io6 



NATURE 



[November 30, 1899 



anemone, larkspur, violet, willowherb, scarlet tropaeolum, red 

 rhododendron, bilberry, flowering currant, scabious, wild 

 thyme, potato, forget-me-not. 



The colouring matter was then withdrawn from these and 

 other petals by macerating them for two days in cold methyl 

 alcohol, the solution was poured off, evaporated to dryness, the 

 residue taken up with warm water, and the solution after filter- 

 ing tested as follows :— (i) One drop HCl or H^PO*, followed 

 by several drops of ammonia ; (2) solution of acetate of |lead 

 followed, or not, by acetic acid ; (3) solution of acetate of 

 magnesium. The results are tabulated as follows : — 



In a few cases the aqueous solution of the pigment, after 

 acidification by HCl, was shaken up with amyl alcohol, and 

 after allowing to separate, the lower acid liquid was withdrawn, 

 and tested with excess of ammonia and of acetate of lead. In 

 this way, rhododendron, red daisy, red tulip, violet, foxglove, 

 Victa cracca, red poppy, gave a brilliant pure blue coloration ; 

 while, on the other hand, flowering currant and woundwort 

 ^ave greens with ammonia, but blue precipitates with acetate of 

 lead. In order, however, to purify the pigment still more 

 thoroughly, its alcoholic or aqueous solution was shaken up at 

 intervals for two days with well-washed hide-powder, and the 

 latter, after filtering off the liquid, was well washed and ex- 

 tracted with very dilute HCl. The bright red liquid thus ob- 

 tained was treated successively with the aforementioned reagents. 

 The result was extremely interesting ; for while flowering 

 currant and rhododendron gave greens, red tulip and purple 

 orchis gave blues. In some cases the Wiesner's experiment was 

 repeated, i.e. the fresh petals were warmed with dilute HCl, 

 and the acid quite washed out with water, and the now red- 

 dened organs placed into solutions of acetate of lead and acetate 

 of zinc, when rhododendron, flowering currant, violet (in some 

 cells), foxglove, Vicia cracca (in some cells), became green ; 

 while, on the contrarj', Geraniuui pratense, bugle, the rest of 

 the cells of violet, and of Vicia cracca became blue. It was 

 evident, therefore, that Wiesner's opinion that anthocyan is 

 invariably blued by alkalis, &c., and never greened, was not 

 confirmed ; inasmuch as at least three petals, when treated in 



the manner he prescribed, were distinctly greened, the pre- 

 sumption being that all yellow intermixture had been obviated. 

 The general conclusion which I think must needs be drawn 

 from these my experiments is, that there are different stages in 

 the development of the floral pigment. In the lower stages 

 the natural colour is red, whatever the chromogen may be ; and 

 so far Berzelius was right. In the higher stages, on the other 

 hand, the natural colour of anthocyan is blue, or rather (at least 

 with some chromogens) it becomes capable of forming blue 

 compounds or lakes with alkalis and certain metallic salts. 

 Moreover, as I have laboured to show elsewhere, chromogens 

 exist which, except under very exceptional conditions and 

 circumstances, are incapable of producing a blue pigment ; and 

 these in all stages naturally develop into a red, the brilliancy 

 of which, when contrasted with that of a blue accidentally 

 obtained in an allied species {e.g. in flax), unequivocally attests 

 its real, original, and proper character. P. Q. Keegan. 



NO. 1570, VOL. 61] 



The Colour of Flints. 



An examination of the pebbles lying on the beach of the coast 

 of the English Channel shows that while these are principally 

 flints they vary considerably in colour. 



The flints derived from the chalk cliffs surrounding this part 

 or the coast, and from which the shingle is generally supposed 

 to be derived, are, so far as my experience goes, invariably 

 black, with a white coating on the exterior. 



Only about one-third of the flints on the beaches of such 

 localities as Eastbourne, Hastings, Brighton, Hythe, Folkestone, 

 Dover, &c., or in 'the large accumulations at Dungeness and at 

 the Chesil Beach are apparently derived from the adjacent chalk 

 cliffs, the remainder being different shades of brown, grey, 

 white and red, the former being the most prevalent. In some 

 cases the outside coating is of a different colour to the interior 

 of the pebble. It follows, then, either that the flints from the 

 chalk undergo some chemical action, either internally or exter- 

 nally, while exposed to the air and salt water of the beach, which 

 changes their colour, or the majority of them must have been 

 derived from inland gravels. 



The first theory does not seem feasible, as flints are to be 

 found in raised, beaches and other positions, where they 

 have been deposited for long periods, still retaining not only 

 their interior black colour, but also the white coaling on the 

 outside. 



If these various coloured beach flints are derived from inland 

 gravel beds, they must have been deposited under different con- 

 ditions from those which now prevail, as there is no action in 

 operation on the south coast which can convey the flints from 

 inland to the .sea. The age of some of these shingle beds must, 

 therefore, be much greater than has been generally supposed. 



There are isolated pockets of gravel at the top of the chalk 

 cliffs in some places, which fall on to the beach where the cliffs 

 are eroded by the sea ; but these are too few in number to ac- 

 count for immen.se deposits such as those at Dungeness, Pevensey 

 and Chesil. 



Failing to obtain any light on this subject from geologists to 

 whom I have mentioned the matter, and whose opinions vary 

 as to the changes flints undergo, I venture to appeal to Nature 

 for a solution. W. H. Wheeler. 



Boston, Lines., November 27. 



THE PROPOSED CHANGES IN THE 

 MATHEMATICAL TRIPOS. 



THE Cambridge Board for Mathematics has presented 

 to the Senate a report on the Mathematical Tripos. 

 This report recommends certain changes in the regula- 

 tions relating to that Tripos. The following note 

 contains an abstract of the proposals made by the 

 Board : — 



The schedule of subjects for Part I. of the Tripos has 

 been reduced by the entire omission of some subjects 

 (calculus of variations, elliptic functions, Bessel's func- 

 tions, hydrodynamics, sound). Other subjects have been 

 limited m extent {e.g. rigid dynamics, electricity, optics, 

 astronomy and others). Care has been taken to specifi- 

 cally exclude parts of some subjects. The arrangement 

 of papers is to be entirely changed and no papers are to be 



