SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934 (Amendment No. 2)

Arch Chemicals, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

_______03937R102_________

(CUSIP Number)

Peter D. Goldstein

GAMCO Investors, Inc.

One Corporate Center

Rye, New York 10580-1435

(914) 921-5000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

______________________October 17, 2011________________________

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box .

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) Gabelli Funds, LLC I.D. No. 13-4044523
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e) X
6	Citizenship or place of organization New York
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) IA, CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) GAMCO Asset Management, Inc. I.D. No. 13-4044521
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization New York
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) IA, CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) Gabelli Securities, Inc. I.D. No. 13-3379374
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization Delaware
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) HC, CO, IA

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) MJG Associates, Inc. I.D. No. 06-1304269
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization Connecticut
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) Gabelli Foundation, Inc. I.D. No. 94-2975159
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization NV
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) 00-Private Foundation

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) MJG-IV Limited Partnership I.D. No. 13-3191826
	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization New York
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) PN

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) GGCP, Inc. I.D. No. 13-3056041
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization Wyoming
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) HC, CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) GAMCO Investors, Inc. I.D. No. 13-4007862
	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization New York
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) HC, CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) Mario J. Gabelli
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization USA
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) IN

Item 1. Security and Issuer

This Amendment No. 2 to Schedule 13D on the Common Stock of Arch Chemicals, Inc. (the “Issuer”) is being filed on behalf of the undersigned to amend the Schedule 13D, as amended (the “Schedule 13D”), which was originally filed on August 5, 2011. Unless otherwise indicated, all capitalized terms used herein but not defined herein shall have the same meaning as set forth in the Schedule 13D.

Item 2. Identity and Background

This statement is being filed by Mario J. Gabelli (“Mario Gabelli”) and various entities which he

directly or indirectly controls or for which he acts as chief investment officer. These entities engage in various aspects of the securities business, primarily as investment adviser to various institutional and individual clients, including registered investment companies and pension plans, and as general partner or the equivalent of various private investment partnerships or private funds. Certain of these entities may also make investments for their own accounts.

The foregoing persons in the aggregate often own beneficially more than 5% of a class of equity securities of a particular issuer. Although several of the foregoing persons are treated as institutional investors for purposes of reporting their beneficial ownership on the short-form Schedule 13G, the holdings of those who do not qualify as institutional investors may exceed the 1% threshold presented for filing on Schedule 13G or implementation of their investment philosophy may from time to time require action which could be viewed as not completely passive. In order to avoid any question as to whether their beneficial ownership is being reported on the proper form and in order to provide greater investment flexibility and administrative uniformity, these persons have decided to file their beneficial ownership reports on the more detailed Schedule 13D form rather than on the short-form Schedule 13G and thereby to provide more expansive disclosure than may be necessary.

(a), (b) and (c) - This statement is being filed by one or more of the following persons: GGCP, Inc. (“GGCP”), GGCP Holdings LLC (“GGCP Holdings”), GAMCO Investors, Inc. (“GBL”), Gabelli Funds, LLC (“Gabelli Funds”), GAMCO Asset Management Inc. (“GAMCO”), Teton Advisors, Inc. (“Teton Advisors”), Gabelli Securities, Inc. (“GSI”), Gabelli & Company, Inc. (“Gabelli & Company”), MJG Associates, Inc. (“MJG Associates”), Gabelli Foundation, Inc. (“Foundation”), MJG-IV Limited Partnership (“MJG-IV”), and Mario Gabelli. Those of the foregoing persons signing this Schedule 13D are hereinafter referred to as the “Reporting Persons”.

GGCP makes investments for its own account and is the manager and a member of GGCP Holdings which is the controlling shareholder of GBL. GBL, a public company listed on the New York Stock Exchange, is the parent company for a variety of companies engaged in the securities business, including those named below.

