580 DAY AND SHEPHERD WATER AND VOLCANIC ACTIVITY 



in the table below. The first column contains the dew-point of air at 

 varying degrees of saturation; the second column the dew-point of the 

 same air to which 1 per cent of S0 2 (air + 1 per cent S0 2 is still respir- 

 able) has been added. All observations are in duplicate. 



Observations of Dew-points 



Air of random water 



The same air -f 



T~HflFcn**iTi 



content 



1 per cent S0 2 



XJlLLClCU 



7.2° 



6.4° 



— 0.8 C 



7.0 



5.8 



— 1.2 



19.2 



18.1 



— 1.1 



19.4 



18.4 



— 0.9 



20.4 



17.5 



— 2.9 



20.2 



18.5 



— 1.7 



21.6 



19.7 



— 1.9 



21.1 



19.4 



— 1.7 



21.5 



19.0 



— 2.5 



21.5 



20.4 



— 1.1 



Dew-point observations in the nature of the case can make no preten- 

 sions to high accuracy, but the eif ect of charging the air with a very small 

 quantity of S0 2 is shown most convincingly. The effect of the addition 

 of S0 3 would have been still greater than that of S0 2 , since it forms 

 H 2 S0 4 , a notable dehydrating agent; but this effect is somewhat more 

 difficult to examine experimentally and so was not undertaken ; indeed, it 

 was unnecessary, in view of the fact that the point at issue is abundantly 

 proved by the observations contained in the table above. Brun has there-, 

 fore proved no more with his hygrometer measurements than that the 

 great white cloud does not consist entirely of water vapor, but it is not 

 possible to estimate the percentage of water contained in it from any 

 figures based on dew-point determinations under the conditions which he 

 describes. 



From this evidence it appears clear that the observations of fact noted 

 by both Green and Brun may for the most part be precisely as described, 

 and still the conclusion that water is not exhaled by the volcano Kilauea 

 remain in doubt. 7 



7 The chemical and physical tests offered by Brun in support of his conclusions (5) 

 and (6), pages 576 and 577, are also somewhat inconclusive. For example, he tests for 

 chlorine with a silver nitrate solution in an atmosphere containing S, S0 2 , and S0 3 , and 

 notes that it immediately becomes clouded, but mentions no test to ascertain whether it 

 was the chloride or the sulphite which was thus precipitated. Similarly, he nowhere 

 offers a chemical analysis of these particular gases which he collected in tubes at 

 Kilauea, but contents himself with presenting two analyses of other gases pumped from 

 lava fragments reheated in vacuo some months afterward. 



