EXHIBIT 3.13

                          CERTIFICATE OF INCORPORATION
                                       OF
                                  AUXITROL CO.

                  1.       The name of the corporation is:

                                  AUXITROL CO.

                  2.       The address of its registered office in the State of
Delaware is Corporation Trust Center, 1209 Orange Street, Wilmington, DE 19801,
County of New Castle. The name of its registered agent at such address is The
Corporation Trust Company.

                  3.       The nature of the business or purposes to be
conducted or promoted is to engage in any lawful act or activity for which
corporations may be organized under the General Corporation Law of Delaware.

                  4.       The total number of shares of stock which the
corporation shall have authority to issue is One Thousand (1,000) and the par
value of such shares is One Dollar ($1.00) amounting in the aggregate to One
Thousand Dollars ($1,000).

                  5.       The board of directors is authorized to make, alter
or repeal the bylaws of the corporation. Election of directors need not be by
ballot.

                  6.       The name and mailing address of the incorporator is:

                           Scott D. Benner
                           Two Union Square
                           601 Union Street
                           Seattle, WA 98101-2346.

                  I, THE UNDERSIGNED, being the incorporator hereinbefore named,
for the purpose of forming a corporation pursuant to the General Corporation Law
of Delaware, do make this certificate, hereby declaring and certifying that this
is my act and deed and that the facts herein stated are true, and accordingly
have hereunto set my hand this 26th day of February, 1992.

                                                       /s/ SCOTT D. BENNER
                                                --------------------------------
                                                Scott D. Benner, Incorporator