Julv, 1928
INDUSTRIAL A N D ENGINEERING CHEMISTRY
747
An Early Type of Chemical Slide Rule’ By J. A. Gunton TRANSYLVANIA COLLEGE,LEXINGTON,K y .
A
MOIYG the treasured heirlooms of the library and museum of Transylvania College there exists a simple piece of chemical apparatus, dating from the early days of chemistry in America, which may be as interesting to others as it is to the author of this description. It is entitled, “An Improved Scale of Chemical Equivalents,” by Lewis C. Beck and Joseph is particularly illumiHenry, AI bany, 1828, 2nd Edition-and nating with respect to the inorganic nomenclature and atomic weights of t h a t period. The scale itself consists of a flat piece of wood about 19 inches long and 2.5 inches wide, fitted with a sliding portion, as is the ordinary slide rule, so that the numbers on the slide may be placed opposite the names of the elements or compounds along either side of the slide. The face of the rule is covered with paper on which is printed the names of the elements and compounds t h a t may be considered in the computations. On the back of the rule is a description of the scale and its construction. The printing on both sides is in good state of preservation and quite readable. The mathematical construction is such t h a t the slider of the scale is graduated into divisions and subdivisions continually decreasing in length from 8 a t the top t o 330 near the bottom. These divisions correspond in relative lengths to the differences of the “logarythms” of the numbers placed opposite them. Now since the division of numbers is performed b y taking the difference of their logs, and since the several divisions on the scale represent the difference of the logs of the numbers placed opposite them, it follows t h a t the distance between any two numbers will be equal t o the distance between any other two that give the same quotient by division. But numbers which give the same quotient have the same ratio t o each other, therefore equality of ratio on the scale is expressed by equality of distance. The chemical explanation of the scale may best be given in the designers’ own words as printed on the back: The application OF the logametric scale to Chemistry is founded on the most important fact in this science; Which is, that all bodies whether simple or compound that enter into chemical combination, always unite z n weights or in multifdes of weights that have the same ratiu to each other. And as these relative weights have the same effect in forming neutral compounds and in producing other changes they are called the chemical equivalents, and may be expressed in numbers referable to a common standard taken as unity. (These have been called the Atomic weights, because philosophers have supposed that in all cases of chemical combination an union takes place between the ultimate atoms of bodies. This is the basis of the Atomic Theory.) On this scale the least combining quantity of hydrogen is taken as the unit; and as eight times as much oxygen enters into combination with hydrogen to form the chemical compound water, oxygen will be expressed by 8 and water by 9. If therefore the slider be placed so that 8 near the top of it coincides with the upper oxygen, the whole scale becomes a synoptical table of these chemical equivalents, having hydrogen as their radix. Thus 16 is the equivalent for Sulphur, 17 for Ammonia, 70 for Barium, 110 for Silver, etc. These substances were placed opposite the respective numbers on the slider as they have been determined by Thomcjon, Brande, and other approved authors. There are included in the list of substances 36 elements and 144 compounds on which calculations may be based. Some of the terms that may be of interest are: “Bi-hydruret of phosphorus, Deut. Oxide Hydrogen, Phosphuret calcium, Muriate of ammonia, Protoiodide mercury, Bi per sulph. copper and 2nd chloride tin.” Presented before t h e Section of History 1 Received March 16, 1923. ef Chemistry a t t h e 63rd Meeting of t h e American Chemical Society, Birmingham, A l a , April 3 t o 7, 1922
As an example of the way in which the slide rule may be used, we may take the case of carbonate of lime. Without moving the slider, the scale shows us that the equivalent weight is 50, and as this substance consists of carbonic acid and lime we find the equivalent of the former to be 22 and of the latter to be 28. The proportion of these ingredients in 100 parts can be determined by placing the slider so that 100 is opposite carbonate of lime. Then i t will be noticed that carbonic acid is opposite 44 and lime opposite 56, which are the proportions of these substances in 100. Again, suppose we wish t o ascertain the constituents of 100 parts of ammonium nitrate. If we move the slider so that 100 is at nitrate of ammonia, which we find has 1 W before it, indicating one proportion of water, then 1 water on the scale is opposite 11.3 on the slider, ammonia is opposite 21.2, and dry nitric acid opposite 67.5. The percentage composition of ammonium nitrate is, therefore, water 11.3, ammonia 21.2, and dry nitric acid 67.5-totaling 100. The designers claim no originality, stating that the invention is due to Dr. Wollaston and that it is stamped with his accuracy and ingenuity. Wollaston’s scale was devised in 1814,2 after he had calculated the equivalent weights of 12 elements and 45 compounds3 from the analyses, mostly by other men, of many compounds. Practical convenience was his sole guide and he thought that the term ‘‘equivalent weight” was less theoretical than the term “atomic weight.” The original instrument was referred to by Thomson in 1817*as Wollaston’s “sliding rule of chemical equivalents so precious in every point of view to the practical chemist.” The scale of Beck and Henry differs from the original in the assumption of hydrogen as the radix or unity, which is of course a n advantage in that it does away with fractional quantities. Also, in order t o diminish the length of the scale and render it more portable, i t commences with oxygen 8 instead of hydrogen 1, and 10 atoms of hydrogen are placed opposite 10 on the slider. For the same reason 2 of carbons, the weight of one atom of which is 6, are placed opposite twelve. The author has been unable to find any reference in the literature of the period to this revised form of Wollaston’s scale, and no record can be located with respect to its history in connection with Transylvania. About 1830, sums of money, enormous for those days, were being spent on books and apparatus, and it may have been included in these purchases. Any information with respect to either point will be appreciated. 2 Pattison Muir, “History of Chemical Theories and Laws,” John Wiley & Sons, Inc., 1909, p 91. 3 Phzl. trans., 1814, P a r t I , 1. 4 “System of Chemistry,” 5th Ed., 3 (1817), 18.
Dr. TViley Honored Harvey W. Wiley, president of the United States Pharmacopeial Convention, 1910 t o 1920, has been elected a n honorary member of the Pharmaceutical Society of Great Britain. This society, like the United States Pharmacopeia1 Convention, is charged with the duty of keeping the Pharmacopeia up t o date. On June 7, 1923, he also had an honorary degree of Master of Arts conferred upon him by the Hahnemann Medical College and Hospital of Philadelphia, at its seventy-fifth annual commencement exercises. On June 20, Dr. Wiley went to Cambridge, Mass., to participate in the festivities in connection with the fiftieth anniversary of his graduation from Harvard University.
