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THE JO
I913
R-V-4L 0 F I LVD 17sT RI d L il S D E S G I LVE E RI S G C H E M I S T R k'
t h a n do t h e official Gunning or official Kjeldahl methods, both of which require from three t o four hours for osidation, depending upon t h e material. BmEAu
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OF
CHEMISTRY
s. DEP.AnT.\lErT O F .kGRICLT,TURE
,
R'ASHIXCTOS
ORTHO-TOLIDINE AS A REAGENT FOR THE COLORIMETRIC ESTIMATION OF SMALL QUANTITIES OF FREE CHLORINE By J. XV. ELLMSA X D S. J. HAUSER Received August 25, 1913
K i t h t h e increasing use of very small quantities of chlorine, either free or in t h e form of hypochlorites for t h e disinfection of m-ater for drinking purposes, a colorimetric method for t h e detection a n d estimation of small a m o u n t s of free chlorine is desirable. S T .IR CH- I O D I D E
31 E T H 0 D
T h e volumetric method in which iodine is liberated f r o m potassium iodide b y t h e chlorine, a n d t h e iodine titrated with sodium thiosulfate. using starch a s a n indicator, offers some difficulties when very small quantities of chlorine are t o be determined. Both t h e sodium thiosulfate a n d t h e potassium iodide solutions deteriorate on standing. Frequent standardizat i o n of t h e sodium thiosulfate is always necessary if accurate estimations are t o be made. Free iodine is liberated from solutions of potassium iodide on standi n g , a n d errors from this source must be constantly guarded against in estimating small quantities of free chlorine. Starch as a n indicator in this method is open t o a n objection on t h e score of not being sensit i v e . unless freshly prepared solutions are used. T h e indefiniteness of t h e color end point, d u e t o t h e liberation of free iodine from t h e potassium iodide, a n d t h e consequent deepening of t h e color are defects which make t h e detection of small a m o u n t s of free chlorine uncertain. Under t h e most favorable conditions t h e .starch-iodide method is capable of detecting quantities of free chlorine n o t lower t h a n 0.03 p a r t per million. This method, therefore, for t h e foregoing reasons lacks reliability for use in determining t h e residual free chlorine which m a y be left in t h e treated water. A C E T I C ACID S O L U T I O N O F O R T H O - T O L I D I S E
T h e ortho-tolidine t e s t for free chlorine, a s suggested b y Earl B. Phelps, in which a n acetic acid solution of this reagent is used. furnishes a delicate qualit a t i v e test. b u t is open t o certain objections for quantitative purposes on account of variations in color produced b y waters of different composition.' According t o this method a one-tenth per cent solution of otolidine in I O per cent acetic acid is employed. With two drops of this reagent in jo cc. of t h e water containing about 0 . 0 ; p a r t per million of free chlorine a yellow color is supposed t o be developed. Dittoe a n d Van Buskirk found t h a t instead of a yello\\- color developing with very small quantities of chlorine, a green color was produced which changed from green t o yellow a n d finally t o deep red as t h e concentration of t h e free chlorine was increased. I n one instance "Report on t h e Public Water Supply of Cleveland with reference t o t h e T r e a t m e n t with Calcium Hypochlorite," by W. H . Dittoe and L. H. I'an Buskirk, Ohio S t a t e Board of Health, Bull. 3, iYo. 1 (January, 1913).
