Croton oil was extracted by the action of ether upon the seeds. The ethereal solution containing croton oil in suspension was acid: it was placed in a glass vessel with two openings. One of them admitted a straight tube, and reached to the bottom of the vessel, admitting the introduction of external air: the other communicated with Woulfe’s apparatus, composed, {174}
1. Of the globular tube after Liebig, containing blue solution of litmus.
2. Another globular tube filled with alcohol.
3. An angular tube in connection with a large vessel full of water, giving an inferior running to the liquid, and causing the air to pass across the thick layer of ethereal oil, to lead the volatile principles in contact with the liquor destined to retain them. The apparatus being arranged, it was put in action by causing the water to run which was contained in the large vessel. The vacuum having begun, air was introduced to the bottom of the ethereal liquid, keeping up this action till the ether was totally evaporated. Consequently, the air has agitated the liquid long enough to remove in a state of vapour all the ether which was contained in the mixture. Nevertheless, the tincture of Turnesol, which opposed the passage of the vapours of ether and water, did not change into red, which would have happened if the volatile principles should have contained any acid. Neither did the alcohol which was acted upon by the same current exhibit any sign of acid. The air saturated with ether arrived in the vessel to replace the water had no acid property; its action upon the eye-lids and nostrils was pungent and irritating, but not that of an acid. Another experiment was made with the same apparatus, having always in view to cause a great quantity of air to pass through croton oil. But this time, instead of causing the current to pass through a mass of ethereal solution, it was caused to pass through pure croton oil. The large vessel was this time not quite filled with water, allowing space to introduce on its upper part two sponges, one filled with oil, the other with ether. Things being thus arranged, the liquid was set running, and the air rushed through the oil, coming in at the bottom of the liquid and spreading through the surface, causing a lengthened ebullition. The mass of air employed in this operation was not below two centimetres. The tincture of litmus contained in the globular tubes was not altered; the oil contained in the sponge was neither acid, pungent, or corrosive. The ether acted upon by too much air had disappeared, the {175} sponge was dry. These two proofs appear to be conclusive, and to show that the croton oil does not contain an active volatile acid, otherwise it would have been made manifest by being carried away by the ether in the first case, or by its proper volatility in the second.
Is it, however, possible to separate the active volatile principle from the mere neutral oil? It has been said by several authors that the croton oil was composed of two different oils, but this was a mere statement which required to be proved by facts. To solve this problem, the oil employed in the experiments was obtained by means of ether. The seeds of croton yield by expression 35 per cent.; treated by ether, they yield from 52 to 55 per cent. If treated by ether, the ether obtained by distillation is free from acid, all the acid remaining in the oil. When a certain fixed quantity of this oil is put in contact with ten times its weight of strong alcohol, the alcohol dissolves 6 per cent. of its own weight, and the oil 50 per cent.
The portion of the insoluble oil has lost its color, its smell, a part of its pungency, and all its acidity.
The portion of oil which has been dissolved in alcohol, when separated from this menstruum by evaporation, is more viscid, more colored, more pungent, and acid. The oil which is not dissolved, can be acted upon again by alcohol; by this second operation, it yields some parts to the alcohol, and the remainder loses all its specific qualities. The action of alcohol upon oil in successive operation, can be followed up to its last limits.
Twenty volumes of oil mixed with 100 volumes of alcohol, will be followed by the reduction of five volumes of oil. In the next operation, when the alcohol is renewed, the volume of the columns of oil lowers only three volumes instead of five. By a fourth operation, the oil loses not a single volume. When reduced to this state, the croton oil is slightly amber-colored, without smell, taste, or acidity; it can be taken in the mouth without causing any sensation. It is soluble in all proportions in ether. Its specific gravity is, 92 compared with that of water. {176}
Thus we find by experiments an evident proof of the co-existence of a sweet oil with the pungent croton oil.
All the specific properties of the croton oil are carried over in that dissolved by alcohol.