EXHIBIT 10.15


             ARCH SUPPLEMENTAL CONTRIBUTING EMPLOYEE OWNERSHIP PLAN
                           Effective February 8, 1999
            As Amended by a First Amendment Dated July 29, 1999 and a
                    Second Amendment dated January 27, 2000

      Arch Chemicals, Inc. ("Arch") hereby establishes a Supplemental
Contributing Employee Ownership Plan (the "Plan" or "SCEOP"), effective February
8, 1999 or, if later, the effective date of the spin-off of Arch from Olin
Corporation (the "Effective Date"). The Plan is intended to be an unfunded,
nonqualified deferred compensation plan for certain management and highly
compensated employees, as described in Section 201(2) and 301(a)(3) of the
Employee Retirement Income Security Act ("ERISA").

      Arch is a participating employer in the multiple employer plan known as
the Olin Corporation Contributing Employee Ownership Plan (as from time to time
amended, the "CEOP"). The purpose of this Plan is to permit certain executive
employees of Arch, whose contributions to the CEOP are limited under Sections
401(a)(17) of the Internal Revenue Code of 1986 and the regulations promulgated
thereunder (the "Code"), with certain supplemental benefits to make up for such
Code-imposed limitations.

                                    ARTICLE I
                       DEFINITIONS AND GENERAL PROVISIONS

      1.1   Except as otherwise provided herein, the terms defined in the CEOP
are used herein with the meanings ascribed to them in the CEOP. In addition,
when used herein, the following definitions shall apply:

            (a)   "Arch Phantom Units" means phantom units of the CEOP's Arch
      Common Stock Fund credited under the SCEOP, such units deemed to consist
      of both Arch Common Stock and cash.

            (b)   "CEOP Percentage" means, with respect to a SCEOP Participant,
      the annual percentage by which such Participant reduces his Maximum
      Eligible Compensation on either a before-tax or after-tax basis in
      calculating Contributions made to the CEOP; provided, however, that, if a
      Participant's CEOP percentage exceeds six percent (6%), the Participant
      may elect, for purposes of this Plan, to limit the CEOP percentage used
      under this Plan to six percent (6%).

            (c)   "Company" or "Arch" means Arch Chemicals, Inc. and its
      affiliated companies.

            (d)   "Compensation" has the same meaning as under the CEOP, except
      that it is not subject to the maximum dollar limitation on compensation
      taken into account for purposes of the CEOP under Section 401(a)(17) of
      the Code.
<PAGE>


            (e)   "Distribution Date" has the same meaning as that specified in
      the Distribution Agreement by and between Olin Corporation and Arch
      Chemicals, Inc.

            (f)   "Dividend Equivalents" means (i) with respect to the Arch
      Phantom Units held in a SCEOP Account of an Arch Participant, the dollar
      amount of regular or special dividends actually paid in cash from time to
      time on the actual number of shares of Arch Common Stock reflected in such
      Arch Phantom Units; (ii) with respect to the Olin Phantom Units held in a
      SCEOP Account of an Arch Participant, the dollar amount of regular or
      special dividends actually paid in cash from time to time on the actual
      number of shares of Olin Common Stock reflected in such Olin Phantom
      Units; and (iii) with respect to Primex Phantom Units held in a SCEOP
      Account of an Arch Participant, the dollar amount of regular or special
      dividends actually paid in cash from time to time on the actual number of
      shares of Primex Technologies, Inc. Common Stock ("Primex Common Stock")
      reflected in such Primex Phantom Units. Any Dividend Equivalents shall be
      deemed reinvested solely in Arch Phantom Units.

            (g)   "Excess Company Matching Contribution" means, with respect to
      a SCEOP Participant for a Plan Year, an amount derived by multiplying (i)
      the percentage used in calculating the Company Matching Contribution (in
      excess of $25 per month) (as of the date hereof, 50%) under the CEOP, as
      such percentage changes from time to time, by (ii) the annual SCEOP
      Participant Contribution for that Participant; provided that, if the
      participant's CEOP Percentage exceeds six percent (6%), the SCEOP
      Participant Contribution will be calculated using six percent (6%) for the
      CEOP Percentage when calculating the Excess Company Matching Contribution.

