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256 THE ADVANCE OF PHOTOGRAPHY
fully brushed to remove any dust, and then placed into the dish. The development which takes place in this solution must be allowed to continue for five minutes, and, of course, produces a negative. Before commencing this it is necessary to have prepared a second bath in which the deposited silver can be dissolved. The stock solution for this is : —
Distilled water . . 1000 c.c.
Bichromate of potash . 8 gms.
Sulphuric acid . . . 12 c.c.
After developing, the negative should be washed for about twenty seconds and then put into a second dish containing about 100-150 c.c. of the second stock solution. The plate having been placed in this bath, while still in total darkness, the subsequent operation should be carried out in ordinary daylight if possible. The plate should be rocked while in this bath and should be kept in it about two minutes. It should then be removed and washed for about half a minute in order to get rid of the bichromate. After this operation place the plate again into the first bath which was used to develop it, and leave it there for about three minutes. In the second development all the bromide of silver which up to that time has been unattacked will turn black, and the negative will by this means be transformed into a positive. After this second development, and washing it in running water for half a minute, the plate may be fixed if desired by placing it for three or four minutes in a bath of the following composition : —
Water .... 1000 c.c.
Sodium hypo-sulphite . 120 gms.
Sodium meta-bisulphite . 30 gms.
After this it should be washed in running water for twenty to thirty minutes before drying. All the various baths should be used at an even temperature of about 65° F.