Colorimetric Determination of Iron with Salicylic Acid d
A Spectrophotometric Study J. P. RIEHLIG. Oregon State College, Corvallis, Ore.
ml. of the ;odium salicylate reagent, the solution TTas made slightly alkaline with 1 to 1 ammonium hydroxide and then just acid with 1 to 1 acetic acid added dropwise. Exactly 10 ml. of acetic acid were then added, and the solution \vas accurately diluted to 100 ml. and thoroughly mixed. The transmittancy curves were determined for a solution thickness of 1.961 cm. The absorption of the glass cell was compensated by placing in the rear beam of light a similar cell filled with distilled water.
By means of the recording photoelectric spectrophotometer, which provides a method of color measurement entirely objective and capable of high accuracy and precision, a critical study has been made of the colorimetric determination of iron by salicylic acid with particular attention to the effects of diverse ions.
Conformity to Beer's Law
T
HE reaction between salicylic acid and ferric ion in acetic acid solution to give an amethyst coloration has been known for many years (7, 9, I S ) , but it was not applied t o the quantitative colorimetric determinabion of iron until 1907 ( 3 ) . Since then the method has been developed and further applied by many workers ( 1 , 8 ,IO, 11) and some of its limitations have been indicated. Snell ( I O ) and Yoe (15) report that hydrochloric, nitric, and sulfuric acids, phosphate, thiosulfate, bisulfite, and fluoride interfere, while Pagaidachnuii and Fiavich (8) say that citrate, tartrate, and oxalate must be absent. The purpose of the work described in thi3 paper v a s t
