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VII. On an Artificial Substance resembling Shell: by Leonard Horner, Esq. F.R.SS. 
Lond. Edinb. With an Account of an Examination of the same : by Sir David 
Brewster, LL.D. F.R.S. 8$c. 
Received October 5, 1835, — Read February 25, 1836. 
While I was, some time ago, officially inspecting the cotton-factory of Messrs. 
J. Finlay and Co., at Catrine, in the county of Ayr, on going over the bleaching- 
establishment attached to it, I was struck with an unusual appearance of a part of 
the machinery, which, at a distance, looked as if it were made of brass. On a closer 
examination, I found that it was a large circular wooden box coated with an incrus- 
tation of a brown compact substance, having a highly polished surface, a metallic 
lustre, in some places beautifully iridescent, and when broken exhibiting a foliated 
texture *. This resemblance in structure and pearly lustre to some species of shells, 
such as the Meleagrina, Malleus, Avicula, Ostrea, Pinna, and others, induced me to 
examine the substance more closely, conceiving that it might possibly throw some 
light on the formation of shell. 
The part of the machinery on which I observed the incrustation is called a Dash- 
wheel, and consists of a circular box, about seven feet in diameter and three feet in 
width, revolving upon a horizontal axis, and having its interior divided into four 
compartments, into each of which there is a circular opening on one side. The pur- 
pose of this wheel is to wash or rinse the cloth in pure water, after it has been boiled 
or steeped in the bleaching-liquors. It makes twenty-two revolutions in a minute, 
which is found to be the proper degree of speed, in order that the cloth may be tossed 
about and dashed against the sides as the wheel turns ; a greater velocity causing it 
to keep at the circumference without shifting its position. 
I was told that the incrustation was a deposit of carbonate of lime, and the source 
of the lime was mentioned. But whence the brown colour, and the metallic nacreous 
lustre? If the substance were analogous to shell, it ought to contain animal matter ; 
and whence could that be derived ? It was necessary to trace the operations from 
the beginning. 
The cotton cloth is brought to the bleach-field in the state in which it is taken from the 
weaver’s loom. The first process is to steep it in water for several hours, after which 
it is immersed in cream of lime. This is made in the following manner : fresh-burned 
lime is slaked and passed through a fine sieve, and added to water in the proportion 
* Specimens are deposited at the British Museum. 
MDCCCXXXVI. 
H 
