790 



SCIENCE 



[N. S. Vol. XXVII. No. 698 



.a most astounding series of libels, against 

 which he seemed to have been utterly power- 

 Hess. 



Robert M. Brown 

 State Nokmai School, 

 WoBCESTEB, Mass. 



A SIMPLE CONTINUOUS ELECTRIC CALORIMETER 

 FOR students' use 



For several years we have been using, with 

 considerable success, a simple form of the 

 continuous-flow calorimeter for measuring 

 -Joule's equivalent in the electrical laboratory 

 work of our elementary students. I venture 

 to describe the apparatus here in the hope that 

 it may commend itself to those engaged in 

 practical work, as being simpler of operation 

 than the older electrical methods of measur- 

 ing this important constant. 



A glass tube, about 50 cm. long and 2 to 

 -3 mm. internal diameter, is cemented at both 

 •ends to brass collars carrying washers and 



mix the water as it flows through. A copper 

 or tin vessel with overflow maintains a con- 

 stant head of water from the city mains at any 

 desired elevation, and a tube conveys the 

 water to the inflow end of the calorimeter. 

 An air trap, made from an inverted thistle 

 tube, serves to catch any air bubbles liberated 

 or carried down by the water. The tempera- 

 ture of the inflowing water is measured on 

 the thermometer. After passing through the 

 flow tube, the water passes out at the outflow 

 end to a suitable measuring vessel. The tem- 

 perature of the outflowing water is recorded 

 at regular intervals on the second ther- 

 mometer. The upper end of the brass T, to 

 which the outflow pipe is attached, is open to 

 the air and establishes the head independent 

 of the exact level of the end of the outflow 

 pipe. Having obtained a reading on the two 

 thermometers before any heating current ia 

 turned on, the electrical circuit is completed, 

 and after four or five minutes, during which 

 the temperature of the outflow water becomes 



//O VOLTS. 



■nuts, which screw into brass castings drilled 

 •out to receive suitable thermometers. A 

 heating wire, of about 10 ohms, coiled in a 

 long helix, passes through the tube and is 

 soldered to the brass collars. The helix serves 

 to break up the stream-lines, and thoroughly 



steady, readings are commenced. These con- 

 sist in measuring the current at regular in- 

 tervals on a tangent galvanometer or a 

 Weston ammeter and reading the inflow and 

 outflow temperatures during the time taken to 

 obtain a suitable amount of water to weigh, 



