Neil A. Maclean Sulfur Dioxide Concentration Slide Rule

This wooden rule has hand-lettered paper labels glued to it. The top of the base has a logarithmic scale for parts per million of sulfur dioxide. The slide has logarithmic scales for pounds of sulfur dioxide and gallons of liquid. By setting the number of gallons next to the desired number of parts per million, the user may find the weight of sulfur dioxide needed to add to the liquid. The lower part of the base is marked: Directions – Set gallons to treat opposite arrow – Read lbs sulfur Dioxide opposite P.P.M. desired. (/) Copyright 1938 Neil A. Maclean Co. 470 - 8th St. San Francisco. Cal.

The back of the rule is stamped: DEC –5 1938. Over this is stamped: [S]URPLUS (/) DUPLICATE around the logo for the Library of Congress. The back is also marked: ©CI 1 pub. 23866. Neil A. Maclean Company (sometimes called NAMCO) was a California distributor of pesticides and agricultural supplies. It deposited this rule with the Library of Congress as part of its application for copyright (23866 is the copyright number for the device). The Library subsequently transferred the instrument to the Smithsonian. Another sample used to procure a copyright is 1983.3009.02.

NAMCO was still on 8th Street in the 1940s, but according to its trademark records, it moved to Milpitas, Calif., by 1971. Van Waters & Rogers, a multinational pest control and chemical supplier now called Univar, acquired the company sometime between 1974 and 1975.

Reference: Library of Congress Copyright Office, Catalog of Copyright Entries: Part 4, Works of Art, Etc., n.s. 34 (1939): 163.

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