In order to see if the poison is volatile with vapor of acetic acid, since this acid is found in the plant and it is thought by some that the poison is volatile, a portion of the tar was distilled under diminished pressure with acetic acid. It was soluble to some extent in the acid.

The temperature did not go higher than 55 during the distillation. A tube containing cotton wet with sweet oil was placed between the receiver and the water suction so that the uncondensed vapors would have to pa.s.s through the cotton. This cotton was rubbed on the skin and was not poisonous. The yellow distillate collected in the receiver was also tested and was not poisonous.

HYDROLYSIS OF THE POISON.

About 5 grams of the poisonous tar free from gallic acid and sugar was dissolved in alcohol, and dilute (2 per cent.) sulphuric acid was added.

Some of the tar separated out on diluting the alcohol with the acid. The mixture was heated on a water bath during work hours for four days. A purple and green fluorescent solution was formed, though much tar was left apparently unchanged. The alcohol was evaporated off and the solution was filtered from tar. The fluorescent filtrate was shaken with ether, by which the green substance was removed, leaving the solution purple. The ether left, on evaporation, a small quant.i.ty of a green substance having a pleasant ester odor. It was not further examined. A portion of the purple solution was exactly neutralized with sodium carbonate. This solution gave a blue-black color with ferric chloride which became red on addition of another drop of sodium carbonate, indicating gallic acid. It also reduced Fehling solution.

Another portion of the purple solution was made alkaline with sodium carbonate. A reddish-brown flocculent precipitate was formed and was filtered off. The filtrate did not give any color with ferric chloride, but it reduced Fehling solution. It also gave the test for rhamnose with alpha-naphthol.

The main portion of the purple solution was made alkaline with sodium carbonate; the precipitate was filtered off and dissolved in acetic acid. This solution was yellow and gave a reaction with ferric chloride similar to that of gallic acid. The filtrate from the precipitate by sodium carbonate was concentrated by evaporation until sodium sulphate began to crystallize out. Alcohol was added to precipitate the sodium sulphate completely, the mixture was heated and filtered. The alcoholic filtrate was concentrated to a syrup which reduced Fehling solution and gave the characteristic tests for rhamnose already described. By this hydrolysis, the tar was split up into rhamnose and some form of gallic acid which could be precipitated by sodium carbonate. This compound, whose acetic acid solution was yellow, probably contained fisetin also.

The reason for this last statement will appear from the following experiment:

DECOMPOSITION OF THE POISON WITH ACETIC ACID.

A portion of the poisonous tar was heated in an open dish with strong acetic acid. The tar seemed to be decomposed to some extent, giving a yellow substance. Acetic acid was added from time to time as it evaporated. After several evaporations, water was added, the mixture was heated to boiling and filtered. This filtrate No. 1 will be mentioned later. The residue in the dish consisted of undecomposed tar and an olive-green flaky substance. This substance was heated with a fresh portion of glacial acetic acid. Water was added, and the mixture was boiled and filtered. The filtrate had a deep yellow color suggesting fisetin. It was shaken out with ethyl acetate which became colored yellow. A portion of the ethyl acetate solution gave an orange red precipitate with lead acetate showing the presence of fisetin. The ethyl acetate was removed from the remainder of the solution by evaporation and the yellow residue was taken up in alcohol. This alcoholic solution gave the characteristic reactions for fisetin with stannous chloride, with pota.s.sium hydroxide, with ferric chloride and with Fehling solution.

Filtrate No. 1 obtained by heating the poisonous tar with acetic acid and hot water as described above was investigated as follows: A portion of it gave a reddish colored precipitate with sodium carbonate as in the case when the tar was hydrolyzed with sulphuric acid. The remainder was nearly neutralized with sodium carbonate and lead acetate was added in excess to remove gallic acid. The excess of lead was removed by sulphuric acid, and the sulphuric acid was removed by barium carbonate.

The solution on evaporation reduced Fehling solution to some extent, but a white precipitate was also formed.

In this experiment, gallic acid and fisetin and probably sugar were formed by decomposition of the poisonous gum with acetic acid, the acid found in the plant by Pfaff. The presence of free gallic acid, fisetin and rhamnose in the plant can therefore be explained by the natural hydrolysis of a complex gum or tar or a const.i.tuent thereof. The poisonous property is lost in the general rearrangement which takes place during hydrolysis.

The poisonous tar was not hydrolyzed by boiling with a dilute solution of sodium carbonate.

