WATER. 



tbelieat will, therefore, be communicated to the furround- 

 ing water, until the heat diftributes itfelf again between the 

 water and the condenfed air, fo that they come to the fame 

 telnperature. In this ftate, if the air is fuffered to rufti out 

 of the veflel, it will fiiddenly expand and recover its former 

 volume, and it muft alfo recover its former (hare of caloric, 

 which it can only do by abftrafting heat from the furround- 

 ing air, or from any fubftance with which it comes in con- 

 taft : hence the coldnefs of the blaft of air. In refpeft to 

 the formation of fnow and ice, it muft be confidered that the 

 air of damp places always contains a confiderable portion of 

 water in a ftate of vapour, and the air in this machine will 

 have taken up more than the ordinary (hare, in confequence 

 of being in contaft with the water. When the air expands 

 itfelf, the heat being fuddenly abftrafted from this watery 

 vapour, it becomes fluid, and accumulates in drops like 

 rain ; which drops, by a farther abftraftion of heat, become 

 folid like fnow or hail. 



An infti-ument which is in common ufe to produce fire, 

 by the fudden compreffion of air, (hews the reverfe of this 

 aftion : it is a fyringe fitted with a pifton, which is air-tight ; 

 at the bottom of the barrel a fmall piece of tinder is placed. 

 Now, if the pifton is very violently and fuddenly forced 

 down to the bottom of the barrel, and the pifton is then 

 withdrawn, the tinder will be found on fire. The heat con- 

 tained in the air which fills the barrel is fo concentrated at 

 the fame time with the air, as to produce aftual fire. If 

 the piftoii is forced flowly down, the air will be condenfed 

 to an equal degree, but no fire will be produced, becaufe 

 the heat has time to efcape through the metal of the barrel, 

 before it arrives at any confiderable degree of concentration. 

 We confider that in all cafes when air (and perhaps other 

 elaftic fluids) is comprefled into a fmaller fpace, part of the 

 heat it before contained will be given out to the furrounding 

 matter ; or if it is fulfered to expand to fill a larger fpace, 

 it will abforb or take up heat from the furrounding matter. 



A larger Machine at Chremnitz. — This does not differ 

 from the original machine, fo as to require a minute defcrip- 

 tion ; but as this machine is not employed in England, and 

 we think it might be ufeful in many cafes in mining diftrifts, 

 we (hall give the proportions and calculations of a larger 

 machioe, as a model for engineers. 



Feet. 



Height of the fource above the place of delivery T 

 or fall of water, which is to work the machine : > 

 defcending pipe 4 inches bore - - -j 



Depth from which the water is to be raifed out of "1 

 the pit to the place of delivery : afcending pipe > 



Cubic Feet. 



4 inches bore 



136 



96 



170 



83 



Upper veflel a copper cylinder 5 feet diameter, 

 and 85 feet high ; metal 2 inches thick ; the 

 defcending pipe goes to within 4 inches of the 

 bottom : contents . . . - - 



The lower veflel a brafs cyhnder 4 feet diameter, 

 and 67^ feet high ; metal 2 inches thick ; the 

 afcendiiig-pipe goes within 3 inches of the bot- 

 tom : rapacity .-.--- 



Air-pipe which communicates between the two 

 vefFels, 2 inches bore, and 96 feet in length 



To ui.derftand the aftion of this machine clearly : — Sup- 

 pofe that the lower cyhnder is charged vi^ith water, and the 

 upper cylinder with air ready for aftion ; when the water 

 from the fource is admitted into the upper cyhnder, if no 

 ifft^ was given to the contained air, the water would enter 

 into the veflel, until the air was compreffed into one-fifth of 



its bulk by the column of 1 36 feet high ; for a column of 

 34 feet nearly balances the ordinary elafticity of the air. 

 But when there is an ilfue given to the air through the air- 

 pipe, it will drive the compreffed air along this pipe, and ir 

 will expel water from the lower cylinder. 



When all the air is expelled from tlie upper cylinder, 

 there will be 34 cubic feet of water expelled from the lower 

 cylinder. Now if the afcending pipe had been carried up 

 more than 136 feet above the lower level, inftead of 96 feet, 

 then the water would have rifen 136 feet high in that pipe, 

 by the intervention of the elaftic air, before it was in equilibrio 

 with the water in the defcending pipe ; but no more water 

 would have been expelled from the lower cylinder than what 

 would fill this pipe. 



But the afcending pipe being only 96 feet high, the water 

 will be thrown out at the top of it with a confiderable velocity. 

 Were it not for the great obftruftions which the water and 

 air muft meet with in their paffage along the pipes, it would 

 iffue from the mouth of the afcending pipe with a velocity 

 of more than 50 feet ptr fecond. It iffues, however, much 

 more (lowly. 



When the upper cylinder is become filled with water, the 

 fupply is ftopped ; but the lower cyhnder ftill contains 34 

 cubic feet of compreffed air of fufiicient elafticity to balance 

 the water in a difcharging-pipe 136 feet high, whereas tha 

 afcending-pipe is only 96 feet. Therefore the water will 

 continue to flow at the mouth of the afcending-pipe till the 

 compreffed air is fo far expanded as to balance only 96 feet 

 of water, that is, until it occupies one-fourth of its ordinary 

 bulk, or one-fourth of the capacity of the upper cylinder, 

 viz. 425 cubic feet. Therefore 425 cubic feet of water 

 will be expelled, and then the efflux will ceafe, leaving tlie 

 lower cylinder about one-lialf full of water. 



When the difcharging-cock of the upper veffel is opened 

 the water iffues with great violence, being preffed by the 

 condenfed air returning from the lower cyhnder. It there- 

 fore iffues with the fum of its own weight, and of this com- 

 preffion. Thefe gradually decreafe together, by the efflux 

 of the water and the expanfion of the air ; and this efflux 

 flops before all the water in the upper veffel has flowed out, 

 becaufe there are only 42I feet of the lower cylinder occu- 

 pied by air. This quantity of water nearly will therefore 

 remain in the upper cylinder. The workman knows this, 

 becaufe the difcharged water from the upper veffel is 

 received firft of all into a veffel containing three-fourths of 

 the capacity of the upper cylinder, which ferves as a mea- 

 fure ; when this is filled, the attendant opens the cock 

 which admits the water into the lower veffel, by a long rod 

 which goes down the (haft : this allows the water of the 

 mine to fill the lower cylinder, and the air returns into the 

 upper cylinder through the air-pipe, and permits the remain- 

 ing water to run out of it ; and when the attendant finds 

 no more water will come out, every thing is brought to its. 

 firft condition. 



The above account of the procedure in working this 

 engine, (hews that the efflux at the mouth of the afcending- 

 pipe becomes very flow near the end. On this account, it is 

 found convenient not to wait for the complete difcharge, but 

 to cut off the fupply when about 30 cubic feet of water 

 have been difcharged, and more work is done in this way. 



A gentleman of great accuracy and knowledge of thefe 

 fubjetts, took the trouble of noticing particularly the per- 

 formance of the machine. He obferved that each ftroke, as 

 it may be called, took up about three minutes and one- 

 eighth, and that 32 cubic feet of water were difcharged, and 

 66 cubic feet were expended. 



The ex pence therefore is 66 cubic feet of water falling 



136 



