250 72 



to be found in the flowing mass, the fluid lava or magma in the interior of the 

 earth, the gas evolution being either the result of the action of the mass on the 

 solid crust of the earth, or else being produced through the gases originally ab- 

 sorbed in the mass being released as the pressure lessens. 



It is evident that when the conditions of the gas evolution are fixed, the 

 gases evolved must have a fixed proportion to each other. At the moment of pro- 

 duction, the carbon dioxide, the hydrogen and the sulphuretted hydrogen appear to 

 be in the proportion 71 : 11.5 : 14.5. As these three gases are very liable to combine 

 with other substances, it is not surprising that the proportion between them is not 

 very constant at the earth's surface. Sulphuretted hydrogen particularly is a very 

 unstable gas, and this is doubtless the reason why the volume of this gas is more 

 liable to variation than that of the two other gases, (carbon dioxide and hydrogen). 



In this class of spring gases carbon dioxide, hydrogen gas and sulphuretted 

 hydrogen constitute nearly 97 "/o of the whole volume. Hence it follows that a 

 decrease in one of these gases must be attended by a corresponding increase in 

 the combined volume of the other two. 



The remainder of the spring gas, amounting to 3 "/o of the entire volume, 

 consists chiefly of nitrogen, and is undoubtedly mostly due to the intermixture of 

 foreign gases of atmospheric origin. The real spring gases in the solfataras and 

 similar hot springs, i. e. the spring gases of which the production is so closely 

 connected with the thermal activity of these springs, are therefore almost exclusively 

 composed of hydrogen gas, carbon dioxide and sulphuretted hydrogen, the remaining 

 gases being treated as a negligible quantity, their percentage being so small. A 

 rise in the percentage of one of these three gases is therefore not so much due to 

 an absolute increase of the gas in question, as to a decrease in the other two gases 

 on account of destruction and absorption. 



The analyses of the spring gases from Kerlingarfjöll and Hengill show that 

 these gases contain some traces of methane, and ditïer in this respect from the 

 spring gases at Myvatn, which contain no hydrocarbon. The gas samples from 

 Hveravellii', Grafarhakki, Laugaras and Reykjafoss also contain a little methane. 



According to my analyses methane must be a rather common constituent of 

 the Icelandic spring gases, although it is nowhere found in large quantities. This 

 does not, however, agree with the results obtained by other analysts. Bunsen in 

 particular states emphatically that he has not been able to find hydrocarbon in 

 any of the spring gases, although he considers that with his instruments he would 

 have been able to detect even a tenth per cent of methane, had it been in any of 

 the samples. The apparatus I used for the analysis being provided with stop 

 cocks, it was not absolutely impossible that the methane came from the grease 

 used for lubricating. I therefore made, in the middle of my analysis work, some 

 experiments with atmospheric air, treating it in the same way as the gas samples 

 under investigation. But in this case no methane could be traced. Another proof 

 experiment was carried out in the following manner. After having proved that a 



