TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 7 
_ glass arm A with the test can 7, located in the retort R, as 
_ described for temperature tests in United States Department of 
Agriculture Bulletin No. 956, entitled “A Study of the Factors Af- 
fecting Temperature Changes in the Container during the Canning 
of Fruit and Vegetables.” Retort temperature is controlled by the 
thermometer 7’. During the test the pressure which causes the level 
of the mercury to fall in arm A is compensated for by raising arm 
B, and the mercury in arm A is therefore maintained at the constant 
level x, corresponding to the zero graduation on scale Y. The vol- 
ume of gas in the retort side of the apparatus is kept constant and 
the pressure in centimeters or inches, as desired, read directly from 
the + portion of the scale. Similarly, the vacuum is read by lowering © 
arm 4, to compensate for the rise of mercury in A, and the vacuum 
is seach directly from the — portion of the scale. The can being at- 
tached to the cover of the small retort, the flexible tube / allows the 
prompt removal of the test can from the retort in a few seconds and 
the cooling of the can either in air or in water, as desired. 
This apparatus is very sensitive to slight changes in pressure, 
demonstrates very quickly any leaks present, and has proved 
very satisfactory. By means of this apparatus the writers have been 
able to conduct tests upon all classes of substances in various quanti- 
ties with different sizes of cans at any initial temperature and retort 
temperature desired. 
DETERMINATION OF TEMPERATURE. 
Data upon temperature changes were obtained in the same manner 
as described in United States Department of Agriculture Bulletin 
No. 956, and all temperatures, both of retort and can, were made with 
special carerally standardized mercury thoumomoters. 
In the paper previously reviewed, Bigelow and his collaborators 
object to the use of a mercury Hheanmeiee for this purpose, on the 
ground that heat is conducted down the stem to the mercury bulb. 
According to Smithsonian conductivity tables, the conductivity of 
glass and water is practically the same. It is evident, therefore, that 
the conductivity of glass is about the same or slightly less than the 
minimum for any food substance. Since, also, the distance from 
the ends of the can to the center is greater than the radius, the heat 
should reach the mercury bulb through the food from the side before 
it could be conducted down the stem of the thermometer. In the 
thermocouple used by Bigelow and his collaborators, which is in- 
serted into the can in the same way as the thermometer, the thermal 
junction is soldered to the end of a bare copper tube, which in turn 
is soldered to the end of a brass tube, the external portion of which 
during processing -is subjected to the full temperature of the retort, 
which allows of rapid conduction of heat into the can. With the 
