June i6, 1893.] 



SCIENCE. 



32; 



carbon containing 0.035 per cent of hydrogen does not tate up 

 chlorine, sugar charcoal, with 0.07 per cent, does take it up. 



The experiments with charcoal and sulphur showed the ab- 

 sorption of from 20 to nearly 47 per cent in charcoal containing 

 much hydrogen and oxygen, while nearly pure amorphous carbon 

 takes up but little sulphur. Professor Mixter regards the sulphur 

 as chemically combined with the carbon, in his experiments, and 

 cites Berzelius in support of this view. 



THE EARTH AS AN ELECTRICAL CONDUCTOR. 



BT A. F. MCKISSICK, ALABAMA POLTfTECHNIC INSTITUTE, AUBUEN, ALA. 



Steinhill, at Munich in 1837, was the first to discover that 

 the earth might be used instead of a return wire, contact being 

 made to the earth at the two ends by means of metal plates sunk 

 in the ground. He discovered this while experimenting on the 

 Nurnberg-Further railroad for the purpose of determining whether 

 the track could be used for telegraphic purposes. He noticed 

 that the current passed from one rail to the other and the idea to 

 use the ground as a return cii-cuit occurred to him, which he 

 afterwards found to be perfectly feasible. The earth is almost 

 universally used as the return circuit in telephone and telegraph 

 lines. While it is true that in the former a complete metallic 

 circuit is sometimes found, it is not on account of the failure of 

 the earth to conduct the current but for the purpose of diminish- 

 ing the induction, caused by the presence of electric light and 

 power circuits. 



The earth-plates are made of zinc or copper and are sunk in 

 moist earth, in a spring, or in the bed of a river. It has been 

 generally considered that the earth offers no resistance at all as 

 its cross-section is so large, although its specific resistance may 

 be very high. While the resistance of the earth may be neglected 

 when we have to deal with telephone and telegraph circuits, we 

 must consider its resistance when it is to be used for conducting 

 currents of large volume. 



The element of danger to life and property forbids its use as a 

 return in commercial lighting and motor circuits. 



In street railway circuits, however, the earth is used partly as 

 a return. It has been found that the earth alone, as a general 

 rule, offers too much resistance, so that it is now almost the uni- 

 versal custom to use in conned ion with the earth the rails bonded 

 together and also a bare copper wire. I had occasion during the 

 past year to notice very closely this resistance in installing a 

 motor at the experirnent station ot the A. and M. College of Ala- 

 bama. I had expected to use the earth as a return, but 

 owing to the very high resistance had to abandon this idea. 

 It was with the idea of finding out how much the resistance of 

 the earth near this motor was, that the following experiments 

 were made. 



An earth-pit was dug six feet deep, eight feet long, and two 

 feet wide, at each end of the line running from generator at col- 

 lege to motor at experiment station. This line is by measure- 

 ment three thousand feet long. A plate of copper, seven by two 

 feet, and a plate of tin of same dimensions, soldered to a No. 

 0000 B and S wire were used as the earth-plate at each end. The 

 plates were packed firmly with charcoal and iron filings and the 

 pit filled with old iron. The water rose in one of the pits to a 

 depth of two feet. With all connections soldered, the resistance 

 measured by a "Wheatstone bridge was found to be 103 ohms. 

 Supposing the earth connection was not a good one at each end 

 of the line, an additional earth connection at each end was made 

 by sinking a large piece of iron in a well. With this additional 

 connection there was no appreciable difference in the resistance. 

 Connections to the earth were then made at different distances 

 from the college by connecting one end of a wire to the overhead 

 wire, the other end soldered and tied to a piece of iron six feet 

 long, driven down flush with the ground. These distances were 

 respectively 500, 1,000, 1,500, 2,000, and 2,500 feet from the col- 

 lege. These connections were made at different times, always 

 removing an earth connection when its resistance had been meas- 

 ured. The resistances in the same order were 307, 567, 153, 707, 

 and 217 ohms. The comparatively small resistances of stations 



3 and 5 are probably explained by the fact that they were lo- 

 cated near branches (small streams). 



From these results we may conclude that the resistance of the 

 earth is a very unknown quantity, and the assumption that the 

 resistance of the earth can be neglected in any soil is an unsafe 

 one when the object in view is to transmit currents without very 

 much loss. 



A VALUABLE FLORIDA DEPOSIT. 



BY THOS. R. BAKER, PH.D. 



There occurs near Bartow, Fla., and at other points as far 

 south as Haines City a geological deposit which has recently been 

 found to be very valuable as a material for covering the sandy 

 side-walks and streets of Florida towns It is popularly known 

 in South Florida by the name "clay," but consists essentially of 

 sand, clay, and oxide of iron, the proportions of which, deter- 

 mined by chemical analysis, are given in the following table: — 



Per cent. 



Moisture 4.20 



Silica 09 03 



Aluminum silicate 18.21 



Iron oxide 8. 58 



Calcium carbonate Trace. 



Geologically considered, the deposit is a sandstone rock, and, 

 although it has to be quarried from its bed, it almost completely 

 disintegrates in the quarrying, and needs no further preparation 

 to fit it for the use to which it is applied. It is of a reddish color, 

 due to the presence of oxide of iron. 



The material is simply spread over the side-walk or street to 

 which it is to be applied to the depth of several inches, and then 

 sprinkled with water, and rolled with a heavy roller. After 

 being walked upon and driven over for a short time it becomes 

 very compact, and fully as hard as it is in its native bed. 



The most valuable constituent of this material, when used as a 

 covering for roads, is undoubtedly the oxide of iron, which acts 

 as a cement, rendering the material capable of becoming compact 

 and hard. That the iron serves this purpose was verified by re- 

 moving it from the compound, and subjecting the mixture of the 

 remaining constituents to tests that had been applied to the origi- 

 nal material. 



The adaptation of this deposit to the improvement of roads was 

 first bi'ought to notice by the South Florida and other railroad 

 companies, who used it for the improvement of railroad crossings, 

 drive-ways about stations, etc , and the first extensive use made 

 of it for streets and side-walks was by the city of Orlando about 

 a year ago. It has given excellent satisfaction in Orlando, noth- 

 ing having been done for the place for years that has so improved 

 it. It has 'been the means of converting streets so sandy that 

 travel over them was very slow and difficult into drive-ways over 

 which travel is easy and pleasant. Now, on Orlando streets, 

 vehicles and horses' hoofs have the familiar rattle and thud that 

 are heard when driving over a macadamized road. It is the 

 opinion of those who have studied the subject that geological de- 

 posits like the one here described are of very rare occurrence. 



NOTES AND NEWS. 

 The next meeting of the Australian Association for the Ad- 

 vancement of Science will be held in Adelaide, South Australia, 

 commencing on September 25th, 1893. The meeting in Adelaide 

 will be presided over by Ralph Tate, F.L S., F.G.S., professor of 

 natural science at the University of Adelaide. At the time fixed 

 for the meeting. South Australia will be at its best. There is no 

 better time at which to visit Australia than when spring is merg- 

 ing into summer. To naturalists, this time of year is specially 

 attractive, and these may be reminded that at the meeting of the 

 Association they will come into contact with men of like tastes 

 from all parts of Australia. Should visitors wish to prolong their 

 trip, they will do well to visit during the months of October and 

 November the principal objects of interest in the mainland, and 

 in December, January, and February to pass on to New Zealand 

 and Tasmania. 



