169 



These results show that the sensitiveness of the test is not impaired by 

 the presence of large amounts of cobalt. 



B. The Tschugaev-Treadwell Method. 



10 cc. portions of 0.0921 molar CoS0 4 , equivalent to 54.31 mg. Co., with 

 varying small amounts of NiS0 4 were heated with ammonia until a clear 

 solution was obtained, hydrogen peroxide added and the solutions heated 

 till excess of peroxide and ammonia was removed, diluted to 50 cc, 1 cc. of 

 dimethylglyoxime solution added and the time required for the red pre- 

 cipitate to appear was observed. Results below. 



TABLE VI. 



NiS0 4 



Mg. Ni. 



Ratio Ni : Co. 





Vol. 



Cone, molar 



Results. 



10 cc 



9 cc 



8 cc 



7 cc 



6 cc 



5 cc 



4 cc 



0.0005 

 . 0005 

 . 0005 

 . 0005 

 . 0005 

 . 0005 

 . 0005 



0.2934 

 .2641 

 .2347 

 .2052 

 .1760 

 .1467 

 .1172 



1 : 185 

 1 : 206 

 1 : 231 

 1 : 264 

 1 : 309 

 1 : 370 

 1 : 462 



Red ppt. 1 hour. 

 Red ppt. 1 hour. 

 Red ppt. 1 hour. 

 Red ppt. 24 hours. 

 Red ppt. 24 hours. 

 Rerl ppt. 24 hours. 

 Red ppt. 24 hours. 



Taking the minimum amount of nickel that could be detected in 1 hour, 

 0.2347 mg., we observed the effect of larger proportions of cobalt. The 

 procedure and final volume were the same as in the experiments recorded 

 In Table VI. 



TABLE VII. 



C0SO4 0.0921 molar 



Mg. Co 



Ratio Ni : CO 



Results. 



10 cc 



54.31 



81.47 



108.62 



135.78 



162.93 



1 : 231 

 1 : 346 

 1 : 462 

 1 : 577 

 1 : 693 



Red ppt. after 1 hr. 





No ppt. after 1 hr. 



20 cc. 



25 cc 



No ppt. after 1 hr. 

 No ppt. after 1 hr. 



30 cc 



No ppt. after 1 hr. 







