234 ? ce an d its Natural History 



the opportunity to make a study of the floating sea-ice. 

 I collected many samples, observed their melting tempera- 

 tures, and determined the percentage of chlorine in the water 

 produced by their fusion. The results obtained showed that 

 their melting temperature was very variable, and always below 

 o C. It was further observed that this temperature was the 

 lower the greater the percentage of chlorine found in the 

 melted ice. The advantage of fractional melting for the 

 purpose of obtaining water of less salinity was confirmed ; 

 but it was found impossible, by any means, to produce pure 

 water by melting the ice. This, combined with the fact that 

 its melting-point was considerably lower than that of pure 

 ice, was for me convincing evidence, at that date, that the salt 

 was present in it in the solid state, and that, consequently, the 

 crystalline body formed by freezing sea-water and similar 

 saline solutions was not pure ice. 



About ten years later Dr Otto Pettersson's treatise 1 on 

 the properties of water and ice came before me, and I studied 

 it with great interest. In it he refers to my " Challenger " 

 work, and rejects the view that " sea-ice is itself wholly desti- 

 tute of salts, and only mechanically encloses a certain quantity 

 of unfrozen and concentrated sea- water." I was much gratified 

 to find that he had, quite independently, arrived at the same 

 conclusion as I had. 



In the careful study which I made of his work, the follow- 

 ing passage, p. 318, arrested my attention: "A thermometer 

 immersed in a mixture of snow and sea-water, which is con- 

 stantly stirred, indicates i'8 C." If this statement was 

 exact, it was clear that the evidence furnished by the melting 

 temperature of the sea-ice was not entitled to the weight 

 which I had attached to it, and that the conclusion, at which 

 we had both independently arrived, was open to doubt. On 

 making the experiment, I was able to confirm his statement. 

 I thereupon decided to proceed without delay to investigate 

 the subject experimentally. 



The question at issue concerned saline solutions generally, 



1 On the Properties of Water and Ice, by Dr Otto Pettersson: Publications of 

 the "Vega" expedition, 1883. 



