of the Oxides of Manganese. 25 



equivalent of the protoxide. I am of opinion that the num- 

 ber assigned by Dr. Thomson is correct, but I am not so cer- 

 tain 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 es- 

 sential to accuracy that the atomic weight of baryta be per- 

 fectly 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 se- 

 parate 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 PoggendorfFs 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 re- 

 mained in the residual liquid ; and on repeating this experi- 

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

 of the baryta was not precipitated. I wish it to be distinctly 

 understood, however, that I do not confidently rely on the 

 accuracy 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 

 error in the atomic weight of barium will at once vitiate an 

 extensive series of his most elaborate analyses. My own ob- 

 servation, however, combined with the remark of Berzelius, 

 has induced me in the mean time to secure my own researches 

 as much as possible from any uncertainty respecting the atomic 

 weight of barium, and I have been therefore induced to ascer- 

 tain the composition of the sulphate of manganese syntheti- 

 cally rather than by analysis. 



Nine grains of pure protoxide of manganese, prepared from 

 the red oxide by means of hydrogen gas, were dissolved in 

 dilute sulphuric acid, the solution was slowly evaporated to 

 perfect dryness in a platinum crucible, and the dry salt exposed 

 for half an hour to a red heat. It then weighed 19'01 grains ; 

 and regarding the increase in weight as owing to the acid com- 

 bined with the protoxide, the resulting sulphate must consist 

 New Series. Vol. 4. No. 19. July 1828. E of 



