LINSEED OIL. 



399 



Tunis. — Susa, Monastir, Media, Sfax, and Biserta, are the best olive 

 districts in the Eegency, there being at the former place upwards of 

 4,000,000 trees, and if the cultivation were more energetically attended 

 to double the crops could easily be produced. The olives are gathered 

 in December and January, the pickers using leather coverings to the 

 fingers. There are two kinds of oil, the " masri," strong in flavour 

 and smell, and the " drup-el-ma," which is deprived of both by being 

 passed through water. 



In the ten years ending with 1871 the quantity of oil shipped from 

 Tunis amounted to 2,639,050 metalli, valued at 100,000,000 piastres. 

 Italy and France receive the largest quantity, England and Austria 

 rank next in order. In 1873 the shipments were 3472 tuns, valued at 

 125,893Z. 



Linseed Oil is obtained from the seed of the flax plant (Linum 

 usitatissimum), formerly called lint-seed. We used to obtain almost 

 all our supply of the seed from Russia, but now we get a good deal 

 from India. Of the imports in 1875, 369,163 quarters came from 

 India, and the rest from the Continent, chiefly Russia. The aggregate 

 value of the seed received was 4,675,242/. As a general rule, the 

 colder the climate in which the seed is grown the greater are the 

 drying properties of the oil, although it is not so good in colour. 

 The East Indian seed is much mixed with rape and other seeds. 



There are two varieties of this oil. The most valuable is the 

 " cold drawn," which is extracted by cold pressure, and is paler, less 

 odorous, and has less taste than that obtained by the aid of heat. By 

 cold expression, the yield of oil is from 21 to 22 per cent, of the 

 seeds ; with the aid of heat, combined with a powerful and long- 

 continued pressure, as much as 28 per cent, can be obtained. If a 

 very fine oil be required, the process of cold expression must be 

 pursued ; and as the utmost degree of purity is the great deside- 

 ratum in varnish-making, this quality is generally employed by 

 makers of high-class varnish. A very good oil, however, may be 

 obtained by a steam heat not exceeding 200°. 



The marc remaining after the expression of the oil is generally 

 known as oilcake, and is an article of great importance to the 

 agriculturists of those countries in which flax is grown, being 

 extensively employed, especially in the winter season, as food for 

 cattle. 



The mode of expressing the oil is as follows : The seed is first 

 passed between iron rollers, in order to crack the husks. They are 

 then introduced into a hopper, through which, by means of a fluted 

 roller, they are caused to descend between the crushing rollers, after 

 passing which they fall into a receiver. They are then passed on to 

 two vertical granite mill-stones, which bruise them to a pasty mass, 

 and this is then heated to a greater or less extent by being placed in 

 pans over an open fire, or in connection with steam or boiling 

 water. 



The object of the heat is to coagulate the albumen contained in the 

 seeds and render the oil more limpid, and, therefore, more easily 

 expressed. The mass is then transferred to a hydraulic press. The 



