EVOLUTION OP GASES FROM HOMOGENEOUS LIQUIDS. 



283 



The results in the lower table show that on reducing the pressure there is a 

 temporary slight increase in the rate of evolution of gas, but afterwards the decomposi- 

 tion proceeds pari passu at the ordinary and at the reduced pressure. 



Decomposition of Ammonium Nitrate into Nitrous Oxide and Steam. 



The effect of variation of pressure on this decomposition was not completely investi- 

 gated ; one experiment was conducted with an apparatus similar to that described 

 above in the case of the decomposition of formic acid, but with a U-tube interposed 

 between the decomposition flask and the SPRENGEL, and surrounded by a freezing 

 mixture to condense the steam evolved. The fused salt having been heated under 

 a pressure of 20 mm., it was observed that a sudden increase of pressure, caused by 

 opening the decomposition flask by removal of the cork, practically stopped the 

 decomposition for some time ; thus, the phenomenon of the retardation, to be followed 

 by a period of acceleration, is much exaggerated. 



Evolution of Hydrogen from Zinc and Sulphuric Acid. 



Various experimenters have from time to time noticed the complete arrestation by 

 pressure of the displacement of acidic hydrogen by zinc and other metals. Thus, so 

 long ago as 1828, BABINET* writes, " Si on opere en vases clos lorsque le gaz (hydrogene) 



* ' Annalcs de Chimic,' [2], vol. 37, p. 183. 

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