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Updated: May 23, 2025
Bichromate prints can be made on albumenized paper by floating it on the solution, and by using a saturated solution of protosulphate of iron and a saturated solution of gallic acid. Very fine prints can be so produced nearly equal to silver prints, and at somewhat less cost, but with a little or no saving of time or labor. Chief Proof Solution.
By producing a "photo-relief" in gelatine sensitised with bichromate of potash, and afterwards exposed first to the sun and then to the action of water an impression in plastic material can be secured, from which, with the use of warm, thin, pigmented gelatine, a hundred copies or more can be printed off in a few minutes.
From four to six cells of a bichromate battery or Faure secondary battery furnish sufficient power to run the machine at a high speed.
Dissolve the bichromate in distilled water, transfer the solution to a liter bottle, and dilute to approximately 1000 cc. Shake thoroughly until the solution is uniform. Transfer the solution to a liter bottle, add 5 cc. concentrated sulphuric acid, make up to about 1000 cc. and shake vigorously to insure uniformity.
Before passing on to consideration of the petrol-driven type of engine, it is necessary to accord brief mention to the dirigible constructed in 1884 by Gaston and Albert Tissandier, who at Grenelle, France, achieved a directed flight in a wind of 8 miles an hour, obtaining their power for the propeller from 1 1/3 horse-power Siemens electric motor, which weighed 121 lbs. and took its current from a bichromate battery weighing 496 lbs.
An ordinary negative picture is taken, and then impressed on a gelatine plate sensitised with bichromate of potash. The parts of the gelatine in light become insoluble, while the parts in shade can be washed away by water.
In Fuller's bichromate cell the zinc is amalgamated with mercury, which is kept in a pool beside it by means of a porous pot. The "plates" are a little rod or pencil of zinc Z, and a strip or wire of silver S, coated with chloride of silver and sheathed in parchment paper.
It was operated by a motor driven by a bichromate of soda battery. The motor weighed 121 lbs. The cells held liquid enough to work for 2-1/2 hours, generating 1-1/3 horse power. The screw had two arms and was over nine feet in circumference. Tissandier made some successful flights. The first dirigible balloon to return whence it started was that known as La France.
Mareschal's system, bichromate of potassa piles may be utilized in a large number of cases where a light of but short duration is required until the battery is exhausted, without the tedious maneuvering of a winch and without inconvenience. The jack permits of a large number of lightings and extinctions being effected before it becomes necessary to wind up its clockwork movement.
As in the case of the bichromate process, it is necessary to reduce the iron completely to the ferrous condition before titration. The reducing agents available are zinc, sulphurous acid, or sulphureted hydrogen. Stannous chloride may also be used when the titration is made in the presence of hydrochloric acid.
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