ANALYSIS. 



a few minutes in order to let the car- 

 bonie arid whicli is mixed with the 

 air of the vial escape, the vial with 

 its contents is again put into the bal- 

 ance. If there has been no disen- 

 gagement of carbonic acid, it is clear 

 that, to restore the equilibrium, it will 

 be sufficient to add to the opposite 

 scale the weight of the earth which 

 was put into the vial ; whatever is 

 wanting of this weight represents 

 precisely the weight of carbonic acid 

 which has been disengaged. Presu- 

 ming this acid to have been combi- 

 ned with lime, the weight of the cal- 

 careous carbonate can be calculated 

 exactly. 



Sulphate of lime is an occasional 

 constituent of soils ; to ascertain its 

 presence and quantity, the following 

 is the method of procedure : 



The earth, well pulverized, is first 

 roasted for a considerable time in a 

 crucible or platinum capsule until all 

 the organic matter is completely de- 

 stroyed ; it is advisable to operate on 

 about 100 grammes, or about 3-2 oun- 

 ces troy of soil. After this operation, 

 the matter is boiled in four or five 

 times its weight of distilled water for 

 some time, water being added to re- 

 place that which is dissipated by 

 evaporation ; we then filter, rewash, 

 and having added all the liquors, we 

 evaporate in a capsule until the vol- 

 ume of the liquid is reduced to a few 

 drachms. To the liquid thus concen- 

 trated we add its own bulk of alcohol. 

 If the solution contains sulphate of 

 lime, it will be deposited, and the de- 

 posite being received upon a filter 

 and washed with weak alcohol, its 

 weight is taken after having been 

 dried and calcined. This salt is fre- 

 quently seen deposited in the form of 

 fine colourless needles on the cooling [ 

 of the sufficiently concentrated solu- i 

 tion ; but the addition of alcohol is | 

 always useful, because the sulphate \ 

 of lime, which is not very soluble in j 

 water, is altogether insoluble in weak 

 spirits, which, on the contrary, dis- ' 

 solves certain alkaline and earthy 

 salts whose presence would interfere 

 with the accuracy of the result. | 



It may be matter of great moment ' 

 18 



to determine the existence and the 

 quantity of ■phosphates contained in 

 a soil destined for cultivation. Al- 

 though the search for phosphoric acid 

 may perhaps require a certain famil- 

 iarity with chemical analysis, I shall 

 nevertheless indicate the method of 

 procedure. It is much to be desired 

 that enlightened agriculturists should 

 not remain strangers to manipula- 

 tions of this kind. 



The soil to be analyzed must be de- 

 prived of all organic matters by cal- 

 cination. 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 hydro- 

 chloric acid. The solution is then 

 diluted with distilled water, and filter- 

 ed ; the matter which remains upon 

 the filter is generally silica or alumina 

 which has escaped the action of the 

 acid. After having reduced the wash- 

 ings by evaporation, and added them 

 to the acid liquor, ammonia in solu- 

 tion is poured in. Taking the sim- 

 plest 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 gelatinous ap- 

 pearance, is received upon a filter, 

 well washed and dried, when the pre- 

 cipitate is readily detached from the 

 filter. It is thrown into a platinum 

 capsule which is raised to a white 

 heat, after which the weight of the 

 residue is taken. The precipitate af- 

 ter calcination is thrown into a small 

 glass matrass, and dissolved by hot 

 hydrochloric acid. If there is any sil- 

 ica 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 un- 

 til 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 



