292 



NATURE 



[June 7, 1917 



chalcid which, instead of adopting a parasitic mode 

 of larval life, lays eggs in apple-seeds, within which 

 the grubs feed. N. E. Mclndoo discusses in No. 3 of 

 the same volume the effects of nicotine as an insecti- 

 cide. He finds that the spray solutions neither pass 

 into the air-tubes nor penetrate the cuticle and skin, 

 but the fumes traverse the air-tubes and are dis- 

 tributed to the tissues, killing insects by paralysis, due 

 to structural changes in the nerve-cells. 



At a meeting of the American Institute of Electrical 

 Engineers in November last Prof. J. B. Whitehead, 

 of Johns Hopldns University, gave an account of a 

 new form of voltmeter he has developed for measur- 

 ing potential differences up to 150 kilovolts. The com- 

 plete paper appears in che April Journal of the Frank- 

 lin Institute. The instrument depends on the con- 

 stancy of the electric field at which the ^orona dis- 

 charge is formed between a wire and a cylinder along 

 the axis of which the wire is placed. In that reading 

 to 100 kilovolts the wire is of nickel-plated tool steel 

 0-6 cm. diameter and about 150 cm. long. It is sur- 

 rounded by a perforated cylindrical electrode 30 cm. 

 diameter and 90 cm. long. Both wire and cylinder 

 are enclosed in a cylindrical vessel in which the pres- 

 sure of the air can be varied from 40 to 140 cm. of 

 mercury. The potential at which the corona forms 

 at the surface of the wire appears to be inde{>endent 

 of the frequency when alternating currents are used, 

 and to be uninfluenced by the presence of moisture 

 in the air. It is a function of the radii of the wire 

 and outer electrode, and of the pressure and tem- 

 perature of the air. The formation of the corona is 

 detected either by an electroscope or a galvanometer 

 connected to the outer electrode, or by a telephone 

 with its transmitter inside and its receiver outside 

 the containing vessel. 



The estimation of toluene in crude petroleum was 

 the subject of a paper read before the Institution of 

 Petroleum Technologists on May 15 by Mr. S. E. 

 Bowrey. It is pointed out that, whilst the process 

 of cracking increases the percentage of aromatics in 

 the oil, there is a serious loss of oil by carbonisation. 

 The experiments were therefore limited to the crude 

 oil. After carefully examining the method of frac- 

 tionation and. of extraction by sulphonation and nitra- 

 tion, all of which possess serious disadvantages, Mr. 

 Bowrey eventually adopted the method of extraction by 

 liquid sulphur dioxide at low temperatures as afford- 

 ing the most satisfactory results. The process is car- 

 ried out in the following manner :— The crude oil is 

 first distilled and the distillate collected up to 150°. 

 The latter is then freed from unsaturated hydro- 

 carbons by shaking with 90 per cent, sulphuric acid, 

 and afterwards with alkali and water. The purified 

 spirit is then extracted with successive quantities of 

 liquid sulphur dioxide at —35°, and the combined 

 extract carefully fractionated with a special form of 

 fractionating apparatus. In this way a series of frac- 

 tions is obtained from which the percentage of 

 benzene, toluene, and xylene can be estimated, and 

 the quantities are further controlled by a specific 

 gravity determination. Each of the steps described 

 has been carefully tested by the use of artificially pre- 

 pared mixtures of light petroleum and the three 

 aromatic hydrocarbons, and the results, considering 

 the difficulties of the problem, appear to be very satis- 

 factory. 



A SHORT paper by Prof. K. C. Browning, of 

 Colombo, on "The Detection of Traces of Mercury 

 Salts for Toxologlcal Purposes" (Journ. Chem. Soc, 

 vol. cxi., p. 236) describes a process whereby the detec- 

 tion of this element can be carried to a point com- 



NO. 2484, VOL. 99] 



parable with that reached in the case of arsenic. The 

 method consists in depositing the mercury on a 

 cathode of gold foil, and then vaporising it in a 

 vacuum tube, where its presence is detected spectro- 

 scopically. Under these conditions one part of mer- 

 curic chloride in 1000 million parts of solution can be 

 detected. Attempts to concentrate liquids containing 

 minute traces of mercury are usually futile, on account 

 of the volatility of the metal and its compounds ; in 

 such cases it is better to use .1 large volume of well- 

 stirred liquid and rely exclusively upon electrolysis for 

 concentration. 



In the issue of the Engineer for May 18 there is an 

 interesting account of the veny important hydro- 

 electric power supply undertaking for Bombay known 

 as the Tata power scheme, by which energy is sup- 

 plied to Bombay over a distance of some forty-three 

 miles. The source of the power is three artificial 

 lakes, or reservoirs, in the Western Ghauts, known 

 respectively as Lake Lonawla (986 acres), Lake Wal- 

 whan (1535 acres), and Lake Shirawta (3174 acres). 

 They stand in order of elevation, commencing with 

 the lowest, which exceeds 2000 ft. above sea-level, 

 and they are capable jointly of storing sixty thousand 

 million gallons of water. The district in wliich the 

 "lakes" are situated is remarkable for its heavy 

 rainfall. During monsoons the precipitation is extra- 

 ordinary, as much as 546 in. (45I ft.) having fallen in 

 the catchment area during a single monsoon, of which 

 quantity 440 in. (36I ft.) fell within thirty-one conse- 

 cutive days. The "lakes" have been formed by the 

 construction of dams, which, though not of remark- 

 able height, are certainly of unusual length. The 

 shortest is 1900 ft. long, and the longest no fexj^er 

 than 8000 ft. — just above i| miles. All the dams are 

 built of masonry, with coursed faces and rubble heart- 

 ing. The Shirawta and Walwhan Lakes are con- 

 nected by a tunnel in hard trap-rock, 5000 ft, in length. 

 The waterways are designed for a water capacity of 

 120,000 h.p., with a maximum velocity of about 5 ft. 

 per second. Sufficient capacity is provided in the fore- 

 bay to keep eight turbines, each of 11,000 b.h.p., 

 working at full load for i\ hours. The length of pipe 

 line from the forebay to the power-house is 13,000 ft., 

 and the difference in level Is 1725 ft. The plant was 

 formally put into service in April, 1915. 



Engineering for May 18 contains an illustrated 

 account of a new 15,000-kw. three-phase turbo-alter- 

 nator recently erected at the Chelsea power station 

 of the Metropolitan District Railway. It is of interest 

 to note that only ten years ago builders were con- 

 sidered greatly daring In constructing turbo-generators 

 of 5000-kw. • capacitv at idoo revolutions per minute. 

 Improvements in generator details have been respon- 

 sible for this notable advance. In view of possible 

 changes In the boiler plant at Chelsea, the new 

 machine was specified to be capable of working with 

 steam at 200 lb. per sq. in, (gauge) and 600° F., but 

 to run its trials at 185 lb, per sq, in. (gauge) and 

 500° F., giving a superheat of 125° F. only. These 

 test conditions give a steam cohsumption of about 

 7 per cent, more than if the tests had been carried 

 out at the higher pressure and temperature. The re- 

 sults under these test conditions, with a vacuum of 

 075 in. absolute back pressure, ar6 as follows : — 



Percentage of econom- 

 ical output 50 75 90 100 126 



Steam consumption, In 

 lb. per kw.-hour ... 129 12-2 11-95 ^^'^ ^2-3 



The makers are Messrs: C. A. Parsons and Co., Ltd.. 

 oi Newcastle; Messrs. Merz and McLellan have acted | 

 as consulting engineers, and have conducted the tests. 



