The method here described is an improvement of that developed by LinderstrømLang, Lanz and Jacobsen (1938, 1940).
A reasonably linear specific gravity gradient is produced in a vertical measuring cylinder by mixing kerosene and bromobenzene, or benzene and chroloform in varying proportions.
In kerosene-bromobenzene mixtures the position of a drop is determined after the drop (diameter 2.0mm) has fallen in 30 sec. Plotting the positions of drops of known solutions of sodium chloride as ordinates against the corresponding specific gravities as abscissae, a nearly straight line is obtained in a coordinate system, from which it is possible, knowing the position of the drop of the unknown solution, to read the specific gravity of the solution with considerable accuracy.
The reading of the positions of drops may be done with the naked eye making use of two sheeves of section papers, each of which are stick on at the diametral wall of measuring cylinder. The eye is kept at the level of the drop and the same position of two scale divisions, in order to eliminate errors due to parallaxis.
In benzene-chloroform mixtures the drops fall more sapid, and come to rest much faster, so that the infusion of the mixtures into the drops will be minimized. At the constant temperature it is not advisable to use of kerosene-bromobenzene mixtures for more than about 1 hour at one experiment, and to use of benzene-chloroform mixtures for more than about 2 hours. Therefore, benzene-chloroform mixtures are more suitable than kerosene-bromobenzene mixtures for the determination of specific gravity. Its accuracy is 0.1 per cent.
