chemical residue

例句：

1. 1. The chemical reactions in the experiment were fascinating.
   实验中的化学反应非常吸引人。
2. 2.Chemical analysis is essential for understanding the origin of a substance.
   化学分析对于理解物质的起源至关重要。
3. 3. The chemical composition of the sample was determined using spectroscopy.
   使用光谱学确定了样本的化学成分。