TEMPERATURE CHANGES IN CANNING FRUITS AND VEGETABLES. 53 



of some viscous substance, as- in the soy beans; or it may be simply 

 a compacting of the material, as happens sometimes in the case of the 

 leafy vegetables; or it may be the evaporation of the liquid, as might 

 happen sometimes in glass where an absolutely tight closure can not 

 be made. 



SUMMARY, 



(1) The mercury thermometer is sufficiently accurate for practical 

 workin the determination of temperature changes in the canning of 

 food materials if it is properly calibrated and standardized. 



(2) A satisfactory apparatus has been devised for measuring the 

 temperature changes at the center of the can during the processing 

 period and the subsequent cooling, which permits the use of the mer- 

 cury thermometer both in the water bath and in the steam retort. 



(3) In a can packed with material having an interspace filled with 

 a free liquid, as in string beans, the rate of change of temperature 

 at the center of the can is very rapid, and in materials of a heavy 

 or pasty nature, as in sweet corn, the rate is very slow unless 

 mechanical agitation is employed. 



(4) In canned materials the character of the pack and the compo- 

 sition of the material very largely determine the rate of change of 

 temperature in the can. The fineness of division and compactness 

 of the material and the amount and viscosity of the free liquid are 

 the factors which influence the rate of change of temperature. Vari- 

 ations in the composition of the material, however, have very little 

 effect if the consistency of the material is such that no convection 

 can occur. 



(5) Sodium chlorid has very little direct effect upon the rate of 

 change of temperature in the can. Dilute sugar solutions have only 

 a small effect, but the concentrated solutions have a considerable 

 effect in retarding the rate of change. Solutions of starch have a 

 very marked retarding effect upon the rate of change of temperature 

 at the center of the can. The retarding effect increases very rap- 

 idly from 2 to 5 per cent. In 5 per cent starch the consistency 

 becomes such that all convection is stopped and the rate of change 

 is very slow. Increasing the percentage of starch further has very 

 little effect upon the temperature changes. Also, any other material 

 of a viscous nature, such as protein or pectin, retards the rate of 

 change of temperature. 



(6) The glass container has a marked retarding effect upon the 

 rate of rise in temperature in those materials in which there is a 

 free liquid, as in string beans, but is of little importance in materials 

 of a heavy consistency, such as sweet corn. On the other hand, glass 

 cools faster in the air than tin, owing to its greater power of 

 radiation. 



