308 
REVIEW. 
manganate was only part of an infinite quantity of impurities 
belonging to the entire mass of the atmosphere, and its 
action required to be extended over a considerable period of 
time, in order to show any-result, he could not accurately 
gauge the amount of septic matter contained in any given 
volume of air at a particular moment. Although in the 
habit, since the year 1856, of demonstrating the presence of 
organic impurities in the atmosphere by means of weak per¬ 
manganate solutions, and of judging comparatively of the 
average purity or impurity of the air of any place, such as a 
room or hospital ward, during a certain lapse of time, he 
had not thought of contriving a definite instrument for 
applying those substances to the examination of the local 
air of the moment. It was reserved for Dr. Angus Smith 
to be the first to make use of the alkaline permanganates 
for this purpose by means of his “ air-test.^^ 
Dr. Smithes air-test consists of a wide-mouthed bottle, of 
the capacity of 100 cubic inches, into which is fitted a 
stopper of caoutchouc, provided with two tubes, one short 
and the other long enough to reach to the bottom of the 
vessel. Through the former the operator withdraws, by 
means of a suitable bellows-pump, the air contained in tlie 
bottle, which is thus replaced by that of the locality where 
the experiment is being made entering through the latter. 
A certain measure of a weak solution of permanganate of 
potash, of ascertained and standard strength, is poured into 
the bottle, and by shaking, brought into contact with the 
air which has just been admitted. When this is impreg¬ 
nated with matter of organic origin, the permanganate 
solution soon loses the pink colour which is peculiar to it. 
A further measure is then added, and repeated till the 
decoloration ceases, accurate note being kept of the number 
required, which furnishes the measure of the amount of 
oxidizable matter present in the 100 cubic inches of air 
operated on. The strength of the permanganate solution is 
graduated by a standard solution of oxalic acid, 1000 grains 
)f which contain one of anhydrous acid ; 5 grains of this 
solution decompose GOO grains of the permanganate solution. 
Mr. Condy, however, thinks that his original method of 
working with permanganate solutions in open vessels, is 
