52 Mr. Phillips on the Hydrates ofBarytes and Sironiia. 



possible, on nccountof the still undetermined resistance of the 

 a'tiier, to predict with any certainty the precise day of the pe- 

 rihelion passage in 1835, without computing the amount of the 

 perturbations from 1607 to 1682. As there is no longer time 

 for this, he has resolved to suspend for the present his calcu- 

 lation of the perturbations from 1759 to 1835, which he has 

 already carried so far as 270° of eccentric anomaly, and to 

 wait the result of experience. He will then resume his cal- 

 culations, and carry them back to 1607, in order that the effect 

 of the resistance of the aether on this comet may be determined 

 with all possible accuracy. 



Olbers. 



VII. On the Quantity of Water contained in crystallized Barytes 

 and Strontia. By Richard Phillips, F.R.S. L.Sf E. S^c, 



Lecturer on Chemistry at St. Thomas's Hospital. 



"PJR. D ALTON in his Chemical Philosophy (vol. i. p. 523.) 

 -■-^ states that he found that 80 grains of fresh crystallized ba- 

 rytes, dissolved in water and saturated with sulphuric acid, gave 

 36 grains of dried sulphate of barytes; and hence he inters, that 

 in the crystals 20 atoms of water are united to one atom of 

 barytes. On looking into chemical works I do not find that 

 any other chemist has attempted to ascertain the quantity of 

 water which these crystals contain ; indeed Dr. Dalton's state- 

 ment is quoted by both Thomson and Turner. 



Not remembering any case in which a binary compound like 

 barytes unites with so many as 20 equivalents of water, and as 

 Dr. Dalton admits that his experience on the crystals of ba- 

 rytes has been limited, I was induced to repeat the experiment, 

 in order to ascertain whether or not these crystals formed an 

 exception to what appears to me to be a general rule. 



With this intention I decomposed some sulphate of barytes 

 by heating it with charcoal, and dissolving the sulphuret of 

 barium in water: the solution was heated with peroxide of 

 copper, and filtered while hot. On cooling, crystals of barytes 

 were plentifully obtained, which were dried, as well as they 

 could be, by repeated pressure between folds of blotting-paper. 

 One hundred parts of these crystals were supersaturated with 

 muriatic acid, and the solution was decomposed by sulphuric 

 acid: in one experiment 72*19 parts and in another 72*15 

 parts of sulphate of barytes were obtained, giving a mean of 

 72*17; now as 116 of sulphate ot" barytes contain 76 of the 

 earth, 72*17 parts contain 1^7*28 of barytes, which, deducted 

 from 100, the crystals employed, leave 52*72 as the quantity 

 of water which they contained. Now a compound of 



