364 The Philippine Journal of Science 
potassium ferro- and ferricyanides interfere. Chromates and 
bichromates tend to give a brown tone to the red color. 
Silver nitrate turns the fiber yellow to brown even in the ab- 
sence of gold; but, unless silver is present in excessive amounts, 
it does not mask the red color produced when gold is present. 
Platinum salts do not color the fiber. Permanganates color the 
fiber brown. Ammonium molybdate and phosphomolybdate 
turn the fiber a light blue color, readily distinguishable from the 
dark blue or bluish red obtained when gold is present. None 
of the other basic or acid radicles interfere. 
In order to express numerically the sensitivity of the fibers 
to gold solutions the following method was adopted: Solutions 
of decreasing concentration of gold were used. A drop of 
constant size was obtained by means of a No. 29 platinum wire 
in the form of a loop 1 millimeter in diameter. The drop de- 
livered by this loop contained 0.00045 cubic centimeter. Start- 
ing with a solution of gold producing a decided color change 
in the fiber when the test drop is evaporated to dryness, solu- 
tions of gold of decreasing concentrations were tested until a 
concentration was reached which failed to give a color in the 
fiber. The most-dilute solution, one drop of which will produce 
a color change in the fiber upon evaporation of the test drop, 
gives the degree of sensitivity. This limit may be expressed 
either in terms of grams per liter or as the absolute amount 
contained in the drop used. The most-dilute solution which 
gave a good color change in the fiber in a drop containing 
0.00045 cubic centimeter was one containing 0.05 gram gold per 
liter. Therefore, the absolute amount of gold detectable by this 
method is 0.000,022 milligram, or 0.022 micromilligram (0.001 
milligram — 1 micromilligram). 
This test for gold is applicable not only in cases where the 
ordinary tests are used but also when the latter cannot be 
used; that is, in exceedingly minute amounts of material or 
upon subjects which must not be disfigured in the testing. 
SUMMARY 
1. Viscose-silk fibers dyed with stannous chloride and pyro- 
gallol give a very sensitive microscopic method for the detection 
of gold. 
2. The test fibers, prepared as described, are stable. No de- 
crease in sensitivity was noted at the end of six months. 
3. A drop of solution containing 0.000,022 milligram of gold 
gives a positive test for gold by this method. 
