IRON AND STEEL. EI>ITEI> l3Y
A
1'. \r
?;IIIMBX.
MODIFICATION of the staiinous chloride method for iron titrations has been proposed 1)y R. W . Slahon ( A m . Chem.J., 15, 360): If mercuric a n d platinic chlorides are added to a solution of ferric chloride, strongly acid with hydrochloric acid, a t or near the boiling point. stannous chloride reduces all the iron first, and the first drops in excess cause the forniatioti of a faint cloud of tilercurow chloride, darkened and rendered instantly perceptible by finel). divided inercury and platiiiuiii ivliich y trace of platinic are precipitated at the same time. A \ ~ r minute chloride present in solutio11 is sufficient to bring about this reaction. This mixture, tlien, of mercuric and platinic chlorides, is an indicator which can be u s e d to advantage i n titrations of iron by stannous chloride. The indicator c;in be iiiatle from solutions of platinic chloride and niercuric cliloritle to coiltain in one liter, 0.05 grain metallic platiiiurn arid 34.d grains mercuric chloride. Fifteen cc. is i: suitable qwiitil>. to be used in each estiniation. T h e standard solution of ferric chloride is atl\-antageousl!made of such strength that one cc. contains 0.01 grain iron, the stannous chloride solution of approxiinately the sa111e strength. The determination of iron in its ores is iIiade as follows : Weigh accurately about one gram of ore into n 250 cc. beaker. Cover with a watch glass and digest in twenty cc. hydrochloric acid of I .zo sp. g r . until deconiposed. .Add now 0.3 gram of potassium chlorate aiid digest a few minutes longer. T h e glass and rim of the beaker are washed C ~ O W I into the solution, which should now be about forty cc. in volume. It is filtered and washed into an Erlennieyer flask; twenty to thirty cc. hydrochloric acid of 1 . 2 0 sp. g r . are atlcletl to the solution bringing its volume up to about 1.5 cc. Sonadd fifteen cc. of the indicator solution and it is ready ior titrntion. H e a t the covered solution to boiliiig. T h e trace of clilorine remaining escapes. Lower the light aiid titrate at incipient boiling. T h e burette should be of IOO cc. capacity. T h e residue is prepared for titration by fusing \\.it11 sodium carbonate, extracting with water and acid, aiid adtliiig fifteen cc. indicator.
