184 HISTORY OF PHOTOGRAPHY. 



or a basic salt which falls as a brownish-yellow pow^cler, has been the 

 principal cause wh_y it has not been so generally employed as the 

 gallic acid. This can be insured by adding a few drops of sulphuric 

 acid and some iron filings to the solution of the protosulphate of iron. 



THE CATALYSOTYPE. 



This process of Doctor Wood's is capable of producing pictures of 

 superior excellence. Owing to the inconstancy of the iodine com- 

 pounds, it is a little uncertain, but, care being taken to insure the 

 same degree of strength in the solutions, a very uniform good result 

 may be obtained. The process and its modifications are thus de- 

 scribed by the inventor: 



Let well-glazed paper (I prefer that called wove post) be steeped in water 

 to which hydrochloric acid has been added in the proportion of 2 drops to 3 

 ounces. When well wet, let it be washed over with a mixture of sirup of 

 iodine of iron, half a dram; water, 2A drams; tincture of iodine, 1 drop. 



When this has remained on the paper for a few minutes, so as to be imbibed, 

 dry it lightly with bibulous paper, and. being removed to a dark room, let it be 

 washed over evenly, by means of a camel-hair pencil, with a solution of nitrate 

 of silver, 10 grains to the ounce of distilled water. The paper is now ready 

 for the camera. The sooner it is used the better, as when the ingredients are 

 not rightl.v mixed it is liable to spoil by keeping. The time I generally allow 

 the paper to be exposed in the camera varies from two to thirty seconds ; in 

 clear weather, without sunshine, the medium is about fifteen seconds. With 

 a bright light the picture obtained is of a rich brown color; with a faint light, 

 or a bright light for a very short time continued, it is black. For portraits 

 out of doors, in the shade on a clear day. the time for sitting is from ten to 

 fifteen seconds. 



If the light is strong and the view to be taken extensive, the operator should 

 be cautious not to leave the paper exposed for a longer period than five or six 

 seconds, as the iiicture will appear confused from all parts being equally 

 acted OD. In all cases the shorter the time in which the picture is taken the 

 better. * 



When the paper is removed from the camera no picture is visible. However, 

 when left in the dark, without any other preparation being used, for a period 

 which varies with the length of time it was exposed and the strength of the 

 light, a negative picture becomes gradually developed until it arrives at a 

 state of perfection which is not attained, I think, by photography produced by 

 any other process.^ It would seem as if the salt of silver, being slightly 

 affected by the light, though not in a degree to produce any visible effect on it 

 if alone, sets up a catalytic action, which is extended to the salts of iron and 

 which continues after the stimulus of the light is withdrawn. The catalysis 

 which then takes place has induced me to name this process, for want of a 



"The picture when developed is not readily injured by exposure to moderate 

 light. It ought, however, to be fixed, which may be done by washing it with 

 a solution of bromide of potassium, 15 or 20 grains to the ounce, iodide of 

 potassium, 5 grains to the ounce. It may either be applied with a camel's-hair 

 liencil or by inniiersion. The picture must then be well washed in water to 

 remove the fixing material, which would cause it to fade by exposure to light. 



