Constants of Igneous Rock. 299 



7. Calorimeter. — A hollow cylindrical box, provided with a 

 hollow hinged lid, through both of which a current of cold 

 water at constant temperature continually circulated, sur- 

 rounded the calorimeter on all sides. Thus the temperature 

 of the environment was sharply given, and the correction for 

 cooling could be found and applied with accuracy. 



The calorimeter was a vessel of thin tinned sheet iron, 

 28 centim. long, 8 centim. in diameter, having a water-value 

 of 19 gramme-calories, and holding a charge of about 1200 

 grammes of water. The inside of the vessel was provided with 

 a fixed helical strip running nearly from top to bottom, and 

 was supported on a hard rubber stem. This could be actuated 

 On the outside of the outer case from below, and served as 

 a vertical axle around which the calorimeter could be rotated. 

 In this way the water within the vessel was churned, and 

 three small hard rubber rowels near the top gave steadiness 

 to the rotation. I pass the description of this apparatus 

 rapidly here, but shall recur to it in connexion with other 

 calorimetric work. 



The box or outer vessel of the calorimeter, with its pro- 

 jecting stem, was movable on a small tramway, the tracks of 

 which lay at right angles to the slides G, G (figs. 1 and 2) , 

 Thus at the proper time the lid of the box was opened and the 

 calorimeter rolled directly under the furnace. After receiving 

 the crucible the calorimeter was again rolled away and the box 

 closed, whereupon the temperature-measurements were made 

 by a sensitive thermometer inserted through a hole in the lid. 



Were I to continue work like the present I should make the 

 crucible bullet-shaped, and provided with a permanent central 

 tube much like fig. 3. The splashing of water by the drop- 

 ping crucible (an annoyance which is sometimes serious) 

 would then be to a great extent obviated. 



Results. 



8. Method of Work. — While waiting for stationary furnace 

 temperature I made the initial measurements for the cooling 

 of the calorimeter in time series. Knowing, therefore, the 

 time at which the body was dropped I also knew the tempe- 

 rature of the water into which it was dropped, accurately. 

 Similarly the three measurements for the temperature of the 

 charge had just before this been made in time series. 



The experiments showed that ten minutes after submer- 

 gence the crucible and charge might safely be considered 

 cold, for the maximum temperature of the calorimeter was 



X 2 



