重量分析法Gravimetric analysis

沉淀重量法最常用：试样溶解 → 加沉淀剂生成沉淀形式 → 陈化 → 过滤、洗涤 → 烘干或灼烧成称量形式 → 称量至恒重 → 计算。例如测硫酸根：加 BaCl₂ 生成 BaSO₄ 沉淀，灼烧后称量；测铁：沉淀为 Fe(OH)₃，灼烧为 Fe₂O₃ 称量。含量 w = m(称量形式) × F / m(试样)，F 为换算因数。理想沉淀要求溶解度小、纯度高、易过滤，称量形式组成固定、稳定、摩尔质量大。

Precipitation gravimetry is most common: dissolve the sample → add precipitant to form the precipitate → digest → filter and wash → dry or ignite to the weighing form → weigh to constant mass → calculate. Sulfate, for example, is precipitated as BaSO₄ with BaCl₂ and ignited; iron is precipitated as Fe(OH)₃ and ignited to Fe₂O₃. Content w = m(weighing form) × F / m(sample), with F the gravimetric factor. A good precipitate is insoluble, pure and easy to filter, and the weighing form has fixed composition, stability and a large molar mass.

重量分析是最古老的定量分析方法之一。18 世纪布莱克、拉瓦锡用精确称量研究化学反应，建立了质量守恒定律。19 世纪贝采利乌斯用重量法精确测定了数十种元素的原子量。1914 年理查兹因精确测定原子量获诺贝尔化学奖，他的工作大量采用重量分析。

Gravimetry is among the oldest quantitative methods. In the eighteenth century Black and Lavoisier studied reactions by accurate weighing and established conservation of mass. In the nineteenth century Berzelius determined the atomic weights of dozens of elements gravimetrically, and Theodore Richards, who received the 1914 Nobel Prize in Chemistry for precise atomic weights, relied heavily on gravimetric analysis.

气化法测定水分、结晶水和灰分（如干燥失重）；电解重量法在电极上析出金属称量（如铜的测定）；热重分析是现代仪器化的重量法。重量法操作繁琐耗时，已在多数场合被仪器分析取代，但仍是校准其他方法的基准方法。

Volatilisation methods determine moisture, water of crystallisation and ash (as loss on drying); electrogravimetry weighs metal deposited on an electrode, as for copper; and thermogravimetric analysis is gravimetry instrumentalised. Gravimetry is slow and laborious and has largely given way to instrumental methods, but it remains a reference method for calibrating others.