474 
Di;. J. H. VIXCEXT OX TRE DEXSITY AXD COEFFICIEXT 
operation was done in such a manner as to ensure that the length of wire thus used 
in the fastening was the same in each experiment. The wire was then pulled tight 
and the little clamp attached with its jaws about 1 centim. distant from o hv the 
method previously mentioned. The whole length of wire used was thus always the 
same. The stopper, P (fig. 4), was then screwed on C and mercury poured into the 
funnel. 
The mercury used throughout these experiments was first cleaned Ijy the ordinary 
chemical methods, then boiled in air, and distilled twice in a vacuum. After being 
used in one experiment it was filtered, boiled and distilled twice again before being 
used in a fresh determination. 
The j)late D was placed on the funnel and the whole was turned on one side to 
enable any air imprisoned under the umbrella to escape. This was repeated until no 
more mercury could be poured into the funnel, when the latter was heaped up with 
mercury and the plate D was slid on to the top of the funnel and firmly screwed into 
position by means of the tri-radiate clamp. It was found necessary to carefully 
grind the Ijearing surfaces of the closing plate and of the funnel together before each 
experiment in order to obtain a perfect fit. 
After thus filling with mercury, the funnel was remo'S'ed from the vice and placed 
in an inverted position on a tripod. The stopj^er was then unscrewed from the 
tube, when the little clamp could l^e seen supported on the top of a straiglit piece of 
wire projecting a few millimetres througli the hole at the end of the tube. The 
mercury reservoir (fig. 8) was slijjped on to the conical tube and the mercury in 
the funnel was then lioiled l)y applying the flame of a large Bunsen ljurner to the 
closing plate. The mercury which came out of the small hole in this process, 
partially filled the reservoir, which on removing the flame was filled with mercurv 
boiled in another vessel. The whole was left to assume the ordinary temperature, and 
then the stopper was inverted and plunged beneath the mercury in the reservoir, 
where it was prevented from rising to the surface by the wire U. 
The boiling was again performed, and then the mercury in the tube and reservoir 
was also boiled. Operations of alternate heating and cooling were continued until I 
felt satisfied that no air or water remained in the funnel. The stopper was then 
taken from the wire in the reservoir, and manipulating it so as never to permit the 
fingers to come beneath its orifice, it was screwed on to the piece C, and the funnel 
was thus closed. 
The reservoir was then removed, and the funnel was again put in the vice ; this 
time with the mercury collar round it ready to be screwed on. The tri-radiate clamp 
and the closing plate were removed and the bearing surfaces were covered with a 
thin film of vaseline before pouring an excess of recently boiled mercury into the 
funnel and sliding the closing plate again into position. The plate was then 
fastened down securely and the mercury collar screwed on. 
The funnel was then installed in the apparatus shown in fig. 9, when the collar was 
