EFFECT OF IRON COLLECTING TUBE 589 



through which to reach the interior of the dome and to insure the capture 

 of the gases at the temperature of emergence from the lava (about 

 1,000°) before any opportunity for cooling or contact with air had been 

 given. 



The effect of this small section of iron pipe on the relations between 

 the gases collected in the tube is not as great as might at first appear. 

 The action of S0 2 on iron at this high temperature is quite vigorous, the 

 iron going over to ferrous oxide and setting free the sulphur. But both 

 these ingredients are present in the lava already, as may be seen from the 

 analyses (table 1), so that no new component is added nor is any new 

 reaction precipitated through the introduction of the iron. It might be 

 assumed, further, that the free hydrogen present would be partly oxidized 

 to water in reducing the ferrous oxide formed from the S0 2 and iron 

 (this is one of the reactions when these components are brought together 

 at this temperature in the laboratory), but if this reaction has had a share 

 in the disposition of our bit of exposed iron we must admit its presence 

 in overwhelming magnitude over the entire inner surface of the dome, 

 which is everywhere lined with liquid lava containing nearly 10 per cent 

 of ferrous oxide. The assumption of this reaction would, therefore, have 

 the immediate effect of establishing the presence of water in quantity 

 among the volcano gases and at the same time relegate the influence of 

 the iron tube to a position of entire insignificance. 



There is still further evidence, if more is needed, that the local reac- 

 tions set up by the iron are of subordinate importance only in their effect 

 on the proportions of the gases collected, and of no effect whatsoever on 

 their identity and chemical relation. Supposing these reactions to have 

 occurred as described, it is then a matter of straightforward computation 

 to show that if the known weight of iron which was dissolved away by 

 the gases, both those which entered the pipe and those which merely 

 played on its outside wall, 13 had reacted in this manner ; and supposing, 

 further, that all the products of the reaction both outside and inside en- 

 tered the collecting tubes (which is obviously impossible), it would have 

 involved pumping through the system some 225 liters of pure hydrogen 

 as an equivalent for the iron consumed, and this still falls short of the 

 quantity required to account for all the water collected by more than 40 

 per cent. Moreover, if the attempt is to be made to account for all the 

 water collected in our tubes through reactions requiring free hydrogen, it 



"The scale on the iron pipe after exposure was found to contain over 85 per cenl of 

 ferrous oxide and about 8 per cent of sulphur. 



XLI — Bull. Geol. Soc. Am., Vol. 24, 1912 



