70 Introduction to the Study of Science 



gained, however, until the age of Scheele, Priestley, and La- 

 voisier. 



Lavoisier's experiments and discoveries. Lavoisier, a 

 Frenchman (1743-1794), who is now called the " father of 

 modern chemistry," proved that combustible materials do not 

 lose, but on the contrary gain weight, when burned in air. This 

 completely upset the old belief. Lavoisier began a series of 

 experiments to discover the source and nature of whatever it 

 is that combines with substances burned in air. He had 

 learned from Joseph Priestley (1733-1804), an English clergy- 

 man, that the air is not a simple substance but is made up of 

 at least two different substances. Lavoisier experimented 

 with many combustible substances, among them lead, which 

 is interesting to work with, has a low melting point, and shows 

 plainly its combination in combustion with some other sub- 

 stance. 



Exercise : Burning lead in air. It is well worth while to perform 

 the following experiment with lead, by means of which Lavoisier 

 made important discoveries. Weigh accurately a small amount of 

 bright lead, the dish in which it is to be melted, and the metal 

 scraper which you will need to remove the burned lead from the dish. 

 Melt the lead and then heat it strongly above the melting point. As 

 a yellowish film is formed over the surface, scrape it to one side with 

 the metal scraper. When all of the bright lead has disappeared, weigh 

 accurately the product, that is, the yellowish substance, and also the 

 dish and the scraper because some of the substance may adhere to 

 them. The result will show that the product or burned lead weighs 

 more than the original lead, and that the dish and the scraper have 

 not lost in weight. This indicates that the increase in weight is due 

 to something probably derived from the air. 



This experiment was followed by another in which Lavoisier 

 sought to ascertain whether all or only a part of the air com- 

 bines with the heated lead. He put a measured quantity of 

 lead into a dish, which was then covered closely. The dish 

 was heated. A very small amount of powder was produced, 

 and in additional experiments it was found that this amount 



