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XXX. On Sensitive Collodion. By Thomas Woods,, M.D. 

 To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, Parsonstown, August 1854. 



TO answer some inquiries which have been addressed to me 

 with respect to the photographic process pubHshed in the 

 July Number of this Magazine, I beg to make the following 

 addenda. 



The mixture of iodide and muriate of iron acts better when it 

 is a few days old ; these salts of iron being formed by the double 

 decomposition which occurs between the iodide of potassium and 

 muriate of soda on the one hand, and the sulphate of iron on 

 the other, and the last-named salt being with difficulty dissolved 

 in the alcohol, the action requires some time before the full effect 

 is produced. 



The picture developed by the sulphate of iron as an exciting 

 agent is a positive one, and if rapidly taken, not deep enough to 

 print from. The usual pyrogallic acid solution (3 grains to the 

 ounce of water, with half a drachm of glacial acetic acid) brings 

 out the picture much more deeply marked. With the pyrogallic 

 acid developing solution I have taken a likeness in about 1|- 

 second which could be printed from very fairly. 



I have found from late experiments that the intensity of 

 the picture may be considerably increased by using collodion 

 without the salt recommended in the paper published last July, 

 but substituting for it one drop of chloroform to the mixture 

 when about to be poured on the glass plate; that is, mixing 

 together 1 part of the solution of iodide of iron, 3 parts of col- 

 lodion, and 1 drop of chloroform to each drachm of this com- 

 pound fluid when about to be poured on the plate. The first 

 effect of the chloroform on the collodion is to precipitate the 

 gun-cotton which comes in contact v/ith it, but it soon redissolves 

 by giving a shake or two to the vessel. 



I am, &c., 



Thomas Woods, 



XXXI. F^'oceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 155.] 

 June 15, 1854. — The Earl of Rosse, President, in the Chair. 



THE following papers were read : — 

 " Examination of the Cerebro-spinal Fluid." By William 

 Turner, Esq., Scholar of St. Bartholomew's Hospital. 



In the Bulletin de TAcademie de Medecine for December 1852, a 

 paper is published by M. Bussy, containing an analysis by M. Des- 