It was found, as has been stated elsewhere, that the lead compound of the poison could not be precipitated in 95 per cent. alcohol. Further experiments, however, showed that on extracting the poisonous gum with 50 per cent. alcohol, a portion of it dissolved, and this solution gave a precipitate with lead acetate which was a true lead compound. The remainder of the purified tar (about 10 gm.) was treated with 50 per cent. alcohol and filtered. Very little dissolved in alcohol of this strength, but on addition of lead acetate in 50 per cent. alcohol to the solution, a light colored precipitate was formed, which became dark on standing. It was filtered off, washed free from lead acetate, decomposed by hydrogen sulphide, and shaken out with ether. The ether left, on evaporation, a yellow resinous substance having a faint odor like garlic. By drying in a desiccator, a small quant.i.ty of a solid yellow resin was obtained which was completely soluble in alcohol. A very small drop of this solution applied to the skin on the end of a gla.s.s rod which had been drawn out to a point caused an eruption in about thirty-six hours. Following the nomenclature used by Maisch and Pfaff, this substance will be designated as _Toxicodendrin_, the ending "in"

indicating its glucoside nature.

The filtrate from the lead precipitate just described was freed from the excess of lead acetate by hydrogen sulphide, was tested for poison, and was found to be poisonous, showing that the precipitation by lead acetate was not complete even in 50 per cent. alcohol. On spontaneous evaporation of the solution, a yellow, sweet smelling resin was left.

A portion of the alcoholic solution of the toxicodendrin gave a dark coloration with ferric chloride, did not reduce Fehling solution and was slightly acid to litmus.

To see whether the toxicodendrin could be hydrolyzed, the remainder was dissolved in alcohol and dilute sulphuric acid was added. A fine, white precipitate was formed at once which rose to the surface on standing as a light flocculent substance. The mixture was heated for several days on a water bath, filtered from unhydrolyzed resin and the filtrate was neutralized and concentrated in the way already described. The solution obtained reduced Fehling solution. Not enough was obtained for further sugar tests, but all the hydrolysis experiments point to the conclusion that the poisonous substance is a rhamnoside, and is the source of the sugar in the plant.

The reaction with ferric chloride observed whenever a lead compound of the poison is decomposed by hydrogen sulphide may be explained by the formation of traces of gallic acid or fisetin through the action of the weak acids present.

The supply of purified poisonous tar having been exhausted in the preceding experiments, further study of the active principle is postponed until more can be prepared. It is highly desirable to investigate the white precipitate formed by addition of sulphuric acid to an alcoholic solution of the toxicodendrin.

OXIDATION OF THE PURIFIED TAR WITH NITRIC ACID.

When the purified poisonous material (p. 32) was extracted with 50 per cent. alcohol, only a small quant.i.ty was dissolved as was stated above.

The insoluble residue was treated with fuming nitric acid. Violent reaction took place at once with copious evolution of red fumes and heat. When the reaction was over, a sticky red gummy ma.s.s was left which was slightly soluble in cold water and readily soluble in warm alcohol.

The water extract was yellow, and the alcoholic solution was red. That the water extract contained picric acid was shown by the following experiments:

(1) A portion was gently warmed with a few drops of a strong solution of pota.s.sium cyanide and two drops of sodium hydroxide. The red color of pota.s.sium isopurpurate was formed.

(2) A portion of the water solution was heated with glucose and a few drops of sodium hydroxide. The deep red color of picraminic acid was produced.

(3) A few drops of an ammoniacal solution of copper sulphate was added to the water extract. A yellow-green precipitate was formed.

(4) The water extract dyed silk, but did not dye cotton cloth.

DISTILLATION OF THE TAR WITH SODA LIME.

About 25 gm. of the tar left after extracting the original material with hot water was dissolved in ether and poured into a gla.s.s retort containing soda lime. The ether was distilled out, leaving the tar intimately mixed with the soda lime. The retort was then gradually heated. Vapors and liquid were given off, both of which turned red litmus blue and had a strong odor like tobacco smoke. No odor of ammonia was detected.[45] At the high temperature of the triple burner, a semi-solid, red, greasy substance collected in and closed the condenser tube. This substance had the same powerful odor as the liquid portion of the distillate. The clear, watery portion of the distillate was separated from the thicker parts, and was found to contain pyrrol and pyridine derivatives by the following characteristic tests:

(1) Wood moistened with hydrochloric acid was turned red by it.

(2) Colorless fumes were formed when brought near hydrochloric acid; mixed with hydrochloric acid, a red insoluble substance was formed.

(3) It precipitated the hydroxides of iron, gave a light blue precipitate with copper sulphate, and a white precipitate with mercuric chloride.

The greasy, semi-solid ma.s.s was extracted with 10 per cent. hydrochloric acid and filtered. On addition of a solution of mercuric chloride to the red filtrate, a brown flocculent precipitate was formed. It was filtered off and distilled with caustic soda, but the distillate did not contain pyridine.

