ON THE LIQUEFACTION OP GASES. 19 
lead is formed by the action of atmospheric air on lead in 
distilled water." 
As to the last question, " to which of the salts contained 
in river-water the non-formation of the white precipitate is 
due," the author states that it is the sulphate of lime, and 
considers that the chloride of sodium, which has been 
generally supposed to be capable of exercising this preser- 
vative power, does not possess it, on account of its forming 
when decomposed a salt of lead partly soluble. 
In conclusion, he remarks that the non-action of rain- 
water which had fallen, after a long continuance of dry 
weather, on lead, is probably due to the small amount of 
carbonate of ammonia which is contained in atmospheric 
air. London Chemical Gazette. 
ART. VI. — ON THE LIQUEFACTION OF GASES. 
BY PROFESSOR FARADAY. 
The author, in a letter to M. Dumas, gives the following 
account of his mode of experimenting : — 
I sought in the first place to obtain a very low tempe- 
rature, and employed for this purpose Thilorier's bath of 
solid carbonic acid and aether, placing it however under the 
recipient of an air-pump. By maintaining a constant 
vacuum, I lowered the temperature to such a degree, that 
the carbonic acid of the bath was not more volatile than 
water at the temperature of 86°, for the barometer of the 
air pump stood at 28.2 inches, the external barometer being 
at 29.4. 
This arrangement made, I joined together, by means of 
corks and stop-cocks, some small glass and copper tubes, so 
