210 



The Allen-Marquardt method, modified according to these suggestions, reads as 

 follows: 



MODIFIED ALLEN-MARQUARDT METHOD. 



Reagents. 



Solutions of sodium thiosulphate. Two solutions of sodium thiosulphate are used, 

 one an approximate three-fourths-normal not standardized, and the other a tenth- 

 normal standardized against pure potassium bichromate whose value has been ob- 

 tained against pure iron. ^ 



Carbon tetrachlorid. The purification of this reagent is a fundamental necessity. 

 (See Breckler's method, p. 209.) 



Potassium iodid solution. Dissolve 1 gram in every cubic centimeter of water 

 taken. 



Bichromate oxidizing solution. Dissolve 200 grams of pulverized potassium bichro- 

 mate in 1,800 cc of water and add 200 cc of concentrated sulphuric acid. 



Determination. 



Proceed with the Allen-Marquardt method for determining fusel oil, as given in 

 Bulletin 107, page 98, to the point of adding the oxidizing mixture. Add exactly 50 

 cc of the oxidizing solution to the blank and the samples by means of a pipette or 

 burette and then oxidize under a high reflux condenser for eight hours. During the 

 oxidation, shaking the flask with a rotary motion will prevent any isolation of spots 

 of bichromate on the flask below the carbon tetrachlorid. Decomposition from over- 

 heating is prevented by placing between the wire gauze and the flask two thicknesses 

 of one-fourth inch asbestos board. 



Remove the flask from the reflux condenser and separate the bichromate from the 

 carbon tetrachlorid in a separating funnel. Care must be taken that in this process 

 no bichromate is lost and that the carbon tetrachlorid is washed free from it. Make 

 up the bichromate solution thus obtained to 500 cc. 



Measure 200 cc of this solution into a liter flask. Add 50 cc of the potassium iodid 

 solution, 50 cc of the approximately three-fourths-normal solution of sodium-thio- 

 sulphate, and then 20 cc of concentrated hydrochloric acid. Titrate the excess of 

 bichromate with the standard tenth-normal thiosulphate solution. If a high content 

 of fusel oil was present in the original sample, the addition of 50 cc of the three-fourths- 

 normal thiosulphate solution may be excessive and if such is the case a smaller amount 

 should be added and the blank titrated in the same manner. 



Treat blanks containing exactly the same amount of the reagents used in running 

 each series of commercial samples in the same way, starting them at the point where 

 the carbon tetrachlorid is washed with sodium chlorid. The titration of this blank, 

 to which has been added the same amount of the three-fourths-normal thiosulphate 

 solution, gives the value of the oxidizing mixture. The difference between this 

 value in cubic centimeters of tenth-normal thiosulphate and that obtained on the 

 reduced oxidizing mixture of the commercial sample in each case gives the amount 

 of bichromate used up by the oxidation of the fusel oil present. This difference is 

 then calculated to grams of amyl alcohol using the following factor: 1 cc of tenth- 

 normal thiosulphate equals 0.001773 gram of amyl alcohol. 



The factor used is an average one obtained by three manipulators in making 60 runs 

 on standards containing amounts of pure amyl alcohol, varying from 0,05 to 0.5 gram 

 as follows: 



Development of factor in the oxidizing process of the Allen-Marquardt method. 



