REPORT ON CHEMISTRY. 
459 
phoric acid. According to his experiments, it would appear 
that the acid after fusion, or as obtained by burning phosphorus, 
is not the same as that contained in the fused phosphate of 
soda. The common acid, the pyro acid obtained by decompo¬ 
sing the pyrophosphate of lead by sulphuretted hydrogen 
after the method of Gay-Lussac, and the meta or fused acid, 
are thus distinguished by Mr. Graham:— 
The common phosphoric does not affect solutions of silver, 
albumen, or barytes. 
The pyrophosphoric gives with silver a white pulverulent 
• • • • 
precipitate (P + 2Ag), but does not affect solutions of albu¬ 
men or of chloride of barium. 
The metaphosphoric gives with nitrate of silver a white ge- 
• • 
• • • • 
latinous precipitate (P + Ag), coagulates albumen, and gives a 
white precipitate with chloride of barium. 
The acids in applying these tests are supposed to be in the 
state of weak solutions, in which state they are perfectly stable. 
Mere concentration is sufficient to change the meta into the 
common acid. 
The metaphosphoric acid is obtained by burning phospho¬ 
rus in an excess of oxygen gas, or by heating to redness the 
common acid. It may also be obtained in composition by fusing 
the diphosphate of soda, dissolving in water and saturating 
with carbonate of soda. To saturate the common biphosphate, 
an atom of carbonate of soda is necessary ; the fused biphosphate 
requires for saturation only half an atom, and the salt is incry- 
stallizable. If the whole acid, therefore, has undergone a like 
change, its saturating power has been diminished one fourth, 
and consequently the weight of the atom of the meta is to that 
of the common acid as 4:3. Such a constitution of the acid, 
if made out, would be sufficiently remarkable. 
But the composition of the fused biphosphate after saturation 
• • • • • • 
• •• • • e • • •••• 
= P+1J So, or 2 P + 3 So, may be represented = (So + P) 
• • 
• • • • 
+ (2 So + P), being a compound of one atom of a biphosphate 
with two atoms of a neutral phosphate. This view obviates the 
necessity of supposing that there is any change in the satura¬ 
ting power,—a necessity which is not borne out by the known 
composition of the white diphosphate of silver thrown down by 
the fused acid. If the acid have a less saturating power when 
combined with soda, it ought to have it also when combined with 
silver. It is possible, however, that during fusion the free acid 
in the diphosphate has alone suffered this new change. If that 
