376 MR. P. O. PEPERSEN ON THE SURFACE-TENSION OF LIQUIDS 



the measurements of the wave-length for orifice III. are carried out with great exact- 

 ness and easiness, just as the determination with orifice VII. is, as a rule, quite good. 

 I have therefore chosen these two orifices and corrected for the too great amplitude of 

 orifice III. by adding 0'5 per cent, to the results, a correction obtained from Table X. 

 In the following this correction is represented by [8]. 



Execution of Observations. 



11. All the experiments to No. 37 are made with ordinary tap-water under 

 constant pressure, produced in the manner explained in 4. In all the other experi- 

 ments the pressure diminished as the liquid ran out. This variation was, however, 

 only small, as the cross-section of the reservoir used was about 400 cm a . and the 

 quantity of liquid used about 1000 cm 3 . The pressure for all the experiments after 

 No. 40 was about 70 cm. 



The measurements themselves took place in the following manner : 



The orifice is closed by a wooden plug. The requisite quantity of liquid is poured 

 into the reservoir, care being taken to fill both the conducting tube and the jet tube 

 completely, the plug is withdrawn and the jet started. Then the jet is adjusted so 

 as to be parallel to the plate-holder and to have the height suitable for the 

 "jet-catcher." The last adjustment is easily controlled by the shadow of the jet on 

 a ground glass placed in the frame and furnished with marks, between which the 

 shadow must fall. At the same time the jet tube is moved until the image (m-n, 

 fig. 14) of the jet is as sharp and clear as possible. In order to enable these 

 adjustments to be made easily, the jet tube is arranged in a bridge that can be moved ^ 

 in all directions by help of screws. 



As the direction of the "jet-catcher " once and for all is parallel to the frame, the jet 

 by the above adjustments is brought into the required position and the measuring of 

 its cross-section can take place. Immediately afterwards the measurements of the 

 discharge begin, after which the plate-holder with an unexposed plate is placed in 

 the frame, which is lying down. The light is then shut off, the shutter removed 

 from the plate- holder and the slide moved into its position, whereupon the frame is 

 brought up to its vertical position and the lamps L t and L 2 lighted. After exposing 

 for about 15 seconds the lamps are turned out, the slide brought back and the 

 shutter replaced in the plate-holder. The entire photographing process takes about 

 40 seconds. Before finishing the measurement of the discharge another photograph 

 is taken in the same manner. 



Finally the necessary weighing takes place and the evaporation is determined as 

 explained in 6. 



In changing from one liquid to another the whole apparatus is cleaned very 

 carefully and finally washed out with distilled water, after which it stands for some 

 time to dry. Before use it is washed out with some of the liquid to be tested. 



