April 2, 1896] 



NATURE 



521 



is only able to state the quantity of sulphur present ; but whether 

 in a dangerous or non-dangerous form, he is unable to say. Mr. 

 Seaton concludes, therefore, that chemical analysis alone is 

 sufficient neither for steel nor for any other combined metal used 

 by the engineer ; while, on the other hand, the microscope 

 reveals the actual structure of the material, and shows most 

 distinctly whether it is a safe or an unsafe one. It appears, there- 

 fore, that the use of the microscope is likely to be of the utmost 

 advantage to the marine engineer. We have not space to give 

 the details by which Mr. Seaton supports his contention. The 

 subject, however, is one well worthy of attention on the part of 

 engineers, and scientific experts who work for them. 



Mr. Stromeyer's paper was also one of interest. He proposes 

 to measure the quantity of water either fed into a boiler, or 

 jiassing through the condenser, by chemical means. A measured 

 quantity of salt water is slowly injected, say into the condenser 

 of an engine while at work ; subsequently a chemical analysis for 

 salt is carried out, both on a sample of sea-water and on a 

 sample of the water to be measured. Their relative salinities 

 would then give the quantity of water pumped, or the amount 

 of steam condensed for any given period. The method is one 

 which will probably be useful for estimating the quantity of 

 circulating water used by the marine engineer, as it is capable of 

 l)eing applied to large quantities of flowing water with com- 

 }5arative facility. For the smaller volumes of water used for 

 feed, which can be passed through pipes of moderate dimensions, 

 the water-metre would, we think, be preferred by the majority of 

 engineers; although, perhaps, the measuring-tank would com- 

 mand the greater confidence than either. 



Mr. Kinghorn's paper, on salvage appliances, was of con- 

 siderable practical interest. It referred to a new system of 

 wreck-raising which has been evolved by certain salvage agents 

 and marine engineers of Liverpool. This country is lamentably 

 deficient in wreck-raising facilities, a fact which has been proved 

 by the resource that has been had to foreign "wrecking" 

 companies, when vessels of exceptionally large size have had to 

 be raised. The case of the battleship Howe, at Ferrol, which 

 was lifted by a Scandinavian company, and of the Atlantic 

 liner Eider, wrecked on our own coast, and lifted by the same 

 company, are instances in point. 



The only evening sitting of the meeting, which was held on 

 Thursday, the 26th ult. , was devoted to the great water-tube 

 boiler question, which is now agitating the marine engineering 

 world. Of the three papers set down for reading, that of 

 Prof. Watkinson was by far the most important. Colonel 

 Soliani proposed a combination of fire-tube and water-tube 

 boiler, which did not meet with universal approval during the 

 discussion, Mr. Watt described certain experiments that he 

 had made many years ago, and which could hardly be described 

 as crucial. Prof. Watkinson attacked the great problem of 

 circulation, the vital question certainly in water-tube boilers, 

 and also to a far greater extent than has been supposed, in 

 boilers of the shell, or fire-tube class The circulation of 

 water and steam in a water-tube boiler involves some very 

 nice questions in physics. Its study affords a good 

 opportunity for those highly skilled in physical science to 

 assist the engineer in arriving at definite conclusions as to 

 what causes govern the flow of water and steam in pipes sub- 

 jected to heat. There were three types of boiler chiefly dealt 

 with by Prof. Watkinson. The Belleville boiler, a French in- 

 vention, which has now been in use for a number of years. It 

 consists of a series of pipes of comparatively large diameter, say 

 four inches to five inches ; these are arranged in a continuous 

 zigzag form, and subjected to the heat of the furnace ; the water 

 flows upward through this serpentine course, steam being gene- 

 rated in its course, and that water which is not converted into 

 steam flows down external pipes, and then again passes into 

 the bottom of the steam generating pipes. In this way a con- 

 tinuous circulation is kept up. The distance the water has to 

 travel through, from one end of the serpentine to the other, is 

 considerable. The various lengths of pipe are not much in- 

 clined from the horizontal, and the sudden bends at the ends 

 of each pipe tend to check the flow. It is believed that for 

 this reason the Belleville boiler will not stand forcing — that is 

 to say, only moderate quantities of coal can be burned to each 

 unit of grate surface. For if rapid evaporation be attempted, 

 the tubes are apt to be denuded of water. Judging by the 

 recent trials of H.M.S. Sharpshooter, there would appear to be 

 some truth in this contention. How far it applies, however, 

 is a matter which experiment alone can reveal, and the results 



NO. 1379, VOL. 53] 



of such experiments, even if made, are not yet available so far 

 as we are aware. 



