自从有了人类，化学便与人类结下了不解之缘。钻木取火，用火烧煮食物，烧制陶器，冶炼青铜器和铁器，都是化学技术的应用。正是这些应用，极大地促进了当时社会生产力的发展，成为人类进步的标志。今天，化学作为一门基础学科，在科学技术和社会生活的方方面面正起着越来越大的作用。从古至今，伴随着人类社会的进步，化学历史的发展经历了哪些时期呢？

1. 远古的工艺化学时期。这时人类的制陶、冶金、酿酒、染色等工艺，主要是在实践经验的直接启发下经过多少万年摸索而来的，化学知识还没有形成。这是化学的萌芽时期。

炼丹术:古代化学雏形

2. 炼丹术和医药化学时期。从公元前1500年到公元1650年，炼丹术士和炼金术士们，在皇宫、在教堂、在自己的家里、在深山老林的烟熏火燎中，为求得长生不老的仙丹，为求得荣华富贵的黄金，开始了最早的化学实验。记载、总结炼丹术的书籍，在中国、阿拉伯、埃及、希腊都有不少。这一时期积累了许多物质间的化学变化，为化学的进一步发展准备了丰富的素材。这是化学史上令我们惊叹的雄浑的一幕。后来，炼丹术、炼金术几经盛衰，使人们更多地看到了它荒唐的一面。

化学方法转而在医药和冶金方面得到了正当发挥。在欧洲文艺复兴时期，出版了一些有关化学的书籍，第一次有了“化学”这个名词。英语的chemistry起源于alchemy，即炼金术。chemist至今还保留着两个相关的含义：化学家和药剂师。这些可以说是化学脱胎于炼金术和制药业的文化遗迹了。

3. 燃素化学时期。从1650年到1775年，随着冶金工业和实验室经验的积累，人们总结感性知识，认为可燃物能够燃烧是因为它含有燃素，燃烧的过程是可燃物中燃素放出的过程，可燃物放出燃素后成为灰烬。

4. 定量化学时期，即近代化学时期。1775年前后，拉瓦锡用定量化学实验阐述了燃烧的氧化学说，开创了定量化学时期。这一时期建立了不少化学基本定律，提出了原子学说，发现了元素周期律，发展了有机结构理论。所有这一切都为现代化学的发展奠定了坚实的基础。

5. 科学相互渗透时期，既现代化学时期。二十世纪初，量子论的发展使化学和物理学有了共同的语言，解决了化学上许多悬而未决的问题；另一方面，化学又向生物学和地质学等学科渗透，使蛋白质、酶的结构问题得到逐步的解决。这里主要讲述近二百多年来的化学史故事。这是化学得到快速发展的时期，是风云变幻英雄辈出的时期。让我们一道去体验当年化学家所经历的艰难险阻,在近代化学史峰回路转的曲折历程中不倦跋涉，领略他们拨开重重迷雾建立新理论、发现新元素、提出新方法时的无限风光。

燃素说的影响

可燃物如炭和硫磺，燃烧以后只剩下很少的一点灰烬；致密的金属煅烧后得到的锻灰较多，但很疏松。这一切给人的印象是，随着火焰的升腾，什么东西被带走了。当冶金工业得到长足发展后，人们希望总结燃烧现象本质的愿望更加强烈了。

1723年，德国哈雷大学的医学与药理学教授施塔尔出版了教科书《化学基础》。他继承并发展了他的老师贝歇尔有关燃烧现象的解释，形成了贯穿整个化学的完整、系统的理论。《化学基础》是燃素说的代表作。

施塔尔认为燃素存在于一切可燃物中，在燃烧过程中释放出来，同时发光发热。

燃烧是分解过程：

可燃物==灰烬+燃素

金属==锻灰+燃素

如果将金属锻灰和木炭混合加热，锻灰就吸收木炭中的燃素，重新变为金属，同时木炭失去燃素变为灰烬。木炭、油脂、蜡都是富含燃素的物质，燃烧起来非常猛烈，而且燃烧后只剩下很少的灰烬；石头、草木灰、黄金不能燃烧，是因为它们不含燃素。酒精是燃素与水的结合物，酒精燃烧时失去燃素，便只剩下了水。

