December 22, 1923] 



NA TURE 



915 



Heat Conduction in Liquids. — In the issue of the 

 Proceedings of the American National Academy of 

 Sciences for October 15, Prof. P. W. Bridgman, of 

 Harvard, gives a summary of the results of his 

 measurements of the heat conductivities of 15 liquids 

 at 30° and 75° C, and at pressures vip to about 12,000 

 atmospheres. The liquids were placed between two 

 concentric metal cylinders, to the inner of which heat 

 was communicated electrically and the difference of 

 temperature of the two measured. For all the liquids 

 tested, with the exception of water, the conductivity 

 decreases as the temperature rises, and increases with 

 rising pressure. For the more compressible liquids 

 the conductivity at a pressure of 12,000 atmospheres 

 is nearly three times that at atmospheric pressure. 

 \i the transfer of energy from molecule to molecule 

 is assumed to take place with the speed v of sound in 

 the liquid, the thermal conductivity should be ^v/d^, 

 where d is the distance apart of the centres of con- 

 secutive molecules. This relation is shown to be 

 satisfied approximately. 



Firing with Pulverised Coal and Blast 

 Furnace Gas. — The firing of coal in a pulverised 

 condition, that is, 90 per cent, through a 100 mesh 

 screen (100 holes to the linear inch) and 65 per cent, 

 through a 200 mesh, is attracting some attention in 

 Great Britain. In the United States about 30,000,000 

 tons of coal per annum is being burnt in the pulver- 

 ised condition, chiefly in the iron and steel, cement, 

 and glass industries. Since 1920 the rapid growth in 

 the application to steam generation has been remark- 

 able, and very soon about 3,000,000 tons per annum 

 will be absorbed in this one operation, although little 

 or no progress has so far been made in Great Britain. 

 One advantage of pulverised coal is that it will work 

 in conjunction with blast furnace gas. In the opera- 

 tions of the blast furnace a large volume of low-grade 

 gas is given off, averaging 90-110 B.Th.U. per cubic 

 foot, with a composition of about 24! per cent, carbon 

 monoxide, 5J per cent, carbon dioxide, 24 per cent, 

 hydrogen, f per cent, methane, and 66^ per cent, 

 nitrogen. As a rule the surplus gas is burnt on very 

 crude lines under steam boilers, and because of the 

 great fluctuations in the supply, generally coal has to 

 be used as an auxiliary fuel. This gives bad results, 

 since it is diflicult to keep pace with the variations 

 in the gas supply. For these conditions, however, 

 pulverised fuel is good, since it is almost as easy as gas 

 to regulate and adjust, and can be started up or shut 

 down in a few minutes. A good example of this 



Erinciple is the huge River Rouge power plant of the 

 brd Motor Co. at Dearborn, Detroit, where 70 per 

 cent, blast furnace gas and 30 per cent, pulverised 

 coal is burnt without difficulty. It has been stated 

 that by neglecting this means of utilising blast furnace 

 HAS, Great Britain is at present wasting more than 

 •DO.ooo h.p. 



The Earth's Electrostatic Field. — In the 

 September issue of Terrestrial Magnetism and Atmo- 

 spheric Electricity, Dr. S. J. Mauchly reviews the 

 evidence now available as to the daily variation of 

 the potential gradient in the air over both land and 

 sea. The land observations were made at nearly 

 20 stations between Cape Thordsen in latitude 78° 

 north and Cape Evans in latitude 77° south, and the 

 ocean observations on board the magnetic observing 

 ship Carnegie in the Pacific, Atlantic, and Indian 

 oceans. Dr. Mauchly finds that as a first approxima- 

 tion the gradient varies daily from 80 or 90 volts per 

 metre at 4 o'clock to no or 120 volts per metre at 

 18 o'clock Greenwich mean time at all land and sea 

 statiniTJ. There appears in be some v.'iri;<t!"»i of t)ie 



,\(». 2825, VOL. I I2J 



magnitude of the daily change and of the time at 

 which the maximum gradient is attained, w'ith the 

 season of the year and with the locality, but these 

 are not sufficient to invalidate the general conclusion. 

 In mid-Pacific and at land stations during June and 

 July, a reduction of the amplitude of the daily change 

 makes it evident that there is also a 12 -hour wave, 

 but the observations are not yet numerous enough 

 to justify conclusions being drawn as to its nature and 

 its generality. 



Synthesis of Benzene. — The classical experiment 

 of Berthelot on the polymerisation of acetylene to 

 benzene, made so far back as 1858, was a fundamental 

 synthesis of benzene, and is still quoted in the text- 

 books. The yield of benzene and allied hydrocarbons, 

 however, was so small that much experimental skill 

 was necessary to prove their presence. The results 

 were not greatly improved by the use of catalysts, 

 the main action in all cases being the decomposition 

 of the acetylene into its elements. In the Comptes 

 rendus of November 5 of the Paris Academy of Sciences, 

 N. D. Zelinsky describes experiments on the poly- 

 merisation of acetylene in the presence of activated 

 wood charcoal at 640° to 650° C. Under the con- 

 ditions described, more than 70 per cent, of the weight 

 of the acetylene passed over the charcoal was con- 

 verted into liquid products. From this liquid 

 absolutely pure synthetic benzene (303 gm.) was 

 obtained, and other substances isolated from the 

 condensate included toluene, p-xylene, styrol, indene, 

 naphthaline, fluorene, and anthracene. 



Scott-Still Marine Engines. — A great deal of 

 experimental work on the Still engine has now been 

 done by Messrs. Scotts' Shipbuilding and Engineering 

 Company of Greenock, and their experience has 

 enabled the firm to consider the appUcation to 

 actual vessels. The m.s. Doiius is now fast approach- 

 ing completion, and is the first in which a large-scale 

 installation of Scott-Still engines has been fitted. 

 In this system the cylinder on one side of the piston 

 is used as an oil engine (two-stroke Diesel cycle) 

 and on the other side as a steam engine. The water 

 in the jackets is kept at working steam pressure, 

 and any heat passing through the cylinder walls is 

 used to generate steam. Heat is also recovered from 

 the exhaust gases by means of a regenerator, and also 

 by a feed heater. The m.s. Doiius is 400 ft. long and 

 has a displacement of 1 1,650 tons. The total power of 

 2500 b.h.p. is divided between two main engines 

 of four cylinders, each 22 in. diameter and 36 in. 

 stroke, and running at 115 to 120 revs, per min., 

 giving a ship speed of about 1 1 knots when fully loaded 

 under service conditions. Steam is generated at 

 about 140 lb. per sq. in., and is first employed at the 

 back of the piston in one cylinder acting as a high- 

 pressure piston, and then is taken to the other three 

 cylinders, which together act as the low-pressure 

 cylinder. Official trials of the engines have been 

 made by the Marine Oil Engine Trials Committee 

 appointed by the Institutions of Mechanical Engineers 

 and Naval Architects. Their report has not yet 

 been i.ssued, but the following summary is available : 

 Average mean effective pressure, oil engine, 77-8 lb. 

 per sq. in. ; average m.e.p. steam cycle referred to 

 oil engine volume, 6-6 lb. per sq. in. ; total average 

 m.e.p., 84-4 lb. per sq. in. ; revs, per min., 122 ; 

 total indicated horse-power, 1425 ; brake horse-power, 

 1 251 ; mechanical efficiency, 87 8 per cent. ; oil 

 consumption per b.h.p. per hour, 0-336 lb. ; steam 

 evaporated per hour, 2400 lb. An account of the 

 engine, with photographs and drawings, appears in 

 Engineering for November 23. 



