ANALYSIS. 



feet means. It is best, however, for 

 agricultural purposes, to discover the 

 preseuce or absence of a given sub- 

 stance, as lime or bone earth, rather 

 than enter into the complete solution 

 of the substance. The ordinary means 

 «f distinguishing the components of 

 a soil is given under Soils. The 

 follownig, from Boussingault, is of a 

 liigher character : 



In examining a soil, attention ought 

 to be directed, 1st, to the sand ; 2d, to 

 the clay ; 3d, to the humus which it 

 contains. It would farther be useful 

 to inquire particularly in regard to 

 certain other principles which exert 

 an unquestionable infhience upon ve- 

 getation, such as certain alkahne and 

 earthy sahs. 



Vegetable earth dried in the air 

 until it becomes quite friable may 

 nevertheless still j-etain a considera- 

 ble quantity of water, and which can 

 only be dissipated by the assistance 

 of a somewhat high temperature. It 

 is therelbre proper, in tlie first in- 

 stance, to bring all the soils whicli it 

 is proposed to examine comparative- 

 ly, to one constant degree of dryness. 

 The best and quickest way of drying 

 such a substance as a portion of soil, 

 is to make use of the oil bath ; a quan- 

 tity of oil contained in a copper ves- 

 sel is readily kept at an almost uni- 

 form temperature by means of a lamp. 

 A thermometer plunged in the bath 

 shows the degree to which it is heat- 

 ed : the substance to be dried is put 

 into a glass tube of no great depth, 

 and sutficiently wide ; or into a por- 

 celain or silver capsule, if the quan- 

 tity to be operated upon be somewhat 

 considerable : these tubes or vessels 

 are placed in the oil so as to be im- 

 mersed 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 ac- 

 curately 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 oper- 

 ate upon from 600 to 700 grains, the 

 drying must be continued during two 

 or three hours ; the weight of the 



I capsule with its contents, after hav- 

 ving been wiped thoroughly clean, is 

 then taken. It is placed anew in the 

 bath, and its weight is taken a sec- 

 ond 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 un- 

 til two consecutive weighings, made 

 at an interval of from fifteen to twen- 

 ty minutes, show anything more than 

 a very trifling difference. Davy points 

 out another and much more simple 

 method, which, although far from ac- 

 curate, may nevertheless suffice in 

 many general trials. The soil to be 

 dried is put into a porcelain capsule 

 heated by a lamp, and a thermome- 

 ter, with which the mass may be stir- 

 red, 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 

 temperature, and one wliich may be 

 reproduced ; for the absolute desicca- 

 tion 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 pie- 

 ces of straw and of roots, which are 

 usuallj' 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 introduced 

 into a matrass, with 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 mo- 

 ment, and then the liquid is decanted 

 into a wide porcelain capsule. The 

 washing is continued, fresh quanti- 

 ties of water being added each time, 

 until the whole of the clay has been 

 removed, which is known by the fluid 

 becoming clear very speedily ; the 

 sand which remains is then washed 

 out into another capsule. The argil- 



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