148 SCIENTIFIC AMUSEMENTS. 



chemical changes taking place arc largely gaseous, and mainly 

 consist of carbonic acid gas, which escapes from the lungs of the 

 animal on exhalation, and from the chimney of the fireplace. Fix 

 a piece of wax-taper or ordinary candle to a wire (fig. 41), and 

 lower the burning candle into a clean dry glass cylinder ; almost 

 immediately you will see that the glass becomes dimmed inside, 

 just as the chimney of a paraffin or moderator oil lamp, or argand 

 gas-burner becomes dimmed and bedewed for a few moments on 

 first putting it over the flame ; this is because water vapour is one 

 of the products of the chemical change going on during burning 

 (in addition to carbonic acid gas), and this vapour condenses on 

 the cool glass as dew (Expt. 43). After the candle has burnt 

 inside the cylinder for a few seconds, quickly pull it out, pour in 

 half a wine-glassful of lime-water, cover the mouth of the jar 

 with the hand (or cork it), and shake up well. If too much time 

 have not been lost, so that the hot gases from the flame may not 

 have all escaped, the lime-water will become milky, just as in the 

 two last experiments, and again for the same reason, viz., that the 

 carbonic acid gas has dissolved in the lime-water, and brought 

 about a chemical change with the lime therein present, resulting 

 in the precipitation of artificial chalk. 



Expt. 155. To dissolve Artificial Chalk in Water by means of 

 a Gas, and reproduce it by Boiling. Fill a wine glass half full of 

 clear lime-water, and then place the deli very tube of a carbon dioxide 

 generator in action inside the wine glass, so that the issuing gas 

 bubbles through the lime-water (fig. 66) ; in a few instants you 

 will see that the lime-water begins to turn milky, owing to the 

 production of artificial chalk (as in the preceding experiments). 

 Continue the stream of gas for a few minutes, and by and by you 

 will see that the milkiness disappears, so that finally you have a 

 clear fluid just as at first. This is owing to the circumstance 

 already mentioned (Expt. 73), that water strongly impregnated 

 with carbonic acid is capable of dissolving chalk and such like 

 substances ; the first portions of carbonic acid gas that dissolved in 

 the lime-water acted chemically on the lime and produced " car- 

 bonate of lime," or artificial chalk, which, being insoluble in plain 

 water, precipitated as a finely-divided solid substance ; but when 

 more carbonic acid became dissolved in the water later on, this 

 solution of carbonic acid redissolved the artificial chalk formed at 

 first, producing a somewhat different chemical substance, some- 

 times called bicarbonate of lime, and differing from " carbonate of 

 lime" in being soluble in water, instead of insoluble. Natural 

 spring-and river- waters generally contain more or less bicarbonate 

 of lime (and sometimes an analogous substance, bicarbonate of 



