36 
Proceedings of Royal Society of Edinburgh. [sess. 
The Relative Densities. 
In order to determine how far the optical method proposed 
by Krummel might be relied upon, Mr H. N. Dickson very kindly 
supplied the author with five samples of sea- water marked l v , 2 V , 
3 V , 4 V , and 5 V , which differed hut little from each other as regards 
“ total salinity.” The samples were first examined as follows: — 
Using a Sprengel tube having a capacity of about 48 c.c., two series 
of determinations of the relative densities at 24° C. were made. 
The tube was first washed out with fuming nitric acid, then with 
distilled water, and finally with absolute alcohol ; it was then dried 
by keeping it thoroughly heated whilst a current of air was passed 
through ; when the tube had become quite cold, it was wiped and 
hung from one arm of the balance, and after an interval of five 
minutes its weight was determined. The tube was then charged with 
recently re-distilled water, and suspended centrally in a large water 
hath, furnished with a rocking stirrer which was kept moving by a 
small water motor; the temperature of the bath was indicated by a 
standardised thermometer reading to 0°T C. With this apparatus 
the maintenance of a constant temperature, which differed very 
little from that of the room, was an extremely easy matter, the 
momentary application of a small Bunsen flame from time to time 
being all that was necessary. It was observed that the tube, 
together with its contents, assumed an almost constant temperature 
in about ten minutes after immersion in the hath ; an approximate 
adjustment of the contents was then made. In every case, how- 
ever, the tube was allowed to remain in the bath for twenty minutes, 
when the liquid was finally adjusted in the usual manner by the 
application of bibulous paper to the capillary. The tube was then 
removed from the bath, carefully wiped, again suspended from one 
arm of the balance, and weighed after five minutes. The contents 
were then discharged, the tube repeatedly washed out with por- 
tions of the sea- water to he examined, and then filled with it, and 
the process described above, repeated. After the first series of 
determinations had been completed, the tube was again thoroughly 
cleaned, dried and weighed, and a second series of determinations 
proceeded with in a manner identical with that described for the 
first series. The weighings were performed with a delicate long- 
