SOIL ITS ANALYSIS. 207 



almost uniform temperature by means of a lamp. A thermometer 

 plunged in the bath shows the degree to which it is heated ; the 

 substance to be dried is put into a glass tube of no great depth, and 

 sufficiently wide ; or into a porcelain or silver capsule, if the quantity 

 to be operated upon be somewhat considerable : these tubes, or ves- 

 sels, are placed in the oil so as to be immersed in it to about two- 

 thirds of their height. For the desiccation of soils, the temperature 

 may be carried to 150" or 160° C, (334° or 352° F.) The weight 

 of the vessel is first accurately taken, and a given weight of the 

 matter to be dried is then thrown into it, after which it is exposed to 

 the action of the bath. If we operate upon from 600 to 700 grains, 

 the drying must be continued during two or three hours; the weight 

 of the capsule with its contents, after having been wiped thoroughly 

 clean, is then taken. It is placed anew in the bath, and its weight is 

 taken a second time after an interval of fifteen or twenty minutes ; 

 if the weight has not diminished, it is a proof that the drying was 

 complete at the time of the first trial. In the contrary case, the 

 operation must be continued, and no drying must be held terminated, 

 until two consecutive weighings* made at an interval of from fifteen 

 to twenty minutes, show any thing more than a very trifling differ- 

 ence. Davy points out another and much more simple method, 

 which, although far from accurate, may, nevertheless, suffice Id 

 many general trials. The soil to be dried is put into a porcelain 

 capsule heated by a lamp, and a thermometer, with which the mass 

 may be stirred, is placed in its middle, and shows the temperature at 

 each moment. Lastly, in many circumstances the marine bath may 

 suffice. In drying, the main point is to do so at a known tem- 

 perature, and one which may be reproduced; for the absolute desic 

 cation of a quantity of soil could not be accomplished except at 

 a heat close upon redness, and this would, of course, alter or destroy 

 the organic matters it contains. 



The organic matters contained in ordinary soils consist, in part, 

 of pieces of straw and of roots, which are usually separated by 

 sifting the earth through a hair sieve ; the gravel and stones which 

 the soil contains are separated in the same way. 



The earth sifted is now washed. To accomplish this, it is intro 

 duced into a matrass, w hh three or four times its bulk of hot distilled 

 water, the whole is shaken well for a. time, the matrass is left to 

 stand for a moment, and then the liquid is decanted into a wide 

 porcelain capsule. The washing is continued, fresh quantities of 

 water being added each time, until the whole of the clay has been re- 

 moved, which is known by the fluid becoming clear very speedily ; 

 the sand which remains, is then washed out into another capsule. 

 The argillaceous particles, or the clay and all the matters held 

 in suspension in the water, are thrown upon a filter and dried ; 

 the desiccation is completed by the same process, and under the 

 same circumstances as that of the soil had been. The sand is, 

 in like manner, dried with the same care. 



If we would ascertain the nature and quantity of the soluble salts^ 

 the whole of the water used in the washing must be put togcthei 



