m 



Dr. H. Stanley Allen on the 



percentage of the initial activity, measured immediately 

 after polishing. 



Table I. 

 Zinc plate in air of room. Fatigue period, 16 minutes. 



I 



100 



100 



100 



100 



100 



II 



75 



# 



77 



76 



77 



Ill 



66 



* 



* 



67 



64 



IV 



57 



58 



* 



* 



58 



V 



54 



55 



55 



# 



* 



VI 



49 



51 



51 



48 



* 



VII 



47 



49 



47 



44 



48 



VIII 



46 



46 



45 



43 



44 



IX 



43 



45 



42 



42 



43 



The fatigue is not affected by shielding the zinc from 

 ultra-violet light for a period of about five minutes, no matter 

 at what stage in the process the shielding takes place. 



In the tests recorded in Table II. the zinc plate was 

 polished with fine emery-paper only. The initial activity is 

 given in arbitrary units in the first row of the table, and 

 below is given the activity at the end of a fatigue period 

 of 16 minutes, expressed as a percentage of the initial 

 activity. 



Table II. 

 Zinc plate in air of room. Fatigue period, 16 minutes. 



f Arbitrary units . . . 

 Initial activity -j 



[ Percentage 



Final activity. Percentage 



a. 



b. 



c. 



d. 



e. 



318 

 100 



47 



290 



100 



44 



288 



100 



43 



237 



100 



44 



211 



100 



46 



In test a the plate was exposed to ultra-violet light con- 

 tinuously. In test b it was shielded from ultra-violet light 

 for 5 minutes, while in tests c, d, and e it was shielded 

 from ultra-violet light for 15 minutes. 



Experiments were also carried out in a closed testing- 

 vessel of brass fitted with a quartz window. The zinc plate 

 was polished with fine emery, placed in position as quickly 

 as possible, and the first reading was taken two minutes after 

 polishing. The initial activity was found by extrapolation, 



