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2019 has been designated the International Year of the Periodic Table as it is the 150th Anniversary of the formulation of Mendeleev's Tabelle I

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1813

Wollaston's Synoptic Scale of Chemical Equivalents

Philosophical Transactions: A Synoptic Scale of Chemical Equivalents by William Hyde Wollaston, M.D. Sec. R.S., or from here.

It is apparent that chemistry the years 1810 to 1850 was largely concerned with discovering the whole number stoichiometric ratios of atoms in chemical compounds.

Wollaston writes in the text above:

"It is impossible in several instances, where only two combinations of the same ingredients are known, to discover which of the compounds is to be regarded as consisting of a pair of single atoms, and since the decision of these questions is purely theoretical, and by no means necessary to the formation of a table adapted to most practical purposes, I have not been desirous of warping my numbers according to an atomic theory, but have endeavored to make practical convenience my sole guide, and have considered the doctrine of simple multiples, on which that of atoms is founded, merely as a valuable assistant in determining, by simple division, the amount of those quantities that are liable to such definite deviations from the original law of Richter."

"Mr. Dalton in his atomic views of chemical combination appears not to have taken much pains to ascertain the actual prevalence of that law of multiple proportions by which the atomic theory is best supported [however] it is in fact to Mr. Dalton that we are indebted for the first correct observation of such an instance of a simple multiple in the union of nitrous gas with oxygen."

"[I have] computed a series of supposed atoms, I [have] assumed oxygen as the decimal unit of my scale [ie. oxygen = 10], in order to facilitate the estimation of those numerous combinations which it forms with other bodies. Though the present table of Equivalents, I have taken care to make oxygen equally prominent on account of the important part it performs in determining the affinities of bodies by the different proportions in which it is united to them.."

Mark Leach writes:

"When Wollaston's equivalent weights are converted from O = 10.00 to the modern value of O = 15.999, the atomic weight values can be seen to be astonishingly accurate.

"However, the language of the article is quite difficult as the meaning of many of the terms is unclear (to me, at least). For example, in modern usage adding 'ia' to a metal implies the oxide: 'magnesia' is magnesium oxide, MgO. I am not clear if this historical usage is consistent. 'Azote' is nitrogen and 'muriatic acid (dry)' is hydrogen chloride gas. I have only analyses/re-calculated the elements and a couple of common/obvious compounds:"

  Wollaston's data Scaled to O = 15.999 Modern Values % error
H (as H2) 1.32 2.112 2.016 5%
O 10.00 15.999 15.999 ref. value
H2O 11.32 18.111 18.015 1%
C 7.74 12.383 12.011 3%
S 20.00 31.998 32.060 0%
P 17.40 27.838 30.974 -11%
N (as N2) 17.54 28.062 28.014 0%
Cl (as Cl2) 44.10 70.556 70.900 0%
Fe 34.50 55.197 55.845 -1%
Cu 40.00 63.996 63.546 1%
Zn 41.00 65.596 65.380 0%
Hg 125.50 200.787 200.590 0%
Pb 129.50 207.187 207.980 0%
Ag 135.00 215.987 107.870 50%
  • The elements hydrogen, nitrogen (azote) and chlorine have clearly been measured as the diatomic molecules, even if this was unknown to Wollaston in 1813.
  • Phosphorus is out by 11%... [fair enough].
  • Only silver is clearly wrong, but it is out by 50% so it looks like a simple stoichiometry error: Perhaps the oxide was assumed to be AgO was instead of the correct Ag2O.

Interestingly, Wollaston's analysis is far better than Daubeny's 1831 data seen in Oxford.

Read more in an entry concerning chemical slide rules.

Thanks to Nawa for the tip!

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© Mark R. Leach 1999-


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