CAR
C 238 )
Carbon is faid by Proull to be capable ofuniting with phofphorus, but this from an ex-periment of Clement and Deformes f appears tobe a miftake.
Two of the metals are known to unite withcharcoal: when in combination with Iron itforms Jleel , and with Copper it forms a peculiarfubltance, firft noticed by Dr. Prieftley, andnamed by him charcoal of copper.
The a£tion of the alkalies upon charcoal hasnot yet been examined into with any accuracy.Cauftic potafh when digefted for fome timeupon charcoal becomes partly carbonated, butthe carbonic acid thus produced is in all proba-bility to be attributed to the decompofition of aportion of water.
The undecompofable acids appear to have noaction on charcoal; but the decompofable onesare deprived by it of their oxygen either inwhole or in part, and the charcoal is convertedinto carbonic acid. Thus fulphuric acid by beingpalled through red-hot charcoal furnilhes ful-phur, fulphureous acid and carbonic acid. Nitricacid yields nitrous gas and carbonic acid; phof-phoric acid yields phofphorus and carbonic acid.If charcoal highly dried and finely pulverized isfhaken into oxymuriatic acid gas, it becomes im-mediately red hot, and falls as a fhower of fireto the bottom of the vefiel.
No affinity has been indicated between char-coal and any of the earths.
Of the neutral and earthy falts thofe withdecompofable acids are ftrikingly altered by theaction of charcoal at a red heat; the othersfuffer no material change. It is worthy of no-tice, that the decompofition which the acidsundergo in thefe circumftances is much morecompleat, owing to their fixity, than when theyare fubjedted alone to the a£tion of charcoal.Thus the lulphats are changed not into fulphitesbut into iulphurets, and the nitrats give out notnitrous gas, but azot. It is remarkable howeverthat phofphat of lime is undecompofable bycharcoal. The metallic falts are all of themdecompofed by charcoal at a greater or lefs de-gree of heat in confequence of the metallic bafebeing deoxygenated, independently of the actionof this fubltance on their acids. Some of themoil eafily decompofable falts, as muriat of goldand nitrat of filver, when perfectly faturatedmay be decompofed in the moift way at a boil-ing heat, or by help of the folar light at theufual temperature by means of charcoal, themetal being depofited on the furface of the1 An. dc Chijn. xlii. p. 149,
CAR
charcoal with all its chara£lerifUc brilliancy atyfcolour.
The effects of charcoal in clarification are-both curious and important. They were firftnoticed by M. Lowitz of Peterfburg, and havebeen for the mod part amply confirmed by fuc-ceeding obfervers. In order to be employedthis way with the greateft fuccefs, it is efientialthat the charcoal fhould be finely pulverized andvery dry. For this purpofe let l'ome well-burntcommon charcoal be rubbed in a mortar (witha few drops of water to prevent the duft fromflying about) and afterwards pafied through afine fieve : fill a crucible with this powder, andlute on a pierced cover. When the vefiel be-gins to be red hot a light blue flame will ifiuefrom the hole in the cover: the heat is to becontinued, gradually increafing it for a fewminutes after the flame has ceafed: being thenwithdrawn from the fire, and placed in a dryfituation till it is fufficiently cool to be handled,it muft be quickly opened, and its contentstransferred without lofs of time into a perfectlydry well flopped bottle, in which the charcoalmay be kept for any length of time without in-jury. The properties of this powder are veryftriking. Being mixed with common vinegar,or any kind of wine, a thick froth rifes to thefurface, and the liquors after filtration are foundto be quite clear and entirely colourlefs. Thefilthiefl and moft putrid ditch water is in likemanner rendered perfectly limpid, inodorous,and infipid, and rancid oils are deprived of theirfmell and tafte by repeated filtration through aftratum of this prepared charcoal. Hence alfoits peculiar efficacy as a dentrifice, its particlesare fufficiently hard to remove the concretionsfrom the teeth without injuring the enamel,while it neutralizes and entirely deftroys thefoetor with which the breath is not unfrequentlytainted from a carious tooth.
The affinity of charcoal for oxygen is fo con-fiderable, that inftances have been known of its.undergoing fpontaneous combuftion by fimplecontact with the air. An occurrence of thiskind took place at the powder-mills of EfTonnein France. ^ A large quantity of recently burntcharcoal had been ground in the ufual manner,and was depofited in a large receptacle forfuture ufe ; fome days after, the door of themagazine being opened in order to remove apart of the charcoal, an extraordinary heat wasperceived, and immediately a train of fire wascbferved fpreading over the furface of the char-.
« An. ii« Chiin. xxxvi. p. 93,