Maboh 2, 1906.] 



SCIENCE. 



339 



calibration of thermometers, although its 

 determination requires more chemical skill 

 than that involving sodic sulphate. 



5. The actual value of the transition tem- 

 perature on the international hydrogen 

 scale is 50.674°. 



, (To be published in the Proceedings of 

 the American Academy and the Journal 

 of the society.) 



A Method of Standardizing Thermometers 

 Below Zero: T. W. Eichards and F. G. 

 Jackson. (Read by the chairman.) 

 This paper describes a simple method of 

 calibrating thermometers at temperatures 

 below the freezing point of water, by using 

 as a standard of comparison the depressions 

 of the freezing point caused by given addi- 

 tions of hydrochloric acid. Data, based 

 upon a very accurate thermometer stan- 

 dardized at the Bureau International at 

 Sevres, are given for the construction of a 

 curve enabling direct comparisons of a 

 thermometer to be made with a minimum 

 of labor. The manipulation consists sim- 

 ply in stirring hydrochloric acid into a mix- 

 ture of pure ice and water until the desired 

 point on the doubtful thermometer is 

 reached. Analysis of the solution then 

 gives, by reference to the curve, the true 

 freezing point; and the difference between 

 this value and that read on the thermom- 

 eter gives the error of the thermometer. 

 The method is shown to be both practically 

 and theoretically satisfactory. This paper 

 is preliminary in nature, and does not pre- 

 tend to give final values, because only a 

 single standardized thermometer was used. 

 (To be published in the Proceedings of 

 the American Academy and the Journal 

 of the society.) 



The Heat of Dilution ' of Eesorcinol in 

 Alcoholic Solutions: S. T. Lincoln. 



The Solubility of Gypsum in Solutions of 

 Ammonium Sulphate: J. M. Bell and 

 W. C. Tabeb. 



The solubility of gypsum in ammonium 

 sulphate solution has been investigated by 

 Droeze, Cohn and Sullivan at temperatures 

 not exceeding 25° C. At 50° C. the au- 

 thors have found that the compositions of 

 solutions lie on three curves, one represent- 

 ing solutions in equilibrium with gypsum, 

 one representing solutions in equilibrium 

 with ammonium sulphate, and the third 

 representing solutions in equilibrium with 

 a double salt which was found to have the 

 composition CaS0^-(NHJ,S0,-2H,0. 



The Solubility of Gypsum in Solutions of 



Magnesium Sidphate: F. K. Cameron 



and J. M. Bell. 



Owing to the difSeulties in determining 

 small amounts of calcium in the presence 

 of large amounts of magnesium the au- 

 thors have adopted the following method 

 for the determination of the solubility of 

 gypsum in solutions of magnesium sul- 

 phate. Weighed plates of selenite were 

 placed in known amounts of solutions of 

 magnesium sulphate of concentrations 

 which had been determined previously. 

 The loss in weight of the plates is a meas- 

 ure of the solubility in these solutions. The 

 solubility curve at 25° is rather remark- 

 able, as it has both a minimum point and a 

 maximum point. At low concentrations 

 of magnesium sulphate the solubility of 

 gypsum decreases as the content of mag- 

 nesium increases, but above 14 grams 

 MgSO^ per liter the solubility of gypsum- 

 increases up to a concentration of about 

 100 grams MgSO^ per liter. From that 

 point the solubility decreases again. The 

 solution in equilibrium with both solid 

 phases contains 355 grams MgS04 and 

 0.50 gram CaSO^ per liter. 



Two tentative explanations are offered 

 to account for the peculiar shape of the 

 curve. The change of density of the 

 solvent due to the presence of solutes (con- 

 cerning which change practically nothing 



