Vol. XXIII. No. 5.] 



POPULAR SCIENCE ITEWS. 



69 



Electrified Steam. — Helniholtz has shown that 

 if an invisible jet of steam be electrified or heated, it 

 becomes visible with bright tints of different colors, 

 according to the potential or the temperature. 



Extremes Meetixc;. — Fort Keogh, Montana, has 

 the widest range of temperature of any place on 

 earth. Last summer the thermometer ranged from 

 120 to 130 degrees above, while recently it marked 

 65 degrees below zero— a total range of 195 degrees. 



Determination of an Alloy of Lead and Tin. 

 — After treating such alloy with nitric acid, in order 

 to convert the tin into insoluble stannic acid, it is 

 necessary to neutralize the excess ot nitric acid by 

 adding a very dilute solution of sodium hydroxide, 

 until a slight precipitate of lead begins to appear. 

 This precipitate is then re-dissolved by means of a 

 few drops of aceticacid, and theanahsis is conducted 

 as usual. 



A New Mineral, of exceptional chemical interest, 

 has been discoverd by Mr. Sperry. of Sudbury, On- 

 tario, Canada. It is an . arsenide of platinum, 

 PtAs2, and is the iirst mineral yet found containing 

 platinum as an important constituent, other than 

 the natural alloys with various metals of the plati- 

 num group. A considerable quantity of the mineral, 

 which takes the form of a heavy, brilliant sand, 

 composed of minute, well-defined crystals, has been 

 thoroughly investigated by Prof. Wells, who names 

 it "sperrylite," after its discoverer. 



A New Use for the Electric Lioht. — A paper 

 on the advantages of the use of the electric light in 

 the observations of marine zoology is published in 

 the Comptes Rendus by M. de Lacaze-Duthiers. An 

 account is given of the system of electric light now 

 in use at the Arago Laboratory of the Banyuls sta- 

 tion, by means of which the author has been enabled 

 to carry out some of the most important recent ob- 

 servations on marine life. The transparent animals 

 especially caf be studied with advantage in a lumin- 

 ous atmosphere, revealing even the embryonic or- 

 ganisms, which cannot be detected in ordinary 

 light. 



The Black Waters of the EqUATORiAL Re- 

 gions. — Certain affluents of the Orinoco and the 

 Amazon have what is called black waters (aguas 

 negras.) When seen in mass they are of a coffee- 

 brown or of a greenish-black. In the shade they 

 are almost black, but in a glass they are brownish- 

 yellow, though very transparent. They have no 

 disagreeable taste, and are preferred for drinking. 

 The samples of these waters brought for analysis by 

 V. Marcano are slightly acid, and contain, per litre, 

 0.028 grm. of humic compounds. There is no lime 

 (less than o.ooi grm. per litre), nitrates are totally 

 absent, and the total inorganic solids do not exceed 

 0.016 grm. per litre. They include silica, alumina, 

 iron, and manganese oxides and potassa, with traces 

 of ammonia. They do not undergo any chemical 

 change on keeping. 



Depth of the Ocean. — The greatest known 

 depth of the ocean is midway between the island of 

 Tristan d'Acunha and the mouth of the Rio de la 

 Plata. The bottom was there reached at a depth of 

 40,236 feet, or eight and three-fourths miles, exceed- 

 ing by more than 17,000 feet the height of Mount 

 Everest, the loftiest mountain in the world. In 

 the North Atlantic ocean, south of Newfoundland, 

 soundings have been made to a depth of 4,580 

 fathoms, or 27,480 feet, while depths equaling 34,- 

 000 feet, or six and one-half miles, are reported 

 south of the Bermuda Islands. The average depth 

 of the Pacific ocean between Japan and California 

 is a little over 2,000 fathoms ; between Chili and the 

 Sandwich Islands, 2,500 fathoms, and between Chili 

 and New Zealand, 1,500 fathoms. The average 

 depth of all the oceans is from 2,000 to 2,500 

 fathoms. 



Practical 6boiiiistry aiid tlje ^rts. 



POTASSIUM AND SODIUM. 



The alkalies potash and soda; have been 

 known from the earliest times. An allusion 

 is made in the ]?ible to a substance translated 

 nitre, but, as the context distinctly refers to 

 its eflervescing when vinegar is poured over 

 it, carbonate of soda (common washing soda) 

 is undoubtedly referred to. The salts of soda 

 and potash were confused with each other 

 until the year 1 756, when the chemist Duha- 

 mel first made clear the ditierence between 

 them. Up to the year 1S07, however, they 

 were considered to be simple substances. In 

 that year, Himiphrey Davy made the most 

 important discovery that they were salts of a 

 metallic base, and succeeded in decompo.sing 

 them with a powerful galvaiiic battery. 



