14 CHEMISTRY. 
obstruction occur in the conducting tube, the gas escapes by the safety 
tube. The column of liquid which under satisfactory circumstances stands 
about e, and in the tube at b, is then driven back into the bulb. The gas 
then ascends through the liquid in the bulb in the form of bubbles, and thus 
escapes. The arrangement of fig. 44 may serve to bring about the same 
result in regard to the conducting tube, by attaching to the latter an appa- , 
vatus similar to that of pl. 31, fig. 61 (the figure is inverted in the plate). 
The end, a, of the latter apparatus is to be placed in the cork of the 
generating vessel. P/. 31, jig. 56, exhibits still another kind of gas 
generator, with two openings, one of them receiving the funnel tube, the 
other the gas conductor. It frequently happens that gases must be freed 
from the watery vapor with which they are combined. This is done 
by interrupting the gas conductor by a wider tube (fig. 56), first partly 
filled with cotton, and next with pieces of chloride of calcium, the latter 
substance absorbing watery vapor with great eagerness. The tub B, in 
pl. 30, fig. 55, is the pneumatic tub or trough as generally used by chemists. 
It has at ce a shelf, provided with grooves and holes, under some of which 
small funnels are attached. Water is poured into the trough to a height 
of an inch or two above the shelf. The receivers are to be filled with 
water, and then inverted and placed on the shelf, over one of the apertures. 
The end of the tube communicating with the gas-generating apparatus is to 
be brought under one of the funnels, which then guides the gas in its ascent 
through the water to the top of the receiver. The general operation is the 
same as already described. The receiver may also be so placed on the 
shelf as to project by less than half its diameter, and the end of the gas tube 
brought under the open space. In this way the holes and funnels may be 
dispensed with. 
Chlorine, at ordinary temperatures, is a gas of a yellowish green color, and 
very corrosive, and poisonous when inhaled. This gas is one of the consti- 
tuents of common salt, which is a combination of chlorine with the metal 
sodium, forming, in chemical nomenclature, the chloride of sodium. Chlorine 
is very conveniently obtained from muriatic or hydrochloric acid, an acid 
procured in large quantities in the manufacture of carbonate of soda from 
common salt. This hydrochloric acid is a combination of chlorine and 
hydrogen, formed under the conditions required for separating the chlorine 
from common salt. Fill the flask A (pl. 31, fig. 14) nearly half full of 
hydrochloric acid, and into it drop some substance rich in oxygen, as the 
peroxyde of manganese: the oxygen of the latter will combine with the 
hydrogen of the acid, forming water, leaving the chlorine free to pass over, 
and to be collected in a receiver, as already described. To accelerate the 
operation, a spirit lamp is placed under the flask, which is fixed by the two 
rings, a and 0, of the retort stand,C. The apparatus (jig. 14) here described 
is applicable to many other purposes. 
444 
