of the Oxides of Manganese. 147 



that salt in atomic proportion with the muriate of baryta, and 

 finding that, after the insoluble precipitate had subsided, no trace 

 of sulphuric acid or baryta could be found in the solution. From 

 this experiment he infers that 36 is the equivalent of the prot- 

 oxide. I am of opinion that the number assigned by Dr THOM- 

 SON is correct, but I am not so certain that the means by which 

 he arrived at this conclusion are altogether free from objection. 

 The principle of his method is unexceptionable, especially if the 

 quantity of the precipitated sulphate be carefully observed at the 

 same time ; but it is essential to accuracy that the atomic weight 

 of baryta be perfectly established. Dr THOMSON supplied this 

 element in the inquiry in the following manner. He dissolved 

 88 parts or one equivalent of sulphate of potash, and 106 parts, 

 or what he considered one equivalent, of the chloride of barium 

 in separate portions of distilled water, and then mixed the solu- 

 tions together. After the precipitate had subsided, the super- 

 natant liquid was found to contain no trace either of sulphu- 

 ric acid or baryta. It hence follows, if no error is committed, 

 that 70 is the true equivalent of barium. But in a recent 

 number of POGGENDORFF'S Annalen der Physik und Chemie 

 (vol. viii. p. 5.), BERZELIUS denies the accuracy of the experi- 

 ment. He declares that after mixing together the sulphate of 

 potash and chloride of barium in the proportions mentioned 

 by Dr THOMSON, 2^ per cent of the chloride of barium remain- 

 ed in the residual liquid ; and on repeating this experiment 

 for my own information, I certainly found that the whole of the 

 baryta was not precipitated. I wish it to be distinctly under- 

 stood, however, that I do not confidently rely on the accu- 

 racy of my result, having been hitherto unable, from want of 

 leisure, to examine the subject with that care which I deem 

 necessary before attempting to decide a point in dispute be- 

 tween chemists, for whose analytical attainments I entertain 

 such high respect. Dr THOMSON will doubtless feel the ne- 

 cessity of verifying his conclusions without delay ; since an er- 



T 2 



