longitudinally to same form as II, ends closed, no angle-irons underneath at middle.

IV. Mild steel, weight 114 lbs., similar to III in all respects, but with two parallel angle-irons across underneath middle, 16 inches apart.

V. Mild steel, weight 95 lbs., length 8 feet 6 inches, width Sinches, Vautherin cross-section, but with raised inclined (1 in 20) rail-bed, 9 inches long, stamped while hot (system Hoesch-Lichthammer).

VI. Mild steel, weight 110 lbs. to 120 lbs., length 8 feet 4 inches to 8 feet 8 inches, variable cross-section on the well-known Post system.1

All the three systems of fastenings referred to in column 9 consist of bolt, clip to hold the rail-foot, and washer.

A. Eccentric bolt with Grover's washer above clip.

B. Ibbotson bolt, large clip with eccentric square washer between it and sleeper (system Roth and Schüler).

C. Eccentric bolt with Verona washer (roughened on both faces) above clip. Price, about 10d. per sleeper.

The ballast in all the twenty-one cases is either cinders, sand, or gravel. The rails are steel, 76 lbs. per yard. The heaviest engine running over the trial-lengths weighs 50 tons, with 13 tons on one pair of wheels. The maximum weight of a train is about 1,000 tons. The maximum speed is about 48 miles per hour. Average day's wage of a plate-layer may be taken at 18. 10d.

In length No. 1 heavy repairs were required in 1886, and continued in 1887. Lengths Nos. 3, 5, and 9 are on marshy ground. W. B. W.

On the Rusting of Permanent-Way in Tunnels. By W. THÖRNER. (Stahl und Eisen, vol. lx., 1889, p. 821.)

The Author was engaged in the years 1887-8 in the technical chemical laboratory at Osnabrück, in an investigation into the causes of the rusting of the permanent-way in the tunnels of the Weilburg and Nassau Railway. The results which have been practically published in official reports now appear in full for the

first time.

The tunnels in the section of line investigated are seven in number as follows:

1. Weilburg Tunnel, 302 metres long, 180 metres straight at north end, 122 metres on 450 metres radius at south end. About half in coarse-grained dolerite, and the remainder in Devonian limestone and shales.

2. Kirschhofen Tunnel, 494 metres, 356 metres at north end on 360

1 Minutes of Proceedings Inst. C. E., vol. xei., p. 492.

5. Rust between rail and) sleeper

2.3 87.22.2

1.2 89.41.8

6. Rust last longitudinal 12.9 sleeper, west side

7. Rusty dust outside of railhead; dry place.

5.32.9 19.616.5 0.6

2.6 78.82.8 0.8 0.222.0

8. Between rail-foot and 21.0 56.34.7 1.2 0.7 1.2

sleeper; dry place

9. Rust under side of lon

11. Rust from longitudinal 7.0 76.34.9 0.6 0.7 1.0

Cramberg

sleeper; near a spring)

12. Rust No. 15 sleeper,

second line

Obernhof

13. Rust, web and foot of 0.7 84.56.6 0.6 0.5 1.8 0.6 L

rail in wet place.

14. Longitudinal sleeper;

wet place.

Hollrich

15. Rust and dust from)

1.7 84.60.8 0.4 0.2 1.1

longitudinal sleeper; 19.7 57:42.2

very dry place

Lengerich

16. Rust from web of rail.

17.

Cochem

foot

0.8 84.33.9

1.6 86.61.89

2.5 1.6 3.1

::

18. Rust between rail and 0.7 88.92.2 ..

1.2

0.2 2.7

0.1 4.2

::

T = traces, L = little, M = much V M = very much.

metres radius, 138 metres straight. Ground generally similar to No. 1.

3. Graeveneck Tunnel, 127 metres long, straight entirely in sound greenstone with columnar structure at either end, above which the village of Graeveneck is built. This, although one of the shortest tunnels, shows the strongest rusting. The rock contains no carbonate of lime.

4. Michelsberg Tunnel, 345 metres, 30 metres straight at north end, 304 metres on 340 metres curved in the middle, 11 metres straight at south end.

5. Cramberg Tunnel, 732 metres, 163 metres on 360 metres radius at west end, 357 metres straight in the middle, 232 metres on 360 metres radius at south-west end.

6. Obernhof Tunnel, 450 metres straight.

7. Hollrich Tunnel, 318 metres on 360 metres curve.

In addition to the above, samples of rust were taken from the following localities:--

8. Lengerich Tunnel. Wanne and Bremen railway 765 metres long, entirely in cretaceous marls containing 80 per cent. of carbonate of lime. The rusting is very slight.

9. Cochem Tunnel. Berlin and Metz railway 4,200 metres long, in Devonian schists poor in lime.

10. Underground Railway, London. (Locality not stated.)

Samples of rust, both from rails and sleepers, as well as of the drainage water, mud, and calcareous deposits in the tunnels, were taken from all of these localities and carefully analysed. The results, so far as the rails and sleepers are concerned, are contained in the following Tables.

