trength of an extract, but he admitted it was occasionally very
valuable for detecting an admixture of extracts of other dyewoods,
such as quercitron bark extract in logwood extract. It was also a good
method of ascertaining the speed of dyeing and hence the relative
proportion of fully developed coloring matter of an extract.--_Jour.
Soc. Chem. Industry._

* * * * *

ORTHOCHROMATIC PHOTOGRAPHY.[1]

[Footnote 1: Read before the Photographic Association of
Brooklyn.]

By OSCAR O. LITZKOW.

What I want to show is the manner in which the process has been
tested. My employer, Mr. Bierstadt, has given me permission to show
you some samples, and also his chart containing the spectrum colors:
violet, indigo blue, green, yellow, orange, red, and black. This chart
has been photographed in the orthochromatic and also in the ordinary
way.

There are many ways of producing an orthochromatic effect; one is the
use of a glass tank placed behind or in front of the lens, in which a
coloring matter from either a vegetable or mineral product is placed;
this tank or cell is, however, only for use in the studio, as for
outdoor photography we have a colored glass screen, so as not to be
bothered with carrying colored solution.

The tank is constructed as follows: Procure two pieces of best white
plate glass, about 6 inches square; between these place a piece of
rubber of the same size square, and about 3/8 of an inch thick. In the
center of this rubber cut out a circle about 4 inches diameter, and
from one of the corners to the center of the circle cut out a narrow
strip 1/4 inch wide; this serves as the mouth of the tank. The two
pieces of glass and the rubber are cemented together with rubber
cement; then, to hold it firmly together, two brass flanges are used
as a clamp, with four screws at an equal distance apart; a thin sheet
of rubber is on the glass side of the flanges to prevent direct
contact with the glass, the center remaining clear for the rays of
light to pass through solution and glass.

One of the best orthochromatic effects made through this tank is with
a three-grains-to-the-ounce solution of bichromatic of ammonia or
bichromate of potassium. In this method there is no preparation used
on the plate. A common rapid dry plate is exposed through this
solution; the exposure, however, is about twenty times longer than it
would be if you removed the tank with the yellow solu