Mix 1 1/2 fluid oz. of each of the strongest nitric and sulphuric acids; put the mixture in a Wedgewood mortar, and when cool add 100 grs. of cotton wool. Stir it with a glass rod, and when it is fully soaked, squeeze out the acid with the pestle or a porcelain spoon, throw the cotton into a large quantity of water, squeeze it again, and wash it under a stream of water till quite free from acid. In the specification, the patentee directs 1 measure of nitric acid, sp. gr. 1.45 or 1.50 to be mixed with 3 measures of sulphuric acid, sp. gr. 1.85; the cotton to be soaked in the acid, then squeezed from it, and left in a covered vessel for an hour; and after washing, to be dipped in a solution of 1 oz. carbonate of potash in a gallon of water, then pressed, and partially dried; again dipped in a weak solution of nitre, then dried in a room heated to 150°. See Pocket Formulary. See Collodion. Gun Powder. A compound of nitre, charcoal, and sulphur. The nitre should be purified by recrystallization, the sulphur by distillation, and the charcoal selected of the best quality - that of the dog-wood, alder, poplar, chestnut, or willow is preferred. The following is the composition of some of the most approved kinds: