406 On the Detection of Baryta or Strontia in union ivith Lime. 



ryta or strontia united to lime may be in this way rendered 

 evident. It is almost unnecessary to add, that when pure lime 

 was treated in a similar manner, no precipitate fell, since sul- 

 phate of lime is nearly four times as soluble in boiling water 

 as lime itself. If however the liquid be raised to the boil- 

 ing point after the addition of the sulphuric acid, one or two 

 crystals of sulphate of lime will sometimes form ; but, as these 

 are transparent and of a distinctly crystalline appearance, it is 

 impossible to mistake them for the sulphate either of baryta or 

 strontia*. In these experiments, I have in general preferred 

 the employment of sulphuric acid to that of a sulphate, as 

 I have found it to be a rather more delicate test, particularly 

 of the presence of strontia. It must of course be carefully 

 purified from sulphate of lead. 



It is generally believed, on the authority of Dr. Hope, that 

 sulphate of strontia is sensibly soluble in water, so that the 

 addition of a barytic salt or an alkaline carbonate to a solu- 

 tion of it, will indicate the presence of both its constituents; 

 and this circumstance has been proposed as a distinguishing 

 test between the sulphates of baryta and strontia. On the 

 other hand, the late Mr. Smithson states that " water or so- 

 lution of sulphate of soda, in which sulphate of strontia had 

 long lain, did not produce the least cloud on the addition of 

 what is commonly called subcarbonate of soda;" and Dr. Thom- 

 son was unable to detect any trace of strontia in the superna- 

 tant liquid which remained after the mutual decomposition of 

 solutions of sulphate of soda and chloride of strontium. I di- 

 gested for some hours sulphate of strontia, obtained by preci- 

 pitation, in pure water, in a solution of sulphate of soda, and 

 in water acidulated with sulphuric acid; carbonate of soda was 

 added to each liquid, and heat applied ; a precipitate appeared 

 in all of them : it was most considerable in the first, while in 

 the last the opalescence was scarcely perceptible ; 900 grains 

 of the solution in pure water were evaporated to dryness, and 

 left a residue of sulphate of strontia which weighed -25 grain ; 

 from which it follows that one part of sulphate of strontia re- 

 quires about 3600 parts of water, at the temperature of 60°, for 

 solution. It also appeiirs that the presence of sulphate of soda 

 and sulphuric acid (in small quantity) diminishes its solubility. 

 I have not examined whether chloride of sodium would pro- 

 duce a similar effect; but the experiments of Dr. Thomson 

 would lead to this conclusion. 



* I added to three different portions of lime-water saturated at 60°, sul- 

 phate of soda, sulphate of ammonia, and sulphuric acid : no precipitate ap- 

 peared at the end of some weeks in the first two liquids; but a large quan- 

 tity of pypseous crystals was slowly deposited in the latter in the course of 

 some days. 



LV. On 



