50 Conductivities and Viscosities in Pure and in Mixed Solvents. 



The calibration curve for the grating and drumhead was calculated 

 from the known grating space, by means of the equation 



,,. . 3000 T + 



X = 33,866.7 Sin 



where T is the number of complete turns of the screw which rotates the 

 grating and R is the reading on the drum. The calibration was also 

 effected by observing the positions of various mercury, sodium, and 

 lithium lines. It was decided that the calculated values are more 

 accurate than the observed; and, accordingly, the dispersion curve 

 based on the calculated values was used. 



SOURCE OF LIGHT. 



A Nernst glower served as the source of light, the electrical energy 

 being supplied by a series of storage batteries. By means of a rheostat 

 the light intensity could be kept quite uniform. The glower was pro- 

 tected from air drafts by means of a box of asbestos wood. Provision 

 was made for the mounting of a nitrogen lamp 1 when it was desired 

 to secure large deflections of the radiomicrometer for wave-lengths of 

 light shorter than X = 0.5ju. 



THE CELLS. 



A very important part of the equipment is the cells which contain 

 the solutions to be investigated. There are two cells made as nearly 

 alike as possible. The cell consists of two brass cylinders which closely 

 telescope into one another. One end of each cylinder is closed by a 

 glass plate held in position by Wood's fusible metal. The four glass 

 ends used hi the cells are all of the same thickness, i. e.,2 mm. Their 

 surfaces are plane, and are parallel to within 5 wave-lengths of light. 

 It is difficult to set these plates in the brass cylinder with Wood's 

 fusible metal, without warping them and destroying their plane- 

 parallelism. The character of the interference fringes which the plates 

 gave with the mercury arc determined when they were correctly 

 adjusted. A fine thread was "chased" on the outer cylinder. This 

 thread carried a nut which, when turned, raised or lowered the inner 

 cylinder a definite amount. Each complete revolution of this nut 

 changed the distance between the plates by 1 mm. The nut contained 

 100 divisions, and by means of this arrangement we could readily 

 adjust the depth of the solutions to within less than 0.01 mm. Each 

 cell was then filled with a layer of water 5 mm. in depth, and the 

 deflections given by the radiomicrometer were noted for a light source 

 of uniform intensity throughout the whole region of the spectrum 

 under investigation, namely, from X = 0.4/z to X = 2.0/x. The deflections 



J Dr. W. R. Whitney, of the General Electric Company, very kindly supplied us with two lamps 

 of special design to be used for this purpose. 



