O.H.M.S. 



the opposite direction. It in there- 

 fore obvious that if R be BO 

 adjusted that the galvanometer is 

 not affected, the resistance of 

 a c => resistance of c d, or deduct- 

 ing equal parts, remittance of It 

 (known) resistance of X. 



In another type of instrument, 

 '. a magnetic needle in sub- 

 jected to the influence of two 

 coils A and B, arranged at right 

 angles to one another. 

 (nil, when current passes through 

 it. tncs to turn the needle into a 

 line parallel to its own axis. A 

 magneto machine supplies current 

 to two screw-posts which are con- 

 nected by coil A, and also by coil B 

 in series with the conductor X 

 under test. Assuming X to <>H.-i 

 infinitely great resistance, all the 

 current will pass through A, and 

 the pointer attached to the needle 

 will move into the infinity position 

 at one end of the scale of the dial. 

 If, however, any current passes 

 through X, coil B acts in opposi- 

 tion to A, and the deflection of the 

 pointer is modified accordingly. 

 The graduation of the dial scale 

 is based upon tests made with 

 resistances of known magnitude. 



O.H.M.S. Abbrev. for On His 

 (or Her) Majesty's Service. 



Ohm's Law. In electricity, a 

 law defining the relationship be- 

 tween electromotive force (E.M.F. ), 

 the resistance of a circuit, and the 

 flow of current through the circuit. 

 It was first investigated by a Ger- 

 man, G. S. Ohm, who stated the 

 law that in any given circuit the 

 ratio of the E.M.F. producing a 

 current to the current produced 

 depends on the resistance of the 

 circuit. Thus, if E= E.M.F. or 

 pressure (in volts), C current (in 

 amperes), R= resistance (in ohms), 

 R=E/C; C=E/R; E=CxR. See 

 Electricity. 



Ohnet, GEORGES (1848-1918). 

 French novelist. He was born in 

 Paris, April 3, 1848, and after the 

 Franco-Prus- 

 sian War suc- 

 cessively edited 

 Le Pays and 

 Le Constitu- 

 tionnel. In 

 | 1877 bis first 

 play, Regina 

 Scarpi, written 

 in collabora- 

 tion, was pro- 

 Georges Ohnet, Hurod and in 

 French novelist A u- t 



1880 his first 



novel, Serge Panine. His most fam- 

 ous story, Le Maitre de Forges, ap- 

 peared in 1881, and in dramatic form 

 achieved a great success both in 

 France and in England, where it 

 was given as The Ironmaster and 

 Lady Clare. He wrote many popu- 

 lar romances of modern life charac- 



5629 



forked by melodramatic ploU and 

 somewhat over-wrought Morion. 

 He died in Parin. May 5, 1918. 



Ohthere (II HMO). Nome navi 

 gator. He entered th Mnrioe of 

 Alfred the Great, who described 

 two of his voyage* in his trans- 

 I it ion of OriMiuH. Ohthere Bailed 

 i. .1111. 1 the North Cape, explored 

 the Murman coast, and discovered 

 the White Sea. 



OIL 



Oich. !.< a Ukeoflni 



-<it land. It is 4 m. long and 

 about J m. broad, and M the 

 rammit level (105 ft.) of the 

 Caledonian Canal Itbasadepthof 

 155 ft., and HIU part of the Great 

 '.i'-i The Glengarry flows into 

 the loch, which M drained by the 

 Oi<h (HJ m. long) into Loch New 

 at Fort Augustus. Trout and 

 nalnion are plentiful 



OIL: ITS PRODUCTION AND USES 



J. T. Smith. Editor of Th Pirolum World 



This is one of a group of articles dealing with the commercial 



Products of the world, the others including Coal, Cotton, and 



Rubber. It is followed by a section on Oils and Fats. See alto 



Mexico; Mining 



Oils may be divided into three 

 groups : mineral oils, and those 

 natural substances present in 

 animal and vegetable organism. 



MINERAL OIL. Petroleum, or 

 rock oil, is a liquid, in most cases of 

 a dark brown, black, or dark green 

 colour, and is the raw material 

 from which petrol, paraffin oil, 

 lubricating oils, fuel oil, paraffin 

 wax for candles, and many other 

 products are manufactured. Its 

 main constituents are carbon and 

 hydrogen. Under various names 

 and in various countries it has been 

 known since ancient times. 

 Methods o! Mining 



The ordinary method of mining 

 for petroleum is by means of wells, 

 which may be of any depth up to 

 4,000 or 5,000 ft, drilled by power- 

 ful machinery, and lined with iron 

 or steel tubes, called casing, 

 through which the petroleum is 

 conveyed to the surface. A tower- 

 like structure of wood or steel, 

 called a derrick, from 80 to 130 ft. 

 in height, is built upon the site of 

 the proposed well, and this is used 

 to contain the drilling machinery 

 and as a support in raising and 

 lowering the drilling tools and the 

 lengths of casing. The stratum 

 in which the petroleum occurs U 

 porous, usually sandstone or lime- 

 stone. In the petroleum industry 

 it is known as the oil sand. If the 

 petroleum, called crude oil or 

 simply oil, is in moderate quantity, 

 it is brought to the surface by 

 pumping or baling. If it is met 

 with in abundance, the flow to the 

 surface takes place of its own ac- 

 cord , and sometimes this flow is 

 of sufficient force to eject the oil 

 scores of feet into the air. Such 

 wells are known as gushers or 

 spouters. Occasionally the flow of 

 oil is so violent as to demolish the 

 derrick and flood the area about 

 the well By far the more nu- 

 merous class of oil wells, however, 

 yield by pumping or baling. 



The crude oil has to be treated 

 for the purpose of obtaining from it 



various products. The first opera- 

 tion is to heat it in a large vessel 

 known as a still. When the oil 

 has reached a moderate tempera- 

 ture, vapours are given off, which 

 are led away by pipes and con- 

 densed, the resultant liquid being 

 known as petrol distillate. This 

 is treated by chemicals to improve 

 its colour and remove any ob- 

 jectionable smell, and it is then 

 ready for use in the motor-car, 

 being known in Great Britain as 

 petrol or motor spirit, and in the 

 United States and Canada as 

 gasoline. Meanwhile the applica 

 tion of greater heat to the remain- 

 ing oil sets free another set of 

 vapours, which when condensed 

 and purified becomes paraffin oil 

 With yet higher ranges or tempera- 

 ture lubricating oils are obtained ; 

 and the residue left in the still mav 

 in some cases be used as fuel oil. 

 Some crude oil is not suitable for 

 distilling as above ; in those cas 

 it is heated sufficiently to remove 

 the petrol, the remainder being 

 used as fuel oil in ships, railway 

 engines, or factories. Again, crude 

 oils of one class yield paraffin w*x, 

 and those of another class yield 

 asphalt 



Transportation ol Crude Oil 

 Crude oil, in countries where it 

 is abundant, is transported through 

 pipe lines, some of which are many 

 hundreds of miles in length. The 

 liquid products mentioned above 

 are, as regards overland carriage, 

 conveyed in railway tank wagons 

 or steel barrels. Tank steamships 

 are the principal means of carriage 

 by sea, and most of the oil pro- 

 ducts brought to the United King- 

 dom come this way, ships with > 

 carrying capacity of over 18,000 

 tons having been constructed in 

 recent yean. Oil and its pro- 

 ducts are usually stored in circular 

 steel tanks, which vary in site 

 .from a few hundred gallons up- 

 wards, the largest having a 

 capacity of about 10,00) > 

 Throughout Great Britain there 



