Phlogiston – Early Science at Work

One of the earlier scientific concepts was phlogiston, and it is of interest to follow why this concept went wrong, if it did. One of the major problems for early theory was that nobody knew very much. Materials had properties, and these were referred to as principles, which tended to be viewed either as abstractions, or as physical but weightless entities. We would not have such difficulties, would we? Um, spacetime?? Anyway, they then observed that metals did something when heated in air:

M   + air +  heat        ÞM(calx) ±  ???  (A calx was what we call an oxide.)

They deduced there had to be a metallic principle that gives the metallic properties, such as ductility, lustre, malleability, etc., but they then noticed that gold refuses to make a calx, which suggested there was something else besides the metallic principle in metals. They also found that the calx was not a mixture, thus rust did not lead to iron being attached to a lodestone. This may seem obvious to us now, but conceptually this was significant. For example, if you mix blue and yellow paint, you get green and they cannot readily be unmixed, nevertheless it is a mixture. Chemical compounds are not mixtures, even though you might make them by mixing two materials. Even more important was the work by Paracelsus, the significance of which is generally overlooked. He noted there were a variety of metals, calces and salts, and he generalized that acid plus metal or acid plus metal calx gave salts, and each salt was specifically different, and depended only on the acid and metal used. He also recognized that what we call chemical compounds were individual entities, that could be, and should be, purified.

It was then that Georg Ernst Stahl introduced into chemistry the concept of phlogiston. It was well established that certain calces reacted with charcoal to produce metals (but some did not) and the calx was usually heavier than the metal. The theory was, the metal took something from the air, which made the calx heavier. This is where things became slightly misleading because burning zinc gave a calx that was lighter than the metal. For consistency, they asserted it should have gained but as evidence poured in that it had not, they put that evidence in a drawer and did not refer to it. Their belief that it should have was correct, and indeed it did, but this avoiding the “data you don’t like” leads to many problems, not the least of which include “inventing” reasons why observations do not fit the theory without taking the trouble to abandon the theory. This time they were right, but that only encourages the act. As to why there was the problem, zinc oxide is relatively volatile and would fume off, so they lost some of the material. Problems with experimental technique and equipment really led to a lot of difficulties, but who amongst us would do better, given what they had?

Stahl knew that various things combusted, so he proposed that flammable substances must contain a common principle, which he called phlogiston. Stahl then argued that metals forming calces was in principle the same as materials like carbon burning, which is correct. He then proposed that phlogiston was usually bound or trapped within solids such as metals and carbon, but in certain cases, could be removed. If so, it was taken up by a suitable air, but because the phlogiston wanted to get back to where it came from, it got as close as it could and took the air with it. It was the phlogiston trying to get back from where it came that held the new compound together. This offered a logical explanation for why the compound actually existed, and was a genuine strength of this theory. He then went wrong by arguing the more phlogiston, the more flammable the body, which is odd, because if he said some but not all such materials could release phlogiston, he might have thought that some might release it more easily than others. He also argued that carbon was particularly rich in phlogiston, which was why carbon turned calces into metals with heat. He also realized that respiration was essentially the same process, and fire or breathing releases phlogiston, to make phlogisticated air, and he also realized that plants absorbed such phlogiston, to make dephlogisticated air.

For those that know, this is all reasonable, but happens to be a strange mix of good and bad conclusions. The big problem for Stahl was he did not know that “air” was a mixture of gases. A lesson here is that very seldom does anyone single-handedly get everything right, and when they do, it is usually because everything covered can be reduced to a very few relationships for which numerical values can be attached, and at least some of these are known in advance. Stahl’s theory was interesting because it got chemistry going in a systemic way, but because we don’t believe in phlogiston, Stahl is essentially forgotten.

