8 Experiments and Observations 
should digest for 3 or 4 days or more, accord- 
ing to the quantity of the materials, the fine- 
ness of the powder, &c. the liquor must then 
be strained through a linen cloth and treated 
as has been mentioned. 
The superphosphate of lime thus obtained, 
when evaporated dry, assumes the appear- 
ance of butter; when rendered liquid by as 
little water as possible, it is of the sp. gravity 
1.44 nearly; it is excessively acid to the taste, 
but not so corrosive as most other acids of 
equal concentration. 
This acid salt is easily analysed. If we 
want to find the quantity of extra-acid, we 
have only to saturate a given portion of it, 
by lime water, marking at the same time the 
quantity of lime water, and previously know- 
ing its saturating power. If we want to find 
the lime the superphosphate contains, we may 
saturate it with caustic soda, when phosphate 
of lime will fall down, and one half of its 
weight must be taken for the lime. 
According to these methods I have not 
found the superphosphate of lime to contain 
more than 11 or 12 per cent. of lime nor less 
than 8 percent., instead of 46, as given by 
Vauquelin. In fact the salt instead of being 
a. biphosphate, is an octophosphate or a dodeca- 
