APPENDIX. 749 



drogen chloride alternately as long as any precipitate is produced. The 

 mixture is then stirred, is allowed to stand for five minutes, and is fil- 

 tered. Alcohol is added to this second filtrate until glvcogen is preci- 

 pitated, which occurs after about 60 per cent of absolute alcohol has 

 been added. The precipitate is then filtered off, and is washed with 

 weak spirit, strong spirit, absolute alcohol (two or three times), and 

 finally with ether. It is then dried on a glass plate at a moderate heat, 

 and, if pure, should remain as a white amorphous powder. If the water 

 has not been completely removed, the glycogen will form a gummy mass; 

 in this case it must again be treated with absolute alcohol. 



Properties. It is freely soluble in water, and its solution looks opa- 

 lescent; it gives a port-wine coloration with iodine, which disappears on 

 heating and returns on cooling. 



It is insoluble in absolute alcohol and in ether. 



It exists in the liver during life, but very soon after death is changed 

 into sugar. It is converted into sugar by diastase ferments, or by boil- 

 ing with dilute acids. 



(c) Dextrin. This substance is made in commerce by heating dry 

 potato starch to a temperature of 400. It is also produced in the pro- 

 cess of the conversion of starch into sugar by diastase, and by the sali- 

 yary and pancreatic ferments. 



Properties. A yellowish amorphous powder, soluble in water, but 

 insoluble in absolute alcohol and in ether. 



It corresponds almost exactly in tests with glycogen; but one variety 

 (achroo-dextrin) does not give the port-wine coloration with iodine. 



(D) Glucose occurs widely diffused in the vegetable kingdom, in 

 diabetic urine, in the blood, etc. ; it is usually obtained from grape-juice, 

 honey, beet-root, or carrots. It really is a mixture of two isomeric 

 bodies, Dextrose or grape-sugar, which turns a ray of polarized light to 

 the right, and Lcevulose or fruit-sugar, which turns the ray to the left. 



Properties. It is easily soluble in water; not so sweet as cane-sugar; 

 the relation of its sweetness to that of cane-sugar is as 3 to 5. 



It is not so easily charred by strong sulphuric acid as cane-sugar. 



It is not entirely soluble in alcohol. 



Tests. (i.) Trommer's. This test depends upon the power sugar 

 possesses of reducing copper salts to their suboxide. It is done in the 

 following way: An excess of caustic potash and then a solution of cop- 

 per sulphate, drop by drop, is added to the solution, containing the 

 sugar in a test-tube, as long as the blue precipitate which forms redis- 

 solves on shaking the tube. The upper portion of the fluid is then 

 heated, and a yellowish-brown precipitate of copper suboxide appears. 



(ii.) Moore's. If a solution of sugar in a test-tube is boiled with 

 caustic potash, a brown coloration appears. 



(iii.) Fermentation If a solution of sugar be kept in the warm 



