It seems to me that sufficient attention has not been paid to the impurities of preserves and to poisoning by compounds of tin. It is only during recent years that chemists and hygienists have given this subject serious consideration. It is the purpose of these pages to make known the facts heretofore proved and to point out certain means for the prevention of like impurities.

Messrs. Nuger and Bodlander were first to call attention to the presence of relatively large amounts of tin in preserved asparagus. Sache found 70 milligrams of tin in 29 pieces of asparagus (see this Revue, 1, 91.) Likewise, Messrs. A. Menthe (Chem. News, July, 1871) and Schner (The Analyst, 1880, p. 318) proved the presence of more or less important quantities of tin, not only in preserved fruit, but in other food materials, liquids, meat, and other preserved foods.

Sedgwick cites for the first time a case of food poisoning which must be unquestionably attributed to tin (Archives de Pharmacie, 1888). The poisoning was caused by pears prepared in a tinned stewpan. [A member of the congress, present session, informs me that a patient died from chronic metallic poisoning, resulting from the prolonged use of metalliferous preserved vegetables.] He afterwards examined several fruits preserved in tin cans and found very pronounced reactions for tin in all of them.

Prof. Beckurts presented some very important data concerning the presence of tin in foods preserved in tin cans, at the session of the congress of German physicians held at Heidelberg, September 25, 1889. He emphasizes the importance of the sulphide of tin, which is formed by the action of the albuminous matter of vegetables, meat, etc., on the tin of cans. At the current session, Dr. Nehring stated 1 hat he had proved the presence of 0.186 grams, 0.3146 grams, and 0.2269 grams, respectively of tin in three tin cans containing asparagus; whence the congress decided that the use of tin cans for the preservation of foods must be interdicted.

During the preceding year Prof. Blarez commmunicated to the journ. de Pharm. et de Chimie that he had found a considerable amount of tin in pears in tin cans. I am not able to confirm this result, as by repeated trials I only obtained traces of tin. I presume that the presence of a considerable quantity of salt has favored the solution of tin in the sample examined by M. Blarez.

Capitaine-Intendant Winckel reported to the Congress of Industrial Hygiene, held at Amsterdam, September 1890 (see No. 3 of this Revue), that 270soldiers became ill after having oaten lettuce and meat preserved in tins. According to the determinations of Prof. Wefers Bettink, of Utrecht, the amount of tin present was from 19 to 72 milligrams per kilogram.

1 Dr. Van Hamel Roos, Rev. Intern, des Falisfications, 4, 10, 179, translated by Mr, E. E. Ewell for this report.

Prof. Kayser, of Nuremberg, reported in this Revue (4, p. 29), that he had found a considerable amount of tin, about 0.19 per cent, in preserved eels. Several persons had become very ill after eating them.

These facts move me to point out the necessity of coating the interior of tin cans with a varnish or substance capable of resisting the action of a weak acid or of organic substances. I am pleased that I am able to say that a Holland manufacturer, C. Verwer, of Krommeiue, has succeeded in preparing a varnish which, according to my investigations, answers the purpose perfectly, especially in regard to the manner of its application to the tinned surface (an important consideration, since the application of this useful invention rests not only upon the composition of the varnish, but in the first place upon the process for making the varnish perfectly adherent to the inner tinned surface).

It is evident that time plays a great role in the question of the solubility of the interior tinned surface. Evident proof of this is furnished by a can of asparagus preserved since 1860, a period of thirty-one years. (This box was opened and its contents were exhibited at the current session.) The tin of this can having entirely disappeared, was dissolved in the liquid.

I will now give the results of my own investigations.

A can containing beef, preserved eight years and weighing 976 grams (beef and liquid), contained 77 milligrams of oxide of tin; a can of asparagus, preserved six years, contained 56 milligrams of oxide of tin, while another can of asparagus which had been kept only four months contained 11 milligrams. Another can of asparagus, preserved two years and having a net weight of 635 grams, contained 36 milligrams of oxide of tin and 6 milligrams of copper. Some appricots contained 20 milligrams per can, and some fine apples, imported from Singapore, a considerable quantity of tin, about 178 milligrams per kilogram. Fortunately the taste of this last sample was so disagreeable that its consumption, if not its sale, was impossible. Several other preserved fruits and vegetables, such as purslane, sauerkraut, pears, carrots, etc., as well as meat and soup, all contained more or less tin, depending, in the case of vegetable and fruits, on the quantity and kind of organic acids. I am perfectly confident of the correctness of the opinion of Prof. H. Wefers Bettink, of Utrecht, as communicated to the Congress, that malic acid is the principal solvent in the case of fruits and vegetables.

In order to determine whether the above-mentioned varnish was capable of preventing the solvent action of acids on tin, some of the most acid foods, such as sauerkraut, buttermilk, and pears in wine, after four to nine months' preservation in varnished tin cans, were subjected to examination. Only imponderable traces of tin were found. The same results were obtained with a sample of beans coming from France, and examined after being preserved twelve years in a varnished can. This latter example is of less importance, since beans and pease free from salt dissolve almost no tin. I have been unable to procure acid foods which have been preserved for as long a time, but in my opinion the experience acquired after four to nine months suffices to heartily recommend the varnishing process, in consideration of the strong reactions which occur in unvarnished cans. In accordance with experience thus far gained, sorrel is the only vegetable whose action the varnish is unable to resist. After a lew months the varnish was already detached and a considerable amount of tin dissolved.

The writer closes his paper by recommending that varnished cans alone be used, especially for acid foods, and deems it important that the various governments give the matter consideration. Several manufacturers have already adopted the process for acid foods and beverages.

The amount of copper in sample No. 6897 is quite large, and is sufficient to condemn the preparation.

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