Oleum Betulae Lentae.
BY GEO. W. KENNEDY, PH.G.
Read at the Pharmaceutical Meeting, January 15, 1884.
In a paper on this subject, read at the last meeting of the American Pharmaceutical Association, I stated that I had considerable correspondence with distillers in reference to the manner of extracting the oil and to the details of the process. After the analysis made by Mr. Pettigrew ("Amer. Jour. Phar.," 1883, page 385), in which he failed to find a terpene in oil of birch, and maintained that on this account it was not identical with oil of teaberry, Prof. Maisch suggested to me in conversation that perhaps the hydrocarbon was lost in the distillation of commercial oil of teaberry either by carelessness or through ignorance of the distiller, or by some defect in the process of extracting it. I immediately put myself in communication with several manufacturers for the sole purpose of ascertaining from them full particulars, more particularly as to the separation of a light oil floating on the surface of the distillate. The replies to these communications, excepting one or two, were alike. To the first interrogation, as to the process of extracting the oil, I find the modus operandi to be very much the same; there is little or no difference. To the second inquiry, as to the separation of a light oil, with one or two exceptions I was informed that this was of frequent occurrence, had been noticed by them for a long time, and was known in the birch fields by the names of "light ring" and "light oil" I was also informed that no care was taken to secure it, as it was considered worthless, of no value whatever, and that it was allowed to run off over the receiving vessel (see "Amer. Jour. Phar.," 1882, page 49).
After such strong proof from the distillers, and similar assurance from two reliable pharmacists, who handle hundreds of pounds of the oil, with whom I was in communication, I came to the conclusion that—provided the oil was properly and carefully extracted—it would contain a hydrocarbon, and it was owing to this strong evidence that, at the Washington meeting, I unhesitatingly said that there was no reason why the oil should not contain the terpene. I believe, under the circumstances, I was justified in so speaking. The interesting discussion which followed the reading of my paper threw out suggestions which caused me to make further investigations.
It was my intention to spend several days in the birch woods, as I had invitations extended to do so, and witness the process of distillation more critically than I did on former occasions, but I was unable to fix a time to suit the convenience of all parties interested, owing to the small amount of oil made. During the past few months the stills were not in operation, the price of the oil being too low to compensate the distillers for their labor. However, my friend Mr. O. M. Briggs, a pharmacist of Carbon county, to whom I am much indebted for many favors, spent a day at one of the best stills in the region, which is worked by a man who thoroughly understands his business, and he obtained for me the product of the distillation of 600 pounds of material, which I here exhibit. The large jar (Mason's fruit jar) contains the oil just as it was made, with some water and dirt. Owing to an accident, about six ounces of the oil were lost. The yield was about one pound, or one-sixth of one per cent., which was small. The amount of "milk" (or water impregnated with oil), condensed in the exhaustion of the bark, amounts to 30 gallons. The jar was used as the receptacle for the oil, and was placed in a pail; as the pail fills with the "milk" it is emptied into a barrel, and put away to be used for another "run," as it is called, meaning the next distillation. The bottle labeled milk is a sample of the product nearing the close of the distillation. When received it was quite milky, but now the oil has separated, and of course the milkiness has disappeared, but by agitation it can be restored; the oily globules of a dirty color can be seen at the bottom of the vial. The "milk" contains about 2 ounces of the oil in every 25 gallons. The pieces of birch exhibited have had the oil taken out, and will give an idea as to the size of the pieces used in the extraction of the oil.
There was also another bottle received by the writer, marked "unknown," and said to contain "light oil," or "light ring," exclusively, and which, from previous information received, was considered to be a hydrocarbon. The vial contained 4 ½ fluidounces, which was reported to me as having been skimmed from five pounds of oil before it was rectified, or just as it came from the still; it was in two layers, and decidedly dirty, the layers occupying about an equal space in the bottle. After freeing it from dirt, by straining through flannel, the layers were separated, and upon examination the light upper layer was found to be nothing but water impregnated with oil. Its specific gravity at 70°F. is 1.001. The lower layer proved to be the oil, the specific gravity of which was taken, and found to be the same as that examined last year, 1.181 at 70°F., thus indicating that it was principally methyl salicylate. This oil was next submitted to a chemical analysis in the same manner as described by Mr. Pettigrew: 50 grams of the oil were decomposed with 25 grams of potassium hydrate, by boiling for six hours upon a sand-bath; at the expiration of this time the oil was perfectly decomposed, and, upon cooling, crystals of salicylate of potassium were obtained, and a clear distillate, without oily layer, nor was such produced upon dilution with water. This observation manifested conclusively the absence of a hydrocarbon. To get at the percentage of salicylic acid and methyl alcohol was the next step taken. The salicylate of potassium, formed as indicated above, was decomposed by hydrochloric acid, which liberated the salicylic acid in small whitish crystals, requiring only to be drained and subsequently recrystallized from ether. The amount obtained from 50 grams of the oil was 40 grams, or about 80 per cent. Another bottle, presented herewith and marked "impure," contains the acid as it is set free from the potassium salt. This was obtained from an old oil, made last year, and has not been recrystallized.
I then proceeded to obtain the methyl alcohol from the oil decomposed as described; the liquid portion was distilled from a sand-bath, until one-fourth the entire amount had passed over; this was redistilled, obtaining one-fourth as before, and this product, to get rid of the water, was distilled twice from lime. The methyl alcohol thus obtained, which is also shown, approximates 8 ½ grams, or 17 per cent. This added to the acid yield would still leave a discrepancy of 3 per cent. to be accounted for.
The rectification (as it is termed) of the oil, to which I referred a year ago, is accomplished by simply straining or filtering through cotton and flannel.
The yield, as I have already stated, from the distillation made Dec. 26, 1884, was small; it required 7 ½ hours' time to make the pound obtained. In the spring, when the sap is in the trees, the yield is from 25 to 35 per cent. larger, and the time consumed one to two hours less.
In concluding this paper I would state that I have endeavored to get all the information it was possible for me to obtain; also, that if all the "light oil" or "light ring" is like that examined by me, there should be no difficulty in giving it a name. The two samples of oil examined, of which one was a year and the other but a few days old, contained no terpene, and the result agrees with Mr. Pettigrew's observation, that oil of birch is nearly pure salicylate of methyl. The "light oil" so called by distillers, is shown to be water and oil; if the chips and dirt were removed from the distillate the oil and water would readily separate.