28 



multiply the solutions, I take the ordinary chloride of gold, used 

 for fixing the impressions, and which is composed of I gramme of 

 chloride of gold, and 4 grammes of hyphosulphite of soda, to a 

 quart of distilled water. 



With respect to chloride of platinum, 2$ decigrammes must be 

 dissolved in three quarts of distilled water ; these two solutions 

 are mixed in equal quantities. 



Modus Operandi. 

 FIRST PREPARATION OF THE PLATE. 



Note. For the sake of brevity in the following description, I 

 will abridge the name of each substance. Thus, I will say, to 

 designate the aqueous solution of bichloride of mercury, sublimate ; 

 for the solution of cyanide of mercury, cyanide ; for the acidulated 

 oil of petroleum, oil ; for the solution of chloride of gold and 

 platinum, gold and platinum ; and for the oxide of iron, rouge 

 only. 



The plate is first polished with sublimate and tripoli, and after- 

 wards with rouge, until a beautiful black is arrived at. Then, the 

 plate is layed on the horizontal plate, and the solution of cyanide is 

 poured on it and heated over a lamp, as in fixing an impression 

 with chloride of gold. The mercury is deposited, and forms a 

 whitish layer. The plate is allowed to cool a little, and, after 

 having poured off the liquid, it is dried by rubbing with cotton 

 and sprinkling it with rouge. 



It is now necessary to polish the whitish layer deposited by the 

 mercury. With a piece of cotton steeped in oil and rouge, this 

 layer is rubbed until it becomes of a fine black. In the last place, 

 it may be rubbed very strongly, but with cotton alone, in order to 

 render the acidulated layer as thin as possible. 



The plate is afterwards placed on the horizontal plane, and Ihe 

 solution of gold and platinum is poured on. It is heated in the 

 ordinary manner ; it is then allowed to cool, the liquid is poured off, 

 and it is dried by gentle friction with cotton and rouge. 



This operation must be performed with care, especially when 

 the impression is not immediately continued ; for, otherwise, some 

 lines of liquid would be left on the plate, which it is difficult to 

 get rid of. After this last friction, the plates should be only dried, 

 and not polished. 



This concludes the first preparation of the plate, which may be 

 made a long time previously. 



