414 Dr. T. M. Lowry on an 



In order to estimate the amount of nitrogen peroxide in 

 the u combined " gas it was necessary to prepare a series of 

 •standard photographs. Some of these are shown in Plate IX., 

 .and indicate that the proportion of nitrogen peroxide in the 

 u combined gas" is not far from 40*00 by volume. The 

 standard photographs were taken with mixtures of nitric 

 oxide and air, prepared with the help of the apparatus 

 shown in fig. 1. The nitric oxide was made from mercury 

 and nitric acid ; its purity was tested by absorption with 

 ferrous sulphate. It was collected in a cylinder funnel, 

 provided with a T- piece and a capillary funnel through 

 which mercury could be poured ; the volume of mercury 

 used in a given time afforded a measure of the volume of 

 nitric oxide transferred to the " mixing-jar." In this jar 

 nitric oxide was diluted with known volumes of air run in 

 from a standard meter. The mixture of nitric oxide and air 

 was taken from the bottom of the mixing-jar and passed on 

 to the trunk for observation. 



Plate X. reveals the remarkable fact that the proportion 

 of nitrogen peroxide in the " combined " gas is but little 

 affected by passing the air through the ozonizer and spark- 

 gaps in the reverse order. Under these conditions the 

 ozonizer alters its function completely and becomes a very 

 efficient generator of nitrogen peroxide, producing this gas 

 in larger quantities even than the series of 17 spark-gaps 

 used for the last exposure on the plate. 



Up to this point the efficiency of the " combined " ar- 

 rangement appeared to be due to some alteration in the 

 function of the spark-discharge when supplied with ozonized 

 air, and of the silent discbarge when supplied with sparked air. 

 Plate XI. shows, however, that the problem is essentially 

 chemical rather than electrical or electrochemical in cha- 

 racter. The three exposures at the top of the plate show 

 that almost equal yields of nitrogen peroxide are produced 

 when part of the air is passed through the ozonizer only, 

 and part through the spark-gaps only, the two products 

 being afterwards mixed on the way to the trunk. In this 

 arrangement a greatly increased yield of nitrogen peroxide 

 is seen to result from the chemical interaction of two parallel 

 currents of air after both have passed away from the electric 

 discharge. 



This result might be interpreted as meaning that the 

 ozone produced by the silent discharge oxidizes to nitrogen 

 peroxide some lower oxide of nitrogen produced by the spark- 

 discharge. But this oxide could only be nitric oxide, as 

 nitrous oxide is too unstable to be produced by sparking. 

 The explanation would therefore amount to a suggestion 



