178 On Steaui and Brines 



crystals. The chlorides of potassium and sodium, though both 

 crystallising in the same form, do not form mixed crystals, 

 and therefore do not eliminate each other from solution. 



These few remarks will show the extent of the subject, 

 and also its great interest. 



The Device of the Elastic Tank of Uniform Depth. 

 In order to provide a standard of comparison between the 

 effect of dissolved salt and that of increased pressure upon 

 the boiling temperature of water, we imagine a quantity of 

 water in a shallow tank kept boiling by steam. The tank is 

 of uniform depth of I centimetre, but it can expand laterally 

 to accommodate condensed steam, the depth of the enlarged 

 tank remaining uniformly i centimetre. In these circum- 

 stances the number expressing the weight, in grammes, of 

 the water, expresses also its volume and its surface in cubic 

 and square centimetres respectively. Let the initial quantity 

 of water be W grammes, and let it be at the boiling tem- 

 perature corresponding to the atmospheric pressure, A, in 

 kilogrammes per square centimetre (k./c. 2 ). If we dissolve 

 a quantity, say one-fifth, of a molecule in grammes of a salt 

 in this quantity of water, the temperature can be raised above 

 the boiling temperature, T, of pure water under the atmo- 

 spheric pressure, A, and if the quantity, W, of water is 

 exactly sufficient to dissolve the fifth of a molecule of salt at 

 its boiling temperature, which is then the temperature of the 

 boiling saturated solution of the salt under atmospheric 

 pressure, A, which we represent by /, then the temperature 

 of the boiling water has been raised from T to / . Now this 

 effect could be produced without adding salt by increasing 

 the load pressing upon the surface, W, of the water. It is 

 already pressed by the weight of the atmosphere A kilogrs. 

 per square centimetre, or a total weight of WA kilogrs. In 

 order to confine the water so as to admit of its temperature 

 being raised from T to /, we must add to WA a certain addi- 

 tional load, b kilogrammes, which is found by consulting 

 Regnault's tables connecting the temperature and tension 

 of saturated steam. In these tables we find directly the 

 tension, / , of saturated steam of temperature /, in millimetres 





