In this phrase, "unto" is there for emphasis. You could say "like bullion" and the result would be the same, though less artful. Bullion is word for gold or silver bars. So the full meaning of the phrase is that he thinks "Jacob Astor" has a similar aesthetic feel to the word "bullion" when he says it. This isn't about the meaning of the words ("Jacob Astor" and "bullion"), so much as it is about the way he feels when he says them.

I can understand only a few words of old English. However I can understand the novel just fine because, although it is a little dated, it's not old English but modern stuff. Well, ok not REALLY modern! 'Like unto' was a common compound preposition 300 years ago. But gradually the 'unto' got left off till it was just 'like.' Translators of Islamic texts seem fond of using the old 'like unto' formula in their modern texts so perhaps it will make a comeback! I do feel that 'like unto' adds a lot of meaning that just 'like' can't give. Only I'm not sure what! Any scholars out there who can tell me why I LIKE 'like unto' ???

@Michael Patrick, this is not Old English, it's just slightly dated Modern English. Old English looks like this: "Þa cydde man me, þæt us mara hearm to fundode, þonne us wel licode", and is quite incomprehensible to speakers of Modern English.

This is Old English. Words like hence, and unto. Do I use these words ? yes,but not that much. Here's a site that goes into the word unto : http://sentence.yourdictionary.com/unto . The word hence though, I do use beacuse it shows off your vocabulary. People of William Shakespear's time used it quite a bit, including Shakespear himself. The one thing I wanted to tell you as yoy learn english is, try not to use the words BUT and the word AND at the beginning of a sentence. The sentence will not flow well. I'm learning Korean right now kind of slowly. at work I see 3 korean people whom I say "Hello", "Thank You", "Have a nice day" and "Goodbye" to everyday. Anyway, I wish you nothing but the best in your quest to learn english.