The French have a happy expression for the less perceptible tendency of yellow and blue towards red: they say the colour has "un œil de rouge," which we might perhaps express by a reddish glance (einen röthlichen blick). [1] Steigerung, literally _gradual ascent_. See the note to par. 523. XXXIX. CULMINATION[1] 523. This is the consequence of still progressing augmentation. Red, in which neither yellow nor blue is to be detected, here constitutes the acme. 524. If we wish to select a striking example of a culmination on the _plus_ side, we again find it in the coloured steel, which attains the bright red acme, and can be arrested at this point. 525. Were we here to employ the terminology before proposed, we should say that the first oxydation produces yellow, the hyper-oxydation yellow-red; that here a kind of maximum exists, and that then an ab-oxydation, and lastly a de-oxydation takes place. 526. High degrees of oxydation produce a bright red. Gold in solution, precipitated by a solution of tin, appears bright red: oxyde of arsenic, in combination, with sulphur, produces a ruby colour. 527. How far, however, a kind of sub-oxydation may co-operate in some culminations, is matter for inquiry; for an influence of alkalis on yellow-red also appears to produce the culmination; the colour reaching the acme by being forced towards the _minus_ side. 528. The Dutch prepare a colour known by the name of vermilion, from the best Hungarian cinnabar, which exhibits the brightest yellow-red. This vermilion is still only a cinnabar, which, however, approximates the pure red, and it may be conjectured that alkalis are used to bring it nearer to the culminating point. 529. Vegetable juices, treated in this way, offer very striking examples of the above effects. The colouring-matter of turmeric, annotto, dyer's saffron,[2] and other vegetables, being extracted with spirits of wine, exhibits tints of yellow, yellow-red, and hyacinth-red; these, by the admixture of alkalis, pass to the culminating point, and even beyond it to blue-red. 530. No instance of a culmination on the _minus_ side has come to my knowledge in the mineral and vegetable kingdoms. In the animal kingdom the juice of the murex is remarkable; of its augmentation and culmination on the _minus_ side, we shall hereafter have occasion to speak. [1] _Culmination_, the original word. It might have been rendered _maximum of colour_, but as the author supposes an _ascent_ through yellow and blue to red, his meaning is better expressed by his own term. [2] Curcuma, Bixa Orellana, Carthamus Tinctorius. XL. FLUCTUATION. 531. The mutability of colour is so great, that even those pigments, which may have been considered to be defined and arrested, still admit of slight variations on one side or the other. This mutability is most remarkable near the culminating point, and is effected in a very striking manner by the alternate employment of acids and alkalis. 532.