SPECIFIC GRAVITY 



17 



which is suspended, by short platinum wires, the scale-pan n. On the under side of this 

 pan is a hook for attaching the fine platinum wire and clip jo, which holds the stone to be 

 tested. This portion hanging from c corresponds to the right-hand scale-pan with short 

 supports of the hydrostatic balance. 



h 



A 



m 



f 



9 



\ 



h 



s: 





wm 





\ 



Fig. 5. Westphal's balance for determining the specific gravity of solids. (Half actual size. ) 



Between the knife-edge I and the end c the beam is divided into ten equal parts, the 

 equally distant lines of division being numbered consecutively from h towards c. The 

 upper side of the beam is notched at these lines of division. TTie weights are of special 

 roiistruction ; some being for the purpose of hanging on the hook under c, and others^ 

 known as riders, rest when in use in the notches on the beam itself, as shown in Figs. 5 and 7. 

 These weights are quite arbitrary, and need not necessarily be multiples or sub-multiples 

 of any recognised" unit ; they are related to each other, however, in a certain definite manner 

 suitable to the purpose of the instrument. The normal weight, N, when placed on the hook 



