6 



BULLETIN 372, U. S. DEPARTMENT OF AGEICULTUEE. 



0.33 per cent, with 67 per cent of phenols. In order to gather 

 further data on this point tests were made in 1912 with plants in 

 various stages of growth harvested from measured areas. The 

 results obtained are summarized in Table II, which also shows the 

 same results reduced to the basis of yield per acre. 



Table II. — Yield of oil and total phenols f 



'■orti horsemint at 



different 



Stages oj 



growth. 





Weight 

 of herb 

 distilled. 



Actual yield. 



Yield per acre. 



stage of growth. 



Oil. 



Total 

 phenols. 



Herb. 



Oil. 



Phenols. 



Plants just beginning to send up flower 

 stalks 



Pounds. 



453 



506 



1,403 



352 



Per cent. 



0.34 



.30 



.24 



.18 



Per cent. 



72 

 76 

 74 

 74 



Pounds. 



9,690 

 10, 590 

 10,000- 



8,500 



Pounds. 

 32.94 

 31.77 

 24 

 1.5.30 



Pounds. 

 23 05 



Budded stage 



24. 14 



Full flower 



18.48 



Flowers fallen 



10 82 







From these results it wiU be seen that the highest yield of phenols 



is secured in the budded stage and that the loss is very rapid as the 



flowering period advances. Since, however, the difference is but 



slight between the first and second stages, it is advisable with a 



large acreage to begm harvesting about the time the flower stalks 



begin to shoot up; otherwise, it may not be possible to harvest part 



of the area until the flowering stage is weU advanced, and thus loss 



will result. 



DISTILLATION. 



Distillation of the horsemint herb is carried on by the usual 

 methods in practice for distilling such volatile oils as peppermint 

 and spearmint. A retort made of wood, galvanized iron, or boiler 

 iron is used to contain the herb. This retort is connected to a con- 

 denser by a pipe of proper size from the top of the retort. The 

 condenser may be of the worm type, such as is used in the distillation 

 of turpentine, or of the tubular type, with flues similar in arrange- 

 ment to a vertical boiler. Steam from a boiler is admitted to the 

 retort at the bottom and passing through the herb enters the con- 

 denser, where the mixed vapors of steam and oil are cooled by a 

 water jacket. The mixture of water and oil flowing from the con- 

 denser should be collected in a receptacle having a side tube entermg 

 the container at the bottom and bent up so that the outlet is only about 

 2 inches below the top of the container. This will allow the water 

 to be discharged through the side tube, while the oil is retained as a 

 layer on top. It has been found advisable to retain the water which 

 flows from the oil receiver, m order to recover the oil dissolved in it, 

 since this recovered oil is very rich in thymol. 



In 1911, 4 gallons of this water was allowed to stand for several 

 days until it was perfectly clear and all the oil globules were removed. 

 When redistilled a yield of 0.114 per cent of oil was secured, containing 



