Chemical Society. 515 



the earliest discovery of the rotatory character of storms, I 

 should certainly not have awarded the honour to Prof. Dove, 

 but to the late Colonel James Capper, of the East India 

 Company's service. We agree with General Reid in giving 

 the merit of first suggesting the theory to Colonel Capper; 

 but we must at the same time claim for Mr. Redfield the 

 greater honour of having fully investigated the subject, and, 

 apparently, established the theory upon an impregnable basis. 

 I am, dear Sir, ever yours, 



D. Brewster. 

 St. Leonard's, St. Andrew's, May 15th, 1841. 



LXXVIII. Proceedings of Learned Societies. 



CHEMICAL SOCIETY OF LONDON. 



April 13, fT^HE following papers were read : — 



IS-il. JL 1. "On the Preparation and Formation of Yellow 

 Prussiate of Potash," by Professor Liebig. 



In order to explain the reaction between animal matters and carbon- 

 ate of potash, when fused together at a red heat, which gives rise to this 

 salt, it is necessary to keep in mind the following properties of the salt : 

 When heated to redness in a close vessel, ferrocyanide of potassium 

 is decomposed into cyanide of potassium, carburet of ii'on and nitro- 

 gen gas ; that is, looliing upon the ferrocyanide of jiotassium as a 

 double cyanide, the cyanide of iron is converted into carburet of 

 iron and nitrogen gas, while the cyanide of potassium escapes de- 

 composition. The cyanides of metals in general which can combine 

 with carbon, are decomposed in the same way as the cyanide of iron ; 

 thus the cyanide of silver when heated gives at first a little cyano- 

 gen, but afterwards it fuses, and glowing suddenly, gives nitrogen 

 gas, the carbon remaining in combination with the silver. The 

 addition of carbonate of potash to the heated ferrocyanide of potas- 

 sium prevents the decomposition of any cyanogen, cyanide of potas- 

 sium being then formed, together with oxide of iron ; and when 

 charcoal forms a third ingredient of the fused mixture, the oxide of 

 iron is reduced to the metallic state. Hence ferrocyanide of potas- 

 sium cannot be supposed ready formed in tlie red-hot mixture of 

 the iron pot in whicli it is manufactured, that mixture containing 

 both charcoal and carbonate of potash. 



A general view is then taken of the process of manufacture of 

 this salt. Animal substances, such as dried blood, horn, hoofs, and 

 bristles, with conmion pearlashes, are the materials employed. The 

 animal matter is used either in its natural state, or it is previously 

 submitted to distillation, as in the jjreparation of ammonia, and the 

 residual charcoal merely employed for the manufacture of the pruS' 

 siate. The i)rqjection of animal matter into tlie melted potash oc- 

 casions a lively effervescence, from the evolution of carbonic acid 

 and some combustible gases. The iitjuid is stirred after each addi- 

 tion of the materials. The usual jjroportions employed are equal 

 2 L 2 