            (h)   "Excess Performance Contribution" means with respect to a
      SCEOP Participant for a Plan Year, the amount derived by multiplying (i)
      the percentage used in calculating the Performance Matching Contribution
      under the formula contained in the CEOP that is applicable to an Arch
      Participant for that year, if any, by (ii) the SCEOP Participant
      Contribution of that Participant for such year; provided that if such
      Participant's CEOP Percentage exceeds six percent (6%), the SCEOP
      Participant Contribution will be calculated using six percent (6%) for the
      CEOP Percentage when calculating the Excess Performance Contribution.

            (i)   "Maximum Eligible Compensation" means the maximum amount of
      Compensation under Section 401(a)(17) of the Code from which a Participant
      is permitted to make Contributions to the CEOP, as such maximum amount is
      adjusted from time to time under the Code.

            (j)   "Olin Phantom Units" means phantom units of the CEOP's Olin
      Common Stock Fund credited under the SCEOP, such units deemed to consist
      of both Olin Stock and cash.

            (k)   "Plan Year" means a twelve-month period ending on December 31.


                                       2
<PAGE>


            (l)   "Primex Phantom Units" means phantom units of the CEOP's
      Primex Stock Fund credited under the SCEOP, such units deemed to consist
      of both Primex Stock and cash.

            (m)   "SCEOP Participant" or "Arch Participant" means an Arch
      employee whose contributions to the CEOP are limited as a result of the
      imposition of the limitations set forth in the Sections 401(a)(17) of the
      Code and who has filed an election to participate in the SCEOP with the
      Committee.

            (n)   "SCEOP Account" for a SCEOP Participant means the Account
      established under the SCEOP for such Participant holding Arch Phantom
      Units, Olin Phantom Units and/or Primex Phantom Units, and/or any other
      phantom securities or units created herein.

            (o)   "SCEOP Participant Contribution" with respect to a SCEOP
      Participant shall mean the annual amount by which the SCEOP Participant
      has elected to reduce his Compensation under this Plan, such amount being
      equal to the CEOP Percentage multiplied by the difference between (i) such
      Participant's Compensation and (ii) his Maximum Eligible Compensation.

                                   ARTICLE II
                          ELIGIBILITY AND PARTICIPATION

      2.1   Any employee of the Company who

            (a)   is a management employee;

            (b)   is a "highly compensated employee" within the meaning of Code
      Section 414(q);

            (c)   is participating in the CEOP; and

            (d)   whose Compensation or rate of pay is in excess of the
      limitation contained in Section 401(a)(17) of the Code

shall be eligible to participate in this Plan (an "Eligible Employee").

      2.2   Each Eligible Employee who was enrolled in the Olin Supplemental
Contributing Employee Ownership Plan ("Olin SCEOP") as of the Distribution Date
shall automatically become a Participant in this Plan as of its Effective Date,
and the salary reduction agreement in effect as of such date shall be carried
over and be effective with respect to this Plan for the remainder of the
calendar year. Each other Eligible Employee wishing to participate in this Plan
must execute and file a salary reduction agreement in a form acceptable to the
Plan Administrator. Initially, such agreement to reduce Compensation shall be
filed within thirty (30) days following such individual becoming an Eligible
Employee. An Eligible Employee not filing such an agreement within the thirty
(30) day period referred to in the preceding sentence


                                       3
<PAGE>


must thereafter file such agreement to reduce Compensation by December 1 of the
calendar year prior to the beginning of the Plan Year for which it will be
effective and prior to the calendar year in which such Compensation would
otherwise be earned. Once filed, agreements to reduce Compensation shall remain
in effect for subsequent Plan Years unless revoked by the Participant in writing
in a form acceptable to the Plan Administrator.

      2.3   Any election to reduce salary shall be irrevocable for the Plan Year
to which it relates, provided, however, that during a Plan Year a Participant
may elect to cease all salary reductions for the remainder of the Plan Year, in
which case, no subsequent election shall be effective until the beginning of the
next Plan Year.

      2.4   No salary reduction election shall be given effect under this Plan
until the Participant has contributed to the CEOP the maximum amount permitted
by the CEOP and by applicable law for the Plan Year to which such salary
reduction election relates.

