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Embrittling of iron by sodium hydroxide
248
H.F.I.
CURRENT TOPICS.
Embrittling of Iron by Sodium Hydroxide.
J. H. ANDREW.
(Tram. Faraday Soc., March, 1914.)--Wrought iron corrodes slowly, becomes highly crystalline, and eventually brittle by immersion in a concentrated aqueous solution of sodium hydroxide at IOO° C. for several months. The corrosion is attributed to electrolytic action between, the two phases, crystalline and amorphous, of which the metal is constituted, iron go~,ng into solution at the anode (forming sodium ferrite), hydrogen being liberated at the cathode. Part of the hydrogen is occluded by the. metal, being first absorbed by the amorphous constituent, thereby forcing the crystals apart, and ultimately causing the iron to become crystalline and brittle. The brittleness decreases with time, an equilibrium being finally established between the metal and the gas, and is due rather to the molecular rearrangement induced by mere occlusion or evolution of hydrogen than to the mere presence of the latter in solution. The potential difference between the amorphous and crystalline phases and hence the rate of corrosion decrease as the latter phase becomes hydrogenized, the passivity of iron produced by immersion in caustic soda being due to this cause. Similar results were obtained with electro-deposited iron, but steel containing o.5 per cent. carbon was much less affected by sodium hydroxide solution. The recrystallization of electro-deposited iron upon cooling through the Ar8 point is also considered to be due to the evolution of hydrogen. Ignition of Gaseous Mixtures by the Electric Discharge. H. F. COWARD,C. COOPER, and J. JACOBS. (Chem. Soc. Trans., cv, io69.)--The inflammability of various gaseous mixtures was compared by determining the lowest pressures at which the mixtures could be ignited with a given sparking arrangement. Mixtures of oxygen and hydrogen were more inflammable as the proportion of oxygen was increased up to 70 per cent. Electrolytic gas at a pressure somewhat too low for ignition became inflammable by adding, without change of volume, either oxygen, hydrogen, nitrogen, carbon dioxide, or argon. Experiments were also made with mixtures of oxygen with carbon monoxide, cyanogen, methane, and ethylene respectively, and with various diluents in each case. Two important factors governing the ignition were the thermal conductivity of the mixture and the energy degraded when the spark was passed; in the case of the mixtures of moist carbon monoxide with oxygen and diluents, a third important factor was the "activation" of oxygen by the discharge.
P R E S S OF j'. B. L I P P I N C O T T COMPANY PHILADELPHIA
H.F.I.
CURRENT TOPICS.
Embrittling of Iron by Sodium Hydroxide.
J. H. ANDREW.
(Tram. Faraday Soc., March, 1914.)--Wrought iron corrodes slowly, becomes highly crystalline, and eventually brittle by immersion in a concentrated aqueous solution of sodium hydroxide at IOO° C. for several months. The corrosion is attributed to electrolytic action between, the two phases, crystalline and amorphous, of which the metal is constituted, iron go~,ng into solution at the anode (forming sodium ferrite), hydrogen being liberated at the cathode. Part of the hydrogen is occluded by the. metal, being first absorbed by the amorphous constituent, thereby forcing the crystals apart, and ultimately causing the iron to become crystalline and brittle. The brittleness decreases with time, an equilibrium being finally established between the metal and the gas, and is due rather to the molecular rearrangement induced by mere occlusion or evolution of hydrogen than to the mere presence of the latter in solution. The potential difference between the amorphous and crystalline phases and hence the rate of corrosion decrease as the latter phase becomes hydrogenized, the passivity of iron produced by immersion in caustic soda being due to this cause. Similar results were obtained with electro-deposited iron, but steel containing o.5 per cent. carbon was much less affected by sodium hydroxide solution. The recrystallization of electro-deposited iron upon cooling through the Ar8 point is also considered to be due to the evolution of hydrogen. Ignition of Gaseous Mixtures by the Electric Discharge. H. F. COWARD,C. COOPER, and J. JACOBS. (Chem. Soc. Trans., cv, io69.)--The inflammability of various gaseous mixtures was compared by determining the lowest pressures at which the mixtures could be ignited with a given sparking arrangement. Mixtures of oxygen and hydrogen were more inflammable as the proportion of oxygen was increased up to 70 per cent. Electrolytic gas at a pressure somewhat too low for ignition became inflammable by adding, without change of volume, either oxygen, hydrogen, nitrogen, carbon dioxide, or argon. Experiments were also made with mixtures of oxygen with carbon monoxide, cyanogen, methane, and ethylene respectively, and with various diluents in each case. Two important factors governing the ignition were the thermal conductivity of the mixture and the energy degraded when the spark was passed; in the case of the mixtures of moist carbon monoxide with oxygen and diluents, a third important factor was the "activation" of oxygen by the discharge.
P R E S S OF j'. B. L I P P I N C O T T COMPANY PHILADELPHIA