VENTILATION. 



■degree in which it would inflame by accefs to a lighted 

 ■candle or to fire. 



Tills improved fyftem of ventilation by double courfes 

 was introduced into the collieries on the Tyne and Wear 

 about the year 1760, and has ever fince continued in ge- 

 neral ufe ; but it is found inadequate to the intended pur- 

 pofe in the following cafes. 



1. When fudden difcharges of inflammable gas mix 

 with and raife the whole circulating mafs of air to the firing 

 point. 



2. When the wind is fouth-eaft, and the weather wet or 

 hazy, and the barometer finks below twenty-nine inches. 



In this cafe the atmofpheric current, which under the 

 mofl favourable ftate of the air is merely fufficient to fweep 

 the noxious effluvia from fome mmes, gets fo contaminated 

 by the difcharge of inflammable gas, and the flownefs of its 

 own progrefs, as to be exceedingly unfafe, and generally 

 inacceflible with candles. 



3. When inflammable air fills a part of the mine 

 between the workmen and the upcaft (haft. 



4. When the gas is ignited by hghtning, as it afcends 

 the upcaft fhaft. 



The prefence of inflammable gas from the flighteft mix- 

 ture, through all its gradations to the firft firing point, is 

 readily difcoverable by an experienced collier, and he judges 

 very correftly of the degree of inflammability and danger 

 which threaten the fafety of the mine, by obferving at- 

 tentively the appearance of the fpire upon the top of his 

 candle. The common pit-candles vary in fize, but thofe 

 generally ufed are forty-five to the pound ; the wick is of 

 cotton, and the candle made of ox or fheep tallow : but 

 clean ox-tallow is beft. 



The mode of trying the candle, as it is called, to afcertain 

 the mixture of inflammable gas, is as follows. 



In the firft place, the liquid fat is wiped off, the wick 

 fnuffed clofe, and carefully cleanfed of red embers, fo that 

 the flames may burn as purely as poflible. The candle, 

 being thus prepared, is held between the fingers and 

 thumb of the one hand, and the palm of the other is placed 

 between the eye of the obferver and the flame, fo that 

 nothing but the fire and the flame can be feen, as it gra- 

 duilly towers over the upper margin of the hand. The 

 obfervation is generally commenced near the floor of the 

 mine, and the light and hand are gently raifed upwards, till 

 the true ftate of the circulating current be afcertained. 

 The firft indication of the prefence of inflammable air, is a 

 flight tinge of blue or a bluei(h-grey colour ftiooting up 

 from the top of the fpire to the candle, and terminating in 

 a fine extended point. The fpire increafes in fize, and re- 

 ceives a deeper tinge of blue as it rifes through an increafed 

 proportion of inflammable gas, till it reaches the firing 

 point ; but the experienced collier knows accurately enough 

 all the gradations of (how (as it is called) upon the candle, 

 and is very rarely fired upon, excepting in fudden difcharges 

 of inflammable gas. The fliow upon the top of the candle 

 varies very much, according to the length of run or diftance 

 which the current of air has pafl'ed through before it is 

 mixed with the inflammable gas. The fliorter the run of 

 the current of air before it is mixed with the inflammable 

 gas, the lefs will be the fliow upon the candle when at the 

 firft firing point, and vue ver/d. 



The fame fize of fpire which would indicate danger in a 

 current which had pafl'ed only one mile, might be perfeftly 

 harmlefs in a current that had ran five or fix miles ; confe- 

 quently the length of run of the current of air is to be taken 

 into confideration, as well as the appearance of the top of 

 the candle. The air-courfe, too, for a (hort diftance be- 



yond a fmall difch.irge of fire-damp may be highly inflam- 

 mable ; but by pafliing a few yards further, it becomes fo 

 diluted as to be perfeftly fecure. The diftance, therefore, 

 within which a blower can be fafely approached with 

 candles, is regulated entirely by the magnitude of the dif- 

 charge and power of the current of air. Long experience 

 and attentive obfervation are confequently neceflary to ob- 

 tain a thorough praftical knowledge of this art. 



The workings of a colliery are very often inacceflible with 

 candles near the downcaft pit, called the firft of the air, 

 while they may be fafely entered with any defcription of 

 fight near the upcaft pit, called the laft of the air. This 

 arifes from the inflammable gas, as it is carried from the 

 place of its difcharge, being gradually diluted by the at- 

 mofpheric current. Hence the advantage of fufBcient ex- 

 tent of pit-room, to obtain length of run to dilute the in- 

 flammable air. It is from the want of pit -room, that the 

 explofions in newly-opened collieries are generally the moft 

 violent. The diftance which the current of air pafles 

 through, between the downcaft and the upcaft pits, varies 

 much according to circumftances. Mr. Buddie has knoWn 

 it to exceed thirty miles. 



After the current of atmofpheric air is fo highly mixed 

 with inflammable air as not to be acceflible with lighted 

 candles, rteel-mills may be employed with fafety. We fliall 

 further notice Mr. Buddie's obfervatlons on fteel-mills, but 

 we believe the difcovery of the fafety-lamp will entirely fu- 

 perfede their ufe. " Although the inflammable air has fre- 

 quently fired at the fparks of the fteel-mills, it only hap- 

 pens, from all the fafts which I have been able to coUeft, 

 when the mills are played near the place where the hydrogen 

 gas is difcharged, and this by due attention may be eafily 

 avoided. 



" I never indeed witnefled an explofion from the fparks of 

 flint ; but from my own obfervations on their appearance in 

 dangerous ftates of the air, as well as from the obfervations 

 of feveral intelligent men, I believe that in moil cafes the 

 change of the appearance of the fparks, if attentively ob- 

 ferved, gives fufficient notice of the threatening danger. 

 When elicited in atmofpheric air, they are of a bright ap- 

 pearance, rather inclining to a reddifh hue, and as they fly 

 from the wheel feem fharp and pointed. In a current of air 

 mixed with inflammable gas above the firing point with 

 candles, they increafe confiderably in fize and become more 

 luminous. On approaching the firing point with fteel-mills, 

 they grow ftlU more luminous, and afl^umc a fort of hquid 

 appearance, nearly refenibling the fparks arlfing under the 

 hammer from iron at the welding heat. They alfo adliere 

 more than ufual to the periphery of the wheel, encompaffing 

 it as it were with a ftream of fire, and the light emanating 

 from them is of a blueifli tint. When the Inflammable gas 

 predominates in the circulating current, the fparks from the 

 fteel-mill are of a blood-red colour ; and as the mixture in- 

 creafes, the mill totally ceafes to elicit fparks. They have, 

 the fame bloody colour in carbonic acid." The fteel-mill 

 here mentioned is what has been ufed till very recently in 

 coal-mines, confifting of a wheel and fpring, which is wound 

 up and let in motion, whereby a conftant coUlfion of flint 

 and fteel is eff'efted, eliciting a copious ftream of fparks. 

 With the concluding remarks of Mr. Buddie's letter we 

 can by no means agree, when he adds, " On the ftrength of 

 my own experience in collieries thus circumttanced, I irct-ly 

 hazard my opinion, that any further application of mechani- 

 cal agency towards preventing explofion In coal-mines would 

 be Ineffeftual." Among the means enumerated by this gen- 

 tleman, the very obvious one of depending on the greater 

 fpecific levity of the carburetted hydrogen gas is entirely 



omitted ; 



