Boiling.

ical shells, 8 in. in external diameter, and of an in. thick; they are cast in sections, 2 or 4 spheres together, are connected by curved necks of 3 in. diameter, and are held together by wrought-iron bolts and caps. The joints are accurately fitted, without packing. See accompanying illus., fig. 9.

The water surface of a boiler is that area of metal which has water within and flame or hot gases without; at this surface the steam is generated. The area which has hot gases without and steam within is superheating surface, at which the steam by the reception of heat acquires greater expansive force. The draught-area, or calorimeter, is the cross section of the area traversed by the hot gases from the fire, and may be taken at any point between the furnace and the chimney. Ordinarily, however, it is restricted to the space around the tubes in the water-tube boilers, and to the section of the flues in flue-boilers. That boiler is most efficient which shows the greatest difference between the furnace temperature and that found at the chimney, since that difference indicates the quantity of heat which has been transferred to the water in the generation of steam. If the combustion is complete, the heat of the furnace will depend on the quantity of air furnished, that is, upon the area of the calorimeter, whence it appears that the calorimeter should be large. But if this space be an unbroken volume, much of the hot gas may pass through without impinging against the boiler surface, and delivering its heat, whence it is desirable that the space should be divided thoroughly; and it is evident that a reduced calorimeter may often give better results than a larger one, not properly arranged. A designer of boilers will find important tables on this point in Appleton's Cyclopædia of Mechanics.

Priming is the tendency of the water in the boiler to form spray by the bursting of the steam bubbles when they come to the surface of the water, the spray going forward with the steam into the cylinder. Here it is cooled and accumulates, especially if the exhaust port is not, either by position or capacity, adequate to its discharge. Water is practically incompressible, and if a quantity of it, greater than the volume of the clearance, is found before the piston, near the end of the stroke, it lies between the piston and the cylinder head as mischievous as a mass of metal would be in the same position. Something must yield. The crank pin may be broken, or the cylinder split, or the head burst out, and all rods and gearing will be ruined. Priming is caused by want of steam room, or of area at the surface of the water in the bodies, or by the use of dirty water. The latter cause may be cured by collecting the water in tanks, and giving it time to settle. The others may be avoided by proper construction of the boiler, by checking the steam at the throttle, or by working the engine more expansively. Any sudden removal of pressure, as the opening of the safety-valve, or of the throttle in starting, tends to produce priming, because while the water had, at the instant of the opening, a capacity for steam corresponding to the higher pressure, the diminished pressure sets free a gush of steam that is entirely disproportioned to the ordinary conditions. Some authorities advise the insertion of a perforated plate through which the steam must pass on its way to the cylinder; the water beating against this plate is arrested, and the steam passes on more freely. In some locomotives the steam is taken by a longitudinal perforated pipe, which serves the purpose of the steam dome of usual designs. Boilers in which the steam does not circulate freely because of the disposition of the tubes, are liable to the annoyance of priming.

The term horse-power, when applied to the boiler, has a meaning scarcely more definite than when used to indicate the capacity of the engine. In either case, the horsepower realized depends as much upon the method of using the mechanism, as upon its original construction. The best authorities agree that the horse-power of the boiler should indicate the actual evaporation of water, instead of the size of the boiler or the efficiency which may be secured through the engine. The ability to evaporate a cubic foot of water per hour, making steam at 212° F., has been suggested as a suitable unit to be called a horse-power. To ascertain the evaporative power of a boiler by experiment, it is necessary to obtain the weights of fuel and water, and to know the quality of the steam produced. A trial should last 24 hours; steam may be raised, and then fire withdrawn, and the ash-pit cleared, the steam meanwhile being maintained with wood. Coal is then added, and as soon as it is fired, the test begins. Note is taken of the height of water in the gauge, and the water is left at the same height at the end of the test. Coal is carefully weighed in regular amounts and at regular intervals to avoid errors. At the end of the trial the fire is withdrawn, and the remaining coal weighed as soon as possible; this weight, plus that of the ashes made during the experiment, taken from the weight of the coal, gives the weight of fuel consumed. To find the quality of the steam, a tank is provided, which is traversed by a pipe leading to the boiler, the whole apparatus being so arranged as to waste as little heat as possible. The tank is filled with water, and steam is admitted through the pipe in such quantity as may be condensed by the water. We have to note the pressure of the steam, the weight and temperature of the water before steam is admitted, the weight and temperature at the close of the test, the weight and temperature of the water formed from the condensed steam, and the time. Experiment must also be made to test the loss of heat by radiation and evaporation, which is done by heating a given quantity of water to a given temperature in the same tank, and noting the loss in weight and temperature during a given time. To illus trate by an example. Suppose a test made, from which these data have been secured:

