36 REPORT — 1844. 



to sunshine, this takes place instantly, and the weight of the precipitate, up to a cer- 

 tain point, is in both these cases a measure of the quantity of light to which the solu- 

 tions have been exposed. A contrary effect to this has also been observed : if a solu- 

 tion of the bichromate of potash be mixed with one of sulphate of copper, and the 

 mixture be set aside in the dark for twelve hours, the glass will become thickly coated 

 with a chromate of copper, but a similar mixture exposed to the sunshine shows no 

 such effect. Several solutions of the salts of silver were exposed to sunshine, whilst 

 portions of the same solutions were kept in the dark. When small quantities of the 

 sulphate of iron were added to these solutions, it was found that those which had been 

 exposed to sunshine gave a precipitate immediately, whereas those which had been 

 preserved in the dark did not precipitate for some time. It has also been noticed, 

 that bichromate of potash, exposed to bright sunshine, precipitated chromate of silver 

 of a much more beautiful colour than a similar solution which had been kept in 

 darkness. A similar effect was seen in precipitating prussian blue by a solution of 

 the ferro-prnssiate of potash whicli had been exposed to the sun, the colour being in- 

 finitely more beautiful than that thrown down by a solution which had not been so 

 exposed. A solution of the iodide of potassium was put into a glass tube, the lower 

 end bein<' closed by a diaphragm ; tliis was put into another vessel containing a solu- 

 tion of nitrate of silver, and a platina wire passed from one solution into the other. 

 Such an arrangement being placed in the dark, a beautiful crystallization of metallic 

 silver took place about the wire, but if placed in the sunshine this crystallization was 

 entirely prevented. The attention of chemists was called to these results, which cer- 

 tainly show that the agency of the chemical rays must in future form an important 

 subject of investigation, particularly when any delicate analysis is desirable. These, 

 and similar experiments, belong to an important branch of chemical science, for which 

 the epithet of Actino-Chemistry has been proposed by Sir John Herschel. 



On the Ferrotype, and the Property of Sulphate of Iron in developing 

 Photographic Images. By Robert Hunt. 



The new photographic process, to which the above name is given, consists essentially 

 in the development of a dormant photographic image, formed on a paper prepared 

 with succinic acid and nitrate of silver, by the deoxidizing power of sulphate of iron. 

 Numerous failures have been communicated to the author, which appeared to arise 

 from the varying rates of solubility jiossessed by succinic acid obtained from different 

 manufacturers. It was now recommended, that five grains of succinic acid should be 

 put into a fluid ounce of distilled water, and allowed entirely to dissolve ; the salt and 

 gum is then to be added to this solution, and the author believes that, with care, the 

 effects will be certain. Recent researches have, however, proved that this property of 

 the sulphate of iron may be made available on any pliotographic paper. On paper 

 merely washed with the nitrate of silver, good camera pictures have been thus ob- 

 tained in a few minutes, and on papers prepared with the chloride of sodium, bromide 

 of potassium, and particularly the iodide of potassium, camera views are procured in 

 less than a minute. Mr. Hunt exhibited a great number of specimens procured on 

 the above and many other salts of silver — the most beautiful being on papers covered 

 with the acetate, the benzoate, the citrate, and other organic salts of silver. These 

 drawings were all fixed by washing with moderately strong ammonia. 



On the Electrolysotype ; a neru Photographic Process. 

 By Thomas Woods, M.D. 



[The following are extracts from this paper]. — While investigating the property 

 that sugar possesses in some cases of preventing precipitation, 1 noticed, that when 

 syrup of ioduret of iron was mixed with solution of nitrate of silver in certain pro- 

 portions, the precipitate was very quickly darkened when exposed to the light, and I 

 thought that if properly used it might be employed with advantage as a photographic 

 agent. 



Let well-glazed paper be steeped in water to which hydrochloric acid has been 

 added, in the proportion of two drops to three ounces ; when well-soaked, let it be 

 cashed over with the following mixture ;— take of syrup of ioduret of iron half a 



