No. K] OF THE PHYSICAL rROPERTIES 01' THE SOIL. 29 



obtaining a comparative result as to the rapidity of drying. The same method 

 may be adopted in regard to the power of the soil to become warm under the 

 influence of the sun's rays. 'I'wo small wooden boxes, containing each a 

 layer of one of the kinds of soil, two inches in depth, may be exposed to the 

 same sunshine for the same length of time, and the heat they severally acquire 

 determined by a thermometer, buried about a (quarter of an inch beneath the 

 surface. Soils are not found to differ so much m the actual temperature they 

 are capable of attaining under such circumstances — most soils becoming 20° 

 or 30° warmer than the surrounding air in the time of summer — as in the re- 

 lative iksree of rapidity with which they acquire this maximum temperature — 

 and this, as stated in the text, appears to depend cliieily upon the darkness of 

 their colour. The detennination of this quality, therefore, except as a matter 

 of curiosity, may,. at the option of the experimenter, be dispensed with. 



n. OF TIIK ORGANIC MATTER PRESENT IN THE SOIL. 



9^. Deter ndnaiion of the pcr-cevtoge of organic viattcr. — The soil must be 

 thoroughly dried in an oven or otherwise, at a temperature not higher than be- 

 tween 250° to 300° F. FTumic and ulmic acids will bear this latter tempera- 

 ture without change. An accurately weighed portion (100 to 200 grains) must 

 then be burned in the open air, till all the blackness disappears. This is best 

 done in a small platinvmi capsule over an argand spirit or gas lamp. The loss 

 indicates the total weight of organic matter present. It is scarcely ever pos- 

 sible, however, to render soils absolutely dry without raising them to a tem- 

 perature so high as to char the organic matter present, and hence its weight, as 

 above determined, will always somewhat exceed the truth, the remaining water 

 being driven off along with the organic matter when the soil is heated to red- 

 ness. This excess, also, will in general be greater in proportion to the quantity 

 of clay in the soil, since this is the ingredient of most soils from which the 

 water is expelled with the greatest difficulty. 



10". Deterndnatinn of tke kuvdc aid. — I'his acid, whether merely mixed with 

 the soil, or combined with some of the lime and alumina it contains, is extracted by 

 boiling with a solution of the common soda of the shops. Into about two ounces 

 by measure of a saturated solution of this salt, contained in a flask, 200 or 300 

 grains of soil, previously reduced to coarse powder, are introduced, an equal 

 bulk of water added, and the whole boiled or digested on the sand bath with 

 occasional shaking for an hour. The flask is then removed from the fire, filled up 

 with water, well shaken, and the particles of soil afterwards allowed to subside. 

 The clear liquid is then poured off. If it has a brown colour it has taken up 

 some humic acid. ]n this case, the process must be repeated once or twice 

 with fresh portions of the soda solution, till the whole of the soluble organic 

 matter appears by the pale colour of the solution to be taken up. These coloured 

 solutions are then to be mixed and filtered, 'i he filtering generally occupies 

 considerable time, the humic and ulmic acids clogging up the pores of the filter 

 in a remarkable manner, and permitting the liquid to pass through sometimes 

 with extreme slowness. 



When filtered, muriatic acid is to be slowly added to the coloured liquid — 

 which should be kept in motion by a glass rod — till effervescence ceases, and 

 the whole has become dictinctly sour. On being set aside the humic acid falls 

 in brown flocks. A filter is now to be dried and carefully weighed,* the liquid 

 filtered through it, and the humic acid thus collected. It must be washed in the 

 filter with pure water — rendered slightly sour by muriatic acidt — till all the soda is 



* This is best effected by piitting the filter into a covered porcelain crucible of knowa 

 wei«ht, and heatinj; it for ten minuies over a lamp or otherwise, at a temperature which 

 just does not discolour the paper, allowing then the crucible to cool under cover, and whien 

 cold weighing it. The increase above the known weight of the crucible is that of the filter 

 which, besides being recorded in the experiment book, should also be marked in sevenu 

 places on the edge of the filter with a black lead pencil. 



t This is to prevent in some measure the humic acid from passing through the filter, 

 which it is very apt to do, when the saline matter is nearly washed out of it. 



