242 PROCEEDINGS OP THE AMERICAN ACADEMY 



Boiling Point Apparatus. 



Upon a horizontal circular brass disk of 18 cm. diameter was brazed, 

 with a heavy collar, a vertical thin brass tube 7.8 cm. diameter and 

 37 cm. high. Eccentrically within this stood a similar tube 6.5 cm. 

 diameter and 34 cm. high, being held in place simply by its weight 

 and by a thin brass collar so near the bottom as to be beneath the 

 surface of the liquid when boiling. Notches cut into the lower edge 

 of the inner tube allowed the vapor formed under this collar to pass 

 into the inner, not into the outer space. A vertical brass tube, open 

 at both ends, about 100 cm. long and 2 cm. diameter, passed through 

 the cover at one side, and extended (by a removable portion) in the 

 outer space of the boiler nearly to the surface of the liquid. This 

 served as an escape and condenser tube, and to its top was attached the 

 exhaustion tube when pressures other than the atmospheric were de- 

 sired. Outside this a glass condenser was placed for water circulation 

 when benzol was used ; with naphthaline and benzophenone this 

 outer jacket was removed. The height to which the vapor extended 

 in the tube could be ascertained by passing a moist cloth along it, and 

 could be readily maintained nearly constant by adjusting the gas flame 

 beneath the boiler. The cover was a brass casting turned and ground 

 to fit a brass ring brazed to the top of the outer tube of the boiler. It 

 was secured to the ring by six screws, and the joint was always very 

 nearly vapor-tight. Through the top were four borings ; one nearly 

 central to admit the stem of the air thermometer, three for the inser- 

 tion of mercurial thermometers to be compared with the air thermom- 

 eter. These borings were closed by perforated screw-plugs, of which 

 the central one was split lengthwise so that it could be placed on the 

 air thermometer stem after this had been passed through the larger 

 hole in the cover. Leakage was reduced to a minimum by an asbestos 

 packing. Thus, when the liquid was boiling, the circulation of vapor 

 was up the inside tube, in which the mercurial and air bulbs were 

 located, down the jacketing space between the tubes, and up into the 

 condenser tube until liquefied, whence it would drip back into the boiler. 

 The depth of liquid in the boiler was from 2 to 5 cm. The sides and 

 top of the boiler were covered with hair felt from one to three inches 

 thick. 



The whole instrument was mounted upon a strong wooden frame in 

 such a way that the cover of the boiler, having the air thermometer 

 rigidly attached to it by a brass bracket, was fixed in place, while the 

 boiler was removable. 



