For the distillation the freshly collected grass tops, tied in bundels, are transferred into the still both through the lateral opening and from above until it is about 3/4 full. For such a charge 1000 bundels with a total weight of about 750 lbs. are required. Then the still is filled to about 1/4 its height with water (about 40 gals.). After the lateral opening has been closed, the helmet placed in position and all cracks luted with cow's dung, fire is started beneath the still. The distillation of a charge lasts from 5 to 6 hrs. and yields 1 to 1 1/2 bottles of 22 oz. each of oil. The oil is allowed to remain in the bottles for some time in order that it may separate from any admixed water, also from deposits (copper salts), and is later transferred to tin-lined iron drums for shipment.
Attempts to cultivate lemongrass in other countries have mostly been carried on with Cymbopogon citratus, Stapf (See p. 202) which yields the inferior West Indian oil.
With the object in view of obtaining a lemongrass oil in every respect the equal of the Malabar oil, the botanical experiment stations in the Leeward Islands have, according to F. Watts and H. A. Tempany1), attempted the cultivation of the genuine Cochin grass of Cymbopogon flexuosus. The grass is said to flourish. However, four experimental distillations made with Cochin grass cultivated in Antigua and Montserrat yielded oils that did not possess the required citral content but 53, 63, 64 and 68 p. c. respectively. Watts and Tempany attribute this to insufficient maturity of the grass since experiments with West Indian grass have shown that both yield of oil as well as citral content increase with maturity. 72,5 kg. of a three months old grass cultivated in Antigua yielded upon distillation 139 cc. of oil with a 58 p. c. citral content, whereas the like amount of grass one year old yielded 206 cc. oil with a 69 p. c. citral content. Additional experiments are going to be made to ascertain the conditions most favorable to the harvest of Cochin grass. From the experiments thus far made at the botanical experiment station it becomes apparent that 2 to 3 cuts can be made in a year and that each cut yields about 6000 to 8000 lbs. of grass per acre. The oil yield was determined at 0,2 to 0,26 p. c.
1) West Indian Bulletin 9 (1908), 267; Report of Schimmel & Co. April 1909, 64.
Similar experiments made in Barbados1) had yielded very favorable results. From a grass raised from Cochin seed, the local government laboratory distilled a readily soluble oil rich in citral.
Composition. Up to 1888 the chemical composition of lemon-grass oil was quite unknown. At that time an aldehyde C10H16 O was discovered as its principal constituent in the laboratory of Schimmel & Co.2). Because of its decided lemon-like odor, the name citral was given to this substance (For properties see vol. I, p. 408). Three years later F. D. Dodge3) described the same aldehyde as citriodora aldehyde. He, however, did not work with the pure aldehyde since he describes it as a dextrogyrate substance boiling at 225°.
Inasmuch as Barbier and Bouveault4) obtained three distinct semicarbazones5) (m. p. 171°, 160° and 135°) by the action of semicarbazide on lemongrass oil, they arrived at the conclusion that the citral of lemongrass oil consists of three isomeric aldehydes. Tiemann1), however, showed that the semicarbazone melting at 135° is a mixture of the other two, a fact later substantiated by Bouveault2). Hence the case is one not of isomeric aldehydes but of isomeric semicarbazones.
1) Report of Schimmel & Co. October 1908, 82.
2) Bericht von Schimmel & Co. October 1888, 17.
3) Americ. chem. Journ. 12 (1890), 553; Berl. Berichte 24 (1891), 90 Ref.; Chem. Zentralbl. 1891, I. 88.
4) Compt. rend. 121 (1895), 1159.
5) The formation of different semicarbazones from citral was first observed by Wallach. Berl. Berichte 28 (1895), 1957; comp. also Tiemann and Semmler, Bed. Berichte 28 (1895), 2133 and Tiemann, Bed. Berichte 31 (1898), 821.
W. Stiehl3) also assumed the existence of three isomeric aldehydes C10H16O in lemongrass oil, viz., citral (geranial), citrio-dora aldehyde and allolemonal. According to Schimmel & Co.4) this citriodora aldehyde corresponds, as to its method of preparation, to the citral of commerce. Inasmuch as this, as was shown by Semmler 5), is identical with the geranial from geraniol, the citral and citriodora aldehyde of Stiehl are identical. In addition Doebner 6) found that the allolemonal of Stiehl consists of about equal parts of citral and non-aldehyde substances.
From the investigations of Tiemann7) it becomes apparent that the bulk of the aldehyde of lemongrass oil is citral. He, however, had to modify his original view of the unity of citral and assumed the presence of two stereoisomeric citrals, a and b (vol. I, pp. 408 and 413), which are readily changed one into the other.
In addition to citral, lemongrass oil possibly contains traces of citronellal 8). Furthermore, Schimmel & Co.9) have demonstrated the presence of traces of an isomeric aldehyde C10H16O (b. p. 68° under 6 mm.; d15o 0,9081; aD + 0°50'; nD20o1,45641), the semicar-bazone of which melts at 188 to 189°. Upon oxidation with moist silver oxide an acid C10H16O2 (b. p. 130° under 9 mm.) was obtained. Still another aldehyde constituent of lemongrass oil, of which likewise mere traces are present, is the n-decylic aldehyde (m. p. of semicarbazone 102°) which upon oxidation yields /7-caprinic acid10).
1) Berl. Berichte 32 (1899), 115. - Chem. Ztg. 22 (1898), 1086.
2) Bull. Soc. chim. III. 21 (1899), 419.
3) Journ. f. prakt. Chem. II. 58 (1898), 51; 59 (1899), 497.
4) Report of Schimmel & Co. October 1898, 58.
5) Berl. Berichte 24 (1891), 203. - Comp. also ibidem 31 (1898), 3001.
6) Ibidem 31 (1898), 3195.
7) Ibidem 31 (1898), 3278, 3297, 3324; 32 (1899), 107, 115; 33 (1900), 877.
8) Doebner, Berl. Berichte 31 (1898), 1891.
9) Report of Schimmel & Co. October 1905, 45.
10) Ibidem 43.