large number of coils to be used, thus obtaining a large radiating area on the surface of the wire, which means that they would dissipate their heat and operate at low temperature, thus reducing oxidation to a minimum.

There were three sections, each consisting of 4 coils, as described, connected in multiple. Each section was separate from the other electrically and was of 2 K. W. capacity on 220 volts. All three sections were, however, mounted on a single strap iron frame and covered with an expanded metal guard. Insulation between element and guard was tested to 1,000 volts. The complete heater was designed to go in a space 28 in. long, 12 in. high, 16 in. wide. The heater has given entire satisfaction.

The cold air enters from the roof through a galvanized iron duct. In traveling to the first section of the heater it passes over a cold air, expansion type, duct thermostat, which is set for 40°. In mild weather, or at such times as the incoming air is above 40° in temperature, the first or outside section of the heater is automatically cut off.

The second and third sections of the heater are controlled by one graduated acting thermostat placed in the apartment supplied by air from this plant. It is located at the fan outlet, where incoming air passes freely over it, thereby allowing close regulation. This thermostat is the usual one employed by the Powers company for graduated damper work. Through its capability to graduate air pressure delivered to the second and third diaphragm motors, which are supplied with differential springs, a range of 2° is maintained by the use of one instrument.

The diaphragm motor controlling the second section of the heater is supplied with a pair of springs which are considerably weaker than those on the third motor, so that it takes less pressure to throw the second switch than it does the third one, the difference being the difference being enough to allow two degrees variation between the opening and closing of the two sections. The graduated thermostat is adjustable over a range of 20°— from 60° to 80°-and can be set for any temperature between these points by

the use of a detachable key which is used to turn a marked dial over a graduated scale plainly shown on the cover of the instrument.

HUMIDIFYING DEVICE.

As explained above, the moisture is admitted to the air which has passed through the main heater. This is accomplished by three electric immersion coils placed in the bottom of an evaporating pan. These coils are kept covered with water automatically; they were designed by Mr. Hewett and are of the type such as are used in electrically heated steam boilers and large capacity water heaters. They consist primarily of a wire wound in spring form about as described in the air heater; in this case, however, a notched piece of mica is put in between each convolution. This is put in in such a way that does not permit it to fall out. The convolutions are therefore insulated from each other, and, as the mica extends beyond the periphery of the coil, it insulates the heating element from the tube in which the element is placed. The mica dividers each have a hole in the center, which permits a 3-16-in. rod to be pushed down the center of the coil, making it a straight rigid unit. Terminal blocks are attached at each end; the central rod forms the electrical return, thus permitting the heater to have its supply terminals at one end.

This unit was slipped into a brass tube, 14-in. outside diameter, No. 16 gauge, which had one end sealed and the other provided with with a flange and threaded for a nut, which permitted the tube to be locked into the wall of the vessel, resting one end on the bottom. The joint was made tight by a gasket.

There are three heaters, each to evaporate about 4 lbs. of water per hour; each heater was of 1,100 watts, 220 volts, single heat, volts, single heat, and was 27 in. long. The wire used in the water heater was altogether different from that used in the air heater. The number of heat units dissipated per unit area on the water heater is large and the element within the tube runs very hot. The wire is a nickel chromium alloy which will stand very high temperature without oxidation. Most forms of insulation

would break down under such a condition, but the large number of mica washers which stand edgewise to support the coil easily stand up under the work. The current of this heating coil is automatically regulated by a Powers. hygrostat placed in the living apartments on the same panel with the thermostat which controls the temperature.

It was impossible to use lengths of galvanized iron pipe, as is the custom on automatic control work, so flexible armored lead tubing was used to supply thermostats and hygrostats with air pressure and also to make connections between these instruments and the four diaphragm motors used. The tubing was extended from the air storage tank, along the under side of the roof, to the flue that leads to the room-from where

it was dropped into the flue and connections made to the controlling instruments by running the lines on the inside. of a cabinet-thus exposing none of it in the rooms. From the thermostats and hygrostats return lines were carried back the same way to the different diaphragm motors. Very little cutting and no patching was necessary to install this system, which is working to the satisfaction to all concerned.

The atmosphere is pleasant and restful, and the effect of the conditioned air is already distinctly beneficial. While it is too early to declare with positiveness that the proper adustment of heat, moisture and ozone has been reached, we have all of these under control and shal be able to meet any particular requirement of the attending physician.

The small share taken by the members of the engineering profession in connection with public affairs, has attracted the attention of the American Institute of Consulting Engineers, which has discussed the subject at several of its recent meetings. Particular attention has been drawn to the fact that the important controlling bodies, such as the public service commissions, have no engineers among their number, although they are dealing with problems of a technical character, necessitating technical knowledge for full consideration.

This condition is so noticeable in connection with many other departments of civic work, that the members of the engineering profession would do well to give the subject consideration.

