326 APPENDIX 



between this weight and that of the empty glass is recorded as the 

 exact weight of the zinc used. Thoroughly clean the hydrogen 

 generator, and raise the delivery-tube in the stopper, so that its 

 end is flush with the bottom of the stopper. With the aid of your 

 wash-bottle rinse the zinc from the watch-glass into the generator- 

 bottle; arrange a bottle, as usual, in the pneumatic trough; but set 

 the gas generator in such a position that the delivery-tube is not 

 under the receiver. Pour one drop of copper sulphate into the 

 funnel, and then so much water that all the air is driven out of 

 the gas-generating apparatus. Now push the end of the delivery- 

 tube under the receiver, and pour 10-15 cc. of strong hydrochlo- 

 ric acid down the funnel tube, cautiously avoiding the carrying 

 down of air bubbles. The evolution of gas will begin at once; 

 should it slacken before the zinc has disappeared, more acid 

 may be added. (The solution of the zinc takes time, and the suc- 

 ceeding experiment may be commenced at this point.) When the 

 zinc has all been dissolved, pour enough water down the funnel to 

 drive all remaining gas from the generator into the receiver. The 

 volume of this gas is now measured and reduced to zero, after 

 ascertaining its actual temperature exactly as in Experiment 14. 

 A cubic centimeter of hydrogen, at zero, weighs approximately 

 .00009 gram; what mass of hydrogen was evolved in this experi- 

 ment ? How many parts of zinc would displace one part of hydro- 

 gen from its combination with chlorine ? 



EXP. 16. Weigh a clean and dry porcelain dish as accurately 

 as possible, add about two grams of zinc and weigh again. Pour 

 small quantities of dilute hydrochloric acid into the dish, until the 

 zinc is all dissolved; profuse addition of acid would result in loss 

 of time. When the zinc has been dissolved, evaporate carefully to 

 complete dryness on the evaporating stove, then transfer the dish 

 to a triangle supported on a ring-stand, where it is cautiously 

 heated until the zinc chloride has just melted, the burner being 

 held in the hand, and the flame being allowed to play down upon 

 the salt. As soon as the latter has melted, cool without delay. As 

 soon as the dish is cool enough to handle without burning the 

 fingers, it may be set in cold water of course without moistening 

 its contents so as to reach room temperature more quickly. Its 

 outside is at once wiped clean and dry and it is reweighed, the 



