A Manual Of Photography

TO DEVELOPE THE IMAGE FORMED ON THE PLATE. 249 card-board, where it is not operated on. The plate is sustained a little above the charged cotton by frames of hard wood var- nished with gum lac. By increasing the distance between the cotton and the plate, or the contrary, we are enabled to suit the arrangement to the temperature of the season, and thus always operate with facility and promptitude. M. Seguier also states, that a single scouring with tripoli, moistened with acidulated water, is sufficient to cleanse the plates thoroughly, and does away with the tedious process of scouring with oil, and afterwards the operation of heating the tablet over a spirit lamp. M. Soliel lias proposed the use of the chloride of silver to determine the time required to produce a good impression on the iodated plate in the camera. His method is to fix at the bottom of a tube, blackened within, a piece of card, on which chloride of silver, mixed with gum or dextrine, is spread. . The tube thus disposed is turned towards the object of which we wish to take the image, and the time that the chloride of silver takes to become of a grayish slate colour will be the time required for the radiations in the camera to produce a good effect on the iodated • silver. These remarks have been introduced as supplementary to the generally approved modes, as they are suggestive in them- selves of still further improvements. Section IV.—To Develops the Image formed on the Plate. The plate, prepared by one of the methods directed, has been placed in the camera, and the image impressed upon it. The more important points to be attended to form the subject of a separate chapter. The image is developed on the daguerreotype plate, as has been already described, by the use of mercurial vapour. In the original process (Big. 10) one form of a mercurial vapour box is given ; and Big. 66, d, represents another. It matters little in what manner the plate is placed in the mercurial bath; the mercury should be volatilized very slowly, and the image allowed to have its full development before it is removed from the box. Care should be taken that the operator avoids as much as possible contact with the mercurial vapour, since continued exposure to its influence might lead to serious inconvenience. M. Claudet has adopted a most admirable arrangement in this respect, as is shewn in the woodcut on the following page.