180 Miscellaneous hiteUlgence. 



the iron is always in the state of protoxide, and that the other 

 base contains twice as much oxygen as the prot-oxide of iron. 

 The acid of these salts is the prussic, composed as M. Gay 

 Lussac has described. Those ferruginous prussiates which 

 effloresce, such as those of potassa, baryta, and lime, lose 

 their water in a vacuum at the temperature of the air. The 

 effloresced salt is no longer a prussiate but a double cyanuret, 

 containing neither oxygen nor hydrogen. When the double 

 cyanuret of iron and potassium, or of iron and barium, are 

 burnt by black oxide of copper, the resulting gas contains 

 three volumes of carbonic acid gas, and two volumes of nitro- 

 gen ; one volume of carbonic acid gas remains with the base, 

 and forms with it a kind of double salt, composed of carbonate 

 and cuprate of potassa and baryta. The double cyanuret of 

 iron and lead, gives gas in the proportion of two volumes of 

 carbonic acid to one volume of nitrogen. In these combustions, 

 only traces of water are obtained, which are inseparable from 

 the pulverized substances. The ferruginous prussiate of am- 

 monia cannot be reduced to a cyanuret. It is composed of 

 prussiate of prot-oxide of iron and prussiate of ammonia. 

 When distilled, it gives prussiate of ammonia, and a little 

 water, formed by the conversion of the prussiate of iron to 

 cyanuret ; the cyanuret then becomes decomposed, and gives 

 nitrogen gas, leaving a carburet of iron composed of four 

 atoms of carbon and one of iron. When this carburet is 

 heated red, it takes fire, and appears to burn as if in oxygen 

 gas, though it is surrounded by nitrogen, and suffers no 

 alteration. The incandescence is analogous to that exhibited by 

 oxide of chrome, oxide of iron, zirconia, §*c., when heated 

 red. The same pheenomena may be remarked in the distil- 

 lation of nearly all the ferruginous metallic prussiates, but 

 with none of them is it so brilliant as with the ferro-prussiate of 

 ammonia. Nearly all the ferruginous prussiates dissolve in 

 concentrated sulphuric acid without decomposition. On at- 

 tracting water from the air, the acid frequently deposits 

 crystals of a combination of sulphuric acid with the prussiate 

 an acid salt with two bases and two acids. M. Berzelius 



