^c|? Expenmenfs and Ohferi' afhns 



proportion to the thicknefs of the enamel which has bcetr 

 thus difiblved : but httlc or no diminution' is obferved in the 

 tooth*, 



Mr, Hunter has noticed this ; and, fpeaking of enam-el, 

 fays, "when foakcd in a gentle acid, there appears no griftly 

 m flefliv pai-t with which the earthy part had been incorpo- 

 rated f." 



Now when the difference, which has been lately ftatcd 

 Between porcellaneous fliell and mother-of-pearl, is confi- 

 d'ered, it is not poffible to avoi-d the compiiring of thefe to 

 enamel and tooth. 



When porcellaneous fliell, whole or in powder, is expofed 

 to the attion of acids, it is completely difiblved without 

 leaving any refiduum. 



Enamel is alfo completely diffolvcd in the like manner. 



Porcellaneous fiiell and enamel when burned emit little 

 or no fmoke, nor fearcely any fmell of burned horn or car- 

 lifcige. 



Their figure, after having been expofed to fire, is not ma- 

 terially changed, except by cracking in fome parts; theip 

 external glofs partly remains, and their colour at mofl be- 

 comes gray, verv different from what happens to mother-of- 

 pearl or tooth. In their fracture they have a fibroiTS texture; 

 and, in (hovt, the only effcntial difference between them ap- 

 pears to be, that porcellaneous fhell confifts of carbonat of 

 lime, and enamel of phofphat of lime, each being cemented 

 by a fmall portion of gluten. 



In Hke manner, if the effefts produced by fire and acid 

 inaiftrua, on fhells compofed of mother-of-pearl, and on 

 thefubflance of teeth and bone, are compared, a great fimi- 

 larity will be found ; for, when expofed to a red heat, 



I ft. They fmoke much, and emit a fmell of burned car^ 

 ■fiTage or horn. 



adty. They become of a dark gray, or black colour. 



■ * I have alfo obferved, that when rafpings of enamel are put into Ji- 

 Jvfted nitric or muriatic acid, ihey are diffolved without any apparent re- 

 fiduum; but when rafpings of tooth or bone are thus treated, portions of 

 membrane or cartilage remain correfponding to the fize of the rafpings. 

 -t Natural Hillory of the Humaa Teeth, p. 55. 



