[LLOYD] PRECIPITATION OF DYES 25 



day changes could be noticed in at least some of the cases, in those, 

 namely, which were most pronounced in their action, e.g. ruthenium 

 red, neutral red, etc. 



Within a very short time it was noticed that some dyes were being 

 rapidly adsorbed, and at the end of twenty-four hours it was clear that 

 fuchsin, erythrosin, corallin, orange G, and methyl orange were not 

 adsorbed, while ruthenium red, neutral red, vesuvin, gentian violet, 

 methylene blue and safranin were, on the contrary, adsorbed, but not 

 with equal vigour. The order in which they are named may be taken 

 as a rough index of their relative vigour; methyl green and methyl blue, 

 of doubtful effect, may be tentatively added. On the seventh day 

 the differences in the viscidity of the mucilage were pronounced, 

 differences which in some instances (ruthenium red, neutral red, 

 vesuvin) could be readily detected much earlier. On the tenth day 

 it was found that the viscidity remained unaltered in orange G, 

 methyl orange, fuchsin, corallin. To these were added, but not with- 

 out doubt at the time, viz. methyl blue, erythrosin, and methyl green. 

 This doubt I removed later as far as erythrosin is concerned. The 

 viscidity was materially lowered or lost entirely in ruthenium red, 

 neutral red, vesuvin, methylene blue, gentian violet, and safranin, the 

 earlier named being the most vigorous. In the preparations in which 

 the first two, at least, occurred, a distinct precipitation of the mucilage 

 on its outer border could be noticed early, and this was so extensive in 

 the case of neutral red that it was clear that the adsorption of the dye 

 accounted for its disappearance from the surrounding fluid. As the 

 precipitation advanced, the outer zones of the adsorption complex 

 disappeared as a suspension. Aside from other details of this kind, 

 which need not be presented, it became evident that those dyes which 

 are adsorbed by the mucilage of Opuntia lower its viscidity with a 

 rapidity directly related to the vigour with which they are adsorbed. 

 Those dyes which are not adsorbed do not alter the viscidity. A 

 considerable number of experiments, done before and after the one 

 above recounted, served to verify the conclusion arrived at. Because 

 of the very minute amounts of ruthenium red at my disposal, my 

 observation of its behaviour was confined to small amount of solution 

 of low concentration, but it was clear that this dye is extremely 

 vigorous, forming flocks and precipitation membranes very quickly. 

 The mucilage of the mallows behaves quite as that of Opuntia, and, it 

 may be added, has an exactly similar cytological origin. That of 

 tragacanth, also, judging from a small series of observations.^ 



■> Lloyd, 1919, I.e. 



