140 Scientific Intelligence. 
that hydrogen arsenide is decomposed both by sap ete sul- 
phuric and hydrochloric acids, depositing, not a ydrogen 
arsenide, but arsenic ee and evolving i in the case ‘of the former, 
sulphurou id. in act with arsenous chloride, hydrogen 
arsenide is property yielding metallic arsenic and hydrochloric 
acid, thus: = AsCl, + AsH,=-(HCl),+-AsAs. 
Hence the author’s ie ee that the attraction of the 
arsenic atoms for each other is greater than their attraction oe 
the chlorine and hydrogen atoms pel aot Finally, on treat- 
ing sodium arsenide with water, gaseo s hydrogen arsenide is 
abundantly evolved, and a brown velvet- ‘like residue is left, which 
gare on analysis the formula AsHL. ——Ber. Berl. Chem. Ges. + Mi, 
~ 1873. G. F. 2 
On the Sensitiveness of silver bromide to the so-called Chem- 
ie rigged rays.—It is well known that with ordinary fii: 
as the line Ein de e gree GEL has now Hassvered the remark- 
able fact that by snttable Seitcieci, silver plates may be rendered 
sensitive to any of the rays of the spectrum at pleasure, even to 
the His attention was called to this subject by observing 
that some dry plates, prepared with silver bromide, received from 
ortley in England, were more sensitive to the green rays, near 
the line E, than to the bright blue, near the line F. This led to 
n inv es tigation into the sensitiveness of silver bromide to the 
various colors of the spectrum. spectrum was produced by 
a direct-vision prism, receiving its i ht from a slit 0°25"™ wide, 
illuminated wih sunlight from a Foucault’s heliostat. The image 
was produced by a ‘Steinheil’s camera lens, the portion 0 
spectrum from D to G being 35™™ in len The experiments 
were all made from 11 to 2 o’clock in the day ‘and during a cloud- 
less sky. The time ef exposure was generally ten minutes, and 
the plates were developed with solution of ferrous sulphate. 
It was at once chacerea that the ‘beens was sensitive to rays 
beyond the line F, rather than short of it, as had been supposed. 
Moreover, while wet plates, with an acid developer, were found to 
be sensitive to rays extending eS to the yellow (to between 
and E), dry plates were affected by rays two millimeters beyond 
D; i. e., rays in the orange. Inthe former case, the most intense 
“pa took place between G and F; diminishing rapidly beyond 
ard E. In the latter, though the action in the blue was 
on ee its decrease was much less rapid. The author con- 
more refran ays. In all the dry plates prepared by him, 
however, a such increase of sensitiveness fro blue toward 
the green was shown as was exhibited by the English dry plates 
above subilidned: In casting about for a reason for this, the 
common explanation of the use of a silver solution as a sensitizer, 
