TEMPERATURE CHAjSTGES IX CANNING FRUITS AXD VEGETABLES. 7 



and so placed as to make direct reading possible at all times during 

 the processing. It is recognized, of course, that the mercury ther- 

 mometer is subject to small inaccuracies, but when it is properly 

 constructed and standardized these are too small to be of practical 

 importance in work of this sort. In the work here reported special 

 long-stemmed thennometers were employed which were calibrated 

 for 6-inch immersion and graduated to read from —10° to +150'^ on 

 the centigrade scale. When tested these thermometers showed a lag of 

 only 15 seconds in passing from 0° to 100° — a lag even less than that 

 of the thermocouple used by Thompson (13). 



The use of long-stemmed thermometers for time-temperature 

 studies is, of course, not new. Bitting (2) and others have em- 

 ployed them for experunents made when processing in the water 

 and chlorid baths, but their use for tests carried on heretofore in the 

 steam retort has not been found feasible. The difficulties have been 

 successfully overcome, and the apparatus here described and illus- 

 trated shows how the temperature at the center of the can may be 

 determined at all times, whether the processing is being done in the 

 water bath or in the steam retort. 



THE STEAM RETORT. 



The steam retort used in these experiments was constructed from a 

 piece of 8-inch water pipe 14 inches long, fitted at one end with a 

 blind flange, Avhich serves as the base of the retort, and at the other 

 with a removable blind-flange cover. By means of :]-incli wrought- 

 iron handles and hinged clamp bolts the cover may be placed in 

 position and securely clamped down in a very few seconds. Steam 

 from a boiler large enough to furnish an ample supply of steam at an}^ 

 pressure desired enters by way of a ^-inch pipe inserted in the side 

 of the retort a few inches above the base, and an exhaust of the same 

 size is provided in the bottom. A carefully tested and standardized 

 pressure gauge is also attached. 



In the cover a pet cock allows the rapid expulsion of air from the 

 retort and also makes possible a continuous flow of steam about the 

 test can during the processing. A 1-inch hole at the center of the 

 cover is threaded to receive a special brass fitting to which the test 

 can is attached. Bj' means of a suitable gasket the joint is made 

 steam tight, and with the brass fitting and the can in place the appa- 

 ratus is ready for the insertion of the thermometer. The thermometer 

 is passed through the brass fitting by way of a §-inch hole until the 

 bulb reaches the center of the test can, as determined by careful 

 measuring beforehand, the funucl-sha})ed depression in the stem of 

 the fitting provided with a siiital>le gasket, and the cap screwed 

 down. The thermometer is thus held securely in jwsition, and a 

 steam-tight closure is easilv made. 



