Helium

(Chem.) In 1868 Prof. Norman Lockyer, while for the first time in the history of science examining the sun with the spectroscope during an eclipse, discovered in the spectrum a line not accordant with any known lines in terrestrial spectra. This was the D-3 line, a bright yellow line near the D line of sodium. As there was then no evidence of the existence in the earth of the substance represented by this line, it was named Helium, after the Greek title for the sun. The line of this hypothetical substance was afterwards discovered in certain stars, and Profe or Cope land saw it in the spectrum of the great nebula of Orion. Until 1895 no trace of this substance was found in the earth; but in that year Profe or Ramsay, while subjecting to the action of heat a rare mineral of Norway, called cleveite , perceived in the spectrum of the gas given off a line that proved to be identical with that of helium. Bröggerite, another mineral, also yielded it, and Ramsay's later researches indicate that it is held by minerals which contain salts of uranium, yttrium and thorium. Oxide of uranium seems capable of retaining it, and it is found plentifully in monazite, a mineral which contains thorium. It has been found also in the waters of certain mineral wells. H. may be a constituent of the atmosphere, but if so must occur in very minute quantity, as no trace of it can be found. Study of its physical characteristics show it to have a density varying in different examinations from 1-874 to 2-133. It is the least soluble in water of all known gases, its solubility at 18° being 0.007. Its refractive index is also very low, being 0146. That of hydrogen is 0-5, or half that of air. Hell Gate, a strait in East River, 8 m. N.E. of the Battery, connecting that river with Long Island Sound, and formed by projecting and underlying rocks that Fig . 2926. GALLERIES IN THE HELL GATE ROCKS UNDER THE EAST RIVER. confine the water to a narrow and crooked channel, causing strong eddies and rapid currents. Extremely dangerous for small ve els, the strait was altogether impa able for ships of considerable tonnage. In view of the fact that the removal of the hindrances to the Sound navigation at Hell Gate would enable ve els to avoid a hundred miles of exposure to a dangerous coast, and bearing in mind, too, the heavy lo es annually sustained on this point, the New York Chamber of Commerce, in 1851, accepted a proposal made them by M. Maillefort, an eminent engineer, which had for its object the removal of three of the smaller-but most dangerous reefs at Hell Gate by means of submarine mining. In the carrying out of his project, M. Maillefort was to a certain degree succe ful; the chief result being the removal of the projection of Pot Rock, and the increased facilities gained thereby for permitting the safe pa age of ve els drawing 16 feet of water. Funds to complete the work falling short, Congre was appealed to in 1852, and an appropriation of $20,000 was made for carrying on operations under the supervision it in hand, and placed it under the charge of Gen. Newton, who energetically pushed it to completion. The removal of Hallett's Point was the most pre ing of the objects to be accomplished, that spit of land project. ing forward 300 feet in such a manner as to divert the Sound tide right upon the dangerous reef known as The Gridiron, over which it broke with irresistible force. The only feasible plan of operation was to work from the shore by sinking a shaft, out of the way of shipping, and after undermining the reef with radiating headings connected by concrete galleries and removing all the rock that could be safely taken out, blow up the roof and its supporting columns at a single explosion, the debris to be either buried in the excavation or removed by grappling, as might be proved most economical. The first step taken, therefore, was to construct, between high and low water, around the mouth of the proposed shaft, a strong coffer-dam, 310 feet in length, extending along four sides of an irregular pentagon, the fifth or shore-line of which was about 145 feet. The dam, consisting of a double shield of heavy timbers securely fastened to the rocks by bolts pa ing through the structure-the space between the walls filled water-tight with sand and clay-was completed and pumped out, so that operations could be begun in the interior. The underground headings radiating from the main shaft were 10 in number, and named, like streets, after persons eminent in American history. The miners employed were Cornishmen, they being found to be the only cla who could work long under water and still retain their health. The drilling of the rock, done in the first place by hand, was, during the latter course of the work, much expedited by the use of drills driven by compre ed air, and acting in connection with the diamond prospecting drill. In this difficult and dangerous task of mining under water about 200 men in all were employed, working by turns. For blasting, dynamite was originally used; but the detonation caused by it being found to be too great, nitro-glycerine was substituted in its place. For the removal of the smaller channel rocks, too distant to be reached by shore tunnelling, and swept by currents too powerful to permit the sinking of a cai on, Gen. Newton invented a special and unique drilling apparatus, worked by divers with the aid of machinery fitted on a scow moored on the surface of the water above the rock to be operated upon. Sept. 24, 1876, the mine was exploded by the electric current. Over 50,000 pounds of explosive compound were used. The concu ion was much le than anticipated, and one of the most succe ful engineering exploits of the age was partly accomplished. Oct. 10, 1885, by a second explosion, far sur pa ing the one of 1876, Flood Rock was blown up. This time 280,000 pounds of explosives were used nearly six times the former quantity. When the débris is fully removed, which has not yet been done, owing to insufficient appropriations, there will be an unobstructed channel 1,200 feet in width and deep enough to permit the pa age of large ve els.