QQ REPORT OP THE COMMISSIONER OP AGRICULTURE. 



juice was j^reviously allowed to stand for about half an hour, to allow 

 included air to escape. 



A weighed portion of the juice was dried, at a.heat not exceeding 

 100° 0., until two successive weights showed but little variation ; the 

 percentage of residue thus found was stated as total solids in juice. 

 These figures can be regarded only as fair approximations, for chemists 

 are well aware of the difficulties attending the perfect desiccation of 

 saccharine juices. In this connection, however, the residts are valuable 

 as checks upon the sugar determinations. 



For determination of sugars in the juice 100 c. c. were taken, and 

 made in every case to 125 c. c. by addition of solution of subacetate of 

 lead and water. Among other substances precipitated by the treatment 

 were chlorophyll, albumenoid matter, gum, and lead salts of the inor- 

 ganic acids of the ash. 



The liquid was filtered perfectly clear through dry paper, and was 

 sometimes colorless and sometimes amber. Every 10 c. c. of this liquid 

 represented 8 c. c. of the original juice. 



For the determination of glucose, 10 c. c. of this filtered liquor were 

 taken, and for sucrose 5 c. c. 



The portion for glucose was treated with considerable excess of Fehl- 

 ing's solution, and carefully heated on the water-bath, a thermometer 

 being inserted in the liquid, which was not allowed to rise above 75^ 0. 

 At this temperature perfectly pure sucrose does not reduce Fehling's 

 solution in the least. 



The portion for sucrose was inverted by boiling half an hour with 

 Blight excess of dilute hydrochloric acid. The inverted sugar thus 

 formed was then treated with large excess of Fehling's solution, exactly 

 as above described, except that it was not necessary to keep the tem- 

 perature lower than the heat of the water bath (100° C). 



The precipitated red suboxide of copper was then thoroughly washed 

 with hot water by decantation and filtration (without aspiration usually) 

 through fine paper. It was then dissolved in an acid (sulphiuic) solu- 

 tion of ferric sulphate, and the amount of ferrous salt determined by 

 titration with potassium permanganate. 



This method for determining glucose depends upon the following facts: 



1. That two molecules (360 parts by weight) of glucose (Cg HiiOe) will 

 reduce from Fehling's solution five molecules of cuprous oxide (5 Cu2 O). 



2. That the five molecules of cuprous oxide thus precipitated will re- 

 duce in acid sol. five molecules of ferric sulphate (Fca (S O4) 3) to form 

 ten molecules (1,520 parts by weight) of ferrous sulphate (Fe S O4) as 

 is explained by the following equation: 



( 5 Cu, O ) , ( 5 Fe^ (S 0^)3 ) , | 5 H2 S O4 ) _ ( 10 Cu S O4 ) , 



\ 715 narls ] ^" \ 2,000 parts ( ' M90 P"i'ts S \ h^-^ V'<^^^^ S ^ 



( 10 Fe S O4 ) , i 5 H2 O - 



1,520 parts 



> ( 5H2O ) 

 I "^ > 90 parts ] . 



The ten molecules of ferrous sulphate thus formed will decolorize one 

 molecule (31G.2 parts by weight) of potassium permanganate (K2 IMua 

 Og), thus: 



( 10 Fe S O4 ( J ( Ko Mn2 Os ) , ( 8 Ha S O4 > _ ( 5 Fe^ (S 04)3 ) . 



\ 1,520 parts S "^ \ 31G.2 parts ] + \ 784 parts S ~~ \ 2,000 parts ^ ^ 



(2MnS04) , ( K2SO4 ) . ( SH2O ) 



\ 302 parts ] "*" \ 174.2 parts i "^ ( 144 parts j 



Bv following this explanation, it appears that two molecules of glu- 

 cose" are exactly represented by one molecule of potassuim permauga- 



