熔点测定Melting-point apparatus

熔点是固液两相蒸气压相等、平衡共存的温度。杂质溶于液相使液相蒸气压降低，按凝固点降低原理，熔点下降且熔程变宽。混合熔点法：把未知物与已知标准品等量混合测熔点，若熔点不降低，二者很可能是同一化合物；若明显降低，则不是。

The melting point is the temperature at which solid and liquid have equal vapour pressures and coexist. An impurity dissolving in the liquid lowers its vapour pressure, so by freezing-point depression the melting point falls and the range widens. In a mixed melting point, an unknown is mixed with an authentic sample: if the melting point does not fall the two are very likely the same compound; if it falls markedly they are not.

毛细管法：把研细干燥的样品装入一端封口的毛细管（高 2–3 mm，夯实），绑在温度计水银球旁，放入盛有浴液（液体石蜡或硅油）的提勒管中加热，利用提勒管侧管的对流使受热均匀；接近熔点时升温速率控制在每分钟 1–2 °C。现代常用数字熔点仪（自动光学检测）、显微熔点仪（可观察晶型变化）和差示扫描量热法（DSC）。

In the capillary method, finely ground dry sample is packed 2–3 mm deep in a capillary sealed at one end, attached beside a thermometer bulb and heated in a Thiele tube of liquid paraffin or silicone oil, whose side arm sets up convection for even heating; near the melting point the rate is held at 1–2 °C per minute. Modern laboratories use digital instruments with optical detection, hot-stage microscopes that show crystal changes, and differential scanning calorimetry (DSC).

1907 年德国化学家约翰内斯·提勒设计了提勒管。在光谱技术出现之前，熔点和混合熔点是有机化学家确认化合物身份的最重要手段之一，至今仍是合成化学中检验产物纯度的快速方法。

The German chemist Johannes Thiele designed the Thiele tube in 1907. Before spectroscopy, melting and mixed melting points were among organic chemists' most important ways to confirm identity, and they remain a quick purity check in synthesis.