NATURAL PHILOSOPHY. 143 



NEW DRY PROCESS. 



At a late meeting of the London Photographic Society, Mr. 

 William England described a dry process which he has found to 

 fulfil better than any other the conditions required in a dry-plate 

 process of photography. We may here premise that the pictures 

 which were exhibited as having been obtained by means of the 

 process in question were excellent, and in no way inferior to any 

 that could have been produced by means of wet collodion from 

 the same subjects. The plates are exceedingly sensitive, judging 

 from the ordinary dry-plate standard ; the certainty seems such as 

 to satisfy even exacting experimenters, while the keeping proper- 

 ties may be deduced from the fact of one of the pictures exhibited 

 having been printed from a negative kept seven weeks previous 

 to development. 



A plate is coated with ordinary collodion and excited in a forty- 

 grain bath. It is then washed until all ** greasiness" disappears, 

 by being transferred first to a bath of distilled water, followed by 

 a similar application of common water. Some plain albumen, to 

 which a few drops of ammonia have been added, is now poured 

 over the. surface and made to travel over every part of the film, 

 for which purpose it should be several times tilted backward and 

 forward. The film is now washed, so as apparently to remove 

 the albumen, some of which, however, will always remain, no 

 matter how prolonged may be the washing to which it is sub- 

 jected. The plate now receives a final sensitizing, by having 

 poured over its surface a thirty-grain solution of nitrate of silver, to 

 which a few drops of acetic acid have been added. The plate is 

 now subjected to a final and thorough washing, and is then dried. 

 The exposure required is about three times that given to a wet 

 collodion plate. A plain solution of pyrogallic acid, of the 

 strength of two or three grains to the ounce, serves to develop 

 all the details, which are afterward strengthened in the usual 

 manner by citric acid and silver. Mr. England prefers to fix 

 with weak cyanide of potassium, although hyposulphite of soda 

 may be employed for the same purpose. British Journal of Pho- 

 tography. 



NEW METHOD OP KEEPING WET PLATES SENSITIVE. 



The value of a bromide in securing immunity from stains, 

 comets, and other markings, has long been known ; but its mode 

 of operation in doing this has not been well understood. Its 

 action in permitting long keeping, however, is easily explained. 

 The process of double decomposition, in which the bromide salts 

 employed in the collodion are changed into bromide of silver, is 

 much slower, as is well known, than is the conversion of iodides; 

 and when a simply bromized collodion is employed, the immer- 

 sion in the nitrate bath needs to be very much prolonged, in order 

 to convert the whole of the bromide in the collodion into bromide 

 of silver. In effecting his purpose Mr. Blanchard pursues the 

 opposite course. Employing a very highly bromized collodion, 



