Int: Bien venuto, Count & Countess Avogadro, and thank you for joining us this evening! Let's begin by asking how you would prefer to be addressed. You have the titles Count, Doctor of Law, and Professor Emeritus. What is your choice as we talk this evening?
AA: Bon giorno! Please just call me Amedeo, and my wife Felicita, or you may use any of the titles if it pleases you.
Int: Amedeo, did you plan to devote your career to the study of chemistry and physics all through your early education?
AA: No, no! My father was a distinguished lawyer, senator, and later advocate general and senate president. He expected that I would follow in his footsteps. Actually, as a young boy I was educated at home. Then later I studied law and took my bachelor in jurisprudence when I was sixteen. I earned my doctorate in ecclesiastical law four years later, in 1796.
Int: Why did you change what appears to have been a very successful career?
AA: Well, I did enjoy practicing law, and pursued the vocation for five years. I also had an interest in natural philosophy, which you would call science, and began studying mathematics and physics in 1800. I would certainly suggest to students of all ages to pursue their specific interests and see what may become of that pursuit.
Int: What area of scientific study first attracted you, Amedeo?
AA: I had been particularly impressed by some discoveries of my compatriot Alessandro Volta. My brother Felice and I turned our attention to the study of electricity during 1803. The satisfaction I received from our experiments and studies convinced me that physical science would be my life's occupation.
Int: Can you tell us what resulted from those experiments?
AA: Si, my brother and I were nominated to the Royal Academy of Sciences of Turin the following year, which is a great honor, you know. Also, I had the opportunity to become a demonstrator at the Royal College of the Provinces.
Int: So you made your living as a scientist rather than a lawyer?
AA: I was still very active in public affairs and held many public offices connected with national statistics, meteorology, and weights and measures. I also was a member of the Superior Council on Public Instruction. But si, the vast majority of my energies were devoted to science and teaching.
Int: Where did you do your teaching, Amedeo?
AA: I was a Professor of Physics and Mathematics at the Royal College in Vercelli from 1809 to 1821. Then I held the Chair of Mathematical Physics at Turin for most of the period from 1821 until my retirement in 1850. There was a time between 1823 to 1833 when political influences disrupted my tenure, and it was held by someone else for part of that time.
Int: Count, were there professional organizations or societies for scientists in Italy at that time?
AA: Si. I became a full member of the Academy of Sciences of Turin in November 1819. However, I did not seek or recieve election to either the Paris Academy or the Royal Society of London.
Int: Let's get back to the personal side for a moment, if you don't mind. I understand you have quite a family, Count Avogadro.
AA: Si, si! Felicita and I rear six sons. None were as interested in the sciences as I, but found the law profession more appealing, as had my father. For instance, Luigi was a general in the Italian army, and Felice (named after his uncle, of course), became president of the Courtof Appeal.
Int: Professor, what inspired your now famous hypothesis?
AA: A contemporary of mine, Gay-Lussac, published a memoir in 1809 which showed that all gases expand to the same extent with rise in temperature. To my mind this made it obvious then that all gases, at a given temperature and pressure, must then contain the same number of particles per unit volume. It is really quite simple....
FA: Forgive my interruption, but my dear husband is far too modest! It was actually a most ingenious and daring interpretation which led him to draw this momentous conclusion. Amedeo never received proper credit at the time you know. It was almost fifty years later that the scientific world finally realized the value of his hypothesis.
Int: Were these conclusions published for the scientific community to review?
FA: I'd like to read from Amedeo's actual memoir of 1811, to demonstrate his now accepted correctness of thought and gentle generosity of spirit, even though at the time his conclusions were rejected by Dalton and ignored by Berzelius:
"M. Gay-Lussac has shown in an interesting memoir... that gases always unite in a very simple proportion by volume, and that when the result of the union is a gas, its volume is very simply related to those of its components. But the quantitative proportions of substances in compounds seem only to depend on the relative number of composite molecules which result. It must be then admitted that very simple relations also exist between the volumes ofgaseous substances and the numbers of simple or compound molecules which form them. The first hypothesis to present itself in this connection, and apparently even the only admissible one, is the supposition that the number of integral molecules in any gas is always the same for equal volumes, or always proportional to the volumes."And the second part of the hypothesis is perhaps more important; it was certainly the most daring.
Int: Really, Countess Felicita! Won't you tell us more about this "second part" that you speak of?
