IIEVIKW. 
307 
sphere, by determining a less copious evolution of the scavenging ozonic 
principle, may suddenly induce an outbreak of zymotic disease; just as 
intemperance, want, uncleanness of person, food or drink, associated as 
they commonly are with overcrowded dwellings, when suffered in an 
extreme degree, will produce a state of concentrated foulness in excess 
of the normal neutralizing power of the atmosphere, which must sooner 
or later engender fevers and other affections of the zymotic class. 
Whether the diseases so origiivated shall be typhus, cholera, yellow fever, 
or plague, will entirely depend on the nature of the country and the race 
to which the sufferers belonjj. In such circumstances, it is no longer 
ozone which predominates, but the downward M^^sanitary scale of oroanic 
cOhtaminations. Here ozonoscope papers cease to be available, since 
they are incapable of affording indications below the ozonic zero. 
Another method of investigation, based on the employment of some 
material with properties fitting it for marking the variations in the 
amount of impurities present in the air, becomes necessary. By means 
of an oxidizable substance the presence of ozone in the atmosphere can 
be detected, and its intensity measured; to indicate the presence of 
oxidizable impurities in the air, and determine with more or less accu¬ 
racy their amount, it would seem natural to have recourse to some agent 
containinij ozone.” 
The use in ozonometrv of substances liable to alteration 
•r 
of colour by contact with ozone, was suggestive to Mr. Concly 
of the choice of a body, capable of indicating, by somewhat 
similar appearances, the presence in the atmosphere of 
matter of a septic nature. Having been for many years 
engaged in the practical study of the purifying properties of 
the alkaline permanganates, and being deeply impressed 
with their extraordinary sensibility to the action of all kinds 
of impure matter, whether solid, liquid or aeriform, he early 
formed the opinion that the remarkable change of colour 
which those salts when decomposing undergo, might be 
taken advantage of for the estimation of atmospheric con¬ 
taminations. He had found that when a weak solution of 
permanganate of potash was left exposed to air impregnated 
with foul gases, or emanations of an organic origin, it rapidly 
lost its fine pink colour, and that the greater the amount of 
impurities present the more rapidly and completely was 
this change effected. Here, then, were the means of recog¬ 
nising and estimating atmospheric impurities. By exposing 
solutions of the alkaline permanganates in shallow vessels, 
he perceived that he could readily ^etect organic matter in 
the air, and by observing the degree of decoloration pro¬ 
duced in them, form a practical estimate of its character 
and amount ; but as the air in contact with the per- 
