1846.] Analysis of Soils. 235 



nia is added to the soil, and the digestion is kept up so long as 

 any color is obtained, and the whole is filtered. The filtered so- 

 lution is then to be saturated, and treated with a slight excess of 

 pure acetic acid, and a solution of acetate of copper is added so 

 long as a brown precipitate falls. This precipitate is apocrenate 

 of copper. The solution is to be placed in a warm place and 

 kept at a temperature of 170 deg. F. until all the apocrenate of 

 copper subsides. Then it is filtered and the apocrenate is col- 

 lected on double counterpoised filters of India paper, and after 

 washing out the excess of acetate of copper, the filters are to be 

 dried at a steam heat, and weighed one against the other. The 

 difference of weight is that of the apocrenate of copper. A por- 

 tion of this apocrenate is removed from the paper and analyzed, 

 and the proportion of the organic acid in the apocrenate is deter- 

 mined. This analysis I shall describe farther on. 



Having thrown down all the apocrenic acid, we next render 

 the solution slightly ammoniacal by means of a solution of car- 

 bonate of ammonia, and crenate of copper precipitates if acetate 

 of copper is in excess. If not add, drop by drop, more acetate of 

 copper until all the crenate is thrown down. This salt is of a 

 pale, greenish w^hite color. The solution is to be allowed to 

 stand for twenty-four hours at least, in a warm place, at a tem- 

 perature of 170 deg. F., until the crenate separates. Then it is 

 to be filtered on double counterpoised India paper filters, washed 

 slightly, dried at a steam heat, and weighed. Then a portion of 

 the crenate is to be removed from the filter and analyzed, and the 

 quantity of crenic acid on the filter will be known. 



We have next to separate the humic acid; in order to do this, 

 we have first to remove all the copper from the solution by pass- 

 ing a current of sulphydric acid gas through the solution until all 

 the copper is precipitated as a sulphuret. Then after allowing 

 the solution to remain in a warm place over night, we filter the 

 solution and then evaporate to near dryness at a temperature be- 

 low boiling, and if possible it should be done in vacuo. The so- 

 lution being now free from sulphydric acid gas, we add a little 

 pure water and then drop in a solution of subacetate of lead, 



