112 Obsei-vations on Liebig's ^^ Crganic Chemistry." 



excrements cannot contain as much as they consume, and 

 hence no manure can return to the soil as much as is taken off; 

 it must be got from the atmosphere, from the ammonia emitted 

 by dead animals. The urine of carnivorous animals, he says, 

 will also contain more nitrogen than that of herbivorous ; and 

 the m-ine is the principal source of ammonia. Yet we find the 

 urine of the cow? to be a very powerful manure to vines ; and 

 the iuice of the vine contains a great deal of ammonia. The 

 benzoic acid, a principle in the urine of herbivorous animals, is 

 useful, he says, to some plants, as the sweet vernal grass, which 

 contains that acid. 



It is much less the quantity of ammonia, he says, yielded 

 by excrements, than the form, which makes it produce fer- 

 tility. Carbonate of ammonia is very volatile, and the other 

 salts of ammonia not so much so; and this, he thinks, is the 

 cause of the influence of gypsum (sulphate of lime) on the 

 fertility of grasses. The sulphuric acid of the lime unites to 

 the ammonia, and forms sulphate of ammonia, a salt not so 

 volatile; and preserves the ammonia. The gypsum acts, he 

 says, on the carbonate of ammonia as long as a trace of it 

 exists : 100 lb. of burned sulphate of lime will fix all the am- 

 monia in 6,250 lb. of horses' urine. Taking Boussingault's 

 estimate of ^^o P^»'t "^ nitrogen in grass, every 4 lb. of gyp- 

 sum would add 100 lb. to the produce. This supposes the 

 produce cannot be made without the nitrogen. In the analysis 

 of the wheats before noticed, it appears plants do not always 

 contain the same proportion of nitrogen to the bulk : the food 

 may be more valuable, but the quantity of nitrogen does not 

 seem to regulate the quantity of produce exactly. Former 

 writers thought the sulphate of lime beneficial to clovers, 

 because it formed a part of clover. Water, he says, is re- 

 quired in great quantity to dissolve the gypsum, in the propor- 

 tion of 400 parts to 1 ; and hence the less benefit from gypsum 

 on dry lands. The decomposition of gypsum by carbonate of 

 ammonia proceeds gradually, and will last for years. Gypsum 

 mio'ht thus be of use in fixing the volatile carbonate of ammonia 

 in nianures and urines. When spread on the ground, however, 

 what will hinder the carbonate of ammonia which has to ap- 

 proach it there, and which is equally soluble, from being taken up 

 as carbonate of ammonia by the roots, adding both carbon and 

 ammonia to the plant. Sulphate of lime is cheap. Chloride of 

 calcium, also, he says, fixes the ammonia. Being generally 

 manufactured from sal ammoniac, it may be high-priced ; if it 

 could be o-ot in a cheap way from salt and lime, it would be 

 beneficial.^ Chloride of lime. Dr. Thomson says, decomposes 

 ammonia. Sulphate of ammonia has been extracted, in a com- 

 mercial way, from soot, to form sulphate of soda, by subliming 



