642 EXPERIMENT STATION RECORD 



"carbohydrates" instead of by tlie longer and less definite term of 

 "nitrog'eu-free extract." This, however, is not warranted, since the 

 nitrogen-free extract necessarily inclndes various materials which, like 

 the carbohydrates, possess the qualities of solubility in water, dilute 

 acid, and dilute alkali, and which are neither carbohydrates, fat, pro- 

 tein, nor ash. All known carl)ohydrates fonnd in nature may occur in 

 the nitrogen -free extract,' consequently a brief resume of the ])rin('ipal 

 groups of carbohydrates may be helpful in considering its nature. 



IIEXOSKS AND THEIR DERIVATIVKS.- 



The hexoses have the general composition OcH] >Ofi. Their derivatives 

 are cane sngar (C12H22O11), hexosans (CeHioOs), etc. 



The various hexoses (monosaccharids, CcniaO,;). — (1) Dextrose (or glu- 

 cose) occurs in sweet fruits, like grapes, strawberries, raspberries, goose- 

 berries, apples, cherries, plums, etc., in larger or smaller quantities, up 

 to 15 or 20 per cent, and is always associated with levulose or cane sugar. 

 Dextrose and levulose are sometimes present in equal molecules, but 

 usually the one or the other sugar predominates, as in the case of grape 

 juice and apple Juice, according to Kulisch and Berend. l^extrose is 

 found in small quantities in the leaves of various plants, in tlie stems 

 of cereals, in maize, sorghum, sugar cane (together with cane sugar), 

 malt, roots and tubers (potato), and in many other i)arts of ])lants. 



(2) Levulose nearly always occurs with dextrose, and sometimes in 

 considerable quantities. Levulose and dextrose may be formed sinuil- 

 taneously in leaves from the carbon dioxid of the air, or they may be 

 produced from cane sugar by hydrolysis, the mixture being known in 

 that case as invert sugar. In all probability the sugars in the leaves 

 of plants are produced by the action of light, with the aid of the 

 chlorophyll of green leaves, from the carbon dioxid of the air; oxygen 

 is liberated, and by the simultaneous action of water formic aldehyde 

 (CH2O) is i>roduced, which is polymerized to 0,;Hi2()(, or other carbo- 

 hydrates. 



(3) Mannose as such has not been recognized with certainty in vege- 

 table materials, although its mother substances, mannan and i)ara- 

 mauuan, occur frequently. 



(4) Galaetose seems also not to occur in nature as such. It is easily 

 produced from galactan and paragahictan, which are of common occur- 

 rence. 



(5) /Sorbose has not been recognized as such in unchanged vege- 

 table materials. 



'A comprehensive, concise treatise on the carbohydrates with very full bibli- 

 ography is given in B. ToUens' Kurzes Handbnch der Kohlenhydrate, vols. 1 and 2, 

 Breslan, 1888 and 1895, to which the reader is referred. 



^The writer nse.s "derivative" in this article in its physiological instead of its 

 analytical sense. That is, starch is regarded as a physiological derivative of 

 hexoso, i)rodnced in the plant by the polymerizing of hexose with the elimination 

 of water. — Ed. 



