STOCK PURCHASE AGREEMENT

            This STOCK PURCHASE AGREEMENT (this "Agreement"), dated as
       of November 4, 1996, between Sid Instruments, Inc., a company
       registered under the laws of Delaware, U.S.A., (the "Seller)  and
       ThermoQuest Corporation, a company registered under the laws of
       Delaware, U.S.A.  (the "Buyer").

                 WHEREAS , the Buyer desires to  purchase from the Seller
       and the Seller desires  to sell to the  Buyer ,all of  the issued
       and outstanding  shares of  capital stock  of Fisons  Instruments
       S.p.A., a  company   registered  under the  laws  of Italy  which,
       subject to the Italian court approval, has changed  its corporate
       name into ThermoQuest Italia S.p.A. (the "Company") owned  by the
       Seller, upon the terms  and subject to  the conditions set  forth
       herein (the "Stock Purchase");

                 WHEREAS, the Company  is engaged in the  import, export
       and marketing of  reagents instruments  to be  used for  chemical
       analysis and other applications  as more accurately described  in
       article 5 of the Company by-laws (the "Business") and has already
       transferred its  ARL and  ELEMENTAL businesses  to Unicam  Italia
       S.p.A.;

                 NOW, THEREFORE, the parties hereto agree as follows:

                                    ARTICLE 1
                               CERTAIN DEFINITIONS

            As used  in this  Agreement, the  following  terms have  the
       following respective meanings:

       "Closing" means the consummation of the Stock Purchase.

       " Shares"  means all of the  366,671 shares of capital stock of the
       Company, par value Lit. 20,000 per share, representing all of the
       issued and outstanding share capital of the Company.

                                    ARTICLE 2
                                  SALE OF STOCK

       2.1  Stock Purchase.   On the  basis of  the representations  and
       warranties, covenants and agreements set forth herein, the Seller
       hereby sells to the  Buyer, and the  Buyer hereby purchases  from
       the Seller,  the  Shares with  all  dividend and  other  economic
       rights attached thereto,  if any,  effective as  from October  1,
       1996. The Buyer  will wire  transfer,   in immediately  available
       funds, to  the account  specified  by the  Seller  the amount  of
       $20,478,000 with respect  to the  Shares (the "Purchase  Price").
       As soon  as possible  upon  payment of  the  Purchase Price,  the
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       Seller  will   cause   (a)   its   respective   duly   authorised
       representative to (i) endorse  the Shares to the  Buyer according
       to the formalities provided by Italian Law; and (ii) deliver such
       duly endorsed Shares to the Buyer or its representatives; and (b)
       a  director  of  the  Company  to  make  an   annotation  in  the
       shareholders book  of  the  Company  of  the  Buyer  as  the  new
       shareholder of the Company.

