Figure 15 is a photograph of the standard kilogram cylinder housed in a small glass bell jar. Covering this bell jar is another larger glass bell jar and covering that bell jar is another even larger glass bell jar. On the top of the largest external bell jar there is a tap and tube connection, used presumably to alter the atmosphere in the jars once they have been placed in position over the standard. Shown next to the jars is a pair of tongs designed for picking up the kilogram cylinder thereby avoiding contact by human hand, which could possibly alter the mass of the cylinder.

 1.2.4 Ammonia synthesis by bulk production