Development. Open the shutter of the dark - slide, tip it towards you with the right hand, and seize the plate by the left upper corner with the left hand, holding it horizontally.

Having prepared your developer before leaving the darkroom, you now quickly pour it completely over the film. There should be no hesitancy about this, lest one part develop more rapidly than the other. Sock the plate back and forth, the eye sharp upon it, to prevent the solution from gathering in uneven greasy patches, until it lies smoothly and does its work properly. If rightly exposed, the image will begin to appear in six seconds. If over- exposed, it will not be so slow about it.

Fig. 38

151 Development 58

151. The developer precipitates the silver from its solutions as a fine metallic powder, and this precipitate is formed also when we pour an iron solution on a collodion plate which is (still wet from an adhering Silver solution. When this solution is not present, sulphate of iron will not develop a picture. Acid has more the property to maintain the development clear than to retard the formation of a precipitate. Acetic acid also causes the developer to flow readily over the collodion film. Like alcohol, it also facilitates the adhesion of water to the collodion. - Dr. H. W. Vogel.

The developed picture, viewed by transmitted light, differs in its appearance, even when possessing equally favorable printing qualities. There are variations of color in the image, and of real or apparent intensity of deposit, which are caused by the changes and relations towards each other of the hath and collodion, as the acidity or neutrality of the one or the other predominates. Likewise, independently of duration of exposure, varieties of appearance are caused by change in the quality of the light; often in the same locality, on the same day, with the identical chemicals, negatives differing in translucence or opacity or color are produced, but which may, notwithstanding their varied character, all have nearly equal properties. - Lake Price.