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LV. On a Method fur preserving the Sensitiveness of Collodion 

 Plates for a considerable time. By John Spiller and Wil- 

 liam Crookes*. 



THE exti-eme sensitiveness of collodion as compared with paper 

 and other photographic surfaces renders this material in- 

 valuable in all cases where rapidity of action is desirable, but up 

 to the present time its use has been greatly restricted by the 

 necessity for preparing the plate and completing the whole of 

 the manipulatory details within a comparatively short space of 

 time, thus rendering this beautiful process practically inap- 

 plicable in all cases where the conveniences of a photographic 

 laboratory are not at hand. 



For some time past we have been investigating the causes 

 which operate to prevent the excited plate retauiing its efficiency 

 for more than a few hours. It seemed highly probable that the 

 permanent sensitiveness of the film was principally dependent 

 on the retention of a moist surface ; and if by any artificial 

 means this end could be secured, the original sensitiveness of the 

 film would be, for at least a reasonable time, preserved unim- 

 paired. 



The only attempts up to the present time to effect this object 

 are, we believe, that of M. Girodf, who proposes to enclose the 

 sensitive collodion film between two plates of glass, with only so 

 much of the exciting silver solution as might be retained by 

 capillary attraction ; and thus by retarding the evaporation of 

 the water, to keep the surface moist, and consequently sensitive, 

 for a longer period; and secondly, that of M. GaudinJ, who 

 suggests the use of perfectly air-tight dark frames or boxes, in 

 which a number of the wet plates could be arranged in a hori- 

 zontal position and there kept until required. Besides these 

 two methods, it is well known that the plate will remain excited 

 for a considerable time if kept immersed in a solution of nitrate 

 of silver ; in fact, a glass bath in the camera has been often used 

 in cases where the length of exposure was likely to be too pro- 

 longed to admit of the plate being placed in the ordinary slide. 



Instead, however, of having recourse to a mechanical means 

 for preventing the evaporation from the surface, we have endea- 

 voured to avail ourselves of a chemical process, by the employ- 

 ment in the bath of substances having a powerful affinity for 

 water ; in the choice of these, however, we are necessarily limited 

 to such as are neutral in constitution, and do not form insoluble 

 compounds with silver. The nitrates and acetates, especially 



* Communicated by the Authors. 



t Jouin. Phot. Soc. No. y. X I'>i'l- >^"- !*'• 