People have blind spots. Priestley also carried out Lavoisier’s experiment:  2HgO  + heat   ⇌   2Hg  + O2and found that mercury was lighter than the calx, so argued phlogiston was lighter than air. He knew there was a gas there, but the fact it must also have weight eluded him. Lavoisier’s explanation was that hot mercuric oxide decomposed to form metal and oxygen. This is clearly a simpler explanation. One of the most important points made by Lavoisier was that in combustion, the weight increase of the products exactly matched the loss of weight by the air, although there is some cause to wonder about the accuracy of his equipment to get “exactly”. Measuring the weight of a gas with a balance is not that easy. However, Lavoisier established the fact that matter is conserved, and that in chemical reactions, various species react according to equivalent weights. Actually, the conservation of mass was discovered much earlier by Mikhail Lomonosov, but because he was in Russia, nobody took any notice. The second assertion caused a lot of trouble because it is not true without a major correction to allow for valence. Lavoisier also disposed of the weightless substance phlogiston simply by ignoring the problem of what held compounds together. In some ways, particularly in the use of the analytical balance, Lavoisier advanced chemistry, but in disposing of phlogiston he significantly retarded chemistry.

So, looking back, did phlogiston have merit as a concept? Most certainly! The metal gives off a weightless substance that sticks to a particular gas can be replaced with the metal gives off an electron to form a cation, and the oxygen accepts the electron to form an anion. Opposite charges attract and try to bind together. This is, for the time, a fair description of the ionic bond. As for weightless, nobody at the time could determine the weight difference between a metal and a metal less one electron, if they could work out how to make it. Of course the next step is to say that the phlogiston is a discrete particle, and now valence falls into place and modern chemistry is around the corner. Part of the problem there was that nobody believed in atoms. Again, Lomonosov apparently did, but as I noted above, nobody took any notice of him. Of course, is it is far easier to see these things in retrospect. My guess is very few modern scientists, if stripped of their modern knowledge and put back in time would do any better. If you think you could, recall that Isaac Newton spent a lot of time trying to unravel chemistry and got nowhere. There are very few ever that are comparable to Newton.


Memories from Fifty Years Ago: Invasion of Czechoslovakia 1.

This post is to remind myself that fifty years ago (1968) my little Ford Anglia and I did a road tour behind some of the old Iron Curtain. I was something of an oddity, and I was sometimes referred to as a “stupid Bulgarian” for putting the GB sticker on back to front. The cobbled roads of Poland did not do a lot of favours for the car, since driving towards Krakow on August 22 the clutch mechanism began leaking hydraulic oil, and finding somewhere to get spare oil was a nightmare. Fixing it was impossible; getting the appropriate parts for a very aged British car behind the Iron Curtain was not going to happen. Interestingly, when I stopped at probably the only garage between Gdansk and Krakow, the Poles there refused to speak German. Germans could go to hell! When I managed to get through to them that I was English (OK, I wasn’t, but why a New Zealander was driving a British car would be to much) they suddenly became very helpful. Memories of the Third Reich had not died down.

Back on the road, and before long I overtook what I assume was a motor rifle Division. Trucks carrying soldiers, tanks, artillery, it seemed to take a lot of the afternoon passing it, with me driving on the left hand side of the road, which, of course, felt like usual driving. It seemed a little ominous because I had one more day on my Polish visa, and if you look at a map, options were limited. Interestingly, when I got into my car the following morning in Krakow, the usual black-market currency trader came up to me, and when he found I was going to Czechoslovakia, he immediately offered Czech crown at a huge discount. Even stranger, he would take zloty instead of the usual hard currency. I emptied out my zloty previously bought at a big discount in exchange for some D-mark, and which I could not find anything to spend them on, and got a big fistful of crowns.

On August 23, 1968, I crossed the border at Cieszyn into Czechoslovakia, as it was then known. Unbeknown to me, the Russian army had crossed the previous night. Getting across the border was interesting, but my expiring Polish visa meant there was nowhere else to go, and I had a legitimate visa for getting into Czechoslovakia. The border guards gave way to a military officer, and when I said I was trying to get to Vienna, he let me through. I stopped at an open square in Frydek-Mystek and bought myself a beer and some lunch. I was glad to taste Czech beer, which was far better than Polish beer, and looked out to see a tank on the other side of the square, and a number of soldiers. It was a beautiful sunny day, and the soldiers seemed to be dozing, while the people ignored them. Someone wanted to put a Czech flag on the aerial of my car, so I let them. Then it occurred to me that the person who let me through the border probably had a Russian uniform. Oops! The next bit of news was all the borders were closed.

