228 Analysis of Soils. [Oct. 



magnesia, that was combined with silicic acid in the insolcible 

 silicate. 



On adding together the products of this analysis, if we are sure 

 we have lost nothing, we may by difference of weight between 

 the insoluble silicates employed and the sum of the ingredients 

 obtained by analysis estimate the weight of the alkalies which 

 we have not separated. It is a good plan to divide the insoluble 

 silicates into two equal parts by weight, and to operate on one- 

 half of it for the alkalies only, while the other operations are 

 done on the other half In that case we have to double the 

 weight of each product in setting down the results of the analysis. 

 On adding up the results of this analysis of the insoluble silicates, 

 we obtain pure silicic acid 72 grains. 



Per-oxide of iron, - - - - 2 



Alumina, _.__-- 3 



Lime, ------- 0.56 



Magnesia, __-_-_ 0.24 



5.80 

 Alkalies by difference, - - - - 20 



6.00 



When we have to determine the alkalies in the insoluble sili- 

 cates, we reduce a given weight of it to fine powder by grinding 

 it in an agate mortar until all grittiness ceases to be felt under 

 the pestle, then the powder is mixed with four times its weight 

 of carbonate of baryta, and is placed in a platina crucible, and 

 fused at a white heat. The silicates are decomposed by the baryta 

 and the whole becomes soluble in chlorohydric acid and water. 

 Dissolve out from the crucible the whole mass, filter, evaporate 

 the acid solution to entire dryness, and redissolve in water and 

 filter again. Treat the filtered solution with a sufficiency of sul- 

 phuric acid to precipitate all the baryta as a sulphate which is 

 insoluble in water and acids; filter, treat the solution with a little 

 nitric acid, and boil; add an excess of aqua ammonia to throw 

 down the alumina and per-oxide of iron. Then add a solution of 