                                   ARTICLE III
                           CONTRIBUTIONS AND ACCOUNTS

      3.1   Each Eligible Employee who, immediately prior to the Distribution
Date, was a participant in the Olin SCEOP shall be credited with an opening
Account Balance under this Plan equal to the same number of Arch Phantom Units,
Olin Phantom Units and Primex Phantom Units (if any) as were credited to his
account under the terms of the Olin SCEOP as of the Distribution Date. Any
Eligible Employee whose employment is transferred to Arch after its spin-off
from Olin, but before February 8, 2000, shall have his or her Olin SCEOP account
balances transferred to this Plan and his or her opening Account Balance shall
be determined based upon the number of Olin Phantom Units, Primex Phantom Units,
and Arch Phantom Units credited to his Olin SCEOP account as of the date he
becomes employed by Arch. No additional Olin Phantom Units or Primex Phantom
Units may be acquired under this Plan, whether through the crediting of Dividend
Equivalents, through contributions to the Plan, or through deemed transfers of
sub-accounts under the Plan. Notwithstanding this Section 3.1, no Eligible
Employee who, immediately prior to his employment by Arch, had an account
balance in the Olin SCEOP shall be credited with an initial Account Balance
under this Plan attributable to his participation in the Olin SCEOP until such
employee has released Olin Corporation and its affiliates, and the Olin SCEOP,
from any liability, or claim for benefits, with respect to the employee's
participation in the Olin SCEOP.

      3.2   In conjunction with establishing this Plan, Arch hereby assumes the
liabilities of Olin for the provision of benefits to participants who,
immediately prior to the Distribution Date, were participants in the Olin SCEOP
and who, as of the Effective Date, transfer to, and become employed by Arch or
its affiliated companies ("Arch Employees"). In consideration of such assumption
of liability, Olin has transferred, as of the Effective Date, to Arch (or to a
rabbi trust established by Arch) the reserves (including any associated assets
held in a rabbi trust or similar vehicle) reflecting the value of the accrued
liabilities being transferred, determined in accordance with Olin's established
policies and accounting methods, uniformly applied for calculating liabilities
under its non-qualified plans.


                                       4
<PAGE>


      3.3   Each SCEOP Participant who so elects for a Plan Year shall defer
SCEOP Participant Contributions on a pre-tax basis. For each SCEOP Participant,
a SCEOP Account will be established. The Account will contain sub-accounts for
each type of contribution credited to the SCEOP Account and for each type of
Phantom Unit credited to his Account. For each Plan Year during which a person
is a SCEOP Participant and making deferrals, the Company (or other Participating
Employer) will credit to the SCEOP Account of each SCEOP Participant the number
of Arch Phantom Units equal in value to the sum of (1) the SCEOP Participant
Contribution, plus (2) the Excess Company Matching Contribution, plus (3) the
Excess Performance Contribution, if any. Such crediting shall occur periodically
in accordance with the timing of contributions to the CEOP, in the case of the
SCEOP Participant Contributions and Excess Company Matching Contributions, and
as soon as administratively feasible following the making of a Performance
Matching Contribution under the CEOP, in the case of an Excess Performance
Contribution.

      3.4   A Participant's SCEOP Account will also be credited with Dividend
Equivalents from time to time, solely in the form of additional Arch Phantom
Units, when such dividends are paid (i) on the actual number of shares of Arch
Common Stock reflected in the Arch Phantom Units held in such Account, (ii) on
the actual number of shares of Olin Common Stock reflected in the Olin Phantom
Units held in such Account and (iii) on the actual number of shares of Primex
Common Stock reflected in Primex Phantom Units held in such Account.

      3.5   For purposes of calculating the number of Arch Phantom Units to be
credited to an Arch Participant's SCEOP Account as a result crediting Dividend
Equivalents or contributions, the SCEOP shall use the Current Market Value for
valuing units in the Arch Common Stock Fund as defined under the CEOP. Phantom
Units will be credited in fractional amounts up to three decimal places. For
purposes of valuing Olin Phantom Units and Primex Phantom Units under this Plan,
the SCEOP shall use the Current Market Value for valuing units in Olin Common
Stock Fund and Primex Common Stock Fund, respectively, as defined in the CEOP.

      3.6   SCEOP Participants may either retain their Olin and/or Primex
Phantom Units or may have their entire Olin and/or Primex Phantom Unit Account
Balance(s) deemed transferred at the then Current Market Value and reinvested in
Arch Phantom Units at the then Current Market Value. Once Olin and/or Primex
Phantom Units are deemed transferred and reinvested, a Participant may not
re-direct investment back into Olin Phantom Units or Primex Phantom Units. No
new investment, whether in the form of Company or Participant contributions or
Dividend Equivalents, shall be permitted in Olin Phantom Units or Primex Phantom
Units.

