lead, and of tallow and lime. Smear the parts to be protected with any one of these mixtures.

Screw Cutting Gears.-Multiply the number of threads cut by equal gears, as indicated on the index, by the number that will give for a product a gear on the index. Place this gear on the spindle or stud. Multiply the number of threads per inch to be cut by the same number and put the resulting gear on the screw. Thus, if a lathe cuts four threads by equal gears and 13 threads per inch are wanted then multiply by five, showing that to cut 13 threads per inch would require a gear of 20 teeth on the spindle or stud and a gear of 65 on the lead screw.

Treating Polished Iron or Steel.-Wash polished iron or steel that has become gray and lusterless, with a stiff brush and ammonia soapsuds. Rinse well and dry by heat if possible. Then apply a plentiful supply of sweet oil and dust thickly with powdered quicklime. Let the lime stay on two days, after which it should be cleaned off with a stiff brush. Polish with a softer brush and rub with cloths until the luster comes out. By leaving the lime on, iron and steel may be kept from rust almost indefinitely.

Speed of Grindstones.-To grind machinist's tools stones should have a speed of about 800 feet a minute at periphery, a 30 inch stone running about 100 revolutions a minute. In grinding carpenter's tools a speed of 600 feet a minute at periphery should be maintained, a 30 inch stone running 75 revolutions a minute.

Cleaning Brass Castings.-Brass castings that are greasy may be cleaned by boiling in lye or potash. The first pickle is composed of one quart of nitric acid, and six to eight quarts of water. After washing in clear warm or hot water the casting should be immersed in the second pickle, composed of one quart of sulphuric acid, twe quarts of nitric acid and a few drops of muriatic acid.

Laying Out Work.-Use blue vitriol and water on the surface of steel or iron in laying out work. This will give a nice copperplate surface, so that all lines will show plainly. A little oil of vitriol will eat off oily surfaces and leave them nicely coppered.

Pipe Joint Cement.-Mix 10 parts of iron filings and three parts of chloride of lime to a paste by means of water. Apply to the joint and clamp. It will be solid in 12 hours.

Drilling.-Use kerosene to drill, ream or turn malleable iron, or to drill or turn aluminum. Turpentine should be used instead of oil for drilling hard steel, as it will cause drilling readily when the metal cannot be touched with oil. By using a combination of turpentine and camphor, glass may be drilled with a common drill. When the point of the drill comes through the hole should be worked with the end of a three-cornered file, having edges ground sharp. Use the corners of the file to scrape rather than as a reamer. Great care must be taken not to crack the glass or flake off pieces of it while finishing. The mixture should be used freely, both while drilling and scraping. It may be used as well to drill hard cast iron and tempered steel.

Body Polish.-A much recommended body polish is made by mixing the following ingredients:

Another scheme is to use a mixture of boiled linseed oil and turpentine, applying it sparingly and rubbing absolutely dry. The use of these polishes will restore even an old car to a degree of brightness that will please the owner. Floor wax is also used, as is furniture polish.

Care of Tops.-Mohair tops should be frequently dusted and brushed off. Pantasote tops and curtains are best cleaned with a soft brush dipped in water to which a little ammonia has been added. Afterwards rub dry. Never attempt to clean top and curtains with gasoline or kerosene. Do not fold the top until it has become thoroughly dry, because any moisture remaining in the folds is apt to cause mildew, besides making the top leaky and unsightly with spots. When a car is not used for some time, it is best to open the top, which keeps it well stretched and smooth.

Care of Leather Upholstery.-Do not use gasoline in cleaning leather upholstery. Plain water with a little ammonia will remove the dirt and a brisk rubbing with a clean woolen or flannel cloth

will do the rest. For still more careful treatment use a regular leather dressing.

Care of Cloth Upholstery.-Do not use an acid solution in cleaning cloth upholstery.

Cloth is not affected by climatic conditions and withstands both heat and cold, and having no oil in its make-up, does not pick up or hold dust readily. To remove ordinary dust, beat cushions and backs lightly with stick or carpet beater, then remove dust with whisk-broom or brush. Grease or oil may be removed by the application of a solution of luke warm water and Ivory soap applied with a woolen cloth. Any of the approved methods for cleaning woolen cloth may be used with success on this upholstery. Gasoline and benzine have a tendency to spread instead of removing the dirt. Their use is not recommended for this reason, although they work no injury to the fabric.

CHAPTER XIV

USEFUL TABLES FOR THE MECHANIC.

Mathematical Tables

Table of Inch Decimal Equivalents-Millimeter Decimal EquivalentsMetric Conversion Tables-General Formulæ in Mensuration-Diagonals of Hexagons and Squares-U. S. Measures and Weights-Trigonometrical Formula-Circumferences and Areas of Circles.

Mechanical Tables

S. A. E. Screw Standard-Standard Hexagon Bolts and Nuts-Machine Screw Table-Dimensions-Pipe Threads-S. A. E. Carburetor Fittings -Standards for Wire Gauges-Calculating Length of Chain-Table of Allowances for Grinding-Sizes of Drills to Use for Hand Taps-Twist Drill Gauge Sizes Speed of Drills-Figuring Emery Wheel SpeedsPulley Sizes-Lathe Gearing for Cutting Threads-Allowances for Fits. Miscellaneous Tables

Time Per Mile Expressed in Miles Per Hour-Comparative Scale, Fahrenheit and Centigrade Thermometers-Horsepower Chart-Compression Pressure- -Approximate Horsepower of Four-Cycle Engines Two-Cycle Engines-Indicated Horsepower-Weights of Metals-Weight of Steel Bars-Weight of Castings to That of Wood Patterns-Table of Gradients-Calculating Grade Percentages-Chart for Determining Speed of Car.

THOSE engaged in mechanical work cannot fail to appreciate the tables which follow, selected with care and with special reference to automobile repairing, machine work and allied industries. These have been compiled from standard authorities on mechanics, standards, metallurgy, automobile construction and design, mathematics, et cetera, and therefore can be divided into three general classes. Those dealing with arithmetic are in one group, those having to do with machine work are in another group, while the remainder deal with miscellaneous subjects. It is believed that the tabulation can be of value in many ways to the motorist as well as to the mechanic. While this data is available to all who can consult different standard works, it is believed that compilation in condensed form, as well as a rearrangement in some cases to simplify the matter, will make it

of real service to the laymen as well as the more expert machinist and repairman. Because of the number of authorities consulted and the many works from which the tables have been made, it is not possible to give individual acknowledgment, especially as many of the tabulations have long been public property and have been gererally used by writers on mechanical subjects.

Table of Decimal Equivalents