空气是带走燃素的必需媒介物。燃素和空气结合，充塞于天地之间。植物从空气中吸收燃素，动物又从植物中获得燃素。所以动植物易燃。

富含燃素的硫磺和白磷燃烧时，燃素逸去，变成了硫酸和磷酸。硫酸与富含燃素的松节油共煮，磷酸（当时指P2O5）与木炭密闭加热，便会重新夺得燃素生成硫磺和白磷。而金属和酸反应时，金属失去燃素生成氢气，氢气极富燃素。铁、锌等金属溶于胆矾（CuSO4·5H2O）溶液置换出铜，是燃素转移到铜中的结果。

燃素说尽管错误，但它把大量的化学事实统一在一个概念之下，解释了冶金过程中的化学反应。燃素说流行的一百多年间，化学家为了解释各种现象，做了大量的实验，积累了丰富的感性材料。特别是燃素说认为化学反应是一种物质转移到另一种物质的过程，化学反应中物质守恒，这些观点奠定了近、现代化学思维的基础。我们现在学习的置换反应，是物质间相互交换成分的过程；氧化还原反应是电子得失的过程；而有机化学中的取代反应是有机物某一结构位置的原子或原子团被其它原子或原子团替换的过程。这些思想方法与燃素说多么相似。

舍勒和普里斯特里发现氧气的制法

令后人尊敬的瑞典化学家舍勒的职业是药剂师——chemist，他长期在小镇彻平的药房工作，生活贫困。白天，他在药房为病人配制各种药剂。一有时间，他就钻进他的实验室忙碌起来。有一次，后院传来一声爆鸣，店主和顾客还在惊诧之中，舍勒满脸是灰地跑来，兴奋地拉着店主去看他新合成的化合物，忘记了一切。对这样的店员，店主是又爱又气，但从来不想辞退他，因为舍勒是这个城市最好的药剂师。

到了晚上，舍勒可以自由支配时间，他更加专心致志地投入到他的实验研究中。对于当时能见到的化学书籍里的实验，他都重做一遍。他所做的大量艰苦的实验，使他合成了许多新化合物，例如氧气、氯气、焦酒石酸、锰酸盐、高锰酸盐、尿酸、硫化氢、升汞（氯化汞）、钼酸、乳酸、乙醚等等，他研究了不少物质的性质和成分，发现了白钨矿等。至今还在使用的绿色颜料舍勒绿（Scheele’s green）,就是舍勒发明的亚砷酸氢铜（CuHAsO3）。如此之多的研究成果在十八世纪是绝无仅有的，但舍勒只发表了其中的一小部分。直到1942年舍勒诞生二百周年的时候，他的全部实验记录、日记和书信才经过整理正式出版，共有八卷之多。其中舍勒与当时不少化学家的通信引人注目。通信中有十分宝贵的想法和实验过程，起到了互相交流和启发的作用。法国化学家拉瓦锡对舍勒十分推崇，使得舍勒在法国的声誉比在瑞典国内还高。

在舍勒与大学教师甘恩的通信中，人们发现，由于舍勒发现了骨灰里有磷，启发甘恩后来证明了骨头里面含有磷。在这之前，人们只知道尿里有磷。

1775年2月4日，33岁的舍勒当选为瑞典科学院院士。这时店主人已经去世，舍勒继承了药店，在他简陋的实验室里继续科学实验。由于经常彻夜工作，加上寒冷和有害气体的侵蚀，舍勒得了哮喘病。他依然不顾危险经常品尝各种物质的味道——他要掌握物质各方面的性质。他品尝氢氰酸的时候，还不知道氢氰酸有剧毒。1786年5月21日，为化学的进步辛劳了一生的舍勒不幸去世，终年只有44岁。

舍勒发现氧气的两种制法是在1773年。

第一种方法是分别将KNO3、Mg（NO3）2、Ag2CO3、HgCO3、HgO加热分解放出氧气：

2KNO3==2KNO2+O2↑

2Mg（NO3）2 == 2MgO+4NO2↑+O2↑↑

2Ag2CO3==4Ag+2CO2↑+O2↑

2HgCO3==2Hg+2CO2↑+O2↑

2HgO==2Hg+O2↑

第二种方法是将软锰矿（MnO2）与浓硫酸共热产生氧气：

2MnO2+2H2SO4（浓）==2MnSO4+2H2O+O2↑

舍勒研究了氧气的性质，他发现可燃物在这种气体中燃烧更为剧烈，燃烧后这种气体便消失了，因而他把氧气叫做“火气”。舍勒是燃素说的信奉者，他认为燃烧是空气中的“火气”与可燃物中的燃素结合的过程，火焰是“火气”与燃素相结合形成的化合物。他将他的发现和观点写成《论空气和火的化学》。这篇论文拖延了4年直到1777年才发表。

