Chemistry and Physics. 417 
this result on the atomic weight of argon was considered. If the 
atomic weight be 19:94, the molecular refraction will be 3°15. 
This figure is almost identical with that belonging to oxygen and 
nitrogen gas, and differs considerably from that of calcium, which 
has a molecular refraction of 10-0 and a specific refractive energy 
of 0-248. These facts tend to suggest an atomic weight of 20 for 
argon, and to place it in the vicinity of the alkali metals.— 
Nature, \ii, 537. 
4, Color Photography.—Zenker, Lehrbuch der Photochromie, 
Berlin, 1868, explained the phenomena of the colors produced 
in sensitized media by the hypothesis of the working of stationary 
light waves. Objections, however, to this hypothesis were raised 
by Schultz-Seilack (Pogg. Ann., cxlili, p. 449, 1871). Lippmann 
(Comptes Rendus, cxii, 1891), however, showed the possibility of 
employing stationary waves in color photography, and his results 
apparently sustained the conclusions of Zenker. Schultz-Sellack, 
in support of his position, showed that. powdered substances had 
served for the reproduction of color. For instance Seebeck used 
paper moistened with a gray preparation of chloride of silver. 
This use of powder has no connection with transparent layers 
formed by Becquerel on good reflecting surfaces, such as silver 
plates which have been covered with a chloride of silver by elec- 
trolysis. The recent researches, however, of Carey Lea throw 
doubt upon the hypothesis of Zenker, for he shows that the colors 
of chloride of silver can be formed in the dark by purely chemi- 
cal processes. H. Krone also, in his treatise on the representa- 
tion of natural colors by photographie (Verlag der deutschen 
Photographenzeitung, p. 43, 1894) asserts that the Poitevin method, 
which consists in bathing paper in different solutions, rests upon 
purely chemical grounds and is radically different from that of 
Lippmann’s. Krone maintains that our present incomplete knowl- 
edge of the production of color in photography rests upon 
Zenker’s theory. Otro WiENeER undertakes in an exhaustive arti- 
cle to settle the question: “‘ Were the colors obtained by the 
early workers in this subject due to interference of waves of light 
or to absorption ?”. His experiments show that Becquerel’s results 
depend upon interference, that in the images obtained by Seebeck 
and Poitevin no color change enters. They are obtained from 
the color of the particles, and Zenker’s hypothesis does not apply 
to them. The color of the particles, body color, kérperfarbe, 
also enters into Becquerel’s results. Wiener addresses himself 
to the question why certain color stuffs give back the color of the 
illumination, and finds the explanation that the color stuff does 
not absorb the light of its own color but reflects it, while the 
other colors are absorbed by the stuff and broken up. It is 
therefore possible that colored illumination in suitable stuffs can 
awaken similar colors in color particles. He calls such material 
color-susceptible, farbenempfangliche. This possibility and the 
knowledge of its conditions leads to the foundation of a new art of 
color photography, which can be termed body color photography, 
