Hydrochloric Acid/ Formic Acid Decalcification Solution is a combination to illustrate the best decalcifying agent by Lillie. Formic acid permits satisfactory nuclear and marrow cell staining. Hydrochloric Acid rapidly decalcifies compact bone in 12 to 24 hours. Like any acid solution, swelling of tissue is characteristic after extended periods. Reagent alcohol may be added to the solution to remedy the swelling action.