li THE ALUMNI JOURNAL 



It is unnecessary to further discuss this method as all who have 

 the occasion to use this method no doubt will condemn it as inac- 

 curate. A great deal could be said about this, but I omit 

 discussions. 



I will next consider a method which is considerably used by the 

 United States Department of Agriculture, and is known as the 

 Chace colorimetric method, and is based on the action of adehyde 

 on fuchsine sulfurous acid ; this method is fairly accurate in experi- 

 enced hands, but usually fails owing to the fact that the color pro- 

 duced by a standard citral solution and the extract or oil in ques- 

 tion are never the same, it requires a very good imagination to 

 match both colors and the results are usually high. 



The most accurate method that I can recommend, and one which 

 has been tried, is the one known as Romeo's method. This method 

 was used on a purified sample of citral and showed after two 

 determinations ioo.i% of citral, and by the bisulphite method 

 98%. The Romeo method has since been used in our laboratory 

 and the oils show the presence of 4.15 to 4.40% citral. The method 

 follows : 



Dissolve 400 grammes of sodium sulphite crystallized 

 (NaoSOy-f 7H2O) in one (i) litre of water and add 200 c. c. of satu- 

 rated solution potassium bisulphite, so that the liquid requires an 

 acidity which is N/2, or 20 c. c. should require 20 c. c. N/2KOH 

 to neutralize it, using rosolic acid as indicator. 



Measure 5 c. c. of oil in an Erlenmeyer flask or an acetilization 

 flask, and weigh accurately; next add rosolic acid as indicator and 

 a few drops of N/io KOH to neutralize any free acidity which 

 might be contained in the oil. Introduce into the flask 25 c. c. of 

 N/2 bisulphite solution, connect with Reflux condenser and heat 

 for one hour; cool solution, taking all the necessary precautions 

 which are always to be observed in determinations of this kind. 

 Titrate excess of N/2 bisulphite solution by means of N/2 KOH. 

 The end point is very sharp. Multiply the number of c. c. required 

 by 0.03802, the prod^et, by 100 and divide by the weight of oil 

 pf lemon taken. 



