1910-11.] 
461 
Isopiestic Expansibility of Water. 
endeavoured to apply a similar electrical method. A great advantage of 
Tait’s method is that for a single immersion of the piezometer in the 
compressor we can get a series of readings for various pressures; while 
with Richards’ only one reading is obtained for a given pressure. Owing 
to the evident advantage to be obtained from a series of readings, I first 
tried to apply Tait’s method. A dilatometer was made of the form shown 
in the figure.* The part AE is made of quartz-glass, while the tube EF 
D 
Fig. 3 a. 
with the contacts had to be of ordinary glass, since the high fusing-point 
and low coefficient of expansion of quartz-glass make it unsuitable for 
the purpose of having metal electrodes fused into it. This means that we 
have a junction of two different materials at E. The junction was made 
by wrapping asbestos paper round the lower end of the glass tube till it 
fitted as tightly as possible, and then coating the whole joint with sealing- 
wax. This is quite an effective junction at ordinary atmospheric pressure, 
but it frequently ceased to be mercury-tight at high pressures, fully 50 
per cent, of the observations being spoiled in this way. Owing to the 
* Fig. 3c. 
