328 APPENDIX 



taining a little strong sulphuric acid. The farther end of the U-tube 

 communicates with a hard-glass tube, by means of a connecting 

 tube and stoppers. While the hydrogen is sweeping the air out of 

 the generator and its connections, weigh the hard-glass tube, fill 

 about half -full of copper oxide, and reweigh. After assuring yourself 

 that the air has been driven out of the generator according to Exp. 1, 

 for which purpose the delivery-tube may be temporarily connected 

 on, put the copper oxide tube in position, supporting its free end 

 with the aid of the ring-stand. Allow a minute for sweeping the air 

 out of this tube, then commence to warm it gradually with a Bunsen 

 flame. Soon steam will issue at the jet, and care must be taken to 

 keep the whole tube beyond the oxide so warm that water may not 

 condense and run back to crack the tube. Whence does this steam 

 come ? Observe what happens to the copper oxide. When the 

 change is complete, allow the tube to cool without interrupting 

 the flow of hydrogen. When cold, disconnect and reweigh. With 

 these data, calculate the ratio in which copper and oxygen combine. 



EXP. 20. Weigh a porcelain crucible without the lid, add about 

 1 gram of finely divided copper, and reweigh. Fill the crucible 

 about a quarter full of nitric acid, cover with a watch-glass, convex 

 side down, and heat very gently until the copper is dissolved; lift 

 off the watch-glass and, with a wash-bottle, rinse down into the 

 crucible the green drops that may have collected on it, and evapo- 

 rate the contents of the crucible to dryness on the stove. When 

 dry, remove with forceps to pipe-stem triangle, and heat over the 

 free flame, cautiously at first, but more strongly toward the end, 

 until all the green copper nitrate has been converted into black 

 copper oxide. Cool and weigh. The gain represents the oxygen 

 which is now combined with the original copper. Compare these 

 two weights with one another. 



ALKALI METALS 



EXP. 21. Remove the kerosene from a small piece of sodium 

 with some dry filter-paper. Drop it, in small bits, into water con- 

 tained in a porcelain crucible, keeping a lid on the latter, as long as 

 chemical action is taking place. When the sodium has disappeared, 

 take a drop of the solution upon the end of a glass rod, and touch 

 it to a piece of red litmus paper; then add hydrochloric acid, drop 



