SOIL. 



considered as mere silicious sand or 

 gravel 



" A good soil is composed of one 

 third coarse sand, one lliirtl very fine 

 sand, and one third iiniialpahle mat- 

 ter, in whieh there is silica in the 

 greatest quantity, alumina and lime 

 in a smaller, and I'rom four to ten per 

 cent, of organic matter, without any 

 appearance of tannin, which is readi- 

 ly di.scoveied by pouring into the wa- 

 ter which has tillered through it a 

 weak solution of sulphate of iron ; if 

 a blackness appears, the gallic acid 

 is present, and in proportion to its 

 quantity the soil is less fertile. In 

 this case quicklime is the best correc- 

 tive. 



" In ascertaining the value of a 

 soil for the purposes of agriculture, 

 two circumstances should be care- 

 fully noticed : the first is the permea- 

 bility of the soil to water ; and the 

 second is its power of absorbing moist- 

 ure from the atmosphere. To ascer- 

 tain the first, it is only required to 

 place an equal weight of different 

 soils in glass tubes of equal diameter, 

 pressing them so that they shall oc- 

 cupy equal spaces, but not filling the 

 tubes ; then pour an equal quantity 

 of water over each soil, and place 

 them upright with cups under them. 

 Examine which has the surface first 

 dry, and how much water runs through 

 each in a given time. That which 

 presents a dry surface, while it holds 

 most water in its pores, is probably 

 the best. To ascertain the compara- 

 tive absorption of moisture, the soils 

 are dried in pairs on a plate of metal 

 heated by steam, or at a heat of 212°, 

 to expel the water ; they are then 

 placed in equal quantities in similar 

 flat cups or dishes, and placed in op- 

 posite scales of a balance, and poised. 

 The apparatus is exposed to a moist 

 atmosphere out of doors, or in a cel- 

 lar, and occasionally examined. That 

 which is heaviest is, in general, the 

 most fertile, and contains most hu- 

 mus. If there are more than two 

 soils, they are compared with each 

 other, and with a third as a stand- 

 ard. 



" By these simple means any per- 

 734 



son, however ignorant of chemistry, 

 or unaccustomed to make accurate 

 experiments, may stion satisfy him- 

 self as to the comparative value of 

 different soils which have never yet 

 been cultivated ; how they may be 

 improved, and what crops are best 

 suited to them : things of the great- 

 est importance to those who go to 

 distant colonies in the hopes of ob- 

 taining good land at a moderate price, 

 and cultivating it to advantage. 



" But we have intimated that there 

 were other means of ascertaining the 

 mechanical texture of soils than by 

 sifting them ; this is by washing with 

 pure water. For this purpose, no- 

 thing is required but a few flat plates 

 and large cups. Some of the soil is 

 formed into a very thin mud by stir- 

 ring it in a cup nearly full of water. 

 The finer particles are successively 

 poured off from the sand or grit, 

 which at last remains pure, so that 

 the water added to it is no longer 

 discoloured : this being dried and 

 weighed, gives the coarse sand. The 

 water and earth poured off are al- 

 lowed to settle : a common soup- 

 plate is found a very convenient ves- 

 sel for this purpose. On the surface 

 of the deposited earth will he found 

 all the undecomposed vegetable mat- 

 ter, which, with a little care, is easily 

 taken off, dried, and weighed. The 

 finer portions of the earth can be 

 poured off successively by shaking 

 the whole moderately till nothing but 

 very fine sand remains. The alumi- 

 na and impalpable silica will remain 

 long suspended in the water, and al- 

 low any sand yet remaining to be de- 

 posited. They may be rapidly sep- 

 arated from the water by filtration 

 through stout blotting paper ; but it 

 is preferable to pour them into a glass 

 tube about one inch in internal di- 

 ameter, with a cork fitted into the 

 lower end. In this tube the earths 

 slowly fall to the bottom, and any 

 variety in the size of the particles 

 causes a line more or less distinct, 

 which can be observed through the 

 glass ; and thus a very good idea 

 may he obtained of the proportion of 

 the different earths as far as regards 



