PREFACE. 



The effect of high temperatures on the absorption spectra of nonaqueous 

 solutions was worked out in the Johns Hopkins University and published 

 in monograph No. 160. By means of a form of apparatus devised by Dr. 

 Strong, this work has now been extended to aqueous solutions and the 

 results are herein recorded. 



Our previous work on the absorption spectra of solutions, which has now 

 been in progress continuously for eight years, had shown that the effect of 

 dilution on absorption spectra is much less than had hitherto been supposed. 

 A form of apparatus and method of procedure were worked out by Professor 

 Anderson, one of my former coworkers in this field, and this method has been 

 applied, with unusual skill, by Dr. Guy, to the effect of dilution on absorp- 

 tion spectra. The results that he has obtained are also recorded in this 

 monograph. 



The grating spectrograph as a means of studying absorption spectra 

 has now supplanted the prism spectroscope. The grating spectrograph, 

 however, has its limitations. The results are photographed. This means 

 that the method is limited to the range of the photographic plate. This is, 

 for the best plates, from about 0.2^t to 0.8ju. It is, however, very desirable 

 to study absorption spectra in the region of wave-lengths which are much 

 greater than 0.8^. For this purpose, some method had to be devised which 

 did not make use of the photographic plate. The i adiomicrometer was the 

 obvious instrument to use, if it could be built sufficiently sensitive and at 

 the same time with sufficiently short period. This has been accomplished 

 by Dr. Guy. 



With this instrument the absorption spectra of a number of salts have 

 already been mapped, and some surprising results have been obtained in 

 reference to the relative absorption of free water as compared with water 

 of hydration. 



It gives me pleasure to express our thanks to Dr. E. J. Shaeffer, who has 

 assisted in making the radiomicrometer readings during the second half 

 of the past year, and who has also aided in the chemical work. Dr. Shaeffer 

 will continue the work on the absorption spectra of solutions, using the 

 radiomicrometer. We are especially indebted to Professor A. H. Pfund for 

 a large number of valuable suggestions, and for frequent advice during the 

 progress of this week. Professor J. S. Ames has kindly placed ample space 

 at our disposal for carrying out this investigation. 



I am deeply grateful to the Carnegie Institution of Washington for 

 financial aid in carrying out this entire work, and in publishing the results 

 obtained. Without this aid, the work recorded in monographs Nos. 60, 

 110, 130, 160, and herein could not have been done. 



Harry C. Jones. 



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