_On preserving the Sensitiveness of Collodion Plates._--_The Philosophical
Magazine_ of the present month contains a very important article by Messrs.
Spiller and Crookes upon this great desideratum in photographic practice.
We have heard from a gentleman of considerable scientific attainments,
that, from the few experiments which he had then made, he is convinced that
the plan is quite feasible. We of course refer our readers to the paper
itself for fuller particulars as to the reasoning which led the writers to
their successful experiment, and for all enumeration of the many advantages
which may result from their discovery. Their process is as follows:
"The plate, coated with collodion (that which we employ contains
iodide, bromide, and chloride of ammonium, in about equal proportions),
is made sensitive by immersion in the ordinary solution of nitrate of
{430} silver (30 grains to the ounce), and after remaining there for
the usual time, is transferred for a second solution of the following
composition:
Nitrate of zinc (fused) 2 ounces.
Nitrate of silver 35 grains.
Water 6 ounces.
The plate must be left in this bath until the zinc solution has
thoroughly penetrated the film (we have found five minutes amply
sufficient for this purpose, although a much longer time is of no
consequence); it should then be taken out, allowed to drain upright on
blotting-paper until all the surface moisture has been absorbed (about
half an hour), and then put by until required. The nitrate of zinc,
which is still retained on the plate, is sufficient to keep it moist
for any length of time, and we see no theoretical or practical reason
why its sensitiveness should not be retained as long: experiments on
this point are in progress; at present, however, we have only subjected
them to the trial of about a week, although at the end of that period
they were hardly deteriorated in any appreciable degree. It is not
necessary that the exposure in the camera should be immediately
followed by the development, as this latter process can be deferred to
any convenient opportunity, provided it be within the week. Previous to
development, the plate should be allowed to remain for a few seconds in
the original thirty-grain silver-bath, then removed and developed with
either pyrogallic acid or a protosalt of iron, and afterwards fixed,
&c. in the usual manner."
* * * * *
Replies to Minor Queries.
_Tippet_ (Vol. ix., p. 370.).--P. C. S. S. cannot help thinking that
_tippet_ is nothing more than a corruption, _per metathesia_, of
_epitogium_. Such, at least, seems to have been the opinion of old Minsheu,
who, in his _Guide to the Tongues_, 1627, describes it thus:
"A habit which universitie men and clergiemen weare over their gownes.
L. _Epitogium_, ab [Greek: epi] and _toga_."