KFtECTS OF HEAT'. ^9 



on fubdances con drained by prelfure, would its a6lion be mo* 

 dified? Would that modification be fuch as is aflumed in the 

 Huttonian theory? 



To thefe queftions Dr. Hutton has replied by arguments Dr. H. has en* 

 founded on general analogy; and has refted the proof of hishy- efliabJrfh thefe 

 pothefis on its agreement with the phenomena of nature* In efFefts from gc* 

 that refpeafew philofophical theories have been fo fortunate; J^°£/^^^'" 

 for its univerfal application to every department of the mineral 

 kingdom, and its folution of all the difficulties, afford a con- ' 

 currenceof probabilities in its favour which prefs on the mind 

 with almoft irrefi(!ible convi6lion. Still it muft be owned that 

 the batis of the fyftem is hypothetical; and a with has been ex*. 

 prefled by every man of fcience who has attended to the fub- 

 je6t, that this bafis fliould be fubmitted to the teft of experi- 

 ment. 



My objefl has been to accomplifti that end, and to bring '^^'^ ^"^^^^f 



^1 • n- ■ . -r^ 1 • ^ , «urs to aftmal 



this great queltion to an experimentum crucis. By placmg tub- experiment* 



fiances in the predicament afligned to them in the Huttonian 



theory, I have endeavoured to imitate the fuppofed procefs of 



nature. In this attempt I have met with great and numerous 



difficulties, but I have at laft fucceeded beyond ray original 



expe^ation, and have obtained refults, which, if I am not 



greatly deceived, eftablith as a law of chemiftry the mod pa^ 



radoxical of Dr. Hutton's pofitions. 



My experiments Ihevv, that when pounded carbonate o^ ^^^^f^^te of 

 lime, produced by the trituration of chalk, of marble, of the (at 22^ Wedg- 

 fliell of a fifti, or of calcareous fpar, after being rammed into wood) in ftrong 

 a fmall tube of porcelain, is expofed in velTels of fufficient becomes ilai-'^ 

 flrength and tightnefs to the heat of 21 or 22 of Wedgwood's ftone. 

 pyrometer (that is to the heat in which pure filver melts,*) 



the 



* I take this opportunity of mentioning that a very material er- 

 ror feems to prevail with refpeft to this point of the pyrometrical 

 fcale. The error is the more formidable that it has been introduced 

 and fanftioned by the highett authority poflible in fuch a cafe j I 

 mean that of Mr. Wedgwood himfelf. In his account of the 

 pyrometer he gives a table, expreffing the efFefts produced at va- 

 rious points of temperature, and ftates 28 as the melting heat of 

 filver. Now it confiits with my knowledge that pure filver melts at 

 22. I learned the fa6^ from Dr. Kennedy, and I have had occafion 

 to confirm the truth of it in numberlefs trials. 



H 2 Thif 



