24 



As a means of shedding some light on the differences occurring in titrating winss 

 with the two indicators, the determinations shown in the following table have been 

 carried out: 



Comparison of litmus and phenol phthalein as indicators in titrating some of the organic 



acids existing in ivines. 



The results shown for volatile acids by the Windisch method (p. 22) are somewhat 

 higher than those obtained by the proposed new method, using phenolphthalein. 

 Such discrepancies, however, lose their significance when it is considered that in 

 the determination of volatile acids by the indirect method not only are the results 

 of the titrations employing litmus as indicator incorrect, but the titrations of total 

 and fixed acids are not made under comparable conditions. While it is unques- 

 tionably true that the volatile acids may be completely driven off by repeated evapo- 

 ration in an open dish, it does not follow that the results obtained by means of the 

 two titrations are correct. It is conceivable that important changes may occur during 

 the prolonged heating of the wine in order to reduce the material a third time to a 

 pasty consistency. At any rate, we have no positive knowledge that the so-called 

 fixed acids occurring in the final residue represent the actual fixed acids in the original 

 wine. A titration of the residue may suffice as an indication of the acids remaining 

 after driving off the volatile constituents by prolonged heating, but to employ the 

 result of such a titration as a factor in the calculation of the actual volatile acids 

 appears to be an unwarranted proceeding. 



In expressing results of analysis the orthodox custom appears to be to calculate 

 the fixed and total acids as tartaric and the volatile acids as acetic. It is impossible 

 to concede any advantages in favor of this custom. It may be safe to assume that in 

 wines the fixed acids are in the main tartaric and the volatile acids acetic; but, even 

 on such assumptions, the results are strictly erroneous and not readily comprehended. 

 Such a method applied to the various fruit juices and ciders would fail to give sig- 

 nificant results in practically all cases, and the case is still worse when one adopts 

 the method of calculating the acids as sulphuric. Instead of these conventional 

 methods it has been found better to adopt the plan of expressing all results for total, 

 volatile, and fixed acids in terms of the number of cubic centimeters of normal acid 

 in a definite measure, say 100 cc, of wine. There will then be afforded results which 

 can be readily compared and comprehended. Furthermore, in case it be required 

 to calculate results in terms of any particular acid, such an operation can easily be 

 carried out. 



RECOMMENDATIONS . 



(1) The standard temperature for the determination of specific gravity should be 

 changed to 20 C. A statement of reasons for this change seems to be unnecessary, as 

 the matter has been fully discussed by others, and many chemists have for some time 



