^l\is Book is the property of t^e OfDanfornm aDoHege of Ph^i^macg ( department of ^itartnacu of the Ifiniocrsitti of California ) f^iresented bn M^JJ_ Bate e ._„,,„,, Cotlege of Pha""*^"^ Digitized by the Internet Archive in 2007 with funding from ■ IVIicrosoft Corporation http://www.archive.org/details/elementsofchemis02grahrich ** LIBRARY OF ILLUSTKATED STANDARD SCIENTIFIC WORKS VOL. XIII. GRAHAM'S ELEMENTS OF CHEMISTRY VOL. IL C&!!fbrri!a Co!!:^c:o of Pharmacy NEW YOEK: CHARLES E. BAILLIERE, 290 BROADWAY. LONDON: HIPPOLYTE BAILLIERE, 219 REGENT STREET. 185t. Entered according to Act of Congress, In the year 1857, by CHARLES E. BAILLli:RE, In the Clerk's Office of the United States DUtrict Court for the Southern District of New York. W, B. TlN»ON, rBISTBB *SD STSRBOinf PER, 4 Classificat ION. Atoms and Equivalents 509 Gerhardt's Unitary System . 513 Types and Radicals. — Rational Formulie 521 Classification of Compounds according to their Chemical Functions 527 Water-type 530 Hydrochloric-acid type 548 Ammonia- type 553 Hydrogen-type 563 Relations between Chemical Composition and Density. Atomic Volume of Liquids . . 569 Atomic Volume of Solids . . 582 Relations between Chemical Composition and Boiling Point. Boiling Points of Alcohols, Fatty Acids, and Com- pound Ethers . . . 583 THE SECOND VOLUME. xi Chemical Affinity. Page Influence of Mass on Chemical Action . 586 Mutual Decomposition of Salts in Solution 591 Decomposition of Insoluble Salts by Soluble Salts . . . . 597 Chemical Decomposition explained by Atomic Motion . . . 600 Diffusion of Liquids. Diffusion of Saline Solutions . . 604 Decomposition of Salts by Diffusion . 613 Diffusion of Salts in the Soil . . 615 Osmose. Passage of Liquids through Porous Earthenware 616 „ ,, „ Membrane 620 Physiological Effects of Osmose . . 623 Diffusion of Gases through Porous Septa . 625 Development of Heat by Chemical Combination. Heat evolved in the Combination of Bodies with Oxygen . . . .625 Heat evolved in the Combination of Bodies with Chlorine . . . 630 Heat evolved in the Combination of Acids with Bases . . . .631 Heat evolved in the Combination of Acids with Water . . . .632 Calorific Effects of the Solution of Salts in Water 633 Cold produced by Chemical Decomposition . 635 an CONTENTS OF THE SECOND VOLUME. NON- METALLIC ELEMENTS. Page Oxygen and Hydrogen - 638 Nitrogen 651 Carbon 658 Boron 667 Silicon 672 Sulphur .679 Selenium 688 Phosphorus 690 Chlorine 702 Bromine 711 Iodine 712 Fluorine 719 Bunsen's Met hod of Vol umetric Analysis 722 Metals of the Alkalies and Earths. Potassium Sodium Ammonium Lithium Barium Strontium Calcium Magnesium Aluminium Glucinum 729 732 736 741 744 746 749 753 756 761 ELEMENTS 0» CHEMISTEY. OEDEE TV, METALS PROPER HAYING PROTOXIDES ISOMORPHOUS WITH MAGNESIA. SECTION I. MANGANESE. Eq. 27-67 or 345-9; Mn. This element is found in the ashes of plants, in the bones of animals, and in many minerals, of which that employed in the preparation of oxygen is one of the richest. The black oxide of manganese was long known as magnesia nigra, from a fancied relation to magnesia alba ; but was first thoroughly studied by Scheele, in 1774, and immediately afterwards by Gahn, who obtained from it the metal now called manganese. From its strong affinity for oxygen, and the very high temperature which it requires for fusion, manganese is one of the most difficult of all the metals proper, to reduce and fuse into a button. Hydrogen and charcoal, at a red heat, reduce the superior oxides of this metal to the state of protoxide, without eliminating the pure metal at that temperature ; but 2 MANGANESE. at a white heat, charcoal deprives the metal of the whole of its oxygen. The following process is recommended by M. John for the reduction of manganese : it illustrates the chief points to be attended to in the reduction of the less tractable metals. Instead of a native oxide, an artificial oxide of manganese, obtained by calcining the carbonate in a well-closed vessel, is operated upon. This oxide, which is preferred from being in a high state of division, is mixed with oil and ignited in a covered crucible, so as to convert the oil into charcoal. After several repetitions of this treatment, the carbonaceous mass is reduced to powder, and made into a firm paste by kneading it with a little oil. Finally, this paste is introduced into a cru- cible lined with charcoal (creuset brasque), the unoccupied portion of which is filled up with charcoal powder. The crucible is first heated merely to redness for half an hour, to dry the mass and decompose the oil ; after which its cover is carefully luted down, and it is exposed for an hour and a half to the most violent heat of a wind-fiimace that the crucible itself can support without undergoing fusion. The metal is obtained in the form of a serai-globular mass or button in the lower part of the crucible, but not quite pure, as it contains traces of carbon and silicon derived from the ashes of the charcoal. By igniting the metal a second time in a charcoal crucible, with a portion of borax, John obtained it more fusible and brilliant, and so free from charcoal that it left no black powder when dissolved in an acid. Manganese is a greyish white metal, ha\ing the appearance of hard cast iron. Its density, according to John, is 801 3; while M. Berthier finds it to be 7*05, and Bergmann made it 6*850 : according to Hjelm, it is 7*0. From its close resem- blance to iron, manganese may be expected to be susceptible of magnetism ; but its magnetic powers are doubtful. Peclet has endeavoured to show that manganese can assume and preserve magnetic polarity from the temperature — 4° up to 70**, but loses it again at higher temperatures. The small OXIDES OF MANGANESE. 4 difference between the atomic weights of iron, manganese, cobalt, and nickel, which are respectively 28, 27*67, 29*52, and 29*57, is remarkable, attended as it is by a great analogy between these metals in many other respects. Manganese oxidates readily in air, soon falling down as a black powder ; in water it occasions a disengagement of hydrogen gas. It is best preserved in naphtha, like potassium, or over mercury. Manganese exhibits five degrees of oxidation, with two intermediate or compound oxides. OXIDES OF MANGANESE. Protoxide or manganous oxide . MnO. Sesquioxide or manganic oxide . Mn203. Bioxide or Peroxide . . . MnOg. Manganoso-manganic oxide or red oxide .... MuaO^, or MnO + MugOg. Varvicite Mn407,orMn203 + 2Mn02. Manganic acid .... MnOg. Permanganic acid , . . M^n20>j. Protoscide of manganese; Manganous oxide; MnO, 35*67 or 445*9. — This is the oxide existing in the ordinary salts of manganese, which are isomorphous with the salts of magnesia. It may be obtained by fusing at a red heat in a platinum crucible, a mixture of equal parts of pure chloride of man- ganese and carbonate of soda, with a small quantity of sal- ammoniac. By the reaction between the first-mentioned salts, chloride of sodium is produced, together with the carbonate of manganese, which is decomposed at a red heat, leaving the protoxide of that metal. The hydrogen of the sal-ammo- niac at the same time reduces to the state of protoxide any bioxide which may be formed by absorption of oxygen from the air. Any one of the superior oxides of manganese, in the state of fine powder, may be converted into protoxide by B 2 4 MANGANESE. passing hydrogen gas over it, in a porcelain tube at a red heat : the bioxide obtained by igniting the nitrate of the protoxide of manganese was recommended by Dr. Turner as the most easily deoxidated. Protoxide of manganese is a powder of a greyish green colour, more or less deep. When obtained by means of hydrogen at a low temperature, it absorbs oxygen from the air, soon becoming brown throughout its whole mass, and is, indeed, sometimes a pyrophorus ; but when prepared by hydrogen at a high temperature, it acquires more cohesion, and is permanent. Protoxide of manganese dissolves readily in acids, and is a strong base. Its salts are of a pale rose tint, which is not destroyed by sulphurous or hydrosulphuric acid, and must be considered as a peculiar character of manganous salts. When the solution is colourless, as it sometimes is, the fact is ex- plained, according to M. Gcirgeu, by the presence of a salt cf iron, nickel, or copper ; the green or blue tint of the latter metals producing white or a scarcely perceptible violet shade when combined with the rose tint of a salt of manganese. Caustic alkalies added to solutions of manganous salts tlirow down the protoxide of manganese in the form of a white hydrate, which soon absorbs oxygen from the air and becomes brown ; when collected on a filter and washed, it ultimately changes into a blackish brown powder, which is the hydrate of the sesquioxide. A similar change is instantaneously produced by the action of chlorine- water upon the white hydrate, or by the addition of chloride of lime to a salt of the protoxide of manganese : but then the hydrated bioxide is formed. Protoxide of manganese resembles magnesia and protoxide of iron, in being but partially precipitated by ammonia. The alkaline monocarbonates precipitate white carbonate of manganese, which does not turn brown in the air, and dissolves sparingly in a cold solution of sal-ammoniac. Bicarbonate of potash precipitates a strong solution imme- OXIDES OF MANGANESE. 5 diately, and renders a dilute solution slightly turbid ; but if the solution contains a free acid, so that an excess of carbonic acid is set free, no precipitate is formed. The earthy carbon- ates do not precipitate manganous salts. Hydrosulphuric acid forms no precipitate in neutral solutions of manganous salts containing any of the stronger acids. In a neutral solution of the acetate, a flesh-coloured precipitate is formed after some time ; but not if the solution contains free acetic acid. Sul- phide of ammonium forms in neutral solutions of manganous salts a flesh-coloured precipitate of hydrated sulphide of man- ganese, insoluble in excess of sulphide of ammonium, but readily soluble in acids. When exposed to the air, it turns brown on the surface, from oxidation. The least trace of iron or cobalt colours it black. Ferrocyanide of potassium forms in neutral solutions of manganous salts a white precipitate, having a tinge of red, and soluble in free acids. Ferricyanide of potassium forms a reddish precipitate, which is insoluble in acids. Manganous salts, and indeed all compounds of man- ganese, heated with borax or phosphorus-salt in the outer blowpipe flame, form an amethyst- coloured bead containing manganoso-manganic oxide, which becomes colourless in the inner flame by reduction of that oxide to the protoxide. This character distinguishes manganese from all other metals. The minutest trace of manganese is discovered by heating the solution with a little bioxide of lead and nitric acid, when a red tint appears due to the formation of permanganic acid (W. Crum). An equally delicate reaction is obtained in the dry way by heating the substance supposed to contain man- ganese with carbonate of soda on platinum foil in the outer blowpipe flame. The smallest trace of manganese is indicated by the formation of green manganate of soda. The delicacy of the reaction may be increased by adding a little nitre to the carbonate of soda. Protosulphide of manganese may be procured in the dry way, by heating a mixture of bioxide of manganese and B 3 6 MANGANESE. sulphur. Sulphurous acid is disengaged, and a green powder remains, which dissolves in acids with disengagement of hydrosulphuric acid. The same compound is obtained in the humid way, when acetate of manganese is decomposed by hydrosulphuric acid, or any manganous salt precipitated by an alkaline sulphide. Protosulphate of manganese, decomposed by hydrogen at a red heat, yields an oxisulphide. A crystal- line sulphide is obtained by passing the vapour of bisulphide of carbon over hydrated manganic oxide ignited in a porcelain tube : the crystals are iron-black rhombic prisms, having a tinge of green, and yielding a dingy green powder ( Volker) . Phosphide of manganese is obtained by exposing an intimate mixture of 10 parts of pure ignited bioxideof manganese, 10 parts of white-burnt bones, 5 parts of white quartz-sand, and 3 parts of ignited lamp-black for an hour i^ a closed Hessian crucible to a heat sufficient to melt cast-iron, — or by strongly igniting 10 parts of ignited phosphate of manganese, 3 parts of ignited lamp-black, and 2 parts of calcined borax in a cru- cible lined with charcoal. The product is a very brittle, crys- talline regulus of the colour of grey cast-iron, and of specific gravity 5*951. It is permanent in the air, glows when heated in contact with air, and bums with an intense light when heated with nitre. It appears to contain ^lusP, and is pro- bably a mixture of MngP and Mn^P, the latter of which compounds is left behind when the substance is treated with hydrochloric acid, while the former dissolves, with evolution of non-spontaneously inflammable phosphuretted hydrogen (Wohler). Protochloride of manganese : MnCl + 4H0 ; 63" 1 7 + 36 or 789*63 + 450. — This salt crystallises in thick tables, which are oblong and quadrilateral, and of a rose colour ; it is very soluble in water, and slightly deliquescent. The residuary liquid obtained in preparing chlorine by dissolving bioxide of manganese in hydrochloric acid, consists of chloride of man- ganese contaminated with a portion of sesquichloride of iron. OXIDES OF MANGANESE. 7 To remove the latter and obtain a pure chloride of manganese, the solution should be boiled down considerably to expel the excess of acid, diluted afterwards with water, and boiled again with carbonate of manganese, which salt precipitates the whole of the sesquioxide of iron, forming chloride of manganese with its acid (Everitt). If about one fourth of the impure solution of chloride of manganese be reserved, and precipitated by carbonate of soda, a quantity of carbonate of manganese will be obtained sufficient to precipitate the iron from the other three-fourths of the liquid, and applicable to that purpose after it has been washed. The iron may likewise be separated by evaporating the solution of the impure chloride to dryness, heating the residue to low redness in a crucible, as long as hydrochloric acid continues to escape ; then leaving it to cool, exhausting with boiling water, and filtering. The hydrated chloride of iron is resolved by the heat into hydro- chloric acid and sesquioxide, while the chloride of manganese remains unaltered, and is easily dissolved out by water, all the iron remaining behind. Chloride of manganese, when free from iron, is precipitated white, without any shade of blue, by ferrocyanide of potassium. The crystals retain one of their four equivalents of water at 212° (Brandes), but may be ren- dered anhydrous at a higher temperature. Brandes finds 100 parts of water to dissolve at 50°, 38-3 ; at 88°, 46-2 ; at 144-5°, 55 parts of the anhydrous salt. A higher temperature, instead of increasing the solubility of this salt, diminishes it. From the aqueous solution, chlorine, with the aid of heat, throws down the black hydrated bioxide of manganese. Hypo- chlorous acid produces a similar result, with evolution of free chlorine. Absolute alcohol dissolves half its weight of the anhydrous chloride of manganese, and afibrds, by evaporation in vacuo, a crystalline alcoate, containing two equivalents of alcohol. Chloride of manganese forms two crystalline double salts with chloride of ammonium. One of these, MnCl. NH^Cl, B 4 8 MANGANESE. forms cubical crystals, containing 1 equiv. water, according to Rammelsberg, and 2 eq. according to Hauer. These crystals when ignited leave manganoso-manganic oxide in microscopic pyramids resembling Hausmanite. The other salt, 2MnCl. NH*C1 + 4H0, forms crystals belonging to the oblique prismatic system (Hautz) . Solution of chloride of manganese containing chloride of ammonium, yields, on addition of ammonia and exposure to the air, a precipitate of hydrated manganoso- manganic oxide (Otto). Protocyanide of manganese is obtained in the form of a yellow- ish or reddish- white precipitate, on adding cyanide of potassium to the solution of a manganous salt. It quickly turns brown on exposure to the air. It is decomposed by the stronger acids, and dissolves in alkaline cyanides. The corresponding fluoride of manganese forms, vMi fluoride of silicon, a double salt which is very soluble in water and crystallises in long regular prisms of six sides. The formula of this double salt is, according to Berzelius, 2SiF3 + 3MnF-}- 21H0. Carbonate of manganese is a white insoluble powder, which acquires a brown tint when exposed in the dry state at 140°. It is decomposed by a red heat. Carbonate of manganese occurs in the mineral kingdom, in the form of manganese-spar y but never in a state of purity, being mixed with the carbonates of lime and iron, which have the same crystalline form, viz. the rhombohedral. Its presence in spathic carbonate of iron is said to be the cause why the latter yields an iron peculiarly adapted for the manufacture of steel. Protosulphate of manganese ; Manganous sulphate ; MnO, SO3 + 7HO. — A solution of this salt, used in dyeing and en- tirely free from iron, is prepared by igniting bioxide of man- ganese mixed with about one-tenth of its weight of pounded coal in a gas retort. The protoxide thus formed is dissolved in sulphmic acid, with the addition of a little hydrochloric acid towards the end of the process ; the sulphate is evaporated to OXIDES OF MANGANESE. 9 dryness, and again heated to redness in the gas retort. The iron is found after ignition in the state of sesquioxide and insoluble, the persulphate of iron being decomposed, while the sulphate of manganese is not injured by the temperature of ignition, and remains soluble. The salt may also be obtained by heating bioxide of manganese, previously freed from the carbonates of lime and magnesia by boiling with dilute sulphuric acid, with an equal weight of strong oil of vitriol, and gently ignit- ing the resulting mass for an hour, to decompose the sulphates of iron and copper formed at the same time. The manganous sulphate, which remains unaltered, is then dissolved in water, and the solution evaporated to the crystallising point. The solution is of an amethystine colour, and does not crystallise readily. When cloth is passed through sulphate of manganese and afterwards through a caustic alkali, protoxide of manganese is precipitated upon it, and rapidly becomes brown in the air ; or it is peroxidised at once by passing the cloth through a solution of chloride of lime. The colour thus produced is called manganese-brown. Crystallised undei 42°, the sulphate of manganese gives crystals containing 7 HO, which have the same form as sul- phate of iron. The crystals wbich form between 45° and 68°, contain 5 HO, and are isomorphous with sulphate of copper. By a higher temperature, from 68° to 86°, a third set of crystals is obtained, which contain 4H0 : their form is a right rhombic prism. The sulphate of iron and other sulphates also assume the same form (Mitscherlich) . This salt loses 3H0 at 243°, but retains 1 eq. even at 400°, like the other magnesian sul- phates. M. Kuhn finds, that when a strong solution of the sulphate of manganese is mixed with sulphuric acid and evapo- rated by heat, a granular salt is precipitated, which contains only one equivalent of water. This sulphate also forms with sulphate of potash a double salt containing 6H0. The anhydrous salt is soluble, according to Brandes, in 2 parts of water at 59°, in 1 part at 122° ; but above the latter tempera- 10 MANGANESE. ture, the salt becomes less soluble. The tetra-hydrated salt dissolves in 0*883 part of water at 43'3° ; in 079 part at 50°; in 0-82 part at 65-8° ; in 0-67 part at 99*5° ; and in 1-079 part at 2'1°. Manganous sulphate is insoluble in absolute alcohol, but dissolves in 500 parts of spirit of the strength of 55 per cent. Hyposulphate of manganese ; MnO . S205-f6HO. For the preparation, see I. 335. — The bioxide of manganese used in preparing it should be previously treated with nitric acid, to dissolve out the hydrated oxide, and be well washed. The salt forms rose-coloured, generally indistinct, crystals, belonging to the doubly oblique prismatic system (Marignac). The oxalate of manganese is a highly insoluble salt. The acetate is soluble in 3^ parts of cold water, and also in alcohol. Bitar- trate of potash dissolves protoxide of manganese, and foiTns a very soluble double salt, the tartrate of potash and manganese j which can be obtained, although with difficulty, in regular crystals. Sesquioxide of manganese; Manganic oxide; MujOg; 79'34 or 991 '8. — This oxide is left of a dark brown, almost black colour, when the nitrate of the protoxide is gently ignited. It also occurs crystallised in the mineral kingdom, although rarely; its density is 4*818, and it is named hraunite as a mineral species. The hydrate of manganic oxide is formed by the oxidation in air of manganous hydrate. Manganic hydrate also frequently occurs in nature of a black colour, both crystallised and amorphous, and is often mixed with the bi- oxide of manganese. It constitutes the mineral species man- ganite, of which the density is 4*3 to 4*4, and the formula Mn203, HO. This hydrate may be artificially prepared by heating finely divided bioxide of manganese with monohy- drated sulphuric acid, decomposing the resulting manganic sulphate with water, and washing it thoroughly (Carius). This oxide colours glass of a red or violet tint. The common violet OXIDES OF MANGANESE. 11 or purple stained glass contains manganic oxide; also the amethyst. Manganic oxide is a base isomorphous with alumina and sesquioxide of iron. It dissolves in cold hydrochloric acid without decomposition. Concentrated sulphuric acid combines with it at a temperature a little above 212°, but does not form a solution. Dilute sulphuric acid does not dissolve it, either in the cold or when gently heated, unless manganous oxide is present, even in very small quantities, in which case a violet solution is formed; hence the commonly received statement that manganic oxide forms a red solution with sulphuric acid (Carius). At somewhat elevated temperatures, acids reduce the sesquioxide of manganese to protoxide, with evolution of oxygen. Manganic sulphate ; MngOg . 3 SO3, — Prepared by mixing finely divided bioxide of manganese (obtained by passing chlorine gas through a solution of carbonate of soda in which carbonate of manganese is suspended) with monohydrated sulphuric acid to the consistence of a pulp, and gradually heating the mixture in an oil-bath to about 276°, at which point the mass becomes dark green and more mobile. It is then drained on a plate of pumice-stone to remove the greater part of the sulphuric acid ; afterwards stirred up in a warm basin with the strongest nitric acid (free from nitrous acid) ; again drained on pumice-stone ; and this treatment repeated several times : lastly, it is dried in the oil-bath at 266°, and preserved in carefully dried tubes. — Manganic sulphate thus obtained is a dark green powder which exhibits no traces of crystallisation. It may be heated to 320° without decompo- sition, but at higher temperatures gives off oxygen and is reduced to manganous sulphate. At ordinary temperatures it is all but insoluble in concentrated sulphuric and nitric acid ; with the former it may be heated nearly to the boil- ing point without alteration, but, when boiled with the acid, it dissolves as manganous sulphate, with evolution of oxygen. 11^ MANGANESE. Heated with concentrated nitric acid to 212°, it turns brown, but resumes its green colour when the acid is evaporated at the lowest possible temperature. In strong hydrochloric acid, it dissolves, like the pure sesquioxide, forming a brown solution, which when heated gives off chlorine till all the sesquioxide of manganese is reduced to protoxide. Organic substances, heated with the dry salt, decompose it with considerable violence. The salt absorbs moisture very rapidly, so that it must always be kept in sealed tubes. Small quantities of it deliquesce in a few seconds, forming a violet solution, which, however, soon becomes brown and turbid from separation of the hydrated oxide. Water decomposes the salt rapidly, especially when heated, separating the pure hydrated sesquioxide. Hence the mode of preparing the hydrate above mentioned. Sul- phuric acid, somewhat diluted, decomposes manganic sulphate, converting it into a red-brown powder, which appears to be a basic salt.* Manganic sulphate forms an alum with sulphate of potash (Mitscherlich) : this salt occurs native in needle- shaped crystals at Alum Point, on the Great Salt Lake in North America (L. D. Gale). Sesquichloride of manganese (MujClg) is formed when the sesquioxide is dissolved in hydrochloric acid at a low tempera- ture. The solution is yellowish brown or black, according to its degree of concentration, and is decomposed by a slight elevation of temperature, with evolution of chlorine. A cor- responding sesquifluoride may be crystallised. Sesquicyanide of manganese. — A compound of tliis cyanide is formed, when manganous acetate is mixed with hydrocyanic acid in excess, then neutralised with potash and evaporated. The manganous cyanide then absorbs oxygen, and is converted into hydrated manganic oxide and manganic cyanide, which last combines with cyanide of potassium, and appears, on the cooling of a concentrated solution, in red crystals, which dissolve easily ♦ Carius, Jnn. Ch. Pharm. xcviii., 53. OXIDES OP MANGANESE. 13 in water (Mitscherlich) . This salt is analogous to red prus- siate of potash^ containing manganese instead of iron, and may, therefore, be represented as containing manganicyanogen — a manganicyanide of potassium, K3(Mn2Cy6). As a double cyanide, its formula would be, SKCy-MugCyg. Red oxide of manganese, MnCMugjOg, named by Berzelius manganoso-manganic oxide, is always produced when any oxide of manganese is heated strongly in air. It is a double oxide, being a compound of single equivalents of protoxide and bioxide of manganese. It forms the mineral Hausmanite, which differs from manganite in having manganous oxide in place of water. Its density is 4i-722. Berthier finds that strong nitric acid dissolves out the protoxide of manganese from the red oxide, and leaves a remarkable hydrate of the bioxide, of which the formula is 4Mn02 + HO. Bioxide or Peroxide of manganese; Black oxide of manga- nese ; MnOg ; 4367 or 545-9. — This is the well-known ore of manganese employed in the preparation of oxygen and chlorine. It generally occurs massive, of an earthy appearance, and con- taminated with various substances, such as sesquioxide of iron, silica, and carbonate of lime ; but sometimes of a fibrous tex- ture, consisting of small prisms radiating from a common centre. Its density varies from 4-819 to 494; as a mineral species it has been named pyrolusite."^ Another important variety of this ore, known as wad, is essentially a hydrate, containing, according to Dr. Turner, 1 eq. of water to 2 eq. of peroxide. A hydrated bioxide, consisting of single equivalents of its constituents, is formed by precipitating the protosalts of manganese with chloride of lime ; and the same compound results from the decomposition of the acids of manganese, when diluted with water or an acid. It is possible that the equiva- lent of this oxide should be doubled, and that its proper * From irvp, fire, and A.u«, I wash ; in allusion to its being employed to discharge the brown and green tints of glass. 14 MANGANESE. formula is Mn204, corresponding with peroxide of chlorine^ CIO4. Bioxide of manganese loses one-fourth of its oxygen at a low red heat, and is changed into sesquioxide ; at a bright red heat it loses more oxygen, and becomes red oxide, the condition into which all the oxides of manganese pass when ignited strongly in the open air. The bioxide does not unite either with acids or with alkalies. When boiled with sulphuric acid, it yields oxygen gas and a sulphate of the protoxide. In hydrochloric acid it dissolves with gentle digestion, evolving chlorine gas, and forming protochloride of manganese (page 6). It is exten- sively used in the arts for preparing chlorine, and also to preserve glass colourless by its oxidating action. In the last application, it is added to the vitreous materials in a relatively small proportion, and becomes protoxide, which is not a colour- ing oxide, while as sesquioxide it would stain glass purple. At the same time it destroys carbonaceous matter, and converts protoxide of iron, which colours glass green, into sesquioxide, which is less injurious. The mineral varvicite was discovered by Mr. R. Phillips among some ores of manganese from Hartshill in Wanvick- shire. It is distinguished from the bioxide by being much harder, having more of a lamellated structure, and by yielding water freely when heated to redness. Its density is 4*531. It may be supposed to consist of 1 eq. of sesquioxide, and 2 eq. of bioxide with 1 eq. of water (Dr. Turner) ; its formula is, therefore, MuaOg . MuaO^ + HO. VALUATION OF BIOXIDE OF MANGANESE. The numerous applications of the higher oxides of manganese depending upon the oxygen which they can furnish, render it important to have the means of easily and expeditiously estimating their value for such purposes. The value of these oxides is exactly proportional to the quantity of chlorine VALUATION OF BIOXIDE OF MANGANESE. 15 wliich they produce when dissolved in hydrochloric acid^ and the chlorine can be estimated by the quantity of protosulphate of iron which it oxidises. Of pure bioxide of manganese 43'7 parts (1 eq.) produce 35'5 parts of chlorine, which oxi- dise 278 parts (2 eq.) of crystallised protosulphate of iron. Hence 50 grains of bioxide of manganese yield chlorine suffi- cient to oxidise 317 grains (more exactly, 316*5 grs.) of proto- sulphate of iron. 50 grains of the powdered oxide of manganese to be examined are weighed out, and also any known quantity, not less than 317 grains, of the sulphate of iron (copperas) em- ployed in chlorimetry. The oxide of manganese is thrown into a flask containing an ounce and a half of strong hydrochloric acid, diluted with half an ounce of water, and a gentle heat applied. The sulphate of iron is gradually added in small quantities to the acid, so as to absorb the chlorine as it is evolved ; and the addition of that salt continued, till the liquid, after being heated, gives a blue precipitate with the red prussiate of potash, and has no smell of chlorine, which are indications that the protosulphate of iron is present in excess. By weighing what remains of the sulphate of iron, the quantity added is ascertained ; say m grains. If the whole manganese were bioxide, it would require 317 grains of sulphate of iron, and that quantity would, therefore, indicate 100 per cent, of bioxide in the specimen ; but if a portion of the manganese only is bioxide, it will consume a proportionally smaller quantity of the sulphate, which quantity will give the propor- tion of the bioxide, by the proportion: as 317 : 100 : : ?/n per-centage required. The per-centage of bioxide of man- ganese is thus obtained by multiplying the number of grains of sulphate of iron oxidised by 0*317. It also follows that the per-centage of chlorine which the same specimen of man- ganese would afford, is obtained by multiplying the number of grains of sulphate of iron oxidised by 0*2588. Another mode of estimation is to pass the chlorine gas. 16 MANGANESE. obtained by heating the manganese in a flask with liydro- chloric acid, into a solution of sulphurous acid, quite free from sulphuric (it should give no precipitate with chloride of barium) ; the chlorine converts an equivalent quantity of sulphurous acid into sulphuric. The liquid is then mixed with chloride of barium, and boiled to expel the excess of sul- phurous acid, after which the sulphate of baryta is thrown on a filter, washed, dried, ignited, and weighed. The 11 6' 64 gr., or 1 eq. of sulphate of baryta, correspond to 43*7 gr., or 1 eq. of bioxide of manganese. The value of commercial oxide of manganese may also be estimated by heating it with hydrochloric acid and oxalic acid. The disengaged chlorine then converts the oxalic acid into carbonic acid, — 2 eq. of carbonic acid representing 1 eq. of chlorine, and therefore 1 eq. of bioxide of manganese : C2HO4 + CI = 2CO2 + HCl. A convenient apparatus for the determination is a small J,- ^ light glass flask (fig. 1), of 3 or 4 oz. capacity, having a lipped edge, and fitted with a perforated cork. A piece of tube, about 3 inches long, drawn out at one end, and filled with frag- ments of chloride of calcium, to absorb water, is fitted by means of a small cork and a bent tube to the mouth of the flask. A short tube closed at one end, and small enough to go into the flask, is used to contain the hydrochloric acid. Fifty grains of the mineral, in the state of very fine powder, are introduced into the flask, together with about half an ounce of cold water, and 100 grains of strong hydrochloric acid in the tube, as shown in the figure : 50 grains of crystallised oxalic acid are then added, the chloride of calcium tube fitted on, and the whole quickly weighed. The flask is then tilted so as to allow the VALUATION OF BIOXIDE OP MANGANESE. 17 hydrocUoric acid to flow out of the tube, and come in contact with the mixture of manganese and oxalic acid, and a gentle heat applied to determine the action. Carbonic acid is then evolved, and escapes through the chloride of calcium tube. To expel the last portions of carbonic acid, the liquid must be ultimately heated till it boils ; after which it is left to cool, and weighed : the loss of weight gives the quantity of carbonic acid. Now, as 43*67, the equivalent of bioxide of manganese, is nearly double that of carbonic acid, which is 22, the loss of weight in the apparatus may be taken to represent the quantity of real bioxide in the 50 grains of the sample. [For other methods, see Appendix.] To obtain a complete appreciation of the value of a sample of manganese, it is not sufiicient to know the per-centage of real bioxide in it, — or, which comes to the same thing, the quantity of chlorine it is capable of yielding, — but we must also know the quantity of hydrochloric acid which must be consumed for evolving this chlorine. If the sample consists of pure bioxide, half the acid used will give up its chlorine ; if it be pure sesquioxide, only a third of the acid wiU be changed into chlorine. The quantity of acid required will therefore be greater in the latter case than in the former in the ratio of 3 : 2. Lastly, if the oxide contains lime, baryta, or oxide of iron, these bases will neutralise a portion of the acid without supplying any chlorine. To determine the ex- penditure of acid, a known weight of the oxide is heated with a known quantity of hydrochloric acid of given strength, the chlorine being sufiered to escape, but the hydrochloric acid which would otherwise escape undecomposed being collected in a small receiver moistened on the inside. When the action is over, the acid thus condensed is added to that in the flask, the whole diluted with water, and the quantity of free acid determined by adding a graduated alkaUne solution, till the precipitate which forms no longer redissolves on agitation. The quantity of free acid thus determined is then to be de« VOL. II. c 18 MANGANESE. ducted from the original quantity, and the difference gives the quantity consumed. Manganic add; MnOgj 51*67 or 645*9. — When bioxide of manganese is strongly ignited with hydrate or carbonate of potash in excess, manganic acid is formed, under the influence of the alkali, together with a lower oxide of manganese. Ignition in open vessels, or with an admixture of nitrate of potash, increases the production of the acid, by the absorption of oxygen which then occurs. The product has long been known as mineral chameleon^ from the property of its solu- tion, which is green at first, to pass rapidly through several shades of colour. But a more convenient process for pre- paring manganate of potash is that recommended by Dr. Gregory. He mixes intimately 4 parts of bioxide of man- ganese in fine powder with 3 J parts of chlorate of potash, and adds them to 5 parts of hydrate of potash dissolved in a small quantity of water. The mixture is evaporated to dryness, powdered, and afterwards ignited in a platinum crucible, but not fused, at a low red heat. The ignited mass, digested in a small quantity of cold water, forms a deep green solution of the alkaline manganate, which may be obtained in crystals of the same colour by evaporating the solution over sulphuric acid in the air-pump. Zwenger, by igniting bioxide of man- ganese with 3 parts of nitric acid, and evaporating the aqueous solution in vacuo, obtained reddish-brown crystals containing KO.MnOg. On exposure to the air, they became dull and dark green. The manganates were discovered by Mitscher- lich to be isomorphous with the sulphates and clu*omates. It has not yet been found possible to isolate manganic acid. Its salts in solution readily undergo decomposition, unless an excess of alkali is present ; and are also destroyed by contact of organic matter, such as paper. Permanganic acid, Mn207; 111*34 or 1391*8. — When the green solution of manganate of potash, prepared as above directed, is diluted with boiling water, hydrated bioxide of VALUATION OF BIOXIDE OP MANGANESE. 19 manganese subsides, and the liquid assumes a beautiful pink or violet colour. The manganic acid is resolved into bioxide of manganese and hypermanganic acid : SMnOg = MnOg + Mn^O^, The permanganate of potash should be rapidly concentrated, without contact of organic matter, and allowed to crystallize. A better process for obtaining this salt is to mix 1 part of bioxide of manganese, in very fine powder, with 1 part of chlorate of potash ; introduce this mixture into a solution of IJ- part of caustic potash in the smallest possible quantity of water ; evaporate to dryness, during which process a con- siderable quantity of manganate of potash is formed ; then heat the mixture slowly to dull redness ; boil the product in water; filter through asbestos, and concentrate by evapora- tion : the liquid, on cooling, deposits permanganate of potash in crystals. It may be purified by solution in a small quan- tity of boiling water, and recrystallisation. The crystals are of a dark purple colour, almost black, and soluble in sixteen times their weight of cold water ; they were found by Mitscher- lich to be isomorphous with perchlorate of potash ; they dis- solve in 16 parts of water at 60° (Regnault). The perman- ganates give out oxygen when heated, and are reconverted into manganates. Their solutions have a rich purple colour, and are so stable that they may be boiled, if concentrated. A small portion of a permanganate imparts a purple colour to a very large quantity of water. When a strong solution of caustic potash is added to a dilute solution of permanganate of potash, the liquid changes colour, assuming first a violet, and afterwards an emerald- green tint. The permanganate is in fact converted into manganate, a double quantity of potash having entered into combination with the acid : KO.MnaOy + KO = 2(KO.Mn03) + O. c 2 20 MANGANESE. The oxygen thus liberated remains dissolved in the water. This transformation is due to the great basic power of the potash. Acids produce the contrary effect, that is to say, they convert manganates into permanganates. The insoluble manganate of baryta may be formed by fusing bioxide of manganese with nitrate of baryta; and when mixed with a little water, and decomposed by an equi- valent quantity of sulphuric acid, affords free permanganic acid. In Mitscherlich's experiments, the free acid appeared to be a body not more stable than bioxide of hydrogen, being decomposed between 86** and 104®, with escape of oxygen gas and precipitation of hydrated bioxide of man- ganese. It bleached powerfully, and was rapidly destroyed by all kinds of organic matter. M. Hunefeld, on the other hand, obtained permanganic acid in a state in which it could be preserved, evaporated, redissolved, &c. He washed the manganate of baryta with hot water, by which it is resolved into bioxide of manganese and permanganate of baryta, and then added to it the quantity of phosphoric acid exactly necessary to neutralise the baryta. The liberated perman- ganic acid was dissolved out, evaporated to dryness, and by a second solution and evaporation, obtained in the form of a reddish-brown mass, crystalline and radiated, which exhibited the lustre of indigo at some points and was entirely soluble in water. When dry permanganic acid was fused in a retort with anhydrous sulphuric acid, and afterwards distilled at a higher temperature, an acicular sublimate of a crimson red colour was obtained, which appeared to be a combination of permanganic and sulphuric acids. (Berzelius^s Traite, i. 522.) When monohydrated sulphuric acid is poured upon a some- what considerable quantity of crystallised permanganate of potash, the salt is decomposed with great evolution of heat, red flames bursting out, oxygen being evolved, and manganic oxide set free in dark-brown flakes and shreds like spider- lines. The red flames seem to show that permanganic acid ISOMORPHOUS RELATIONS OF MANGANESE. 21. is gaseous at the high temperature produced by the reaction* (Wohler.) Perchloride of manganese^ Mn2Cl7, is a greenish yellow gas, which condenses at (f F. into a liquid of a greenish- brown colour. This liquid diffuses purple fumes, owing to the formation of hydrochloric and permanganic acids, by the decomposition of the moisture of the air. It was formed by Dumas by dissolving manganate of potash in oil of vitriol, pouring the solution into a tubulated retort, and addiug by degrees small portions of chloride of sodium or potassium, completely freed from water by fusion. The perchloride of manganese is the result of a reaction between the liberated hypermanganic and hydrochloric acids : MngOy + 7HCl=Mn2Cl7 + 7H0. A corresponding perfluoride of manganese was formed by Wohler by distilling, in a platinum retort, a mixture of manganate of potash and fluor-spar in powder, with fuming sulphuric acid. It is a greenish-yeUow gas, which likewise produces purple fumes in damp air. Isomorphous relations of manganese. — There is no other element whose compounds enter into so many isomorphous groups, and connect so large a proportion of the elements by the tie of isomorphism, as manganese. The salts of its prot- oxide are strictly isomorphous with the salts of magnesia and its class ; so that manganese belongs to and represents the magnesian famUy of elements. The same metal connects the sulphur family with the magnesian, by the isomorphism of the sulphates and manganates ; and, therefore, sulphur, se- lenium, and tellurium are thus allied to the magnesian metals. An equally interesting relation is that of permanganic with perchloric acid, and the isomorphism, which it establishes, of 2 equivalents of manganese with 1 equivalent of chlorine, and the other members of its family. c 3 22 MANOANESE. ESTIMATION OP MANGANESE, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. The usual method of precipitating manganese from the so- lution of a manganous salt, is to add carbonate of soda at a boiling heat. The precipitated carbonate of manganese is then well washed with boiling water, and calcined at a strong red heat, whereby it is converted into manganoso-manganic oxide, Mn304, containing 72*11 per cent, of manganese. If the solution contains a considerable quantity of ammoniacal salts, it must be evaporated after mixing it with excess of carbonate of soda, and the soluble salts dissolved out of the residue by water. Manganese is separated from the alkali-metals by means of carbonate of soda or sulphide of ammonium, which latter precipitates it in the form of sulphide. The sulphide is washed with water containing a small quantity of sulphide of ammonium ; then redissolved in acid ; and the manganese precipitated from the solution by carbonate of soda. From barium and strontium, manganese is easily separated by means of sulphate of soda, which throwsdown the barytaand strontia as sulphates ; also by sulphide of ammonium. From lime and manganese it is separated by sulphide of ammonium, which, if the solution be sufficiently dilute, precipitates the manganese alone in the form of sulphide. The separation from lime may also be effected by means of oxalate of ammo- nia, after the addition of chloride of ammonium to keep the manganese in solution. From alumiQa and glucina, manganese, if in small or mode- rate quantity only, may be separated by boiling the solution with potash in an open vessel. The manganese is then pre- cipitated in the form of sesquioxide, while the alumina and glucina are dissolved by the potash. If, however, the propor- tion of manganese be considerable, this method cannot be used, because the oxide of manganese carries down with it IRON. 23 considerable quantities of alumina and glucina. In this case, the liquid must be mixed with sal-ammoniac and the alumina and glucina precipitated by ammonia. The precipitate, how- ever, always contains small quantities of manganese, which must be separated by subsequent treatment with potash. SECTION II. IRON. Eq, 28 or 350 j Fe (ferrum). The most remarkable of the metals; the production of which, from the numerous and important applications it possesses, appears to be an indispensable condition of civilisation. Meteoric masses of iron, often so pure as to be malleable, are found widely although thinly scattered over the eartVs surface, and probably first attracted the attention of mankind to this metal. Of the occurrence of metallic iron as a terres- trial mineral in situ, the best established instances are the species of native iron which accompanies the Uralian platinum, and a thin vein about two inches in thickness, observed in chlorite slate, near Canaan in the United States. In a state of combination, iron is extensively diffused, being found in small quantity in the soil, and in most minerals, and as sulphide, oxide, and carbonate, in quantities which afford an inexhaust- ible supply of the metal and its preparations, for economical purposes. Iron differs from all other metals in two points, which greatly affect the methods of reducing it. Its particles agglu- tinate at a full red heat, although the pure metal is nearly infusible. The oxides of iron, which are easily reduced by combustible matter, thus yield in the furnace a spongy metallic mass, which may admit of being compacted by subsequent c 4 24t IRON. heating and hammering, if the oxide has originally been free from earthy and other foreign matter. Such probably was everywhere the earliest mode of treating the ores of iron, and we find it still followed among rude nations. But iron is also singular in forming, at an elevated temperature, a fusible compound with carbon (cast iron), the production of which facilitates the separation of the metal from every thing extra- neous in the ore, and is the basis of the only method of extract- ing iron extensively practised. The ore of iron most abundant in the primary formations is the black oxide or magnetic ore, which affords the most celebrated and valuable irons of Sweden and the north of Europe, but of which the application is greatly circumscribed from its not being associated with coal. In the secondary and tertiary formations, the anhydrous and hydrated sesqui- oxide of iron, red and brown hematite, occur occasionally in considerable quantity, often massive, reniform, and quite pure, at other times pulverulent and mixed with clay. It is em- ployed to some extent in England in the last condition, but only for the purpose of mixing with the more common ore. The crystallised carbonate of iron, or spathic iron, is smelted in some parts of the continent, and gives an iron often remark- able for a large proportion of manganese. The celebrated iron of Elba is derived from specular or oligistic iron, a crystallised sesquioxide. But the consumption of all these ores is inconsiderable, compared with that of the clay iron- stone of the coal measures. This is the carbonate of the protoxide of iron mixed with variable quantities of clay and carbonates of lime, magnesia, &c. ; it is often called the argil- laceous carbonate of iron. It is a sedimentary rock wholly without crystallisation, resembhng a dark-coloured limestone, but of higher density, from 2-936 to 3-471, and not effer- vescing so strongly in an acid. It occurs in strata, beds, or bands, as they are also named, from 2 to 10 or 14 inches in thickness, alternating with beds of coal, clay, bituminous SMELTING CLAY IRON-STONE. 25 schist, and often limestone. The proportion of iron in this ore varies considerably, but averages about 30 per cent., and after it has been calcined, to expel carbonic acid and water, about 40 per cent.* SMELTING CLAY IRON-STONE. The Ijlast furnace, in which the ore is reduced, is of the form represented below, 40 to 65 feet in height, with rig. 2. * Accurate analyses of several Scotch varieties of this ore have been pub- lished by Dr. H. Colquhoun (Brewster's Journal^ vii. 234 j or Dr. Thomson's Outlines of Mineralogy and Geology^ i, 446) ; and of the French ores, by 26 IRON. an interior diameter of from 14 to 17 feet at the widest part. The cavity of the furnace is entirely filled with fuel and the other materials, which are continuously supplied from an opening near the top; and the combustion maintained by air thrown in at two or more openings, called tuyeres, near the bottom, under a pressure of about 6 inches of mercury, from a blowing apparatus, so as to maintain the whole con- tents of the furnace in a state of intense ignition. When the air to support the combustion has attained a temperature of 600° or 700°, by passing through heated iron tubes, before it is thrown into the furnace, raw coal may be used as the fuel ; but with cold air, the coal must be previously charred to expel its volatile matter, and converted into coke, other- wise the heat produced by its combustion is insufficient. "With the ore and fuel, a third substance is added, generally limestone, the object of which is to form a fusible compound with the earthy matter of the ore ; it is, therefore, called a flux. Two liquid products accumulate at the bottom of the furnace, namely, a glass composed of the flux in combination with the earthy impurities of the ore, which when drawn off forms a solid slag, and the carbide of iron, or metal, which is the heavier of the two. It may be drawn from observations made by Dr. Clark, in 1833, on the working of the Scotch blast furnaces, under the hot blast, that the relative pro- portions of the materials, including air, and product of cast iron, are as follows* : — Coal Weight, 5 Roasted iron-stone 5 Limestone ..... Air Average product of cast iron 1 . 11 2 M. Berthier, in his Traite des essais par la voie seche, ii. 252, a work which is invaluable for the metallurgic student, and Mitchell'e Practical Assaying^ 8vo. • Edinburgh Phil. Trans. toI. 13. SMELTING CLAY IRON-STONE. 27 ^he ultimate fixed products are the slag and carburet of iron, but the formation of these is preceded by several in- teresting changes which the ore successively undergoes in the course of its descent in the furnace. A portion of the oxide of iron is certainly reduced to the metallic state, soon after its introduction, in the upper part of the furnace, by carbonic oxide and volatile combustible matter ; but the reduced metal does not then fuse. A large portion of the oxide of iron must combine also, at the same time, with the silica and alumina present in the ore, which act as acids, and a glass be formed, the oxide of iron in which is scarcely reducible by carbon. But this injurious effect of the acid earths is coun- teracted by the lime of the flux, which, being a more powerful base than oxide of iron, liberates that oxide from the glass when the proportions of the materials introduced into the furnace are properly adjusted, and neutralises the silica; so that the slag eventually becomes a silicate of lime and alumina, with scarcely a trace of oxide of iron. The whole oxide of iron comes thus to be exposed to the reducing action of the volatile combustible, and consequently the whole iron is pro- bably, at one time, in the condition of pure or malleable iron. But when the metal descends somewhat farther in the fur- nace, it attains the high temperature at which it combines with the carbon of the coke in contact with it, and it fuses for the first time, in the form of carburet of iron. It has not yet, however, attained its ultimate condition. When it reaches, in its descent, the region of the furnace where the heat is most intense, its carbon reacts on the silica, alumina, lime, and other alkaline oxides contained in the fluid slag with which it is accompanied, reducing portions of silicon, alumi- num, calcium, and other alkaline metals, which combine with the iron. The proportion of carbon replaced by silicon and metallic bases is generally found to be greater in iron pre- pared by the hot than by the cold blast, owing, it is presumed, to the higher temperature of the furnace with the hot blast. 28 IRON. The introduction of air already heated to support the com- bustion of the blast furnace, for which a patent was obtained by Mr. J. B. Neilson, has greatly reduced the proportion of coal required to smelt a given weight of ore, enabHng the iron-master, indeed, to effect a saving of more than three- fourths of the coal where it is of a bituminous quality. The air is heated between the blowing apparatus and the furnace, by being made to circulate through a set of arched tubes of moderate diameter, heated by a fire beneath them. The air can be heated in this manner to low redness, or to near 1000**, but there is found to be no proportional advantage in raising its temperature much above the melting point of lead (612°), which is already higher than the point at which charcoal inflames. Considering the great weight of air that enters the furnace, the temperature of that material must greatly affect the whole temperature of the furnace, particularly of the lower part, where the air is admitted, and which part it is desirable should be hottest. Now a certain elevated temperature is required for the proper smelting of the ore, and, unless attained in the fiimace, the fuel is consumed to no purpose. The removal of the negative influence of the low temperature of the air, appears to permit the heat to rise to the proper point, which otherwise is attained with difficulty and by a wasteful consumption of fuel. Professor Reich, of Freiberg, has ob- served that heating the air likewise alters the relative tem- peratures of different parts of the furnace, depressing in par- ticular, and bringing nearer the tuyeres, the zone of highest temperature. The admixture of steam with the air has, he finds, precisely the opposite effect, elevating the zone of highest temperature in the furnace ; so that the effect of the hot blast may be exactly neutralised by mixing steam with the hot air. Cast iron. — The fused metal is run into channels formed in sand, and thus cast into ingots or pigs, as they are called. WHITE CAST IRON. 29 Cast iron is an exceedingly variable mixture of reduced sub- stances, of which the principal is iron combined with carbon. The theoretical constitution to which that variety of it, most definite in its composition, approaches, is the following : — WHITE CAST IRON. 4 equivalents of iron . , . 94*9 1 equivalent of carbon , , 5*1 100-0 The difference in appearance and quality of the varieties of cast iron is not well accounted for by their composition. The grey or mottled cast iron, forming the qualities Nos. 1 and 2, presents a fracture composed of small crystals, is easily cut by the file, and is preferred for castings. It is generally sup- posed that a portion of uncombined carbon is diffused through the iron of these qualities, in the form of graphite. No. 3, or white cast iron, is more homogeneous ; its fracture exhibits crystalline plates, like that of antimony, and is nearly white ; it is exceedingly hard and brittle. Malleable iron. — The great proportion of cast iron manu- factured is afterwards refined, or converted into bar or malleable iron. The mode of effecting this conversion varies with the nature of the fuel. Where coal or coke is used, as in this country, the process consists of two stages. In the first, which is called refining, the pig-iron is heated in contact with the fuel in small low furnaces called refineries, while air is blown over its surface by means of tuyeres. The effect of this operation is to deprive the iron of a great portion of the carbon and nearly all the silicon associated with it. The metal thus far purified is run out into a trench, and suddenly cooled by pouring cold water upon it. It then forms a greyish- white very brittle mass, blistered on the surface. In 30 this state it is called fine metal. It is then ready for the second and principal operation, called the puddling process, which consists in heating masses of the iron with a certain access of air in a kind of reverberatory furnace, called the puddling furnace, of which Fig. 3. represents a vertical sec- tion. This furnace has four doors, two of which, F and G, serve for the introduction of fuel to the grate ; the charge of metal is introduced at E; and D serves for the insertion of a long poker or spatula, with which the metal is stirred about. The hearth of the furnace has an aperture B at the back, for removing the slag. The furnace having been brought to a bright red heat, about four or five hundred- weight of fine metal is introduced, together with one hun- dred-weight of rich scoriae or forge cinders (scale-oxide). The metal then fuses, and in this state the workman stirs it about with the poker, so as to expose every part to the flame. The carbon is thus gradually burnt out, partly by the direct action of oxygen in the flame, and partly by cementation with the oxide of iron ; and the metal becomes STEEL. 81 less fusible, and thick and tenacious, so that it sticks together, and is easily formed into four or five large balls, called blooms. In this condition it is removed by tongs, com- pressed into a cylindrical form by a few blows of a loaded hammer, and quickly converted into a bar, by pressing it between grooved rollers. The tenacity of the metal is further increased by welding several bars together ; a faggot of bars is brought to a white heat in an oblong furnace, and then extended between the grooved rollers into a single bar. The texture of malleable iron is fibrous. Although the purest commercial form of the metal, it still contains about one-half per cent, of carbon, with traces of silicon and other metals. Pure iron may^ however, be obtained by introducing into a Hessian crucible 4 parts of iron wire cut into small pieces, and 1 part of black oxide of iron; placing above these a mixtui'e of white sand, lime, and carbonate of potash, in the proportions used for glass-making ; covering the crucible with a closely fitting lid ; and exposing it to a very high tempera- ture. A button of pure metal is thus obtained, the traces of carbon and silicon in the iron having been removed by the oxygen of the oxide. (Mitscherlich.) Steel. — Only the best qualities of malleable iron, those prepared from a pure ore, and reduced by means of charcoal, such as the Swedish iron, are converted into steel. An iron box is filled with flat bars of such iron and charcoal powder, in alternate layers, and kept at a red heat for forty-eight hours, or longer. The surface of the bars is found after- wards to be blistered, and they have absorbed from 1-3 to 1*75 per cent, of carbon. This is the process of cementa- tion. It is known that iron can be converted into steel without being in actual contact with charcoal, provided the iron and charcoal are in a close vessel together, and oxygen be present, the carbon reaching the surface of the metal in 33 IRON. the form of carbonic oxide gas. The iron becomes harder by this change, and more fusible, but can still be hammered into shape, and cut with a file. The property in which steel differs most from soft iron, is the capacity it has acquired of becoming excessively hard and elastic, when heated to red- ness and suddenly cooled by plunging it into cold water or oil. This hardness makes steel invaluable for files, knives, and all kinds of cutting instruments. But the steel, when hardened in the manner described, is harder than is required for most of its applications, and also very brittle. Any portion of its original softness can be restored to the steel by heating it up to particular temperatures, — which are judged of by the colour of the film of oxide upon its surface, which passes from pale yellow at about 430**, through straw yellow, bro\\Ti yellow, and red purple into a deep blue at 580**, — and allowing the steel afterwards to cool slowly. Articles of steel are tempered in this manner. A simple and expeditious method of converting crude or pig-iron into malleable iron and steel, vnthout the aid of fuel, has lately been proposed by Mr. H. Bessemer. This process consists in causing cold air to bubble through the liquid iron ; under which circumstances the oxygen of the air combines with the carbon of the iron, removing it in the form of car- bonic oxide, and generating sufficient heat to keep the iron in the liquid state without external heating, and to sustain the action till the whole, or any required proportion, of the car- bon is burnt away. As the quantity of carbon in the metal diminishes, part of the oxygen combines with the iron, con- verting it into an oxide, which, at the very high tem- perature then existing in the vessel, melts, and forms a powerful solvent for the earthy bases associated with the iron. At a certain stage of the process, the whole of the crude iron is said to be converted into cast steel of ordinary quality. By continuing the process, the steel thus formed is gradually deprived of its small remaining portion of carbon, and passes PROPERTIES OF IRON. 33 successively from hard to soft steely steely iron, and ulti- mately to very soft iron.* Properties of iron. — Iron is of a bluish- white colour, and admits of a high polish. It is remarkably malleable, parti- cularly at a high temperature, and of great tenacity. Its mean density is 7'7, which is increased by fusion to 7'8439. When kept for a considerable time at a red heat, its particles often form large cubic or octohedral crystals, and the metal becomes brittle. Malleable iron softens before entering into fusion, and in this state it can be welded, or two pieces united by hammering them together. The point of fusion of cast iron is 3479° ; that of malleable iron is much higher. Cast-iron expands in becoming solid, and therefore takes the impression of a mould with exactness. Iron is attracted by the magnet at all temperatures under an orange-red heat. It is then itself magnetic by induction, but immediately loses its polarity, if pure, when withdrawn from the magnet. If it contains carbon, as steel and cast iron, it is affected less strongly, but more durably, by the proximity of a magnet, becoming then permanently magnetic. Among the native compounds of iron, the black oxide, which forms the load- stone, and the corresponding sulphide, are those which share this property with the metal in the highest degree. A steel magnet loses its polarity at the boiling point of almond oil ; a loadstone, just below visible ignition (Faraday). Iron reduced from the oxide by hydrogen at a heat under redness, forms a spongy mass, which, when exposed to air, takes fire spontaneously at the usual temperature, oxide of iron being reproduced (Magnus). But iron, in mass, appears to undergo no change in dry air, and to be incapable of decom- posing pure water at ordinary temperatures. Nor does it * Cliemical Gazette, 1856. p. 336. VOL. II. » 31 IRON. appear to be acted upon by oxygen and water together ; but the presence of carbonic acid in the water causes the iron to be rapidly oxidated, with evolution of hydrogen gas. In the ordinary rusting of iron, the carbonate of the protoxide appears to be first produced, but that compound gradually passes into the hyd rated sesquioxide, and the carbonic acid is evolved. The rust of iron always contains ammonia, probably absorbed from the air ; the native oxides of iron also contain ammonia. Iron remains bright in solutions of the alkalies and in lime-water, which appear to protect it from oxidation ; but neutral, and more particularly acid salts, have the opposite effect. The coiTosion of iron under water appears, in general, to be immediately occasioned by the formation of a subsalt of that metal with excess of oxide, the acid of which is supplied by the saline matter in so- lution. Articles of iron may be completely defended from the injury occasioned in this way, by contact with the more positive metal zinc, as in galvanized iron (I., 257), while the protecting metal itself wastes away very slowly. Cast iron is converted into a species of graphite by many years' immersion in sea-water, the greater part of the iron being dissolved w hile the carbon remains.* In open air, iron burns at a high temperature with vivacity, and its surface becomes covered with a fused oxide, which forms smithy ashes. Iron also decomposes steam at a red heat, and the same oxide is formed as by the combustion of the metal in air, namely, the magnetic or black oxide, FeO.FcgOg. Iron dissolves readily in diluted acids, by substitution for hydrogen, which is evolved as gas. Strong nitric acid acts violently upon iron, yielding oxygen to it, and undergoing decomposition. But the relations of iron to that acid when * Mr. Mallet has collected much information respecting the corrosion of iron, in his First Report to the British Association, on the action of sea and river water upon cast and wroui;ht ii'on, 1839. PASSIVE CONDITION OF IRON. 35 slightly diluted are exceedingly singular; they have been particularly studied by Professor Schonbein. Passive condition of iron. — Pure malleable iron, such as a piece of clean stocking wire, usually dissolves in nitric acid of sp. gr. 1-3 to 1-35, with effervescence; but it may be thrown into a condition in which it is said by Schonbein to be passive, as it is no longer dissolved by that acid, and may be preserved in it for any length of time without change : — 1. By oxidating the extremity of the wire slightly, by holding it for a few seconds in the flame of a lamp, and after it is cool dipping it gradually in the nitric acid, introducing the oxidated end first. 2. By dipping the extremity of the wire once or twice in con- centrated nitric acid, and washing it with water. 3. By placing a platinum wire first in the acid, and then introducing the iron wire, preserving it in contact with the former, which may afterwards be withdrawn. 4. A fresh iron wire may be intro- duced in the same manner into the nitric acid, in contact with a wire already passive ; this may render passive a third wire, and so on. 5. By making the wire the positive pole or zincoid of a voltaic battery, introducing it after the negative pole or chloroid has been placed in the acid. Oxygen gas is then evolved from the surface of the iron wire, without combining with it, as if the wire were of platinum. As the passive state can be communicated by contact of passive iron, so it may be destroyed by contact Tvith active iron (or zinc) undergoing, at the moment, solution in the acid. If passive iron be made a negative pole (chlorous) in nitric acid, it also ceases to resist solution. The indifference to chemical action exhibited by iron when passive, is not confined to nitric acid of the density mentioned, but extends to various saline solutions which are usually acted upon by iron. An indifference to nitric acid of the same kind can also be acquired by other metals as well as iron, particularly by bismuth (Dr. Andrews), but in a much less degree. To account for this remarkable phenomenon various theories have been proposed. Schonbein and Wetzlar attri- D 2 36 IRON. bute it to a peculiar electro-dynamic condition of the surface of the metal, similar to that of the platinum in Grove's gas battery (I. 268 — 270). Mousson attributes it to a coating of nitrous acid. By others again it has been ascribed to a peculiar antagonism between two forces acting simultaneously on the metal, the one tending to oxidate it at the expense of the nitric acid, the other to cause it to take the place of hydrogen in the nitrate of water, just as when it dissolves in sulphuric acid.* But perhaps the most probable explanation is that which attri- butes the passive condition of iron to the formation on its sur- face of a thin film of anhydrous ferric oxide, similar to specular iron. This view is supported by the fact that iron which has been ignited, and is therefore completely covered with black oxide, exhibits tlie same characters, excepting that, from the greater thickness of the coating, the passive state is more complete. It may also be observed, that iron becomes passive only in liquids which give up oxygen, and that in the voltaic circuit it becomes passive precisely under the circumstances in which it is exposed to oxidation, i. e. when it is made the zincoid or positive pole, and that it becomes active again when made the negative pole, that is to say, when the oxide is reduced. The same view is supported by the observation that iron rendered passive in nitric acid immediately begins to dis- solve on the addition of hydrochloric acid. PROTOCOMPOUNDS OF IRON ; FERROUS COMPOUNDS. Protoxide of iron, Ferrous oxide ; FeO ; 36 or 450. — Iron appears to admit of three degrees of oxidation, the protoxide * Dr. Andrews indeed concludes from observation, that the ordinary chemical action of a hjdrated acid upon the metals which dissolve in it, is in general diminished, when the acid is concentrated, by the voltaic association of these metals with such metals as gold, platinum, &c. ; while, on the con- trary, it is increased when the acid is diluted. — Trans, of the Koyal Irish Academy, 1838 ; or, Bccquercl, vol. v. pt. 2, p. 187. FERROUS COMPOUNDS. 37 and sesquioxide, whicli are both basic and correspond respec- tively with manganous and manganic oxide, and ferric acid. The protoxide is not easily obtained in a dry state, from the avidity with which it absorbs oxygen. The purest anhydrous protoxide is obtained by igniting the oxalate out of contact of air; but even this, according to Liebig, contains a small quantity of metallic iron. The protoxide exists in the sulphate and other salts of iron, formed when the metal dissolves in an acid with evolution of hydrogen. Solutions of ferrous salts have a green colour. Potash or soda added to them throws down the protoxide as a white hydrate, which becomes black on boiling, from loss of water. The colour of the white precipitate changes by exposure to air, to grey, then to green, bluish black, and finally to an ochrey red, when it is entirely sesquioxide. Ammonia exer- cises a similar action, but does not precipitate the whole of the oxide, because the precipitate dissolves in the ammoniacal salt produced. Alkaline carbonates form a precipitate of carbonate of iron, which is white at first, but soon becomes of a dirty green, and undergoes the same subsequent changes from oxidation. Ferrous salts are not precipitated by hydro- sulphuric acid, the sulphide of iron being dissolved by strong acids, but give a black sulphide with solutions of alkaline sul- phides. They give a white precipitate with ferrocyanide of potassium, which gradually becomes of a deep blue when exposed to air ; with the ferricyanide, a precipitate which is at once of an intense blue, being one of the varieties of Prussian blue. The infusion of gall-nuts does not afiect a solution of the protoxide of iron when completely free from sesquioxide. Protosulphide of iron is prepared by heating to redness, in a covered crucible, a mixture of iron filings and crude sulphur, in the proportion of 7 of the former to 4 of the latter. It dissolves in sulphuric and hydrochloric acids, with evolution of hydrosulphuric acid gas (I. 420.). D 3 SS IRON. A subsulphide of iron, ^^cfi, appears to be formed wlien tlic sulphate of iron is reduced by hydrogen^ one-half of the sul- phur coming off in the form of sulphurous acid. This sub- sulphide is analogous to the subsulphidcs of copper and lead, which crystallise in octahedi'ons. Protochloride of iroii crystallises with 4H0, and is very soluble. Like all soluble ferrous salts, it is of a green colour, gives a green solution, and has a great avidity for oxygen. Protiodide of iron is formed when iodine is digested with water and iron wire, the latter being in excess, and is obtained as a crystalliue mass by evaporating to dryness. It was introduced into medical use by Dr. A. T. Thomson. A piece of iron wire is placed in the solution of this salt to preserve it from oxidising. The protiodide of iron dissolves a large quantity of iodine, without becoming periodide, as the excess of iodine may be precipitated by starch. Protocyanide of iron C2NFe or FeCy, is as difficult to obtain as the protoxide of iron. "When cyanide of potassium is added to a protosalt of iron, a yellowish-red precipitate appears, which dissolves in an excess of the alkaline cyanide, and forms the ferrocyanide of potassium (I., 529.). A grey powder re- mains on distilling the ferrocyanide of ammonium at a gentle heat ; and a white insoluble substance on digesting recently precipitated prussian blue in sulphuretted hydi'ogen water, contained in a well-stopped phial ; these products, although they differ considerably in properties, have both been looked upon as protocyanide of iron. This compound is also obtained as a white deposit on boiling an aqueous solution of hydro- ferrocyanic acid, HgFeCyg. The same solution heated with red oxide of mercury forms cyanide of mercury and white proto- cyanide of iron. The most remarkable property of this cy- anide is its tendency to combine with other cyanides of all classes, and to form double cyanides, or to enter as a con- stituent into the salt-radicals ferrocyanogen and ferricyanogen, CyaEe and CjoFe^, FERROUS COMPOUNDS, 39 Hijdroferrocyanic acid; H2reCy3 or 2HCy,FeCy. This compound was discovered by Mr. Porrett. It may be ob- tained by decomposing ferrocyanide of barium witb sulphuric acid, or ferrocyanide of potassium witb an alcoholic solution of tartaric acid, or ferrocyanide of lead with hydrosulphuric acid. It is soluble in water and alcohol, insoluble in ether, and crystallises by spontaneous evaporation in cubes or four- sided prisms, or sometimes in tetrahedrons. When dry, it may be kept for a long time without alteration in close vessels; but is decomposed on exposure to the air with evolution of hydrocyanic acid, and formation of prussian blue. Hydroferrocyanic acid unites with most salifiable bases, forming the salts called ferrocyanides, whose general formula is M2reCy3, the symbol M denoting a metal. The ferro- cyanides of ammonium, potassium, sodium, barium, stron- tium, calcium, and magnesium, dissolve readily in water ; the rest are insoluble or sparingly soluble. Some of them, as the copper and uranium salts, are very highly colom*ed. Ferro- cyanide of potassium has been already described (I. 529.). Ferrocyanide of potassium and iron ; Kre2Cy3 = (KFe), (CygFe). — The bluish- white precipitate which falls on testing a protosalt of iron with the ferrocyanide of potassium or yellow prussiate of potash, e. g.y with the protochloride : KaFeCyg + FeCl = KCl + KFcaCya- It is also obtained in the form of a white crystalline salt (mixed with bisulphate of potash), in the preparation of hydro- cyanic acid, by distilling ferrocyanide of potassium with dilute sulphuric acid : 2K2FeCy3 + 6S03 + 6HO = 3(KO,HO,2S03) +3HCy F-KFcaCy,. Exposed to the air, it absorbs oxygen and becomes blue. It then affords ferrocyanide of potassium to water, and after all soluble salts are removed, a compound remains, which Liebig names the basic sesquiferrocyanide of iron, and repre- sents by the formula Fe4.3(Cy3Fe) -f FegOg, corresponding, D 4 40 IRON. as will be seen hereafter, with 1 eq. of prussian blue + 1 eq. of sesquioxide of iron. This basic compound is dissolved entirely by continued washing, and affords a beautiful deep blue solution. The addition of any salt causes the separation of this compound. Its solution may be evaporated to dryness without decomposition. The white ferrocyanide of iron and potassium likewise turns blue when treated with chlorine- water or nitric acid, being thereby converted into fern- cyanide of iron and potassium (KFe4Cy6). 2KFe2Cy3 + CI = KFe^Cyg + KCl. This latter compound, which when dry is of a beautiful violet colour, may be regarded as ferricyanide of potassium K3re2Cy6, in which 2 eq. of potassium are replaced by iron (Williamson) . Ferricyanide of iroUy TkimbuIVs blue; !Fe3(Cy6Fe2). — This is the beautiful blue precipitate which falls on adding the ferricyanide of potassium (red prussiate of potash) to a proto- salt of iron. It is formed by the substitution of 3 eq. of iron for the 3 eq. of potassium of the latter salt (I. 530). The same blue precipitate may be obtained by adding to a proto- salt of iron a mixture of yellow prussiate of potash, chloride of soda, and hydrochloric acid. The tint of this blue is lighter and more delicate than that of prussian blue. It is occasionally used by the calico-printer, who mixes it with permuriate of tin, and prints the mixture, which is in a great measure soluble, upon Turkey-red cloth, raising the blue colour afterwards by passing the cloth through a solution of chloride of lime containing an excess of lime. The chief object of that operation is indeed different, namely, to dis- charge the red and produce white patterns, where tartaric acid is printed upon the cloth ; but it has also the effect in- cidentally of precipitating the blue pigment and peroxide of tin together on the cloth, by neutralising the acid of the pre- muriate of tin. This blue is believed to resist the action of FERROUS COMPOUNDS. 41 alkalies longer than ordinary prnssian blue. It is distin- guished from Prussian blue by yielding, when treated with caustic potash or carbonate of potash, a solution of ferro- cyanide of potassium, and a residue of ferroso-ferric oxide : SFe^Cye + 4K0 = SK^FeCy, + ^630, ; whereas prussian blue treated in the same manner yields ferric oxide (Williamson). Carbonate of iron is obtained on adding carbonate of soda to the protosulphate of iron, as a white or greenish- white pre- cipitate, which may be washed and preserved in a humid con- dition in a close vessel, but cannot be dried without losing carbonic acid and becoming sesquioxide of iron. It is soluble, like the carbonate of lime, in carbonic acid water, and exists under that form in most natm-al chalybeates. Carbonate of iron occurs also crystallised in the rhombohedral form of calc- spar, forming the mineral spathic iron, which generally con- tains portions of the carbonates of lime, magnesia, and man- ganese. It is generally of a cream colour or black, and its density rarely exceeds 3*8. This anhydrous carbonate does not absorb oxygen from the air. Carbonate of iron is also the basis of clay iron-stone. There is no carbonate of the sesquioxide. Protosulphate of iron. Ferrous sulphate. Green vitriol, Cop- peras ; FeO.SOg, HO + 6H0; 7Q 4- 63 or 950 + 787-5.— This salt may be formed by dissolving iron in sulphuric acid diluted with 4 or 5 times its bulk of water, filtering the solu- tion while hot, and setting it aside to crystallise. But the large quantities of sulphate of iron consumed in the arts are prepared simultaneously with alum, by the oxidation of iron pyrites (I. 606). The commercial salt forms large crystals, derived from an oblique rhomboidal prism, which effloresce slightly in dry air, and, when at all damp, absorb oxygen and become of a rusty 43 IRON. red colour; hence the origin of the Erench term couperose applied to this salt^ and comipted in our language into cop- peras. If these crystals be crushed and deprived of all hygro- metric moisture by strong pressure between folds of cotton cloth or filter paper^ they may afterwards be preserved in a bottle without any change from oxidation. Of the 7H0 which sulphate of iron contains, it loses 6H0 at 238°, but retains 1 eq. even at 535°. It may, however, be rendered perfectly anhy- drous, with proper caution, without any appreciable loss of acid. The anhydrous salt is also obtained in very small crystalline scales by immersing the hydrated crystals in strong boiling sulphuric acid, and leaving the liquid to cool. The salt was observed by Mitscherlich to crystallise at 176°, with 4H0, in a right rhombic prism, like the corresponding sulphate of manganese. "When its solution containing an excess of acid is evaporated by heat, a saline crust is deposited, which, according to Kuhn, contains 3110. The sulphate of iron appears to form neither acid nor basic salts. One part of copperas requires to dissolve it, the following quantities of water, at the particular temperatures indicated above each quantity, according to the observations of Brandes and Firnhaber : — 50° 59° 75-2° 109-1.° 111° 110-0° 183-2° 191° 212° 1-64 1-13 0-87 0-6G Oil 038 0-37 027 0-30 Ferrous sulphate undergoes decomposition at a red heat, changing into ferric sulphate, and leaves, after all the acid is expelled, the red sesquioxide known as colcothar. This sulphate, like all the magnesian sulphates, forms with sul- phate of potash a double salt containing 6H0. A solution of the sulphate of iron absorbs nitric oxide, and becomes quite black ; according to Peligot, it takes up the gas in the pro- portion of 9 parts to 100 anhydrous salt, or one-fourth of an equivalent (1., 342). Protonitrate of iron. Ferrous nitrate, may be formed by FERRIC COMPOUNDS. 43 dissolving the protosulpliide in cold dilute nitric acid; the solution evaporated in vacuo yields pale green^ very soluble crystals. The solution of the neutral salt is decomposed near the boiling heat^ with evolution of nitric acid and copious pre- cipitation of a ferric subnitrate. Iron turnings dissolve in dilute nitric acid and form the same salt, without evolution of gas, the water and acid being decomposed in such a manner as to form ammonia, at the same time that they oxidate the iron. ' Protoacetate of iron, Ferrous acetate, is obtained by dis- solving the metal or its sulphide in acetic acid. It forms small green prisms which decompose very readily in the air. Tartrate of potash and iron, Potassio -ferrous tartrate, is prepared by boiling bitartrate of potash with half its weight of iron turnings and a small quantity of water. Hydrogen is evolved, and a white, granular, sparingly soluble salt formed which blackens in the air from absorption of oxygen. It is used medicinally. The iron of this salt is not precipitated by hydrate or carbonate of potash. SESQUICOMPOUNDS OF IRON; FERRIC COMPOUNDS. Sesquioxide of iron ; Peroxide of iron ; Ferric oxide, 80 or 1000. — Occurs very abundantly in nature : 1. as oligistic or specular iron, in crystals derived from a rhombohedron very near the cube, which are of a brilliant metallic black and highly iridescent. Their powder is red ; their density, from 5-01 to 5-22. This oxide forms the celebrated Elba ore. — 2. As red hematite, in fibrous, mammillated, or kidney-shaped masses, of a dull red colour, very hard, and of sp. gr. from 4* 8 to 5*0. This mineral when cut forms the burnishers of blood- stone. — 3. also in combination with water, as brown hematite, which is much more abundantly diflPused than the anhydrous sesquioxide, the granular variety supplying, according to M. 44 IRON. BertMer, more than three-fourtlis of the iron-fumaces in France. Its density is 3*922; its powder is brown vnth a shade of yellow^ and it dissolves readily in acid, which the anhydrous sesquioxide does not. From analyses by Dr. Thomson and M. Berthier, this mineral appears to unite with 1 eq. of water, as HO.Fe203, analogous to the magnetic oxide of iron, FeO.Fe203. The hydrated sesquioxide produced by the oxidation of iron pyrites, of which it retains the form, contains 1 eq. of water, or lO'Sl percent., and that from the oxidation of the carbonate of iron, 3 eq. of water, or 14' 71 per cent., to 2 eq. of sesquioxide (Mitscherlich, Lehrbuch, II. 23, 1840). The hydrate is the yellow colouring matter of clay, and with silica and clay it forms the several varieties of ochre. When metallic iron is oxidated gradually in a large quantity of water, there forms around it a light precipitate of a bright orange yeUow colour, which, according to Berzelius, is a ferric hydrate, and of which the empirical formula is 2Fe203 + 3HO, the usual composition of broT\-n hematite. When iron is oxidated in deep water, it is converted, according to E. Davy, into the magnetic oxide, which is possibly formed by cemen- tation from the hydrated sesquioxide. The hydrated sesqui- oxide is also obtained, by precipitation from ferric salts, by ammonia and by hydrated or carbonated alkali; but never pure, as when an insufficient quantity of alkali is added, a sub- salt containing acid is precipitated; and wlien the alkali is added in excess, a portion of it goes down in combination with the oxide, and cannot be entirely removed by washing. When ammonia is used, the water and excess of the precipi- tant may be expelled by ignition, and the pure sesquioxide obtained. The latter is not magnetic, and after ignition dis- solves mth difficulty in acids. When ignited strongly, it loses oxygen and becomes magnetic. Ferric oxide and its compounds are stiictly isomorphous with alumina and the compounds of that earth, and remark- ably analogous to them in properties. It is a weak base. FERRIC COMPOUNDS. 45 of whicli the salts have a strong acid reaction, and are decomposed by all the magnesian carbonates, as well as by the magnesian oxides themselves. The solutions of its salts, which are neutral in composition, have generally a yellow tint ; but they are all capable, when rather concentrated, of dissolv- ing a great excess of ferric oxide, and then become red. Very dilute solutions of the neutral salts of ferric oxide are decom- posed by ebullition, and the oxide entirely precipitated, the acid of the salt then uniting with water as a base ( S cheer er). Iron is most conveniently distinguished by tests, or pre- cipitated for quantitative estimation, when in the state of sesquioxide. The solution of a ferrous salt is usually oxidised by transmitting a current of chlorine through it, or by adding to it, at the boiling point, nitric acid, in small quantities, so long as eflPervescence is occasioned from the escape of nitric oxide. Alkalies and alkaline carbonates throw down a red-brown precipitate of hydrated sesquioxide. Hy^ drosulphuric acid converts a sesquisalt of iron into a proto- salt, with precipitation of sulphur. Ferrocyanide of potassium throws down prussian blue, but the ferricyanide has no effect upon ferric salts beyond slightly changing the colour of the solution. Suljjhocyanide of potassium produces a deep wine-red solution with ferric salts, which becomes perfectly colourless when considerably diluted with water, provided the iron salt is not in great excess. Infusion of gall-nuts produces a bluish-black precipitate — the basis of common writing ink. A remarkable insoluble modification of the hydrated sesqui- oxide is produced by boiling the ordinary hydrate (precipitated from the chloride by ammonia) in water for 7 or 8 hours. The colour then changes from ochre-yellow to brick-red, and the hydrate thus altered is scarcely acted upon by strong boil- ing nitric acid, and but very slowly by hydrochloric acid. In acetic acid, or dilute nitric or hydrochloric acid, it dissolves, forming a red liquid, which is clear by transmitted but turbid 46 IRON. by reflected light ; is precipitated by tlie smallest quantity of an alkali-salt or a sulphate ; and on addition of strong nitric or hydrochloric acid, yields a red granular precipitate ^vhich re-dissolves on diluting the liquid -with water. The modified hydrate does not form prussian blue with ferrocyanide of po- tassium and acetic acid. It appears to be FcoOg.HO, the ordinary precipitated hydrate, after drying in vacuo, being 2Fe203.3IIO. This insoluble hydrate is likewise precipi- tated when a solution of the ordinary hydrate in acetic acid is rapidly boiled. The same solution, if kept for some time at 212° in a close vessel, becomes light in colour, no longer forms prussian blue with ferrocyanide of potassium, or exhibits any deepening of colour on addition of a sulphocyanide ; strong hydi'ochloric or nitric acid, or a trace of an alkali-salt, or sulphuric acid, throws down all the ferric oxide in the form of the insoluble hydrate.* It has also been observed that ferric hydrate becomes crystalline and less soluble by long immersion in water, and by exposure to a low temperature. Black or magnetic oxide of iron, Ferroso -ferric oxide, FeO.FcaOa, an important ore of iron, is a compound of the two oxides. It crystallises in regular octohcdrons. In this compound, the sesquioxide of iron may be replaced by alu- mina and by oxide of chromium, and the protoxide of iron by oxide of zinc, magnesia, and protoxide of manganese, with- out change of form. It was produced artificially, by Liebig and Wohler, by mixing the dry protochloride of iron with an excess of carbonate of soda, calcining the mixture in a crucible, and treating the mass with water. The double oxide then remains as a black powder, which may be washed and dried without further oxidation. The same chemists, by dissolving the black oxide in hydrochloric acid, and preci- pitating by ammonia, obtained a hydrate of the double oxide. It was attracted by the magnet, even when in the state of a » Pean de St. Gilles, Ann. Clt. Phjs. [3], xlvi. 47. FERRIC COMPOUNDS. 47 flocculent precipitate suspended in water. When ignited and anhydrous, this double oxide is much more magnetic than iron itself. Scale-OMde, 6Fe0.re2 03. — When iron is heated to redness in contact with air, two layers of scale-oxide are formed, which may be easily separated. The inner layer, which has the composition just given, is blackish grey, porous, brittle, and attracted by the magnet. The outer layer con- tains a larger proportion of ferric oxide ; it is of a reddish iron-black colour, dense, brittle, yields a black powder, and is more strongly attracted by the magnet than the inner layer. The proportion of ferric oxide in the outer layer is between 32 and 37 per cent., and on the very surface as much as 52*8 per cent. (Mosander). The specific gravity of the scale- oxide is 5-48 (Boullay). Sesquisulphide of iron, or Ferric sulphide, Yq^ S3, corre- sponding with the sesquioxide, may be prepared by pouring a solution of a sesquisalt of iron, drop by drop, into a solution of an alkaline sulphide, the latter being preserved in excess. At a low red heat, it loses 2-9ths of its sulphur, and becomes magnetic pyrites. The common yellow iron pyrites is the bisulphide of iron. It crystallises in cubes or other forms of the regular system; its density is 4*981. It may be formed artificially by mixing the protosulphide with half its weight of sulphur, and distilling in a retort at a temperature short of redness. The metallic sulphide combines with a quantity of sulphur equal to that which it abeady possesses, and forms a bulky powder of a deep yellow colour and metallic lustre, upon which sulphuric and hydrochloric acids have no action. This sulphide appears to be of a stable nature, but the lower sulphides of iron oxidate, when moistened, with great avidity. Stromeyer found the native magnetic sulphide of iron to con- sist of 100 parts of iron combined with 68 of sulphur; and the sulphide left on distilling iron with sulphur at a high temperature, to be of the same composition. It may be 48 IRON. viewed as BFeS.FcaSg (Berzelius). It is said to be this compound which is almost always formed when sulphide of iron is prepared in the usual manner. Sesquichloride of iron. Ferric chloride, Fcg CI3, is formed when iron is burned in an excess of chlorine. It is volatile at a red heat. Its solution, which is used in medicine, is obtained by dissolving the hydrated sesquioxide of iron in dilute hydrochloric acid. When greatly concentrated, the solution of sesquichloride of iron yields, sometimes orange- yellow crystalline needles, radiating from a centre, which are FcjClg + 12H0, at other times, large dark yellowish-red crystals, Ye^ CI3 + 5H0. Mixed with sal-ammoniac, and evaporated in vacuo, it affords beautiful ruby-red octohedral.^ crystals, consisting of 2 eq. of chloride of ammonium, and 1 eq. sesquichloride of iron, with 2 eq. of water, Fcj CI3. 2NH4 CI I- 2H0. Of this water, the double salt loses 1 eq. at 150°, and the other when dried above 300° (Graham). There is a similar double salt, containing chloride of potassium, but not so easily formed. Sesquichloride of iron is soluble both in alcohol and ether. A strong aqueous solution was found by Mr. R. Phillips to dissolve not less than 4 eq. of freshly precipitated ferric hydrate, becoming deep red and opaque. Sesqui-iodide of iron is formed in similar circumstances to the preceding sesquicliloride. Sesquicyanide of iron, Ferric cyanide, Ye^Cj^, is unknown in the pure state. A solution of it, which is decomposed by evaporation, is obtained by precipitating the potash of the red prussiate by fluoride of silicon. It forms a numerous class of double cyanides. A compound of the two cyanides of iron, like the compound oxide, is obtained as a green powder, when a solution of the yellow prussiate of potash, charged with excess of chlorine, is heated or exposed to air. The precipitate should be boiled with eight or ten times its weight of concen- FERRIC COMPOUNDS. 49 trated hydrochloric acid, and well washed. Its formula is, FeCy. Fe2Cy3 + 4H0.* Hydroferricyanic acid; H3Fe2Cy6, or H3.(Cy3Fc)2, or 3HCy.Fe2Cy3, is obtained by decomposing ferricyanide of lead with sulphuric or hydrosulphuric acid. The decanted yellow solution yields, by careful evaporation, brownish needles, which redden litmus strongly, and have a rough sour taste. This solution gives a deep blue precipitate (TumbulPs blue), with ferrous salts. This acid, united with salifiable bases, forms the ferricyanides M3Fe2Cy6. The potassium salt is described in Vol. I. p. 530. Prussian blue, Fe^ • 3(Cy3Fe), or 3FeCy. 2Fe2Cy3. — This ' remarkable substance is precipitated whenever the yellow prussiate of potash is added to a sesquisalt of iron. Thus with the sesquichloride : 3K2FeCy3 + 2Fe2Cl3"= Fe4.3(Cy3Fe) + 6KCI3. Care must be taken to avoid an excess of the yellow prussiate, as the precipitate is apt to carry down a portion of that salt. The precipitate also contains water which cannot be separated from it without decomposition. On the large scale, prussian blue is sometimes prepared by precipitating green vitriol with yellow prussiate of potash, and subjecting the white precipi- tate, KFe2Cy3, to the action of oxidising agents, such as chlorine or nitric acid. This process, however, is likely to yield ferricyanide of iron and potassium, KFe4Cy6 (p. 40.), rather than prussian blue, properly so called. Prussian blue, dried at the temperature of the air, is a light porous body, of a rich velvety blue colour ; dried at a higher temperature it is more compact, and exhibits in mass a cop- pery lustre. It is tasteless, and not poisonous. Alkalies de- compose it, precipitating sesquioxide of iron and reproducing an alkaline ferrocyanide. This renders prussian blue of little value in dyeing, as it is injured by washing with soap. Ked * Pelouze, Ann. Ch. Phys. [2], Ixix. 40. VOL. II. E 50 IRON. oxide of mercury boiled with prussian blue, affords the soluble cyanide of mercury, with an insoluble mixture of oxide and cyanide of iron. Prussian blue is destroyed by fuming nitric acid, but combines with oil of vitriol, forming a white pasty mass, which is decomposed by water. The combination of prussian bhic and sesquioxide of iron, called basic prussian blue^ was noticed at page 40. Although there is no carbonate of the sesquioxide of iron, the hydrated sesquioxide is dissolved by alkaline bicai'bonates, under certain conditions which are not well understood, and d red solution is formed. Ferric sulphates. — The neutral sulphate, Fe203. SSOg, is formed by adding to a solution of the protosulphate, half as much sulphuric acid as it already contains, and oxidising by nitric acid. It gives a syrupy liquid, without crystallising. This salt is found native in Chili, forming a bed of consider- able thickness. It is generally massive, but forms also six- sided prisms, with right summits, which are colourless, and contain OHO (Rose). Ferric sulphate is soluble in alcohol. It may be rendered anhydrous by a low red heat ; but after ignition, it dissolves in water with extreme slowness, like calcined alum. When hydrated ferric oxide is digested in the neutral sul- phate, a red solution is formed, which, according to Maus, is the compound FcjOg. 2SO3. The rusty precipitate which is formed in a solution of the protosulphate from absorption of oxygen, is another subsulphate, of which the empirical formula is 2Fe203. SO3. The decomposition may be represented by the following equation: — lOlFeO.SOg) + 50 = 2Fe203.S03 + SlFcaOg-SSOa). The neutral ferric sulphate remains in solution. A potassio-ferric sulphate, or iron alum, is formed by eva- poratmg a solution of the mixed salts to their point of crystal- FERRIC SULPHATES. 51 lisation. It is colourless and exactly analogous in composition to ordinary alum (I. 606.). Its formula is KO • SO3 + ¥efiy 3SO3 + 24HO. Another double sulphate is formed, which crystallises in large six-sided tables, and of which the formula is 2(K0 • SO^j + FcaOg • 2SO3 + 6HO (Maus), when potash is added gradually to a concentrated solution of ferric sulphate, till the precipitate formed ceases to redissolve, and the solu- tion is evaporated in vacuo. Berzelius designates as ferroso-ferric sulphate a combination containing FeO * S03 + re203 • 3SO3. It is the salt produced when a solution of the neutral protosulphate of iron is ex- posed to the air, till no more ochre is precipitated. The solution, which is yellowish red, does not crystallise, but gives the black oxide of iron when precipitated by an alkali. A salt of the same constituents, but in different proportions, forms large stalactites, composed of little transparent crys- tals, in the copper mine of Fahlun. This last is represented by SFeO • 2S03 4-3(Fe203 • 2S03)-h36HO (Berzelius). Ferric nitrate. — By dissolving iron in nitric acid, without heat, as in Schoenbein^s experiments (page 35), a salt is ob- tained in large, transparent, colourless crystals. From more than one analysis, Pelouze found the constituents of this salt to be in the proportion of 2Fe203.3N05 + 1^110. Its solution is decomposed by heat, with deposition of ferric oxide. Ordway*, by digesting metallic iron in nitric acid of sp. gr. 1'20, obtained, first a greenish solution, then a red, and ultimately a rusty brown precipitate ; and on adding an equal volume of nitric acid of sp. gr. 1*43 as soon as the last pre- cipitate began to form, and cooling the liquid below 60°, — or by evaporating the greenish solution, adding a large excess of nitric acid and cooling, — colourless, oblique, rhombic prisms, were formed containing Fe203 • 3 NO5 + 18 HO ; they * Sm. Am. J. [2], k. 30. B 2 53 IRON. were deliquescent, sparingly soluble in nitric acid, melted at about 116° to a red liquid, and gave off their acid partly at 212^, completely at a red beat. Two ounces of these crystals pounded and mixed with an equal weight of pulverised bicarbonate of ammonia, produced a fall of temperature from +58° to —5°. By adding this compound to recently precipitated ferric hydrate, Ordway obtained basic salts con- taining from 1 to 8 eq. oxide to 1 eq. acid. The solutions of these salts were of a deep red colour ; were not decomposed by boiling or dilution; but when they contained a large excess of oxide, were decomposed by the addition of chloride of sodium and other salts. Hausmann*, by evaporating the solution of iron in nitric acid to a syrup, adding half the volume of strong nitric acid, and leaving the solution to crystallise, obtained colourless prisms containing FcaOg. 3 NO5 + 12 HO. By mixing a very concentrated solution of this neutral salt with water till the colour became reddish yellow, then boiling, and adding nitric acid after cooling, an ochre-coloured precipitate was formed, containing 8 FcgOg • 2 NO5 + 3 HO. By adding a very large quantity of water to a highly concentrated and slightly acid solution of the nitrate, an ochre-coloured precipitate was sometimes formed, containing 36 Fe203.N05 + 48HO. By treating iron in excess wath nitric acid, a precipitate was obtained having the composition 8Fe203.NO^ + 12H0. Ferric oxalate is very soluble and does not crystallise. It forms a double salt with oxalate of potash, of a rich green colour, of which the formula is 3(KO.C203) + re203.3C203 + 6H0. The crystals effloresce in dry air. In this double salt, the ferric oxide may be replaced by alumina or oxide of chromium. This salt is formed by dissolving hydrated ferric oxide to saturation in bioxalate of potash (salt of sorrel), and crystallises readily from a concentrated • Ann. Ch. Pharm. Ixxxix. 100. FERRIC ACID. ^ 53 Solution. The circumstance of its being the salt of sesqui- oxide of iron most easily obtained and preserved in a dry state should recommend it as a pharmaceutical preparation. The henzoate and succinate of ferric oxide are insoluble precipitates. Hence the benzoate and succinate of ammonia are employed to separate iron from manganese. As both these precipitates are dissolved by acids, the iron solution should be made as neutral as possible. The formula of the succinate is, Fe203.S. Ferric acid, FeOg. — This compound, which is analogous to manganic acid, is obtained in the form of a potash-salt by exposing metallic iron or ferric oxide to the action of powerful oxidising agents. 1. A mixture of 1 part iron-filings and 2 parts nitre is projected into a capacious crucible kept at a dull red heat, and the crucible removed from the fire as soon as the mixture begins to deflagrate and form a white cloud ; if the heat is too strong, the compound decomposes as fast as it is formed. The soft, somewhat friable mass of ferrate of potash thus obtained, may be taken out with an iron spoon, and preserved in well stoppered bottles ; or the ferrate of potash may be obtained in solution by treating the fused mass with ice-cold water, leaving the liquid to stand to allow the un- dissolved ferric oxide to settle down, and then decanting ; the solution must not be filtered, as it is immediately decomposed by contact with organic matter. 2. Ferrate of potash is also formed by igniting ferric oxide with hydrate of potash in an open crucible, or with a mixture of hydrate of potash and nitre. 3. Chlorine gas is passed through a very strong solu- tion of caustic pctash containing hydrated ferric oxide in suspension, fragments of solid potash being continually added in order to maintain a large excess of alkali in the liquid. The ferrate of potash, being almost insoluble in the strong alkaline liquid, is deposited in the form of a black powder, which may be freed from the greater part of the mother -liquor by drying it on a plate of porous earthenware. E 3 54 IRON. Ferrate of potash is a very unstable compound, and has not been obtained in the crystalline form. Its solution is of a deep red colour, like that of permanganate of potash. The acid has not been obtained in the free state ; it appears in- deed to be scarcely capable of existing in that state, decom- posing, as soon as liberated, into oxygen and ferric oxide. Ferrate of baryta is formed by adding a solution of ferrate of potash to a dilute solution of a baryta-salt; it then fails down as a deep carmine-coloured precipitate, which may be washed and dried without changing colour. It gives off oxygen when heated, and is readily decomposed by acids. Nitroprussic acid; Fe2Cy5(N02).H2. This acid and its salts were discovered by Dr. Lyon Playfair.* It is formed by the action of nitric acid (or rather of nitric oxide) on hydro- ferrocyanic acid or a ferrocyanide. The hydroferrocyanic acid is first converted into hydroferricyanic acid : 4H2reCy3 + NO2 = 2H3Fe2Cy6 + 2H0 + N ; and afterwards, by the further action of the nitric oxide, into nitroprussic acid : HjFejCye + NO, = Pe,Cy,(NO,).H^ + HCy. Cyanogen is also evolved and oxamide deposited ; but these products are due to a secondary action. To prepare the potassium or sodium salt, ferrocyanide of potassium (2 eq.) is digested in the cold with ordinaiy nitric acid (5 eq.) diluted with an equal bulk of water, till it is completely dissolved ; the solution boiled till it forms with ferrous salts no longer a dark blue, but a green or slate- coloured precipitate, and then left to crystaUise, where- upon it deposits a large quantity of nitre, together with oxamide. The strongly coloured mother-liquor is neutralised with carbonate of potash or soda ; boiled ; filtered to separate * Phil. Trans. 1849, ii. 477. NITROPRUSSIC ACID. 55 a green or brown precipitate ; and again left to crystallise. Nitrate of potash or soda then crystallises out first; and afterwards, by further evaporation, the nitroprussiate. The sodium-salt crystallises most readily, forming large ruby- coloured prisms, which dissolve in 2i parts of water at 60°, and in a smaller quantity of hot water. From the solution of this salt, the silver-salt may be obtained by double decom- position j and this, when decomposed by hydrochloric acid, yields nitroprussic acid. This acid crystallises in dark red, very deliquescent, oblique prisms, which dissolve very readily in water, alcohol, and ether. The aqueous solution is very prone to decomposition. The general formula of the nitroprussiates or nitroprussides is FcgCyg (N02).M2* : the radical (which might be called nitro- ferro cyanogen) may be regarded as 2 eq. of ferrocyanogen, or 1 eq. of ferricyanogen, Fe2Cy6, in which 1 eq. of cyanogen is replaced by nitric oxide, NO2. Most of them are strongly coloured; the ammonium, potassium, sodium, barium, stron- tium, calcium, and lead salts, dissolve readily in water, forming deep red solutions from which the salts are not precipitated by alcohol. The other nitroprussiates are inso- luble, or sparingly soluble. A solution of a nitroprussiate forms, with the solution of an alkaline sulphide, a splendid blue or purple colour, which affords an extremely delicate test of the presence, either of a nitroprussiate, or of an alkaline sulphide. * This formula was proposed by Gerhardt. Playfair originally gave the formula EegCyi2(NO)3.Mg ; and subsequently {P//il. Mag. [3.] xxxvi. 360) suggested the simpler formula, Fe2Cy3(NO) .M2. G-erhardt's formula, however, agrees quite as well with the analyses of the best defined nitroprussiates as either of these, and is more in accordance with certain reactions; viz., that nitroprussiate of sodium, exposed to sunshine, actually gives off nitric oxide j and that when a solution of the barium-salt is treated with red oxide of mer- cury, part of the nitrogen is converted into nitric acid. £ 4 56 IRON. QUANTITATIVE ESTIMATION OF IRON. Iron is always estimated in the form of sesquioxide. If the solution contains protoxide, either alone or mixed with sesquioxide, it is first boiled mth a sufficient quantity of nitric acid to convert the whole of the protoxide into sesquioxide, and then treated with ammonia in excess to precipitate the latter. The precipitate is collected on a filter, washed, dried, and ignited at a moderate red heat; too high a temperature expels a portion of the oxygen. Every 10 parts of pure sesquioxide correspond to 7 parts of metallic iron. In some cases, however, it is necessary to use potash as the precipitant. In that case, the precipitated ferric oxide is very apt to carry down with it a portion of the potash, which is exceedingly difficult to remove by washing. It is best therefore, after having washed it two or three times with hot w^ater, to re-dissolve it in acid and precipitate by ammonia. In other cases, as when the solu- tion contains organic matter, the iron must be precipitated by sulphide of ammonium, because such substances prevent the precipitation of the oxide. The precipitated sulphide, after being washed, is then dissolved in nitric acid, and the iron precipitated by ammonia as before. Volumetric method. — The quantity of iron in a solution may also be estimated by reducing it aU to the state of protoxide, either by sulphurous acid or by metallic zinc (in the former case the excess of sulphurous acid must be ex- pelled by boiling), and then adding, from a graduated burette, a quantity of solution of permanganate of potash, sufficient to convert all the protoxide of iron into sesquioxide : KO • MusOy + 10FeO= 2MnO + KO -VhY^jdy The liquid must contain an excess of acid, to hold the oxide of manganese in solution. The first portions of perman- QUANTITATIVE ESTIMATION OP IRON. 57 ganate added produce no visible effect ; but as soon as all the protoxide of iron is converted into sesquioxide, the addition of another drop of the permanganate imparts a rose tint to the liquid. The value of the solution of the permanganate must be previously ascertained by dissolving 1 gramme of iron (harpsichord wire) in hydrochloric acid, and determin- ing the number of divisions of the burette occupied by the quantity of the solution required to convert that quantity of iron into sesquioxide. (Margueritte, Ann. Ch. Phys. [3], 18,244.) The preceding method may also be applied to determine the quantities of protoxide and sesquioxide of iron in a solu- tion when they occur together, — viz., by first treating a portion of the solution, as it is, in the manner just described ; then taking another equal portion, reducing all the iron in it to protoxide by sulphurous acid, and applying the same method to the solution thus reduced. The first determina- tion gives the quantity of iron in the state of protoxide ; the second, the total quantity present : the difference is therefore the quantity in the form of sesquioxide. Separation of iron from the metals previously described. — From the alkalies and alkaline earths, iron is separated by ammonia, after having been brought to the state of sesqui- oxide. In the case of the alkaline earths, care must be taken to add but a slight excess of ammonia, to filter quickly, and exclude the air as completely as possible during the filtration ; otherwise the free ammonia will absorb carbonic acid from the air, and then throw down the earths in the form of carbonates, together with the ferric oxide. Should such precipitation occur, — which may generally be known by the colour of the oxide, — the precipitate must be re-dissolved and the treatment with ammonia repeated. If the solution contains fixed organic substances, such as sugar, tartaric acid, &c., the iron must be precipitated by sulphide of am- 58 IRON. monium, and the precipitate treated in the manner already described (p. 56.) From alumina and glucina, iron is separated by potash, which precipitates the iron, but holds the alumina or glucina in solution. The precipitate, which always contains potash, must then be re-dissolved in acid, and the iron re-precipitated by ammonia. The separation of iron from zirconia, yttriay and thorina, is effected by adding a sufficient quantity of tartaric acid to prevent the earths from being precipitated when the solution is rendered alkahne, and throwing down the iron by sulphide of ammonium. From magnesia and from manganous oxide, iron is most effectually separated by succinate or benzoate of ammonia. The solution, after all the iron has been brought to the state of sesquioxide, is mixed with a sufficient quantity of sal- ammoniac to hold the magnesia or manganous oxide in solu- tion, and very carefully neutralised with ammonia; it is then treated with benzoate or succinate of ammonia, which throws down the iron as ferric benzoate or succinate, leaving the magnesia or manganous oxide in solution. The precipitate is washed and dried, and ignited in an open platinum crucible, so that the air may have sufficient access to it to prevent any reduction of the iron by the carbon of the organic acid. Should such reduction take place, the iron must be re-oxidized by nitric acid. The success of this mode of separation depends entirely on the care with which the acid in the solution is neutralised with ammonia before add- ing the benzoate or succinate. If too much ammonia has been added, manganese or magnesia goes down with the iron ; if too little, a portion of iron remains in solution. The addition of ammonia should be continued till a small quan- tity of ferric oxide is precipitated, and does not re-dissolve on agitation. The supernatant liquid has then a deep brown colour, the greater part of the iron being still in the solution. COBALT. 59 The separation of ferric oxide from manganous oxide may also be effected by agitating the solution with excess of car- bonate of lime or baryta, which precipitates the iron but not the manganese. According to J. Schiel*, manganese may be separated from iron by mixing the solution with acetate of soda and passing chlorine through it ; bioxide of manganese is then alone precipitated. The methods of separation given at page 7. serve very well for preparing a pure salt of man- ganese from a solution containing that metal together with iron, but are not adapted for quantitative analysis. Aridium ? This name was given by Ullgren to a metal which he be- lieved to exist in the chrome-iron ores of Roros in Sweden, and in the iron ores of Oernstolso. Its characters very much resemble those of iron. It forms two oxides analogous to those of iron, and presenting, both with liquid reagents and with the blowpipe, characters which might be exliibited by oxides of iron containing a little chromium (vid. Chem. Gaz. 1854, 289} ; Bahr {Ann. Ch. Fharm. Ixxxvii. 264), endeavoured to prepare the supposed new metal by Ullgren's process, and came to the conclusion that it was merely iron containing a little phosphorus, and perhaps also chromium. SECTION III. COBALT. %. 29-52, 07-369; Co. Cobalt occurs in the mineral kingdom chiefly in combina- tion with arsenic, as arsenical cobalt, CoAs ; or with sulphur and arsenic, as grey cobalt ore, CoAs.CoSg, but contaminated with iron, nickel, and other metals. Its name is that of the Kobolds or evil spirits of mines, and was applied to it by the •SeU. Am. J. [2], XV. 275. 60 COBALT. superstitious miners of the middle ages, who were often de- ceived by the favourable appearance of its ores. These remained without value, till the middle of the sixteenth century, when they were first applied to colour glass blue. They are now consumed in great quantity for the blue colours of porcelain and stoneware. Cobalt is likewise found in almost all meteoric stones. To obtain metallic cobalt, the native arsenide is repeatedly roasted, by which the greater part of the arsenic is converted into arsenious acid, and carried off in vapour, while the impure oxide of cobalt, known as zaffre, remains. This is dissolved in hydrochloric Jicid, and the remaining arsenic precipitated as sulphide, by passing a stream of sulphuretted hydrogen through the solution. To get rid of the iron present, the last solution, after filtration, is boiled with a little nitric acid, to peroxidise that metal ; and carbonate of potash is added in excess, which throws down carbonate of cobalt and sesquioxide of iron. The precipitate is treated with oxalic acid, which forms an insoluble oxalate of cobalt and soluble ferric oxalate. The oxalate of cobalt is dried and decomposed by ignition in a covered crucible, when the oxide is reduced by the carbon of the acid, which goes off as carbonic acid, while the metallic cobalt remains as a black powder. To separate cobalt from nickel, with which it is almost always associated, the mixed oxalates of cobalt and nickel, obtained by the preceding pro- cess, are dissolved in ammonia, after which the liquid is diluted and exposed to the air in a shallow basin for several days. The ammonia evaporates, and the salt of nickel precipitates as a green powder, while the salt of cobalt remains in solution. The liquid is then decanted, and if no additional precipitate subsides from it in twenty-four hours, it is free from nickel, and may be evaporated to. dryness. The precipitate of nickel contains a little cobalt.* Cobalt is a brittle metal, of a reddish grey colour, some- * For other methods of separating nickel and cobalt, see Nickel. SALTS OF COBALT. 61 what more- fusible than iron, and of the density 8'5131 (Berzelius). Rammelsberg, in five experiments with cobalt reduced by hydrogen, found the specific gravity to vary from 8-132 to 9-495 ; the mean is 8-957. Pure cobalt is mag- netic, but a minute quantity of arsenic causes it to lose that property. Cobalt is less oxidable in the air or by acids than iron, dis- solving slowly in diluted hydrochloric or sulphuric acid, when heated, with evolution of hydrogen ; but it is readily oxidised by nitric acid. This metal forms a protoxide and sesqui- oxide, CoO and C02O3, corresponding with the oxides of iron, and three intermediate oxides, viz., €0304 = 000.00203; 0o6O7 = 40oO.0o2O3; and 0o8O9=60oO.0o2O3. According to Fremy, the first of these, viz., O03O4 is a salifiable base com- bining directly with acetic acid, and existing in several am- monio-salts of cobalt. Fremy has also obtained compound salts of this nature containing a bioxide of cobalt OoOg Protoxide of cobalt, Cobaltous oxide, CoO, 37-52 or 469. — Prepared by the ignition of the carbonate. This oxide is a powder of an ash-grey colour. It colours glass blue, even when in minute quantity, no other colouring matter having so much intensity. Smalt blue is a pounded potash-glass containing cobalt. All compounds of cobalt, when heated with borax or phosphorus -salt, either in the inner or in the outer blowpipe-flame, impart a splendid blue colour to the bead. This coloration afibrds an extremely delicate test for cobalt. The salts of protoxide of cobalt have a reddish colour in solution. Potash or soda added to these solutions forms a blue precipitate of the hydrated oxide, insoluble in excess of the reagent. Ammonia also forms a blue precipitate, which dissolves in excess of ammonia, yielding a red-brown solution. If the cobalt solution contains a large quantity of free acid or of an ammoniacal salt, no precipitate is formed by ammonia. Alkaline carbonates precipitate a pink carbonate of cobalt. 62 COBALT. soluble in carbonate of ammonia. Hydromlphuric add does not precipitate a solution of cobalt xjontaining either of the stronger acids ; but in a solution of acetate of cobalt, or of any cobalt- salt mixed with acetate of ammonia, it forms a black precipitate of protosulphide of cobalt. Alkaline ml- pJiides throw down the same precipitate from all solutions of protoxide of cobalt. Oxide of cobalt appears to combine with alkalies and earths as well as with acids. It dissolves in fused potash, and imparts a blue colour to the compound. IMagnesia mixed with a drop of nitrate of cobalt, and then dried and ignited, assumes a feeble but characteristic rose tint. A compound of oxide of cobalt with alumina is obtained by mixing the solution of a salt of cobalt, which must be perfectly free from iron or nickel, with a solution of equally pure alum, precipitating the liquor by an alkaline carbonate, washing the precipitate with care, then drying and igniting it strongly. It forms a beautiful blue pigment, known as cobalt-blue, which may be compared in purity of tint with ultramarine. A compound of oxide of cobalt with oxide of zinc of a fine green colour may be prepared in a similar manner. These coloured compounds often aftbrd useful confirmatory tests of the presence of zinc, alumina, or magnesia. The substance to be examined is placed on pla- tinum foil, moistened with nitrate of cobalt, then dried, and strongly heated in the blo^vpipe-flame. Chloride of cobalt, Co CI, is obtained by dissolving zaffre or the oxide in hydrochloric acid. Its solution is pink-red, and affords hydrated ciystals of the same colour ; but when highly concentrated, assumes an intense blue colour, and then affords blue crystals of chloride of cobalt, which are anhydrous (Proust). The red solution is used as a sympathetic ink; characters written with it on paper are colourless and invisible, or nearly so, but when the paper is warmed by holding it near a fire or against a stove, the writing becomes visible and appears of a beautiful blue. After a while, as the salt absorbs SALTS OF COBALT. 63 moisture, the colour again disappears, but may be reproduced by the action of heat. If the paper be exposed to too high a temperature, the writing becomes black, and does not after- wards disappear. The addition of a salt of nickel to the sym- pathetic ink gives a green instead of blue. The neutral carbonate of cobalt is unknown, oxide of cobalt, like magnesia, being thrown down from its solutions by alka- line carbonates, as a carbonate with excess of oxide. The sub- carbonate of cobalt is a pale red powder, which contains, according to Setterberger, 2 eq. of carbonic acid, 5 eq. of oxide of cobalt, and 4 eq. of water. Besides the sulphate of cobalt corresponding with green vitriol, another salt was crystallised by Mitscherlich between 68** and 86°, containing 6 eq. of water, C0O.SO34-6HO, iso- morphous with a corresponding sulphate of magnesia. Sulphate of cobalt forms the usual double salts with the sulphates of potash and ammonia, containing 6H0. Nitrate of cobalt, C0O.NO5 — is obtained by dissolving the metal, the protoxide, or the carbonate in dilute nitric acid. Its solution is carmine -coloured, and on evaporation yields red crystals containing 6 eq. of water ; they deliquesce in the air, fuse below 100°, and at a higher temperature give off water and melt into a violet-red liquid, which afterwards becomes green and thick, and is ultimately converted, with violent intumescence and evolution of nitrous fumes, into black sesquioxide of cobalt. Characters written on paper with a solu- tion of this salt assume a peach-blossom colour when heated. A seocbasic nitrate, 6CoO.NOg + 5Aq., is obtained on adding excess of ammonia to a well boiled solution of the neutral nitrate, carefully protected from the air. It then falls down as a blue precipitate, but on the slightest access of air quickly assumes a grass-green colour and partly redissolves in the liquid. Cobalt-yellow, CoO.KO.N208.--This compound is formed by adding a solution of nitrite of potash (obtained by passing 64 COBALT. the nitrous fumes evolved from a heated mixture of nitric acid and starch into caustic potash) to an acid solution of nitrate of cobalt ; nitric oxide and nitrate of potash are then formed, and the cobalt-compound separates in the form of a beautiful yellow crystalline powder : C0O.NO5 + 2NO5 -h 4(KO.N03) = 3(KO.N05) + 2NO2 + N2O8.C0O.KO. It is likewise obtained by adding potash, not in excess, to solution of nitrate of cobalt, so as to precipitate a blue basic salt, treating this with a slight excess of nitrite of potash, and adding nitric acid in a thin stream, by means of a pipette. Also by treating nitrate of cobalt with a slight excess of potash, so as to throw do^vn the rose-coloured hydrated oxide, and passing nitric oxide gas into the mixture. This last reac- tion is so rapid that it may be exhibited as a lecture-experi- ment. The compound crystallises in microscopic four-sided prisms with pyramidal summits. It is insoluble in cold water, also in alcohol and ether, but when boiled with water gradually dissolves with evolution of acid vapours ; the solu- tion yields on evaporation a lemon-yellow salt of different composition. Nitric acid and hydrochloric acid do not act upon it in the cold, but decompose it at a boiling heat, with evolution of nitrous fumes. Hydrosulphuric acid decom- poses it very slowly, sulphide of ammonium immediately, forming black sulphide of cobalt. When heated, it assumes an orange-yellow colour, gives off water and aftei'wards fumes of nitric and hyponitric acids, and leaves sesquioxide of cobalt mixed with nitrite of potash. Its beautiful colour, its perma- nence, and the facility with which it mixes with other colours, render it well adapted for artistic purposes.* According to A. Stromeyerf, this salt is a nitrite of co- * St. Evre, Ann. Ch. Phys. [3], xxxviii. 177. t Ann. Ch. Pharm. xcvi. 218. SALTS OF COBALT. 65 baltic oxide and potash, Co203.2N03 + 3(KO.N03), and its formation may be represented by the equation, 2(CoO.S03) + 5(KO.N03) + 0= [Co203.2N03 4-3(KO.N03)] + 2(KO.S03). When a solution of lead is mixed with nitrite of potash and acetic acid, the liquid assumes a yellow colour, but no precipi- tation takes place ; but on adding a cobalt-salt, a yellowish green precipitate (or brownish black and crystalline from dilute solutions) is formed, whose composition is that of the yellow cobalt-compound with half the potash replaced by oxide of lead (Stromeyer). Phosphate of cobalt , 2CoO.HO.PO5, is an insoluble preci- pitate of a deep violet colour. When 2 parts of this phosphate or 1 part of the arseniate of cobalt are carefully mixed with 16 parts of alumina and strongly ignited for a considerable time, a beautiful blue pigment is obtained, resembling ultra- marine ; it was discovered by Thenard. Arseniate of cobalt, SCoO.AsOg + 8H0, exists as a crystal- line mineral called cobalt-bloom. Sesquioxide of cobalt , Cobaltic oooide, C02O3, is formed when chlorine is transmitted through water in which the hydrated protoxide is suspended, or when a salt of the protoxide is precipi- tated by a solution of chloride of lime. In the former case, water is decomposed by the chlorine, and hydrochloric acid produced, while the oxygen of the water peroxidises the cobalt ; 2CoO + HO + CI = C02O3 + HCl. The sesquioxide of cobalt is precipitated as a black hydrate, containing 2H0. This hydrate, when cautiously heated tt 600° or 700°, yields the black anhydrous oxide. When sesqui- oxide of cobalt is digested in hydrochloric acid, clilorine is evolved, and the protochloride formed. Exposed to a low red heat, the sesquioxide loses oxygen, and the compound oxide, C0O.C02O3, is produced. (Hess.) When protoxide of VOL. II. r 66 COBALT. cobalt is calcined with a borax glass, at a moderate heat^ it absorbs oxygen, and a black mass is obtained, which mixed with manganic oxide, serves as a black colour in enamel painting. Sesquioxide of cobalt acts as a weak base. Phosphoric, sul- phuric, nitric, and hydrochloric acids dissolve its hydrate in the cold, without decomposition at first, but the resulting salts are afterwards reduced to salts of the protoxide. A protosalt of cobalt containing a small quantity of a sesquisalt is some- what deepened in coloiu*. The most permanent of the sesqui- salts is the acetate ; the hydrated sesquioxide while yet moist dissolves in acetic acid, slowly but completely. The solution, which has an intense brown colour, forms a brown precipitate with alkalies and alkaline carbonates. With ferrocyanide of potassium it forms a dark precipitate, which, if the precipitant is in excess, gives up cyanogen to it, converting it into ferri- cyanide of potassium and being itself converted into green ferrocyanide of cobalt. Alkaline oxalates colour the solution yellow, forming an oxalate of the oxide C03O4. According to Fremy, the oxide C03O4 combines also with other acids. The acetate of this oxide is obtained by digesting in dilute acetic acid the hydrated oxide obtained by continued action of oxygen on the blue precipitate tlirown down from ordinary cobalt-salts by potash not in excess. Fremy also states that when chlorine is passed into the solution of ordi- nary acetate of cobalt, a browTiish yellow salt is formed con- taining the base CO3CIO3, or C03O4 in which 1 eq. of O is replaced by CI. This chlorine base exists also in some of the amraonio -compounds of cobalt (pp. 68-72) . The oxide C03OJ is obtained in the free state by heating the nitrate or oxalate of cobalt, or the hydrated sesquioxide to redness in contact with the air (Hess, Rammelsberg) ; but according to Beetz and Winkclblech, the oxide thus obtained is CogO^. When the residue obtained by gently igniting the oxalate in contact with the air is digested in strong boiling hydrochloric acid, the oxide C03O4 remains in liard, brittle, greyish-black micro- SALTS OF COBALT. 67 scopic octohedrons having a metallic lustre. The same crys- talline compound is obtained by igniting dry protochloride of cobalt, alone or mixed with sal-ammoniac, in dry air or oxygen gas (Schwarzenberg). A cobaltic acidj C03O5, is obtained in combination with potash by strongly igniting the oxide C03O4, or the protoxide, or the carbonate, with pure hydrate of potash. A crystalline salt is then formed which, when dried at 100° C, contains KO.3C03O5 + 3HO, and gives of 1 eq. of water at 130° (Schwarzenberg) . Bioxide of cobalt, C0O2J has not been obtained in the free state, but exists according to Fremy in the oxycobaltiac salts, (p. 68.) There exist three sulphides of cobalt, a protosulphide, sesqui- sulphide, and bisulphide. Sesquicyanide of cobalt has not been obtained in the sepa- rate state, but it exists in a class of double cyanidbs, of which the radical is cobalticyanogen, CygCo2, analogous to ferri- cyanogen. The cobalticyanide of potassium, corresponding with the red prussiate of potash, is formed when protoxide of cobalt or its carbonate is dissolved in caustic potash which has been treated with an excess of hydrocyanic acid. It is an anhydrous salt, pale yellow and nearly colourless when pure, and of the same form as the ferricyanide of potassium. Its solution does not affect the salts of iron, but forms a rose- coloured precipitate with those of the protoxide of cobalt.* K phosphide of cobalt, C03P, was obtained by Rose, as a grey powder, on passing hydrogen over the subphosphate of cobalt ignited in a porcelain tube. It is also produced by the action of phosphuretted hydrogen on the chloride of cobalt, and may be looked upon as analogous in composition to the former compound, II3P. * For further details on the cobaltioyanides, vide Gmelin's Handbook (trans- lation), vii. 492-497. F 2 68 COBALT. Ammoniacal salts of cobalt. — Cobalt-salts treated with excess of ammonia in a vessel from wliicli the air is excluded, unite with the ammonia, forming compounds to which Fremy gives the name of ammonio- cobalt salts. Most of them con- tain 3 eq. ammonia to 1 eq. of the cobalt-salt ; thus the cliloride contains C0CI.3NH3 + HO : the nitrate C0O.N05.3NH3 + 2H0. They are mostly cry st alii sable and of a rose-colour, soluble without decomposition in ammonia, but decomposed by water with separation of a basic salt. (Fremy.) H. Rose, by treating dry chloride of cobalt with ammoniacal gas, obtained the compound C0CI.2NH3; and similarly an anhydrous sul- phate containing C0O.SO3.3NH3. When an ammoniacal solution of a cobalt salt is exposed to the air, oxygen is absorbed, the liquid turns brown, and new salts are formed containing a higher oxide of cobalt (C02O3 or CO2), and therefore designated generally ^speroa^idised ammo- niO'Cobalt salts. Several of these salts containing different bases are often formed at the same time. Fremy* distinguishes four classes of these compounds, viz., salts of occijcobaltia, luteocobaltia, fitscocobaltia, and roseocobaltia. The oxycobaltia-salts are formed by the action of the air on concentrated solutions of ammonio-cobalt salts. Tlicy have generally an ohve colour, are sparingly soluble in the am- moniacal liquid, and are decomposed by water, especially when hot, with evolution of pure oxygen, liberation of am- monia, and separation of a green basic salt containing cobal- toso-cobaltic oxide CO3O4, They contain 5 cq. of ammonia associated with 2 eq. of a monobasic salt of bi-oxide of cobalt, C0O2; thus the nitrate is composed of 2(Co02.N05).5NIi3. The nitrate and sulphate crystallise in small prisms contain- ing water of crystallisation (Fremy). The luteocobaltia-salts are formed: 1. By the action of the air on dilute solutions of ammonio-cobalt salts ; 2. By the action of a small quantity of water on crystallised oxycobal- * Ann. Ch. Phys., [3], xxxv. 257. ; Chem. Gaz. 1853, 201. SALTS OF COBALT. 69 tia-salts ; 3, By treating the brown solution, formed by the action of oxygen in excess on ammonio-cobalt salts, with di- lute acids; 4. By treating roseocobaltia- salts with excess of ammonia. These salts are of a fine yellow colour, crystallise readily, are tolerably permanent, and resist for some time the action of boiling water. They give no precipitates with alkaline phosphates or carbonates at ordinary temperatures, but are decomposed by boiling potash, with evolution of am- monia and separation of C02O3HO. Dilute acids precipitate them from their aqueous solution in the crystalline state. They contain 1 eq. of a sesquisalt of cobalt, associated with 6 eq. of ammonia ; thus, the sulphate = {Co203.3S03).6NH3 ; the chloride = C02CI3.6NH3. (Fremy.) This last salt was previously obtained by Bogojski*, who regarded it as the hydrochlorate of dicobaltinamine ClH.NgHgCO [co = fCo]. He likewise obtained the other salts of the same base by double decomposition. Fuscocobaltia-salts are formed when an ammoniacal solu- tion of a protosalt of cobalt is exposed to the air, and by the action of water on the oxycobaltia- salts. They are aU un- crystaUisable, but may be obtained in the solid state by pre- cipitation with alcohol or excess of ammonia. They are slowly decomposed by boiling with water, but quickly on the addition of an alkali, with evolution of ammonia, and precipitation of hydrated sesquioxide of cobalt. They are of a brown colour, and appear to contain basic salts of sesquioxide of cobalt, united with 4 or 5 eq. of ammonia. The nitrate contains C02O3. 2NO5.4NH3.3HO. Ammonio-chloride of cobalt, after exposure to the air, yields by evaporation in vacuo, an uncrystallisable residue having the characters of the fuscocobaltia-salts, but contain- ing a chlorine-base ; its formula is C02CI2O.4NH3.3HO. By exposing the solution of the ammonio-chloride to the air for * J. pr. Cliera. Ivi. 491. F 3 70 COB.\LT. two or three weeks, and then boiling with sal-ammoniac^ roseocobaltiacal chloride separates out first, and afterwards a l)lack crystalline compound containing CO3CIO3.NH3 + 5HO. The roseocobaltia-salts are obtained : 1 . By slightly acidu- lating the solution of an ammonio-cobalt salt, w hich has been exposed to the air; 2. By boiling the solution of an ammonio- cobalt salt, which has been exposed to the air for two or three days, and contains a fuscocobaltia-salt, with a salt of ammonia; 3. By mixing oxycobaltia-salts with boiling solutions of am- moniacal salts. They have a fine red or rose colour, and some of them crystallise readily. Their reactions are similar to those of the luteocobaltia-salts. The nitrate and the neutral sulphate contain 3 eq. of C02O3.3NO5, or €0203,3803, with 5 eq. ammonia. There is also an acid sulphate containing (Co203.5S03)5NH3 + 5HO, obtained by adding sulphuric acid in excess to an ammoniacal solution of sulphate of cobalt which has stood for some days in contact with the air. Baryta- water added to the solution of the sulphate, throws do^ni roseocobalti- acal oxide, which is rose-colom'cd, has a strong alkaline reaction, and decomposes on boiling, giving off ammonia and depositing C02O3. Tlie chloride, C02CI3.5NH3.HO, is obtained by boiling the ammonio-chloride of cobalt, or the chlorine-comiX)und C02CI2O.4NH3 (p. 69.), or a salt of oxycobaltia, with chlo- ride of ammonium (Fremy) . Genth * and F. Claudetf have also described a compound ■which appears to be the same as Fremy's hydrochlorate of 30seocobaltia, although each assigns to it a different formula. "When sulphate or chloride of cobalt is mixed with a large quantity of chloride of ammonium and an excess of ammonia, exposed for some time to the air, and then boiled with excess of hydrochloric acid, a crimson powder gradually separates, oxygen is evolved, and the liquid becomes colourless. This compound dissolves in 244 parts of cold water, and in a smaller * Ann. Cli. Pharm. Ixxx. 275. ; Chem. Gaz. 1851, 266, t Pliil. Mag. [4], ii. 253. ; Chem. Soc. Qu. J. iv. 35a SALTS OF COBALT. 71 quantity of boiling water, but is decomposed by continued boiling, unless hydrocbloric acid be added ; in that case a solu- tion is obtained, from which the compound crystallises on cooling in ruby- coloured regular octohedrons. Genth assigns to this compound the formula C02O3.3NH4CI, regarding it as the chloride of a conjugated radical C02O3.3NH4. Claudet finds it to contain 3C1, 2Co, 5N and 16H, and expresses its com- position by one of the following formulae : — (NH2C02 ) , V CE \ 3NH4CI + 2NH2C0; CWNH3NH4 }; C1NK,M ^.2C1N 2 (NHNH4 ) ^ ^^^^ ^^^'^ According to the two latter formulae, the compound is sup- posed to contain ammonium in which part of the hydrogen is replaced by NH4. It might also be regarded as the hydro- chlorate of pentacobaltosamine N5H13C02.3HCI, the base being formed of 5 eq. of ammonia in which 2 eq. of hydrogen are replaced by cobalt. Gregory* assigns to it the formula C02CI3 . 5NH3, making it identical with Fremy's roseoco- baltiacal chloride. The compound heated in a glass tube gives off ammonia and sal-ammoniac, and leaves CoCl. When the aqueous solu- tion is boiled, ammonia is evolved, and a precipitate formed probably consisting of C03O4.3HO, combined with nitride of cobalt. The chlorine compound treated with recently preci- pitated oxide of silver, yields the oxygen-compound of the same radical ; and by double decomposition with various silver- salts, the other salts of the base. The ammonia in all these compounds is in a peculiar state, not exhibiting its usual basic properties, or being recognisable by the usual reagents or replaceable by other bases. Glaus attributes this circumstance to the ammonia being in a passive state, which is merely another way of expressing the fact, but * Ann. Cli. Pharm. Ixxxvii. 125. F 4 72 COBALT. affords no explanation. Weltzien supposes the compounds in question to contain compound ammonium-molecules, in which 1 or 2 at. hydrogen are replaced by ammonium itself (an idea first suggested by Mr. Graham), viz., ammo-cobaltammo- nium NHgAmCo, and biammo-cobalt ammonium NHAmjCo [the symbol Am standing for NH^]. Thus the ammonio- cobalt salts J containing 2NH3, may be regarded as neutral salts of ammo-cobaltammonium, and those which contain 3NH3 as neutral salts of biammo-cobaltammonium ; thus — C0CI.2NH3 = NH2AmCo.Clj and CoBr.SNHy = NHA^o.Br. The fuscocobaltia-salts may be regarded as basic salts of the sesquioxide of ammo-cobaltammonium, e. g. — C02O3.2NO5.4NH3 = (NH^cijA-^NOs. The luteocobaltia-s&\ts, as neutral salts of the sesquioxide of biammo-cobaltammonium, e. g. — C02O3.3NO5.GNH3 = (NHAm2Co)203.3N05 ; The roseocobaltia-svAts as neutral sesquisalts containing 1 at. of each of the above-mentioned ammoniums, thus — Co,Cl3.5NH3 ^NH^AmCo NHAmXo •CI3; And the oxycobaltia-salts as basic salts of the same two ammonium-molecules, e. g, — 2CoO2.2SO3.5NH3 = ^^M;^0 NHAm2Co 0,.2S03. ESTIMATION OF COBALT. 73 ESTIMATION OF COBALT, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. Cobalt is generally precipitated from its solutions by caustic potash. The precipitate is bluish, and consists of a basic salt, which, however, when heated, is converted into the hydrated protoxide of a dingy rose colour. It must then be washed in hot water, dried and ignited in an atmosphere of hydrogen, by which it is reduced to the metallic state, after which it is weighed. According to Beetz*, the reduction to the metallic state may be dispensed with, an accurate result being obtained by igniting the precipitated oxide till it no longer varies in weight, its composition being then 4C0.C02O3 or CogO^ ; but the reduction by hydrogen is perhaps the surer method. Cobalt is separated from the alkalies and alkaline earths by sulphide of ammonium, the black sulphide of cobalt being then dissolved in nitro-hydrochloric acid, and the oxide preci- pitated by potash as above. From magnesia it may also be separated by sulphide of ammonium, sufficient chloride of ammonium being added to hold the magnesia in solution. From alumina and glucina it is separated by potash. The separation of cobalt from manganese is difficult. It is best effected by heating the mixed oxides in hydrochloric acid gas, which converts them into chlorides, and then heating the chlorides in a stream of hydrogen, which reduces the cobalt to the metallic state, but leaves the chloride of manganese undecomposed ; the latter is then dissolved out by water. Another mode of separation is to digest the mixed oxides in a solution of pentasulphide of calcium, which dissolves the sulphide of cobalt, but leaves the sulphide of manganese un- dissolved, f Cobalt is separated from iron in the same manner as man- * Pogg. Ann. Ixi. 472. t Cloez, J. Pharm. [3.] vii. 157. 74 NICKEL. gancse (p. 58.), viz. by bringing the iron to the state of sesquioxide, then adding chloride of ammonium, neutralising ^yiih ammonia, and precipitating the iron by succinate of ammonia. SECTION IV. NICKEL. Eg. 29-57 or 369'6. This metal resembles iron and cobalt more than any others, and is associated with these metals in meteorites, and in most of the terrestrial minerals which contain it. The principal ore of nickel is arsenical nickel, a mineral having the colour of metallic copper, to which the German miners, having attempted in vain to extract copper from it, gave the name kupfer-nickely or false copper. This mineral was found by Cronstedt of Sweden, in 1751, to contain a particular metal, which he called nickel. Nickel imparts a remarkable white- ness to the metallic alloys which contain it, on which account it has come of late to be valued in the arts, being added to brass to form the well-known imitations of silver. The metal is prepared from the native arsenide, or from an artificial arsenide called speiss, which contains about 54 per cent of nickel, and has been observed by Wohler to occur in octohedrons with a square base, having the composition NiyAs. Speiss is a metallic substance which collects at the bottom of the crucibles in which smalt or cobalt-blue is prepared. In that operation, a mixture of quartzy sand, potashes, and the roasted ore of cobalt is fused. The previous roasting never being perfect, a part of the metals escapes oxidation ; and hence when the mixture described is fused, the cobalt, which NICKEL. 75 is more oxidable than nickel and copper, reacts upon the oxides of these metals^ and reduces them, while it is itself oxidated : the nickel and copper concentrate in the speiss, while the smalt contains scarcely any of them. A salt of nickel may be obtained by treating speiss in fine powder with an equal weight of sulphuric acid, diluted with four or five times its bulk of water, and gradually adding an equal weight of nitric acid, which occasions the oxidation of both the nickel and the arsenic. The green solution thus obtained, when cooled and allowed to stand for twenty-four hours, deposits much arsenious acid, from which it may be separated by filtra- tion. A quantity of carbonate of potash, equal to half the weight of the speiss, is then added to the solution, which is concentrated and set aside to crystallise. The double sulphate of nickel and potash, NiO.SOg + KO.SOg-f 6H0, forms easily, and may be obtained free from arsenic by a second crystallisa- tion. (Dr. Thomson.) The perfect separation of small quan- tities of cobalt and copper, which these crystals may still contain, requires additional processes.* With the view of ob- taining the metal, the insoluble oxalate of nickel may be preci- pitated from the preceding salt by oxalate of ammonia, washed, dried, and ignited gently in a covered crucible. The oxalic acid reduces the oxide of nickel, and the metal remains in a spongy state. It is pyrophoric, like manganese and iron prepared in the same manner, if the temperature of reduction has been low. To obtain the metal in a solid mass, it should be fused in a crucible covered with pounded glass. The oxide of nickel is very easily reduced both by carbonic oxide and by hydrogen. Nickel, when free from cobalt, is silver- white, unalterable in air, and highly ductile. Its density, according to Richter, is 8*279, and after being forged 8*666. Nickel is magnetic nearly to the same extent as iron. Magnets composed of this metal lose their polarity at 630° (Faraday). It is somewhat more fusible than iron. Nickel forms two oxides correspond- * Bcrzelius, Traite. tcm. i. p. 486. ; see also pp. 78—80. of this volume. 76 NICKEL. ing with the protoxide and sesquioxide of iron ; but the doable compound of the two oxides of nickel^ corresponding with the black oxide of iron, has not been observed. Protoxide of nickel,'NiO,S7'67j or 469'6, may be obtained by the ignition of the carbonate or nitrate of nickel, or by pre- cipitation from its salts by an alkali, as a dark ash-coloured powder, or as a bulky hydrate of an apple- green colour, NiO HO. Oxide of nickel is very soluble in acids, but not in pot- ash or soda. Ammonia dissolves it, and forms an azure -blue solution, from which oxide of nickel is precipitated by potash, baryta, and strontia, having a considerable tendency to com- bine with salifiable bases. The solutions of its salts have all a green colour, much more intense than tliat of the ferrous salts. They are not precipitated by hydrosulphuric acid when a strong acid is present, but afford a black sulphide with alka- line sulphides. Carbonate of nickel is of a pale green-colour and soluble in carbonate of ammonia. Peroxide or sesquioxide of nickel, Ni203, is obtained as a black powder, by exposing the hydrated protoxide suspended in water to a stream of chlorine gas. It does not combine with acids, and in other respects resembles sesquioxide of cobalt. Besides a protosulphide, NiS, a subsuljjhide of nickel, ^\2^, is formed, like that of manganese, by decomposing the ignited sulphate of nickel with hydrogen. A bisulphide of nickel also exists in combination as a constituent of the mineral nickel- glance, NiSj.NiAs. Chloride of nickel NiCl, forms a solution of an emerald- green colour, and yields by evaporation a hydrated salt of the same colour, which becomes yellow when deprived of its water of crystallisation. Chloride of nickel, sublimed at a high tem- perature without access of air, forms golden scales which dissolve with difficulty. Sulphate of nickel crystallises from a strong solution in slen- der green prisms, isomorphous with Epsom salt, of which the composition is NiO-SOg^- 7H0. At a higher temperature, it ESTIMATION OF NICKEL. Tt crystallises with 6 eq. of water NiO.SOa + CHO, like the magnesia and cobalt salts, and in the same form. Mitscher- lich made the singular observation, that when the crystals containing 7 eq. of water are exposed, in a close glass vessel, to a day of sunshine, or kept for some time in a temperate place, the}'^ change their form, becoming a mass of small crys- tals, of which the form is the regular octohedron. The original crystals become opaque from this change, but lose none of their combined water. Sulphate of nickel forms the usual double salts with the sulphates of potash and ammonia. Nickel also forms ammonio -compounds analogous to the ammonio-cobalt salts; e. g, the ammonio-chloride — SNHg.NiCl = NHAm2Ni.Cl ; ammonio-sulphate — 3NH3. NiS04 = NHAm2Ni.S04, &c. The useful white alloy of nickel, German silver or packfong, is formed by fusing together 100 parts of copper, 60 of zinc, and 40 of nickel. ESTIMATION OF NICKEL, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. Nickel isbest precipitated from its solutions by caustic potash which throws down an apple-green precipitate of the hydrated protoxide, and if the liquid be heated, leaves not a trace of nickel in the solution. The precipitate must be washed with hot water, dried, ignited, and weighed ; it then consists of pure protoxide of nickel, containing 78*57 per cent of the metal. In separating nickel from other metals, it is often necessary to precipitate it by sulphide of ammonium; this precipitation is attended with difficulties, because the sulphide of nickel is somewhat soluble in the alkaline sulphide. To make the pre- cipitation as complete as possible, Rose directs that the solu- tion be diluted with a considerable quantity of water, and then treated with sulphide of ammonium, as nearly colourless as it can be obtained, avoiding a large excess of the precipitant and 78 NICKEL. likewise an excess of ammonia ; the glass is then to be covered up with filtering paper, and left in a warm place. Under these circumstances, the excess of sulphide of ammonium is decom- posed by the oxygen and carbonic acid of the air, without risk of the sulphide of nickel being oxidised. As soon as the super- natant liquid has lost its brown colour, the precipitate is col- lected on a filter and washed, as quickly as possible, with water containing a little sulphide of ammonium. It must then be dissolved in nitro-hydrochloric acid, and the nickel preci- pitated by potash as above. The methods of separating nickel from all the preceding metals except cobalt, are the same as those given for cobalt (p. 73.). The separation of nickel from cobalt itself is diflBicult. The be3t method is perhaps that given by H. Rose*, depending on the fact that protoxide of cobalt in solution is converted by chlo- rine into sesquioxide, whereas with nickel this change does not take place. The metals or their oxides being dissolved in excess of hydrochloric acid, the solution is diluted with a large quantity of water, about a pound of water to a gramme of the metals or their oxides. Chlorine gas is then passed through the solution for several hours, till in fact the space above the liquid becomes permanently filled with the gas ; carbonate of baryta is then added in excess, the whole left to stand for 12 or 18 hours, and shaken up from time to time. The precipitate, consisting of sesquioxide of cobalt and carbonate of baryta, is then collected on a filter, and washed with cold water. The filtered liquid, which has a pure green colour, contains all the nickel without a trace of cobalt. The precipitate is boiled with hydrochloric acid to convert the sesquioxide of cobalt into protoxide, and dissolve it together ^dth the baryta ; the latter is then precipitated by sulphuric acid, and the cobalt from the filtrate by potash. The nickel is also precipitated by potash after the removal of any baryta that the solution majr contain * ITaiulbuch dor Analyiisclicn Chemie (Corlin, 1S51), ii. 10k SEPARATION OF NICKEL FROM COBALT. 79 by sulphuric acid. This method, if properly executed, gives very exact results. The chief precautions to be attended to, are to add a large excess of chlorine, and not to filter too soon, because the precipitation of sesquioxide of cobalt by carbonate of baryta takes a long time. Liebig has given several methods of separating these two metals, founded on the difference of their reactions with cyanide of potassium. 1. The oxides of the two metals are treated with hydrocyanic acid and then with potash, and the liquid warmed till the whole is dissolved (pure cyanide of potassium, free from cyanatemay also be used as the solvent). The reddish-yellow solution is boiled to expel free hydro- cyanic acid, whereupon the cobaltocyanide of potassium (K2CoCy3), formed in the cold, is converted into cobalticya- nide (K3Co2Cy6), while the nickel remains in the form of cyanide of nickel and potassium (KNiCy2). Pure and finely- divided red oxide of mercury is then added to the solution while yet warm, whereby the whole of the nickel is precipi- tated partly as oxide, partly as cyanide, the mercury taking its place in the solution. The precipitate contains all the nickel, together with excess of mercuric oxide ; after washing and ignition, it yields pure oxide of nickel. The filtered solution contains all the cobalt in the form of cobalticyanide of potassium. It is supersaturated with acetic acid, boiled with sulphate of copper, which precipitates the cobalt in the form of cobalticyanide of copper (Cu3Co2Cyg.7HO), and the precipitate retained in the liquid at a boiling-heat till it has lost its glutinous character. It is then washed, dried, and ignited, dissolved in hydrochloric acid mixed with a little nitric acid, the copper precipitated by hydrosulphuric acid, and the filtrate, after boiling for a minute to expel the excess of that gas, mixed with boiling caustic potash to preci- pitate the cobalt.* — 2. Instead of adding the oxide of mercury, the solution containing the mixed cyanides may, after cooling, * Ann Ch. Pharm. Ixv. 214. 80 NICKEL. be supersaturated with chlorine, the precipitate of cyanide of nickel thereby produced being continually redissolved by caustic potash or soda. The chlorine produces no change on the cobalticyanide of potassium, but decomposes the nickel- compound, the whole of the nickel being ultimately preci- pitated in the form of black sesquioxide.* Liebig's first methodf which consisted in treating the solution of the mixed cyanides with excess of hydrochloric or sulphuric acid, whereby the nickel was precipitated as cobalticyanide of nickel, leaving a solution of pure cobalticyanide of potassium, has been found, both by himself and others, not to give per- fectly satisfactory results. The method by oxalic acid (p. 75.), and the precipitation of nickel from an ammoniacal solution of the two metals by potash (p. 76.) arc not sufficiently accu- rate for quantitative analysis. r. Claudet proposes to separate cobalt from nickel and other metals in the form of the ammonio-compound described on page 70., that compound being very insoluble, while cor- responding compounds of the other metals do not appear to be formed under the same circumstances. The separation of cobalt from nickel (also from zinc and the previously described metals) may likewise be effected by means of St. Evre's yellow compound, which is regarded by A. Stromeyer as a nitrite of cobaltic oxide and potash (p. 65.). The solution containing the mixed metals is diluted with water till about 300 parts of water are present to 1 part of protoxide of cobalt ; a somewhat concentrated solution of nitrite of potash J then added, and a sufficient quantity of acetic acid to redissolve any precipitated carbonates ; and the * Ann. Ch. Pharm. Ixxxvii. 128. t Ibid. xli. 291. + The nitrite of potash is prepared by fusing 1 part of nitre in contact with 2 parts of metallic lead, first at a low and then at a bright-red heat, ex- hausting the cooled, mass with water, precipitating a small quantity of lead by carbonic acid, and then by sulphide of ammonium, evaporating to dryness, and heating to the melting-point to decompose any hyposulphite of potash that may have been formed. ZINC. 81 solution left to stand for 12 to 24 hours in a covered vessel, then filtered and washed, first with acetate of potash, after- wards with alcohol. The precipitate contains all the cobalt in the form of the above-mentioned salts, and none of the other metals.* SECTION V. ZINC 32-52 ; Zn. or Eg. 406*6. The principal ores of zinc are calamine, or the carbonate, a pulverulent mineral generally of a reddish or flesh colour, and zinc -blende J a massive mineral of an adamantine lustre, and often black. The oxide, from the carbonate or from the calcined sulphide, is mixed with about ^ of its weight of carbonaceous matter, and heated to a low white heat in re- torts, or similar vessels of earthenware or iron. The zinc is then reduced and volatilised, and condenses in the colder part of the apparatus. In Silesia, the mixture of zinc-oxide and charcoal, or coke, is heated in muffles (Fig. 4.) 