1846.] Analysis of Soils. 225 



obtained. Let us suppose we obtained 1 per cent of carbonate 

 of lime. Next we have to examine the solution from which we 

 have precipitated the lime, and the next substance we shall find 

 in it will be magnesia. This is best thrown down by adding a 

 solution of phosphate of soda, and if ammonia is not present in 

 excess a little aqua ammonia is to be added and the magnesia 

 will be thrown down as a phosphate of magnesia and ammonia, 

 which requires some time to form and precipitate. Therefore 

 leave the solution in a warm place for twenty-four hours. The 

 phosphate may then be collected on a filter, as in the previous 

 cases, and washed with water containing a little ammonia. 

 This precipitate when ignited is converted into the biphosphate 

 of magnesia, on which it is customary to estimate 40 per cent of 

 it as magnesia, which gives a very close approximation to the 

 true proportion. Let us suppose the weight of the biphosphate of 

 magnesia obtained was 2 per cent; this would be equal to 0.8 

 per cent of magnesia in the soil. We shall have by other opera- 

 tions to determine in what state this substance actually existed in 

 the soil, and then we can calculate the salts discovered. Potash 

 and soda, which may have been present in the solution, we can 

 only determine by difference in the weight of the products offered 

 and that of the matter dissolved. ' We may estimate them thus 

 for the present, but shall have to determine them more accurately 

 by other operations. Let us then add up our substances, and we 

 shall see what we have already separated, and the difference will 

 be the weight of those salts which we have not yet determined. 



Potash and soda, or some of their saline combinations, which 

 are to be sought for by separate operations, will probably com- 

 plete the weight of the matter operated upon. 

 In the present stage of the analysis we have. 



Organic matters, - _ _ _ § grs. 

 Insoluble silicates, _ - - 84 



Alumina, per-oxide of iron, &c., - 5 



Carbonate of lime. - - - _ i 

 Magnesia, - - _ _ _ 0.8 



No. VIII. 5 98.8 



