Spratts Patent Ltd was a UK dog cakes (biscuit) company. Very collectible but not civil war. From Wikipedia: "Spratt's was the world's first large-scale manufacturer of dog biscuits. Its "Meat Fibrine Dog Cake" was the brainchild of American entrepreneur James Spratt who launched the biscuit in London circa 1860. The company began operations in the United States of America in the 1870s and, after Spratt's death in 1880, the company went public and became known as Spratt's Patent, Limited, and Spratt's Patent (America) Limited. Spratt's pioneered the concept of animal life stages with appropriate foods for each stage."
Maybe the container was used to store gunpowder?