234 ANNUAL OF SCIENTIFIC DISCOVERY. 



a good washing, a solution made by dissolving 180 grains of pure gelatine 

 in twenty ounces of water, filtering whilst hot, and when nearly cold, adding 

 three ounces of glycerine of specific gravity 1.3000, is poured upon the plate 

 for a few seconds, and the plate is then dried. Plates prepared in this way 

 have been kept for thirty-eight days without producing any diminution of sen- 

 sitiveness. Previous to developing, the plate is immersed in cold water for 

 five minutes, the development being accomplished either with gallic acid 

 and nitrate of silver, or pyrogallic acid. 



Newell' 's Photographic Portraits. A new invention by Mr. Newell, of 

 Philadelphia, consists in crystallizing a photograph or other picture on paper, 

 and securing the photograph thus prepared between two plates of glass by a 

 transparent cement, which renders the whole impervious to air or dampness, 

 securing durability in any climate. The coloring is then applied, which, 

 being transmitted through this transparent medium, produces the peculiar 

 softness and natural appearance of texture, while it preserves every line, ex- 

 pression, and feature precisely as taken by the camera. The whole effect is 

 to produce a picture more exact in tints, shadows, and colors, and more per- 

 fect in its minutest details, than has heretofore been obtained ; at the same 

 time there is a roundness and stereoscopic appearance which no other picture 

 possesses without the aid of the stereoscope itself. 



Crai/on Photographs. The shading of the so-called Crayon photographs, 

 invented by Mr. Mayall of London, and called Crayon, from their close re- 

 semblance to crayon drawings, is effected by means of a revolving disc in 

 which the opening is in the form of a small star. This is interposed between 

 the object, or sitter, and the camera ; and the central portion of the star is 

 made large enough to admit the rays from that part of the object which is 

 to be shown in strong light, whilst the rays from those parts which arc to be 

 gradually shaded off to a dark background, are partially intercepted by the 

 points of the star 



DRY COLLODION PROCESSES. 



Mr. G. Pi. Berry has recently published in the Chemist the following re- 

 sume of the various dry collodion processes now in use in photography : 

 We will take first the ordinary collodion process, which is thus divided : 



1. Preparation of the collodion. 



2. Preparation of the nitrate of silver bath. 



3. Preparation of the developing solution positive and negative. 



4. Removal of the surplus chemicals. 



5. Varnishing. 



Collodion is, as all are aware, a solution of one of the pyroxyline com- 

 pounds, in a mixture of alcohol and ether, and holding also in solution an 

 iodide, or a mixture of iodide and bromide of potassium, ammonium, cad- 

 mium, or other bases. The number of these is not very extensive, as the 

 case will admit only those soluble in the menstruum before mentioned, but 

 if the ingredients are few in number, the variations in quantity and relative 

 adjustment are almost infinite, as every photographer has his series of pet 

 fancies, and to this fact nearly all the disheartening failures of amateurs are 



