Alphabet of lines

The alphabet of lines shows the various line types that, when used together, create an engineering drawing of an object. 

Engineers must be able to communicate graphically using the alphabet of lines. 

The labels s, p, d, and f are used for historical reasons. They originally referred to characteristics of lines observed in the atomic spectra s (sharp), p (principal), d (diffuse), and f (fundamental). Beyond f the letters become alphabetic g, h,..., skipping , which is reserved as a symbol for angular momentum. 

A single unstable compound of known composition is placed in the main first volume and is located on the basis of its empirical molecular formula expressed in the Hill system used by Chemical Abstracts (C and H if present, then all other element symbols alphabetically). The use of this indexing basis permits a compound to be located if its structure can be drawn, irrespective of whether a valid name is known for it. A representation of the structure of each compound is given on the third bold title line while the name of the compound appears as the first bold title line. References to the information source are given, followed by a statement of the observed hazard, with any relevant explanation. Cross-reference to similar compounds, often in a group entry, completes the entry. See Trifluoroacetyl nitrite p. 244. 

For ease of reference, the terms in each section, sub-section, etc. are listed alphabetically and numbered sequentially. Cross references to terms defined elsewhere in the document are denoted in italic typeface. If there are two terms in an entry on successive lines, the second is a synonym. 

The solvents in Table I are listed with upper case letters alphabetically, with the names which seemed best known. Many solvents with two or more common names are listed in each place. Cross references save the repetition of the accompanying data, when more than five lines are required. 

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