August 6, 1896] 



NA TURE 



329 



means of transmission to larger power. As a result of a number 

 of experiments he found that the following were the best ratios 

 of diameters for ropes and pulleys : — 



i\ inch diam. rope 3 feet diam. pulley ratio I to 2S'8 



li .. .• 4 -. .. ,. I to 32-0 



li ,. „ 5 .. ,. -. 11034-3 



2 I. ., 6 „ ,, ,, I to 36'0 



In regard to power transmitted, it was found that when working 

 under ordinary conditions the foregoing sizes of rope transmit, 

 for each 100 revolutions per minute made by the pulley, the 

 following : — 



Rope \\ inch diam. on 3 feet pulley would give 5 I.H.P. 

 ,, I* „ 4 ., ,, 8 ,, 



,. Ij „ 5 .. ,, II ,. 



,.2 ,.6 „ „ 15 „ 



These figures may be exceeded under more favourable cir- 

 cumstances. The best angle of the groove on the pulley was 

 foun<l to be 45°, and the best speed of rope 3300 feet per 

 minute. Illustrations and descriptions were given of many very 

 ingenious forms of rope driving, by which power was conveyed 

 from a driver to a single driven pulley under conditions that 

 would have been impossible with belts, or in any case unless 

 conijilicated trains of wheel gearing had been employed. 

 In the discussion which followed the reading of this paper, a 

 good deal of light for the uninitiated was thrown on rope driving 

 practice. The importance of splicing was brought to the fore, 

 and on this depends to a large extent the durability of ropes 

 used for conveying power. A short splice will not do at all, and 

 even the "long splice" ordinarily made by the inariner is 

 insufficient. For 3-inch ropes the splice has to be 12 feet long ; 

 the strands being cut and divided, so as to avoid producing what 

 sailors call a "gouty" length ; that is, one where there is an 

 increased diameter. Three patterns of rope are used ; the three 

 strand, four strand, and the served rope. The former is far the 

 easier to splice, the latter the most difficult. A served rope, 

 however, has the greatest flexibility ; a very prominent virtue 

 in a driving rope, as it leads to longevity, and enables smaller 

 pulleys to be used without ill effect. In regard to material, 

 cotton appears to be the favourite. It is almost universally used 

 in England ; naturally so in the Lancashire district, where 

 rope-driving practice is so largely followed. In Ireland manilla 

 appears to be most often used. There was one speaker, who 

 came from India, and who said that he had used coir rope with 

 great success ; this is made from the fibrous material of the 

 husk of the cocoanut. We should have thought this substance 

 would have been altogether too elastic for the purpose. Another 

 speaker, Mr. McLaren, had used rope-driving for ploughing 

 l>urposes, but had gone far beyond the proportions advised by 

 the author in his table. For instance, he had used a i-inch 

 lope to transmit 40 horse-power, whilst his pulleys were no more 

 than 20 inches in diameter. This rope we understood him to 

 say was a manilla one, but the proportions seem altogether extra- 

 ordinary. We should have thought a wire rope would have been 

 more likely to answer the purpose. The speaker, however, 

 <lrew the moral that too high a factor of safety was demanded 

 by engineers in rope driving. Later on Prof. Goodman 

 stated that he had calculated the average factor of safety in 

 rope driving at about 90 per cent. 



One of the excursions during the meeting was made from 

 lielfast to Lame Harbour, to visit the alumina factory there 

 situated. A description of this factory formed the basis of Mr. 

 Sutherland's paper. Although, as is universally known, alu- 

 minium is one of the most abundant metals found in ihe earth, 

 there are not many of the compounds containing it which render 

 themselves readily to the extraction of the inetal. Bauxite is 

 (lie one generally used for its production, and large deposits of 

 this have been found in County Antrim. The analysis is as 

 follows: — Alumina is 56 percent., corresponding to aluminium 

 29 9 per cent., peroxide of iron 3 per cent., silica 12 per cent., 

 titanic acid 3 per cent., water 26 per cent. The peroxide of 

 iron, silica, and titanic acid have to be separated out before Ihe 

 extraction of the metal from the alumina is attempted ; and it is 

 the function of the Larne works to carry on these operations ; 

 the smelting of the ore being done by electrical meihoils at 

 Foyers. That, however, is an operatif)n which does not come 

 within the scope of the paper now before us, but may form the 

 .subject later on of another contrilmtiun in the transactions of 

 the inst.tulion. 



