Sensitive Indicator for Volumetric Determination of Boiler Feedwater Alkalinity

Abstract

N A lime-soda process for the treatment of raw water for I boiler consumption, accurate laboratory tests on the effluent water provide the fundamental bases for efficient softener control. Volumetric determinations of treated water alkalinities form a most important phase of such laboratory tests, and the chemist should have available accurate and positive color indicators in order to make the analyses with the highest degree of precision.An ideal indicator would show a sharp point of color transition coincident with the equilibrium point for the completion of the neutralization reaction. This point was computed for boiler feedwaters a t about 4.89 by interpolating the data reported by Cooper (8) to a millimolarity of 0.333, the average sodium carbonate content of such waters.The use of methyl orange for alkalinity titrations of water has received almost universal application and has been adopted as standard (I). This indicator, however, possesses a color change rather difficult to detect and, more important, has been shown by Cooper (8) to have a p H color response in disagreement with the equivalence point for complete neutralization.The reduction of such indicator uncertainty has been reported by various investigators through the application of mixtures of indicators and of indicators and dyes, and these mixtures are dwcribed in the literature (6). I n the htter type of mixture, the dye is added to supplement the color of the indicator and produce a color other than that of the indicator itself. For example, an inert dye, xylene cyanole FF, has been proposed by Hickman and Linstead (3) to augment methyl orange, giving a green color with the alkaline yellow of the indicator and a magenta red color with the acid orange. The application of this mixture to feedwater titrations is subject to criticism in that the pH of the color transition is 3.8, according to Willard and Furman (71, making the indicator less suitable than methyl orange itself.Johnson and Green (4) have investigated the use of an alcoholic solution of methyl red and alphazurine (6) for alkalinity determinations, and this mixture was applied as an indicator in titrating treated water alkalinities at the laboratory of the Federal Central Heating Plant, Washington, D. C. A modification in the ratio of dye to indicator was made to improve the color transitions. The mixture showed great promise, but after standing several weeks the methyl red separated from solution and the color response of the indicator became less pronounced. These difficulties were eliminated by substituting the sodium salt of methyl red (dimethylaminobenzene sodium carbonate) in place of the methyl red and water in place of the alcohol, The aqueous solution was found to be stable and its u8e avoided the necessity of using alcohol. The indicator was prepared by dissolving 0.45 gram of methyl red sodium salt and 0.55 gram of alphazurine in 1 liter of distilled water. The pH value of the solution was observed to be approximately 7.3.The indicator was checked for accuracy by titrating ...

Comparative strengths of four organic bases in benzene

“…With an unhindered amine a high yield of the desired product can be obtained, but with triethylamine and other hindered amines the yields are greatly reduced, in consonance with the experience of Brown and hi coworkers in their studies of addition reactions. 19 Brown has stated [32] that the ability of hinder ed amines such as triethylamine "to r eact with aqueous acids is not noticeably affected because of the low steric requirements of t h e proton. " It should be borne in mind, however, that in water, as in other m edia, the proton do es not have an independent existence.…”

“…In the titrations, samples weighing approxima tely 0.5 to 0.7 g wer e dissol ved in redis tilled 95-percen t ethanol and titrated with approximately O.I -N s tandard aqueous h ydrochloric a cid, with an aqueou s mixture of m ethyl r ed sodium salt and alphazurine [19] as indicator.…”

Volumetric Determination of Phosphorus

“…Phenolphthalein very closely approached the monosodium to disodium phosphate end point. The mixed indicator methyl purple (4) corresponded to the disodium to monosodium phosphate end point. Also, these two indicators were mutually compatible.…”

Water Analysis

“…The dyes of the stilbene group are advantageous for use in industrial work because they register a color change in the pH region between 4.0 and 5.0. In a later paper Taras (138) describes two otjier indicators of the stilbene group which register a color change immediately above pH 4.6. For the preparation of a more stable methyl red indicator solution, Fleisher (44) suggests that instead of dissolving in alcohol, alphazurine be mixed with methyl red sodium salt and dissolved in distilled water.…”