A filtering arrangement devised by F.
The tri-iodide, AsI3 prepared by subliming arsenic and iodine together in a retort, by leading arsine into an alcoholic iodine solution, or by boiling powdered arsenic and iodine with water, filtering and evaporating, forms brick-red hexagonal tables, of specific gravity 4.39, soluble in alcohol, ether and benzene, and in a large excess of water; in the presence of a small quantity of water, it is decomposed with formation of hydriodic acid and an insoluble basic salt of the composition 4AsOI.
Large doors at the side of the cistern are then opened, and as soon as the bags are cool enough they are removed at the expense of very exacting labour and considerable time, and fresh bags and sheaths are fixed in their places ready for filtering fresh liquor.
Mastication, and by filtering through wire-gauze filters, is kept warm by a steam-jacket.
The crude phosphorus is purified by melting under water and then filtering through animal black and afterwards through chamois leather, or by treating it, when molten, with chromic acid or a mixture of potassium bichromate and sulphuric acid; this causes the impurities to rise to the surface as a scum which can be skimmed off.
This process is now shortened by filtering oils through filter presses, or otherwise brightening them, e.g.
Deep wells owe their comparative immunity from pollution to the circumstances that the larger quantity of water yielded renders it worth while to pump that water and convey it by pipes from comparatively unpolluted areas; and that any impurities in the water must have passed through a considerable depth, and by far the larger part of them through a great length of filtering material, and must have taken so long a time to reach the well that their organic character has disappeared.
The amalgam is cleaned out periodically - fortnightly or monthly - and after filtering through linen bags to remove the excess of mercury, it is transferred to retorts for distillation (see below).
Imagine when the twenty-cent computer in your eyeglasses begins filtering out high levels of radiation the moment it is detected, and the dime computer in your skillet warns you of salmonella in your eggs (see box at right).
As the liquor goes on filtering through the bags they gradually get filled up with slime and sludge, and the clear liquor ceases to run.