406 



Dr. A. Gait on the Heat of Combination or 



sides, two oval-shaped openings into the globe. 



glas 



The 



a certain 

 bored in 



selected. 

 that the 



Fisr. 1. 



tube was free to move np and down 

 distance through one of two holes 

 a short common cork, specially 

 Particular care being taken to see 

 globe was clean and dry, it was 

 drawn down from the cork about 6 centims. 

 and the cork was then fixed in a clamp. 

 The filings (*5 gramme was the quantity gene- 

 rally used in the experiments) were then most 

 carefully inserted into the bottom of the globe 

 through one of the openings, and the globe 

 was then drawn up close to the cork. Through 

 the other hole in the cork a thin short-range 

 thermometer, whose marked divisions corre- 

 spond to 0*05° O.j was passed. The cork, 

 carrying the globe and attached tube and the 

 thermometer, was then carefully fixed in the 

 neck of a small flask of thin glass containing 

 a definite quantity of nitric acid of density 

 P360 at 15° C. To avoid possible heating 

 effects from the hand the rim of the flask was 

 not held by the ringers ; instead the rim was 

 placed in a slit made near the bottom of each 

 hinged limb of a small wooden tripod I or 5 

 inches long, a rubber band round this part 

 tightening the grip. 



Holding the flask by the top of the tripod, 

 it was gently shaken so as to give the acid a 

 rotating motion; in this way the flask and 

 acid soon attained a uniform and steady tem- 

 perature which was usually about that of the 

 room, and it was carefully noted.- The globe 

 containing the filings was now plunged to 

 near the bottom of the flask by quickly 

 pushing down the glass tube to which it was 

 attached, the downward movement being- 

 arrested by the knob on the tube. 



If the method of pouring the acid on the filings or of 

 dropping the tilings into the acid had been adopted, a violent 

 action would have occurred, and it would not have been 

 possible to prevent the loss of heat due to escape of fumes. 

 But the plan adopted effectually got rid of this difficulty by 

 the almost instantaneous projection of the globe containing 

 the filings to the bottom of the acid*. It was interesting to 



* Andrews, • Scientific Papers,' p. 214: — "Every chemist is familiar 



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