102 Conchology. 



which were examined, were different species of volula and 

 cyprasa. When they were exposed to a red heat for a quarter 

 of an hour, they crackled and lost the colors of their 

 enamelled surface. No apparent smoke, and no smell, like 

 that of burnt horn or cartilage, were emitted during the 

 process. The figure remained the same, excepting a few 

 ilaws ; and they became of an opaque white, partially tinged 

 with pale gray. When they were dissolved in acids, after 

 being burnt, they deposited a small quantity of animal coal, 

 which proves that they contain some portion of gluten. 

 Shells, which had not been exposed to the fire, dissolved with 

 great effervescence in the different acids, and the solution re- 

 mained transparent and colorless ; from which it appears, that 

 the proportion of gluten is small, since it could not be traced 

 in the solution of the unburnt shells. 



In examining the different solutions of shells, whether burnt 

 or unburnt, by chemical tests, it was found that no trace of 

 phosphate of lime, or of any other combination of phosphoric 

 acid, existed in these substances ; and it appeared, from many 

 experiments, that the component parts of porcellaneous shells 

 are carbonate of lime, cemented with very small portions of 

 animal gluten. 



Some species of patella, which were brought from Madeira, 

 were also subjected to chemical examination by the same phi- 

 losopher. When exposed to a red heat, in a crucible, they 

 emitted a perceptible smell of burnt horn or feathers ; and, by 

 farther examination, by solution, the proportion of carbonic 

 matter deposited, appeared to be greater, and the proportion 

 of carbonate of lime less, than what was indicated by the re- 

 sult of the experiments on porcellaneous shells. When un- 

 burnt shells, belonging to the same species, were immersed 

 in nitric acid, very much diluted, the epidermis separated, 

 and the whole of the carbonate of lime was dissolved. A 

 gelatinous substance, nearly in a liquid state, remained, but 

 it did not retain the figure of the shell, and exhibited no ap- 

 pearance of a fibrous structure. These shells, therefore, con- 

 tain a larger portion of gelatinous matter than the porcella- 

 neous shells ; but the other component part consists entirely 

 of carbonate of lime. 



Shells composed of Mother of Pearl. Shells of this 

 description were subjected to similar experiments with the 

 former. When the common oyster was exposed to a red 

 heat, the effects were the same as those which were produced 

 by the same process on the species of patella from Madeira. 



