TRANSACTIONS OP THE SECTIONS. 37 



drachm, of water two and a half drachms, and of iodine one or two drops ; mix. When 

 it has remained wet for a little time let it be dried lightly with bibulous paper, and 

 brashed over again with the same mixture ; let it be again dried with the bibulous 

 23aper, and being removed to a dark room, let it be washed evenly over with a solution 

 of nitrate of silver — twelve grains to the ounce of water. The iodide of silver which 

 is formed should be disturbed as little as possible by the camel's hair pencil with which 

 the nitrate of silver is laid on. The paper is now ready for use ; the sooner it is used the 

 better, as when the ingredients are not rightly proportioned it is liable to be spoiled 

 by keeping. I have obtained pictures with it when prepared for twelve hours, but I 

 have not tried it after having kept it for a longer period. The time I generally allow the 

 paper to be exposed, when used in the camera, varies from one second to half a minute 

 in clear weather. With a bright light the picture obtained is of a rich brown colour ; 

 with a faint light, or a bright light for a short time continued, it is black. If the 

 paper be left exposed for too long a time the minute parts of the picture are confused. 

 For taking portraits in the shade out of doors on a clear day, fifteen seconds will be 

 the time for sitting. When the paper is removed from the camera, no picture is 

 visible ; however, when left in the dark for some time, the duration of which will vary 

 with the time it was exposed to light, it gradually developes itself, until it arrives at a 

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

 other process. The action set up by the light is continued in the dark, an electro- 

 lysis taking place by which the picture is brought out ; and for this reason I have 

 ventured to name the process, for want of a better word, the Electrolysotype. Sir J. 

 Herschel observed long ago this fact of the action of light continuing after its influence 

 is apparently removed, especially in the salts of iron ; but I do not know of any pro- 

 cess being employed for photographic purposes which depends on this action for its 

 development except my own. The pictures are fixed by first steeping them well in 

 water, then in a solution of bromide of potassium, twenty grains to the ounce ; and 

 then again in water, to remove the bromide from the paper. 



If the acid solution is too strong, it impairs the sensibility of the paper. If the ni- 

 trate of silver solution is too strong, the paper blackens in the dark after having been 

 for some time kept ; if too weak, it remains yellow, even though exposed to the light. 

 If the ioduret of iron is in too great quantity, the picture becomes dotted over with 

 black spots in the dark, which are rapidly bleached by the light. 



Of the specimens exhibited. No. 1 was a paper darkened by the moonlight in fifteen 

 minutes. 



On Photography. By Professor Grove. 



Mr. Grove communicated experiments he Ijad made with some success in obtaining a 

 paper capable of giving positive photographs by one process, and avoiding the necessity 

 of transfer, by which the imperfections of the paper are shown. As light favours many 

 chemical actions, Mr. Grove thought that a paper darkened by the sun (which dark- 

 ening is supposed to result from the precipitation of silver), might be bleached by using 

 a solvent which would not attack the silver in the dark, but would do so in the light. 

 Among other acids tried, nitric acid succeeded best. Thus a darkened calotype paper 

 is re-iodized by iodide of potassium, and then drawn over dilute nitric acid, one part 

 acid to two and a half water ; when so prepared it is rapidly bleached by exposure to 

 light, and perfectly fixed by washing in water and dipping in hyposulphite of soda, or 

 bromide of potassium, if tlie acid be strong, say one-half water, the paper will be 

 bleached in ten seconds by the sun, but then it partially bleaches in the dark. 



Mr. Grove showed some lithographs copied by this process ; but stated, that in the 

 very few trials he had made with the camera the images had not been clear; that 

 he had then tried the following method : — Let an ordinary calotype image or portrait 

 be taken in a camera and developed by gallic acid, then drawn over iodide of potas- 

 sium and nitric acid, and exposed to full sunshine ; while bleaching the dark parts, 

 the light is re-darkening the newly precipitated iodide in the lighter portions, and thus 

 the negative picture is converted into a positive one. It is, however, faint, and gallic 

 acid will not develope it; possibly some other solutions, such as those of iron, may; 

 but Mr. Grove had not had time to try them. He believed from what he had ob- 

 served, that a great many cases would be found in which a negative picture might be 

 changed to a positive one, and that in some of these very good positive eiFects would 

 probably be obtained. 



