Reviews — Dr. A. Brim's Volcanic Researches. 315 



his head. Obviously, then, Brun is not yet numbered among the 

 Saints of Science, and equally obviously the cloud did not consist 

 of drops of water ! 



Brun now summarizes his results regarding the part played by 

 water in volcanic action, and states them as Laws. 



To quote these laws would involve too much repetition, but we may 

 note his observations regarding the volatile constituents of dead rocks. 

 These J atter, heated in vacuo, frequently yield large quantities of water 

 accompanied by oxides of carbon, free hydrogen, and subordinate 

 nitrogen. The dead rocks differ from the active rocks both in the 

 abundance of water and hydrogen which they liberate, and also, 

 apparently, in their failure to produce volatile chlorine compounds 

 (JSa CI, K CI, N H 4 CI, H CI, etc.) and free chlorine. 



AVe now come to the general conclusions, and a sketch is given 

 of the manner in which in nature the emanation is often separated 

 into various fractions, owing sometimes to condensation and sometimes 

 to solution. At a late stage in the history of a volcano secondary 

 emanations resulting from slow oxidation may still be important. 



The primary exhalation is not necessarily violent, eruptive, and 

 tumultuous, as one might imagine from hearing so much about 

 paroxynis ; an obsidian can crystallize, with concomitant emission of 

 volatile constituents, very slowly and tranquilly, if only it be 

 maintained at a suitable temperature for a sufficient length of time. 

 Take, for instance, Lipari obsidian with 75*4 per cent, silica and an 

 explosion temperature of 830°-902° C. It crystallizes at 523°-530° C. 

 in radiating spherulites which gradually transform the whole mass. 

 It is even possible to follow the change with the microscope. Carbon 

 is expelled and localized between the spherulites; gas is given off; 

 salts, which in the colloid were masked and insoluble in water, now 

 concentrate and become soluble. All the substances are rejected 

 through the crystallization of the silicates; but though rejected with 

 the rest the salts probably play an essential role, as catalytic agents, 

 in bringing about the crystallization. In support of this contention 

 Brun points out that he has found no difficulty in obtaining quartz by 

 heating amorphous silica with anhydrous chlorides. 



And now the dethronement of water seems well nigh complete, but 

 the micas of the granites still remain ; they remind Brun of the old 

 regime, and accordingly their heads are in danger; he remarks that 

 the crystallization of granite must occur at a temperature very close to 

 the destruction temperature of the micas, and adds that probably the 

 formation of these micas takes place a posteriori through hydration. 

 If by a posteriori he means to infer that the micas of granites are 

 secondary in the ordinary sense of the term, then, with a vengeance, 

 this is new wine for the new bottles, and of a brand that will find 

 little favour with sober scientists. But if, as is more probable, lie 

 merely suggests a hydration of the magma from outside sources during 

 crystallization, he has evidently raised a debatable point. It does not, 

 however, seem obvious that outside help is necessary to account for 

 the presence of the micas, or even of the water so often recorded from 

 cavities in granitic quartz. According to Brun himself the volcanic 

 exhalation contains abundant hydrogen (as jSTHg, H CI, etc.) and 



