THE NITROGEN-FREE EXTRACT OF FEEDING STUFFS. 649 



leguminous plants (leguniiu aud couglutin) contain, according- to liitt- 

 hauseu, 17 to 18 per cent of nitrogen, and some globulins contain 

 nearly li> per cent. On the other hand, some of the proteids of milk 

 are found to luive only 15 per cent of nitrogen; and other nitrogenous 

 substances, as amids, etc., have still other nitrogen contents.' Ilence, 

 by usiug the average factor 6.25 a greater or less error in the protein 

 content wUl sometimes be involved, which is naturally reflected in the 

 nitrogen-free extract. But the various uncertainties in connection with 

 the determination of crude fiber are of much greater influence on the 

 amount of nitrogen-free extract, as will be seen below. 



UNCERTAINTIES IN THE DETERMINATION OF CRUDE FIBER. 



The fact that the crude liber is not wholly insoluble in the reagents 

 used in the Weende method is a disturbing element in the determina- 

 tion of nitrogen- free extract by difference. If some of the crude fiber 

 is dissolved by the dilute acid and alkali the nitrogen -free extract will 

 be too high; and, on the other hand, if the crude fiber is not suffi- 

 ciently j)ure the nitrogen-free extract will be too low. 



In this connection, the questions arise, What is crude hber, and upon 

 what is its determination based? 



Heuneberg designated as crude fiber the residue remaining after 

 treating the feeding stuff with 1.25 per cent sulphuric acid, water, 1.25 

 per cent potassium hydroxid, water, alcohol and ether, and which con- 

 sisted i)rincipally of the cellulose of the plant. He stated' that this 

 name was preferable to woody fiber (cellulose), and furthermore that 

 crude fiber was of a mixed nature. 



Besides true cellulose, crude fiber contains some of the lignin sub- 

 stances which are entirely different from cellulose in their physiological 

 action. These substances sometimes remain almost comi:)letely intact 

 during the boiling with acid and alkali, but sometimes they are more 

 or less dissolved. This will naturally depend primarily on the exact 

 method of analysis employed; and as Henueberg's original method has 

 been variously modified from time to time, it will be of interest to notice 

 some of the original communications on the method. 



The methods of crude fiber determination. — Henueberg ' gives the fol- 

 lowing directions for his methods : About 3 gm. of the well ground sub- 

 stance is boiled for ouehalf hour in a porcelain dish with a mixture of 

 50 cc. of 5 per cent sulphuric acid and 150 cc. of water, the volume 

 being ke])t constant by the addition of water as it e\aporates. In 

 order to keep the volume constant at 200 cc, it was recommended, as a 

 result of the investigations of Wattenberg,^ carried on in Henneberg's 



'Conceiuiu!;' this (juestion, see a recent article by Ritthauseu in Lauclw. Vers. 

 Stat., 47(1896), p. 391 (E. S. R., «, p. 279). 

 - Weeiuler I5eitr;i,ne, vol. 2, j). 49. 



^Hennebci'g and Stohnianu, Weender Beitriige, vol. 2, p. 48. 

 ■'Jour. Laiidw,, 2S (1880), p. 273. 



1178G— i^o. 8 2 



