1820.] the Atoms of Barytes, Potash, Soda, ^-c. 337 



traces either of chromic acid, or of oxide of lead. It deserves 

 the attention of the practical chemist that 1 repeated this expe- 

 riment a number of times before I could succeed. The hquid 

 after the precipitation of the chromate of lead always contained 

 a minute but variable quantity of oxide of lead. I discovered at 

 last, though not without a good deal of trouble, that my chro- 

 mate of potash was not absolutely free from nitrate of potash. 

 Before I was perfectly successful in the experiment, I found it 

 necessary to prepare pure chromate of potash by saturating a 

 solution of bichromate of potash with potash, and then crystal- 

 lizino- the salt. With perfectly pure chromate of potash thus 

 prepaVed, the experiment may be repeated without difficulty. It 

 was in consequence of this very difficult separation of all the 

 saltpetre from chromate of potash that I have preferred using 

 the bichromate instead of the chromate. It is much easier to 

 procure the former in a state of purity than the latter. 



Unless I am mistaken in my conclusions altogether, I have 

 demonstrated in this essay the true atomic weights of eight 

 very important substances, and I have shown that neither the 

 atomic weights of these bodies given by Dalton, Wollaston, nor 

 Bei-zelius, are absolutely correct, or capable of standing the test 

 which Richter long ago applied to the analyses of Kirwan, Wen- 

 zel, and Bergman. My numbers, on the contrary, stand that 

 severe test perfectly well, and consequently are accurate. 



I shall conclude this essay by laying these weights again 

 before my readers, and with requesting them to endeavour to 

 remember the respective numbers ; because they indicate the 

 weights of the different acids and bases which just saturate each 

 other, and will be found of infinite value to the practical chemist. 



Weight of atom. 



Barytes 9-75 



Potash 6-00 



Soda 4-00 



Protoxide of lead 14-00 



Sulphuric acid 5*00 



Nitric acid 6-75 



Muriatic acid 4-625 



Chromic acid 6-5 



Henceforth these numbers may be used with perfect confidence 

 by practical chemists. 



Vol. XVI. N° V. 



