Chemical slide rule

W. D. Williams, Some early chemical slide rules , Bull. Hist. Chem., 1992,12, 24-29. 

In other words, much of the structure of chemical theory serves to enhance our inferential capacities. Nor is articulation of this structure the only means by which chemistry supports reliable reasoning. In the eighteenth century, Macquer s tables assisted prediction via an orderly repository of a large number of chemical reaction types. The nineteenth century witnessed the manufacture and commercial sale of several "chemical slide rules" for calculating chemical equivalents, and the technology was frequently combined with a standard slide rule in the first half of this century (Williams, 1992). As we have seen, the periodic table itself supports many qualitative and comparative modes of reasoning. 

Williams, William D. 1992. "Some Early Chemical Slide Rules." Bulletin for the History of Chemistry, 12 24-29. 

The above is an incomplete list, given to illustrate the level of preparation we are presuming in this text. If you find very much of this list partly or wholly unfamiliar, you don t have to give up, but have a good general chemistry textbook available for study and reference—and use it Some useful general chemistry books are listed at the end of the chapter. A four-place table of logarithms will be necessary a set of ball-and-stick models and a chemical handbook will be very helpful, as would be a small electronic calculator or slide rule to carry out the simple arithmetic required for many of the exercises. 

In nearly all practical chemical calculations, a precision of only two to four significant figures is required. Therefore the student need not perform multiplications and divisions manually. Even if an electronic calculator is not available, an inexpensive 10-in slide rule is accurate to three significant figures, and a table of 4-place logarithms is accurate to four significant figures. 

In general, chemical problems may be solved by using a slide rule for the numerical work. This gives about three reliable figures in the answer, which is often all that is justified by the accuracy of the data. Sometimes the data are more reliable, and logarithms or long-hand calculations might be used to obtain the answer with the accuracy called foit. 

I remember his lectures in Oxford in early 1948. The lecture hall was too small to hold all who wished to attend there was standing room only. He told those of us who had never studied electrostatics to go home and read Sir James Jeans s book on that subject before coming to his lectures on chemical bonding. I had never studied electrostatics but I stayed, spellbound. I had never heard anyone quite like him, with his jokes, his relaxed manner, his seraphic smile, his slide-rule calculations and his spontaneous flow of ideas. (Only much later did I realize that much of that apparent spontaneity was carefully studied.) He had great histrionic skills. 

Wollaston describes a synoptic scale of chemical equivalents in the form of a logarithmic slide-rule. These scales, and tables of equivalents accompanying them, were sold by Newman, Regent St., London, and some are still in existence. ... 

Wollaston s paper on equivalents and his slide-rule introduced confusion into chemical theory, since some of his numbers are not equivalents at all, and they no doubt popularised the use of Gmelin s equivalents (Vol. IV) instead of Berzelius s true atomic weights. Wollaston mentions Richter and points out that Wenzel s results are incompatible with the law of neutrality. 

Figure 18 An operational version of the pAa slide rule. See text for explanation. (Reproduced from Gilli et al., 2009 American Chemical Society, 2009).

The pAa slide rule toward the solution of a long-lasting problem. Accounts of Chemical Research, 42, 33-44. 

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