156 



MR J. Y. BUCHANAN ON THE 



of a solution can be determined with a minimum quantity of liquid. With instruments 

 of this form it is necessary to use mercury as ballast, not only in order to keep the 



Fig. 3. 



Fig. 4. 



Fig. 5. 



centre of gravity as low as possible, but also because, when free in a wide cylinder and 

 not confined in a small sphere, a quantity of shot does not necessarily rest with its upper 

 surface quite perpendicular to the direction of gravity. 



