930 SUGAR 



liquid having been changed by the addition of the hydrochloric acid, the deviation 

 observed a', must be replaced by the deviation, -r- a", which would have been ob- 

 served if the inversion could have been produced without the addition of hydrochloric 

 acid. Admitting therefore that.a quantity of cane-sugar which effects a deviation, x, gives 

 rise to a quantity of noncrystallisable sugar which effects a deviation, r x, we have- 

 Before the inversion, x+y = a,'. 



10 

 After the inversion, y + r x = <r a". 



From these two equations the quantities x and y may be determined. The co- 

 efficient of inversion, r, is determined once for all by a special experiment performed 

 upon pure cane-sugar at the temperature at which the experiments have afterwards 

 to be made. According to Biot, this coefficient is 0'038 for hydrochloric acid at a 

 temperature of 71*6. 



The process is the same when the cane-sugar is mixed with noncrystallisable sugar, 

 turning the plane of polarisation to the left. In this case the initial deviation a', of 

 the liquid is the difference between the deviation to the right r, of the cane-sugar, 

 and the deviation z, to the left of the noncrystallisable sugar. After treating with 

 hydrochloric acid, the deviation, a' 1 , is composed of the deviations of the original 

 noncrystallisable sugar, and of that produced by the action of the hydrochloric acid. 

 We then have 



Before the inversion, x z = a'. 

 10 



After the inversion, z + r x = - a". 



It is important in examining optically noncrystallisable sugar always to employ 

 the same temperature, because a change of temperature materially affects the rotatory 

 power of this kind of sugar. 



The Table appended on the following pages includes each degree of temperature 

 from + 10 to + 35 Centigrade, and for qualities increasing in hundredths, this range 

 being found sufficient for all practical purposes either in Europe or the Colonies. 



To note the temperature at which the observation is made, a tube z s, fig. 1919, pro- 

 vided with a vertical branch, is employed. In this branch a thermometer, t, is placed. 



The following are two examples of the use of the Table : 



1. A solution of a saccharine substance prepared in the normal pro- 

 portions of weight and volume recommended, and giving before acidu- 



lation a notation on the left-hand part of the scale of . . . .75 divisions. 



And after the inversion (the temperature being +15) a notation in 

 the opposite direction of 20 divisions. 



Sum of the inversions 95 divisions. 



2. Another liquor similarly prepared, giving before the inversion a 



notation on the left of . .80 divisions. 



And after the inversion, at the temperature of + 20, another notation 

 of the same direction, but only of 26 divisions. 



Difference expressing the value of the inversion . 54 divisions. 



The strength of the two solutions will be found thus : for the first, by seeing what 

 is the figure of the column representing 15, which is the nearest to the sum of the 

 inversion, 65 divisions : it will be observed that this figure is 95'5, and that it corre- 

 sponds to quality 70, shown on the same horizontal line in the last column but one, A ; 

 hence we conclude that the substance contained 70 per cent, of sugar. 



As to the second solution, the figure nearest 54 is 53'6, in the column for the tem- 

 perature of + 20, and the strength sought will be 40 per cent, on the same line in the 

 column of qualities. Finally, we shall find, besides, in the last column, B, of the 

 table, the quantity in grammes and centigrammes of the sugar contained per litre in 

 the solution, which is 1 14 grs. 45 cgrs. for the first, and 65 grs. 40 cgrs. for the second. 



Other methods for the estimation of sugar have been adopted. We have already 

 described Peligot's method by means of lime. When sugar is formed from starch, its 

 complete saccharification may be determined by the action of sulphuric acid, for if on 

 a strong solution of imperfectly-formed grape-sugar, nearly boiling hot, one drop of 

 strong sulphuric acid be added, no perceptible change will ensue, but if the acid be 

 dropped into solutions of either cane- or perfectly-formed grape-sugar, black carbo- 

 naceous particles will make their appearance. 



