HYD

HYD ( 558 )

rapidly to the ceiling of the room and burfl by{inking againfl it.

It is incapable, of itfelf, of fuppovting com-builion for a moment, a lighted taper dipped init being immediately extinguifhed. But whenpure hydrogen is put in contaft with commonair or ftill more with oxygen, and the furface ofcontaft touched with a lighted taper or a red-hot iron, .it immediately kindles at this placewith a flight fnapping noife, and burns with afaint blueifh-white flame without any fmokeand fcarcely vifible in the day time, and con-tinues to burn gradually as long as the contactof air is continued, till the whole is confumed.This is amufingly fhewn by filling a long-neckedretort or long tube with pure hydrogen, placingit with the open end downwards (by which thegas on account of its levity is prevented fromel'caping) and kindling it with a taper. A ringof faint blue flame immediately appears at theopen mouth, and continues flowly to travel upthe tube till the whole is burnt out. If duringthe combuftion the tube is fuddenly turned up,the remaining hydrogen rifes through the ringof flame, forming a large and fudden flafh, andis immediately exhaufted.

The combuftion of pure hydrogen thereforeis perfedtly tranquil and progreffive through themafs following the progreffive contact of air,but if it be previoufly mixed with common air(or ftill more ftrikingly with oxygen) and agi-tated, and a lighted taper then applied, thewhole takes fire inflantly and burns with alarge blue flafh attended with a pretty vio-lent explofion relatively to the quantity of ma-terials. The electric fpark kindles this mixtureas well as a lighted body. It is on account ofthis property of fudden combuftion with ex-plofion that care fliould be taken not to kindleany portion of a large quantity of hydrogen,through however fmall an orifice, before theoperator is lure of the purity of the gas within,for if it be mixed with any fenfible quantity ofoxygen, the flame inflantly communicates tothe whole mafs, and a dangerous explofionmight enfue. The force and danger of explofionis of courfe regulated (other things being thefame) by the degree in which the gas is con-fined by the veflel in which it is made. Thusa common phial, holding half a pint of a mix-ture of hydrogen and common air in due pro-portions, will not burfl by being kindled at themouth, much of the force lpending itfelf at theopen orifice; and even, if the phial ij flout, thefame quantity of hydrogen and oxygen will

hardly burfl by the explofion, though as loud asthat of a common gun; whereas a very fewinches of the fame mixture confined in a verythick and clofe glafs tube and fired by the elec-tric fpark, will often fhiver it to pieces.

The proportion of oxygen required for theperfefl combuftion of hydrogen, is about onepart in bulk of oxygen to two and a half ofhydrogen, fuppofing each to be pure, or moreaccurately 85 parts by weight of oxygen to 15 ofhydrogen. If common air be ufed, the pro-portions acquired for compleat combuftion areabout 6, in bulk, of common air, to 2 of hydro-gen. After explofion the bulk of the whole isreduced to about 5 parts, and is chiefly theazotic refidue of the common air, which appearsto be quite paffive in this operation.

The great circumfiances which diflinguifhthe combuftion of hydrogen whether flowly orby fudden explofion, are the total deftrudtionof the two gaffes, relatively to their gafleousform, the entire abfence of all vifible vapour o'f'fmoke, and efpecinlly the production of a quan-tity of moifture, which precipitates in the formof a thick dew on the fides of the veflel where-in the combuftion is carried on, and looncollects in fufficient quantity to trickle down inevident drops that continue as long as the pro-cefs is going on. Thefe drops when collectedand examined by every chemical tell are foundto be, when the gaffes are as pure as poffible,nothing but water.

The particulars of many moft laborious andaccurate experiments that prove this importantfact, with the circumfiances under which appa-rently contradictory refults have been obtained,will be further mentioned under the article.Water.

Inflammable air proves almoft inflantly fatalto fmall animals introduced in it, as was afcer-tamed by the experiments of Dr. Prieflley.-Scheele however found that he could refpirethe fame quantity of this air in and out of abladder alternately for feveral times, withoutmaterial inconvenience. Many other experi-ments of Fontana a on this fubject prove, that-tliis is owing to the great dilution which it un-.dergoes in the latter cafe, by mixing with thelarge quantity of common air always prefent inthe lungs •, whereas when a fmall animal is im-merfed in an atmofphere of hydrogen, the air inits lungs makes no fenfible proportion to thehydrogen. Both thefe were proved by exa-mining each air by nitrous gas, which does notin the leafl diminifh in bulk with hydrogen

* Phil. Tranf, vol. 69.