Dave,
A list I have from a pal gives the 1940 version of The Chemical Mine as part V with a total of 6 parts in the pamphlet:
MTP No. 32, The Tactical and Technical Employment of Chemical Weapons
Part I, Chemical Warfare Units, Organization, Employment and Training, April 1940
Part II, The Projector, 1940
Part III, The Cylinder, 1940
Part IV, The Bulk Contamination Vehicle, June 1940, Amendments (No. 1) 1941
Part V, The Chemical Mine, February 1940
Part VI, Bombs, Ground, 6-lb, March 1940, reprinted in Canada April 1940
Sad as it may sound I appreciate knowing what the printer's imprint is for these pamphlets [reads something like
B121 Wt1234 23,000 10/41 H&S Gp123)