The effect of the two arsenical dips, viz.: Cooper's powder dip and sodium arsenite, on the fleece has been studied from several angles. The process of dipping, results in the leaching out of suint constituents, thereby influencing the hygroscopicity of the raw wool, especially at 100 per cent. humidity. The use of arsenicals as dips results in the contamination of the fleece with arsenic, some of this arsenic remaining in the fibres even after scouring. When using the correct concentrations, the dips themselves do not cause any noticeable damage to the fibre, except that Cooper's dip tends to stain the fleece yellow by depositing its insoluble constituents. Should, however, the alkalinity of the dips rise above pH 10•3, the soundness of the fibres may be seriously affected. Under normal conditions, however, the undesirable effect of dipping on the fibre soundness must be ascribed to the process of clipping as such, and not to the use of the chemicals here studied. In-vitro studies have shown that this dipping effect in turn is merely a secondary cause of damage, the initiative and primary cause of fibre damage being the effect of the ultra-violet radiations of ordinary sunlight. In this respect arsenates and arsenites would appear to protect the fibre, rather than causing further damage, since pure water is appreciably more deleterious to such radiated wools than arsenite solutions. Cooper's dip renders additional protection to the fibre, the yellow film staining the fibres impeding the penetration of the ultra-violet rays to the fibre itself. The theoretical implications of these observations have been discussed and explained. The natural grease and suint on the fibres were not found to afford sufficient protection against the effects of sunlight. In how far these observations affect the fleece on the sheep's back must still be further investigated. It may be expected, however, that repeated dipping would aggravate this photo-chemical effect, since the staple-formation is thereby destroyed, thus exposing a greater portion of the fleece to direct radiation.
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