398 Intelligence and Miscellaneous Articles. 



less dense, though colder, than that of the Red Sea, flows into the 

 latter on both sides of the Island of Perim. This colder water could 

 be detected half a degree north of the Straits. After some further 

 remarks about this current, the authors pass on to the 



Arabian Sea — in which they found 

 From long. 44° to 50° East from Greenwich, temp. 2S 0, 8, reduced sp. gr. 1-0275. 

 From the merid. of Cape Guardafui to Bombay, temp. 27° to 28 CI ) red. sp. gr. T0278. 



LVI. Intelligence and Miscellaneous Articles. 



ON SENSITIVE COLLODION. BY THOMAS WOODS, M.D. 



IN the Number of the Photographic Journal for December last, 

 Mr. Doyle asked me a question about the quantity of the gun- 

 cotton which is precipitated by the solution of salt I recommend to 

 be added to the collodion to prepare it for my process. I sent an 

 answer to the succeeding Number of the Journal, but I was not aware 

 at that time how much I ought to have explained. Questions since 

 put to me on the same subject caused me to read over carefully the 

 paper originally sent to the Philosophical Magazine of July last, and 

 I find I have in it made an omission which no doubt has caused the 

 process to be unsuccessful. When I recommended a saturated solu- 

 tion of salt to be used, I meant the solution to be made with alcohol, 

 not with water. If made with the latter, it not only would preci- 

 pitate too largely, but otherwise destroy the mixture ; and I am 

 afraid such has been the case with the operators who have tried the 

 process. As my experience of the process with the iodide of iron 

 has quite answered my own expectations, and, when the proper 

 solutions have been used, in the hands of others the promises I have 

 made for it, I am tempted to rewrite the formula I use, exactly as it 

 should be, at the risk of occupying too much space by a repetition. 

 It may not, however, be without its value just now, as the season is 

 becoming more favourable for photographic operations, and I know 

 of no process more sensitive or certain than that I describe. 

 Take of — 



Sulphate of iron 40 grs. 



Iodide of potassium 24 grs. 



Chloride of sodium (common salt) 6 grs. 



Alcohol - . 2 ozs. 



Strong water of ammonia 3 drops. 



Mix the powdered salts together and add them to the alcohol, then 

 the water of ammonia. A few pieces of iron wire must be kept in 

 the mixture to prevent the iron becoming peroxidized. 



One part of this mixture is to be added to three parts of collodion 

 holding in solution an alcoholic solution of common salt in the pro- 

 portion of 1 fluid drachm of salt to 4 ozs. of collodion. Or, neglect- 

 ing the salt solution, 5 drops of chloroform may be added to 1 drachm 

 of the solution of iodide of iron and 3 drachms of plain collodion. 

 The mixture of collodion and iodide of iron ought to be used shortly 



