PRODUCTION OF DYES 311 



discoverer of mauve, the first of these artificial colouring matters, 

 was attracted to the subject by noticing the beautiful tints dis- 

 played by a film of tar floating on water. Such colours are, of 

 course, due to the thinness of the film, and have nothing what- 

 ever to do with its composition. 



In order to render intelligible the chemical changes which are 

 involved in the successive stages of the production of the numerous 

 synthetic dyes, drugs, perfumes, and other so-called organic 

 compounds, a very brief statement of the meaning of chemical 

 symbols is necessary. How they are arrived at, and the full 

 extent of their meaning, are questions which are beyond the 

 scope of this work, but can be answered by reference to any one 

 of the best textbooks of chemistry. 



A chemical symbol such as C or H is usually the initial letter 

 of the name of an element, carbon or hydrogen for example. It 

 is used to signify one atom of the element, and when two such 

 symbols stand side by side, the elements are represented in 

 combination, thus H 2 means that two atoms of the element 

 hydrogen are combined with one atom of the element oxygen, 

 forming one molecule of the compound, water. The symbols are 

 also used for the purpose of displaying what is believed to be the 

 order in which the elements in a compound are joined together. 

 Thus the formula for water, H 2 0, may be written H.O.H or 

 H-O-H, by which expressions the idea is conveyed that the 

 atoms united together in a molecule of water are not jumbled 

 together irregularly, but that each atom of hydrogen is attached 

 to the oxygen and is unconnected, at least directly, with the 

 other atom of hydrogen. Similarly any number of atoms of 

 carbon may be joined together, and at the same time combined 

 with hydrogen or other elements as in the formulae for 



Alcohol CH 3 .CH 2 .OH and 

 Acetic acid CH 3 .CO.OH. 



Such expressions may be expanded if necessary so as to show 

 the manner in which each atom is joined to the others as in the 

 case of acetic acid : 



H 



I II 

 H C C H. 



H 



