================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 14A
                                 (RULE 14A-101)

                            SCHEDULE 14A INFORMATION

PROXY STATEMENT PURSUANT TO SECTION 14(A) OF THE SECURITIES EXCHANGE ACT OF 1934

FILED BY THE REGISTRANT  [ ]

FILED BY A PARTY OTHER THAN THE REGISTRANT  [X]

CHECK THE APPROPRIATE BOX:

[ ]   PRELIMINARY PROXY STATEMENT
[ ]   DEFINITIVE PROXY STATEMENT            [ ]  CONFIDENTIAL, FOR USE OF THE
[X]   DEFINITIVE ADDITIONAL MATERIALS            COMMISSION ONLY (AS PERMITTED)
[ ]   SOLICITING MATERIAL PURSUANT TO            BY RULE 14A-6(E)(2)
      RULE 14A-12

                             HERCULES INCORPORATED
--------------------------------------------------------------------------------
                (NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)


                      INTERNATIONAL SPECIALTY PRODUCTS INC.
--------------------------------------------------------------------------------
    (NAME OF PERSON(S) FILING PROXY STATEMENT, IF OTHER THAN THE REGISTRANT)



PAYMENT OF FILING FEE (CHECK THE APPROPRIATE BOX):

[X]  NO FEE REQUIRED.

[ ] FEE COMPUTED ON TABLE BELOW PER EXCHANGE ACT RULES 14A-6(I)(4) AND 0-11.

      (1)   TITLE OF EACH CLASS OF SECURITIES TO WHICH TRANSACTION APPLIES:
            NOT APPLICABLE

      --------------------------------------------------------------------------
      (2)   AGGREGATE NUMBER OF SECURITIES TO WHICH TRANSACTION APPLIES:  NOT
            APPLICABLE.

      --------------------------------------------------------------------------
      (3)   PER UNIT PRICE OR OTHER UNDERLYING VALUE OF TRANSACTION
            COMPUTED PURSUANT TO EXCHANGE ACT RULE 0-11 (SET FORTH THE
            AMOUNT ON WHICH THE FILING FEE IS CALCULATED AND STATE HOW
            IT WAS DETERMINED): NOT APPLICABLE.

      --------------------------------------------------------------------------



      (4)   PROPOSED MAXIMUM AGGREGATE VALUE OF TRANSACTION:  NOT APPLICABLE.

      --------------------------------------------------------------------------
      (5)   TOTAL FEE PAID:  NOT APPLICABLE.

      --------------------------------------------------------------------------

[ ]  FEE PAID PREVIOUSLY WITH PRELIMINARY MATERIALS:

[ ]  CHECK BOX IF ANY PART OF THE FEE IS OFFSET AS PROVIDED BY EXCHANGE
     ACT RULE 0-11(A)(2) AND IDENTIFY THE FILING FOR WHICH THE OFFSETTING
     FEE WAS PAID PREVIOUSLY. IDENTIFY THE PREVIOUS FILING BY REGISTRATION
     STATEMENT NUMBER, OR THE FORM OR SCHEDULE AND THE DATE OF ITS FILING.

      (1)       AMOUNT PREVIOUSLY PAID:  NOT APPLICABLE.

      --------------------------------------------------------------------------
      (2)       FORM, SCHEDULE OR REGISTRATION STATEMENT NO.:  NOT APPLICABLE.

      --------------------------------------------------------------------------
      (3)       FILING PARTY:  NOT APPLICABLE.

      --------------------------------------------------------------------------
      (4)       DATE FILED:  NOT APPLICABLE.

