Attack on his " First Principles of Chemistry " 221 



I determined the atomic weight of barytes. The muriate of 

 barytes of commerce always contains lead. The reason I 

 take to be, that it is manufactured from the carbonate of ba- 

 rytes of Anglesark, which is probably mixed with some car- 

 bonate of lead. I do not recollect whether the chloride of 

 barium which I emj)loyed was prejiared by myself, oi- pur- 

 chased. Supposing it purchased, it was possible that my 

 number might have been affected by the lead present, which 

 would undoubtedly tend to increase the apparent weight of 

 the atom of barytes. To obviate this uncertainty, I purified a 

 quantity of muriate of barytes by passing a current of sulphu- 

 retted hydrogen through its solution. It was then crystallized 

 and ionited. With this purified chloride I made several of 

 my practical pupils in succession, at least as many as six of 

 them, make the following experiment : 1 1 grains of sulphate 

 of potash and 13-25 grains of chloride of barium were dis- 

 solved each in a minimum of water. The solutions were 

 mixed, and after standing for twenty-hours were tested for 

 sulphuric acid and barytes, and in no one case was the least 

 trace of either found. I consider these experiments as more 

 satisfactory than if I had made them myself, because the ex- 

 perimenters could have no undue leaning to my numbers. 

 When 1 see Berzelius's observations, I shall be able to judge 

 whether any additional experiments are necessary. 



The only atomic weights given in my First Piiiicijjles, which 

 I have since found to be inaccurate, are the following : 



Chromium I stated to have an atomic weight of 3*5. This 

 was merely from analogy. 1 had determined the atomic 

 weight of chromic acid to be 6*5 ; and as there were three com- 

 pounds of chromium and oxygen, I was led to consider them 

 as composed of 1 atom chromium, and 1, 2, and 3 atoms 

 oxygen respectively, which would make the atoms of chro- 

 mium 3-5. Since that time I have examined the atomic 

 weight of chromium and its oxides with much care. The 

 reader will find the result of this investigation in the Philoso- 

 phical Transactions for 1827. I found the supposed deut- 

 oxide of chromium to be merely the protoxide contaminated 

 with a little chromic acid. The atom of chromium I found 

 to be 4, that of protoxide 5, and that of chromic acid 6-5. 



I find the atomic weight of the phosphoric acid which exists 

 in earth of bones and in the phosphate of soda of connnerce 

 to be 4-5, and not 3-5 as I state it in my First Princiji/cs. My 

 number 3-5 was obtained from the analysis of a phosphate of 

 soda whicli I had prepared myself many years ago in Eilin- 

 burgh. My stock of this jjhosphate was considerable, and it 

 was only exhausted in the summer of 1825. On using some 



phosphate 



