198 HOW TO TEST CANE JUICE. 
weigh. Or ignite the suboxide of copper with access of 
air, and convert it completely into oxide by treating with 
fuming nitric acid. 
“100 parts of anhydrous grape sugar correspond to 
220:05* of oxide of copper, or 198°2 of suboxide of cop- 
per,t or 155-55 of iron converted from the state of sesqui- 
chloride to that of protochloride. In the application of 
this method, it must be borne in mind that the separated 
suboxide of copper will, upon cooling of the supernatant 
fluid, gradually redissolve to oxide, being reconverted into 
this by the oxygen of the atmosphere. Hence the neces- 
sity of washing the precipitate by decantation with boiling 
water.” 
The details of this method are thus given at length, for 
the reason that it is the test most depended upon for de- 
termining the quantity of grape sugar in asolution. With 
the exception, perhaps, of that given below, it is the only 
purely chemical process known that may be implicitly relied 
upon for its accuracy, and by means of which the result is 
reached with facility and dispatch. 
An elegant quantitative test for cane and grape sugar has 
been proposed by M. Peligot, which I have found to give 
uniform results. I give this method as described by Dr. 
Ure. ‘‘Peligot’s method depends upon the definite consti- 
tution of sugar lime (or saccharate of lime), its greater 
solubility in water than in lime alone, and the unalterability 
of this solution by heat. Soubeiran found sugar lime to 
consist of three equivalents of lime to 2 equivalents of 
* Fehling obtained as highest result 219-4 grammes of oxide of copper. 
+ Neubauer found in his experiments with starch that 0°05 of the latter 
correspond to 0°112 of suboxide of copper. As 90 of starch gives 100 of 
grape sugar, 0°05 of the former correspond to 0°0555 of the latter. Ac- 
cordingly 100 of grape sugar gives actually 201-62 of suboxide of copper, 
instead of 198-2. 
