Analytical chemistry - Tapa blanda

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1895 Excerpt: ...Cyanogen is a colourless gas (condensing to a liquid at--21 C.) which has a characteristic odour and, when lighted, burns with a violet flame. It is prepared by the ignition of mercuric or silver cyanide. The cyanides are obtained by the action of nitrogen or its compounds upon carbon in presence of the alkali metals or their oxides and at a high temperature. Potassium cyanide is usually obtained as the product of the reaction, and all the other cyanides are prepared from this salt. Anothev and equally important method is based upon the formation of cyanides by the withdrawal of water from the amides of organic acids. Thus, cyanogen is formed when the constituents of water are split off from the amide of oxalic acid: co-m, C=n I = +2H.O. CO-NH2 C=N Hydrocyanic acid (Prussic acid) is prepared by distilling cyanides with sulphuric acid. It is a liquid boiling (in the anhydrous state) at 27 C., soluble in water, and having a strong odour of bitter almonds. Hydrocyanic acid is a deadly poison, either in solution or in the gaseous state. The soluble cyanides and simple compounds of hydrocyanic acid are likewise poisonous, and extreme caution must be taken in operations which involve their use. Cyanides (salts of hydrocyanic acid).--The salts of the metals of Groups I. and II., and of mercury, are soluble in water and alcohol. Their aqueous solutions, however, are unstable; the final products of decomposition being formic acid and ammonia: KCN + 2H20 = HCOOK + NH3. The alkali cyanides are stable at a high temperature, but on fusion in the air with oxidising agents (such as the peroxides of manganese or lead) they are converted into cyanates, e.g., KCNO. They also unite directly with sulphur to form the sulphocyanates (KCNS). The employment of potassium cyanide as...