20 



volatile acids ex-cure when 500 cc of distillate have passed over. On this basis the 

 results show that the proportion of volatile acids collected in the first 300 cc of distil- 

 late ranges from 90 to 95.7 per cent, only four samples showing a proportion slightly 

 greater than 95 per cent. Thus, even in the present provisional method of the asso- 

 ciation, if the entire apparatus be of fixed dimensions and relations in addition to 

 the other conditions stipulated, a large part of the fundamental error is still retained 

 even by carrying the distillation to 300 cc. If the distillation be conducted slowly 

 and the.volume of the wine permitted to become too large, an insufiicient amount of 

 volatile acids will pass over; if the distillation be too rapid and the volume of wine 

 be permitted to diminish too much, there may occur an overheating and the amount 

 of volatile acids will be too great. Finally , in order to obtain the greatest possible 

 concordance in results, the distillation must be watched from beginning to end with 

 the greatest care. 



It has also been recognized that the agreement in results obtained by several dis- 

 t illations on a given sample fails to reach as high a degree as ought to be expected, 

 even in approximately exact determinations. When the distillations are carried 

 to 400 cc, or even until the vanishing point of acidity is fairly reached, the results 

 often fail to agree within reasonable limits. A difference in the results of the titra- 

 ti'-n< amounting to from 0.3 to 0.5 cc of tenth-normal alkali has often been noted; 

 .UK! the differences are commonly far greater at the close of the 200 cc period, amount- 

 ing to from 0.6 to 0.8 cc in several instances. 



Briefly, then, the objections to the present provisional method are: 



(1) The method is complicated, requiring rather elaborate apparatus and tiresome 

 supervision. 



(2) The prolonged heating of the wine by the direct action of the flame doubtless 

 affects in some manner the constitution of the acid ingredients. 



(3) The results do not to a sufficient extent represent the total volatile acids. 



(4) The results are not reasonably concordant in the hands of different persons or 

 even in the hands of a single individual. 



Owing to these considerations, various chemists have proposed the abandonment 

 of the direct method of determining volatile acids in favor of an indirect course of 

 procedure. After a prolonged examination of the relative merits of these two general 

 methods, Windisch" proposes the following: 



Twenty-five cubic centimeters of wine are titrated in the usual manner for total 

 acids, using litmus or litmus paper as indicator. Another 25 cc portion is then evap- 

 orated on a water-bath in a porcelain dish to 3 to 5 cc, the residue dissolved in about 

 25 cc of hot water, the liquor again evaporated to 3 to 5 cc, the residue again dissolved 

 in about 25 cc of hot water, and the liquor evaporated a third time to 3 to 5 cc. Finally, 

 the residue is dissolved in hot water and the fixed acids titrated, using litmus as an 

 indicator. From the difference between these titrations the volatile acids are calcu- 

 lated: 



The advantages of this over the present provisional direct method are obvious, 

 and have been adequately demonstrated by Windisch and others. The wine is 

 never heated above the temperature of the w r ater-bath and the volatile acids are 

 undoubtedly all driven out, leaving the fixed acids probably unchanged. Further- 

 more, the results appear to be reasonably concordant and satisfactory. Various 

 modifications of the indirect method of obtaining the volatile acids have appeared. & 



Sellier c has described a simple apparatus which consists of a small wide-neck flask 

 into which is fitted a cylindrical-shaped flask. In the bottom of the latter flask is a 



Zts. Xahr. Genussm., 1905, 9: 70. 



f> Methods proposed by Roos and Mestrezat, Guerin, Curtel, and Robin: Bui. assoc. 

 chim. sucr., 1907,25: 41-49; J. pharm. chim., 1907, 25: 491^92; Ann. chim. anal., 

 1901, 6: 361; J. pharm. chim., 1904, 19: 531-533. 



'Ann. chim. anal., 1901, 6: 414. 



