384 CARNEGIE INSTITUTION OF WASHINGTON. 



the violet. The color of fluorescence is a blend of the colors of the 

 two bands, the color of phosphorescence goinj^ over rapidly to that 

 of the band of long duration. The band of short duration has never 

 been subjected to quantitative study, but it is possible to do so, since 

 (as was shown in the paper just cited) the band of long duration 

 disappears at low temperatures. Doctors ]^ercy Hodge and Howes 

 have in progress the determination of the law of decay of this band and 

 also of its location in the spectrum. 



Lenard has shown that there are in the violet and ultra-violet two 

 and sometimes three narrow, well-defined regions, varying in position 

 for each preparation, which strongly excite the phosphorescence of 

 these sulphides. Dr. H. E. Howe, using the large quartz spectro- 

 graph, has obtained the absorption spectra of several of the sulphides 

 and finds absorption bands coincident with these regions, so that it 

 appears that the so-called "bands of excitation" of Lenard owe their 

 activity to the fact that they are regions in which the incident light 

 is strongly absorbed by the phosphorescent material. 



Dr. H. E. Howe has also completed a critical study of the sector 

 disk method of measuring ultra-violet absorption and has found it 

 possible to greatly simplify the procedure. The modified method 

 may be employed with any photographic plate which is sensitive in 

 the region studied. A spark between aluminum temiinals sub- 

 merged in distilled water was used as a source of light, and with 

 suitable devices to secure steadiness was found to be extremely satis- 

 factory as far as 0.2l^i. With this source Dr. Howe has used the 

 sector disk method in mapping the ultra-violet absorption spectra for 

 a number of derivatives of fluoran prepared by Professor W. R. Orn- 

 dorff. The results of this investigation are now ready for publication. 



More recently Dr. Howe has mapped the ultra-violet absorption 

 spectra of alcoholic solutions of phenolphthalein and five of its halogen 

 derivatives, while Dr. K. S. Gibson (whose work on the effect of 

 temperature on the absorption of the synthetic ruby^ is completed), 

 has detemiined the absorption of the same substances in the visible 

 region by spectrophotometric methods. The agreement in the results 

 obtained by these widely different methods in the region where they 

 overlap affords a highly gratifying check upon the accuracy of the work. 



The chief object of this study of the phenolphthalein derivatives 

 was to determine what changes in the spectrum accompany the 

 appearance of color that is observed when alkali is added. It was 

 found that the type of the absorption curve changes gradually as the 

 amount of alkali is increased. The great differences in the value of 

 the constants of molecular absorption in the visible regions, for the 

 several solutions, and the apjiroximate equality of this constant in 

 the ultra-violet band, indicate the presence in the solutions of two 



'Gibson, K. S., Physical Review (2), viii, p. ;is (191f>). 



