SYNTHESIS, Chemical. The building up or formation of chemical compounds from their elements or groups of their elements. The op posite of analysis, one meaning of which is the breaking up or decomposition of a chemical compound into its elements. Thus the forma tion of water from its elements hydrogen and oxygen is synthesis, while the decomposition of water into hydrogen and oxygen is analysis. Many of the most important manufacturing processes are synthetical. The synthesis of compounds from their individual elements is of great scientific but of little technical interest. However, the recent synthetical process of unit ing moist nitrogen and oxygen to form nitric acid by use of the electrical discharge bids fair to be of great interest to mankind because of the use of nitrates as fertilizers. The syn thesis of compounds from groups of their ele ments is of very great industrial importance. Sometimes only a singie and simple chemical reaction is required, as, for example, the action' of water on quicklime to form slaked lime, while others, such as the manufacture of in digo from naphthalene, require many and com plicated changes. There is a great difference as to the ease with which elements or groups of elements unite to form compounds. Some unite readily under ordinary atmospheric conditions of temperature and pressure, while others may require the action of heat, light, electricity, presence of water, etc. Phosphorus and iodine unite the moment they come in contact. Phos phorus and oxygen unite slowly at ordinary temperatures but with violence if the tempera ture is raised; sulphur and iron do not act at all at room temperature but do so when heated highly; hydrogen and chlorine do not act in the dark at ordinary temperatures but do so with explosive violence if exposed to the light ; ammonia and hydrochloric acid or the mixture of bicarbonate of soda and cream of tartar used in baking powder do not react when dry but do so in the presence of water.
Up to 1828 it was thought that all organic chemical compounds, those formed in or pro duced by animals and plants, could not be pre pared in the laboratory by synthetical processes. The action of a "vital principle' or "vital force' was thought to be necessary. Wohler showed this to be not true when (1828) he prepared urea, an organic substance produced by animals, from ammonium cyanate. Since that time an immense number of other organic substances have been prepared by synthetic processes. Some of the well-known ones are oil of winter green, indigo, caffeine, alizarine, etc. The pro cesses used in synthesis have been so thoroughly studied that the chemist has only to find out the exact chemical structure of a compound to be able to prepare it in the laboratory. Sometimes these laboratory processes are too costly to be of technical importance, but often they are of great commercial value. See Imitoo; ALIZARIN.
Many substances are prepared by synthesis that never existed in any plant or animal. They are purely laboratory products. To this class belong most dyestuffs, many valuable medicines and a large number of perfumes and flavoring substances. Consult Berthelot, P. E. M., synthese chimique) (Paris 1876) Posner, The odor, 'Lehrbuch der synthetischen Methoden' (Leipzig 1903) ' • Lassar-Cohn, 'Arbeitsmethoden fiir organisch-chemische (2 vols., Hamburg 1907).