368 Proceedings of Royal Society of Edinburgh. [sess. 
was then placed in position, and the vessel immersed in crushed ice 
contained in a large glass jar protected by thick felt. The ice was 
heaped up above the level of the stopper so as to surround the tubes 
which acted as collars. The thermometer was now removed from 
the ice and water in which the bulb was constantly kept when it was 
not in use, and introduced through the tube C, being at the same 
time attached to the stage of the observing microscope. A thick felt 
cover was now placed on the top of the ice, and the stirrer was 
moved up and down a few times for the purpose of thoroughly 
mixing the ice and water, the process being assisted by the hand- 
blower, which also served to saturate the water with air. The 
position of the thermometer relatively to the vessel was always the 
same as measured on a millimeter scale. 
The reading on the thermometer was generally constant as soon as 
the stirring was over. Observations were made from time to time 
during at least fifteen minutes with intermittent stirring, if the 
reading changed appreciably the thermometer was so far raised out 
of the solution as to alter slightly the position of the mercury on 
the scale, and then replaced in the liquid. In every case, with one 
exception, the reading was then constant for at least fifteen minutes. 
The rubber tube of the band-blower was now removed from the 
top of the stirrer, down which was delivered, by means of a gradu- 
ated pipette, a sufficient quantity of cooled normal acetic acid 
solution to give approximately the required freezing-point depres- 
sion. The stirring tube was then washed down with a little 
cooled distilled water. The blower was now reattached and the 
solution thoroughly mixed by means of a rapid stream of air 
bubbles and the vertical motion of the stirrer. The thermometer 
at once adjusted itself to a new position of equilibrium. Stirring 
and reading were then continued intermittently as before, and 
after the lapse of at least half an hour the liquid was filtered off. 
During the stirring the filter was kept at the top of the liquid, 
but before filtration it was lowered so as to be on a level with the 
bulb of the thermometer. The upper end of the filtering tube 
was connected to a tube passing through the stopper of a filter 
flask, which was in its turn connected with a 100 c.c. pipette filled 
with water and used as an aspirator. Two separate portions, of 
about 30 c.c. each, were then filtered off and analysed separately. 