GAMCO, a wholly-owned subsidiary of GBL, is an investment adviser registered under the Investment Advisers Act of 1940, as amended (“Advisers Act”). GAMCO is an investment manager providing discretionary managed account services for employee benefit plans, private investors, endowments, foundations and others.

GSI, a majority-owned subsidiary of GBL, is an investment adviser registered under the Advisers Act and serves as a general partner or investment manager to limited partnerships and offshore investment companies and other accounts. As a part of its business, GSI may purchase or sell securities for its own account. GSI is a general partner or investment manager of a number of funds or partnerships, including Gabelli Associates Fund, L.P., Gabelli Associates Fund II, L.P., Gabelli Associates Limited, Gabelli Associates Limited II E, ALCE Partners, L.P., Gabelli Capital Structure Arbitrage Fund LP, Gabelli Capital Structure Arbitrage Fund Limited, Gabelli Intermediate Credit Fund L.P., Gabelli Japanese Value Partners L.P., GAMA Select Energy + L.P., GAMCO Medical Opportunities L.P., GAMCO Long/Short Equity Fund, L.P., Gabelli Multimedia Partners, L.P, Gabelli International Gold Fund Limited and Gabelli Green Long/Short Fund, L.P.

Gabelli & Company, a wholly-owned subsidiary of GSI, is a broker-dealer registered under the Securities Exchange Act of 1934, as amended (“1934 Act”), which as a part of its business regularly purchases and sells securities for its own account.

Gabelli Funds, a wholly owned subsidiary of GBL, is a limited liability company. Gabelli Funds is an investment adviser registered under the Advisers Act which provides advisory services for The Gabelli Equity Trust Inc., The Gabelli Asset Fund, The GAMCO Growth Fund, The Gabelli Convertible and Income Securities Fund Inc., The Gabelli Value Fund Inc., The Gabelli Small Cap Growth Fund, The Gabelli Equity Income Fund, The Gabelli ABC Fund, The GAMCO Global Telecommunications Fund, GAMCO Gold Fund, Inc., The Gabelli Global Multimedia Trust Inc., The GAMCO Global Convertible Securities Fund, Gabelli Capital Asset Fund, GAMCO International Growth Fund, Inc., The GAMCO Global Growth Fund, The Gabelli Utility Trust, The GAMCO Global Opportunity Fund, The Gabelli Utilities Fund, The Gabelli Blue Chip Value Fund, The GAMCO Mathers Fund, The Gabelli Woodland Small Cap Value Fund, The Comstock Capital Value Fund, The Gabelli Dividend and Income Trust, The Gabelli Global Utility & Income Trust, The Gabelli Global Gold, Natural Resources, & Income Trust, The Gabelli Global Deal Fund, Gabelli Enterprise Mergers & Acquisitions Fund, The Gabelli SRI Green Fund, Inc., and The Gabelli Healthcare & Wellness Rx Trust, (collectively, the “Funds”), which are registered investment companies. Gabelli Funds is also the investment adviser to The GAMCO International SICAV (sub-funds GAMCO Stategic Value and GAMCO Merger Arbitrage), a UCITS III vehicle.

Teton Advisors, an investment adviser registered under the Advisers Act, provides discretionary advisory services to The GAMCO Westwood Mighty Mitessm Fund, The GAMCO Westwood Income Fund and The GAMCO Westwood SmallCap Equity Fund.

MJG Associates provides advisory services to private investment partnerships and offshore funds. Mario Gabelli is the sole shareholder, director and employee of MJG Associates. MJG Associates is the Investment Manager of Gabelli International Limited and Gabelli Fund, LDC. Mario J. Gabelli is the general partner of Gabelli Performance Partnership, LP.

The Foundation is a private foundation. Mario Gabelli is the Chairman, a Trustee and the

Investment Manager of the Foundation. Elisa M. Wilson is the President of the Foundation.

