24 IOWA ACADEMY OF SCIENCES. 



or levity. During this period of theory gone utterly wrong, 

 facts were accumulated by the investigation of many able men, 

 and these were soon to serve a purpose in the establishment 

 of a new theory by which they also were to be co-ordinated 

 and explained. 



The work of Lavoisier marks an epoch in chemical history, 

 and paves the way for a general theory. He first employed 

 the balance systematically, and clearly showed that calcination 

 and combustion were processes of union of oxygeu with other 

 substances, and his work marks the overthrow of phlogiston. 

 Thera arose again with his work true ideas of element, com- 

 pound and chemical reaction. 



Probably most chemists accustomed to use the atomic theory 

 with as much confidence as the carpenter uses his square and 

 pencil in marking out his work, would place the origin of 

 scientific chemistry at the announcement of the rudiments of 

 the atomic theory by John Dalton, ia 1803. This theory was 

 the outgrowth of the law of definite proportions demonstrated 

 by Proust, 1799-1807, against the determined opposition of 

 Berthellot and his school, who argued that the constitution of 

 one and the same compound is variable, and the law of multi- 

 ple proportions discovered by Dalton himself. The theory 

 accounts for these laws; it is, therefore, the result of legitimate 

 scientific work, and is not to be confused with the speculative 

 theory of atoms of the Greeks. That Chemistry passed the 

 date 1800 without an atomic theory of any kind, sufficiently 

 indicates its condition. No further comment is necessary. 



To th's period belongs the discovery of nitrogen, phos- 

 phorus, chlorine, hydrogen, oxygen, manganese, cobalt, 

 nickel, platinum, though they were not regarded as elements, 

 and many of their compounds were made; the distinction 

 between caustic and mild alkalies, and the relations of acids, 

 bases and salts, were pointed out; many new gases were 

 stuaied and the foundations of analysis were laid. To this 

 period belongs a long array of illustrious nam-.s — Black, Cav- 

 endish, Priestley, Galen, Scheele, Hales, Mayow, Bergman and 

 Hoffmann, who paved the way for Lavoisier and Dalton. The 

 theory of phlogiston, though wrong, served to explain and 

 group certain related phenomena, and to that extent there was 

 science of chemistry. 