As one who has taken an active part in local civic problems, the writer is able to state, from his experience, that an engineer is better equipped to aid in dealing with such subjects, from the public point of view, than a member of any other profession. It is safe to say that at least one-half of a city's problems are more. or less intimately connected with technical matters. In all such problems, the training of an engineer will enable him to aid his fellow-citizens in securing needed improvements, in investigating

municipal and governmental methods, and in analyzing figures. The latter is one of the most difficult problems in civic work, as a large majority of our citizens, including those who are most active and interested in such problems, are unacquainted with the meaning and effect of figures and are often entirely. unable to determine their bearing upon a municipal or governmental problem.

All these considerations indicate that the engineer can do good and effective work by taking a share in betterment and uplift problems, and there is no reason, other than the modesty and reticence of the members of the profession, why they should not form the leading element in these good works.

As an instance that is directly of interest to the members of the profession of heating and ventilating, the great subject of the ventiliation of New York City's public schools is now being dealt with by the Board of Education composed, as Mr. John Martin has recently. stated, entirely of untechnical laymen, dependent upon information derived from some one engineer engaged for the purpose, or, as is more generally the case, dispensing entirely with any technical assistance. Why should a board charged with the important duty of caring for the

health of the children of a city, be without a single technical member? This has simply come about because engineers have not drawn the attention of the appointing authorities to the need for such an appointment, and because these appointing authorities are in ninety-nine cases out of one hundred, members of the legal profession, whose knowledge and opinion of the engineering profession is usually narrow and restricted.

Our technical societies are not free from blame in this connection; one of the

leading engineering societies adopted the attitude some years ago of standing aloof from all public affairs and refusing even to present a list of eligible and experienced members for appointment upon public duties.

The best course to remedy the existing condition is for all engineers to unite in demanding recognition, but while that process is going on, to get out into public affairs and take an active part in the work of voluntary associations, on committees and on the public platform.

CONNECTION WITH

Among the many problems which confront manufacturing industries in thickly populated communities, that of dust removal is frequently very serious. This applies to industries where pneumatic conveying of light material is employed or in whose processes large quantities of dust are formed which necessitate continuous removal by fan exhaust systems. This dust is valuable in some cases and purely waste in others.

Regardless of its value, the scattering of it over the neighborhood often becomes an annoyance, giving rise to injunctions, threats of damage suits, etc. Complete shutting down of a plant with its attendant expense is not infrequent, pending the installation of apparatus to abate the nuisance. In such emergencies ineffective make-shifts and costly experiments are the rule. The result is, perhaps, a partial suppression of the annoyance which may temporarily relieve the situation; the same condition often has to be met again and all previous expenditure of time and money is wasted.

As its almost universal application indicates, the centrifugal type of dust collector has proven to be the most practical device, to date, for the separation of solid matter from air. The efficiency of a dust separator varies widely, depending chiefly on the character of the material, other things being equal. An important fact is that the percentage of material escaping consists of the finer

CLOUD OF DUST ENSUING FROM SEPARATOR IN ORDINARY EXHAUST SYSTEM.

the combination of a dust collector and an air washer. That it has not been more generally known is due to the fact that exploitation was deemed inadvisable until the pioneer systems had proven practical and continuously efficient. The success of the several systems now in operation for reclamation service has far exceeded the expectations of both the owners and manufacturers.

In one large and well-known plant of an Eastern manufacturing company three successive systems were installed. The first was installed to abate a nuisance, but it was soon found that the material removed was suitable for reworking. The owners state that the actual saving the first year exceeded the cost of the entire installation. The second apparatus was installed to remove sawdust; it presented some rather perplexing problems because of the behavior of the material when wet, and its large quantity. About 50 cu. ft. of sawdust, in the form of an almost impalpable powder, is removed every working day. The third apparatus is similar to

the first and performs the same kind of service.

The air washer becomes a practical device for this work chiefly when used in conjunction with a dust collector, since the former is not able to handle large quantities of material with the same facilities as the latter.

An air washer designed for this service will remove from 90 to 95% of the dust escaping from a dust collector. Assuming that a collector has an efficiency of only 50% for an extremely difficult material and that the air washer will remove but 90% of that escaping, the plant efficiency will be about 95%; with less difficult materials to handle the efficiency becomes practically 100%. Under any conditions, then, the efficiency will be such that it will in effect abate any dust nuisance.

Briefly, the scheme involves a dust. collector the air discharge outlet of which is connected to a specially designed air washer. The design of such an air washer is a matter dependent in many respects on the character of the

material to be handled and upon local conditions. Naturally there are some broad principles which form the basis of design, but beyond this, individual treatment is required in each case.

Preliminary to the designing of such a system it is necessary to conduct extensive tests in an experimental apparatus with the material to be removed. The behavior of the dust under various forms of spray, its affinity for various materials, etc., are noted. The arrangement of nozzles and spray heads, form of eliminator, disposition of additional washing surface in some cases and many other considerations affect the final lay-out.

Back pressure upon the dust collector lowers its efficiency greatly, with corresponding increase of work for the air washer. The equipment in connection. with the dust collector must, therefore, be taken into consideration, since excessive back pressure might create serious disturbances.

It is obvious that in work of this character spray devices must be used which do not readily clog. They must

be simple, since unskilled labor is usu