NATURAL PHILOSOPHY. 145 



mide may, we presume, be used without impropriety. Photo- 

 graphic News. 



IMPROVEMENTS IN PHOTOGRAPHY. 



Chloro-Iodized Collodion. A friend of ours is working entirely, 

 both in the gallery and the field, with chloro-iodized collodion ; 

 the results are excellent; we are inclined to believe they are bet- 

 ter than can be obtained with a bromo-iodized collodion. Our 

 own experience with a similar collodion is equally satisfactoiy ; 

 we get more detail and better work in general with the chloro- 

 iodized than with the bromo-iodized collodion. 



The following is the formula: Alcohol, 4 ounces; ether, 4 

 ounces ; pyroxyline, 48 grains (mofe or less) ; iodide of ammo- 

 nium, 40 grains; chloride of ammonium or magnesium, 8 grains. 



Chloride of magnesium is more easily soluble in alcohol and 

 ether, and therefore preferable. Our friend has 24 grains of chlo- 

 ride of ammonium in this quantity of collodion ; but we are certain 

 so much will not dissolve. Humphrey^ Journal. 



Prints in Bitumen. Mr. Swan has shown us a curiosity in car- 

 bon printing, prints pro'duced in the following novel manner: 

 Paper was saturated with a solution of asphalt, of such consistence 

 that when dry no gloss appears on the paper. After exposure 

 under a negative, an image was developed by means of turpen- 

 tine, applied so that the soluble asphalt shall find its way out of 

 the paper from the side opposite to that exposed to light, so leav- 

 ing the insoluble asphalt to form a print with half tone. The 

 same principle is, of course, applicable with chromo-gelatine 

 printing ; the material saturated with the chromo-gelatine being 

 of an open texture (woven materials, for an example), and the 

 coloring matter being of course soluble with the gelatine. Prints 

 by Mr. Swan's processes are regularly published in Paris. Pho- 

 tographic News. 



Leptographic Paper. This is the name given to a species of 

 new photographic paper which is prepared by a company in Paris, 

 and sold, ready sensitized, at a comparatively low price. It con- 

 sists of the ordinary paper upon which a sensitizing collodion or 

 film has been poured and dried. Exactly what the film is com- 

 posed of does not yet appear. It was at first supposed to be noth- 

 ing more than paper covered with collodio-chloride, as in Simp- 

 son's process ; but the leptographic film seems to be different from 

 that, as it is more insoluble, keeps better, is harder, etc. 



The leptographic paper possesses some very peculiar and val- 

 uable qualities : The paper being prepared beforehand and prop- 

 erly protected from the light, is ready for use at any moment ; it 

 may be left, indeed, in the printing-frame, if the weather is unfa- 

 vorable, and then exposed again two or three days afterward, in 

 order to finish the impression already commenced, and all this 

 without any inconvenience or detriment to the whites, a con- 

 venience which is very agreeable, and which occurs with no other 

 paper. It has been demonstrated by experience that this paper is 

 as sensitive at the expiration of half a year as on the day of its 

 preparation. 



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