Substances in the Wet Way. 



381 



this transfer is of no 

 The following results 



lized to the receiver ; but since the chromic acid thus pro 



duced is reduced later by the arsenit* 



account in the working of the process. 



were thus obtained. 



Table V. 



As 2 3 r As 2 3 



taken. found, 



grm. grm. grm. 



5-1025 0-1144 4-9447 



5*0799 0-0526 4'9849 



5-0801 0-0582 4'9782 



5-0706 0-0908 4'9365 



K 2 Cr 2 7 



taken. 



grm. 



5-0002 

 5-0018 

 5-0005 

 5-0013 



K 2 Cr 2 0; 

 found. 



Error on 



K 2 Cr 2 7 . 



grm. 



0-0555 — 

 0-0169 — 

 0*0223 — 

 0-0648 — 



The cause of the error shown in these experiments was 

 traced finally to too great concentration of the sulphuric acid 

 in the process. When the boiling begins the chromate is 

 reduced gradually and if the evaporation of the water is 

 pushed too rapidly, the sulphuric acid may reach a strength at 

 which it begins to cause the reduction of the chromic acid 

 with the evolution of oxygen instead of chlorine. 



The obvious remedy is to conduct the boiling operation 

 more slowly. It was found that, if from 5-6 hours time was 

 taken for the proper concentration of the contents of the Voit 

 flask, the presence of the sulphuric acid worked no harm, as 

 will be seen from the following results. Experiments (1) and 

 (5) were made with 5 cm3 of sulphuric acid present and the 

 others with 20 cm3 , as used before. 









Table VI. 









K 2 Cr 2 7 



As 2 3 



As 2 3 



K 2 Cr 2 7 



Error on 





taken. 



taken. 



found. 



found. 



K 2 Cr 2 7 . 





grm. 



grm. 



grm. 



grm. 



grm. 



1. 



10004 



1-0500 



0-0398 



1-0014 



0-0014 + 



2. 



1-0007 



1-0531 



0-0437 



1-0006 



o-oooi — 



3. 



2-0013 



2-0501 



0-0299 



20026 



00013 + 



4. 



2-0037 



2-0727 



0-0502 



2-0049 



00012 + 



5. 



5-0020 



5-1002 



0-0495 



5-0068 



0*0048 + 



6, 



5-0037 



5-1018 



0-0513 



5-0066 



0*0029 + 



In applying this method to the determination of oxygen 

 used in the oxidation of an organic substance, the carbon 

 determination was made as already described, the amount of 

 water used being such as to leave 60-80 cm3 of liquid in the 

 boiling flask after the carbon dioxide had been driven to the 

 absorption flask by boiling. This liquid was then washed into 

 the Voit flask and the chromic acid remaining determined by a 

 second distillation (this time with hydrochloric acid) in the 

 manner described above. In each of the experiments recorded 



* Browning, this Journal, 1896, vol. i, 35. 



