The study of the Bible was Kaulen's aim from the beginning. He kept it before his mind even when engaged in the ministry or in the conferences at the theological school of Bonn; and nearly all his works refer to it or kindred subjects. His principal works are:
"Lingu Mandschuric Institutiones", a grammar of the Manchu language
"Librum Jonae exposuit Fr. Kaulen", or a commentary on the Book of Jonas
"Geschichte der Vulgata", or a history of the Vulgate
"Sprachliches Handbuch zur biblischen Vulgata", or a linguistic manual to the Latin Vulgate
"Einleitung in die Heilige Schrift Alten und Neuen Testamentes", or Introduction to the Sacred Scripture of the Old and New Testament
"Assyrien und Babylonien"
"Der biblische Schöpfungsbericht", or the Biblical account of the creation
"Thomas von Villanova, ein Büchlein von der göttlichen Liebe", or a book on Divine love
three books of devotion, "Alleluja", "Brot der Engel" or Bread of the Angels, and "Die ewige Anbetung" or the perpetual adoration.
The grammar to the Vulgate, the "Introduction" and "Assyria and Babylon" passed through several editions. The work on Babel was attacked by August Friedrich Pott, in an 1863 book Anti-Kaulen. A lasting monument of his theological learning is found in the second edition of the "Kirchenlexikon". The first edition of his work which comprised 11 volumes, a supplement, and a general index, was issued by the publishing firm of Benjamin Herder. A second edition soon appeared necessary: in 1877 the editorship was entrusted to Joseph Hergenröther, then professor in Würzburg, but, at the elevation of the latter to the cardinalate in 1879, was finally given to Kaulen, who presided over the work until it was completed. The new or second edition comprises twelve volumes and a general index; the first volume appeared in 1886, the last in 1901, and the index, prepared by Hermann Joseph Kamp, with an introduction on the divisions of theology by Melchior Abfalter, in 1903. Kaulen was helped by Hermann Streber, by A. M. Weiss, O.P., who prepared the catalogue of subjects, and by a large number of learned contributors, the list of whom is given at the end of the last volume. The part taken by Kaulen consisted in editing the articles contributed, in revising several articles taken over from the first edition, and in contributing many articles of his own; the enumeration of his personal contributions fills almost five columns in the general list of contributors.
