I wouldn't fool around with 10 year old cakey chemistry. Whatever caused it to become cakey is not going to be of benefit when using it.
I've switched to Arm & Hammer Super Washing Soda, it is all Sodiulm Carb - Mono with no perfumes or phosphates. It sells for about $2.30 for a 55 Oz. box and is available in almost any grochery store. Just make sure it is washing SODA, not degergent.