462 FOODS AND FOOD ADULTERANTS. 



drain the same leugth of time (thirty seconds). The bottle is then placed 

 in the steam-bath, together with a blank, containing no fat. After 

 saponifieation is complete and the bottles cooled, the contents are 

 titrated with accurately semi-normal hydrochloric acid, using phenolph- 

 thalein as an indicator. The number of cubic centimeters of the acid 

 used for the sample deducted from the number required for the blank 

 gives the number of cubic centimeters which combines with the fat, 

 and the saponification equivalent is calculated by the following formula, 

 in which W equals the weight of fat taken in milligrams and N the 

 number of cubic centimeters which have combined with the fat. 



2W 



Sap. equiv. = >r- 



If it is desirable to express the number of milligrams of potash for 

 each gram of fat employed, it can be done by dividing 5,G10 by the 

 saponification equivalent and multiplying the quotient by 10. 



PRESERVATION OF THE REAGENTS USED IN DETERMINING THE VOLATILE ACIDS AND 

 SAPONIFICATION EQUIVALENTS. 



In order to secure uniformity of strength in the deci normal and ap- 

 proximately semi-normal alkali solution employed in the above opera- 

 tions, it is necessary that they be preserved out of contact with the car- 

 bonic acid in the air. This is best done by the apparatus used for sup- 

 plying burettes. In the U tu ^ e of this apparatus is placed some of the 

 solution which is to be preserved in the flask itself. The air, therefore, 

 which enters the bottle as the solutions are withdrawn is entirely de- 

 prived of carbonic acid by passing through the tube. 



(c) Iodine number Reagents. Twenty-live grams of pure iodine dis- 

 solved in 500cc of strong alcohol. Thirty grams of mercuric chloride 

 dissolved in 500cc of strong alcohol. 



The solution of mercuric chloride is to be poured into the iodine solu- 

 tion. The iodine solution undergoes a constant change, by which its 

 percentage of free iodine is diminished. This has been ascribed to the 

 presence of impurities in the alcohol, but is doubtless due to a conver- 

 sion of the iodine into hydroiodic acid and to the disturbing influence 

 of the chloroform used in the subsequent process. There are, however, 

 local changes in the strength of the iodine solution which are noticed 

 from day to day, as is indicated in the examples which follow, .the iodine 

 solution being apparently stronger some days than others. These local 

 variations may also be ascribed to the influence of the chloroform on t he 

 iodine solution. It is therefore of the utmost importance that the blank 

 titrations in which the strength of the iodine solution is determined 

 should be made on the measured portion of the solution, Ireatcd with 

 the same amount of chloroform, and allowed to stand the same length 

 of time as the samples containing the oils or fats whose iodine numbers 

 are to be determined. By this method, although the strength of the 

 iodine solution may appear to vary from day to day, yet this variation 

 \s ill take place pt'ri /m.s.s/t with the change in the strength of the iodine 



