Mae. 5. 1853.] 



NOTES AND QUEEIES. 



245 



oi 2l fifty-grain solution of iodide of potassium, by 

 which a precipitate of iodide of silver will be 

 formed, the supernatant fluid containing the 

 excess of iodide of potassium and the nitrate of 

 potash formed by the decomposition. Add drop 

 by drop a solution of the cyanide of potassium, 

 until the iodide of silver is redissolved, and the 

 liquid becomes limpid, and then four ounces more 

 of distilled water, making up five ounces alto- 

 gether. The paper should then be washed over 

 with the above and dried, after which it may be 

 floated on water slightly acidulated with sulphuric 

 acid for a few minutes, and after being again dried, 

 either wholly, or else partially with blotting-paper, 

 may be rendered sensitive with a weak solution of 

 nitrate of silver. Here are two or three points 

 admitting doubt : first. Would it not be better to 

 "wash away the nitrate of potash and free iodide of 

 potash first, and then dissolve the iodide of silver 

 in solution of cyanide of potassium ? Secondly, 

 Would not a slight soaking in plain water after 

 the acidulated bath be of advantage ? Thirdly, 

 Js it better to dry the paper again before ren- 

 dering it sensitive ? and fourthly. What strength 

 of nitrate of silver solution should be used to 

 render it sensitive ; and ought it to have any acetic 

 or gallic acid, or both ? George Shadbolt. 



Animal Charcoal in Photography. — Perhaps you 

 or one of your photographic correspondents would 

 inform me whether the animal charcoal, recom- 

 mended for the aceto-nitrate of silver solution, 

 should be used as a filter, or simply allowed to 

 remain in the bottom of the bottle ? A. B. C. 



Oxford. 



Sir W. Newton on Use of Common Soda and 

 Alum. — In reply to W. Adrian Delferier, who 

 is desirous of knowing the " rationale of the action 

 of the common soda and powdered alum, &c.," my 

 motive for using common soda to cleanse the ne- 

 gatives is, that It not only removes the hyposul- 

 phite of soda more readily, but any impurities 

 which may be in the paper, as well as the whole of 

 the size, such being absolutely necessary for the 

 -after waxing process ; which, when done, the ne- 

 gative should appear nearly as transparent as 

 glass. 



The reason why I prefer alum for the positives 

 is, that while It has the effect of removing the 

 hyposulphite of soda and other impurities In the 

 paper, It does not act upon the size, which In this 

 instance It is desirous to retain. 



^ I have been induced to make a series of expe- 

 riments, with a view to prevent the fading of the 

 positives, or. Indeed, that any portion should be, 

 AS It were, eaten away in parts ; and since I have 

 adopted the foregoing. In no one Instance has any 

 change taken place whatever. W. J. Newton. 



6. Argyle Street. 



Difficulties in Photographic Practice. — Having 

 met with some of the difficulties that your corre- 

 spondent G. H. mentions in his communication 

 (Vol.vii., p.218.), I beg to offer a few hints which 

 I think will be of service to those who are trying 

 the waxed-paper process. 



With regard to the spots, It is not easy to know 

 whether they are produced by particles of Iron in 

 the paper, or by the oxide of silver. Le Gray 

 says : " If spots should form, produced by the 

 oxide of silver, they may be removed by pouring 

 over the negative some acetic acid, and passing a 

 brush lightly over it." 



The second difficulty, want of depth of tone or 

 Intensity In the negative, may have been caused by 

 too short an exposure In the camera, or not having 

 used the proper proportion of developing solution. 

 Try the following : 



4 oz. dist. water. 

 8 grains gallic acid. 



When this solution has been filtered, add to it 

 ^ drachm of the aceto-nitr. of silver solution, and 

 1 drachm of acetic acid. I have generally put a 

 little camphor In the gallic acid solution, as re- 

 commended by Laborde. It prevents the decom- 

 position of the gallic acid, and renders the image 

 clearer and free from spots. A piece about the 

 size of a pea for four or five ounces of solution. 



As to the third difficulty, I believe nothing but 

 replacing the porcelain dishes by glass ones will 

 prevent the dirty marbled appearance in the bot- 

 tom of the dishes made of porcelain ; they are 

 generally rough and uneven on the surface, and 

 there are often what Is called "kiln-cracks" In the 

 angular parts. Two months ago I bought two 

 glass dishes; although they are more than double 

 the price of porcelain, I expect the annoyance of 

 dirty dishes Is prevented. The glass ones are 

 made quite round at the sides and ends, and of 

 course will be easily cleaned. I am informed they 

 are made in France, but they could be had of 

 English manufacture. 



The animal charcoal in the sensitive solution 

 must be shaken up In the aceto-nitrate solution ; 

 and when It has become quite clear, the solution 

 before using must be filtered into the dish. 



E. Elliott. 



Penslur Iron Works. 



The Countess of Pembroke's Letter (Vol. i., 

 pp. 28. 119. 154.; Vol. vil., p. 154.).— None of 

 your correspondents seem to be aware that the 

 paper In the World (No. XIV. April 5, 1753), in 

 which this questioned letter first appeared, was 

 written by Horace Walpole, and was afterwards 

 reproduced by him In his Royal and Nolle Au- 

 thors. These facts may help to guide inquirers, 



