6 



ABSORPTION SPECTRA OF SOLUTIONS 



speculum mirror M on the slit S. A similar arrangement was used for the 

 fused silica cell. DTS is a double-throw switch, by means of which either 

 the Nernst glower or the spark gap may be thrown in circuit. B is a bal- 

 last. R is a variable resistance, by means of which the current in the Nernst 

 glower, as shown by the ammeter A, may be kept constant. OC is an oil- 

 condenser. IC isjm X-ray induction coil and R* is a resistance in the 

 primary circuit of this coil. 



Fig. A. 



In a recent paper Merton 1 states that he has studied the effect of pressure 

 on the absorption spectra of solutions. This was studied here by Jones and 

 Strong and the results published in the American Chemical Journal. 2 The 

 quotation of a paragraph from our earlier paper will show what was found : 



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

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

 being made so as to fit into this pump. It was not at all difficult to obtain pressures of 

 200 atmospheres with water and alcohol solutions. Spectrograms were made of the 

 absorption spectra of neodymium solutions 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 an expansion of the cell due to heating. 



It should be stated that in all of the work on absorption spectra which has 

 been carried out in this laboratory for the past seven years, a grating spec- 

 troscope has been used. The arrangement of the heated cell, the grating, 

 photographic plate, etc., will now be discussed. 



1 Proc. Roy. Soc, (A) 87, 146. 2 Amer. Chem. Journ., 47, 32, January 1912. 



