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Reviews — Dr. A. Brans Volcanic Researches. 



Water does not enter into the results given above, since these are 

 wholly concerned with volatile matter released at the explosion 

 temperature. The Arran pitchstone is regarded as a typical hydrated 

 obsidian of moderate antiquity. It has much water, which it loses 

 almost entirely at 200° C, whereas its explosion temperature is 

 about 900° C. 



It is important to realize that the anhydrous gases which are 

 liberated from a lava heated in vacuo to its explosion temperature, 

 are more than sufficient to explain the paroxj'smal phenomena 

 observed in nature. We have already seen that in the Krakatoa 

 eruption of 1883 every kilogram of obsidian involved gave about 

 373 c.c. of gases (0° C. and 760 mm.). In the laboratory experiments 

 457 c.c. have been obtained, not to mention 45*7 mg. of ammonium 

 chloride. 



To bring these results into closer touch with nature is the next 

 step. Brun finds that freshly fallen ashes contain soluble chlorides, 

 including ammonium chloride and greasy hydrocarbons, which later 

 can be extracted with chloroform. They also always give an acid 

 reaction. It thus appears that the stony matter of the ashes is mixed 

 with the same volatile products as are generated in the artificial 

 distillation of a magma under anhydrous conditions in vacuo. Samples 

 of the 1906 ash of Vesuvius, collected during the eruption at 

 thirty-five different localities, contained from 1 to 1£ per cent, by 

 weight of soluble salts, about equally proportioned between the 

 sulphates and the chlorides. The abundance of sulphates is a feature 

 of which no mention is made in connexion with the laboratory 

 experiments. 



The salts deposited by dry fumaroles and on the walls of craters are 

 found to agree with those associated with ashes. 



Secondary exhalation. — A specimen of lava, which has already been 

 heated to its explosion temperature in vacuo, will give a fresh supply 

 of gas if oxidized by heating to a moderate temperature in air or 

 oxygen or by melting with some such reagent as ferric oxide. The 

 gases produced under these circumstances constitute what Brun 

 appropriately terms the secondary exhalation. A few examples are 

 given in the subjoined table. It must be clearly understood that the 

 secondary exhalations here tabulated are additional to the primary 

 exhalations previously quoted. 



