Official Announcement of Various Unit Standardisation from the Mining and Metallurgy Institute

Posted By Richard Jefferson on 04 December 2014

Posted in The Vintage Machinery Almanac

This article was originally published in Electrochemical and Metallurgical Industry Publication of December 1907. Information within this article is therefore correct as of 1907. The publication of this material aims to provide historical insight on the subject and its place in industry.

The Institution of Mining and Metallurgy (London) has sent out an official announcement, stating that the following definitions have been adopted by the institution:

1) The word "ton" shall represent a weight of 2,000 pounds avoirdupois (29,166.6 ounces troy). It is advisable to abandon the use of the terms hundredweights and quarters, and to express fractions of a ton in pounds or in decimals of a ton.

2) The term "miners inch" shall represent a flow of 1.5 cubic feet of water per minute; and the term "sluice head" shall represent a flow of 60 cubic feet of water per minute. It is advisable, however, to abandon the use of both terms, as being merely of local usage, in favor of definite expressions of the flow of water per minute, or per second, in cubic feet or in gallons.

3) The word "gallon" shall represent the imperial gallon measure of 10 pounds of water.

4) Temperatures shall be expressed in degrees centigrade.

5) Returns of gold and silver shall be expressed in terms of fine gold and fine silver, respectively, not as "bullion."

6) Gold contents of ores, etc. determined by assay, shall be expressed in money values as well as in weights; and in this connection the value shall be taken (as a convenient constant) at 85 shillings, or $20.67 United States currency, per troy ounce of fine gold.

Mesh of Wire Cloth.— The following table of "I. M. M. Standard Laboratory Screens" is intended for use in making grading tests and for the correlation of screens used in commercial or other work. When screens other than the I. M. M. standards are employed, the diameters of apertures should be given in any published results, so that comparisons may be made. When screens are described simply by the number of meshes per linear inch, it will be understood that the I. M. M. standard is referred to. The number of sizes standardized has been reduced to a minimum, as it is desirable to abandon excessive refinements in grading tests. It is believed that the I. M. M. standards will meet all necessary requirements of the laboratory. In reporting grading tests it is desirable to state whether wet or dry screening has been employed.

Mesh or Pertures
Per Linear Inch
Wire Diameter (inch)
Wire Diameter (mm)
Aperture (inch)
Apperture (mm)
Screening %
 5  0.1
 2.540  0.1
 2.540  25.00
 8  0.063  1.600  0.62  1.574  24.60
 10  0.05  1.270  0.05  1.270  25.00
 12  0.0417  1.059  0.0416  1.056  24.92
 16  0.0313  0.795  0.0312  0.792  24.92
 20  0.025  0.635  0.025  0.635  25.00
 30  0.0167  0.424  0.0166  0.421  24.80
 40  0.0125  0.317  0.0125  0.317  25.00
 50  0.01  0.254  0.01  0.254  25.00
 60  0.0083  0.211  0.0083  0.211  24.80
 70  0.0071  0.180  0.0071  0.180  24.70
 80  0.0063  0.160  0.0052  0.157  24.60
 90  0.0055  0.139  0.0055  0.139  24.50
 100  0.005  0.127  0.005  0.127  25.00
 120  0.0041  0.104  0.0042  0.107  25.40
 150  0.0033  0.084  0.0033  0.084  24.50
 200  0.0025  0.063
 0.0025  0.063

Whilst absolute accuracy to the fourth place of decimals of an inch is impracticable in the manufacture of wire cloth, a sufficiently close approximation to the above standards is attainable.

The adoption of a screening area of 25 per cent, necessitating equality of size of wire and aperture, secures perfect interlocking and consequent permanence of aperture.

Some of the finer mesh screens can only be woven in what is known as "twilled."

Image Credit: Smithsonian Institution