SOIL ITS ANALYSIS. 209 



just criticised, inasmuch as the volume of gas collected varies with 

 every difference of heat employed. 



The only method in my opinion which we have of learning the 

 quantity of humus, of organic debris, which is contained in a soil, 

 is that of an elementary analysis. It is by burning a known quanti- 

 ty of earth thoroughly dried by means of the oxide of copper, aided 

 by a current of oxygen, that the carbon and hydrogen may be de- 

 termined. But the most important point of all is to ascertain the 

 amount of azote included in the organic remains of the soil ; and we 

 have happily precise means in our elementary analysis of ascertain- 

 ing the quantity of azote, from which the amount of azotized organic 

 matter may be accurately inferred. 



It may be very useful to determine the presence or absence of 

 carbonate of lime in a so 1 ; this knowledge would of course guide 

 us in our applications of lime, marl, &c. Two modes may be em- 

 ployed for this purpose ; 1st. the soil may be treated by nitric acid 

 slightly diluted with water. Any effervescence will denote the 

 presence, in all probability, of carbonate of lime. I say in all proba- 

 bility, because the disengagement of carbonic acid gas under such 

 circumstances generally indicates the presence of carbonate of lime ; 

 it is not, however, a special character, because the disengagement 

 may be due to the presence of any other carbonate. It is well to 

 boil the acid solution upon the sample of soil that is analyzed ; the 

 part which is not dissolved is thrown upon a filter and washed with 

 distilled or rain-water boiling hot. Into the clear filtered liquor 

 which results from all the portions of water used in the washing, a 

 little ammonia is added ; if any precipitate falls, it is collected upon 

 a filter and washed : to the new liquors obtained by this washing, a 

 solution of oxalate of ammonia is added. If there be any lime pres- 

 ent, it is thrown down in the state of oxalate, and the liquor, having 

 been left at rest for five or six hours, becomes completely clear ; the 

 addition of a few drops of the solution of oxalate of ammonia to this 

 clear fluid satisfies us whether the whole of the lime has been pre- 

 cipitated or not. The oxalate of lime is received upon a filter, wash- 

 ed, and dried ; it is then thrown into a platinum capsule along with 

 the piece of filtering paper upon which it was collected, and is heat- 

 ed to a dull red, until the paper of the filter is completely consumed 

 and no further trace of carbon appears ; the capsule is then taken 

 from the fire or from over the spirit lamp, and cooled ; when cold, 

 the matter which it contains is moistened with a concentrated solu- 

 tion of carbonate of ammonia. 



The matter is then dried, great care being taken that nothing is 

 lost by particles flying out, and the capsule is again heated to a dull 

 red ; when cold, it is weighed accurately, and the quantity of matter 

 contained then becomes known. This matter is carbonate of lime, 

 100 of which represent 56.3 of lime and 43.7 of carbonic acid. I 

 have said that in arable soil other carbonates may be met with be- 

 sides that of lime ; calcareous soils, for example, very commonly 

 contain carbonate of magnesia. If we would ascertain the quantity 

 of this earth, the mode of proceeding which I have just particularly 



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