This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Precipitated sulphur is made by boiling sulphur and lime together in water, filtering, and then precipitating with muriatic acid. Certain chemical reactions between the lime and sulphur, through which both are dissolved, are inverted by the muriatic acid, which reacts with the ingredients of the lime so as to form chloride of calcium and water, while the sulphur is separated and deposited, carrying with it a portion of loosely combined water.
Precipitated sulphur is in the form of powder or pulverulent lumps, of a whitish colour, soft to the touch, not gritty between the teeth like the flowers, of a feeble odour, and a slight sulphurous taste. its properties are not materially different from those of the sublimed sulphur. it was at one time supposed to be a hydrate; but, when thoroughly dried, it contains very little if any water; certainly not enough to form an equivalent combination with the sulphur. According to Berzelius, it becomes yellow when melted, giving out a little sulphuretted hydrogen; to the presence of which, therefore, the colour has been ascribed.
It is very apt to contain sulphate of lime, arising from the use of sulphuric acid as the precipitant instead of muriatic acid, the former giving rise to a nearly insoluble, the latter a very soluble compound. The presence of this impurity may be suspected, when the preparation is of a purely white colour. it is left behind when the sulphur is either burned or volatilized.
The effects, therapeutic uses, and dose of the precipitated sulphur are the same as those of the flowers; and its only advantage is its more impalpable condition, and probably somewhat greater facility of being acted on in the primae viae, so as to become absorbable. Dr. Fuller, of London, employs it externally in chronic rheumatism, and especially sciatica, causing the whole affected limb to be wrapped in flannel thickly sprinkled with it, and confined by means of a bandage, over which is placed a covering of oiled silk. it is said that the sulphur is absorbed, as proved by the odour of the breath, urine, and cutaneous exhalation. (On Rheumatism, etc., II. 456-t.)