238 PROCEEDINGS OP THE AMERICAN ACADEMY 



competent investigation other substances could be had which at other 

 temperatures should fulfil the conditions just named as rendering 

 steam so useful. 



The investigations in this direction by Prof. J. M. Crafts — in part 

 published * — contribute far more than any others to the establishment 

 of such fixed reference temperatures. The results of Mills's f measure- 

 ments of melting points are also important. Independent study of the 

 same substances by various observers is valuable, even when the check 

 results cannot claim all the accuracy of the most elaborate investiga- 

 tions. For it is of material importance to answer in this way for each 

 substance the questions: Is the substance reproducible with sufficient 

 certainty to give wholly independent workers sensibly the same tem- 

 perature ? What is this temperature in absolute degrees (of Thomson 

 scale) as a function of the vapor pressure, errors in thermometric 

 methods being eliminated? Is the substance readily reproducible 

 without great expense ? 



The following is a brief account of a study of naphthaline, benzo- 

 phenone, and benzol, undertaken with these points in view, and with 

 special reference to attempting to check the results of Professor Crafts. 

 It is probable that, owing to superior facilities and greater experi- 

 ence, he has obtained results entitled to decidedly greater weight than 

 those which we give. But it is believed that the conditions under 

 which our work was done, and the pains taken in the system of air 

 thermometry, entitle the temperature measurements to consideration. 



In designing the apparatus we departed somewhat widely from the 

 published descriptions of Crafts's apparatus in almost all details. Our 

 thermometer contained air dried and freed from C0. 2 , while Crafts's 

 contained hydrogen ; its bulb was large (about 200 cc.) ; the sub- 

 stances studied were either commercially obtained or prepared by 

 methods differing from those of Crafts ; and the vapor pressures were 

 under control by a regulator, and were extended through a greater 

 range. We have since learned from Professor Crafts that the form 

 of gas thermometer whose description had been published was not 

 invariably employed, but that others of various capacities and forms 

 had been used. 



The concordance of our results with those of Professor Crafts for 

 naphthaline (p. 246) is certainly as close as could be anticipated, and 

 is within the limits of error in even the most elaborate use of the 



* Crafts. Bulletin de la Soc. Chim., xxxix. 196, 277 (1883). 

 t Mills. Phil. Mag., (5,) xiv. 1 (1882). 



