化学 1662

关于空气弹性的新物理-力学实验

罗伯特·玻意耳

把气体压进一半的空间，它就反推两倍的力——压强乘体积，守恒不变。

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In depth · the introduction

用大拇指堵住打气筒的出气口，再往下压——你压得越狠，里头封住的空气就把你顶得越凶。玻意耳找到了这股反顶背后那条精确的规则。

压一压，它就回顶——而且有准数

空气有一股弹性，玻意耳称之为「空气的弹性」：它向外挤压，你越压它，它顶得越凶。他的发现，是「凶」出了多少。

把一团封住的空气压进一半的空间，它就回顶整整两倍的力。压进三分之一的空间，回顶三倍。体积往下，压强往上，步调分毫不乱——于是体积乘压强，永远是同一个数。这就是玻意耳定律。

一根管子、一位批评者，与一条借名而来的假说

罗伯特·玻意耳是位富有的英裔爱尔兰绅士，也是皇家学会的创建人之一，在牛津做研究，身边有位年轻助手罗伯特·胡克，替他造了一台抽气机。1660 年，他发表实验，主张空气是有弹性的。一位名叫弗朗西斯·莱纳斯的耶稣会士不以为然，说撑起东西的是一根看不见的线，而非什么弹簧。

为了一锤定音，玻意耳弯了一根 J 形玻璃管，把空气封在封闭的短臂里，再往长臂倒水银去压它——一格一格地读出体积与压强。他找到的那条利落的反比规则，却老老实实归功于另一个人，称它为「汤利先生的假说」，纪念最先提出它的理查德·汤利。玻意耳的本事，是把它量得足够干净，足以证实它。

它为何重要

这是头一回，有人把无形的气体钉死在一个硬邦邦的数上。看似什么都不是的空气，竟服从一条像钟表一样精确的定律。这条单一、可重复的关系——以及玻意耳那种摆仪器、列数据、当众论证的方式——帮着向世人显示：新生的实验科学，到底能做到什么。

一根你能称量的弹簧

把封住的空气，想成打气筒里的一根弹簧。把活塞压到一半，弹簧就以两倍的力抵抗；压到三分之一，就以三倍抵抗。玻意耳定律说，一团气体正是这样一根弹簧——而且不像金属弹簧，天下任何一种气体，在任何地方，都服从同一条规则。

它在故事里的位置

玻意耳定律，是气体定律里的头一条。一个世纪后，查理把体积系于温度，盖-吕萨克把压强系于温度；阿伏伽德罗（见 avogadro-1811）则把体积系于分子的数目。四者编在一起，便成了理想气体定律 PV = nRT。而那个更深的「为什么」——气体究竟为何会回弹——要等到动理学理论才到来：那时人们才明白，压强原来是小到看不见的分子无休止的擂击，正是道尔顿（见 dalton-1808）与阿伏伽德罗当年学着去清点的那些分子。

The original document

Original source text

Robert Boyle · New Experiments Physico-Mechanical, Touching the Spring of the Air · Oxford, 1660 · the law in the “Defence…” appendix, 2nd edition 1662

The spring of the air

In 1660, working with an air-pump that his assistant Robert Hooke had designed and built, Boyle argued that air is elastic — that it behaves like a fleece of tiny coiled springs, pressing outward and pressing harder the more it is compressed. He named this elasticity the spring of the air.

Linus's objection

The Jesuit Francis Linus rejected the idea, holding that an invisible thread-like pull — his “funicular hypothesis” — held up the mercury, rather than any spring. In the second edition of his book (1662) Boyle added an appendix, A Defence of the Doctrine Touching the Spring and Weight of the Air, to answer him with measurement instead of argument.

The J-tube experiment

Boyle bent a glass tube into the shape of a J, sealed at the short end. Pouring mercury into the long open arm trapped a column of air at the top of the short one. He marked the trapped air in equal spaces and read the height of mercury that balanced it. As more mercury was added the air shrank and the pressure on it rose — from 48 equal spaces at 29 1/8 inches of mercury down to 12 spaces at 117 9/16 inches, a fourfold squeeze answered by a fourfold pressure.

the same air being brought to a degree of density about twice as great as it had before, obtains a spring twice as strong as formerly.

The relation — that pressure and volume stand in reciprocal proportion — Boyle credited not to himself but to Richard Towneley, calling it “Mr Towneley's hypothesis.” He set his measured pressures beside the values the hypothesis predicted, column against column, and left the reader to judge how closely they agreed.

[ … ]

Boyle never wrote an equation, nor used “pressure,” “volume,” and “temperature” in their modern senses; he reasoned with the spring and the density of the air, keeping the warmth of the room steady without isolating it. In France the same law is named for Edme Mariotte, who published it independently in 1679 and added the condition Boyle had left tacit — that the temperature must be held constant.

Oxford · 1662