OBSERVATIONS. 43 
proportion is to take the mean refult of 
many experiments. 
§ *• 
Half an ounce of this tin-ore was 
heated red hot in a fmall glafs retort. 
When cold, about two drops of a fluid, 
which proved to be volatile fulphureous 
acid, were found in the receive^. In the 
neck of the retort was a little grey yel¬ 
low fublimate, about one-fourth of a grain. 
This fublimate carefully collected and 
placed upon a red hot charcoal, fmelled 
and burned at firft like fulphur, but af¬ 
terwards a fmell of arfenic was perceived. 
The refiduum had loft 3 grains. 
■ ...... 
| a. 
Two drams of this ore were flowly 
heated in an earthen veffel, till no fmell 
. of 
/ 
; 