3 feet long and 18 inches high. Fig. 4. six of which are laid in one furnace (Fig. 5.), three side by side. The evolved mixture of carbonic oxide and zmc -vapour passes from the upper and fore part of the muffles M, through * A. Stromeyer, Ann. Ch. Pharrn. xcvi. p. 218. ; see also Liebig and Kopp'a Jaliresbericht, 1854, p. 357. VOL. II. G 82 ZINC. a knee-shaped channel b c d^ and the zinc condenses therein and drops down from the lower aperture d into the reservoirs t (Fig. 5.) placed beneath. Fig. 5. Fig. 6. Part of the zinc- vapour, and likewise some cadmium -vapour, escapes uncondensed, together with the carbonic oxide gas, and bums in the air, producing the substance called Silesian zinc-flowers. Silesia furnishes the greater part of the zinc used in the arts. In Belgium, the reduction is performed in earthenware tubes, laid side by side ; and tlie zinc as it condenses in the fore part of these tubes, is scraped out from time to time in the hquid state. In England, a number of cast- iron pots are arranged in a circle in the furnace (Fig. 6.). Through tlie bottom of each of these pots, there passes an iron tube / 1', which is con- tinued downwards through an aper- ture in the bottom of the furnace. The upper end of the tube is stopped with a plug of wood, which is cliarrcd during the operation, and l)ccomes sufficiently porous to allow ZINC. 83 the passage of the zinc-vapour, but at the same time prevents the solid matter from falling through. Each pot is fitted with a cover well luted with clay. The fire-place F, is in the middle. The distilled zinc condenses in the tubes //', and falls in drops into a receiver u, placed beneath. This process is called destillatio per descensum. Zinc may be purified by a second distillation in a porcelain retort ; but the first portions of that metal which come over should be rejected, as they generally contain cadmium and arsenic. Zinc is a white metal, with a shade of blue, capable of being polished and then assuming a bright metallic lustre. It is usually brittle, and its fracture exhibits a crystalline structure. But zinc, if pure, may be hammered into thin leaves, at the usual temperature ; and commercial zinc, which is impure and brittle at a low temperature, acquires the same malleability between 210° and 300°: it may then be laminated ; and the metal is now consumed in the form of sheet zinc for a variety of useful purposes. At 400° it again becomes brittle, and may be reduced to powder in a mortar of that temperature. The density of cast zinc is 6*862, but it may be increased by forging to 7*21. Its point of fusion is 773° (Daniell). At a red heat, zinc rises in vapour and takes fire in the air, burning with a white flame like that of phosphorus ; the white oxide produced is carried up mechanically in the air, although itself a fixed substance. Laminated zinc is a valuable substance, from its little disposi- tion to undergo oxidation. When exposed to air or placed in water, its surface becomes covered with a grey film of sub- oxide, which does not increase ; this film is better calculated to resist both the mechanical and chemical effects of other bodies than the metal itself, and preserves it. Zinc dissolves with facility in dilute hydrochloric, sulphuric and other hydrated acids, by substitution for hydrogen. In contact G 2 :84 ZINC. with iron, it protects the latter from oxidation in any saline fluid. Zinc appears to form three oxides, the suboxide above re- ferred to, the protoxide, and a peroxide, which last is produced when the hydrated protoxide is acted upon by a solution of peroxide of hydrogen ; but of these, the first and last have not been studied, and the protoxide is, therefore, the only well known oxide of zinc. Protoxide of zinc ; ZnO; 40'52 or 5066. — This oxide may be obtained, in the form of an anhydrous white powder, by the combustion of the metal in a stoneware crucible, or as a white hydrate, by precipitation from its salts by an alkali. It is of a yellow colour at high temperatures, but becomes colourless again on cooling. By the oxidation of zinc in air and water, without access of carbonic acid, a hydrate, 3ZnO -f HO, has been obtained in crystalline needles (Mitscherlich). Oxide of zinc combines with acids and forms salts, which are colourless, like those of magnesia. Caustic alkalies form with zinc-salts a white gelatinous precipitate of the hydrated oxide, soluble in excess of the alkali. Carbonate of potash or soda throws down white carbonate of zinc, insoluble in excess ; carbonate of ammonia, the same precipitate, soluble in excess. Ferrocyanide of potassium, and the alkaline phos- phates and arseniates, also foiTQ white precipitates. Zinc- salts containing a strong acid in excess, are not affected by hydrosulphuric acid, but give a white hydrated sulphide with alkaline sulphides. A solution of acetate of zinc is readily decomposed by hydrosulphuric acid. The native sulphide of zinc, or zinc-blende, ZnS, crystal- lises in octohedrons. Its colour is variable, being sometimes yellow, red, brown, or black. Chloride of zinc, ZnCl, is produced by the combustion of zinc in chlorine, and by dissolving the metal in hydrochloric acid. It is fusible at 212°, volatile at a red heat, and perhaps the most deliquescent of salts. Chloride of zinc-ammonium, SALTS OF ZINC. 85 NHgZn.Cl, is obtained, according to Ritthansen, in white prismatic crystals, when zinc and copper, or zinc and silver, are placed in contact in a solution of sal-ammoniac, or by the action of zinc on a solution of sal-ammoniac containing chloride of copper. Iodide of zinc is formed by digesting iodine, zinc, and water together, and resembles the chloride. The compound Znl.SNHg, or NH2(NH4)Zn.I, forms crystals belonging to the rhombic system (Rammelsberg) . The neutral carbonate of zinc forms the ore called calamine. When precipitated by an alkaline carbonate, the salts of zinc, like those of magnesia, yield the neutral car- bonate in combination with hydrated oxide, 2(ZnO.C02) + 3(ZnO.HO). The mineral substance, zinc-bloom, is of the same composition. Precipitated in the cold, the carbonate is ZnO.COg + 2(ZnO.HO), but is contaminated with sulphate of soda (Mitscherlich). Sulphate of zinc, White vitriol, ZnO.SOg + THO. — This salt is formed by the oxidation of the native sulphide at high temperatures, or by dissolving the metal in dilute sulphuric acid. It crystallises in colourless prismatic crystals, contain- ing 7 eq. of water, the form of which is a right rhombic prism. This, like all the other magnesian sulphates, gives up 6 eq. of its water at about 212°, while the seventh or constitutional equivalent requires a heat of 400° to expel it. The crystals are soluble in 24 times their weight of water, at the usual temperature, and fuse in their water of crystallisation when heated. The salt also crystallises above 86°, with 6 eq. of water, in oblique rhombic prisms (Mitscherlich). According to Kiihn, another hydrate is formed and precipitated as a white powder, containing 2 eq. of water, when a concentrated solution of sulphate of zinc is mixed with oil of vitriol. Sul- phate of zinc forms the usual double salt with sulphate of potash, ZnO.SOa + KO.SOg-l-eHO. The double sulphate of zinc and o 3 86 ZINC. soda contains 4 atoms of water, ZnO.S03 + NaO.S03 + 4HO. It is formed by a singular decomposition (I. 228.). "When a solution of the sulphate is mixed with a quantity of alkali less than suflficient for complete precipitation, a subsulphate of zinc precipitates, which, according to the analyses of several chemists, contains 4 eq. of oxide of zinc to 1 eq. of sulphuric acid, besides water. A concentrated solution of sulphate of zinc dissolves the preceding subsalt, and, when saturated, contains a compound of 1 eq. of acid and 2 eq. of base, ac- cording to Schindler, and docs not crystallise. From this solution, Schindler obtained the former insoluble subsalt with two different proportions of water, in long crystalline needles, containing lOHO, by spontaneous evaporation of the solution, and in brilliant crystalline plates containing 2 HO, which were deposited on boiling the solution. By diluting the same solution with a large quantity of water, he also ob- tained another subsalt, as a light bulky precipitate, which contained 1 eq. of acid, 8 eq. of oxide of zinc, and 2 eq. of water. The insoluble matter, which precipitates when sul- phate of zinc-ammonium (NH3Zn)O.S03 is thrown into water, is considered by Kane as a third subsulphate of zinc, containing 1 eq. of acid, 6 eq. of oxide of zinc, and 10 eq. of water. All these subsulphates afford neutral sulphate of zinc to water, after being heated to redness ; so that, whatever their constitution may be when hydrated, it is certaiidy different from what it is in their anhydrous condition. Nitrate of zinc, ZnO.NOg -1-6110, is very soluble in water, and moderately deliquescent. Phosphate of zinc, ZnOj.HO.POg 4- 2HO, is obtained in minute silvery plates, which are nearly insoluble, on mixing dilute solutions of phosphate of soda and sulphate of zinc. Silicate of zinc is foimd as a crystalline mineral, which has received the name of the electrical oxide of zinc, because it acquires, like the tourmalin, a high degree of electrical ESTIMATION OF ZINC. 87 polarity when heated. It contains water, and may be repre- sented by the formula 2(3ZnO.Si03) +3H0. The most important alloys of zinc are those with copper, which form the varieties of brass. Zinc also combines readily with iron, and is contaminated by that metal, when fused in an iron crucible. OTHER METALS. Zinc is precipitated from its solutions by carbonate of soda, which, when added in excess and boiled with the solu- tion, throws down carbonate of zinc. It is best, however^ to pour the zinc-solution into the hot solution of the alkaline carbonate, because, in that case, we may be sure of not form- ing a basic salt. If the zinc-solution contains ammoniacal salts, it must be boiled with a quantity of carbonate of soda sufficient to decompose those salts ; then evaporated to dry- ness ; the residue treated with a large quantity of water to dissolve out the soluble salts; and the carbonate of zinc collected on a filter and weU washed with hot water. The evaporation should be conducted as quickly as possible. The carbonate of zinc, when dried and ignited, yields oxide of zinc containing 80*26 per cent, of the metal. In separating zinc from other metals, it is often necessary to precipitate ' by sulphide of ammonium. If the solution is acid, it must be previously neutralised by ammonia. The precipitate must not be thrown on the filter immediately, but left to settle down completely, after which the clear liquid must first be passed through the filter, and then the preci- pitate thrown on it. If this precaution be neglected, the sulphide of zinc will stop up the pores of the filter. The precipitate is washed with water containing a little sulphide of ammonium ; then dissolved in hydrochloric acid ; the solution o 4 88 ZINC. boiled to drive off the hydrosulphuric acid; and the zinc precipitated by carbonate of soda as above. Zinc is separated from the alkalies and alkaline eartJis (baryta, strontia, and lime) by means of sulphide of am- monium. In the case of the alkaline earths, however, great care must be taken to prevent the ammoniacal liquid from absorbing carbonic acid from the air, as that would occasion a precipitation of the earth in the form of carbonate. For this purpose, the filtration must be effected as quickly as possible, and the liquid well protected from the air. The separation of zinc from baryta may also be effected by sul- phuric acid, and from lime by oxalate of ammonia. From magnesia^ zinc may be separated by sulphide of am- monium, a sufficient quantity of chloride of ammonium being previously added to prevent the precipitation of the magnesia. Or the separation may be effected by converting the zinc and magnesia into acetates, and precipitatmg the zinc as sulphide by hydrosulphuric acid. The separation of zinc from alumina and glucina may also be effected by converting the two bases into acetates and pre- cipitating the zinc by hydrosulphuric acid ; or hy dissolving in potash, and precipitating the zinc by hydrosulphuric acid ; but the former method is to be preferred. The conversion into acetates and precipitation by hydrosul- phuric acid likewise serves to separate zinc from zirconia, yttria, thorina, and manganese. The separation from man- ganese may also be effected by converting the two metals into chlorides, passing chlorine gas through the solution to convert the manganese into bioxide, and completing the pre- cipitation of the latter by carbonate of baryta. From iron, zinc may be separated by ammonia, or better by succinate of ammonia, the same precautions being used as in the separation of iron from manganese by the same method (p. 58.). The iron (in the state of sesquioxide) may also be precipitated by carbonate of lime or carbonate of baryta. CADMIUM. 89 From cobalt and nickel, zinc is separated "by dissolving the oxides of both metals in excess of acetic acid, and precipi- tating the zinc by hydrosulphuric acid. Nickel and cobalt are completely precipitated by hydrosulphuric acid from the neutral solutions of their acetates, but not when a consider- able excess of acetic acid is present. But in separating zinc from cobalt and nickel in this manner, a small quantity of the latter metals is generally precipitated with the zinc towards the end of the process, the precipitate then becoming greyish black. In that case it must be redissolved in hydrochloric acid, the chlorides converted into acetates, and the precipita- tion repeated. Another method of separation is to convert the metals into chlorides, and ignite the dry chlorides in a stream of hydrogen gas : the nickel or cobalt is then reduced to the metallic state, while the chloride of zinc remains un- altered, and may be dissolved out by water. (For the separa- tion of cobalt from zinc, see also p. 80.) In precipitating zinc from its acetic acid solution by hydro- sulphuric acid, it is necessary that the solution be quite free from inorganic acids, which would interfere with the precipitation. This may be effected either by precipitating the metals with carbonate of soda, washing the precipitate and dissolving it in acetic acid, or by boiling the solution with excess of sulphuric acid to drive off the inorganic acids (if vola- tile) and decomposing the sulphate with acetate of baryta. SECTION VI. CADMIUM. J^Jg. 65-74 or 696-77; Cd. This metal is frequently found in smaU quantity, associated with zinc, and derives the name cadmium, applied to it by Stromeyer, from cadmia fossilis, a denomination by which the 90 CADMIUM. common ore of zinc was formerly desi^ated. In the process of reducing ores of zinc, the cadmium which they contain comes over among the first products of distillation, owing to its greater volatility. It may be separated from zinc, in an acid solution, by hydrosulphuric acid, which throws down cadmium as a yellow sulphide. This sulphide dissolves in concentrated hydrochloric acid, affording the chloride of cadmium, from which the carbonate may be precipitated by an excess of car- bonate of ammonia. Carbonate of cadmium is converted by ignition into the oxide ; and the latter yields the metal when mixed with one-tenth of its weight of pounded coal, and dis- tilled in a glass or porcelain retort, at a low red heat. Cadmium is a white metal, like tin, very ductile and mal- leable. It fuses considerably under a red heat, and is nearly as volatile as mercury. The density of cadmium, cast in a mould, is 8*604, after being hammered, 8-6914. Cadmium may be dissolved in the more powerful acids, by substitution for hydrogen, with the aid of heat ; but nitric acid is its proper solvent. Oxide of cadmium, CdO; 6374 or 796'77.— The only known oxide of cadmium is obtained by the combustion of the metal, or by the ignition of its carbonate, as a powder of an orange colour, or as a white hydrate by precipitation from its salts by an alkali. Its density, in the anhydrous condition, is 8' 183 (Herapath). By igniting the nitrate, the oxide is obtained in microscopic octohedrons, which are dark bluish black by reflected, and dark brown with a tinge of violet by transmitted light (Schuler). This oxide is soluble in am- monia, but not in its carbonate (differing in the last property from zinc and copper) nor in the fixed alkalies. Its salts are white, and greatly resemble those of zinc. They are precipi- tated of a fine yellow colour by hydrosulphuric acid. Sulphide of cadmium is distinguished from sulphide of arsenic, which it resembles in colour, by being insoluble in potash and in sulphide of ammonium, and by sustaining a red SALTS OF CADMIUM. 91 heat without subliming. A crystalline sulphide is obtained by fusing 1 part of the precipitated sulphide with 5 parts of carbonate of potash and 5 parts of sulphur; or by passing dry hydrosulphuric acid gas over strongly-heated chloride of cadmium. Chloride of cadmium forms a crystalline hydrate, containing CdCl + 2H0. It also forms crystalline compounds with the chlorides of ammonium, potassium_, sodium, barium, stron- tium, calcium, magnesium, manganese, iron, cobalt, nickeb and copper. A solution of chloride of cadmium, mixed with excess of ammonia, yields by spontaneous evaporation the compound NH2CdCl (C. v. Hauer). The same ammoniacal solution treated with excess of hydro- chloric acid deposits crystalline crusts, which, according to Sclmler, contain CdCl.SNHg or NH(NHJ^.C1. Sul- phurous acid gas passed through the ammoniacal solution throws down a white crystalline precipitate containing CdO.SO24-NH4O.SO2 (Schiller). Iodide of cadmium forms a crystalline compound with water. Bromide of cadmium mixed in equivalent quantity with bromide of potassium in solution, yields crystals, first of 2CdBr.KBr + 2H0, afterwards of CdBr.2KBr (C.v. Hauer). Sulphate of cadmium forms efflorescent crystals contain- ing CdO.SOg + 4H0 (Stromeyer). According to Kiihn and Von Hauer, an acid solution of the salt concentrated at the boiling heat, deposits nodular crystals, which contain CdO.SOs + HO, and give oiF their water at 212°. The crys- tals obtained by evaporation at ordinary temperatures contain 3(CdO.S03)+ 8H0, give off nearly 3 eq. water at 212°, and the rest at a low red heat (C. v. Hauer). Sulphate of cad- mium forms with sulphate of potash the compound CdO.SOg + KO.SO3 + 6H0, and similar double salts with the sul- phates of soda and ammonia. Several definite alloys of cadmium have been formed. At a red heat, 100 parts of platinum retain 1 1 7'3 parts of cadmium. 92 COTPER. giving a compound = CdgPt : 100 parts of copper retain, at a red heat, 82'2 of cadmium, which approaches nearly to the pro- portion of CdCug. Cadmium forms an amalgam with mer- cury, which crystallises in octohedrons, and consists of 21 '74 parts of cadmium, and 78*26 of mercury. Cor dHgg. Estimation of cadmium, and method of separating it from the preceding metals. — Cadmium is best precipitated from its solutions by carbonate of soda ; it is thereby obtained as a carbonate, which by ignition yields the brown oxide containing 87*45 per cent, of the metal. From all the preceding metals cadmium may be separated by hydrosulphuric acid ; the sulphide of cadmium being then dissolved by nitric acid, and the metal precipitated by carbonate of soda as above. SECTION VII. COPPER. Eg. 31*66 or 395*7; Cu {aiprum). Copper, if not the most abundant, is certainly one of the most generally diffused of the metals. Its ores arc often accompanied by metallic copper, crystallised in cubes or octo- hedrons. Very large masses of native copper have been found near Lake Superior in North America, one of which w^eighed 2200 pounds ; in the Cliff mine, on the Eagle river, a mass has been found weighing 50 tons. Native copper is also found in considerable quantities in the decomposed basalt of Rheinbreitenbach, near Recsk in Hungaiy, and near Harlech, North Wales. The richest mines of this country are those in Cornwall and Anglesea. The common ore of this metal is copper pyrites, a compound of subsulphide of copper and ses- quisulphide of iron, or a sulphui'-salt, CuS -f FcgSg, but in COPPER. 93 which the two sulphides are also found in other proportions, and which often contains an admixture of the bisulphide of iron. Few metallurgic processes require more skill and atten- tion than the extraction of copper from this ore. The ore is first roasted at a high temperature in a reverberatory or flame- furnace (Fig. 7.) J whereby the sulphide of iron is in great part Fig. 7. converted into oxide^ while the sulphide of copper remains un- altered. The product of this operation is then strongly heated with silicious sand_, which combines with the oxide of iron, form- ing a fusible slag, and separates from the heavier copper com- pound. This operation is performed in a reverberatory furnace similar to the former, but of smaller dimensions. These pro- cesses are several times repeated, whereby the quantity of iron is continually diminished, and the sulphide of copper begins to decompose, giving it up its sulphur and absorbing oxygen ; the temperature is then raised high enough to reduce the resulting oxide by the aid of carbonaceous matter. The coarse copper thus obtained, containing from 80 to 90 per cent, of copper, is then melted under the action of a strong blast of air, to complete the expulsion of volatile matter, and the copper is partially oxidised. Lastly, to free it from oxide, which renders it brittle, it is again melted with its surface well covered with charcoal, and a pole of birchwood is thrust into it ; this causes considerable ebullition, the oxide being reduced 94 COPPER. by the carbonaceous matter, and carbonic acid escaping. Samples of the metal are taken out from time to time, and tested by the hammer, the process being discontinued as soon as the right degree of toughness is attained. If the poling is continued too long, the copper takes up carbon, and then becomes even more brittle than in its former oxidised state : it is then said to be over-poled, and must be again melted in contact with the air to bum away the carbon.* Copper is the only metal of a red colour. The crystals of native copper, and of that obtained in the humid way by pre- cipitation with iron, belong to the regidar system ; but the crystals which form in the cooling of melted copper were found by Seebeck to be rhomboidal, and to have a different place in the thermo-electric series from the other crystals. The density of copper when cast is about 8*83, and when laminated or forged 8*95 (Berzelius). It is less fusible than silver, but more so than gold, its point of fusion being 1996° (Daniell) . It is one of the most highly malleable metals, and in tenacity is inferior only to iron. It has much less affinity for oxygen than iron, and decomposes water only at a bright red heat, and to a small extent. In damp air, it acquires a green coating of subcarbonate of copper, and its oxidation is remarkably promoted by the presence of acids. The weaker acids, such as acetic, have no effect upon copper, unless with the concurrence of the oxygen of the air, when the copper rapidly combines with that oxygen, and a salt of the acid is formed. Copper scarcely decomposes the hydratcd acids by displacing hydrogen ; when boiled in hydrochloric acid, it dis- engages only the smallest traces of that gas. But hydrogen does not precipitate metallic copper from solution. Copper acts violently on nitric acid, occasioning its decomposition, with evolution of nitric oxide, and dissolving as a nitrate. * A minute account of the process of copper-smelting as practised at Swansea, lias lately been given by Mr. Napier, in the '* Philosophical Maga- zine," 1th Scries, vols. iv. and v. CUPROUS OXIDE. 95 Dioxide of copper, Red oxide of copper, Cuprous oxide, CugO j 71'32 or 891'4. — This degree of oxidation is better marked in copper than in any other metal of the magnesian class. The dioxide of copper is found native in octohedral crystals, and may be prepared artificially by heating to red- ness, in a covered crucible, a mixture of 5 parts of the black oxide of copper with 4 parts of copper-filings. It is a reddish-brown powder, which undergoes no change in the air. The surface of vessels of polished copper is often converted into red oxide, or bronzed, to enable them to resist the action of air and moisture : this is done by covering them with a paste of sesquioxide of iron, heating to a certain point, and after- wards cleaning them, to remove the oxide of iron ; or other- wise, by means of a boiling solution of acetate of copper. Dilute acids decompose red oxide of copper, dissolving the protoxide, and leaving metallic copper. Undiluted hydro- chloric acid dissolves the red oxide, without decomposition, or rather forms a corresponding chloride of copper, CU2CI, which is soluble in hydrochloric acid. The hydrated alkalies precipitate hydrated cuprous oxide from that solution, of a lively yellow colom", which changes rapidly in air from absorp- tion of oxygen. Cuprous oxide is also formed when copper is placed in a dilute solution of ammonia containing air, and is dissolved by the alkali. If the ammonia has been corked up in a bottle with copper for some time, the liquid is colourless ; but on pouring it out in a thin stream, it immediately becomes blue, by absorbing oxygen. The liquid may be again deprived of colour by returning it to the bottle, and closing it up, in con- tact with the metal. Cuprous oxide is also readily obtained by the reducing action of glucose (grape-sugar) on the prot- oxide or its salts. When a solution of 1 part of common sul- phate of copper and 1 part of glucose is mixed with a sufficient quantity of caustic potash or soda to redissolve the precipitate first formed, and the liquid gently warmed, cuprous oxide is 9G COPPER. abundantly precipitated in the form of a yellowish-red crystal- line powder. Cane-sngar produces the same effects, but more slowly, apparently because it must first be converted into glucose. Compounds have been obtained of cuprous-oxide with several acids, particularly with sulphurous acid, the sulphite forming a double salt with sulphite of potash, CU2O.SO2 + 2(KO.S02) (Muspratt) ; also with hyposulphurous, sulphuric, carbonic and acetic acids. When fused with vitreous matter, cuprous oxide gives a beautiful ruby-red glass; but it is difficult to prevent the cuprous oxide from absorbing oxygen, in which case the glass becomes green. Hydride of copper , Cuprous hydride, Cu^H. — When a solution of cupricsulphate and hypophosphorous acid is heated not above 158°, this compound is deposited as a yellow pre- cipitate, which soon turns red-brown. It gives off hydrogen when heated, takes fire in chlorine gas, and when treated with hydrochloric acid, is converted into dichloride of copper, with evolution of a double quantity of hydrogen, the acid in fact giving up its hydrogen as well as the copper-compound (Wurtz) : CuJI + HCl = Cu^Cl + HH. This action is very remarkable, inasmuch as metallic copper is scarcely acted upon by hydrochloric acid. It appears to arise from the two atoms of hydrogen contained in the acid and the hydride being in opposite states, the former being basylous or positive, the latter chlorous or negative, and so disposed to combine togetheVy just as the hydrogen of the hydrochloric acid combines under similar circumstances with the oxygen of the compound CU2O. The reduction of certain metallic oxides by peroxide of hydrogen affords another example of the same kind of action. Disulphide of copper, Cuprous sulphide, CU2S, forms the mineral copper -glance, and is also a constituent of copper CUPROUS SALTS. 97 pyrites. It is a powerful sulphur-base. Copper-filings, mixed with half their weight of sulphur, unite, when heated, with in- tense ignition, and form this disulphide. Bichloride of copper^ Cuprous chloride, CU2CI, may be pre- pared by heating copper-filings with twice their weight of corrosive sublimate. It was obtained by Mitscherlich in tetrahedrons, by dissolving in hydrochloric acid the dichloride of copper formed on mixing solutions of the protochlorides of copper and tin, and allowing the concentrated solution to cool. Dichloride of cojjper so prepared is white, insoluble in water, soluble in hydrochloric acid, but precipitated by dilution. It is dissolved by a boiling solution of chloride of potassium, and the resulting solution, if allowed to cool in a close vessel, yields large octohedral crystals of a double chloride : CU2CI.2KCI ; they are anhydrous. It is remarkable that the forms of this double salt, and of both its constituents, aU belong to the regular system.* When finely-divided metallic copper is boiled in a saturated solution of sal-ammoniac, ammonia is evolved and a white salt formed, which crystallises in rhombic dodecahedrons : it contains NH3.CU2CI, and may be regarded as a dichloride of copper and cuprammonium ^^ !ci. A solution of this salt exposed to the air yields blue crystals of the compound NH3.Cu2Ci + NH3CUCI+HO ; and the mother-liquor, after further exposure to the air, contains the salt NH3.CUCI + NH4CI, which at a lower temperature crystallises in large cubes (Ritthausen). Diniodide of copper, Cuprous iodide, CU2I, is a white in- soluble precipitate, obtained on mixing a solution of 1 part of sulphate of copper and 2-^ parts of protosulphate of iron, with a solution of iodide of potassium. Dicyanide of copper, Cuprous cyanide, CugCy. — Obtained as a white curdy precipitate on adding hydrocyanic acid or * Mitscherlich in Poggendorff 's Annalen, xlix. 401., 1840. VOL. II. H 98 COPPER. cyanide of potassium to a solution of dichloride of copper in hydrochloric acid, or to a solution of protochloride of copper mixed with sulphurous acid. It forms a colomiess solution with ammonia, and a yellow solution with strong hydrochloric acid, from which it is precipitated by potash. Dicyanide of copper unites with the cyanides of the alkali- and earth-metals, and with the cyanides of manganese, ii'on, zinc, cadmium, lead, tin, uranium, and silver, forming double salts, some of which have the composition MCy.Cu2Cy, others SMCy.Cu^Cy (the symbol M denoting a metal). CvprosO'Cujjric cyanide, CugCy . CuCy, is obtained as a green hydrate by adding hydrocyanic acid or cuproso-potassic cyanide, KCy.Cu2Cy, to sulphate of copper. It forms three compounds with ammonia, viz., NH3.Cu3Cy2.HO, obtained by adding cyanide of ammonium to a protosalt of copper, and the compounds 2NH3.Cu3Cy2 and 3NIl3.Cu3Cy2, formed by the action of ammonia on the first compound. Cuprous hyj)osiiIj)hite, CU2O.3S2O2 + 2H0, separates in microscopic needles, having a golden lustre, on adding a saturated solution of hyposulphite of soda to a concentrated solution of cupric sulphite, till a deep yeUow colour is pro- duced. It dissolves in aqueous sal-ammoniac, and the solu- tion deposits the compound CU2O.3S2O2 4- NHgCuCl + HO. (C. v. Hauer). Cuprous sulphite is said by some chemists to be obtained in a definite state by the action of sulphurous acid on cupric oxide ; but according to Rammelsbcrg and Pean de St. Gilles, it exists only in combination with cupric sulphite, forming the compound CU2O.SO2 -f CUO.SO2, which crystallises with 3 and 5 eq. of water, — and with the sulphites of the alkalies. By treating dichloride of copper with excess of sulphite of ammonia, prismatic crystals are formed containing CU2O.SO2 + 7(NH40.S02) + 10 Aq. ; and by saturating the solution of this salt with sulphurous acid, the salt CU2O.S2O2 + NH4O.SO3 is obtained. A concentrated solution of sulphite CUPRIC OXIDE. 99 of ammonia and cupric sulphate saturated with sulphurous acid gas, yields light green crystals containing fCu20.S02 + NH4O . SO2) + (CU2O . SO2 + CuO . SO2) + 5 aq. Corre- sponding double salts are formed by the sulphites of potash and soda, but they are very unstable. Protoxide of copper , Black oxide of copper j Cupric oxide, CuO; 495*7 or 39*66. — The base of the ordinary salts of copper, or cupric salts. It is formed by the oxidation of copper at a red heat, but is generally prepared by igniting the nitrate of copper. It is black like charcoal, and fuses at a high temperature. This oxide is remarkable for the facility with which it is reduced, at a low red heat, by hydrogen and carbon, which it converts into water and carbonic acid. It is this property which re- commends oxide of copper for the combustion of organic substances, in close vessels, by which their ultimate analysis is effected. Oxide of copper is a powerful base. Its salts, the cupric salts, are generally blue or green, when hydrated, but white when anhydrous. Although neutral in composition, they have a strong acid reaction. They are poisonous ; but their effect upon the animal system is counteracted in some degree by sugar. Liquid albumen forms insoluble compounds with these salts, and is an antidote to their poisonous action. Copper is separated in the metallic state from its salts by zinc, iron, lead, and the more oxidable metals, which are dissolved, and take the place of the former metal. Potash or soda added to the solution of a cupric salt, throws down at first a blue precipitate of hydrated cupric oxide, which, however, on agitation, takes up a portion of the unde- composed salt, and forms with it a green basic salt. An excess of the alkali throws down the hydrated oxide in bulky blue flakes, which, on boiling the mixture, collect together in the form of a black powder, consisting of the anhydrous oxide. This reaction is greatly modified by the presence of fixed or- H 2 loo COPPER. ganic substances, such as sugar, tartaric acid, &c. In a solu- tion of sulphate of copper, containing such substances in sufficient quantity, potash either produces no precipitate, or one Tvhich is quickly redissolved, forming a blue solution ; and from this solution, when boiled, the copper is sometimes wholly precipitated as red or yellow cuprous oxide, as when grape- sugar is present, — or partially, as with cane-sugar, or not at all, as with tartaric acid. Ammonia, added by degrees, and with constant agitation, to the solution of a cupric salt, first throws down a green basic salt, and afterwards the blue hydrate : an excess of ammonia dissolves the precipitate, forming a deep blue solution. A copper solution diluted so far as to be colourless, becomes distinctly blue on the addition of ammonia. The blue colour thus produced is still visible, according to Lassaigne, in a solution containing 1 part of copper in 100,000 parts of liquid. Carbonate of potash or soda throws down, with evolution of carbonic acid, a greenish blue preci- pitate of a basic carbonate of copper, which on boiling is converted into the black oxide. Carbonate of ammonia pro- duces the same precipitate, but when added in excess, dissolves it abundantly, forming a blue solution. Hydro- sulphuric acid and solutions of alkaline sulphides throw down a brownish black precipitate of protosulphide of copper, in- soluble in sulphide of potassium or sodium, slightly soluble in sulphide of ammonium. Ferrocyanide of potassium forms with cupric salts a deep chocolate -coloured precipitate of ferrocyanide of copper. To very dilute solutions it imparts a reddish colour, which is even more delicate in its indications than the ammonia reaction, being still visible in a solution containing 1 part of copper in 400,000 parts of liquid, according to Lassaigne, and in 1,000,000 parts, according to Sarzeau. Ferrocyanide of copper dissolves in aqueous ammonia, and reappears when the ammonia is evaporated. This reaction serves to detect extremely small quantities of copper, even when associated with other metals. Thus, if a solution CUPIUC SALTS. 101 containing copper and iron be treated with excess of ammonia, a few drops of ferrocyanide of potassium added, the liquid filtered, and the filtrate left to evaporate in a small white porcelain capsule*, ferrocyanide of copper will be left behind, exhibiting its characteristic red colour (Warington). Salts of copper impart a green colour to flame. The black oxide of copper dissolves by fusion in a vitreous flux, and produces a green glass. Any compound of copper fused with borax in the oxidising flame of the blowpipe forms a trans- parent glass, which is green while hot, but assumes a beautiful blue colour when cold. In the reducing flame, the glass becomes opaque, and covered on the surface with liver-coloured streaks of cuprous oxide, or metallic copper. This last reaction is somewhat difficult to obtain^ especially when the quantity of copper is small, but it may always be ensured by fusing a small piece of metallic tin in the bead. Copper salts mixed with carbonate of soda or cyanide of potassium, and heated on charcoal before the blowpipe, yield metallic copper. Thenard obtained a higher oxide of copper, CuOg, by the action of diluted bioxide of hydrogen on the hydrated prot. oxide of copper. Chloride of copper , cupric chloride, CuCl, is obtained by dissolving the black oxide in hydrochloric acid. Its solution is green when concentrated, but blue wheu more dilute, and the salt forms blue prismatic crystals, containing two atoms of water. It combines with chloride of potassium, and more readily with chloride of ammonium, forming the double salts KCl.CuCl + 2H0, and NH^Cl.CuCl + 2H0. Another chloride of copper and ammonium, containing NH4CI.2CUCI + 4H0, is obtained in fine bluish-green crys- tals, by mixing the solutions of 1 eq. sal-ammoniac and 2 eq. chloride of copper. Chloride of copper likewise combines with ammonia, form- ing the three following compounds: — a. SNHy.CuCl. This compound is obtained by saturating dry protochloride of H 3 102 COPPER. copper with ammoniacal gas: it forms a blue powder. — b. 2NH3. CuCl. Formed by passing ammoniacal gas through a hot satu- rated solution of protochloride of copper, till the precipitate first formed is completely redissolved. During this process, the liquid is kept almost boiling by the heat developed by the absorption of the gas; and the resulting solution yields, on cooling, small dark blue octohedrons and square prisms yni\\ four-sided summits. — c. NHg.CuCl. Obtained by heating a or b to 300°, or by saturating dry chloride of copper, at a high temperature, with ammoniacal gas. Forms a green powder. The compound c may also be regarded as chloride of citprammo- nium, NH3CU.CI, or hydrochlorate of cupr amine , NHjCu.HCl, the base being ammonium or ammonia in which 1 II is replaced by Cu. Similarly, b may be regarded as a basic hijdrochhrate of dicupr amine, NjHgCu.HCl, the base being formed by the union of two atoms of ammonia into one, and the substitution therein of ICu for IH. Lastly, a may be regarded as basic hydrochlorate of tricupramine, NgHgCu.HCl ; or again, a may be regarded as NHAm2Cu.Cl, and b as NH2AmCu.Cl. Carbonates of copper. — When a salt of copper is precipitated by an alkaline carbonate, a hydrated subcarbonate is produced containing 2 eq. of oxide of copper to 1 cq. carbonic acid. It is a pale blue bulky precipitate, which becomes denser and green when treated with boiling water. It is used as a pig- ment, and known as mineral green. The beautiful native green carbonate of copper, malachite, is of the same composi- tion, CUO.CO2 + CuO.HO. The finely crystallised blue copper ore is another subcarbonate. It may be represented as the neutral hydrated carbonate of copper, in combination with a similar carbonate of copper, in which the constitutional water is replaced by oxide of copper : CCuO.COa + HO. ^CuO.C02 + CuO. In the green carbonate, the constitutional water of the neutral CUPRTC SALTS. 103 carbonate of copper is replaced by hydrate of copper. The neutral carbonate of copper itself, of which the formula would be CuO.COg + HO, is unknown. According to Thomson*, the anhydrous subcarbonate 2CuO . CO2, occurs in the form of mysorinej which contains also ferric oxide and silica. Sulphate of copper, Cupric sulphate, Blue vitriol, CUO.SO3. HO + 4H0; 79-66 or 995*7 + 562-5.— This salt may be formed by dissolving copper in sulphuric acid diluted with half its bulk of water, with ebullition; the metal is then oxidated with formation of sulphurous acid. But the sul- phate of copper is more generally prepared, on the large scale, by the roasting and oxidation of sulphide of copper; or by dissolving in sulphuric acid the oxide formed by exposing sheets of metallic copper to air at a red heat. It forms large rhombo'idal crystals of a sapphire-blue colour, contain- ing 5 eq. of water, which lose their transparency in dry air : they are soluble in four times their weight of cold, and twice their weight of boiling water. Like the other soluble salts of copper, the sulphate has an acid reaction; it is used as an escharotic. The water in this salt may be reduced to 1 eq. at 212°; above 400° the salt is anhydrous and white. Although sulphate of copper does not crystallise alone with 7 HO, yet, when mixed with the sulphates of magnesia, zinc, nickel, and iron, it crystallises along with these isomorphous salts in the form of sulphate of iron. At a strong red heat it melts and loses acid. The anhydrous sulphate absorbs 2J eq. of ammonia, and forms a light powder of a deep blue colour (H Rose). When ammonia is added to a solution of sulphate of copper, an in- soluble subsulphate is first thrown down, which is redissolved as the addition of ammonia is continued, and the usual deep azure- blue ammoniacal solution formed. The ammoniacal sulphate may be obtained in beautiful indigo-blue crystals, by passing • Outlines of Mineralogy. n 4 lOl corpteii. a stream of ammoniacal gas into a saturated liot solution of tlie sulphate: it is CuO.S03.HO + 2^H3 (Berzelius). These crystals lose 1 eq. ammonia and 1 eq. water at 390° (Kane), and are converted into a green powder, CuO.SOg + NH3, or (NHgCuO) . SO3 ; by the cautious application of a heat not exceeding 500°, the whole of the ammonia may be got rid of, and sulphate of copper quite pure remains behind. Sul- phate of copper forms the usual double salts with sulphate of potash and with sulphate of ammonia. A saturated hot solution of the double sulphate of copper and potash allows a remarkable double subsalt to precipitate in crystalline grains, KO.S03 + 3(CuO.S03) 4- CuO.HO + 3HO. A corresponding seleniate is deposited, below the boiling point, and always in crystals. The ammoniacal and double salts of sulphate of copper may be represented thus : — Sulphate of copper (blue vitriol) . . . CuO.SOa.HO + 4II0 Sulpliate of copper and potash .... CuO.S03,(KO.S03) + 6H0 Ilydrated ammoniacal sulphate of copper CuO.S03,HO + 2NH3 Preceding salt dried at 300^ (NH3.CuO).S03 Rose's ammoniacal sulphate CUO.SO3+ (Nn3CuO)S03 + 4NIl3 Do. heated to 350° CUO.SO3 + (NH3CuO)S03 The hydrated ammoniacal sulphate may also be regarded as NH2(NHJCu.S04 j and Rosens ammoniacal sulphate as ^^^^- Uso,. NHlNHJ^Cu ) Several subsiilphates of copper have been formed. By digesting hydrated oxide of copper in a solution of sulphate of copper, a green powder is obtained, of which the constituents are, according to Berzelius, 3CUO.SO3 + 3H0. The bhiish- green precipitate which falls when ammonia is added to sul- phate of copper, or potash added in moderate quantity to the same salt, contains, according to Kane^s and Graham^s analyses 4CUO.SO3 -f 4H0. By a larger quantity of potash, Kane precipitated a clear grass-green subsulphate, containing CUPRIC SALTS. 105 SCaO.SOg-f 12H0. The last subsulpliate loses exactly half its water at 300^* ] Nitrate of copper, CuO.NOg 4- 3 HO, is formed by dissolving copper in nitric acid. It crystallises from a strong solution in blue prisms which contain 3 atoms of water, or in rhom- boidal plates which contain 6 atoms of water. This salt acts upon granulated tin, with nearly as much energy as hydrated nitric acid. A crystallised ammoniacal nitrate of copper is obtained by conducting a stream of ammoniacal gas into a saturated solution of nitrate of copper. It is anhydrous, and contains NOg.CuO + 2NH3 (Kane). It may be regarded as NH^lNHJCu.NOg. Subnitrate of copper, CuO.NOg + 3(CuO . HO), according to the analyses of Gerhardt, Gladstone-f, and Kuhnf, is a green powder, produced by the action of heat upon the neutral nitrate, at any temperature between 160° and 600° ; or by adding to that salt a quantity of alkali insufficient for complete precipitation. When oxide of copper is drenched with the most concentrated nitric acid (HO.NO5), ^^ ^^ ^^^^^ subsalt, singular as it may appear, which is formed, even when the acid is in great excess. Oxalate of copper and potash is obtained by dissolving oxide of copper in binoxalate of potash ; it crystallises with 2 and with 4 eq. of water. Acetates of copper. — The neutral acetate, CuO.(C^H303) + HO, or C^H^CuO* + HO, is obtained by dissolving oxide of copper in acetic acid. It forms fine crystals of a deep green colour, containing 1 eq. of water, which lose their trans- parency in air, and are soluble in 5 times their weight of boiling water. This salt, when it separates from an acid solution below 40°, also forms blue crystals containing 5 HO * Transactions of the Eoyal Irish Academy, vol. xix. p. 1. ; or Ann. Ch. Phys. t. Ixxii. p. 272. t Chem. Soc. Mem. iii. 480. % Arch. Pliarm. [2.], 1. 283. lOG COPPER. (Wohler). The green salt is found in commerce under the improper name of distilled verdigris. The acetates of copper and potash unite in single equivalents, and form a double salt in fine blue crystals, containing 8H0. Verdigris is a sub- acetate of copper, formed by placing plates of the metal in contact with the fermenting marc of the grape, or with cloth dipped in vinegar. The bluer species, which con- sists of minute crystalline plates, is a definite compound of 1 eq. acetic acid, 2 cq. oxide of copper, and 6 eq. of water, C^IIaCuO^.C^^O + 6H0. The ordinary green species is a mixture of the sesqui- and tribasic acetates of copper, with the preceding bibasic acetate. Water dissolves out from verdigris the sesquibasic acetate^ which presents itself on evaporating the solution, sometimes as an amorphous mass, and some- times in crystalline grains of a pale blue colour. The sesqui- basic acetate consists of 2 eq. of acetic acid, 3 eq. of oxide of copper, and G eq. of water; it loses 3 cq. of water at 212°. The tribasic acetate is the insoluble residue which remains after the lixiviation of verdigris. It is a clear green powder, which loses nothing at 212^. It contains 2 cq. of acetic acid, 6 eq. oxide of copper, and 3 cq. of water (Berzclius). Acetate of copper also combines with acetate of lime, and "with several other salts. The double acetate and arsenite of copper is a crystalline powder of a brilliant sea-green colour, which is used as a pigment, under the name of Schweinfurt green. It is obtained by mixing boiling solutions of equal parts of arsenious acid and neutral acetate of copper, adding to the mixture its own volume of cold water, and leaving the whole at rest for several days. It is a highly poisonous sul)- stance. From the analysis of Ehrmann, its formula is CJI,CuO^ + 3(CuO.As03). The most important alloys of copper are those which it forms with tin and zinc : 100 parts of copper with 5 tin (or 4 tin +1 zinc) form the bronze used for coin. ESTIMATION OP COPPER. 107 100 parts copper with 10 tin, form bronze and gun-metal. 100 parts copper with 20 to 25 tin, form bell-metal. 100 parts copper with 30 to 35 tin, form speculum-metal. A little arsenic is generally added to the last alloy, to increase its whiteness. The different varieties of brass are prepared, either by fusing together the two metals, copper and zinc, or by heating cop- per under a mixture of charcoal and calamine — an operation in which zinc is reduced and its vapour absorbed by the copper. Two or three parts of copper to one of zinc form common brass. The brass known as Muntz^s white metal, which re- sists the solvent action of sea-water much better than pure copper, and is, in consequence largely used for the sheathing of ships, consists of 60 parts copper to 40 parts zinc, and appeai-s to be the atomic compound Ca2Zn. Equal parts of copper and zinc, or four of the former and one of the latter, give an alloy of a higher coloui*, resembling gold, and on that account called similor. ESTIMATION OF COPPER, AND METHODS OP SEPARATING IT PROM OTHER METALS. Copper is best precipitated by caustic potash, which when added to a boUing solution of a cupric salt, throws down the protoxide of copper in the form of a heavy black powder. From tliis precipitate every trace of potash may be removed by washing with hot water ; and the washed precipitate may then be dried and ignited in a platinum or porcelain crucible. It must be weighed immediately after cooling, with the cover on the crucible, because it absorbs moisture rapidly firom the air. It contains 79*82 per cent, of copper (H. Rose). Copper is often precipitated from its solutions by hydro- sulphuric acid. In that case the precipitated sulphide must be washed as quickly as possible with water containing hy- drosulphuric acid, to prevent oxidation ; the precipitate mav 108 COPPER. then be dried, and the filter burnt with the precipitate on it, in a porcelain basin ; after which the precipitate is treated with concentrated nitric acid, which dissolves it, with separa- tion of sulphur, and the copper precipitated from the filtered solution by potash as above. The chief precaution to be attended to in this process is to wash the precipitated sulphide quickly, and to preserve it as completely as possible from contact with the air; otherwise the sulphide becomes par- tially oxidised and converted into sulphate, which being soluble, runs through the filter ; when this takes place, the filtrate becomes brown, because the copper thus carried through, is again precipitated by hydrosulphuric acid. Volumetric methods. — Copper may be volumetrically deter- mined by means of a solution of permanganate of potash, by a process founded on that adopted by Margueritte for the deter- mination of iron (p. 56.). The copper compound having been weighed and dissolved in acid, is mixed in a porcelain basin, with neutral tartrate of potash and excess of caustic potash, and then heated with a quantity of milk-sugar, or honey, sufficient to precipitate all the copper as cuprous oxide, the completion of the precipitation being indicated by the brown colour which the liquid then acquires. The precipitated cuprous oxide is then filtered, washed with hot water, and gently heated, together with the filter, with a mixture of pure scsquichloride of iron and dilute hydrochloric acid. It is thereby dissolved in the form of protochloride of copper, the scsquichloride of iron being at the same time reduced to protocldoride : CU2O + Fe^Clg + HCl = 2CuCH- 2reCl + HO. In the filtered liquid, diluted to a convenient strength and heated to about 86°, the quantity of iron in the state of proto- chloride is determined by a graduated solution of permanganate of potash in the manner already described (p. 56.), and thence the equivalent quantity of copper is readily determined. The presence of lead, zinc, bismuth, manganese, or iron, in the ESTIMATION OF COPPER. 109 alkaline solution does not interfere with the process ; silver or mercury must be separated before the precipitation of the cuprous oxide. Another method, which appears to give very exact results, is to treat the copper-solution with iodide of potassium, whereby diniodide of copper is precipitated and iodine set free : 2(CuO.N05) + 2KI = CU2I 4- I + 2(KO.N05), and remove the free iodine by means of a standard solution of hyposulphite of soda, whereby iodide of sodium and tetrathio- nate of soda are produced : 2(NaO.S202) + I = Nal + KaCS^Og. The copper- compound, if solid, an alloy for example, is dissolved in nitric acid j carbonate of soda added till a slight precipitate is formed; and this precipitate redissolved in acetic acid (free nitric acid would vitiate the result by decomposing the iodide of potassium) . A quantity of iodide of potassium is next added, equal to at least six times the weight of the copper to be determined, and then the standard solution of hyposulphite of soda, in sufficient quantity to remove the greater part of the free iodine, which point will be indicated by the colour of the liquid changing from brown to yellow. Lastly, a clear solution of starch is added, and the addition of the hyposulphite of soda cautiously continued till the blue colour of the iodide of starch is completely destroyed. The solution of hyposulphite of soda is graduated by dissolving a known weight of pui-e electrotype copper in nitric acid, and proceeding as above. If the copper-compound contains a large quantity of lead or iron, these metals must be removed before commencing the determination, because the yellow colour of the iodide of lead and the red of the acetate of iron might interfere with the result (E. O. Brown).* * In a paper read before the Cliemical Society, Nor 17th, 1856, and to be Published in the 10th Yolumc of the Society's Journal. 110 COPPER. Pelouze's method, which consists in treating the copper solution with excess of ammonia, and precipitating the copper as oxysulphide, CuO.SCuS, by adding a graduated solution of sulphide of sodium tiU the blue colour is completely destroyed, appears, from Mr. Brown's experiments, to be liable to uncertainty from two causes : first, because the oxysulphide of copper reduces a portion of the protoxide of copper to dioxide, thereby rendering the solution colourless before the precipitation is complete ; and secondly, because a portion of the sulphide of sodium is oxidised and converted into hyposul- phite of soda. Copper is separated from all the preceding metals, except cadmium, by means of hydrosulphuric acid, the solution being preWously acidulated with hydrochloric or sulphuric acid. When zinc, nickel, or cobalt is present, a considerable excess of acid must be added, otherwise a portion of these metals will be precipitated together with the copper. From cadmium^ copper may be separated by carbonate of ammonia, which dissolves the copper and leaves the cadmium. The deposition of the cadmium is not complete till the liquid has been exposed for some time to the air. The separation is, however, better effected by adding to the solution of the two metals a quantity of cyanide of potassium, sufficient to rc- dissolve the precipitate first formed, and then passing hydro- sulphuric acid through the solution. Sulphide of cadium is then precipitated, and on driving off the excess of hydrosulphuric acid by heat, and adding more cyanide of potassium, the sulphide of copper remains completely dis- solved. The copper may be precipitated as sulphide by mixing the filtrate with hydrochloric acid : but it is better to boil the filtrate with aqua-regia, till all the hydrocyanic acid is expelled, and then precipitate the copper by potash (Haidlen and Fresenius). LEAD. Ill SECTION VIII. LEAD. Eq, 103-56 or 1294-5; Pb [jMmbum). Lead was one of tlie earliest known of the metals. A con- siderable number of its compounds are found in nature,, but the sulphide, or galena, is the only one which is important as an ore of lead. The reduction of the metal is effected by heating the sulphide with exposure to air (or roasting), by which much of the sulphur is burned and escapes as sulphu- rous acid, and a fusible mixture of oxide of lead and sulphate of lead is produced. A fresh portion of the ore is added, which reacts upon the oxide of lead, the sulphur and oxygen forming sulphurous acid, and the lead of both oxide and sulphide being consequently reduced. Lime also is added, which de- composes the sulphate of lead, and exposes the oxide to be reduced by the fuel or by sulphide. Lead has a bluish grey colour and strong metallic lustre, is very malleable, and so soft, when it has not been cooled rapidly, as to produce a metallic streak upon paper. Its density is 11*445, and is not increased by hammering. Its tenacity is less than that of any other ductile metal. The melting point of lead is 612° ; on solidifying, this metal shrinks con- siderably, so that bullets cast in a mould are never quite round. Lead, like most other metals, assumes the octohedral form on crystallising. Lead is one of the less oxidable metals, at least when massive ; its surface soon tarnishes, and is covered with a grey pellicle, which appears to defend the metal from further change. Rain or soft water cannot be preserved with safety in leaden cisterns, owing to the rapid formation of a white hydratcd oxide at the line where the metal is exposed 112 LEAD. to both air and water ; the oxide formed is soluble in pure water, and highly poisonous. But a small quantity of car- bonic acid, which spring and well ^yater usually contain, arrests the corrosion of the lead, by converting the oxide of lead into an insoluble salt, and prevents the contamination of the water.* Lead is not directly attacked by hydrochloric and sulphuric acids, at the usual temperature, but they favour its union with oxygen from the air. Its best solvent is nitric acid. Besides a protoxide, PbO, which is a powerful base, lead forms a suboxide Pb20, and a bioxide PbO^, wliich do not combine with acids. Suboxide of lead, Pb20, was discovered by Dulong, and is best obtained by heating the oxalate of lead to low redness in a small retort. It is dark grey, almost black, and pulverulent, and is not affected by metallic mercury. According to tlie analysis of Boussingault, it contains 1 eq. of oxygen to 2 eq. of lead. The grey pellicle which forms upon lead exposed to the air is, according to Berzelius, the same suboxide. Protoxide of lead, PbO, 111*56 or 1394*5. — When a stream of air is thrown upon the surface of melted lead, the metal is rapidly converted into the protoxide, of a sulphur-yellow colour. The oxidated skimmings of the metal are, in this condition, termed massicot, and were at one time used as a yellow pigment. This preparation is fused at a bright red heat, and the oxide is thus separated from some metallic lead, with which it is intermixed in massicot. The fused oxide, on solidifying, forms a brick-red mass, which divides easily into crystalline scales, tough and not easily pulverised ; they form litharge. The protoxide of lead can be obtained distinctly crystallised by various processes, but always presents itself in the same form, an octohedron with a rhombic base (Mitscherlich). By igniting the subnitrate of lead, the prot- oxide is obtained very pure, and of a rich lemon-yellow colour. Its density after fusion is 9*4214. * Dr. Cliristison's Treatise on Poisons. PROTOXIDE OF LEAD. 113 When the acetate^ or any other salt of lead, is precipitated by potash, the protoxide falls as a white hydrate, which may be dried at 212'' without decomposition. It contains 3^ per cent, water, and is, therefore, the hydrate 2PbO . HO (Mitscherlich). Oxide of lead likewise crystallises anhydrous, from solution, at the usual temperature, when precipitated under such circumstances that it cannot find water to com- bine with. This oxide dissolves in above 12,000 times its weiglit of distilled water, which acquires thereby an alkaline reaction, but not in water containing any saline matter. It is soluble in potash or soda ; and the solutions, when evapo- rated, yield small crystals of an alkaline compound. A com- pound of lime and oxide of lead is obtained in needles, when hydrate of lime and that oxide are heated together, and the solution allowed to evaporate with exclusion of air. This solution has been employed to dye the hair black. Oxide of lead combines readily with the earths and metallic oxides by fusion, and when added to the materials of glass, imparts bril- liancy to it and increased fusibility. Oxide of lead is a powerful base, resembling baryta and strontia, and affords a class of salts which often agree in form and in general properties with the salts of these earths. Its carbonate occurs in plumbocalcite, in the form of carbonate of lime, an isomorphism by which the protoxide of lead is connected with the magnesian oxides. All its soluble salts are poisonous, although no salt of lead, with the exception of the insoluble carbonate, is highly so (Dr. A. T. Thomson). In a case of accidental poisoning by the carbonate, acetic acid proved a sufficient antidote. Caustic alkalies precipitate lead from its solutions as a white hydrate, soluble in potash and soda, insoluble in am- • monia. Alkaline cirhonates throw down a white precipitate of carbonate of lead, insoluble in excess of the reagent. Hy- drochloric acid and soluble chlorides produce in moderately strong lead-solutions, a white crystalline precipitate of chloride VOL. ir. 1 114 LEAP. of lead, easily soluble in potash, insoluble in ammonia, soluble in a considerable quantity of Avater ; in dilute solutions {e. y. in a solution of 1 part of nitrate of lead in 100 parts of water) no precipitate is formed. Sulphuric acid and soluble sulphates throw down, even from very dilute solutions, a white, pul- verulent precipitate of sulphate of lead, easily soluble in potash, soluble also, though slowly, in hydrochloric and nitric acid ; but by adding a considerable excess of sulphuric acid, lead may be completely precipitated even from solutions con- taining hydrochloric or nitric acid. According to Lassaigne, 1 part of oxide of lead (in the form of nitrate) dissolved in 25,000 parts of water, gives an opalescence with sulphate of soda, after a quarter of an hour. Hydrosulphuric acid and alkaline sulphides produce a black precipitate of sulphide of lead, insoluble in sulphide of ammonium. In very dilute solutions, cnly a brown colouring is produced, the limit of the reaction being attained, according to Lassaigne, with 1 part of oxide of lead (in the form of nitrate) dissolved in 350,(){)() parts of water. If the solution of the lead-salt contains free hydrochloric acid, the precipitate is red or yellow, and a large excess of hydrochloric acid prevents it altogether. Iodide of potassium produces a bright yellow precipitate of iodide of lead, which dissolves in boiling water and separates again on cooling in crystalline spangles, exhibiting a beautiful play of colours. Chromate and bichromate of potash throw down yellow chromate of lead, easily soluble in caustic potash. The limit of this reaction is attained with 1 part of oxide of lead (in the form of nitrate) dissolved in 70,000 parts of water (Harting). Iron and zinc throw down metallic lead. If a mass of zinc be suspended in a solution, made by dis- solving one ounce of acetate of lead in two pounds of distilled water, the lead is precipitated in beautiful crystalline plates, which are deposited not only in metallic contact with the zinc, but extend from it to a considerable distance in the liquid, forming what is called the lead-tree. Lead-salts, mixed with PROTOXIDE OF LEAD. 115 carbonate of soda or cyanide of potassium, and ignited on cliarcoal before the blow-pipe, yield a malleable button of lead. The oxides of lead are reduced by simply heating them with the blowpipe flame on charcoal. Sesquioxide of lead, Pb203. — Hypochlorite of soda throws down from lead-salts a reddish yellow mixture of sesquioxide and chloride of lead. The sesquioxide may be obtained free from chloride by supersaturating a solution of nitrate of lead with potash, in quantity sufficient to redissolve the precipitated hydrate, and then treating it with hypochlorite of soda. The sesquioxide is converted by acids into bioxide and an ordinary salt of lead (Winkelblech). Bioxide or peroxide of lead, Pb02, may be obtained in the same manner as the peroxides of cobalt and nickel, by ex- posing the protoxide suspended in water to a stream of chlorine ; also by fusing protoxide of lead with chlorate of potash at a temperature short of redness ; or by digesting the following intermediate oxide, minium, in diluted nitric acid, which dissolves the protoxide of lead, decanting off the nitrate of lead, and washing the powder which remains with boiling water. "VVohler precipitates a solution of 4 parts of acetate of lead with a solution of 3 parts or rather more of crystallised carbonate of soda, and passes chlorine gas through the result- ing thin pulpy mass, till the whole of the carbonate of lead is converted into brown bioxide, amounting to 2i parts, which may then be washed. No chloride of lead is formed in this reaction, the whole of the chlorine combining with the sodium, while acetic and carbonic acid are set free. Bioxide of lead is of a dark earthy-brown colour. It loses half its oxygen by ignition; absorbs sulphurous acid with great avidity, and becomes sulphate of lead; and affords chlorine when digested in hydrochloric acid. Minium or red lead is formed by heating massicot or pro- toxide of lead, which has not been fused, to incipient redness in a flat furnace, of a particular construction, and directing a I 2 116 LEAD. current of air upon its surface. Oxygen is absorbed, and an oxide formed of a fine red colour, with a shade of yellow. It is not constant in composition. The proportion of oxygen, when the absorption is least considerable, approaches that of a compound containing 3PbO.Pb02; and such was the com- position of a crystallised compound of a fine red colour, formed })y accident in a minium furnace, and analysed by Houton- Labillardiere. But when the absorption is favoured by time and most considerable, it approaches but never exceeds 2*4 per cent, of the original weight of the protoxide. This re- sult agrees with the formula Pb304, and accordingly minium may be regarded as a compound of protoxide and ])ioxidc of lead 2PbO.Pb02, or of protoxide and sesquioxide PbO.Pb203. A sample of minium analysed by Longchamps contained SPbO.PbOg. The finest minium is obtained by calcining oxide of lead from the carbonate, at about G00°. Minium is not altered by being heated in a solution of acetate of lead, which is capable of dissolving free protoxide of lead. AY hen heated to redness, it loses oxygen, and leaves the protoxide. It does not combine with acids, but is resolved by a strong acid into bioxide of lead and protoxide, the latter combining with the acid. When minium is treated with concentrated acetic acid, it first becomes white, and then dissolves entirely in a new quantity of acid without colouring it. But the solution gradually decomposes, and bioxide of lead separates from it of a blackish- brown colour (Berzelius). Protosiilphide of lead, PbS, is thrown down from salts of lead, by hydrosulphui'ic acid, as a black precipitate, which is insoluble in diluted acids or in alkalies. It forms also the ore galena, which crystallises in the cube and other forms of the regular system ; its density is 7'585. Sulphide of lead is decomposed easily by nitric acid, and converted into nitrate and sulphate of lead, with separation of a little sulphur. The more concentrated the nitric acid, the greater is the quantity of sulphate produced Recently precipitated sulphide of lead SULPHIDE Of LEAD. 117 may be completely dissolved in the form of nitrate by boiling with dilute nitric acid. Concentrated and boiling hydro- chloric acid dissolves sulphide of lead, with disengagement of hydrosulphuric acid gas. Galena may be united by fusion with more lead, and gives the subsulphides Pb4S, and PbgS. When a solution of persulphide of potassium is added to a salt of lead, a blood-red precipitate appears, which is a per- sulphide of lead, but is almost immediately changed into the black protosulphide of lead and free sulphur. Chloride of lead, PbCl, 139*06 or 1738-25. — Lead dissolves slowly in hydrochloric acid, by substitution for hydrogen, forming the chloride of lead, but only when assisted by the action of the air. The same compound is obtained by digest- ing oxide of lead in hydrochloric acid, and also falls as a white precipitate, when a salt of lead is added to any soluble chloride. The chloride of lead is soluble in 135 times its weight of cold water, and more so in hot water, from which it crystallises on cooling in long flattened acicular crystals, which are anhydrous. It is very fusible, and may be sublimed at a higher temperature Oxy chloride of lead. — Chloride of lead combines in five different proportions with the protoxide, forming the follow- ing compounds : — a. 3PbCl.PbO. Four parts of chloride of lead ignited with 1 part of litharge yield a fused, laminar, pearl-grey mixture, which, when triturated with water, swells up to a bulky mass having the above composition (Vauquelin). The same substance is obtained by Mr. Pattinson, by decom- posing carbonate of lead with lime-water, and used as a white pigment. — b. PbCl.PbO. Formed by igniting chloride of lead in contact with air till it no longer fumes, or by fusing chlor- ide and carbonate of lead together. Carbonic acid is then set free, and a compound formed which is of a deep yellow colour while fused, but as it cools assumes a lemon-yellow colour, and becomes nacreous and crystalline (Dobereiner). — c. PbC1.2PbO. This compound forms the mineral Mendi^nte, I 3 118 LEAD. found at Mendip,in Somersetshire, where it occui's in yellowish- wliite, right rhombic prisms, which are harder than gypsum, translucent, and have an adamantine lustre (Berzelius). It also occurs, and in a state of greater purity, at Brilon, near Stadtbergen, in Westphalia ; the crystals there found are white, translucent, and have a mother-of-pearl lustre on the cleavage surfaces.* — d. PbCl.SPbO. ' Obtained by fusing 1 eq. chlor- ide of lead with 3 eq. of the protoxide ; also in the hydrated state, PbC1.3PbO + HO or 4PbO.HCl, by decomposing chlor- ide of lead with ammonia; by precipitating subacetate of lead with common salt ; and by decomposing a solution of common salt with protoxide of lead. The hydrate is a white flocculent mass, and when fused yields the anhydrous com- pound, which is a greenish yellow laminated mass, forming a yellow powder. — e. PbC1.5PbO. Obtained by fusing 1 eq. chloride of lead with 5 cq. of the protoxide. Orange-yellow substance, yielding a deep yellow powder. — /. PbC1.7PbO, is produced on fusing by heat a mixture of 10 parts of pure oxide of lead and 1 part of pui'e sal-ammoniac, a portion of the lead being at the same time reduced. The surbasic chloride when fused affords cubic crystals on cooling slowly. It forms in that state a beautiful yellow pigment, known as Turner's yellow in this country, and Cassel yellow in Ger- many. It was prepared in England by digesting litharge with half its weight of common salt, a j)ortion of which is converted into caustic soda, and afterwards washing . and fusing the oxychloride formed. But it is sufficient to use 1 part of salt to 7 parts of oxide of lead in this decomposition. Bichloride of lead , PbClj. — Bioxide of lead dissolves, with- out evolution of gas, in cold dilute hydrochloric acid, form- ing a rose-coloured liquid, from which alkalies throw down the bioxide in its original state. The rose-coloured acid solution, evaporated in vacuo over strong potash-ley, yields crystals « Khodius, Ann. Cb. Pharra. Ixii. 373. CARBONATE OF LEAD. 119 of chloride of lead PbCl, togtlier with crystals of a different character, which appear to consist of PbClg (Rivot, Beudant, and Daguin). Bromide of lead, PbBr, is much less soluble in water than the chloride; hence, in a liquid containing hydrochloric and hydrobromic acids, if the bromine be precipitated by acetate of lead, the filtered liquid will still contain chlorine, which may then be detected by adding nitrate of silver (H. Rose). Iodide of lead, Pbl, 229*92 or 2874. — Appears as a beautiful lemon-yellow powder, when iodide of potassium is added to a salt of lead. It is soluble in 194 parts of boiling water, and in 1235 parts of water at the usual temperature, and may b^ obtained from solution in brilliant hexagonal scales of a golden- yellow colour. A compound of a paler yellow, which appears in dilute solutions and when the salt of lead is in excess, is a basic iodide. M. Denot finds three oxy-iodides of lead, con- taining 1 eq. of iodide of lead to 1 eq., 2 eq., and 5 eq. of oxide of lead, and always 1 eq. of water, which last they do not lose below a temperature of about 400°. Neutral iodide of lead, Pbl, is decomposed by metallic chlorides, yielding, when the iodide is in excess, compounds which may be regarded as iodide of lead, in which part of the iodine is replaced by chlorine. Sesquichloride of iron and protochloride of copper separate free iodine (A. Engelhardt). Cyanide of lead, PbCy, is a white insoluble powder, obtained by precipitation. Carbonate of lead, ceruse, white lead; PbO.C02; 133*56 or 1669*5. — Occurs in nature well crystallised, in the form of carbonate of baryta. It is precipitated as a white powder, of which the grains, although very minute, are crystalline, when an alkaline carbonate is added to the acetate or nitrate of lead. The precipitate is anhydrous. When oxide of lead is left covered with water in an open vessel, it absorbs car- bonic acid, and becomes white, forming the subcarbonate PbO.COa+PbO.HO. I 4 120 LEAD. Carbonate of lead is invaluable as a white pij^mcnt, from its great opacity, which gives it that property called body by painters, and enables it to cover well. As precipitated by an alkaline carbonate, it is deficient in body, owing to the transparency of the crystalline grains composing the precipi- tate. It is also a neutral carbonate, as thus prepared, and differs in composition from the ceruse of commerce, which Mulder finds always to contain hydrated oxide of lead in combination with the carbonate of lead. The result of Mulder's analyses of numerous specimens of white lead, is, that there are three varieties of that substance, the composi- tion of which is expressed by the three following formuUe : — 2(PbO.C02) + PbO.HO; 5iPbO.C02)+3(PbO.HO); and 3(PbO.C02)-}-PbO.HO. Mr. J. A. Phillips has also examined several specimens of white lead prepared by tlie Dutch process. Four samples gave by analysis the formula, 2iPbO.C02) + PbO.HO; one gave 3(PbO.C02) + PbO.IIO; another, SlPbO.COj) + PbO.HO.* Dr. T. Richardson also found that varieties of white lead contain a portion of oxide of lead, in addition to the carbonate, and so far confirms the conclusions of Mulder. In the old or Dutch mode of preparing white lead, which is still extensively practised, thin sheets of the metal arc placed over gallipots containing weak acetic acid (water with about 2i per cent, dry acid), themselves imbedded in fermenting tan, the temperature of which varies from 1 10° to 150°. The action is often very rapid, and the metal disappears in a few weeks to the centre of the sheet. In this process, from 2 to 2\ tons of lead (4480 to 5600 pounds) are converted into carbonate, by a quantity of vinegar which does not contain more than the small quantity of 50 pounds of dry acetic acid. Hence the metal is certainly neither oxidised nor carbonated in this process, at the expense of the acetic acid. The oxygen * Chem. Soc. Qu Vi. iv. p. 165. SALTS OF LEAD. 121 must be derived from the air, and the carbonic acid from the fermenting tan. In the newer process, litharge, without any preparation, is mixed with water and about 1 per cent, of acetate of lead, and carbonic acid gas passed over it ; the oxide of lead is rapidly converted into excellent ceruse. There can be little doubt that all the oxide of lead is successively dis- solved by the acetate, and presented to the carbonic acid as a soluble subacetate ; a compound which, it is known, absorbs carbonic acid with the greatest avidity, and allows its excess of oxide to precipitate as carbonate of lead. The new process supplies likewise the theory of the old one, the function of the acetic acid being manifestly the same in both processes. Nitrate of lead has been substituted for the acetate, with other things the same as in the last process. Sulphate of lead ; PbO, SO3; 151-56 or 1894-5. — This salt is precipitated when sulphuric acid or a soluble sulphate is added to a solution of acetate or nitrate of lead, as a white, dense, insoluble precipitate, which appears by the microscope to be composed of minute crystals. It is also formed by the action of strong nitric acid on sulphide of lead. Sulphate of lead contains in 100 parts, 26'44 sulphuric acid and 73-56 oxide of lead, and may be exposed to a red heat without de- composition. Dr. Richardson finds that this salt acquires considerable opacity, and may be substituted for ceruse, when prepared in a mode analogous to the new process for that substance ; namely, by supplying sulphuric acid, in a gradual manner, to a thick mixture of litharge and water containing a small proportion of acetate of lead. In this manner the sulphate of lead may be obtained united with any desirable excess of oxide of lead. Nitrate of lead ; PbO.NOs; 165-56 or 2069-5. — Obtained by dissolving litharge, at the boiling point, in slightly diluted nitric acid, which should be free from hydrochloric and sul- phuric acids. The neutral nitrate crystallises in large octo- hedrons, with the secondary faces of the cube, sometimes 122 LEAD. transparent, although generally white and opaque. The crystals are anhydrous ; they are soluble in 7^ times their weight oi cold, and in a much smaller quantity of hot water. Nitrate of lead is decomposed by an incipient red heat, yielding a mixture of oxygen gas and peroxide of nitrogen (which is pre- pared in this way), and leaving the yellow oxide of lead. When a small quantity of ammonia is added to nitrate of lead, or w^hen a dilute solution of the neutral salt is boiled with oxide of lead in fine powder, a soluble bibasic nitrate of lead is formed PbO.NOg + PbO. It crystallises during evaporation in fine scales, or in little opaque grains, which are anhydrous. The granular crystals decrepitate when heated, with extraor- dinary force. The tribasic nitrate of lead precipitates when ammonia is added in very slight excess to a solution of nitrate of lead. Its constituents are 2(3PbO.N05)4-3HO (Berzelius). It is a white powder, which is soluble to a small extent in pure water. When nitrate of lead is digested with a considerable excess of ammonia, the decomposition stops at the point at which 6 eq. of oxide of lead arc combined with 1 eq. of nitric acid. The sexbasic nitrate of lead contains 2(6PbO.N05)+ 3H0 (Berzelius). Nitrites of lead. — When a solution of 100 parts of nitrate of lead is boiled with 78 parts of metallic lead in thin turn- ings, the lead is dissolved, and a little nitric oxide is evolved, in consequence of a partial decomposition of nitrous acid previously formed. The solution is alkaline and yellow ; and gives, on cooling, brilliant crystalline plates of a golden yellow colour, which consist of the bibasic nitrite of leady 2PbO.N03. By dissolving 100 parts of this salt in water at 107° (75° C), and then mixing with the solution 35 parts of oil of vitriol, previously diluted with four times its weight of water, one half of the oxide of lead is precipitated as sulphate of lead, and a solution is obtained of a deep yellow colour, from which the neutral nitrite of lead, PbO.NOg + HO, crystallises. This salt gives yellow crystals, resembling the nitrate in form. Its SALTS or LEAD. l;^3 solution absorbs oxygen from the air, and, like all the nitrites, gives off nitric oxide at 176° (80° C), while a subnitrite of lead precipitates. Berzelius, to whom we are indebted for the preceding facts, also formed a quadribasic nitrite of lead, con- taining N03.4PbO + HO, by boiling 1 part of nitrate of lead, and 1 \ parts or more of metallic lead, in a long-necked flask for 12 hours, then filtering and leaving the solution to crys- tallise by cooling : it thus yields pale, flesh-coloured, silky needles, or, if rapidly cooled, a white powder. The nitrites of lead have also been examined by other chemists, who have obtained results differing from those of Berzelius. Thus, Peligot and others found that Berzelius^s bibasic nitrite contains the elements of 2 eq. of oxide of lead, 1 eq. of hyponitric acid, NO4, and 1 eq. of water. Gerhardt therefore regards it as a compound of bibasic nitrate and bibasic nitrite of lead : — 2(PbO.N04) = 2PbO.N03 + 2PbO.N05. and expresses its formation by the equation : — 2(PbO.N©5) + 2Pb = 2PbO.N05 + 2PbO.N03. If the action of the metallic lead be further continued, a fresh portion of nitrate is deoxidised, and the result is an orange- coloured salt, containing 7Pb0.2N04 (Peligot),which Gerhardt regards as a double salt more basic than the former : 7Pb0.2N04 = 4PbO.N03 + SPbO.NO^. Finally, by the continued action of the lead, the subnitrate contained in these two salts is likewise reduced, and a sub- nitrite is formed, viz., either Berzelius^s quadrobasic salt, 4PbO.N03, or a bibasic nitrite 2PbO.N03, obtained by Bromeis. The last salt crystallises in long golden-yeUow needles containing 1 eq. of water.* Phosphate of lead. — On mixing nitrate of lead with ordi- * For a more detailed account of the nitrates and nitrites of lead, see Gmelin's Handbook, Translation, v. 152—157. 12 i LEAD. nary phosphate of soda, a precipitate is formed coutaiiiing the two salts SPbO.PO^ and 2PbO.IIO.PO5. The latter is obtained pure by precipitating a boiling solution of nitrate of lead with pure phosphoric acid. This salt dissolves in nitric acid and fixed alkalies, but very sparingly in acetic acid; ammonia converts it into SPbO.POg. It fuses readily before the blow- pipe, and crystallises on coolmg in well defined polyhedrons. When strongly ignited with charcoal, it gives off phosphorus and carbonic oxide, and leaves metallic lead. Chlorite of lead, PbO.ClO^, is obtained in sulphur-yellow crystalline scales by precipitating nitrate of lead T\dth an excess of chlorite of barj^ta containing free chlorous acid. It decora- poses at 259° with a kind of explosion, and sets fire to flowers of sulphur triturated with it. Sulphuric acid diluted with an equal weight of water, decomposes it, especially between 104° and 122°, evolving pure chlorous acid gas, and leaving 88'75 per cent, of sulphate of lead (Millon). Chlorate of lead, PbO.ClOg + HO, is obtained by cooling a hot solution of oxide of lead in aqueous chloric acid, in rhom- boidal prisms belonging to the oblique prismatic system, and isomorphous with the analogously constituted crystals of chlorate of baryta. These crystals, when heated, leave the yellow oxychloride Pb0.2PbCl (Vauquelin, Wiichter, Yogel). Perchlorate of lead, Pl)O.C107. — The solution of oxide of lead in warm aqueous perchloric acid, yields small prisms having a sweet but highly astringent taste, soluble in their own weight of water, but not deliquescent (Serullas). By boiling a concentrated solution of this salt with carbonate of lead, a solution of a basic salt is obtained, which if the excess of base is very large, yields by evaporation, dull, indistinct crystals, which are resolved by water into a solution of bibasic salt, and a white insoluble residue. AVlien the excess of base is less, or when the solution of the bibasic salt is left to evapo- rate, ci^stals of two different forms are obtained ; both, how- ever, containing 2PbO.C107 + 21IO (Marignac). SALTS OF LEAD. 123 Chlorophosphate of had^ PbCl + 3(3PbO.P05), occurs as pyromorphite and green and brown lead- ore. The crystals belong to the hexagonal system, and have the hardness of apatite. It fuses readily, and on cooling solidifies with vivid incandescence into an angular crystalline mass. In some of these ores, the chloride of lead is partly replaced by fiuoride of calcium, and the triphosphate of lead by the triphosphate of calcium or trisarscniate of lead. The calcareous ores may be regarded as mixtures of apatite and pyromorphite. The same compound containing, however, an atom of water, is formed artificially on pouring a boiling solution of chloride of lead into a boiling solution of phosphate of soda, the latter being in excess (Ileintz). When, on the contrary, a boiling solution of phosphate of soda is poured into an excess of chloride of lead, a precipitate is formed, which, according to Heintz, is 2(3PbO.P05) + PbCl, but, according to Gerhardt, 2PbO.HO.P05 + PbCl. Acetate of lead, PbO.(C4H303) h3H0.— This salt is met with well crystallised, and in a state of great purity, in com- merce. It is generally prepared by dissolving litharge in the acetic acid procured by the distillation of wood. It crystal- lises in flattened four-sided prisms ; has a taste which is first sweet and then astringent ; is very soluble in water, 100 parts of water dissolving 59 of the salt at 60°; and dissolves in 8 parts of alcohol. It effloresces in air, and is apt to be partially decomposed by the carbonic acid of the air, and thus to become partially insoluble. It loses the whole of its water when dried at the usual temperature in vacuo. M. Payen crystallised the anhydrous acetate from solution in absolute alcohol. Tribasic subacetate of lead, PbO.(C4ll303) -f 2PbO,is formed by digesting oxide of lead in a solution of the neutral salt, till it is strongly alkaline. This salt does not crystallise when so prepared, but may be dried, and then contains no water. It is very soluble, but must be dissolved in distilled water, as the carbonic, hydrochloric and other acids in well wa.er precipi- 126 LEAD. tate its oxide of lead. M. Payen lias observed that the tribasic subacetate crystallises readily, in fine prismatic needles, when formed by adding ammonia to a moderately strong solu- tion of the neutral acetate. The crystals contain 1 eq. of water, which they lose at 212°. The acetate of ammonia, formed at the same time, appears to give stability to the sub- acetate of lead in solution, and prevents an excess of a whole equivalent of ammonia from throwing down any oxide of lead from the solution. This ammoniacal solution of the subacetate of lead, prepared without an excess of ammonia, is a con- venient form in which to apply that salt as a reagent.* Sesquibasic acetate of lead, 3Pb0.2(C^Il303)-f HO.— This salt was obtained by Payen by adding 1 cq. of the neutral acetate to a concentrated and boiling solution of 1 eq. of the tribasic acetate. It is also produced when the neutral and anhydrous acetate of lead is heated in a retort or porcelain capsule, till the whole, after being liquid, becomes a white and porous mass. The sesquibasic acetate is then formed by the decomposition of 3 eq. of neutral acetate of lead, from which there separate the elements of 1 eq. of acetic acid, in the form of carbonic acid and acetone (Matteucci and Wohler). This basic salt is very soluble, and crystallises in plates of a pearly lustre. Another method of obtaining it is to digest an aqueous solution of 2 eq. of the neutral acetate with 1 eq. of protoxide of lead free from carbonate, till it dissolves, and evaporate the filtrate in vacuo over oil of vitriol. A sexbasic acetate of lead, 6PbO.(C4H303), is formed on dropping a solution of the neutral, or of triliasic acetate of lead, into excess of ammonia. It is a white precipitate, which when examined by the microscope, has a crystalline aspect. It contains a little water, which it loses when dried in vacuo. A bibasic acetate, 2PbO.(C4H303), is also formed, accord- • Memoire sur lee Acetates et le Protoxide de Plomb, par M. Pajen, An. de Chim, et de Phys. t. Ixvi. p. 37. ALLOYS OF LEAD. 127 ing to Dobereiner and Scliindler, by boiling 1 eq. of neutral acetate of lead with 1 eq. of the protoxide. The common extrokctum Saturni of the pharmacopoeias ap- pears to consist chiefly of bibasic acetate_, containing more or less of the tribasic and sesquibasic salts. Alloys of lead. — Lead and tin may be fused together in all proportions. M. E-udberg finds that these metals combine in certain definite proportions^ having fixed points of congela- tion : — 1 atom of lead and 3 atoms of tin^ congeal at 368*6°. 1 atom of lead and 1 atom of tin, at 464°. 2 atoms of lead and 1 atom of tin, at 518°. 3 atoms of lead and 1 atom of tin, at 536°. A thermometer placed in a fluid alloy of 1 atom of lead and 2 atoms of tin, becomes stationary when the temperature falls to 392° ; a portion then solidifies, and a more fusible alloy separates; the temperature again falls, and afterwards be- comes stationary at 368*6°, the crystallising point of the alloy composed of 1 atom of lead and 3 atoms of tin. If the alloy contains so much tin that its point of complete congelation is below 368*6°, the last compound always separates from it at that point, and the thermometer remains stationary for a time, whatever may be the proportion of the metals in the alloy.* Fine solder is an alloy of 2 parts of tin and 1 of lead ; it fuses at about 360°, and is much employed in tinning copper. Coarse solder contains one fourth of tin, and fuses at about 500° ; it is the substance employed for soldering by plumbers. Lead, as reduced from the native sulphide, always contains a little silver. The latter is separated by allowing two or three tons of the melted metal to cool slowly in a hemispherical iron pot, when the lead, as it solidifies, separates in crystals, which can be raked out. The silver remains almost wholly in the * Eudborg, An. Ch. Phys. [2.] xlviii. 363. 128 LEAD. more fusible portion, or wliat may be looked upon as tlie mother- liquor of these crystals; so that by this operation the argentiferous alloy is greatly concentrated. This mode of separation was discovered by Mr. Pattinson of Newcastle. To separate the remaining lead, much of it is converted into massicot, by the action of air upon its surface, in the shallow furnace used for that preparation ; and the last portions of lead are removed by continuing the oxidation upon a porous bason or cupel of bone-earth, whicli imbibes the fused oxide of lead, while the melted silver is found in a state of purity upon the surface of the cupel, not being oxidable at a high tem- perature. ESTIMATION OF LEAD, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. Lead may be estimated either as protoxide or as sul- phate. For the former mode of estimation, it is best to pre- cipitate by oxalate of ammonia, the solution being neutral or rendered very slightly alkaline by ammonia. The oxalate of lead, after being washed and dried, is then to be ignited in an open porcelain crucible, whereby it is converted into protoxide. As lead is very easily reduced by carbonaceous matter at a red heat, the precipitate must not be ignited in contact with the filter ; but the filter, after the greater part of the precipitate has been removed from it, must be held on the point of a fine platinum wire above the cru- cible, and set* on fire, so that the ashes may drop in ; the precipitate may then be added, and the ignition completed. The protoxide contains 92-83 per cent, of metallic lead. Lead may also be precipitated by carbonate of ammonia, to which a little free ammonia has been added, and the carbonate of lead treated as above. In precipitating lead as sulphate, if the solution be neutral, the precipitation is best eftectcd by sulphate of soda ; the sul- ALLOYS OF LEAD. 129 phate of lead may then be washed on a filter, dried and ignited ; but if the solution contains free nitric acid, it is best to precipitate by excess of sulphuric acid, then evaporate to dryness, and ignite till all excess of acid is driven off; treat the residue with water to dissolve out any soluble salts that may be present ; wash the sulphate of lead on a filter, and then dry and ignite it, burning the filter separately as above. The sulphate contains 68*32 per cent, of lead. From the alkalies and earths, and from manganese, iron, cobalt, nickel, and zinc, lead is easily separated by hydrosulphuric acid, the solution being previously acidulated with nitric acid. The precipitated sulphide is washed and dried, then placed, together with the filter (which should be as small as possible), in a porcelain dish, covered over with a glass plate or a funnel, and treated with fuming nitric acid, added cautiously and by small portions at a time. Violent action takes place, and the sulphide of lead is converted into sulphate. A portion may, however, be converted into nitrate, with separation of sul- phur: hence, to insure complete conversion into sulphate, it is necessary to add a few drops of strong sulphuric acid. The product must then be strongly ignited to drive off the excess of sulphuric acid, and burn away the remaining organic matter of the filter. From cadmium and copper, lead is easily separated by sul- phuric acid. VOL. II. 130 TIN. ORDER V. OTHER METALS PROPER HAVING ISOMORPHOUS RELATIONS WITH THE MAGNESIAN FAMILY. SECTION I. TIN. Eq. 58-82 or 735*25; Sn (siannum). Tin does not occur native, but its common ore is reduced by a simple process, and mankind appear to have been in possession of this metal from the earliest ages. The most productive mines of tin are those of Cornwall, from which the ancients appear to have derived their principal supply of this metal, and those of the peninsula of Malacca and island of Banca in India. The only important ore of tin is the bioxide, which is found in Cornwall, both in veins traversing the primary rocks, and in alluvial deposits in their neighbourhood. In the latter case, the ore presents itself in rounded grains of greater or less size, which form together a bed covered by clay and gravel. This ore has evidently been removed from its original situation, and the grains rounded by the action of water, which has at the same time divested it of the other metallic ores with which it is accompanied in the vein; these being softer are more easily reduced to powder, and have been carried away by the stream. This ore, called stream tin, is easily reduced by coal, and gives the purest tin. The metal from the ore of the veins is contaminated with iron, copper, arsenic, and antimony, from which a portion of it is par- tially purified by liquation. Bars of the impure metal arc PROTOXIDE OF TIN. 131 exposed to a moderate heat, by wliicli the pure tin is first melted, and separates it from a less fusible alloy containing the foreign metals. The pm^er portion is called grain tin, and the other, ordinary tin or block tin. The mass of grain tin is heated till it becomes brittle, and then let fall from a height. By this it splits into irregular prisms, somewhat resembling basaltic columns. This splitting is a mark of the purity of the tin, for it does not happen when the tin is contaminated by other metals. Pure tin is white, with a bluish tinge, very soft, and so malleable, that it may be beaten into thin leaves, tinfoil not being more than 1- 1000th of an inch in thickness. When a bar of tin is bent, it emits a grating sound, which is cha- racteristic; and when bent backwards and forwards rapidly, several times in succession, becomes so hot that it cannot be held in the hand. At the temperature of boiling water, tin can be drawn out into wire, which is very soft and flexible, but deficient in tenacity. The density of pure tin is 7*285, or 7*293 after being laminated; that of the tin of com- merce is said to vary from 7*56 to 7'Q. Its point of fusion is 442°, according to Crichton and Rudberg; 4456°, according to KupfFer. Tin is volatile at a very high temperature. The brilliancy of the surface of tin is but slowly impaired by exposure to air, and even in water it is scarcely acted upon. Hence the great value of this metal for culinary vessels, and for covering the more oxidable metals, such as ii'on and copper, when employed as such. Three oxides of tin are known, the protoxide SnO, sesquioxide Sn203, and bioxide Sn02. Protoxide of tin. Stannous oxide; SnO, 66*82 or 835*25. Tin dissolves in undiluted hydrochloric acid, at the boiling temperature, by substitution for hydrogen, and forms the pro- tochloride of tin. From this the protoxide is precipitated by an alkaline carbonate, as a white hydrate, which may be washed with tepid water and dried at a temperature not ex- ceeding 176°. It does not contain a trace of carbonic acid. z 2 132 TIN. This white powder dried more strongly in a retort filled with carbonic acid, and heated to redness, gives the anhydrous oxide as a black powder, the density of which is 6*666. In this state, the oxide is permanent; but if a body at a red heat is brought in contact with it in open air, it takes fire and burns, and is entirely converted into bioxide. If hydrated stan- nous oxide be boiled with a quantity of potash not sufficient to dissolve it entirely, the undissolved portion is converted into small, hard, shining, black crystals of anhydrous stan- nous oxide, which, when heated to 392°, decrepitate, swell up, fall to pieces, and are converted into an olive-green powder, consisting also of the anhydrous protoxide. Again, on evaporating a very dilute solution of sal-ammoniac, in which hydrated stannous oxide is diff'used, that compound is converted, as soon as the sal-ammoniac crystalli.es, into anhydrous stannous oxide, having the form of a cinnabar- coloiu-ed po-\vder. There are, therefore, three modifications of stannous oxide, black, olive-green, and red (Fremy). The red modification is also obtained by digesting thoroughly washed hydrated stannous oxide at a temperature of 133°, in a slightly acid solution of stannous acetate, having a density of 1-06 (Roth). Protoxide of tin dissolves in acids, and with more faci- lity when hydrated than after being ignited. This oxide is also dissolved by potash and soda, but the solution after a time undergoes decomposition ; metallic tin is deposited, and the bioxide is found in solution. The solution of a stannous salt, and of a stannic salt also, is apt to undergo decomposition, when largely diluted with water, and to deposit a subsalt. Stannous salts absorb oxygen from the air, and have a great affinity for that element ; they convert the sesquioxide of iron into protoxide, and throw down mer- cury, silver and platinum in the metallic state from their solutions. Chloride of gold produces a purple precipitate in a stannous salt, consisting, it is believed, of the l)ioxide of STANNOUS COMPOUNDS. 138 tin in combination with protoxide of gold, a test by which the protoxide of tin may always be distinguished. Hydrosulphuric acid produces in neutral or acid solutions of stannous salts, a brown-black precipitate of protosulphide of tin, which, when gently heated with a considerable quantity of sulphide of am- monium containing excess of sulphur, is converted into the bisulphide and dissolved; acids added in excess to this solu- tion precipitate the yellow bisulphide. Caustic alkalies and alkaline carbonates, added to stannous salts, throw down a white precipitate of hydrated stannous oxide, soluble in caustic potash or soda, but not in ammonia. Ferrocyanide of potas- sium produces a white precipitate, soluble in hydrochloric acid. Protosulphide of tin, SnS, is formed when sulphur is mixed with tin heated above its melting point ; it is also obtained in small dark grey crystalline laminse, of sp. gr. 4*973, by adding the hydrated sulphide precipitated from a stannous salt by hydrosulphuric acid, to anhydrous protochloride of tin in the melted state, and removing the excess of the proto- chloride with dilute hydrochloric acid. It is decomposed by dilute hydrochloric acid, with evolution of hydrosulphuric acid. Protochloride of tin, Salt of tin ; SnCl. — This salt may be obtained in the anhydrous state by gradually heating a mixture of equal weights of calomel and tin, and finally dis- tilling the protochloride at a strong red heat. The fused mass on cooling forms a grey solid, of considerable lustre, and having a vitreous fracture. The hydrated chloride, known in commerce as salt of tin, is procured by evaporating the solution of tin in concentrated hydrochloric acid to the point of crystallisation. It is thus obtained in needles, or in larger four-sided prismatic crystals containing 2 eq. of water. They fuse between 100° and 105°. The specific gravity of the crystals is 2*710 at 60° ; that of the fused mass at 100°, is 2-588 (Penny). The salt parts with the greater portion, if not the whole of its water at 212°, but if distilled K 3 13i TIN. at a higher temperature, loses hydrochloric acid also, and leaves an oxychloride of tin. It dissolves completely in a small quantity of water ; but when treated with a large quan- tity, is partly decomposed, hydrochloric acid being dissolved, and a light milk-Avhite powder separating, which is a basic chloride, or oxy chloride, SnCl.SnO + 2 HO. Both the crys- tals and the solution absorb oxygen from the air, and then a basic salt of the sesquioxide is formed which is also insoluble in water. From both these causes, a complete and clear solu- tion of the salt of tin is rarely obtained, imlcss the water is previously acidulated with hydrochloric acid. This salt is en- tirely soluble in caustic alkali, but the solution is liable to an ulterior change already mentioned. One part of crystallised protochloride of tin dissolved, together with 3 parts of tartaric acid, in a sufficient quantity of hot water, and carefully neu- tralised with potash, forms a clear sohition, whicli may be boiled and mixed with any quantity of water without becoming turbid: the white precipitate which forms in it on the addition of a little more potash, especially on heating, is redissolved by a lai'ger quantity of potash (R. Schneider) . When protochloride of tin is heated with a mixture of hydrochloric and sulphurous acids, a yellow precipitate of bi- sulphide of tin is formed: 6SnCH- 2S0.^ + 4liCl= SnS2 4- SSnClj -r 4110. This reaction serves as a test for sulphurous acid. The protochloride of tin is used in calico-printing, not only as a mordant, but also as a deoxidising agent, particularly to deoxidise indigo, and to reduce to a lower state of oxidation and discharge the sesquioxides of iron and manganese fixed upon cloth. Protochloride of tin and potassium ; SnCl.KCl. — Proto- chloride of tin forms a double salt w ith chloride of potassium, and also with chloride of ammonium, which compounds crys- tallise in the anhydrous state, and also with 3 eq. of water, or, according to Rammelsberg, with only 1 equivalent. STANNOUS COMPOUNDS. 135 Anhydrous protochloride of tin fused in ammoniacal gas, absorbs half an equivalent of that gas_, according to Persoz, forming 2SnCl.NH3, or rather perhaps SnCL(NH3Sn)Cl. Protiodide of tiny SnI, is formed by heating a mixture of granulated tin and iodine. It is obtained in beautiful shining yellowish red prisms by gently boiling concentrated hydriodic acid with strips of tinfoil in a long glass tube for a day, or more readily by heating the acid with the tin in a sealed glass tube to a 'temperature of 248°, or at most 302° for an hour ; after cooling, the remaining portion of tin is found to be covered with crystals. When tinfoil and iodide of amyl were heated together in a sealed tube for a day to 356°, the tinfoil became covered with yellowish-red quadratic octohedrons at the part where the tube cooled most quickly ; but at the part which was immersed in the oil-bath, and therefore cooled more slowly, the metal was covered with sulphur-yellow prisms, which became yellowish-red when taken out (Wohler). Stannous iodide was found by Boullay, jun., to form double salts with other iodides, particularly with the iodides of the alkaline and earthy metals, in which two atoms of the stannous iodide are combined with one of the other iodide. Carbonic acid does not combine with either of the oxides of tin. Protosulphate of tin j SnO.SOg. — Tin dissolves in sulphuric acid, concentrated or a little diluted, yielding a saline mass, which forms a brown solution in water and deposits small crystalline needles on cooling. Protonitrate of tin, SnO.NOg, is obtained by dissolving hydrated protoxide of tin in nitric acid ; the solution cannot be concentrated and is easily altered. Tartrate of potash and tin, KO.SnO.(C8H40iQ) or C8H4(KSn)Oi2- — Bitartrate of potash dissolves protoxide of tin, and forms a very soluble salt of potash and tin, which, like most of the tartrates, is not precipitated either by caustic alkalies or by alkaline carbonates. An addition of bitartrate K 4t 136 TIN. of potash is occasionally made to the solution of tin used in dyeing. Sesquioxide of tirij Sn203. — Was obtained by M. Fuchs, by diffusing recently precipitated sesquioxide of iron in a solution of protochloride of tin containing no excess of acid, and afterwards boiling the mixture. A double decomposition occurs, in which sesquioxide of tin precipitates, and proto- chloride of iron is retained in solution : 2SnCl + Fe203 = Sn^Og + 2FeCl. The sesquioxide thus obtained is a slimy grey matter, and usually yellow from adhering oxide of iron. Ammonia dis- solves it easily, and without residue, a character which distin- guishes this oxide from the protoxide of tin, the latter being insoluble, or nearly so, in that menstruum. Sesquioxide of tin is dissolved by concentrated hydrochloric acid ; the taste of the solution is not metallic. It is distinguished from a salt of the bioxide of tin, by producing the purple precipitate with chloride of gold. A sesquisulphide exists, corresponding with this oxide. The salts of sesquioxide of tin have not been examined. Bioxide of tin, Stannic oxide, SnOj, 74*82 or 935-25. — This constitutes the common ore of tin, which is generally crystal- lised. The crystals oi tin-stone are sometimes brownish-yellow and translucent, at other times dark brown and almost black, and contain small quantities of the protoxides of iron and manganese. Their primitive form is an obtuse octohedron with a square base ; their density from 6*92 to 6*96. Bioxide of tin in this state does not dissolve in acids, unless previously ignited with an alkali. Anhydrous stannic oxide may be ob- tained in colourless crystals derived from a right rhomboi'dal prism, which scratch glass, and have a density of 5 '72, by de- composing vapour of bichloride of tin with water at a red heat. These crystals are isomorphous with one of the native varieties of titanic acid (brookite), whereas the crystals of native tin- BIOXIDE OF TIN. 137 stone are isomorphous with another variety of titanic acid (rutile) . Bioxide of tin is susceptible of two modifications called stannic and metastannic acid, distinguished from one another by the proportions of water and metallic oxide with which they combine. Stannic acid, or Hydrated stannic oxide, SnOg.HO, is ob- tained by decomposing bichloride of tin with water, or by precipitating a soluble stannate with an acid. It is white, gelatinous, insoluble in water, but dissolves readily in dilute acids. A moderate heat converts it into metastannic acid. At a red heat, it gives off all its water, and becomes very hard. Solutions of stannic oxide in acids (the hydrated bichloride for example), are decomposed by zinc and cadmium, the tin being precipitated in an arborescent form. Hydro sulphuric acid and sulphide of ammonium throw down the yellow bisul- phide soluble in alkalies and in sulphide of ammonium. Am- monia throws down a white bulky hydrate, soluble with some turbidity in a large excess of ammonia. The presence of tartaric acid prevents the precipitation. Potash throws down a white bulky hydrate (probably containing potash), easily soluble in excess. Carbonate of potash gives a white precipi- tate, consisting, according to Fremy, of stannate of potash, which dissolves in excess of the reagent, but separates com- pletely after a while. Bicarbonate of potash and sesquicar- bonate of ammonia throw down the hydrated oxides, insoluble in excess of the reagent. Chloride of gold gives no preci- jiitate with stannic salts. All salts of tin are easily reduced to the metallic state when heated on charcoal before the blowpipe with carbonate of soda or cyanide of potassium. The compounds of stannic acid with bases are represented by the general formula MO.SnOg. The stannates of the alkalies crystallise readily, and may be obtained in the anhy- drous state. They are prepared by dissolving stannic acid in 138 TIN. alkalies, or by calcining metastannic acid or the metastannates in contact with an excess of base. Siannate of potash, KO . Sn02 + 4HO, is white, very soluble in water, insoluble in alcohol ; it crystallises in oblique rhombo'idal prisms, which are transparent, sometimes very large, and slowly absorb moisture fi'om the air. It has a caustic taste and strong alka- line reaction. Water appears to decompose it after a while into potash and metastannate of potash. It is precipitated from its solution by nearly all soluble salts, even by those of potash, soda and ammonia. Stannate of soda, NaO.SnOj + 4HO, resembles the potash- salt, and is obtained in a similar manner. It crystallises in hexagonal tables, dissolves in cold more readily than in hot water, is insoluble in alcohol, and has a strong alkaline reaction (Fremy). The stannatcs of all other bases are insoluble in water, and may be formed by double decomposition. The scsquioxide of tin may be regarded as a stannate of stannous oxide, SuO.SnOj (Fremy). Metastannic acid, Sn^OiQ. — Tin treated with strong nitric acid is completely transformed into a white powder, which, when dried in the air at ordinary temperatures, contains SngOiQ.lOHO ; after being heated for some time to 212°, it is reduced to SujOio-SHO. It is white, cr\^stalline, insoluble in water, and in dilute nitric acid and sulphuric acid. Monohy- drated sulphuric acid dissolves it in considerable quantity, forming a compound which is not decomposed by water or alcohol. It dissolves in dilute hydrochloric acid, forming a liquid, which, when treated with excess of acid, yields a white amorphous precipitate, differing considerably from hydrated bichloride of tin. Metastannic acid also combines with certain organic acids. The acid prepared with nitric acid is completely insoluble in ammonia, but when dissolved in potash and pre- cipitated by an acid, it becomes gelatinous and soluble in ammonia ; in that state, it contains more water than in the crystalline state ; but by the slightest desiccation, or even by STANNIC COMPOUNDS. 139 boiling for a few minutes, it gives up part of its water, and is reconverted into the modification insoluble in ammonia. Other hydrates of metastannic acid appear also to exist, possessing different properties. The metastannates are represented by the general formula (M0.4H0.) SugOiQ. They can only exist in the hydrated state, being decomposed when deprived of their basic water. The potash and soda-salts, heated with excess of base, are transformed into stannates. They are soluble in basic water. The other metastannates are insoluble, and are obtained by double decomposition. Metastannate of potash, (K0.4H0). Sn^OjQ, is prepared by dissolving metastannic acid in cold potash ; it may be precipitated in the solid state by adding pieces of potash to the liquid. It is gummy, uncrystallisable, and strongly alkaline. At a red heat, it gives off its water and is decomposed ; the calcined mass, digested in water, yields up all its alkali and leaves insoluble metastannic acid. The soda-salt, (Na0.4HO).Sn50io, closely resembles the potash- salt, but is crystalline, dissolves slowly in water, and is decom- posed by boiling water. Metastannate of stannous oxide, (Sn0.4HO).Sn50io, is obtained by placing metastannic acid in contact with protochloride of tin. It is yellow, and in- soluble in water ; when heated in contact with the air, it is transformed into anhydrous stannic acid (Fremy). Oxide of tin is employed in the preparation of the white glass known as enamel ; and the ignited and finely levigated oxide forms jeioeller's putty, which is used in polishing hard objects. The hydrated oxide resembles alumina in forming insoluble compounds with the organic colouring matters; hence its salts are much prized as mordants. Bisulphide of tin, Stannic sulphide, SnS2, is precipitated from stannic salts, of a dull yellow colour, by hydrosulphuric acid gas. Prepared in the dry way, by igniting a mixture of stannic oxide, sulphur, and sal-ammoniac in a covered crucible, it forms the aurum musivum or mosaic gold of the alchemists. In 140 TIN. this operation, tlie sal- ammoniac is indispensable, although it seems to serve no other purpose than to prevent the elevation of temperature which results from the sulphuration. Mosaic gold when well prepared has the yellow colour of gold, and con- sists of brilliant translucent scales, which are soft to the touch. No acid dissolves it, except aqua-regia. It is decomposed by dry chlorine, yielding the compound SnCl2.SCl2. Bichloride of tin, Permuriate of tin, Stannic chloride, SnCl2 ; 129'82 or 162275. — The anhydrous bichloride of tin, known as the fuming liquor of Libavius, is procured by distilling, at a gentle heat, a mixture of 4 parts of corrosive sublimate and 1 part of tin in filings, or tin amalgamated with a little mercury, and then reduced to powder. A colourless, highly limpid liquid is found in the condenser, which fumes strongly in humid air. The bichloride boils at 218°; the density of its vapour, observed by Dumas, is 9* 1997. It forms a solid saline mass with one third of its weight of water, and dissolves in a larger quantity of water. The same salt is obtained in solution, by conducting a stream of chlorine gas into a strong solution of the protochloride of tin, till the latter is saturated, which is shown by the solution ceasing to precipitate mercury from a solution of corrosive sublimate. A solution of this salt extensively used in dyeing, and known as the nitromuriate of tin, is generally prepared by oxidising crystallised protochloride of tin with nitric acid ; or by dissolving tin in a mixture of hydrochloric and nitric acids, avoiding any considerable eleva- tion of temperature. Ammonio-bichloride of tin, SnClj.NHg or (NH3Sn)Cl2. — An- hydrous bichloride of tin absorbs ammoniacal gas, and forms a white powder, which may be sublimed without decomposition ; after sublimation it is entirely soluble in water (Rose). Chlorosulphide of tin, SnS2.2SnCl2. — Hydrosulphuric acid gas is rapidly absorbed by bichloride of tin, with formation of hydrocliloric acid gas ; SSnCla + 2HS = SnS2.2SnCl2 + 2HC1. ALLOYS or TIN. 141 The compound obtained by perfect saturation with hydro- sulphuric acid is a yellowish or reddish liquid^ heavier than water. When heated^ it gives off bichloride of tin, and leaves the bisulphide (Dumas). Bichloride of tin and sulphur, SnCl2.2SCl2. — Formed by the action of chlorine gas on bisulphide of tin at ordinary temperatures : SnS2 + 6C1 = SnCl2.2SCl2. Large yellow crystals, which fuse when heated, and sublime without decomposition ; they fame in the air more strongly than the bichloride. Bichloride of tin with Pentachloride of phosphorus, 2SnCl2. PCI5. — When a mixture of the last-described compound with terchloride of phosphorus is moderately heated in a stream of hydrochloric acid gas, a rapid action takes place, and this compound is formed, together with other products : 2(SnCl2.2SCl2) + 3PCI3 = 2SnCl2.PCl5 + 2PCI5 + 2S2CI. If the retort in which the action takes place is connected with a receiver surrounded with ice, a pasty, yellomsh mass collects in the receiver, and an amorphous white body remains in the retort. On heating the yellowish mass to between 212° and 250°, dichloride of sulphur escapes, and there re- mains a mixture of pentachloride of phosphorus with the double chloride, identical, in fact, with the amorphous white mass in the retort. On heating this mixture to a tempe- rature between 284° and 320°, the pentachloride of phosphorus is also driven off, leaving the double chloride, which sublimes between 392° and 428°, in highly lustrous colourless needles, which, however, soon crumble to an amorphous powder, even when kept in close vessels. The compound fumes strongly in the air, and rapidly absorbs water, being thereby converted into transparent colourless crystals containing water of crys- tallisation.* * Casselmann, Ann. Cli. Pharm. Ixxxiii. 257. 142 ALLOYS OF TIN. Bichloride of tin toith Oxy chloride of phosjjhorus, 2SnCl2 + PO2CI3. — Obtained by the action of oxychloridc of phos- phorus on bichloride of tin : if an excess of either substance is present, the compound separates in large isolated crystals. It has a peculiar odour, melts at 131°, and boils at 356°, and distils without alteration if kept from contact with moist air. It fumes in the air and is decomposed by water. When oxychloride of phosphorus comes in contact in a close vessel with the compound SnCl2.2SCl2, the whole dissolves, forming a yellowish liquid, from which, after a while, the compound 2SnCl2 . PO2CI3 crystallises; and above the crystals there remains a yellow liquid, probably SCI2 (Casselmann) . Bichloride of tin ivith Phosphuretted hydrogen, 3SnCl2.PH3. ' — These two bodies unite without production of hydi'ochloric acid; the compound is solid (Rose). Bichloride of tinwithpotassiuin, SnCl2.KCl. — The solution of bichloride of tin, when mixed with an equivalent quantity of chloride of potassium and evaporated, yields this double salt in anhydrous regular octohedrons having a vitreous lustre. A similar double salt is formed with chloride of ammonium. A sulphate and nitrate of dioxide of tin, have been crystal- lised ; this base forms no carbonate. Both the sulphide and bisulphide of tin act as sulphur-acids, combining with alkaline sulphide. The bisulphide of tin dissolves with digestion in sulphide of sodium, and the con- centrated solution yields fine crystals of the salt, 2NaS.SnS2 + 12H0. By gradually adding tin to melted pentasulphide of sodium, treating the resulting mass with water, and then filtering and evaporating, yellowish octohedral crystals are obtained, containing NaS.SnSj + 2H0.* The bisulphide of tin is found combined with the subsulphides of copper and iron, forming tin pyrites, a rare mineral, 2Fe2S.SnS2 4- 2Cu2S.SnS2. Alloys of tin. — Tin alloyed with small quantities of anti- ♦ Kiihn, Pogg. Ann. Ixxxv. 293. ALLOYS or TIN. 143 mony, copper, and bismuth, forms the best kind of pewter, possessing the peculiar whiteness of metallic tin. The most fusible compound of tin and bismuth is that of an atom of each metal, Bi.Sn; it melts at 289*4° (Rudberg). When the metals are mixed in other ratios, a portion first congeals at a higher temperature, separating from the compound mentioned, which remains liquid till the temperature falls to 289*4°. Although tin precipitates copper from its solutions in acids, yet it is possible to precipitate tin upon copper, and to cover the latter with tin, as is proved by the tinning of pins. Tin is dissolved in a mixture of 1 part of bitartrate of potash, 2 of alum, 2 of common salt, and a certain quantity of water, and the pins which consist of brass wire are introduced at the boiling temperature. The pins undergo no change in this liquor, supposing it to contain no undissolved tin, but the moment a fragment of tin touches the pins, all those in contact with each other are tinned. Dr. Odlings finds that pure copper boiled in a moderately dilute and rather acid solution of stannous chloride, also becomes coated with tin.* ESTIMATION OF TIN, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. Tin is estimated in the state of bioxide, a compound which contains 78-62 per cent, of the metal. If the tin is united with other metals in the form of an alloy, the alloy must be treated with nitric acid of sp. gr. about 1-3. The tin is then converted into bioxide, while the other metals (with the ex- ception of antimony) are dissolved by the acid. The oxide of tin must then be thoroughly washed, afterwards dried, ignited, and weighed. To insure complete oxidation, the alloy should be finely divided. When the tin is in solution in hydrochloric acid (which is its usual solvent) it must first be precipitated as a stdphide * Chem. Soc. Qu. J. ix. 291. 144 ALLOYS OF TI\. by hydrosulplmric acid, and tlie sulphide then converted into bioxide by roasting in an open porcelain crucible_, a small quantity of nitric acid being added to insure complete oxida- tion. Precipitation by hydrosulphuric acid serves also to separate tin from all metals which are not thrown down by that reagent from their acid solutions. From cadmium, copper, and lead, tin may be separated by treating the solution with a slight excess of ammonia, and then adding sulphide of ammonium containing excess of sul- phur. All the metals are thereby converted into sulphides, but the sulphide of tin dissolves, while the others are left undissolved. Volumetric estimation of tin. — The following method of estimating the amount of tin in the commercial protochloride is given by Dr. Penny* ; it is basecl on the conversion of proto- chloride of tin into bichloride by the action of chromic acid in presence of free hydrochloric acid : 3SnCl + K0.2Cr03 -f 7HC1 = SSnCla H KCl + Cr^Clg + 7H0. The solution of the tin-salt is mixed with a sufficient quantity of hydrochloric acid and gently heated, and a solution of bichromate of potash gradually added, till a drop of the liqui d added to acetate of lead (a solution of 1 part of that salt in 8 parts of water being scattered in large drops on a porcelain plate) produces a faint yellow colour ; or tiU the liquid pro- duces a dark broAvn or red colouring in an acidulated mixture of sulphocyanide of potassium and a pure protosalt of iron. With the commercial solution of the protochloride of tin, the contrary method is adopted; that is to say, the tin solution, diluted and reduced to a definite volume, is poured into a so- lution of bichromate of potash containing a known weight of that salt. Penny finds, by direct experiments, that 83*2 parts of pure bichromate of potash correspond to ICO parts of tin. * Chem. Soc. Qii. J. iv. 249, TITANIUM. 1J5 SECTION II. TITANIUM. Eq. 24-33 or 3037; Ti. This metal was discovered in 1791, by Mr. Gregor of Corn- wall, and afterwards by Klaprotb, who gave it tlie name titanium. In the form of titanic acid it constitutes several minerals, as rutile, anatase, menachanite, &c. ; and as titanate of protoxide of iron, it forms ilmenite and other species. When titaniferous iron-ores are smelted in the blast furnace, small cubic crystals of a bright copper colour are found on the slag which adheres to the lower part of the furnace. These crystals were long supposed to be metallic titanium ; but Wohler* has shown that they also contain carbon and nitrogen, being, in fact, a compound of cyanide of titanium with nitride of titanium, CyTi.SNTig. Pure titanium is obtained by heating the double fluoride of potassium and titanium with potassium in a covered crucible. The metal is then set free with vivid incandescence, and the fluoride of potassium may be removed by washing with water. Titanium thus obtained is a dark green, heavy, amorphous powder, which does not exhibit any shade of copper colour, even after pressure ; under the microscope it appears as a cemented mass, having the colour and lustre of iron. Metallic titanium is also obtained by mixing titanic acid with one-sixth of its weight of charcoal and exposing it to the strongest heat of a wind-furnace. It was thus obtained in the form of a copper- coloured or gold- coloured powder by Vauquelin, Lampadius, and others ; but possibly the charcoal which they used may have contained nitrogen, and that element united with the reduced metal. * Ann. Ch. Pbarra. Ixxiii. 34. ; Chem. Soc. Qu. J. ii. 352. VOL. II. L 1 10 TITANIUM. Pure titanium (prepared from the double fluoride) burns with great splendour when heated in the air, and, if sprinkled into a flame, is consumed, with brilliant scintillations, at a considerable distance above the point of the flame. When heated to redness in oxygen-gas, it bums with a splendour resembling a discharge of electricity. In chlorine-gas it exhibits similar phenomena, requiring also the aid of heat to set it on fire. Mixed with red lead and heated, it bums with such violence that the mass is thrown out of the vessel, with loud detonation. Titanium does not decompose water at ordinary temperatures, but on heating the water to the boiling point, hydrogen begins to escape. Warm hydrochloric acid dissolves titanium with brisk evolution of hydrogen. Ammonia added to the solution throws down a black oxide ; and, on heating the liquid, hydrogen is evolved, and the precipitate first turns blue, and is afterwards converted into white titanic acid. Titanium forms three compounds with oxygen : viz. the protoxide, TiO, whose composition is, however, doubtful ; the sesquioxide, Ti203 ; and titanic acid, TiOg. Protoxide of titanium, TiO, 32-33. or 403-7 — Is formed when titanic acid is exposed in a charcoal crucible, to the highest temperature of a wind-furnace. Where the acid was in contact with the charcoal, a thin coating of metallic titanium is formed ; but within, it is changed into a black mass, which is insoluble in all acids, and not otherwise affected by them, and is oxidated with difficulty when heated in contact with air, or by fusion with nitre. Protoxide of titanium is also obtained by the moist way, in the form of a deep purple powder, when a fragment of zinc or iron is introduced into a solution of titanic acid in hydrochloric acid ; but it alters so quickly by absorption of oxygen, that no opportunity has yet been ob- tained of studying its properties. The composition assigned to it above is, therefore, hypothetical. The blue powder is, OXIDES or TITANIUM. 147 perhaps, a compound of protoxide of titanium with oxide of zinc or iron. Sesquioxide of titanium, Ti203. — When anhydrous titanic acid is strongly ignited in a current of hydrogen gas, it be- comes black and loses considerably in weight. From a deter- mination of the actual loss of weight, Ebelmen concludes that sesquioxide of titanium is produced. The residue is not acted upon by nitric or hydrochloric acid, but dissolves in sulphuric acid, forming a violet solution. * Titanic acid, Ti02, 40*33 or 503" 7. — In the mineral rutile, titanic acid is crystallised in the form of tinstone, the link by which tin is connected with titanium. Again, ilmenite and other varieties of titanate of iron, reO.Ti02 are isomorphous with sesquioxide of iron ; and thus tin comes to be con- nected through titanium with the last order of metals. But titanic acid is dimorphous, and crystallises, in anatase, in an unconnected form. The best method of obtaining pure titanic acid is to fuse titanate of iron, reduced to powder and levigated with sulphur. The sulphur has no action upon the titanic acid, but converts the protoxide of iron into a sulphide of iron, which is dissolved by hydrochloric acid. If iron is still retained by the titanic acid, the latter is heated in a stream of hydrosulphuric acid gas, by which every particle of iron is converted into sulphide, and then removed by hydrochloric acid. Titanic acid is a white powder, which acquires a yellow tint by exposure to a high temperature ; it is infusible and insoluble in water. Titanic acid is considerably analogous in properties to silica ; like that acid it has a soluble modifica- tion, formed by igniting titanic acid with an alkaline car- bonate, which is soluble in dilute hydrochloric acid. The acid solution of titanic acid gives an orange-red precipitate with an infusion of gall-nuts, which is characteristic of titanic acid. « Ann. Cli. Phys. [3.] xx. 385. L 2 118 TITANIUM. On neutralising the acid solution with ammonia, the soluble modification of titanic acid is thrown down as a white gela- tinous precipitate. When this precipitate is dried and heated, it glows, and the titanic acid is then no longer soluble in acids. When a solution of bichloride of titanium, or of the sulphate of titanic acid in water, is boiled for some time, titanic acid precipitates in the insoluble modification. Titanic acid mixed with borax, or better with phosphorus-salt, forms in the outer blowpipe-flame a colourless glass, but in the inner flame, a glass which is yellow while hot, but assumes a violet colour on cooling. The same character is exhibited by those salts of titanic acid whose bases do not themselves impart any colour to the bead. If the titanic acid contains iron, the colour of the bead is brown-red or blood-red instead of violet. Many titanates yield the blue colour only with phosphorus- salt, not with borax. The colour is produced more readily by heating the substance on charcoal than on platiimm wire. The above characters suffice to distinguish titanic acid from all other substances. Bisulphide of titanium, TiS2, was discovered by Rose, who formed it by passing the vapour of bisulphide of carbon over titanic acid, in a porcelain tube maintained at a bright red lieat. Bichloride of titanium, TiCl2, was formed by Mr. George of Leeds, by transmitting chlorine over metallic titanium at a red heat. It is a transparent colourless liquid, resembling bichloride of tin, and boiling a little above 212°. The density of its vapour is 0-615 (Dumas). Bichloride of titanium combines with ammonia, and forms a white saline mass, TiCl2.2NH3. Metallic titanium is most easily obtained by heating this compound to redness. Bichloride of titanium also absorbs phosphurctted hydrogen, and forms a dry brown powder. From this compound when heated, a lemon-yellow sublimate rises, which Rose found to contain 3 atoms of bi- chloride of titanium, combined with 1 atom of a compound of phosphurctted hydrogen and hydrochloric acid, analogous to NITRIDES OF TITANIUM. 149 sal-ammoniac, but wliich could not be isolated. Bichloride of titanium combines with the alkaline chlorides, forming double salts, which are colourless and capable of crystaUising. It also combines with chloride of cyanogen, forming a yellow crystal- line compound containing CyCl . 2TiCl2, and with anhydrous hydrocyanic acid, forming the compound HCy . TiCl2, a yellow pulverulent substance which sublimes below Ji]2°, in trans- parent, shining, lemon-yellow ci'ystals. Bromide of titanium^ TiBr2, is obtained by passing bromine vapour over an intimate mixture of titanic acid and carbon, heated to bright redness, and distilling the resulting brown liquid with excess of mercury to remove free bromine. It is an amber-yellow crystalline body of specific gravity 2*6. It melts at 102°, and boils at 356°. It attracts moisture with the greatest avidity, and is converted into titanic and hydro- bromic acids (F. B. Duppa). A volatile bifluoride of titanium, TiF2, was obtained by Unverdorben, by distilling titanic acid in a platinum ap- paratus with fluor spar in powder and fuming sulphuric acid. A definite sulphate of titanic acid, Ti02 . SO3, is obtained by dissolving titanic acid in sulphuric acid, and evaporating to dryness at a heat below redness. Nitrides of titanium. — H. Bose, by heating the double chloride of titanium and ammonium in ammoniacal gas, or by heating the ammonio-chloride of titanium, 2NH3 . TiClg, with sodium, obtained a copper-coloured substance which he supposed to be metallic titanium, but which Wohler has shown to consist of nitride of titanium, Ti3N2, or more probably TigN^ = 3TiN . Ti3N ; it contains 28 per cent, of nitrogen. This compound is redder than the cubic crystals of the blast-furnaces, which have a tinge of yellow. Another nitride of titanium, TiN, is produced when titanic acid is strongly heated in a stream of ammoniacal gas. Its powder is dark violet with a tinge of copper-colour ; in small pieces it exhibits a violet copper-colour and metallic lustre. A third L 3 150 TITANIUM. nitride, TigNg, or more probably 2TiN . TigN, is formed wben Rose's titanium is subjected to tbe action of a stream of hydrogen at a strong red heat. It has a brassy or almost gold-yellow colour and a metallic lustre. It is also obtained (mixed however with carbon) when titanic acid is heated to redness in a stream of cyanogen gas or hydrocyanic acid vapour; no cyanide of titanium is formed in this reaction. All these three nitrides of titanium sustain without decompo- sition, a temperature at least equal to that of melting silver. Mixed in the state of powder with the oxides of copper, lead, or mercury, and heated, they emit a lively sparkling flame, and reduce the oxides to the metallic state. When fused with hydrate of potash, they give off ammoniacal gas (Wohler). Nitrocyanide of titanium, C2NTi . STigN. — This is the copper-coloured compound already s2)oken of as occurring in the iron furnaces, and formerly mistaken for metallic titanium. Its formation appears to be connected with that of cyanide of potassium, so constantly observed in the blast- furnaces. It sometimes occurs in very large masses ; in a furnace at Rubeland in the Ilartz, a mass of it was found, weighing 80 pounds. This compound forms cubic crystals harder than quartz, and of specific gravity 5*3. It contains 18 per cent, of nitrogen and 4 of carbon. In its chemical characters, it resembles the nitrides just described, giving off ammonia when heated with potash, and reducing the oxides of lead, copper, and mercury, when heated with them. A similar product may be formed by placing a mixture of titanic acid and ferrocyanide of potassium in a well closed crucible, and exposing it for an hour to a heat sufl&cient to melt nickel. (Wohler.) ESTIMATION OF TITANIUM. J.51 ESTIMATION OF TITANIUM, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. Titanium is always estimated in the form of titanic acid. This compound is best precipitated from its solutions in acids by ammonia, which throws it down in the form of a very bulky precipitate, resembling hydrate of alumina. A great excess of ammonia must be avoided, as it would redissolve a small portion of the titanic acid. The precipitate after ignition contains 60 per cent, of titanium. If the titanic acid, after precipitation by ammonia, is to be redissolved in acids, which is sometimes necessary in order to separate it from other metals, great care must be taken in the precipitation to avoid all rise of temperature, and the precipitate must be washed with cold water, because heat has the effect of rendering titanic acid more or less insoluble in acids. Titanic acid may also in some cases be separated from its acid solutions by boiling ; from the solution in sulphuric acid, complete precipitation is effected by this method ; but when hydrochloric acid is the solvent, a small portion of titanic acid always remains in solution after boiling. Protoxide of titanium is precipitated from its solutions by ammonia, and the precipitate, after standing from 24 to 36 hours, is converted, with evolution of hydrogen, into titanic acid, in which form it may be estimated. From the alkalies and alkaline earths, titanic acid may be separated by ammonia, the solution in the latter case being carefully excluded from the air. Baryta may also be separated by sulphuric acid. Titanic acid is separated from magnesia by boiling, if the two are dissolved in sulphuric acid, and by precipitation with carbonate of baryta, when hydrochloric acid is the solvent. The separation from alumina and glucina is also effected by boiling the sulphuric acid solution. L 4 152 CHROMIUM. From the metals which are precipitated as sulphides by sulphide of ammonium, viz. , manganese^ iron, cobalt, nickel, and zinc, titanic acid is separated by mixing the acid solution with tartaric acid and excess of ammonia (which then forms no precipitate), and adding sulphide of ammonium, which pre- cipitates everything but the titanic acid. The filtered solution is then evaporated to dryness, and the residue ignited in a platinum crucible to expel ammoniacal salts and burn away the carbon of the tartaric acid. As this carbonaceous matter is very difficult to burn, the ignition should either be performed in a muffle furnace, or a stream of oxygen should be very gently directed into the crucible. The residue consists of titanic acid, which may then be weighed. From cadmium, copper, lead, and tin, titanium is easily separated by hydrosulphuric acid. SECTION III. CHROMIUM. Eq. 26-8 or 335 ; Cr. This metal, so remarkable for the variety and beauty of its coloured preparations, was discovered by Yauquclin in 17^7, in the red mineral now known as chromate of lead. It has since been found in other minerals, more particularly chrome- iron (FeO . Cr203), a mineral which many countries possess in considerable quantity. It is from this ore that the com- pounds of chromium, used in the arts, are actually derived. The metal may be procured by the reduction of its oxide, in the usual way; but the reduction is as difficult as that of manganese. Chromium is a greyish-white metal, of density 5*9, very difficult to fuse, and not magnetic. It does not undergo oxidation in the air. It dissolves in hydrofluoric acid with evolution of hydrogen. Chromium is also obtained CHROMIC OXIDE. 153 as a brown powder, when sesqnichloride of chromium is heated in ammoniacal gas (Liebig). Chromium forms several compounds with oxygen; viz. jivotoxide of chromium, or chromous oxide, CrO, isomorphous with ferrous oxide, &c. ; sesquioxide of chromium, or chromic oxide, Cr203, isomorphous with ferric oxide and alumina ; and chromic acid, CrOg, isomorphous with sulphuric acid ; also a chromosO'Ckromic oxide, Cr304, or CrO.Cr203, and four oxides intermediate between chromic oxide and chromic acid, which may, in fact, be regarded as chromates of chromic oxide; viz. monochromute of chromic oxide, or Cr203.Cr03 = Cr30g ; the bichromate, Cr203.2Cr03 = Cr40g; the neutral chromate, Cr203.3Cr03 = Cr50i2, and the acid chromate, Cr203.4Cr03 = CrgOis- Protoxide of chromium, Chromous oxide, CrO ; 34*8 or 435. — This oxide probably exists in chrome-iron, and in pyrope. It is precipitated in the form of a hydrate by the action of potash on a solution of the protochloride. The anhydrous protoxide has not yet been obtained. The hydrate is very unstable, decomposes water, even at ordinary temperatures, and if the air be not excluded by filling the apparatus with hydrogen, is converted, almost as soon as formed, into chromoso-chromic oxide Cr304, with evolution of hydrogen (Peligot). It is yellow when recently precipitated, brown when dry, and may be preserved unaltered in dry air. When ignited it gives off hydrogen, and the oxygen thereby liberated converts the remaining protoxide into sesquioxide (Moberg). Hydrated chromous oxide is insoluble in dilute acids, but dissolves slowly in strong acids. The chromous salts are best prepared by mixing a solution of the protochloride with the corresponding potash or soda salts, access of air being carefully prevented. They are generally of a red colour, sometimes inclining to blue ; dissolve but sparingly in cold water, but more readily in hot water. Like ferrous salts, they dissolve large quantities of nitric oxide, forming dark brown solutions. 154 CHROMIUM. Protochlonde of chromium, Chromom chloride, CrCl ; 62*3 or 778" 75. — Obtained by passing hydrogen gas over perfectly anhydrous sesquichloride of cliromium very gently heated, as long as hydrocldoric acid gas continues to escape. The hydrogen must be previously freed from all traces of oxygen by passing it through a solution of protochloride of tin in caustic potash, then through tubes containing sulphuric acid and chloride of calcium, and lastly over red-hot metallic copper. The protochloride is also formed by passing dry chlorine gas over a red-hot mixture of charcoal and chromic oxide. The first method yields the protochloride in the form of a white, velvety substance, retaining the form of the sesqui- chloride from which it has been formed ; the second method yields it in fine while crystals, usually mixed, however, with chromic oxide, chromic chloride, and charcoal. Protochloride of chromium dissolves in water, with evolution of heat, forming a blue solution, which rapidly turns green when exposed to the air or to chlorine gas. AVith potash it forms a dark brown precipitate (yellow, according to !Moberg, if the air be completely excluded) of hydrated chromous oxide, which, however, quickly changes to light brown chromoso- chromic oxide, with evolution of hydrogen. Ammonia forms a greenish white precipitate, without evolution of hydrogen. With ammonia and sal-ammoiiiac, a blue liquid is formed which turns red on exposure to the air. Sulphide of ammo- nium or potassium forms a black precipitate of chromous sulphide. The solution of protochloride of chromium is one of the most powerful deoxidising agents known. With a solu- tion of monochromate of potash, it forms a dark brown preci- pitate of chromoso-chromic oxide, which, however, disappears on the addition of an excess of the protochloride, and forms a green solution. It precipitates calomel from a solution of corrosive sublimate. With cupric salts, it forms at first a white precipitate of cuprous chloride ; but when added in excess throws down red cuprous oxide. It instantly converts tungstic CHROMIC OXIDE. 155 acid into blue oxide of tungsten, and precipitates gold from the solution of the chloride. Chromous carbonate is formed by adding a solution of the chloride to carbonate of potash ; its precipitate is red or red- brown, if the alkaline solution is hot, but in the form of dense yellow or bluish green flakes, if it is cold ; the preci- pitate appears, however, to have the same composition in all cases (Moberg). Chromous sulphite is obtained by double decomposition in the form of a brick-red precipitate, which becomes bluish- green on exposure to the air (Moberg) . Chromous sulphate. — When the metallic powder obtained by treating sesquichloride of chromium with potassium is treated with dilute sulphuric acid, hydrogen is evolved, and a solution obtained which exhibits the characters of a chromous salt (Peligot). Chromoso-chromic oxide , CrgO^ = CrO . Cr203. — Formed when the protoxide comes in contact with water, and conse- quently at the moment of its precipitation by potash, from a solution of the protochloride. After washing with water and drying in vacuo, it has the colour of Spanish tobacco. It is but feebly attacked by acids. The hydrate is composed of Cr304 . HO ; when heated, it is converted into chromic oxide with evolution of hydrogen. Sesquioxide of chromium, Chromic oxide, 77*6 or 970.— This oxide exists in chrome-iron, but is not immediately derived from that mineral. When chromate of mercury, the orange precipitate obtained on mixing nitrate of mercury and chro- mate of potash, is strongly ignited, chromic oxide remains as a powder of a good green colour. Chromic oxide is also obtained, by deoxidising the chromic acid of bichromate of potash in various ways ; by ignition with sulphur, for instance, or by igniting together 1 part of bichromate of potash with 1-i- parts of sal-ammoniac and 1 part of carbonate of potash, whereby chloride of potassium and sesquioxide of chromium 156 CHROMIUM. are formed, the chromic acid losing half its oxygen, which is converted into water by the hydrogen of the ammonia. Another process, interesting from affording the oxide in the state of crystals, is to pass the vapour of chlorochromic acid (Cr02Cl) through a tube heated to whiteness, when oxygen and chlorine gases are disengaged, and chromic oxide attaches itself to the surface of the tube. The crystals have a metallic lustre, and are of so deep a green as to appear black ; they have the same form as specular iron ore, a density of 5*21, and are as hard as corundum (Woliler). The ignited oxide is not soluble in acids ; heated with access of air, and in contact with an alkali, it absorbs oxygen and is converted into chromic acid. Fused with borax or other vitreous substances, scsquioxide of chromium produces a beautiful green colour; it is the colouring matter of the emerald, and is employed to produce a green colour upon earthenware. Scsquioxide of chromium (and not chromic acid) is also the colouring matter of jnnk colour applied to stoneware. This substance is formed by strongly igniting a mixture of 100 parts of bioxide of tin, 33 parts of chalk, and not more than one part of scsquioxide of chromium.* To obtain the same oxide in the hydrated state, a solution of bichromate of potash is brought to the boiling point, and hydrochloric acid and alcohol added alternately in small quantities, till the solution passes from a red to a deep green colour, and no longer effers'csces from escape of carbonic acid gas, on addition of either the acid or alcohol. In this experiment, the chromic acid liberated by the hydro- chloric acid, is deprived of half its oxygen by the hydrogen and carbon of the alcohol, and the resulting scsquioxide of chromium is dissolved by the excess of hydrochloric acid pre- * Malaguti, Ann. Ch. Phys. [3.] Ixi. p. 433. Mr. O. Sims finds that sesquioxide of iron and bioxide of manganese may be substituted for oxide of chromium in pink colour, so that the coloration of that substance is of a very peculiar character. CHROMIC SALTS. 157 sent, and in fact converted into the corresponding sesqui- chloride of chromium. Many other organic substances may be used in place of alcohol in this experiment, such as sugar, oxalic acid, &c. The reduction may also be effected by hydrc- sulphuric acid or even by hydrochloric acid alone, if added in sufficient excess ; in this last case, sesquichloride of chromium and chloride of potassium are then formed, and part of the chlorine escapes as gas ; thus : KO. 2Cr03 + 7HC1 = KCl + Cr^Clg + 7H0 + 3C1. The oxide of chromium is precipitated from the green solution by ammonia, and falls as a pale bluish-green hydrate. The same oxide is obtained more directly, when to a boiling solu- tion of bichromate of potash a hot solution of pentasulphide of potassium is added, the chromic acid then giving half its oxygen to the sulphur. Ilydrated chromic oxide is soluble in acids, and forms salts. It is also dissolved by potash and soda, but not to a great extent by ammonia. Its salts have a sweet taste, and are poisonous. The oxide itself becomes of a greener colour when dried, and loses water. A moderate heat affects its relations to acids, the sulphate of the heated (or green) oxide not forming a double salt, for -instance, with sulphate of potash. When heated to redness, it glows, or undergoes the same cliange as zirconia, bioxide of tin, and many other hydrated oxides when made anhydrous ; becomes denser, assumes a pure green colour, and ceases to be soluble in acids. The salts of chromic oxide exhibit two different modifica- tions, green and violet; some acids, e. g., sulphuric and hydrochloric, produce both modifications; others only one. Ammonia produces, in solutions of the green salts, a bluish-gray precipitate, but in solutions of the violet salts, a greenish-gray precipitate, both of which, however, yield green solutions w hen dissolved in sulphuric or hydrochloric acid (Regnault) ; accord- ing to II. Rose, hov ever, the precipitate is bluish-gray in both 158 CHROMlUxM. cases. The liquid above the precipitate has a reddish colour, und contains a small quantity of chromic acid. Potash and soda form similar precipitates, which dissolve in excess of the alkali, forming green solutions from which the chromic oxide is precipitated by boiling. The alkaline carbonates form greenish precipitates (violet by cc ndle-light), which dissolve to a considerable extent in excess of the reagent. Hydtosulphuric acid forms no precipitate ; sidphide of ammonium throws down the hydi'ated sesquioxide. ZinCf immersed in a solution of chrome alum or sesqui- chloride of chromium excluded from the air, gradually reduces the chromic salt to a chromous salt, the liquid after a few hours acquiring a fine blue colour, and hydrogen being evolved by decomposition of water. If the zinc be left in the liquid after the change of colour from green to blue is complete, hydrogen continues to escape slowly, and the liquid after some weeks or months, is found no longer to contain chromium, the whole of that metal being precipitated in the form of a basic salt, and its place taken by zinc. Tin, at a boiling heat, like- wise reduces the chromic salt to a chromous salt, but only to a limited extent ; and on lea\ing the liquid to cool after the action has ceased, a contrary action takes place, the proto- chloridc of chromium decomposing the protochloridc of tin previously formed, reducing the tin to the metallic state, and being itself reconverted into sesquichloride. Iron does not reduce chromic salts to chromous salts, but merely precipi- tates a basic sulphate of chromic oxide, or an oxychloride, as the case may be. * Sesquioxide (and also the protoxide) of chromium, ignited with an alkaline carbonate, or better with a mixture of the carbonate and nitre, is converted into chromic acid, which unites with the alkali ; and en dissolving the fused product in water, filtering if necessary, and neutralising with acetic acid, the characteristic reactions of chromic acid (p. 164.) • H. Loewpl, Ann. Ch. Phya. [3.1 xl. 42. CHROMIC SALTS. 159 may be obtained with lead and silver-salts. An oxide of chromium fused with borax, in either blowpipe flame, yields an emerald-green glass. The same character is exhibited by those salts of chromic acid whose bases do not of themselves impart decided colours to the bead. A sesquisulphide of chromium, Cr2S3, corresponding with the oxide, is obtained by exposing the latter, in a porcelain tube, to the vapour of bisulphide cf carbon, at a bright red heat. It is a substance of a dark grey colour, which is dissolved by nitric acid. Sesquichloride of chromium, Chromic chloride, Cr2Cl3; 160*1 or 2001*2. — This salt is obtained as a sublimate of a peach- purple colour, when chlorine is passed over a mixture of oxide of chromium and charcoal, ignited in a porcelain tube : or in the hydrated state by evaporating the solution of sesquichloride of chromium to dryness. The salt obtained by the latter process is a green powder containing Cr^Clg -\- 9H0. When heated, it gives off water and hydrochloric acid, and leaves a residue of oxy chloride of chromium. Heated in a current of hydro- chloric acid gas, it likewise parts with its water, and is con- verted into the violet anhydrous sesquichloride. The solution, evaporated in vacuo, leaves an amorphous mass which dissolves in water with evolution of heat, and consists of Cr2Cl3H-6HO (Peligot). Anhydrous sesquichloride of chromium is perfectly insoluble in cold water, and dissolves but very slowly in boiling water ; but if to cold water in which the sesquichloride is im- mersed, there be added a very small quantity, even -ttitu-o, of protochloride of chromium, a green solution is formed identical Avith that which is obtained by dissolving chromic oxide in hydrochloric acid (Peligot). Chromic sulphate, Cr2 03.3S03; 197*6 or 247*0. — Chromic oxide is dissolved by sulphuric acid, but the salt does not crystallise. Chromic sulphate exhibits a violet and a green modification. The violet sulphate is obtained by leaving 8 parts of hydrated chromic oxide, dried at 212*^, and 8 or 10 IGO ' CHROMIUM. parts of strong sulphuric acid in a loosely stoppered bottle for several weeks. Tlie solution, wliich is green at first, gra- dually becomes blue, and deposits a greenish blue crystalline mass. On dissolving this substance in water, and adding alcohol, a violet-blue crystalline precipitate is formed; and by dissolving this precipitate in very weak alcohol, and leav- ing the solution to itself for some time, small regular octa- hedrons are deposited, containing Cr203.3S03 + 15110. The green sulphate is prepared by dissolving cliromic oxide in strong sulphuric acid at a temperature between 122° and 140°; also by boiling a solution of the violet sulphate. The liquid, when quickly evaporated, yields a green crystalline salt, having the same composition as the violet sulphate. The green sulj hate dissolves readily in alcohol, forming a blue solution; but the violet salt is insoluble in alcohol. The solution of the green sulphate is not completely decomposed by soluble baryta-salts at ordinary temperatures, a boiling heat being required to complete it ; the violet sulphate, on the contrary, is deprived of all its sulphuric acid by baryta- salts at ordinary temperatures. When either the green or the violet sulphate is heated to 390°, with excess of sulphuric acid, a light yellow mass is obtained, which, when further heated, leaves a residue cf anhydrous chromic sulphate, having a red colour. This anhydrous salt is completely insoluble in water, and dissolves with difficulty even in acid liquids.* Chromic sulphate forms a crystallisable double salt with sul- phate of potash, viz., chrome-alum, KO.SO.3-f Cr203.3S03^- 21•HO. Tliis salt is produced when a mixture of its con- stituent salts, with a little free sulphuric acid, is left to spon- taneous evaporation. The best mode of preparing it is to mix three parts of a saturated solution of neutral chromate of potash, first with one part of oil of vitriol, and then with two parts of alcohol, which is to be added by small portions to the * Rognault, Cours de Cliimie. CHEOME-ALUM. 161 mixture of acid and chromatCj and not to apply artificial heat. The chromic acid is thus deoxidised in a gradual manner, and large crystals of the double sulphate are slowly deposited (Fischer). The octohedral crystals of chrome-alum are of a dark purple colour, and of a beautiful ruby-red, when so small as to be transparent. The solution is bluish- purple, but when heated to 140° or 180° becomes green, and, according to Fischer, either deposits on evaporation a bright- green amorphous, difficultly soluble mass, or yields crystals of sulphate of potash, while green chromic sulphate remains in solution. According to Loewel*, on the contrary, the change of the purple into the green salt does not arise from a separation of the two simple salts, but merely from loss of water of crystallisation. A solution of chrome-alum, which has become green and uncrystallisable by heating, does not deposit any sulphate of potash even when concentrated; neither does that salt separate when the crystals are melted in a sealed tube ; but the green liquid obtained by either of these processes yields, when heated to 77° and 86° in a dry atmosphere, a dark green mass containing Cr203.3S03 -f- KO.SO3, with scarcely 6 eq. water (Loewel). The violet crystals containing 24 Aq., when left for several days in dry air at a temperature between 11^ and 86°, give off 12 Aq., and assume a lilac colour. At 212°, another quantity of water goes off, and the crystals become green; and, by gradually raising the temperature to about 660°, the whole of the water may be expelled without causing the salt to melt. The anhydrous crystals are green, and dissolve without residue in boiling water, but at a temperature somewhat above 660°, they suddenly become greenish-yellow, without perceptible loss of weight, and are afterwards perfectly in, soluble in water. Oxalate of chromium andpotashjS{KO.C20^) + Cr203,3C203 H- 6H0. — This is another beautiful double salt of chromium. * Ann. Ch. Phys. [3.] xliv. 313. VOL. IT. M 163 CHROMIUM. It is easily prepared by the following process of Dr. Gregory : — One part of bichromate of potash, two parts of binoxalatc of potash, and two parts of crystallised oxalic acid are dissolved together in hot water. A copious evolution of carbonic acid gas takes place, arising from the deoxidation of the chromic acid, at the expense of a portion of the oxalic acid; and nothing fixed remains, except the salt in question, of which a pretty concentrated solution crystallises upon cooling in pris- matic crystals, which are black by reflected light, but of a splendid blue by transmitted light, when sufficiently thin to be translucent. The oxide of chromium is not completely precipitated from this salt by an alkaline carbonate ; and it is remarkable that only a small portion of the oxalic acid is thrown down from it by chloride of calcium. When fully dried and then carefully ignited, this salt is completely de- composed, and leaves a mixture of chromate and carbonate of potash. The corresponding double oxalate of chromium and soda contains OHO, according to Mitscherlich. In the analo- gous oxalate of ferric oxide and soda, the proportion of water appeared to the author to be lOHO. The mineral chrome-iron^ FeO-CrjOg, crystallises in octo- hedrons, and corresponds with the magnetic oxide of iron, having the sesquioxide of iron replaced by sesquioxide of chromium. Its density is 4*5 ; it is about as soft as felspar, and infusible. When exposed to long-continued calcination, in contact with carbonate of potash, in a reverberatory fur- nace, the oxide of chromium of this compound absorbs oxygen, and combines as chromic acid with the potash, while the protoxide of iron becomes sesquioxide. The addition of nitre increases the rapidity of oxidation, but is not absolutely required in the process. A yellow alkaline solution of car- bonate and chromate of potash is obtained by lixiviating the calcined matter, which is generally converted into the red chromate or bichromate of potash, by the addition of the proper quantity of sulphuric acid, the latter salt being CHROMIC ACID. 163 more easily purified by crystallisation than the neutral cliro- mate. Chromic acid, CrOg, 52*19 or 651'8. — This acid is not liberated from the chromates in a state of purity by any acid except the fluosilicic; it is also easily altered. Fluosilicic acid gas is ccmducted into a warm solution of bichromate of potash, till the potash is completely separated as the insoluble fluoride of silicon and potassium, which may be ascertained by testing a few drops of the solution with tartaric acid or chloride of platinum. The solution is evaporated to dryness by a steam heat, and the chromic acid redissolved by water ; it gives an opaque, dull red solution. Chromic acid may also be obtained anhydrous and in acicular crystals, by distilling, in a platinum retort, a mixture of 4 parts of chromate of lead, 3 parts of finely pulverised fluor spar, and 7 parts of Nord- hausen sulphuric acid; sulphate of lime is formed, together with perfluoride of chromium, the vapour of which is received in a large platinum crucible, covered with wet paper and used as a condenser. The perfluoride is decomposed by the aqueous vapour from the paper, being resolved into hydrofluoric acid and beautiful orange-red acicular crystals of chromic acid, which fill the crucible. A third and easier method of pre- paring chromic acid is to mix a solution of bichromate of potash, saturated between 122° and 140°, with IJ times its volume of strong sulphuric acid, adding the acid by successive small portions. Bisulphate of potash is then formed, which remains in solution, and the liquid, as it cools, deposits the chromic acid in long red needles. These may be drained, first in a funnel, afterwards on a brick; then dissolved in water ; the solution treated with a small quantity of chromate of baryta to remove the last portion of sulphuric acid ; and the filtered liquid evaporated in vacuo. Chromic acid difters remarkably from sulphuric acid, in having but little affinity for basic water, so that it may be obtained anhydrous by evaporating its solution to dryness. Indeed, the chromate of M 2 164 CHROMIUM. water is not known to exist, even in combination, both the bichromate and terchromate of potash being anhydrous salts. The free acid is a powerful oxidizing agent, and bleaclies organic colouring matters : chromic acid then loses half its oxygen, and becomes oxide of chromium. It is also con- verted into sesquichloride of chromium by hydrochloric acid, with evolution of chlorine : 2Cr03 + 6HC1 = Cr2Cl3 -f- 6H0 + 3C1; and into sesquioxide by hydrosulphuric acid, with precipitation of sulphur : 2Cr03 + 3HS = Cr203 + 3110 + 3S. Sulphurous acid passed through a sclution of chromic acid, or its salts, throws down a brown precipitate, consisting of monochromate of chromic oxide, or bioxide of chromium; Cr203.Cr03 = 3Cr02. The other intermediate oxides, or chromates of chromic oxide mentioned on page 153., are formed by other imperfect reductions of chromic acid, or by the imperfect oxidation of chromic oxide. They are all brown substances, soluble in potash and in nitric acid. One of them, the bichromate, dissolves also without decomposition in hydrochloric and sulphuric acid ; the others are reduced by hydrochloric acid to sesquichloride, with evolution of chlorine, and resolved by sulphuric acid into chromic acid and sulphate of chromic oxide.* Chromic acid forms bibasic, monobasic, biacid, and a few tri-acid salts. Themonochromates of the alkalies are yellow, the bichromates red ; the chromates of the metals proper are bright yellow, red, or occasionally of some other colour. All chromates heated with oil of vitriol give off oxygen, and form sulphate of chromic oxide, together with another sulphate. When heated with hydrochloric acid, they give ojff chlorine * For a full account of these brown oxides, see the translation of QmeKn's Handbook, ir. 113. CHROMATES. 