a?i artificial Suhstajice resemhliiig Shell, 203 



Chemical examination of the Substance. 



1 . The external deposit, — Exposed to the flame of a wax 

 candle, it blackens, and gives out the usual smell of burning 

 animal matter, the thin laminae of which it is composed sepa- 

 rating and curling up like films of horn ; appearances similar 

 to those exhibited by membranous shells when heated. When 

 the flame is urged by the blowpipe, the laminae separate still 

 more, and are changed into an extremely light and brittle 

 enamel, pure white, and having a pearly lustre. A fragment 

 moistened on the back of the hand gives a sensation of heat, as 

 quicklime does when so treated. The substance, when thrown 

 into dilute muriatic acid, is entirely dissolved; the fluid is 

 tinged yellow, and the effervescence produces a froth, like beer. 

 When the acid is very much diluted, and a portion of the sub- 

 stance is suspended in it, the solution takes place gradually, 

 minute flocculi of animal matter being separated, and floating 

 in the fluid. 



2. The internal deposit, — This is separable into extremely 

 thin laminae, and these, when in small fragments, are hardly 

 distinguishable from scales of brown mica, showing also the 

 most beautiful play of colours. The action of heat produces 

 the same effect as on the external deposit, except that the sepa- 

 rated laminae are thinner. The action of muriatic acid is the 

 same, but the yellow tinge is deeper, and the froth is more 

 permanent, indicating a larger proportion of animal matter than 

 in the other. The nacreous lustre is also much more conspi- 

 cuous in this. 



Mr. Gray, in his paper on the Structure of the Shells of 

 Molluscous Animals, observes that the pearly or iridescent 

 lustre appears to be confined to shells of the concretionary 

 structure, which when broken exhibit a nearly uniform texture, 

 but separate when heated into numerous thicker or thinner 

 laminae ; and he adverts to the observation of Mr. Hatchett, 

 that when they are digested in weak muriatic acid, the lime is 

 dissolved, leaving a great number of thin plates of animal mat- 

 ter, which retain the original shape of the shell. He adds, 

 '' This variety of structure is found to constitute the whole 

 shell of the Anomice and Placuncc^ and to form the inner coat of 

 those shells which have pearly insides, as the Turbines, Ha- 

 liotides, Uniones, &c., as well as the laminar portion of the 

 Pinnce and Mother-of-pearl shells *," 



Besides the laminated structure, there is, in the case of the 



* Phil. Trans., 1833, p. 794. [An abstract of Mr. Gray's paper here re- 

 ferred to will be found in Lond. and Edinb. Phil. Mag., vol. iii. p. Ab2. 

 Mr. Hatchett's paper was reprinted entire in Phil. Mag., First Series, voJ, vi- 

 p, 31. —Edit.] 



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