19S ANNUAL OP SCIENTIFIC DISCOVERY. 



to the amount of gas passed into the camera, the light, temperature, 

 electric state of the atmosphere, &c., instead of requiring from three 

 to five hours, as in the original process, and the colors of the picture 

 will be impressed on the plate in all their original beauty. This ex- 

 periment may be very easily performed, it only requiring a few grains 

 of zinc in a small vial, containing dilute sulphuric acid. The vial and 

 its contents may be placed in the camera, and the hydrogen being 

 nascent, is in its most active state, and as it is perfectly transparent, it 

 permits the light to act on the plate, while it is itself engaged in re- 

 ducing the chloride, which it is only capable of doing in sunlight. 



The hydrogen, probably from its affinity for oxygen, hastens the 

 decomposition of the organic matter, and assists in reducing the chlo- 

 ride, thus acting as a deoxydating and dechloridating agent. There is, 

 however, sufficient hydrogen contained in the combined organic mat- 

 ter, to effect the reduction of the chloride, hence it is probable that 

 the excess merely hastens the decomposition. 



Following this train of investigation, I have tried many other re- 

 ducing agents both liquid and gaseous. The most important liquid 

 agents tried have been the proto-sulphate and nitrate of iron, ferocy- 

 anide of potassium, protochloride of tin, and the fluorides of potassi- 

 um and sodium. The principal gaseous agents tried are hydrogen 

 alone, and in combination with carbon and sulphur, ammonia, sulphur- 

 ic ether in vapor, chloroform vapor, sulphuret of carbon, chloride of 

 sulphur, hydro-sulphuret of ammonia, and sulphurous acid. As very 

 remarkable results followed from the application of the gases, I will 

 speak of them more particularly. Sulphurous acid has a strong ten- 

 dency to abstract oxygen from organic bodies, it also unites with chlo- 

 rine in sunlight, and so do light and heavy carburetted hydrogen, the 

 latter, indeed, without the influence of light. Sulphurous acid ab- 

 stracts oxygen from organic bodies, with which it combines, forming 

 sulphuric acid, and sulphuric acid renders chloride of silver unchange- 

 able to light by destroying the organic matter with which it is com- 

 bined. I hence inferred that it might be used for the double purpose 

 of reducing and fixing the picture. That it is a powerful accelerator 

 is certain ; the fixing requires further experiment. 



Pictures may be obtained with this gas in half an hour, by passing 

 it nascent and in sufficient quantity in the camera, and the colors are 

 preserved. There is, however, sometimes a little sulphur deposited 

 under the enamel, which gives the light parts of the picture a yellow- 

 ish cast. This color may sometimes be removed by heating the plate. 

 Carburetted hydrogen acts still quicker, probably from the free car- 

 bon which results from its decomposition being a powerful reducing 

 agent, and as the carbon is not left under the enamel, it probably pass- 

 es off under the form of the volatile chloride of carbon. I obtained 

 one picture in five minutes, by passing into the camera the gases gen- 

 erated from distilling alcohol and sulphuric acid in a retort. The 

 gases formed were olefiant gas and sulphurous acid, mixed with a little 

 light carburetted hydrogen and sulphuric ether. The colors were 

 very fairly represented, but not as good as I had previously obtained. 



