Page:Popular Science Monthly Volume 21.djvu/724

708 Then the clover that had been thrown away attracted their attention, and they ate greedily even of that which was musty. A small extemporized silo was tentatively made, in the natural ground where it was well drained, without walling, and was filled with green clover. The ensilage came out in perfect condition and entirely palatable. The result of the last experiment shows how persons living where the subsoil is very compact might make a silo with either very light walls or with none at all.

How Oölite may be formed.—Mr. F. W. Putnam, in giving an account of a visit he made some months ago to the Mammoth Cave, remarks that in one of the newly discovered chambers he noticed that many fragments of stalactites and small pieces from the walls of the cave, which had fallen into a little pool, were worn round and smooth by constant attrition, occasioned by the dropping of water from the high ceiling of the chamber. Should the water cease to drip in this place, as it probably will, and that in the pool evaporate, leaving the lime to crystallize about these small pebbles, a conglomerate would be formed which would have some resemblance to oolitic limestone, pebbles of which occurred in the pool, probably derived from fragments detached from the walls of the chamber. Calling attention to the formation of "cave pearls," which he had found in Grand Avenue Cave some years ago, he remarked that should such a mass of small pearl-like lime-concretions as were found in the last named cave ever be cemented together, the resemblance to oölite would be very marked. While he did not wish to be understood as stating that the oölitic limestone was formed in this way, he could not help thinking that a rock of similar appearance might be locally so produced under the conditions he had observed.

Lead in Food and the Industrial Arts.—M. Armand Gautier has recently published a memorandum on the dangers arising from the use of lead in food-vessels and in various arts, and on the means of counteracting them. He shows that lead may be detected in preserved vegetables, fish, lobsters, meats, in drinking-water, and water artificially charged with carbonic acid, in acid foods and drinks preserved in glass vessels, in tin dishes, in the coverings of our walls and furniture, in the leather of our boots, in our dishes, and in our glazed table-cloths. He gives a simple and practical test for the presence of lead in solder or tinned or solid metal, and for estimating the proportion of the poison that may be there. It consists in turning on two drops of acetic acid upon the surface of the metallic object, allowing it to evaporate in the air, then touching with a solution of chromate of potash, letting dry, and washing with water. The yellow chromate of lead, thus obtained, adheres to the metal, and does not change color for several days, so that the spot can be kept in evidence. When a tin thus treated shows a yellow spot it should be rejected; if it is used in a food-can the contents should be regarded as suspicious, even if the soldering has all been done on the outside, as the latest regulations require. The general use of food preparations done up in metallic boxes that are soldered with an alloy of lead necessarily results in the introduction of a little lead into the economy, and, according to M. Gautier, the proportions of lead thus absorbed, generally very weak with vegetables, are much stronger in foods rich with fats, and especially in fish preserved in oil; the oils that surround the fish are still more strongly charged with it; and preserved meats contain it in widely varying proportions. The lead appears to exist in vegetables in the shape of an albuminate soluble in the acids of the stomach, in fat-substances as an oleate and a palminate dissolved in the fats, and absorbable with them when they undergo emulsion in the digestive tube. The use of lead in a multitude of arts and trades, too numerous to be named here, leads to more perceptible and extensive poisoning than the minute quantities of the metal that reach us through our foods and food-vessels, the importance of which is indicated by the admission of an average number of seven hundred workmen suffering from it to the hospitals of Paris every year. The compounds of lead with which these workmen come in contact are absorbed by the skin, the mouth, the nostrils, and in breathing. To workmen exposed to such