162 MORRIS LOEB 



tools and built machines, many centuries before the birth of 

 Watt and Arkwright. Just so, many operations that involve 

 a change of substance, and are therefore properly classed 

 among chemical processes, had their origin in prehistoric 

 times. Ore-smelting, tanning, dyeing, the making of cement, 

 pottery and glass are good examples of industries now pe- 

 culiarly within the chemist's control, but which were prac- 

 ticed by rule of thumb, by skilled artisans, ever since the 

 dawn of civilization. 



Then, again, the preparation of perfumes and cosmetics, 

 medicines and poisons, had been perfected long before the 

 Roman era, and these arts were preserved by Jews and Arabs 

 during the barbarous relapse of mediaeval Europe; so that 

 there was a constant development, from the magic of the 

 Egyptian priesthood, through the alchemy of a Geber and an 

 Albertus Magnus, the spagirism of a Paracelsus and a Glauber, 

 to the chemistry of a Becher and a Boyle. By the middle of 

 the eighteenth century, scientific chemistry had reached a 

 point where it could give a rational explanation of some of 

 the industrial processes of the period, and could seek to con- 

 trol their operations by distinct tests and to improve them 

 upon the basis of laboratory experiments. But the essential 

 step toward the domination of scientific theory over empir- 

 ical manufacture was taken when Bergman, Lavoisier and 

 their contemporaries recognized the constant quantitative 

 composition of chemical substance; for now it became certain 

 that the proportion of ingredients which proved most ad- 

 vantageous in a laboratory experiment must be the ratio to 

 which the manufacturer should adhere; the percentage of 

 useful substances contained in raw materials from various 

 sources could be estimated. At times it would be discovered 

 that certain admixtures, prescribed for centuries by tradi- 

 tional formularies, contributed nothing to the desired com- 



