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Quantities of Materials (Cont'd.)

IV. Special Methods of Measurement of Quantities.

2. Weights of Metals

Method of Measurement.

To illustrate the application let us suppose we have a piece of iron of the shape shown in Fig 4. of Plate 4 the total weight of which is required and that the given figure is an accurate drawing of the article drawn to any convenient scale— say ½ inch to 1 foot.

Since the scale of the given drawing is ½ inch to 1 foot, one actual square inch of the drawn figure will represent an area of 4 square feet of metal.

Since the material is Iron and 1 sq. ft. of Iron taken as 1 inch thick weighs 40.0 lbs., and since 1 sq. inch of actual area of the drawing represents an area of 4 sq. ft., the weight represented by 1 sq. inch of actual area will be 40 × 4 = 160 lbs., and the total weight of the article will be 160 lbs., taken as many times as there are square inched of actual area in the drawing of the figure.

If then we adjust the Planimeter to that Setting which will give a Reading of 1600 Vernier Units for each square inch of actual area of figure traced, it is evident that the Reading due to tracing the given figure will be ten times its weight in lbs., and to obtain the weight of any piece of flat iron drawn to a scale of ½ inch to 1 foot we trace the outline of the given figure with the Planimeter adjusted as described and the resultant Reading divided by 10 or multiplied by .1 will be the desired weight in lbs. assuming the iron to be 1 inch thick. Multiplying this result by the thickness of the iron in inches will evidently give the total weight required.

Table 11 has been calculated in the manner just described and gives the Settings, Vernier Units and other factors for all scales used in plotting construction work or similar nature.

The table has been calculated on the assumption that the metal measured was 1 inch in thickness or length and the result of any tracing must be multiplied by the total thickness or length in inches of the metal measured.

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