492 PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 



is ground, and is then exposed to heat in a pan heated by steam, 

 a small quantity of water being added to it in the pan. The seed 

 is then introduced into bags made of a coarse kind of cloth, and 

 exposed to powerful pressure in hydraulic presses. The quantity 

 of oil obtained in this way depends, of course, on that existing in 

 the seed, and also on the length of time it is exposed to pressure, 

 which is usually about ten minutes. The oil then obtained 

 amounts to rather more than one-fourth of the seed, and the- 

 remainder constitutes the cake. In making my calculations, I 

 have assumed that in every case the residual oil amounts to 9 

 per cent., and that the water added in damping the seed amounts 

 to 4 per cent. When the calculation is made on this footing, it 

 will be seen that the result approximates closely to that of average 

 oil-cakes. 



Irish Linseed. — This sample was remarkably clean and uni- 

 form in size of seeds and appearance throughout, the seeds being- 

 small and fiat. It contained only 1-5 per cent of impurity. It 

 contained — 



A moment's inspection shows that the calculated composition of 

 the cake which this seed should yield tallies well with that of 

 an ordinary average quality. The ash, indeed, is somewhat lower 

 than is usually found, but it must be remembered that in this 

 case every impurity was separated, while in practice the best of 

 linseed must always contain dust and a few foreign seeds. In 

 this particular case the impurity contained in the seeds consisted 

 chiefly of a small seed, apparently charlock or wild mustard, and 

 its quantity was far too small to have any effect on the composi- 

 tion of the cake. 



St Petersburg Linseed, No. 1. — A good sample, with 447 per 

 cent, of impurities, consisting of a mixture of all the seeds 

 usually found in linseed. 



