18 CHEMISTRY. 
apparatus has thus been replaced by hydrogen, the lamp (fig. 11) is to be 
brought under the bulb of b, and the oxyde of iron heated to a slight glow. 
When this has ensued the hydrogen combines with the oxygen of the 
oxyde to form water, which is carried by the succeeding hydrogen into the 
calcium tube c, and there absorbed. After a time the oxyde in b will be 
found. completely reduced to metallic iron. The lamp must now be 
removed and the whole apparatus allowed to cool. The bulb containing 
the iron is again to be provided with the cocks and the air exhausted; on 
weighing it, the difference between this weighing and the preceding will be 
the weight of the oxygen, and the difference between this last weighing and 
the first will be the weight of the iron. In experiments tending to great 
accuracy, the chloride of calcium tube, c, is likewise weighed before and 
after the operation. This tube will be increased in weight by the water 
absorbed, and as the composition of water is well known, the amount of 
oxygen in the estimated weight of water must coincide with the amount 
lost by the oxyde of iron. 
Il. Tue Evements anp THEIR ComMBINATIONS. 
It has already been remarked that by far the greater number of bodies 
surrounding us are chemically compound in their character. Of this we 
are abundantly convinced by the possibility of reproducing certain 
compounds from the elements which we had obtained from them. In this 
way we are enabled very conveniently to form certain substances whose 
composition has been first ascertained by analysis. 
It is a very general, if not universal law, that a simple body combines 
only with another simple body, rarely with one that is already compound. 
In this manner are produced chemical combinations of the first degree, or 
binary compounds, containing two elements. When two binary compounds 
unite, a ternary compound is produced. The number of these ternary 
compounds far exceeds that of any of the others. 
Different names are given to particular classes of these compounds. 
Thus the binary compounds of oxygen with any other element are either 
oxydes or acids. When the same element combines with oxygen to form 
an oxyde in more than one proportion, that containing the least quantity of 
oxygen is called the protoxyde; the next, deutoxyde; the third, tritoxyde ; 
&c.: the highest proportion gives us the peroxyde. The acid combinations 
of oxygen have the name of the combining element with a termination of 
ic. Thus nitrogen and oxygen form nitric acid. If there be two acid 
compounds, the one with least oxygen ends in ows, as nitrous acid. 
The most remarkable law of chemistry, and at the same time the one on 
which the whole science depends, is, that the elements always combine in 
definite proportions by weight. An entirely new attribute is thus added to 
our previous idea of an element, namely, its capacity of combining, 
according to definite laws, with all the others. Thus carbon never 
combines with oxygen in any other ratio than that of 6:8, while sulphur 
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