Mr Clark ori the Arseniate of Soda. 309 



as we know that the ore of gold would be trodden over by men, 

 and remain unfound, if it were unsought. 

 August 15th, 1827. 



Art. XVIII. — On the Arseniate of Soda. By Mr Thomas 

 Clauk, Lecturer on Chemistry and Mechanics in the 

 Glasgow Mechanics' Institution. Communicated by the 

 Author. 



In making the experiments on arseniate of soda, alluded to in 

 the preceding paper, I made an observation, which, though I 

 now find it is not original, is likely to be new to the chemists 

 of this country, as it was new to myself. 



Professor Mitscherlich describes the arseniate of soda, as of 

 the same crystalline form with phosphate of soda. But in pre- 

 paring the arseniate of soda, I found it very rare to get cry- 

 stals of this form, the crystals which most commonly occurred 

 being distinctly different. On submitting these crystals for 

 crystallographic examination to Mr Haidinger, I was inform- 

 ed by that gentleman that they had been previously discover- 

 ed by Professor Marx of Brunswick, and examined chemical- 

 ly by Dr L. Gmelin of Tubingen. They differ, chemically 

 from the other arseniate only in their water of crystallization ; 

 and the last proportion of it cannot be expelled without red heat, 

 just as with the other arseniate, and with the phosphate of soda. 



To ascertain the water of crystallization, and especially to 

 distinguish what was mechanical water, I made one experiment 

 on crystals, two others on crystals pounded and dried in the 

 corner of a handkerchief, and lastly two on pounded crystals, 

 dried in blotting paper. I put down the result as if the dry 

 arseniate of soda had turned out 22.226 in each case ; this be- 

 ing Dr Berzelius's combining proportion for this salt, and con- 

 taining 7 proportions of oxygen ; namely 5 in the acid and 2 

 in the base. 



Water, expelled by sand-bath 

 Water expelled by red heat 

 Dry arseniate of soda 



40.842 39.791 39.120 



