AMMONIA. —Sulphate of Ammonium. 197

Ammonium sulphate is found native (Mascagnite),usually in mealy crusts and stalaetitie forms. Itcollects about the solfatara of Naples , round vol-canoes, and in the fissures of the lava, as at Etna ,Vesuvius , and the Lipari Isles. This mineral isnamed after its discoverer, Professor Mascagni .

Manufacture .—Sulphate of ammonia is obtainedfrom gas liquor by the following process:—Alarge pipe conveys a quantity of gas liquor to alarge boiler placed over a fire, the flue from whichcirculates round the bottom and sides; a large pipeissues from its upper surface top, and descendsthrough an adjoining tun, containing sulphuricacid, to its bottom. By bringing the contents ofthe boiler to ebullition, the free ammonia is drivenoff through the pipe into the tun containing acid;here it is absorbed by the sulphuric acid, giving riseto ammonium sulphate. Distillation is continuedtill no more ammoniacal vapours are given off, andthen the fire is checked, while the residual liquor isdrawn off and mixed with sufficient quicklime togive it a strong alkaline reaction; the whole is thenrun into a second and larger boiler, like the preced-ing, on the principle of a still; under this a brisk fireis applied, and the ammoniacal vapours liberated bythe action of the lime are transmitted through thesulphuric acid solution in the tun. After all theammonia is obtained, the waste liquor is run off.

During the time the ammonia vapour is blownthrough the sulphuric acid liquor, much water isremoved from the solution by the heat from thesteam and ammoniacal gas, so that less fuel is re-quired in further concentrating the liquor. Theevaporating pans are similar to those used for boilingdown the chloride of ammonium solution. Muchmore care is requisite when fire is applied directly tothe pans, than when the concentration is effected ata steam heat; for the organic matter which the liquorcontains partially decomposes the sulphate into sul-phide, which reacts upon the iron pans, or by theexcess of acid present is decomposed, giving off sul-phurous acid or sulphuretted hydrogen gas. Theoperative watches carefully for any traces of theodour resembling that of rotten eggs, which charac-terizes sulphide of hydrogen, because this tells himthat decomposition is taking place, and of courseadmonishes him that it should be prevented by im-mediately withdrawing or slacking the fire.

Crystallized sulphate of ammonia obtained in thefirst operation is much purer than the chloride ofammonium already described, in consequence of theimpurities of the crude liquor being removed by thedistillation. After the crystallization, the crudeliquor which is still acid is returned to the tun, tocombine with further quantities of ammonia.

Besides the ordinary gas liquor, the impure chlo-ride from the packing-house and the refuse of thesublimers are decomposed by lime, and the eliminatedammonia either transmitted through the acid solu-tion to form sulphate, or used to prepare thecarbonate. The sublimation of the crystallizedsulphate cannot well be effected; but ammoniumchloride may be prepared from it, by mixing it

with a proportionate quantity of chloride of sodium,and then heating; the chloride is sublimed, and sul-phate of soda remains in the bottom of the sublimer.

In subliming ammoniacal salts, considerable ad-vantage results from the use of large vessels, as thelabour of attending them is less in proportion, andthe fire which is requisite to heat a pan of 3 feet indiameter would serve, with very little addition, tosublime the contents of one of 9 feet; the time re-quired also in working the charge of each sublimer,whether it be 3, 5, or 9 feet diameter, is nearly thesame, though the quantity of salt produced by thelarger ones is very different. A great advantage inspeed of working is gained by making the bottomrise in the centre instead of being flat. The heat isthus sooner communicated to the mass of the mate-rial, and the time required for sublimation is muchshortened. Ammoniacal gas liquor yields from J lbto lb. of sal-ammoniac per gallon of liquor, butthis quantity is subject to much variation from manycauses.

In the manufacture of ammonium chloride asalready described, if the purification of the liquorbe not effected before crystallizing the salt, sometraces of ferrous chloride are generally present, some-times in large proportions. When the crystals arcsubmitted to heat in sublimation, the ferrous chlorideis volatilized, and blends with the ammoniacal saltin the colourless as well as in the dark or brownseams of the cake.

Wurtz, who examined this substance, states thatneither the brown nor colourless portions of thesublimate give any indications of iron with theusual reagents, until nitric acid has been added toconvert the ferrous salt into the ferric modification,after which the addition of potassium ferrocyanideproduces a very distinct precipitate of Prussian blue ,and potassium sulphocyanide a red coloration. Itwas not generally considered that the colourlesschloride of ammonium contained iron till Wurtzdiscovered this reaction. It seems that the ironmight be present in the lie as ferric chloride, and issubsequently converted into ferrous chloride by thereducing action of ammonium chloride. The reac-tion may be represented as follows :—

Ferric

Ammonium

Ferrous

Hydrochloric

Amidogen.

chloride.

chloride.

chloride.

acid.

*'eAf

+ 2 NII 4 CI =

2FeCl 2

+ 4II Cl +

2NII a ;

Ferric

Ammonium

Ferrous

Hydrochloric

Nitrogen.

chloride.

chloride.

chloride.

acid.

3Fc 2 C1 6 + 2NII 4 C1 = GB'eCL, + 8HC1 + 2N.

In either case the ferric chloride is converted intoferrous chloride.

Repeated crystallizations would remove the ironcompound, but this would cause a loss of time, fuel,and material. The smallest trace of this salt can beseparated at very slight cost by passing a few bubblesof chlorine gas through a concentrated hot solutionof the salt in the crude state, which reconverts theferrous chloride into ferric chloride ; this in turn isdecomposed by free ammonia, with the precipitationof hydrated ferric oxide of iron and the formation