APPARATUS. 243 



other two expressed, respectively, the required depth of solution and the 

 distance from the lower plane surface of the quartz plate M to the plane of 

 the lower end of the brass cylinder E. As an example from practice, for a 

 depth of 2cm. the sum was 1.34+2.00+0.69 = 4.03 cm. ;/. c., the two cylinders 

 E and I had to be screwed around each other until the fiducial line to the 

 flange was equal to 4.03 cm. 



Conversely, knowing this distance, as well as the two-cell data, it was 

 merely a matter of algebraic addition to obtain the effective depth of the cell. 



The remaining parts of the apparatus had the characteristics described 

 below and were assembled as follows: L denotes the handle of a stout, hollow 

 cylindrical plate, which formed the bottom of the complete cell. The inte- 

 rior of this plate was turned out so as to leave a flange at the bottom upon 

 which the rubber washer P was placed. The three pillars mentioned above 

 projected vertically from and were rigidly attached to the plate L. Two 

 holes had been tapped out of this plate to correspond accurately to the smooth 

 holes of the flange of I. After laying the washer P on the flange of L, and 

 after pushing and turning the quartz plate M tight up into the conical holes 

 of the glass tube F, the transparent system was set vertically with its lower 

 end resting symmetrically on the washer. The thickness and the smallest 

 diameter of this quartz plate were, respectively, 4.6 mm. and 19 mm. The 

 solution to be studied, N, was next poured into the vessel constituted by F 

 and O. It was necessary to measure the depth of the liquid, and it was 

 found convenient to make this depth 2 mm. greater than the effective depth 

 of the cell. 



The assembled system of parts A,B,C, D,G. I,M,R,was next let down over 

 the glass tube F, until the upper flange inside the cylinder I rested on top 

 of this tube. The three pillars H guided the system into the correct position, 

 and prevented any rotation of the cylinders I and L around each other. 

 Lastly, the two little screws were passed through the holes in the lower rim 

 of I, and the two cylinders were screwed tightly together. This operation 

 completed the adjustment of the cell. It is seen at once from the preceding 

 explanation, that the liquid or solution in question came only in contact 

 with glass and quartz surfaces, while the vapor touched both glass and brass 

 walls. Since the vapors of the solutions studied did not act on brass, glass, 

 and quartz, and since the apparatus did not leak, the cell gave entire satisfac- 

 tion. For vapors that would attack brass but not the silicates, it is easy 

 to see how a system could be designed that would differ from the system 

 just described, in having coaxial glass tubes dip into a trap of some neutral 

 liquid instead of the brass cylinders E and I. Moreover, it would be quite 

 possible to design the parts of the cell in such a way as to impart to the liquid 

 the shape of a wedge or prism of adjustable angle and depth. 



