TRANSACTIONS OF SECTION G. 877 



bearings not only diminish the first cost of construction, but lessen the cost of 

 personal attention, and show a great saving in working cost.' 



Many experiments by the author led to the introduction of a material known 

 as carboid, composed of finely powdered carbon mixed with steatite, the mixture 

 having the advantages of plumbago as regards lubricating properties, but showing- 

 little sigDS of wear after tests extending to two years' constant use. 



Professor Sellers finds that the coefficient of friction Avith the dry bearings he 

 experimented on was lower than with metal bearings as usually operated, and 

 points out the advantage they possess of having a constant frictional resistance 

 whether the bearing is run warm or cold, so that the friction can be provided for 

 in the power. Professor Unwin's experiments with carboid show that the co- 

 efficient is independent of the area of contact, and only increases if the temperature 

 becomes excessive, but not with increased pressure, and tends to diminish with 

 increased speed. 



General Deductions. — First cost of a dry bearing used for shafting or ordinary 

 machinery is less than with the usual brass or patent metal bearing, and, besides, 

 the economy shown by the absence of lubricants, there is saving in the wa^es- 

 required for oiling and cleaning ; and in trades where unskilled labour is employed 

 the risk of oiling machinery in motion is entirely obviated ; also in mills the drip 

 from oil-cups, besides damaging goods, renders the floors highly inflammable. 



Applications of Carboid. — Up to the present time these have been principally 

 for shafting and the bushing of loose pulleys; also for steam-heated rolls such 

 as are used in cloth factories and paper mills. It has been shown experimentally 

 that it can be adapted for use in axle-boxes of tramway cars and for ligbt rollino- 

 stock generally, the existing brass being either replaced or a carboid liner 

 cemented in. 



8. Notes on the Design of Steam Generators especially wlapted for High 

 Pressures.^ By B. II. Thvvaite, G.E., F.G.S., of Liverpool. 



The increasing and laudable desire of engineers to obtain a higher efficiency 

 from their thermo-dynamic motors and steam-generating equipment has directed 

 attention more particularly to the defects and large margin for improvement in the 

 steam generators of the Cornish, Lancashire, and Marine types. 



These types the author, in bis analysis, unavoidably condemns, and shows that 

 in their design eflects of a thermo-chemical and thermo-physical nature, of high 

 importance, are ignored. These effects, he explains, are responsible for the reduc- 

 tion of the strength integrity of the joints, and consequent safety of the steam 

 boiler, and cause structural defects and weakness, requiring constant attention. 



The irregular method of heat application in these internal flue-boilers, specified,. 

 is criticised, and the result of careful tests in this connection are recorded. 



The author formulates a series of axioms that he considers should be respected 

 by the designers of steam-generators, but especially those requiring to withstand 

 very high-working pressures. 



The author submits designs of high-pressure safety steam-generators, in which 

 the formulated canons of design of a perfect steam-generator are applied as far as 

 practicable. 



The designs submitted are boilers constructed by Messrs. Clark, Chapman & 

 Co., Gateshead, and are of the class known as the tubular type, designed so as to- 

 permit the highest pressures to be obtained with safety and with comparatively 

 light metallic proportion of constructional parts. 



Smokeless combustion arrangements are described, and methods by which 

 perfect erosive or scale removal circulation is established, and also arrangements 

 by which a certain flexibility of heating surface is obtained, so as to permit of free- 

 dilatation or expansion of the transmitting elements of the steam generator. 



' The paper is published in Industries, vol. i. 1892. 



