m. Experiments aiicL Ohfervdtions 



Upon itnmerfing an unburned ilicll in dilute nitric acid, 

 a rapid folution and effervefcence at firft took place, but gra- 

 dually became lefs, fo that the difengagement of the carbonic 

 acid gas was to be perceived only at .intervals. 



At the end of two days T found nearly the whole of the 

 carbonate of liinediflblved, but a feries of membranes re- 

 taining the figure of the fliell remained, of which the epi- 

 dermis conftituted the firft. 



In the besiinningr the carbonate of lime was readily dif- 

 folved, becaufe the acid menllruum had an eafy accefs; but 

 after this it had more difficulty to infinuate itfelf between the 

 different membranes, ahd of courfe the folution of the car- 

 bonate of lime was flower. 



During the folution the carbonic acid gas was entangled, 

 and retained in many places between the membranes, fo as 

 to give to the whole a cellular appearance. 



The haliotis iris and the turbo olearius refembled this 

 mufcle, excepting that their membranaceous parts were 

 more compaft and denfe. 



Thefe fliells, when deprived, by an acid menftruum, of 

 their hardening fubftance, or carbonate of lime, appear to be 

 formed of various membranes applied ftratum fuper ftratum. 



Each membrane has a corrcfponding coat or cruft of car- 

 bonate of lime; which is fo fituated that it is al^v,'^ys between 

 every two membranes, beginning with the epidermis, and 

 ending with the laft formed internal membrane. 



The animals which inhabit thcfe ftratified (hells, increafe 

 their habitation by the addition of a ftratum of carbonate of 

 lime, fccured by a new membrane ; and as every additional 

 ftratum exceeds in extent that which was previoufly formed, 

 the fhell becomes ftronger in proportion as it is enlarged, and 

 the growth and age of the animal becomes denoted by the 

 ninmber of the ftrata which concur to form the fliell. 



Although the haliotis iris and the turbo olearius are com- 

 pofed of the true mother-of-pearl, I was induced to repeat 

 the foregoing experiments on fome detached pieces of mother- 

 of-pearl, fuch as are brought from China. 



Thefe experiments I need not defcribe, as the refults were 

 precifely the fame. 



\ muft,^ 



