272 Professor Davy’s Account of 
parts, 4, of chlorine gas, which, by absorption was reduced to about 5, the remain- 
2 of the measure was now filled with common air, and being mixed, a bit of the 
INS so 
test was dropped into the tube, when it readily exploded. 
The foregoing experiments seem to prove that the new fulminating silver is a very 
delicate test of the presence of chlorine gas, nor does its delicacy appear to be im- 
paired by exposure to the air, the light, or the sun’s rays. Thus, some of the com- 
pound made last spring, was exposed on the sand bath during the summer months ; 
part of it became of a dark brown, and part of a black colour. Some of the com- 
pound was exposed to the direct agencies of the sun’s rays for some time, but the 
changes of colour it thus underwent, did not prevent it from instantly exploding in 
all cases in which it was put into chlorine gas, or into mixtures of this gas with other 
gases. I may also remark, that on exposing some of the test to the action of boiling 
water for some time, and then drying it, it exploded under the same circumstances as 
before. 
The properties which appear to be regarded as most characteristic of chlorine, are its 
colour and odour. Though chlorine is easily recognised by its yellowish green colour ; 
in cases when it is pure or nearly so, or when it forms the greater part of a gaseous 
mixture on which it does not act; yet it may, as is well known, be present in conside- 
rable quantity without exhibiting the least vestige of colour. Thus, in the common 
modes of making the gas, a considerable quantity must be generated, before any co- 
lour is apparent. And the purest chlorine, when mixed with a certain portion of 
common air, or other gases, on which it exerts no immediate action, is no longer dis- 
tinguishable by its colour. Whereas the new test readily detects chlorine in the first 
bottle of air that comes over in the usual modes of making the gas; in cases when 
the gas is mixed with 0.98 or 0.99 of common air, and also, when even a solution 
of the gas in water is transferred from one bottle to another. 
The odowr of chlorine, though perhaps sufficiently characteristic, when the gas is 
mixed with other gases on which it exerts no action, or which have no powerful odour ; 
yet it ceases to be so, when certain pungent gases or vapours are diffused through it. 
Thus, when a portion of chlorine was mingled with muriatic acid, or nitrous acid gas, 
or with the strongest liquid muriatic or nitric acid, the chlorine could not be satisfac- 
torily distinguished ; but in every instance of the kind the test exploded with flame an 
indefinite number of times. From a number of experiments I have made, I am dis- 
posed to regard what is commonly called the odour of chlorine, as a vague, and by no 
means a discriminative character, and that this odour exists in cases where we have no 
evidence of the presence of chlorine, or where, according to received opinions, it 
caunot exist. Thus, after exposing solutions of chlorine in water for several weeks 
or even months to the action of the sun’s rays in summer, they are found still to have 
a strong odour which has been, I think, erroneously referred to chlorine. 
I have hitherto said little concerning the specific action of chlorine gas, on the new 
