December 13, 1894J 



NATURE 



161 



Ephemeris for Berlin Midnight. 



1894. R.A. (app.) Decl. (app.) Brightness. 



h. m. s. 



Dec. 13 ... 23 21 36 ... -s 339 



,, 15 ••• 26 46 ... 4 557 •• 0'53 



„ 17 •• 31 52 ■•• 4 17-9 



,, 19 •■• 36 54 ■•• 3 40'S ■■• 0-48 



„ 21 ... 41 53 ■ ■ 3 35 



,, 23 ... 23 46 48 ... -2 26-9 ... 0-43 



The brightness of the comet oa November 21 has been taken 

 as unity. 



A New Star? — The Rev. T. E. Espin has announced that 

 a very red star of the eighth magnitude, not in the Bonn 

 DurchmusteruDi;, was found by him on November 29, in R..\. 

 '7h. 54'3ni. Decl. + 58' 14'. The spectrum belongs to 

 Secchi's Type IV. 



PROF. VICTOR MEYER'S NEW METHOD OF 

 DETERMINING HIGH MELTING POINTS. 



A DESCRIPTION of improved apparatus for the determina- 

 ■^ lion of high melting points, by his admirable new method, 

 is contributed to the current Bcrichte by Prof. V'ictor Meyer, in 

 conjunction with hisstudents Messrs. Riddleand Lamb. The sim- 

 plicity of the method will doubtless cause it to take rank immedi- 

 ately among the standard processes for the determination of 

 physical constants, and alongside the universally popular method 

 of determining vapour densities, which we likewise owe to the dis- 

 tinguished Heidelberg professor. Naturally, however, operations 

 at temperatures higher than those at which the hardest varieties 

 of glass soften, must perforce be conducted in apparatus con- 

 structed of platinum, just as in the cases of the determinations 

 of vapour density at the same high temperatures. One of the 

 main advantages of the method is that it only necessitates the 

 use of a very small quantity of the substance whose melting 

 point is to be determined, thus enabling it to be extended to 

 compounds of the most extreme rarity. 



The method is based upon the principle of measuring the 

 temperature by means of a miniature air thermometer constructed 

 of platinum, the air contained in which is expelled, at the 

 moment when the fusion of the substance under investigation 

 occurs, by means of a soluble gas into a gas-measuring vessel 

 filled with a liquid capable of dissolving; the expelling gas. The 

 substance whose melting point is to be determined is placed in 

 a small and very narrow platinum tube, which is fixed to the 

 bulb of the air thermometer during the operation, and both are 

 immersed in a bath of a fused salt whose melting point is con- 

 siderably below that of the substance under investigation. Hence 

 the operation of determining a high melting point by this method 

 is perfectly analogous to that usually adopted in determining 

 ordinary melting points lower than the temperature of boiling 

 mercury. 



The air thermometer is simplicity itself. It consists of a 

 spherical platinum bulb of about 25 c.c. capacity, from which 

 rise parallel to each other two relatively long capillary tube.s, 

 also of platinum. One of the tubes passes down into the 

 interior of the sphere, almost touching the opposite inner sur- 

 face, while the other only just pierces the envelope. Both are 

 bent at right angles at their upper extremities, in opposite 

 directions. In order to eliminate all errors due to the capillary 

 tubes a compensator is also employed, consisting of a long 

 capillary U-tube of the same bore and bent at right angles at 

 the extremities, so as to form an exact counterpart of the 

 capillary portion of the air thermometer. The small tube con- 

 taining the substance is firmly fixed by means of stout platinum 

 wire so that its lower portion is in close contact with the 

 sphere ; the walls of the tube are of the same thickness as those 

 of the sphere. The salt employed for the purposes of a bath is 

 contained in a capacious platinum crucible, supported over a 

 table furnace in a miniature basket of platinum gauze. One of 

 the capillary tubes of the air thermometer is ready to be con- 

 nected with an apparatus for generating pure carbon dioxide, 

 and the other is attached to a gas-measuring burette similar 

 to the well-known Schiff nitrogen apparatus, but some- 

 what narrower, and surrounded by the outer tube of a I.iebig's 

 condenser, through which a stream of cold water is continually 

 passed. This arrangement enables the air to be collected and 

 measured in the proximity of the furnace. The measuring 



NO. 131 I, VOL. 51] 



burette is filled with a concentrated solution of caustic potash. 

