170 



NATURE 



[August 5, 1909 



bonding with it. Sandstone, as a rulf, is loo soft, porous, 

 and absorbent for use in reiiiforced-concreie work. It 

 may be salely, u.sed if it will stand about \\ tons per 

 square incli under a crushing test, and also if the differ- 

 ence in weight when clean and dry,. and after being two 

 days under water, does not exceed 8 per cent. . Quartzite 

 stone is fairly good if not too soft and open in texture, 

 . in which case the same precautions apply as for sand- 

 stone. It should be noted that the test pieces for crush- 

 ing tests should have an area of at least lo inches or 

 12 inches. 



With reference to artificially produced aggregates, 

 broken earthenware and stoneware from the , Potteries 

 district make a good aggregate, but these must be un- 

 glazed, as the glaze prevents the proper adhesion of the 

 cement. Burnt clay and gault inay be used provided thev 

 are tough and hard, and do not soften or crumble after 

 being left in water for two or three days. In general, 

 broken bricks are not a good aggregate for reinforced 

 concrete. They may be employed safely if hard and close 

 in texture and free from mortar. Coke-breeze is cheap 

 and readily obtained, but cannot be regarded as being 

 really fire-proof. The effect of any sulphur present must 

 also be considered, .^shcs and clinkers mav be used. In 

 the case of ashes, only those which will float in water 

 and are of uniform colour and texture, as well as being 

 c|uite free from coal and dirt, should be used. Reallv 

 hard and clean clinker alone is serviceable. In both of 

 these sulphur must be considered. Slag from blast 

 furnaces and cupolas makes a good aggregate if hard, 

 tough, and free from dust ; any sulphur present must be 

 noted. 



Sulphur is apt to attack the reinforcing steel with 

 disastrous results. The maximum allowable percentage nf 

 sulphur in reinforced concrete aggregates is now being 

 made the subject of experiments, and it is hoped an 

 authoritative statement will soon be made. In the form 

 of a sulphate sulphur is practically harmless, but is very 

 deleterious if in the form of a sulphide. 



It is of importance that no free lime be present in 

 artificial aggregates ; carbonate of lime is practicallv harm- 

 less. Washing and exposure to the air and sun 'will do 

 much to convert sulphides into sulphates and free lime into 

 carbonates. Good and accessible aggregates are often con- 

 demned because no discretion is exercised as to the form 

 in which lime and sulpfiur occur. 



A certain amount of sand is absolutciv necessary in 

 concrete, and no other material is at present known which 

 can be .substituted for it. Generally speaking, the better 

 a sand is for moulding purposes the worse it is for re- 

 inforced concrete. Dirt in the form of slime, mud, or 

 vegetable refuse is bad, but a little loam, enough to soil 

 the fingers, but not enough to cause the sand 'to adhere 

 to them, is no detriment. Small particles or nodules of 

 clay do_ not appear to affect the strength of the concrete, 

 but it is better to avoid them if possible. It is not good 

 practice to use the stone aggregate, and its smalls and 

 dust, together with some sand, upon the chance that they 

 will be in proper proportion, and that the voids and spaces 

 will be properly filled. Such a practice should not be 

 allowed in reinforced work, where absolute homogeneitv 

 is so essential. 



With reference to cement, anv user is safe if he insists 

 that his cement shall pass the' British standard specifica- 

 tion in every detail, and purchases from a trustworthy 

 maker. It should not be one of the many mixtures 

 imported into this country as cement, which do not deserve 

 the name, and are costly at anv price. 



Methods of inserting the reinforcement in beams, slabs, 

 columns, &c., together with hints on erecting various 

 structures._ take up the remainder of this valuable paper. 



Prof. Unwin spoke of reinforced concrete construction 

 as demanding excellent execution and supervision to be 

 successful. In regard to formula- of the empirical class, 

 largely employed in this subject, the range of experimentai 

 work should rule the trustworthiness of the formula;. 

 Much of the present methods of design is based on guess- 

 work. He took the opportunity of urging the necessity 

 for more extended experiments. 



In presenting his paper on the advance of marine 

 engineering in the early twentieth century, Mr. .\rthur J. 

