Page:Popular Science Monthly Volume 1.djvu/520

504 a nuisance of a very obnoxious character. Oxide of iron absorbs sulphuretted hydrogen equally well, and has the great superiority that, when taken out of the purifiers and exposed to the air, it not only creates no nuisance, but becomes in a short time fit to be used again. The same oxide may thus be used over and over again for twenty times or more, and when it becomes unfit for the purifiers it is still more valuable on account of the quantity of sulphur it contains.

But neither lime nor oxide of iron exerts any action on the other sulphur impurity, the compound of sulphur and carbon, and at the present time this bisulphide of carbon remains in the gas without any attempt being made to remove it.

The bisulphide of carbon, when burnt, forms for the most part sulphurous acid, which, being a gas, is removed with the carbonic acid by efficient ventilation. But a small part of the sulphur in this compound is converted into sulphuric acid, which, with the aqueous vapor formed, condenses on the walls of the apartments, and has been proved to destroy the leather bindings of books, and the canvas of pictures.

If coal-gas is to be burnt in rooms as freely as oil or candles, it is absolutely essential that the amount of sulphur it contains should be reduced to the smallest possible quantity.

One means by which the elimination of sulphur may be achieved, a process by which the amount of sulphur may be brought down to one-fifth of the present legal maximum, namely, 30 grains in 100 cubic feet, is the following:

The coal-gas is made to pass through tubes which are filled with fragments of iron and heated to redness. When dry hydrogen, contaminated with the vapor of bisulphide of carbon, is passed through a heated glass tube, carbon is deposited, and sulphuretted hydrogen is produced. The action is precisely the same when coal-gas containing bisulphide of carbon is made to pass over strongly-heated surfaces; the bisulphide is decomposed, and sulphuretted hydrogen formed, which is speedily removed by the ordinary purifying apparatus.

Mr. Harcourt showed, by means of a jet-photometer, that there was no appreciable difference in illuminating power between the coal-gas which had passed through an iron tube filled with nails and heated to redness, and that of ordinary cannel-coal gas. He also demonstrated the truth of his statement that, after being thus treated, but one-fifth the quantity of sulphur remained that is found in common illuminating gas.

Facts in relation to Rainfall.—From observations at Fulwell, near Twickenham, England, it appears that the rainfall for that locality during the year 1871 was 22.42 inches. This is nearly the amount which falls at Paris and at San Francisco, California. A calculation made by John James Hall, which was published in Nature, April 18th, and corrected in a subsequent number, gives some interesting statistics of the rainfall at Fulwell:

He states that one inch upon an acre of ground gives 22,623 gallons. Now, 640 times this amount, multiplied by the depth of rainfall, 22.42 inches, gives the quantity on a square mile as 324,612,902 gallons.

If this amount be multiplied by 10, the number of pounds of water to the gallon, and the result divided by 2,000 for tons, we shall have, for the quantity of rainfall on the square mile, nearly 1,623,064 tons.

The coal-carriages used on railways in England and in the United States carry from 8 to 10 tons of coal each. We will assume the former number, and find that 202,883 such carriages would be required to convey the weight of the rainfall above given, and, if each carriage measures 20 feet in length, they would form a train 768 miles long.

The quantity of rain which falls at Flatbush, Long Island, in the immediate vicinity of New York City, is 43 inches yearly. This is based upon observations made during 26 years. It will be seen that this amount is nearly twice as great as that which falls in a year at Fulwell, and is not far from the annual average that falls on our coast from Maine to Florida.

The computation which gives the results for Fulwell will give the quantity for each square mile of our own coast. For Flatbush, with an annual rainfall of 43 inches, we have the enormous quantity of 622,594,960 gallons nearly, or 3,112,974 tons of 2,000