July i6, 1891] 



NATURE 



259 



will be published under the auspices of the Minister of Public 

 Instruction of France. 



The annual publication of the very useful " Correspondance 

 botanique" ceased with the death of its editor, Prof. E. Morren, 

 of Liege. With the aim of supplying its place, the Interna- 

 tional Library, 4 Rue de la Sorbonne, Paris, has now issued a 

 " Nouvelle Correspondance botanique : liste des botanistes de 

 tous les pays, et des etablissements, societes, et journaux de 

 botanique." 



Prince Roland Bonaparte has issued, at his own expense, 

 a handsome book on Corsica, recording his travels and the 

 history of the island. He also gives a full bibliography relating 

 to the subject. 



A NEW quarterly scientific journal has made its first appear- 

 ance in Paris, under the title Revue des Sciences naturelles de 

 rOuest, devoted to the interests of zoology, botany, geology, 

 mineralogy, anthropology, embryology, and teratology. 



A MONTHLY journal of natural science, which may have many 

 opportunities of doing good work, has just been started in Malta. 

 It is called The Mediterranean Naturalist, and is edited by Mr. 

 JohnH. Cooke, F.G.S. 



The " Dictionnaire d' Agriculture," by J. A. Barral and H. 

 Sagnier, will soon be completed. Vol. iv. is nearly ready, and 

 will be quickly followed by Vol. v. 



A NEW edition of the Great Eastern Railway Company's 

 " Tourist Guide to the Continent," edited by Mr. Percy Lindley, 

 has been published. New editions of Mr. Lindley's "Walks 

 in the Ardennes" and "Walks in Epping Forest " have also 

 been published ; and he has compiled two other useful little 

 hand-books, " Walks in Holland " and " Holidays in Belgium." 



Messrs. Guv and Co., Cork, send us "Guy's South of 

 Ireland Pictorial Guide," in which are described and illustrated 

 much fine scenery and various things interesting to students of 

 natural history and archaeology. 



Messrs. Dulau and Co. have issued a catalogue of the 

 works on geology which they are offering for sale. 



The results of an investigation concerning the cause of the 

 insolubility of pure metals in acids are contributed by Dr. Weeren 

 to the current number of the Berichte. De la Rive, so long ago as 

 the year 1830, pointed out that chemically pure zinc is almost 

 perfectly insoluble in dilute sulphuric acid. Hitherto, however, 

 the hypotheses put forward attempting to account for this singular 

 fact have been anything but satisfactory. The theory of Dr. 

 Weeren is extremely simple, and is fully supported by the most 

 varied experiments, physical and chemical. It may be stated as 

 follows : "Chemically pure zinc and also many other metals in a 

 state of purity are insoluble or only very slightly soluble in acids, 

 because, at the moment of their introduction into the acid, they 

 become surrounded by an atmosphere of condensed hydrogen, 

 which under normal circumstances effectually protects the metal 

 from further attack on the part of the acid." It is found that 

 when a piece of pure zinc is immersed in dilute sulphuric acid, a 

 slight action does occur during the first few succeeding moments, 

 zinc sulphate and free hydrogen being formed in minute quantity. 

 The free hydrogen, however, instead of escaping, becomes con- 

 densed by the molecular action of the zinc upon the surface of 

 the latter, and is retained there with great tenacity as a thin 

 mantle of highly compressed hydrogen gas, capable of affording 

 perfect protection against further inroad of the acid. The 

 experiments from which this simple and very probable explana- 

 tion has been derived were briefly as follows. The amount of 

 chemically pure zinc dissolved by the acid was first determined. 

 It was, of course, an exceedingly minute quantity. Considering 

 this amount as unity, it was next sought to determine what 

 NO. I 133, VOL. 44] 



difference would be effected by performing the experiment in 

 vacuo, when of course the escape of the hydrogen would be 

 greatly facilitated. The solubility was found under these 

 circumstances to be increased sevenfold. Next the experiment 

 was performed at the boiling temperature of the dilute acid, first 

 when ebullition was prevented by increasing the pressure, and 

 secondly when ebullition was unhindered, thus again facilitating 

 the removal of the hydrogen film. In the first case, when ebullition 

 was prevented, the solubility was practically the same as in the 

 cold ; while in the second case, with uninterrupted ebullition, the 

 solubility was increased twenty-four times. Finally, experiments 

 were made to ascertain the effect of introducing into the acid a 

 small quantity of an oxidizing agent capable of converting the 

 hydrogen film to water. When a little chromic acid was thus 

 introduced the solubility was increased 175 times, and when 

 hydrogen peroxide was employed the solubility was increased 

 three-hundred-fold. The explanation of the ease with which the 

 metal becomes attacked when the ordinary impurities are present 

 is that the hydrogen is not then liberated upon the surface 

 of the zinc, but rather upon the more electro-negative impurities, 

 leaving the pure zinc itself open to the continued attack of the 

 acid. The same of course occurs when a plate of platinum is 

 placed in contact with a plate of pure zinc in the acid. The 

 action of nitric acid, the only common acid which does attack 

 pure metals, is evidently due to the oxidation of the hydrogen 

 film by further quantities of the acid, with formation of water and 

 production of the lower oxides of nitrogen, and even under certain 

 circumstances of ammonia. 



The additions to the Zoological Society's Gardens during the 

 past week include a Macaque Monkey {Macacus cynoniolgus) 

 from India, presented by Mr. R. Armstrong ; two Senegal 

 Touracous {Corythaix persa) from West Africa, presented by 

 Sir Brandforth Griffith, Bart. ; two Rock Thrushes {Monlicola 

 saxatilis) from Italy, presented by the Rev. Hubert D. Astley ; 

 two Larger Hill-Mynahs {Gracula intermedia) from China, 

 deposited ; two Mule Deer (Cariacus macrotis), three Summer 

 Ducks {/£x sponsa), seven Mandarin Ducks {/Ex galericulata), 

 five Chilian Pintails {Dafila spinicauda), two Australian Wild 

 Ducks {Anasi. superciliosa), a Spotted-billed Duck [Anas 

 pcccilorhyncha), three Night Herons {Nycticorax griseus), bred 

 in the Gardens. 



OUR ASTRONOMICAL COLUMN. 



The Stellar Cluster x Persel — Mr. O. A. L. Pihl has 

 completed a micrometric examination, begun in 1870, of the 

 group X of the great star cluster iu Perseus, and the results are 

 published by Grondahl and Son, Christiania. His survey in- 

 cludes all stars down to lo'6 magnitude, and a number of 

 fainter ones down to 117 magnitude, the total number of stars 

 measured being 236. The positions obtained, joined to those 

 determined iu the b group by I'rof. Kriiger, with the Bonn 

 heliometer, lorm one continuous survey of both components of 

 the cluster. Prof. Vogel has determined the positions of 178 

 stars in the central part of the x group, but Mr. Pihl's investi- 

 gation covers more than four times the area. A comparison of 

 the right ascensions of the stars measured by these two obser- 

 vers brought to light difierences ol a systematic character which 

 appeared to be neither the result of observational errors nor of 

 calculation. Upon closely inspecting the measures, Mr. Pihl 

 found that his value for right ascension was less than Prof. 

 Vogel's in the case of those stars which were brighter than the 

 star to which positions were referred ; whereas for all stars 

 fainter than this his value was larger, and the fainter the star 

 the greater the difference. 



A ling and a bar micrometer were used in the observations, 

 and the reductions were made by the ordinary method of taking 

 half the sum of the moments of ingres^^s and egress in the cal- 

 culation — a mode of proceeding which depends upon the sup- 

 position that the half sum denotes the instant of the passage of 



