118 HOW CROPS GROW. 
Exp. 20. Further account of them will be given under 
the metals. 
CHLORINE AND ITS COMPOUNDS. 
Chlorine, Sym. Cl, at. wé. 35.5—This element exists in 
the free state as a greenish-yellow, suffocating gas, which 
has a peculiar odor, and the property of bleaching vege- 
table colors. It is endowed with the most vigorous 
affinities for many other elements, and hence is never met 
with, naturally, in the free state. 
Sprengel claims to have found that Glaux maritima and Salicornia her- 
bacea, plants growing in salt marshes, exhale chlorine. He says that the 
chlorine thus evolved is very quickly converted into chlorhydric acid, 
by acting on the vapor of water which exists in the atmosphere. Such 
an exhalation of chlorine is manifestly impossible. The gas, were it 
eliminated within the plant, would be consumed before it could escape 
into the atmosphere. Chlorhydric acid is evolved from the mud of salt 
marshes when left bare by ebb of the tide, and:exposed to the heat of 
the summer sun. It comes from the mutual decomposition of chloride 
of magnesium and water, ; 
Me Cl, + H,O = MgO + 2HCL 
Exe. 55.—Chlorine may be prepared by heating a mixture of chlor- 
hydric acid and black oxide of manganese or red-lead. The gas being 
nearly five times as heavy as common air, may be collected in glass bot- 
tles by passing the tube which delivers it to the bottom of the receiving 
vessel. Care must be taken not to inhale it, as it energetically attacks 
the interior of the breathing passages, producing the disagreeable 
symptoms of a cold. 
Chlorine dissolves in water, forming a yellow solution. 
Very weak chlorine water was found by Humboldt to fa- 
cilitate the sprouting of seeds. 
In some form of combination chlorine is distributed over 
the whole earth, and is never absent from the plant. 
The compounds of chlorine are termed chlorides, and 
may be prepared, in most cases, by simply putting their 
elements in contact, at ordinary or slightly elevated tem- 
‘peratures. 
Chiorhydric acid, also Hydrochloric acid, Sym. H Cl, mo. wt. 
36.5.—When Chlorine and Hydrogen gases are mingled together, they 
slowly combine if exposed to diffused light; butif placed in the sun- 
shine, they unite explosively, and chloride of hydrogen or chlorhydrie 
