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such collodion remains colourless and fit for photographic use for a very 
long period, and is, in this respect, greatly superior to that prepared with 
the iodide of ammonium. In this explanation it cannot be the author’s 
intention to assert that the removal of the hyponitric elements is more 
than partial, else the ultimate product, cotton itself, would in time be 
precipitated from the etherial solution. No such result has yet been 
observed, and if Dr. Phipson’s suggestion be limited to the reduction of the 
trinitro compound, C x 2 j O x 0 , usually employed in the manufacture 
of photographic collodion, to one of the lower modifications of pyloidine, 
containing two, or even a fewer number of atoms of nitrogen, and which 
are still soluble in mixtures of alcohol and ether, a feasible explanation is 
at once provided, and one which more nearly coincides with the facts of 
the case than that formerly advanced by Mr. Hardwich, to the effect that 
ozone was mainly instrumental in promoting this change by time. 
We have already more than once had occasion to refer to the employ- 
ment of the sulphocyanide of ammonium as a fixing agent, which may 
possibly, at no distant period, supersede altogether the use of hyposulphite 
of soda. The favourable report regarding its efficacy made by the com- 
mittee appointed by the Marseilles Photographic Society tends to 
strengthen this conviction. The paramount obstacle which has hitherto 
stood in the way of its introduction, viz., its high price, seems likely to be 
soon overcome ; for already M. Meynier, to whom we are indebted for the 
original proposal, has succeeded in producing it with such facility, that 
he is enabled to offer it for sale at the rate of three francs per kilogramme, 
which in English money is nearly equivalent to one shilling and two- 
pence per pound. 
The efficacy of ebonite as a material for photographic baths, trays, and 
other apparatus intended to be used in contact with nitrate of silver, has 
been much questioned of late, and it appears, from evidence given upon 
this subject by Captain Dennis Wright, Mr. J. Spiller, and others, that 
there are a variety of materials met with in commerce under the name of 
ebonite, Some kinds of which appear to have been manufactured from 
condemned india-rubber goods, and in consequence are liable to contain 
bronze powders, pigments, and other metallic impurities, which exert a 
reducing action upon the nitrate of silver. There is, however, a better 
class of goods to be met with to which these objections do not apply, and 
it is suggested that the guarantee afforded by the name or stamp of the 
maker should be the guide in selecting articles of this description for 
photographic employment. 
Dr. Phipson proposes to measure the chemical action of the sun’s rays 
by the employment of molybdic acid, dissolved in sulphuric acid. On 
exposure to light this solution becomes coloured of a bluish green tint, due 
to the reduction of the molybdic acid to the state of an inferior oxide ; 
whilst the oxygen, liberated from the first-named compound, is said to 
unite with the elements of water, producing the binoxide of hydrogen. 
During the night this “ oxygenated water ” gives back the oxygen which 
has been withdrawn from its combination with molybdenum, and the 
mixture thus becomes again fitted to undergo the same chemical change by 
