PROCEEDINGS 



OF 



THE ROYAL SOCIETY. 



1835-1836. No. 24. 



February 25, 1836. 



HENRY HOLLAND, M.D., Vice-President, in the Chair. 



A paper was read, " On an artificial Substance resembling Shell ; 

 by Leonard Horner, Esq., F.R.S. L. and Ed. : with an account of 

 the examination of the same; by Sir David Brewster, K.H., LL.D., 

 F.R.S., &c." 



The author, having noticed a singular incrustation on both the in- 

 ternal and external surfaces of a wooden dash-wheel, used in bleach- 

 ing, at the Cotton Factory of Messrs. J. Finlay and Co., at Catrine, 

 in Ayrshire, instituted a minute examination of the properties and 

 composition of this new substance. He describes it as being compact 

 in its texture, of a brown colour, and highly polished surface, with a 

 metallic lustre, and presenting in some parts a beautiful iridescent 

 appearance : when broken, it exhibits a foliated structure. Its ob- 

 vious resemblance, in all these respects, to many kinds of shell, led 

 the author to inquire into its intimate mechanical structure, and into 

 the circumstances of its formation. He found, by chemical analysis, 

 that it was composed of precisely the same ingredients as shell ; 

 namely, carbonate of lime and animal matter. The presence of the 

 former was easily accounted for $ as the cotton cloths which are placed 

 in the compartments of the wheel, in order that they may be tho- 

 roughly cleansed by being dashed against its sides, during its rapid 

 revolutions, have been previously steeped and boiled in lime water. 

 But it was more difficult to ascertain the source of the animal matter; 

 this, however, was at length traced to the small portion of glue, which, 

 in the factory where the cloth had been manufactured, was employed 

 as an ingredient in forming the paste, or dressing, used to smooth 

 and stiffen the warp before it is put into the loom. These two ma- 

 terials, namely lime and gelatine, being present in the water in a state 

 of extreme division, are deposited very slowly by evaporation; and 

 thus compose a substance which has a remarkable analogy to shell, 

 not only in external appearance, and even pearly lustre, but also in 

 its internal foliated structure, and which likewise exhibits the same 

 optical properties with respect to double refraction and polarizing 

 powers. 



A letter from Sir David Brewster, to whom the author had sub- 



2 F 



