XXIII] FATS AND OILS 305 



16 DETERMINATION. 



Weigh about 0.500 gram of fat, or 0.250 gram of oil (0.100-0.200 gram in the case 

 of drying oils which have a very high absorbent power), into a 500 cc. glass-stoppered 

 flask or bottle. Dissolve the fat or oil in 10 cc. of chloroform. Add 30 cc. of the 

 HiJbl iodin solution in the case of fats, or 40-50 cc. in the case of oils. Place the 

 bottle in a dark place and allow to stand for 3 hours, shaking occasionally. 



This time must be adhered to closely in order to obtain good results. The time 

 allowed does not give the complete iodin absorption power of an oil or fat and can 

 not be compared with determinations in which 6-12 hours have been used. It gives 

 very satisfactory comparative results, but the time factor must be closely observed. 



The excess of iodin should be at least as much as is absorbed. Add 20 cc. of the 

 15% potassium iodid solution, shake thoroughly and then add 100 cc. of water, wash- 

 ing down any free iodin that may be found on the stopper. Titrate the iodin with 

 the N/10 sodium thiosulphate, adding the latter gradually, with constant shaking, 

 until the yellow color of the solution has almost disappeared. Add a few drops of 

 the starch indicator and continue the titration until the blue color has entirely 

 disappeared. Toward the end of the titration, stopper the bottle and shake vio- 

 lently, so that any iodin remaining in solution in the chloroform may be taken up 

 by the potassium iodid solution. Conduct 2 blank determinations along with that 

 on the sample. The number of cc. of the N/10 sodium thiosulphate required by the 

 blank less the amount used in the determination gives the thiosulphate equivalent 

 of the iodin absorbed by the fat or oil. Ascertain the iodin number by calculating 

 the per cent by weight of iodin absorbed. 



Haniis Method. — Official. 



17 REAGENTS. 



Hanus' iodin solution. — Dissolve 13.2 grams of iodin in 1 liter of glacial acetic 

 acid (99.5%) which shows no reduction with dichromate and sulphuric acid. Add 

 enough bromin to double the halogen content as determined by titration (3 cc. of 

 bromin are about the proper amount). The iodin may be dissolved by heating 

 but the solution should be cold when the bromin is added. 



A convenient way to prepare the Hanus solution is as follows: Measure 825 cc. 

 of acetic acid which has shown no reduction by the dichromate test and dissolve in 

 it 13.615 grams of iodin with the aid of heat. Cool and titrate 25 cc. of this solu- 

 tion against the N/10 sodium thiosulphate. Add 3 cc. of bromin to 200 cc. of acetic 

 acid and titrate 5 cc. of the solution against the N/10 sodium thiosulphate. Cal- 

 culate the quantity of bromin solution required exactly to double the halogen con- 

 tent of the remaining 800 cc. of iodin solution as follows: 



A = p in which 



A = cc. of bromin solution required; 



B = 800 X the thiosulphate equivalent of 1 cc. of iodin solution; 



C = the thiosulphate equivalent of 1 cc. of bromin solution. 

 Example: 136.15 grams of iodin are dissolved in S2.50 cc. of acetic acid. 30 cc. 

 of bromin are dissolved in 2000 cc. of acetic acid. Titrating 50 cc. of the iodin 

 solution against the standard thiosulphate shows that 1 cc. of the iodin solution 

 equals 1.1 cc. of the thiosulphate (0.01G5 gram of iodin). Titrating 5 cc. of the bro- 

 min solution shows that 1 cc. of the bromin solution equals 4.6 cc. of the thiosulphate. 

 Then the quantity of bromin solution required to double the halogen content of 



8200 X 1 1 

 the remaining 8200 cc. of iodin solution is equivalent to . „ — '— or 1961 cc. Upon 



