paratively small diameter are used. These are filled with water and the gases from the furnace pass around and between the tubes, heating the water contained in them. An advantage of the water tube boiler is the possibility of making it light, powerful, and compact. It is especially well adapted for forced draught, and steam can be raised quickly. These boilers are the safest against explosions. For these and other reasons they are largely used on war vessels and especially torpedo boats.
The most frequent cause of boiler explosions is the inability of the boiler to resist the regular working pressure. A boiler may be weak through various reasons, and old boilers are likely to be weakened by rust and general decay. See Steam.
BOILING, in general, the change of a substance from the liquid to the gaseous state which takes place throughout the liquid. The boiling point, in science, is the point of degree of the thermometer at which any liquid boils. The boiling point of any liquid is always the same, if the physical conditions are the same. The boiling point of distilled water under pressure of 760 millimeters is 100° C., or 212° F. A difference of height of about 327 meters lowers the boiling point of water about 1° C., or 597 feet ascent lowers it 1° F. The boiling point of organic compounds is generally higher as the constitution is more complex. In a homologous series the boiling point rises about 19° for every additional CH₂ in normal alcohols, and 22° in the normal fatty acids, as ethylic alcohol, C₂H. (OH) 78.4°; propylic alcohol, C3H₂(OH) 97°; acetic acid, CH.CO.OH. 118°; propionic acid, C₂H.CO.OH 149.6°. The secondary and tertiary alcohols have lower boiling points than the primary alcohols. The replacement of hydrogen in a hydrocarbon by chlorine, or by a radical, raises the boiling point, as benzene C.H. 82⁰, chlorbenzene C.H.bl. 135°, amidobenzene CH(NH,) 182°.
Liquids are not increased in heat after they once begin to boil; a fierce fire only makes them boil more rapidly. The following boiling points have been stated:
| Deg. Fahr. | |
| Mercury | 662 |
| Sulphuric acid. | 610 |
| Olive oil | 600 |
| Phosphorus | 554 |
| Iodine | 347 |
| Naphtha | 320 |
| Oil of turpentine | 314 |
| Water | 212 |
| Nitric acid. | 210 |
| Alcohol | 173 |
| Sulphuric ether | 113 |
| Muriatic ether | 134 |
In cookery, an important preliminary rule in boiling rests on the fact 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° F. 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. For boiling 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 pound, 3½ ounces; beef, in 1 pound, 4 ounces. Meat that has been salted and dried has its outer coat already 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.
Before boiling poultry or fish, it is advisable to rub the outside skin with a cut lemon. This insures a snowy white appearance in the cooked food. 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.
BOIS D'ARC (bwä-dark') (sometimes corrupted into Bodock), also bow-wood, or osage orange (maclura aurantiaca), a tree belonging to the artocarpaceæ, sub--order moraceæ, is a native of the southern United States. Its large, beautiful, orange-like fruits are scarcely eatable, but its spines make it useful as a hedge plant. Its wood is strong, and hard, and elastic, and hence was used by the Indians in the manufacture of their bows.
BOIS DE BOULOGNE (bwä dè bölōn'), a wood near the gates on the W. of Paris, so named after the suburb Boulogne-sur-Seine. It is one of the pleasantest Parisian holiday promenades and a famous dueling ground.
BOISE, city, capital of the State of Idaho, and county-seat of Ada co.; on the Boise river and the Oregon Short Line railroad; 45 miles S. W. of Idaho City. It occupies the site of a former trading post of the Hudson's Bay Company; is in an agricultural and a rich mining region; and is supplied with pure hot water from a flowing boiling well. It contains the State Capitol, erected in 1885-1887, a penitentiary, United States Assay Office, State Library, National banks, public li-
