156 



JUNIOR GRADE SCIENCE 



these plates are supported two glass test-tubes of equal capacity, and the 

 tubes and part of the funnel are filled with water to which has been added a 

 little sulphuric acid, as otherwise the liquid offers great resistance to the 

 passage of the electric current. The wires from a battery of three or four 

 cells are connected with the ends of the platinum wires, and as soon as the 

 connection with the batter} 1 is complete, provided there is clean metal at 

 every junction, bubbles of gas are seen to rise from each platinum plate, 

 and to ascend into the tube and displace the contained liquid. After the 

 experiment has gone on for half an hour, the gases may be tested and their 

 volumes measured. It will be found that the volume of one gas is double 

 that of the other, and that the gas of which there is the larger amount is 

 hydrogen, whilst the other is oxygen. 



Formation of water by burning hydrogen. When a jet of burning 

 hydrogen is brought into contact with a cold surface, such as a cold 

 glass, the product of combustion, the oxide of hydrogen, is condensed. 

 If after a sufficient quantity of the liquid has been collected it is 

 examined, it is found (a) to have a density of 1, (b) to freeze at C., 

 and (c) to boil at 100 C. These are the physical characteristics of 

 water and of no other substance, so we are justified in stating that 

 this liquid, formed when hydrogen burns, is water. 



From these experiments the evidence is conclusive, that hydrogen 

 and oxygen are the sole constituents of pure water, and therefore water 

 is an oxide of hydrogen. The reason for giving the inflammable gas 

 the name hydrogen, which comes from Greek words meaning " water 

 producer," is now apparent. 



77. COMPOSITION OF WATER BY WEIGHT. 



i. Action of hydrogen on heated copper oxide. Arrange an apparatus 

 like that shown in Fig. 109, in which a flask .4 for the making of hydrogen 



BLACK OXIDE 



^^-|K if 



T "*T^~^ni ** 



HYDROGEN STRONG 

 JLASK SULPHURIC ACID 



FlO. 109. When hydrogen is passed over heated oxide of copper it extracts the 

 oxygen, with which it forms water, and leaves copper behind. 



is connected with the bottle B containing strong sulphuric acid. The 

 passage of the hydrogen through the strong acid completely dries the gas. 



