INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
May 15,1934
(special arsenic-free hydrochloric acid gives a perfect blank for this work) are added by means of a dropping funnel. Some operators may prefer to use 100 cc. of 1 to 1 phosphoric or sulfuric acid to eliminate the necessity for a moist cotton plug for absorbing any escaping hydrochloric acid fumes. The contents of the flask are heated to boiling and a stream of nitrogen (about 5 mm. of pressure) is continually passed through the system until all sulfide has been evolved. The residual gas is washed out of the flask by increasing the nitrogen stream (to about 30 mm. pres-
n
for absorbinn HC1 tumes
Rubber tubing
