ANALYSIS. 



ANALYSIS. 



tion of its fertility. It cannot, however, be 

 eniirely relied upon in the absence of other 

 proofs ; for there may be many different mix- 

 tures of earths which will have the same spe- 

 cific gravity, although they may differ greatly 

 in their fertility ; biu ; t will facilitate the 

 analysis, and often detect -nistakes in the pro- 

 cess, if the result does not acrord with the sne- 

 cific gravity found. We proceed now to the 

 analysis. The portion of soil which has been 

 deprived of all its water, as described above, 

 must be sifted through metallic sieves of dif- 

 ferent fineness; the first is made of a perforated 

 tin plate, the holes of which are about one- 

 twentieth of an inch in diameter : whatever 

 does not go through this is put by. The re- 

 mainder is successively passed through two or 

 three more sieves, increasing in fineness to the 

 last ; which is of the finest wire-cloth, having 

 from 150 to 170 threads in an inch: whatever 

 passes through this is an impalpable powder. 

 Thus we have already a division of the soil, 

 according to the size of its particles : 1, the 

 coarse grit left in the first sieve ; 2, the finer 

 grit in No. 2 ; 3, fine sand in No. 3 ; and 4, im- 

 palpable powder, which has passed through 

 the last sieve. To facilitate this part of the 

 operation, the sieves may be made so as to fit 

 into one another, like the filterers in a coffee- 

 biggin, the last fitting into a tin pot which will 

 hold about a pint of water ; a cover being 

 made to fit on the top sieve, the instrument is 

 complete. (See fig.) Thus, all 

 the sifting may be done at 

 once without any loss. Any 

 lumps which are not tho- 

 1 roughly pulverized must be 

 broken. The coarser sand 

 left in the sieve, No. 1, must 

 L now be washed with pure 

 water, to detach any fine dust 

 adhering to it ; what runs 



3 through may be used to wash 

 No. 2, in the same manner; 

 and then may pass through 

 No. 3 to the impalpable mat- 

 ter which passed through all 



4 the sieves. A sufficient quan- 

 tity of water must be used to 



render the whole of this last nearly fluid. 

 There will then be three different portions of 

 the washed soil left in the sieves, and a por- 

 tion of impalpable matter diffused through the 

 water in the lower division of the instrument. 

 This last is the principal object of analysis, 

 and that to which Sir Humphry Davy usually 

 confined his attention, merely noticing the pro- 

 portion of coarser sand in the soil. It contains, 

 no doubt, the great principle of fertility and 

 nutrition ; and the effect of the coarser parts 

 may be considered as chiefly mechanical ; but 

 they may much affect the fertility of the finer 

 parts, and are of the greatest importance to 

 the sou in which they are blended: they con- 

 sequently deserve a more minute examination, 

 to which we will return. 



In the mean time, our attention shall be di- 

 lected to the composition of the finer earth in 

 No. 4, which is mixed with water in a semi- 

 fluid state. This is well shaken, and suddenly 

 88 



poured into a deep glass vessel, and allowed 

 to settle for a few minutes, when the heavier 

 earth, which is sand, will be deposited, and the 

 lighter may be poured off suspended in the 

 water. It requires some little practice to effect 

 this at once, but a few trials will soon enable 

 any one to do it. This operation may be re- 

 peated until all sand, of which the particles 

 are visible to the naked eye, is separated. The 

 earth and water decanted out of this last vessel 

 are now poured into a glass tube, eighteen 

 inches long, No. 1, the bore of which is less 

 than an inch ; one end is stopped with a cork 

 fitted into it, and the other has a small lip for 

 the convenience of pouring out the contents. 

 In a short time, there will be a further deposi- 

 tion of earth, which will be principally alu- 

 mina. What remains suspended in the water 

 over it is gently poured off into another similar 

 tube (No. 2) ; this will contain nearly the 

 whole of the humus, which will take some 

 hours to be deposited in the form of a fine 

 brown mud. The contents of the tube No. 1 

 may now have a little more water added to 

 them: after being well shaken, the tube may 

 be set upright, and left for half an hour to 

 settle : what remains suspended in the water 

 after this, must be added to the humus in the 

 tube No. 2. After some time, this will also be 

 deposited, and the clear water may be decanted 

 off. The mud which remains is put on filtering 

 paper in a glass funnel ; and when all the 

 water has drained from it, it is dried over the 

 fire, and weighed. 



This is the most important portion of the 

 soil. The fine earths deposited in the tube 

 No. 1 will consist of very fine particles of 

 sand, clay, and perhaps carbonate of lime. 

 The sand will appear deposited in the bottom 

 of the tube. The clay may be easily diffused 

 in the water above it, by stirring it carefully 

 with a small rod, without reaching the sand. It 

 may then be decanted with the water into 

 another tube (No. 3), and allowed to settle. 

 This part of the operation may be carried to 

 much perfection by great care, and by examin- 

 ing the results occasionally with a small mi- 

 croscope; but for all common practical pur- 

 poses it is sufficient to separate the vegetable 

 earth from the mineral, and the particles of 

 sand from the finer. The contents of No. 1 

 having been collected, as well as those of 

 No. 3, are dried over the fire, and accurately 

 weighed. The same is done with the earth 

 which remains on the sieves. All the water 

 in which the earths have been diffused and 

 washed is collected and passed through filter- 

 ing paper, and then set over the fire in a com- 

 mon saucepan. It is boiled away gently, untiJ 

 it is reduced to a small portion, which begins 

 to look turbid. The complete evaporation is 

 finished in an evaporating dish as slowly as 

 possible ; and the residue is the soluble matter 

 contained in the soil. It will be sufficient to 

 dry and weigh this, as its further analysis 

 would require more skill and chemical know- 

 ledge than we suppose in the operation. Salts 

 may be detected by the taste, or by the crystals 

 formed in the evaporation ; but unless there is 

 a decided saline taste, the whole may be consi 



