A Manual Of Photography

NATITBALLT-COLOUBED PHOTOGRAPHS. 175 in general, and to that of alcohol in particular. If we prepare a plate of silver and pass it into water saturated with chlorine to which is added some chloride of strontian, and when thus pre- pared we place upon it a coloured design of red and other colours, and then expose it to the sunshine, after six or seven minutes we shall perceive that the colours of the image are reproduced upon the plate, hut the reds much more decidedly than the others. When we would produce successfully the other rays of the solar spectrum, we operate in the same manner as we have indicated for the red ray—employing for the orange the chloride of calcium, or that of uranium for the yellow, or the hypochlorite of soda, or the chlorides of sodium or potassium. Very fine yellows have been obtained with a bath composed of water slightly acidulated with muriatic acid and a salt of copper. The green rays are obtained with boracic acid or the chloride of nickel ; also with all the salts of copper. The blue and indigo rays are obtained with the double chloride of copper and ammonia. The violet rays are obtained with the chloride of strontian and sulphate of copper. Those substances whicli give white flames, as the chloride of antimony, the chlorate of lead, and the chloride of zinc, yield no colour by luminous action. All the colours of a picture have been produced by preparing a bath composed of the deuto-chloride of copper ; and M. Niepce states that this salt thrown into burning alcohol produces a variegated flame according to the intensity of the fire, and it is nearly the same with all the salts of copper mixed with chlorine. Niepce says— “If we put a salt of copper in liquid chlorine we obtain a very sensitive surface by a single immersion in the bath; but the colorific result of this mixture is seldom good. I prefer a mixture of equal parts of chloride of copper and of chloride of iron, with three or four parts of water: the chloride of iron has, as those of copper, the property of being impressed on the plates of silver and of producing many colours, but they are infinitely more feeble, and the yellow always predominates ; and this agrees with the yellow colour produced in flame by this salt.” It should be understood that when the plate of silver, being previously connected with a voltaic battery, is plunged into the bath and the circuit completed, it becomes covered with a dark coating, probably of a sub-chloride of silver mixed with the salt on whicli the colour to be produced by solar radiation depends' If we form a bath composed of all the substances which separately give a dominant colour, we obtain very lively colours• but the great difficulty is the mixing of the salts in such propor- tions as to give an equality to the tints, as it commonly happens that some colours are excluded by others. We cannot always