      3.7   A Participant shall at all times be fully vested in his SCEOP
Participant Contribution Account Balance, and shall vest in his Excess Company
Matching and Excess Performance Contribution Account Balances in accordance with
the vesting schedule contained in the CEOP. Each Participant shall be deemed
vested in his SCEOP Account Balance to the same extent that he is actually
vested in his CEOP Account Balance. For purposes of determining an Arch
Participant's vested percentage under this SCEOP, such Participant's past
service with Olin shall be recognized to the same extent as if such service had
been rendered with Arch. A Participant shall be fully vested in his SCEOP
Account Balance upon his death,


                                       5
<PAGE>


upon his termination of service from the Company and all affiliates after
reaching a retirement date under the CEOP, or upon his termination of service
due to his Permanent Disability as defined in the CEOP.

      3.8   In the event that the Compensation Committee of the Board ("the
Committee") determines that any dividend or other distribution,
recapitalization, stock split, reverse stock split, reorganization, merger,
consolidation, split-up, spin-off, combination, repurchase or exchange of Arch
Common Stock, Olin Common Stock, Primex Common Stock, or any other securities of
Arch, Olin or Primex, issuance of warrants or other rights to purchase Arch,
Common Stock, Olin Common Stock, Primex Common Stock or other securities of
these companies, or other similar corporate transaction or event occurs that
affects Arch, Olin or Primex Common Stock such that the Committee determines an
adjustment in Phantom Units under the Plan is appropriate in order to prevent
dilution or enlargement of the benefits intended to be made available under this
Plan, then the Committee shall, in such manner as it deems equitable, adjust
Participants' SCEOP Accounts. In the case of a spin-off, split-up, issuance of
an extraordinary stock dividend, or similar transaction, such adjustment, in the
Committee's discretion, may result in creation of phantom shares in a separate
phantom stock fund, reinvestment of such phantom shares in Arch Phantom Units,
and the like. Notwithstanding the foregoing, a Participant to whom Dividend
Equivalents have been allocated shall not be entitled to receive a non-cash
special or extraordinary dividend or distribution unless the Committee expressly
authorizes such receipt.

      3.9   TRANSFERS BETWEEN ARCH AND OLIN. It is contemplated that Plan
Participants may transfer their employment after the Distribution Date and on or
before February 8, 2000 from Arch to Olin and VICE VERSA and commence, or
resume, participation in the SCEOP of the new employer.

      (a)   TRANSFER TO OLIN FROM ARCH. In the event that a Plan Participant
transfers employment to Olin after the Distribution Date and on or prior to
February 8, 2000, benefit accrual under this Plan shall cease and Arch shall
remain liable for payment of any benefits accrued under this Plan to the date of
transfer. No reserves shall be transferred with respect to such Participant. No
separation from service shall be deemed to occur under this Plan permitting a
distribution under this Plan and benefits hereunder shall not commence until the
Participant has terminated his employment with Olin and has otherwise qualified
for benefits hereunder. Arch shall continue to recognize a Participant's service
with Olin and its affiliates subsequent to his transfer to Olin solely for
purposes of determining the Participant's vesting under this Plan.

      (b)   TRANSFER FROM OLIN TO ARCH. In the event that an Olin employee
transfers employment to Arch from Olin after the Distribution Date and on or
prior to February 8, 2000, benefit accrual under the Olin SCEOP shall cease and
Olin shall remain liable for payment of any benefits accrued under that Plan to
the employee's date of transfer to Arch. No reserves shall be transferred from
Olin or the Olin SCEOP with respect to such Olin employee. Benefits shall not
commence under the Olin SCEOP until the former Olin employee terminates service
with Arch and its affiliates and has otherwise qualified for benefits under the
Olin SCEOP. Following such transfer, Olin shall continue to credit such
employee's service with Arch and its affiliates


                                       6
<PAGE>


subsequent to his transfer to Arch solely for purposes of determining his
vesting under the Olin SCEOP.

