evolution of black smoke at a low level, and of acid fumes. The acid fumes are produced (1) by the decomposition of magnesic chloride; (2) by sulphurous acid produced by burning the slack; (3) by a reaction between sulphurous acid gas and sodic chloride; (4) decomposition of sodic chloride by the silica of the bricks, silicate of soda being formed and hydrochloric acid produced. The acid fumes are therefore mainly hydrochloric acid with some sulphurous acid.

There is also some nuisance caused by waste heaps. Several patents have been taken out for a more economical method of salt manufacture enabling manufacturers to dispense with the use of open pans altogether. So long as the system of open pan evaporation continues the abatement of these nuisances is difficult.

The sulphurous acid can be much diminished by the use of a good form of slack or coal containing only a small proportion of sulphur; the fear of injuring the long chimney shafts from subsidence is said not to be so great as the manufacturers make out, at all events light long sheet iron chimneys lined with fire brick and secured by wire rope stays could surely be used?

(215) The Manufacture of Chloride of Lime (Bleaching Powder). The ordinary process is the decomposition of hydrochloric acid by manganese dioxide; the chlorine evolved is conducted to chambers where hydrated lime is exposed to its action in thin layers. The decomposition takes place in a square chamber made of Yorkshire flags, and the reaction is aided by means of steam. The residue is a strong acid solution of manganese chloride.

The Weldon process of making chlorine differs from this in recovering the manganese and using it over again. The solution of manganese chloride is neutralized by means of limestone, which precipitates the impurities, viz., oxide of iron, alumina and carbonate of lime; these are allowed to settle, and the clear liquid, containing calcic chloride, manganese chloride and some calcic sulphate, is transferred to an iron cylinder where it is mixed with milk of lime; manganese protoxide is precipitated as a thick black mud. Air is blown through this mud, which effects an oxidation, oxidizing the protoxide into binoxide of manganese.

In the Deacon process hydrochloric acid gas is passed at a high

temperature over bricks saturated with sulphate of copper solution; under these circumstances the acid gas is decomposed, the hydrogen forming with the oxygen of the air, water and the chlorine passing on in the free state. The gas is washed with water and dried by means of strong sulphuric acid. It is then pure enough to be used to saturate the lime.

The Deacon process, Dr. Ballard says, is free from nuisance outside the works.

The source of nuisance from bleaching works is the escape of chlorine from leakage, and from chlorine being only mechanically, not chemically, combined with the lime, from the chambers themselves, and lastly from the packing and transferring the powder to casks or other receptacles.

One method of reducing the "chamber" nuisance is as follows:the door of the chamber is slightly opened, and by means of a fan the chlorine atmosphere is driven into another chamber in which there are layers of fresh lime; another good plan is to use divided chambers, that is, chambers divided into two by a partition, and then when one part is saturated, remove the partition and thus allow the excess of chlorine to be absorbed.

It has also been proved that with proper arrangements the transference into casks need cause no nuisance. For instance in Messrs. Deacon's works the powder is transferred direct to the cask from the chamber through a tube of sacking.

(216) The Manufacture of Glass.

In the manufacture of glass, especially that of the poorer kinds, sulphate. of soda and common salt are heated with silica and other substances, the result being that sulphuric and hydrochloric acids are expelled. There is besides generally a considerable amount of nuisance from smoke. Where the works are large, the amount of acid sent into the atmosphere is of course proportionate; for instance at the St. Helen's plate glass works more than 190 tons. of sodic sulphate are decomposed weekly.

No way of abating the acid emanations from glass works which will not interfere seriously with the trade itself has yet been devised; of course neither sodic sulphate nor sodic chloride are essential to use at all, it would be far better to employ sodic

carbonate, but it is said the great competition, especially with foreign manufacturers, prohibits the use of the dearer material.

A good deal has been effected to remedy the smoke nuisance, e.g. with the Siemens gas furnace there is no nuisance from smoke. There are also several improved furnaces which with careful stoking consume most of their own smoke.

(217) The Calcining of Ironstone and Tap Cinder.

Ironstone whether in the form of "clay band" or "black band' is calcined in order to drive off carbonic acid, to peroxidize the iron, burn off the sulphur, and reduce the bulk of the ore. The calcining is done either in clamps or in kilns. The slag drawn from puddling furnaces is treated similarly.

In both instances there is nuisance from smoke and sulphurous acid gas. Kiln burning is much less offensive than clamp burning, and where the nature of the stone will allow of this process to be used, it should be insisted upon.

