Di THE DETECTION OF MERCURY IN EXPLOSIVES 
of explosive. At the end of two hours heating the tube 
containing the silver had gained 1.4 milligrams, and after 
another two hours had gained a further 0.4 nulligrams 
or 1.8 milligrams recovered from two milligrams added. 
The silver foil was transferred to a small combustion 
tube 40 mm. long by 5 mm. diameter with ground top, 
which fitted into a hole in a thick copper plate in the usual 
way. A microscope slide was placed on top of the tube 
and a little water on the slide to keep it cool. The tube 
was heated to redness, and the sublimed mercury condensed 
on the microscope slide. It was visible as a grey stain 
to the naked eye, and with a power of 118 diameters under 
the microscope, the mercury globules were easily dis- 
tinguished. 
Several other experiments were made with the addition 
of known quantities of mercury chloride, and in every case 
a recovery of nearly 90 per cent. in 3 hours heating was 
obtained. | 
This experiment was repeated with French chalk, to 
which had been added 1 cc. of mercuric chloride solution 
containing 0.1 milligram per cc. .equivalent to one part of 
mercuric chloride in one million of explosive. No attempt 
was made in this case to weigh the tube, nor was a stain 
visible to the naked eye on the microscope slide, but under 
a power of 118 diameters many globules of mercury were 
distinctly visible, so that even smaller proportions than one 
in a million could be detected with certainty. 
A sample of explosive which gave no reaction in the 
Abel Heat Test in three hours, but which gave the reaction 
in 17 minutes when thoroughly ground with one leaf of 
silver foil, gave an increase of 1.4 milligrams in the tube 
containing the silver foil in the first two hours and a further 
increase of 0.4 milligrams in the second two: hours, thus 
agreeing exactly with the experiment in which one part 
of mercuric chloride had been added to 50,000 parts of 
explosive. On heating the silver as before, globules of 
mercury were easily recognised with the microscope. <A 
second test of this explosive gave exactly similar results. 
Another brand of explosive where the heat test had 
been lowered from 63 minutes to 9 minutes by grinding 
with one leaf of silver, gave a gain of 1.6 milligrams in the 
