3. Mr Croll (Patent dated 1849) converts the crude ammoniacal vapours that issue with the gas from the common retorts into the hydrochlorate, and obtains a solution of it by passing the gas through a solution of crude CHLORIDE OF MANGANESE[54] (1 cwt. of the salt to about 40 galls. of water), contained in one of the ordinary vessels used for purifying coal-gas. The manganic solution absorbs the ammonia and its salts, converting them into the hydrochlorate, whilst a corresponding proportion of oxide of manganese is precipitated. As soon as the liquor in the purifier is fully saturated, it is drawn off, and replaced by a fresh quantity; whilst the saturated liquor containing the hydrochlorate, after subsidence, or filtration, is evaporated, &c., as before. Crude CHLORIDE OF IRON may be substituted for the chloride of manganese, in the above process: as may also SULPHATE OF MANGANESE, but then the product, of course, will be sulphate of ammonia, instead of the hydrochlorate. [Footnote 54: Obtained from the chloride-of-lime works. The portion of the precipitated oxide of manganese saved from the process may be reconverted into the chloride, by mixing 3 parts of it with 4 parts of common salt, and heating the mixture to low redness, scarcely perceptible in the dark, for 2 to 3 hours. 140 _lbs._ of the calcined mass, with 40 galls. of water, forms a solution that may be again pumped into the purifier.] 4. Mr Laming (Patent dated 1850) also proposes the use of various salts and mixtures for retaining and condensing the ammoniacal vapour of coal-gas as it passes from the retorts through the purifiers. Of these the principal are CHLORIDE OF CALCIUM obtained by decomposing chloride of iron by hydrate of lime; CHLORIDE OF IRON, obtained by decomposing sulphate of iron with chloride of sodium; CHLORIDE OF MAGNESIUM; a mixture of SULPHATE OF LIME and SULPHATE OF IRON; or of moist precipitated oxide of iron with carbonate of lime, carbonate of magnesia, or magnesian limestone; or one containing sulphate of magnesia, or chloride of magnesium or calcium, or one or more of them, in combination with oxide of copper, either with or without lime or magnesia, or with both or either of them or their carbonates. These salts, or compounds, are mingled with sawdust, or some other porous substance not acted on by the gas, before being put into the purifiers; and after they become saturated with the vapour, the newly-formed hydrochlorate or sulphate (according to the salt or mixture employed) is washed out of the mass with water. Besides the usual sources of SAL AMMONIAC (and the other ammonia-salts of commerce) it has been proposed to obtain it from guano, peat, shale, &c., as noticed under SESQUICARBONATE OF AMMONIA (_suprà_); the substance employed to effect the neutralisation or decomposition of the ammoniacal liquor being, in this case either hydrochloric acid or a chloride.