1818.] Triple Prussiate of Potash. 107 



47"6 per cent. The third and fourth jars contained respectively 

 15 and 20 per cent, of nitrous gas. The remainder of the gas 

 possessed the properties of azote. 



4. It is well known to chemists, from preceding experiments, 

 that the triple prussiate of potash contains the following ingre- 

 dients : 



1. Water. 



2. Potash. 



3. An acid composed of iron united to 

 the constituents of prussic acid. 



I shall relate the experiments to which I subjected it in order 

 to determine the proportions of these different constituents. 



(1.) Water. — When the salt is exposed to a gentle heat, it 

 becomes white, owing to the escape of its water; and it gradually 

 loses its transparency and becomes opaque ; but it does not fall 

 to powder, nor lose its crystalline form. If we heat the salt in a 

 retort, the water passes over into the receiver.- It is colourless 

 and tasteless, if two much heat has not been applied ; but if the 

 heat has been too great, a portion of the acid is decomposed, 

 and the water acquires a slightly saline taste. The salt in that 

 case is not completely soluble in water, but leaves behind it a 

 dark brown insoluble residue. One hundred grains of the salt 

 when kept for an hour in a strong red heat lose 23*2 grains of 

 their weight ; but a considerable portion of the acid is destroyed, 

 for the salt has become strongly alkaline, though it still conti- 

 nues to strike a blue with persulphate of iron. The greatest 

 quantity of water which I was able to separate from this salt, 

 without altering its nature, was 13 per cent. When the loss of 

 weight amounted to 14 per cent, the salt was never quite soluble 

 in water, a sensible portion of brown insoluble matter always 

 remaining behind. I think, therefore, we may conclude, that 

 triple prussiate of potash when regularly crystallized contains 

 13 percent, of water. 



(2.) Potash. — When a given weight of triple prussiate of 

 potash is treated with nitric or sulphuric acid and heated till the 

 acid of the salt is completely decomposed, if we digest the 

 residue in water, filter and evaporate, we obtain a salt, which in 

 the first case is nitre ; and in the second, bisulphute of potash. 

 This last salt may be converted into sulphate of potash by 

 exposure to a strong hesnt. I conceive that the proportion of 

 potash in the triple prussiate may be determined with sufficient 

 precision by ascertaining the weight, of nitre or of sulphate of 

 potash that may be obtained from a given weight of it. By 

 three successive experiments 1 ascertained that the nitre obtain- 

 able from 100 grains of the triple prussiate weighed 88-5 grains. 

 Now this is equivalent to 41*04 grains of potash. 1 tried some 

 experiments with sulphuric acid to obtain the potash in the state 

 of sulphate of potash ; but did not find this method quite so 



