There was a Reformed Presbyterian minister in the 19th century by the name of Nathan Robinson Johnston (1820-1904, known for his missionary endeavors among the Chinese in California, among other things), who wrote a fascinating biography titled Looking Back From the Sunset Land; or, People Worth Knowing (1898). He was "a lineal descendant of Sir Archibald Johnston, or Lord Warriston whom the Scotch Covenant-breakers hung in Edinburgh," as he himself notes. Among the interesting vignettes of which he writes, there is one involving Sankey that is very poignant. As a Reformed Presbyterian, he held to the practice of exclusive psalmody -- that is, singing the Psalms alone in worship. But he writes candidly of an encounter with Sankey that resonates over a century later.
...together we listened with rapture to Mr. Moody's song companion, Ira D. Sankey. By the way, if ever an 'old Psalm-singer' is tempted to become a hymn-singer it must be at those meetings where everybody joins in chorus with Mr. Sankey in some of his songs as no other can sing them. By the way again, Ira D. Sankey might not be the last one to be brought to our belief in the exclusive use of the inspired songs of the Bible. He has a great admiration for them, and he once said to me that he would like to use them if they were more beautifully versified. His emphasized statement is that in his public singing he is only 'singing the Gospel.' As yet, however, he is far from accurate in his views. Some years ago, in pleasant talk with him in San Francisco, I could not convince him that the 'psalms, hymns, and spiritual songs' mentioned by Paul are all found in the book of the Bible called the 'Book of Psalms.' Nor is Mr. Sankey alone in his opinion. Some good people believe that the 'hymn' which Jesus and his disciples sang after the Passover and before he went out to the Mount of Olives, was only the effusion of some poetic genius among his followers. (Looking Back From the Sunset Land, pp. 569-570)