380 On the Action of Nitric Acid upon Pyrophosphate of Magnesia. 



lines, and, further (a theory I am alone responsible for), to deepen 

 them in parts more considerably when, from various causes, 

 the grinding power of the ice was unusually powerful, especially 

 where, as in the lowlands of Switzerland, the Miocene strata are 

 comparatively soft. But for details on this point I must refer to 

 my memoir in the Journal of the Geological Society. 



L. On the Action of Nitric Acid upon Pyrophosphate of Mag- 

 nesia. By Dugald Campbell, Analytical Chemist to the 

 Brompton Hospital , London*. 



WHEN pyrophosphate of magnesia, obtained by heating to 

 redness the phosphate of magnesia and ammonia, was 

 mixed with nitric acid and heated to about 320° F. for a long 

 time and until the weight was constant, it was found that a 

 large percentage of nitric acid remained with the pyrophosphate ; 

 at a very much higher temperature, nitric acid was still retained, 

 and the nitric acid was not entirely driven off until the tempe- 

 rature was raised to a bright red or almost white heat, when it 

 was observed that a considerable quantity of the pyrophosphate 

 of magnesia w T as also volatilized along with it. 



Pyrophosphate of magnesia, dissolved in ordinary nitric acid 

 and exposed in an open capsule to temperatures ranging from 

 320° F. to 550° F. till the weight became constant for each 

 temperature, was invariably found to have increased very much 

 in weight, although not always to the same extent, as shown 

 below. 



Temperature. Percentage increase of weight. Difference. 



320° F. 22 to 30 8 per cent. 



420 19 „ 21 2 „ 



550 13-5 „ 14-5 1 „ 



When the pyrophosphate of magnesia, still retaining nitric 

 acid, but constant in weight at 320° F., was heated sufficiently 

 to drive off all the nitric acid, it was found to have decreased in 

 weight, not to a uniform amount, but varying from 9 to 15 per 

 cent., according to the greater or less rapid application of heat ; 

 on heating in the same manner the pyrophosphates of magnesia 

 retaining nitric acid and constant in weight at 420° F. and 550° F., 

 they were found likewise to have decreased much in weight, 

 although not to so great an extent. 



It is inferred from these experiments that nitric acid has a 

 stronger affinity for magnesia than pyrophosphoric acid has, and 

 that on adding nitric acid to pyrophosphate of magnesia, nitrate 



* Communicated by the Author, being an abstract of a paper read at 

 the Cambridge Meeting of the British Association, October 1862. 



