BLO 



612 



BLO 



Block Ma- section, the highest point of which forms the cutting 



clnncrv, et lge. The tool is held in the same manner as the 

 Blockade. . r ,i . 

 . gouge the shaping engine. 



Machine After being turned, the pins are burnished in a 



for bur- curious machine. It has a revolving spindle, placed 

 niihing the vertically. The pin is fixed at the end of this, and, 

 I" 1 ' " as it turns round, is forced down between three dies, 



or smooth pieces of hard steel, highly polished. These 

 are fitted in a frame, and have screws behind them, 

 by which they can be thrust forwards against the 

 pin, to grasp it tight, and make such a pressure as 

 will burnish down all the spiral scorings left by the 

 turning lathe. The dies are immersed in oil to faci- 

 litate the operation, and prevent the dies from heat- 

 ing. The pins after this process are highly polished 

 and fit for use. 



Having now explained the mode of making all the 

 parts of a block, its shell, sheave, and pin, it only re- 

 mains to put them together, in which operation there 

 is nothing singular or worthy of detail. 



We shall conclude this article by observing, that 

 these machines, with alterations, might be adapted to 

 many useful purposes in the mechanical arts ; particu- 

 larly the mortising machine, which would be a most 

 excellent tool for forming mortises in any pieces of 

 work where a great number of similar pieces are re- 

 quired, so as to render it worth while to erect such 

 an engine. Any person who has had the patience to 

 stand by a carpenter while performing the tedious 

 and laborious process of mortising through a large 

 beam of wood, will judge of the importance of a ma- 

 chine which makes from 110 to 150 strokes per mi- 

 nute, and cuts at every stroke a chip as thick as 

 pasteboard, with the most perfect accuracy, (j. f.) 



We are proud in having had it in our power to pre- 

 sent our readers with the first account of these valu- 

 able machines that has yet been given to the world ; 

 and we are fully compensated by this feeling, for 

 the great labour and expence by which this object 

 has been obtained. We hope, in the course of our 

 work, to lay before our readers, other proofs of the 

 great mechanical genius of Mr Brunell. (Ed.) 



BLOCKADE. See Military Tactics. 



BLOIS, the Blesje, or Castrum Blesense of 

 the Romans, a town of France, and capital of the 

 department of the Loire and Cher, agreeably situated 

 in a pleasant country, partly on a small eminence, 

 and partly in a plain near the river Loire. Though 

 the town itself is ill built, yet many of the public 

 edifices are deserving of notice. The castle, which 

 at first sight has the appearance of two separate 

 buildings, that communicate by a passage through 

 the rock, is the chief ornament of the town. A part 

 of it was demolished in 1632 by the duke of Orleans, 

 who built in its place a superb edifice, which is 

 still unfinished. This castle was the birth-place of 

 Louis XII. and the chambers in it are still shewn 

 where the duke of Guise and his brother were assas- 

 sinated, on the 23d December 1587, by order of 

 Henry III. In the extensive court before the castle 

 is situated the Church of St Saviour, which is a hand- 

 some and large building. The cathedral, called the 

 Church of St Solenne, the bridge of seven arches 

 over the Loire, the Jesuits college, and the gates of 

 the city, are the only other objects worthy of atten- 

 tion. The town is supplied with water by a large 

 aqueduct, supposed to be built by the Romans, into 

 which the water descends from the clefts of a rock, 

 about three-quarters of a mile from the city. The 

 water is distributed from a large reservoir near the 

 walls into fountains in different parts of the town. 

 About six miles from Blois is the castle of Cham- 

 bord, built by Francis I. and belonging to Marshal 

 Saxe, who died there in 1751. 



The commerce of Blois consists chiefly of brandy 

 and wines, which are carried by the Loire to Orleans, 

 Paris, Tours, Angers, Laval, and sometimes by 

 land carriage to Normandy. 



Blois carries on a considerable trade in serges, 

 ticken, skins, gloves, hats, stockings, knives, &c. 

 About 600 or 700 pieces of serges, Sec. made of the 

 wool of the country, are manufactured annually. 

 The gloves of this place have been long held in great 

 estimation. Population 13,312. E. Long. 1" 20' 

 10", N. Lat. 47 35' 20". (*) 



BLOOD. See Anatomy and Chemistry, but 

 particularly Physiology. 



Blois, 



blood. 



BLO W-P I P E. 



Blow-pipe. 







Ijlow-Pipe, in chemistry, mineralogy, and the arts, 

 is an extremely useful instrument, employed to raise 

 an intense heat by the flame of a lamp or candle. It 

 operates by throwing a rapid current of air through 

 the flame, and by this :neans urging it violently against 

 the object to be heated, which must necessarily be 

 of small size. The blow-pipe is capable of throwing 

 such a heat on a small object as would be difficult to 

 obtain for a larger quantity of the same substance 

 in the most powerful furnaces, and with this advan- 

 tage, that the process is all the time under the in- 

 spection of the operator, whereas he can only con- 

 jecture what passes in the centre of a furnace. The 

 stream of air for blow-pipes is usually raised by a 

 Vlat from the mouth ; in some instances by the va- 



pour of boiling alcohol; and in others from bellows, Blow- pipe 

 or other pneumatic machines. We shall begin with ' v~ 

 blow-pipes of the first kind, as being the most simple 

 and convenient. The common blow-pipe in use 

 among artificers, consists of a conical metal tube, re- 

 gularly tapering from the size convenient to be held 

 in the mouth to the size of a small pin : The snll 

 end is bent with a regular curvature, so as to be 

 nearly at right angles to the main tube. This pipe 

 being held in the mouth, and a regular stream of air 

 discharged through it into the flame of a candle, the 

 flame is projected sidewise into a long conical spi- 

 racle of fire, which is of a blue colour at its root, or 

 the part where it joins the flame ; farther on it is of 

 a yellow cast, growing more and more faint towards 



