The following process for making photographic copies of drawings in blue lines on white background was invented by H. Pellet, and is based on the property of perchloride of iron of being converted into protochloride on exposure to light. Prussiate of potash when brought into contact with the perchloride of iron immediately turns the latter blue, but it does not affect the protochloride.
A bath is first prepared consisting of ten parts perchloride of iron, five parts oxalic or some other vegetable acid, and one hundred parts water. Should the paper to be used not be sufficiently sized, dextrine, gelatine, isinglass, or some similar substance must be added to the solution. The paper is sensitized by dipping in this solution and then dried in the dark, and may be kept for some length of time. To take a copy of a drawing made on cloth or transparent paper, it is laid on a sheet of the sensitive paper, and exposed to light in a printing frame or under 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.[1]
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.