COMBUSTION IX OXYGEN. 201 



place at least two vaporous or gaseous products, water vapour and 

 carbon dioxide gas. If a candle be burnt under such circum- 

 stances that the oxygen of the air used in burning can be weighed, 

 and if this weight be added to the weight of the candle which has 

 disappeared, it will be found that the total weight of materials 

 undergoing chemical change is exactly equal to the weight of the 

 products formed by the change, viz., the water and carbon dioxide 

 gas. To carry out this experiment accurately, however, requires 

 much skill and a variety of complex apparatus. 



Expt. 224. To burn Charcoal in Oxygen. Collect a jar of 

 oxygen (Expt. 177) ; fix a piece of hard charcoal (preferably that 

 made from boxwood) to the end of a wire by coiling the wire 

 round one end of the charcoal (copper bell wire answers well). 

 Light the charcoal by holding it in a flame, so that it is glowing 

 and burning at the far end, and then plunge it into the jar of 

 oxygen ; the combustion will be greatly accelerated, and the 

 charcoal will burn and " scintillate " or throw out sparks vigorously. 

 After the combustion is over let the jar stand awhile to cool (so 

 as to avoid cracking it if the sides are hot), with a cork in the 

 mouth or covered over with a saucer^ &c., then pour in some lime- 

 water and shake up ; the limewater will become milky, showing 

 that carbon dioxide has been formed by the combustion, i.e., the 

 solid charcoal has become changed into an invisible gas. 



Precisely the same result occurs when charcoal is burnt in air ; 

 but in this case the rate of chemical action is much slower, and 

 one result of this difference is that a different gas, called carbon 

 monoxide (Expt. 219), is often produced as well as carbon dioxide. 

 As carbon monoxide is poisonous when inhaled, charcoal fires in 

 badly ventilated apartments are somewhat dangerous from this cause. 



Expt. 225. To burn Sulphur in Oxygen. Fill a bell jar with 

 oxygen, the top having an orifice fitted with a stopper or cork. 

 Through this introduce a deflagrating ladle with a little burning- 

 sulphur in the bowl (fig. 79); the sulphur will burn much more 

 brilliantly in the oxygen, producing the same suffocating gas 

 (sulphur dioxide) formed when it burns in air. After the com- 

 bustion is over shake up a little distilled water in the jar; it will 

 dissolve some of the sulphur dioxide, forming a solution of sul- 

 phurous acid capable of discharging the blue colour given to starch 

 paste by a drop of solution of iodine (Expt. 164). 



Expt. 226. To produce a stream of Blue Fire. Melt some 

 sulphur in an iron ladle covered over with a lid of metal or 

 earthenware (a bit of tile, the round bottom of a canister, &c.) and 

 continue the heat until the sulphur is hot enough to burn. From 

 an open window above a stone pavement or gravel walk, &c., pour 



