MINERAL SALTS. 145 



of carbon in the same time. He has received, then, of carbon 4,500 

 grains, and of nitrogen 500 grains, while he has given ofl' in respira- 

 tion 3,500 grains, but very little or no nitrogen. Hence there is left 

 to be converted into the body, or to be rejected, 1000 grains of car- 

 bon and 500 grains of nitrogen. Vegetable food is freed of much of 

 its carbon by expiration ; its nitrogen, of course, mostly remaining. 

 In the food above mentioned the carbon was to the nitrogen as 9 to 1, 

 and after the expiration of the carbon, it is in the proportion of 2 to 1. 

 This residue of nitrogen, or so much of it as is not carried off in per- 

 .spiration or voided, is incorporated with the body ; and, although this 

 is proportionably very small, it ultimately constitutes a considerable 

 portion of the body. It is contained principally in the blood, muscles, 

 tendons, and the gelatinous parts of the bones, and is most abundant, 

 in young persons, or animals, and therefore less escapes from the body 

 of such than from older ones. 



Mineral waters applied to plants afford many of the important salts 

 we have before spoken of. Nitrates of soda and of pot-ash impart to 

 the leaves a rich dark green color, and hence they are advantageously 

 applied to grass and young grains, in the proportion of 1 to l cwt. 

 per acre. The nitric acid contained in them affords the nitrogen ; 

 and the soda and pot-ash also serve important purposes, as we have 

 seen by the analysis of plants. For clovers, grasses, and other green, 

 crops, sulphate of soda is recommended ; and, mixed with nitrate of 

 soda, it is remarkably productive on crops of potatoes. Sulphate of 

 magnesia may also be applied with equal success to the grains and 

 grasses. This may be obtained from our alum works at a nominal 

 price. Sulphate of lime, or common gypsum, is applied extensively in 

 this country to grass land, and indeed to those of almost every kind of 

 crop. But it should be ascertained, before this is applied, if the soil 

 does not contain within itself the salt or salts applied ; for lime is often 

 used without beneficial results, and therefore thrown away on soils 

 alrpady containing it. Common Salt on very many soils is undoubtedly 

 highly fertilizing and essential to the healthy condition of many crops, 

 especially on inlands and highlands much washed by rains. 



Kelp, or the ash left by burning sea-weed is valuable. It contains 

 pot-ash, soda, sulphur, silica and chlorine, with other inorganic mat- 

 ter required for the food of plants. Sea-weed, partly charred, is thus 

 used with much success. The common pearl-ash, though in an im- 

 pure state, with sulphate and silicate of pot-ash, all contained in com- 

 mon wood ashes, show that this is often very successfully applied to 

 soils. 



Lime, it is well known, is extensively used in practical agriculture, 

 and has been from the earliest period. All the varieties of its forms, 

 as lime-stones, shells, chalk, etc., are composed of carbonic acid and. 

 lime, and hence is carbonate of lime. But when submitted to heat 



