1919] 



DODGE — TYROSINASE REACTION 



75 



tural formula of ty rosin shows that there are three readily 

 reacting groups for which more or less well-defined methods 

 of determination exist. These are the amino group, which 

 may be determined by the Van Slyke method, the carboxyl 

 group, which may be determined by titration, and the phenol 

 group, which may also be titrated by a suitable method. If 

 ammonia is split off, this is easily determined in several ways. 

 Determination of amino-nitrogen. — The " micro' ' Van Slyke 

 apparatus, with certain modifications, was used for the deter- 

 mination in the earlier experiments. By taking extreme care 

 in manipulation, 8 cc. of the solution analyzed could be used 

 in a determination instead of the usual 2 cc. In this case it 

 was convenient to use 60 per cent sodium nitrite solution 

 instead of 30 per cent. Caprylic alcohol was employed occa- 

 sionally if the mixture started to foam. Later it was found 

 possible to use a "micro" burette with the "macro" form of 

 apparatus, providing proper attention was paid to the amount 

 of nitrogen liberated from the nitrite in the check. It was noted 

 that after all of the air was expelled from the apparatus, 

 successive burettefuls of the oxides of nitrogen gave a series 

 of readings as follows: 0.12 cc, 0.10 cc, 0.10 cc, 0.10 cc, 

 0.09 cc, 0.10 cc Much care must be taken to be sure that 

 the alkaline permanganate solution is absorbing properly. In 

 the usual procedure, all of the nitrogen is contained in the 

 first buretteful, or in the first few cubic centimeters of the 

 second buretteful, hence the error due to not taking into con- 

 sideration the total gas volume before absorption was neg- 

 ligible. However, when dealing with such a dilute solution, 

 this precaution was found necessary, as the amount of nitrite 

 is in such large excess of the amount actually needed for the 

 reaction. 



Determination of ammonia. — The permutit method of am- 

 monia determination as described by Folin and Bell ('17) 

 was found to be adequate for our purpose. Two grams of 

 permutit were placed in the bottoms of each of the required 

 number of 100-cc volumetric flasks, the solution to be 

 analyzed or the standard, as the case might be, was added, 

 and the flasks shaken by a mechanical shaker for 5 minutes. 



