The Detection of Phenols in Water
Journal of Industrial & Engineering Chemistry
A1203 and, therefore, in such cases, the more probable result. These results are included in Table VII . SUMMARY' 1-The methods here compared all turn on t h e titration of the aluminium salt with a n alkali, using phenolphthalein as indicator. 2-The manipulation details t o be observed in A N D E N G I N E E R I N G C H E M I S T R Y 1'01. 13, No. 5 carrying out this principle are all-important and constit u t e t h e differences between t h e methods. 3-Methods A and B alone are both
... hy and convenient. &Method B has some slight advantage over A, especially in t h e presence of iron. 5-It is quite essential t o use a n alkali of titer not more t h a n 0.5 N . The presence of very small quantities of phenols in certain public water supplies has been found t o cause quite offensive tastes and odors, which are greatly intensified if the raw water is chlorinated, owing probably t o the formation of chlorophenols. The detection of traces of phenols in such waters by chemical tests has been impossible until recently. While numerous tests for phenols are known, none sensitive enough t o detect these minute quantities was available until Folin and Denis3 presented their colorimetric test, widely used in the estimation of phenols in urine. To 750 cc. of water add 100 g. of sodium tungstate, 20 g. of phosphomolybdic acid, and 50 cc. of 85 per cent phosphoric acid. Boil for 2 hrs. under a reflux condenser, cool, and dilute t o one liter. (Owing t o the fact t h a t several formulas may be found for phosphomolybdic acid, it would seem desirable t o substitute for it 18 g. of 85 per cent molybdenum trioxide. This change has been found t o give satisfactory results in practice.) One t o two cc. of this reagent are mixed with a n equal volume of t h e solution t o be tested, 3 t o 10 cc. of saturated sodium carbonate solution are added, and, in the presence of phenols, a blue color is produced. I n addition t o phenols, the authors mention tyrosine, protein, and uric acid as producing the same color. Folin and Wu4 mention cuprous oxide. Tisdal15 mentions indol and ferrous iron. Thus t h e original test is by no means specific. It is believed t h a t t h e method was first applied t o water examination by C. E. Trowbridge, chemist a t the Newcastle (Pennsylvania) Filtration Plant, his adaptation being: T o 100 cc. of t h e sample add 1 cc. of phenol reagent, then 5 cc. of sodium carbonate solution. Trowbridge states t h a t amounts as low as 1 part in 20,000,000 give a positive test. Numerous tests made by the writer on natural waters t o which phenol was added indicated t h a t amounts a t least as low as 0.5 p. p. m. could be detected. However, i t was found t h a t tannin in dilute solution also gives t h e test. This was not surprising, The reagent is prepared as follows: 1 Since writing the above, the author has met with the recent paper of I. M. Kolthoff in Z. anoyg. Chcm., 112 (1920), 172. He describes a titration of aluminium salts essentially similar to Method B, but with variations which would destroy its accuracy in certain circumstances. * Received January 24, 1920. * J . B i d . Ckem.. 12, 239. 4 Ibad., SS, 106. 6 Ibad., 44, 409. in view of its composition, b u t presented a complication in the practical use of t h e method. Later this test for tannin was used in connection with a n investigation of stream pollution b y waste from a leather products factory, and effort was made t o distinguish between tannins and phenols by other colorimetric methods. It was found t h a t the ferric chloride test, using 1 cc. of 1 per cent FeC13.6HzO t o 100 cc. of sample, produced a blue color with as little as 2 p. p. m. of tannin, b u t not with less t h a n 500 p. p. m. of phenol. This, however, would not distinguish between them if less t h a n 2 p. p. m. of either were present. Distillation proved a n effective means of separation. It was found, on acidifying and distilling tannin solutions of various strengths, t h a t t h e distillates gave no test with t h e Folin phenol reagent. With phenol solutions t h e distillates all gave positive tests. Distillation has certain other advantages. 1-A slight degree of concentration takes place in the first portions of distillate, thus making possible the detection of appreciably smaller amounts than when the test is made on the original sample. 2-The precipitate of calcium carbonate, which is formed in many waters on the addition of sodium carbonate, is eliminated. 3-As applied to water examination, the test becomes practically specific for phenols.