. The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass. Fig. 43. THE DARK ROOM. 93 of cast iron. The latter is best for large is apt to be suspicious of trusting a silversolution in an iron vessel, even when enamelled, butthese basins are certainly in use in many of thelargest establishments without any disadvantage beingknown. The porcelain basins are undoubtedly themost cleanly, and a careful worker will prefer them. To determine when the bath has been boiled downto the right strength, it is a good plan to have a specificgravity bulb.
. The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass. Fig. 43. THE DARK ROOM. 93 of cast iron. The latter is best for large is apt to be suspicious of trusting a silversolution in an iron vessel, even when enamelled, butthese basins are certainly in use in many of thelargest establishments without any disadvantage beingknown. The porcelain basins are undoubtedly themost cleanly, and a careful worker will prefer them. To determine when the bath has been boiled downto the right strength, it is a good plan to have a specificgravity bulb. This is graduated to float in a givenstrength of solution. The bulb is thrown in when theboiling commences, and when it comes to the surfaceand remains floating it is known that the operation iscompleted. The specific gravity of a freshly made silver bath of. Fig. 44. the correct strength, namely, thirty-five grains to theounce, will be about ro6g, and when boiled down tohalf strength it will be 1-035, so that the latter 1S thefigure the bulb should be chosen for. 94 THE HALF-TONE PROCESS. In the colonies and in country districts where a supplyof distilled water is not easily obtainable, a still will befound a good investment for obtaining a supply of purewater for the bath. There are several very cheappatterns on the market for the purpose, the orthodoxform being as fig. 44. A small laboratory Bunsen burner is a useful ac-cessory in or near the dark room for rapidly drying offnegatives, warming negatives for varnishing, warmingsolutions, etc. A couple of plate racks, one for the clean glass andthe other for finished negatives, are necessary, and mostoperators believe there has been nothing better inventedthan the old fashioned V-shape folding rack, but itshould be of a substantial pattern. The V-shape madefixed (non-folding) is the best i
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