Mario Gabelli is the controlling stockholder, Chief Executive Officer and a director of GGCP and Chairman and Chief Executive Officer of GBL. Mario Gabelli is also a member of GGCP Holdings. Mario Gabelli is the controlling shareholder of Teton.

MJG-IV is a family partnership in which Mario Gabelli is the general partner. Mario Gabelli has less than a 100% interest in MJG-IV. MJG-IV makes investments for its own account. Mario Gabelli disclaims ownership of the securities held by MJG-IV beyond his pecuniary interest.

The Reporting Persons do not admit that they constitute a group.

GBL, GAMCO, and Gabelli & Company are New York corporations and GSI and Teton Advisors are Delaware corporations, each having its principal business office at One Corporate Center, Rye, New York 10580. GGCP is a Wyoming corporation having its principal business office at 140 Greenwich Avenue, Greenwich, CT 06830. GGCP Holdings is a Delaware limited liability corporation having its principal business office at 140 Greenwich Avenue, Greenwich, CT 06830. Gabelli Funds is a New York limited liability company having its principal business office at One Corporate Center, Rye, New York 10580. MJG Associates is a Connecticut corporation having its principal business office at 140 Greenwich Avenue, Greenwich, CT 06830. The Foundation is a Nevada corporation having its principal offices at 165 West Liberty Street, Reno, Nevada 89501.

For information required by instruction C to Schedule 13D with respect to the executive officers and directors of the foregoing entities and other related persons (collectively, “Covered Persons”), reference is made to Schedule I annexed hereto and incorporated herein by reference.

(d) – Not applicable.

(e) – On April 24, 2008, Gabelli Funds settled an administrative proceeding with the Securities and Exchange Commission (“Commission”) regarding frequent trading in shares of a mutual fund it advises, without admitting or denying the findings or allegations of the Commission. The inquiry involved Gabelli Funds’ treatment of one investor who had engaged in frequent trading in one fund (the prospectus of which did not at that time impose limits on frequent trading), and who had subsequently made an investment in a hedge fund managed by an affiliate of Gabelli Funds. The investor was banned from the fund in August 2002, only after certain other investors were banned. The principal terms of the settlement include an administrative cease and desist order from violating Section 206(2) of the Investment Advisers Act of 1940, Section 17(d) of the Investment Company Act of 1940 (“Company Act”), and Rule 17d-1 thereunder, and Section 12(d)(1)(B)(1) of the Company Act, and the payment of $11 million in disgorgement and prejudgment interest and $5 million in a civil monetary penalty. Gabelli Funds was also required to retain an independent distribution consultant to develop a plan and oversee distribution to shareholders of the monies paid to the Commission, and to make certain other undertakings.

On January 12, 2009, Gabelli Funds settled an administrative proceeding with the Commission without admitting or denying the findings or allegations of the Commission, regarding Section 19(a) of the Company Act and Rule 19a-1 thereunder by two closed-end funds. Section 19(a) and Rule 19a-1 require registered investment companies, when making a distribution in the nature of a dividend from sources other than net investment income, to contemporaneously provide written statements to shareholders that adequately disclose the source or sources of such distribution. While the two funds sent annual statements and provided other materials containing this information, the shareholders did not receive the notices required by Rule 19a-1 with any of the distributions that were made for 2002 and 2003. As part of the settlement Gabelli Funds agreed to pay a civil monetary penalty of $450,000 and to cease and desist from causing violations of Section 19(a) and Rule 19a-1. In connection with the settlement, the Commission noted the remedial actions previously undertaken by Gabelli Funds.

(f) – Reference is made to Schedule I hereto.

Item 5. Interest In Securities Of The Issuer

Item 5 to Schedule 13D is amended, in pertinent part, as follows:

(a) As a result of the completion of the tender offer by Lonza Group Ltd. for the Issuer’s outstanding shares, the Reporting Persons no longer have beneficial ownership of any of the Issuer’s shares.

