TABLE II.

10

mp.
lp.
total

Total feed-water per I.H.P.)

195.3

323.6

255.8

774.7

78.4

118.7

85.0

282.1

Discussion.

Sir JOHN COODE, President, said that having regard to the Sir John Coode, exhaustive manner in which the Author had treated the subject, and more especially to the way in which he had dwelt upon and elucidated the principles involved, the Paper could not fail to be of great service to all who were concerned in the design or in the use of steam-boilers.

croft.

Mr. JOHN I. THORNYCROFT said there was only one remark he desired Mr. Thornyto make before the discussion commenced. He had been asked by several persons how tubes were fastened into the tube-plate. The mode adopted was simply that of using Dudgeon's mandril in the ordinary way; and in boilers in which the tubes were not sufficiently large for a man to get in, the mandril was worked by bevel-gearing.

Professor ALEXANDER B. W. KENNEDY observed that at the end Professor of the Paper there was an Appendix containing a statement giving Kennedy. the results of some experiments which he had made for the Author; and as, for obvious reasons, this statement had not been read, it might be convenient if he gave a few particulars of the results of some of the experiments described in it. Of course, so very novel a boiler might be regarded from various points of view. Its merits might be discussed from the point of view of cost and lightness, or from the cost of maintenance and ease of repairs; but the only matters on which he had occasion to examine it were with reference to its economy, that was its efficiency as a water evaporator. He had to do that under the most varying conditions, because a boiler of a torpedo-boat might have to exert powers that varied more widely than the powers of any corresponding land boiler, or indeed any other marine boiler. The trials he had to make were in fact a graduated series of trials at different air-pressures in the stoke-hold; a trial with natural draught, a trial with about inch air-pressure, a trial with inch, and a trial with about 2 inches air-pressure. He did his best to get all the measurements as complete as possible, and he believed that the figures obtained were as accurate as such figures could be, the errors being only such as would occur with the most careful measurements. He would not say anything about the methods of measurement, but would mention the results of two of the trials, the first with natural draught, and the second with 2 inches of air-pressure in the stoke-hold. In the first case, the boiler was

Professor very much underworked, so to speak, and in the latter case Kennedy. it was very much overworked. In the first case it was evaporating

about 1 ton of water per hour, and burning something under 8 lbs. of coal per square foot of grate; and in the second case it was evaporating 7 tons of water per hour, and burning nearly 70 lbs. of coal per square foot of grate; so that there was about nine times the rate of combustion in the second case that there was in the first. In reference to a remark made in the Paper, he might say that the stoke-hold was about 10° cooler in the latter trial than in the former trial. The volume of air blown into it, even with the pressure of 2 inches of water, was sufficient to keep down the temperature to 60° or 61°, while formerly it was 70°, 71°, or 72°; and the actual pressure was not so great but that it was possible to get in and out the stoke-hold by opening the doors, without the least trouble or without any interference with the regularity of work. The trial with a natural draught and with a very slow rate of combustion, namely, 7 lbs. of coal per square foot of grate, resulted in a figure which he did not hesitate to give, because he had no doubt it was right; but which he thought, at least as far as his experience went, was what was technically known as a "record," for he did not think any other trials had been made of any considerable length in which as much as, or at any rate inore than, 13.4 lbs. of water had been evaporated by 1 lb. even of the very best coal. The coal used was of very high quality, so that that particular evaporation amounted to 86.8 per cent. of the whole heat of combustion. The coal was Nixon's Navigation. coal, giving about 2 per cent. of ash. Plate 3, Fig. 5, showed clearly the results of the trials, this particular trial being represented by the left-hand vertical ordinates. The meaning of the area under each curve in the diagram was marked on it. The largest and lowest area showed the quantity of heat taken up by the feed-water; the area above showed the quantity of heat taken up in raising the temperature of the furnace gases; the area above that showed the heat lost by the formation of carbonic oxide, or by incomplete combustion; while finally the area at the top showed the total quantity that could not be accounted for. He supposed that when an evaporation of 13.4 lbs. of water per lb. of coal was suggested, the question whether there was any priming would naturally be asked. He knew of no method of measuring priming water with accuracy at sea, and he did not make any attempt to measure it. But as the boiler would without difficulty evaporate seven or eight times the amount of water which it was raising on that particular trial, he thought there was no