THE ALUMNI JOURNAL 131 



THE ASSAY OF PEPSIN U. S. P. 



In makinj>- the U. S. P. assay of pepsin care must be taken to disin- 

 tegrate thorouohly the coagulated egg albumen in order to be fair with 

 the pepsin sample. To do this well by means of a glass rod tipped with 

 cork or rubber tubing as the pharmacopoeia directs is very difficult. A 

 few vigorous shakes will accomplish the result more efifectually. On the 

 other hand, to insure the stringency of the U. S. P. test, the method 

 of ap-itation every ten minutes during the digestion, by inverting the 

 bottle once, should be rigidly adhered to. A more vigorous shakmg 

 every ten minutes gives the sample too great an advantage. 



VALUE OF lODEOSIN AS AN INDICATOR IN ALKALOIDAL ASSAYS. 



It is to be regretted that our new Pharmacopoeia does not more em- 

 phatically advocate the use of iodeosin as an indicator in pharmaceutical 

 assaying. In the assays of nux vomica and physostigma and their 

 preparations, iodeosin is directed, but in the case of belladonna, hen- 

 bane, stramonium, scopola, coca, and pilocarpus the use of iodeosin is 

 made optional. It is in in the assay of drugs containing mydriatic 

 alkaloids that I deem its use especially desirable. Although directions 

 for making iodeosin indicator are to be found in the appendix of the 

 Pharmacopccia I prefer to make the titration as follows : 



A solution of alkaloidal residue in excess of standard acid is trans- 

 ferred to an 8-ounce bottle, diluted to about lOO Cc. with distilled 

 water, about 30 Cc. of ether added, and lastly 5 to 8 drops of a 5 per 

 cent, solution of iodeosin in alcohol. The bottle is stoppered and vig- 

 orously shaken after each addition of centi-normal potassi. The end 

 reaction is marked by the appearance of a rose pink tinting the lower 

 aqueous layer. The ether, which I prefer to use in amounts somewhat 

 in excess of those advocated in the LT. S. P., serves the double purpose 

 of holding the indicator itself in position while the aqueous layer is still 

 acid, and of dissolving and holding in solution the coloring matter 

 present in the alkaloidal residue being titrated, thereby enabling the 

 color change of the end reaction to be more clearly seen in the practi- 

 cally colorless lower layer. 



I have found, however, that the most delicate reading can be obtained 

 with this indicator by observing the color change in the agitated mix- 

 ture of water-ether layers. In this way I have been able in assay work 

 to note the end reaction on the addition of two drops (about 1-20 Cc.) 

 of N_ioo alkali, the milky looking mixture during the vigorous shak- 