Boiling.

Coal used, 5980 lbs. ; feed water used, 42,320 lbs.; coal withdrawn at end of test, with ashes, 1830 lbs.; hence, coal burned in the test, 5980 minus 1830-4150 lbs. The apparent evaporation per pound of coal is, 42,320÷4150=10.2 lbs., if the steam were dry. To test the quality of the steam the described apparatus has been used, and these data noted: Pressure of steam at gauge, 80 lbs.; weight of steam condensed at 95°, 204 lbs.; initial temperature of water for condensing, 60; final temperature, 92°; head of water in tank, 27 in.; time of trial, 24 hours; and by former tests it appears that 4 cu. ft. of water, weighing 62.2 lbs. per ft., pass from the tank per hour, and that the loss of heat by evaporation and radiation is 1480 thermal units per hour. The heat given to the water by the condensing steam in one hour was 4×62.2× (95 minus 60) +1480-8708 thermal units. The steam condensed per hour was 204÷24-8.5 lbs., hence each pound of steam communicated to the water 8708÷8.5=1024.5 thermal units of heat. But this condensed steam was discharged at 95°; to bring it down to the standard of 32° there must have been a farther reduction of 95 minus 30=65 thermal units, showing that the quantity of heat above freezing standard held by a pound of steam as it issued from the boiler was 1024.5+65-1089.5 thermal units. The total heat, above freezing standard, of a pound of dry steam at 80 lbs. pressure (see Rankine, Steam Engine, or Appleton's Cyc. of Mechanics), is 1177.1; it is therefore evident that the steam used in the test contained some moisture. As the temperature of the feed-water was 60°, it had already 28 thermal units of heat per pound above water at 32°, and would require 1177.1 minus 28-1149.1 thermal units to change it to dry steam; but it required 1089.5 minus 28=1061.5 thermal units to change it to steam of the quality observed, hence the actual evaporation was 1061.5÷1149.1=0.91506 of the apparent evaporation. But the apparent evaporation was 8.5 lbs. per pound of coal, and the actual was therefore 7.778 lbs. If the feed-water were at 212, 998.5 thermal units would be required to convert a pound of water into steam. Hence, 1061.5÷998.5=10.6= nearly the evaporation per pound from and at 212°.

