July, 1913. 



KNOWLEDGE. 



267 



EFFECT OF TARRED ROADS UPON VEGETATION 

 — -Various criticisms have been brought against the use of tar 

 upon roads on the grounds of their effect upon vegetation and 

 animal life, and a general outline of these is given in the 

 current issue of The Journal of Industrial and Engineering 

 Chemistry (1913, V, 428). In 1910 it was shown by MM. True 

 and Fleig (Comptes Rendus, 1910, CLI, 593) that although 

 bituminous vapours had but little influence upon the eyes 

 the dust from old roads produced, through its mechanical 

 action, inflammation and other troubles. 



The following year M. Mirande (Comptes Rendus, 1911, 

 CLI I, 204) tested the effect of various coal tar products, such 

 as creosote and the like, and came to the conclusion that these 

 all had a destructive influence upon plant life, blackening the 

 leaves and causing death. Mainly on the results of this investi- 

 gation has grown up the belief that the tarring of roads is 

 injurious to the neighbouring vegetation ; but quite recently 

 this has been refuted by other investigators. For example, it 

 has been pointed out by French engineers that tar has been 

 used in Bordeaux for many years without any injurious effects 

 upon the trees. In another town, however, tar was apparently 

 responsible for the destruction of the trees in a large square ; 

 but here its action was purely mechanical, for it had been 

 spread so closely to the trunks that it prevented water from 

 reaching the roots. 



The conclusions of M. Mirande have also been called in 

 question in Germany, and the results of experiments made by 

 Dr. H. F. Fischer to determine the point are to be brought 

 before the International Road Congress which will have met 

 (June) in London prior to the appearance of this note. 



STUDIES ON THE ELEMENT ZIRCONIUM.— 

 Pure zirconium cannot be prepared by reduction with 

 aluminium or magnesium, but a product containing about 

 ninety-eight per cent, of the metal has been obtained by Herr 

 Wedekind (Annalen, 1913, CCCXCV, 149) by the following 

 method. Pure zirconium oxide was mixed with finely divided 

 metallic calcium, and the mixture placed in an iron tube, from 

 which the air was subsequently removed with an air-pump. 

 The reaction between the calcium and zirconium oxide was 

 started by heating the bottom of the tube, after which the 

 exterior of the tube was cooled by means of a current of air, 

 and finally by placing it in cold water. 



After cooling, the contents of the tube were rapidly powdered, 

 and treated first with water, then with acetic acid, and finally 

 with dilute hydrochloric acid, care being taken to exclude air 

 throughout the whole process. This treatment was continued 

 until the whole of the calcium had been removed, the water 

 being then expelled, and the powder dried first in a vacuum and 

 finally at a high temperature in a porcelain tube from which 

 the air had previously been extracted. The final product, 

 which contained a small quantity of iron, had a specific 

 gravity of 6-44 in the melted state. It melted at 1530°C, 

 and at higher temperatures oxidised readily. The solidified 

 metal when filed and polished had a fine surface, which did 

 not tarnish on exposure. 



A new compound, zirconium nitride (Zr 3 N 2 ) was prepared 

 by heating the metal in an atmosphere of nitrogen, and 

 this could be decomposed by hydrogen at a high temperature 

 with the formation of the theoretical amount of ammonia. 



IMITATION PEARLS FROM GELATIN.— An ingenious 

 adaptation of the process of diffusion of salts through a gelatin 

 film is described by Dr. R. Liesegang (Zeit. Chetn. hid. 

 Kolloide, 1913, XII, 181). It is based upon the fact that when 

 certain saline solutions diffuse into gelatin the film becomes 

 iridescent. The best results are obtained with dilute solutions 

 of alkali phosphates and pure gelatin in the form of a ten 

 per cent, solution. Beads intended to serve as the foundation 

 for the imitation pearls are dipped into the warm gelatin 

 solution and placed on a glass plate which has previously been 

 coated with gelatin. Round each bead is then painted a ring 

 of the ten per cent, phosphate solution, or in place of this a 

 mixture of the phosphate and gelatin may be used for coating 

 the glass plate. 



