84 PROXIMATE PRINCIPLES OF THE SECOND CLASS. 



honey is prepared in some way by the bee from materials of vege- 

 table origin. 



These varieties differ but little in their ultimate chemical compo- 

 sition. The following formulae have been established for three of 

 them. 



Cane sugar = C 24 H 22 22 



..Milk sugar . . . ' . . . = C 24 H 24 21 

 Glucose = C 24 H 28 O 23 



Cane sugar is sweeter than most of the other varieties, and more 

 soluble in water. Some sugars, such as liver sugar and sugar of 

 honey, crystallize only with great difficulty ; but this is probably 

 owing to their being mingled witn other substances, from which it 

 is difficult to separate them completely. If they could be obtained 

 in a state of purity, they would doubtless crystallize as perfectly as 

 Vane sugar. The different sugars vary also in the readiness with 

 which they undergo fermentation. Some of them, as grape sugar 

 and liver sugar, enter into fermentation very promptly ; others, 

 such as milk and cane sugar, with considerable difficulty. 



The above are not to be regarded as the only varieties of sugar 

 existing in nature. On the contrary, it is probable that nearly 

 every different species of .animal and vegetable produces a distinct 

 kind of sugar, differing slightly from the rest in its degree of sweet- 

 ness, its solubility, its crystallization, its aptitude for fermentation, 

 and perhaps in its elementary composition. Nevertheless, there is 

 so close a resemblance between them that they are all properly 

 regarded as belonging to a single group. 



The test most commonly employed for detecting the presence of 

 sugar is that known as Trommels test. It depends upon the fact 

 that the saccharine substances have the power of reducing the 

 persalts of copper when heated with them in an alkaline solution. 

 The test is applied in the following manner : A very small quantity 

 of sulphate of copper in solution should be added to the suspected 

 liquid, and the mixture then rendered distinctly alkaline by the 

 addition of caustic potassa. The whole solution then takes a deep 

 blue color. On boiling the mixture, if sugar be present, the in- 

 soluble suboxide of copper is thrown down as an opaque red, 

 yellow, or orange-colored deposit; otherwise no change of color 

 takes place. 



This test requires some precautions in its application. In the 

 first place, it is not applicable to all varieties of sugar. Cane 

 sugar, for example, when pure, has no power of reducing the salts 



