812 Mr Clark ofi a New Phosphate of Soda. 



crystals containing less water of crystallization, I exposed a 

 concentrated solution of phosphate of soda, to evaporation in 

 a calico-printer's stove which was kept hot night and day, com- 

 monly at a temperature of about 90° Fahr. Crystals have been 

 deposited since the preceding papers were written ; and I have 

 the happiness to find that they are just the kind I was seeking 

 for ; similiform with the arseniate of soda, and containing the 

 same proportion of combined water ! In the following expe- 

 riment, the water was separated from crystals, which had been 

 pounded and dried in a handkerchief. 



Water expelled by sand-bath - - 16.303 

 Water expelled by red heat -. - 1.186 



Dry pyrophosphate of soda - - 16.741 



Compare the water in this phosphate with that in the simi- 

 liform arseniate, as stated in the preceding paper; this salt 

 having undergone the same treatment. 



Water expelled by sand-bath - - 16.386 

 Water expelled by red heat - - 1.179 



Dry arseniate of soda _ - - 22.226 



I need hardly remind the reader that, in Dr Berzelius's 

 tables, 16.741 of pyrophosphate of soda is equivalent to 

 22.226 arseniate of soda ; each of these numbers representing 

 one combining proportion. Comparing the above experiments 

 together, there can be no doubt of the identity of the propor- 

 tion of water of crystallization. 



A solution of the new phosphate in water has the same pro- 

 perties as those of the common phosphate, crystals of which 

 it yields by the usual treatment. The new phosphate does 

 not lose its water by exposure at ordinary temperatures ; but 

 it is difficult to remove completely from its surface, the mother 

 liquor which almost immediately forms a thin covering of efflo- 

 rescing phosphate to the salt, and speedily, by losing its water, 

 gives to the new phosphate the appearance of an efflorescing 

 salt. 



Professor Mitscherlich may look to the discovery of the 

 new phosphate of soda, not without triumph. The arseniate 

 of soda, which does not effloresce, seems originally to have 



