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POPULAR SCIENCE REVIEW. 
than carbonic oxide, nitrous oxide (N 2 0) a better absorber 
than nitric oxide {NO), and ammonia (NH S ) superior to 
either. This circumstance may be beautifully observed in 
the case of nitric oxide. The gas is quite colourless and 
transparent like air, but, as soon as it comes in contact with 
oxygen, both combine, and form pernitric oxide, a gas of 
a deep brown colour. 
Nitric oxide. Oxygen. Pem'.tric oxide. 
Pure nitric oxide caused an absorption expressed by the 
number 1590, but as soon as air or oxygen was admitted to 
it, the effect or radiant heat was increased more than twenty- 
fold. Pernitric oxide is nearly of the colour of bromine 
vapour; but, notwithstanding this, the nitrogen compound 
possesses perhaps more than a hundred times the absorbing 
energy of bromine for radiant heat. 
Results similar to the above were obtained with ozone. 
Pure oxygen, made in the ordinary way, deflects, as will 
be remembered, the needle one degree. Electrolytic oxygen 
(obtained by decomposing water with a galvanic current) gave 
Mr. Tyndall deflections ranging from 20° to 136°, according to 
the conditions observed in the preparation of the oxygen gas. 
If the plates which conducted the current into the water 
were of small size, an oxygen was obtained which gave greater 
deflections than was the case when larger plates were used ; 
also a more energetic oxygen was developed when the 
temperature of the decomposing liquid was kept near the 
freezing-point. Oxygen which escaped from a decomposing 
cell, surrounded by salt and ice, gave an absorption of 136. 
Now, it is known that electrolytic oxygen contains variable 
quantities of ozone — in all cases, probably, much less than 
one per cent. Those specimens, which, according to the 
mode of their preparation, ought to have been rich in ozone, 
also proved the best absorbers of radiant heat. If, on the 
other hand, the ozone was removed from the oxygen, then the 
latter lost most of its absorbing energy, and sunk down to the 
level of pure oxygen. 
It has been remarked that compound bodies are far superior 
to the elements as absorbers of radiant heat : hence Pro- 
fessor Tyndall concludes, if ozone be a modified oxygen, two 
or more atoms of ordinary oxygen must have collapsed and 
formed a compound group or molecule. If so, ozone ought 
to occupy less space than oxygen. These conclusions of Pro- 
fessor Tyndall are in harmony with the investigations of 
Andrews and Tait, and of the more recent ones of Yon Babo. 
Oxygen may be converted, under the influence of electricity 
