Photochemical Experiments. 257 
rify them. At 120° C. they become brown, and at a higher temperature 
they melt with a black color. For moulding, the material is excellent. 
It is in a high degree electric, and may be used for making electrical 
plates or the electrophorus. It readily destroys any tissues to which it 
may be applied. 
Bromid of sulphur has properties analogous to those of the chlorid. 
, presiding especially over 
chemical phenomena, Niepce de St. Victor will have had a prominent 
part in the discovery. But a few months since, he ascertained the funda- 
atk, &@ positive image immediatel ars having the maroon 
tint. To fix it, it is -e nec a he it with pure water. If the 
titrate of silver is replaced by chlorid of gold, the image appears of a 
deep blue, These pictures resist the action of the cyamd of potassium, 
photographs 
increases the sensibility of the reaction. For on covering with a plate of 
ton heated to 50° C. both the pasteboard which bears the impression 
a 
ey the image will appear at the end of a few minutes, while at 0° C. 
int impression. 
general result of the researches of Mr. Niepce is this, that the 
bodies which preserve the greatest activity with a dose of the sun are, 
With the exception of the salts of uranium, those which are the least dis- 
Posed to fluorescence. Wiis 
is canal activity which certain bodies may contract under the 
ence ’ ‘ 
i 
the nature of the substance; it has its limits; when a substance has 
thing to - maximum of activity continued exposure does not add any- 
it, 
‘Paper prepared with the nitrate of uranium changes color in the light 
“me becomes insoluble; in the dark it is decolorized, and it becomes solu- 
¢ after some hours, to be colored again in the light. It reduces the 
‘alts of gold and silver, so much as to become colored and insoluble. 
A rendered active by the sun will Cg this activity by con- 
‘act in the dark to another body—tartaric acid, for example. 
