Page:Popular Science Monthly Volume 4.djvu/133

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form, and probably not in origin. There are many Yosemites. Many of the great glacial valleys become deep, narrow cañons, with precipitous walls near the junction of the granites with the slates. This is the position of Yosemite. It occurs in the valley of the American River and the valley of Hetch Hetchy, which, says the author, almost rivals the Yosemite in grandeur, and, in his opinion, all these deep, perpendicular slots have been sawed out by the action of glaciers, the verticality of the walls having been determined by the perpendicular cleavage of the rocks.

Origin of the Potato-Disease.—Messrs. T. & E. Brice, of Plymtree, England, claim to have discovered the cause of the potato and the foot and mouth diseases, which they assert to be nothing else but the employment of chemical manures. It is remarkable, say they, that both of these diseases made their appearance about the same period. It is some 250 years since the potato was introduced into Britain, and there is no record that the disease ever existed until the year 1845, when, subsequently to a continued rain for some days together, the potato was found to be diseased generally throughout the kingdom. Previous to that time the chemical manures had been introduced, and they were used in great abundance the same season that the potato-disease first appeared. Messrs. Brice were then of opinion that the manure was the cause, and, having since investigated its principles and action, they find that it contains a very active poison—sulphuric acid: "Its particles readily attract the particles of water, producing fermentation, and sometimes causing putrefaction of the compound they adhere to. If the chemical manures are distributed over the land in a dry season, and there is not enough rain to cause fermentation, the sulphuric acid remains fixed on the earth; if it is applied in a wet season, the rain causes fermentation; the effluvium ascends in the atmosphere, and, mixing with the vapors, helps to constitute clouds, when there is a return in poisoned rain and dew on the potatoes, and other bodies as well. Putrefaction of the potato is the consequence, and it has a very offensive smell." The authors have made some experiments with a mixture of water and sulphuric acid. Fermentation and poisoning of the water were the result, and an application of the mixture to the potato caused disease.

But the question naturally arises, Why should the sulphuric acid cause disease only in the potato and not in other plants? and on this point the Messrs. Brice leave us in the dark. Here we may mention another theory which has been proposed to account for this potato-blight. It has been observed that the electrical state of the atmosphere has something to do with the matter, and in Ireland the potato-crop is described as wearing a blighted appearance after a protracted thunder-storm. The theory is, that the electrical condition of the atmosphere causes the conversion of the starch into dextrine, sugar, etc., and the tuber then melts away. But again we ask, Why did not the same causes produce the same effects previous to 1845?

As regards the foot and mouth disease, the cattle and other animals travel and browse where the poison has fallen, and it is taken in with their food. The active particles adhere to their feet, lips, and mouth, destroying the scarf-skin and mucous membrane of the mouth and throat. The symptoms are such as might be produced by sulphuric and other corrosive acids.

A Substitute for Parchment.—Parchment-paper has several properties in common with animal membrane. It is obtained by the action of sulphuric acid or chloride-of-zinc solution on unsized paper. When sulphuric acid is employed, the best solution is one kilogramme (2.20485 pounds) English concentrated sulphuric acid to 125 grammes (about 4.4 ounces) of water. The paper is dipped into the acid so as to moisten both sides uniformly. The length of time it is to remain in the bath depends on its own thickness and density. The minimum time for the ordinary unsized paper of commerce is 5 seconds, the maximum 20. When the acid has acted a sufficient length of time, the paper is first dipped in cold water, then in dilute ammonia, again in water, to remove the acid, and finally it