      --------------------------------------------------------------------------






                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 13D
                    Under the Securities Exchange Act of 1934

                                (Amendment No. 9)

                         ------------------------------

                              HERCULES INCORPORATED
                                (Name of Issuer)

COMMON STOCK, $25/48 STATED VALUE PER SHARE                      427056106
       (Title of class of securities)                          (CUSIP number)

                            RICHARD A. WEINBERG, ESQ.
                        C/O ISP MANAGEMENT COMPANY, INC.
                                 1361 ALPS ROAD
                             WAYNE, NEW JERSEY 07470
                                 (973) 628-4000
            (Name, address and telephone number of person authorized
                     to receive notices and communications)

                                 WITH A COPY TO:

                             STEPHEN E. JACOBS, ESQ.
                           WEIL, GOTSHAL & MANGES LLP
                                767 FIFTH AVENUE
                          NEW YORK, NEW YORK 10153-0119
                                 (212) 310-8000

                                  APRIL 3, 2001
             (Date of event which requires filing of this statement)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition that is the subject of this Schedule 13D, and is filing this
schedule because of ss.ss. 240.13d-1(e), 240.13d-1(f) or 240.13d-(g), check the
following box. [ ]

Note: Schedules filed in paper format shall include a signed original and five
copies of the schedule, including all exhibits. Seess. 240.13d-7 for other
parties to whom copies are to be sent.

* The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purposes of Section 18 of the Securities Exchange Act of
1934 (the "Act") or otherwise subject to the liabilities of that section of the
Act but shall be subject to all other provisions of the Act. (However, see the
Notes.)

                         (Continued on following pages)

                               (Page 1 of 7 Pages)


================================================================================


NY2:\1031597\01\M3ZH01!.DOC\54104.0018




-----------------------------------------------------------              --------------------------------------------------------
                                                                                                         
CUSIP No. 427056106                                             13D                                            Page 2 of 7 Pages
-----------------------------------------------------------              --------------------------------------------------------

----------------------    -------------------------------------------------------------------------------------------------------
          1               NAME OF REPORTING PERSON                                ISP OPCO HOLDINGS INC.
                          S.S. OR I.R.S. IDENTIFICATION NO.
                          OF ABOVE PERSON
----------------------    -------------------------------------------------------------------------------------------------------
          2               CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                    (a) [ ]
                                                                                                               (b) [X]
----------------------    -------------------------------------------------------------------------------------------------------
          3               SEC USE ONLY
----------------------    -------------------------------------------------------------------------------------------------------
          4               SOURCE OF FUNDS:                                                  OO
----------------------    -------------------------------------------------------------------------------------------------------
          5               CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
                          PURSUANT TO ITEM 2(d) OR 2(e):                                                            [ ]
----------------------    -------------------------------------------------------------------------------------------------------
          6               CITIZENSHIP OR PLACE OF ORGANIZATION:                                               Delaware
----------------------    -------------------------------------------------------------------------------------------------------
                                  7               SOLE VOTING POWER:                                                 0
      NUMBER OF
        SHARES
                          -------------------     -------------------------------------------------------------------------------
     BENEFICIALLY                 8               SHARED VOTING POWER:                                       10,719,200
       OWNED BY

         EACH             -------------------     -------------------------------------------------------------------------------
      REPORTING                   9               SOLE DISPOSITIVE POWER:                                             0

     PERSON WITH
                          -------------------     -------------------------------------------------------------------------------
                                  10              SHARED DISPOSITIVE POWER:                                  10,719,200


----------------------    -------------------------------------------------------------------------------------------------------
         11               AGGREGATE AMOUNT BENEFICIALLY OWNED BY REPORTING PERSON:                           10,719,200
----------------------    -------------------------------------------------------------------------------------------------------
         12               CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                         [ ]
----------------------    -------------------------------------------------------------------------------------------------------
         13               PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):                                           9.91%
----------------------    -------------------------------------------------------------------------------------------------------
         14               TYPE OF REPORTING PERSON:                               CO
----------------------    -------------------------------------------------------------------------------------------------------




-----------------------------------------------------------              --------------------------------------------------------
CUSIP No. 427056106                                             13D                                            Page 3 of 7 Pages
-----------------------------------------------------------              --------------------------------------------------------

