172 



SCIENCE 



[N. S. Vol. LIV. No. 1391 



urge authors to be extra patient in the matter 

 of receiving their reprints. If the present 

 composition force is diverted to work on re- 

 prints, the issue of each of the journals of the 

 society would be delayed to that extent. We 

 have, therefore, taken the liberty of authoriz- 

 ing the printer to postpone the making up of 

 reprints from this Journal, and to put all 

 emphasis upon catching up with the regular 

 schedule of publication. We are confident of 

 an extension of loyal cooperation on the part 

 of our contributors. 



To adopt the language of the Weather Bu- 

 reau : " For to-morrow : fair weather." — Jour- 

 nal of Industrial and Engineering Chemistry. 



SPECIAL ARTICLES 



NOTE ON THE USE OF THE DUBOSCQ TYPE OF 

 COLORIMETER FOR THE DEMONSTRA- 

 TION OF DIFFERENCES IN SUR- 

 FACE TENSION 



Although there are many interesting ex- 

 periments by which the phenomena of surface 

 tension can be demonstrated to students, as a 

 rule they fail to give a basis of direct visual 

 evidence of the main force concerned. Conse- 

 quently any procedure which will enable the 

 student to demonstrate to himself in a semi- 

 quantitative manner, that there are differences 

 in the ability of different liquids to sustain 

 themselves by the forces inherent in their sur- 

 faces, should assist in an understanding of the 

 underlying principles. 



Such a demonstration can be staged by the 

 use of the Duboscq type of colorimeter. 

 Moreover the effects of the additions of mi- 

 nute amounts of various substances to water, 

 on the surface tension of the latter can be 

 strikingly shown. 



If that point on the scale at which the dry 

 lower surface of the plunger just comes in 

 contact with the surface of a liquid in the 

 cup or small beaker of about 5 cm. diameter 

 resting upon the cup support is taken as the 

 base line, it is possible to measure with a con- 

 siderable degree of constancy the height in 

 tenths of millimeters to which the plunger can 

 be raised above the surface of the liquid be- 

 fore the clinging column of fluid breaks con- 

 tact and slides back into the container. This 



affords a clear idea of the principle of surface 

 tension from the fact that an obviously weigh- 

 able volume of liquid is lifted and held above 

 the main surface of fluid by the force of the 

 liquid surface in contact with the plunger. 



When a comparison is made of the height to 

 which the plunger can be raised from contact 

 with the surface of such substances as water, 

 ether, absolute alcohol, acetone and toluol, it 

 becomes at once evident that different liquids 

 have different abilities to cling to the plunger 

 surface and hence different surface tensions. 

 When a bit of soap is swished around in the 

 water in the beaker and then removed, the 

 marked decrease in surface force is made plain 

 by the decrease in the height to which the 

 plunger can be raised before contact is broken. 

 A similar result is obtained when a trace of 

 amyl alcohol is added to the water. When a 

 bit of picric acid is dissolved in the water in 

 the beaker the opposite effect is observed and 

 is of sufficient magnitude to demonstrate why 

 picric acid solutions " bump " when heated. 



TABLE 



Substance Height In 0.1 mm. a^mm'^ 



Water 40 14.68 



Toluol 29 6.72 



Acetone 28 6.18 



Absolute alcohol 27 5.08 



Ether 25 4.61 



Water plus soap 36 



Water plus amyl alcohol 33 



Water plus picric acid 42 



The accompanying table shows the values 

 obtained for the substances mentioned. The 

 second column of figures gives the values for 

 the same compounds as copied from Landolt, 

 Bernstein and Eoth's tables, 4th edition, in 

 terms of a'mm'. The correspondence is pleas- 

 ingly close, but is of course accidental since 

 contributing factors other than the height 

 in millimeters are obviously involved, though 

 in this group they happen to be mutually com- 



These few examples suggest the availability 

 of the plunger-cup mechanism as a basis for 

 the development of an accurately calibrated 

 piece of apparatus for the determination of 



