CLARK. — SURFACE TENSION BETWEEN LIQUIDS AND VAPORS. 371 



the stopper entering the narrow place at d, effectually closes the open- 

 ing. The expanded part M prevents the tube from being pressed up 

 through the stopper. This form of joint is perfectly tight up to 100 

 atmospheres and probably would be at much higher pressures. The 

 joint is very flexible and the tube may be rotated very easily. After 

 the insertion of the tube, the heater is lowered as far as possible, the 

 tube b is sealed on to the retort containing the 

 liquid to be distilled in. There is a stop-cock 

 in this tube. The tube e (Figure 6) is attached 

 to the air-pump also through a cock. Next 

 the narrow parts in the two tubes are drawn 

 out very small and when cool the air-pump 

 is started and the lower part of the tube is 

 heated. The mercury iu the steel chamber 

 is allowed to rise very slowly, being kept very 

 hot to drive out air and moisture. This is 

 continued until the part a is partly filled. 

 The tube a is now allowed to cool. The 

 air-pump still operating, b is gradually heated 

 with a coil of wire to ensure the driving out 

 of any air that may have entered during the 

 filling. Now a is kept cool with ice, and b 

 hot with the electric current, and the liquid 

 distilled over from the retort. The first dis- 

 tillate is boiled away to carry off any air still 

 remaining. Then the liquid is distilled over 

 and when the proper amount is obtained the 

 cock to the still is closed, the narrow part 

 sealed off, then the other tube sealed off, and 



the tube is complete. The tube is now rotated until in the best position 

 for observation, the heater is raised to the proper height and the cover 

 put on, thermometers inserted, and the experiment begun. 



Figure 8. 



Manometer. 



The manometer is patterned after Amagat's and was made from draw- 

 ings loaned by Professor Barus of Brown University, the sizes of the 

 pistons being changed to suit the work in hand. The large piston is 

 5 cm. in diameter and the small one about 1 cm., the reduction factor 

 being 24.42. A complete description of this manometer is given in 



