Category of the First Term in the Partitive Construction

Question

Are the words in bold type in the following sentences determiners?

1. One of the books was written by X
2. I want two of those
3. 8 percent of the population has X
4. I ate some of that cake

In a treatise on partitives, the author identifies them as determiners. But I don't see a noun following these 'determiners'. Without a following noun, they more resemble a pronoun referring to that absent noun.

Online Oxford Dictionary defines partitive as:

1. A partitive construction
   1.1. A noun or pronoun used as the first term in a partitive construction

From the definition it seems that the first term, which I think is the word or a group of words before of, is either a noun or a pronoun.

Answer 1

There are three ways to consider polysemous words:

1) as several parts-of-speech that must be disambiguated by context.

2) as new parts-of-speech that share properties of multiple existing POS.

3) as single parts-of-speech that occur with other POS elided for brevity.

By method (3) they are determiners:

One [book] of the books ...

I want two [things] of those [things].

8 [people] per_cent=one_hundred [people] of the population=people ...

I ate some [cake/part] of that [one] cake.