S48 On the Purification 
the air; let them stand together* and stir them up several 
times for the first twenty-four hours; then let them stand 
a day* and the lime-water will sink below the oil* which 
must be carefully separated from them. Take this oil* 
if not sufficiently purified for your purpose* and treat it 
as directed in Process the Third* diminishing the quanth 
ty of pearl-ashes to one ounce* and omitting the lime and 
chalks 
ILobert Dossie, 
No. 67.. 
On the Purification of Rapeseed Oil . By C. Thenard.* 
TO purify oil of rapeseed* mix one hundred parts of 
the oil with from one and a half to two parts of sulphuric 
acid* and stir the mixture. The oil will immediately 
change its colour; it will become turbid and assume a 
blackish-green tint* and at the end of three quarters of 
an hour it will be full of flakes. You must then give 
over stirring it* and add gradually double its weight of 
water to remove the sulphuric acid* which* if allow- 
ed to remain too long with the oil* would not fail to 
exercise too strong an action on it* and to char it. 
The mixture must then be beat for at least half an hour* 
to bring the molecule of the oil* the acid* and water* 
into contact with each other; after which it is to be left at 
rest. 
When it has rested about eight days* the oil will float 
on the surface of the water* and the latter will itself float 
on a black matter* precipitated from the oil by the sub 
* The dregs remaining after the sundry processes above mentioned will form 
an excellent manure, as has been since noticed in Dr. Hunter’s Georgical 
Essays. 
f Tilloch, voh 10, p. 68, From the Journal de Physique , Floreal, an. 9. 
