A Little History Of Science: The ‘New Chemistry’
If you have a chemistry set then you may already know about litmus paper. These small strips of special paper can tell you whether a solution is acid or alkaline. If you stir some vinegar in water (making it acidic) and dip in the blue paper, it will turn red.
If you try it with bleach (which is alkaline), the red paper will turn blue. Next time you use a piece of litmus paper, think of Robert Boyle, for he created the test more than 300 years ago.
Boyle (1627–91) was born into a large aristocratic family in Ireland. He was the youngest son, and never had to worry about money. Unlike a lot of wealthy people, Boyle was always generous with his fortune, and he donated a good deal of it to charity. He paid for the Bible to be translated into an American Indian language. Religion and science played equally big parts in his life.
He spent a few years at Eton, the elite English school, and then travelled in Europe, where he had a series of private tutors. Boyle
returned to England where the Civil War was raging; some of his family sided with King Charles I, and some with the Parliamentarians, who sought to overthrow the king and establish a republic. His sister convinced him to join the Parliamentarians, and through her, he met an enthusiastic social, political and scientific reformer called Samuel Hartlib. Like Francis Bacon, Hartlib believed that science had the power to improve the lives of human beings, and convinced the young Boyle that studying agriculture and medicine could lead to such improvements. Boyle began with medicine and looked at the cures for various diseases, gaining along the way a lifelong fascination with chemistry.
Some religious people fear exposing themselves or their children to new ideas because they think the ideas might undermine their faith. Robert Boyle was not one of these people: his religious belief was so secure that he read whatever was related to his wide scientific interests. Descartes and Galileo were controversial figures in Boyle’s early days, but he studied them both carefully – he read Galileo’s Starry Messenger in 1642 in Florence, the very same year and place in which Galileo died – and used their insights in his own work. Boyle was also interested in the atomists of ancient times (Chapter 3), though he was not altogether convinced by their belief that the universe consists of nothing but ‘atoms and the void’.
He knew, however, that there were some basic units of matter in the universe, which he called ‘corpuscles’, but he could go about his work without the godless (atheistic) associations of ancient Greek atomism.
Boyle was equally unsatisfied with Aristotle’s theory of the four elements – air, earth, fire and water – and he showed by experiment that it was not correct. He burnt a stick of fresh wood and showed that the smoke that came off it was not air. Nor was the fluid that oozed out of the end of the burning wood ordinary water. The flame differed depending on what was burnt, so that was not pure fire, and the ash that was left was not earth. By carefully analysing the results of these simple experiments, Boyle did enough to show that some- thing as common as wood was not made of air, earth, fire and water.
He also pointed out that some substances, like gold, could not be broken down further. When heated, gold melted and ran but it didn’t change like wood did when it was burnt: when gold grew cold, it returned to its original form. Boyle recognised that the things that surround us in our daily lives, such as wooden tables and chairs, and woollen dresses and hats, were made up of a variety of components, but they could not be reduced to the four Greek elements, or to the three elements of Paracelsus. Some believe that Boyle came up with the modern definition of a chemical element. He certainly came close when he described elements as things ‘not being made of other bodies, or of one another’. But he didn’t take this any further, nor did he use it in his own chemical experiments.
Instead, Boyle’s notion of the ‘corpuscle’ as a unit of matter suited his experimental purposes very well. Boyle was a tireless experimenter, spending hours in his private laboratory either alone or with friends, and writing up his experiments in great detail in books. It is partly this attention to detail that makes Boyle so special in the history of science. He and his friends wanted science to be open and public, and for others to be able to use the knowledge they gained. No longer was it enough to claim to have found out some deep secret of nature, as Paracelsus had done. A scientist needed to be able to demonstrate that deep secret to others, either in person or through written descriptions.
This insistence on openness was one of the guiding rules in the scientific circles in which Boyle moved. The first of these was an informal group in Oxford, where he lived in the 1650s; when most of the group moved to London, they joined with others to establish what became, in 1662, the Royal Society of London, still one of the leading scientific societies in the world. They knew that they were doing something that Francis Bacon had called for half a century earlier. Boyle was a leading light in this club devoted to increasing knowledge. From the beginning, the Fellows – as the Royal Society’s members were called – were keen that the new knowledge they uncovered and discussed at their meetings should be useful.
