PART III.

Alkalies and Neutral Salts.

587

Dublin." Take of muriate of ammonia, reduced to powder gndwell dried, carbonate of soda, dried, each half a pound. Mix:then put them into an earthen retort, and sublime with a heatgradually increased, into a receiver kept cold."

Syn. Carbonate d'ammoniaque (F.), Kolilcusiiures ammonium (G.), Sotto-carbonato d'ammoniaco (/•)•

This salt is produced by a double decomposition of the sub-stances employed. The lime of the chalk attracts the muriaticacid of the muriate of ammonia, while the carbonic acid isattracted by the ammonia. The muriate of lime whichformed remains in the retort, while the subcarbonateammonia sublimes and concretes into a cake on the sides

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the receiver. The theory of the Dublin process, in whichthe carbonate of soda is ordered instead of chalk, is preciselythe same, only less heat is required; but it is too expensiveto be generally employed. The chalk, or the carbonate ofsoda, should be extremely well dried, and the ingredientsvery intimately mixed, that the decomposition may be ascomplete as possible. The retort should have a wide cylin-drical neck; and the receiver have a nearly cylindrical form,to permit the concreted salt to be taken out without breakingthe glass. '

Qualities. — Subcarbonate of ammonia has an ammoniacalpungent odour, and a slightly acrid, yet cooling taste. It isusually in a white, semitransparent, hard mass, which breakswith a striated fracture; has the specific gravity of 0 - 966 "- ;and is totally volatilized, when pure, in a moderate heat.It is soluble in less than three parts of water at 60°, in anequal weight of warm water; but in the latter it effervesces,and is partially decomposed: it is insoluble in alcohol, whichcoagulates to a spongy mass a strong solution of the salt. Itchanges the vegetable blues to green. Exposed to the air itgradually effloresces, and loses its pungent odour, owing eitherto the volatilization bf the superabundant ammonia it contains,or to the absorption of carbonic acid from the air. 3

Bergman makes its constituents to be 45 parts of carbonicacid, 43 ammonia, and 12 water, — in 100 parts; but thisstatement has been shown to be erroneous; and I am inclinedrather to adopt that of Mr. Phillips 4 , who makes the propor-tions to be 50 carbonic acid, 89 ammonia, and 11 of water.Sir H. Davy, however, has found that the quantity of alkalivaries according to the temperature that has been employed in

' This salt is prepared, on a large scale, by sublimation from an iron pot, towhich the heat is directly applied, and which is connected with a large earthen orleaden receiver. Murray's System of Materia Medica, ii. 228.

4 Annates tie Chimie, xxviii. 12. 3 The neutral carbonate is inodorous.

* Remarks on the Edilio Altera of the Piiarm. LomU p. 16.