GLUCOSE, 283 



lead in definite proportions : its aqueous solution takes up a large 

 quantity of this oxide ; an insoluble compound is obtained from 

 glucose and a solution of acetate of lead treated with ammonia. 



The combination of glucose with chloride of sodium, C 12 H 12 O 12 

 + 2HO + C 12 H 12 O 12 .NaCl, may be obtained by the direct mixture 

 of the solutions of the two constituents and by spontaneous eva- 

 poration, in very large, colourless, four-sided, double pyramids. 

 These crystals are hard, easily^, pulverisable, of 1*5441 specific 

 gravity, transparent, unaffected by the atmosphere, of a saline 

 and sweetish taste, soluble in 3*685 parts of cold water, and 

 difficult of solution in alcohol. At 100 the powdered crystals 

 begin to cake together, and lose 4f of water ; when rapidly heated 

 to 120 they melt in their water of crystallisation, and begin to 

 become brown at + 160. The crystals contain 13'3^ of chloride of 

 sodium. 



Preparation. This sugar is not only, as is well known, widely 

 diffused throughout the vegetable kingdon, but may be formed 

 from other kinds of sugar and from carbo-hydrates (starch, wood- 

 fibre, &c.) by digestion with dilute acids; hence it may be pre- 

 pared in many different ways. On the large scale it is commonly 

 obtained from starch ; but all that concerns us here is its mode of 

 preparation from diabetic urine. The following is the ordinary 

 mode of proceeding. Diabetic urine is treated with basic acetate of 

 lead, and the excess of lead removed from the filtered fluid by 

 sulphuretted hydrogen ; the fluid is then evaporated, and extracted 

 with alcohol, from which the sugar crystallises ; but sugar thus 

 obtained always contains acetates. In order to obtain the sugar I 

 am in the habit of evaporating the urine to nearly the thickness of 

 a syrup ; provided it has not been too powerfully evaporated, the 

 whole residue, after a variable time, becomes converted into a solid 

 yellowish white mass, which must be extracted with absolute 

 alcohol and subsequently with hot spirit. The sugar dissolved in 

 the latter is removed, after it has crystallised, by filtration, while 

 the spirit is submitted to evaporation, and then treated with a little 

 water in order to facilitate further crystallisation. In this way we 

 obtain the sugar in a state of greater purity than by the ordinary 

 method. 



In order to obtain diabetic sugar in a state of chemical purity, I 

 prepared the chloride of sodium compound by saturating the 

 aqueous solution of the alcoholic extract with chloride of sodium, 

 and by repeated crystallisation obtained it in perfectly transparent 

 crystals, which I dissolved in water, and cautiously precipitated with 



