374 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



fit the seat, which is relieved at the tip. These cocks always close 

 tightly and do not break down at critical times as do such cocks when 

 seated with some soft metal like tin or lead. 



All joints, whether containing mercury or oil, are heated, smeared with 

 marine glue, and screwed together hot, and never leak. 



Microscope. 



The observing is done with a micrometer microscope whose working 

 focal length is 10 cm. It is carried on a micrometer slide so that the 

 stationary wire of the eyepiece may be kept on the surface of the liquid 

 in the outer part of the experimental tube, one observation only being 

 required to measure the capillary height. One division of the eyepiece 

 micrometer corresponds to .005 mm. The 

 whole system is supported on a rigid iron 

 base, whose height is adjustable. The 

 thermometers used were made by Baudin, 

 readings being taken to ^ G ° . 



Method of Experimentation. 



The microscope is focused on the tube 

 and the stationary wire set on the base 

 level, the movable one on the meniscus, 

 and several readings made on each of 

 the instruments. The current is turned 

 on and the regulator set for the next 

 higher temperature. As the tempera- 

 ture rises, there is always a slight displacement of the liquid in the ex- 

 perimental tube which is easily compensated by the compressor. It is 

 desirable that the volume should be kept as nearly constant as possible, 

 since any considerable change may produce decided changes in tempera- 

 ture, especially at high temperatures. After the temperature is steady, 

 as shown by the thermometer, readings were taken on the manometer to 

 ensure constancy of temperature. 



The entire run with one tube occupies from ten to fifteen hours when 

 there are no accidents. 



The density of the heavier liquids was determined with a pyknometer, 

 being treated in the heater at various temperatures and then weighed 

 with the contents. 



Figure 10. 



