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solution and acid

PYROCATECHIN (Formula, C,H, (OH), ; synonyms. catechol, oxypjecnic acid, brenexatechin, pyromorintannic acid).—Obtained by the dry distillation of catechu extracted from the inner bark wood of the Acacia catechu, and also from Kino, another similar extract. The leaves of the Virginia creeper contain pyrocatechin. It is also obtained by fusing phenol-sulphonatic acid with caustic potash, and is present in crude pyroligneous acid, distilled from wood.

Pyrocatechin crystallizes in quadratic prisms soluble in water, alcohol, and ether. They fuse at C , and boil at 245° C. In presence of alkalies it absorbs oxygen from the air, and becomes brown. Nitric acid oxidises it to oxalic acid. It is a reducing agent, and for this reason has been recommended as a developer for dry plates.

The first investigator was M. Benoist, who published his formula in La Nature, as follows: To develop a io x 8 plate take 1 c.c. of A solution and from five to ten c.c. of B in about 7o

c.c. of water. For instantaneous drop-shutter work, more of solution A must be used.

Dr. Eder speaks highly of this developer, but notifies the importance of obtaining pure pyrocatechin. His formula is: For use, mix one volume of A with two volumes of B.

The advantages claimed for this developing agent are—freedom from fog, non-actinicity of solution, simplicity in preparation, high energy at low temperature, and a negative color that facilitates printing. According to Dr. Arnold, the plates lose their sensitiveness to light as soon as they are immersed in the developing solution, and may be developed at a distance of twenty inches from a gas flame, or in weak daylight. Further, the solution does not stain the fingers.