Feb., 1919] Salt, Iron, and Acidity of the Ash 227 



The conditions of the eruption were reducing, and sulphuretted 

 hydrogen, together with hydrochloric acid, are still important 

 volcanic emanations of this region. The ash contains con- 

 siderable quantities of ferrous iron, and this acted upon by the 

 acid fumes would give water soluble ferrous iron. Some of 

 the streams leaching the slopes of Mt. Katmai are strongly 

 impregnated with alum, indicating plenty of sulphates in the 

 ash deposit. The finely divided, water deposited ash of Samples 

 No. 1 and No. 6 are very compact and practically impervious 

 to atmospheric oxygen; consequently the iron has had little 

 opportunity to pass to the ferric condition. Moreover, the 

 absence of humus and of soluble calcium salts prevents the 

 fixing of the toxic ferrous iron into compounds non-injurious 

 to plant growth. 



Numerous observations in the field showed that ferrous 

 iron and acidity were always associated with finely divided, 

 river deposited ash saturated with water. This formed a 

 compact impervious mass, through which an exchange of water 

 soluble substances would not occur; for, being saturated from 

 below, any rainfall on its surface immediately runs off without 

 appreciably affecting the content of the mass. Even the ash 

 deposit on Pillar Mountain, although wind deposited, was 

 nevertheless of this character, for it was very finely divided and 

 saturated from the seepage of the hill upon which it rested. All 

 deposits of the ash, where composed of coarser materials, were 

 found to be free from water soluble ferrous iron and sulphuric 

 acid. This was no doubt due to efficient drainage, with con- 

 sequent aeration and prevention of the accumulation of these 

 toxic compounds. 



THE WATER SOLUBLE SALT CONTENT OF KATMAI VOLCANIC ASH. 



The water soluble salt content of a number of samples of the 

 Katmai volcanic ash was determined by the Electrical Bridge, 

 according to the method recommended by Davis and Bryan 2 , 

 for the determination of alkali in soils. The measurements 

 were carried out on samples of the ash, treated with distilled 

 water, until just a little more than saturated, The instru- 

 ment used was the latest form of the Electrical Bridge, 

 as described by Davis and Bryan in the above mentioned 

 bulletin, and the calculations for the salt content from the 

 Bridge readings were based on their factor 1.45 as the ratio 



2 Davis, R. O. E. and Bryan, H. The Electrical Bridge for the Determination 

 of Soluble Salts in Soils. U. S. Dept. of Agriculture, Bureau of Soils, Bull. 61 1910. 



