178 On the Physical Properties of Soil 



III. The firmness and consistencj^ of a soil in its dry and in its 



moist state. 



IV. Its different capability of becoming dry on exposure to the air. 

 V. Its diminution in bulk on drying. 



VI. Its absorption of humidity from the atmosphere. 

 VII. Its absorption of oxygen from the atmosphere. 

 VIII. Its power of retaining heat. 

 IX. Its capability of becoming more or less warmed by the 

 sun's rays. 



X. Its capability of developing heat on being moistened. 

 XI. Its electric polarity and capability of conducting electricity. 



We will now consider these several properties more narrowly, 

 and give the process of testing soils in regard to them ; to which 

 w^e mil subjoin a comparative arrangement of them, in reference 

 to those earths and soils which come most frequently under the 

 notice of the agriculturist : we have selected for this purpose, — 



1. Siliceous sand. 



2. Calcareous sand. 



3. Finely powdered carbonate of lime, obtained from burnt lime- 

 stone, which, by long exposure to the atmosphere, has returned to 

 the state of perfect carbonate. 



4. A common grey clay, consisting of 68 per cent, of silica, 36.2 of 

 alumina, and 5.8 per cent, of protoxide of iron. 



5. Stiff clay or brick-earth, loam, and sandy clay. 



6. Earthy gypsum, or g}^3sum-powder, resulting from the pulveriza- 

 tion of the natural white gypsum. 



*7. A somewhat fine-slaty, red-brown clay marl, frequently found 

 in the Keuper formation of Wiirtemberg, consisting of 84.8 per 

 cent, of clay with oxide of iron, 6.5 per cent, of carbonate of lime, 

 7.2 of carbonate of magnesia, and 1.3 per cent, of loosely com- 

 bined oxide of iron. 



8. Humus, or humic acid ; and with these investigations should be 

 connected the animal-vegetable humic acid, which is known to be 

 of especial effect on vegetation. 



9. Carbonate of magnesia, obtained from the precipitation of solutions 

 of magnesia in acids by alkalies. 



10. A fertile, light, black garden-mould, consisting of 52.4 per cent, 

 of clay, 36.5 per cent, of sihceous sand, 1.8 per cent, of calcareous 

 sand, 2 per cent, of lime, and 7.2 per cent, of mild humus and 

 organic remains. 



11. A common fertile arable soil, consisting of 51.1 per cent, of 

 clay, 42.7 of siliceous sand, 0.4 of calcareous sand, 2.3 per cent, 

 of lime, and 3.4 per cent, of mild humus and organic remains. 



In testing the several properties, we employed, for compa- 

 rison, white pipe-clay, as one of the purest native clays ; fine 

 lime, prepared by precipitation of acid solutions, by means of 

 alkalies; and several other kinds of earth, of which particular 

 mention will be made when we come to discuss the special pro- 

 perties of soils individually. 



