Researches into dips and dipping. A. Lime-sulphur dips. Paper IV. Further studies on the colorimetric method as a rapid means of control of polysulphide solutions

Abstract

As a continuation of the preliminary study of the colorimetric method as a rapid means of control of polysulphide solutions, the effect of free alkali on sodium polysulphide solutions at room temperature was studied, since in the process of dipping the washing-out of the suint of the fleece results in the interaction of clipwash with alkali and in the formation of alkali polysulphides. It was found that the chemical interaction, as revealed by ordinary chemical analysis, is slight, though the colorimetric study reveals a marked change in chemical nature. This change was ascribed, either to the formation of a complex compound between the alkali and the polysulphide, or to the existence of different isomers of the polysulphides in solution. The observation that field samples of lime-sulphur cannot be directly compared calorimetrically is thus partially explained. It was further shown that the addition of excess sodium carbonate and alcohol causes immediate precipitation of all turbidity-forming materials, rendering a perfectly clear solution of the alkali polysulphides which can be matched against a potassium dichromate standard. In this way fairly accurate values were obtained with both used and unused lime-sulphur clip washes. It is proposed to apply this colorimetric principle for evolving a simple field method of control.