350 



GLUCOSE. 



there are supposed, therefore, to have been 

 a succession of glacial epochs between which 

 occurred epochs when the mean temperature 

 went as much higher as in the stage of great- 

 est cold it stood lower than the present mean 

 temperature. At the end of this period, when 

 the variations were least, the mean tempera- 

 ture of the coldest month is estimated to have 

 been 20 Fahr. less in the latitude of London 

 than now, and the summer twenty days short- 

 er at the cold epoch of the cycle. The excava- 

 tion of the basins of lakes is now ascribed to 

 glacial action. Professor Ramsay divides lakes 

 into three classes: those which are due to ir- 

 regular accumulations of drift, and which are 

 generally very shallow ; those formed by mo- 

 raines ; and those occupying true basins, which 

 have been scooped out of the rocks by glacier 

 ice. The glaciers which, according to this the- 

 ory, formed the basins of the Swiss and Italian 

 lakes must have been of enormous size, the 

 Lake of Geneva being 984, the Lake of Brienz 

 2,000, the Lake of Como 1,929, and Lago Mag- 

 giore 2,625 feet deep. The ice which formed 

 the valley of Geneva Lake must have been at 

 least 2,700 feet thick. 



GLUCOSE. Glucose and grape-sugar are 

 the terms employed to designate the saccharine 

 constituents of grapes and other fruits, and 

 honey, the sugar of malt, and the saccharine 

 products which are artificially formed from the 

 starches. In ordinary commercial usage, glu- 

 cose is employed exclusively as the name of 

 the thick sirup which is made from corn-starch, 

 while grape-sugar is applied to the solid product 

 from the same source. In chemistry the term 

 glucose is used to describe either substance, the 

 composition of which may be equally indicated 

 by the formula CgHnOg + HaO. 



Chemists distinguish between two kinds of 

 glucose : dextroglucose, which turns the plane 

 of polarization to the right ; and laevoglucose, 

 which turns it to the left. Dextroglucose, with 

 which commercial glucose is identified, has 

 received various names, such as granular sugar 

 (Kriimehuclcer), grape-sugar, fruit-sugar, hon- 

 ey-sugar, starch-sugar, diabetic sugar, sugar of 

 nrine, chestnut-sugar, rag-sugar, etc. It occurs 

 abundantly in sweet fruits, frequently together 

 with cane-sugar and IsBvo-rotatory fruit-sugar, 

 but is only rarely isolated in nature ; in honey, 

 with cane-sugar and inverted sugar ; and in 

 many animal liquids and tissues. Dextroglu- 

 cose separates from its aqueous solution in 

 white, opaque, granular, hemispherical or cauli- 

 flower-shaped masses, consisting of a hydrate. 

 From alcohol of 95 per cent and upward it 

 separates in anhydrous, microscopic, sharply 

 defined needles, which are, however, often 

 mixed with small portions of the hydrate, and 

 which melt at 284 to a colorless, transparent 

 mass. Anhydrous glucose is also obtained as 

 a white powder by heating the hydrate to 131 

 or 140 in a stream of dry air, and as a fused 

 transparent mass by heating the hydrate to 

 212. Dextr.oglucose is much less soluble in 



water than cane-sugar, requiring for solution 

 one and a half times its weight of cold water, 

 but dissolves in all proportions in boiling water, 

 forming a sirup which has a very sweet taste, 

 but is not as ropy as the sirup of cane-sugar. 

 It is also less soluble than cane-sugar in alco- 

 hol ; and the solution, saturated at the boiling 

 heat, deposits crystals which retain a portion 

 of the alcohol with considerable force. Lsevo- 

 glucose is isomeric with dextroglucose, but is 

 distinguished from it by turning the plane of 

 polarization in the opposite way, or to the left. 

 It occurs, together with dextroglucose, in honey, 

 in many fruits, and in other sacchariferous 

 vegetable organs. The mixture of these two 

 sugars in equal numbers of atoms constitutes 

 fruit-sugar, or inverted sugar, which is itself 

 lasvo-rotatory, because the specific rotatory 

 power of laevoglucose is greater than that of 

 dextroglucose. It is a colorless, uncrystallizable 

 sirup or amorphous solid mass, is as sweet as 

 cane-sugar, acts as a purgative, and is more 

 soluble in alcohol than dextroglucose. 



Commercial glucose is a thick, tenacious sirup 

 of a yellowish tint, or almost colorless, with an 

 average specific gravity at 20 C. or 68 Fahr. 

 of 1'412. That which is made for summer con- 

 sumption is a little more dense than that man- 

 ufactured for winter use. The sweetness of 

 glucose varies greatly with different specimens, 

 and depends inversely on the extent to which 

 chemical changes are allowed to proceed in the 

 manufacture, that resulting from processes in 

 which the conversion is stopped as soon as the 

 starch has all disappeared having the maximum 

 of sweetness. If the manufacture has been well 

 conducted, the grape-sugar made from corn- 

 starch is at first of a pure white color, but has 

 a tendency to assume a yellowish tint when 

 old. It is hard and brittle, does not usually 

 take on a visible crystalline structure, and dis- 

 solves more slowly in water than cane-sugar. 

 Its specific gravity has been found to be as 

 high as l - 6. It is much less sweet than cane- 

 sugar, and leaves a faint but perceptible bitter 

 taste when dissolved in the mouth. 



The manufacture of glucose has attained a 

 very considerable magnitude, indicating an ex- 

 tensive use of the sugar and the sirup in the 

 arts and in trade. Nineteen factories were in 

 operation or ready to go into operation during 

 1881, in the States of New York, Ohio, Illinois, 

 Michigan, Iowa, and Missouri, which together 

 had a capacity for consuming more than thirty- 

 five thousand bushels of corn daily, and eleven 

 million bushels during the year. The works 

 are estimated to represent more than two mill- 

 ion dollars of capital, and to give employment 

 to twenty-one hundred men. 



Glucose is made at the factories from Indian 

 corn by the conversion of the starch in the 

 grain through the action of sulphuric acid, 

 between twenty-six and thirty-two pounds 

 being obtained from a bushel of corn. The 

 corn is first soaked for two or three days in 

 warm water, and is then ground on specially 





