INFERIOR DRUGS AND METHODS OF DECEPTION. 11 



the determination of tannin can be employed to advantage only when 

 considerable work of this character is done. F. Penny's" process 

 appears to have many advocates. The basis of this method is the 

 oxidation of the coloring" material in an alkaline solution by means of 

 a 1 per cent solution of potassium ferricyanid. It is executed by 

 digesting together, on a water bath, for one hour, 1 gram of powdered 

 cochineal and 5 grams of caustic potash, dissolved in 20 cc of distilled 

 water. Avoid dissipation of the water, dilute the resulting mixture 

 to 100 cc, and titrate an aliquot part by means of the potassium fer- 

 ricyanid solution. The carmine red color is changed to a brownish 

 yellow. The transition of color is indistinct and the exact end reac- 

 tion is difficult to determine. In this work 20 cc of cochineal solution 

 were used for each titration. 



Except in cases where cochineal is to be used for special purposes, a 

 simple colorimetric method gives satisfactory results. For this pur- 

 pose the following process is suggested: 



Digest on the water bath for one hour, 1 gram of powdered cochi- 

 neal and 1 gram of potassium hydroxid, dissolved in 20 cc of water; 

 replenish the water as it evaporates and make the mixture up to 100 cc 

 with distilled water. Dilute 10 cc of this solution to 400 cc. The 

 color thus obtained, from a cochineal of known purity, is taken as the 

 basis and called 100. If pure cochineal always possessed the same 

 tinctorial value and were a well-known commercial article, the color 

 obtained by the above procedure could be utilized as a standard. A 

 readily available uniform standard is, however, found in a properly 

 diluted aqueous solution of potassium permanganate. It has been 

 found that by diluting 12.5 cc of a centinormal potassium permanga- 

 nate solution (0.316 gram of pure potassium permanganate dissolved in 

 1 liter of distilled water) to 100 cc. a tint of color is obtained, when 

 observed in a Nessler tube held at a right angle to the eye of the worker, 

 which is identical to that prepared from pure cochineal by the proc- 

 ess described above. By adopting this potassium permanganate solu- 

 tion as a standard, and calling it 100, the tinctorial value of every 

 sample of cochineal can be ascertained and definitely expressed. If a 

 sample of cochineal should be found in the future possessing a higher 

 coloring equivalent than any met in this work, the standard of com- 

 parison would not need to be changed, but could be expressed by 110, 

 125, etc., as the case may be. 



According to the above method, Nos. 157, 158, and 165 are of good and 

 equal quality, No. 159 is of fair quality, and Nos. 3 and 156 are decid- 

 edly inferior, having only about one-half and two-thirds, respectively, 

 the coloring value of a normal cochineal. A microscopic examination 

 of No. 159 indicates that the silvering is due to rod-shaped bodies, 

 like bacilli, but the usual bacterial stains would not effect them. It 



Rept. Brit. Assor. Advanr. Science, 1855, pt. 2, p. 68. 



