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Chemical Abstracts

CA coverChemical Abstracts was published in print from 1907 to 2009 by the American Chemical Society.  In the decades before computer databases, large indexes like CA were the standard entry point into the scientific literature.  Using them effectively was a skill that required learning, dedication, and practice.  A complete set of CA, with Collective Indexes, from 1907 through 2001, is located in remote storage.


There were 26 weekly issues per semiannual "volume." Each Abstract issue was divided into 80 Subject Sections. An abstract appeared in just one section, based on the novelty of the process or substance being reported in the literature. Each weekly issue also contained indexes by author, subject keyword (not official headings), and patent number. The issue indexes were superseded first by a volume index published every six months, and then by the 5-year Collective Index. (The library did not retain the issue and volume indexes.)

Collective Indexes
Every five years CAS published a Collective Index (CI). The 14th CI was published in 2002 and covers the years 1997-2001. The library has all Collective Indexes up to this point. They are divided into:

  • Author Index, 1907-2001
  • Subject Index 1907-71 (included chemical substance names through 1971)
  • Chemical Substance Index, 1972-2001 (includes all CA Index Names used during the specific index period)
  • General Subject Index, 1972-2001 (includes all subject and compound-class terms that are not systematic CA Index Names)
  • Formula Index, 1920-2001
  • Patent Index, 1907-2001

Index Guides
The Index Guide (IG) for each Collective Index period provides cross-references from commonly used chemical names to official CA Index Names (with registry numbers) used in the corresponding Chemical Substance Index. It also serves as a thesaurus of all controlled-vocabulary subject headings used in the General Subject Index. The Index Guide should always be consulted before looking up a chemical name or subject term in the Collective Indexes.

Ring Systems Handbook
The RSH leads you from a ring or cage structure to the CA Index Name and Registry Number of a ring parent compound, for searching in the Chemical Substance Index. Entries are in ring analysis order and are indexed by molecular formula and Index Name.

Registry Handbook
The Registry Handbook - Number Section was a cumulative numerical listing of Registry Numbers assigned to chemical substances from 1965 to 1996. If you have only a registry number and need the CA Index Name for that compound, look it up here first and then use the name to consult the Chemical Substance Indexes. A corresponding Names Section issued on microfiche provided registry numbers for several hundred thousand of the most-indexed common names.

CASSI (Chemical Abstracts Service Source Index) is the comprehensive and retrospective list of publications that have been indexed by Chemical Abstracts since it began in 1907. It includes journals, books, conferences, and other series, arranged by CA abbreviation. This is the source you use to translate journal title abbreviations into full titles for searching in the library catalog and other finding aids. The last print edition of CASSI (1907-2004) is kept in the Librarian's office. It is also available in a somewhat limited form on the web:

Doing a manual search in printed Chemical Abstracts is a tedious, mutli-step process.  This is how it was done.

  1. Select an appropriate Index volume based on the type of search you want to do (author, substance, or subject) and the time period desired.
    • Author: Entries are arranged by last name, then by first and second initials (not by first name). Qualifying text is the title of the document. Coauthors are cross-referenced to first author.
    • Formula: Entries contain only abstract numbers unless there is a large number of them, and no qualifying text. It's best to use the Formula Index to get the corresponding CA Index Name, then look up that name in the corresponding Chemical Substance or Subject (1907-71) index, where the entries are more detailed. Formulas are listed in Hill order: C, then H, then other elements in alphabetical order.
    • Chemical Substance name: Start with the Index Guide to see if there's an entry for the name you have. If not, use the Formula Index or Ring Systems Handbook to get the name. In the CSI you must use only the specific CA Index Name for that CI period. There are no cross references to earlier or generic names. Names are arranged by "parent" (the structural skeleton) followed by substituents and modifications. Qualifying text in each entry indicates what the document is primarily about, followed by an abstract number. About 600 of the most frequently indexed compounds are called "Qualified Substances." Their document entries are grouped into seven categories: Analysis, Biological studies, Occurrence, Preparation, Properties, Reactions, Uses and miscellaneous.
    • Subject term: Check the Index Guide first to find an appropriate term to look up in the Subject Index (1907-71) or General Subject Index (1972- ). Classes of compounds (e.g. Carcinogens), undefined compounds and mixtures (e.g. Gasoline), processes, plant/animal species, and other general topical terms are found in this index, along with cross references and scope notes.
    • Patent number: Arranged by issuing country/organization, then by patent number. CA abstracts only the first member of a patent family, and links later equivalent patents to this parent patent. Equivalents are cross-referenced to the parent. Prior to 1981 the equivalents were listed in the Patent Concordance.
  2. Note Abstract Numbers from the entries of interest. Abstract numbers prefixed "R" indicate a review; "P" indicates a patent.
  3. Go to the corresponding Abstracts volume and look up the abstract by its number.
  4. Repeat this process for earlier or later index periods. Remember that Index Names and subject headings changed over time, so consult the Index Guide for each CI period.
  5. A booklet called "How To Search Printed CA" is available in the library with the CA indexes.


