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THE POPULAR SCIENCE MONTHLY. 



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 con- 

 tains. 



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 car- 

 bonic 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 es- 

 sential that the amount of sulphur it con- 

 tains 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 hy- 

 drogen, contaminated with the vapor of bi- 

 sulphide 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 bi- 

 sulphide 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 state- 

 ment 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 Twicken- 

 ham, 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 Na- 

 ture, April 18th, and corrected in a sub- 

 sequent 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 as- 

 sume 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 Flat- 

 bush, 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 gal- 

 lons nearly, or 3,112,974 tons of 2,000 



