"Sir,—Wishing a few days since, to calcine some tin, I weighed out two pounds six ounces of the finest sort, from England, put it into an iron vessel fitted to an open furnace, and keeping it continually stirred over a strong fire, without adding any thing, I converted it in six hours, into a very white . I weighed it to ascertain the loss, and found there were two pounds thirteen ounces of it. This occasioned me incredible astonishment, not being able to imagine, from whence the seven ounces of increase could be derived. I made the same trial with lead, of which I calcined six pounds, but in this I found a loss of six ounces. I have inquired the cause of many learned men, particularly of Dr. N. but no one has been able to declare it."