108 BOARD OF AGRICULTURE. 



material be reduced, as it can be, in a new form of mill machinery 

 which is at work in the vicinity of Boston, to an impalpable dust, 

 and it becomes quite soluble, so that the water passing through 

 it drinks it up in large quantities, and would furnish it most 

 liberally to the roots of living plants. These, then, are simple 

 illustrations of the enormous influence exercised by mere 

 mechanical aggregation on the value of soils. Of course, this 

 is no novelty to those who hear me ; but it seems to me that the 

 importance of the fact has not been duly weighed or sufficiently 

 recognized in practical agriculture. I might in like manner 

 illustrate the influence of the color of soils as aflecting their 

 capacity for absorbing the solar rays, and in the same connection 

 speak of the relative powers of difierent soils as to the conduc- 

 tion and retention of heat, and I might dwell on the still more 

 important diversities which depend on the permeability of soils 

 to moisture, and their power of retaining it when received ; 

 but I must pass over these leading considerations to ar fact of 

 special interest less generally known, which was first clearly 

 established a few years since by the great agricultural chemist 

 Boussingualt. This able observer ascertained that in soils con- 

 taining much organic matter intimately blended in the mass, 

 there exists and is continually evolved a marked amount of 

 carbonic acid in the gaseous state. He found that the air 

 occupying the interstices of the soil, forming often one-half of 

 the entire volume, was not the common atmospheric air of the 

 surface, but that it was air impregnated with carbonic acid, 

 amounting in the case of certain deep organic loams to a 

 considerable percentage of the whole bulk. 



Now, carbonic acid, you know, is one of the materials which 

 contribute directly to the nourishment of plants, the substance 

 which chiefly furnishes the carbon, building up, as it were, the 

 solid framework of the vegetable structure, while the oxygen 

 previously combined with the carbon in the gas, is, in the pro- 

 cesses of the vital economy, exhaled again into the atmosphere. 

 Now, observe what an important element here is, which yet is 

 not detected by the ordinary analysis of the soil. The soil is 

 dried, the water is expelled, the gases it held are freed and 

 escape, and the soil is then analyzed as a dry, solid material, 

 leaving us in ignorance of one of its most important characters 

 — the capacity it possesses through the chemical change of its 



