RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY— AGROTECHNY. 



Fruit juices, F. Thompson and A. C. Whittiee (Delaware Sta. Bui. 102, pp. 

 2S, figs. 7). — This is an account of preliminary work on an investigation of tlie 

 exact nature of tlie chemical compounds which exist in fruits at various stages 

 of maturity and the reactions taking place therein. The fruits studied were 

 one variety each of strawberries, peaches, pears, apples, and grapes. The first 

 samples of fruit were taken soon after they were set and the analyses were 

 continued from time to time until complete maturity. In the work the sugars 

 present in the juices were assumed to be sucrose, dextrose, and levulose. 



In polarizing at high temperatures with the ordinary water -jacketed polari- 

 scope tube, much difiiculty was experienced in obtaining a clear and unob- 

 structed field of vision. For correcting this a modified form of instrument 

 (which is illustrated) was employed which permits the introduction of a hot 

 water oven between the analyzer and polarizer whereby a uniform temperature 

 may be maintained (at any point within 0.1°) throughout the length of the 

 tube, and a clear field of vision is obtained. The heating chamber is entirely 

 separate from the optical parts of the instrument. For inverting sucrose 

 Hudson's invertase method (E. S. R., 22, p. 412) was employed. 



The results seem to show that dextrose and levulose are the first sugars to 

 appear and that they are the dominant sugars until maturity. Both of these 

 monosaccharids are almost present in the proportion of inveii; sugar, i. e., the 

 dextrose content is slightly higher. In the grape, levulose and dextrose are 

 present practically as invert sugar at all stages and no sucrose was noted at 

 any stage (E. S. R., 25, p. 504). 



It was also found that the average molecular weight of the solids in the juice 

 increases as tlie fruit arrives at maturity. This is particularly true of the 

 fruits which carry sucrose. The gain in weight, however, is greater than can 

 be accounted for with sucrose. " From calculated molecular weights deter- 

 mined, it is evident that in the peach there are bodies of low molecular weights 

 being formed along with the sucrose, counterbalancing to some extent the 

 effect of the increasing sucrose." The principal sugar present in the peach 

 is sucrose. Dextrose and levulose exist in almost equal proportions. 



In the apples and i)ears examined, the principal sugar present throughout 

 the ripening process was levulose. Sucrose appeared early in the apple, and 

 dextrose when the fruit was almost mature, but only in small quantity. Both 

 of these fruits are the only ones of the 5 examined which contained starch in 

 appreciable amounts, and the appearance of the starch seemed to be accom- 

 panied by a disappearance of the dextrose. 



The osmotic pressure of the fruit juices increased considerably up to the 

 final stage of ripeness but most rapidly in the later stages. An exception was 

 the strawberry, which maintained a low osmotic pressure during all stages. 

 " Ionization as shown by the depression of the freezing point was sliglJ^ in all 

 the juices with the exception of the grape juice, which showed a high ioniza- 



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