**3.2 Hydro diffusion**

Hydro Diffusion method for extraction of oils is a type of steam distillation and is only different in the way in which steam enters the container of the still. This method is preferred when the plant material has been dried and is not deteriorate at boiling temperature [24]. The steam in this method is drenched from the topmost onto the phytophagous matter and thus leads to impregnate the plants even more and less time. Hydrodiffusion method is superior to steam distillation because of shorter processing time and a higher oil yield with less steam used [11].

## **3.3 Steam distillation**

One of the most widely used methods of extracting essential oils from their sources is steam distillation, and it is one of the preferred methods due to its low cost. In this method, the essential oil and aromatic components of the plant are gathered by utilize heating water or vapor and thus cause damage to plant cells and lead to release these materials [21, 25]. This method is applied in isolation of essential oils at temperatures approach to 100°C, and next with condensation to produce an immiscible fluid that can clarify it to isolate the oil*,* so it is used in the conservation of compounds that might rupture at elevated temperatures [23, 26, 27].

#### **3.4 Solvent extraction**

In this method, the extraction of the essential oil occur after utilization of a hydrocarbon solvent which is acts as dissolving material when added to the plant and leads to the formation of mixture contain the essential oil with other material. The next step includes purification by concentration and filtration of the mixture and then added of absolute alcohol that when evaporate left the oil behind it. This method represents the best in the formation of big amounts from the product oil because of the least display to high temperatures or air but on the other hand the residue that results by the way after the extraction had bad effects on the health and immunity [28].

#### **3.5 Cold pressing**

Uses large machinery to either grind the seeds/fruits to squeeze out the oil or pierce the rind and peel of the fruit while it is rotating to extract the oil. Cold pressing is used to extract the essential oils from citrus rinds such as orange, lemon, grapefruit and bergamot. In this method the heat is generated internally where it result from the revolving of the mixture and the friction lead to disconnect of the oil from the mixture and the next step include filtration of the oil to discard any residue and ensure the purification process [29].

#### **3.6 Enfleurage**

An intense and classical method of elicit essential oil from petals of flowers. The procedure includes coating fats above petals of the flower which act on the soak up the oils, and then utilize alcohol to isolate the essential oils from the fat, then let alcohol be evaporated and thus the essential oils are gathered [29].

#### **3.7 Carbondioxide extraction**

This method is traditional where it uses the liquid CO2 via pressurized it and the essential oils of the plants dissolved in this liquid. The next step includes return

**33**

*Essential Oils*

**4. List of essential oils**

*DOI: http://dx.doi.org/10.5772/intechopen.92216*

**1** Allspice (Pimento Berry, Jamaica Pepper)

**2** Amyris (Torchwood, West Indian Sandalwood)

back of CO2 to the state of gases thus gathered left the oil, so the positive feature of this method was kept the essential oil from damage by high temperatures [29].

This list is organized alphabetically by the common essential oil name (**Table 1**).

23 Cassia

24 Catnip

40 Cumin

Sweet Bay)

**NO. Essential oils NO. Essential oils**

**3** Angelica Root 25 Cedarwood Atlas **4** Anise (Aniseed) 26 Cedarwood Himalayan **5** Arborvitae (Western Red Cedar) 27 Cedarwood Virginian

**6** Balsam Peru (Peru Balsam) 28 Celery Seed

 Birch (Sweet Birch) 33 Citronella Black Pepper 34 Clary Sage Black Spruce 35 Clementine Blue Cypress Blue Tansy 36 Clove Bud Buddha Wood (Desert Rosewood) 37 Coffee

**8** Bay Leaf 30 Cinnamon Bark **9** Bergamot 31 Cinnamon Leaf

**7** Basil (Sweet Basil, Basil Linalool 29 Cilantro (Coriander Leaf)

**10** Bergamot Mint 32 Cistus (Labdanum, Rock Rose)

**16** Blue Tansy (Moroccan Blue Chamomile) 38 Copaiba (Copaiba Balsam)

**17** Cajeput (Cajuput, White Tea Tree) 39 Coriander Seed

**21** Carrot Seed 43 Dill Weed/Dill Seed **22** Cardamom 44 Douglas Fir **NO.** Essential oils NO. Essential oils

**45** Elemi 73 Juniper Berry (Juniper)

**49** *Eucalyptus smithii* 77 Laurel Leaf (Bay Leaf, Bay Laurel,

**52** Fir Balsam(Canadian Fir Needle) 80 Lavender (Spike Lavender)

**19** Cannabis 41 Cypress **20** Caraway Seed 42 Davana

**46** *Eucalyptus dives* 74 Key Lime **47** *Eucalyptus globulus* 75 Kunzea **48** *Eucalyptus radiata* 76 Labdanum

**50** Everlasting (see Helichrysum) 78 Lavandin **51** Fennel (Sweet Fennel) 79 Lavender

**18** Camphor (White Camphor, Camphor

Laurel)

back of CO2 to the state of gases thus gathered left the oil, so the positive feature of this method was kept the essential oil from damage by high temperatures [29].
