2 THE DETECTION OF MERCURY IN EXPLOSIVES 
ot 
Hargreaves, we also adopted the volatilisation method, 
that he and Dr. Dupré had found useful, and with our 
method of abstracting the mercury from the vapour found 
the detection of mercury easy both qualitatively and 
approximately quantitatively. 
A number of preliminary experiments were made 
and we determined that mercuric chloride could be easily 
and completely volatilised at 100 degrees C., that a very 
small quantity of silver foil absorbed the mercuric chloride 
vapour quantitatively at 100 degrees C., and that on heating 
the silver after the >xperiment in a combustion tube in the 
usual manner the mercury could be readily recognised 
even in smali feactions of a milligram. 
The apparatus shown in sketch was then construct >d. 
The water bath is 450 mm. long by 150 mm. wide and 150 
mm. deep, cn legs 200 mm. long. At each end is a hole 
70 mm. diameter, with a short collar projecting 20 mm. 
An indiarubber cork fits each hole, and a glass tube 30mm. 
in diameter and 510 mm. long passes through the rubber 
corks, thus enabling the tube to be surrovnded with boiling 
water. 100 grammes of the explosive to be tested is ground 
up with 100 grammes of the French chalk prepared for 
heat test work, and the mixture run into the tube while 
it is held nearly vertical, a temporary stopper being put 
in the tube 60 mm. from ore end. We found it convenient 
to do this while the tube was in place in the bath. The 
200 grammes of mixture then loosely occupy about 350 mm. 
of the tube. At the shorter unoccupied end of the tube, 
a glass “‘thimble”’ about 25 mm. in diameter is inserted 
close to the mixture to prevent back currents and in the 
end of the tube is inserted a cork and through the cork 
passes an open glass tube of about 5 mm. diameter. This 
provides for the inlet of air. A perforated cork is fitted 
into the other end of the large tube and through the perfora- 
tion is fitted a small glass tube about 5 mm. diameter and 
140 mm. long. Close to the inner end of this narrow tube 
there is a constriction and pushed up against the constric- 
tion so as to loosely fit the tube are two leaves of silver foil, 
occupying about 15 mm. in length of the tube. By this 
means the mercuric chloride vapour never comes into 
eontact with a cold surface, the tube and silver foil being 