英国化学家 普里斯特里

而英国化学家普里斯特里在1774年发现氧气后，很快就发表了论文。

普里斯特里始终坚信燃素说，甚至在拉瓦锡用他们发现的氧气做实验，推翻了燃素说之后依然故我。他将氧气叫做“脱燃素气”。他写到：

“我把老鼠放在‘脱燃素气’里，发现它们过得非常舒服后，我自己受了好奇心的驱使，又亲自加以实验，我想读者是不会觉得惊异的。我自己实验时，是用玻璃吸管从放满这种气体的大瓶里吸取的。当时我的肺部所得的感觉，和平时吸入普通空气一样；但自从吸过这种气体以后，经过好长时间，身心一直觉得十分轻快舒畅。有谁能说这种气体将来不会变成通用品呢？不过现在只有两只老鼠和我，才有享受呼吸这种气体的权利罢了。”

普里斯特里一生的大部分时间是在英国的利兹作牧师，业余爱好化学。1773年他结识了著名的美国科学家兼政治家富兰克林，他们后来成了经常书信往来的好朋友。普里斯特里受到好朋友多方的启发和鼓励。他在化学、电学、自然哲学、神学四个方面都有很多著述。

1774年普里斯特里到欧洲大陆参观旅行。在巴黎，他与拉瓦锡交换了好多化学方面的看法。正直的普里斯特里同情法国大革命，曾在英国公开做了几次演讲。英国一批反对法国大革命的人烧毁了他的住宅和实验室。普里斯特里于1794年他六十一岁的时候不得已移居美国，在宾夕法尼亚大学任化学教授。美国化学会认为他是美国最早研究化学的学者之一。他住过的房子现在已建成纪念馆，以他的名字命名的普里斯特里奖章已成为美国化学界的最高荣誉。

近代化学之父 拉瓦锡

拉瓦锡和他的天平

燃素说的推翻者，法国化学家拉瓦锡原来是学法律的。1763年，他20岁的时候就取得了法律学士学位，并且获得律师开业证书。他的父亲是一位律师，家里很富有。所以拉瓦锡不急于当律师，而是对植物学发生了兴趣。经常上山采集标本使他对气象学也产生了兴趣。后来，拉瓦锡在他的老师，地质学家葛太德的建议下，师从巴黎有名的鲁伊勒教授学习化学。

拉瓦锡的第一篇化学论文是关于石膏成分的研究。他用硫酸和石灰合成了石膏。当他加热石膏时放出了水蒸气。拉瓦锡用天平仔细测定了不同温度下石膏失去水蒸气的质量。从此，他的老师鲁伊勒就开始使用“结晶水”这个名词了。

这次成功使拉瓦锡开始经常使用天平，并总结出了质量守恒定律。质量守恒定律成为他的信念，成为他进行定量实验、思维和计算的基础。例如他曾经应用这一思想，把糖转变为酒精的发酵过程表示为下面的等式：

葡萄糖 == 碳酸（CO2）+ 酒精

这正是现代化学方程式的雏形。用等号而不用箭头表示变化过程，表明了他守恒的思想。拉瓦锡为了进一步阐明这种表达方式的深刻含义，又具体地写到：

“我可以设想，把参加发酵的物质和发酵后的生成物列成一个代数式。再逐个假定方程式中的某一项是未知数，然后分别通过实验，逐个算出它们的值。这样以来，就可以用计算来检验我们的实验，再用实验来验证我们的计算。我经常卓有成效地用这种方法修正实验的初步结果，使我能通过正确的途径重新进行实验，直到获得成功。”

早在拉瓦锡出生之时，多才多艺的俄罗斯科学家罗蒙诺索夫就提出了质量守恒定律，他当时称之为“物质不灭定律”，其中含有更多的哲学意蕴。但由于“物质不灭定律”缺乏丰富的实验根据，特别是当时俄罗斯的科学还很落后，西欧对沙俄的科学成果不重视，“物质不灭定律”没有得到广泛的传播。

1772年秋天，拉瓦锡照习惯称量了一定质量的白磷使之燃烧，冷却后又称量了燃烧产物P2O5的质量，发现质量增加了！他又燃烧硫磺，同样发现燃烧产物的质量大于硫磺的质量。他想这一定是什么气体被白磷和硫磺吸收了。他于是又做了更细致的实验：将白磷放在水银面上，扣上一个钟罩，钟罩里留有一部分空气。加热水银到40℃时白磷就迅速燃烧，之后水银面上升。拉瓦锡描述道：“这表明部分空气被消耗，剩下的空气不能使白磷燃烧，并可使燃烧着的蜡烛熄灭；1盎司的白磷大约可得到2.7盎司的白色粉末（P2O5，应该是2.3盎司）。增加的重量和所消耗的1/5容积的空气重量接近相同。”

