POTASH AND POTASSIUM. L 253 



mine the composition of saltpetre ; for the loss of 

 weight would indicate the quantity of nitric acid, 

 while the residual matter in the crucible would 

 be the potash ; and if we were possessed of any 

 vessel upon which red hot saltpetre would not 

 act, and if potash were absolutely fixed in the 

 fire, this method would be a good one ; but I 

 have not been able to obtain satisfactory results 

 by decomposing this salt by heat. The process, 

 which answered best, was to triturate a given 

 weight of saltpetre with twice as much siliceous 

 sand, and to fuse the mixture in a platinum 

 crucible. When 12'75 grains of saltpetre were 

 employed, the loss of weight approached very 

 near 6*75 grains, though it always somewhat 

 exceeded that quantity. 



2. Sulphate of potash affords an easy method 

 of determining the atomic weight of potash with 

 precision. Before relating the experiment by 

 which this object was attained, it may be pro- 

 per to remind the reader that the atomic weight 

 of sulphuric acid is 5 ; and that 13-&5 grains of 

 chloride of barium yield a quantity of barytes 

 just capable of neutralizing 5 grains of sulphuric 

 acid. 



11 grains of sulphate of potash, and 13 '25 

 grains of chloride of barium, were dissolved in 

 separate portions of distilled water. The two 

 solutions being mixed, a double decomposition 

 took place, and sulphate of barytes precipitated 



