835 



the specific gravity of which is known with an uncertainty of one 

 or two units in the fifth decimal figure. 



The agreement of the result of our measurement with that of 

 Osborne and Mac Kelvy proves a posteriori that our thermometer 

 agrees down to one or a few 0,01° with that of Washington. 



It is clear that Von Baumhauer's measurement is among the less 

 accurate ones. The cause of this must be ascribed to his rather 

 inaccurate way of determination of the specific gravity, which he 

 has carried out by hydrostatic weighing with an immersion body of 

 53 ccm., in which method especially the adjustment of the tempera- 

 ture meets with great difficulties, and the attraction of moisture 

 from the atmosphere is also difTicult to avoid. 



Besides many objections are to be made to the determinations of 

 the specific gravity of mixtures of alcohol and water which have 

 been carried out by Von Baumhauer, and which he executed with 

 a small pearshaped "body" of only 13 ccm. capacity, which allows 

 only a measurement of the sp. gr. down to 0,0001 even with the 

 present better constructed chemical balances. In v. B.'s values, 

 however, differences of as much as 0,0007 could be demonstrated 

 between two measurements of mixtures of the same concentration 

 (86,9 7o vol.). And yet von Baumhauer claims for his results an 

 accuracy of 0,00001. It is certainly not exaggerated when in general 

 we assume a possible error in Von Baumhauer's determinations of 

 0,0005, and consider only the third decimal of his sp. gr. as 

 valid. 



We have accurately determined the sp. gr. ^ (1.1.) of a number 

 of mixtures of absolute alcohol and water, and found the best 

 agreement with Osborne and Mac Kei.vy's results (Washington). It 

 appears from the subjoined table that this agreement is so much 

 better than that with the results of Von Baumhauer, and even better 

 than with those of Mendelejeff, that we do not hesitate to recommend 

 the table of the Bureau of Standards (Washington) as the very best 

 that is known at present. 



In order to be able to compose tables for different temperatures 



t 

 from 10° to 30° we have also accurately determined the sp. gr. — 



4 



(1.1.) both at 25° and at 15° for the mixtures of the mentioned 

 table and for some others, and calculated from this the modulus 

 of expansion between these temperatures for different con- 

 centrations by graphical interpolation. In order to be able to 

 compare our results with those of other investigators we have had 

 to assume the modulus of expansion between 10° and 30° as inde- 



