176 



Capt. Abney. On the Effect of the [Dec. 15, 



Similar paper was washed, some was used in this state and other 

 was afterwards treated with a solution of sodium chloride and again 

 washed, leaving thus only a trace of an organic salt of silver in the 

 fibre. The action of the spectrum on the simply washed paper is 

 shown in fig. 37. With a short preliminary exposure, traces of an 

 impression between F and C were obtained, tending to show that 

 the preliminary action in fig. 36 was effective on the chloride besides 

 on the organic compound of silver. Fig. 38 gives the action of the 

 spectrum in the chloride which had all traces of silver nitrate removed 

 by the wash of sodium chloride. 



To obtain an emulsion of silver chloride in collodion, 20 grains 

 of calcium chloride were dissolved in 1 oz. of collodion, and 1 gr. 

 more, or 1 gr. less, according as excess or defect of silver nitrate was re- 

 quired, than the equivalent of silver nitrate dissolved in another ounce 

 of collodion ; the former solution was poured in the later, shaking at 

 intervals, till a perfect emulsion was obtained. In some cases the 

 emulsion was washed in the ordinary way known to photographers, 

 and in others used when made as above, and the films washed or 

 exposed in their natural state. In no case did any difference in the 

 resulting impression of the spectrum appear. I may also state that 

 other chlorides were tried, and there is no apparent difference from 

 those obtained where sodium chloride was employed. Fig. 38 also 

 gives the action of the spectrum on such emulsion, there being no 

 apparent difference between the washed emulsion or the emulsion 

 exposed with an excess of silver nitrate, or with an excess of the 

 soluble chloride, unless it be one of general sensitiveness. In other 

 words, the spectrum seemed to act on the silver chloride in one and 

 the same manner. Fig. 39 shows the printing action on the chloride 

 when enveloped in gelatine. The emulsion was formed in the usual 

 manner habitual amongst photographers, each ounce of emulsion con- 

 taining about 25 grs, of converted silver nitrate. Fig. 39 has refer- 

 ence to this emulsion after it was heated to its boiling point for half 

 an hour, and when treated with ammonia ; when used unboiled it took 

 an impression similar to fig. 38. 



When these same preparations of the chloride in gelatine are 

 exposed for a short time to the spectrum and developed with ferrous 

 citro-oxalate developer, or with gallic acid and silver, we get figs. 42, 

 43, 44 and 45, the first two expressing the result of the unboiled 

 emulsion which transmits yellow-orange light, and the two latter 

 numbers that on the boiled emulsion which transmits a blue-grey light. 



visibly darkened by the light. This, as is well known, is impressed throughout the 

 ipectruni, and takes the approximate colour of the spectrum. This is true whatever 

 vehicle is used to hold the silver chloride, and also whether exposed in the presence 

 of an excess of silver nitrate or other sensitiser, and also when organic compounds of 

 silver are mixed with it. 



