A L K

A L K

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decomposes upon the iron turnings, and fnuchturbid hydrogen gas comes over. At the sametime however the potassium is produced and isalso vaporized within the furnace, but imme-diately condenses, partly in the extremity ofthe barrel, D. and partly in the copper recipient,all of which are, as before, kept cool by wettedcloths. When the efllux of gas begins to'slacken, an additional portion of potash is sentdown, by shifting the hanging trough of char-coal a little higher, and so on till' the whole-has been heated almost to the extremity A..It is of importance not to send over too muchalkali at once, as this would damp the heat ofthe iron turnings, and lessen the product ofpotassium,, and this too is one reason why thepotash is put in in large pieces. It is a signthat the operation is going on well when theproduct of hydrogen at the lower extremityis pretty steady and abundant, but not very■ cloudy. The distillation i3 terminated whenall the alkali has been successively melted down,which takes about an hour from the timethat the gun-barrel is first made white-hot,and it then only remains to collect the product,,which requires a little dexterity and caution.

The potassium being volatile condenses forthe most part in the end of the barrel at D.and thence falls down into the copper recipientG. II. where it solidifies. To collect it,remove the barrel when the distillation is over,stop the upper end A. with a little lute, andhasten the cooling of the barrel by strippingoh the lute and wetting the outside, then pulloff the copper recipient (immediately stoppingthe end D. of the gun-barrel that'is thus ex-posed) separate it into 'its two parts, pour intoeach a little naphtha, and detach all the potas-sium with a knife, throwing it into a bottle ofnaphtha as soon as separated. As some of thepotassium remains in the end of the gun-barrelnearest to the recipient, it is the best way tocut off that end with a file, (as the barrel willnever serve for a second operation) and topush out all the potassium into oil with a solidmould made for the purpose. This is generallymixed with a little potash from which it maybe freed by melting in oil and pressing the whole.

The product of two experiments is given bythe authors, in which it appears, that in one,70 grammes (about 18 drams troy) of potashwas employed of which nearly yths was re-covered undecomposed from the iron turnings,and the product of potassium was 15.5 grammes(231 grains troy.) In the other experiment

81. gramme^ of potash were used, mid theproduct of potassium was 20. 2 grammes ornearly a third more than in the former case.

Sometimes the efflux of hydrogen gas fromthe lower part of the barrel ceases suddenly,and appears at the upper extremity. Thismay be owing to the stoppage of the. end D.by a collection of condensed potash, when thefire has not been kept hot enough or when thealkali has been sent down too fast. This maysometimes be removed' by heating the tubewith charcoal on the outside, and melting awaythe obstruction. But if no gas is sent outfrom- either end,, it generally shews that thebarrel has partly fused down owing to someimperfection in the lute, in which- case theprocess must be discontinued and renewedafterwards either with a fresh barrel or betterluting. If a very large barrel is used, a freshcharge of potash may be thrown into the upperpart, and the process kept up for an additionaltime provided enough of iron turnings areintroduced at first.

After the operation, if the gun-barrel isdivided in different parts where it has beenexposed to the furnace, it is found to containa very hard agglutinated mass of alkali, oxydof iron, alloy of iron and potassium, and un-altered iron turnings, which' require consider-able digestion in water to dissolve out thealkali. The quantity of alkali recovered fromfile iron, is full half of what has been used,and yet a large portion of the iron turningsretain their metallic appearance and their form,so that there is probably much loss of potassiumby its alloy with part of the iron, which returnsto the state of potash when moistened.

It may be of some assistance to the chemicaloperator to give Dr. Henry’s very clear direc-tions for preparing potassium, according to aprocess just described, but with some littlevariation in the apparatus. 0

The apparatus consists of a common gun-barrel, curved and drawn out at one end torather a small diameter, (see plate, fig. 3).To one end ’is adapted an iron tube a. withan iron stopper) of the capacity of two cubicinches, for containing the potash. At thebottom of this tqbe is a small hole h throughwhich the potash gradually flows. This tubeis shewn separately in fig. 4. To the oppositeend of the gun-barrel a tube of safety e is tobe cemented ; and into this a sufficient quantitypoured either of mercury or naphtha. Into thegun-barrel 2\ parts of very clean iron turnings-

* Elements of experimental Chemistry, Gth. edition, vol. 1.

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