Dmitri Mendeleev — "It is the duty of the chemist to teach the world how to use the elements wisely."

"The edifice of science not only requires material, but also a plan. Without the material, the plan alone is but a castle in the air—a mere possibility; whilst the material without a plan is but useles…"

"Experiment itself cannot give truth, but it gives the means of destroying erroneous representations whilst confirming those which are true in all their consequences."

"The knowledge of the properties of the elements is the foundation of all chemistry."

"The periodic law is the most important generalization in chemistry, and it has no equal in any other branch of science."

"I consider it my duty to warn against this tendency to make a science of alchemy."