and always in operating methods and conditions. Individual plants had to be studied and individual instruction given. The present situation in the fuel market is such that practically the only fuel available for use in Illinois is bituminous coal. It must be accepted and used for residences and apartment buildings as well as for industrial purposes. This condition still further complicates the smoke problem, because house heaters which burn pocahontas or anthracite satisfactorily generally require much greater care and more frequent attention when bituminous coal is used. Without undertaking a detailed discussion of furnaces and heaters, and their operation, it may be said that smokeless combustion of bituminous coal, and its economical use, involves compliance with certain definite principles: I. The fresh coal should be introduced into the fire-box at such a point and distributed in such manner that the combustible gases distilled from it will be required to pass over incandescent portions of the fire or over surfaces which are maintained at a high temperature. Observance of this principle promotes the ignition and combustion of the distillates. 2. The steam of gases arising from the fresh fuel must be heated quickly and must be kept at a high temperature until the process of combustion is well advanced. The use of a fire-brick arch, under which the distillates may be burned, is an aid in securing this condition. 3. An ample supply of air, under proper control, should be available to aid the combustion of the gases which arise from bituminous coal. 4. The proportions of the furnace and the fire-box should be such as to provide an ample flame-way. This condition is necessary in order to allow sufficient time for the burning of the gases. The length of flame-way in many types of furnaces may be increased by the use of baffle walls or arches. The engineering experiment station of the University of Illinois has recently issued a circular, designed to meet the needs of the layman rather than the engineer, which sets forth certain fundamental principles involved in the economical operation of house heaters. Abstracts of this prepared for the state council of defense are available. The station also has in preparation circulars dealing with small power plants and with steam locomotives. The bureau of mines and the United States fuel administration at Washington are reported to be developing some information for the public on these and allied subjects. The object of all of these is to promote economy in the use of fuel, but one of the coordinate benefits should undoubtedly be seen in the production of less smoke. With reference to the broader phases of atmospheric pollution, in which every city official is interested, it should be recognized that: I. Smoke has three distinct characteristics to each of which a suitable standard of measure may be applied. These are: (a) visible properties (b) solid particles (c) gaseous products. 2. Smoke is responsible for only approximately two-thirds of the pollution in the air, the remaining one-third having its origin in sources the disposition of which is a relatively simple and inexpensive matter. By "visible properties" of smoke are meant those properties which impart visibility to it or make it apparent to the eye. Public interest has been centered in this aspect of smoke, and it has been assumed that a chimney which did not give forth a discharge visible to the eye, was not a source of atmospheric pollution. This assumption is not borne out by the facts. Tests have shown that stationary plants discharging through the smoke stack as much as two per cent of the fuel fired, may appear smokeless to the eye. On the other hand it has been shown that stacks recording a smoke discharge of high visible density may be emitting in the form of solid particles only a small fraction of one per cent of the fuel fired. Thus there is apparently no relationship between these two aspects of smoke. Both are objectionable. Visible smoke is offensive to the eye and solid particles or dust from smoke stacks is injurious to property, to vegetation and to animal life. In densely populated cities the discharge of solid particles amounts to about 600 tons per square mile per annum : even in cities of moderate size the deposit is as much as 300 or 400 tons per square mile per annum. In determining the extent of the smoke nuisance created by any fuel consuming plant or the amount of smoke emitted from the smoke stack, the relation between the amount of fuel fired and the discharges through the stack is studied. Discharges may be rated according to the Ringelmann method (visible smoke) or they may be analyzed to determine their physical and chemical properties by means of filtering and sampling apparatus designed for the purpose. The correction of the smoke nuisance is very largely a matter of improving the practice in each individual plant. While the plant owner should be made responsible, the city official should not fail to give proper advice based upon a knowledge of conditions. While the abatement of smoke is a problem involving expense, study and the constant attention of a competent engineer, there is much that city officials may do to help purify the atmosphere by merely seeing that municipal housekeeping is well done. More than a third of all the dust and dirt in the atmosphere of the average city has its origin in poorly cleaned streets, in the careless handling of materials in transit, in street construction, in unimproved streets and alleys, in building operations, in neglected backyards and roofs, in rubbish heaps, and in vacant lots. Slide 19. Mercury seal and filter case for air and tests Slide 29. Slide 30. Slide 31. Slide 32. Slide 33. Sources of Pollution-street construction Slide 34. Slide 35. Sources of Pollution-materials in transit Slide 36. Sources of Pollution-rubbish heaps Slide 37. Sources of Pollution-vacant lot Slide 38. Sources of Pollution-roof accumulations Slide 39. Sources of Pollution-roof activities This brief survey of the problem of atmospheric sanitation does not of course touch all aspects of it, nor concern itself with details of procedure. It is a problem which all cities sooner or later must face and solve, and I think it is obvious that it is one for the engineer or for the city official who is trained in a knowledge of the details involved. It is a job in which it will pay to do right. JAMES ELMO SMITH The two problems, refuse collection and refuse disposal, are so intimately related that it is not easy to discuss one without involving the other, but an effort will be made to consider only the methods of disposing of city wastes and more particularly the method known as cremation, incineration, or destruction, that is, disposal by burning or rapid oxidation. The terms crematory, incinerator and destructor are commonly used loosely and interchangeably, but among manufacturers and engineers or technical men they usually are assigned distinct meanings. The word furnace is a general term covering all types. Crematory may also apply to all furnaces but is frequently applied, as is the term incinerator, only to low temperature furnaces. The term destructor is almost universally applied to furnaces producing high temperatures. Another classification which is frequently made is by the country where developed, as English type and American type. The incinerator or low temperature furnace is often spoken of as the American type and the destructor or high temperature furnace as the English type. Low temperature is considered as being below 1200° F.; high temperature applies to temperatures above 1200° F. Burning or cremation suggests itself at once as the most effective and sanitary method conceivable for the complete disposal of the waste or refuse of cities. The higher the temperature the more rapid and complete will be the oxidation and more thorough will be the destruction. Crude furnaces or ovens as are frequently seen in our alleys back of the stores in the business. district, consisting of brick walls arched over or covered with a piece of sheet iron, or a section of a boiler stack in which papers, excelsior, boxes and other rubbish are burned have been in use for years, and perhaps centuries, but the high temperature furnace is a comparatively modern invention. The combustion in |