ll. Musee de l'Industrie_.

[Illustration: SCHURICHTS FILTERING APPARATUS. Fig. 2.]

* * * * *

LARGE BLUE PRINTS.

By W.B. PARSONS, JR., C.E.

I send you a description of a device that I got up for the N.Y., L.E.,
and W.R.R. division office at Port Jervis, by which I overcame the
difficulties incident to large glasses. The glass was 58 inches long,
84 inches wide, and 3/8 inch thick. It was heavily framed with ash. In
order to keep the back from warping out of shape, I had it made of
thoroughly seasoned ash strips 1" x 1". Each strip was carefully
planed, and then they were glued and screwed together, while across
the ends were fastened strips with their grain running transversely.
This back was then covered on side next to the glass with four
thicknesses of common gray blanketing. Instead of applying the holding
pressure by thumb cleats at the periphery, it was effected by two long
pressure strips running across the back placed at about one quarter
the length of the frame from the ends, and held by a screw at the
center. The ends of these strips were made so as to fit in slots in
the frame at a slight angle, so that as the pressure strips were
turned it gave them a binding pressure at the same time. In other
words, it is the same principle as is commonly used to keep backs in
small picture frames. This arrangement, instead of holding the back at
the edges only, and so allowing the center to fall away from the
glass, distributed it evenly over the whole surface and always kept it
in position. The frame was run in and out of the printing room on a
little railway on which it rested on four grooved brass sheaves, one
pair being at one end, while the other was just beyond the center, so
the frame could be revolved in direction of its length without
trouble. In order to raise the heavy back, I had a pulley-wheel
fastened to the ceiling, through which a rope passed, with a ring that
could be attached to a corresponding hook at the side of the back, in
order to hoist it or lower it. Although that is an extremely large
apparatus, yet by means of the above device it was worked easily and
rapidly, and gave every satisfaction.

The solution used was of the same proportions as had been adopted in
the other engineering offices of the road:

Citrate iron and ammonium 1-7/8 oz.
Red prussiate potash (C.P.) 1-1/4 oz.

Dissolve separately in 4 oz. distilled water each, and mix