12 



BTILLETIlSr 956, U. S. DEPARTMEl^T OE AGKICULTTJEE. 



sadden drop in the temperature at the center of the can. It falls 

 to 30° in a very few minutes, the rate of cooling being only slightly 

 slower than the rate of rise in temperature. As will be seen, the 

 cooling in air is very slow when contrasted with the cooling in water. 

 No cooling tests of glass in water, of course, could be made In 

 these tests in the cooling in air the glass cooled considerably faster 

 than the tin The diameter of the No. 2 tin can is less than that 

 of the quart glass jar, yet the quart jar cools faster. This may have 

 been caused in part by leakage around the cover of the jar, since a 

 steam-tight closure was not possible, but it must be due largely to 



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 TIME IN MINUTES 



Fig. 4. — Time-temperature relations for distilled water -when processed in No. 2 tin cans 

 at 100°, 109°, 116°, and 121° C. and also when cooled in air and in water. The 

 curves representing the rise In temperature during processing and the fall in tempera- 

 ture during cooling in water were plotted from readings made at intervals of 30 sec- 

 onds ; curves representing cooling in air, from readings made at intervals of 5 to 10 

 minutes. Rise in temperature when processed : A, At 100° C. ; B, at 109° C. ; C, at 

 116° C. ; D, at 121° C. Fall when cooled : a'. From 100° C. in water at 17° C. ; V, from 

 109° C. in water at 15° C. ; c' , from 116° C. in water at 16° C. ; d' , from 121° C. in 

 water at 16° C. ; a, from 100° C. in air at 17° to 20° C. ; 'b, from 109° C. in air at 20° 

 to 24° C. ; c, from 116° C. in air at 25° C. ; d, from 121° C. in air at 25° C. 



the fact that glass radiates heat faster than tin. The rate of cooling 

 in tin is in the order of the diameter of the cans, the No. 10 being 

 slowest, the No. 3 next, and the No. 2 fastest. The pint glass jar is 

 faster than the quart glass jar or the No. 2 tin can. The temperature 

 of the room was not constant, varying between 16° and 20° C. The 

 length of time necessary for any container to reach any specific tem- 

 perature is shown by the curves. 



In figures 4 to 7 are shown the curves representing the tempera- 

 ture changes at the center of the various cans of distilled water when 

 processed at 100°, 109°, 116°, and 121° C. Since a steam-tight 

 closure could not be made in the glass, any temperature above 100° 



