1070 Traxsactioxs of the American Ikstitute. 



ment in tlie working quality of an old bath after long continued 

 exposure to sunlight. The old method of exposing for one or two 

 days, only served to begin the action which, if allowed to continue 

 by long exposure, produced changes which were unmistakably bene- 

 ficial. 



Mr. l^ewton said he had made some modifications in his developer 

 since giving the formula at the last meeting of the Section. lie 

 found that the gelatine was precipitated by the ammonia, when tho 

 solution was kept in the dark, therefore he had discontinued its use. 

 He also adds eight, instead of four grains, of tartaric acid, as given 

 in his formula. The developer was designed for dry plates only. 



j\Ir. Boyle suggested photographing clouds for the stereoscope by 

 the simultaneous work of two photographers located at somewhat 

 distant points, say one-eighth or one quarter of a mile, so as to be 

 able to signalize for exposure. 



After discussion and calculation, it was decided that tho proper 

 distance between the cameras should be about sixty feet. 



Mr. Chapman thought that the distance between the operatoi-s 

 should be greater than that suggested by Mr. Bayley, as the ordinary 

 stereoscopic camera gives good relief only to such objects as are 

 vrithin a distance of eighty rods.* 



Mr. D. C. Chapman then read the following paper : 



Preparations of Collobio-Bromide Plates. 



Mr. President and Gentlemen — The subject to which I wish to 

 call your attention for a few minutes this evening, is the preparation 

 of dry plates without a silver bath, the collodion being sensitized 

 before flowing upon the plate. Three years ago I tried this process 

 and had very fair success, but found that there was a marked differ- 

 ence between the compounds prepared at different times, but what 

 made that difference I was not then able to discover. 



This spiing, having occasion to use some dry plates, I again tried 

 this same process, with several kinds of preservatives, such as tannin, 

 gallic acid and sugar of milk. Gallic acid, acetate of lead and acetic 

 acid, as published by Mr. Cary Lee, also coffee and sugar of milk, as 

 used by Mr. Newton, and am decidedly in favor of the latter. 



The manner in which I work is as follows : 



To eight ounces of ether add ninety-six grains of gun cotton, one 

 huudred and twenty-eight grains of bromide of cadmium, thirty-two 

 grains of bromide of ammonium, and one ounce of alcohol. This 

 bromized collodion should stand three or four weeks, then carefully 



