bath is as usual. Iron is deposited on the cathode in the separated chamber -the equivalent of what is dissolved from the article in pickle, and the free acid equivalent is liberated at the anode in the pickling bath, so maintaining its condition.

So far as can be gathered from galvanisers who have tried it, the objections are:

(1) Want of uniformity in the pickling-pitting and rough surfaces. (2) Cost of current as compared with fresh acid.

(3) Peeling.

A method of recovering hydrochloric acid pickle, and one that has met with more success, seeing that it has been installed and in successful operation some years, is that of Mr Thos. Turner. In this process the pickle is fed into the hearth of a reverberating furnace A (fig. 117), in front of which at B a coke fire is kept burning.

On concentration ferric chloride is deposited, and upon hard firing hydrochloric acid passes with the fire products along the pipes C and is condensed in the ordinary muriatic towers D and E. The ferric chloride is fished forward at the hand holes in the furnace wall and the process kept going continually.

The iron oxide is of some value as fettling for puddling furnaces, yielding a few shillings per ton. The two furnaces at Messrs Walker Brothers' works together treat 1000 gallons of waste per day, yielding about 300 to 350 gallons per day of 75 per cent. commercial strength (29° Twaddell). Its actual strength Twaddell is not a reliable indication of its acidity, owing to the ferric chloride it contains, formed from particles of iron oxide which pass over in the draught and are dissolved by and come down with it. This in small quantities, however, is no drawback to the system, as the formation and elimination alternately of ferric chloride really form the cycle. An average sample of the acid contained 8.8 per cent. by weight of ferric chloride; and 10 parts by volume of the acid required for neutralisation contained 62.5 parts of normal alkali, its specific gravity being 1.115 or 23° Twaddell. The ferric oxide contained 97.6 per cent. of black magnetic oxide and 2 per cent. of carbon and ash. About one cwt. of the oxide is produced daily, and about four tons of coke are used every week. The ferric chloride in crystallising out in the pot does not always sink to the bottom immediately, but forms a scum on the surface, which, owing to the high temperature, is to a certain extent decomposed in the pot. A sample extracted from the surface contained

Ferric chloride,

Ferric oxide,

Moisture,

Carbon and insoluble matter, .

Two men are required to attend to the plant, one being on duty during the day and the other at night. The average cost of recovery is about 8s. per ton.

Up to the present all attempts in the direction of rivers pollution prevention in the Black Country have resulted in but little so far as the galvanisers' pickle is concerned. In no other district of England, probably, do the industries so overlap each other-galvanised sheets, iron bars, fencing, harness, chains, general hardware-and in no other district probably do manufacturing interests as represented on the local governing bodies so preponderate. The particular classes of industry here followed are also very liable to suffer from both home and foreign competition, and it is therefore hardly surprising that efforts put forth to compel the traders to purify waste, the presence of which in streams is an eyesore rather than a nuisance, are not received with unanimous approval. The stage arrived at as yet appears to be no more than this-that the galvanising trade is prepared to neutralise the pickle with lime if the aggrieved authorities provide it, and if the canal companies will carry it to the point of application.

Various industries not referred to in this volume-such as the manufacture of Starch, Sugar, Jam, Pickles, Paints, etc.-produce waste liquids the general principles for the purification of which are outlined herein, though special circumstances may call for additional or modified treatment.

The author nevertheless trusts that the current practice as to preventing pollution caused by the commoner forms of liquid waste, together with hints as to the best modes of procedure in special cases, have been plainly set forth, and hopes to deal at a future date and in another volume with the utilisation and disposal of Trades Waste of a purely solid character.

THE END.

INDEX.

Bradford, city of, reports on wool scouring
liquors, etc., 84, 86.

Corporation, special clause in Tram-
way and Improvement Act, 106.

at Wolverhampton Sewage Brewery, Anglo-Bavarian, Shepton Mallet,