This section is from the book "A Research On The Eucalypts Especially In Regard To Their Essential Oils", by Richard T. Baker, Henry G. Smith. Also available from Amazon: A Research On The Eucalypts And Their Essential Oils.
(R.T.B. & H.G.S., in Euc. and their Ess. Oils, 1st Edit., 1902.) River Red Gum.
Systematic. - It has long been known by stockmen that cattle will eat the leaves of only one kind of "River Gum" (E. rostrata, Schl.), but which kind it does not seem possible to differentiate in the herbarium. Morphologically, no variations could be detected between the Murray River specimens and those received from Broken Hill and Nyngan, but they differed, however, in chemical constituents, and this probably partly accounts for this choice of trees by stock. After our experience with E. apiculata, we have little doubt but that morphological differences do exist between these two Eucalypts, and will yet be found, so that a systematic description can be given for each species. On chemical grounds, we have decided to separate the Northern "River Gum" from the Southern "River Gum" under the varietal name of borealis.
For the data in reference to the type E. rostrata, see under that species.
ESSENTIAL OIL. - Leaves and terminal branchlets for distillation were obtained from Nyngan, New South Wales, in December, 1899. The yield of oil was 0.8 per cent. Pinene was found, but phellandrene was quite absent. Constituents having a high-boiling point were present only in small amount.
The oil of this tree is rich in cineol, and the leaves might be distilled commercially, but oil could not be profitably extracted from the leaves of the type E. rostrata.
The crude oil had specific gravity at 15° C. = 0.9109; rotation aD + 5.46°; refractive index at 200 = 1.4654, and was soluble in 1 3/4 volumes 70 per cent, alcohol. The saponification number for the esters and free acid was 4.8.
On rectification 2 per cent, distilled below 1700 C. (corr.). Between 170-1830, 85 per cent, distilled; between 183-2500, 5 per cent, distilled.
The specific gravity of the first fraction at 150 C. = 0.909, of the second fraction = 0.9142. The rotation of the first fraction aD + 6.37°.
The cineol determined by the phosphoric acid method in the first fraction was 52 per cent.. (O.M.), indicating about 45 per cent, in the crude oil.
Material of this species was also obtained from near Broken Hill, New South Wales, in July, 1898. The yield of oil was 1.19 per cent. The constituents in this oil and its general characters agreed very well with that from the Nyngan material. The specific gravity at 150 = 0.9065, saponification number = 8, and the oil was soluble in 1 3/4 volumes 70 per cent, alcohol. The cineol determined by the phosphoric acid method in the crude oil was 48 per cent. (O.M.).
Oil was distilled from this species by Mr. P. R. H. St. John in 1916, from trees cultivated in Melbourne, and forwarded to the Museum for investigation. The yield of oil he obtained was 0.83 per cent. The crude oil had specific gravity at 150 = 0.9153; rotation aD + 3.5°; refractive index 1.4583, and was soluble in 1 1/4 volumes 70 per cent, alcohol. The saponification number for the esters and free acid was 6.6. The cineol in the crude oil determined by the resorcinol method was 69 per cent. It is thus seen that this oil agrees fairly well with the above samples from Nyngan and Broken Hill, and differs entirely from the oil of the type E. rostrata, which species gives equally constant oil results. (See under that species.)