304 Mr Clark on the Pyrophosphate of Soda. 



This result agrees sufficiently well with the mean result of 

 the former experiments on the crystallized phosphate of soda, 

 so far as regards the action of red heat. 



Water by sand-bath heat, - - .6167 



Loss by red heat, now ascertained to be water, - .0248 

 Dry pyrophosphate of soda, - .3585 



1.0000 

 But though it is thus proved that .0248 of water is not se- 

 parated from the common crystals of phosphate of soda, with- 

 out the application of a red heat ; yet the question remained : 

 Did not the power to retain this portion of water belong also 

 to the crystals of pyrophosphate of soda.? 



To determine this point, I subjected very fine, pure, and 

 hard crystals of pyrophosphate of soda to the same treatment 

 the common phosphate had undergone : that is, I exposed it 

 to the same sand-bath heat, and then to a red heat ; noting 

 the loss by each operation. 



Experiment 



I. II. Mean. 



Water expelled by sand-bath heat, - .4061 .4065 .4063 



Water expelled by red heat, - .0011 .0007 .0009 



Dry pyrophosphate of soda, - - .5928 .5928 .5928 



Now .0009 of water on .5528 of pyrophosphate of soda is 

 not so much as .0006 on .3585. But .3585 retained ,0248 of 

 water under the same treatment, when it was the ordinary 

 crystals cf phosphate of soda, instead of those of pyrophos- 

 phate, that were subjected to the heat of redness, after under- 

 going that of the sand bath. Thus it seems established, that 

 phosphate of soda so long as it may be dissolved in water with- 

 out change of properties, retains .0248, or rather perhaps 

 (.0248— .0006) = .0242 of its weight of water, which, in the 

 state of pyrophosphate, it does not retain. 



Before we can reflect with advantage on the probable func- 

 tion of this last portion of water, which is separated by a red 

 heat, it will be necessary to consider the quantity of water in 

 crystals of phosphate and pyrophosphate of soda, with refer- 

 ence to the doctrine of combining proportions. I have already 

 hinted at the differences between Doctors Thomson and Ber- 

 zelius respecting the combining proportions t)f the phosphates. 



