CARBON AND SOME OF ITS COMPOUNDS 173 



would lose if heated strongly, seeing that a given mass of chalk loses 

 the amount noticed. 



Percentage loss of mass of chalk when strongly heated. 

 Whenever chalk or limestone no matter from what locality is 

 strongly heated in a kiln or in a laboratory furnace, it loses about 



BEFORE BURNING AFTER BURNING 



100 IBS OF CHALK 56 IBS OF LIME 



FIG. 118. When 100 Ibs. of chalk are heated, 56 Ibs. of lime are produced. 



44 per cent, of its mass, as shown in the above experiment. That is 

 to say, 100 grams, or pounds, or tons, of chalk lose 44 grams, or pounds, 

 or tons, in mass when strongly heated. But it has been learnt before, 

 that this loss in mass is due to the escape of a gas which puts out flames 

 and is called carbon dioxide, so that when 100 grams of chalk are 

 strongly heated, 44 grams of the gas, carbon dioxide, are driven out 

 and 56 grams of quicklime are left behind. 



83. QUANTITATIVE STUDY OF THE ACTION OF 

 ACIDS ON CHALK. 



i. Composition of chalk. Place a few small pieces of chalk in a test- 

 tube. Add dilute hydrochloric acid until the effervescence, due to the 

 production of carbon dioxide, ceas.es (Expt. 81 i.). Filter the solution 

 remaining in the test-tube and evaporate it. Notice the substance left; 

 it is not chalk, but calcium chloride. 



ii. Solution of lime in acids. 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 experiments under the name of calcium chloride. 



iii. Loss of mass when an acid acts on chalk. Into a flask A (Fig. 

 119) fitted with india-rubber stopper and tubes, as shown, pour some dilute 

 hydrochloric acid, and weigh the flask with the contained acid. Weigh 

 a small test-tube B (i) empty, (ii) with some chalk in it. Place this in the 

 flask, taking care not to allow the acid to reach the inside of the tube. 

 Kf place the cork and shake the flask so as to allow the acid and chalk to 

 come in contact with one another. The gas (carbon dioxide) formed 



