4.1

The thermometer bulb must be made from a type of glass which assures that the depression of zero, determined in accordance with the specifications given in Annex B, does not exceed . The glass must be identified visibly and indelibly:

• either by the glass manufacturer

• or by the manufacturer of the thermometer (see 7.1.3)

4.2

The types of glass used for the maximum device, capillary tube, and bulb must meet the following requirements:

When the glass is analyzed according to the requirements of ISO Recommendation R 719-1968 (Determination of the hydrolytic resistance of glass grains at ), the quantity of alkali passed into solution for of glass must correspond to no more than of NaO.

4.3

The scale-bearing strip of an enclosed-scale thermometer must be made of opaline glass, metal, or a material having an equivalent dimensional stability.

4.4

The protective sheath of an enclosed-scale thermometer must be made of glass.