The Chemical Relations of Water 291 



to the edge of a Bunsen flame. See that the mouth 

 of the bottle is pointing towards a wall, and not in the 

 direction of any person in the neighbourhood. When 

 the mixture of gases within the bottle reaches the 

 composition required for explosion, this will occur, 

 with the result that the cork will be ejected to a 

 considerable distance, and the flame of the Bunsen 

 burner will be extinguished. 



A mixture of hydrogen and oxygen affords a sharper 

 and more forcible explosion than the above. In this 

 case it is best to use one of the thick-walled glass 

 tubes sold for the purpose, and to dispense with the 

 cork. 



201. A simple chemical test was given for the 

 detection of the presence of water in the liquid formed 

 by the combination of hydrogen and oxygen. To 

 prove that a sample thus produced consists entirely 

 of pure water, the following points should be ob- 

 served : 



The liquid must be colourless, tasteless, and odour- 

 less. It must leave no residue on evaporation to 

 dryness. It must be of unit specific gravity. Its 

 freezing-point must be C. and its boiling-point, 

 under a pressure of 760 mm., must be 100 C. It must 

 not affect the colour of either red or blue litmus paper. 

 It must turn white copper sulphate blue. 



202. A distinctive test, in addition to those above 

 enumerated, is to be found in the peculiar behaviour 

 of water when heated from the freezing-point up- 

 ward. 



EXPERIMENT 136. Obtain a piece of lead piping 

 " compo " piping, as it is called by plumbers, will do 

 excellently about 2 ft. long. Seal one end of the 

 piping by hammering the edges together. Coil the 



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