10 THE SPECIFIC HEAT OF WOOD. 



through the small opening in the tip of the arm E. After a cer- 

 tain interval of time this cup is removed and weighed again. The 

 loss of weight tells the amount of mercury which the melting of 

 the ice caused to be drawn into the calorimeter from the cup. In 

 these determinations two cups were used, one of which was attached 

 to the instrument while the other was being weighed. The cups 

 were changed every 5 or 10 minutes during the course of each 

 experiment. 



The second modification was necessitated by the use of lake ice 

 instead of newly fallen snow for maintaining the calorimeter at the 

 freezing point. It consists in suspending the calorimeter in an empty 

 glass j ar, the air in which affords good insulation between the calorim- 

 eter and the ice in which the jar is packed. The idea is due to 

 Boys. 1 The jar is provided with a vulcanite cover, H, which has holes 

 to accommodate the central tube and the side arm. Suspension is 

 effected by wrapping electrician's friction tape tightly around the 

 central tube after passing it through this cover. A rubber stopper 

 with a suitable hole is split and placed around the side arm to close 

 the opening through which the arm passes. The jar is placed in an 

 asbestos-covered galvanized-iron ice can, I, upon a block of wood, K, 

 resting in a rack, L, near the bottom of the can. The metal cover, 

 M, of the can has lour holes through which the ice may be replen- 

 ished These may be opened or closed by revolving a circular piece 

 of linoleum as shown in Plate I. The metal cover is also cut away in 

 the center and a vulcanite cover, N, fitted into the opening. Cover N 

 has suitable holes to permit the passage of the central tube and the 

 side arm of the calorimeter. The ice in the can may, if desired, be 

 replenished by removing the arm E and the metal cap M instead of by 

 simply revolving the linoleum. The can is provided with a cock, O, 

 for draining off water. 



Before starting the experiments the calorimeter was thoroughly 

 cleaned and cautiously filled with carefully prepared water of high 

 purity and with freshly distilled mercury. To start the formation of 

 ice, the calorimeter was immersed in a freezing mixture. In this way 

 frondlike crystals were formed through the whole body of water. 

 These were melted almost completely away and the water was then 

 frozen again by evaporating ether in the central tube. The ice so 

 formed was vitreous, developing a tubercular structure on thawing. 

 Ether was used to renew the ice in the calorimeter from time to time 



The flow of mercury between the calorimeter, and the weighed cup 

 was noted for a sufficient period before and after each run to furnish 

 a correction for heat lost or gained from sources other than the 

 heated wood. 



i Boys, C. V. On an addition to Bunsen's ice calorimeter. Phil. Mag. 5 ser. XXIV, pp. 214-217. 1887. 



