146 



NON-METALS AND THEIR COMBINATIONS. 



After having ascertained that all atmospheric air has been expelled from the 

 flask, the gas may be ignited directly at the mouth of the delivery tube, after 

 moving it out of the water. 



Continue to add acid until the zinc is nearly all dissolved, remembering that 

 the action is not instantaneous and some time should be allowed before the 

 next addition of acid. Warming the flask will hasten the action, and as long 

 as small gas-bubbles arise from the zinc, action is not over. Avoid adding too 

 much acid, but if there is an excess, it may be removed by adding more zinc. 

 Note the dark particles floating in the liquid and the bad odor of the hydrogen, 

 which are due to the impurities in the zinc. Finally, filter the solution (by 

 folding a circle of filter-paper twice at right angles through the center, open- 

 ing it into a cone, placing in a funnel, wetting with water, and pouring the 

 solution into it), and evaporate it to about one-third its volume at a tempera- 

 ture a little below boiling. Set aside a day to cool and crystallize. If no 

 crystals appear, evaporate further, The crystals are zinc sulphate, the same 



FIG. 38. 



Apparatus for generating hydrogen. 



as is used in medicine. They are an illustration of the formation of a salt by 

 the action of an add on a metal. Filter the crystals and examine them care- 

 fully. Expose some to the air for several days. Does any change take place ? 

 Save the crystals for Experiment 37. 



Experiment 4. Pour into a test-tube of not less than 50 c.c. capacity, 5 c.c. of 

 hydrochloric acid, fill up with water, close the tube with the thumb and set it 

 inverted into a porcelain dish partly filled with water. Weigh of metallic 

 zinc 0.04 gramme, and bring it quickly under the mouth of the test-tube, so 

 that the generated hydrogen rises in the tube. Prepare a second tube in the 

 same manner, and introduce 0.04 gramme of metallic magnesium. In case the 

 decomposition of the acids by the metals should proceed too slowly, a little 

 more acid may be poured into the dishes. 



When the metals are completely dissolved it will be seen that the volumes 

 of hydrogen in the two tubes bear a relation to each other of about 10 to 27. 



In order to measure the gas volumes as correctly as the simple apparatus 

 permits, the tubes should be transferred to a large beaker filled with cold water, 



