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expect that the latter substance would blue guaiacum resin, and my experiments 
have shown that such is really the case. If one brings a strip of filter paper which 
has been saturated with guaiacum tincture into strongly ozonized air, prepared by 
means of phosphorus, the paper at once takes on a blue color. As a matter of fact, 
guaiacum resin is as sensitive a reagent for ozone as the potassium iodide and starch 
mixture. If one allows the strips to remain for a somewhat longer time in the ozonized 
atmosphere, the color changes from blue to yellowish brown, as is the case with chlo- 
rine. Ozone therefore conducts itself towards guaiacum resin in precisely the same 
way as chlorine. It is scarcely necessary to point out that ozone produced by the 
other two methods, namely, by the electrolysis of water and by the action of the electric 
discharge on air or moist oxygen, acts in the same way toward guaiacum. Since the 
bluing of guaiacum undoubtedly depends on the action of oxygen, and since free 
oxygen does not act on the resinous mass, this element must first be gotten into a state 
of chemical activity in order to oxidize the guaiacum. This condition seems to be 
called forth even by sunlight. It is not known, however, whether dry oxygen can act 
on the water-free resin in the sunlight. It may well be that in the absence of water 
the guaiacum resin can, as is the case with other organic substances, take up oxygen 
at ordinary temperatures to a slight extent. Be this as it may, it is nevertheless a 
fact that the oxygen which is in association with certain other substances has such 
chemical activity that it can act upon guaiacum, or upon a substance with which it is 
in combination, at ordinary temperatures. If one believes, as indicated by the older 
theories, that chlorine, bromine, and iodine are the peroxides of murium, bromium, 
and iodium, one must believe that there exists in these compounds an equivalent of 
oxygen which is in this chemically active state, and that it is this oxygen which calls 
forth the above-described color change in guaiacum resin. If, as we hold, ozone is to 
be looked upon as a compound of oxygen with water, it is the chemically excited 
oxygen of this compound which blues the guaiacum. As I have elsewhere pointed 
out, compounds of certain of the metals act upon guaiacum in the same way as do 
chlorine and ozone. For example, if one mixes pure lead or manganese peroxide in 
water with a solution of guaiacum, the latter is instantly colored blue just as if brought 
into chlorine water. It is remarkable, and so far as I know a new fact, that guaiacum 
which has been blued in this way loses its color again if it is introduced into an atmos- 
phere containing hydrogen sulfide or sulfur dioxide, or when added to a solution of 
stannous chloride; under these conditions the oxygen in combination with the 
guaiacum appears to be again removed. Finally, I have observed that all those sub- 
stances which color a potassium iodide solution yellow to brownish red, or blue the 
potassium iodide and starch mixture — that is, all substances which have the power 
to cause the separation of iodine; for example, chlorine, bromine, ozone, nitrous 
acid, and the peroxides of manganese, lead, and gold — have also the power to blue 
the tincture of guaiacum. Conversely, those substances which have the power to 
remove the yellow color from potassium iodide solutions and the blue color from 
the potassium iodide and starch mixture — for example, hydrogen sulfide, sulfur di- 
oxide, and stannous chloride — have also the power to destroy the blue color of guaia- 
cum resin. 
In a further note on guaiacum resin Schoenbein ( 371 ) shows that 
guaiacum is also blued by the products of the slow combustion of 
ether, for the reason that an ozonid is produced. Schoenbein ( 372 ) 
next makes use of the bluing of guaiacum as a reaction for indicating 
the presence of an electric current, he ( 373 ) having observed that strips 
of paper saturated with tincture of guaiacum are colored blue when 
exposed to the oxygen liberated from water by electrolysis and to the 
