EXHIBIT 10.4



                   AMENDMENT NO. 1 TO SHAREHOLDERS' AGREEMENT

             WHEREAS, Elson T. Killam Associates, Inc., a New Jersey
        corporation ("Killam"), Engineering, Technology and Knowledge
        Corporation, a Delaware corporation (formerly known as
        Environmental, Technology and Knowledge Corporation ("ETKC"), and
        certain persons (individually, a "Shareholder" and collectively,
        the "Shareholders") are parties to that certain Shareholders'
        Agreement dated as of the 29th day of January, 1995 (the
        "Shareholders' Agreement"); 

             WHEREAS, ETKC owns 100% of the outstanding capital stock of
        Killam (the "Killam Stock") and the Shareholders collectively own
        vested options (the "Killam Options") to purchase, in the
        aggregate, 1,590 additional shares of Killam Stock;

             WHEREAS, in the absence of any public trading market for
        Killam Stock, the Shareholders' Agreement contains certain
        provisions intended under certain identified circumstances to
        provide the Shareholders with liquidity with respect to their
        shares of Killam Stock;

             WHEREAS, pursuant to a Stock Purchase and Sale Agreement of
        even date herewith, Thermo Process Systems Inc., a Delaware
        corporation ("Thermo"), has acquired 100% of the outstanding
        capital stock of ETKC;

             WHEREAS, as of the date hereof, the Killam Options (after
        taking into account the cancellation of certain of the Killam
        Options) have been assumed by Thermo and have been converted into
        options to purchase shares of the common stock of Thermo, which
        shares are listed for trading on the American Stock Exchange and
        are freely tradable under U.S. securities laws in the public
        securities markets; and

             WHEREAS, the parties wish to clarify the Shareholders'
        Agreement to establish such public markets as the means to
        provide the Shareholders with the liquidity guaranteed by the
        Shareholders' Agreement;

             NOW, THEREFORE, in consideration of the foregoing, of the
        mutual promises set forth herein, and intending to be legally
        bound, the parties hereto hereby agree as follows:
         
             1.   The Shareholders' Agreement is amended by deleting
        Section 1.8 thereof in its entirety and substituting therefor the
        following:

                  "1.8 "SHARES" shall mean shares of the common stock of
             Thermo Process Systems Inc. acquired upon the exercise of

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             options received by the Shareholders as of February 6, 1995
             (the "Thermo Options") upon the conversion of
             then-outstanding options to purchase shares of the capital
             stock of Killam." 

             2.   The Shareholders' Agreement is amended by deleting
        Section 2.2 thereof in its entirety and substituting therefor the
        following:

                  "2.2 FUTURE SHARES.  The Shareholders agree to be bound
             by this Agreement only with respect to the Shares.  This
             Agreement shall not apply to any other shares of stock of
             Thermo Process Systems Inc. acquired by the Shareholders." 

             3.   The Shareholders' Agreement is amended by deleting
        Article 3, Sections 4.2, 4.3, 4.4 and 4.5 and Article 7 thereof
        in their entirety.

             4.   The Shareholders' Agreement is amended by deleting
        Section 5.1 thereof in its entirety and substituting therefor the
        following:

                  "5.1 DEATH.   Upon the death of a Shareholder, the
             estate or personal representative of such deceased
             Shareholder may sell, transfer or otherwise dispose of any
             Shares owned by such deceased Shareholder to any third party
             on such terms as such estate or personal representative and
             such third party may agree.  Any such third party shall take
             such Shares free and clear of any restriction imposed on the
             Shareholder by this Agreement."  

             5.   The Shareholders' Agreement is amended by deleting
        Section 5.2 thereof in its entirety and substituting therefor the
        following:

                  "5.2 DISABILITY.   In the event that a Shareholder
             becomes Disabled, such Disabled Shareholder or the legal
             guardian of such Disabled Shareholder may sell, transfer or
             otherwise dispose of any Shares owned by such Disabled
             Shareholder to any third party on such terms as such
             Disabled Shareholder or such legal guardian and such third
             party may agree.  Any such third party shall take such
             Shares free and clear of any restriction imposed on the
             Shareholder by this Agreement."  

             6.   The Shareholders' Agreement is amended by deleting
        Section 5.3 thereof in its entirety and substituting therefor the
        following:

                  "5.3 INVOLUNTARY TERMINATION OF EMPLOYMENT.  If any
             Shareholder ceases to be employed by Killam, or any Related
             Corporation, on account of an involuntary termination, such
             Shareholder may sell, transfer or otherwise dispose of any
             Shares owned by such Shareholder to any third party on such

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             terms as such Shareholder and such third party may agree.
             Any such third party shall take such Shares free and clear
             of any restriction imposed on the Shareholder by this
             Agreement."  

             7.   The Shareholders' Agreement is amended by deleting
        Section 5.4 thereof in its entirety and substituting therefor the
        following:

                  "5.4 VOLUNTARY TERMINATION OF EMPLOYMENT.  If any
             Shareholder ceases to be employed by Killam, or any Related
             Corporation, on account of a voluntary termination, such
             Shareholder may sell, transfer or otherwise dispose of any
             Shares owned by such Shareholder to any third party on such
             terms as such Shareholder and such third party may agree.
             Any such third party shall take such Shares free and clear
             of any restriction imposed on the Shareholder by this
             Agreement."  

