化学 1789

化学基础论

安托万-洛朗·拉瓦锡

在每一次反应中，物质都守恒——称一称，化学便成了一门精确的科学。

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In depth · the introduction

点一支蜡烛，让一枚铁钉生锈——几个世纪里，没人说得清这究竟是怎么回事，直到有个人决定：把这一切都放到天平上去称。

核心想法

拉瓦锡的想法，简单得有些出人意料：称量一切。把一个反应封进罐子，总重量便始终不变——于是凡是看似消失或凭空出现的东西，其实都只是移动了位置，或彼此化合了。仅凭这一条规则，他便证明：燃烧不是失去什么，而是从空气中获得了什么；空气与水都不是简单物质；而物质，可以被归入一小张「元素」的清单。

它使化学从一堆配方，变成一门测量的科学。如果数目对不上，那你对这场反应的说法，就是错的。

它是如何诞生的

在十八世纪的大部分时间里，化学家用「燃素」来解释火——一种燃烧物据说会释放出的、看不见的东西。拉瓦锡并不相信它，因为金属在空气中加热后会变重、而非变轻，这对一个「正在失去某种物质」的东西来说，方向恰好反了。于是他以近乎执拗的细心去称量，把金属与空气封进密闭容器，追踪每一格令。

他发现，金属增加的重量，恰好等于被封住的空气所失去的重量。燃烧是化合，而非丧失。他把空气中活跃的那一部分命名为「氧」，又把呼吸重释为一种缓慢的火，并在 1789 年把这一切汇成了这部教科书——其中大量的实验工作，是与他的妻子、合作者玛丽-安娜一道完成的，那些器械的图，也出自她之手。五年后，革命把他送上断头台；数学家拉格朗日说，砍下那颗头颅只在一瞬，而一百年也未必能再长出一颗这样的来。

它为何重要

这部书，给了化学一套方法，也给了它一种语言。那方法——一切论断都由天平裁断——至今仍是这门科学的运作之道。而那套理性的命名，使一种物质的名字便道出它由什么构成，让各国的化学家终于能彼此听懂。现代化学，自此开始。

一个可以想象的画面

想象一位一丝不苟的会计的账本：没有任何东西能不留记录地离开账面。如果一支燃烧的蜡烛变轻了，那失去的重量并未消失——它化作看不见的气体飘走了。把那气体也捕住、也称一称，账目便分毫不差地平衡。一场化学反应，不过是物质在各栏之间被挪动，既不被创造，也不被消灭。

它的位置

在拉瓦锡之前，化学仍带着炼金术与燃素说的习气。是他，让化学变得定量——成为他那个世纪的物理学的姊妹，也成为贯穿其间的诸守恒律的表亲（他的「热质」，不久便会被卡诺热机里的「热」所取代）。在他之后，这条线径直向前：1808 年道尔顿的原子，给那守恒的物质添上了颗粒；而他最先列成表的元素，终将被排布成元素周期表。

The original document

Original source text

Antoine-Laurent Lavoisier · Traité élémentaire de chimie, présenté dans un ordre nouveau et d'après les découvertes modernes · Paris: Cuchet, 1789

A textbook in three parts, written to teach chemistry as a measuring science under a reformed language. Its English title, in Robert Kerr's 1790 translation, is "Elements of Chemistry, in a New Systematic Order, Containing all the Modern Discoveries."

Preface of the Author

Lavoisier argues that a science cannot be improved without improving its language, and that we should reason only from facts established by experiment, never assuming what we set out to prove. He resolves to admit as elements only those bodies that no experiment has yet decomposed.

Part I — On the formation and decomposition of aëriform fluids, on the combustion of simple bodies, and the formation of acids

Heat is treated as a subtle fluid, "caloric," that swells bodies into gases. Combustion and the calcination of metals are recast: a burning or calcining body does not lose a "phlogiston" but combines with oxygen drawn from the air. Water, decomposed and recomposed, is shown to be a compound of oxygen and hydrogen, not an element.

In the chapter on the vinous fermentation, Lavoisier lays out a reaction as a balance sheet — the sugar of the grape must on one side, carbonic acid gas and alcohol on the other — and states the principle that governs the whole book:

We may lay it down as an incontestible axiom, that, in all the operations of art and nature, nothing is created; an equal quantity of matter exists both before and after the experiment; the quality and quantity of the elements remain precisely the same; and nothing takes place beyond changes and modifications in the combination of these elements. Upon this principle, the whole art of performing chemical experiments depends.

[ … ]

Part II — On the combination of acids with bases, and the formation of neutral salts

A table of thirty-three "simple substances" — bodies not yet resolved into anything simpler — stands as the first modern list of the chemical elements. (It still counts light and caloric among them, and a handful of "earths" later shown to be metal oxides.) From it Lavoisier and his collaborators build a systematic nomenclature in which a compound's name announces its composition: sulphuric acid, sulphates, oxides.

[ … ]

Part III — Description of the instruments and operations of chemistry

A manual of apparatus and precise measurement — the gasometer, the calorimeter, the careful weighing on which the whole method rests — illustrated by thirteen folding plates drawn and engraved by Marie-Anne Paulze Lavoisier, his wife and laboratory collaborator.

Paris · 1789