanks' process of lixiviation, 76. Shellac, 344. " Shivering " of pottery, 187. " Short flame burning," 18. Siemens' gas producer, 31. regenerative furnace, 32. Sienna, 207. INDEX 539 Silent spirit, 409. Silk, 438. bleaching, 457. " boiled off," 439. dyeing, 483, 484, 486, 489. ecru, 440. glue, 438. souple', 440. tussur, 441. Silver nitrate, 123. Simon-Carve's coke oven, 29. " Singeing " of cotton cloth, 448. Sisal, 437. Sizing of paper, 510. " Skipping " of sugar, 381. Skins, 515. " Skivers," 520. Slabber machine for soap, 326. Slag cement, 153. fertilizers, 145. " Slip " (prepared clay), 182. Slow-cook sulphite process, 505. Smalt, 201. Smokeless powder, 425, 430. Soap, 321. Castile, 322. "boiled down, "326. "cold process, "323, 324. laundry, 323. milled, 328. mottled, 323, 327. remelted, 328. soft, 322. toilet, 323, 327. transparent, 328. Soap boiling, 324. frames, 326. kettles, 323. " Sod-oil," 523. Soda-ash, 89. Soda crystals, 79. industry, 73. process for wood pulp, 502. Sodium alum, 246. acetate, 263. arsenate, 230. arsenite, 230. bisulphite, 44. bromide, 218. chlorate, 112. hyposulphite, 44. manganate, 255. nitrate, 119. peroxide, 233. sulphate, 72. thiosulphate, 45. Soffioni, 225. Soft sugars, 382. porcelain, 183. Sole leather, 519. Solar salt, 62. " Solidified " bromine, 217. Solid solution theory of dyeing, 480. Solvent naphtha from coal-tar, 282. "Souring, "447, 450. Sour process for wheat starch, 358. Spanish grass, 508. " Sparger," 400. Spence's burner, 51. Spent tan-bark as fuel, 25. Spermaceti, 319. Spindle oils, 295. Spirits of turpentine, 336. Spirit varnishes, 345. Splitting of skins, 520. Spraying, petroleum oils, 293. Sprengel explosives, 432. " Spueing " of leather, 515. Staking of skins, 521. Starch, 353. cassava, 362. corn, 354. potato, 359. rice, 360. sago, 361. wheat, 358. Stassfurt salts, 132. Steam style (textile printing) , 497. Stearin, 303. Stearine, 330. Stick lac, 344. Still, Coffey, 9. Coupler's, 8. French column, 9. Stockholm tar, 264. Stoneware, 184. Stout, 404. "Stoving" of wool in bleaching, 456. " Strike pan " for sugar, 374. Strontium nitrate, 124. process for recovery of sugar from beet molasses, 377. " Stuffing " in leather, 520. "Stuffing and saddening" (in dyeing), 486. Style (in textile printing) , 497. Sublimation, 10. Sublimed white lead, 196. Sucrose, 370. " Sugar of lead," 263. Sugar recovery from beet molasses, 377. Sugar refining, 378. Suint, 131, 320, 444. Sulphates, 237. Sulphate process for wood pulp, 506. Sulphite process for wood pulp, 503. Sulphite digester, 504. Sulphur, 39. 540 INDEX Sulphur dioxide, 43. purification, 42. recovered, 42. Sulphuric acid, 45. Sumach, 464. Superphosphates, 143. Suspenders for tanning hides, 519. " Sweating " of hides, 517. " Sweet waters " (glycerine), 332. (glucose) , 368. Tallow, 317. bone, 318. Tankage, 139. Tank furnace for glass, 169. liquor, 77. waste, 76, 82. Tanning processes, 518. Tanning with oils, 522. Tannins, 463. Tapioca, 362. Tar stills for petroleum residuum, 293. Tawing of skins, 521. Taylor's gas producer, 31. Tempered glass, 175. " Tempering" of bone-char, 367. Temporary hardness in water, 35. Terra alba, 197. cotta, 187. verde, 205. Tessie du Motay process for oxygen, 235. Testing of cement, 160. Textile industries, 433. printing, 494. Thelen'span, 79, 89. Thenard's process for white lead, 193. Thionines, 473. Thymol, 337. Tiles, 185. Time of setting of cement, 161. Tin salts as mordants, 461. "Tin spirits," 461. Tinkal, 227. Tissue paper, 512. Tough glass, 175. Tragacanth, 351. " Trying out" of animal fats, 305. Turkey-red oil, 312. bleach, 451. dyeing process, 487. Turmeric, 470. Turnbull's blue, 201. Turpentine varnish, 345. Twaddell's hydrometer, 22. Udells, 218. Ultramarine blue, 198. green, 199, 202. Ultramarine red, 200. violet, 200. Umber, 213. Ungumming of silk, 439. Unhairing process (in tanning) , 516. Up-draught kiln, 184. Upper leather, 520. V Valonia, 465. Vandyke brown, 213. Van Ruymbeke process for glycerine, 332. Varec as source of iodine, 218. Varnish, 345. Vaseline, 295. Vegetable drying oils, 308. tannage, 518. Vellum, 524. Venetian red, 210. Vermilion, 210. Vermilionettes, 211. Verdigris, 204. Vinasse, 131. Vinegar, 412. " Vinegar mother," 412. Violet glass, 177. Viscosity test for oils, 297. Vitrified tiles, 185. Vitriol, oil of, 45. blue, 239. green, 237. white, 240. Vulcanization of rubber, 348. Vulcanite, 349. W Washing machine for cotton, 447. Wash leather, 520. Water, hard, 35. purification of, 36. saline, 35. soft, 35. sources of, 34. Water gas, 266. Lowe process, 266. Wilkinson process, 268. as fuel, 33. Water-glass, 230. Water-marks in paper, 512. Wax, bee's, 319. carnauba, 320. Chinese, 320. insect, 320. Japan, 317. Waxes, liquid, 318. solid, 319. Wedgwood ware, 184. Weiss-bier, 404. Weldon process for manganese recovery in chlorine making, 96. INDEX 541 Weldon-Pechiney chlorine process, 102. " Weldon mud," 97. Westphal's balance, 23. Whiskey, 408, 410. White arsenic, 229. glass, 177. lead, 190. pigments, 190. vitriol, 240. zinc, 197. Whiting, 198. Willisden paper, 513. Window glass, 174. Wine, 389. artificial, 392. currant, 393. palm, 393. Wood as fuel, 24. pulp, 502. spirit, 259. Wood-tar, 203. Wool, 442. bleaching, 455. dyeing, 483, 484, 485, 488, 490. grease, 320, 444. scouring, 444. Wort, 399. Wove paper, 512. Wrapping paper, 512. Writing paper, 512. Yamamai silk, ^41. Yaryan evaporator, 6. Yeasts, 386. bottom, 387. compressed, 388. top, 387. "wild," 388. Yellow glass, 176. lake, 213. ochre, 207. pigments, 205. phosphorus, 223. prussiate of potash, 249. " Yellow liquors," 83. Yorkshire grease, 445. Young fustic, 470. Zinc chromate, 206. sulphate, 240. sulphide, 197. RETURN TO the circulation desk of any University of California Library or to the NORTHERN REGIONAL LIBRARY FACILITY Bldg. 400, Richmond Field Station University of California Richmond, CA 94804-4698 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS 2-month loans may be renewed by calling (510)642-6753 1-year loans may be recharged by bringing books to NRLF Renewals and recharges may be made 4 days prior to due date. DUE AS STAMPED BELOW DEC u u ^ uuu 12,000(11/95) YC 6920! UNIVERSITY OF CALIFORNIA LIBRARY