2 
SkEY.—On the Movements of Camphor on Water. 408 
The effect of a gentle heat in obliterating photographie impressions (4) 
is no doubt called into play, where, as Claudet observes, ** exposure to the 
red rays neutralizes the effect previously produced on a sensitive surface by 
white light." 
From results Nos. 7, 8, 9, and 10, it is seen that these silver salts have a 
predisposition to combine with small or even minute quantities of certain 
substances, the same as molybdic acid and its congeners have in relation to 
phosphoric acid, and this, without doubt, indicates a molecular change 
throughout, and one which, at least in the case of argentic-iodide, is possibly 
of the same nature in respect to structural form as that which light induces. 
It has been ascertained by Vogel that in the case of this salt (argentic- 
iodide) no'silver or iodine is liberated by light—the change is molecular 
only; so that the experimental results detailed above may have a signifi- 
cance in regard to the mode in which light produces this. But being a 
change apparently of this character only, it is not a little singular that 
water, or its constituents, is necessary for its production; and it was this 
that led me to make experiment (5), under the idea that water is assimi- 
lated by this salt when photographic effect takes place upon it. The result, 
however, as is seen, does not show this to be the case; but further experi- 
ments seem necessary here. 
From the results last described (11, 12) it is seen that most oxidizing 
substances have the property of putting argentic-iodide, altered by light, 
back to its normal state, and that this salt comports itself with ammonia 
according as ‘to whether light has been permitted to exert its influence 
thereupon or not, results which have no doubt an intimate relation to the 
phenomena under consideration, but in what way it is difficult as yet to 
discover. The primary effect of ammonia, however, in the last result is, 
it would seem, merely to form feebly ammoniacal compounds with the silver 
salts, which are so unstable as to be decomposable by water. 
Arr. LXII.— Further Notes upon the Movements of Camphor on Water. By 
Wurm Srey, Analyst to the Geological Survey Department. 
[Read before the Wellington Philosophical Society, 21st February, 1880.) 
Scoe my paper “On the Movements of Camphor on Water”* was read 
before you, I have learned that this subject has been especially treated by 
Professor Tomlinson, in one of a series of **experimental essays," dated 1868. 
This work I eannot get hold of; but the theory which this scientist there 
* Trans. N.Z. Inst., Vol. XL, p. 473. 