燃素说认为燃烧是分解过程，燃烧产物应该比可燃物质量轻。而拉瓦锡实验的结果却是截然相反。他把实验结果写成论文交给法国科学院。从此他做了很多实验来证明燃素说的错误。在1773年2月，他在实验记录本上写到：“我所做的实验使物理和化学发生了根本的变化。”他将“新化学”命名为“反燃素化学”。

1774年，拉瓦锡做了焙烧锡和铅的实验。他将称量后的金属分别放入大小不等的曲颈瓶中，密封后再称量金属和瓶的质量，然后充分加热。冷却后再次称量金属和瓶的质量，发现没有变化。打开瓶口，有空气进入，这一次质量增加了，显然增加量是进入的空气的质量（设为A）。他再次打开瓶口取出金属锻灰（在容积小的瓶中还有剩余的金属）称量，发现增加的质量正和进入瓶中的空气的质量相同（即也为A）。这表明锻灰是金属与空气的化合物。

拉瓦锡进一步想，如果设法从金属锻灰中直接分离出空气来，就更能说明问题。他曾经试图分解铁锻灰（即铁锈），但实验没有成功。

拉瓦锡制得氧气之后

到了这年的10月，普里斯特里访问巴黎。在欢迎宴会上他谈到“从红色沉淀（HgO）和铅丹（Pb3O4）可得到‘脱燃素气’”。对于正在无奈中的拉瓦锡来说，这条信息是很直接的启发。11月，拉瓦锡加热红色的汞灰制得了氧气。在舍勒的启发下，拉瓦锡甚至制造了火车头大小的加热装置，其中心是聚光镜。平台下面是六个大轮子，以便跟着太阳随时转动。

1775年，拉瓦锡的实验中心已从分解金属锻灰转移到了对氧气的研究。他发现燃烧时增加的质量恰好是氧气减少的质量。以前认为可燃物燃烧时吸收了一部分空气，其实是吸收了氧气，与氧气化合，即氧化。这就是推翻了燃素说的燃烧的氧化理论。

与此同时，拉瓦锡还用动物实验，研究了呼吸作用，认为“是氧气在动物体内与碳化合，生成二氧化碳的同时放出热来。这和在实验室中燃烧有机物的情况完全一样。”这就解答了体温的来源问题。

空气中既然含有1/4的氧气(数据来自原文），就应该含有其余的气体，拉瓦锡将它称为“碳气”。研究了空气的组成后，拉瓦锡总结道：“大气中不是全部空气都是可以呼吸的；金属焙烧时，与金属化合的那部分空气是合乎卫生的，最适宜呼吸的；剩下的部分是一种‘碳气’，不能维持动物的呼吸，也不能助燃。”他把燃烧与呼吸统一了起来，也结束了空气是一种纯净物质的错误见解。

1777年，拉瓦锡明确地讥讽和批判了燃素说：“化学家从燃素说只能得出模糊的要素，它十分不确定，因此可以用来任意地解释各种事物。有时这一要素是有重量的，有时又没有重量；有时它是自由之火，有时又说它与土素相化合成火；有时说它能通过容器壁的微孔，有时又说它不能透过；它能同时用来解释碱性和非碱性、透明性和非透明性、有颜色和无色。它真是只变色虫，每时每刻都在改变它的面貌。”

这年的9月5日，拉瓦锡向法国科学院提交了划时代的《燃烧概论》，系统地阐述了燃烧的氧化学说，将燃素说倒立的化学正立过来。这本书后来被翻译成多国语言，逐渐扫清了燃素说的影响。化学自此切断了与古代炼丹术的联系，揭掉了神秘和臆测的面纱，代之以科学的实验和定量的研究。化学进入了定量化学（即近代化学）时期。所以我们说拉瓦锡是近代化学的奠基者。

