M '\ Wedgwood's Experiments upon Black Wadd. 285 
Mr. woodward, as well as Mr. da costa, has defcribecl 
this earth fo minutely, that it cannot eafily be miffaken ; but 
from the following experiments it will appear, that it fhould 
not be clafled amongft the Ochres not adted upon by acids ; and 
that it may, with as great propriety, be called Manganefe as 
Ochre. 
exp. 1. Mixed with porcelain bifcuit body, it gives darker 
or lighter fhades of black and brown, as the quantity is greater 
or lefs in proportion to the body. 
exp. 2. Mixed with linieed oil, in the quantity of a few 
penny-weights only, into a pafte, it dried very flowly, with- 
out producing any perceptible fmoke or heat. The quantity, 
perhaps, was too fmall for ignition, and, I believe, it was 
ever-dofed with oil. 
exp. 3. When the mineral w-as previoufly calcined with a 
flight red heat about half an hour, the mixture of it with the 
oil dried much fooner and harder ; a circumftance which, if 
not already known, may render it ffill more valuable to the 
painter. In other refpedts no difference could be obferved. 
exp. 4. Ill the above low heat it buffers no alteration of co- 
lour or texture. In a heat of 30°, by my thermometer for 
meafuring high degrees of heat, it lofes its property of flain- 
ing the hands, diminifhes very confiderably in bulk, acquires 
a little hardnefs, though it ffill proves friable between the fin- 
gers, and has its colour changed from a brownifh to ablueifh 
black. In a heat of 8o° it begins to melt; and at 95° runs 
into a black fcoria. 
exp. 5. With black flux, in a heat of 90 , by the above- 
mentioned thermometer, it yielded a button of lead, amount- 
ing, in one experiment, to 21 ; and in another to 22 grains 
from an ounce, or nearly T * T . 
EXP. 
