CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



THE USE OF THE TRANSITION TEMPERATURES OF 



COMPLEX SYSTEMS AS FIXED POINTS IN 



THERMOMETRY. 



By Theodore William Richards and Jesse Briggs Churchill. 



Received November 14, 1898. Presented November 23, 1898. 



In a brief paper upon the transition temperature of sodic sulphate,* we 

 have recently shown that this non-variant point is cajmble of being repro- 

 duced in practice with great certainty, and that it is therefore admirably 

 suited for use as a standard of reference in thermometry. We pointed 

 out the fact that many other systems composed of two or more com- 

 ponents might answer equally well, and declared our intention of fixing 

 as many points as possible in order to simplify the accurate measurement 

 of temperature. The subsequent appearance of a hastily written note by 

 Messrs. Meyerhoffer and Saunders,! claiming for themselves a part of 

 this scheme, has prompted the present paper, which has as its object a 

 more detailed statement of the plan. 



It is obvious that, while any number of components might be employed 

 simultaneously for this service, the simpler systems will be on the whole 

 the most useful. Water is so omnipresent as to be difficult to exclude 

 from any kind of experiment, hence the investigator is almost forced to 

 adopt it as one of the components. The choice is then of the other 

 material or materials, and the first step was obviously to study all com- 

 mon substances with a view to discover the probable usefulness of the 

 transition temperatures of their aqueous crystals. If a complete tem- 

 perature scale could not be built up from such simple data it would 

 obviously become necessary to investigate quintuple points, of which a 

 very great number could be devised. This additional complication could 

 not but be regretted, however; for it involves the necessity of preparing 

 two salts instead of one in a pure state, it renders less easy the use of 



* American Journal of Science, VI. 201 (1898); also Zeitschr. phys. Chem., 

 XXVI. 690. 



t Zeitschr. phys. Chera., XXVII. 367, October, 1898. 



