321 



VIII. — Distillation with Water. 



In the preceding analytical course the volatile oils have found 

 no place, though theh- presence might have been conspicuous 

 sometimes, especially in the ethereous extract. For their produc- 

 tion and examination another sample of the substance must be 

 employed, but not less than 1 kilogram, or much more on 

 account of the comparatively small amount of volatile oil contained 

 in most plants. 



Besides volatile oils there are other ingredients of plants that 

 have been obtained in the preceding analysis in too small a quan- 

 tity or not at all, and the discovery of which becomes easier with 

 a larger amount of raw material. 



The production of these two classes of bodies may be combined 

 in the following way : — 



(a) Macerate the substance with water for one or two days and 

 distil, preferably on the water-bath and by means of steam, in a 

 Beindorf 's apparatus, described on p. 277, and provided with a good 

 refrigerator. From what will be seen afterwards the weight of the 

 empty tin still (without head or other accessories) must be deter- 

 mined and engraved on the tin. As recipient, a Florentine flask 

 or a similar contrivance is employed. 



The distilling water dissolves invariably certahi quantities of 

 oil. Either more oil is present than requisite for saturating the 

 water, or there is less of it. In the first case the oil separates on 

 or under the water, according to its density. To claiify the at 

 first usually turbid oil allow to stand undisturbed for a few days, 

 and prevent the solidifying of some oils by keeping them in a 

 moderately warm place. After it has become clear, and if it 

 floats on the water, remove it by means of a thin cotton wick, 

 used as a syphon ; if it be heavier than water, pour ofi" the latter 

 and remove the rest by means of the same syphon. 



If no volatile oil has been separated in the distillate, i.e., if 

 the water has not been saturated with it, a saturation or se2:»ara- 

 tion may be obtained in most cases by submitting the distillate to 

 another distillation with a fresh quantity of raw material so as to 

 increase the amount of oil in the same qiiantity of water. Some- 

 times this process (cohobation) must be repeated a thii-d time. 

 Shovild it be desirable to obtain the oil without distilling two or 

 three times, the aqueous distillate must be shaken with one-fifth 

 its volume of ether for half-an-hour. Allow the mixture to become 

 clear, pour ofi" the ether and let evaporate spontaneously in a 

 beaker. The volatile oil, mixed with a few drops of water, re- 

 mains,' though only in very small quantity. 



In order to enable an investigation of more thair the external 

 characters of a volatile oil (colour, smell, taste, density) at least 50 



Y 



