78 



SIXES' S HYDROMETER. 



V ~ 



A 

 E 



oh 



(1) 



which gives the ratio of the specific gravities of the two 

 liquids. 



COR. If the second liquid be the standard, s' = 1, and 

 s, the specific gravity of the first liquid, is given in (1). 



38. Sikes's Hydrometer.* This instrument differs 

 from the common hydrometer in the shape of the stem, 

 which is a flat bar and very thin, so that it is 

 exceedingly sensitive. It is generally construct- 

 ed of brass, and is accompanied by a series of 

 small weights F, which can be slipped over the 

 stem above C, so as to rest on C. 



The weights are used to compensate for the 

 great sensitiveness of the instrument, which, 

 without the weights, would render it applicable 

 only to liquids of very nearly the same density. 



Let Tc = the area of a section of the stem, 

 v = the volume, and w = the weight of the 

 hydrometer. When the instrument floats in a liquid whose 

 specific gravity is s, let w' = the weight on C so that the 

 level D of the stem shall be in the surface ; and when it 

 floats in a liquid whose specific gravity is *', let w" = the 

 weight on C so that the level E shall be in the surface ; and 

 let v' and v" be the volumes of w' and w". Then (Art. 34, 

 Hem.) we have for the weights of the liquid displaced in the 

 first and second cases, respectively, 



w + w' = s (v -f v' &-AD), 

 w + w" = s' (v -f- v" Tc- AE) ; 



w + w' v + v" &-AE 



w 4- w" v 



&-AD 



(1) 



Pesant's Hydrostatics, p. 127. 



