WATER BLOW TNG MACHINE.. v 55 



which teamen term a fquall, and is fufficiently violent to carry- 

 away tlie -mails of a (hip, if the fails be net reduced in time. 



It is evident that this engine poffelTes the defireable qualities 

 of cheapnefs and fimplicity; and Lewis who has written 

 fomewhat fully upon it, in his Piiilofophical Commerce of 

 Arts, from experiments of his own, afferts, that it requires 

 much lefs water for working it than any other kind of bellows 

 in ufe. I have no doubt but that many occafions muft offer 

 in which it would be beneficial; but whether its expence of 

 water be comparatively finall, and its power in any cafe 

 equal to the fupply of our fmeiting furnaces, may be deferving 

 of more enquiry. 



In the excellent paper of Mr. Roebuck on the Devon iron Numerical 



works, inferred in the fifth Volume of the Edinburgh Tranf. ? T atemen f b * 



& Mr. Roebuck, 



actions, and alfo in the Quarto Series of this Journal, there 6f the effect or a 

 are fome numerical fads refpe&ing the blaft afforded to iron team engine in 

 furnaces by iron cylinder bellows worked by the fleam engine ; f air, 

 and as they agree very well with others given in my Chemical 

 Dictionary, under the article Trompe, I will flate them in 

 this place.;- Mr. Roebuck affirms, that one iron furnace was 

 excited by a blowing cylinder, which gave 155 cubic feet of 

 air 16 times per minute, which numbers give a product of 

 24-80 cubic feet. This is §\ times the quantity emitted by the 

 blowing engine in the text. The fleam engine was efiimated 

 to act by a preflure of 13062 lbs. anfwering to 2| lbs. on the 

 fquare inch of the air piflon, and this multiplied by four feet 

 eight inches, the length of ftroke, and by 16, the number of 

 ilrokes, gives 975296/or the weight multiplied by its fall in feet. 



Now the machine in the text was worked by 173 cubic compared with 

 ket t or 10812 lbs. of water falling through 21 feet, which jjj SjJJjT 

 gives a product of 227052, or mote than one fourth of the 

 fii ft mover of the fleam engine blafl, inftead of one fifth and a 

 half. The blowing engine therefore confumed more water by 

 one fourth than would have been required to produce its 

 effect, according to what was done' by the fleam engine 

 But the fleam engine drove out its air under a reaction of 

 between five and fix inches of mercury in the gage ; a velocity 

 which being more than Mr. Roebuck found neceffary, was 

 a difadvantageous wafle of power. The velocity of the The fteam 

 water blowing engine produced by its preffure of two inches, "JJ" " m0rC 

 is moll probably too fmal! ; and if fo, the multiplication of 



thefe 



