428 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Although the brass jacket was designed especially for experiments on 

 compressibility, it was found convenient to insert the dilatometer in 

 it. Figure 6 shows the brass jacket with the dilatometer in position. 

 Part of one side is removed to show the dilatometer in the interior. 



Pressure Gauge. 



For the measurement of the pressure on the liquid an open manom- 

 eter of the form shown in Figure 7 was used. In this figure parts of the 

 vertical tubes are omitted. The manometer was made of heavy glass 

 tubing with an internal diameter of 1.2 cm. The U-shaped part of the 

 tube was filled with clean mercury to a height of 120 cm. Between the 

 branches A Band CD of the U-shaped part of the tube were placed 



Figure 6. 



meter rods, end to end, on which one read off the difference in height 

 of the mercury in the two parts of the tube. One had, of course, to 

 read the barometer each time in order to get the absolute pressure on 

 the liquid. From H and G the pressure gauge was connected by means 

 of pressure tubing to the capillary tube of the piezometer or the dila- 

 tometer and to the small tube in the top of the brass jacket. Hence 

 the internal and the external pressure on the walls of the piezometer or 

 of the dilatometer were the same. By means of the stopcock Ki the 

 pressure gauge could be made to communicate with the external atmos- 

 phere. The large tube I, which was 42 cm. long and 5.5 cm. in diam- 

 eter, served as an air-chamber into which air could be forced or from 

 which it could be exhausted. By turning the stopcock Kj the pres- 

 sure on the liquid could be increased or decreased by as small an amount 

 as one wished. The other end of I was closed with the stopcock K3. 



