10 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



entire contents of a can through a sausage mill as directed above. Remove sausage 

 from the casings and mix by repeated grinding in a sausage mill. Dry that portion 

 of the sample which is not needed for analysis, extract with gasoline which boils 

 below 60 C, allow the gasoline to evaporate spontaneously, and expel the last traces 

 by heating for a short time on the steam bath. Neither the meat nor the separated 

 fat should be heated longer than necessary, owing to the tendency of the latter to 

 decompose. Reserve the fat for examination according to the methods given under 

 the examination of edible fats and oils (page 20) . Fat must be kept in a cool place, 

 and its examination finished before it becomes rancid. 



4. DETERMINATION OF WATER. a 



Dry to constant weight about 2 grams of the macerated sample, in a tared, flat- 

 bottomed dish ac the temperature of boiling water. The dish may be of aluminum 

 or platinum, or a tin bottle cap answers admirably for this purpose. On account of 

 the oxidation of the fat, meats may be dried to advantage in a current of hydrogen 

 or -in vacuo, although satisfactory results are obtained in the above way. Drying 

 usually requires about five hours. 



5. DETERMINATION OF ASH. a 



Ignite the residue from the determination of water to low redness as long as smoke 

 or inflammable gases are given off. Exhaust the charred mass with 5 or 10 cc of 

 water, transfer to a filter, and wash with hot water till the greater part of the soluble 

 salts are removed. Transfer filter paper and contents to the original dish and ignite 

 at bright red heat till combustion is complete (a white ash can rarely be obtained) . 

 Transfer the soluble portion to the dish, add a few drops of ammonium-carbonate 

 solution, evaporate to dryness, heat for a moment in a free flame to very low redness, 

 cool in a desiccator and weigh. Satisfactory results may often be obtained without 

 exhaustion by igniting 0.5 gram of the substance in a porcelain crucible cover. 



6. DETERMINATION OF ETHER EXTRACT. 



It has recently been shown that fat can not be completely extracted from meat by 

 means of ether. A complete extraction can be obtained only after digesting the pro- 

 teids and muscular tissue with pepsin and extracting again with an organic solvent. 

 Voit b extracts first with alcohol, to remove the last traces of water, and then with 

 ether in a continuous extractor. This process leaves ^ery little fat in the sample. 

 Comparative results which are satisfactory in all ordinary examinations of meat may 

 be obtained by extracting 2 grams of the dried,- finely divided sample with ether for 

 16 hours in a continuous extractor. Fat may be determined by extracting the ether 

 extract with low boiling-point petroleum ether. 



7. DETERMINATION OF NITROGENOUS SUBSTANCES. 



(a) TOTAL NITROGEN. 



Employ either the Kjeldahl or the Gunning method, using about 2 grams of the 

 sample. The digestion with sulphuric acid should be continued at least 4 hours. 



(b) COAGULATED PROTEIDS. 



Thoroughly exhaust 2 grams of the sample with cold water after extraction with 

 ether, filter, and determine nitrogen in the insoluble residue as directed under " Total 

 nitrogen." Multiply the percentage of nitrogen so obtained by 6.25 for the percent- 



See Appendix, p. 149. b Ztschr. f. Biol., 1897, 35, 555. 



