N I T

NIT

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The proportion of nitre afforded by thefeartificial beds it is not eafy to afcertain. InFrance , where the cuftom is to lixiviate once intwo years, the produce may be eftimated atfrom 7 to 12 ounces of nitre from 100 lbs. ofmaterials: of this about half is nitrat of potafh,and the reft nitrat of lime, requiring thereforethe addition of potafh to convert it into truenitre.

Concerning the theory of nitrification muchhas been written, but with the exception of anadmirable memoir by M. Thouvenel, to littlepurpofe. The chemifts of the modern fchoolhaving difcovered that nitric acid is compofedof oxygen and azot, and that animal mattersabound in condenfed azot, content themfelveswith faying that the azot as it is evolved by theprogrefs of putrefaction combines with theoxygenous part of the air, and thus forms nitricacid, which is prevented from efcaping by thelime and other alkaline bafes with which it is incontaft. This however from the little hithertoknown on the fubjeCt appears to be a very•imperfeCt reprefentation of the matter ; we (halltherefore proceed to detail the principal refultsof M. Thouvenel’s experiments, which, imper-feCt as they are, throw more light on thiscurious and important fubjeCt than any otherswith which we are acquainted. 0

Several open veffels containing each three lbs.of pure and well wafhed chalk moiftened withdiftilled water, were for the fpace of feven oreight months expofed to the putrid vapours ofprivies, cellars and prifons, being then lixiviatedthey afforded from 50 to 90 grs. of nitre each,of which the principal part was nitrat of limebut mixed in general with a little nitrat ofpotafh. From other fimilar experiments M.Thouvenel afcertained that in clofe confinedfituations where there was hardly any circula-tion of air, and on the other hand that in placeswhere the external air palled in a free current,the production of nitre was by no means fo; copious as where the putrid fumes remained fora long time in contact with the chalk, andwere only occafionally diluted with atmofphericair. In thofe places molt favourable to thegeneration of nitre were expofed together withthe veffels containing chalk, others with a likequantity of quicklime, with magnefia both mildand cauftic, with earth of alum and with thefixed alkalies both mild and cauftic. Theywere all examined after the expiration of 8months: the faline contents of the chalk wehave juft mentioned; the quicklime, the caufticand mild magnefia afforded from 6 to 7 grs. of

earthy nitrat mixed with a little ammoniacatnitrat; the earth of alum yielded a ftill fmallerproportion of nitrat, and the fixed alkalies noneat all. The refults of thefe experiments beingafcertained, another feries was undertaken andconducted in the following manner. An earth-en cucurbit was fitted to a very large receiverof the fame materials pierced with a few fmallholes fo as to allow of a partial communicationbetween its contents and the outer air: in theCucurbit was put fome putrid blood, and in thereceiver were placed open veffels containing afew ounces of lime, magnefia, earth of alum,and the fixed alkalies both mild and calcined:21 other receivers furnifhed in the fame mannerwere connected with cucurbits charged withvarious putrefcent mixtures. The gas as it wasdifengaged from the materials in the cucurbitpaffed into the receiver mixing with the atmo-fpherical air, and furrounding the inclofedearth and alkalies. After this procefs hadbeen continued for a year or more the contentsof the receivers were examined; in all of themthe chalk was found to contain nitrat of limebut varying in proportion from one to 5 grainsper oz. The quicklime, the magnefia andearth of alum in moft of the experiments hadacquired no nitric acid, but in fome a littleearthy nitrat was formed. The fixed alkalies,as in the former experiments, had acquired nonitric acid whatever. It was further obfervedthat although the chalk in moft of ,the experi-ments fhowed figns of nitrification in about amonth’s time and proceeded rapidly for thefirft three months, yet after this period theprogrefs was very flow, no doubt becaufe theoxygen of the atmofpheric air originally con-tained in the receivers having been confumed,the gradual pouring in of putrid gas from thecucurbit almoft entirely preventing the externalair from entering through the fmall holes thathad been drilled for this purpofe.

It appearing from the above experiments thatthe fixed alkalies and the alkaline earths them-felves when cauftic are very little capable ofabforbing nitric acid from a mixture of putridgas and atmofpheric air, M. Thouvenel wasinduced to try whether this was owing to anychange produced on the putrid gas by thefebodies. For this purpofe having charged aretort with putrefying materials, he connectedwith it three receivers in the manner of Woulfebottles, the laft of which terminated in a tubecommunicating with a pneumatic apparatus.Four different fets of this apparatus were em-ployed at the fame time. In the firft of thefe.

* Mem, jEtrang de l’Acad. des Sciences xi. p. no.