Gradually there is a diffusion of the phosphate into the 



gelatin, and the desired iridescent effect is obtained. Special 

 precautions are taken to prevent the beads drying too rapidly, 

 and finally the gelatin may be hardened and rendered in- 

 soluble by exposure to the vapours of formaldehyde. 



OCCURRENCE OF FORMALDEHYDE IN PLANTS. 

 — A method of detecting formaldehyde in plant juices has 

 been discovered by MM. Angelico and Catalano (Gazz.Chim. 

 Hal., 1913, XLIII, 38). It is based upon the fact that the 

 plant Atractylis gummifera contains an active glucosidal 

 principle (atractiline) which gives a specific reaction with 

 formaldehyde, and will detect a mere trace of that compound. 

 When the juice of the plant is brought into contact with 

 atractiline and sulphuric acid, a violet coloration is imme- 

 diately produced when formaldehyde is present. 



By means of this test the aldehyde has been detected in 

 the juices of eleven plants, including lupins, maize, and so on ; 

 and its formation is apparently connected with the chlorophyll 

 function. This is indicated by the fact that when the same 

 plants were kept for twenty-four hours in the dark no formal- 

 dehyde could be found. The juices and distillates from 

 several species of fungi contained no trace of formaldehyde. 



GEOGRAPHY. 



Bv Alex. Stevens, M.A., B.Sc. 



BIOGEOGRAPHY OF THE ATLANTIC ISLES.— The 

 bathymetric charts of the Atlantic reveal a long submarine 

 plateau running along the axis of the present ocean and 

 bounded by symmetrical valleys on the east and west. The 

 surface of the plateau is irregular, rising into peaks which 

 project here and there in groups as the Atlantic Isles. Far 

 out the Azores rise from the " oceanic axis," while the 

 foundations of the Madeiras, the Canaries, and the Cape 

 Verde Islands lie in the eastern trough. These archipelagos 

 are of volcanic origin, and were the seat of a recent, Neolithic, 

 it is thought, and considerable vulcanicity. The Madeiras are 

 continuous with the Great Atlas. The materials of the 

 islands are uniform — trachytes, basalts, and tuffs — and all the 

 isles present the same appearance of towering mountains, 

 trenched by deep valleys, cut off at the sea by vertical cliffs or 

 running out into long promontories continued by tails of islets. 

 The ocean platform also is covered with lavas which were 

 certainly poured forth on dry land, but were covered by the 

 sea before subaerial denudation could leave its mark on them. 



A second group of the Atlantic Isles embraces those in 

 the Gulf of Guinea and the distant Ascension and St. 

 Helena. But these are remnants of the foundered Gondwana- 

 land, and display a characteristic tropical African fauna. 

 Louis Germain (" Annales de Geographie ") has worked out 

 faunal and floral connections for the northerly groups, 

 particularly by means of insects and fossil and living molluscs; 

 but he draws evidence from other phyla, worms, and 

 arthropods generally. The islands are remarkably poor in 

 vertebrates, notably in mammals; and this poverty has been 

 used by Wallace, who considered the few vertebrates found 

 in the archipelagos to be imported, as an argument against 

 the possibility of a former continental connection. But 

 Scharff has shown that the mammals are indigenous and 

 came from Europe by a land passage, while Osborn, less 

 convincingly, derives the rabbit from America. It is a matter 

 for regret, nevertheless, that no traces of a possible extinct but 

 once flourishing mammal fauna have been brought to light 

 for purposes of comparison with American forms. On the 

 whole the much larger part of the fauna is circummediter- 

 ranean and the smaller American. 



Where the Atlantic now rolls an old - time continent 

 supported a large and varied fauna and flora. By the close 

 of the Cretaceous the southern Gondwanaland portion was 

 passing beneath the waves and a narrow gulf divided the 

 northern part from America. Later, and perhaps within the 

 memory of the human race, this too — possibly the Atlantis of 

 Plato and the ancients, recalled only by uncertain oral 

 tradition — passed. The waters encroached from the west, 

 and the shore creatures of a fauna common to Atlantis and 