One of Boyle’s favourite collaborators was another Robert, a few years younger than him: Robert Hooke (1635–1702). Hooke was even cleverer than Boyle, but unlike Boyle, he came from a poor family. He always had to earn his way in life by his wits. Hooke was employed by the Royal Society to perform experiments at each of its meetings. He became very skilled at inventing and handling all kinds of scientific equipment. Hooke devised many experiments; for example, to measure the speed of sound, or to examine what happens when blood is transfused from one dog to another. In some cases the dog that had been given new blood seemed more energetic, and the men were encouraged to experiment with humans. They transfused blood from a lamb into a human being, but it didn’t work; in Paris, too, one person who had been given a transfusion died, so these experiments were given up. Hooke’s task at the Royal Society’s weekly meetings was to prepare two or three less deadly experiments to entertain and stimulate the Fellows.
Hooke was one of the earliest ‘savants’ to make good use of the microscope. (A ‘savant’ literally means ‘one who knows’, and the term was often used to describe what we would now call scientists.) He used his microscope to reveal a new world of things invisible to the naked eye, uncovering structures in plants, animals and other objects that could never be seen without using it. The fellows loved to peer through the microscope at their meetings, and in addition to Hooke’s demonstrations, they also received many communications from another famous early microscopist, a Dutchman named Antonie van Leeuwenhoek (1632–1723). Leeuwenhoek worked as a cloth merchant, but in his spare time he ground and polished very small lenses that could magnify things more than 200 times.
He had to make a new lens for each observation, and crafted hundreds during his long life. He would place each lens in a metal holder with the small object that he wanted to examine behind it.
He found tiny organisms in pond water, bacteria in the scrapings of his teeth and many other wondrous things. Hooke too believed that his microscope could take the observer closer to nature, and the illustrations in his book, Micrographia, published in 1665 (the very year of the London plague), caused a sensation. Many of these illustrations look odd to us, for they show very large, magnified insects, such as flies or lice, and these pictures have become quite famous. Yet he also filled his book with observations and speculations on the structures and functions of other things he could see through his microscope. He showed one picture of a thin section of cork, from the cork tree – the material used to close wine bottles. He called the little boxy structures he saw there ‘cells’. They weren’t actually what we now call cells, but the name stuck.
Both Boyle and Hooke had a favourite mechanical device: their version of the air pump. Hooke and Boyle’s air pump worked in the same way as the pumps we use to put air into bicycle tyres or foot- balls. It had a large central cavity, with a tight fitting that could be opened at the top, and another opening in the bottom, where there was a valve through which gases could be drawn in or let out. It might not seem very exciting, but it helped solve one of the major puzzles of science during the period: whether it was possible to have a vacuum, that is, completely empty space, not even containing air. Descartes had insisted that vacuums were impossible (‘Nature abhors a vacuum’ was the common phrase expressing this idea).
But if, as Boyle had argued, matter was ultimately composed of separate corpuscles, in different forms, there ought to be some space between them. If something like water is heated, so that it evaporates and turns into a gas, the same corpuscles would still be there, said Boyle, but the gas occupies more space than the liquid had done. After lots of experiments heating liquids to gases, he saw that all gases behaved pretty much the same when they were in the air pump. Boyle and Hooke came to a conclusion that is still known as Boyle’s Law. At a constant temperature, the volume that any gas occupies has a special mathematical relationship to the pressure that it is under. We say that its volume is directly influenced by the pressure around it. So, if you increase the pressure by decreasing the space it occupies, the gas squeezes into the available space. (If you increase the temperature, the gas expands, and a new pressure comes into effect, but it’s the same basic principle.) In the future, Boyle’s Law would help the development of the steam engine, so remember him when we get there.
Boyle and Hooke used their air pump to examine the characteristics of many gases, including the ‘air’ that we breathe. Air was, remember, one of the Ancients’ elements, but it was becoming clear to many people in the seventeenth century that the air that surrounds us and keeps us alive is not a simple substance. It was obviously involved in breathing, since we draw air into our lungs when we take a breath. But what else did it do? Boyle and Hooke, both individually and together, were very interested in what happens when a piece of wood or charcoal burns. They also wondered why blood was dark red before it went into the lungs and bright red when it came out of them. Hooke linked these two questions together and suggested that what happens in the lungs is a special kind of combustion, with the ‘air’ being the substance that connected both the breathing and the burning. Hooke pretty much left it at that, but the problems surrounding both the composition and nature of ‘air’, as well as what happens during respiration (breathing) and combustion, continued to intrigue scientists for more than a century after Boyle and Hooke, as people repeated and developed their experiments.
There was hardly any area of science that Robert Hooke did not think about. He invented a watch run by a set of springs (a great improvement in time-keeping), wondered about the origin of fossils, and investigated the nature of light. He also had brilliant things to say about a problem we have encountered before, and will look at in more detail in the next chapter: the physics of movement and force. Hooke was investigating these subjects at the same time as Isaac Newton. As we shall see, Newton himself is one of the reasons that everybody has heard of Sir Isaac, but few people know about Mr Hooke.