212 III. DIGESTIBILITY OF FATS 



making use of a filter stick, approximately 150 ml. of 5% sulfuric acid (by 

 weight) are added. In the course of this addition, the material adhering 

 to the filter stick is washed into the flask ; the mixture is then refluxed for 

 one hour and filtered. The residue is again washed with hot water, 

 ethanol, and finally with diethyl ether, and is dried while remaining in the 

 flask. Following this, 20 ml. of 72% sulfuric acid are added to the flask, 

 and it is allowed to stand for two hours, with occasional stirring. Then 

 125 ml. of water are added; the residue is filtered and is washed with 15 

 to 20 ml. of hot water. Again the residue from the filter stick is returned 

 to the flask with the aid of 3% sulfuric acid; the volume is made up to 

 150 ml. and the mixture is refluxed for two hours. After filtering into 

 a Gooch or alundum crucible, the residue is washed with hot distilled 

 water until free from acid. Lignin is determined by the loss of weight of 

 the substance (dried at 105° to 110°C.) on ignition at 600°C. 



b. Chromic Oxide. Several methods have been employed in the deter- 

 mination of chromic oxide in food or feces. These include the method of 

 Paloheimo and Paloheimo, 59 Edin et al., 2i the "reference-substance" 

 method of Barnicoat, 28 that of Kane and associates, 19 and of Schurch, 

 Lloyd, and Crampton. 35 



According to the method of Schurch et al., a sample of 1 to 2 g. of food 

 or feces, containing 20 to 50 mg. of chromic oxide, is ashed in 75 ml. nickel 

 crucible at about 600°C. When this is cooled, about 1 g. of sodium per- 

 oxide is added, it is well mixed with the ash by swirling the crucible, and 

 the mixture is fused at a low red heat until liquid. The heating is con- 

 tinued for five minutes at low red heat, during which time the mixture in 

 the crucible is swirled occasionally. After cooling, the crucible is placed 

 in a 500 ml. beaker. Cold distilled water is added to the crucible; after 

 an interval of five to ten minutes, to allow for dissolving the residue, the 

 solution is poured into the beaker and the crucible is washed several times 

 with hot distilled water. After the solution has stood for thirty minutes 

 in the beaker, it is filtered. The residue is washed with warm distilled 

 water, this filtrate is added to the original solution, and the extract is 

 made up to 500 ml. The concentration can be determined on a photo- 

 electric colorimeter, using a 440 m/x filter or a spectrophotometer. The 

 concentration of Cr 2 3 is then read from a calibration curve. 



(8) Special Methods for the Calculation of Digestibility of Lipids 



When the diets contain large amounts of indigestible material, the cal- 



59 1.. Paloheimo and I. Paloheimo, Bieder mantis Zentr., Abt. B., Tierernahr., 7, 317— 

 324 (1935). 



