316 CARNEGIE INSTITUTION OF WASHINGTON. 



Nichols, E. L., Cornell University, Ithaca, New York. Systematic studies of 

 the properties of matter through a wide range of temperatures. (For previ- 

 ous reports see Year Books Nos. 4-16.) 



The Luminescence of Calcite. 



The discovery that certain uranyl salts excited by kathode rays at 

 a temperature of — 180° exhibit phosphorescence of long duration, 

 although the same substances under photo-excitation glow for a few 

 thousandths of a second only,* has been extended to the calcite of the 

 Franklin Furnace region. f We have studied the ruddy luminescence 

 of this calcite in detail and have established the following facts :| 



(1) Under photo-excitation the phosphorescence vanishes in about 

 0.3 second. 



(2) The curve of decay corresponds with that previously found in 

 the case of the photo-luminescence of the uranyl salts and hitherto 

 supposed to be characteristic of and confined to those substances. § 



(3) The color, intensity, and duration of the luminescence are not 

 strikingly modified through a considerable range of temperature, but 

 the color appears to be of a purer red at — 180° than at +20° and 

 tends toward yellow at still higher temperatures. This observation 

 was verified for the higher temperatures by measurements of the 

 relative brightness of two regions of the phosphorescence spectrum 

 (0.65m and 0.52^) at temperatures between +20° and +300°. 



(4) At about +350° the activity of this calcite, like that of the 

 calcites from Joplin, Missouri, and Fort Collins, Colorado, long since 

 described by Headden,^ ceases entirely and becomes non-luminescent. 



(5) The calcites studied by Headden are strongly thermo-lumines- 

 cent between about 60° and +200°, a statement which we have had 

 the pleasure of verifying from specimens kindly furnished by that 

 observer. The Franklin Furnace calcite, on the other hand, displays 

 no thermo-luminescence whatever under the above conditions. 



(6) The luminescence is unquenched by red or infra-red radiation 

 applied during or subsequent to excitation. 



(7) The Franklin Furnace calcite contains appreciable amounts of 

 manganese and it appears that the characteristic ruddy luminescence 

 of this mineral depends upon this admixture. One writer (Wilber) 

 showed that a similar luminescence could be produced in pure calcite 

 by the addition of a manganese salt and suitable heat treatment. 



(8) Although the luminescence spectrum appears to the eye to 

 consist of a single broad band extending from red to blue, detailed 

 spectro-photometric measurements indicate a complex structure. 

 The spectrum consists of at least two systems of components having 



* Wick and McDowell; Physical Review (2), xi, p. 421 (1918). 

 t Nichols, Howes, and Wilber: Proc. Nat. Acad. Sci. (1918). 

 j Nirhols, Howes, and Wilber: Physical Review (2), xii, 351 (1918). 

 § Nichols and Howes: Physical Review (2), x, 293 (1917). 

 1 Headden: Amer. Jour. Sci., (4). xxi, 301 (1906). 



