METALS. 



its purity afterward tested. In tho fil- 

 110 trace of coloring could be 



e\tn :I!!.T eonceiitratioll to g^ of its 



nine, the presence of lead could not be de- 

 te. 1. '1 his result was to be expected from 

 il-knouii fact that lead salts are pre- 

 pitated by metallic iron, and that spongy 

 n is a much more energetic, precipitant than 

 n in other form-. This property, too, is an 

 portant and welcome audition to the em- 

 o\meiit of .spongy iron for purifying water 

 Although applicable- to tho purification of 

 MI mi extended scale, as shown by the 

 erini. nts of one of tbe London water corn- 

 author thinks that spongy iron will 

 found most effective and economical in 

 all filters designed for domestic use. On 

 this point, which is one of great practical im- 

 portance, ho says: 



J' would prefer to see it used in small domestic fil- 

 , and in this case, if such a filter were to contain 

 gallon by volume of spongy iron (or 10 Ibs. to 12 

 . weight), a vield of 2.000 gallons of purified 

 with an undiminishea action of the spongy 

 iron would inor<- approach u practical result. Sup- 

 ]">Mnir ten gallons of water a day for cooking and 

 drinking, such a domestic filter would, as far as the 

 of the spongy iron is concerned, purify as en- 

 :illy after 200 days as on the first any; so 

 that, doing away with all hypothesis, it would cer- 

 tainly not require a renewal under less than six 

 months of constant use, and at a cost of hardly one 

 shilling. Of course, in such domestic filters, the 

 filtration can be made much slower in order to effect 

 a more complete piyiflcation than would be practi- 

 cable for water companies. I should think that one 

 gallon in half an hour, or even in an hour, is a suf- 

 ficient speed for domestic filters. 



Improved Tin-Dressing Machinery. In a 

 paper on this subject, read before the London 

 Society of Engineers, Mr. S. Cox called atten- 

 tion to the following as the most important im- 

 provements that have of late years been made 

 in tin-dressing machinery. Shool's atmos- 

 pheric stamps for crushing the ore were first 

 mentioned, and their advantages over the old 

 system pointed out. Briefly these were stated 

 to be : 1. A greater length of stroke, by which 

 the weight of the heads is reduced from 5 cwt. 

 to 3 cwt.; 2. A greater speed, the relative 

 velocities being respectively 150 and 60 blows 

 per minute ; 8. The additional momentum pro- 

 duced by the compressed air and the power thus 

 afforded of regulating the length of the stroke. 

 The Propeller Knife Buddie recently intro- 

 duced at Restronguet Steam Tin- Works, as well 

 a- Collom's Patent Jigger, were then described. 

 The last machine consists of hutches with fine 

 wire sieves placed upon the top, the sieves be- 

 ing covered with a layer of coarse ore and the 

 machine being kept full of water under press- 

 ure. Each hutch is in connection with a trunk 

 in which a piston fits loosely and works with a 

 short vertical stroke. At each stroke the water 

 is forced through the sieves, and partially floats 

 the tin-stuff, the return-stroke allowing the 

 heavier particles of tin to subside. 



The author stated it to be a very important 

 point with both of these machines to first sepa- 



rate tho ore into various degree* of coarsenou, 



aii.l for that purpose a machine known as Cox's 

 i(..r was proposed to be employed. In 

 thU machine a column of u ai. r n.-ri-niling in a 

 coiiiral hopper meets with descend ing tin 

 whieh is supplied from tho stamps. The flow 

 of water is regulated so as only to allow the 

 coarser particles to fall, the lighter ones being 

 carried by the water into a second machine of 

 tho same kind with a less strong flow of water. 

 An additional washing action is produced by 

 supply ing the wuter through a perforated case, 

 and tin- upward tlow of the water is regulated 

 by means of a hollow cone which fits into the 

 bottom of the hopper, and round the top of 

 which quarter-inch holes are drilled in a hori- 

 zontal direction. An active agitation is kept 

 up by the water passing through the holes, and 

 meeting the ascending column of water at right 

 angles. 



Mr. Cox then described Stephens's Pulver- 

 izer, in which, by means of strips of wood 

 placed in slots in the covering plate, the rotat- 

 ing action of the water is turned into a jigging 

 one, thus carrying the' pulverized ore through 

 the covering plate, whence it is conveyed away 

 by launders. 



Nickel and Cobalt Ore*. The folio wing notes 

 on the nickel and cobalt ores of foreign coun- 

 tries are published in Iron. The ores of nickel 

 and cobalt are found in almost all parts of the 

 world where other minerals exist, but those 

 which yield the chief supply of these metals 

 abroad, are found in Norway, Sweden, and 

 Hungary. The mineral from which nickel is 

 derived in Sweden and Norway is an iron py- 

 rite, which is in most cases magnetic, but is 

 nearly free from cobalt. These ores are exceed- 

 ingly poor, never containing more than 3 per 

 cent, of nickel. In some cases they are worked 

 when yielding only 1 per cent, of the metal. 

 The nickel-ores are found abundantly in Hun- 

 gary, where the nickel is always in association 

 with cobalt. The ore generally contains 15 

 per cent, of the former metal, and 5 per cent, 

 of the latter. This is a very valuable mineral, 

 and the mines have been worked profitably for 

 the last thirty or forty years. The ore is com- 

 posed of an arsenical mundic, highly impreg- 

 nated with tho more valuable metals, and in 

 this respect differs from the Norwegian and 

 Swedish ores, insomuch that the latter contain 

 little or no arsenic, and appear simply as sul- 

 phides. 



Precipitation of Copper with Tin-Scrap. 

 Prof. 1. Sterry Hunt has patented an im- 

 proved method for the precipitation of metallic 

 copper from solution by the employment of 

 tin-scrap : 



This invention consists in using tin-plate scrap or 

 waste for the precipitation of copper from the solu- 

 tions obtained in the various wet processes of copper 

 extraction, and in saving in the operation the adner- 

 ing tin. The copper solution must contain at the 

 same time protocnloride of copper (otherwise called 

 cupric chloride) and sulphate of soda, or some other 



