fumes from copper works, is to have large deposit flues so as to lessen the velocity of the vapour, the flues terminating in lofty shafts.

(225) Lime Burning,

Lime is either burnt in a close or open kiln. Nuisance may arise from lime burning if low class fuel is used, especially fuel containing much vegetable or animal matter, also if the gases, which always contain some considerable proportion of carbon oxide, get entrance into adjacent dwellings. In Dr. Ballard's report on effluvium nuisances there is a distinct case of chronic carbon oxide poisoning from this cause. Lime burned in close kilns, the vapours being carried into the upper part of the atmosphere, appears to be productive of little or no nuisance.

(226) Manufacture of Coke and Breeze.

In principle the manufacture of coke and breeze is nothing more than destructive distillation of carbonaceous matter by the agency of heat, the air being partially excluded; water, compounds of hydrogen and carbon, and volatile matters generally, are driven off, and there is left, if the process is stopped at a certain time, an impure carbon with incombustible mineral matters. The manufacture is either done in heaps, " pile coking," or in ovens. Pile coking is most productive of nuisance, dense volumes of smoke are emitted at a low elevation with sulphurous acids and other irritating gases. The amount of sulphurous acid gas depends on the amount of sulphur in the fuel which is coked, some classes of fuel containing but a small quantity, other classes containing much pyrites and therefore a large quantity. The mean quantity of sulphur in coal is a little under 1 per cent., but some of the Welsh coal contains as much as 5 per cent. of sulphur. One method of pile coking is to build a hollow, permanent, brick dome, perforated at intervals; around the base are iron pipes for the admission of air extending radially like the spokes of a wheel ; the coal to be coked is piled up around the dome, the whole being covered with coke dust, such a pile is lighted at the centre and burns slowly to the circumference. The burning is continued for five or six days, and then the fire is extinguished by covering the

heaps with damped coke dust. Dr. Ballard describes a fairly effectual means of mitigating the nuisance from coke-pile burning, the invention of Mr. E. Jones; it briefly consists in connecting a flue with the central dome, drawing off the products of combustion by means of a fan through underground flues, and condensing the products by passing them through a water jacketed condenser. These condensed products are commercially valuable.

When coking is done in ovens, the vapours are passed into a tall chimney shaft, and are thus discharged at a sufficient elevation to abate more or less the nuisance.

(227) Brick Burning.

Bricks are burnt either in clamps or kilns. Clamp burning, is burning the bricks in a quadrangular pile. The green bricks made of clay and mixed with a small proportion of ashes being arranged in layers alternating with breeze. The breeze is set alight by means of small fires of wood and coal.

(a) Kiln Burning.-In kiln burning no combustible substance is mixed with the brick material. The bricks are burned by the aid of coal. The kilns are either open, that is the smoke finds its way from the top of the kiln into the atmosphere, or the kilns are provided with a special flue for discharging the smoke.

(b) Clamp Burning.-Clamp burning is especially offensive. The emanations are watery vapour, thick smoke, the usual gases of combustion, very often sulphuretted hydrogen, and certain pyroligneous matters which have an offensive odour. Where, as is often the case, household refuse is used containing animal and other organic matter, the odour is intensely disagreeable. The emanations are often acid, irritating to the mucous membranes and injurious to vegetation.

The fumes from burning bricks differ in composition very much in the different stages of the process, the clay used, and the fuel employed. Clamp burning as the most offensive process should be entirely prohibited in the neighbourhood of large towns. Kiln burning by careful stoking, by the use of certain special kilns, and by the aid of a long chimney shaft, can be carried on with but trifling offence.

(228) Ballast Burning.

Ballast burning is converting stiff clay by the agency of heat into a bricklike material for use on the roads. The clay is usually burned in heaps mixed with breeze and ashes. It is, without doubt, a great nuisance. Dr. Ballard remarks, "Should it at any time be held essential that clay should be burned where the burning is likely to be a nuisance, it should be burned in such a way as to bring the effluvia under control. I see no reason why it should not, under such circumstances, be burned in a kiln with due provision against nuisance from the empyreumatic vapours and smoke emitted. If it is absolutely necessary that ballast should be burned in heaps, it appears to me that the method adopted by Mr. Jones (see page 306) to prevent coking in heaps, or some similar method, would be applicable. If it is worth while to burn the clay at all it ought also to be considered worth while to do it inoffensively.

(229) The Manufacture of Portland Cement.

Two kinds of hydraulic cement are in use-the one, "Roman cement," made from the septaria nodules found in the London clay formations; the other, "Portland cement," made from an artificial mixture of clay and limestone. In the manufacture of the Roman cement the stones are calcined in open kilns, like limekilns, and there is but little nuisance. The manufacture of Portland cement has, however, often been complained of, and has formed the subject for injunction. The chalk and clay are mixed under water, and then the mixture is either run into depositing-tanks, or when only a small quantity of water is used (Goreham process), the substances are ground together. In either case a wet mud is produced, which is technically called "slurry." The slurry has to be dried, and then burned in kilns. The chief nuisance is in the burning, and especially if this is done in open kilns. The emanations consist of gases, some of which, like carbon dioxide and sulphuretted hydrogen, are poisonous. In certain cases, when the clay used contains much nitrogenous matter, it appears to be definitely proved that either hydrocyanic acid or a volatile cyanide is produced. At Southampton, for instance, the fume from a cement

works was observed to colour the gravel in its neighbourhood blue, and the blue colour Dr. Dupré found to be produced by cyanide of iron; moreover, the gases drawn from the kiln were found to contain volatile cyanides. The emanations from a cement-kiln vary according to the different stages; this is well shown in some analyses by Dr. Russell and Mr. Fleming, made in 1877, of gases from an open kiln at Greenhithe :

Besides gaseous products there are also sublimations and dusty matter; these are composed of soot, cement dust, and sulphates of lime and potash, chlorides of the alkalies, with silica, alumina and some lime compounds. Some of these collect as a white deposit in the neighbourhood of the kiln.

Dr. Ballard's report gives good grounds for saying that emanations from open kilns during the process of manufacturing Portland cement are positively injurious to health.

There have been attempts to mitigate the nuisance of cementmaking in three directions-viz., washing the fume with water; passing it through fire; and delivering it at a high elevation by means of a tall chimney shaft. The first method seems not to have been very successful; burning the fume has to a certain extent been found to answer, but the best method of dealing with it, according to experience, is to discharge it from a tall chimney shaft, that is one from 150 feet to 200 feet high.

(230) The Firing of Pottery-Salt-glazing.

In salt-glazing, the articles of clay are subjected to a high heat with common salt. A decomposition of part of the salt takes place: silicate of soda is formed, producing a glaze, and hydrochloric acid gas escapes with the portion of salt in excess; there is also always some sulphurous acid gas from the fuel employed, and more or less smoke. It has been hitherto found impracticable to arrest the acid vapours by scrubbers, because their interposition interferes with the draught necessary to properly fire the articles, and the only feasible means to mitigate the nuisance is to convey the vapours into the upper regions of the atmosphere by a tall chimney shaft.