Which Christian denomination removed trinitarian language from the hymn "Holy, Holy, Holy"?

In a [brief article on the Trinity](https://en.wikisource.org/wiki/Articles_on_the_Westminster_Confession_of_Faith/4) by Gordon H. Clark, he makes a surprising claim about a popular trinitarian hymn: > The hymn book of one denomination has rewritten "Holy, Holy, Holy," so as to exclude all reference to "God in Three Persons, Blessed Trinity." I'd like to know what hymn book and denomination he's referring to. [Wikipedia](https://en.wikipedia.org/wiki/Holy,_Holy,_Holy) doesn't mention any such rendition, and he doesn't provide any other identifying information about this denomination. It's possible that the following paragraph's contrast to the "Presbyterian church" indicates that the change was made in a non-presbyterian hymnal, but that's not definitive. And this article was written in 1954, so the hymnal must have been published before then, but probably not long before. Which denomination and hymnal is Clark likely referring to?