402 Transactions.— Chemistry. 
added thereto produces the same kind of change. This may be an oxy- 
chloride. If, on the other hand, an alkali is omitted, the silver salt 
acquires a pale-reddish colour, and undergoes that chemical change which is 
generally imputed to it when subjected to light,—that is, it passes to 
argentous-chloride with evolution of chlorine; while hydrochloric acid is 
also produced in a secondary way (no doubt from the chlorine), and this, 
being free, is antagonistic to the formation of that dark product which 
results, as I have said, when photographic effect is produced in the presence 
of alkaline matter. 
7. Iodide of silver forms, as I have before shown,* a bright yellow 
compound with mercuric-iodide, as administered thereto in the form of 
mercuro-iodide of potassium. This compound, I have just ascertained, 
contains only about one-quarter per cent. of mercuric-iodide. 
8. The quantity of mercuric-chloride which has to be present in argentic- 
chloride so as to render it insensitive to light, need not be more than 1:16 
per cent. of the whole compound. 
9. Most of the aniline dyes are absorbed to a small extent by these 
silver salts. 
10. Argentic-chloride is to a very slight extent hygroscopic. In the 
dark at 22? C. a well washed sample of this compound gained :11 per cent. 
of water. 
11. Oxidizing agents generally, when applied to argentic-iodide which 
has been faded by light, turn its colour to a full yellow. 
12. Argentic-iodide precipitated from an excess of argentic-nitrate has 
its dull yellow colour changed to bright yellow by ammonia; but this yellow 
relapses to the normal hue upon the addition of water thereto in quantity. 
But if the argentic-iodide prepared in this manner is first thoroughly modi- 
fied by light, ammonia then browns in the place of yellowing it, and the 
addition of water causes a relapse to its former colour. 
I will for the present only make the following few remarks upon these 
notes. 
In 1 and 2 is shown in a marked manner the necessity of water in some 
form for the production of photographic effect upon argentic-iodide, and 
also of a temperature very far below its fusing point, facts which should, 
when fully realized by chemists, lead to a knowledge of. the exact molecular 
change which such an effect involves. 
The opposing effect of sodic-chloride to the aetion of light on silver 
salts (8), when taken in connection with results 8, 9, and 10, seems due to 
the formation of a double salt therewith which is not sensitive to this 
agent. 
* Trans. N. Z. Institute, Vol. IX., p. 555. 
