Vol. XIII. 



ROCHESTER, N. Y., MARCH, 1852. 



No. HI. 



AGRICULTURAL CHEMISTRY. 



NUMBER III. 



Specific Gravity of Soils. — Cohesion. — Tlie specific gravity of soils is ascertained 

 by finding how much water a given weight of dry soil displaces. To dry a soil where 

 one has no apparatus designed expressly for the purpose, it may be spread to the amount 

 of four hundred grains on a quarter of a sheet of white foolscap writing paper, which 

 may be placed on another piece of white paper laid on a heated stove. This should bo 

 as hot as it can be and not char or burn the paper. The soil should be stirred with a 

 glass or steel rod, or with the blade of a clean knife, to hasten the drying. A paper 

 with soil upon it may be put upon an earthen plate and set in a common cooking stove 

 hot enough nearly to bake bread, where it will, if properly spread out on the paper, dry 

 in thirty minutes. Any heat that does not burn the paper will not consume nor char 

 the mold, or organic matter in the soil. Of this dried soil, weigh out say 357 grains, 

 Avhich may be put into a specific gravity bottle which will hold 1000 grains. (One of 

 a difterent weight will answer, if the weight be known.) A bottle holding 1000 grains 

 of water ought, when 35*7 grains of dry soil are added, to weigh 135 V grains, provided 

 none of the water was displaced by the earth. But it is obvious that so much space in 

 the bottle as the solid matter introduced really filled, the water must leave as the soil 

 was added. 



Again ; if the soil weighed precisely the same per cubic inch as the water, then it is 

 clear that if the bottle were half filled with water and half with earth, the two together 

 would still weigh 1000 grains, or the same that the water alone did; but the result of 

 the experiment may show that the addition of 357 grains increases the weight of the 

 contents of the bottle from 1000 to 1285 grains. Now, as the whole of the water and 

 soil weigh 1357 grains, it is plain that if we subtract 1285 from 1357, the diflference is 

 72 grains, which is the exact weight of the water displaced, and the exact volume of the 

 soil weighing in the air 35.7 grains — water being the standard. As 72 is to 357, or as 

 the weight of the water is to that of the solid of equal volume, so is 1000 to 4958. In 

 this case the soil or other mineral is 4 and nearly 96-100 times the specific gravity of 

 water. This is heavier than any soil, but not so heavy as iron filings. 



The specific gravity of solid bodies of considerable size can not be determined in the 

 manner above described ; but it may be the circumstance that water partly supports 

 solids immersed in it, which support is greater or smaller as the body is lighter or 

 heavier compared with its volume. A solid, in order to sink in a liquid, has to displace 

 and push upward a quantity of it equal to its own bulk, and to resist the weight of the 

 Hquid, or its tendency to sink down again. To illustrate the principle of the phenome- 

 non under consideration, let us suppose one has a gold coin which, weighed in the air, 



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