554 SCIENCE PROGRESS 



(b) that the compression of the small volume of mercury 



which they contain involves but little dilution of the 

 contents of the cell; 



(c) that only small volumes of the specially purified mercury 



are required. 



(a) (b) 



(a) For moderate pressures. 

 (&) For high pressures. 



Fig. 2. — Osmotic cell complete. Fig. 3. — Manometers. 



On the other hand : 



(d) the meniscus is more troublesome ; 



(e) the capillary depression is large and varies so greatly 



with the bore of the tube that it can only be deter- 

 mined by direct calibration ; 