So, where to go? The next step was fairly obvious: Olomouc. From there, roads went to Brno or Praha. Brno is near the border with the route to Vienna, but there were likely to be far more westerners in Praha, which meant that with more options, it was more likely a border would open soon. It was also reasonably obvious that I would have to stay the night somewhere, so that somewhere might as well be Olomouc. When I got there, all was not well because it was late afternoon. I tried the odd hotel, and met someone who would make a cameo appearance in one of my novels: he spoke 13 languages, so he claimed, but none were English, French or German. So, on the road again. I took the road towards Praha (and I cannot recall whether this was a decision or accidental) and nothing much happened except it started to get darker, then it was clearly night. I was going at about 60 mph, and came over a hill when I saw a small fire to the left and something not right. Emergency avoidance! I swerved left and went into a four-wheel drift, sending a shower of stones towards some clearly frightened soldiers (they would see a ton of steel heading their way). Fortunately, my youthful time spent doing drifts on gravel roads came to my assistance as I held the car and carefully made it back onto the road. (Hint – returning to the road is the most dangerous part as it is easy to overcompensate and start rolling.) Going left was pure instinct. Nevertheless, I had avoided colliding with a tank parked in the centre of the road and covered with camouflage netting to hide its shape. All the same, I decided I had better stop driving soon.

I came to a little village where the road turned right, but there was a further road going left and straight ahead. The road signs had been switched, directing traffic to Praha straight ahead. I stopped, and the Czech flag did a good thing – it brought someone who spoke English. He told me the obvious, but I said I really needed somewhere to stop. He took me to a hotel down to the left, and I found it was illegal to be moving. My guide said he would burn down the hotel if the manager didn’t accept me. Would I permit him to register me from the day before? Of course. Everyone was happy. After ensuring my belongings were in the room, I went back to the cross-roads where part of a Division was passing through. There was a Czech out there indicating the false road, where the sign was pointing but the soldiers were not to be fooled. There was a gap in the traffic, and I approached my new friend, and suggested he get the Czech on the road to point the right way: the drivers would not believe a Czech was trying to be helpful. So when the next part of the Division arrived, the Czech was ignored and the trucks started going down the wrong way. This went on for about half an hour, when a driver was almost going down the wrong way but he realised his mistake and hit the brakes. Everybody stopped behind him. He flung his truck into reverse and shot backwards, furious at the agitated crowd. What he forgot was he had a trailer with an artillery piece on the back, the barrel of which smashed the following truck’s window and the driver only just evaded. The crowd roared. Eventually, this was sorted and what was left of the Division went the correct way. I later learned that a Polish Division was split into five parts that night and it took three days or so to get them all back together. My small contribution to military history!

Next morning I was off to Hradec Kralove, where I found a garage. They could not sell petrol, but I did get a litre of hydraulic oil. They refused payment; it was illegal to sell anything under the occupation. My Czech flag was working! I took the road to Praha and all was well on another gorgeous morning. I passed a detour sign, but I knew better. (I had passed lots of them before.) I kept driving and I must have been fairly close to Praha when there was a minor disaster in the making. There was a dry riverbed, but no bridge. On the other side the road went behind a belt of trees. The last detour sign appeared to be true, but I had only two gallons of petrol left and there was no way I could make it around the detour. I took something of a deep breath, put the car in second gear and went down the bank to the streambed and floored the accelerator. I got up to about 45 mph by the other side, sustaining ferocious bouncing, then up the other side. I had just enough momentum to get over the lip and onto the road. Joy! Through the belt of trees and . . . Oops. I was at the back of a Russian military camp. This Czech flag may not be working in my favour now . . .

More next week for those interested.