Chemical and Physical Notes 29 



pushed into the sea. If it had a temperature below 29 R, it 

 would freeze the sea-water round it until it had got rid of its 

 excessive cold ; and if it had a temperature above 29 F., the 

 sea-water round it would melt its ice until it had got rid of 

 its excessive heat. The representative freezing temperature 

 of sea-water is taken as 29 F., but it varies with the salinity. 

 In this respect sea-water was found to agree closely with 

 a solution of chloride of sodium containing the same per- 

 centage of chlorine. The subject was carefully investigated 

 during the winter 1886-87, ar >d the results were communicated 

 to the Royal Society of Edinburgh, in a paper which was read 

 on March 21, I887 1 . The rule regulating the appearance or 

 disappearance of ice in a solution of chloride of sodium is 

 very simple. The number expressing the percentage by 

 weight of chlorine in the solution expresses on Celsius' scale 

 the depression of the freezing-point of the solution below that 

 of distilled water, and by consequence the temperature at 

 which pure ice begins to melt in the same solution. Thus 

 the freezing-point of a solution of chloride of sodium, con- 

 taining i per cent, of chlorine, is - i'O C. ; if it contains 

 175 per cent, chlorine, its freezing-point is i75 C. ; and so 

 on for concentrations not exceeding that of the saltest ocean 

 water. Sea-water, the solid contents of which consist chiefly 

 of chlorides, follows this rule approximately, but not exactly. 

 The following table, from p. 133 of the memoir, is derived 

 from twenty-five determinations made with the greatest care 

 in sea-waters of different degrees of concentration and freezing 

 at temperatures between o'5 C. and 2'22 C. 



Freezing temperature -2'oC. -i'5C. -i-oC. -o'^C. 



Per cent, by weight of chlorine 1-940 1-445 0*963 0-475 



Difference 0-060 0-055 '37 ' O2 5 



From this we have the following approximate rule: The 

 number expressing on Celsius scale the depression of the 

 freezing-point of a sea-water below that of distilled water is 

 found by adding 0-04 to the number expressing the percentage 



1 ' On Ice and Brines,' by J. Y. Buchanan (1887). Free. K. S. ., vol. xiv. 

 p. 129; also Nature, vol. xxxv. pp. 516, 608, and vol. xxxvi. p. 9. (Below, p. 130.) 



