phlogosin

例句：

1. 1. The phlogiston theory was a major scientific theory in the 18th century.
   燃素理论是18世纪的主要科学理论。
2. 2. Phlogiston is a chemical element that was once believed to be essential for life.
   燃素是一种化学元素，曾经被认为是生命所必需的。
3. 3. In modern chemistry, phlogiston has been replaced by other theories about the nature of matter.
   在现代化学中，燃素已被其他关于物质本质的理论所取代。