Their experiments on fluoric acid are exceedingly valuable. They first obtained that acid in a state of purity, and ascertained its properties. Their attempts to decompose it as well as those of Davy, ended in disappointment. But Ampere conceived the idea that this acid, like muriatic acid, is a compound of hydrogen with an unknown supporter of combustion, to which the name _fluorine_ was given. This opinion was adopted by Davy, and his experiments, though they do not absolutely prove the truth of the opinion, give it at least considerable probability, and have disposed chemists in general to adopt it. The subsequent researches of Berzelius, while they have added a great deal to our former knowledge respecting fluoric acid and its compounds, have all tended to confirm and establish the doctrine that it is a hydracid, and similar in its nature to the other hydracids. But such is the tendency of fluorine to combine with every substance, that hitherto it has been impossible to obtain it in an insulated state. We want therefore, still, a decisive proof of the accuracy of the opinion. To the experiments of Gay-Lussac and Thenard on chlorine and muriatic acid, I have already alluded in a former part of this chapter. It was during their investigations connected with this subject, that they discovered _fluoboric_ acid gas, which certainly adds considerably to the probability of the theory of Ampere respecting the nature of fluoric acid. I pass over a vast number of other new and important facts and observations contained in this admirable work, which ought to be studied with minute attention by every person who aspires at becoming a chemist. Besides the numerous discoveries contained in the Recherches Physico-chimique, Gay-Lussac is the author of two of so much importance that it would be wrong to omit them. He showed that cyanogen is one of the constituents of prussic acid; succeeded in determining the composition of cyanogen, and showing it to be a compound of two atoms of carbon and one atom of azote. Prussic acid is a compound of one atom of hydrogen and one atom of cyanogen. Sulpho-cyanic acid, discovered by Mr. Porrett, is a compound of one atom sulphuric, and one atom cyanogen; chloro-cyanic acid, discovered by Berthollet, is a compound of one atom chlorine and one atom cyanogen; while cyanic acid, discovered by Wöhler, is a compound of one atom oxygen and one atom cyanogen. I take no notice of the fulminic acid; because, although Gay-Lussac's experiments are exceedingly ingenious, and his reasoning very plausible, it is not quite convincing; especially as the results obtained by Mr. Edmund Davy, and detailed by him in his late interesting memoir on this subject, are somewhat different.