FRUITS AND FRUIT PRODUCTS. 75 



preservatives, or coloring matter, examination of the liquor would be sufficient. 

 The relative weights of liquor and fruit may be of value in detecting the presence of 

 an excessive amount of water. A. S. Mitchell* has noted the presence of free sul- 

 phuric acid in jellies. The methods for determination of mineral acids in vinegar 

 can be readily applied to fruit products. The presence of phosphoric acid would be 

 shown in the examination of the ash. 



The determination of solids by drying at 100 C. gives lower results than drying in 

 vucuo at lower temperature, or calculation from the specific gravity of the solution, 

 the reason undoubtedly being that levulose is dehydrated at 100 C. 1 ' But as few 

 laboratories are equipped to use the drying in vacno method, and as it is not possible 

 to determine specific gravity in all cases, it is necessary to adopt some method which 

 will give uniform results. In such a method the empirical rules have to be followed 

 closely in order to obtain comparative results. 



2. PREPARATION OF SAMPLE. 

 (a) JUICES, JELLIES, AND SIRUPS. 



Prepare the fresh juices by pressing in a jelly bag the well pulped fruit and filter- 

 ing through muslin. In the case of fresh fruit juices and fresh fruits the determina- 

 tion of total and volatile acids and sugars, and the polarization should be made at 

 once, as fermentation takes place in a very short time. Portions for polarization 

 and reducing sugar may lie weighed out and an excess of lead sub-acetate added. 

 They can then be kept for several days, if denied, without fermentation. All 

 samples must be transferred without delay to glass-stoppered bottles and kept in a 

 cool place. 



In the case of jellies, thoroughly mix to ensure uniformity in sampling. Weigh 

 60 grams into a 300-cc flask, dissolve in water by means of frequent shaking, make 

 up to the mark with water, and use aliquot portions for the various determinations. 

 With jellies that contain starch or other insoluble material, thoroughly mix before 

 taking aliquot portions for the various determinations. 



1 >ealcoholize sirups by evaporation to one-third their volume and dilute with 

 water till they contain from 15 to 20 per cent of solids. 



(b) FUKSII nirns. 



Pulp the whole, well-cleaned fruit in a large nun-tar or by means of a food chopper 

 and mix thoroughly. Incase of stone fruits remove the pits and determine their 

 proportion in a weighed sample. 



(C) JAMS, MARMALADES, I'KKSKKYES, AND CANNED FRUITS. 



Thoroughly pulp the entire contents of the jar or can, as directed under fresh 

 fruits; with stone fruits remove the pits, and if desired determine their proportion in 

 a weighed sample. In the examination of canned fruits it is often sufficient to merely 

 examine the sirups in which the fruits are preserved. In such cases the liquor may 

 be separated and treated as is prescribed for juices. 



3. DETERMINATION OF TOTAL SOLIDS, 

 (a) IN JUICES, JELLIES, AND SIRUPS. 



(1) By direct cfetmrnnotfon. Measure 25 cc fl of a 20 percent solution [see 2 (a)] of 

 jelly, or weigh 25 grams of juice, into a large flat-bottomed dish which contains 



Coiiiiiiuniented hy letter. 



bCarr >md Sunburn, r. S. Dept. of \KT.. Division of Chemistry, llnl. 17. j>. i:il. 



It'll pipette )>e used it must lie ^radiiMted so us to deliver M definite volume of a 20 per cent sugar 

 solution lifter draining M delinite time. 



