Book III. ANALYSIS OF SOILS. :U7 



SuBSECT. 2. Of discovering the Qualities of Soils by Chemical Analysis. 



2133. Chemical analysis is much too nice an operation for general purposes. It is not 

 likely that many practical cultivators will ever be able to conduct the analytic process 

 with sufficient accuracy, to enable them to depend on the result : but, still, such a know- 

 ledge of chemistry as shall enable the cultivator to understand the nature of the process 

 and its results, when made and presented to him by others, is calculated to be highly 

 useful, and ought to be acquired by every man whose object is to join theoretical to 

 practical knowledge. If it so happens that he can perform the operations of analysis 

 himself, so much the better, as far as that point is concerned ; but, on the whole, such 

 knowledge and adroitness are not to be expected from men who have so many other 

 points demanding their attention, and who will, therefore, effect their purpose much 

 better by collecting proper specimens of the soils to be studied, and sending them for 

 analysis to a respectable operative chemist. 



2134. In selecting specimens, where the general nature of the soil of a field is to be 

 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 of 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 silicious ; 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 col- 

 lected in dry weather, and exposed to the atmosphere till it becomes dry to the touch. 



2135. The soil best suited for ctdture, according to the analysis of Bergman, contains 

 four parts of clay, three of sand, tw o 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, probably derived from the decomposition of water, 

 either by the chemical affinities of the ingredients of the soil, or by the process of vege- 

 tation, while the carbonic acid or fixed air may be absorbed from the atmosphere, or 

 produced by living vegetables under certain circumstances. The following is the ana- 

 lysis of a fertile soil, as occurring in the neighbourhood of Bristol : In 400 grains, 

 there were of water, 52 ; silicious 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 ingre- 

 dients 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 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 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 sufficiently favourable 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. 



2136. Use of the remit of analysis. In the present state of chemical science. Dr. Ure 

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

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

 amply repaid by the certainty vsdth 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 plant?, 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 labour and expense. 

 {Diet, of Chem., art. Sod.) 