BOILING (of liquids)-BOILING-POINT. When heat is applied to a vessel containing water, the temperature gradually rises, and vapor comes silently off the surface; but at a certain degree of heat, steam (q.v.) begins to be formed in small explosive bursts at the bottom, and rising through the liquid in considerable bubbles, throws it into commotion. If, after this, the steam is allowed freely to escape, the temperature of the water rises no higher, however great the heat of the fire. The water is then said to boil, and the temperature at which it remains permanent is its boiling-point. The boilingpoint of water is ordinarily 212°; but every liquid has a point of its own. Thus, sulphuric ether boils at 96°; alcohol, at 176°; oil of turpentine, at 316; sulphuric acid, at 620°; and mercury, at 662°. The boiling-point of liquids is constant, under the same conditions, but is liable to be altered by various circumstances. Water with common salt in it, e.g., requires greater heat to make it boil than pure water. The nature of the vessel, too, exerts an influence; in a glass vessel, the boiling-point of water is a degree or two higher than in one of metal, owing to the greater attraction that there is between water and glass than between water and a metal. But what most affects the boilingpoint is variation of pressure. It is only when the barometer stands at 80 in., showing an atmospheric pressure of 15 lbs. on the sq. in., that the boiling-point of water is 212. When the barometer falls, or when part of the pressure is in any other way removed, it boils before coming to 212°, and when the pressure is increased, the boiling-point rises. -Thus, in elevated positions, where there is less air above the liquid to press on its surface, the boiling point is lower than at the level of the sea. An elevation of 510 ft. above the sea-level, makes a diminution of a degree; at higher levels, the difference of elevation corresponding to a degree of temperature in the boiling-point increases; but the rate of variation once ascertained, a method is thus furnished of measuring the heights of mountains. See HEIGHTS, MEASUREMENT OF. At the city of Mexico, 7000 ft. above the sea, water boils at 200°; at Quito, 9000 ft., at 194°; and on Donkia mountain, in the Himalaya, at the height of 18,000 ft., Dr. Hooker found it to boil at 180°. Boiling water is thus not always equally hot, and in elevated places, many substances cannot be cooked by boiling. Under the receiver of an air-pump, the same effect is still more strikingly seen; water may be made to boil at the temperature of summer, and ether when colder than ice. In complete vacuo, liquids, in general, boil at a temperature 140° lower than in the open air. The knowledge of this effect of diminished pressure is now largely turned to account in sugar-boiling, in distilling vegetable essences, and in other processes where the substances are apt to be injured by a high temperature, -By increasing the pressure, again, water may be heated to any degree without boiling. Papin's Digester (q.v.) is formed on this principle. Under a pressure of two atmos pheres, the boiling point rises to 234°; of four atmospheres, it is 294°; of ten atmospheres, 359; of fifty atmospheres, 510°.

In a deep vessel, the water at the bottom has to sustain the pressure not only of the atmosphere, but also of the water above it. At a depth of 34 ft., the pressure of the water above is equal to an atmosphere, or 15 lbs. on the sq. in.; and thus, at the bottom of a vessel of that depth, the water must be heated to 234° before it is at its boilingpoint. This principle has been successfully applied to explain the phenomena of the Geysers (q.v.).

If a small quantity of water be poured into a silver basin, heated above the boiling

point, but below redness, it will begin to boil violently, or perhaps burst into steam at once. But if the basin is heated to redness, the water will gather itself into a globule, and roll about on the hot surface, without becoming heated to the boiling-point. For the explanation of this and other interesting phenomena connected with it, see SPHE ROIDAL CONDITION OF LIQUIDS.

BOILING OF LIQUIDS (ante). As will be understood from the above, the terms liquid and boiling-point are entirely relative, depending upon external agents and upon each other. The statement that water is a liquid is only true under certain conditions In the arctic regions it is a solid, and in a vessel heated to 212° under ordinary atmos pheric pressure it is a vapor or gas. Nitrous oxide is a liquid under ordinary atmos pheric pressure when reduced below 126° below zero, and the same is true of carbonic acid when reduced to 108.76°. Pressure, however, is capable of reducing both these gases to liquids, and modern experiments with various substances are now common in which carbonic acid is liquefied by pressure. Ammonia, commonly a gas, is a liquid when reduced to -28.66°. This substance is capable of being absorbed by a very small volume of water under heavy pressure, or, at least, of occupying a very small volume; for we cannot say that the gas is really absorbed; the water assists the pressure in holding the gas in a liquid form. Advantage is taken of this in the working of a certain class of ice-making machines, called ammonia machines (q.v.). Some of the machines, however, depend upon the vaporization of ammonia, anhydrous, or nearly so, for the absorption of sensible heat. The following is a table of the boiling points of various substances:

The investigations of prof. Kopp indicate certain remarkable laws connecting the boiling points of classes of liquids with their chemical constitution. The following tables, calculated from the observations of prof. Kopp and others, show that in the group of alcohols, and the acids derived from them by oxidation—both of which differ in constitution by one molecule of CH2-there is a difference of very nearly 19° C. between successive members of the series; and that, moreover, the difference in the boiling-points between the alcohols and their respectively derived acids is about 40° C.