舍勒和普里斯特里先于拉瓦锡发现氧气，但由于他们思维不够广阔，更多地只是关心具体物质的性质，没有能冲破燃素说的束缚。与真理擦肩而过是很遗憾的。

拉瓦锡对化学的另一大贡献是否定了古希腊哲学家的四元素说和三要素说，辨证地阐述了建立在科学实验基础上的化学元素的概念：“如果元素表示构成物质的最简单组分，那么目前我们可能难以判断什么是元素；如果相反，我们把元素与目前化学分析最后达到的极限概念联系起来，那么，我们现在用任何方法都不能再加以分解的一切物质，对我们来说，就算是元素了。”

在1789年出版的历时四年写就的《化学概要》里，拉瓦锡列出了第一张元素一览表，元素被分为四大类：

1.简单物质，普遍存在于动物、植物、矿物界，可以看作是物质元素：光、热、氧、氮、氢。

2.简单的非金属物质，其氧化物为酸：硫、磷、碳、盐酸素、氟酸素、硼酸素。

3.简单的金属物质，被氧化后生成可以中和酸的盐基：锑、银、铋、钴、铜、锡、铁、锰、汞、钼、镍、金、铂、铅、钨、锌。

4.简单物质，能成盐的土质：石灰、镁土、钡土、铝土、硅土。

拉瓦锡对燃素说和其它陈腐观点的讥讽和批判是无情和激烈的。这使他在创建科学勋绩的同时得罪了一大批同时代和老一辈的科学家。在《影响世界历史的一百位人物》中，在许多有关历史、科学史、化学史的书籍中，作者都对拉瓦锡总是突出自己的人格特点进行低调的描述和评价，指责他在《化学概要》里没有提起舍勒和普里斯特里对他的启示和帮助。但我们得看到，拉瓦锡确实具有非凡的科学洞察力和勇往直前的无畏精神。虽然不是他最先发现氧气的制法，但他通过制取氧气分析了空气的组成，建立了燃烧的氧化学说。氧气因此不同于其它气体，被赋予非凡的科学意义。

拉瓦锡十分勤奋，每天六点起床，从六点到八点进行实验研究，八点到下午七点从事火药局长或法国科学院院士的工作，七点到晚上十点，又专心从事他的科学研究。星期天不休息，专门进行一整天的实验工作。

拉瓦锡28岁结婚时，他的妻子只有14岁。他们一生没有孩子，但生活非常愉快。她帮助拉瓦锡实验，经常陪伴在他身边。在拉瓦锡的著作里，有很多插图都是他的妻子画的。

1789年法国大革命爆发，三年后拉瓦锡被解除了火药局长的职务。1793年11月，国民议会下令逮捕旧王朝的包税官。拉瓦锡由于曾经担任过包税官而自首入狱。极左派马拉曾与拉瓦锡有过激烈的科学争论，心存嫉恨，便诬陷拉瓦锡与法国的敌人有来往，犯有叛国罪，于1794年5月8日把他送上了断头台。对此，当时科学界的很多人感到非常惋惜。著名的法籍意大利数学家拉格朗日痛心地说：“他们可以一瞬间把他的头割下，而他那样的头脑一百年也许长不出一个来。” Sincethe existence of human beings, chemistry and human beings have formed anindissoluble bond. Drilling wood to make fire, cooking food with fire, firingpottery, smelting bronze and iron, are all applications of chemical technology.It was these applications that greatly promoted the development of socialproductive forces at that time and became the symbol of human progress. Today,as a basic subject, chemistry is playing an increasingly important role in allaspects of science, technology and social life. From ancient times to thepresent, with the progress of human society, the development of the history ofchemistry has experienced what periods?

1. The ancient process chemistry period. Atthis time, people's pottery, metallurgy, wine making, dyeing and other crafts,mainly under the direct inspiration of practical experience after thousands ofyears of exploration and exploration, chemical knowledge had not yet formed.This was the beginning of chemistry.

Alchemy: Ancient chemical rudiments

2. The period of Alchemy and Medicinalchemistry. From 1500 BC to 1650 AD, alchemists and alchemists, in the palace,in the church, in their own homes, in the smoke of the mountains and forests,in order to obtain the elixir of immortality, in order to obtain glory andwealth of gold, began the earliest chemical experiments. There are many booksthat record and summarize alchemy in China, Arabia, Egypt and Greece. Duringthis period, many chemical changes between substances were accumulated, whichprepared rich materials for the further development of chemistry. This is oneof the most spectacular scenes in the history of chemistry. Later, alchemy,alchemy several ups and downs, so that people see more of its absurd side.

