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XLII. Researches on the Methods of preserving the Sensitiveness 

 of Collodion Plates. By John Spiller and William 

 Crookes.* 



IT is now nearly two years since we had the honour of pre- 

 senting to the photographic world our first experiments 

 made with the view of preserving the sensitiveness of collodion 

 plates. In the Philosophical Magazine for May 1854 (an abs- 

 tract appearing in the Photographic Journal of that month) we 

 communicated the possibility of securing this end by taking 

 advantage of the deliquescent nature of certain neutral salts, 

 which, by retaining water in the film, enabled us to prolong or 

 defer the exposure of the sensitive plate for a length of time 

 which was not practicable by the ordinary collodion process. 

 For this purpose we proposed the use of the nitrates of zinc, 

 manganese, lime or magnesia, and, as the type of a class of sub- 

 stances equally suitable in the organic kingdom, glycerine; 

 sugar also had been tried, but with no good result. In conse- 

 quence of public attention being again drawn to glycerine, by 

 the lecture recently delivered before the Society of Arts, we 

 think it but right to assert our claim of priority iu suggesting 

 the application of this body to the purpose under consideration. 

 We quote from the article of May 1854. " Glycerine at first 

 seemed to promise vei'y good results, but the principal difficulty 

 was the necessary impurity of the commercial product, in con- 

 sequence of its being obtained from the exhausted leys of the 

 soap boilers." Now, however, that an improved process of 

 manufacture has been introduced at the works of Price's Patent 

 Candle Company, where it is obtained as a bye product in the 

 decomposition of fatty matters by high-pressure steam, it became 

 a point of interest to determine whether the purer article might 

 not well serve the object in view. With this intention we pro- 

 cured a sample of Price's glycerine as soon as it became an 

 article of commerce, and although the result of our experiments 

 coincides to a certain extent with those of Mr. Pollock and 

 others, we nevertheless think it worth while to specify the par- 

 ticiilar points of difference in manipulation, some of which will, 

 we believe, materially facilitate the preparation of the plates in 

 this way. 



Our first care was to ascertain the action of glycerine upon an 

 aqueous solution of nitrate of silver. For this purpose, a mixture 

 was made and divided into two portions, one of which was ex- 

 posed to a full southern aspect, and the other carefully protected 

 from every gleam of light ; after a few days a thin but distinct 

 coating of metallic silver was found lining the interior of the 



* Communicated by the Authors. 



