258 Correspondence of J. Nicklés. 
Mr. Niepce proposes to investigate whether the permanent aetivity 
municated to a body by the solar rays is capable of determining the 
combination of chlorine and hydrogen, and whether it can be acquired 
in a luminous vacuum. engravi j un Te 
produces itself on sensitive paper. But i some mall 
meters of water, the effect fails, even with a solution of a salt of uranium 
or tartaric acid. 
Th h ; ference for demonsi 
e reagents which Mr. Ni s by preference for 
g epee employs by p cual 
ese 
In many substances that have been exposed to the sun the activily wd 
municated is apparent in the insolubility; it is on a similar principle ac 
quired under the sun’s action by gelatine containing a : potas, 
and humidity 
romptly cause the loss of thi ty. . 
promptly s of this property ts are obtained 
on inverting the course of operations; thus, a leaf of paper imprest 
with gallic acid and exposed to the sun, treated by iodid of pola 
gives'a feeble image which becomes very decided e ve we “a and 
. orid of mereury, 
exposed to the sun gives an image with chlorid of tin, chlorid i 
soda, potash, and sulphuret of sodium. In the same manner image 
pregnated with chlorid of tin, and exposed to the sun, gives (ce An?) 
draw2 
facts are still A 
z 
Ores . 
is d to the vapors of phosphorus burning slowly m Ss 
black parts alone become impregnated with the ear it is tue after 8 
quarter of an hour of contact, the engraving is represented OP", | 
t, g g ich when it is sufficient!) 
