On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
An important item in the extension of the work of the Bureau of Chemistry has been the establishment of inspection for imported food products. . As a result food products imported to this country have been greatly improved. In former years the United States was regarded as the dumping ground for the refuse teas of the commerce of the world. Many years ago, in order to overcome this evil, a system of inspection of imported teas was established and has since been maintained. Under the beneficent working of this system Americans are now certain of being able to purchas pure and wholesome tea, since it is almost impossible for spurious and adulterated teas to find their way into this country. Congress has now extended this system of inspectioi to all foods, beverages, and condiments imported into the United States. There is every reason to believe that when this system is thoroughly established an improved condition comparable to that which has taken place in teas may be anticipated. The bactericidal effect of wall-paints has been studied ately by Dr. Beaufils (see Revue Gnrale des Sciences) according to the following method: A layer of paint having been spread out on wooden boards or glass plates, a culture of microbes was placed on this layer after being dried, and the plate thus prepared was kept in the laboratory protected against dust. At regular intervals some microbe colonies were removed and spread out on an appropriate medium or used in inoculating animals. An unpainted check-plate served to ascertain the action exerted by the paint on the vitality and virulence of the microbes, this action being shown generally to be distinctly bactericidal while varying according to the nature of the painting. The colors of enameled porcelain are for instance found to be much more active than oil colors, especially in regard to the bacillus of tuberculosis. The fact that these paints exert a constraining action on the latter bacillus would seem to be the most important practical result of these researches. When chloride of silver is exposed to sunlight it assumes a violet tint and gives off chlorine. A chemical change thus occurs, and the change of color must be attributed to the formation of a new compound. But there seems to be a great difference of opinion as to the nature of this effect. D. Tommasi, in taking up the question, considers that the chloride of silver, under the influence of the rays, undergoes a partial decomposition which is proportional to the surface, the exposure, and strength of the light. A very small quantity of silver chloride is transformed into AgaCl or Ag,Cl.., (this chloride has been directly obtained by Von Bibra) which is finally decomposed into silver and chlorine by a long exposure to the sun, so that the violet chloride of silver contains variable quantities of Ag CI and the two chlorides mentioned above, and also metallic silver. As there are some differences of opinion as to many of the properties of silver chloride, M.. Tommasi undertook the study of these properties, and gives the following results. The white chloride of silver when exposed to the sun in a glass-stoppered flask containing water saturated with chlorine, in a short time acquires a slight violet tint which does not become any darker on a long exposure. Here a state of equilibrium is formed between the action of the light upon the white chloride and the action of the chlorine upon the violet chloride, which has the effect of preventing the light from blackening the white chloride, and the chlorine to bleach the violet chloride. Again, dried white chloride in a sealed glass tube becomes violet when exposed to the sun and becomes white again when the tube is placed in the dark. When the dry violet salt is shaken with chlorine water in the dark, it whitens in a short time. He also finds that when the violet chloride is boiled with nitric acid, it is not bleached. Bromide of silver acts in an analogous manner, but the iodide is not affected by exposure to the sun.
