578 DAY AND SHEPHERD WATER AND VOLCANIC ACTIVITY 



does not in the least suggest either a change in the composition or a 

 diminution in the total quantity of the gases given off by the volcano. 



When the lava level in the lake has fallen 10 or 20 feet (which is an 

 almost daily occurrence and often takes place within an hour), only part 

 of the gases set free come from the free surface of the lava, and consider- 

 able quantities now appear through the shattered floor surrounding the 

 basin. The gases bubbling out from the lava basin remain as transparent 

 as before and for the same reasons, but the gases appearing from the 

 cracks in the floor and from the surrounding talus are now cooled in pass- 

 ing through the cracks to such an extent that they.no longer burn on 

 reaching the oxygen Of the air. Free sulphur is then set free in consider- 

 able quantities, unburned; this we were able to collect without trouble, 

 both at the point of emergence and on the crater rim. It is this finely 

 divided free sulphur which is mainly responsible for the beautiful white 

 cloud (plate 18) above the crater and not crystalline chlorides, as sup- 

 posed by Brun. In fact only a minute quantity of chlorine or its salts 

 (less than 0.02 per cent) could be found in the emanations from the 

 Kilauea basin during the period of our visit. 



Our observation of the appearance and behavior of this cloud is there- 

 fore in full accord with the observations of both Green and Brun, so far 

 as recorded, but there is nothing in the facts thus established to show 

 whether the sulphur is accompanied by water vapor or not. 



Herein is also to be found a sufficient explanation of Bran's observa- 

 tions — (1), (2), and (3), page 576 — that the cloud when present does 

 not evaporate after leaving the crater, that it gives no optical phenomena 

 in sunlight, and that it is immediately visible as it emerges from the floor 

 cracks and talus, without a transparent zone separating the point of emer- 

 gence from the visible cloud— results which would be expected if the 

 cloud consisted only of steam, but not if it contains much sulphur. 



Brun's hygrometric Observations 



The remainder of Bran's observations of the apparent absence of water 

 vapor may find appropriate explanation in the fact that they were made 

 in an unsaturated atmosphere (as shown by his elaborate records of the 

 hygroscopic state of the air during his observations) at a distance of more 

 than 250 feet from the point of emergence of the gases, and the further 

 fact that the cloud not only carries sulphur, but two of its oxidation 

 products, S0 2 and S0 3 , both of which in these circumstances are effective 

 drying agents. It may very well happen that water is given off in con- 

 siderable amount by the volcano and yet remains invisible; for, in addi- 



