306 Mr Clark on the Pyrophosphate of Soda* 



About a fourth part of the crystals however escaped pound- 

 ing. I ascertained the water in one experiment where the 

 salt had been thus treated, and where, it is evident, some me- 

 chanical water was likely to remain ; and I made two experi- 

 ments where the salt had been pounded and dried in blotting 

 paper, and where of course there was risk of efflorescence. 

 The following are the results : 



Pounded in a Dried in 



Crystals. Handkerchiel". Blotting Paper. 



Pyrophosphate of soda 16.741* 16.741 16.741 



Water expelled by red heat 1.158 1.188 1.112 



Water expelled by sand bath-heat 28.786 27.305 26.803 



The oxygen in the water expelled by a red heat is 

 1.03 1.05 .99 Mean 1.024 



This ought evidently to be 1. 



The water expelled by the sand bath contains of oxygen 

 25.59 24.27 23.83. 



But as the first quantity includes mechanical water, as like- 

 wise probably the second, though in a much less degree; and 

 as the water in the third was more likely to be in deficiency 

 than in excess ; we may safely conclude that the true quantity 

 lies between the second and third. In this view, twenty-four 

 must be the proportion of oxygen. Thus, exclusive of me- 

 chanical water, one proportion of crystallized phosphate of 

 soda contains twenty-five proportions of water ; of which twen- 

 ty-four are separable by a sand bath heat, and the remaining 

 one by a red heat ; and, in losing this last one proportion of 

 water, phosphate of soda becomes pyrophosphate of soda. 



In what light are we to view this last proportion of water ? 

 Is it in combination with the salt, like the other twenty-four 

 proportions of water of crystallization ? Is it in combination 

 with the soda, forming, with one half of it, a hydrate ? Or, 

 Is it in combination with the acid ? Though one proportion 

 of water is separated, let us recollect that this does not neces- 

 sarily imply that one proportion of water existed : it may be, 

 that the salt contained merely the elements of this water; 

 namely, one proportion of oxygen and one proportion of hy- 

 drogen ; and that the water is, not merely separated, but pro- 

 duced, by the action of heat ; as we know nitrate of ammonia 

 to be resolved by heat into nitrous oxide and water, neither, of 



