SOIL — ITS ANALYSIS. 211 



indicate the method of procedure. It is much to be desired that en- 

 ligfhtened agriculturists should not remain strangers to manipulations 

 of this kind. 



The soil to be analyzed must be first deprived of all organic mat- 

 ters by calcination. After having reduced it to a very fine powder 

 it is to be boiled for about an hour with three or four times its weight 

 of nitric or hydrochloric acid. The solution is then diluted with 

 distilled water, and filtered ; the matter which remains upon the 

 filter is generally silica or alumina which has escaped the action 

 of the acid. After having reduced the washings by evaporation, 

 and added them to the acid liquor, ammonia in solution is poured 

 in. Taking the simplest instance, the precipitate which falls upon 

 the addition of this alkali may contain, 1st, phosphoric acid in union 

 with the peroxide of iron and lime ; 2d. oxide of iron and of man- 

 ganese ; 3d. silica. This precipitate, which is usually of a gelatin- 

 ous appearance, is received upon a filter, well washed and dried, 

 when the precipitate is readily detached from the filter. Tt is thrown 

 into a platinum capsule which is raised to a white heat, after vi'hich 

 the weight of the residue is taken. The precipitate after calcina- 

 tion is thrown into a small glass matrass, and dissolved by hot hy- 

 drochloric acid. If there is any silica undissolved, its quantity is 

 merely estimated, if it be very small ; if it be a larger quantity, it is 

 to be collected upon a filter and weighed. To the new acid solution, 

 about three times its weight of alcohol is added : the mixture is 

 shaken, and pure sulphuric acid is then instilled drop by drop until 

 there is no longer any precipitate. The precipitate is sulphate of 

 lime, which is thrown upon a filter, where it is washed with diluted 

 alcohol ; it is then dried, calcined, and the weight of the sulphate of 

 lime obtained, permits us to calculate that of the lime which formed 

 part of the precipitate throv^'n down by the ammonia in the first in- 

 stance. 100 of sulphate of lime are equivalent to 41.5 of pure lime. 



The alcoholic liquor is concentrated in order to expel the spirit ; 

 as it is acid, it is saturated with ammonia until a slight precipitate 

 begins to be formed, which is not redissolved upon shaking the 

 mixture. A few drops of the hydrosulphate of ammonia are then 

 added, upon which the iron and the manganese fall in the state of 

 sulphurets. As a part of the metals has been precipitated in the 

 state of oxide by the ammonia added in the hydrosulphate, it is well 

 to digest for eight or ten hours, because the hydrosulphate of am- 

 monia always ends by changing the metals present into sulphurets, 

 which being washed, dried, and reduced to the state of oxides by 

 calcination in a platinum capsule, are weighed. 



If the first ammoniacal precipitate did not contain phosphoric acid, 

 its weight ought to be reproduced by adding that of the lime to that 

 of the metallic oxides proceeding from the calcination of the sul- 

 phurets. Any loss which is noted after this, is due, if the process 

 has been well conducted, to phosphoric acid, which had not been 

 collected, but which has remained in the state of phosphate of am- 

 monia in the liquid treated by the hydrosulphate. To determine 

 with precision the presence of phosphoric acid, the liquid in questioj* 



