Distilled water is a colorless, limpid liquid, without odor or taste, and of neutral reaction. On evaporating one liter of distilled water no fixed residue should remain. The transparency or color of distilled water should not be affected by hydrosulphuric acid or sulphide of ammonium (absence of metals), by test solutions of chloride of barium (sulphate), nitrate of silver (chloride), oxalate of ammonium (calcium), or mercuric chloride, with or without the subsequent addition of carbonate of potassium (ammonia and ammonium salts). On heating 100 com. of distilled water acidulated with 10 ccm. of diluted sulphuric acid to boiling, add enough of a dilute solution of permanganate of potassium (1 in 1000) to impart to the liquid a decided rose-red tint; this tint should not be entirely destroyed by boiling for five minutes (absence of organic or other oxidizable matters). - U. S. Distilled water should not be affected by solution of lime (absence of carbonic acid) - Br. On continued exposure to the air distilled water will dissolve carbonic acid gas, and then become cloudy with clear lime-water.

Fig. 3.   Water Distilling Apparatus

Fig. 3. - Water Distilling Apparatus.

A, Copper still, tin-lined; B, Condenser; C, Charcoal filter; D, Receiver or carboy; a, Steam inlet; 6, Steam coil; c, Steam outlet; d, Discharge cock; e, Iron support; /, Water guage; g, Water inlet; h, Water supply pipe; i, Condensing-pipe, with block tin coil; k, Water-main; I, Stop-cock; m. Supply valve; n, Water inlet for condenser; o, Water outlet; p, Waste pipe; r, Water supply-pipe for condenser.

To this valuable information we may add, that the distilled water ought to be stored in clean carboys or carefully rinsed barrels, both closed air-tight, and disinfecting or cleansing should be resorted to between successive supplies. The particular smell which distilled water is almost invariably possessed of can be got rid of by filtering it through animal charcoal, and this should always be done, as it tends to its preservation.

The above illustration shows the arrangement of a distilling apparatus with an extra tin-lined copper still, and condenser and filter attached.

The inlet of the distilled water in filter C is practically closed by a perforated cork, also the outlet of condensing pipe, and both are connected with a glass tube fitted in the corks. The outlet-tube leading to carboy and the mouth of the latter are protected by a layer of cotton, which allows the air free access and acts as a vent but retains its spores.

An ingenious condensing apparatus and filter for distilled water we find illustrated in Barnett & Foster's catalogue, and reproduce here for the benefit of the trade.

The steam is caused to pass along narrow grooves having very small capacity but large surface; the steam is thus very rapidly condensed to water, which has great effect on the main body of steam in the tube. The steam is moreover caused to rub continually against edges or angles, which are most easily cooled by the circulating water. The steam inlet is fitted with a dirt arrester - a special contrivance to prevent dirt or scale passing into coils. This condenser and filter combined is indeed an efficient and practical arrangement in water-distilling apparatus.

Instead of charcoal, it was recommended to filter distilled water through paper or paper pulp; but when filtered through paper, distilled water soon exhibits a fatty sediment, which is never found when filtered through sponge. The latter therefore would be preferable to paper; however, animal charcoal is the proper filter material for distilled water. It is, of course, frequently to be renewed or regenerated.