196 GEOLOGY AND CHEMISTRY OF SOILS. 



most moisture, are richest in vegetable mould or geine, and 

 by comparing this power in different soils, we may arrive at 

 valuable knowledge as to their comparative fertility. 



2. The next step in the process is to bruise the whole, so 

 that no lumps can be found in it, and then sift it through the 

 coarse sieve. What remains too coarse to pass through, will 

 consist of pebbles and fibres of wood. This may now be 

 weighed and tested. The pebbles may be broken with a 

 hammer, and their nature ascertained by inspection, or they 

 may be tested by acids. 



To test them by acids, a few grains may be bruised, if 

 need be, put into a clean glass, flask or tumbler, and cover- 

 ed with water. Half as much hydrochloric (muriatic) acid as 

 water may be added, and if they are calcareous, small bub- 

 bles of gas will pass up through the water. If they are 

 wholly carbonate of lime, the acid will completely dissolve 

 thefti. But this is not to be expected in any of our soils. 

 It is very rare, that the least trace of carbonate of lime will 

 be found in this portion. If the coarse parts do not effer- 

 vesce with acids, they are composed entirely of silica and 

 alumina, or of a mixture of both, which is generally the case. 

 These two bodies may easily be distinguished from each oth- 

 er. The silica is rough like sand, scratches glass, etc., and 

 the alumina is soft and unctuous to the touch. If any ani- 

 mal or vegetable substance is mixed with the coarse parti- 

 cles, by burning a portion of them, the odor of peat or sponge 

 will be given off, then by carefully weighing a quantity 

 before and after burning, the amount of organic matter may 

 be ascertained. 



3. Sift the soil again through the fine sieve, and weigh 

 the quantity which remains in the sieve. It will consist of 

 sand and fine vegetable fibres. This may be tested in the 

 same way with the coarser particles, and the amount ascer- 

 tained. 



Take now the fine powder, which passes the gauze sieve, 



