FIXED OILS. 207 



limpid. This method of purification is equally ap- 

 plicable to all other seed oils. Another process has 

 been recently recommended somewhat similar to the 

 above, which consists in the admixture of dilute 

 sulphuric acid, and the subsequent introduction of 

 steam into the oil, whereby it is more entirely freed 

 from all acid. This is said to be an improvement 

 on M. Thenard's method. 



Rape oil thus prepared has very little smell ; it is 

 of a yellow colour, and of rather a sweet taste. This 

 oil has the advantage of remaining limpid at a much 

 lower temperature than most other oils, which useful 

 property causes it to be used in preference for street 

 lamps. 



It is of the same specific gravity as olive oil. 



The very extensive cultivation of rape for oil, 

 which has been made of late years on the Continent, 

 has seriously affected the trade of Italy in olive oil. 

 Besides in soap, rape-seed oil is now made to enter 

 into several other manufactures, for which, until 

 recently, Italian olive oil (chiefly from Gallipoli) was 

 always employed. In consequence of this, in 1827, 

 the value of those estates in the kingdom of Naples, 

 whose main produce was oil, was very considerably 

 reduced. 



LINSEED OIL. 



The oil drawn from the seeds of the flax plant or 

 linseed is of very general application in the arts, 

 especially in oil painting and in the composition of 

 varnishes. Linseed oil as it is first extracted is of a 

 dark brown colour. Many methods have been pro- 

 posed for divesting it of this tint, which in some 

 kinds of varnishes is an obstacle to its use. One 

 process for bleaching it, is to add litharge in the 

 proportion of two ounces to every gallon of oil. 



