283 ELEMENTARY GENERAL SCIENCE CHAP. 



or amorphous state are coke, and gas carbon, which result from 

 the heating of coal ; lampblack, which is the carbon deposited by 

 oils, &c., burning in an insufficient supply of oxygen ; wood 

 charcoal, &c., obtained by heating wood, in closed retorts or in 

 stacks under earth. 



Charcoal has the power of absorbing many gases, and also of 

 absorbing colouring matter, and on the latter account it is used 

 for decolorising solutions coloured by organic matter. Coal con- 

 tains large quantities of carbon, especially the harder or anthra- 

 cite coals, where the quantity may reach 94 per cent., being, 

 however, only about 65 in the brown coal or lignite. Animal 

 charcoal is really a misleading term, as the quantity of carbon 

 present is usually only about 10 or 12 per cent. , the remainder 

 being chiefly bone-ash. 



Compounds of Carbon. Carbonates. It has been already 

 stated that when carbon burns it forms an oxide, which is called 

 carbon dioxide. This is known to be a colourless gas, with a 

 very faint smell ; it may be recognised by the turbidity it 

 produces in lime-water. We must now study this gas further, 

 and investigate the change it produces in lime-water ; but before 

 doing this, it will be necessary to know something concerning 

 the latter, so that we shall first examine lime. 



Lime. Lime is a white solid, which is unchanged on heating ; 

 but which, if heated sufficiently, glows and emits a brilliant white 

 light. It is on this account employed for the production of the 

 limelight, where a small, hard cylinder of lime is strongly heated 

 in an oxy-hydrogen or oxy-coal-gas flame. 



EXPT. 291. Dissolve some lime in hydrochloric acid, and 

 evaporate the solution to dryness. Note the formation of 

 a white solid, which rapidly absorbs moisture from the air 

 and liquefies. It has been previously used in some of our 

 experiments under the name of calcium chloride. 



Try the effects of other acids, and observe that lime yields 

 with nitric acid a white soluble solid, and with sulphuric acid 

 a white insoluble solid. 



EXPT. 292. Test some wet lime with litmus papers. 

 Observe it changes red litmus to blue. 



Lime is obtained from chalk, or from limestone, the rock 

 being strongly heated in kilns, from which, after the burning, 



