Spallanzani, la chimica e la "variazione accettabile"

On April 1st 1795, after three months of laboratory experiments on respiration, something odd caught Lazzaro Spallanzani’s attention: to his great surprise, he noticed an increasing presence of nitrogen in the air flowing through the lungs of test subjects. Following this observation, Spallanzani started verifying the experimental data obtained by the German chemist J.F.A. Göttling, who – against Lavoisierians – believed nitrogen capable of reactivity. This paper reconstructs the evolution of Spallanzani from his early endorsement of Göttling’s thesis to its complete refutation (1796). In doing so, Spallanzani developed a well-structured experimental procedure and successfully used the concept of “acceptable variation.” Still, his gruelling work on gases had no substantial impact on his biological research. The production of nitrogen remained an unexplained fact, and until his death (1799) he continued his search for acceptable coefficients of variation. But in this case, he did not find firm criteria to separate – as he said – the “costante” from the “accidentale”.