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arranged that when a rise of temperature causes expansion of the mercury in rising in the tube it makes a contact; and the wires from these tubes are in connection with an electric bell, indexboard, and battery in the captain's room ; so that the moment the temperature is reached to which the thermometers have been set the bell rings, and will continue to ring, until the temperature again sinks, the spot in which the heating is taking place being indicated by the index-board. In the evidence given before the Commissioners in 1875, Mr. J. Glover strongly advocated the use of carbon dioxide, or carbonic-acid gas, as it is more usually termed, for extinguishing ignition when it had broken out in a coal cargo, and for stopping heating when it had reached a dangerous pitch. His proposal was to generate the gas by the action of hydrochloric acid upon chalk, and to lead it by gas pipes to the compartment affected; and this gas, being heavier than air, and a non-supporter of combustion, was to displace the air and. its contained oxygen, and so to prevent further action by surrounding the coal with an atmosphere which could not carry on combustion. The idea was a good one, but there were many difficulties in the way of carrying it out, one being that, for every 1,000 tons of coal carried, 80 cwt. of hydrochloric acid would have had to be shipped ; also the gas could not have been driven down into the hold if any serious heating had taken place, as an upcurrent would have been formed, and would have carried it away ; whilst in the state of gas, it fails to give any great cooling effect, and so would have exercised but little influence upon the mass of red-hot fuel. These objections weighed so strongly with the Commissioners that, in their final report, we find the following sentences : ' Several methods for generating carbonic-acid gas, and applying it to the ignited portion sf a coal cargo, have been proposed for our consideration. We consider, however, that although this gas might be useful for excluding atmospheric air (which is essential to support combustion), yet it will not, as water does, exert any very sensible cooling effect, which is a point of vital importance in the case of a mass of ignited coal. We are of opinion that water and steam are the only agents practically available for the purpose of extinguishing fire in coal cargoes.' Applied in the way which, was suggested, there is no doubt but that the carbonicacid gas would have been practically useless ; but there is another way in which it could be used, which would make it a most powerful cooling agent, an instantaneous quencher of fire, and would prevent any further tendency to heat on the part of the coal treated with it. If carbonic acid gas is compressed under a pressure of 36 atmospheres at a temperature of 32° Fahr. (0° C), it is condensed to the liquid state, and can be obtained in steel vessels closed with screw-valves. On opening the valve some of the liquid is ejected into the air, and, in coming into the ordinary atmospheric pressure, is in a moment converted in a large volume of gas. Conversion from the liquid to the gaseous state means the absorption of a large amount of heat; and so great is this, that everything near the stream of new-born gas is cooled down, and some of the escaping liquid is frozen to a solid, having a temperature of —78° C, or —108-4° Fahr. This liquid carbonic-acid gas is now extensively manufactured, and is used abroad to a large extent for aerating waters, driving torpedoes, and for freezing-machines ; and I should suggest its rise in the following way for the checking of ignition in the coal cargo : The nozzle attached to the screw-valve on the bottle of condensed gas should have a short metal nose-piece screwed on to it, the tube in which should be cast in solid, with an alloy of tin, lead, bismuth, and cadmium, which can be so made as to melt at exactly 200° Fahr. (93° C). The valve should then be opened, and the steel battle buried in the coal during the process of loading. The temperature at which the fusible metal plug will melt is well above the temperature which could be reached by any legitimate cause, and would mean that active heating was going on in the coal; and under these conditions the pressure in the steel cylinder would have reached something like 1,7001b., and the moment the plug melted the whole contents of the bottle would be blown out of it into the surrounding coal, producing a large zone of intense cold, and cooling the surrounding mass to a comparatively low temperature. The action, moreover, would not stop here, as the cold, heavy gas would remain for some time in contact with the coal, diffusion taking place but slowly through the small exit-pipe. " When the coal has absorbed as much oxygen as it can it still retains the power of absorbing a considerable volume of carbonic-acid gas; and when coal has heated, and then been rapidly quenched, the amount of gas so absorbed is very large indeed, and the inert gas so taken up remains in the pores of the coal, and prevents any further tendency of heating; indeed, a coal which has once heated, if only to a slight degree, and has then cooled down, is perfectly harmless, and will not heat a second time. It is not by any means necessary to replace the whole of the air in the interstices of the coal with the gas, as a long series of experiments show that 60 per cent, of carbonic-acid gas prevents the ignition of the most pyrophoric substances. One hundred cubic feet of gas can be condensed in the liquid state in a steel cylinder lft. long and 3in. diameter, and it has been shown that a ton of coal contains air-spaces equal to about 12 cubic feet; therefore, one of these cylinders would have to be put in for every eight tons of coal, as, although the gas formed at the first moment would only occupy a small space, on account of its low temperature, it would rapidly expand in contact with the hot coal. These cylinders should be distributed evenly throughout the cargo and near the alarm - thermometers, which should be set to ring a degree or two below the point at which the fusible plug would melt. The bell ringing in the captain's room would warn him that heating was taking place, and the bell would continue to ring until the cylinder had discharged its contents, and had cooled the cargo down to a safe degree, so that the whole arrangement would be purely automatic, and yet the officers would know if everything was safe. This liquid is now being made at a comparatively cheap rate, and, with any demand for it, machinery could be put up at the principal coaling-ports to charge empty cylinders at a very low rate ; so that, the initial cost of the steel cylinders once got over, the expenses would not be worth considering, more especially as only one, or two at most, of the cylinders in use wo aid be likely to go off. If the precautions advocated were taken no danger could arise until the arrival of the ship at her destination, and the commonest precautions would then suffice. On removing the hatches no naked light must be allowed near them, and no one 19—C. 3.