10 M. Gay-Liissac on the [Jan, 



it crystallizes retaining seven portions of water, 79*3, for one 

 proportion of salt, 74-6, each number which expresses the solu- 

 bility, must be increased by this number multiplied by the ratio 

 of 79-3 to 74-6, and the corresponding quantity of water dimi- 

 nished as much. We shall thus have for the solubihty of crystal- 

 lized sulphate of magnesia the following results : 



Temperature. 



14-58° 103-69 



39-86 178-34 



49-08 212-61 



64-35 295-13 



97-03 644-44 



These results are no longer proportional to the temperatures ; 

 they augment in a much greater ratio. 



Solubility of Sulphate of Soda. 



Salt soluble in iOO water. 

 Temperature. Anhydrous. Crystallized. 



0-00° 6-02 1-2-17 



11-67 10-12 26-38 



13-30 11-74 31-33 



17-91 16-73 48-28 



25-05 28-11 99-48 



28-76 37-35 161-53 



30-75 43-05 215-77' 



31-84 47-37 270-22 



32-73 60-65 322-12 



33-88 60-04 312-11 



40-15 48-78 291-44 



45-04 47-81 276-91 



50-40 46-82 262-35 



59-79 45-42 



70-61 44-35 



84-42 42-96 



103-17 42-65 ,. 



We see by these results that the solubility of sulphate of soda 

 follows a very singular law. After having increased rapidly to 

 about the temperature of 33°, where it is at its maximum, it 

 diminishes to 103-17°, and at that point it is nearly the same as 

 at 30-6°. The sulphate of soda presents the second example of 

 a body whose solubility diminishes as the temperature augments ; 

 for Mr. Dalton has already observed the same property in lime. 

 In the plate, the line of solubility of anhydrous sulphate of soda 

 is traced. It consists of two branches convex towards the axis 

 of the abscissas, and having a point of contrary flexure corre- 

 sponding nearly to the temperature of 33°. It was not possible 

 to represent more than a small portion of the hne of solubility of 

 crystallized sulphate, on account of the great extent of the ordi- 

 nates ; besides, this line could not be of use beyond 50°, because 



