Page:Outlines of Physical Chemistry - 1899.djvu/23

 FUNDAMENTAL THEOEIES 3*

n atoms of another, p atoms of a third, m, n, p being in- variable numbers. That is, the same elements must be united in the same proportions, as stated by the second law above.

8. If m atoms of one element can combine with n, 2 n, or 8 n atoms of another element with formation of different substances, it is evident that the weights of the latter element will be in the ratio 1:2:8, that is, in simple numerical relation.

There is no difficulty in expressing the law of reciprocal proportions in the same manner, i.e. in atomic language. In fact, the three first fundamental laws, based on the works of Lavoisier, Berthollet, Proust, and Dalton, have enabled the last-mentioned to establish the great probability

If this book pretended to be a complete treatise on theoretical chemistry, there would have to be inserted here a very important chapter on ' The Determination of the Proportional Numbers ' (also called equivalents or atomic weights according to the authors and the epochs of their discovery). 2 But for a study of this question, to which the most famous men of science, BerzeUus, Dumas, Stas, and

��1 Dalton, New System of Chemical Philosophy, 1808-1810.

part in the history of chemistry (Wollaston, 1814 ; Gmelin, about 1840). They were represented by the symbols of the elements, and were -used to give a simple expression to the results of analytical researches and to the quantitative composition of various substances. The symbol of hydrogen represented one part by weight of this element, that of chlorine 35*5 parts, that of oxygen 8 parts. Similarly the equivalents of the following elements were expressed by their respective symbols, representing the following number of parts by weight: Br = 7995; S = 16 ; N = 14 ; P = 31; C = 6 ; Si = 14 ; Al = J3-75; Fe = 28; Ca = 20; Mg = 12; Na = 23; K = 39*1; and so on.
 * The equivalents have on several occasions played an important

The formula HO represented perfectly the quantitative composi- tion of water : 8 parts of oxygen and 1 part of hydrogen. Sulphu- retted hydrogen was represented by HS (16 parts of sulphur and 1 part of hydrogen). Sulphuric anhydride was written SO, (24 parts of oxygen and 16 parts of sulphur). In an analogous

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