CHEMISTRY. 19 
combines with oxygen in the proportion of 16:8. The same numbers, six 
and sixteen, expressing the ratio of combination for carbon and sulphur 
with oxygen, express also the ratio of their mutual combination. Their 
ratios experience no other modifications than those obtained by multiplying 
the first or second term. This same law of definite proportions applies not 
only to carbon, sulphur, and oxygen, but to all elements. Knowing, then, 
the ratio in which all the elements combine with oxygen, we shall have the 
ratio of their combinations with each other. This’ ratio may be expressed 
either by the numbers themselves, or by their multiplication into some 
definite progression. This progression may be the series of numbers from 
one to five, and in some cases fractions intermediate to these. The 
numbers thus obtained for the different elements are known by the terms, 
atomic weights, combining numbers, or chemical equivalents, and were first 
established with remarkable accuracy by Berzelius, and afterwards 
corrected by other chemists. In the following table we present the 
elements already known to chemists, with their symbols and equivalents. 
For greater convenience we have given two series of equivalents, the one 
where hydrogen is taken as unity and oxygen as 8, the other assuming 
12.5 as the equivalent of hydrogen, and 100 as that of oxygen. 
The equivalents adopted in the table are taken from the third volume of 
the fifth (German) edition of Berzelius’ Treatise on Chemistry, a few more 
recent determinations by Marignac being added. Many chemists consider 
the equivalents of Calcium, Magnesium, Iron, Silver, Mercury, Sulphur, and 
some others, as exact multiples of that of Hydrogen ; but experiment has not 
yet established this point in a perfectly satisfactory manner. 
Tantalum, Niobium, and Pelopium occur associated in nature, and have 
not yet been perfectly separated. The name Columbium was applied to the 
metal obtained from the Columbite of Connecticut by Dr. Wollaston. Rese 
has recently ascertained its identity with Niobium, and it is therefore better 
to drop the old name, which has only been employed by American 
writers. 
The symbols are abbreviations of the English or classical names, 
employed for greater convenience of reference. Those elements to which 
no equivalent is appended, have either been discovered quite recently, or 
else elements supposed to be pure, have been ascertained to be compounded 
with some other elements, and the equivalents previously determined must 
therefore be rejected. 
The circumstances under which chemical combinations of simple bodies 
take place, are very various. Temperature exerts a great influence, 
although its action differs much under different circumstances. Many 
bodies require to be cooled in order that a combination may take place. 
Thus chlorine only combines with water at and under a temperature of about 
32° F.; others combine directly at ordinary temperatures, whenever brought 
into communication, as potassium and oxygen. By far the greater number 
of combinations, however, are produced through the instrumentality of heat, 
while others again are decomposed by the same agency. Of all simple 
elements, oxygen exhibits the greatest tendency to combine with the rest, 
ICONOGRAPHIC ENCYCLOPADIA.—VOL. I. 29 449 
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