50 Operation and Tests. 
yall, place in a shallow orifice or cone-shaped 
cavity made in the charcoal. Now play upon it with 
the desired flame, and note the kind of colors forming 
the coatings on the coal around the assay, also note the 
color of bead as before, the escaping fumes and their 
odor and whether or not a globule of metal would be 
given out with further blowing. 
(f) TESTS ON PLASTER OR BONE-ASH. 
In case of the presence of lead or other heavy metals 
in large quantities, a prepared surface of dried clay or 
bone-ash may be advantageously substituted for the 
charcoal, but whether the test be made on coal or plaster, 
if the mineral is not previously roasted, the desired col- 
orations are rendered obscure in the presence of volatile 
substances. 
(g) TESTS IN CLOSED TUBE (MATRASS). 
In closed tube, either heated directly over the Bunsen 
burner, or in the blowpipe flame, volatile substances of 
the assay within the tube are vaporized and condensed 
in the upper or colder part of the tube, where they may 
be examined by a lense, if necessary, or by further 
heating. The odor given off may be noted; also the 
acidity of any fumes by inserting a small strip of litmus 
paper in the mouth of the tube. Acid fumes turn blue 
litmus red, and alkalies turns red litmus blue. The closed 
tube is used to observe all the effects that may take place 
when the mineral is heated out of contact with the air. 
The substance, of course, must be finely pulverized be- 
fore going into the tube and only a minute quantity 
taken. 
(h) TESTS IN THE OPEN TUBE. 
This tube being open at both ends the 
atmosphere passes through in the heating and 
so modifies the result. The assay is placed 
