Hard to Hemlock

Heating to He1ical angle

resistance wire ()r other material.
Heating. (Forg.) Placing a piece in a forge or fire until it is of a tempera­ture to be properly worked.
Heating effect of current. (Elec.) The heating effect of a current is in direct proportion to the current flow.
Heating of bearings. Rise in tem­perature of bearings, commonly due to faulty lubrication; may cause the axle and bearing to stick or to wear rapidly.
Heating of dynamos. (Elec.) Three factors contribute to the heating of dynamos: mechanical friction in the bearings, core losses due to eddy currents and "hysterisis, and losses in the windings.
Heating surface. AJI surfaces of a boiler which ~ve hot gases on one side and steam or water on the other.
Heating unit. (Elec.) That part of any" electrical heating device in which the heat is generated.
Heat of fusion. The heat required per unit mass of a given solid at its melting point for complete conver­sion of the solid to a liquid at the same temperature.
Heat of vaporization. The heat required per unit mass of a liquid at its boiling point for complete conversion of the liquid to a gas at the same temperature. "
Heat mark. (Plast.) An extremely shallow, regular, or irregular depres­sion or groove in the surface of a plastic, visible only because of a sharply defined rim or roughened surface.
Heat pump. A .device that, by means of compressible refrigerant, trans­

fers heat from one body to an­other body, as a building, the process being reversible.
Heat seal. (Plast.) To bond or weld a material to itself or to another material by heat alone.
Heat sink. A device employed in association with transistors to displace unwanted h~t and prevent thennal runaway; a system that is considered to absorb heat at a con­stant temperature, the concept is useful in thennodynamics, as in the operation of a heat engine.
Heat time. (Weld.) The time of du­ration of each current impulse in pulsation welding.
Heat treatment. (Metal.) The care­fuJly controJled heating and cool­ing of steel to bring it to its highest efficiency. The treatment pre­scribed by the ~anufacturer for any particular kind of steel must be rigidly followed as different steels requ~re different treatment.
Heavy duty. Made or designed to withstand great physical strain.
Heavy joist. (Wood wkg.) Timber over four inches and less than six inches in thickness and eight inches or over in width.
Hectograph. A gelatine pad for mak­ing multiple copies of drawing or writing.
Heel. (Arch.) The end of a rafter or beam which rests on the wall plate.
Height. (Arch.) Of an arch, the dis­tance from the middle line of the chord to the intrados.
Helical angle. (Mach.) The angle which any portion of a helix or screw makes with a line drawn at

Helical gear to Hemlock
right angles to its axis.
Helical gear. (Mach.) A tooth gear in which the wheel teeth, instead of being at right angles with their faces, are set at some other angle therewith. Often incorrectly called spiral gear. It may be used to transmit power between (I) parallel shafts, (2) shaft at right angles and not intersecting, (3) shafts inclined at any angle and not intersecting. It gives greater strength and smoother operation, but develops considerable end thrust.
Helical groove. (Shopwk.) A groove of uniform-advance. The amount of advance in one revolution in a sin­gle helical groove is called the ':pitch"; in the case of a multiple helical groove, as double or triple, the amount of advance in one revo­lution is spoken of as the '~Iead."
Helical spring. (Mach.) A compres- .. sion-type spring shaped like the frustum of a cone.
Helicoid. Coiled in such a manner as to resemble a helix.
Helicoid. (Aero.) A type of aircraft supported by one or more rotors turning in a horizontal plane which can rise or descend vertically; fly in any direction, forward, backward, or sideways; or. hover motionless. The first practical helicopter was developed by Igor Sikorsky.
Heliport. (Aero.) An area for the land­ing and takeoff of helicopters.
Helium. One of the rarest elements. It exists in certain uranium miner­als and to a small extent in the air. Its chief source is in the natural gas of southwestern United States.
Helix. (Draft.) A curve, as would be obtained by winding a thread around a cylinder in suct) a manner that there would be a uniform amount of advance with each revo­lution.
Helix angle. (Mach.) The angle made by the helix of the thread at the pitch diameter with a plane per­pendicular to the axis.
HeUbox. (Print.) A box into which is thrown all kinds of broken and battered type and all useless print­ing material.
Helper. One who serves as an assis­. tant. working with and under the direction of someone more skilled. Halve. The handle of a hatchet or axe. Hematite. An important iron ore.
HeniicoUoids. (Chern. Plast.) Poly­mers of molecular weight up to
10,000 corresponding to an order of polymerization equal to 20 to 100 monomeric units. They dis­solve without swelling and give solutions .of IQW viscosity. .Precipi­tation from solution yields pow­dery masses.
Hemisphere. A half sphere.
Hemlock. (Wood) A tree of the pine family. Its wood is like spruce in appearance; much used in framing.
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