BATES AND PHELPS : TESTING OF SUGARS 317 



titration of the acid remaining unneutralized or less frequently by- 

 allowing gas to pass until a change is shown by the indicator used. 



The choice of the proper indicator to use for this determination 

 is of greater importance than the choice of apparatus. The indi- 

 cators which were found to be most suitable for the determination 

 of ammonia in gas were sodium alizarinsulphonate, cochineal, and 

 paranitrophenol. The presence of glass beads which are used in 

 some of the absorption apparatus may lead to erroneous results 

 for two reasons: First, the beads may yield alkali on contact 

 with the absorbing liquid; second, washing of the beads may be 

 incomplete. It is recommended that the operator test the solu- 

 bility of any beads he may use; the method of washing out the 

 apparatus should also be tested. 



Five different forms of apparatus were tested: The Referees 

 apparatus, the Emmerling tower, the Lacy apparatus, the com- 

 mon form of gas wash bottle, and a modified form of the Gumming 

 gas bottle. The relative efficiency, and from this the probable 

 accuracy, of the different forms of apparatus was determined by 

 running them in parallel, using gas from a common supply. As 

 a result of this comparison it was found that the Emmerling tower 

 gave results which were somewhat higher than those obtained with 

 the other forms and that the wash bottle gave results consistently 

 lower. With careful operation any one of the five forms of appa- 

 ratus tested would ordinarily give results that are well within the 

 limits of accuracy required for this determination, either for 

 commercial control work or for the purpose of gas inspection. 



PHYSICAL CHEMISTRY.— r/ie influence of atmospheric co7idi- 

 tions in the testing of sugars.'^ F. J. Bates and F. P. Phelps. 

 Communicated by G. K. Burgess. 

 A simplified form of Marvin's evaporation equation has been 



applied to the evaporation of raw sugar solution during filtration. 



Marvin's formula reduces to — rr = C (Pg — Pa) or Q = C 



(Pg — Pa) T, which, it is shown, fits the observations satisfactorily. 

 Q = the change due to evaporation in the time T, Pg = the vapor 

 pressure of the sugar solution, Pa = the saturation vapor pressure 

 in the air at the temperature of the dew point. 



^To appear in full as Bureau of Standards Scientific Paper 221 (in press). 