165 and form sesquichloride of chromium, together with another metallic chloride. Heated in the anhydrous state with com- mon salt and sulphuric acid, they give off red vapours of chlorochroraic acid, which condense to a brownish red liquid. Similarly, when heated with fluor spar and sulphuric acid, they give off red vapours of terfluoride of chromium. A few only of the chromates, more particularly those of the alkalies, are soluble in water, but they all dissolve in nitric acid. Solu- tions of the alkaline chromates form a pale yellow precipitate wdth baryta salts ; bright yellow with lead-salts ; brick red with mercurous salts ; and crimson with silver salts. Chromate of potash , Yellow chromate of potash, KO.CrOg ; 97'8 or 1222*5. — This salt is produced in the treatment of the chrome ore, but is seldom crystallised. It may be formed from the bichromate, by fusing that salt with an equivalent quantity of carbonate of potash ; or by adding caustic potash to a red solution of the bichromate, till its colour becomes a pure golden yellow. The solution of chromate of potash has a great tendency to effloresce upon the sides of the basin when evaporated. Its crystals are of a yellow colour, anhy- drous, and isomorphous with sulphate of potash. One hundred parts of water at 10° dissolve 48^^ parts of this salt ; the solu- tion preserves its yellow colour, even when diluted to a great degree. Bichromate of potash. Red chromate of potash. — K0.2Cr03 ; 148*6 or 1857*5. — This beautiful salt, of which a large quan- tity is consumed in the arts, crystallises in prisms or in large four-sided tables, of a fine orange-red colour. It fuses below a red heat, and forms on cooling a crystalline mass, the crys- tals of which have, according to Mitscherlich, the same form as those obtained from an aqueous solution ; but this mass falls to powder as it cools, from the unequal contraction of the crystals in different directions. At 60°, water dissolves -rV of its weight of this salt, and at the boiling point a con- siderably greater quantity. M 3 166 CHROMIUM. Bichromate of chloride of potassium, Peligofs salt, KCl. 2Cr03. — This salt, which we are obliged to designate as if it contained chloride of potassium combined as a base with chromic acid, is formed by dissohing together, with the aid of heat, about three parts of bichromate of potash and four of concentrated hydrochloric acid, with a small quantity of water, avoiding the evolution of chlorine. It ciystallises in fiat red quadrangular prisms, and is decomposed by solution in pure water. Terchromate of potash, KO.SCrOg, is obtained crj^stallised when a solution of the bichromate is mixed with nitric acid, and evaporated. Bichromates of soda and silver exist which are anhydrous, like the bichromate of potash (Warington). Chromate of soda, NaO-CrOg + lOHO.— By the evapora- tion of a concentrated solution of this salt, it is obtained in large fine crystals, having the form of glaubcr salt. The bichromate crystallises in thin, hyacinth-red, six-sided prisms, bevelled at the ends. Chromate of ammonia, NH40.Cr03 is prepared by evapora- ting a mixture of chromic acid with a slight excess of ammo- nia. It crystallises in lemon-yellow needles, very soluble in water, and having an alkaline reaction and pungent saline taste. When heated, they give off ammonia, water, and oxygen, and leave sesquioxide of chromium. The bichromate, NH40.2Cr03, forms orange-yellow or reddish bro^vn rhombic tables, which at a heat below redness are decomposed, with emission of light and feeble detonation, leaving the sesqui- oxide. It combines with chloride of mercury, forming crys- talline compounds, containing NH40.2Cr03.HgCl + HO, and 3(NH40.2Cr03).HgCl (Richmond and Abel).* Rammelsberg has obtained an acid salt composed of NH4O.6CrO3 + 10HO. Chromate of baryta, BaO.CrOg is a lemon-yellow powder obtainedby precipitating a baryta-salt with an alkaline chromate. * Chem. Soc. Qu. J. iii 139. CHROMATES. 167 It is insoluble in water, but dissolves easily in nitric, hydro- chloric, or chromic acid. When a baryta-salt is precipitated with neutral chromate of potash, and sulphuric acid added, the pre- cipitate dissolves with partial decomposition, and on diluting with water, mixing the filtered solution with chromic acid, and evaporating in vacuo, neutral chromate of baryta first separates, then crystals of a bichromate, Ba0.2Cr03 + 2HO, and afterwards a double salt containing 2(Ba0.3Cr03.HO) + (KO.3CrO3.HO). (Bahr.)* Neutral chromate of lime, CaO.Cr03, is obtained by treating carbonate of lime with aqueous chromic acid ; and by treating the neutral salt with excess of chromic acid and evaporating, a bichromate, Cr0.2Cr03 + 2H0, is obtained. Chloride of calcium mixed with monochromate of potash, yields a double salt containing 5(CaO.Cr03) + KO.CrOg. (Bahr.) Chromate of magnesia forms, according to the author's ob- servations, yellow crystals which are very soluble, and contain 5 HO. It does not form a double salt with chromate of potash, as sulphate of magnesia does with sulphate of potash. It is remarked that the insoluble metallic chromates generally carry down portions of the neutral precipitating salts, or of subsalts, and their analysis is often unsatisfactory from that cause. When the magnesian chromates are compared with the sulphates of the same family, the former are found to have their water readily replaced by metallic oxides, but not by salts; so that subchromates with excess of oxide are numerous, while few or no double chromates exist. Chromate of lead, PbO.CrOg ; 162*4 or 2030.— This com- pound, so well known as chrome-yellow, is obtained by mixing nitrate or acetate of lead with chromate or bichromate of potash. The precipitate is of a lighter shade from dilute than from concentrated solutions. It is entirely soluble in potash or soda, but not in dilate acids. Subchromate of lead, 2PbO.Cr03, is of a red colour. It is * J. pr. Chem. Ix. 60. If 4k 168 • CHROMIUM. formed when a solution of neutral chromate of potash^ mixed with as much free alkali as it already contains, is added to a solution of nitrate of lead. But the finest vermilion-red subchromate is formed when one part of the neutral chromate of lead is thrown into five parts of nitre in a state of fusion by heat. Water dissolves the chromate and nitrate of potash in the fused mass, and leaves the subchromate of lead as a crys- talline powder, (Liebig and Wohler). An orange pigment may be obtained very economically, by boiling the sulphate of lead, which is a waste product in making acetate of alumina from alum by means of acetate of lead, with a solution of chromate of potash. The subchromate of lead forms a beau- tiful orange upon cloth, which is even more stable than the yellow chromate, not being acted upon by cither alkalies or acids. One method of dyeing chrome-orange, is to fix the yellow chromate of lead first in the calico, by dipping it suc- cessively in acetate of lead and bichromate of potash, and then washing it. This should be repeated, in order to precipitate a considerable quantity of the chromate in the calico. A milk of lime is then heated in an open pan ; and when it is at the point of ebullition, the yellow calico is immersed in it, and instantly becomes orange, being deprived of a portion of its chromic acid by the lime, which forms a soluble chromate of lime. At a lower temperature, lime-water dissolves the chromate of lead entirely, and leaves the cloth white. Chromate of silver falls as a reddish brown precipitate when nitrate of silver is added to neutral chromate of potash. Dis- solved in hot and concentrated solution of ammonia, it yields, on cooling, large well formed crystals, AgO CrOg + 2NH3, isomorphous with the analogous ammoniacal sulphate and seleniate of silver. Chlorochromic acid, CrOgCl, or 2Cr03.CrCl3. — This is a volatile liquid, obtained by distilling, in a glass retort, at a gentle heat, 3 parts of bichromate of potash and 3 J parts of common salt, previously reduced to powder and mixed ESTIMATION OF CHROMIUM. 169 together, with 5 parts by water-measure of oil of vitriol, discontinuing the distillation when the vapours, from being of a deep orange-red, become pale — that change arising from watery vapour. The compound is a heavy red liquid, decom- posed by water. The density of its vapour is 5*9. Terfluoride of chromium, CvY^, is obtained in the manner already mentioned under the preparation of chromic acid. It is a blood-red liquid. No corresponding terchloride of chro- mium has been obtained in an isolated state. Per chromic acid, CrgO^. — When peroxide of hydrogen dissolved in water is mixed with a solution of chromic acid, the liquid assumes a deep indigo-blue colour, but often loses this colour very rapidly, giving off oxygen at the same time. The same blue colour is formed by adding a mixture of aqueous peroxide of hydrogen and sulphuric or hydrochloric acid to bichromate of potash; but, in a very short time, oxygen is evolved, and a potash-salt, together with a chromic salt, left in solution. For each atom of K0.2Cr03, four atoms of oxygen are evolved, provided an excess of HOg be present : K0.2Cr03 + O + 4SO3 = KO.SO3 + Cr203.3S03 + 40. The peroxide of hydrogen first gives up 1 at. O to the 2 at. of Cr03, and forms Crfiyj ; and this compound is subsequently resolved into Cr203 and 40. With ether, perchromic acid forms a more stable blue mixture than with water, and in this state may be made to unite with ammonia and with certain organic bases, forming very stable compounds, from which stronger acids separate the blue acid. ESTIMATION OF CHROMIUM, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. Chromium is usually estimated in the state of sesquioxide. When it exists in solution in that state, it may be precipitated 170 CHROMIUM. by ammonia, care being taken to avoid a large excess of that reagent (which would dissolve a portion), and to heat the liquid for some time. The chromic oxide is then completely precipitated, and the precipitate, after washing and drying, is reduced by ignition to the state of anhydrous sesquioxide, con- taining 70-1 per cent, of the metal. When chromium exists in solution in the state of chromic acid, it is best to precipitate it by a solution of mercurous nitrate ; the mercurous chromate thereby thrown down yields by ignition the anhydrous sesquioxide. The chromic acid might also be precipitated and estimated in the form of a baryta or lead salt. Chromic acid may also be estimated by means of oxalic acid, which reduces it to sesquioxide, being itself converted into carbonic acid. The quantity of carbonic acid evolved determines the quantity of chromic acid present, 3 eq. CO2 corresponding to 1 eq. CrOg, as shown by the equation : 2Cr03 + 3C2O3 = Cr203 + GCO2. The mode of proceeding is the same as that adopted for the valuation of black oxide of manganese (p. 17). If the object be merely to determine the quantity of chromium present, any salt of oxalic acid may be used ; but if the alkalies are also to be estimated in the remaining liquid, the ammonia or baryta salt must be used. Chromic oxide, in the state of neutral or acid solution, is easily separated from the alkalies or alkaline earths, by pre- cipitation with ammonia, care being taken in the latter case to protect the liquid and precipitate from the air. The same method, with addition of sal-ammoniac, serves to separate chromic oxide from magnesia. The separation from the alkaline earths and from magnesia may also be effected by precipitating the whole with an alkaline carbonate, and igniting the precipitate with a mixture of carbonate of soda and nitre. The chromium is then converted into chromate of soda, which ESTIMATION OF CHROMIUM. 171 may be dissolved out, and the solution, after neutralisation with nitric or acetic acid, treated with mercurous nitrate as above. From alumina and glucina, chromic oxide may be separated by treating the solution with excess of potash, and boiling the liquid to precipitate the chromic oxide. The separation is, however, more completely effected by fusing with nitre and carbonate of soda, treating the fused mass with water, adding an excess of nitric acid to dissolve anything that may be insoluble in water, and precipitating the alumina or glucina by ammonia. Another method of converting chromic oxide into chromic acid, and thereby effecting its separation from the above- mentioned oxides, is to treat the mixture with excess of potash, and heat the solution gently with bioxide of lead. The whole of the chromium is then converted into chromic acid, and remains dissolved as chromate of lead in the alkaline liquid ; and on filtering from the excess of bioxide of lead, and any other insoluble matter that may be present, and supersaturating the filtrate with acetic acid, the chromate of lead is precipitated (Chancel).* Chromic acid may be separated from the alkalies in neutral solutions by precipitation with mercurous nitrate; also by reducing it to chromic oxide with hydrochloric acid and alcohol, and precipitating by ammonia. From the earths it may also be separated by this latter method, or, again, by fusing with carbonate of soda, dissolving out with water, &c. From manganese, iron (in the state of protoxide), cobalt, nickel, and zinc, chromium in the state of sesquioxide may be separated by agitation with carbonate of baryta, which precipitates the chromic oxide, leaving the protoxides in solution. The precipitate is then treated with dilute sulphuric acid, which dissolves the chromic oxide and leaves the baryta, * Compt. rend, xliii. 927. 172 • VANADIUM. and the filtrate treated with ammonia to precipitate the chromic oxide. Chromium may also be separated from all these metals, except manganese, by fusion with nitre and carbonate of soda, or with the carbonate alone if it is already in the form of chromic acid. Or, again, the separation may be effected by means of potash and bioxide of lead, according to ChancePs method above described. From cadmium, copper , lead, and tin, chromium is easily separated by hydrosulphuric acid. When sesquioxide of chromium and chromic acid occur together in a solution, the chromic acid may be precipitated by mercurous nitrate, the solution being first completely neutralised, and the sesquioxide precipitated from the filtrate by ammonia, which at the same time throws down a mercury- compound, to be afterwards separated from the chromic acid by ignition. SECTION IV. VANADIUM. Eg. 68-55 or 856-9; V. Vanadium, so named from Vanadis, a Scandinavian deity, was discovered by Sefstroem in 1830, in the iron prepared from the iron ore of Taberg, in Sweden, and procured after- wards in larger quantity from the slag of that ore. It was found afterwards by Mr. Johnston, in a new mineral dis- covered by him, the vanadiate of lead, from Wanlockhead. It is one of the rarest of the elements. The metal itself has considerable resemblance in properties to chromium. It combines with oxygen in three proportions, forming the protoxide of vanadium, VO, bioxide, VO2, and vanadic acid, VO3. OXIDES OF VANADIUM. 173 Protoxide of vanadium, VO, 76*55 or 956*9, is produced by the action of charcoal or hydrogen upon vanadic acid. It is a black powder of semi-metallic lustre, and when made coherent by pressure, conducts electricity like a metal. It does not combine with acids, and exhibits none of the cha- racters of an alkaline base. It is readily oxidised when heated in the open air, and passes into the following com- pound. Bioocide of vanadium, Vanadic oxide, VOg, 84*55 or 1056*9, is produced by the action of hydrosulphuric acid and other deoxidating substances upon vanadic acid. When pure, it is a black pulverulent substance, quite free from any acid or alkaline reaction. It dissolves in acids, and forms salts, most of which are of a blue colour. Vanadic salts form, with the hydrates and monocarbonates of the fixed alkalies, a greyish- white precipitate of hydrated vanadic oxide, which dissolves in a moderate excess of the reagent, but is precipitated by a large excess in the form of a vanadite of the alkali. Ammonia in excess produces a brown precipitate, soluble in pure water, but insoluble in water containing ammonia. Ferrocyanide of potassium forms a yellow precipitate, which turns green on exposure to the air. Hydrosulphuric acid produces no pre- cipitate. Sulphide of ammonium forms a black-brown pre- cipitate, soluble in excess. Tincture of galls forms a finely- divided black precipitate, which gives to the liquid the appearance of ink. Bioxide of vanadium is also capable of acting as an acid, and forms compounds with alkaline bases, some of which are crystallisable. It is hence called vanadous acid, and its salts vanadites. These salts in the dry state are brown or black ; they are all insoluble in water, excepting those of the alkalies. The solutions of the alkaline vanadites are brown, but when treated with hydrosulphuric acid, they acquire a splendid red- purple colour, arising from the formation of a sulphur-salt. Acids colour them blue, by forming a double salt of vanadic 174 VANADIUM. oxide and the alkali. Tincture of galls colours them blackish- blue. The insoluble vanadites, when moistened or covered with water, become green, and are converted into salts of vanadic acid. Vanadic acid, VO3; 92-55 or 1156-9. — It is in this state that vanadium occurs in the slag of the iron-ore of Taberg, and in the vanadiate of lead. It is obtained by dissolving the latter mineral in nitric acid, and precipitating the lead and arsenic, with which the vanadium is accompanied, by hydro- sulphuric acid. A blue solution of bioxide of vanadium remains, which becomes vanadic acid when evaporated to dryness. Vanadic acid fuses but retains its oxygen at a strong red heat. It is very sparingly soluble, water taking up only l-lOOth of its weight of this compound, thereby acquiring a yellow colour and an acid reaction. It acts the part of a base to stronger acids. An interesting double phosphate of silica and vanadic acid was observed in crystalline scales, of which the formula is 2Si03.P05 + 2VO3.PO5 + 6H0. Vanadic acid forms, with bases, neutral and acid salts, the first of which admit of an isomeric modification, being both white and yellow, while the acid salts are of a fine orange-red. Vanadic and chromic acids are the only acids of which the solution is red, while they are distinguished from each other by the vanadic acid becoming blue, and the chromic acid green, when they are deoxidised. All the vanadiates are, more or less soluble in water; some of them, however, as the baryta and lead salts, are very sparingly soluble. The vanadiates of the alkalies are sparingly soluble in cold water, especially if it contains a free alkali or another alkaline salt ; e. g.j vanadiate of ammonia is nearly insoluble in water con- taining sal-ammoniac; hence on treating a solution of vana- diate of potash with excess of sal-ammoniac, a precipitate of vanadiate of ammonia is produced. The aqueous solutions of the vanadiates are coloured red by the stronger acids, but the mixture often becomes colourless again after a while. They ESTIMATION OF VANADIUM. 175 give orange-red precipitates with the salts of teroxide of antimony, protoxide of lead, protoxide of copper, and prot- oxide of mercury. Hydrosulphuric acid produces in neutral solutions of the vanadiates a mixed precipitate of sulphur and hydrated vanadic oxide ; in acid solutions, it merely throws down sulphur and reduces the vanadic acid to vanadic oxide. Sulphide of ammonium imparts to solutions of the vanadiates a brown-red colour, and, on adding an acid to the solution, a light brown precipitate is formed, consisting of vanadic sul- phide mixed with sulphur; the liquid at the same time generally acquires a blue colour. All compounds of vanadium heated with borax or phos^ p)horus salt in the outer blowpipe flame, produce a clear bead, which is colourless if the quantity of vanadium be small, yellow if it be large; in the inner flame, the bead acquires a beautiful green colour. Sulphides and chlorides of vanadium, corresponding with the bioxide and vanadic acid have likewise been formed.* ESTIMATION OF VANADIUM, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. Vanadium, in the state of vanadic oxide or vanadic acid, is estimated by reducing it to the state of protoxide by ignition in a stream of hydrogen ; 100 parts of the protoxide contain 90-54 of the metal. In solutions of vanadous salts, the vanadium is precipitated by mixing the solution with excess of mercuric chloride (cor- rosive sublimate), and then with ammonia. The precipitate, consisting of mercuric vanadiate, and amido- chloride of mer- cury, is ignited, whereupon vanadic acid remains mixed only with a small quantity of mercuric oxide, from which it is separated by solution in carbonate of ammonia. * Berzeliua, Ann. Cli. Pliys. [2.] xlvii. 337. 176 TUNGSTEN. When vanadic acid is dissolved in a liquid, it may be ob- tained by evaporating the liquid, and if volatile acids or ammonia are also present, by igniting the residue. Vanadic acid may be separated from many acids and other substances, by causing it to unite with ammonia, expelling the excess of ammonia by evaporation, and then adding a saturated solution of sal-ammoniac, in which vanadiate of ammonia is insoluble. The precipitate is then washed on a filter, first with solution of sal-ammoniac, then with alcohol, and the ammonia driven ofi* by ignition. This method serves to separate vanadic acid from the fixed alkalies. Vanadium may be separated from many of the preceding metals by the solubility of its sulphide in sulphide of ammo- nium ; and from others, which are precipitated from their acid solutions by hydrosulphuric acid, by acidulating the liquid, and passing hydrosulphuric acid gas through it ; the vanadium then remains dissolved in the form of vanadic oxide. From leadf baryta, and strontia, vanadic acid may be separated by fusion mth bisulphate of potash ; on treating the fused mass with water, sulphate of lead, baryta, or stron- tia remains, while vanadiate of potash is dissolved. Sulphuric acid cannot be used to effect this separation, because the pre- cipitated sulphate always carries down with it a portion of the vanadium. SECTION V. TUNGSTEN. Syn. WOLFRAM. Eq. 94*64, or 1183 ; W. This element exists in the form of tungstic acid in several minerals, the most important of which are the native tungstate of lime CaO.WOg, and wolfram, or the tungstate of manganese and iron, MnO.WOg H-3(FeO.W03). Its name tungsten TUNGSTEN". 177 ineatis in Swedisii_, heavy stone, and is expressive of the great density of its compounds. Tungstic acid parts with oxygen easily, and may be reduced in a glass tube, by means of dry hydrogen gas, at a red heat. The metal is thus obtained in the state of a dense, dark grey powder, which it is necessary to expose to a very violent heat to fuse into globules, for tungsten is even less fusible than manganese. The metal, when fused, has the colour and lustre of iron, and is not altered in air : it is one of the densest of the metals, its specific gravity being from 17*22 to 17*6. By passing the vapour of chloride or oxy chloride of tungsten mixed with hydrogen, through a red-hot glass tube, the metal is obtained in the form of a dense specular film of steel-grey colour, and sp. gr. 16-54 (Wohler). When heated to redness in the pulverulent form, it takes fire, burns, and is converted into tungstic acid. Tungsten forms two com- pounds with oxygen, viz., tungstic oxide, WO2, and tungstic acid, WO3. Tungstic oxide, WO2, 110-64 or 1383.— This oxide is ob- tained as a brown powder when tungstic acid is reduced by hydrogen at a temperature not exceeding low redness. Tung- stic acid may also be deprived of oxygen in the humid way, by pouring diluted hydrochloric acid over it, and placing zinc in the liquor; the tungstic acid then gradually changes into tungstic oxide, in the form of brilliant crystalline plates of a copper-red colour. No saline compounds of this oxide with acids are known. When digested in a strong solution of hydrate of potash, it dissolves, with disengagement of hydrogen gas and formation of tungstate of potash. A compound of tungstic oxide and soda, Na0.2W02, of a very singular nature, was discovered by Wohler. It is obtained by adding to fused tungstate of soda as much tungstic acid as it will take up, and exposing the mass at a red heat to hydrogen gas. After dissolving out the neutral undecomposed tungstate by water, the new compound remains in golden VOL. II. N 178 TUNGSTEN. yellow scales and regular cubes, possessing tlie metallic lustre of, and a striking resemblance to gold. This compound is not decomposed by aqua rcgia, sulphuric or nitric acid, or by alkaline solutions, but yields to hydrofluoric acid. It cannot be prepared by uniting soda directly Avith tungstic oxide. Tungsttc acid, WO3 ; 118'G1< or 1483, is most conveniently obtained by decomposing the*native tungstate of lime, finely pulverised, by hydrochloric acid ; chloride of calcium is dis- solved, and tungstic acid precipitates. It is also obtained from wolfram by digesting that mineral in nitro-hydrochloric acid, which dissolves the oxides of iron and manganese, and leaves the tungstic acid in the form of a yellow powder — or by fusing the mineral ^-ith four times its weight of nitre ; treating the fused mass with water to dissolve out the tungstate of potash thereby produced ; adding chloride of calcium to the filtrate to throw down the tungstic acid as tungstate of lime; and decomposing the washed lime-salt with nitric acid. Dissolved in ammonia and reprecipitated by acids, tungstic acid always forms a compound with the acid employed. It may be ob- tained in the separate state by heating the tungstate of ammonia to redness. It is an orange-yellow powder, which becomes didl green when strongly heated. Its density is 6*12. It is quite insoluble in water and in acids, but dissolves in alkaline solutions. Tungstic acid forms both neutral and acid salts with the alkalies. Neutral tungstate of potash KO.WO3 is a very soluble salt, which may be obtained in small crystals by evaporating its solution. When a little acid is added to the solution, an acid salt precipitates, which is very slightly soluble in water. The neutral tungstate of soda is also very soluble, but may be obtained in good crystals, which contain a large quantity of water of crystallisation. The acid tung- state of soda Na0.2\V03 is very crystallisable, and soluble in eight parts of water. A combination of tungstic acid with tungstic oxide, WO2.WO3, is obtained as a fine blue powder when tungstate of ammonia is heated to redness in a TUNGSTIC ACID. 179 retort, and is also produced under other circumstances. Malaguti is disposed to consider this compound as a distinct acid of tungsten, W2O5. * All the salts of tungstic acid have a very high specific gra- vity. The alkaline and earthy tungstates are colourless. The only soluble tungstates are those of the alkalies and magnesia. Solutions of the alkaline tungstates give, with hydrochloric, nitric, sulphuric, and phosphoric acid, white precipitates con- sisting of compounds of tungstic acid with the other acid. The precipitate formed by phosphoric acid dissolves in excess of that reagent ; the precipitates formed by the other three acids turn yellow on boiling. A solution of an alkaline tungstate supersaturated with sulphuric, hydrochloric, phosphoric, oxalic, or acetic acid, yields, on the introduction of a piece of zinc, a beautiful blue colour arising from the formation of bljie oxide of tungsten ; this effect is not produced with nitric, tartaric, or citric acid. Solutions of alkaline tungstates form with lime- water and with salts of baryta, lime, zinc, lead, mercury, and silver, white precipitates consisting of tungstates of those bases. A soluble tungstate mixed with sulphide of ammonium and then with an acid in excess, yields a light brown precipi* tate of sulphide of tungsten, soluble in sulphide of ammonium. With borax and phosphorus-salt in the outer blow-pipe flame, tungstic acid forms a colourless bead; in the inner flame it forms with borax, a yellow glass, if the quantity of tung- sten present be somewhat considerable, but colourless with a smaller quantity. With phosphorus- salt in the inner flame it forms a glass of a pure blue colour, unless iron is also present, in which case the colour is blood-red; the addition of tin, however, renders it blue. The above mentioned characters of tungstic acid, though general, are not invariable. Tungstic acid appears to be sus- ceptible of certain modifications analogous to those of phos- phoric acid, and depending upon the proportions in which it * Ann. Ch. Phys. [2], Ix. 271. N 2 180 TUNOSTEN. unites with water and other bases. In some of these modifi- cations it is much more soluble than in others^ and is not precipitated by nitric or hydrochloric acid. Laurent distinguished five or six classes of tungstates, viz., 1. Ordinary tungstates, WO3MO, with or without water (M denoting a metal or hydrogen). To this class belong the neu- tral potash, soda, and baryta-salts, and most of the insoluble salts of tungstic acid. No acid salts of this class appear to exist. The solution of an ordinary tungstate dropped into excess of dilute nitric acid produces a gelatinous precipitate. The hy- drated tungstic acid obtained by the action of aqua regia on wolfram belongs to this variety, its formula being WO3.HO. 2. ParatungstateSj W^Oij-SMO, with or without water. To this class belong the salts commonly called bitungstates of potash, soda, ammonia, baryta, &x;. They all, excepting the soda-salt, dissolve but sparingly in water. The solutions give no precipitate on the addition of very small quantities of nitric acid, or of very weak hydrochloric acid. They give precipitates with the ammoniacal solutions of nitrate of mag- nesia, zinc, and silver, which the ordinary tungstates do not. 3. MetatungstateSy \V3O9.MO, with or without water. The ammonia-salt of tliis variety is formed by boiling a solution of the paratungstate for several hours ; the solution filtered when cold and then evaporated to a syrup, yields very soluble octohedrons. The solution is not precipitated by concentrated hydrochloric acid — 4. Isotung states, WjOg.MO, with or with- out water. The ammonia-salt is formed by boiling meta- tuugstate of ammonia with excess of ammonia; it is but slightly soluble in water. The acid, which may be separated from it by means of another acid, is principally characterised by reproducing the isotungstate when treated with ammonia. 5. Poly tungstates J WgOig.SMO. When the yellow acid ob- tained from wolfram is treated with ammonia, and the solution slowly evaporated, paratungstate of ammonia is first deposited and afterwards the isotungstate. The mother-liquor separates TUNGSTATES. 181 into two layers, one of whicli is brown and syrupy, and changes on drying to an easily soluble crystalline mass, probably a double salt of ammonia and iron. Boiled with strong nitric acid, it yields a precipitate which is not gelatinous, and does not turn yellow when boiled. Polystungstic acid is further characterised by forming with ammonia a very soluble salt, which becomes gummy on evaporation. 6. Laurent also, mentioned another class of tungstates, viz., Homotungstates, containing WgO^g . MO. According to Margueritte * also there exist acid tungstates containing 3, 4, 5 and 6 eq. of acid to 1 eq. of base. The composition of the tungstates has also been recently examined by W. Lotz f, whose results differ in many points from the preceding. According to Lotz, crude tungstic acid, obtained from wolfram by the action of hydrochloric and a small quantity of nitric acid, yields by digestion with ammo- nia and evaporation at a very gentle heat, yellow needles of an ammonia-salt containing 3NH4O . 7WO3 + 6H0, or 2(NH40.2W03) + NH4O . 3WO3 + 6H0. By mixing warm concentrated solutions of 1 eq. of monotungstate of soda, and rather more than 1 eq. chloride of ammonium, a double salt is obtained, composed of (2NH4O . WO3) + NaO . WO3 + 3H0; and by adding 1 eq. metatungatate of soda to a boiling solu- tion of 2 eq. chloride of ammonium, another double salt is formed containing 3NaO . 7WO3 + 4(3NH40 . 7WO3) + 14H0. The needle-shaped ammonia- salt mixed wdth solutions of the neutral salts of barium, strontium, manganese, nickel, and lead, yields precipitates of the general formula 3MO . 7WO3. With alumina a white curdy precipitate is formed containing AI2O3 . 7WO3 -f 9H0. Sesquioxide of chromium forms a salt of a similar constitution. With magnesia, a sparingly soluble crystalline double salt is formed, containing 2(MgO . 2WO3) + NH4O . 3W03H- lOHO ; a similar double salt with zinc. Cad- * Ann. Ch. Phys. [3], xvii. 475. t Ann. Cli. Phann. xci. 49. K 3 182 TUNGSTEN. mium also forms a double salt containing SNH^O . 7WO3 + 4(3CdO . 7W3O) + 35HO. To the octoliedral tungstate of am- monia, "which was regarded by Margueritte as NH^O . 3WO3 + 5 HO, and by Laurent as a metastungstate containing (NH4)^H.W30,o + 5IIO,or^^^^4^l I8WO3 + 3OHO. Lotz assigns the formula 2(NH40 . 4WO3) + 15 eq. The solution of this salt is not precipitated by nitric or hydrochloric acid at ordinary temperatures, but after continued boiling yields a yellow precipitate ; but if it be previously mixed with potash, the addition of an acid produces an immediate white precipi- tate, which turns yellow on boiling ; the needle-shaped salt gives an immediate precipitate with acids, witliout previous addition of alkali. The octohedral salt diftcrs from the needle-shaped salt also, in not forming precipitates with solutions of the earths and other metallic oxides, except when previously mixed with ammonia, by which, indeed, it is con- verted into the salt 3NH4O . TWOj. Sulphides of tungsten. — The bisulphide is prepared by mix- ing one part of tungsten with six parts of cinnabar, and exposing the mixture, covered witli charcoal, in a crucible, to a white heat ; or, according to Roche, by fusing bitung- state of potash with an equal weight of sulphur, and washing the fused mass with water. The tersulphide is formed by dissolving tungstic acid in an alkaline sulphide, and precipi- tating by an acid. It is of a liver-brown colour, and becomes black on drying. The tersulphide of tungsten has a certain degree of solubility in water containing no saline matter, and is a strong sulphur-acid. The salt KS.WS3 fonns pale red crystals. Two parts of this sulphur-salt dissolved in water with one part of nitre, give large and beautiful ruby-red crystals of a double salt, KS.\VS3H-KO.K05. Phosphides of tungsten. — Phosphorus and tungsten com- bine directly, but without emission of light and heat, when finely pounded metallic tungsten contained in a glass tube is CHLORIDES OF TUNGSTEN. 183 lieated to redness in phosphorus vapour. The resulting compound is a dull, dark grey powder, very difficult to oxidise, and containing W3P2- Another compound, W^P, is obtained in magnificent crystalline groups, having exactly the appear- ance of natural geodes, by reducing a mixture of 2 eq. phos- phoric and 1 eq. tungstic acids at a very high temperature in a crucible lined with charcoal. The crystals are six-sided prisms, sometimes an inch long, of a steel-grey colour, and strong lustre; their specific gravity is 5 '207. This compound is a perfect conductor of electricity; undergoes no change when heated to the melting point of manganese in a close vessel, and remains nearly unaltered when heated to redness in the air; but burns with great splendour on charcoal in a stream of oxygen, or on fused chlorate of potash ; it is not attacked by any acid, not even by aqua-regia (Wohler).* Bichloride of tungsten, WCI2, is formed when metallic tungsten is heated in chlorine gas. It condenses in dark red needles, which are very fusible and volatile. This chloride is decomposed by water, and tungstic oxide with hydrochloric acid formed. Terchloride of tungsten, WCI3, is produced at the same time as the last compound, and also when the sulphide of tungsten is heated in chlorine gas. It forms a sublimate of beautiful red crystals, which are resolved by water into tungstic and hydrochloric acids. A chlorotungstic acid, or double com- pound of terchloride of tungsten and tungstic acid, WO2CI, or WCI3 . 2WO3, is prepared by heating tungstic oxide, in chlorine gas. It condenses in yellow crystalline scales : when suddenly heated, it is resolved into tungstic acid, bichloride of tungsten, and chlorine. Another compound is known, containing 2WCI3 . WO3 (Bonnet). According to A. Richef, the terchloride of tungsten is the only product obtained when tungsten is heated in pure dry * Chem. Soc. Qu. J. v. 94. f Compt. rend. xlii. 203. N 4 184 j:STIMATION OF TUNGSTEN. chlorine gas : it crystallises in needles, not of a red but of a steel-grey colour. The bichloride is formed in small quan- tity, as a blackish-brown mass, by heating the terchloride in dry hydrogen ; and the red oxychloride WCI2O, by passing chlorine gas over a mixture of tungstic acid and charcoal, and distilHng the product in an atmosphere of hydrogen. ESTIMATION OF TUNGSTEN, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. Tungsten is always estimated in the form of tungstic acid. When this acid exists in a solution not containing any other fixed substance, it is sufficient to evaporate to dryness and ignite the residue. The tungstic acid is then obtained in a state of purity, and contains 79*7G per cent, of the metal. Tungstic oxide is easily converted into tungstic acid by fusion with carbonate of soda. The best method of separating tungstic acid from the fixed alkalies is to treat the solution, after exact neutralisation with nitric acid, with a solution of mercurous nitrate. Mercurous tungstate is then precipitated, and the mercury may be ex- pelled from the dried precipitate by careful ignition in a good draught. The separation of tungstic acid from the earths may be eflPected by decomposing the compound with nitric acid, and treating the decomposed mass with carbonate of ammonia, which dissolves the tungstic acid. Tungstic acid may be readily separated from many metallic oxides, such as the oxides of iron, manganese, nickel, cobalt, /fflc?, &c., by fusing the whole Avith carbonate of soda, and digesting the fused mass with water, which dissolves the tungstic acid and leaves the oxides undissolved. From titanic acid, tungstic acid is separated by ammonia, which dissolves only the latter. The best mode of separating tungstic acid from chromic MOLYBDENUM. 185 acid, is to treat the concentrated solution with excess of hydrochloric acid^ which precipitates the greater part of the tungstic acid ; then boil with alcohol to reduce the chromic acid to chromic oxide; and dissolve the tungstic acid by ammonia. SECTION VI. MOLYBDENUM. Eq. 47-88 or 598*5 ; Mo. This metal is closely allied to tungsten. Its native sul- phide was first distinguished from plumbago by Scheele, in 1778; and a few years afterwards^ molybdic acid^ w^hich he had formed, was reduced, and molybdenum obtained from it, by another Swedish chemist, Hjelm. The name molybdenum is derived from the Greek term for plumbago. The oxides of molybdenum are easily reduced, when exposed to a strong heat in a crucible lined with charcoal, but the metal itself is very refractory. Bucholz, who obtained it in rounded buttons, found it to be a white metal, of density between 8'615 and 8-636. It may be reduced from its chlo- rides by hydrogen, like tungsten (p. 177.), and then forms a light steel- grey specular deposit, adhering to the glass (Wohler). It is not acted upon by hydrochloric, hydro- fluoric, or diluted sulphuric acid; but is dissolved by con- centrated sulphuric acid, by nitric acid, and by' aqua-regia. Hydrate of potash does not dissolve this metal in the humid way. Molybdenum combines in three proportions with oxy- gen, forming molybdous oxide, MoO, molybdic oxide, MoO-y and molybdic acid, M0O3. Molybdous oxide, MoO, 55-88 or 698-5. — This oxide is obtained by adding to the concentrated solution of any 18G MOLYBDENUM. molybdate, so mucli hydrochloric acid as to redissolve the molybdic acid which is at first thrown down, and placing zinc in the liquid ; this becomes first blue, then reddish-brown, and finally black, and contains the chloride of zinc and proto- . chloride of molybdenum. To separate the oxide of molyb- denum from the oxide of zinc, ammonia is added to the liquid in quantity no more than sufficient to precipitate the former, while the latter remains in solution. The molybdous oxide carries down with it a portion of oxide of zinc, from which it may be freed by washing with ammonia : it is thus obtained as a hydrate of a black colour. The hydrate of molybdous oxide dissolves with difficulty in acids, forming solutions which are almost black and opaque, and which do not yield crystallisable salts. These solutions yield with the alkalies and their carbonates a brownish-black precipitate of the hydrated oxide, insoluble in the caustic alkalies, slightly soluble in the neutral carbonates, but readily soluble in bicar- bonate of potash or carbonate of ammonia. HydrosulpJiuric acid throws down a brown-black precipitate, and sidphide of ammonium a yellowish-brown precipitate of sulphide of molybdenum, easily soluble in sulphide of ammonium. FeiTo- cyanide or ferricyanide of potassium forms a dark-brown precipitate, insoluble in excess. Phosphate of soda forms a brownish-white precipitate. Molybdous oxide resists, after ignition, the action of all acids. Molybdic oxide, MoOg ; 6388 or 798-5. — This oxide may be obtained by igniting molybdate of ammonia in a covered crucible, but mixed with a little molybdic acid. It is better procured by igniting rapidly, in a covered crucible, a mixture of anhydrous molybdate of soda (which may contain an excess of soda) with sal-ammoniac. Water poured upon the fused mass dissolves common salt, and leaves a brown powder almost black. But molybdic oxide prepared in this way is insoluble in acids. The hydrated oxide may MOLYBDIC ACID. 183? be obtained in various ways, one of which consists in digesting molybdic acid with hydrochloric acid and copper, till all the molybdic acid is dissolved. From the solution, which is of a deep-red colour, molybdic oxide is precipitated, in appearance exactly similar to the hydrated sesquioxide of iron, by ammonia added in sufficient excess to retain all the oxide of copper in solution. The hydrate has a certain degree of solubility in pure water, and should, therefore, be washed with solution of sal-ammoniac, and lastly with alcohol. This hydrate reddens litmus paper, but possesses no other property of an acid. It is not dissolved by the hydrated alkalies, but is soluble in their carbonates, like several earths and metallic oxides. It dissolves in acids and forms salts, which are red when they contain water of crystallisation, and black when anhydrous. The aqueous solutions of these salts have a reddish-brown colour, and a rough, somewhat acid and subsequently metallic taste. When heated in the air, they have a tendency to become blue by oxidation. With zinc, they first blacken, and then yield a black precipitate of hydrated molybdous oxide. Their behaviour with alkalies, hydrosulphuric acid &c., is similar to that of the molybdous salts, excepting that the precipitates are lighter in colour. The oxalate of molybdic oxide may be obtained in crystals by spontaneous evaporation. Molybdic acid, M0O3 ; 71*88 or 898*5. — The native sulphide of molybdenum, in fine powder, is roasted in an open crucible, with constant stirring, at a heat not exceeding low redness, so long as sulphurous acid goes off. It leaves a dull yellow powder, which is impure molybdic acid. This is dissolved in ammonia, and the molybdate of ammonia purified by evapora- tion, during which some foreign matters are deposited, and crystallised. The crystallised salt, exposed to a moderate heat, so as to avoid fusion, gives off its ammonia, and leaves molybdic acid in a state of purity. The acid thus prepared is 188 MOLYBDENUM. a white and light porous mass, which may be diffused in water, and divides into little crystalline scales of a silky lustre. It fuses at a red heat, and forms on cooling a straw-coloured crystalline mass, the density of which is 3*49. This acid forms no hydrate. It requires 570 times its weight of water to dis- solve it. Before being ignited, it is soluble in acids, and forms a class of compounds, in which it appears to play the part of base, but of which not much is known. When boiled with bitartrate of potash, molybdic acid dissolves, even after being fused by heat. "WTien a solution of bichloride of molybdenum is poured into a saturated or nearly saturated solution of molybdate of ammonia, a blue precipitate falls, which is a molybdate of molybdic oxidCy MO2.2MO3. This compound is likewise readily formed in a variety of other circumstances. The salts of molybdic acid are colourless, when their base is not coloured. When they are treated with other acids, molybdic acid is precipitated, but dissolves in an excess of the acid. It forms both neutral and acid salts with the alkalies. Tliese alkaline molybdatcs are the only ones that are easily soluble in water; of the rest, some dissolve sparingly, and others are completely insoluble. Solutions of the alka- line molybdatcs are coloured yellow by hydrosulphuric acid from formation of a siilphomolybdate of the alkali-metal (MS,MoS3), and then yield with acids a brown precipitate of tersulphide of molybdenum. This is an extremely delicate test for molybdic acid. They form white precipitates with salts of the earths, and precipitates of various colours with salts of the heavy metals ; e. g. white with lead and silver salts ; yellow with ferric salts ; and yellowish- white with merciirous salts. — Protochloride of tin produces immediately a greenish blue precipitate, soluble in hydrochloric acid forming a green solution ; which turns blue on the addition of a very small quantity of the tin-solution. — When tribasic phosphoric acid, or a liquid containing it, is added to the MOLYBDATES. 189 solution of molybdate of ammonia, together with an excess of hydrochloric acid_, the liquid turns yellow, and after a while deposits a yellow precipitate of molybdic acid combined with small quantities of phosphoric acid and ammonia. This pre- cipitate is soluble in ammonia and likewise in excess of the phosphate. The reaction is therefore especially adapted for the detection of small quantities of phosphoric acid. The bibasic and monobasic phosphates do not produce the yellow precipitate. Arsenic acid gives a similar reaction. According to Seligsohn*, the yellow precipitate is sl phosphomolybdate of ammonia 2(Sl>illfi . PO5) + 15(H0 . 4M0O3). By digesting it in a dilute solution of acetate of potash or soda, crystal- line double salts are formed, containing 2(3NH40.P05) + ^ q|.4Mo03J. With acetate of baryta, a double salt is formed, containing SNH^O.POg + 30(BaO.MoO3); and similarly with acetate of lead. Molybdic acid and other compounds of molybdenum form a colourless bead with borax and phosphorus-salt in the outer blowpipe flame. In the inner flame, they form a brown bead with borax and a green bead with phosphorus-salt. Molybdates of potash. — The monomolybdatCj KO.M0O3, i^ obtained by agitating the termolybdate with- an alcoholic solution of potash : it then separates as an oily mass, which, when dried over lime and sulphuric acid, crystallises in four- sided prisms containing 2(KO.Mo03) 4- HO. It is also ob- tained by mixing a solution of molybdate of ammonia with excess of carbonate of potash, and evaporating to a syrup. Bimolybdate of potash does not appear to exist. When a solution of molybdic acid in carbonate of potash is mixed with strong nitric or hydrochloric acid till a slight permanent pre- cipitate is produced, the liquid after a while yields crystals of a salt containing 4KO.9M0O3 + 6H0 : and this salt is decom- * J. pr. Cliem. Ixvii. 474. 190 MOLYBDENUM. posed by water into monomolybdate, which dissolves readily, and termolybdate which is sparingly soluble : 2(4K0.9Mo03) = 3(KO.Mo03) + 5(K0.3Mo03). The termolybdate dissolves easily in Ipoiling water, and separates as a bulky white precipitate when the solution is quickly cooled ; but by slow cooling it is obtained in needles, having a beautiful silky lustre and containing KO.3M0O3 + 3 HO. Nitric acid added in excess to a solution of molybdic acid in carbonate of potash throws down a white precipitate consisting sometimes of quadromolybdate and sometimes of poitamo- lybdate of potash, both anhydrous (Svanberg and Struve).* Monomohjbdatc of soda, NaO.MoOa + 2110, is obtained by fusing molybdic acid with an equivalent quantity of carbonate of soda. It is easily soluble in water, and crystallises in small rhombohcdrons, which melt easily and give off their water. The bimolybdate, Na0.2Mo03 + IIO, is obtained in a similar manner. It crystallises in needles, and dissolves sparingly in cold, readily in boiling water. The termolybdate is obtained by adding nitric acid to a solution of molybdic acid in car- bonate of soda, as a bulky white precipitate, more soluble than the corresponding potash-salt. The solution yields crys- tals containing Na0.3Mo03 -f 7110. Nitric acid added in excess to a solution of molybdate of soda throws down nothing but molybdic acid (Svanberg and Struve). f Monomolybdate of ammonia, NH4O.M0O3, obtained by treating molybdic acid in excess with strong solution of ammonia in a closed vessel, then precipitating with alcohol, and drying over quick lime, forms microscopic four-sided prisms, which are anhydrous. The bimolybdate, NH40.^Mo03, is deposited as a white crystalline powder when a solution of molybdic acid in excess of ammonia is quickly evaporated. A solution of molybdic acid in ammonia, evaporated by heat to * Ann. Cli. Pharm. Ixviii. 494. f Ann. Cli. Pliarm. Ixviii. 404. MOLYfiDATES. 191 the crystallising point, or left to evaporate in the air_, deposits large transparent six-sided prisms containing NH4O.2M0O3 + NH4O.3M0O3 + 3H0 (Svanberg and Struve). Monomolybdate of baryta^ BaO.MoOa, is precipitated as a sparingly soluble crystalline powder gn adding chloride of barium to a solution of molybdic acid in excess of ammonia* Baryta-salts, containing BaO.SMoOg + SHO and Ba0.2Mo03 -f- Ba023Mo03 + 6H0, are obtained by precipitating the cor- responding potash and ammonia-salts with chloride of barium. By decomposing monomolybdate of baryta with dilute nitric acid, an acid salt is formed containing Ba0.9Mo03 + 4HO ; it crystallises in small six-sided prisms, fusible and insoluble in water (Svanberg and Struve). Monomolybdate of magnesia^ MgO.Mo03 4- 5H0, is obtained in distinct crystals by boiling molybdic acid and magnesia alba with water, and evaporating the filtrate; it gives off 3 eq. water at 212'' (Struve).* Molybdate of manganous oxide, MnO.Mo03 •\- HO, is ob* tained as a heavy white powder, by treating carbonate of manganese with termolybdate of potash or soda. Protosulphate of iron added to a solution of molybdate of potash, reduces the molybdic acid to a lower state of oxida- tion j but if chlorine gas be passed through the solution at the same time, a bulky precipitate is formed, which, when dried in the air, forms a light yellow powder, consisting oi pentamo- lybdate of ferric oxide, re203.5Mo03 + 16H0. By boiling the solution of termolybdate of potash or soda, or acid molybdate of ammonia, with hydrate of alumina, man- ganic oxide, ferric oxide, or chromic oxide, and evaporating to the crystallising point, double salts are obtained. The com- position of the double salts containing alumina, ferric oxide, or chromic oxide with potash or oxide of ammonium, may be represented by that of the alumina and potash-salt, viz., * Ann. Ch. Pharm. xcvi. 266. 192 MOLYBDENUM. AI2O3.6M0O3 + 3(K0.2Mo03) + 20HO. The potassio-man ^amc salt contains Mn203.6Mo03+ 5(KO,2Mo03) + 12H0. The ammonio -manganic salt is similarly constituted. The sodio-chromic salt contains Cr203.6Mo03 + 3(Na0.2Mo03) + 21 HO (Struve). Acid molybdate of ammonia, added to a boiling solution of sulphate of copper, throws down a heavy green amorphous powder, consisting of basic molybdate of copper y 4CUO.3M0O3 -1- 5H0. By adding molybdate of ammonia in excess to a cold solution of sulphate of copper, a double salt is formed, consisting of CUO.2M0O3 + NH4O.3M0O3 + 9H0. It is a white-blue crystalline powder, which gives off 4 eq. of water at 212° and 4 eq. more at 266° (Struve). Molybdate of lead, PbO.Mo03, is formed by precipitating nitrate of lead with termolybdate of potash. It is a heavy white powder which melts only at a high temperature. It occurs finely crystallised as a mineral. Chromate of lead is dimorphous, and corresponds in the least usual of its forms with molybdate of lead : hence molybdenum is connected with the magnesian metals, and tungsten also with the same class, from the isomorphism of the tungstates and molybdates. Sulphides of molybdenum. — The bisulphide is the ore from which the compounds of this metal are derived. It occurs in many parts of Sweden, and might be procured in quantity if any useful application of the metal were discovered. It is a lead-grey mineral, having the metallic lustre, composed of flexible lamince. soft to the touch, and making a streak upon paper like plumbago. Nitric acid oxidates it easily, without dissolving it. Its density is from 4*138 to 4*569. A tersuU phide of mohjbdenum is obtained in the same way as the corresponding compound of tungsten, and affords crystallisa])le sulphur-salts which are red. The sulphomolybdate of potas- sium combines likewise with nitrate of potash. When a solution of the former salt is boiled with tersul phide of molyb- denum in excess, the latter is converted into l^isulpliide of ESTIMATION OP MOLYBDENUM. 193 molybdenum, and a quadrisulphide of molyhdenum dissolves in combination with the sulphide of potassium. The quadrisul- phide may be precipitated by hydrochloric acid, and when dried is a cinnamon-brown powder. Chlorides of molybdenum. — A protochloride is formed when molybdous oxide is dissolved in hydrochloric acid j the bichlo- ride when molybdenum is heated dry in chlorine gas, as a dark -red gas which condenses in crystals, like those of iodine. It forms a crystallisable double salt with sal-ammoniac. Chloromolybdic acid, or a compound of terchloride of molyb- denum and molybdic acid, M0O2CI, or M0CI3 -1- 2M0O3, is formed with (molybdic acid), when molybdic oxide is exposed to chlorine gas at a red heat. It sublimes below a red heat, and condenses in crystalline scales, which are white with a shade of yellow. ESTIMATION OP MOLYBDENUM, AND METHODS OP SEPARATING IT FROM THE PRECEDING METALS. The determination of molybdic acid is more difRcult than that of tungstic acid, on account of its partial volatility. The best mode of estimating it is to convert it into molybdic oxide by ignition in an atmosphere of hydrogen ; the oxide which is perfectly fixed may then be weighed ; it contains 74*95 per cent, of the metal. When molybdic acid exists in solution in ammonia or in other acids, the solution must be care- fully evaporated to dryness, and the residue treated as above. Molybdic acid is separated from most metallic oxides by its solubility in sulphide of ammonium. The filtered solution is then treated with an excess of very dilute nitric acid, to precipitate the tersulphide of molybdenum ; the precipitate collected on a weighed filter, and its quantity determined ; after which, a weighed quantity of it is ignited in an atmosphere of VOL. II. o 194 TELLURIUM. hydrogen, to convert it into the bisulphide, MoS^, from the weight of which the amount of molybdenum is calculated. Molybdic acid is separated from the earths by fusing with carbonate of soda, and digesting the fused mass in water, which dissolves molybdate of soda, and leaves the earth in the form of carbonate. From the fixed alkalies, molybdic acid may be separated by precipitation with mercurous nitrate, and its quantity esti- mated from the weight of the precipitate. SECTION VII. TELLURIUM. ^g. 64-14 or 801-8 J Te. Tellurium is a metal of rare occurrence, and appeared at one time to be almost confined to certain gold mines in Transyl- vania; but it has been found lately, in considerable abun- dance, at Schemnitz, in Hungary, combined with bismuth; and in the silver mine of Sadovinski in the Altai, united with silver and with lead. It was first described as a new metal by Klaproth, who gave it the name of tellurium, from telluSj the earth. Tellurium is chiefly obtained from telluride of bismuth. The ore, after being freed from the matrix by pounding and washing, is mixed with an equal weight of carbonate of potash or soda, the mixture made up into a paste with olive oil, and heated in a well closed crucible, carefully at first to prevent frothing, and afterwards to a full white heat. The fused mass is then digested in water ; which leaves the bis- muth and the excess of charcoal undissolved, and dissolves the tellurium in the form of telluride of potassium or sodium ^ which imparts a port-wine colour to the liquid. The solution deposits metallic tellurium when exposed to the air, or more TELLURIUM. 195 quickly when air is blown througli it ; and the precipitated metal is purified by washing with acidulated water, and sub- sequent distillation in an atmosphere of hydrogen (Berzelius) . The metal is also obtained from the ore called foliated tel- lur'nnn, which contains 13 per cent, of tellurium^ and 63 per cent, of lead, together with copper, gold, antimony, and sul- phur. The finely pounded mineral is freed from the sulphide of lead and antimony by repeated boiling with strong hydro- chloric acid and washing with water; the residual telluride o^ gold treated with strong nitric acid ; the tellurium -solution poured off from the gold and evaporated to dryness; the residue dissolved in hydrochloric acid ; and the tellurium pre- cipitated from the solution by sulphurous acid (Berthier). * In a state of purity, tellurium is silver- white and very bril- liant. It is very crystallisable, assuming a rhombohedral form, in which it is isomorphous with arsenic and antimony. It is brittle for a metal, and an indifferent conductor of heat and electricity. Its density is from 6*2324 to 6*2578, according to Berzelius. Tellurium is about as fusible as antimony, and may be distilled at a high temperature. It burns in air, at a high temperature, with a lively blue flame, green at the borders, and diffuses a dense wiiite smoke, which generally has the odour of decaying horse-radish, from the presence of a little selenium. Tellurium belongs to the sulphur-class of elements. Like selenium and sulphur, it dissolves to a small extent in concentrated sulphuric acid, and communicates to it a fine purple-red colour. In this solution, the metal is not oxidated, for it is precipitated again, in the metallic state, by water. This metal has also considerable analogy \vith anti- mony, and may probably connect together the sulphur and * For further details respecting the extraction of tellurium, vide Berzelius, Traite de Chiruie, i. 344; and the translation of Gmelin's Handbook, iv. 303. Wohler states, in a note to his paper on telluride of ethyl (Ann. Cli. Pharra. Ixxxiv. 70), that tellurium may be obtained in considerable quantities from the residues of the Transylvanian gold-extraction, which have hitherto been throwa away as worthless. o 2 196 TELLURIUM. phosphorus families. Tellurium combines in two propor- tions with oxygen, forming tellurous acid, Te02, ^^^ telluric acid, TeOg. Tellurous acid, TeOa ; 80-14 or 1001-8.— This acid differs remarkably in properties according as it is anhydrous or hydrated.* Hydrated tellurous acid is obtained by pre- cipitating bichloride of tellurium with cold water; or by fusing anhydrous tellurous acid with an equal weight of carbonate of potash, as long as carbonic acid is disengaged, dissolving the tellurite of potash in water, and adding nitric acid to it till the liquor distinctly reddens litmus paper. A white and bulky precipitate is produced, which is washed with ice-cold water, and afterwards dried without artificial heat. Tellurium likewise dissolves with violence in pure nitric acid of density 1*25, and if after the first five minutes, the clear liquid be poured into water, tellurous acid is precipitated in white flocks. But if not immediately precipitated, the nitric acid solution undergoes a change. The hydrated acid obtained by these processes forms a light, white, earthy mass, of a bitter and metallic taste. It instantly reddens litmus paper, and while still moist, dissolves to a sensible extent in water. It is very soluble in acids, and the solutions are not subject to change, except that which is formed by nitric acid. Ammonia and the alkaline carbonates also dissolve hydrated tellurous acid with facility, the latter becoming bicarbonates. Anhydrous tellurous acid. — When the solution of tellurous acid in water is heated to 140°, it deposits the anhydrous acid in grains, and loses its acid reaction. The same change occurs when an attempt is made to dry the hydrated tellurous acid by heat : it parts with combined water, and becomes granular. The solution of tellurous acid in nitric acid changes spon- * "Berzelius regarded the hydrated and anhydrous acids as containing dif- ferent modifications of the same compomid, and distinguished them as a-tel- lurous and /S-telhirous acid. TELLURITES. 197 tar ecusly in a few hours, and in a quarter of an hour when heat is applied to it, and allows the anhydrous acid to precipi- tate. When the deposition of the acid is slow, it forms a crystalline mass of fine grains, among which octohedral crys- tals may be perceived by the microscope. The acid is then anhydrous. In this state it does not redden litmus, or not till after a time. It is but very slightly soluble in water, and the solution has no acid reaction. At a low red heat, it fuses into a clear transparent liquid of a deep yellow colour, which on cooling becomes a white and highly crystalline mass, easily detached from a crucible. Tellurous acid is volatile, although less so than the metal itself. The solutions of hydrated tellurous acid in the stronger acids yield a black precipitate of metallic tellurium, when treated with powerful deoxidising agents, such as zinc, phos- phorus, protochloride of tin, sulphurous acid, and the alkaline bisulphates. Hydrosulphuric acid and sulphide of ammonium throw down black-brown sulphide of tellurium, easily soluble in excess of sulphide of ammonium. The tellurites, or compounds of tellurous acid with salifiable bases, contain 1 atom of base united with 1, 2, or 4 atoms of acid. They are fusible, and generally solidify in the crystalline form on cooling ; the quadrotellurites, however, form a glass. Tellurites are colourless unless they contain a coloured base ; those which are soluble have a metallic taste. Most of them, when heated to redness with charcoal, yield metallic tellurium, sometimes with slight detonation ; and the reduced metal volatilises readily, being at the same time reoxidised and forming a Avliite deposit on the charcoal ; it likewise imparts a green colour to the flame ; the tellurites, when ignited with potassium, or with charcoal and carbonate of potash, yield telluride of potassium which dissolves in water, forming a port- wine coloured solution ; with the zinc and silver-salts, how- ever, and a few others, this reduction does not take place. The tellurites of ammonia, potash and soda are easily soluble 198 TELLURIUM. in water; those of baryta, strontia, and lime are sparingly soluble ; the rest, insoluble. An aqueous solution of a tellu- rite is decomposed by the carbonic acid of the air. Nearly all tellurites dissolve in strong hydrochloric acid without evolv- ing chlorine when heated ; tlie solution exhibits the above- mentioned characters of a solution of tellurous acid in the stronger acids, except in so far as it may be interfered with by the presence of another base. The solution when diluted in water yields a white precipitate of tellurous acid, provided the excess of hydrochloric acid present is not too great. Monotellurite of potash j KO . TeOg, is obtained by heating 1 eq. tellurous acid with eq. of carbonate of potash. The fused mass on cooling forms crystals of large size. The salt dissolves slowly in cold, more quickly in warm water, llitel- lurite of potash, KO-TcjO^, is obtained by fusing two atoms of tellurous acid with one atom of carbonate of potash. It appears to be capable of existing in a hot solution, and of crystallising in certain circumstances ; but it is decomposed by cold water, which resolves it into the neutral salt, which dissolves, and a quadritelhirite of potash, KO.Tc^Og -f 1-H0. The latter salt cannot be redissolved in water, without de- composition. In losing its water when heated, it swells up like borax. Telluric acid, TeO,; 88 14 or 1101 -8.— This acid is obtained in combination with potash, by fusing tellurous acid with nitre. It may then be transferred to baryta, and the insoluble telluratc of baryta decomposed by sulphuric acid. The solu- tion of telluric acid gives bulky, hexagonal, prismatic crystals. Its taste is not acid, but metallic, resembling that of nitrate of silver. Indeed, it appears to be but a feeble acid, redden- ing litmus but slightly, when the solution is diluted. The crystallised acid contains 3110, of which it loses 2H0 by efflorescence, a little above 212°. It then appears insoluble in cold water, but may be completely redissolved by long digestion, particularly with ebullition, and is not permanently altered. TELLURIC ACID. 1C9 Anhydrous telluric acid. — The crystals of hydrated telluric acid give off all their water at a heat below redness, and are converted into a mass of a fine orange-yellow colour, without changing their form. This yellow matter, which is distin- guished, as alpha-tellaric acid by Berzelius, is remarkable for its indifference to chemical reagents, being completely in- soluble in cold or boiling water, in hot hydrochloric and nitric acids, and in potash-ley. At a high temperature, it is decomposed, evolving oxygen, and leaving tellurous acid white and pulverulent. Telluric acid has but slight affinity for bases. The hydrated acid withdraws from alkaline carbonates, only so much alkali as to form a biacid salt. Telluric acid forms bibasic, sesqui- basic, monobasic, biacid, and quadracid salts. The tellurates are colourless, unless they contain a coloured base. At a red heat, they give off oxygen and are converted into tellurites. Before the blowpipe, they behave like tlie tellurites ; also with reducing agents, such as protochloride of tin, and sulphurous acid,' excepting that the reduction does not take place so quickly, and in some cases requires the application of heat. Ilydrosulphuric acid, added to the solution of a tellurate, produces no change at first ; but if the liquid be placed in a stoppered bottle and left for a while in a warm place, a brown precipitate of sulphide of tellurium is formed. Tellurates dissolve in cold strong hydrochloric acid without decomposi- tion. The solutions are not yellow, like those of the tel- lurites in hydrochloric acid, and may be diluted with water without becoming milky, even though the excess of hydro- chloric acid be but small. But on boiling the solution, chlorine is evolved, and the liquid, if subsequently mixed with water, gives a precipitate of tellurous acid, provided the excess of hydrochloric acid is not too great. Neutral tellurate of potash is KO.TeOg + 5H0; the bitel- lurate of pot ash , KO.Te206 + 4H0 ; the quadritellurate of potash, K0.Te^0i2 + 4H0. All these salts may be obtained 200 TELLURIUM. directly, in the humid way, by dissolving the proper pro- portions of hydrated acid and carbonate of potash together, in hot water. A portion of the combined water in the last two salts is unquestionably basic, but how much of it is so has not been determined. They cannot be made anhydrous by heat without being essentially altered in properties. The neutral tellurate of potash undergoes no change in constitution under the influence of heat, resembling in that respect those tribasic phosphates of which the whole three atoms of base are fixed. The bi tellurate of potash loses its water and becomes yellow at a temperature below redness, and is changed into a quadritellurate, which is insoluble both in water and in dilute acids. Water dissolves out neutral tel- lurate from the yellow mass. The insoluble salt is named, by Berzelius, the alpha-quadritellurate of potash. The elements of this compound are united by a powerful affinity. It is formed when hydrated telluric acid is intimately mixed with a potash-salt, such as nitre or chloride of potassium, and the mixture calcined at a temperature which should be much below a red heat ; also when tellurous acid is ignited with chlorate of potash, and in other circumstances. Hydrate of potash dissolves the alpha-quadritellurate by fusion, and nitric acid by a long continued ebullition ; but in both cases, the acid set free in the solution exhibits the properties of ordinary telluric acid. Telluretted hydrogen^ Hydrotellmric acid, TeH, is a gaseous compound of tellurium and hydrogen, analogous in constitu- tion and properties to sulphuretted hydrogen. It is obtained by fusing tellurium with zinc or with tin, and acting on the mixture with hydrochloric acid. Definite sulphides of tellurium have been obtained, corre- sponding with tellurous and telluric acids. They are sulphur- acids. Two chlorides of tellurium have been formed, a protochloride, TeCl, to which there is no corresponding oxide, and a bichlo- ESTIMATION OP TELLURIUM. 201 ride, TeCl2. No higher chloride_, corresponding with telluric acid, has been obtained. Tellurium forms alloys with several metals, e.g., with potas- sium, sodium, aluminum, bismuth, zinc, tin, lead, iron, copper, mercury, silver, and gold. Some of these alloys, as those of bismuth, silver, and gold, are found native. Telluride of potassium is prepared by mixing 1 part of tel- lurium powder with 10 parts of burnt tartar ; introducing the mixture into a porcelain retort fitted with a glass tube bent downwards at right angles ; heating the retort to redness for three or four hours, as long, indeed, as carbonic oxide con- tinues to escape ; and then introducing the end of the bent tube into a flask kept full of carbonic acid gas, to prevent access of air ; this latter precaution is necessary on account of the highly pyrophoric character of the product (Wohler) . The compound may also be obtained by heating tellurium with potassium, in a retort filled with hydrogen ; combination then takes place attended with vivid combustion. TeUuride of potassium dis- solves in water, forming a port- wine coloured solution, which on exposure to the air becomes decolorised, and deposits tellurium in shining scales ; with acids it evolves teUuretted hydrogen gas. Telluride of sodium is prepared by similar methods, and possesses similar properties. ESTIMATION OF TELLURIUM, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. When tellurium exists in solution in the form of t^llurous acid it is reduced to the metallic state by sulphurous acid or an alkaUne bisulphite. The reduced tellurium is then collected on a weighed filter, and carefully dried at gentle heat. If the solution is alkaline, it must be previously acidulated with hydrochloric acid ; if it contains nitric acid, which might redis- solve a portion of the precipitated tellurium, it must be boiled YOL. II. p 202 TELLURIUM. with hydrochloric acid till all the nitric acid is decomposed, then diluted with water, and treated with sulplmrous acid as above. If the tellurium is in the state of telluric acid, that compound must first be reduced to tellurous acid by boiling with hydrochloric acid, and the tellurium then reduced by sulphurous acid. Tellurium may be separated from the alkalies and earths, and from manganese, iron, cobalt, nickel, zinc, and chromium, by means of hydrosulphuric acid. If the precipitated sulphide of tellurium is quite pure and definite, it may be collected on a weighed filter, dried and weighed, and the amount of tellu- rium calculated from it. But if it contains excess of sulphur, which is often the case, it must be boiled with aqua-regia till it is completely decomposed ; the solution filtered from the separated sulphur ; freed from nitric acid in the manner above described ; and the tellurium precipitated by sulphurous acid. The separation of tellurium from cadmium, copper, and lead, may be effected by means of sulphide of ammonium, in which the sulphide of tellurium is easily soluble. The filtered solu- tion is then treated mth excess of hydrochloric acid to pre- cipitate the sulphide of tellurium, which is then decomposed by aqua-regia as just described. Tellurium may be separated from tin in solution by means of sulphurous acid. The quantity of metallic tellurium in an aUoy may be estimated by heating the alloy in a current of chlorine gas ; passing the volatile chloride of tellurium into water acidulated with hydrochloric acid, which dissolves it ; and reducing the tellurium by sulphurous acid. ARSENIC. 203 ORDER VI. METALS ISOMOEPHOUS WITH PHOSPHORUS. SECTION I. ARSENIC. Eq. 75 or 9375. This metal is found native, but more generally in combina- nation with other metals, particularly cobalt and nickel, and is largely condensed, during the roasting of their ores, in the state of arsenious acid. The metal may be easily obtained, in a state of purity, by subliming a portion of native arsenic in a glass tube or retort, by the heat of a lamp, or by reducing a mixture of one part of arsenious acid and three parts of black flux, in the same apparatus. The metal in condensing forms a crust, of a steel-grey colour and bright metallic lastre. It has been observed to crystallise by subli- mation in rhombohedral crystals, and is isomorphous with tellurium and antimony. It is a brittle metal, and very easily pulverised. The density of arsenic is from 5 to 5*96. It rises in vapour at 356° (180° Cent.) without first undergoing fusion. Arsenic vapour is colourless; its density is 10*370; and, like phosphorus and oxygen, its combining measure is one volume. It has as strong an effect upon the organ of smell as selenium; its odour resembles that of garlic. Arsenic combines in three proportions with oxygen, forming by spon- taneous oxidation in air a grey sub-oxide, the composition of which is undetermined; it also forms arsenious and arsenic acids, AsOg and AsOg. VOL. II. Q 201- ARSENIC. Arsenious acid, 99 or 1237*5. — This compoimd is formed wlien metallic arsenic is volatilised in contact mth the air. It is obtained in large quantity, as an accessary product, in the roasting of arsenical ores of tin, cobalt, and nickel, and as principal product in the roasting of arsenical pyrites. These operations are performed in reverberatory furnaces, communicating with chambers in which the arsenious acid condenses. The product is purified by a second sublimation in vessels of cast-iron, or, on a small scale, in glass or earthen retorts. Arsenious acid heated in a tube closed at both ends melts into a colourless liquid ; but under the ordinary atmospheric pressure, it volatilises at about 380° (at 444° according to Mitchell), without previous fusion, producing a colourless vapour, which has a density of 13850, and is therefore com- posed of 1 volume of arsenic vapour and 3 volumes of oxygen, condensed into 1 volume. The vapour is inodorous when pure, but if the acid be volatilised in contact with any easily oxidisable substance, as when it is thrown on red-hot coals or iron, the garlic odour of metallic arsenic becomes perceptible. In the solid state, arsenious acid exhibits three modifi- cations, one amorphous, and two crystalline. (1.) When the sides of the vessel in which the acid is distilled become strongly heated, the vapour condenses, at a temperature near the melting point of the acid, into a transparent vitreous mass, having a conchoidal fracture. (2.) When arsenious acid is sublimed in a glass tube, or under any circumstances which allow the vapour to condense suddenly, and solidify at once, without passing through the semi-fused state, it assumes the form of regular octohcdrons, which, if the sublimation be slowly conducted, are distinct, and have an adamantine lustre. Similar octohedral crystals are obtained when arsenious acid separates from its solution in water or in ammonia. (3.) In the roasting of arsenical cobalt ores, arsenious acid is some- times obtained in the form of thin transparent flexible plates, ARSENIOUS ACID. 205 derived from a right rhombic prism (Wohler). Crystals of similar form are obtained by saturating a boiling solution of caustic potash with arsenious acid, and then leaving it to cool or mixing it with water (Pasteur) . Vitreous arsenious acid, even when completely protected from air and moisture, gradually loses its transparency, and becomes an opaque white mass, passing in fact into the octohedral variety. The specific gravity of transparent vitreous arsenious acid is 3*7385, that of the octohedral variety 3*699 (Guibourt). The vitreous acid dissolves in water more quickly and more abundantly than the opaque crystalline acid ; the same quan- tity of water which at 54° or 55° will take up 36 or 38 parts of the former, will not take up more than 12 or 14 of the latter (Bussy). According to Guibourt, on the contrary, 100 parts of boiling water dissolve 9*68 parts of the vitreous, and 11*47 of the opaque acid; and when the solutions are left to cool to 60°, the first retains 1*78 parts, and the latter 2*9 parts of the acid. The discrepancy of these statements and of various others respecting the solubility of arsenious acid, may perhaps be reconciled by the great facility with which the amorphous variety passes into the crystalline, and vice versa. It appears indeed that heat tends to transform the opaque into the vitreous acid, and cold to produce the contrary change, and this tendency is manifested even in presence of water. Thus the opaque acid is converted into the vitreous by long boiling ^Yith. water, the contrary change taking place gradually in the solution when cold. The aqueous solution of arsenious acid is transparent and colourless, and reddens litmus slightly. Hydrosulphuric add colours it yellow, and on the addition of hydrochloric acid throws down a yellow precipitate of AsSg. On the addition of a small quantity of ammonia, it gives a yellow precipitate with nitrate of silver, and a peculiar light green (Scheele^s green) with sulphate of copper ; these precipitates are easily soluble in excess of ammonia. Mixed vrith hydrochloric acid Q 2 206 ARSENIC. it produces a grey metallic deposit on copper. With zinc and sulphuric or hydrochloric acid, it evolves arseniuretted hydrogen gas (p. 211.). Arsenious acid dissolves in many acids, in hydrochloric acid for example, with much greater facility than in water, but without forming any definite compounds. It is dissolved, however, by bitartrate of potash, with formation of a crys- tallisable salt analogous to the potash-tartrate of antimony. The vitreous acid dissolved in boiling dilute hydrochloric acid crystallises on cooling in regular octohcdrons, the deposition of each crystal being accompanied by a flash of light. Agita- tion increases the number of crj^stals produced, and the intensity of the light. The opaque acid dissolved in hydro- chloric acid does not emit any light on crystallising ; the same is the case with the crystals obtained by cooling a solution of the vitreous acid in hydrochloric acid, when these crystals are redissolved in hydrochloric acid. Hence it appears that the vitreous acid dissolves as such in hydrochloric acid, and that the emission of light at the moment of crystallisation is due to the change from the amorphous to the crystalline state. Arsenious acid is dissolved by potash y soda, and ammonia, also by alkaline carbonates, but from these latter solu- tions it is sometimes deposited in the free state, so that it is doubtful whether arsenious acid displaces carbonic acid in the humid way. The ai'senites of the earths and metallic oxides are insoluble in water, but soluble in acids. With potash, arsenious acid forms the salts 2K0 . AsOg, KO . ASO3, and KO . HO . 2ASO3 ; similar salts with soda. With baryta, it forms 2BaO . AsOg and BaO . AsOg ; and with lime, 2CaO . AsOg. With nickel, cobalt, and silver, it forms bibasic and sesquibasic salts. The neutral solutions of the alkaline arsenites give a yellow precipitate with nitrate of silver, and Scheele's green with copper salts. Acidulated with hydrochloric acid, they give ARSENIC ACID. 207 with hydrosulphuric acid, &c., the same reactions as aqueous arsenious acid. Nitric acid and aqua regia transform arsenious into arsenic acid. Hydrogen, charcoal, and other reducing agents easily reduce it to the metallic state. Arsenious acid has a rough taste_, slightly metallic, and afterwards sweetish. It is one of the most violent among acrid poisons. The principal industrial use of arsenious acid is in cahco- printing ; it is also used in glass-making, serving to transform the protoxide of iron into sesquioxide, which produces glasses less highly coloured than the protoxide. Arsenic acid, AsOg, 115 or 1437*5. — This acid is obtained by heating powdered arsenious acid in a basin with an equal quantity of water, and adding nitric acid in small quantities to the mixture at the boiling point, so long as ruddy fumes escape. An addition of hydrochloric acid to the water is generally made, to increase the solubility of the arsenious acid, but it is not absolutely necessary. The solution of arsenic acid is then evaporated to dryness, to expel the remaining nitric and hydrochloric acids ; but the dry mass must not be heated above the melting point of lead, otherwise oxygen gas is emitted and arsenious acid reproduced. Arsenic acid thus obtained is milk-white, and contains no water. Exposed to air, it slowly deliquesces, and runs into a liquid. But notwith- standing this, when strongly dried, it does not dissolve com- pletely in water at once, and a portion of it appears to be insoluble ; but the whole is dissolved by continued digestion. Arsenic acid, in absorbing moisture from the air, sometimes forms hydrated crystals, which are highly deliquescent ; but this acid is easily made anhydrous, and does not retain basic water with force, like phosphoric acid. Its solution has a sour taste, and reddens vegetable blues. Arsenic acid, indeed, is a strong acid, and with the aid of heat expels all the volatile Q3 208 ARSENIC. acids from their combinations. Arsenic acid undergoes fusion at a red heat, and at a higher temperature is completely dis- sipated in the form of arsenious acid and oxygen. When an equivalent of arsenic acid is ignited with an excess of carbonate of soda, three equivalents of carbonic acid are expelled, and a tribasic arseniate of soda formed, which when dissolved in water, crystallises with 24 equivalents of water, forming the salt 3NaO . As05H-24HO, isomorphous with the subphosphate of soda. The same salt is obtained by treating arsenic acid in solution with an excess of caustic soda. Wlien carbonate of soda is added to a hot solution of arsenic acid, so long as there is eflfervescence, a salt is obtained by evaporation corresponding with the common phosphate of soda, containing 2 eq. of soda and 1 eq. of water as bases. This salt affects the same two multiples, in its water of crystallisation, as phosphate of soda, namely, 24HO and 14H0, but most fre- quently assumes the smaller proportion, forming the salt 2NaO. HO. AsOg + liHO. This arseniate is more soluble than the phosphate, and slightly deliquescent in damp air. When to the last salt a quantity of arsenic acid is added equal to that which it already contains, and the solution is highly concentrated, the salt named biarseniate of soda crystallises at a low temperature. This salt contains 1 eq. of soda and 2 eq. of water as bases, with 2 eq, of water of crystallisation, and corresponds with the biphosphate of soda. Its formula is Na0.2HO.As05 + 2HO. The biarseniate of potash, which is analogous in composition, is a highly crystallisable salt. It is sometimes prepared by deflagrating arsenious acid with an equal weight of nitrate of potash. These arseniates of the alkalies, which contain water as base, all lose that element at a red heat ; but, unlike the phosphates, they recover it when redissolved in water. Arsenic acid, therefore, fonns only one, and that a tribasic class of salts. The arseniates of the earths and other metallic oxides are insoluble in water, but soluble in acids. Arseniate of silver (3AgO . AsOg) falls as a preci- SULPHIDES OF ARSENIC. 209 pitate of a chocolate-brown colour, when nitrate of silver is added to the solution of an arseniate, and affords an indication of the presence of arsenic acid. On treating a solution of arsenic acid with ammonia in excess, chloride of ammonium, and sulphate of magnesia, a white crystalline precipitate is formed, consisting of arseniate of magnesia and ammonia, 2MgO . NH4O . AsOg + 12 Aq., similar in appearance and ana- logous in constitution to the ammonio-magnesian phosphate. Hydrosulphuric acid produces a yellow precipitate of AsSg after a considerable time ; but if the solution be previously mixed with sulphurous acid, which reduces the arsenic acid to arsenious acid, a precipitate of AsSg is immediately produced. Sulphides of arsenic. — "When the bisulphide, realgar, is digested in caustic potash, it gives off sulphur and leaves a brownish black powder, having some resemblance to bioxide of lead, which, according to Berzelius, is the sulphide AsgS. Bisulphide of arsenic, As 85, is obtained by fusing sulphur with an excess of arsenic or arsenious acid. It is transparent and of a fine ruby colour after cooling, and may be distilled without decomposition. It forms the crystalline mineral realgar. Sulph- arsenious acid, or orpiment, ASS3, also occurs native. It may be prepared by decomposing a solution of arsenious acid in hydro- chloric acid, by hydrosulphuric acid or by an alkaline sulphide. This sulphide has a rich yellow colour, and is the basis of the pigment called hinges yellow. It is insoluble in acids, but soluble to a small extent in water containing hydrosulphuric acid, and also in pure water, but is precipitated by ebullition with a little hydrochloric acid. When heated, it fuses readily and becomes crystalline on cooling. It is readily dissolved by ammonia and solutions of the fixed alkalies, and is indeed a powerful sulphur-acid. Sulpharsenic acid, AsSg, falls as a yellow precipitate, having much the appearance of orjnment, when a solution of arsenic acid somewhat concentrated is decomposed by hydrosulphuric acid. It may be sublimed Q 4 210 ARSENIC. without change, and after cooling forms a non- crystalline mass. It is also a powerful sulphur-acid, forming salts called sulpharseniates. Persulphide of arsenic , AsSjg, is obtained by precipitating neutral solution of sulpharseniate of potassium with alcohol, filtering the liquid, and evaporating off two- thirds of the alcohol; the concentrated solution, when left to cool, deposits the persulphide of arsenic in shining yellow crystalline laminae. Chlorides of arsenic. — A tercMoride, As CI3, corresponding with arsenious acid, is formed when arsenic is introduced into chlorine gas, in which it takes fire and bums spontaneously. The same compound is obtained by distilling a mixture of 1 part of arsenic with 6 parts of corrosive sublimate ; also by distilling arsenious acid with excess of hydrochloric acid, or of common salt and sulphuric acid. It is a colourless, oily, and very dense liquid, which is resolved by water into arse- nious and hydrochloric acids. When a mixture of arsenic and calomel is distilled, a dark brown sublimate is formed, consist- ing partly of Hg2ClAs, partly of Hg4ClAs. No chloride cor- responding with arsenic acid is known. Bromide of arsenic y AsBrg, is formed by the direct combination of its elements. Iodide of arsenic. As I3, is formed, according to Plisson, by digesting 3 parts of arsenic with 10 of iodine and 100 of water, as long as the odour of iodine is perceived. The liquid yields by evaporation red crystals of the iodide. Fluo- ride of arsenic, AsFg, is obtained by distilling a mixture of fluor spar and arsenious acid with sulphuric acid. It is a fuming, colourless liquid ; the density of its vapour is 2730 (Unverdorben). Arsenic and hydrogen. — A solid arsenide of hydrogen was obtained by Davy, by using metallic arsenic as the negative pole (the chloroid) in decomposing water. Gay-Lussac and Thenard have also shown that the same compound precipitates when arsenide of potassium is dissolved in water. It is a chestnut-brown powder, which may be dried without change. TESTING FOR ARSENIC. 211 Its composition has not been determined with accuracy. Arseniuretted hydrogen, AsHg, a gas analogous in constitu- tion to ammonia, is obtained by dissolving arseniate of potas- sium or sodium in water, or an alloy of equal parts of zinc and arsenic in sulphuric acid diluted with three times its weight of water; or again, when zinc dissolves in hydro- chloric or dilute sulphuric acid, with which arsenious acid is mixed : 6Zn -h 3H0 + AsOg + 6SO3 = 6(ZnO . SO3) + AsHg. It is a dangerous poison, when inhaled even in the most minute quantity, and should, therefore, be prepared with the greatest caution. The density of this gas is 2695 (Dumas). It is liquefied by a cold of — 40°. When passed through a glass tube heated to redness by a spirit lamp, it is decom- posed and deposits metallic arsenic. The flame of this gas, when burned in air, also deposits metallic arsenic upon a cold object exposed to it. No combination of arseniuretted hydrogen is known with either acids or bases. It precipitates many of the metallic solutions which are precipitated by hy- drosulphuric acid, but not oxide of lead, its hydrogen alone being oxidated, and the arsenic being precipitated in com- bination with the metal. From the salts of silver, gold, platinum, and rhadium, it precipitates the metals, while arse- nious acid remains in solution. This gas, when pure, is completely absorbed by a solution of sulphate of copper, and AsCug precipitated. TESTING FOR ARSENIC. Poisoning from arsenious acid is much more frequent than from any other substance. Hence, a more than usual degree of importance is attached to the modes of detecting the pre- sence of arsenic in minute quantity. Of the diflPerent prepa- rations of the metal, arsenic acid, and after it arsenious acid. 212 ARSENIC. are the most poisonous ; the salts and sulphides are so in a much less degree. Arsenious acid in the solid form and un- mixed with foreign matters, is easily recognised as a white heavy powder, which is tasteless or nearly so, is entirely volatilised by heat, and diffuses a garlic odour in the re- ducing flame of a lamp. When dissolved in water, arsenious acid may be detected by the fluid tests, already mentioned (pp. 205, 206.). The silver and copper tests are most con- veniently applied in the following forms. 1. Ammonio-niirate of silver. — This is an exceedingly deli- cate test of arsenious acid, whether free, or in combination with an alkali. It is prepared by adding diluted ammonia to a solution of nitrate of silver, till the oxide of silver, which is first thrown down, is redissolved. When the ammonia has been added in proper quantity and not in excess, the odour of that substance is scarcely perceptible, and the liquid con- tains in solution the crystallisable ammonio-nitrate of silver, AgO.NOg . 2NH3. This test-liquid throws down from arse- nious acid, the yellow arsenite of silver, which is redissolved both by acids and by ammonia. A solution of nitrate of silver, gives the same indication as the prepared ammonio-nitrate in an alkaline but not in an acid solution of arsenious acid. Nitrate of silver produces, in phosphate of soda or any other soluble phosphate, a yellow precipitate of phosphate of silver of the same colour as the arsenite of silver, and which might, therefore, be mistaken for the latter; but the action of the ammonio-nitrate is not liable to tliat ambiguity, as it does not produce a yellow precipitate in an alkaline solution of phos- phoric acid, the phosphate of silver being then retained in so- lution by the ammonia of the reagent, although arsenite of silver is precipitated in the same circumstances. Both phos- phate and arseniate of silver are indeed considerably more soluble in ammonia than the arsenite of the same metal. 2. Ammonio -sulphate of copper gives a beautiful green pre- cipitate, the arsenite of copper, in both alkaline and acid solu- TESTING FOR ARSENIC. 213 tions of arsenious acid; sulphate of copper gives the same precipitate in the former, but not in the latter. But in solutions containing organic matter, the indications of these tests are sometimes delusive, and often doubtful. Eecourse is then had to the proper means of obtaining arsenic in the metallic form, from the liquid suspected to contain arsenious acid. Indeed, even where the indica- tions of the fluid tests are clear, the reduction test should never be omitted, the evidence which it affords being of a superior and completely demonstrative character. The reduction test of arsenic is practised in two different ways : (1.) by the reduction of the sulphide of arsenic by means of charcoal and carbonate of potash, and (2.) by the production, and subsequent decomposition of the gaseous compound of arsenic and hydrogen. The following operations are neces- sary in the practice of the first method : — REDUCTION TEST OF ARSENIC. I. Preparation of the fluid : 1. Heat the mass with about one-fourth of its weight of strong sulphuric acid in a retort, to which is adapted a receiver having its inner surface wetted, till the organic matter is carbonised. 2. Pulverise the residue, and treat it with nitric acid mixed with a little hydrochloric acid, in order to bring the arsenic to the state of arsenic acid, which is easily soluble. 3. Boil with water ; filter ; and mix the filtrate with the liquid in the receiver.* * This is the mode of preparation most generally adopted, and it is appli- cable to all cases of searching for mineral poisons. Another method, which is especially applicable when the matter to be examined contains a large quan- tity of fat, is to heat the mass with strong hydrochloric acid, or aqua-regia, in 214 ARSENIC. IT. Precipitation of the sulphide of arsenic : 1. Transmit a stream of hydrosulphuric acid gas through the liquid for half an hour.* 2. Heat the liquid in an open vessel for a few minutes, to cause the precipitate to separate. 3. Wash the precipitate by aflPusion of water acidulated with hydrochloric acid, and subsidence. 4. Dry the precipitate at a temperature not exceeding 300°. III. Reduction of the sulphide of arsenic : 1. Mix the dried precipitate intimately with twice its bulk of dry black flux (carbonate of potash and charcoal), or with a mixture of pounded charcoal and dry carbonate of soda, or with cyanide of potassium, and heat to redness in a glass tube, of the form and size of a or b, exhibited below. 2. Heat slowly a particle of the metallic crust in a glass tube c, and observe the formation of a white crystalline sublimate of arsenious acid. 3. Dissolve the sublimate in a small quantity of boiling water, and test with ammonio-nitrate of silver, &c., as above. Fig. 8. ( ' O C a large retort ; the greater part of the arsenic is then converted into chloride, and may be collected in a receiver containing water. * As the arsenic is in the state of arsenic acid, it is best to mix the liquid with sulphurous acid before passing the hydrosulphuric acid gas through it. TESTING FOR ARSENIC. 215 Fig. 9. Marshes test, — Hydrogen cannot be evolved in contact with any preparation of arsenic, soluble or insoluble, without com- bining with the metal, which is thus removed from the liquor, in the form of arseniuretted hydrogen gas. Mr. Marsh has founded, upon this fact, a simple and elegant mode of obtain- ing metallic arsenic from arsenical liquors. The stopcock being removed from the bulb-apparatus re- presented in the figure, a fragment of zinc is placed in the lower bulb, and diluted sul- phuric acid poured upon it. The stopcock being replaced and closed, the lower bulb is soon filled with hydrogen gas, and the acid liquid forced into the upper bulb. It is ne- cessary to test this hydrogen for arsenic, which will be found in it, if the zinc itself contains that metal. The gas for this pur- pose is kindled at the stopcock and allowed to burn with a small flame. If a stoneware plate be depressed upon the flame, a black spot of a steel- grey colour and bright metallic lustre, is formed, in a few seconds, upon the surface of the plate, sup- posing the gas to contain arsenic ; or if a cold piece of glass be held over the flame, at a smaU height above it, a white sublimate of arsenious acid condenses upon the glass. But if the zinc employed contains no arsenic, neither of these eflPects is produced. The zinc being proved to be free from arsenic, a portion of the liquor to be tested is introduced into the lower bulb, in addition to the acid and zinc already there ; and when the bulb is again filled with hydrogen gas, the latter is burned and examined precisely as before. If the liquor is loaded with organic matter, as generally happens with the liquids submitted to examination in actual cases of poisoning, the gas may be filled with froth, and the evolution of it very slow. But in the course of a night, the gas is 216 ARSENIC. generally obtained in suflBcient quantity, and in a proper state, to permit of examination. It is much better, however, first to remove the organic matter by one of the methods above given; the gas is then evolved freely and without frothing, and a plain bottle with a cork and glass jet will be sufficient for this reduction experiment. Then also, instead of burning the gas at the jet, it may be allowed to escape by a horizontal tube, such as that in figure 10., a portion of which is heated to redness by ^S' 10. a spirit lamp. The arsenic / ^ I condenses within the tube, be- yond the flame and nearer the 'jl Tp aperture, and forms a metallic crust, which may be converted by sublimation into arsenious acid; the sublimate may then be dissolved in a small quan- tity of boiling water, and the solution tested with ammonio- nitrate of silver, &c., as before. Wlien the liquid examined contains antimony, that metal combines with the nascent hydrogen, and comes off as anti- moniuretted hydrogen, a gas which, when burned, or heated in a glass tube, gives the metal and a white sublimate, in the same circumstances as arsenic (L. Thompson). Antimony, however, may be recognised by a peciUiarity of its reduction in the ignited tube. This metal is deposited in the tube, on both sides of the heated portion of it, and closer to the flame than arsenic, owing to the inferior volatility of antimony. The white sublimate also, if dissolved in water containing a drop of ammonia, will not give the proper indications with the fluid tests of arsenic, if the metal be antimony. Another dis- tinction is, that the arsenical deposit is soluble in hypochlorite of soda, whereas the antimonial deposit is not. ESTIMATION OF ARSENIC. 217 Antidotes to arsenious acid, — When hydrated sesquioxide of iron is mixed with a solution of arsenious acid to the con- sistence of a thin paste, a reaction occurs by which the ar- senious acid disappears in a few minutes, and the mass ceases to be poisonous. The arsenious acid takes oxygen from the sesquioxide of iron, and becomes arsenic acid, while the sesquioxide of iron is reduced to protoxide, a protarseniate of iron being the result, which is insoluble and inert : SFcaOa + AsOg = 4FeO . AsOg. The constitution of this arseniate of iron is probably 2FeO.HO.AsO5 + 2FeO. Sesquioxide of iron, when used as an antidote to arsenious acid, should be in a gelatinous state, as it is obtained by precipitation, without drying. It may be prepared extemporaneously, by adding bicarbonate of soda in excess to any tincture or red solution of iron. Cal- cined magnesia may likewise be used as an antidote to arsenic. Care should be taken in preparing the latter not to employ too great a heat, which would render it very dense, and cause it to combine but slowly with the arsenious acid. ESTIMATION OF AKSENIC, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. When arsenic is contained in a solution entirely in the form of arsenic acid, the best mode of estimating it is to pre- cipitate it in the form of ammonio-magnesian arseniate, 2MgO . NH4O . ASO5 + 12H0. The solution is mixed with excess of ammonia, and then with sulphate of magnesia, to which a quantity of chloride of ammonium has been added, sufficient to prevent the precipitation of the magnesia by am- monia. The liquid is then left to stand for about twelve 218 ARSENIC. hours ; the precipitate collected on a weighed filter ; washed with water containing ammonia ; and dried over sulphuric acid in vacuo at ordinary temperatures ; it has then the com- position expressed by the above formula. It may also be dried, and more expeditiously, by exposing it to a temperature of exactly 212° F., whereby it loses 11 eq. of water, and is reduced to 2MgO.NH40.As05 + HO. Exposure to a higher temperature occasions loss of arsenic. If the liquid contains arsenious acid, that compound may be converted into arsenic acid by mixing the solution with hydrochloric acid, and adding chlorate of potash by small quantities. The vessel must be left in a moderately warm place till the odour of free chlorine has entirely disappeared. Aqua regia may also be used to effect the oxidation, but it is less convenient. In either case, the liquid must be consider- ably diluted with water, otherwise part of the arsenic will be converted into chloride, and volatilised. It is best, perhaps, to perform the oxidation in a capacious retort having a receiver adapted to it. Arsenious acid may also be estimated by its action on terchloride of gold. The arsenious acid is thereby converted into arsenic acid, and gold is precipitated in the metallic state. The quantity of gold thus reduced gives the quantity of arsenious acid present : 2 AUCI3 + 6110 + 3 ASO3 = 2 Au + 6HC1 -f SAsOg. The gold solution used for the purpose is the sodio-chloridc, or ammonio-chloride of gold. It must be free from nitric acid ; but the presence of hydrochloric acid, even in large excess, does not interfere with the action. The liquid, after the addition of the arsenic solution, must be left to itself for a considerable time to enable the gold to settle down completely. When arsenic and arsenious acids exist together in solution SEPARATION OP ARSENIC. 219 the former may be precipitated as ammonio-magnesian arseniate (a considerable quantity of sal-ammoniac being added to prevent the simultaneous precipitation of the ar- senious acid); the arsenious acid converted into arsenic acid by oxidation with chlorate of potash and hydrochloric acid, and then precipitated in a similar manner ; or the arsenious acid may be estimated by chloride of gold, as last described. The separation of arsenic in solution from the alkalies, earths, and those metals which are not precipitated from their acid solutions by hydrosulphuric acid, is effected by passing a stream of that gas through the acid liquid for a considerable time, then leaving it to stand, and heating it gently to ensure the complete precipitation of the sulphide of arsenic. If the arsenic is in the form of arsenic acid, that compound must be previously reduced to arsenious acid by means of sulphurous acid. The tersulphide of arsenic is collected on a weighed filter, thoroughly washed, and dried at a moderate heat. If quite pure, it may be weighed with the filter, and the quantity of arsenic thereby directly determined. But as it almost always contains an excess of sulphur, it is better to take a weighed quantity of it from the filter, oxidise it in a capacious flask by means of dilute hydrochloric acid and chlorate of potash, continuing the operation till the greater part of the sulphur is converted into sulphuric acid, and the remainder collects at the bottom of the liquid in a compact yellow globule ; then decant the liquid, wash the globule of sulphur, and weigh it ; and, finally, estimate the quantity of sulphur in the solution by precipitation with chloride of barium, adding the quantity thus found to the weight of the globule. The proportion of sulphur in the precipitated sul- phide of arsenic being thus ascertained, the amount of arsenic is easily calculated. From cadmium, copper, and lead, arsenic may be separated by means of sulphide of ammonium. The filtered ammoniacal solution is then treated with excess of hydrochloric or acetic VOL. II. R 220 ARSENIC. acid to throw down the sulphide of arsenic, and the precipi- tate treated in the manner just described. The separation of arsenic from tin is attended with con- siderable difficulty. One of the best methods is to convert the two metals into sulphides, and separate them, after drying and weighing the whole, by ignition in a stream of hydro- sulphuric acid gas. The mixed sulphides are introduced into a weighed glass bulb, having a tube attached to it on each side. One of these tubes, the exit-tube, must be at least a quarter of an inch in diameter, to prevent stoppage, and bent downwards so as to dip into a flask containing am- monia. The whole is then weighed, hydi-osidphuric acid gas passed through the apparatus, and the bidb heated till the whole of the sulphide of arsenic is sublimed. Part of the sulphide of arsenic passes into the ammoniacal liquid, by which it is dissolved, and the rest sublimes in the wide tube. When the operation is ended, and the apparatus has cooled, the wide tube is cut off at a short distance from the bulb, then broken, and the pieces digested in caustic potash to dissolve out the sulphide of arsenic. The solution thus ob- tained is added to the ammoniacal liquid in the flask ; the sulphide of arsenic precipitated by hydrochloric acid, oxidised without previous filtration with hydrochloric acid and chlo- rate of potash ; and the resulting arsenic acid precipitated by ammonia and sulphate of magnesia. The sulphide of tin remaining in the bulb is converted into stannic oxide by treating it with strong nitric acid. When arsenic is combined with other metals in the form of an alloy, the whole may be dissolved or oxidised by means of aqua regia, or, better, with hydrochloric acid and chlorate of potash, and the arsenic separated by one of the preceding methods. In the case of tin, however, it is best to fuse the alloy in thin laminae with five times its weight of carbonate of soda and an equal quantity of sulphur, whereby a mixture of sulpharseniate and sulphostannate of soda is obtained, which ANTIMONY. 221 dissolves completely in hot water. The sulphides of tin and arsenic may then be precipitated by hydrochloric acid, and separated as above.* SECTION II. ANTIMONY. Eq. 120-24 or 1503t; Sb {stibium). This metal was well known to the alchemists, and is one of the metals the preparations of which were first introduced into medicine. Its sulphide is not an uncommon mineral, and is the source from which the metal and its compounds are always derived. The sulphide of antimony is easily reduced to the metallic state by mixing together 4 parts of that substance, 3 parts of crude tartar, and \\ parts of nitre, and projecting the mixture by small quantities at a time into a red hot crucible. The sulphide is also sometimes reduced by fusion with small iron nails, which combine with the sulphur and disengage the antimony. Or it may be obtained in a state of greater purity by strongly igniting in a crucible a quantity of the potash- tartrate of antimony, and placing the resulting metallic mass in water to remove any potassium it may have acquired. Antimony is a white and brilliant metal, generally pos- sessing a highly lamellated structure. It is easily obtained * For a full account of the methods of estimating arsenic and separating it from other metals, vide H. Rose, *' Ilandbuch der analytischen Chemie," 1851, ii. 381. t The number 129, given by Berzelius for the equivalent of antimony, and hitherto generally adopted, appears from recent experiments by Schneider (Pogg. Ann. xcviii. 293) and by H. Rose (Berl. Akad. Ber. 1856, p. 229) to be much too high. Schneider, by reducing the tersulphide of antimony with hydrogen, finds the equivalent to be 120'24 ; and Rose, by decomposing the terchloride with hydrosulphuric acid, and precipitating tlie chlorine with nitrate of silver, finds the number 120-69. B 2 222 ANTIMONY. in rhombohedral crystals of the same form as arsenic and tellurium. Its density is from 6*702 to 6-86. It under- goes no change in the air. The point of fusion of antimony is estimated at 797°; it may be distilled at a Avhite heat. This metal bums in air at a red heat, and produces copious fumes of oxide of antimony. Antimony combines in three proportions with oxygen, form- ing oxide of antimony and antimonic acid, SbOg and SbOg, which correspond respectively with arsenious and arsenic acids ; and antimonious acid, Sb04, which is probably an intermediate or compound oxide, analogous to the black oxide of iron. Teroxide of antimony, Antimonic oxide, Antimonious acid, SbOg, 144-24 or 1803.— This oxide may be obtained by dis- solving the sulphide, finely pounded and in the condition in which it is known as prepared sulphide of antimony, in four times its weight of concentrated hydrochloric acid. Pure hydrosulplmric acid goes oflP, and the antimony is converted into terchloride : SbSg + 3HC1 = SbClg + 3HS. The clear solution may be poured off, and precipitated at the boiling heat by a solution of carbonate of potash added in excess, the carbonic acid, which does not combine with oxide of antimony, escaping as gas. Teroxide of antimony, so prepared, is anhydrous, but is slightly soluble in water: it is white, but assumes a yellow tint when heated. It is fusible at a red heat, and sublimes at a high temperature in a close vessel, where it cannot pass into a higher state of oxidation. The brilliant crystalline needles which condense about antimony in a state of combustion likewise consist of this oxide. They possess the unusual prismatic form of ar- senious acid observed by Wohler. Oxide of antimony also crystallises as frequently in regular octohedrons, the other form of arsenious acid. It occurs in the prismatic form as a rare mineral, whose density is 5 '227. SALTS OF ANTIMONY. 223 When a solution of potash is poured upon the bulky hydrate of teroxide of antimony, which is precipitated from the chloride by water, a portion of the oxide is dissolved, but the greater part loses its water, and is reduced in a few seconds to a fine greyish, crystalline powder, which is a neutral combination of teroxide of antimony with potash. Teroxide of antimony also combines with acids, forming the salts of antimony y or an- timonic salts. The solutions of these salts giv^e with hydrosulphuric acid a brick-red precipitate of tersulphide of antimony, easily soluble in sulphide of ammonium, and reprecipitated by acids. This precipitate dissolves in strong boiling hydrochloric acid, forming the terchloride, which when thrown into water yields a precipitate of the oxychloride. This reaction with hydro- sulphuric acid distinguishes antimony from all other metals.* Zinc or iron precipitates antimony from its solutions in the form of a black powder, which, when fased on charcoal before the blow-pipe, yields a brittle button of the metal. According to Dr. Odlingtj antimony is also precipitated by copper, in the form of a brilliant metallic film, which may be dissolved ofi* the copper by a solution of permanganate of potash, yielding a solution which will give the characteristic red precipitate with hydrosulphuric acid. This reaction affords a ready method of separating antimony from liquids containing organic matter, — as in medico-legal inquiries. All compounds of antimony fused upon charcoal with carbonate of soda or cyanide of potassium, yield a brittle globule of antimony, a thick white fume being at the same time given off, and the charcoal covered to some distance around with a white de- posit of antimonic oxide. The reduction with cyanide of potassium may also be performed in a porcelain crucible, without charcoal. A solution of terchloride of gold added to * For the reactions of antimonic salts witli alkalies, see terchloride of aniU movy and tartar-emetic. t Guj's Hospital Reports, [3.] ii. 249. B 3 324 ANTIMONY. the solution of a salt of teroxide of antimony, forms a yellow precipitate of metallic gold, tlie oxide of antimony being at the same time converted into antimonic acid, which com- pound is precipitated as a white powder, together with the gold, unless the solution contains a very large excess of hydro- chloric acid. In a solution of oxide of antimony in potash, terchloride of gold produces a Mack precipitate, which is not altered by heating. This reaction is extremely delicate. Tersulphide of antimony , SbSg, 168-24 or 2103. — The com- mon ore of antimony is a tersulphide, SbSg, corresponding with the preceding oxide of antimony. It is rarely free from sul- phide of arsenic, which thus often enters into the antimonial preparations derived from the sulphide of antimony, but into tartar-emetic less frequently than the others. The same sulphide is formed when salts of the oxide of antimony, such as tartar- emetic, are precipitated by hydrosulphuric acid; but it is then of an orange-red colour. When the precipitated sulphide is dried, it loses water and becomes anhydrous, still remaining of a dull orange colour ; but when heated more strongly, it shrinks at a particular temperature, and assumes the black colour and metallic lustre of the native sulphide. This sulphide is also obtained of a dark brown colom* by boiling the prepared sulphide of antimony in a solution of carbonate of potash, and allowing the solution to cool; by fusing 2} parts of the prepared sulphide with 1 part of car- bonate of potash; or dissolving it in a boiling solution of caustic potash, and afterwards adding an acid. The last pre- paration is known as Kermes mineral. It has a much duller colour than the precipitated sulphide, but differs from it only in containing small quantities of oxide and pentasulphide of antimony, together with an alkaline sulphide which can- not be removed by washing (Berzelius). When the cooled mother-liquor from which kermes is deposited is mixed with hydrochloric acid, a precipitate is obtained, consisting, like the kermes, of SbS3 mixed with SbOa and SbSg, but of a redder I TERCHLORIDE OF ANTIMONY. 226 colour. It is sometimes called the golden sulphwret of antimony. When the sulphide of antimony is oxidated at a red heat, much sulphur is burned off, and an impure oxide of antimony remains. This matter forms, when fused, the glass of anti- mony, which contains a considerable quantity of undecomposed sulphide. The glass, reduced to powder, is boiled with bitar- trate of potash as a source of oxide of antimony, in the pharmaceutical preparation of tartar- emetic. The oxide of antimony is dissolved out from the glass by acids, and a sub- stance is left which is called saffron of antimony. This last is a definite compound of oxide and sulphide of antimony, Sb03 . SSbSg, which also occurs as a mineral — namely, red antimony ore. Terchloride of antimony, SbClg, is obtained by distilling either metallic antimony or the tersulphide of antimony with corrosive sublimate. When heated it flows like an oil, and becomes a crystalline mass on cooling. It is a powerful cautery. This salt deliquesces in air, and becomes turbid, owing to the deposition of a subsalt. A concentrated solution of chloride of antimony is also obtained by dissolving the sulphide of antimony in hydrochloric acid. When this solution is thrown into water, it gives a white bulky precipitate, which after a time resolves itself into groups of small crystals, having usually a fawn colour ; it was formerly called the powder of Algaroth. These small crystals are an oxychloride of anti- mony, which, according to the analyses of Johnston and Malaguti, contains SSbClg . 9Sb03. A solution of terchloride of antimony, to which water is added, and then a sufficient quantity of hydrochloric acid to redissolve the precipitate thereby produced, gives with potash a white precipitate of the hydrated teroxide, soluble in a very large excess of the alkali. Ammonia forms the same preci- pitate insoluble in excess. Carbonate of potash, or soda, pro- duces also a white precipitate of the hydrated teroxide, which B 4 226 ANTIMONY. is soluble in excess, especially of the potash-salt, but re- appears after a while. These reactions are greatly modified by the presence of fixed organic acids, especially of tartaric acid. In such a case, water forms no precipitate, ammonia but a slight one and after some time only, and the precipi- tate formed by potash dissolves easily in excess of the alkali. (See Tartar-emetic.) Terfluoride of antimony y SbFg, is obtained, by treating the teroxide with strong hydrofluoric acid, in colourless crystals which dissolve in water without decomposition. It unites with fluoride of potassium, forming the compound 3KF . SbFa and similarly with fluoride of sodium and fluoride of ammo- nium. Sulphate of antimony, SbOg . SSOg, is obtained, by boiling metallic antimony with concentrated sulphuric acid, as a white saline mass, which is decomposed by water. Oxalate of jmtash and antimony ^ KO . C2O3 4- SbOg . 3C2O3. — This is a double crystallisable salt of antimony, which, like the tartrate of potash and antimony, may be dissolved in water without decomposition. It is prepared by satur- ating binoxalate of potash with oxide of antimony. It is soluble at 48° in ten times its weight of Avater (Lassaigne). According to Bussy, when binoxalate of potash is digested upon oxide of antimony in excess, two salts are formed, one in oblique prisms, and another less soluble, in intricate small crystals ; but neither is very stable. The former is decom- posed by a large quantity of water : its analysis gave 3(KO . C2O,) + SbOg . 3C2O3 + GHO.* Tartrate of potash and antimony, KO . Sb O3 + C8H4O1Q.2HO. — This salt, the tartar-emetic or potash tartrate of anti- mony of pharmacy, is prepared by neutralising bitartrate of potash with oxide of antimony ; the oxide obtained by de- composing the chloride or sulphate of antimony with water answers best for the purpose. A quantity of oxide of anti- • J. Pharm. 1838, p. 509. f TARTAR-EMETIC. 227 mony may be boiled with three or four times its weight of water, and bitartrate of potash added in small quantities till the oxide is entirely dissolved. The filtered solution yields the salt, on cooling, in large transparent crystals, the form of which is an octohedron with a rhombic base ; they become white in the air, and lose their water of crystallisation. They are soluble in 14 times their weight of cold water, and in 1'88 parts of boiling water, but not in alcohol. The mother-liquor of these crystals becomes a syrupy liquid, and dries up into a gummy mass without crystallising, when oxide of antimony has been dissolved in excess by the acid tartrate in prepar- ing the salt. Potash added to a solution of the salt throws down the teroxide of antimony, but the precipitate is easily soluble in excess of potash. Ammonia forms no precipitate at first, and but a slight one after standing. Alkaline car^ bonates form a precipitate of the teroxide insoluble in excess of the reagent. With hydrosulphuric acid, the reaction is the same as with other salts of antimony. (See p. 224.) Salts of the earths and basic metallic oxides, such as baryta and oxide of silver J throw down from its solution a compound of the tartrate of antimony with tartrate of baryta, tartrate of silver, &c. (Wallquist.) Strong acids decompose the salt, and produce a precipitate which is a mixture of bitartrate of potash with oxide of antimony, or with a subsalt of that oxide. This salt was formerly described as a double tartrate of potash and antimony, or, abstracting its water of crystallisa- tion, which is differently stated at 2 and 3 equivalents, as KO . (C4H2O5) + SbOa . (C4H2O5) . When the atomic weight of tartaric acid is doubled, and it is represented as a bibasic acid, the formula for dry tartar-emetic becomes KO . SbOg. (CgH^Ojo). In comparing the last formula with that of bi- tartrate of potash, represented also as a bibasic salt, KO . HO . (CgH^Oio), it is observed that 1 eq. of oxide of anti- mony takes the place of I eq. of water as base, although the 228 ANTIMONY. former contains 3 eq. of oxygen, and the latter only one. Tar- trate of potash and antimony is, in this respect, an anomalous salt. Another equally remarkable fact respecting this salt has been observed by M. Dumas, namely, that 2 eq. of water are separated from the anhydrous salt at 428°, leaving a substance of which the elements are CgH20j2 SbK. The first part of this formula C8H2O12, M. Dumas looks upon as a quadribasic salt-radical, existing in the tartrates, which in hydrated tartaric acid is united with 4H, in bitartrate of potash with 311 + K, and in tartrate of antimony and potash with Sb + K. Here Sb is found equivalent to and capable of replacing 3H. Tartrate of antimony and potash might, therefore, be represented by KSb(C8H20i2) + 2H0 + water of crystallisation. If Sb02 be regarded as a radical capable of replacing 1 eq. of hydrogen (similar to uranyl, U2O2, the hypothetical radical of the uranic salts), the formula of tartar-emetic dried at 212° may be written as CgH^K (Sb02)Oi2, and that of the salt dried between 392° and 428°, as C8H2K(Sb02)Oio. Antimonic acid, SbO^,! 60*24 or 2003. — This compound is obtained in the hydrated state : 1 . By treating antimony with nitric acid, or with aqua-regia containing excess of nitric acid. 2. By decomposing pentachloride of antimony with water. 3. By precipitating a solution of antimoniate of potash with an acid. The hydrated acid obtained by either of these methods gives off its water at a moderate heat, and yields anhydrous antimonic acid in the form of a yellowish powder, which is tasteless, insoluble in water, decomposes alkaline carbonates, and, when heated to redness, gives off oxygen, and is con- verted into antimoniate of antimonic oxide, SbOg . SbOg. The hydrates obtained by the three methods above de- scribed are by no means identical. The acid in the first is monobasic, whereas in the other two it is bibasic. The bi- basic acid is distinguished by the name of met antimonic acid. ANTIMONIATES. 229 while the monobasic acid is called simply antimonic acid (Fremy) . Antimonic acid forms neutral or normal salts, containing MO . SbOg, and acid salts whose formula is MO . (Sb05)2. Met- antimonic acid forms neutral salts containing (MO) 2 . SbOg, and acid salts containing (MO)2.(Sb05)2, or MO.SbOg, so that the acid metantimoniates are isomeric or polymeric with the neutral antimoniates. An acid metantimoniate easily changes into a neutral antimoniate. The metanti- moniates of potash, soda, and ammonia are crystalline ; the antimoniates of the same bases are gelatinous and uncrystal- lisable. The soluble acid metantimoniates form a crystalline precipitate with salts of soda; the soluble antimoniates do not form any such precipitate (Fremy). Antimoniates of potash. — The neutral salt, KO.SbO5.5HO, is obtained by fusing 1 part of antimony with 4 parts of nitre, digesting the fused mass in tepid water to remove nitrate and nitrite of potash, and boiling the residue for an hour or two with water. The white insoluble mass of anhydrous anti- moniate is thereby transformed into a hydrate containing 5 eq. water, which is soluble. The solution when evaporated leaves this hydrate in the form of a gummy uncrystallisable mass, which gives off 2 eq. of water at 320°, and the whole at a higher temperature. Acid antimoniate of potash, KO . (Sb05)2 is obtained by passing carbonic acid gas through a solution of the neutral antimoniate. It is white, crystalline, perfectly insoluble in water, and is converted into the neutral salt when heated with excess of potash. This salt is the antimonium diapho- reticum lavatum of the pharmacopoeias (Fremy) . Neutral metantimoniate of potash, 21L0.^h0^y is prepared by fusing antimonic acid or neutral antimoniate of potash with a large excess of potash. The fused mass dissolves in a small quantity of water, and the solution evaporated in vacuo yields crystals of the neutral metantimoniate. This salt 230 ANTIMONY. dissolves freely and without decomposition in warm water containing excess of potash; but cold water or alcohol de- composes it into potash and the acid metantimoniatc. Hence the aqueous solution of this salt gives a precipitate, after a while, with salts of soda (Fremy) . Acid metantimoniate of potash, KO . SbOg + THO, some- times called granular antimoniate of potash. — This salt is used as a test for soda. To obtain it, the neutral antimoniate is first prepared and dissolved in the manner above described ; the solution filtered to separate any acid antimoniate that may remain undissolved; then evaporated to a syrup in a silver vessel ; and hydrate of potash added in lumps to convert the antimoniate into metantimoniate. The evaporation is continued till the liquid begins to crystallise, which is ascer- tained by taking out a drop now and then upon a glass rod, and the liquid is left to cool. A crystalline mass is thus obtained, consisting of neutral and acid metantimoniate of potash ; the alkaline liquor is then decanted, and the salt di'ied upon filtering paper or unglazed porcelain (Fremy). This salt may also be prepared by treating terchloridc of antimony with an excess of potash sufficient to redissolve the precipitate first formed, and adding permanganate of potash till the solution acquires a faint rose colour. The liquid, filtered and evaporated, yields crystals of the granular metantimoniate (Reynoso). This salt is sparingly soluble in cold water, but dissolves readily in water between 113° and 122°. When boiled with water for a few minutes, or kept in contact with water for some time, it is converted into the neutral anti- moniate. It must therefore be preserved in the solid state, and dissolved just before it is required for use. A small quantity of it is then treated with about twice its weight of cold water to remove excess of potash, and convert any neutral metantimoniate into the acid salt; the liquid de- canted; the remaining salt rapidly washed three or four times with cold water ; then left in contact with water for a ANTIMONIATES. 231 few minutes, and the liquid filtered. On adding to the solu- tion thus obtained, a small quantity of any soda-salt, a crys- talline precipitate is formed, consisting of acid metantimo- niate of soda, NaO . SbOg + 7H0. This reaction is apparent in a solution containing only 1 part of soda in 300. In strong solutions of soda, the precipitate appears immediately, but in dilute solutions only after a while, the crystals being depo- sited on the sides of the vessel. An excess of potash in the reagent also retards the precipitation (Fremy*) . Antimoniates of ammonia. — ^When the metantimonic acid, obtained by decomposing pentachloride of antimony with water, is treated with ammonia, part of it dissolves, and a solution is formed containing neutral metantimoniate of am- monia. A few drops of alcohol added to the solution, throw down a precipitate consisting of acid metantimoniate of am- monia, NH^O . SbOg + 6H0. This salt is slightly soluble, and its solution precipitates soda-salts. It changes spontaneously in a few days, even when kept in a close vessel, into neutral an- timoniate of ammonia, which is completely insoluble in water. The same change is instantly produced in it by heat (Fremy) . Antimoniate of lead, PbO . SbOg, may be obtained as a yellow powder by fusing antimonic acid with oxide of lead, or as a white hydrate by precipitation : the hydrate gives off its water when heated, and turns yellow. This salt is used as a pigment under the denomination of Naples yellow. Antimoniate of antimoni/, SbOg.SbOg. or Sb04, is obtained by the action of heat upon antimonic acid, by roasting the * Traite de Cliimie Generale, par Pelouze et Fremy, 2me. ed. t. 3. pp. 151. 157. According to Heflfter (Pogg. Ann. Ixxxvi. 418.), the granular antimoniate of potash is KO .HO + 12(KO.Sb05 + 7HO) ; the precipitated soda-salt is similarly constituted ; and by treating the solution of this salt in boiling water with salts of the earths and metallic oxide?, precipitates are obtained, also of similar composition, or differing only in the water which they contain. Heffter's formulae were calculated according to the old equivalent of antimony, 129 ; but Schneider has shown that, on re-calculating the analyses with the lower equivalent 120'24, the numbers of the equivalents of base and acid come out equal. 233 ANTIMONY. teroxide or tersulphide, or by treating powdered antimony with excess of nitric acid. It is white, infusible, and unalterable by heat ; slightly soluble in water. It was formerly regarded as a distinct acid, Sb04, ^'^^ called antimonious acid ; but it does not form salts; and, when boiled with bitartrate of potash, it is resolved into cream of tartar, which dissolves, and a residue of antimonic acid. Pentasulphide of antimony, Sulphantimonic acid, SbOg, is obtained by passing hydrosulphuric acid gas into an acid solution of pentachloride of antimony, or into the solution of an alkaline antimoniate. It has an orange-colour much less red than the tersulphide; it is the golden sulphuret of antimony of several pharmacopoeias. It combines with basic metallic sulphides, forming the sulphantimoniates. The sodium- salt, 3NaS . SbSg, which is sometimes used in medicine, is obtained by mixing 18 parts of finely pounded tersulphide of antimony, 12 parts of dry carbonate of soda, 13 parts of lime, and 3 J parts of sulphur ; triturating the mixture for about half an hour ; leaving it for two or three days in a flask filled with water, and shaking it from time to time ; then filtering and evaporating, first over tlie open fire, afterwards in vacuo. The salt is thus obtained in large regular tetrahedrons of a pale yel- low colour. It is very soluble in water, and is decomposed by acids, which throw down hydrated pentasulphide of antimony. Pentachloride of antimony, SbClg, is obtained by heating metalUc antimony in a current of dry chlorine, and distilhng the product in a dry retort, rejecting the first portions of the distillate, which contain excess of chlorine. It is a yellowish, very volatile liquid, which emits suffocating vapours. Water first converts it into a crystalline hydrate, and then decomposes it, forming antimonic acid : SbCl5 4-5HO = Sb05 + 5HCl. It absorbs ammonia and phosphurctted hydrogen, forming red-brown solid compounds. It absorbs olefiant gas as readily as chlorine, and forms Dutch liquid. It likewise absorbs hydrosulphuric acid gas at ordinary temperatures, forming a ANTIMONIURETTED HYDROGEN. 233 white crystalline mass, consisting oi chlorosulphide of antimony j SbClgSg, exactly analogous to chlorosulphide of phosphorus PCI3S2. Pentasulphide of antimony, treated with dry chlorine aided by heat, forms a white pulverulent compound, containing SbClgSg, or SbClg.SSClj this compound is decomposed at 572° (300° C.) into chlorine, chloride of sulphur, and ter- chloride of antimony. Pentachloride of antimony combines with hydrocyanic acid, forming a white, crystalline, volatile compound, composed of SbClg.SHCy. It also combines with chloride of cyanogen. Antimoniuretted hydrogen. — This compound is obtained by dissolving an alloy of zinc and antimony in hydrochloric or dilute sulphuric acid, or by dissolving zinc in either of these dilute acids containing oxide or chloride of antimony, tartar- emetic, &c. The gas, however, always contains more or less free hydrogen. Its comparative purity may be tested by means of a solution of nitrate of silver, which absorbs the antimoniuretted hydrogen, and leaves the free hydrogen. An alloy of 2 parts zinc and 1 part antimony yields the purest gas; an alloy containing a larger proportion of antimony gives more free hydrogen ; and an alloy of equal parts of the two metals yields scarcely anything but free hydrogen. As the compound has never been obtained in a state of purity, its composition has not been correctly ascertained, but it is probably SbH3. Antimoniuretted hydrogen is a colourless gas, and when free from arsenic, quite inodorous. It is insoluble in water, and in alkaline liquids ; with solutions of silver or mercury it forms precipitates containing silver or mercury, together with antimony. When burned from a jet, it deposits, on a plate of porcelain, metallic spots, greatly resembling those of arsenic, but differing from the latter in possessing less lustre and in not being soluble in hypochlorite of soda. They may also be dissolved in aqua-regia or in permanganate of potash (p. 224), and the solution wiU give the characteristic orange 231 ANTIMONY. precipitate with hydrosulphuric acid. A metallic deposit may also be obtained by heating a glass tube through which the gas is passed ; and this deposit, when sublimed, will not exhibit the characters of arsenic (p. 216). Alloys of antimony with potassium or sodium may be ob- tained by igniting metallic antimony, or its oxide or sulphide, with an organic salt of potasli or soda. Thus, when 5 parts of crude tartar and 4 parts of antimony are slowly heated in a covered crucible till the mixture becomes charred, then heated to whiteness for an hour, and left to cool, a crystalline regulus is obtained containing 12 per cent, of potassium. This alloy decomposes water rapidly, and oxidises slowly in the air when in the compact state, but becomes heated and takes fire when rubbed to powder. A mixture of 7 parts of antimony and 3 parts of iron, heated to whiteness in a crucible lined with charcoal, forms a white, very hard, slightly magnetic alloy, which gives sparks when filed. It is always formed when sulphide of antimony is reduced by iron in excess. With zinc, antimony forms alloys of definite crystalline character. A fused mixture of the two metals, containing from 43 to 70 per cent, of zinc, deposits by partial cooling, silver-white rhombic prisms, containing from 43 to 64 per cent, of zinc. The alloy containing exactly 43 per cent, of zinc, appears to be a definite compound, stibiotinzincyl, SbZug. Mixtures containing from 33 to 20 per cent, of zinc deposit rhombic crystals containing from 35 to 21 per cent, of zinc. The alloy containing exactly 33 per cent, is stibiobizincyl, SbZn2. These alloys, especially SbZn3, decompose water with evolution of hydrogen at the boiling heat, and very rapidly under the influence of acids (J. P. Cooke *). Type-metal, is an alloy of antimony and lead, usually con- taining 76 per cent, of lead, which corresponds nearly with the formula V\^h. * Sm. Aui. J. [2.] xviii. 229; xx. 222. ESTIMATION OF ANTIMONY. 235 ESTIMATION OF ANTIMONY, AND METHODS OP SEPARATING IT FROM THE PRECEDING METALS. Antimony cannot be estimated in the form of antimonious or antimonic acid, because we can never be sure of the purity of those bodies. The best mode of proceeding is to precipi- tate it by hydrosulphuric acid, collect the sulphide of anti- mony on a weighed filter, and, after ascertaining the total quantity of the precipitate, estimate the proportion of sulphur in it in the manner already described with reference to sul- phide of arsenic (p. 219). Or the sulphide of antimony may be decomposed by heating it in a current of hydrogen gas, whereupon hydrosulphuric acid and sulphur-vapour escape, and metallic antimony remains behind. For this purpose, a weighed portion of the sulphide is placed in a small porcelain crucible ha^dng a hole in its cover, through which a tube passes to convey the hydrogen. The temperature is gradually raised, and the process continued till the weight of the cru- cible no longer varies. The reduction may also be performed in a bulb-tube. When antimonious and antimonic acids occur together in solution, the total quantity of antimony may be ascertained by treating one portion of the liquid in the manner just described, and the quantity existing as antimonious acid may be determined in another portion by means of terchloride of gold, 2 eq. of precipitated gold corresponding to 3 eq. of anti- monious acid : 2AUCI3 -I- 6H0 + 3Sb03 = 2Au + 6HC1 + 3Sb05. The separation of antimony from the alkalies and earths j and from those metals which are not precipitated from their acid solutions by hydrosulphuric acid, is effected by means of that reagent. To separate antimony from cadmium^ copper , and leadj the VOL. II. s 236 ANTIMONY. solution, after being neutralised with ammonia, is mixed with sulphide of ammonium containing excess of sulphur. The sulphide of antimony then dissolves, the other sulphides remaining undissolved ; and on mixing the filtrate with acetic acid (hydrochloric acid might redissolve a portion of the pre- cipitate, especially as the liquid becomes heated), the sulphide of antimony is reprecipitated, and may be treated as above. When antimony is combined with any of the preceding metals in the form of an alloy, it may be separated by treating the alloy with nitric acid, whereby the other metals are dissolved, and the antimony converted into insoluble antimonic acid. This method is, however, not rigidly exact; for the nitric acid dissolves a small portion of the antimony. Separation of antimony from arsenic and tin. — The separa- tion of these metals is attended with considerable difficulty. The best mode of effecting it is to convert them into arsen- iate, stannate, and antimoniatc of soda, and treat the mixture with dilute alcohol, which dissolves the arseniate and stannate of soda, and leaves the antimoniate undissolved. If the three metals exist together in solution, they must be precipitated as sulphides by hydrosulphuric acid, and the precipitate treated by one of the following methods : — (1.) The precipitated sulphides are fused in a silver cru- cible with a mixture of hydrate of soda and nitre : or, better, they are oxidised by heating them with strong nitric acid ; the solution, together Avith the insoluble stannic and anti- monic acids, mixed with excess of caustic soda, and evapo- rated to a small bulk ; then transferred to a silver crucible, evaporated to dryness, and kept for some time in a state of red hot fusion. The fused mass, consisting of arseniate, stannate, and antimoniate of soda, is disintegrated by diges- tion in warm water; the contents of the crucible trans- feiTcd to a beaker-glass; and the crucible well rinsed out with a measured quantity of water. The greater part of the arseniate and stannate of soda then dissolves, while the anti- SEPARATION OF ANTIMONY FROM TIN AND ARSENIC. 237 moniate remains undissolved. But to effect complete separa- tion, a quantity of alcohol of sp. gr. 0'833 is added, equal in bulk to one-third of the water used; the mixture left to stand for 24 hours and frequently stirred ; and the anti- moniate of soda, which has then completely settled down, is collected on a filter and washed, first, with a mixture of 1 volume of the same alcohol to 3 vols, of water, then with 1 vol. alcohol to 2 vols, water ; next, with a mixture of equal measures of water and alcohol; and, lastly, with 3 vols, alcohol to 1 vol. water (H. Eose).* (2.) The precipitated sulphides of the three metals are dissolved in a mixture of sulphide of sodium and caustic soda, and the liquid mixed with a solution of hypochlorite of soda. The sulphides are thereby oxidised and converted into arsenic, stannic, and antimonic acids, which combine with the soda, and may be separated by treatment with dilute alcohol, and washing, as in Rosens process. This method is due to Dr. Williamson; it is easier of execution than the former, as the fused mixture of the soda-salts is very hard, and difficult to disintegrate by water. The antimoniate of soda, separated by either of these pro- cesses, is digested in a mixture of hydrochloric and tartaric acids, which dissolves it completely ; the antimony then pre- cipitated by hydrosulphuric acid ; and its quantity estimated in the manner already described (p. 235). The filtrate containing the arseniate and stannate of soda is supersaturated with hydrochloric acid, which throws down a bulky precipitate of arseniate of stannic oxide ; hydrosul- phuric acid gas passed through the liquid till the white preci- pitate is completely converted into a brown mixture of the sulphides of tin and arsenic ; the whole left to stand till the odour of hydrosulphuric acid is no longer perceptible; the precipitate collected on a weighed filter; and the filtrate * Handb. d. anal. Chem. 1851. ii. 429. s 2 238 ANTIMONY. heated for some time to expel the greater part of the alcohol ; then mixed with sulphurous acid, and again treated with hydrosulphuric acid, whereby a small quantity of sulphide of -arsenic is generally precipitated. This quantity of sulphide of arsenic being quite free from tin, need not be added to the mixed sulphides on the filter. These mixed sulphides are dried at 212°, their total weight determined, and a known quantity heated in a stream of hydrosulphuric acid gas in the manner described at page 220. The residual sulphide of tin is then converted into stannic oxide, and the sublimed sulphide of arsenic, together with the small quantity separately precipitated, is converted into arsenic acid by treatment with hydrochloric acid and chlorate of potash, and the arsenic precipitated as ammonio-magnesian arseniate (H. Rose). If the three metals are in the state of solid oxides, the mixture may be dissolved in hydrochloric acid, with addition of tartaric acid, and the metals precipitated as sulphides as before. If the metals are mixed in the form of an alloy, they may be dissolved in aqua-regia, tlie solution mixed with tar- taric acid, then diluted, and precipitated in the same manner. The method just described may, of course, be applied to the separation of antimony from tin or from arsenic alone. In these cases, however, simpler methods may often be ad- vantageously adopted. Separation of antimony from tin — When these two metals exist together in solution, and the sum of their weights is known, the separation may be effected, and the weights of the two determined, by immersing in the solution a piece of pure tin, which precipitates the antimony in the form of a l^lack powder. To render the precipitation complete, a gentle heat must be applied, and the solution must contain excess of acid. The antimony is collected on a weighed filter, dried at a gentle heat, and weighed. If the sum of the weights is not previously known, the metals must be precipitated together SEPARATION OF ANTIMONY TROM ARSENIC. 239 by zinc from a known quantity of the solution, and the anti- mony precipitated by tin from another portion. When the two metals exist together in an alloy, a portion of the alloy must be weighed, then dissolved in aqua-regia, and the solu- tion mixed with tartaric acid, diluted with water, and treated as above. Another method of separation is to precipitate the two metals with zinc, and treat the precipitate with strong hydro- chloric acid without previously decanting the solution of chloride of zinc. The tin then dissolves, while the antimony remains undissolved, the presence of the chloride of zinc diminishing its tendency to dissolve in the acid. The tin may afterwards be precipitated by hydrosulphuric acid, and the sulphide converted into stannic oxide, by treating it with strong nitric acid (Levol).* Separation of antimony from arsenic. — When these two metals are associated in the metallic state, they may be com- pletely separated by heating the alloy in a stream of carbonic acid, the arsenic then volatilising, and the antimony remain- ing. Antimony is, however, the only metal from which ar- senic can be completely separated in this manner ; hence, if the alloy contains any other metal, some of the arsenic will be retained, and the method is no longer applicable. When this is the case, the alloy may be dissolved in aqua regia, or in hydrochloric acid to which chlorate of potash is gradually added ; the solution diluted with water after addi- tion of tartaric acid ; then mixed with a considerable quantity of chloride of ammonium and excess of ammonia; and the arsenic precipitated as ammonio-magnesian arseniate by addi- tion of sulphate of magnesia. The antimony may then be precipitated from the filtrate by hydrosulphuric acid. * Ann. Ch. Phys. [3.] xiii. 125. S 3 240 BISMUTH. SECTION III. BISMUTH. Eq. 213, or 26625; Bi. Bismuth is generally found in the metallic state, disseminated in quartz-rock ; but occurs also as an oxide, carbonate, and sulphide, either alone or associated with other metals ; also in combination with tellurium. Native bismuth is, however, the only mineral which occui*s in sufficient abundance for the economical extraction of the metal. The process of extraction as performed in Saxony, whence all the bismuth of commerce is obtained, is veiy simple, the mineral being merely heated in close vessels, so as to melt the bismuth, and thereby separate it from the gangue or accompanying rock. The fusion is per- formed in iron tubes, laid in an inclined position, in a furnace. {Fig. 11.) The ore is introduced at the upper end, d, which is then plugged. The other end, 6, is closed with an iron plate having an aperture, 0, through which the melted metal runs into earthen pots, a, heated by a few coals placed in the space, K, below, so as to keep the metal in the melted state. It is then ladled out and run into moulds. The crude metal thus obtained is afterwards fused with 1-lOth of its weight of nitre, to free it from sulphur, arsenic, and certain foreign metals. Commercial bismuth, however, is still somewhat impure. To free it completely from other metals, it is dissolved in Fii?. 11. OXIDES OF BISMUTH. 241 nitric acid, the clear liquid decanted and mixed with water, which throws down a subnitrate of bismuth; and this com- pound is reduced at a moderate heat, either with black flux, or in a crucible lined with charcoal. Bismuth crystallises in octohedrons and cubes. It may be obtained in very beautiful crystals, by fusing several pounds of the ordinary metal in a crucible or iron ladle, adding nitre from time to time, and stirring, till a portion of the fused metal, taken out and exposed to the air, no longer assumes an indigo colour, changing to violet or rose and dis- appearing on cooling, but a fine green or golden tint, which it retains on cooling ; then leaving the metal to cool slowly, on a hot sand-bath, for instance, till a crust forms on the surface ; piercing this crust with a hot coal ; and pouring out the por- tion which still remains liquid. On subsequently detaching the crust, the inner surface of the metal is found to be covered with beautiful fretted cubes, like those of common salt. Bismuth is moderately hard, slightly sonorous, and brittle, but may be somewhat extended by careful hammering. Its colour is reddish tin- white, with moderate lustre. The specific gravity of pure bismuth is 96542 (Karsten), 9'799 (Marchand and Scherer) ; of commercial bismuth, 9' 822 (Brisson), 9'833 (Herapath), 9*861 (Bergman). Strong pres- sure rather diminishes than increases the density. Bismuth melts at 480° (Crichton) ; at 507° (Rudberg) ; at 509^ (Hermann) ; and expands in solidifying. It boils at an inci- pient white heat, and if the air be excluded, sublimes in laminae. Bismuth forms four compounds with oxygen, viz., the bioxide, Bi02; the teroxide, BiOg; the quadroxide Bi04; and bismuthic acid, BiOg. Bioxide or suboxide of ^i^mM^A.-— Bismuth oxidises slowly when exposed to the air at ordinary temperatures, becoming covered with a brownish film of suboxide. When heated in the air till it fuses, it oxidates more rapidly, becoming covered S 4 242 BISMUTH. with the same brown oxide, which is renewed as often as it is removed, till the whole of the metal is oxidised. This sub- oxide is also formed when subnitrate of bismuth is heated with protochloride of tin. By pouring a hydrochloric acid solution of equivalent quantities of teroxide of bismuth and proto- chloride of tin into excess of moderately strong potash, a black-brown precipitate is formed, consisting of a lower oxide of bismuth combined with stannic acid ; and on treating this com- pound with stronger potash, the stannic acid dissolves and an oxide of bismuth remains, which, when dried in vacuo, or at 100°, out of contact with the air, forms a blackish-grey crystal- line powder, consisting of 610.2, retaining, however, a small quantity of water. It shows but little disposition to absorb oxygen at ordinary temperatures, but when heated, it is instantly converted, with a glimmering light, into teroxide. Acids de- compose it into metallic bismuth and teroxide. AVhen ignited in an atmosphere of carbonic acid, it becomes perfectly anhy- drous, and in that state does not undergo any perceptible alteration by exposure to the air at ordinary temperatures, and oxidises but slowly even at a red heat (R. Schneider).* Teroxide of Bismuth, BiOg ; 237 or 3662-5. — Bismuth heated in the air till it boils, takes fire and bums with a faint bluish white flame, forming teroxide of ])ismuth, the vapour of which condenses on the surface of cold bodies in the form of flowers of bismuth. The same oxide is obtained in solution by acting on bismuth with nitric acid, the metal being then dissolved with evolution of nitrous fumes. Strong sul- phuric acid likewise dissolves it at a boiling heat, with evolution of sulphurous acid. Hydrochloric acid acts but slightly on it, even with the aid of heat. Wlien the solution of the nitrate is mixed with water, a white precipitate of subnitrate is produced; and this, when gently ignited, yields the ter- oxide in the form of a lemon-yellow powder. By fusing the * Pogg. Ann. Ixxxviii. 45. OXIDES OF BISMUTH. 243 hydrated oxide with hydrate of potash, or boiling it with potash-ley, the anhydrous oxide may be obtained in yellow shining needles. Teroxide of bismuth fuses at a strong red heat, and solidifies in a crystalline mass on cooling. It is easily reduced to the metallic state by potassium or sodium at a gentle heat, and by charcoal before the blowpipe. Teroxide of bismuth combines with acids, forming salts which are very heavy, colourless, unless the acid itself is coloured, and exert a poisonous action. Heated on charcoal with carbonate of soda, they yield a button of metal. ZinCf tin, cadmium, iron, and lead, precipitate the metal from the so- lutions of these salts. Water decomposes most bismuth-salts — provided they do not contain too large an excess of acid, throwing down a sparingly soluble basic salt, while the acid remains in solution, together with a small quantity of oxide. Hydrosulphuric acid produces a brown-black precipitate of tersulphide of bismuth, insoluble in sulphide of ammonium. Caustic alkalies, at ordinary temperatures, throw down the white hydrated oxide, but at a boiling heat, especially if they are concentrated, they produce a yellow precipitate of the anhydrous oxide : these precipitates are insoluble in excess of the alkali. Alkaline carbonates throw down a white preci- pitate of carbonate of bismuth, slightly soluble in excess, but precipitated from the solution by a caustic alkali. Chromate or bichromate of potash throws down a yellow chromate of bismuth, insoluble in caustic potash, whereby it is distin- guished from chromate of lead. Sulphuric acid produces no precipitate. Quadr oxide of bismuth, Bi04. — When a bismuth-salt con- tains free chlorine, caustic potash produces in it, not a white but a yellow precipitate, which consists of the hydrate of a higher oxide, but cannot be obtained free from chlorine. When this yellow hydrate is boiled with an alkaline chlorite having a strong alkaline reaction, it turns brown, like peroxide of lead, and is converted into the quadroxide of bismuth (Arppe). 244 BISMUTH. This oxide is completely dissolved by boiling nitric acid ; any yellow or green residue that may be left, consists of bismuthic acid. It is perhaps a compound of teroxidc of bismuth with bismuthic acid : BiOg'BiOg. Bismuthic acid, BiOg. — Prepared by passing chlorine through a strong solution of potash in which finely divided teroxide of bismuth is suspended ; also, by heating a mixture of potash and teroxide of bismuth for a long time in contact with the air, — or better, by calcining a mixture of teroxide of bismuth, caustic potash, and chlorate of potash. Bismuthic acid, prepared by any of these methods, is always more or less mixed with teroxide of bismuth, which, however, may be dis- solved out by weak nitric acid. Bismuthic acid is a light red powder, which, at a temperature a little above 212°, gives off part of its oxygen, and is converted into quadroxide of bis- muth. Strong acids also decompose it, reducing it to the state of teroxidc of bismuth, which then unites with the acid. Bismuthic acid combines with potash, and forms a few double salts, whose bases are the alkali and teroxide of bismuth. Bisulphide of bismuth, BiS2, separates in crystals from a fused mixture of metallic bismuth and the tersulphide, and may also be obtained by fusing 10 parts of bismuth wnith 3 parts of sulphur, melting the resulting mixture three times with fresh sulphur, and cooling quickly. Hydrochloric acid decomposes this compound, yielding metallic bismuth and the terchloride. Hence, and jfrom the fact that its crystalline form is the same as that of the tersulphide, and that by fusing the tersulphide with metallic bismuth, in certain pro- portions, crystals may be obtained of the same form but containing less sulphur, Schneider concludes that the sup- posed bisulphide is merely a mixture of the tersulphide with metallic bismuth. Tersulphide of bismuth, BiSg, occurs native as bismuth- glance, and may be formed artificially by fusing bismuth with CHLORIDES OF BISMUTH. 245 sulphur, and by decomposing bismuth-salts with hydrosul- phuric acid» The native variety forms right rhombic prisms, isomorphous with sulphide of antimony : its colour is light lead-grey; specific gravity from 6*4 to 6-5. Tersulphide of bismuth is decomposed by heat ; the native sulphids, heated in a tube, yields sublimed sulphur ; and the artificial sulphide, when fused and left to cool, yields globules of metallic bismuth as it solidifies. Selenide of bismuth, BiSe3, is obtained by melting together 1 eq. of bismuth and 3 eq. of selenium, and remelting the product with fresh selenium out of contact with the air. On a recently fractured surface, it exhibits a steel-grey colour, me- tallic lustre, and a distinct crystalline laminated texture. Its density is 6*82; hardness equal to that of galena: it may be readily pulverised. It is scarcely attacked by hydrochloric acid, but nitric acid and aqua regia decompose it readily (Schneider). Bichloride of bismuth, BiCl2, is formed by the action of dry hydrogen on the terchloride of bismuth and ammonium, 2NH4Cl.BiCl3, at about 570°, or by heating 1 part of pul- verised bismuth with 2 parts of subchloride of mercury in a sealed tube, at about 460°, and purifying the product by repeated fusion in sealed tubes. It is a black hygroscopic mass, which, by heating in the air, and by the action of acids, is resolved into metallic bismuth and the terchloride. Terchloride of bismuth, BiClg. — Pulverised bismuth thrown into chlorine gas takes fire and burns with a pale blue light, forming the terchloride. This compound may also be ob- tained by heating 1 part of bismuth with 2 parts of proto- chloride of mercury, or by evaporating to dryness the solution of teroxide of bismuth in hydrochloric acid, and distilling the residue out of contact with the air. It is a white opaque solid, with a slight tinge of brown or grey, and a granular frac- ture ; melts very readily, forming an oily liquid. The hydrated 246 BISMUTH. terchloride is obtained in crystals by dissolving tlie teroxide in hydrochloric acid, and evaporating. The anhydrous chloride, the crystals, and the solution are decomposed by water, yield- ing oxy chloride of bismuth, BiClg . 2Bi03, in the form of an insoluble white powder, commonly known as pearl-white^ — and hydrochloric acid holding a small quantity of bismuth in solution. A sulphochloHde, of analogous composition, BiClg . 2BiS3, is obtained by heating chloride of bismuth and ammonium with sulphur or tersulphide of bismuth, or by passing hydrosulphuric acid gas over the same compound, heated to a temperature between 485° and 572°, and after- wards heating the product to its melting point in the same gas:— SBiClg -f 6HS = BiCla . 2BiS3 + GIICl. The product of either of these operations, after being waslied, first with water containing so much hydrochloric acid as not to give a precipitate with the terchloride, then with water slightly acidulated, and lastly with pure water, forms small, dark grey, crystalline needles, which, when heated in the air, give ofi*, first, chloride of bismuth, then sulphurous acid, and leave a mixture of oxychloride and basic sulphate of bismuth (Schneider). A seleniochloride, BiCl3 . 2BiSe3, is obtained by adding terselenide of bismuth to fused chloride of bismuth and ammonium. It forms small needle-shaped crystals, having a dark steel-grey colour and metallic lustre (Schneider). Terchloride of bismuth and ammonium. — A solution of 1 eq. of terchloride of bismuth and 2 eq. of sal-ammoniac, yields, by evaporation, double six-sided pyramids containing 2NH4CI . BiClg, isomorphous with the corresponding ter- chloride of antimony and ammonium ( Jacquelain) . A solution of 1 eq. terchloride of bismuth and 6 eq. sal-ammoniac yields rhombic crystals, containing 3NH^C1 . BiClg (Arppe). SALTS OF BISMUTH. 247 Bismuth dissolves in a boiling solution of protochloride of copper, the liquid being decolorised_, and appearing to con- tain the compound, 3CU2CI. BiClg. Bismuth dissolves in a similar manner in other cupric salts (Schneider). Teriodide of bismuth, Bilg. — Obtained as a crystalline sublimate by heating 1 eq. (32 parts) of tersulphide of bis- muth with 3 eq. (475 parts) of iodine. Large, thin, crystal- line laminae, having the form of regular six-sided prisms, of a blackish grey colour with a tinge of brown and a strong lustre. The compound, heated in the air, volatilises for the most part, leaving a small quantity of basic oxide of bismuth of a red-brown colour. Boiling water converts it into the same compound. Aqueous potash decomposes it, forming iodate of bismuth, BiOg . 