DETECTION OF ADULTERATION.

NOTES ON THE MICROSCOPICAL EXAMINATION OF SICILIAN SUMAC AND ITS ADULTERANTS.

By B. J. HOWARD, Chief, Microchemical Laboratory.

The differentiation of pure and adulterated sumac by means of the microscope is not at all a new procedure, but it does not appear to be generally employed by the trade in this country. The work done in this laboratory indicates that this is a convenient and quick method of identifying certain of the common adulterants in Italian sumac leaves, and that in the detection of the most common adulterant, Pistacia lentiscus, no great experience is necessary to obtain reliable results. The examinations here reported include only commercial samples, most of which were in a powdered form, and hence no studies of sections were made. The investigations have been in progress since 1903. The paper by Priestman" will be found very useful to beginners along this line, but the technique of the method as there described seems to leave something to be desired in the way of simplification. As will be shown, the technique adopted in this laboratory is quite different, and, it is believed, has some advantages over Priestman's. '

APPARATUS AND REAGENTS.

The most important apparatus required is a good compound microscope giving a range of magnification of from about 75 to 200 diameters. Magnifications of 90 and 180 were actually used in the work here reported, but if approximately these powers are used, giving good definition, no trouble should be experienced. The instrument should have fine and coarse adjustments and a substage condenser with iris diaphragm. A mechanical stage with wide range of movement (about 2.5 cm or more) will be found very convenient, though it is not really necessary.

Microscope slides 25 by 75 mm (1 by 3 inches) and cover-glasses, round or square, are required, round covers of 0.75 inch diameter and from 0.17 to 0.25 mm in thickness, listed by some dealers in microscopical apparatus as No 2, are preferred. Some device for producing a small flame, such as a micro-bunsen burner or small alcohol

a J. Soc. Chem. Ind., 1905, 24: 231.

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lamp, is required. In addition to the above, a pair of teasing-needles, a pair of small forceps, and a scalpel should be secured.

As a clearing agent a chloral hydrate solution made up as follows was almost exclusively used: Chloral hydrate, 150 grams; water, 100 cc.

Among other reagents of occasional value the following should be noted: Alcohol of two strengths, 70 per cent and 95 per cent; two grades of glycerin, 100 per cent and 50 per cent (glycerin and water 1:1 by volume), and glycerin jelly are needed if permanent specimens are to be made, and this will almost always be done by careful workers.

a

The glycerin jelly is made up as follows: Best gelatin, 1.5 parts; water, 3 parts, and glycerin, 4 parts. Some persons " prefer to use only 1 part of gelatin, since it gives a jelly more easily worked than the amount mentioned. Soak the gelatin in the water until it is soft, add the glycerin, and heat over a water bath, finally adding two or three drops of carbolic acid as a preservative.

TECHNIQUE.

The difficulty encountered on examining specimens mounted in water or glycerin direct is due to the fact that they are too opaque and contain considerable air. Some means of clearing the fragments are necessary. Priestman treated the sample with nitric acid, which attacked the more delicate tissues of the leaf first, and if the action was stopped at the right time, the leaf epidermis could be mounted as nearly clean tissues. This method is laborious if a large number of samples is to be tested, and seems to require considerable judgment as to just the stage at which the action is to be stopped, and hence is not desirable unless one is very familiar with microscopical technique.

In this work the chloral hydrate solution before mentioned was used. A small amount of the specimen is placed upon a slide with two or three drops of the solution and gently heated to boiling over the micro-bunsen burner or alcohol flame and kept gently boiling for about one minute. If the chloral hydrate solution boils away before the heating is finished, a few drops more are added, for if the specimens become dry the object of the treatment is defeated. After the boiling is completed the specimen is allowed to cool down somewhat, a cover-glass is placed over it and the specimen is ready for examination. If too much of the original specimen has been used, the mass will be too dense to give satisfactory results. A few tests, however, will demonstrate to the worker the most satisfactory amount

a Clark's Practical Methods in Microscopy, 2d edition, 1896, p. 243.

b Loc. cit.

to use. It is well to make several slides from the specimen, so as to get a good idea of its character.

Another method of procedure which some may prefer, and which lends itself readily to the examination of finely powdered samples, is the following: Place in a test tube a portion of the sample equal in size to a hazelnut, add a few cubic centimeters of the chloral hydrate solution and boil slowly for two or three minutes, allow to stand until the larger pieces have settled to the bottom and then remove a part of them with a pipette and mount on a slide in the usual manner.

Such treatment is all that is necessary in the preparation of samples for immediate examination. It is often desirable, however, to prepare specimens for future reference. For this purpose the specimen is cleared with chloral hydrate as described, the excess liquid is removed by a piece of filter paper, and then mounted in glycerin or glycerin jelly. To mount in glycerin, add to the moist fragments a small drop of the 50 per cent glycerin and after covering seal with a good microscopical cement. In order to mount in glycerin jelly, the sample is cleared and the excess chloral hydrate solution removed as previously directed, a tiny drop of 50 per cent glycerin is mixed with the moist fragments, and then a small piece of glycerin jelly (about a quarter of the size of a pea) is placed on the slide. The whole is gently heated until the jelly melts, and the fragments are mixed with the jelly by means of a teasing-needle or scalpel, care being exercised not to make bubbles in the mass, as they are difficult to remove. Care should also be taken not to heat the glycerin jelly on the slide enough to produce bubbles.

Permanent samples can be made, after clearing in chloral hydrate, by dehydrating in alcohol, clearing in xylol, and mounting in xylol canada balsam. This method is not satisfactory, however, unless the sample is stained; and with many small fragments, as is usual in a powdered sumac, this step is somewhat difficult and tedious.

SOME HISTOLOGICAL FEATURES.

A short description of the most characteristic histological features of sumac and the most important of its adulterants may be of value. Although written descriptions and photographs aid greatly, in beginning such investigations the microscopist should, of course, first work on samples of known purity, then on known mixtures, and finally on mixtures of a content unknown to him but prepared from authentic samples.

SICILIAN SUMAC (Rhus coriaria).

The upper epidermis of Rhus coriaria (Pl. I, fig.1) is made up of cells about 35μ in diameter (varying from 20μ to 50μ). They appear in the surface view to be bounded by walls with fairly straight sides

FIG. 2.-SICILIAN SUMAC (RHUS CORIARIA). LOWER SURFACE. X150.