At the age of 25, Antoine Lavoisier bought a share in a consortium that collected taxes for the king of France. His work as a tax administrator not only made him a wealthy man but also influenced his approach to science. Like a bookkeeper, he paid obsessive attention to the weights of his chemical ingredients before and after each reaction — an approach that became a model for all future chemists. Before and after work each day, Lavoisier spent hours in a private laboratory equipped with the finest instruments money could buy. One day a week he welcomed others into his lab to take part in his ambitious experiments, but his most important collaborator was his wife, Marie Anne, who brought her own extraordinary talents to their partnership.