244 f fe ana it* Natural History 



In the same paper (above, p. 148), the very low values 

 found by Dr Pettersson for the latent heat of fusion of 

 different samples of ice- prepared by freezing sea-water, were 

 quantitatively explained on the basis of the above law ; and 

 the conclusion was experimentally confirmed by the thermal 

 exchanges which were observed to take place in the freezing 

 of a sample of sea-water, as the result of which chemical 

 analysis showed that the ratio Cl : SO 3 was the same in the 

 original water, in the ice formed, and in the brine remaining. 



I give these quotations from my paper of 1887 at length 

 because, though published so many years ago, they appear to 

 have been but little read. I know of no manual of physical 

 chemistry in which the above demonstration of the funda- 

 mental fact of cryoscopic chemistry is given, nor am I 

 acquainted with any recent treatise on natural ice in which 

 the influence of the nature of the medium, in which it melts, 

 on the melting temperature of ice at constant pressure is even 

 mentioned, still less taken into account. 



For these reasons, in preparing the lecture, I have given 

 the greatest space to this all-important subject, and I proceed 

 with its development. 



In Table I we have, under v, the volume, in cubic centi- 

 metres, of ice, the melting of which is induced at the tempe- 

 rature / ( by the presence of i'5iO5 gram chloride of sodium. 

 The values of v are derived from determinations of the 

 freezing-point of solutions of chloride of sodium. Under 

 w( = O'gi6jv), we have the volume of water so produced, and 

 under c(=v w), the contraction due to the melting. The 

 cryohydric temperature of solution of chloride of sodium is 

 taken as 2i72, and its concentration as 29^97 grams salt in 

 100 grams water. 



The coefficient of cubic dilatation by heat of pure ice is 

 taken as 0*00016, and it is assumed to be constant at the 

 temperatures under consideration. The specific gravity of 

 pure ice at / referred to that of water at the same temperature, 

 is taken as O'9i67. The volume of the salt diffused through 

 the ice is disregarded. 



Using these constants, and those of Table I, we will apply 



