328 Prof. Graham on Water as a Constituent of Salts, 



paid to the subject. The most highly concentrated sulphuric 

 acid retains one atom of water, and is supposed to be a sul- 

 phate of water. In the case, too, of sucl) a supersalt as bi- 

 sulphate of potash or bitartrate of potash, the single atom of 

 water which is known to be persistently attached to the salt, 

 has been viewed of late, by our most enlightened chemical 

 theorists, as essential to its constitution, and the possibility 

 admitted that such salts may really be double salts; the bisul- 

 phate of potash, a sulphate of potash combined with sulphate 

 of water, and the bitartrate of potash, a tartrate of potash 

 combined with tartrate of water. 



In a late publication I have developed this view of water 

 acting as a base in the case of phosphoric acid*. That acid is 

 capable of combining with water in three different propor- 

 tions ; and the number of atoms of water with which the acid 

 combines at any time, depends upon circumstances which are 

 understood. That the water is basic in these different hy- 

 drates, follows from the fact, that, on treating them with an 

 alkali, the water is constantly replaced by a quantity of alkali 

 chemically equivalent to the water. By nitrate of silver, the 

 same precipitate is thrown down from any phosphate of soda 

 and from the corresponding phosphate of water ; the compo- 

 sition of the precipitate being determined in both cases by the 

 same double decomposition. The peculiarity of phosphoric 

 acid is, that it is capable of uniting with water as a base, in 

 several proportions, while all other acids combine with water 

 as a base in one proportion only, so far as is yet known. By 

 these discoveries in regard to phosphoric acid and its salts, 

 the ordinary conceptions entertained of the constitution of 

 salts were completely deranged. The salts called biphosphate 

 of soda, phosphate of soda, and subphosphate of soda, are all 

 tribasic salts. The common idea of a supersalt is inapplicable 

 to any of them. 



I have subsequently found water to exist in a different state 

 in certain salts, not possessed of a true basic function, being 

 replaceable by a salt^ and not by an alkaline base. To illus- 

 trate this new function of water as a constituent of salts, is 

 my principal object in the present communication. 



The tendency of phosphate of soda to unite with an addi- 

 tional dose of soda, and form a subsalt, I had traced to the 

 existence of basic water in the former. The inquiry sug- 

 gested itself, Is there any analogous provision in the constitu- 

 tion of such salts as have a tendency to combine with other 



• [Abstracts of Prof. Graham's papers on this subject published in the 

 Philosophical Transactions, will be found in Lond. and Edinb. Phil. Mag., 

 vol. iii. pp. 451, 459: see also his " Reply to Mr. Phillips's Additional Ob- 

 servations on Chemical Symbols," in vol. v. p. 401. — Edit.] 



