232 



NATURE 



[January 4, 1894 



Cuivre," by M. Paul Weiss, in which the origin, mode of 

 occurrence, properties, metallurgy, applications, and alloys of 

 copper are fully treated. The author has visited the chief 

 copper mines and works in Europe, and his book is a very use- 

 ful resume o{ \.\\Q. fundamental principles of the copper industry. 

 The ninety-six figures inserted in the text include twelve excel- 

 lent sections illustrating the molecular structure of various metals 

 and alloys. 



The structure of snow-cryslals photographed by G. Norden- 

 skiold formed the subject of an article in our last volume. 

 Another important contribution to the subject has recently been 

 published, namely. Prof. G. Helimann's " Schneekrystalle " 

 (Rudolf Miickenberger, Berlin). The work begins with a brief 

 history of the study of snow-crystals, illustrated by reproduc- 

 tions of the various forms observed and drawn by different 

 observers, from the spikes, crescents, and daggers of Magnus in 

 the sixteenth century, to the elaborate and perfectly symmetrical 

 stars designed by Glaisher. But in meteorology as in astronomy, 

 photography is rapidly taking the place of the observer ; so much, 

 indeed, is this the case that the modern meteorologist and physical 

 astronomer views visual observations with more or less sus- 

 picion. At any rate, the remarkably fine series of micro- 

 photographs of snow-crystals obtained by Dr. Neuhauss during 

 the winter 1892-3, and reproduced in Prof. Helimann's work, 

 indicates that eye-observations of their forms are no longer 

 necessary. After discussing the structure of snow-crystals. Prof. 

 Hellmann proposes a classification into tabular and columnar 

 crystals, the former class being subdivided into radiating stars, 

 plates, and a combination of the two, and the latter into 

 prisms and pyramids. A descriptive bibliography is given, thus 

 increasing the value of a work upon a subject of which much 

 more can yet be said. 



The cause of the violent explosion which usually occurs 

 when any considerable quantity of metallic sodium is brought 

 in contact with water in a more or less confined space, forms 

 the subject of a communication to the journal filr praktisclie 

 CJiemie, by Prof. Rosenfeld. It has been hitherto supposed to 

 be due to the formation of a quantity of sodium peroxide, by 

 the decomposition of which oxygen is liberated, which mixes 

 with the hydrogen produced in the main reaction, thus forming 

 an explosive mixture. Prof. Rosenfeld has fully investigated 

 the question experimentally. It was first established that steam 

 may with impuoity be passed over sodium contained in a slightly 

 bent iron tube, no explosion ever occurring under these con- 

 ditions. This would be quite compatible with the above 

 explanation of the cause of the explosions, for any explosive 

 mixture would be rapidly carried from the seat of the reaction 

 by the escaping hydrogen or the excess of water vapour. No 

 oxygen, however, was ever detected in the gas thus liberated. 

 In all the experiments in which explosion was brought about by 

 the action of water, whether in open vessels or in vessels closed 

 by a water column, it was invariably observed that the sodium 

 was blown to powder from the centre outwards — that is to say, 

 the seat of the explosion was the interior of the piece of metal 

 experimented with. Prof. Rosenfeld comes to the conclusion, 

 from the whole of the phenomena observed, that the explosion 

 is brought about by the sudden dissociation of a hydride of 

 sodium which is formed in the first stage of the reaction. As 

 such a compound can only be produced in an atmosphere of 

 hydrogen, the only safe mode of decomposing water by metallic 

 sodium is considered to be that previously mentioned, of passing 

 a rapid current of steam over the metal ; for the hydrogen is 

 then removed from the sodium as quickly as it is produced, and 

 the formation of hydride, and therefore all risk of explosion, is 

 NO. 1262, VOL. 49] 



consequently avoided. In order 'to carry out this reaction an 

 iron crucible is best employed which is capable of being closed 

 in a gas-tight manner by means of an iron plate, which can 

 be pressed firmly down against a flange on the edge of the 

 crucible by means of a screw threading through a suitably sup- 

 ported nut. Steam is blown into the body of the crucible con- 

 taining the sodium by means of a side tube, and the escaping 

 hydrogen is led away by a similar tubulus upon the other side. , 

 If the supply of steam is arrested the moment hydrogen ceases 

 to escape, solid caustic soda is obtained, mixed in a curious 

 manner with more or less finely divided iron, probably owing to 

 the formation of a quantity of an alloy of iron and sodium, 

 which is subsequently decomposed with liberation of iron. 

 Silver is likewise attacked in a similar manner. The method 

 may also be employed to prepare solutions of soda of known 

 strength. Thus, if twenty-three grams of sodium are employed, 

 and the escaping hydrogen is washed through a little water, an 

 exactly normal solution of soda can at once be obtained by dis- 

 solving the product in water, adding the wash water, and making 

 up to a litre. 



An interesting investigation of the amount and nature of the 

 gases occluded in the coal derived from several collieries in the 

 Durham coal field has been carried out by Mr. W. McConnell, 

 of the Durham College of Science. The collieries from which 

 samples were taken are situate at different points along the 

 same seam, known in Durham as the Hutton seam. It is 

 bituminous coal used as gas-coal and as steam-coal. The coal 

 or coal-dust was placed in an apparatus constructed entirely of 

 glass, and which was capable of continuous exhaustion while 

 heated in baths to known temperatures varying from 100' to 

 180° ; the gas previously occluded by the coal was delivered by 

 the pump into a receiving gas-holder, and subsequently measured 

 and analysed. The coals from the Ryhope colliery were found 

 to contain as combustible gases considerable quantities of 

 occluded free hydrogen, marsh gas, ethane, and other members 

 of the paraffin series of hydrocarbons as far as pentane. More- 

 over, a portion of the gas, consisting chiefly of the higher 

 members of the paraffins and smaller quantities of olefines, is so 

 firmly retained that crushing to fine powder and heating to 180° 

 under reduced pressure is insufficient to remove it. It is also 

 singular that the coal retains a remarkably high proportion of 

 free oxygen in the occluded form, even after heating to 180°. 

 In the case of the Hebburn colliery, a notably " gassy " mine, 

 in which frequent "blowers" are met with, the results are 

 especially interesting. The "blowers" deliver such large 

 quantities of gas that some of it is actually " piped " up to the 

 bank and burnt under the boilers. The combustible constituent 

 of the gas thus utilised is found to be entirely marsh gas. The 

 coal itself is found to contain a relatively very large volume of 

 occluded gas, the combustible constituents being mainly marsh 

 gas and ethane ; and the ground coal and coal-dust yield in 

 addition considerable quantities of higher members of the 

 paraffin series. From the whole of the results derived from the 

 various collieries, there can be no doubt that the coal-dust 

 largely owes its sensitiveness to ignition to the denser occluded 

 gaseous hydrocarbons which it retains so tenaciously. 



The additions to the Zoological Society's Gardens during the 

 past week include a Leopard [Felts pardus, 6 , black variety), 

 from India, pre.'iented by the Duke of Newcastle ; a Her- 

 ring Gull {Lams argentatus) from Jersey, presented by Mr. 

 John Stanton ; an Alligator {Alligator mississippiaisis) from 

 the Mississippi, presented by Mr. C. Knox Shaw ; a Diamond 

 Snake {Morelia spilotes) from Australia, presented by Com- 

 mander A. Burgess, R.N.R. ; a Diamond Snake {Morelia 

 spilotes) from Australia, purchased. 



