For a limited number of substances the same CAS-number applies to the pure substance and to the substance in an aqueous solution. The European Union has than two Index-numbers assigned to the same CAS-number. Other substances are available in different physical forms (large or small particles, for example), or with or without a “mixing component”. Also in these cases two Index-number ate assigned to the same CAS-numbers.
IN DOHSBase Compare the CAS-number is our unique key. To avoid problems with the uniqueness of the CAS-number we have chosen fore these situations to change the last digit of the CAS-number (a checksum) to the %-sign for the aqueous solutions, and the letter i for the substances with two physical states.
F.i.: the CAS-number for “Hydrogen chloride” is 7647-01-0 (with Index-number 017-002-00-2), and for “Hydrochloric acid … %” the CAS-number 7647-01-% was assigned by us (with Index-number 017-002-01-X).
OELV’s and measurement methods are only associated with the “original” CAS-number, without % or i in the checksum.
This list shows all substances with and % or i as the checksum in the CAS-number.