362 



MR. P. O. PEDERSEN ON THE SURFACE-TENSION OF LIQUIDS 



the pendulum completing two whole swings, the corresponding loss, p s , being 

 determined in the same manner as above. In a similar manner p 3 , />, and p b are 

 determined. We have then 



In Table II. are arranged the results of these determinations for water and alcohol 

 (98*04 per cent). 



TABLE II. 



In the following it is always assumed that a = 0'88. A small error in the 

 determination of a is of no great importance. If the worst case in this paper 

 is taken, P is almost equal to 230 mg. and jp s = 25 mg. ; we have then 

 P + op 5 = 252 mg. An error in a of 0'04 will give an error in the concluding weight 

 of 1 mg. or of 0'4 per cent. The corresponding error in the surface-tension is about 

 0'2 per cent. 



As the determination of p^ always takes place under the same conditions 

 temperature, humidity, and air pressure as those under which the " cutting off" 

 takes place, the determination of this correction is quite certain and cannot cause 

 great errors. 



In Table III. are shown some of the values found for a.j) 6 corresponding to orifice 

 No. III. All the weighings are corrected for the buoyancy of the air. 



Besides the sources of error investigated there are several other circumstances that 

 possibly could cause irregularities in the exactness of the measurements. Thus it is 

 necessary that the vessels K of the "jet-catcher " have a certain shape, so that they can 

 without loss receive and hold the portions of the jet cut off. With the form shown 

 in fig. 6 I have never noticed any loss of liquid. 



It is further obvious that if the speed of the "jet-catcher" when passing the jet is too 

 slow, the disturbance in the jet produced by the first knife will have time to reach 

 the second knife before it has cut the jet through. It is also possible that the 

 movement in the air resulting from the movement of the pendulum and the " jet-catcher " 



