202^ Mr. Horner and Sir David Brewster on 



sieve, and added to water in the proportion of 38 lbs. of dry 

 lime to 1000 lbs. of cloth. The cloth is boiled in this liquor from 

 four to six hours, the lime acting as an alkali; and it is used 

 only from being consitlerably cheaper than potash or soda. 

 After this boiling, the cloth is taken to the dash-wheel to be 

 thoroughly cleared of the lime, which is effected by its being 

 tossed about for ten minutes in clear water in the interior of 

 one of the compartments into which the wheel is divided. 

 Here, then, is the source of the calcareous matter of the in- 

 crustation ; and we have the lime dissolved or suspended in 

 the water in a state of extremely minute division, and from 

 which it is deposited, most probably, by a partial evaporation. 

 It is difficult to say whether the deposit takes place while the 

 wheel is revolving, by the water being broken into a kind of 

 spray, and so presenting a greater surface for evaporation, or 

 during the night, when the wheel is still : some of the proper- 

 ties, to be afterwards described, render the latter supposition 

 the most probable. But in whatever way it takes place, the 

 operation is an exceedingly gradual one ; for the wheel had 

 been in constant use for ten years, and the coating in the inte- 

 rior did not exceed one tenth of an inch in thickness. It had 

 been in operation about two years before any perceptible depo- 

 sit showed itself in the inside ; but it had not been going half a 

 year before an incrustation began to be formed on the outside 

 of the wheel. I remarked that the deposit was in greatest 

 quantity around the orifice where the cloth is put in and taken 

 out. llie deposit in the interior, and which coated the whole 

 surface of the compartment, was of a darker brown colour, 

 and was as smooth and splendent as a lining of highly polished 

 bronze would have been. The high polish is no doubt partly 

 produced by friction ; and I observed that it was highest on 

 that part of the outside nearest the opening. 



So far we have calcareous^ but no animal, matter; but in 

 going a little further back in the history of the process to which 

 the cotton had been subjected, before it came to the bleach- 

 field, I discovered that animal matter might be contained in 

 the incrustation. I learned that the cloth had been woven 

 in power-looms ; and on making inquiry as to the composition 

 of the dressing or paste used to smooth and stiffen the warp be- 

 fore it is put into the loom, I was told that in the factory from 

 whence the cloth had come, it is the practice to mix glue with 

 the wheaten flour, generally in equal proportions by weight. 



We have thus lime and gelatine, the same materials which 

 are employed by the molluscous animal in the formation of its 

 covering, and apparently in the same degree of minute divi- 

 sion as that in which they are exuded from its mantle. 



