classification of substances from a chemical standpoint than that of superficial outward appearance was demanded is not strange, when we recollect that at this period and, indeed, down to the close of the eighteenth century, the transmutation of metals was a popular belief of the common people and was not disproved by the chemist. There was no underlying, unchangeable principle at the basis of the different substances with which the chemist had to deal.
Lavoisier—government medallist at twenty-one, adjunct member of the French Academy at twenty-five, chemist, geologist, mineralogist and mathematician, man of business and amasser of wealth, financier, reformer, fermier general, imprisoned by Kobespierre on the trumped- up charge of having adulterated tobacco with water, guillotined in 1794, when only just past fifty years old—this is the man whom the French, with much justice, call the 'Father of Chemistry,' the man who made chemistr}^ possible as a science by furnishing it with a foundation, the doctrine of the indestructibility of matter. This he accomplished by the use of the balance. A familiar experiment had often been used to support the old idea of transmutation. When water has been boiled for a long time in a glass vessel, on evaporating the water an earthy residue is obtained, and this, said the chemists of that day, is conclu- sive evidence that water can be transmuted into earth by boiling; and, if water into earth, why not other substances; and why not, if we only knew the method, even the base metals into gold? Wlien less than thirty years old, Lavoisier repeated this experiment, but he took the precaution of weighing his glass vessel with its contained water. After a hundred days' boiling, he found that there was no change in weight. On then evaporating the water he found, indeed, an earthy residue, but the glass vessel had lost an amount exactly equal in weight to that recovered from the w^ater. In other words, the water, so far from being changed into earth, had merely dissolved out a small por- tion of the glass container. This and many other similar experiments the keen-witted Frenchman used to prove the indestructibility of mat- ter, and on this fundamental doctrine the superstructure of scientific chemistry began to rise.
With this doctrine established, it became possible to consider the nature of matter from a new standpoint, and to define with some ac- curacy a chemical element. Back in the days of Greek philosophers, elements were very variously conceived of. To Pherekides earth was the primal element; to Anaximenes, air; to Herakleitos, fire; while Thales found in water the first principle of all things, and the followers of the Milesian philosopher were not a few for more than two mil- lenniums. Empedokles accepted all four of these elements, and to them Aristotle added a fifth, ether, the quintessence, subtler and more divine than the other foxir. With these the alchemists placed a number of