1-1000th of its volume of the bisulphide, and yields it up again on distilling; the solution possessing a burning taste, with the odour of the bisulphide. Many substances insoluble in water are soluble in this liquid-such as sulphur, phosphorus, iodine, caoutchouc, fats, and oils. Carbon disulphide boils at 46° C. Its vapour, when mixed with three times its volume of oxygen, ignites with explosion; forming sulphurous and carbonic acid gases, thus :

The vapour of carbon disulphide, when mixed with nitric oxide, burns with a blue flame, which is very rich in rays of high refrangibility, and has, on this account, been used in photography. On passing the vapour through a tube heated to bright redness, it is partly resolved into its elements; carbon depositing, and sulphur passing off with the undecomposed portions. The vapour of bisulphide of carbon has an excessively low igniting-point, and will take fire at a temperature of 300° F. (149° C.). But the trace present in coal-gas is so minute that it could not affect its point of ignition; besides which Dr. Frankland has shown that even the smallest trace of ethylene in a gaseous mixture which contains the vapour of bisulphide of carbon destroys this great inflammability.

"The formation of the bisulphide of carbon vapour found in coal-gas is due to the direct action of sulphur vapour upon the red-hot carbon. If powdered charcoal or coke be mixed with powdered sulphur, and the mass heated, sulphur vapour distils off, and no bisulphide of carbon is produced, because the sulphur has all volatilized before the carbon is in a sufficiently heated condition to bring about combination; and if the sulphur in the coal were in the free state, the same thing would happen. When coal is put into the hot retort, the portions in contact with the sides are rapidly raised in temperature, and the

sulphur which is liberated by the breaking up of the disulphide of iron, pyrites or brasses,' vaporizes, and combines with free hydrogen to form sulphuretted hydrogen. But by the time the pyrites in the centre of the mass of coal are sufficiently heated to yield sulphur vapour, the outer surface of the partly coked mass is at a temperature high enough to form with it small traces of bisulphide of carbon; and the higher the temperature used, the more of the sulphur compounds other than sulphuretted hydrogen' are produced" (Professor Lewes).

In the following table, obtained from experiments made by Mr. Lewis T. Wright, this is shown very clearly; the yield of gas per ton of coal being taken to give an idea of the temperature, while the grains per 100 cubic feet of sulphur compounds in the gas, are after purification from sulphuretted hydrogen-the same coal being used in each case:

The injurious action of CS, in coal-gas is due to the fact that sulphuric acid is one of the products of its combustion, but the actual amount of carbon bisulphide generally present in purified gas is exceedingly small, and there is a great difference of opinion as to the effects produced when coal-gas containing CS, is burnt. The following are the views of Professor Lewes, who has minutely investigated. the question. (See "Journal of Gas-lighting," February 20th, 1894):

"In considering the effect of these sulphur compounds in the products of combustion, it must be borne in mind

that, when coal-gas is burnt the sulphur is liberated in the form of sulphur dioxide; and many most misleading statements and ideas have gained ground as to the quantity of this which becomes converted into sulphuric acid in the atmosphere. My own experiments, as well as those of Mr. Harold B. Dixon, all prove that when traces of sulphur dioxide, as minute in quantity as those which are given off in the combustion of gas, are present in the air, they show no tendency to oxidize to sulphuric acid, even though the air is highly charged with moisture, unless the temperature falls to such a point that water is deposited. from it. This water then takes up the sulphur dioxide, which slowly becomes oxidized to sulphuric acid. For this reason it is perfectly possible to find traces of sulphuric acid and sulphates upon window-panes where the cold air outside has caused moisture to condense on the windows; and the same action will take place where you have ammonia or other alkaline substances present in the air or dust, fixing the sulphurous acid. But it is manifestly incorrect to suppose that this action goes on unless the temperature of the room has fallen to the condensing point of the water vapour; for, if this did take place, even with the highly-purified London gas, there is not a sittingroom in London in which the draperies would not become rotted in a very short space of time, as the smallest deposit of sulphuric acid, no matter how dilute, would, by slow and cumulative action, become sufficiently strong to burn away the fabric. The test of time has shown the fallacy of any such injurious action.

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In order to prove the deleterious effects of this hypothetical formation of sulphuric acid, certain observers have brought forward many experiments to show that, in passing the air through absorbing solutions, sulphates could be detected in them in small and varying quantities. This, however, certainly does not prove that sulphates

were present in the air, as, directly the sulphur dioxide is absorbed by the liquid, the oxidation to sulphuric acid takes place with considerable rapidity. It is this that has given rise to wrong deductions from the observed facts of sulphuric acid, either free or in combination, being found in wetted fabrics, or on moistened plates or liquid absorbents exposed to the air of rooms in which gas has been burnt, also on lamp-glasses and in ventilating-tubes, especially in towns where no limit is placed on the amount of sulphur present in the gas.

“It has also been considered a proof of the formation of sulphuric acid from the products of combustion of gas containing sulphur compounds, that dust collected in a room in which such gas is being burnt contains small quantities of sulphates.. But here again several important factors of error have been overlooked. The dust which is found in a room has not been formed in that room, but has filtered in from the outside air, under the sashes and other openings; and it must, of necessity, contain sulphur compounds, which have been produced by the fixation of the sulphur produced by the burning of coal and coke, by the ammonia and other alkaline bases present in the air. An analysis of dust from rooms in which no gas has been burnt will also show the presence of these bodies in as large quantities as from the rooms in which gas has been consumed in very considerable volume. Dust collected in my study at Greenwich, in which gas is very freely burnt, gave 305 per cent. of sulphur as sulphates; while dust. collected in an attic in a disused portion of the same building, in which there has never been a gas-fitting, gave 44 per cent. This mistake has been caused by the fact that rain-washed dust collected on exposed outside sills often contains only a small percentage of sulphur. The closeness and oppressive feeling which can be distinguished in a room that is not properly ventilated, when gas is

being burnt, is not due to the presence of sulphur compounds, but to carbon dioxide, and to the traces of the products of incomplete combustion. It is also partly

owing to the organic emanations from the bodies and lungs of the occupants of such a room being unable to rise into the zone of highly-heated air which exists above the gasburners in the room, and so being kept down to the level from which the air for respiration is being drawn.”

As remarked under condensation, the first stage of the purifying process begins when the crude gas leaves the retort and travels along the hydraulic main, a partial deposition of the tarry and aqueous vapours taking place, together with a small portion of the ammonia which is absorbed by the condensed aqueous vapour, but very little purification is effected here, however, as the gas is still in a heated condition, and it is not until its passage through the condenser, where it becomes reduced to the normal temperature, that purification proper can be said to commence. Passing through the condenser nearly the whole of the tarry vapours previously held in suspension are deposited, collecting as liquid tar, together with a quantity of weak ammoniacal liquor, about one half of the total ammonia in the gas being deposited by the time the latter reaches the outlet of the condensers.

It is of the utmost importance that the condensing power should.be properly proportioned to the make of gas, for, if the temperature of the gas is not properly reduced before it enters the scrubbers, these vessels will not do their work efficiently, and, as a consequence, extra work will be thrown upon the purifiers proper. In addition to being cooled down to the normal temperature, the gas should be quite free from suspended tarry particles, which would tend to block up and impede the action of the washers or scrubbers.

The last-mentioned plant is employed for the removal