ALTHOUGH it is no part of my duty to teach chemistry, I have on several occasions had to perform an experiment which Mr. Marle quotes (p. 428) as being dangerous, viz. the collection of hydrogen from the action of sodium on water. I can fully endorse his warning. Twice a violent explosion took place; but I found that if the piece of sodium is carefully cleaned so that all its surfaces are bright, and cold water used, the experiment can be carried out in safety. I do not know if these important details have found their way into the practical manuals in use in chemical laboratories. If not, I trust that this experiment is not one that beginners are directed to make.