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Page 12
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 when ready
to use. But by putting mixture in dark bottle, and that in a tight box
impervious to light, it can be kept two or three weeks.
In some frames used at the School of Mines for making large blue
prints a similar device has been in use for several years. Instead,
however, of the heavy and cumbrous back used by Mr. Parsons, a light,
somewhat flexible back of one-quarter inch pine is employed, covered
with heavy Canton flannel and several thicknesses of newspaper. The
pressure is applied by light pressure strips of ash somewhat thicker
at the middle than at the ends, which give a fairly uniform pressure
across the width of the frame sufficient to hold the back firmly
against the glass at all points. This system has been used with
success for frames twenty-seven by forty-two inches, about half as
large as the one described by Mr. Parsons. A frame of this size can be
easily handled without mechanical aids. Care should be taken to avoid
too great thickness and too much spring in the pressure strips, or the
plate glass may be broken by excessive pressure. The strips used are
about five-eighths of an inch thick at the middle, and taper to about
three-eighths of an inch at the ends.
The formul� for the solution given by Whittaker, Laudy, and Parsons
are practically identical so far as the proportions of citrate of iron
and ammonia and of red prussiate of potash, 3 of the former to 2 of
the latter, but differ in the amount of water. Laudy's formula calls
for about 5 parts of water to 1 of the salts, Whittaker's for 4 parts,
and Parson's for a little more than 2 parts. The stronger the solution
the longer the exposure required. With very strong solutions a large
portion of the Prussian blue formed comes off in the washwater, and
when printing from glass negatives the fine lines and lighter tints
are apt to suffer. The blue color, however, will be deep and the
whites clear. With weak solutions the blues will be fainter and the
whites bluish. Heavily sized paper gives the best results. The
addition of a little mucilage to the solution is sometimes an
advantage, producing the same results as strength of solution, by
increasing the amount adhering to the paper. With paper deficient in
sizing the mucilage also makes the whites clearer.--_H.S.M., Sch. of
M. Quarterly._
* * * * *
HOUSE DRAINAGE AND REFUSE.
A course of lectures on sanitary engineering has been delivered during
the past few weeks before the officers of the Royal Engineers
stationed at Chatham, by Captain Douglas Galton, C.B., D.C.L., F.R.S.
The refuse which has to be dealt with, observed Captain Galton,
whether in towns or in barracks or in camp, falls under the following
five heads: 1, ashes; 2, kitchen refuse; 3, stable manure; 4, solid or
liquid ejections; and 5, rainwater and domestic waste water, including
water from personal ablutions, kitchen washing up, washings of
passages, stables, yards, and pavements. In a camp you have the
simplest form of dealing with these matters. The water supply is
limited. Waste water and liquid ejection are absorbed by the ground;
but a camp unprovided with latrines would always be in a state of
danger from epidemic disease. One of the most frequent causes of an
unhealthy condition of the air of a camp in former times has been
either neglecting to provide latrines, so that the ground outside the
camp becomes covered with filth, or constructing the latrines too
shallow, and exposing too large a surface to rain, sun, and air. The
Quartermaster-General's regulations provide against these
contingencies; but I may as well here recapitulate the general
principles which govern camp latrines. Latrines should be so managed
that no smell from them should ever reach the men's tents. To insure
this very simple precautions only are required:
1. The latrines should be placed to leeward with respect to prevailing
winds, and at as great a distance from the tents as is compatible with
convenience. 2. They should be dug narrow and deep, and their contents
covered over every evening with at least a foot of fresh earth. A
certain bulk and thickness of earth are required to absorb the
putrescent gas, otherwise it will disperse itself and pollute the air
to a considerable distance round. 3. When the latrine is filled to
within 2 ft. 6 in. or 3 ft. of the surface, earth should be thrown
into it, and heaped over it like a grave to mark its site. 4. Great
care should be taken not to place latrines near existing wells, nor to
dig wells near where latrines have been placed. The necessity of these
precautions to prevent wells becoming polluted is obvious. Screens
made out of any available material are, of course, required for
latrines. This arrangement applies to a temporary camp, and is only
admissible under such conditions.
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