Other analogous correspondences in the boiling-points of liquids and their chemical constitution were observed; thus in the series of hydrocarbons, homologous with benzole, C.He, a difference in the series of CH, was attended with a difference of boiling. point of about 20° C.

The molecular constitution, or, more strictly speaking, the mutual relations between the molecules of liquids, particularly as regards water, whose affinities are so numerous, exerts a great influence not only upon the boiling-point, but upon the nature or manner of ebullition. Thus, if a clean glass flask is partially filled with ordinary, and, of course, more or less aerated spring water, and heated rapidly with a spirit-lamp, nearly all the air will be expelled first, but before all the air is thus expelled ebullition will commence, and at a point very slightly below 212°. After a little tine, more of the air having disappeared, but not entirely, the boiling-point (at 30 in. mercurial pressure) will be 212°. By continuing the boiling, however, the mode of ebullition will be found to have

Boiling.

changed. If the flask is held quite still there will be intervals of time-although the application of heat is constant-when ebullition will cease; and during these intervals the temperature will rise. If the heat is taken away for a few moments so as to allow the water to come to a state of comparative rest, and then reapplied, the temperature may be raised to 220° before ebullition commences, when it will be decidedly explosive. If now the flask is corked tight, and a partial vacuum formed in the space occupied by vapor, boiling will go on until the water is quite cool, but the boiling will be of the explosive character observed in the later periods of application of heat, and when quite cool will be more irregular, partly in consequence of the reduction of atmospheric pressure, but more particularly, probably because of the increased cohesion between the contiguous molecules of water by reduction of heat.

BOILING, in cookery. One important preliminary rule in boiling rests on the fact. explained in a preceding article, that water cannot be heated in an open vessel, or in one with the ordinary fitting lid of a cooking utensil, to a higher point than 212°. When a vessel, then, has once begun to boil, a stronger fire than is just sufficient to keep it boiling, will only evaporate, or waste, the water in steam, but will not cook the food any faster; on the contrary, the outside will be rendered so hard by the quick boiling, that the interior will not be reached by the heat.

By long soaking in cold or tepid water, fresh meat loses much of its albumen and nutritive juice. When a piece of meat is to be boiled, it is necessary, for the preservation of these juices, and its consequent tenderness and nutritious quality, that the outside should be sealed up, by immersing it in boiling water, and keeping up the temperature for a minute; this closes up the pores, and coagulates the albumen of the exterior. The boiling water should then be taken off, and as much cold put in as will reduce it to a tepid state; it should then be gradually warmed until it reaches a degree slightly under the boiling-point, called simmering; at this point it must be kept without suffering any interruption of the heat, till the time elapses that is allowed for cooking the food. The cooking goes on through the agency of the natural moisture of the flesh. Converted into vapor by the heat, a kind of steaming takes place within the piece of meat; it is, when skillfully done, cooked by its own steam."