915
when testing for chlorine in a sample of t h e water supplied t o t h e city of Columbus, Ohio, a light blue color developed on adding o-tolidine. S o explanation for these color changes is a t t e m p t e d b y t h e above writers. It is a p p a r e n t , however, t h a t o-tolidine could not be very well employed in a colorimetric estimation, unless these color changes were e h i i n a t e d . X limited a m o u n t of s t u d y of t h e various factors affecting these color changes has been undertaken b y t h e authors, a n d a reliable mode of procedure for a colorimetric determination worked out. -4 possible esplanation of t h e reactions inl-olJ-ed is offered, which seems t o account for some of the color changes. although t h e authors h a r e not had t h e opportunity of making a sufficiently thorough investigation t o enable t h e m t o esplain completely all of these complex reactions. In using t h e acetic acid solution of o-tolidine with small a m o u n t s of chlorine. it was found t h a t different shades of color were produced. ranging from a yellowish green t o a blue. -Although in this test t h e dyes are produced in a n acid solution. nevertheless t h e variations in t h e colors formed appeared t o be intimately associated with t h e original degree of alkalinity of t h e water. Waters t h a t are naturally alkaline from t h e carbonates of calcium and magnesium, which t h e y contain, or those rendered artificially so b y a n y of the fixed alkalies, act similarly. T h e higher t h e original alkalinity of t h e water containing free chlorine, t h e bluer is t h e shade of color produced. T h e more nearly neutral is the water being examined, t h e yellower is t h e t i n t . In natural waters of moderate hardness, which have not been materially modified b y some method of purification, t h e usual t i n t obtained is a yellowish green. B y increasing t h e concentration of t h e acetic acid a more yellowish green color is produced; b u t only b y adding very large quantities of acid is a yellow color formed. On t h e other h a n d t h e addition of a very small quantity of a highly dissociated acid, such as hydrochloric or sulfuric, produces a deep yellow color with small amounts of free chlorine. This yellow color is not affected b y t h e original degree of alkalinity of t h e water being tested, nor is t h e t i n t modified b y a n y change in t h e concentration of the acid. By increasing t h e a m o u n t of free chlorine, t h e acetic acid solution of o-tolidine produces first a solution with a yellowish green color, changing t o an orange a n d t h e n t o a deep red. Still larger quantities of chlorine produce a d a r k red precipitate. Small quantities of bromine a n d iodine produce, with an acetic acid solution of D - t oli dine, green- c ol or e d solutions. K i t h larger a m o u n t s bromine acts as does chlorine, but iodine tends t o f o r m a precipitate more readily. a n d i t is of a bluish color. K i t h increasing concentrations of solutions of potassium bichromate or potassium permanganate. b u t with no halogens present t h e acetic acid solution of o-tolidine produces first green-colored solutions, then yellow solutions and finally deposits brown-colored precipitates. These precipitates are soluble in hydrochloric acid a n d give yellow- colored solutions. On t h e addition of nitric acid t o a n acetic acid solution
.4*l7D EAVGIAVEERILVG C H E M I S T R Y of
o-tolidine a yellow- colored solution is formed. T h e acetic acid solution of o-tolidine darkens on standing, a n d especially so when exposed t o t h e light. Old solutions give slightly different shades of color with small a m o u n t s of free chlorine. t h a n do those which are freshly prepared. T h e green colors produced with small a m o u n t s of free chlorine fade within a few minutes, and are probably n o t reliable for longer t h a n five minutes for colorimetric estimation against standards prepared with known amounts of chlorine. This reagent is sufficiently delicate t o detect quantities of free chlorine a s low as 0.01 p a r t per million. T h e objections t o malting use of the acetic acid solution of o-tolidine for t h e quantitative determination of small a m o u n t s of free chlorine m a y be summed u p as follows: 1st. Watersof varyingdegreesof alkalinityproduce differentshadesof color withsimilar amountsof freechlorine. 2nd. Fading of t h e colors occurs within a few minutes. 3rd. Deterioration of t h e reagent with age, especially in t h e light. HYDROCHLORIC
ACID S O L U T I O S O F O R T H O - T O L I D I S E
Since t h e addition of small a m o u n t s of highly dissociated acids. such as hydrochloric a n d sulfuric. was found t o give a yellon- color with small a m o u n t s of free chlorine, when using t h e o-tolidine reagent, a n d since this color was neither affected b y t h e degree of alkalinity of t h e water being tested. nor b y changes in t h e concentration of t h e acid. i t led t o t h e preparation of a hydrochloric acid solution of o-tolidine in place of t h e acetic acid solution. T h e strength of this hydrochloric acid solution was one-tenth per cent o-tolidine in a I O per cent solution of hydrochloric acid. This reagent does not deteriorate on standing. I t produces with small quantities of free chlorine a yellow color. T h e yellow color is produced uniformly with small a m o u n t s of free chlorine, regardless of t h e soluble constituents of t h e water being tested. T h e alkalinity of t h e water in no way affects t h e shade or t i n t produced. T h e presence of sulfates. chlorides a n d nitrates of t h e alkalies a n d alkaline earth bases d o n o t interfere with t h e test. T h e yellow color develops in about three minutes a n d is permanent for a t least one-half hour. There is a good gradation of color for increasing a m o u n t s of free chlorine. T h e test is delicate enough t o detect o . o o j p a r t per million of free chlorine. K i t h large amounts of free chlorine, t h e hydrochloric acid solution of o-tolidine changes from yellow t o orange t h e n t o red a n d finally throws down a dark red precipitate. Bromine a n d iodine both produce yellowcolored solutions with this reagent. Large quantities of bromine behave as does chlorine, b u t iodine solutions do not appear t o form precipitates. Solutions of potassium permanganate a n d potassium bichromate produce a yellow color with this reagent, which deepens with increased concentration of t h e above compounds, b u t do not form precipitates. Nitric acid gives a yellow-colored solution with this reagent, which could b e due either t o t h e oxidizing action of t h e nitric acid. or of t h e chlorine formed b y t h e oxidation of t h e hydrochloric acid of t h e o-tolidine solution.
