168 Foreign and Miscellaneous Intelligence. 



phoric acid. Gay-Lussac then gave further light on the subject, 

 and now M. Stromeyer has published an investigation of the sub- 

 ject, which adds Very much to what was before known. 



M. Stromeyer first compares the two salts of silver, namely, the 

 phosphate and pyrosphosphate, as those compounds which most 

 strikingly exhibit the new characters impressed on the acid. Both 

 these salts are pulverulent, and, when well dried, anhydrous ; the 

 first is yellow, the second white ; the first has a specific gravity of 

 7.321, the second of 5.306. The first fuses with great difficulty, 

 requiring a very high temperature, and cools into a yellow mass. 

 The second fuses beneath a red heat into a brown liquid, which, by 

 cooling, becomes a colourless, crystalline mass. Both salts are 

 insoluble in water, both dissolve in nitric and sulphuric acid, and 

 are precipitated unchanged ; but when the pyrophosphate is heated 

 in solution, it becomes ordinary phosphate. Muriatic acid decom- 

 poses it, but without changing the peculiar character of the acid. 



All the metallic pyrophosphates, boiled with phosphate of soda, 

 become phosphates, and form pyrophosphates of soda the reverse 

 does not take place. Hence pyrophosphoric acid should be placed 

 after phosphoric acid in chemical affinity ; and this alone establishes 

 an important distinction between the two. Most of the pyrophosphates 

 recently precipitated dissolve freely in the solution of pyrophosphate 

 of soda. The same effect does not happen with the phosphates and 

 phosphate of soda. 



Hence, that a great difference exists between the phosphoric and 

 the pyrophosphoric acid is evident, although the latter is obtained 

 by calcining the former, or by burning phosphorus in oxygen ; still 

 there are plenty of reasons why the difference should not be due to 

 either an excess or deficiency of oxygenation in this respect. M. 

 Stromeyer shews that both are alike ; neither does it depend upon 

 more or less water combined, for the two salts of silver are both 

 anhydrous, and yet their properties are distinct. 



M. Stromeyer determined the composition of these two salts, 

 and, by various modes of experimenting, proved that they contained 

 different proportions of acid and base. The result of all his experi- 

 ments was, that the proportions per cent, were as follows : 



Oxide of Silver. Acid. 



In the phosphate . . 83.454 . 16.545 

 pyrophosphate . 75.390 . 24.610 



for equal quantities of acid, therefore, the quantity of oxide of silver 

 in the two salts is as 3 : 5. This great difference in saturating 

 power is the cause why, when a neutral phosphate of soda is calcined, 

 it becomes strongly alkaline, for the phosphoric acid present, by be- 

 coming pyrophosphoric acid, loses two-fifths of its neutralising power, 

 and yet this extraordinary effect happens without any loss of acid, 

 or any change in the quantity of its constituents. The whole dif- 

 ference depends upon the manner in which the elements combine, 

 and it is one more added to the very few decisive cases previously 

 known, in which the mere mode of combination, and that too in a 



