256 THE POPULAR SCIENCE MONTHLY, 



rated, at as low a temperature as possible, to the required concentra- 

 tion. If grape-sugar is to be made, the process of conversion is not 

 stopped as soon as the starch has disappeared, but is carried on still 

 further to a point which can only be determined by trial. After con- 

 centration it is conveyed into tanks, where the j^rocess of solidification 

 begins and continues for several days. 



Glucose, on the other hand, will not harden, whatever the degree 

 of concentration may be, or, at least, if it do so, only partially and 

 after many months. 



The habit of bleaching both glucose and grape-sugar by means of 

 sulphurous acid is sometimes practiced, but is reprehensible. By the 

 oxidation of the sulphurous acid, free sulphuric acid is likely to occur 

 in the finished product. 



Glucose and grape-sugar are mixtures of several chemical sub- 

 stances. Starch, which is composed of six atoms of carbon, ten of 

 hydrogen, and five of oxygen, when subjected to the action of dilute 

 sulphuric acid, appears to undergo a molecular condensation and hy- 

 dration. Among the substances formed may be reckoned dextrine, 

 glucose, and a substance isomeric with cane-sugar. This latter sub- 

 stance appears to be one of the early products of conversion, and this 

 is the reason that the poorly converted glucoses are sweeter than the 

 well converted. It is only after prolonged boiling with dilute acid 

 that the product becomes chemically homogeneous, with a constitution 

 which is probably represented by the symbol CgHj^OgH^O. 



Glucose presents several anomalies when examined with polarized 

 light. Its highest rotatory power is found when it is made with the 

 least possible amount of conversion i. e., when the process of con- 

 version is stopped as soon as the starch has disappeared. Continued 

 boiling with dilute acid causes a gradual decrease of rotatory power. 

 It is only after six to eight hours* heating to a temperature of 104 C. 

 that a constant rotatory power is reached. This power is only about 

 half that exhibited by the glucose as a maximum. This minimum 

 rotatory power, however, is greater than that possessed by cane-sugar. 



Glucose, like many other bodies, has the property of reducing a hot 

 alkaline copper solution and separating the metal as a red sub-oxide. 

 This power in glucose is always inversely as the rotating power. I 

 have shown this fully and conclusively in the paper already referred 

 to. The relation between reducing power and rotating power is a con- 

 stant one, and hence the percentage of reducing power can be calcu- 

 lated from the polarimetric observations. This, however, is of more 

 interest to the practical chemist than to the general reader, and I there- 

 fore pass it by. 



The question of most practical importance is, " Is glucose a whole- 

 some article of food ? " I do not hesitate to answer this question 

 in the affirmative, I mean by this, however, a glucose which is 

 properly made. Such a glucose contains only a very little sulphuric 



