CHAMBERS'S INFORMATION FOR THE PEOPLE. 



salt crystallises out in large tabular crystals contain- 

 ing two molecules of water of crystallisation. In 

 the fusion, cyanide of potassium is formed by the 

 union of the nitrogen and carbon of the animal 

 matter with the potassium of the potash ; and the 

 cyanide of potassium, by the action of water, oxy- 

 gen, and iron, is converted into the ferrocyanide, 

 thus : 6KCN -f Fe + H 2 O + O = 2KHO + 

 4KCN,Fe(CN)2. Ferrocyanide of potassium, when 

 treated with dilute sulphuric acid, yields hydrocy- 

 anic acid, which, being volatile, can be distilled off 

 from the residue, consisting of sulphate of potash 

 and a substance called ' Everitt's salt.' 



Prussic acid is an extremely poisonous sub- 

 stance, and this character belongs also to most of 

 the cyanides. The ferrocyanides are, however, 

 exceptions. By the action of chlorine, ferrocyanide 

 of potassium is converted into ferricyanide of po- 

 tassium or red prussiate of potash, 4KCN,Fe(CN) 2 

 + Cl = 3KCN,Fe(CN) 3 + KC1. The most import- 

 ant cyanides are : Cyanide of potassium, KCN ; 

 cyanide of silver, AgCN ; mercuric cyanide, 

 Hg(CN) 2 , formed by dissolving mercuric oxide in 

 aqueous hydrocyanic acid, and crystallising. Ferro- 

 cyanide and ferricyanide of potassium. Ferric fer- 

 rocyanide (Prussian blue) and ferrous ferricyanide 

 (TurnbuU's blue). Mercuric cyanide, when heated, 

 decomposes into metallic mercury and cyanogen. 

 Part of the cyanogen passes off as cyanogen gas, 

 (CN) 2 or C 2 N 2 , part remains as brown solid of the 

 same composition, known as paracyanogen. Just 

 as chlorine, when passed into a cold solution of 

 caustic potash, gives chloride of potassium, and 

 hypochlorite of potash, KC1 and KC1O, so cyano- 

 gen, under the same conditions, gives cyanide 

 of potassium, KCN, and cyanate of potash, KCNO. 

 Cyanate of potash can also be formed by the 

 oxidation of cyanide of potassium by means of 

 red oxide of lead or black oxide of manganese. 



ORGANIC BASES. 



It has already been pointed out that the alcohols 

 have a great resemblance in their mode of action 

 upon acids to hydrated bases (p. 333) ; but there 

 are other organic compounds which are much 

 more completely analogous to the bases of inor- 

 ganic chemistry, forming, with acids, salts, which 

 are usually crystalline, and which undergo double 

 decomposition exactly as the salts of metallic 

 oxides do. Many of these organic bases, or alka- 

 loids, as they are called, are soluble in water, and 

 have an alkaline reaction. Some of them can be 

 formed artificially, and some occur as salts in the 

 juices of various plants. Thus, in opium, the dried 

 juice of the unripe heads of the white poppy (Pa- 

 paver somniferum), there occur salts of morphia, 

 codeia, narcotine, thebaine, papaverine, narceine, 

 and some other less completely investigated alka- 

 loids. The juice of the deadly nightshade (Atropa 

 belladonna) contains a salt of the alkaloid atropia. 

 Nux-vomica contains salts of strychnia and brucia ; 

 cinchona bark, salts of quina and cinchona ; 

 henbane (Hyoscyamus niger) contains a salt of 

 hyoscyamine ; tobacco (Nicotiana tabacum) con- 

 tains a salt of nicotine ; hemlock (Conium macu- 

 latutn), a salt of conia; and so on. In most cases, 

 the plant owes its special action on the animal 

 system, as a poison or drug, to the alkaloid or 

 alkaloids contained in it, so that it is possible to 

 substitute a salt of the alkaloid as a medicine 



336 



for the extract or tincture of the plant, with the 

 advantage of having a substance of constant com- 

 position and action, instead of a mixture which 

 sometimes contains more, sometimes less, of the 

 alkaloid which is its really active ingredient. 



For detailed accounts of these vegetable alka- 

 loids, we must refer the reader to the larger hand- 

 books of chemistry. They all contain nitrogen, 

 and may be regarded as ammonia in which the 

 hydrogen has been replaced by organic radicals ; 

 thus, trimethylamine, a base which occurs in 

 herring-brine, is N(CH 3 ) 3 , corresponding to am- 

 monia, NH 3 . The other natural bases have a 

 similar, though, in most cases, a much more com- 

 plicated constitution. 



VOLATILE OR ESSENTIAL OILS 



are obtained from many plants by distillation 

 with water, the oil coming over with the water, 

 and collecting in the receiver, partly dissolved in 

 the water, partly floating upon its surface. The 

 watery solution has the odour of the oil. In this 

 way, oil (or attar) of roses and rose-water, oil of 

 lavender and lavender water, &c. are prepared. 

 Many of these oils, so different in odour, have the 

 same composition as oil of turpentine namely, 

 C 6 H 8 . Of these we may name oil of lemons, 

 of bergamot, of juniper, of thyme, of parsley. 

 Others contain various volatile substances. Thus, 

 oil of bitter almonds is a mixture of benzoic alde- 

 hyd (C 7 H 6 O) and prussic acid ; oil of meadow- 

 sweet is salicylic aldehyd (C 7 H 6 O 2 ) ; oil of mus- 

 tard, C 4 H 6 NS. 



ALBUMINOUS OR PROTEIN COMPOUNDS. 



The white of egg consists chiefly of a watery 

 solution of a substance called albumine; a similar 

 substance occurs in the serum of blood and in 

 dropsical fluids. Fibrine occurs in the clot of 

 blood ; caseine is that constituent of milk which is 

 curdled by rennet or by the addition of an acid to 

 the milk. These substances have many properties 

 in common, and have nearly the same composi- 

 tion. We now know a considerable number of 

 such bodies. They form essential constituents of 

 animal organisms, and also occur in plants. They 

 are produced in the plant from simpler substances. 

 In the animal system they are never formed, but 

 only undergo transformation. They are thus 

 necessary ingredients in the food of animals (see 

 HUMAN PHYSIOLOGY). They exist both in the 

 soluble and in the insoluble condition, and are 

 easily changed from the one to the other. Thus, 

 albumine occurs in solution in white of egg, but 

 when the egg is boiled, the albumen becomes 

 insoluble. Caseine is in solution in milk, but 

 when the milk is curdled, the caseine is rendered 

 insoluble. By the process of digestion in the 

 stomach, insoluble albuminous substances are 

 rendered soluble, and capable of being absorbed. 

 These albuminous substances have an extremely 

 complex composition, and chemists are not yet 

 able to give formula for them. Analysis gives 

 the following results : 



Carbon 52-7 to 54-5 per cent. 



Hydrogen 6-9 ir 7-3 11 



Nitrogen 15-4 ,, 16-5 n 



Oxygen 20-9 H 23-5 n 



Sulphur 0-8 ii 1-6 ti 