3IO3 : the same change is more slowly produced by alkaline carbonates. Alkaline sul- phides decompose it, forming tersulphide of bismuth. Hydro- chloric acid dissolves it without decomposition ; nitric acid, with separation of iodine. Sulphates of bismuth. — When bismuth is heated with strong sulphuric acid, sulphurous acid is evolved, and the metal is converted into a white insoluble powder, consisting of ter sulphate of bismuth, Bi03 . 3SO3, which is decomposed by water, yielding a very acid salt which dissolves, and a monobasic sulphate, Bi03 . SO3 + HO, which remains. There is also a bisulphate of bism,uth, which is obtained in small delicate needles when an acid solution of nitrate of bismuth is mixed with sulphuric acid (Heintz). Carbonate of bismuth, Bi03 . CO2, is obtained by adding nitrate of bismuth to the solution of an alkaline carbonate : this salt is used in medicine. Nitrates of bismuth. — The neutral or ternitrate, Bi03. 3NO5+ lOHO, is obtained by dissolving bismuth in hot nitric acid, evaporating the solution, and leaving it to cool. The salt then separates in transparent oblique prisms of six or eight sides, and tenninated with several faces. At 212° 218 BISMUTH. they separate into a solid and a liquid portion, the latter solidifying as it cools. At 302°, they are reduced to the mononitrate, BiOg . NO5 + HO ; which, when further heated to 500°, gives up all its acid and water, and leaves oxide of bismuth. Siibnitrates of bismuth. — a. Ternitrate of bismuth dissolves without decomposition in a sfnall quantity of water, especially if a few drops of nitric acid are added. But a larger quan- tity of water decomposes it, forming a white precipitate of a subsalt, commonly called magistery of bismuth. This sub- stance is generally regarded as a mononitrate containing one atom of water, Bi03 . NO5 + HO ; but, according to Becker *, the basic nitrate obtained directly by treating the ternitrate with cold water, consists of BiOa . NO5 + 2 HO. This precipitate, when recently formed, dissolves somewhat freely in water, especially if the water contains nitric acid. Hence, if, after the precipitation of the basic salt, the super- natant liquid be mixed with a large quantity of water, the precipitate is completely redissolved; but after a while, a basic salt separates, containing SBiOg . 4N05-}-9Aq ; this, according to Becker, is the tnie magistery of bismuth, inasmuch as, in the usual mode of preparing that sub- stance, the same change takes place in washing the precipitate. Boiling water decomposes this salt, extracting all the nitric acid, excepting about 1 per cent. — b. A salt containing 5Bi03.4N05-f-12HO, is obtained by evaporating a solution of the ternitrate at a strong heat. When the precipitate first obtained by the action of cold water on a solution of the ter- nitrate is heated in contact with a free acid, or when the same acid solution is poured into hot water, a -s^hite, very loose powder is precipitated, containing GBiOg . oNOg + 9H0. This salt is decomposed by water more readily than the preceding. If it be washed with water as long as the filtrate continues to * Arcliir. riiarni. Iv. 31. and 129. SALTS OF BISMUTH. 249 exhibit a strong acid reaction_, a crystalline residue is left on the filter, containing 4Bi03 • ^^^5 • 9-A.q. Duflos obtained a magistery of bismuth having the same composition, by treat- ing the crystals of the neutral nitrate with 24 times their weight of water. Lastly, if the mononitrate, completely freed from the adhering acid liquid, be treated with water likewise free from acid, it dissolves completely ; but the liquid after a while becomes milky, and after long standing deposits a white amorphous powder, containing SBiOg . SNOg + 8HO. This salt may be formed, in addition to the true magistery of bismuth, if, in the preparation, of that substance, too large a quantity of water be used, and the greater part of the acid liquid removed (Becker.) Magistery of bismuth is used as a cosmetic, but has the serious disadvantage of being black- ened by hydrosulphuric acid. Bichromate of bismuth, BiOg . 2Cr03. — When a solution of ternitrate of bismuth, containing as little free acid as possible, is poured into a moderately concentrated solution of bichromate of potash, bichromate of bismuth is obtained in the form of a yellow flocculent precipitate, which becomes dense and crystalline after a while, or immediately if heated. It may be dried without decomposition between 212° and 257°, but becomes blackish- green at a red heat. It contains 69'48 per cent, of teroxide of bismuth (J. Lowe.) The alloys of bismuth are remarkable for their fusibility. The amalgam of this metal is liquid. An alloy of 8 parts bismuth, 5 lead, and 3 tin, melts at 202° j another mixtui-e of 2 bismuth, 1 lead, and 1 tin, at 200*75° ; these mixtures are known by the name of fusible metal. Bismuth is also added to the alloy of tin and lead used for casting stereotype plates. Besides increased fusibility, bismuth communicates to this alloy the property of expanding on becoming solid, by which it is rendered capable of taking an accurate impression. 250 BISMUTH. ESTIMATION OF BISMUTH^ AND METHODS OF SEPARATING IT PROM THE PRECEDING METALS. The best reagent for precipitating bismuth from its solu- tions is carbonate of ammonia ; which, when added in excess, throws down the bismuth completely : the liquid must, how- ever, be left to stand for some hours in a warm place, other- wise a considerable quantity of the bismuth w ill remain in solution. The precipitate, after being washed and dried, must be separated from the filter as completely as possible, the filter separately burned, and the precipitate ignited in a porcelain crucible : a platinum crucible would be attacked by it : after ignition, it consists of teroxide of bismuth contain- ing 89'66 per cent, of the metal. If the solution contains hydrochloric acid, the bismuth cannot be estimated by precipitation with carbonate of am- monia, or any other alkali, because the precipitate so pro- duced would contain oxychloride of bismuth (p. 255). In this case, therefore, the bismuth must be precipitated by hydrosulphuric acid; the sulphide of bismuth oxidised and dissolved by nitric acid ; and the diluted solution treated with carbonate of ammonia, as above. Bismuth is separated from the alkalies and earths, and from iron, cobalt, nickel, zinc, and chromium , hy hydrosul- phuric acid ; from tin, arsenic, and antimony, by sulphide of ammonium ; from lead, by sidphuric acid ; and from copper and cadminni by ammonia. The separation of bismuth from cadmium may also be effected by cyanide of potassium, which dissolves the latter as cyanide of cadmium and potas- sium, and precipitates the bismuth. The precipitated bis- muth, however, always contains potash, and must therefore be dissolved in nitric acid and precipitated by carbonate of ammonia. These two metals may also be separated by means of bichromate of potash, which throws down the bis- muth as Bi03 . 2 Cr03, and retains the cadmium in solution. URANIUM. 251 ORDEE VII. METALS NOT INCLUDED IN THE EOEE GOING CLASSES, WHOSE OXIDES AEE NOT EEDUCED BY HEAT ALONE. SECTION L URANIUM. Eq. 60, or 750; U. This metal is obtained from pitchblende, a mineral con- taining from 40 to 95 per cent, of uranoso-uranic oxide, U3O4, associated witli sulphur, arsenic, lead, iron, and several otlier metals. The mineral is finely pounded ; freed by elu- triation from the finer earthy impurities ; roasted for a short time, to remove part of the sulphur and arsenic ; then dissolved in nitric acid, and the solution evaporated to dryness. The residue is exhausted with water ; the solution filtered from the brick-red residue of ferric oxide, ferric arseniate, and lead- sulphate ; the greenish yellow filtrate slightly concentrated by evaporation, and left to cool, whereupon it deposits crystals ; and the resulting radiated mass of crystallised uranic nitrate drained on a funnel, and then washed with a small quantity of cold water. As the water dissolves a portion of the crystals, it is used in a subsequent operation to redissolve the residue obtained by evaporating the solution of pitchblende in nitric acid. The uranic nitrate, after being dried in the air, is introduced into a wide-mouthed bottle containing ether, in which it immediately dissolves ; the yellow solution is left to evaporate in the air ; and the resulting crystals are purified VOL. II. T 252 URANIUM. by solution in hot water and recrystallisation. The mixed mother-liquids, after dilution with water, are treated with hydrosulphuric acid to precipitate arsenic, lead, and copper, and the filtrate is freed from oxide of iron by evaporating to dryness and digesting the residue in water. The solution thus obtained yields a fresh crop of crystals of uranic nitrate. This salt is converted by ignition into uranoso-uranic oxide, U3O4, and from this the protoxide is obtained by ignition with reducing agents (Peligot). Metallic uranium is obtained by decomposing the proto- chloride with potassium or sodium. If the mixture be heated in a platinum crucible over a spirit-lamp, and the soluble alkaline chloride washed out by water, the m'anium is ob- tained in the form of a black powder, or sometimes aggre- gated on the sides of the crucible in small plates, having a silvery lustre and a certain degree of malleability. But, by introducing into a porcelain crucible, first, a layer of sodium, then chloride of potassium, and then a mixture of chloride of potassium and protochloride of uranium (the use of the chloride of potassium being to moderate the action, which is otherwise very violent), placing the porcelain crucible within a closed earthen crucible lined with charcoal, and heating it, first moderately, till the reduction takes place, and then strongly in a blast-furnace for 15 or 20 minutes, the metal is obtained in fused globules (Peligot). Uranium, in its compact state, is somewhat malleable and hard, but is scratched by steel. Its specific gravity is 18*4 ; its colour is like that of nickel or iron. When exposed to the air, it soon tarnishes and assumes a yellowish colour. At a red heat it oxidises with vivid incandescence, and becomes covered with a bulky layer of black oxide, which protects the interior from oxidation. In the pulverulent state, it takes fire at about 402°, burning with great splendour, and forming a dark-green oxide. It is permanent in the air at ordi- nary temperatures, and does not decompose cold water. OXIDES OP URANIUM. 253 It dissolves with evolution of hydrogen in dilute acids, forming green solutions. It combines directly with chlorine, giving out great light and heat, and forming a green vola- tile chloride. It unites directly with sulphur at a slightly elevated temperature (Peligot). Uranium forms four compounds with oxygen, viz., the protoxide, UO ; the sesquioxidej U2O3 ; and two intermediate oxides, U4O5, and, U3O4, which may be regarded as com- pounds of the other two, viz., 2UO.U203and UO.U2O3. Protoxide of uranium ; Uranous oxide, UO, 68, or 850. — This oxide is obtained by exposing uranoso-uranic oxide, mixed with charcoal powder, bullock^s blood, or oil, to the strongest heat of a blast-furnace ; by heating the same oxide to redness in a current of dry hydrogen ; by igniting uranic oxalate out of contact of air, or better, in a current of hydrogen ; or by igniting the chloride of uranyl and potassium (p. 257), either alone or in a current of hydrogen. Protoxide of uranium has sometimes the form of an earthy powder of a grey or brown colour ; sometimes of crystalline scales having the me- tallic lustre. It was for a long time regarded as metallic uranium,* till Peligot f pointed out its true nature, and ob- tained the real metal in the manner above mentioned. Uranous oxide, after ignition, is insoluble in boiling dilute hydrochloric or sulphuric acid, but dissolves in strong sul- phuric acid. The hydrated oxide dissolves readily in acids. Solutions of uranous salts are green, and, when treated with alkalies or alkaline carbonates, or with carbonate of lime, yield a reddish-brown gelatinous hydrate of uranous oxide, which dissolves in alkaline carbonates, especially in carbonate of ammonia, forming a green solution. Alkaline hydrosul- phates yield a black precipitate of uranous sulphide. Uranous salts are converted into uranic salts by exposure to the air, by * See the first edition of this work, page 643. t Ann. Ch. Phys. [3,], v. 5. ; and xii. 258. T 2 254 URANIUM. the action of nitric acid, and by gold and silver salts; the action in the last case being accompanied by precipitation of metallic gold or silver. Protochloride of uranium ; Uranous chloride, UCl, is ob- tained by burning uranium in chlorine gas, or by passing that gas over an intimate mixture of charcoal and either of the oxides of uranium, strongly heated in a tube of very refractory glass. It crystallises in dark-green regular octohe- drons, which have a metallic lustre, and, when heated to red- ness, volatilise in red vapours and form a sublimate. It fumes strongly on exposure to the air, and dissolves very readily in water, forming a green solution. Uranous sulphate, UO.SO3, is found native as uranium,' vitriol, and may be formed artificially by dissolving uranoso- uranic oxide in boiling oil of vitriol; or hydrated uranous oxide in dilute sulphuric acid ; or by decomposing a con- centrated solution of uranous chloride with sulphuric acid. Crystallises with two and with four atoms of water. A bibasic uranous sulphate is obtained by treating the normal salt with a large quantity of water ; by exposing the alcoholic solution of that salt to the sun*s rays ; by careful addition of ammonia to its aqueous solution ; and by boiling that solution with green uranoso-uranic oxide. It forms a light-green powder haviug a silky lustre. Uranoso-uranic oxide, U3O4, or UO.UjOg. — This oxide forms the principal constituent of pitchblende. It is obtained artificially by burning the metal or the protoxide in the air ; by heating the protoxide to redness in an atmosphere of aqueous vapour ; and by gentle ignition of uranic oxide or uranic nitrate. It is a dark-green powder which dissolves in acids, forming green solutions, exhibiting characters inter- mediate between those of uranous and uranic salts, and probably consisting of mere mixtures of the two. Another intermediate oxide, U4O5, or 2UO.U2O3, is said to be formed by strongly igniting the last oxide or the sesqui- URANIC SALTS. 255 oxide. It is black, and dissolves in acids, like the last ; but it is probably a mere mixture of U3O4 with the protoxide. Sesquioxide of uranium ; Uranic oxide^ ^2^3 ^ -^^^ ^^ 1800. — Uranium and its lower oxides dissolve in nitric acid, with evolution of nitric oxide and formation of uranic nitrate. When a solution of this salt in absolute alcohol is evaporated at a gentle heat, till nitrous ether begins to escape, an orange- yellow spongy mass is obtained, consisting of hydrated uranic oxide mixed with undecomposed nitrate : the nitrate may be dissolved out by water, and the hydrated oxide then remains, exhibiting a lemon-yellow or orange-yellow colour. This hydrate is permanent in the air, and does not absorb carbonic acid. At 572°, it yields anhydrous uranic oxide, which is also yellow ; and at a low red heat, it is converted into green uranoso-uranic oxide. The uranic salts are obtained by oxidising uranous or uranoso-uranic salts with nitric acid, or by exposing them to the air. Most of them contain one equivalent of uranic oxide combined with one equivalent of an acid. Now, as this is con- trary to the usual analogy of the normal salts of sesquioxides, most of which contain three equivalents of acid to one equiva- lent of base, e.g., ferric sulphate = Fe203 . 3SO3 j sulphate of alumina= AI2O3 . 3SO3, — Peligot is of opinion that the base of these salts is not really a sesquioxide, but the protoxide of a compound radical uranyl, U2O2, made up of the elements of 2 equivalents of uranous oxide : 1X203= (U2O2) O. To abbre- viate the formulae, we shall denote the compound radical, uranyl, by the symbol U' ; we have then for the formula of uranic sulphate : U2O3 . SO3 = (U2O2) O . SO3 = U'O . SO3. Uranic salts are yellow; they are mostly soluble in water, and, in solution, have a very rough taste, without any metallic after-taste. They are reduced to uranous salts by hydrosuU phuric acid ; also by alcohol or ether , in sunshine. Caustic alkalies added to uranic solutions throw down a yellow preci- pitate, consisting of a uranate of the alkali, which is insoluble T 3 256 URANIUM. in excess of the reagent. Alkaline carbonates produce a yellow precipitate, consisting of a carbonate of nrauic oxide and the alkali, soluble in excess, especially in bicarbonate of potash or sesquicarbonate of ammonia. Potash added to these solutions throws down all the uranic oxide. From the solution in carbonate of ammonia, the uranic oxide is like- wise precipitated by boiling. Carbonate of baryta precipitates uranic oxide completely from its solutions at ordinary tem- peratures. Phosphate of soda, added to uranic salts not containing too much free acid, produces a white precipitate of uranic phosphate, having a sliglit tinge of yellow. Sulphide of ammonium produces a black precipitate of uranic sulphide, which remains for a long time suspended in the liquid. Hy- drosulphuric acid produces no precipitate. Ferrocyanide of potassium produces a dark red-brown precipitate; ferriq/- anide of potassium, none. Metallic zinc does not precipitate uranium in the metallic state from uranic solutions, but, after a long time, produces a yellow precipitate of uranic oxide. Uranic oxide and its salts, fused with phosphorus-salt in the outer blowpipe flame, produce a clear yellow glass which becomes greenish on cooling. In the inner flame, the glass assumes a green colour, becoming still greener when cold. Similar colours with borax. The oxides of uranium are not reduced to the metallic state by fusion with carbonate of soda on charcoal. Uranic oxide is used for imparting a delicate yellow tint to glass ; the glass thus coloured is called canary glass. Chloride of uranyl, U202C1=U'C1. — When dry chlorine gas is passed over uranous oxide at a red heat, the tube be- comes filled with an orange-yellow vapour of this compound, which solidifies in a yellow crystalline mass, easily fusible, but not very volatile. Dissolved in water, it forms hydrated chloride of uranyl, or hydrochlorate of uranic oxide : U2O2CI + HO = U2O3. HCl. URANIC PHOSPHATES. 257 Chloride of uranyt and potassium, KCl . U CI + 2Aq., is formed by evaporating an aqueous mixture of uranic chloride and chloride of potassium. By heating the hydrated crystals to 212°, the anhydrous compound is obtained. Uranic sulphate; sulphate of uranyl, — The monosulphate V'O.SOg + SAq. is obtained by dissolving uranoso-uranic oxide in strong sulphuric acid, diluting the solution with water, and oxidising with nitric acid ; also by decomposing a solution of uranic nitrate with sulphuric acid, expelling the excess of acid by heat, dissolving the residue in water, evapo- rating the solution to a syrup, and leaving it to crystallise. Forms small lemon-yellow prisms. According to Berzelius, a bisulphate and a tersulphate are obtained by dissolving the monosulphate in sulphuric acid; but Peligot denies their existence. A basic sulphate is found native in the form of a yellow powder. The monosulphate forms, with sulphate of potash, a crystalline double salt, whose formula is : KO . SO3 + U2O3 . SO3 + 2H0 = ^, I 2SO4 + 2H0. Uranic nitrate ; nitrate of uranyl ; U203.N05 = U'O.N05, is formed by treating the metal or either of its oxides with nitric acid. It crystallises in lemon-yellow prisms. The solution of this salt possesses the power of lowering the re- frangibility of rays of light which fall upon it, producing the peculiar phenomenon called fluorescence. This property is likewise exhibited by other compounds of uranium, especially by canary-glass. A basic nitrate is formed by gently igniting the normal salt. Uranic phosphates ; phosphates of uranyl. — Three of these salts are known, all containing 3 atoms of base to 1 atom of acid. When uranic oxide is digested in a small quantity of aqueous phosphoric acid, a yellow saline mass is produced, part of which dissolves in boiling water, leaving a light yellow powder, which is the neutral phosphate (2U'0 . HO) . PO5. The aqueous solution concentrated by heat, and then left T 4 258 URANIUM. to evaporate in vacuo over oil of vitriol, deposits a lernon- yellow crystalline salt, consisting of the acid phosphate (U'O . 2H0) . PO5. The basic phosphate has not been ob- tained in the separate state ; but when uranic nitrate is mixed with a moderate excess of basic phosphate of soda (3NaO . PO5), a dark yellow precipitate is formed containing (Na0.2U'0) . PO5 + 3U'0 . PO5 (Wertheim) * When uranic acetate is added to a solution of any soluble phosphate containing an abundance of ammonia and free acetic acid, a yellow precipitate is formed consisting of ammonio-uranic phosphate, 2U'0 . NH4O.PO5, which, when ignited, leaves iiranic pyrophosphate, 2U'0 . PO5. This reaction affords a ready and exact method of estimating phosphoric acid. The insoluble phosphates, even those of alumina and sesquioxide of iron, are also decomposed by boiling with uranic acetate in presence of a large excess of acetate of ammonia and free acetic acid, the bases dissolving, while the phosphoric remains undissolved in the form of the ammonio-uranic phosphate above described. To separate phosphoric acid from iron in this manner requires, however, a very large excess of the uranium-salt (W. Knop).t A neutral and an acid arseniate of uramjlj analogous in composition to the phospliatcs, have also been obtained by similar means. The composition of these phosphates and arseniates affords a strong argument in favour of the uranyl theory. Compounds of uranic oxide with bases, — Uranic oxide combines as an acid with the alkalies, earths, and other me- tallic oxides, forming salts which may be called uranates. The uranates of the alkalies are obtained by precipitating a solution of uranic oxide in an acid with an alkali; the uranates of the earths and heavy metallic oxides, by adding ammonia to a solution of an uranic salt mixed with one of * J. pr. Chem. xliii. 321. f Chem. Gaz. 1856, 467. ESTIMATION OF URANIUM. 259 these bases. The uranates are for the most part yellow, and after ignition orange-yellow. The soda-compound, NaO . 2U2O3 -H 6H0, is used for colouring glass, and is pre- pared on the large scale by roasting pitchblende with lime-< stone in a reverberatory furnace; treating the resulting uranate of lime with dilute sulphuric acid, by which the uranic oxide is almost completely dissolved ; mixing the green solution with crude carbonate of soda, by which the uranium is precipitated together with other metals, but redissolved tolerably free from impurities by excess of the alkali; and treating the liquid with dilute sulphuric acid as long as effervescence is produced. The uranate of soda is then precipitated in a form well adapted for the manufacture of yellow glass. ESTIMATION OF URANIUM, AND METHODS OF SEPARATING IT FROM THE PRECEDING METALS. Uranium is completely precipitated from uranic solutions by ammonia. The precipitate, which consists of hydrated uranic oxide containing ammonia, must be washed with water containing sal-ammoniac, as it runs through the filter when washed with pure water. It is then dried and ignited in an open crucible, whereby it is converted into uranoso-uranic oxide, U3O4 ; but to obtain a perfectly definite result, and prevent further oxidation during cooling, it is necessary to put the cover on the crucible while the substance is still red- hot, and keep it there till the crucible is quite cold. The oxide thus obtained contains 84^*90 per cent, of uranium. An accurate result is likewise obtained by igniting the ses- quioxide in an atmosphere of hydrogen, whereby it is reduced to protoxide containing 88*24 per cent, of the metal. If the uranic solution contains a considerable quantity of an earth or a fixed alkali, the precipitate formed by ammonia carries down with it a certain portion of the earth or alkali ; 260 URANIUM. to free it from which it must, before ignition, be redissolved in hydrochloric acid and reprecipitated by ammonia. From the fixed alkalies, uranium, in the state of sesqui- oxide, is separated by ammonia, attention being paid to the precaution just mentioned. From batata it is separated by sulphuric acid ; from strontia and limej also by sulphuric acid with addition of alcohol. From magnesia, manganese, cobalt, nickel, and zinc, these metals being in the state of protoxide, and the uranium in the state of sesquioxide, it is separated by precipitation with carbonate of baryta. Fi'om iron it is separated by carbonate of ammonia, both metals being in the state of sesquioxide; the uranic oxide then dissolves, while the ferric oxide remains undissolved. Care must, however, be taken that the carbonate of ammonia be really monocarbonate, quite free from excess of carbonic acid, otherwise the iron will also be dissolved. To ensure this condition, the carbonate of ammonia must be previously boiled, and the solution of the oxides, if acid, must be neutralised with ammonia till a slight permanent precipitate begins to form : the solution should then be diluted with water. The uranic oxide is separated from the filtrate either by boiling, or by supersaturation with hydrochloric acid and precipitation by ammonia. From alumina, uranium is also separated by carbonate of ammonia, and with greater facility. From cadmium, copper, lead, tin, arsenic, antimony, and bismuth, uranium is separated by hydrosulphuric acid ; from titanium and chromium in the same manner as iron is sepa- rated from those metals (pp. 152. 171.) ; and from vanadium, tungsten, molybdenum, and tellurium, by sulphide of am- monium, in which the sulphides of the last named metals are soluble. OXIDES OF CERIUM. 261 SECTION IL CERIUM. Eq. 47-26, or 590*87. Ce. This metal, wliich was discovered in 1803, simultaneously by Klaproth, and by Hisinger and Berzelius, exists, together with lanthanum and didymium, in cerite, allanite, orthite, yttro-cerite, and a few other minerals, all of somewhat rare occurrence. The most abundant of them is cerite, which is a compound of silicic acid with the oxides of cerium, lan- thanum, and didymium, together with small quantities of lime and oxide of iron. To extract the oxides of the three metals, the cerite is finely pounded and boiled for some hours with strong hydrochloric acid, or aqua-regia, which dissolves the metallic oxides, leaving nothing but silica. The filtered solution is then treated with a slight excess of ammonia, which precipitates everything but the lime ; the precipitate is redissolved in hydrochloric acid, and the solution treated with excess of oxalic acid. A white or faintly rose-coloured preci- pitate is then obtained, consisting of the oxalates of cerium, lanthanum, and didymium : it is curdy at first, but in a few minutes becomes crystalline, and easily settles down. When dried and ignited, it yields a red-brown powder, containing the three metals in the state of oxide. The finely pounded cerite may also be mixed with strong sulphuric acid to the consistence of a thick paste, the mixture gently heated till it is converted into a dry white powder, and this powder heated somewhat below redness in an earthen crucible. The three metals are thus brought to the state of basic sulphates, which dissolve completely when very gradually added to cold water ; and the solution treated with oxalic acid yields a precipitate of the mixed oxalates, which may be ignited as before. From the red-brown mixture of the oxides of cerium, lan- thanum, and didymium thus obtained, a pure oxide of cerium 262 CERIUM. may be prepared by either of the folloAving processes : — 1 . The mixed oxides are heated with strong hydrochloric acid, which dissolves the whole, with evolution of chlorine ; the solution precipitated with excess of caustic potash ; and chlorine gas passed through the liquid with the precipitate suspended in it. The cerium is thereby brought to the state of sesqui- oxide, which is left undissolved in the form of a bright yellow precipitate, while the lanthanum and didymium re- main in the state of protoxides, and dissolve. To ensure complete separation, the passage of the chlorine must be continued till the liquid is completely saturated with it, and the solution, together >vith the precipitate, left for several hours in a stoppered bottle, and agitated now and then. The liquid is then filtered, the washed precipitate treated with strong boiling hydrochloric acid, which dissolves it with evo- lution of chlorine, and forms a colourless solution of proto- chloride of cerium ; and this, when treated with oxalic acid or oxalate of ammonia, yields a perfectly white precipitate of oxalate of cerium, which may be converted into oxide by ignition (Mosander). 2. The red-brown mixture of the three oxides is treated with very dilute nitric acid (I part of nitric acid of ordinary strength to between 50 and 100 parts of water), which dissolves the greater part of the oxides of lan- thanum and didymium, and leaves the oxide of t erium ; and by treating the residue with very strong nitric acid, the last traces of lanthanum and didymium may be extracted (Mo- sander, Marignac). 3. The red-brown mixture of the three oxides is boiled for several hours in a strong solution of chloride of ammonium. The oxides of lanthanum and didy- mium then dissolve, with evolution of ammonia, and eerie or ceroso-ceric oxide is left in a state of purity. It must be collected on a filter and washed with a solution of sal-am- moniac, because, when washed with pure water, it first runs through the filter, and then stops it up (Watts).* » Cbem. Soc. Qu. J. ii. 147. CEROUS OXIDE. 263 Metallic cerium is obtained by heating the pure anhydrous protochloride with potassium or sodium. It is a grey powder which acquires the metallic lustre by pressure. It oxidises readily, decomposes water slowly at ordinary temperatures, quickly at the boiling heat, and dissolves rapidly in dilute acids, with evolution of hydrogen, forming a solution of a cerous salt. Protoxide of cerium ; Cerous oxide, CeO ; 55*26 or 690*8. — • This oxide is scarcely known in the anhydrous state. The sesquioxide, exposed to the strongest heat of a wind-furnace, in a crucible lined with charcoal, yields a residue chiefly con- sisting of protoxide, but the reduction is never complete. The hydrated protoxide is easily obtained by precipitating the chloride with a caustic alkali. It dissolves readily in acids, forming the protosalts of cerium or cerous salts, the solutions of which are distinguished by the following cha- racters : Caustic potash or soda produces a white precipitate of the hydrated protoxide, which is insoluble in excess, and is converted into the yellow sesquioxide by the action of chlorine or hypochlorous acid. Ammonia precipitates a basic salt. Alkaline carbonates form a white precipitate of cerous carbonate insoluble in excess. Oxalic acid or oxalate of ammonia produces a white precipitate of cerous oxalate, gelatinous at first, but quickly assuming the crystal- line character, and converted by ignition in an open vessel into a salmon-coloured powder, consisting of sesquioxide of cerium mixed with protoxide. Hydrosulphuric acid produces no precipitate. Sulphide of ammonium throws down the hydrated protoxide. Ferrocyanide of potassium produces a white pulverulent precipitate ; ferricyanide of potassium, none. Sulphate of potash produces a white crystalline precipitate of potassio-cerous sulphate, nearly insoluble in pure water, and quite insoluble in excess of sulphate of potash. With dilute solutions the precipitate takes some time to form. This cha- racter, together with the beha\4our of the oxalate, and the 2G4 CERIUM. yellow coloration of the hydrated protoxide by cblonne, serves to distinguish cerium from all other metals. Cerous salts in solution have a sweet astringent taste, and redden litmus, even when tlie acid is perfectly saturated. All compounds of cerium, ignited with borax or phosphorus -salt in the outer blowpipe-flame, yield a glass which is deep red while hot, but becomes colourless on cooling. In the inner flame a colour- less bead is formed, but when ignited with excess of oxide of cerium, it forms a yellow enamel. Sesquioxide of cerium; Ceric oxide, Ce203. — It is doubtful whether this oxide has been obtained in the separate state. The hydrated protoxide, the nitrate, and the oxalate, yield, when ignited in the acid, a salmon-coloured powder, which is generally regarded as ceric oxide ; but, according to Marignac, it is a mixture or compound of the sesquioxide and protoxide of cerium, not quite constant in composition, but containing on the average 82* 15 percent of metal, and there- fore nearly agreeing with the formula CCyOg or 3Ce0.2Ce203. When mixed with oxide of didymium, its colour is red- brown. This oxide is nearly insoluble in strong nitric and hydrochloric acids, even at the boiling heat, but strong boiling sulphuric acid dissolves it. Hydrochloric acid, with the aid of reducing agents, such as alcohol, dissolves it slowly at the boiling heat, forming a solution of cerous chloride. If mixed with the oxide of lanthanum or didymium, it dissolves readily in strong boiling hydrochloric acid, with evolution of chlorine. The solution of this oxide in strong sulphuric acid has a bright yellow colour, and deposits yellow prismatic crys- tals, which, according to Marignac, consist of a ceroso-ceric- sulphate, containing Ce^Og. 4S03-f 7H0. Potash, added to the solution of this salt, throws down a yellow hydrate, which dissolves readily in acids. The solutions are yellow, and, when boiled with hydrochloric acid, are converted into cerous salts. Protosulphide of cerium, CeS, is obtained by igniting the SALTS OF CERIUM. 265 carbonate in vapour of bisulphide of carbon, or by heating an oxide of cerium with sulphide of potassium. The first process yields a light powder of the colour of red lead ; the second, a product resembling mosaic gold. The sesquisulphide of cerium is not known in the free state, but exists in certain sulphur-salts. Protochloride of ceriunij CeCl. — Cerium burns vividly when heated in chlorine gas, and forms this compound. The anhydrous chloride may be prepared by igniting the sulphide, or the residue obtained by evaporating to dryness a solution of the chloride mixed with sal-ammoniac, in a current of chlorine gas. If the air is not completely excluded, an oxychloride is also produced. The anhydrous chloride is a white porous mass, fusible at a red heat, and perfectly soluble in water. A hydrated chloride is obtained in colourless four- sided prisms, by dissolving the hydrated oxide or the car- bonate in hydrochloric acid, and evaporating to a syrup. The solution, when exposed to the air, turns yellow, from formation of a eerie salt. Sesquichloride of cerium. — The hydrated sesquioxide dis- solves in cold hydrochloric acid, forming a red solution, which, however, soon gives off chlorine, and is reduced, more or less completely, to protochloride. Protofluoride of cerium is formed by precipitating the pro- tochloride with an alkaline fluoride. The sesquifluoride occurs native in six-sided prisms, mixed with half its weight of protofluoride ; also with the fluorides of yttrium and calcium, in yttrocerite. An oxyfluoride of cerium, Ce4F303-|-3HO, is also found native. Cerous carbonate, CeO . COg + SHO, is formed by exposing the hydrated protoxide to the air, or by precipitation. Cerous oxalate, 0400203, is precipitated from cerous salts by oxalic acid or oxalate of ammonia added in excess, even when the solution contains a considerable quantity of free nitric or hydrochloric acid. It is at first curdy, but soon becomes 266 CERIUM. very dense and crystalline. When ignited with free access of air, it yields ceroso-ccric oxide. Cerous sulphate^ CeO . SO3. — The anhydrous salt is a white powder, which, when sprinkled with a small quantity of water, becomes very hot, and condenses into a solid mass, veiy diffi- cult to dissolve. It forms two crystallme hydrates, viz., 2 (CeO . SO3) + 3H0 and (CeO . SO3) + 3H0. The anliydrous salt, heated in a close vessel, leaves a basic cerous sulphate ; but, with free contact of air, it leaves a basic eerie or ceroso- ceric sulphate. Cerous sulphate forms with sulphate of potash a crystalline double salt, containing CcO . SO3 + KO . SO3, which is nearly insoluble in water. Cerous phosphate. — Obtained by precipitating a cerous salt with phosphate of soda. It also occurs native (associated with the phosphates of lanthanum and didymiura), in several forms. In Monazite and Edwardsite, it occurs in oblique rhombic prisms ; in the former it is associated with thorina, and smaU quantities of lime, manganese, and tin; in the latter, with alumina, zirconia, and silica. Cryptolite is a tribasic phosphate of cerium, occurring in the rose-coloured apatite of Arendal in Norway, and is separated by dissolv- ing the apatite in nitric acid. It then remains in the form of a crystalline powder, appearing under the micro- scope to consist of hexagonal prisms. Sp. gr. 4*6 (Wohler).* Phosphocerite is a mineral similar in composition to cryp- tolite. It was discovered by Mr. O. Sims in the cobalt-ore of Johannisberg in Sweden, of which it forms about one- thousandth part. It remains as a residual product when the ore after calcination is treated with hydrochloric acid for the purpose of extracting the cobalt. It is a greyish yellow crystalline powder, mixed with a small quantity of minute dark purple crystals, which are strongly attracted by the magnet, and consist chiefly of magnetic oxide of iron. The crystals of phosphocerite, when examined by the microscope, » Ann. Ch. Pharm. Ivii. 268. ESTIMATION OF CERIUM. 267 exhibit two forms, one an octohedron, the other, a four-sided prism with quadrilateral summits, both forms apparently- belonging to the right prismatic system. Sp. gr. 4-78. The mineral contains 64*68 per cent, protoxide of cerium, &c., 38-46 phosphoric acid, 2*83 oxide of iron, and 3*41 oxide of cobalt, silica, &c. It is very rich in didymium. Strong sulphuric acid, aided by gentle heat, decomposes it, forming a pasty mass, which dissolves in cold water with the exception of a small quantity of silica (Watts).* ESTIMATION OF CERIUM, AND METHODS OP SEPARATING IT FROM THE PRECEDING METALS. Cerium is precipitated from neutral solutions of cerous salts by potash, as cerous hydrate; or by oxalate of am- monia, as cerous oxalate; and either of these compounds is converted by ignition in an open vessel into ceroso-ceric oxide. This oxide, as already observed, is not perfectly de- finite in constitution; it may be stated approximately to contain 96'5 per cent, of cerous oxide, or 82"5 per cent, of the metal, and this estimate may be adopted where great accuracy is not required. A more exact method, however, is to dissolve the hydrate precipitated by potash in dilute sul- phuric acid, then evaporate, and heat the residue to com- mencing redness, whereby it is converted into the anhydrous sulphate CeO . SO3, containing 57*6 per cent, of the protoxide of cerium, or 49' 6 per cent, of the metal. Hydrosulphuric acid serves to separate cerium from all metals which are precipitated by that reagent from their acid solutions. From manganese^ iron, cobalt, nickel, zinc, titanium, chromium, vanadium, and tungsten, cerium may be separated by means of a saturated solution of sulphate of potash. • Chem. Soc. Qu. J., ii. 131. VOL. TI. U 268 LANTHANUM. From alumina it may be separated by carbonate of baiyta, which precipitates alumina and not cerous oxide ; from ylucina by sulphate of potash. From yttria, with which it is often associated in minerals, it is separated by a saturated solution of sulphate of potash added in excess, the sulphate of yttria and potash being soluble in excess of sulphate of potash, while the cerous double salt remains undissolved. From zirconia, cerium is separated by treating the boihng acid solution with sulphate of potash, whereby the greater part of the zirconia is precipitated as basic sulphate, while the cerium remains dissolved ; to complete the precipitation, a small quantity of ammonia must be added, but not sufficient to saturate the acid (H. Rose). From magnesia also cerium may be separated by sulphate of potash; from baryta, strontia, and lime, it is separated by ammonia added in slight excess ; or from baryta by sulphuric acid, and from strontia and lime by sulphuric acid and alcohol ; and from the fixed alkalies by precipitation with oxalate of ammonia. SECTION VI. LANTHANUM. -Ey. 47, or 588; La. The red-brown oxide obtained from cerite by the methods already described (p. 2G1), and originally regarded as the oxide of a single metal, cerium, was shown by Mosander *, in 1839, to contain the oxide of another metal, to which he gave the name lanthanum. Subsequently, in 1841 f, Mosan- der discovered that even this supposed simple oxide contained two distinct metals, for one of which the name of lantbanmn « Pogg. Ann. xlvi. G48 j xlrii. 207. f Ibid. Ivi. 504. LANTHANUM. 269 was retained^ while the other was called didymium. These two metals appear to be constantly associated with cerium, though not always in the same proportion. The separation of lanthanum and didymium from cerium may be effected by either of the methods already described (p. 262) j the second and third are easier and more expe- ditious than the first. If the solution obtained by treating the crude red-brown oxide with dilute nitric acid be evapo- rated to dryness, and the residue treated with nitric acid diluted with at least 200 parts of water, a solution will be obtained quite free from cerium (Marignac). Boiling the red-brown oxide with chloride of ammonium also yields a solu- tion of lanthanum and didymium free from cerium. In both cases, however, it is best to test a portion of the solution for cerium by precipitating with excess of caustic potash, and passing chlorine through the solution. The presence of cerium, even in very small quantity, will be indicated by the formation of a yellow precipitate, after the liquid, supersatu- rated with chlorine, has been left in a close vessel for several hours. A solution free from cerium having been obtained, the separation of the lanthanum and didymium is effected by the different solubilities of their sulphates. To convert them into sulphates, the solution is treated with excess of a caustic alkali, and the washed precipitate dissolved in dilute sulphuric acid. The mode of proceeding varies according as the lanthanum or the didymium is in excess. 1. When the lanthanum is in excess, in which case the solution has but a faint amethyst tinge, the liquid is evapo- rated to dryness, and the residue heated in a platinum- dish to a temperature just below redness, to drive off the excess of acid, and render the sulphates perfectly anhydrous. The residue is then dissolved in rather less than six times its weight of water, at about 36° Fah. (2° or 3° C), the salt being reduced to powder and added in successive small portions, r 2 270 LANTHANUM. and the vessel containing the liquid being immersed in ice-cold water. Without these precautions, the temperature of the liquid may be raised several degrees, in consequence of the heat evolved by the combination of the anhydrous sulphates with water; and, in that case, crj'stallisation will commence, and rapidly extend through the whole mass of liquid, as these sulphates are much less soluble in warm than in cold water ; but if the liquid be properly cooled, the whole dissolves com- pletely. The solution is next to be heated in the water-bath to about 104° F. (40° C.) ; the sulphate of lanthanum theu crystallises out, accompanied by only a small quantity of sulphate of didymium. To purify it completely, it is again rendered anhydrous, redissolved in ice-cold water, &c., and the entire process repeated ton or twelve times. The test of purity is perfect whiteness, the smallest quantity of didymium imparting an amethyst tinge (Mosander). 2. When the didymium-salt is in excess, in which case the liquid has a decided rose-colour, separation may be effected by leaving the solution containing excess of acid, in a warm place for a day or two. The sulphate of didymium then sepa- rates in large rhombohedral crj^stals modified with numerous secondary faces; and, at the same time, slender, needle- shaped, violet-coloured crystals are formed, containing the two sulphates mixed. The rhomboliedral crystals, which are nearly free from lanthanum, are removed, and the needles, together with the mother-liquid, treated as in the first method, to obtain sulphate of lanthanum (Mosander). In both cases, the separation may be greatly facilitated by first dissolving the mixed oxides of the two metals in a large excess of nitric acid, and precipitating in successive portions by oxalic acid : the first precipitates thus formed have a much deeper rose-colour, and are much richer in didymium than the latter. The separation thus effected is very imperfect in itself, but it greatly facilitates the subsequent separation of the sulphates, which is much more rapid, when one of the LANTHANUM. ^71; sulphates is in great excess with regard to the other (Ma- rignac) . Metallic lanthanum is obtained by decomposing the anhy- drous chloride with sodium, and dissolving out the chloride of sodium with alcohol of sp. gr. 0-833. It is a dark, lead- grey powder, soft to the touch, and adhering when pressed. Protoxide of lanthanum, LaO, 55 or 688, is obtained in the anhydrous state by igniting the precipitated hydrate or carbonate in a covered crucible. It is a white powder, which turns brown when heated in the air, probably from partial conversion into a higher oxide. The hydrated oxide is formed when the metal or the anhydrous oxide is immersed in warm water, or when a salt of lanthanum is precipitated by caustic potash. It is a white substance, viscid while moist, and slightly alkaline to test-paper. It absorbs carbonic acid from the air with great rapidity. Oxide of lanthanum, even after strong ignition, dissolves very easily in acids. When boiled with a solution of chloride of ammonium, it dissolves and expels the ammonia. The salts of lanthanum are perfectly colourless when free from didymium. The soluble salts have an astringent taste. Potash and soda, added to the solutions, throw down the hydrated oxide, which dissolves completely in chlorine-water, Avithout forming any yellow deposit. Ammonia throws down a basic salt. Oxalic acid or oxalate of ammonia, throws down a white flocculent precipitate, which does not become crystalline. In other respects, the solutions resemble those of cerous salts. Compounds of lanthanum do not impart any colour to borax or phosphorus-salt. Chloride of lanthanum is obtained in the anhydrous state by igniting the oxide in a current of hydrochloric acid gas, and as a hydrate by evaporating a solution of the oxide in hydrochloric acid. It dissolves very readily in water. Carbonate of lanthanum is found native in small crystalline scales, containing traces of protoxide of cerium. When ob- u 3 272 ESTIMATION OF LANTHANUM. tained by precipitation, it forms a gelatinous mass, which gradually changes into shining crystalline scales (Mosander). Sulphate of lanthanum, LaO . SO3, is obtained by spon- taneous evaporation in small prismatic crystals, containing 3 eq. of water of crystallisatipn. It parts with its water at a low red heat, and with half its acid at a strong red heat. It is much less soluble in hot than in cold water (p. 272). It forms with sidphate of potash a very sparingly soluble double salt, similar to the sulphate of cerium and potassium. Nitrate of lanthanum crystallises in deliquescent colourless prisms, very easily soluble in water and in alcohol. When carefully heated, so as not to expel any of the acid, it fuses, and solidifies into a colourless glass on cooling. If the heat is raised, so as to drive off a portion of the acid, a fused mass remains which, on cooling, forms a kind of enamel, but almost immediately afterwards crumbles to a bulky white powder, and with such force that the particles are scattered about to a considerable distance (Mosander). ESTIMATION OF LANTHANUM. Lanthanum is precipitated from its solutions by potash, or by oxalate of ammonia, and the precipitate converted by ignition in a covered platinum crucible into the anhydroils oxide, containing 85*7 per cent, of the metal. The methods of separating lanthanum from other metals are the same as those adopted for cerium. The separation of lanthanum from cerium itself may be effected by boiling the mixed oxides in a solution of chloride of ammonium (p. 262) . DIDYMIUM. 273 SECTION VII. DIDYMIUM. Eq. 48 or 600; Di. Didymium was discovered by Mosander in 1841*; and its compounds liave since been more minutely examined by Marignac.f A pure salt of didymium is obtained by recrystallising the rose-coloured rbombobedrons wbich separate from an acid solution of the mixed sulphates of lanthanum and didymium by spontaneous evaporation ; and from the pure sulphate thus prepared, the other compounds of the metal may be formed. Metallic didymium is obtained by heating potassium with an excess of chloride of didymium, and washing out the soluble chlorides with cold water. It is thus obtained, for the most part, as a grey metallic powder ; but partly, also, in fused globules. The powder, thrown into the flame of a spirit-lamp, burns with bright sparks like iron-filings. The powder decomposes water at ordinary temperatures ; the fused granules do not : in either form, however, the metal dissolves rapidly in dilute acids, with evolution of hydrogen. Protoxide of didymium, DiO, 56 or 700. — Obtained in the anhydrous state by strongly igniting the nitrate, oxalate, or the precipitated hydrate in a covered crucible. It is per- fectly white ; is slowly converted into a hydrate by immersion in warm water ; dissolves readily in the weakest acids ; and expels ammonia from ammoniacal salts when boiled with them. The hydrate, DiO. HO, is a gelatinous mass resembling alumina, but having a very pale rose-colour. It contracts much by desiccation. * Pogg. Ann. Ivi. 504. t Ann. Ch. Phjs. [3], xxxviii. 148 j Chem. Soc. Qu, J., vi. 260. U 4 274 DIDYMIUM. The salts of didymium have either a pure rose-colour, like the sulphate, or slightly inclining to violet, like the nitrate in the state of strong solution. Potash, soda, and ammonia precipitate the hydrate ; so does sulphide of ammonium. Carbonate of baryta also throws down the hydrated oxide slowly, but completely. Oxalate of ammonia precipitates didymium completely from neutral solutions; and oxalic acid almost completely, unless the solution contains a large excess of acid. The sulphates of potash, soda, and ammonia form, immediately in strong, and gradually in weak solutions, rose- white precipitates of double sulphates, shghtly soluble in water, less soluble in excess of the reagent ; the soda-salt is the least soluble of the three. Phosphoric and arsenic acids, at a boiling heat, form precipitates sparingly soluble in acids. All compounds of didymium impart to borax and phosphorus- salt a very pale rose-colour. They do not colour carbonate of soda before the blowpipe. Peroxide of didymium. — When the oxalate, nitrate, car- bonate, or hydrate of didymium is ignited in contact with the air, and not very strongly, a dark brown oxide is obtained, containing from 0-32 to 0*88 per cent, of oxygen more than the protoxide. 'V\Tien treated with acids it dissolves readily, giving off the excess of oxygen, and forming a solution containing the protoxide. It is probably a mixture of the protoxide with a small quantity of a higher oxide of definite composition. By strong ignition in a close vessel, it is con- verted into the white protoxide. Sulphide of didymium, DiS, is obtained by igniting the oxide in the vapour of bisulphide of carbon. It is a light, brownish g^-een powder, which dissolves in acids, with evo- lution of hydrosulphuric acid. A greyish-white oxysulphide, 2DiO.DlS, is obtained by igniting the oxide with carbonate of soda and excess of sulphur, and digesting the fused mass in water (Marignac). Chloride of didymium is obtained as a hydrate in rose- DIDYMIUM. 275 coloured crystals of considerable size, by evaporating a solution of the oxide in hydrochloric acid. The crystals, which are very soluble in water and alcohol, contain DiC1.4H0. The solution, when evaporated, gives off hydrochloric acid, and leaves an oxychloride, not however of constant composition (Marignac). Carbonate of didymium, DiO . COg. — Precipitated as a white, bulky hydrate, tinged with rose-colour, on adding an alkaline carbonate or bicarbonate to a salt of didymium. The precipitate formed in the cold with nitrate of didymium and bicarbonate of ammonia, contains, after drying in vacuo j DiO.Cl2 + 2HO. At 212°, it gives off l^- eq. water and a small quantity of carbonic acid (Marignac). Oxalate of didymium,, C4Di208, is precipitated from neutral solutions as a rose-white powder, which dissolves in warm nitric or hydrochloric acid, and separates, on cooling, in the form of a granular crystalline powder, sometimes even in small rose-coloured prismatic crystals. After drying in the air, it contains 8 eq. water, 6 eq. of which go off at 212° (Ma- rignac) . Sulphate of didymium, DiO.S03. — Formed by dissolving the oxide or carbonate in dilute sulphuric acid. The solution is rose-coloured, and deposits, by spontaneous evaporation, dark rose-coloured, shining crystals, having the form of an oblique rhomboidal prism (Mosander), and cleaving readily and distinctly in a direction parallel to the base. They con- tain 3(DiO.S03) + 8 Aq., and give off the whole of their water at 392° F. (200° C), leaving an anhydrous powder, which may be heated to redness without further alteration. A solution of the sulphate, when heated, especially to the boiling point, deposits a crystalline precipitate containing DiO.SOg + 2H0. The following table exhibits the solu- bility of the anhydrous salt, and of the two crystalline hydrates in water at different temperatures : — 276 DIDYMIUM. perature. Anhydrous Sulphate. \ Sulphate with 2 eq. water. Sulphate crystallised iu the cold. 12° C 431 — — 14 39-3 — — 18 25-8 16-4 — 19 — — 11-7 25 20-6 — — 38 130 — 4D — — 8-8 50 110 — 6-5 00 — — 1-7 The anhydrous sulphate, exposed to the heat of an intense charcoal fire, gives off two-thirds of its sulphuric acid, and leaves a tribasic sulphatCy 3DiO.S03 (Mariguac). Sulphate of didymium, mixed in solution with sulphate of potash, forms a crystalline double salt, which appears to con- tain KO.SO3 + 3(DiO.S03) + 2H0; it dissolves in sixty- three times its weight of cold water. With sulphate of soda it forms the anhydrous double salt, NaO.SOg + 3(DiO.S03), which requires two hundred times its weight of water to dis- solve it, and is still less soluble in a solution of sulphate of soda. With sulphate of ammonia, it forms the salt NH^O.SOg -I- 3(DiO.S03) + 8H0, soluble in eighteen times its weight of water (Marignac). Sulphite of didymium, DiO.SOs + 2H0. — Oxide of didy- mium suspended in water, is readily dissolved by a stream of sulphurous acid gas, forming a rose-coloured solution which becomes tui'bid when heated, forming a light bulky precipitate, which redissolves as the liquid cools, unless the temperature has been raised to the boiling point, in which case it remains undissolved (Marignac) . Nitrate of didymium, DiO.NOg. — This salt is very soluble in water and in alcohol of the strength of 96 per cent. The aqueous solution has a pure rose colour when dilute, but appears violet by reflected light when strong. A syrupy solu- TANTALUM. 27 f tion solidifies on cooling into a deliquescent crystalline mass, which, when carefully heated to 300° C, melts, becomes per- fectly anhydrous, and exhibits the composition of the neutral nitrate. At a higher temperature, it is decomposed, giving off nitrous fumes, and leaving a residue from which water extracts a portion of neutral nitrate, and leaves a basic salt containing 4DiO.N05 + 5 HO. (Marignac) . Phosphate of didymium, SDiO.POg + 2H0. — Precipi- tated, after a few hours, as a white powder, on adding a strong solution of phosphoric acid to a strong solution of nitrate of didymium. It is insoluble in water, very sparingly soluble in dilute acids ; but dissolves readily in the stronger acids when coDcentrated; gives off its water when ignited (Marignac). Arse7iiate of didymium, 5Di0.2As05 + 2H0. — Obtained as a pulverulent precipitate by the action of arsenic acid on solutions of didymium at the boiling heat, or as a gelatinous precipitate by the action of neutral arseniate of potash at ordinary temperatures. It is but slightly soluble in dilute acids (Marignac). The quantitative estimation of didymium is effected in the same manner as that of lanthanum. The anhydrous prot- oxide contains 85*7 per cent, of the metal. The methods of separating didymium from the preceding metals are also the same as for lanthanum. For separating it from lanthanum itself, no method has yet been devised sufficiently exact for quantitative analysis. SECTION VIII. TANTALUM. Eq. 68-82 or 860'3 ; Ta. This metal was discovered by Ekeberg in 1802. It is a rare metal, occurring only in a few minerals, the principal of which are Swedish tantalite and yttro-tantalite. 278 TANTALUM. Tantalum is obtained, in the metallic state, by heating the fluoride of tantalum and potassium, or fluoride of tantalum and sodium, with sodium, in a well covered iron crucible, and afterwards washing out the soluble salts by water. The re- duced metal thus obtained is not quite piu'e, being more or less contaminated with acid tantalate of soda, the quantity of which may, however, be diminished by covering the mixture in the crucible witli chloride of potassium. Tantalum is a black powder, which, according to II. Rose, is a good conductor of electricity. When heated in the air, it bums with a bright light, and is converted, tliough with difficulty, into tantalic acid. It is not attacked by sulphuric, liydi'ochloric, or nitric acid, or even by aqua regia. It dis- solves slowly in warm aqueous hydrofluoric acid, with evolu- tion of hydrogen, and very rapidly in a mixture of hydrofluoric and nitric acids. Tantalum forms two compounds with oxygen, viz., tantalous acid, probably TaO, and tantalic acid, TaOj. Tantalous acid is ol)tained by placing tantalic acid in a small cavity in a crucible filled with charcoal, and exposing it to the strongest heat of a blast-furnace ; a thin film on the outside is at the same time reduced to the state of metal. It is a dark grey mass which scratches glass, and acquires metallic lustre by bm'nishing. Tantalic acid, TslO^; 84-82 or 1060-3.* — This compound is formed when tartalum bums in the air; also by the action of water on chloride of tantalum; and, in the form of a potash-salt, by fusing metallic tantalum or tantalous acid * The composition of tantalic acid is usually represented by the formula TaOg, which, according to the original analysis of that compound by Ber- relius (88'5 per cent, tantalum + 11-5 per cent, oxygen), gives for tantalum the equivalent number 185. But according to the recent experiments of H. Rose (Berl. Akad. Ber. 1856, 385), the tantalum-compounds appear to con- tain 2 eq. of the chlorous element, viz., the chloride, TaCla, tantalic acid, TaOo, &c. ; he also finds the cliloride to contain 49-25 per cent, of tantalum, making the equivalent of tantalum 6882. TANTALIC ACID. 279 -with hydrate, carbonate, or bisulphate of potash. It exists, in combination with various bases, in the minerals above mentioned, and is usually extracted from tantalite, which con- tains the oxides of iron and manganese, together with small quantities of stannic and tungstic acids, by one of the follow- ing processes: — 1. The mineral, after being pulverised and levigated, is fused with twice its weight of hydrate of potash ; the fused mass digested in hot water; and the filtered solution supersaturated with hydrochloric or nitric acid : hydrated tantalic acid is then precipitated in white flakes, which may be purified by washing with water (Berzelius). 2. A better method, however, is to fuse the levigated tantalite in a platinum crucible with six or eight times its weight of bisulphate of potash ; pulverise the mass when cold ; and boil it repeatedly with fresh quantities of water till no more sul- phate of potash, iron, or manganese is dissolved out of it. The residue, which consists of hydrated tantalic acid mixed with ferric oxide, stannic acid, and tungstic acid, is then digested in sulphide of ammonium containing excess of sulphur, which removes the stannic and tungstic acids, and converts the iron into sulphide ; the liquid is filtered, and the tantalic acid washed with water containing sulphide of am- monia, then boiled with strong hydrochloric acid to remove the iron, and finally washed with boiling water. The hydrated tantalic acid thus prepared is converted into the anhydrous acid by ignition. It may still, however, contain silica, to re- move which, it is dissolved in aqueous hydrofluoric acid, the filtered solution mixed with sulphuric acid and evaporated to dryness, and the residue ignited as long as its weight con- tinues to diminish : the silica is then expelled as gaseous fluoride of silicon (Berzelius) . Anhydrous tantalic acid is a white powder, which remains white when heated, or acquires but a very faint tinge of yellow. Its specific gravity varies from 7'022 to 8-264, in- creasing with the temperature to which the acid has been 280 TANTALUM. exposed (H. Rose). It neither melts nor volatilises wlien heated, and is destitute of taste and smell. It is reduced to the metallic state in the circuit of a very powerful voltaic battery ; partially also by very strong ignition in contact with charcoal. When ignited in the vapour of bisulphide of carbon, it yields sulphide of tantalum : 2Ta02 + 4CS2 = Ta2S3 + 4C0 + 58. It is insoluble in all acids, and can only be rendered soluble by fusion with hydrate or carbonate of potash. Hydrated tantalic acid, obtained by precipitating an aqueous solution of tantalate of potash with hydrochloric acid, or by decomposing chloride of tantalum with water containing a small quantity of ammonia, is a snow-white bulky powder, which reddens litmus-paper while moist, and dissolves in hydrochloric and hydrofluoric acids. AVhen strongly heated it gives off its water and becomes incandescent. The hydrate, obtained by fusing tantalite with bisulphate of potash in the manner above described, is of a denser and more ciystalline character, is insoluble in all acids excepting strong sulphuric acid, and is precipitated from the solution by water. When heated, it becomes anhydrous, but does not emit light. Tantalic acid combines with banes much more readily than with acids. When fused with hydrate of potash in a silver ciiicible, it forms a transparent mass of tantalate of potash, which, after cooling, dissolves completely in water. With hydi^ate of soda it fuses into an opaque turl)id mass, and ultimately deposits a sediment, which is not taken up by fusion with any excess of the alkali. Water poured upon the fused mass when cokl dissolves out the excess of soda, but not a trace of tantalic acid ; and the residue, when treated with fresh water, dissolves and forms an opalescent solution of acid tantalate of soda, which salt is completely insoluble in a strong solution of caustic soda, and is therefore precipitated on mixing the liquid with the solution of soda previously TANTALIC ACID. 281 obtained by treating the fused mass with water. When tan- talic acid is fused with carbonate of potash or soda^ the fused mass is not completely soluble in water. Hydrochloric acid, added in excess to the solution of an alkaline tantalate, first precipitates the tantalic acid, and then redissolves it, forming a slightly opalescent liquid, Sulphuric acid also precipitates the tantalic acid, but does not redissolve it when added in excess. Carbonic acid gas, passed through the solution of an alkaline tantalate, precipitates the whole of the tantalic acid in the form of an acid salt. Chloride or sulphate of ammonium also pre- cipitates the tantalic acid from these solutions in the form of hydrate, mixed with small quantities of ammonia and the fixed alkali. The presence of carbonate of potash or soda prevents the formation of this precipitate at ordinary tem- peratures ; but it then appears after boiling for some time. Sulphide of ammonium produces no precipitate. Chloride of barium or calcium forms a precipitate of tantalate of baryta or lime, insoluble in water and in ammoniacal salts. Nitrate of silver forms, in the solution of a neutral alkaline tantalate, a white precipitate, which is turned brown by a small quantity of ammonia, and dissolves in a larger quantity. A solution of basic mercurous nitrate forms a yellowish white precipitate, which turns black when heated. Ferrocyanide of potassium, added to a very slightly acidulated solution of an alkaline tantalate, forms a yellow precipitate ; ferricyanide of potassium a white precipitate. Infusion of galls, added to a solution of an alkaline tantalate acidulated with sulphuric or hydrochloric acid, forms a light yellow precipitate soluble in alkalies. Zinc, immersed in the solution of an alkaline tantalate acidu- lated with hydrochloric acid, does not produce any blue colour ; neither is that colour produced, or but very faintly, on addition of sulphuric acid. But if chloride of tantalum be dissolved in strong sulphm-ic acid, and then water and metallic zinc added, a fine blue colour is produced, which does 282 TANTALUM. not change to brown, but soon disappears. The blue eolour is also produced on placing zinc in a solution of chloride of tantalum in hydrochloric acid, to which a small quantity of water has been added ; too much water, however, prevents its formation. Before the blowpipe, tantalic acid dissolves abundantly in phosphorus-salt, forming a clear, colourless glass, which un- dergoes no alteration when heated in the inner flame, and does not turn red on addition of protosulphate of iron. AVith borax also it forms a transparent glass, which, however, if the quantity of tantalic acid is somewhat large, may be rendered opaque by interrupted blowing, or flaming, as it is technically called, but recovers its transparency by long exposure to a continued blast. A very large quantity of tantalic acid ren- ders the glass opaque. No alteration takes place in the inner flame. With carbonate of soda on charcoal, tantalic acid produces efibrvescence, but does not fuse into a bead or undergo reduction. The above-described characters are sufficient to distinguish tantalic acid from all the substances previously described. From titanic acid, which it most resembles, it is distinguished, first, by its behaviour before the blowpipe ; secondly, l)y its per- fect insolubility in strong suli)huric acid after ignition, ignited titanic acid, when finely pulverised, being soluble in that acid ; and, thirdly, by the fact that, when it is fused with bi- sulphate of potash, and the fused mass treated with cold water, the tantalic acid remains undissolved in combination with sulphuric acid; whereas titanic acid, similarly treated, yields a fused mass, which dissolves completely in a con- siderable quantity of cold water, provided the fusion has been continued long enough. From silica, tantalic acid is distin- guished by its behaviour before the blowpipe, silica being in- soluble in phosphorus-salt, and fusing to a transparent bead when heated on charcoal with a small quantity of carbonate of soda. The behaviour of tantalic acid with zinc, with tine- CHLORIDE OF TANTALUM. 28S ture of galls^ and with hydrofluoric acid, also distinguishes it from silica. Sulphide of tantalum, TagSg. — Obtained by igniting tan- talic acid in the vapour of bisulphide of carbon, or by ex- posing chloride of tantalum to the action of hydrosulphuria acid gas. The product is not perfectly definite in either case. The second process yields a sulphide containing 24*08 per cent, sulphur, whereas the formula Ta2S3 requires 25 -86 per cent. The former process gives a product containing 28*5 per cent, sulphur. Sulphide of tantalum is a black substance, which acquires a brass-yellow colour by trituration in an agate mortar. Heated in an atmosphere of chlorine gas, it is converted into chloride of tantalum and chloride of sulphur (H. Rose). Chloride of tantalum, TaClg. — Prepared by passing chlorine gas over a heated mixture of tantalic acid and charcoal. Tantalic acid is mixed with starch or sugar, and the mixture completely charred by ignition in a covered crucible. It is then introduced in small pieces into a glass tube which is strongly heated by a charcoal fire, while a stream of dry carbonic acid is passed through it. As soon as all the moisture is expelled, the tube is left to cool, the flow of car- bonic acid being still kept up ; the carbonic acid apparatus is then replaced by a chlorine apparatus, and the tube again heated after the carbonic acid and atmospheric air have been completely expelled by the chlorine. Chloride of tantalum is then obtained in the form of a sublimate of a pure yellow colour. If, however, the tantalic acid contains tungstic acid, the colour of the sublimate is red ; and if stannic or titanic acid is present, yellow drops of liquid chloride are also produced. Chloride of tantalum melts at 430°, and volatilises at 291°. Water decomposes it, forming hydrochloric and tantalic acids; but the decomposition is not complete even at the boiling heat : water containing a small quantity of ammonia decomposes the chloride perfectly even at ordinary tempera- VOL. 11. X USL TANTALUM. tures. According to the recent experiments of II. Rose, chloride of tantalum contains 81*14 per cent, of tantalum. Bromide of tantalum is prepared in the same manner as the chloride ; when freed from excess of bromine, it has a yellowish colour. Fluoride of tantalum, TaF^. — Ignited tantalic acid does not dissolve in aqueous hydrofluoric acid; but the hydrate dissolves, forming a clear solution, which, when evaporated, partly gives off the tantalum as fluoride, but also leaves a white residue of oxyfluoride. Fluoride of tantalum forms with fluoride of potassium a crystalline double salt, containing KF.2TaF2; and with fluoride of sodium the salt, NaF.TaFj (H. Rose). ESTIMATION AND SEPARATION OF TANTALUM. Tantalum is estimated in the form of anhydrous tantalic acid, containing 81*13 per cent, of the metal. It occurs in nature associated with lime, magnesia, yttria, and the oxides of iron and manganese, and occasionally with zirconia, titanic acid, and a few other substances. From these it is separated by fusion with hydrate of potash, or, better, with bisulphate of potash, in the manner already described (p. 279). Some comjjounds of tantalic acid may be decomposed by sulphuric acid, the tantalic acid being separated in the insoluble state, and all the bases passing into the solution. Tantalate of zirconia may be decomposed in this manner. On treating that compound with strong sulphuric acid, and digesting the cooled mass for some time with a large quantity of water, sulphate of zirconia dissolves, and tantalic acid re- mains hehind in combination with sulphuric acid, from which it may be purified by repeated boiling with water. From titanic acid, with which it sometimes occurs in nature, tantalic acid is separated by fusing the mineral with bisulphate of potash, and treating the fused mass with a large quantity of COLUMBIUM. 285 water. Titanic acid then dissolves, especially if the water is slightly acidulated with hydrochloric acid, while sulphate of tantalic acid remains undissolved. The titanic acid is preci- pitated from the solution by boiling : the separation is, how- ever, not very complete. In some cases, the decomposition may be effected by sulphuric acid. From the alkalies, tantalic acid may be completely separated by sulphuric acid, provided the compound is soluble in water. In the contrary case, it must first be fused with carbonate or hydrate of potash. If, however, the quantity of alkali is to be likewise estimated, the compound must be rendered soluble by fusion with sulphate of ammonia.* SECTION IX, COLUMBIUM. Synonyme. Niobium ; Cb. This metal was discovered by Hatchett in 1801, in a black mineral (columbite), from Massachusetts, in North America ; it was thence named Columbium. Wollaston, in 1809, ex- amined it further, and pronounced it to be identical with the tantalum discovered by Ekeberg, in Swedish tantalite. This idea of the identity of the two metals remained current till 1846, when H. Rosef, by a more careful investigation of the matter, was led to conclude that the American columbite, and the tantalite from Bodenmais, in Bavaria, contained two acids bearing a very close resemblance to tantalic acid, but never- theless, distinct from it and from each other. To the metals supposed to exist in these acids he assigned the names Niobium and Pelopium. But by a later investigation J, he finds that * IT. Rose, Handb. d. Anal. Chem. 1851, ii. 326—335. t Pogg. Ann. Ixiii. 317 ; Ixix. 115. X Pogg. Ann. xc. 456 ; Ann. Ch. Pharm. Ixxxviii. 245. X 2 286 COLUMBIUM. these two acids really contain the same metal, associated with different quantities of oxygen ; he therefore discards the name pelopium, and proposes to designate by niobium the metal contained in American columbite and Bavarian tantalite. As, however, this metal is clearly the one discovered fifty years ago by Hatchett, wc cannot do better than retain for it the name originally proposed by its discoverer, viz., Colu^ibium.* Columbium likewise occurs, associated with yttrium, ura- nium, iron, and small quantities of other metals, in a Siberian mineral called urano-tantalite, y ttro-ilmenite, or samarskite ; also in pyrochlore, cukolite or wohlerite, euxenite, and in a variety of pitchblende from Satersdiilcn. Metallic columbium is obtained by passing dry ammoniacal gas over the chloride. It is a black powder, which oxidises when heated in the air. Nitric acid and aqua-regia have no effect upon it ; but a mixture of hydrofluoric and nitric acids attacks it at ordinary temperatures. It combines with oxygen in two proportions, forming cohimbous and Columbia acids, formerly supposed by Rose to contain different metals, and called respectively niobic and pelopic acids. The composition of these acids has not yet been determined. Columboiis acid, or a mixture of that acid with columbic acid, is separated from the minerals containing it by processes similar to those already described for the preparation of tan- talic acid (p. 279) ; and when the acid, or mixture of acids, tlius obtained, is mixed with charcoal and heated in a stream of chlorine gas, w ith the precautions already detailed for the preparation of chloride of tantalum (p. 285), it is generally converted into two chlorides, — the one white, volatile, but not fusible; the other yellow, likewise volatile, and easily fusible : the latter contains the larger proportion of chlorine. It was the formation of these two chlorides which led Rose to con- clude that certain varieties of tantalite contained two distinct * See a paper " On the Nomenclature of the Metals contained in Colum- bite and Tantalite," by Prof. Connell, Phil. Mag. [4]. CHLORIDES OP COLUMBIUM. 287 inetals, niobium and pelopium ; he now finds, however, that the substance which he regarded as perfectly pure niobic acid, obtained by the action of water on the white chloride, may, by mixing it with a large excess of charcoal, and gently igniting the mixture in a stream of chlorine gas, with strict attention to all the precautions above alluded to, be com- pletely converted into the yellow chloride, — the so-called chloride of pelopium. But if a smaller quantity of charcoal be used, or if the mixture be too strongly ignited during the action of the chlorine, especially at the commencement, the white and less volatile chloride (chloride of niobium), is obtained, as well as the yellow compound. Columbium appears, then, to be capable of uniting with chlorine in two proportions ; and the chlorides thus formed yield, when treated with water, two acids of corresponding constitution, viz., Columbous and Columbic acids, the latter, which contains the larger proportion of oxygen, being formed from the yellow chloride. Columbous acid (Rosens niobic acid) may, like tantalic acid, be obtained in the amorphous and the crystalline state, viz., by the rapid or gradual action of water on the chloride. Its specific gravity is lower than that of tantalic acid, and is subject to similar variations. Samples of the acid, prepared from various sources, exhibited, after ignition over a spirit- lamp to the point of incandescence, specific gravities ranging from 4-66 to 5-26; by stronger ignition, the density was diminished. The mean density of the amorphous acid was found to be greater than that of the crystalline in the ratio of 1 to 0*875. The acid is colourless both in the anhy- drous and hydrated states, but when heated assumes a yellow colour, much deeper than that of heated tantalic acid. The hydrated acid becomes incandescent during its transition to the anhydrous state. Columbous acid is decomposed by ignition in a stream of hydrosulphuric acid, and converted into sulphide of colum- X 3 288 COLUMBIUM. bium. When i^ited in ammoniacal gas, it turns black, and yields a large quantity of water. Columbous acid, after ignition, is insoluble in all acids. The hydrated acid is but very sparingly soluble in hydro- cliloric acid ; so that when an alkaline columbite is precipi- tated by excess of hydrochloric acid, the filtrate retains only a trace of columbous acid in solution. The hydrated acid dis- Bolves, to a certain extent, in oxalic and in hydrofluoric acid. The alkaline columbites are soluble in water, in solutions of potash and carbonate of potash, but dissolve with great difficulty in excess of soda and carbonate of soda, more sparingly even than tantalate of soda. Columbous acid is precipitated from its alkaline solutions by acids, especially by sulphuric acid, even at ordinary temperatures ; whereas the precipitation of tantalic acid requires the aid of heat. Oxalic acid does not affect alkaline colurabites; but carbonic acid gas precipitates an acid salt soluble in a large quantity of water; acetic acid and sal-ammoniac also form precipitates. A solution of an alkaline columbite, acidulated with sul- phuric or hydrochloric acid, forms a red precipitate with ferrocyanide of potassium, bright yellow with the ferri- cyanidCy and orange-red with infusion of galls. A piece of zinCy immersed in the acidulated solution, forms a beautiful blue precipitate, which after a while changes to brown. Before the blowpipe, especially in the inner flame, colum- bous acid assumes a greenish yellow colour while hot, but becomes colourless on cooling. With borax it forms in the outer flame a colourless bead, which, if the acid is in sufficient quantity, becomes opaque by flaming. In the inner flame, the bead assumes a greyish blue colour, provided it contains a suflScient quantity of acid to produce opacity on cooling. In phosphorus-salt, the acid dissolves in large quan- tity, forming a colourless bead in the outer flame, and in the inner, a violet-coloured, or, if the bead be saturated with the COLITMBIC ACID. 289 acid, a beautiful blue bead, the colour disappearing in the outer flame. The addition "of protosulphate of iron changes the colour to blood-red. These characters, together with the above-mentioned precipitates, sufficiently distinguish colum- bous from tantalic acid. Columbic acid (Rose's pelopic acid) bears a very strong re- semblance to tantalic acid, and is intermediate in its pro- perties between that acid and columbic acid. Its specific gravity ranges from 5*5 to 6'7, It appears to be susceptible of three modifications; viz., amorphous, crystalline before ignition, and crystalline after ignition at the heat of a porce- lain-furnace. It is insoluble in all acids after ignition. It is precipitated from its alkaline solutions by the same reagents as columbous acid. The precipitate formed by hydrochloric acid redissolves in excess, forming an opalescent solution from which the acid is completely precipitated by sulphuric acid at a boiling heat. The acidulated solutions yield a brownish-red precipitate with, f err o cyanide of potassium^ white with ferricyanide, and orange-yellow with infusion of galls. Zinc behaves with these solutions in the same manner as with solutions of tantalic acid. A fine blue colour is obtained by treating the yellow chloride of columbium with hydrochloric acid, diluting with water, and adding a piece of zinc. With borate before the blowpipe, columbic acid behaves like tantalic acid. In phosphorus-salt it dissolves in large quantity, forming a colourless bead in the outer flame. In the inner flame, the bead assumes a light-brown colour, tinged with violet, the colour disappearing again after a while in the outer flame. The addition of protosulphate of iron changes the brown colour to crimson. It is remarkable that columbic acid cannot be formed directly from columbous acid, even by the most powerful oxidising agents. It appears, however, to be deprived of a portion of its oxygen by certain reducing agents. X 4, 290 COLUMBIUM. The methods of estimating cohimbium and separating it from other metals are the same as for tantalum. No method is known of separating columbium from tantalum ; but these metals have not hitherto been found occurring together. Ilmenium. (?) — According to the observations of K Hermaim*, it would appear that Siberian yttrotantalite or yttroilmenite contains a peculiar metal, Hmenium, which forms an acid, ilmenic acid, very closely resembling colum- bous acid, but nevertheless distinct from it ; the chief pohits of difference being the lower specific gravity, viz., 4'1 to 4'2 ; the insolubility of the hydrate in hydrochloric acid ; and the formation of a compound witli sul- phuric acid which is decomposed by a large quantity of water, leaving a residue of hydrated ilmenic acid. H. Rosef, however, is of opinion that the supposed ilmenic acid is merely columbous [niobic] acid, more or less impure. Tlie question must, for the present, be regarded as undecided. Kose likewise regards yttroUmenite as identical >^ith urano-tantalite or samarskite. * J. pr. Chem. ixxviii. 91, 119 ; xl. 475 ; Ixv. 54. t Pogg. Ann. Ixxi. 157. MERCURY. 29i ORDEE VIII. METALS WHOSE OXIDES AEE EEDUCED TO THE METALLIC STATE BY HEAT (NOBLE METALS). SECTION I. MERCURY. Eq. 100 or 1250; Hg. Mercury_, or quicksilver, as it is named from its fluidity, has been known from all antiquity. It is found to a small extent in the metallic state, but its principal ore is the native sulphide cinnabar. The most valuable European mines of mercury arc, those of Almaden in Spain, and of Idria in Illyria. At Almaden the cinnabar is found in veins, often nearly fifty feet thick, traversing micaceous schists of the older transition period : in Illyria it is disseminated in beds of grit, bitu- minous schist, or compact limestone of more recent date. The mode of extraction in both these localities, consists in simply roasting the ore in a distillatory apparatus, whereby the sulphur is burned and converted into sulphurous acid, while the mercury is set free in the form of vapour, and condenses in chambers or vessels provided for it. The arrangement adopted in Illyria is represented in figures 12, 13, 14. A is a large furnace (figs. 12 and 14), on each side of which is a series of condensing chambers, CCCCCD. The space V, separated from the fire-place by the perforated arch n n', is filled with the ore in large lumps ; smaller pieces are introduced into the next compartment above the arch pp^; and on the uppermost arch, r r\ are laid a number of earthen capsules, containing the pulverised ore and the mercurial resi- dues of preceding operations. The fire being lighted, and the 292 MERCURY. Fig. 12. Fig. 13. Fig. 14. heat gradually raised, the sulphur is bui-ncd by the air which enters through channels opening into the spaces G, H ; and the mixture of mercurial vapour, sulphurous acid, and smoke from the fire, passes through the horizontal channel at the top of the furnace, then up and down through the condensing chambers, C C C C, and finally escapes into the air. EXTRACTION OF MERCURY. 293 The greater part of the mercury condenses in the first three chambers_, whence it runs into the channels abed, a'h'c'd' , which conduct it into a reservoir. To facilitate the condensation of the last portions of mercury in the chambers DD, the vapours are made to pass between a series of boards placed from side to side of these chambers in an inclined position, and having a stream of water continually running over them. As the mercury ivhich condenses in these last chambers is mixed with a considerable quantity of dust, it is collected in separate channels, then filtered, and the residues returned to the furnace as already described. The mercury obtained by this process is purified by fil- tration through coarse linen cloth, and sent into the market in wrought-iron bottles, each containing about fifty pounds. At Almaden, the mercury is also extracted from the cin- nabar by roasting, the operation being conducted in furnaces called buytrones. (Figs. 15 and 16.) Fig. 15. Fig. 16. 294 MEKCURY. The fire is made at A, and the space B, above it, is filled with the ore, the largest pieces being laid on tlie perforated arch at the bottom, smaller pieces above, and the whole covered with lumps of a mixture of clay, powdered ore, and the residues of preceding operations. The vapours pass through an aperture p, in the upper part of the furnace, into a series of tubular vessels called alndels, open at both ends and fitting one into the other. These are laid on a surface Cy bj a, called the aludel-bath, first descending a little, then ascending, and finally opening into the chimney. The form and disposition of the aludels is shown in figure 17. The con- densed mercury escapes at the joints of the aludels, and runs into the channel b b, by which it is conveyed into the reser- voirs m, n n. The uncondensed mercurial vapour passes into the chamber E, where it deposits a mercurial dust, whicli yields by filtration an additional quantity of liquid mcrcur}^, and a residue which is mixed with clay and pounded ore, and returned to the furnace in the manner above mentioned. The heating of the furnace is Fig 17. Fig. 18. continued for twelve or thirteen hours : it is then left to cool for three or four days, after which it is cleared out and arranged for another operation. In the duchy of Deux Ponts, a mixture of cin- nabar iind limestone is heated to redness in retorts of earthenware or cast-iron placed side by side in an oblong furnace (fig. 18), rURinCATION OF MERCURY. 295 and provided witli receivers containing a certain quantity of water. Sulphide of calcium and sulphate of lime are then formed, and the mercury is evolved in vapour, which con- denses in the receivers. At Horzowitz, in Bohemia, a mixture of cinnabar and smithy-scales is placed in iron dishes, which are attached one above the other by the centres of their bases to a vertical iron axis, and covered with an iron receiver, closed at top and dipping into water at the bottom. The upper part of the receiver is surrounded by the furnace, and imparts its heat to the dishes, from which the mercury rises in vapour and collects in the water below. The mercury of commerce is generally very pure; it is sometimes, however, contaminated with foreign metals, and in that case its fluidity is remarkably impaired. Mercury may be purified by distilling it from half its weight of iron- turnings, or by digesting it with a small quan- tity of nitric acid, or with a solution of corrosive sublimate, which rids it of metals more oxidable than itself. The purification may also be effected by agitating the mercury with a small quantity of solution of sesquichloride of iron. Pure mercury should leave no residue when dissolved in nitric acid, evaporated, and ignited; when made to run down a slightly inclined surface, it should retain its round form, and not drag a tail; and when agitated in a bottle with dry air, it should not yield any black powder. Mercury is liquid at ordinary temperatures. Its colour is white, with a shade of blue when compared with that of silver, and it has a high metallic lustre. At 39° or 40° below zero, it becomes solid, and crystallises in regular octohedrons. According to M. Kupffer, the density of mercuiy at 39 2° is 13-5886; at 62-6'^, 13'5569; and at 78-8°, 13-535 (according to Kopp, it is 13-595 at 39-2°). In the solid state, its density is about 14-0. Mercury boils at 662°, forming a colourless vapour, the density of which was observed, by Dumas, to 296 MERCURY. be 6976 ; the theoretical density is 6930. Mercury emits a sensible vapour between 68° and 80°, but not under 20° {Faraday). When heated near its boiling point, mercury a])sorbs oxygen from the air, and forms crystalline scales of the red oxide. It is not affected by boiling hydrochloric or dilute sulphuric acid, but is readily dissolved by dilute nitric acid. This metal never dissolves in hydrated acids by sub- stitution for hydrogen. Mercury combines with oxygen in two proportions, forming the black oxide, IIg20, and the red oxide, composed of single equivalents, HgO, both of which are bases. According to these formula;, the equivalent of mercury is assumed to be 100 ; but whether it should be this number or a multiple of it by 2, no certain means exist of deciding, while we are in ignorance of any isomorphous relation of mercury with the magnesian metals. MERCUROUS COMPOUNDS. Dioxide of mercury [black oxide), Mercurous oxide, Hg20, 208 or 2600. — This oxide is obtained by the action of a cold solution of potash, used in excess, upon calomel. The sub- stances should be mixed briskly together in a mortar, in order that the decomposition may be as rapid as possible, and the oxide be left to dry spontaneously in a dark place. Mr. Donovan finds these precautions necessary, from the dis- position of this oxide to resolve itself into metallic mercury and the higher oxide. The decomposition of mercurous oxide is promoted by elevation of temperature, and by ex- posure to light. Mercurous oxide is a black powder, whose density is 10*69 (J. Herapath) ; it unites with acids and forms salts. Its soluble salts are all partially decomposed by pure water, which com- bines with a portion of their acid, and throws down a subsalt containing an excess of oxide. They are precipitated black by hydrosulphuric acid and alkaline sulphides. Caustic alka- MERCUROUS COMPOUNDS. 297 lies throw down a black precipitate of mercurous oxide. The alkaline carbonates precipitate white mercurous carbonate, which soon turns black from decomposition. Carbonate of baryta also decomposes mercurous salts, forming a mercuric salt which remains in solution, and a precipitate of metallic mercury. Mercurous salts are decomposed by hydrochloric add and soluble chlorides, with precipitation of calomel as a white powder, a property by which they are distinguished from the salts of the red oxide of mercury. In very dilute solutions, only an opalescence is produced. The precipitate turns black when treated with potash or ammonia. Mer- curous salts form with phosphate of soda a white precipitate of mercurous phosphate, and with alkaline chromateSy a brick- red precipitate of mercurous chromate. Oxalic acid and alkaline oxalates form a white precipitate of mercurous oxalate. Ferrocyanide of potassium produces a thick white precipitate, Siiid ferricyanide of potassium a red-brown precipitate. Tinc- ture of galls yields a brownish-yellow precipitate. The salts of this, and also of the red oxide, are reduced to the metallic state by copper and the more oxidable metals, and by the proto-compounds of tin ; also by phosphorous and sulphurous acids. The precipitated mercury often takes the form of a grey powder, in which no metallic globules are per- ceptible, and remains in this condition while moist. Mercury in this divided state possesses the medicinal qualities of the milder mercurials, and has often been mistaken for black oxide. To obtain precipitated mercury, equal weights of crystallised protochloride of tin (salt of tin) and corrosive sublimate may be dissolved, the first in dilute hydrochloric acid and the second in hot water, and the solutions mixed, with stirring. The salt of tin takes up all the chlorine of the corrosive sublimate, becoming bichloride of tin, which remains in solution, while the mercury is liberated, and forms so fine a precipitate, that it requires several hours to subside. It may be washed by affusion of hot water and subsidence, and 298 MERCURY. slightly drained on a filter, but not allowed to dry. There can be no doubt that it is in this divided state, and not as the black oxide, that mercury is obtained by trituration with fat, turpentine, syrup, saliva, &c., in many pharmaceutical pre- parations. Bisulphide of mercury ^ HgjS, is obtained, as a black pre- cipitate, by the action of hydrosulphuric acid on a solution of mercurous nitrate or upon calomel. This sulphide is decom- posed by a gentle heat, and resolved into globules of mercury and the higher sulphide. Dichloride of mercury y Mercurous chloride, Calomel, Hg2Cl, 235-5 or 2913-75. — A variety of processes are given for the preparation of this remarkable substance. It may be obtained in the humid way, by digesting IJ parts of mercury with 1 part of pure nitric acid, of density from 1*2 to 1-25, till the metal ceases to dissolve, and the liquid has begun to assume a yellow tint. A solution is also prepared of 1 part of cldoride of sodium in 32 parts of distilled water, to which a certain quantity of hydrochloric acid is added ; and this, when heated to near the boiling point, is mixed with the mercurial salt. The mercury takes up the chlorine of the common salt, and the subehloride of mercury formed precipitates as a white powder, while the nitric acid and oxygen are given up by the mercury to the sodium, which becomes nitrate of soda : NaCl + HgaO . NO5 = Hg2Cl + NaO . NO5. The excess of acid in this process is intended to prevent the precipitation of any subnitrate of mercury, which the dilution of the nitrate of mercury, on mixing the solutions, might occasion. Calomel is also obtained by rubbing together, in a mortar, 4 parts of protochloride of mercury (corrosive sub- limate) with 3 parts of running mercury. The mixture is afterwards introduced into a glass balloon, and sublimed by a heat gradually increased. Here the protochloride of mercury combines with mercury, and the dichloride is produced. The MERCUROUS COMPOUNDS. 299 same result is obtained by mixing mercuric sulphate witb as much mercury as it already contains, and about one-third of its weight of chloride of sodium, and subliming the mixture. The vapour of the dichloride of mercury, in these sublima- tions, is advantageously condensed by conducting it into a vessel containing hot water; the vapour of the water then condenses the salt in an extremely fine and beautifully white powder. The product of this operation is recommended by its purity, as well as by its minute division ; for the water dissolves out all the protochloride of mercury by which the dichloride is accompanied. It appears that whenever the dichloride is sublimed, a small portion of it is resolved into mercury and the protochloride. As the calomel usually con- denses in a solid cake, it must, to prepare it for medical use, be reduced to a fine powder, and washed with hot water to remove the soluble chloride. Dichloride of mercury is obtained by sublimation, in four- sided prisms, terminated by summits of four faces. When the solid cake is finely pounded, the salt acquires a yellow tinge. The density of this salt in the solid condition is 6'5 ; in the state of vapour 8350. One volume of the vapour con- tains one volume of vapour of mercury and half a volume of chlorine. This salt is so very sparingly soluble in water, that when mercurous nitrate is added to hydrochloric acid diluted even with 250,000 times its weight of water, a sensible pre- cipitate of dichloride of mercury appears. When boiled for a long time in hydrochloric acid, this salt is resolved into proto- chloride of mercury which dissolves, and mercury which is reduced. Action of ammonia on dichloride of mercury. — The dry dichloride was found by Rose to absorb an equivalent of ammonia, and to become black. Exposed to air, the com- pound loses its ammonia, and the dichloride of mercury recovers its' white colour. This ammoniacal compound is VOL. II, Y 300 MERCURY. HgjCl.NHg, and may be regarded as 3„g iq\^ ^i^at is, as dichloride of mercury in -which 1 eq. of mercury is replaced by mercurammonium, NHgHg. Or again, if we suppose the mercurous salts to contain, not two distinct atoms, but a double atom of mercury (Hg' = Hgj), this double atom being the equivalent of one atom of hydrogen — thus, calomel = Hg'Cl j black oxide of mercury = Hg'O, &c., — then the ammoniacal compound HgjCl.NHg may be regarded as chloride of mercurosammonium, NHgHg' . CI, or chloride of ammonium in which one eq. H is replaced by a double atom of mercury. When calomel is digested in aqueous ammonia, it turns black, and was found by Kane to be converted into mercurous amido-chloride, Hg2Cl.Hg2NH2, sal-ammoniac being formed at the same time : SHg^Cl + 2NH3 = Hg2Cl.Hg2NH2 + NH4CI. This compound may also be regarded as chloride of bimercu- 7'osammonium, NH2Hg'2 . CI. It is not altered by boiling water ; when quite dry, it is of a grey colour. Dibromide of inercury, Mercurous bromide, Hg2Br, is a white insoluble powder, resembling in all respects the di- chloride, and formed in similar circumstances. A boiling solution of bromide of strontium was found by Loewig to dis- solve three equivalents of dibromide of mercury, of which one equivalent precipitated during the cooling of the solution. When the filtered solution was evaporated, it deposited a salt in small crystals, containing SrBr. 2Hg2Br. These crystals were decomposed by pure water, and resolved into the insoluble dibromide, Hg2Br, and a double salt, SrBr . rig2Br, which dissolved easily, and crj'stallised by evaporation. Diniodide of mercury, Mercurous iodide, HgjT, is obtained by precipitation as a green powder, which is red when heated. It is also formed by triturating mercury and iodine together MERCUROUS COMPOUNDS. 301 in a mortar, with a few drops of alcohol, in the proportion of 2 eq. of the former to 1 eq. of the latter. No dicyanide of mercury exists ; and it is doubtful whether a difluoride, corresponding with the dioxide, has been formed. Mercurous carbonate, Carbonate of black oxide of mercury, Hg*02.C02, precipitates as a white powder, when an alkaline carbonate is added to the nitrate of the same oxide. The precipitate becomes grey when the liquid containing it is boiled, and carbonic acid escapes. This carbonate is soluble both in carbonic acid water, and, to a slight extent, in an excess of alkaline carbonate. Mercurous sulphate, Sulphate of black oxide of mercury, Hg20.S03; 248 or 3100. — This salt is obtained by digesting 1 part of mercury in 1^ parts of sulphuric acid, avoiding a high temperature, and interrupting the process as soon as all the mercury is converted into a white salt. It is also pre- cipitated when sulphuric acid is added to a solution of mer- curous nitrate. The salt may be washed with a little cold water. It crystallises in prisms, and requires 500 times its weight of cold and 300 of hot water to dissolve it. With aqueous ammonia this salt forms a dark grey powder, con- taining ammonia or its elements. Mercurous seleniate. — Aqueous solutions of seleniate of soda and mercurous nitrate form a white precipitate, probably consisting of the neutral salt, Hg20 . SeOg, which, however, gradually turns yellow during washing, and, when dried at 100°, is found to be reduced to 6Hg20 .SSeOg (Komer). Mercurous selenite. — The neutral salt Hg20.Se02 is found native as onofrite, a yellow earthy mineral, occurring, together with horn-quicksilver and native mercury, at San Onofrio, in Mexico. It is also obtained by double decomposition as a white powder, which melts at 356°, and when heated above that point, is converted into a brick-red, opaque, crystalline mass of the salt 3Hg20.4Se02 (Kohler).* * Pogg. Ann. Ixxxix. 146. Y 2 302 MERCURY. Mercurom nitrates, Nitrates of black oxide of mercury. — The neutral nitrate is obtained when mercury is dissolved in an excess of cold nitric acid : it crystallises readily in trans- parent rhombs. It is soluble with heat in a small quantity of water, but is decomposed by a large quantity of water, and an insoluble subsalt formed, unless nitric acid be added to the water. The formula of this salt is Hg20.N05 + 2H0. A subnitrate is formed when the black oxide is dissolved in a solution of the preceding salt, or when an excess of mercury is digested in diluted nitric acid at the usual temperature. It crystallises readily in white, opaque rhombic prisms, which contain, according to both G. Mitscherlich and Kane, 3Hg20.2N05 -f 3H0; or, according to Marignac, 4Hg20.3N03 + HO. This salt was observed by G. Mit- scherlich to be dimorphous. "When dissolved by dilutp nitric acid, it yields the neutral salt. The subnitrate is soluble in a little water, but when treated with a large quantity, it leaves imdissolvcd, like the neutral nitrate, a white powder, which retains its colour so long as the supernatant liquid is acid, Ijut becomes yellow when washed with water. The yellow sub- nitrate of mercury was found to contain 2lIg.2O.NO5 + HO (Kane). Another subnitrate, containing, according to Ma- rignac, SHgjO.SNOg -f 2H0, is obtained by boiling the solution or the mother-liquor of the neutral or the sesqui- basic nitrate with excess of mercury for several hours. This salt crystallises in colourless or slightly yellow crystals, derived from an unsymmetrical oblique prism ; it appears to be the most stable of all the mercurous subnitrates. When very dilute ammonia is added to the preceding soluble nitrates, without neutralising the whole acid, a velvety black precipi- tate falls, known as Hahnemann's soluble mercury. This salt contains, according to the analysis of C. G. Mitscherlich, SHgjO.NOg + NH3. But when pains were taken to avoid decomposition of the salt in washing it, its composition was found by Kane to be 2IIg20.N05 + NH3. Bibasic mer- MERCURIC COMPOUNDS. 303 curous nitrate, mixed in solution with nitrate of lead, yields a crystalline double salt, containing 2(PbO.N05) + 2Hg20.N05; and similar double salts with the nitrates of baryta and stron- tia (G. Staedeler). Mercurous acetate, HggO . C4H3O3, falls when acetic acid, or an acetate, is added to the iiitrate, in crystalline scales of a pearly lustre. It is anhydrous, and sparingly soluble in water. MERCURIC COMPOUNDS. Protoxide of mercury [red oxide). Mercuric oxide, HgO, 108 or 1351. — This compound is formed, as described, by the oxidation of mercury at a high temperatm*e, or by heat- ing the nitrate of mercmy till all the nitric acid is expelled, and the mass, calcined almost to redness, no longer emits vapoui-s of nitric oxide. As prepared by the latter process, protoxide of mercmy forms a brilliant orange-red powder, crystallised in plates, and having the density 11*074. It is very dark red at a high temperature, but becomes paler as it cools. When reduced to a line powder, it becomes yellow, like litharge, without any shade of red. It was found by ]\Ir. Donovan to be soluble to a small extent in water, form- ing a solution which has a slight alkaline reaction. If con- taminated with nitric acid, it gives off nitrous fumes when heated in a glass tube, and forms a yeUow sublimate of sub- nitrate. This oxide is known in pharmacy as red precipitate, Tiie same compound is obtained by precipitation, when a solution of corrosive sublimate is mixed with an excess of caustic potash ; it then forms a dense powder of a lemon- yellow colour. It is necessary to use the potash in excess, otlierwise a dark brown oxychloride is formed. The preci- pitated oxide parts with a little moistiu*e when gently heated, but does not change in appearance. This yellow precipitated oxide differs in some respects from the red oxide ; it combines T 3 304 MERCURY. in the cold with oxalic acid, whereas the red oxide does not ; it is converted into black oxychloride by the action of an alcoholic solution of mercuric chloride, which has no action on the red oxide, and it is attacked by chlorine much more readily than the latter. At a red heat, the oxide of mer- cury is entirely volatilised in the form of oxygen and metallic mercury; the same decomposition takes place more slowly under the influence of light. The oxide detonates when heated with sulphur, and converts chlorine into hypochlorous acid. The salts of mercuric oxide, when they do not contain a coloured acid, are colourless in the neutral, and yellow in the basic state. They have a disagreeable metallic taste, and act as violent acrid poisons. Some of them, e. g. the nitrate and sulphate, are resolved by water into a soluble acid salt, and an insoluble basic salt. From their aqueous solutions the mercury is, for the most part, precipitated in the metallic state by the same substances as from mercurous salts ; but the complete reduction of the mercury is often preceded by the formation of a mercurous salt : such, for example, is the action of phosphorous acid, sulphurous acid, protochloride of tin, metallic copper, &c. Gold does not by itself reduce mercury from its salts ; but if a drop of a mercm'ic solution be laid on a piece of gold, and a bar of zinc, tin, or iron be brought in contact with the moistened surface, an electrolytic action is set up, and the gold becomes amalgamated at the point of contact. Hydrosul/jhuric acid and alkaline sulphides, added in excess to mercuric salts, throw down a black pre- cipitate of mercuric sulphide, insoluble in strong nitric acid. If, however, the quantity of the re-agent added is not suffi- cient for complete decomposition, a white precipitate is formed consisting of a compound of mercuric sulphide with the original salt, and often coloured yellow or brown by excess of the sulphide : this re-action is quite peculiar to mercuric salts. Ammonia and carbonate of ammonia form white precipitates. MERCURIC COMPOUNDS. 305 generally consisting of a compound of the mercuric salt with amide of mercury. The fixed alkalies throw down a yellow precipitate of mercuric oxide (not hydrated), insoluble in excess. If, however^ the solution contains a large quantity of free acid^ no red precipitate is formed, or only a slight one after a considerable time. Monocarbonate of potash or soda throws down red-brown mercuric carbonate. But if any ammoniacal salt is present in the solution, the fixed alkalies and their carbonates throw down the white precipitate above mentioned. Bicarbonate of potash or soda also gives a brown- red precipitate, with mercuric nitrate or sulphate ; but with the chloride it forms a white precipitate which afterwards turns red. The carbonates of baryta, strontia, and lime precipitate mercuric oxide from the solutions of the sulphate and nitrate, but not from the chloride. Phosphate of soda throws down white mercuric phosphate from the sulphate and nitrate, but not from the chloride. Chromate of potash forms a yellowish red precipitate. Ferrocyanide of potassium forms, in solutions not too dilute, a white precipitate which gradually turns blue. Tincture of galls forms an orange- yellow precipitate with all mercuric solutions except the chloride. Iodide of potassium produces a scarlet precipitate of mercuric iodide, soluble in excess either of the mercuric salt or of iodide of potassium. When aqueous ammonia is digested for several days upon precipitated oxide of mercury, the latter is converted into a yellowish white powder, which Kane regards as 2HgO . HgNH2 + 3HO, or as a hydrated compound of amide and oxide of mercury, which may be called oxyamide of mer- cury. According to Millon*, on the other hand, its compo- sition is 4IigO.NH3 + 2HO, or rather 3HgO . HgNH2.HO -I- 2H0. This substance, when placed in vacuo over quick lime, gives off 2 eq. water, turns brown, and in that state undergoes no further alteration by exposure to the air * Compt. rend. xxi. 826. Y 4 306 MERCURY. at ordinary temperatures; but between 100° and 130° C, it gives off a third atom of water and is reduced to the anhy- drous compound 3HgO . HgNHg. The yellow hydrated com- pound rapidly absorbs carbonic acid from the air, and turns white. Dilute potash has no action upon it ; but very strong potash, at a boiling heat, decomposes it, with evolution of ammonia. The brown anhydrous compound resists the action of aqueous potash even at the boiling heat, but is decomposed by fusion with hydrate of potash. Oxyamide of mercury is a power- ful base, and expels ammonia from its salts. One equivalent of this compound, represented by the formula 3HgO . HgNH^, saturates 1 eq. of sulphuric acid, nitric acid, &c. ; thus the sulphate is 3HgO . HgNHa . SO3; the nitrate, 31IgO.IIgNH2. NO5 + HO, &c. &c. Nitride of mercury , M er cur ammonia , NIIg3. — This com- pound is formed by passing dry ammoniacal gas over precipi- tated mercuric oxide previously well washed and dried : 3Hg04-NH3^NHg3H-3HO. After removing the excess of mercuric oxide by dilute ni- tric acid, the mercurammonia is obtained in the form of a dark flea-brown powder, which explodes, by heat, friction, percussion, or by contact with oil of vitriol, almost as violently as iodide of nitrogen. When carefully heated with hydrate of potash, it is decomposed witliout detonation, yielding am- moniacal gas and sublimed metallic mercury. It is also decomposed by hydrochloric acid, sulphuric, and concentrated nitric acid, yielding an ammoniacal and a mercuric salt. It may be regarded as ammonia in which the hj^drogen is entirely replaced by an equivalent quantity of mercury (Plantamour).* By the action of various ammoniacal salts at a boiling heat on mercuric oxide, compounds are obtained consisting of nitride of mercury combined with mercuric salts : e. g. with * Ann. Cli. Pliarm. xl. 115. MERCURIC COMPOUNDS. 307 nitrate of ammoma, the compound NHg3 + 2(3HgO . NO5) is obtained ; with phosphate of ammonia, the compound NHgg + 3HgO . PO5 + 3H0 ; with carbonate of ammonia, the com- pound 2(NHg3+ HgO . CO2 + 2HO) + HO j with chromate of ammonia, the compound NHgg . HgO . 2HO + 4(HgO.Cr03), which when treated with ammonia is converted into NHg3 + HgO . Cr03 + 2HO; with acetate of ammonia, the compound NHg3 + C^H3Hg04 + 4HO, &c. &c. (Hirzel) * Protosulphide of mercury, Mercuric sulphide, Cinnabar, HgS; 116 or 1450. — This is the common ore of mercury, and sometimes occurs crystallised, forming a beautiful ver- milion. It is prepared artificially by fusing one part of sul- phur in a crucible, and adding to it by degrees six or seven parts of mercury, stirring it after each addition, and covering it to preserve it from contact of air, when it inflames, from the heat evolved in the combination. The product is exposed to a sand-bath heat, to expel the sulphur uncombined with mercury, and afterwards sublimed in a glass matrass at a red heat. A brilliant red mass of a crystalline structure is thus obtained, which, when reduced to fine powder, forms the lively red pigment vermilion. This sulphide is black before sublimation. It is precipitated black also when hydrosul- phuric acid is passed through a solution of corrosive sublimate, but is of the same composition in both states. The sulphide of mercury, however, may be obtained of a red colour without sublimation, or in the humid way, by several methods. Liebig recommends for this purpose to moisten the pre- paration called white precipitate, recently prepared, with sulphide of ammonium, and allow them to digest together. The black sulphide is instantly produced, which in a few minutes passes into a fine red cinnabar, the colour of which is improved by digesting it at a gentle heat in a strong solution of hydrate of potash. The sulphide of ammonium used in this experiment is prepared by dissolving sulphur to saturation * Ann. Ch. Pharm. Ixxxiv. 258. 308 MERCURY. in hydrosulphate of ammonia. Cinnabar is not attacked by sulphuric, nitric or hydrocldoric acid, or by solutions of the alkalies, but is dissolved by aqua-regia. Protochloride of mercury, Mercuric chloride, Corrosive sub- limate, 135-5 or 1693*75. — This compound may be formed by dissolving red oxide of mercury in hydrochloric acid, or by adding hydrocldoric acid to any soluble salt of that oxide ; but it is generally prepared in a different manner. Four parts of mercury are added to five parts of sulphuric acid, and the mixture boiled tiQ it is converted into a dry saline mass. The mercuric sulphate thus obtained is mixed with an equal weight of common salt, and heated strongly in a retort by a sand- bath; chloride of mercury sublimes and condenses in the upper part and neck of the retort, while sulphate of soda remains behind with the excess of chloride of sodium. The mercury and sodium have exchanged places in the salts : NaCl + HgO . SO3 = HgCl + NaO . SO3. Mercury, when heated in a stream of chlorine gas, burns with a pale flame, and is converted into a white sublimate of chloride. The salt has been prepared on a large scale in this manner, which was suggested as a manufacturing process by Dr. A. T. Thomson. The sublimed chloride of mercury forms a crystalline mass, the density of which is 6*5 ; it fuses at 509°, and boils at about 563°. The vapour of chloride of mercury is colourless, its density 94.20, one volume of it containing 1 volume of mercury vapour and 1 volume of chlorine gas. This salt is soluble in 16 parts of cold and in 3 parts of boiling water, in 2} parts of cold and in 1^ part of boiling alcohol, and in 3 parts of cold ether. It is not decomposed by sulphuric or nitric acid; is largely dissolved by the latter, and also by hydrochloric acid. It is obtained by sublimation and from solution in two different crystalline forms. The solutions of chloride of mercury exposed to the direct rays of the sun MERCURIC COMPOUNDS. 309 evolve oxygen^ while hydrochloric acid is dissolved and dichloride of mercury precipitates. The decomposition of this salt by the action of light is much more rapid when the solution contains organic matter. The poisonous ac- tion of chloride of mercury, which is scarcely inferior to that of arsenious acid, is best counteracted by liquid albu- men, with which chloride of mercury forms an insoluble and inert compound. Many metals, viz. arsenic, antimony, bismuth, zinc, tin, lead, iron, nickel, and copper, decompose mercuric chloride in ^he dry way, withdrawing the half or the whole of its chlorine, and separating calomel or metallic mercury, which latter forms an amalgam with the excess of the other metal. Arsenic forms terchloride of arsenic and a brown sublimate. An intimate mixture of 3 pts. antimony and 1 pt. corrosive sublimate, well pressed into a glass, becomes hot and liquid in the course of half an hour, and on the application of heat yields terchloride of antimony and metallic mercury. Tin heated with corrosive sublimate yields a distillate of bichlo- ride of tin, and a grey residue containing calomel and proto- chloride of tin. Many metals also reduce the mercury from the aqueous or alcoholic solution of the chloride (p. 306) . Most metals throw down calomel together with the mercury ; but zinc, cadmium, and iron precipitate nothing but mercury, zinc being thereby converted into a semi-fluid amalgam, and cadmium forming an amalgam which crystallises in beautiful needles. The other reactions of mercuric chloride in solution have been already described (p. 306, 307.). Chloride of mercury with ammonia. — 1. When chloride of mercury is gently heated in a stream of ammoniacal gas, the latter is absorbed, and the compound fuses from heat evolved in the combination. The product was found by Rose to con- tain 2HgCl . NH3. This compound boils at 590°, and may be distilled without loss of ammonia; it is decomposed by water. — 2. Fusible white precipitate. When the double 310 MERCURY. chloride of mercury and ammonium, called sal alembroth, is precipitated by potash in the cold, a white powder is obtained, which was first distinguished by Wohler from the compound next described ; its composition may be expressed, according to Kane's analysis, by the formula HgCl . NH3. The same compound is also formed when ammonia is added to a solution of sal-ammoniac, the liquid brought to the boiling point, and chloride of mercury dropt into it so long as the precipitate which is produced is redissolved. The compound appears, on the cooling of the solution, in small crystals, which are garnet dodecahedrons (Mitscherlich) . The crystalline form of this compound belongs, therefore, to the regular system, like that of sal-ammoniac. 3. Mercuric amido-chloride. — The compound known as white precipitate f and sometimes infusible white jjrecipitatey to distinguish it from the preceding, is formed when ammonia is added to a solution of chloride of mercury. When first pro- duced, it is bulky and milk-white ; it is decomposed by hot water or by much washing with cold water, and acquires a yellow tinge. Kane has shown that white precipitate is free from oxygen, and contains nothing but the elements of a double chloride and amide of mercury, and represents it by the formula HgCl . HgNH2. White precipitate is distin- guished from calomel by solution of ammonia, w hich does not alter the former, but blackens the latter : it is readily dis- solved by acids. 4. Nitrochloricle of mercury. — Mitscherlich has observed that when white precipitate is gradually heated in a metal bath, and the heat continued for a long time, three atoms of it give off two atoms of ammonia and one atom of chloride of mercury, while a red matter remains in crystalline scales, having much the appearance of red oxide of mercury pro- duced by the oxidation of the metal in air, and containing two atoms of cliloride of mercuiy united with a com- pound of one atom of nitrogen and three atoms of mercury, WHITE PRECIPITATE. 311 2HgCl.NHg3. He concludes that the atom of white preci- pitate should be multiplied by three ; its decomposition by the heat of the metal bath will then be represented by the equation : — 3(HgCl . HgNH2) = 2HgCl . NHgg + 2NH3 + HgCl. The red compound is itself decomposed by a temperature above 680°, and resolved into chloride of mercury, mercury, and nitrogen. It is insoluble in water, and is not altered in boiling solutions of the alkalies. It may be boiled without change in diluted or concentrated nitric acid, and in pretty concentrated sulphuric acid, but it is decomposed and dissolved when boiled in the most concentrated sulphuric acid or in hy- drochloric acid ; no gas is evolved, but ammonia and chloride of mercury are found in the acid solution. The compound NHg3 is not isolated by passing ammonia over the heated red compound. Mercury conducts itself in these compounds in the same way as potassium with ammonia, the olive- coloured substance produced by the action of dry ammonia upon potassium being the amide of potassium, 3(K.NH2), and the plumbago-looking substance left on heating the amide of potassium, when ammonia escapes, a compound of nitrogen and potassium, NK3.* 5. When white precipitate is boiled in water, it is changed into a heavy canary-yellow powder, which Kane regards as a compound of the amido-chloride of mercury with oxide of mercury, HgCl.HgNH2.2HgO. Two atoms of water are decomposed in its formation, yielding the two atoms of oxy- gen which are found in the yellow compound, while the two atoms of hydrogen, added to an atom of chlorine and an atom of amidogen, form an atom of hydrochlorate of ammonia, which is found in solution : 2 (HgCl . HgNH^) + 2H0 = HgCl . HgNH^ . 2HgO + NH^Cl. * Mitscherlicli in Poggeudorff's Annalen, toI. xxxix. p. 409. 313 MERCURY. Solutions of potash and soda convert white precipitate into the same yellow substance, while a metallic chloride is formed and ammonia evolved (Kane). The five compounds just described may be regarded as salts of metalloidal radicals formed from ammonium (NHJ in which the whole or part of *the hydrogen is replaced by an equivalent quantity of mercurj'. Thus, the fusible white precipitate, HgCl.NHg, may be regarded as a chloride of fTT mercurammonium, —Q\J^\^j^ •, the preceding compound, SHgCl.NHg, as a double chloride consisting of the same compound united with chloride of mercury, namely as ClHg 4- Cl.N I TT^ . similarly, infusible white precipitate, {TT Ho- * the yellow powder obtained by boiling this compound with water is a chloride of tetramercurammoninm combined ydth two atoms of water, = ClNIIg^ + 2H0 ; and the red com- pound, 2IIgCl.NHg3, may be regarded as a compound of this same chloride with chloride of mercury, namely as ClHg.ClNHg^. Oxy chloride of mercury. — When a solution of corrosive sublimate is precipitated by potash or soda, mercuric oxide goes down, in combination with a portion of chloride, as a brown precipitate, unless a considerable excess of alkali be employed. The same oxychloride is produced by an alkaline carbonate; but a double carbonate is then also foiTned. Chloride of mercury is not immediately precipitated by the bicarbonates of potash and soda ; and hence that salt may be employed to detect the presence of a neutral alkaline car- bonate in these bicarbonates. This oxychloride may also be formed by passing chlorine through a mixture of ^vater and oxide of mercury. It may be obtained crystalline and of a very dark colour, almost black, by mixing corrosive subli- CHLORIDES OF MERCURY. 313 mate with chloride of lime, and boiling the liquid, or by treating a solution of corrosive sublimate with bicarbonate of potash, and allowing the solution to stand in an open vessel, when carbonic acid gradually escapes, and the compound HgCl . .4HgO is deposited. This oxychloride is decomposed by a moderate heat, chloride of mercury subliming, while the red oxide remains. Sulpho chloride of mercury, HgC1.2HgS. — When hydro- sulphuric acid gas is passed through a solution of chloride of mercury, the precipitate which first appears, and does not subside readily, is white ; it has been shown by Rose to be a compound of chloride and sulphide of mercury. This sub- stance is changed entirely into sulphide of mercury, when left in water containing hydrosulphuric acid. On the other hand, precipitated sulphide of mercury digested in a solution of chloride of mercury, takes down that salt, and forms the compound in question. The same compound may be formed in the dry way, by fusing protosulphide of mercury (either black or red) with eight or ten times its weight of corrosive sublimate, in a sealed tube, and dissolving out the excess of chloride by boiling water ; the sulphochloride then remains in the form of a dirty -white powder having a distinctly crys- talline structure (R. Schneider). Sulphide of mercury com- bines likewise with the bromide, iodide, fluoride, and nitrate of mercury, and always in the proportion of two atoms of the sulphide to one atom of the other salt. Double salts of chloride of mercury. — Chloride of mercury was found by M. Bonsdorff" to combine with chloride of potas^ sium in three different proportions, forming a series of salts in which the chloride of potassium remains as one equivalent, while the chloride of mercury goes on increasing. They are KCl.HgCl.HO, which crystallises in large transparent rhom- boidal prisms ; KCl . 2HgCl . 2H0 crystallising in fine needle- like amianths; and KCl + 4HgCl + 4HO, which crystallises also in fine needles. Chloride of sodium forms only one com- 314 MERCURY. pound, NaCl . 2HgCl . 4H0, which crystallises in fine regular hexahedral prisms. One of the double salts of chloride of ammonium has long been known as sal alembroth. It crystal- lises in flattened rhomboidal prisms, NH^Cl . HgCl . HO, and is isomorphous with the corresponding potassium salt. When exposed to dry air, it gives off its water without change of form. Kane has also obtained NH^Cl . 2HgCl, and the same with an atom of water, NH^Cl . 2IIgCl . HO, the first in a rhomboidal form, and the second in long silky needles. All these double chlorides are obtained by dissolving their constituent salts together in the proper proportions. The chlorides of barium and strontium form well-crystallised com- pounds with chloride of mei^curi/y viz. BaCl. 2HgCl. 4H0, and SrCl . 2HgCl . 2H0. Chloride of calcium combines in two proportions with mercuric chloride. When chloride of mercury is dissolved to saturation in chloride of calcium, tetrahedral crystals separate from the solution, which are tolerably persistent in air, and contain CaCl . 5HgCl . 8HO. After the deposition of these crystals, the liquid yields, when evaporated by a gentle heat, a second crop of large prismatic crystals, CaCl . 2HgCl. 6H0, which are very deliquescent. Chloride of magnesium also forais two salts, MgCl.SHgCl. HO, and MgCl . HgCl . GHO, both deliquescent. Chloride of nickel gives two compounds, one of which crystallises in tetrahedrons, like the chloride of calcium salt. Chloride of manganese forms a compound in good crystals, MnCl . HgCl . 4H0. The chlorides of iron and zinc form similar isomorphous salts, FeCl . HgCl . HO, and ZnCl . HgCl . HO. The double chlo- rides of zinc and of manganese are remarkable in one respect, that chloride of mercury dissolved by them in excess crystallises by evaporation in fine large crystals, such as cannot be obtained in any other way. The chlorides of cobalt, nickel, and copper form similar crystallisable salts; but chloride of lead does not appear to form a double salt with chloride of mercury. (Bonsdorff.) PROTIODIDE OF MERCURY. 315 Mercuric chloride likewise forms definite compounds with alkaline chromates. A hot solution of equal parts of mercuric chloride and bichromate of ammonia deposits, on cooling, large hexagonal prisms, of a splendid red colour, containing NH4O . 2Cr03 + HgCl + HO, and the mother-liquor deposits a further crop of red, somewhat needle-shaped crystals, contain- ing 3 (NH40.2Cr03) +HgCl. (Richmond and Abel.*) Mono^ chromate of potash forms with mercuric chloride a brick-red precipitate of mercuric chromate ; and, on evaporating the filtered liquid, small pale red crystals are obtained of a double salt, containing KO . Cr03 + HgCl. A solution of equivalent quantities of mercuric chloride and bichromate of potash yields beautiful red pointed crystals, containing KO . 2Cr03 + HgCl. (Darby.t) On mixing the cold saturated aqueous solutions of acetate of copper and mercuric chloride, and leaving the mixture to evaporate, deep blue, concentric, radiated hemi- spheres are obtained, containing CuO . C4H3CUO4 + HgCl. (Wohler and Hutteroth.)t Protobromide of mercury , Mercuric bromide, HgBr; 180 or 2250. — This salt is obtained by treating mercury with water and bromine. It is colourless, soluble in water and alcohol, and when heated, fuses and sublimes, exhibiting a great ana- logy to chloride of mercury in its properties. Its density in the state of vapour is 12370. Bromide of mercury forms a similar compound with sulphide of mercury HgBr . 2HgS, which is yelloAvish. It was also combined, by BonsdorfF, with a variety of alkaline and earthy bromides. Bromide of mer- cury combines with half an equivalent of ammonia, in the dry way, and also gives, with solution of ammonia, a white precipitate, analogous to that derived from chloride of mer- cury. Protiodide of mercury, mercuric iodide, Hgl, 226 '36 or * Chem. Soc. Qu. J. iii. 202. f Chem. Soc. Qu. J. i. 24. X Ann. Ch. Pharni. lui. 142. VOL. II. Z 316 MERCURY. 2829*5. — Falls as a precipitate of a fine scarlet colour, wlieu iodide of potassium is added to a solution of chloride of mer- cury. It may also be obtained by triturating its constituents together, in the proper proportion, ^nth a few drops of alcohol. To procure it in crystals, Mitscherlich dissolves iodide of mer- cury to saturation, in a hot concentrated solution of the iodide of potassium and mercury, and allows the solution to cool gradually. When heated moderately, mercuric iodide becomes yellow ; at a higher temperature, it fuses and sublimes, con- densing in rhomboidal plates of a fine yellow colour. The forms of the red and yellow crystals are totally different, so that the change of colour is due to the dimorphism of mer- curic iodide. The yellow crystals generally return gradually into the red state when cold ; and this change may be deter- mined at once by scratching the surface of a crystal, or by crushing it. The density of mercuric iodide in the state of vapour is 15630; it is the heaviest of gaseous bodies. Mer- curic iodide is slightly soluble in water, but requires more than 6000 times its weight of water to dissolve it. It is much more soluble in alcohol and in acids, particularly with the assistance of heat. Mercuric iodide is very soluble in iodide of potassium ; it is also dissolved by a solution of mercuric chloride, especially when hot. Hence, when a few drops of iodide of potassium solution are added to a solution of corro- sive sublimate, a precipitate is formed, which redissolves on agitating the liquid ; a somewhat larger quantity of iodide of potassium renders the precipitate permanent ; and a still further addition causes it to disappear entirely. When treated with sulphuretted hydrogen water, mercuric iodide forms the compound Hgl . 2HgS, which is yeUow. Mcrcmic iodide unites with other iodides, and forms a class of salts as extensive as the compounds of chloride of mercury. They have been studied by M. P. BouUay.* Mercuric iodide * Ann. Ch. Plijs. [2], xxxiv. 337. MERCURIC IODIDE. 317 also combines with chlorides ; it is dissolved by a hot solution of mercuric chloride, and two compounds have been obtained on the cooling of the solution, viz., a yellow powder, Hgl . HgCl, and white dendritic crystals, HgI.2HgCl. Mercuric iodide treated with very strong aqueous ammonia forms the compound NHgHg . I ; with somewhat less concen- trated ammonia it yields white needles of the compoimd NHg.SHgl or NHgHgl + Hgl, and a red-brown powder con- sisting of iodide of tetramercurammonium with 2 eq. water NHg4lH-2HO. The formation of this last compound is represented by the equation : 4HgI + 4NH3 + 2HO = NHgJ . 2H0 + SNHJ. Iodide of tetramercurammonium is also formed by passing ammoniacal gas over mercuric oxy-iodide : Hgl . 3HgO + NH3 = NHgJ . 2H0 + HO ; by digesting the chloride of tetramercurammonium in aqueous iodide of potassium (Rammelsberg) ; and by adding ammonia to a solution of iodide of mercury and potassium mixed with caustic potash (Nessler *) : 4(HgI . KI) + NH3 + 3K0 = NHg^I . 2H0 + 7KI + HO. This last reaction affords an extremely delicate test for am- monia. A solution of iodide of mercury and potassium is prepared by adding iodide of potassium to a solution of corrosive sublimate, till a portion only of the resulting red precipitate is redissolved, then filtering, and mixing the filtrate with caustic potash. The liquid thus obtained pro- duces a brown precipitate with a very small quantity of ammonia, either free or in the form of an ammoniacal salt. The precipitate is soluble in excess of iodide of potassium (Nessler). * Cheni. Gaz. 1856, 445. 463. z 2 318 MERCURY. Mercuroso-merciiric iodide, Hg^Ig or Hg2l . 2HgI. — This compound is obtained by precipitating a solution of mercurous nitrate with hydriodic acid or iodide of potassium, and col- lecting the precipitate on a filter after the green colour has changed to yellow ; or by dissoMng in aqueous iodide of potassium half as much iodine as it already contains, and adding the solution to a solution of mercurous nitrate. It is a yellow powder, which turns red when heated. Cyanide of mercury, HgCy, 126 or 1575. — This salt is most easily obtained by saturating hydrocyanic acid Avith red oxide of mercury. To prepare the hydrocyanic acid required, the process of Winkler may be followed. Fifteen parts of ferrocyanide of potassium are distilled with 13 parts of oil of vitriol diluted with 100 parts of water, and the distillation continued by a moderate heat nearly to dryness. The vapour should be made to pass through a Liebig's condensing tube, and be afterwards received in a flask containing 30 parts of water. A portion of the condensed hydrocyanic acid is put aside, and the remainder mixed with 16 parts of oxide of mer- cury in fine powder, and well agitated till the odour of hydro- cyanic acid is no longer perceptible. The solution is drawn off from the undissolved oxide of mercury, and the reserved portion of hydrocyanic acid mixed with it. The last addition is necessary to saturate a portion of oxide of mercury, which cyanide of mercury dissolves in excess. This operation yields 12 parts of the salt in question. Cyanide of mercury may also be obtained by boiling 1 pt. of ferrocyanide of potassium for ten minutes with 2 pts. of neutral mercuric sulphate and 8 pts. of water, filtering the liquid, and leaving it to crystallise by cooling. The reaction may be represented by the equation : K2FeCy3 + 3HgO = 3HgCy + 2K0 + FeO. A third method of preparing tliis compound is to heat the red oxide of mercury with about an equal weight of pure and CYANIDE OP MERCURY. 319 finely pounded Prussian blue, and a large quantity of water, stirring the mixture frequently; then boil the filtrate with oxide of mercury to throw down the last portions of iron; and neutralise the excess of mercuric oxide in the liquid with hydrocyanic acid. Cyanide of mercury crystallises in square prisms which are anhydrous, and resembles chloride of mercury in its solubility and poisonous qualities. The red oxide of mercury, even when dry, absorbs hydrocyanic acid, with formation of water and evolution of heat. The affinity of mercury for cyanogen appears to be particularly intense, oxide of mercury decom- posing all the cyanides, even cyanide of potassium, and libe- rating potash. Cyanide of mercury is consequently not precipitated by potash. Nor is it decomposed by any acid, with the exception of hydrochloric, hydriodic, and hydrosul- phuric acids. By a heat approaching to redness, cyanide of mercury is decomposed, and resolved into mercury and cyanogen gas. When exposed in the moist state to the action of chlorine in a dark place, it is converted into mer- curic chloride and gaseous chloride of cyanogen : HgCy -i- 3C1 = HgCl + CyCl. But in strong sunshine, a difierent action takes place, attended with considerable rise of temperature, and yielding sal-am- moniac, mercuric chloride, a pecidiar yellow oil, a small quan- tity of gaseous chloride of cyanogen, and a trace of carbonic acid (Serullas). When hydrocyanic acid is digested upon mercurous oxide, the mercuric cyanide dissolves, and metallic mercury is liberated. Oxy cyanide of mercury , HgCy . HgO, is produced as a white powder intermixed with the red oxide, when hydrocyanic acid of considerable strength (10 or 20 per cent.) is agitated with red oxide of mercury in large excess. It is sparingly soluble in cold water, but may be dissolved out by hot water, and crystallises on cooling in transparent, four-sided, acicular z 3 320 * MERCURY. prisms. When heated gently, it blackens slightly, and then explodes (Johnston).* Cyanide of mercury, digested upon red oxide of mercury, dissolves a large quantity of it, and forms, according to Kuhn, a tribasic cyanide of mercury , HgCy . 3HgO, which is more soluble in water than the neutral cyanide, and crystallises with less facility in small acicular crystals. Cyanide of mercury and potassium , KyCy . HgCy, is formed on dissolving cyanide of mercury in a solution of cyanide of potassium, and crystallises in regular octohedrons. Cyanide of mercury also forms crystallisable double salts with other cyanides, such as the cyanides of sodium, barium, calcium, magnesium, &c. It also combines with chlorides, bromides, iodides, and with several oxi-salts, such as cliromate and formiate of potash, with which it forms the compounds 2(K0 . CrOg) 4- HgCy and C2HKO, . IlgCy. Mercuric sulphate, HgO . SO3; 148 or 1850. — This salt is formed by boiling 5 parts of sulphuric acid upon 4 parts of mercury, till the metal is converted into a dry saline mass. Mercuric sulphate is a white crystalline salt, neutral in com- position, but, like most of the neutral salts of mercury, cannot exist in solution. Water decomposes it, forming a dense yellow subsulphate, and a solution of an acid sulphate. This subsulphate is known as turbith mineral^ a name applied to it by the older chemists, because it was supposed to produce effects in medicine analogous to those of a root formerly employed, and known as convolvulus turpcthura. The com- position of turbith mineral is 3HgO . SO3 or HgO . SO3 + 2HgO (Kane). Solution of ammonia converts both the neutral sul- phate and turbith mineral into a hea^y powder, which Kane names ammonio-turbith, and finds to be HgO.S03 + Hg.NH2 -|-2HgO. It is, therefore, analogous in composition to the yellow powder produced by the decomposition of white pre- * PhU. Trans. 1839, p. 113. MERCURIC SELENITES. 321 cipitate^ and may be regarded as a sulphate of tetramercuram- monium with 2 eq. water : NHg^ . SO4 + 2H0. Mercuric sulphites. — The neutral sulphite, HgO . SO2, may be formed by precipitating the nitrate, HgO . NO5, with an alkaline sulphate ; but it is very unstable, and resolves itself spontaneously into mercuric sulphate and metallic mercury. The basic sulphite^ 2HgO . SO2, is obtained by precipitating a solution of the basic nitrate, 2HgO . NO5, with an alkaline sulphite. It is a white, heavy powder, insoluble in water, and changing, when slightly heated, into mercurous sulphate; 2HgO . S02=Hg20. SO3. Iodide of potassium converts it into red mercuric iodide (Pean de St. Gilles).* A bisulphite, HgO . 2SO2 4- HO, is obtained as a white crystalline powder by pouring a saturated solution of bisulphite of soda on solid mercuric chloride. It dissolves readily in water, and is de- composed by heat, whether in solution or in the solid state, with separation of metallic mercury (Wicke).t By treating mercuric chloride with a solution of neutral sulphite of potash, a double salt, HgO . SO2 + HO, is obtained in small needle- shaped crystals, whose solution is neutral to test-paper. Similar salts are formed with the neutral sulphites of soda and ammonia. By treating mercuric chloride in excess with neutral sulphiteof soda, thesalt,2 (HgO. SOg) -f NaO. SOg + HO, is obtained, which is alkaline to test-paper. The solutions of these double sulphites are precipitated by hydrosulphuric acid and soluble sulphides, but not by alkalies. (Pean de St. GiUes.) Mercuric seleniate. — A hot aqueous solution of selenic acid forms with mercuric oxide prepared by precipitation, a soluble neutral seleniate, HgO . SeOg + HO, and a red insoluble basic salt, containing 2(3HgO . Se03) + H0 (Korner).t Mercuric selenite. — Mercuric oxide forms with aqueous * Ann. Ch. Phys. [3], xxxvi. 80. f Ann. Ch. Pharm. xcv. 176. % Pogg. Ann. Ixxxix. 146. z 4 323 MERCURY. selenious acid^ according to Berzelius, an insoluble neutral and a soluble acid selenite ; according to Kohler, on the other hand, selenious acid does not form any soluble salt with mer- curic oxide, but only a pale yellow amorphous salt, containing 7Hg0.4SeOj. Nitrates of the red oxide of mercury , Mercuric nitrates. — The neutral nitrate cannot be crystallised, but it is formed in solution when chloride of mercury is precipitated by nitrate of silver. When red oxide of mercury is dissolved in nitric acid, or when the metal is dissolved in the same acid with ebullition, till a drop of the solution no longer occasions a precipitate in water containing a soluble chloride, a subnitrate is formed, crystallising in small prisms, which are deliquescent in damp air. Its composition is expressed by the formula 2HgO .NOg-f 2H0. It is the only crystallisable nitrate of this oxide. Decomposed by water, this salt yields a yellow subnitrate, which, after washing with warm but not boiling water, is 3HgO . NO5 + HO. When the subnitrate is pre- pared by boiling water, it has a red colour, and probably consists of 6HgO . NO5 (Kane). Nitrate of mercury yields several compounds when treated with ammonia. («.) When a dilute and not very acid solu- tion of that salt is treated in the cold, witli weak solution of ammonia not added in excess, a pure milk-Avliitc precipitate appears, which is not granular, and remains suspended in the liquid for a considerable time. It was analysed by C. G. Mitscherlich, and to distinguish it from some other salts con- taining the same constituents, may be called Mitscherlich^ s ammonia-subnitrate. It contains 2HgO . IS O5 + HgNHg. [b.) The preceding compound is altered in its appearance by boiling water, and becomes much heavier and more granular, forming Soubeiraji's ammonia-subnitrate, the composition of which is found by Kane to be HgO . NO5 -f Hg . NH2 + 2HgO, or it resembles in constitution the bodies already described containing chlorine and sulphuric acid. This compound is MERCURIC NITRATES. 323 also formed by decomposing a dilute solution of mercuric nitrate with a slight excess of ammonia (Soubeiran). (c.) A third compound, the yellow crysialline ammonia-subnitrate, was obtained by C. G. Mitscherlich by boiling the ammonia subnitrate («) with excess of ammonia, and adding nitrate of ammonia, by which a portion of the powder is dissolved ; the solution, as it cools and loses ammonia, yields small crystalline plates of a pale yellow colour. The constituents of this salt are 2HgO . NO5 and NH3. Kane doubles its equivalent, and represents it as a compound of Soubeiran^s salt with nitrate of ammonia, as it appears to be produced by the solution of the former salt in the latter, (HgO . NO5 + Hg .NH2 + HgO) + NH4O . NO5. [d.) Soubeiran's ammonia subnitrate {a) is dissolved in considerable quantity, when boiled in a strong solution of nitrate of ammonia, and the solution deposits, on cooling, small but very brilliant needles, which were observed and analysed by Kane. This salt, which may be called Kane's ammonia subnitrate, is decomposed by water, nitrate of am- monia dissolving, and Soubeiran^s subsalt being left undis- solved. It contains the elements of 3(NH40 . NO5) and 4HgO. Kane believes that it is most likely to contain Soubeiran^s subnitrate ready formed, which leaves two atoms of nitrate of ammonia and two atoms of water to be otherwise disposed of.* These ammonia-nitrates, like the corresponding chlorides and sulphates, may be regarded as nitrates of mercuram- moniums, containing one or more atoms of mercury in place of hydrogen. Thus, Mitscherlich' s ammonia-subnitrate [a) is NHHgg.NOg + HO = nitrate of trimercurammonium with 1 eq. water; Soubeiran's salt {b) is NHg^ . N06 + 2HO = nitrate of tetramercurammonium with 2 eq. water; the crystal- line salt (c) is NH2Hg2 . NOg + HO = nitrate of bimercur- ammonium with 1 eq. water ; and [d) is a compound of [b) * Trans, of the Royal Irish Academy, toI. xix. pt. i. ; or, Ann. Ch. Phys. [2], Ixxii. 225. 324 MERCURY. with nitrate of ammonia and water = 2(NH4.N06) + 2H0 + (NHg^ . NOg + 2H0) . Nitrate of mercury forms an insoluble compound with sulphide of mercury, IlgO . NOg + SHgS, resembling the compounds of the sulphate and chloride with sulphide of mercury. It also forms double salts with iodide and cyanide of mercury. Alloys of mercury or amalgams. — Mercury combines with a great number of metals, forming compounds called amalgams , which are liquid or solid according as the mercury or the other metal predominates. A very small quantity of a foreign metal suffices to impair the fluidity of mercury in a very great degree. All amalgams are decomposed by heat, the mercury volatilising and the other metal remaining. The union of mercury with potassium and sodium is attended with considerable disengagement of heat ; the re- sulting amalgams are of a pasty consistence, and decompose water. The amalgams of tin and lead, when heated till they are quite liquid, and then left to cool slowly, yield solid crys- talline amalgams of definite constitution. An amalgam of silver, HgjAg, is found native in the form of regular dodeca- hedrons. An amalgam of tin is used for silvering glass. For this purpose a sheet of tinfoil is laid on a horizontal table, and mercury poured over the whole surface, so as to form a layer about l-5th or l-6th of an inch thick. The plate of glass is then slid along the surface in such a manner as to cut this layer in halves horizontally, which prevents the introduction of air-bubbles. The glass is then loaded with weights, so as to press out the excess of mercury ; and after a few days, the surface is found to be covered with a closely-adhering layer of an amalgam containing about 5 parts of tin to 1 of mercury. Mercury combines very readily with bismuth. An amal- gam obtained by heating a mixture of 497 pai'ts of bismuth. SEPARATION OP MERCURY. 325 310 lead, 177 tin, and 100 mercury, is very well adapted for injecting anatomical preparations : it is solid at ordinary tem- peratures, and has a silvery lustre, melts at 171*5 (Fah.), and solidifies at 140°. An amalgam of lead and tin, sometimes also containing bismuth, is used for covering the cushions of electrical machines. ESTIMATION OF MERCURY, AND METHODS OF SEPARATING IT «* FROM THE PRECEDING METALS. Mercury is generally estimated in the metallic state ; some- times, however, as sulphide, HgS, or as dichloride, Hg2Cl. To separate it from its compounds in the metallic state, it may be distilled with quicklime, in a tube of hard glass sealed at one end. Into this tube is introduced, first a layer of carbonate of lime, about an inch long ; then the mixture of the substance with quicklime; lastly, a layer of quick- lime about two inches long, and a plug of asbestos to keep the lime in its place. The open end of the tube is next drawn out into a narrow neck, and bent at an obtuse angle. The tube is laid in a combustion-furnace, the same as that which is used for organic analysis (I, 373), the neck being turned downwards and made to pass into a narrow-mouthed bottle containing water, so as to terminate just above the surface of the water. The tube is then gradually heated by laying pieces of red-hot charcoal round it, beginning at the part near the neck, containing the pure quicklime. This portion having been brought to a full red heat, the heat is carefully extended towards the middle part, to decompose the com- pound and volatilise the mercury : any portion of the com- pound that may volatilise undecomposed, will be decomposed in passing over the red-hot lime at the end. Lastly, the back part of the tube containing the carbonate is heated, so as to evolve carbonic acid gas and sweep out all the mercury vapour contained in the tube. The quantity of carbonic acid thus 326 MERCURY. evolved may be increased by mixing the carbonate of lime with bicarbonate of soda. The mercury condenses under the water in the bottle, which must be kept cold. The water is poured off as completely as possible ; the mercury transferred to a weighed porcelain crucible ; the greater part of the water which still adheres to it removed by means of blotting-paper ; the drying completed over sulphuric acid ; and the mercury finally weighed. Mercury may also be precipitated from its solutions in the metallic state by protochloride of tin, or by phosphorous acid ; the solution then decanted ; the mercury washed with water ; and dried in the manner just described. Mercury is also frequently precipitated from its solutions, as a sulphide, by hydrosulphuric acid. In that case, if the precipitate consists of the pure protosulphide, HgS, as when it is thrown down from a solution of corrosive sublimate, the precipitate may be simply collected on a weighed filter, washed, dried over the water-bath, weighed, and the quantity of mercury thence determined. But if, as is generally the case, the precipitate also contains free sulphur, as when it is thrown down from a solution containing a ferric salt, or a considerable excess of nitric acid, — or if it be precipitated in conjunction with the sulphides of other metals, then the mer- cury must be separated from it by distillation with lime, as above described. Or again, the mixture of sulphides may be converted into chlorides by gentle heating in a stream of chlorine gas, the volatile chloride of mercury passed into water, and the mercury precipitated from the solution by protochloride of tin. The precipitation of mercury in the form of dichloride is best effected by means of hydrochloric acid and formiate of potash or soda. If the mercury is contained in an alloy, the alloy must be dissolved in aqua-regia ; if it is contained in solution in the form of mercuric nitrate, hydrochloric acid must be added, the solution, in either case, nearly neutralised SEPARATION OF MERCURY. 327 ^vith potash, formiate of potash or soda thea added, and the whole exposed for some days to a temperature between 140° and 176° F. (at the boiling heat, the mercury would be re- duced to the metallic state.) The dichloride then precipitates, and must be collected on a weighed filter, washed, dried at a gentle heat, and weighed. The quantity of mercurous oonide present in a solution may also be determined by precipitation with hydrochloric acid. The solution must, however, be very dilute, and be kept cool ; it must also contain but a very small quantity of free nitric acid, as a larger quantity would convert the dichloride of mercury into protochloride. To determine the proportions of mercurous and mercuric oxide, when they exist together in solution, the mercurous oxide is first precipitated with hydro- chloric acid, and the remaining mercury by protocjiloride of tin or hydrosulphuric acid. Mercury may be separated from all other metals, except arsenic and antimony, by its superior volatility. When it exists in the form of an amalgam, the compound is simply heated, and the quantity of mercury determined by the loss of weight. If it exists as an oxide, chloride, &c., combined with compounds of other metals, it may be separated by dis- tillation with quicklime, as above described. Its separation from the alkalies and earths, and from uranium, manganese, nickel, cobalt, iron, zinc, and chromium, may also be effected by precipitation with hydrosulphuric acid. From bismuth and cadmium it may be separated by reduction with proto- chloride of tin; from copper, by mixing the solution with excess of cyanide of potassium, and passing hydrosulphuric acid through the liquid, whereby the mercury is precipitated as sulphide, while the copper remains dissolved ; from lead, by precipitating that metal with sulphuric acid; also by treating the solution with excess of cyanide of potassium, which precipitates the lead, but not the mercury. From arsenic, tin and antimony, mercury is separated by the solubility of the sulphides of those metals in sulphide of ammonium. 328 SILVER. SECTION 11. SILVER. Eq. 108, or 1350; Ag [argentum). This metal is found iii various parts of the world, and oc- curring often in the metallic state, and being easily melted, must have attrabted the attention of mankind at an early period. Before the discovery of America, the silver mines of Saxony were of considerable importance ; but the silver mines of Mexico and Peru far exceed in value the whole of the European and Asiatic mines, the former having furaished during the last three centuries, according to Humboldt, 316 millions of pounds troy of pure silver. A considerable quantity of silver is obtained from ores of lead by cupellation, as described under that metal. From argentiferous copper ores also the silver is exti'actcd by a pro- cess called liquation^ which consists in fusing the coarse copper (p. 93.) with three times its weight of lead ; a mix- ture of two alloys is then obtained, the more fusible of which, containing the greater part of the lead and nearly all the silver, is separated by the application of a moderate heat, and yields the silver by cupellation. Native silver, which is in the form of threads or thin leaves, is separated from the gangue or accompanying rock, by amaU gamation, a process which is also followed in the treatment of the most frequent ore of silver, the sulphide, when it is not accompanied by sulphide of lead. At Freiberg, in Saxony, the sulphide of silver, ground to powder, is roasted in a reverbera- tory furnace with 10 per cent, of chloride of sodium, by which the silver is converted into chloride. It is then introduced into barrels (fig. 19.), with water, iron, and a quantity of metallic SILVER. 329 mercury, and the materials kept in a state of agitation for eighteen hours by the revolution of the barrels on their axes. The chloride of silver. ^- ,q ' iug. ly. although insoluble, is reduced to. the metallic state by the iron, and chloride of iron is produced, while the silver forms a fluid compound with the mercury. By adding more water, and turning the barrels more slowly, the fluid amalgam separates and subsides. It is drawn off and subjected to pressure in a chamois leather bag, the mercury passing through the leather^ while a soft amalgam of silver remains in the bag. The mercury is afterwards separated from this amalgam by a species of distillation, per descen- swTij and the silver remains. In South America, where fuel is scarce, a different process is adopted. The ore, in a finely divided and moist condition, is exposed for a considerable time to the successive action of common salt, sulphate of copper (obtained by roasting copper pyrites), and mercury, the materials being spread on a paved floor, and trodden by men or horses to effect an intimate mix- ture ; and the silver amalgam thus obtained is separated from the exhausted ore by washing with water. In this process, the chloride of sodium and sulphate of copper form sulphate of soda and protochloride of copper. The latter gives up chlorine, converting part of the silver into chloride, and separates the sulphur, provided an excess of chloride of sodium is present to dissolve the dichloride of copper as it forms. The dichloride of copper then acts upon another portion of the sulphide of silver, forming disulphide of copper and chloride of silver: Cu^Cl + AgSrrrCu^S + AgCl. The chloride of silver thus produced, dissolves in the chloride of sodium, and is decomposed by the mercury subsequently 330 SILVER. added, yielding calomel and metallic silver. This process is always attended with considerable loss of mercury, which however may be diminished by the previous addition of iron. Mr. P. Johnston proposes to diminish the loss of mercury, as soluble chloride, which occurs in this process, by using an amalgam of zinc and mercury, instead of pure mercury. Silver is obtained free from other metals, and in a state of purity, for chemical and other purposes, by the following processes : — 1 . The metal is dissolved in pure nitric acid slightly diluted, and precipitated by a solution of chloride of sodium, the salts of the other metals present remaining in solution. The insoluble chloride of silver, thus obtained, is thoroughly washed upon a filter with hot water and dried. A quantity of carbonate of potash, equal to twice the weight of the silver, is then fused in a crucible, and the chloride of silver gradually added to it, whereupon cldoridc of potassium is formed, and carbonic acid and oxygen escape with effer- vescence. The crucible is then exposed to a heat sufficient to fuse the reduced silver, which subsides to the bottom. — 2. The mode of separating silver from the common metals, in the ordinaiy practice of assaying, is, like many mctallurgic opera- tions, an exceedingly elegant and refined process. A portion of the silver alloy, the assay, is fused with several times its weight of pure lead (an alloy of 1 copper and 15 silver with 96 lead, for instance) upon a bone-earth cupel, which is sup- ported in a little oven or muffle, heated by a proper furnace. Air being allowed access to the assay, the lead is rapidly oxi- dated, and its highly fusible oxide imbibed, as it is produced, by the porous cupel. The disposition of copper and other common metals to oxidate is increased by the presence of the lead; and their oxides, which form fusible compounds with oxide of lead, are removed in company with the latter, ^hen the foreign metal is almost entirely removed, the assay is observed to become rounder and more brilliant, and the last trace of fused oxide occasions a beautiful play of prismatic SILVER. 