Chemical methods were in turn justified inmedicine and metallurgy. During the Renaissance in Europe, books on chemistrywere published, and the term "chemistry" first came into being. TheEnglish word chemistry comes from alchemy. Chemist still retains two relatedmeanings today: chemist and chemist. These are the cultural relics ofchemistry's origins in alchemy and medicine.

3. Phlogiston chemical period. From 1650 to1775, with the accumulation of metallurgical industry and laboratoryexperience, people summarized perceptual knowledge that combustible materialscan be burned because they contain phlogiston, and the combustion process isthe process of releasing phlogiston from combustible materials, which will becomeashes after releasing phlogiston.

4. The quantitative chemical period, namelythe modern chemical period. Around 1775, Lavoisier used quantitative chemicalexperiments to explain the oxidation theory of combustion, which opened theperiod of quantitative chemistry. During this period, many basic laws ofchemistry were established, the atomic theory was put forward, the periodic lawof elements was discovered, and the theory of organic structure was developed.All these laid a solid foundation for the development of modern chemistry.

5. The period of interpenetration ofscience is the period of modern chemistry. At the beginning of the twentiethcentury, the development of quantum theory made chemistry and physics have acommon language, and solved many outstanding problems in chemistry. On theother hand, chemistry has penetrated into biology and geology and otherdisciplines, so that the structural problems of proteins and enzymes have beengradually solved. Here mainly tells the story of the history of chemistry inthe past two hundred years. This was a period of rapid development ofchemistry, a time of great changes and great heroes. Let us experience theHARDSHIPS and difficulties experienced by CHEMists in those days, trektirelessly through the twists and turns of the modern history of chemistry, andappreciate the infinite scenery when they cleared through the fog to establishnew theories, discover new elements, and propose new methods.

The effect of the fugualism

Combustibles, such as charcoal and sulfur,burn with little ash; After calcination of dense metal, the forged ash is more,but very loose. All this gave the impression that something was being carriedaway as the flames rose. As the metallurgical industry developed, the desire tosummarize the nature of combustion became stronger.

In 1723, Starr, a professor of medicine andpharmacology at the University of Halle in Germany, published a textbook calledThe Foundations of Chemistry. He inherited and developed his teacher Becher'sexplanation of the phenomenon of combustion, forming a complete and systematictheory throughout chemistry. Fundamentals of Chemistry is a representative workof the theory of fuels.

Starr believed that phlogiston was presentin all combustible materials, and that it was released during the combustionprocess, as well as giving off light and heat.

Combustion is a decomposition process:

Combustible == Ash + phlogiston

Metal == Forged ash + phlogiston

If the metal forging ash and charcoal mixedheating, the forging ash will absorb the charcoal phlogiston, back into metal,at the same time the charcoal lost phlogiston into ash. Charcoal, grease, andwax are all substances rich in phlogiston, which burn fiercely, and leave verylittle ash; Stone, ash, and gold do not burn because they do not containphlogiston. Alcohol is a combination of phlogiston and water. When alcoholburns, it loses phlogiston, leaving only water.

Air is an essential medium for the removalof phlogiston. Phlogiston combines with air and fills the space between heavenand earth. Plants get phlogiston from the air, and animals get phlogiston fromplants. So plants and animals are flammable.

When phlogistin-rich sulfur and whitephosphorus burn, phlogistin-rich sulfur escapes and becomes sulfuric andphosphoric acid. Sulfuric acid was BOILED WITH phlogistIN-rich turpentINE, andPHOSPHORIC acid (P2O5 IN those days) was heated IN CLOSE QUARTERS with CHARCOALTO recapture PHlogistIN-PRODUCING sulfur and white phosphorus. When a metalreacts with an acid, it loses phlogiston to produce hydrogen, which is rich inphlogiston. Copper is replaced by iron, zinc and other metals dissolved in thesolution of CuSO4·5H2O, which is the result of phlogiston transferred tocopper.

Although wrong, the theory of fuel unites alarge number of chemical facts under a single concept, which explains thechemical reactions in metallurgical processes. During the more than one hundredyears since the fuxin theory was popular, chemists have done a lot ofexperiments and accumulated a wealth of perceptual materials in order toexplain various phenomena. In particular, phlogiston's view of chemicalreactions as the transfer of one substance to another, and the conservation ofmatter in chemical reactions, formed the basis of recent and modern chemicalthinking. The substitution reaction that we're studying now, is the exchange ofcomponents between substances; REDOX reactions are electron gain and lossprocesses; Substitution reaction in organic chemistry is the process in whichatoms or groups of atoms in a certain structural position of organic matter arereplaced by other atoms or groups of atoms. How similar these ideas are to thetheory of fuel.

