The ordinary method of intensifying is to adhere to the use of one solution as a blackening agent; but it frequently happens that the same degree of increment is neither desirable nor necessary, then choice may be made from the above solutions. Mr. Chapman Jones has tabulated in convenient form the action of many of these. He says : - " In the following series of opera-tions each change is supposed to be thorough - that is, that the change of colour in every case shall be visible clearly at the back of the plate in the densest part of the negative, (i) Mercuric chloride, followed, after well rinsing, with sodium sulphite, gives the little addition of brilliancy sometimes wanted in a carefully made and successful negative; (2) mercuric chloride on the original negatives, followed, after thorough washing, by ferrous oxalate, gives about as much increase of density, as compared with No. I., as No. I. gives when compared with the original negative; (3) a repetition of the application of mercuric chloride and ferrous oxalate - that is, these re-agents applied to the result of No. II. - gives another step in the intensification ; * (4) the result of No. III. may be treated again with mercuric chloride and ferrous oxalate, and so on, as may be necessary ; (5) the fourth or fifth consecutive application of mercuric chloride and ferrous oxalate will probably give a result equal to that of the uranium intensifier acting upon the original negative; (6) if a still greater effect is desired, the lead intensifier may be used on the original negative." Continuing this series we may say that the action of No. V. is fully equal to, if not slightly greater than, mercuric chloride, followed by ammonia; whilst No. VI. gives as great increase as the lead intensifier if desired. No. VII. about the same as No. V. Instead of hydrochloric acid in the bleaching or mercuric chloride solution, many recommend potas-sium bromide or ammonium chloride ; either may be used, with-out any difference in results being detected. Nos. II. and Ill-solutions give about the same density ; Nos. V., VI., and VII. are all poisonous, as is also the mercuric chloride solution. The bleached negative should not be allowed to remain too long in No. V., or else the shadows are attacked. When the negative is placed in No. VI. it turns first bright yellow, then much darker brown. At this stage it is very dense, and only extremely thin
* The result of this treatment is about equal to the action of mercuric chloride, followed by ammonia, upon the original negative.