331 colours upon its surface, after which the assay becomes, in an instant, much whiter, ov flashes, an indication that the cupel- lation is completed. Pure silver may also be obtained from an alloy containing only silver and copper, by precipitating the two metals with excess of carbonate of soda with the aid of heat, boiling the precipitate for about ten minutes with a solution of grape- sugar, whereby the copper is reduced to the state of red oxide, and the silver to the metallic state, and treating the moist precipitate with a hot solution of carbonate of ammonia: the copper then dissolves, and pure silver remains. Pure silver is the whitest of the metals, and susceptible of the highest polish ; when granulated by being poured from a height of a few feet into water, its surface is rough, but its aspect peculiarly beautiful. It crystallises in cubes and regular octohedrons, both from a state of fusion and by precipitation from solution. Silver is in the highest degree ductile and malleable; its density varies between 10-474 and 10*542; it fuses at 1873^ When in the liquid state, it is capable of absorbing oxygen gas from the air, which is discharged again in the solidification of the metal, and gives rise to a sort of vegetation upon its surface, or even occasions the projection of small portions of the silver to a distance, an accident which is known in assaying as the spitting of the metal, Gay-Lussac observed, that when a little nitre was thrown upon the surface of melted silver in a crucible, and the whole kept in a state of fusion for half an hour, a very considerable absorption of oxygen took place. "When the crucible was removed from the fire and quickly placed under a bell-jar filled with water, which can be done without danger, the silver discharged a quantity of oxygen equal to 20 times its volume. This property is possessed only by pure silver, and does not appear at all in silver con- taining 1 or 2 per cent, of copper. As oxide of silver is re- duced by a red heat, the absorption of the oxygen by the VOL. II. A A 332 SILVER. fluid metal must be a phenomenon of a different nature from simple oxidation. Silver does not combine witli the oxygen of the air at the usual temperature, nor even when heated ; the tarnishing of polished silver in air is occasioned by the formation of sul- phide of silver. Silver does not dissolve in any hydrated acid, by substitution for hydrogen, but on the contrary is dis- placed from solution in an acid by hydrogen, and precipi- tated in the metallic state. This metal is also precipitated by mercury and by all the more oxidable metals. Its salts are reduced at the usual temperature by sulphate of iron, the protoxide in which is converted into sesquioxidc. But if the ferric sulphate is boiled upon the precipitated silver, the latter is dissolved again, and oxide of silver and protoxide of iron reproduced. Silver, however, is oxidated when fused or heated strongly in contact with substances for which oxide of silver has a great affinity, as with a siliceous glass, and stains the glass yellow. It is oxidated by concentrated sulphuric acid, with evolution of sulphurous acid. Silver is readily dissolved by nitric acid, at a gentle heat, and with much violence, at a high temperature, nitrate of silver being formed, and nitric oxide escaping. Silver combines in three propor- tions with oxygen, forming a suboxide, AgjO, a protoxide AgO, and a peroxide, AgOg. Suboxide of silver, K^j^- — I*^^e protoxide of silver is com- pletely reduced to the state of metal by hydrogen gas, at 212° ; but the oxide contained in citrate of silver loses only half its oxygen under the same circumstances, the suboxide being formed and remaining in combination with one half of the citric acid of the former salt. The aqueous solution of the suboxide salt is dark brown, and the suboxide is precipi- tated black from it by potash. When the solutioYi of the subsalt is heated, it becomes colourless, and metallic silver appears in it. The salt dissolves with a brown colour in ammonia. Several other salts of silver, containing organic PROTOXIDE OP SILVER. 333 acids^ comport themselves in the same way as the citrate, when heated in hydrogen.* A solution of protoxide of silver in ammonia deposits on exposure to the air, a grey suboxide, containing 108 parts of silver to 5*4 parts oxygen. When heated, it gives off oxygen and leaves metallic silver (Fara- day). f Protoxide of silver, AgO, 116 or 1450. — This oxide is thrown down, when potash or lime-water is added to a solution of nitrate of silver, as a brown powder, which becomes of a darker colour when dried. The powder was found to be anhydrous by Gay-Lussac and Thenard j its density is 7*143, according to J. Herapath ; 7'250, according to P. Boullay ; 8*2558, according to Karsten. Oxide of silver is decomposed by light, or at a red heat, into oxygen gas and metallic silver. Hydrogen reduces it even at 212°. It is also reduced by an aqueous solution of phosphorous acid. When recently preci- pitated, it is decomposed by aqueous sulphurous acid, yielding metallic silver and sulphate of silver; but the decomposition is only partial, even when aided by heat. When immersed in water, it is reduced by zinc, cadmium, tin, and copper, but not by iron or mercury. In an aqueous solution of hypochlorous acid, it is converted into chloride of silver, oxygen being evolved together with a small quantity of chlorine. Oxide of silver is a powerful base, and forms salts, several of which have been found isomorphous with the corresponding salts of soda. Like oxide of lead, it dissolves to a small extent in pure water free from saline matter, and the solution has an alkaline reaction. Oxide of silver is not dissolved by solutions of the hydrates of potash and soda. Its salts are precipitated black by hydrosulphuric acid and alkaline sul- phides. When treated with hydrochloric acid or a soluble chloride, they yield a white cm^dy precipitate, the chloride of silver, which soon becomes purple, if exposed, while moist, to * Ann. Ch. Pharm. xxx. 1. f Ann. Ch. Pbys. [2], ix. 107. A A 2 33i SILVER. the direct rays of the sun. This precipitate is not dissolved by nitric acid^ but is dissolved by ammonia in common with most of the insoluble salts of silver. This precipitate is visible, according to Lassaigne, even in solutions containing only 1 part of silver in 800,000 parts of liquid. In a solution containing 1 part of silver in 200,000 parts, hydrochloric acid or common salt produces a slight tm-bidity ; with 1 part of silver in 400,000, the same reagents produce a scarcely per- ceptible opalescence ; and if the proportion of liquid amounts to 800,000 parts, the opalescence does not show itself for a quarter of an hour. Hydrobromic acid and soluble metallic bromides J added to solutions of silver salts, throw down all the silver in the form of yellowish white bromide, insoluble in nitric acid, and sparingly soluble in ammonia. Hydriodic acid and soluble iodides form a pale yellow precipitate of iodide of silver, likewise insoluble in nitric acid, and still less soluble in ammonia. Hydrocyanic acid and soluble cyanides throw down a white precipitate of cyanide of silver, easily soluble in ammonia, insoluble in cold dilute nitric acid, but dissolved by strong nitric acid at a boiling heat, with evolu- tion of nitric oxide. Ammonia added in very small quantity to perfectly neutral silver-salts, produces a slight brown pre- cipitate of oxide of silver, easily soluble in excess ; but if the solution contains excess of acid, ammonia produces no preci- pitate. Potash added to the ammoniacal solution produces a white precipitate, provided the excess of ammonia be but small. The fixed alkalies form, in neutral or acid solutions of silver-salts, a brown precipitate of oxide of silver, insoluble in excess. Alkaline carbonates precipitate white carbonate of silver, soluble in ammonia and carbonate of ammonia. Ordinary tribasic phosphate of soda forms a yellow precipi- tate; pyrophosphate and metaphosphate of soda form white precipitates. Chromate of potash forms a dark crimson pre- cipitate of chromate of silver. Alkaline arsenites form a canary-yellow precipitate of arsenite of silver. Oxalic acid PROTOXIDE OF SILVER. 335 forms a white pulverulent precipitate of oxalate of silver. Silver is precipitated from its solutions in the metallic state by phosphorus, phosphorous acid, phosphuretted hydrogen, and sulphurous acid (imperfectly) ; by various metals, viz., zinc, cadmium, tin, lead, iron, manganese, copper, mercury, bis- muth, tellurium, antimony, and arsenic ; also by protoxide of uranium, hydrated protoxide of manganese, and protoxide of tin; and by various organic substances at a boiling heat, e. g., charcoal, sugar, aldehyde, formic acid, tincture or infusion of galls, and volatile oils. Many organic substances added to a solution of nitrate of silver mixed with excess of ammonia, throw down metallic silver in the form of a beautiful specular film lining the sides of the vessel. This eflPect is produced by aldehyde, saccharic acid, salicylous acid, pyromeconic acid, and various essential oils. A mixture of oil of cinnamon and oil of cloves is found to produce an exceedingly brilliant speculum, and has indeed been used for silvering mirrors in place of the ordinary process with tin and mercury ; it is par- ticularly adapted for silvering curved surfaces. A very bright and regular specular surface is also produced by adding a solution of milk-sugar to an ammoniacal solution of nitrate of silver mixed with caustic potash or soda; the precipitation then takes place without the application of heat (Liebig) .* Oxide of silver combines with ammonia and forms the ful- minating ammoniuret of silver, a substance of a dangerous character from the violence with which it explodes. The ammoniuret may be formed by digesting newly precipitated oxide of silver in strong ammonia, or more readily by dis- solving nitrate of silver in ammonia, and precipitating the liquor by potash in slight excess. If this substance be pressed by a hard body, while still moist, it explodes with unequalled violence ; when dry, the touch of a feather is_ often sufficient to cause it to fulminate. The explosion is obviously occa- * Ann. Ph. Pharm. xcviii. 132. A A 3 336 SILVER. sioned by the reduction of the silver from the combination of its oxygen with the hydrogen of the ammonia, and the evolu- tion of nitrogen gas. Sulphide of silver j AgS, 124 or 1550. — Sulphur and silver may be combined together by fusion ; the excess of sulphur escapes,, and at a high temperature the sulphide melts; it forms^ on coohng, a crystalline mass. This compound has a lead-grey colour and metallic lustre. It is so soft that it may be cut ^dth a knife, and is malleable. The sulphide of silver is also rcmai'kable for conducting electricity, like a metal, when warmed. The same compound occurs in nature, some- times crystallised in octohedi'ons with secondary faces. This sulphide is particularly interestmg from being isomorphous with the subsulphide of copper, AgS with CujS (page 144). These two sulphides replace each other in indeterminate pro- portions in several double sulphides of silver and other metals, as in polybasite and fahl-ores, the composition of which may be expressed by the following formulae, the symbols placed above each other representing constituents, of which cither the one or the other may be present : Polybasite . O^^^f +^^^3 -p ,, /,ZnS^ SbSA , o/.AgS , SbSA Fahl-orcs {^^^.^^ +AsS3) + H^Cu,S+AsS3)- Chloride of silver, AgCl, 143*5 or 1793-75. — This salt contains in 100 parts, 21*G9 parts of chlorine, and 75-31 parts of silver. It is found native as horn-silver , in trans- lucent cubes or octohedrons of a greyish-white colour, and specific gravity 5-55. The same compound is also thrown down as a white precipitate, at first very bulky and curdy, when hydrochloric acid or a soluble chloride is added to any soluble salt of silver, except the hyposulphite. It is wholly insoluble in water, and the most miimte quantity of hydro- chloric acid contained in water may be detected by adding to CHLORIDE OF SILVER. 337 it a drop of a solution of nitrate of silver (p. 336.) Hydro- cUoric acid, when concentrated, dissolves chloride of silver, which crystallises from it in octohedrons, when the solution is evaporated. This salt dissolves easily in solution of am- monia, and crystallises also as the ammonia evaporates. When heated, it fuses at about 500°, forming a transparent yellowish liquid, which becomes, after cooling, a mass that may be cut with a knife, and has considerable resemblance to horn: a property to which it was indebted for the name of horn-silver, applied to it by the older chemists. It is not volatile. Chloride of silver is not affected by a concentrated solution of potash. It is easily reduced to the state of metal by zinc or iron with water. Chloride of silver may be dissolved out in this way by means of zinc and acidulated water, from a porcelain crucible in which it has been fused. To obtain pure silver by this mode of reduction, it is necessary to use zinc free from lead, otherwise that metal, not being dissolved by the sulphuric acid, remains mixed with the silver. A better mode of reduction is to boil the chloride of silver with an equal weight of starch-sugar and a solution of one part of carbonate of soda in three parts of water (Bottger). The chloride and other salts of silver acquire a dark colour when exposed to light ; chlorine escapes, and a portion of the salt appears to be reduced to the metallic state, as the blackened surface conducts electricity. According to Wetzlar, the black substance contains an inferior chloride of silver, and is not attacked by nitric acid, or soluble in ammonia. It has also been supposed that the blackening is due, not to any chemical decomposition, but merely to a change in the state of aggre- gation of the particles. It appears, however, from some recent experiments by Dr. F. Guthrie, that the chloride is com- pletely decomposed and metallic silver separated, even in presence of free nitric acid. Paper charged with chloride of silver is very sensitive to the impression of light, and is the material used for positive photographs, tlie unaltered chloride A A 4 338 SILVER. being afterwards dissolved out by a solution of hyposulphite of soda. One hundred parts of chloride of silver absorb 17'9 parts of ammoniacal gas, forming the compound, 3NH3 . 2AgCl, or N H(NH4)2Ag| ^^^^ ,pj^.g compound gives off its ammonia in the air. Chloride of silver is dissolved by concentrated and boiling solutions of the chlorides of potassium, sodium, and ammonium, and, on cooling, a double salt is deposited in crystals, generally cubes. Chloride of silver is also dissolved by cyanide of potassium, and the solution yields a double salt by evaporation (Liebig). Bromide of silver^ AgBr, 188 or 2350. — This salt consists in 100 parts, of 42*56 bromine and 57*M' silver. It is found native in Mexico and in Bretagne ; sometimes in small amorphous masses, sometimes in greenish-yellow octohedral crystals. It is insoluble in water, and falls as a precipitate which is white at first, but becomes pale yellow when col- lected. When fused and cooled, it yields a mass of a pure and intense yellow colour. It has most of the properties of chloride of silver, but dissolves very sparingly in ammonia. Iodide of silver, Agl, 231-36 or 2929-5.— This salt con- tains in 100 parts, 53*87 of iodine and 16*13 of silver. It is found native, sometimes in regular hexagonal prisms. It is insoluble in water, like the chloride, and is prepared in a similar manner by precipitation, but is distinguished from that salt by its colour, which is pale yellow, by the difficulty with which it is dissolved in ammonia, ])eing even less soluble than the bromide, and by being blackened more slowly by the action of light. According to Martini, 2500 parts of am- monia, of density 0-960, are required to dissolve one part of iodide of silver. It is soluble to a large extent, at the boiling temperature, in concentrated solutions of the alkaline and earthy iodides, and forms with them double salts. Silver is rapidly dissolved by hydriodic acid, ^vith evolution SALTS OF SILVER. 339 of hydrogen. If the action is assisted by heat, the solution deposits, on cooling, a colourless crystalline salt, resembling nitrate of silver, but decomposing as soon as it is sepa- rated from the liquid : it appears to consist of an iodide of silver and hydrogen. The mother-liquor, when left to itself, deposits iodide of silver in large regular six-sided prisms, resembling the native iodide (H. Ste.-Claire Deville).* Fluoride of silver, AgF, is obtained by dissolving the oxide or carbonate in hydrofluoric acid. It is very soluble in water, and is partly decomposed by evaporation. Cyanide of silver, AgCy; 134 or 1675. — This salt contains, in 100 parts, 19*41 cyanogen and 8059 silver. It falls as a white powder when hydrocyanic acid is added to a solution of nitrate of silver. It is distinguished from chloride of silver by dissolving in concentrated nitric and sulphuric acids, when heated. It is readily decomposed by hydrochloric acid, and yields hydrocyanic acid, 100 parts of cyanide of silver giving 20-36 parts of hydrocyanic acid. It is decomposed by a red heat, giving off half its cyanogen and leaving paracyanide of silver, AggCya- Cyanide of silver is dissolved by cyanide of potassium, and other soluble cyanides. The double cy- anide of potassium and silver crystallises in octohedrons, KCy.AgCy. Carbonate of silver, AgO . CO2, is a white insoluble powder. Sulphate of silver, AgO.SOaJ 156 or 1950.— Obtained by dissolving silver, with heat, in concentrated sulphuric acid, or by precipitating a solution of nitrate of silver with sulphate of potash. It is soluble in 88 times its weight of boiling water, and crystallises, on cooling, in the form of anhydrous sulphate of soda. This salt is highly soluble in ammonia, and gives, by evaporation, an ammoniacal sulphate of silver in fine transparent crystals, which are persistent in air; AgO.SOg + 2NH3, or NHalNHJAg . SO4. Chromate and * Compt. rend. xlii. 894. 340 SILVER. seleniate of silver form analogous compoands with am- monia, which are all isomorphous. The bichromate of silver is also isomorphous with bichromate of soda. Hyposulphate of silver ^ AgO . S2O5, is soluble in water, and crystallises in the same form ;is hyposulphate of soda. It crystallises also with ammonia, as AgO . S20g -f 2NIi3, or Hyposulphite of silver, AgO . SjOg. — Hyposulphurous acid appears to have a greater affinity for oxide of silver than for any other base. Oxide of silver decomposes the alkaline hyposulphites, liberating one-half of their alkali, and forming a double hyposulphite of the alkali and silver. These double salts are best prepared by adding chloride of silver in small portions to the soluble hyposulphite of potash, soda, ammonia, or lime in the cold, till the liquid is saturated ; after w hich, the solution is filtered, and mixed with a large quantity of alcohol, which precipitates the double salt; the potash and soda salts are crystallisable. Herschel considers the double salts obtained in this manner as probably containing one eq. of hyposulphite of silver to two eq. of the other hyposulpliite. The solution of one of these double salts dissolves more oxide of silver, and forms a double salt, which is believed to contain single equivalents of the salts, and precipitates as a white crystalline, pulverulent, bulky mass. The second com- pound is sparingly soluble in water, but dissolves in ammonia, and communicates to the liquor an intensely sweet taste. The hyposulphite of silver itself is an insoluble substance ; it is prone to undergo decomposition, changing spontaneously into sulphate and sulphide of silver. When to a dilute solu- tion of nitrate of silver, a dilute solution of hyposulphite of soda is added by small quantities, a white precipitate of hypo- sulphite of silver falls, which dissolves again in a few seconds, from the formation of the soluble double hyposulphite of soda and silver. When enough of hyposulphite of soda has been NITRATE OF SILVER. 341 gradually added to render the precipitate permanent, without, however, decomposing the whole silver salt, a flocculent mass is obtained of a dull grey colour, which is permanent. The liquor contains much hyposulphite of silver, and has an in- tensely sweet taste, not at all metallic ; the silver is not pre- cipitated from it by hydrochloric acid or the chlorides. An excess of hyposulphite of soda destroys the precipitated hypo- sulphite of silver, converting it into sulphide of silver. Nitrate of silver, AgO . NO5; 170 or 2125, — When a piece of pure silver is suspended in nitric acid, it dissolves for a time without effervescence at a low temperature, nitrous acid being produced, which colours the liquid blue ; but if heat be applied or the temperature allowed to rise, then the metal dis- solves with violent effervescence, from the escape of nitric oxide. The nitrate of silver crystallises on cooling in colour- less tables, which are anhydrous. It is soluble in 1 part of cold, in \ part of hot water, and in 4 parts of boiling alcohol. The solution of this salt does not redden litmus paper, like most metallic salts, but is exactly neutral. Nitrate of silver fuses at 426°, and forms a crystalline mass on cooling ; it is cast into little cylinders for the use of surgeons. It is some- times adulterated in this state with nitrate of potash, which may be detected by the alkaline residue which the salt then leaves when heated before the blowpipe, — or with nitrate of lead, in which case the solution of the salt is precipitated by iodide of potassium, of a full yellow colour. When applied to the flesh of animals, it instantly destroys the organisation and vitality of the part. It forms insoluble compounds with many kinds of animal matter, and is employed to remove it j&'om solution. When organic substances, to which a solution of nitrate of silver has been applied, are exposed to light, they become black from the reduction of the oxide of silver to the metallic state. A solution of nitrate of silver in ether is em- ployed to dye the hair black. One part of nitrate of silver and 4 parts of gum arable dissolved in 4 parts of water, and 342 SILVER. blackened with a small quantity of Indian ink, form the inde- lible marking ink used to write upon linen. The part of the linen to be marked should be first wetted with a solution of carbonate of soda and dried, and the writing should be exposed to the light of the sun. For this ink, which is expensive, another liquid has been substituted by bleachers, namely coal tar, made sufficiently thin with naphtha to write with, which is found to resist chlorine, and to answer well as a marking ink. A strong solution of nitrate of silver absorbs two equivalents of ammoniacal gas, and forms the crystallisable Ammoniacal nitrate of silver, AgO .NOg-f 2NH3=N H^lNIIJAg'.NOe. The dry nitrate in powder absorbs three atoms of ammonia, AgO.N06 + 3NH3=NH(NHj2Ag\ NOg. Nitrate of silver forms a double salt with nitrate of the red oxide of mercury, which crystallises in prisms. Nitrate of silver and cyanide of mercury also form a double salt, when hot solutions of them are mixed : AgO.N05 + 2HgCy + 8HO. Cyanide of silver is soluble in a boiling solution of nitrate of silver, and forms a crystalline compound, AgO . NO5 + 2 AgCy, which is decomposed by water. Nitrite of silver, AgO . NO3 ; 154 or 1925. — Nitrate of soda is fused at a red heat, till it is wholly converted into ni- trite by loss of oxygen ; the latter salt then begins to give off nitrous acid, and a small portion of the salt dissolved in water will be found to precipitate silver brown. The fusion is then interrupted, the salt dissolved in boiling water, precipitated by nitrate of silver, and filtered while still very hot. The nitrite of silver, which requires 120 times its weight of water at 60° to dissolve it, is precipitated as the solution cools. The other nitrites are prepared by rubbing this salt in a mortar with chlorides taken in equivalent quantities. It appears from experiments of Proust, that two subnitrites of silver exist, one soluble and the other insoluble. Acetate of silver, wliich is soluble in 100 times its weight ALLOYS OF SILVER. 343 of cold water, is precipitated when acetate of copper is mixed witli a concentrated solution of nitrate of silver. It crys- tallises from solution in boiling water in anhydrous needles. Oxalate of silver is an insoluble powder. A double oxalate of potash and silver is formed by saturating binoxalate of potash with carbonate of silver. It is very soluble, and forms rhomboidal crystals, which are persistent in air. Peroxide of silver. — A superior oxide of silver is deposited upon the positive pole or zincoid of a voltaic battery in a weak solution of nitrate of silver, in the form of needles of 3 or 4 lines in length, which are black and have a metallic lustre, while metallic silver is, at the same time, deposited in crystals upon the negative pole or chloroid. The former crystals are converted by sulphuric acid into oxide of silver and oxygen, and yield with hydrochloric acid, chloride of silver and chlorine. According to Fischer, whose observa- tions are confirmed by L. Gmelin, the peroxide prepared as above from nitrate of silver always retains nitric acid, and if prepared in a similar manner from the sulphate, it always retains sulphuric acid.* Alloys of silver. — Silver may be readily alloyed with most metals. It combines by fusion with iron, from which it cannot be separated by cupellation. Native silver is always associated with gold ; the two metals are found crystallised together in all proportions in the same cubic or octohedral crystals. Gold may be detected in a silver coin, by dissolving the latter in pure nitric acid, when a small quantity of black powder remains, which after being washed with water, will be found to dissolve in nitro-hydrochloric acid, giving a yellow solution, in which protochloride of tin produces a pre- cipitate of the purple powder of Cassius. Pure silver, being very soft, is always alloyed in coin and plate, with a certain * Gmelin's Handbook, Translation, vi. 145. 344 SILVER. quantity of copper, to make it harder. The standard silver of England is an alloy of 222 pennyweights of silver with 18 pennyweights of copper.,, or it contains 92*5 per cent, of silver. The standard of the Spanish dollar, of the French and most other coinages, is 90 per cent, of silver. The alloy of silver and copper of greatest stability consists of 71*9 silver, and 28" 1 copper, and corresponds with the formida AgCu^.^ ESTIMATION OF SILVER, AND METHODS OF SEPARATING IT FROM OTHER METALS. Silver, when in the state of solution, is always estimated as chloride. The solution, if not already acid, is slightly acidu- lated with nitric acid; the silver precipitated with hydro- chloric acid, and the liquid placed for some hours in a warm situation to cause the precipitated chloride of silver to settle down. The precipitate is collected on a filter, which should be as small as possible, washed with water, and dried at 212°. It must then be separated as completely as possible from the filter; introduced into a porcelain crucible, previously weighed ; the filter burnt to ashes outside the crucible ; the ashes added to the contents of the crucible ; and the whole strongly heated over a lamp till the chloride of silver is brought to a state of tranquil fusion, after which it is left to cool and weighed. It contains 75-2G per cent, of silver. This mode of estimation is affected with an error, arising from the partial reduction of the chloride of silver by the organic matter of the filter. The error thus occasioned is but slight when the process is well conducted, and may always be obviated by treating the fused chloride after cool- ing with nitric acid to dissolve the reduced silver; then adding hydrochloric acid, evaporating to dryness, and again fusing the residue. Another mode of proceeding is to collect the chloride of silver on a weighed filter, and dry it in an oil- ■ * Levol, Ann. Ch. Phys. [3], xxxvi. 220. ESTIMATION OF SILVER. 345 bath, at about 300° P. The chloride may also be washed by decantation, and the use of a filter avoided altogether ; but the washing requires very careful manipulation. The quantity of silver in a solution may also be determined by precipitating it with a solution of chloride of sodium of known strength. The solution of chloride of sodium is made of such a strength that a cubic decimetre of it exactly pre- cipitates 1 gramme of pure silver. It is added to the silver solution from a burette, divided into cubic centimetres, the liquid being well shaken after each addition, to cause the precipitate to settle down. The number of cubic centimetres of solution thus added determines the quantity of silver present. As silver is reduced from many of its salts by the mere action of heat, the quantity of silver in such compounds may be readily determined by simply igniting them in a porcelain crucible. This method is applicable to nearly all salts of silver which contain organic acids. It must be observed, however, that in some cases, a certain quantity of carbon re- mains combined with the silver, and that some organic silver compounds containing nitrogen leave cyanide of silver when ignited. The method of precipitating by hydrochloric acid serves to separate silver from all other metals. If lead be present in solution with silver, the liquid must be diluted with a large quantity of water before the hydrochloric acid is added; because the chloride of lead is but sparingly soluble. The separation of silver from lead may also be effected by pre- cipitating both the metals as chlorides, and dissolving the chloride of silver in ammonia. To separate silver from mer- cury, the latter metal, if in the state of mercurous oxide, must first be converted into mercuric oxide by oxidation with nitric acid. The estimation of the quantity of silver in alloys, such as coins, is usually effected either by cupellation in the manner 34() GOLD. already described (p. 332.), or by dissolving the alloy in nitric acid, and precipitating the silver with a graduated solution of chloride of sodium.* The cupellation of silver is always attended with a certain loss, arising partly from a portion of the melted silver being absorbed by the cupel, and partly by volatilisation. The loss thus occasioned varies with the proportion of lead employed in the cupellation, with the proportion of silver in the aUoy, and likewise with the heat of the furnace : hence the results obtained require a certain correction, the amount of which must be determined by special trials made upon alloys of known composition and with different proportions of lead. SECTION III. GOLD. Eq. 98-33 or 1229*16; Au. (Aurum.) Gold is found in small quantity in most countries, some- times mixed with iron pyrites, copper pyrites, and galena, but generally native, massive, and disseminated in threads through crystalline rocks, such as quartz, or in grains among the sand of rivers, and in allmial deposits formed by the disintegration of ancient rocks. In these deposits, some of which are of great extent, gold is occasionally found in masses of consider- able size, called iiuggets. Formerly, the principal supply of this metal was from the mines of South America, Ilungarj^, and the Uralian mountains; but of late years, the largest quantities have been obtained from California and Australia. Native gold is sometimes pure, but is more frequently asso- ciated in various proportions with silver. * The process, by Guy-Lussac, for lliis purpose is described, with the re- quisite Tables, in the Parhaniciitary Keport upon the Koyal Mint, 1837, Appendix, p. 145. See also Dr. Mdler's Elemcuis of Chemistry^ p. 1035. GOLD. ' 347 Gold is separated from the substances with which it is me- chanically associated, either by washing with water, whereby the earthy matters are carried away while the heavy gold particles remain behind, or by amalgamation. The small quantity of gold which occurs, generally associated with silver, in certain lead and copper ores, is extracted by liqua- tion and cupellation, in the manner already described for silver. By these processes, gold is obtained free from all other metals except silver, and from this it may be separated by nitric acid, which dissolves the silver, but only when it forms a large proportion of the alloy. When nitric acid does not dissolve the silver, the alloy is submitted to an operation termed quartation, which consists in fusing it with four times its weight of silver, after which the whole of the silver may be dissolved out by nitric acid. Pure gold may be obtained from any alloy containing it, by dissolving the alloy in a mixture of two measures of hy- drochloric and one measure of nitric acid; separating the solution from insoluble chloride of silver by filtration ; eva- porating it over the water-bath till acid vapours cease to be exhaled ; then dissolving the residue in water acidulated with hydrochloric acid; and adding protosulphate of iron, which completely precipitates the gold in the form of a brown or brownish-yellow powder, the protosulphate of iron being at the same time converted into sesquisulphate and sesqui- chloride : 6(FeO . SO3) + AU2CI3 = 2(Fe203 . 3SO3) + re2Cl3 + 2Au. The gold thus precipitated is quite destitute of metallic lustre, but acquires that character by burnishing. From alloys of gold and silver, or of gold, silver, and copper, the gold may also be separated by the action of strong sulphuric acid. The alloy, after being granulated by pouring it in the melted state into water, is heated in a platinum or cast-iron vessel with 2 J times its weight of sulphuric acid VOL. II. B B 348 GOLD. of specific gravity 1*815 (66° Baume), the heat being con- tinued as long as sulphurous acid is evolved. The silver and copper are thereby converted into sulphates, while the gold remains unattacked. The solution is boiled for a quarter of an hour with an additional quantity of sulphuric acid of specific gravity 1*653, or 58° Bauni6 (obtained by concen- trating the acid mother-liquors of sulphate of copper pro- duced in the operation), and afterwards left at rest. The gold then settles down, and the liquid, after being diluted with water, is transferred to a leaden vessel and again boiled with sheets of copper immersed in it. The silver is then precipitated in the metallic state, while the copper is con- verted into sulphate, and dissolves. The gold deposited in the manner above described still retains a small quantity of silver, from which it is separated by treating it a second and a third time with strong sulphuric acid : it then retains only 0*005 of silver. This process is not applicable to alloys con- taining more than 20 per cent, of gold ; richer alloys must first be fused with the requisite quantity of silver. It is applied on the large scale to the extraction of gold, chiefly from alloys which contain but little of that metal, such as native silver and old silver coins, and, as now practised, is economically available even when the amount of gold does not exceed one part in 2000. Gold is the only metal of a yeUow colour. When pure, it is more malleable than any other metal, and nearly as soft as lead. Its ductility appears to have scarcely a limit. A single grain of gold has been drawn into a wire 500 feet in length, and this metal is beaten out into leaves which have not more than 1 -200,000th of an inch of thickness. The coating of gold on gilt silver wire is still thinner. Gold, when very thin, is transparent, thin gold leaf appearing green by transmitted light. The green colour passes into a ruby red when highly attenuated gold is heated : in the red gold-glass, the gold is in the metallic state (Faraday). The point of fusion of this AUROUS COMPOUNDS. 349 metal is 2192°, according to Pouillet; 2518°, according to Guy ton-Morveau ; and 2590°, according to Daniell : it con- tracts considerably upon becoming solid. The density of gold varies from 19*258 to 19-367, according as it has been more or less compressed. Gold does not oxidate or tarnish in air, at the usual temperature, nor when strongly ignited. Bat this and the other noble metals are dissipated and partly oxidated, when a powerful electric charge is sent through them in thin leaves. It is not dissolved by nitric, hydro- chloric, or sulphuric acid, or indeed by any single acid. It is acted upon by chlorine, which converts it into sesquichloride, and by acid-mixtures, such as aqua-regia, which evolve chlo- rine. It combines in two proportions with oxygen, forming the two oxides AuqO and AU2O3, which show but little tendency to combine with acids. Some chemists, however, double the atomic weight of gold, and regard these oxides as protoxide, AuO, and teroxide, AUO3, respectively. Oxide of gold, Aurous oxide, AU2O, 204i'66 or 2558*25. — This oxide is obtained as a green powder by decomposing the corresponding chloride of gold with a cold solution of potash. It is partly dissolved by the alkali, and soon begins to un- dergo decomposition, being resolved into the higher oxide and metallic gold. The latter forms upon the sides of the vessel a thin film, which is green by transmitted light, like gold leaf. Chloride of gold, Aurous chloride, AU2CI, is obtained by evaporating a solution of the sesquichloride to dryness, and heating the powder thus obtained in a sand-bath, retaining it at about the temperature of melting tin, and constantly stirring it, so long as chlorine is evolved. It is a white, saline mass, having a tinge of yellow, and quite insoluble in water. In the dry state it is permanent, but in contact with water it gradually undergoes decomposition, and is converted into gold and the sesquichloride. This change takes place almost instantaneously at the boiling temperature. B B 2 350 GOLD. Aurous iodide, Auol, is formed by the action of hydriodic acid on auric oxide, water being formed and two-tbirds of tbe iodine set free : AU2O3 + SHI = AU2I + 3H0 + 21; also by adding iodide of potassium in proper proportion, and in successive small quantities, to an aqueous solution of auric chloride : AU2CI3 + SKI = Au^I -f 3KC1 + 21. It is a lemon-yellow, crystalline powder, insoluble in cold water, and very sparingly soluble in boiling water. Aurous sulphide is formed when hydrosulphuric acid gas is passed into a boiling solution of the sesqui chloride of gold. It is dark-brown, almost black. Aurous sulphide combines with the protosulphides of potassium and sodium, forming double salts containing 1 eq. of aurous sulphide with 1 eq. of the alkaline sulphide. The sodium- salt is obtained by fusing together 2 eq. protosulphide of sodium, 1 eq. gold, and 6 eq. sulphur; digesting the fused mass in water; filtering the yellow solution in an atmosphere of nitrogen ; and concen- trating in vacuo over sulphuric acid. Yellow crystals are then obtained, having the form of oblique hexagonal prisms with trilateral or quadrilateral summits, and containing NaS . Au^S -I- 8Aq. They are soluble in water and alcohol. The potassium-salt, which is obtained in a similar manner, forms indistinct crystals (Col. Yorke).* Sesquioxide of gold, Auric oxide, AU2O3, 220*66 or 2758'25. — This oxide has many of the properties of an acid. It is obtained by digesting magnesia in a solution of sesquichloride of gold, when an insoluble compound of auric oxide and mag- nesia is formed, which is collected upon a filter and weL washed. The compound is afterwards digested in nitric acid, which dissolves the magnesia, with traces of auric oxide, but * Cliem. Soc. Qu. J. i. 236. AUROUS COMPOUNDS. 351 leaves the greater part of the latter undissolved. It is left in the state of a reddish-yellow hydrate, which when dried in air becomes chestnut-brown. When precipitated by an alkali, auric oxide carries down a portion of the latter, of which it may be deprived by nitric acid. Dried at 212°, it abandons its water, becomes black, and is in part reduced. When exposed to light, particularly to the direct rays of the sun, its reduction is very rapid. It is decomposed by an incipient red heat. Hydrochloric acid is the only acid which dissolves and retains this oxide, and then sesquichloride of gold is formed. It is dissolved by concentrated nitric and sulphuric acid, but precipitated from these solutions by water. The affinity of this oxide for 'alkaline oxides, on the contrary, is so great that, when boiled in a solution of chloride of potassium, it is dissolved, the liquid becoming alkaline, and aurate of potash, or a compound of auric oxide and potash, being formed. The compounds of auric oxide with the alkalies and alkaline oxides are nearly colourless, and are not decomposed by water. They appear to be of two different degrees of saturation, aurates which are soluble, and superaurates which are in- soluble. The only one of these compounds which has been studied in some degree is the aurate of ammonia, or ful- minating gold as it is named, from its violently explosive character. Aurate of ammonia. — When the solution of gold is precipi- tated by a small quantity of ammonia, a powder of a deep yellow colour is obtained, which is a compound of aurate of ammonia with a portion of sesquichloride of gold. This com- pound explodes by heat, but the detonation is not strong. But when the solution of gold is treated with an excess of ammonia, and the precipitate well washed by ebullition in a solution of ammonia, or better in water containing potash, the fulminating gold has a yellowish brown colour with a tinge of purple. When dry, it explodes very easily with a loud report, accompanied by a feeble flame. It may be ex- B B 3 352 GOLD. ploded by a heat a little above the boiling point of water, or by the blow of a hammer. Its composition has not been exactly determined ; but if the ammonia is present in double the proportion that would contain the hydrogen necessary to bum the oxygen of the auric oxide, which Berzelius considers probable, its constituents may be AU2O3 . 2NH3 H HO. The affinity of auric oxide for ammonia is so great, that it takes that alkali from all acids. Thus, when auric oxide is digested in sulphate of ammonia, fulminating gold is formed, and the liquid becomes acid. Aurate of potash, KO . Au^Og + 6H0. — Obtained in the crystalline state by evaporating a solution of sesquioxide of gold in a slight excess of pure potash, first over the open fire and afterwards in vacuo : the crystals may be freed from adhering potash by recrystallisation from water, then drained on un- glazed porcelain and dried in vacuo. Aurate of potash is very soluble in water, and forms a yellowish strongly alkaline solution, which is decomposed by nearly all organic bodies, the gold being precipitated in the metallic state : it is also de- composed by heat. With most metallic salts it forms pre- cipitates of aurates, which are insoluble in water, but soluble in excess of the precipitant ; thus, chloride of calcium forms a precipitate of aurate of lime, soluble in excess of chloride of calcium. The solution of aurate of potash may be used as a bath for electro-gilding. Aurosulphite of potash, KO. Au203 + 4(KO . 2SO2) + 5H0 ; or 5K0LgX 3 4- 5 HO. — Deposited in beautiful yellow needles when sulphite of potash is added drop by drop to an alkaline solution of aurate of potash. It is nearly insoluble in alkaline solutions, but dissolves with decomposition in pure water, especially if hot, giving off sulphurous acid and de- positing metallic gold. Acids decompose it in a similar manner. After drying in vacuo, it may be preserved for two or three months, in well-closed bottles, but ultimately decom- PURPLE OP CASSIUS. 353 poses_, giving off sulphurous acid and leaving metallic gold and sulphate of potash. The same decomposition takes place more quickly when the salt is heated (Fremy).* Purple of Cassius. — When protochloride of tin is added to a dilute solution of gold^ a purple- coloured powder falls, which has received that name. It is obtained of a finer tint when protochloride of tin is added to a solution of the sesquichloride of iron, till the colour of the liquid takes a shade of green, and the liquid in that state added, drop by drop, to a solution of sesquichloride of gold free from nitric acid, and very dilute. After 24 hours, a brown powder is deposited, which is slightly transparent and purple-red by transmitted light. When dried and rubbed to powder, it is of a dull blue colour. Heated to red- ness, it loses a little water, but no oxygen, and retains its former appearance. If washed with ammonia on the filter while still moist, it is dissolved, and a purple liquid passes thi'ough, which rivals the hypermanganate of potash in beauty. From this liquid, the colouring matter separates very gradually, weeks elapsing before the upper strata of the liquid become colour- less ; but it is precipitated more rapidly when heated in a close vessel between 140° and 180°. The powder of Cassius is inso- luble in solutions of potash and soda. It may also be formed by fusing together 2 parts of gold, 3^ parts of tin, and 15 parts of silver, under borax, to prevent the oxidation of the tin, and treating the alloy with nitric acid to dissolve out the silver ; a purple residue is left containing the tin and gold that were employed. The powder of Cassius is certainly, after ignition, a mixture of binoxide of tin and metallic gold, from which the gold can be dissolved out by aqua-regia, wliile the binoxide of tin is left ; and the last mode of preparing it, favours the idea that its constitution is the same before ignition ; but the solubility of the unignited powder in ammonia, and the fact that mercury does not dissolve out gold from the powder when properly * Ann. Ch. Pharm. lyi. 315. B B 4 854 GOLD. prepared, appear to be conclusive against that opinion. The proportions of its constituents vary so much, that there must be more than one compound ; or more likely the colour- ing compound combines with more than one proportion of binoxide of tin. Berzelius proposed the theory that the powder of Cassius may contain the true protoxide of gold combined with sesquioxide of tin, AuO . Sn203, a kind of combination containing an association of three atoms of metal, which is exemplified in black oxide of iron, spinell, gahnite, franklinite, and other minerals, and which we have repeatedly observed to be usually attended with great stability. A glance at its formula shows how readily the powder of Cassius, as tlms repre- sented, may pass into gold and binoxide of tin ; AuO . Sn203 = Au -f 2Sn02. The existence of a purple oxide of gold, AuO, is not established ; but it is probably the substance formed when a solution of gold is applied to the skin or nails, and which dyes them purple. Paper, coloured purple by a solution of gold, becomes gilt when placed in the moist state in phosphuretted hydrogen gas, which reduces the gold to the metallic state. Pelletier gives the following method of preparing a purple of Cassius of constant composition : — 20 grammes of gold are dissolved in 100 grammes of aqua-regia containing 20 parts nitric to 80 parts of commercial hydrochloric acid ; the solution is evaporated to dryness over the water-bath ; the residue dissolved in water ; the filtered solution diluted with 7 or 8 decilitres of water; and tin filings introduced into it: in a few minutes the liquid becomes brown and turbid, and deposits a purple precipitate, which merely requires to be washed and dried at a gentle heat. The purple thus prepared contains in 100 parts: 32'746 stannic acid, 14"618 protoxide of tin, 44772 aureus oxide (AU2O) and 7*864 water. The precipitate obtained by treating sesquichloride of gold with pure protochloride of tin is always brown. To obtain a fine purple precipitate, the chloride of gold should be treated with AURIC COMPOUNDS. 855 a mixture of protochloride and bicliloride of tin. The follow- ing process gives a fine purple : — a. A neutral solution is prepared of 1 part of tin in hydrochloric acid ; h. A solution of 2 parts tin in cold aqua-regia (I part hydrochloric acid to 3 nitric), the liquid being merely heated towards the end of the process, that it may not contain any protoxide of tin j c. Seven parts of gold are dissolved in aqua-regia (6 hydro- chloric to 1 nitric), and the solution, which is nearly neutral, diluted with 3500 parts of water. To this solution c, the solution h is first added, and then the solution «, drop by drop, till the proper colour is produced. If the quantity of a be too small, the precipitate is violet ; if too large, it is brown. It must be washed quickly, so that the liquid may not act upon it too long. It weighs 6| parts (Bouisson).* Sesquisulphide of gold, AU2S3, or Auric sulphide, is formed when a dilute solution of gold is precipitated cold by hydro- sulphuric acid. It is a flocculent matter of a strong yellow colour, which becomes deeper by drying ; it loses its sulphur at a moderate heat. Sesquichloride of gold, Perchloride of gold, Auric chloride, AU2CI3, 303*16 or 3789*5. — This compound is formed when gold is dissolved in aqua-regia. The solution is yellow, and becomes paler with an excess of acid, but is of a deep red when neutral in composition. It is obtained in the last condition by evaporating the solution of gold, till the liquid is of a dark ruby colour, and begins to emit chlorine. It forms on cooling a dark red crystalline mass, which de- liquesces quickly in air. But the only method of procuring auric chloride perfectly free from acid salt, is to decompose aurous chloride with water. A compound of chloride of gold and hydrochloric acid crystallises easily from an acid solution, in long needles of a pale yellow colour, which are permanent in dry air, but run into a liquid in damp air. The solution of this salt deposits gold on its surface, and * J. Pharm. [2], xvi. 629. 356 GOLD. on the side of the vessel turned to the light. The gold is also precipitated in the metallic state by phosphorus, by most metals, by fen'ous salts, by arsenious and antimonious acids, and by many vegetable and animal substances, by vegetable acids, by oxalate of potash, &c., carbonic acid then escaping. Hydrosulphuric acid and sulphide of ammonium throw down black sulphide of gold, soluble in excess of the latter re- agent. Ammonia and carbonate of ammonia produce a yellow precipitate of fulminating gold. Potash added in excess forms no precipitate, unless it contains organic matter, in which case a slight precipitate of aurous oxide is pro- duced. Cyanide of potassium produces a yellow precipitate soluble in excess. Tincture of gaUs throws down metallic gold. Chloride of gold is soluble in ether and in some essential oils. It forms double salts with most other chlo- rides, which are almost all orange-coloured when crystallised ; in efflorescing, they acquire a lemon-yellow colour, but in the anhydrous state they are of an intense red. They are obtained by evaporating the mixed solutions of the two salts. Chloride of gold and potassium, KCl . AugCl.^ + 5H0. — Crystallises in striated prisms with right summits, or in thin hexagonal tables which are very efflorescent; becomes an- hydrous at 212°. The anhydrous salt fuses readily when heated, but loses chlorine and becomes a liquid, which is black while hot, and yellow when cold. It is then a compound of aurous chloride with chloride of potassium. Chloride of gold and ammonium ciystallises in transparent prismatic needles, which become opaque in air ; Mr. Johnston found their com- position to be NH4CI . AU2CI3 + 2H0. Chloride of gold and sodium crystallises in long four-sided prisms, and is persistent in air. Its composition is NaCl . AU2CI3 4- 4H0. Bonsdorff has prepared similar double salts with the chlorides of barium, strontium, calcium, magnesium, manganese, zinc, cadmium, cobalt, and nickel. The salt of lime contains sLx, and the salt pf magnesia twelve equivalents of water. AURIC COMPOUNDS. 357 Sesquibromide of gold, Au2Br3, is formed by dissolving gold in a mixture of nitric and hydrobromic acids. It greatly resembles the sesquichloride, and forms also an extensive series of double salts. Auric iodide, AU2I3, is formed by gradually adding a neutral solution of auric chloride to a solution of iodide of potassium : the liquid then acquires a dark-green colour, and yields a dark-green precipitate of Augig, which redissolves on agitation; but after 1 eq. of the auric chloride has been added to 4 eqs. of iodide of potassium, a farther addition of the gold-solution decolorizes the liquid and forms a permanent precipitate of auric iodide, because the iodide of gold and potassium at first produced is thereby decomposed. The successive actions are represented by the following equa- tions : — (1.) 4KI + AU2CI3 = 3KC1 + KI . AU2I3 ; (2.) 3(KI . AU2I3) + AU2CI3 = 3KC1 + 4AU2T3. Auric iodide is a very unstable compound; when exposed to the air at ordinary temperatures, it is gradually converted into yellow aureus iodide, and afterwards into metallic gold. It combines with hydriodic acid and with the more basic metallic iodides, forming a series of very dark-coloured salts ; e. g. iodo-aurate of potassium, KI . AU2T3. The oxides of gold show but little tendency to combine with oxygen-acids : the sesquioxide dissolves in strong nitric acid, but the solution is decomposed by evaporation or dilu- tion. , Hyposulphite of aurous oxide and soda : Au20.S202 + 3(NaO.S202) + 4HO; or ^^^Oj^g^Q^.^ ^jjq This salt is prepared by mixing concentrated solutions of sesquichloride of gold and hyposulphite of soda, and preci- 358 GOLD. pitating with alcohol. When purified by repeated solution in water and precipitation by alcohol, it forms delicate, colour- less needles. It has a sweetish taste, dissolves very easily in water, but very sparingly in alcohol. It is decomposed by heat and by nitric acid, with deposition of metallic gold. Its solution gives a blackish precipitate Avith hydrosulphuric acid and soluble sulphides. The presence of gold in this solution is not indicated by protosulphate of iron, protochloride of tin, or oxalic acid ; and, on the other hand, sulphuric acid, hydro- chloric acid, and the vegetable acids neither precipitate sulphur nor expel sulphurous acid from it. When mixed with chloride of barium, it yields a gelatinous precipitate of Hyposulphite of aurous oxide and baryta, containing o g^Q | ^8202- Sulphuric acid removes all the baryta from this salt, and leaves hydrated aurous hyposulphite^ which is uncrystallisable, strongly acid, and tolerably stable at ordinary temperatures. The solution of the soda-salt is used for fixing daguerreotype pictures (Fordos and Gelis).* A hyposulphite of auric oxide and soda appears also to be formed by dropping a neutral solution of chloride of gold into aqueous hyposulphite of soda (Fordos and Gelis). Alloys of gold. — Gold unites with nearly all metals ; but its most important alloys are those which it forms with silver and copper. Gold which is used for coins, watches, articles of jewellery, &c., is always alloyed with copper, to increase its nardness, pure gold being much too soft for any of these pur- poses. The standard for coin in the United Kingdom is II gold with I alloy; in France and the United States of America, 9 gold to 1 alloy. For articles of jewellery, gold is also frequently alloyed with silver, which gives it a lighter colour. The alloys of gold, both with silver and with copper, arc more fusible than gold itself. The solder used for gold * Ann. Ch Phys. [3], xiii. 394. AURIC COMPOUNDS. 359 trinkets is composed of 5 parts gold and 1 part copper, or of 4 parts gold, 1 part copper, and 1 part silver. Amalgam of gold. — Gold unites readily with mercury, forming a white amalgam ; the smallest quantity of mercurial vapour coming in contact with gold is sufficient to turn it white. Mercury is capable of dissolving a large quantity of gold without losing its fluidity, but, when quite saturated, it acquires a waxy consistence. When the liquid amalgam is strained through chamois-leather, mercury passes through together with a very small quantity of gold, and there remains a white amalgam, of pasty consistence, containing about 2 parts of gold to 1 part of mercury. By dissolving 1 part of gold in 1000 parts of mercury, pressing through chamois- leather, and treating the residue with dilute nitric acid at a moderate heat, a solid amalgam, AugHg, is obtained, which crystallises in shining four-sided prisms, retains its lustre in the air, is not decomposed by boiling nitric acid, and does not melt even when heated till the mercury volatilises (T. H. Henry).* Gilding and silvering. — The pasty amalgam of 2 parts gold and 1 part mercury is used for gilding ornamental articles of copper and bronze. The surface of the object is first thoroughly cleaned by heating it to redness, then plunging it into dilute sulphuric acid, and sometimes for an instant also into strong nitric acid; it is then amalgamated by washing it with a solution of nitrate of mercury, and afterwards pressed upon the pasty amalgam, a portion of which adheres to it. The mercury is then expelled by heat, and the gold-surface finally polished. Silver may be gilt by similar processes. By substituting an amalgam of silver for the amalgam of gold, articles of copper, bronze, and brass may be silvered or plated. Articles of copper, chiefly copper trinkets, are also gilt by * Phil. Mag. [4], ix. 468. 360 GOLD. immersion in a boiling solution of chloride of gold in an alka- line carbonate, after having been cleaned by processes similar to those just described. But the process now most generally adopted is that of electro-gilding, which is performed by immersing the objects to be gilt in a solution of 10 parts of cyanide of potassium and 1 part of cyanide of gold in 100 parts of distilled water, and connecting them with the negative pole of a voltaic battery, while the positive pole is connected with a bar of gold also immersed in the liquid. The solution is then de- composed by the current, the gold being deposited on the objects at the negative pole, while the gold connected with the positive pole dissolves and keeps the solution at a nearly uniform strength. The cyanide of potassium in the solution is sometimes replaced by ferrocyanide of potas- sium, and the cyanide of gold by sesquioxidc of gold, chloride of gold and potassium, or sidphide of gold ; but the composition above given is that which is most generally adopted. This mode of gUding may be at once applied to copper, brass, bronze, silver, or platinum. To gild iron, steel, or tin, it is necessary first to deposit a layer of copper on the surface, which is effected by immersion for a few seconds in a bath of cyanide of copper and potassium. Electro-silvering or electro-plating is performed in a similar manner, with a bath composed of 1 part of cyanide of silver and 10 parts of cyanide of potassium dissolved in 100 parts of water ; it is principally applied to articles made of nickel- silver. Platinum may also be deposited in a similar manner on copper or silver ; but it does not adhere very firmly. ESTIMATION OF GOLD. 361 ESTIMATION OF GOLD, AND METHODS OF SEPARATING IT FROM OTHER METALS. Gold is always estimated in tlie metallic state. It is gene- rally precipitated from its solution in aqua-regia by proto- sulpliate of iron or oxalic acid. Protosulphate of iron pre- cipitates the gold in the form of a fine brown powder. K the gold solution is quite neutral, it must first be acidulated with hydrochloric acid, otherwise the precipitated gold will be contaminated with sesquioxide of iron formed by the action of the air on the solution of the protosulphate. If the gold solution contains much free nitric acid, there is a risk of some of the precipitated gold being redissolved by the aqua- regia present. To prevent this, the excess of nitric acid must be destroyed by adding hydrochloric acid, and boiling before the iron solution is added. Oxalic acid reduces gold slowly but completely ; the gold solution must be digested with it for 24 or 48 hours. These methods of precipitation serve to separate gold from most other metals. In such cases, oxalic acid is mostly to be preferred as the precipitating agent, because, when the quan- tities of the other metals are also to be determined, the presence of a large amount of iron in solution is very incon- venient. The separation of gold in alloys may generally be efiected by dissolving out the baser metals with nitric, or sometimes with hydrochloric or sulphuric acid. When, however, the proportion of gold is considerable, it may happen that the alloy is but very slowly attacked by nitric acid, especially if the other metal be silver or lead. In such a case, it is best to treat the alloy with aqua-regia, and precipitate the gold with oxalic acid. Or, again, the alloy may be fused with a known weight of lead or silver, as in the method of quarta- tion (p. 349.), and thereby rendered decomposable by nitric acid. 362 GOLD. The analysis or assay of an alloy of gold and copper is usually made by cupcllation with lead. The weight of the button remaining on the cupel gives directly the amount of gold in the alloy after certain corrections similar to those required in the case of silver (p. 348.). Alloys containing both silver and copper are cupelled with lead and a quantity of silver sufficient to bring the proportion of gold and silver in the alloy to 1 part gold and 3 parts sUver. The button obtained by cupcllation then consists of an alloy of gold and silver, from which the silver may be dissolved out by nitric acid. Small ornamental articles, which would be destroyed if submitted to any of the preceding processes, are approxi- mately assayed by rubbing them on a peculiar kind of black stone, called the touchstone^ so as to leave a streak of metal, the appearance of which may be compared with that of similar streaks produced from alloys of known composition. A further comparison is obtained by examining the appear- ance which the streaks present when treated with acids. This method is also sometimes used in the assaying of coins, to afford an indication of the quantity of silver required in the cupcllation. The touchstone, which is a peculiar kind of bituminous quartz, was originally obtained from Lydia; but stones of similar quality are now found in Bohemia, Saxony, and Silesia. PLATINUM. 363 OEDEE IX. METALS IN NATIVE PLATINUM. SECTION I. PLATINUM. Eq. 98-68 or 1233-5 ; Pt. This metal was discovered in the auriferous sand of certain rivers in America. Its name is a diminutive of plata, silver, and was applied to it on account of its whiteness. It occurs in the form of rounded or flattened grains of a metallic lustre. It has been found in Brazil, Colombia, Mexico, St. Domingo, and on the eastern declivity of the Ural chain; in small quantity also in certain copper-ores from the Alps; it is everywhere associated with the debris of a rock, easily recog- nised as belonging to one of the earliest volcanic formations. The grains of native platinum contain from 75 to 87 per cent, of that metal, a quantity of iron generally sufficient to render them magnetic, from J to 1 per cent, of palladium, but sometimes much less, with small quantities of copper, rhodium, osmium, iridium, and ruthenium. To separate the platinum from these bodies, the ore is digested in a retort with hydro- chloric acid, to which additions of nitric acid are made from time to time. When the hydrochloric acid is nearly saturated, the liquid is evaporated in the retort to a syrup, then diluted with water, and drawn off" from the insoluble residue. If the mineral is not completely decomposed, more aqua-regia is added and the distillation continued. A portion always remains undissolved, consisting of grains of a compound of VOL. II. c c 364 PLATINUM. osmium and iridium^ and little brilliant plates of the same alloy, besides foreign mineral substances which may be mixed with the ore. The solution is generally deep red, and emits chlorine from the presence of perchloride of palladium; to decompose which the liquid is boiled, whereupon chlorine escapes, and the palladium is reduced to protochloride. Chloride of potassium is then added, which precipitates the platinum as a sparingly soluble double chloride of platinum and potassium, wliich has a yellow colour if pure, but red if it is accompanied by the double chloride of iridium and potassium. The precipitate is collected on a filter, and washed ^\dth a dilute solution of chloride of potassium. By igniting this double salt with twice its weight of carbonate of potash to the point of fusion, the platinum is reduced to the metallic state, while a portion of the iridium remains as peroxide. The soluble potash-salts are then removed by washing with hot water, and the platinum is dissolved by aqua-regia, in which the peroxide of iridium remains untouched. To com- plete the separation of the iridium, the precipitation by chloride of potassium and ignition vnth carbonate of potash may require to be repeated several times. The platinum- solution thus freed from iridium is mixed with sal-ammoniac, which throws down a yellow precipitate of the double chloride of platinum and ammonium. From this precipitate, when heated to redness, chlorine and sal-ammoniac are given oflP, and the platinum remains in the form of a loosely coherent mass, called sjjongy plathmm. When it is not required to have platinum absolutely pure, the solution first obtained from the ore is precipitated by sal-ammoniac, and the pre- cipitate treated in the manner just described : much of the platinum of commerce is obtained in that way. The small trace of iridium which is left in commercial platinum greatly increases its hardness and tenacity. Platinum is too refractory to be fused in coal furnaces : but at a high temperature its particles cohere like those of ii'on. PLATINUM. 365 Fig. 19. and it may, like that metal, be welded, and thereby rendered malleable. For this purpose, the spongy platinum obtained by igniting the double chloride of platinum and ammonium, is introduced into a brass cylinder efg h {Fig. 20), the lower part of which fits into a steel socket abed. The cylinder being half filled with spongy platinum, a steel piston ik, which fits it exactly, is introduced, and driven down by blows of a hammer, gently at first, but afterwards with greater force. The spongy platinum is thereby much reduced in bulk, and after a while is converted into a coherent disc of metal. This disc is heated to whiteness in a muffle, and after- wards hammered on a steel anvil. By repeating these operations several times, the platinum is rendered perfectly malleable and ductile, and may be rolled into sheets. Platinum in this state is the densest body at present known ; its specific gravity was fixed by Dr. WoUaston at 21*53. This metal may be fused by the oxyhydrogen blow-pipe, or even made to boil, and be dissipated with scintillations. It is not acted upon by any single acid, not even by concentrated and boiling sul- phuric acid. Its resistance to the action of acids, conjoined with its difficult fusibility, renders platinum invaluable for chemical experiments, and for some purposes in the chemical arts, particularly for the concentration of oil of vitriol. The remarkable influence of a clean surface of platinum in determining the combustion of oxygen and hydrogen, has already been considered. This property platinum shares with osmium, iridium, palladium, and rhodium. It is exhibited in the greatest degree by the highly divided metal, such as pla- tinum-sponge, the condition in which the metal is left on igniting the double chloride of platinum and ammonium. Platinum precipitated from solution by zinc, causes the com- c c 2 366 PLATINUM. bustion of alcohol vapour. The black powder of platinum, commonly called platinum-black, is the form in which that metal is most active. This is prepared by dissolving the pro- tochloride of platinum in a hot and concentrated solution of potash, and pouring alcohol into it while still hot, by small quantities at a time ; violent effervescence then occurs from the escape of carbonic acid gas, by which the contents of the vessel, unless capacious, may be thrown out. The liquor is decanted from the black powder which appears, and the latter boiled successively with alcohol, hydrochloric acid, and potash, and finally four or five times with water, to divest it of all foreign matters. Platinum-black may also be obtained by decomposing a hot solution of sulphate of platinum with alcohol ; and by boiling a solution of the bichloride with car- bonate of soda and sugar ; chloride of sodium is then formed, water and carbonic acid are produced by oxidation of the sugar, and the platinum is precipitated in the finely-divided state. The powder, when dried, resembles lamp-black, and soils the fingers, but still it is only metallic platinum ex- tremely divided, and may be heated to full redness without any change of appearance or properties. It loses these pro- perties, however, by the effect of a white heat, and assumes a metallic aspect. Platinum-black, like wood charcoal, absorbs and condenses gases in its pores, with evolution of heat, a property which must assist its action on oxygen and hydrogen, although not essential to that action. When moistened with alcohol, it determines the oxidation of that substance in air, and the formation of acetic acid ; and, in a similar manner, it converts wood-spirit into formic acid. Platinum is insoluble in all acids except aqua-regia. It may be oxidated in the dry way by fusing it with hydrate of potash or nitre. Palladium, osmium, and iridium resemble platinum in their chemical relations, the corresponding com- pounds of these four metals being isomorphous; platinum and iridium have also the same atomic weight. Of platinum. PLATINOUS COMPOUNDS. 369^ only two degrees of oxidation are known witn certainty, the protoxide, PtO, and binoxide, Pt02. Protoxide of platinum, Platinous oxide, PtO, 106*68 or 1333-5. — This oxide is obtained by digesting the corres- ponding chloride of platinum with potash, as a black powder, which is a hydrate. It is dissolved by an excess of the alkali, and forms a green solution, which may become black like ink with a large quantity of oxide. Protoxide of platinum forms the platinous class of salts, which have a greenish, or, some- times red colour, and are distinguished from the platinic salts by not being precipitated by sal-ammoniac. With hydrosuU phuric acid and hydrosulphate of ammonia, they form a black precipitate, soluble in a large excess of the latter ; with mer- curous nitrate, a black precipitate; with potash, no precipitate; with carbonate of potash or soda, a brownish precipitate. Am- monia added to the hydrochloric acid solution throws down a green crystalline precipitate of ammonio-platinous chloride ; carbonate of ammonia forms no precipitate. Protosulphide of platinum, PtS, is thrown down as a black precipitate, when the protochloride of platinum is decomposed by hydrosulphuric acid. It. may be washed and dried without decomposition. Protochloride of platinum, Platinous chloride, PtCl, is ob- tained by evaporating a solution of the bichloride of platinum to dryness; triturating the dry mass; and heating it in a porcelain capsule by a sand-bath at the melting point of tin, taking care to stir it at the same time, so long as chlorine is evolved. It remains as a greenish grey powder, quite insoluble in water, and repelling that liquid so as not to be moistened by it. This chloride is not decomposed by sulphuric or nitric acid, but is partially soluble in boiling and concentrated hy- drochloric acid. From the last solution, alkalies throw down a black precipitate of protoxide. When the calcination of the bichloride of platinum, at 420° or 460"^, is interrupted before the whole of the chlorine is expelled, the residue yields to c c 3 368 PLATINUM. water a compound of a bro^vn colour, so deep, that the liquid becomes opaque. This, Professor Magnus believes to be a combination of the two clilorides of platinum. A double protochloride of platinum and potassium^ or chloroplaiinite of potassium, PtCl . KCl, is obtained on adding chloride of potassium to the solution of platinous chloride in hydrochloric acid, and evaporating the liquid. The salt crystallises in red four-sided prisms, the form of which is the same as that of a corresponding salt of palladium ; it is anhydrous. A proto- chloride of platinum and sodium also exists, but does not crystallise easily. Corresponding platinous iodides and cyanides have been formed. The cyanide forms a numerous class of double salts, called platinocyanides, whose general formula is MCy.PtCy. The potassium salt is obtained by heating spongy platinum with fcrrocyanide of potassium ; exhausting the mass with hot water and crystallising; or by treating platinous chloride with aqueous cyanide of potassium. The salt crystallises in needles and rhombic prisms, pale yeUow by transmitted light, yellow or blue by reflected light, according to the direction in which they are. viewed. From the solution of this salt, the platino-cyanides of zinc, lead, copper, mer- cury, and silver, which are insoluble, are obtained by precipi- tation. The sodium, barium, strontium, and calcium-salts, which are soluble, are obtained by treating the copper-salt with caustic soda, baryta, &c. ; and the magnesium and aluminum- salts, by precipitating the barium-salt with sulphate of magnesia or alumina. The ammonium-salt is prepared like the potassium-salt. Platinous oxide has also been united with several acids, particularly sulphuric, nitric, oxalic, and acetic acids ; but none of these salts have been crystallised, except the oxalate. Bioxide of platinum. Peroxide of platinum, Platinic oxide, PtO.2, 111'68 07^ 1433-5. — By precipitating sulphate of pla- tinum with nitrate of baryta, nitrate of platinum is obtained. PLATINIC COMPOUNDS. 369 One half of its oxide may be precipitated by soda, from the last salt, but when a larger quantity of alkali is added, a sub- salt is thrown down. The precipitated oxide is hydrated, very bulky, and exactly resembles sesquioxide of iron precipi- tated by ammonia. When heated, it first loses its water, and becomes black, then its oxygen, and leaves metallic platinum. Bioxide of platinum combines with acids, and forms a class of salts, which are either yellow or reddish-brown. From, the solutions of these salts, the platinum is precipitated in the metallic state by phosphorus and by most metals. Hydrosul- phuric acid and sulphide of ammonium form a black precipitate soluble in a large excess of the latter. In a solution of pla- tinic chloride, potash or ammonia forms a yellow crystalline precipitate of chloroplatinate of potassium or ammonium; so likewise do the chlorides of potassium or ammonium ; sodium-salts form no precipitate. In the solution of platinic nitrate or sulphate, potash or ammonia forms a yellow-brown precipitate ; chloride of potassium or ammonium produces, after some time, a slight yellow precipitate of the double chloride. Platinic oxide has also a decided affinity for bases, and forms insoluble compounds with the alkalies, earths, and many metallic oxides. It forms also, like sesquioxide of gold, a fulminating ammoniacal compound, discovered by Mr. E. Davy. Bisulphide of platinum, PtS2, is formed by adding a solution of bichloride of platinum, drop by drop, to a solution of sul- phide of potassium. It is dark brown and becomes black by desiccation. When dried in open air, a portion of its sulphur is converted into sulphuric acid, by absorption of oxygen, and the mass becomes strongly acid. Bichloride of platinum, PtCl2, 2121 or 169'68, is obtained by concentrating the solution of platinum in aqua-regia, as a red saline mass, which becomes brown when deprived of its water of crystallisation by heat. The solution of this salt when pure has an intense and unmixed yellow colour, the red c c 4 370 PLATINUM. colour whicli it usually exhibits being due to iridium or to protocbloride of platinum. Bichloride of platinum is soluble in alcohol, and the solution is used to separate potash and ammonia in analysis. Chloride of platinum and potassium, Chloroplatinate of potassium, KCl . PtCl2, is the salt which falls on mixing chloride of platinum with chloride of potassium or any other salt of potash. The crystalline grains of which it is composed are regular octohedrons. This salt is soluble to a certain extent in water, but is wholly insoluble in alcohol. It is anhydrous. A very intense red-heat is required for its com- plete decomposition. Chloroplatinate of sodium, NaCl . PtClj + 6H0, crystallises in beautiful transparent prisms of a bright yellow colour. It is soluble in alcohol as well as in water. When a solution of this salt in alcohol is distilled till only one-fourth of the liquid remains, the solution yields by evaporation a salt containing the elements of ether, and be- longing to a class of compounds discovered by Professor Zeise, and known as the etherised salts of Zeise. Chloroplatinate of ammonium resembles the double salt of potassium. When ignited, it leaves metallic platinum in the spongy state. Bonsdorflf has formed a large class of com- pounds of bichloride of platinum with the alkaline, earthy, and metallic chlorides, in all of which the salts are united in single equivalents. The bromides and iodides of platinum have likewise been formed, and classes of double salts derived from them. Bioxide of platinum has also been combined with acids ; but none of its salts, with the exception of the oxalate, is obtained in a crystalline state. Bicyanide of platinum, or platinic cyanide, does not appear to exist in the separate state ; but it forms double salts with the cyanides of potassium and ammonium ; it likewise com- bines with chloride of potassium, forming the compound KCl . PtCy^. The sulphocyanides of platinum, PtCySg, and Pt, (CyS2)2.. PLATINUM SALTS. 371 likewise form two series of double salts, viz. the platino- bisulphocyanides or sulphocyanoplatinites = MPt(CyS2)2^ oi' MCyS2 + PtCyS2, and theplatino-tersulphocyanides or sulpho- cyanoplatinates = MPt (€782)3, or MCyS2 + Pt (0782)2- The potassium salts are formed b7 the action of sulphoc7anide of potassium on protochloride and bichloride of platinum re- spectively. All these salts are strongly coloured, exhibiting all shades of colour from light yellow to deep red. They are quickly decomposed by heat (G. B. Buckton).* AMMONIACAL PLATINUM SALTS. The oxides, chlorides, sulphates, &c., of platinum are capable of taking up the elements of 1 or 2 equivalents of ammonia, giving rise to four series of compounds, whose composition may be represented by the following general formulae, in which the symbols R, B' denote acid elements : 1. Ammonio-platinous compounds, or protosalts of pi at am- monium, NH3PtR=NH^P?.R. 2. Biammonio-platinous compounds, or protosalts of ammo- platammonium, N2H6PtB=NH3raj5t . R. 3. Ammonio-platinic compounds, or bisalts of platammo- nium, NH3Pt{„,&=NH;Ft.{„^g|,,_ 4. Biammonio-platinic compounds, or bisalts of ammo- platammonium. The third and fourth classes of these compounds may also be regai^ded as protosalts of compound ammoniums, in which * Chem. Soc. Qu. J. rii. 22. 372 PLATINUM. 1 eq. of hydrogen is replaced by PtO or PtCl ; for example, the bichloride NH3PtCl2=NH^(PtCi) .CI; the chloronitrate N2H6PtClN06=NH^(NHJPtCl . NOg. 1. Ammonio-platinous compounds, or Protosalts of Plat- ammonium. — These compounds are formed by the action of heat on those of the follo^ving series, half the ammonia of the latter being then given off. They are for the most part insoluble in water, but dissolve in ammonia, reproducing the biammoniacal platinous compounds ; they detonate when heated. Oxide, NH3PtO=NH3Pt.O.— Obtained by heating the hydrated oxide of biammo-platammonium to 230°. It is a greyish mass which, when heated to 392° in a close vessel, gives off water, ammonia, and nitrogen, and leaves metallic platinum. Probably the compound, Pt3N, is first produced and is afterwards resolved into nitrogen and platinum : 3NH3PtO=Pt3N + 3H0 + 2NH3. The oxide, heated to 392° in contact with the air, becomes incandescent, and burns vividly, leaving a residue of platinum. Chloride, NHaPtCl = NHgPt . CI. — Of this compound three isomeric modifications exist : a. Yelloiv, obtained by adding hydrochloric acid, or a soluble chloride, to a solu- tion of nitrate or sulphate of platammonium. Or, by boiliug the green modification, y, with nitrate or sulphate of am- monia, whereupon it dissolves and forms a solution which, on cooling, deposits the yellow salt. Or, by neutralising a solu- tion of platinous chloride in hydrochloric acid with carbonate of ammonia, heating the mixture to the boiling point, and adding a quantity of ammonia equal to that already contained in the liquid, filtering from a dingy green substance, which deposits after a while, then leaving the solution to cool, and decanting the supernatant liquid as soon as the yellow salt is PLA.TINUM SALTS. 373 deposited. /3. Red. — If, in the last mode of preparation, the carbonate of ammonia, instead of being added at once in excess, be added drop by drop to the hydrochloric acid solu- tion of platinous chloride, the liquid on cooling deposits small garnet-coloured crystals having the form of six-sided tables. This red modification may also be obtained in other ways (Peyrone).* y. Green. — This modification, usually denomi- nated the green salt of Magnus, was the first discovered of the ammoniacal platinum compounds. It is obtained by gra- dually adding an acid solution of platinous chloride to caustic ammonia, or by passing sulphurous acid gas into a boiling solution of bichloride of platinum till it is completely con- verted into protochloride (and therefore no longer gives a precipitate with sal-ammoniac), and neutralising the solution with ammonia ; the compound is then deposited in green needles. The same modification of the salt may also be ob- tained by adding an acid solution of platinous chloride to a solution of biammonio-platinous chloride, N2HgPtCl. Hence it would appear that the true formula of this green salt is (NH3PtCl)2=PtCl + NH^(NHJP"t . CI, that of the yeUow or red modification being simply NHaPtCl. Either modifica- tion of the salt, when heated to 572°, gives off nitrogen, hydrochloric acid, and sal-ammoniac, and leaves a residue of platinum. A red crystalline compound of chloride of platammonium with chloride of ammonium, viz. NHgPtCl + NH^Cl, is formed when a solution of chloride of ammo-platammonium, contain- ing a large quantity of sal-ammoniac, is evaporated to the crystallising point. Thus, when a solution of platinous chlo- ride in hydrochloric acid is precipitated by ammonia, and the green salt of Magnus thereby formed is heated, while still in the liquid, with excess of ammonia, to convert it into chloride of ammo-platammonium, the red compound separates at a * Vide Translation of Gmelin's Handbook, vi. 303. 374 PLATINUM. certain degree of concentration^ together with tlie chloride of ammo-plataramonium (Grimm).* Iodide J NHaPtl. — Yellow powder, obtained by boiling the aqueous solution of the compound N2H6PtI. It dissolves in ammonia, and is thereby reconverted into the latter com- pound. Cyanide, NHgPtCy. — Obtained by adding hydrocyanic acid to a solution of biammonio-platinous oxide, cyanide of ammoniimi being formed at the same time (Reiset) : NaHgPtO + 2HCy = NHgPtCy + NH^Cy + HO. Also, by digesting ammonio-platinous chloride with cyanide of silver. It crystallises in fine regular needles of a pale yellow colour, soluble with tolerable facility in water and ammonia. An isomeric modification of this compound, (NH3PtCy)2= N2H6PtCy 4- PtCy, is formed by passing cyanogen gas into a moderately concentrated solution of biammonio-platinous oxide; the cyanogen then decomposes the water, forming hydrocyanic and cyanic acids, and the hydrocyanic acid acts upon the biammonio-platinous oxide, forming the compound (NH3PtCy)2, together with ammonia and water : 2 (N2H6PtO) + 2HCy = (NH3PtCy)2 + 2NH3 + 2H0. The compound, (NH3PtCy)2, crystallises out and may be purified by recry stall isation from water. It is also obtained by mixing a solution of biammonio-platinous chloride with cyanide of potassium. It forms crystals which, under the microscope, appear like six-sided tables arranged in stellate groups ; it dissolves without decomposition in potash, hydro- chloric acid, and dilute sulphuric acid, but is decomposed by strong sulphuric and by nitric acids (Buckton).t The sulphate^^YL^Vi.^O^.TiO, and the nitrate, NHgPt.NOg, are obtained by boihng the iodide with sulphate and nitrate * Ann. Ch. Pharm. xcix. 95. t Chem. Soc. Qu. J., iv. 34. AMMONIACAL PLATINUM SALTS. 375 of silver ; they are crystalline, and have a strong acid reaction. The sulphate retains one atom of water, which cannot be re- moved without decomposing the salt. 2. Biammonio-platindus compounds, or Protosalts of Ammo- platammonium.— Oxide, NaHgPtO . HO = NH2(NH4)Pt .0 + HO. — Obtained by decomposing the solution of the sulphate with an equivalent quantity of baryta- water, and evaporating the filtrate in vacuo; a crystalline mass is then left, con- taining N2H6PtO . HO. The oxide is not known in the anhy- drous state. The hydrate is strongly alkaline and caustic, like potash, absorbs carbonic acid rapidly from the air, and precipitates oxide of silver from the solution of the nitrate. It is a strong base, neutralising acids completely, and ex- pelling ammonia from its salts. It melts at 230°, giving off water and ammonia, and leaving the compound NH3PtO. Its aqueous solution does not give off ammonia, even when boiled. Chloride, N2H6PtCl = NH2(NH4)Pt . CI.— This compound is prepared by boUing protochloride of platinum, or the green salt of Magnus, with aqueous ammonia, till the whole is dis- solved, and evaporating the liquid to the crystallising point. Or, by passing sulphurous acid gas into bichloride of platinum till the solution is completely decolorised, precipitating with carbonate of soda, dissolving the precipitate of sodio-platinous sulphite in hydrochloric acid, saturating the resulting solution of chloride of sodium and platinous chloride with ammonia, and dissolving the precipitate of N2H6PtCl and NHgPtCl in boiling hydrochloric acid. The filtered liquid on cooling deposits NHgPtCl, while the biammoniacal compound remains in solution and may be obtained by evaporation, mixed how- ever, with sal-ammoniac. It separates in bulky crystals of a faint yellow colour, containing 1 eq. water, which is com- pletely given off at 230°. At 482° it gives off ammonia, and leaves NHaPtCl. The anhydrous compound rapidly absorbs 376 PLATINUM. water from the air. The hydrate does not give off ammonia when treated with caustic alkalies in the cold, and is but very slowly decomposed by them, even with the aid of heat. Chloride of ammo-platammonium forms two compounds with bichloride of platinum. The first, whose formula is 2(NH2 (NH^) Pt. CI) + PtClg, is obtained as an olive-green precipitate on adding bichloride of platinum to a solution of NH7(NHJPt . CI ; the second, Nh7(NH J Pt . CI -f PtCl^, by treating the preceding with excess of bichloride of pla- tinum. The bromide and iodide of this series are obtained by treating the solution of the sulphate with bromide or iodide of barium : they crystallise in cubes. X * . The sulphate, NH2 (NH^) Pt . SO4, and the nitrate, NH2(NH4)Pt.N06, are obtained by decomposing the chloride with sulphate or nitrate of silver; they are neutral, and crystallise easily. Carbonates. — The hydrated oxide absorbs carbonic acid rapidly from the air, forming first, a neutral carbonate, NH2 (NH4) Pt . CO3 + no, and afterwards an acid salt, NH2(NH,)Pt.C03 + CO3H. 3. AmmoniO'platinic compounds; or, Bi-salts of platam- monium. — The oxide, l^Yi^iO<^=^VL.^t .O^j may also be regarded as oxide of oxy plat ammonium, NH3 (PtO) .0. It is obtained by adding ammonium to a boiling solution of am- monio-platinic nitrate ; it is then precipitated in the form of a heavy, yellowish, crystalline powder, composed of small, shining, rhomboid al prisms; it is nearly insoluble in boiling water, and resists the action of boiling potash. Heated in a close vessel, it gives off water and ammonia, and leaves metallic platinum. It dissolves readily in dilute acids, even in acetic AMMONIACAL PLATINUM SALTS. 377 acid, and forms a large number of crystallisable salts, both neutral and acid, having a yellow colour, and sparingly soluble in water (Gerhardt).* Another compound of platinic oxide with ammonia, called fulminating platinum, whose compo- sition has not been exactly ascertained, is produced by de- composing chloroplatinate of ammonium with aqueous potash. It is a straw-coloured powder which detonates slightly when suddenly heated, but strongly when exposed to a gradually increasing heat. Chloride, NH3PtCl2 = NH^. CI2 = NH3 (PtCl) . CI. — Obtained by passing chlorine gas into boiling water in which the compound NHgPtCl (the yellow modification) is sus- pended. This compound is insoluble in cold water, and very slightly soluble in boiling water, or in water containing hy- drochloric acid. It dissolves in ammonia at a boiling heat, and the solution, on cooling, deposits a yellow precipitate, consisting of biammoniacal platinic chloride. The compound NHgPt . CI2 dissolves in boiling potash without evolving am- monia. An isomeric compound, (NHaPtCl,), = N^HePtCl, + PtCl^ is obtained by passing chlorine into water in which Magnuses green salt is suspended. A red crystalline powder is at first precipitated, consisting of N2HgPtCl + PtCl2; but on con- tinuing the passage of the chlorine, this precipitate redis- solves, and the solution yields, by evaporation, the crystalline compound (NH3PtCl2)2- The sulphate, NHgPt . (804)3, ^^ obtained by dissolving the oxide in dilute sulphuric acid, and evaporating. It is a yellow powder, having an acid taste, and is soluble in boiling water. Nitrates. — A mononitrate, NH3Pt02 . NO5 + 3H0, or oxynitrate, NH3Pt . | q^ + 3H0, or nitrate of oxyplat- * Comptes Eendus des Traraux de Chimie, 1849, p. 273. 378 PLATINUM. ammonium^ NH3 (PtO) . NOg + 3H0, is obtained by boiling the chloride NH3PtCl2 for several hours with a dilute solution of nitrate of silver. It is a yellow, crystalline powder, spar- ingly soluble in cold, more soluble in boiling water. The binitrate, NHgPt . 2N06 + 2H0, is obtained by dissolving the mononitrate in nitric acid : it is yellowish, insoluble in cold water, soluble in hot nitric acid. The oxalate, ^"H^ViO^.C^O^ + 2H0, or NHgPtI ^2^4 ^ 2H0, or NH3 (PtO). C20^ + 2H0, is formed by decomposing the nitrate with oxalate of ammonia. It is a light yellow precipitate, soluble in boiling water, and detonating when heated. 4. BiammoniO'platinic compounds, or Bi-salts of ammo- plat ammonium. — The oxide of this series has not yet been isolated. Chloride. —-^^ HePtCl^ = N H^IN HJ Pt . CI2 = NH2 (NH J (PtCl) . CI. — Obtained by passing chlorine gas into a solution of biammonio-platinous chloride, N2H6PtCl; by dissolving ammonio-platinic chloride, NH3PtCl2, in am- monia, and expelling the excess of ammonia by evaporation ; or by precipitating a solution of one of the nitrates, N2HgPt02 . NO5, or N2H6PtC10 . NO5, with hydrochloric acid. It is white, and dissolves in small quantity in boiling water, jfrom which solution it is deposited in the form of transparent, regular octohedrons, having a faint yellow tint. When a solution of this salt is treated with nitrate of silver, one half of the chlorine is very easily precipitated, but to remove even a small portion of the re- mainder requires a long -continued action of the silver-salt; a result easily explained if the salt be regarded as a chlo- AMMONIACAL PLATINUM SALTS. 379 ride of ammo-chlorplatammonium, NH2 (NHJ (PtCl) . CI (Grimm.)* A compound having the formula N2H5PtCl, containing, therefore, 1 eq. CI and 1 eq. H less than the pre- ceding, is obtained by dissolving chloroplatinate of ammonium in ammonia, and precipitating by alcohol; but it does not crystallise, merely drying up to a pale yellow, resinous mass : hence its composition is doubtful. Nitrates. — A mononitrate, N2HgPt02.N05,or oxynitrateof ammoplatammonium,NH2(NH4)Pt| q^ or nitrate of am- moxyplatammonium, NH2 (NH4) (PtO) . NOg, is obtained by boiling the following salt 5, with ammonia : it is a white amorphous powder, slightly soluble in cold, more soluble in boiling water. Sesquinitrate, 2(N2H6Pt02) .SNOg, or 2('NH2(NH,)PtY "^^^^ or , .^-. pNOg.- V / i ^ NH2(NHJ(PtN06)J Formed by boiling the mononitrate of ammoplat ammonium with nitric acid. It is a colourless, crystalline, detonating salt, slightly soluble in cold water, more soluble in boiling water, insoluble in nitric acid (Gerhardt). Chloronitrates.—a. NaHfiPtClO .NO.; or NH^^NEgPt . { "^ci' «^ NH^(NlSj^Pta) . NOg. — This salt was discovered by Gros. It is obtained by treating Magnuses green salt with strong nitric acid. The green compound first turns brown, and is afterwards converted into a mixture of platinum and a white powder, which is dissolved out by boil- ing water, and crystallises on cooling in shining flattened prisms, colourless, or having a pale yellow tint. The reaction may be thus represented : — 2(NH3PtCl) + HO . N05=N2H6PtCl . NOg f I*t-f HCl. * Ann. Cli. Pharm. xcix. 77. VOL. TI. D D 380 PLATINUM. This compound dissolves readily in water, especially T\'hcn heated. The chlorine and platinum contained in the solution cannot be detected by the ordinary reagents ; thus, nitrate of silver and hydrosulphuric acid yield but very trifling precipi- tates, even after a long time. b, 4NH3 . PtaClOa . 2NO5, or ^IWH4)(PtCl) | gNOg. NH2(NHJ(PtCl)) Discovered by Raewsky. When Magnus's green salt is boiled with a large excess of nitric acid, red fumes are evolved, and the resulting solution deposits this salt in small, brilliant, needle-shaped prisms, which deflagrate when heated, giving off water and chloride of ammonium, and leaving metallic platinum. Raewsky assigns to this salt the formula 4NH3 . PtjClOg . 2NO5 ; but the formula above given, which is deduced from Gerhardt's analysis, and contains 20 less, is much more probable, as it accords with the constitution of the other compounds of the series. The 2 atoms of nitric acid contained in this salt may be replaced by 2 atoms of carbonic or oxalic acid, yielding sparingly soluble ci-ystalline salts of exactly similar constitution. There is also a phos- phate containing iNH, . Pt2C103 . PO5 . HO, o])tained by mixing the solution of the nitrate with ordinary phosphate of soda. According to Raewsky, the mother-liquor from which the preceding nitrate has crystallised, contains another nitrate whose formula is 4NH3.Pt2Cl2O4.2NO5; but Gerhardt finds this salt to be identical with the nitrate discovered by Gros. Chlorosulphate, N2H6PtClS04=NH^(NlSj^Ptci) . SO^.— Obtained by treating biammonio-platinic chloride, or Gros's nitrate, with dilute sulphuric acid, or by mixing the solution of the nitrate with a strong solution of a soluble sulphate. It crystallises in slender needles, sparingly soluble in cold water, but dissohdng with tolerable facility in boiling water. The AMMONIACAL PLATINUM SALTS. 381 sulphuric acid in the solution is not precipitated by baryta- salts. The salt is, however, decomposed by hydrochloric or nitric acid, either of which takes the place of the sulphuric acid, reproducing the chloride or nitrate (Gros). Chloroxalate, NaHgPtClO . C2O3 = NH2(NH4)Pt | ^ cl "^ NH2(NH4)(PtCl) . C2O4. — Oxalic acid or an alkaline oxalate added to the solution of the corresponding sulphate or nitrate, throws down this salt in the form of a white granular pre- cipitate, insoluble in water. Oxalonitrates. — a. N2HgPt02 . NO5 . C2O3 = NH^mjpt. [c^\ = nh^cnhIkpIno;) . c A- Deposited as a white crystalline body from a solution of the following salt b in dilute nitric acid. b. 2(N2H6Pt02) . NO5 . 2C2O3 = 2(NH^(]NT^ .1 NO^ = ^ ■ . i O NH2(Nh') (PtNOg) } 2C20,.-Obtained by adding oxalate of ammonia to a solution of the sesquinitrate ; it is insoluble in water (Gerhardt). GERHARDt's theory of the AMMONIACAL PLATINUM COMPOUNDS. These compounds may be regarded as salts of peculiar bases or alkalies, formed from ammonia by the substitution of one or two atoms of platinum for hydrogen ; admitting, however, that platinum (like other metals) may enter into its com- pounds with two different equivalent weights, viz., in the platinow* compounds, as Platinosum = 98*68 = Pt, and in the platinic compounds, as Platinicum = 49*34 = pt. This being- admitted, the ammonio-platinous compounds may be regarded as salts of an alkali, called Platosamine = NH2Pt, formed from ammonia by the substitution of 1 atom of platinosum for 1 atom of hydrogen ; and the biammonio-platinous compounds, D D 2 382 PLATINUM. as salts of Diplatosamine = NgH^Pt, formed by the union of two atoms of ammonia into one, and the substitution therein of 1 Pt for IH : thus for the chlorides : — NH3PtCl= Hydrochlorate of Platosamine = NH2Pt . HCl ; N2H6PtCl=HydrochlorateofDiplatosamine=N2ll5Pt.HCl; and for the nitrates : — NH3Pt.N06= Nitrate of Platosamine=NH2Pt . HNOg; NsHgPt.NOgrr: Nitrate of Diplatosamine =N2H5Pt . HNOg. In a similar manner, the ammonio-platinic compounds may be regarded as salts of Platinamine = NHpt2, and the biammonio-platinic compounds as salts of Diplatinamine = N2H4pt2; thus — NHaPtClj = Bihydrochlorate of Platinamine = NHpt2 . 2HC1. N2ll6PtCl2 = Bihydrochlorate of Diplatinamine = N2H4pt2 . 2HC1. Diplatinamine forms three kinds of salts, viz., mono-acid, sesqui-acid, and bi-acid salts ; and, moreover, exhibits a peculiar tendency to form double salts containing two acids : thus, the salts discovered by Gros may be regarded as bi-acid salts, and those discovered by Raewsky, as sesqui-acid salts of diplatinamine containing hydrochloric together with another acidj thus: — Mononitrate =N2H6Pt02 . N05 = N2H4pt2 . HN06 + HO. Sesquinitrate=2(N2H6Pt02) . SNOg = 2N2H4pt2 . SHNOg + HO. fSSre)} =N,H«PtC10.N0, = N,H,pt,. |HC1^^ Oxalonitrate = N2H6Pt02 . NO5 . C2O3 = N2H4pt2 . | ^^^q * Sesqui-oxalonitrate = 2(N2H6Pt02) . NO5 . 2C2O3 = 2N2H,pt2.f^5g^ + HO. ESTIMATION OF PLATINUM. 383 ESTIMATION AND SEPARATION OP PLATINUM. For quantitative estimation, platinum is usually precipitated from its solutions in the form of cMoroplatinate of ammonium. The acid solution of platinum, after sufficient concentration, is mixed with a very strong solution of sal-ammoniac, and a sufficient quantity of strong alcohol added to render the pre- cipitation complete. The precipitate of chloroplatinate of ammonium is then washed with alcohol, to which a small quantity of sal-ammoniac has been added, and then heated to redness in a weighed porcelain crucible, whereupon it is de- composed and leaves metallic platinum. Great care must, however, be taken in the ignition to prevent loss, as the evolved vapours are very apt to carry away small particles of the salt and of the reduced metal. The best mode of avoiding this source of error is to place the precipitate in the crucible enclosed in the filter, and expose it for some time to a moderate heat, with the cover on the crucible, till the filter is charred, and then to a somewhat higher temperature to expel the chlorine and chloride of ammonium. The crucible is then partially opened and the carbonaceous matter of the filter burnt away in the usual manner. When these precautions are duly observed, not a particle of platinum is lost. Instead of igniting the precipitate and weighing the platinum, the precipitate is sometimes collected on a weighed filter, dried over the water-bath and weighed ; but this method is less accurate, because the precipitate always contains an excess of sal-ammoniac (H. Eose). Chloride of potassium may also be used instead of chloride of ammonium to precipitate platinum, the concentrated so- lution of the platinum being previously mixed with a sufficient quantity of strong alcohol to bring the per centage of alcohol in the liquid to between 60 and 70 per cent. The precipitated chloroplatinate of potassium is then washed with alcohol of D D 3 384 PALLADIUxM. 60 to 70 per cent, and decomposed by simple ignition in a porcelain crucible, if its quantity is small, or in an atmo- sphere of hydrogen if its quantity is larger ; the chloride of potassium washed out by water; and the platinum dried, ignited, and weighed. Potash and ammonia may also be estimated by precipitat- ing their solutions with chloride of platinum, and treating the precipitates in the manner just described. Every 100 parts of platinum correspond to 47*83 parts of potash, and 17*25 parts of ammonia. The same methods of precipitation serve also for the separation of platinum from most of the preceding metals. To separate platinum from silver, when tlie two metals are combined in an alloy, the best method is to heat the alloy with pure and strong sulphuric acid, diluted with about half its weight of water, till the sulphuric acid begins to escape in dense fumes. The silver is thereby converted into sulphate, and the platinum remains behind in the metallic state. The sulphate of silver is dissolved by a large quantity of hot water, the platinimi washed with hot water, and again treated with sulphuric acid, to separate the last traces of silver. SECTION II. PALLADIUM. ^g. 53*36 or 665*9; Pd. This metal was discovered in 1803 by Dr. Wollaston. It is precipitated by cyanide of mercury from the solution of the ore of platinum, after the removal of that metal by sal-ammoniac, and is gradually deposited as a yellowish white flocculent powder, which is cyanide of palladium, and yields the metal when calcined. Palladium likewise occurs, asso- ciated with a larger quantity of gold and a small quantity of PROTOXIDE OF PALLADIUM. 385 silver_, in a peculiar gold-ore from Brazil, called oropudre. This mineral, which contains 10 per cent, of palladium, and is the chief source of that metal, is dissolved in aqua-regia, the acid solution saturated with potash, and the palladium precipitated by cyanide of mercury. In external characters, palladium closely resembles pla- tinum. It is nearly as infusible, but can more easily be welded. The density of the fused metal is 11-3 ; after being laminated, 11'8. At a certain temperature, the surface of palladium tarnishes and becomes blue from oxidation, but at a stronger heat the oxide is reduced. Palladium is very slightly attacked by boiling and concentrated hydrochloric and sulphuric acids. It dissolves in nitric acid, communi- cating a brownish red colour to the acid, while no gas is evolved if the temperature is low, the nitric acid being con- verted into nitrous acid. Palladium dissolves with facility in aqua-regia; its surface is blackened by tincture of iodine, which has no effect upon platinum. Palladium is sometimes used for making the divided scales of astronomical instruments ; being nearly as white as silver, and not blackened by sulphurous emanations, it is well adapted for that purpose. An alloy of palladium with I -10th of its weight of silver is used by dentists. Palladium has a much greater affinity for oxygen than platinum. It forms two oxides, the protoxide PdO, and the bioxide Pd02. Protoxide of palladium, Palladous oxide, PdO, 61 '27 or 765*9. — This oxide is obtained by dissolving palladium in nitric acid, evaporating the solution to dryness, and calcining the nitrate at a gentle heat. It forms a black mass, which dissolves with difficulty in acids. When carbonate of potash or soda is added in excess to a palladous salt, the hydrated protoxide precipitates of a very dark brown colour. This oxide is easily deprived of its water by heat, but a violent calcination is necessary to reduce it to the metallic state. D D 4 386 PALLADIUM. The palladous salts are for the most part brown or red ; their taste is astringent, but not metallic. AVhen ignited alone, or when gently heated in hydrogen gas, they yield metallic palladium. The metal is precipitated from the solu- tions of palladous salts by phosphorus, by sulphurous acid, by nitrite of potash, by all the metals which reduce silver, by forrniate of potash, and by alcohol at a boUing heat. Hydro- sulphuric acid and hydrosulphate of ammonia throw down the brown sulpliide of palladium, insoluble in the latter reagent. Hydriodic acid and iodide of potassium throw down a black precipitate of iodide of palladium, visible even to the 500,000th degree of dilution. This reaction serves for the separation of iodine from bromine ; for alkaline bromides do not precipitate palladous salts. Potash or soda forms a brown precipitate of a basic salt, soluble, with the aid of heat, in excess of the reagent. Ammonia produces no precipitate in a solution of palladous nitrate; but from a solution of the chloride it throws down a flesh-coloured precipitate of ammonio-chloride of palladium, soluble in excess of ammonia. The carbonates of potash and soda form a brown precipitate of hydratcd palladous oxide. Carbonate of ammonia acts like ammonia. Phosphate of soda forms a brown precipitate. Ferroryanide and ferricyanide of potassium form no preci- pitates, but the liquid after a while coagulates into a jelly. Cyanide of mercury throws down a white precipitate of cyanide of palladium. Protochloride of tin forms a black precipitate, which dissolves with intense green colour in hydrochloric acid. Protosulphate of iron precipitates palla- dium slowly from the nitrate, but not from the chloride. The reactions of palladium with hydrosulphuric acid, cyanide of mercury, and iodide of potassium taken together, serve to distinguish it from all other metals. Protosulphide of palladium, PdS, is obtained by precipi- tating a palladous salt by hydrosulphuric acid, and is of a dark PALLADOUS COMPOUNDS. 387 brown colour ; it may also be prepared by the direct union of its elements. Protochloride of palladium , PdCl^ is prepared by dissolving palladium in hydrochloric acid^ to which a little nitric acid is added, and evaporating the solution to dryness, to expel the excess of acid. The compound is a mass of a dark brown colour, which becomes black when made anhydrous by heat, and may be fused in a glass vessel. When heated in platinum vessels, it becomes contaminated with the protochloride of that metal. When dissolved with chloride of potassium, it forms a double salt, KCl . PdCl, which is soluble in cold, and consi- derably more so in hot water, and crystallises in fonr-sided prisms, of a dull yellow colour. Protochloride of palladium also combines with chloride of ammonium and chloride of sodium, according to BonsdorfF, and forms double salts with most other chlorides. Protocyanide of palladium, PdCy, is always formed when cyanide of mercury is added to a neutral solution of palladium, as a light-coloured precipitate, which becomes grey after dry- ing. When the solution of palladium is acid, no precipitate is formed, and when the solution contains copper, the preci- pitate has a green colour. Palladium appears to have a greater affinity for cyanogen than any other metal. Even cyanide of mercury is decomposed when boiled with protoxide of palladium, and cyanide of palladium formed. When this cyanide is dissolved in ammonia, and the excess of the latter allowed to escape by evaporation, a precipitate of brilliant, colourless, crystalline plates is formed, which appears to con- sist of ammoniacal cyanide of palladium. Nitrate of palladium, PdO . NO5, is formed by dissolving the metal in nitric acid -, the solution dries up into a dark red saline mass. When an excess of ammonia is added to an acid solution of this salt, and the solution evaporated by a gentle heat, a colourless nitrate of palladium and ammonium is deposited in rectangular tables. 388 PALLADIUM. Bioxide of palladium, Peroxide of palladium, Palladia oxide, PdOj, 69-27 or 865*9. — To prepare this oxide, Berzelius re- commends a solution of the liydrate or carbonate of potash to be added by small quantities at a time, to the dry bichloride of palladium and potassium, mixing well after each addition. A yellowish brown powder separates, which is the hydrated bioxide, retaining a little alkali. Washed with boiling water, it loses the greater part of its combined water and becomes black. This oxide dissolves with difficulty in acids ; the solu- tions are yellow. The corresponding bisulphide of palladium has not been formed. Bichloride of palladium, Pd CI2, is obtained in solution, when the protochloride is dissolved in concentrated aqua- regia, and the solution only slightly heated. Its solution is of so dark a brown as to appear black, and gives a red preci- pitate with chloride of potassium. When the solution is diluted or heated, chlorine gas is evolved, and protochloride of palladium reproduced. The double salt of this chloride and chloride of potassium is obtained by treating the double protochloride of palladium and potassium in fine powder with aqua-rcgia, and evaporating the sujiernatant fluid to dryness. It forms a cinnabar red powder, in which little octohedral crystals can be perceived, both the palladic and palladous double chlorides being isomorphous with the corresponding compounds of platinum. When treated Avith hot water, this double salt emits chlorine, and is in a great measure decom- posed. The salts of bioxide of palladium are scarcely known. Ammoniacal compounds of palladium. — A moderately con- centrated solution of protochloride of palladium treated with a slight excess of ammonia, yields a beautiful flesh-coloured or rose-coloured precipitate, consisting of NHgPdCl. This precipitate dissolves in a larger excess of ammonia; and the ammoniacal solution, when treated with acids, yields a yellow precipitate having the same composition. This yellow modi- fication is likewise obtained by heating the red compound in AMMONIACAL COMPOUNDS OF PALLADIUM. 389 the moist state to 212°, or in the dry state to 392°. The yellow compound dissolves abundantly in aqueous potash, forming a yellow solution, but without giving off ammonia, even when the liquid is heated to the boiling point ; the red compound behaves in a similar manner, but, before,dissolving, is converted into the yellow modification. For this reason, Hugo Miiller, who has lately made the ammoniacal compounds of palladium the subject of an elaborate examination, regards the red compound as ammomo-palladous chloride, NHg.PdCl, and the yellow, as chloride of palladammonium, NHgPd . CI. The yellow compound, digested with water and oxide of silver, yields the oa7ic?e of palladammonium {or palladamine),'N}l^Vd.O. This compound is a strong base, analogous to oacide of plat- ammonium (p. 374). It is soluble in water, to which it com- municates a strong alkaline taste and reaction ; by evaporating the solution in vacuo, the base is obtained in the form of a crystalline mass, which absorbs carbonic acid rapidly from the air, especially when moist. It unites with acids, forming definite salts. Its solution precipitates the salts of silver and copper, and an excess of it does not redissolve the precipi- tates. Sulphite of palladammonium, NH3Pd . SO3, is formed by saturating the solution of the oxide with sulphurous acid, or by the action of that acid on the yellow chlorine-compound : it crystallises in orange-yellow octohedrons. The sulphate, NH3Pd . SO4, crystallises in a similar manner. The nitrate, iodide, and bromide have also been formed. The fluoride is obtained by adding the chloride to a solution of fluoride of silver. Chloride of ammopalladammonium (or chloride of pallad^ diamine, according to Miiller), 2NH3 . PdCl = NH2 (NliJ Pd . CI, separates from the ammoniacal solution of chloride of pal- ladammonium, in colourless, oblique rhombic prisms, which 390 PALLADIUM. at 392° give off half tlieir ammonia and are reduced to NHgPd . CI. The iodide and bromide of ammopalladam- monium are likewise obtained by treating the solutions of iodide and bromide of palladium or palladammonium with ammonia. ^ They both crystallise readily. The fluoride is obtained by adding ammonia to the solution of chloride of palladammonium in fluoride of silver, and evaporating : it forms oblique rhombic prisms. The silico-fluoride is obtained in crystalline scales on adding hydrofluosilicic acid to any so- luble salt of ammopalladammonium. Oxide of ammopalladam- monium^ NHgPd . O. — By decomposing the solution of the chloride with oxide of silver, — or better, the sulphate with hydrate of baryta, a strongly alkaline solution is obtained, which, on evaporation, leaves the hydrated oxide in the form of a crystalline mass, though not quite pure. The solution precipitates the salts of aluminium, iron, cobalt, nickel, and copper, but not those of silver ; expels ammonia from cliloride of ammonium, on boihng ; and absorbs carbonic acid from the air. The carbonate obtained in this manner, or by de- composing the chloride with carbonate of silver, or the sulphate with carl)onate of baryta, crystallises in shining, colourless prisms, which turn yellow a little above 212°; the solution is strongly alkaline, and gives copious precipitates with salts of lime, baryta, copper, and silver. The sulphite^ NH2 (NH^) Pd . SO3, obtained by direct combination, or by the action of ammonia on sulphite of palladammonium, forms small prismatic crystals, sparingly soluble in water, insoluble in alcohol, and turning yellow at about 392°. The sulphate obtained by treating palladous sulphate with excess of am- monia, forms small colourless prisms, easily soluble in water, but insoluble in alcohol (Hugo MuUer).* * Ann. Ch. Pharm. Ixxxvi. 311. IlilDIUM. 391 ESTIMATION AND SEPARATION OF PALLADIUM. Palladiuin is always estimated in the metallic state. It is precipitated from its solutions in the form of cyanide by means of a solution of cyanide of mercury, the liquid not containing any excess of acid. The precipitated cyanide of palladium is then reduced to the metallic state by calcination. Palladium may be separated from nearly all other metals either by precipitation as cyanide, or by precipitation with hydrosulphuric acid, or by the solubihty of its oxide in am- monia. But to separate it from copper, with which it is associated in platinum ore, the two metals are precipitated together by hydrosulphuric acid, and the precipitate, while still moist, roasted, together with the filter, as long as sul- phurous acid continues to escape. The metals are thereby converted into basic sulphates, which must be dissolved in hydrochloric acid, the solution mixed with nitric acid and chloride of potassium, and evaporated to dryness. A dark saline mass is thus obtained, consisting of chloride of potas- sium, chloride of copper and potassium, and chloride of pal- ladium and potassium ; and on treating this mass mth alcohol of sp. gr. 0-833, the two former salts are dissolved, and the double chloride of palladium and potassium remains. SECTION III. IRIDIUM. Eq. 98-68, or 1233-5; Ir. The black scales which remain when native platinum is dissolved in aqua-regia, were discovered by Mr. Smithson Tennant to contain iridium and osmium.* The same alloy * PhU. Trans. 1804. 392 IRIDIUM. occurs in flat white metallic grains in native platinum. Iri- dium has also been observed in combination with about 20 per cent, of platinum^ crystallised in octohedrons, which are whiter than platinum, and are said to have a greater density, namely 22*66. The separation of the osmium and iridium is effected by the following methods : — 1 . The osmide of iridium is mixed with an equal weight of common salt, and subjected to the action of a stream of chlorine in a porcelain tube heated to redness. Double chlorides of iridium and sodium, and of osmium and sodium, are then formed ; and if the chlorine is moist, a certain quantity of osmic acid, which volatilises, and may be condensed in aqueous ammonia. The mixture of the double chlorides is detached from the tube and boiled with nitric acid. Osmic acid is then evolved, and may be con- densed in an alkaline solution, while the chloride of sodium and iridium remains in the solution, and, when mixed with sal-ammoniac, yields a precipitate of chloride of iridium and ammonium, which, on ignition, leaves pure metallic iridium (Wohler). — 2. A mixture of 100 grammes of osmide of iridium and 300 grammes of nitre is placed in an earthen crucible, and heated to bright redness for an hour, the re- sulting mixture of osmiate and iridiate of potash poured out on a cold metal plate, then introduced into a tubulated retort, and distilled with a large excess of nitric acid. A large quantity of osmic acid then volatilises and condenses in the receiver in beautiful white ciystals. As soon as the evolution of osmic acid ceases, water is added, and the residue, con- sisting of oxide of iridium, with a certain quantity of oxide of osmium, is collected on a filter and boiled with aqua-regia, which dissolves the two metals as chlorides. The solution is then mixed with sal-ammoniac, which precipitates chloride of osmium and ammonium, and bichloride of iridium and am- monium ; and the mixed precipitate suspended in water and ex- posed to a current of sulphurous acid, whereby the compound IRIDIUM. 393 IrCl2.NIl4Cl, is converted into IrCl.NH^Cl, which dissolves, ■while the chloride of osmium and ammonium remains un- altered and does not dissolve : this latter chloride yields pure metallic osmium by calcination. The solution of protochloride of iridium and ammonium leaves, when evaporated, beautiful brown crystals, which yield metallic iridium by calcination. Iridium is obtained immediately from the chloride, by decomposing that salt with hydrogen at a gentle heat, or by exposing it alone to a very high temperature, in the form of a grey metallic powder, much resembling spongy platinum; also, as above described, from the chloride of iridium and ammonium. It is one of the most refractory bodies known, not being fused by the oxyhydrogen blowpipe. Mr. Chil- dren, however, succeeded in fusing a portion of iridium into a globule, by the discharge of a very large voltaic battery. This globule was white and very brilliant, but still a little porous; its density was 18*68. Iridium is neither ductile nor malleable ; but it may be obtained in the form of a com- pact mass, very hard, and capable of taking a good polish, by moistening the pulverulent metal with a small quantity of water, compressing it lightly at first with filtering paper, afterwards very forcibly in a press, and calcining it at a strong white heat in a forge fire. The metal thus aggregated is very porous, and its density does not exceed 16*0. Iridium be- comes white and brilliant by strong ignition, without fusion, and is afterwards insoluble in acids. If reduced by hydrogen at a low temperature, it oxidates slowly when heated to red- ness, or when digested in aqua-regia. This metal is generally rendered soluble by one or other of the following operations. It is calcined with hydrate of potash or nitre, or with a mixture of these salts, which gives a compound of sesqui- oxide of iridium and potassium. Or, the metal is reduced to a fine powder, and intimately mixed with an equal weight of chloride of potassium or sodium, and the mixture heated to low redness in a stream of chlorine gas. The metal then 391 IRIDIUM. combines with chlorine, and the double chloride of iridium and potassium or sodium is formed, which is soluble in water. Oxides of iridium. — Iridium forms four compounds wiih oxygen, which are obtained by decomposing the corresponding chlorides. The protoxide of- iridium^ IrO, is obtained from the chloride produced when iridium is heated in chlorine gas; also by precipitating the double chloride of iridium and potas- sium (KCl . IrCl) with carbonate of potash. The hydrate is then obtained of a greenish grey colour, which is soluble in an excess of the alkaline carbonate. This oxide is the base of a class of salts. The sesquioxide cf iridium, Ir203, is formed when the metal is calcined with hydrate of potash or nitre. Berzelius recommends as the best process for pro- curing it, to mix the double bichloride of iridium and potas- sium (KCl + IrCl2) with twice its weight of carbonate of potash, and expose it to a low red heat. On dissolving out the alkaline salt, the sesquioxide remains as a very fine pow- der, of a black colour with a shade of blue. A heat above the melting point of silver is required to expel the oxygen from this oxide. It is reduced to the metallic state by hydro- gen gas at the usual temperature, an effect which appears to arise from the oxide of iridium having the property, as well as the metal, to determine the oxidation of hydrogen, a reaction which causes the oxide to be heated to the temperature at which it is itself reduced by hydrogen. The hydrate of this oxide dissolves in acids and forms a particular class of salts, the solutions of which are sometimes of a very dark colour, resembling a mixture of water and venous blood. Bioxide of iridium, or Iridic oxide, IrOj. — A solution of sesquichloride of iridium mixed with potash yields no preci- pitate at first ; but if the liquid be heated out of contact with the air, it quickly assumes an indigo colour, absorbs oxygen from the air, and deposits hydrated iridic oxide, IrOg . 2H0, which may be rendered anhydrous by calcination. This oxide is likewise obtained by dissolving the hydrated sesquioxide in SALTS OP IRIDIUM. 395" potash, and treating the solution with an acid. A greenish- blue precipitate is then formed, which gradually absorbs oxygen from the air, and assumes an indigo colour (Claus). This oxide forms salts whose solutions are of a dark, brown- red colour and almost opaque when concentrated, but reddish- yellow when dilute. Hydrosulphuric acid decolorises the solutions at first, and afterwards forms a brovm precipitate ; hydrosulphate of ammonia also forms a brown precipitate. Potash and ammonia decolorise the solution, and produce only a slight black precipitate ; but the liquid, on exposure to the air, soon acquires a very fine blue colour. Carbonate of potash forms a red-brown precipitate, which gradually dis- solves, the liquid afterwards turning blue when exposed to the air. Carbonate of ammonia imparts a blue colour to the liquid under the influence of the air. Chloride of ammonium forms a dark, cherry-red pulverulent precipitate of bichloride of iridium and ammonium. Ferrocyanide of potassium and protosulphate of iron decolorise the solution. Protochloride of tin forms a light brown precipitate. Zinc precipitates metallic iridium as a black powder. Teroxide of iridium, IrOg, is formed in small quantity when the alloy of osmium and iridium fused in nitre is digested in aqua-regia. The double terchloride of iridium and potassium then formed yields a rose-red solution, which, when treated with an alkali, slowly deposits the teroxide as a greenish-yellow precipitate, retaining, however, a cer- tain quantity of the alkali. The salts of the protoxide and teroxide afford blue and purple solutions when mixed, depending probably on the formation of one or more com- binations of these oxides. The name iridium (from Iris) was applied to this metal, from the variety of colours which its preparations exhibit. Sulphides of iridium, corresponding with the oxides of the same metal, have been formed. Chlorides of iridium. — The protochloride, IrCl, is formed VOL. II. E E 396 IRIDIUM. when iridium in powder is heated to low redness in chlorine gas. As thus prepared, it is insoluble in water, but slightly- soluble in hydrochloric acid. It forms double salts with the chlorides of potassium, ammonium, and sodium. The sesquichloride, Ir2Cl3, is prepared by dissolving the sesquioxide in hydrochloric acid. It is black, deliquescent, and does not crystallise. It forms soluble double chlorides, which are decomposed by ebullition into iridous double chlo- rides (containing IrCl), which remain in solution, and iridic double chlorides (containing IrClg), which are precipitated. Glaus has obtained the compounds, 3KC1 . Ir2Cl3 -h 6H0 ; 3NH4CI . Ir^Clg + 3H0 ; and 3NaCl . Ir2Cl3 + 2 IHO. The bichloride, IrCl2, is obtained by dissolving very finely- divided iridium, or one of its oxides, in aqua-regia. the liquid being heated to the boiling point. It dissolves in water, forming a reddish-yellow solution. It combines with other chlorides, forming very definite salts. The potassium-salt, chloridiate of j^otassium, IrClg.KCl.IIO, crystallises in black octohedrons, yielding a red powder, and soluble in water, to which it imparts a red colour. Chloridiate of ammoniu7n, IrClg . NH4CI .HO, is obtained, on mixing the solutions of the two chlorides, as a very dark brown precipitate, which dissolves in boiling water, and crystallises in octohedrons on cooling. Its colouring power is very great, 1 part of it sufficing to impart a distinct coloration to 40,000 parts of water. The red colour often exhibited by chloroplatinate of ammonium is due to traces of this salt. Chloridiate of am- monium dissolves in sulphurous acid, and is thereby converted in a soluble and crystallisable compound of NH4CI, and IrCl ; the separation of iridium and osmium depends upon this property. Bichloride of iridium, free or combined with other chlorides, is also reduced to the s':ate of protochloride by potash, hydrosulphuric acid, ferrocyanide of potassium, and alcohol. According to Claus,* the bichloride is converted * Liebig and Kopp's Jahresbericht, 1855, p. 427. AMMOx\IACAL COMPOUNDS OF IRIDIUM. 397 by potash into tlie olive-green sesquichloride, hypochlorite of potash being formed at the same time. The alkaline solution when heated becomes colourless, and afterwards violet-red, and yields a blue precipitate of the hydrated bioxide; the decolorised alkaline solution, mixed with a few drops of alcohol and heated, deposits metallic iridium. Nitrate of silver added to the solution of the bichloride forms a blue pre- cipitate, which quickly loses its colour and passes into the compound Ir2Cl3 . 3AgCl. Mercurous nitrate forms a light ochre-yellow precipitate of IrgClg . 3Hg2Cl. Terchloride of iridium, IrClg, is formed by treating an oxide or a lower chloride of iridium with very strong aqua- regia, at a temperature not exceeding 104° or 122° (40° or 50° C). Its colour is a deep brown, nearly approaching to black; it is soluble in water, and deliquescent. It forms double chlorides with the chlorides of the alkali-metals. Carburet of iridium. — When a coherent mass of iridium is held in the flame of a spirit lamp, black masses appear on its surface, which are a carburet, containing 19*83 per cent, of carbon, or IrC^. The carbon bums off readily in the air. Iridic sulphate is obtained by dissolving bisulphide of iridium in nitric acid and expelling the excess of acid by evaporation. It dissolves in water and alcohol, forming orange-yellow solutions, which on evaporation leave the salt in the form of a syrupy uncrystallisable mass. Ammoniacal Compounds of Iridium, — Ammonio-iridious chloride, NH3 . IrCl, or Chloride of iridammonium, NH3lr . CI. — Prepared by heating bichloride of iridium till it is converted into protochloride, dissolving the brown resinous residue in carbonate of ammonia, and adding hydrochloric acid in slight excess. The compound then separates in the form of a yellow granular precipitate, insoluble in water. The oxide correspond- ing to this chloride has not been obtained in the free state. The sulphate NH3lr . SO4 is obtained by heating the chloride £ £ 2 398 IRIDIUM. with dilute sulphuric acid. It crystallises in large orange- yellow laminae, easily soluble in water. Biammonio-iridiotis chloride, 2NH3 . IrCl, or Chloride of ammiridammonium, ^ ' NH2(NH4)Ir. CI, is obtained, as a white precipitate, by boiling the compound, NHglr . CI, with excess of ammonia. Treated with moderately strong sulphuric acid, it yields the corresponding sulphate, NH2(NH4)Ir . SO4, in rhombic prisms ; and, by decomposing this salt with nitrate of baryta, or decomposing the chloride with nitric acid, the nitrate is obtained in yellow needles, which dissolve readily in water, melt when heated, and then suddenly decompose T^dth flame. A chloronitraie of ammiridammonium, NH2(NH4)Ir.| ^p or nitrate of ammochlonHdammonium, NH2(NH4)(IrCl).NOg, analogous to Groses platinum-nitrate (p. 379), is obtained as a yellowish, crystalline, granular mass, by heating the chloride of iridammonium, NHglr . CI, with strong nitric acid ; when recrystallised from water, it forms shining yellow, laminar crystals. Bichloride of ammiridammonium, NH2(NH^)Ir . Clj, . ^ or chloride of ammO'Chloriridammonium,'^!^^^^ ^^^^^) • CI, is obtained by treating the last-mentioned salt with hydro- chloric acid, in the form of a violet precipitate, which dissolves readily in hot water, and separates from the solution in violet crystals. Nitrate of silver added to the solution throws down only half the chlorine. The nitrate, treated with dilute sul- phuric acid, yields the chlorosulphate of ammiridammonium in delicate greenish, needle-shaped crystals (Skoblikoff). The compound SNH, . IrClg, or ^ H2(NHJI r| ^^^^ .^ ^^_ NH(NHj2lr^ taincd by mixing a dilute solution of Ir2C]3 + SNH^Cl, mixed with excess of ammonia, and leaving the mixture in a well- closed and completely filled bottle for some weeks in a warm place; heating the liquid, which has then acquired a rose- ESTIMATION OF IRIDIUM. 399 colour, to expel the excess of ammonia; neutralising with, hydrochloric acid ; evaporating to dryness ; and treating the greenish yellow residue with cold water to extract the chloride of ammonium. A light flesh-coloured, finely crystalline powder then remains, which, when dissolved in boiling water, acidulated with hydrochloric acid, yields, on cooling, a crys- talline precipitate of 5NH3 . Ir2Cl3 mixed with sesquichloride of iridium. This compound when dissolved in a boiling solu- tion of ammonia, is partially decomposed, with separation of blue hydrated bioxide of iridium ; when digested with water and oxide of silver, it yields a rose-coloured alkaline solution of the base 5NH3 . Ir203. This solution, saturated with various acids, yields : — the carbonate, 5NH3 . Ir203 . 3C02 + 3HO, in the form of a finely crystalline powder, having a light flesh- colour and alkaline reaction; i\iQ nitrate, 5NH3.Ir2O3.3NO5, in indistinct, light flesh-coloured, neutral prisms ; and the sulphate, 5NH3 . Ir203 . 380^, as a neutral crystalline salt of similar colour. All these salts are soluble in water (Claus). ESTIMATION AND SEPARATION OF IRIDIUM. The quantitative estimation of iridium is effected in the same manner as that of platinum, viz. by precipitating with sal-ammoniac and igniting the precipitate. The same method serves to separate iridium from all the preceding metals except platinum. The separation of these two metals is effected by the method already described for the preparation of pure platinum (p. 336) ; viz. by precipitating with chloride of potassium, fusing the precipitate with carbonate of potash, and dissolving out the platinum with aqua-regia. £ E 3 400 OSMIUM. SECTION IV. OSMIUM. Eq, 99-56 or 12445 ; Os. In the treatment of the aUoy of iridium and osmium, the latter is separated as a volatile oxide, or osmic acid (p. 394) . To obtain the metal, a solution of osmic acid is mixed with hydrochloric acid, and digested with mercury in a well closed bottle at a temperature of 104° (40° Cent.). The osmium is reduced by the mercury, and an amalgam formed, which is distilled in a retort, through which a stream of hydrogen is passed, till all the mercury and calomel formed are re- moved : osmium then remains as a black powder without metallic lustre. Metallic osmium is also obtained by igniting the sesquichloride of osmium and ammonium mixed with sal- ammoniac. When rendered coherent, osmium is a white metal, less brilliant than platinum, and very easily pulverised. Its den- sity is about 10. As obtained from the amalgam, osmium is highly combustible ; when a mass of it is ignited at a point, it continues to redden, and burns without residue, being con- verted into the volatile oxide or osmic acid. Osmium in the same condition is oxidated by nitric acid or aqua-regia, and the osmic acid formed distills over with the water and acid. But after being exposed to a red heat, osmium becomes much less combustible in air, and is not oxidated by the humid way, resembling silicon and titanium in that respect. Six different oxides of this metal have been obtained, namely, OsO; OS2O3 ; OSO2 ; OSO3 ; OsO^ ; and OsOg. The three lowest of these oxides are analogous in composition to the oxides of iridium. Chlorides and oxides of osmium. — When osmium is heated in a long glass tube by a spirit lamp, and chlorine gas passed CHLORIDES AND OXIDES OF OSMIUM. 401 over it, two chlorides are formed, which condense separately in the tube, owing to a difference in their volatility. The protochloride, OsCl, which is the least volatile, crystallises in needles of a deep green colour. It is deliquescent, and forms a green solution remarkable for its beauty. This solution is instantly discoloured by great dilution, metallic osmium being deposited, and hydrochloric and osmic acids remaining in solution. Chloride of osmium combines with alkaline chlorides, and acquires greater stability. The protoxide, OsO, is obtained by adding potash to a solution of protochloride of osmium and potassium; after some hours, a deep green, almost black, powder is precipitated, which is the hydrated oxide. This hydrate contains alkali. It dissolves slowly but completely in acids, and gives solutions of a deep green colour. Sesquioxide of osmium, OS2O3, is not known in the separate state ; but when a mixture of osmic acid and ammonia is kept for some hours at a temperature of 100° to 120°, nitrogen gas is evolved, and a black substance is deposited, containing the sesquioxide in combination with ammonia. It dissolves slowly in acids, and forms yellowish brown solutions, which become brown-black when they contain much oxide. The metal is not precipitated from these solutions by zinc or iron. The corresponding sesquichloride of osmium is obtained in combination with chloride of potassium as a double salt, when the preceding oxide containing ammonia is dissolved in hydrochloric acid, and evaporated to dryness ; the compound is not crystalline. Bichloride of osmium, OsClg, is the more volatile chloride produced when osmium is heated in chlorine. It condenses as a dark red floury powder. Exposed to air, it attracts a little moisture, and forms dendritic crystals. It is soluble in a small quantity of water, giving a yellow solution, but is de- composed by a large quantity, like the protochloride. The bichloride of osmium and potassium is prepared in the same manner as the corresponding salt of iridium. In powder, it E E 4 402 OSMIUM. is of a red colour like minium, but forms also the usual octo- hedral crystals, KCl . OSCI2, which are brown. A solution of this double salt, mixed with carbonate of potash or soda, affords after a time, or immediately, if heated, the correspond- ing bioxide of osmium or os-mic oocide, OSO2, as a brown powder, which appears black when collected. This oxide, like the peroxide of iridium, is reduced by hydrogen at ordinary temperatures. It is a base capable of uniting with acids at the moment of its formation. Osmic sulphate is obtained by treating one of the sulphides of osmium with nitric acid ; when diied as completely as pos- sible, it forms a dark yellowish brown syrup, which dissolves in water. The reactions of osmic salts {e. g. of the bichloride of osmium and potassium) in solution, are as follows : — Potash forms a black precipitate, slowly in the cold, im- mediately on boiling; ammonia^ a brown precipitate, after some time ; carbonate of potash, the same ; chloride of am- monium, a red precipitate ; protochloride of tin, a brown precipitate ; mercurous nitrate, yellowish white ; nitrate of silver, dark olive-green; hydrosulpJiuric acid, a yellowish brown precipitate after some time ; hydrosulphate of ammonia, a yellowish brown precipitate insoluble in excess. No pre- cipitate is formed by oxalic acid, ferrocyanide or ferricyanide of potassium, or ferrous sulphate. Zinc throws down part of the osmium in the metallic state. Iodide of potassium does not form any precipitate, but imparts a deep purple-red colour, which does not disappear when the liquid is heated. Tannic acid imparts a deep blue colour. Osmious acid, OsOg. — This acid is not known in the separate state, being resolved at the moment of separation from its combinations, into osmic acid and osmic oxide, 2OSO3 = OSO4 + OSO2. Osmite of potash, KO . OsOg + 2H0, is obtained by the action of reducing agents on the osmiate ; thus, when a few drops of alcohol are added to a solution of osmiate of potash, the osmite is precipitated in the OSMIC ACID. 403 form of a rose-coloured crystalline powder, a strong odour of aldehyde being at the same time evolved, due to the oxidation of the alcohol. Osmite of potash may be obtained in octo- hedral crystals of considerable size, by mixing a solution of osmiate with nitrite of potash, and leaving the mixture to evaporate slowly. The salt is likewise obtained by dissolving osmic oxide in osmiate of potash. It is rose-coloured, soluble in water, insoluble in alcohol and ether, permanent in dry air, but changes into osmiate under the influence of air and water. Chlorine converts it into osmic oxide and osmiate of potash. It is decomposed by acids, even by the weakest, osmic oxide being precipitated and osmic acid evolved. Sulphurous acid introduced into a solution of this salt, previously rendered alkaline, throws down a yellow crystalline precipitate, con- taining a salt whose acid is formed of osmium, oxygen, and sulphur. Chloride of ammonium decomposes osmite of potash, forming a nearly insoluble yellow salt, NH^Cl . OSO2NH2, which may be regarded as a compound of sal-ammoniac with osmiamide, OSO2NH2. This compound, heated in a stream of hydrogen, gives off ammonia and sal-ammoniac, and leaves metallic osmium. Osmite of soda is prepared in the same manner as osmite of potash, but does not crystallise so easily ; its solutions are rose-coloured. Osmious acid does not com- bine with ammonia; the osmites of potash and soda are rapidly reduced by ammonia. A terchloride of osmium has been obtained in combination with chloride of ammonium, as a double salt, when osmic acid is saturated with ammonia, and treated after a while with ex- cess of hydrochloric acid, mercury being also placed in contact with it. After a few days, the liquid loses the odour of osmic acid, and when evaporated to dryness, leaves the double salt in brown dendritic crystals. Osmic acid, OSO4, or the volatile oxide of osmium, is best obtained by the combustion of osmium in a glass tube through which a stream of oxygen gas is passed ; it is also obtained 404 OSMIUM. by the action of nitric acid on osmium, and in the decomposi- tion of osmites or osmates by acids. It condenses in long, coloui'less, regular prismatic needles. The odour of this com- pound is extremely acid and penetrating, resembling that of the chloride of suiphiu*. It- was from this property of its acid, which is so constantly observed when the oxidable com- pounds of osmium are heated in air, that osmium obtained its name (from oa-fios, odour). Its taste is acrid and burning, but not acid. It becomes soft like wax by the heat of the hand, melts into a colourless liquid like water considerably below 212°, and enters into ebullition a very little above its point of fusion. It is dissolved slowly, but in considerable quantity, by water. The solution has no acid reaction. Osmic acid is also soluble in alcohol and ether, but these solutions are apt to deposit metallic osmium. It is a weak acid, being incapable of displacing carbonic acid from the carbonates, in the humid way, but forms a class of salts, the osmiates. Osmic acid is expelled by heat from most of its combinations with bases. An acid containing more oxygen than osmic acid, and apparently having the formula OsOg, is formed by submitting the osmiates to the action of oxygen and oxidising agents. It is very unstable ; its potash and soda-salts have a dark brown colour, and sometimes crystallise in the alkaline liquids. If the formida OsOg be correct, the oxidation- series of osmium will present remarkable analogies with those of nitrogen, phosphorus, and arsenic (Fremy). Osmiamic acid, OS2NO5. — Formed by the action of am- monia on osmic acid, 2OSO4 + NH3 . OsgNOg + 3H0. Its potash-salt is obtained by adding ammonia to a hot solution of osmic acid in excess of potash j the deep orange colour of the liquid soon changes to light yellow, and osmiamate of potash separates in the form of a yellow crystalline powder. The osmiamates of the alkalies and alkaline earths and the zinc-salt are soluble in water ; the lead, mercury, and silver- salts insoluble. The aqueous acid is obtained by decomposing ESTIMATION OF OSMIUM. 405 the baryta-salt with sulphuric, or the silver-salt with hydro- chloric acid. It may be kept for some days when dilute^ but soon decomposes in the concentrated state. It is a powerful acid, decomposing not only the carbonates, but even chloride of potassium. Fritzsche and Struve,* who discovered this acid, assign to it the formula OS2NO4, regarding it as a compound of nitride of osmium with osmic acid ; OsN . OSO4. Gerhardt, on the contrary,t assigns to it the formula above given, viz., OS2NO5, which is the more probable of the two, inasmuch as, if Fritzsche and Struve's were correct, the formation of the acid must be attended with the evolution of 1 eq. oxygen; but they particularly observe that no escape of gas takes place. Sulphides of osmium. — Osmium has a great affinity for sulphur, and burns in its vapour. Five sulphides of osmium are known, corresponding to all the oxides except the highest, viz., OsS, OS2S3, OSS2, OSS3, OSS4. The first four of these sulphides are obtained by decomposing the corresponding chlorides with hydrosulphuric acid. The tetrasulphide is pre- pared by passing hydrosulphuric acid gas into a solution of osmic acid : it is a sulphur-acid, completely insoluble in water ; whereas the others are sulphur bases, slightly soluble in water, and forming deep yellow solutions. ESTIMATION AND SEPARATION OF OSMIUM. Osmium is generally estimated in the metallic state. The best mode of separating it from the metals with which it is usually accompanied, is to volatilise it in the form of osmic acid — by distillation with aqua-regia, if the compound be per- fectly soluble therein, or by roasting in a stream of oxygen — receiving the vapours of osmic acid in a strong solution of * J. pr. Chem. xli. 97. t Compt. rend, de Trans, en Chimie, 1847, 304. 406 ESTIMATION OF OSMIUM. potash ; and to reduce this salt, by the addition of a few drops of alcohol, to osmite of potash, which is insoluble in the alcoholic liquor. The osmite of potash is then digested in a cold solution of sal-ammoniac, whereby the compound NH4CI . OSO2NH2 is produced, and the osmium reduced to the metallic state by igniting this last-mentioned compound in a current of hydrogen gas (Fremy). Another mode of proceeding is to condense the acid vapours evolved by distilling a compound of osmium with aqua-regia in a well-cooled receiver, and precipitate the osmium from the solution by metallic mercury. A precipitate is thereby obtained consisting of calomel, a pulverulent amalgam of osmium, and metallic mercury containing a very small quan- tity of osmium. This mixture is heated in a glass bulb, through which a stream of hydrogen is passed, whereupon the mercury and its chloride volatilise, and metallic osmium is left in the form of a black powder. The liquid, however, still retains a small quantity of osmium, which may be iso- lated by saturating the liquid with ammonia, evaporating to dryness, and calcining the residue (Berzelius). The osmium may also be precipitated from the distilled liquid l)y hydro- sulphuric acid, the solution, after complete saturation, being left for several days in a stoppered bottle, till the sulphide of osmium is completely deposited. The sulphide is then washed, dried, and weighed ; but as it is apt to retain moisture, and, moreover, oxidises to a certain extent in the air, the method is not very exact. It is recommended, however, for the estimation of small quantities of osmium, the method of precipitating by mercury being better adapted for larger quantities (Berzelius). OXIDES or KHODIUM. 407 SECTION V. RHODIUM. Eq. 52 or 651-4; R. This metal was discovered, by WoUaston, in the ore of platinum. He found the ore from Brazil to contain 0*4 per cent ; native platinum from another locality has been found with as much as 3 per cent, of rhodium. After the precipitation of the palladium from the solution of native platinum, by cyanide of mercury, the solution, in order to obtain the rhodium, may be mixed with carbonate of soda and excess of hydrochloric acid, and evaporated to dry- ness. The cyanide of mercury in excess is decomposed by the hydrochloric acid, and converted into chloride of mercury. The dried mass is reduced to a very fine powder, and washed with alcohol of density 0*837, which takes up the double chlorides of sodium with platinum and iridium, the copper and the mercury, but leaves the double chloride of rhodium and sodium in the form of a fine deep red powder. The rhodium is most easily reduced by gently heating the double chloride in a stream of hydrogen gas, and afterwards washing out the ' chloride of sodium by water. Rhodium, when rendered coherent, is a white metal like platinum; its density is about 10*6. It is brittle and very hard, and may be reduced to powder. When pure, it is not dissolved by any acid ; but when alloyed with certain metals, such as platinum, copper, bismuth, or lead, and exposed to aqua-regia, it dissolves along with those metals. When fused with gold or silver, however, it is not dissolved with the other metal. But the most eligible mode of rendering rhodium soluble, is to mix it in fine powder with chloride of potassium or sodium, and to heat the mixture to low redness in a stream of chlorine gas. A double chloride is then formed, as with 408 RHODIUM. the other platinum metals in similar circumstances, which is very soluble in water. The solutions of rhodium have a beautiful red colour, the circumstance from which the metal derives its name (from pbBov, a rose) . Rhodium may also be rendered soluble in the dry way, by fusing it with bisulphatc of potash, when the metal is oxidated with escape of sul- phurous acid gas. Rhodium is the most oxidable of the platinum metals, combining with oxygen when heated to redness in an open vessel, and very readily when in fine powder and heated to a cherry-red heat. It appears to form two oxides, the rhodous and the rhodic, of which, however, the last only has been completely isolated. Oxides of rhodium. — The protoodde or rhodous oxide, RO, is formed when rhodium is ignited in contact with the air. One hundred parts of rhodium thus treated quickly increase to 115-3 parts, corresponding to the protoxide; then slowly, if the ignition be continued, to 11807 parts; a black powder being formed, consisting of 3R0 . R2O3 (Berzelius). Rhodic oxide, R2O3, is produced when the metal is ignited with hydrate of potash and a little nitre, in a silver crucible. The metal swells up, assumes a coffee-brown colour, and is converted into a compound of rhodic oxide and potash, which must be washed with water, and afterwards digested in hydro- chloric acid ; the hydrated oxide remains of a grey colour, with a shade of green, and insoluble in acids. The same hydrated oxide, as obtained from the double chloride of rho- dium and potassium or sodium, by precipitation with an alkali and evaporation, dissolves slowly in acids, together with a certain quantity of alkali which is attached to it, assuming a yellow coloiir, and producing double salts. The solution in hydrochloric acid is also pale, although it contains chloride of potassium, while a solution of the double chloride, pre- pared in the way formerly mentioned, has a fine red colour. Hence Berzelius infers that there are two isomeric modifi- cations of this oxide, whose compounds, when in solution, are SALTS OF RHODIUM. 409 respectively yellow and rose-coloured. Hydrated rhodic oxide contains one atom of water, ^2^3 -HO. Two compounds of rhodic oxide with the protoxide of the same metal appear to exist : ^2^3 • 3^0^ ^^^ ^^2^3 • 2K-0. The known com- pounds of rhodium are not isomorphous with compounds of platinmn ; but this may arise from these two metals affecting combination in different proportions, so that their compounds are not analogous in composition. Their association and resemblance in other respects afford a strong presumption of their being isomorphous bodies. Solutions of rhodic salts yield, with hydrosulphuric acid, a brown precipitate of protosulphide, which is slowly deposited ; with hydrosulphate of ammonia a brown precipitate, insoluble in excess ; with sulphurous acid and sulphites, a pale yellow precipitate; with potash, a yellow precipitate of hydrated rhodic oxide, soluble in excess ; with ammonia, a yellow pre- cipitate of rhodate of ammonia, which, however, does not form immediately; with alkaline carbonates, a yellow precipitate after a while. Iodide of potassium produces a slight yellow precipitate ; protochloride of tin imparts a dark colour to the solutions, but forms no precipitate. Acetate of lead, mercu- rous nitrate, and nitrate of silver form precipitates analogous in composition to the iridium-salts already mentioned (p. 397). Zinc precipitates metallic rhodium. In a solution of rhodium mixed with excess of potash, alcohol forms, even at ordinary temperatures, a black precipitate, probably consisting of me- tallic rhodium ; with the other platinum-metals, this reaction takes place only when the liquid is heated. No precipitate is formed by phosphate of soda, sal-ammoniac, chloride of potassium, chromate of potash, oxalic acid, cyanide of potas- sium, cyanide of mercury, ferrocyanide or ferricyanide of potassium, or gallic acid. Hydrogen gas reduces the anhy- drous salts at a moderate heat. Sulphide of rhodium. — Rhodium may be united with sul- phur by either the dry or the humid way. The sulphide of 410 RHODIUM. rhodium was used by Wollaston to obtain the metal in a coherent mass. Protochloride of rhodium^ RCl, is obtained by heating the protosulphate (precipitated from rhodic salts by hydrosul- phuric acid) in a stream of chlorine ; or by digesting one of the intermediate oxides with hydrochloric acid, whereupon the sesquichloride dissolves, and the protochloride remains in the form of a reddish grey powder insoluble in water. Sesquichloride of rhodium, R2CI3, is obtained from the double chloride of rhodium and potassium, by precipitating the latter metal with fluosilicic acid. The dry salt thus obtained is brown black, and not crystalline; it requires a pretty high tempcratui'c to decompose it, and then resolves itself at once into clilorine and rhodium. This salt deliquesces in air ; its solution in water is of a beautiful red colour (Ber- zelius). Sesquichloride of rhodium is also obtained in the form of a rose-red powder by heating the metal to low redness in a stream of chlorine (Clans) . This red powder, which was regarded by Berzelius as R2CI3 . 211C1, is slowly decomposed when heated in hydrogen gas, is insoluble in strong hydro- chloric and aqua-rcgia even at the boiling heat, is coloured yellow by continued boiling with potash, and if afterwards boiled with strong hydrochloric acid, dissolves in small quan- tity, forming a rosc-colom'cd solution, the greater part, how- ever, remaining unaltered. A chloride of rhodium and potassium, containing 2KCl.R2d3 + 2H0, is obtained by the action of chlorine on a mixture of rhodium and chloride of potassium, or by evaporating a solution of the sesquichloride of rhodium and sodium with chloride of potassium. It forms brown, doubly oblique prisms, which dissolve sparingly in water. Another double salt, containing 3KC1 . R2CI3 + 6II0, is obtained in dark red, sparingly soluble, efflorescent prisms, by spontaneous evaporation of a solution of the hydratcd sesquioxide in hydrochloric acid mixed with chloride of potassium. The sodium double-salt, ESTIMATION OF RHODIUM. 411 3NaCl . ^2^13 + 24HO, forms doubly oblique prisms of a deep cherry-red colour. With chloride of ammonium, two double salts are obtained, viz., 2NH4CI . ^2^\ + 2H0, and 3NH4CI . R2CI3 + 3H0, both of which form red prismatic crystals. By precipitating either of the above double chlorides containing 2 or 3 eq. of the basic chloride to 1 eq. R2CI3, with acetate of lead, mercurous nitrate, or nitrate of silver, rose-coloured precipitates are formed, containing 2 or 3 eq. of PbCl, Hg2Cl, or AgCl, to 1 eq. of R^Clg (Claus). A sulphate of rhodium is formed when rhodium is ignited with bisulphate of potash ; it gives a yellow solution. Another sulphate in combination with sulphate of potash gradually falls as a white powder, when sulphuric acid is added to a solution of the double chloride of these bases. It is nearly insoluble in water; its formula is KO . SO^ + 203-3^03. Nitrate of rhodium is formed by dissolving the oxide in nitric acid. It forms a deliquescent salt of a dark red colour, II2O3 • 3NO5 ; the last salt combines with nitrate of soda, forming dark red crystals soluble in water but not in alcohol : NaO . NO5 + R2O3 • 3NO5. The salts of rhodium are often mixed with peculiar rose- coloured salts, whose nature is not exactly known. These new salts are not precipitated, either by iodide of potassium in the cold, or by sulphurous acid, or by ammonia ; they form, with chloride of ammonium, double salts, which crystallise, not in scales, but in red prisms (Fremy). ESTIMATION AND SEPARATION OF RHODIUM. Rhodium is estimated in the metallic state. The solution containing it is mixed with excess of carbonate of soda and evaporated to dryness, the residue ignited, and the calcined mass treated with cold water : oxide of rhodium then remains, and may be reduced by hydrogen. VOL. II. F F 4^' 4 412 RHODIUM. Rhodium is separated from many metals with which it may be alloyed, by fusing the alloy with bisulphate of potash ; the rhodium is thereby converted into sulphate of rhodium and potassium, which may be dissolved out by water. The method of separating it from platinum and the allied metals has already been given. The separation of rhodium from other metals in solution is somewhat difficult, because it is not completely precipitated by hydrosulphuric acid. To separate rhodium from copper , the solution is saturated with hydrosulphuric acid and left to stand in a stoppered bottle for twelve hours, then filtered, and the filtrate heated to separate an additional portion of sulphide of rhodium. The whole of the precipitate is then roasted in a platinum crucible till the sulphides are completely oxidised, and the product treated with strong hydrochloric acid, which dissolves the copper and leaves the oxide of rhodium. The liquid filtered from the hydrosulphuric acid precipitate still contains a small portion of rhodium, which may be precipi- tated by carbonate of soda and converted into oxide as above. The whole of the oxide is then reduced by hydrogen. To separate rhodium from iron, the rhodium is precipitated as completely as possible by hydrosulphuric acid ; the liquid filtered ; and the iron in the filtrate precipitated by ammonia, after having been brought to the state of sesquioxide. The iron-precipitate carries down with it a certain portion of rho- dium, which may be separated by igniting the precipitate in a current of hydrogen, and treating the reduced metals with hydrochloric acid, which dissolves the iron and leaves the rhodium : the latter is then converted into oxide by ignition in the air. The precipitated sulphide of rhodium is likewise oxidised by roasting. The small quantity of rhodium which remains in solution after precipitation by ammonia is preci- pitated by carbonate of soda, and converted into oxide by ignition. The whole of the oxide of rhodium is then reduced to the metallic state by hydrogen. RUTHENIUM. 413 The separation of rhodium from the alkali-metals is easily- effected by converting the metals into chlorides, and igniting the chlorides in a current of hydrogen, which reduces only the chloride of rhodium. SECTION YI. RUTHENIUM. :E.q, 52'1 or 651-25 ; Ru. This metal was discovered hy Clans in 1846. It occurs in platinum ores, chiefly in the native osmide of iridium, which contains from 3 to 6 per cent, of it. To separate it, the osmide of iridium is pulverised, mixed with about half its weight of common salt, and heated to low redness in a current of moist chlorine gas. The disintegrated mass is then digested in cold water, and the concentrated solution, which is brown- red and almost opaque, mixed with a few drops of ammonia and gently heated, whereupon it deposits a copious black- brown precipitate, consisting of sesquioxide of ruthenium and bioxide of osmium. This precipitate, after being washed with nitric acid, is heated in a retort, till the osmium is ex- pelled in the form of osmic acid. The residue is then ignited for an hour in a silver crucible with caustic potash free from silica, and the ignited mass softened and dissolved by cold distilled water. The solution is left in a corked bottle for two hours to clarify ; after which the perfectly transparent orange- coloured liquid is separated by a siphon, and neutralised with nitric acid. It then deposits velvet-black sesquioxide of ruthenium, which, when washed, dried, and ignited in an atmosphere of hydrogen, yields the pure metal. Ruthenium is a grey metal, very much Hke iridium. Its FP 2 414 RUTHENIUM. specific gravity is 8'6. * It is very brittle, does not fuse even in the flame of the oxy-hydrogen blowpipe, and is scarcely attacked by aqua-regia. It combines with oxygen in four proportions, forming the three oxides, RuO, RU2O3, KuOj, and ruthenic acid, RUO3. Its affinity for oxygen is greater than that of any of the other platinum metals, except osmium. When heated to redness in the air, it oxidises readily, forming a ]3luish black oxide, which does not part with its oxygen at a white heat. When fused with nitre or with caustic potash, it is converted into rutheniate of potash. It is not dissolved by fused bisulphate of potash. Protoxide of ruthenium, RuO. — Obtained by igniting the protochloride with carbonate of soda, in a stream of carbonic acid gas, and washing the residue with water. It is a blackish grey powder, containing 13*4 per cent, of oxygen. It is in- soluble in acids, and consequently its salts have not been directly formed. The p7'otochloride, RuCl, is obtained in the anhydrous state, by heating the metal to low redness in a stream of chlorine. It is a black crystalline substance, insoluble in water and acids, and imperfectly decomposed by alkalies. A soluble pix)tochloride appears, however, to be formed by passing hydrosulphuric acid gas through a solution of the sesquicldoride. Sesquioxide of rutJienium, Ru^^Og. — Pulverulent ruthenium, strongly heated before a powerful blowpipe turns black, and rapidly absorbs oxygen, 100 parts of the metal increasing to 118 parts; afterwards the oxidation slowly proceeds further till the oxide acquires a blackish blue colour, and contains 23 or 24 parts of oxygen to 100 parts of metal, which is about the proportion required for the sesquioxide. The hydrated * This is much less than the density usually attributed to iridium (p. 395.)' It is probable, however, that the two metals do not really differ much in density ; for a specimen of porous iridium prepared from the blue oxide, by reduction with hydrogen, exliibitcd a density of only 9"3 (Claus). SESQUIOXIDE OF RUTHENIUM. 