230 SCIENCE PROGRESS 



0-OI43 c.c. The accuracy of Morgan's method is exempUfied 

 by his results with six different hquids : using the equations 



TlMJdY = K{t, -t-6) 



and mgt = TJC 



we get mgt{M/d) *= K/C {t, - t - 6) 



where mgt is the weight of a drop at the temperature /. 



Tt is the surface tension at the same temperature, 

 M is the molecular weight and d the density of the liquid. 



and tc its critical temperature. 



The value of K should be constant in the surface tension equation, 

 and that of KjC in the weight of a drop equation if the same tip 

 be used with all the liquids : for the six liquids Morgan found 

 KjC = 2-5694 ± 0-0013, i.e. 0-05 per cent, variation from the 

 average; while Renault and Guye, using the capillaryrise method, 

 found for the same six liquids K— 2-116 i 0-0965, i.e. a varia- 

 tion of 4-6 per cent, from the mean. The laboratory form of 

 Morgan's apparatus is made entirely of glass, the various parts 

 fitting together by means of ground-glass joints. It consists 

 essentially of two stoppered straight-sided weighing bottles 

 2 cm. diameter connected by an inverted capillary U-tube, one 

 limb being slightly shorter (i cm.) than the other. The weigh- 

 ing bottles, by means of their stoppers, fit into a perforated disc, 

 which in its turn fits into a larger weighing bottle, the latter 

 serving as an air-bath. The two weighing bottles and the outer 

 air-bath are all supplied with a ventilation tube, and a ther- 

 mometer is attached having its bulb close to the U-tube. The 

 inverted tube is the " capillary " drop tube, and has the shorter 

 end ground accurately cylindrical for a length of i cm. to 

 take the tip : the bore of this tube is 0-2 mm. Tips of various 

 sizes can be fitted ; the bottom of the tips is made plane and 

 perpendicular to the sides, a clean sharp edge being very im- 

 portant. When the apparatus is fitted with a fresh tip, great 

 care should be taken to get the bottom of the tip exactly parallel 

 to the cover of the apparatus, so that the tip can afterwards be 

 set exactly level by levelling the cover. Before using, the 

 apparatus is very thoroughly cleaned with the usual liquids. 

 A rubber bulb is connected to the ventilation tube, which fits 

 into the weighing bottle on the tip side ; the compression of the 

 bulb can be accurately controlled by means of a screw. The 

 empty weighing bottle on the tip side is put on first, and then 

 that containing the liquid is fitted in position on the supply 

 side, and the outer vessel is attached : the whole apparatus is 

 placed in the thermostat and allowed to remain for twenty to 

 forty minutes to attain thermal equilibrium, the capillary being 



