46 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



resistance being changed by varying the length of the acid column contained between 

 two electrodes immersed therein, one of which is movable. a 



6. DETERMINATION OF ETHER EXTRACT IN CONFECTIONERY. 



Measure 25 cc of the 20 per cent mixture or solution 2(c)(l)(6) into a very 

 thin, readily frangible glass evaporating shell (Hoffmeitter's Schalchen), containing 5 

 to 7 grams of freshly ignited asbestos fiber; or, if impossible to thus obtain a uniform 

 sample, weigh out 5 grams of the mixed, finely divided sample into a dish, and wash 

 with water into the asbestos in the evaporating shell, using, if necessary, a small por- 

 tion of the asbestos fiber on a stirring rod to transfer the last traces of the sample 

 from dish to shell. Dry to constant weight at 100, after which cool, wrap loosely in 

 smooth paper, and crush into rather small fragments between the fingers, carefully 

 transferring the pieces with the aid of a camel's hair brush to an extraction tube or 

 a Schleicher and Schull cartridge for fat extraction. Extract with anhydrous ether 

 or with petroleum ether in a continuous extraction apparatus for at least 25 hours. 

 Transfer the solution to a tared flask, evaporate off the ether, dry in an oven at 

 100 C. to constant weight, and weigh. 



Unless the ether is absolutely anhydrous, sugar will be dissolved. Ether which gives 

 off hydrogen when treated with metallic sodium is unfit to use without purification. 

 To purify it, let it stand for some time with calcium chlorid in the container, then 

 pour off and distill over metallic sodium. 



If petroleum ether is employed, it should be purified by fractional distillation so 

 that it boils between 45 and 60 C. and leaves absolutely no residue. 



7. DETERMINATION OF PARAFFIN IN CONFECTIONERY. 



Add to the ether extract in the flask as above obtained, 10 cc of 95 per cent alco- 

 hol and 2 cc of 1:1 sodium hydroxid solution, connect the flask with a reflux con- 

 denser, and heat for an hour on the water bath or until saponification is complete. 

 Remove the condenser, and allow the flask to remain on the bath till the alcohol is 

 evaporated off and a dry residue is left. Treat the residue with about 40 cc of water 

 and heat on the bath, with frequent shaking, till everything soluble is in solution. 

 Wash into a separatory funnel, cool, and extract with four successive portions of 

 petroleum ether, which are collected in a tared flask or capsule. Remove the 

 petroleum ether by evaporation and dry in the oven to constant weight. 



It should be noted that any phytosterol or cholesterol present in the fat would 

 come down with the paraffin, but the amount would be so insignificant that except 

 in the most exacting work it may be disregarded. The character of the final residue 

 should, however, be confirmed by determining its melting point and specific gravity, 

 and by subjecting it to examination in the butyro-refractometer. The melting point 

 of paraffin is about 54.5 C.; its specific gravity at 15.5 is from 0.868 to 0.915, and 

 on the refractometer (Zeiss's scale) the reading at 65 C. is from 11 to 14.5. 



8. DETERMINATION OF NITROGEN. 



Use 5 grams of the sample for this determination, and follow the details of the 

 regular Gunning method. b 



9. DETERMINATION OF STARCH IN CONFECTIONERY. c 



Measure gradually 25 cc of the 20 per cent solution or uniform mixture (2 (c) (1) 

 (6)) into a hardened filter or Gooch crucible, or transfer by washing 5 grams of the 

 finely powdered substance to the filter or Gooch, and allow the residue on the filter 

 to become air-dried. Extract with 5 successive portions of 10 cc of ether, then wash 



a Wiley, Principles of Agricultural Analyses, vol. 3, p. 152. 

 b U. S. Dept. of Agr., Div. of Chem., Bui. 46 revised, p. 16. 

 C U. S. Dept. of Agr., Div. of Chem., Bui. 46 revised, p. 25. 