415 sesqmoxide is formed by precipitating a solution of the sesquichloride with an alkali, by decomposing a solution of rutheniate of potash with nitric acid, or by heating the aqueous solution of the sesquichloride. It is a black-brown powder, which becomes suddenly incandescent when heated. Hydrogen gas reduces it imperfectly at ordinary temperatures. It is insoluble in alkalies, but dissolves in acids, forming orange-yellow solutions. The solution in hydrochloric acid exhibits the following reactions : — Hydrosulphuric acid partly precipitates the ruthenium in the form of a black sulphide, but at the same time reduces the sesquichloride to proto- chloride, the reduction being attended with a change of colour from orange-yellow to a fine azure blue : this reaction is ex- tremely delicate, and very characteristic of ruthenium. Zinc effects the same reduction. Hydrosulphate of ammonia throws down the greater part of the ruthenium in the form of a black- brown sulphide, not perceptibly soluble in excess. The caustic alkalies J alkaline carbonates , and phosphate of soda precipitate the black sesquioxide, insoluble in excess of the reagent. Borax forms no precipitate at first, but, on heating the solu- tion, the hydrated sesquioxide is thrown down. Sulphurous acid, oxalic acid, and formiate of soda do not precipitate the metal, but merely decolorise the solution. Ferrocyanide of potassium decolorises the solution at first, but afterwards turns it bluish green. Acetate of lead forms a purple-red precipi- tate, inclining to black. Cyanide of mercury colours the solution blue, and throws down a blue precipitate. Nitrate of silver forms a black precipitate, which is a mLxture of chloride of silver and sesquioxide of ruthenium ; the oxide dissolves, after a while, in the nitric acid, leaving a white residue of chloride of silver ; and, if ammonia be then added in excess, the chloride of silver dissolves, and the sesquioxide of ruthenium is reprecipitated : this is also a very delicate reaction. The chlorides of potassium and ammo)iium throw down from concentrated solutions, crystalline precipitates 416 RUTHENIUM. of double chlorides, exhibiting a play of colorirs inclining to violet. Sesquichloride of ruthenium, Itu2Cl3, is obtained in the solid state by evaporating the solution of the sesquioxide in hydro- chloric acid. The residue is deliquescent, has a very astringent but not metallic taste, and dissolves in water and alcohol, forming beautiful orange-coloured solutions, but leaving a yellow basic compound undissolved. When heated, it turns green and blue. The dilute solution is resolved by heat into hydrochloric acid and the hydrated sesquioxide (pp.414, 415). The sesquichloride forms double salts with the chlorides of potassium and ammonium, and apparently also with those of sodium and barium. Bioxide of rutheniumy Ruthenic oxide, RuOj, is formed by roasting and igniting the bisulphide, or by strongly igniting the sulphate, RuOj . 2SO3 ; the former method yields a black- blue powder, with a tinge of green ; the latter, grey particles with metallic lustre and bluish or greenish iridescence. The hydrate, RuOj . 2H0, is obtained as a gelatinous precipitate by decomposing the bichloride of ruthenium and potassium with carbonate of soda. The precipitate, when dried and heated in a platinum spoon, deflagrates with vivid incan- descence, and is scattered about. It dissolves in acids, forming solutions which are yellow when dilute and rose- coloured when concentrated. The bichloride is not known in the separate state, but forms with chloride of potassium a double salt, KCl,RuCl2, which is obtained by treating the sesquichloride of ruthenium and potassium with aqua-regia. This double salt is very soluble in water, but insoluble in alcohol ; its colour is brown inclining to rose-red. The aqueous solution has a deep rose- colour, strongly resembling that of sesquichloride of rhodium. Hydrosulphuric acid acts but slowly on this solution, pro- ducing first a milky turbidity from precipitated sulphur, and afterwards throwing doAvn a yellowish brown sulphide ; the RUTHENIC ACID. 417 solution, however, still retains a deep rose-colour and does not turn blue. Ruthenic sulphate, RuOg.SSOg. — When the sulphide ob- tained by treating the sesquichloride with hydrosulphuric acid is digested in moderately strong nitric acid, an orange-yellow solution is formed, which, on evaporation, yields this salt in the form of a yellowish brown amorphous mass. It is deli- quescent, and dissolves readily in water. Alkalies added to the solution form no precipitate at first ; but, on evaporating, a yellowish brown gelatinous precipitate is obtained, consist- ing of hydrated ruthenic oxide, and strongly resembling impure rhodic oxide. The solution of this salt does not turn blue when treated with hydrosulphuric acid. Ruthenic acid, E-uOg, is known only in the form of a potash- salt, which is obtained by igniting ruthenium with a mixture of potash and nitrate or chlorate of potash. It dissolves in water, forming an orange-yellow solution, which has an astrin- gent taste, colours organic substances black by coating them with oxide, and is decomposed by acids, yielding a precipitate of the sesquioxide. Sulphides of ruthenium. — This metal probably forms with sulphur a series of compounds analogous to the oxides ; but it is difficult to obtain them in a definite state. Sulphur and ruthenium do not combine directly, and the precipitates thrown down by hydrosulphuric acid from the chlorides always contain excess of sulphur. When the sulphide ob- tained by precipitation from the sesquichloride is heated in an atmosphere of carbonic acid, incandescence and explosion take place, sulphur and water pass ofi^, and a blackish grey metallic powder is left, whose analysis agrees with the formula IIU2S3. All the sulphides are dissolved by nitric acid of ordinary strength (Claus). L-' 418 RUTHENIUM, ESTIMATION AND SEPARATION OF RUTHENIUM. This metal is precipitated from its solutions in the form of oxide, and generally as sesquioxide, viz. from a solution of the sesquichloridej either by alkalies or by simply heating the solution, and from a solution of riithcniate of potash by nitric acid. The precipitated oxide is reduced to the metallic state by ignition in an atmosphere of hydrogen. As, however, the precipitate generally contains alkali, which cannot be removed by washing, the reduced mass must be treated with water ; the liquid filtered from the ruthenium ; and the metal, be- fore weighing, must be again ignited and left to cool in an atmosphere of hydrogen, as it oxidises when heated in the air. Ruthenium has hitherto been found only associated with the metals of the platinum-residues, and from these it is separated by the method described at page 413., depending on the resolution of the aqueous scsquichloride by heat into hydrochloric acid and sesquioxide of ruthenium. NEW METHOD OF TREATING PLATINUM-RESIDUES.* When platinum-ore has been exhausted by aqua-regia, a residue is left, commonly known by the name of osmide of iridium. This residue is a mixture of two different sub- stances, one of which is scaly, and consists of osmium, iridium, and ruthenium ; while the other, which is granular, contains but mere traces of osmium and ruthenium, but is very rich in iridium and rhodium. Now oxide of ruthenium can bear a red heat without decomposing, and osmium is actually roasted by the action of oxygen, producing a volatile acid, just as sulphur and arsenic do; hence the residue of platinum- ore may be decomposed by roasting ; and by submitting it to * Fremy, Compt. rend, xxxviii. 1008 ; also Traits do Chimie Generale, par Pelouze et Fremv, iii. 452. TREATMENT OF PLATINUM-RESIDUES. 419 this operation, osmic acid is produced in large quantity and very pure, and oxide of ruthenium is obtained in well-defined crystals. The roasting is performed as follows : — About 200 grammes of platinum-residue (the scaly and granular alloys together) are heated to bright redness in a porcelain tube placed in a long furnace. Air is drawn through the tube by means of an aspirator, being first made to pass through solution of potash to free it from carbonic acid, and through strong sulphuric acid to remove organic matter. The air thus purified passes over the heated platinum-residue, and forms osmic acid and oxide of ruthenium. The latter crystal- lises in the colder parts of the roasting tube, while the more volatile osmic acid is carried forward, first into a series of empty tubes, in which part of it settles in the form of crys- tals, and then through two bottles filled with solution of potash, which retains the uncondensed vapours : the apparatus terminates with an aspirator. The products of the operation are : — 1. Oxide of ruthenium, in violet crystals, the form of which is similar to that of native oxide of iron ; 2. Osmic acid, very pure, and sometimes amounting to 40 per cent, of the platinum-residue used ; 3. Osmiate of potash, which, by the addition of a few drops of alcohol, may be converted into osmite of potash, a salt from which metallic osmium may be obtained (p. 403) ; 4. An alloy of iridium and rhodium, which remains in the roasting tube. This last residue may be used for the preparation of iridium and rhodium. For this purpose, it is calcined in an earthen crucible with four times its weight of nitre, care being taken not to carry the process too far ; and the residue is exhausted with boiling water and filtered. A copious precipitate is thereby formed, which remains on the filter, and the filtrate consists of an alkaline liquid, which, when left to evaporate, deposits crystals of osmite of potash, the osmium never being completely removed by the previous roasting. The precipitate which remains on the filter and retains a VOL. II. G G 420 PLATINUM-RESIDUES. considerable quantity of potash, is subjected to the action of aqua-regia, which converts the iridium into chloriridiate of potassium, nearly insoluble in cold water : the action of the aqua-regia must be continued for several hours. The mass is then treated with boiling water, which dissolves the chlor- iridiate of potassium, the washing being continued tiU the extract no longer exhibits a brown colour. The solutions are then evaporated, and the chloriridiate of potassium obtained in crystals. The undissolved portion, which contains the rhodium, is dried, mixed with an equal weight of chloride of sodium, and subjected for three or four hours to the action of dry chlorine at a dull red heat. Chlororhodiate of sodium is thereby formed, and may be obtained, by solution in water and evaporation, in beautiful rose-coloured octohedral crystals, resembling chrome-alum. Rhodium is likewise obtained in another stage of the treat- ment of platinum-ore. When this ore is treated with aqua- regia a certain quantity of rhodium is dissolved together with the platinum, althougli rhodium by itself is insoluble in aqua- regia. The solution is evaporated to drj^ness, the residue dissolved in water, and the solution mixed with sal-ammoniac to precipitate the platinum. The rhodium then remains in solution, together with a small quantity of platinum, to sepa- rate which a plate of iron is immersed in the liquid, and the pulverulent mixture of platinum and rhodium thereby pre- cipitated is digested in weak aqua-regia, which dissolves the platinum and leaves the rhodium nearly pure. From this residue, pure well-defined crystals of chlororhodiate of sodium may be obtained in the manner just described (Fremy). SUPPLEMENT. HEAT EXPANSION OF SOLIDS. The following determinations of the amount of the cubical expansion of solids for each degree Centigrade, at tempera- tures not exceeding 100° C, are given by H. Kopp*, the volume of the solid at 0° being taken equal to 1 : — Table I. — Cubical Expansion of Solids. Cubical Cubical Substance. Formula. Exp. for PC Substance. Formula. Exp. for lOC. Copper Cu 0-000051 Arragonite . CaO.CO, 0000065 Lead . Pb 0-000089 Calcspar CaO.CO, 0-000018 Tin . Iron . Sn Fe 0-000069 0-000037 Bitterspar . { CaO.CO^ -1 + MgO.CO, J 0-000035 Zinc . Cadmium . Zn Cd 0-000089 0-000094 Iron- spar . Fe(Mn,Mg)0. "1 C02 J 0-000035 Bismuth Bi 0-000040 i Heavy spar . BaO.SOg 0-000058 Antimony . Sb 0-000033 Coelestin SrCSOg 0-000061 Sulphur s 0-000183 Quartz Si03 { 0-000042 Galena PbS 0000068 0-000039 Zinc-blende ZnS 0-000036 Orthoclase . KO.SiOg 1 + A1.^03.3Si03 J 0000026 Iron pyrites EeS^ 0-000034 0-000017 Rutilc . TiO^ 0-000032 Soft soda Tin stone . SnO„ 0-000016 glass . 0-000026 Iron-glance . Fe,03 0000040 Another sort . 0-000024 Magnetic iron Hard potash ore . FCgO^ 0-000029 glass . . 0-000021 Fluor-spar . CaF 0-000062 VOL. II. * Ann. Ch. Pharm. Ixxxi. II II 422 EXPANSION OF SOLIDS. The mode of experimenting consisted in taking the specific gravity of the solid substance at a lower and at a higher temperature, by ascertaining the quantity of water together with a known weight of the solid substance, and also the quantity of water alone, which filled a vessel of constant capacity at the different temperatures. The determinations in the instances of iron and glass, and the second determina- tions of quartz and orthoclase, were made with mercury in- stead of water, and calculated in a similar manner. Kopp has also determined the expansion of some other solids, especially near the melting points.* Most bodies, at temperatures near their melting points, exhibit a sudden increase in the rate of expansion. The increase of volume which a substance exhibits in the fused state, as compared with the same substance at lower temperatures, arises, partly from the great expansion which it undergoes as it approaches the melting point, partly from the sudden expansion which takes place in fusing. In some substances, however, only one of these modes of expansion is at all considerable. FhospJioriis (the yellow modification), of sp. gr. 1*826 at 10° C. (50° F.), expands uniformly up to its melting point 44° C. (111*2° F.), at which temperature its volume is 1*017 of the volume at 0° C. ; but, at the moment of fusion, it ex- hibits a sudden expansion amounting to 3*4 per cent., so that its liquid volume at 44° C. is 1-052. Sulphur (native crystals, sp. gr. 2-069) expands irregularly near its melting point (115° C. or 239° F.). Its volume being latO°C.,isl-010at50°C.(122°F.); 1*037 at 100° C; 1-096 at 115° C; at the moment of fusion, the expansion amounts to 5 per cent., the volume then increasing to 1*150. Wa.v (bleached beeswax, sp. gr. 0-976 at 10° C.) expands very rapidly as it approaches its melting point (64° C. or * Ann. Ch. Pharm. xciii. 129. EXPANSION OF LIQUIDS. 423 147*2° F.), but only 0*4 per cent, more at the moment of fusion. If the volume at 0° C. is 1, the volume at 50° C. (122° F.) is 1-068 ; at 60° C. (14*0° F.) is 1-128 ; at 64° C. (147-2° F.) is 1*161, and increases bj fusion to 1-166. Water expands at the moment of freezing by about 10 per cent. 1-1 volume of ice gives 1 volume of water at 0° C, which, when heated to 4° C. (39*2° F.), contracts to 0-99988, but expands progressively at higher temperatures, its volume at 100° being 1-043. Solid hydrated salts, on the contrary, expand at the moment of fusion; e. g, chloride of calcium (CaCl + 6H0), by 9*6 per cent. ; ordinary phosphate of soda (2NaO.HO.P05+ 24HO) and hyposulphite of soda (NaOSgOg + 5H0), each by 5*1 per cent. Roses fusible metal (2 parts bismuth, 1 part tin, and 1 part lead, sp. gr. 8*906 at 10° 0.) expands, when heated from 0°"to 59° C. (32° to 138*2° F.), in the ratio of 1 to 1-0027 ; but con- tracts when further heated, its volume at 82° C. (179*6° F.) being equal to that at 0° C, and at 95° C. (203° F.) equal to 0*9947 ; in fusing, between 95° and 98° C, it expands by 1-55 per cent., so that at 98° C. (208-4° F.) its volume is equal to 1*0101. This alloy, therefore, contracts from 59° C. up to its melting point. EXPANSION OF LIQUIDS. M. Pierre's researches on this subject have been con- tinued.* The expansions of a great number of liquids have also been determined by H. Kopp. f * Annales de Chimie et de Physique, [3], xxi. 118, xxxiii. 119. f Pogg. Ann. Ixxii. 1 and 223 ; and Ann. Ch. Pharm. xciii. 157 ; xciv. 257 ; xcv. 307 ; xcviii. 367. H H 2 424 EXPANSION OF LIQUIDS. Pierre concludes from Ins experiments that isomeric liquids in general do not contract equally at an equal number of degrees below their respective boiling points; an exception is, however, presented by acetate of methyl (CgHgO . C4H3O3) and formiate of ethyl (C^H^O . C2HO3), in which the con- traction for equal intervals below the boiling points appears to be equal.* Table II. exhibits the contractions of several groups of isomeric liquids, at D° centigrade below the boiling point, as determined by Pierre and by Kopp. Table IL — Expaksion of Liquids. D. Aldehyde. Butyric Acid, CsHhO^. AceUte of Ethyl, CbH^O,. D. Pierre (B. P. 2'iO). Cio'so). Pierre (163°). (?««;. Pierre (74-1°). (^Tc?). 10000 10000 10000 10000 10000 10000 10 9817 9830 9872 9867 9846 9843 10 25 9567 9596 9688 9677 9629 9622 25 45 9284 . 9453 9439 9359 9352 45 60 9094 . 9288 9271 9172 9165 60 75 . . 9128 9112 8996 8988 75 110 • • 8781 8765 8633 • 110 D. Chloride of Ethy- lene, C^H,Cl2 Pierre (84-90). Mono- chlorinated Chloride of Ethvl, C,H,dl,. Pierre (64-80). • Mono. chlorinater Chloride o! Ethylene, C4H3CI3. Pierre {114- 2°). Blchlo- rinated Chloride of Ethyl, C4H3CI3. Pierre (74 -90). Formiate of Ethyl, CeHfiO^. Acetate of Methyl, CfiHgO,. D. Pierre (52-90). <»,. Pierre Kopp (56 36). 10000 10000 10000 10000 10000 10000 10000 10000 25 9677 9669 9693 9648 9632 9631 9633 9631 25 55 9331 9300 9350 9267 9241 9243 9243 9243 55 80 9068 9003 9090 8988 8953 • 8955 ♦ 80 ♦ The contrary statement originally made by Pierre, and quoted at p. 7. Vol. L of this work, was founded on an error of calculation. EXPANSION OF LIQUIDS. 425 Expansion of water. — Table III. contains the results ob- tained by Kopp*, and also those of Pierre as calculated by Frankenheimf, with regard to the expansion of water between 0° and 100° C, the volume at zero being taken as the unit. Table III. — Expansion of Water. Volumfe. Volume. Temp. Temp. Kopp. Pierre. Kopp. Pierre. - 1 0° C. 1-003758 19° 1-001370 -10 , 1-001658 20 1-001567 1-001594 - 5 , 1-000582 21 1-001776 1-000000 1-000000 22 1-001995 I 0-999947 23 1-002225 2 0-999908 24 1-002465 3 0-999885 25 1002715 1-002708 4 0-999877 30 1-004064 1-004071 5 0-999883 0-999890 35 1-005697 1-005677 6 0-999903 40 1-007531 1-007512 7 0-999938 45 1-009541 1-009563 8 0-999986 50 1-011766 1 011815 9 1-000048 55 1-014100 1-014360 10 1-000124 1-000148 60 1-016590 1-017118 11 1-000213 65 1-019302 1019947 12 1-000314 70 1-022246 1022938 13 1-000429 75 1-025440 1-026078 14 1-000556 80 1-028581 1-029360 ' 15 1-000695 1-000728 85 1-031894 1-032769 16 1-000846 90 1-035397 1-036294 17 1-001010 95 1-039094 1-039925 18 1-001184 100 1-042986 1-043649 The maximum density Frankenheim finds, from the same data, to exist at the temperature of 3*86° C. or 38*95° F. ; Playfair and Joule J fix the point of maximum density at 3-945° C. or 39*1° F. ; Plucker and Gessler§, at 38° C. or 38-8° F. * Pogg. Ann. Ixxii. 223. X PhiL Mag. [3], xxx. 41. t Pogg. Ann. Ixxxvi. 451. § Pogg. Ann. Ixxxv. 238. II H 3 426 SPECIFIC HEAT. Absolute expansion of mercury. — From numerous measure- ments of the pressures exerted by columns of mercury of equal height but different temperatures, Regnault* finds that if the volume of mercury at 0° C. be = 1, the volume at f of the air-thermometer is given by the formula — 1 + 0-0001 79007i + 0-0000000252316 t\ Hence, the values in Table IV. — Extansion of Mercury. Temp. Volume. Temp. Volume. 50° 100 150 200 1-009013 1-018153 1027419 1036811 250° 300 350 1046329 1-055973 1-065743 Militzer has also determined the absolute expansion of mercury by similar means, but only at ordinary tempera- tures, the temperature of the colder column of mercury ranging, in his experiments, between 2° and 4° C, and that of the warmer column between 19° and 23°. The mean coefficient of expansion for 1°, deduced from these experi- ments, is 0-00017405 + 0-00000082.t The experiments of Dulong and Petit (i. 8.) give for 1° the coefficient 0-00018018. * " Relations des Experiences cntreprises, pour dct.rrainer les princi- pales lois physiques ct les donnees numeriques qui entrent dans le calcul des machines a vapcur." Paris, 1847. f Pogg. Ann. Lxxx 55. SPECIFIC HEAT. 427 SPECIFIC HEAT. The specific heat of most bodies is greater in the liquid than in the solid state. The following determinations are by Regnault ; — Table V. — Specific Heat. Solid. Liquid. Substance. Temperature. Sp. Heat. Temperature. Sp. Heat. Lead . 0° to 100° C. 0-0314 350° to 450° C. 00402 Bromine . -78 „ -20 0-08432 10 „ 48 0-1109 Iodine „ 100 0-05412 0-10822 Mercury . -78 „ -40 0-0247 „ 100 0-0333 Sulphur „ 100 0-2026 120 „ 150 0-234 Bismuth . „ 100 0-03084 280 „ 380 0-0363 Zinc . „ 100 0-0956 Tin . „ 100 00562 250 „ 350 0-0637 Phosphorus 10 „ 30 0-1887 50 „ 100 0-2120 Amorphous 15 „ 98 0-1700 Water below 0-502 „ 20 1-0000 Crystallised chlo- ride of calcium below 0-345 33 „ 80 0-555 Nitrate of soda . to 100 0-27821 320 „ 430 0-413 Nitrate of potash „ 100 0-23875 350 „ 435 0-3319 Table YI. exhibits the specific heats of several liquids as determined by H. Kopp*, and by Favre and Silbermann.f The second column shows the intervals of temperature in Kopp's determinations. Those of Favre and Silbermann were made by cooling the liquids in a mercurial calorimeter of peculiar construction, from their several boiling points to temperatures nearly equal to that of the surrounding atmosphere. * Pogg. Ann. Ixxv. 98. t Comptes Rendus, xxiii. 524. HH 4 428 SPECIFIC HEAT. Table VI. — Specific Heat. Liquids. Temperature. Sp. Heat. Observers. Mercury 440 to 24°C. 0.0332 Kopp. Iodine .... . 0-10822 F. S. Bromine 45 „ 11 0.107 Andrews. Sulphuric acid . 46 „ 21 343 Kopp, Wood-spirit 43 „ 23 . 0-645 Kopp. 0-6713 F. S. Alcohol 43 „ 23 0-615 Kopp. 6438 F. S. Fusel-oil 44 „ 26 0-564 0-5873 Kopp. Ethal .... , , 0*5059 F. S. Ether .... • 0-50342 t» Formic acid 45 „ 24 0-536 Kopp. Acetic acid 45 „ 24 0-509 »» Butyric acid 45 „ 21 503 »» Formiate of ethyl 39 „ 20 0-513 ti Acetate of methyl 41 „ 21 0-507 »» Acetate of ethyl 45 „ 21 0-496 »» 0-48344 F. S. Butyratc of methyl 45 „ 21 0-487 Kopp. 0-49176 F. S. Valerate of methyl 45 „ 21 0-491 Kopp. Acetone 41 „ 20 0-530 »» Benzoic. 46 „ 19 0-450 » Oil of mustard . 48 „ 28 0-432 >» Oil of turpentine 0-46727 F. S. The specific heat of water at different temperatures lias been determined by Regnault*, from whose experiments it appears that the quantity of heat expressed in heat-units^ wljich one gramme of water loses in cooling down from f to 0° C. is given by the formula — Q = < -f 0-00002 ^2 + 0-0000003 ^ ; and the specific heat C at the temperature f, that is to say, the quantity of heat required to raise one gramme of water from f to (^ + 1)°, is — C = 1 + 0-00004 t + 0-0000009 <^ * " Relations," &c. (see note, p. 426), 729. t See page 448. SPECIFIC HEAT. 429 From this formula, the following numbers are obtained: Table VII. — Specific Heat. t. Q. C. t. 150° 200 230 Q. C. 0° 60 100 0000 50-087 100-500 1 -0000 1-0042 1-0130 151-462 203-200 234-708 10262 1-0440 0-0568 Specific heat of gases and vapours. — On this subject numerous experiments have been made by Kegnault *, who finds, con- trary to the statement of Delaroche and Berard, that the specific heat of a gas does not vary, either with its density or with its temperature. The specific heat of atmospheric air, referred to water as unity, is found to be 0*2377 between ~ 30° and + 10° C. ; it is 0*2379 between 10* and 100°; and 0-2376 between 100° and 225°. Table YIII. contains Regnault's determinations of the specific heats of a considerable number of gases; in column A, as referred to equal weights (water = 1) ; in column B, as referred to equal volumes. Table VIII. — Specific Heat of Gases (Regnatjlt). Oxygen . Nitrogen . Hydrogen Chlorine . Bromine . Nitrous oxide . Nitric oxide . Carbonic oxide Carbonic acid . Sulphide of carbon . Sulphurous acid Hydrochloric acid . Hydrosulphuric acid Ammonia Marsh -gas Olefiant gas Water-vapour . Alcohol -vapour A. B. 1 0-2182 0-2412 ! 0-2440 0-2370 3-4046 0-2356 0-1214 0-2967 0-0552 0-2992 0-2238 0-3413 ! 0-2315 0-2406 0-2479 0-2399 ! 5-2164 0-3308 i 0-1575 0-4146 0-1553 0-3489 i 0-1845 2302 1 0-2423 0-2886 1 0-5080 02994 0-5929 0-3277 0-3694 0-3572 , 0-4750. 0-2950 ; 04513 0-7171 1 1 Ether Chloride of ethyl Bromide of ethyl Sulphide of ethyl . Cyanide of ethyl Chloroform Chloride of ethylene Acetate of ethyl Acetone . Benzole . Oil of turpentine Terchloride of phos- phorus Chloride of arsenic . Chloride of silicon . Bichloride of tin Bichloride of titanium A. B. 0-4810 1-2296 0-2737 0-6117 0-1816 0-6717 0-4005 1-2568 0-4255 0-8293 0-1568 0-8310 0-2293 0-7911 0-4008 1-2184 0-4125 08341 0-3754 10114 0-5061 2-3776 0-1346 0-6386 0-1122 0-7013 0-1329 0-7788 00939 0-8639 0-1263 8634 Compt. Rend, xxxvi, 676. 430 SPECIFIC nEAT. LIQUEFACTION. The melting point of a body appears to be influenced to a minute but certain amount, by the pressure to which it is subjected. W. Thomson*, by enclosing transparent pieces of ice and water in an Oersted's water-compressing apparatus, found that the melting point of the ice was lowered 0-059° C. by a pressure of 8*1 atmospheres, and 0*129° by a pressure of 16*8 atmospheres. Bunsenf has obtained similar results with spermaceti and paraffin. SPERMACETI. PARAFFIK. Tressure in Solidifving ricssurc in JSulidil'ying Atmospheres. Point. Atmosplicrcs. Point. 1 ... 47-7" C. 1 . . . 46-3° G 29 ... 48-3 85 . . , . 48-9 96 . . . 49-7 100 . . . 49-9 141 ... 50-5 156 ... 50-9 Such results are in conformity with the deductions by J. Thomson J from the mechanical theory of heat. The latent heat of water was found by Regnault, and by Provostaye and Desains, to be 79° C. or 142 F. According to Person, this number denotes the quantity of heat required to convert ice at 0° C. into water, but not the total quantity of the latent heat in the water, inasmuch as a certain additional portion of heat is rendered latent as the temperature of the ice rises from — 2° to 0°.§ In six experiments on tjie fusion of ice previously cooled to temperatures between —2° and —21°, the latent heat was found to vary between 79*9 and 80*1, the mean quantity being 80° C, or 144° Pah. Regnault also found greater values for the latent heat of water in proportion * Phil. Mag. [3], xxxvii. 123. f Pogg. Ann. Ixxxi. 562. t Edinb. PhiL Trans, vol. xvi. § Ann. Ch. Phyg. [3j, xxx. 73. LATENT HEAT OF VAPOURS. 431 as the ice used in the experiments had been cooled to a lower temperature. According to Hess, the true latent heat of water is 80-34° C. = 144*6° Fah. For the specific heat of ice, Hess finds the number 0*533 ; Person finds 0*48 for the tempe- ratures between — 21° and — 2°, the specific heat of water being 1. Table IX. contains the latent heats of fusion, and the melting points of various solids, as determined by Person.* Table IX. — Latent Heat of Fusion. Substances. Melting point. Latent Heat. Tin . 235° C. 14-3 Bismuth 270 12-4 Lead 332 5-15 Alloy Pb., Siij Big 96 5-96 Alloy Pb Sna Bi 145 7-63 Phosphorus 44-2 471 Sulphur 115 9-175 Nitrate of Soda 310.5 62-98 Nitrate of Potash 339 46-18 A mixture of 1 eq. Nitrate of Soda and 1 eq. Nitrate of Potash . 219-8 51-4 Phosphate of Soda 2NaO, HC ), PO5 + 24HO 36-4 66-80 Chloride of Calcium CaCl, 6t 10 . . 28-5 40-70 Bees-wax (yellow) 62-0 43-51 Zinc . 423-0 27-46 LATENT HEAT OP VAPOURS. Water, — It is stated at page 5S, vol. i. of this work^ that the sum of the latent and sensible heats of steam is the same at all temperatures. This is commonly known as Watt's law. Southern, on the other hand, maintained that the latent heat alone is constant at all temperatures. But the late elaborate researches of Regnault f have shown that both these * Pogg. Ann. Ixx. 300 ; Ann. Ch. Phys. [3], xxvii. 250. ■f "Relations des Experiences," &c. (see Note, p. 426), 271; also "Works of Cavendish Society," i. 294. 432 LATENT HEAT OF VAPOURS. statements are incorrect, and that the total quantity of heat (expressed in heat-units*), which a unit of weight of saturated aqueous vapour contains at the temperature f centigrade, exceeds the amount contained in the same weight of water at 0°, bj the quantity — X = 606-5 + 0-305 t If from this, we subtract the quantity of heat which a unit of weight of water at f contains, beyond tliat which is con- tained in the same weight of water at 0° (see Regnault's determinations of the specific heat of water at different tem- peratures, p. 428), we sliall obtain the latent heat L of the vapour of water at the temperature f. The values of X and L for various temperatures are given in Table X., together with the tensions expressed in millimetres and in atmospheres. Table X. — Latent Heat of Steam. Temperature. Tension. X L. mm. atm. 0°C 4-60 0.006 60G-5 606-5 50 91-98 0-121 621-7 571-6 100 76000 1-000 637-0 536-5 150 3581-23 4-712 652-2 500-7 200 11688-96 15-380 667-5 464-3 230 20926-40 27-535 676-6 441-9 The latent heats of the vapours of several other liquids at their boiling points have been determined by Andrews f, and by Favre and Silbermann.J The results are given in — * A unit of heat is the quantity required to raise the temperature of a unit of weight (1 gramme, 1 pound, &c.) of water at 0°, by 1° Centigrade, t Chem. Soc. Qu. J. i. 27. + Ann. Ch. Thys. [3], xxxvii. 461. TENSION OF VAPOURS. 433 Table XI. — Latent Heat op Vapours. Substances. Boiling point Latent Heat of Vapour. Observers. Water . . . 100° at 760 mm. 535-9 Andrews. »» • • • 100 536 F. andS. Iodine , 23-95 i> Bromine 58 ' „ 76*0 45-60 A, Sulphurous acid , 94-56 F. and S. Terchloride of phosphorus . 78-5 „ 767 51-42 A. Bichloride of tin 112-5 „ 752 3-053 >» Bisulphide of carbon 46-2 „ 769 86-67 »> Alcohol 77-9 „ 760 202-40 „ »» ... 78-4 208-92 F. S. Wood-spirit . 65-8 „ 767 263-70 A. i» • • • 66-5 263-86 F. S. Fusel-oil 132 121-37 »> Ether 35-6 91-11 »» » ... 34-9 „ 752 90-45 A. Amylic ether 113 69-40 F. S. Acetic acid . 120 101-91 ^^ Formic acid . 100 120-72 » Valerianic acid 175 103-52 ji Butyric acid 16.4 114 67 F. S Acetate of ethyl 74 105.80 »» »> • • 74-6 „ 762 92-68 A. Acetate of methyl 55 „ 762 110-20 »> Formiate of ethyl 54-3 „ 762 105-30 '» Formiate of methyl . 32-9 „ 752 117-10 Iodide of ethyl 71-3 „ 760 46-87 »> Iodide of methyl 42-2 „ 752 4607 Oxalate of ethyl 184-4 „ 779 72-72 >» Butyrate of methyl . 93-02 ^^ 779 87-33 F. S. Ethal 360-0» 58-48 >» Oil of turpentine 156 68-73 »> Terebene 156 67-21 )) Oil of lemons 165 70-02 n Hydrocarbons — (a)C.,H,, . . 198 59-9 »» (6)C,,H,, . . 255 59-7 M TENSION OF VAPOURS. Regnault* has made a vast number of observations on the tension of aqueous vapour in vacuo, between the temperatures of —32° and + 147*5° C, and given formulaB of interpola- tion for calculating the tension at any given temperature between those limits. Ann. Ch. Phys. [3], xi. 273 434 TENSION OF VAPOURS. For temperatures between 0° and 100° the interpolation formula is — log e = a + hcc* + c/3' ; in which t denotes the temperature, e the tension, and a, h, c, a, /3 are constants whose values are determined by five equations of condition, obtained by substituting in the preceding equation the cprresponding observed values of t and e for the temperatures 0°, 25°, 50°, 75°, and 100°. (See Table, p. 65, vol. i.) The values thus obtained are — log a = 0-006865036 log c = 0-6116485 log /3 = 1-9967249 a = + 4-7384380. log h = 2-1340339 For temperatures below 0°, Regnault adopts the formula — e ■= a -\- ba' ; in which — a; = < - 32 ; log 5 = T-4724984 ; log u = 0-0371566 ; a = + 0-131765. For temperatures above 100° C. the interpolation formula is — log e = a — ha.' \ X ^=- t — 100° ; in which — log a = 1-9977641 ; log ^^ = 0*4692291 ; a = + 5-8267890. It has not yet been found possible to include the whole series of observations in one formula of interpolation. From the first and second of these formulae, the follow- ing table of tensions* is calculated for every half degree between —10° and +35°. This table (which is the one alluded to in the note at page 94, vol. i.) is of great utility in hygrometric observations ; — * Ann. Ch. Phys. [3], xv. 1 33. TENSION OF VAPOURS. Table XIL Tension of Aqueous Vapour from —10° to +35° C 435 Degrees. -100 9-5 90 8-5 80 7-5 7-0 6-5 6-0 5-5 5-0 45 4-0 3-5 3-0 2-5 20 1-5 1-0 0-5 00 + 0-5 1-0 1-5 2-0 2-5 30 3-5 40 4-5 Tension. mm. 2-078 2-168 2-261 2-356 2-456 2-561 2-666 2-776 2-890 3010 3-131 3-257 3 387 3-522 3-662 3-807 3-955 4-109 4267 4-430 4-600 4-767 4-940 5-118 5-302 5-491 5-687 5-889 6-097 6-313 Diff. 0-090 0-093 0-095 0-100 0105 0-105 0-110 0-114 0-120 121 0-126 0130 0-135 0-140 0145 0-148 0-154 0158 0-163 0-170 0-167 0-173 0-178 0-184 0-189 0-196 0-202 0-208 0-216 Degrees. + 5-0 5-5 6-0 6-5 7-0 7-5 8-0 85 90 9-5 10-0 10-5 110 11-5 12-0 12-5 13-0 13-5 140 14-5 15-0 155 16-0 16-5 17-0 17-5 18-0 18-5 19-0 19-5 Tension. mm. 6-534 6-763 6-998 7242 7-492 7-751 8-017 8-291 8-574 8-865 9-165 9-474 9-792 10-120 10-457 10-804 11-162 11 530 11-908 12-298 12-699 13-112 13-536 13-972 14-421 14-882 15-357 15-845 16-346 16-861 Diflf. 0-229 0-235 0-244 0-250 0-259 0-265 0-274 0-283 0-291 0-300 0-309 0-318 I 328 0-337 0-347 0-358 0-368 0-378 0-390 0-401 0-413 0-424 0436 0-449 0-461 0-475 0-488 0-501 0-515 Degrees. + 20-0 20-5 21-0 21-5 22-0 22-5 23-0 23-5 24-0 24-5 25-0 25-5 260 26-5 27-0 27-5 28-0 28-5 29-0 29-5 30-0 30-5 31-0 31-5 32-0 32-5 33-0 33-5 34-0 34-5 35*0 Tension. mm. 17-391 17-935 18-495 19069 19-659 20-265 20-888 21-528 22-184 22*858 23550 24-261 24-988 25-738 26-505 27-294 28-101 28-931 29-782 30-654 31-548 32-463 33-405 34 368 35-359 36-370 37-410 38-473 39-565 40-680 41-827 Diff. 0-544 0-560 0-574 0-690 0-601 0-623 0-640 0-656 674 0-692 0711 0-727 0-750 0-767 0-789 0-807 0-830 0-851 0-872 0-894 0-915 0-942 0963 0-991 1-011 1-030 1-063 1092 1 115 1-147 Regnault has also determined the tensions of several other liquids in vacuo. The results (given in Table XIIT.) were obtained either by direct measurement of the elastic forces in vacuo, or by determining the temperature of the vapour of a boiling liquid under the pressure of an artificial atmosphere. The former method was adopted for low, the latter for high temperatures. The series of experiments made by the two methods were, however, in all cases made to include a certain common range of temperature, so that the corresponding 436 TENSION OF VAPOURS. curves of tension might overlap each other within that range. With liquids which could be obtained perfectly pure, such as water and sulphide of carbon, the two curves thus obtained were found to coincide exactly ; but with alcohol, ether, and still more with chloroform, which are more difficult to purify, the presence of foreign substances gave rise to more or less divergence in the results. Thus the tension of chloroform vapour at 36°, was found to be 342*2 mm. by the first method, and 313*4 mm. by the second. Regnault finds that an extremely small amount of impurity may be detected in this manner. Table XIIL — Tension op Vapours. Temperature. Alcohol. Ether. Sulphide of Carbon. Chloroform. Oil of Turpentine. mm. mm. mm. mm. mm. -21° C. 312 -20 3*34 69-2 -16 , . 58-8 -10 6-50 113-2 790 12-73 182-3 127-3 . 2-1 10 2408 286-5 199-3 130-4 2-3 20 44-00 434-8 298-2 190-2 4-3 30 78-4 637-0 434-6 276-1 7-0 40 134-10 913-6 617-5 364-0 11-2 50 220-3 1268-0 8527 524-3 17-2 60 350-0 1730 3 1162-6 738-0 26-9 70 539-2 2309-5 15490 976-2 41-9 80 812-8 2947-2 2030-5 1367-8 61-2 90 1190-4 3899-0 2623-1 1811-5 910 100 16850 4920-4 3321-3 2354-6 134-9 no 2351-8 6243-0 4136-3 3020 4 187-3 116 . 7076*2 120 3207-8 5121-6 3818-0 257-0 130 4351-2 6260-6 4721-0 347-0 136 7029-2 140 5637-7 462-3 150 7257-8 604-5 152 7617-3 160 777*2 170 . 989-0 180 . 12250 190 . 1514-7 200 . 1865-6 210 . 2251-2 220 . 2690-3 222 2778-5 TENSION OF VAPOURS. 437 Vapours of saliiie solutions. — It is well known that the boiling point of a saline solution is higher than that of pure water, the affinity of the water for the salt being, in fact, an additional obstacle which the heat must overcome before ebul- lition can take place. Nevertheless, it appeared to Rudberg that the vapours rising from such solutions do not exhibit a higher temperature than steam from boiling water ; a result' which was attributed to the sudden expansion which the vapour undergoes at the moment of escaping from the liquid. Regnault finds, however, that a thermometer having its bulb immersed in the vapour of a boiling saline solution does not give a correct indication of the temperature of that vapour, because the bulb becomes covered with a film of condensed water, and, therefore, the thermometer exhibits only the temperature due to the boiling of that water. But when proper precautions are taken, by the interposition of screens, to prevent, as far as possible, this deposition of water, the temperature of the vapour appears very nearly equal to that of the liquid. It is, however, extremely difficult to remove this source of error completely. The observation of the elastic force of a vapour arising from a saline solution appears to afford excellent means of detecting chemical changes in the constitution of the liquid, every such change being indicated by the occurrence of a singular point in the curve which represents the law of the tension. For example, in the case of salts, like the sulphates of sodium, copper, iron, manganese, &c., which crystallise at different temperatures with different proportions of water, Regnault suggests that the variations in the tension of the vapour might indicate whether the water is chemically com- bined with the salt while still in solution, or whether the combination takes place at the moment of crystallisation. Mixtures of vapours and gases, — The law of Dalton, that the tension of any saturated vapour in air is the same for VOL. II. I I 438 TENSION OF VAPOURS. any given temperature as in vacuo, must be received with certain limitations. It has been ah'eadj stated (i. 91) that Regnault found the tension of saturated aqueous vapour in air to be always somewhat less than in vacuo ; the differences, however, seldom exceeding 2 per cent, of the entire value. The following are a few of the results obtained : — Table XIV. Temperature. Obierved Tension in Air. Calculated Tension in Vacuo. ^ Difference. mm. mm. 0°C. 4-47 460 -0-13 12-59 10-31 10-85 -0-54 15 12-38 12-70 -0-32 21 18-27 18-49 -0-22 24-69 22-70 23-13 -0-40 31 32-97 33-41 -0-44 35-97 43-39 44-13 -0-74 38 48-70 49-30 -0-60 Similar differences are observed with other liquids, ether the following results are obtained : — With Table XV. Temperature. Tension of Ether-vapour. In Air. In Vacuo. Difference. 33-62° C 30-97 26.52 22-63 20-05 19-99 14-26 mm. 705-09 645-52 552-67 479-63 429-69 428-88 337-71 mm. 7260 659-0 559-2 484-0 433-9 4330 3410 mm. 20-9 13-4 6-5 4-4 4-2 4-1 3 3 In air and in hydrogen gas, the tension of ether vapour was found to be always lower than in vacuo, unless the gas was strongly compressed; in carbonic acid gas, which (as a liquid) TENSION OF VAPOURS. 439 dissolves ether in considerable quantity, the tension never becomes equal to that in vacuo. The tension of a vapour in a gas is very much affected by the condensation of the vapour on the sides of the vessel, an effect which takes place considerably below the point of saturation. Regnault is of opinion that Dalton'3 law with regard to the tensions of vapours in gases could never be strictly true, unless the gas were enclosed in a vessel whose walls were, to a certain thickness, formed of the liquid itself. Vapours of mixed liquids. — Gay-Lussac found that the tension of the vapour arising from two or more mixed liquids is equal to the sum of the tensions of the vapours which each would produce separately. The more recent experiments of Magnus and of Kegnault have shown that this law is true, or nearly true, only when the liquids are quite immiscible, such as benzol and water. When the liquids are mutually soluble, but not in all proportions, the tension of the mixed vapour is much less than the sum of the separate tensions. With ether and water it scarcely differs from the tension of the ether- vapour alone ; thus : — Table XVI. Temperature. Tension of water- vapour. Tension of ether-vapour. Sura of tensions. Observed tens'.on of mixed vapour. 15-66° C. 24-21 33-08 mm. 1316 2-2-47 37-58 mm.' 361-8 510-0 711-1 mm. 374*96 532-47 748-68 mm. 362-95 51008 71002 When the mixed liquids dissolve in one another in all pro- portions, the tension of the mixed vapour is in most cases greater than that of the less volatile, but less than that of the more volatile substance ; such, for example, is the case with mixtures of ether and sulphide of carbon. In a mixture of benzol and alcohol, however, the tension of the mixed vapour II 2 440 CONDUCTION OF HEAT. is greater than that of either of the separate vapours. With this mixture Regnault obtained the results given in — Table XVIL Temperature. Tension of vapour, J Of the mixture. OfalcohoL Of benzol. 7-22° C. 4317 40-4 201 9-98 50-22 46-8 24-2 13-11 59-66 54-4 29-2 16-05 69-43 62-7 350 18-59 79-35 71-0 41-0 When the liquids do not mix, but dispose themselves in layers, the more volatile liquid forming the lower stratum, and the ebullition being but feeble, the temperature and corresponding vapour-tension agree with Gay-Lussac's law. But with a brisk fire and violent ebullition, the temperature remains nearly at the limit at which the more volatile liquid would boil by itself under the same pressure. CONDUCTION OF HEAT. In metals, — From the experiments of Wiedemann and Franz*, it appears that the metals follow each other with regard to their heat-conducting power, in the same order as with regard to their power of conducting electricity ; and, moreover, that the numbers which express their relative heat-conducting powers, do not differ from those which express their relative powers of conducting electricity, more than the latter numbers, as determined by different observers, differ from each other. The heat-conducting power of metals appears also to di- minish as their temperature rises. * Phil. Mag. [4], vii. 33. CONDUCTION OF HEAT. Table XVni. 441 Electric-conducting power according to Heat- conducting power. Metals. Riess. Becquerel. Lenz. Silver 100 100 100 100 Copper 66-7 91-5 73-3 73-6 Gold 59-0 64-9 58-5 53-2 Brass 18-4 21-5 23-6 Tin . 10 140 22-6 14-5 Iron . 120 12-35 13-0 11-9 Steel 11-6 Lead 7-0 8-27 10-7 8-5 Platinum 10-5 7-93 10-3 8-4 German silver . 5-9 6-3 Bismuth . 1-9 1-8 Conduction of heat in crystallised bodies. — Bodies of perfectly homogeneous structure conduct heat with equal facility in all directions ; so likewise do crystallised bodies belonging to the regular system ; but in crystals belonging to any other system, the rate of conduction is different in different directions. This subject has been very ingeniously investigated by Senar- rnont*, whose method of observation was as follows: — A small tube of platinum was inserted through the centre of a flat cylindrical plate of the crystal in the direction of the axis J the tube being bent at right angles at the lower ex- tremity and heated by a lamp, and a current of air made to pass through the tube by means of an aspirator. The two bases of the cylindrical plate were covered with wax, which, being melted by the heat, traced on the surface a curve line, whose form was determined by the conducting power of the crystal in diflPerent directions. Plates of non-crystalline sub- stances, such as glass and zinc, treated in this manner, gave circles having their centres in the axis of the platinum-tube. On a plate of calc-spar, cut perpendicularly to the axis of symmetry (the optic axis), the curves are circles with their centres in the axis. On plates parallel to the direction of * Ann. Ch. Phys. [3], xxi. 45. I I 3 442 CONDUCTION OF HEAT. natural cleavage, the curves are also circles, having a slight tendency to elongate in the direction of the principal section. On plates cut parallel to the axis of symmetry, and at right angles to one of the faces of the primary rhombohedron, tlie curves are ellipses, having their transverse diameter in the direction of the axis of symmetry. The ratio of the axes of the ellipse thus formed is I'llS : 1. Similar results are obtained with quartz, the ratio of the axes being 1*31 : 1; also with crystals belonging to the square prismatic system, such as rutile, idocrase, and subchloride of mercury. In crystals belonging to the right prismatic, oblique prismatic, and doubly oblique prismatic systems, — that is to say, in crj'stals having two axes of double refraction, — three direc- tions are found at right angles to each other, in which the thermal curves, obtained in the manner above described, are ellipses. Hence it is inferred that : — 1. In crystalline media having two optic axes, supposing the medium to be indefinitely extended in all directions, and a centre of heat to exist within it, the isothermal surfaces are ellipsoids with three unequal axes. 2. In crystals with one optic axis, the isothermal surfaces are ellipsoids of revolution round that axis. 3. In crystals belonging to the regular system, and in homogeneous uncrystallised media, the isothermal surfaces are spherical. Uncrystallised bodies, however, acquire axes of different heat-conducting power when their molecular structure is altered by pressure, traction, or hardening. Plates of glass subjected to lateral pressure, and heated in the manner above described, exhibit distinct thermic ellipses, having their shorter axes in the direction of the pressure, that is, of the greatest density (Senarmont). It is well known that glass, and other transparent non-crystalline bodies, when similarly treated, acquire the power of double refraction. Crystalline media likewise exhibit peculiar characters in CONDUCTION OF HEAT. 443 the transmission of heat by radiation as well as by conduction. Through crystals with one optic axis, heat is radiated in diflferent quantity and also of different quality (i. 37), accord- ing as it passes in a direction parallel or perpendicular to that axis. In crystals with two optic axes, the quantity and quality of the transmitted heat differ according as the direction of transmission coincides with one or other of the three axes of elasticity (Knoblauch).* Conducting power of wood. — The dependence of heat-con- duction upon molecular arrangement is exhibited by organic structures as distinctly as by crystalline media. This subject has been very ingeniously investigated by Dr. Tyndall f, who has examined the conducting power of various organic sub- stances, especially of wood. The bodies cut into cubes of equal size, were enclosed between two chambers filled with mercury, that liquid being confined on the sides next the cube by membranous diaphragms, with which the cube was in close contact. The mercury in one of the chambers was heated by a spiral of platinum wire immersed in it, and connected with a galvanic battery. The heat thus generated was trans- mitted through the organic substance to the mercury in the other chamber, and the quantity of heat thus communicated in a given time, was measured by means of a thermo-electric couple connected with a galvanometer. By transmitting heat in this manner through cubes of wood in different directions, it was found that ; At all points not situated in the centre of the tree, wood possesses three unequal axes of calorific conduction. The first and principal axis is parallel to the fibres of the wood ; the second and intermediate axis is perpendicular to the fibres and to the ligneous layers ; and the third, and least axis, is perpendicular to the fibre and parallel to the layers. These axes of heat-conduction coincide with the axes of * Pogg. Ann. Ixxxv. 169 ; xciv 161. f rhil. Mag. [4], vi. 121. II 4 444 MECHANICAL EQUIVAJ.ENT OF HEAT. elasticity, which Savart discovered by observing the figures of sand formed on plates of wood when thrown into acoustic vibration. The same directions are likewise axes of cohesion and of permeability to liquids, AYood of any kind may be most easily split by laying the blade of the cutting instru- ment parallel to the fibres and across the annual rings ; the direction of least cohesion is, therefore, perpendicular to the fibres, and parallel or tangential to the rings. The direction of greatest resistance is parallel to the fibres. With regard to permeability, it is well known that plates of wood cut perpendicularly to the fibres are not fit for the bottoms of casks to hold liquids ; also, that in cutting staves for casks, it is indispensable to cdt them across the woody layers, the direction parallel to the layers being that of least per- meability. It may, therefore, be stated as a general law, that : the axes of calorific conduction in wood coincide with the axes of elasticity, cohesion and permeability to liquids, the greatest with the greatest, and the least icith the least The heat-conducting power of wood does not bear any definite relation to its density. American birch, which is one of the lightest woods, conducts heat better than any other. Oak and Coromandel wood, which are very dense, conduct nearly as well ; but iron-wood, which has the enor- mous density of 1*426, is very low in the scale of conduction. RELATION BETWEEN HEAT AND MECHANICAL FORCE OR WORK. — DYNAMICAL THEORY OF HEAT. Heat and motion are convertible one into the other. The powerful mechanical effects produced by the elasticity of the vapours evolved from heated liquids afford abundant illus- tration of the conversion of heat into motion ; and the production of heat by friction shows with equal clearness that motion may be converted into heat. That the rise of MECHANICAL EQUIVALENT OF HEAT. 445 temperature thus produced is not due to any change in the heat-capacity of the bodies, is strikingly shown in Davy's experiment of melting ice by rubbing two plates of the substance together in vacuo (i. 101); and Count Rumford's observations on the heat produced by the boring of ordnance point to the same conclusion. In these and all similar cases, the heat appears as a direct result of the force expended: the motion is converted into heat. But the connection between heat and mechanical force appears still more intimate when it is shown that they are related by an exact numerical law, a given quantity of the one being always convertible into a determinate quantity of the other. The first approximate determination of this numerical relation — the mechanical equivalent of heat — was made by Count Rumford in the following manner: A brass cylinder, enclosed in a box containing a known weight of water at 60° F., was bored by a steel borer made to revolve by horse-power, and the time noted which elapsed before the water was raised to the boiling-point by the heat resulting from the friction. In this manner it was found that the heat required to raise the temperature of a pound of water, 1° F., is equivalent to 1034 times the force expended in raising a pound weight one foot high, or to 1034 foot-pounds, as it is technically expressed. This estimate is now known to be too high, no account having been taken of the heat communicated to the containing vessels, or of that which was lost by dispersion during the progress of the experiment. For the most exact determinations of the mechanical equi- valent of heat, we are indebted to the careful and elaborate experiments of Mr. J. P. Joule. From experiments made in the years 1840-1843, on the relations between the heat and mechanical power generated by the electric current, Mr. Joule was led to conclude that the heat required to raise the temperature of a pound of water 1° F., is equiva- lent to 838 foot-pounds ; and a nearly equal result was 446 MECHANICAL EQUIVALENT OF HEAT. afterwards obtained by experiments on the condensation and rarefaction of gases ; but this estimate has since been found to be likewise too high. The most trustworthy results are, however, obtained by measuring the quantity of heat generated by the friction between solids and liquids. It was for a long time believed that no heat was evolved by the friction of liquids and gases. But, in 1842, Meyer showed that the temperature of water may be raised 22° or 23° F. by agitating it. The warmth of the sea after a few days of stormy weather is also, pro- bably, an effect of fluid friction. In 1843 Mr. Joule showed that heat is evolved in the passage of water through narrow tubes, and that each degree of heat per pound of water required for its evolution in this way a force of 770 foot-pounds. In subsequent experiments, a paddle-wheel was employed to produce fluid friction, and the equivalents 781*5, 782*1 and 787*6 obtained from the agitation of water, sperm-oil, and mercury respectively. The apparatus finally employed by Mr. Joule* in the determination of this important constant, by means of the ■p. 21 friction of water, consisted of a brass paddle- wheel furnished with eight sets of revolving vanes, working between four sets of stationary vanes. This revolving apparatus, of which fig. 21 shows a vertical and fig. 22 a Fig. 2L horizontal section, was firmly fitted into a copper vessel (A, fig. 23) containing water, in the lid of which were two necks, one for the axis to revolve in without touching, the other for the insertion of a thermometer. A similar apparatus, but made of iron, and of smaller size, and having six rotatory and eight sets of stationary vanes, was used for experiments on the friction of mercury. The apparatus for the friction of solids con- * Phil. Trans. 1850, i. 61 ; Chem. Soc. Qu. J. iii. 316. MECHANICAL EQUIVALENT OF HEAT. 447 sisted of a vertical axis carrying a bevelled cast-iron wheel, against which a fixed bevelled wheel was pressed by a lever. The wheels were enclosed in a cast-iron vessel filled with mercury, the axis passing through the lid. In each apparatus Fig. 23. motion was given to the axis by the descent of leaden weights suspended by strings from the axes of two wooden pulleys w, one of which is shown at p (fig. 23), their axes being supported on friction-wheels dd; and the pulleys were connected by fine twine with a wooden roller r, which, by means of a pin, could be easily attached to or removed from the friction apparatus. The mode of experimenting was as follows : The tempera- ture of the frictional apparatus having been ascertained, and the weights wound up, the roller was fixed to the axis, and the pre- cise height of the weights ascertained, after which the roller was set at liberty, and allowed to revolve till the weights touched the floor. The roller was then detached, the weights wound up again, and the friction renew^ed. This having been repeated twenty times, the experiment was concluded with another observation of the temperature of the apparatus. The mean temperature of the apartment was ascertained by observations made at the beginning, middle, and end of each experiment. Corrections were made for the effects of radia- tion and conduction ; and, in the experiments with water, for the quantities of heat absorbed by the copper vessel and the 448 MECHANICAL EQUIVALENT OF HEAT. paddle-wheel. In the experiments with mercury and cast- iron, the heat-capacity of the entire apparatus was ascer- tained by observing the heating effect which it produced on a known quantity of water in which it was immersed. In all the experiments, corrections were also made for the velocity with which the weights came to the ground, and for the friction and rigidity of the strings. The thermometers used were capable of indicating a variation of temperature as small as -j^-Q of a degree Fahrenheit The following table contains a summary of the results obtained by this method ; the second column gives the results as they were obtained in air ; the third column, the same results corrected for a vacuum. Material Equivalent Equivalent employed. in air. in vacuo. Mean. Water . . . 773-640 772-692 772-692 r 773-762 772-814] ^^. ^.„ Mercury . .[^^^_^^^ ^^^.^^J 774-083 Cast-iron . . ( "''"^^^ l''-'"'] 1U-9S1 1774-880 773-930 J In the experiments with cast-iron, the friction of the wheels produced a considerable vibration of the frame-work of the apparatus and a loud sound ; it was therefore necessary to make allowance for the quantity of force expended in pro- ducing these effects. The number 772*692, obtained by the friction of water, is regarded as the most trustworthy ; but even this may be a little too high ; because, even in the friction of fluids, it is imjoossible entirely to avoid vibration and sound. The conclusions deduced from these experiments are — 1. TJiat the quantity of heat proditced hy the friction of bodies, ivhether solid or liquid, is alicays proportional to the force expended, 2, That the quantity of heat capable of increasing the tempera- ture of \ lb. of loater {weighed in vacuo, and betioeen 55° and 60°) by 1° F., requires for its evolution the expenditure of a mechanical DYNAMICAL THEORY OF HEAT. 449 force represented by the fall of 772 lbs. through the space of 1 foot Or, the heat capable of increasing the temperature of 1 gramme of water by 1° cent,, is equivalent to a force represented by the fall of 423*55 grammes through the space of 1 metre. This is con- sequ£ntly the effect of a " unit of heat^"* Kupffer* has also determined the mechanical equivalent of heat by comparing the expansion which a metal wire suffers by heat with the elongation produced by stretching it with a given weight. By this method, which does not appear to be quite so accurate as that above described, it is found that the heat necessary to raise a pound of water 1° Fahrenheit, is equivalent to 661 foot-pounds. DYNAMICAL THEORY OF HEAT. The constant relation between heat and work affords a powerful argument in favour of the mechanical or dynamical theory of heat — the theory which rests on the hypothesis that HEAT IS MOTION. This theory has received, of late years, many important additions and developments, chiefly by the labours of Clausius, Joule, Rankine, and W. Thompson. It is impossible, within the limits of this Supplement, to give even a brief account of the whole of these valuable researches ; but the leading points of the theory may, perhaps, be suffi- ciently elucidated by the following summary of two remark- able papers lately published in " Poggendorff 's Annalen," one by Kronig, entitled "Fundamental Principles of a Theory of Gases ; "f the other, by Clausius, '^ On the Kind of Motion which we call Heat." % * Phil. Mag. [4], xli. 393. f Grundzuge einer Theorie der Gase ; von A. Kronig. Pogg. Ann. xcix. 315. X Ueber die Art der Bewegung welche wir Warme nennen ; von R. Clausius. Pogg. Ann. c. 353. See also a former paper by Clausius, " Ueber die bewegende Kraft der Warme," ibid. Ixxix. 394. 450 DYNAMICAL THEORY OF HEAT. First, then, it is assumed that the particles of all bodies are in constant motion, and that this motion constitutes heat, the kind and quantity of motion varying according to the state of the body, whether solid, liquid, or gaseous. In gases, the molecules — each molecule being an aggregate of atoms — are supposed to be constantly moving forward in straight lines, and with a constant velocity, till they impinge against each other or against an impenetrable wall. This constant impact of the molecules produces the expansive tendency or elasticity, which is the peculiar characteristic of the gaseous state. The rectilinear movement is not, however, the only one with which the particles are affected. For the impact of two molecules, unless it takes place exactly in the line joining their centres of gravity, must give rise to a rotatory motion ; and, moreover, the ultimate atoms of which the molecules are composed may be supposed to vibrate within certain limits, being, in fact, thrown into vibration by the impact of the molecules. This vibratory motion is called, by Clausius, the motion of the constituent atoms (^Deicegimgen der Bestandtheile). The total quantity of heat in the gas is made up of the progressive motion of the molecules, together with the vibratory and other motions of the constituent atoms ; but the progressive motion alone, which is the cause of the expansive tendency, determines the temperature. Now, the outward pressure exerted by the gas against the con- taining envelope, arises, according to our hypothesis, from the impact of a great number of gaseous molecules against the sides of the vessel. But, at any given temperature, that is, with any given velocity, the number of such impacts taking place in a given time, must vary inversely as the volume of the given quantity of gas ; hence the pressure varies inversely as the volume or directly as the density, which is Mariotte's law. When the volume of the gas is constant, the pressure resulting from the impact of the molecules is proportional to the sum of the masses of all the molecules multiplied into DYNAMICAL THEORY OF HEAT. 451 the squares of their velocities ; in other words, to the so- called vis viva or living force of the progressive motion. If, for example, the velocity be doubled, each molecule will strike the sides of the vessel with a two-fold force, and its number of impacts in a given time will also be doubled ; hence the total pressure will be quadrupled. Now we know that when a given quantity of any perfect gas is maintained at a constant volume, it tends to expand by -j^ of its bulk for each degree centigrade. Hence the pressure or elastic force increases proportionately to the tem- perature reckoned from — 273° C. ; that is to say, to the absolute temperature. Consequently, the absolute temperature is proportional to the vis viva of the progressive motion,* Moreover, as the motions of the constituent particles of a gas depend on the manner in which its atoms are united, it follows that in any given gas the different motions must be to one another in a constant ratio ; and therefore the vis viva of the progressive motion must be an aliquot part of the entire vis viva of the gas ; hence, also, the absolute tempera- ture is proportional to the total vis viva arising from all the motions of the particles of the gas. From this it follows that the quantity of heat which must be added to a gas of constant volume in order to raise its * Suppose a vessel of the form of a rectangular parallelopiped, the length of whose sides are x, y, z, to contain n gas-molecules, each having the mass m. Suppose, also, the space enclosed by this vessel to be divided into — equal cubes ; and at a given instant let there be in each of these cubes six gas- molecules, moving severally in the directions -f x, — x, +y, — y, + z, — z, and with the common velocity c. Let it also be supposed that the molecules exert no mutual action upon each other, but pass without hindrance from side to side of the vessel. It is required to determine the pressure which the gas exerts against one of the sides, i/z, of the vessel. The pressure arising from the impact of a single gas-molecule is mca, if a denote the number of impacts which take place in a unit of time. Now, a molecule moving at right angles to yz, or parallel to x, strikes against yz every time that it passes over the space 2x ; therefore «=— To find the total pressure P upon i/z, the quantity, mca, must be multiplied 452 DYNAMICAL THEORY OF HEAT. temperature by a given amount, is constant and independent of the temperature. In other words, the specific heat of a gas referred to a given volume, is constant, a result wliicli agrees with the experiments of Regnault, mentioned at page 429. This result may be otherwise expressed as follows; The total vis viva of the gas is to the vis viva of the progressive motion of the molecules, ichich is the measure of the temperature^ in a constant ratio. This ratio is different for different gases, and is greater as the gas is more complex in its constitution ; in other words, as its molecules are made up of a greater number of atoms. The specific heat referred to a constant pressure is known to differ from the true specific heat only by a constant quantity. The relations just considered between the pressure, volume and temperature of gases, presuppose, however, certain con- ditions of molecular constitution, which are, perhaps, never rigidly fulfilled ; and accordingly, the experiments of Magnus and Regnault show (i. 13) that gases do exhibit slight deviations from Gay-Lussac and Mariotte's laws. What the conditions are which strict adherence to these laws would by the number of molecules which move parallel to x, which number, since two atoms out of every six arc parallel to x, is — . Hence P = m.c , — * - ^ ^ '3 •2x 3- And the pressure p upon a unit of surface of the side yz/\B p= m.c . — - ~ — ; 2x 3 1/z or if we put xyz = v, and leave out the constant factor : nmc* This expression shows that the pressure exerted upon a unit of surfiice is tlie same for each side of the vessel ; also, that the pressure is inversely in proportion to the volume of the gas, which is Mariotte's law. The product, mc"; or the vis viva of an atom, is tlie expression of the tem- perature reckoned from the absolute zero, or — 273° C. If, in the preceding value of p, we put vie- = t, we have nt, p=i; that is to say, when the volume is constant, the pressure varies directly as the absolute temperature (Kronig). DYNAMICAL THEORY OF HEAT. 453 require, will be better understood by considering the differ- ences of molecular constitution which must exist in the solid, liquid, and gaseous states. A movement of molecules must be supposed to exist in all three states. In the solid state, the motion is such that the molecules oscillate about certain positions of equilibrium, which they do not quit, unless they are acted upon by external forces. This vibratory motion may, however, be of a very complicated character. The constituent atoms of a molecule may vibrate separately ; the entire molecules may also vibrate as such about their centres of gravity, and the vibrations may be either rectilinear or rotatory. Moreover, when extraneous forces act upon the body, as in shocks, the molecules may permanently alter their relative positions. In the liquid state, the molecules have no determinate positions of equilibrium. They may rotate completely about their centres of gravity, and may also move forward into other positions. But the repulsive action arising from the motion is not strong enough to overcome the mutual attraction of the molecules and separate them completely from each other. A molecule is not permanently associated with its neighbours, as in the solid state; it does not leave them spontaneously, but only under the influence of forces exerted upon it by other molecules, with which it then comes into the same relation as with the former. There exists, therefore, in the liquid state, a vibratory, rotatory and progressive move- ment of the molecules, but so regulated, that they are not thereby forced asunder, but remain within a certain volume without exerting any outward pressure. In the gaseous state, on the other hand, the molecules are removed quite beyond the sphere of their mutual attractions, and travel onward in straight lines according to the ordinary laws of motion. When two such molecules meet, they fly apart from each other, for the most part, with a velocity equal to that with which they came togetlier. The perfection VOL. II. K K 454 DYNAMICAL THEORY OF HEAT. of the gaseous state, however, implies : 1. That the space actually occupied by the molecules of the gas be infinitely small in comparison with the entire volume of the gas. 2. That the time occupied in the impact of a molecule, either against another molecule or against the sides of the vessel, be infinitely small in comparison with the interval between any two impacts. 3. That the influence of the molecular forces be infinitely small. When these conditions are not com- pletely fulfilled, the gas partakes more or less of the nature of a liquid, and exhibits certain deviations from Gay-Lussac and Mariotte's laws. Such is, indeed, the case with all known gases ; to a very slight extent with those which have not yet been reduced into the liquid state ; but to a greater extent with vapours and condensable gases, especially near the points of condensation. Let us now return to the consideration of the liquid state. It has been said that the molecule of a liquid, when it leaves those with which it is associated, ultimately takes up a similar position with regard to other molecules. Tiiis, how- ever, does not preclude the existence of considerable irregu- larities in the actual movements. Now, at the surface of the liquid, it may happen that a particle, by a peculiar combina- tion of the rectilinear, rotatory, and vibratory movements, may be projected from the neighbouring molecules with such force as to throw it completely out of their sphere of action, before its projectile velocity can be annihilated by the attractive force which they exert upon it. The molecule will then be driven forward into the space above the liquid, as if it belonged to a gas, and that space, if originally empty, will, in consequence of the action just described, become more and more filled with these projected molecules, which will comport themselves within it exactly like a gas, impinging and exerting pressure upon the sides of the envelope. One of these sides, however, is formed by the surface of the liquid ; and when a molecule impinges upon this surface, it DYNAMICAL THEORY OF HEAT. 455 will, in general, not be driven back, but retained by the attractive forces of the other molecules. A state of equili- brium, not static, but dynamic, will therefore be attained, when the number of molecules projected in a given time into the space above, is equal to the number which in the same time impinge upon and are retained by the surface of the liquid. This is the process of vaporisation. The density of the vapour required to ensure the compensation just mentioned, depends upon the rate at which the particles are projected from the surface of the liquid, and this again upon the rapidity of their movement within the liquid, that is to say, upon the temperature. It is clear, therefore, that the density of a saturated vapour must increase with the tem- perature. If the space above the liquid is previously filled with a gas, the molecules of this gas will impinge upon the surface of the liquid, and thereby exert pressure upon it ; but as these gas- molecules occupy but an extremely small proportion of the space above the liquid, the particles of the liquid will be pro- jected into that space almost as if it were empty. In the middle of the liquid, however, the external pressure of the gas acts in a different manner. There also it may happen that the molecules may be separated with such force as to produce a small vacuum in the midst of the liquid. But this space is surrounded on all sides by masses which afford no passage to the disturbed molecules; and in order that they may increase to a permanent vapour-bubble, the number of molecules projected from the inner surface of the vessel must be such as to produce a pressure outwards, equal to the external pressure tending to compress the vapour-bubble. The boiling point of the liquid will, therefore, be higher as the external pressure is greater. According to this view of the process of vaporisation, it is possible that vapour may rise from a solid as well as from a liquid ; but it by no means necessarily follows that vapour R K 2 456^ DYNAMICAL THEORY OF HEAT. must be formed from all bodies at all temperatures. The force which holds together the molecules of a body may be too great to be overcome by any combination of molecular movements, so long as the temperature does not exceed a certain limit. The production and consumption of heat which accompany changes in the state of aggregation, or of the volume of bodies, are easily explained, according to the preceding principles, by taking account of the work done by the acting forces. This work is partly external to the body, partly internal To consider first the internal work : When the molecules of a body change their relative posi- tions, the change may take place either in accordance with or in opposition to the action of the molecular forces existing within the body. In the former case, the molecules, during the passage from one state to the other, have a certain velocity imparted to them, which is immediately converted into heat ; in the latter case, the velocity of their movement, and consequently the temperature of the body, is diminished. In the passage from the solid to the liquid state, the mole- cules, although not removed from the spheres of their mutual attractions, nevertheless change their relative positions in opposition to the molecular forces, which forces have, therefore, to be overcome. In evaporation, a certain number of the molecules are completely separated from the remainder, which again implies the overcoming of opposing forces. In both cases, therefore, work is done, and a certain portion of the vis viva of the molecules, that is, of the heat of the body, is lost. But when once the perfect gaseous state is attained, the molecular forces are completely overcome, and any- further expansion may take place without internal work, and, therefore, without loss of heat, provided there is no external resistance. But in nearly all cases of change of state or volume, there is a certain amount of external resistance to be overcoiue. POLARISATION OP LIGHT. 457 and a corresponding loss of heat. When the pressure of a gas, that is to say, the impact of its atoms, is exerted against a movable obstacle, such as a piston, the molecules lose just so much of their moving power as they have imparted to the piston, and, consequently, their velocity is diminished and the temperature lowered. On the contrary, when a gas is compressed by the motion of a piston, its molecules are driven back with greater velocity than that with which they impinged on the piston, and, consequently, the temperature of the gas is raised. When a liquid is converted into vapour, the molecules have to overcome the atmospheric pressure or other external resistance, and, in consequence of this, together with the internal work already spoken of, a large quantity of heat disappears, or is rendered latent, the quantity thus consumed being to a considerable extent affected by the external pres- sure. The liquefaction of a solid not being attended with much increase of volume, involves but little work ; never- theless, the atmospheric pressure does influence, in a slight amount, both the latent heat of fusion and the melting point. LIGHT. POLARISATION. The phenomena of circular polarisation have lately ac- quired so much importance in chemistry, as to make it highly necessary for the student to be acquainted with them. But to render a description of these phenomena intelligible, a a few elementary explanations of the subject of polarisation in general must first be offered. Suppose a ray of light, A C (fig. 24), to fall upon a plate K K 3 458 POLARISATION OF LIGHT. of glass (not silvered, but blackened at the lower surface) at C, making an angle of 54^° with the normal P C, or 35^° Fig. 24. with the reflecting surface. This ray will be reflected in tho direction C D, making an angle P C D = A C P, and in the same plane as A C and C P. Now suppose the reflected rajr to fall upon a second surface of glass at the same angle of 54^° with the normal. If, then, the second mirror be so placed, that its plane of reflection is parallel to the plane of reflection from the first surface (see left-hand figure), then the ray will be reflected from the second surface in the direction D E, just as if it proceeded directly from a luminous source, and had not undergone previous reflection; but if the second mirror be so adjusted that its plane of reflection is perpendicular to that of the first (see right-hand figure), then the ray, CD, will not be reflected from it at all. In intermediate positions, still at the same angle of incidence, the ray, C D, will be partially reflected, the quantity of light in the reflected ray, D E, being greater as the planes of reflection of the two mirrors are more nearly parallel. The ray, after reflection from glass at an angle of 54-|-*' appears then to exhibit difi'erent properties, according to the direction in which it is a second time reflected; one side of the ray appearing to be reflectible, and the other side not so. The ray has now different properties on different sides, and is said to be polarised. The angle, 54^°, is called the polarising angle for glass. POLARISATION OF LIGHT. 459 For every medium there is a particular polarising angle, the magnitude of which depends upon the refracting power of the medium.* Now, as the different coloured rajs which compose white light, differ in refrangibility (i. 104), there must be for each coloured ray a distinct polarising angle. Hence it is evident that only homogeneous light can be completely polarised by reflection. Solar light, or ordinary gas or candle-light, can never be made to disappear completely in the manner above mentioned. The plane in which a polarised ray is most easily reflected is called its plane of polarisation : it coincides with the plane of reflection (or of incidence). Light is also polarised by refraction, and the refracted ray is polarised in a plane perpendicular to the plane of refrac- tion, or of incidence, and, therefore, also perpendicular to the plane of polarisation of the reflected ray ; so that it would be reflected from a surface of glass at an angle of 54^°, just under the circumstances in which the ray polarised by re- flection would not. Light, however, is never completely polarised by one refraction ; but by successive refractions through a number of surfaces of glass, or other medium, it may be brought within any assigned limit of complete polarisation. * In all cases, the polarisinfr angle, A C P (fig. 25), is that for which the refracted ray, C D, is perpendicular to the reflected ray, C B. Let m denote the index of refraction, then : m = ""^ A C P. Fig. 25. sin qciV but angle A.C P = B CP [= 0] ; and since B C is perpendicular to C D, and QC to CN, angle QCD = BCN = 90° - e ; therefore cosO that is to say, the polarising avgle is t/ie angle whose tanyent is equal to the index of refraction. K K 4 46U POLARISATION OF LIGHT. All crystalline bodies not belonging to the regular system, possess the power of double refraction (i. 103), that is to say, a ray of light entering such a medium is split up into two rays of equal intensity, which traverse the crystal in different directions. In all such media, however, there are either one or two directions in which double refraction does not take place, and these lines are called the optic axes of the crystal. Transparent calcspar, or Iceland spar, which crys- tallises in rhombohedrons, and exhibits double refraction more distinctly than any other substance, is a crystal with one optic axis, the direction of that axis being parallel to the line joining the obtuse summits of the rhomb. A ray traversing the crystal in a direction parallel to this axis is not divided into two ; but in all other directions the ray is doubly refracted ; and the two rays into which it is thus divided are both completely polarised, the one in the principal section, that is to say, in a plane passing through the optic axis and the direction in which the ray traverses the crystal ; the other at right angles to that plane. The ray which is polarised in the principal section follows the ordinary laws of refraction, remaining always in the plane of incidence, and having for all incidences a constant index of refraction ; but the ray polarised perpendicularly to the principal section follows different laws of refraction, its direction not being confined within the plane of incidence, unless that plane coin- cides with or is perpendicular to the principal section, and its index of refraction, excepting in the last-mentioned case, varying continually with the angle of incidence. The former of these rays is called the ordinaryy the latter the extra- ordinary ray. When these two oppositely polarised rays fall on a plate of glass at the angle of 54^-°, so placed that the plane of reflection is parallel to the principal section of the crystal, the ordinary ray is reflected, and the extraordinary ray is not, the contrary effect taking place when these planes are at POLARISATION OP LIGHT. 461 right angles to each other. When the plane of reflection is inclined to the principal section at any angle between 0° and 90°, both rays are reflected, but with diff*erent intensities. NichoVs Prism, — It is often desirable to get rid of one of the images produced by a double-refracting crystal. This is efi*ected by the arrangement shown in ^''S- 26. fig. 26, which consists of two similar prisms of calcspar, A B C D, C D E F, ce- mented together with Canada balsam at the faces, C D. The faces, A B, E F, are cut so as to make an angle of 68° with the obtuse edges, A E, B F, of the na- tural crystal (the natural faces make an angle of 71° with the obtuse edges), and the faces, C D, are perpendicular to A B and E F. With this arrangement, it is found that of the two rays, no, ne, into which an incident ray, m n, is divided, the ordinary ray, n o, on reaching the surface of Canada balsam (whose index of refraction is less than that of the ordinary and greater than that of the extraordinary ray), suffers total reflection in the direction o P, while the extraordinary ray passes on in the direction ef, and emerges in/^, parallel to m n. An eye placed at /, therefore, sees but one image, viz., that formed by the extraordinary ray. This apparatus, called a Nichol's prism, is of great use in experiments with polarised light. For, as it transmits only the extraordinary ray, a beam of ordinary light passing through it will be polarised in a plane perpen- dicular to the principal section — that is to Fig. 27. say, to the shorter diagonal of the rhomb, ab ^ (fig. 27); and a ray, already polarised, will be stopped by the prism if its plane of polari- sation is parallel to a b, but will pass freely 462 POLARISATION OF LIGHT. through it when the plane of polarisation is perpendicular to ah, or parallel to the longer diagonal, cd. Hence, also, two NichoPs prisms, placed one behind the other, appear perfectly opaque when their principal sections are at right angles to each other, perfectly transparent when the principal sections are parallel, and transmit light with diminished inten- sity in intermediate positions. Polarisaiion hy Tourmalines. — The tourmaline, which is a crystallised mineral having one optic axis, possesses the remarkable property of transmitting liglit only when polar- ised in a plane perpendicular to that axis. Hence, a plate of tourmaline cut with faces parallel to the optic axis, acts exactly like a Nichol's prism, and may be used in the same manner. It is, however, less convenient, on account of its colour, which, in the best tourmalines, is rather a dark yellow-brown. Nature of Polarised Light, — Light is supposed to consist of undulations excited in an ethereal medium pervading all space, and filling up the intervals between the particles of ponderable bodies. Moreover, the particles of this ether are supposed to vibrate, not in the direction of the ray, like the particles of air in conveying sound, but in planes at right angles to the length of the ray, like the transverse vibrations of a stretched cord. Further, the difference between ordinary and polarised light, is supposed to be this ; that in the former, the particles Fig. 28. of the ether vibrate in all imagi- nable directions, at right angles, to the length of the ray ; while, in the latter, they are confined to one particular plane. Thus, if A (fig. 28) represents the projection of an unpolarised ray, travelling at right angles to the plane of the paper, the particles of the ether at POLARISATION OF LIGHT. 463 all points of this ray vibrate parallel to the plane of the paper, but some may move in the direction a a', others in h b', c c\ d df, &c. Now imagine all these vibrations to be reduced to one plane, in the direction a a', for example. Then the ray will become polarised. In fact, since its particles now vibrate in one direction only, it is no longer a matter of indifference whether the ray is presented to a reflecting surface on one side or the other ; whereas the unpolarised ray, whose particles vibrate in all directions, will be reflected in the same manner on whichever side it meets the surface of any medium. Now, from considerations into which we cannot at present enter, it is found that a plate of tourmaline transmits only those vibrations which are parallel to its axis. Since then, a ray of polarised light is transmitted through a tourmaline only when its plane of polarisation is perpendicular to the axis of the tourmaline (p. 461), it follows that the plane of polarisation of the ray is perpendicular to the plane of vibration. Hence, also, the plane of vibration of a ray polarised by reflection is at right angles to the plane of incidence (or of reflection) ; the plane of vibration of a ray polarised by refraction is parallel to the plane of incidence ; and of the two rays into which a beam of light is divided by double re- fraction through a rhomb of calcspar, the ordinary ray vibrates at right angles to the principal section, and the extraordinary ray parallel to that section. The vibrations of a ray polarised by passing through a Nichol's prism, are, therefore, parallel to to the principal section, that is, to the shorter diagonal of the prism (fig. 27). Let mn (fig. 29), be the plane of vibration of a polarised ray moving at right angles to the plane of the paper, and meeting it at the point a. If this ray enters 464 CIRCULAR POLARISATION. a plate of tourmaline, whose axis is parallel to m n, or a Nicbol's prism, whose principal section is in that direction, the ray will be transmitted with its full intensity. But if the axis of the tourmaline or the principal section of the prism be turned round into the position rnfii', the intensity of the transmitted light will be diminished, because the tourmaline or the prism will only transmit vibrations in the direction a m, and there is always a loss of power in changing the direction of motion. Let ah represent the utmost length of the excursion of a particle of the ether in the original direction of vibration, in other words, the original intensity of the light. Draw i c at right angles to a m' ; then a c represents the component of the force a b in the direction a m', and a c is clearly less than a b. If the tourmaline or the prism be turned still further into the position m'' w'' the reduced portion of the intensity a c' will be found to be still less; and, lastly, when the axis or the principal section is perpendicular to mw, the reduced portion of the motion becomes equal to nothing, and there is no light transmitted. Generally, if u be the original intensity of the light, and 6 the angle between the old and new planes of vibration, the reduced intensity will be u cos 6. Circular Polarisation. — Some media possess the singular property of changing the direction of vibration of a ray of polarised light ; in other words, of causing the plane of pola- risation to rotate through a certain angle, either to the right or to the left. This property is exhibited in a remark- able degree, by quartz or rock-crystal, a mineral which crystallises in six-sided prisms terminated by six-sided pyra- mids, the axis being a straight line joining the two pyramidal summits. Suppose now, a ray polarised by passing through a Nichol's prism to be viewed through another such prism, having its principal section at right angles to that of the first. The field will, of course, appear dark. Then let a plate of quartz, bounded by parallel faces cut perpen- dicularly to its axis, be interposed between tlie two prisms. CIRCULAR POLARISATION. 465 Immediately the field of view will appear brilliantly illumi- nated and coloured, exliibiting a tint of red, yellow, green, blue, &c., according to the thickness of the quartz-plate. If the Nichol's prism, which serves as the eye-piece, be turned on its axis, the colours will go through the regular prismatic series, from red to violet, or the contrary, according to the direction of rotation; but no alteration of colour is produced by rotating the quartz-plate while the eye-piece remains stationary. Exactly similar effects are produced if either of the Nichol's prisms be replaced by a tourmaline or a glass reflector, or a bundle of glass plates which polarise by ordinary refraction ; but the two NichoPs prisms form by far the most convenient apparatus, and we shall therefore suppose them to be always used. For distinction, the one is called the polarising prism or polariser, the other, the eye-piece. To understand the phenomena just described, we must examine what takes place when homogeneous light is used. Suppose, then, a plate of dark-red glass coloured with red oxide of copper, to be interposed anywhere between the two prisms placed as before, with their principal sections at right angles, so that no light is transmitted by the eye-piece. On interposing the plate of quartz, a red light immediately makes its appearance, and, to render the field again dark, it is necessary to turn the eye-piece through a certain angle, either to the right or to the left. Now, as the Nichol's prism stops a ray of light only when the plane of vibration of that ray is perpendicular to its principal section, it follows that the ray which has traversed the quartz must have had its plane of vibration thereby deflected through an angle equal to that through which the eye-piece has been moved. This effect is called circular polarisation. Precisely similar effects are produced with yellow, green, violet, or any other kind of homogeneous light; but the angle of rotation varies according to the nature of the ray, being least for red, and greatest for violet light. 466 CIRCULAR POLARISATION. Some crystals of quartz rotate the plane of polarisation of a ray to the right, others to the left ; the former are called right-handed, the latter left-handed quartz. But in whichever direction the rotation takes place, a plate of quartz of given thickness always produces the same amount of angular deviation for a ray of given refrangibility ; and for plates of different thickness, the deviation for any particular ray increases in direct proportion to the thickness. The following table gives the angles of deviation for the principal rays of the spectrum produced by plates of quartz of the thickness of 1 millimeter and 3*75 millimeters. Angle of Rotation. Colour*. Plate Plate 1 mm. thick. 3-75 mm. thick. Medium red .... 15° .561° „ orange 19 71i „ yellow 24 90 green 27 101] blue . 32 120 „ indigo 38 142^ „ violet . 44 165 Fig. 30. We can now explain the succession of colours produced when ordinary daylight is used. Suppose a beam of white light, polarised by a Nichol's prism, whose principal section is parallel to A A' (fig. 30 ), to pass through a plate of right- handed quartz, 3*75 mm. thick. The vibrations of the several coloured rays composing the beam of polarised light, are all at first parallel to A A' ; but by passing through the quartz, their planes of vibration are deflected through the several angles given in the above table, CIRCULAR POLARISATION. 467 the red ray then vibrating in the line rv', the yellow in yy, the violet in v v', &c. Now, let the ray be viewed through another Nichol's prism, placed with its principal section also parallel to A A' ; then, by reference to the explanation given at page 463, it will be seen that the red and violet rays w^ill be transmitted with but slightly diminished intensity, the orange and blue with less, the yellow with still less, and the green not at all. The result will, therefore, be a purple tint. Now let the eye-piece be turned from left to right. As the principal section passes successively over the lines rr, oo\ &c., the red, orange, yellow, &c., will, in suc- cession, be more fully transmitted than the other rays, so that a succession of tints will be produced agreeing nearly with the colours of the spectrum and following in the same order, from red through yellow to violet. If the eye-piece be turned the contrary w^ay, the order of the tints will be reversed. If the quartz were left-handed, the phenomena would be precisely similar, excepting that the colours would change from red through yellow to violet, when the eye-piece was turned from right to left. Similar changes of colour will be produced with a plate of quartz of any other thickness ; but the tint produced at any given inclination of the polariser and eye-piece, will of course be different. The tint produced with a quartz-plate S'15 mm. thick, when the prncipal sections of the polariser and eye-piece are parallel to one another, deserves particular notice. This tint, as already observed, is a purple, and more- over changes ver}^ quickly to red or to violet, when the eye- piece is turned one way or the other, the change of colour thus produced being, in fact, very much more rapid and de- cided than in any other part of the circuit. It is accordingly distinguished by the term sensitive tint, or transition-tint {couleur sensible, teinte de passage). On account of the facility and certainty with which it may be recognised, it is frequently 468 CIRCULAR POLARISATION. adopted as the standard tint in measuring the angles of rotation produced by different substances ; it is, in fact, much easier to determine when this particular colour makes its ap- pearance, than to seize the exact moment when a ray of red, yellow, or other homogeneous light completely disappears. The rotatory power of quartz is essentially related to its crystalline forml It is not exhibited by opal, or any other amorphous variety of silica, or by silica dissolved in potash or fused by the oxy-hydrogen blowpipe. The same is true with regard to a few other inorganic compounds possessing the rotatory power, viz. chlorate of soda, bromate of soda, and acetate of uranic oxide and soda ; these salts exhibiting that power only when crystallised, not in solution. Circular Polarisation in Organic Bodies. — The power of rotating the plane of vibration of a polarised ray, is much more widely diffused in the organic, than in the inorganic world ; moreover, inorganic bodies possess it in the liqui4> as well as in the crystalline state. Among organic compounds which rotate the plane of polarisation to the right, may be men- tioned: — Cane-sugar, grape-sugar, diabetic sugar, milk-sugar, dextrin, camphor, asparagin, cinchonine, quinidine, narcotine, tartaric acid, camphoric acid, aspartic acid, oil of lemons, castor-oil, croton-oil. The following rotate to the left: — uncrystallisable sugar of fruits, starch, albumen, amygdalin, quinine, nicotine, strychnine, brucine, morphine, codeine, malic acid, anti-tartaric acid, oil of turpentine, oil of valerian. By passing a polarised ray through tubes of different lengths, filled with the same solution of cane-sugar, or other rotatory substance, it is found that the angle of deviation is proportional to the length of the column of liquid ; and, by filling the same tube with solutions containing different quan- tities of sugar, &c., it is found that the angle of deviation is proportional to the quantity of the substance contained in a column of given length. Generally, then, the angle of deviation is proportionate to the number of active particles which the light has to pass. CIRCULAR POLARISATION. 469 If, then, s be the quantity of active substance contained in a unit of weight of the solution, I the length of the column, and a the observed angle of rotation for a particular tint, the transition-tint, for example, the angle of rotation for the unit of length, and supposing the entire column to be filled with the optically active substance, will be — -. But as the solution of a substance is often attended with condensation of volume, it is best, in order to obtain a measure of the rotatory power, independent of such irregularities, to refer the observed angle of deviation to a hypothetical unit of density, that is to say, to divide the quantitv by the " s I density 8 of the solution. The fraction thus obtained, viz., [a] = — ttj is called the specific rotatory 'power, and expresses the angle of rotation which the pure substance in a column of the unit of length and density = 1 would impart to the ray corresponding to the transition-tint. For example, a solution containing 155 milligrammes of cane-sugar in a gramme of liquid, has a specific gravity = 1 '06, and deflects the tran- sition-tint by 24°, in a column 20 centimeters long ; its specific rotatory power is therefore — [a] = '^ 7-3° ^ ^ 0-155 . 20 . 106 Saccharimetry, — An important practical application of the principles just explained relates to the determination of the quantity of sugar contained in saccharine solutions. The apparatus used for this purpose consists of a glass tube (fig. 31), surrounded with a case of wood or brass, and closed Fig. 31. at both ends with plate-glass discs ground to fit water-tight VOL. II. L L 470 CIRCULAR POLARISATION. and pressed against the tube by mOans of screw-caps. The tube being completely filled with the liquid, is placed on the supports, cd (fig. 32), between two Nichol's prisms, one of which, A, serves as a polariser, the other, B, as an eye- piece. The latter carries a vernier, 7n, moving round a Fig. 32. graduated circle. The simplest way of using this apparatus is to interpose between the tube and the polariser a glass coloured with sub-oxide of copper, the tint of which corre- sponds with the red of the fixed line C of the spectrum — and having set the eye-piece with its principal section at right angles to that of the polariser (which makes the field of view dark so long as the tube is not interposed), to adjust the tube in its place, and turn the eye-piece round till the red light completely disappears. The angle through which the eye-piece is turned measures the deviation produced by the saccharine liquid. A solution of 164*71 grammes of pure and dry cane-sugar in a litre of water, produces in a tube, 20 centimeters long. ^ CIRCULAR POLARISATION. 471 an optical effect equal to that of a plate of right-handed quartz, 1 millimeter thick, that is to say, it turns the plane of polarisation of the red ray corresponding to the fixed line C, through an angle of 15*3°. Hence, if any other solution of cane-sugar in a tube of the same length produces a deviation of a degrees, one litre of that solution will contain . 164*71 grammes of sugar. lO'o The direct measurement of the rotation of the red ray is, however, by no means the best mode of observation, because, as already observed (p. 468), it is difficult to tell with pre- cision when the light completely disappears. For this reason it is better to introduce behind the polarising prism, instead of the red glass, a plate of quartz 3*75 millimeters thick, which, when the polariser and eye-piece are set with their principal sections parallel, exhibits the transition-tint The interposition of the saccharine liquid, which rotates to the right, causes this tint to change ; and the rotation is measured by the number of degrees through which the prism must be turned to restore the transition-tint. Greater exactness is obtained by using a double plate of quartz 3*75 millimeters thick, one-half being composed of right-handed, the other half of left-handed quartz. • Such a plate will exhibit the transition-tint with perfect uniformity on both halves, when the polariser and eye-piece are set with their principal sections parallel ; but on turning the eye-piece to the right, one-half of the plate will incline to red, and the other to blue. The same change will, of course, take place on introducing the tube containing the saccharine liquid ; and to restore the uniformity of tint, the eye-piece must be turned a certain number of degrees the contrary way. If the liquid has but a slight rotatory power, this method is quite satisfactory ; but if the rotatory power is considerable, an LL 2 472 CIRCULAR POLARISATION. error arises from the different angles of rotation imparted to the different coloured rays. To obviate this last source of inaccuracy, a contrivance^ called the compensatory has been invented. It consists of two prismatic plates of quartz, r/ (fig. 33), having their faces, > "' '| """"".m i M!m i :ii i iimii ' nii i iii c c', perpendicular to the crystallographic axis, and the oppo- site faces inclined to this axis at equal angles. These prisms are introduced into the polarising apparatus between the tube and the eye-piece, and one of them is made to slide over the other by means of a rack and pinion, so that the two together form a plate of variable thickness. To the frame of one of these prisms is attached a linear scale, a h, and to the other an index, or a vernier, v v'. One hundred divisions of the scale correspond to an increase of 1 millimeter in the thick- ness of the compound plate. Suppose now these two prisms to consist of left-handed quartz ; a flat plate of right-handed quartz, whose thickness is equal to that of the two compen- sating prisms together when the index points to 0°, is likewise introduced between the tube and the eye-piece. This plate then completely neutralises the action of the compensator, and the effect is the same as if neither the compensator nor the plate of right-handed quartz were introduced, the double quartz-plate (p. 471) still exhibiting the transition- tint on its two halves, when the tube containing the saccha- rine solution is not in its place. Now let the tube containing the dextro-rotatory saccharine liquid be introduced. Imme- diately the two halves of the double-plate assume different CIRCULAR POLARISATIOlSr. 473 colours ; and to restore the uniformity of tint, the compensator must be shifted so as to give the combined left-handed prisms a greater thickness. Suppose that, to produce this compen- sation, the index is moved through eighteen divisions of the scale. Then the rotatory action of the liquid in the tube is equal to that of a quartz-plate having a thickness of -^^ of a millimeter, that is to say, it turns the red ray through an angle of 15-3° x -^\ = 2f . . In order that the preceding method may be directly applied to determine the strength of a solution of any optically active substance, it is necessary : 1. That the solution contain only one such substance. 2. That the quantity of the active substance present be proportioned to the angle of rotation. 3. That the rotation of the red ray be known for one given degree of concentration. Now, in determining the quantity of crystallisable sugar in the syrups obtained from plants, in molasses, &c., a diffi- culty arises from the presence of other kinds of sugar, viz., glucose, and, more especially, the uncrystallisable sugar of fruits, which rotates to the left. This difficulty may, in most cases, be obviated by boiling the liquid with hydrochloric acid, whereby the crystallisable sugar (cane-sugar) is con- verted into the las vo- rotatory sugar of fruits, while the other kinds of sugar remain unaltered. The rotatory power of cane-sugar is not sensibly affected by heat ; but that of un- crystallisable sugar decreases considerably as the tempera- ture rises. Thus, when cane-sugar is heated with hydrochloric acid to 68° C, the resulting fruit-sugar exhibits at different temperatures the following rotatory powers : — Temperature 10° 15° 20° 25° 30° 35° Rotatory power (that of cane- 1 g sugar)=100° J"^^ "^^ "^^ ^^^ 2^ 2^^ Suppose, now, a solution of cane-sugar containing 164*71 grammes in a litre, which, in a column 20 centimeters long, L L 3 474 CIRCULAR POLARISATION. deflects the red ray 15*3° to the right, to be heated to 68° C, with -^ of its volume of hydrochloric acid, and the liquid, after cooling to 15° C, to be introduced into the polarising apparatus in a tube 22 centimeters long, which will contain the same number of atoms of sugar as a tube 20 centimeters long of the liquid before the addition of the acid. The red ray will then be deflected to the left by 0-36 X 15-3° = d'S''. Consequently, the diff*erence in the positions of the eye-piece before and after the conversion will amount to 15-3° + d-d"" = 20-8°. If, then, any mixed solution of cane-sugar and uncrys- tallisable fruit-sugar, containing 164*71 grammes of sugar in a litre, be treated as above, and the difference in the positions in the eye-piece before and after the conversion be 5*2°, tho temperature being 15° C, the amount of crystallisable sugar 5*2 in the mixture is . 164*71 = 41*2 grammes.* 20-8 If the mixture contains grape or starch-sugar mixed with cane-sugar, it must be heated to 80° C. before being intro- duced into the saccharimeter, because the rotatory power of grape or starch-sugar decreases considerably after a while • Let n be the observed deviation before inversion, n' the dcxtro- rotation produced by the crystallisable sugar, n" the laivo-rotation produced by tho uncrystallisable fruit-sugar. Also, let n, be the observed deviation in a column of liquid of the same length, after the liquid has been heated with -^^ of its volume of hydrochloric acid ; and suppose that a quantity of cane-sugar which produces a deviation of n' to the right, yields, when thus treated, a quantity of uncrystallisable sugar, which produces a deviation of Kn' to the left (at 15°C., JT = 0-36). Then, for the determination of n' and n", we have the two equations : — n =n' - n" A mixture of cane-sugar with starch-sugar or grape-sugar may be treated in exactly the same manner, since only the cane-sugar has its direction of rotation reversed ; and in this case, n' and n" will be determined by the equations : — n = n' + n" '-in,=n"-Kn! CIRCULAR POLARISATION. 475 at ordinary temperatures, but quickly attains its minimum value when the liquid is heated to 80°. If grape or starch sugar is present together with uncrys- tallisable fruit-sugar, the problem is indeterminate, because neither of these sugars has its rotating action reversed by treatment with acids. The following table contains a few of the results obtained by the method just described. If the liquid to be examined contains nothing but crystallisable sugar, we have merely to look in the last column but one for the number of degrees read off on the compensator ; and the corresponding number in the last column gives the number of grammes of sugar in a litre of the liquid. If other optically active substances are present, and inversion is consequently necessary, the results are found by means of the readings in the first six columns. Table for the Analysis op Sacchakine Solutions.* Sum or difference of the readings before and after the inversion of the sugar, the last reading being made at the temperature of Degrees. Grammes of sugar in a litre. lOO 150 20° 250 30O 35° 1-4 1-4 1-3 1-3 1-3 1-3 1 1-64 13-9 13-6 13-4 13-1 12-9 12-6 10 16-47 27-8 27-3 26-8 26-3 25-8 25-3 20 32-94 41-7 40-9 40-2 39-4 38-7 37-9 30 49-41 55-6 54-6 53-6 52-6 51-6 50-6 40 65-88 69-5 68-2 67-0 65-7 64-5 63-2 50 82-35 83-4 81-9 80-4 78-9 77-4 75-9 60 98-82 97-3 95-5 93-8 92-0 90-3 88-5 70 115-29 111-2 109-2 107-2 105-2 103-2 1012 80 131-76 125-1 122-8 120-6 118-3 116-1 113-9 90 148-23 139-0 136-5 134-0 131-5 1290 126-5 100 164-71 152-9 150-1 147-4 144-6 141-9 139-1 110 181-18 166-8 163-8 160-8 157-8 154-8 151-8 120 197-65 180-7 177-4 174-2 170-9 167-7 164-4 130 214-21 ♦ This table is extracted from the much more extensive one given in the " Traitc de Chimie Goneralo " par Pelouzo ct Fremy. Paris, 1855, t It. pp. 620—622. L L 4 476 CIRCULAR POLARISATION. Relations between Rotatory Power and Crystalline Form, — It has already been observed that silica and a few other inorganic bodies exhibit circular polarisation, only when crystallised. Moreover, crystals of the same substance — quartz, for example — which exert opposite actions on polarised light, often exhibit a remarkable opposition in their crys- talline forms. Thus, the ordinary form of quartz, the six- sided prism with pjTamidal six-sided summits, is sometimes found modified in the manner shown in figs. 34, 35, the solid angles formed by the meeting of two pyramidal with two Fig. 34. Fig. 35. prismatic faces, being truncated with faces, a, obliquely inclined to the faces of the prism ; these truncation faces, however, are only six in number, whereas to form a complete holohedral combination (since these faces are unequally inclined to those of the prism), there should be twenty-four of them, two at each of the twelve angles above-mentioned : the form is therefore tetartohedral.* But, further, these * Hdohedral forms are those which are bounded by similar faces occurring in the greatest possible number consistent with the law of symmetry which de- termines their position ; if the number of such faces is only one-half of what it might be, the form is hemihedral ; if only one-fourth, it is tetartohedral. The regular octohedron is a holohedral crystal, and tlie tetrahedron is the hemi- hedral form coiTcsponding to it ; similarly, the rhombohedron is the hemihedral form of the double six-sided pyramid. Hemihedral and tetartohedral forms often occur associated with holohedral fonus in the same crystal. CIRCULAR POLARISATION. 477 tetartohedral faces are not always placed alike, occurring in some crystals on the right of a prismatic face above, and on the left below, and the contrary in others, as shown in the above figures. The two forms of crystal thus produced, though their faces are alike in number and in form, are evidently not superposible, but the one may be regarded as the reflected image of the other. Now, the crystals of the one kind invariably exhibit dextro-rotatory, and those of the other kind Isevo-rotatory, power. The same kind of opposite tetartohedry, and accompanied by a corresponding opposition of rotatory power, is found in the few other inorganic com- pounds (p. 468) which exhibit circular polarisation. This remarkable relation between rotatory power and crystalline form is, however, much more strikingly exhibited by certain organic compounds. Tartaric acid and its salts turn the plane of polarisation to the right ; racemic acid, which is identical in chemical com- position with tartaric acid, and agrees with it in nearly all its chemical relations, has no action whatever on polarised light, either in the free state of the acid or when combined with bases. Now, the crystals of tartaric acid and the tartrates are hemihedral, those of racemic acid and the racemates, with one exception, are holohedral The exception alluded to is the racemate of soda and ammonia. A solution of racemate of soda and racemate of ammonia, in equivalent proportions, yields by evaporation crystals of a double salt, the form of which is represented in figs. 36, 37. It is a right rectangular prism P, M, T, having its lateral edges replaced by the faces b^, and the intersection of these latter faces, with the face T, replaced by a face A. If the crystal were holohedral, there would be eight of these faces, four above, and four below ; but, as the figures show, there are but four of them, placed alternately: moreover, these hemihedral faces occupy in different crystals, not similar, but opposite positions ; so that, as in the case of quartz, the 478 CIRCULAR POLARISATION. one kind of crystal is, as it were, the reflected image of the other. Fig. 36. Fig. 37. But further ; by carefully picking out the two kinds of crystals, and dissolving them separately in water, solutions are obtained, which, at the same degree of concentration, exert equal and opposite actions upon polarised light, the one deflecting the plane of polarisation to the right, the other, by an equal amount, to the left. Moreover, the solu- tions of the right and left-handed crystals, yield, by evapora- tion, crystals, each of its own kind only ; and by mixing tho solutions of these crystals with chloride of calcium, lime-salts are obtained, which, when decomposed by sulphuric acid, yield acids, agreeing with each other in composition, and in every other respect, except that their crystalline forms exhibit opposite hemihedral modifications, and their solutions, when reduced to the same degree of concentration, exhibit equal and opposite effects on polarised light. Of the two acids thus obtained, the one which turns the plane of polarisation to the right is identical in every respect with ordinary tartaric acid. The other may be called, for distinction, antitartaric acid. When equal weights of these two acids are dissolved in water, and the solutions mixed, a liquid is obtained, which has no action whatever on polarised light, and yields by evaporation, holohedral crystals of racemic acid, A similar result is obtained by mixing equal quantities of any of the salts of the two acids, excepting the double salt of soda and ammonia. CIRCULAR POLARISATION. 470 Hence it appears that racemic acid, a body which has no action upon polarised light, and crystallises in holohedral forms, is a compound of two acids (tartaric and antitar- taric*), which have equal and opposite effects on polarised light, and crystallise in similar but opposite hemihedral forms. There is also another property in which these acids differ, viz. in their pyro-electric relations. The crystals of both these acids become electric when heated, but the corre- sponding extremities of the two exhibit opposite electrical states. Racemic acid is not pyro-electric. Tartaric acid may be converted into racemic acid by the action of heat, provided only it be associated with some sub- stance which will enable it to bear a somewhat high tempe- rature without decomposing. There are many substances whose effect on polarised light is altered by heat. This is remarkably the case with the alkaloids of the cinchona bark. When cinchonine, or any of its salts (which rotate to the right), is heated in such a manner as not to produce decomposition, it is transformed into an isomeric alkaloid, cinchonicine, which turns the plane of polarisation to the left. Similarly, quinine, which rotates the plane of polarisation to the left, is converted by heat into quinicine, which turns it to the right. Now, when tartrate of cinchonine is heated, it is first converted into tartrate of cinchonicine, and if the heat be then continued, the change extends to the tartaric acid, half of which is converted into antitartaric acid. If the process be stopped at a certain point, and the fused mass treated with water, a solution is obtained which yields, first, crystals of antitartrate, and afterwards, of tartrate of cinchonicine. But if the heat be longer continued, the two acids unite, and form racemate of cinchonicine, from which racemic acid may be prepared, identical in every respect with ordinary race- mic acid, and separable by the same means into the two opposite tartaric acids. * Thence also called respectively dextro-racemie and lavo-raceniic acids. 480 CIRCULAR rOLARlSATION. But, what is very remarkable, there is formed at the same time a modification of tartaric acid, which has no action whatever on polarised light, and yet is not separable into the two opposite acids. In fact, when the fused mass obtained by heating tartrate of cinchonine is treated with water, and chloride of calcium added, a precipitate is formed, consisting of racemate of lime, and the filtrate, if left at rest, deposits crystals of the lime-salt of inactive tartaric acid. There are other organic compounds which are also opti- cally active in their ordinary forms, but exhibit inactive and inseparable modifications. Malic acid, as it exists in fruits, turns the plane of polarisation to the right ; so likewise does aspartic acid obtained by the action of acids and alkalies on asparagin. Now both these acids may be formed from fu- maric acid, an optically inactive substance. Acid fumarate of ammonia is C8H3(NH4)08=C8H7N08, which is also the formula of aspartic acid, and this acid is actually formed by heating the acid fumarate of ammonia. But the aspartic acid thus produced is, like fumaric acid, optically inactive. Again, aspartic acid is converted into malic acid by the action of nitrous acid : — CgH^NOg + NO3 = CgHgOjo + 2N + IIO. Aspartic acid. Malic acid. Both active and inactive aspartic acids undergo this trans- formation ; but active aspartic acid yields active malic acid, and inactive aspartic acid yields inactive malic acid. Neither inactive aspartic nor inactive malic acid can be separated into two acids oppositely active. Common oil of turpentine possesses considerable dextro- rotatory power; but the isomeric substance obtained by heating the artificial solid camphor of turpentine with quick- lime is optically inactive. Fusel oil has lately been shown by Pasteur to be a mix- ture of two kinds of amylic alcohol, which differ slightly in FLUORESCENCE. 481 boiling point. One of these alcohols is optically active, the other inactive. Rotatory Power induced by Magnetic Action. — Faraday lias made the remarkable discovery, that bodies which, in their ordinary state, exert no particular action on polarised light, acquire the circular-polarising structure when subjected to the action of powerful electric or magnetic forces. A polar- ised ray passing along the axis of a prism or cylinder of any transparent substance, such as water or glass, has its plane of polarisation deflected to the right or left, as soon as the medium is subjected to the action of an electric current passing round it at right angles to the axis, or to that of two powerful opposite magnetic poles, so placed that their line of junction shall be parallel to the axis of the column of the transparent substance. The rotation ceases as soon as the electric or magnetic force ceases to act ; its amount varies directly as the strength of the current; and its direction changes with that of the current or of the magnetic force. If the medium has a rotatory power of its own, the total effect is equal to the sum or difference of the natural and induced rotations, according as the electric or magnetic force acts with or against the natural rotatory power of the medium. CHANGE OF REFRANGIBILITY OF LIGHT. — FLUORESCENCE. It was observed some years ago by Sir John Herschel, that a solution of sulphate of quinine, though perfectly colourless by transmitted light, exhibits in certain aspects a peculiar blue colour. This blue light was found to be produced only by a very thin stratum of the liquid adjacent to the surface by which the light entered ; and the incident beam, after having passed through the stratum from which the blue light came, was not sensibly weakened or coloured, but had lost the power of producing the usual blue colour when admitted into another 482 FLUOKESCENCE. solution of sulphate of quinine. Light thus modified was said by Sir J. Herschel to be epipolised. Similar phenomena were observed by Sir D. Brewster in an alcoholic solution of chlorophyll, the green colouring matter of leaves, the path of a beam of sunlight admitted into the green solution being marked by a bright light of a blood- red colour. The same appearance was afterwards observed in various vegetable solutions and essential oils, and in some solids. Brewster distinguished this phenomenon by the name of internal dispersion, attributing it to the irregular reflection of the light from coloured particles suspended in the liquid, and was of opinion that Herschel's epipolic dispersion was only a particular case of this internal dispersion. The true explanation of these remarkable phenomena has, however, been given by Professor Stokes*, who has submitted the whole subject to the most searching investigation, and shown that the peculiar dispersion produced by sulphate of quinine, and the other liquids above mentioned, is due to a change of refrangihility in the rays of light. The following experiment renders this evident : — A solar spectrum is formed by means of an achromatic lens, and one or more prisms of flint glass, sufficiently pure to render visible the principal fixed lines, and a tube filled with a solution of sulphate of quinine is passed along this spectrum, from the red towards the violet end. Nothing peculiar is observed while the tube is held in the less refrangible part of the spectrum, the light passing through it freely and without sensible modification ; but just before it reaches the extremity of the violet, a peculiar blue diffused light makes its appear- ance at the surface of the fluid by which the light enters, and remains visible even after the tube has passed beyond the violet into the invisible portion of the spectrum, acquiring in fact its greatest intensity at a certain distance beyond the ex- treme violet. * Phil. Trans. 1852. ii. 463. FLUORESCENCE. 48S The stratum of liquid from which the diffused blue light emanates is thinner in proportion as the incident rajs are more refrangible ; and, from a little beyond the extreme violet to the end of the spectrum, the blue space is reduced to an excessively thin stratum adjacent to the surface by which the rays enter. It appears, therefore, that the solution, though transparent with respect to nearly the whole of the visible rays, is of an inky blackness with respect to the invisible rays more refrangible than the violet. Nevertheless, these rays, when once they have been converted into the visible blue light, pass through the liquid with facility. They must, therefore, be essentially altered in character. Now a change in the quality of light must consist, either in a modification of its state of polarisation, or in its period of undulation. The former sup- position is excluded by the fact that the light thus modified is not polarised at all. It must, therefore, have undergone a change in its rate of vibration, and consequently a change of refrangibility. The existence of this change is, moreover, distinctly proved by examining the diffused light with a prism. It is then found to be by no means homogeneous, but to be resolvable into rays of unequal refrangibility, the whole of which are however comprised within the limits of the visible spectrum. The diffused blue light consists of the chemical rays rendered visible by a change in their refrangibility. The diffusion thus produced is entirely distinct from that which is due to reflection from irregularities or suspended particles. The two phenomena are often produced together in the same medium ; but they are easily distinguished by the fact that the light diffused by irregular reflection is more or less polarised, whereas the light diffused in the manner above described is entirely unpolarised, even if the incident rays were themselves polarised. This phenomenon, to which Pro- fessor Stokes originally gave the name of true diffusion, to distinguish it from the false diffusion produced by irregular reflection, is now called Fluorescence. 484 FLUORESCENCE. It is exhibited by many solutions, and by many solid bodies, opaque as well as transparent, the colour of the diffused light varying with the nature of the medium. An aqueous infusion of horse-chestnut bark exhibits it very strongly, producing the same blue colour as sulphate of quinine. Many compounds of sesquioxide of uranium are also highly fluorescent, and diffuse a greenish-blue light, especially the nitrate, and canary-glass (ii. 256). A decoction of madder mixed with alum gives a yellow or orange-yellow fluorescence ; tincture of turmeric and alcoholic extract of thorn-apple seeds diffuse a greenish light ; an alcoholic solution of chlorophyll, a red light. When the fluorescence is strong, as with sulphate of qui- nine, it may be seen by merely viewing the substance by ordinary diffused daylight. For more accurate observation, and for detecting fluorescence when it exists only in a slight degree, the following method is recommended by Professor Stokes*: — Light is admitted into a darkened room through a hole several inches in diameter in the window shutter, and the object to be examined is placed on a small shelf, blackened at the top, and fixed just below. The hole is covered with an absorbing medium, called the pHncipal absorbent, so selected as to transmit only the feebly luminous and invisible rays of high refrangibility. The body on the shelf is viewed through the second medium, the complementary absorbent, which is chosen so as to be as transparent as possible to those rays which are absorbed by the first, and to absorb all the rays which are transmitted by the first. If the media are well selected, they produce a very near approach to perfect darkness ; and if the object appears unduly luminous, that effect most pro- bably arises from fluorescence. To determine whether the illumination is really due to that cause, the complementary absorbent is removed from before the eyes to the front of the aperture, when the illumination, if really due to fluorescence, * Phil. Mag. [4], vi. 304, FLUORESCENCE. 485 almost wholly disappears ; whereas, if it be due merely to scattered light capable of passing through both media, it remains. In examining feebly fluorescent substances, how- ever, it is better to keep the second medium in its place before the eye, and to us© a third medium, the transfer-medium, placing the last alternately in the path of the incident rays, and between the object and the eye. Still greater delicacy of observation is attained by placing the substance side by side with a small white porcelain tablet, which is quite destitute of fluorescence, and examining the two as above. Or, again, the object being placed on the tablet, a slit is held close to it, in such a position as to be seen projected, partly on the object, partly on the tablet, and the slit is viewed through a prism. The fluorescence of the object is evidenced by light appearing in regions of the spectrum, in which the rays coming through the principal absorbent, and scattered by the tablet, produce nothing but darkness. These methods are delicate enough to show the fluorescence of white paper, even on a very gloomy day. It is not merely the most refrangible rays that are capable of producing fluorescence ; the rays of any part of the spec- trum may undergo this change. By examining different media with the spectrum in the manner already described, it is seen that the fluorescence begins, sometimes in the blue, sometimes in the yellow. With an alcoholic solution of chlorophyll, it begins in the red. But wherever the change of refrangibility may begin, it is always in one direction, con- sisting in a diminution of the index of refraction, and a con- sequent depression of the light in the scale of colours. In other words, the length of the wave w increased, and its velocity of undulation diminished. The vibrations of the ether in the incident ray appear to excite disturbances within the complex molecules of the fluorescent medium, whereby new vibrations are excited in the ether, differing in period from those of the incident ray. The portion of the light which has produced VOL. IL M M 486 FLUORESCENCE. this molecular disturbance is used up, or absorbed, and thereby lost to visual perception, just as heat is converted into mechanical work. It is probable that the absorption of light always takes place in this manner. The well-known fact of the conversion of luminous rays into invisible calorific rays, is a striking instance of diminution of refrangibility accompanied by absorption. As the most refrangible rays are the most active in pro- ducing fluorescence, it is natural that this effect should be most strikingly exhibited by the light of flames which are rich in those rays, — the flame of alcohol and of sulphur, for example. These flames do, in fact, produce the effect in a higher degree even than sunlight. An extremely beautiful effect is produced by exposing a number of highly fluorescent media, such as sulphate of quinine, infusion of horse-chestnut bark, and canary-glass, to the flame of sulphur burning in oxygen in a dark room. The similarity of the blue light diffused by most fluorescent media to the phosphorescence exhibited by certain bodies, might lead us to suppose that the two phenomena proceed from the same cause. Such, however, is not the case: for fluorescence is entirely dependent on the incidence of certain rays, whereas phosphorescence is not ; and, moreover, there is no apparent connection between fluorescent and phosphorescent bodies. So far as observation has yet gone, phosphorescent bodies are not fluorescent. SPECTRA EXHIBITED BY COLOURED MEDIA. The colour of an object depends upon the rays which it reflects or transmits to the eye ; it is, in fact, the mixture or resultant of all the rays which the body does not absorb. We cannot, however, from observation with the unassisted eye, judge with certainty of the rays which are transmitted or reflected ; because the same, or nearly the same, com- SPECTRA PRODUCED BY COLOURED MEDIA. 487 pound tint may result from the union of very different pri- mary colours. Thus a body may exhibit an indigo or violet tint, either because it absorbs all the rays excepting those which form the indigo or violet portions of the spectrum, or because it reflects or transmits the red and blue rays in cer- tain proportions ; similarly, a green colour may be the pure green of the spectrum, or a mixture of yellow and blue. In such cases, examination with the prism will show of what primary rays the colour is composed, and may thus afford the means of distinguishing between substances which, to ordinary observation, appear of the same colour. Dr. Gladstone, who has lately made some very inte- resting observations on the absorption of light by coloured liquids*, introduces the liquid into a wedge-shaped vessel placed before a slit in the window-shutter of a darkened room, so that the line of light may be seen through various thicknesses of the liquid, from the thinnest possible fihn to a stratum perhaps three-quarters of an inch thick, and examines this line of coloured light with a prism held with its refracting angle parallel to the line of light. The whitish portion of the line, where the light traverses but a thin film of the liquid, is thereby expanded into a spectrum differing but little from that which is given by unaltered day- light ; but as the line of light is viewed through deeper portions of the liquid, some rays are seen to diminish in intensity, others gradually to die out, while others almost im- mediately disappear, giving place to perfect darkness. With a good prism, on a tolerably clear day, the most conspicuous of Fraunhofer's lines may be seen. The appearances pre- sented may be understood from the following representations of the effects produced by solutions of sesquichloride of chromium (Fig. 38) and permanganate of potash (Fig. 39).t * Chem. Soc. Qu. J. x. 79. f For representations of the spectra exhibited by a considerab'o number of ^Imiv^H liniiirla spft Dr. Cilsiflstone's nsiner nhnvp. rp.fp.rrp.d to. ]» M 2 488 LIGHT. The right-hand side of these figures corresponds with the red extremity of the spectrum : the letters refer to Fraunhofer's lines. Fig. 38. Fig. 39. G^ F Ji B A comparison of the spectra exhibited by different salts, only one constituent of which is coloured, shows that, with very few exceptions, all the compounds of the same base or acid have the same effect on the rays of light. This law is seen to hold good in many instances which at first sight appear exceptional. Thus it is well known that some salts of chromic oxide are green, others red or purple. Now these differently-coloured chromic salts all exhibit the same general form of spectrum (Fig. 38), in which the violet and indigo rays are very soon cut off; and as the thickness increases, the light is more and more concentrated about two points, one in the red, the other in the bluish green, the red ray penetrating with the greatest facility. Hence it is that the chloride and other salts of chromium, which are green in moderately dilute solutions, appear purple or red when we look through a strong or very deep solution. The acetate absorbs the green rays more readily, and therefore appears green only in very weak solutions, or in thin strata, while the " red potassio- oxalate" absorbs the green so speedily that the thinnest portion of it appears bluish red. SPECTRA PRODUCED BY COLOURED MEDIA. 489 Salts composed of a coloured base and a coloured acid exhibit colours compounded of the rays which are not absorbed by either, the resultant colour bearing, in many instances, but little resemblance to the original colours. Thus, the acid chro- mate of chromic oxide, a compound of two substances which give respectively yellow and green solutions, is not bright green, but brownish-red, because the chromic acid cuts off nearly all the blue and violet rays, while the oxide of chromium absorbs the yellow and the greater part of the green. Some salts, which are but slightly coloured, nevertheless exhibit very characteristic spectra. Thus, a solution of sul- phate of didyraium, which has but a faint rose colour, exhibits, when examined by the hollow wedge and prism, a spectrum containing two very black lines, one in the yellow, the other in the green. These lines are visible in very weak solutions of didymium, and therefore serve as a delicate test for that metal ; they moreover afford the means of distinguishing it from cerium and lanthanum, in the spectra of which they do not occur. MEASUREMENT OF THE CHEMICAL ACTION OF LIGHT. Chlorine and hydrogen combine under the influence of light, and form hydrochloric acid. Moreover, if the gaseous mix- ture is in contact with water, the resulting hydrochloric acid is immediately absorbed, and the diminution of volume thus produced affords a measure of the amount of chemical action. This mode of measurement was first adopted by Dr. Draper, of New York, whose experiments led to the important con- clusion that the chemical action of light varies in direct propor- tion to the intensity of the light, and to the time of exposure. But to give to this method all the exactness of which it is susceptible, certain conditions require to be fulfilled; the chief of which are perfect uniformity in the gaseous mixture, M M 3 490 MEASUREMENT OF TUB constancy of pressure on the gas and liquids througliout the apparatus, and elimination of the disturbing action of radiant heat. These and other essential conditions are completely fulfilled in the apparatus used by Professor Bunsen and Dr. H. Roscoe in their late elaborate researches on the chemical action of light.* This apparatus is represented in figure 40. To furnish the mixture of chlorine and hydrogen gases required, hydro- chloric acid is decomposed in the glass vessel a, containing two carbon poles, connected by platinum wires with the four- celled Bunsen's battery, C. Between the battery and this vessel is interposed an instrument called the gyrotrope, by means of which the current may be made to pass either directly through the acid vessel a, or previously through the vessel d containing very slightly acidulated water, whereby the current is greatly weakened, and the evolution of gas in the vessel a reduced to a small amount. The mixture of chlorine and hydrogen passes from the vessel a through the washing- tube to, containing water, then forward through a horizontal tube provided with a glass cock, h, into the insolation vessel i, where the gases are exposed to the action of light. The lower part of this vessel, containing water, is blackened to protect it from the action of the light. From the insolation vessel, the gas passes through the horizontal measuring-tube K, pro- vided with a millimeter scale, then through the water in the small vessel /, and finally into a vessel filled with fragments of charcoal and hydrate of lime, to absorb the excess of chlorino When the gas is made to stream through the apparatus, the liquids in «, to, z, and /, become gradually saturated w^ith gas; and as the saturation goes on, the composition of the gas varies. At length, however, after the stream of gas has been continued for three or four days, the liquids become saturated, and then the evolved gas is found to consist of exactly equal volumes * Pogg. Ann. c. 43, 481 ; abstr. Proceedings of the Royal Society, viii. 235, 23G, 516. CHEMICAL ACTION OP LIGHT. 491 of chlorine and hydrogen. This normal state having been attained, the apparatus is ready for use, and retains its constant sensibility for weeks, req uiring only a short saturation each day, previous to the actual observations. To make an obser- vation, the stop-cock h is closed, and the light allowed to act on the gas in the upper part of the vessel z. Combina- tion then takes place, accompanied by di- minution of volume, and the external pres- sure forces the water in I through the tube K towards i. The position of the end of the column in the scale measures the diminution of vo- lume. The pressure on the gas in the in- solation vessel and the measurinfj-tube during the observa- tions, is necessarily uniform from the construction of the apparatus ; but it is further necessary that uniformity of pressure be ensured in all parts of the apparatus M 3f 4 492 CHEMICAL ACTION OF LIGHT. in the intervals between the observations ; otherwise the com- position of the gaseous mixture will be altered, and the results will no longer be exact. To ensure this uniformity of pres- sure, the gas, after the stopcock h is closed, is made to pass through the bent tube m v v, containing water, and thence through the tube p, which dips under the water in the vessel F, the pressure being regulated by raising or depressing this tube through the caoutchouc mouthpiece t. From the vessel F the gas is conveyed by a flexible tube into the condensing vessel G, containing charcoal and hydrate of lime. As soon as the stopcock h is closed, the gyrotrope wire is turned, so as to cause the current to pass through the vessel (Z, and thereby slacken the evolution of gas. When the stopcock h is open, the gas will pass one way or the other, according to the depth at which the tube p is immersed below the water in F. To prevent any disturbance from the effects of radiant heat, the light from a coal gas flame, or other source, after being condensed by the convex lens tti, is made to pass through the cylinder n, closed with plate-glass ends, and filled with water. A screen is placed in front of the insolation vessel, to prevent radiation of heat from the body of the observer ; and this, together with the screen L, serves also to prevent radiation from extenial objects. The heat evolved in the insolation vessel by the combustion of the mixed gases, was found by direct experiment, not to exert any sensible influence on the results. All the parts of the apparatus between a and I are connected by ground-glass joints or by fusing; no caoutchouc, or any other organic matter, which could be acted upon by the chlorine, being introduced, excepting in those parts which merely serve to carry away the waste gas. Fhoto-chemical Induction, — On exposing the gas to the light, the quantity of hydrochloric acid formed does not at once attain the maximum : a certain time always elapses before any PHOTO-CHEMICAL INDUCTION. 493 alteration of volume is perceptible; a slight alteration is, however, soon observed, and this gradually increases till the permanent maximum is reached* This remarkable fact was first observed by Draper, who explained it by supposing that the chlorine underwent, by exposure to light, a permanent allotropic modification, in which it possessed more than usually active properties. But Bunsen and Roscoe have shown that neither chlorine nor hydrogen, when separately insolated, undergoes any such modification, no difference being indeed perceptible between the action of light on a mixture of the gases which have been separately insolated before mixing, and on a mixture of the same gases evolved and previously kept in the dark. The light appears then to act by increasing the attraction between the chemically active molecules, or by overcoming certain resistances which oppose their combination. This peculiar action is called photo-chemical induction. The time which elapses from the beginning of the exposure till the maximum action is attained, varies considerably accord- ing to circumstances, the maximum being sometimes reached in fifteen minutes, sometimes in three or four minutes. In one instance, the first action was visible only after six minutes' insolation, whilst in some experiments a considerable action was observed in the first minute. The duration of the inductive action varies with the mass of the gas, and with the amount of light. With a constant quantity of light, it increases with the volume of the exposed gas. With a constant volume of gas it is found : — 1, That the time necessary to effect the first action decreases with increase of light, and in a greater ratio than the increase of light. — 2. That the time which elapses until the maximum is attained, also decreases with increase of light, but in a less ratio. — 3. That the increase of the induction proceeds at first in an ex- panding series, and then converges till the true maximum is attained. The condition of increased combining power into which the mixture of chlorine and hydrogen is brought by the action of 494 CHEMICAL ACTION OF LIGHT. light, is not permanent ; on the contrary, the resistance to combination overcome by the influence of the light, is soon restored when the gas is allowed to stand in the dark. The resistance to combination which prevents the union of the gases until the action is assisted by light, may be increased by various circumstances, especially by the presence of foreign gases, even in very small quantity. An excess of y^oT ^^ hydrogen above that contained in the normal mixture, reduces the action from 100 to 38. Oxygen, in quantity amounting to only j-^-o of the total volume of gas, diminishes the action from 100 to 4*7 ; and yoq-q reduces it from 100 to 1'3. An excess of Y^^ of chlorine reduces the action from 100 to 60-2; and f^ from 100 to 41-3. A small quantity of hydrochloric acid gas does not produce any appreciable diminution ; y^q-q of the non-insolated mixture reduces the action from 100 to 55. ■ The increase in the rate at which combination goes on up to a certain point under the influence of light, appears to arise, not from any peculiar property of light, but rather from the mode of action of chemical affinity itself. Chemical induction is in fact observed in cases in which there is nothing but pure chemical action to produce the alteration. Thus, when a dilute aqueous solution of bromine mixed with tartaric acid is left in the dark, hydrobromic acid is formed ; and, by deter- mining the amount of free bromine present in the liquid at different times, it is found that the rate at which the produc- tion of hydrobromic acid goes on is not uniform, but increases up to a certain point, according to a law similar to that which is observed in photo-chemical induction. These phenomena seem to point to the conclusion that the affinity between any two bodies is in itself a force of constant amount, but that its action is liable to be modified by opposing forces, similar to those which affect the conduction of heat or electricity, or the distribution of magnetism in steel. We overcome these resistances when we accelerate the formation of a precipitate by agitation, or a decomposition by insolation. EXTINCTION OF THE CHEMICAL RAYS. 495 Optical and Chemical Extinction of the Chemical Rays, — When light passes through any medium/ part of it is lost by reflection at the surface, another portion by absorption within the medium, so that the quantity of emergent light is only a fraction of the incident light. This is true with regard to the chemical as well as to the luminous rays. By passing light from a constant source through cylinders with plate-glass ends filled with dry chlorine, it is found that, with a given length of cylinder, the quantity of the chemical rays trans- mitted, when no chemical action takes place, is to the quan- tity in the incident light in a constant ratio ; in other words, the absorption of the chemical rays is proportional to the in- tensity of the light. It is also found that the quantity of chemical rays transmitted varies proportionally to the density of the absorbing medium. But further, when light passes through a medium in which it excites chemical action, it is found that, in addition to the optical extinction already spoken of, a quantity of light is lost proportional to the amount of chemical action produced. The depth of pure chlorine at 0° C and 0*76 mm. pressure, through which the light of a coal-gas flame must pass in order to be reduced to ^, is found to be 173*3 millimeters. Hence, since the quantity of light absorbed varies as the density, the depth of chlorine diluted with an equal volume of air, or other chemically inactive gas, required to produce the same amount of extinction, would be 346*6 mm. But when the sensitive mixture of equal volumes of chlorine and hydrogen is used, the depth of the mixture which the light must penetrate to be reduced to J^-, is found to be only 234 mm. Hence, it appears that light is absorbed in doing chemical work. With light from other sources, results are obtained similar in character, but differing in amount. Diffuse morning light reflected from the zenith of a cloudless sky is reduced to -^^ by passing through 45 '6 mm. of chlorine, and through 73*5 mm. of the sensitive mixture ; diffuse evening light is reduced to j\ by passing through 19*7 mm. of chlorine and through 496 ELECTRICITY. 57*4 mm. of the standard mixture. Hence it appears that the chemical rays of diffuse morning light are absorbed by chlorine much more quickly than those of lamp-light ; and those of evening light with still greater facility. From this we may conclude that the chemical rays reflected at different times and hours, possess, not only quantitative but also quali- tative differences, similar to the various coloured rays of the visible spectrum. It is a fact well known to photographers, that the amount of light photometrically estimated gives no measure of the time in which a given photochemical effect is produced. For the taking of pictures, a less intense morning light is always preferred to a bright evening light. ELECTRICITY. Measurement of the Force of Electric Currents, — There are two methods by which the forces of electric currents are com- pared with each other, viz., the chemical or electrolytic, and the electromagnetic methods. Faraday has shown that the amount of chemical work done is the same in all parts of the circuit ; that, if two decomposing cells be introduced, one containing dilute sulphuric, the other hydrochloric acid, the quantity of hydrogen evolved is the same in both, and equal to the hydrogen evolved (by true current action) in each cell of the battery ; moreover, that the quantities of different elements eliminated in any part of the circuit, are always in the ratio of their equivalent weights. The voltameter (I. 290) affords, therefore, a true and exact measure of the amount of the chemical or electrical force developed by the battery. But its indications are not always sufficiently rapid. In fact, in using this instrument, it is necessary to wait till a measurable quantity of gas is collected. It will, therefore, indicate the relative quantity of electricity THE TANGENT COMPASS. 497 which has passed through the circuit in a certain j&nite inter- val, say in a minute; but it gives no information of any variations that may have taken place during that interval ; moreover, it can only be used to measure currents of con- siderable strength. The Tangent-compass, — To supply these deficiencies, and obtain exact and instantaneous indications of the relative forces of electric currents, recourse is had to the electro- magnetic method, which consists in observing the deflection of a magnetic needle produced by the current. Instruments for this purpose are called Galvanometers or Rheometers, The effect of a coil of wire in intensifying the effect of the current upon a magnetic needle, is described at page 290. Vol. I., of this work. But the kind of instrument there described, though commonly called a galvanometer, is really only a galvanoscope, or multiplier. It indicates with great delicacy the existence and direction of an electric current, but it is not constructed for quantitative determinations. In the true galvanometer (Fig. 41) the current, instead of passing through a long coil of wire placed close to the needle, is made to pass through a broad circular band of brass or copper, p Q, of considerable dimensions, in the centre of which is placed a mag- netic needle, n, the length of which is very small in comparison with the diameter of the circular con- ductor, so that the distance of the extremity of the needle from the conductor P Q, and consequently the force exerted upon it by the cur- rent, is sensibly the same at all angles of deflection. The instrument 498 ELECTRICITY. is so placed that the plane of the circle P Q coincides with the magnetic meridian. To determine the relation which exists under these circumstances between the deflection of the needle and the force of the current, let p q (Fig. 42) repre- sent the circular conductor seen from above ; a z the direction of the needle under the influence of the current. The extre- mity of the needle is then acted upon by two forces, viz, the force of terrestrial magnetism acting Fijr. 42. parallel to P Q, and the force of the current acting at right angles to that direction. Let these forces be represented in magnitude and direc- tion by the lines ah, a c. Draw also the line /a d perpendicular to a z, and hf, c d, perpendicular to df. Then the lines af, a d represent the resolved portions of the forces a b, a c, which act at right angles to the needle, and tend to turn it one way or the other. In order, therefore, that the needle may be at rest, a d must be equal to af, or a c . cos c a d = ah, sin ah f. Now the angle c a cZ is equal to v, the angle of deflection of the needle from the meridian, because a c is perpendicular to p Q, and a d to a z ; and the angle a h f is also equal to u, because a 6 is parallel to p Q, and hfXo a z. Hence the preceding equation becomes a c sin V therefore cos V ^ a h a c := a h , tan v. Or, if we denote the force of the earth's magnetism by M, and that of the electric current by E, we have E = M tan v. ohm's formulae. 499 Consequently, since the magnetic force of the earth is constant at the same place (at least for short intervals of time), the magnetic force of the current is proportional to the tangent of the angle of deflection : hence the name of the instrument. Comparison between the chemical and magnetic actions of the current, — By introducing into the same voltaic curcuit, a voltameter and a tangent-compass, it is found that the chemical action of the current is directly proportional to its magnetic action. The tangent-compass affords, therefore, a measure of the chemical as well as of the magnetic force of the current, the quantity of chemical or electrical force in the circuit being proportional to the tangent of the angle of deflection of the needle. If m milligrammes of hydrogen are evolved in a second in the voltameter, when the galvanometer exhibits a de- flection of 45°, and therefore a current force = 1 (since tan 45° = 1), then, when the same galvanometer shows a deflection = a, the quantity of hydrogen evolved in t seconds will be m . ^ . tan a. The quantity of any other element eliminated in the same circuit, will be found by multiplying this quantity by the equivalent weight of that element. With a tangent -compass, the diameter of whose conductor measures one decimeter, it is found that, when the deflection is 45°, one milligramme, or 11*2 cubic centimeters (at 0° C. and Bar. 0*76 met.) of hydrogen is eliminated in 32*3 seconds. Hence with any other circular current whose radius is r deci- meters and force = tan ot, the time t in which 1 milligramme of hydrogen is evolved, or 9 milligrammes of water are decomposed, is 32-3 t = tan et OhrrCs Formulce. — The amount of electrical or chemical power developed in the voltaic circuit, — or, in other words. 500 ELECTRICITY. the quantity of electricity which passes through a transverse section of the circuit, in a unit of time, evidently depends upon two conditions ; viz., the power, or electromotive force of the battery, and the resistance offered to the passage of the current by the conductors, liquid or solid, which it has to traverse. With a given amount of resistance, the power of the battery is proportional to the quantity of electricity deve- loped in a given time ; and by a double or treble resistance, we mean simply that which, with a given amount of exciting power in the battery, reduces the quantity of electricity deve- loped, or work done, to one-half or one-third. If, then, we denote the electromotive force of the battery by Ey and the resistance by 72, we have, for the quantity of electricity pass- ing through the circuit in a unit of time, the expression : ^=i w This is called Ohm's law, from the name of the distinguished mathematician who first announced it. It must be under- stood, not as a theorem, but as a definition. To say that the strength of the current varies directly as the electromotive force, and inversely as the resistance, is simply to define what we mean by electromotive force and what we mean by resistance.* Let us now endeavour, by means of the formula (1), to estimate the effect produced on the strength of the current by increasing the number and size of the plates of the battery. The resistance R consists of two parts ; viz. that which the current experiences in passing through the cells of the battery itself, and that which is offered by the external conductor which joins the poles. This conductor may consist either wholly of metal, or partly of metal and partly of electrolytic liquids. ♦ It must be remembered that we are here merely comparing the strength of electric currents one with the other, not reducing the current force to ab- solute mechanical measure, or even comparing it with the electro-static forces of attraction and repulsion. (See page 506.) ohm's formula. 501 Let the resistance within the battery be r, and the external resistance v' ; then, in the one-celled battery, we have 1 = VT^ (2) Now suppose the battery to consist of n cells perfectly similar ; then the" electromotive force becomes nE, the resistance within the battery nri if, then, the external resistance remains the same, the strength of the current will be denoted by nE E nr -\- t' , r' r +- n (3) If r' be small, this expression has nearly the same value jp as ^ ; that is to say, if the circuit be closed by a good conductor, such as a short thick wire, the quantity of elec- tricity developed by the compound battery of n cells, is sensibly the same as that evolved by a single cell of the same dimensions. But if r' is of considerable amount, as when the circuit is closed by a long thin wire, or when an electrolyte is interposed, the strength of the current increases considerably with the number of plates. In fact, the expression (3) is always greater than (2) ; for — nE __ E ^ {n -I) Er" ^ ^ _l_ / 7* + r' (nr -^ r')(r -\- r') ' a quantity which is necessarily positive when n is greater than unity. Suppose, in the next place, that the size of the plates is increased, while their number remains the same. Then, according to the chemical theory, an increase in the surface of metal acted upon must produce a proportionate increase in the quantity of electricity developed, provided the conducting power of the circuit is sufficient to give it passage. According to the theory which attributes the development of the elec- VOL. II. N N 502 ELECTRICITY. tricity to tlie contact of dissimilar metals, an increase in tlie size of the plates does not increase the electromotive force, but it diminishes the resistance within the cells of the battery by offering a wider passage to the electricity. Hence in the single cell, if the surface of the plates, and therefore the trans- verse section of the liquid, be increased m times, the expression for the strength of the current becomes E _ mE r , , • r -\- mr^' — 4- r m If / be small, this expression is nearly the same as ,, that is to say, the quantity of electricity in the current in- creases very nearly in the same ratio as the size of the plates ; but when the external resistance is considerable, the advantage gained by increasing the size of the plates is much less. We may conclude, then, that when the resistance in the circuit is small, as in electro-magnetic experiments, a small number of large plates is the most advantageous form of battery ; but in overcoming great resistances, power is gained by increasing the number rather than the size of the plates. Electric Resutance of Metals. — The preceding principles enable us to determine the manner in which the resistance of a metallic wire varies with its length. For this purpose suppose a one-celled battery (Daniell's) to be used, which maintains a constant action during the time of the experiment. First let the current be made to pass directly through the. tangent- compass, and afterwards let wires, of uniform thick- ness and of the lengths of 5, 10, 40, 70, and 100 meters, be interposed in the circuit, and the resulting deflections ob- served. Now, as the force of the battery is constant, the resistance is inversely as the strength of the current. But the total resistance is made up of that of the interposed wires, together with that of the battery itself, and that of the con- ductor of the tangent-compass. These last two resistances ELECTRIC RESISTANCE OF METALS. 503 we may suppose to be equal to that of a wire of the same thickness as the above, and of a certain unknown length, x. Instead, therefore, of the lengths of wire 5, 10, 40, &c., we must substitute x + 5^ os + \0, x + AOy &c. An experiment of this kind* gave the following results : — Length of Wire. Observed Deflection. Tangent of Deflection. X meters 62° 0' 1-880 X + 5 40 20 0-849 X + 10 28 30 543 x + 40 9 45 0-172 X + Id 6 0-105 X + 100 4 15 0074 Now, let us assume, as most probable, that the resistance of a wire increases in direct proportion to its length, then, according to Ohm's law, the first two experiments give : — ^ : ^ + 5 = 0-849 : 1*880 whence, x = 4*11. And, by combining in a similar manner the first experiment with all the others, we obtain for x the several values 4*06, 4*03, 4*14, 4*09, the mean of the whole being 4-08. Substituting this value for x in the preceding table, and calculating the corresponding deflections on the supposition that the strength of the current varies inversely as the resistance, that is as the length of the conductor, we obtain the following results : — Length of Conductor. Calculated Deflection. Observed Deflection. Difference. 4-08 meters 62° 0' 62° 0' 9-08 40 18 40 20 + 2' 14-08 28 41 28 30 - 11 44-08 9 56 9 45 - 11 7408 5 57 6 + 3 104-08 4 14 4 15 + 1 * Miiller, Lehrbuch der Physik. 