CLARK. SURFACE TENSION BETWEEN LIQUIDS AND VAPORS. 367 



distance of 7 cm. from the conical end. Then they are 1.2 cm. in 

 diameter for the remainder of the length. The copper box rests on the 

 shoulders thus formed, while the iron 

 box rests on the points. Thus, when- 

 ever it is necessary to take down the 

 apparatus, it may be put together 

 again in perfect alignment with very 

 little trouble. The whole system, 

 which weighs about 40 kg., is slung 

 from the ceiling by rope and pulleys. 

 The case is supported by heavy iron 

 straps and is also provided with large 

 screw-eyes which slide on two upright 

 steel rods, securely fastened to the 

 work-table. This allows vertical ad- 

 justment and prevents swaying and 

 tipping. F is a porcelain tube in- 

 serted in the heated space to protect 

 the experimental tube from becoming 

 heated too rapidly, since otherwise 

 the lower part of the latter, being 

 filled with mercury, would be unduly 

 heated in the warming-up stages and 

 cause distillation of the liquid in the 

 tube above. 



The resistance of the heater is 10 

 ohms, and is used on the 110-volt 

 alternating lighting circuit. This, 

 though unsteady through a small 

 range of voltage, answers very well, 

 since the changes of temperature in 

 the heater take place slowly. 



It remains now to describe the au- 

 tomatic part of the regulator. Since 

 the thermostat was designed for tem- 

 peratures between room temperature 



and .300° C, an overflow chamber of adjustable capacity is necessary. 

 This is shown in Figure 3. 



A cast-iron cylinder A, with an opening for a glass tube B in the 

 upper end, and a stuffing-box C with screw D in the lower end, is screwed 



Figure 3. 



