1910-11.] 
Isopiestic Expansibility of Water. 
463 
General Procedure. 
The following account refers more particularly to the procedure in 
the case of a dilatometer of the form last described ; but the variations 
necessary in the other cases will be clear. 
The dilatometer is carefully cleaned and weighed empty. Let its 
weight be W r 
By means of exhaustion under the air-pump, or by gently heating, it 
is filled with mercury approximately to the point F. To bring it to a 
uniform temperature, it is immersed in a beaker of water at 15° C. and 
allowed to stand for some minutes. After removal, the wires HIT are 
introduced and connected with the galvanometer circuit, the dilatometer 
being clamped so as to stand vertically. Mercury is added or removed 
so that contact is just made at F. The dilatometer and contents are then 
weighed. Let this weight be W 2 . 
By means of a long thin glass tube some water is introduced round to C, 
and, by gently tapping with the finger, it is made to rise into the bulb AB. 
A gentle heat was sometimes also necessary. After bringing the whole once 
more to a uniform temperature, we remove mercury from GF until contact 
is again just made at F. The dilatometer and contents are again weighed. 
Let this weight be W 3 . 
Finally, an amount of mercury, depending on the volume of the liquid 
in the bulb and on the temperature to be worked at, is removed from EF 
and weighed. Let its weight be W 4 . 
Assuming the density of mercury at the said temperature to be 13*56, 
and the density of the liquid to be 1*00, and neglecting corrections which 
will be discussed later, we have: (1) Original volume of liquid at 15° C. 
is equal to 
w 2 -w 3 
12*56 
(21 Change in volume necessary before contact is again made at F is given by 
13*56 
After the removal of the mercury (W 4 ), the remaining space EG is filled 
with pure distilled water to prevent impurities coming in from the com- 
pression-cylinder in the course of the experiment and spoiling the contacts. 
The wire-system HE is then tied by means of thread to MM' in the same 
definite position as it was when used to determine the volumes above. 
The plug K 2 with the oven 0 is removed from the compression-cylinder, 