 NO. 2075, VOL. 81] 



Maginnis naturally devotes a great deal of his space to 

 the marine steam turbine. While the use of turbines has 

 produced practicallv no advance or improvement in fuel 

 consumption since 1901', still, an advance has to be re- 

 corded in that a greater speed has been attained. During 

 the past eight years experience has shown the trustworthi- 

 ness of ■ the Parsons turbine machinery. Notwithstanding 

 that there are now more than seventy steamers continu- 

 ously plying to and- fro.- no sailing schedules have been 

 upset by a failure of machinery, nor has a- turbine steamer 

 ever had to be towed into port. The author has no 

 hesitation in stating that rotary machinery must eventually 

 replace the present system in cargo steamers as well as 

 in liners. - - 



Combined systems of reciprocating and turbine machinery 

 were referred to, but the author does not think that an 

 extensive adoption of this system will be made. ' In 

 evidence of the saving in weight -in - the boilers - where 

 turbines are installed, owing to the lower steam pressure 

 which mav be used, the author states that in the case of 

 the LH5/ta»ia and Maiirctania the saving in weight on the 

 boilers alone is about 120 tons over and above that which 

 would have been required if triple or quadruple piston 

 engines had been used. 



The author gives a sun-imary of the results attained by 

 marine engineering to date as follows ; — vessels of clo-^e 

 upon 800 feet length and more than 38,000 tons dis- 

 placement are being propelled across the Atlantic at an 

 average speed of 255 knots by turbine machinery work- 

 ing up to about 70,000 horse-power, having a consump- 

 tion of upwards of 1000 tons per day. Similar results 

 have been obtained in the turbine-propelled warship 

 Ituloniitahle^ of more th;in 40,000 horse-power, and main- 

 tained across the .Atlantic with water-tube boilers. 



The electrical operation of textile factories formed the 

 subject of a paper by Mr. Herbert W. Wilson. The prin- 

 cipal advantage claimed lies in the fact that a i-nuch 

 greater steadiness of drive can be obtained, with conse- 

 quent higher average speed and increased output. Slight 

 variations in speed above that corresponding to the maxi- 

 mum safe tension breaks the threads, and unless abso- 

 lutely constant speed can be obtained, it is necessary 

 to allow a margin of safety and to run at a speed 

 materially below the breaking point. In one case in 

 Lancashire, with two mills under the same management 

 iuid of about the same size, and working under the same 

 general conditions, the results obtained from the electrically 

 driven factor}- have been distinctlv superior to those from 

 the mechanically driven one. The improvement in the 

 quality of yarn was so noticeable that the output from the 

 electricallv driven mill fetched a distinctly better price than 

 that from the other factory, the increase being stated at 

 about 24 per cent. .As regards increase in production, 

 mills in this country which have adopted electrical driving 

 may be estimated as showing an improvement of 5 per 

 cent. 



.\ paper on the indicating of gas engines was contributed 

 bv Prof. F. W. Burstall, of Birmingham University. The 

 Standards Committee of the Institution of Civil Engineers 

 expressed the opinion in their igo6 report that the in- 

 dicating of gas engines was open to very much greater 

 errors than was the case with steam engines, and this 

 matter has been considered by the Research Committee of 

 the Institution of Mechanical Engineers. In the tests 

 undertaken by the author, two indicators were used 

 simultaneously, one of the ordinary string type and the 

 other an optical indicator. A Premier gas engine was 

 used having a cylinder 16 inches in diameter by 24 inches 

 stroke, running at 165 revolutions per minute. The only 

 variation in the four tests recorded was the amount of 

 gas admitted, the me.-in pressure varying from 55 kg. per 

 cm.° up to about 7^ kg. per cm.° 



The string indicator emploved was of the Crosby type, 

 selected for these tests by the Crosby Company. Before 

 and .-ifter each set of trials the indicator was tested for 

 backlash and friction, and the spring also calibrated. 

 The backlash was in all cases negligible, and the friction 

 amounted to less than i lb. with a spring having a scale 

 of 400 lb. per square inch. The optic indicator was lent 

 by Prof. Hopkinson, and was calibrated at the University. 



Both indicators were mounted on a branch piece con- 



