Observations on Liehig's " Organic Chemistry.^' 129 



the organic constituents, tie recommends fallow plants, as clover, 

 rye, buckwheat, &c., ploughed into the soil when nearly in bloom, 

 to supply humus. Lucerne, he says, is most effectual; it re- 

 quires few inoi-ganic matters, and, till a certain period of the 

 growth, retains all the carbonic acid and ammonia which may 

 have been conveyed to the plants by rain and air, and the great 

 breadth of foliage prevents the escape of ammonia into the air. 

 When the green principle is produced in leaves, by light and 

 heat stimulating the action of the organs, the remainder of what 

 was absorbed by them is returned as excrements to the soil ; 

 and, after the lapse of a few years, he says, every fibre of the 

 roots will be surrounded with them. As these excrements 

 remain for some time soluble, they will act as poison ; and the 

 fields will produce barren places till the excrement is decom- 

 posed, when they will again become fertile. The roots, as they 

 continue to extend, should partly leave this excrement. We 

 must replace all the other substances, as well as carbon and 

 nitrogen ; and it is for this, he says, that manures are wanted. 



Every constituent of the body of animals is derived from 

 plants; during their life they return the inorganic substances 

 not needed, as excrement. After death their nitrogen and 

 carbon pass into the air in the form of carbonic acid and 

 ammonia. Nothing remains except the phosphates of lime, &c., 

 and other substances in their bones ; which must, he says, be a 

 powerful manure for plants, if every thing is to be restored to 

 the land which is taken from it. In the enquiry as to what the 

 excrements yield, he notices that, though animals are fed on 

 substances containing nitrogen, there is very little of it in their 

 excrement, the greater part being assimilated by themselves. In 

 100 parts of the excrement of a horse, analysed by Macaire 

 and Marcet, only 0"8 of nitrogen was found in 100; and in that 

 of the cow by Boussingault only 0'506. 25 lb. of hay, the food 

 of the cow for a day, should yield ^\h. of nitrogen ; and this is 

 the quantity found in 8*3lb. of flesh in its natural condition ; and 

 as the daily increase of size in a cow is much less than this, the 

 remainder of the nitrogen must be found in the milk and urine. 

 The nitrogen is therefore found in greatest quantity in the liquid, 

 not the solid, excrements of animals. The quantities of salts and 

 earthy matters contained in horse-dung, he says, is very variable, 

 from 10 to 27 per cent. 1000 lb. of horse-dung, he calculates, 

 will yield inorganic substances to 6000 lb. of hay, the crop on 

 nearly 2^ acres; or 8,300 lb, of oats on more than 3 acres; and 

 the same quantity would yield phosphates to If crop of wheat. 

 The excrements of cows, black cattle, and sheep contain phos- 

 phate of lime, common salt, and silicate of lime, the weight of 

 which varies from 9 to 28 per cent. The fresh excrement of the 

 cow contains from 80 to 90 per cent of water ; that of the horse 

 1841. — III. .SdSer. K 



