QQ4: PROCEEDINGS OF THE AMERICAN ACADEMY. 



The Hot Thermostat. 



As has been said, the new method requires the two solutions should 

 mix quickly and completely. To accomplish this, glass pipettes, each of 

 about 0.23 liter capacity, were constructed to contain the liquids, and 

 provided with ground-glass stoppers inside the lower ends of their bulbs, 

 as illustrated below. These stoppers could be pulled out simultane- 

 ously by means of long silver wires. The entrance tubes were made 

 of large enough bore to admit easily both the silver wires and large 

 Beckmann thermometers. The exit tubes had bores of 10 mm. and 

 therefore permitted a very rapid outflow of the liquids. These tubes 

 were bent at such an angle that, when the pipettes were in place, the 

 issuing streams met before striking the walls and floor of the receiving 

 vessel in the calorimeter. 



The method further required that the solutions in these pipettes 

 should be kept at constant temperatures, one above, the other below, 

 that of the room. The temperature of the solutions must be known to 

 within the thousandth of a degree, and the development and construction 

 of thermostats which would permit this was the main difliculty of the 

 research. 



Thermostats maintaining a temperature above that of the room, with 

 the required constancy, have been constructed by Bradley,* Geer,t and 

 others. In the present research, that of Bradley was chosen, as offering 

 the fewest difficulties of construction. The action of the thermostat 

 depends on the automatic regulation of an inflowing stream of hot water. 

 This regulation is accomplished by the alternate contraction and expan- 

 sion of a suitable liquid, inclosed in a long spiral tube, whereby a column 

 of mercury is raised or lowered, and thus made to open or close the end 

 of a capillary tube through which the warm water enters. 



The thermostat, as used here, is partially illustrated in the diagram. J 

 It differs in several respects from the instrument as described by Bradley. 



* Journ. Pliys. Chem., 6, p. 118 (1902). 



t Ibid., p. 85 (1902). 



t The following designations will assist in the understanding of the diagram: — 



B, B'. Stoppers in pipettes. N. Vertically movable supporting 



C. Calorimeter for mixing. stand for calorimeter. 



II. Hot thermostat. P, P. Pulleys for driving stirrers. 



I. Cold thermostat. S. Motor shafting. 



M. Platinum ring and tripod to pre- T^, To, T3. Thermometers. 



vent spattering. W, W^. Wires for pulling stoppers 

 M'. Perspective view of same, removed. (B, B'). 



