PRUSSIATES. 109 



lime, all tlie lead is precipitated as PbCl + PbO,HO, at 212°, 

 or PbCl + PbO when dried between 212° and 350°. The 

 great brilliancy and body of this white oxichloride induced 

 the inventor to take a patent for its application as a pigment. 



An excellent essay on the effects of preparing this pigment 

 on the health of the operative, was made by M. Combes to 

 the Academic des Sciences, and appears as a translation in 

 the Lond. Journ. xxxvi. 184-193. We may state that in most 

 of our establishments in the United States, the corroded 

 sheets of lead are ground in water, whereby the greatest evils 

 of the former mode of dry grinding are avoided. 



3. Prussiates. — Yellow Prussiate of Potash is usually pre- 

 pared by heating common pearlash or potash to fusion in an 

 iron vessel, and adding to the melted mass, dried blood, horn- 

 shavings, cracklings, &c. The excess of carbon in the animal 

 matter probably reduces the potassium, while the nitrogen 

 and carbon form cyanogen, which unites with the potassium. 

 The formation of cyanogen, or rather of cyanide of potas- 

 sium, from the nitrogen of the air, in part at least, was clearly 

 shown by Bunsen, in his investigations on the blast-furnace. A 

 patent had been taken out in England for making prussiate 

 from the air and coal, but the process was not successfully 

 carried out. 



Possy and Bossiere (Comptes Rendus, xxvi. 203) have suc- 

 ceeded in manufacturing yellow prussiate of potash, upon a 

 large scale, by means of the nitrogen of the atmosphere. 

 The daily product of their works, at Newcastle-upon-Tyne, 

 is about 1000 kilogrammes (a ton), at a cost not exceeding 

 2000 francs ($400) for that quantity. The apparatus, as now 

 constructed, will resist, for several years, the destructive action 

 of the potassa and fire. It consists of a vertical cylinder set in 

 refractory brick-work. The interior diameter of the cylinder is 

 about 18 inches. The height, heated to bright redness, is about 

 10 feet. The cylinder, being heated to bright redness and 

 charged with lumps of charcoal impregnated with 30 per cent 

 of carbonate of potassa, is kept filled with burned air, which 

 is injected, across a heated channel, by means of a forcing- 

 K 



