Phelps — Estimation of Chlorates and Bromates. 201 



Art. XYII. — The Use of Ferrous Sulphate in the Estima- 

 tion of Chlorates and Bromates ; by I. K. Phelps. 



[Contributions from the Kent Chemical Laboratory of Yale University — CXXV.] 



In a recent article, * a method for the titrimetric estimation 

 of nitric acid or nitrates was described. It consisted, briefly, 

 in the measurement of the amount of ferrous salt oxidized in 

 the reduction of the nitric acid to nitric oxide by an excess of 

 ferrous sulphate in the presence of hydrochloric acid. The 

 value of ferrous sulphate as a reducing agent in analytical pro- 

 cesses has been long recognized on account of its ready avail- 

 ability, the high degree of precision with which it may be 

 determined, and the extreme slowness with which it is oxidized 

 by atmospheric oxygen. This last fact was clearly shown by 

 Peters and Moodyf for solutions which had been allowed to 

 stand until all active oxygen, dissolved in the water, or other- 

 wise present, had produced its effect. The author was surprised 

 to find that, in boiling such solutions in the open air and 

 cooling with stirring in running water, no distinctly perceptible 

 change could be noted, although the oxidation from day to day 

 was plainly evident. 



CarotJ has suggested the use of ferrous sulphate for deter- 

 mining the oxygen in hypochlorites and chlorates in admixture 

 with chlorides but gives no evidence to show the degree of 

 accuracy of the process. Table I records experiments made with 

 the purest potassium chlorate of commerce to test this point. 

 The dry salt was weighed out, treated with an excess of stand- 

 ardized ferrous sulphate solution approximately ' - ), and with 



15 cm3 of sulphuric acid (1 : 4). This mixture was brought to the 

 boiling point in a trapped flask, cooled to room temperature by 

 immersion in running water, diluted to a volume of 600 cm3 , and, 

 after the addition of 1-2 grms. of manganous chloride, titrated 

 to color with standard potassium permanganate solution. 



Table I. 





Oxygen value 



Oxygen value 





KC10 3 



of ferrous salt 



of ferrous salt 



Error on 



taken. 



taken. 



found. 



KCIO3. 



grm. 



grm. 



grm. 



grm. 



0*0500 



0-02756 



0*00814 



0-0004 — 



0-0500 



0-02739 



0-00781 



o-oooo± 



o-iooo 



0-04934 



0-01024 



0-0002 — 



o-iooo 



0-04951 



0-01043 



0-0002 — 



0-2000 



0-09086 



0-01247 



0-0002 4- 



0-2000 



0-09078 



001277 



0-0008 — 



0*5000 



0-20552 



0-00993 



0-0006 — 



0-5000 



0-20543 



0-00980 



0-0005- 



* This Journal, xiv, 440 (1902). f This Journal, xii, 369 (1901). 



X Compt. Eend., cxxii, 449. 



Am. Jour. Scl— Fourth Series, Vol. XYII, No. 99.— March, 1904. 

 14 



