Count (number) and Noncount (amount) Nouns
Some nouns can be counted: examples, for example
1, 2, 3, 4 examples? YES
A number of examples
Some nouns cannot be counted: evidence, for example
1, 2, 3, 4, evidences? NO
The amount of evidence
Just as you would never say 3 evidences, you should also never say: The amount of examples I offer in my essays.
Since they can be counted, those examples are referred to as the number of examples you include in your essays.
On the other hand, no matter how many pieces of evidence you bring to your essay, you would never refer to the number of evidences. The pieces can be counted, but evidence cannot, so we refer to the amount of evidence.