40 PROCEEDINGS OF THE AMERICAN ACADEMY 



ANALYSIS. 



Sterlingite. Damourite. 



Oxygen. 1. 2. Oxygen. 



SiO, 43.87 23.40 45.22 43.41 23.15 



AlOs 36.45 17.00 37.85 35.17 16.39 



Fe^Os 3.36 1.00 4.62 1.39 



MgO 1.40 0.56 



K,0 10.86 1.84 11.20 10.90 1.85 



if^O 5.19 4.61 5.25 4.50 4.00 



99.73 99.52 100.00 



Of the two analyses of Damourite, No. 1 is by Delesse, of the 

 mineral found in the gangue of cyanite, at Poutivy in Brittany, and 

 No. 2 is by Igelstrom, of the similar mineral, found at Horrsjoberg, 

 Wermland. The analysis of Sterlingite was made by Mr. C. E. Munroe, 

 Assistant in the Chemical Laboratory of Harvard College, and the 

 above numbers have been abundantly confirmed in repeated analyses 

 by various students in the same laboratory. The alkalies were treated 

 by Smith's process, and the potassium was weighed as PtK.^ Cl^. This 

 value, compared with the total weight of the alkaline chlorides, and that 

 of the chlorine also determined, showed that the alkali in the mineral 

 was almost wholly potash, although the presence of lithium and sodium 

 was plainly indicated by the spectroscope. The water was determined 

 by igniting the mineral in coarse powder, previously dried at 100° C. 

 Even after ignition, the finely pulverized mineral is only j^artially 

 decomposed by hydrochloric acid, and in the above analysis it was 

 decomposed by fusion with sodic carbonate. The usual tests failed to 

 indicate the presence of fluorine. 



Regarding the water as basic, and as forming a part of the protox- 

 ides, the atomic ratio in Sterlingite, between the silicon, the sesqui- 

 oxide radicals, and the protoxide radicals, is 



IV VI It 



Si : R : R = 23.40 : 18 : 6.45, ornearly 4:3:1. 



The deviation from the simple ratio will not appear so great, as seems 

 at first sight, if it is noticed that a difference of one-half per cent in 

 the amount of water would make the ratio almost exact. 



The corresponding ratio in the Damourite from Wermland is 



23.15 : 17.78 : 6.41, or, as before, nearly 4:3:1. 



These ratios point to the general formula : — 



n VI 



