Exhibit 2.2


                            Stock Purchase Agreement


             This Stock Purchase Agreement dated May 9, 1995 is entered
        into by Thermo Instrument Systems Inc., a Delaware corporation
        (the "Seller"), and Thermo Process Systems Inc., a Delaware
        corporation (the "Buyer").  

             WHEREAS, Seller owns 100% of the issued and outstanding
        shares (the "Shares") of the capital stock of each of Eberline
        Analytical Corporation, Skinner & Sherman, Inc., TMA/NORCAL Inc.,
        Normandeau Associates Inc., Bettigole Andrews & Clark Inc.,
        Fellows, Read & Associates Inc., and Thermo Consulting Engineers
        Inc. (collectively, the "Corporations"); and 

             WHEREAS, Buyer wishes to purchase, and Seller wishes to
        sell, the Shares, upon the terms and conditions set forth below; 

             NOW, THEREFORE, in consideration of the promises set forth
        below and for other good and valuable consideration, the receipt
        and sufficiency of which are hereby acknowledged, Seller and
        Buyer hereby agree as follows:

             1.   Delivery of Outstanding Shares.  At the Closing (as
        defined in Section 3 hereof), and subject to the terms and
        conditions contained in this Agreement, Seller shall transfer to
        Buyer and Buyer shall acquire from Seller, all right, title and
        interest in and to the Shares, free and clear of all liens,
        encumbrances, charges, equities or restrictions.

             2.   Purchase Price.  In exchange for the Shares, and
        subject to the terms and conditions contained in this Agreement,
        Buyer shall pay to Seller at the Closing $34,267,000 in cash (the
        "Purchase Price").  

             3.   Time and Place of Closing.  The closing of the
        transactions contemplated by this Agreement (the "Closing") shall
        take place immediately upon the execution of this Agreement by
        the parties hereto or at such other time and place as the parties
        may agree.  

             4.   Closing Deliveries.  At the Closing, in addition to the
        taking of such other action as may be provided in this Agreement,
        (i) Seller shall deliver certificates for the Shares to Buyer,
        duly endorsed by Seller or accompanied by duly executed stock
        powers, (ii) Buyer shall deliver the Purchase Price to Seller,
        and (iii) Seller and Buyer shall each deliver such closing
        certificates, documents and opinions of counsel, if any, as may
        be requested the other.
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             5.   Representations and Warranties of Seller.  Seller
        represents and warrants to Buyer that, as of the Closing Date:

                  (a)  Organization and Qualification.  Seller is a
        corporation validly existing and in good standing under the laws
        of the State of Delaware.  

                  (b)  Authority.  The execution and delivery of this
        Agreement, and the consummation of the transactions contemplated
        hereby to be performed by Seller, have been duly and validly
        authorized by all necessary corporate action on the part of
        Seller.  This Agreement constitutes the valid and binding
        obligation of Seller enforceable against Seller in accordance
        with the terms hereof.  

                  (c)  Ownership of Shares; Authority to Transfer.  The
        Shares are not encumbered and are freely transferable by Seller.
        Seller holds good and marketable title to the Shares to be
        transferred to Buyer hereunder and no third party is entitled to
        claim any right thereto or make any claim thereon.  The transfer
        of the Shares to Buyer pursuant to this Agreement will vest in
        Buyer title to the Shares, free and clear of all liens, claims,
        equities, options, calls, voting trusts, agreements, commitments
        and encumbrances whatsoever.  

                  (d)  SELLER DISCLAIMS ANY REPRESENTATIONS OR WARRANTIES
        WITH RESPECT TO THE CORPORATIONS OR THEIR RESPECTIVE BUSINESSES,
        ASSETS AND/OR LIABILITIES.  THE TRANSFER OF THE SHARES TO BUYER
        IS  MADE "AS IS" AND ALL WARRANTIES OF CONDITION,
        MERCHANTABILITY, QUALITY OR FITNESS FOR USE, OR ANY OTHER
        WARRANTY, EXPRESSED OR IMPLIED, WITH THE EXCEPTION OF WARRANTIES
        OF TITLE SET FORTH HEREIN ARE HEREBY DISCLAIMED.

             6.   Representations and Warranties of Buyer.  Buyer
        represents and warrants to Seller that, as of the Closing Date:

                  (a)  Organization and Qualification.  Buyer is a
        corporation validly existing and in good standing under the laws
        of the State of Delaware.  

                  (b)  Authority.  The execution and delivery of this
        Agreement, and the consummation of the transactions contemplated
        hereby to be performed by Buyer, have been duly and validly
        authorized by all necessary corporate action on the part of
        Buyer.  This Agreement constitutes the valid and binding
        obligation of Buyer enforceable against Buyer in accordance with
        the terms hereof.  

             7.    Further Assurances.  From time to time and at any time
        after the Closing, and without further expense to the requesting
        party, each party will execute and furnish to the requesting
        party all documents and will do or cause to be done all other
        things that the requesting party may reasonably request in order

                                      - 2 -PAGE



        to give full effect to this Agreement and to effectuate the
        intent of the parties.

             8.   Confidentiality of Information.  Seller agrees that (a)
        it has obtained confidential and proprietary information about
        the Corporations, including, but not limited to, the
        Corporations' business plans strategies, customer lists, and
        financial and statistical information and (b) it will not
        disclose, directly or indirectly, such information or use it for
        any purpose other than for Buyer's benefit.  

             9.   Successors and Assigns.  Each and every provision
        hereof shall be binding upon and shall inure to the benefit of
        the parties and their respective successors and assigns.

             10.  Entire Agreement.  This Agreement constitutes the full
        and complete agreement of the parties hereto with respect to the
        subject matter hereof.  

             11.  Captions.  Titles or captions of sections contained in
        this Agreement are inserted only as a matter of convenience and
        for reference, and in no way define, limit, extend or describe
        the scope of this Agreement or the intent of any provision
        hereof.  

             13.  Counterparts.  This Agreement may be executed in
        counterparts, all of which together shall for all purposes
        constitute one Agreement, binding on the parties hereto
        notwithstanding that such parties have not signed the same
        counterpart.  

             14.  Applicable Law.  This Agreement and the rights and
        obligations of the parties hereunder shall be governed by and
        interpreted, construed and enforced in accordance with the laws
        of the Commonwealth of Massachusetts. 

             15.  Creditors.  None of the provisions of this Agreement
        shall be for the benefit of or enforceable by any creditor of any
        party hereto.

             IN WITNESS WHEREOF, the parties have executed this Agreement
        on May 9, 1995.  

        SELLER:                            BUYER:

        THERMO INSTRUMENT SYSTEMS INC.     THERMO PROCESS SYSTEMS INC.


        By: Arvin H. Smith                 By: John P. Appleton
            ------------------                 --------------------
                Arvin H. Smith                     John P. Appleton
                President                          President

        AA951430011