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XLV. On an Artificial Substance resembling Shell, Bj/ 

 Leonard Horner, Esq.y F,R,SS. LomL and Edinb. With 

 an Account of an Examination of the same. By Sir D win 

 Brewster, LL,D., RR.S., ^c* 



'll/'HILE I was, some time ago, officially inspecting the cot- 

 ^^ ton-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 incrustation 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 f. This resemblance 

 in structure and pearl}' lustre to some species of shells, such 

 as the Meleagrina, Malleus^ Avicula, Ostrea^ Pinna, and others, 

 induced me to examine the substance more closelj', conceiving 

 that it might possibly throvv some light on the formation of 

 shell. 



The part of the machinery on which I observed the incrus- 

 tation is called a Dashwheel, 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 purpose 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. 



1 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 im- 

 mersed in cream of lime. This is made in the following man- 

 ner ; fresh-burned lime is slaked and passed through a fine 



• From the Philo«opliical Transactions for 1836, p. 49. 

 t Specimens arc deposited at the British Museum. 

 Third Series. Vol. 10. No. 60. March 1837. 2 D 



