in Ferric Salts and in Chromic Acid. o05 



Iron. — Results obtained with metallic iron are shown in 

 Table II, the first experiment, as before, being recorded in 

 detail as an example. The calculation of the constants from 

 the titrations is here somewhat different, since for every two 

 molecules of ferrous iron formed by reduction of the ferric 

 sulphate one more is formed by solution of the metal. The 

 concentration of: ferric salt at any instant is therefore measured 

 by the value of the expression C — <? — f (c — c„), in which C is 

 the total iron, c the initial ferrous iron, and c the ferrous iron 

 at time t, all expressed in the same units. In the table these 

 units, as before, are cubic centimeters of 0*02 normal perman- 

 ganate, and the values refer to 20 cm 3 of solution. The metal 

 used was " American Ingot Iron," a special grade of commer- 

 cial iron which has a purity of about 99*9 per cent. 



Table II. 

 Metal: Iron. E [ Fe(S0 4 )2 , 0'05 molar. 



No. of 

 Exp. 







EUSO* , 



O'Ol molar. 









1. 



= 



50-00 c< 



, = 0'44 











K 





v = 



580 



560 



540 



520 500 



480 



460 







At= 



8 



8 



8 



8 8 



8 



8 







c — 





4-36 



8-20 11-93 15-68 



19-15 22 



•68 



25-67 





hi = 



3-90 



3-93 



3-90 



399 3-78 



3-59 



373 







k = 



3-87 



3-91 



3-89 

 H 2 S0 4 , 



3-99 3-79 

 0'05 molar. 



3-58 



3-73 



382 



2. 



k = 



3-97 



3-97 



3-64 

 H 2 S0 4 , 



(lost) 3-76 

 025 molar. 



3-96 



3-80 



385 



3. 



k = 



4-00 



3-92 



3-95 



3-98 391 



3-94 



399 



396 



4. 



k = 



391 



3-90 



3-82 

 H 2 S0 4 , 



3-80 3-85 

 1'25 molar. 



3 92 



3-92 



387 



5. 



k = 



3-42 



3-38 



3-31 



3-42 3-35 



335 



3-34 



337 



6. 



k = 



3-45 



3-38 



3;29 

 EUSO. 



3-44 3-33 

 1 , 5 molar. 



3-45 



3-31 



338 



7. 



k = 



1-77 



1-79 



1-74 



1-79 1-75 



1-78 



1-69 



176 



8. 



k = 



1-75 



1-71 



1-69 



1-67 1-63 



1-64 



1-62 



1'67 



9. 



k = 



1-79 



1-74 



1-74 



1-72 1-73 



1-72 



1-74 



174 



10. 



k = 



1-80 



1-79 



1-76 



1-76 1-76 



1-76 



1-78 



1-77 



For the lower acidities, O'Ol and 0'05 molar, the results are 

 less trustworthy than the rest and probably slightly too low, 

 for the disk became covered during the experiment with a 

 blackish coating which seemed to consist chiefly of hydroxide, 

 since it turned to a rust-red color on drying. In the presence 

 of 0-25 molar sulphuric acid the coating was very slight, and 

 at higher acidities entirely absent. 