                                   ARTICLE IV
                                  DISTRIBUTIONS

      4.1   No amounts credited to a Participant's SCEOP Account under this Plan
may be withdrawn or distributed prior to the Participant's termination of
employment with the Company and all affiliates thereof, including, but not
limited to any other corporation in the same controlled group with Arch (within
the meaning of Section 414(b), (c) and (m) of the Code). Amounts credited to a
Participant's Account under this Plan may not be loaned to such Participant. A
Participant's SCEOP Account will be distributed in the form elected under
Section 4.2 upon the earliest to occur of the Participant's death, termination
of service due to Permanent Disability, retirement or termination of active
service from the Company and all affiliates. In the event that an Arch Employee
is re-employed by Olin on or prior to February 8, 2000, and again participates
in the Olin SCEOP, no separation from service shall be deemed to occur
permitting a distribution of benefits from this Plan.

      4.2   Upon becoming a SCEOP Participant, such SCEOP Participant shall
elect to receive the value of his SCEOP Account Balance either (i) in a lump
sum, or (ii) in annual installments for a period not to exceed fifteen (15)
years, commencing on the earliest to occur of the Participant's death,
retirement, termination of service due to Permanent Disability or termination of
active employment from Arch and its affiliated companies. A SCEOP Participant
may change such election upon written notice to the Plan Administrator, provided
no such change shall be given effect if the SCEOP Participant becomes eligible
for a distribution from this Plan within twelve (12) months of such change.

      4.3   Installment payments shall commence to be paid as soon as
administratively feasible and generally effective as of the first day of the
month following a Participant's termination of active service. The Company may
delay the payment of any benefit owed hereunder in order to complete the orderly
processing of such benefit.

      4.4   Distributions to a SCEOP Participant of his SCEOP Account Balance
shall be made only in the form of cash. Except as provided in Section 7.3, the
value of the amount of any distribution shall be based on the Current Market
Value of units in the Arch Common Stock Fund and, if applicable, the Olin Common
Stock Fund and Primex Common Stock Fund, as calculated in accordance with the
CEOP at the close of business on the last business day immediately preceding the
date on which the distribution is to be effective.

      4.5   Any benefit payable under this Plan on account of the death of a
Participant shall be paid to the Participant's beneficiary as designated or
determined under the terms of the CEOP; however, a Participant may, by filing
with the Plan Administrator prior to death on a form supplied by the Plan
Administrator, designate a different individual or entity to be the designated
Beneficiary of such Participant for purposes of this Plan, in which case the
subsequent designation will supercede any designation of a beneficiary under the
CEOP.


                                       7
<PAGE>


                                    ARTICLE V
                              LIABILITY FOR PAYMENT

      5.1   The Company (and each other Participating Employer) shall pay the
benefits provided hereunder with respect to SCEOP Participants who are employed
or were formerly employed by it during their participation in the Plan. In the
case of a SCEOP Participant who was employed by more than one Participating
Employer, the Committee shall allocate the cost of such benefits among such
Participating Employers in such manner as it deems equitable. The obligations of
the Participating Employer hereunder shall not be funded in any manner. The
rights of any person to receive benefits under this Plan are limited to those of
a general creditor of the Participating Employer liable for such benefits
hereunder.

                                   ARTICLE VI
                           ADMINISTRATION OF THE PLAN

      6.1   The Pension Administration and Review Committee shall be the named
Plan Administrator of this Plan. The Plan Administrator shall administer the
Plan for the exclusive benefit of the Participants (and their Beneficiaries), in
accordance with the terms of the Plan. The Plan Administrator shall have the
absolute discretion and power to determine all questions arising in connection
with the administration, interpretation and application of the Plan. Any such
determination by the Plan Administrator shall be conclusive and binding upon all
persons. The Plan Administrator may correct any defect or reconcile any
inconsistency in such manner and to such extent as shall be deemed necessary or
advisable to carry out the purposes of the Plan; provided, however, that such
interpretation or construction shall be done in a non-discriminatory manner and
shall be consistent with the intent of the Plan, the Code and ERISA.

      The Plan Administrator shall:

            (a)   determine all questions relating to eligibility of Employees
      to participate or continue participation in the Plan;

            (b)   maintain all necessary records for the administration of the
      Plan;

            (c)   interpret the provisions of the Plan and make and publish such
      rules for regulation of the Plan as are consistent with the terms hereof;

            (d)   assist any Participant regarding his rights, benefits or
      elections available under the Plan; and

            (e)   communicate to Employees, Participants and their Beneficiaries
      concerning the provisions of the Plan.

