638 TRANS. ST. LOUIS ACAD. SCIENCE. 



demann. As this method has not hitherto been published, I asked 

 and obtained permission of its author to describe it here. 



The method is based on the following principle: — A known 

 quantity of pure mercury, heated to a known temperature, is run 

 into a known quantity of the liquid substance whose specific heat 

 it is desired to determine, and whose initial and final tempera- 

 tures are observed. Knowing the specific heat of mercury, we 

 have thus all data for our determination. 



Herewith I give the detail of the apparatus. By means of 

 steam, generated in a boiler (see Fig. I.), the cast-iron vessel .4, 

 which contains the mercury, entirely surrounded by the brass. 

 mantle B, can be heated to a very constant temperature closely 

 approaching 100° C. The brass mantle consists of a lid (Z)r 

 which is first traversed by the steam, and which is perforated by 

 canals to admit to the cast-iron vessel an iron stirrer and a ther- 

 mometer. Thus the mercury can be stirred and its temperature 

 very exactly determined. From the lid the steam passes to the 

 lower part of the mantle B through tubing a, and then into a 

 condenser. The cast-iron vessel is large enough to hold from 2 to 

 3 klgs. of pure mercury, which can be tapped by means of the 

 stopcock S; below this stopcock there is a metal plate perforated 

 by many small holes ; by this means the mercury is tapped into- 

 the calorimeter in a shower and loses its heat almost instantly, at 

 the same time stirring the liquid quite thoroughly. The losing of 

 the heat during the fall is mostly avoided by the walls at m and n^ 

 that are part of the brass mantle. To screen the calorimeter from 

 the radiation of the brass mantle the hollow circular brass plate 

 /?, traversed by water of the temperature of the room, is inter- 

 posed. A little screen just below the opening is thrown aside auto- 

 matically at the moment when the stopcock is turned. A vertical 

 screen (^) preserves the calorimeter from the radiations before 

 and after the experiment. 



The method of procedure in an examination is the following : 

 The mercury is first raised to the constant temperature by the 

 steam, an operation requiring but a very short time. The calor- 

 imeter has weighed out in it the substance to be examined, and 

 is then placed on cork supports within a mantle (J/), which in 

 turu rests on the slide F. Either a thermometer bent at right 

 angles, or one inserted through the side of the calorimeter, may 



