198 Liebig on the Constitution of the Compounds of Mellone. 



C12 j\x2 ]v;8^ and Gerhardt represented tliem as C'^ h M^ N^, and 

 the radical hydromellone as C'^ H^ N^. 



The latter view is quite incorrect. After a careful study, the 

 author had found that in the formation of mellonide of potassium 

 the materials, sulphur and dried ferrocyanide of potassium, 

 united to form sulphocyanide of iron, and that the mellonide of 

 potassium resulted from the decomposition of this body at a 

 very high temperature. The formation, under these circum- 

 stances, of a hydrogen compound from materials which were free 

 from it was impossible. Furthei-, in the analysis of hydrogen 

 compounds, there is always an excess of water found, but in all 

 the very careful and accurate analyses of mellone compounds, 

 there had never been more thaii half the quantity of hydrogen 

 found which Gerhardt's formula requires. Some criticism is 

 devoted to Gerhardt^s views of the products obtained by Henne- 

 berg in the decomposition of mellonide of potassium by alkalies, 

 and in the other compounds derived from luellone. Liebig 

 charges Gerhardt with a tendency to reject formulae derived from 

 accurate experiments on insufficient grounds, merely because 

 they do not favour his personal opinions. 



Henneberg's investigation of the decomposition of mellonide 

 of potassium led the author to resume the study of the subject. 



If the author^s old formula for mellonide of potassium were 

 correct, it must give on decomposition, along with other pro- 

 ducts, formic acid. But careful experiments showed that under 

 no circumstances was this acid a product of decomposition, and 

 the old fornmla must be rejected. After much investigation 

 results were obtained which led to the unexpected formula 

 Q18 ]Nji3 JJ3 fo^. hydromellonic acid. 



The acid was obtained by precipitating corrosive sublimate 

 with mellonide of potassium, dissolving the mellonide of mercury 

 formed in hydrocyanic acid, precipitating the mercury by sul- 

 phuretted hydrogen, filtering, and expelling the hydrocyanic 

 acid by gentle heat. 



In the acid either one or all the equivalents of hydrogen are 

 replaceable by metals. As mellonide of potassium is the best 

 source for the other compounds, the author devoted a good deal 

 of attention to its preparation, and goes into the particulars of 

 the different processes in some detail. 



A great many analyses were made of the different salts. 

 There are three potash salts, a neutral one, whose formula is 

 C18N13K3 + 10HO j an acid insoluble salt, C'^Ni^K^H, and 

 an acid soluble one, C'«N'M<: H^ + GHO. The silver salt has 

 the formula C'^Ag^N'^. Numerous accurate analyses of the 

 dry salt, effectually disproved the idea of Gerhardt that the 

 radical contains hydrogen. 



