■682 L. V. PIRSSON 



in decomposing the substance and went into solution. The 

 .analysis by Hunter' gave the following results: 



99.53 



The substance just sank in the heavy liquid with specific 

 gravity of 2.31, and this may be taken as being very close to its 

 own specific gravity. 



Of the above analysis about 96 per cent, is made up of 

 silica, alumina, alkalies, and water, the rest is composed of the 

 oxides of the microlites taken into solution. It will be seen 

 that the oxides first mentioned are very close in their molecular 

 ratios, given in the second column, to 4 : i : i : 2, but a slight 

 excess of silica belonging to the lime, iron, and magnesia is 

 present. The state of oxidation of the iron is uncertain, as it is 

 not mentioned whether ferrous iron was determined or not. If 

 we assume that the lime, iron, and magnesia are present accor- 

 ding to the general formula of the amphibole group, RSiOg, 

 the microlites having been determined as amphibole, and deduct 

 the requisite number of silica molecules to satisfy them, the 

 remainder becomes 



The base has therefore the chemical composition Na Al 



■(5103)2 ^2^' with a little of the soda replaced by potash, or, 



in other words, it has the exact chemical contpositioti, the exact spe- 



-cific gravity, the property of gelatiiiizing with acids, a?id the optical 



■ 'Op. cit.,p. 454. 



