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                                                       EXHIBIT 10 (iii)A10

March 1, 1998


Patrick C. Mackey
11 Stony Point Road
Westport, Connecticut 06831


Dear Pat:

        The purpose of this letter agreement (the "Agreement") is to set forth
the terms of your employment with Witco Corporation (the "Company").

1.      Effective Date.

        The "Effective Date" of this Agreement shall be March 1, 1998.

2.      Term of Employment.

        The Term of Employment (the "Term") shall be the period of time between
the Effective Date and the date on which your employment with the Company is
terminated by you or by the Company (the "Termination Date").

3.      Position, Reporting, Responsibilities.

        (a) Position, Reporting. You will be employed as the Company's Group
Vice President, Polymer Chemicals (and in such other positions in the Company,
its subsidiaries or affiliates as may later be determined), and will have the
powers, responsibilities and authorities customarily associated with such
position. You will report to me, Dr. E. Gary Cook, Chairman of the Board, Chief
Executive Officer, and President, or to such other senior officer that I, in my
discretion, determine.

        (b) Responsibilities. During the Term, you agree to devote your working
time, on a full-time basis, to the performance of services for the Company and
its subsidiaries and affiliates, and to perform such services faithfully and to
the best of your ability. You further agree to abide by the terms of Witco's
Conflict of Interest Policy and Code of Business Conduct. Notwithstanding the
foregoing, nothing in this Agreement shall preclude you from: (i) serving on the
boards of directors of other companies, subject to my consent (or the consent of
my successor), (ii) engaging in charitable and community affairs, and (iii)
managing your own personal investments.

4.      Compensation.

        (a) Base Salary. Your base salary shall initially be established at
$340,000 per year and shall be payable in substantially equal installments in
accordance with the Company's payroll practices. Thereafter, your base salary is
subject to adjustment in accordance with the Company's compensation practices in
effect in the United States.

        (b) Bonus. Beginning in 1998, you will be eligible to participate in the
Witco Corporation Officers' Annual Incentive Plan ("OAIP") in accordance with
the terms of such Plan. Your "Target Percentage of Salary" (as defined in the
OAIP) will be 50%.











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        (c) One-Time Signing Bonus. The Company will provide you with a one-time
Signing Bonus in the amount of $50,000, which will be paid to you no later than
the Effective Date.

        (d) Equity-based Compensation. You will receive an option to purchase
25,000 shares of Witco Common Stock, par value $5, with an option price of
$44.1875. This option will become exercisable with respect to 50% of the grant
on December 2, 1998 and with respect to the remainder of the grant, the option
is exercisable on December 2, 1999. Vesting of your option will not accelerate
if your employment terminates for any reason (other than Change in Control, as
defined in the Stock Incentive Plan) before the option is exercisable as
described.

        From time to time the Organization and Compensation Committee of the
Company's Board of Directors may in its complete discretion cause you to
participate in other equity-based compensation programs.

        (e) Long Term Incentive Plan. You will be eligible to participate in the
Company's Long Term Incentive Plan ("LTIP") for the 1998-2000 cycle. This is a
rolling three year plan with Restricted Shares awarded at the end of a three
year period assuming specific Corporate performance goals are met. Full details
of this plan will be provided to you in a separate letter.

        (f) Shareholder Value Incentive Plan. Additionally, you will be eligible
to participate in the Company's Shareholder Value Incentive Plan and you will be
given 10,000 preferred shares under that plan, subject to approval of the
Organization and Compensation Committee of the Board of Directors.

5.      Employee Benefits and Perquisites.

        During the Term, the Company will provide you with the following
benefits and perquisites:

        (a) Medical, Dental, Life Insurance, Disability. The Company will
provide you with medical, dental, life insurance and disability coverage on the
same terms as provided to its other employees covered by U.S. benefit plans.

        (b) Supplemental Executive Retirement Plan. You will be designated a
participant in the Company's Supplemental Executive Retirement Plan ("SERP") and
will be eligible to retire and receive the retirement benefits described in the
SERP at or after age 62 (subject to approval of the Board of Directors). In the
event that you elect to retire at age 58 1/2, Witco shall pay to you the lump
sum of (pound)283,096, grossed up in respect of any income taxes payable, as
compensation for lost DuPont early retirement benefits.

