A sound level meter is used for acoustic sound that travels through air measurements. It is commonly a hand-held instrument with a microphone. The best type of microphone for sound level meters is the condenser microphone, which combines precision with stability and reliability. The diaphragm of the microphone responds to changes in air pressure caused by sound waves. That is why the instrument is sometimes referred to as a Sound Pressure Level SPL Meter. 

 

Chloroscope is an instrument used to check the residual chlorine in drinking water. In this test, a chlorinated water sample is taken in a glass tube after the required contact period. To this, a stipulated quantity of chemical reagent is added. The color formed is observed after 5 minutes. The formation of yellow color normally indicates the presence of chlorine (either combined or free) in the water. The more yellow color, the greater is the chlorine residual. The amount of residual chlorine can be ascertained by comparing the colour developed in the glass tube with the standard colors already kept in the laboratory. This test, is therefore, very simple and does not require much technique or time.