AMMONIA.— Preparation froji Ammoniacal Salts.

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peculiar facilities in the preparation of many com-pounds on account of its great volatility, as also thatof its salts, and as being an almost universal precipi-tant of the oxides of the heavy metals. In medicine,ammonia is used to a moderate extent to alleviatespasms, for rousing the vascular and respiratorysystem, as an antacid, and in various other cases.It is extensively employed in bleaching and calico-printing, in colour manufactories, for making arti-ficial manures, and other important trades.

When ammonia is manufactured on the large scalefrom ammoniacal salts, the sulphate of the alkali isfor the most part preferred; but there is no materialdeviation from the directions already laid down, ex-cept that another kind of apparatus is used, to avoidthe loss of retorts which is incurred when preparingit in the laboratory. It is particularly necessary,when working upon the large scale with condensersin the form of Woulfe’s bottles, to have the jointswell luted; this is effected by covering each connec-tion with a paste made of white of egg and chalkintimately ground. A better composition is producedby blending wax, resin, and turpentine together;

Fig. 3.

this should bo applied upon the connection of thetubes and tubulures of the condensers in moderatethickness. If this point is not attended to with care,the pressure upon the gas forces it through intothe atmosphere, causing the workmen considerableannoyance till arrested.

Fig. 3 is a vertical section of an apparatus whichanswers well for the preparation of ammonia on alargo scale.

A is an iron retort, placed in sand, over the fire g,of which 7j is the ash-pit, and x the chimney; a is thestopper, and b an iron pipe connected to the neek ofthe retort, and reaching some distance from the fur-nace to the end of the tube, c, which may be eitherof glass or lead. B is the first condensing vessel, andis supplied with three tubulures, through the middleone of which a safety tube is inserted, e is a stop-cock and pipe, by which the contents of b are drawnoff when requisite. This vessel is left nearly empty,for the purpose of purifying the gas of any traces ofammoniacal salt which may be earned over, and also forretaining traces of oily matters which are invariablypresent, eitherfrom the impurity of the salt employed,or from the grease with which the stopper is smeared

to prevent it from adhering too tightly in its place.B is connected with other condensers, of which onlyone, c, is seen in the figure; these vessels are filledto about three-fourths of their capacity with water,and so rapid is the absorption of the gas, that scarcelya trace of ammonia escapes from C till the solutioncontained in it is completely saturated.

When this happens, the solution of ammonia isdrawn off by the stopcock, d, and the very weakliquor in the third condenser supplied instead, or it isrecharged with a fresh quantity of water.

In this process it is very easy to produce, at eachoperation, an ammoniacal liquor of any standardstrength, by furnishing each condenser with a g’assgauge pipe, graduated into equal parts, showing thebulk of liquid in the interior. Whatever bo thequantity of water introduced, it expands in the ratioof six to ten, as before stated, on being completelysaturated with the alkaline vapour, or in less propor-tion according as its gravity is reduced. At the firstworking, the measure of water employed is noted,and also the proportion of expansion, till it approachesthat point which, by calculation, is found to corres-pond with the strength of the liquid required; thismay be corroborated by drawing off portions re-peatedly, and taking their density, and from thisnumber the quantity of ammonia is ascertained bythe aid of tables, which will be found further on. Assoon as the exact point is gained, the gauge isscratched at the level of the liquid, and this one testwill serve for all future operations where the am-monia is to be made of the same strength; but it isnecessary that the bulk of liquid should be alwaysequal to that used in the first experiment.

When gas ceases to be evolved from the mixturein the retort, the fire is partly urged, and the stopperremoved by moans of a lever. If the stopper be sofirmly fixed that it cannot be readily displaced, acloth moistened with cold water should be carefullywrapped round it, without touching the neck of theretort; this refrigeration causes a contraction in itsparticles, and will enable the operator to remove itwith facility. The residue—which is fused chlorideof calcium, in the event.of the chloride of ammoniumbeing used—is then ladled out. Should sulphate ofammonia be operated upon considerable quantities ofwater are employed, and the distillation should neverbo allowed to proceed to dryness, as in such a casethe sulphate of lime formed would constitute a con-crete on the bottom of the retort, which could not beremoved without much labour and loss of time.

All the ammoniacal impurities which have collectedin B during the first distillation are drawn off, andintroduced into the retort in the second operation, toobtain the ammonia which they hold, and a smallquantity of fresh water is substituted, to cover thelower end of the safety tube, as in the precedingoperation. This apparatus, when once erected, willlast for a long time.

A modification of the foregoing apparatus repre-sented in the annexed cut—Fig. 4 —is sometimesemployed.

a is an iron kettle, to which a metallic lid, b b, is