JUVENILE LECTURES.

On Wednesday afternoon, December 31st, 1902, Professor EDWARD B. POULTON, M.A., D.Sc., F.R.S., delivered the first lecture of his course addressed to a juvenile audience, on the "Means of Defence in the Struggle for Life among Animals."

The special subject of this lecture was the "Methods by which animals hide in order to escape their enemies and catch their prey."

The main object of the defenceless animals was to escape from their enemies. by assimilating themselves with their surroundings, thus also enabling them to obtain food with safety. In a series of lantern slides the lecturer showed the different animals alone, and concealed by their surroundings. Fishes were shown with no evident means of protection, and again hidden in the midst of the grass which they mimicked. The fish held itself upright in the water, and imitated the motions of the grass which it resembled and by which it was surrounded. The next series of slides showed creatures which imitated different parts of a plant. Thus Professor Gregory gathered in British East Africa what he supposed to be a foxglove, but which really consisted of green and

pink insects that flew away when the stalk was disturbed. Another similar case was recorded in that country, which differed in certain respects, but the lecturer thought that it would be possible to reconcile the conflicting evidence.

Professor Poulton said that it was not necessary to go to the Tropics for these examples of protection, because if they were sought for at home they would be found. Certain moths, daddy long legs, and caterpillars when in their proper positions, were often SO wonderfully like their surroundings that it was by no means easy to distinguish them. In the slides, many of the animals were likely to have escaped notice if they had not been pointed out by the lecturer.

Many fish alter their colour in accordance with their surroundings, and Lord Lister discovered that this was due to the effect the of light on eye. The lecturer did not think that this held good in respect to insects, whose change of appearance, he believed, was effected through the nerves of the skin. He made special experiments on chrysalises, which changed in colour in adapting themselves to their surroundings. In one family of caterpillars fed on the same food each individual changed its appearance in accordance with the colour of the twig upon which it was placed.

It was said by some that the cases of mimicry were not so common as was supposed by the advocates of the theory, but the lecturer pointed out that in general we see only what we look for. He had himself found many cases of butterflies insufficiently protected which had been pecked at by the birds. The reason why attention had not been generally drawn to these cases was that the injured specimens were thrown away by the collectors. If, however, it was wished to collect these, plenty of specimens would be found to reward the search.

The lecturer referred to the different kinds of markings on the zebra and on the tiger which make these animals specially noticeable when they are seen in confinement, but which in their natural surroundings helped to hide them, the zebra from its enemies and the tiger from its prey. In conclusion, the Brazilian frog was shown alone, and also in the hole which it scoops out for itself when it lurks for prey. Professor Poulton said that he had shown many instances of the protection of animals from enemies, and few exhibiting the power of hiding from prey, but this was the proportion in which the two occurred in nature.

CANTOR LECTURES.

THE FUTURE OF COAL GAS AND ALLIED ILLUMINANTS."

BY PROFESSOR VIVIAN B. Lewes, Royal Naval College, Greenwich.

Lecture II.-Delivered Dec. 1st, 1902.

In the last lecture I traced the changes that had taken place in the conditions of gas supply, and showed why an illuminating gas of comparatively low light-giving power and good calorific value would be the need of the future. We can now proceed with the discussion of how this gas is to be best obtained; and, having gone into the question of what may be expected from high temperatures in carbonisation, can proceed to consider the effect of blue water gas as an economical diluent, taking as a dominating factor that we must not add more than 40 to 43 volumes of blue water gas to 100 of coal gas, for fear of raising the percentage of carbon monoxide in the mixed gases above the advisable limit, and also because directly that amount is exceeded it begins to interfere with the action of atmospheric burners as adjusted for coal gas, and tends to cause flashing back.

