10 



COMMENTS BY ANALYSTS. 



K. v. BAUER-BREITENFELD. 



Preparation of the samples. The two methods shaking, and pouring from one 

 beaker into the other showed practically no difference in the results, the specific 

 gravity being the same according to both methods. The amount of alcohol, after 

 shaking the sample, was only 0.01 per cent higher than after pouring. Both 

 methods, furthermore, secure a complete separation of the carbonic-acid gas. 



Determination of specific gravity. We made all three determinations of specific 

 gravity at the temperatures of 15, 17.5, and 20 C., using, of course, in the calcula- 

 tion three different water weights of the pycnometer, corresponding to the temper- 

 ature employed. We did not find any important differences between the determi- 

 nations, the specific gravity increasing 'only slightly with the lowering of the temper- 

 atures. The differences in the extreme cases amounted to 

 0.00007 in the specific gravity of alcohol. 

 0.00011 in the specific gravity of the real extract. 

 0.00014 in the specific gravity of the beer itself. 



As the difference between the two temperatures was never higher than indicated 

 above, they can practically be substituted for one another. For this reason we would 

 be in favor of the employment of the temperature of 20 C. as a normal temperature 

 for the determination of specific gravities. 



The tables of Ellion and Balling give almost the same results with respect to the 

 amount of extract, while the table of Schultz and Ostermann indicates a somewhat 

 higher extract. 



Determination of alcohol. We determined the alcohol by the distillation method 

 strictly according to your suggestions, but having no Zeiss immersion refractometer at 

 our disposal used instead of this the refractometer of Tornoe. The results obtained 

 by this instrument, and by the distillation method, with regard to the amount of 

 alcohol or real extract, never differed more than 0.1 per cent. Between the alcohol 

 tables of Squibb and Baumhauer no considerable difference appears to exist. 



Determination of extract. No considerable difference between the methods of 

 evaporating to dryness, distillation, and Tornoe's refractometer could be detected. 

 The first method," however, takes too long a time to come into practical use. 



Total acids. Instead of using neutral litmus paper as an indicator, we prefer the 

 red phenolphthalein solution, prepared by adding 12 drops of the ordinary alcoholic 

 solution of phenolphthalein and 0.2 cc of normal alkali to 20 cc of water. The end 

 point of the titration is determined by transferring one drop of the solution to a 

 porcelain plate and adding one drop of the beer as soon as the red color of the indi- 

 cator does not appear. 



In answer to an inquiry, K. v. Baur-Breitenfeld submitted the fol- 

 lowing* method for the determination of dextrin by means of the 

 polar iscope, together with other notes: 



Twenty-five cubic centimeters of beer are clarified with 5 cc of alumina cream and 

 filtered after the addition of water until the volume amounts to 50 cc. The clarified 

 filtrate is polarized in the 200 mm tube, using the Soleil Ventzke apparatus. The 

 reading in degrees is multiplied b 2 on account of the dilution, and from the total 

 rotation is deducted the rotation of the corresponding amount of maltose in 100 cc 

 of beer, determined by the gravimetric-analytical method. One gram of maltose 

 dissolved in 100 cc in the 200 mm tube rotates 8.1+, and the quantity of maltose 

 found must, therefore, be multiplied by 8.1. 



After the deduction of this rotation from the total rotation, the result corresponds 

 to the quantity of dextrin in 100 cc of beer. As 1 gram of dextrin in 100 cc of solution 

 in the 200 mm tube rotates 11. 6+, the quantity of dextrin is found by dividing the 

 polarization-difference by 11.6. 



Inasmuch as in fermented normal beer the reducing sugar consists almost exclu- 

 sively of maltose and very small quantities of .reducing malto-dextrins, it is possible 

 to deduce from an abnormally low amount of dextrin obtained by the polarization 

 method, that in the production of the beer, aside from malt and unmalted cereals, 

 large quantities of dextrose (glucose and grape sugar) have been used. 



As far as the use of the refractometer of Tornoe is concerned in connection with 

 the examination of beer, we have found that the results obtained in this way corre- 

 spond very well with those obtained by the analytical method. In our laboratory 

 almost all the beers are examined according to both methods, which gives us an 

 excellent control of our work and its accuracy. 



[Cir. 33] 



