Feb. 24, 1 881] 



NA TURE 



391 



necessary to prepare pure orthonitrophenylpropiolic acid ; 

 if orthonitrocinnamic acid (No. 2 above) be treated with 

 bromine, then with alcoholic potash, and lastly with 

 grape-sugar, without separating the various products 

 indigo-blue is produced. C)rthonitrocinnamic acid may 

 be prepared, without difficulty, froQi oil of bitter almonds. 



Artificial indigo may be directly printed on cloth by 

 mixing orthonitrophenylpropiolic acid — or orthonitro- 

 phcnyloxyaoylic acid described below — with soda and 

 grape- or milk-sugar, and after proper thickening, soak- 

 ing the cloth in the mixture, and heating : or the material 

 may be simply soaked in orthonitrophenyloxyacrylic acid 

 and heated. 



OrtlwnitropSicnyloxyacrylic acid is prepared by the 

 action of alcoholic potash on an alcoholic solution of 

 orthonitrophenylchlorolactic acid (itself prepared by the 

 action of chlorine on orthonitrocinnamic acid), in accord- 

 ance with the equation — 



C H ^^^■'■ 



^""-'XCHjOCl. COoH +2K0H = 



C H '^^"^•^ 



^'^"^CjHsO . COjK + KCl + H.p. 



By boiling an aqueous solution of orthonitrocinnamic 

 acid dibromide (No. 3 above) with sodium carbonate, 

 indigo blue separates out. M. M. P. M. 



MICROSCOPIC STRUCTURE OF MALLEABLE 

 METALS 



'X'HE following observations on the minute structure of 

 •'■ metals, which have been hammered into thin leaves, 

 are instructive. Notwithstanding the great opacity of 

 metals, it is quite possible to procure, by chemical means, 

 metaUic leaves sufficiently thin to examine beneath the 

 microscope by transmitted light. Silver leaf, for instance, 

 when mounted upon a glass slip and immersed for a 

 short time in a solution of potassium cyanide, perchloride 

 of iron, or iron-alum, becomes reduced in thickness to any 

 required extent. The structure of silver leaf may also be 

 conveniently examined by converting it into a transparent 

 salt by the action upon it of chlorine, iodine, or bromine. 

 Similar suitable means may also be found for rendering 

 more or less transparent most of the other metals which 

 can be obtained in leaf. 



An examination of such metallic sections will show two 

 principal types of structure, one being essentially granular, 

 and the other fibrous. 



The granular metals, of which tin may be taken as an 

 example, present the appearance of exceedingly minute 

 grains, each one being perfectly isolated from its neigh- 

 bours by still smaller interspaces. The cohesion of such 

 leaves is very small. 



The fibrous metals, on the other hand, such as silver 

 and gold, have a very marked structure. Silver, especially, 

 has the appearance of a mass of fine, elongated fibres, 

 which are matted and interlaced in a manner which very 

 much resembles hair. In gold this fibrous structure, 

 although present, is far less marked. The influence of 

 extreme pressure upon gold and silver seems to be, there- 

 fore, to develop a definite internal_structure. Gold and 

 silver in fact appear to behave in some respects hke 

 plastic bodies. When forced to spread out in the direc- 

 tion of least resistance their molecules do not move uni- 

 forml)', but neighbouring molecules, having different 

 velocities, glide over one another, causing a pronounced 

 arrangement of particles in straight lines. 



This development of a fibrous structure, by means of 

 pressure, in a homogeneous substance like silver, is an 

 interesting lesson in experimental geology, which may 

 serve to illustrate the probable origin of the fibrous 

 structure of the comparatively homogeneous limestones 

 of the Pyrenees, Scotland, and the Tyrol. 



J. Vincent Elsden 



ISLAND LIFE-' 

 II. 



IN the second half of his volume Mr. Wallace proceeds 

 to apply to the elucidation of the history of the 

 characteristic assemblages of plants and animals in 

 islands, the principles laid down with so much explicitness 

 in the first half. He points out that for the purposes of 

 the naturalist a fundamental difference exists between 

 islands that have once formed part of continents and 

 those which have not. Continental islands are those 

 which, by geological revolutions at more or less remote 

 periods, have been severed from the continental masses 

 in their neighbourhood. They are recognisably portions 

 of the continental ridges of the earth's surface. This 

 relation is usually made strikingly apparent by the chart 

 of soundings between them and the nearest mainland 

 (Fig. 2). Further, in geological structure they resemble 

 parts of the continents, like which they contain both 

 old and new formations, with or without volcanic ac- 

 cumulations. In some cases the evidence of recent 

 severance from the adjacent continent is abundant. 

 In others it is less distinct ; for example, where the 

 islands are separated from the nearest land by a depres- 

 sion of a thousand fathoms or more, and where their 

 fauna, though abundant, is of a fragmentary nature, almost 

 all the species being distinct, many of them forming dis- 

 tinct and peculiar genera or families, while many of the 

 characteristic continental orders or families are entirely 

 absent, and in their place come animals to which the 

 nearest allies are to be found only in remote parts of the 

 world. Oceanic islands, on the other hand, exhibit no 

 geological connection with any continental area, but owe 

 their birth either to upheaval of the ocean floor or to the 

 piling up of lavas and tuffs round submarine vents ot 

 eruption. Their geological structure is of the simplest 

 kind. As Mr. Darwin long ago showed, they consist of 

 volcanic rocks or of coral reefs, or of volcanic and coral- 

 line formations combined. Ancient formations, so cha- 

 racteristic of continental islands, are wholly wanting. 

 These islands lie far removed from a continent, and rise 

 from water of profound depth. Their fauna is in curious 

 keeping with this isolation, for it contains no indigenous 

 land-mammals or amphibians, but abounds in birds 

 and insects, and usually possesses some reptiles. These 

 animals or their ancestors must have reached the islands 

 by crossing the ocean. 



Mr. Wallace first attacks the problems presented by 

 the Oceanic Islands (Fig. i). He describes the characters 

 of the flora and fauna of the Azores, Bermuda, the 

 Galapagos, St. Helena, and the Sandwich Islands, and 

 endeavours in each case to show how the resemblances 

 and differences between them and the plants and animals 

 of the continents may be accounted for. The contrast 

 offered by two groups of islands on either side of the 

 American continent— the Bermudas and Galapagos — 

 brings vividly before the mind the nature of the diffi- 

 culties with which the author grapples, and the methods 

 by which he seeks to solve them. In the case of the 

 Bermuda group a series of coral islets having a total area 

 of no more than fifty square miles rises from the very 

 deepest depression in the Atlantic basin in 32° N. lat. at 

 a distance of 700 miles from North Carolina. The chief 

 elements in the fauna of these islands are birds and land- 

 shells. Upwards of 180 species of birds have been 

 observed, more than half of which belong to wading and 

 swimming orders, while eighty-five are land-birds, of which 

 twenty species are frequent visitors. Only ten species 

 live as permanent residents on the island, and these are all 

 common North American birds. No bird, and indeed no 

 vertebrate animal, save a species of lizard, is peculiar to 

 Bermuda. The feathered population of the islands is de- 



' " Island Life : or. the Phenomen.i and Causes of Iniular Faunas and 

 Floras.- &c. Ey Alfred Russel Wallace. (London: Macmillan and Co., 

 18S0.) Continued from p. 359 



