~Effect of Varying Temperature.~--In these experiments the bulk was in
each case 100 c.c., and 10 c.c. of dilute sulphuric acid were present.
The permanganate required by
1 c.c. of ferrous sulphate was, at 15° 1.0 c.c., and at 70° 1.1 c.c.
10 " " " 9.7 " 9.8 "
100 " " " 97.7 " 96.8 "
The lower result with the 100 c.c. may be due to oxidation from
exposure.
~Effect of Varying Bulk.~--The following experiments show that
considerable variations in bulk have no practical effect. In each case
20 c.c. of ferrous sulphate solution and 10 c.c. of dilute acid were
used.
Bulk of assay 30 c.c. 100 c.c. 500 c.c. 1000 c.c.
Permanganate required 20.0 " 20.0 " 20.2 " 20.5 "
~Effect of Free Sulphuric Acid.~--Free acid is necessary for these
assays; if there is an insufficiency, the assay solution, instead of
immediately decolorising the permanganate, assumes a brown colour. The
addition of 10 c.c. of dilute sulphuric acid suffices to meet
requirements and keep the assay clear throughout. The following
experiments show that a considerable excess of acid may be used without
in the least affecting the results. In each case 20 c.c. of ferrous
sulphate were used.
Dilute sulphuric
acid 1.
Pages:
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451