ALUMINOUS CHALYBEATE SPRING IN I. O? WIGHT. gf 



3. ft appears therefore, that the aggregate of the analy- Difference be- 

 tical results would indicate 79 grs. of ignited sulphate of l *^ n *• J"** 

 barytes, instead of the 74 grs. obtained by a single direct recalculated 

 operation. This difference 1 apprehend to be in a great and obtained, 

 degree owing to my estimate of the proportion of acid in 

 sulphate of alumine being overrated, from the circumstance 

 of not having been able to obtain a neutral sulphate of alu- 

 mine in the experiment ju9t related from whk:h that estimate 

 was deduced. 



Sect. XVI. Silica. 

 -,. . . . „, .., . .,-r Examination 



I. During the various solutions of the residue in acid, I forsilex. 



had repeatedly observed, that, beside the selenite, (the 

 solution of which was attended with some difficulty y and re* 



two equal portions, one of which was precipitated by succinate of am- 

 monia, and the other by nitrate of barytes, yielded 45 grs. of ignited 

 alumine, for 21 grs. of ignited sulphate of barytes. From which it 

 may be inferred, that the 38 grs. of ignited alumine, found in a pint of 

 the water, were combined with a quantity of acid equal to iff grs. of 

 ignited sulphate of barytes. But it is assumed in this computation, 

 that the artificial sulphate of alumine subjected to analysis, was in 

 the same state of combination as that which exists in the water, a sup- 

 position which may not be strictly accurate. 



X The quantity of sulphate of barytes, produced by the precipitation p . f 



of a given quantity of sulphate of lime, was ascertained in the following sulphate of 

 manner ; some pulverized crystals of native selenite, apparently per- barytes to sul- 

 fectly pure, were dissolved in water and afterwards slowly precipitated phate of lime. 

 by evaporation. The object of this previous operation was to obtain 

 the sulphate of lime in a state more fit for subsequent redissolution. 

 Fifteen grains of this selenitic residue, dried at a red heat, were dis- 

 solved in water, slightly acidulated by muriatic acid, in order to super- 

 sede the necessity of using large quantity of water ; and the solution, 

 after fating neutralized by pure ammonia, was precipitated by muriate 

 of barytes. The sulphate of barytes, thus obtained, weighed, after 

 careful edulcoration and ignition in a platina cruciblf , 26-75 grs. which 

 are equivalent to 175 6 grs. of sulphate of barytes for 100 grs. of ignited 

 sulph-)tfc of lime. 



|| According to Dr. Henry 100 grs. of crystallized sulphate of mag- 

 nesia give 111 grs. of ignited sulphate of barytes. See Philos. Traat. 

 1S10, p. 114. [Journ. vol. xxvi, p. 2?8.] 



§ These proportions were deduced from the following experiment: 

 40 grs. of crystallized sulphate of soda, being dissolved in water and 

 precipitated by nitrate of barytes, the sulphate of barytes, well edul- 

 corated and ignited, weighed 29 1 grs. 



Vol. XXXIL— June 1 SIS. H q«ir*4 



