Perhaps the most curious of all these works is the _Rosarium_, which is intended as a complete compend of all the alchymy of his time. The first part of it on the theory of the art is plain enough; but the second part on the practice, which is subdivided into thirty-two chapters, and which professes to teach the art of making the philosopher’s stone, is in many places quite unintelligible to me. He considered, like his predecessors, mercury as a constituent of metals, and he professed a knowledge of the philosopher’s stone, which he could increase at pleasure. Gold and gold-water was, in his opinion, one of the most precious of medicines. He employed mercury in medicine. He seems to designate bismuth under the name _marcasite_. He was in the habit of preparing oil of turpentine, oil of rosemary, and spirit of rosemary, which afterwards became famous under the name of Hungary-water. These distillations were made in a glazed earthen vessel with a glass top and helm. His works were published at Venice in a single folio volume, in the year 1505. There were seven subsequent editions, the last of which appeared at Strasburg in 1613. 6. John Isaac Hollandus and his countryman of the same name, were either two brothers or a father and son; it is uncertain which. For very few circumstances respecting these two laborious and meritorious men have been handed down to posterity. They were born in the village of Stolk in Holland, it is supposed in the 13th century. They certainly were after Arnoldus de Villa Nova, because they refer to him in their writings. They wrote many treatises on chemistry, remarkable, considering the time when they wrote, for clearness and precision, describing their processes with accuracy, and even giving figures of the instruments which they employed. This makes their books intelligible, and they deserve attention because they show that various processes, generally supposed of a more modern date were known to them. Their treatises are written partly in Latin and partly in German. The following list contains the names of most of them: 1. Opera Vegetabilia ad ejus alia Opera Intelligenda Necessaria. 2. Opera Mineralia seu de Lapide Philosophico Libri duo. 3. Tractat vom stein der Weisen. 4. Fragmenta Quædam Chemica. 5. De Triplice Ordine Elixiris et Lapidis Theorea. 6. Tractatus de Salibus et Oleis Metallorum. 7. Fragmentum de Opere Philosophorum. 8. Rariores Chemiæ Operationes. 9. Opus Saturni. 10. De Spiritu Urinæ. 11. Hand der Philosopher.