The following information is extracted from the British Official History of the Great War.
Military Operations Egypt & Palestine. From the Outbreak of War with Germany to June 1917 page 328 notes that 4,000 rounds of 4.5 inch gas shells were brought into the theatre before the Second Battle of Gaza (April 1917). Page 336 states that during the Second Phase of the British attack the field howitzers were to fire gas shells for the first 40 minutes; then employ high explosive for the remainder of the two hours preliminary bombardment. The gas shells were directed mainly against enemy artillery positions but were unsuccessful in silencing these batteries.
Military Operations Egypt & Palestine. From June 1917 to the End of the War. Part I page 65 records that during the Third Battle of Gaza (October-November 1917) "Bombardments of enemy batteries with gas shells were carried out on the 29th, 30th and 31st October, but appear to have had little or no effect."
The low concentration of gas shells and the effect of hot, windy weather appear to have neutralised the effect of the gas.