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VIII. Researches on the Action of Organic Substances on the Ultra-violet Rays of the 
Spectrum. 
By W. N. Hartley, F. Inst. Chem., F.R.S.E., F.C.S., Demonstrator of Chemistry, 
Kings College, London ; and A. K. Huntington, F. Inst. Chem., A.R.S.M., F.C.S. 
Communicated by Professor G. G. Stokes, Sec. R.S. 
Received October 10, 1878,—Read January 9, 1879. 
[Plates 21-34.] 
PART I. 
Method of Experimenting.—Examination of Alcohols and Fatty Acids. 
In the year 1863 the late Dr. W. A. Miller described his method of examining the 
diactinic properties of various saline solutions and organic substances. (Miller, “ On 
the Photographic Transparency of Various Bodies, &c.,” Phil. Trans., 1863, 1.) 
He found that the spectrum transmitted by lenses and prisms of rock-crystal was 
far superior in length as determined by sensitive photographic plates, to that 
obtained when lenses and prisms of glass and other materials were employed. He 
found particularly that the spectrum produced by passing electric sparks between 
silver points was very rich in photographic rays, and he ascertained how far various 
substances were transparent to these rays. Professor Stokes at the same time com¬ 
municated results he had obtained when studying the long spectrum of the electric 
light by receiving the rays on a fluorescent screen. (Stokes, “ On the Long Spectrum 
ol Electric Light,” Phil. Trans., 1863, 1.) He discovered the fact that certain solutions 
showed light and dark bands which were otherwise invisible. More recently, M. Soret 
has studied the absorption of the ultra-violet rays of the spectrum transmitted by 
various substances, using for the purpose a spectroscope of his invention, which has a 
fluorescent eye-piece. (Soret, “ Recherches sur 1’A bsorption des Bayons Ultra-violets 
par diverses substances,” ‘ Archives des Sciences Physiques et Naturelles; ’ Geneva, 
January, 1878.) In 1872 the apparatus of Dr. Miller was reconstructed by one of 
us, and certain improvements were introduced. The intention of repeating his experi¬ 
ments and carrying them out in a more complete manner was prompted by a desire 
to know what relation, if any, exists between the molecular constitution and the 
actinic absorption of organic substances. No encouragement to pursue this line of 
research was offered by the results of Dr. Miller, since he states, “ I have not been 
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