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Tests for Pure Air

A simple method of ascertaining the presence of impurity (carbonic acid) in the atmosphere, is to nearly fill a glass tumbler with limewater, and blackish precipitate, insoluble in muriatic acid. of ammonia give a black precipitate, insoluble Sulphuretted hydrogen and hydrosulphuret in simple acids.

Ammonia gives a reddish-yellow precipitate (fulminating gold) with tolerably concentrated solutions, either at once, or on boiling the liquid. Liquor of potassa gives, with neutral solutions of gold, a similar precipitate to that formed by ammonia, insoluble in excess. to place it in any convenient position, as on 4077. Fused Nitrate of Silver. Take the mantelpiece of a room. The rapidity with which a pellicle forms on its surface, or the water becomes cloudy, corresponds to the amount of the carbonic acid present in the atmosphere that surrounds it.

A little moist carbonate of lead put on a plate or saucer, and exposed in the same way, will turn black, should any sulphuretted hydrogen be contained in the air. This is a very delicate test for that destructive gas M 3 ounces refined silver, 2 fluid ounces nitric acid, and 5 fluid ounces distilled water; mix in a glass flask and apply a gentle heat until the metal is dissolved. Transfer the solution to a porcelain capsule or crucible, decanting it off a heavy black powder which appears at the bottom of the flask; evaporate the solution to dryness; raise the heat, in a dárk room, until the mass liquefies, then pour it into hinged brass or iron moulds furnished with cylindrical cavities of the size of a goose-quill.

Keep the product, which is Lunar Caustic, or fused nitrate of silver, in well stopped tion until it will crystallize on cooling very slowly. (See No. 3216.) 4078. iscellaneous Chemi- bottles, impervious to the light. cals. It is proposed, in this place, ver is obtained by dissolving grain silver Crystallized (or crystals of) Nitrate of Sil- Crystallized (or crystals of) Nitrate of Silto give a concise description of the chemical (see No. 3217) in nitric acid diluted with twice compounds referred to in the various depart- its weight of water; evaporating the soluments of this book. A complete list of chemicals would not be necessary for the scope of the work, which is a purely practical one; such information only is therefore given as is deemed necessary to render the whole thoroughly intelligible, and as complete as possible. A considerable number of them are inserted, for the sake of clearness, in connection with the process or special purpose for which their use is directed. These will be found in their proper place by reference to the INDEX.