NON-NITKOGENOUS ORGANIC CELL-CONSTITUENTS. 117 



calcium carbonate being added to neutralize the acid reaction. After 

 filtering and concentration, inulin separates from the extract in the form 

 of crystals. By boiling with dilute acid, inuliu is converted into 

 Isevulose. 



(6) THE GLUCOSES, OR GRAPE-SUGAR GROUP ?i(C 6 H 12 6 ). This group 

 comprises grape-sugar, or dextrose, galactose, inosite, and Isevulose, or 

 sugar of fruits. 



1. Grape-Sugar (C 6 H 12 O 6 -|-H 2 O). Grape-sugar, or glucose, is widely 

 distributed throughout the vegetable kingdom, as a rule accompanying 

 fruit-sugar, and Js also normally found dissolved in many of the animal 

 j uices. It owes its name to its being found in grapes, where it is associated 

 with Isevulose. It rotates the plane of polarized light to the right, and is 

 consequently designated as dextrose. As a product of the action of 

 the diastatic ferments on starch and the majorit3 T of the carbo-l^-drates, 

 it acquires an especial importance for the animal organism. Grape-sugar 

 also occurs in the vegetable kingdom associated with other bodies to form 

 glucosideSj from which it may be separated by treatment with acids or 

 ferments. Most of these bodies contain only C, H, and O; some, such 

 as solanin and amygdalin, contain N in addition, and in others S is also 

 found. Grape-sugar seldom occurs in well-formed crystals, but ordinarily 

 in crumbly, white masses, which, under the microscope, are seen to consist 

 of small, rhombic tables. It has a sweetish taste, and is soluble in water 

 and alcohol. At 100 C. grape-sugar melts and loses its water of 

 ciystallization. At higher temperatures it becomes brown, and is con- 

 verted into caramel, CuH^Oj,. At still higher temperatures it is 

 completely decomposed into CO, C0 2 , marsh-gas, acetic acid, acetone, 

 aldehyde, and other products. If heated with a strong solution of 

 caustic potash grape-sugar decomposes, with heat production, into lactic 

 acid, brenzcatechin, formic acid, and other products, accompanied by 

 the development of a brown color. If nitric acid is then added, an odor 

 of burnt sugar and formic acid is produced. Grape-sugar is readily 

 soluble in water, but less so than cane-sugar. It is also less sweet than 

 cane-sugar. It is very slightly soluble in alcohol and insoluble in ether. 

 Glucose combines with different acids and bases to form glycosates or 

 saccharates. Grape-sugar has a great affinity for oxygen, and it is 

 therefore a powerful reducing agent. This property is seen in the 

 reduction of cupric oxide in an alkaline solution, and has been made use 

 of for a qualitative and quantitative test of its presence. Thus, if one 

 molecule of grape-sugar is mixed with five molecules of cupric sulphate 

 and eleven molecules of sodic hydrate the copper will be precipitated 

 completely, and the filtrate will be free from sugar. In watery solutions 

 grape-sugar is unstable, since it is readily decomposed under the action 

 of ferments. This fermentation, produced under the influence of yeast 



