The density of gas can be measured by using a scale!
Fill a container with gas and weigh it, then use a vacuum pump to evacuate the container, then weigh the container again.
The difference in weight is the weight of the gas.
A very common instrument for the direct measurement of the density of a liquid is the hydrometer, which measures the volume displaced by an object of known mass. A common laboratory device for measuring fluid density is apycnometer; a related device for measuring the absolute density of a solid is a gas pycnometer. Another instrument used to determine the density of a liquidor a gas is the digital density meter - based on the oscillating U-tube principle.
The instrument that can measure the density of an earthquake is called an seismometer. The first seismoscope dates back to 132 AD.
Density = Mass / Volume. There is not an instrument that will measure both so you will need to measure them separately and calculate the density.
You do the Mass of the object then, divide the Volume away from it.
A seismograph records the intensity measured by the Ritcher Scale.
respiromterrespirometer
Lactometerlactometer
An argon gas analyzer measures the purity of Argon gas. The analyzer can be used to determine the actual content of Argon gas in a specific sample.
A hydrometer is an instrument that measures the density of liquids. Auto batteries could be checked to see the strength of the acid in each cell before sealed batteries were made. I don't know of an instrument for solids or gases.
Pressure guage
Usually in homes its just the gas meter that is checked often by city workers.
A manometer is an instrument that can be used to measure the pressure in an enclosed container that is filled with gas. The manometer is sometimes called a pressure gauge.