238 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



may be cut from an ordinary boxwood slide-rule by a skilful car- 

 penter. They are very useful in a variety of physical work, but less 

 so than the ruled paper. 



Proof of the Method. — The method rests for demonstration on the 

 fact that logarithmic plots thus made for the six calibrations above 

 cited, each containing observations on naphthalin, sulphur, aluminum, 

 gold, and platinum, and using the above temperatures, were straight 

 lines well within the limits of variable error of the observations with 

 but one exception, when the platinum point showed a wide divergence, 

 presumably due to mistake, or possibly to faulty setting up of the 

 instrument. 



Apparatus and Procedure in Calibrating : Sidphur. — For this boil- 

 ing point, in order to obtain as good results as the instrument is 



capable of, the boiling point tube 

 shown in the sketch is satisfactory, 

 and a duplicate serves well for 

 naphthalin. The glass tube is about 

 an inch in diameter, and twelve 

 inches long, terminating below pref- 

 erably in a bulb about two inches 

 in diameter. The tube, to within 

 two inches of the top, is wrapped 

 with asbestos cloth of a thickness 

 of at least a quarter of an inch, to 

 prevent radiation and superheating. 

 An asbestos cover closes the top. 

 The clear part of the tube serves 

 as a condenser, which may be made 

 more efficient by a spiral coil of 

 jl wire, S. It is easy to regulate the 



rate of boiling so that the visible 

 line of condensation in the tube is nearly steady in position. The 

 bulb rests on a diaphragm of asbestos board, having an opening about 

 half an inch smaller in diameter than the bulb. The whole apparatus 

 is supported in a clamp stand. The flame plays upon the bulb where 

 it is exposed by the hole, but the diaphragm (six or eight inches in 

 diameter) prevents the hot gases from passing up around the tube, 

 which would cause superheating. Two overlapping diaphragms, I) 

 and E, about an inch above the sulphur and half an inch apart, pre- 

 vent spattering and radiation from the liquid to the thermal junction. 

 The wires of the couple extend downward through the cover to a 



