what is the purpose of the double bell jars that surround the international prototype of the kilogram in Paris?
Isn't it to keep the air out and reduce the chance of oxidation?
Is there a vacuum under the jars or is it just been air sealed with air already under it?
There is a vacumn.
The purpose of the double bell jars that surround the International Prototype of the Kilogram in Paris is to protect the kilogram from any external influences that could potentially alter its mass. These bell jars, made of special material, create an isolated and stable environment for the prototype.
To understand why the bell jars are necessary, let's delve into the concept of the International Prototype of the Kilogram. Historically, the kilogram was defined as the mass of a specific platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM) in France. However, over time, it was discovered that this physical object, known as the "Big K," was subject to slight variations in mass.
In order to overcome this issue, a new definition of the kilogram was introduced. Since 2019, the kilogram is defined by a fundamental constant of nature called the Planck constant. This constant is used to determine the mass of the kilogram through precise measurements.
However, the International Prototype of the Kilogram is still crucial for historical and practical purposes, and it serves as a reference against which measurements are compared. Hence, it must be protected from any factors that could lead to a change in its mass.
The double bell jars provide a controlled environment to minimize the impact of external factors such as dust, humidity, and contamination. The jars are designed to maintain a stable and low-pressure atmosphere, shielding the prototype from any disturbances that might affect its mass.
In summary, the double bell jars surrounding the International Prototype of the Kilogram in Paris protect it from external factors that could alter its mass, ensuring its accuracy as a reference for kilogram measurements.