EXHIBIT 2.2A November 18, 1996 First Mississippi Corporation 700 North Street Jackson, MS 39202-3095 Ladies and Gentlemen: Reference is made to the Agreement and Plan of Merger and Reorganization (the "Merger Agreement"), dated as of August 27, 1996,...

                                                                    EXHIBIT 2.2A
 
                               November 18, 1996



First Mississippi Corporation
000 Xxxxx Xxxxxx
Xxxxxxx, XX  00000-0000

Ladies and Gentlemen:

       Reference is made to the Agreement and Plan of Merger and Reorganization
(the "Merger Agreement"), dated as of August 27, 1996, by and among Mississippi
Chemical Corporation, a Mississippi corporation ("Mississippi Chemical"), MISS
SUB, INC., a Mississippi Corporation ("Miss Sub"), and First Mississippi
Corporation, a Mississippi corporation ("First Mississippi").  Capitalized terms
not defined in this letter agreement have the meanings given to them in the
Merger Agreement.

       This letter constitutes an agreement between Mississippi Chemical and
First Mississippi not to waive certain Closing conditions related to the receipt
of certain tax opinions of Xxxxxx & Xxxx, L.L.P. and Skadden, Arps, Slate,
Xxxxxxx & Xxxx (Illinios).  In consideration of the foregoing and for good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Buyer and the Seller hereby agree as follows:

1.  Mississippi Chemical will not waive the conditions to Closing contained in
    Sections in 7.2(d) and 7.2(e) of the Merger Agreement.

2.  First Mississippi will not waive the conditions to Closing contained in
    Section 7.3(d) of the Merger Agreement.


       This letter agreement may be executed in counterparts, all of which will
be considered one and the same agreement and will become effective when a
counterpart has been signed by each of the parties, it being understood that all
parties need not sign the same counterpart.


                SIGNATURES ARE INCLUDED ON THE FOLLOWING PAGE.

 
       If the foregoing accurately reflects our agreement, please execute this
letter in the space provided below and return an executed copy to the
undersigned.

                              MISSISSIPPI CHEMICAL CORPORATION


                              By:    /s/ XXXXXX X. XXXXX
                                    -----------------------------
                              Name:  Xxxxxx X. Xxxxx 
                                    -----------------------------
                              Title: Senior Vice President and
                                    -----------------------------
                                     General Counsel 
                                     
Accepted and agreed:

FIRST MISSISSIPPI CORPORATION


By:     /s/ X. X. XXXXXXXXXX
       ---------------------------
Name:   X. X. Xxxxxxxxxx
       ---------------------------
Title:  Vice President & Chief 
       ---------------------------
        Financial Officer