700 POISONS : THEIR EFFECTS AND DETECTION. [§ 893 . 
substance is mixed with two or three times its weight of litharge, and 
introduced into the tube at a. The portion of the tube containing the 
mercury is at first heated gently, but finally brought to a temperature 
sufficient to fuse the substance and soften the glass. The mercury 
collects in an annular film at b in the cooler limb, and may now, with a 
little management of the lamp, be concentrated in a well-defined ring ; 
the portion of the tube containing this ring is cut off, weighed, then 
cleansed from mercury, and reweighed. Many of the pharmaceutical 
preparations do not require litharge, which is specially adapted for ores, 
and heating with sodic carbonate (in great excess) will suffice. Mercury 
mixed with organic matter muse be first separated as described, by copper 
or gold, the silvered foil rolled up, dried, introduced into the bent tube, 
and simply heated without admixture with any substance ; the weight 
may be obtained either by weighing the foil before and after the opera¬ 
tion, or as above. 
Alexander Charles Gumming and John Macleod ( Journ . Chem. Soc., 
T., 1913) have shown that mercury, whether as sulphide or iodide, 
can be accurately estimated as metal by dry distillation. A piece of 
glass tubing about 20 cm. in length and 5 mm. in diameter is closed at 
one end and a small bulb blown at the closed end ; a second bulb is blown 
some 15 cm. from the first. By means of a long funnel, a suitable 
quantity of the dry substance is introduced into the end bulb : weighing 
the tube before and after this operation gives the weight taken. A mixture 
of iron filings and calcium oxide is now introduced and mixed up by 
rotating the tube : the final mixture should occupy about 8 cm. A small 
plug of asbestos is pushed down so as to retain the whole in place. The 
extreme end of the tube is next drawn out to a fine capillary. The end 
bulb of the tube is wrapped in asbestos paper, and heated in an iron 
tube. The bulb adjacent to the capillary protrudes from the tube, and 
is protected from heat by an asbestos shield; it is also cooled by wet 
filter paper. The heat is at first gradual; .finally the iron tube is brought 
to a low red heat; in about an hour the operation is finished, and the 
flame allowed to play directly on to a portion of the projecting tube, 
which is now drawn out and then broken. The mercury is now in the 
bulb; it is dried by drawing dry air through, and weighed, then the 
mercury shaken out and the empty tube weighed. The authors found 
that it was necessary in the analysis of the sulphides to add to the 
calcium oxide and iron filings also lead chromate. 0-5 to 0-9 grin, of 
cinnabar, mercuric sulphide, mercuric chloride, and mercuric iodide were 
assayed by this method and excellent results obtained. 
§ 893. Volumetric Processes for the Estimation of Mercury.— 
When a great number of mercurial preparations are to be examined, a 
volumetric process is extremely convenient. There are several of these 
processes, some adapted more particularly for mercuric, and others for 
