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V O L U M E 19, N O . 5, M A Y 1 9 4 7 Importance of a Specific Acid Medium. Of the common laboratory acids dilute hydrochloric acid alone supports a spontaneous reaction between chlorine and methyl orange. Sulfuric, nitric, and acetic acids proved unsatisfactory by virtue of a delayed response. Several minutes elapsed before the reaction was completed in their presence. Temperature. The reaction between methyl orange a n d chlorine is independent of sample temperature. Samples verging on 0' C. can be determined with the same facility as those a t normal room temperature. Interference. In the normal course of events manganic mangancw m a y be regarded as the sole interfering ion in the methyl orange rctacst ion. -1 survey of colloidal manganese dioxide revealed that eonccntrations of manganic ion of the order 0.10 p.p.ni. giye false reedings of 0.10 p.p.m. in terms of chlorine. JVhen the manganic concentration is lowered to 0.05 p.p.ni. interference is eliminated. The methyl orange reagent, therefore, is coequally sensitiw t o manganic ion and elementary chlorine. Kitrites impart an orange tint to the methyl orange reagent. T h e orange color is out of harmony Ll-ith the standards. However, nitrite is incompatible with free chlorine owing to the ordinary oxidative process. Accordingly, interference from this source is improbable. Fcrric. iron, as ferric chloride, can be tolerated in substantial quantities. Interference in the form of a n orange color occurs only after the reaction is allowed to proceed for several minutes. The chlorine dioxide employed in water treatment ( 1 ) contains a 1 0 0 7 excess of free chlorine to ensure the complete convci,sion of sodium chlorite. The colorimetric anal3 containing 1.5 p,p.ni. of chlorine dioxide disclosed the presence of thc excess chlorine.
Reaction with Chloramines. The chloramine evperiments were performed on synthetic solutions prepared in the normal manner from ammonium sulfate and ammonium chloride. Judging from the results, chloramine strengths conventionally encountered in water works practice offer no trouble. Concentrations as high as 1.25 p,p,m. of chloramine, formed by dosing 0.1 p.p.m. of ammonia, are handled with ease. Color reduction at this abnormal concentration approximates 0.10 p.p.m. when the reaction time is prolonged for 7 minutes and 0.25 p.p.m. a t the end of 30 minutes. Seedless to say, loiyer chloramine concentrations exert a corresponding minor effect. DISCUSSION
number of'advantages accrue to the use of methyl orange, outstanding among which is the preparation of the permanent standards from the reagent itself. 11ethyl orange is one of the few indicators found on every reagent shelf. Thus, the same stock solution can function in the dual role of neutralization indicator and chlorine rcxagent. The stability of the stock solution is: unimpaired by long standing. Furthermore, the reagent can serve equally in laboratories where the chlorine determination is a routine or an occasional necessity. Finally, the reaction is instantaneous and capable of a high degree of ipecificity, particularly in differentiating between elementary chlorine and chloramine. LITER4TURE CITED
(1) Synan, J . F., MscMahon, J. D., and T'incent, G . P., J . Am. TTater TT'orks dssoc., 37, 889-73 (1945). ( 2 ) Taras, &I., I h i d . , 38, 114G-50 (1940).
Electronically Controlled Apparatus for Distillation of Fluorine as Hydrofluosilicic Acid 1IOB.iRT H. FILLARU, T.IFT Y. TORIBARA, AND LEWIS University of M i c h i g a n , A n n A r b o r , .Mich.
N. HOLLiND
. i n electronically controlled apparatus is described for steani-distilling fluorine as hydroflnosilicic acid at a fairly constant temperature in the determination of fluorine or in the decomposition of insoluble silicates.
T
HE distillation of fluoride as hydrofluosilicic acid, proposed
by Willard and Winter ( 2 ) , serves to separate fluorine from interfering ions in a wide variety of materials. This quantitative method for the removal of fluorine also conveniently removes the remaining fluoride in the decomposition of a silicate ( 1 ) for the 'determination of potasium by the perchlorate method. The method demands the attention of the operator t o maintain the tlir. 4. C'ompactness, as the \rriclgi~rircuit and povier supply are all contained in a single unit. 5. Siniple construction of all parts a t a low cost. LITEII A T U R E CITED
(1) TVillard, H. H., LiFgett, L. SI..and Diehl. H., IXD. Ex(;. CHEX, .Is\L.ED.,14, 284 (1942). ( 2 ) K l l a v d , H. H., and Winter, 0 . R . , Zhid., 5, 7 (1933).
