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Proceedings of the Royal Society of Edinburgh. [Sess. 
scale division. The compression screw, in addition to being the means of 
attaining high pressures, is useful as a fine adjustment. The cylinder was 
kept immersed in a tank of water of about 9 cubic feet capacity. The 
water was kept stirred by a system of propellers driven by a hot-air 
engine, and the temperature maintained constant at 15° C. by incandescent 
lamps worked by a regulator and relay. 
The electrical method of measuring compressibility, first used by Tait 
and Amagat, and modified by Richards, was employed. The piezometers 
had the shape shown in the figure, i.e. with no stopcock. AB is a bulb about 
15 cm. long and of 45 c.c. capacity. The portion BD was made thicker in the 
walls, as otherwise it was found liable to break under pressure. It became 
A 
narrower at D (about 1 mm. diameter), where one platinum wire was fused 
in, and widened out again in DE. Another platinum wire was inserted at C. 
The piezometer was completely filled under the receiver of an air-pump with 
the solution in question, then placed in the thermostat, and after it had at- 
tained the temperature of 15° C., liquid was removed from DE until the surface 
stood at D. The piezometer was then carefully dried and weighed. Mercury 
was then added to fill the space BD, the adjustment of the level of the 
mercury at D at 15° being made with the aid of a battery and galvanoscope 
circuit. The piezometer and contents were again weighed. Knowing the 
weight of the empty piezometer, the volume of the solution can now be ob- 
tained. A small quantity of mercury was then weighed and added in DE ; 
above it was placed pure distilled water; a cap of paper was tied round 
the top of the tube at E, and the piezometer was then ready to go into the 
compression cylinder. A metal framework was permanently attached to 
the lower end of the plug, to which the piezometer was bound. The wires 
