444 On the Assay of Minerals ly means of the Blowpipe. 
The charcoal which serves for the stud fulfils this object : but 
in order to increase the effect, it must be reduced to powder, and 
mixed with the mineral, before submitting it to the blowpipe. 
Oil is also a very good reductive when applied to the mineral 
in powder. In the assays with additional substances we observe 
the way in which the mineral acts with the flux, if it is fusible, or 
resists fusion. If fusible, we must notice, ist, if it be tranquil- 
ly; 2d, if it be with the disengagement of gas, as in the fusion 
of gray manganese with borax; 3d, if it be in the form of 
froth. ‘ 
We observe what is the time necessary for the fusion, and whe- 
ther it be quickly or slowly performed; the colour of the flux ; 
and whether it be permanent or fugacious. 
The colour may also change when we hold the mineral in va- 
rious parts of the flame: for instance, the glass of borax, with 
a slight addition of manganese, is a violet-blue colour while we 
hold it in the oxidating part of the flame, and it loses this colour 
when we make it pass into the reductive part. 
We observe, also, if a mineral has the property of being re-. 
duced, and whether its reduction be complete or incomplete, as 
in the red ore of copper when treated with borax. Detona- 
tion is another phenomenon in the combustion of inflammable 
bodies, which must be observed. 
The products of assays may be: 
1. 4 glass: i, e. a transparent or translucid body with a 
glossy or shelly fracture. We must observe if it be compact, ho- 
neycombed, or frothy, as in the obsidian and pechstein, or clean 
and transparent, coloured or colourless. 
2. An enamel: i, e. an opaque body with a fracture like 
wax, and the same observations with the above must be made. 
3. A scoria: 1. e. a body generally opaque, or at most trans+ 
lucid, with a surface honeycombed: we observe if its fracture 
be dull, vitreous, or metallic, and its colour black or brown, &c. 
We observe if it possesses any polarity, like that of chlorite, 
some micas, &c. 
4, dfritte: i.e. a body the fracture of which presents vi- 
treous particles, and others not vitreous. 
5. A regulus: i. e. a metallic globule. 
6. An ochre, or earthy substance containing a metallic ox- 
ide: we observe its colour. 
7. A coke, a charry and cellular residue of coal, having 
much consistence after the combustion of its bituminous part. — 
8. A charcoal, a black, light, friable substance composed of 
hydrogen and oxydulated carbon. 
9. Ashes, an earthy, pulverulent, alkaline substance contain- 
ing molecules of metallic oxides ; that is, the residue of the com- 
bustion _ 
