118 On the Measurement of the Specific Gravitij of Liquids. 



maker (all fitted with Tralles's scales) ; and 4th, one of Gay- 

 Lussac's hydrometers made by Nissen of Copenhagen. 



The error in the division scale, or h — //, was determined in 

 the following manner : — A glass cylinder, of radius 17*821 mil- 

 lims., was placed upright in the spirit to be examined ; a fine 

 steel needle, also upright, was fitted to the cylinder in such man- 

 ner that it could be elevated and depressed by means of a micro- 

 meter-screw, so that its point could be brought into contact with 

 the surface of the liquid. By means of a very exact catheto- 

 metcr, the distance between the upper end of the needle and the 

 raised edge of the surface of the capillary ring of liquid was 

 measured, and thus the length of the needle being known, the 

 height H was determined. As the specific gravity of the spirit 

 under examination was known, m, T, and h—h' could then be 

 calculated. 



For several samples of spirit the following values of H, m, 

 and T were found (1 millimetre being taken as the unit of 

 length) : — 



If the per-centage of alcohol be taken as the abscissa and T 

 as the ordinate, the curve representing the tension will be seen 

 to be convex towards the axis of x. From to 40 per cent, it 

 falls rapidly, but afterwards it presents only a slight curvature. 

 This is still more obvious if the weight per cent, of alcohol be 

 substituted for the volume per cent. The curve, then, between 

 30 and 80 per cent, is very nearly a straight line, and the tension 

 T can, between these limits, be calculated with sufficient prac- 

 tical accuracy from the formula T:=:a—bp, where a = 3'96798, 

 4 = 0*0204867, and jo is the weight per cent, of alcohol. In this 

 manner, for instance, we find 



