Why does the test tube face downwards in gas production?

In the preparation of $$\ce{NH3}$$ from $$\ce{NH4Cl}$$ and $$\ce{Ba(OH)2}$$, my teacher said that when heating the test tube, the test tube faces downwards as opposed to upwards. Why is this so? Wouldn't the solid just fall out?

• This is from the Royal Society of Chemistry in 2016: edu.rsc.org/resources/making-and-testing-ammonia/433.article . The figures show the reaction test tube as horizontal and a suggestion is to put some CaO in that test tube to trap (some of) the water produced.
– Ed V
Mar 6 '20 at 22:55
• "As adverbs the difference between downward and downwards is that downward is toward a lower level, whether in physical space, in a hierarchy, or in amount or value while downwards is towards a lower place; towards what is below." and "In British English, downward (with no final -s) is normally only used as an adjective." Not sure which one is appropriate here. Mar 7 '20 at 21:46