ADBOLT as to my meaning. I have very rarely any "spottings"
in my pictures; but I always drop the plates once or twice into the
bath, after the two minutes' immersion, to wash off any loose particles.
I also drain off all I can of the nitrate of silver solution before
placing the glass in the camera, and for three reasons:--1. Because it
saves material; 2. Because the lower part of dark frame is kept free
from liquid; 3. Because a "flowing sheet" of liquid must interfere
somewhat with the passage of light to the film, and consequently with
the sharpness of the picture. I think it is clear, from MR. SHADBOLT'S
directions to MR. MERITT, that it is no very easy thing to cement a
glass bath with marine glue.

J. L. SISSON.

_Colouring Collodion Pictures_ (Vol. vii., p. 388.).--In your impression
of April 16, there is a typographical error of some importance relative
to lifting the collodion in and out of the bath: "The plate, after being
plunged in, should be allowed to repose quietly from twenty to thirty
_minutes_," &c. This should be _seconds_. The error arose, in all {415}
probability, from my having used the contractions 20" to 30".

It may appear somewhat droll for any one to answer a question on which
he has _not_ had experience; but I beg to offer as a _suggestion_ to
PHOTO, that if he wishes to use collodion pictures for the purpose of
dissolving views, he should first copy them in the camera as transparent
objects so as to _reverse_ the light and shade, then varnish them with
DR. DIAMOND'S solution of amber in chloroform, when they will bear the
application of transparent colours ground in varnish, such as are used
for painting magic-lantern slides.

GEO. SHADBOLT.

_Gutta Percha Baths_ (Vol. vii., p. 314.).--In "N. & Q." for March 26, I
ventured to recommend to H. HENDERSON gutta percha, as a material for
nitrate of silver baths. I did this from a knowledge that hundreds of
them were in use, but chiefly because I have found them answer so well.
In the same Number the Editor gives MR. HENDERSON very opposite advice;
and, had I seen his opinion before my notes appeared, I should certainly
have kept them back. But it is, I think, a matter of some importance,
especially to beginners, to have it settled, whether gutta percha has
the effect of causing "unpleasant markings" in collodion pictures or
not. With all due deference to the Editor's opinion, I do not believe
that gutta percha baths are injurious to th