Dr. Fordyce on the Cause of the additional Weight, &c. 375 
be easily repeated by any person who is at all versed in che- 
mistry, and possesses those most necessary qualifications in 
this science, patience and accuracy. I am, Sir, 
Your most obliged humble servant, 
G. FORDYCE. 
It has been a great desideratum among chemists to deter- 
mine the cause of the additional weight which metals acquire 
when they are calcined. To investigate this subject, I had 
begun the following experiment many years ago, but various 
other engagements have so much interrupted me, that I have 
had but little time to pursue any other chemical inquiry than 
such as were necessary to form the catalogue of the ores and 
minerals in Dr. Hunter's museum. 
There is great difficulty in choosing the metal on which in- 
quiry should be instituted, on account of the differences of their 
calces. After a number of trials, I chose zinc, as that whose 
calces appeared to differ the least from one another ; in other 
respects there are great objections to it likewise, but which 
may be got over. 
I took a portion of the zinc I employed, and dissolved it in 
Vitriolic acid, with which it made a clear solution (without 
any of that black matter which commonly separates during its 
solution when we employ zinc imported from abroad). After 
precipitating it by an alkali, and exposing the calx to the air, 
it remained of a pure white ; so that it could contain no iron. 
This zinc was reduced to its perfect metallic form by breaking 
it into small particles, and melting it with black flux, taking 
that part of it only which was at the bottom of the crucible. 
SC2 
