The international standard Kilogram in Paris is stored under double bell jars. What is the prupose of the jars?

Is it because the jars create a vacuum to prevent the standard from gaining mass due to oxidation? If so, why double jars? Are there any other reasons?

An interesting question. I would imagine that the bell jars serve several purposes, for example a) reducing the airborne contaminations that the standard picks up and b) ensuring that the mass is at the same temperature as the room. I believe the mass is stored in atmospheric air.

I know that the standard is periodically cleaned and there is a complicated protocol to do this.

You could try googling for the standard kilogram and see what you can find.

I hope this helps.

The purpose of storing the international standard Kilogram under double bell jars in Paris is primarily to protect it from contaminants and external influences that could affect its mass. Let's break down why the jars are used and why there are two of them.

1. Protection from contaminants: The double bell jars help create a controlled environment around the Kilogram to shield it from dust, gases, and other pollutants that could potentially affect its mass. The jars act as a barrier against these contaminants, preventing any interaction between the standard and its surroundings.

2. Vacuum sealing: One of the key reasons for using the double bell jars is to create a vacuum. By removing the air inside the jars, the standard is isolated from the oxygen in the atmosphere. This prevents oxidation, as you mentioned, which could potentially alter the mass of the Kilogram. Oxidation can lead to the formation of a thin layer on the surface of the standard, affecting its weight.

3. Stability and redundancy: Having two jars serves as a safety measure to ensure the stability and accuracy of the standard Kilogram. In case one of the jars becomes compromised or contaminated, the second jar provides redundancy and continuing protection for the standard. This redundancy helps minimize any potential impact on the mass of the Kilogram due to external factors.

It is important to note that the double bell jars are not the only means used to prevent the standard Kilogram from gaining mass. The jars are part of a comprehensive system that includes periodic cleaning and calibration processes to maintain the accuracy and integrity of the standard over time.