CANNED VEGETABLES. 51 



tion of liquor, owing to excess of water added, will be detected. Then thoroughly 

 grind the entire contents of the can, cither in a mortar or by means of a food chopper; 

 mix thoroughly and preserve in a glass-stoppered bottle for analysis. Unless the 

 analysis is to be completed within a reasonably short time it is best to dry the entire 

 sample after the determination of moisture is made. After thorough drying, the 

 material is allowed to stand exposed to the air for several hours, or until it has 

 become air dry. A second moisture determination is necessary with this procedure. 



4. PROXIMATE ANALYSIS. 



For methods of proximate analysis, see Bulletin 13, part 8, U. S. Department of 

 Agriculture, Division of Chemistry, page 1028. 



5. DETECTION OF SACCHARIN. 



Saccharin is quite extensively used in canned sweet corn as a sweetening agent. 

 For its detection add from 25 to 40 cc of water to about 20 grains of the sample; 

 macerate and strain through muslin; acidify with 2 cc of sulphuric acid (1 to 3) and 

 extract with ether. Separate the ether layer, allow the ether to evaporate sponta- 

 neously, and take up the residue with water. If saccharin lx> present its presence 

 will be indicated by the sweet taste imparted to the water. To conlirm this test add 

 from 1 to 2 grams of sodium hydroxid, and place the dish in an oil bath. Maintain 

 the temperature of the oil at 250 C. for twenty minutes, when the saccharin will be 

 converted into salicylic acid. After cooling and acidifying with sulphuric acid 

 extract in the usual way and test for salicylic acid. This test, of course, presupposes 

 the absence of salicylic acid in the original sample. If salicylic acid is present in 

 the original sample it must be removed before making the test for saccharin. 



6. DETERMINATION OF SULPHITES. 



Sulphites are largely used with certain classes of vegetables, notably corn and 

 asparagus, as a bleaching agent; they may also find use with this class of foods as a 

 preservative. 



(a) DISTILLATION METHOD. 



For their determination place 50 grams of the material in a distilling flask, add 

 about 5 cc of a saturated solution of glacial phosphoric acid, and proceed with the 

 distillation and the titration of the sulphite as directed on p. 90. Where only a 

 qualitative test is desired, take the first few cubic centimeters of the distillate, add 

 a slight excess of iodin solution, boil to expel the excess of iodin, then acidify with 

 hydrochloric acid and add barium chlorid solution. This test is verv delicate and is 

 easily applied. 



(b) REDUCTION METHOD.* 



To about 25 grams of the sample placed in a 200-cc Erlenmeyer flask add some 

 pure zinc and several cubic centimeters of hydrochloric acid. In the presence of 

 sulphites, hydrogen sulphid will be generated and may be tested for with lead paper. 

 Traces of metallic sulphids are occasionally present in vegetables, and by the above 

 test will indicate sulphites. Hence positive results obtained by this method should 

 be verified by the distillation method. 



It is always advisable to make the quantitative determination of sulphites, owing 

 to the danger that the test may be due to traces of sulphids. A trace is not to be 

 considered sufficient either as a bleaching agent or as a preservative. 



7. DETECTION OF PRESERVATIVES. 

 See methods given under Preservatives (p. 107, and following). 



I>ept. of Agr., Div. of Clu-m., Bui. 13, pt. , p. 1032. 



