181 i.j On Mr. Hume's Paper on Banjtes. 433 



rcsulte demandant bcaucoup d'eau pour sa dissolution, so precipite 

 aussitot qu'il se forme, comme l'a observe M. Ivlaproth." 



" L'acide marin dissout avec effervescence le spath pesant acre : 

 le sel qui en resulte se precipite aussitot. L'acide marin qui surnage, 

 ne tient point en dissolution de sel a base do teroe pesante." 



The next discovery claimed by Mr. Hume to which I shall 

 advert is, that " sulphate of strontian has a capacity for super- 

 saturation, forming an acidulous sulphate in solution, and decom- 

 posable by water; " and of this fact he asserts that " no author has 

 given any account." 



That this statement as to sulphate of strontian is correct, and the 

 assertion respecting it erroneous, is proved by the following extract 

 from p. 331, vol. i. of the English Translation of Klaproth's 

 Analytical Essays, published in I SOI ; and the original was printed 

 in Crell's Annals for 17'.>"> : — -" Upon 60 grains of pulverized stron- 

 tianite, introduced into a retort, 1 poured by degrees two ounces of 

 concentrated sulphuric acid. The first portion that was effused 

 caused a great frothing. The contents of the retort were then 

 brought to hoiling in a sand heat. After cooling, the earth was 

 found entirely dissolved, and the solution colourless ; but it is again 

 decomposed as soon as any water is added." 



The remaining parts of Mr. Hume's paper which I shall notice 

 are contained in the following quotations: — " Sulphate of barytes 

 is completely soluble in sulphuric acid ; forming a saline fluid or 

 acidulous sulphate, analogous, in some of its characters, to phos- 

 phate of lime and many other sails, with capacity for excess of 

 acid ; decomposable by water alone, which returns it to simple 

 sulphate ; and this salt," says Mr. Hume, " never has been enume- 

 rated by any author." 



" Carbonate of barytes is also totally decomposed by, and soluble 

 in, sulphuric acid, forming, of course, the same acidulous sulphate. 

 Respecting any figure this new salt may put on, 1 have not yet been 

 able fully to determine ; but 1 strongly suspect it may, under par- 

 ticular circumstances, be made to crystallize." 



Notwithstanding the unqualified assertion by which some of these 

 facts, as well as those respecting strontian, are accompanied, it will 

 appear that all of them were well known, and had been repeatedly 

 described, before the appearance of Mr. Hume's paper, in French, 

 German, and English. 



I. The solution of sulphate of barytes in sulphuric acid, the 

 crystallization of the solution, and its decomposition by water, are 

 all stated in a letter from Morveau to Bergman : Journal de Phy- 

 sique, vol. xviii. p. JU'.f, \JK\. 



'_'. The^e facts, with the additional one of the decomposition of 

 the carbonate of barytes by sulphuric acid, arc all described by Dr. 

 Withering : Phil. Trims. I "SI. 



■i. Excepting the crystallization of the solution of the sulphate 

 of barytes, tbe same circun, ■ < ices are related by Sage in the paper 

 already quoted: Memoirei deTAcademie, &c. I ;* 



Voil. IV. V VI. 2 E 



