put a piece of pasteboard of the same size on the back,
to protect the silvering, and stick around the edge in
the same manner as in putting up a picture. Take a sheet
of tin for the large size, or a half sheet for the other;
place the glass crosswise in the centre; bend the ends of the tin
over the edge of the glass and turn them back so as to form a groove
to hold the glass, and still allow it to slide out and in.
These ends of the tin must be turned out flaring, that they
may not reflect in the glass.

Have a tin band about an inch wide made to fit close on the end
of the camera tube; place it on, and taking the tin containing
the glass, bring it to an angle of forty-five degrees with the tube,
extending nearly the whole length of the glass in front of the lenses;
lap the loose ends of the tin on each side of the tin rim,
and having your camera turned on the side to throw the view lengthwise,
arrange the exact angle by examining the image on the ground-glass. When
you have it exactly right, hold it while it is soldered fast to the band.
Take out your glass and stain the tin black, to prevent reflection.



CHEMICALS.

CHAPTER III.

Bromine and its Compounds--Iodine and its Compounds--
Chlorine and its compounds--Cyanide of Potassium--
Hyposulphite of Soda--Hyposulphite of Gold--Nitric Acid--
Nitro-Muriatic Acid--Hydrochloric Acid--Hydrofluoric Acid--