J»4 M'Xptrments on the Heat excited b^ Fr'iSlmi, 



mud have been confumed, in order that, in burning equably, it fhould have produced by com- 

 buflion the fame quantity of heat in the fame time. 



in one of Dr. Crawford's e-xperiments, (fee his Treatifc on Heat, p. ^21) 371b. 70Z. 

 troy= 1 8 1920 grains of water were heated 2, '5 degrees of Fahrenheit's thermometer, with 

 the heat generated in the combuftion of 26 grains of wax. This gives 382032 grains of 

 water heated i degree witli 26 grains of wax; or I469,3[J grains of water heated i de- 

 gree, or 't|?'=8i.63i grains, heated 1 80 degrees with the heat generated iuthecombuf- 

 tion of I grain of wax. 



The quantity of ice-cold M-ater, which might have been heated 180 degrees with, the 

 heat generated by friflion in t!ie before-mentioned e.xperiment, was found to be 26.5Slb. 

 — 1 88060 grains ; and, as 81.631 grains of ice-coM water require the heat generated in the 

 combullion of I grain of wax to heat it 1 80 degrees, the former quantity of ice-cold wa- 

 ter, namely, 1S8060 grains, would require the combuftion of no lefs than 2303.8 grains 

 (=:4-j\oz. troy) of wax to heat it iSo degrees. 



As the experiment (No. 3.) in which the given quantity of l>eat was generated by fric- 

 tion lafted 2 hours 30 minutes — 150 minutes ; it is necelFary, for the purpofe of afcertain- 

 ing how many wax candles of any given fize mail burn together, in order that, in the 

 combuftion of them, the given quantity of heat may be geserated in the given time, and 

 confequently ivith the fame celerity as that with which the heat was generated by fri£lion in 

 the experiment, that the fize of the candles fliould be determined, and the quantity of wa.\ 

 confumed in a given time by each candle in burning equably fhould be known- 



Now, I found by an experiment made on purpofe to finifli thefe computations, that 

 when a good wax candle of a moderate fize, -|^ of an inch in diameter, burns with a clear 

 flame, juft 49 grains of wax are confumed in 6 minutes.- Hence it appears, that 24J 

 grains of wax would be confumed in 30 minutes ; and that to burn the quantity of wax 

 ( = 2303,8 grains) neceflary to produce the quantity of heat adually obtained by friftion, 

 in the experiment in quefljon, and in the given time (150 minutes), nine candles burning 

 at once would not be fufiicient ; for 9 multiplied into 245 (the number of grains confumed 

 by each candle in 150 minutes) amounts to no more than 2205 grains; whereas the quan- 

 tity of wax necefTary to be burned, in order to procure the given qnatitity of heat, wa3 

 found to be 2303.8 grains. 



From the refult of thefe computations it appears, that the quantity of heat produced 

 equably, or in a continual flream (if 1 may ufe that expreffion), by the friction of the blunt' 

 fteel boreu agarnft the bottom of the hollow metallic cylinder, in the experiment under con- 

 fideration, was greater than that produced equably in the combuftion of 9 wax candles, 

 each |. of an inch in diameter, all burning together, or at the fame time, with clear bright 

 flames. 



As the machinery ufed in this experiment could eafily be carried round by the forcfe oF 

 one horfe (though, to render the work lighter, two horres were actually employed in do- 

 ing it), thefe computations fliow farther how large a quantity of heat might be produced by 

 proper mechanical contrivance, merely by the ftrength of a horfe, without either fire, lighti 

 combuftion, or chemical decompolition ; and, in a cafe ofneceffity, the heat thus produced 

 might be ufed in cooking viftuab. • • 



But 



