Such a statement as this, although suited to the conceptions of that time, could not be received when Lavoisier had shown chemists how Nature ought be examined. With the definite conception of element introduced by the new chemistry, came an attempt to prove that organic compounds were built up of elements which were rarely found together in any one compound of inorganic origin. Substances of vegetable origin were said by Lavoisier to be composed of carbon, hydrogen and oxygen, while phosphorus and nitrogen, in addition to those three elements, entered into the composition of substances derived from animals. But neither could this definition of organic compounds be upheld in the face of facts. Wax and many oils contained only carbon and hydrogen, yet they were undoubtedly substances of vegetable or animal origin. If the presence of any two of the three elements, carbon, hydrogen and oxygen, were to be regarded as a sufficient criterion for the classification of a compound, then it was necessary that carbonic acid--obtained by the action of a mineral acid on chalk--should be called an organic compound.
To Berzelius belongs the honour of being the chemist who first applied the general laws of chemical combination to all compounds alike, whether derived from minerals, animals, or vegetables. The ultimate particles, or molecules, of every compound were regarded by Berzelius as built up of two parts, each of which might itself be an elementary atom, or a group of elementary atoms. One of these parts, he said, was characterized by positive, the other by negative electricity. Every compound molecule, whatever was the nature or number of the elementary atoms composing it, was a dual structure (see p. 164). Organic chemistry came again to be a term somewhat loosely applied to the compounds derived from animals or vegetables, or in the formation of which the agency of living things was necessary. Most, if not all of these compounds contained carbon and some other element or elements, especially hydrogen, oxygen and nitrogen.
But the progress of this branch of chemistry was impeded by the want of any trustworthy methods for analysing compounds containing carbon, oxygen and hydrogen. This want was to be supplied, and the science of organic chemistry, and so of chemistry in general, was to be immensely advanced by the labours of a new school of chemists, chief among whom were Liebig and Dumas.