412 



NA TURE 



[Mar. 26, 1874 



First, then, with regard to chemistry. What is chemistry? 

 It is a science which deals with the matter which surrounds us, 

 and of which the whole planet and we ourselves are built up. 

 We see everywhere around us an enormous number of apparently 

 perfectly distinct things, some of them having vital properties, some 

 of them lifeless, motion'ess ; but out of this apparently infinite 

 diversity chemistry presents us with an almost perfect simplicity. 

 It tells us that everything which exists here is really made up of 

 only sixty-three different things ; that the whale of the animal 

 kingdom, the vegetable kingdom, the mineral kingdom— every- 

 thing— is made up of only sixty-three dififerent substance-. That 

 is a wonderful simpHlication, and science always simplifies. 



Now we may look upon those sLxtythree elements in tvi'o 

 distinct points of view. We may consider them in their physical 

 relations, or we may regard them in a more purely chemical 

 aspect. If we lo>k upon them in relation to their physical 

 conditions, we find that amongst tliem are fifty-six solids, two 

 liquids, and five gases. If we look upon them chemically, 

 dropping all distinctions between solids, liquids, and gases, we 

 say that some of them are metals, some metalloids ; and of some, 

 it may be truly said that it is very difficult to place them exactly 

 — to determine whether they are on the side of the metals or on 

 the side of the metalloids — in the same way as the biolo- 

 gist finds it absolutely impossible to put his finger upon any 

 particular part of the organic world and say, Here the vege- 

 table, or here the animal, kingdom begins. All these chemical 

 distinctions, then, are quite independent of physical conditions. 

 For instance, I shall have to show you that amongst the niDst 

 metallic ol the metals is a gas. Again, among the metals we 

 have a liquid — mercury; so that we have a co'uplete chain of 

 gas, liquid and solid among the metals, although popularly the 

 term metal is often imagined to apply only to such solids as 

 gold, silver, and iron. On the metalloid side, again, we have 

 gases among them the familiar oxygen and nitrogen ; we have the 

 liquid bromine, and so on, added to other unmistakable metal- 

 loids, such as phosphorus, sulphur, carbon, and iodine, generally 

 thought of in their solid form. 



Now what are the chemist's tools by which he has brought 

 about this marvellous simplicity, what the processes by which he 

 carries on his operations ? 1 answer, in the main vibrations. 

 He finds the world composed of molecules in millionfold com- 

 plexities, combinations, and sizes, and he acts upon these mole- 

 cules by vibrations. For gross molecules he finds in heat most 

 that he wants, but when the molecules are more delicate, then 

 electricity is called in, and electricity does fi^r these what heat 

 did for the others. 



Let me here endeavour to make my meaning clear. I 

 want you to assume a long series of vibrations, long at one 

 end of the series and short at the other. We know that 

 heat consists of vibrations, we know that light consists of 

 vibrations. I will also ask you to think of electricity as 

 connected wiih vibrations, and I ask you further to assume 

 these vibrations to be short. We get heat from the sun, 

 and among these vibrations are some to which our eye 

 is tuned. We get an immense vibration of heat from the oxy- 

 hydrogen flame, a llanie the heat of which is due to the forma- 

 tion of the gaseous molecules of water, but we get, practically 

 speaking, no light. Many of the electric il phenomena with 

 which we are acquainted take place unseen, and without heat, 

 showing they are not long- wave phenomena ; others are exquisitely 

 visible to us, beciuse the vibrations are within our ken ; but, to 

 get associated heat, we want presmre, and with pressure we can 

 render the oxyhydrogen flame luminous. In fact — and here let 

 me be perfectly frank with you — I call your attention to the 

 " tts if "- -it is as if we have long heat-waves at one end of a 

 long scale, and short electricity-waves at the other, each with 

 different functions, heat giving us with solids and liquids visible 

 phemonena, because of added shorter waves, electricity giving us 

 visible phenomena with gases and vapours, because of added longer 

 waves; heat passing invisibly through gases, electricity passing 

 invisibly through solids ; heat bringing; about chemical changes 

 in solids and liquids, electricity bringing about s'lnilar changes 

 in the case of gases. 



