evident with either the square tubes shown at A or the zigzag passages outlined at B a large amount of metal surface compared to volume of water is exposed to the action of the air currents and the heat is readily extracted from the liquid. The end view of a typical honeycomb section made up of tubes as shown at B is outlined and

it will be noticed that the ends of the tubes are swaged together and firmly soldered in order to make water-tight joints.

Q. Name advantages and defects of large water passages in radiator.

A. Methods of radiator construction, which provide larger passages for the water than those previously discussed, are shown at Figs. 140 and 141. The general construction of the section outlined

Fig. 140.-Part Sectional View of Honey-Comb Radiator Section Showing Small Water Spaces and Large Air Spaces.

at Fig. 140 is very similar to that of a honey-comb radiator but the tubes are so assembled that larger water spaces are provided between them for the water to pass through. At Fig. 141 the tubes are flattened and the effective radiating surface is augmented by means of flat cooling flanges through which the tubes are passed and to which they are firmly secured by solder when building up the radiator. The front of the section shown at Fig. 141 is provided

with a series of vertical strips which give the effect of the conventional honey-comb cooler. When water is circulated in large passages there is no retarding effect offered by the friction of the tubing walls and as the passages are direct they are not liable to become clogged with rust or other foreign matter in the water. The disadvantages of the large water passages are that a greater volume of water is needed on account of the reduced cooling effect. When water is spread out in thin sheets it is easy to cool the entire mass but when

Fig. 141.-Sectional View of Flat Tube Radiator Showing Large Water Spaces Provided by this Construction.

it passes through tubes of large bore only the outside of the column of water is exposed to the cool walls of the metal tube and the inner core remains warm. Water coolers having large tubes are better adapted for the natural or thermo-syphon cooling systems.

Q. How is air circulated through radiators?

A. The usual method of supplying a stream of air is to use some form of simple fan placed immediately back of the radiator to draw the air through the spaces between the tubes while in those forms

where the radiator is carried at the rear of the hood, as shown at Fig. 138, a fan blade flywheel is often employed to produce the air draft.

Q. How are various members of the cooling system coupled together?

A. As is clearly outlined at Fig. 134 the various members of a cooling system are joined together by means of rubber and metal piping. Metal pipe is used at all points where the members are held rigid and are not liable to vibrate, while rubber hose joins two members which are liable to have motion relative to each other. For instance, in practically all cars the radiator is joined to the water jackets at the motor top and to the circulating pump by means of flexible non-metallic conductors. If metal pipe is used, the vibration is apt to crystallize it or open the joints.

Q. How are tight joints insured with the various forms of pipe?

A. Water conductors of metal are usually provided with flanged fittings which join them to the water jackets and other parts, and a tight joint is insured by interposing a gasket or packing member which is tightly squeezed between the pipe flange and the member to which it is connected and thus forms an effective seal to prevent leakage of water. In some constructions the ends of the metal pipe are pushed into a suitable opening made to receive them and a tight joint is insured by a packing gland and hemp wicking. Tight joints may be made with rubber hose by using the regular form of hose clamps which constrict around the hose and bring it in firm contact with the pipe over which it is slipped.

Q. Name two methods of constructing water manifolds.

A. Water manifolds may be cast in one piece or may be built up of various cast fittings and lengths of tubing joined together by a brazing or soldering process.

Q. Why are built-up metal manifolds preferable to cast manifolds?

A. The usual form of cast manifold unless of very large volume has rough interior walls that are apt to impede the flow of water