216° Mr. P. Henry on the Action ‘of, &c, 
gas, de-coloured the oils more powerfully than moft 
of the metallic oxydes, and equally with any of 
them. This earth has a ftrong attraction for colour- 
ing matter, and on this property depends its ufe in 
dying. 
“But on the fuppofition that the above theory is 
juft, it may be expected not only that the oil may be 
deprived of colour, but that rancid oils may be re- 
Rtored to {weetnefs by the metallic oxydes.. My 
Father formerly found,* that rancid oil, expofed to 
ftreams of carbonic gas, was fweetened. The fame 
effe&t may be produced by the fame gas formed in 
the procefs; and indeed, though I was not particu- 
larly attentive to this circumftance, I thought the 
train oi! was diminifhed in rancidity ; and the Sper- 
ma Ceti oil, which was kept for feveral months, after 
expofure to heat, continued {weet. 
Another circumftance, worthy of remark, is, 
that though concentrated vitriolic acid, on addition to 
oils, blackens them, and gives out a fulphureous 
{mell; yet when dropped into oils, in which the 
metallic calces have been digefted, it combines with 
the calces, and precipitates them, without either 
difcolouring the oils, or changing their odour. 
* Henry’s Experiments and Obfervations, page 129; 
