106 Dr. Thomson on [August, 



solution of triple prussiate of potash in nitric acid, an efferves- 

 cence speedily commences, and gas is extricated copiously. 

 After some time, the liquid in the retort becomes viscid, and 

 swells so much that considerable caution is requisite to regulate 

 the heat so as to prevent on the one hand part of the contents of 

 the retort from being driven out of the vessel, and on the other 

 to guard against the water making its way into the retort and 

 diluting the mixture. In a few minutes this viscidity disappears, 

 the matter in the retort becomes manifestly a mixture of solid 

 and liquid matter, and the evolution of gas still continues. When 

 the portion of liquid present is diminished to a certain extent, 

 the matter in the retort catches fire, and burns at intervals with 

 considerable brilliancy. The extrication of gas still continues 

 mixed with white vapours and red coloured fumes, owing 

 obviously to a mixture of aqueous vapour and nitrous acid. 

 When the evolution of gas is completely at an end, nothing 

 remains in the retort but a spongy mass, having the appearance 

 of rust of iron. It is a mixture of nitre and peroxide of iron. 

 If water be poured into the retort, the nitre dissolves, and may 

 be obtained by evaporating that liquid, while the peroxide of 

 iron subsides in the form of a red powder. 



The proportion of gas formed, and even its nature, seems to 

 be influenced by the degree of heat applied, and, perhaps, also 

 by the proportion of nitric acid. From 50 grains of the triple 

 prussiate treated in this way, I obtained over mercury 50 cubic 

 inches of gas, and the whole gas was not collected. In another 

 experiment from 200 grains of triple prussinte, I obtained over 

 water 250-5 cubic inches of gas. The first portions of gas that 

 come over are pure cyanogen ; at least they have the smell of 

 that gas, burn with the same coloured flame, and are absorbable 

 by water. The succeeding portions which are evolved after the 

 application of heat contain likewise cyanogen ; but they consist 

 chiefly of azote, carbonic acid, and nitrous gas. It would 

 appear that the prussic acid is completely decomposed ; the 

 carbon and hydrogen are converted respectively into carbonic 

 acid and water, while the azote is evolved in the state of gas. 

 In one experiment I collected, after the evolution of the cyanogen 

 over mercury, 10 cubic inches of an inflammable gas, which 

 burned with a bluish white flame, and gave out but little light. 

 This gas seemed to possess peculiar properties, but I did not 

 examine it with sufficient care to determine its composition. 



The 250-5 cubic inches of gas were collected over water in 

 four separate glass jars. The first jar contained 10 cubic inches 

 of gas, the second, 35 ; the third, 145 ; and the fourth, 60-5 

 cubic inches. All of these jars, except the last (collected during 

 the combustion of the matter in the retort), smelled so strong of 

 cyanogen that the odour could not be supported. The first jar 

 contained no carbonic acid gas ; the second jar contained 52*2 

 per cent of it ; the third jar, 40 per cent ; and the fourth jar, 