The only successful processes used in Europe and America for the production of water gas have depended on the system introduced by Gillard, in 1849, in which the temperature of a burning carbonaceous fuel, such as coke or anthracite, was raised to incandescence by means of an air blast, and then steam was passed through the incandescent fuel with formation of water gas until the temperature had been lowered to a point at which carbon dioxide began to appear in the gas to a serious extent, when the steam was cut off and the fuel again blown up to the required temperature by the air blast. the only differences in the systems adopted being in the form of plant and the arrangement of valves employed.

In all forms, however, up to 1895 but little attention was paid to the ratio existing between the air blast employed and the fuel in the generator. The result of urging the carbonaceous fuel to incandescence was to obtain a gaseous product generally known as producer gas, the composition of which is :

This, under certain circumstances; can be used as a fuel gas, as it contains some 32 per cent. of combustible matter.

In order to raise the temperature of the fuel, however, to a sufficiently high point for the formation of 1,000 cubic feet of water gas by the passage of steam through it, 44 lbs. of carbon had to be consumed during the blow, which yielded 4,000 cubic feet of producer gas. This in the processes for making blue water gas was blown to waste at the mouth of the generator, whilst another 15 lbs. of carbon was consumed by the action of the steam in making the 1,000 cubic feet of water gas itself; so that this amount of gas meant the consumption of about 60 lbs. of carbon. The average yield of water gas per ton of coke by this process was 34,000 cubic feet, which represents only some 34 per cent. of the thermal value of the carbon from which it was formed, and it is quite clear that such a loss as this would prevent the economic use of water gas made by such a process from being successful.

The plea put forward in favour of blue water gas as a fuel at this period was that you had the fuel in the form most easy of application, and that also, by utilising the producer gas as a fuel, the heat to be obtained from it brought the total calorific value of the two mixtures up to 80 per cent. of the thermal value of the carbon used.

This argument however, as regards thermal efficiency, was purely fallacious in practice, as the two gases, being produced intermittently, would have to be stored in order to utilise them separately, and the enormous bulk of the producer gas as compared with its thermal efficiency would have required such an amount of storage room as to render such use of it impossible, whilst if stored and therefore cold, it would have to be re-heated before it could be got to burn, owing to the 68 per cent. of nitrogen and carbon dioxide diluting the combustible gases.

The introduction of carburetted water gas however provided a really successful method of utilising the heat given off during combustion of the producer gas, as in the beautiful forms of apparatus devised for making the carburetted water gas, you really have a heat engine which does its work in a perfect way.

During the blow the producer gas, red hot from the generator, was consumed with the requisite quantity of air in the checker-brick cracking and fixing chambers, which decompose the oil and convert it into a permanent gas. By the time the right degree of incandescence has been arrived at in the generator, the chambers designed for the oil gas manufacture have also reached the required temperature, so that when the air blast is cut off and steam admitted to the incandescent coke in the generator, and a stream or spray of oil passed into the cracking chambers, you have at once a process for making carburetted water gas proceeding under the best conditions; as the hot water gas, sweeping forward through the cracking and fixing chambers, washes out from them the oil gas as it is produced, and saves it from over-decomposition by contact with the heated walls of the chambers, so that in reality, in all those forms of carburetted water gas apparatus which have arisen as improvements of Lowe's original ideas, you have the full thermal value of both the producer and water gas being utilised.

On the Continent, however, where the oil supply is not under such favourable conditions as in this country, an economical method of producing blue water gas still remained one of the greatest needs of the technical world, and in 1896 Carl Dellwik gave a method of making water gas to the manufacturers, which in simplicity and ease of working could not be surpassed, and which in one step did away with the production of the well-nigh useless producer gas, and doubled the production of water gas per ton of fuel.

In the spring of 1897 I had the privilege of investigating this process at the little Westphalian town of Warstein, where Dellwik had the process installed. In the June of that year I gave a lecture before the Incorporated Gas Institute, at their Bath meeting, in which I gave the results I had obtained whilst working with the apparatus; and at the present day I gather considerable amusement and pleasure from looking back to the criticisms and remarks which were aroused at that time. An American correspondent of mine took the trouble of writing to one of the leading gas experts in Germany, asking for his opinion on the figures I had given. The reply received was that the results were absolutely impossible; and the writer was evidently not clear in his own mind as to whether I had been sufficiently intoxicated to have seen the results double, or

was so incapable as not to be able to perform the experiments. I was, however, pleased to see a year later that the same gentleman had investigated the process himself and given the same figures, and is now one of the most ardent supporters of the process.

