TRANSACTIONS OF THE SECTIONS. 43 
have the two surfaces of the glass very carefully ground, in the same manner as 
the bell-glasses for an air-pump are prepared; by these means glass vessels of 
almost any required dimensions can be used, provided care is taken that the form 
is such as will resist the pressure of the atmosphere. 
The potash necessary to absorb the residue of the carbonic acid after the exhaus- 
tion by the air-pump, may be placed at the bottom of the vessel, and gently heated 
on a sand-bath or by a spirit-lamp, or it may be placed in a tube, and subsequently 
sealed off by the blowpipe. 
On the Essential Oil of Bay, and other Aromatic Oils. 
By J. H. Guapsrone, Ph.D., FBS. 
This paper consisted of—1st. A description of the essential oils of Bay, Bergamot, 
Carraway, Cassia, Cedar-wood, Cedrat, Citronella, Cloves, Indian Geranium, 
Layender, Lemon Grass, Mint, Neroli, Nutmeg, Patchouli, Petit-grain, Portugal, 
Rose, Santal-wood, Turpentine, and Winter-green, with the specific gravities and 
powers of refraction, dispersion, and circular polarization. 2nd. Some remarks on 
the isomeric hydrocarbons, which may be derived from the majority of the essen- 
tial oils, and which generally resemble each other very closely, though they are 
rarely identical: 3rd. Notices of some of the oxidized bodies present in these oils, 
which are generally more refractive and more aromatic than the hydrocarbons of 
which they are oxygen substitution products. 
Among the observations were the following :—Oil of Bay consists of a hydrocarbon 
of the bet hary type, C,, H,,, and eugenic acid. Oil of Neroli contains two hydro- 
carbons, one of which is a fluorescent body. The essential oil of Petit-grain, which 
is derived from the leaves of the orange-tree, contains a hydrocarbon resembling the 
more volatile one from oil of Neroli, which is prepared from the orange flower; and 
so does the oil of Portugal, from the orange peel. Otto of roses is an oxidized oil; 
the crystallizable portion of it has a great attraction for ether vapour. The oils of 
Citronella and of Lemon-grass, from different species of Andropogon, cultivated 
in Ceylon, consist mainly of oxidized oils which are nearly if not quite identical. 
There is a very wide difference in the action on the polarized ray exerted by dif- 
ferent essential oils, both in regard to amount and direction. 
On the Means of observing the Lines of the Solar Spectrum due to the Terres- 
trial Atmosphere. By J. H. Guapstone, Ph.D., PRS. 
The object of this communication was to incite observers in various parts to 
notice those lines and bands which appear in the spectrum when the sun is near 
the horizon. They vary under different atmospheric conditions, and probably in 
different parts of this and other countries. The author had found one of Crookes’s 
pocket spectroscopes sufficiently powerful to exhibit all the most important of 
them, and very convenient for taking up mountains, &c. All observations should 
be referred to the map published in the Philosophical Transactions for 1860, 
On a particular Case of induced Chemical Action. 
By A. Vernon Harcourt, M.A. 
It has been observed by Mohr, Scheurer-Kestner, and other chemists, that when 
a protosalt of tin is determined by means of a standard permanganate solution, the 
results obtained vary according to the degree in which the solution of tin-salt is 
diluted. The greater the dilution, the less is the amount of permanganate required. 
This variation is justly ascribed by the two chemists above named to the influence 
of the oxygen which the water used in diluting holds dissolved. With recently 
boiled water, the effect is less; with water which has been absolutely freed from 
air, it disappears. 
If these facts stood alone, their explanation would seem simple, viz. that chloride 
of tin is speedily oxidized when mixed with water containing oxygen. But this 
is not the case, especially when much free acid has been added. If iodine, or per- 
chloride of iron, or sulphate of copper is used as the oxidizing agent, the result of 
the determination is the same, whether the tin solution be little or much diluted. 