1-01.
j,
SO.I I
METHOD OF A S A L T S I S
T h e method of making t h e colorimetric test consists in adding I cc. of t h e one-tenth per cent o-tolidine solution in I O per cent hydrochloric acid t o I O O cc. of t h e water t o be tested for free chlorine. When t h e free chlorine exceeds 3 p a r t s per million i t is necessary t o use more of t h e reagent. T h e water a n d the reagent are well mixed a n d are allowed t o s t a n d for five minutes. T h e y are t h e n compared with standards of known strength prepared a t t h e same time or with permanent standards as described below. F r o m a solution of chlorine, standardized b y means of a -V/I O O thiosulfate solution, a series of standards are prepared b y dilution with redistilled water. T h e strength of t h e chlorine solution should be determined a t t h e t i m e t h e standards are t o be prepared. T h e l a t t e r must be freshly made a n d immediately compared rTith t h e samples being tested. Water for dilution of s t a n d a r d s should be a s free from organic m a t t e r as redistillation with alkaline potassium permanganate will make i t . Ordinary distilled water contains enough organic m a t t e r t o quickly reduce t h e chlorine a n d t h u s cause i t t o disappear. T o avoid t h e difficulties inherent in preparing standards as above described, permanent standards m a y be made from solutions of copper sulfate a n d potassium bichromate in sulfuric acid solution. For standards between 0.01 p a r t per million a n d I O p a r t s per million t h e proportionate volumes of t h e t w o solutions are given below. Copper sulfate Potassium bichromate P a r t s per million cc. cc. 0.01 ... 0.8 0.02 ... 2.1 0.03 ... 3.2 0.04 ... 4.3 0.05 0.4 5 .5 0.06 0.8 6.6 0.0i 1.2 7.5 0.08 1.5 8.7 0.09 l.i 9.0 0.10 1.8 10.0 SorE-Potassium bichromate solution: 0.025 gram 0.1 cc. concentrated sulfuric acid diluted t o 100 cc. with distilled water. 1 cc. concentrated Copper sulfate solution: 1.5 gram5 CuSOa.SH?O sulfuric acid diluted t o 100 CC. with distilled water.
+
+
Standards higher t h a n 0. I O p a r t per million require a stronger potassium bichromate solution; i. e . , 0.2; gram I cc. concentrated sulfuric acid diluted t o I O O cc. with distilled water.
+
Copper sulfate Potassium bichromate solution solution P a r t s per million 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
cc. 1.8 1.9 1.9 2 0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0
cc.
1. o 2 0 3.0 3 .8 4.5
5,l 5.8 6.3 6.7 7.2 12.0 21 . 0 30.0 39.0 46.0 56.0 63.0 70.0 75.0
1 - 0IT., I 9I3
T H E J O 1 7 R S d L O F I S D L - S T R I A L . 4 S D ESGIAVEERILVG C H E M I S T R Y COLOR
S U G G E S T I O S S AS T O T H E C.AL*SES F O R C O L O R C H - I S G E S
Ortho-tolidine is a n organic compound of t h e formula C14H11,S2.1I t is a homolog of benzidine a n d is a powder melting a t 1 2 9 O C. I t m a y be prepared from o-nitrotoluene b y reduction with zinc dust a n d sodium hydroxide. T h e resulting hydrazo-toluene is converted i n t o t h e o-tolidine b y boiling with hydrochloric acid. I t m a y be purified in a manner similar t o t h a t of benzidine. I t s structural formula m a y be written as a t ( I ) : 1
OF
S e u t r a l alcoholic soI u 1ion Aniline Yellow-green-brown h-H?