      The Plan Administrator shall keep a record of all actions taken and shall
keep such other books of account, records and other information that may be
necessary for proper administration of the Plan. The Plan Administrator shall
file and distribute all reports that may be required by


                                       8
<PAGE>


the Internal Revenue Service, Department of Labor or others, as required by law.
The Plan Administrator may appoint accountants, actuaries, counsel, advisors and
other persons that it deems necessary or desirable in connection with the
administration of the Plan.

      6.2   Except as otherwise provided herein, all provisions set forth in the
CEOP with respect to the administration of that plan shall also be applicable
with respect to this Plan. For purposes of this Plan, the Company shall be
entitled to rely conclusively upon all tables, valuations, certificates,
opinions and reports furnished by any actuary, accountant, controller, counsel
or other person employed or engaged by the Company or by Olin Corporation with
respect to the CEOP.

                                   ARTICLE VII
                  AMENDMENT, TERMINATION AND CHANGE OF CONTROL

      7.1   The Company reserves the right to amend or terminate this Plan at
any time, by action of the Company's Board of Directors, the Compensation
Committee of the Board, or such other committee from time to time designated by
the Board, and without the consent of any employee or other person.

      7.2   Notwithstanding Section 7.1 above, no amendment or termination of
the Plan shall directly or indirectly reduce the balance to the credit of any
Participant hereunder as of the effective date of such amendment or termination.
Upon termination of the Plan, no additional amounts shall be credited under the
terms of the Plan. Notwithstanding the termination of this Plan, amounts
credited hereunder shall not be distributed to Participants except as provided
in Article IV, above.

      7.3   Upon a Change of Control (as defined below), the Plan shall
terminate and the Account Balance of a SCEOP Participant shall be paid in cash
to such Participant as promptly as practicable, but in no event later than 30
days following the Change in Control. The spin-off of Arch Chemicals from Olin
Corporation shall not be deemed to be a change of control entitling any
Participant herein to benefits under this Plan or the prior Olin Supplemental
Contributing Ownership Plan. For purposes of the Plan, a "Change in Control" of
the Company shall have occurred in the event that

            (i)   the Company ceases to be, directly or indirectly, owned of
            record by at least 1,000 stockholders;

            (ii)  a person, partnership, joint venture, corporation or other
            entity, or two or more of any of the foregoing acting as "person"
            within the meaning of Section 13(d)(3) of the Securities Exchange
            Act of 1934, as amended (the "Act"), other than the Company, a
            majority-owned subsidiary of the Company or an employee benefit plan
            of the Company or such subsidiary (or such plan's related trust),
            become(s) the "beneficial owner" (as defined in Rule 13d-3 of the
            Act) of 20% or more of the then outstanding voting stock of the
            Company; or


                                       9
<PAGE>


            (iii) during any period of two consecutive years, individuals who at
            the beginning of such period constitute the Company's Board of
            Directors (together with any new Director whose election by the
            Company's Board or whose nomination for election by the Company's
            stockholders, was approved by a vote of at least two-thirds of the
            Directors of the Company then still in office who either were
            Directors at the beginning of such period or whose election or
            nomination for election was previously so approved) cease for any
            reason to constitute a majority of the Directors then in office; or

            (iv)  all or substantially all of the business of the Company is
            disposed of pursuant to a merger, consolidation or other transaction
            in which the Company is not the surviving corporation or the Company
            combines with another company and is the surviving corporation
            (unless the shareholders of the Company immediately following such
            merger, consolidation, combination, or other transaction
            beneficially own, directly or indirectly, more than 50% of the
            aggregate voting stock or other ownership interests of (x) the
            entities, if any, that succeed to the business of the Company or (y)
            the combined company); or

            (v)   the shareholders of the Company approve a sale of all or
            substantially all of the assets of the Company or a liquidation or
            dissolution of the Company

For purposes of computing the payout under this Section 7.3, the cash value of
the SCEOP Account of a Participant shall be determined by:

      (i)   multiplying the actual number of shares of Arch Common Stock
      reflected in a Participant's Arch Phantom Units by the greater of (a) the
      highest Current Market Value of the Common Stock (as defined in the CEOP
      Plan) on any date within the period commencing thirty (30) days prior to
      such Change in Control and ending on the date of the Change in Control, or
      (b) if the Change in Control occurs as a result of a tender or exchange
      offer or consummation of a corporate transaction, then the highest price
      paid per share of Common Stock pursuant thereto;

      (ii)  adding any cash portion attributable to a Participant's Arch Phantom
      Units held in his SCEOP Account; then

      (iii) adding the then Current Market Value of that portion of a
      Participant's SCEOP Account which is deemed invested in Olin Phantom Units
      and Primex Phantom Units (and any other phantom units or stock fund
      established in the SCEOP).


