r a sheet of glass. The length of exposure varies with the state
of the weather from 15 to 30 seconds in summer to from 40 to 70 seconds
in winter, in full sunlight. In the shade, in clear weather, 2 to 6
minutes, and in cloudy weather, 15 to 40 minutes may be necessary. The
printing may also be done by electric light. The print is now immersed
in a bath consisting of 15 to 18 parts of prussiate of potash per 100
parts of water. Those parts protected from the light by the lines of the
drawing immediately turn blue, while the rest of the paper, where the
coating has been converted into protochloride by the effects of light,
will remain white. Next, the image is freely washed in water, and then
passed through a bath consisting of 8 to 10 parts of hydrochloric acid
to 100 parts of water, for the purpose of removing protoxide of iron
salt.

It is now again washed well in clean water and finally dried, when the
drawing will appear in blue on a white background.--_Proc. Eng. Club,
Phila._

* * * * *

[PROCEEDINGS OF THE ENGINEERS' CLUB OF PHILADELPHIA.]

RELATIVE COSTS OF FLUID AND SOLID FUELS.

[Footnote: Read June 20, 1885.]

By JAMES BEATTY, JR., Member of the Club.

During the past twenty-five years there have been numerous efforts to
introduce fluid fuels as substitutes for coal, for the evaporation of
water in boilers, metallurgical operations, and, on a small scale, for
domestic purposes.

The advantages claimed for these fuels are: Reduction in the number of
stokers, one man being able to do the work of four using solid fuel.
Reduction in weight, amounting to one-half with the better classes.
Reduction in bulk; for petroleum amounting to about thirty-six per
cent., and with the gases, depending on the amount of compression. Ease
of kindling and extinguishing fires, and of regulation of temperature.
Almost perfect combustion and cleanliness.

Siemens used gas, distilled from coal and burnt in his well known
regenerative furnace.

Deville experimented with petroleum on two locomotives running on the
Paris and Strassburg Railroad.

Selwyn experimented with creosote in a small steam yacht, and under the
boilers of steamship Oberlin.

Holland experimented with water-gas in the furnace of a locomotive
running on the Long Island Railroad.

Isherwood experimented with petroleum under the boilers of United States
steamers.

Three railroads in Russia are using naphtha in