34 On the Analysis of Soili. 



This may be done with sufficient precision, by heating it 

 to strong ignition in a crucible over a common fire till no 

 blackness remains in the mass. It should be often stirred 

 with a metallic wire, so as to exyiose new surlaces continu- 

 ally to the air; the loss of weight that it undergoes denotes 

 the quantity of the substance that ii contains destructible 

 by fire and air. 



It is not possible to ascertain whether this substance is 

 wholly animal or vegetable matter, or a mixture of both. 

 Wh.cn the smell emitted during the incineration is similar 

 JLo ihat of burnt feathers, it is a certain indication of some 

 auimal matter; and a copious blue flame at the time of ig- 

 rCtion almost always denotes a considerable proportion of 

 vegetable matter. In cases when the experiment is needed 

 to be very quickly performed, the destruction of the de- 

 composable substances may be assisted by the agency of ni- 

 trate of ammonia, which, at the time of ignition, ntiay be 

 throvi'n gradually upon the heated mass, in the quantity of 

 twenty grains for every hundred of residual soil. It af- 

 fords the principle nccessarv tothe combustion of the animal 

 and vegetable matter, which it causes to be converted into 

 elastic fluids; and it is itself at the same ti\ne decomposed 

 and lost. 



XI. Mode of separating Aliiminovs and Siliceous JMatter 

 and Oxide of Iron. ., 



The substances remaining after the decomposition of the 

 vegetable and animal matter, are generally minuie particles 

 of earthy matter containing usually alumine and silex with 

 combined oxide of iron. 



To separate these from each othi-r, the solid matter 

 should be boiled for two or three hours with sulphuric acid, 

 diluted with four tipies its weight of v/ater ; the quantity 

 of the acid should be regulated by the quantity of solid re-, 

 siduum to be acted on, allowino- for every hundred grains 

 two drachms or one hundred and twenty grains of acid. 



The substance remaining after the action of the acid may 

 be considered as biliceous ; and it must be separated and its 

 weight ascertained, after washing and drying in the usual 

 manner. 



The alumine and the oxide of iron, if they exist, arc 

 both dissolved by the sulphuric acid ; they may be separa- 

 ted by carbonate of ammonia, added to excess ; it throws 

 down the alumine, and leaves the oxide of iron in solu- 

 tion ; and this substance may be separated from the liquid 

 by boilino". 



Slrould 



