PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 501 



sometimes tempted to hurry on the process, so as to get a larger 

 amount of material through his hands, in which case more oil is 

 left in the cake. 



In the calculated composition of the cakes which would be 

 yielded by the different seeds analysed, I have sought to avoid 

 all questions depending on the mode of pressing, by assuming 

 that this operation has been performed in an exactly similar 

 manner in all cases. The variable results, therefore, which 

 these calculations show, are due to the difference in composition 

 of the seeds alone. In regard to the amount of oil, the varia- 

 tion is very small, and scarcely exceeds 1 per cent., while in 

 most cases it is less even than this. The quantity of water 

 varies to a greater extent ; because I have assumed that in all 

 cases, no matter what amount of that substance was contained 

 in the seed, the same quantity was used in moistening before 

 going into the press, and hence possibly I may sometimes have 

 overrated the quantity of water which would be found in actual 

 practice. I have thought it better, however, to adopt a uniform 

 system, than to make any allowance in particular cases. 



Turning to the other constituents of the cakes, we notice a cheater 

 amount of variation, and this is seen most conspicuously in the 

 albuminous compounds, to which, and to the nitrogen, which is 

 only another mode of expressing the percentage of albuminous 

 compounds, I shall mainly direct attention. The latter, it will be 

 seen, can always be calculated from the former by multiplying by 

 6 - 25. The amount of nitrogen, therefore, measures that of albumin- 

 ous compounds. Now, to the percentage of nitrogen or albuminous 

 compounds great importance must be attached in estimating the 

 quality of different oil-cakes. In regard to the estimation of the 

 feeding qualities of different substances a good deal of difference 

 of opinion exists among different authorities. Some have sup- 

 posed that, inasmuch as the process of fattening consists to a 

 great extent of the accumulation of fat in the animal frame, the 

 respiratory or fat-forming constituents of the food must possess 

 the highest value ; while others attribute, if not the chief, at least 

 a most important, influence to the nitrogenous or flesh-forming 

 substances. Without entering here on the discussion of this 

 difficult question, it may be said that oil-cake, which is the most 

 highly nitrogenous food, has been found by experience to be that 

 best fitted to promote the fattening process ; and without under- 

 rating the importance of the respiratory substances, it is impossible 

 to doubt that it is the abundance of the former which makes 

 oil-cake surpass other foods which are quite as rich, or even 

 richer in the latter. As indicating the quality of oil-cake, great 

 importance must be attached to the quantity of nitrogen. From 

 the calculated composition of the cake from pure linseed, it 

 appears that the nitrogen may vary from 3 55 up to 5 02. It is 