The other two kinds of boiler dealt with were of what is 

 known as the " express" type— that is to say, they are boilers 

 which will bear forcing, so that large quantities of fuel can be 

 burned in a given time, and the rate of evaporation thus made 

 very high. These arc the well-known Thornycroft and Yarrow 

 types of boiler, which have been so successfully applied to the 

 torpedo-boat destroyers, which have given such remarkable re- 

 .suUs of late, in the matter of quick steaming. Although both 

 the Yarrow and Thornycroft boiler have small tubes, say about 

 one inch in diameter, which are comparatively short in length, 

 each tube connecting directly with the top and bottom vessel, 

 yet the two types have fundamental points of difference. The 

 Thornycroft boiler has outside down-comers and bent tubes which 

 discharge into the top drum above water. The Yarrow boiler has 

 straight "drowned" tubes. These expressions require some 

 further explanation. Each boiler consists essentially of a top 

 drum or steam vessel, and two bottom drums or wing cylinders. 

 Looked at in sectional elevation, these three drums form the 

 points of a triangle standing on its base. The sides of the 

 triangle are composed of the steam-generating tubes ; the base 

 is composed of the fire-grate. The products of combustion ascend 

 from the grate amongst the tubes, and pass off" to the furnace. 

 In the Thornycroft boiler the outline formed by the three cylin- 

 drical ves.sels, and the connecting steam-generating tubes, is not 

 strictly triangular, as the tubes are bent, as already stated. This 

 bending enables them to be inserted into the top drum above 

 the water-level carried into the latter. In the \'arrow boiler, 

 the straight tubes pass in a direct line from the bottom vessels 

 to the top drum, and therefore enter the bottom part of the 

 latter, and, consequently, are below the water-level. 



We will first trace the course of circulation of water in the 

 Yarrow boiler. As there are several rows of tubes on each side 

 of the furnace, those on the inside are naturally subjected to the 

 greater heat. In them, as steam is first generated, the bubbles 

 of steam rise, and water flows with them. To make up the 

 deficiency thus caused in the content of the tube, water flows 

 down the back tubes furthest from the fire, into the bottom 

 vessel, which is common to all tubes on that side of the furnace, 

 and then ascends those tubes where steam has been generated. 

 In this way a continuous circulation is kept up. In the Thorny- 

 croft boiler this cycle cannot exist, as the tubes deliver above 

 water, therefore special down-comer tubes have to be fitted ; 

 these enter the top drum below the water-level. Circulation 

 takes place as follows. When the hot gases ascend among the 

 bent steam-generating tubes, steam is generated. The tubes 

 being small, it forces upward a certain quantity of water, which 

 then falls into the top drum, and flowing down the downcomers, 

 is able to rise again in the generating tubes to make up the 

 deficiency. Circulation is, of course, due to the difference in 

 specific gravity of the upward and downward columns of water 

 in the generating tubes, and the down-comers, respectively. For 

 some time past controversy has ranged between two schools — 

 one favouring drowned tubes and anti-down-comers, the other 

 undrowned tubes and down-comers, each maintaining that 

 boilers constructed according to their views have most efficient 

 circulation. Prof. Watkinson's paper dealt with this question, 

 but no final opinion was expressed as to the respective values of 

 the two types of boiler. The Professor had brought from 

 Glasgow the glass model boilers with which he had made a 

 number of experiments. Unfortunately, when he attempted to 

 repeat these at the meeting, the breakage of tubes prevented him 

 from carrying out his full programme. This is much to be 

 regretted, as the experiments are of a very interesting nature. 

 It is to be hoped that at no distant date Prof. Watkinson will 

 have an opportunity of repeating them. 



The last day of the meeting was devoted to two papers on. 

 pitching and rolling of ships. Mr. Froude's paper was practi- 

 cally a reply to one recently contributed by M. Emile Bertin, 

 the eminent French naval architect, at the last meeting of the 

 Institution ; which in turn was a continuation of a paper by the 

 said author read at a previous meeting. Without referring at 

 length to these two papers it would be useless to attempt to give 

 the -substance of Mr. Froude's contribution, even if we had space 

 to do so. It may be said, however, that Mr. Froude does not 

 agree generally with M. Bertin. What the points of dis- 

 agreement are, it would be impossible to explain without the aid 

 of many diagrams, upon which the author relied for making his. 

 explanation clear. We must therefore refer our readers to the 



