O X Y
O X Y
( 198 )
heat given out during combuftion is chieflyderived from the oxygen, that the inci'eafe oftemperature is generally pretty accurately pro-portioned to the quantity of oxygen confumed,as was found by Meffrs. Lavoifier and La Place,in their experiments with the calorimeter.
Several objections of weight however oppofethe hypothecs that light is alfo a conftituentpart of oxygen gas, or of oxygen in any flatefit to fupport combuftion. One of the ftrongeftis, that the quantity of light given out in thisprocefs, is not proportioned to the quantity ofheat, and the circumftance of the various colourwhich the flame affumes, according to the na-ture of the combuftible body, would feem ratherto indicate that it is this latter, and not theoxygen gas, which is the principal fource of thelight.
•i his opinion has been adopted by feveralehemifts of late years, among whom are Grenand Brugnatelli, and Dr. Thomfon. So thataccording to this fyftem-the procefs of com-buftion is in fa£t a double decompofition, inwhich the combuftible body unites with oxygento form an oxyd, or water, or an acid, accordingto circumftances, whilft the light of the com-buftible combines with the caloric of the oxygen,and produces the flame or fire
It will be eafily feen that this fyftem in onepart bears a refemblance to the ancient hypo-thefis of phlogifton, infomuch that both of themfuppofe a fomething to be contributed by thecombuftible body itfelf towards the compofitionof the fire or flame, and this too appears on thewhole more confonant with the general pheno-mena of combuftion and oxygenation ; but (tillthere remain a vaft number of difficulties to becleared up before it can be fully admitted.
The lateft, the moft laboured, and certainlyone of the moft ingenious theories of com-buftion, is that of Dr. Thompfon, who adoptsthe above-mentioned modification of the phlo-gistic fyftem, and has given a very fatisfaclory.view of the actual phenomena as far as they areknown, to which we {hall refer the reader b
OXYMURIATIC ACID. 1 Acide muriatiqueoxygens. Fr. Oxygenifirte Salzsdure. Germ.Dephlogifticated Marine Acid of Scheele.
This acid was firft difeovered by Scheele inconfequence of digefting the black oxyd ofmanganefe with muriatic acid. It is bell pre-pared in the following way. Charge a long-necked tubulated glafs retort not more thanene-fourth full of 8 parts, by weight, of muri-£ted foda, and 3 parts of black oxyd of manga-
nefe, thefe ingredients being in fine powder,and accurately mixed together; then add 5parts of fulphuric acid, diluted with 4 parts ofwater : the beak of the retort being now intro-duced into a common water bath filled withwarm water, and a gentle heat being commu-nicated to the ingredients by means of a lamp,a fpeedy effervefcence will take place, the com-mon air will be driven out of the retort by alight yellow coloured gas, which is oxymuriaticacid, and may be collected in inverted vials inthe ufual manner. The rationale of the procefsis this : fulphuric acid when heated with blackoxyd of manganefe, drives off part of its oxygen,and then forms with the remaining fub-oxydfulphat of manganefe: muriat of foda is alfodecompofed by fulphuric acid, the muriatic acidbeing feparated by the fuperior affinity of thefulphuric. But if thefe two diftinrit decompo-fitions take place at the fame time and in thefame veffel, the oxygen and muriatic acid gaffeswhile in a nafeent flate, combine togetherproducing a new compound, oxymuriatic gas,which being but little foluble in warm water, iscollected as we have juft deferibed 5 any por-tion of common muriatic acid that might beaccidentally mixed with, it being compleatlyfeparated by means of the water through whichit paffes. This gas may alfo be procured in amore Ample, though not quite fo eligible amanner, by digefting ftrong muriatic acid withabout half its weight of black oxyd of manga-nefe.
Oxymuriatic acid gas is of a light yellowifligreen colour: its fpecific gravity has not beenafeertained. Its odour is more penetrating andfuffocating than even that of fulphureous a'cid,occafioning a long - continued and convulfivecough, even when largely mixed with commonair; when pure, or nearly fo, it is inftantane-oufly fatal to animal life. A cubic inch ofwater at 43 0 Fahr. is capable of abforbing1.07 grains troy of this gas, and thereby ac-quires a denfity of 1.003 : but though coldwater takes up this gas without much difficulty,it is nearly infoluble in hot water : hence theheft method of obtaining the liquid acid is bymeans of a Woulfe’s apparatus, the bottles ofwhich are furrounded with ice; by this ma-nagement, when the water is nearly faturatedwith the gas, it depofits thin lamellar cryflalsof oxymuriatic acid, which again diffolve andmix with the reft of the fluid on a fmallincreafe of temperature ; and at a higher heat,part of the acid efcapes in an elaftic form.