----------------------    -------------------------------------------------------------------------------------------------------
          1               NAME OF REPORTING PERSON                                ISP INVESTMENTS INC.
                          S.S. OR I.R.S. IDENTIFICATION NO.
                          OF ABOVE PERSON
----------------------    -------------------------------------------------------------------------------------------------------
          2               CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                    (a) [ ]
                                                                                                               (b) [X]
----------------------    -------------------------------------------------------------------------------------------------------
          3               SEC USE ONLY
----------------------    -------------------------------------------------------------------------------------------------------
          4               SOURCE OF FUNDS:                                                  WC, OO
----------------------    -------------------------------------------------------------------------------------------------------
          5               CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
                          PURSUANT TO ITEM 2(d) OR 2(e):                                                           [ ]
----------------------    -------------------------------------------------------------------------------------------------------
          6               CITIZENSHIP OR PLACE OF ORGANIZATION:                                              Delaware
----------------------    -------------------------------------------------------------------------------------------------------
                                  7               SOLE VOTING POWER:                                         10,719,200
      NUMBER OF
        SHARES
                          -------------------     -------------------------------------------------------------------------------
     BENEFICIALLY                 8               SHARED VOTING POWER:                                                0
       OWNED BY

         EACH             -------------------     -------------------------------------------------------------------------------
      REPORTING                   9               SOLE DISPOSITIVE POWER:                                    10,719,200

     PERSON WITH
                          -------------------     -------------------------------------------------------------------------------
                                  10              SHARED DISPOSITIVE POWER:                                           0


----------------------    -------------------------------------------------------------------------------------------------------
         11               AGGREGATE AMOUNT BENEFICIALLY OWNED BY REPORTING PERSON:                           10,719,200
----------------------    -------------------------------------------------------------------------------------------------------
         12               CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                         [ ]
----------------------    -------------------------------------------------------------------------------------------------------
         13               PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):                                           9.91%
----------------------    -------------------------------------------------------------------------------------------------------
         14               TYPE OF REPORTING PERSON:                               CO
----------------------    -------------------------------------------------------------------------------------------------------




-----------------------------------------------------------              --------------------------------------------------------
CUSIP No. 427056106                                             13D                                            Page 4 of 7 Pages
-----------------------------------------------------------              --------------------------------------------------------

----------------------    -------------------------------------------------------------------------------------------------------
          1               NAME OF REPORTING PERSON                                INTERNATIONAL SPECIALTY PRODUCTS INC.
                          S.S. OR I.R.S. IDENTIFICATION NO.
                          OF ABOVE PERSON
----------------------    -------------------------------------------------------------------------------------------------------
          2               CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                    (a) [ ]
                                                                                                               (b) [X]
----------------------    -------------------------------------------------------------------------------------------------------
          3               SEC USE ONLY
----------------------    -------------------------------------------------------------------------------------------------------
          4               SOURCE OF FUNDS:                                                  OO
----------------------    -------------------------------------------------------------------------------------------------------
          5               CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
                          PURSUANT TO ITEM 2(d) OR 2(e):                                                           [ ]
----------------------    -------------------------------------------------------------------------------------------------------
          6               CITIZENSHIP OR PLACE OF ORGANIZATION:                                              Delaware
----------------------    -------------------------------------------------------------------------------------------------------
                                  7               SOLE VOTING POWER:                                                  0
      NUMBER OF
        SHARES
                          -------------------     -------------------------------------------------------------------------------
     BENEFICIALLY                 8               SHARED VOTING POWER:                                       10,719,200
       OWNED BY

         EACH             -------------------     -------------------------------------------------------------------------------
      REPORTING                   9               SOLE DISPOSITIVE POWER:                                             0

     PERSON WITH
                          -------------------     -------------------------------------------------------------------------------
                                  10              SHARED DISPOSITIVE POWER:                                  10,719,200


----------------------    -------------------------------------------------------------------------------------------------------
         11               AGGREGATE AMOUNT BENEFICIALLY OWNED BY REPORTING PERSON:                           10,719,200
----------------------    -------------------------------------------------------------------------------------------------------
         12               CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                         [ ]
----------------------    -------------------------------------------------------------------------------------------------------
         13               PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):                                           9.91%
----------------------    -------------------------------------------------------------------------------------------------------
         14               TYPE OF REPORTING PERSON:                               CO
----------------------    -------------------------------------------------------------------------------------------------------





