314 SCIENCE OF AGRICULTURE. Part II. 



and another part siliceous ; and in this case, and in analogous cases, the portions dif- 

 ferent from each other should be separately submitted to experiment. Soils, when 

 collected, if they cannot be immediately examined, should be preserved in phials quite 

 filled with them, and closed with ground glass stoppers. The quantity of soil most 

 convenient for a perfect analysis is from two to four hundred grains. It should 

 be collected in dry weather, and exposed to the atmosphere till it becomes dry to the 

 touch. 



2085. The soil best suited for culture, according to the analysis of Bergman, contains 

 four parts of clay, three of sand, two of calcareous earth, and one of magnesia ; and, 

 according to the analysis of Fourcroy and Hassenfratz, 9216 parts of fertile soil con- 

 tained 305 parts of carbon, together with 279 parts of oil; of which, according to the 

 calculations of Lavoisier, 220 parts may be regarded as carbon : so that the whole of the 

 carbon contained in the soil in question may be estimated at about 525 parts, exclusive 

 of the roots of vegetables, or to about one sixteenth of its weight. Young observed that 

 equal weights of different soils, when dried and reduced to powder, yielded by distillation 

 quantities of air somewhat corresponding to the ratio of their values. The air was a 

 mixture of fixed and inflammable airs, proceeding probably from decomposition of the 

 water; but, partly, it may be presumed, from its capacity of abstracting a portion of air 

 from the atmosphere, which the soil at least is capable of doing. The following is the 

 analysis of a fertile soil, as occurring in the neighborhood of Bristol : In 400 grains, 

 there were of water, 52 ; siliceous sand, 240 ; vegetable fibre, 5 ; vegetable extract, 3 ; 

 alumine, 48; magnesia, 2; oxide of iron, 14; calcareous earth, 30; loss, 6. But 

 Kirwan has shown in his Geological Essays, that the fertility of a soil depends in a great 

 measure upon its capacity for retaining water ; and if so, soils containing the same in- 

 gredients must be also equally fertile, all other circumstances being the same ; though it 

 is plain that their actual fertility will depend ultimately upon the quantity of rain that 

 fells, because the quantity suited to a wet soil cannot be the same that is suited to a dry 

 soil. And hence it often happens that the ingredients of the soil do not correspond to 

 the character of the climate. Silica exists in the soil under the modification of sand, and 

 alumine under the modification of clay. But the one or the other is often to be met 

 with in excess or defect. Soils in which the sand preponderates retain the least mois- 

 ture ; and soils in which the clay preponderates retain the most : the former are dry soils, 

 the latter are wet soils. But it may happen that neither of them is sufficiently favorable 

 to culture ; in which case, their peculiar defect or excess must be supplied or retrenched 

 before they can be brought to a state of fertility. 



2086. Use of the result of analysis. In the present state of chemical science, Dr. Ure 

 observes, no certain system can be devised for the improvement of lands, independently 

 of experiment ; but there are few cases in which the labor of analytical trials will not be 

 amply repaid by the certainty with which they denote the best methods of melioration ; 

 and this will particularly happen, when the defect of composition is found in the propor- 

 tions of the primitive earths. In supplying organic matter, a temporary food only is 

 provided for plants, which is in all cases exhausted by means of a certain number of 

 crops ; but when a soil is rendered of the best possible constitution and texture, with re- 

 gard to its earthy parts, its fertility may be considered as permanently established. It 

 becomes capable of attracting a very large portion of vegetable nourishment from the 

 atmosphere, and of producing its crops with comparatively little labor and expense. 

 {Diet. ofChenu art. Soil.) 



SuBSECT. 3. Of discovering the Qualities of a Soil mechanically and emjnrically. 



2087. The j)hysical j)roperties of soils, and some of their most important constituents 

 relatively to the cultivator, may be ascertained to a certain extent by various and very 

 simple means. 



2088. The specific gravity of a soil, or the relation of its weight to that of water, may 

 be ascertained by introducing into a phial, which will contain a known quantity of water, 

 equal volumes of water and of soil, and this may be easily done by pouring in water till 

 it is half full, and then adding the soil till the fluid rises to the mouth ; the difference 

 between the weight of the soil and that of the water will give the result. Thus if the 

 bottle contains four hundred grains of water, and gains two hundred grains when 

 half filled with water and half with soil, the specific gravity of the soil will be 2, that is, 

 it will be twice as heavy as water, and if it gained one hundred and sixty-five grains, its 

 specific gravity would be 1825, water being 1000. 



2089. The presence of clay and sand in any soil is known, the first by its tenacity, the 

 other by its roughness to the touch, and by scratching glass when rubbed on it. 



2090. The presence of calcareous matter in soil may be ascertained by simply pouring 

 any acid on it, and observing if it effervescea freely. Calcareous soils are also softer to 

 the touch than any other. 