             8.   The Shareholders' Agreement is amended by deleting
        Section 5.5 thereof in its entirety and substituting therefor the
        following:

                  "5.5 RETIREMENT.  If any Shareholder ceases to be
             employed by Killam, or any Related Corporation, on account
             of Retirement, such Shareholder may sell, transfer or
             otherwise dispose of any Shares owned by such Shareholder to
             any third party on such terms as such Shareholder and such
             third party may agree.  Any such third party shall take such
             Shares free and clear of any restriction imposed on the
             Shareholder by this Agreement."  

             9.   The Shareholders' Agreement is amended by deleting
        Section 6.1 thereof in its entirety and substituting therefor the
        following:

                  "6.1 SALE OF SHARES.  Notwithstanding the provisions
             contained in Article 4, (a) on and after January 1, 1997,
             each Shareholder may sell up to 25% of his Shares to any
             third party on such terms as such Shareholder and such third
             party may agree; (b) on and after January 1, 1998, each
             Shareholder may sell up to 25% of his Shares to any third
             party on such terms as such Shareholder and such third party
             may agree; (c) on and after January 1, 1999 each Shareholder
             may sell up to 25% of his Shares to any third party on such
             terms as such Shareholder and such third party may agree;
             and (d) on and after January 1, 2000 each Shareholder may
             sell up to 25% of his Shares to any third party on such
             terms as such Shareholder and such third party may agree;
             such that beginning on January 1, 1997, each Shareholder
             will have been entitled to sell one-fourth of his total
             Shares on and after each such date.  Any such third party
             shall take such Shares free and clear of any restriction
             imposed on the Shareholder by this Agreement.  This Section

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             6.1 shall not limit the ability of each Shareholder to sell
             Shares as set forth in Article 5." 

             10.  The Shareholders' Agreement is amended by adding the
        following Section 13.11 immediately after Section 13.10:

                  "13.11  FLOOR PRICE ON SHARES.  In the event that a
             Shareholder desires to sell in the open market any or all of
             his Shares at any time prior to January 29, 2002 (subject to
             the resale restrictions set forth in this Agreement), but
             cannot do so at prices equal to at least $8.00 per Share, as
             adjusted for stock dividends, stock splits,
             reclassifications and similar events (the "Floor Price"),
             Killam's parent company, Thermo Process Systems Inc.
             ("Thermo") will either, in its discretion, buy any such
             Shares that cannot be sold for at least the Floor Price for
             an amount equal to the Floor Price or (ii) permit the
             Shareholder to sell such Shares in the open market at such
             price or prices as may be obtainable and pay to the
             Shareholder an amount which is equal to the difference
             between the Floor Price and the amount which such
             Shareholder received (before taking into account
             commissions, taxes and other transaction costs) upon such
             sales.  The Shareholders agree, as a condition to such
             agreements by Thermo, to give Thermo reasonable prior
             written notice of any such intention to sell such Shares and
             to consult with Thermo as to the timing of such sales."

             11.  The Shareholders' Agreement is amended by adding the
        following Section 13.12 immediately after Section 13.11:

                  "13.12  PLEDGES.  Notwithstanding any other provision
             of this Agreement, each Shareholder may pledge any or all of
             his Shares as collateral for any loans that may be needed to
             enable such Shareholder to pay any alternative minimum tax
             or other income tax due as a result of the exercise of the
             Thermo Options, provided, however, that any lender accepting
             such Shares as collateral shall continue to be prohibited
             from disposing of such Shares except in accordance with the
             provisions of Section 6.1 of this Agreement."

             12.  Except as expressly amended hereby, the Shareholders'
        Agreement shall remain in full force and effect in accordance
        with the terms thereof.

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             IN WITNESS WHEREOF, the parties have executed this Amendment
        No. 1 as of the day and year first written above.

        ELSON T. KILLAM ASSOCIATES, INC.   ENGINEERING, TECHNOLOGY 
                                           AND KNOWLEDGE CORPORATION

        By: /s/ Emil C. Herkert            By: /s/ John P. Appleton
        Printed Name: Emil C. Herkert      Printed Name: John P. 
        Title: President                      Appleton
                                           Title: President


        /s/ Emil C. Herkert                /s/ Kenneth L. Zippler
        Emil C. Herkert                    Kenneth L. Zippler


        /s/ Franklin O. Williamson, Jr.    /s/ Fletcher N. Platt, Jr.
        Franklin O. Williamson, Jr.                  Fletcher N. Platt,
        Jr.


        /s/ Eugene J. Destefano            /s/ Meint Olthof
        Eugene J. Destefano                Meint Olthof


        /s/ Stanley P. Kaltnecker, Jr.
        Stanley P. Kaltnecker, Jr.











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        for purposes of SectionS 10 and 11 hereof only:

        THERMO PROCESS SYSTEMS INC.


        By:  /s/ John P. Appleton

        Printed Name:  John P. Appleton

        Title:  President