10 BULLETIN 956, U. S. DEPARTMENT OF AGRICULTURE. 



one, therefore, desiring to undertake time-temperature studies with 

 canned foods need not hesitate to make use of this or a similar 

 device. 



THERMOCOUPLES. 



The thermocouples used were constructed of copper and constantan 

 wires by Dr. R. B. Harvey, of the. Office of Plant Physiological 

 and Fermentation Investigations, to whom the writers are greatly 

 indebted for assistance in installing and standardizing the thermo- 

 electrical equipment. The constant junction was located in an ice 

 bath maintained at 0° C. by means of a thermos bottle filled with an 

 ice and water mixture, and the variable junction was placed in the 

 center of the container of material under test. The potential was 

 measured with a potentiometer of recognized standard and a re- 

 flection type of galvanometer. 



THE WATER BATH. 



In all time-temperature experiments conducted at 100° C, a water 

 bath was used. This consisted of a wooden tank 18 by 18 by 30 

 inches lined with galvanized iron and heated by means of a steam 

 coil constructed from f-inch pipe. The water was maintained at a 

 constant level and kept vigorously boiling throughout the tests. 

 Owing to the large volume of water in the bath, there was no cessa- 

 tion of boiling when the cans and jars were introduced. The tem- 

 perature was therefore always 100° C, a condition which often does 

 not obtain when small kettles or pots are used for the purpose. 



PRELIMINARY EXPERIMENTS. 



To obtain a thorough understanding of the factors influencing tem- 

 perature changes in the can during the processing period and the 

 subsequent cooling it was considered advisable to make some pre- 

 liminary experiments which would serve as a basis for comparison. 

 In these experiments distilled water, brines of various concentrations, 

 and solutions of sugar and starch were treated as here described. 

 The processing was done in the water bath at 100° C, and in the case 

 of distilled water also in the retort at 109°, 116°, and 121° C. 



DISTILLED WATER. 



The first of these experiments was carried out with distilled water, 

 using No. 2, No. 3, and No. 10 tin cans and pint and quart glass jars. 

 In the case of the tin cans the water was filled to within one-fourth of 

 an inch of the top and the device for holding the thermometer 

 soldered to the can, making a steam-tight joint. In the glass a steam- 



