D. CHEMISTRY AND METALLURGY. 219 



is by laying it on a sheet of zinc in a basin of diluted sul- 

 phuric acid. The hydrogen generated by the action of the 

 acid on the zinc is given off on the surface of the iron; and 

 two minutes or less will suffice to charge a piece of iron with 

 hydrogen, and alter its properties completely. This alteration 

 is not confined to a diminution of toughness, which may be 

 reduced to one quarter of its original value, but is also ac- 

 companied by a marked decrease in tensile strength, amount- 

 ing in cast steel to upward of twenty per cent. ; but in the 

 case of iron-ware to only six per cent. The electrical re- 

 sistance is increased by this occlusion of hydrogen. It is 

 probable that repeatedly rusting iron occludes hydrogen, 

 and it is thereby deteriorated in strength and toughness. 

 Nature, II., 903. 



THE COMPOSITION OF BLEACHIXG-POWDER. 



The question of the composition of the so-called " chloride 

 of lime" lias lately been much agitated. The generally re- 

 ceived view of Gay Lussac, that it is a true calcium hypo- 

 chlorite, has been attacked by Goepner, who regards it as 

 merely a molecular compound of lime and chlorine, contain- 

 ing no hypochlorous acid. Mr. Ferdinand Kopfer now sub- 

 mits the subject to the test of a long series of careful exper- 

 iments, and decides in favor of the old view. He finds that 

 when a dilute mineral acid, just sufficient to saturate the 

 calcium present, is added to a solution of bleaching-powder, 

 no smell of free chlorine can be detected, but only the char- 

 acteristic odor of hypochlorous acid. The solution thus ob- 

 tained, shaken up with a large excess of mercury, yields the 

 brown oxychloride of the metal, again proving the presence 

 of hypochlorous acid. Jour. Chem. JSoe., August, 1875. 



THE INCOMPLETE COMBUSTION OF GASES. 



The habilitation thesis of Dr. Ernst Meyer on the incom- 

 plete combustion of j^ases contains the following- suo-o-est- 

 ive sentences: The studies upon inflammability, which, ac- 

 cording to the experiments contained in this essay, stand in 

 a closer connection with the phenomena of affinity than we 

 should at first suspect, indicate the importance that must be 

 attributed to the thermal relations of the o-ases. The com- 

 bustion of carburetted hydrogen in a closed tube, which, be- 



