Final answer:
The main purpose of the band on the upper end of a Draeger Tube is to indicate the starting point for gas or vapor concentration measurements and align the tube with the concentration scale.
Step-by-step explanation:
The main purpose for the band (frosted portion) on the upper end of a Draeger Tube is to indicate the starting point for measuring a gas or vapor concentration. This band is called the measuring range indicator (MRI) and is used to align the bottom of the tube with the corresponding concentration scale for accurate measurements.
For example, let's say you are measuring the concentration of a specific gas using a Draeger Tube. You would first break off the tips of both ends of the tube, and then locate the band on the upper end. This band represents the starting point for gas measurement, and you would align it with the appropriate concentration scale on the tube. As you draw air through the tube, the chemicals inside react with the gas of interest, and the length of the color change, which occurs within the tube, is used to determine the concentration of the gas. By aligning the band with the concentration scale, you ensure accurate measurements.
In summary, the band or frosted portion on the upper end of a Draeger Tube, known as the measuring range indicator (MRI), is used to align the tube with the corresponding concentration scale and serves as the starting point for accurate gas or vapor concentration measurements.