KILLING MICROBES BY PRESSURE

Evening Star, Issue 17234, 26 December 1919, Page 5

KILLING MICROBES BY PRESSURE

Although tho sterilisation of liquids by nigh pressures can hardly have a. wide field of application in industry or medicine the investigations in this direction lately earned out afc the West Virginia University fcxpenmental Station by Professor B. H. Hite and his associates are of considerable interest. Very high pressures, ranging up j tons *° 1131 * 1 inch, are used, and special cylinders of enormous strength are _ required to withstand tho bursting strains. This will be readily appreciated when it is remembered that th« abovementioned pressure is mora than double that in tho breech of a 15in gun just after the __ cljarge has been fired. The cylinder uscq in tho experiments consisted of a block of steel with a hole through it measuring slightly over five-eighths of an inch in diameter. The bottom end of, the hole was closed by a 6teel plug, while a steel plunger was inserted at tho top. It would have been impossible to make such a plunger tight by any known form of packing if actually in contact -with tho liquid; the latter was therefore sealed up in a thin lead tube. Pressure was applied by an Olsen testing-machine, such as is ordinarily used for testing bars of steel and other rnetals. It was found that no micro-organisms can withstand a pressure of 100,0001b to tho square inch, while "most bacteria," 6ays the 'Scientific American,' "including those responsible for typhoid, tuberculosis, and diphtheria," are killed in three minutes by a pressure of 75,0001b. As might ba expected, the time of exposure has an important bearing upon the results obtained, longer exposures being required with lower pressures. Temperature also affects the destructive power of high pressures, this being enhanced by increasing tho temperature. For sterilising, the media employed in the culture of bacteria a pressure of 100,0001b to the square inch is applied at temperatures of from 40 to 4-5 degrees centigrade.