30 THE ABSORPTION SPECTRA OF SOLUTIONS. 



the spectroscope (containing the grating G, photographic plate holder C, and 

 slit S) was kept in a vertical position, a 45 quartz prism was used to change 

 the horizontal beam of light into a vertical beam, the beam being totally 

 reflected by the hypothenuse surface of Q. The source of light N.G. (Nernst 

 glower) or S.G. (spark gap) was focused by the concave speculum mirror M 

 on the slit S. A similar arrangement was used with the fused silica cell. 

 D.T.S. represents a double throw switch, by means of which either the Nernst 

 glower or the spark gap may be thrown in circuit. B is a ballast. R is a 

 variable resistance, by means of which the current (read by the ammeter A) 

 in the Nernst glower may be kept constant. 



O.C. is an oil condenser. Some trouble was given by the condensers, 

 especially when a large spark gap (2 or more centimeters) was used for 

 several hours. Paraffin condensers often become heated so that the paraffin 

 melts. A condenser was made of transformer oil. Unfortunately, the box 

 part was made of wood and it is very difficult to prevent the leaking of the 

 oil from such a box, especially when it becomes heated. I.C. is an X-ray 

 induction coil and R 2 is a resistance in the primary circuit of this coil. 



Some preliminary tests were made with the cells at high pressure. The 

 Cailletet pump belonging to the University was used for this purpose , the cell 

 represented in fig. 3 being made so as to fit on this pump. It was not at all 

 difficult to obtain pressures of 200 atmospheres with water and alcohol solu- 

 tions. Spectrograms were made of the absorption spectra of neodymium solu- 

 tions under pressures as high as 275 atmospheres. No effect of pressure was 

 detected. The work at high pressures is easier than at high temperatures, on 

 account of the fact that there is no expansion of the cell due to heating. 



