NIT

NIT

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its materials being duly lixiviated, a large quan-tity of nitre will be obtained. This methodtvas adopted in many parts of Germany withreafonable fuccefs, but requiring much manuallabour was at length abandoned for more eco-nomical precedes.

In direCt oppofition to the inftruftions onthis fubjeft by Glauber who had clearly fhownthe abfolute neceffity of the prefence of air to theformation of nitre, feveral very large experimentswere made, chiefly in Sweden and Germany toprepare this fait by filling large trenches withanimal and vegetable refufe of various kindsmixed with quicklime and wood allies and dulywatered with urine. But though all othercircumftances, were tolerably favourable theexclufion of air from the greater part of themafs fo delayed the production of nitre, thatafter the expiration of 20 years a fmallcr quan-tity of this fait was thus obtained than is yieldedby the fame materials in two or three years whenthe air is freely admitted to them. Attemptswere made to remedy thefe defedts by the infer-tion of pipes and air {hafts, but with little fuc-cefs compared to the trouble and expence; fothatat length, inftru&ed by experience, the Swedesadopted that mode, which with a few modifi-cations they ftill retain, and the advantages ofwhich are daily more and more apparent.Upon a fquare floor of brick or fbone, is laid abed a few inches thick compofed of woodafhes,lime, and mellow vegetable earth moiftened withurine, and the mother water obtained in therefining of nitre: upon this is placed a layer offtraw or old thatch, then another of the com-pofition, and fo on alternately till a pyramid 8or 9 feet high is conllructed. In order to pre-ferve thefe piles from the rain and fnow whichwould wafh out the fait as fall as it formed, anumber of ftout poles are ftuck in the groundall round the floor, the tops of which are tiedtogether, and their interftices carefully clofedwith intertwifted twigs, thus excluding therain, but admitting the air. Thefe pyramidsare watered from time to time with putridurine, and in about a year faline efflorefcencesbegin to appear on their furface: lhortly after,the nitre thus generated is fwept off', and thepiles then yield regular crops of this fubftanceevery week or ten days, except during frofty■weather, for about nine years. At the expira-tion of this period the efflorefcence ceafes, andthe nitre yet remaining in the pile is obtained

y ixmation: the infoluble refidue is an excel-lent manure and much in requeft for flax andJ»emp. la i ruffiu, nitre is obtained from mud

walls compofed of loamy earth, night foil, mudfrom ponds, liable litter, and any other vege-table or animal fubftances: thefe being mixedtogether and tempered to the confiftence offtiff mortar by urine and dunghill drainings,are raifed into walls four feet high and abouttwo feet thick, and topped with a flight copingof thatch in order to Ihoot off the rain: inprocefs of time the ftraw and other vegetableswhich the walls contain decay, by which it isrendered more porous and the air gets admiflionmore or lefs to its interior fubftance. Manyhowever are the objections to this method ofpreparing nitre. In the firft place the labourrequired for the conftruclion of thefe walls isvery confiderable: fecondly, the clayey loamwhich is neceflary to give the mafs a due con-fiftence for the formation of walls, prevents itfrom being fufficiently porous even after theftraw, &c. has decayed: thirdly, there is feldoma proper quantity of calcareous matter, fo thatmuch of the nitrous acid flies off for want of afit bafe to detain it: and fourthly, the veryimperfeCt protection from the weather whichthefe walls receive from their thatch coping,fubjedts a confiderable quantity of the fait whenformed to be wafhed out by the rain and thusloft. For thefe reafons it is feldom worthwhile to lixiviate this earth oftener than once inabout fix or eight years, and even then theproduce is very fcanty.

In France the nitre-beds are compofed ofnitrous earth from farm-yards, ftables, &c. offtreet fweepings, of mild calcareous earth, fuch.as old mortar or plaifter, chalk, tufa, or thefweepings of roads paved with limeftone; ofanimal matter, fuch as night-foil, blood, refufefrom the Ikinners and tanners, bones and other,offal; of vegetable matter, fuch as ftraw andliable litter, leaves, fawduft, fpent tanner’s-bark, &c. Thefe are all mixed in fomewhatcafual proportions, care, being only taken that aluflicient quantity of calcareous matter is pre-fent; they are laid as lightly as polfible in longbeds or pyramids under covered roofs to protect'them from the weather, and are kept dulymoiftened with putrid water or urine: by this-management they yield every other year by,lixiviation a confiderable quantity of nitratedlime, which by the addition of woodalhes or-potalh is converted into true nitre. The cir—cumllance in which the French nitre bedsdiffer principally from thofe of Sweden andGermany is that they fcarcely ever containwoodalhes, the requifite portion of alkali being-added in a fubfequent part of the manufacture*