CHEMICAL APPARATUS. 69 



air, and permits the fluid to rise. This instrument is not 

 capable of measuring variations of temperature through any 

 very considerable range, and it is liable to other objections ; 

 yet, notwithstanding, it is still applicable, from its great de- 

 licacy, to many purposes. 



Fig. 504. Fig. 505. Price ' with Aiding scale (Fig. 505) $1 .00. 

 " without, " $0.50. 



" tube only (Fig. 504) - $0.19. 



o 



Fig. 506. 



Fig. 507. 



Boyle's Thermometer. (Fig. 506, as above.) One of the 

 earlier, and consequently more imperfect thermometers. It 

 is, however, superior to any previously in use. It is simply 

 a glass tube, open at both ends ; one end cemented into a 

 bottle half full of some liquid ; the cement preventing any 

 escape of the air which is above the liquid. Any increase 

 of temperature rarifies the air, and drives the liquid further 

 up the tube ; on the contrary, a decrease of temperature 

 occasions it to subside. There was no scale attached to this 

 thermometer. 



Evaporating Dishes. (Fig. 507, as above.) These are 

 best made of Wedgewood's ware, and are employed in the 

 evaporation of solutions, so as to enable the dissolved body 

 to assume the crystalline form. These dishes are made in 

 such a manner, that a large surface of the liquid to be evapo- 

 rated, may be exposed to the air at one time. They usually 

 have a lip for the convenient pouring off of any remaining 

 liquid, after the crystals are formed on the bottom of the 

 dish. They are made of a variety of sizes, usually from 

 two to seven inches in diameter. Price, 25cts. to 63cts. 



