104 USE OF THE BLOWPIPE. 



Should the student still find a difficulty in using the instru- 

 ment, he has only to apply to the first working-jeweller at 

 hand, for full instructions on the subject. 



The blowpipe is usually placed in two different positions 

 with reference to the flame, which will be best explained by 

 the following figures. The first represents the outer, or 

 oxidating flame (fig. 54). 



To produce this, it is necessary to use the blowpipe with the 



larger orifice, and to insert 

 it about the tenth of an 

 inch into the flame, and 

 about the same distance 

 above the wick, while the 

 assay, which is supported 

 on a platinum hook, is held at the point of the flame. 



The inner or reducing flame is managed as follows : the 

 blowpipe should have a smaller orifice than that employed 

 for the outer, or oxidating flame ; 

 it is necessary to blow a little 

 stronger than in the first experi- 

 ment, and the position of the 

 assay should be such that it is sur- 

 rounded by flame (fig. 55). 

 FJG 55 The small fragment of mineral 



submitted for examination to the 



blowpipe is called the assay ; and with respect to size, the 

 beginner should not attempt a piece larger than a grain 

 of mustard-seed. It is a common fault to commence with 

 specimens which are too large. It ought, if possible, to 

 be chipped off, in the shape of a small scale, with a sharp 

 edge, or point, because these points are more easily acted 

 on than those which are thicker ; and in proportion as the 

 point becomes rounded, or retains it sharpness, it may be 

 considered fusible or infusible. Next take a piece of char- 

 coal, (that prepared from alder is best,) and, with a borer 

 made for the purpose, make a neat little hole about the 

 eighth of an inch deep, and the fourth of an inch wide, and 

 situate between the centre and the edge of the piece of 

 charcoal. It will be expedient to saw the charcoal into sticks 

 an inch square, and to support them on a piece of tin, bent 

 at the end to hold them firmly, 



