Synthesis requires exact knowledge of all the elements and forces involved in the object of its investigation, and looks to the inductive or analytic method to furnish these data. There must be no unknown quantities in the problem to be solved, for synthesis seeks not to build from the unknown but only to re-form the known. Hence it properly awaits to receive verified facts from chemical analysis, which has yet been able to compass but a fractional part of the organic compounds.
Chemical elements are the basis of chemical science; they are neither produced nor destroyed, but are the enduring and constant factors in the many series of changes in the properties of matter, which represent the desideratum of this science. And yet the knowledge of molecules is very meager; the weights of but a few are known, even among the commonest elements and compounds; and but little account has been taken of atomic motion, which furnishes the most perfect explanation of chemical reaction.
Of the highly complex series of albuminoid substances, which neither crystallize nor possess any combining equivalent, and therefore can not be expressed by exact symbols, analytic chemistry knows but little, and hence it would be in vain to attempt their reproduction by synthesis. Notwithstanding our ignorance of essential facts, the progress of synthetic chemistry has been great, and the prospect is favorable for more brilliant achievements in the future.
Wöhler, in 1828, first, by synthesis, formed urea from ammonia cyanate. It was claimed by the critics that urea, being a nitrogenous metabolite, a product of animal decomposition, was a mineral, rather than an element of the animal tissues; but when Fownes, in 1841, prepared cyanogen itself direct from its elements, and, from this salt, urea, the fact was recognized and accepted, although it was affirmed that a "vital force" was necessary to account for the more complicated organic compounds, of which series urea was a member having only simple combinations. This was disproved by Berthelot in 1856, when he obtained the potassium salt of formic acid. Then followed the production of acetylene, marsh-gas, ethylene, and other hydrocarbons, from inorganic materials. Marsh-gas was converted into methyl alcohol, and ethylene into ethyl alcohol, and from these alcohols formic and acetic acids were made.
Startling as these results were, the substances formed were, relatively, simple in nature, and the "vital force" still ruled in the more complicated bodies of organic origin.
Synthetic work continued to achieve brilliant results and added to its list of vegetable compounds oxalic, valeric, malic, citric, tartaric, and salicylic acids, the oils of garlic, mustard, and wintergreen, also conine, alizarine, and indigo.
Of animal compounds, leucin, creatin, sarcosin, and taurin are added to the large and growing list of substances from which analysis and synthesis have banished the vital force, and harmonized the facts