COMPOSITION OF SLAGS. 703 



One problem is solved the slags are magnetic, because they contain free mag- 

 netite disseminated throughout their mass ; the magnetite is not combined, since it 

 can be thus isolated in a state of purity, and it is evidently to this substance that the 

 intense black color of slags is chiefly due. To this substance also they partially owe 

 their opacity. 



Magnetite can be isolated by a process much more simple and more rapid than 

 the one previously described. Sifted slag is attacked in a platinum vessel by a mix- 

 ture of weak nitric and hydrofluoric acids ; the solution is decanted, the residue is 

 treated with a boiling solution of caustic potash, and this residue is washed with water 

 and weak hydrochloric acid. In a few minutes pure magnetite is isolated. 



3. The pulverized slag is treated by a boiling solution of caustic potash; after a 

 few minutes ebullition the potash is charged with sulphide of potassium, and in a few 

 minutes more it takes the rich yellow color of persulphide of potassium. Only one 

 among the sulphides that can possibly exist in the slags is capable of producing this 

 reaction ; it is sulphide of calcium. The existence of this sulphide, which has long 

 been suspected and often reported, is demonstrated here beyond a doubt. Whether 

 all the sulphur of slag exists in the state of sulphide of calcium is another question. 

 That most of the sulphur is in that condition there is no doubt, but from the general 

 behavior of slag, the writer is almost inclined to think that small quantities of sul- 

 phides of iron, manganese, zinc, and even lead exist there also. A great number 

 of experiments were made to ascertain this, but in every case the presence of metallic 

 sulphides might be attributed to secondary reactions, so they will not be described. 



4. The pulverized slag is treated by a strong solution of cold potash. A consid- 

 erable quantity of oxide of lead is dissolved ; consequently there can be no doubt as to 

 the state in which lead exists in slags. It is in the state of silicate of oxide. 



5. Slags contain always a little chlorine, whose quantity is proportionate to the 

 quantity of silver found; hence there is little doubt that silver exists in the slag in 

 the state of chloride which has escaped decomposition. This fact is important because 

 it explains why there is no relation between the quantities of lead and silver found in 

 slag. The slag in indistinct but large crystals behaves with reagents exactly like the 

 distinctly crystalline one ; magnetite can be extracted by the processes previously 

 described, but this oxide, instead of being crystalline to the eye, forms an apparently 

 amorphous powder. The non-crystalline, fine-grained siags possess the same proper- 

 ties as the former. They are more easily attacked under the same circumstances and 

 yield only traces of magnetite; yet they contain almost as much peroxide of iron as 

 the former, but in this case peroxide of iron exists in the state of silicate. 



Most slags in Leadville belong to the two types just described: the lustrous crys- 

 talline slag known as acid slag, which may be defined as a silicate of sulphides and 

 oxides, colored by magnetite, and the fine-grained, non-crystalline known as basic slag, 

 and which may be termed a silicate of sulphides and oxides, colored by sulphide of 

 iron. 



