156 
GARDENING AS A SCIENCE. 
White pure Cojoo/, the products are — Carbon = , 76°811 
Oxygen and Hydrogen . . . 12*052 
Hydrogen m excess . , . 11'137 
100 
There are other resinous substances produced by plants of warm climates, which 
are highly fragrant, odorous, or foetid. They are partially soluble in water, and 
therefore have been termed Gum-resins ; — the fragrant balsam of tolu ; Gum Ben- 
zoin, frankincence, ammoniacum, assafoetida, olibanum, rank among these compounds. 
14. Camphor. In noticing this singular substance, we must depart from the 
authority of Davy, as recent discoveries refer it to the volatile or essential oils. 
15. Fixed Oils — or, for example, those of the olive, walnut, almond, beech-nut, 
rape-seed, poppy-seed, mustard, sun-flower-seed, — kernels of plum, cacao (called 
cocoa) — from the Tkeohroma, the chocolate nut; laurel-berry, &c. &c., are nutritive 
substances, of great importance, not only in the arts, but in domestic economy, 
and for the preparation of fine soaps. Olive Oil has been analysed by the two 
French chemists named before, and found to yield of Carbon 77*213 : Oxygen 
9*427: Hydrogen 13-360. 
16. Volatile, or Essential Oils, approach to the quality of resins — they evapo- 
rate by heat ; are soluble in alcohol ; which the fat or fixed oils are not ; — and are 
very slightly soluble in water, A strong and peculiar odour characterises each of 
them ; they inflame very readily, and by combustion afibrd different proportions of 
the same elements, namely, water, carbonic acid, and charcoal. 
These oils are deposited in cells of the leaves and bark, and may be seen in the 
leaves of the myrtle tribe, and particularly in those of the cinnamon leaves and 
bark: this fact presents a strong proof of the immediate connection which exists 
between the foliage and liher of trees. 
The essential oils are of great utility to man. Some are medicinal ; such are 
the oils of peppermint, spearmint, carraway, cloves, cinnamon, cassia, aniseed. As 
perfumes, we are indebted entirely to the oils of lavender, orange blossom (neroli), 
lemons, bergamot, and rhodium. Yet, perhaps the most important of the essential 
oils is the Oil or Spirit of Turpentine, termed also Camphogen, or Camphine. 
From this material we now possess the means of obtaining a light so pure and 
brilliant, that imagination can scarcely conceive a thing more beautiful ; yet it is 
attended with considerable danger. Turpentine yields a dense vapour, which the 
chemist Dumas supposes to consist of 500 volumes of carbon vapour, and 800 of 
hydrogen, condensed into 100 volumes. 
Camphor, the product of Laurus Camphora, is supposed by Dumas to be an 
oxide of an hydro-carbon, identical in composition with pure oil of turpentine. 
Hence, the addition of oxygen only, is thought necessary to convert turpentine to 
camphor, and by analysis we find 100 parts of camphor to produce. 
According to Dumas— Carbon . . 79*28 Or, to Dr. Ure . , 78-02 
Hydrogen . 10-36 11-58 
Oxygen . . 10-36 ..... 10-40 