       2.2. Price Adjustment .   The  Buyer and  Seller  acknowledge and
       agree that the Purchase Price  represents the sum of (i)  the net
       tangible assets of the Company  (assumed to be $7,095,000 ) as of
       the date of the Seller's acquisition of the Shares as part of the
       acquisition on March  29, 1996 by  the Thermo Instrument  Systems
       Inc. ("THI") and its subsidiaries of certain businesses of Fisons
       plc  (the  "Fisons  Businesses")  pursuant  to  the  Amended  and
       Restated Asset and Stock Purchase Agreement dated as of March 29,
       1996 among the  THI, Thermo Electron  Corporation and Fisons  plc
       (the "Restated Agreement"), plus  (ii) a percentage of  the total
       goodwill  associated  with  THI's   acquisition  of  the   Fisons
       Businesses equal to  the sales of  the Carlo Erba  chromatography
       business of  the  Company for  the  1994  and 1995  fiscal  years
       relative to the  total sales  of the Fisons  Businesses for  such
       years (the "CE Percentage"), plus (iii) the CE  Percentage of the
       total costs incurred  by THI in  acquiring the Fisons  Businesses
       and in restructuring  the sales and  service organization of  the
       Fisons Businesses  (the  "Restructuring  Costs") .   The parties
       acknowledge that  the purchase  price  paid by  the  THI for  the
       Fisons Businesses is subject  to a post-closing adjustment  based
       on the difference between the value of the net tangible assets of
       the Fisons Businesses as shown on the closing balance sheet dated
       as of March 29, 1996 (the "Closing Balance Sheet") and the target
       net tangible asset value provided for in the  Restated Agreement.
       In the  event of  such adjustment,  the Purchase  Price shall  be
       recalculated in  accordance  with  the  third  sentence  of  this
       paragraph to account for (A)  any adjustment in the  net tangible
       assets (other than cash) of  the Company as shown on  the Closing
       Balance Sheet  from $7,095,000, and       (B)  any adjustment  in
       total goodwill associated  with THI's  acquisition of the  Fisons
       Businesses.  In addition, the purchase price shall  be subject to
       recalculation in  accordance  with  the third  sentence  of  this
       paragraph in the event that the Restructuring Costs  incurred are
       less than $1,686,000.  If any recalculation made pursuant to this
       paragraph results in an increase in the Purchase Price, the Buyer
       shall pay the amount of such  increase to the Seller, and  if any
       such recalculation results in  a decrease in the  Purchase Price,
       the Seller shall pay  the amount of  such decrease to the  Buyer.
       Any payment made pursuant to the preceding sentence shall be made
       within ten days after the Closing Balance Sheet  has become final
       (in the  case of  an adjustment  related to  the Closing  Balance
       Sheet) and  no later  than  March 29,  1997 (in  the  case of  an
       adjustment related to the Restructuring Costs) and shall  also be
       accompanied by  interest  from  the  date  hereof  calculated  as
       provided in Section 4.1 of the Restated Agreement  which is known
       to the parties.
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                                    ARTICLE 3
                  REPRESENTATIONS AND WARRANTIES OF THE SELLER

       The Seller makes the following representations and warranties and
       acknowledges that the Buyer is relying upon  such representations
       and warranties  in connection  with  the purchase  by  it of  the
       Shares.
       3.1  Due  Incorporation.   The   Seller   and  the   Company  are
       corporations duly  constituted,  validly  existing  and  in  good
       standing under  the laws  of  their respective  jurisdictions  of
       organization.

       3.2  Approval of  Transactions .   The  Seller  has  obtained all
       necessary corporate authorizations and  approvals, and has  taken
       all actions  required  for the  execution  and delivery  of  this
       Agreement and the consummation  of the transactions  contemplated
       hereby.

       3.3  No conflict.   Neither the  execution nor  delivery of  this
       Agreement,  nor  the  consummation  of  the  transactions  herein
       contemplated, nor the fulfilment of or compliance with  the terms
       and provisions hereof will  (1) conflict with the  Certificate of
       Incorporation or  By-laws  of  the  Seller or  the  Company,  (2)
       violate any current provisions of law, administrative regulation,
       or court decree applicable  to the Seller  or the Company or  (3)
       conflict with  or  result  in  a  breach of  any  of  the  terms,
       conditions or  provisions  of  or constitute  default  under  any
       material agreement  or  instrument to  which  the Seller  or  the
       Company is a party or by which either of them is bound.

       3.4  Authorized Capital .   The  Company  has  an authorized  and
       issued capital stock of   Lit. 7,333,420,000  and all the  Shares
       have been duly and validly issued and are fully paid.

       3.5  Title to Shares. The Shares are owned by the  Seller with a
       good and valid title thereto and are free and clear of any liens,
       options, charges and encumbrances of any kind. 

                                    ARTICLE 4
                   REPRESENTATIONS AND WARRANTIES OF THE BUYER

       The Buyer makes the following representations and  warranties and
       acknowledges that the Seller is relying upon such representations
       and warranties in connection with the sale by it of the Shares.

       4.1  Due Incorporation.  The  Buyer   is   a   corporation   duly
       incorporated, validly  existing and  in good  standing under  the
       laws of Delaware, U.S.A.

