1879.] 



Volumetric Estimation of Sugar. 



263 



Fehling's solution, and if it comported itself in the same manner as 

 the latter, 10 cub. centims. of it would stand equivalent to "005 grm. 

 of grape sugar. In working with this liquid the results obtained 

 were so accordant in relation to each other that I had no misgiving 

 about its uniformity of action ; but I felt that before being definitely 

 accepted they ought to be checked against known amounts of sugar. 

 The accomplishment of this proceeding, however, is not altogether 

 unattended with difficulty, on account of the uncertainty of obtaining 

 grape sugar free from impurity and in a perfectly dried state. 



The method I have adopted has been to operate upon weighed 

 amounts of cane sugar and produce inversion by boiling with an acid. 

 I first found that the cane sugar, which is sold in coarse colourless 

 crystals — that which is known as " white crystal," and used for 

 sweetening coffee — stood the test on examination for purity with 

 Laurent's polarimeter. A weighed quantity was taken, and, after 

 being inverted by boiling with hydrochloric acid, tlie acid neutralised, 

 and the liquid brought to a known volume, subjected to treatment 

 with the ammoniated copper liquid. Repeated trials were made with 

 varying quantities, and it was found that the results stood in har- 

 monious relation to each other, but that the amount of sugar indicated 

 was larger than the calculated amount of invert sugar from the 

 weighed quantity of cane sugar taken. At first I was at a loss for an 

 explanation of this result, but subsequent observation has revealed 

 that in the case of the ammoniated liquid, 6 atoms of oxide of copper 

 are appropriated by 1 atom of sugar, instead of 5, as in that of 

 Fehling's solution used in the ordinary way. When the reckoning is 

 made upon this basis the results exactly correspond with, the actual 

 amount of sugar known to be present. Moreover, with solutions of 

 ordinary grape sugar and diabetic sugar, examined comparatively with. 

 Fehling's solution used in the ordinary way and the ammoniated 

 copper liquid, the results exactly accord under the reckoning that 5 

 atoms of oxide of copper are appropriated in the one case and 6 atoms 

 in the other by 1 atom of sugar. 



To be quite satisfied upon this point, a large number of observations ' 

 under varying conditions have been made, and whilst what I have 

 stated holds good for the ammoniated copper liquid prepared from 

 Fehling's solution, without any further addition of alkali, and with, 

 the addition of potash to the extent of 1 grm. to 20 cub. centims. of 

 the ammoniated test, yet a larger quantity of potash alters the action, 

 and with 5 grms., and anything beyond, the behaviour is brought to 

 the same as that of Fehling's solution used in the ordinary way, viz., 

 5 atoms only of oxide of copper are appropriated by 1 atom of sugar. 

 With quantities of potash between the 1 and 5 grms., the results 

 stand between the 5 and 6 atoms of cupric oxide. 



I may mention that observation has further shown that whilst 



