11 



pressing the plate hard and evenly against it, and changing the 

 direction frequently, bnt always ending by polishing in a direction 

 which will cross the picture you wish to obtain upon it ; that is, 

 if the plate is to be placed upright in the camera, finish it 

 from side to side, and vice versa. The last polish should be given 

 a short time before the plate is to be used ; and any dust which 

 may remain on it should be removed carefully, holding the plate 

 in an inverted position, wth a piece of cotton or a camel's hair 

 pencil, just before the process of iodizing. 



IODIZING THE PLATES. 



The best way of securing an even coat of iodine on the plate, is 

 to use the chloride of iodine, diluted with water, two or three 

 drops to an ounce, until it assumes the colour of pale sherry. A 

 little of this mixture being poured into the trough, (described p. 7) 

 sufficient to cover the bottom to about a quarter of an inch in 

 depth ; the plate must then be placed in the frame, and carefully 

 put over this solution to expose it to its vapour : in about a minute 

 and a half, or two minutes, according to the temperature of the 

 atmosphere, the plate will be found, on inspection, to have acquired 

 a yellow tint, which will vary from a pale to a rich golden tint, 

 according to the time the plate is allowed to remain in contact with 

 the vapour. This degree of intensity must be varied, to suit the 

 quality of the accelerating liquid employed, as will presently be 

 explained ; but care must be taken that the tint on the plate does 

 not pass to the violet, or its sensitiveness will be diminished. The 

 colour of the plate may be inspected, by raising it and turning it 

 towards a white light, replacing it quickly on the trough. When 

 sufficiently iodized, it may be laid aside in the frame with its face 

 downwards, without injury. The same mixture may be used again 

 several times ; but it is better to renew it after each time of prepa- 

 ration. Iodine strewed at the bottom of the trough, and covered 

 with fine sand, may replace the chloride mixture, and will last much 

 longer, if carefully covered after use with an air-tight glass or 

 slate cover. 



ACCELERATING LIQUIDS. 



There are many varieties of these known by the names of Eau 

 Bromee, Bromide of Iodine, Redman's Sensitive Solution, Hunga- 

 rian Liquid, etc., etc. The two latter are much used in England, 



