FRAGMENTS OF SCIENCE. 



cathode, are put the following ingre- 

 dients: Fluoride of calcium, 234 parts 

 by weight; double fluoride of cryolite, 

 421 parts by weight; fluoride of alumi- 

 num, 845 parts by weight. To these 

 add three to four per cent of a suitable 

 chloride — for example, calcium chloride. 

 To this add alumina sufficient to form a 

 very stiff mixture. Before electrolysis 

 can begin the above are fused by means 

 of heat, which should not exceed 1,210° 

 F. The heat is obtained from a furnace 

 heated by gas, coke, or charcoal, care 

 being taken that no gases from the fur- 

 nace enter the crucible. The bath fused, 

 the electrodes are dipped into it, the cur- 

 rent switched on, and the metal is depos- 

 ited (in the best and largest of these 

 crucibles) at the rate of one pound per 

 five electrical horse-power hours. The 

 current pressure required is six to eight 

 volts, at a density of one and a half am- 

 peres per square inch. The metal from 

 time to time is removed from the cruci- 

 ble by means of a siphon or a ladle, 

 care being taken to remove as little of 

 the haloid salts as possible. There is an- 

 other method of extraction equally suc- 

 cessful with this, but also more econom- 

 ical. In this other method a set of sim- 

 ilar ingredients are placed in a crucible 

 having one or more vertically movable 

 carbon electrodes, which are used as one, 

 or a collective anode, respectively. The 

 crucible, though lined principally with 

 carbon, has some metal exposed to act as 

 a cathode at the beginning of the process, 

 this to generate heat enough to fuse the 

 bath, after which the anode is placed so 

 that the extracted aluminum acts as a 

 cathode. The molten metal is from 

 time to time run out of a tap-hole into 

 a mold, and thence cast into ingots, or 

 granulated by being poured into cold 

 water. The same particulars as to re- 

 sults apply to this crucible furnace 

 process also, only that not nearly so 

 much of the bath is wasted in it, and 

 the metal needs less purifying when 

 molten. There are, also, no loss of time 

 and money from the use of gas, coke, or 

 charcoal, and of an extra furnace in 

 this method. 



" A Mechanical Bootblack." — A 

 bootblacking apparatus is one of the 

 latest developments of the nickel-in-the- 

 slot machine, a specimen of which is 

 undergoing trial in a French public gar- 



den. The customer drops his coin— in 

 the present case a ten centime, or a two- 

 and-a-half-cent piece — into the recepta- 

 ele, which opens the way to a compart- 

 ment where a brush cleans his boots; 

 he next puts his feet into a second com- 

 partment and has them blackened; and 

 then into a third, where they are pol- 

 ished. The operation takes about a 

 minute and a half, and during the time 

 the customer may watch the indications 



of its progress as they are shown upon 

 the dial. The machinery working in 

 the inside is very simple. An electric 

 motor of small power — about eighteen 

 kilogrammetres per second — controls 

 the shaft on which the three rotary 

 brushes are fixed, and the customer has 

 only to unlock the machine, the same 

 as all others of its kind, with his coin, 

 and move the handle which opens the 

 circuit and starts the motion. A repre- 

 sentation of the machine at work is 

 given in the accompanying illustration, 

 for which we are indebted to La Nature. 



The " Barisal Guns." — A curious 

 phenomenon of unexplained sounds like 

 those of explosions, occasionally heard 

 in different places over the earth, has 

 attracted much attention, has been 

 made the subject of a book recording 

 several hundred accounts of it, by M. 

 Ernest Van den Broeck, of Brussels, and 

 has already been mentioned in the Popu- 

 lar Science Monthly. The phenomenon 

 has been most carefully observed in 

 India, where it seems to have assumed 



