VIII.; 



CH: 



115 



btieka, and placing an argand lamp, similar 

 ,,nder it. This is 



a sand-bath. Sometimes the 

 is placed over boiling 

 water in another vessel, which is called a 

 water-bath. >uvenient manner 



of evaporating small 

 portions of i. 

 to hold a small slip 

 of glass over the 

 flame of a spirit- 

 lamp, as in i 

 Occasionally an eva- 

 poratii. 



over a spirit- l.-tiup 

 *' l7 - by means of a pair of 



tongs (?& 18) bent near the points. These 

 tongs ; .iseful, being frequently 



Fig. IS. 



required for lifting small crucibles from 

 sand-baths, or furnaces. 



86. T. What is ignition ? 



/'. This scarcely requires explanation, 

 because nearly everybody knows that bodies 

 become luminous when exposed to a high 

 degree of heat (800 in the dark, and about 

 1000 in the daylight), and radiate caloric 

 without undergoing any great marked 

 chemical change. body looks 



red hot it is said to be ignited ; but when it 

 appears paler, or what is called white hot, 



(indetctnt. 

 T What is distillation? 



lie condensation of the vapour 

 of a liquid or solid, by means of a particu- 

 lar kind of apparatus. Forexampl* 

 preparation of alcohol and distilled waters, 

 the common still is used. The n. 



to be distilled are placed in one part called 



, which has a pipe connected with 

 : : \v end ; this pipe passes through 

 cold water contained in a tub or other 

 vessel, and as the pipe (or worm, :. 

 technically called) is coiled within the tub, 

 every part of it is exposed to 

 rating action of the eold v. 

 requires to be renewed occasionally. It 

 may be conducted on a smaller scale by 

 using a common glass retort, which may 

 be fitted with a stopper, being then called 



F>g. 19. 



tubulated, as (a) in The neck of 



the retort is inserted into n flask immersed 

 :n of cold water, and the heat main- 

 tained by a lamp (b) placed under the retort. 



ttAL (irKSTIONS ON LF.SSOX VII. 



1. How is caloric measured ? 



2. What changes may be ascribed to 

 caloric ? 



3. Give the relative conducting power 

 of bodies ? 



4. Give examples of the degrees of the 

 heat of fluid 



t by convcc 



of the bub- 

 i motion of! 

 .v are high temperatures nu 



ns of expan- 

 . vaporisation, evapora- 

 tion, ignition, and < 



III. 



ve look around us, and sec the many improvement* made in objects that are 

 daily I/: r our notice, we are struck with the great benefits conferred upon us 



by Chemistry. The luxuriant crops of the farmer, the improvements in dyeing, 

 bleaching, soap and candle-making, flax-dressing, smelting, photography and 

 dagucrreotyping, baking, brewing, distilling, calico-printing, nml sugar-refining, are 



.liar instance* of the obligations we arc under to Chcmistr t not 



