12 ~~ Experiments and Observations 
salt was in reality a biphosphate of soda, or 
was constituted of 2 atoms of acid and 1 of 
soda. 
A saturated solution of the biphosphate in 
water is of the sp. gr. 1.032. Though con- 
stituted of 2 atoms of acid to 1 of base, it is 
remarkably alkaline by the colour test, and 
in fact requires the acid to be doubled before 
it is neutral. Or it may be neutralized by 
adding any other acid sufficient to engage 
one half of the soda. Hence the neutral 
phosphate is a guadriphosphate of soda. 
If to a solution of biphosphate of soda we 
add as much more caustic soda as is in the so- 
lution, we reduce the salt to a simple phos- 
phate, or one atom to one; and this is the 
salt that should be used in most cases as a 
chemical agent in the analysis of metallic 
and other salts. It is more soluble than bi- 
phosphate ; it crystallizes in very fine needle 
shaped crystals in a liquid of 1.086 sp. gr.; 
whereas those of the biphosphate are rhom- 
boidal and the liquid is 1.032 sp. gr. 
It appears then that there are at least 3 
distinct combinations of phosphoric acid and 
soda; the phosphate just mentioned; the com- 
mon salt or biphosphate, and the quadriphos- 
phate or neutral salt. 
