154 Intelligence and Miscellaneous Articles. 



12 per cent.) ; and the metals which are insoluble in aqua regia 

 (rhodium, iridium, and ruthenium) then remain in the state of 

 peculiar products, without metallic lustre, which seem to be an 

 allotropic modification of the true alloys possessing a metallic 

 appearance. 



The action of zinc upon the osmide of iridium is thus accounted 

 for naturally. If the heat liberated in the combination of iridium 

 and zinc much exceeds the heat of combination of osmium and 

 iridium, the osmide, in conformity with the laws of thermo- 

 chemistry, will be destroyed by the zinc ; the osmium dissolves 

 and may crystallize in the excess of metal ; the iridium and the 

 other metals remain combined with the zinc. It is the residue 

 from the action of the hydrochloric acid upon this alloy with excess 

 of zinc that constitutes the explosive substance above considered. 

 In fact the heat liberated in the union of zinc with iridium, 

 ruthenium, and rhodium, which are the dominant metals of the 

 osmide, is truly enormous : on adding, for instance, 1 part of iridium 

 to 30 or 40 per cent, of melted zinc at a temperature below a red 

 heat, there is combination accompanied by actual incandescence of 

 the whole mass of metal ; it is the same with the two other metals. 

 If all the zinc be driven out by heat (as was clone by us in our old 

 experiments), the hardly fusible metals of the osmide, free or 

 alloyed, remain in a state of extreme division, in which they aiv 

 much more readily attacked than the natural osmide. 



In an early Note we shall speak of facts observed in the solution 

 of the platinum metals in copper. — Comptes Bendus de VAcademie 

 dp? Sciences, June 12, 1882, t. xciv. pp. 1557-1560. 



OX THE REACTION-CURRENT OF THE ELECTRIC ARC. BY M. .TAMIX, 

 WITH THE ASSISTANCE OF M. G. MANEUVRIER. 



The two currents, in alternately opposite directions, given by 

 Gramme's self-exciting machine are absolutely equal ; consequently 

 they do not decompose water, and a tangent-compass intercalated 

 in the circuit undergoes no deflection, since the contrary effects 

 following at very close intervals destroy one another. This de- 

 struction of the effects is kept up when one or several burners are 

 put into the circuit, provided that the two carbons are equal, dis- 

 posed in exactly the same manner, and are heated equally. 



If eight or ten Bunsen elements be introduced into the total 

 circuit, they communicate to the compass a deflection § when the 

 machine is at rest, and a deflection B', absolutely equal to c. when 

 the machine is working. 



o. 6'. 



First experiment 32 33 



Second experiment 38 38-45 



Third experiment 33 34-10 



This equality proves that the resistance of the wires of the 

 machine does not vary, whether the machine be at rest or in motion : 



