Dana and Penfield — Miner alogical Notes. 137 



SO,.... 



...43-59 



•545 



Na 3 . 



...40-86 



•659 



CO,... 



... 5-42 



■3 23 



K .... 



... 2-33 



•060 



CI .... 



... 2-13 



•060 



In sol 



... 4-41 





Ign. 



1-32 





Ratio. 

 and 



•545 = 



= 43-59 S0 3 ) 

 33-23 Na 9 \ 



•536 



•123 



7-63 Na 3 } 



•123 



5-42 C0 3 f 





2'33 K } 





2-13 CI \ 



100-06 

 This corresponds then to 



Na 2 S0 4 76-82 



Na 2 C0 3 13-05 



KC1 4-46 



Insol. .. 4*41 



Ign 1-32 



100-06 



The insoluble portion is apparently clay ; a section exam- 

 ined in the microscope showed the impurity densely distributed 

 in bands parallel to the prismatic faces. The fact that in the 

 analysis the potassium and chlorine are present in exactly the 

 amounts required to form potassium chloride may be only a 

 coincidence, and the chlorine may in fact be combined with 

 sodium, and the potassium may in part replace the sodium in 

 the sulphate. It is immaterial which explanation is adopted, 

 but in any case it is quite certain that the potassium (or 

 sodium) chloride is present as an impurity, for in the thin sec- 

 tion numerous rectangular crystals, some of them apparently 

 cubes, were visible. It seems proper, therefore, to deduct 

 these elements from the analysis, leaving only the sodium sul- 

 phate and sodium carbonate. The result, calculated to 100 

 per cent, is 



Na 3 S0 4 .. 85-48 



Na 2 C0 3 14-52 



This corresponds, though approximately only, to the formula 

 4Na 3 S0 4 +Na 3 C0 3 



which requires 



Na 2 S0 4 84-27 



Na 2 C0 3 15-73 



100-00 



Am. Jour. Sci. — Third Series, Vol. XXX, No. 176. — August, 1! 

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