736 



PHUSSIC ACID. 



of cyanogen. Though a compound body, it has a 

 remarkable tendency to combine with elementary 

 bodies. Thus it is capable of uniting with the sim- 

 ple non-metailic bodies, and evinces a strong attrac- 

 tion for the metals. It enters into direct combina- 

 tion with a few alkaline bases only, and these com- 

 pounds are by no means permanent; hence it has 

 no claim to be considered as an acid. To return 

 to the properties of prussic acid, before we describe 

 the other compounds of cyanogen. Barytes, heat- 

 ed in prussic acid, yields its barium to the cyanogen 

 of the acid to form a cyanuret of barium, while the 

 hydrogen of the acid and the oxygen of the earth 

 unite to form water. Potash and soda behave in 

 a similar manner, as respects their bases. Prussic 

 acid is the most violent of all poisons. When a rod 

 dipped into it is brought in contact with the tongue 

 of an animal, death ensues before the rod can 

 be withdrawn. Doctor Magendie has, however, 

 introduced its employment into medicine. He 

 found it beneficial against phthisis and chronic 

 catarrhs. His formula is the following: Mix one 

 part of the pure prussic acid with 83 of water by 

 weight. To this mixture he gives the name of 

 medicinal prussic acid. Of this he takes 1 gros or 

 59 grs. troy, distilled water I lb., or 7560 grs., pure 

 sugar lg oz., or 708f grs., and, mixing the ingre- 

 dients well together, he administers a table spoon- 

 ful every morning and evening. One ten thousandth 

 of prussic acid may be detected in water, by the 

 addition of a few drops of solution of sulphate of 

 iron. This test, though delicate, is surpassed by 

 another, in which copper is used, and which will 

 detect one twenty thousandth of prussic acid in 

 water. To employ it, we must render the liquid 

 containing the prussic acid slightly alkaline with 

 potash, add a few drops of sulphate of copper, and, 

 afterwards, sufficient muriatic acid to redissolve the 

 excess of oxide of copper. The liquid will appear 

 more or less milky, according to the quantity of 

 prussic acid present. Prussic acid is formed in a 

 great many chemical operations; as, for instance, 

 by transmitting ammoniacal gas over ignited char- 

 coal contained in a tube; as also by heating in a 

 glass tube, closed at one end, a mixture of oxalate 

 of ammonia and oxalate of manganese. Prussic 

 acid exists in the vegetable kingdom. The pecu- 

 liar smell of bitter almonds, peach flowers, and the 

 leaves of the lauro-cerasus, and of other vege- 

 tables, is owing to this substance. Prussic acid is 

 often obtained from the peach and apricot kernels. 

 The bark of the prunus padus contains much of it, 

 and water distilled from it is capable of killing ani- 

 mals. Cyanogen unites with oxygen, and gives 

 rise to a compound called cyanic acid. It consists 

 of cyanogen twenty-six parts, and oxygen sixteen. 

 It crystallizes in oblique rhomboidal prisms, which 

 are colourless and transparent, insoluble in cold 

 water, but are dissolved in hot water, as well as in 

 the strong acids. Its most remarkable property is, 

 that it allows of being boiled with the strong acids 

 without undergoing decomposition or change. With 

 the metalic oxides it forms salts that do not deto- 

 nate. The cyanous acid contains just half as much 

 oxygen as the cyanic, and is characterized by the 

 facility with which it is resolved by water into car- 

 bonic acid and ammonia, and by the property of de- 

 tonation, when in union with the oxides of mercury 

 and silver. It is, in fact, the same substance as 

 the fulminic acid, which is essential in the fulmina- 

 ting compounds of these metals. (See Fulmina- 

 tion, and Fulminating Silver, and Mercury, under 

 these metals respectively. ) We have also two com- 

 pounds of the radical of prussic acid with chlorine, 

 called the chloride of cyanogen, and the bichloride 



of cyanogen. The former of these is solid at of 

 Fuhi . Between 5 and 10 S', it is liquid, and al- 

 so at 68, under a pressure of four atmospheres; 

 !)ut, at the common pressure and temperature, it is 

 a colourless gas. In the liquid state, it is as limpid 

 and colourless as water. It has a very offensive 

 odour, irritates the eyes, and is highly injurious to 

 animal life. It consists of thirty-six parts chlorine 

 and twenty-six of cyanogen. The bichloride of 

 cyanogen contains twice as much chlorine as the 

 preceding compound. It is solid at common tem- 

 peratures; at 284 it fuses, and boils at 374. Its 

 vapour is acrid, and excites a flow of tears, and is 

 injurious to life. Its odour is similar to that of 

 chlorine. When boiled in water, it is converted 

 into muriatic and cyanic acid. There is a com- 

 pound of iodine and cyanogen of somewhat similar 

 properties. It has a caustic taste and a penetrating 

 odour. It is very volatile, and sustains a tempera- 

 ture above 212, without decomposition. Bromide 

 of cyanogen has also been formed, and resembles 

 the last mentioned compound. Cyanogen forms an 

 acid compound by a union with hydrogen and iron. 

 It is neither volatile nor poisonous in small quanti- 

 ties, and is destitute of odour. It is gradually de- 

 composed by exposure to the light, forming prussic 

 acid and prussian blue. It decomposes some salts 

 of the more powerful acids: peroxide of iron, for 

 example, unites with it in preference to sulphuric 

 acid, unless the latter is concentrated. As this 

 acid contains no oxygen, but simply consists of car- 

 bon, hydrogen, nitrogen and metallic iron, the name 

 of ferrureted chyazic acid (chyazic, from the initials 

 of carbon, hydrogen and azote} has been proposed; 

 but the term ferro cyanic acid is more generally em- 

 ployed. Of the salts formed by this acid, the most 

 important in chemistry is the ferrocyanate of potash 

 (formerly called the prussiate of potash). It is 

 transparent, and of a beautiful lemon yellow colour. 

 In large crystals, it possesses a certain kind of 

 toughness, and in thin scales, a degree of elasticity. 

 Its solution is not affected by alkalies, but it is de- 

 composed by almost all the salts of the permanent 

 metals. The following table presents a view of the 

 colours of the metallic precipitates thus obtained: 



Solutions of Give a 



Manganese . . . White precipitate. 



Protoxide of iron . . Copious white. 



Deutoxide of iron . . Copious clear blue. 



Tritoxide of iron . . Copious dark blue. 



Tin White. 



Zinc ' 



Antimony 



Uranium .... Blood red. 



Cerium .... White. 



Chalt Grass green. 



Titanium . Green. 



Bismuth .... White. 

 Protoxide of copper 



Deutoxide of copper . Crimson brown. 



Nickel .... Apple green. 



Lead White. 



Deutoxide of mercury . 



Silver . . . . f passing to 



1 blue iu the air. 



Palladium .... Olive. 



Rhodium, platina and gold None. 



Iron, though contained in the ferrocyanic acid and 

 all its salts, cannot be detected in them by the usual 

 tests of iron; for the liquid tests are fitted only for 

 detecting oxid of iron as existing in a salt, and 

 therefore cannot be expected to indicate the pre- 

 sence of metallic iron, while forming one of the 

 elements of an acid. The beautiful dye, called 

 prussian blue, is a ferrocyanate of the peroxide of 

 iron, and is always formed when ferrocyanic acid or 

 its salts are mixed in a solution with a persalt of iron. 

 The usual mode of manufacture is by mixing to- 

 gether one part of the ferrocyanate of potash, one 

 part of copperas and four of alum, each previously 



