AN APPARATUS FOR THE RAPID MEASUREMENT OF 

 SURFACE TENSION' 



ROBERT G. GREEN 

 Department of Bactenology and Immunology, University of Minnesota 



Investigations carried on in these laboratories concerning the 

 role of surface tension in certain bacteriological phenomena 

 (Larson, 1921), have led to the development of an apparatus for 

 the rapid determination of surface tension by the drop-weight 

 method. After using the more common methods of surface tension 

 measurement the belief is expressed that the most rehable and 

 constant results for both pure and biological hquids can be obtained 

 from their drop weights. The apparatus here described repre- 

 sents a means of determining the surface tension of a liquid by 

 the drop-weight method without any mathematical calculation 

 or the determination of the drop weights and is termed a surface 

 tension balance. The apparatus is designed primarily for 

 rapiditj-- of measurement and an accuracy is obtained which 

 is consistent with ordinary experimental conditions. 



In general the apparatus consists of three mechanical parts, 

 a dropping pipette, a balance beam mounted on a torsion wire 

 and an adjustable scale. 



The dropping pipette (A) differs in no way from those already 

 in use and all the inaccuracies and corrections, which have been 

 recorded for this method, occur but such errors may be mini- 

 mized and reduced to an order of magnitude which is of no 

 concern to the biologist, by using a dropping surface of the proper 

 dimensions (Morgan, 1911). The rate at which the drops fall 

 may be easily controlled by using a fine capillary tube for an air 

 inlet protected by larger tubing (/). 



* Aided by a grant from the National Dental Research Association. 

 Presented at Twenty-third Meeting of the Society of American Bacteriologists, 

 December 26, 1921. 



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