140 JUNIOR GRADE SCIENCE 



with a tightly fitting rubber stopper. Warm the flask very gently, avoiding 

 the spot where the phosphorus lies. As soon as the phosphorus is ignited 

 discontinue heating. When the flask is cool, weigh it. Remove the stopper 

 and weigh again. 



Indestructibility of matter. Although in many experiments there 

 appears at first sight to be a loss of the materials employed ; it is 

 found that when care is taken to collect and preserve all the products 

 that the total mass of the substances used remains unaltered through- 

 out an experiment. When a small piece of phosphorus is burned in 

 a closed flask, it is found the mass of the flask and contents is the 

 same before and aiter the experiment. When oir is admitted to the 

 flask after the burning there is a decided increase in mass. During 

 the process of burning a portion of the air is used up in forming phos- 

 phorus oxide, but the amount of mass lost by the air is exactly counter- 

 balanced by the gain in mass of the phosphorus (Section 56, iv.). 

 In the same -manner, in every case it can be shown than an apparent 

 loss of mass in one substance is compensated for by an increase in 

 mass of something else. 



This fact is generally stated as follows : Matter cannot be created or 

 destroyed, although it may be changed from one form to another; or, 

 from the chemical point of view, it may be put in a slightly different 

 way although the meaning is the same. The quantity of matter which 

 takes part in a chemical reaction remains unaltered throughout. This 

 statement is known as the "Law of the Indestructibility of matter." 



QUESTIONS ON CHAPTER XXII. 



106. What do you understand by an element ? Water was formerly 

 regarded as an element on what grounds ? What experimental evidence 

 can you quote to show that this view was incorrect ? Classify the following 

 substances into elements and compounds : lime, copper, mercury, litharge, 

 salt, nitre. 



107. Tabulate the properties of alum, sulphur and iron rust according to 

 the following scheme : 



(a) Whether element or compound. 



(6) Effect of water. 



(d) Possibility of obtaining the crystalline forms. 



(d) Effect of strongly heating. 



108. What do you understand by a law ? Illustrate your answer by 

 examples in both Physics and Chemistry. 



109. The older chemists asserted that there were only four elements, viz. 

 earth, air, fire and water. How would you proceed to show that the above 

 are not elements in the chemical sense of the word ? 



