1885.] Solubility of Calcium Sulphate in Water. 331 



II. On the Solubility of Calcium Sulphate in Water in the 

 presence of Chlorides." By. William A. Tllden, D.Sc, 

 F.R.S., Professor of Chemistry in the Mason Science 

 College, Birmingham, and W. A. Shenstone, F.I.C., F.C.S., 

 Lecturer on Chemistry, Clifton College, Bristol. Received 

 April 27, 1885. 



It has long been known* that the solubility of calcium sulphate in 

 water attains a maximum at about 35° C, also that the solubility of 

 this compound is increased by the presence of common salt. But 

 accurate determinations of the extent to which the solubility is thus 

 influenced have not hitherto been published. Having the means of 

 determining solubilities at temperatures above the boiling point of 

 water, and considering the interest from both a theoretical and 

 practical point of view attaching to these determinations, we under- 

 took the following experiments. When our work was nearly com- 

 pleted we observed a paper by Professor Lunge on the same subject 

 in the Journal of the Society of Chemical Industry for January 

 last. We venture to think, however, that our results are still of 

 interest as being more systematic, and since every experiment was 

 done with every precaution and very great care, they are probably 

 more accurate. The solubilities at temperatures above 100° have 

 never before been determined. 



Our former experiments on solubilities at high temperaturesf were 

 made in a gun-metal tube coated with silver, but in the present series 

 of experiments the silver was not found to resist the action of the 

 solutions, and we have therefore employed a tube of platinum. The 

 platinum tube is shown in the accompanying figure. 



The part A is 87 mm., B 123 mm. long. Both are closed at one 

 end, and the open ends are ground to fit the union piece C, which 

 contains a small screen d, and has two small holes at e and /. The 

 internal diameter of the arrangement is 12 mm. When joined 

 together, the three pieces form a compound tube C, 245 mm. long. 



The salt and solvent are placed in B, a small strainer of platinum 

 gauze is introduced at g, and the tubes are fitted together. The 

 whole is then enclosed in the strong gun-metal]tube and heated in the 

 paraffin bath as already described ("Phil. Trans."). After four or 

 five hours at the desired temperature the solution is drained into A, 

 and after turning the tube so that the screen may arrest the flow of 

 any subsequent drainings into A, the whole is allowed to cool. The 

 small hole at e allows any drops of liquid that may be stopped by the 

 screen to escape into the outer tube. 



* Poggiale, "Ann. Chim. Phys." [3], viii, 469. 

 t " Phil. Trans." 1884, I, 23. 



