BURNING WATCH SPRINGS. 205 



they absorb oxygen, a chemical action being set up sufficiently 

 energetic to cause "combustion." In all cases, the action is far 

 more energetic in pure oxygen than in ordinary air. 



Expt. 233. To burn " a Steel Watchspring in Oxygen. 

 Obtain some old watchsprings from a watchmaker, and straighten 

 them by holding them in a flame and then bending with pliers 

 whilst red hot ; tie two or three straightened springs together in 

 several places with thread, and warm one end of the bundle and 

 then dip it into flowers of sulphur ; a little of the sulphur will 

 stick to the steel, tipping it something like a match ; light the 

 sulphur tip at a candle and then plunge the bundle in a jar of 

 oxygen ; the heat given out by the burning sulphur will be 

 sufficient to light the steel, which will burn brilliantly throwing 

 out " scintillations " or sparks on all directions. An oxide of 

 iron is thus formed which will drop down in molten globules, 

 which will usually be hot enough to melt their way into the glass 

 if a bottle of oxygen be used, or into the glaze of the saucer if a 

 bell jar and earthenware saucer be employed, even though there 

 be a layer of water half an inch deep at the bottom. 



In the preceding experiment the result of the chemical actions tak- 

 ing place between the solid and gas employed was to produce a solid 

 product, viz., the oxides of magnesium, iron, and zinc respectively. 

 If the experiment is made in such a way that the whole of the solid 

 product formed can be collected and weighed, it is always found 

 that the weight of the oxide formed is greater than that of the sub- 

 stance burnt, the excess of weight in the product being exactly 

 equal to the weight of the oxygen fixed by the metal during 

 the chemical change ; in other words, the weight of the materials 

 employed is exactly equal to the weight of the product formed, so 

 that on the whole there is neither gain nor loss of weight during 

 a chemical change, but only an alteration in the form and pro- 

 perties of the substances used. This is an in-variable law in all 

 chemical changes, whether the products and materials are solid, 

 liquid, or gaseous. 



Expt. 234. To burn Phosphorus in Oxygen. Cut under 

 water a small piece of solid phosphorus about the size of a pea, 

 dry it with blotting paper, and place it in the bowl of a deflagrating 

 ladle (not hot from any previous experiment, and not wet) ; touch 

 the phosphorus with a hot wire and it will immediately take fire ; 

 introduce the ladle and burning phosphorus into a jar of oxygen, 

 and a most brilliant light will be produced. 



Caution. Phosphorus is a highly inflammable waxy solid 

 which requires to be kept under water, and is best cut into pieces 

 also under cold water ; it ignites easily on slightly warming, and 



