Page:The New International Encyclopædia 1st ed. v. 17.djvu/72

* KESINS. mar, dragon's blood, fiaukincense, lac, mastic, and snndarac. Consult: Wiesner, Die iechnisch vcrwciideten GummUirtcn, Harze und Balsame (Erlangen IS(Jl)) : Theniiis, Die llarzc und Hire Producte ('iinna 1S70) : Cameron, Oils, Resins, and Var- nishes (t^ondon, 1880). BESIN WEED. See Compass Plant. RESISTANCE, Electrical. That property of a ronilm-tcir whic-li determines the intensity of an eleetrie eurrent llowing through it for a jjiven dilVerenee of potential at its terminals. The re- sistanee of a eonduc-tor varies with its tempera- ture, but is the same for all currents. The unit of resistance, the ohm (q.v.) is such a resistance as will cause a current of one ampere to flow over a conductor when there is difference of potential of one volt between its terminals. Tliis relation is given by Ohm's law that C = g. where C stands for the current, E for the electromotive force, and R for the resistance. The resistance of a homogeneous conductor will vary directly as its length and inversely as the area of its cross-sec- tion, or in the case of a round wire inversely as the square of the diameter. Specific resistance is the resistance of a centimeter cube of a sub- stance in microhms, while the relative conduc- tivity of a conductor is its relative resistance to some standard substance, generally annealed copper. Resistance may be measured by means of the Whealstone bridge (q.v) or by substituting known resistances for iinknowii, so as to pro- duce an equivalent current, which is indicated by the deflection of the galvanometer (q.v.). An- other method is to use the difl'erential galvanom- eter and so arrange the known resistances that the same current flows through each set of coils, wliile there are also methods where use is made of the condenser and ballistic galvanometer. See Electricity; Conductor; Ohm; Electrical, Units. RES JUDICATA (Lat., thing adjudged). In law, a matter of controversy which has been finally decided and determined on its merits by a court of competent jurisdiction. This implies that there has been no fraud or collusion by which the court has been misled. The importance of this doctrine lies in the fact that if a matter is once judicially determined it cannot again be litigated. To make the entire subject-matter of an action res judieata all the parties interested must be made parties thereto, either as plaintifTs or defendants. Only the points actually decided come within this rule. See Jeopardy : .Judg- IIENT, RESOLUTION, In law, an act or official cxi>rcssion of the will of a legislative body, cor- poration, or organized assembly. The term is sometimes used as being synonymous with ordi- nnnee. when applied to an act of a municipal coTUieil or a board of aldermen. However, reso- lutions are usually adopted to authorize min- isterial acts, or to express the sentiment or regard of a body, whereas ordinances are passed to prescribe permanent rules of conduct or law. For example: If a common council desii-es to regulate the speed of vehicles, it would be done by an ordinance; whereas, if the freedom of the city were to be extended to a distinguished guest, it would be done by a resolution. 56 RESORCIN. In the civil law the discharge of a valid con- tract by consent of the parties or by decree of a court is said to be a resolution of the contract. This is distinguished from a rescission, which implies that the contract was void 06 initio. RESONANCE (OP. resonnance, Fr, risen- nance, from Lat. resonantia, echo, from resonare, to sound back, from re-, back again, anew -)- sonare, to sound, from sonus, sound; connected with Skt, svan, to sound). A general mechanical property which has many illustrations in nature. If a large bell is to be set in motion, it is only necessary to apply a series of impulses regulaily timed at intervals to correspond with the natural period of the body. The colunm of air in a bottle or tube may be set in vibration by waves whose period is the same as that of the column of air. (This is illustrated by the strengthening of cer- tain sounds heard when a bottle or a large sea- shell is put near the ear, for in any room there are present waves of all periods.) If a train of ether-waves passes through some nuiterial medium the minute portions of which have a frequency the same as that of the waves, it will set these portions of matter vibrating. The waves thus lose energy, which is gained by the matter. See Radiation ; Absorption op Waves. RESONATOR. A device used in acoustics (q.v.) to reinforce or strengthen a given tone. Resonators, which are used largely in the analy- sis of sound, consist of hollow vessels usually bulb- shaped or cylindrical. The air of such a vessel has a natural period of vibration, and when the resonator is brought near a sounding body which is emitting waves of the same frequency the for- mer will take up the vibration and will emit the sound. In analyzing sound which is made up of numerous harmonies or overtones the resonator will select a particular sound, which it will re- inforce, and if a diapliragm is placed so that it will vibrate under the action of the air in the resonator, the motion can be communicated to a small gas flame, as in Koenig's manometric capsule. Resonators in the form of wooden boxes are frequently used to mount tuning forks on and are constructed of such dimensions that the contained air will vibrate in uni.son with the fork and so strengthen the sound. RESORCIN, or RESORCINOL (from res-in -f orcin), CeH4(0H)^. A diatomic phenol first obtained by Hlasiwetz and Earth in 1804, by fusing resins with potassium hydroxide. It has since been obtained by various other reac- tions. On an industrial scale it is made by fusing the sodium salt of meta-benzene-disulphonic acid with caustic soda, resorcin being thus produced according to the following chemical equation: CeH, ( S03Na ), + 2NaOH = CaH. ( OH ), -f 'ZNa^SO^ Sodium Cau.«tic Resorcin Sodium m-bpnzene- soda sulphite disulphoimte The mixture is acidified with livdrocbloric acid, and the resorcin is separated by means of ether or some other liquid in which it is soluble. The crude resorcin thus obtained is purified by dis- tillation. It may be added that the meta-ben- zene-disulphonic acid used in making resorcin is obtained by heating benzene with fuming sul- phuric acid. Pure resorcin is a colorless crys- talline substance melting at 119° C. (•240.2° F.) and boiling at 270.5° C. (529.7° F.), It has a faint odor and a sweetish taste, but leaves a dis-