ulsion a good shaking, and when all bubbles have
subsided, pour it into the funnel, and it will go through in five
minutes. The filtered emulsion will be found to be a soft, smooth, creamy
fluid, flowing easily and equally over the plates. Coat with it six
plates in succession, and place each, as you coat it, into the water. By
the time the sixth is in, the first will be ready to come out. Take it
out, see that all greasiness is gone, and place it in the preservative,
going on till all the plates are so treated.

A very handy way of drying is to have a flat tin box of the usual hot
plate description, which fill with hot water, then screw on the cap; on
this flat tin box place the plates to dry, which they will do rapidly;
when dry, store away in your plate box, and you will have a supply of
really excellent dry collodion plates.

Just a word as to the preparation of the glasses before coating. It is
very generally considered that it is better the glasses receive either a
substratum of albumen or very weak gelatine. I use the latter on account
of the great ease of its preparation. After your glasses are well
cleaned, place them in, and rub them with a weak solution of hydrochloric
acid of the strength of 2 ounces acid to 18 ounces water.

Prepare a solution of gelatine 1 grain to the ounce of water, rinse the
plate after removal from the acid mixtures, and coat twice with the above
gelatine substratum; the first coating is to remove the surplus water,
and should be rejected. Rear the plates up to drain, and dry in a plate
rack or against a wall, and be careful to prevent any dust adhering to
the surface while wet.

Having now described the plates I intend to use, let us next consider
what a transparency is, that we may understand the nature of the work we
are undertaking. You are all aware that if we take a negative, and in
contact with it place a sheet of sensitized paper, we obtain a positive
picture. Substitute for the paper a sensitive glass plate, and we obtain
also a positive picture, but, unlike the paper print, the collodion or
other plate will require to be developed to bring the image into view.
Now this is what is termed making a transparency by contact. It often
happens, however, that a lantern slide 31/4 by 31/4 has to embrace the whole
of a picture contained in a much larger negative, so that recourse must
be had to the camera, and the picture reduced with the aid of a short
focus lens to within the lant