From a review of this book by Dutch theologian Tjeu van den Berk,study of Mozart's opera The Magic Flute from a Jungian and alchemical point of view:

Mozart held exactly the same view of alchemy. He belonged to a branch of the Freemasons closely linked to the Rosicrucians. Both spiritual and practical alchemy flourished in Vienna towards the end of the eighteenth century. Around the year 1780 an English visitor estimated that Vienna counted some 3000 practising alchemists.

And, for more scholarly examples of his Masonic and Rosicrucian ties, see the synopsis of this book, which includes:

Appendix II is a photo reproduction and translation of the complete article "Ueber die Mysterien der Aegyptier", written by the Master of one of the most important and active Masonic lodges in Vienna in the 1780's, Ignaz von Born. It is said to have inspired some of the plot and detail in The Magic Flute.

According to other sources Mozart attended the same Masonic Lodge as Haydn.

I have had the privilege of seeing the Charter for the Masonic Lodge in Northampton, Massachusetts which contains the signatures of its founding members, including Lafayette.

kat