6 
BULLETIN 372, U. S. DEPARTMENT OF AGRICULTURE. 
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 from horsemint at different stages of 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 
15.30 
Pounds. 
23.05 
Budded stage 
24. 14 
Full flower 
18.48 
Flowers fallen 
10.82 
From these results it will 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 begin 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 well 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 entering 
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, in 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 0.1 14 per cent of oil was secured, containing 
