ELISIIA iMITCHELL SCIENTIFIC SOCIETY. 53 



about one minute adil 15 or 20 cc. water, and observ-e the 

 shades of color. This observation must be made ivithin jive 

 minutes, as the air and bVht will soon cause all to be unifbrmlv 

 blue. 



By comparison with the shades of color ])roduced by these 

 standard dilutions, you can easily estimate the strength of any 

 sam[)le of laudanum with much accuracy. The sample must, 

 of course, be dilut^nl with an equal part of dilute alcohol. The 

 presence of tannin interferes with this method, but opium does 

 not contain tanuiii. Tannin is easily detected with a solution 

 of a salt of iron. The ferridcyanide mixture must be freshly 

 prepared and the glasses must be cleari and dear, as the slightest 

 bluish tinge interferes. Wash them with caustic soda and then 

 with hydrochloric acid and rinse if they are soiled with Turn- 

 bull's Blue. 



The ferridcyanide mixture is probably the best confirmatory 

 test for morphine. If one drop of water containing .000001 

 gram of morphine is mixed on a white slab with one drop of 

 the ferridcyanide mixture a blue color will be developed within 

 one minute. With water alone the mixture will become of a 

 bluish shade in about ten minutes, owing to the action of air and 

 light. 



P. S. — To estimate the strength of vinous or aqueous com- 

 pounds of opium they must be brought to about the same spe- 

 cific gravity as the "standard dilutions'' with alcohol, that the 

 drops may be uniform in size. 



COLORIMETRIC METHOD FOR ESTIMATING TANNIN IN 



BARKS, ICTC. 



Dissolve 0.04 gram potassic ferridcyanide in 500 cc. water, 

 and add to it 1.5 cc. (about 22 drops) liquor ferri chloridi. 

 Call this Iron Mixture. 



Dissolve 0.04 gram "pure tannin (gallotannic acid) which has 

 been dried at 212° F. in 500 cc. of water. Call this Tannin 

 Solution. 



