564 JAMES H. HANCE 



move "E" to the left index on "D." The reading on "C" under 

 "E" is 301, which means that 30. i per cent of albite is equivalent 

 to 3.55 per cent of Na20. Similarly, to find the amount of AI2O3 

 needed to combine with 3.55 per cent NazO in the albite molecule 

 move ''E" to 195 on ''D." This will then cross "C" at 587, which 

 indicates a requirement of 5.87 per cent of AI2O3. The sliding 

 portion of the rule (carrying scales "B" and "C") has been set 

 but once for both these readings. Now suppose that the Si02 

 value in albite corresponding to 3 . 55 per cent Na20 is desired. In 

 the table the Si02 percentage is 68.8. This value on "D" is not 

 under "C" at all in the present setting. The next operation cor- 

 responds merely to doubling the length of the scale on "C." 

 Place "E" on the right index of "C" and then move "C" to the 

 right until the left index of "C" is under "E." Then move "E" 

 to 688 on "D" and it is found to cross "C" at 20.7 which is the 

 SiOz value required. A check on the correctness of these values 

 thus obtained is to total the constituents and compare with the 

 total obtained on "C." 



Total on "C" Separate Percentages 



Albite — 30. 1 per cent NaaO — 3. 55 per cent 



AlA-5-87 " " 

 SiOs— 20.7 " " 



Total — 30. 12 per cent 



Now suppose we consider the potash in Analysis II which prob- 

 ably was present as leucite (7.78 per cent). Table I shows the 

 composition of leucite as follows: 



K2O— 2 1.5; AI2O3— 23 . 3 ; Si02— 55 . 2 



Set "E" on 215 on "D" and move the slide so that 778 on ''C" 

 is under "E," or is opposite 215 on "D." Move "E" to the left 

 index on "D" and it is found to cross "C" at 36.19, which is the 

 percentage of leucite present. In order to get the corresponding 

 value of AI2O3 move " E " to 233 on " D." In this position it crosses 

 "C" at 8.43, the percentage of AI2O3. The silica value, 55.2 on 

 "D," again falls under the blank space in the rule, so set "E" on 

 the right index of "C," move the slide to the right so that the left 



