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[645]

cloudiness j the vitriolic acid and the chalk precipitate to-gether, and the nitrous acid and mineral alcali remain inthe liquor, which accordingly, on crystallization, yields atrue cubic nitre. The solutions ought to be well satu-rated, that the milkiness, which grows fainter and fainteras we continue to add more of the calcareous solution,may be the better distinguished; and aster the cloudinessseems to have entirely ceased, a little more of this last so-lution may be dropt in, for a small excess in its quantitywill be of no inconvenience, but a small deficiency, byleaving part of the sal mirabile undecompounded, will oc-casion the mineral alcali, for which this process is onlypreparatory, to be impure, as will appear in the followingoperation.

3. Separation of the mineral alcali from cubic nitre.

The marine alcali being by the above methods com-bined with the nitrous acid, the acid is to be separatedfrom it by deflagration with inflammable substances. Mixthe cubic nitre with one fifth or one sixth of its weight ofpowdered charcoal, grinding them thoroughly together :the coal of animal substances is preferable to that of vege-tables, as the latter will leave, after burning, some smallportion of an alcaline salt, of a different nature from thatwhich is here required. Throw the mixture, by a verylittle at a time, into a large crucible made just red hot,covering the crucible, as speedily and as close as may be,after each injection, to prevent the matter from being dis-sipated by the strong deflagration which ensues. Whenthe mixture has been all thrown in, and the detonationhas ceased, the fire may be augmented, and a pretty strongred heat kept up for half an hour or more, the crucibleduring this time being left uncovered. The nitrous acidbeing thus burnt out, there remains in the crucible a blu-

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