Mr Clark on the P^.roj)hosj)hale of Soda. 301 



of crystals, obviously different in their form from the common 

 phosphate of soda. I refrain, however, from all description 

 of their form, as that has been in disinterested kindness under- 

 taken by Mr Haidinger ; a gentleman who has established a 

 peculiar claim to the gratitude of scientific men in this coun- 

 try, by his devotion to crystallography, at a time when that 

 science is ripe for the efforts of genius, and is destined, by its 

 successful efforts, to rise high in dignity among the sciences. 

 The new crystals, being dissolved again in water, afforded a 

 .white precipitate with nitrate of silver. They were much less 

 soluble in water than the common phosphate ; they contained 

 not more than two-thirds the water of crystallization in the 

 same weight of crystals ; they did not, like the common phos- 

 phate, become dim on the surface by loss of water after many 

 days, exposure to the air ; like the commoti phosphate they 

 were alkaline in their action on vegetable colours, and in their 

 laste ; but unlike it they did not feel cooling to the tongue. 

 The mother liquor, from which these crystals were separated, 

 was concentrated and crystallized ; and the operation was re- 

 peated, till the whole liquor was converted into crystals. 

 Among these, none of the common crystals of phosphate of 

 soda could be detected ; and the last crop contained only a 

 small quantity of foreign soda salts, just as if the crystalliza- 

 tion had been made without previous exposure to red heat. 



It was quite obvious then, that by simply drying the com- 

 mon phosphate of soda and heating it to redness, an entirely 

 new salt had been produced. This new salt I shall,, in the 

 sequel of this paper, call Pyrophosphate of soda, a provisional 

 name which it will probably be well to retain, till all doubts 

 are removed respecting the constitution of this salt. 



The question which now remained was : Did the phosphate 

 of soda lose, or did it acquire any component in becoming the 

 pyrophosphate of soda ? 



An observation to which I have not yet adverted, directed 

 me, in the prosecution of this inquiry. 



I soon found that phosphate of soda might undergo a con- 

 siderable heat, without being converted into the pyrophosphate. 

 The temperature of the sand-bath at which I operated can- 

 not have been less than that of melting lead or boiling mer- 



