BETWEE^r THE VISCOSITY OF LIQUIDS AHD THEIE CHEMICAL NATURE. 411 
chrometer shall be constant and shall be known. Let ns suppose that an observation 
is to be made in the rigdit limb; the liquid level in the left limb is just broug’ht into 
coincidence with the mark when any excess of liquid will flow over into the trap 
T'; hence the effective head of liquid extends from to k^, and is thus known. A 
similar proceeding is carried out for the left limb observations, using the mark k^ and 
trap Th The marks k^ and /r have been placed by trial in such positions that the 
volume from k^ to is almost equal to, but slightly greater than, that from P to 
The reason for this will be given subsequently. The volumes k^ and /w are the 
working volumes of liquid used in the observations. 
From what has been said it will be seen that at the bemnninff of an observation in 
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the right limb the liquid level is at Hk In order to allow the observer time to get 
ready to take the necessary readings before the liquid level falls to which time is but 
short in the case of mobile liquids, the limb is expanded into a bulb, as shown in fig. 1, 
just above m^. After the liquid has fallen to m‘^ and the time has been noted, readings of 
temperature, pressure, &c., have to be taken immediately; to give the necessary time 
for these readings, the limb is again enlarged below the mark, so that they can be 
taken before the level in the right limb falls to k^, and the level in the left rises to Hh 
Similar reasons explain the shape of the left limb. The lower extremities of the limbs 
are also expanded and bulb-shaped. This form was given to them, so that, if by any 
mischance any solid particles were present in the liquid under experiment, they would 
tend to collect in the hollow under the end of the capillary. 
The instrument was made of thin glass to facilitate the passage of heat through its 
walls. It was therefore somewhat fragile, and would probably not have lasted 
throughout_^ the observations had pains not been taken in its treatment. When 
immersed in the bath it was attached by light brass clips to a brass framework (see 
fig. 3). Whenever possible it was only manipulated when attached to this frame, and 
in this way it could be filled with liquid and cleaned with little risk of breakage. 
The general arrangement of the whole apparatus is shown in fig. 2. The scale is -po" 
A bath B, which for observations at temperatures below 100° contains water, and for 
higher temperatures glycerin, is supported on an iron stand, which is placed on a 
table in front of a window.* The bath is divided into two compartments. The inner 
compartment is provided back and front with plate glass walls; the rest of the bath 
i/3 made of brass. The outer compartment bounds the inner at the sides, and under¬ 
neath, and is fitted with a tap for adjusting the quantity of liquid which it contains. 
The brass framework carrying the glischrometer, and thermometer T, can be lowered 
into vertical slots in the lateral walls of the inner compartment; when thus situated 
the glischrometer occupies a central position in the bath. The walls of both compart¬ 
ments are provided with guides, along which move stirrers consisting of brass plates 
pierced with holes, which are attached to suitable rods and cross pieces, and are 
worked by a small water-motor W, M, which is connected with the upper cross piece 
* In practice two baths were used, one containing water, the other glycerin. 
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