Ascientist working at a pharmaceutical company is conducting a research project on a new medicine that will be used to treat the common cold. why is it important for the scientist to keep accurate notes about his investigation?

There are several reasons behind why they must keep accurate notes.
There may be a mistake or an anomaly that occurs during the process, and something completely different than the desired compound may be created and the process may need to be repeated.
The investigation may be successful and may need to be repeated. 
The investigator may need to prove that the project was done by him and the notes may help him to do so. (hence why they must be dated and signed.)
The investigator may need them to protect him from legal action.
The pharmaceutical company may need proof that the possible medicine is safe and effective, and that it works as it should.

The gas would begin to expand, and eventually the can would burst or explode.

Putting salt in vinegar water