According to "Preliminary Inventories, Number 101, War Department Collection of Confederate Records," published by the National Archives in 1957, "the identification of many of the volumes described in this inventory by chapter and volume numbers has its origin in the early determination by the Federal Congress to publish documents relating to the War of the Rebellion....It was in the course of selecting suitable documents for this publication [The War of the Rebellion: A Compilation of the Official Records of the Union and Confederate Armies], apparently, that the bound volumes were classified, according to a crude approximation of provenance, into groups called 'chapters,' and the volumes numbered serially within each 'chapter'." So, the reference you have is from Chapter 10, volume 21. These records, according to the Preliminary Inventory, were among those of Chapter 10 -- the Confederate Department of the Treasury, Second Auditors Office -- and volume 21 --Record of Deceased Soldiers' Money Effects That Were Turned Over to Quartermasters. This volume "shows date money was received, receipt number, deceased soldier's name, rank, organization, and amount of money received. Entries are arranged alphabetically by initial letter of soldier's name." Hope this helps.