APPENDIX 331 



EXP. 34. Weigh about a gram of gypsum carefully in a porce- 

 lain crucible, heat strongly, cool and reweigh. Heat a second time, 

 to see whether a second loss of weight occurs. This loss of weight 

 is due to the driving off of water of crystallization. How much 

 water was present in the natural gypsum ? Shake the residue into 

 a watch-glass, stir up with a few drops of water, and observe the 

 result. 



EXP. 35. Prepare three test-tubes containing calcium chloride, 

 strontium chloride, and barium chloride, respectively, each diluted 

 with about four times their volume of water. To these three test 

 tubes add equal quantities of calcium sulphate solutions (about 25 

 drops for each). Observe and discuss results. 



ZINC, CADMIUM, AND MAGNESIUM 



Hydrogen sulphide, which is used in this exercise, may be obtained from taps in 

 the room set apart for the purpose. The student must affix his own glass 

 tube to the rubber hose set on these taps. As the number of outlets is limited, 

 considerable time will be saved if the students will prepare the solutions 

 required for the following four experiments at one time, and carry the test 

 tubes on a rack into the sulphuretted hydrogen room. If the gas is passed into 

 the test tubes in the prescribed order, the glass delivery tube need not be 

 cleansed between the experiments. It should finally be cleaned with a little 

 strong acid. 



EXP. 36. Dilute about 5 cc. of zinc chloride with an equal 

 amount of water. If the solution is acid, neutralize as nearly as 

 possible with ammonium hydroxide. Treat with hydrogen sulphide. 



EXP. 37. Acidify a similar solution of zinc chloride with hydro- 

 chloric acid and treat with hydrogen sulphide. 



EXP. 38. Dilute about 5 cc. of cadmium chloride solution to 

 one-half its original strength. Acidify with hydrochloric acid and 

 treat with hydrogen sulphide. 



EXP. 39. Mix approximately equal volumes of the solutions of 

 zinc and cadmium chlorides. Dilute somewhat, acidify with hydro- 

 chloric acid and pass hydrogen sulphide into the mixture until no 

 more precipitate forms. Separate the precipitate from the solution 

 by filtration, allowing the liquid to run into an evaporating dish. 

 Set the latter upon the evaporating stove in your fume closet 

 and concentrate to dryness. Meanwhile wash the precipitate once 



