154 JUNIOR GRADE SCIENCE 



acid (one part acid to four parts water). The method is described 

 in the experimental work. Owing to the slight solubility of hydrogen 

 in water, it can be collected in the same way as oxygen over the pneu- 

 matic trough. If, when the chemical action in the flask has completely 

 stopped, the liquid is filtered from the still undissolved zinc, as previously 



FIG. 106. Crystals of zinc sulphate. 



explained, and then partially evaporated in a basin and afterwards 

 allowed to crystallise, a quantity of clear colourless crystals is formed. 

 These crystals melt if heated in a tube, give off water, and leave a white 

 powder. They consist of a compound formed from the /inc and part 

 of the sulphuric acid and known as zinc sulphate (Fig. 106). 



We may therefore state that sulphuric acid a-iid zinc form hydrogen 

 and zinc sulphate. Or, the same fact may be expressed in another way : 



when 

 SULPHURIC 'tcfcod ,Zi\c 



with 



Properties of hydrogen. Having now a means of obtaining hydrogen 

 in considerable quantity, it can be observed that it is a colourless, odour- 

 less gas, considerably lighter than air ; it burns, but does not support 

 combustion, and it forms a highly explosive mixture when mixed with 

 air. It is now necessary to obtain and examine the compound which 

 is produced by the burning of hydrogen that is, the oxide of hydrogen. 



76. EXAMINATION OF THE LIQUID WHICH IS FORMED 

 WHEN HYDROGEN BURNS. 



i. Liquid formed by burning hydrogen. (a) Arrange a flask as before 

 for the production of hydrogen. Pass the gas through a tube containing 

 chloride of calcium in order to dry it thoroughly. Allow it to burn under 



