CHEMISTRY. 



aurochloride of potassium (KCl,AuCl 3 ), auro- 

 chloride of sodium (NaCl,AuCl 3 ), platinochloride 

 of potassium (2KCl,PtCl 4 ), platinochloride of 

 sodium (2NaCl,PtCl4). Platinochloride of potas- 

 sium is sparingly soluble in water, insoluble in a 

 mixture of alcohol and ether ; very similar to it is 

 the platinochloride of ammonium (2NH 4 Cl,PtCl4). 

 When the latter salt is heated, chloride of ammo- 

 nium, hydrochloric acid, and nitrogen are given 

 off, and metallic platinum is left as a spongy, 

 porous mass (spongy platinum). British standard 

 gold is an alloy of gold and copper, containing in 

 12 parts, ii of gold and i of copper. 



6. The metals of the Antimony group resemble, 

 in many respects, the non-metallic elements ; 

 arsenic, antimony, and bismuth being analogues 

 of phosphorus ; while tin has many points of 

 resemblance to silicon. Vanadium, molybdenum, 

 and tungsten are comparatively rare metals. 



Arsenic occurs in nature combined with sulphur 

 in realgar (AsS) and orpiment (As 2 S 3 ) ; with 

 metals, particularly iron, in mispickel and arsen- 

 ical pyrites (almost all specimens of iron pyrites 

 contain some arsenic, which thus occurs in sul- 

 phuric acid prepared from pyrites (see CHEMISTRY 

 APPLIED TO THE ARTS. When arsenical ores 

 are heated in a current of air, the arsenic is 

 converted into 'white arsenic,' or arsenious acid 

 (As 2 O 3 ). Arsenious acid, when heated with 

 nitric acid, is oxidised to form arsenic acid 

 (3H 2 O,As 2 O 6 ), an acid very closely resembling 

 phosphoric acid (3H 2 O,P 2 O 5 ). Arsenious and 

 arsenic acids form arsenites and arseniates with 

 bases. Arsenite of copper is the green pigment 

 known as ' Scheele's green.' ' Schweinfurt green ' 

 is a compound of arsenite of copper and acetate 

 of copper. All these compounds of arsenic are 

 highly poisonous. 



Antimony occurs in nature chiefly as sulphide 

 of antimony (Sb 2 S 3 ). Its most important com- 

 pounds are : Antimonious oxide (Sb 2 O 3 ), a weak 

 base, forming salts with some acids. Tartar emetic 

 is the double tartrate Jsee p. 335) of potash and 

 antimony (K 2 O,Sb 2 O 3 ,T, where T stands for an- 

 hydrous tartaric acid). Chloride of antimony 

 (SbClg) is formed by the action of strong hydro- 

 chloric acid on sulphide of antimony ; when 

 poured into water, it forms a white precipitate, 

 'powder of algaroth,' or oxychloride of anti- 

 mony (3SbCl 3 + 3H 2 O = 6HC1 +Sb 2 O 3 ,SbCl 3 or 

 SbCL, + H 2 O = 2HC1 + SbOCl). 



Tin occurs in nature as 'tinstone' or stannic 

 oxide (SnO 2 ), corresponding to silica (SiO 2 ). The 

 most important compounds of tin are : Stannous 

 chloride, ' salt of tin,' or ' pink salt ' (SnCLj), 

 formed by the action of hydrochloric acid on tin 

 (Sn + 2HC1 = H 2 + SnClg). It is soluble in water, 

 and is used as a mordant in dyeing (see 

 CHEMISTRY APPLIED TO THE ARTS). Stannic 

 chloride (SnCl 4 ), formed by the addition of 

 chlorine to stannous chloride. It is a colourless, 

 volatile liquid. Stannic oxide acts as an anhy- 

 drous acid, and forms salts called stannates. 



Compounds of the metals with one another are 

 called alloys. They resemble metals in their 

 physical characters. We shall mention a few of 

 the most important. 



Brass, 64 parts copper and 36 parts zinc ; 

 German silver, 51 parts copper, 30-5 parts zinc, 

 and 18-5 parts nickel; bell-metal, 78 parts copper 

 and 22 parts tin ; bronze, 80 parts copper, 4 parts 



zinc, and 16 parts tin ; coinage bronze, 95 parts 

 copper, I part zinc, and 4 parts tin ; aluminium 

 bronze, 90 parts copper and 10 parts aluminium ; 

 spider, from 2 parts tin and I part lead, to i part 

 tin and 2 parts lead ; pewter, 4 parts tin and r 

 part lead; Britannia metal, pewter with a little 

 copper and antimony; type-metal, 2 parts lead, 

 i part tin, and i part antimony ; standard (or 22 

 carat) gold contains in 24 parts, 22 of gold and 2 

 of copper. Alloys containing less gold are used 

 in jewellery such as i8-carat gold, containing 18 

 parts gold in 24; i6-carat gold, containing ot 

 pure gold ; &c. 



Standard silver, as already stated, contains 7-5 

 per cent, of copper. 



The alloys of mercury are called amalgams. 

 Tin amalgam is used for silvering looking-glasses. 

 For details respecting the metals, the reader is 

 referred to the article on METALS AND METAL- 

 LURGY. 



ORGANIC CHEMISTRY. 



The term ' Organic Chemistry ' was first em- 

 ployed to express that department of chemistry 

 which treats of the substances peculiar to animals 

 and vegetables, and the direct derivatives of these 

 substances. As almost all these substances con- 

 tain carbon, and as almost all compounds of 

 carbon are practically obtained from animal or 

 vegetable products, it is now found more con- 

 venient to group all carbon compounds together, 

 and to define organic chemistry as the chemistry 

 of the compounds of carbon. These compounds 

 are so numerous, and many of them so complex, 

 that it is impossible in a sketch like this to do 

 more than shortly describe the relations of a few 

 of them, selected on account of their practical 

 importance. 



Some of the simpler carbon compounds car- 

 bonic acid, carbonic oxide, marsh gas, and olefiant 

 gas have already been described (p. 323), and 

 are therefore omitted here. We shall begin with 

 a large and very important group of compounds 

 known as the 'carbohydrates.' This name implies, 

 not that they contain carbon and water, but that 

 they contain carbon, hydrogen, and oxygen, and 

 that the hydrogen and oxygen are present in them 

 in the same proportion as in water. The most im- 

 portant members of the group are : I. The sugars ; 

 2. Starch, gum, and inulin ; and 3. Cellulose. 



i. Sugars are substances, soluble in water, hav- 

 ing a sweet taste, and capable of undergoing the 

 peculiar chemical change called the vinous fer- 

 mentation, which will be described farther on 

 (p. 332). They may be divided into two sets : i. 

 Those analogous to grape-sugar ; and 2. Those 

 analogous to cane-sugar. Honey and the juice 

 of sweet fruits contain principally grape-sugar. 

 These can also be prepared from cane-sugar and 

 its analogues, and from starch, inulin, or cellulose. 

 The formula of grape-sugar is C 6 H 12 O ? . Cane- 

 sugar and milk-sugar are the most important 

 sugars of the second set. Cane-sugar is obtained 

 from the juice of the sugar-cane, from the juice of 

 the beetroot, from the sugar-maple, and from the 

 sugar-palms. It occurs mixed with sugars of the 

 first set in most sweet fruits. Milk-sugar is con- 

 tained in the milk of all mammals, and is obtained 

 by evaporating the whey, and allowing the sugar 



