APPARATUS AND METHODS. 11 



INTERPRETING THE INDICATIONS. 



In order to interpret the changes in weight observed, it is necessary 

 to know the weight of mercury drawn in the calorimeter when one 

 calorie of heat is introduced. This amount can be calculated directly 

 from physical data, and can also be determined experimentally. 

 The method of calculation from physical data was pointed out by 

 Bunsen, and is extremely simple. Let W be the weight in grams 

 of mercury drawn in for one calorie: then 



where Vi is the specific volume of ice, V w is the specific volume of 

 water, D m is the density of mercury, and H is the latent heat of fusion 

 of ice, all at C. 



But, since neither Vi nor H is known with sufficient accuracy, 

 this calculation fails to give reliable results. Bunsen l actually 

 calibrated his calorimeter by introducing a definite weight of water 

 at 100 C. and noting the change which resulted. He then determined 

 Vi in a separate experiment, and used the formula to calculate H. 

 He found that the introduction of one mean calorie caused a con- 

 traction of 0.001133 cubic centimeter, which is the volume occupied 

 by 15.41 milligrams of mercury. 



Schuller and Wartha 2 repeated this calibration, using the same 

 method: They found, as the mean of five very concordant results, 

 that the introduction of one mean calorie caused the inflow of 15.442 

 milligrams of mercury. An accuracy greater than one-tenth of 1 per 

 cent is claimed for this value, and it is generally recognized as the 

 most reliable that has been secured. Velten 3 found 15.47 for this 

 value. 



Dieterici 4 accepted the value obtained by Schuller and Wartha, 

 after discarding the last place as insignificant, and pointed out that 

 it was the mean of the values obtained by Bunsen and by Velten. 

 He accepted and used this result without checking it. 



Von Than, 5 Nessen, 6 and Chappuis 7 contributed nothing to the 

 knowledge of this factor. Mond, Ramsay, and Shields 8 followed 



i Bunsen, R.; 1. c. 



* Schuller, A., and Wartha, V. Calorimetrische Untersuchungen. Wied, Ann. II, pp. 359-393. 1877. 

 Velten, A. W. Das specifische Warme des Wassers. Wied. Ann. XXI, 31-64. 1884. 

 Dieterici, C. Ueber eine Bestimmung des mechanischen Aequivalentes der Warme und iiber die 

 specifische Warme des Wassers. Wied. Ann. XXXIII, pp. 417-444. 1888. 



6 V. Than, C. Die Verbrennungswarme des Knallgases in geschlossenen Gefassen. X, Ber. d. deutschen 

 chem. Gesellschaft, pp. 947, 952. 1877. Thermoschemische Untersuchungen. Wied. Ann. XIII, pp. 84- 

 105. 1881. 



Nessen, F. Ueber die specifische Warme des Wassers. Wied. Ann. XVIII, pp. 369-386. 1883. 



7 Chappuis, J. Sur les chaleurs latentes de vaporisation de qulques substances tres volatiles. Ann. de 

 Chem. et Phys. 6 ser. XV, pp. 498-517. 1888. 



8 Mond, L., Ramsay, W., und Shields, J. Ueber die Okklusion von Sauerstoff und Wasserstoff durch 

 Platinschwarz. II. Zeitsch.fiir Phys. Chemie, XXV, pp. 657-685. 1898. 