Now, this being so, let us assume, for the purposes of the 

 present statement, that the mode of motion heat, with its long 

 waves, chiefly affects the larger molecules, that is, comjiound 

 bodies, and the mode of motion electricity, whatever electricity 

 may be, chiefly affects the smaller molecules, that is, the atoms of 

 simple substances. We shall find, in accordance with this 

 assumption, that if a chemist wishes to reduce the millions of 



compound molecules in that very compound molecule a piece of 

 ice, he applies heat, and he gets a physical simplitication, but 

 not a chemical one, when water is produced ; a still further, and 

 exactly similar, stage is reached when this water takes tlie form 

 of steam, but it is not till an enormous temperature, with its 

 addel short vibrations, or electricity, is employed, that the com- 

 pound molecule breaks up into the simple things oxygen and 

 hydrogen, unless another vibration is superadded of a molecule 

 of another simple thing (or element) which shall aid in shaking 

 them apart. 



As instances of the action of heat, I will show you one or 

 two experiments to indicate that in a great deal of chemical 

 action the heat vibration requisite to bring about that 

 simplification by means of which the simple bodies have 

 been determined to exist as such is supplied by the chemical 

 action itself ; it is the heat of arrested motion. In other cases 

 we have to supply the heat artificially ; but alsj bear this in 

 mind, that whenever we apply artificial heat the heat is none of 

 our making. It also is the result of a chemical combination. 

 For instance, if I take some potassium and thrjw it int.) water, 

 that potassium will instantly burst into flame. You will see that 

 we have a perfectly cool metal put into perfectly cool water, and, 

 as you see, it at oice takes fire in consequence of the heat of 

 combination which has been brought about by the attraction 

 between the potassiunr and the water. And if I had time I could 

 show you that as the result of that heat-vibration thus introduced 

 the water has been simplified, one of its constituent simple things, 

 hydrogen, has been liberated, and I might have collected ii in a 

 bell jar. 



Another illustr.ition is to be got from a mixture of water and 

 sulphuric acid. I have, in a test-tube, some ether, and I have 

 the water. When I pour the water into a glass you will see 

 that the ether in the test-tube placed in the glass will remain as 

 if nothing had happened. But no.v I will pour some sulphuric 

 acid into the water, and what happens ? We get an attraction 

 between these two things : we get a heat vibration as the result 

 of chemical combination ; and, as the result of the heat vibration 

 produced in that nnnner, the water gets hot and the ether boils, 

 the boiling point of ether being below that of water. 



Here is another experiment, and I have chosen these out of 

 many others which might have been brought before you, 

 to show the changes brought about by heat vibrations. Here 

 we have some bichromate of potassium, and on the application 

 of heat it will be inUantly reduced. When I say instantly re- 

 duced, probably a few seconds will be required in order to allow 

 the heat vibration to act, and you will then have a change of 

 colour in the solution brought about by the application of heat, 

 artificial, so to speak, in this case, although, as I have already 

 cautioned you, the heat of the Bunsen burner which we employ 

 is really an effect of chemical combination. 



But not only have we heat with its long waves to bring about 

 chemical action and its result, simplification, but, as I have said, 

 we have another agent, electricity. I have here two tubes 

 filled with water, and a battery, and in each tube connected with 

 this battery is a strip of platinum. The instant that the 

 circuit is made complete you see that the water is decomposed, 

 bubbles rise from the platinum foil, which bubbles in the one 

 case are bubbles of hydrogen, and in the other case bubbles of the 

 other constituent of the water — oxygen. Here you see, by 

 means not of the long wave; of heat, but by means of elec- 

 trici'y, we bring about a coaiplete dissociation or a co.nplete 

 separation of the elements of the water which originally was 

 in these two tubes. Anl if we were to allow the experiment to 

 go on a little longer, you would see that not only is there the 

 evolution of gas in each of the tubes, but that the evolution will 

 be greater in one tube than in the other, for this reason, that 

 in the water there are two equivalents of hydrogen to one of 

 oxygen. 



These then are instancis of simplificatio.i brought about by 

 heat and electricity. I quit this part of the subject by the remark 

 that the ultimate particles of an element are called atoms ; that 

 agglomerations of atoms are termed molecules ; elementary mole- 

 cules when the atoms are alike ; compound molecules when the 

 atoms are dissimilar. The heat-waves generally help us to 

 get at the molecule, and electricity helps us to get at the 

 atom; and ma-k, I only say ^Liicrally. It might be univer- 

 sally true if all elementary atoms were alike ; but on that point 

 we must be content to say that we do not know. But 1 ini'ilit 

 place much evidence before you which indicates that they are 

 vastly different. We can only study them by their vibrations ; 



