GLUCOSE. 281 



characters may be. They are so indifferent that it is only with few 

 other bodies, and in these cases with considerable difficulty, that they 

 can be made to combine, and then they enter into combination in 

 multiple proportions, so that it is always difficult to determine their 

 atomic weights with any degree of certainty. Almost the only 

 physical properties which they have in common are deficiency in 

 colour and smell. They are all decomposed by heat, and yield 

 acid products of distillation. By digestion with dilute mineral 

 acids, they are for the most part converted into glucose or grape- 

 sugar. When decomposed by nitric acid, they yield oxalic acid, 

 saccharic acid and mucic acid, and, perhaps, also, conjugated nitric 

 acids. When treated with concentrated sulphuric acid these bodies 

 become brown or black, and in addition to humin-like substances, 

 form conjugated sulphuric acids. 



The only substances of this group of any zoo-chemical importance 

 are glucose or grape-sugar, milk-sugar, [inosite* or muscle-sugar] 

 and cellulose. 



GLUCOSE. C 12 H 12 O 12 . 



Chemical Relations. 



Properties. Glucose, which is the name applied to grape-sugar 

 by the French chemists, is identical with diabetic sugar* and crys- 

 tallises with 2 atoms of water in wart-like masses consisting of 

 minute plates arranged in a cauliflower form ; these plates are rhombic 

 and not square (as Saussure believed) ; when this substance separates 

 rapidly from a solution, we may observe under the microscope that 

 it occurs in irregularly striated, roundish masses, and not in 

 plates ; it is white, devoid of odour, and not so sweet as cane- 

 sugar but sweeter than milk-sugar ; it is only half as soluble in 

 water as cane-sugar, but more soluble than milk-sugar ; it is only 

 slightly soluble in alcohol, and insoluble in ether; its aqueous 

 solution turns the plane of polarisation of a ray of light to the 

 right, and is devoid of action on vegetable colours. 



At a few degrees below 100 it begins to cake together, but it 

 melts perfectly at 100 with the loss of its 2 atoms of water ; at 140 it 

 becomes converted into caramel, and developes a sweetish odour; 

 at a higher temperature it becomes frothy, grows brown, developes 

 a pungent vapour, and leaves a voluminous charcoal. 



In contact with nitrogenous bodies, and especially with casein, 



* [Inosite or muscle-sugar has been discovered by Scherer since the original 

 Publication of this volume. Its formula is C 12 H 16 16 . It will be noticed in a future 

 ^art of this work. G. E. D.] 