       4.2  Approval of  Transactions .   The Buyer  has  obtained  all
       necessary corporate authorizations and  approvals, and has  taken
       all actions  required for  the execution  and   delivery of  this
       Agreement and the consummation  of the transactions  contemplated
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       hereby.

       4.3  No Conflict . Neither the  execution nor  delivery of  this
       Agreement,  nor  the  consummation  of  the  transactions  herein
       contemplated, nor the fulfillment of or compliance with the terms
       and provisions hereof will  (1) conflict with the  Certificate of
       Incorporation or By-laws  of the Buyer,  (2) violate any  current
       provisions of  law, administrative  regulation,  or court  decree
       applicable to  the Buyer  or (3)  conflict with  or  result in  a
       breach of  any  of the  terms,  conditions  or provisions  of  or
       constitute default under any material agreement or  instrument to
       which the Buyer is a party or by which it is bound.

                                    ARTICLE 5
                                 INDEMNIFICATION

       5.1  Indemnification  by  the  Seller . The  Seller  agrees  to
       indemnify and hold harmless the  Buyer from any and  all damages,
       losses  liabilities,  costs  and  expenses   (including,  without
       limitation, settlement costs and any reasonable legal, accounting
       or other expenses for  investigating or defending any  actions or
       threatened actions) incurred by the Buyer as a result  of (i) the
       inaccuracy of any representation or warranty contained in Section
       3 hereof; (ii) the breach by the Seller of  any provision hereof;
       or (iii)   any  third party  claim  arising  due  to  the act  of
       omissions of the Seller  or the Company  from March 29, 1996  and
       prior to the date hereof.  

       5.2  Indemnification by the Buyer.  The Buyer agrees to indemnify
       and hold harmless the  Seller from any  and all damages,  losses,
       liabilities, costs and  expenses (including, without  limitation,
       settlement costs and  any reasonable  legal, accounting or  other
       expenses for investigating or defending any actions or threatened
       actions) incurred by the Seller as a result of (i) the inaccuracy
       of any representation or warranty contained in Section  4 hereof,
       or (ii) the breach of the Buyer of any provision hereof.

       5.3  Notice of  Claim.        Whenever  any  claim  shall  arise
       indemnification hereunder, the party seeking indemnification (the
       "Indemnified Party") shall promptly  notify the other party  (the
       "Indemnifying Party")  of the  claim and,  when  known the  facts
       constituting the basis for such claim.  In the event  of any such
       claim  for  indemnification  hereunder   resulting  from  or   in
       connection with any claim or legal proceedings by  a third party,
       the notice to the Indemnifying Party shall specify, if known, the
       amount or  an estimate  of the  amount of  the liability  arising
       therefrom.  The Indemnified Party shall not settle  or compromise
       any claim by  a third party  for which  the Indemnified Party  is
       entitled to indemnification hereunder  without the prior  consent
       of the Indemnifying Party, unless suit shall have been instituted
       against the Indemnified  Party and  Indemnifying Party shall  not
       have taken control  of such  suit after  notification thereof  as
       provided in Section 6.4 of this Agreement.
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       5.4  Defense of the claim .  In connection  with any claim giving
       rise to indemnity hereunder resulting from or arising  out of any
       claim or legal proceeding by a person who is not a  party to this
       Agreement, the Indemnifying  Party at its  sole cost and  expense
       may, upon notice to the Indemnified Party, assume  the defense of
       any such claim  or legal  proceeding to the  extent permitted  by
       applicable law, if it  acknowledges to the Indemnified  Party its
       obligations to indemnify  the Indemnified  Party with respect  to
       all elements  of such  claim.   The  Indemnified  Party shall  be
       entitled to participate in (but  not control) the defense  of any
       such action, with  its counsel and  at its own  expense.  If  the
       Indemnifying Party does not assume the defense of  any such claim
       or litigation resulting therefrom  within 30 days after  the date
       the Indemnifying  Party is  notified of  such  claim pursuant  to
       paragragh 5.3  hereof,  (i)  the  Indemnified  Party  may  defend
       against such claim or litigation, after giving notice of the same
       to the Indemnifying Party,  on such terms  as are appropriate  in
       the  Indemnified  Party's  reasonable  judgemen ,  and  (ii)  the
       Indemnifying Party shall be  entitled to participate in  (but not
       control) the defense of such action, with its counsel  and at its
       own expense.

