. The book of photography; practical, theoretical and applied. tly, more work may be done,and a greater amount of silver reduced,in the same time, or by the expenditureof the same energy ; therefore, the platebecomes more rapid. As this is a pointthat will be dealt with in a later sectionof the book, nothing further need be saidon the subject, except that attention maybe called to the fact that a similar ex-planation may be given as to why theproportion of emulsion on the plate affectsthe sensitiveness. Weighing. Tliis nuist be done with extreme accur-acy. The rough sort of weighing practisedb
. The book of photography; practical, theoretical and applied. tly, more work may be done,and a greater amount of silver reduced,in the same time, or by the expenditureof the same energy ; therefore, the platebecomes more rapid. As this is a pointthat will be dealt with in a later sectionof the book, nothing further need be saidon the subject, except that attention maybe called to the fact that a similar ex-planation may be given as to why theproportion of emulsion on the plate affectsthe sensitiveness. Weighing. Tliis nuist be done with extreme accur-acy. The rough sort of weighing practisedby many photographers is only likely tQ 62 THE BOOK OF PHOTOGRAPHY. lead to disaster. A chemical balance,the pattern shown in either Fig. 128 orFig. 129 being quite suitable for thispurpose, should be employed in prefer-ence to those in general use. It neednot, however, possess the extreme deli-cacy of adjustment of the best of sucliinstruments. Place filter paper on the panof each scale. Having weighed out the sub-*i>tances, place ^ach aside on a separate. Fig. 130.—BoiLiXG Tdbe paper ; be careful not to get them mixed,although there should be no fear of doingso, except perhaps in the case of thegelatine, as the silver nitrate and potas-sium bromide are easily distinguishablecrystals, the former occurring in flakes andthe latter in cubes. In using a balanceof the above kind, the substance should beplaced upon the scales and then the armgently raised. If the pointer indicates toomuch or too little, the arm should belowered before the alteration is 240 grains need not be weighed upat the present time. The other gelatineshould be of a soft variety. Nelsons No. 1being very suitable. Silver nitrate shouldbe recrystallised and absolutely pure,while the same remark applies to thepotassium bromide ; needless to say, dis-tilled water should be used throughout theoperation. a little water on the gelatine, con-tained in a beaker or a jam jar, rinse round rapi
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