596 Mr. J. Y. Buchanan on Chemical Work 



Having obtained the specific gravity of the water in question at a 

 temperature which depends upon that of the air at the time, it is 

 necessary, in order that the results may be comparable, to reduce them 

 to their values at one common temperature. For this purpose a know- 

 ledge of the law of expansion of sea-water with temperature is neces- 

 sary. This had been determined with sufficient accuracy for low tem- 

 peratures by Despretz and others ; but as the temperatures at which 

 specific-gravity observations are usually made are comparatively high, 

 their results were of but little use, directed as they were chiefly to the 

 determination of the freezing and maximum -density points. When the 

 late Captain Maury was developing his theory of oceanic circulation, owing 

 to difference of density of the water in its different parts, he found the 

 want of information on this important subject. At his request the late 

 Professor Hubbard, of the National Observatory, U.S., instituted a series 

 of experiments, from which he was enabled to lay down a curve of the 

 volumes of sea-water at all temperatures from considerably below the 

 freezing-point to much above what obtains even in the hottest seas. 

 The results are published in Maury's ' Sailing Directions,' 1858, vol. i. 

 p. 237, and have evidently been carried out with great care. The 

 composition of different oceanic waters varies, even in extreme cases, 

 within such close limits, that the law of thermal expansion is sensibly 

 the same for all of them ; of this Hubbard's experiments afford satis- 

 factory proof. In the Table which gives the results of all his experiments 

 he takes the volume of water at 60° F. as his unit. In order to avoid 

 much useless calculation, I have been in the habit of reducing my results 

 to the same temperature (15 0, 56 C), while, for a like reason, I have 

 retained the specific gravity of distilled water at 4° C. as the unit. The 

 choice of a common temperature to which the results should be reduced, 

 and of a unit of specific gravities, is a purely conventional matter ; and 

 in choosing the above-mentioned ones, in the first instance, I was moved 

 solely by a desire to save calculation. For every water, however, there 

 is one temperature to which it would be natural to reduce its specific 

 gravity, namely, the temperature which the water had when in its place 

 in the ocean ; and in this sense all my results during the cruise have 

 been reduced. Hubbard's Table of the change of volume of a mass of 

 sea-water with change of temperature enables us very easily to reduce 

 any observed specific gravity from the temperature of observation to any 

 other temperature, say 15 0, 56 0. In the paper it is transcribed from the 

 ' Sailing Directions.' 



In the following Table the volumes for every Centigrade degree from 



- 1° C, to + 30° C. are given :— 



