Dr. Isaac Van Alphen was Postmaster General during the Transvaal Second Republic,"The Transvaal - A Challenge" by Alan Drysdall in Gibbons Stamp Monthly, June 1997, pp. 47-49. appointed on April 1, 1885.
See also Friederich Jeppe Postage stamps and postal history of Transvaal
References
External links
https://www.nytimes.com/1897/06/03/archives/kruegers-namesake-dead-transvaals-postmaster-general-learns-of-his.html