In order to show how synthetic remedies have been built up from simple products it will be convenient to take a few typical examples in the order of increasing chemical complexity, rather than with strict regard to chronological progression. ALCOHOL, ETHER, ALDEHYDE, ACETIC ACID. Ethyl (that is, ordinary) alcohol forms a convenient starting point. It has been already stated that the molecule of this substance is represented by the formula C_{2}H_{5}OH but for centuries before its constitution was unravelled it had been prepared in a more or less pure condition, as it still is, by a process of fermentation followed by distillation. Alcohol can be built up from its elements thus:--When an electric arc burns between carbon rods in an atmosphere of hydrogen, acetylene is formed; acetylene can be made to combine with hydrogen, forming ethane; ethane reacts with chlorine, yielding ethyl chloride; and this acted upon by an aqueous solution of potash gives alcohol as a result. The steps of the process are shown below:-- CH CH{3} CH{2}Cl CH{2}OH | --> | --> | --> | CH CH{3} CH{3} CH{3} Acetylene. Ethane. Ethyl chloride. Ethyl alcohol. Alcohol is the basis of a number of substances used in medicine. On treating it with a dehydrating agent such as strong sulphuric acid, the elements of water are removed, and two molecules of alcohol unite into one, the resulting product being ether (diethyl oxide). The reaction is rather more complicated than is explained here, but the net result is as stated. The process was described by the German physician, Valerius Cordus, and was incorporated in the “Dispensatory” published after his death by the Senate of Nuremberg, under the title of “Oleum vitriole dulce verum.” As explained in the article on Ether (Vol. I. p. 347), the chemical reaction was, until recent times, a favourite topic for investigation. When alcohol (C_{2}H_{5}OH) is oxidised, a substance known as aldehyde (CH_{3}CHO) is formed. This was first prepared and described by Fourcroy and Döbereiner, but its constitution was explained by Kolbe. On further oxidation acetic acid (CH_{3}COOH) is formed. The relationship between the alcohol, aldehyde and acetic acid was traced by Liebig. CHLORAL HYDRATE AND CHLOROFORM.