92 JUNIOR GRADE SCIENCE 



platinum are malleable, but gold has more malleability than any other 

 solid. Lead can be bent and does not spring back ; its shape, after 

 bending or twisting, remains just as it was left ; it is on this account 

 said to be pliable. Substances like india-rubber which do spring back 

 to their first shape and size after being forced out of it are called 

 elastic. 



Other properties. It frequently happens that a body has some 

 special or characteristic property not included under the foregoing 

 headings, e.g. salt becomes moist when exposed in damp air. It is 

 most important to note and record all such proj>erties, as they may be 

 a means of distinguishing a body from others of a similar nature. 



Litmus. It has been found that many substances have the power 

 of altering the colour of certain vegetable colouring matters. For 

 example, a variety of cabbage which when freshly cut is a purple 

 colour changes to a reddish colour on adding vinegar to it. This 

 property has been found useful in classifying substances, and even 

 although its significance will not be understood yet, it will be used in 

 the examination of the properties of substances. The colouring matter 

 most commonly used in the laboratory is litmus, which is obtained 

 from a certain lichen, and from a kind of spurge common in South 

 Europe. When treated with water a purple solution is obtained. 

 Litmus paper is made by soaking unsized paper in the solution and 

 drjdng. The paper should always be moistened with water before 

 applying as a test. 



34. EFFECT OF HEAT ON SUBSTANCES. 



Effect of heat on substances. From the very earliest times it 

 has been customary to try the effect of heat on substances, and no 

 wonder, for of all the experiments performed, perhaps the most in- 

 teresting effects are obtained by this means. But to obtain the fullest 

 information it is most important that great care should be taken, and 

 the experiment closely watched. If the substance under examination 

 is a solid, a little of it should be placed in a test-tube and heated, using 

 a very smatt flame. Every change should be noted, and the sides of the 

 test-tube examined from time to time, when there is no further change 

 apparent as a result of gentle heating, the heat may be increased and 

 careful observations again made. The properties of a residue left 

 after heating should always be described, and if fumes are given off 

 their action on moist litmus should be noted. 



Source of heat. For the purpose of heating substances it is de- 

 sirable that we should have a flame which is not smoky. A spirit 



