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SECOND REPORT— 1 832 . 
phosphoric. The advantage to be gained by the adoption of 
such a general prefix is obvious, both in simplifying nomencla¬ 
ture and in keeping before the mind the true relations subsist¬ 
ing between the several groups of isomeric compounds : but it is 
to be regretted that Berzelius should have thought it necessary 
to transfer to the new modification a term so long applied to 
the old one. The only reason given for the change will also 
be set aside, should the observations of Mr. Graham on the 
zractaphosphoric acid prove correct. 
Metaphosphoric acid .—The differences between the two 
acids above mentioned, as they are at present received, are the 
following:— 
1°. The common acid gives a yellow precipitate with nitrate 
of silver ; the fused, a white precipitate. 
2°. The common does not affect a solution of albumen; the 
fused, coagulates it. 
3°. The common is changed into the new acid by fusion at a 
high temperature ; the new again into the common by solution 
in water, more speedily by boiling, and by the aid of a small 
quantity of another acid. 
4°. The common phosphate of soda contains \2\ atoms of 
water: after heating to redness and resolution it crystallizes with 
only ten atoms of water. It has been stated that the precipitates 
with nitrate of silver by solutions of newly heated phosphoric 
acid and of the heated phosphate of soda, are both white, and 
similar in appearance. But by the analysis of Berzelius the 
precipitate from the acid is a bisalt = P + Ag, while that from 
• • • • 
the solution of the heated soda salt is neutral = P + 2Ag. 
This difference in composition it was easy to account for 
from the presence of an excess of acid in the case where the 
double salt was formed, without supposing that there was any 
difference between the acids combined with the silver in the 
two precipitates. 
Dumas in his Chemistry (vol. ii. p. 239,) states distinctly, 
however, that there is a third modification of the phosphoric 
acid, though he does not specif}^ its distinctive properties. He 
says that when the common phosphate of soda is boiled for 
some time it crystallizes in a peculiar form, which it obstinately 
retains. 
Mr. Graham lias lately directed his attention to this sub¬ 
ject, and has made out, it would appear satisfactorily, that 
there is in reality a sufficiently distinct third acid, which, with 
his consent, I shall here distinguish by the term wetophos- 
