^oe Experimtnts and Oifervatiom en Shell and Bone. 



many experiments U appeared, that porcellaneous (hells confift of carbonate of lime, ce- 

 mented by a very fmall portion of animal gluten. 



Previous to the experiments on (hells compofed of nacre, or mother of pearl, I examined 

 fbme patellae from Madeira. 



When thefe were expofed to a red heat in a crucible, there was a perceptible fmell, like 

 that of horn^ hair, or feathers. 



The proportion of carbonic matter depoGted by the fubfequent folution, was more con- 

 fiderable than that of the (hells above mentioned } and the proportion of caibonate of lime 

 relative to their weight was lefs. 



When the recent (hells were immerfed in very dilute nitric acid, the epidermis was 

 feparated, the whole of the carbonate of lime was diflblved, and a gelatinous fubftance, 

 nearly liquid, remained, but without retaining the figure of the (liell, and without any 

 fibrous appearance. 



Thefe (hells evidently, therefore, contain a larger portion of a more vlfcid gelatinous 

 fubftance, than thofe before mentioned; but the folution feparated from the gelatinous 

 fubftance alForded nothing but carbonate of lime. 



Experiments on Shells compofed of Nacre, or Mather of Pearl. 



When the ftiell of the common oyfter was expofed to a red heat, the effects were the 

 fame as thofe obferved in the patella, and the folution of the unburned (hell was limilar, 

 only the gelatinous part was of a greater confiftency. 



A fpecies of the river mufcle was next fubje£led to experiment. This when burned in a 

 crucible emitted much fmoke, with a ftrong fmell of burned cartilage, or horn ; the (hell 

 throughout became of a dark grey, and exfoliated. By folution in the acids a large quan- 

 tity of carbonic matter was feparated ; and much lefs of carbonate of lime was obtained 

 from a given weight of the (hell, than from thofe already mentioned. 



Upon immerfing an unburned (hell in dilute nitric acid, a rapid folution and clFervef- 

 cence at firft took place, but gradually became lefs, fo that the difengagement of the car- 

 bonic acid gas was to be perceived only at intervals. 



At the end of two days I found nearly the whole of the carbonate of lime dilTolved, but 

 a feries of membranes retaining the figure of the (hell remained, of which the epidermis 

 conftituted the firft. 



In the beginning the carbonate of lime was readily dllTolved, becaufe the acid menftruum 

 had an eafy accefs ; but after this it had more difficulty to infinuate itfelf between the dif- 

 ferent membranes, and of courfe the folution of the carbonate of lime was (lower. 



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 rcfembled this mufcle, excepting that their mem- 

 branaceous parts were more compaft and denfe. 



4 Thcjfr 



