222 SCIENCE OF GARDENING. PART U. 



ascertained, portions of it should be taken from different places, two or three inches below 

 the surface, and examined as to the similarity of their properties. It sometimes happens, 

 that upon plains, the whole of the upper stratum cf the land is of the same kind, and in 

 this case, one analysis will be sufficient ; but in valleys, and near the beds of rivers, there 

 are very great differences, and it now and then occurs that one part of a field is calcareous, 

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

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

 lected, 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. 



1041. The soilbest 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, accord- 

 ing to the analysis of Fourcroy and Hassenfratz, 9216 parts of fertile soil contained 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 neighbourhood 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 ingredients 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 falls, 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 modifi- 

 cation 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 moisture ; 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 suffi- 

 ciently 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. 



1042. 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 proportions 

 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 regard 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. \Dict. of Chem. 

 art. SoiL) 



SUBSECT. 3. Of discovering the Qualities of a Soil mechanically and empirically. 



1043. The physical properties 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. 



1044. 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 differ- 

 ence 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. 



