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XV. Further researches on the Methods of Preserving the Sensi- 

 tiveness of Collodion Plates. By John Spiller and William 

 Crookes*. 



THE object of our former paper in the Philosophical Maga- 

 zine for May, was to draw attention to the principle of 

 preserving the collodion surface moist by taking advantage of 

 the deliquescent character of certain bodies ; and we preferred 

 that method of communicating our discovery, as, although theo- 

 retically correct, it was not sufficiently developed to warrant our 

 laying it before practical photographers, but required further 

 experiments by which the comparative merits of the different 

 substances at our disposal could be determined. 



Having decided against the use of nitrate of zinc, we tried 

 other substances, and among the rest the acetate of potash ; but 

 although by its use we succeeded in obtaining very good results, 

 yet the sparing solubility of acetate of silver necessitates so many 

 precautions, that we determined if possible to find an equally 

 efficacious salt among the nitrates. 



On giving the nitrate of magnesia a further trial, under cir- 

 cumstances which later experience had shown to be necessary, 

 our former difficulties vanished, and we are now enabled to com- 

 municate to the Society the following process, which, in our 

 opinion, scarcely admits of an improvement. 



The plate coated with collodion in the usual manner is to be 

 rendered sensitive in a 30-grain nitrate of silver bath, in which 

 it should remain rather longer than is generally considered ne- 

 cessary (about five minutes), it must then be slightly drained 

 and immersed in a second bath, consisting of — 



Nitrate of magnesia . . 4 ounces. 

 Nitrate of silver ... 12 grains. 

 Glacial acetic acid ... 1 drachm. 

 Water .13 ounces. 



and there left for about five minutes, then removed and placed 

 in a vertical position on blotting-paper, until all the surface- 

 moisture has drained off and been absorbed ; this generally takes 

 about half an hour, and they may then be packed away in any 

 convenient box until required for use. 



Not only is the sensitiveness unimpaired by this treatment, 

 but we think, on the contrary, that it is slightly increased; 

 instantaneous negatives have been taken on plates which had 

 been prepared some days previously. We are not yet in a posi- 

 tion to give the length of time that may elapse between the pre- 

 paration of the plate and development of the picture ; such expe- 



* From the Journal of the Photographic Society, July 21, 1854. 



