<TABLE>
                                                                      EXHIBIT 4.2

<S>                <C>              <C>                               <C>
                   COMMON STOCK     [LOGO]  IONICS                    COMMON STOCK
                   Par Value $1             ____________________      Par Value $1
 Number            Per Share                IONICS, INCORPORATED      Per Share
FBU______                           Incorporated under the laws of      [Shares]
                                    the Commonwealth of Massachusetts
                   This certificate    (see reverse for certain
                   is transferable          restrictions)             CUSIP ___________
                   in Boston or in                                    See Reverse for
                   New York City                                      Certain Definitions


                   THIS CERTIFIES THAT


                   is the owner of

                                      CERTIFICATE OF STOCK
                   FULLY PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK OF
                   Ionics, Incorporated, transferable on the books of the Corporation by the
                   holder hereof, in person or by duly authorized attorney, upon surrender of
                   this certificate property endorsed or assigned.

                   This certificate and the shares represented hereby are subject to the laws of
                   The Commonwealth of Massachusetts and to the Restated Articles of Organization
                   and By-laws of the Corporation, as from time to time amended.

                   This certificate is not valid until countersigned and registered by the
                   Transfer Agent and Registrar.

                   In Witness Whereof, Ionics, Incorporated has caused this certificate to be
                   signed by the facsimile signatures of its duly authorized officers and to be
                   sealed with a facsimile of its corporate seal.

[CORPORATE SEAL]   Dated

                   /s/Theodore G. Papastavros                        /s/Arthur L. Goldstein
                   __________________________                        ______________________
                   Treasurer                                         Chairman and Chief
                                                                     Executive Officer

                   COUNTERSIGNED AND REGISTERED:
                      STATE STREET BANK AND TRUST COMPANY

                   By               Transfer Agent
                                     and Registrar


                                    Authorized Signature
</TABLE>
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     This certificate also evidences and entitles the holder hereof to
certain Rights as set forth in the Renewed Rights Agreement between
Ionics, Incorporated (the "Company") and BankBoston, N.A. (the "Rights
Agent") dated as of August 19, 1997, as the same may be amended, restated,
renewed or extended from time to time (the "Rights Agreement"), the terms
of which are hereby incorporated herein by reference and a copy of which
is on file at the principal offices of the Company.  Under certain
circumstances, as set forth in the Rights Agreement, such Rights will be
evidenced by separate certificates and will no longer be evidenced by this
certificate.  The Company will mail to the holder of this certificate a
copy of the Rights Agreement, as in effect on the date of mailing, without
charge, promptly after receipt of a written request therefor.  Under
certain circumstances set forth in the Rights Agreement, Rights
beneficially owned (as such term is defined in the Rights Agreement) by
any Person who is, was or becomes an Acquiring Person or any Affiliate or
Associate thereof (as such terms are defined in the Rights Agreement),
whether currently held by or on behalf of such Person or by any subsequent
holder, may become null and void.  The Rights shall not be exercisable,
and shall be void so long as held, by a holder in any jurisdiction where
the requisite qualification to the issuance to such holder, or the
exercise by such holder, of the Rights in such jurisdiction shall not have
been obtained or be obtainable.

     The following abbreviations, when used in the inscription on the face
of this certificate, shall be construed as though they were written out in
full according to applicable laws or regulations:
<TABLE>
     <S>                                      <C>
     TEN COM -- as tenants in common          UNIF GIFT MIN ACT -- _________Custodian_________
     TEN ENT -- as tenants by the entireties                        (Cust)           (Minor)
     JT TEN  -- as joint tenants with right                         under Uniform Gifts to Minors
                of survivorship and not as                          Act____________
                tenants in common                                       (State)
                   Additional abbreviations may also be used though not in the above list.
</TABLE>













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For value received_____hereby sell, assign and transfer unto

PLEASE INSERT SOCIAL SECURITY OR OTHER
     IDENTIFYING NUMBER OF ASSIGNEE
[                                   ]___________________________________
________________________________________________________________________
PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS INCLUDING POSTAL ZIP CODE OF
ASSIGNEE
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
of the capital stock represented by the within Certificate, and do hereby
irrevocably constitute and
appoint_________________________________________________________________
________________________________________________________________________
Attorney to transfer the said stock on the books of the within-named
Corporation with full power of substitution in the premises.

Dated_________________

                             ______________________________
                             NOTICE:  The signature to this assignment must
                             correspond with the name as written upon the face
                             of this Certificate, in every particular, without
                             alteration or enlargement, or any change whatever.

Signature(s) guaranteed:

____________________________________________
The signature(s) should be guaranteed by an
eligible guarantor institution (banks stockbrokers,
savings and loan associations with membership in an
approved signature guarantee medallion program),
pursuant to S.E.C. Rule 17Ad-15.















/63