220 GLUCOSES, SACCHAROSES, ETC. 



§ 207. Saccharoses. — Cane-sugar differs from the glucoses in 

 composition ; its formula, CjoH.„Oj^, is the same as that of certain 

 carbohydrates of the vegetable gum group, triticin, etc. It crystal- 

 lizes with tolerable facility in anhydrous monoclinic crystals, is 

 freely soluble in cold water, insoluble in ether, and in cold absolute 

 alcohol ; the latter, when heated to boiling, dissolves about 1 '25 

 per cent. An aqueous solution is dextro-rotatory. Hesse ^ found 

 the rotatory power for («)„ to be +67 95°(^ = 1) and +66-50° 

 0^= 10);2Tollens,3 +66 -649°, and + 66 •47o°(^j = 10); and Schmitz, 

 + 66 •527°. Heated for some time to about 160^, cane-sugar is con- 

 verted into dextrose and levulosan (C^JHJQ05); at a higher tempera- 

 ture it is decomposed into caramel and other products. It does 

 not reduce alkaline copper solution in the cold ; prolonged boil- 

 ing, however, causes the gradual separation of cuprous oxide. 

 Cane-sugar is only indirectly fermentable, being first gradually 

 converted into glucose by the invertin of the yeast (§ 230). It 

 has already been observed (§§ 86, 88, etc.) that a similar change 

 is easily brought about by the action of dilute acids ; the principal 

 means of distinguishing cane-sugar from the more important 

 glucoses have also been mentioned (see §§ 200 to 204 and § 206). 



The following saccharoses are isomeric with cane-sugar and 

 classed with it. 



Milk-sugar, which has not yet been detected with certainty in 

 the vegetable kingdom, forms rhombic crystals containing 1 

 molecule of water of crystallization and soluble in 7 parts of water 

 at 10°. Its rotatory power (in solutions that have been previously 

 heated) is (a)D= +53-63° (7? = 2); Hesse found for freshly pre- 

 pared cold solutions (a)ü = +80-68°. It is not directly ferment- 

 able, ]jut, like cane-sugar, is gradually inverted by yeast. The 

 action of dilute acids results in the production of galactose 

 (i^205); by oxidation with nitric acid it yields large quantities 

 of mucic acid. Milk-sugar reduces ammoniacal silver and alkaline 

 copper solution in the cold, l)ut the extent to whicli icduction is 

 efiectcd when boiled Avith the latter reagent is less than is the case 

 with dextrose. When converted into galactose the leducing power 



^ Loc. c'd. Caldunm found (n)]j = G7"09° (Journ. do Tharm. et de. Chim. 

 xxiv. 437, 187C). 



- For the decrease in rotatory power caused by the i^resence of certain salts 

 see Muntz, Ber. d. d. chem. Ges. ix. !)02, 187G. 



•' Ber. d. d. chem. Ges. x. 1403, 1877 ; xi. 1800, 1878. See also Schmitz, 

 ibid. X. 1414. 



