8 THE SPECIFIC HEAT OF WOOD. 



between the initial and final temperatures of the wood in degrees 

 centigrade, and by its weight in grams, gives the mean specific heat 

 of the wood through the range of temperature involved. 



THE OVEN. 



A copper drying oven, liquid jacketed, was used to bring the wood 

 to the oven-dry condition and also to warm it before its introduction 

 into the calorimeter. The oven was heated by gas. The jacket was 

 filled with a mixture of water and glycerine, in about the proportion 

 of 3 to 5, by volume. This mixture, when boiling, gave a temperature 

 inside the oven from 5 to 10 above the boiling point of water. A 

 reflux condenser maintained the constancy of the mixture in the 

 jacket. The oven is shown in Plate I (frontispiece). 



The temperature inside the oven was determined by means of an 

 ordinary mercury-in-glass thermometer inserted through the top of 

 the oven, with its bulb free in the air, near the center of the oven. 

 This thermometer was calibrated in the oven against a carefully 

 calibrated thermometer of the same type, and was read to twentieths 

 of a degree centigrade. 



THE CALORIMETER. 



Bunsen's ice calorimeter, 1 in a slightly modified form, was used 

 for measuring heat. The chief advantage of this calorimeter is that 

 no radiation correction is necessary, because the introduction of 

 heat is not indicated by a rise in temperature. This feature is par- 

 ticularly advantageous, since wood cools slowly. 



The ice calorimeter depends for its indications upon the difference 

 between the specific volumes of ice and water at the freezing point. 

 It consists essentially of a mercury-sealed reservoir of water. After 

 the water has been partially frozen the calorimeter is packed in melt- 

 ing ice, which prevents either freezing or thawing. The introduction 

 of a hot body supplies heat and melts a portion of the ice, so that the 

 amount of ice in the reservoir is diminished and the amount of water 

 is increased while both remain at the melting point of ice. The heat 

 produces no rise in temperature, but is entirely consumed in melting 

 a portion of the ice. Since ice occupies 9 per cent more volume than 

 does the water from which it is frozen, the melting of a portion of the 

 ice in the reservoir causes the contents to contract. The measure- 

 ment of this contraction indicates the amount of heat introduced. 



The calorimeter used is shown in section in figure 1. The long 

 glass tube at the axis is provided for the reception of the heated wood ; 

 its lower end, A, projects into the cylindrical jacket B. The upper 

 end of this jacket is sealed to the tube, and the lower end opens into 



i Bunsen, R. Calorimetrische Untersuchungen. Pogg. Ann. CXLI, pp. 1-31, 1870. 