        (c) Vacation. You will be eligible for five (5) weeks' paid vacation per
year, which vacation may be taken at such times as you elect, with due regard to
the needs of the Company. Additionally, you will receive two (2) paid floating
holidays and ten (10) paid Company holidays in accordance with Company policy.

        (d) 1997 DuPont Incentive Compensation. The Company shall pay to you the
difference, if any, between your anticipated 1997 DuPont Incentive Compensation
of $135,000, and the amount of 1997 Incentive Compensation you actually receive
from DuPont. Any such difference will be calculated so as to take account of any
differential between combined federal and state/local tax imposed in the United
States on the sum of $135,000, and any tax that would have been imposed on this
sum overseas had you not relocated to the United States. Any such difference
will be paid to you within fifteen (15) business days of Witco's receipt of
documentation regarding your actual 1997 DuPont Incentive Compensation.











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        (e) Severance. In the event the Company terminates your employment, you
will be eligible for the payments and benefits described in Section 6. Except as
otherwise provided in Section 6, and notwithstanding the terms of any plan or
program to the contrary, you will be ineligible for severance pay under any plan
or program sponsored by the Company from time to time.

        (f) Travel Documents. The Company will provide you with (and, where
applicable, assume related expenses in securing) all documents required for you
to work in the United States.

        (g)  Housing.

               (i)    Temporary Housing. Until the earlier of three (3) months
                      following the Effective Date, or the date on which you
                      relocate to long-term housing, the Company will reimburse
                      you for the reasonable cost of renting temporary,
                      furnished accommodations that are comparable to the
                      accommodations an executive officer would inhabit in the
                      United States.

               (ii)   Long-Term Housing. In the event that you purchase a home
                      in the Greenwich, Connecticut area during the Term, the
                      Company will: (i) provide you with an interest-free loan
                      of ten percent (10%) of the purchase price of the home,
                      which loan will be secured by your mortgage on the home;
                      and (ii) reimburse you in monthly installments during the
                      Term for housing expenses up to $49,600 per year (grossed
                      up in respect of any income taxes payable).

        (h) Company Car. The Company will provide you with a car for business
and personal use throughout the Term in accordance with the Company's U.S. Car
Policy. Additionally, with respect to the two cars you own overseas and are
intending to sell, the Company will reimburse you for any reasonable difference
between your actual sale price and the retail "book value" of these cars as of
the date of sale.

        (i) Relocation Expenses. The Company will reimburse you for the
reasonable cost of relocating household goods and personal effects from
Switzerland to the United States, and for the reasonable cost of relocating
household goods and personal effects from the United States to the location of
your choice upon the termination of your employment with the Company.

        (j) Tax Counseling and Preparation Services. In accordance with
applicable Company policy, the Company will arrange to have professional tax
advisors (A) provide you with tax counseling services and (B) prepare your
income tax returns in the United States and, if applicable, Switzerland. The
fees for said services will be grossed up in respect of any income taxes
payable.

        (k) Family Visits. The Company will reimburse you for the round trip
cost of business class travel for you and your spouse to Europe from the United
States twice per year. Additionally, the Company will reimburse you for the
round trip cost of business class travel for your son, Peter Mackey, to the
Greenwich, Connecticut area from the United Kingdom twice per year. The airfares
for these family visits will be grossed up in respect of any income taxes
payable.

        (l) Tuition Reimbursement. The Company will reimburse you for your son's
tuition at the University of Edinburgh from October 1997 to the earlier of (i)
June 2002, (ii) your son's graduation date; or (iii) your Termination Date.
Reimbursement will be paid on an annual basis within fifteen (15) days after the
Company receives proof of tuition payment. Your son's tuition will be grossed up
in respect of any income taxes payable.











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6.      Termination of Employment.

        (a) Termination of Employment. At any time on or after the Effective
Date, the Company shall have the right to terminate your employment, and you
shall have the right to resign your employment with the Company for any reason
or no stated reason.

        (b)  Termination without "Cause".

