[ocr errors][merged small][merged small][merged small]


The pronunciation of the words that form the titles of the articles is indicated in two ways: 1st, By re-writing the word in a different form and according to a simple system of transliteration. 2d, By marking the syllable on which the chief accent falls. Entries which simply have their accentuation marked are English or foreign words that present little difficulty, and in regard to which readers can hardly go far wrong. A great many of the entries, however, cannot be treated in this way, but must have their pronunciation represented by a uniform series of symbols, so that it shall be unmistakable. In doing this the same letter or combination of letters is made use of to represent the same sound, no matter by what letter or letters the sound may be represented in the word whose pronunciation is shown. The key to the pronunciation by this means is greatly simplified, the reader having only to remember one character for each sound. Sounds and letters, it may be remarked, are often very different things. In the English language there are over forty sounds, while in the English alphabet there are only twenty-six letters to represent them. Our alphabet is, therefore, very far from being adequate to the duties required of it, and still more inadequate to represent the various sounds of foreign languages.

The most typical vowel sounds (including diphthongs) are as shown in the following list, which gives also the characters that are used in the Cyclopedia to show their pronunciation, most of these being distinguished by diacritical marks.

[blocks in formation]

Of the consonants, b, d, f, h, j, k, l, m, n, ng, p, sh, t, v, z, always have their common English sounds, when used to transliterate foreign words. The letter c is not used by itself in re-writing for pronunciation, s or k being respectively used instead. The only consonantal symbols, therefore, that require explanation are the following:

[blocks in formation]



Potamogeton (-moj'e- ton), a genus of aquatic plants belonging to the natural order Naiadaceæ. It has a perfect flower, a four-pointed perianth, four sessile anthers, four ovaries, and four drupes or nuts. Several species are indigenous to Britain, where they are known by the name of pond-weed. Potash, or POTASSA, an alkaline substance obtained from the ley of vegetable ashes which is mixed with quicklime and boiled down in iron pots, and the residuum ignited, the substance remaining after ignition being common potash. It derives its name from the ashes and the pots (called potash kettles) in which the lixivium is (or used to be) boiled down. An old name was regetable alkali. Potash in this crude state is an impure carbonate of potassium, which when purified is known in commerce as pearl. ash. It is used in the making of glass and soap, and large quantities of it are now produced from certain ‘potash minerals' (especially carnallite), instead of from wood ashes. What is known as caustic potash (hydrate of potassium, KHO) is prepared from ordinary potash. It is solid, white, and extremely caustic, eating into animal and vegetable tissues with great readiness. It changes the purple of violets to green, restores reddened litmus to blue and yellow turmeric to reddish-brown. It rapidly attracts humidity from the air, and

becomes semi-fluid. It is fusible at a heat of 300, and is volatilized at low ignition. It is used in surgery under the name of lapis infernalis or lapis causticus for destroying warts, fungoid growths, &c., and may be applied beneficially to the bites of dogs, venomons serpents, &c. In chemistry it is very extensively employed, both in manufactures and as an agent in analysis. It is the basis of the common soft soaps, for which purpose, however, it is not used in its pure state. See Potassium.

Potash Water, an aerated water pro

[blocks in formation]

duced by mixing bicarbonate of potash with carbonic acid water in the proportion of 20 grains to each bottle of the water, or about half an ounce to the gallon. Bisulphate of potash, as being cheaper than tartaric acid, is sometimes used (but should not be) with carbonate of soda to produce the common effervescing drink. A valuable medicinal water is compounded of a certain proportion of bromide of potassium. See Acrated Waters.

Potassium (a latinized term from potash), a name given to the metallic basis of potash, discovered by Davy in 1807, and one of the first-fruits of his electro-chemical researches; symbol, K; atomic weight, 391. Next to lithium it is the lightest metallic substance known, its specific gravity being 0:865 at the temperature of 60°. At ordinary temperatures it may be cut with a knife and worked with the fingers. At 32° it is hard and brittle, with a crystalline texture; at 50° it becomes malleable, and in lustre resembles polished silver; at 150' it is perfectly liquid. Potassium has a very powerful affinity for oxygen, which it takes from many other compounds. A freshly-exposed surface of potassium instantly becomes covered with a film of oxide. The metal must therefore be preserved under a liquid free from oxygen, rock-oil or naphtha being generally employed. It conducts electricity like the common metals. When thrown upon water it decomposes that liquid with evolution of hydrogen, which burns with a pale violet flame, owing to the presence in it of potash vapour. Chloride of potassium (K (1) is known in commerce as 'muriate of potash,' and closely resembles common salt (chloride of sodium). It is obtained from potassic minerals, the ashes of marine plants (kelp), and from sea-water or brine springs. It enters into the manufacture of. saltpetre, alum, artificial manures, &c. Bromide and iodide of potassium are useful drugs. (For



