12 



and will be found to answer well if properly applied. The liquid is 

 diluted witli water in the proportion of about one dram to an ounce 

 and a half. A sufficient quantity having been poured into the 

 trough, the plate is placed over it, and allowed to remain until it 

 acquires a red colour, approaching in some cases to violet. The 

 following rules will guide the experimenter in using the different 

 liquids. If bromide of iodine be used as the accelerating agent, 

 the plate should remain over the iodine solution, until it is of a 

 deep yellow tint: and over the bromide, till of a deep rose colour. 

 If Redman's solution, or the Hungarian liquid, a pale yellow and 

 light rose will be found to answer best. As a general rule : if the 

 yellow colour produced by the iodine be pale, the red should be 

 pale also ; if deep, the red must incline to violet. When several 

 plates are to be prepared at the one time, the same solution will 

 serve for all ; but it seldom answers to preserve the mixtures for 

 any time ; and its use, after keeping, is one great cause of the 

 failures which so annoy amateurs. The bromine contained in these 

 solutions is very subtle, and escapes, leaving little else but iodine 

 remaining, which will, after some little time, give a red colour to 

 the plate, without rendering it sensitive, entirely disappointing 

 the expectations of the operator. The colour of the plate may be 

 examined as before, but care must be taken to replace the plate 

 over the solution for a few seconds, which removes the effect of the 

 light. When the liquid is renewed at each operation, one inspection, 

 at an interval determined by experience, will be generally sufficient. 

 From thirty to sixty seconds, according to temperature, are usually 

 required to produce the effect; in certain states of the atmos- 

 phere, a much longer time may be necessary. The plate is now 

 ready for the camera, and may be kept for twelve or eighteen hours, 

 if due care is taken to keep it secure from light or dust. Plates 

 prepared over night are often considered more sensitive than those 

 prepared immediately before using. Frames to carry prepared 

 plates, may be purchased at the opticians. The prepared plate 

 must be transferred to the camera frame with extreme care neither 

 to expose it to light, or rub the surface. 



EXPOSURE IN THE CAMERA. 



The form of camera most suitable for the purpose, has been 

 already described, page 5. The inside should be carefully dusted 

 before using. Having been placed opposite to the object to be 

 copied, and made perfectly steady, a clear and distinct representa- 



