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fome dry fand, and a ftratum of iron filings overall. In this arrangement therefore the carbonicacid, gas expelled from the chalk by heat wouldhave to traverfe a ftratum of fand three inchesthick before it would reach the iron filings. Thegafeous products of the diftillation were a quan-tity of undecompofed carbonic acid, togetherwith a large proportion of the inflammable gas,and the iron filings were found confiderably oxi-dated when taken out. The decompofition ofcarbonic acid by metals does therefore take placewhen the acid is in the gafeous form, but by nomeans fo perfedtly as in its nafcent ftate. Afimilar decompofition was alfo effected by for-cing the fame carbonic acid gas fucceffivelybackwards and forwards through an iron tube,the middle of which was full of iron filings, andwas kept red hot by a fmall furnace beneath it.A bladder was tied to each extremity of the tubeto receive the gas. By twenty times pallingthe gas {lowly through the red-hot part of thetube two-thirds of it were converted into in-flammable gas, and, by continuing the procefs,three-fourths.

Solution of Carbon in Carbonic Acid .

It is obvious that increafing the oxidable bafeof any fubftance already united with oxygenmuft have the fame relative effect, as abftrafit-ing a portion of its oxygen ; and this offers ano-ther mode of converting carbonic acid into theinflammable oxyd of carbon, which has beeniuccefsfully prafitifed by Meffrs. Deformes andClement.

Pelletier in his valuable experiments on barytesand ftrontian, d difcovered that the native car-bonat of barytes, though fcarcely calculable perfe in any fire, would readily part with its car-bonic acid by calcination if previoufly rubbed tofine powder, and mixed with a fmall quantityof charcoal. The chemifts above-mentioned onrepeating this experiment with three parts ofcarbonat of barytes and one of charcoal obtaineda large quantity of gas, compofed of about £ 0 fcarbonic oxyd, and £ of carbonic acid, and inthe retort the barytes was left quite cauftic.Here, therefore, it is to be fuppofed that the car-bonic acid is fuperfaturated with its own bafe,and thus rendered much more volatile thanbefore.

A more direct combination of carbon withcarbonic acid was alfo obtained by the famechemifts, precifely with the fame apparatuswhich Mr. Cruiklhank had- employed for pall-ing the carbonic acid gas over red-hot iron,that is, with a tube filled in the middle with

charcoal, and with a bladder faftened to eachextremity, which was kept alternately full orempty as the gas was preffed backwards andforwards through the tube. The firft fenfibleeffect produced on the calcined gas was a con-fiderable dilatation, which was exclufive of theexpanfion by mere heat, and arofe from the fo-lution of a part of the heated charcoal in thegas as it palled over. After each experimentby far the greater part of the carbonic acid wasfound changed into the inflammable gafeousoxyd of carbon, the proportions of the 1 formervarying from about T *o to The remainingcharcoal taken out and weighed was foundto have loft confiderably, but the lofs wasgreater when iron tubes were ufed than withthofe of glafs or porcelain. Reckoning, there-fore, the quantity of charcoal taken up by thecarbonic acid in the different procefles to beindicated by the lofs of charcoal from the tubes,the compofition of the gafeous oxyd into whichthe carbonic acid was converted was found tobe, when iron tubes were ufed, about 48 ofoxygen to 52 of carbon; and when porcelainor earthen tubes were employed it confifted ofabout 53 of oxygen to 47 of carbon.

It would appear from the refult of feveral ex-periments that the inflammable gas is the pureftwhen prepared from chalk and iron, or zincfilings; for when charcoal and the metallicoxyds are employed, or charcoal in any way,fome admixture of a gas always appears, whichcaufes the production of a portion of waterwhen the whole is burnt with oxygen, andtherefore muft be hydrogen but this is not thecafe with the inflammable air from chalk orcarbonat of barytes and metallic filings. Thisif taken after the firft portions have palfed overand walhed with lime-water or cauftic alkali, tofeparate any carbonic acid it may contain, maybe confidered as pure gafeous oxyd of carbon, orcarbonous oxyd, and its charaCteriftic properties,(according to Cruiklhank where not otherwifefpcified) are the following, to which may beadded the diftincHve marks whereby it is foundto differ from carburetted hydrogen.

Carbonous oxyd is nearly of the famefpecificgravity as atmofpheric air, heing lighter thancommon air only in the proportion of 22 : to 23.Its fpecific gravity therefore will be about 1.177(water.being 1000. and common air 1.2308).On the other hand, the average weight of thetrue carburetted hydrogen is not more than halfthat of common air.

d Kemoires de relit, tier..