                                       10
<PAGE>


                                  ARTICLE VIII
                               GENERAL PROVISIONS

      8.1   The Plan at all times shall be entirely unfunded and no provision
shall at any time be made with respect to segregating any assets of the Company
for payment of any distribution hereunder. The right of a Participant or his
designated Beneficiary to receive a distribution hereunder shall be an unsecured
claim against the general assets of the Company, and neither the Participant nor
a designated Beneficiary shall have any rights in or against any specific assets
of the Company. All amounts credited to the SCEOP Accounts of Participants shall
constitute general assets of the Company and may be disposed of by the Company
at such time and for such purposes as it may deem appropriate.

      8.2   Nothing contained in the Plan shall constitute a guaranty by the
Company or any other person or entity that the assets of the Company will be
sufficient to pay any benefit hereunder.

      8.3   No Participant shall have any right to receive a distribution of
contributions made under the Plan except in accordance with the terms of the
Plan. Establishment of the Plan shall not be construed to give any Participant
the right to be retained in the service of the Company.

      8.4   No interest of any person or entity in, or right to receive a
distribution under, the Plan shall be subject in any manner to sale, transfer,
assignment, pledge, attachment, garnishment or other alienation or encumbrance
of any kind; nor may such interest or right to receive a distribution be taken,
either voluntarily or involuntarily for the satisfaction of the debts of, or
other obligations or claims against, such person or entity, including claims for
alimony, support, separate maintenance and claims in bankruptcy proceedings.

      8.5   The Plan shall be construed and administered under the laws of the
State of Connecticut, to the extent not preempted by federal law.

      8.6   If any person entitled to a distribution under the Plan is deemed by
the Company to be incapable of personally receiving and giving a valid receipt
for such payment, then, unless and until claim therefor shall have been made by
a duly appointed guardian or other legal representative of such person, the
Company may provide for such payment or any part thereof to be made to any other
person or institution then contributing toward or providing for the care and
maintenance of such person. Any such payment shall be a payment for the account
of such person and a complete discharge of any liability of the Company and the
Plan therefor.

      8.7   The Plan shall not be automatically terminated by a transfer or sale
of all or substantially all of the assets of the Company or by the merger or
consolidation of the Company into or with any other corporation or other entity,
but the Plan shall be continued after such sale, merger or consolidation only if
and to the extent that the transferee, purchaser or successor entity agrees to
continue the Plan. In the event that the Plan is not continued by the
transferee, purchaser or successor entity, then the Plan shall terminate,
subject to the provisions of Section 7.2.


                                       11
<PAGE>


      8.8   Each Participant shall keep the Company informed of his current
address and the current address of his designated Beneficiary. The Company shall
not be obligated to search for the whereabouts of any person. If the location of
a Participant is not made known to the Company within three (3) years after the
date on which payment of any or all of the Participant's Accounts may first be
made, payment may be made as though the Participant had died at the end of the
three-year period. If, within one additional year after such three-year period
has elapsed, or, within three years after the actual death of a Participant, the
Company is unable to locate any designated Beneficiary of the Participant, then
the Company shall have no further obligation to pay any benefit hereunder to
such Participant or designated Beneficiary and such benefit shall be irrevocably
forfeited.

      8.9   This Plan shall constitute the entire agreement between the Company
and its executives concerning the provision of supplemental CEOP benefits.

      8.10  Notwithstanding any of the preceding provisions of the Plan, neither
the Company nor any individual acting as employee or agent of the Company shall
be liable to any Participant, former Participant or other person for any claim,
loss, liability or expense incurred in connection with the Plan.


      IN WITNESS WHEREOF, Arch Chemicals, Inc. has caused this Plan to be
executed by its duly authorized officer as of February 8, 1999.

                                     ARCH CHEMICALS, INC.



                                     By: /s/ Mark A. Killian
                                         Its Vice President of Human Resources