6 



B. Dextrin may be determined by the following differential method based on the 

 difference between its optical activity and that of maltose: 



p = A (MX8.1) when D=ol ex t r i n in grams per 100 cc; A=total rotation in 



11. o 



degrees Ventzke in 200 mm tube, and M= percentage of maltose as determined 

 gravimetrically. 



DIRECT POLARIZATION. 



Read the polarization of the original sample in degrees Ventzke in a 200 mm 

 tube. If the beer is turbid clarify by shaking with alumina cream. 



INVERT POLARIZATION. 



To 10 cc of the beer in a small flask add 1 cc of concentrated hydrochloric acid, 

 invert by slowly heating to 68 C., cool, polarize in a 200 mm tube and increase the 

 reading one-tenth to allow for dilution. 



GLYCEROL. 



Proceed as directed on page 82, Bulletin 65. The milk of lime is added during 

 evaporation after the carbon dioxid has been expelled. It is advisable that the 

 filtrate, after being evaporated to a sirupy consistency, be treated again with 5 cc 

 of absolute alcohojand two portions of 7.5 cc each of absolute ether. If clear, con- 

 tinue as directed; if not clear, it is necessary to treat as above. 



ASH. 



Evaporate 25 cc of the sample to dryness, ignite at low redness until thoroughly 

 charred, place in a muffle, and continue the ignition until ash is white. Leaching 

 is rarely necessary. 



PHOSPHORIC ACID. 



Measure out 50 cc of the beer, free from carbon dioxid, into a small beaker. Add 

 5 cc of an acid solution of sodium acetate and heat to boiling. Run in from a burette, 

 standard uranium acetate solution 0.5 cc at a time, testing each time until a drop of 

 the beer, when placed on a white plate, colors a drop of potassium ferrocyanid 

 slightly brown. The number of cubic centimeters of the uranium acetate solution 

 necessary, multiplied by 0.01, gives the grains per 100 cc of phosphoric acid in the 

 beer. If the beer is very dark, employ the official method, gravimetric or volumet- 

 ric, using the residue obtained in the determination of the ash. 



PROTEIN. 



Evaporate 25 cc of the original beer, to which has been added a small amount of 

 tannin to prevent frothing, and proceed according to the Kjeldahl or Gunning 

 method for the determination of nitrogen, and multiply the result by 6.25. 



CARBON DIOXID. 

 Proceed as directed in Bulletin 65, page 95. 



PRESERVATIVES. 



Add 5 cc of dilute sulphuric acid to the remaining residue after distillation, and 

 shake out with an equal volume of a mixture of ether and benzene. Pour off the 

 supernatent liquid and test for salicylic acid, benzoic acid, and saccharin in the usual 

 manner. It is well to reserve 2 or 3 cc of the liquid in a test tube for the salicylic 

 acid test before evaporating the remainder to dryness in a small porcelain evaporat- 

 ing disk. 



Determine sulphites and sulphurous acid as determined under wines, page 90, Bul- 

 letin 65, employing the method of direct determination on 50 cc of the sample. 



Determine flourids by the method of Blarez as follows: Thoroughly mix the sample 

 and heat 150 cc of the sample to boiling. Add to the boiling liquor 5 cc of a 10 per 

 cent solution of barium acetate. Collect the precipitate in a compact mass, using to- 

 advantage a centrifuge, wash upon a small filter, and dry in the oven. Transfer to a 

 platinum crucible, first breaking up the dry precipitate and then adding the filter 

 ash to the crucible. 



[Cir. 33] 