(218) Hardening of Steel Springs and Saws.

In the tempering of various steel articles the red hot steel is plunged into a bath of oil. The result is the evolution of irritating fumes of acrolein and other volatile substances. The nuisance can be remedied like others of the same kind, viz., by conducting the evolved vapours through a furnace fire and thus burning them up.

(219) The Calcining of Spelter.

In the smelting of zinc ores, containing sulphur such as blende, copious sulphurous acid fumes are evolved. There is also much dust in the form of oxide of zinc produced. Dr. Ballard states that in one instance the nuisance from the fumes was successfully abated by carrying them up a flue 300 yards long and then into a tall chimney shaft. This effectually removed the vapours from the vicinity of inhabited houses.

(220) Galvanizing Iron.

The iron is first chemically cleaned by means of acid, it is then dipped into a bath of melted zinc. During this process hydrogen is evolved, and very frequently some hydrocarbons, the hydrogen

uniting with the carbon of the iron. Should the iron contain sulphur or phosphorus, then sulphuretted or phosphuretted hydrogen gases are likely to be eliminated. Where chloride of ammonium is sprinkled upon the bath from time to time then chloride of arsenic is evolved. In most cases there is indeed an arsenical odour from the fumes during the galvanizing of iron. The spent pickle is a strongly acid solution of chloride of iron.

There can be no question that the fumes from galvanizing iron are directly injurious to health, and should be removed from the works by suitable fans, hoods, and flues, and either properly condensed or discharged at a considerable height into the upper layers of the atmosphere. If the spent pickle is likely to damage the sewers it should be neutralized by means of limestone.

(221) Tin Plate Manufacture.

The plates are first pickled in acid. The pickle consists of slightly diluted oil of vitriol heated up to boiling point by means of steam. After pickling, the plates are immersed in a series of dipping pots, the first of which is filled with palm oil, and the others contain melted tin covered with a layer of palm oil.

The emanations from tin plate works consist of acid fumes, of odours of palm oil and acrolein. There is also more or less hydrogen gas evolved, the gas having a peculiar odour. The practice seems to be to use a number of small chimneys, instead of collecting the fumes into one large shaft. So long as the traditions of the trade remain unbroken, great difficulty will be necessarily experienced in effectually dealing with the vapours. There is little doubt that the general principles of conveying the various fumes collected by hoods and flues to scrubbers and then to a furnace fire, would arrest the acid and burn up the organic emanations.

The strongly acid spent pickle is often concentrated by boiling for the purpose of crystallizing out the iron sulphate it contains; this is necessarily accompanied by the evolution of acid fumes. Any nuisance from this source can be readily obviated by covering the concentrating vessels and condensing the fumes in a scrubber. Where the spent pickle is not dealt with in this way it should not. be cast down the sewers until neutralized with limestone or some form of lime.

(222) Tin Burning.

Tin burning is the burning by fire of refuse heaps containing old tins for the purpose of extra ting the solder they contain. If the refuse does not already contain enough combustible matter, wood shavings are added in alternate layers. From the ashes solder and other saleable matter are picked out by hand. Tin burning generally gives rise to much offence, the vapours are often most irritating, especially when the refuse contains an oily matter, such as paint, there is also a large volume of smoke given off at a low level. Tin burning is only practised by the very poor in large cities, hence the crude method employed. Of the nuisance of the process there can be little doubt.

(223) The Calcining of Arsenic and Arsenical Ores.

In the roasting of arsenical pyrites and in the refining of arsenic large volumes of sulphurous acid are given off, the sublimed arsenic also is a real danger to the work people. It appears, unfortunately, that attempts to wash the sulphurous acid fumes, which are always mixed with a large volume of air, have not been successful, for the washing always interferes with the draught of the furnaces. Where it can be done, the uncondensed fumes should be discharged at such an elevation and at such a distance. from inhabited houses that they shall be thoroughly dispersed before they have time to fall in such quantities as to occasion nuisance.

(224) The Smelting of Copper Ores.

In the various complicated operations in use for the smelting of copper ores containing sulphur, there are volatile emanations consisting of sulphurous acid gas, arsenious acid, and, if fluorine be present, fluoride of silicon, with dust and smoke. The vapour well-known as "copper smoke" is a mixture of these volatile and dusty matters. The copper will occasionally travel some distance, but the arsenic has not been discovered save in the immediate neighbourhood of the works.

According to Mr. Hussey Vivian's evidence before the "Noxious Vapours Commission" the principle to be adopted in lessening the