114 Temperature of the Sea and the Air 



The degrees were 1-6 mm. apart, so that there was no difficulty 

 in estimating tenths of a degree. Its zero was verified on 

 board by immersing it in pounded ice, and found correct. 

 The ice was well pounded in a clean towel, and a tall 

 tumbler was filled with it; the thermometer was then thrust 

 into it and allowed to remain till sufficient ice had melted 

 to fill up the interstices, producing a perfect magma of ice and 

 water down to the bottom. The mercury remained constant 

 on the zero line. The temperature of the air was 25 C. 



Having plenty of pounded ice at my disposal I poured off the water 

 which had formed by melting, and replaced it by sea-water, containing 

 35'65 grammes salt per kilogramme, and then immersed the thermometer; 

 it fell rapidly below zero, and remained constant at - i. I then strained 

 away the sea-water from the ice and replaced it by a mixture of equal 

 volumes sea-water and distilled water: the thermometer fell to -0-45, 

 and remained constant for some time at that temperature. When the ice 

 was mixed with distilled water alone, the thermometer again stood at 

 o C. These experiments were made to verify some observations of 

 Pettersson, quoted in his investigations into the nature of ice formed 

 from waters of different degrees of salinity, in connection with the voyage 

 of the "Vega." He there says, referring to the melting temperature 

 of different kinds of ice, that pure fresh-water ice, when immersed in 

 sea-water, melts at a temperature considerably below o C. Writing 

 from memory, I think he puts the melting point at from - i to - 2 C. 

 Having both the ice and the sea-water ready at hand, I repeated this 

 remarkable experiment. The result showed that Pettersson's observa- 

 tion is quite correct, and that the lowering of the melting point is roughly 

 proportional to the salt held in solution. When equal volumes of the 

 sea-water and distilled water of the same temperature were mixed, there 

 was no change of temperature. I do not remember if Dr Pettersson 

 furnished an explanation of this remarkable phenomenon, and I am 

 unable to supply one myself, but it must necessarily affect the validity 

 of conclusions as to the composition of sea-water ice drawn from its melting 

 point. When the "Challenger" was in Antarctic waters I made a number 

 of observations on the melting point of ice collected from broken pieces of 

 the pack, and found that it began to melt a little below - i C. I concluded 

 that either it was one solid substance or a mixture of several solids. But 

 if pure ice melts at a different temperature according to the medium 

 in which it is placed, then this reasoning is faulty, for inclosed brine would 

 have much the same effect as inclosed salt or crystalline hydrate. 



Temperature of the water. The water was collected in a 

 small bucket, well clear of the side of the ship, and on the 

 opposite side from that through which the condensing water 

 of the engine is discharged. Its temperature was determined 

 as soon as the sample was brought on board. 



