432 
MESSRS. T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
rate of each was determined from time to time by running it for 12 hours against 
an astronomical clock controlled by hourly signals from the Royal Observatory, 
Greenwich, and suitable corrections, which were in all cases very slight, were 
introduced into the observed times of flow. 
Purity of the Liquids Employed. 
As regards the purity of the liquids investigated, we mainly relied upon their origin 
and mode of preparation, but we give, whenever possible, as criteria, the boiling- 
point and vapour density, and in some cases the density of the liquid emploj^ed for 
the viscosity determinations. 
The boiling-point was in almost all cases determined by means of the apparatus 
seen in fig. 4, constructed on a principle similar to that already employed by 
Berthelot. It is made entirely of glass in order to exclude dust and extraneous 
organic matter, and is so arranged that the mercurial column of the thermometer is 
jacketed for by far the greater part of its length, and is completely surrounded by 
vapour during a distillation. Hence the correction for the emergent column, which is 
especially unsatisfactory in the case of thermometers of the Geissler pattern, is 
* obviated. For this reason it is only in the case of a few liquids which were distilled 
from ordinary flasks that there is any correction for emergent cokimn involved in the 
boiling-points as given by us. 
Fig, 4. 
The neck of the flask is constricted just below the cork supporting the thermometer, 
so that the cork may never be moistened by the liquid. 
The observations on boiling-points are reduced to a standard atmosphere by the 
formulse of Crafts (‘Ber.,’ 20, 709) and of Ramsay and Young (‘Phil. Mag.,’ 
1885, 515). In certain cases where the vapour pressures have been studied the 
corrections have been deduced from the curves of vapour pressure. 
In cases in which it was necessary to carry out a fractionation the same 
apparatus was employed ; on account of the large radiating surface and the peculiar 
construction of its neck, the flask was found to be very well adapted to this purpose. 
