116 METHODS OF ANALYSIS. 



50 cc of the liquid at room temperature. The liquid must be saturated with 

 the salt, but a large excess should be avoided, as it is likely to cause bumping 

 in the subsequent determination of nitrogen. Let stand several hours, filter, and 

 wash the precipitate with snturated zinc sulphate. In case the precipitate is 

 voluminous, which rarely happens, mr.ke up the mixture to a definite volume 

 with saturated zinc sulphate, filter, and determine the nitrogen in an aliquot 

 of the filtrate ; determine the nitrogen of the precipitated proteids by difference. 



(g) GELATIN STUTZER'S METHOD MODIFIED. 6 PROVISIONAL. 



Boil 10 grams of the sample for a few minutes with water ; filter, wash, and 

 evaporate the filtrate to dry ness in a porcelain dish of about 10 cm diameter, 

 after the addition of about 20 grams of sand which has been freed from dust by 

 sifting, and thoroughly ignited. Exhaust the residue with four 100 cc portions 

 of absolute alcohol and pass the supernatant liquid through an asbestos filter, 

 whi:-h rests on a porous plate of about 4 cm diameter, in a funnel. The funnel 

 is surrounded by pounded ice and attached to an aspirator, by means of which 

 gentle and gradually increasing suction may be applied. Take care to trans- 

 fer as little as possible of the insoluble residue to the filter. Extract the 

 residue repeatedly with 100 cc portions of a mixture containing 100 cc of 95 per 

 oent alcohol, 300 grams of ice, and 600 grams of cold water, taking care that 

 the temperature shall not exceed 5 C. Continue the extraction until the vari- 

 ous portions of solvent used are entirely colorless. Filter the extract through 

 the funnel employed for the alcohol extract. Finally, return the asbestos filter 

 to the beaker which contains the exhausted residue and thoroughly extract the 

 whole with boiling water. Receive the hot water extract in a Kjeldahl flask, 

 determine nitrogen, and multiply the percentage of nitrogen by 5.55 to obtain 

 the percentage of gelatin. 



(h) PROTEOSES. PROVISIONAL. 



Deduct the nitrogen in the gelatin precipitate (g) from that of the proteose 

 and gelatin precipitate. Multiply by 6.25 to obtain the percentage of proteoses. 



(i) MEAT BASES. PROVISIONAL. 



Deduct from the total nitrogen (a) the sum of the nitrogen (b), (c), (d), 

 (f). and (g). Multiply the difference by 3.12 to obtain the percentage of meat 

 bases. 



8. Glycogen. Provisional. 

 Proceed as directed on page 110, under "Meat." 



9. Detection of Preservatives. 

 Proceed as directed under " XXVII. Food Preservatives," page 179. 



" Zts. anal. Chem., 1895, 84: 568. 



" U. 8. Dept. of Agr., Bureau of Chemistry, Bui. 1.",. Tart 10, p. 1397. The results ob- 

 i by this method do not include the products found by the protracted digestion of 

 latin with acids or boiling water 



