74 BURTON EDWARD LIVINGSTON 



have been corrected to the Livingston standard, may be re- 

 garded as comparable for all practical purposes, regardless as to 

 whether 6-cm. or 8-cm. instruments were employed. 



Further study of the behavior of these instruments, and of 

 other modifications as to form and size, will be necessary before 

 we shall be able to state within what sort of limits of external 

 conditions the relation between the evaporating powers of two 

 different kinds of cup may be considered approximately constant. 

 Where the greatest accuracy is derived it is advisable to employ 

 cups whose coefficients are alike. 



This matter of cup size and shape has no reference, of course, 

 to modifications of the cups, produced by dust, handling, impure 

 water, etc., which are apt to occur with use. With these altera- 

 tions we shall deal below, in considering the operation of the 

 instrument. This is, however, the place to mention one feature 

 of this general problem, which is involved in the standardiza- 

 tion procedure. It has been stated that serious changes in the 

 standard cup have been avoided by frequently replacing the 

 standard with a new cup, unused since its standardization. It has 

 also been stated that serious alterations in cup surface may usually 

 be prevented by frequent cleansing. The question then arises, 

 would it not be better to hold the same standard continuously 

 and to cleanse it from time to time instead of replacing? This 

 suggestion is perfectly feasible with the insoluble cup, which 

 is permanently glazed at base, but is to be followed with caution 

 in the case of the regular form. The latter has been thought to 

 be soft enough so that repeated rubbing might alter the porcelain 

 surface, and there is little doubt that such treatment would 

 alter the shellac coating. Recently the new form of insoluble 

 cup, quite like the regular cup in size and form, has been em- 

 ployed as standard. With thorough cleaning between standard- 

 ization series, a single one of these cups may be repeatedly used. 



{To be confirmed.) 



