Constitution of organic compounds.—One of the most difficult, but at the same time most interesting and important problems which present themselves to the chemist, is the internal arrangement or constitution of organic compounds. A child may no far investigate a watch for instance, as to discover that it consists of silver, steel, and glass, nay he might even without difficulty make his research a quantitative one, and ascertain the weights of these different materials, which enter into the composition of the instrument, but such an investigation would obviously leave the most interesting part of the history of the watch untouched ; it would tell him nothing either of the arrangement of these materials or of the respective functions of the wheels, the springs, the hands, &c., the investigation of which would obviously involve a much more laborious and especially a much more intellectual inquiry. So in chemistry, the mere determination of the composition of a compound stops short of the more interesting attributes of the body—its internal arrangement and the functions performed by its several constituents. Hence the higher problem, difficult as its solu tion undoubtedly is, has never been lost sight of by the chemical investigator. With a view to its solution he on the one hand submits
organic compounds to various processes, in order to take them to pieces ; and on the other, he brings together what he conceives to be their proximate constituents, in order if possible to build up the substance be is investigating; and thus he endeavours from both the points of view thus afforded to arrive at some conclusion as to their internal constitution.
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It would be easy greatly to extend this view of the constitution of organic carbon compounds, but the above examples are sufficient to indicate its general application. It is from carbonic acid, water and ammonia that nature constructs her most complex organic compounds; these inorganic substances are the essential food of plants, which thus find ready formed in the air and earth the moulds in which to cast their most complicated chemical compounds, just as animals find ready formed in their vegetable food, the plastic constituents which they employ for the construction of the various parts of their organisms.