                                    ARTICLE 6
                                  MISCELLANEOUS

       6.1   Amendment-Modification-Waiver. No amendment,  modification,
       or waiver of this Agreement will be binding or  effective for any
       purpose unless it is made in writing signed by  the party against
       whom enforcement of  such amendment,  modification, or waiver  is
       sought.

       6.2  Counterparts.  This Agreement may be executed in one or more
       counterparts, all of which  will be considered  one and the  same
       agreement,  and   will  become   effective  when   one  or   more
       counterparts have been signed by each party and  delivered to the
       other party.

       6.3  Governing  Law,  Jurisdiction.       This  Agreement
       governed by and construed  in accordance with  the laws of  Italy
       without reference to the choice  of law principles thereof.   The
       Court of Milan shall have exclusive jurisdiction over any dispute
       which may arise from this Agreement.

       6.4  Notices.          Every  notice or  other  communication
       contemplated, or permitted by  this Agreement by any  party shall
       be in writing and shall be delivered either by personal delivery,
       telegram, facsimile, private courier service, or by  certified or
       registered  mail,  postage  prepaid,  return  receipt  requested,
       addressed to the party to whom intended at the following address:

                 (a)  If to the Seller, to:

                      SID INSTRUMENTS INC.
                      81 Wyman Street
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                      Waltham, MA 
                      01921 U.S.A.
                      Attention:   General Counsel
                      Telephone: 001 617 622 1000
                      Fax: 001 622 1283

            (b)  If to Buyer, to:

                      THERMOQUEST CORPORATION
                      81 Wyman Street
                      Waltham, MA 
                      01921 U.S.A.
                      Attention:   General Counsel
                      Telephone: 001 617 622 1000
                      Fax: 001 622 1283

       or at such  other address  as the intended  recipient shall  from
       time to time designate by written notice delivered  in accordance
       herewith.   Notice by  courier or  certified  or registered  mail
       shall be  effective on  the date  it is  sent.   All notices  and
       communications  required,  contemplated,  or  permitted  by  this
       Agreement to be delivered in person shall be deemed  to have been
       delivered  to  and  received  by  the  addressee,  and  shall  be
       effective,  on  the  date  of  personal  delivery.    Any  notice
       transmitted by telegram or facsimile shall be deemed to have been
       delivered  to  and  received  by  the  addressee,  and  shall  be
       effective, on the date said  notice is delivered to  the telegram
       company or facsimile operator for transmission.

       6.5   Assignment   .   No  party  hereto may  assign  its rights
       delegate its obligations under this Agreement without the written
       consent of the other party thereto.

       6.6  Burden and Benefit.  This  Agreement will be binding upon,
       and inure  to  the  benefit  of, the  parties  hereto  and  their
       respective successors and permitted assigns.

       6.7   Interpretation. Article  and Section headings contained  in
       this Agreement are inserted for convenience of reference only and
       are  not  a  part  of,  and  will  not  affect   the  meaning  or
       interpretation of,  this Agreement.    The references  herein  to
       Articles and  Sections,  unless  otherwise  indicated,  refer  to
       Articles and Sections of this Agreement.
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            IN WITNESS WHEREOF,  this Agreement has been signed by  or on
       behalf of each of the parties as of the day first above written.


       SELLER                             BUYER

       SID INSTRUMENTS, INC.              THERMOQUEST CORPORATION



       By:   Earl R. Lewis                 By:   Richard W.K. Chapman
          ------------------                 ------------------------
       Name: Earl R. Lewis                Name:  Richard W.K. Chapman
       Title: President                   Title: President