364 INDEX. 



Silica, enters into the composition of arable soils, 18. — Its mixture 

 with alumina., ibid. — Process for obtaining it pure, 30. — Abundant 

 in vegetables, 31. — Properties, 35. 



Sirups, processes for making them, 187. 



Soda, extraction of it from marine plants, 173. 



Soils, their nature, their elements, 18, 19, 23, 24, 25. — Mixtures of 

 them, 27, 28. — Their fertility, as affected by their composition and 

 exposure, 40, 41. — Exhausted by long cultivation, 110. 



Stables and Sheepfolds, purification of the air in, 286. 



Starch or Fecula, 136. — Its use, 136, 137. — Process for obtaining 

 it, 137 et seq. 



Straw, a weak manure, 63. 



Sugar, to what the name is applied, 140. — Three kinds known, ibid. 

 — Vegetables which yield them, 140, 141. — Their specific gravity, 

 141. — Extraction of sugar from beets. See Beet. 



Sulphur, fumigation with it for purifying sheepfolds, 286. 



Sweat, animal, 61. — Its analysis, ibid. 



Tannin, its characteristics, proper uses, and the mode of extracting it, 

 158. — Improvement of the art of the tanner, 158. — Combination 

 of tannin with gelatine, 203. 



Tar, how obtained, 148. — Process for improving it, ibid. 



Tax, upon salt, a public calamity, xxvii. 



Temperature, its variations and eifects, 11, 12. 



Tillage, its advantages, varieties, appropriate periods, depth, accord- 

 ing to the nature of soils and plants, 42. — Soils which require more 

 or less tillage, 107, 108 et seq. 



Trees, resinous, 147, 148. 



Trenches, suited to the preservation of grains, 190, 194. 



U. 



Urine, as a manure, 57. — Varieties in the urine of animals, ibid — 

 Its efficiency in composts, 58. — Its combination with plaster and 

 lime, ibid. 



V. 



Vapors, aqueous, their effects, 32, 33. 

 Vegetable acids. See Acids. 

 Vitality, its laws, xviii. 