Potassium is a silvery white metal, with a 

 specific gravity of 0.875, being the lightest 

 metal known, except lithium. It melts at 

 144.5", '*"'' '^''*' such an intense affinity for 

 oxygen, that, in ordinary air, it rapidly unites 

 with it, forming a cru.st of caustic potash on 

 the surface of the metal. In perfectly pure 

 and dry air, however, no change occurs. 

 When thrown upon water, it rapidly decom- 

 po.ses it, imiting with the oxygen, and setting 

 the hydrogen free, which, owing to the great 

 heat developed in the reaction, takes~fire and 

 burns with a violet-colored flame. We have 

 thus, apparently, the remarkable phenomena 

 of a metal which takes fire when thrown upon 

 water. Towards the end of the experiment, 

 the hot globule of potash usually explodes, 

 and it is a wise precaution to cover the metal 

 with a bell gla.ss as soon as it is thrown upon 

 the water. Only a small piece should be 

 used lor the experiment, and it must not be 

 handled by the fingers, or warmed in any 

 way, or a dangerous explosion may occur 

 when it is brought in contact with water. 

 On account of this remarkable affinity for 

 oxygen, potassium must be kept in a bottle 

 filled with kerosene, or some other liquid 

 free from oxygen. 



Potassiinn is made in larger quantities by 

 reducing from a mixture of carbon and 

 potassic carbonate, at an inten.se heat. An 

 intimate mixture of these two substances is 

 olitained by heating crude tartar (hydro- 

 potassic tartrate) in a closed crucible until a 

 charred mass is obtained. This is introduced 

 into an iron retort, coated with fire-clay, and 

 submitted to an intense heat. The carbon 

 reduces the potash to the metallic state, and 

 the vapor of potassium passes out through a 

 tube into a condenser, consisting of a shallow 

 iron box, where it is rapidly cooled, and the 

 melted metal runs off into a vessel of oil 

 placed to receive it. The rapid condensation 

 of the potassium vapor is a very important 

 point, as otherwise it is liable to form a pecu- 

 I liar black compound, K2QO,j, which is ex- 



cessively explosive. When the ' metal first 

 began to be prepared, accidents frequently 

 happened from this cause, and even rtow the 

 process is one that requires a great amount of 

 care and skill. 



Potassium is one of the most powerfid 

 reducing agents known, but it is of little use 

 in the arts, and is rarely seen outside of a 

 laboratory. Its nearest relative, sodium, how- 

 ever, has recently come into great importance, 

 and is at present made in very large quantities 

 by a new and improved process. 



Sodium closely resembles potassium, but is 

 less active chemically. In large pieces it 

 may be kept in the air with but slight oxida- 

 tion. When thrown on water, it decompo.ses 

 it, like potassium, setting hydrogen free, but 

 there is not sufficient heat generated to ignite 

 the gas. If thrown on wet blotting paper, 

 however, so that the metal camiot move about, 

 the escaping Indrogen will take fire. The 

 same precautions are advisable as in the case 

 of potassium. 



Sodium was formerly made like potassium, 

 by heating a mixture of soda-ash, coal, and 

 chalk. Recently, however, a Mr. Castner, of 

 New York, has invented an improved pro- 

 cess, bv which the reduction takes place at a 

 lower temperature, and the amoiuit of the 

 product is much increased, while the cost is 

 greatly reduced. It consists in melting a 

 mixture of caustic soda, and an artificial car- 

 bide of iron, prepared by coking an intimate 

 mixture of finelv divided iron and pitch, or 

 other hydro-carbon. This artificial carbide of 

 iron is finely ground, and added to the caustic 

 soda in iron retorts. Upon heating, the me- 

 tallic sodium distills over, and is received and 

 condensed in suitable vessels. 



The exact chemical reactions which take 

 place in the Castner process are not fully un- 

 derstood. It is probable that the action is 

 partly mechanical, the heavy particles of iron 

 holding the carbon down below the surface of 

 the melted soda, so as to keep the mixture 

 uniform and render theVeduction more rapid 

 and certain. At any rate, the process is a 

 very cheap and effective one, and immense 

 quantities of sodiimi are now made by it, one 

 establishment in England having a capacity 

 of a ton a day. 



Sodium is a powerful reducing agent, and, 

 being cheaper and more manageable than 

 potassium, is used in the preparation o( mag- 

 nesium, and especiallv aluminiinn. This 

 valuable metal can be reduced from its ores at 

 a cost which bears a direct relation to that of 

 sodiimi. The greatest importance of the 

 Castner process is, that by giving us cheap 

 sodium, we can obtain cheap aluminium. 

 At present, the price of the latter metal is 

 about ten dollars a pound, but, as further im- 

 provements are made in the process, we may 

 expect to see it still cheaper, although we are 

 not as sanguine as some, who predict that it 



