prove this rule.  Essential oil of orange-peel, and of lemon-peel, are frequently termed in the trade “Essence” of orange and “Essence” of lemons, instead of essential oil or otto of lemons, &c.  The sooner the correct nomenclature is used in perfumery, as well as in the allied arts, the better, and the fewer blunders will be made in the dispensatory.  It appears to the writer, that if the nomenclature of these substances were revised, it would be serviceable; and he would suggest that, as a significant, brief, and comprehensive term, Otto be used as a prefix to denote that such and such a body is the odoriferous principle of the plant.  We should then have otto of lavender instead of essential oil of lavender, &c. &c.  In this work it will be seen that the writer has generally used the word OTTO in place of “essential oil,” in accordance with his views.  Where there exists a solution of an essential oil in a fat oil, the necessity of some such significant distinction is rendered obvious, for commercially such articles are still called “oils”—­oil of jasmine, oil of roses, &c.  It cannot be expected that the public will use the words “fat” oil and “essential” oil, to distinguish these differences of composition.

There are several good reasons why the odoriferous principle of plants should not be denominated oils.  In the first place, it is a bad principle to give any class of substances the same signification as those belonging to another.  Surely, there are enough distinguishing qualities in their composition, their physical character, and chemical reaction, to warrant the application of a significant name to that large class of substances known as the aroma of plants!

When the chemical nomenclature was last revised, the organic bodies were little dealt with.  We know that we owe this universal “oil” to the old alchemist, much in the same way as “spirit” has been used, but a little consideration quickly indicates the folly of its continued use.  We can no longer call otto of rosemary, or otto of nutmegs, essential oil of rosemary or nutmegs, with any more propriety than we can term sulphuric acid “oil” of vitriol.  All the chemical works speak of the odoriferous bodies as “essential” or “volatile” oils, and of the greasy bodies as “fat” or “unctuous” oils.  Oils, properly so called, unite with salifiable bases and form soap; whereas the essential or volatile oils, i.e. what we would please to call the ottos, do no such thing.  On the contrary, they unite with acids in the majority of instances.

The word oil must hereafter be confined to those bodies to which its literal meaning refers—­fat, unctuous, inodorous (when pure), greasy substances—­and can no longer be applied to those odoriferous materials which possess qualities diametrically opposite to oil.  We have grappled with “spirit,” and fixed its meaning in a chemical sense; we have no longer “spirit” of salt, or “spirit” of hartshorn.  Let us no longer have almond oil “essential,” almond oil “unctuous,” and the like.