'Tis pure delight without alloy. J. Watts. [Divine Love Desired.] Published in his Horae Lyricae, 1706, Bk. i., in 6 stanzas of 4 lines and headed, "Ascending to Him in Heaven." In the American Methodist Episcopal Hymns, 1849, and in their Hymnal, 1878, it is given with the omission of stanza iv. as, "O 'tis delight without alloy." It is from the original, as above, that Watts took a portion for his hymn, "Happy the heart where graces reign."
--John Julian, Dictionary of Hymnology (1907)