Potassium

A metal of a bright silver-white color, derived in 1807 by Sir Humphrey Davy from potash. It is prepared by heating together potash and carbon to a high temperature in an iron retort. It is lighter than water, brittle at 320 Fahrenheit, malleable at a little higher temperature, melts at 62°, and when heated to a temperature below red heat it yields a fine green colored vapor. It has a strong affinity for oxygen, taking fire when thrown upon water or ice, and oxidizes so readily that to be preserved it must be kept in substances which contain no oxygen, as naphtha or kerosene. Its com pounds are very important, being used in gla and soap making, in artificial manures, and in many drugs OF COMMON THINGS 119 and chemicals. The most important of the salts of pota ium are potash, nitre or saltpetre, chlorate of potash, and cream of tartar. [Span, patata, potato, from the native American word (probably batata) in Hayti.] Next to the cereals or grains, the potato is the most valuable of all plants used for food. It is a native of South America, and was introduced into Great Britain by Sir Walter Raleigh in the sixteenth century. The potato plant has a portion of its stem underground, and this part sends out roots and real branches. It is at the ends of these branches that potatoes are formed. Every part of the potato plant except the tuber dies off on the approach of winter, and the tuber is the special provision made by the plant for reproduction. The eyes of the potato are real buds, and the solid flesh of the tuber consists mainly of starcti, the destined food of the young plant. Potatoes are largely cultivated in all mild climates. There are very many varieties, differ¬ ing in time of ripening, form, size, color, and quality. New varieties are raised from the seed, but potatoes are grown by planting the tubers or cuttings of them, care being taken to have at least one eye in each piece. About three-fourths of the weight of a full-grown potato is water, and of the other fourth about one-sixth is gluten and five-sixths starch. [Fr. poterie.~\ The term applied to all objects made out of baked clay. The art of forming utensils of clay is of very ancient origin, extending back to the early days of mankind. Its rudimentary condition, that of merely molding soft clay into the desired form and drying it by the heat of the sun, was suc¬ ceeded by baking it in a fire to make it harder and le brittle. Other substances were after¬ wards mixed with the clay so as to make finer and more delicate pottery. Gradually the potter enhanced the value of the art by forming graceful designs, and by painting and decorating them, until at the present day the art of the potter is one of the most important. Pottery may be divided as regards material and baking into three kinds—earthenware, stoneware, and porcelain or china. The term pottery is applied to all ware of the opaque kind, while porcelain applies to that which is translucent. [Fr., from Low L. prataria; L. pratum, a meadow.] A large level tract of country, bare of trees, covered with coarse gra , and generally of a fertile soil. This name is applied to the treele plains of the Mi i ippi valley. Similar plains in the South are called Savannahs. A small rodent animal, allied to the marmot, and found in the prairies west of the Mi i ippi. It is gregarious in habit, dwells in largely arid districts, makes deep burrows in the earth, and throws up mounds. On these the animal often sits, and, if disturbed, gives a warning cry somewhat like the bark of a small dog. stones. Minerals which are used in jewelry on account of their rarity and beauty. They include the diamond, ruby, emerald, sapphire, and many others. 695