﻿THE CRATER OF TAAL. 119 



will readily be seen if their composition is only casually considered. 

 These lakes are largely solutions of aluminium and iron chlorides and 

 sulphates. The determinations of the different elements were made 

 directly, both in the present analyses and in the former ones, as it is 

 evident that where iron and aluminium chlorides are present in such 

 large quantities, analyses of the solid residues would not give the true 

 composition of the waters; it is also evident that the total solids obtained 

 by drying for six hours at 110° only approximately represent the quan- 

 tities of salts originally present, for a solid residue obtained in this way 

 can not give true values, because it is impossible to obtain constant weight 

 unless the dish is heated for a sufficient length of time to drive off most 

 of the combined chlorine, in which case iron and aluminium will also 

 be lost. 3 



If one calculates the number of anion and kation forming elements 

 from the analyses, some rather interesting and what at first appear to 

 be rather surprising results, are obtained. In Water No. 1 the number 

 of anions largely exceeds that of the kations and this would be expected, 

 as sulphur dioxide is continually bubbling through the boiling crater 

 lake. In Waters JSTos. 2 and 3, as well as in the two which I examined 

 last year, the number of kations exceeds the number of anions, but that 

 this condition should exist and the waters still be very acid, seems to 

 be contradictory. However, if the behavior of solutions of aluminium 

 and iron chlorides on evaporation are considered, then the behavior of 

 these waters at once becomes clear. 



It is well-known that the so-called neutral salts of aluminium are 

 very acid, acting on metallic iron or zinc just as do dilute acids; the 

 salts of aluminium easily dissolve alumina to form basic salts 4 and from 

 such salts, aluminium oxide and the various hydroxides are only gradually 

 precipitated, the rate depending upon the concentration of acid present, 

 the temperature and other factors. 5 The conclusion is therefore valid 

 that basic salts of aluminium and iron are present in these waters, which 

 are capable of sufficient hydrolysis to give hydrogen ions. It is hardly 

 necessary to state that all determinations have been made in duplicate. 

 The precipitation of alumina from such basic salts must take place with 

 comparative slowness, for it was found that the salts in these waters 

 were not yet in dynamic equilibrium. The filtered samples, analyzed 



3 It would be possible to determine the real amounts of free acid in these 

 waters by a study of the electrical conductivity of these waters as well as of 

 their constituent salts, obtaining the speed of migration of the various ions 

 according to the methods developed by Bredig. Such a determination could also 

 be made by a study of the hydrolysis of esters or of cane sugar. 



Such a study would involve very many factors, and would consume so much 

 time, that for the purpose of the present paper it was not considered advisable. 



1 Dammer : Handbuch der anorganischon Chemie (1893)', 3, 91. 



"Tornasi: Bl. Soc. chim. (Paris) (1882), (2) 37, 443. 



