OILS, VOLATILE 



455 



is to substitute nitric acid, saturated TFith hyponitric acid, for the nitrate-of-mercury 

 solution. The sample to be tested is shaken with two or three per cent, of this acid, 

 and then placed in a cool place, and the moment of solidification noticed. It is always 

 better also to treat a sample of oil of known purity to the same test at the same time, 

 and compare the results. If the sample tested be pure, it will solidify quite as quickly 

 as the sample which serves for comparison. One hundredth of poppy oil present will 

 delay the solidification 40 minutes ( Gerhardt}, and of course the greater the quantity 

 of admixture, the more will it be delayed. 



M. Maumeno takes advantage of the greater amount of heat given out by the ad- 

 mixture of concentrated sulphuric acid with the drying oils than takes place with 

 olive oil under the same circumstances. MM. Heydenreich and Penot employ 

 sulphuric acid also to detect the different oils, but they notice the peculiar colorations 

 which take place on contact of the concentrated acid with the different kinds of oils. 

 Their test is thus performed: one drop of concentrated sulphuric acid is added 

 to 8 or 10 drops of the oil, placed on a piece of white glass, resting on a sheet of 

 white paper ; different colorations appear, which they state are characteristic of the 

 different oils ; thus olive oil gives a deep yellow tint, becoming greenish by degrees ; 

 colza oil, a greenish blue ; poppy oil, a pale yellow tint, with a dirty grey outline ; 

 hempseed oil, a very deep emerald tint; and linseed oil becomes brownish red, passing 

 directly into blackish brown, &c. These reactions are, however, uncertain ; the age 

 of the oil, mode of extraction, &c., altering them greatly. 



Marchand states that a mixture of poppy oil and olive oil, when thus treated, 

 developes, after a certain time, on their outline, a series of colours, rose, lilac, then blue, 

 and more or less violet-coloured, according to the proportion of poppy oil, while pure 

 olive oil becomes of a dirty grey, then yellow and brown. 



As the means of detecting the various fraudulent admixtures is of great commercial 

 value, the late F. C. Calvert's valuable paper on the adulteration of oils is referred to. 

 Pharmaceutical Journal, xiii. 356. 



The accompanying table of reactions (see opposite page) will be found very useful. 



Of the more important oils we imported in the years from 1868 to 1873 inclusive, 

 as follows : 



OIXiS, VOLATILE, ETHEREOUS, OR ESSENTIAL. The volatile oils 

 occur in every part of odoriferous plants, whose aroma they diffuse by their exhala- 

 tion ; but in different organs of different species. Certain plants, such as thyme and 

 the scented Labiatce in general, contain volatile oil in all their parts ; but others con- 

 tain it only in the blossoms, the seeds, the leaves, the root, or the bark. It some- 

 times happens that different parts of the same plant contain different oils ; the 

 orange, for example, furnishes three different oils, one of which resides in the flowers, 

 another in the leaves, and a third in the skin or epidermis of the fruit. The quantity 

 of oil varies not only with the species, but also in the same plant with the soil, and 

 especially witli the climate ; thus, in hot countries it is generated most profusely. 

 In several plants the volatile oil is contained in peculiar orders of vessels, which 

 confine it so closely that it does not escape in the drying, nor is dissipated by 

 keeping the plants for many years. In other species, and particularly in flowers, 

 it is formed continually upon their surface, and flies off at the moment of its for- 

 mation. 



Volatile oils are usually obtained by distillation. For this purpose the plant is 

 introduced into a still, water is poured upon it, and, heat being applied, the oil is 

 volatilised by the aid of the watery vapour at the temperature of 212, though when 

 alone it would probably not distil over unless the heat were 100 more. 



There are a few essential oils which may be obtained by expression from the sub- 

 stances which contain them ; such as the oils of lemons and bergamot, found in the 

 pellicle of the ripe fruits of the Citrus limonum and C. beryamia, or the lemon and 

 the bergamot. The oil conies out in this case, with the juice of the peel, and collects 

 upon its surface. 



