378 
ON WATER ANALYSIS. 
approaching completion, the mercury gradually rises in the tube from the 
trough m. t. below until it stands at about 30 inches, or the height of the column 
of mercury in the barometer. This then is the apparatus employed to extract 
the gases from the combustion tube when they have been produced by the 
burning of the organic matters. The pump is first set to work to remove the 
air contained in the combustion tube, and other portions of the apparatus 
connected with it; and when this is accomplished, the combustion is proceeded 
with in the ordinary manner. The copper is first made red-hot and then 
the heat is continued backwards until the operation is finished. The Sprengel 
pump is then again worked whilst the tube is still hot, and the gases produced 
are driven downwards, and by means of the upturned extremity of the vertical 
tube are collected in a small mercurial trough placed at the bottom. The gases, 
of which there is usually about half a test-tube full, are next transferred to 
the receiver, a, filled with mercury, and standing in a mercurial trough. 
The arrangement of which this forms a part is a simplified modification of 
the apparatus invented some years ago by the author and Mr. Ward, for the per¬ 
formance of gasometric operations in such a manner as to avoid the inconveniences 
usually introduced by variations of temperature. It consists, in its present form, of 
a tube rather more than an inch in internal diameter, bent, as shown in the draw¬ 
ing, so as to form two upright limbs. The shorter is carefully joined by the blow¬ 
pipe to a tube, < 7 , of about half its own diameter, both being carefully graduated. 
Tiie upper end of the narrow tube, < 7 , is again sealed on to another of capillary 
bore, similar to thermometer tubing ; this is bent at right angles, and, by a 
peculiar ground-steel joint, the invention of M. Regnault, is connected with 
