Potassium as an Oxydizing mixture. 195 
Place a weighed quantity of the powdered mineral together 
with some chlorate of potassium in a porcelain dish—Five 
ams of a variety of pyrites containing about 18 per cent of 
copper was found to be enough for one analysis, and a quan- 
tity of chlorate of potassium equal to a small teaspoonful, was 
added to the ore——Invert a glass funnel with bent stem in the 
dish above the pyrites and pour upon the latter rather more 
ordinary strong nitric acid than wou sufficient to 
completely cover the powder. Place the dish upon a water- 
bath, and, from time to time, throw into it small quantities of 
chlorate of potassium. The doses of the chlorate must be re- 
render silica insoluble in case any silica be present. J ; 
Pour water upon the cold residue, and, without filtering the 
: , and keep the mixture at a temperature near boil- 
ing during four or five minutes, in order to destroy the small 
quantity of nitric acid which has escaped decomposition in 
Spite of the evaporation with chlorhydric acid. 
The ferrous salt seldom or never acts instantaneously, but 
the reducing action proceeds rapidly and perfectly satisfactorily 
When once begun. If need be, add more of the ferrous solu- 
tion, little by little, until the entire contents of the beaker 
became dark colored, or almost black, and no more gas is disen- 
gag 
__ In order to be sure that all the nitric acid has been reduced, 
it is well enough, after the mixture of liquid and solution of 
ferrous sulphate has been duly heated, to place a drop of the 
mixture upon porcelain and test it with ferricyanid of potas- 