(c) Information with respect to all transactions in the Securities which were effected during the past sixty days or since the most recent filing on Schedule 13D, whichever is less, by each of the Reporting Persons and Covered Persons is set forth on Schedule II annexed hereto and incorporated herein by reference.

(e) The Reporting Persons ceased to be beneficial owners of 5% or more of the Issuer’s common stock on October 17, 2011.

Signature

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: October 19, 2011

GGCP, INC.

MARIO J. GABELLI

MJG ASSOCIATES, INC.

GABELLI FOUNDATION, INC.

MJG-IV LIMITED PARTNERSHIP

By:/s/ Douglas R. Jamieson

Douglas R. Jamieson

Attorney-in-Fact

GABELLI FUNDS, LLC

By:/s/ Bruce N. Alpert

Bruce N. Alpert

Chief Operating Officer – Gabelli Funds, LLC

GAMCO ASSET MANAGEMENT INC.

GAMCO INVESTORS, INC.

GABELLI SECURITIES, INC.

By:/s/ Douglas R. Jamieson

Douglas R. Jamieson

President & Chief Operating Officer – GAMCO Investors, Inc.

President – GAMCO Asset Management Inc.

President – Gabelli Securities, Inc.

Schedule I

Information with Respect to Executive

Officers and Directors of the Undersigned

Schedule I to Schedule 13D is amended, in pertinent part, as follows:

The following sets forth as to each of the executive officers and directors of the undersigned: his name; his business address; his present principal occupation or employment and the name, principal business and address of any corporation or other organization in which such employment is conducted. Unless otherwise specified, the principal employer of each such individual is GAMCO Asset Management Inc., Gabelli Funds, LLC, Gabelli Securities, Inc., Gabelli & Company, Inc., Teton Advisors, Inc., or GAMCO Investors, Inc., the business address of each of which is One Corporate Center, Rye, New York 10580, and each such individual identified below is a citizen of the United States. To the knowledge of the undersigned, during the last five years, no such person has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors), and no such person was a party to a civil proceeding of a judicial or administrative body of competent jurisdiction as a result of which he was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities law or finding any violation with respect to such laws except as reported in Item 2(d) and (e) of this Schedule 13D.

GGCP, Inc. Directors:
Mario J. Gabelli	Chief Executive Officer of GGCP, Inc., and Chairman & Chief Executive Officer of GAMCO Investors, Inc.; Director/Trustee of all registered investment companies advised by Gabelli Funds, LLC.
Marc J. Gabelli	Chairman of The LGL Group, Inc. 2525 Shader Road Orlando, FL 32804
Matthew R. Gabelli	Vice President – Trading Gabelli & Company, Inc. One Corporate Center Rye, NY 10580
Charles C. Baum	Secretary & Treasurer United Holdings Co., Inc. 2545 Wilkens Avenue Baltimore, MD 21223
Fredric V. Salerno	Chairman; Former Vice Chairman and Chief Financial Officer Verizon Communications

Officers:
Mario J. Gabelli	Chief Executive Officer and Chief Investment Officer
Marc J. Gabelli	President
Michael G. Chieco	Vice President, Chief Financial Officer, Secretary
Silvio A. Berni	Vice President, Assistant Secretary and Controller

GGCP Holdings LLC Members: GGCP, Inc. Mario J. Gabelli	Manager and Member Member

GAMCO Investors, Inc. Directors:
Edwin L. Artzt Raymond C. Avansino Richard L. Bready	Former Chairman and Chief Executive Officer Procter & Gamble Company 900 Adams Crossing Cincinnati, OH 45202 Chairman & Chief Executive Officer E.L. Wiegand Foundation 165 West Liberty Street Reno, NV 89501 Former Chairman and Chief Executive Officer Nortek, Inc. 50 Kennedy Plaza Providence, RI 02903
Mario J. Gabelli Elisa M. Wilson	See above Director c/o GAMCO Investors, Inc. One Corporate Center Rye, NY 10580