1853, ii. 177. NN 2 504 ELECTRICITY. From the results of this and similar experiments, it is inferred that — the resistance of a conductor of uniform thickness varies directly as its length. The Rheostat or Current-regulator, — The various forms of the so-called constant battery, Daniell's for example (I. 284), attain their end but imperfectly, a galvanometer included in the circuit always exhibiting more or less variation. A really constant current can only be obtained by interposing in the circuit a conducting wire of variable length, so that the resistance may be increased or diminished as the action of the battery becomes stronger or weaker. Various instruments have been contrived for this purpose. The one most used, invented by Professor Wheatstone, is represented in fig. 43. A and B are two cylinders of the pjg, 43. same dimensions — the first of dry wood, the second of brass — placed with their axes parallel to each other. The wooden cylinder A has a fine screw cut on its surface, and around it, following tlie thread of the screw, is coiled a thin ht^ss wire. One extremity of this wire is attached to a brass ring, r, at the nearer end of the wooden cylinder, and the other to the farther extremity of the brass cylinder. The ring v and the nearer end of the brass cylin- der are connected with the wires of the battery through the medium of the screw-joints CD. A movable handle, /i, serves to turn the cylinders alternately round their axes. By turning b to the right, the wire is uncoiled from A and coiled upon B ; and the contrary when A is turned to the left. The number of coils of wire upon A are indicated by a scale placed between the cylinders, the fractions of a turn being measured by an index moving round the ring v, which is graduated accordingly. As the coils of the wire are insulated THE KHEOSTAT. 505 on the wooden cylinder, but not on the brass, it is evident that the path of the current will be longer, and therefore the resistance greater, in proportion to the number of coils of wire upon the wooden cylinder. By means of the rheostat and the tangent-compass, the resistances afforded by different conductors to the passage of the current may be measured with great facility. Suppose that when the wire of the rheostat is completely uncoiled from the wooden cylinder (the index then standing at 0°), a tangent-compass introduced into the circuit shows a deflection of 46°. Then let a copper wire four yards long and -^ih of an inch thick, be introduced into any part of the same circuit. The galvanometer-needle will then exhibit a smaller deflection, say 37°. On removing the wire, the galvanometer will again exhibit its former deflection of 46°. Now let the rheostat wire be coiled round the wooden cylinder till the needle returns to 37°, and suppose that to produce this effect twenty turns of the rheostat wire are necessary. This length of the rheostat wire produces a resistance equal to that of the wire under examination. Next let a similar experiment be made with a wire of the same length but of twice the thickness, and consequently having a transverse section four times as great as that of the former. It will be found that five turns of the rheostat wire, or one-fourth of the former length, are sufficient to produce a resistance equal to that of the second wire. By experiments thus conducted it is found that: The resistance of a wire or any other conductor of given length varies inversely as its transverse section. And comparing this result with that which was established at page 503, we find that : Conductors of the same inaterial offer equal resistances, when their lengths are to one another in the same proportion as their transverse sections. In a similar manner, the relative conducting powers of different metals may be ascertained. Taking the resistance of pure copper as the unit, it is found that that of iron is N N 3 506 ELECTRICITY. 7*02, of brass 3*95, of German silver 15-47. The conducting powers are of course inversely as these numbers (II. 441). Heating Power of the Voltaic Current, — The degree of heat excited in a metallic wire by the passage of the current, increases with the strength of the current and with the resistance of the wire. To determine the numerical relations of this phenomenon, the wire to be heated is formed into a spiral and enclosed within a vessel containing strong alcohol, or some other non-conducting liquid, in order that the cur- rent may pass entirely through the wire, and not through the liquid itself. The rise of temperature in the liquid is noted by a delicate thermometer ; the strength of the current mea- sured by the tangent-compass ; and the resistance of the wire afterwards determined in the manner above described. By this method Lenz* has shown that: — The quantity of heat evolved in a given time is directly propor- tioned to the resistance of the wire, and to the square of the quan- tity of electricity lohich passes through it. The same result has been obtained by Joule f, both for wires and liquid conductors ; by E. Becquerel for liquids ; and by RiessJ for the heat produced by the discharge of the electricity accumulated in a Leydcn jar. Reduction of the Force of the Current to absolute mechanical Measure: — This important determination has been made the subject of an extensive research by Weber and Kohlrausch. § To understand tlio results obtained by these philosophers, it is necessary to define exactly the several units of measurement adopted : a. The unit of. electric fluid is the quantity which, when concentrated in a point, and acting on an equal quantity of * Pogg. Ann. Ixi. 18. f Phil. Mag. [3], xix. 210. X Pogg. Ann. xl. 335 ; xliil 47 ; xlv. 1. § Abhandlungen derMathematisch-physischcn Classe der Kiinigl. Sachsis- chen Gescllsch. d. Wiss. Leipzig. 1856. FORCE OF THE VOLTAIC CURRENT MEASURED. 507 the same fluid also concentrated in a point, and at the unit of distance, exerts a repulsion equal to the unit of force. b. The unit of electrochemical intensity is the force of the current which, in a unit of time, decomposes a unit of weight of water, or an equivalent quantity of any other electrolyte. c. The unit of electromagnetic force, is the force of a current which — when it traverses a circular conductor whose area is equal to the unit of surface, and acts upon a magnet whose magnetic moment is equal to unity, the magnet being placed at a great distance, and In such a manner that its axis is parallel to the plane of the conductor, and its centre on a line drawn through the centre of the circular conductor, and perpendicular to its plane — exerts upon the magnet a rotatory force equal to unity divided by the cube of the dis- tance between the centre of the needle and the centre of the conductor. "Weber had shown by previous experiments that the unit of electrochemical force is to that of electromagnetic force as 106f to 1. It remained, therefore, to determine the relation between the electromagnetic unit and the electrostatic unit (1), and thus to establish a numerical relation between statical and dynamical electricity. The mode of experimenting was as follows : — 1. A Leyden jar having been strongly charged, its knob was touched with a large metallic ball, which took from it a certain portion of its charge, determined by previous experi- ments. The charge of the ball was then transferred to the torsion-balance, and the repulsive force measured. At the same time, the remainder of the charge of the jar was made to traverse the wire of a galvanometer, previously, however, having been passed through a long column of water, in order to give it a sensible duration, and prevent it from passing from one coil of the wire to another in the form of a spark. In this manner, a relation was established between the statical and dynamical effects of the charge of the jar. — 2. The N N 4 508 ELECTRICITY. intensity and duration of a voltaic current were determined, which imparted to the galvanometer needle the same deflection as that produced hy the discharge of the Ley den jar. The results of the experiments were as follows: — Through each section of a conductor traversed by a current whose force is equal to the electromagnetic unit, there passes in a second of time a quantity of positive electricity equal to 155,370 X 10^ statical units (p. 506, a), and an equal quantity of negative electricity travelling in the opposite direction. The quantity of electricity required to decompose one milligramme of water, amounts to 106f times this quantity, or 16,573 x 10^ units of electricity, of each kind. To decom- pose nine milligrammes of water, or one equivalent, requires of course nine times this amount of electricity. This quantity of positive electricity (9 x 16,573 x 10^) accumulated on a cloud situated 1000 meters above the surface of the earth, and acting on an equal quantity of negative electricity on the surface of the earth below the cloud, would exert an attrac- tive force equal to 226,800 kilogrammes, or 208 tons. From the same data it is calculated that, if all the particles of hydrogen in one milligramme of water in the form of a column one millimeter long, were attached to a thread, and all the particles of oxygen to another thread, then, to effect the decomposition of the water in a second, the two threads would require to be drawn in opposite directions, each with a force of 147,380 kilogrammes, or 145 tons. If the water were decomposed with less velocity, the tension would be propor- tionally less. 509 CHEMICAL NOTATION AND CLASSIFICATION. ATOMS AND EQUIVALENTS. Equivalent quantities of any two substances are such as can replace one another in combination, producing compounds of similar chemical character. Thus, when copper is immersed in a solution of nitrate of silver, 31*7 parts of copper take the place of 108 parts of silver, forming a neutral nitrate of copper. Similarly, the 31*7 parts of copper may be replaced by 32*5 parts of zinc, and these again by 39 parts of potassium, the product of the substitution being in each case a neutral salt. These quantities of silver, copper, zinc, and potassium, are therefore equivalent to one another : they discharge analogous chemical functions. In like manner, 47 parts of potash, and 31 parts of soda are equivalent, because they unite with the same quantity of an acid to form neutral salts. Equivalent numbers cannot, however, be always determined by actual substitution. Six parts of carbon are said to be equivalent to 14 parts of nitrogen; but there is no known instance of the direct replacement of nitrogen by carbon. Moreover, certain quantities of sulphuric acid and soda are spoken of as equivalent to one another, although it is plainly impossible that bodies so opposite in character should dis- charge the same chemical function. In fact, the term equi- valent is frequently used, not in its strict etymological sense, but as synonymous with combinirig number. Eight parts of oxygen are said to be equivalent to 1 part of hydrogen, because the bodies unite in this proportion to form water (I. 123). This confusion of the terms equivalent and combining number. 510 . CHEMICAL NOTATION. arises from tlie circumstance that the combining numbers in o most general use have been selected so as to represent, in many cases, the true equivalents. Nevertheless, the ideas of equivalent and combining proportion are essentially different, and the numbers which relate to them cannot be made to coincide in all cases. The numbers which represent the pro- portions in which bodies combine, though to a certain extent arbitrary, may be regarded as fixed when once selected ; but the equivalent of a body varies according to the chemical function which it discharges. When iron dissolves in hydro- chloric acid, producing ferrous chloride, FeCl, every grain of hydrogen expelled from the acid is replaced by 28 grains of iron; but when the same metal dissolves in aqudregia, forming ferric chloride, FcgClg or Fe^Cl, each grain of hydrogen in the acid is replaced by 18^ grains of iron ; in other words, the equivalent of iron (H = 1) is 28 in the ferrous acid, 18f in the ferric compounds. Similarly, the equivalent of mercury is 200 in the mercurous, 100 in the mercuric compounds. By comparing the perchlorates with the permanganates, it appears that 55*7 parts of manganese are equivalent to 35*5 parts of chlorine. Now this same quantity of chlorine is equivalent to 8 parts of oxygen, and to 16 parts of sulphur : moreover, the analogy of the sulphates and manganates shows that 16 parts of sulphur are equivalent to 27*7 parts of manganese, i. e, half the former quantity. Lastly, by comparing the manganous with the manganic salts, it appears that if the equivalent of man- ganese be 27*7 in the former, it must be 18*5 in the latter. Manganese has, therefore, three different equivalents, according to the kind of compound into which it enters ; and, generally, the number of equivalents which may be assigned to a body is equal to the number of chemical func- tions which it discharges. The so-called tables of equivalents are really, as already observed, tables of combining proportion. How are these combining proportions determined ? Most bodies unite with ATOMS AND EQUIVALENTS. 511 others in more than one proportion. Eight parts of oxygen combine with 14, 7, 4*7, 3*5, and 2*8 parts of nitrogen. Which of these numbers is to be taken as the combining number of nitrogen? Again, — 1 part of hydrogen unites with 4|- parts of nitrogen, and yet the combining number of nitrogen (H = 1), is said to be not 4f, but three times that number, viz. 14. Why is this last number adopted? The solution of such questions leads to a variety of considerations. Obviously, the combining numbers should be so selected as to represent all series of compounds by the simplest formulae, and to express analogous combinations by similar formulae. Practically, however, this rule is not found to be a sufficient guide in all cases ; and, in the actual determination of com- bining numbers, reference is constantly made to considerations intimately related to the atomic theory, such as isomorphism, the specific heat of atoms, vapour-densities, and the basicity of acids. Suppose, for example, the combining number of an acid is to be determined ; the first thing to be ascertained is its saturating pow-er. But then arises the question, — is the acid monobasic, bibasic, or tribasic ? Now, on the system of com- bining numbers or equivalents, viewed without reference to atomic constitution, such a question has no meaning. Why, for example, is citric acid said to be tribasic ? Because the formula of a neutral citrate is C12M3O14 ; a formula which does not admit of division by 3, without introducing a frac- tional number of oxygen-atoms. But if the symbols merely denote combining numbers or equivalents, there can be no valid objection to the use of such fractional numbers. There is nothing absurd in the idea of ^ of the quantity of oxygen which unites with one pound of hydrogen to form water. But if the symbols denote atoms, the case is altered, the idea of a divided atom being self-contradictory. This is but one instance out of many of the influence exerted by the atomic theory on the construction of chemical formulae, and consequently on the determination of combining numbers. 512 CHEMICAL NOTATION. These numbers do, in fact, represent the supposed relative weights of atoms. Different views may be entertained of the atomic constitution of bodies ; and, in the present state of chemical knowledge, the determinations of the atomic weight of a body from different points of view may not always agree : the specific heat, for example, sometimes leading to one conclusion, the vapour-density to another ; but the idea of atoms and of their relative weights, and of the building up of compounds by the juxta-position of elementary atoms, is perfectly definite, and affords the only satisfactory explanation yet given of the observed laws of chemical combination (I. 135). GERHARDTS UNITARY SYSTEM. There are three systems of atomic weight in use among chemists: — 1. The system adopted in this work, which is the same as that in Gmelin's Hand-book. In this system, water is represented by the formula HO, and the metallic oxides (protoxides) most resembling it by the formula MO. The atomic weights correspond, for the most part, with the equi- valents, substitution being supposed to take place, atom for atom. 2. The system of Berzelius, based upon the hypothesis that all elementary gases contain equal numbers of atoms in equal volumes, so that the atomic constitution of a compound corresponds with its constitution by volume. Thus, water being composed of 2 vol. H to 1 vol. O, is HgO ; hydrochloric acid, being composed of equal volumes of chlorine and hydro- gen, is HCl, &c. The atomic weights in this system are the same as those in the former (I. 108), excepting those of hydrogen, nitrogen, phosphorus, chlorine, bromine, iodine, and fluorine, which have half the values there assigned to them, viz. : — (O = 8) ; H = 0-5 ; N = 7 ; P = 16-01 ; CI = 17-75; I = 63-18; Br = 40; F = 9*35. Metallic gerhardt's unitary system. 513 protoxides are represented by the formula MO : e. g, potash = KO ; black oxide of copper = CuO, 3. The system of Gerhardt, based, like that of Berzelius, on the hypothesis that all simple gases contain equal numbers of atoms in equal volumes, but carrying out that system more consistently. The formula of water in Gerhardt's system is HgO, as in that of Berzelius. Moreover, as the vapour-density of mercury is to that of oxygen as 6976 : 1106 (I. 149), and mercuric oxide contains 8 parts by weight of oxygen to 100 parts of mercury, it follows that the proportions by volume of mercury-vapour and oxygen which compose this oxide must be 2 vol. mercury to 1 vol. oxygen : for 2 x 6976 : 1106 = 100 : 8 (nearly). Hence mercuric oxide is HggO ; and from the analogy of cupric oxide, ferrous oxide, potash, soda, &c., with mercuric oxide, it follows that these oxides must be CugO, FcgO, KgO, NagO, &c. ; or, generally, the formula of a protoxide is MgO, analogous to that of water, HgO. If O = 8, the atomic weights of sulphur, selenium, tel- lurium, and carbon are the same in Gerhardt's system as in that adopted in the present work, but those of all the other elements have only half the usual values: — H = 0-5, CI = 17 '75, K = 19 5, &c. Or, what is more convenient, assuming PI = 1, the atomic weights of O, S, Se, Te, and C will be doubled, while those of all the other elements will remain the same.* In the following explanations and applications of Gerhardt's system, these double atomic weights of oxygen, &c., will, to avoid confusion, be denoted by letters with bars through the middle : thus, O = 16, -S = 32, €• = 12. The following table presents a comparative view of the * Gmelin, in his Handbook (Translation, vol. vii. p. 27), objects to Gerhardt's atomic weights, that they do not correspond with the equivalent numbers ; but this, as already shown (p. 510), must necessarily be the case with all systems of atomic weights or combining numbers, inasmuch as a body may have several equivalents, but can have only one atomic weight. 514 CHEMICAL NOTATION. formulao of some of the most important chemical compounds in the ordinary notation, and in that of Gerhardt. Ordinary System. Gerliardt's System. Water HO H,f> Peroxide of hydrogen H0„ HO Hydrosulphuric acid HS H28 Sulphuric acid (anhydrous) SO, Htfj „ (hydrated) . / . SHO, KH,e, Hydrochloric acid . HCl HCl Hypochlorous acid (anhydrous CIO 9»^ „ (hydrated) C1H0» CIHO Carbonic oxide CO •ee Carbonic acid (anhydrous) co„ €f>a Nitric acid (anhydrous) . NO, xM* „ „ (hydrated) . NHOg NHOa Phosphoric acid (anhydrous) PO, P,e. „ „ (hydrated) PH3O, ^M* Protoxides (anhydrous) . MO M^e „ . (hydrated) . r MHO, "l t or MO. HO J MHO Sesquioxides (anhydrous) M,0, M,03 Sulphate of potash (neutral) SKO^ SK,tt, „ (acid) s,Kno« ■SKHO, Nitrate of potash NKO« J^^^^.. Alum (anhydrous) . S.KAl^O.o -&,KALe8 Hydrocyanic acid . C,NH eNH Cyanic acid C,NIIOa eNH-O Cyanate of soda CjNNaOj €NNaO Hydrosulphocyanic acid . CsNHS, eNLis , Siilphocyanidc of silver . C^NAgS, -GNAg* Alcohol C,H,0, 0,11,0 Ether C,H,0 ^.H.oO Acetic acid (hydrated) . cji.o, €,H,4>, „ (anhydrous) . C4H3O3 eji.e. Benzoic acid (hydrated) . CuHeO, €,H,0, „ „ (anhydrous) C.,H,03 Ou".o^3 Benzoate of potash . C.,H,K0, ■e^H^KOa 4,H,0, Oxalic acid C,H,0« These two systems of notation possess in common tlie advantage of representing the metallic protoxides by formulae analogous to that of water, whereas in the system of Ber- zelius, this analogy is lost, water being represented by Hg-Q, and the protoxides of the metals by MO. But the repre- sentation of water by HHO, as in Gerliardt's system, pos- sesses the additional advantage of corresponding with the 515 important fact, that it is possible to replace either the half or the whole of the hydrogen in water by a metal. Thus potassium thrown into water displaces half the hydrogen, and forms hydrate of potash, HKO ; and when this compound, in the solid state, is heated with an additional quantity of potas- sium, the remaining half of the hydrogen is displaced, and an- hydrous potash, KKO, is formed. On the contrary, when potassium acts on hydrochloric acid, HCl, it displaces the whole of the hydrogen, and forms chloride of potassium KCl. This is an important difference, which is easily under- stood on the supposition that water contains two atoms and hydrochloric acid only one atom of hydrogen ; whereas, if these two compounds are represented by the analogous formulas HO and HCl, the cause of the difference of action is by no means apparent. Assuming as the unit of vapour- volume the space occupied by 1 gramme of hydrogen (or by 16 grammes of oxygen, 14 of nitrogen, 35*5 of chlorine, &c.), and calculating by formulae analogous to those in the third column of the preceding table, the weights of the compound atoms or molecules of those com- pounds which are capable of assuming the gaseous form, it will be found that they correspond to 2 volumes of vapour. Thus, for hydrochloric acid: H + Cl = 1 +35*5 = 36*5; and as the density of hydrochloric acid gas is 18*25 times that of hy- drogen (see Table I. p. 150.), it follows, that the number 36*5 represents the weight of 2 volumes of vapour. Similarly, for water: H20= 2 + 16 = 18, which is also the weight of 2 volumes of vapour, the specific gravity of aqueous vapour compared with hydrogen as the unit being 9. Alcohol = -G2HgO= 24 + 6 + 16=46 : and the specific gravity of alcohol vapour (H= 1) is 23. Ether=-G4Hioa=48 + 10 + 16 = 74, which is twice 37, the weight of a unit- volume of ether- vapour. In the formula? of the second column, this uniformity of vapour-volume is not observed. Some of them, as those of water HO, ether C^HgO, anhydrous acetic acid C4II3O3, and 516 CHEMICAL NOTATION. lijdrated sulphuric acid SHO^, represent 1 volume of vapour, when referred to the unit above-mentioned, viz. the space occu- pied by 1 gramme of hydrogen, or 2 volumes, if compared with the volume of half a gramme of hydrogen, or 8 grammes of oxygen; while the rest, for example, hydrochloric acid, HCl, and hydrated acetic acid, C^H^O^, represent 2 volumes or 4 volumes of vapour, according to the unit adopted. (See the table in Vol. L, pp. 149-155.) To bring all these for- mulae to the same standard of vapour- volume, it is necessary, therefore, to double those first mentioned, thus : water = HgO^ ; ether, C8H,o02 ; anhydrous acetic acid, CgHgOg ; hydrated sulphuric acid, SgHgOg, &c. ; and if the corresponding change be made in the formulae of the analogous compounds, which are not known to exist in the gaseous state, e. g. anhydrous metallic protoxides, MgOg*, neutral sulphate of potash, S2K2O8, &c., it will be found that Gerhardt's formulae may, in all cases, be converted into those of the ordinary notation, by doubling the number of atoms of carbon, oxygen, sulphur, selenium, and tellurium.* There is yet one class of bodies whose atomic weights repre- sent, not two, but one volume of vapour, viz. the elementary bodies. To reduce these bodies to the same standard, it is necessary to assume that each molecule of an elementary body in the free state consists of two elementary atoms, e. g. hy- drogen, HH ; chlorine, ClCl. This hypothesis is justified by numerous considerations. First: It accords with the polar view of the constitution of bodies suggested by the phenomena of electrolysis (I. 238). Secondly: It is justified by certain relations of boiling point * Gerhardt applied the term unitary to his system of notation, because it is based on the reduction of all formulae to one common standard, the formulaj being derived one from the other by substitution. The ordinary system, being founded rather on the formation of compounds in successive binary groups (c. g. potash = KO ; sulphuric acid = SO3 ; sulphate of potash = KG . SO3), is called the Dualistic system. erhardt's unitary system. 517 and vapour-density, to be considered hereafter. Thirdly: There are numerous instances of chemical action in which two atoms of an elementary body unite together at the moment of chemical change, just like heterogeneous atoms. Thus, when the hydride of copper, CU2H, is decomposed by hydrochloric acid, cuprous chloride is formed, and a quantity of hydrogen evolved equal to twice that which is contained in the hydride itself: — Cu^H + HCl = Cu^Cl + HH. This action is analogous to that of hydrochloric acid on cuprous oxide : — Cu,0 + 2HC1 = 2CU2CI + H^a. In the latter case, the hydrogen separated from the hydro- chloric acid unites with oxygen ; in the former, with hydrogen. When solutions of sulphurous and hydrosulphuric acids are mixed, the whole of the sulphur is precipitated: — SOa + 2H2S = 2H2a + S. S2, the action being similar to that of sulphurous acid on hydro- selenic acid : — SO2 + 2H2^ = 2U^Q + S . Se^. In the one case, a sulphide of selenium is formed; in the other, a sulphide of sulphur. The precipitation of iodine which takes place on mixing hydriodic with iodic acid, affords a similar instance of the combination of homogeneous atoms. The reduction of certain metallic oxides by peroxide of hy- drogen, is another striking example of this kind of action. When oxide of silver is thrown into this liquid, water is formed ; the silver is reduced to the metallic state ; and a quantity of oxygen is evolved equal to twice that which is contained in the oxide of silver. It appears, indeed, as if atoms could not exist in a state of isolation. An atom of an elementary body VOL. II. O O 518 CHEMICAL NOTATIOJf. must unite, either with an atom of another element, or witli one of its own kind. The same tendency of homogeneous atoms to combine together is exhibited by certain groups of atoms called com- pound radicals, which behave in most respects like elementary substances, and pass as entire groups from one state of com- bination to another. Thus there is a series of hydrocarbons called the alcohol-radicals (p. 531), e.g. methyl, ^^Hg ; ethyl, ^2^5, which may be regarded as compound metals, capable of taking the place of hydrogen in combination with chlorine, iodine, oxygen, &c., just as simple metals do. Now when zinc-ethyl, ^^^HaZn, and iodide of methyl, ^^Ilgl, are heated together, double decomposition takes place, the products being iodide of zinc, and methyl- ethyl : — C,H,.Zn + CH,I = Znl + (4:,H,) . (GH,). And when zinc-ethyl is heated with iodide of ethyl, a similar action takes place, but attended with formation of free ethyl : — C,H..Zn + e.HJ =: Znl + (<;,H,) . (e,H,). Moreover, the boiling points and vapour-densities of these radicals are related to each other and to those of the com- pound radicals, methyl-ethyl, butyl-amyl, &c., in a manner which can only be explained by supposing the radicals in the free state to consist of double atoms. This will be seen from the following Table ; — Sp. gr. at ( P C. Vapour-density. Boiling-point. Ethyl-butyl . e,H, . 0,H, 0-7011 3053 62° C. Ethyl- amy 1 . ^H, . ^.H„ 0-7069 3522 88 Butyl <^.H, • ^4H9 0-7057 4070 106 Butyl-amyl . ^.H, . <^sH„ 0-7247 4-465 132 Amyl . ^.H„ • ^.H, 0-7413 4-956 158 Butyl-caproyl 4i,U, . ^«H„ ? 4-917 155 Caproyl . <^6U,3 . 0,H.3 0-7564 5-983 202 gerhardt's unitary system. 519 The regular gradation of these densities and boiling points plainly shows that the proper places of butyl, amyl, and caproyi in the series, are those which they occupy in the table, and consequently that their atomic weights in the free state are double of those which appertain to them in com- bination: e.g., amyl in combination = ^-^n = 71; free amjl = (C,H„), = 142. Fourthly : Elementary bodies frequently act upon others as if their atoms were associated in binary groups. Thus chlorine acting upon potash forms two compounds, chloride of potassium and hypochlorite of potash : — KKa + ClCl = CIK + CIKO; just as chloride of cj'anogen would form chloride of potas- sium and cyanate of potash. The quantity of chlorine which acts upon an atom of potash, is not 1 at. = 35 '5, but 2 at. = 70. Similarly, when metallic sulphides oxidise in the air, both the metal and the sulphur enter into combina- tion with oxygen. Sulphur acting upon potash forms a sulphide and a hyposulphite. Lastly, when zinc-ethyl is exposed to the action of chlorine, iodine, &c., these elements unite separately with the zinc and with the ethyl, thus : — Qr^H.Zn + ClCl = ^^H.Cl + ZnCL Double Decomposition regarded as the Type of Chemical Action in general. — Double decomposition is generally understood as an action taking place between four elements or groups of elements ; but since it appears that homogeneous atoms may exhibit towards one another the same chemical relations as atoms of different bodies, it follows that the same kind of action may be supposed to take place when less than four bodies are concerned. The extension of this view of chemical action to cases in which three elements or groups of elements come into play, is sufficiently illustrated by the examples just given. But w^e may proceed still further in the same o o 2 520 CHEMICAL NOTATION. direction, and regard as double decompositions those reactions which are commonly viewed as the simple combination or separation of two elements, or as the substitution of one ele- ment for another. Thus, when potassium burns in chlorine gas, the reaction may be supposed to take place between two atoms of chlorine and two atoms of potassium: — KK + ClCl = KCl + KCl. Again, the decomposition of cyanide of mercury by heat may be represented thus: — CyHg. CyHg = CyCy + Hgllg. The simple replacement of one element by another may also be regarded as a double decomposition, by supposing the for- mation of an intermediate compound to take place. Thus, the action of zinc upon hydrochloric acid may be supposed to consist of two stages : — ZnZn + HCl = ZnH + ZnCl, and ZnH + HCl = ZnCl + HH. It is true that the formation of the intermediate compound, the hydride of zinc, cannot be actually demonstrated in this case, because it is decomposed as fast as it is formed ; but in other cases the two stages of the action can be distinctly traced. Thus, it is well known that hydrochloric acid does not dissolve copper ; but an alloy of zinc and copper, CugZn, dissolves in it readily, with evolution of hydrogen. Here it may be supposed that the first products are chloride of zinc and hydride of copper, a known compound : — Cu^Zn + HCl = Cu^H + ZnCl; and that the hydride is afterwards acted upon by the acid in the manner already explained. Again, when zinc and iodide of ethyl are heated together in a sealed tube, iodide of zinc and zinc-ethyl are obtained, thus: — ZnZn 4- (^2^5). I = Znl + Zn (^^JIJ; TYPES AND RADICALS. 521 and the zinc-ethyl, when heated with excess of iodide of ethjl, yields iodide of zinc and free ethyl : — Zn (G,H,) + (C,HJ. I = Znl + (e,H,) (C,H,). In this manner, all chemical reactions may be reduced to one type, viz., a mutual interchange of atoms between two binary groups. TYPES AND RADICALS. — RATIONAL FORMULA. The rational formula of a compound is inferred from its modes of formation and decomposition. When cyanide of sodium is mixed with nitrate of silver, an interchange of elements takes place, resulting in the formation of nitrate of soda and cyanide of silver : — ^N. Na + NO3. Ag = ^N . Ag + NOg.Na. Here the group, or radical NO3 passes from the silver to the sodium, and in a similar manner it may be transferred to potassium, barium, copper, &c. Hence it may be inferred that the nitrates consist of NO3 associated with a metal. Similarly, -GN may be regarded as the radical of the cyanides; ■SO^ of the sulphates, &c. When alcohol, -GgHgO, is treated with potassium, one-sixth of the hydrogen is evolved, and the compound Q^H^KQ^ is formed. Again, — alcohol treated with chloride, bromide, and iodide of phosphorus, yields the com- pounds, •G2H5CI, Q,fifir, and -G-gH^I ; and when the com- pound -G-gngKO is treated with -GgHgT, iodide of potassium and ether are formed : — G,HJ + •^»5'}0 = KI + g^H^jO. From these and other reactions, alcohol and its derivatives are supposed to contain the radical ethyl, -GgHg, alcohol being o o 3 522 TYPES AND RADICALS. its liydrated oxide, ^tt^J^j analogous to hydrate of potash, XT JO, and ether its anhydrous oxide, jQ^tt'] O, analogous It must be especially observed, however, that the reason for admitting the existence of ethyl as a radical in the alcohol compounds, is that this supposition affords the readiest ex- planation of certain reactions. Other reactions may point to a different conclusion. Thus, since alcohol heated to a high temperature with strong sulphuric acid is resolved into defiant gas and water, it may be regarded as a hydrate of defiant gas, Ojll^ . IlgO. Again, — certain sulphates, when heated to redness, give off anhydrous sulphuric acid; and sul})hatc of baryta may be formed by the direct combination of the same anhydrous acid with anhydrous baryta. Such reactions might lead to the conclusion that oxygen-salts are compounds of anhydrous metallic oxides with anhydrous acids, rather than of metals with salt- radicals, which is, in fact, the ordinary view. Similarly, ammoniacal salts are re- garded as compounds of NHg with hyd rated acids, or of NH^ with acid radicals, according to the reactions specially under consideration. It appears, then, that the same compound may have several rational formulae. This of course implies that the formula is an expression, not of the constitution of the body in a state of rest, but of the manner in which the atoms are supposed to arrange themselves when subjected to certain influences. It is no longer the question what the absolute constitution of a substance may be, but of how many forms of constitution the substance fulfils the conditions. For in chemical sub- stances, as in the objects of a branch of natural history, any one individual exhibits more or less distinctly the features of every other. The greater the number of elementary atoms entering into TYPES AND RADICALS. 523 tlie constitution of a compound, the more numerous will be the possible arrangements of those atoms, and the greater, therefore, the number of rational formulae which may be assigned to the compound. Practically, however, it is found that a small number of rational formulae — seldom more than two or three — suffices for each compound ; and moreover, - that the formulae of all bodies whatever may be reduced to a small number of general types. Of these, Gerhardt adopts four, viz. : — Water, tt] ^> from which are derived the oxides, sulphides, selenides, and tellurides. Hydrochloric acid, HCl, the type of the chlorides, bromides, iodides, fluorides, and cyanides. Ammonia, N]H, the type of the nitrides, phosphides, ^H arsenides, &c. Hydrogen, HH, the tj'-pe of the elementary bodies, com- pound radicals, hydrides of metals and radicals, &c. These typical formulae all correspond to 2 volumes of vapour. The formulae of the several compounds included under each of these types are obtained by replacing one or more of the ele- mentary atoms contained in them by another radical, simple or compound. The derivative compound is called primary, secondary, or tertiary, according to the number of atoms of hydrogen in the type which are thus replaced. For example, the hydrated metallic oxides, which are formed from the type water by the substitution of 1 at. of a metal for 1 at. hydrogen, are primary oxides ; e. ^. hydrate of potash, t^]0; the an- hydrous oxides, in which both atoms of hydrogen arc similarly o o 4 524 TYPES AND RADICALS. replaced, as in anhydrous potash, tt-JO, are secondary oxides. The replacement of 1 at. H in ammonia by ethyl, "CgHg, forms a primary nitride, viz., ethylamine, N(-G^H5)n2 ; similarly, biethylamine, N(-G2H5)2H, is a secondary nitride; and tri- cthylamine, N (02115)3, a tertiary nitride. Equivalent Values of Radicals. — A radical is monatomic, hiatomicy triatomicy &c., according as its atom or molecule is equivalent to one, two, three, &c., atoms of hydrogen. Potas- sium and ethyl arc monatomic radicals. Sulphuryl, -SOg, is a biatomic radical, and by replacing 2 at. H in two molecules TT Sill of water, tt^]^2' forii^s hydrated sulphuric acid, ti^]^' Fhosplioryl, PO, is a triatomic radical, and by replacing TT 3 atoms of hydrogen in three molecules of water, TT^jOg, forms the ordinary hydrate of phosphoric acid, PH3O4 = tt jOg. When a metal forms two classes of salts, its atom has a different equivalent value in each. Thus, in the platinous compounds, Pt (= 98) is monatomic ; in the platinic salts, it CI is biatomic: thus, platinic chloride = Pt {p,. In the ferrous compounds, Fe (= 28) is monatomic; in the ferric com- pounds, it is sesquiatomic, Fe2 being equivalent to H3, or TT Fe-| to H: thus, ferric oxide = ^ ^jOg. In the mercuric compounds, Hg( = 100) is monatomic; in the mercurous compounds, it is semi-atomic; the double atom, Hg2(= 200), being the equivalent of 1 atom of hydrogen. In arsenious acid, ASgOg, which is derived from 3 molecules of water, Asg is equivalent to Hg, and therefore As to II3; but in arsenic acid, AsgOg, derived from 5 molecules of water. As is equivalent to H^.* * If the notion of equivalents be strictly adhered to, independently of the atomic theory, the formuloe of bisalts and scsquisalts may be dispensed with, TYPES AND RADICAL S. 525 Since a compound may have several rational formulae, or, in other words, maj be represented as containing different radicals, it is necessary to determine the relation which exists between the equivalents of such radicals. This relation is determined by the following general law : — Every equivalent of hydrogcji added to a radical diminishes by unity the equivalent value of the entire radical; and every equivalent of hydrogen sub- tracted from a radical increases by unity the total equivalent value of the entire radical. Thus, nitric acid may be represented by the three following formula : — In the first of these formulae, which represents nitric acid as formed from one molecule of water, HgO, the radical nitryl, ISTOg, is equivalent to 1 atom of hydrogen; in the second, which is formed from 2 molecules of water, H^O^, the radical azotyl, NO, formed from nitryl by abstraction of O, the equivalent of Hg, takes the place of 3 atoms of hydrogen ; and in the third, which is formed from 3 molecules of water, HgOg, the radical nitricum, N, formed from nitryl by abstraction of Oo, the equivalent of H^, takes the place of 5 atoms of hydrogen. Again, uranic oxide may be represented either as tt^JOs, and the different classes of salts of the same metal regarded as containing different radicals : thus the mercurous salts may be regarded as salts of viercuroswn, Hg=200 ; the mercuric salts as containing mercuricum, hg = lOO : thus — Mercurous chloride or chloride of mercurosum . . HgCl = 200 4 35'5 Mercuric chloride or chloride of mercuricum . . . hgCl=100+35-5 Ecrrous chloride or chloride of ferrosum .... FeCl = 28 +35-5 Ferric chloride or chloride of ferricum .... feCl = 185 + 35-5 This mode of representation might be made consistent with the atomic theory, by supposing that the ultimate atom of iron weighs 9^ ; that a double atom of iron constitutes ferricum = 18§ ; and a triple atom, ferrosum, = 28 : similarly, the atom of mercury weighing 100, a double atom constitutes mer- curosum. In organic compounds, such relations between radicals are actually observed : thus, ethylene, G2II4, = 2 x GHj ; propylene, C.II^, = 3 x Gllj ; buty- Icuc, G^Hg = 4 X OII2, &c. 526 TYPES AND RADICALS. or as TT^riJ^' The first of these formulae represents three molecules of water, HgOa, and contains the radical Ug = H3 ; the second represents one molecule of water, and contains the radical ui^anyl, U2O, equivalent to H; and accordingly, Ug — O, is equivalent to Hg — Hg = H. Another example of the general law above stated is afforded by the radicals of the monatomic, biatomic, and triatomic alcohols (p. 531). Conjugate Radicals. — Ax\j compound radical may be regarded as a compound of two or more simpler radicals. Thus, ethyl, •G2H5, may be represented as CHg + CH3, or as -GgHg + Hg ; acetyl, -GgHgO, the radical of acetic acid, may be regarded as .GO+'GH3, or as -G^Hg -j- O, &c. Radicals viewed in this manner are said to be conjugated. A radical may be conjugated either by addition, as in the preceding examples, or by sub- stitution of another radical for one or more atoms of hy- drogen; e.g., from benzoyl, -GyH^O, is formed nitro-benzoyl, G7H4(N02)0, by substitution of a molecule of nitryl, NOg, for 1 at. H. Similarly, from acetyl, -GgHa-Q, are formed mono- chloracetyl, Qji^S^\)Q>, and tcrchloracetyl, Gr^Q\jl^. An important class of conjugate radicals consists of those which are formed of certain metals — arsenic, antimony, tin, bismuth, &c. — associated with the alcohol-radicals. For ex- ample: cacodyl, or arsen-bimethyl, A^{Grl\).-^\ stibethyl, Sb(-G2H5)3; arsenethylium, As(G2H5)4; stannethyl, Sn..G2H5. The same radicals may be regarded as conjugated by substi- tution : e. g.y arsenethyl, As(-G2H5)3, as formed from ammonia, NH3, the 3 at. H being replaced by ethyl, and tlie nitrogen by arsenic. In like manner, arsenethylium, As(G2H5)4, may be derived from ammonium, NH^. The equivalent in hydrogen of a conjugate radical may be determined by the two following rules, deduced from the general law given at page 525 : — 1. The equivalent in hydrogen of a radical conjugated hy addition is equal to the difference of the equivalents of the con- CLASSIFICATION. 527 stituent radicals. Thus, acetyl (^3113)0, which is equivalent to H, is composed of acetosyl, ^2^3» ^^* ^° ^> ^^^ ^ ^^* to Hg ; arsenethyl As (■^•2115)3, which is equivalent to Hg, is composed of As (arsenicum), eq. to H5*, and (^2^^o)3» ^^' to H3 ; cacodjl, As (^H3)2, which is equivalent to H, is com- posed of As (arsenosum), eq. to H3, and (•GH3)2 eq. to Hg. 2. The equivalent in hydrogen of a radical conjugated by substitution is equal to the difference between the sum of the equivalents of the constituent radicals and the equivalent of the hydrogen replaced. For example, — acetyl ^2^3'^^ which is equivalent to H, may be regarded as Q^^d + ^ (^9.* ^^ H + Hg) minus Hg. CLASSIFICATION OF CHEMICAL COMPOUNDS. Bodies may be classified in two ways. 1. According to their origin, as when the acids, salts, oxides, &c., of copper are made to form one group ; those of chromium another, those of ethyl a third, &c. 2. According to their chemical functions, independently of origin; the acids forming one group, the bases a second, the alcohols a third, the ethers a fourth, &c. The former mode of classification is best adapted to tlie detailed description of compounds; the latter forgiving a general view of their mutual relations. The following table exhibits Gerhardt's system of clas- sification by types, or according to chemical functions : — ♦ Oxide of arsenethyl is As(0^H5)3O or As2(C2Hg)g02 ; now as (^Ji^)^ is equivalent to -O; this last formula may be derived from that of arsenic acid, AS2O5 or AS2O3.O2 by the substitution of (€-2Si^)Q for -Gg ; hence As has in oxide of arsenethyl the same equivalent value that it has in arsenic acid ; that is to say, it is equivalent to H^, On the other hand, oxide of cacodyl is As2(-e-H3)4-6-; which has the same equivalent value as ASg . O2O, or As^Og, which is the formula of arsenioas acid. Hence the radical As in cacodyl has the same value as in arsenious acid, viz., equivalent to H^. CLASSIFICATION OF BODIES ACCORDING WATER TYPE, OXIDES. r Bases proper. Deriva- tives with Positive Radicals. I. Primary or hydrated bases (hydrate of potash ^■O, hydrate of ar- Dcriva- ' tives with Negative Radicals. Inter- mediate Deriva- tives. senethylium). 2. Secondary or anhydrous bases (oxide of potas- sium). Aleoliols or Hydrocar- tourettcd Bases. 1. Primary or alcohols proper (vinic alcohol, hydrate of phenyl, gly- col, glycerine). 2. Secondary alcohols or ethers (oxide of ethyl). Aldehydes. 1. Primary (acetic alde- hyde, bitter almond oil). 2. Secondary. Acids. 1. Primary or hydrated acids (sulphuric, acetic, cyanic acids). 2. Secondary or anhydrous acids. Oxygen-salts. Sulphates, nitrates, cyan- ates. Compound Ethers. Sulphate, cyanatc, oxalate of etliyl, glyceridcs, stearin, &c. Compound Aldehydes. SULPHIDES (Selenides, Tellurides). Basic Sulphides. 1, Primary or hydrosul- phates (hydrosulphate of potassium). 2. Secondary or metallic sulphides (sulphide of potassium). Alcoholic Sulphides. 1. Primary or mercaptans (hydrosulphate of ethyl) 2 Secondary or hydrosul- phuric ethers (sulphide of ethyl). Aldehydic Sulphides. 1. Primary (sulphobenzol) 2. Secondary. Acid Sulphides. 1. Primary (hydrosulpho- cyanic acid). 2. Secondary (sulphide of benzoyl). Sulphur-salts. Sulphocyanidcs, sulphan- timoniates. Compound Sulpliur- ethers. Thiacetate of ethyl, sul- phocyanide of ethyl. Compound Sulphur- aldehydes. HYDROCHLORIC- HCl. CHLORIDES (Bromides, Iodides, Fluorides). Basic Chlorides. Metallic chlorides (chlo- ride of potassium). Alcoholic Chlorides. Hydrochloric ethers(ch\o- ride of ethyl). Aldehydic Chlorides. Chloride of aldchy dene. Acid Chlorides. Chloride of acetyl, oxy- chloride of phospho- rus, chloride of cyan- ogen, free chlorine. TO THEIR CHEMICAL FUNCTIONS. ACID-TYPE, CYANIDES. Basic Cyanides. Metallic cyanides (cyanide of potassium, ferrocy- anide of potassium). Alcoholic Cyanides. Hydrocyanic ethers or nitriles (acetonitrile, hydrocyanic acid). Aldeliydic Cyanides. Acid Cyanides. Cyanide of benzoyl, free cyanogen. AMMONIA TYPE, H. N^ H, NITRIDES (Phosphides). Basic Nitrides. 1. Primary (amide of potas- sium). 2. Secondary. 3. Tertiary (nitride of po- tassium). Alcoholic Nitrides. 1. Primary (ethylamine). 2. Secondary (biethylamine). 3. Tertiary (triethylamine). Aldehydic Nitrides. 1. Primary. 2. Secondary. 3. Tertiary. Acid Nitrides. 1. Primary (benzamide, cy- anamide, succinamide). 2. Secondary (succinimide, benzoyl-phenylamide). 3. Tertiary (bibenzoyl-sali- cylamide, boramide, free nitrogen). Amido^en -salts. Benzamidate of mercury. Alcalamides. Oxanilide, eth3'lacetamide. HYDROGEN TYPE, HH. METALS (Metalloids). Basic Metals. 1. Primary or metallic hydrides (hydride of copper). 2. Secondary or metals proper (potassium, stibethyl, tctre- thylium). Alcoholic Metals. L Primary or alcoholic hydrides (marsh-gas, benzin^. 2. Secondary : the so-called alcohol-radicals (ethyl, amyl, phenyl). Aldehydic Metals. 1. Primary or aldehydic hy- drides (olefiant gas). 2. Secondary. Acid Metals. L Primary or acid hydrides (hydride of benzoyl, hydro- chloric acid, hydrocyanic acid). 2. Secondary or metalloids (benzoyl, chlorine, cyano- gen). Here might be placed many compounds already included in the preceding classes : e.g.^ the cyanides of ethyl, &c., contain- ing the radical of cyanic acid and an alcohol-radical. 530 CLASSIFICATION. WATER-TYPE. Positive Oxides. — A, Bases proper, or Metallic Oxides. — These compounds are formed by the substitution of a metallic radical, simple or compound, for the hydrogen, in one, two, or three molecules of water: — oi, Monatomic. — Hydrate of potash, tt]0; anhydrous pot- ash or oxide of potassium, t^]0; — cupric hydrate, ttJO; — cupric oxide, p ]0; — hydrate of ammonium, tt'*]0; — hydrate of tetramercurammonium, tt'^'*] O ; — hydrate of tetrethylium,-^<^^^5 )4]0;— oxide of cacody l,^^g^,'^^3)2 1^.__ oxide of arsenethylium, a //^^tt^\?0. /3. Biatomic. — Platinic hydrate, tt jOg; platinic oxide, ^JjO^ ; oxide of stibethyl, Itjc^J' i'^^^** y. Triatomic. — Hydrate of alumina, tt ^] ^3 ; anhydrous alumina, * 1* j O3 ; antimonic hydrate, tt ] O3 ; antimonic oxide, mlOg; teroxide of bismuth, r^.j-Qg Certain triatomic bases may be represented as monatomic, by supposing a portion of the oxygen to be associated with the positive radical ; thus, sesquioxide of uranium U4O3 may be represented as protoxide of uranyl, tt^£a] O; and teroxide of antimony, Sb203, as protoxide of antimony 1, ci^riiO. Non- * The radical stibethyl is biatomic, like arsencthyl (p. 527). ALCOHOLS. 531 basic bioxides, or peroxides, may be represented in a similar manner; e.g., peroxide of hydrogen, = tt^"^' B, AlcoJwls. — These bodies, all of which belong to organic chemistry, are also monatomic, biatomic, or triatomic. The primary monatomic alcohols, or alcohols proper, are derived from water by the replacement of 1 atom of hydrogen by a hydrocarbon of the form -G-nHan+i ; -^011211-1 ; or ^0^20-7. a. Alcohols containing radicals of the form ^nll2n+i« The number of these at present known is ten, viz. : — Methylic alcohol, wood-spirit, or^ __ .QH3 i^ hydrate of methyl (protyl) . .5 ^ ~ H ■* * Ethylic alcohol, spirit of wine, oro tt £> _ -^2^5 7 ^v hydrate of ethyl (deutyl) . .5^2^^^ - h ^^• Propylic alcohol, or hydrate of^ _ QJJ . trityl J^3^8^ - H ^^• Butylic alcohol, or hydrate ofi^^ ^^ -^4^9 m tetryl 5 ^ 10 H -^ * Amylic alcohol, or hydrate ofi ^ = ^-^n]Q. amyl(pentyl) 5 ^ 12 - H ^ ' Caproic alcohol, or hydrate of^ ^^e^ulCL hexyl iH^H^ - H ^^• Caprylic alcohol, or hydrate of^^ _ "^sHni/:!. octyl .3^«^i«^ - H ^^• Cetylic alcohol, or hydrate of) r\ ^^le^siln cetyl ^^16^34^- H ^^• Cerylic alcohol, or hydrate ofo^ ^ ^^-^zT^ssm ceryl 5 27 se H ^ ' Melissic alcohol, or hydrate ofi n-^so^eilri meiissyl ^^30^^62^ - H ^^• The first of these liquids is found among the products of the destructive distillation of wood ; the second, third, fourth, and fifth, are formed by the fermentation of saccharine sub- 532 WATER TYPE. stances ; caprylic alcohol is obtained by saponifying castor-oil with hydrate of potash and distilling the product with excess of the alkali at a high temperature ; cetylic alcohol is obtained from spermaceti ; cerylic alcohol from Chinese wax, and me- lissic alcohol from bees-wax. Compounds, whose formulae differ from one another by n . •GHg, are said to be Jiomologous : e. g., the alcohols, the fatty acids (p. 538), the compound ethers (p. 545), &;c. /3. Alcohols containing radicals of the form CnHsn-i : — jn TT Acrylic or allylic alcohol, -GgHgO = ^tt^]^' This is the only term of the series at present known. y. Alcohols containing the radicals, OJi^n-i ' — Of this series, there are two isomeric groups, distinguished by their be- haviour with oxidising agents, the bodies of the one group being thereby converted into aldehydes, the others not. To the first group belong : — . Benzoic alcohol . . -GyHg-Q = ^'g']©. Cuminic alcohol . . -GjoHi^Q = ^'°g>3]©. To the second : — Phenylic alcohol, car-^ bazotic acid, or hy- -QgHgO = drate of phenyl . J ^lf=}©. Cresylic alcohol . . -G^HgO = ^IjH']©. All these alcohols contain 1 atom of hydrogen replaceable by a metal ; thus : common alcohol, treated with potassium, gives off one sixth of its hydrogen, and yields ethylate of potassium, r\ TT \r ^] '^' I* is not found possible to replace another atom of hydrogen in a similar manner. Biatomic Alcohols, or Glycols. — The general formula of these /"I TT compounds is tt ^"]^2- Three of them have been obtained. ALCOHOLS. . 533 viz., ethjlic glycol, |j ^j ^2^ propylic glycol, ^ ^] O2; and amylic glycol, tt ^°] Og. The 2 at. hydrogen in each of these formulae, may be replaced by other radicals positive or negative ; so that the glycols are bibasic and biacid. By mixing iodide of ethylene, ^2^4 • -^ 2 ^'^^^ ^ atoms of acetate of silver, and distilling the product, a distillate of acetate of gly- col is obtained, while iodide of silver remains behind : — e.HJ, + 2gg^ = 2 Agl + (^^2^5^ Acetate of silver. Acetate of glycol. and acetate of glycol distilled with hydrate of potash yields glycol and acetate of potash : — ^ The propylic and amylic glycols are obtained in a similar manner with bromide of propylene and bromide of amylene. Tr {atomic Alcohols, or Glycerines, — The general formula of P TT these compounds is "tt^"~M'^3' 'The three atoms of hy- drogen which they contain may be wholly or partly replaced by radicals positive or negative. One term of the series has been long known, viz. : ordinary glycerine, ■QgHgOg = jT^ TT V] O3. The neutral fats, olein, stearin, palmitin, &c., consist of glycerin, in which the 3 atoms of free hydrogen are replaced by acid radicals; eg., stearin, G^-j^hqQ-q = jQ TT /£2 TT A\ ] ^3- A great number of similar compounds have been formed artificially by heating glycerine with acids. Conversely, when neutral fats, stearin for example, are heated VOL. II. P P 534 WATER TYPE. with hydrate of potash, or other metallic oxides, the acid radical passes to the metal, forming a salt, and glycerine is formed, e.g., (e?sb%)3^^3+ 3 (go) =3 f . A.O)o3+ ^^Is ja. This is the process of saponification. Glycerine may also be formed synthetically, viz. by heating the terbromide of allyl, ^^gHgBrg with acetate of silver. Teracetate of glycerine (tri- acetin) is thus formed ; and this, when heated with hydrate of baryta, yields glycerine. The other glycerines have not yet been obtained in the free state ; but the acetate of ethyl- d XT glycerine, /ri TT o^ ^ ^s' '^^ obtained at the same time as gly- col, by the action of iodide of ethylene on acetate of silver. The secondary alcoJiols, or Ethers, bear the same relation to the primary alcohols that anhydrous metallic oxides bear to Q XT the hydrates; e.^., amy lie alcohol, ^tt^^J-Q-; amylic ether, Q H ^ ^5" 11 There are likewise ethers containing two different radicals ; e, g., methyl-amylic ether, ^ tt^ ]0. Ethers may be formed ■^5^^ 11 by the action of the iodides of methyl, ethyl, &c., on alcohols in which 1 atom of hydrogen is replaced by potassium ; thus, common alcohol treated with potassium gives off hydrogen, and yields CgHgKO; and this compound treated with iodide of amyl, yields ethyl-amylic ether : — ^»K=]a + G,H„I = KI + §H° ^^- The same potassium-alcohol treated with iodide of ethyl, yields common ether : — ^2H5p + ^^H,. I = KI + §{5;}0. ACIDS. 535 Ethers are also formed by the action of strong sulphuric acid on the alcohols, as will be more fully explained hereafter. C. — Aldehydes. — These compounds differ from the alcohols, in containing 2 atoms of hydrogen less. Thus, to an alcohol, ^nH2n+ij^^ there corresponds an aldehyde, ^"^^^-^lO. They are obtained by the action of oxidising agents on the alcohols. Thus, common alcohol treated with bichromate of potash and sulphuric acid, yields ethylic or acetic aldehyde, H ^^• There are likewise aldehydes corresponding to the other series of alcohols. Thus, to the alcohols containing the radicals, ^J^2vi-v there correspond aldehydes containing radicals of rj, XT the form ^nH2n_9. Oil of bitter almonds, •G7HgO= ^tt^]0, belongs to the series. The aldehydes are especially distinguished by forming crys- talline compounds with the alkaline bisulphites ; 6. g., sulphite of acetosyl and sodium, Cg^sNaO, -802= £^ TT -vr \^2' One atom of hydrogen in the radical of an aldehyde may be replaced by an alcohol-radical ; the compounds thus pro- duced are called ketones. Thus, acetone, GgHgO, the ketone of the acetic series, is ^ ^^ tt^ ]^» Acids, or Negative Oxides. — These, like the positive oxides, are divided into primary or hydrated, and secondary or anhydrous. Thus, hydrated nitric acid, -rj ^ JO ; anhydrous nitric acid, -vtm^]^- Acids are also monatomic, like nitric acid just noticed, and acetic acid, ^ a j^. biatomic, like sulphuric acid, tt ^l-O-g; p p 2 536 WATER TYPE. or triatomic, as phosphoric acid, tt 1 -Og ; citric acid, A monatomic hydrated acid, having only one atom of re- placeable hydrogen, is necessarily monobasic ; a biatomic acid, having two atoms of replaceable hydrogen, is generally (but not necessarily) bibasic ; a triatomic acid, generally tri- basic. The determination of the basicity of an acid is a matter of some difficulty. In many cases, the formation or non- formation of acid and double salts may serve as a distinction. Thus, tartaric acid, which is a bibasic acid, ^tt"^ '^]^2'> iCj H" O. forms a neutral tartrate of potash, '^j^'* '*]'^2> ^"^ ^" ^^'^^ tartrate, 4^tt ''j-^2 5 ^^f likewise, sulphuric acid forms 'S'K204, and •S-KH04 ; whereas nitric acid, having but one atom of hydrogen, forms but one potash-salt, viz. NKO3. But acetic acid, generally regarded as monobasic, Q^llJ^^^ ^ 3 JQ^ also forms, not only a neutral potash-salt, Q^H^KQ^^^ but like- wise, an acid potash-salt, usually represented by the formula ^gHgKOg . 'G2H4O2 ; but if the formula of acetic acid be doubled, making it C^HgO^, the neutral potash-salt will be •G^HgKgO^, and the acid salt, QJiQ(K}l)Q-^. Acetic acid will thus be represented as a bibasic acid; and in fact, this quantity, e^HgO^ (= 120), is the equivalent of ^SHgO^ ( = 98), that is to say, it saturates the same quantity of potash. Why, then, is acetic acid universally regarded as monobasic ? On this point, we shall quote the observations ofGerhardt: — " The basicity of acids is a question, not of equivalents, but of molecules. . . . If we examine, under the same volume, the composition of the vapour of certain volatile bodies, correspond- ing to the acids, and compare together the similar terms, such as the chlorides of the acid radicals, or the neutral compound ethers, we observe perfectly regular differences, which are ACIDS. 537 always related to the chemical properties of the corresponding bodies: thus, — , „ f Chloride of acetyl . contain CI . -GgHgO. 1 Chloride of sulphuryl „ Clg . -SOg. 2 vol. of, Acetate of methyl . contain j^A JO, 3 Sulphate of methyl . „ mH^ ^^2* In the same volume^ therefore, chloride of acetyl contains the radical chlorine once, while chloride of sulphuryl contains it twice : In the same volume, again, sulphate of methyl contains twice the quantity of methyl that is contained in the acetate. With these differences of composition of the chlorides and neutral ethers, are connected other properties, such as the fol- lowing: — Acetic acid forms but one compound ether (p. 545), whereas sulphuric acid forms two, a neutral. and an acid ether; acetic acid forms but one amide (p. 557) ; sulphuric acid forms several, &c. In short, on inquiring what are the smallest quan- tities of the radicals, acetyl and sulphuryl, that are concerned in chemical metamorphoses, we find that they are QJIJ^, equivalent to H^ and -SOg equivalent to Hg ; hence, we are led to represent the molecule of acetic acid as monatomic, and that of sulphuric acid as biatomic." The principal monobasic inorganic acids are nitric, -rj ^JO, hypochlorous, ttI-O-, chloric, tt ^]0, and metaphosphoric. Of monobasic organic acids, the most important are the so-called fatty acids, whose general formula is — c„H,„a, = '^»H|"-'^ia They correspond to the alcohols -G-nHsn+iO, and those which contain the same number of carbon atoms as the known alcohols may be obtained from the latter by the action of p p 3 Formic acid -GH^e^ CEnanthylic acid €7 Hi^Og Palmitic Acetic „ e,H, o. Caprylic „ €-, H.^-^^ Stearic Propionic „ •03H,0, Pelargonic „ O9 HjgOj Cerotic Butyric „ ^4Hs^, Rutic or capric „ OjoHjoOa Melissic Valerianic „ "^5Hio"^2 Laurie „ OijHj^Os Caproic „ ^eH.A Myristic „ G^^Hag-Ga 538 WATER TYPE. oxidising agents, such as chromic acid. The number of these acids at present known to exist is sixteen, viz. : — These acids occur in the vegetable and animal organism ; they are formed by the saponification of fats, and by the action of oxidising agents on fatty and waxy matters, and on albumin, fibrin, casein, &c. The first ten acids of the series are liquid at ordinary temperatures; the next four are solid fats; the last two are waxy. Cerotic acid is obtained from Chinese wax ; melissic acid from bees-wax. A second series of monobasic organic acids consists of acids whose radical is of the form QJlzn-zO-; e.g., oleic acid, ■GigHg^Og = ^^Ti^^]0'j obtained by the saponification of various fixed oils. A third series consists of acids whose radical has the form -G-nHau.g-Q. These are called the aromatic acids ; p TT r\ only three of them are known, viz. benzoic acid, ^tt^ JO; toluicacid, ^tt^ jO, and cuminic acid, ^^xj^^ ]0. There are a few monatomic organic acids not included in either of these groups, among which, must be particularly men- tioned cyanic acid, tt ] '^' The cyanates are formed from the cyanides by oxidation ; thus, cyanide of potassium fused with oxide of lead, or bioxide of manganese, yields cyanate of potash, ^NKO. Bibasic acids. — These acids, as already observed, generally form two salts, a neutral and an acid salt, and are peculiarly inclined to form double salts ; e. g. potassio-cupric sulphate, ifa'^^^; tartrate of potash and soda, ^i^^^i'^2- ACIDS. 539 With the alcohols they form two compound ethers, a neutral and an acid ether ; e. g., neutral oxalate of ethyl, fjrh\ i^2» acid oxalate of ethyl, or oxalovinic acid, tt fjr^TJ^\ S ^2* Within the same vapour volume, the neutral ethers of the hihasic acids contain twice as much of the alcohol-radical as the neutral ethers of the monobasic acids (p. 545). Thus, 2 vols, oxalate of ethyl = .So \ ]0; 2 vols, benzoate of ethyl = ^^^JO. (,■^2 "^5/2 ^2"^5 The chlorides of hihasic acids (obtained by the action of pentachloride of phosphorus on the acids) contain, within a given vapour volume, twice as much chlorine as the chlorides of the monobasic acids (p. 549). The principal bibasic inorganic acids are carbonic, tt j -^2 > sulphurous, TT ]'02 5 sulphuric, Tr^jOg; and chromic acid, A ^jOg. Pyro-phosphoric acid, PgH^O^, may be regarded as p TT jQ bibasic acid, containing the radical PgHgQ^; viz., ^tt^ ^ j q.^ . or as a compound of metaphosphoric and ordinary phosphoric acid. The greater number of the bibasic organic acids may be arranged in three groups, viz. : — a.— Acids whose general formula is " g""* ^l^a* Eight of these are known, viz.: — Oxalic acid, |t ^] Og; succinic acid (^4); pyro-tartaric (-G-g); adipic (^g); pimelic (-G;) ; suberic (-Gg) ; anchoic (>Gg) ; and sebacic acid (-Gjq). They are formed by the action of oxidising agents on fatty matters, and are related to the monobasic fatty acids GJl^vf^i ^7 the relation — - '^nH2n^2^4 = ^^^2 + ^n-lH2n^2^2 e.g., fiHA. = €0, + G^,^ Succinic acid. Propionic acid, p p 4 540 WATER TYPE. ^.-General formula: (^"^fn- A)2j ^^^ For example, ■"2 lactic acid = Qq^i^^q = ^^^^^^^Q^. y.— General formula: ^"^ff ^^^^j^^. Two acids of this group are known, viz., phthalic acid, ^gHg04, obtained by the action of nitric acid on bichloride of naphthalin, and insolinic acid, •Q9H8O4, bj the action of chromic acid on cuminic acid. They are related to the aromatic acids in the same manner as the acids a to the fatty acids. Thus : — e^HgO^ = QQ, -f ^sHgO^ Insolinic acid. Toluic acid. Of bibasic acids not included in the preceding groups, the jQ XT Q most important are malic acid, •G^HgOg = ^tt'' ^]^2' ^'"^^ tartaric acid, ^411606 = ^^S^'^^jOg. Trihasic acids. — These acids, containing three atoms of re- placeable hydrogen, form three kinds of salts, viz., one neutral, and two acid salts. Thus, from tribasic phosphoric acid, PH3O4 = -^jOg are formed PH2Ka4, PHK2a4, and PK3©,. With alcohols they form three compound ethers. Phos- phoric acid and common alcohol yield ethylophosphoric acid, VUJ^Qfi,)(^,', bi-ethylophosphoric acid, VI{{Q^YL,\Q>^i phosphoric ether, P(.G2H5)304. The neutral ethers of trihasic acids contain^ within a given vapour volume, three times as much of the alcohol radical as the ethers of the monobasic acids. Thus, 2 vols, citric ether contain ^^^^ja,; and 2 vols, acetic ether contain *S,^^^0. (^2^5)3' ' -^2^5 ^ The chlorides of the tribasic acid radicals contain , within a given volume, three times as much chlorine as the chlorides of the monobasic acid radicals. Thus, 2 vols, chloride of phosphoryl ACIDS. 541 (oxychloride of phosphorus) contain PO . CI3 ; and 2 vols, chloride of benzoyl contain Q^llfi- .01. The tribasic mineral acids are, — boracic acid, BH3O3; phosphorous acid, PH3O3; phosphoric acid, PH3O4; and arsenic acid, AsHgOg. Five tribasic organic acids are known, viz. : — Cyanuric acid e6H3N303 = ^I^]^y Citric acid . CfiHgO^ = ^^^'^^jOa. Aconitic acid. GtqH^Q-q = "^Su^^'lOg. Meconic acid . Q^ll^Q^ = ^^u^^jOg. Chelidonic acid Q^U.O, = ^^^^'}Q^. Cyanuric acid may be regarded as a triple molecule of cyanic acid. It is formed by the destructive distillation of uric acid, by the action of chlorine gas on urea, and by the action of water on fixed chloride of cyanogen, CygClg. Aconitic acid is obtained by the destructive distillation of citric acid. Meconic acid is contained in opium, and chelidonic acid in the chelidonmm majus. Conjugated acids, — This name is given to acids contain- ing a conjugated radical. Thus, there are chloro-, hromo-, and iodo-conjugated acids, containing chlorine, bromine, or iodine in place of hydrogen in the radical ; e, g., chloracetic acid,'^2(Cl2H)Oj^. terchloracetic acid, ^^^^^j O ; mtro- conjugated acids, containing NOg; e.g., nitro-benzoic acid, 7 4V 2/^j Q . sulpho-conjugated acids, containing SQ^ ; e ^., sulpho-benzoic acid, ^ '^Vr ^^ iQ^, 8ic, 542 WATER TYPE. These acids are formed by the action of sulphuric acid, nitric acid, chlorine, &c., on the primitive acids : — a. — Jmidogen acids. — These are derived from hydrate of NIT ammonium, ^ '' jO, by the substitution of an acid radical for two or more atoms of the hydrogen in ammonium. Thus : — Sulphamic acid . . SHgNOa = "^^l^^ ^O. Phosphamic acid . PH^NO^ = ^^^^) jO. Osmiamicacid . . Os^HNOg = ^(^2^2) jq. Oxamicacid . . e^HgNOg = ^^2(^2^2) jq. These acids are formed by the action of ammonia on the anhydrides, or by the action of heat on the acid am- monia-salts of bibasic acids, an atom of water being thus eliminated : — •^2^2 la _« TT £1 — ^"^2(^2^2)^1:1 " ~r ~- — ' *~~~" Y Acid oxalate of Oxamic acid, ammonia. Anhydrous Acids, or Anhydrides. — These com- pounds are formed by the substitution of an acid radical for the whole of the hydrogen in one or two molecules of water, thus: — citric anhydride NgOg^ vro^}^; sulphuric anhydride •^Q3 = SQ2.0; phosphoric anhydride PgO^ = ANHYDRIDES. 543 Anhydrous nitric acid is obtained by the action of chlorine on dry nitrate of silver. The anhydrides of bibasic acids may be formed by the abstraction of water from the hydrated acids, either by heat or by the action of anhydrous phosphoric acid ; e. g, : — ^2 ^^ r ' ^-^-i— X.— i*^--' Succinic Succinic acid. anhydride. The bibasic acids may, indeed, be supposed to contain water. Thus, succinic acid = -Q^H^Og . O + HgO. But the anhy- drides of the monobasic acids cannot be obtained in this way ; in fact, according to the formulae of the unitary system, they do not contain water, and even supposing HgO to be abstracted from them, the remainder will not be the formula of the anhydrides : thus, the formula of acetic acid being ^ a \ Q,^ the abstraction of HgO would leave ^2^2^ J whereas, the p TT r \ formula of anhydrous acetic acid is riTx^r\\ 0=2 x Q^fi^, This is a fact which the ordinary formulae do not explain. If the formula of hydrated acetic acid be C4H4O4 = C4H3O3. HO, it is by no means evident why the HO should not be separated from it, and leave the anhydrous acid. The anhydrides of organic monobasic acids are obtained by the action of the chlorides of their radicals on the alkaline salts of the acids ; thus : — ^A^ja + e^HgO.ci = KCi + ^^H^^Jo. ^~-- Y -^ Chloride of ."- — ; — ^^ ^ Acetate of acetyl. Acetic anhydride, potash. There are some organic anhydrides containing two different radicals ; thus, by the action of chloride of benzoyl on acetate of potash, aceto*benzoic anhydride is formed : — ^^^a^jo + a^Hsa.ci = KOI + ^^Ho^^- 544 WATER TYPE. These compounds are resolved by heat into the simple anhydrides, thus : — Oxygen-salts, or Intermediate Oxides. — Salts are formed by the substitution of a metal or other positive radical for the basic hydrogen of an acid, and may there- fore be regarded as water, the hydrogen of which is re- placed partly by a basic, partly by an acid radical. If all the basic hydrogen of the acid is thus replaced, the salt is neutral or normal; if only part of the hydrogen is thus re- placed, the salt is acid ; and such salts may be regarded as compounds of neutral salts with the free acid, thus : — / gp , N so ■> so ]o,) = ^^]o, + ^;]o, Bisulphate of Sulphuric acid. Neutral sulphate soda. of soda. (^2"^3^)2]ri — ■^2"^3^ ? o I ■^2^3'^ ^n. KH i^2 - H i^ + K ^^' Biacetate of potash. Acetic acid. Neutral acetate of potash. Basic salts may be regarded as compounds of a neutral salt and an oxide, or as double or triple molecules of water, in which the hydrogen is replaced by a positive radical in a larger proportion than is required to form a neutral salt; thus : — Pbg 3 ^2 - pbi ^ + Pb J ^• Subacetate of Oxide of lead. Neutral acetate lead. of lead. Subsulphate Oxide of Neutral sulphate of copper. copper. of copper. COMPOUND ETHERS. 545 In the neutral salts of sesquioxides, as in the oxides them- selves, 3 at. hydrogen of the type water are replaced by 2 at. of the metal ; thus — (-^^2/3 1 o. . (^^2)3 1 o. Fe^ -J^a' Fe^ ^ ^«* Ferric nitrate. Ferric sulphate. Compound ethers. When the basic hydrogen of an acid is replaced by an alcohol-radical, the product is a compound ether ; these compounds may also be regarded as alcohols in which one atom of hydrogen is replaced by an acid radical. As already observed, monobasic acids form but one compound ether ; bibasic acids form two, a neutral and an acid ether ; and tribasic acids, one neutral and two acid ethers. The acid ethers are true acids, and form salts. Thus, from sulphuric acid are formed — Neutral sulphate of ethyl = //-. tt^n ] Oo, and SO Acid sulphate of ethyl, or __ tt^ ( jQ sulphovinic acid "" £1 TT ^ ^' The remaining atom of hydrogen in the latter may be re- placed by K, Na, &c. From citric acid are formed — Neutral citrate of methyl . . . /^'u'P'J ^3 Citrobimethylic acid (monobasic) . (-^113)2 > O3 H ^ Citromonomethylic acid (bibasic) . -GHg / O3 The glycerides or neutral fats (p. 533) also belong to the compound ethers, being derived from a triatomic alcohol or glycerine by the substitution of an acid radical for the replace- r\ XT able hydrogen ; e,g.y triacetin = ,^ A An jOg. V'^2"3^>'3 546 WATER TYPE. SULPHIDES, SELENIDES, TELLURIDES. The formulae of these bodies are precisely similar to those of the oxides, being derived from hydrosulphuric acid, Tr]^t &c. just as the oxides are derived from w^ater. These series, however, especially the selenides and tellurides, are much less complete than that of the oxides. The analogy between the metallic sulphides and oxides has been sufficiently pointed out in the preceding part of this work. The alkali-metals, potassium, sodium, &c., form hydrated sul- phides, or hydro-sulphates, such as tt]^^ ttJ'^^&c.; and K anhydrous sulphides, tA ^9 &c. Most of the other metals form only anhydrous sulphides. The alcoJiolic sulphides, primary and secondary, bear the same relation to hydrosulphuric acid that the alcohols and ethers bear to water. The primary alcoholic sulphides, jQ TT °TT^°'*'^} "S, generally called mercaptans, are fetid oils, or crys- talline solids, which are obtained by the action of the alkaline hydrosulphates on the chlorides of the alcohol radicals ; — C,H,C1 + ^]» = KCl + ^^2^}S; Chloride of Ethylic mer- ethyl. captan. or by tlie action of the same alkaline hydrosulphates on the sulphovinates or homologous salts : — The basic hydrogen in the mercaptans may be replaced by metals, forming compounds called mercaptides; e. g., A ^] ^. SULPHUR-ACIDS. 547 The secondary alcoholic sulphides or hydrosulphuric ethers are obtained by the action of the anhydrous alkaline sulphides ' on the chlorides of the alcohol-radicals : — 2€2H,C1 4- |]^ = 2KC1 + q'^']^' Sulphur-acids. — The mineral sulphur-acids are but little known in the hydrated state. The anhydrous sulphur-acids are analogous to the oxygen-acids. Thus, sulpharsenious acid, A ] ^3, sulpharsenic acid, * J'S-g, the arsenic being triatomic ^ in the former, and pentatomic in the latter. But few organic sulphur-acids have been obtained. Hydro- sulphocyanic acid, -GNH^ = tt } S'j is analogous to cyanic acid, Tj ]0. Its potassium-salt is obtained by heating sul- phur with ferrocyanide of potassium (I. 532). Thiacetic acid ^ 3 j^^ jg obtained by the action of pentasulphide of phosphorus on acetic acid : — This reaction is instructive when viewed in relation to that of pentachloride of phosphorus on acetic acid ; the latter giving rise to two chlorides, Q^Yi^Q^ . CI, and HCl, whereas the action of the sulphide of phosphorus yields not two, but one sulphur •d TT O compound, ^ s | §^ ^ similar difference is observed in the action of the sulphide and chloride of phosphorus on al- cohol, the former producing a single compound, viz. mercap- tan, the sulphide of ethyl and hydrogen, ^tt^]^» the latter producing two separate compounds, viz. Q.fi^CX, and HCl. This difference of action shows in a striking manner the pro- 548 HYDROCHLORIC ACID TYPE. priety of representing the oxides and sulphides by a type containing two atoms of hydrogen, and the chlorides, bro- mides, &c., by a type containing only one atom of hydrogen. Sulphur-salts. — These compounds are formed from the type TT tt}S, by the substitution of a positive and a negative radical for the tvv'o atoms of hydrogen ; Thus, monobasic sulph- arseniate of potassium, -it- j-Sj ; tribasic sulpharseniate of AsS potassium, ^ jSg; these formulas are evidently analogous to those of the monobasic and tribasic phosphates. The compound sulphur-ethers are sulphur-salts, in which the positive element is an alcohol radical:— For example, sulpho- cyanide of ethyl, ^-L ]S; sulphocyanide of allyl, or oil of mustard, = p, X } S. Sulphide of acetyl and ethyl, or thiacetic ether, is obtained by the action of persulphide of phosphorus on acetic acid: — HYDROCHLORIC ACID TYPE. Chlorides. — The basic metallic chlorides are, like the oxides, either monatomic or polyatomic ; e. g. — KCl PtClg Fe^Clg.AuClg. monatomic. biatomic, triatomic. The biatomic and triatomic chlorides unite with the mon- atomic chlorides, forming crystalline compounds, whose com- position may be illustrated by the formulae of — Chloro-aurate of sodium . . NaCl.AuCl3= Au^^^*' CHLORIDES. 549f ■M"TT Chloroplatinate of ammonium, NH^Cl . PtClg = pf '^ 1 ^h' The chlorides of gold and platinum form similar compounds ■with the hydrochlorates of the organic bases, which may be represented by analogous formulae. Thus, chloroplatinate of ethylamine, ^^Ha NH rC H ^. H [N.HCI + PtCl^ = ^^^3^^2^^^]Cl3. The hydrochlorate of any organic alkali may be represented as the chloride of a basic radical containing an additional atom of hydrogen, just as sal-ammoniac may be represented either as NH3 . HCl, or as NH^Cl. Thus, hydrochlorate of ethyla- mine, NH^Ce^Hs). HCl = NH3(€2H5) . CI. The chlorides of the alcohol-radicals, or hydrochloric ethers, are obtained either by the action of hydrochloric acid, or one of the chlorides of phosphorus, on the alcohols: — ^Ajo + HCl = ^]Q + G,U,.Cl. (C.H.to) PCI3 = l]0, + 3 (^H^). ' Chloride of Alcohol. Phosphorous ethyl. acid. These chlorides are more volatile than the corresponding alcohols. The acid, or negative chlorides, are also monatomic, biatomic, or triatomic, according to the acids from which they are derived. The monatomic chlorides, derived from one atom of hydro- chloric acid, contain, in two vapour-volumes, one atom of chlorine, capable of forming a metallic chloride with mineral alkalies ; e.g., chloride of cyanogen, .GNCl = Cy . CI ; chloride of acetyl, = ■G2H3O.CI. They are obtained by the action of one of the chlorides of phosphorus on the acids, thus : — VOL. IL . Q Q 550 HYDROCHLORIC ACID TYPE. Perchloride of *" 1 ^ Oxychloride phosphorus. Chloride of acetyl of phosphorus. + hydrochloric acid. 3(^A©]o) + PCI3 = |j©3 + 3(C,H30.C1). Or, by the action of oxychloride of phosphorus on an alkaline salt of the same acid: — (^A^ja) + PO. CI3 = ^^}03 + 3 (G,H30.C1), The biatomic diloridesj derived from two molecules of hydro- chloric acid, contain, within two vapour-volumes, two atoms of chlorine, capable of forming a metallic chloride with alkalies : — Chloride of carbonyl, oxychloride of carbon, or phosgene = ^O . Clj Chloride of sulphuryl = ^Og . Clg Chloride of succinyl = -Q^H^O^ . Clg Chloride of chromyl, or chloro- chromic acid ....... = CrgOg . Clg These chlorides may be obtained by the action of penta- chloride of phosphorus upon the corresponding anhydrous acids. The action of pentachloride of phosphorus on a bibasic acid is supposed by Gerhardt to consist of two stages, — the first being the formation of an anhydrous acid, the second the con- version of that compound into a chloride. For example : — ^'^'h' ; O ^ + ^^^2 • CI3 = Gfl,^2 ' ^ + 2HC1 + POCI3 ; and a.H.O^.O + VC\,.C\,= QJI,Q,.C\, -f- FQC],; whereas, in the case of a monobasic acid, the action consists of one stage only. This difference is connected by Gerhardt CHLORIDES. 551 with the fact, that a bibasic acid may be supposed to contain water, whereas a monobasic acid cannot (p. 543). According to Williamson, on the contrary, the two stages of the reaction, in the case of a bibasic acid, are precisely similar to one another, and to the single reaction which takes place wuth monobasic acids. Thus, with sulphuric acid — ^2]o, + PGl^. CI3 = ^|]0 + HCl + POCI3, and hqI ]0 + PCI2 . CI3 = SQ, . Cl^ -f HCl + POCla. The difference in the two views of the reaction is this: — that the former supposes the first stage of the action to consist in the formation of an anhydrous acid ; the second supposes an intermediate compound, — a chloro-hydrate of the acid, to be produced. The formation of this chloro-hydrate has been shown by Professor Williamson to take place with sulphuric acid. If, however, one of the two molecules of hydrochloric acid in Gerhardt's first equation be supposed to remain asso- ciated with the anhydrous acid, the two views will nearly coincide. In every case, indeed, the reaction consists essentially in the interchange of O and CI 3. The triatomic chlorides, or terchlorides, contain, within two vapour volumes, three atoms of chlorine capable of forming a metallic chloride when acted upon by the mineral alkalies. The following acid chlorides are triatomic : — Terchloride of phosphorus P. CI3 Chloride of phosphoryl (oxychloride of phos- phorus PO.CI3 Chloride of sulphophosphoryl (sulphochloride of phosphorus) PS . CI3 Chloride of chlorophosphoryl (pentachloride of phosphorus) PCI 2 . CI 3 QQ 2 552 HTDROCHLORIC ACID TYPE. Chloride of boron B . CI3 Chloride of cy anury 1 (solid chloride of cyanogen) Cy3 . CI3 The BROMIDES, IODIDES, and FLUORIDES, are exactly analogous to the chlorides. There are \ery few organic fluorides known. The CYANIDES are also analogous to the chlorides. The metallic cyanides have a great tendency to unite and form double cyanides, which may be regarded as derivatives of two or more atoms of hydrochloric acid. Thus, the ferro- Fe 1 cyanides may be represented by the formula ^ i^y^y ^^^^ the ferricyanides, by -^ ^ ] Cyg ; the Fcg in the latter formula being equivalent to H3. The cyanides of the alcohol-radicals are obtained by dis- tilling a sulphovinate or homologous salt witli cyanide of potassium: thus, — Kf£,H,^^2 + KCy = *|^]©. + CA.Cy; or by the action of anhydrous phosphoric acid on the animon- iacal salts of the fatty acids, the action of the phosphoric acid consisting in the abstraction of water : thus, — ^^ ■—" Cyanide of Acetate of methyl, ammonia. or, generally, ^°NH;'^^^ - 2H,a = CN.G„_,H,„.,. The ammonia- salt of each acid in the series yields when thus treated, the cyanide, not of the corresponding alcohol-radical, but of the next lowest ; thus : the propionate yields cyanide of ethyl ; the acetate, cyanide of methyl ; and the formiate, cyanide of hydrogen, or hydrocyanic acid. AMMONIA TYPE. 553 When these cyanides are heated with caustic alkalies, the opposite change takes place ; that is to say, an alkaline salt of the acid corresponding to the next highest alcohol is formed, and ammonia is evolved : thus, — CNH + ^]Q + H^ = ^I^JO + NH, ; Cyanide of hy Formiate of drogen. potash. Q^QU, + ]^]a + H.O = ^'^^IQ + NH3 ; Cyanide of " -^ — — ^ methyl. Acetate of potash. These alcoholic cyanides may also be regarded as nitriles : thus, — Cyanide Formo- Cyanide of Aceto- of hy- nitrile. methyl. nitrile drogen. generally : GN . -GnHgn + ^ = N . €„ + ^ Hgn + 1- AMMONIA TYPE. Nitrides. — a. Positive. — These compounds are chiefly organic, constituting in fact the organic bases or alkaloids. A few mineral nitrides have, however, been obtained by the action of ammonia on the metals or their oxides; e.g., amide of potassium, N(H2K) ; nitride of potassium, NK3 ; nitride of mercury NHgg. The primary nitrides of the alcohol-radicals, such as methylamine, GH^N = N(GH3 . Hj), amylamine -GsHjgN = QQ 3 554 AMMONIA TYPE. N(C5Hii. H2), are obtained : — 1. By the action of the bromides or iodides of the alcohol-radicals on ammonia : — £2 TJ NH3 + Q,ll,l = HI + N j H Iodide of ethyl Ethylamine. 2. By the action of potash on the cyanates or cyanurates of the same radicals : — Cyan ate of Hydrate of Carbonate of ' ^ ^ ethyl. potash. potash. Ethylamine. 3. By the action of reducing agents, such as hydrosulphuric acid, or acetate of iron, on certain nitro-conjugated hydro- carbons; thus: — ■C H ^eH^CNO^) + 3H„^ = N^ h'+ 2B^Q +3^. . — — ( H Nitrobenzol. Aniline or phenylamine. They are also frequently produced in the destructive dis- tillation of nitrogenised organic substances, and are conse- quently found in coal-tar, bone-oil, &c. These bodies are all volatile liquids, having more or less of an ammoniacal odour. The bases of the same series — for instance, those formed 'from the alcohol-radicals ^0^20+1 — are less volatile and more oily, as they contain more carbon. They all combine with acids in the same manner as ammonia, and form crystallisable double salts with bichloride of plati- num. Nitrous acid converts them into alcohols or nitrous ethers, with elimination of nitrogen : — ^2^5 ) 1^ r: XT H N + Jj ] 03 = NN + ^^« j O2 + H,0; H ' . _ ^ ^ "rrr ; — r" Nitrous acid. Nitrite of ethyl. Ethylamnie. NITRIDES. 555 A h1 V^N^^3 = 2NN + 2(^A|©) + H,©. " . .;7 ^ 2 jnol. hydrate ^°^l^°e. of phenyl. Secondary alcoholic nitrides, — The constitution of these bodies maj be understood from the following examples : — p TT Biethylamine, QJIn^ . . = -Q^hJ N. H> Metethylamine, ^gHgN . . = ^Hg^N. Ethaniline, or ethyphenylamine^CgHjjN = ^gHgVN. H * They are obtained by the action of the bromides or iodides of the alcohol-radicals on the primary nitrides : — Q2H5) ^2^3) H ^N + e^HgBr = QJiS N + HBr. H> H> Tertiary alcoholic nitrides, or nitrile bases : — Triethylamine, •GgHigN = qIr, In. €A ) Biethamylamine CqHo.N = ■Q2H5 f-N. Methamylaniline G,»H,„N = GsH-.^N. These compounds are formed by the action of the iodides and bromides of the alcohol-radicals on the secondary alco- holic nitrides ; also by the distillation of the ammonium-bases, thus : — Q Q 4 556 AMMONIA TYPE. N(€A),^ O = (^H^yj + G,H, + H,a. "^ — zi~y 7^ Triethylamine. Ethylene. Hydrate of tetrethylium. Triethylamine is likewise obtained by the action of ethylate of potassium on cyanate of ethyl : — "t: ' ■' ^ :;<- — ^ „ "X^^" ' Triethylamine. Cyanate of 2 at. ethylate of Carbonate ethyl. potassium. of potash. This action is analogous to that of hydrate of potash or cyanate of ethyl (p. 554). The other tertiary alcoholic nitrides might doubtless be obtained in a similar manner. There are also nitrides containing conjugated alcohol - radicals; e.g. Bichlorethylamine esH^Cl^N H ) Chloraniline . G,H„C1N = H tN. H S Nitraniline . . . €eHe(NO,)N CoH,(N©,) H h- Nitrides of aldehyde- radicals. — These bodies are but little known. Acetosylamine, N(H2 . -^2^3)^ ^^ obtained by the action of ammonia on chloride of ethylene (chloride of acetosyl and hydrogen) : — H'i^^2 + 2NH3 = 'h|n.HC1 +NH,C1. •G-oH, Chloride of aceto- syl and hydrogen. Hydrochlorate of acetosylamine. AMIDES. 557 The natural vegeto-alkalies, morphine, strychnine, &c., are most probably of similar nature to these artificial alkalies, but they have not yet been reduced to regular series. h. Negative or acid nitrides. — These are the compounds generally called amides. Primary amides. — In these compounds, one-third of the hy- drogen in 1, 2, or 3 molecules of ammonia is replaced by an acid radical. a. Monatomic e^HgO Acetamide, or nitride of acetyl ^^^ir" tr isj£i_Tyj) ^u hydrogen j ^ iH Butyramide, or nitride of butyryl and?^^ -rr fjn—isjj \t^ hydrogen ( H p TT Q Benzamide, or nitride of benzoyl ^^^^n TT l^JiH— "\r\ Vr^ hydrogen 5 v 7 < H * These amides differ from the corresponding ammoniacal salts by the elements of one atom of water : — NH4 ^^ y±2^-^i JJ2 • Acetate of ammonia. Acetamide. They are produced by the action of ammonia on the anhy- drous acids: — 1^ + NH3 = ^1=^ + N[^|^; Benzoic anhydride. Benzoic acid. Benzamide. by the action of ammonia on the acid chlorides : — ^yH^O-Cl + NH3 = HCl + NJ^^H^O. and by the action of ammonia on the compound ethers : — 558 AMMONIA TYPE. %H^^]0 + NH3 = \H.j^ ^ NJ^I^O Acetate of ethyl. Alcohol. These amides are neutral crystalline bodies, which, when boiled with aqueous acids or alkalies, take up water, and are converted into ammonia-salts. When treated with anhydrous phosphoric acid, they give up the elements of 1 at. water, and are converted into cyanides of the alcohol radicals : — ^- r-~ — ' Cyanide of methyl. Acetamide. /3. Biatomic. Primary biamides or diamides : — Oxamide, or nitride of oxalyl and)^^ TT "NT jQ — TsT < TT hydrogen ^2422 ^(jj ■^Ttj'T^n 2 2 [GO Succinamide, or nitride of succinvl) r^ tt at /-k xt 1 ^tt'* and hydrogen ) ^ H Urea and carbamide, or nitride ofj^^Tj -m- ri — "Nr i TT carbonyl and hydrogen . . . ) ^ ^ ^ ( jj Tartramide, or nitride of tartryl > ^ tt 7^- p. _ isj j w and hydrogen Jt,,H,WM-^.| H, They are produced by the action of heat on the neutral ammonia-salts of bibasic acids : — Oxalate of ammonia. by the combination of ammonia with secondary amides : — N{^ + NH3 = nJ H,; « — , — ' >^ Hg Cyanic acid <--, — ' or cai'bonimide. Urea. AMIDES. 559 and by the action of ammonia on compound ethers or acid chlorides : — (^^+ 2NH3 = (ej^^ja, + n£|^^ Oxalate of ethyl. 2 at. alcohol. Oxamide. ^.H.a^.CI^ + 2NH3 = 2HC1 + Nj^^^*^^ Chloride of H4 succinyl. Succinamide. y. — Triatomic. Primary triamides : — Triphosphamide, or nitride of^ rPO phosphoryl and hydrogen : 1 ". ih Citramide, or nitride of citrjl^ N O =N J^e^sO^ and hydrogen j 6 11 3 4 ^i Hg Melamine and melam, or nitride ) ^ tt ^y -^ ^ Cy of cyanuryl and hydro^ren J 3 6 6 — ^ i jj jyanuryl and hydrogei Secondary amides. — In these compounds, two-thirds of the hydrogen in a molecule of ammonia are replaced by acid radicals, viz. : 1. By two monatomic radicals ; e.g.i — Nitride of bisulphophenyh^ ^ ^&^l and hydrogen . . . .) *^ " ^ * ' H Nitride of sulphophenyl, J^.^H^NSA = nJ efll^' benzoyl, and hydrogen J ^^ ^^ ^ ^ ' H These amides are produced by the action of acid chlorides on the primary amides or their metallic salts. Ni '^6-*^5^^2 ^ ^A-tl.'i'^'^o , H 4 aH,O.Cl = N^ ^.H^O + HCI. ^ H ^ H 2. The two atoms of hydrogen are replaced by one molecule of a biatomic radical. These compounds are called imides. 560 AMMONIA TYPE. Carbon imide (cyanic acid)or nitrides r CO of carbonyl and hydrogen . . I ~ ^ H Succinimide, or nitride of succinyU ^ ^^ ^^.^^H^O,. and hydrogen J 4 s 2 I jj Most of them are produced by the action of heat on the acid ammoniacal salts of bibasic acids, the change consisting in the elimination of 2 molecules of water : — H fa, - 2H,0 = l' NH, Acid succinate of ammonia. Succinimide. by the action of heat on the biamides of bibasic acids, ammonia being then given off: — (G4H4O2 f/2 TT jQ nJ H, - NH3 = N p^ti^^^ Succinamide. Succinimide. or by the action of heat on the amidogen acids. Tertiary Amides. — In these compounds, all the hydrogen in ammonia is replaced by acid radicals. a. Monatomic. — 1. The hydrogen is replaced by three monatomic radicals ; e.g.: — rCeH,SO, Nitride of sulphophenyl, benzoyl, and acetyl . NJ-G^HsO Nitride of sulphophenyl and benzoyl .... N-^G^HsO 2. One atom of hydrogen is replaced by a monatomic, and the other two by a biatomic radical ; — jC TT O Nitride of succinyl and sulphophenyl . . ^{ri''H^S.(4 INTERMEDIATE NITRIDES. 561 These amides are formed by the action of acid chlorides on the secondary amides or their silver-salts. 3. All the hydrogen is replaced by a triatomic radical. The composition of several inorganic compounds may be ex- pressed in this manner : — Monophosphamide, or nitride of phosphoryl = N . PO. Boramide, or nitride of boron .... = N . B. Free nitrogen, or nitride of nitrogen, the ^ __ at iv amide of nitrous acid Protoxide of nitrogen, or nitride of azo-^ tyl, the amide of nitric acid ... /3. Biatomic. — Compounds in which all the hydrogen of 2 molecules of ammonia is replaced by monatomic or biatomic radicals : — Trisuccinamide, or biamide of trisuccinyl . N9^■G4H402 Biamide of succinyl, bibenzoyl, and bi-> -kt S^A Ac sulphophenyl j . IN 2 1(^7^5^ These tertiary hiamides are produced by the action of acid chlorides on other amides or biamides. Intermediate nitrides, or amidog en- salts, — These are com- pounds in which the hydrogen of ammonia is replaced partly by a basic, partly by an acid radical. Most of the primary and secondary- amides form such salts, which are produced by the direct action of the amides on the corresponding oxides or their salts ; e. g.i — Benzamidate of mercury . . . • Nj Hg When the positive radical is an alcohol-radical, the com- pounds are called alcalamides ; those which contain phenyl, •GgHfi, are also called anilides : thus, — 562 AMMONIA TYPE. ^«H^ Phenjl-acetamide or acetanilide . . Nj^gHgO ^ H Ethyl-cyanamide N) Cy. I H Phosphides. — These compounds are derived from the type ammonia by the substitution of phosphorus for nitrogen, and of various radicals for the hydrogen. Phosphuretted hydro- gen, PHg, is analogous to ammonia, and forms with hydriodic acid a compound, PH3 . HI, or PH^I, which crystallises in cubes like iodide of ammonium, or iodide of potassium. With the alcohol-radicals, phosphorus forms compounds analogous to the alcoholic nitrides, and like those bodies pos- sessing alkaline properties ; e. g., triphosphomethylamine, or trimethyphosphine, V{Gil^y These compounds may be obtained by the action of terchloride of phosphorus on zinc- methyl, zinc-ethyl, &c., the reaction being expressed by the following general equation : — PCig -f 34;„H2n + iZn = 3ZnCl + PC^nH^n + Og. These phosphides, treated with the iodides of the corre- sponding alcohol-radicals, yield compounds analogous to the ammonium bases : thus, — P(eH,)3 + CAi = gg3),^P.i. The only negative or acid phosphide known is chloracety- phide, or phosphide of terchloracetyl = V{Qr^Q\^Q- . H . H). Arsenides and Antimonides.— Arsenic and antimony also form compounds of the ammonia type; e. g., AsHg; SbHg; As(-G2H5)3 ; S^-GgHg) ; but the arsenides and antimonides of the alcohol-radicals differ considerably in their properties from the nitrides and phosphides, not combining with hydro- chloric acid, &c., in the same manner as ammonia, but rather combining with oxygen, chlorine, iodine, &c., like metals. They belong, therefore, rather to the hydrogen type (p. 567). HYDROGEN TYPE. 563 HYDROGEN TYPE. The primary derivatives of this type are : — 1. The hydrides of the metals proper, A small number only of these are known, viz., CugH, AsHg, and SbHg. The two latter may also be regarded as derivatives of ammonia. 2. The hydrides of the alcohol-radicals, Q'Jl2n-\-\i viz., marsh-gas, or hydride of methyl, GrYi^ = H . -GHg ; hydride of ethyl, e,H,= H.e,H,;hjdrideofan.yl,e,H„= H.C,H„, &c. These compounds are formed by the action of zinc on the chlorides or iodides of the corresponding alcohol-radicals : — 2Gr^Yi,\ + Zn Zn = 2ZnI + H.e^H^ + ^gH^; Iodide of Hydride of Ethylene, ethyl. ethyl. also by the action of water on zinc-methyl, zinc- ethyl, &c. : — Zn.G,H, + giO = H.e,H, + |"}0; occasionally also in the destructive distillation or spontaneous decomposition of vegetable and animal substances. Marsh- gas, for example, is formed by the putrefaction of vegetable matter under water (I. 375). The hydrides of methyl and ethyl are gaseous at ordinary temperatures, the rest are liquid or solid. They are decomposed by chlorine, with form- ation of substitution-products ; thus — H.^^H, + ClCl = H.€2(H,CI) + HCl. There are likewise hydrides of alcohol-radicals of the form H.-GnH2n-75 the best known of which is benzol, or hydride of phenyl, -GgHg or H . ^^gH^. These compounds are obtained in the destructive distillation of many organic substances ; benzol, for instance, by the distillation of coal. They are also formed by the dry distillation of the monobasic 564 HYDROGEN TYPE. acids ^nHga-gO, with excess of lime or baryta, a carbonate of the base being formed at the same time : — Benzoic Acid. Benzol. 3. The hydrides of the aldehyde- radicals, Q^ Hgn-i. These are : — Ethylene, olefiant gas, or hydride of acetosyl ^2^4 = ^ • "^2^3 Propylene, or hydride of propionyl . . . Q^11q = II .Q^H^ Butylene, or hydride of butyryl .... QJl^ = ll.QJij Amy lene, or hydride of valeryl . . . ■G5Hjo = H. -GgHg These compounds might also be regarded as hydrides of the alcohol-radicals -GnH^n-i; for example, propylene as hydride of allyl (p. 532). Possibly, however, there may be two isomeric series of these compounds, the one derived from the alcohols, the other from the aldehydes. These hydro- carbons are formed by the destructive dis- tillation of organic substances, several of them being found among the products of the distillation of coal. They are also produced by the action of strong sulphuric acid at a high temperature on the alcohols, the change consisting in the abstraction of the elements of water : thus : — Alcohol. Ethylene. The only body of the series which is gaseous at ordinary temperatures is ethylene (L 384) ; the rest are liquid or solid. The first term, methylene, has not been obtained in the free state. These compounds are especially distinguished by combining with two atoms of chlorine, bromine, &c., forming compounds homologous with Dutch liquid or chloride of ethylene, -GgH^ , C\^ ; whereas the hydrides of the radicals •G„H.2n + 1 are decomposed by chlorine. The lower compounds of the series also combine with an- hydrous sulphuric acid. Thus, olefiant gas is immediately HYDRIDES or ACIDS. 5Q5 absorbed by the anhydrous acid, or by a coke ball soaked in fuming oil of vitriol. This property, and that of forming liquid compounds with chlorine and bromine, is made available for separating olefiant gas, and the other more volatile hydro- carbons of the series, from gaseous mixtures. 4. The hydrides of the acid radicals. a. Monatomic. — The hydrides of the acid radicals ^nH2u_iO, are evidently the aldehydes of the fatty acids (p. 535): thus: — Acetic aldehyde = H . ^^HOg = ^^gs jo Butyric aldehyde = H . ^.H^O = ^^^^JO Benzoic aldehyde .^ ^ ^rH^O j^ (bitter almond oil)) ^ ^ H ^ The following compounds may be regarded as the alde- hydes of monobasic mineral acids ; that is to say, as the hydrides of the radicals contained in those acids considered as derivatives of water : — Nitrous acid, or aldehyde of nitric acid NHOg = H . NO2 Hydrochloric acid, or aldehyde of hypo- chlorous acid CIH = H . CI Hydrocyanic acid, or aldehyde of cyanic acid \ , . . €HN = H.Cy Spontaneously inflammable phosphuret- ted hydrogen, or aldehyde of hy pophos- phorous acid PH = H . P /3. Hydrides of biatomic acid radicals : — Hydrosulphuric acid, or aldehyde of hyposulphurous acid -S-Hg = Hg . S Hydroselenic acid, or aldehyde of liy- poselenlous acid -S-eHg = Hg . Se V . VOL. XI. . it.R ... 566 ALCOHOL METALS. y Hydrides of triatomic acid radicals : — Non-spontaneouslj inflammable phosphu- retted hydrogen, or aldehyde of phos- phorous acid PH3 = H3 . P Antimoniuretted hydrogen, or aldehyde of antimonious acid SbHg = Hg . Sb The secondary derivatives of the hydrogen-type are — 1. The ordinary metals: — Potassium, KK, derived from HH ; antimony, SbSb, derived from H3H3 ; aluminium, AlgAlg, derived from H3H3, &c. 2. The alcoliol-metahi derived from the type HH, both atoms of hydrogen being replaced by alcohol radicals. The only bodies of this class which have yet been obtained are those containing the radicals -GnHan+i; viz. (a.) Those in which the two atoms of hydrogen are replaced by the same radical : methyl, ^Hg . ^Hg ; ethyl, ^^^s • "^2-^5 > i>utyl or tetryl, JQ4H9 . •G4H9 ; amyl, ^5-^11 • ^s^n » Cf^P'^^oyl or hexyl, •GgHjg . -GgHjg ; and capryl or octyl, ^gHj^ . -GgHj^. — (6.) Those in which the two atoms of hydrogen are replaced by different radicals : ethylo-butyl, ethyl-amyl, methylo-caproyl, butyl-amyl, and butylo-caproyl. The reasons for representing the bodies of the class (a.) in the free state, by the double formulae, have been already given (p. 518). These alcohol-metals are obtained by the action of zinc on the iodides of the alcohol-radicals (p. 531); by the action of sodium on the chlorides of the same radicals; and by the electrolysis of the alkaline salts of the fatty acids, carbonic acid and hydrogen being evolved at the same time : — 2 (^^-^g^ja) + H,a = (^Hg), + H, +f^2 + ^J^r Acetate of potash. Methyl. of^PoS? The alcohol-metals, containing two different radicals, are MIXED METALS. 567 obtained by the action of sodium on a mixture of the corre- sponding iodides : thus, with the iodides of ethyl and butyl — e^H.I + Na Na = Nal + Na^^H, and Qfi,l + Na^^H^ = Nal + QJI,.QJi,; also, by the electrolysis of a mixture of the alkaline salts of two of the fatty acids. Methyl and ethyl are gaseous at ordinary temperatures ; the other alcohol-metals are liquids more or less volatile. They exhibit but little tendency to unite with other bodies. The alcohols and ethers cannot be formed from them directly. Oxygen and sulphur do not act upon them, and chlorine and bromine do not unite with them, but decompose them, form- ing substitution-products; they are not attacked by hydro- chloric acid or by potash. For their boiling points and vapour-densities, see page 518. 3. Mixed metals, containing a metal proper and an alcohol- radical; e.g. zinc-methyl, GH^.Zn; zinc-ethyl, Q^H^.Zn; zinc- amy I, CgHj^Zn; stannethyl, -GgH^Sn; arsenethyl, (^2^5)3 As; stihmethyl, (CH3)Sb, &c. These compounds are obtained by the action of iodide of ethyl, &c., on the corresponding metals, or their alloys with potassium or sodium ; thus, the compounds of ethyl and ar- senic are obtained by distilling iodide of ethyl with arsenide of sodium ; arsen-bimethyl or cacodyl, (GH3)2As, is likewise produced by the dry distillation of a mixture of acetate of soda and arsenious acid. To understand this reaction, it must be remembered that the radical of acetic acid, ^gHgO, may be supposed to consist of QQ- conjugated with methyl, -GHg : — Acetate of soda. Oxide of cacodyl. These compounds are liquids more or less volatile, and B R 2 568 CONJUGATE METALS. generally having a very offensive odour ; they oxidise rapidly in the air, and sometimes take fire. Zinc-methyl, zinc-ethyl, and cacodyl take fire instantly on coming in contact with the air. Zinc-methyl, zinc-ethyl, and zinc-amyl differ in some re- spects from the other mixed metals in their behaviour with oxygen, sulphur, chlorine, iodine, &c. When these metals are exposed to the air, but not freely enough to cause them to take fire, they are converted into mixed ethers ; thus, — 2 (^Hg. Zn) + oa == 2 (^^^i a). Similarly with sulphur. Chlorine, bromine, and iodine, on the other hand, decompose them, producing a chloride of the metal and a chloride of the alcohol-radical : — ^Hg. Zn + ClCl = ^Hg. CI + ZnCl. This difference of reaction is in perfect accordance with the bibasic character of oxygen and sulphur, and the monobasic character of chlorine, bromine, and iodine (compare pp. 515, 547). The same mixed metals decompose water, forming a hydrate of zinc and a hydride of the alcohol-radical; — ^HgZn + ][^] O == H . ^Hg -f- ^^]0. The other mixed metals — thence called conjugate metals — containing tin, antimony, arsenic, bismuth, lead, and mercury, combine as simple radicals with oxygen, chlorine, &c., form- ing oxides, chlorides, &c. The oxides of these conjugate metals may be regarded as derivatives of the oxides of the simple metals contained in them, one or more atoms of oxygen being replaced by its equivalent quantity of ethyl, &;c. ; that is, O by (■€•2115)2, &c. This will be seen from the following table, in which the symbol Et stands for (^2^5)2 • — CONJUGATE METALS. 569 Type. Derivative. Arsenious acid, ASgOg . Oxide of arsen-biethyl As2(Et20) = j jt^sCG^U) Arsenic acid, AsjOg . . Oxide of arsen-triethyl AsaCEtaOj) = O2 1 ^3^^=^ jjy Arsenic acid, As^Q^ . . Oxide of arsenethylium As^(Et^Q■)=^\ As(cV) Stannic oxide, SngO^ . Oxide of stannethyl SuaCEtO) =0 1 gn/^-^H^ Stannic oxide (2 at.), 1 /-w -a eo . *i, 1 d /tti* r»N r\ fSnoCOaH-), Sn,0, ....\./:) Oxide of 5-stannethyl Sn,(Et3O)=02|sn2(GX)3 Me^c^uncoxide(2at.),|Q^.^^ of--«-ethyl Hg,(EtO) ^. O^ { g jgg^j The method of determining the equivalent in hydrogen of these conjugate radicals has been already explained (p. 526). Acid metals, or metalloids. — These are the elements com- monly called negative or chlorous : e. g. oxygen, sulphur, phosphorus, &c. RELATIONS BETWEEN CHEMICAL COMPOSI- TION AND DENSITY. Atomic Volume of Liquids * — The atomic volumes of bodies are the spaces occupied by quantities proportional to their atomic v^eights, and are calculated by dividing the atomic weights by the specific gravities (I. 210); thus, the atomic weights of copper and silver being, on the hydrogen scale, 31*7 and 108*1, and their specific gravities (water =1) being 31*7 8-93 and 10*57, their atomic volumes are, respectively, 8*93 * H. Kopp, Ann. Ch. Pharm. xcvi. 2, 330. H R 3 570 ATOMIC VOLUME OF LIQUIDS. and r , or 3*6 and 10-2. These numbers are. of course, 1057 only relative; their actual values depend en the units of atomic volume and density adopted. It has already been observed, that the relations between atomic weight and density are much less simple in solids and liquids than in gases, the diversities in the rates of expansion by heat of liquid and solid bodies being alone sufficient to complicate these relations to a considerable extent. With regard to liquids in particular, the researches of Professor Kopp have shown that their atomic volumes are comparable only at temperatures for which the tensions of the vapours are equal ; for example, at the boiling points of the liquids. If the atomic weights of liquids are compared with their den- sities at equal temperatures, no regular relations can be per- ceived ; but when the same comparison is made at the boiling temperatures of the respective liquids, several remarkable laws become apparent. The density of a liquid at its boiling point cannot be ascertained by direct experiment ; but when the density at any one point, say at 15*5° C. (60° F.), has been ascertained, and the rate of expansion is also known, the density at the boiling point may be calculated. Abundant data for these calculations are supplied by the labours of Kopp and Pierre (II. 433). The following table contains Kopp's determinations of the atomic volumes of a considerable number of liquids contain- ing carbon, hydrogen, and oxygen at their boiling points. The atomic weights are those of the hydrogen-scale. The calculated atomic volumes in the fourth column are deter- mined by a method to be presently described; the observed atomic volumes in the fifth column are the quotients of the atomic weights, on the hydrogen-scale, divided by the specific gravities referred to water as unity. ATOMIC VOLUME OF LIQUIDS. 571 Table A. Atomic Volumes of Liquids containing Carbon, Hydrogen, and Oxygen. Atomic Volume at the Boiling Point. Substance. Formula. Atomic Weight. Calculated. Observed. / Benzol GeH, 78 99-0 96-0... 99-7 at 80° Cymol 134 187-0 183-5. ..185-2 „ 175 ^ \ Naphthalia . S ^Aldehyde . "Z < Valeraldehyde . 128 1540 149-2 . . „ 218 0,HA 44 56-2 56-0... 56-9 , 21 O.H.oO, 86 122-2 117 3.. .120-3 „ 101 ^ 1 Bitter almond oil . G.HgO 106 122-2 118-4 . . , 179 H / Cuminol O.oHeO 148 188-2 189-2 . . , 236 1 Butyl .... ^sH.e 114 187-0 184-5. ..186-8 , 108 \ Acetone 0,H,0 58 78-2 77-3... 77-6 , 56 "Water . • . HoO 18 18-8 18-8 . . , 100 Wood-spirit . €H,0 32 40-8 41-9... 42-2 , 59 Alcohol O^HgO 46 62-8 61-8... 62-5 , 78 Amylic alcohol 0,H,,0 88 128-8 123 6.. .124-4 , 135 Phenylic alcohol . ^eHeO 94 106-8 103-6.. .104-0 , 194 Benzoic alcohol , G.HgO 108 128-8 123-7 . . „ 213 Formic acid . 0H,0, 46 420 40-9... 41-8 , 99 Acetic acid . e,H,o, 60 64-0 63-5... 63-8 , , 118 Propionic acid G^HgO, 74 86-0 85-4 . . , 137 Butyric acid e^HA 88 108-0 106-4.. .107-8 , 156 Valerianic acid ^5H,o02 102 130-0 130-2. ..131-2 , 175 Benzoic acid ^tH^O^ 122 130-0 126-9 . . , 253 Vinic ether . e,H,„& 74 106-8 105-6... 106-4 , 34 O Acetic acid (anhydrous) G,H,03 102 109-2 109-9. ..110-1 , 138 a Formiate of methyl G,H,0, 60 640 63-4 . . „ 36 w^ Acetate of methyl 0,H,0, 74 86-0 83-7... 85-8 , 55 a Formiate of ethyl . G3H,0, 74 86-0 84-9... 85-7 , 55 ^ Acetate of ethyl . e.H^o, 88 108-0 107-4. ..107-8 , 74 Butyrate of methyl e5HioO, 102 130-0 125-7... 127-3 , 93 Propionate of ethyl e^H.oO, 102 130-0 125-8 . . , 93 Valerate of methyl ^eH.A 116 152-0 148-7... 149-6 , 112 Butyrate of ethyl . G.H.A 116 1520 149-1. ..149-4 , 112' Acetate of butyl . G,H„0, 116 1520 149-3 . . , 112 Formiate of amyl . 0,Hj,0, 116 152-0 149-4... 150-2 , 112 Valerate of ethyl . e,H„o, 130 174-0 173-5. ..173-6 , 131 Acetate of amyl . 0,H.A 130 174-0 173-3. ..175-5 , 131 Valerate of amyl . ^lo^ao^a 172 240-0 244-1 . . , 188 Benzoate of methyl G,H,^, 136 152-0 148-5.. .150-3 „ 190 Benzoate of ethyl . e.H^O, 150 174-0 172-4... 174-8 , 209 Benzoate of amyl . e„H„0, 192 240-0 247-7 . . , 266 ^Cinnamate of ethyl ^uH.A 176 207-0 211-3 . . „ 260 <^ /Acid salicylate of methyl e^H.Og 152 159-8 156-2.. .157-0 , 223 a ^ Carbonate of ethyl e^H.oOa 118 137-8 138-8.. .139-4 „ 126 S ; Oxalate of methyl O.H^O, 118 117-0 116-3 . . „ 162 ^ Oxalate of ethyl . Qh \ Succinate of ethyl e6H,o^4 146 161-0 166-8. ..167-1 „ 186 ^bHmO. 174 205-0 209-0 . . „ 217 R E 4 5-72 ATOMIC VOLUME OF LIQUIDS. A comparison of the numbers in this table leads to the following remarkable results : — \» Differences of atomic volume are in numerous instances proportional to the differences between the corresponding chemical formuke. — Thus liquids, whose formulae differ by n . -GHg, differ in atomic volume by n . 22 ; for example, the atomic volumes of formiate of methyl, -GgH^Og, and butyrate of ethyl, -GgHgOg, differ by nearly 4 x 22. Acetate of ethyl, -G^HgOg, and butyrate of methyl, -G-gHioOg, whose formulas differ by -GHg, differ in atomic volume by nearly 22. The same law holds good with respect to liquids containing sulphur, chlorine, iodine, bromine, and nitrogen (see Tables B, C, D). Again : by comparing the atomic volumes of analogous chlorine and bromine compounds, it is found that the substitution of 1, 2, or 3 atoms of bromine for an equivalent quantity of chlorine, increases the atomic volume of a compound by once, twice, or three times 5. This will be seen by comparing the atomic volumes of PBrg and PCI3; Q^^fi^ and 'G2H5CI, &c. (Table C.) 2. Isomeric liquids belonging to the same chemical type have equal atomic volumes. — The atomic volume of acetic acid, ^2^^]0, is between 63-5 and 63-8; that of formiate of methyl, £^TT jO, is 63 4 ; the atomic volume of butyric acid^ ^A^jO, is between 106-4 and 107*8 ; that of acetate of ethyl, ^^^aOj^^ -^ ij^tween 107-4 and 107-8. 3. In liquids of the same chemical type, the replacement of hydrogen by an equivalent quantity of oxygen (that is to say, of 1 pt. of hydrogen by 8 pts. of oxygen) makes but a slight alteration in the atomic volume. — This may be seen by com- paring the atomic volumes of alcohol, ^^fi-, and acetic acid, JG2H4O2 ; of ether, G^HjoO, acetate of ethyl, ^G^HgOg, and anhydrous acetic acid, 4^411^03 ; of cymol, Gj^Hj^, and ATOMIC VOLUME OF LIQUIDS. 573 cuminol, C^qR^^Q. The alteration caused by the substitution of O for Hg is always an increase. 4. In liquids of the same chemical type, the replacement of 2 at H by I at. Q (I pt. by weight of hydrogen by 6 parts of carbon) makes no alteration in the atomic volume, — Such, for example, is the case with benzoate of ethyl, -GgHjoOg, and valerate of ethyl, ^^Hj^Og, and with the corresponding ben- zoates and valerates in general; also with bitter almond oil, C-^HgO, and valeraldehyde, -G^HjoO. In liquids belonging to different types, the same relations are not found to hold good. Moreover, the types within which these relations are observed, are precisely those of Gerhardt's classification (II. 528). Further, when liquid compounds are represented by rational formulas founded on these types, their atomic volumes may be calculated from certain fundamental values of the atomic volumes of the elements, on the supposition that the atomic volume of a liquid compound is equal to the sum of the atomic volumes of its constituent elements. Since the addition of •G-H2 to a compound increases the atomic volume by 22, this number may be taken to represent the atomic volume of "GHg ; moreover, since Q- (or Og) may take the place of Hg in combination, without altering the atomic volume of the compound, it follows that the atomic volume of •€• must be equal to that of Hg ; and therefore the 22 atomic volume of G= — = 11, and that of Hg also equal to 11, or that of H=5'5. Further, as the substitution of O for Hg produces a slight increase in the atomic volume of a compound, the atomic volume of O must be rather greater than 11 ; and it is found that, by assuming the atomic volume of O, when it takes the place of Hg (that is to say, in a radical, as when acetyl, -GgHgO, is formed from ethyl, GgH^), to be equal to 12-2, results are obtained agreeing very nearly with those of abservation. But when oxygen occupies the 574 ATOMIC VOLUME OF LIQUIDS. XT position which it has in water, ttO, its atomic volume is smaller. The specific gravity of water at the boiling point is 0-9579 ; hence its atomic volume at that temperature is 18 — — 18*8 ; now the 2 atoms of hydrogen occupy a space u * yo 7 y equal to 11; hence the volume of the oxygen is 7*8. The same value of the atomic volume substituted for Q in the formulae of the several compounds belonging to the water- type, in which it occupies a similar place, that is to say, outside the radical, gives results agreeing nearly with obser- vation. That a given quantity of a substance should occupy different spaces, under different circumstances, is a fact easily explained, when it is remembered that the particles of a body cannot be supposed to be in absolute contact, but are sepa- rated by certain spaces, which increase or diminish according to the temperature of the body, and according as it is in the solid, liquid, or gaseous state. From these values of the atomic volumes of the elements carbon, hydrogen, and oxygen ; viz. — Atomic volume of ^G . . . . = 11 „ „ xl . . , . = o'o „ „ O (within the radical) = 12*2 ,, Si ^ (without the radical) = 7*8 ; the calculated values of the atomic volumes of liquids, in the fourth column of Table A, are deduced. The method of calculation may be understood from the following ex- amples : Benzol, QJi^ = Q^U, . H. Atomic volume of -Gg . . . , = 66 a 99 -Hg • • • • = oo ,, „ benzol . . . = 99 ATOMIC VOLUME OF LIQUIDS. 575 Aldehyde, ^,H,0 = : e,H3©. ,H. ,ic volume of -Gg , , . = 22 3> i9 ^A • • • . = 22 „ „ O (within the radical) = 12-2 „ aldehyde . . . = 56*2 Alcohol, G^HgO = ^AjQ, Atomic volume of Q^ . . . . = 22 39 39 H, . . . . = 33 99 99 O (without the radical) = 7*8 99 99 alcohol . . . = 62-8 Acetic acid, Q^U^Q, = ^^^^^]Q. Atomic volume of Q^ • • • . = 22 99 99 H, . . . . = 22 99 99 O (within the radical) =12-2 JJ 39 O (without the radical) = 7*8 99 39 acetic acid . . . = 64*0 Anhydrous acetic acid, ■G^HgOg = jC^TT^ri^^* Atomic volume of G^ . . . . = 44 J5 >J Hg . . . . = 33 33 J> Og (within the radical) = 24-4 33 33 O (without the radical) = 7*8 JJ 39 anhydrous acetic acid . = 109*2 Oxalate of methyl, G^HgO^ = (q^\ ]^2' Atomic volume of ^4 . . . , = 44 99 33 Hg . . . . = 33 « 33 O2 (within the radical) = 24*4 93 93 O2 (without the radical) = 15-6 99 39 oxalate of methyl . = 117*0 576 AT03IIC VOLUME OF LIQUIDS. Liquids containing Sulphur. — Sulphur enters into combina- tion in various ways ; sometimes taking the place of oxygen in the type HH . O (as in mercaptan) ; sometimes taking the place of carbon within a radical (as in anhydrous sulphurous acid) iSO . O, compared with anhydrous carbonic acid €0 . 0; sometimes replacing oxygen within a radical (as in sulphide of carbon), CS . -S, compared with anhydrous carbonic acid. In the first and second cases, the atomic volume of sulphur- compounds may be calculated by attributing to sulphur (S= 32), the atomic volume 22*6, those of the other elements re- maining as above ; in the third case, the atomic volume of sulphur appears to be greater; viz., 28-6. Examples. — Mercaptan, -GgHgS = Atomic volume of -Gg • «< He €„H. ]^. H . = 22 = 33 , = 22-6 77-6 „ „ mercaptan . Sulphide of carbon, -GSg = GS*S. Atomic volume of -Q . . . . = 11 „ „ ^ (within the radical) = 28*6 „ „ S (without the radical) = 22-6 sulphide of carbon = 62-2 Table B. Atomic Volumes of Liquid Sulphur-compounds, Substance. Formula. Atomic Volume at the Boiling Point. Weight. Calculated. Observed. Mercaptan . Amylic mercaptan Sulphide of methyl Sulphide of ethyl . Bisulphide of methyl . Sulphurous acid . Sulphite of ethyl . Bisulphide of carbon . €8, 62 104 62 90 94 64 138 76 77-6 143-6 77-6 121-6 100-2 42-6 149-4 62-2 76-0... 76-1 at 36° C. 140-1. ..140-5 „ 120 75-7 . . „ 41 1205... 121-5 „ 91 100-6. ..100-7 „ 114 43-9 . . „ -8 148-8... 149-5 „ 160 62-2... 62-4 „ 47 ATOMIC VOLUME OF LIQUIDS. 577 Chlorides, Bromides, and Iodides. — In liquid compounds of this class, the atomic volume of CI is supposed to be 22*8, that of Br = 27*8, and that of I = 37 '5, those of the other elements remaining as above. Table C. Atomic Volumes of Liquid Chlorides, Bromides, and Iodides. Atomic Volume at the Boiling Point. Substance. Formula. Atomic Weight. ^^ Iculatec 1. ObserTed. Bichlorinated ethylene . OJi^Cla 97 78-6 79-9 . . at 37° C. Chloride of carbon o,ci. 166 113-2 115-4 . . „ 123 Chloride of ethylene G,H,C], 99 896 85-8... 86-4 „ 85 , monochlorinated GJifih 133'5 106-9 105-4... 107-2 „ 115 , bichlorinated . G,H,C1, 168 124-2 120-7. ..121-4 „ 137 G2HCI5 ono.f; 141*'i 143 . . „ 129-5.. .133-7 „ 154 123 Chloride of butylene O.HgCfz 127 It 1 133-6 Monochlorinated chloride of methyl . GH2CI2 85 676 64-5 . . „ 30-5 Chloroform . OHCI3 119-5 84-9 84-8... 85-7 „ 62 Chloride of carbon CCI4 154 102-2 104-3. ..107-0 „ 78 Chloride of ethyl . ©aHsCl 64-5 72-3 71-2... 74-5 „ 11 , monochlorinated G2H4CI2 99 89-6 86-9... 89-9 „ 64 , bichlorinated . O2H3CI3 133-5 106-9 105-6... 109-7 „ 75 Chloride of amyl . O^H.jCl lOG-5 138-3 135-4.. .137-0 „ 102 Chloral GJICI3O 147-5 108-1 108-4.. .108-9 „ 96 Chloride of acetyl . C^H.OCl 78-5 73-5 74-4... 75-2 „ 55 Chloride of benzoyl G,H,0Q1 140-5 139-5 134-2. ..137-8 „ 198 Bromine Br, 160 55-6 54 ... 57-4 „ 63 Bromide of methyl OH^Br 95 55-3 58-2 . . „ 13 Bromide of ethyl . G^H.Br 109 77-3 78-4 . . „ 41 Bromide of amyl . 0,H„Br 151 143-3 149-2 . . „ 119 Bromide of ethylene 0,H,Br, 188 99-6 97-5... 99-9 „ 130 Iodide of methyl . GH3I 142-1 65-0 65-4... 68-3 „ 43 Iodide of ethyl G,H,I 156-1 87-0 85-9... 86-4 „ 71 Iodide of amyl €^5HuI 198-1 153-0 152-5... 155-8 „ 147 Chloride of sulphur SCI 6T-5 45-7 . . „ 140 Chloride of phosphorus . PCI3 137-5 93-9 . . „ 78 Bromide of i)hosi)horus . PBr3 271 108-6 . . „ 175 Chloride of silicon SiCL 127-8 91-6 . . „ 59 Bromide of silicon SiBrg 261-3 108-2 . . „ 153 Chloride of arsenic AsClg 181-5 94-8 . . „ 133 Chloride of antimony . SbCl3 2355 100-7 . . „ 223 Bromide of antimony , SbBrg 369 116-8 . . „ 275 Chloride of tin SnCL 129 65-7 . . „ 115 Chloride of titanium TiCl, 96 63-0 . . „ 136 ^7^ ATOMIC VOLUME OF LIQUIDS. The compounds PCI3, SiClg, and AsClg have nearly equal atomic volumes, whence it may be inferred that phosphorus, silicon, and arsenic, in their liquid compounds, have equal atomic volumes. The same conclusion may be drawn regard- ing tin and titanium, since the atomic volumes of SnClg and TiClg are equal. Nitrogen-compounds. — In compounds belonging to the ammonia type, the atomic volume of nitrogen is 2*3. This result is deduced from the observed atomic volume of ani- line, ^gH^N, which is 106 '8. Now the atomic volume of 6 € + 7 H = 6 . 11 + 7 . 5-5 = 104*5, which number, deducted from 106 8, leaves 2*3 for the atomic volume of nitrogen. The atomic volume of cyanogen deduced from the observed at. vol. of cyanide of phenyl, ^N . ^^5, or -Q^HgN, is nearly 28. Thus— Atomic volume of ^^HgN = 121*6 9> 99 "^6^5 ^^ 93*5 „ „ €N = 28-1 A similar calculation, founded on the observed atomic volume of cyanide of methyl, ^gHgN, gives, for the at. vol. of cyanogen, the number 26*8. The atomic volume of liquid cyanogen determined directly at 37° or 39° C. above its boiling point, is between 28*9 and 30*0. As a mean of these values, the atomic volume of cyanogen may be assumed to be 28 ; and with this value the atomic volumes of the liquid cyanides are calculated. Thus, for Oil of mustard (sulpho-cyanide of allyl),€4H5NS = ^^ JS. Atomic volume of C3H5 . . . = 60*5 „ „ GN . . .= 28-0 „ „ S (without the radical) = 22*6 oil of mustard . . = 111*1 ATOMIC VOLUME OF LIQUIDS. 579 The atomic volumes of compounds containing the radical NO2 are calculated on the hypothesis that the at. vol. of that radical is 33, which agrees nearly with the observed atomic volume of liquid peroxide of nitrogen. Thus : — the at. vol. of nitrite of amyl, ^gHj^NOg = at. vol. of Q^B^^i + at. vol. of NO2 = 115-5 + 33 = 148-5. Table D. Atomic Volumes of Liquids containing Nitrogen. Atomic Volume at the Boiling Point. Substance. Formula. Atomic Weight. Calculated. Observed. Ammonia H3N 17 18-8 22-4... 23-3 at 10°. ..16°* Ethylamine . G,H,N 45 62-8 65-3 . . at 18-7 Butylamine . 0,H„N 73 106-8 Amylamine . G,H,3N 87 128-8 125-0 . . . „ 94 Caprylamine GgHjgN 129 194*8 190-0 . . . M 170 Aniline G,H,N 93 106-8 106-4.. .106-8 . „ 184 Toluidine aHoN 107 1288 Ethaniline 0,H„N 121 150-8 1.50-6 . „ 204 Biethaniline . 0,oH,,N 149 194-8 190-5 . . . „ 213-5 Cyanogen €N 26 28-0 28-9... 300 . „ 16 1 Hydrocyanic acid . GHN 27 33-5 391 . . . „ 27 Cyanide of methyl e,H3N 41 55-5 54-3 . . . „ 74 Cyanide of ethyl . ^aH.N 55 77-5 77-2 . . „ 88 Cyanide of butyl . G,H,N 83 121-5 Cyanide of phenyl . e,H,N O2H3NS 103 121-5 121-6. ..121-9 „ 191 Sulphocyanide of methyl 73 78-1 75-2... 78-2 „ 133 Sulphocyanide of ethyl . ^gH^NS 87 100-1 99-1 . . ,, 146 Oil of mustard a.H^NS 99 111-1 1131. ..114-2 „ 148 Cyanate of ethyl . OgHsNO 71 85-3 84-3... 84-8 „ 60 Peroxide of nitrogen NO3 30 33-0 31-7... 32-4 >, 40 1 Nitrate of methyl . GH3NO3 77 68-3 69-4 . . » 66 Nitrate of ethyl O.H^NOg 101 90-3 90-0... 90-1 » 86 Nitrobenzol GgH.NO, 123 126-5 122-6.., 124-9 „ 218 Nitrite of methyl . eH3NO, 61 60-5 61-6 . » 14§ Nitrite of ethyl G,H,NO, 75 82-5 79-2... 84-6 » 18 Nitrite of amyl e,H„NO, 117 148-5 148-4 . . „ 95 * Between 44° and 50° above the boiling point, f Between 37° and 39° above the boiling point. % About 35° above the boiling point. § 27° above the boiling point. 580 ATOMIC VOLUME OF LIQUIDS. From the preceding observations and calculations, it appears that the atomic volume of a compound depends, not merely on its empirical, but likewise on its rational formula ; in other words, not merely on the number of atoms of its elements, but further on the manner in which those atoms are arranged. Now it has been shown (p. 522) that a com- pound may have more than one rational formula, according to the manner in which it decomposes ; and hence it might appear that the calculation of atomic volumes must be attended with considerable uncertainty, inasmuch as the atomic volumes of certain elements, as oxygen and sulphur, vary according to the manner in which they enter into the compound. Aldehyde, for example, may be represented cither as ^tt^J^^ or ^s ^^ [; and, as the atomic volume of oxygen is 12*2 or 7*8, according as it is within or with- out the radical, the atomic volume of aldehyde will be 56*2 if deduced from the type HH, and 51 '8 if deduced from the type HH . O. But the atomic weight of aldehyde, and its specific gravity at a given temperature are invariable ; it cannot, therefore, have two different atomic volumes. It must be remembered, however, that, in speaking of a compound as bavins several rational formulae, we consider it rather in a dynamical than in a statical point of view; as under the influence of disturbing forces, and on the point of undergoing chemical change. But if, on the other hand, we regard a compound in its fixed statical condition, as a body possessing definite physical properties, a certain specific gravity, a cer- tain boiling point, rate of expansion, refractive power, &c., we can scarcely avoid attributing to it a fixed molecular arrangement, or, at all events, supposing that the disposition of its atoms is confined within those limits which constitute chemical types. It is found, indeed, that isomeric liquids exhibit equal atomic volumes only when they belong to the same chemical type. If this view be correct, the relation ATOMIC VOLUME OF LIQUIDS. 581 between the atomic volumes of elements and compounds, may often render valuable service in determining the rational formula which belongs to a compound in the state of rest. Thus, of the two atomic volumes just calculated for aldehyde, the number 56*2, deduced from the formula Q^H^Q . H, agrees with the observed atomic volume of aldehyde, which is between 56*0 and 56*9, better than 51*8, the number deduced from ^2^3^^^ This result leads to the conclusion that the aldehydes belong to the hydrogen-type (p. 565), rather than to the water- type. There are many groups of liquid compounds, irrespective of isomerism or similarity of type, the members of which have equal or nearly equal atomic volumes. The following table exhibits the calculated atomic volumes of several of these groups : — Atomic Volume of Liquids. Water H^O 18-8 Ether 0,H,oO 106-8 Ammonia NH3 18-8 Butylic alcohol «^ 106-8 Phenylic alcohol 0,H,0 106-8 Bromine . Br, 55-6 Butylamine 0,H.,N 1068 Cyanogen (ON), 56-0 Aniline . 4H7N 106-8 Aldehyde O2H4O 56-2 Butyric acid . O4H8O, 108 Cyanide of methyl . O^HgN 55-5 Acetate of ethyl 0,H,O, 108-0 Bromide of methyl . O^HaBr 55-3 Anhydrous acetic acid 0,H,03 109-2 Chloral . O2HCIO 108-1 Alcohol . 0,HeO 62-8 Bichlorinated chlo- Acetic acid 0,H,0, 64-0 ride of ethyl 0,H3Cl3 106-9 Formiate of methyl . 0,H,0, 64-0 Monochlorinated chlo- Cyanate of methyl . 0,H3NO, 63-3 ride of ethylene . 02H3C13 1069 Ethylamine O.H.N 62-8 Bromide of phos- Sulphide of carbon . 0^; 62-3 phorus . PBr3 108-6 Iodide of methyl 0H3I 65-0 Valeraldehyde . 0,H.,0 122-2 Acetone . OaHeO 78-2 Cyanide of butyl 0,H,N 121-5 Cyanide of ethyl e3H,N 77-6 Bitter almond oil 0,H,O 122-2 Sulphocyanide ofme- Cyanide of phenyl . O^H.N 121-5 thyl . O^HgNS 78-1 Sulphide of ethyl . 0,H,„S 121-6 Sulphide of methyl . e.H,S 77-6 These groups exhibit an approach to the uniformity of atomic volume which is observed in the gaseous state. Berthelot has adduced a number of examples, showing that VOL. II. S S 582 ATOMIC VOLUME OF SOLIDS. when a liquid compound is formed by the union of two other liquids, whose specific volumes are denoted by A and B, with elimination of x atoms of water, the specific volume of the compound is nearly = A -f- B— .-cC (the atomic volume of water being denoted by C). Berthelot's observations, how- ever, were made at medium temperatures, not at the boiling points of the liquids. Atomk, Volume of Solids, — The principal results obtained by Kopp, with reference to the atomic volume of solid bodies, are given in Yol. I. pp. 210 — 216.* The difficulty of reducing the results to general laws is similar to that which has been noticed in the case of liquids, but exists to a still greater extent, inasmuch as our knowledge of the expansion of solids by heat is much more limited than that of liquids. It is probable that the atomic volumes of solids should be com- pared at their melting points ; since it is only at those tem- peratures that the effects of heat upon different solids can be said to be equal. Now the specific gravities of most solids are determined only at medium temperatures, from which the melting points of different solids are separated by intervals of very different magnitude ; moreover, there are but few solids whose rate of expansion at different temperatures has been ascertained with sufficient accuracy to render it possible to calculate the specific gravities at the melting points. A further complication arises from the different densities which the same solid often exhibits, according as it is amorphous or crystalline, or according to the particular form in which it crystallises. * The numbers there given refer to the oxygen-scale of atomic weights. (0 = 100.) RELATIONS OF COMPOSITION AND BOILING POINT. 583 RELATIONS BETWEEN CHEMICAL COMPOSI- TION AND BOILING POINT.* In compounds of similar constitution, and especially among the members of homologous series (p. 532), difference of boiling point is frequently proportional to difference of composition. 1. In the alcohols, ^0^20+2^* the fatty acids, ^uHgnOg, and the compound ethers (p. 545) isomeric with the fatty acids, a difference of ^Hg in the formula corresponds to a difference of 19° C. in the boiling point. 2. The boiling point of a fatty acid, ^..HanOg, is higher by 40° C. than that of the corresponding alcohol, ^nIl2n+2^» 3. The boiling point of a compound ether, ^nH2n02, is lower by 82° C. than that of the isomeric acid. Starting from the observed boiling point of common alcohol, 78° C, and calculating by these rules the boiling points of the other alcohols and of the fatty acids and ethers, we obtain the numbers in the third column of the following table, which do not differ from the observed boiling points in the fourth column, more than these latter, as determined by different observers, differ from one another. Substance. Alcohols. Methylic alcohol Propylic alcohol Butylic alcohol Amy lie alcohol Cetylic alcohol Formula. Boiling point. Calculated. 59° 97 116 135 344 Observed. 60° 61 64-9 65 96 109 1 ?0-4 132 132 360 at 744 mm. ,, 755 „ 754 „ 752 „ ? „ ? „ 742 „ 760 ,, 766 Observers. Kane. DelfFs. H. Kopp. H. Kopp. Chancel. Wurtz. H. Kopp. Cahours. DelfFs. Favre and Silbermann. * H. Kopp. Ann. Ch. Pharm. xcvi. 2, 330. S s 2 584 RELATIONS OP COMPOSITION AND BOILING POINT. Boiling point. Substance. Formula. Observed. Calculate i. Observed. Acids. Formic acid . €HA 99 r 98-5 . 105-4 . . at 753 . „ 764 mm. It Liebig. H. Kopp. Acetic acid . 0,H,0, 118 • " 116-9 . 116 . . „ 750 . „ 754 »» H. Kopp. Delffs. Propionic acid 03HeO, 137 ^ 141-6 . L 141 . . „ 754-6 „ H. Kopp. Limpricht and V. Uslar. Butyric acid . 0,H«0, 156 r 156 . L 163 . . „ 733 . „ 751 >» H. Kopp. L Pierre. Valerianic acid ^5H.o^2 175 174-5 . L 175-8 . . „ 762 „ . „ 746-5 „ Delffs. H. Kopp. Caproic acid . ^6 "12^2 194 198 . . „ ? » Brazier and Gossleth. Caprylic acid . O^H.eO, 232 236 . . „ ? »» Fehling. Pelargonic acid Q,R,,^, 251 260 . . » ? » Cahours. Compound Ethers. Formiate of methyl. 0,HA 36 ■ r 32-7 . L 22-9 . . « 741 . „ 752 » H. Kopp. Andrews. '■ 55 . . „ 762 ti Andrews. Acetate of methyl . GgHgO, 55 • 55-7 . . „ 757 it H. Kopp. 59-5 . . „ 761 »> L Pierre. ' 52-9 . . „ 752 >» L Pierre. Formiate of ethyl . ^sHe^a 55 53 . . „ 736 )> Delffs. 54-7 . . ,, 754 »» H. Kopp. Acetate of ethyl . e,H30, 74 ■ ' 73-7 . L 74-1 . . » 745 . „ 766 »» H. Kopp. I. Pierre. 93 . . „ 744 » Delffs. Butyrate of methyl. e^H.oO, 93 95-1 . 102-1 . . „ 742 . » 744 >» H. Kopp. L Pierre. Acetate of propyl . e^H.oO., 93 90 (abou t) Berthelot. Propionate of ethyl. G,H,oO, 93 95-8... 9 8 >» H. Kopp. Valerate of methyl . G,H.,0, 112 114 ...11 5 „ 756 »» H. Kopp. Butyrate of ethyl . GeH,,0, 112 f 114-6 . 119 . . „ 756 . » 747 » H. Kopp. I. Pierre. Formiate of amyl . ^6H,20, 112 '■ 114 . 116 (abou . „ 771 t) »» Delffs. H. Kopp. Acetate of butyl , €,H,,0, 112 114 Wurtz. Valerate of ethyl . G,H.,0, 131 ' 131-3 . 133-2 . . „ 735 . „ 754 Delffs. H. Kopp. 133 . . „ 760 " Delffs. Acetate of amyl ^vH.A 131 133-3 . . M 749 H. Kopp. 137-6 . . „ 746 11 H. Kopp. Valerate of amyl . e.oH,oO» 188 187-8. ..18 8-3 „ 730 >» H. Kopp. It appears from this table that isomeric compound ethers have equal boiHng points, e.g, formiate of ethyl and acetate of RELATIONS OF COMPOSITION AND BOILING POINT. 585 methyl boil at 66° ; valerate of methyl, butyrate of ethyl, for- miate of amy I, and acetate of butyl, boil at 1 1 2°. It follows, also, from the preceding laws, that the boiling point of an acid, QJl2x/^2i ^^ ^^° higher than that of its methylic ether, 44° higher than that of its ethylic ether, and 13° lower than that of its amylic ether: thus, valerianic acid boils at 175°; valerate of methyl at 112° ; valerate of ethyl at 131° ; valerate of amyl at 188°. Common ether, ("^2^5)2^^ ^^ ^^® ethyl-salt p XT of alcohol, A ^]0, regarded as an acid; that is to say, it bears the same relation to alcohol that acetate of ethyl bears to acetic acid : hence its boiling point should be 78° — 44° = 34°. The actual observations of the boiling point of ether vary from 34° to 35-7°. In the same series of homologous compounds, it is found that the addition of w -G raises the boiling point by w . 29° ; and the addition of ^^ H lowers the boiling point by n . 5° [conse- quently, the addition of nGHg raises it by w. (29 — 2x5) = n, 19°]. The same law is likewise observed in other series of compounds of similar character. Thus, benzoate of ethyl, GgHjoOg, boils at 209°, which is higher by 4 x 29, or 116, than the boiling point of the ethers G^Hj^Og, — butyrate of methyl for example. The boiling point of angelic acid, GgHgOg, is higher by 29° than that of butyric acid, C^HgOg ; and 2 x 5, or 10°, higher than that of valerianic acid, -GgHjoOg. The boiling point of phenylic alcohol, GgHgO, is higher by about 4 x 29, or 116°, than that of common alcohol, Grfi.fi- ; and about 8 x 5, or 40°, higher than that of caproic alcohol, GgH^^O. Constant relations of composition and boiling point are observed also in other series of homologous compounds ; but the difference of boiling point corresponding with a difference of GH2, is not always 19°. In the series of hydrocarbons : — benzol, -GsHe (B.P.^80°), toluol, G^Hg, xylol, GgH^o, cumol, G9H12, cymol, ^iqHj^, the difference is 24°; in the homologous s s 3 586 CHEMICAL AFFINITY. compounds: — bromide of ethylene, 4^2H4Br2, bromide of pro- pylene, Q^HqEv^, bromide of butylene, QJIfir^, it is 15°, their boiling points being 130°, 145°, and 160°, respectively. In the series of alcohol-radicals (in the free state), the difference is about 23° ; in the anhydrous acids, homologous with an- hydrous acetic acid, it is about 13°. These differences of boiling point would probably be the same in all series of homologous compounds, if the boiling points were determined at different pressures. It is not, indeed, to be expected that two substances should exhibit the same difference of boiling point under all pressures ; for if B and B' denote the boiling points of two liquids at the ordinary atmospheric pressure, b and b', the boiling points of the same liquids at another pressure ; and if we suppose that B _ B' = b - b', it will follow that B - b = B'-V; that is to say, the boiling points of the two liquids would vary equally for equal differences of pressure, which is contrary to observation. CHEMICAL AFFINITY. Tnjfluenoe of mass on chemical action. — That the relative degrees of affinity of a body for a number of others to which it is simultaneously presented, are greatly modified by their relative masses, was first pointed out by Berthollet The law laid down by that philosopher respecting the action of masses, is this : — A body to which two different substances, capable of uniting with it chemically , are presented in different proportions, divides itself between them in the ratio of the products of their 7nasses, and the absolute strenaths of their affnities for the first CHEMICAL AFFINITY. 587 hodij. Thus, if we denote by A and B the masses of the two bodies which are present in excess, by a and /3, the coefficients of their absohite affinities for the body C ; and by a and 6, the quantities of A and B, which actually combine with C, the law just stated will be expressed by the proportion: — a : h := uA : ^B, If this view be correct, any alteration, however small, in the relative quantities of A and B, must produce a corresponding alteration in the relative quantities of the two which unite with C, That this is not the case under all circumstances, is shown by the following experiments of Bunsen and of Debus. Bunsen's experiments,* which were made in such a manner that all the phenomena of combination concerned in them took place simultaneously, lead to the following remarkable laws : — • 1. When two or more bodies, B B' , . , are presented in excess to the body JL, under circumstances favourable to their combination with it, the body A always selects of the bodies B B' , , , quantities which stand to one another in a simple atomic relation, so that for 1, 2, 3 . . . atoms of the one com- pound, there are always formed 1, 2, 3 . . . atoms of the other ; and if in this manner there is formed an atom of the compound AB', in conjunction with an atom of AB, the mass of the body B may be increased relatively to that of B^, up to a certain limit, without producing any alteration in the atomic pro- portion. When carbonic oxide and hydrogen are exploded with a quantity of oxygen not sufficient to burn them completely, the oxygen divides itself between the two gases in such a manner that the quantities of carbonic acid and water produced stand to one another in a simple atomic proportion. The results of Bunsen's experiments are given in the following table, the numbers in which denote volumes : — ♦ Ann CIi. Fliann. Ixxxv. j37. s s 4 588 CHEMICAL AFFINITY. Composition of Gaseous Mixture. Quantities of CO and H con- sumed by Detonation. Ratio of CO: H. 72-57 CO . 18-29 H . 9*14 59-93 „ . 26-71 „ . 13-36 „ 36-70 „ . 42-17 „ . 21-13 „ 40-12 „ . 47-15 „ . 12-73 „ 12-18 CO . 6-10 H 13-06 „ . 13-66 „ 10-79 „ . 31-47 „ 4-97 „ . 20-49 „ 2 : 1 1 : 1 1 :3 1 : 4 The results were the same whether the explosion took place in the dark, in diffused daylight, or in sunshine ; and were not affected by the pressure to which the gaseous mixture was subjected. The proportions of hydrogen and carbonic acid consumed in these several experiments, correspond with the composition of five hydrates of carbonic acid, containing, respectively — HO.2CO2; HO. CO, 2H0.C0 2 ' 3HO.CO2; 4H0.C0, but the results cannot be attributed to the actual formation of these hydrates, inasmuch as hydrates of acids containing several atoms of water are incapable of existing at high temperatures. 2. When a body. A, exerts a reducing action on a com- pound, BC, present in excess, so that A and JB combine together, and C is set free ; then, if C can, in its turn, exert a reducing action on the newly-formed compound, AB, the final result of the action is, that the reduced portion of BC is to the unreduced portion in a simple atomic proportion. In this case, also, the mass of the one constituent may, without altering the existing atomic relation, be increased to a certain limit, above which that relation undergoes changes by definite steps, but always in the proportion of simple rational numbers. When vapour of water is passed over red-hot charcoal, the carbon is oxidised and hydrogen is separated ; but the process does not go on so far as the complete formation of carbonic acid, but stops at the point at which 1 vol. carbonic acid and 2 vol. carbonic oxide are formed to every 4 vol. of hydrogen. CHEMICAL AFFINITY. 589 In the imperfect combustion of cyanogen — the gaseous mixture being so far diluted that it will but just explode, in order that the temperature may not rise too high, and the result be consequently vitiated by the partial oxidation of the nitrogen — carbonic acid and carbonic oxide are formed, and nitrogen set free, likewise in simple atomic proportion. A mixture of 18*05 vol. cyanogen, 28*87 oxygen, and 53*08 nitrogen, gave, by detonation, 2 vol. carbonic oxide, and 4 vol. carbonic acid to 3 vol. nitrogen. In the combustion of a mixture of carbonic acid, hydrogen, and oxygen, in which the carbonic acid is exposed at the same time to the reducing action of the hydrogen and the oxidising action of the oxygen, the reduced portion of the carbonic acid is likewise found to bear to the unreduced portion a simple atomic relation. In the combustion of a mixture of 8*52 carbonic acid, 70*33 hydrogen, and 21*15 oxygen, the result- ing carbonic oxide was to the reduced carbonic acid in the ratio of 3 .* 2. After the combustion of a mixture of 4*41 vol. carbonic oxide, 2*96 carbonic acid, 68*37 hydrogen, and 24* Z. 6 oxygen, the volume of the carbonic oxide converted into carbonic acid by oxidation, was to that of the residual carbonic oxide as 1:3. That these remarkable laws had not been previously observed is attributed by Bunsen to the fact that they held good only when the phenomena of combination, which are regulated by them, take place simultaneously ; for, even if a body A, were originally to select for combination from the bodies B and (7, quantities bearing to one another a simple atomic relation, but the combination of A and B were to take place in a shorter time than that of A and C, it would follow of necessity, that during the whole of the process, the ratio of B to C, and therefore, also the atomic relations of the associated compounds, would change, so that the observed proportion would be no longer definite. The same result must follow if the bodies which are combining side by side are not homogeneously mixed in the beginning. 590 CHEMICAL AFFINITY. With regard to the bearing of these results on Berthollet's law, it might be objected that, in some of the experiments, as in the combustion of a mixture of carbonic oxide, hydrogen, and oxygen, one of the products, viz. the water, is removed from the sphere of action by condensation, and that the circum- stances are therefore similar to the removal of an insoluble product by precipitation (I. 231). It is scarcely conceivable, however, that a reverse action would take place, even if tlie gaseous mixture were to remain at the temperature which exists during the combustion. Moreover, in the decomposition of vapour of water by red-hot charcoal, the whole of the pro- ducts remain in the gaseous state. Debus* has obtained results similar to those of Bunsen by precipitating mixtures of lime and baryta-water with aqueous carbonic acid, or mixtures of cliloride of barium and chloride of calcium, with carbonate of soda. A small quantity of a very dilute solution of carbonate of soda, added to a liquid containing 5 pts. of chloride of barium to 1 pt. of chloride of calcium, threw down nearly pure carbonate of lime; but when the proportion of the chloride of barium in the mixture was 5*7 times as great as that of the chloride of cal- cium, 2*3 pts. of the former were decomposed to 1 pt. of the latter. Hence it appears that, in this reaction also, limits exist at which the ratio of the affinities undergoes a sudden change. In these experiments, however, the products are imme- diately removed from tlie sphere of action, and the results are therefore not comparable with those which are obtained when all the substances present remain mixed and free to act upon each other. The latter condition is most completely fulfilled in the mutual actions of liquid compounds, such as solutions of salts, when all the possible products of their mutual actions are likewise soluble ; as, for example, when nitrate of soda in solution is mixed with sulphate of copper. Tlie question to be solved in such cases is this. Suppose two salts AB, CD, * Ann. Ch. Pliarm. Ixxxv. 103. ; Ixxxvi. 156. j Ixxxvii. 238. CHEMICAL AFFINITY. 591 the elements of which can form only soluble products by their mutual interchange, to be mixed together in solution. Will these elements, according to their relative affinities, either remain in their original state of combination, as AB and CD, or pass completely into the new arrangement AD and CB ? — or will each of the two acids divide itself between each of the two bases, producing the four compounds AB, AD, BC, BD ? — and, if so, in what manner will the relative quantities of these four compounds be affected by the original quantities of the two salts ? Do the amounts of AD and CB, produced by the reaction, increase progressively with the regular increase of AB, as required by Berthollet's theory? or do sudden tran- sitions occur, like those observed in the experiments of Bunsen and Debus ? The solution of this question is attended with considerable difficulty. For when two salts in solution are mixed, and nothing separates out, it is by no means easy to ascertain what changes may have taken place in the liquid. The ordinary methods of ascertaining the composition of the mixture, such as concentration, or precipitation by re-agents, are inadmis- sible, because any such treatment immediately alters the mutual relation of the substances present. In some cases, however, the mixture of two salts is attended with a decided change of colour, without any separation of either of the con- stituents, and such alterations of colour may afford indications of the changes which take place in the arrangement of the molecules. This method has been employed by Dr. Glad- stone*, who has carefully examined the changes of colour attending the mixture of a great variety of salts, and applied the results to the determination of the effect of mass in influencing chemical action. Dr. Gladstone's principal experiments were made with the blood-red sulphocyanide of iron, which is formed on adding hydro-sulphocyanic acid or any soluble sulphocyanide to a solution of a ferric salt (I. 532). On mixing known quantities * PhiL Trans, 1855, 179 ; Chem. Soc. Qu. Jo. ix. 54. 592 CHEMICAL AFFINITY. of different ferric salts with known quantities of different sulphocyanides, it was found that the iron was never com- pletely converted into the red salt; that the amount of it so converted depended on the nature both of the acid combined with the ferric oxide, and of the base combined with the sul- phocyanogen; and that it mattered not how the bases and acids had been combined previous to their mixture, so long as the same quantities were brought together in solution. The effect of mass was tried by mixing equivalent proportions of ferric salts and sulphocyanides, and then adding known amounts of one or the other compound. It was found that, in either case, the amount of the red salt was increased, and in a regular progression according to the quantity added. When sulphocyanide of potassium was mixed in various pro- portions with ferric nitrate, chloride, or sulphate, the rate of variation appeared to be the same, but with hydrosulpho- cyanic acid it was different. The deepest colour was pro- duced when ferric nitrate was mixed with sulphocyanide of potassium ; but even on mixing 1 eq. of the former with 3 eq. of the latter, only 0*194 eq. of the red sulphocyanide of iron was formed; and even when 375 eq. of sulphocyanide of potassium had been added, there w^as still a recognisable amount of ferric nitrate undecomposed. The results of a series of experiments with ferric nitrate and sulphocyanide of potassium are given in the following table : — Ferric Sulphocyanide of Red Salt Ferric Sulpliocyanide of Potassium. Red Salt Nitrate. Potassium. produced. Nitrate. produced. 1 equiv. 3 equiv. 88 1 equiv. 63 equiv. 356 6 „ 127 99 „ 419 1 J 96 „ 156 135 „ 487 12-6 „ 176 189 „ 508 16-2 „ 195 243 „ 539 1 19-2 „ 213 1 297 „ 560 28-2 „ 266 375 „ 587 46-2 „ 318 CHEMICAL AFFINITT. 593 The addition of a colourless salt reduced the colour of a solution of ferric sulphocjanide, the reduction increasing in a regularly progressive ratio, according to the mass of the colourless salt. Similar results were obtained with other ferric salts, viz., with the black gallate, the red meconate and pyromeconate, the blue solution of Prussian blue in oxalic acid, &c., and likewise with the coloured salts of other metals, e. g, the scarlet bromide of gold, the red iodide of platinum, the blue sulphate of copper, when treated with different chlorides, &c. The amount of fluorescence exhibited by a solution of acid sulphate of quinine w^as found to be affected by the mixture of a chloride, bromide, or iodide, according to the nature and mass of the salt added ; and the addition of sulphuric, phos- phoric, nitric, and other acids was found to produce a fluo- rescence in solutions of hydrochlorate of quinine or of sulphate which had been rendered non-fluorescent by the addition of hydrochloric acid. Solutions of horse-chestnut bark, and of tincture of thorn-apple, yielded similar results. The conclusions to be drawn from Dr. Gladstone's experi- ments, which afford a complete confirmation of BerthoUet's theory, so far at least as relates to the action of substances in solution, are as follows : — When two or more binary compounds are mixed under such circumstances that all the resulting compounds are free to act and react, each electro-positive element enters into combination with each electro-negative element in certain constant proportions, which are independent of the manner in which the different elements are primarily arranged, and are not merely the resultant of the various strengths of affinity of the several substances for each other, but are dependent also on the mass of each of the substances present in the mixture. All deductions respecting the arrangement of substances in solu- tion, drawn from such empirical rules as that the strongest acid combines with the strongest base, must therefore be fallacious. 594 CHEMICAL AFFINITY. An alteration in the mass of any of the binary compounds present alters the amount of every one of the otlier binary compounds, and that in a regularly progressive ratio, sudden transitions only occurring where a substance is present which is capable of combining with another in more than one pro- portion. This equilibrium of affinities arranges itself in most cases in an inappreciably short time ; but, in certain instances, the elements do not attain their final state of combination for hours. Totally different phenomena present themselves where pre- cipitation, volatilisation, crystallisation, and perhaps other actions occur, simply because one of the substances is thus removed from the field of action, and the equilibrium, which was at first established, is thus destroyed (I. 231). The reciprocal action of salts in solution has also been examined by Malaguti*, whose method consists in taking two salts, both of which are soluble in w*ater, but only one of which is soluble in alcohol, mixing them in equivalent pro- portions in water, then pouring the aqueous solution into a large quantity of alcohol, and analysing the precipitate, in order to ascertain the quantities of the original salts which have been decomposed. Malaguti concludes from his experi- ments that, in the mutual action of two salts, if nothing se- parates from the liquid, the decomposition is most complete when the strongest acid and the strongest base are not origi- nally united in the same salt, and that two experiments of this kind, made in opposite ways, must lead to the same final result ; that, for example, when 1 eq. of acetate of baryta is added to 1 eq. of nitrate of lead, the quantities of nitrate of baryta and nitrate of lead ultimately present in the liquid are the same as when 1 eq. nitrate of baryta is mixed with 1 eq. acetate of lead. The greater the quantity of the two salts decomposed in the one case, the smaller will be the quantity ♦ Ann. Ch. Phys. [3], xxxvii. 198. CHEMICAL AFFINITY. 595 decomposed in the other : so that if the quantity of any salt, out of 100 parts, which is decomposed by the action of another salt (always supposing that the whole remains in solution) be called the coefficient of decomposition , the law of the reaction is, that the sum of the coefficients of decomposition in the two cases is always equal to 100. For example : if 1 at. sulphate of potash and 1 at. acetate of soda act upon each other, and -^-^^ of the original quantity of sulphate of potash remain in solution as such, the coefficient of decomposition is 36. The numerical values of the coefficients of decomposi- tion, determined in several cases by the method above de- scribed, are given in the following table : — Salts. Acetate of potash . Nitrate of lead . . Chloride of potassium Sulphate of zinc . . Acetate of baryta . Nitrate of lead , . Chloride of sodium . Sulphate of zinc . . Acetate of baryta . Nitrate of potash . Acetate of potash . Nitrate of strontia . Acetate of strontia . Nitrate of lead . . Acetate of potash . Sulphate of soda Chloride of potassium Manganous sulphate Chloride of potassium Sulphate of magnesia Chloride of sodium Sulphate of magnesia Coefficient of Decom- position. 920 84-0 77-0 72-0 72-0 67-0 65 5 62-0 58-0 56-0 54 5 Salts. Acetate of lead . Nitrate of potash Chloride of zinc . Sulphate of potash Acetate of lead . Nitrate of baryta Chloride of zinc . Sulphate of soda Acetate of potash Nitrate of baryta Acetate of stronti i Nitrate of potash Acetate of lead . Nitrate of strontia Acetate of soda . Nitrate of potash Mangiinous chloride Sulphate of potash Chloride of magnesium "^ Sulphate of potash Chloride of magnesium Sulphate of soda Coefficient of Decom- position. 90 17-6 22-0 29-0 27-0 36-0 33 36-5 42-5 43-0 45-8 In all these cases, except one, the coefficients of decompo- sition are greatest when the strongest acid and the strongest base are not originally united in the same salt. The ex- ceptional case is presented by the mixture of nitric acid. 596 CHEMICAL AFFINITY. acetic acid, potash, and baryta, in which the greatest co- efficient of decomposition is obtained when the nitric acid is at first united, not with the baryta, but with the potash. A similar result was obtained by the action of potash on nitrate of baryta and of baryta on nitrate of potash, wood-spirit being used as ther precipitating agent instead of alcohol. The coefficient of decomposition was 6*9 in the former case, and 93-6 in the latter. It is not easy to determine how far the particular numerical results of these experiments were influenced by the presence of the alcohol ; but as its action was the same in both cases of each pair of experiments, the results certainly justify the conclusion that the two salts, when mixed, resolve themselves into four ; that the partition takes place in a definite manner ; and that the proportions of the resulting salts are independent of the manner in which their elements were originally combined. Experiments bearing on the same point, have' also been published by Margueritte *, who finds that two salts in solu- tion mutually decompose each other, even when one of them is already the least soluble of the four salts that may be pro- duced from the two acids and the two bases present. A saturated solution of chlorate of potash, to which chloride of sodium is added, becomes capable of dissolving an additional quantity of chlorate of potash, showing that a portion of the chlorate has been decomposed, and a more soluble salt formed. Chloride of ammonium is precipitated from its saturated aqueous solution on addition of a small quantity of nitrate of ammonia; but the previous addition of chlorate of potash prevents the precipitation ; whence it would appear tliat the chlorate of potash and chloride of ammonium are partially con- verted into chlorate of ammonia and chloride of potassium. The precipitation of sulphate of lime from its aqueous solu- tion by alcohol, is prevented by the presence of the nitrates ♦ Compt. rend xxxviii. 304. CHEMICAL AFFINITY. 597 or chlorides of potassium, sodium, or ammonium, evidently because a portion of the sulphate is converted into nitrate or chloride. A solution of chloride of ammonium dissolves the carbonates of baryta, strontia, and lime more readily than pure water, because it partially converts them into chlorides, the liquid at the same time acquiring an alkaline reaction, in consequence of the formation of carbonate of ammonia. The decomposition of insoluble by soluble salts affords a striking instance of the tendency of atoms to interchange, and of the influence of mass on chemical action. According to H. Rose*, sulphate of baryta is completely decomposed by boiling with solutions of alkaline carbonates, provided that each equivalent of sulphate of baryta is acted upon by at least 15 eq. of the alkaline carbonate. If 1 eq. of sulphate of baryta is boiled with only 1 eq. of carbonate of potash, only J- of it is decomposed, and only -^ by boiling with 1 eq. of carbonate of soda, further decomposition being prevented by the presence of the alkaline sulphate already formed. If, however, the liquid be decanted after a while, the residue boiled with a fresh portion of the alkaline carbonate, and these operations repeated several times, complete decomposi- tion is effected. Carbonate of baryta is converted into sul- phate by the action of an aqueous solution of sulphate of potash or soda, even at ordinary temperatures. Solution of carbonate of ammonia does not decompose sulphate of baryta either at ordinary or at higher temperatures ; carbonate of baryta is not decomposed by sulphate of ammonia at ordinary temperatures, but easily on boiling. Sulphate of baryta is not decomposed by boiling with caustic potash-solution, pro- vided the carbonic acid of the air be excluded ; but by fusion with hydrate of potash, it is decomposed, with formation of carbonate of baryta, because the carbonic acid of the air cannot then be completely excluded. Hydrochloric and * Pogg. Ann. xciv. 481 ; xcv. 96, 284. VOL. II. T T 598 CHEMICAL AFFINITY. nitric acids, left in contact at ordinary temperatures with sulphate of baryta, either crystallised or precipitated, dissolve only traces of it; at the boiling heat, a somewhat larger quantity is dissolved, and the solution forms a cloud, both with a dilute solution of chloride of barium and with dilute sulphuric acid. Sulphate of strontia is dissolved by hydro- chloric acid at ordinary temperatures, sufficiently to form a slight precipitate with dilute sulphuric acid, and with chloride of strontium. Sulphate of lime treated with hydrochloric acid, either cold or boiling, yields a liquid in which a preci- pitate is formed, after a while, by dilute sulphuric acid, but not by chloride of calcium. Sulphate of strontia and sulphate of lime are completely decomposed by solutions of the alkaline carbonates and bi- carbonates at ordinary temperatures, and more quickly on boiling, even if considerable quantities of an alkaline sulphate are added to the solution : the decomposition is also effected by carbonate of ammonia, even at ordinary temperatures. The carbonates of strontia and lime are not decomposed by solutions of the sulphates of potash or soda at any tempera- ture ; sulphate of ammonia does not decompose them at ordi- nary temperatures, but readily with the aid of heat. Sulphate of lead is completely converted into carbonate by solutions of the alkaline carbonates and bicarbonates, even at ordinary temperatures, the neutral carbonates, but not the bicarbonates, then dissolving small quantities of oxide of lead. Carbonate of lead is not decomposed by solutions of the alka- line sulphates, either at ordinary temperatures or on boiling. Chromate of baryta is decomposed at ordinary tempe- ratures by solutions of the neutral alkaline carbonates, and much more easily by boiling with excess of an alkaline bicarbonate. When equivalent quantities of the chromate of baryta and carbonate of soda are boiled with water, ^ of the whole is decomposed ; when the same quantities of the salts CHEMICAL AFFINITY. 599 are fused together, and the mass treated with water, only -^ of the baryta-salt is decomposed. Carbonate of baryta is completely converted into chromate by digestion with a solu- tion of an alkaline monochromate ; and the decomposition of chromate of baryta by alkaline carbonates, even at the boiling heat, is completely prevented by' the presence of a certain quantity of an alkaline monochromate. Seleniate of baryta is easily and completely decomposed by solutions of alkaline carbonates, even at ordinary tempe- ratures: this salt is somewhat soluble in water, and more readily in dilute acids. Oxalate of lime is decomposed by alkaline carbonates even at ordinary temperatures ; but to effect complete decompo- sition the liquid must be frequently decanted and renewed. The decomposition takes place rapidly at the boiling heat; but in all cases it is completely prevented by the presence of a certain quantity of a neutral alkaline oxalate. When the salts are mixed in equivalent proportions, ^ of the oxalate of lime are decomposed at ordinary temperatures, and ^ on boiling. Carbonate of lime is partially converted into oxalate by the action of a solution of neutral oxalate of potash at ordinary temperatures, and more quickly on boiling; — but the decomposition is never complete, even when the liquid is frequently decanted and renewed. — Oxalate of lead is com- pletely converted into carbonate at ordinary temperatures by the solution of an alkaline carbonate, a small portion of the carbonate of lead dissolving in the liquid. (Rose.) The preceding experiments exhibit in a striking manner the influence of difference of solubility in determining the order of decomposition. Sulphate of baryta is less soluble than the carbonate, and, accordingly, carbonate of baryta is more readily decomposed by alkaline sulphates, than the sulphate by alkaline carbonates. Precisely the contrary relations are exhibited by the sulphates and carbonates of T T 2 600 CHEMICAL AFFINITY. strontia* and lime, both as regards solubility and order of decomposition. On the other hand, oxalate of lime is less soluble than the carbonate, and yet its decomposition by alkaline carbonates takes place more easily than the opposite reaction : in this case, the order of decomposition appears rather to be determined, as in Malaguti's experiments, by the tendency of the strongest acid to unite with the strongest base. The effect of a soluble sulphate, &c., in arresting the de- composition of the corresponding insoluble salts by alkaline carbonates, is evidently due to its tendency to produce the reverse action : hence the acceleration produced by decanting and renewing the liquid. Some insoluble salts, however, phos- phate of lime for example, are never completely decomposed, even by this treatment. The constant tendency to interchange of atoms, exhibited in the phenomena above described, and, indeed, in all cases of chemical action, suggests the idea that the atoms of all bodies, at least in the fluid state, are in constant motion. We have already seen that the same idea is suggested by the phenomena of heat, and leads to a consistent theory of those phenomena (II. 449). On a similar hypothesis. Professor Williamson proposes to construct a general theory of chemical action.f The fundamental notion of this theory is, that the atoms of all compounds, whether similar or dissimilar, are continually changing places, the interchange taking place more readily as the atoms resemble each other more closely. Thus, in a mass of hydrochloric acid, each atom of hydrogen is supposed, not to remain quietly in juxta-position with the atom of chlorine with which it happens to be first united, but to be continually changing places with other atoms of hydro- gen, or, what comes to the same thing, continually becoming associated with other atoms of chlorine. This interchange is * According to Fresenius, carbonate of strontia dissolves in 11,862 parts, and the sulphate in 6895 parts of cold water, t Chem. Soc. Qii. J., ix. 110. CHEMICAL AFFINITY. 