| "I read somewhere that
bicarbonate of soda is really useful
for cleaning. You should try it.**
Is this ethos and if so why

The sentence given above is Ethos, since it explains the belief where that belief is verbally conveyed to other person.

Explanation:

Ethos can be defined as the characteristic spirit of a culture, era, or community as manifested in its beliefs and aspirations. Ethos also refers to the power of music to influence emotions, behaviors, and even morals. Hence in the given sentence, the usage of bicarbonate soda was explained and it was conveyed as the fact was read somewhere else. Hence this matches to Ethos.