522 



Tlie Traprain Law PJtonolite. 



Total 



100-44 



99-4 



It will be seen, that, with the exception of the alkalies, the new 

 analysis agrees very closely with that of Player. The new figures 

 for potash and soda, which confirm the partial analysis of Dr. Pollard, 

 diSer from those of Player, both in the total and in the relative 

 proportions of the two oxides. The only other constituent in which 

 any serious divergence occurs between the two analyses is the 

 alumina, but, after making allowance for the j)hosphoric anhydride 

 not determined by Player, the discrepancy amounts to only 0-4 per 

 cent Phosphoric anhydride and chlorine, of which no mention is 

 made by Player, have been found in quite appreciable quantity. 

 Special interest attaches to the determination of these constituents, 

 owing to their importance in the calculation of the amount of 

 sodalite. If the phosphoric anhydride is assumed to be present as 

 chlorapatite, the 0-15 per cent of PgOg found will require 0-02 per 

 cent of chlorine to form SCa^PjjOg . CaClo. The remaining 0-20 per 

 cent of chlorine calculated to 3(Na20,Ai203,2Si02) 2NaCl gives 2-7 

 a,s the percentage of sodalite in the rock. 



The mineral composition of the rock has been calculated from the 

 chemical analysis in the following way and the results are appended 

 below. After determining the amounts of ilmenite from the titania 

 and chlorapatite from the phosphoric anhydride, the residual chlorine 

 is allotted to sodalite. Total potash is calculated as orthoclase, 

 and water above 105° C. as analcite. The soda remaining after 

 allowing for that in sodalite and analcite is divided between albite 

 and nepheline, the relative amounts of these being determined by 

 the silica available after all other silicates have been satisfied. As 



