The second concerned the nature of "oxymuriatic acid" (chlorine).
Among the substances of which he investigated the composition were ammonia, sulphuretted hydrogen and prussic acid, and his experiments on chlorine, which he regarded, not as an element, but as oxygenated muriatic (oxymuriatic) acid, led him to propose it as a bleaching agent in 1785.
Next year, in a paper read in July and in his fifth Bakerian lecture in November, he argued that oxymuriatic acid, contrary to his previous belief, was a simple body, and proposed for it the name "chlorine."