Since chemistry has been studied as a science, it has been an object with its cultivators to arrange the bodies which have been the subjects of their attention, into groups in which the individuals should have a natural relation to each other. Probably at no time in the history of the science has the importance of such a classification been more strongly felt than at the present day, not only on account of the number of known elements, but also from the number of compound bodies appearing to act as elements, which organic chemistry has made known. Although great advances have been made in this direction, the place of the element silicon in such a series as above alluded to, is very doubtful. Yet the binary compound of this element, silicon with oxygen, is familiar to every one; it constitutes by itself a considerable portion of the crust of the earth, and enters into a long series of definite crystallized compounds. It has been satisfactorily determined that this substance, silica, belongs to the class of bodies designated as acids, but one essential point is wanting to enable chemists to give it, or its peculiar element, its proper position, and that is, the formula of this silica or silicic acid.