93 



purity of nitre or of Chili saltpetre, by its expulsion at a 

 high temperature by another acid, as silicic or chromic, 

 that is not volatile at such a temperature. 



Fuse a quantity of the salt, free from carbonic acid, 

 ammonic salts, or organic matter, at the lowest possible 

 temperature, pour it on a warm porcelain plate, pulverize 

 the cake, and dry the powder thoroughly ; then put 2-3 

 grms. of finely powdered quartz in a platinum crucible, 

 and ignite it strongly; add to this about 0.5 grra., care- 

 fully weighed, of the nitrate prepared as above directed, 

 mix the two substances carefully with a dry glass rod, 

 wipe oif the rod with a little more of the quartz powder, 

 and weigh the whole ; ignite the well-covered crucible 

 with its contents, for half an hour, at a barely visible red 

 heat, weigh, and count the loss as nitric anhydride. Sul- 

 phates or chlorides are not decomposed under these cir- 

 cumstances, but, if carbonates are present, they must be 

 removed by previous treatment of the salt with hydro- 

 chloric acid in slightest possible excess, and evaporation 

 to dryness on the water-bath. 



c. A very convenient method for determining nitric 

 acid in nitrates is given by C. Noellner. {Fres. Zeitschrift 

 6, 375). It depends upon the solubility of ammonic nitrate 

 in absolute alcohol, and the insolubility of other salts of 

 the alkalies and alkaline earths. 



Heat a quantity of the salt containing not more than 

 0.2 grm. of the nitre with a small quantity of a solution of 

 ammonic sulphate ; ammonic nitrate is formed, and this 

 remains in solution while all other salts are precipitated, 

 when absolute alcohol is added to the liquid ; let the mix- 

 ture stand a few minutes, filter it, wash the precipitate, 

 add an alcoholic solution of potassa to the filtrate, collect 

 the precipitated potassic nitrate on a dried and weighed 

 filter, wash it with alcohol, dry it at 100°, and weigh it. 



