The Daguerreotype and its Applications. 141 



hour; one of American manufacture, an hour or longer ; and if 

 it assumed a yellow coat in burning, it should not be placed in 

 the camera for several hours. 



The possibility of obtaining impressions on an iodized surface 

 in any kind of weather, has been amply demonstrated. Gene- 

 rally, however, to obtain proofs successfully, a dry atmosphere, 

 a pure white light, and a clear blue sky, are required. Attempts 

 made to obtain them the day after one of rain, — when snow is 

 melting rapidly,— or when the sun's light is of a yellowish tint, 

 will generally be fruitless. The proofs taken with the light of a 

 yellowish cast, are frequently black. 



In removing the sensitive coat, care should be taken not to em- 

 ploy the same solution too long. If it remains unchanged, mer- 

 cury is liable to be precipitated from it on the proof, producing 

 unsightly spots. The method of removing the iodine introduced 

 by Prof Draper, is now generally abandoned, in consequence of 

 the tarnishing of the proof after a time. The plate being placed 

 in a weak solution of common salt, becomes one of the elements 

 of a galvanic pair, if it is touched under the fluid with another 

 metal. The iodine is apparently entirely removed by touching 

 successivel^r its corners with a clean piece of zinc. Distilled, or 

 even rain water, is unnecessary in the last washing, if a little dex- 

 terity is employed in the manipulations. Immediately after pour- 

 ing the water on the proof, one corner is dried in the flame of a 

 spirit lamp ; this is seized by a pair of forceps, and the plate held 

 in an inclined position over the flame, the operator at the same 

 time blowing over the surface of the plate, A film of water can 

 in this way be made to traverse the whole length of the proof, 

 leaving it free from stains or dirt. If any stain remains it will be 

 on a corner, or an edge of the plate, and can be easily concealed 

 by the mounting of the frame. A process has recently been em- 

 ployed in France which fixes the picture and changes its color ; 

 it also removes the unpleasant reflection from the silver surface, 

 and renders the use of glass protectors unnecessary. A gramme 

 of neutral chloride of gold, and three grammes of hyposulphite 

 of soda, are dissolved in half a litre of water, i. e. one pint. The 

 plate having the view on it, supported, by a wire frame, has some 

 of the liquid poured evenly over its surface ; heat is then applied 

 from below by a spirit lamp, with a large wick. The view pre- 

 sently turns dark ; it should then be removed and well washed 



