THE ROSIWAL METHOD FOR MINERALS 



219 



140-150 gms. This was quartered, and one-fourth of each 

 quarter was used to make two samples for determination. 

 For this particular rock, grains passing through a 60-mesh sieve 

 and remaining on a 100 mesh seemed to be very suitable. 



TABLE IV 



Magnetite. . 



Biotite 



Hornblende 



Augite 



Plagioclase . 



Quartz 



Orthoclase. . 



I 



Sp. gr. 



II 



Mesh 

 80-100 



1.38 

 II . 10 



6.66 



37.87 

 19. 21 

 23.07 



III 



Mesh 

 80-100 



I .09 

 9-49 



6-93 

 37.10 

 21 . II 

 24.25 



IV 

 Mesh 

 60-100 



I .42 



9-94 



6.66 



34.60 



21-35 

 26.00 



V 

 Mesh 

 60-100 



9-74 

 6.44 



31-65 

 23. 22 

 27.06 



99.29 99.97 99-97 99-23 100.04 100.43 99-OI 



VI 



Mesh 

 60-100 



1.36 

 9.88 



6.31 



32-82 

 24.65 

 25.02 



VII 



Mesh 

 60-100 



1.30 

 9-72 

 6.25 



33-40 

 23-70 

 26.06 



VIII 



Average 



1 .26 

 9.98 



6-54 



34-57 

 22. 21 



25-25 



Comparing now the final results of each of the three methods, 

 we have the results given in Table V. 



TABLE V 



Quartz. . . , 

 Orthoclase . 

 Plagioclase, 

 Biotite. . . 

 Pyribole. . 

 Magnetite . 

 Pyrite, etc. 



Calculated 



from Analysis 



99-15 



Weight 



Percentage 



Rosiwal 



99-9 



Heavy Solution 



22. 21 

 25-24 



34-57 

 9.98 

 6-54 

 1 . 26 



99-83 



The amount of quartz in the calculated analysis is practically 

 the same as in the specific -gravity determination, and the Rosiwal 

 value is only slightly less. 



The orthoclase is low in the calculated analysis and practically 

 the same in columns 2 and 3, while the calculated plagioclase is 

 high as compared with the other two determinations. This is 

 unquestionably due to the fact that the orthoclase carries soda. 

 In the computation of the analysis by Cross, Iddings, Pirsson, and 