Eugene R. McGrath	Former Chairman and Chief Executive Officer Consolidated Edison, Inc. 4 Irving Place New York, NY 10003
Robert S. Prather	President & Chief Operating Officer Gray Television, Inc. 4370 Peachtree Road, NE Atlanta, GA 30319
Officers:
Mario J. Gabelli	Chairman and Chief Executive Officer
Douglas R. Jamieson Henry G. Van der Eb Bruce N. Alpert Agnes Mullady Robert S. Zuccaro Christopher Michailoff	President and Chief Operating Officer Senior Vice President Senior Vice President Senior Vice President Executive Vice President and Chief Financial Officer Acting Secretary

GAMCO Asset Management Inc. Directors:
Douglas R. Jamieson Regina M. Pitaro William S. Selby
Officers:
Mario J. Gabelli	Chief Executive Officer and Chief Investment Officer – Value Portfolios

Douglas R. Jamieson Robert S. Zuccaro Chistopher J. Michailoff	President Chief Financial Officer General Counsel and Secretary
Gabelli Funds, LLC Officers:
Mario J. Gabelli	Chief Investment Officer – Value Portfolios
Bruce N. Alpert	Executive Vice President and Chief Operating Officer
Agnes Mullady	President and Chief Operating Officer – Open End Fund Division
Robert S. Zuccaro	Chief Financial Officer
Teton Advisors, Inc. Directors:
Howard F. Ward Bruce N. Alpert Nicholas F. Galluccio Robert S. Zuccaro	Chairman See above Chief Executive Officer and President Chief Financial Officer
Officers:
Howard F. Ward Nicholas F. Galluccio Robert S. Zuccaro Christopher J. Michailoff	See above See above See above Acting Secretary

Gabelli Securities, Inc.
Directors:
Robert W. Blake	President of W. R. Blake & Sons, Inc. 196-20 Northern Boulevard Flushing, NY 11358
Douglas G. DeVivo	DeVivo Asset Management Company LLC P.O. Box 2048 Menlo Park, CA 94027
Douglas R. Jamieson	President

Officers:
Douglas R. Jamieson Christopher J. Michailoff Robert S. Zuccaro	See above Secretary Chief Financial Officer
Gabelli & Company, Inc. Directors:
James G. Webster, III	Chairman
Irene Smolicz	Senior Trader Gabelli & Company, Inc.
Officers:
Daniel Miller	Office of the President
Bruce N. Alpert Diane M. LaPointe Douglas R. Jamieson	Vice President - Mutual Funds Treasurer Secretary
Gabelli Foundation, Inc. Officers:
Mario J. Gabelli	Chairman, Trustee & Chief Investment Officer
Elisa M. Wilson Marc J. Gabelli Matthew R. Gabelli Michael Gabelli	President Trustee Trustee Trustee
MJG-IV Limited Partnership Officers:
Mario J. Gabelli	General Partner

SCHEDULE II
INFORMATION WITH RESPECT TO
TRANSACTIONS EFFECTED DURING THE PAST SIXTY DAYS OR
SINCE THE MOST RECENT FILING ON SCHEDULE 13D (1)
SHARES PURCHASED AVERAGE
DATE SOLD(-) PRICE(2)

COMMON STOCK-ARCH CHEMICALS INC.

