I40 



NA TURE 



[December 9, 1897 



metal or of the circulating water to carry off the heat. In many 

 cases condensation was diminished by films of oil or grease, or 

 by accumulations of hair, or by other incrustations or deposits, 

 but these were not considered in the paper. 



The authors found, on the contrary, as the result of their 

 experiments on a steam-engine running under normal conditions, 

 that a practically clean and dry metal surface was not immedi- 

 ately heated to the temperature of the saturated steam in contact 

 with it, that the rate of condensation of steam was not infinite, 

 but finite and measurable, and that the amount of condensation 

 in any given .case was limited chiefly by this finite rate of con- 

 densation, and could be calculated in terms of it. 



The cyclical variations of temperature in the metallic walls of 

 the cylinder, with each stroke of the engine, were measured by 

 means of thermo-couples inserted at various distances from the 

 inner surface. It was possible thus to deduce the amount of 

 heat absorbed and given out by the metal, and to infer the 

 quantity of steam condensed and re-evaporated at different points 

 of the stroke. The temperature-cycles of the steam were simul- 

 taneously measured by a very sensitive platinum thermometer. 

 The observations showed that the temperature of the steam in 

 different parts of the cylinder differed in a systematic way from 

 the saturation temperature as deduced from indicator diagrams. 



In order to deduce the condensation from the observed tem- 

 perature-cycles, it was necessary to determine the conductivity 

 and specific heat of cast iron. A series of experiments were 

 made upon a four-inch bar of cast iron, and the result found for 

 the conductivity was nearly 30 per cent, smaller than that 

 generally assumed. 



At the lowest speed of the experiments, namely, forty-five 

 revolutions per minute, the temperature of the surface of the 

 metal at the end of the admission period was found to be never 

 raised higher than within 20° F. of the temperature of the steam, 

 and the rate of condensation at any moment was simply pro- 

 portional to the difference between the temperature of the steam . 

 and the surface. The numerical value found for the rate of con- 

 densation waso74 B.T. U. per second per square foot of surface 

 per degree Fahrenheit of difference between the temperature of 

 the steam and the surface. This was equivalent to the condensa- 

 tion of 27 pounds of steam per square foot per hour at 300° F. , 

 for a difference of temperature of 10° F. Assuming this law, 

 the total amount of condensation at any point of the stroke 

 cculd be inferred by measuring the "Condensation Areas " on 

 the temperature-cycle diagram, i.e. the areas included between 

 the curves representing the temperatures of the steam and of the 

 metal surface. 



To compare the results thus found with the missing steam 

 deduced from the indicator diagrams and the feed measurements, 

 the leakage of the valve and piston was determined as nearly as 

 possible under the conditions of running. It was found to be pro- 

 portional to the difference of pressure and nearly independent of 

 the speed through a considerable range. The usual test for 

 leakage with the valve stationary was found to be of little or no 

 value. From a comparison of leakage tests, it was inferred 

 that a valve in motion, however well fitted, was subject to 

 leakage of a definite type. The leakage took place chiefly in 

 the form of water, by condensation and re-evaporation on the 

 moving surfaces, and was directly proportional to the perimeter 

 of the ports and inversely to the width of the bearing surfaces. 

 The amount of condensation observed during the admission 

 period in a single-acting non-condensing cylinder 105 inches in 

 diameter with a stroke of 12 inches, was only 20 per cent, of 

 the feed at a speed of 100 revolutions per minute. The small- 

 ness of this result was probably due to the early compression 

 and the dryness of the steam supply. It was found that re- 

 evaporation was completed very quickly, and that the walls 

 were dry for the greater part of the cycle. It was inferred 

 from the form of the temperature curves and from other 

 evidence that the rate of re-evaporation was the same as that of 

 condensation. 



From the form of the law of condensation it was possible to 

 make an important theoretical deduction with regard to cases in 

 which re-evaporation was incomplete, and the walls remained 

 wet throughout the whole cycle. Under these conditions the 

 mean temperature of the walls should be the same as the time 

 average of the temperature of the steam to which they were 

 exposed, and the cyclical condensation was the maximum pos- 

 sible for the given steam cycle. If the extent of the clearance 

 surfaces was known, this limiting value of the condensation in 

 any case might be easily deduced from the indicator diagram. 



