POISONING BY TIN. 931 



Prof. Kayser, of Nuremberg, reported in this Eevue (4, p. 29), that he had tound 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 man- 

 ner 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 var- 

 nish, but in the first place upon the process for making the varnish perfectly adher- 

 ent to the inner tinned surface). 



It is evident that time plays a great role in the question of the solubility of the in- 

 terior tinned surface. Evident proof of this is furnished by a can of asparagus pre- 

 served since 1860, a period of thirty-one years. (This box was opened and its con- 

 tents were exhibited at the current session.) The tin of this can having entirely dis- 

 appeared, 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 keptonly four months contained 11 milligrams. Another can of asparagus, pre- 

 served 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 disagreea- 

 ble 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 correct- 

 ness of the opinion of Prof. H. Wefers Bettiuk, 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 pre- 

 venting the solvent action of acids on tin, some of the most acid foods, such as sauer- 

 kraut, 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 al- 

 most 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 amouiit of copper in sample No. 6897 is quite large, and is suffi- 

 cient to condemn the preparation. 

 20o93 No. 13 5 



