The oils of certain Eucalypts, when freshly distilled, contain a constituent which slowly changes its character and eventually deposits an insoluble precipitate. This constituent is never present in great quantity, and in some instances only in traces. In the majority of species it is absent, and appears to follow the general rule of all Eucalyptus oil constituents, in increasing in amount through a range of species until a maximum is reached in one or more of them.

Very many Eucalyptus oils, from authentic species, have now been under observation for several years in the Museum, and we have thus been able to determine in which of them this deposit has formed.

Reference was made to it in the first edition of this work, but the evidence then available was insufficient to enable general conclusions to be drawn. It may now be stated that none of the oils of species belonging to the groups yielding the more pronounced pinene oils, in which cineol is only present in small amount, has any signs of the deposit appeared, nor in that of any member belonging to

Plate LXXXVIII.

The Deposit which forms in the Oils of some Specie 277

Crude Oil of Eucalyrtus goniocalyx. Illustrating the deposit (A) and (B) the diminution in volume.

the typical "Boxes," E. hemiphloia, etc, and closely agreeing Eucalypts. In no species, the oil of which contains phellandrene, has it been detected, but is most in evidence in oils distilled from Eucalypts belonging to the typical "Gum" group: - E. globulus, E. goniocalyx, etc, and closely-related species.

The oils of these Eucalypts usually contain a fairly large amount of cineol, together with pinene, and in the case of many members belonging to these groups, the cineol increases in amount when the oils are stored. By reason of this peculiarity it was thought that the formation of this deposit was connected, in some way, with this increase in cineol, but the evidence available hardly supports that supposition, particularly as the oils of E. goniocalyx, E. punctata, and E. maculosa have not increased their cineol content during twenty years, although the deposit was quite pronounced in all three. It may also be mentioned that the cineol has increased in the oil of E. eugenioides, and one or two others, in which no precipitate has formed.

Although the deposit is so insoluble in all organic solvents, except chloroform, yet it has been found in solution in the oil itself in two or three instances, and precipitated when these were fractionated. One sample was distilled in Western Australia from a species growing in that State, and forwarded to us by Mr. C. E. Lane Poole; another sample was from Queensland, and sent to us by the late Mr. P. McMahon. In neither case was botanical material available, so that the species remain undetermined.

Plate lxxxviii will serve to show the appearance of the deposit after the precipitation was complete, and the amount so derived from the quantity of oil in the bottle. When originally placed in the show-case the oil was quite clear.

The following list records the species in the oils of which this deposit has formed. The percentages of cineol in the crude oils, when first distilled, are given, also percentages in some of the same samples about twenty years afterwards; in both cases the determinations were made by the phosphoric acid method: -

Cineol when

first

distilled.

Cineol after

about 20

years.

Eucalyptits accedens...

43

.....

E.

bicolor ...

48

62

E.

cordata ..

55

65

E.

cosmophylla...

43

....

E.

costata ...

57

....

E.

dealbata ...

52

73

E.

dumosa ...

44

.....

E.

elœophora ..

58

66

E.

globulus ...

57

64

E.

goniocalyx ...

56

56

E.

gracilis ...

19

30

E.

hemilampra ...

35

50

E.

intertexla ...

35

60

E.

Lehmanni ...

20

....

E.

leucoxylon ...

27

......

E.

maculosa ....

55

55

E.

microcorys ...

10

30

Cineol when

first

distilled.

Cineol

after

about 20

years.

Eucalyptus Morrisii ....

60

64

E.

Muelleri ...

57

...

E.

occidentalis ...

36

...

E.

odorata ....

63

...

E.

oleosa ...

52

62

E.

platypus ...

48

...

E.

populiifolia ...

62

70

E.

propinqua ...

32

39

E.

punctata ...

55

55

E.

quadrangulata..

32

54

E.

redunca ....

38

...

E.

Rodwayi ...

50

...

E.

Seeana ...

52

58

E.

squamosa ...

56

70

E.

urnigera ...

53

....

E.

vernicosa ....

52

...

In the diagram illustrating the article dealing with the probable evolution of the Eucalypts, all the above species will be found towards the left, and if a line be drawn from E. maculata to E. tereticornis, and another from E. tereticornis to E. apiculata, not one of the species in the above list will be found to the right of those lines. It is thus seen that only about one-fifth of the oils so far investigated appear to contain the constituent which on alteration forms this deposit, and these were all distilled from species belonging to closely related groups, the principal oil constituents of which are cineol and pinene.

That the deposit consists of a polymerised body is shown from its general character and exceedingly high molecular weight; it also shows a fairly constant composition with most species in which it occurs, as is evident from the results of the analyses, and the closely agreeing molecular weight determinations.

Its composition and chemical behaviour, as well as its alteration when heated, apparently show it to be associated with the neutral resins. After three or four years the polymerisation appeared to be complete, as no further formation of the deposit took place in the filtered oils after that period.

Experimental

The substance was purified by filtering off the deposit which was thus obtained as a jelly-like mass; it was spread upon porous plates to absorb the adhering oil, finely ground, dissolved in chloroform and precipitated by the addition of an excess of alcohol. The process was repeated several times, when in most cases the finely-ground powder was quite white and had little cohesion.

When purified as above all the samples contained minute traces of manganese or alumina, and occasionally iron, but neither lime nor magnesia was detected. In those cases where a reaction for iron was obtained the powder was slightly tinted, and it did not appear possible to remove this by repeated solution and reprecipitation.

The powder was quite neutral, was insoluble in alkalis and in all the usual organic solvents except dry chloroform. It was soluble in sulphuric acid with the formation of an orange-brown solution, but on addition of water was again precipitated apparently unchanged.

The melting point was very high, in most cases about 280-290° C, although that of E. punctata melted fairly well at 265-270° C. The melted substance was a brown brittle resin, mostly soluble in alcohol and in hot aqueous alkalis; the portion soluble in alcohol melted at 125-130° C. When heated in the tube to slight decomposition it evolved an odour reminding one of an aromatic resin, and gave off a small quantity of a volatile liquid which was acid to litmus.