. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. e understood from pre-ceding chapters ; any furtherremarks it is to be hoped willbe unnecessary, except that asheet of blackened card shouldbe interposed between theapparatus and the screen, soas to protect the latter fromall scattered light. This lastis the only objection to thearrangement, but is not greatif the condenser beam, mirror,&c, are carefully adjusted. Ifhowever it be at hand, pro-jections of this kind are bettershown, and more quicklyadjusted, with a vertical at-tachment, in cel
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. e understood from pre-ceding chapters ; any furtherremarks it is to be hoped willbe unnecessary, except that asheet of blackened card shouldbe interposed between theapparatus and the screen, soas to protect the latter fromall scattered light. This lastis the only objection to thearrangement, but is not greatif the condenser beam, mirror,&c, are carefully adjusted. Ifhowever it be at hand, pro-jections of this kind are bettershown, and more quicklyadjusted, with a vertical at-tachment, in cells resemblingfig. 117. Any demonstrator will beable from these hints toelaborate any number of ex-periments according to hisown requirements. The chiefpoint is to ascertain by trialo?i the screen the most effectivestrength for his various solu-tions. The phenomena of crystallisation, &c, belong to aprevious chapter, and those of electro-decomposition will betouched upon later. 133. Photography. — The formation, development, andfixing of a photographic image is rather an attractive lantern. Fig. 129—Vertical Projection CHEMISTRY 247 demonstration, and easily carried out by anyone practically ex-perienced in photography. A developing glass tank must beprovided of proper size, and the plate cut small enough to dipeasily into it. This plate should be a chloride plate and nota bromide, which is too opaque, while the chloride plate is alsoso much less sensitive as to be more manageable. A suitablenegative being provided, and superposed in a proper frame uponthe chloride plate, may be exposed in the parallel beam from thecondensers, time 5 to 15 seconds, according to the power ofthe jet. The developing tank is then placed in the stage, witha plate of ruby glass between it and the condensers, and aplate of glass with some black diagram being placed in it, inthe position the photographic plate will occupy, is being withdrawn, the plate is taken from the frame andplaced
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