POTa.s.sIUM PERMANGANATE AS A REMEDY FOR RHUS POISONING.[46]

In the early stages of this work some experiments were made to see if pota.s.sium permanganate could be used to purify the lead precipitate by oxidizing the tar brought down in precipitation. It was found that the permanganate attacked the lead precipitate as well as the other organic matter in the vessel. This fact and the well-known value of permanganate in treating skin diseases, its use as an antidote for some kinds of alkaloid poisoning,[47] as an antidote given to cattle poisoned by plants,[48] and as an antidote for snake bites,[49] suggested its use as a remedy for Rhus poisoning. Maisch[50] mentioned that he had used it with success, but it never came into general use, probably on account of its staining the skin and clothing. In carrying out this work abundant opportunities for testing its value as a remedy for the dermat.i.tis caused by poison ivy were afforded by many cases of accidental and intentional poisoning. The best example of the latter was obtained with the ether solution from the extraction of the lead precipitate in the Soxhlet apparatus (page 28). After removing the ether, a small drop of the residue was applied to the wrist as described. An itching red spot about the size of a dime was noticed in thirty-six hours, and it steadily increased in size. Nearly two days after the application of the poison, a dilute solution of pota.s.sium permanganate containing a little caustic potash was rubbed into the spot until the pimples were destroyed. A little black spot was left wherever there had been a pimple, showing that the permanganate had been reduced to oxide in the skin. The place was washed and nothing more was thought of it until the morning following, when it was noticed that the wrist had commenced to swell during the night, and the characteristic watery secretion was running from the poisoned spot. More permanganate solution was applied without potash and the wrist was bandaged, thinking that this would prevent the spreading of the eruption, but it really facilitated spreading by becoming saturated with the poisonous fluid and keeping it in contact with a larger surface of skin. In the meantime the swelling and inflammation had extended nearly to the elbow. The arm now had the appearance of having been bitten by a snake. To reduce the swelling it was immersed in hot water. This seemed to bring out the eruption very quickly and the blisters were treated with permanganate as fast as they appeared. The swelling was reduced, but returned during the night. On the evening following, the forearm was immersed in a bowl of hot permanganate solution containing a little caustic potash. The solution was kept as hot as could be borne for about half an hour. After this bath, the poison was completely oxidized, for the swelling was reduced and did not return, nor was there any fresh eruption. What appeared to be a severe case of poisoning was thus cured very quickly. The use of hot water not only reduces the swelling, but also helps to destroy the poison. The action of permanganate is also more rapid at high temperatures.

The oxidizing power of permanganate, as is well known, is greater in acid solution than in alkaline, five atoms of oxygen being available in the former and three in the latter, according to these equations:

2 KMnO_{4} + 3 H_{2}SO_{4} = K_{2}SO_{4} + 2 MnSO_{4} + 3 H_{2}O + 5 O.

2 KMnO_{4} + H_{2}O = 2 MnO_{2} + 2 KOH + 3 O.

Permanganate was used as a remedy in some cases mixed with dilute sulphuric acid, and in others, with zinc sulphate; also with lime water.

It was found to be satisfactory whether used alone or with any of the substances mentioned, provided it was well rubbed into the skin. The concentration of the solution used was varied according to the location and condition of the eruption. Where the skin was thin or already broken, dilute solutions (one per cent.) were used. In one case, the eruption appeared in the palm of the hand where the skin was so thick that it was necessary to open it before the remedies could reach the poison. The difficulty of getting the remedy in contact with the poison in the skin is the reason why the eruption is hard to cure.

The remedy most commonly used for this eruption is an alcoholic solution of lead acetate. This remedy is unsatisfactory for the reason that its action consists in depositing an unstable lead compound of the poison in the skin where the conditions of moisture and temperature are favorable for its decomposition, liberating the poison with all its irritant properties. Moreover, alcoholic preparations should not be used because the alcohol dissolves the poison and, on evaporation, leaves it spread over a larger surface like a varnish. Pota.s.sium permanganate, however, oxidizes the poison completely. The only objection to the use of permanganate of which the writer is aware is that it stains the skin.

The stain can be removed by vigorous scrubbing with soap, or it will wear off gradually in a few days. It can be removed at once by certain acids, but these should not be used by persons not familiar with their action.

With the knowledge of the facts mentioned, many solutions were tested for poison by applying them to the skin, and when an eruption appeared, it was cured quickly and permanently by rubbing in a permanganate solution, usually mixed with dilute sulphuric acid.

FOOTNOTES:

[16] Nitrogen was found very readily by the soda lime test in the tar left after extracting the original material with 50 per cent. alcohol, but was not found by the La.s.saign test.

[17] Stevens. Amer. Jour. Pharm. 77, 255, June, 1905.

[18] Whenever it is stated in this paper that a solution was poisonous or not poisonous, the test was made by the writer upon himself.

[19] Liebig's Annalen, CXI, p. 215.

[20] uber Mategerbstoff, p. 20.

[21] Bull. Soc. Chim. (II), Vol. 2, 95 (1864).

[22] Berichte 19, 1735 (1886).