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weight that it undergoes denotes the quantity of 
the substance that it contains destructible by fire 
and air. 
It is not possible, without very refined and dif- 
ficult experiments, to ascertain whether this sub- 
stance is wholly animal or vegetable matter, or a 
mixture of both. When the smell emitted during 
the incineration is similar to that of burnt feathers, 
it is a certain indication of some substance either 
animal or analogous to animal matter ; and a 
copious blue flame at the time of ignition almost 
always denotes a considerable proportion of vege- 
table matter. In cases when it is necessary that 
the experiment should be very quickly performed, 
the destruction of the decomposable substances 
may be assisted by the agency of nitrate of ammo- 
niac, which at the time of ignition may be thrown 
gradually upon the heated mass, in the quantity of 
twenty grains for every hundred of residual soil. 
It accelerates the dissipation of the animal and 
vegetable matter, which it causes to be converted 
into elastic fluids ; and it is itself at the same time 
decomposed and lost. 
7. The substances remaining after the destruc- 
tion of the vegetable and animal matter are gene- 
rally minute particles of earthy matter, containing 
usually alumina and silica, with combined oxide of 
iron, or of manganesum. 
To separate these from each other, the solid 
matter should be boiled for two or three hours with 
sulphuric acid, diluted with four times its weight 
of water : the quantity of the acid should be regu- 
lated by the quantity of solid residuum to be acted 