MJG-IV LIMITED PARTNERSHIP
10/17/11 25,000- 47.2000
GABELLI FOUNDATION, INC.
10/17/11 40,000- 47.2000
MARIO J. GABELLI
10/17/11 63,000- 47.2000
10/17/11 15,000- 47.2000
10/12/11 5,000- 47.0800
GABELLI SECURITIES, INC.
10/17/11 33,200- 47.2000
10/17/11 7,000- 47.2000
10/13/11 300 47.0539
10/12/11 2,000- 47.0800
10/07/11 1,000 46.6678
10/06/11 1,200 46.7610
10/05/11 2,700 46.7524
10/03/11 100 46.8768
9/29/11 700 47.0124
9/27/11 4,500 46.9725
9/22/11 700 46.8007
9/21/11 1,200 46.8552
GABELLI ASSOCIATES LIMITED II E
10/17/11 58,200- 47.2000
9/30/11 3,000- 46.9967
9/29/11 1,600 47.0124
9/28/11 300 46.9500
9/27/11 9,500 46.9725
9/22/11 1,300 46.8007
9/21/11 2,700 46.8552
GABELLI ASSOCIATES LIMITED
10/17/11 89,293- 47.2000
10/13/11 900 47.0539
10/07/11 4,400 46.6678
10/06/11 3,500 46.7610
10/05/11 3,600 46.7524
10/03/11 900 46.8768
9/29/11 2,100 47.0124
9/28/11 300 46.9500
9/27/11 11,900 46.9725
9/22/11 1,800 46.8007
9/21/11 3,300 46.8552
GABELLI ASSOCIATES FUND II
10/17/11 70,800- 47.2000
10/07/11 2,000 46.6678
10/06/11 2,800 46.7610
10/05/11 4,500 46.7524
10/03/11 800 46.8768
9/29/11 1,700 47.0124
9/28/11 200 46.9500
9/27/11 9,600 46.9725
9/22/11 1,300 46.8007
9/21/11 2,700 46.8552
GABELLI ASSOCIATES FUND
10/17/11 155,424- 47.2000
10/13/11 1,400 47.0539
10/07/11 7,800 46.6678
10/06/11 6,300 46.7610
10/05/11 6,100 46.7524
10/03/11 3,900 46.8768
9/29/11 3,466 47.0124
9/28/11 600 46.9500
9/27/11 20,441 46.9725
9/22/11 2,800 46.8007
9/21/11 6,041 46.8552
MJG ASSOCIATES, INC.
GABELLI INTERNATIONAL LIMITED
10/17/11 5,000- 47.2000
GAMCO INVESTORS, INC.
10/17/11 32,000- 47.2000
10/17/11 128,000- 47.2000
10/17/11 276,780- 47.2000
10/13/11 200 47.0539
10/12/11 4,489- 47.0600
10/11/11 1,011- 47.0452
10/10/11 5,000 46.8319
10/07/11 800 46.6678
10/06/11 1,700 46.7610
10/05/11 1,600 46.7524
10/05/11 1,000 46.7500
10/03/11 100 46.8768
9/30/11 2,800 46.9700
9/29/11 7,200 *DI
9/29/11 700 47.0124
9/28/11 100 46.9500
9/27/11 4,300 46.9725
9/22/11 2,000 46.8800
9/22/11 700 46.8007
9/21/11 1,300 46.8552
GABELLI FUNDS, LLC.
GABELLI SMALL CAP GROWTH FUND
10/17/11 100,078- 47.2000
10/03/11 24,000 46.8800
THE GDL FUND
10/17/11 370,000- 47.2000
GABELLI ENTERPRISE M&A FUND
10/17/11 70,000- 47.2000
GAMCO MERGER ARBITRAGE
10/17/11 8,249- 47.2000
10/13/11 5,100 47.0539
10/11/11 2,749 47.0389
10/03/11 400 46.8768
GABELLI ABC FUND
10/17/11 260,025- 47.2000

(1) UNLESS OTHERWISE INDICATED, ALL TRANSACTIONS WERE EFFECTED
ON THE NY STOCK EXCHANGE.

(2) PRICE EXCLUDES COMMISSION.

(3) THE TRANSACTIONS ON 10/17/11 ARE A RESULT OF THE COMPLETION OF
THE TENDER OFFER BY LONZA GROUP LTD. FOR THE ISSUER'S OUTSTANDING
SHARES.

(*) RESULTS IN CHANGE OF DISPOSITIVE POWER AND BENEFICIAL OWNERSHIP.

ARCH CHEMICALS INC SC 13D/A