917
PRECIPIT.4TE IX Alcohol a n d acetic acid. Brown-purple-red
Alcohol a n d HC1. Yellow-purplr-red
0 o-Toluidine I'ellow-orange-brown
3"'^
Purple-blue-red
Purple-red
SH2
.,
Benzidine Yellow -oran gc-red SH?
0
I t is a p - 2-diamido-nz-2-dimethyldiphenylcomp o u n d , a n d probably produces dyes of t h e same general t y p e a s those derived from benzidine. Oxidation of o-tolidine probably produces a nitroso compound of formulb ( 2 ) : this compound is probably blue in color. Salts of o-tolidine upon oxidation produce a yellow dye. a possible formula for t h e acetic acid salt being ( 3 ) . T h e green color produced b y t h e action of t h e chlorine on t h e acetic acid solution of o-tolidine is probably a mixture of t h e blue compound ( 2 ) a n d t h e yellow compound 13). I n t h e hydrochloric acid solution of o-tolidine. HCl is merely substituted f o r H O O C C H , . T h e slight dissociation of acetic acid a n d t h e hydrolysis of t h e acetate perhaps account f o r t h e slow formation of t h e yellow dye in t h e acetic acid solution, while t h e large dissociation of hydrochloric acid might be t h e reason for t h e rapid development of t h e yellow color in t h e hydrochloric acid solution. T h e red color a n d red precipitate produced b y large a m o u n t s of chlorine m a y be a substitution product of t h e nitroso compound resulting from t h e complete oxidation of all t h e o-tolidine present. Xniline t r e a t e d with a solution of bleaching p o n d e r produces certain color reactions, b u t i t requires a considerable a m o u n t of chlorine for their development. Si mi 1ar 1y or t h o - t ol ui din e for m s c ol or e d solutions with chlorine. \T-hich are likewise slon-ly developed. although someivhat more rapidly t h a n in t h e case of aniline. -4s has been previously noted benzidine readily produces colored solutions n-ith chlorine, similar t o those formed with o-tolidine. I t s sensitiveness t o chlorine is much greater t h a n is t h a t of aniline or o-toluidine b u t somewhat less t h a n t h a t of o-tolidine. T h e colors produced b y a solution of bleaching powder in gradually increasing quantities with neutral a n d m-ith acid alcoholic solutions of aniline, o-toluidine, benzidine a n d o-tolidine are shown in t h e following table: 3rd edition, Vol. 4, page 980
1-ellow-orange-red
Green-orange-red
tellow orange-red
A
0
1 Beilstein,
Green-orange-red
SHz o-Tolidine Y e l l o w - o r a n p r e d
OCH3 SH:
X b!ue color reaction produced b y t h e action of hypochlorites o n methyl-aniline and ethyl-aniline h a s been recently reported b y Leech.' H e suggests t h a t t h e blue dye. possibly a member of t h e "indo" series of dyes. results from t h e oxidation of t h e methyl or ethyl group. It seems t o t h e authors t h a t in t h e case of o-toluidine a n d o-tolidine t h a t t h e dyes are produced as a result of t h e oxidation of t h e amido group, a n d n o t t h e methyl group, since in aniline a n d benzidine. having no methyl groups, similar dyes are formed b y t h e action of hypochlorites. CISCISSAT1 F I L S R A T I O h - P L A N T CINCINNASI, OHIO
THE QUANTITATIVE ESTIMATION OF GLIADIN I N FLOUR AND GLUTEN B y GEO. A. OLSON Received July 26, 1913
Since Einhof? separated alcohol-soluble proteins from wheat, r y e a n d barley, much interesting research work has been done on prolamines. It was n o t . however. until Osborne a n d Voorhees? presented a s t u d y on t h e proteins of t h e wheat kernel t h a t a clear understanding as t o t h e n a t u r e of vegetable proteins was established. Of particular interest was t h e research on gliadin. t h e prolamine of wheat. It has been further belie\-ed t h a t t h e proportion of gliadin t o glutenin determines t h e quality of t h e gluten which in t u r n 1 "A Color Reaction of Hypochlorites with Methyl-Aniline a n d EthJ-1. m . Chrm. Soc., 36, No. 8 (August, 1911). Aniline," b y Paul S . Leech, J O U YA 2 See "The Proteins of t h e Wheat Kernel a n d Vegetable Proteins," by T h o m a s B. Osborne. Also Trans. of the Canadian Instilufe, 7, 1903, b y George G. Nasmith. Amer. Chem. J . , 16, 392 (1893).