The format of the CA Abstract Number changed over time. Only 1967-forward abstract numbers are searchable as "document identifiers" in SciFinder. "CAN" numbers displayed in SciFinder for pre-1967 records do not correspond to the printed CA abstract number.

Dates Example Notes
1967-present 74:23628c Represents a single specific abstract; searchable in SciFinder. The final control character appears only in the print abstracts and should be ignored.
1947-66 45:1541e Volume:Column number/column fraction letter a-h. Abstract numbers prior to 1967 do not necessarily represent a specific abstract, but rather the position in a column or page where that abstract begins.
1934-46 28:37145 Volume:Column number/column fraction digit 1-9
1907-33 6:571 Volume:page only.

For Librarians:  Retention of Chemical Abstracts

old CAS logoFor most libraries, the increasingly rare use of historical print CA may no longer warrant the large amount of space it occupies. It ceased print production in 2009, and many libraries stopped taking it long before that.  Ultimately, the decision must be based on local needs and situations. If space needs are urgent, it is quite difficult to justify keeping CA in place. If you have the luxury of considering the finer points, these are some pieces of collective wisdom gathered from experts over the years.


  • Here's the most important consideration: It's highly unlikely that any scientist born after the mid-1970s would have any experience using print CA (or any printed index for that matter), or even be aware of its existence. Therefore academic libraries should expect all potential use to be initiated and mediated by a library staff member or senior faculty member who has working knowledge of this tool. If no such persons remain on the campus, then print CA is almost certainly a waste of space. (Similarly, there is no longer any practical reason to teach students how to use it!)
  • SciFinder is not identical to Chemical Abstracts. All (or nearly all) the metadata content of the latter is included in the CAPLUS file and robustly substance-indexed via the Registry file. But it is inaccurate to say that you can do everything in SciFinder that you could do in the print.
  • The Collective subject/substance/formula indexes allow browsing of chemical names, formulas, and subject headings in a way that isn't possible in SciFinder. SciFinder is great for snapshots, but it provides only a limited view of the hierarchical structure of the CA database, or its indexing and nomenclature practices; nor does it allow easy browsing for derivatives, salts, and other variants of a parent structure. In other words, you can't browse online for nearby entries like you can in the print, which removes a serendipity factor. For some purposes, this is an important distinction. Browsing and searching CA indexing terms for concepts, chemical classes, and taxonomic vocabulary from the CAS Lexicon (thesaurus) is possible in SciFinder, as of 2023.
  • When you can't figure out how CAS has defined the structure or formula of certain types of compounds, especially inorganic (salts, hydrates, ions, decimals, etc), coordination compounds, and multicomponent substances, SciFinder can be frustrating. Using the Index Guide and Chemical Substance Index can actually save some time, and when you find the Registry number then you can go back to SciFinder, locate the substance record and complete the literature search. (Of course, this method only works for compounds registered before your last Collective Index.)
  • Pre-1967 CA abstract numbers are not searchable or displayed in SciFinder, and can only be looked up or verified in the print. These numbers were occasionally cited in the older literature, especially as stand-ins for obscure and foreign documents.
  • Some older printed abstracts may contain structure graphics that aren't duplicated online.
  • If you have bound any of the six-month volume indexes, and you have the equivalent Collectives and their Index Guides, the former are expendable and should be discarded to save space. And hopefully the indexes in the back of the weekly issues were sliced out and discarded before binding -- those are indeed useless and add a significant amount of linear footage.
  • Production of printed CA ceased in 2009, and the hardcopy is now only applicable to historical searching. It is not a viable substitute for any form of current online searching.
  • Even if you decide to discard the bulk of CA, consider retaining the most valuable parts, such as the Index Guides (potentially useful for finding contemporary index terms, synonyms, controlled vocabulary, Registry Numbers, etc.). If you wish to split the run by time period, collective wisdom suggests that the older (and smaller) pre-1967 portion of CA is more useful than the post-1967 volumes.
  • Indexes stored remotely in closed-stacks facilities will almost certainly never be used again.
    • If the facility lacks space and staff who can retrieve and consult CA volumes to mediate a reference question, stored CA can't be used as designed.
    • If storage space is at a premium, it's difficult to justify the space CA would occupy there. (A complete set of CA with indexes can occupy as much as 1000 linear feet of shelving, depending on how a library has bound it.)  The trend toward shared/consortial storage may allow multiple institutions to share a single print copy.
    • If the item-specific metadata in your catalog don't include abstract number ranges -- as opposed to issue numbers, which are useless -- remote usage/retrieval of CA volumes becomes even less practical.
    • UT's copy is in remote storage because it is one of the last copies in Texas.
  • ACS does not require institutions to retain print CA for chemistry program approval. (There's no requirement for SciFinder either. See ACS Committee on Professional Training guidelines for more information.)

Further Reading

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