                  This Amendment No. 9 ("Amendment No. 9") amends the statement
of beneficial ownership on Schedule 13D ("Schedule 13D") filed on July 24, 2000,
as amended by Amendment No. 1 filed on October 11, 2000, Amendment No. 2 filed
on January 23, 2001, Amendment No. 3 filed on February 7, 2001, Amendment No. 4
filed on February 20, 2001, Amendment No. 5 filed on February 28, 2001,
Amendment No. 6 filed on March 7, 2001, Amendment No. 7 filed on March 9, 2001,
and Amendment No. 8 filed on March 12, 2001, by and on behalf of ISP Opco
Holdings Inc. ("ISP Opco"), ISP Investments Inc. ("ISP Investments"), and
International Specialty Products Inc. ("ISP" and together with ISP Investments
and ISP Opco, the "Reporting Persons") with respect to their ownership of common
stock, stated value $25/48 per share ("Common Stock"), of Hercules Incorporated
(the "Company"). Capitalized terms used herein and not defined herein have the
meanings ascribed thereto in the Schedule 13D, as previously amended.

ITEM 4. PURPOSE OF TRANSACTION

                  On April 3, 2001, Samuel J. Heyman, Chairman of the Board of
ISP, sent the following letter to Mr. Thomas Gossage, Chairman, CEO and
President of the Company:

Mr. Thomas Gossage
Chairman, CEO and President
Hercules Incorporated
Hercules Plaza
1313 North Market Street
Wilmington, Delaware 19894-0001

Dear Tom:

                  I note from the Board's announcement yesterday that Hercules
has not only postponed the Annual Meeting to May 24th but made no commitment not
to attempt a further delay.

                  The action Hercules took yesterday, we believe, is a
disservice to Hercules stockholders. In addition, I would remind you that we had
suggested several weeks ago a short continuance if you really needed it in
connection with the Company's "sale process", Hercules instead insisted on going
forward with the April 26th date, your people gave us no heads-up as to the
postponement, and this has caused everyone a lot of needless effort and expense.

                  Putting that all aside, we would request the commitment of the
Hercules Board not to seek any further delays. I believe this is in the
interests of all concerned, and I would appreciate your prompt response.

                                   Sincerely,

                                   /s/ Samuel J. Heyman


ITEM 5. INTEREST IN SECURITIES OF THE ISSUER

                  As of the filing of this Amendment No. 9, the Reporting
Persons beneficially owned (or are deemed, solely for purposes of Rule 13d-3, to
beneficially own), directly or indirectly, an aggregate of 10,719,200 Shares,
representing approximately 9.91% of the Common Stock outstanding on April 4,
2001 (based on 108,115,824 shares of Common Stock outstanding as of March 6,
2001, as set forth in the Company's Preliminary Proxy Statement on Schedule 14A
dated April 4, 2001). ISP Investments has direct beneficial ownership of all of
such Shares.



                                       5


                  ISP Investments has the sole power to vote, direct the voting
of, dispose of and direct the disposition of the Shares. ISP Opco, by virtue of
its ownership of all of the outstanding capital stock of ISP Investments, may be
deemed to own beneficially (solely for purposes of Rule 13d-3) the Shares. ISP,
by virtue of its ownership of all of the outstanding common stock of ISP Opco,
may be deemed to own beneficially (solely for purposes of Rule 13d-3) the
Shares. Mr. Heyman, by virtue of his beneficial ownership (as defined in Rule
13d-3) of approximately 79% of the capital stock of ISP, may be deemed to own
beneficially (solely for purposes of Rule 13d-3) the Shares.


             [The remainder of this page intentionally left blank.]















                                       6


                                   SIGNATURES

                  After reasonable inquiry and to the best of their knowledge
and belief, the undersigned certify that the information set forth in this
Statement is true, complete and correct.

Dated: April 4, 2001

                            ISP OPCO HOLDINGS INC.
                            ISP INVESTMENTS INC.
                            INTERNATIONAL SPECIALTY PRODUCTS INC.


                            By:    /s/ Susan B. Yoss
                                   --------------------------------------------
                                   Susan B. Yoss
                                   Executive Vice President and Treasurer














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