O. H. Koyl—Oolors of Thin Blowpipe Deposits. 187 
Art. XXIII.— The Colors of Thin Blowpipe Deposits; by 
C. H. Korn, B.A., Student of Physics in Johns Hopkins 
University. 
SOME examples of the action of very fine particles of matter 
upon light, having lately come to my notice, it may be inter- 
esting to make them public, as they have heretofore, I believe, 
been unexplained. 
Those who are familiar with the methods of blowpipe anal- 
ysis have observed faint borders occasionally surrounding 
some of the colored charcoal coatings, the colors of these borders 
seemingly bearing no relation to the characteristic colors of the 
adjoining oxides. For instance, the white coating of antimony 
is generally accompanied with a blue border, the brownish 
oxide of cadmium occasionally with a green, while the lead 
and bismuth yellows not unfrequently have a whitish ring 
inclosing them. As these oceur only and always where the 
coating is very thin they have a significance different from 
that of the ordinary colors, and as they may be produced at 
pleasure from the purest specimens they cannot be due to 
mixtures of the metals. A possible analogy with the antimony 
blue was suggested by a consideration of the colors of the sky, 
and to prove the connection it was simply necessary to show 
the similarity of attendant phenomena. As is well known, it 
is believed that the blue of the sky is due to the presence in 
the atmosphere of suspended particles, so fine that they are 
unable to reflect the longer rays of the spectrum which accord- 
ingly are transmitted and the union of the remainder gives to 
the sky its blueness. At evening, the sky is red because we 
get the rays of the sun directly transmitted or reflected from 
the clouds. Thirdly, the light of the sky, reflected at an angle 
of 90° with the sun, is plane polarized. ; 
When an antimony coating had been produced which gave, 
beyond the white oxide, a blue well defined and full, the whole 
was illuminated in a dark room by a sodium flame and that 
the blueness was no psychical or physiological effect as distin- 
guished from ordinary vision was proved by the fact that here it 
almost completely vanished while the white presented the usual 
ghastly appeardnce. A blue book-cover, treated in the same 
manner, gave more reflection than did the blue coating. 
Experiments with the polariscope were at first inconclusive 
from the fact that though the light from the blue coating was 
largely polarized, so, to some extent, was also that irregularly 
reflected from the charcoal, and it was found necessary to cover 
the block with a thin layer of carbon from a gas-flame. The 
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