THE CALORIMETER. 27 



tion of the stem is held in a vertical position by a clamp. The pail is filled 

 with water, thereby insuring a large mass of water and slow temperature 

 fluctuations, and the water is stirred by means of an electrically driven 

 turbine stirrer. 



The Beckmann thermometers, of which two are used, are so adjusted 

 that they overlap each other and thus allow a range of 8 to 14 C. without 

 resetting. For all temperatures above 14 C., the standard Eichter ther- 

 mometer can be used directly. For temperatures at 8 C. or below, a large 

 funnel filled with cracked ice is placed with the stem dipping into the water. 

 As the ice melts, the cooling effect on the large mass of water is sufficient 

 to maintain the temperature constant and compensate the heating effect of 

 the surrounding room-air. The thermometers are tapped and read as nearly 

 simultaneously as possible. A number of readings are taken at each point 

 and the average readings used in the calculations. Making due allowance 

 for the corrections on the Beckmann thermometers, the temperature differ- 

 ences can be determined to less than 0.01 C. The data obtained from the 

 calibrations are therefore used for comparison and a table of corrections is 

 prepared for each set of thermometers used. It is especially important that 

 these thermometers be compared among themselves with great accuracy, 

 since as used in the calorimeter the temperature of the ingoing water is 

 measured on one thermometer and the temperature of the outgoing water 

 on another. 



Thermometers of this type are extremely fragile. The long angle with 

 an arm some 35 centimeters in length makes it difficult to handle them 

 without breakage, but they are extremely sensitive and accurate and have 

 given great satisfaction. The construction of the bulb is such, however, 

 that the slightest pressure on it raises the column of mercury very percep- 

 tibly, and hence it is important in practical use to note the influence of the 

 pressure of the water upon the bulbs and make corrections therefor. The 

 influence of such pressure upon thermometers used in an apparatus of this 

 type was first pointed out by Armsby,* and with high rates of flow, amount- 

 ing to 1 liter or more per minute, there may be a correction on these ther- 

 mometers amounting to several hundredths of a degree. We have found 

 that, as installed at present, with a rate of flow of less than 400 cubic cen- 

 timeters per minute, there is no correction for water pressure. 



In installing a thermometer it is of the greatest importance that there 

 be no pressure against the side of the tube through which the thermometer 

 is inserted. The slightest pressure will cause considerable rise in the mer- 

 cury column. Special precautions must also be taken to insulate the tube 

 through which the water passes, as the passage of the water along the tube 

 does not insure ordinarily a thorough mixing, and by moving the thermom- 



* Armsby: U. S. Dept. of Agr., Bureau of Animal Industry Bull. 51, p 34 

 (1903.) 



