On Steam and Brines 173 



and W . If we consider experiments Nos. i to 9, it will be 

 seen that the values of W in experiments i to 3, which were 

 made in Edinburgh, are lower than those found in Nos. 4 to 9, 

 which were made at high levels, and therefore at lower tem- 

 peratures, in Switzerland. 



It must also be noted that the weight of the salt taken 

 was less exactly ascertained in Switzerland than in my labora- 

 tory in Edinburgh. The Swiss weighings were made with a 

 pair of hand scales, and were exact to the nearest ox>5 grm., 

 that is to say, generally to 0*025 grm. In the Edinburgh 

 experiments quoted in Table IV the weights are exact to the 

 nearest O'OI grm., or to + 0*005 g rm - The quantity of salt 

 usually taken was one-fifth of a molecule in grammes. In the 

 case of KC1, which has a medium molecular weight, this repre- 

 sents I4'92 grms., and we see that even the roughest of the 

 weighings would be exact to within less than one-half 

 per cent. 



The earlier experiments in Switzerland were not always 

 made with equivalent weights of the salts ; all such cases 

 have been recalculated for this table. While the usual 

 quantity taken is one-fifth of a gramme-molecule, on some 

 occasions two-fifths have been taken ; and in the case of 

 sparingly soluble salts as little as one-tenth or one-twentieth 

 has been taken. The values of W are given for the quantity 

 of salt quoted in the headline (M). The products have been 

 all reduced to their value for one-fifth of a molecule of salt. 



The physical meaning of the expression W(t T) is im- 

 portant. W is a weight of water expressed in grammes, and 

 (t T} is the excess of the boiling temperature in degrees 

 Celsius of that water, when it holds in solution a certain 

 amount of a given salt, above its boiling temperature when 

 in a state of purity ; therefore W (t T) expresses, in gramme- 

 degrees (g. C.), the quantity of heat required to be in the 

 water when it is boiling with salt dissolved in it above what 

 is required when it is pure. If the values of W(t 7) were 

 constant for each salt at all dilutions, then the law connecting 

 the dilution of a saline solution and the elevation of its 

 boiling-point would be graphically expressed by a hyperbola, 



