Everyone knows that electric lamps sometimes have to be shifted in a shop until the desired illumination has been obtained. The advice of an acoustic specialist in particularly noisy shops may save some experimenting in this respect.

Musical sounds differ from one another in the following three respects: In pitch, high or low; in intensity, loud or soft; and in quality (timbre), such as brass, reed, string instruments, human voice, etc. Noise is a nonharmonic combination of such sounds, and can be analyzed into its components. These fundamentals of acoustics are now being applied to the solution of industrial problems, and the science of industrial acoustic engineering is rapidly growing, bringing with it increased economy and efficiency.

There are engineering concerns which specialize in acoustic signals and in intercommunication problems, just as other engineering concerns specialize in factory illumination, ventilation or sanitation. They have accumulated considerable experience in installing signals in noisy places and it would pay a foundry manager to get advantage of their advice in laying out a new code-calling system.

The following are the principal sources of noise in a fully equipped foundry:

Molding Department.-Vibrators for loosening sand from patterns, jar-ramming machines, cranes, trolleys, hissing of compressed air; noise of conveyors, trucks, wheelbarrows, etc.

Cleaning or Trimming Room.-Tumbling barrels, air chisels, pneumatic drills, grinding wheels, scrapers, band saws, conveyors, sand-blast machines, hissing of escaping air.

Sand Mixing Room.-Gears, chains, disintegrator ham-. mers, magnetic separator for iron stays, and electric motors.

Melting Room.-Roar of blowers and of combustion (especially when burning oil); cranes and conveyors. Not very noisy.

Core Department.-Hammering, jar-ramming machines, escaping air, gas or oil furnaces, sand conveyor, a traveling crane, and trucks.

Welding Department.-Roar of the oil-burning furnaces for preheating defective castings; hissing of the oxyacetylene flames; handling, hammering and dragging of castings.

Discussion Audible Signals

PROF. KARAPETOFF.-Loud speaking telephones are in use in some railroad stations, in offices and on warships, and those who have had experience, especially in railway stations, know that sometimes it takes a good deal of imagination to know just where the train is going. Undoubtedly loud speaking telephones find their place where there are no loud noises; but in a shop, where it is difficult to even understand each other without shouting, I doubt very much if, at the present stage of development, a loud speaking telephone would be feasible at all, not to speak of its added expense. The only advantage that a loud speaking telephone might have over code calling would be in conveying a more definite message. Such messages are readily taken care of by a more elaborate code, without the necessity of listening as closely as one would have to listen to a human voice. One of such combinations might mean "Come to the telephone when through with present engagement." This would do away with the objection that a busy executive may be unnecessarily interrupted by code calls. Such an extended code answers any possible objection to code calling. Of course we all hope that the day will come when telephones will be either loud or else everyone can carry a wireless receiver about him and hear conversations by means of electric waves, but at the present stage of the development, I do not believe that is feasible. In offices loud speaking telephones are doing splendid service and I can recommend them.

MR. TOPPATE.-I would like to know if the professor has had any experience in using colored lights?

PROF. KARAPETOFF.-Colored lights are good in some places and I have seen them in use in some department stores where the floor walker can readily see them, and where audible signals may be objectionable to the customers. I am not at all opposed to colored lights or to any system of signals whatever. Any system of signals has to be properly designed in application to the problem on hand, designed by a specialist who understands all kinds of signals and who knows the local conditions.

The Testing of Clays for Foundry

Uses

BY HOMER F. STALEY, Washington, D. C.

The clays in common use in foundries are all plastic fire clays, that is, soft clays with comparatively high melting, or softening, points. However, plastic fire clays may be divided into eight classes or varieties. The first division is into clays of low and high plasticity. Clays in the first division are usually sandy, slake rapidly in water and have low bonding power when wet, while those in the latter are commonly fat and sticky, contain little sand, slake slowly and have high bonding power when wet. Each of these divisions may be subdivided into vitrifying clays, that is, clays that burn hard and dense at temperatures below 1200 degrees Cent. (2200 degrees Fahr.) and nonvitrifying clays, which do not burn hard and dense until temperatures above 1200 degrees Cent. are reached. Each of these subdivisions may be divided into two classes, first, refractory clays which soften at temperatures above 1550 degrees Cent. (2820 degrees Fahr.) and second, nonrefractory clays which soften at temperatures below that point. The relations of these classes of clays to each other can be seen in Table II.

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Clays are used in foundries for three purposes: First, mortar in the construction of fireclay brick linings for cupolas and furnaces; second, as daubing material for lining ladles and the repair of cupolas; third, as a binder in sand mixtures in making molds for steel castings. The requirements for satisfactory service in these three uses vary, and therefore the tests to be applied to determine the suitability of clays for each of these services should vary also. The object of this paper is to discuss the relation of the properties

of clays to the requirements of the service to be performed in different foundry operations and to describe tests that will determine the fitness of a particular clay for a given use.

High Temperature Mortars and Cements

The Importance of Proper Mortar Joints.-In general, foundrymen seem to fail to realize the importance of the use of the proper kind of mortar in furnace construction and lining of cupolas. They complacently follow the old custom of specifying that fire-clay brick shall be laid in the same clay that is used in making the brick. While brick manufacturers will furnish clay on these specifications, they cannot meet them literally. Fire-clay brick are made from a mixture of soft plastic fire clay and hard rock-like flint fire clay. The latter is very refractory but in the shape in which it is used in fire bricks is wholly unfit for use as mortar. Very rarely finely ground flint clay is mixed with plastic clay and sold as mortar material. The fire clay furnished for mortar is usually one of eight plastic varieties. In general it is less refractory than the fire brick of which it is one component. According to its properties and the conditions of service to be met, it may or may not be suitable for use as mortar in a given piece of furnace construction. It is perfectly possible that a more satisfactory mortar could be secured by the use of some other material.

Construction of Mortar Joints. In the construction of fire brick parts of furnaces that are to be exposed to heat, the mortar joints should be kept as thin as possible, much thinner than the ordinary bricklayer is willing to make them. The essential difference between a bricklayer and a successful furnace builder is that the latter understands the necessity for thin mortar joints while the former cannot be made to realize it. It has been found in practice that when thick mortar joints are used in furnace building the structures fail

very quickly at the joints. In good furnace construction, therefore, fire clay is never used in the shape of thick mortar but only as a thin batter into which the brick are dipped immediately before being put into place. Bricks and shapes that are too irregular in form to permit the making of sufficiently tight walls in this manner with slight rubbing should not be used. If a trustworthy furnace builder is employed, the use of trowels for laying extremely thin joints may be permitted.

Furnaces should be, and generally are, so constructed that there is no necessity for the mortar to act to any marked degree as a binding material either before or after the furnace has been put into service. The function of the thin coating of clay batter is simply to fill small crevices between the brick. Of course, most raw clays and all hardburned clays exert some bonding action, but this should not be considered as a factor in furnace construction or in selecting a clay for this work.

Table I-Classes of Plastic Fire Clays

Fineness Test of Raw Clay.-As far as properties in the raw state are concerned the only essential is that the clay shall work up with water to a thin fine-grained batter. This requirement is met by most plastic fire clays. A simple sieve test is sufficient to determine the suitability of a clay in this regard. All of the batter should pass readily through a 20mesh sieve. If it does not do so, it should be put through a sieve of that mesh. The presence of coarse granules of clay prevents the making of a brick wall with thin tight joints. Of course the clay could be sieved dry through a 20-mesh sieve before the batter is made. Often, however,