Scheele and Priestley discovered how tomake oxygen

The respected Swedish chemist Scheele'sprofession is pharmacist - chemist, he long in the small town Chepin pharmacywork, living in poverty. During the day, he makes various medicines forpatients in the pharmacy. Whenever he has time, he gets into his laboratory andgets busy. Once, when the shopkeeper and his customers were still amazed by aloud noise in the backyard, Scheele came running with a face full of ashes andexcitedly pulled the shopkeeper to see his new compound, forgetting everything.The shopkeeper loved and hated the clerk, but he never wanted to fire himbecause Scheele was the best pharmacist in the city.

In the evenings, when Scheele had freetime, he devoted himself more intently to his experimental studies. He repeatedevery experiment in the chemistry books available at the time. His painstakingexperiments led him to synthesize many new compounds, such as oxygen, chlorine,tartaric acid, manganate, permanganate, uric acid, hydrogen sulfide, mercuric (mercuricchloride), molybdate, lactic acid, diethyl ether, etc. He studied theproperties and composition of many substances and discovered scheelite, etc.Scheele's green, a green pigment still in use today, is Scheele's invention ofcopper hydrogen arsenite (CuHAsO3). Such a large body of work was unprecedentedin the eighteenth century, but Scheele published only a small fraction of it.It was not until 1942, the bicentennial of Scheele's birth, that all hisexperimental records, diaries and letters were collated and published in eightvolumes. The correspondence between Scheele and many chemists at that time isremarkable. There are valuable ideas and experimental processes in thecorrespondence, which play the role of mutual communication and inspiration.The French chemist Lavoisier was a great admirer of Scheele, making him morefamous in France than in Sweden.

In correspondence between Scheele anduniversity teacher Gunn, it was discovered that Scheele's discovery ofphosphorus in ashes inspired Gunn to prove that phosphorus was present inbones. Until now, phosphorus was only known to be in urine.

On February 4, 1775, Scheele was elected amember of the Swedish Academy of Sciences at the age of 33. The owner had died,and Scheele inherited the pharmacy and continued scientific experiments in hishumble laboratory. As a result of working all night, coupled with the cold andthe erosion of harmful gases, Scheele developed asthma. He was still constantlytasting the taste of matter in spite of the danger -- he wanted to master thenature of matter in all its aspects. When he tasted hydrocyanic acid, he didnot know that it was highly poisonous. On May 21, 1786, Scheele, who had workedhard all his life for the progress of chemistry, died at the age of 44.

Scheele discovered two ways of makingoxygen in 1773.

The first method is to decompose KNO3, Mg(NO3) 2, Ag2CO3, HgCO3 and HgO by heating to release oxygen:

2 - kno3 = = 2 kno2 + O2 write

2Mg (NO3) 2 == 2MgO+4NO2↑+O2↑↑

Write 2 ag2co3 = = 4 ag + 2 co2 + O2 write

2 hgco3 = = 2 hg + 2 co2 + O2 write write

2 hgo = = 2 hg + O2 write

The second method is to coheat pyrolusite(MnO2) with concentrated sulfuric acid to produce oxygen:

2MnO2+2H2SO4 (concentrated) == 2MnSO4+2H2O+O2↑

Scheele studied the properties of oxygen.He found that combustibilites burned more violently in this gas, and afterburning the gas disappeared, so he called oxygen "fire gas." Scheelewas a believer in the phlogiston theory. He believed that combustion was theprocess by which "fire" in the air combined with phlogiston incombustible materials, and flame was a compound formed by the combination of"fire" and phlogiston. He wrote his findings and ideas in "On theChemistry of Air and Fire". The paper was delayed for four years until1777.

-- John Priestley, British chemist

British chemist John Priestley discoveredoxygen in 1774 and soon published a paper.

Priestley continued to believe in the fueltheory, even after Lavoisier disproved it by experimenting with oxygen, whichthey had discovered. He called oxygen "phlogiston gas." He wrote:

"I do not think it will surprise thereader that, having found the mice to be very comfortable in the air ofdephlogiston, my curiosity led me to experiment with them myself. In my ownexperiments, I sucked the gas through a glass straw from a large bottle filledwith it. The sensation in my lungs was the same as when I breathed ordinaryair; But it has been a long time since I breathed in the gas, and I have beenfeeling quite buoyant. Who is to say that this gas will not become a common usein the future? But now only two mice and I have the right to breathe it."

