BY MEANS OF THE RADIOMICROMETER. 11 



sion by the solution it was desired to measure, was made to fall upon 

 the junction after passing through the solution, by turning the cali- 

 brated drum-head to the proper point. The deflection when the deeper 

 layer was in the path of the beam of light was noted, and as quickly as 

 possible the cell containing the more shallow layer was placed in the 

 position formerly occupied by the deeper layer. This was accom- 

 plished by a carefully adjusted sliding carriage. The deflection when 

 the more shallow layer was in the path of the beam of light was noted. 

 The deflection produced when the light passed through the deeper 

 layer of solution, divided by the deflection when the more shallow layer 

 was in the path of the light, gave the absolute percentage transmission 

 of 20 mm. of the solution, for the wave-length of light in question. 



In work such as this, involving as it does so many distinct and 

 separate operations, it is highly desirable to duplicate all of the meas- 

 urements. This has been done in nearly all of the work the results 

 of which are herein recorded. In only some cases are the duplicate 

 results given. In every series of measurements, duplications were 

 made for certain wave-lengths of light. After filling the cells with 

 solution or solvent, and making the necessary adjustments as accu- 

 rately as possible, the percentage transmission was determined several 

 times for wave-length X 706. When 20 mm. of the solution or solvent 

 was employed this was always about 95.5 per cent. After taking about 

 ten readings farther down in the infra-red, wave-length of light X 706 

 was again passed through the solution and thrown upon the junction. 

 The transmission for this wave-length was repeatedly determined dur- 

 ing the entire series of measurements. Usually we obtained the same 

 percentage transmission in the two cases, to within the limit of error of 

 the method. This showed that comparable conditions were maintained 

 in both cells during the time required to make the intermediate read- 

 ings. Duplicate results are given for the wave-lengths X = 0.706/1, 

 X = 1.00/x, and X = 1.24yu. These were secured after the entire series of 

 measurements had been completed. To obtain reliable readings great 

 care had to be exercised in adjusting the cells in the carriage, so that 

 there was the same distribution of light from the glower upon the 

 slit when either cell was placed in the path of the light. 



THE CELLS. 



The cells for holding the solutions and solvent are among the most 

 important parts of the apparatus, and the reliability of the results is 

 largely dependent upon how they meet various requirements. Two 

 cells were made for this work, and they were made as nearly alike as 

 possible. Each cell consisted essentially of two brass cylinders, which 

 telescoped neatly into one another. Glass plates were set into the 

 ends of each cylinder by means of Wood's fusible metal, so that their 

 surfaces were parallel to one another. The question as to whether the 



