VENTILATOR. 



omitted ; nor is it even ftated, that the general inclination of 



the flrata prefent facilities for the afcent of the inflammable 

 air, were requifite precautions taken to conduft it by chan- 

 nels to the mouth of the upcaft pit, which in many fituations 

 might be done at a trifling expence. 



The public have been given to underlland, that an im- 

 proved and complete fyftem of ventilation, depending on 

 this principle, had been introduced into fome of the Staiford- 

 fhire colUeries ; but on recent inquiry at the place, we were 

 informed, that the method of ventilation propofed by Mr. 

 Ryan had never been carried into praftice to the full extent 

 ftated, but confiderable advantage had been derived from 

 a partial application of the principle, by making channels 

 near the roof of the mine for the efcape of the inflammable 

 gas. 



Where the ftrata rife regularly for a confiderable ex- 

 tent, unbroken By faults, it appears eafy to difcharge the 

 inflammable gas as faft as it is generated. The fpecific 

 gravity of carburetted hy^drogen is little more than one- 

 half the weight of atmoipheric air, being as .555 to 1000. 

 If, therefore, it were condufted along the roof by an un- 

 obftrufted paflage to the upcaft Ihaft, it would rife and 

 difcharge itfelf. 



Explofions not unfrequently take place at the upcaft 

 ftiaft, from the inflammable air palling near the fire placed 

 at tlie bottom to rarefy the air and increafe the circulation. 

 The only expedient at prefent fuggefted is the ufe of char- 

 coal, as the gas will not ignite at a red heat without flame ; 

 but charcoal does not promote fo rapid a circulation of air 

 as coal or wood, which produce fmoke and flame. The 

 carbonic acid gas generated by the combultion of charcoal, 

 being alfo heavier than atmofpheric air, would in fome de- 

 gree retard the afcent of air from the upcaft fliaft ; and if a 

 imall particle of coal fell upon tlic charcoal fire, it would 

 produce flame, which might caufe an explofion. 



A feries of moft interefting experiments was undex-taken 

 by-fir H. Davy in 1815, on the degree of inflammability of 

 diff^erent admixtures of carburetted hydrogen when pafled 

 through fmall tubes or apertures, which led to the very im- 

 portant and unexpected refult, that carburetted hydrogen, 

 mixed with atmofpheric air in the proportion which is moft 

 explofive, and then ignited, will not fet fire to another por- 

 tion of the fame air, feparated from it by a fieve of fmall 

 wire, the meflies of which amount to two hundred and fifty 

 in the fquare inch. On this principle he conftrutled a lamp 

 furrounded by a fmall wire-fieve in the place of horn or 

 glafs, having no aperture for the admiffion or tranfmiflion 

 of air but through the mdhes of the fieve. This lamp, 

 when hghted, was found to burn in explofive mixtures with 

 perfeft fafety, the flame being confined within the lamp by 

 the intervening wire-ileve. This lamp has fince undergone 

 confiderable improvements, and fome of the objeftions to 

 which it was firft expofed have been removed. Important 

 additions to it are ftill making by its illuftrious inventor. 

 For a fuU account of its conftruftion and recent improve- 

 ments, we muft refer to the article WlKE-Ga;/z^ Safety- 

 Lamp, 



VENTILATOR, a machine by which the noxious air 

 of any clofe place, as an hofpital, gaol, fliip, chamber, &c. 

 may be difcharged and changed for frefli. 



The noxious quahties of bad air have been long known ; 

 and no one has taken greater pairs to fet the mifchiefs 

 arifing from foul air in a juft hght than Dr. Hales ; who 

 has alfo propofed an eafy and eifeftual remedy by the ufe 

 of his ventilators ; his account qf which was read to the 

 Royal Society in May, 1741. In the November follow- 

 ing, Mr. Triewald, military architeft to the king of 



Sweden, informed Dr. Mortimer, fecretary- to the Royal 

 Society, that he had in the preceding fpring invented a 

 machine for the ufe of his majefty's men of war, in order to 

 draw out the bad air from under their decks, the leaft of 

 which exhaufted 36,172 cubic feet of air in an hour, or at 

 the rate of 21,732 tons in twenty-four hours. In 1742 he 

 fent one of them, formed for a fixty-gun fliip, to France ; 

 which was approved of by the Royal Academy of Sciences 

 at Paris ; and the king of France ordered all the men of 

 war to be furniftied vnXh the like ventilators. 



