588

Distilled Waters.

part 111.

viscid matter forms in them, owing to the essential oil theycontain, undergoing decomposition, and changing into mu-cilage. The addition of the spirit is intended to prevent thisfrom taking place, but it is not adequate to the effect in-tended ; and a much preferable mode is to redistil the waters,after which they will keep good for several years.

Several of these waters are prepared on a great scale, of asuperior quality to any that the apothecary can prepare, andcheaper.

AQUA DISTILLATA. Lond.' Distilled Water." Take of water, ten gallons. First distil four pints, whichare to be rejected, and then distil four gallons. Preserve thedistilled water in a glass bottle."

Edinburgh." Let water be distilled in clean vessels, until two thirds ofthe quantity employed have distilled over."

Dublin." Take of spring water, twenty pounds. Put them into aglass retort, and having rejected the first pound which comesover, let one gallon be distilled over with a gentle heat."

Water is almost universally diffused over the surface of theearth, but it is not found perfectly pure in any place, which isowing to its great solvent powers enabling it to take up a por-tion of many substances with which it must come into con-tact in its natural state. These impregnations, however, inspring and in river water, are not sufficient in general to givethem any very sensible taste, or render them unfit for the ordi-nary purposes of life; but for many pharmaceutical purposesit is necessary that the water be absolutely free from every fo-reign ingredient. Rain water is the purest kind of naturalwater, but it nevertheless contains a portion of carbonic acidgas, and minute quantities of carbonate of lime, and of muriateof lime; in spring water, besides these ingredients, is found asmall portion of muriate of soda: VoeU water, which is springwater obtained from a greater depth, holds in solution a muchlarger portion of carbonic acid, and several earthy salts, theprincipal of which are sulphate and carbonate of lime; andriver water is impregnated with different proportions of carbo-nate of lime, sulphate of lime, and muriate of soda. By dis-tillation water is freed from these ingredients, and renderednearly pure. The process should be conducted slowly, with amoderate degree of heat, and not continued longer than thetime specified in the formulae, otherwise a minute portion of

i Eau distill^ (F.) Einfaches dcsullirtea Wasser (G.) Acqua Distillata (J.) Aguadislillada (S.)