NO. 1467, VOL. 57] 



If the surfaces were dry during part of the stroke, the con- 

 densation was less than the limit, and it was necessary to know 

 the mean temperature of the clearance surfaces in addition. 

 Upon these views of the nature of condensation and leakage, 

 the missing quantity of steam W in pounds per hour might be 

 expressed by an equation of the general type, W = S {f — f) 

 -}- L (/ -/"), — where the first term represented condensation 

 and the second term leakage, S being the equivalent clearance 

 surface in square feet, and t' — f the mean difference of 

 temperature, in degrees Fahrenheit, between the walls and the 

 steam during admission reduced to one-half cut-off. L, the 

 rate of leakage per pound difference of pressure p' -p", might 

 be taken to vary approximately as the product of the diameter 

 and the square root of the normal piston-speed, for engines of 

 different sizes. It would appear from this formula that the 

 effect of leakage on the performance was relatively more im- 

 portant in small engines and at high pressures, and that the loss 

 due to condensation was most effectively reduced by increase of 

 piston-speed. 



As an indirect verification of this law of condensation, the 

 temperature of the clearance surface in cases in which water 

 was present in the cylinder was measured, and was found to 

 agree with that of the mean of the steam cycle. The amount 

 of condensation was also correctly calculated in several cases of 

 published tests in which sufficient data were available. The 

 rate of condensation deduced was also directly verified by an 

 entirely different method. The experiments gave approximately 

 the same rate of condensation, and appeared to show that the 

 water-drops condensed on the metallic surface, owing probably 

 to their rapid action, did not appreciably diminish the rate. 

 Assuming it possible to estimate the condensation occurring in 

 any given case by the method indicated, from a knowledge of 

 the indicator diagram and of the temperature and area of the 

 clearance surfaces, it then became possible to determine the 

 amount of leakage under the actual conditions of running. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge. — The Institution of Civil Engineers has resolved 

 to exempt Bachelors of Arts who obtain honours in the 

 Mechanical Sciences Tripos from the examination prescribed for 

 the Associate Membership of the Institution. 



The Managers of the John Lucas Walker Studentship have 

 elected Mr. J. W. W. Stephens, of Caius College, to the 

 studentship in Pathology, and Dr. Hamilton K. Wright, of 

 McGill University, Montreal, to an Exhibition of the value of 

 50/. 



The proposal to authorise the Examiners for the Natural 

 Sciences Tripos Part II. to inspect the laboratory note-books of 

 candidates for honours was carried in the Senate by forty-seven 

 votes to eighteen. 



Dr. H. A. Giles has been elected to the Professorship of 

 Chinese. Dr. W. H. R. Rivers, of St. John's College, has 

 been appointed University Lecturer in Physiological and Ex- 

 perimental Psychology. Mr. W. L. H. Duckworth, Fellow of 

 Jesus College, has been recognised as a Lecturer in Anthro- 

 pology. 



The Walsingham Medals for research in Biology, including 

 Physiology, have been awarded to Mr. V. H. Blackman, of 

 St. John's College, and Mr. W. M. Fletcher, of Trinity College. 

 The electors report that the essays of four other candidates 

 were of a high order of merit. 



The election to the Isaac Newton Studentship in Astronomical 

 Physics will be held in the Lent Term 1898. Candidates must 

 be Bachelors of Arts of less than twenty -five years of age on 

 January i. The student.ship is of the value of 200/. a year for 

 three years. Applications are to be sent to the Vice-Chancellor 

 between January 14 and 24. 



The University delegates to the International Congress of 

 Hygiene at Madrid, next April, are Dr. Kanthack, Dr. D. 

 MacAlister, and Dr. Anningson. 



The death is announced of Dr. Brownless, Chancellor oi 

 Melbourne University. 



Dr. H. H. Hoffert has been promoted to a senior inspec- 

 torship under the Science and Art Department, and Mr. S. J. 

 Cartlidge— at present head-master of the Hanley School of Art 

 — has been appointed to the vacant inspectorship. 



