1910-11.] Specific Gravity and Displacement of Saline Solutions. 635 
XLIV. — Experimental Researches on the Specific Gravity and the 
Displacement of some Saline Solutions. By J. Y. Buchanan, 
F.R.S. 
[Abstract. — Extended jpajper in Transactions R.S.E.] 
(MS. received July 20, 1911. Read July 14, 1911.) 
In this paper are collected and discussed the observations of the specific 
gravity of saline solutions of moderate and high dilution made during the 
course of the last ten years. The instrument employed was the hydrometer, 
of the type used by me during the cruise of the Challenger in the years 
1872 to 1876. The results then obtained were such as to convince me 
that the instrument, in capable hands, and with strict attention to the 
obligatory conditions of experiment, gives more exact results than any 
other instrument in use for such work. In the course of the last forty 
years the method has been improved in the sense that more and more 
attention has been paid to the conditions, especially those of temperature, 
under which the experiment is made, because it was found that the method 
is so delicate that it responds to every increase of care in experimenting 
by greater exactness in the results which it furnishes. Almost the whole 
of the work of the Challenger was done between latitudes 40° N. and 40° S., 
where the temperature of the air is high and subject to very small diurnal 
variation. Besides this natural advantage, the conditions obtaining in a 
laboratory on the main deck of a wooden man-of-war of the ancient type 
were all that could be wished for the performance of physical experiments 
requiring invariability of temperature. For this reason the results obtained 
during the cruise were exceptionally good. 
When I took the subject up again in the climate of the British Islands 
it was a long time before I was able to manage the climate of the 
laboratory so as to produce the desired temperature in the liquid, and to 
maintain it without variation during the time that the experiment lasted. 
In this I have had the good fortune to be aided by assistants of rare 
ability and perseverance, with the result that any variation of the 
temperature of the liquid during the experiment, which is sensible on a 
thermometer divided into tenths of a degree Centigrade, each such interval 
occupying a length of 1 millimetre, is considered an imperfection. 
In the extended paper the principal solutions of moderate and high 
dilution considered are those of the chlorides, bromides, iodides, nitrates, 
