206 ASH OF THE REFINING HEARTH. 



The quantitative analysis of the ordinary compact 

 slag is far more difficult and -complex, since it may 

 contain, in addition to the above principal constituents, 

 small variable quantities of the protoxides of copper, 

 nickel, cobalt, and manganese, besides the oxides of 

 chromium, molybdenum and vanadium, together with 

 alumina, potassa, lime, magnesia, arsenic and phos- 

 phoric acids. 



Several of these constituents can only be discovered 

 by a qualitative analysis, for which a large amount of 

 slag is employed. The process is conducted as fol- 

 lows : 



A pound of the slag, powdered as finely as possible, 

 is intimately mixed with a.i equal weight of nitre, and 

 as much carbonate of potassa,* and exposed for an hour, 

 in a crucible, to a moderate red heat. The mass is 

 finely powdered, boiled out with water, the solution 

 filtered off, and the residue washed several times with 

 hot water. 



The solution may contain, besides alkaline carbonates 

 and nitrites, vanadic acid, chromic acid, molybdic acid, 

 arsenic acid, phosphoric acid, silicic acid, and alumina. 

 A yellow color indicates the presence of chromic acid. 



It is now carefully mixed with nitric acid, so that it 

 may still remain alkaline, and any silica which may be 

 precipitated is filtered off. A yellow color at this 

 stage of the process denotes the presence of vanadic 

 acid. The liquid is then evaporated to crystallization, 

 and the greater part of the alkaline nitrate allowed to 

 crystallize out in as cool a place as possible. The 

 mother-liquor is poured off from the crystals, which 

 are washed several times with a little perfectly cold 

 water ; the washings are mixed with the mother-liquor, 

 and acetate of lead added as long as any precipitate is 

 produced. This precipitate contains all the substances 



* Perhaps smaller quantities of both might be employed. 



