O X Y

O X Y

( 195 )

pure enough for moft experiments may be got red nitrous oxyd is ufually fubftitutqd. (Seemuch cheaper by other ways. the articles Mercury and Altnofpherical Air.,-

The black oxyd of manganefe contains a Thefe oxyds yield about f of their weig togreat abundance of oxygen fo loofely combined oxygen gas. This gas is however at nr aas to be expelled by a moderate red heat, and little impregnated with mercurial vapour, whicftthis is the method ufually purfued. An earthen is depofited as a white film on the furface^ot•or iron retort (the latter of which are made for the water over which the gas fhould hand mrthis exprefs purpofe) is to be filled with the a day. _

black oxyd of manganefe in powder, and heated Turbith mineral (the fulphated oxyd of mer-•in a briik fire. The firft produft of gas comes cury) yields much oxygen m this way, mixedover when the manganefe is faintly red, and with fome fulphureous acid,coilfifts chiefly of carbonic acid, fo that a taper The Red oxyd of Lead or Minium heated to■is immediately extinguifhed. After this if rednefs in an earthen retort gives abundance offmall famples of the gas are examined as it oxygen, but mixed with fome carbonic acid gas.comes over by dipping a bit of kindled wood Ail the oxyds of iron when heated to fullin it, the fire will foon be found to burn with rednefs begin to give out oxygen in confiderableencreafed flame and brightnefs, a fign of the purity.

prefence of oxygen foon after which it may Oxygen gas may alfo be obtained very cneapbe code&ed for ufe. If the manganefe be and confiderably pure, by the deftrudive dif-very good, one pound of it (which will lie in filiation of nitre in a moderate red heat. Thisa very fmall retort' will give about 1400 cubic procefs which highly illuftrates the decompo-inches of oxygen of great purity, that is, con- lition of nitric acid, has been already notice*!taining perhaps no more than a tenth of car- under the article Nitrat of Potajh. io obtainbonic acid or any other gas. The oxygen oxygen from it, put fome dry nitre m a coatedbegins to come over in quantity when the glafs or an earthen retort, lute a tube to it tomanganefe is red-hot, and a full red heat fhould convey away the gas to the proper veffels, filledbe continued as long as any gas comes over, with and inverted over water, and apply a heatThe refidue is a dark grey oxyd. gradually raifed to rednefs. When red-hot,

• Manganefe if moiltened wich fulphuric acid the acid of the nitre is decompofed, and a verywill alio give out much oxygen on applying no large quantity of oxygen is given out for agreater heat than that of a taper, and hence it confiderable time, till at laft all the acid ismay be obtained very expeditioufly with the diflipated in the form of oxygen and azot, andfimpleft apparatus poffible. But a great difFe- cauftic potafh remains in the retort, which laftrence is found in this refpedf in the different if the operation be puflied to the utmoft,fpecies of manganefe. corrodes the retort and renders it unfit for a

All the oxyds of mercury when heated red fecond charge. The oxygen is confiderablyhot are decompofed, the metal returns to the pure in this way, but is mixed with a portionftate of running mercury, (which is driven up of azot, particularly towards the laft. It isin vapour and foon condenfes) and the oxygen obtained fimpler and cheaper by fubftituting towhich it contained appears in the gafteous the retort two earthen crucibles^" one invertedform, mixed with any acid, if fuch exifted in over the other, and the point of contact be-the oxyd. Hence the calcined mercury or pre- tween the two well luted, and a tube proceed-cipitate per fe , which is a fimple combination of ing from the upper crucible to convey away theoxygen and mercury, when heated in a retort gas b Nitrat of foda will anfwer as well, asto a low red heat, yields only oxygen gas and will moft of the metallic nitrats, and manymercury in vapour, the whole of the oxyd is other fubftances moiftened with nitric acid,decompofed, the mercurial vapour condenfes Dr. Prieftley obtained from 2 oz. of nitre :mto extremely pure running mercury, and the heated in an earthen retort, about 812 oz.° x ygen gas remains. This was the way in meafures, and the vefiel melted with the alkaliis ^ r ‘ Prieftle y obtained this gas, and before the procefs was finiflied.

■ °* tet1 prafififed when a very pure oxygen gas All the nitrats (nitrated ammonia excepted)y a i nted> as k ma Y be done in a glafs retort will yield oxygen gatT when expofed to a heat7 c °ated, held over a pan of charcoal fo fufficient to decompofe the acid,d ’ eat / t . to moderate rednefs. But as the Moft of the green parts of vegetables whileoxya perfe ls a very ex penfive preparation, the living, yield oxygen gas when expofed to the

fc An. Chim. Tom. p. 187.

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