31:19 



Pj. If P^ iy turned in a horizontal direction, tlie screws A^ and yl,, 

 as well as the springs F-^ and F.^, (fixed at one end only) will glide 

 along the upper disc P,, the whole ui)per part thus remaining in its 

 original positioji. It appeared to be necessary to use a third screw 

 B for the adjustment of the capillary tube. It is first completely 

 loosened from F^, then after F^ and F^ have been brought into the 

 desired relative position, the screw B is turned so as to touch the 

 disc Pj slightly : in this way the relative position of the two plates 

 is completely fixed. The tubes S and Y, (not shown in fig. 3«) are 

 bent rectangnlarly upwards, and fitted, to the spiral tul)es G. By this 

 arrangement an undesirable motion of the apparatus (during the 

 adjustment of the capillary tube), due to the influence of the stress and 

 weight of the connecting-tubes, could be sufficienly prevented, while 

 the micrometerscrew }[ at the same time remained in working 

 condition. This screw .1/, fitted with a drum iV and a scale D, 

 serves to move the discs Pi and P, together through a known ver- 

 tical distance. The screw has a pitch of 1 mm. exactly, the circum- 

 ference being divided into one hundred equal parts, it thus permits a 

 vertical motion of 0,01 mm. to be measured at D. This is more 

 than sufficient, because experience proves, that no adjustment of the 

 capillary tube in contact with the surface of the liquid, can be 

 made with greater accuracy than about 0,1 mm. During this vertical 

 motion the drum N and the micrometerscrew M remain in their 

 original positions, because they can only move in a horizontal direction 

 round the fixed part V of the apparatus. A vertical scale Z, provided 

 with divisions for about 30 mm., is moved at the same time with 

 the two discs Pi and P„. In this way the number of revolutions of 

 N can be read directly. Concerning the adjustment of the capillary 

 tube with respect to the surface of the liquid, which can be made 

 either visually, or with the aid of the manometer-readings, the neces- 

 sary directions will be given below. 



§ 6. It was soon found, that the adjustment of the slight diffe- 

 rences of pressure in the long connecting-tubes happened so slowly, 

 that considerable errors in the measurements must inevitably occur. 

 For this reason all the capillary tubes, with which the apparatus 

 was originally equipped, were replaced by 5 mm. gas-tight tubes. 

 These tubes were made in part of lead, in part of aluminium ^) and, 



1) Also tubes of cellpn, made hy ihe Bheinisch-Westphalische Sprengstoffe A.G. 

 in Cöbi a/Rh., and which may be bent in hot water, can be recommended for 

 such purposes. The material is gastiglit and fire-proof; however it is difficult to 

 obtain it from the plant in any desired shape. 



