Lao-Kiun

One of the more misfitted sections of Art Magic reads as follows:

Lao-Kiun, a cotemporary (sic) of the great Chinese Sage Confucius, founded a school, which, for the spirituality of its doctrines, far transcended the teachings of Confucius. His text of religious faith was: "Tao (meaning God) produced one; one produced two, two produced three, and three produced all things." During the lifetime of this philosopher, a book containing the names and offices of innumerable companies of spirits was found, as it was asserted, suspended on the royal gate of Pekin, placed there by no mortal hand, and supposed to be full of direct revelations from heaven. This miraculous volume is said have contained magical formulae for the evocation and control of spirits; directions how to cast out devils and heal diseases; also the profoundest secrets of alchemy, namely the composition of the philosopher's stone and the elixir vitae. To satisfy the bigotry and superstitious fears of succeeding generations, this book, together with all other magical writings, was destroyed. Still, it was asserted, that private copies had been
made and circulated of its contents. From a curious and very ancient roll of MSS., in the royal library of Pekin, the author has had the privilege of copying a fine astrological chart, and a magical evocation of elementary spirits, assumed to have been first written in the aforesaid book.

Leaving aside the annoying fact that we must now add China to the list of places visited by Louis de B_________, it shouldn't be too hard to track down the source of this interestingly specific anecdote.

L(ydia) Maria (Francis) Child tells it, substantially, in her The Progress of Religious Ideas Through Successive Ages (1855).

And, in all the books indexed by Google Books, that is the only location in which the anecdote appears.

That Emma ran into Maria Child in the anti-abolitionist, women's-rights circles of New York in the late 1850s is, really, quite plausible.

That a Prussian occultist and religious scholar would crib an anecdote -- involving a text he claims to have seen, directly, in China -- from a radical American proto-feminist is really beyond belief.