2. Since the parts of animals—their blood, muscles, tendons, and the gelatinous portion of the bones—contain much nitrogen, young beasts which are growing, must appropriate to their own use, and work up into flesh and bone, a portion of the nitrogen contained in the _non-respired_ part of their food. But the more they thus appropriate, the less will pass off into the fold-yard; and hence it is natural to suppose that the manure, either liquid or solid, which is prepared where many growing cattle are fed, will not be so rich as that which is yielded by full grown animals. I am not aware how far this deterioration has been observed in practice, but it may with some degree of certainty be expected to take place,—unless by giving a richer food to the young cattle, the difference to the farm-yard be made up.[18] [18] Though I have dwelt as long upon these interesting and, I believe, novel considerations, as the limits of this little work will permit, yet I must refer the reader for fuller details, and to perhaps a clearer exposition of the principles above advanced than I have here been able to give, to my “LECTURES _on Agricultural Chemistry and Geology_.” SECTION V.—OF MINERAL WATERS. The general nature and mode of operation of such mineral substances as are capable of acting as manures, will be in some measure understood from what has already been so fully stated in regard to the necessity of inorganic food to living plants, and to the kinds of such food which they specially require. A slight notice, therefore, of the more important of these manures now in use will here be sufficient. 1. _Nitrates of Potash and Soda._—Saltpetre and nitrate of soda have been deservedly commended for their beneficial action, especially upon _young_ vegetation. They are distinguished by imparting to the leaves a beautiful dark green colour, and are applied with advantage to grass and young corn, at the rate of 1 cwt. to ½ cwt. per acre. The nitric acid they contain yields nitrogen to the plant, while potash and soda are also put within reach of its roots, and no doubt serve many beneficial purposes. _Sulphate of Soda_, or Glauber’s salt, has lately been recommended in this country for clovers, grasses, and green crops. Mixed with nitrate of soda it produces remarkable crops of potatoes.[19] [19] See the author’s “_Suggestions for Experiments in Practical Agriculture_,” Nos. 1 & 2. _Sulphate of Magnesia_, or Epsom salts, might also be beneficially applied in agriculture, probably to clovers and corn crops. As it can be had in pure crystals at 10s. a cwt., and in an impure state at a much less price, from the alum works, it might readily be submitted to trial. _Sulphate of Lime_, or Gypsum, is in Germany applied to grass lands with great success, over large tracts of country. In the United States it is used for every kind of crop. It is especially adapted to clovers and legumes.