1898. J on Some Becent Besults of Physico-CJiemical Inquiry. G13 



tinuously filled with the viscous substance. He then described the 

 different modes of measuring viscosity, and explained the general 

 principle of the method and the features of the particular apparatus 

 employed in the investigation made by Mr. Rodger and himself. The 

 princij^le was that of Poiseuille, and consisted in observing the time 

 required for a definite volume of liquid under a definite pressure to 

 pass through a capillary tube of known size, the temperature being- 

 known and kept constant during the interval. The actual apparatus, 

 however, differed in many important features from any previously 

 designed for the same purpose, and admitted of the determination, in 

 absolute measure, of the coefiicient for a tempemture range from 

 0° up to the ordinary boiling point of the liquid. In most of the 

 instruments used by previous observers, the liquid, after passing 

 through the capillary, was allowed to escape, and hence the apparatus 

 had to be recharged before another observation 

 could be made. In the newer form, the time ^ '^ 



spent in recharging was saved, by arranging 

 that in all the observations on any one liquid 

 the same sample could be used repeatedly ; and 

 further economy in time was obtained by ar- 

 ranging that observations could be taken while 

 the liquid was flowing in either direction through 

 the capillary tube, and that while an observation 

 was in progress and liquid was leaving one por- 

 tion of the instrument, it was entering another 

 portion and getting into position for a fresh ob- 

 servation. It was also desirable to avoid the use 

 of corks or caoutchouc in such parts as would be 

 in contact with the liquid, and it was therefore 

 necessary that the instrument should be made 

 entirely of glass. 



The form of apparatus designed to meet these 

 requirements is shown in Fig. 1 ; it may be 

 termed a glischrometer. It consists of two up- 

 right limbs L and R (left and right), connected 

 near their lower ends by a cross piece. Within 

 the cross piece is the capillary tube C P, the 

 bore of which is about • 008 centimetres radius, 

 and the thickness of the wall about 2 millimetres, 

 the internal radius of the cross piece being a 

 millimetre or so greater than the external radius 

 of the capillary. At the zone R, R'^, the walls of 

 the cross piece are constricted and made con- 

 tinuous with those of the capillary : the latter 

 is thus gripped at its middle portion and held axially within the 

 cross piece. Care is of course taken that the bore of the capillary is 

 in no wise disturbed during the process of sealing. 



On one side of each limb of the instrument three fine horizontal 



