B L A 



577 



BLA 



Blasting. Mr Farey mentions his having witnessed, near 

 ' v ' Aylesbury, a method of blasting large rooks without 

 gunpowder. The rock was undermined for about a 

 yard in length, and half a yard in depth, and a small 

 faggot of brushwood, furze, or a bundle of straw-, 

 was introduced into the cavity. As soon as it was 

 set on fire, the expansive force of the air, confined 

 in the stone, burst it into innumerable fragments. 



Mr Headrick proposes to blast rocks by introdu- 

 cing the purest quicklime into the cylindrical hole, 

 instead of gunpowder. By suddenly slaking the 

 lime, he conceives, that the expansive force would 

 rend the stone in pieces. See Nicholson's Journal, 

 vol. x. p. 230.; vol. xi. p. 241. Communications to 

 the Board of Agriculture, vol. ii. Philosophical 

 Magazine, vol. xx. p. 208. (o) 



BLASTING Screw, the name of a simple appa- 



ratus for blasting logs of wood by the explosion of 

 gunpowder, invented by Mr Richard Knight. The 

 instrument is a screw, having a small hole drilled 

 through its centre. When a log of wood is to be 

 split, a cylindrical hole is bored, to a proper depth, 

 with an auger, and a quantity of gunpowder intro- 

 duced. The screw is then screwed into the cylindri- 

 cal hole, till it nearly touches the powder, and a 

 match is put down through the hole in the screw 

 till it touches the charge. This match, which is 

 about 18 inches long, and made of twine or linen 

 thread, steeped in a solution of saltpetre, is then set 

 on fire, and the log is broken in pieces. See Trans- 

 actions of the Society of Arts, for 1802 ; and Ni- 

 cholson's Journal^ vol. v. p. 31. (sr) 



BLATTA, a genus of hymenopterous insects. 

 See Entomology. 



Biatta. 



BLEACHING. 



Bleaching. JJleachixc, is the art by which those manufac- 

 ~ v tures which have vegetable substances for their raw 

 material, are freed from the colouring matter with 

 which such substances are naturally combined, or 

 accidentally stained ; and the pure vegetable fibre, 

 deprived of these coloured matters, is left to reflect 

 the different rays of light in due proportion, so as to 

 appear white. 



Besides the spoils of animals, mankind, to supply 

 their natural want of covering, have, in all countries, 

 had recourse to vegetable substances, preferring 

 those whose fibres excelled in strength, durability, 

 and pliancy ; and experience having proved, that 

 flax and cotton were well adapted to such purposes, 

 these substances have been very generally adopted, 

 and formed into such cloths as the skill and industry 

 qf the wearers could execute. 



It would soon be observed, that the action of wa- 

 ter, together with that of the sun and air, rendered 

 those rude cloths whiter than they were at their first 

 formation ; and, since the first step towards refine- 

 ment is to add beauty to utility, as the state of so- 

 ciety improved, a desire to give them a pure and 

 spotless white would naturally arise. The idea of 

 white raiment being the emblem of innocence and 

 peace, which seems to have been very early enter- 

 tained, would make every means for facilitating the 

 removal of natural or adventitious stains more ear- 

 nestly studied. 



Accident would probably discover, that a certain 

 degree of putrid fermentation carried off colouring 

 matters from vegetable fibres. Hence the practice 

 of macerating cloth in water, mixed with putrid 

 urine, and the dung of domestic animals, which lias 

 been continued to our days. 



From the earliest accounts we have of India, E- Bleaching, 

 gypt, and Syria, it appears, that these enlightened ' - v - ' 

 nations knew the efficacy of natron, (the nitre of 

 scripture,) an impure mineral alkali found in these 

 countries, for combining with and carrying off the 

 colouring matters with which cloth is stained ; and 

 it is still found in great abundance by the present in- 

 habitants, and used for the same purpose. We arc 

 also informed by Pliny, (lib. xviii. c. 51.) that the 

 ancient Gauls were acquainted with the use of a lixi- 

 vium, extracted from the ashes of burnt vegetables 

 as a detergent, and knew how to combine this lixi- 

 vium with animal oil to form soap. 



But, though these nations appear to have early 

 acquired some- knowledge of the art of bleaching, 

 the progress of improvement which they made in it, 

 when compared with the advantages which some of 

 them enjoyed, was very inconsiderable. The same 

 practices seem to have been handed down from one 

 generation to another, without any material improve- 

 ment. In India, it would appear, that the art of 

 bleaching, as well as that #f staining cloths of vari- 

 ous colours, are not in greater perfection at present, 

 than they are described to have been in the days of 

 Herodotus. Even in Europe, where the arts, after 

 they have been once introduced, have generally 

 made rapid progress, the art of bleaching made very 

 slow advances till towards the end of the 18th cen- 

 tury. 



At this period, the oxymuriatic acid, and its ef- Discovery 

 fects, were discovered by the justly celebrated Mr of 'lie oxy- 

 Scheele ; and its application to the art of bleaching, muriatic 

 by Mr Berthollet, has given it an impulse towards au * 

 perfection unknown in the history of any other art. * 

 It now became evident, that oxygen had an affinity 



As the facts reacting the introduction 01* the new method of bleaching are not generally known, and have been greatly 

 misrepresented by some late writers on that subject, we shall make no apology for laying them before our readers. 



The first attempt to apply the oxymuriatic acid to the art of bleaching, appears to have been made by Berthollet about 

 the year 17H(i, (.Inn. de Chin, ii. 160.) Influenced by the most liberal views, he made no secret > f his experiments; and 

 exhibited some of them in presence of Rfa Watt of Birmingham, who was instantly impressed with the importance of the 

 discovery, (/4.) Karl; in the year 1788, an attempt was made by some foreigners to obtain a parliamentary grant ; and, 



VOL. III. TART IV. 4 D 



