46 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



The water was heated by a number of Bunsen flames. After the 

 water had begun to boil the can was lowered suddenly into it, 

 and the temperature readings made at frequent intervals. 



The temperature readings were made with a thermocouple and 

 sensitive galvanometer (1.88 x lO'^ volt/mm.) The thermocouple 

 was of constantan (No. 27) and copper (No. 30) mounted as 

 sliown in Fig. 5. The wires were protected by enclosure in glass 

 and rubber tubing. The glass tube was narrowed down to about 

 2 mm. diameter at the point where it enters the can. The can 

 was supported by a brass tube held fast by solder. In order to 

 make the interchange of cans easy the brass tube was made in 

 two pieces and held together by a collar. The wires of the 

 thermo-junction were allowed to project about 2 mm. beyond the 

 end of the glass tube and were sealed in shellac. This did not 

 form a permanent seal and was renewed for each set of readings. 

 The whole outfit was mounted as compactly as possible by use of 

 laboratory' clamps and rods to enable the can to be lowered 

 readily into the bath. 



The temperature readings made with this arrangement are ac- 

 curate to within about 1°C. For calibration purposes a mercury 

 thermometer was used as a standard. 



Wlien the steam bath was used it was necessarj'- to lead the 

 thermocouple wires in through a steam tight joint capable of 

 withstanding a pressure of twenty pdunds per square inch gauge. 

 This was accomplished by inserting the couple in a thin glass tube 

 closed at one end, and held in place by a rubber gasket as shown 

 in Figure 6 ; the closed end which contains and protects the 

 junction being placed at the center .of the can. The presence of 

 the thin glass surrounding the ju,nction did not prevent the 

 junction from attaining the temperature of the surrounding ma- 

 terial promptly. A test showed that in about one-half minute 

 after immersion in boiling water the junction was practically at 

 the temperature of the water. 



BIBLIOGRAPHY. 



1. J. Kochs and K. Weinhausen, Bericht der Agl. Gartnerlehranstalt 

 Zu Dahlem, 1906-07, pp. 146-161. 



2. A. W. Bitting and K. G. Bitting, Bulletin No. 14, National Can- 

 ners Association Research Laboratory, pp. 32-38. 



3. Carslaw, Introduction to the Theory of Fourier's Series and In- 

 tegrals, pp. 203 and 312. Macmillan & Co., 1906. Preston, Theory of 



