1002.] of the Blood by Hammerschlag's Method. 173 



Table I. 





No. 1. 



No. 2. 



No. 3. 



No. 4. 





15-3118 



11-367 



3-81 



2-868 





3 '95 



4-37 



3-55 



3-13 



Length of first division of scale 



(i fi 1 '000 tn 1 'Ortl^ in mm 



1 -29 



0-74 



0-417 



0-398 



Eeading of scale in a chloroform 

 benzol mixture of specific gravity 



- 1 -ooo 



1 -002 



1-003 



1 -0095 



1-010 



No. 1 hydrometer is a more sensitive instrument than the ordinary urinometer, 

 Laving a large barrel and a comparatively fine stem. No. 2 is an ordinary urino- 

 meter such as is in general use in hospitals. Hydrometers Nos. 3 and 4 are 

 considerably smaller instruments, and are similar to those which have been 

 employed in this laboratory for use in connection with Hammerschlag's method. 



immersion which corresponds to the mark 1 -000 on the stem when the 

 hydrometer is floating in water. 



If the same hydrometer is floated in a chloroform and benzol mix- 

 ture of sp. gr. = 1 "000, the same volume of mixture is displaced, but, 

 as in this case the liquid possesses a lower surface tension, the pull 

 upon the stem is less powerful, and hence less of it is immersed from 

 this cause than in the case of water, the degree of surface tension 

 immersion being, in the two instances, in direct proportion to the 

 respective values of the surface tensions. The mark 1*000 on the 

 stem, therefore, floats a little distance above the surface of the mixture, 

 and the hydrometer hence shows a reading which is higher than the 

 actual specific gravity. 



The length of the divisions and the diameter of the stem of any 

 hydrometer being known, the error due to surface tension may be 

 calculated. 



The value of surface tension may be readily expressed in milli- 

 grammes for each millimetre of the circumference of the stem on 

 which its acts. The surface tension of water is estimated by Van der 

 Mensbrugghe as 7*3 milligrammes per mm. Other observers have 

 found higher values, but it is difficult to obtain water sufficiently 

 clean to exhibit even the surface tension of 7*3 milligrammes, for an 

 exceedingly slight contamination of the surface by greasy matter 

 suffices to appreciably reduce the tension. 



The surface tensions of chloroform and benzol are very nearly equal 



