E620") 
XIII. Account of the Proceffes ufed by Mr. SHzLDRAKE fe 
- feparate the Mucilage from Lanfied Oil, and to diffolve 
Copal in Spirit of Turpentine, and in Alcohol *, 
To feparate the Mucilage from Linfeed Oil, 
I HAD read in fome book, the title of which I do not 
recollect, that linfeed oil might be purified by fhaking it 
with water, which would imbibe the impurities, and leave 
the oil more limpid. I tried this experiment by fhaking 
linfeed oil with warm water; and was furprifed to find they 
did not feparate, but remained united in the form of emul- 
fion. I then boiled them together, and found their tendency 
to feparate diminifh. As it is the known property of gums 
or mucilage to keep oil and water united in this ftate, T was 
induced to fufpect the prefence of mucilage in linfeed oil. 
I had read-in Doffie a method of preparing what he calls 
fat ail, Tt is effected by placing linfeed oil in a fhallow pe 
expofed to the heat of the fun, and ftirring it frequently : 
a certain time it lofes its property of drying, thickens, sc 
acquires a degree of tenacity that makes it proper for a fize 
or cement for gilders, &c. A fimilar fubftance is alluded to 
by Leonardo da Vinci. 
Taking the exiftenece of mucilage in this oil for granted, 
T conjectured that the alteration, produced in its texture by 
Doffie’s procefs, arofe from the evaporation of fome of its 
principles, and the more intimate union of the reft in con- - 
fequence of that evaporation. To verify this conjecture, I 
tried the following experiment : 
I filled a half-pint phial full of linfeed oil, corked and tied 
it fecurely over with a bladder. This I expofed to the heat 
of the fun in fummer, during the whole day: after it had 
remained a few days in this fituation, the upper part of the 
* From the Tran/a‘tions of the Society for the Encouragemeni of Arts, &c. 
Vol. XVil. The prefent may be confidered as a continuation of Mr, 
Sheldrake’s paper on Painting in Oil, in a manner fimilar to that praétifed 
in the ancient Venetian School, publifhed in Yol. XVI: for a copy of 
which fee Phil. Mag. Vol. I. ‘ 
phial 
