The following is a table by H. E. Tolman showing displacement on ground glass of objects in motion : INTENSIFICATION.—Any method of increasing the opacity of a negative. It frequently happens that either from under-exposure, insufficient development, or other cause, the negative does not possess sufficient density to yield satisfactory prints. It will then be necessary to " intensify " it, or increase the opacity by " intensification " with an " intensifier." There are two chief methods of intensification very distinct from each other in the actions of the chemicals used. The first is a method of increasing the density by thickening the deposit of metallic silver, and the second is by substituting another metal for the silver, having a more opaque color, causing the negative to become less transparent. There are also other methods of A method of intensifying that has found considerable favor with practical workers is the following : The plate is first of all thoroughly freed from the hypo, and immersed in a ten per cent, solution of perchloride of mercury until the image becomes bleached and appears quite white on both sides of the film. It is then thoroughly washed. A solution of silver nitrate (too grains in to ounces of water) is then taken, and sufficient potassium cyanide in solution added, to nearly dissolve the precipitate first formed on making the addition. In this solution the bleached negative is laid, when it will at once commence to darken. When the required density is obtained it is removed. It will be necessary to bear in mind that the negative, while wet, will appear slightly denser than when dry. Also the plate should not be allowed to remain too long
in the silver cyanide solution or reduction will take place. The chemical actions that take place with this method are briefly these. The mercuric chloride becomes reduced when it comes into contact with the silver image, and forms calomel mercurous chloride and silver chloride, thus 2 + 2Ag = + 2AgCI.
The potassium cyanide and silver can be taken as a solution of silver cyanide, reduced by the mercurious chloride to a dense black deposit of metallic silver.
There are a number of other methods of intensifying the image, by first bleaching it with mercury and afterwards darkening it with other chemical agents.
The negative is laid in the bleaching solution composed of— Mercury perchloride too grains Potassium bromide too grains I )istilled water to ounces until the silver image is whitened. To do this properly it is absolutely necessary that the nega tive be free from hyposulphite of silver, otherwise stains will be the inevitable result.* When the negative is perfectly white when viewed both from the front and back of the film, the plate is removed and thoroughly washed. We have now to change the color of the image to a more opaque one. This can he done in several ways.. If the plate be immersed in a weak solution of ammonia, the chloride of silver will become dissolved away, and the mercurous chloride is changed into mercurous ammonium chloride (a dark colored substance) and ammonium chloride, thus