In this process (which I have described already on more than one occasion, and which I need only now, therefore, touch upon), by careful regulation of the grate surface, the height of the fuel bed, and the air blast, instead of bringing about incomplete combustion in the generator whilst blowing up to incandescence, and getting producer gas as a by-product, the ratios are so arranged as to give complete combustion aud to yield practically ordinary flue gas during this process, This means that the carbon monoxide produced in the old process of blowing was now burnt in the generator itself instead of in a supplementary chamber, as in the case of the Lowe process, and the extra temperature due to its combustion is given to the fuel, thereby raising it to incandescence in much shorter time than had been the case heretofore, and so reducing the amount of fuel consumed.

Burnt up by the excess of air during the blow, the carbon is converted into carbon dioxide and not carbon monoxide, so that instead of developing 2,400 pound-centigrade heat units per pound of carbon, it develops 8,080 for the same consumption, or an amount 3.37 times as great.

Having reached incandescence in this, the only rational and economical way, the fuel is then subjected to the action of steam. But the steam supply is so regulated that it is never at any time in excess of the quantity required for the formation of water gas. By this means oxidation of the carbon monoxide to carbon dioxide by steam, which always takes place to a small extent in the old process, is here avoided, and the result is that with a decent coke it is possible to produce 70,000 cubic feet of water gas per ton of carbon, as against 34,000 cubic feet with the old processes, a result which now makes water gas the most important factor in obtaining high temperatures. It is by this process that the blue water gas will have to be made in the future if it is to be successfully employed as an adjunct in the manufacture of an economical low grade gas.

Many experiments have been made with a view of seeing if the generators utilised for making water gas for the formation of carburetted water gas could be used on the Dellwik lines. It was soon found that the alterations necessary cost far more than a new plant, and

that an increase in the amount of air blast is by no means the only thing necessary to give the improved results, as unless this is accompanied by a careful regulation of the ratio between the fuel, grate area, and air blast, little improvement can be obtained. In America many attempts have been made to get away from the Dellwik patents by experiments in this direction, aad I was pleased to hear the other day from one of the leading water gas makers in America, that although he had blown his generators until, as he put it, the country round was an inch deep in ashes, he had absolutely failed to get any result approaching that given by the Dellwik plant.

Taking now our water gas made in the most economical way, we can proceed to see how it can be best used for diluting coal gas down to such standards as may hereafter be fixed upon. Mr. T. C. Paterson, in his inaugural address to the Incorporated Gas Institute last year, gave some most valuable figures on the relation of illuminating power and calorific value in gases, and tabulated the effect of diluting coal gas with uncarburetted water gas as follows::

My first series of experiments in the direction of trying how best to make a low grade gas of satisfactory heating power was to test the effect of diluting coal gas of different calorific values with blue water gas, the gases being mixed pro rata as they flowed into the holder, and being allowed to stand over night to complete the mixing.

In practice, if a 16 per cent. limit was fixed by Parliament for the carbon monoxide in the gas, it would be manifestly unwise to approach the limit too closely, as during a press of work owing to fog or other causes that threw a strain on the resources of the works, a slight want of uniformity in mixing might bring the percentage above the limit. In these experiments 40 volumes of blue water gas were added to 100 of coal gas, which would give 28.5 per cent. of water gas in the mixture and bring the carbon monoxide up to about 14 per cent. The gases were measured through a meter before mixing, and the resulting mixture was tested for calorific value in a Junker's calorimeter. The blue water gas used was purified from carbon dioxide, and had a calorific value of Gross.

Nett.

Coal gas Thermal Value:

35'0 3175

Coal gas.