In some instances the upper dusty layer of the rust analysed above was scraped off and specially examined. The numbers correspond with those in the preceding Table.

21. Underground, London 34 0 39.14.1 2.2 0.3 7.9

On comparing these results it appears that the composition of rust in tunnels, apart from Nos. 2 and 6, which, being the result of calcareous infiltrations, may be regarded as ferruginous stalagmite, is [THE INST. C.E. VOL. XCIX.]

2 H

substantially similar from all localities. The essential constituent is ferric oxide, partly present as hydrate, with variable, but always small quantities of silica, alumina, lime, and magnesia; carbonic acid, when present, being in connection with the two latter bases. The only abnormal constituent is sulphuric acid, or, more correctly, an oxidized sulphur compound, which occurs in all proportions from 0.3 to 7.9 per cent., the actual state of combination being doubtful. Most probably it is in the form of basic ferric sulphate. Nearly all the samples show a slightly acid reaction, but only give a very small amount of sulphuric acid when exhausted with water. No rust contains iron as sulphide.

The origin of the sulphuric acid may be most readily ascribed to the oxidation of sulphurous acid derived from sulphur in coal and dissolved in the condensed steam from locomotives. This, trickling down the walls, is absorbed by the ballast and slowly oxidized by atmospheric air, producing sulphuric acid, which, penetrating to the rails by capillarity, attacks them, forming ferrous and ferric sulphates.

This, however, does not account entirely for the result, as samples of rust taken from rails in sections of the line open to the air, as well as from many different samples of ironwork from town buildings, and also newly formed rust obtained by exposure of clean iron wire to air and rain in a garden at Osnabrück, contained sulphuric acid in quantities (0·8 to 5.5 per cent.),1 quite comparable to those observed in the tunnels, and in these cases the sulphurous acid in the exhaust steam of the locomotives could not contribute, except in a very indirect manner. A further series of experiments showed that nitrous acid and nitrites are formed by the direct action of iron upon air and water, and these substances are well known to act most energetically in the conversion of sulphurous into sulphuric acid. A more potent cause has, however, been discovered by the Author in the existence of free sulphuric acid in the exhaust steam of a locomotive which was determined experimentally on a heavy goods engine travelling at the speed of 30 miles per hour. The absorption apparatus consisted of a large Woolf bottle, half filled with water for taking up sulphuric acid and ammonia, a second tube with a solution of sulphate of cadmium, for detecting sulphuretted hydrogen, and a third with a solution of iodine in iodide of potassium for collecting and oxidizing sulphurous acid.

The apparatus was placed in front of the smoke-box of the engine, and connected on one side with the funnel by a tin tube, and on the other with a steam-jet aspirator, allowing a continuous current of the gases and steam to pass through. Towards the end of the trial the steam-jet connection was closed so as to leave the absorption vessels full of gas, which was afterwards collected and analysed. The results of two trials, each of one hour's duration, gave:

1 Details of these and numerous other analyses are given in the original, p. 825. -H. B.

The water in the Woolf bottle contained free sulphuric acid, ammonia, and ferric oxide, but no nitrous oxide. No sulphuretted hydrogen was detected, but the third tube, as might be imagined, contained a considerable amount of sulphuric acid due to the oxidation of the sulphurous acid which was emitted in large quantity.

The amount of sulphuric acid evolved per hour by the engine was estimated by the Author, after deducting that required to saturate the small proportion of ammonia present, at 2,228 grammes, or very nearly 5 lbs., a quantity which under appropriate conditions is likely to act very destructively upon ironwork. The action is likely to be strongest in tunnels where the rock is not very wet, and the exhaust steam is without means of rapid escape, and especially in those where the rock is poor in carbonate of lime. Where the ground is very wet and provision is made for drainage, the soluble gases are taken up by the water, and removed in a very diluted form, before they have much chance of doing harm. Carbonate of lime acts beneficially by directly neutralizing the sulphuric acid, and converting it into gypsum.

The heaviest rusting seems to take place between rail and sleeper when both are of iron, the acid water being introduced by capillary action, forms layers of rust which by continual accretion attains a thickness of 10 to 15 millimetres, and drives rail and sleeper upward; wooden sleepers, on the other hand, protect the iron on account of their low conductivity, which prevents the precipitation of the acid gases, if the surface of the latter is sufficiently covered up in the ballast.

The methods best suited for the prevention of rusting in tunnels seems to be as follows:

1. Covering the ironwork as far as possible with heavy or socalled carbonized tar (not ordinary gas tar) or asphalt. These are excellent preservatives if applied to the metal in a properly clean condition and renewed at intervals.

2. The precipitation being greatest at the coldest points in the tunnel, that is on the ironwork, the latter should as far as possible