Collecting gases made on a laboratory scale

The diagrams show four ways of collecting gases that have been prepared on a laboratory scale. 
Which of these is appropriate depends on the water solubility and density of the gas.

 
Water displacement
Can be used for gases of any density provided the water solubility is low
Gas syringe
Can be used  for collection of any gas.

Upward delivery
Can be used for gases with density less than air.

Once collected, the gas test-tube should be kept upside down (or its contents will be displaced by air).
Downward delivery
Can be used for gases that have a higher density than air.