To prepare meat for B., it should be trimmed, washed, and dried before it is placed in the water. As it simmers, the water should be kept well skimmed with a skimmingspoon, as frequently as any scum is thrown up, but with due remembrance of the fact, that raising the lid of the vessel lowers the temperature of the water; and the preservation of an equal degree of heat throughout the operation is of the greatest importance. For fresh meat, 20 minutes is the allowance for each pound. The weather must also be considered: in frosty weather, or with very thick joints, extra 20 minutes should be given. Mutton loses in boiling, in 1 lb., 34 oz.; beef, in 1 lb., 4 oz. Meat that has been salted and dried has its outer coat alrealy sealed up; it requires, therefore, to be thoroughly washed, soaked for two hours in cold water, dried, and put to boil in cold water, gradually brought to the boiling-point, and kept simmering for a time, proportioned to the size of the piece. Hams and tongues to be eaten cold, should be allowed to cool in the water in which they have been boiled. The following is a time-table for the cooking of these meats, reckoning from the time the water boils: A ham of 16 lbs. takes 4 hours; a tongue of 16 lbs., 2 to 4 hours; a pig's face of 16 lbs., 2 hours; a piece of bacon of 4 lbs., 2 hours.

Poultry and white meats, as veal or rabbit, should be put at once into tepid water, gradually brought to the boiling point, drawn back immediately, and simmered, carefully skimming the water as scum rises. A chicken, or small fowl, or rabbit, will take 35 minutes; a fowl. or old rabbit, an hour, or an hour and a half, according to size. Some cooks add milk to the water, but this is apt to cause the scum to stick to the meat in streaks; some also use a cloth to inclose the meat, but this frequently imparts to it a disagreeable taste. Having trimmed, washed, and dried the meat, all that is necessary to keep it white, is to use a perfectly clean utensil, to be attentive to the skimming, and careful that no soot falls from the lid into the pot when doing this. Meat should only just be covered with water; if it wastes, a cupful of water at the same temperature should be added. The liquor in which fresh meat has been boiled is an excellent foundation for soups and gravies.

Fish should be well cleaned and scraped; liver and roe should be carefully preserved, and boiled with the fish, in a fine net: they are used to garnish the fish. The sound of cod should be carefully cleaned, and left in the fish. Fish should be placed in cold water. in which a tablespoonful of salt and one of vinegar is mixed; should be gradually brought to the boiling-point, and simmered carefully, lest the outer part should crack before the thick part is done. If on drawing up the fish-plate, a thin knife will easily divide the flesh from the bone in the thick parts, and if the eyes contract, and become like balls, the fish is sufficiently cooked. Drain by laying the plate across the kettle covered with the lid, and dish perfectly dry on the strainer, which should be covered with a napkin.

Vegetables require generally to be well washed, and placed in B. is mixed a large spoonful of salt. When they sink, they are done. should be well picked, soaked in salt and water, drained and boiled in in a vessel without a lid. Cabbage requires two waters; spinach, very

water, in which Green vegetables plenty of water, little, as it is full

Bojar.

of moisture. Peas and beans should not soak, but be merely rinsed in a colander. Winter potatoes should soak for an hour or more; whether they should be placed in cold or B. water, depends on the sort. A piece of soda the size of a small marble assists the B. of peas and cabbage, if the water is very hard.

For B. meat, the best vessel is one made of iron, tinned inside or not, but one kept perfectly dry, and free from grease or rust. Tinned vessels are proper for B. fish and veg etables; they require to be kept very dry, the moisture entering between the metals rusts the iron, and makes holes that cannot be mended. A tinned vessel in daily use should be polished once a week with fine whiting and oil; too frequent polishing wears off the tin. The advantage of a tin over an iron utensil is, that it gains heat sooner.

BOIS D'ARC. See OSAGE ORANGE,

BOIS BLANC, an island of the United States of America, situated in lake Huron, between Michillimackinac and Michigan. It measures 10 m. by 3, and has a lighthouse at its east end.

BOIS-DE-BOULOGNE. See BOULOGNE.

