276 Mr. J. Prideaux 071 the Compositioti of 



for the future, sure of its position within ten or fifteen minutes 

 of a degree, would appear to have been the cause that this 

 planet, the first-discovered of the small ones, has been least ob- 

 served in recent years ; — at any rate I have not succeeded in 

 obtaining accurate observations of Ceres at the times of its op- 

 position, even since the period that the oppositions of the other 

 small planets have been regularly observed by meridian instru- 

 ments in German observatories. It is possible that some oppo- 

 sitions have really been entirely neglected. It is the more de- 

 sirable that the future oppositions should not pass by unno- 

 ticed, as Ceres might likewise afford additional means of de- 

 termining the mass of Jupiter, or might assist in answering 

 the question which has lately been agitated, Whether for all 

 planets, the attraction is rigorously proportional to their mass? 



XXXIX. On the Compositio7i of Chloride of Barium, Nitrate 

 of Lead, and Phosphoric Acid : and on the Atomic Weights 

 of Iodine and Bromine. By Mr. John Prideaux. 



To the Editors of the Philoso^ihical Magazine a?id A?inals. 

 Gentlemen, 

 TN a letter published in the Phil. Mag. and Annals, vol. vi. 



p. 166, I mentioned a scale of equivalents which, having 

 found convenient in my own practice, I was induced to pre- 

 pare for publication. This was deferred in consequence of 

 Dr. Turner's experiments on chloride of barium ; most of 

 the equivalent numbers having been taken from Dr. Thom- 

 son's " First Principles," which those experiments tended to 

 call in question. And it seemed desirable to wait the result 

 of the further investigations promised in Dr. Turner's paper; 

 in the mean while, having seldom found reason to be dissatis- 

 fied with the scale as it stood, employing my occasional lei- 

 sure in testing it by more accurate experiments. 



Not having seen any further progress reported by the Lon- 

 don Professor, I send you the following account of some of 

 these experiments. 



So far as had occurred to me, chloride of barium and the 

 sulphates precipitated each other completely in Dr. Thom- 

 son's proportions ; as did nitrate of lead, and oxalate of am- 

 monia: and on these equivalents depended the accuracj' of 

 many of the numbers in the " First Principles." If the ex- 

 periment of Thomson, Berzelius, and Turner, with sulphate 

 of potass,, had been repeated by me, I should not presume to 

 report it publicly: beside that, it is objectionable, without cer- 

 tain 



