This section is from the book "A Practitioner's Handbook Of Materia Medica And Therapeutics", by Thos. S. Blair. Also available from Amazon: A Practitioner's handbook of Materia Medica and Therapeutics.
Silicea, Precipitated Silica. This is a supposedly medicinal substance peculiar to the biochemists. They believe it to be indicated in a great many conditions. There is a small amount of silica in the skin and the nails and traces of it in some other tissues; and indurated and suppurative states are frequently characterized by a lack of this substance. It is, therefore, probably of some use in these conditions, and may be of service in rachitic children, suppurative processes upon the skin, quinsy, styes, affections of the finger nails, and indurated tumors. I have had no experience with it at all, except that in casting about for a remedy for mild indurations and cracked finger nails, due to x-ray burns, I hit upon silicea. For several years in my hospital service I have been very much overexposed to the x-ray, and find the IX of silicea to be of considerable aid in some of the lesions. While some of the contentions made in its favor by its advocates appear very ridiculous, yet it must be classed as a tissue food neglected in regular medicine, but probably just as much indicated as manganese and other substances found in traces in living tissues. If one does not care to use this sectarian preparation, Squibb can supply the wet process silicic acid, which is really silicic oxide or precipitated silica. The natural silicic acid is infusorial earth, and is used for filtering acids. This would not do. The wet process silica should, of course, be well triturated.