222 ELEMENTARY GENERAL SCIENCE CHAP. 



water (i.e. some of the clear liquid which is formed if lime and 

 water be shaken together and allowed to stand. It is really 

 a solution of lime in water). Notice that it turns milky owing 

 to a white powder being diffused through the liquid. 



EXPT. 217. In the second jar burn some phosphorus con- 

 tained in the deflagrating spoon. Note the great brilliancy of 

 the combustion and the dense white fumes. Add water and 

 shake the fumes dissolve. In the solution put a little blue 

 litmus paper. Observe that it is turned red. 



EXPT. 218. Third jar. Perform a similar experiment with 

 sulphur. There are few fumes, but a strongly smelling gas is 

 obtained, also soluble, turning the blue litmus red. 



EXPT. 219. In a dry deflagrating spoon put a small piece of 

 the metal sodium, 1 light it and put it in the .fourth jar of the 

 gas. Observe the fumes formed. Dissolve these in water- and 

 try the effect of the solution on litmus paper. It does not 

 turn the blue colour to red but has exactly the reverse effect, 

 and changes the red litmus blue. Feel the water, it has a 

 peculiar soapy feel. 



EXPT. 220. Obtain a piece of iron wire (a thin steel watch 

 spring will do), and dip one end into a little melted sulphur, 

 and when the sulphur is burning place the wire in the fifth jar 

 of oxygen. Observe that the sulphur burns and also starts the 

 combustion of the iron which continues to burn with a 

 brilliant shower of sparks. After the burning has ended, 

 observe that a quantity of an insoluble solid (iron rust) has 

 been formed. 



Oxides and their Properties. In all these cases of burn- 

 ing, both the substance burnt and the oxygen disappear and 

 a new product is found. They have in fact combined to form a 

 compound which we term an oxide, the name given to the com- 

 pound of oxygen with some other element. We have noticed 

 also that the oxides differ completely in their action upon 

 litmus, for whereas some turn the blue litmus red, others 

 do exactly the reverse. Substances which, like the solution of 

 the oxide of phosphorus or sulphur, change the blue litmus red 

 are acids. 



1 Great care must be taken when using sodium, which must never be allowed 

 to touch damp materials. It is kept under naphtha until used, and should never 

 be handled with the fingers. It should be dried by blotting paper when taken 

 from the bottle and cut with a clean knife, the pieces not used being immediately 

 replaced in the bottle. 



