BLOWPIPE REACTIONS. 83 
prevent the assay from falling out. The strength of the 
draught depends upon the inclination of the tube, and in special 
cases it should be inclined as much as possible. 
The most common fluxes are borax (sodium bi-borate), salt 
of phosphorus (sodium and ammonium phosphate), and soda 
sodium carbonate, either the carbonate or bi-carbonate of soda 
of the shops.) These substances, when fused and highly heated, 
are very powerful solvents for metallic oxides. ‘They should 
be pure preparations. The borax and soda are much the most 
important. In using the platinum wire, the loop may be highiy 
heated, and then a portion of the borax or soda may be taken 
up by it, and by successive repetitions of this process the re- 
quisite amount of the flux may be obtained on the wire. Then, 
by bringing the melted flux of the loop into contact with one 
or more grains of the pulverized mineral, the assay 1s made 
ready for the trial. With soda and quartz a perfectly clear 
globule is obtained, cold as well as hot, if the flux is used in 
the right proportion. Some oxides impart a deep and charac- 
teristic color to a bead of borax. In other cases the color 
obtained is more characteristic when salt of phosphorus is em- 
ployed. The color obtained in the outer flame is often differ- 
ent from that which is obtained in the inner flame. The beads 
are sometimes transparent and sometimes opaque. If too much 
substance is employed the beads will be opaque when it is de- 
sired that they should be transparent. In such cases the 
experiment may be repeated with less substance. In inany 
cases pulverized mineral and the flux, a little moistened, are 
mixed together into. a ball upon charcoal, especially in the ex- 
periments with soda. 
In the examination of sulphides, arsenides, antimonides and 
related ores, the assay should be roasted pefore using a flux, in 
order to pone the substance into an oxide. This is done by 
spreading the substance out on a piece of charcoal and exposing 
it to a gentle heat in the oxidizing flame. The sulphur, arsenic, 
antimony, etc., then pass off as oxides in the form of vapors, 
leaving the non-volatile metals behind as oxides. ‘The escap- 
ing sulphurous acid gives the ordinary odor of burning sulphur; 
arsenous acid, from arsenic present, the odor of garlic, or an 
alliaceous odor; selenous acid, from selenium present, the odor 
of decaying horse-radish ; while antimony fumes are dense white, 
and have no odor. 
The following is the scale of fusibility which has been adopted, 
beginning with the most fusible : 
STIBNITE.—Fusible in large pieces in the candle flame. 