Priestley spent most of his life as aclergyman in Leeds, England, with a hobby in chemistry. In 1773 he metFranklin, a famous American scientist and politician, and they later becamegood friends who often wrote to each other. Priestley was inspired andencouraged in many ways by his good friends. He wrote extensively on chemistry,electricity, natural philosophy and theology.

In 1774 Priestley made a tour of thecontinent. In Paris, he and Lavoisier exchanged many ideas about chemistry. Therighteous Priestley sympathized with the French Revolution and made severalpublic speeches in England. A group of English opponents of the FrenchRevolution burned down his house and laboratory. Priestley was forced to moveto America in 1794 at the age of sixty-one and became a professor of chemistryat the University of Pennsylvania. The American Chemical Society recognized himas one of the earliest scholars of chemistry in the United States. The housewhere he lived is now a memorial, and the Priestley Medal in his name is thehighest honor in American chemistry.

Lavoisier, the father of modern chemistry

Lavoisier and his scales

Lavoisier, the French chemist who overthrewphlogiston, was trained in law. In 1763, at the age of 20, he received hisBachelor's degree in law and his bar certificate. His father was a lawyer, andthe family was wealthy. So Lavoisier was not eager to become a lawyer, butbecame interested in botany. Frequent trips to the mountains to collectspecimens led him to become interested in meteorology. Later, on the advice ofhis teacher, geologist Gotede, Lavoisier studied chemistry under the famousProfessor Ruillers in Paris.

Lavoisier's first chemistry paper was onthe composition of gypsum. He made gypsum from sulfuric acid and lime. Steamwas released when he heated the plaster. Lavoisier used a balance to carefullymeasure the amount of water vapor lost by gypsum at different temperatures.From then on, his teacher Ruille began to use the term "water ofcrystal".

This success led Lavoisier to use scalesregularly and to formulate the law of conservation of mass. The law ofconservation of mass became his belief and the basis of his quantitativeexperiments, thinking and calculations. He used this idea, for example, toexpress the fermentation of sugar into alcohol as the following equation:

Glucose == carbonic acid (CO2) + alcohol

This was the beginning of the modernchemical equation. Using equals instead of arrows to show the process of changeshows his idea of conservation. In order to further clarify the profoundmeaning of this way of expression, Lavoisier specifically wrote:

"I can imagine that the substancesthat take part in fermentation and the products after fermentation are listedin an algebraic form. Then assume that one of the terms in the equation isunknown, and then through the experiment, each of them is calculated. In thisway, our experiments can be checked by calculation, and our calculations can beverified by experiment. I have often and fruitfully corrected the preliminaryresults of experiments in this way, so that I can repeat them in the right wayuntil I succeed."

As early as Lavoisier was born, theversatile Russian scientist Lomonosov put forward the law of conservation ofmass, which he called the "law of the indefiability of matter", whichhad more philosophical implications. However, due to the lack of richexperimental basis for the "law of the indefatigability of matter",especially at that time, Russian science was still backward, and Western Europedid not pay attention to the scientific achievements of Tsarist Russia, the"law of the indefatigability of matter" was not widely spread.

In the fall of 1772, Lavoisier, ascustomary, weighed a certain mass of white phosphorus to make it burn. Aftercooling, he weighed the mass of the combustion product P2O5, and found that themass had increased! He burned sulfur and again found that the mass of theproduct was greater than the mass of the sulfur. He thought it must be somekind of gas absorbed by the white phosphorus and sulfur. He then made a moredetailed experiment: white phosphorus was placed on a surface of mercury, and abell jar was fastened, leaving some air in it. Heat the mercury to 40℃ and thewhite phosphorus burns rapidly, after which the mercury surface rises. As Lavoisierdescribed it, "This shows that part of the air is consumed, and that theremaining air does not make the white phosphorus burn, and extinguishes theburning candle; One ounce of white phosphorus yields approximately 2.7 ouncesof white powder (P2O5, should be 2.3 ounces). The weight gained is close to thesame as the weight of the one-fifth volume of air consumed."

The fuel theory holds that combustion is adecomposition process and that the products of combustion should be lighterthan the fuel. The result of Lavoisier's experiment was quite the opposite. Hesubmitted his results to the French Academy of Sciences in a paper. Since then,he has done many experiments to prove the fuguin theory wrong. In February1773, he wrote in his experiment notebook, "The experiments I haveperformed have brought about fundamental changes in physics andchemistry." He named "New chemistry"