404 



BLOWPIPE 



BLOODSTONE. A very hard, compact variety of haematite iron ore, which, 

 when reduced to a suitable form, fixed into a handle, and well polished, forms the best 

 description of burnisher for producing a high lustre on gilt coat-buttons. The gold 

 on china is burnished by the same means. 



Bloodstone is a name also applied to the jaspery variety of quartz known as the 

 heliotrope, coloured deep green, with interspersed blood-red spots like drops of blood. 

 BLOOM. The name given to a mass of iron after it leaves the puddling furnace. 

 See IKON. 



BLOOiyiARY. The old iron-furnaces were so called. 



BLOWING MACHINE and FANS. See IRON, METALLURGY, VENTILATION. 

 BLOWPIPE. (Chalwneau, Fr. ; Lb'throhr, Ger.) Jewellers, mineralogists, che- 

 mists, enamellers, &c., make frequent use of a tube, usually bent near the end, 

 terminated with a finely-pointed nozzle, for blowing through the flame of a lamp, 

 candle, or gas-jet, and producing thereby a small conical 

 flame possessing a very intense heat. 



The blowpipe is so extremely useful to the manufacturer 

 and to the miner that a more exact description of the in- 

 strument is required. 



When we propel a flame by means of a current of air 

 blown into or upon it, the flame thus produced may be 

 divided into two parts, as possessing different properties 

 that of reducing under one condition, and of oxidising 

 under another. 



The reducing flame is produced by blowing the ordinary 

 flame of a lamp or candle simply aside by a weak current 

 of air impinging on its outer surface ; it is therefore un- 

 changed except in its direction. Unconsumed carbon, at 

 a white heat, giving the yellow colour to the flame, coming 

 in contact with the substance aids in its reduction. 



The oxidising flame is formed by pouring a strong blast 

 of air into the interior of the flame ; combustion is thus 

 thoroughly established, and if a small fragment of an 

 oxidisable body is held just beyond the point of the 

 flame, it becomes intensely heated, and, being exposed 

 freely to the action of the surrounding air, it is rapidly 

 oxidised. 



The best form of blowpipe is the annexed (fig. 144), 

 which, with the description, is copied from Blanford's 

 excellent translation of Dr. Theodore Scheerer's ' Introduc- 

 tion to the Use of the Mouth Blowpipe." 



The tube and nozzle of the instrument are usually made 

 of German silver, or silver with a platinum point, and a 

 trumpet-shaped mouth-piece of horn or ivory. Many blow- 

 pipes have no mouth-pieces of this form, but are simply 

 tipped with ivory, or some similar material. The air- 

 chamber A serves in some degree to regulate the blast and 

 receives the stem B, and the nozzle a, which are made 

 separately, and accurately ground into it, so that they may 

 be put together or taken apart at pleasure. The point b is 

 best made of platinum, to allow of its being readily cleaned, 

 and is of the form shown in the woodcut. When the in- 

 strument is used, the mouth-piece is pressed against the 

 lips, or, if this is wanting, the end of the stem must be 

 held between the lips of the operator. The former mode is far less wearying than 

 the latter ; and whereas, with the trumpet mouth-piece, it is easy to maintain a 

 continued blast for five or ten minutes, without it it is almost impossible to sustain an 

 unbroken blast of more than two or three minutes' duration. While blowing, the 

 operator breathes through his nostrils only, and, using the epiglottis as a valve, 

 forces the air through the blowpipe by means of the cheek muscles. 



Some years since, Mr. John Prideaux, of Plymouth, printed some valuable ' Sug- 

 gestions ' for the use of the blowpipe by working miners. Some portions of this 

 paper appear so useful, especially under circumstances which may preclude the use of 

 superior instruments, &c., that it is thought advisable to transfer them to these pages. 

 For ordinary metallurgic assays, the common blowpipe does very well. A mere 

 tapering tube, 10 inches long, A inch diameter at one end, and the opening at the 

 other scarcely equal to admit a pin of the smallest kind, the smaller end curved off for 

 1 inch to a right angle. A bulb at the bend, to contain the vapour condensed from 



