BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 561. sists of two metallic vessels, 



placed one within the other, 

 with a space between them ; 

 each vessel being furnished 

 with a stop -cock at bottom. 

 The vessels have each a closely 

 fitting cover, which covers 

 have also a space between 

 them. If the space between 

 the vessels be filled with melt- 

 ing ice or snow, this will gradu- 

 ally melt away, and the water 

 formed run out by the cock, A ; 

 by this arrangement the tem- 

 perature of the inner vessel will 

 always be that of the freezing point, or the thawing point, 

 which is the same thing. A third vessel, B, is now placed 

 within the second, and the space between the two inner ves- 

 sels also filled with melting ice. It is evident that the ice 

 contained in the second vessel, cannot be affected by the 

 external air ; there-fore, when a heated substance is placed 

 within B, it will melt a certain proportion of the inner 

 stratum of ice, the quantity of which melted, and conse- 

 quently the quantity of heat parted with, to lower it to 32, 

 is ascertained by the quantity of water which flows out 

 of c. PriceJS.OO. 



Fig. 562. 



Reflectors, d*c., for Radiation of Heat. (Fig. 562.) 

 Reflectors arranged for the radiation of heat, commonly 

 called Pictet's Apparatus, consist of two concave reflectors, 

 or mirrors of brass, or planished tin, twelve inches or more 

 in diameter, and mounted on mahogany stands, having rods, 