The ventilators invented by Dr. Hales confift of a fquare 

 box A BCD (Plate XV II. Pneumatics, fg. i.) of any 

 fize : in the middle of one fide of this box a broad partition, 

 or midriff, is fixed by hinges X, and it moves up and down, 

 fi'om A to C, by means of an iron rod Z R, fixed at a 

 proper diftance from the other end of the m.idiiff^, and paffincr 

 through a fmall hole in the cover of the box up to R. 

 Two boxes of this kind may be employed at once, and the 

 two iron rods may be fixed to a lever FG [fg' 2.) 

 moving 011 a fixed centre O ; fo that by the alternate 

 raifing and prefling down of the lever F G, the midriffs are 

 alfo alternately raifed and depreffed, by which tliefe double 

 bellows are at the fame time both drawing in air, and pour- 

 ing it out through apertures with valves made on the fame 

 fide with, and placed both above and below the hinges of 

 the midrifl^s. In order to render the midriffs light, they are 

 made of four bars lengthwife, and as many acrofs them 

 brcadthwifc, the vacant fpaces being filled up with thin 

 paniiels of fir-board ; and that they may move to and fro 

 witli the greater eafe, and without touching the fides of the 

 boxes, there is an iron regulator fixed upright to the middle 

 of the end of the box A C (jff. I. ) from N to L, with a 

 notch cut into the middle of the end of the midriff^ at Z, fo 

 that the midriffs, in rifing and falling, fuffer no other friftion 

 than what is made between the regulator and the notch. 

 Moreover, as the midriff Z X moves with its edges only 

 one-twentieth of an inch from the fides of the bos 

 A B C D F E, very little air will efcape by the edges, 

 and, therefore, there will be no need of leathern fides, as in 

 the common bellows. The end of the box at A C is made 

 a httle circular, that it may be better adapted between A 

 and C to the rifing and falling midriff ; and at the other clid, 

 X, of the midriff, a flip of leather may be nailed over the 

 joints, if needful. The eight large valves, through which 

 the air is to pafs, are placed at the hinge-end of the boxes 

 B K {Jig- 2.) as at I, 2, 3, &c. The valve I opens 

 inward to admit the air to enter, when the midriff is de- 

 preffed at the other end, by means of the lever F G. And 

 at the fame time the valve 3 in the lower ventilator is ftiut by 

 the compreffed air which paffes out at the valve 4. But 

 when that midriff is raifed, the valve i (huts, and the air 

 paffes out at the valve 2. And it is the fame with the 

 valves 5, 6, &c. of the other box ; fo that the midriffs are 

 alternately rifing and falling, and two of the ventilators 

 drawing in air, and two blowing it out ; the air entering at 

 the valves l, 3, 6, 8, and paffing out at the valves 2, 4, 5, 7. 

 Before thefe laft valves there is fixed to the ventilator a box 

 Q Q N M [Jig- 3.), as a common receptacle for all the air 

 which comes out of thefe valves : which air paffes off by the 

 trunk P, through the wall of a building. 



For a farther account of this machine we refer to the au- 

 thor himfelf, who gives a full detail of it, and of its manner 

 of working. See Defcription of Ventilators, by Stephen 

 Hales, D.D. Lond. 1743, 8vo. 



The doftor has fliewn the ufe of his ventilators very fully. 

 As to (hips, in particular, he obferves, that the rj^-'md-fail, 

 (iee WiND-iSa/V, ) made ufe of at iea to introduce fre(h air 



between 



