“As the new compound in its purest form is possessed of a bright yellow-green colour, it may be expedient to designate it by a name expressive of this circumstance and its relation to oxymuriatic gas. As I have named that elastic fluid Chlorine; so I venture to propose for this substance the name Euchlorine, or Euchloric gas from ευ and χλωρος. The point of nomenclature I am not inclined to dwell upon. I shall be content to adopt any name that may be considered as most appropriate by the able chemical philosophers attached to this Society” [the Royal Society]. Euchlorine was subsequently discovered by Soubeiran to be a mixture of chlorine and chlorine peroxide, a gas which Davy himself afterwards isolated in a pure state. It is however obvious from the accounts he gives that even in his first paper he must have been experimenting with a fairly pure product, due probably to the circumstance that he had collected the mixed gases over mercury, which retains the greater part of the chlorine. Former experimenters had collected the gas over water, which dissolves the chlorine peroxide more readily than the chlorine. Madame de Staël once observed that an interesting book might be written on the important consequences which have sprung from little differences. It ought to be noted, however, that Davy had himself doubts whether his euchlorine was not a mixture of chlorine and the gas which he subsequently discovered, and to which he says: “I shall not propose to give any name till it is determined whether euchlorine is a mixture or a definite compound.” It has been stated that Davy discovered the two chlorides of phosphorus. In a paper read to the Royal Society on June 18th, 1812, “On some Combinations of Phosphorus and Sulphur and on some other Subjects of Chemical Inquiry,” he reverts to these substances, as they “offer decided evidences in favour of an idea that has been for some time prevalent among many enlightened chemists and which I have defended in former papers published in the Philosophical Transactions; namely that bodies unite in definite proportions, and that there is a relation between the quantities in which the same element unites with different elements.” He first makes a determination, singularly accurate for the time, of the amount of chlorine contained in the lower chloride, and finds that 13·6 grains on decomposition with water afforded 43 grains of horn-silver; theory requires 42·6 grains. By synthetical experiments he came to the conclusion that the amount of chlorine absorbed by phosphorus to form the higher chloride was exactly double that contained in the lower chloride: he found that 3 grains of phosphorus combined with 20 grains of chlorine: in reality it should require only 17¾ grains.