HORNS, NAILS, AND SCALES. 311 



it in alcohol and ether. When burnt it left 0*7 per cent, of 

 ashes. Its constituents were, 



Carbon, . 51-578 



Hydrogen, . 6-712 



Azote, . 17-284 



Oxygen, | 



Sulphur, / 



100- 



He gives us an empirical formula, C 48 H 34 Az 7 O 17 . So that 

 its constitution is the same as that of hair, namely, one atom 

 protein -f one atom ammonia + three atoms oxygen. 



If we precipitate an alkaline solution of hair or horn with 

 acetic acid, sulphuretted hydrogen escapes and a precipitate falls, 

 which is soluble in acetic acid, and possesses the characters and 

 constitution of protein. 



The nails, which cover the extremities of the fingers, are at- 

 tached to the epidermis, and come off along with it. Mr Hat- 

 chett has ascertained that they are composed chiefly of a mem- 

 branous substance, which possesses the properties of coagulated 

 albumen. They seem to contain also a little phosphate of lime. 

 Water softens but does not dissolve them ; but they are readily 

 dissolved and decomposed by concentrated acids and alkalies. 

 Hence it appears that nails agree with horn in their nature and 

 composition. Under the head of nails must be comprehended the 

 talons and claws of the inferior animals, and likewise their hoofs, 

 which differ in no respect from horn. 



The substance called tortoise-shell is very different from shells 

 in its composition, and approaches much nearer to the nature of 

 nail ; for that reason I have placed it here. When long mace- 

 rated in nitric acid, it softens, and appears to be composed of 

 membranes laid over each other, and possessing the properties of 

 coagulated albumen. When burnt, 500 grains of it yield three 

 of earthy matter, consisting of phosphate of lime and soda, with a 

 little iron.* 



The scales of animals are of two kinds ; some, as those of 

 serpents and other amphibious animals, have a striking resem- 

 blance to horn ; while those of fish bear a greater resemblance to 

 mother-of-pearl. The composition of these two kinds of shells 

 is very different 



* Hatchett, Phil, Trans. 1799, p. 332. 



