WATER AND VOLCANIC ACTIVITY DAY AND SHEPHERD. 279 



the basin. When the lava is high enough to completely flood the 

 floor of the basin, these cracks are closed and all the gases emitted 

 emerge directly from the surface of the lava into the atmosphere 

 and have the temperature appropriate to the surface of the liquid 

 (1,000° to 1,200° centigrade). At this temperature the gases (sul- 

 phur and hydrogen, for example) burn promptly on contact with the 

 oxygen of the air and remain nearly or quite invisible. A thin blue 

 haze can sometimes be distinguished above a bursting bubble ^ when 

 conditions are exceptionally favorable, but this haze is so thin that 

 spectators watching for it from the rim will generally disagree about 

 its existence. 



This is the condition of no cloud (pi. 1) described by Green, and 

 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 considerable 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 surround- 

 ing- talus are now cooled in passing 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 considerable quantities, unburned; 

 this Ave were able to collect without trouble, both at the point of 

 emergence and on the crater rim. It is this finely divided free sul- 

 phur which is mainly responsible for the beautiful white cloud 

 (pi. 2) above the crater and not crystalline chlorides, as supposed 

 by Bruij. 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 

 therefore in full accord with the observations of both Green and 

 Brun, so far as i-ecorded, but there is nothing in the facts thus estab- 

 lished to show whether the sulphur is accompanied by water vapor 

 or not. 



Herein is also to be found a sufficient explanation of Brun's ob- 

 servations — (1), (2), and (3), page 277, 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 emergence from the visible cloud — results 

 which would be expected if the cloud consisted only of steam, but not 

 if it contains much sulphur. 



1 Cf. Frank A. Ferret : " The circulatory system in the Halemaumau Lava Lake during 

 the summer of 1911." Amer. .Tourn. Sel. (4), vol. 35, 1913, p. 341. 



