August 



1 90 1 



NA rURE 



413 



the weather side. Thus the increase of amplitude is a steady 

 process, whereas the increase of the wave-length (if determined 

 by measurement along one or two sections of a few ridges) takes 

 \)\?LCt per salttim, or, as Dalton might have said, in "multiple 

 proportion." 



It is pointed out that the tidal sand ridges, by their size, 

 orientation, and lateral extension, afford an admirable means of 

 mapping the tidal currents in those estuaries in which circum- 

 stances secure their preservation on the sand-banks visible above 

 low-water mark. 



Between the date of the writing and the publication of this 

 paper the author observed in Canada the formation of long 

 trains of waves of snow, by a process similar to that which 

 creates these sand waves. They are 



distinct altogether from the ripples <. 



of drifted granular snow, which were Ridge 

 also observed. 



the water ; after a few hours the infusion will be found of a pale 

 yellow colour, having, when cold, a green fluorescence. If an 

 alkali be added to this infusion and air blown through it, indigo 

 blue is precipitated on the further addition of an acid. Woollen 

 articles dipped into this alkalised infusion become, on exposure 

 to the atmosphere, a pale azure blue. This change, however, 

 takes place far more rapidly if they be dipped into acidulated 

 water. The indigo thus obtained is, however, very apt to 

 contain impurities ; notably, to pass into a condition known as 

 indigo-brown, in which an insoluble black-brown substance is 

 formed which is useless to the dyer and cannot be reconverted 

 into indigo blue. During the unsettled state of Europe towards 

 the end of the eighteenth and beginning of the nineteenth 



60 FEET 



IVOAD AS A BLUE DYE} 



\l\ R. E. CORDER - has so tho- 

 "^ roughly gone into the matter of 

 East Anglian woad culture and pre- 

 paration that the present remarks 

 must be regarded as quite supple- 

 mental to his paper, having been, in 

 fact, inspired by it. Frequent visits 

 have been made to the Parson Drove 

 Woad Mill, and a long series of ex- 

 periments conducted before the blue 

 colour, the indigo in fact, in this 

 woad could be demonstrated. Curi- 

 ously enough, the subject has engaged 

 the attention of Prof. Beyerinck, of 

 Delft, and by his help the presence of 

 indigo was easily shown in the fresh 

 plant from Parson Drove. The blue 

 colour of woad is indigo — the same 

 substance chemically as that obtained 

 from Indigo/era tinctoria and Poly- 

 gonum tinctoria. There is this great 

 difference however : in the last named 

 plants it exists in a form which is 

 easily extractable, whereas in woad 

 it exists in a condition which is the 

 very reverse. 



In 1855, Dr. E. Schunck, in an 

 exhaustive paper on the chemistry of 

 woad, drew attention to the fact that 

 indigo did not exist as ready formed 

 indigo-white in this plant. He showed 

 that the glucoside indican was the form 

 from which indigo-white was produced 

 by oxidation. In 1877, M. Alvarez 

 attributed the formation of indigo to 

 the action of bacteria, but in iSgS 

 Breaudat demonstrated that microbic 

 life was not necessary. 



Marchlewski and Radcliffe consider 

 indican consists of sugar and a very 

 unstable substance called indoxyl. 

 Prof. M. W. Beyerinck holds the 

 view that the indigo producing plants 



may be divided into two groups, in one of which this substance 

 exists as indican {Indigofera tinctoria and Polygonum tinctoria), 

 while in the other (of which woad, Isatis tinctoria, is the type) 

 it exists as indoxyl. More recently, however, Beyerinck has 

 come to the conclusion that even indoxyl does not e.xist ready 

 formed in woad, but that it exists as a " loose compound " isatan, 

 which by an enzyme isatase also present in woad is easily 

 decomposed into indoxyl. 



Be this as it may, it is not difficult to extract indigo blue from 

 fresh woad leaves by the process given by Beyerinck. This 

 consists in packing fresh woad leaves into a stoppered bottle 

 and filling the bottle entirely with boiling water, inserting the 

 stopper so that no air-bubble is left between it and the top of 



B. Plowright: 



1 Abridged from a paper by Di 

 of tbe Norfolk and Norwich Naturalists' t 

 = Corder, E. Tr.tns. Norfolk and Norwi 



NO. 1660, VOL. 64] 



ety, vol. . 



the Transactions 

 . TQoo-jgoi. 

 8go, vol. v. p. 144. 



succeeding days, Dovey Estuary. 



century, numerous attempts were made to manufacture indigo 

 directly from woad ; prizes were offered by various Governments 

 for the attainment of this object in order that the use of foreign 

 indigo might be obviated, as it could only be obtained with 

 difficulty. None of these processes were ever practically success- 

 ful. Many of them were entirely theoretical. Some sought to 

 obtain indigo by m.acerating fresh woad leaves in cold water, 

 others in warm water, others by infusing them in boiling water and 

 subsequently washing with cold. 



To demonstrate the presence of indigo in the woad leaf, the 

 process of Dr. Hans Molisch is the best. This consists in keep- 

 ing the fresh leaves in a wide-mouth stoppered bottle, filled 

 with gaseous ammonia for twenty-four hours, and then dissolving 

 out the chlorophyll by immersing the leaves for a like period in 

 absolute alcohol. Sections show that the indigo is confined to 

 those tissues which contain chlorophyll, and that the hairs, 



