214 ODOEOGEAPHIA. 



years of acre, if kept in well-filled vessels, should dissolve readily 

 in alcohol in all proportions, making a clear solution without need 

 of filtration.* 



When a few drops of the oil are placed upon white paper and 

 held over a lamp or gas jet, it should volatilize quickly and 

 perfectly without undergoing change or leaving any residue. When 

 3 drops of the oil are placed upon 4 grains of resublimed iodine (or 

 such quantity as will thoroughly saturate, but not drown the 

 iodine), there should be but a slight reaction, and what little 

 vapour is produced should be almost invisible, becoming entirely 

 so after having arisen about twelve inches above the mixture, the 

 colour of the vapour assuming a bluish cast. The colour of the 

 mixture in this test should be carefully noticed, which, in the case 

 of pure peppermint, is of a brown, or brownish-black colour, the 

 iodine dissolving slowly and imperfectly. If oil of turpentine, 

 erigeron, " Fire-weed," or other terebinthinate oils are present, 

 there will be quite a violent reaction (according to the quantity of 

 the adulterant) with the evolution of considerable heat, and a red 

 or recldish-yellow vapour will be produced, of a rank odour, par- 

 taking considerably of the nature of the adulterant, and the 

 mixture will change to a bright violet. If the colour of the 

 mixture is most carefully noted, a very slight quantity of such 

 adulterants can be detected. When to 25 drops of alcohol, 1 drop 

 of nitric acid, sp. gr. 1*2, is added, and then one drop of pure oil of 

 peppermint, there will be produced, within about half an hour, a 

 blue or bluish-green colour, which will remain permanent for a 

 long time. 



Oil of pennyroyal and of Mentha arvensis produce no coloration. 

 A much more intense coloration will be produced when one drop 

 of nitric acid, of the strength as stated, is mixed with 50 or 60 



* This test would appear to apply only to the English oil, at all events 

 with any degree of reliability. The " Hotchkiss " oil, which is the most 

 esteemed brand in the Wayne County, was formerly perfectly soluble in 

 rectified spirit, 56 o. p. one part to seven, but consumers have since found that 

 spirit of even 60 o. p. only makes a milky solution, which no kind or extent of 

 paper filtering will clear. Such a mixture, when first made, and for a consider- 

 able time after, is unsaleable ; but in the course of four or five months it 

 partially loses its turbidity, and becomes comparatively clear, depositing on the 

 sides and bottom of the vessel in which it is made a dirty precipitate. This 

 precipitate is of a resinous nature. It has been recommended to clear the 

 milkiness from the solution, to add a little carbonate of magnesia, shake 

 occasionally for a few days, then filter. 



