440 On the Assay of Minerals ly means of the Blowpipe. 
As to the method of presenting the fragment to the flame ef 
the blowpipe, we may place it, 1. Half within the flame. 2. In 
the yellow part of the flame, which produces oxidation. 3. In 
the blue part, which effects the process of reduction. 
Duration of the experiment.—lIt depends on the different 
parts of the flame where the fragment is exposed, and upon the 
degree of intensity of the heat. This intensity depends on the 
volume of air which the blowpipe gives out according to the 
breadth of its aperture, which we may vary occasionally if the 
blowpipe be properly constructed : the best is of metal, and in 
three pieces, a tube, a reservoir, and a point in the form of a 
cone; the reservoir, placed between the tube and the point, re- 
tains ‘the humidity of the breath, and serves at the same time as 
a moderator, by means of the compressed air which it contains, 
We may adapt to this reservoir tubes of different diameters and 
points with different apertures. We may also procure a stronger 
or weaker current of air. The abundance of the current of air 
depends on the power of the blowing instrument : the air is fur- 
nished to the blowpipe either by means of a bellows with a dou- 
ble vent, or by means of the mouth: the air is taken in through 
the nostrils, and blown out through the mouth. ‘This is the me- 
thod most in use and most convenient, and renders the opefator 
more master of the experiment. The stud or support of the 
fragment assayed is to be held in the left hand, and the blowpipe 
in the right, with the elbows resting on the table. We may also 
manage the experiment by placing the fragment on a fixed or 
moveable support ; but it is better to hold it in the hand, 
The intensity of the flame is different ; 
1. According to the state of the air which issues from the — 
blowpipe, it is clear that the stream furnished by the bellows is 
better than that from the mouth ;: the difference has but little in- 
fluence, however, on the result of the experiment, 
2. This intensity is different according to the nature of the 
light employed: a candle, lamp, or taper. A candle is better 
than a lamp, but a wax taper is best of all,, The wick as well 
as the taper ought to be flat, and the flame has of course a flat 
appearance. The current of air should be so directed as to 
make the flame act upon the fragment at an angle of 45 degrees. 
3. Its intensity is different according to the different parts of 
the flame where the fragment. is exposed. The place where this 
intensity is strongest is the extremity of the blue point of the 
flame. We get at this point by management, moving the fragment 
about till we find it reddish. 
In the course of the experiment we ought to observe the va- 
rious phenomena presented by the fragments under assay. 
In those which exhibit no considerable change we remark. the 
various 
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