NO. 1397, VOL. 54] 



It is the Bayer process which is used at Larne. The bauxite, 

 as received from the mines, is first ground and sifted, after 

 which it is taken to a calciner in order to remove the organic 

 matter present, which would prevent the subsequent separation 

 of the alumina from the caustic soda. The calciner is an iron 

 tube lined with fire-brick, and caused to revolve on rollers. It 

 is inclined at a necessary angle, the heat from the furnace pass- 

 ing up through the tube. As the tube inclines, the bauxite 

 travels to the lower end, and falls out into a receptacle. The 

 alumina is extracted from the ground bauxite by treating it 

 with a strong solution of cau.nic soda under pressure. This 

 operation is carried out in Kiers. A soluble compound of 

 alumina and soda (aluminate of soda) is thereby formed, while 

 the peroxide of iron, silica, and titanic acid remain as an 

 insoluble compound. The Kiers are steam-jacketed, and 

 have paddles mechanically actuated to agitate the mixture. 

 The steam pressure in the jacket is carried up to 70 or 80 pounds, 

 and the mixture is subjected to the heat corresponding to the 

 pressure for two or three hours until decomposition is complete. 

 The liquid product of the Kiers is then passed through filter 

 presses, the impurities being insoluble are retained, while the 

 liquid aluminate runs into tanks. The residue, or cakes of im- 

 purities, are afterwards washed to extract as much of the 

 aluminate of soda as possible ; and the washings are used for 

 diluting the product of the Kiers. Centrifugal pumps are em- 

 ployed for this purpose. At present the red mud forming the 

 residue is useless, and there is an opportunity for any chemist 

 to suggest a means by which it could be utilised. Experiinents 

 are being conducted in this direction by the Company. The 

 lyes from the presses contained in the filter tank are afterwards 

 subjected to another filtering process, being passed through cel- 

 lulose, consisting of paper-makers' pulp. About fifty pounds of 

 cellulose is boiled with water to a thin pulp, and is run upon 

 sieves ; it soon settles down, and is then ready to receive the 

 lyes, arresting all finely divided, insoluble particles that have 

 escaped from the filter presses. Finally, there is another filtering 

 process. 



It is now necessary to separate the alumina from the soda. 

 This is brought about by the addition of excess of more hydrate 

 ot alumina to the hydrate of alumina itself, and in this way 

 about 70 per cent, of the alumina in combination with the 

 soda separates out in thirty-six hours. The hydrate of alumina 

 is then pumped out of the decomposing cylinders, in which the 

 latter process has taken place, .sufficient however being allowed 

 to remain behind in the cylinder for beginning the decomposi- 

 tion of the next charge of liquor admitted. The hydrate of 

 alumina pumped out is filtered through filter-presses, and the 

 last traces of soda are removed by washing. The hydrate of 

 alumina is then taken to the calcining furnace, where the water 

 of hydration is driven off at a low temperature, leaving the 

 alumina perfectly anhydrous. It will, however, take up water 

 again readily, and to prevent this it is heated to about 

 2000° F. , when it becomes crystalline, and not so liable to 

 absorb moisture. The weak soda liquors which are obtained 

 are concentrated by a triple-effect evaporator. 



On the afternoon of Wednesday he members and their 

 friends were shown these processes in operation at Larne. 



The last paper read was that by Mr. Stelfox. It was not 

 discussed, the time for the conclusion of the meeting having 

 arrived. 



The Belfast meeting was a complete success, the whole 

 arrangements being carried out most .satisfactorily. A large 

 number of the works of Belfast were visited by members, 

 manufacturers being most liberal in opening their establi.shments 

 to members, and generally showing that hospitality for which 

 Ireland is renowned. The .summer meeting of next year is to 

 be held in Birmingham, the city in which the Institution of 

 Mechanical Engineers had its origin fifty years ago next year. 



OLD WORLD METEOROLOGY} 



T N the year 1508 a book was published in t;ermany under the 

 ^ title of the " Bauern-Pracktik." This book had a wide cir- 

 culation. It taught the farmer, the sailor, the merchant — all, 

 indeed, who were interested in the weather — what would be its 



1 " Die Bauern Praktick. Neudrucke 

 Meteorologie und Erdmagnetismus." I 

 Hellmaim. (Berlin : A. .\sher .ind Co., ) 



Schriften und Karten iiber 

 ■isgegcben von Prof. Dr. G. 



