CHEMISTRY

THE CHEMISTRY of the eighteenth century had put the science on the road to development by the discovery of many of the gases, some inkling of the permanence of matter, and the true theory in general of combustion and respiration. The great step made in the first third of the nineteenth century was the scientific development of the atomic theory.

The theory first suggested itself to Dalton about 1804, while experimenting on marsh gas and olefiant gas. He noted that marsh gas seemed to contain exactly twice the weight of hydrogen combined in olefiant gas: also that carbonic acid gas seemed to contain just twice as much oxygen as carbonic oxide gas. To explain these facts he went back to the old idea of the atom-that matter is composed of indivisible atoms with definite weights, the ratio of which to the weight of an atom of hydrogen could be expressed by definite numbers. The weight of the smallest particle of a compound, then, would be equal to the sum of the weights of the atoms composing it. Dalton's new theory was given to the world in Thomson's System of Chemistry, 1807.

The next step in the theory was made by Gay-Lussac in 1808. This was that a definite volume of oxygen combines with just twice its bulk of hydrogen, and in fact, that there always exists a simple relation between the volumes of gases that combine with each other and that the volume of the compound bears, also, a simple relation to the amount. of gas of which the less is used. Thus, three volumes of hydrogen combining with one of nitrogen make two of ammonia; or one of chlorine with one of hydrogen makes two of hydrochloric acid gas. Therefore,

NTONIE WATTEAU was born in Valenciennes, France, in 1684. He went to Paris while very young and was employed first by an artist named Métayer, then with Claude Gillot, a scene-painter, and afterwards with a far more able man, Claude Audran. Watteau quarrelled with Audran and went his way because he thought Audran had blamed his first picture out of jealousy, for he had sold the work. He now went back to his native Valenciennes where he produced a second work, a Regiment Halting, which also sold in Paris, thus enabling him to pursue his studies in a more formal way. Both of these paintings were military subjects and are only preserved in engravings. He was about twenty-one now. In 1717 he was received in the Academy of Fine Arts and designated a "painter of court pastorals." In 1720 he went to England where he lived for a year, but, his health failing, he returned to France and died July 18, 1721, at Nogent-sur-Seine.