FA: You see, Amedeo realized that Gay-Lussac's experiments also showed that particles did not have to be individual atoms, but rather could be combinations of atoms. For instance, hydrogen gas particles could be made up of two atoms of hydrogen, and water could be three atoms per particle-- two of hydrogen and one of oxygen. I read again from the memoir:
"We suppose... that the constituent molecules of any simple gas whatever...are not formed of a solitary elementary molecule (atom), but are made up of a certain number of these molecules united by attraction to form a single one."AA: That's the part that Dalton and Berzelius couldn't accept, you know, especially the diatomic molecules. It meant that many of the atomic weights that Dalton had put forward were wrong. According to my hypothesis hydrogen was 1/16 as heavy as oxygen, not 1/8 as he thought.
Int: Let's talk more about this particle controversy. I understand that there was some confusion about the use of the words "atom" and "molecule" in your memoir.
AA: In the original paper, which was published in 1811, I avoided using the word "atom." Looking back now, that may have been a mistake, but things were very different then, you understand. There was no real agreement on what an atom was. Rather, I distinguished between the various types of particles using the terminology suggested earlier by Macquer and Fourcroy:
AA: As I said, perhaps a mistake...
Int: It certainly sounds like this hypothesis of yours had people thinking! What effect did it have on theories of the time?
AA: An important contribution was in deriving relative weights of individual molecules. If the number of particles in equal volumes of gases is equal, it allows a very useful relationship: the ratio of the weights of equal volumes of gases is equal to the ratio of the weights of single particles of each individual gas. For example:
thus, individual oxygen particles are 16 times as heavy as individual hydrogen particles.
Int: So, was this famous hypothesis the end of your scientific work?
AA: Oh no, I continued to studies in physics and chemistry almost to the end of my life.
Int: I'm glad you brought that up, Count, since it's a bit of a touchy subject. When did you die?
AA: On July 9, 1856, in Turin. The same city that saw my birth eighty years before.
Int: And I understand that it was some time after your death that this famous hypothesis was finally accepted.
AA: Si. My countryman Cannizzaro presented a paper at the Karlsruhe Congress in 1860, which expounded a system of atomic weight determinations based largely on my work. It was favorably received.
Int: Any comments as to why you think it took so long for your hypothesis to gain recognition?
FA: Please, may I answer once again for my dear husband? I'm afraid he is too close to this topic to answer objectively, and there are several reasons his work was neglected for so long.
Int: By all means, Countess!
FA: First of all, there's that lack of clarity in the use of the term "molecule." Also, Amedeo was not known for his experimental techniques, and he did not have an impressive accumulation of results to support his hypothesis. He was predominantly a theorist, not an experimenter. Then he tried to extend his theory of polyatomic molecules to metallic elements with no experimental evidence. That didn't help his credibility.
Int: No, I imagine it didn't. I understand also that organic chemistry was getting most of the attention in the first half of the 19th century. Analysis and classification of organics were really the hot topic.
FA: Si, a good point. Also, Berzelius' view of similar atoms repelling was the dominant view of the time. Amedeo's diatomic molecule conflicted sharply with this view. I think the biggest problem, however, was that Amedeo was intellectually isolated from the chemical community. He was on the Italian side of the Alps doing his research while the French chemists were in the eye of the scientific community. Amedeo did value his privacy, and his family always came first.
Int: Well, it sounds like the influential chemists of the day just weren't ready to give your work a very careful hearing during your lifetime, Professor. Now, of course, your hypothesis is considered a keystone of modern chemistry, providing a vital link between Dalton's atomic hypothesis and Cannizzaro's atomic theory.
Thank you again, Count and Countess Avogadro, for helping us to understand a little better this important hypothesis and the times in which it was developed. Good bye to you both!
Eduard Forber, Ed., Great Chemists, Interscience Publications, 1961.
Charles Coulston Gillispie, Ed., Dictionary of Scientific Biography, Vol. I, Charles Scribners' Sons, N.Y., 1970.
Mario Morselli, Amedeo Avogadro, A Scientific Biography, Kluwer Academic Publishers, USA, 1984.
"Review," a review of the book Avogadro and Dalton: The Standing in Chemistry of Their Hypotheses, by Dr. Andrew Meldrum, Nature, No. 1926, Vol. 74, Sept. 27, 1906, pp.537-8.
Edgar C. Smith, "Amedeo Avogadro," Nature, No 2196, Vol. 88, Nov. 30, 1911, pp. 142-3.
Sir William A. Tilden, Famous Chemists: The Men and Their Work, 1921, 1968.
Trevor I. Williams, Ed., A Biographical Dictionary of Scientists, Halsted Press/John Wiley & Sons, 1974.