 The temperature of the water-jacket is measured by a thermo- 

 meter immersed in a small accessory reservoir, through which 

 the water passes immediately after leaving the jacket. A very 

 simple device has been adopted for determining the exact 

 moment when fusion occurs. Before the experiment the little 

 test-tube is heated until the substance melts ; a fine platinum 

 wire, furnished with a thickened end, is then inserted in it, and 

 allowed to become fixed by the solidification of the substance. 

 The fine wire is then passed over a pulley some distance over- 

 head, and the free depending end is attached to a weight ; just 

 below the weight a bell is hung. 



When everything is ready for the actual operation of deter- 

 mining a melting point, the salt in the crucible is fused, the 

 lower part of the air thermometer and its attached substance- 

 tube are inserted in the bath of liquid, as is likewise the com- 

 pensator, connection with the measuring burette is made, and 

 the carbon dioxide apparatus is arranged to be delivering the 

 pure gas. When the temperature of the bath at length attains 

 that of the melting point of the substance, the portion of the 

 latter in immediate contact with the walls of the platinum tube 

 fuses, and instantly the wire is released, and the weight falls 

 and strikes the bell. The moment the sound is heard, connec- 

 tion with the carbon dioxide apparatus is established, and the 

 air contained in the thermometer is displaced and driven into 

 the measuring burette. The compensator is similarly treated, 

 and the quantity of air which it contained deducted from that 

 contained in the thermometer. From the resulting volume, 

 together with the knowledge previously obtained concerning 

 the capacity of the thermometer and compensator and the known 

 expansion of air, the melting point is obtained by a very simple 

 calculation. 



Four groups of interesting results have already been obtained 

 by use of the new method, indicating the dependence of the 

 melting point upon atomic weight. They are as follows : 



Melting q , Melting 



point. point. 



Salt. 



Potassium chloride 

 Potassium bromide 

 Potassium iodide 



Sodium chloride 

 Sodium bromide 

 Sodium iodide 



800 o 

 7220 



684- 7 



815-4 



7577 

 661 '4 



Potassium iodide 

 Rubidium iodide 

 C.vsium iodide 



6847 

 641-5 

 62 1 'O 



Calcium chloride 8o6'4 

 Strontium chloride 832 o 

 Barium chloride 9218 



It will be observed that in the halogen salts of both sodium 

 and potassium a diminution of melting point accompanies a rise 

 in the atomic weight of the halogen ; also that a lowering of the 

 melting point accompanies a rise in the weight of the metallic 

 atom in the case of the iodides of the alkali metals potassium, 

 rubidium, and cxsium, while the reverse occurs with respect to 

 the chlorides of the alkaline earthy metals calcium, strontium, 

 and barium. Whether there is rise or fall of the melting point 

 with ascending atomic weight, however, the salt of intermediate 

 molecular weight invariably exhibits an intermediate melting 

 point. .\. E. Tl-tton. 



SCIENCE IN THE MAGAZINES. 



T^HERE are very few articles on purely scientific subjects in 

 •*■ the magazines received by us this month. Apparently 

 the magazine-reading public thinks a scientific pabulum un- 

 suitable for Christmas reading ; or is it that men of science are 

 too deeply engrossed in their researches to cultivate the art of 

 writing interestingly upon the wonders of n.iture ? Literary men 

 frequently play fast and loose with natural phenomena and laws, 

 and are often pilloried fordoing so ; but, on the other hand, 

 many men of science do not pay due regard to the literary 

 polish which is essential to an attractive style. 



The first number of the Fortnightly under the new editor, 

 Mr. W. L. Courtenay, contains two articles of interest to our 

 readers, one on " .\ True University of London," by Mr. 

 Montague Crackenthorpe, and the other on "The Spread nf 

 Dijihtheria," by Dr. Robson Roose. Mr. Crackenthorpe deals 

 broadly with the whole question of the expediency of establish- 

 ing in London a University which shall teach as well as examine. 

 He defines the work of a true metropolitan University as follows : 

 (l) To do the work of the higher teaching by its own pro- 

 fessorial staff, and to superintend .and aid its being done by other 

 educational agencies in the metropolis. (2) To examine and to 



