We have no data to enable us to determine the shape of these atoms. The most generally received opinion is, that they are spheres or spheroids; though there are difficulties in the way of admitting such an opinion, in the present state of our knowledge, nearly insurmountable. The probability is, that all the supporters have the property of uniting with all the bases, in at least three proportions. But by far the greater number of these compounds still remain unknown. The greatest progress has been made in our knowledge of the compounds of oxygen; but even there much remains to be investigated; owing, in a great measure, to the scarcity of several of the bases which prevent chemists from subjecting them to the requisite number of experiments. The compounds of chlorine have also been a good deal investigated; but bromine and iodine have been known for so short a time, that chemists have not yet had leisure to contrive the requisite processes for causing them to unite with bases. The acids at present known amount to a very great number. The oxygen acids have been most investigated. They consist of two sets: those consisting of oxygen united to a single base, and those in which it is united to two or more bases. The last set are derived from the animal and vegetable kingdoms: it does not seem likely that the electro-chemical theory of Davy applies to them. They must derive their acid qualities from some electric principle not yet adverted to; for, from Davy's experiments, there can be little doubt that they are electro-negative, as well as the other acids. The acid compounds of oxygen and a single base are about thirty-two in number. Their names are Hyponitrous acid Nitrous acid? Nitric acid Carbonic acid Oxalic acid Boracic acid Silicic acid Hypophosphorous acid Phosphorous acid Phosphoric acid Hyposulphurous acid Subsulphurous acid Sulphurous acid Sulphuric acid Hyposulphuric acid Selenious acid Selenic acid Arsenious acid Arsenic acid Antimonious acid Antimonic acid Oxide of tellurium Chromic acid Uranic acid Molybdic acid Tungstic acid Titanic acid Columbic acid Manganesic acid Chloric acid Bromic acid Iodic acid. The acids from the vegetable and animal kingdoms (not reckoning a considerable number which consist of combinations of sulphuric acid with a vegetable or animal body), amount to about forty-three: so that at present we are acquainted with very nearly eighty acids which contain oxygen as an essential constituent. The other classes of acids have been but imperfectly investigated. Hydrogen enters into combination and forms powerful acids with all the supporters except oxygen. These have been called hydracids. They are Muriatic acid, or hydrochloric acid Hydrobromic acid Hydriodic acid Hydrofluoric acid, or fluoric acid Hydrosulphuric acid Hydroselenic acid Hydrotelluric acid