BOIS-LE-DUC (Dutch, 's Hertogenbosch, "Duke's Forest"), the capital of the Nether lands province of n. Brabant, is situated at the junction of the Dommel and the Aa. The fortifications are greatly strengthened by the natural situation, as the surrounding country can be flooded, leaving only two roads passable. It is a clean, well-built town, about 5 m. in circumference, intersected by canals, and has a citadel called Papenbril. B. has a very fine cathedral, and academy of arts, a grammar-school, several hospitals, etc. Iron-founding, making ultramarine, book-printing, refining salt, beer-brewing, distilling spirits, manufacturing linen-thread, ribbons, cutlery, etc., are the principal industries. Pop. (Jan. 1, 1883), 25,517. B. is a place of considerable antiquity, having been founded in 1184 by Godfrey III., duke of Brabant. The surrounding forest was cut down by his son and successor Henry, who strengthened the town with walls. In the 16th c., B. separated itself from the states, and was ineffectually besieged, in 1601 and 1603, by prince Maurice of Nassau, but had to surrender to a Dutch force in 1629. In 1794, B. was taken by the French; and in 1814, retaken by the Prussians.

BOISÉ, a co. in s.w. Idaho, on the Payette river; about 3300 sq.m.; pop. '80, 3204 -1225 Chinese. It is a mining region. Co. seat, Idaho City.

BOISE CITY, in Idaho, capital and chief city of the state, on the Boisé river, 285 m. n.w. of Salt Lake City, and 520 m. n.e. of San Francisco. It has a government assay office, and a penitentiary. It is on the site of an old trading-post of the Hudson's Bay company. Pop. '80, 1899.

BOISSEREE, SULPIZ, a celebrated archæologist, was b. at Cologne in 1783. A visit which he and his brother Melchior (born 1786), along with their friend Joh. Bapt. Bertram, paid to Paris in 1803, inspired the trio with the idea of collecting and preserving the scattered specimens of early German art. The realization of this idea became the single object of their lives. After many years of patient and unwearied research, they gathered together 200 pictures, which received the name of "the Boisserean collection." The king of Würtemberg having presented the brothers with a spacious edifice in Stuttgart, the pictures were transferred thither, and skillfully arranged, according to their age and importance. This brought to light a very important historical fact, previously unknown-viz., that in the 14th c. Germany possessed a school of art based on Byzantine traditions. Great light was also thrown upon many of the Flemish masters, and especially on the influence exerted by Jan Van Eyck. The collection was divided into three sections corresponding to three historical periods-the first comprising the works of the Cologne school in the 14th c.; the second, those of Van Eyck and his disciples in the 15th; and the third, those of the German painters at the close of the 15th and beginning of the 16th centuries. In 1827, the collection was sold to the king of Bavaria; and in 1836 was transferred to the picture-gallery (pinakothek) in Munich, whither the brothers followed it. Sulpiz died in 1841, and Melchior in 1851. The former has left several interesting and valuable works; such as Monuments of Architecture on the Lower Rhine, from the 7th to the 13th c. (Munich, 1830-33); Concerning the Temple of the Holy Grail, 1834; Collection of Old Low and High German Paintings, with Notices of the Early Painters, by Sulpiz and Melchior B. and Joh. Bapt. Bertram, lithographed by J. V. Strizner (1822-39); and a very magnificent work, entitled Views, Plans, Sections, and Details of the Cathedral of Cologne, with Restorations after the Original Plan, accompanied by Researches on the Architecture of Ancient Cathedrals, etc. (1823–32).

BOISSONADE, JOHN FRANCIS, a distinguished classical scholar, b. at Paris, Aug. 12, 1774, of a noble Gascon family. He was originally intended for the administrative career, but after experiencing some of its more violent vicissitudes, he renounced it for philology, in which he had always found his favorite recreation. He soon made himself known to the critical world by his acute and learned contributions to the literary journals, was appointed professor of Greek in the academy of Paris in 1809, and entered on the active duties of the chair in 1812. In 1813, he was admitted into the academy of inscriptions; and in 1828, he succeeded Gail as professor of Greek literature in the college of France. Beyond this high position he never aspired, but pursued his investigations with an energy which no mere social or public ambition could distract. His more