École d'Orgue was first published in 1862. The edition by Gigout in 1920 seems to be the more well-known edition of the work. The numbering of the pieces in other editions of École d'Orgue (see the editions on IMSLP) refer to his edition, although he emits 8 of the pieces present in the original edition.
This Communion belongs between numbers 11 and 12 of the Gigout edition. In editions since Gigout it is therefore referred to as 11b.
Pierre Gouin has published them all, and his edition is readily available on IMSLP. Nr 11b is here: http://imslp.org/wiki/Special:ImagefromIndex/130909
The score indicates a play between f and p. But since every sentence is divided into three segments, I make it a play between the three manuals, from f to p to pp.