CAR

CAR

( 26 3 )

and the whole lofs of weight, deducting that ofthe carbonic acid thus expelled, was luppofedto be the weight of the charcoal: but charcoalthat had been foaked in hot water can by nomeans be dried at a temperature below a redheat, and therefore a large deduction mull bemade from the charcoal, on account of thewater contained in it.

On referring to the refults of the analyfis wefind 250 grs. fet down as dry cauftic foda, butfomewhat impure: this is entirely founded ona grofs blunder. Among the cryftalline faitdepofited by the lixivium was a portion of 346grs.: this confided of “ a mixture of vegetable“ and mineral alkali, with a proportion of ex-u tra£!ive matter and fome digeftive fait.” The(( mere alkali” contained in this is eftimatedby Mr. K. at 253 grs.: but this is impoffrble,for 250 grs. of mere foda would produce 1136grs. of carbonated foda, whereas the fait in quef-tion with all its impurities, amounted only to346 grs. A fimilar objeftion may be made tothe 127 grs. fet down as dry cauftic foda mixedwith muriated foda. Mr. K. fays, “ I obtained* £ 127 grs. of a mixture of mineral alkali and

common faitbut this like the former wasprocured by cryftallization, and therefore the127 grs. even if they were pure carbonated fodawould indicate no more than 28 grs. of purefoda.

Kelp is made of what is vulgarly called fea-weed or fea wrack (whence the French termfoude de varech ) that is of fuch of the leafy fuci,principally the veficulofus and ferr at us, as growon rocks in the fea between the high and thelow-water mark. The moft favourable fituationfor thefe plants is a fheltered bay full of cal-careous rocks: for limeftone is not only morefavourable to the growth of thefe fuci than anyother kind of ftone, but from its lying generallyin nearly horrizontal beds is more acceflible atlow-water than thofe rocks which affedt a morevertical inclination, and therefore form narrowridges. The feafon for gathering the plants isfrom May to Auguft. On the Britifh coaftsthey are cut with a fcythe as clofe to the rockas poflible, and then bound up into large bundles,which being faftened to one end of a long rope,the other extremity of it is tied to a boat, andthus the labour of two or three men is capableof towing feveral tons weight to the fhore. Thepradtice of cutting the Items is however by nomeans fo judicious as the French method oftearing them up by the roots with inftrumentslike rakes; for it has been clearly fhown 11 that

b Mem. des Sciences, 1772, Part ii. p,

the items when once cut never throw out anymore leaves, and the root being a long time indecaying, occupies unprofitably the fpace whichotherwife would be filled by young plants. Thelarge bundles when landed are to be opened andtheir contents fpread thinly on the fhore todry, turning them from time to time, left theyfhould ferment, by which both the quantity and'quality of the kelp would be greatly deterio-rated. The ware when dry ihould be Hackedfecure from rain for a few weeks till it becomescovered with a white faline efflorefcence, andthen it is ready to be burnt. The furnace em-ployed for this purpofe ufed to be, and in manyparts ftill is, nothing but a round pit three orfour feet deep, and feven or eight feet acrofs,lined with ftones : the more fkilful kelp-burnershowever make ufe of a kiln of the followingconftruction. * It is built of ftone in the iliapeof a long open coffer, being 28 inches wide inthe clear, about 2§ feet high, and from 8 to 18feet long. The bottom of the kiln being coveredwith bruih-wood or heath, a thin ftratum of thedried ware is ihaken lightly upon it, and fire ijapplied to the leeward end of the kiln. It mullnow be gradually fupplied with freih warethrown lightly on wherever the combuftionreaches the furface : if the weather is perfe&lycalm no further precautions are required than totake care that the fire is not ftifled, but if itblows ever fo little the windward fide of the kilnmuft be covered with fods, and even both fidesif the weather is at all boifterous. When allthe ware has been thrown on that is intendedto be ufed at one time, care muft ftill be takento cover every fpot where the fire reaches thefurface with a little of the charred, or leaft burntpart, laid lightly on by means of a fork. Aftera time that part of the mafs which is neareft tothe fides is feen to foften or melt, and now be-gins the moft critical part of the whole procefs.An iron bar previoufly heated is to be intro*duced among the foft matter, which by thismeans is to be llowly ftirred up and incorpo-rated, adding by degrees fome of the lefs burntportions, and in this manner the whole is to bekneaded together till it becomes a pafty femi-fluid mafs. It is a matter of confiderable dex-terity fo to perform this procefs as to be ableto mix the dull and fragments of a precedingburning with the prefent, without too muchcooling the whole. If when this incorporationof the materials is begun the mafs is too hardand dry, by waiting a Ihort time it will be foundto have acquired the neceffary temper, but if it70. ■ Repertory xii. p. *46,