was / were

"Were". The subject (milliliters) is plural. I sense an argument coming along, but that's my take.

was. It's a quantity, implying singular.

A cupful was added.
50 ml was added.

I have just realised that sodium chloride is a solid, normally found in granules as common salt.

So it would normally be measured in grams, not ml.

But I suppose the question is not about chemistry.

Quantities or measurements of time, money, distance and weight usually take singular verbs when they refer to a unit, and plural when they refer to separate items.

Fifty yards is a short distance.

Ten years have passed since I finished college.

Fifty grams of sodium cloride was/were added to the mixture.

Should be 'was' or 'were'?

Many thanks.

You have already been told. Read the answers, where they mention weight.

Told, and then confused...

Tang, it's "was".