               (i)    If your employment is terminated by the Company without
                      Cause, you will be eligible to receive the following,
                      provided you execute a Release in the form attached hereto
                      as Exhibit A upon the termination of your employment:

                      (A)    continuation of salary payments for two (2) years
                             after the Termination Date, as if your employment
                             had not terminated;

                      (B)    relocation expenses as described in Section 5(i) of
                             this Agreement.

                      (C)    payment for any vacation days not taken in the year
                             employment is terminated.

               The Company may, in its discretion, choose to accelerate all or a
               portion of the cash payments to be made pursuant to this Section
               and pay you such amount in one lump sum.

               (ii)   For purposes of this Agreement, "Cause" shall mean (A)
                      your gross misconduct in the performance of your duties
                      with the Company, (B) your engaging in illegal conduct
                      (other than any misdemeanor, traffic violation or similar
                      misconduct) in connection with your performance of duties
                      for the Company, or (C) your commission of a felony. The
                      determination as to whether "Cause" exists will be made by
                      me, Dr. E. Gary Cook (or such other individual who may
                      become your immediate supervisor). In the event that you
                      are terminated for cause, you will be eligible to receive
                      only those items specifically described in Section
                      6(b)(i)(B) and (C).

7.      Confidentiality.

        (a) Disclosure or Use of Confidential Information. During your
employment and thereafter, you agree that you will not without the Company's
consent, disclose or use for the benefit of any person other than the Company
any Confidential Information. For this purpose, "Confidential Information" shall
mean information relating to the products, services, business, personnel or
commercial activities of the Company (and its subsidiaries, affiliates, and
partners), which information is not generally known to the public and which
either derives economic value (actual or potential) from not being generally
known or has a character such that the Company has a legitimate interest in
maintaining its secrecy. The term, "Confidential Information" shall include but
not be restricted to, formulas, compilations, programs, devices, concepts,
inventions (regardless of whether patentable), designs, methods, techniques,
customer lists, pricing information, marketing and commercial strategies and
future plans therefor, processes, data concepts, know-how, and unique
combinations of separate items which individually may or may not be
confidential. Information contained in documents may be considered Confidential
Information regardless of whether the documents are marked with any proprietary
notice or legend.

        (b) Procedure Upon Termination of Employment. Upon leaving the Company's
employ, you agree you will not, without the Company's consent, take with you any
Confidential Information including, without limitation, any (i) books, drawings,
blueprints, specifications, memoranda, or documents or anything detailing











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any formulae or secret processes, (ii) sales lists, price books, customer data,
customer lists, or any documents detailing the foregoing.

        (c) Remedies. You hereby acknowledge that money damages for any breach
or threatened breach of Section 7 of this Agreement would be inadequate and
therefore agree that the Company may be entitled to injunctive relief, in rights
and remedies available; provided, however, that nothing contained in this
Section shall be construed as prohibiting the Company from pursuing any other
remedies available for any such breach or threatened breach.

8.      Governing Law; Severability.

        You agree that this Agreement shall be construed and interpreted in
accordance with the laws of the State of Connecticut and the United States of
America (without regard to any conflict of laws provisions). In the event it is
determined that any provision of this Agreement is invalid or unenforceable
under applicable law, you agree that this Agreement shall be deemed modified so
as to be enforceable in accordance with its scope and intent.

9.      Arbitration; Jurisdiction.

        In the event of any dispute or controversy arising under or in
connection with this Agreement you agree that the exclusive method for settling
this dispute shall be by arbitration, conducted before an arbitrator in the
State of Connecticut in accordance with the rules and procedures of
J*A*M*S/Endispute. You further agree that judgment may be entered on the
arbitrator's award in any court in the State of Connecticut and hereby consent
to the jurisdiction of the Connecticut courts for purposes of enforcing any such
award.

10.     Entire Agreement.

        This Agreement represents the entire agreement between you and the
Company regarding your employment with the Company.

        Please indicate your acceptance of the terms of this Agreement by
signing below and returning it to the Company.


                                     Very truly yours,


                                     /s/ E. Gary Cook

                                     E. Gary Cook
                                     Chairman of the Board,
                                     President and Chief Executive Officer

AGREED TO AND ACCEPTED BY:

PATRICK C. MACKEY



Signature:     /s/ Patrick C. Mackey
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Dated:         March 23, 1998




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