化學 1789

化學基礎論

安托萬-洛朗·拉瓦節

在每一次反應中，物質都守恆——稱一稱，化學便成了一門精確的科學。

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In depth · the introduction

點一支蠟燭，讓一枚鐵釘生鏽——幾個世紀裡，沒人說得清這究竟是怎麼回事，直到有個人決定：把這一切都放到天平上去稱。

核心想法

拉瓦錫的想法，簡單得有些出人意料：稱量一切。把一個反應封進罐子，總重量便始終不變——於是凡是看似消失或憑空出現的東西，其實都只是移動了位置，或彼此化合了。僅憑這一條規則，他便證明：燃燒不是失去什麼，而是從空氣中獲得了什麼；空氣與水都不是簡單物質；而物質，可以被歸入一小張「元素」的清單。

它使化學從一堆配方，變成一門測量的科學。如果數目對不上，那你對這場反應的說法，就是錯的。

它是如何誕生的

在十八世紀的大部分時間裡，化學家用「燃素」來解釋火——一種燃燒物據說會釋放出的、看不見的東西。拉瓦錫並不相信它，因為金屬在空氣中加熱後會變重、而非變輕，這對一個「正在失去某種物質」的東西來說，方向恰好反了。於是他以近乎執拗的細心去稱量，把金屬與空氣封進密閉容器，追蹤每一格令。

他發現，金屬增加的重量，恰好等於被封住的空氣所失去的重量。燃燒是化合，而非喪失。他把空氣中活躍的那一部分命名為「氧」，又把呼吸重釋為一種緩慢的火，並在 1789 年把這一切匯成了這部教科書——其中大量的實驗工作，是與他的妻子、合作者瑪麗-安娜一道完成的，那些器械的圖，也出自她之手。五年後，革命把他送上斷頭台；數學家拉格朗日說，砍下那顆頭顱只在一瞬，而一百年也未必能再長出一顆這樣的來。

它為何重要

這部書，給了化學一套方法，也給了它一種語言。那方法——一切論斷都由天平裁斷——至今仍是這門科學的運作之道。而那套理性的命名，使一種物質的名字便道出它由什麼構成，讓各國的化學家終於能彼此聽懂。現代化學，自此開始。

一個可以想像的畫面

想像一位一絲不苟的會計的帳本：沒有任何東西能不留記錄地離開帳面。如果一支燃燒的蠟燭變輕了，那失去的重量並未消失——它化作看不見的氣體飄走了。把那氣體也捕住、也稱一稱，帳目便分毫不差地平衡。一場化學反應，不過是物質在各欄之間被挪動，既不被創造，也不被消滅。

它的位置

在拉瓦錫之前，化學仍帶著煉金術與燃素說的習氣。是他，讓化學變得定量——成為他那個世紀的物理學的姊妹，也成為貫穿其間的諸守恆律的表親（他的「熱質」，不久便會被卡諾熱機裡的「熱」所取代）。在他之後，這條線徑直向前：1808 年道爾頓的原子，給那守恆的物質添上了顆粒；而他最先列成表的元素，終將被排布成元素週期表。

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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