In any legal proceedings, evidence as to the nature of the whole or part of a sample of a thing –

(a) taken from a parcel of the thing; or

(b) taken from a quantity of the thing that was, at the time when the sample was so taken, represented as being, or as being part of, a bulk lot of the thing –

in the performance of a function conferred by this Act, is evidence as to the nature of the whole of the contents of the parcel or bulk lot, as the case may be.