308 Mi* Clnrk on the Pyrophosphate of Soda. 



soda into pyrophosphate, but merely a concomitant, and, it 

 may^be, an independent effect of heat. 



Are we, then, to conceive that a red heat has produced a 

 decisive change on the constitution and properties of phosphate 

 of soda, without causing the addition or the separation of any 

 constituent whatever ? This, I think, to be at least conceiva- 

 ble ; and I will explain how. Any compound, it is generally 

 admitted, containing one proportion of sulphur and one pro- 

 portion of sodium, united with oxygen in any proportion less 

 than sufficient to form the sulphate of soda, is convertible by 

 heat into sulphate of soda, and sulphuret of sodium. Thus, 

 sulphite of soda, being heated red, forms sulphate of soda out 

 of three-fourths of the sulphur, three-fourths of the sodium, 

 and the whole of the oxygen, and also sulphuret of sodium 

 out of the remaining fourth of sulphur, and the remaining 

 fourth of sodium. These two compounds sulphate of soda, 

 and sulphuret of sodium would probably be separable by cry- 

 stallization from a watery solution of the heated product. But 

 it is conceivable at least, that the sulphate of soda, and the 

 sulphuret of sodium might remain in combination, forming a 

 sort of compound salt. In this case, (water being out of the 

 question) a red heat, without altering the weight of the sul- 

 phite, would produce a salt, whose solution would exhibit new 

 properties, and afford crystals of a new form. Is it not ad- 

 missible at least, that a red heat may produce some analogous 

 change on the phosphate of soda ? 



I repeat, however, that the constitution of the pyrophosphate 

 of soda must be decided by a more extended examination 

 (particularly of the effects of heat on salts) than has yet been 

 undertaken. Obliged by my avocations to relinquish experi- 

 mental research for a few months to come, I can only hope 

 that the interesting and extensive subject, which I am happy 

 enough in introducing to the notice of chemists, will be taken 

 up speedily, and prosecuted zealously, by others. In an age 

 of unexampled enterprise in chemical investigation, it is impos- 

 sible but that changes, analogous to the one which is the sub- 

 ject of this paper, will be discovered from time to time. But 

 it is better to seek for such discoveries, than to wait for them ; 



