STEAM AND BRINES. 547 



one type, mixtures of the chlorides of potassium and sodium may be taken as an example. 



For a mixture of equal molecules 0*2 — - — -CI t-T is 11*87° C. at sea level, and 



W = 20"7 grms. The concentration of its boiling mixture is, therefore, 50 per cent. 



greater than that of chloride of sodium alone. In other words, a boiling saturated 



solution of either KC1 or NaCl has still plenty of room for the other. 



Mixtures of the nitrates of strontium and lead give an example of another type. 



The amount of steam condensed is exactly the sum of the amounts required by the 



quantities of the respective salts separately. For Sr(N0 3 ) 2 (t — T) = 6'53° C, and for 



Sr. + Pb 

 Pb(N0 3 ) 2 (*-T) = 3-29. In the mixture 0-2— ^ (N0 3 ) 2 a constant value of 



£-T = 5'98° C. is observed for thirteen out of the twenty-five minutes that were 

 required to dissolve all the salt. Therefore the saturation temperature of the mixture 

 lies between those of the components. A third type is furnished by a mixture of the 

 nitrates of strontium and barium. The elevation of boiling point is not as great as 

 with Sr(N0 3 ) 2 alone, and the maximum temperature does not remain constant for even 

 one minute out of the fifty minutes which were required to dissolve the fifth of a 

 molecule used. The water required to dissolve this mixture is about 25 per cent, more 

 than is required to dissolve the salts separately. 



The nitrates of strontium, barium, and lead are isomorphous salts, and no doubt are 

 capable of forming mixed 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. 



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 1 centimetre, but it can expand laterally to accommodate condensed steam, the depth 

 of the enlarged tank remaining uniformly 1 centimetre. In these circumstances 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 temperature 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 

 atmospheric pressure, A, and if the quantity, W, of water is exactly sufficient to dissolve 

 the fifth of a molecule salt at its boiling temperature, which is then the temperature of 

 the boiling saturated solution of the salt under atmospheric pressure, A, which we repre- 

 sent by t , then the temperature of the boiling water has been raised from T to t . 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 



