CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. LIBRARY 



NEW V 



CONCERNING THE USE OF ELECTRICAL HEATING IN botanic a i 

 FRACTIONAL DISTILLATION. Qarden. 



By Theodore William Richards and Joseph Howard Mathews. 



Received May 18, 1908. 



In the course of a research 1 now in progress in this laboratory it 

 became necessary to fractionate a number of organic liquids in order 

 to prepare them in a state sufficiently pure for investigation. The 

 process of distillation was at first carried out in the usual manner, but 

 some of the substances required very many successive systematic dis- 

 tillations in order to furnish enough material boiling within a reason- 

 able limit of temperature, and, indeed, in more than one case the task 

 seemed hopeless. 



A part of the research in question involved the determination of the 

 latent heat of vaporization of the various substances by means of a 

 modification of Kahlenberg's method, 2 to be described later. In the 

 course of these experiments it was noticed that each organic liquid 

 boiled at a much more constant temperature wben heated electrically 

 by the platinum coil of this apparatus than it bad during its previous 

 fractional distillations in an ordinary boiling flask. This led to the 

 use of the hot platinum coil instead of the gas burner as a source of 

 heat in the preliminary fractional distillation, with a very great gain 

 in the efficiency of this process. 



Probably the reason for this difference in efficiency between the two 

 methods lies in the difference in the extent of superheating. The suc- 

 cess of fractional distillation might be supposed to be impaired when 

 superheating occurs, for in this case the higher boiling fractions would 

 naturally have more tendency to come over with those of lower boiling 

 point. In order that the most effective separation may be made, the 



1 J. Am. Chem. Soc, 30, 8 (1908) ; also Z. phys. Chem., 61, 449 (1908). 



2 Kahlenberg, Journ. Phys. Chem., 5, 215 (1895). 



