Technikatörténeti szemle 10. (1978)

A MÉRÉS ÉS A MÉRTÉKEK AZ EMBER MŰVELŐDÉSÉBEN című konferencián Budapesten, 1976. április 27–30-án elhangzott előadások II. - Szabadváry F.: Tömegmegmaradás elve; mérés és számolás a kémiában

only transformations take place." We can be certain that Lavoisier, if he had meant this to be a novel discovery, would have announced it with much more ado. None the less, there is something new in this statement as compared to those of his predecessors. In those formulations the thesis is general, it refers, as it were, to the totality of the universe, as become philosophers. Lavoisier's formulation brings it down from its sublimity to the fermentation of must, to a partial phenomenon, and pronounces its validity separately for every chemical process. However, there is no question of a balance. Lavoisier, to be sure, did use balances, very often and very accurate ones. Among others, in 1772, when he demonstrated that when tin is being burned in a sealed flask, the weight of the flask does not change. From this experiment he developed

—implicitly assuming the principle of conservation of matter

— the new combustion theory. Lomonosov demonstrated the same in 1756, also using a balance. So good weighing can lead to good conclusions. Both of them proved that the similar experiment carried out by Boyle at the end of the 17th century was erroneous. Boyle found a weight increase when burning tin under similar conditions. Apparently there was some error in the experiment, presumably the seal was not tight. Boyle's erroneous statement contributed to the establishment of the phlogiston theory. Theories can be based on errors, and the more distinguished the person who errs, the greater the authority of the erroneous theory. It is, however, evident that already Boyle used weighing. From erroneous weighing, wrong conclusions can be drawn, like Boyle did, assuming that the fire particles pass through the wall of the flask. Indeed, the human mind is capable of finding an explanation for anything. Before Boyle, Helmont also came to a conclusion, around 1600, from weighing, concerning the final component of matter. He attempted to refute Aristotle's millenial doctrine of the four elements (fire, water, earth, air) by weighing 200 pounds of dried earth into a big vessel and planting a willow twig weighing 5 pounds into it. He covered the vessel with a fine screen and watered the twig every day with rain water. After five years he ended the experiment. He took out the earth, dried it and weighed it. He found that only two ounces of the original weight were lacking. He also weighed the willow tree that had developed from the twig. Its weight was 164 pounds. Since he had only added water, he assumed that it was this water that had been transformed into a tree. This reasoning necessarily presumes that nothing comes into being from nothing, matter does not come into being, but is only transformed. Helmont then burnt the tree, whereby air (carbon dioxide) was formed and a small amount of earth (ash) was left. So he reasoned that these also originated from water. The final element, consequently, is water. This example demonstrates that wrong conclusions can be drawn from good experimental results, since conclusions are always limited, to a certain extent, by the general notions of the given period on Nature and its phenomena, and these limits are not easy to cross. '' All these experiments and theories based on weighing, in their own period, fundamentally contributed to the development of chemistry as a whole, even if progress sometimes followed a zigzag line. Anyhow, the use of the balance is much more ancient in chemistry than is often proclaimed. In fact, it has always been an indispensable tool of the laboratory. The balance is much older than the laboratory, since it exists for 6000 years, whereas alchemy and with it, the chemical laboratory was born only 2000 years ago in that same Egypt where the balance had a dominant