vessel; B, the crank driving the pumps;
C, a pump with piston in position; D, delivery tube of the pump; E,
the silver guide plate to conduct the emulsion down to the glass; F,
the spreading cylinder; G, the cords regulating the distance of the
cylinder from the glass plates; H, soft camel's hair brush; K,
friction roller; L L L, three plates passing under the emulsion tank;
M, knife edged wheels in the hot water tank, N; the "plucking roller,"
P, has a hot water tank of its own, and travels at slightly greater
speed than the other rollers; R is the beginning of the cooling bands;
T, the driving cords; and W, a level of the emulsion in the trough. Y
represents one of the bucket pistons of the pumps, detached. The
construction of the crank itself is such that, by adjustment of the
connecting rods, more or less emulsion may be put upon the plates. Mr.
Cowan, however, intends to adjust the pumps once for all, and to
regulate the amount of emulsion delivered upon the plates by means of
driving wheels of different diameters upon the cranks.

[Illustration: Fig. 10.]

Fig. 10 is a section of the hollow spreading cylinder, made of sheet
silver as thin as paper, so that its weight is light. For coating
large plates it is divided in the center, so as to adapt itself
somewhat to irregularities in the surface of each plate. In this case
it is supported by a third and central thread, as represented in the
cut. Otherwise the cylinder would touch the center of the plate. Its
two halves are held together by a slip of India rubber.--_The
Engineer_.

* * * * *

THE USE OF AMMONIA AS A REFRIGERATING AGENT.[1]

[Footnote 1: Paper lately read before the Civil and Mechanical
Engineers' Society.]

BY MR. T.B. LIGHTFOOT, M.I.C.E.

Within the last few years considerable progress has been made in the
application of refrigerating processes to industrial purposes, and the
demand for refrigerating apparatus thus created has led to the
production of machines employing various substances as the
refrigerating agent. In a paper read by the author before the
Institution of Mechanical Engineers, in May, 1886, these systems were
shortly described, and general comparisons given as to their
respective merits, scope of application, and cost of working. In the
present paper it is proposed to deal entirely with the use of ammonia
as a refrigerating agent, and to deal with it in a more full and
comprehensi