The Life and Science of Percy Julian
Activities and Readings
3B (Lab Activity)

Repeating Experiments


In the 1920s many chemists in Europe were studying chemicals found in plants and trying to figure out how to mimic nature and make, or synthesize, these substances in the lab. Ernst Späth was among the leaders in this field. Späth had synthesized nicotine, found in the tobacco plant, for the first time. We now know nicotine as the substance that makes cigarettes addictive, but in the 1920s chemists were just beginning to study substances like this.

Julian had read about Späth’s work and wanted to learn more. So he began to duplicate Späth’s experiments in his own lab as a way to learn more about the chemistry of natural products. But what could he hope to learn? Hadn’t Späth already learned everything that we needed to know about how to produce nicotine?

Chemists often try to duplicate someone else’s experiment in order to check on the original procedure and results, and to learn new ideas. This idea of checking each other’s work is very important in chemistry and in most sciences. Without it, scientists wouldn’t pass along the skills to do cutting-edge research on new topics.


In this lab activity your group will write out a tentative procedure for a common process, carry out the procedure, revise the procedure if necessary, and then give it to another group to repeat. Your challenge is to write the procedure so clearly that the other group can do the experiment exactly the way you did and get the same results.


Wear your safety goggles while working on this activity.


  1. Your teacher will give your lab group a brief description of a process.
  2. In your lab group, come up with a procedure to carry out the process assigned to you. Briefly jot down the steps of the procedure on a piece of paper.
  3. Your group should then carry out the process and carefully record the exact steps you follow. If the steps you first thought of turn out to be incorrect when you try to carry them out, modify the steps until you have a successful procedure. Be sure to modify your notes.
  4. Record your results.
  5. Someone in your group should make a neat written copy of the steps in your procedure on a separate sheet of paper. This copy should NOT include your results.
  6. Give the procedure to your teacher, who will then give it to another lab group in your class. Your teacher will, in turn, also give your group a procedure designed by another group in your class.
  7. You are to follow the other group's written steps exactly. Do not add any steps of your own, and do not attempt to ask questions of the group that wrote the original procedure. Record all your results. Note any problems you encounter in following the procedure.
  8. Post-Lab Discussion
    After you are finished working, compare your results with the group whose work you repeated. Your teacher will tell you which group to meet with. This group will have tried to follow your procedure.
  9. In your meeting with the other lab group, discuss the following questions:
    1. Were both procedures written clearly and were the steps easy to follow?
    2. If any steps were unclear, discuss what problems this caused and discuss how the problems could have been eliminated.
    3. Show the other group the results your group found for their procedure. Compare your results with theirs.
    4. If the results were different, discuss why.
  10. Reporting Your Work
    Each member of your group should write a few sentences summarizing the discussion in step 9. Write these answers on the Post-lab Discussion Report Sheet given to you by your teacher. Include in this a summary of what you learned about replicating the work of others in the lab.

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