33'3

nett B.T.U.'s gross nett

80

Mixture.

404'5 370'7

15.1 15.2 13°4 13.9 15.1 14.6 1374 13.3 This Table shows that given an ordinary gas coal, such as we should in practice use, yielding 10,000 cubic feet per ton of a 15 to 16 candle power gas, it may have added to the 10,000 cubic feet 4,000 cubic feet of blue water gas, with a reduction of only 13 to 15 per cent. in ther:nal value.

The experiments made by Mr. Paterson and others show that the reduction in candle power is practically proportional to the volume of water gas added, as one would expect, so that

the candle feet per ton of coal carbonised would be practically the same whether they were present in 10,000 cubic feet of coal gas or 14,000 cubic feet of the mixture.

Instead, however, of mixing the blue water gas with the cold coal gas, a distinct advantage is to be gained by passing the gas into the foul main. This is done at several places in Germany, notably at Erfurt, and it is found that a distinct gain in candle power is obtained owing to the water gas becoming to a slight extent carburetted with benzol vapour present in the hot gas, which if allowed to cool would be taken up by the tar.

I regret to say that I have no direct figures which show the result of percentage admixtures made in this way, of blue gas and coal gas, as in all the works where it is used, the mixed gases are benzolised, i.e., enriched to a small extent by benzol before being sent out. The saving is found by less benzol being required to bring the gas up to a given candle power when the mixture is made in this way than when, as is done in some other places, the water gas is enriched with benzol, and is then afterwards mixed in with the coal gas.

In utilising water gas for the dilution of coal gas, it is possible, however, to make it perform a far more important function than that of merely increasing the volume. One of the weakest points in the manufacture of coal gas is to be found in the process of carbonisation, which has undergone little or no change since the earliest days of the gas industry. When the coal is placed in the hot retort, evolution of gas at once commences with great rapidity, and working with a five hours' charge, the largest proportion and the richest portion of the coal gas is evolved during the first three hours. The general course of the reactions are well shown in the following Table of results found by Mr. Lewis T. Wright in his studies on carbonisation :

A moment's consideration of the actions taking place during carbonisation shows that whereas, in order to obtain the best results, the coal gas during retorting ought to remain under absolutely uniform and reliable conditions of temperature and time of exposure to the heat of the retort, yet these are the very factors which it is absolutely impossible to obtain under existing circumstances. The gas and vapours generated from the coal at the mouth end of the retort have only a very short exposure to radiant heat from the walls of the retort, as they are hurried out by the volume of gas behind them, and therefore they leave almost unacted upon by the heat, whilst the gas from the extreme end of the retort, having nothing to urge it forward, gets largely decomposed by overheating, with the result that not only are many of the heavy hydrocarbons, which would have been of the greatest value as illuminants to the gas, broken down into methane, hydrogen, and carbon, but also the over-baking yields a large percentage of the naphthalene found in the tar and mains.

It has always been a dream of the gas manager to devise some process which would enable him to decompose the tar formed during destructive distillation, and by getting from it hydrocarbons of high illuminating value, to do away with enrichment by other and more costly processes. Many attempts have been made in this direction, but, so far, the only way in which tar has shown itself of value as an enricher has been to separate the benzol from it, and then return that benzol to the gas in the carburettor.

I have many times pointed out that when once formed tar is one of the most difficult bodies to decompose. Its formation is really due to two distinct sets of actions, a primary action in which liquid hydrocarbons distil as vapours from the less heated portions of the coal in the retort, and escaping decomposition by the radiant heat from the crown of the retort, condense as liquids again on cooling, whilst a secondary reaction is of a synthetic character, and results in the formation of naphthalene, carbon and many of the heavier constituents of the tar, by the polymerisations and decompositions taking place in the heated crown of the retort at the expense of hydrocarbon gases which ought to find their way unaltered into the gas. I have also pointed out that the only rational method of getting the benefit of the hydrocarbons which are at present lost as