. The microscope; an introduction to microscopic methods and to histology. Microscopes. 240 PHOTO-MICROGRAPHY [CH. VIlI tincture of iodine, nitric acid in various degrees of strength, hydrochloric acid, etc., are used or one may use electricity, the metal being immersed in an indiffer- ent liquid. See numerous articles in the Metallographist for methods and micro- graphs. After the etching, the surface should be washed well with water to remove the etcher. Le Chatelier recommends that the etched surface when dry be coated with a very thin coating of collodion to avoid tarnishing. The preparati
. The microscope; an introduction to microscopic methods and to histology. Microscopes. 240 PHOTO-MICROGRAPHY [CH. VIlI tincture of iodine, nitric acid in various degrees of strength, hydrochloric acid, etc., are used or one may use electricity, the metal being immersed in an indiffer- ent liquid. See numerous articles in the Metallographist for methods and micro- graphs. After the etching, the surface should be washed well with water to remove the etcher. Le Chatelier recommends that the etched surface when dry be coated with a very thin coating of collodion to avoid tarnishing. The preparation will then last for several months untarnished. I 387. Mounting the Preparations of Metal.—In order to get a satisfactory image the flat, polished and etched face should be at right angles to the optic axis. For preliminary observation one can approximate this by mounting the specimen on a piece of beeswax. (Behrens). Very elaborate arrangements of the stage have also been devised (Reichert). A simple and effective device is shown in Fig. 193 in which the specimen is held against the under side of the plane face of the stage attachment. Rubber bands answer well to support the metal, and only one side need be flat. § 388. Photographing Opaque Objects.—The general directions given in § 347 should be followed with the necessary modifications. The time of exposure is usually considerably greater with opaque objects than with transparent ones. Very few such objects can be photgraphed in less than 30 seconds, even with day- light For metallic surfaces and magnifications of 100, 150, 250 to 500, with the electric arc light as illuminant the time required for favorable objects is I, 2, 4 and 7 seconds ; with the Wellsbacb lamp the time is 5, 10, 30 and 60 minutes (Sauveur).. Fig. 194. Rack for drying negatives (Rochester Opt. Co). Fig. 194. References to Ch. VIII. See the works and journals dealing with photography. For Photo-Micrography see Pringle, Bousfield, Neuhauss, Sternb
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