The Practical Use of the Ortho‐tolidine‐Arsenite Test for Residual Chlorine

Abstract

FIELD laboratory tests that can be performed quickly and with a minimum of equipment are essential for the control of the water supply treatment required to maintain safe sanitary quality under emergency as well as ordinary conditions.

Development of Instrumentation in Chlorination

“…There has been steady progress in the application of instrumentation to chlorination. This has been required by and resulted from: [1] the demand for automatic and remote control, [2] the need to record chlorination rate and residual level, [3] the use of chlorine in water treatment for purposes other than disinfection, [4] the recognition of different types of chlorine residuals, [5] the employment of free residual chlorination and chlorineammonia treatment, and [6] the need of controls to effect efficient operation.…”

“…Introduction of the free residual chlorination process wherein free available and combined available chlorine residuals may be present at the same time led to much research work directed toward differentiating between such residuals. Several colorimetric methods were evolved, the most practical of which used sodium arsenite in a modification of the orthotolidine test (6) . This modification produced the ortholidine-arsenite (OTA) test which appeared in the 9th and 10th editions of Standard Methods.…”

Water Analysis

“…cause no serious difficulties. The o-tolidine-arsenite (48,49,58,61) test is considered a quantitative method for differentiation of active chlorine from chloramine, and interference from manganese, nitrite, and iron seems to be eliminated.…”

Contemporary Chlorination Practices

“…combined available chlorine and interfering substances in water. Gilcreas and Hallinan (7) have studied the practical use of this test and report it fully applicable to plant and field conditions. The simple procedure of the orthotolidine-arsenite (OTA) test provides the best method at present available for the control of chlorination.…”