CAR ( 243 ) CAR

then clofed up, leaving only a very fmall open-ing for the heated air to efcape. After heatingthe tube red hot for a few minutes it was re-moved from the fire, and when cold, was broken.It contained a black powder, confuting of char-coal mixed with a compound of phofphat oflime or lime united with phofphoric acid, and ofphofphuret of lime or lime with phofphorus.The phofphat of lime, and the lime of the phof-phuret were feparated from the charcoal byfolution in an acid and filtration, the remainingphofphorus was expelled by fublimation in aclofe veffel, and thus the charcoal was left pure.This in no way differed from common charcoalof wood, deflagrating with nitre, and yield-ing carbonic acid by the combultion. In theabove experiment therefore a part of the phof-phorus is oxygenated at the expence of the car-bonic acid, and the decompofition of the latterappears to be effected by complicated affinities,namely by that of a part of the phofphorus forthe oxygen of the carbonic acid, of another partof the phofphorus for the lime of the marble,and of the phofphoric acid (as foon as formed)alio for the lime. Therefore the experimentfucceeds better if the marble is firft flightly cal-cined, that the furface may afford cauftic limefor the phofphorus immediately to act upon.Phofphorus alone ha9 lefs aifinity for oxygenthan charcoal has, otherwife it could not be pro-duced by the Ample heating of a mixture ofphofphoric K acid and charcoal.

A iimilar decompofition of carbonic acid waseffected by Dr. Pearfon with phofphorus andcarbonat of foda, dried fo as to expel all itswater of cryftallization, but not its carbonicacid. After heating red-hot for twenty minutes,the contents of the tube, which were partlymelted to the glafs, confifted of fome undecom-pofed carbonat of foda, of phofphat of foda, andof a black powder, which when feparated andanalyfed was found by many fatisfadtory. trialsto be pure charcoal. The quantity of it variedin different experiments from 32 to above 40grains, from 200 grains of phofphorus and 800of dry carbonated foda of the firft materials.

Befides this entire decompofition of carbonicacid, a partial deoxygenation takes place in agreat' variety of inftances, and the product isthat kind of inflammable gas, the nature ofwhich was long unknown and confoundedwith hydrogen and with hydro-carbonat gas,rill the late experiment's of Mr. Cruikfhank,who firft pointed out the true grounds of dif~tmttiou, and has dcmonltratcd the leading pro-

* Obf. on Ail

perties of this fubflance, intermediate betweencarbon and carbonic acid, to which agreeably tothe prefent fyftem of nomenclature, the nameof Gafeous Oxyd of Carbon, or Carbonous Oxyd hasvery properly been given. This will be defcribedin the next article, and to it may be referredmany curious experiments on the decompofitionof carbonic acid by electricity, performed byPrieftley and others.

Befides the fources of carbonic acid alreadymentioned, it is produced in abundance by theaction of nitrous acid on charcoal, and even onany fubftance containing a carbonous bafe. ThusDr. Prieftley k procured it from alcohol and-fuming nitrous acid. Under the article Nitrous.Acid, it will be feen how far the a£tion of this-acid refembles the effects of common combuf-tion, and hence it may generally be inferred thatwherever carbonic acid would be generated bycombuftion, it would alfo be produced by the.aftion of the nitrous acid on the combuftiblefubftance.

Many liquids abforb carbonic acid with greateafe, fuch as alcohol, oil, &c. but it appears to be:retained by no ftronger adhefion than to water,and to be expelled by heat or other means, with-out having produced any fenfible change. Inlike manner it mixes readily with every gas, butthe only perceived effect is to render the air lefsable to maintain combuftion (when at all fo)and it does not feem to enter into any. chemicalunion with any of the gaffes. Ammoniacal gasmuft be excepted however, for with this it unites,inftantly, and a denfe white cloud arifes on mix-ture, which condenfes into a folid carbonat ofammonia.

The affinity of carbonic acid with the alka-lies, earths, and metals, is fo weak that it is dif-placed in molt inftances by every other acid,the boracic perhaps excepted. Hence it is that-a carbonated alkali will ejfervefce with any other-acid, being expelled from, the alkali in form ofgas. This tendency to afliime the gafeous formcontributes much to the weaknefs of its affi-nity.

The order of the affinities of this acid are—barytes, ftrontian, lime, potafli, foda, magnefia,.and ammonia. With regard to the two laft,.their affinities are fo nearly balanced that nei-ther will entirely decompofe the carbonat of-the other fubftance, and the difference of a fewdegrees of temperature makes an effential alter-ation in the relative force of affinity.

The tendency of carbonic acid to quit all its-combinations when ftrongly heated, renders , it:

■, vol. i. 134,

2H.2.