402 Tranaactioih'i. — Chemistfy. 



added tbercto produces the same kind of change. This may be an oxy- 

 chloride. If, on the other hand, an alkaH 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 hydi-ochloric 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 

 compomid 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 yeUow 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 folloAvmg 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 action of light on silver 

 salts (3), 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. 



