6 



Prof. T. S. Humpidge. 



of cold water flows. In this way the chamber (B) into which the 

 calorimeter has to be run is kept quite cool. A double tin screen 

 (not shown in the figure) serves also to prevent the calorimeter 

 from receiving extraneous heat. The whole operation of trans- 

 ferring the substance from the heater to the calorimeter can be 

 performed in less than two seconds, and the gain of heat by the 

 calorimeter during this period cannot be measured. In a series of 

 blank experiments it was found that when the calorimeter remained 

 under the heater (at 300°) for 15 seconds, the thermometer £ 4 rose 

 j-i-Q . The temperature of the substance in the heater was measured 

 by three delicate thermometers from Greissler. Their fixed points 

 were determined in ice, water, naphthalene, and benzophenone, but 

 they were not calibrated. The gas supply for this heater was regu- 

 lated by three regulators made by Griroud, of Paris, burning 60, 80, 

 and 110 litres of gas per hour, and giving temperatures of 200°, 240°, 

 and 310° respectively. With these regulators the temperature could 

 be kept constant to about provided there were no great fluctua- 

 tions in the gas pressure. I have sadly felt the need of a good regu- 

 lator for high temperatures.* The suspension of the substance (S) in 

 the heater was by a small pair of tongs, made so that the jaws open 

 when the arms are closed. The tongs with the substance are sup- 

 ported by a thin platinum wire which is attached, outside the heater, 

 to a thread passing over pulleys and fastened to a catch (K). When 

 this catch is released the tongs fall by their own weight until they 

 reach the ring X ; this brings the arms closer together, and the sub- 

 stance drops into the calorimeter. The connexions are so arranged 

 that when the calorimeter is run under the heater, the lid of the 

 calorimeter casing is first opened, then the slider under the heater, 

 and finally the catch is released, and the substance falls. As the 

 calorimeter returns the two sliders are again closed. 



The liquid used in the calorimeter was purified turpentine, of 

 which the specific was determined as follows : — 



(i.) By the method of mixtures, using metallic magnesium, of 

 which the specific had been found to be c 1 1 ( jj ) =0"2442. This gave for 

 the turpentine A; 10 =0 , 4146.f 



(ii.) By Andrews' calorifierj the mean of two series of experiments 

 gave & 10 =0'4103. 



(iii.) By Pfaundler's apparatus§ (Joule's principle), in which equal 

 weights of water and turpentine contained in two similar calorimeters 

 are heated by two platinum wires of equal resistance, through which 



* I am much indebted to Professor L. Meyer for advice and assistance in the 

 construction of these two heaters. 



f For details of these and the following experiments, see Appendix C. 

 + " Ann. Chim. et Phys." [3], xiv, 92. 

 § " Wien. Akad. Ber.," lix. 



