190 MANURE. *■ , 



becomes of great agricultural value. From an accurate 

 experiment on 106,504 lbs. of coal, I find the quantity of this 

 ash, collecting about flues, is 5.09 per cent, of the coal con- 

 sumed. 



227. Among the mixed manures, is the salt, or spent lye 

 of the soap-boiler. It seems to offer a natural passage from 

 this class to those consisting of salts only. To understand 

 its components, the chemical composition of oil and fat must 

 be briefly studied. No products of life are now better 

 understood than the fatty bodies. They are all acids, com- 

 bined with a peculiar organic base, which acts the part of an 

 oxide. This is never obtained except in combination with 

 oxygen and water. In this state it has long been known 

 under the name of glycerine. The acids combined with it, 

 are stearic, margaric, and oleic. By the union of these acids 

 with glycerine, stearine, and margarine, or fats, an oleine 

 or oil is produced. In soap-making, the alkali used decom- 

 poses stearine and oleine, combining with their acids, which 

 thus are converted into stearates, margarates, and oleates of 

 alkali, or soap, while the glycerine remains free in the spent 

 lye with the salts which that contains. 



228. The proportion of glycerine in fat and oil, is about 

 8 per cent. Its composition is — 



Carbon, 40.07 f These are in such ^ Carbon, 24.77 



Oxygen, 51.00 \ ST^e cli'Td \ or Car. hyd. 17 85 

 Hydrogen, 8.92 I "^^""^^"^^ ^y^^'^s^"- J Water, 57.37 



Glycerine is transparent and liquid, and was called the 

 sweet principle of oils, from its sweet taste. 



229. The glycerine is thus the organic, or geine part of 

 salt lye. Its proportion in that will vary, if the spent lye is 

 boiled, as is usual, upon a fresh portion of tallow, which adds 



