Vol. 8, 1922 
PHYSICS: DAVIS AND TERRILL 
59 
binations have already been prepared and isolated. Whether they form 
an intermediate step in the process of oxidation cannot be stated at present 
with certainty. It has also been observed that the oxidation proceeds 
rapidly even in air, and quite as well in alcohol as in water. 
Research is now in progress dealing with the oxidation of hydroquinol, 
and its homologues toluquinol, xyloquinol, etc., in the presence of various 
aliphatic amines. The detailed results of this work will be published 
later in the Journal oj the American Chemical Society. 
^ National Research Fellow in Chemistry. 
2W6hler, Ann., 51, 1844 (145-63). 
3 F. Mylius, Ber., 18, 1885 (467). 
4 F. Kehrmann, Ihid., 23, 1890 (906). 
5 A. Hofmann, Jahr., 1863 (415). 
« F. Fichter, Ann., 361, 1908 (397, 400). 
7 F. Fichter, and A. Willmann, Ber., 37, 1904 (2388). 
8 Th. Zincke, Ihid., 14, 1881 (94). 
9 R. T. Plimpton, /. Chem. Soc, 37, 1880 (637). 
THE GRA TING SPACE OF MICA AND THE INTENSITIES OF THE 
SPECTRAL ORDERS 
By Bkrgkn Davis and H. M. Thrrii.Iv 
Phoenix Physical Laboratory, Columbia University 
Communicated by W. Duane, February 28, 1922 
In attempting to determine the reflectivity from its principal cleavage 
planes, it was found desirable to know the grating space and incidentally 
the relative intensities of the several spectral orders. 
We would like to point out that perhaps the grating space of mica may 
not be constant. The thickness of a piece of mica may be altered by pres- 
sure to a small extent without apparently destroying its crystalline struc- 
ture. In this case we should expect nautral specimens even of the same 
chemical constitution to show differences due to the variable pressures 
to which they may have been subjected in their natural positions in the 
native rocks. 
The specimen of mica here reported on was a clear sheet about one milli- 
meter in thickness. It was selected for its smoothness of surface and free- 
dom from flaws. Nevertheless it was not optically plane as shown by 
viewing a distant straight edge by reflection from the surface. Small 
local departures from a plane surface were evident. 
The measurements were made by an ionization spectrometer, the stand- 
ards of wave-lengths were the Kq;i(X = .710) and the K^,(X = .633) 
emitted from a Coolidge tube having a molybdenum target. The slit 
of the ionization chamber was left open wide, the readings of angular 
position being made only on the crystal verniers. 
