of acidulated
water; the cotton is divided into parcels and allowed to dry in the open
air until it feels dry to the touch, though in this condition it still
contains 20 per cent. of water. It is next inclosed in a covered jar,
which is heated to a temperature of 65 deg. C.; the desiccation therefore
takes place in the closed space, and the conversion of the material
is completed in about two or three hours. In this way a very perfect
hydro-cellulose is obtained, and in the best form for producing
excellent pyroxyline.--_Corresp. Photo Mews_.
* * * * *
PHOTO TRACINGS IN BLACK AND COLOR.
Two new processes for taking photo tracings in black and color have
recently been published--"Nigrography" and "Anthrakotype"--both of which
represent a real advance in photographic art. By these two processes we
are enabled for the first time to accomplish the rapid production of
positive copies in black of plans and other line drawings. Each of
these new methods has its own sphere of action; both, therefore, should
deserve equally descriptive notices.
For large plans, drawn with lines of even breadth, and showing no
gradated lines, or such as shade into gray, the process styled
"nigrography," invented by Itterbeim, of Vienna, and patented both
in Germany and Austria, will be found best adapted. The base of this
process is a solution of gum, with which large sheets of paper can be
more readily coated than with one of gelatine; it is, therefore, very
suitable for the preparation of tracings of the largest size.
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