601 not perceptible to the eye, because one molecule of hydro- chloric acid is exactly like another. But suppose the hydro- chloric acid to be mixed with a solution of sulphate of copper (the component atoms of which are likewise undergoing a change of place), the basylous elements, hydrogen and copper, then no longer limit their change of place to the circle of atoms with which they were at first combined, but the hy- drogen and copper likewise change places with each other, forming chloride of copper and sulphuric acid. Thus it is that, when two salts are mixed in solution, and nothing separates out in consequence of their mutual action, the bases are divided between the acids, and four salts are produced. If, however, the analogous elements of the two compounds are very dissimilar, and, consequently, interchange but slowly, it may happen that the stronger acid and the stronger base remain almost entirely together, leaving the weaker ones combined with each other. This is strikingly seen in a mix- ture of sulphuric acid (sulphate of hydrogen) and borate of soda, which soon becomes almost w^holly converted into sul- phate of soda and free boracic acid (borate of hydrogen). Now suppose that, instead of sulphate of copper, sulphate of silver is added to the hydrochloric acid. At the first moment the interchange of elements may be supposed to take place as above, and the four compounds, -SO^Hg, SO^Agg, CIH, and ClAg, to be formed ; but the last, being insoluble, is immediately removed by precipitation ; the remaining ele- ments then act upon each other in the same way, and this action goes on till all the chlorine or all the silver is removed in the form of chloride of silver ; if the original compounds are mixed in exactly equivalent proportions, the final result is the formation of only two salts, viz., in this case, -^04112 and ClAg. A similar result is produced when one of the pro- ducts of the decomposition is volatile at the existing tempera- ture, as when hydrate or carbonate of soda is boiled with chloride of ammonium. tt 3 602 CHEMICAL AFFINITY. This theory affords a simple explanation of the action of sulphuric acid upon alcohol, whereby sulphovinic acid (sulphate of ethyl and hydrogen) is first formed, and after- wards, at a certain temperature, ether and water are elimi- nated (I. 226). When alcohol, ^^^^j O, and sulphuric acid, XT XT } ^^4, are mixed together, the interchange between the atoms of ethyl in the former and of hydrogen in the latter gives rise to the formation of sulphovinic acid and water : — But the change does not stop here, for the sulphovinic acid thus produced, meeting with fresh molecules of alcohol, exchanges its ethyl for the hydrogen of the alcohol, producing ether and sulphuric acid : — The sulphuric acid is thus restored to its original state, and is ready to act upon fresh quantities of alcohol ; so that if alcohol be allowed to run into the mixture in a constant stream, the temperature being kept within certain limits (between 140° and 160° C), the process goes on without in*- terruption, ether and water continually distil over, and the same quantity of sulphuric acid suffices for the etherification of an unlimited quantity of alcohol. This is the peculiarity of the process ; it has given rise to a variety of explanations ; in fact, the process of etherification has long been a battle- ground of chemical theories.* The discussion of these various theories would be foreign to the present purpose ; it is suffi- cient to remark that the hypothesis of atomic interchange aff'ords a ready explanation of the most obscure point in the * See the translation of Gmelin's Handbook, vol. viii. pp. 231—237. CHEMICAL AFFINITY. 603 reaction, viz., the formation and decomposition of sulphovinic acid following each other continuously, without any change of temperature or other determining cause. If it be admitted that the atoms of ethyl and hydrogen in the mixture are con- tinually interchanging in all possible ways, this series of alter- nate actions follows as a necessary consequence. The formation of ether by the mutual action of sulphovinic acid and alcohol is also analogous to its production by the action of iodide of ethyl on potassium-alcohol (p. 534) : — ^aHsjo + ^^H.I = J^H^ja + KI. The same view is corroborated by the fact recorded by Wil- liamson, in the paper above quoted, that sulphamylic acid (sulphate of amyl and hydrogen) distilled with common alcohol, yields an ether containing both ethyl and amyl : — %^^^, + %'}G^ = §i;jo + |]sa, ; and that the same compound is obtained by distilling a mix- ture of vinic and amylic alcohols with sulphuric acid ; also with the fact discovered by Chancel, that sulphovinate of potassium distilled with potassium-alcohol, yields ether : — K ]^^4 + ^K^}^ "" QJlJ^ "^ k]'^*^4; and that the same salt distilled with methylate of potassium, ^HgKO, yields methamylic ether, jno^]"^* 3 The idea of atomic motion is in accordance with physical as well as chemical phenomena. To suppose that rest, rather than motion, is the normal state of the particles of matter, is at variance with all that we know of the effects of light, heat, and electricity. In the heat-theory of Clausius, (II. 449), the particles of bodies are supposed to be affected T T 4 604 DIFFUSION OF LIQUIDS. with progressive, as well as with rotatory and vibratory move- ments ; and this same hypothesis of progressive movement which, of course, implies change of relative position among the particles, affords, as already stated, a ready explanation of certain chemical reactions, otherwise somewhat obscure. It is worth while to observe that, in the heat-theory of Clausius, the progressive motion of the particles is supposed to exist only in the liquid and gaseous states, the particles of solid bodies merely performing rotatory and vibratory move- ments about certain positions of equilibrium. This is quite in accordance with the well-known fact that chemical reaction rarely takes place between solid bodies. DIFFUSION OF LIQUIDS. Intimately connected with the interchange of atoms re- sulting in chemical decomposition, is the process by which a saline, or other soluble substance, is spread or diffused uni- formly through the mass of the solvent ; in some cases, in- deed, as will presently be seen, the decomposition of salts is greatly facilitated by the tendency of one or more of the products of decomposition to diffuse into the surrounding liquid. The phenomena of liquid diffusion have been minutely investigated by Mr. Graham.* The apparatus used consisted of a set of phials, of nearly equal capacity, cast in the same mould, and further adjusted by grinding to a uniform size of aperture. The phials were 3-8 inches high, with a neck 0*5 inch in depth, and aperture 1*25 inch wide; capacity to base of neck equal to 2080 grains of water, or between 4 and 5 ounces. For each diffiision-pliial, a plain glass ivatev" * Phil. Trans. 1850, pp. 1, 805 ; Chem. Soc. Qu. J. ii. 60, 257 ; iv, 83. DIFFUSION OF LIQUIDS. 605 jar was also provided, 4 inches in diameter and 7 inches deep. (Fig. 43). The difFusion-phial was filled with the saline solution, sal-ammoniac for instance, to the base of the neck, or more correctly to a distance of 0*5 inch from the ground surface of the lip. The neck of the phial was then filled up with distilled water, a light float being first placed on the surface of the solution, and care being taken to avoid agitation. After the phial had been placed within the jar, water was poured into the jar, so as to cover the open phial to the depth of an inch which required about 20 ounces of water. The saline liquid in the phial is thus allowed to communicate freely with the water in the jar. The diffusion is interrupted by placing a small plate of ground glass on the mouth of the phial, and raising the latter out of the jar. The amount of salt diffused, called the diffusion-product, or diffusaie, is ascertained by evaporating the water in the jar to dryness, or, in the case of chlorides, by precipitating with nitrate of silver. The results of several series of experiments made in this manner are given in the following Table, the second column of which shows the quantity of salt in 100 parts of the solu- tion ; the third, the time of diffusion ; the fourth, the tempe- rature, on the Fahrenheit scale ; the fifth, the quantity of salt diffused : — 606 DIFFUSION OF LIQUIDS. Diffusion of Saline Solutions. Substance. Per Cent. Days. Fahr. Diffusate. r 1 5 51° 7-41 2 5 51 15-04 Hydrochloric acid . 2 5 59-7 16-55 4 5 51 30-72 I 8 5 51 67-68 Hydriodic acid 2 5 51 1511 Hydrobromic acid . 2 6 59-7 16-58 Bromine 0-864 10 60-1 5-84 Hydrocyanic acid . 1-766 5 64-2 11-68 1 5 51-2 6-99 Hydrated nitric acid (NO^H) . • 2 4 5 5 51-2 51-2 14-74 28-76 8 5 51-2 57-92 r 1 10 49-7 8-69 Hydrated sulphuric acid (SO4H) 2 4 10 10 49-7 49-7 16-91 33-89 8 10 49-7 68-96 Chromic acid .... 1-762 10 67-3 19-78 2 10 48-8 11-31 Acetic acid (C^H^OJ . 4 10 48-8 22-02 8 10 48-8 41-80 1 10 68-1 8-09 Sulphurous acid 2 4 10 10 68-1 68-1 16-96 33-00 8 10 68-1 66-38 1 4-04 63-4 4-93 Ammonia . . . . < 2 4 4-04 4-04 63-4 63-4 9*59 19-72 8 4-04 63-4 41-22 2 10 48-7 8-62 Alcohol ■ 4 10 48-7 16-12 8 10 48-7 35-50 1 11-43 64-1 7-72 Nitrate of baiyta 2 4 11-43 11-43 64-1 64-1 15-04 29-60 8 11-43 64-1 54-50 Nitrate of strontia . 0-82 11-43 51-5 5-59* 1 11-43 64-1 7-66 Nitrate of lime 2 4 11-43 11-43 64-1 64-1 15-01 29-04 8 11-43 64-1 55-10 Acetate of baryta . 1 16-17 53-5 7-50 Acetate of lead 1 16-17 53-1 7-84 1 8-57 6-3 6-32 Chloride of barium . 2 4 8-57 8-57 6-3 6-3 12-07 23-96 8 8-57 6-3 45-92 1 8-57 6-3 6-09 Chloride of strontium 2 4 8-57 8-57 6-3 6-3 11-66 23-56 8 8-57 6-3 44-46 DIFFUSION OF LIQUIDS. Diffusion of Salike Solvtio^b — continued. 607 Substance. Per Cent. Days. Fahr. Diffusate. r 1 11-43 63-8° 7-92 2 11'43 63-8 15-35 Chloride of calcium 4 11-43 63-8 30-78 8 11-43 63-8 61-56 1 11-43 50-8 6-51 Chloride of manganese . 1 11-43 50-8 6-63 Nitrate of magnesia 1 11-43 50-8 6-49 Nitrate of copper . 1 11-43 50-8 6-44 Chloride of zinc 1 11-43 50-8 6-29 Chloride of magnesium . 1 11-43 50-8 6-17 Cupric chloride 1 11-43 50-8 6-06 Ferrous chloride 1 11-43 53-5 6-30 / 1 16-17 65-4 7-31 2 16-17 65-4 12-79 \ 4 16-17 65-4 23-46 Sulphate of magnesia . . < 8 16-17 65-4 42-82 1 8 16-17 62-8 42-66 16 16-17 62-8 75-06 \ 24 16-17 62-8 102-04 / 1 16-17 65-4 6-67 / 2 16-17 65-4 12-22 1 4 16-17 65-4 23-12 Sulphate of zinc . . . < 8 16-17 65-4 42-26 i 8 16-17 62-8 39-62 f 16 16-17 62-8 74-40 V 24 16-17 62-8 101-42 ' 1 16-17 65-4 5-48 Sulphate of alumina. 2 4 16-17 16-17 65-4 65-4 10-21 19-28 8 16-17 65-4 33-52 r 2 7 63-4 13-61 Nitrate of silver 4 7 63-4 26-34 8 7 63-4 51-88 ■ 2 7 63-4 12-35 Nitrate of soda 4 7 63-4 23-56 8 7 63'4 47-74 ' 1 7 63-4 6-32 2 7 63-4 12-37 Chloride of sodium . 4 7 63-4 24-96 8 7 63-4 48-44 2 7 63-4 12-14 Iodide of sodium 2 7 59-8 12-18 Bromide of sodium . 2 7 59-8 12-14 Chloride of potassium 2 5-716 59-8 12-24 Bromide of potassium 2 5-716 59-8 12-46 Iodide of potassium 2 5-716 59-8 12-51 Chloride of ammonium . 1 5-716 59-8 5-99 " 1 8-08 68-2 7-23 Bicarbonate of potash 2 4 8-08 8-08 68-2 68-2 14-05 26-72 8 8-08 68-2 52-01 Bicarbonate of ammonia . . ■ 1 2 8-08 8-08 68-2 68-2 6-91 13-65 608 DIFFUSION OF LIQUIDS. Diffusion of Saline Solutions — continued. Substance. Per Cent. Days. Fahr. Diffusate. Bicarbonate of ammonia . 4 8 8-08 8-08 68-2° 68-2 27-00 50-10 1 9-87 68-2 7-31 Bicarbonate of soda . . ■ 2 4 9-87 9-87 68-2 68-2 13-81 26-70 8 9-87 68-2 52-38 1 4-04 63-3 6-56 Hydrate of potash . 2 4 4-04 4-04 63-3 63-3 12-84 25-04 8 4-04 63-3 52-24 " 1 4-95 632 5-81 Hydrate of soda, 2 4 4-95 4-95 63-2 63-2 11-09 20-86 8 4-95 63-2 40-44 I 8-08 63-6 6-13 Carbonate of potash 2 4 8-08 8-08 63-6 63-6 11-92 22-88 8 8-08 63-6 45-44 1 9-9 63-4 6-02 Carbonate of soda . 2 4 9-9 9-9 63-4 63-4 11-70 21-42 8 9-9 63-4 39-74 Sulphate of potash . 1 8-08 60-2 6-16 2 8-08 60-2 11-60 4 8-08 60-2 22-70 8 8-08 60-2 43-92 ' 1 9-9 59-9 6-33 Sulphate of soda 2 4 9-9 9-9 59-9 59-9 12-00 21-96 8 9-9 59-9 41-38 Sulpliite of potash . 2 808 59-5 11-63 Sulphite of soda 2 9-9 59-5 11-83 Hyposulphite of potash . 2 8-08 59-7 12-37 Hyposulphite of soda 2 9-9 59-9 11-89 Sulphovinate of potash . 2 8-08 59-7 12-60 Sulphovinate of soda 2 9-9 59-5 13-03 r 1 8-08 .59-9 6-20 Oxalate of potash . . . 'V 2* [Forthe amides ofphosphoricacid, seepage 695.] All salts of ammonium, heated with fixed caustic alkalies, give oif ammonia, which may be absorbed by hydrochloric acid, and its quantity then determined either by evaporating the solution of chloride of ammonium over the water-bath, or, more exactly, by precipitation with bichloride of platinum (p. 385). LITHIUM. Preparation.- — Pure chloride of lithium is fused over a spirit-lamp, in a small porcelain crucible, and decomposed by a zinc-carbon battery of four or six cells. The positive pole is a small splinter of gas-coke (the hard carbon deposited in the gas-retorts), and the negative pole an iron wire about VOL. IL 3 E 742 LITHIUM. the thickness of a knitting-needle.* After a few seconds, a small silver-white regulus is formed under the fused chloride, round the iron wire and adhering to it, and after two or three minutes attains the size of a small pea. To obtain the metal, the wire pole and regulus are lifted out of the fused mass, by a small, flat, spoon-shaped iron spatula. The wire may then be withdrawn from the still melted metal, which is protected from oxidation by a coating of chloride of lithium. The metal may now be easily removed from the spatula with a pen-knife, after having been cooled under rock-oil. These operations may be repeated every three minutes ; and thus an ounce of the chloride may be reduced in a very short time. Lithium, on a freshly-cut surface, has the colour of silver, but quickly tarnishes on exposure to the air, becom- ing slightly yellow. It melts at 180° C. (356° F.), and if pressed at that temperature between two glass plates, exhibits the colour and brightness of polished silver. It is harder than potassium or sodium, but softer than lead, and may, like that metal, be drawn out into wire. It tears much more easily than a lead wire of the same dimensions. It may be welded by pressure at ordinary temperatures. It swims on rock-oil, and is the lightest of all known solids, its specific gravity being only 0-5986. Taking the atomic weight at 6*5, its atomic volume is therefore 1*06, being nearly the same as that of calcium. Lithium is much less oxidable than potassium or sodium. It makes a lead-grey streak on paper. It ignites at a tempe- rature much higher than its melting point, burning quietly, and with an intense white light. It burns when heated in * The decomposing power of an electric current depends chiefly upon its density, i. e. upon the quotient obtained by dividing the strength of the current by the surface of the pole at which the electrolysis takes place. Thus, a current of constant strength passed through an aqueous solution of terchloride of chromium, eliminates, as its density is successively diminished (or the cross- section of the reducing pole increased), metallic chromium, chromous oxide, chromic oxide, and, lastly, hydrogen. (Bunsen, Fogg. Ann. xci. 619.) ESTIMATION OF LITHIUM. 743 oxygen, chlorine, bromine, iodine, or dry carbonic acid, and with great brilliancy on boiling sulphur. When thrown on water, it oxidises, but does not fuse like sodium. Nitric acid acts on it so violently, that it melts and often takes fire. Strong sul- phuric acid attacks it slowly; dilute sulphuric acid and hydro- chloric acid, quickly. Silica, glass, and porcelain are attacked by lithium at temperatures even below 200° C. (Bunsen.*) According to Dr. Mallett f, the atomic weight of lithium is 6*95 ; and accordingly that of sodium is exactly the mean between those of lithium and potassium. Nitrate of Lithia. — This salt has a strong tendency to form supersaturated solutions. Above 10° or 15° C, it crystallises in rhombic prisms, resembling those of common nitre, but below 10° in rhorabohedrons ; both kinds of crystals are deliquescent. The crystals which separate from the super- saturated solution at 1° C. are slender needles. (Kremers.J) Phosphate of Lithia, — According to W. Mayer §, the pre- cipitate formed en adding phosphate of soda to the solution of a lithia-salt, is not a double phosphate of lithia and soda, as commonly supposed, but a tribasic phos{)hate of lithia, SLiO.POg. The same precipitate is also produced when a lithia-salt is treated with phosphate of potash or phosphate of ammonia, mixed with free alkali. Estimation of Lithium. — This element, when separated from other metals, may be estimated in the form of sulphate or chloride, in the same manner as potassium or sodium. From potassium it is separated by precipitating the latter with bi- chloride of platinum ; and from sodium, by converting the two bases into chlorides, and treating the dried chlorides, in a well- closed bottle, with a mixture of absolute alcohol and ether, which, after a few^ days, dissolves the whole of the chloride of lithium, and leaves the chloride of sodium undissolved. * Ann. Cli. Pharm. xciv. 107 ; Chem. Soc. Qn. J. viii. 143. t Sill. Ann. J. [2], xxii. 349. % Pogg. Ann. xcii. 520. § Ann. Ch. Pharm. xcviii. ] 93. 3 E 2 744 BARIUM. BARIUM. Bunsen has obtained this metal by subjecting chloride of barium, mixed up to a paste with water and a little hydrochloric acid, at a temperature of 100° C, to the ac- tion of the electric current, using an amalgamated platinum wire as the negative pole. In this manner, the metal is ob- tained as a solid, silver-white, highly-crystalline amalgam, which, when placed in a little boat made of thoroughly ignited charcoal, and heated in a stream of hydrogen, yields barium in the form of a tumefied mass, darkly tarnished on the sur- face, but often exhibiting a silver-white lustre in the cavities.* Matthiessen has obtained barium by a method similar to that adopted for strontium (p. 756), but only in the form of a metallic powder. Binoxide or Peroxide of Barium, — A solution of this oxide in dilute hydrochloric acid acts as a reducing agent on various metallic oxides, a portion of its oxygen uniting, at the moment of separation, with the oxygen of the other metallic oxide (p. 517). When peroxide of barium is introduced into a solu- tion of bichromate of potash acidulated with hydrochloric acid, oxygen is abundantly evolved (its evolution being, how- ever, preceded, in the case of cold dilute solutions, by the formation of a blue compound, first observed by Barreswil, and supposed by him to be a perchromic acid, Orfi^) ; and according to Brodie's experiments, the reaction, when a great excess of bichromate of potash is present, takes place as shown by the equation, 2Cr03 + 4Ba02 = Cr^Og + 70 + 4BaO, the chromic acid being reduced to sesquioxide of chromium. The quantity of oxygen evolved affords the means of calcu- ♦ Pogg. Ann. xci. 619. CARBONATE OF BARYTA. 745 lating the per centage of real BaOg in the sample used. Oxide, chloride, sulphate, or carbonate of silver introduced into an acid solution of a peroxide of barium, is partly reduced to metallic silver, the quantity of metal thus reduced being, however, always less than that which is equivalent to the oxygen which exists in the peroxide together with baryta. The quantity reduced increases with the amount of the silver compound used, and diminishes as the temperature is higher. A small quantity of the silver-compound, or of any similar substance, is capable of decomposing a large quantity of the peroxide. Iodine, on the other hand, decomposes only an equivalent quantity, according to the equation, BaO^ + I = Bal -f O^ (Brodie*). [For the separation of oxygen from the air by first convert- ing baryta into the peroxide, and then decomposing the latter, see p. 638.] Peroxide of barium, heated over a large spirit-lamp in a rapid current of carbonic acid gas, becomes white-hot, and at the same time small white flames burst out from its surface, probably arising from the evolution of oxygen from the still undecomposed peroxide. A similar, but much more brilliant appearance is presented when the peroxide is heated in sul- phurous acid gas. (Wohler.f) Carbonate of Baryta^ mixed with carbonate of lime and charcoal, and heated to redness in a stream of aqueous vapour, is decomposed, and yields caustic baryta. This pro- cess is recommended by JacquelainJ for the preparation of caustic baryta. According to Boussingault§, a solution of chloride of ba- rium, mixed with the native sesquicarbonate of soda called * Phil. Trans. 1850, 759. f Ann. Ch. Pharm. Ixxviii. 175. X Ann. Ch. Phys. [3], xxxii. 421. § Ibid. xxix. 397. 3 E 3 746 STRONTIUM. Uras, yields a precipitate of 2Ba0.3C02. Laurent assigns to this precipitate the formula 2BaO. SCOg + HO. H. Rose*, on the other hand, finds that chloride of barium and bicar- bonate of soda always yield a precipitate consisting merely of BaO . COj, and similarly with lime. Recently-precipitated sulphate of baryta, enclosed, with a solution of bicarbonate of soda, or with dilute sulphuric acid, in a sealed glass tube, and heated for 60 hours to 250° C. (472° F.), dissolves to a slight extent, and separates out on the sides of the tube in microscopic crystals, whose form agrees with that of heavy spar. Pure water or a solution of sulphide of sodium does not perceptibly dissolve sulphate of baryta under similar circumstances. (Senarmont.f) Estimation of Barium. — Barium is almost always estimated in the form of sulphate, the precipitation and filtration being performed in the manner already described for the estimation of sulphuric acid (p. 686). Precipitation with a soluble sulphate likewise serves to separate barium from all other metals except strontium, calcium, and lead. Barium is also sometimes estimated as carbonate, beinsr precipitated by carbonate of ammonia with addition of caustic ammonia, and the liquid boiled to render the precipitation complete. The carbonate is not decomposed by ignition. STRONTIUM. Preparation. — This metal is also obtained by the electro- lysis of its chloride in the fused state. A small crucible, with a porous cell in the middle, is filled with anhydrous chloride of strontium, mixed with a little chloride of ammo- nium, and in such a manner that the level of the fused chloride within the cell may be much higher than in the cru- * Pogg, Ann. Ixxxvi. 293. f Ann. Ch. Phys. [3], xxxii. 129. ESTIMATION OF STRONTIUM. 747 cible. The negative pole placed in the cell consists of a very fine iron wire wound round a thicker one, and then covered with a piece of tobacco-pipe stem, so that only ^th of an inch of it appears below ; the positive pole is an iron cylinder, placed in the crucible round the cell. The heat should be regulated during the experiment, so that a crust may form in the cell ; the metal will then collect under this crust without coming in contact with the sides of the crucible. In this manner, pieces of the metal weighing half a gramme are sometimes obtained. Strontium resembles calcium in colour (p. 749), being only a shade darker ; it oxidises much more quickly than that metal. Its specific gravity is 2*5418. Its place in the elec- trical series, with water as the exciting liquid, is as follows : + - K, Na, Li, Ca, Sr, Mg, &c. Strontium burns like calcium, and acts similarly to it when heated in chlorine, oxygen, bromine, or iodine, or on boiling sulphur, or when thrown on water or acids. (Matthiessen.*) Estimation of Strontium, — Strontium, like barium, may be estimated in the form of sulphate ; but as sulphate of stron- tia is slightly soluble in water, it is necessary, in order to ensure complete precipitation, to add alcohol to the liquid, which may be done if there are no other substances present which are insoluble in alcohol. Generally speaking, however, it is better to precipitate strontium in the form of a carbonate, by adding carbonate of ammonia and caustic ammonia, and heating the liquid. The precipitation of strontia in this form is more complete than that of baryta. The precipitate may be ignited on a lamp without giving off carbonic acid. It contains 59*27 per cent, of strontium, and 70*14 of strontia. * Chem. Soc. Qu. J. viii. 107. 3e 4 748 STRONTIUM. The same mode of precipitation serves to separate strontia from the alkalies. The separation of strontia from baryta is best effected by means of hydrofluosilicic acid, which precipitates barium in the form of a crystalline silicofluoride, leaving the strontium in solution. The precipitate must be left to settle down for two or three hours ; and its deposition may be accelerated by a gentle heat. It may then be collected on a weighed filter, washed with water, and dried at 100° C. The filtrate con- taining the strontium is then mixed with sulphuric acid, evaporated, and ignited, whereby it is converted into sulphate. The quantities of barium and strontium in a mixture may likewise be determined by an indirect method, viz. by weigh- ing them, first in the form of chlorides or carbonates, and afterwards as sulphates. Thus, suppose them to be first precipitated as carbonates, the united weight of which is found to be w, then converted into sulphates, the weight of which is w\ Then, to determine the quantity of baryta, x, and strontium, ?/, in the mixture, we have the equations BaC SrC BaS SrS Ba Sr Ba Sr 98-7 73-7 116-7 91-7 or, j^x ^-j^^^y^iv; -^^^ x + ^i:^y=io'. A similar method may be applied in all cases in which two substances in a mixture can be weighed in two distinct forms. Such methods, however, give exact results only when the quantities of the substances to be determined are not very unequal. CALCIUM. 749 CALCIUM. Preparation, — A mixture of 2 at. chloride of calcium and 1 at. chloride of strontium, with a small quantity of chloride of ammonium (this mixture being more fusible than chloride of cal- cium alone), is melted in a small porcelain crucible, in which a carbon positive pole is placed, while a thin harpsichord wire wound round a thicker one, and dipping only just below the sur- face of the melted salt, forms the negative pole. The calcium is then reduced in beads, which hang on to the fine wire, and may be separated by withdrawing the negative pole every two or three minutes, together with the small crust which forms round it. A surer method, however of obtaining the metal, though in very small beads, is to place a pointed iron wire so as merely to touch the surface of the liquid ; the great heat evolved, owing to the resistance of the current, causes the reduced metal to fuse and drop off from the point of the wire, and the bead is taken out of the liquid with a small iron spatula. Or, thirdly, the disposition of the apparatus may be the same as that for the reduction of strontium (p. 746). Properties. — Calcium is a light yellow metal, of the colour of gold alloyed with silver ; on a freshly cut surface, the lustre somewhat diminishes the yellow colour, which becomes more apparent when the light is reflected several times from two surfaces of calcium, or when the surface is slightly oxidised. It is about as hard as gold, very ductile, and may be cut, filed, or hammered out into plates having the thickness of the finest paper. Its specific gravity is 1*5778. In dry air the metal retains its colour and lustre for a few days, but in damp air the whole mass is slowly oxidised. Heated on platinum-foil over a spirit-lamp, it burns with a very bright flash. It is not quickly acted upon by dry chlorine at ordi- nary temperatures ; but when heated, burns in that gas with 750 CALCIUM. a most brilliant light ; also in iodine, bromine, oxygen, sul- phur, &c. With phosphorus, it combines without ignition, forming phosphide of calcium. Heated mercury dissolves it as a white amalgam. Calcium rapidly decomposes water, and is still more rapidly acted on by dilute nitric, hydro- chloric, and sulphuric acids, nitric acid often causing ignition. Strong nitric acid does not act upon it below the boiling heat. In the voltaic circuit, with water as the liquid element, cal- cium is negative to potassium and sodium, but positive to magnesium. It is not, however reduced by potassium or sodium from its chloride by electrolysis. On the contrary, a fused mixture of CaCl with KCl or NaCl, in certain pro- portions, yields potassium or sodium, when subjected in a cer- tain manner to electric action (p. 730) ; hence it appears that the metal formerly obtained by reducing chloride of calcium with potassium or sodium, could not be calcium, but was, probably, a mixture of potassium or sodium with aluminium, silicon, &c. (Matthiessen.*) Lime, — According to Wittsteinf, 1 part by weight of lime dissolves in 729 to 723 pts. of water, at ordinary temperatures, and in 1310 to 1569 pts. of boiling water. The carbonate of lime deposited from lime-water on exposure to the air is really the neutral carbonate, CaO . COg. Marchand and Scheerer find that calcspar begins to give off carbonic acid at 200° C, but that a certain quantity of that acid remains with the lime, even after the most violent ignition.J Sulphate of Lime dissolves in water containing sal-ammo- niac more abundantly than in pure water, part of it appearing to be decomposed into chloride of calcium and sulphate of ammonia. The presence of nitrate of potash likewise in- cceases the solubility of gypsum. (A. Yogel, jun.§) * Chem. Soc. Qu. J. viii. 28. f Repert. Pharm. [3], i. 182. X J. pr. Chem. 1. 237. § Repert. Pharm. [3], v. 342. ESTIMATION OF CALCIUM. 751 Sulphate of Lime and Potash, KO . SO3 + CaO . SO3 + HO. — This salt is obtained as an accessory product in the manufac- ture of tartaric acid from cream of tartar. The latter salt is converted, bj treatment with carbonate of lime, into tartrate of lime and neutral tartrate of potash ; and by the action of sul- phate of lime, all the tartaric acid is obtained in combination with lime, together with an impure solution of sulphate of potash. This solution, when evaporated, yields a hard depo- sit, and in slowly evaporating large quantities of it, transparent laminated crystals are obtained, having the composition ex- pressed by the above formula ; they are sparingly soluble in water, more easily in dilute hydrochloric acid. The non- crystalline deposit contains about Q5 per cent, of this double salt, together with sulphate, carbonate, and phosphate of lime, carbonate of magnesia, silicate of potash, oxide of iron, alumina, water, and traces of organic matter. (J. A. Phillips.*) Phosphate of Lime. — According to H. Ludwigf, the preci- tate produced by ordinary phosphate of soda in a solution of chloride of calcium mixed with ammonia, has, after washing and drying in the air, the composition 3CaO . PO5 + 5|-H0 ; after keeping for two years in a loosely stoppered bottle, it is reduced to 3CaO . PO5 + S^-HO, and of these 3iH0, 2\ go off below 100°. The precipitate was free from chlorine, but contained a trace of ammonia. According to Forchhammerij:, apatite may be artificially crystallised by fusing tribasic phosphate of lime, or bone-ash, with four times its weight of chloride of sodium, and leaving the fused mass to cool slowly. The mass when cold exhibits cavities containing numerous delicate six-sided prisms, having the composition of apatite. Estimation of Calcium. — The metal may be estimated either as carbonate or as sulphate. The best method of precipitating * Chem. Soc. Qti. J. iii. 348. f Pharm. Centr. 1852, 345. X Pogg. Ann. xci. 588. 752 CALCIUM. it is, in most cases, by means of oxalate of ammonia, the oxalate being the least soluble of all the salts of calcium. If the solution contains an excess of any strong acid, such as nitric or hydrochloric acid, it must be neutralised with am- monia before adding the oxalate of ammonia, because oxalate of lime is soluble in the stronger acids. The precipitate, after being washed with hot water and dried, is heated over a lamp, care being taken not to allow the heat to rise above redress. It is thereby converted into carbonate of lime, con- taining 40-15 p. c. of calcium and 56-12 of lime. If, however, the solution contains any acid which forms with lime a compound insoluble in water, phosphoric or boracic acid for example, this method of precipitation cannot be adopted ; because, on neutralising with ammonia, the lime would be precipitated in combination with that acid, and would not be converted into oxalate on addition of oxalate of ammonia. In such a case, the lime may be precipitated as sulphate by adding pure dilute sulphuric acid and alcohol. The sulphate, when dried, contains 41*25 per cent, of lime. Phosphate of lime may, however, be precipitated from its acid solutions by oxalate of ammonia, with addition of acetate of ammonia, because oxalate of lime is insoluble in acetic acid, which dissolves the phosphate with facility. From the alJcalies, lime is easily separated eitlier by oxalate of ammonia, or by sulphuric acid and alcohol. Lime is separated from baryta by precipitating both the earths as carbonates, dissolving the carbonates in nitric acid, evaporating to dryness, and digesting the residue in absolute alcohol, which dissolves nitrate of lime, but not nitrate of baryta. They may also be separated in this manner in the form of chlorides, but the separation is less complete, because chloride of barium is not quite insoluble in absolute alcohol. From strontia, lime is separated in the same manner, nitrate of strontia being likewise insoluble in alsolute alcohol. When baryta, strontia, and lime occur together, the baryta MAGNESIUM. 753 is first separated by hydro-fluosilicic acid ; the strontia and lime in the filtrate are then converted into sulphates ; these sulphates, after being weighed, converted into carbonates by fusion vidth carbonate of soda, or by boiling with the aqueous solution of that salt (p. 598); the carbonates weighed; and the quantities of strontia and lime determined from the equations : 91-7 51-7^ + 68 28 y = w 73-7 51-7 "^ + 50 28 y = w'; in which x is the weight of strontia, y that of the lime, w that of the sulphates, and w^ that of the carbonates of the two bases. Or the carbonates may be dissolved in nitric acid, and the nitrates separated by absolute alcohol. MAGNESIUM. Bunsen prepares this metal by the electrolysis of the fused chloride. A porcelain crucible is divided in its upper part into two halves by a vertical diaphragm (made out of a thin porcelain crucible-cover), and fitted with a cover (filed from a tile), through which the extremities of the carbon-poles of a galvanic battery are introduced into the two halves of the crucible. The crucible is then heated to redness, together with the cover and the poles ; filled with fused chloride of magnesium (I. 595) ; and subjected to the action of a battery of 10 zinc-carbon elements. The negative pole is cut like a saw, so that the magnesium, as it separates, may lodge in the cavities, and not float on the surface of the specifically heavier liquid.* According to Matthiessen f, the metal may be much more easily obtained from a fused mixture of 4 at. chloride of magnesium and 3 at. chloride of potassium, which is pre- * Ann. Ch. Pharm. 82, 137. f Chem. Soc. Qu. J. viii. 107. 754 MAGNESIUM. pared with more facility than the pure anhyorous chloride of magnesium. The two salts mixed in the proper proportions* with a little chloride of ammonium may be fused and elec- trolysed in Bunsen's apparatus just described, the cutting of the negative pole being, however, dispensed with, as the metal is heavier than the fused mixture. A very simple and convenient way of reducing the metal, especially for the lecture-table, is to fuse the mixture in a common clay tobacco- pipe over an argand spirit-lamp or gas-burner, the negative pole being an iron wire passed up the pipe-stem, and the positive a piece of gas-coke, just touching the surface of the fused chlorides. (Matthiessen.) Magnesium may, however, be obtained in much larger quantity, by heating a mixture of 600 grammes of chloride of magnesium, 100 grms. fused chloride of sodium, and 100 grms. of pulverised fluoride of calcium, with 100 grms. of sodium, to bright redness, in a covered earthen crucible. The magnesium is thereby obtained in globules, which are after- wards heated nearly to whiteness in a boat of compact char- coal placed within an inclined tube of the same material, through which a stream of dry hydrogen is passed. The magnesium then volatilises and condenses in the upper part of the tube. Lastly, it is remelted with a flux composed of chloride of magnesium, chloride of sodium, and fluoride of calcium, and is thus obtained in large globules. (H. Deville and Caron.f) Magnesium on the recently fractured surface is sometimes slightly crystalline and coarsely laminated ; sometimes fine- grained. In the former cases it is silver- white and shining ; in the latter, bluish grey and dull. Its specific gravity is 1-7430 at H- 5° C. (Bunsen); 1-75, according to Deville and Caron. It is about as hard as calcspar, and may be easily filed, bored, sawn, and flattened to a certain extent, but is scarcely more duc- * The solution of the chloride of magiiesium mny be evjiporated almost to dryness and analysed to find the pioportiun of anhydrous salt present. t Ann. Ch. Pharm. ci. 359. ESTIMATION OF MAGNESIUM. 755 tile than zinc at ordinary temperatures. It melts at a moderate red heat (Bunsen) ; melts and volatilises at about the same tem- perature as zinc (Deville and Caron). It does not alter in a dry atmosphere, but in damp air soon becomes covered with a film of hydrate of magnesia. Heated to redness in the air, or in oxygen gas, it burns with a dazzling white light, and forms magnesia. It decomposes pure cold water but slowly, acidulated water very quickly ; when thrown on aqueous hydrochloric acid, it takes fire momentarily ; strong sulphuric acid dissolves it but slowly ; a mixture of sulphuric acid and fuming nitric acid does not act upon it at ordinary temper- atures. It burns when heated in chlorine gas ; also in bromine-vapour, though with less facility ; in sulphur and iodine- vapour very brilliantly (Bunsen). Estimation of Magnesium. — When magnesia occurs in a solution not containing any other fixed substance, its quantity may be determined by evaporating to dryness, igniting the residue, then moistening it with sulphuric acid slightly diluted with water, and expelling the excess of that acid at a low red heat ; sulphate of magnesia then remains, containing 33*7 per cent, of magnesia. If the solution contains other fixed substances, the magnesia must be precipitated by the addition of ammonia in excess and phosphate of soda. The precipitated ammoniomagnesian phosphate is then treated in the manner described at p. 700, The pyrophosphate of magnesia obtained by igniting it contains 36 33 per cent, of magnesia. From baryta and strontia, magnesia is separated by sulphuric acid ; from lime, by oxalate of ammonia, with addition of chlo- ride of ammonium to prevent the precipitation of the magnesia. From the alkalies, magnesia may be separated by con- verting the bases into sulphates, and adding baryta-water. The magnesia is then precipitated in the form of hydrate, together with sulphate of baryta. The precipitate, after washing, is digested with dilute sulphuric acid, which extracts 756 ALUMINIUM. the magnesia in the form of sulphate ; and the filtrate con- taining the alkalies together with the excess of baryta, is also treated with sulphuric acid, which precipitates the baryta, and converts the alkalies into sulphates. ALUMINIUM OR ALUMINUM. Preparation, — This metal is now obtained in considerable quantity by decomposing the chloride or fluoride with sodium. The chloride of aluminium is prepared on the large scale by passing chlorine over a previously ignited mixture of clay and coal-tar in retorts like those used in the preparation of coal- gas, and is either made to pass into a chamber lined with plates of earthenware, where it condenses into a compact crystalline mass ; or the vapour is made to pass over chloride of sodium at a red heat, whereby it is converted into the double chloride of aluminium and sodium. To effect the reduction, 400 pts. of this double salt, 200 pts. of chloride of sodium, 200 pts. of fluor-spar (or better, of cryolite), all per- fectly dry and finely pounded, are mixed together, and the mixture placed, together with 75 or 80 parts of sodium, in an earthern crucible, the saline mixture and the sodium being deposited in alternate layers. The crucible is then moderately heated till the action begins, afterwards to redness, the melted mass stirred with an earthenware rod, and afterwards poured out. Twenty parts of aluminium are thus obtained in a com- pact lump, and about 5 parts in globules encrusted with a grey mass. (H. Ste-Claire Deville.*) Aluminium may also be prepared in a similar manner from cryolite, the native fluoride of aluminium and sodium which is now imported in large quantities from Greenland. (H. Rose.f) Instead of this natural mineral, an artificial cry- • Ann. Ch. Phys. [3], xlvi. 415 ; see also Compt. rend, xxxviii. 279 ; xl. 1298. t ^^SS' Ann. xcvi. 152. ALUMINIUM. 757 blite may be used, jrepared by mixing 1 part of burnt clay with 3 parts, or rather more, of anhydrous carbonate of soda, supersaturating the mixture with hydrofluoric acid, then dry- ing and fusing it at a red heat. A fluoride of aluminium and potassium possessing analogous properties may be prepared by a similar process. (Deville.*) Aluminium may likewise be obtained by the electrolysis of the double chloride of aluminium and sodium, the process being similar to that adopted by Bunsen for the electrolysis of chloride of magnesium. (Deville, Bunsen.) Pure aluminium is a white metal, with a faint bluish irides- cence ; when recently fused, it is soft like pure silver, and has a density of 2*56 ; but after hammering or rolling, it is as hard as iron, and has a density of 2*67. A bar of it is very sonorous. It conducts electricity eight times as well as iron, and ia slightly magnetic. Its melting point is between those of zinc and silver: when solidified from fusion, or reduced by electro- lysis, it exhibits crystalline forms, apparently regular octo- hedrons. It does not oxidise in the air, even at a strong red heat ; neither does it decompose water, excepting at the strongest red heat, — and even then but slowly. It does not dissolve in nitric acid, either dilute or concentrated, at ordinary temperatures, and but very slowly in boiling nitric acid ; dilute sulphuric acid scarcely attacks it at ordinary temperatures, even after a long time ; but hydrochloric acid, at any degree of concentration, dissolves it readily, even at low temperatures, with evolution of hydrogen. It is not attacked by hydrosul- phuric acid, or by the fused hydrates of the alkalies. It does not combine with mercury, and when fused with lead, takes up only traces of that metal. With copper it unites in various proportions, forming light, very hard, white alloys, and it combines also with silver and iron. (Deville.) * Ann. Ch. Phys. [3], xlix. 83. VOL. IL 3 F 758 ALUMINIUM. Alumina. — The specific gravity of alumina ignited over a spirit-lamp is from 3*87 to 3*90 ; after 6 hours' ignition in an air-furnace, 3*75 to 3*725 ; and after ignition in a porcelain furnace, 3 999, which agrees very nearly with that of naturally crystallised alumina as it occurs in the ruby, sapphire, and corundum. (H. Rose.*) Bihydrate of Alumina, soluble in ivater, Alfi^ + 2 HO. When a dilute solution of biacetate of alumina (see page 760), is exposed to heat for several days, the whole of the acetic acid appears to become free, and the alumina passes into an allotropic state in which it is soluble in water, and is no longer capable of acting as a mordant, or of entering into any definite combination. This allotropic alumina retains 2 at. water when dried at 100° C. Its solution is coagulated by mineral acids and by most vegetable acids, by alkalies, by a great number of neutral salts, and by decoctions of dye- woods. It is insoluble in the stronger acids, but soluble in acetic acid, unless it has been previously coagulated in the manner just mentioned. Boiling potash changes it into the ordinary terhydrate. Its coagulum with dye-woods has the colour of the infusion, but is translucent, and entirely different from the dense opaque cakes which ordinary alumina forms with the same colouring matters. (Walter Crum.f) According to Phillips J, hydrate of alumina when kept after precipitation in a moist atmosphere or under water, becomes after a few days difficult to dissolve in acids. Alum, — By fusing ignited alumina with four times its weight of bisulphate of potash, a mass is obtained, which when treated with warm water, leaves an insoluble residue, consisting of thin microscopic six-sided tables, which refract light singly. They contain 23 per cent, potash, 30*7 sulphu- ric acid, and 46*3 alumina, and appear to consist of crystallised anhydrous alum. (Salm-Horstmar.§) * Pogg. Ann. Ixxiv, 430. f Chcm. Soc. Qu. J. vii. 225. t Chcm. Gaz. 1848, 319. § J. pr. Clioni. lii. 319. II Sill. Am. J. [2], ix. 30. ACETATES OF ALUMINA. 759 Nitrate of Alumina, — According to Ordway||, a concen- trated and somewhat acid solution of alumina in nitric acid, de- posits colourless, flattened, oblique rhombic prisms, containing AI2O3.3NO5 4 18H0. These crystals melt at 72-8'' C. into a colourless liquid which solidifies in the crystalline form on cooling ; they are deliquescent, and dissolve in water and in nitric acid. Half an ounce of the pulverised crystals mixed with an equal weight of bicarbonate of ammonia, lowered the temperature from 10*5'' to — 23*3° C. By the action of this salt upon hydrate of alumina, basic salts appear to be formed. Salm-Horstmar*, by evaporating and cooling a solution of hydrate of alumina in nitric acid of 26*3 per cent, likewise obtained a salt which crystallised in rhombic prisms and (by truncation) in hexagonal tables ; but after repeated solution in water, it no longer crystallised distinctly ; and its aqueous solution was decomposed by evaporation at a somewhat ele- vated temperature. Acetates of Alumina. — By decomposing tersulphate of alumina (I., p. 605), with neutral acetate of lead, a solution is formed, consisting apparently of a mixture of biacetate of alumina with 1 at. free acetic acid. When this aluminous solution is evaporated at a low tem- perature and with sufficient rapidity, — as by spreading the concentrated solution very thinly over sheets of glass or porce- lain, exposing it to a temperature not exceeding 100° F., and, as it runs together in drops, rubbing it constantly with a platinum or silver spatula, — a dry substance is obtained which may be redissolved easily and entirely by water. This is the biacetate of alumina, AlgOg . 2C4H3O3 + 4HO : the alumina contained in it retains all its usual properties. When the first aluminous solution, containing not less than 4 or 5 per cent, of alumina, is left for some days in the cold, a salt is deposited in the form of a white crust, which is an allotropic biacetate of alumina insoluble in water. Heat effects * J. pr. Chem. Hx. 208. 3f 2 760 ALUMINIUM. the same change in the aluminous solution more rapidly, and the insoluble biacetate then separates in the form of a granular powder. At the boiling temperature, the liquid is thus de- prived, in half an hour, of the whole of its alumina, which goes down with | of the acetic acid, leaving ^ in tlie liquid. The soluble biacetate of alumina is decomposed by heat, yielding the bihydrate of alumina soluble in water already described (p. 758). The insoluble biacetate of alumina, when digested in a large quantity of water, is gradually changed into the soluble biacetate, part of which, however, is decom- posed during the process into acetic acid and the allotropic bihydrate of alumina. The precipitate which is formed on the application of heat to a mixed solution of acetate of alumina and sulphate of potash, and which is soluble in cold acetic acid, is a bibasic sulphate of alumina, 2AI2O3 . SO3 -f- lOHO. Common salt added to a solution of teracetate of alumina forms, on the application of heat, a very finely divided white precipitate containing 44*66 per cent, alumina, 21*96 acetic acid, 5*51 hydrochloric acid, 25*90 water, and 1-97 chloride of sodium. A similar precipitate is formed by nitrate of potash (Walter Crum.*) Estimation of Alumina, — Alumina is precipitated from its solutions in the form of hydrate by ammonia, carbonate of ammonia, or sulphide of ammonium; the precipitate when ignited yields pure anhydrous alumina, containing 53*26 per cent, of the metal. Precipitation with ammonia or sulphide of ammonium serves also to separate alumina from the preceding bases. In thus separating it from the alkaline earths, care must be taken not to expose the liquid to the air ; otherwise carbonic acid will be absorbed by the excess of ammonia, and the alkaline earths precipitated as carbonates. From baryta, alumina is most readily separated by sulphuric acid. * Chcm. Soc. Qu. J. vii. 217. GLUCINUM. 761 GLUCINUM. This metal and its compounds have been minutely ex- amined by Debray.* The metal may be obtained from the chloride by reduction with sodium. It is a white metal, whose density is 2*1. It may be^ forged, and rolled into sheets like gold. Its melting-point is below that of silver. It may be melted in the outer blowpipe-flame, without ex- hibiting the phenomenon of ignition presented by zinc and iron under the same circumstances ; it cannot even be set on fire in an atmosphere of pure oxygen, but in both experiments becomes covered with a thin coat of oxide, which seems to protect it from further change. It does not appear to com- bine with sulphur under any circumstances, but unites directly with chlorine and iodine with the aid of heat. Silicon unites readily with glucinum, forming a hard brittle substance sus- ceptible of a high polish ; this alloy is always formed when glucinum is reduced in porcelain vessels. Glucinum does not decompose water at a boiling heat, or even when heated to whiteness. Sulphuric and hydrochloric acid dissolve it, with evolution of hydrogen. Nitric acid, even when concentrated, does not act upon it at ordinary temperatures, and dissolves it but slowly at a boiling heat. Glucinum is not attacked by ammonia, but dissolves readily in caustic potash. I'he above-mentioned properties differ considerably from those of the metal which Wohler obtained by igniting chloride of glucinum with potassium in a platinum crucible ; the metal thus obtained being a grey powder, very refractory in the fire, but combining with oxygen, sulphur, and chlorine much more energetically than Debray's metal. The differences appear to be due, partly to the different states of aggregation, and partly to the contamination of Wohler's metal with platinum and potassium. * Ann. Ch. Tliys. [3], xliv. 5. 3 F 3 762 GLUCINUM. Glucina. — Debray prepares this earth from the emerald of Limoges by the following process. The mineral, finely pounded (levigation with water is quite superfluous), is fused with half its weight of quicklime in an air-furnace, and the glass thus obtained is treated, first with dilute, and then with strong nitric acid, till it is reduced to a homogeneous jelly. The product is then evaporated to dryness, and heated suffi- ciently to decompose the nitrates of alumina, glucina, and iron, and a small portion of the nitrate of lime; and the residue, consisting of silica, alumina, glucina, sesquioxide of iron, nitrate of lime, and a small quantity of free lime, is boiled with water containing sal-ammoniac, which dissolves the nitrate of lime immediately, and the free lime after a while, with evolution of ammonia. (If no ammonia is evolved, the calcination has not been carried far enough and must be repeated.) The liquid is then decanted ; the precipitate, after thorough washing, treated with boiling nitric acid ; and the resulting solution of alumina, glucina, and iron poured into a solution of carbonate of ammonia mixed with free ammonia. The earths are thereby precipitated without evolution of car- bonic acid, and the glucina redissolves, after seven or eight days, in the excess of carbonate of ammonia. As the car- bonate of ammonia may also dissolve a small quantity of iron, it should be mixed with a little sulphide of ammonium to precipitate the iron completely. Lastly, the carbonate of ammonia is distilled off, and the carbonate of glucina which remains yields pure glucina by calcination. Glucina is not hardened by heat like alumina, but merely rendered less soluble in acids. Ebelmen has obtained it in hexagonal prisms by exposing a solution of glucina in fused boracic acid to a powerful and long-continued heat. It may be more easily obtained in microscopic crystals, apparently of the same form, by decomposing the sulphate at a high tem- perature in presence of sulphate of potash, also by calcining the double carbonate of glucina and ammonia. GLUCINA. 763 Hydrate of glucina dissolves in potash like alumina, but is reprecipitated bj boiling when the solution is diluted with water to a certain extent. It is likewise soluble in carbonate of potash or soda, sulphurous acid, and bisulphite of ammonia. When precipitated by ammonia, especially from the oxalate or acetate, it is completely redissolved by prolonged ebullition. Glucina was regarded by Berzelius as a sesquioxide, GlgOj, while Awdejew and others regard it as a protoxide, GIO. The latter formula appears preferable, first because it gives more simple formulaB for the salts of glucina than the former, and secondly, because glucina, on the whole, exhibits a closer re- semblance to known protoxides, such as magnesia, than to sesquioxides, such as alumina. The greater simplicity of the formulaB derived from the formula GIO, will be seen from the following table : Neutral sulphate of glucina . • { or Glfd3^s63 +?2H0. Sulphate of glucina and potash . { or f(KO ^f^G^^^^^^^ Carbonate of glucina and am-f 3(NH40.C02) + 4G10.3C02 + H0 mouia \or9(NH40.C02)+4Gl203.9C02 + 3HO. Oxalate of glucina and potash .{^^ ^(KO^So'lffG&'^^SC^^^^ The reasons which induced Berzelius to regard glucina as a sesquioxide, were founded on the resemblance of glucina and alumina in the hydrated state, from the volatility of the chlorides, and from the supposed capability of glucina and alumina to replace one another in minerals, as in cymophane and in emerald. This last point has been completely settled by the researches of Awdejew and of Damour, from which it appears that cymophane, the native aluminate of glucina, has always the same composition (GlO.AlgOg), from whatever locality it may be derived. With regard to the hydrates, it is true that alumina and glucina are precipitated under the same circumstances ; but there the resemblance ends. Glu- cina, when dried in the air, absorbs carbonic acid and forms a 3 F 4 764 GLUCINUM. carbonate, which alumina does not. The existence of a defi- nitely crystallised carbonate of ammonia and glucina (obtained by boiling a solution of glucina in carbonate of ammonia, stop- ping the ebullition as soon as turbidity appears, then filtering, and adding alcohol) constitutes another important difference between that earth and alumina. The anhydrous oxides likewise differ essentially. Glucina volatilises, like magnesia, without melting, whereas alumina fuses under the same cir- cumstances. Glucina cannot be fused with lime, like alu- mina, the presence of another body, such as silica or alumina, being required to enable the fusion to take place. In this respect again glucina resembles magnesia. The identity of crystalline form which has been observed between glucina and alumina is merely an isolated fact, which would be im- portant if the two bodies possessed similar chemical properties, but not otherwise. Chloride of glucinum exhibits at first sight considerable resemblance to chloride of aluminium, and is prepared in a similar manner ; but the resemblance does not go far. Chlo- ride of glucinum is less volatile than chloride of aluminium : thus, when a mixture of finely powdered emerald and char- coal, made into a paste with oil, is calcined in a crucible, then powdered, and heated in a porcelain tube through which chlorine gas is passed, chloride of glucinum and chloride of aluminium are formed together ; but the chloride of glucinum passes over first, and may be separately condensed. Chloride of glucinum is, in fact, about as volatile as chloride of zinc. Chloride of aluminium unites with the alkaline chlorides, forming compounds which may be called spinelles, and are re- presented by the general formula MCI + AlgClg ; but chloride of glucinum does not form any similar compound. It must, however, be remembered that glucina does not exhibit any very close analogy to the class of protoxides. It is not isomorphous with lime or magiiesia. Cymo[)hanc may be represented by the general formula of the spinelles, SILICON AND HYDROGEN, 765 GIO . AI2O3 ; but the dissimilarity of its crystalline form prevents it from being included in that class of minerals. The emerald also differs completely in crystalline form from the generality of silicates of the same composition, whose general formula is MO. SiOg + M/Og. SSiOg. Neither is there any greater analogy between the double sulphates, carbonates, and oxalates of glucina and those of lime or mag- nesia. On the whole, glucina appears to be intermediate in its properties between the protoxides and sesquioxides. Glucina is precipitated from its solutions for quantitative analysis in the same manner as alumina. From the latter it is separated by carbonate of ammonia. Note to Page 675. Chloride of Silicon and Hydrogen, Si2Cl8 . 2HC1. — This is the compound which Wohler and Buff obtained by heating crystalline silicon in a current of dry hydrochloric acid gas. It is a colourless, very mobile liquid, of sp. gr. 1*65, and boiling at 42° C. It has a very pungent odour, and fumes strongly in the air. Its vapour is as inflammable as ether- vapour, and burns with a faint greenish flame, diffusing vapours of silica and hydrochloric acid. When passed through a red-hot tube, it is decomposed, yielding hydro- chloric acid, terchloride of silicon, and a specular deposit of amorphous silicon. The compound is decomposed by water with formation of a corresponding oxide. The compounds SigBrg . 2HBr, and Sijg. 2HI, are obtained in a similar manner. The former is liquid, the latter solid, at ordinary temperatures. Ilydrated Oxide of Silicon, — 81203. 2H0, is formed by 766 NOTE. the action of water on either of the preceding compounds, but most easily from the chloride. It is a snow-white amor- phous, very bulky powder, which floats on water. It is in- soluble in all acids except hydrofluoric acid. Alkalies, even ammonia, dissolve it readily, with evolution of hydrogen and formation of an alkaline silicate. It may be heated to 300° C. without alteration ; but at higher temperatures, it glows brightly, and gives off* sponta- neously inflammable hydrogen gas (containing siliciuretted hydrogen). A lower oxide of silicon (SiO ?) and the corresponding chloride appear also to exist.* * Ann. Ch. Pharm., Oct. 1857, p. 94. 76 r TABLE A. FOR CONVERTING FRENCH DECIMAL MEASURES AND WEIGHTS INTO ENGLISH MEASURES AND WEIGHTS. 1 Meter 1-0936331 English yards. 3-2808992 „ feet. 39-37079 „ inches. 1 Liter = 0-2209687 Imperial gallons. = 1-7677496 „ pints. = 0-35317 cubic feet. = 61-02710 „ inches. 1 Kilogramme = 0-0196969 cwt. = 2-20606 lb. (avoird.) = 2-68098 lb. (troy). 1 Gramme 15-44242 grains. These values are taken from the " Table of Constants " at the end of the Tables of Logarithms published by the Society for the Diffusion of Useful Knowledge. The Imperial Gallon is equal to 277-24 cubic inches, and contains 10 lbs. avoirdupois of water at 60° Fahr. 768 TABLE B. BABOBIETER SCALE IN MILLIMETERS AND INCHES. Mm. In. Mm. In. Mm. In. 700 = 27-560 730 = 28-741 760 = 29-922 701 = 27-599 731 = 28 780 761 = 29-962 702 = 27-639 732 = 28-820 762 = 30-001 703 = 27-678 733 = 28-859 763 = 30-040 704 = 27-717 734 = 28-899 764 = 30-080 705 = 27-756 735 = 28-938 765 = 30-119 706 = 27-795 736 = 28-977 766 =- 30-159 707 = 27-835 737 = 29-017 767 = 30-198 708 = 27-875 738 = 29-056 768 = 30-237 709 = 27 914 739 = 29-096 769 = 30277 710 = 27-954 740 = 29-135 770 = 30-316 711 = 27-993 741 = 29-174 771 = 30-355 712 = 28-032 742 = 29-214 772 = 30-395 713 = 28-072 743 = 29-253 773 = 30-434 714 = 28-111 744 = 29-292 774 = 30-474 715 = 28-151 745 = 29-332 775 = 30-513 716 = 28-190 746 = 29-371 776 = 30-552 717 = 28-229 747 = 29-411 777 = 30-592 718 = 28-269 748 = 29-450 778 = 30-631 719 = 28-308 749 = 29-489 779 = 30-671 720 = 28-347 750 = 29-529 780 = 30-710 721 = 28-387 751 = 29-568 781 = 30-749 722 = 28-426 752 = 29-607 782 = 30-788 723 = 28-466 753 = 29-647 783 =. 30-828 724 = 28-505 754 = 29-686 784 = 30-867 725 = 28-544 755 = 29-725 785 = 30-907 726 = 28-584 756 = 29-765 786 = 30-946 727 = 28 623 757 = 29-804 787 = 30-985 728 = 28 662 758 = 29-844 788 = 31-025 729 = 28-702 759 = 29-882 789 = 31064 28 inches = 711-187 millimeters. 29 „ = 736-587 „ 30 „ = 761-986 „ 31 „ = 787-386 1 millimeter = 0-03937079 inch. | 1 inch = 25-39954 millimeters. 760 TABLE C. FOR CONVERTING DEGREES OP THE CENTIGRADE THERMOMETER INTO DEGREES OF FAHRENHEIT'S SCALE. Cent Fah. 100° ... - 148-0° 99 ... 146-2 98 ... 144-4 97 ... 142-6 96 ... 140-8 95 ... 1390 94 ... 137-2 93 ... 135-4 92 ... 1336 91 ... 131-8 90 ... 1300 89 ... 128 2 88 ... 126-4 87 ... 124-6 86 ... 122-8 85 ... 121-0 84 ... 119-2 83 ... 117-4 82 ... 115-6 81 ... 113-8 80 ... 1120 79 ... 110-2 78 ... 108-4 77 ... 106-6 76 ... 104-8 75 ... 1030 74 ... 101-2 73 ... 99-4 72 ... 97-6 71 ... 958 70 ... 940 69 ... 92-2 68 ... 90-4 67 ... 88-6 66 ... 86-8 65 ... 850 64 ... 83-2 63 ... 81-4 62 ... 79-6 61 ... 77-8 60 ... 76-0 59 ... 74-2 58 ... 72-4 57 ... 70-6 56 ... 68-8 55 ... 67-0 54 ... 65-2 53 ... 634 52 ... 61-6 51 ... 59-8 Cent. Fah. 50° ... - 58-0° 49 ... 56-2 48 ... 54-4 47 ... 52-6 46 ... 50-8 45 ... 49-0 44 ... 47-2 43 ... 45-4 42 ... 43-6 41 ... 41-8 40 ... 40-0 39 ... 38-2 38 ... 36-4 37 ... 34-6 36 ... 32-8 35 ... 31-0 34 ... 29-2 33 ... 27-4 32 ... 25-6 31 ... 23-8 30 ... 22-0 29 ... 20-2 28 ... 18-4 27 ... 16-6 26 ... 14-8 25 ... 13-0 24 ... 11-2 23 ... 9-4 22 ... 7-6 21 ... 5-8 20 ... 4-0 19 ... 2-2 18 ... 0-4 17 ... + 1-4 16 ... 3-2 15 ... 5-0 14 ... 6-8 13 ... 8-6 12 ... 10-4 11 ... 12-2 10 ... 14-0 9 ... 15-8 8 ... 17-6 7 ... 19-4 6 ... 21-2 5 ... 230 4 ... 24-8 3 ... 266 2 ... 28-4 1 ... 30-2 Cent. Fah. 0^... + 32-0° 1 ... 33-8 2 ... 35-6 a ... 37-4 4 ... 39-2 5 ... 41-0 6 ... 42-8 7 ... 44-6 8 ... 46-4 9 ... 48-2 10 ... 50-0 11 ... 51-8 12 ... 53-6 13 ... 55-4 14 ... 57-2 15 ... 59-0 16 ... 60-8 17 ... 62-6 18 ... 64-4 19 ... 66-2 20 ... 68-0 21 ... 69-8 22 ... 71-6 23 ... 73-4 24 ... 75-2 25 ... 77-0 26 ... 78-8 27 ... 80 6 28 ... 82-4 29 ... 84-2 30 ... 86-0 31 ... 87-8 32 ... 89-6 33 ... 91-4 34 ... 93-2 35 ... 95-0 36 ... 96-8 37 ... 98-6 38 ... 100-4 39 ... 102-2 40 ... 104-0 41 ... 105-8 42 ... 107-6 43 ... 109-4 44 ... 111-2 45 ... 113-0 46 ... 114-8 47 ... 116-6 48 ... 118-4 49 ... 120-2 770 TABLE C— (continued.) Cent. Fah. Cent Fah. Cent. Fall. + 50° .. . + 122-0° + 100° .. . + 212-0° + 150° .. . + 302-0° 51 .. 123-8 101 .. . ■ 213-8 151 .. 303-8 52 .. 125-6 102 .. 215-6 152 .. 305-6 53 .. 127-4 103 .. 217-4 153 .. 307-4 54 .. 129-2 104 .. 219-2 154 .. 309-2 55 .. 131-0 105 .. 2210 155 .. 311-0 56 .. 1328 106 .. 222-8 156 .. 312-8 57 .. 134-6 107 .. 221-6 157 .. 314-6 58 .. 1364 108 ,. 226-4 158 .. 316-4 59 .. 138-2 109 .. 228-2 159 .. 318-2 60 .. 1400 110 .. 230-0 160 .. 330-0 61 .. 141-8 Ill .. 231-8 161 .. 321-8 62 .. 143-6 112 .. 233-6 162 .. 323-6 63 .. 145-4 113 .. 235-4 163 .. 325-4 64 .. 147-2 114 .. 237-2 164 .. 327-2 65 .. 1490 115 .. 239-0 165 .. 329 66 .. 150-8 116 .. 240-8 166 .. 330-8 67 .. 152-6 117 .. 242-6 167 .. 332-6 68 .. 154-4 118 .. 244-4 168 .. 334-4 69 .. 156-2 119 .. 246-2 169 .. 336-2 70 .. 158-0 120 .. 248-0 170 .. 338-0 71 .. 159-8 121 .. 249-8 171 .. 339-8 72 .. 161-6 122 .. 251-6 172 .. 341-6 73 .. 163-4 123 .. 253-4 173 .. 343-4 74 .. 165-2 124 .. 255 2 174 .. 345-2 75 .. 167-0 125 .. 257-0 175 .. 347-0 76 .. 168-8 126 .. 258-8 176 .. 348-8 77 .. 170-6 127 .. 260-6 177 .. 350-6 78 .. 172-4 128 .. 262-4 178 .. 352-4 79 .. 174-2 129 .. 264-2 179 .. 354-2 80 .. 176-0 130 .. 266-0 180 .. 3560 81 .. 177-8 131 .. 267-8 181 .. 357-8 82 .. 179-6 132 .. 269-6 182 .. 359-6 83 .. 181-4 133 .. 271-4 183 .. 361-4 84 .. 183-2 134 .. 273-2 184 .. 363-2 85 .. 185-0 135 .. 275-0 185 .. 365-0 86 .. 186-8 136 .. 276-8 186 .. 366-8 87 .. 188-6 137 .. 278-6 187 .. 368-6 88 .. 190-4 138 .. 280-4 188 .. 370-4 89 .. 192-2 139 .. 282-2 189 .. 3722 90 .. 194-0 140 .. 284-0 190 .. 374-0 91 .. 195-8 141 .. 285-8 191 .. 375-8 92 .. 197-6 142 .. 287-6 192 .. 377-6 93 .. 199-4 143 ,. 289-4 193 .. 379-4 94 .. 201-2 144 .. 291-2 194 .. 381-2 95 .. 203-0 145 .. 293-0 195 .. 383-0 96 .. 204-8 146 .. 294-8 196 .. 384-8 97 .. 206-6 147 .. 296-6 197 .. 386-6 98 .. 208-4 148 .. 298-4 198 .. 388-4 99 .. 210-2 149 .. 300-2 199 .. 390-2 TABLE C- -(continued.) Cent. Fah. Cent. Fah. Cent. Fah. + 200° ... + 392-0° + 250° ... + 482-0° + 300° ... + 572-0° 201 393-8 251 ... 483-8 301 573-8 202 395 6 252 ... 485-6 302 575-6 203 397-4 253 ... 487-4 303 577-4 204 399-2 254 ... 489-2 304 .579-2 205 401-0 255 ... 491-0 305 581-0 206 402-8 256 ... 492-8 306 582-8 207 404-6 257 ... 494-6 307 584-6 208 406-4 258 ... 496-4 308 586-4 209 408-2 259 ... 498-2 309 588-2 210 410-0 260 ... 500-0 310 590-0 211 411-8 261 ... 501-8 311 591-8 212 413-6 262 ... 503-6 312 593-6 213 415-4 263 ... 505-4 313 595-4 214 417-2 264 ... 507-2 314 597-2 215 419-0 265 ... 5090 315 599-0 216 420-8 266 ... 510-8 316 600-8 217 422-6 267 ... 512-6 317 602-6 218 424-4 268 ... 514-4 318 604-4 219 426-2 269 ... 516-2 319 606-2 220 428-0 270 ... 518-0 320 608-0 221 4298 27] ... 519-8 321 609-8 222 431-6 272 ... 521-6 322 611-6 223 433-4 273 ... 523-4 323 613-4 224 435-2 274 ... 525-2 324 615-2 225 437-0 275 ... 527-0 325 617 226 438-8 276 ... 528-8 326 618-8 227 440-6 277 ... 530-6 327 620-6 228 442-4 278 ... 532-4 328 622-4 229 444-2 279 ... 534-2 329 624-2 230 446-0 280 ... 536-0 330 626-0 231 447-8 281 ... 537-8 331 627-8 232 449-6 282 ... 539-6 332 6296 233 451-4 283 ... 541-4 333 631-4 234 453-2 284 ... 543-2 334 633-2 235 455-0 285 ... 545-0 335 635-0 236 456-8 286 ... 546-8 336 '636-8 237 458 6 287 ... 548-6 337 638-6 238 460-4 288 ... 550-4 338 640-4 239 462-2 289 ... 552-2 339 642-2 240 464-0 290 ... 554-0 340 644-0 241 465-8 291 ... 555-8 341 645-8 242 467-6 292 ... 557-6 342 647-6 243 469-4 293 ... 559-4 343 649-4 244 471-2 294 ... 561-2 344 651-2 245 473-0 295 ... 563-0 345 663-0 246 474-8 296 ... 564-8 346 654-8 247 476-6 297 ... 566-6 347 656-6 248 478-4 298 ... 568-4 348 658-4 249 480-2 299 ... 570-2 349 660-2 772 TABLE D. COMPARISON OF TUB DEORKES OF BAUMe's HYDROMETER WITH THE REAL SPECIFIC GRAVITIES. 1. For Liquids heavier than Water. Degrees. Specific Gravity. Degrees. Specific Gravity. Degrees. Specific Gravity. 1-000 26 1-206 52 1-520 1 1-007 27 1-216 53 1-535 2 1-013 28 1-225 54 1-551 3 1-020 29 1-235 55 1-567 4 1-027 30 1-245 56 1-583 5 1-034 31 1-256 57 1-600 6 1-041 32 1-267 58 1-617 7 1048 33 1-277 59 1-634 8 1-056 34 1-288 60 1-652 9 1063 35 1-299 61 1-670 10 1-070 36 1-310 62 1-689 11 1-078 37 1-321 63 • 1-708 12 1-085 38 1-333 64 1-727 13 1-094 39 1-345 65 1-747 14 1-101 40 1-357 66 1-767 15 1-109 41 1-369 67 1-788 16 1118 42 1-381 68 1-809 17 1-126 43 1-395 69 1-831 18 1134 44 1-407 70 1-854 19 1143 45 1-420 71 1-877 20 1-152 46 1-434 72 1-900 21 1-160 47 1-448 73 1-924 22 1169 48 1-462 74 1 949 23 1-178 49 1-476 75 1-974 24 1-188 50 1-490 76 2 000 25 1-197 51 1-495 773 TABLE D. -- (continued). 2. Baumi's Hydrometer for Liquids lighter than Water, Degrees. Specific Gravity. Degrees. Specific Gravity. Degrees. Specific Gravity. 10 1-000 27 0-896 44 0-811 11 0-993. 28 0-890 45. 0-807 12 0-986 29 ' 0-883 46 0-802 13 0-98Q. 30' 0-880,' 47 0-798 14 0-973 31 0-874 48 0-794 15 0-967 32 X 0-869 49 0789 16 0-960 33-^. 34^ 0-864 St) 0-785 17' 0-9 54f 0-859* 61 0-781 1-8 0-948 35. ^ 0-854-*,. 62 ; 0-777 . 19 0-942 36 0-840 5^ 0-773 20 0-93^ 3> 0-844"*- 54 0-7^8 21 0-930 38 0-839. •55 0-764 22 0-924 39, 0-831 66 0-760 23 0-918 40 0-830 57 ^ 0-757 24 0-913 41 0-825 58 0-753 25 0-907 42 0-820 59 0-740.. 26 0-901 43 0-816 60 0-743. Baume's hydrometer is very commonly used on the Continent, especially for liquids heavier than water. In the United Kingdom, Twaddcll's hydrometer is a good deal used for dense liquids. This instrument is so graduated that ihe real specific gravity can be deduced by an extremely simple method from the degree of the hydrometer, namely, by multiplying the latter by 5, and adding 1000 ; the sum is the specific gravity, water being 1000. Thus 10° Twaddell indicates a specific gravity of 1050, or 105 ; 90° Twaddell, 1450, or 1-45. VOL. 11, 3 a 774 TABLE E. SHOWING THE PROPORTION BY WEIGHT OP ABSOLUTE OR REAL ALCOHOL IN 100 PARTS OP SPIRITS OF DIFFERENT SPECIFIC GRAVITIES. (fOWNES.) Sp. Gr. at Percentage of Sp. Gr. at Percentage of Sp. Gr. at Percentage of real Alcohol. 60OF. real Alcohol. GQOF. real Alcohol. 60OF. •9991 0-5 •9511 34 •8769 68 •9981 1 •9490 35 •8745 69 •9965 2 •9470 36 •8721 70 •9947 3 •9452 37 •8696 71 •9930 4 •9434 38 •8672 72 •9914 5 •9416 39 •8649 73 •9898 G •9396 40 •8625 74 •9884 7 •9376 41 •8603 75 •9869 8 •9356 42 •8581 76 •9855 9 •9335 43 •8557 77 •9841 10 •9314 44 •8533 78 •9828 11 •9292 45 •8508 79 •9815 12 •9270 46 •8483 80 •9802 13 •9249 47 •8459 81 •9789 14 •9228 48 •8434 82 •9778 15 •9206 49 •8408 83 •9766 16 •9184 50 •8382 84 •9753 17 •9160 51 •8357 85 •9741 18 •9135 52 •8331 86 •9728 19 •9113 53 •8305 87 •9716 20 •9090 54 •8279 88 •9704 21 •9069 55 •8254 89 •9691 22 •9047 56 •8228 90 •9678 23 •9025 57 •8199 91 •9665 24 •9001 58 •8172 92 •9652 25 •8979 59 •8145 93 •9638 26 •8956 60 •8118 94 •9623 27 •8932 61 •8089 95 •9609 28 •8908 62 •8061 96 •9593 29 •8886 63 •8031 97 •9578 30 •8863 64 •8001 98 •9560 31 •8840 65 •7969 99 •9544 32 •8816 66 •7938 100 •9528 33 •8793 67 INDEX, A. Absolute Expansion of Mercury, ii. 4. Absorption, Coefficients of, ii, 649. of Gases by Liquids, ii, 647. Water, Heat evolved in the, ii. 633, Acetate, Ferrous, ii. 43. Mercurous, ii. 303. Acetates of Alumina, ii. 759. Copper, ii. 105. Lead, ii. 125. Acid, Anhydrous Sulphuric, i. 188. Antimonic, ii. 228. Antimonious, ii. 222. Antitartaric, ii. 478. Arsenic, ii. 207. Arsenious, ii. 203. Azophosphoric, ii. 699. Azoto-sulphuric, i. 412. Bismuthic, ii. 243. Bisul-hyposulphuric, i. 418. Boracic, i. 390 ; ii. 669. Bromic, i. 490. Carbonic, i. 363. Chloric, i. 129, 473. Chlorocarbosulphurous, ii. 705. Chloromethylosulphurous, ii. 705. Chloronitric, i. 479. Chloronitrous, i. 480. Chlorochromic, ii. 169. Chlorosulphuric, i. 410 ; ii. 551, 709. Chlorous, i. 477. Chromic, ii. 163. Cobaltic, ii. 67. Columbic, ii. 289. Columbous, ii. 286. Deutazophosphoric, ii. 699. Ferric, ii. 51. Fluoboric, i. 507. Acid, Fluosilicic, i. 508, Hydriotic, i. 497. Hydrobromic, i. 489, Hydrochloric, i. 464. Hydroferricyanic, ii. 39. Hydroferrocyanic, ii. 49. Hydrofluoric, i. 504. Hydrofluosilicic, i. 509. Hydrotelluric, ii. 200. Hydrosulphuric, i, 419, 445, Hypochloric, i, 478. Hypochlorous, i. 469. Hypoiodic, ii. 712. Hypophosphorous, i. 434. Hyposulphuric, i. 413. Hyposulphurous, i, 115, 415. Iodic, i. 498. Manganic, ii. 18. Mellitic, Croconic, Rhodizonic, L 371. Metaphosphorie, i. 448 ; ii, 693, Metastannic, ii. 138. Methylosulphurous, ii. 706. Molybdic, ii. 187. Monosul-hyposulphuric, i. 417. Nitric, i. 346. Nitroprussic, ii. 55. Nitrosulphuric, i. 411. Nitrous, i. 341. Osmiamic, ii. 404. Osmic, ii. '403. Osmious, ii. 402. Oxalic, i. 372. Oxamic, ii. 740. Penta-iodic, i. 501, Pentathionic, i. 418. Perchloric, i. 115, 475. Perchlorocarbosulphurous, ii. 705. Pei'chromic, ii. 169. Periodic, i. 501. Permanganic, ii. 18. Phosphamic, ii. 697. 3 o 2 776 INDEX. Acid, Phosphoric, i. 438. Phosphoric, Amides of, ii. 695. Phosphorous, i. 434. Pyrophosphamic, ii. 700. Racemic, ii. 477. Radicals, Hydrides of, ii. 565. Ruthenic, ii. 416. Selenic, i. 429. Selenious, i. 428. Silicic, i. 396 ; ii. 677. Stannic, ii. 137. Sulpharaic, ii. 741. Sulphuric, i. 402. Sulphurous, i. 399- Sulphantimonic, ii. 232. Tantalic, ii. 278. Tantalous, ii. 278. Thionamic, ii. 741. Telluric, ii. 198. Tellurous, ii. 196. Tetrathionic, i. 418. Titanic, ii. 147. Trisul-hyposulphuric, i. 418. Trithionic, i. 417. Tungstic, ii. 178. Vanadic, ii. 174. Acids, Action of Ammonia on Anhydrous, ii. 557. Anhydrous, ii. 542. Aromatic, ii. 538. Basicity of, ii. 536. Bibasic, ii. 538. Conjugated, ii. 541. Fatty, Boiling Points of, ii. 584. Fatty, Table of, ii. 538. Heat evolved in the Combination of, with Water, ii. 632. Monobasic, ii. 538. or Negative Oxides, ii. 535. Oxygen, i. 186. Sulphur, ii. 547. Theory of, i. 187. Tartaric and Antitartaric, ii. 478. Tribasic, ii. 540. with Bases, Heat produced by Combination of, ii. 631. AflSnity, Chemical, i. 217 ; ii. 586. of Solution, i. 218. Order of, i. 223. Tables of, i. 224. Air, Analysis of, i. 331. Composition of dry Air by Volume, i. 336. Air, Diffusion of Vapours into, i. 90. Extraction of Oxygen from Atmo- spheric, ii. 638. Researches on the Expansion of, i. 13. Weight of, i. 324. Alcohol, Action of Sulphuric Acid on, ii. 602. Alcoholic Nitrides, Secondary and Ter- tiary, ii. 555. Sulphides, ii. 546. Alcohol-metals, derived from Type HH, ii. 566. Alcohol-radicals, ii. 518, 531. Action of Ammonia on the Bromides and Iodides of, ii. 554. Chlorides of, ii. 548. Cyanides of, ii. 552. Hydrides of, ii. 563. Primary Nitrides of, ii. 563. Alcohols, Biatomic, ii. 532. Boiling Points of, ii. 583. Classification of Primary, ii. 531. Secondary, or Ethers, ii. 534. Triatomic, ii. 533. Aldehyde-radicals, Hydrides of, ii. 564. Nitrides of, ii. 556. Aldehydes, ii. 534. Alkalamides, ii. 561. Alkalies, Estimation of in Silicates, ii. 678. Separation of Magnesia from, 755. Alkalimetry, i. 547. Gay-Lussac's Method of, i. 550. Allotropy, i. 176—180. Alloys of Antimony, ii. 234. Bismuth, ii. 249. Cadmium, ii. 91. Copper, ii. 106. Gold, ii. 358. Lead, ii. 127. Mercury, ii. 324. Nickel, ii 77. Silver, ii. 343. Tin, ii. 143. Zinc, ii. 87. Alum, i. 606 ; ii. 758. Basic, i. 608. Stone, i. 607. Alumina, i. 602; ii. 757. Acetates of, ii. 759. and Potash, Sulphate of, i. 117. Estimation and Separation of, ii. 760. Hydrates of, i. 603 ; ii. 758. Nitrate of, i. 602, 610. Phosphate of, i, 610. Salts of, i. 605. Silicates of, i. 610. Silicates of Lime and of, i. 316. INDEX. 777 Alumina, Sulphate of, i. 605. and Potash, Alum, i. 606. Aluminium, i. 601. Chloride of, i. 604. Fluoride of, i. 605. Preparation of, i. 601 ; ii. 756. Properties of, i. 601 ; ii. 757. Sulphide of, i. 604. Sulphocyanide of, i. 605. Amalgam of Gold, ii. 358. Amalgamation of Silver, ii. 328. of the Zinc Plate of the Voltaic Battery, j. 246. Amalgams, ii. 324. Amides of Phosphoric Acid, ii. 695. Primary, ii. 556. Secondary, ii. 559. Tertiary, ii. 560. Amido-chloride Mercuric, ii. 310. Amidogen- Acids, ii. 542. Salts, ii. 561. and Amides, i. 204, Ammon-compounds, ii. 741. Ammonia, Action of, on Anhydrous Acids, ii. 557. Acid Chlorides, ii. 558. Compound Ethers, ii. 557. Dichloride of Mer- j cury, ii. 299. the Bromides and Io- dides of the Al- cohol-radicals, ii. 554. and Glucina, Carbonate of, ii. 763. Antimoniates of, ii. 231. Aurate of, ii. 351. Chromates of, ii. 166. Estimation of, ii. 384, 741. Molybdate of, ii. 190. Nessler's Test for, ii. 317. Phosphate of, i. 563. Preparation of, i. 353. Properties of, i. 355. Salts of, i. 202, Why is it a Base ? i. 207. Ammoniacal Amalgam, i. 203. Compounds of Iridium, ii. 397. Compounds of Palladium, ii. 388—390. Platinum Salts, ii. 371 — 382. Salts, Decomposition of, i. 205. Ammoniacal Salts of Cobalt, ii. 68. Ammonia-salts, Anhydrous, ii. 741. Ammonia type, ii. 523, 553. Ammonio-Bichloride of Tin, ii. 140. Compounds of Nickel, ii. 77. Nitrate of Silver, ii. 212, 342. Nitrates, Mercuric, ii. 322. Platinic Compounds, ii. 376 — 378. Platinous Compounds, ii. 372 —374. Sulphate of Copper, ii. 212. Ammonium and Bismuth, Terchloride of, ii. 246. Chloride of, ii. 736. Carbonates of, ii. 738. Chloroplatinate of, ii. 370. Nitrate of, ii. 738. Oxalates of, ii. 740. Phosphates of, ii. 739. Sulphate of, ii. 739. Sulphides of. ii. 737. Ammo-platamraonium, Bisalts of, ii. 378 —381. Proto-salts of, ii. 375, 376. Amphigen, or Leucite, i. 612. Amylic Alcohol, active and inactive, ii. 480. Analcime, i. 613. Analysis of Organic Bodies, i. 373 ; ii. 662. Sea- water, i. 319. Silicates, ii. 677. Volumetric, Bunscn's gene- ral Method of, ii. 722 Anhydrides, or Anhydrous Acids, ii. 542. Anhydrous Acids, Action of Ammonia on, ii. 557. Nitric Acid, ii. 652. Sulphuric Acid, Formation of, i. 403 ; ii. 622. Sulphuric Acid, Action of, on the Pentachloride of Phos- phorus, ii. 551, 709. Telluric Acid, ii. 199. Tellurous Acid, ii. 196. Animal Charcoal, i. 361. Anthracite, i. 358. Antidotes to Arsenious Acid, ii. 217. Antimoniate of Antimony, ii. 231. Antimoniates of Lead, ii. 231. Ammonia, ii. 231. Potash, ii. 229. Antiraonic Acid, ii. 228. Oxide, ii. 222. Acid, Action of, on Penta- chloride of Phosphorus, ii. 710. 3 C 3 778 INDEX. Antimonides, ii. 562. Antiraonious Acid, ii. 222. Antimoniuretted Hydrogen, ii. 233. Antimony, Sources and Extraction of, ii. 221. Alloys of, ii. 234. and Arsenic, Separation of, ii. 239. Potash, Oxalate of, ii. 226. Tartrate of, ii. 226. Tin, Separation of, ii. 238. Oxide of, ii. 222. Pentachloride of, ii. 232. Pentasulphide of, ii. 232. Estimation and Separation of, ii. 235. Separation of, from Arsenic and Tin, ii. 236. Sulphate of, ii. 226. Terchloride of, ii. 225. Terfluoride of, ii. 225. Tersulphide of, ii. 223. Antitartaric Acid, ii. 478. Antithetic, or Polar Formula;, i. 204. Aqueous Vapour, Tension of, i. 435. Argentiferous Copper, Liquation of, ii. 328. Aridmm, ii. 59. Arseniate of Cobalt, ii. 65. Didymium,ii. 277. Uranyl, ii. 258. Arsenic and Antimony, Separation of, ii. 239. Hydrogen, ii. 210. Acid, ii. 207. considered Tribasic, i. 208. Chlorides of, ii. 210. Estimation and Separation of, ii. 217. Reduction, Test for, ii. 213. Persulphide of, ii. 209. Separation of, from Antimony and Tin, ii. 236. Sources and Extraction of, ii. 203. Sulphides of, ii. 209. Testing for, ii. 211, Arsenides, ii. 562. Arsenious Acid, ii. 203. Antidotes of, ii, 217. Ash, Analysis of Black, i. 560. Aspartic Acid, active and inactive, ii. 480. Assay of Gold, ii. 361. Silver, ii. 346. Atmosphere, i. 324, 327. Density of the, i. 325. Temperature of the, i. 325. Atomic Motion, ii. 600. Representation of a double De- composition, i. 237. Theory, i. 133. Atomic Volume, dependent upon ra- tional Formula, ii. 580. of Liquids, ii. 569. Solids, i. 209, 210; ii. 582. and Specific Gravity of Elements, i. 211. of Salts, i. 213. Oxides, i. 215. "Weights, Gerhardt's, ii. 513. Relations between the, and Volumes of Bo- dies in the Gaseous State, i. 142—148. Atoms and Equivalents, ii. 509. Specific Heat of, i. 135. Table of Specific Heat of, i. 136. A urate of Potash, ii. 352. Auric Bromide, ii. 356. Chloride, ii. 355. ' Iodide, ii. 357. Oxide, ii. 350. and Soda, Hvposulphite of, ii. 358. Sulphide, ii. 355. Aurosulphite of Potash, ii. 352. Aurous Chloride, ii. 349. Oxide, ii. 349. and Soda, Hyposulphite of, ii. 357. Baryta, ii. 358. Sulphide, ii. 352. Azophosphoric Acid, ii. 699. Azoto sulphuric Acid, i. 412. B. Barilla, i. 562. Barium, i. 575 ; ii. 744. Binoxide of, i. 577 ; ii. 742. Chloride of, i. 577. Class of Elements, i. 169. Decomposition of Peroxide of, by Aqueous Vapour, ii. 638. Estimation and Separation of, ii. 746. Formation of Peroxide of, ii. 638. Protoxide of, i. 575. Baryta and Aurous Oxide, Hyposulphite of, ii. 358. Carbonate of, i. 577; ii. 745. Chromate of, ii. 166. Estimation of, ii. 746. Hydrate of, i. 576. Molybdate of, ii. 191. Nitrate of, i. 578. Sulphate of, i. 578. INDEX. 779 Bases and Acids, Heat developed by Combination of, ii. 631. Nitrile, ii. 555. Proper or Metallic Oxides, ii. 530. Basic Alum, i. 608. Basicity of Acids, ii. 536. Basyl Class of Compound Radicals, i. 186. Battery, Bird's, i. 287. Bunsen's, i. 286. Daniell's, i. 283. Grove's, i. 269, 285. Beilstein's Experiments on Liquid Diffu- sion, ii. 612. Benzoate Ferric, ii. 53. Beryl, or Emerald, i. 617. Beryllia, or Glucina, i. 616. Beryllium, i. 615. Biamides, Primary, or Diamides, ii. 558. Tertiary, ii. 561. Bi-ammonio-platinic Compounds, ii. 378. —381. Bi-ammonio-platinous Compounds, ii. 375, 376. Bibasic Phosphate of Water, i. 441. Salts, i. 193. Biborate of Soda, i.-565. Bicarbonate of Potash, i. 533. and Magnesia, i. 597. Soda, i. 552. Bicarburetted Hydrogen, of Faraday, i. 386. Preparation of, i. 385. Bichloride of Bismuth, ii. ?45. Iridium, ii. 396. Lead, ii. 118. Osmium, ii. 401. Platinum, ii. 369. Tin with Oxychloride of Phosphorus, ii. 142. Tin with Peutachloride of Phosphorus, ii. 141. Titanium, ii. 148. Tin, ii. 140. Tin and Potassium, ii. 142. Tin and Sulphur, ii. 141. Bichromate of Bismuth, ii. 249. Chloride of Potassium, ii. 166. Potash, ii. 165. Bifluoride of Titanium, ii. 149. Bihydrosulphate of Potash, i. 528. Bimcjcurammonium, Chloride of, ii. 312. Nitrate of, ii. 324. Binoxide or Bioxide of Barium, i. 577. Hydrogen, i. 319. Manganese and Hydrochlo- ric Acid, Preparation of Chlorine from, i. 458. Nitrogen, Compound of,with Chlorine, i. 472. Properties of, i, 341. Preparation of, i. 341. Strontium, i. 580. Cobalt, ii. 67. Bismuth, ii. 241. Iridium, ii. 395. * Lead, ii. 115. Manganese, ii. 13, 14. Platinum, ii. 368. Ruthenium, ii. 415. Tin, ii. 136. Vanadium, ii. 173. Bird's Battery and Decomposing Cell, i. 287. Bi-salts of Ammo-platammonium, ii. 378, 381. Platammonium, ii. 376, 378. Bismuth and Ammonium, Terchloride of, ii. 246. Bichloride of, ii. 245, Bichromate of, ii. 249. Bioxide of, 241. Bisulphide of, ii. 244. Carbonate of, ii. 249. Nitrates of, ii. 247. Quadroxide of, ii, 243. Selenide of, ii. 24 i. Sources and extraction of, ii. 239. Subnitrates of, ii. 247. Sulphates of, ii. 247. Terchloride of, ii. 245. Teriodide of, ii. 246. Teroxide of, ii. 242. Tersulphide of, ii. 244. Bismuthic Acid, ii. 243. Bisul-hyposulphuric Acid, i. 418. Bisulphate of Soda, i. 562. Bisulphide of Bismuth, ii. 244. Carbon, i. 425. Action of Chlorine on, ii. 703. Action of Nascent Hydrogen on, ii. '685. decomposed by heating with Water and with Sahs in sealed tubes, ii. 585, 3 G 4 780 INDEX. Bisulphide of Hydrogen, i. 423. Iron, ii. 47. Platinum, ii. 369. Titanium, ii. 148. Tin, ii. 139. Bittern, i. 542. Black Sulphur, ii. 681. Black's Views on Fluidity, i. 43. Bleaching Powder, i. 591. Bodies, Compound, i. 113. Relation between the Atomic Weights and the Volumes of, in the Gaseous State, i. 142. Boilers, Construction of, i. 61, 62. Boiling Point and Chemical Composition, Relations between, ii. 583. Points of Acids, ii. 583. Alcohols, ii. 583. Compound Ethers, ii. 584. Homologous Com- pounds, ii. 585. Table of, i. 52. Boracic Acid, Estimation of, ii. 671. Reactions of, ii. 669. Boracite, i. 600. Borate of Magnesia, i. 599. Borates, i. 391. Borax, i. 565. Borofluoride of Potassium, ii. 671. Boron, Chloride of, i. 484. Allotropic modifications of, ii. 667. Estimation of, ii. 671. Fluoride of, i. 507. Nitride of, ii. 670. its Preparation, Properties, i. 389. Boutigny, Experimeats on the Ebullition of Water, i. 49. Brewster on Light, i. 326. Brix, Experiments of Vaporisation on, i. 56, 57. on the Latent Heat of Vapour of Water, i. 56. Bromic Acid, i. 490. Bromide, Auric, ii. 356. Mercuric, ii. 315. Mercurous, or Dibromide of Mercury, ii. 300. of Alcohol-radicals, Action of Ammonium, ii. 554. Cadmium, ii. 91. Iodine, i. 502. Lead, ii. 119. Nitrogen, ii. 711. Phosphorus, i. 491. Silver, ii. 338. Silicon, i. 491. and Hydrogen, ii. 765. Bromide of Sulphur, i. 490. Tantalum, ii. 284. Titanium, ii. 149. Bromides, ii. 552. Atomic Volume of Liquid, ii. 577. Bromine, Chloride of, i. 490. Preparation of, i. 488. Properties of, i. 489. Separation of from Chlorine, ii. 717. Iodine, ii. 719. Volumetric Estimation of, ii. 724. Bude Light, Gurney's, i. 384. Bunsen, Carbo-zinc Battery, i. 286. Eudiometers, i. 381. Experiments on the Absorption of Gases, ii. 647. Experiments on the influence of Mass on Chemical Action, ii. 587. General Method of Volumetric Analysis, ii. 722. and Roscoe, Measurement of the chemical action of Light, 489. Burette, Description of, i. 551. Bussy, Table of the Efficiency of different Charcoals, i. 361. Cadmium, Alloys of, ii. 92. Chloride, Bromide, Iodide, and Sulphate of, ii. 91. Estimation and Separation of, ii. 92. Oxide, ii. 90. Sources and Extraction of, ii. 98. Sulphide of, ii. 90. Calcium, i. 581, 593. Binoxide, Protosulphide, Phos- phide, Chloride of, i. 584-85. Estimation of, ii. 752. Fluoride of, i. 586. Hydrate of the Binoxide of, i. 584. Preparation and Properties of, ii. 749. Separation of, from Barium and Strontium, ii. 752. Separation of, from Magnesium, and the Alkali-metals, ii. 752, 755. Calomel, Dichloride of Mercury, or Mer- curous Chloride, ii. 298. INDEX. 781 Caloric, i. 1. Calorimeters, ii. 626. Canary-glass, Fluoresence of, ii. 257, 484. Capillary Tabes, i. 15. Carbamide, ii. 558, 741. Oarbides, i. 362. Carbon and Hydrogen, Compounds of, i. 374. Nitrogen, Cyanogen, i. 387. Sulphur, i. 425. Bisulphide of, i. 425; ii. 685, 703. Chlorides of, i. 481. Class of Elements, i.l74. from Wood, i. 360. Estimation of, by Combustion with Oxide of Copper, &c. ii. 662. Hydrogen, and Oxygen, Atomic Volume of Liquids containing, ii. 37. Perchloride of, i. 483. Protochloride of, i. 483. Protosulphide of, ii. 684. Relation between Heat of Com- bustion and Specific Heat of, ii. 629. Solid Sulphide of, i. 427. Specific Heat, and Heat of Com- bustion of Varieties of, i. 139; ii. 629. Subchloride of, i. 483. Sulphides of, i. 425; ii. 684, 685. Sulphite of Perchloride of,ii. 703. Sulphite of Protochloride of, ii. 704. Uses of, i. 363. Volatility of, ii. 656. Carbonate of Baryta, i. 577; ii. 745. Bismuth, ii. 247. Cerous, ii. 265. Chromous, ii. 155. Mercurous, ii. 301. of Cobalt, ii. 63. Copper, ii. 101. Didymium, ii. 275. Glucina, ii. 763. Glucina and Potash, ii. 763. Iron, ii. 41. Lanthanum, ii. 271. Lead, ii. 119. Lime, i. 587. Lithia, i. 574. Magnesia, i. 596. Manganese, ii. 8. Potash, i. 532. Silver, ii. 339. Soda, i. 544. Hydrates of, ii. 732. Carbonate of Soda, Preparation of, from theSulphate, i. 557. Solubility of, ii. 733. Strontia, i. 580. Zinc. ii. 85. Carbonates, i. 368. Decomposition of insoluble, by soluble Sulphates, ii. 597. Decomposition of insolu- ble Salts by Alkaline, ii. 597. of Ammonium, ii. 738. Table of, i. 213. Carbonic Acid, Composition of, i. 366. Estimation of, ii. 663. Preparation of, i. 363. Properties of, i. 364. Uses of, i. 368. Vapour, Tension of, i. 73. Oxide, absorption of by Di- chloride of Copper, ii. 661. Estimation of, ii. 664. Preparation, i. 369. Properties, i. 370. Carburet of Iridium, ii. 397. Carburets or Carbides, i. 362. Cast-iron, ii. 28. Catalysis or Decomposition by contact, i. 233. Cavendish, Experiments on Hydrogen, i. 311. Celsius's Thermometer, i. 18. Ceric Oxide, ii. 264. Cerium, ii. 261. Estimation and Separation of, ii. 267. Metallic, ii. 263. Protochloride of, ii. 265. Protofluoride of, ii. 265. Protosulphide of, ii. 264. Protoxide of, ii. 263. Sesquichloride of, ii. 265. Sesquioxide of, ii. 263. Cerous Carbonate, ii. 265. Oxalate, ii. 265. Oxide, ii. 263. Phosphate, ii. 266. Sulphate, ii. 266. Ceruse, ii. 119. Chalybeate Waters, i. 319. Charcoal, i. 358. Animal, i. 361. as a Disinfectant, ii. 659. Platinised, ii. 660. Chemical Action, Development of Heat by, ii. 625. 782 INDEX. Chemical Action, Influence of Mass on, ii. 586. of Light, Measure- ment of, ii. 489. Chemical Affinity, i. 217; ii. 586. and Magnetic Actions of the Current compared, ii. 499. and Optical Extinction of the Chemical Rays, ii. 495. Composition and Boiling Point, Relations between, ii. 583. Composition and Density, Re- lations between, ii. 669. Compounds, Classification of, ii. 527. Decomposition, Cold produced by, ii. 635. Functions, Classification of Bodies according to their, ii. 528. Nomenclature, i. 117. Notation and Classification, i. 108; ii. 509. Rays, Extinction of, ii. 495. Chlorate of Lead, ii. 124. Potash, i. 537. Chlorates, i. 474. Chloric Acid, i. 473. Composition of, i. 474. Resolution of, into Per- oxide of Chlorine and Hyperchloric Acid, i. 475. Chloride, Auric, ii. 355. Aurous, ii. 349. Chromic, ii. 159. Chromous, ii. 154. Cupric, ii. 101. Cuprous, ii. 97. Ferric, ii. 490. Ferrous, ii. 48. Mercuric, ii. 308. Mercurous, ii. 298. Platinic, ii. 369. Platinous, ii. 367. Stannic, ii. 140. Stannous, ii. 133. Uranous, ii. 254. of Aluminium, i. 604. Ammonium, ii. 736. Barium, i. 577. Bimercurammonium, ii. 312. Boron, i. 484. Bromine, i. 490. Cadmium, ii. 91. Calcium, i. 595. Carbon, i. 431. Cobalt, ii. 62. Didymium, ii. 274. Chloride of Gold, ii. 349. and Potassium, ii. 356. Iodine, i. 502. Lanthanum, ii. 271. Lead, ii. 117. Lime, i. 591. Volumetric Estima- tion of, i. 592; ii. 726. Magnesium, i. 595. Mercurammonium, ii. 312. Mercury with Ammonia, ii. 309. Mercury, Double Salts of, ii. 313. Nickel, ii. 76. Nitrogen, i. 480; ii. 702. Phosphorus, i. 487. Phosphoryl, ii. 551. Potassium, i. 528. Bichromate of, ii. 166. Rhodium and Potassium, ii. 410. Silicon, i. 484. and Hydrogen, ii. 765. Silver, ii. 336. Sodium, i. 542. Strontium, i. 580. Sulphuryl, ii. 550, 709. Tantalum, ii. 283. Tetramercurammonium, ii. 312. Thionyl, ii. 708. Uranyl, ii. 256. and Potassium, ii. 257. Zinc, ii. 84. Chlorides, i. 123, 463; ii. 548. Acid or Negative, ii. 549. Action of Ammoniaon Acid, ii. 558. and Oxides of Osmium, ii. 400. Atomic Volume of Liquid, ii. 577. Basic Metallic, ii. 548. Classification of, ii. 548. of Alcohol-Radicals, ii. 549. Tables for Atomic Volumes of 1st and 2nd Class of, i. 214, 215. of Arsenic, ii. 210. Bibasic Acids, ii. 539. Iridium, ii. 396. Manganese, ii. 7, 12, 21. Palladium, ii. 387, 388. Platinum, ii. 367, 3G9. Tellurium, ii. 200. INDEX. 783 Chlorides of Tribasic Acids, ii. 540. Tungsten, ii. 183. Chlorimetry, i. 592. Chlorine, i. 114, 455. Action of, on Potash, i. 473. and Binoxide of Nitrogen, i. 479. Oxygen, Compounds of, i. 469. Sulphur, i. 485. Class of Elements, i. 171. Estimation of, ii. 716. Heat of Combination of Metals -with, ii. 630. Peroxide of, i. 478. Preparation of, i. 456. Process for, from Hydrochloric Acid and Binoxide of Man- ganese, i. 458. Process for, from Chloride of Sodium, Binoxide of Manga- nese, and Sulphuric Acid, i. 460. Properties of, i. 460. Separation of, from Iodine, ii. 719. Uses of, i. 462. Volumetric Estimation of, ii. 724. Chlorite of Lead, ii. 124. Chlorites, Volumetric Estimation of, ii. 725. Chlorocarbosulpliurous acid, ii. 705. Chlorochromic Acid, ii. 169. ('hloromethylosulphurous Acid, ii. 705. Chloronitric Acid, i. 479. Chloronitrous Acid, i. 480. Chlorophosphate of Lead, ii. 125. Chlorophosphide of Nitrogen, ii. 710. Chloroplatinate of Ammonium, ii. 370. Potassium, ii. 370. Sodium, ii. 370. Chloroplatinite of Po- tassium, ii. 368. Chlorosulphide of Phosphorus, i. 487; ii. 707. Tin, ii. 140. Chlorosulphuric Acid, i. 410; ii. 550, 709. Chlorous x\cid, i. 477. Chloroxicarbonic Gas, i. 484. Chloroxide of Phosphorus, i. ^187. Chromate of Baryta, ii, 166. Lead, ii. 167. Lime, ii. 167. Magnesia, ii. 167. Potash, ii. 165. Silver, ii. 168. Soda, ii. 166. Chromates and Tungstates, Table of, i. 214. Chromates, Compounds of Mercuric Chloride with Alkaline, ii. 31.5. Decomposition of Insolu- ble, by Alkaline Car- bonates, ii. 599. of Ammonia, ii. 1 66. Volumetric Estimation of, ii. 726. Chrome Iron, ii. 162. Chromic Acid, ii. 163. Chloride, ii. 159. Oxide, ii. 155. Salts, Reactions of, ii. 1 56. Sulphate, ii. 159. Chromium and Potassium, Oxalate of, ii. 161. Estimation and Separation of, ii. 1 69. Protochloride of, ii. 154. Protoxide of, ii. 1 53. Sesquichloride of, ii. 159. Sesquioxide of, ii. 155. Sesquisulphide of, ii. 159. Sources and Extraction of, ii. 152. Terfluoride of, ii. 169. Chromoso-chromic Oxide, ii. 155. Chromous Carbonate, ii. 155. Chloride, ii. 154. Oxide, ii. 153. Sulphate, ii. 155. Sulphite, ii. 155. Chrysoberyl, i. 617. Cinnabar, ii. 307. Circular Polarisation, ii. 464. in Organic Bodies, ii. 468. Claudet, Analysis of Black Ash, i. 560. Clay, i. 610, 614. Iron Stone, Smelting of, ii. 25. Classification and Notation, Chemical, ii. 509. of Bodies according to their Chemical Functions, ii. 527. of Elements, i. 168. Coal Gas, i. 378. Henry's Analysis of, i. 880. Cobalt, Ammoniacal Salts of, ii. 68. Arseniate of, ii. 65. Bioxide of, ii. 67. Carbonate of, ii. 63. Estimation and Separation of, ii. 73. Chloride of, ii. 62. Nitrate of, ii. 63. Phosphate of, ii. 65. Phosphide of, ii. 67. Protoxide of, ii. 6L 784 INDEX. Cobalt, Separation of, from Nickel, ii. 78. Sesquicyanide of, ii. 67. Sesquioxide of, ii. 65. Sources and Extraction of, ii. 59. Sulphide of, ii. 67. Cobaltic Acid, ii. 67. Oxide, ii. 65. Cobaltous Oxide, ii. 61. Cobalt-yellow, ii. 63. Coefficients of Diffusion, ii. 612. Gas-absorption, ii. 648. Cohesion, i. 217. Axes of, in Wood, ii. 444. Cold produced by Chemical Decomposi- tion, ii. 635. Columbic Acid, ii. 289. Columbium, ii. 285. Columbous Acid, ii. 286. Columbites, ii. 288. Coloured Media, Spectra exhibited by, ii. 487. Combining Measure, i. 145. Numbers, ii. 510. Proportions, i. 121 — 132. Combustion, Heat of, i. 299; ii. 625. in Air, i. 301. Common Salt, i. 542. Compound Ethers, ii. 545. Action of Ammonia on, ii. 557. Boiling Points of, ii. 584. Compounds, Formation of, by Substitu- tion, i. 227. Formula} of, i. 118. Condensing Tube, i. 63. Conduction of Heat, i 28; ii. 441. Conjugate Metals, ii. 568. Kadicals, ii. 527. Conjugated Acids, ii. 541. Contraction of Liquids from the Boiling Point, i. 7 ; ii. 424. Water, i. 9. Copper, Acetates of, ii. 105. Action of Nitric Acid upon, i. 341. Alloys of, ii. 107. Ammonio-sulphate of, ii. 212. and Potash, Oxalate of, ii. 105. Diohloride of, ii. 97. Dicyanide of, ii. 97. Diniodide of, ii. 97. Dioxide of, ii. 95. Disulphide of, ii. 96. Esfimation and Separation of, ii. 107. Hydride of, ii. 96. Liquation of Argentiferous, ii. 328. Nitrates of, ii. 105. Protochloride of, ii. 101. Copper, Protoxide of, ii. 99. Sources and Extraction of, ii. 92. Sulphate of, ii. 103. Volumetric Estimation of, ii. 108. Cordier, Investigation on Heat, i. 40. Corrosive Sublimate, ii. 308. Crichton's Thermometer, i. 17. Cryophorus, Dr. Wollaston's, i. 66. Crystalline Form and Rotatory Power, Relations between, ii. 476. Crystallised Bodies, Conduction of Heat in, ii. 441. Cupellation of Silver, ii. 346. Cuprammonium, i. 203; ii. 102. Cuproso-cupric Cyanide, ii. 98. Cuprous Chloride, Iodide, and Cyanide, ii. 97. Hyposulphite, ii. 98. Oxide, ii. 95. Carbonate, ii. 102. Chloride, ii. 101. Nitrate, ii. 105. Oxide, ii. 99. Salts, Reactions of, ii. 99. Sulphate, ii. 105. Sulphite, ii. 98. Current, Heating Power of the Voltaic, ii. 506. Reduction of the Force of the, to absolute Mechanical Mea- sure, ii. 506. Regulator, ii. 504. Electric, Measurement of, ii. 496. Cyanide, Cuproso-cupric, ii. 98. Cuprous, ii. 97. Ferric, ii. 48. of Lead, ii. 119. Mercury, ii. 318. Mercury and Potassium, ii. 320. Palladium, ii. 387. Potassium, i. 530. Silver, ii. 339. Cyanides, Compound, i. 200. of the Alcohol-radicals, ii. 552. of Platinum, ii. 368, 379. Cyanogen, i. 337. D. Dalton on Evaporation of Water, i. 91. Dalton's Atomic Theory, i. 133. Law of the Dilatation of Gases, i. 12. Miscibility of Gases, i. 85. INDEX. 785 Daniell's Constant Battery, i. 285. Hygrometer, i. 95. Pyrometer, i. 20. Debus' Experiments on the Influence of Mass on Chemical Action, ii. 590. Decomposition, i. 225. by Contact, i. 233. Cold produced by, i. 635. Circumstances which af- fect the order of, ii. 225 ; ii. 591—604. Decompositions, Secondary, i. 262. Delarive and Marcet, Haycraft, Dulong, Apjohn, Suermann, Delaroche, Berard, on Specific Heat of Gases, i. 26. Density and Chemical Composition, Re- lations between, ii. 569. Deutazophosphoric Acid, ii. 699. Deuto-hydrate of Phosphoric acid, i. 441. Dew, Deposition of, i. 38. Well's Experiments on, i. 39. Diamagnetic Bodies, i. 282. Diamides, or Primary Biamides, ii. 558. Diamond, i. 357. -boron, ii. 668. -silicon, ii. 673. Diaphragm, Two Polar Liquids sepa- rated by a Porous, i. 263. Dibromide of Mercury, ii. 300. Dichloride of Mercury, ii. 298. Action of Ammo- nia on, ii. 299. Dicyanide of Copper, ii, 97. Didymium, Arseniate of, ii. 277. Carbonate of, ii. 275. Chloride of, ii. 274. Estimation of, ii. 274. Metallic, ii. 273. Nitrate of, ii. 276. Oxalate of, ii. 275. Peroxide of, ii. 274. Phosphate of, ii. 277. Protoxide of, ii. 273. Salts of, ii. 274. Sources and Extraction of, ii. 73. Sulphate of, ii. 275. Sulphide of, ii. 274. Sulphite of, ii. 276. Diffusion-coefficients, ii. 612. Diffusion of a Salt into the Solution of another Salt, ii. 610. Gases, i. 84. through Porous Septa, ii. 624. Liquids, ii. 604. Diffusion of Liquids through Porous Septa, ii. 616. Dilatation of Solids by Heat, i. 3 ; ii. 421. Dimetaphosphoric Acid, ii. 693. Dimorphism, i. 176. Diniodide of Copper, ii. 97. Mercury, ii. 300. Dioxide of copper, ii. 95. Diplatosamine and Diplatinamine, ii. 382. Disinfecting Properties of Charcoal, ii. 659. Dissipation of Heat, i. 32, Distillation, Natural Sequel to Vaporisa- tion, i. 62. Disulphide of Copper, ii. 96. Mercury, ii. 298. Dolomite, i. 592. Double Decomposition of Salts, i. 229; ii. 591, regarded as the Type of Chemical Action in general, ii. 519. Refraction, Polarisation by, ii. 459. Salts, i. 197. Dutch Liquid, i. 386. Dynamical Theory of Heat, ii. 449. £. Earthenware and Porcelain, I 613. Elasticity, Axes of, in Wood, ii. 444. Electric Current, Heating Power of, ii. 506. reduced to absolute Mechanical Mea- sure, ii. 506. Currents, Measurement of the Force of, ii. 496. Resistance of Metals, ii. 502. Electro gilding, ii. 359. Electrolysis, i. 260. Electro-silvering, ii. 360. Elementary Bodies, Atomic Weights, and Formula of, in the free State, ii. 516. Substances, Table of, i. 108 — 110. Elements, Arrangement of, in Compounds, i. 184. Atomic Volume and Specific Gravity of, Table L, i. 211. 786 index; Elements, Barium Class of, i. 169. Carbon Class of, i. 174. Chlorine Class of, i. 171. Classification of, i. 168. Gold Class of, i. 173. Magnesian Class of, i. 168. Metallic, i. 510. Non-metallic, i. 291 ; ii. 638. Phosphorus Class of, i. 1 72. Platinum Class of, i. 173. Potassium, Class of, i. 170. Sulphur, Class of, i. 168. Symbols of the, i. 118. Tin, Class of, i. 173. Tungsten, Class of, i. 174. Emerald, or Beryl, i. 617. Enamel, i. 571. Endosmose andExosmose, ii. 616. Equivalent of Heat, Mechanical, ii. 445. Values of Radicals, ii. 524, Equivalents and Atoms, ii. 509. Table of, i. 108-110. Erbia, i. 618. Erbium, i. 617. Etherification explained by Atomic Mo- tion, ii. 602. Ethers, ii. 534. Action of Ammonia on Com- pound, ii. 557. Boiling Points of Compound, ii. 584. Compound, ii. 545. Sulphur, ii. 548. Hydrosulphuric, ii. 547. of Bibasic Acids, ii. 539. Tribasic Acids, ii, 540. Ethylene, ii. 564. Euchlorine Gas, i. 472. Euclase, i. 617. - Eudiometers for Measuring Gases, i. 381. of Bunsen, i. 381. Evaporation in Vacuo, i. 64. Spontaneous, i. 90. Dalton and Regnault on the, of Water, i. 91. Expansion and the Thermometer, i, 2. of Gases, i. 12. Liquids, i. 5, 7 ; ii. 423. Mercury, absolute, ii. 425. Solids, i.2; ii. 221. Water, ii. 424. Extinction of the Chemical Rays, ii. 495. F. Fahl-ores, ii. 336. Faraday, on the Liquefaction of Gases, i. 71. on Relation between Light and Magnetism, i. 201 ; ii. 481. Fatty Acids, ii. 538. Boiling Points of, ii. 584. Felspar, i. 612. Ferric Acid, ii. 53. Compounds, ii. 43. Oxide, ii. 43. Sulphide, ii. 47. Ferrocyanide of Iron, ii. 40. Potassium, i. 29. and Iron, ii. 39. Ferroso-ferric Oxide, ii. 46. Sulphate, ii. 51. Ferrous Compounds, ii. 36. Oxide, ii. 36. Volumetric estimation of, ii. 728. Pick's Experiments on Liquid Diffusion, ii. 611. Flame, Structure of, i. 381. Fluidity, as an effect of Heat, i. 41. Black's Views on, i. 43. Table of, i. 42. Fluoboric Acid, i. 507. Fluoboride of Silicon, i. 508. Fluorescence, ii. 481. Fluoride of Aluminium, i. 605. Boron, i. 507. Calcium, i. 586. Manganese, ii. 8. Silver, ii. 339. Tantalum, ii. 284. Fluorides, ii. 552. Fluorine, i. 503. Detection of minute quantities of, ii. 720. Estimation of, ii. 721. Isolation of, ii. 720. Sources of, ii. 719. Fluor-Spar, i. 505, 586. Fluosilicic Acid, i. 508. Formula?, Rational, ii. 521. Formulae, Antithetic or Polar, i. 204. of Compounds, i. 118. Freezing Apparatus, i. 586. of Water, i. 66. Mixtures, i. 556. Fulminating Gold, ii. 351. Functions, Classification of Bodies, ac- cording to their Chemical, ii. 528. Fusco-cobaltia Salts, ii. 69. INDEX. 787 Galvanometer, i. 290 ; ii. 497. Garnet, i. 613. • Gas-Battery, Grove's, i. 269. Gases and Vapours, Specific Heat of, ii. 429. Air and, are imperfect Conductors, i. 31. Absorption of, by Liquids, i. 75, 316; ii. 647. Dalton on Miscibility of, i. 15. Density of, i. 79, 80. Determination of the Specific Heat of, i. 25. Diffusion of, i. 86. through Porous Septa, ii. 624. Effusion of, i. 78. Expansion of, i. 12. Faraday's Experiments on, i. 71. Heat evolved by the Solution of, in Water, ii. 633. Passage of, through Membranes, i. 89. Permanent, i. 68. Priestley, on Diffusion of, i. 85. Table of the Specific Gravity of, and Vapours, i. 149 — 155. Thilorier's Machine for the Lique- faction of Carbonic Acid, i. 69. Transpiration of, i 82. Gerhardt's Atomic Weights, ii. 513. Formulae of Salts, i. 201. Theory of the Ammoniacal Platinum Compounds, ii. 38 1 . Types, ii. 523. Unitary System, ii. 512. German Silver, ii. 77. Gilding and Silvering, ii. 359, Glass, i. 568. Analysis of, i. 569. Bohemian, i. 570. Composition of. Varieties of, i. 569. Crown, i. 570. Crystal, i. 571. Devitrification of, 572. Flint, i. 571. Green or Bottle, i. 572. Window, i. 569. Glauber's Salts, i. 555. Glucina and Ammonia, Carbonate of, ii. ii. 763. Potash, Oxalate of, ii. 763. Carbonate of, ii. 764. Glucina, Estimation and Separation of, ii. 765. Glucina, Properties, Rational Formula and Preparation of, ii. 762. Glucinum, i. 615; ii. 761. Gladstone's Experiments on the Influence of Mass on Chemical Action, ii. 391. Glycerines, ii. 533. Glycols, ii. 532. Gold, Alloys of, ii. 358. Amalgam of, ii. 358. and Potassium, Chloride of, ii. 356. Glass, i. 173. Estimation and Separation of, ii. 360. Extraction of, ii. 347. Oxide of, ii. 349. Fulminating, ii. 351. Properties of, ii. 348. Sesquichloride of, ii. 355. Sesquioxide of, ii. 350. Sesquisulphide of, ii. 335. Sources of, ii. 346. Graham's Experiments on Liquid Diffu- sion, ii. 602. Researches on Osmose, ii. 619. Graphite, i. 358. Preparation of pure, finely divided, ii. 661. Graphitoidal Boron, ii. 668. Silicon, ii. 672. Gunpowder, i. 536. Gurney's Bude Light, i. 384. Gypsum, i. 589. H. Hail, i. 330. Heat, Absorption and Reflection of Radi- ated, i. 34. Bache's Experiments on the Radia- tion of, i. 33. Capacity of Different Bodies for, i. 24. Central, i. 40. Conduction of, i. 28 ; ii. 441. Developed by Chemical Combina- tion, ii. 625. Dilatation of Solids by, i. 3; ii. 421. Distribution of the Rays of, i. 106. Despretz and Dulong's Experiments on Latent, i. 58. Dynamical Theory of, ii. 449. Evolved by the Solution of Gases in Water, ii. 632. Effects of, on Glass, i. 5. Evolved in the Combination of Acids with Water, ii, 632. Experiments of Melloni on the Transmission of, i. 35 ; ii. 430. 788 INDEX. Heat, Fluidity, as an Effect of, i. 41. Latent, i. 57 ; ii. 430. Mechanical Equivalent of, ii. 445. Nature of, i. 99, 101; ii. 449. of Combination of Acids with Bases, ii. 631, 632. Combinations of Metals with Chlorine, ii. 630. of combination of Metals, &c. with Oxygen, ii. 627. Combustion and Specific Heat, Relations between, ii. 62. or Cold produced by Solution of Salts in Water, ii. 633. Radiation of, i. 31. Regnault's Table of the Capacity of Bodies for, i. 25. Rumford's Experiments on the Ra- diation of, i. 32. Specific, i. 24 ; ii. 426. Table of the Conduction of, by Building Materials, i. 29. Transmission of, i. 35. Radiant, through Me- dia and the Effects of Screens, i. 34. Transparency of Bodies to, i. 36. Heating Power of the Voltaic Current, ii. .506. Hedyphar, i. 590. Hemihedry, ii. 476. Hexametaphosphoric Acid, ii. 694. Henry, on Coal Gas, i. 380. Hepar Sulphuris, i. 528. Homologous Compounds, Boiling Points of, ii. 585. Homologous Series, ii. 532. Horse-chestnut Bark, Fluorescence of Infusion of, ii. 484. Humboldite, i. 372. Hydracids, i. 468. Hydrate of the Binoxide of Calcium, i. 584. Potash, Preparation of, from the Nitrate, ii. 731. Hydrated Bisulphate of Potash, i. 534. Sesquisulphate of Potash, i. 534. Tantalic Acid, ii. 278. Hydrates of Alumina, i. 602 ; ii. 758. Copper, ii. 96. Silicic Acid, i. 394. Sulphuric Acid, i. 409. the Alcohol-radicals, ii. 563. Aldehyde-radicals, ii. 564. Metals Proper, ii. 563. Hydraulic Mortar, i. 584. Hydride of Phosphorus (Liquid), i. 453. Hydrides of Carbon, i. 374. Hydriodic Acid, i. 497. Hydroboracite, i. 600. Hydrobromic Acid, i. 489. Hydrochlorate of Ammonia, ii. 736. Hydrochloric Acid and Binoxide of Man- ganese, process for preparing Chlorine from, ii. 454. Preparation of, i. 464. Table of the Specific Gravity of, i. 467. Type, ii. 523, 548. Hydrocyanic Acid, i. 531. Hydroferricyanic Acid, ii. 49. Hydroferrocyanic Acid, ii. 39. ' Hydrofluoric Acid, i. 504, 505. Anhydrous, ii. 720. Hydrofluosilicic Acid, i. 509. Hydrogen and Arsenic, ii. 210. Nitrogen, Ammonia,i. 353. Phosphorus, i. 451. Sulphur, i. 419. Antinioniuretted, ii. 233. Bicarburetted, i. 384. Binoxide of, i. 320, Bisulphide of, i. 423. Cavendish's Experiments on, i. 311. Peroxide of, i. 334. Preparation of, i. 305. Properties of, i. 307. Protocai'buretted, i. 375. Protoxide of, i. 311. Quantitative Estimation of, ii. 645. Siliciurettcd, ii. 676. Teroxide of, ii. 640. Hydrogen-type, ii. 523, 563. Hydrosulphate of Ammonia, ii. 737. Hydrosulphuric Acid, i. 419. Ethers, ii. 547. Hygrometer, i. 92. Condensing (Regnault's), i. 96. Daniell's, i. 95. Differential, i. 93. Wet Bulb, i. 93. Hy perchloric Acid, i. 475. Hypochloric Acid, i. 478, Hypoclilorite of Lime, i. 591. Hypochlorites, i. 472. Volumetric Estimation of, ii. 725. Hypochlorous Acid, i. 469. Hypo-iodic Acid. ii. 712. Hypophosphorous Acid, i. 434. Analysis of, i. 437. Hyposulphate of Magnesia, i. 599. Hyposulphate of Manganese, ii. 10. Silver, ii. 340. INDEX. '89 Hyposulphite, Cuprous, ii. 98. of Auric Oxide and Soda, ii. 358. Aurous Oxide and Soda, ii. 357. Baryta, ii, 358. Silver, ii. 340. Strontia, i. 580. Hyposulphuric Acid, i. 413. Hyposulphurous Acid, i. 415. Estimation of, ii. 687. Hydrotelluric Acid, ii. 200. I. Ilmenium, ii. 290. Imides, ii. 559. Inactive Tartaric Acid, ii. 480. Induction, Photo-chemical, ii. 493 Insolubility, influence of, on Chemical Decomposition, i. 227 ; ii. 601. Insoluble Salts, Decomposition of, by Soluble Salts, ii. 597. lodate of Potash, i. 539. lodates, i. 500. Iodic Acid, i. 498. Iodide, Auric, ii. 327. Cuprous, ii. 97. Platinous, ii. 368. of Cadmium, ii. 91. Lead, ii. 119. Nitrogen,!. 501 j ii. 713. Palladium, ii. 386, 718. Potassium, i. 529. Sulphur, i. 502. Stannous, ii. 135. Silver, ii. 338. Tetramercurammonium, ii. 3 1 7. Zinc, ii. 85. Iodides, ii. 496 ; ii. 552. AtomicVolume of Liquid, ii. 577. Ferric and Ferrous, ii. 38, 48. of Alcohol-radicals, Action of Ammonia on, ii. 554. Mercury, ii. 300. 316. Phosphorus, i. 502 ; ii. 715. Iodine, Bromides of, i. 503. Chlorides of, i. 502. Compounds of, i. 497. Estimation of, ii. 718. Preparation of, i. 491. Properties of, i. 494. Separation of, from Bromine and Chlorine, ii. 719. Sources of, i. 491 ; ii. 712. Uses of, i. 495. Volumetric Estimation of, ii. 723. lodo-aurate of Potassium, ii. 357. Ions, Transference of the, i. 265. Iridic Sulphate, ii. 397. Iridium, Ammoniacal Compounds of, ii. 397. Carburet of, ii. 397. Chlorides of, ii. 396. Oxides of, ii. 394, 395. Properties of, ii. 393. Sources and Extraction of, ii. 391. Sulphides of, ii. 395. Iron and Potassium, Ferrocyanide of, ii.39. Bisulphide of, ii. 47. Black or Magnetic Oxide of, ii. 46. Carbonate of, ii. 41. Cast, ii. 28. Ferricyanide of, ii. 40. Malleable, ii. 20. > Metallurgy of, ii. 23. Ores of, ii. 24. Passive condition of, ii. 35. Properties of, ii. 32. Protoacetate of, ii. 41. Protochloride of, ii. 38. Protocompounds of, ii. 36. Protocyanide of, ii. 38. Protiodide of, ii. 38. Protosulphate of, ii. 41. Protosulphide of, ii. 37. Protoxide of, ii. 36. Puddling of, ii. 30. Pyrites, ii. 47. Quantitative Estimation of, ii. 56. Scale Oxide of, ii. 47. Separation of, from other Metals, ii. 57. Sf squichloride of, ii. 48. Sesquicompounds of, ii. 43. Sesquicyanide of, ii. 48. Sesquiiodide of, ii. 48. Sesquioxide or Peroxide of, ii. 43. Sesquisulphide of, ii. 47. Sources of, ii. 23. Subsulphide of, ii. 39. Volumetric Estimation of,ii. 56,728. Isomerism, i. 181. Isomorphism, i. 159 — 167. Isomorphous relations of Manganese, ii. 2 1 . K. Kelp, i. 562. Lanthanum, Carbonate of, ii. 271. Chloride of, ii. 271. Estimation of, ii. 272. Metallic, ii. 271. VOL. II. 3 H 790 INDEX. Lanthanum, Nitrate of, ii. 272. Protoxide of, ii. 271. Sources and Extraction of, ii. 268. Sulphate of, ii. 272. Latent Heat, i. 44 ; ii. 430. Lead, Acetates of, ii. 125. Alloys of, ii. 127. Antimoniates of, ii. 231. Bichloride of, ii. 118. Bioxide or Peroxide of, ii. 115 Bromide, Iodide, and Cyanide of, ii. 119. Carbonate of, ii. 119. Chlorate of, ii. 124. Chloride of, ii. 117. Chlorite of, ii. 124. Chlorophosphate of, iL 125. Chromate of, ii. 169. Estimation and Separation of, ii.l28. Nitrate of, ii. 121. Nitrites of, ii. 122. Oxychloride of, ii. 1 1 7. Perchlorate of, ii. 124. ^ Phosphate of, ii. 123. Protoxide of, ii. 112. Salts, Reactions of, ii. 113. Sesquioxide of, ii. 115. Sources and Extraction of, ii. HI. Suboxide of, ii. 112. Sulphate of, ii. 121. Sulphide of, ii. 116. Leslie, Radiation of Heat, i. 32. Leucite, or Amphigen, i. 612. Liebig's Condensing Tube, i. 63. Light, Brewster (Sir D.)on,i. 105, 326. Change of Refrangibilityof, ii. 481 . Common, i. 103. Decomposition of, 104. Difference of Chemical Power in Morning and Evening, ii. 496. Double Refraction of, i. 103 ; ii. 459. Forbes on, i. 326. Gurney's Bude, i. 384. Measurement of the Chemical Ac- tion of ii. 489. Polarisation of, i. 103 ; ii. 457. Faraday's Experiments on the Re- lations between Magnetism and, i. 281 ; ii. 481. Lime, i. 581. and Alumina, Silicates of, i. 613. Potash, Sulphate of, ii. 751. Carbonate of, i. 587. Chromate of, ii. 167. Estimation of, ii. 751. Hydrate of, i. 582. Hypochlorite of, i. 591. Lime, Hyposulphite of, i. 590. Nitrate of, i. 590. Phosphate of, i. 590 ; ii. 751. Salts of, i. 587. Separation of, from Baryta and Strontia, ii. 752. from Magnesia and the Alkalies, ii. 752. Solubility of, ii. 750. Sulphate of, i. 589. Volumetric Estimation of Chloride of, i, 592 ; ii. 726. Liquation of Argentiferous Copper, ii. 328, Liquefaction, i. 41 ; ii. 429. Liquids, Absorption of Gases by, ii. 647. Atomic Volume of, ii. 569. Circular Polarisation in, ii. 468. Contraction of, from the boiling point, i. 7 ; ii. 424. Diffusion of, ii. 604. through porous Sep- ta, ii. 616. Expansion of, i. 57; ii. 423. Latent Heat of, ii. 431. Specific Heat of, ii. 427. Tension of Vapours of mixed, ii. 439. Vaporisation of, i. 52. Lithia, i. 573. Carbonate of, i. 574. Estimation and Separation of, ii. 743. Hydrate of, i. 574. Nitrate of, ii. 743. Phosphate of, ii. 743. Sulphate of, i. 674. Lithium, i. 573 ; ii. 741. Chloride of, i. 574. Luteo-Cobaltia Salts, ii. 68. M. Madder-stove, i. 98. Magnesia, i. 594. Alba, i. 596. Bicarbonate of Potash and, i. 597. Borate of, i. 599. Carbonate of, i. 596. Chromate of, ii. 167. Estimation and Separation of, ii. 755. Hyposulphate of, i. 599. Nitrate of, i. 599. Phosphate of and Ammonia, i. 599. Silicates of, i. 600. INDEX. t9l Magnesia, Sulphate of, i. 697. Magnesian Class of Elements, i. 168. Magnesium, i. 594 ; ii. 753. Chloride of, i. 595. Magnetic Action, Rotatory Power in- duced by, ii. 481. and Chemical Actions of the Current compared, ii. 499. Oxide of Iron, ii. 47. Magnetic Polarity, i. 235. Malaguti's Experiments on the Recipro- cal Action of Salts, ii. 594. Malic Acid, Active and Inactive, ii. 480. Malleability, i. 511. Malleable Iron, ii. 29. Manganese, Bioxide or Peroxide of, ii. 13. Carbonate of, ii. 8. Estimation and Separation of, ii. 22. Fluoride of, ii. 8. Hyposulphate of, ii. 1 1. Isomorphous relations of, ii. 21. Molybdate of, ii. 191. Oxides of, ii. 3. Perchloride of, ii. 21. Phosphide of, ii. 6. Protochloride of, ii. 7. Protocyanide of, ii. 8. Protosulphide of, ii. 5. Protoxide, ii. 3. Protosulphate of, ii. 8. Reactions of, ii. 4. Red Oxide of, ii. 13 Sources and Extraction of, ii. 1. Sesquioxide of, ii. 10. Valuation of Bioxide of, ii. 14, Manganic Acid, ii. 18. Sulphate, ii. 11. Manganous Oxide, ii. 3. Margueritte's Experiments on the Reci- procal Action of Salts, ii. 594. Mariotte, Deviation from the Law of, in Gases, i. 76. Law of Compression of Gases, i. 75. Marsh Gas, ii. 563. Marsh's Test for Arsenic, ii. 215. Mass, Influence of, on Chemical Action, ii. 586. Measurement of the Force of Electric Currents, ii. 496. Mechanical Equivalent of Heat, ii. 445. Mechanical Measure of the Electric Current, ii. 506. Mellon (Liebig), i. 388. Melting Point of Sulphur, i. 396 ; ii. 681. Mercaptans, ii. 546. Mercurammonia, ii. 306. Mercurammonium, Chloride of, ii 312. Mercuric Amidochloride, ii. 318. Ammonio-nitrates, Bromide, ii. 315. Chloride, ii. 308. Compounds, ii. 303. Iodide, ii. 315. Nitrates, ii. 321. Oxide, ii. 303. Seleniate and Selenite, ii. 321. Sulphate, ii. 320. Sulphide, ii. 307. Sulphites, ii. 321. Mercuroso-mercuric Iodide, ii. 318. Murcurous Acetate, ii. 303. Bromide, or Dibromide of Mercury, ii. 300. Carbonate, or Carbonate of Black Oxide of Mercury, ii. 301. Chloride, DicLloride of Mer- cury, or Calomel, ii. 298. Compounds, ii. 296. Iodide, or Diniodide of Mer- cury, ii. 300. Nitrates, or Nitrates of Black Oxide of Mercury, ii. 302. ii. 301. Sulphates, or Sulphate of Black Oxide of Mercury, ii. 301, Seleniate, ii. 301. Selenite, ii. 301. Mercury, Absolute Expansion of, ii. 425. Action of Ammonia on Bi- chloride of, ii. 299. Alloys of, and Potassium,ii.324. Calorimeter, ii. 626. Nitride of, ii. 306. Nitrochloride of, ii. 310. Chloride of, with Ammonia, iL 309. Cyanide of, ii. 318. Dibromide of, ii. 300. Dichloride of, ii. 298. ♦ Diniodide of, ii. 300. Disulphide of, ii. 298. Double Salts of Chloride of, ii. 313. Estimation and Separation of, ii. 325. Oxy chloride of, i. 117 ; ii. 312. Oxycyanide of, ii. 319. Protobromide of, ii, 315. Protochloride of, ii, 308. Protoxide of, ii. 303. Protosulphide of, ii. 307. Sulphochloride of, ii. 313. 792 INDEX. Metalloids or Acid Metals, ii. 567. Metals, Alcohol-, il 566. Combinations of, i. 514. Conduction of Heat in, ii. 440. Conjugate, ii. 567. Diamagnetic, i. 282. Electric Resistance of, i. 502. Found in Native Platinum, i. 519; ii. 363. General Observations on, i. 510 Heat of Combination of, with Chlorine, ii. 630. Heat of Combination of, with Oxygen, ii. 627. Isomorphous with Phosphorus, i. 518; ii. 203. in Native Platinum, ii. 363. Mixed, ii. 567. Noble, ii. 291. of the Alkalies, i. 517 ; ii. 729. Alkaline Earths, i. 518; ii. 744. Earths Proper, i. 5 1 8 ; 7 63. Oxidability of, i. 513. Physical Properties of, i. 511. Proper, having Isomorphous Re- lations with the Magnesian Family, i. 518 ; ii. 130. Proper, having Protoxides iso- morphous with Magnesia, i. 518 ; ii. 1. Proper, Hydrides of, ii. 563. Proper, of which the Oxides are reduced by Heat to the Me- tallic state, i. 519; ii. 291. Protoxides of, i. 514. Table of the, i. 510. Fusibility of dif- ferent, i. 512. Metameric Bodies, i. 183. Metaphosphates, i. 442. Action of Water on the, ii. 694. Metaphosphoric Acid, i. 448 ; ii. 692. Metastannates, ii. 139. Metastannic Acid, ii. 138. Methylosulphurous Acid, ii. 706. Microcosmic Salt, i. 563. Minium, ii. 115. Mitchell's Experiments on Diffusion of Gases, i. 90. Mixed Liquids, Tension of Vapours of, ii. 439. Metals, ii. 567. Molybdate of Lead, ii. 192. Manganese, ii. 191. Molybdates of Ammonia, ii. 190. Baryta, ii. 191. Potash, ii. 189. Molybdates of Soda, ii. 190. Molybdenum, Chlorides of, ii. 193. Estimation and Separation of, ii. 193. Sources of, ii. 185. Sulphides of, ii. 192. Molybdic Acid, ii. 187. Oxide, ii. 186. Molybdous Oxide, ii. 185. Monobasic Salts, i. 193. Monometaphosphoric Acid, ii. 693. Monophosphamide, ii. 697. Monosul-hyposulphuric Acid, i. 417. Motion, Atomic, i. 660. N. Neutral Metantimoniate of Potash, ii. 229. Nichol's Prism, ii. 460. Nickel, Ammonio- Compounds of, ii. 77. Chloride of, ii. 76. Estimation and Separation of, ii. 77. Oxides of, ii. 76. Sources and Extraction of, ii. 74. Sulphate of, ii. 76. Niobium, ii. 285. Nitrate, Cupric, ii. 105. Ferric, ii. 51. of Alumina, i. 610. Ammonium, ii 738. Argentammonium, ii. 342. ' Baryta, i. 578. Bimercurammonium, ii. 323. Cobalt, ii. 63. Didymium, ii. 276. Lanthanum, ii. 272. Lead, ii. 121 Lime, i. 590. Lithia, ii. 743. Magnesia, i. 599. Palladium, ii. 387. Potash, i, 535. Silver, ii. 341. Soda, i. 562. Strontia, i. 580. Tetramercurammonium, ii. 323. Trimercurammonium, ii. 323. Uranyl, ii. 257. Zinc, ii. 86. Stannous, ii. 135. Uranic, ii. 257. Nitrates, Mercuric, ii. 322. Mercurous, ii. 302. of Bismuth, ii. 247. Table of, i. 535. INDEX. 793 Nitre, i. 535. valuation of, ii. 657. Nitric Acid, Action of, upon Copper, i. 341. Anhydrous, ii. 652. Battery (Grove's), i. 285. Estimation of, ii. 655. Preparation of, i. 346. Properties of, i, 341, 348. Uses, i. 352. Nitric Oxide, Preparation of, ii. 652. Nitride of Boron, ii. 670. Mercury, ii. 306. Nitrides, Intermediate, ii. 561. Negative or Acid, of the Alcohol-radicals, pri- mary, ii. 553. Alcohol-radicals, se- condary and tertiary, ii. 555. Aldehyde-radicals, ii. 556. Titanium, ii. 149. Positive, ii. 553. Kitrile Bases, ii. 555. ' Nitrite of Silver, ii. 342. Nitrites of Lead, ii. 122. Nitrochloride of Mercury, ii. 310. Nitrogen, i. 124. and Hydrogen, Ammonia, i. 353. Phosphorus, i. 454. Sulphur, i. 424. Binoxide of, i. 341. Bromide of, ii. 711. Chloride of, i. 480 ; ii. 702. Chlorophosphide of, ii. 710. Compounds, Atomic Volume of Liquid, ii. 578. Compounds containing Phos- phorus and, ii. 695. Iodide of, i. 501; ii. 713. Peroxide of, i. 344. Preparation of, i. 322, 337 ; ii. 651. Properties of, i. 323. Protoxide of, i. 337. Quantitative Estimation of, ii. 653. Sulphide of, i. 424; ii. 682. Nitrocyanide of Titanium, ii. 150. Nitroprussic Acid, ii. 52. Nitroprussides, ii. 55. Niti'osulphuric Acid, i. 411. Nitrous Acid, i. 343. Oxide, ii. 652. Noble Metals, ii. 291. Non-metallic Elements, i. 291 ; ii. 638. Mormal Acid Fluid, i. 550. Notation and Chemical Nomenclature, i. 108-112. Classification, Chemical, ii. 509. Octohedral Boron, ii. 668. Silicon, ii. 673. Ohm's Formulae, ii. 500. Oil Gas, i. 386. of Vitriol, i. 405. Specific Gravity of the Vapour of, i. 157. Olefiant Gas, or Ethylene, i. 384 ; ii. 564. Optical and Chemical Extinction of the Chemical Rays, ii. 495. Organic Compounds, Circular Polarisation in, ii. 468. Estimation of Carbon and Hydrogen in, ii. 662. Estimation of Chlo- rine in, ii. 717. Estimation of Nitro- gen in, ii. 652. Estimation of Sul- phur in, ii. 687. Osmiamic Acid, ii. 404. Osmic Acid, ii. 403. Sulphate, ii. 401. Osmious Acid, ii. 402. Osmium, Bichloride of, ii. 401. Estimation and Separation of, ii. 405. Oxides and Chlorides of, ii. 400. Sources and Extraction of, ii. 399. Sesquioxide of, ii. 400. Sulphides of, ii. 405. Terchloride of ii. 403. Osmose through Membrane, ii. 620. Physiological Action of, ii. 623. through Porous Earthenware, ii. 619. Jolly's researches on, ii. 617. Graham's researches on, ii. 619. Oxalate, Cerous, ii. 265. Ferric, ii. 53. of Chromium and Potassium, ii. 161. Copper and Potash, ii. 105. Didymium, ii. 275. Glucina and Potash, ii. 763. Potash and Antimony, ii. 226. Silver, ii. 343. Oxalates, Decomposition of Insoluble by Alkaline Carbonates, ii. 599. 3 H 3 794 INDEX. Oxalates of Ammonium, ii. 740. Oxamide, ii. 558, 740, Oxalic Acid, i. 372. Estimation of, ii. 665. Oxamic Acid, ii. 542, 740. Oxide, Antimonic, ii. 222. Auric, ii. 350. Aurous, ii. 349. Ceric, ii. 264. Cerous, ii. 263. Chromic, ii. 155. Chromoso-chromic, ii. 155. Chromous, ii, 153. Cobaltic, ii. 65. Cobaltous, ii. 61. Cupric, ii. 99. Cuprous, ii. 95. Mercuric, ii. 303. Molybdic, ii. 186. Molybdous, ii. 185. of Antimony, ii. 222. Cadmium, ii, 30. Gold, ii 349. Iridium, ii, 394, 395. Iron, Volumetric Estimation of, ii. 728. Manganese, ii. 3, 10, 13. Rhodium, ii, 407. Silver, ii, 333, Phosphorus, i. 633. Potassium, Salts of, i. 532, Vanadium, ii. 174. Zinc, ii. 84. Palladous, ii. 385. Platinic, ii. 368. Platinous, ii, 367. Rhodic, ii, 407. Ruthenic, ii. 415. Stannic, ii. 136. Stannous, ii. 131. Tungstic, ii. 177- Uranic, ii. 255. Uranosouranic, ii. 254. Uranous, ii, 253. Oxides and Chlorides of Osmium, ii. 400. Atomic Volume and Specific Gravity of, i. 215, 216. Intermediate, or Oxygen Salts, ii. 544, Metallic, Classification of, ii. 530. Negative or Acid, ii. 535. Positive, ii. 530, Oxy chloric Acid, i. 475. Oxy bromide of Phosphorus, ii. 711. Oxychloride of Lead, ii, 1 1 7. Mercury, ii. 312. Oxycobaltia-salts, ii, 68, Oxy cyanide of Mercury, ii. 319. Oxygen, i. 123. Oxygen -Acids, i. 186. Active Modification of, ii. 641, 644. Compounds of Chlorine and, i, 469. Extraction of, from Atmosphe- ric Air, ii, 638. Heat produced by combination -with, ii. 627. Preparation of, i. 291. Properties of, i, 296. Quantitative Estimation of, ii. 645. Oxygenated Water, i. 185, Oxygen-Salts or Intermediate Oxides, ii. 644. Ozone, i. 304 ; ii. 639. Packfong, ii, 77. Palladium, Ammoniacal Compounds of, ii, 388-390. Chlorides of, ii, 387, 388. Cyanide of, ii. 387. Estimation and Separation of, ii. 391. Nitrate of, ii. 387. Properties of, ii, 385. Protoxide of, ii. 385. Reactions of, ii. 386. Sources and Extraction of, ii. 384. Sulphide of, ii. 386. Passive condition of Iron, ii. 35. Pearl- Ash, i. 533. Pentachloride of Antimony, ii, 232. Phosphorus, i. 487. Action of Acids on, ii. 708. Pentaiodic Acid, i. 501. Pentasulphide of Antimony, ii. 232. Pentathioaic Acid, i. 418. Perchlorate of Lead, ii, 1 24, Potash, i. 539. Perchloric Acid, i, 475.^ Perchloride of Carbon, i. 483. Sulphite of, ii, 751 Manganese, ii, 21. Periodates, i, 501. Periodic Acid, i. 501. Permanganic Acid, ii. 18. Permeability to Liquids, Axes of, in Wood, ii. 444. Persulphide of Arsenic, ii. 209 Peroxide of Chlorine, i, 478. Didymium, ii, 274. Iron, ii. 43. x INDEX. 795 Peroxide of Lead, ii. 116. Manganese, ii. 13. Nitrogen, i. 344. Potassium, i. 527. Silver, ii. 343. Peroxides, Volumetric Estimation of, ii. 727. Phospham, ii. 698. Pliosphamic Acid, ii. 697. Phosphate, Cerous, ii. 266. of Alumina, i. 610. Cobalt, ii. 65. Didymium, ii. 279. Lead, ii. 123. Lime, i. 590; ii. 751. Lithia, ii. 743. Magnesia, i. 599. and Ammonia, i. 599. Phosphates, i. 43. Analysis of, i. 449 ; ii. 700. Bibasic, i. 444. of Ammonium, ii. 739. of Uranyl, ii. 257. Zinc, ii. 86. Tribasic, i. 444. Uranic, ii. 257. Phosphide of Cobalt, ii. 67- Manganese, ii. 6. Nitrogen, i. 454; ii. 699. Tungsten, ii. 182. Phosphides, ii. 562. Phosphites, i. 437. Phosphocerite, ii. 266. Phosphoric Acid, Analysis of, i. 449. Action of, onPentachlo- ride of Phosphorus, ii. 710. Amides of, ii. 695. considered Tribasic, i. 208. Deuto-hydrate of. Acid or Bibasic Phosphate of Water, i. 441. Estimation of, ii. 700. Separation of, from Bases, ii. 701. Preparation of, i. 438. Protohydrate of, i. 442. Terhydrate of, or Tri- basic Phosphate of Water, i. 440. Phosphorous Acid, Analysis of, i. 437. Estimation of, ii. 702. Preparation of, i. 436. Properties of, i. 437. Phosphorus, i. 429. Atomic Weight of, ii. 692. Phosphorus and Hydrogen, i. 451. Nitrogen, i. 454; ii. 695. Sulphur, i. 454. Bromide of, i. 491. Chloride of, i. 487. Chlorosulphide of, i. 487. Chloroxide of, i. 487. Class of Elements, i. 172. Estimation of, ii. 701. Iodides of, i. 502; ii. 715. Liquid Hydride of, i. 453. Oxide of, i. 433. Oxy bromide of, ii. 711- Pentachloride of, i. 487. Properties of, i. 431. Red or Amorphous, ii. 690. Solid Hydride of, i. 451. Sulphides of, i. 454 ; ii. 695. Sulphobromide of, ii. 711. Terchloride of, i. 487. Phosphoryl, Chloride of, ii. 551. Phosphuretted Hydrogen Gas, i. 151. Photo-Chemical Induction, ii. 493. Platinic Chloride, ii. 369. Oxide, ii. 368. Platinised Charcoal, ii. 660. Platinocyanides, ii. 367. Platinous Chloride, ii. 367. Cyanide, ii. 308. Iodide, ii. 368. Oxide, ii. 367. Platammonium, Bisalts of, ii. 376, 378. Proto-saltsofjii. 372-374. Platinum Black, ii. 365. Bichloride of, ii. 339. Bioxide of, ii. 368. Bisulphide of, ii. 36 Class of Elements, ii. 173. Estimation and Separation of, ii. 383. Extraction of, ii. 363. Inflammation of Mixed Oxy- gen and Hydrogen by, i. 269. Metals in Native, ii. 363. Process of rendering malle- able, ii. 365. Protochloride of, ii. 367, Protosulphide of, ii. 367. Protoxide of, ii. 367. Residues, New Method of treat- ing, ii. 417. Salts, Ammoniacal, ii. 371-382. Sources of, ii. 363. Spongy, ii. 364. Sulphocyanides of, ii. 371. Platosamine and Platinamine, ii. 382. Polar Chains, i. 275. Formulae, i. 204. Liquids, Separation of, i. 263. 3 H 4 796 INDEX. Polarisation, Circular, ii. 464. of Light, i. 103, 281 ; ii. 457. Polarised Light, Nature of, ii. 461. Polarisation hy Reflection, ii. 457. Refraction, Single and Double, ii. 459. Tourmalines, ii. 461. Polarity, Chemical, i. 235. Illustrations from Magnetical, i. 235. of Arrangement, i. 243. Polybasite, ii. 336. Polythionic Series, i. 417. Porcelain and Earthenware, i. 613. Potash, i. 524. Acid Antimoniate of, ii. 229. Metantimoniate of, ii. 229. Action of Chlorine upon, i. 473. Antimoniates of, ii. 229. and Antimony, Oxalate of, ii. 226. Tartrate of, ii. 226. Glucina, Oxalate of, ii. 763. Lime, Sulphate of, ii. 751. Soda, Carbonate of, i. 554. Sulphate of, ii. 735. Aurate of, ii. 352. Aurosulphite of, ii. 852. Bicarbonate of, i. 533. Bichromate of, ii. 165. Bihydrosulphate of, i. 528. Chlorate of, i. 537. Chromate of, ii. 165. Estimation of ii. 731. Felspar, i. 612. Hydrate of, i. 524. ii. 731. Hydrated Bisulphate of, i. 534. Sesquisulphate of, i. 534. Hydriodate of, i. 529. lodate of, i. 539. Ley, i. 525. Mulybdates of, ii. 189. Neutral Metantimoniate of, ii. 229. Nitrate of, i. 535. Valuation of, ii. 657. Perchlorate of, i. 538. Preparation of Hydrate of, from the Nitrate,ii. 731. Red Prussiate of, i. 530. Sulphate of, i. 534. Tellurate of, ii. 199. Terchromate of, ii. 166. Yellow Prussiate of, i. 529. Potassio-ferrous Tartrate, ii. 43. Potashes, i. 533. Potassa, i. 524. Potassium, Chloride of, i. 528. and Gold, Chloride of, 356. I Potassium and Iron, Ferrocyanide of, ii. 39. Mercury, Cyanide of, ii. 320. Rhodium, Chloride of, ii. 410. Chloroplatinate of, ii. 370. Chloroplatinite of, ii. 368. Class of Elements, i. 170. Compounds of, i. 524. Cyanide of, i. 530. Estimation of, ii. 731. Ferricyanide of, i. 530. Ferrocyanide of, i. 529. Improvements in the Prepa- paration of, by Maresca and Donny, ii. 729. Iodide of, i. 528. lodo-aurate of, ii. 357. Pentasulphide of, i. 528. Peroxide of, i. 527. Preparation of, i. 519. by Electro- lysis, ii. 729. Properties of, i. 523. Protosulphide of, i. 527. Salts of Oxide of, i. 532. Separation of, from Sodium, ii. 735. Sulphides of, i. 527. Sulphocyauide of, i. 532. Telluride of, ii. 201. Trisulphide of, i. 528. Priestley on Diflfusion of Gases, i. 85. Prism, Nichol's, ii. 460. Proto-acetate of Iron, ii. 43. Protobromide of Mercury, ii. 315. Protocarburetted Hydrogen : — Experi- ments on, i. 380. Preparation and, i 375. Properties of, i. 375, 376. Protochloride of Carbon, i. 483. Sulphite of, ii. 704. Cerium, ii. 265. Chromium, ii. 154. Copper, ii. 101. Iridium, ii. 396. Iron, ii. 38. Mercury, ii. 308. Platinum, ii. 367, Rhodium, ii. 409. Ruthenium, ii. 414. Sulphur, i. 486. Tin, ii. 133. Tin and Potassium, ii. 135. Uranium, ii. 254. Protocyanide of Iron, ii. 38. INDEX. 797 Protofluoride of Cerium, ii. 268. Proto- hydrate of Phosphoric Acid, i. 442. Protiodide of Mercury, ii. 315. Protosulphurets i. 410. Protoxide of Cerium, ii. 263. Chromium, ii. 153. Cobalt, ii. 61. Copper, ii. 99. Didymium, ii. 273. Iridium, ii. 394. Iron, ii. 36. Lanthanum, ii. 271. Lead, ii. 112. Mercury, ii. 303. Nickel, ii. 76. Nitrogen, i. 337. Palladium, ii. 385. Platinum, ii. 367. Ruthenium, ii. 413. Tin, ii. 131. Titanium, ii. 146. Silver, ii. 333. Uranium, ii. 253. Vanadium, ii. 173. Protoxides of Metals, i. 514; ii. 514, 530. Protosalts of Ammo-platammonium, ii. 375, 376. Platammonium, ii. 372 — 374. Protosulphate of Iron, ii. 41. Protosulphide of Carbon, ii. 684, Cerium, ii. 264. Iron, ii. 37. Mercury, ii. 307. Platinum, ii. 367. Tin, ii. 133. Prussian Blue, ii. 49. Prussine, i. 200. Psychrometer, i. 93. 94. Purple of Cassius, ii. 353. Pyrites Iron. ii. 47. Pyrometer, Daniell's and Wedgwood's, i. 19, 20. Pyrophosphamic Acid, ii. 700. Pyrophosphate of Soda. i. 444. Pyrophosphoric Acid, i. 442. Quadroxide of Bismuth, ii. 243. Quartation of Gold and Silver, ii. 347. Quartz, Left and Right-handed, ii. 465. Quinine, Fluorescence of Salts of, ii. 482. R. Racemic Acid, Composition of, ii. 479. Radiant Heat, i. 34. Radicals and Types, ii. 521. Radicals Conjugate, ii. 526. Equivalent Values of, ii. 524. Rain, Mean Fall of, in London, i. 330. in Northern Europe, Central Eu- rope, and in South Europe, L 330. in York, i. 330. Rational Formula and Atomic Volume, Relation between, ii. 580. Formulae, ii. 521. Rays, Chemical, i. 107. Deoxidising, i. 107. Reaumur, Thermometer of, i. 18. Reciprocal Action of Salts, ii. 544. Red Lead, ii. 115. Oxide of Copper, ii. d5. Phosphorus, ii. 690. Sulphur, ii. 681. Reduction of the Force of the Electric Current to absolute Mecha- nical Measure, ii. 517. Test for Arsenic, ii. 2 1 3. Reflection, Polarisation by, ii. 457. Refraction, Polarisation by, ii. 459. Refrangibility of Light, Change of, ii. 481. Regnault, Condenser-Hygrometer, i. 96. Experiments on Gases, i. 77. Oxygen, i. 296. on Atomic Heat, i. 1 39. Evaporation of Water, i. 9 1 . the Weight of Air, i. 324. Table of Specific Heat, i. 25. the Specific Heat of Compounds i. 141, 142. Gases, ii. 429. Tension of Vapour of Water in Vacuo, i. 65; ii.435. Resistance of Metals, Electric, ii. 502. Respirators, Charcoal, ii. 658. Rheometers, ii. 497. Rheostat, ii. 504. Rhodic Acid, ii.407. Rhodium and .Potassium, Chloride of, ii. 410. Estimation and Separation of, ii 411. Oxides of, ii. 407. Protochloride of, ii. 409. Sesquichloride of, ii. 409. Sources and Extraction of, ii. 406. Sulphate of, ii. 410. Sulphide of, ii. 409. Rose's Fusible Metal, i. 11, Roseocobaltia Salts, ii. 70. Rotatory Power and Crystalline Form, Relations between, ii. 476. 798 INDKX. Rotatory Power induced by Magnetic Action, i. 281 ; ii. 481. Power, Specific, ii. 469. Ruthenic Acid, ii. 416. Oxide, ii. 415. Sulphate, ii. 416. Ruthenium, Bioxide of, ii. 415. Bichloride of, ii. 416. Estimation and Separation of, ii. 417. Protochloride of, ii. 414. Protoxide of, ii. 413. Sesquichloride of, ii. 41 5. Sources and Extraction of, ii. 412. Sesquioxide of, ii. 414. Sulphides of, ii. 417. Rutherford's Thermometer, i. 27. Saccharimetry, ii. 469. Saccharine Solutions, Table for the Ana- lysis of, ii. 475. Safety Lamp, Davy's, i. 377. Sal- alembroth, ii. 314. Saline Solutions, Tension of Vapours of, ii. 437. Waters, i. 319. Sal-prunelle, i. 535. Salt, Microcosmic, i. 563. Saltpetre, i. 535. Valuation of, ii. 657. Salts of Cobalt, Ammoniacal, ii. 68. Tin, ii. 133. Salts, i. 130. Acid, Neutral, and Basic, ii. 544. Amidogen, or Intermediate Nitrides, ii. 561. Analysis of (Wenzel), i. 131. Atomic Volume and Specific Gra- vity of, Table IL, i. 213. Bibasic, i. 193. Calorific Effect of Solution of, in Water, ii. 633. Constitution of, L 186 — 201. Decomposition of Ammoniacal, i. 205. , Insoluble, by Soluble, ii. 597. by Diffusion, ii. 613. Derivations of Double by Substitu- tion, i. 199. Diffusion of, ii. 606. Double, i. 197. Salts, Double Decomposition of, i. 229 — 233. Formation of, by Substitution, i. 201. Glauber's, i. 555. Heat produced in the Formation of, ii. 631. Monobasic, i. 193. the Type of Red Chro- mateof Potash, i. 196. Oxygen, or Intermediate Oxides, ii. 544. Reciprocal Action of, ii. 591 — 604. Solubility of, in 100 parts of Water, i. 220. Solution of, i. 219. Sulphur, ii. 548. Table of, i. 141. Tribasic, i. 194. usually denominated Subsalts, i. 194. Scale-oxide of Iron, ii. 47, Scales of Chemical Equivalents, i. 131. Schweitzer, Analysis of Sea- water, i. 319. Sea- salt, i, 642. Sea- water. Analysis of, i. 319. Secondary Decomposition, i. 262. Seleniate and Selenite, Mercuric, ii. 327. Mercurous, ii. 301. of Baryta, Decomposition of, by Alkaline Carbonates, ii. 599. Selenic Acid, i. 429. Selenide of Bismuth, ii. 244. Selenides, ii. 546. Selenious Acid, i. 428. Selenium, Allotropic Modifications of, ii. 688. Estimation of, ii. 689. Preparation of, ii. 688. Properties of, i. 427. Sesquicarbonate of Soda, i. 553. Sesquichloride of Carbon, i. 481. Cerium, ii. 265. Chromium, ii. 139. Gold, ii. 355. Iridium, ii. 396. Iron, ii. 48. Ruthenium, ii. 415. Sesquicom pounds of Iron, ii. 43. Sesquicyanide of Cobalt, ii. 67. Iron, ii. 48. Sesquioxide of Cerium, ii. 263. Chromium, ii. 155. Cobalt, ii. 65. Gold, ii. 350. Iron, ii. 43. Lead, ii. 115. Manganese, ii. 10. Nickel, ii. 76. INDEX. 799 Sesquioxide of Osmium, ii. 400. Ruthenium, ii. 414. Titanium, ii. 147. Tin, ii. 136. Uranium, ii. 255. Sesquisulphide of Chromium, ii. 159. Iron, ii. 47. Gold, ii. 355. Silica or Silicic Acid: — Dissolved by Acids, i. 393. Hydrates of, i. 394; ii. 675. Preparation and Properties of, i. 393. Silicate of Soda and Lime, i. 569. Zinc, ii. 87. Silicates, i. 395. Analysis of, ii. 677. of Alumina, i. 572, 610. Lime and of Alumina, i. 613. Magnesia, i. 600. Potash and Lead, i. 571. Soda, i. 567. Silicic Acid dissolved by Acids, i. 393. Estimation of, ii. 677. Formula of, ii. 674. Hydrates of, ii. 675. Siliciuretted Hydrogen, ii. 676. Silicon or Silicium, AUotropic Modifica- tions of, ii. 672. Atomic Weight of, ii. 674. Estimation of, ii. 677. Silicon and Hydrogen, Chloride, Bro- mide, and Iodide of, ii. 765. Silicon, Hydrated Oxide of, ii. 765. Chloride of, i. 484. Bromide of, i. 491. Preparation of, i. 391 ; ii. 672. Properties of, i. 392. Silver, Alloys of, ii. 343. Ammonio-nitrate of, ii. 212. Assay of, ii. 345. Bromide of, ii. 338. Carbonate of, ii. 339. Chromate of, ii. 169. Cupellation of, ii. 346. Cyanide of, ii. 339. Estimation and Separation of, ii. 344. Fluoride of, ii. 339. Hyposulphate of, ii. 340. Hyposulphite of, ii. 340. Iodide of, ii. 338. Metallurgy of, ii. 328. Nitrate of, ii. 341. Nitrite of, ii. 342. Oxalate of, ii. 343. Peroxide of, ii. 343. Silver, Properties of, ii. 331. Protoxide of, ii. 333. Sources of, ii. 328. Suboxide of, ii. 332. Sulphate of, ii. 339. Sulphide of, ii. 336. Silvering, ii. 359. Silver-ores, Treatment of, ii. 328. Silver-salts, Reactions of, ii. 334. Simmler and Wilde's Researches on Li- quid Diffusion, ii. 613. Six's Thermometer, i. 22. Soda, i. 526, 540. and Auric Oxide, Hyposulphite of, ii. 358. Aurous Oxide, Hyposulphite of, ii. 357. Potash, Carbonate of, i. 554. Sulphate of, ii. 735. Ash, i. 546. Alum, i. 609. Biborate of (Borax), i. 565. Bicarbonate of, i. 582. Biphosphate, i. 563. Bipyrophosphate of, i. 564. Bisulphate of, i. 562. Carbonate of, i. 544. Chlorate of, i. 562. Chromate of, ii. 166. Furnace, i. 558. Hydrates of Carbonate of, ii. 733. Hyposulphite of, i. 550. Metaphosphate of, i. 444, 564. Molybdates of, ii. 190. Nitrate of, i. 562. Phosphates of, i. 562—563. Preparation of Carbonate of, from the Sulphate, i. 557. Preparation of Sulphate of, i. 558. Pyrophosphate of, i. 444, 564, Salt, i. 546. Sesquicarbonate of, i. 553. Silicates of, i. 567. Solubility of Carbonate of, ii. 733. Sulphate of, ii. 735. Solution of Caustic, i. 541. Sub phosphate of, i. 563. Sulphate of, i. 665. Sulphite of, i. 554. Sodium, i. 540. Chloride of, i. 542. Chloroplatinate of, ii. 370. Compounds of, i. 540. Estimation and Separation of, ii. 735. Preparation of, i. 540 ; ii. 732. Salts of Oxide of, i. 544. Sulphides, i. 541. Telluride of, ii. 201 800 INDEX. Solid Bodies, Atomic Volume of, i. 209 ; ii. 582. Expansion of, i. 2 ; ii. 221. Specific Heat of, ii. 427. Soluble Glass,!. 568. Solution, Density of Salts, 600. of Salts in Water, Calorific Effect, ii. 633. Soils, Estimation of Nitrates in, ii. 656. Spectra exhibited by Coloured Media, ii. 486. Specific Heat, i. 24 ; ii. 426. and Heat of Combustion, Relations between, ii.629. of Gases i. 27. Atoms, i. 135. Carbon, i. 139. Gravity of Gases and Table of, i. 149—155. Rotatory Power, ii. 469. Stannic Acid, ii. 137. Chloride, ii. 140. Salts, Reactions of, ii. 137. Oxide, ii. 136. Oxide, Sulphate and Nitrate of, ii. 142. Sulphide, ii. 139. Stannous Iodide, ii. 135. Oxide, ii. 131. Salts, Reactions of, ii. 133. Sulphate and Nitrate, ii. 135. Steam as a Moving Power, i. 59 — 62. Latent Heat of, i. 57 ; ii. 432. Steel, ii. 31. Stoneware, i. 614. Strontia, i. 579. Estimation of, ii. 747. Separation of, from Baryta, ii. 748. Lime, ii. 752. Sulphate, Hyposulphite, and Ni- trate of, Carbonate of, i. 580. Strontium, Binoxide and Chloride of, i. 580. Preparation and Properties of, i. 579 ; ii. 146. Subchloride of Carbon, i. 483. Subnitrates or Bismuth, ii. 247. Copper, ii. 105. Suboxide or Bioxide of Bismuth, ii. 241. Lead, ii. 112. Silver, ii. 332. Subsalts, i. 194. Substances, Table of Elementary, i, 108 -112. Substitution, Formation of Compounds by, i. 227. Subsulphide of Iron, ii. 38. Succinate, Ferric, ii 51. Sugars, Optical Rotatory Power of, ii. 469-475. Sulphamide, ii. 741. Sulphantimonic Acid, ii. 232. Sulphate and Nitrate of Stannic Oxide, ii. 142. Ceroso-ceric ii. 264. Cerous, ii. 266. Chromic, ii. 159. Chromous, ii. 1 55. Cupric, ii. 103. Ferric, ii. 50. Ferroso- Ferric, ii. 51. Ferrous, ii. 41. Iridic, ii. 397. Manganic, ii. 11. Manganous, ii. 8. Mercuric, ii. 320. Mercurous, ii 301. of Alumina, i. 605. Ammonium, ii. 739. Antimony, ii. 226. Bismuth, ii. 247. Cadmium, ii. 91. Didymium, ii. 275. Didymium, Solubility of, ii. 276. Lanthanum, ii. 272. Lead, ii. 121. Lime, i. 589. and Potash, ii. 751. Magnesia, i. 597. Nickel, ii. 76. Potash, i 534. and Soda, ii. 735. Rhodium, ii. 410. Silver, ii. 339. Soda, Solubility of, ii. 735, Strontia, i. 584. Titanic Acid, ii. 149. Uranyl, ii. 257. Zinc, ii. 85. Osmic, ii. 401. Potassio-Ferric. ii. 50. Stannous, ii. 135. Ruthenic, ii. 416. Uranic, ii. 257. Uranous, ii. 254. Sulphates, i. 409. Earthy, decomposition of, by Alkaline Carbonates, ii. 597. Formula; of Neutral, i. 190. Atomic Volume of First and Second Class, i. 214. Sulphide, Auric, ii. 355. Aurous, ii. 350. Cuprous, ii. 96. Ferric, ii. 47. INDEX. 801' Sulphide, Ferrous, ii. 37. Mercuric, ii. 307. Mercurous, ii. 298. Staunic, ii. 139. Stannous, ii. 133. of Aluminium, i. 604. Carbon, solid, i. 427. Didymium, ii. 274. Lead, ii. 116. Manganese, ii. 5. Nitrogen, i. 424 ; ii. 682. Rhodium, ii. 409. Silver, ii. 336. Tantalum, ii. 283. Zinc, ii. 84. Sulphides, Alcoholic, ii. 546. Classification of, ii. 546. of Ammonium, ii. 737. Arsenic, ii. 209. Carbon, i. 425 ; ii. 684. Cobalt, ii. 67. Iridium, ii. 395. Molybdenum, ii. 192. Osmium, ii. 405. Phosphorus, i. 454 ; ii. 695. Potassium, i. 527. Ruthenium, ii. 417. Tellurium, ii. 200. Tungsten, ii. 182. Sulphite, Chromous, ii. 155. Cuprous, ii. 98. of Cadmium, ii. 90. Didymium, ii. 276. Perchloride of Carbon, ii. 703. Protochloride of Carbon, ii. 704. Soda, i. 554. Sulphites, Mercuric, ii. 321. their uses, i. 401. Sulphobromide of Phosphorus, ii. 711. Sulphocarbonic Acid, i. 425. Sulphochloride of Mercury, ii. 313. Sulphocyanide of Aluminium, i. 605. Platinum, ii. 371. Potassium, i. 532. Sulphur, AUotropic modifications of, i. 396 ; ii. 679. and Carbon, i. 425 ; ii. 684. Chlorine, i. 485 ; ii. 706. Hydrogen, i. 419. Nitrogen, i. 424 ; ii. 682. Phosphorus, i. 454 ; ii. 695. Bromide of, i. 490. Chlorides of, i. 485 ; ii. 706. Class of Elements, i. 168. Estimation of, ii. 686. Heat of, Combustion of, in various states, ii. 630. Iodide of, i. 502. Sulphur, Melting Point of,- i. 396 ; ii. 681. Properties of, i. 396. Protochloride of, i. 486. Uses of, i. 398. Sulphur- Acids, ii. 547. Sulphur- Compounds, Atomic Volume of Liquids, ii. 577. Sulphur- Ethers, Compound, ii. 543. Sulphur-Salts, ii. 548. Sulphuric Acid, Action of, on Penta- chloride of Phospho- rus, ii. 709. Density of, i. 408. Estimation of, ii. 686. Formation of, Anhy- drous, ii. 682. Heat evolved in the Hydration of, ii. 632. Hydrates of, i. 409. Manufacture of, i. 404. Preparation of, i. 402. Properties of, L 406. Uses, i. 410. Sulphurous Acid, Action of, on Penta- chloride of Phospho- rus, ii. 708. Estimation of, ii. 687. its Preparation, i. 399. Properties of, i. 400. Series, i. 402. Volumetric Estimation of, ii. 722. Water, i. 369. Sulphuryl, Chloride of, ii. 550, 709. Supersaturated Solutions of Carbonate of Soda, ii. 732. Sulphate of, i. 555. Symbols, i. 118. T. Tangent- Compass, ii. 497. Tantalic Acid, ii. 278. Hydrated, ii. 280. Reactions of, ii. 287. Tantalous Acid, ii. 273. Tantalum, ii. 277. Bromide of, ii. 284, Chloride of, ii. 283. Estimation and Separation of, ii. 284. Fluoride of, ii. 284. Sulphate of, ii. 283. Tartar- emetic, ii. 226. Tartaric Acid, Circular Polarisation of, ii. 477. Inactive, ii. 480. 802 INDEX. Tartaric Acid, Pyro-electricity of, ii.479. Tartrate of Potash and Antimony, ii.226. Potassio- ferrous, ii. 43. Tartrate of Tin and Potassium, ii. 135. Telluretted Hydrogen, ii, 200. TeUuric Acid, ii. 198. Anhydrous, ii. 199. Tellurides, ii. 201. 546. Tellurium, ii. 194. Chlorides of, ii. 200. Estimation and Separation of, ii. 201. Sulphides of, ii. 200. Tellurous Acid, ii. 196. Anhydrous, ii. 196. Temperature, Capt. Parry and Back on, i. 41. Equilibrium of, i. 38. of the Atmosphere, i. 325. Table of interesting Cir- cumstances in the Range of, i. 23. Tension of Vapours, ii. 434. Terbia, i. 618. Terbium, i. 617. Terchloride of Antimony, ii. 225. Bismuth, ii. 245. Bismuth and Ammonium, ii. 246. Iridium, ii. 397. Osmium, ii. 403. Phosphorus, i. 486. Terchromate of Potash, ii. 166. Terfluoride of Antimony, ii. 225. Chromium, ii. 169. Teriodide of Bismuth, ii. 246. Teroxide of Bismuth, ii. 242. Hydrogen, ii. 640. Iridium, ii. 395. Tersulphide of Antimony, ii. 223. Bismuth, ii. 244. Test- Acid, i. 550. Tetramercurammonium, Chloride of, ii. 312. Iodide of, ii. 307. Nitrate of, ii. 322. Tetrametaphosphoric Acid, ii. 694. Tetrathionic Acid, i. 418. Tetartohedry, ii. 476. Thenardite, i. 557. Thionamic Acid, ii. 741. Thionamide, ii. 709, 741. Theory of Heat, Dynamical, ii. 449. Thionyl, Chloride of, ii. 708. Thermometer, Celsius, i. 18. Crichton's, i. 17. Description of the, i. 14. Regnault's and Pierre's Remarks on the, i. 1 7. Thermometer, Reaumur's, L 18. Rutherford's, i. 21. Sanctorio's and Sir John Leslie's, i. 14. Six's, i. 22. Thermo-multiplier, i. 35. Thorina, i. 618. Thorium, i. 615. 618. Tin, ii. 130. Alloys of, ii. 143. AmmoniO' Chloride of, ii. 140. and Antimony, Separation of, ii. 238. Potassium, Bichloride of, ii. 1 42. Protochioride of, ii, 134. Tartrate of, ii. 135. Sulphur, Bichloride of, ii. 141. Bichloride of, with Oxychloride of Phosphorus, ii. 142. Bichloride of, with Pentachloride of Phosphorus, ii. 141. Bioxide of, ii. 136. Bisulphide of, ii. 139. Chlorosulphide of, ii. 141. Class, i. 173. Estimation and Separation of, ii. 143. Protochioride of, ii. 133. Protiodide of, ii. 135. Protoxide, ii. 131. Protosulphateof, ii. 135. Protosulphide of, ii. 133. Separation of, from Antimony and Arsenic, ii. 236. Sesquioxide of, ii. 136. Volumetric Estimation of, ii. 144. Tinkal, i. 565. Titanic Acid, Sulphate of, ii. 149. Titanic Oxide, ii. 147. Titanium, ii. 145. Bichloride of, ii. 148. Bifluoride of, ii. 149. Bisulphide of, ii. 148. Bromide of, ii. 149. Estimation and Separation of, ii. 151. Nitrides of, ii. 149. Nitro-cyanide of, ii. 150. Protoxide of, ii. 146. Sesquioxide of, ii. 147. Touchstone, ii. 362. Tourmalines, Polarisation by, ii. 461. Transpiration of Gases, i. 83. Triamides, Primary, ii. 559. Tribasic Phosphate of Water, i. 440. Salts, i. 194. Trimetaphosphoric Acid, ii. 694. Trimercurammonium, Nitrate of, ii. 323. Triphosph amide, ii. 695. INDEX. 803 Trisul-hyposulphuric Acid, i, 418. Trithionic Acid, i. 417. Tungstates, ii. 180. and Chromates, Atomic Vo- lume of, i. 214. Tungsten, ii. 176, Class of Elements, i. 173. Chlorides of, ii. 183. Estimation and Separation of, ii. 184. Phosphides of, ii. 182. Sulphides of, ii. 182. Tungstic Acid, ii. 178. Action of, on Pentachloride of Phosphorus, ii. 710. Oxide, ii. 177. Turnbull's Blue, ii. 40. Type-Metal, ii. 234. Types and Radicals, ii. 521. U. Ultramarine, i. 573. Unitary System, Gerhardt's, ii. 512. Uranic Nitrate, ii. 257. Oxide, ii. 255. Oxide, Compounds of, with Bases, ii. 258. Phosphates, ii. 257. Salts, Fluorescence of, ii. 257, 484. Sulphate, ii. 257. Uranium, Estimation and Separation of, ii. 258. Sources and Extraction of, ii. 251. Protochloride of, ii. 254. Protoxide of, ii. 253. Sesquioxide of, ii. 255. Ui-anoso-uranic Oxide, ii. 254. Uranous Chloride, ii. 254. Oxide, ii. 253. Sulphate, 254. Uranyl and Potassium, Chloride of, ii. 257. Arseniate of, ii. 258. Chloride of, ii. 256. Nitrate of, ii. 257. Phosphates of, ii. 257. Sulphate of, ii. 257. Utricular Sulphur, ii. 681. V. Vanadic Acid, ii. 174. Vanadium, ii. 173. Bioxide of, ii, 173. Vanadium, Estimation and Separation of, ii. 175. Protoxide of, ii. 173. Vaporisation, i. 47 — 68. Brix's Experiments on, i. 56, 67. Despretz's Experiments on, i. 57. Table of Elastic Force of Steam, i. 55. Vapour, i. 328. of Water, i. 314. Vapours and Gases, Specific Heat of, ii. 429." Table of the Specific Gravity of Gases and, i. 149, 155. Latent Heat of, ii. 431. Tension of, ii. 434. of Saline Solutions, Tension of, ii. 437. Vapour-volume, Uniformity of, ii. 515. Varvicite, ii. 14. Ventilators, Charcoal, ii. 659. Voltaic Circle, Applicationof the, to Che- mical Synthesis, i. 264. (Compound), i. 250. Liquid Elements of the, i. 258. (Simple), i. 242. Solid Elements of the, i. 255. ■without a Positive Metal, i. 267. with the Connecting Wire unbroken, i. 245. with the Connecting Wire broken, i. 249. Theoretical Considera- tions on, i. 272. Battery, i. 253. Current, Heating Power of, ii. 506. Endosmose, i. 266. Instruments, i. 283, 290. Protection of Metals, i. 256. Secondary Decomposition, i. 262. Transference of Ions, i. 265. Voltameter, L 290. Volume, Atomic, of Liquids, ii. 569. Volume, Atomic, of Solids, i. 213 ; ii. 582. Volumetric Analysis, Bunsen's General Method of, ii. 722. Volatility of Carbon, ii. 658. W. Water, Absorption of Gases by, i. 75. 316; ii. 647. Boutigny's Experiments on the Ebullition of, i. 49. 804 INDEX. Water, Calorific Effect of Solution of Salt§ in, ii. 633. Calprimeter, ii. 626. Capacity of, for Heat, i. 26. Chalybeate, i. 319. Circulation of, i. 11. Constitutional, i. 195. Contraction of, i. 9. Ebullition of, i. 48, Estimation of, ii. 646. Expansion of, i. 1 1 ; ii. 424. Estimation of Nitrogen in,ii. 656. Evaporation of (Dalton), i. 91. Filter, i. 317. Heat evolved in the combination of Sulphuric Acid with,ii. 632. Latent Heat of, i. 44 ; ii. 430. Vapour of, i. 44 ; ii. 432. Leslie's Process for Freezing of, i. 66. Oxygenated, i. 185. Properties of, i. 313. Saline, i. 319. Schweitzer's Analysis of Sea- Water, i. 319. Specific Heat of, ii. 428. Sulphurous, i. 319. Table of Boiling Point of, i. 52. Tension of Vapour of, i. 65 ; ii. 435. Tribasic Phosphate of, i. 440. Type, ii. 523, 530. Uses of, i. 316. Vapour of, i. 314. Wedgwood's Pyrometer, i. 20. White Lead, ii. 119. Williamson's Theory of Chemical Action, ii. 600. Winds, i. 326. Wood, Heat-conducting Power of, ii. 443. Y. Yellow Prussiate of Potash, i. 529. Yttria, i. 617. Yttrium, i. 615, 617. Z. Zinc, i. 128, 256; ii. 81. Alloys of, ii. 87. Carbonate of, ii. 85. Chloride of, ii. 84. Estimation and Separation of, ii. 87. Iodide of, ii. 85. Nitrate of, ii. 86. Oxide of, ii. 84. Phosphate of, ii 86. 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Histoire naturelle des drogues simples, ou Cours 'I'histoire naturelle professe a I'Ecole de Pharmacie, quatrieme edition, augmentee. 4 vo. , Svo., avec 600 fig. inter- calees dans le texte. Paris, 1849 . . . . . . 7 50 Half bound in Paris . . . . . .9 60 [Cet ouvrage, que tous les pharmaciens considerent comme un Vade-mecum de pre- miere necessite, puree que la grande exactitude apportee par I'auteur dans la descrip- tion des drogues leur permet dedistinguer les diverses especes et varietes qui se rencon- trent dans le commerce, ainsi que les falsifications qu'on leur fait subir. Cette quatrieme edition a ete soumise a une revision generiile, et les augmentations out ete telleuient importantes, qu'on peut la considercr cotnme un ouvrage eutierement neuf. C'est un CourH i'A/mplet (V kifttoire naturelle pharmaceutique et medicale, que les medecins con3ult«ront toujours avec fruit.] Guitard. Histoire de I'Electricite. 12rao. Paris, 1854 . . . . 1 00 Gurney. Lectures on Chemistry. Svo. 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Esquisse d'une nouvelle classification Cliimique des Corps. 4to. . . 26 ^ Combust:. )n de Ja vapeur alcoolique et etheree, autour d'un fil de Platine. 4to, . z5 Sur la theorie Chimique de la Respiration et de la Chaleur Animal. 4to, . 50 Martins (A.) Handbuch der Photographie. Dritte aullage. Svo. Wien, 1852 . 2 3: ITIatlier (Ja,nies). Coal Mines, their Dangers and Means of Safety. Svo., woodcuts. London, 1S53 . . . . . . . . . 1 12 mattenci. Cours Special sur I'Induction, le Magnetisme et sur les relations entre la P6rce Magnetique et les Actions Moleculaires. Svo. Paris, 1854 . . . . 1 50 IVatteucci et Savl. Traite des phenomenes Electro-Physiologiques des animaux. Svo. Paris, 1844 . . . . . . . . 2 00 ]IIatthe'%vs (W.) Compendium cf Gas Lighting. 12mo. London . . . 1 25 Historical Sketch and Origin of Gas Lighting. 12mo. London . . 2 25 menioires d'Agriculture, d'Economie Rurale et Domestiqne, publics et par la Societe Im- periale et Centrale d'Agriculture. Annee 1854. lere partie, Svo. Paris, 1855 . 1 50 Messier. Observations sur les grandes Chaleurs, la Secheresse, etc., de la Seine a Paris, 4to. Pendant 1793 . . . . . . , . 50 Metcalfe (S. T.) Caloric; its Mechanical, Chymical, and Vital Agencies in the Pheno- mena of Nature. 2 vols., Svo. . . . . . , . 10 50 Mialhe. Chimie appliquee a la Physiologie et a la Therapeutiqae. Svo. Paris, 1855 . 2 6tf Miller (W. A.) Elements of Chemistry, Theoretical and Practical, extensively illus- trated. 8 vols. Svo. London, 1855^7 . . . . . 14 00 Just Completed. Millar (James). Elements of Chemistry. Svo. London . . . 8 75 Miller {VV.) (Cashier to the Bank of England.) Decimal Tables used at the Bank of England, for reducing Gross weight of Gold and Silver to Standard. 4to. London, 1854 1 25 Millon (M. E.) Etudes de Chimie Organique faites en vue des Applications Physiolo- logiques et Medicales. Svo. Lille, 1849 . . . . . . 76 XT. Sailliere, 290 Broadway^ JIT. IT. m 10 Standard Scientific Works » inillon (ITf . E.) Dea Plienomenes qui se produisent du contact de I'Eau et du Ble et de leur Consequences, Industrielles. 8vo. Paris, 1854 . . . . 60 mitcliell (•>.) Manual of Practical Assaying, intended for the use of Metallurgists, Captains of Mines, and Assuyers in general. With a copious table, for the purpose of ascertaining in Assays of Gold and Silver the precise amount, in ounces, pennyweigiits, and grains, of noble metal contained in one ton of ore, from a given quantity. 1 vol., Svo. 2nd edit. London, 1854 . . . . . . . 5 00 • Treatise on the Adulterations of Pood, and the Chemical means employed to detect them. Containing Water, Flour, Bread, Milk, Cream, Beer, Cider, Wines, Spirit- uous Liquors, Coffee, Tea, Chocolate, Sugar, Honey, Lozenges, Cheese, Vinegar, Pickles, Anchovy Sauce and Pasta, Catsup, Olive (Salad) Oil, Pepper, Mustard. 12mo. Lon- don, 1848 . . . . . . . . . 1 50 Moig^no. Traite de Telegraphic Electrique. 8vo., and atlas. Paris, 1852 . . 8 76 , Repertoire d'Optique. 4 vols., 8vo. Paris, 1849-50. (Very scarce.) l^orebead (•.) Essay on Inebriating Liquors and Distillation. Svo. London . 4 75 Illorfit (C) A Treatise on Chemistry applied to the Manufacture of Soap and Candles. New edition. 8vo., woodcuts. Philadelphia, 1856 . . . . 6 00 mulder (G, J.) The Chemistry of Vegetable and Animal Physiology, with intro- duction and notes by J. E. W. Johnston, and twenty illustrations, colored and plain. 8vo., cloth . . . . . . . . . 8 50 niuller. Principles of Physics and Meteorology. Illustrated with 600 Woodcuts, and 2 colored plates. 8vo. London, 1847 ...... Murphy (Rev, R.) Elementary Principles of the Theories of Electricity, Heat, and Molecular Actions. Part I. Svo. Cambridge (England), 1832 Murpliy (P.) Rudiments of the primary forces of Gravity, Magnetism, and Electricity in their Agency on the Heavenly Bodies. Svo. London, 1880 Murray. 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Baudrimont, 1 ; Berzellus, 2; Pelouze & Fremy, 11. Handbook. Gmelin, 6. History. Hoefer, 7 ; Thomson, 13. Inorg'a.nic. Campbell, 3; Berzellus, 2 ; Gmelin, 6 ; Gregory, 6 ; Outlines of, 7 ; Thomson, 13. Liectures. Gurney, 6. ITI a, n U a I . Bernay, 2 ; Brande, 3 ; Fyfe, 5 ; Glover, 6. iVlanipulation. Faraday, 5 ; Noad 10; Benoit. jTIemoirs. Dumas, 5 ; Graham, 6. Non-Metaliir. Faraday, 5. Orsranic. Brande, 2 ; Dumas, 5 ; Ger- hardt, 6 ; Gmelin, 6; Gregory, 6 ; Lowig, 9; Millon, 9; Raspail, 12; Thomson, 13; Wolff, 14. Philr-sopliy. Dalton, 4; Daniell,4; Davy, 4 ; Webster, 14 ; Weekes, 14. Practical. Bowman, 2. Progress of. Berzellus, 2; Liebig and Kopp, — Treatise. Gregory, 6. Crystailograpliy. Descloizeaux,4; Lau- rent, 8 ; Regnault, 12. Colors and Painting. Chevreul,3; Co- loriate, 4. Cyclopned.ia* Oooley, 4; Francis, 5 ; Pre- chtl, 11 ; Thomson, 1 ; Tomlinson, 13. Dictionary (Ciieinical; etc.) Cheval- lier, 3 ; Crabb, 4 ; lloefer, 7 ; Laboulaye, 8; Lassaigne, 8; Nesbit, 10; Ottley, 10; ToUhausen, 13 ; Ure, 14. DistillinK'. Dubrunfaut, 5 ; Duplais, 5 ; La- cambre, 8; Le Normand, 9; Morewood, 10. Dyeiuiir and Scouring:. Berthollet, 2 ; Blanchiment, 2 ; Brande, 2; Love, 9 ; Na- pier, 10; Parnel, 10 ; Persoz, 11 ; Kunze,12 ; Smith, 13; Thomson, 18. 16 Alphabetical Index, Electricity. Becquerel, 2; Chalmers, 8; Cummiug, 4 ; De la Rive, 4 ; De Bois Ray- mond, 4; Faraday, 5; Harris, 7; Matteuci,9; Murphy, 10 ; Noad, 10. Electrlc-Telegrraph* Highton.T; Moigno, 10. Electro-metallurgy. Dorure, 4; Gal- vanoplastie, 5 ; Gore, 6 ; Napier, 10 ; Rose- leur, 12 ; Smee, 18 ; Walker et Fau, 14. Falsifications. Ohevallier, 3 ; HassaU, 7; Hureaux, 7; Marcet,.9 ; Mitchell, 10. Food. See FaUifioaUont. Oas. Accum, 1 ; Clegg, 4 ; Knapp, 8 ; Journal of, 6 ; Matthews, 9 ; Peckston, 11 ; Pelouze, 11. Geological Chemistry. Bischoff, 2. Olue. Colles,4. Heat. Avogrado, 1 ; Cooper, 4 ; Dove, 6 ; Gavarret, 6 ; Lardner, 8 ; Metcalfe, 9 ; Pe- clet, 11 ; Poisson, 11 ; Prideaux, 11 ; Reech, 12 ; Regnault, 12 ; Thomson, 13 ; Williams, 14. Ink. Encres, 4. magnetism. Becquerel, 2. Meteorology, Arago, 1 ; Cotte, 4 ; Hop- kins, 7; Houzeau,7; Howard, 7; Kaemtz,8; Lambert, 8 ; Nicollet, 10 ; Peltier. 11 ; Pouil- let, 11 ; Prout, 11 ; Robertson, 12 ; Sabine, 12. mineral "Waters. Bouquet, 2 ; Faure, 5. Optics and Light. Biot, 2 ; Brewster, 8 ; Claudet, 4; Du Moncel, 5 ; Gorham, 6; Har- dy, 7 ; Hunt, 7 ; Kyan, 8 ; Light, 9 ; Moigno, 10 ; Scantini, 12 ; Scoffern, 18. Perfumery. Piesse, 11. Pharmacy. Deschamps, 4; Goebel, 6; Guibourt, 6 ; Jourdain, 8 ; Pharmaceutical Journal, 11 ; Repertoire de, 12 ; Soubeiran, 18; Wittstein, 14. Pharmacopeia. Codex, 4 ; New London, 11 J Trousseau and Reveil, 14. Photography. Barreswil and Davanne, 1 ; Blanquart, 2; Brebisson, 3; Ohevallier, 3 ; Cundall, 4; David, 4; Delaiiiotte, 4; De- souge, 4; Disderi, 4; Fau, 5; Gaudin, 6; Hardwicke, 7 ; Heath, 7 ; Henuah, 7 ; Her- ling, 7; Howlett, 7; Hunt, 7 ; Lacan, 8; Legray, 8 ; Lerebours, 9 ; Long, 9 ; Mar- tens; 9 ; Rintoul, 12 ; Sutton, 18 , Thorn- thwaite, 18. Physics. Aime Martin, 1 ; Ajasson de Grandsagne, 1 ; Archanibault, 1 ; Biot, 2 Bird, 2 ; Boutigny, 2 ; Brown, 3 ; Cabart, 3 Coulomb,4; Cuvier,4; Daguin,4;Desains,4: Durand, 5 ; Fau and Ohevallier, 5; Ganot,5 Grove, 6; Gruyer, 6 ; Guitard,6, Hinds, 7 Julien,8; Lame, 8; Lardner, 8; Liebig, 9 McGauley, 9; Muller, Id; Peclet, 11 ; Pou illet, 11 ; Quetelet, 11 ; Regnault, 12; Roichen. bach, 12; Scoffern, 13; Scoresby, 13 ; Sou beiran, 13 ; Thieme, 13. Platina. Billard, 2. Polarization. Biot, 2 ; Pereira, 11 ; Wood- ward, 14. Precious Metals. Faucher, 5. Pyrotecliny. Chertier, 8. Rural Economy. Bouchardat,2; Bous- singault, 2. Safety Lamps for Miners. Davy, 4; Knapp, 8. Sugar. Baudrimont, 2 ; Kerr, 8 ; Scoflfern, 13 ; Shier, 13. Ventilation. Amott, 1 ; Dunn, 5 ; Hed- ley, 7; Hood, 7; Mather, 8; Reid, 12; Richardson, 12. l¥eaviug'* Etoffes Imprimees, 5 ; Persoz,ll. ♦ 4 . •*^99e J St ^~ ' •■•, --U .ilQ(;0 .U^^^tiJ. ^„