Photographical Section Pboceedixgs. 1107 



•dry plate. Experiments have not been made with a view of finding 

 something which would keep a plate longer than tannin, but to iind 

 something which was as good a preservative as tannin, and at the same 

 time possessed qualities which would enable it to retain its sensitive- 

 ness. A number of experimenters claim to have succeeded in pro- 

 ducing such plates. I have tried almost every published formula, and 

 I have no hesitation in saying, that there are a large number of form- 

 ulas which will, if carefully worked, produce plates superior in every 

 respect, to tannin plates. 



The keeping qualities, of course, can only be decided by time ; it 

 is a fair inference, however, that if a plate will keep through the 

 summer months without suft'ering any detrimental change, that it is 

 good for a year. The coffee plates have been kept two years without'- 

 .showing any change, which is much longer, under ordinary circum- 

 stances, than would ever be required. After a plate lias kept well 

 for a year, the fact that it will keep another year adds nothing to its 

 value. As I have previously observed, the object of those experi- 

 menting with dry plates has been to discover something that would 

 make them approximate as near as possible in their sensitiveness to 

 wet ones. The great drawback to the tannin plates has been their 

 lack of sensitiveness. About a year since, the use of the acetate of 

 morphia was introduced as a preservative, but it proved to be only a 

 sensitiver, and without any of the qualities requisite for a preserva- 

 tive. Plates prepared with it were very nearly as sensitive as wet 

 ■ones, but they kept no longer, if they did as long, than when they 

 were simply washed. I tried it also for paper negatives with the 

 same results. The idea came to me, that by combining the acetate 

 of morphia with tannin, I might retain the sensitive qualities of the 

 morphia, and the keeping qualities of the tannin, I made a few 

 plates, and kept them several weeks ; they showed no signs of 

 change, and were as sensitive as those prepared with morphia only ; 

 and I exhibited some negatives made on those plates to this society, 

 which were exposed thirty seconds according to my recollection, I 

 found, however, in a short time that there was a lack of harmony in 

 the solution ; it had undergone a change which rendered it unfit for 

 use as a preservative, I then made a compound of opium, sugar of 

 milk and tannin, calculating to get the morphia of the opium in a 

 form that would not be as susceptible to change. After a few trials, 

 I ascertained that the following proportions answered my purpose, 

 not only makino; a verv clear and brilliant solution, but one that will 



