< Page:Popular Science Monthly Volume 76.djvu
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509
JOHN DALTON

stituents in fixed and invariable proportions." Notice, in the words I have italicized, the unanimous trend towards quantitative measurements and accuracy, the ruling notion being that of numerical ratio. We come to closer quarters with our central theme in the work of Richter (1762-1807), an investigator, it is important to note, obsessed by mathematical methods. Despite his obvious idiosyncrasy, Richter arrived at the law of equivalent ratios—"The qualities of acids and bases equivalent in one neutralization are equivalent in all." In 1802 Fischer made Richter's conclusions known to Berthollet, and chemical ratios became an integral part of the science. As Wollaston says, in 1814:

It is to Richter we are originally indebted for the possibility of representing the proportions in which the different substances unite with each other in such terms that the same substance shall always be represented by the same number. He discovered the law of permanent proportions.[1]

The experimental proof was clinched by Berzelius in 1811-12, and the law of "permanent" or "definite" ratios, as it is called now, put the problem of composition on a practicable footing.[2] It should be noted also that, in stating the numerical values of the elements, Dalton employed some determinations of other chemists, at all events as checks.

We are now in a position to see that series of complicated researches, all looking to quantitative results, furnished Dalton with material which enabled him to render the atomic theory perspicuous and applicable from the very outset. Notwithstanding, to him must be given sole credit for the final simplification, which had been exercising his mind for some eighteen years—since 1790, in fact. A quotation from Berthollet's "Essai" (1803) may suffice to emphasize the long step due to Dalton's insight.

Some chemists, influenced by having found determinate proportions in several combinations, have frequently considered it as a general law that combinations should be formed in invariable proportions; so that, according to them, when a neutral salt acquires an excess of acid or alkali, the homogeneous substance resulting from it is a solution of the neutral salt in a portion of the free acid or alkali. This is a hypothesis which has no foundation, but a distinction between solution and combination.[3]

Undoubtedly, events tended towards the new climate of opinion, nay, this had become so far prevalent that the Irishman, William Higgins (17?-1825) came nigh playing Wallace to Dalton's Darwin. Indeed, in 1814, he raised a claim to priority, which was disproved at once by Thomson, the Glasgow chemist who had made Dalton known. This Higgins is to be distinguished from his uncle, Bryan Higgins

  1. ↑ The italics are mine.
  2. ↑ Reference should be made to the classical experiments in further confirmation by Stas (1865).
  3. ↑ Cf. Lambert's English translation, p. 39.
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