21,4 Cole: Detection of Gold 363 
weakened the fiber so that it could not be handled without break- 
ing. 
In the experiments discussed in this paper, when stannous 
chloride solution is mentioned it means that a filtered solution 
of stannous chloride crystals dissolved in water was used. 
Viscose silk boiled for ten minutes in 0.5 per cent, 1 per cent, 
and 10 per cent solutions of tannic acid gave a faint blue color- 
ation in gold solution. 
Fibers treated with a solution of stannous chloride and quinol 
(hydroquinone) gave almost no color with gold solution. 
Fibers treated with stannous chloride and resorcinol gave a 
pink coloration with gold solution. 
All the fibers prepared as above mentioned were left exposed 
to the air and light for six months and tested from time to 
time. No marked decrease in sensitivity was noted even after 
six months’ exposure to air. It was noted, however, that the 
fiber after several days’ exposure to air turned dark blue in 
concentrated gold solution, but red to purple in dilute solution. 
Freshly prepared fibers gave red to purple in either dilute or 
- concentrated gold solution. 
The final method of preparation of the test fibers was as 
follows: Ten grams of stannous chloride crystals were dissolved 
in 95 cubic centimeters distilled water and 5 cubic centimeters 
concentrated hydrochloric acid and filtered; 10 grams of pyro- 
gallol were added to the filtrate. The viscose-silk fibers were 
heated in this solution for ten minutes on the water bath. The 
fibers were then removed and washed well with water and dried 
between filter paper. 
The test for gold with the stannous chloride-pyrogallol fiber 
is best carried out as follows: Place upon an object slide a 
drop of the solution (neutral) to be tested. Insert into it a 
fiber 5 millimeters long for only part of its length. Move the 
preparation on the stage of the microscope until a portion of 
the fiber both in and out of the drop falls within the field of 
vision. Note the change of color if any. Let the drop evapo- 
rate to dryness spontaneously. A red to purple color denotes 
gold. Strong solutions of gold immediately turn freshly prepared 
fibers dark red, and older fibers dark blue; weaker solutions give 
a red or blue color in the fiber only upon evaporation of the 
drop to dryness. Alkali prevents the formation of the color. 
Mineral acids retard the formation of the color. Reducing and 
oxidizing agents in general interfere. Ferrous and ferric salts, 
