TEMPERATURE CHANGES IN CANNING FRUITS AND VEGETABLES. 15 



100 



SO 



SO 



in the can, comparative tests were made with 10 per cent, 30 per cent, 

 and 60 per cent cane-sugar solutions. This series of tests was made 

 with No. 3 tin cans in the boiling-water bath as the 

 heating medium, and in circulating water at 17° C. 

 as the medium for cooling. In each of the tests 

 the cans were filled with the solution to within 

 one-fourth of an inch of the top. The device for 

 holding the thermometer was soldered in place and 

 the thermometer so placed that the bulb was at the 

 center of the can. The curves in figure 9 show the 

 results obtained. The sugar solutions show no 

 marked effect upon the rate of changes of temper- 

 ature at the center of the can, where the concen- 

 tration is 10 per cent or less. Even in a 60 per cent 



solution of susar 



70 







ki so 



<?o 



too 



90 



BO 





*o 



30 



20, 



fyb 

















































































































30 



AffB 



;=— 



to 



60 



the effect is less 

 marked than 

 might be ex- 

 pected. The ef- 

 fect of the sugar 

 solution upon the 

 rate of change of 

 temperature at 

 the center of the 

 can is due to the 

 greater viscosity, 

 which decreases 



the rate of convection in the sugar 

 solutions. The value of the force 

 which tends to produce convection 

 currents in the solution depends 

 upon the steepness of the gradient 

 between the temperature at the 



o /o 20 



T/ME /HM/MUTES 



Fig. 8. — Time-tem- 

 perature relations 

 for distilled water 

 and saturated brine 

 when processed in 

 No. 3 tin cans at 

 100° C. These 

 curves were plotted 

 from temperature 

 readings made at 

 intervals of 1 min- 

 ute. A, Distilled 

 water; B, satu- 

 rated brine. 



20 30 -90 GO 



T/M£ V/V M/A/UTE3 



Fig. 9. — Time-temperature relations for 

 10 per cent, 30 per cent, and 60 per 

 cent cane-sugar sirup when processed 

 in No. 3 tin cans at 100° C. and also 

 when cooled in water. These curves 

 were plotted from temperature read- 

 ings made at intervals of 1 minute. 

 Rise in temperature : A, For 10 per 



cent sirup ; b, for 30 per cent sirup ; center of the can and the tempera- 



C, for 60 per cent sirup. Fall in tem- 

 perature from 100° when cooled : 

 a', For 10 per cent sirup in water at SO that the force tending to produce 



for 30 per cent sirup in convec tion currents becomes less and 



ture at the margin of the solution, 



12|° C. ; V 



water at 17° C. ; c', for 60 per cent 



sirup in water at 15|° C. 



less as the temperature at the center 

 of the can approaches that of the bath. It is known that the vis- 

 cosity of the sugar solutions decreases as the temperature increases. 

 It is this characteristic of sugar solutions that makes the temperature 

 shown by the upward curves follow so closely that of distilled water. 



