With respect to No. 3, Mr. William Crookes has shown, that when a saturated solution of gallic acid is required in large quantities, that it is better to dissolve at once two ounces of gallic acid in six ounces of alcohol (60° over proof); to hasten solution, the flask may be conveniently heated by immersion in hot water; when cold it should be filtered, mixed with half a drachm of glacial acetic acid, and preserved in a stoppered bottle for use; so prepared it will keep unaltered for a considerable length of time. The gallic acid is not precipitated from this solution by the addition of water; consequently, if in any case desirable, the development of a picture may be effected with a much stronger bath than the one usually employed. To obtain a solution of about the same strength as a saturated aqueous solution, such as No. 3, half a drachm of the alcoholic solution is mixed with two ounces of water; but for my particular purpose, says Mr. Crookes, referring to the wax-paper process, "I prefer a weaker bath, which is prepared by mixing half a drachm with ten ounces of water." In either case it [Page 143] will be found necessary to add solution of nitrate of silver in small quantities, as the developing picture seems to require it. Returning again to the solutions marked 1, 2, 3, the numbers will assist the memory in mixing the proportions of each. If the paper is required to be used _at once_, a drachm of each may be mixed together and spread over the iodized paper (of course, in a dark room), which is then transferred to a clean blotting-book of white bibulous paper, and being placed in the paper-holder may be taken to the camera and exposed at once. If the paper is not required to be used immediately, the solutions are mixed in the proportions of the numbers--viz., one of No. 1, two of No. 2, three of No. 3; and in making the mixture, it is advisable to keep a measure specially for No. 3, the gallic acid, or else the measure, if used for the three solutions, will have to be washed out every time, which is very troublesome, particularly where water is not plentiful. If the excited paper is required to be kept some hours before use, No. 3 must be added in still larger proportion, as much as ten or even twenty measures of No. 3 to two of No. 2, and one of No. 1, being used, and even this large dilution is frequently insufficient to prevent the paper spoiling in hot weather; therefore if the temperature is high, too much reliance must not be placed on this paper, as it is peculiarly disappointing, after walking some miles to romantic and beautiful scenery, to find, when developing the pictures in the evening, that the paper used was all spoilt before exposure; and it will be seen presently that when the excited paper is to be carried about for use, it is better to adopt the wax-paper process.