the carbonate of potassium see Potash.) Bicarbonate of potassium is obtained by exposing a solution of the carbonate to the air, carbonic acid being imbibed from the atmosphere, and crystals being deposited; or it is formed more directly by passing a current of carbonic acid gas through a solution of the carbonate of such a strength that crys tals form spontaneously. It is much used in medicine for making effervescing drinks. Nitrate of potassium is nitre, or saltpetre. (See Nitre.) Sulphate of potassium (K2SO) is used medicinally as a mild laxative, in making some kinds of glass and alum, and in manures. The bi-sulphate (KHSO4) is used as a chemical reagent, and in calicoprinting and dyeing. Chlorate of potassium (KClO3) is employed in the manufacture of lucifer matches, in certain operations in calico-printing, and for filling friction-tubes for firing cannon. It is a well-known source of oxygen. The bi-chromate (K2CrO4) is also used in calico-printing and dyeing. Cyanide of potassium (K C;) is much used in photography.

Potato (Solanum tuberōsum), a plant belonging to the natural order Solanaceae, which also includes such poisonous plants as nightshade, henbane, thorn-apple, and tobacco. We owe this esculent to western South America, where it still grows wild chiefly in the region of the Andes, producing small, tasteless, watery tubers. The potato was first introduced into Europe by the Spaniards after the conquest of Peru, by whom it was spread over the Netherlands, Burgundy, and Italy before the middle of the 16th century. In Germany it is first heard of as a rarity in the time of Charles V. Sir John Hawkins, Sir Francis Drake, and Sir Walter Raleigh are all credited with the first introduction of the tuber into England (1565). Although the potato was tolerably widely distributed on the continent of Europe before its appearance in Britain it seems to have been cultivated more as a curiosity than as an article of food, and Ireland is said to have been the country in which it was first cultivated on a large scale for food. In the course of the 18th century it became a favourite article of food with the poorer classes in Germany; but in France there existed so violent a prejudice against it that it did not come into general use until towards the end of the century. The potato is a perennial plant, with angular herbaceous stems, growing to the height of 2 or 3 feet; leaves pinnate; flowers pretty large, numerous, disposed in

corymbs, and coloured violet, bluish, reddish, or whitish. The fruit is globular, about the size of a gooseberry, reddish-brown or purplish when ripe, and contains numerous small seeds. The tubers, which furnish so large an amount of the food of mankind, are really underground shoots abnormally dilated, their increase in size having been greatly fostered by cultivation. Their true nature is proved by the existence of the 'eyes' upon them. These are leaf-buds, from which, if a tuber or a portion of it containing an eye is put into earth, a young plant will sprout, the starchy matter of the tuber itself supplying nutriment until it throws out roots and leaves, and so attains an independent existence. The potato succeeds best in a light sandy loam containing a certain proportion of vegetable matter. The varieties are very numerous, differing in the time of ripening, in their form, size, colour, and quality. New ones are readily procured by sowing the seeds, which will produce tubers the third year, and a full crop the fourth. But the plant is usually propagated by sowing or planting the tubers, and it is only in this way that any one variety can be kept in cultivation. Like all plants that are extensively cultivated, and under very different circumstances of soil, climate, and artificial treatment, the potato is extremely subject to disease. Among the diseases to which it is liable are the 'curl,' the 'scab,' the 'dry-rot,' and the 'wetrot,' besides the more destructive potato disease proper. The principal feature of the curl is the curling of the shoots soon after their first appearance. After that they make little progress, and sometimes disappear altogether. The plants produce no tubers, or only a few minute ones, which are unfit for food. The scab is a disease that attacks the tubers, which become covered with brown spots on the outside, while underneath the skin is a fungus called Tubercinia scabies. The dry-rot is characterized by a hardening of the tissues, which are completely gorged with mycelium (the vegetative part of fungi). In the disease called wet-rot the potato is affected much in the same way as by the dry rot; but the tubers, instead of becoming hard and dry, are soft. The fungus present in wet-rot is supposed to be the same that accompanies dryrot. The potato disease par excellence was prevalent on both sides of the Atlantic in the year 1845. Usually the first sign of this disease is the appearance of brown

« ElőzőTovább »