i68 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
Apparatus 
The instrument employed for this purpose was a form of' differential densimeter,' 
which, after passing through many modifications, took the form represented in the 
accompanying sketch (Fig. i), which is drawn approximately to a scale of one- 
quarter. 
The two tubes shown are exactly similar, and are graduated in cubic centimetres 
and tenths in the upper portion, and in centimetres in the lower and wider portion. 
The tubes are connected as shown by means of thick-walled rubber tubing and 
a glass Y-piece to a stout glass mercury receiver capable of holding more than enough 
mercury to fill both tubes and their connexions. 
Fig. i. — Diagram of Differential Densimeter. 
The tubes are held in a vertical position by clamps attached to the strong vertical 
iron bar of a massive retort stand, and each tube is capable of being moved in its 
clamp vertically up and down for purposes of adjusting the mercury levels. 
