CARBON, SILICON, BO RON. 181 



Examine the gas for its high specific gravity by pouring it from one vessel 

 into another ; for its power of extinguishing flames, by mixing it with an equal 

 volume of air, which mixture will be found not to support the combustion of 

 a taper notwithstanding that oxygen is contained in it. Add to one portion of 

 the collected gas some lime-water, shake it, and notice that it becomes turbid. 

 Blow air exhaled from the lungs through a glass tube into lime-water, and 

 notice that it also turns turbid. 



Continue to pass the gas through the turbid liquid, and notice that it becomes 

 clear in consequence of the dissolving action of carbonic acid water on calcium 

 carbonate. On heating the solution carbon dioxide is expelled and calcium 

 carbonate is reprecipitated. (So-called " hard " waters often contain calcium 

 carbonate dissolved by carbonic acid. On heating these hard waters they 

 become "soft," because the dissolved carbonate is precipitated.) 



If marble has been used for the experiment, neutralize the liquid in the flask, 

 if acid, by adding more marble until action ceases, filter, and evaporate it in a 

 dish to dry ness. The solid residue is a salt, calcium chloride. Expose some 

 of it to the air for a long time and note that it absorbs moisture or deliquesces. 

 What method of salt formation is illustrated by this experiment? 



If sodium carbonate has been used, neutralize the liquid by adding acid 

 or carbonate, as may be required, filter, and evaporate it to dryness. Taste 

 the residue. What is it ? Taste also sodium carbonate and the acid. 



Carbon dioxide is a colorless, odorless gas, having a faintly acid 

 taste. By a pressure of 38 atmospheres, at a temperature of C. 

 (32 F.), carbon dioxide is converted into a colorless liquid, which by 

 intense cold ( 79 C., 110 F.) may be converted into a white, 

 solid, crystalline, snow-like substance. The specific gravity of carbon 

 dioxide is 1.529 ; it is consequently about one-half heavier than 

 atmospheric air. One liter at C. and 760 mm. pressure weighs 

 1.977 grammes. 



Cold water absorbs at the ordinary pressure about its own volume 

 of carbon dioxide, but the solubility is increased one volume for every 

 increase of one atmosphere in pressure (soda water). 



Carbon dioxide is not combustible, and not a supporter of combus- 

 tion ; on the contrary, it has a decided tendency to extinguish flames, 

 air containing one-tenth of its volume of carbon dioxide being unable 

 to support the combustion of a candle. While not poisonous when 

 taken into the stomach, carbon dioxide acts indirectly as a poison 

 when inhaled, because it cannot support respiration, and prevents, 

 moreover, the proper exchange between the carbon dioxide of the 

 blood and the oxygen of the atmospheric air. 



Common atmospheric air contains about 4 volumes of carbon 

 dioxide in 10,000 of air, or 0.04 per cent. In the process of respira- 

 tion this air is inhaled, and a portion of the oxygen is absorbed in 

 the lungs by the blood, which conveys it to the different portions of the 



