Understanding the Difference Between Troy and Avoirdupois Systems: A Chemist's Explanation

Many questions arise when dealing with the various systems of measurement used for precious metals. The saying, 'In America, is an ounce of silver heavier than an ounce of lead but a pound of lead is heavier than a pound of silver,' encapsulates this confusion. This article aims to clarify these concepts from a chemist's perspective, helping to rectify misconceptions.

Overview of Measurement Systems

In the United States, two distinct systems of measurement are commonly used: the Troy system and the Avoirdupois system. Each system serves different purposes and can lead to confusion when comparing weights of materials like silver and lead.

Troy System: Used for Precious Metals

The Troy system, named after the French town of Troyes where it was used in the 14th century, is specifically designed for measuring precious metals such as gold and silver. It is based on a Troy ounce, which is heavier than the more common avoirdupois ounce. A Troy ounce is standardized at approximately 31.1035 grams.

Avoirdupois System: Used for General Weights

In contrast, the Avoirdupois system is used for general weights and measures, particularly for non-precious metals and other commodities. An avoirdupois ounce is lighter, with a standardized weight of exactly 28.349523125 grams.

Difference Between Troy and Avoirdupois Ounces

While an avoirdupois ounce of lead is lighter than a Troy ounce of silver, the weight comparison changes when comparing pounds. Here's the breakdown:

An avoirdupois ounce is approximately 28.3495 grams, whereas a Troy ounce is 31.1035 grams. Therefore, a Troy ounce of silver weighs more than an avoirdupois ounce of lead. However, when comparing pounds, the picture changes:

Since a Troy pound has fewer ounces (12), it is lighter than an avoirdupois pound, even though each Troy ounce is heavier than each avoirdupois ounce. Thus, a pound of lead (avoirdupois pound) is heavier than a pound of silver (Troy pound).

Confusion and Misconceptions

The saying, 'In America, is an ounce of silver heavier than an ounce of lead but a pound of lead is heavier than a pound of silver,' can be misleading because it fails to distinguish between the units of measurement. It simplifies comparisons and overlooks the standardized weights inherent to each system.

Conclusion

Understanding the differences between the Troy and Avoirdupois systems is crucial for accurate measurements in industries dealing with precious metals and other commodities. While an ounce of silver may be heavier than an ounce of lead, a pound of lead can be heavier due to the different unit structures of the two systems. This confusion highlights the need for precise and consistent use of measurement units in specific contexts.