Apparatus for freezing Water by the aid of Sulphuric Acid. 133 



allow of the slightest leakage. If a pump has been used previously 

 for freezing, by the vaporization of ether, it will not be competent for 

 the experiment in question, unless it be taken apart and cleaned. 



Cocks of the ordinary construction, are rarely if ever perfectly air 

 tight, and their imperfection always increases with wear. Under 

 these impressions, having, cleansed my air pump, and put it into the 



