METALS. 



419 



it with gas-tar, resin, petroleum, or some such 

 substance, making it into a stiff paste, which 

 is divided into pellets, which are dried in an 

 oven, then placed in a strong retort or tube, 

 which is lined with a coating of plumbago. 

 They are then exposed to a cherry-red heat. 

 The retort must be sufficiently strong to stand 

 a pressure of from 25 to 30 Ibs. on the square 

 inch, and be so arranged that, by means of a 

 safety-valve or tube, the necessary amount of 

 some carburetted hydrogen gas can be intro- 

 duced into the retort among the heated mixture, 

 and the pressure of from 20 to 30 Ibs. on the 

 square inch be maintained. The gas alluded 

 to is forced into the retort by means of a force- 

 pump. By this process the alumina is reduced, 

 and the aluminium remains as a spongy mass, 

 mixed with carbon. This mixture is remelted 

 with metallic zinc, and, when the aluminium 

 has collected in a metallic state, the zinc is 

 driven off by heat. The reduction is due to 

 the carburetted hydrogen gas under pressure. 

 The time required for reducing one hundred 

 pounds of alumina earth, cryolite, or other 

 compound of alumina, should not be more than 

 four hours ; when the gas. can be applied in a 

 previously - heated as well as strongly-com- 

 pressed state, the reduction takes place in a 

 still shorter period. 



Platinizing Copper. The Quarterly Jour- 

 nal of Science publishes the following : 



In order to obtain a platinizing fluid capable of 

 platinizing copper, yellow metal, and brass, add, to a 

 moderately-concentrated solution of chloride of plati- 

 num, finely-powdered carbonate of soda, until effer- 

 vescence ceases; next some glucose, and afterward 

 just so much common salt as will cause a whitish- 

 colored precipitate. > When it is desired to apply this 

 mixture for platinizing, the objects to be treated are 

 placed in a vessel made of zinc and perforated with 

 holes. The vessel is then placed, with its contentSj for 

 a, few seconds, in the mixture just described, which, 

 just previous to using, should be heated to 60 C. 

 On being removed from the zinc vessel, the objects 

 are to he washed with water and dried in sawdust. 



Preventing Silver Waste. The loss of silver, 

 from the formation of a sulphide of silver on 

 the surface of plate and its subsequent wash- 

 ing off, is enormous. The -cause of the for- 

 mation is well known to 'be the sulphurous 

 products of the combustion of gas in streets, 

 houses, and shops, which products unite with 

 the exposed silver, causing a black appearance 

 on its surface not only tarnishing it, but di- 

 minishing the quantity of metallic silver in the 

 articles so affected. Various expedients have 

 been tried by silversmiths to prevent this dis- 

 coloration of their wares, and also the loss in 

 their weight, but without complete success, 

 until Herr Strolberger, of Munich, hit upon 

 the thought of coating his goods with a thin 

 film of collodion, which effectually prevents 

 the sulphur formations, and keeps silver, no 

 matter how freely exposed to the deleterious 

 influences of gas-lights, bright for an indefinite 

 time. He first warms the article to be- coated, 

 and then, with a wide, soft brush, gives it a 

 coating with a thia collodion diluted with al- 



cohol. One operation generally suffices to pro- 

 duce the result. 



Tinning Brass and Copper Vessels. Dr. 

 Hiller proposes the following method of tin- 

 ning vessels of copper and brass : A solution is 

 made of one part of crystallized protochloride 

 of tin and ten parts of water. Another solu- 

 tion is prepared with two parts of caustic soda 

 or potash, and twenty parts of water, and the 

 two solutions are mixed together. The mixed 

 liquor will be milky at first, but becomes clear 

 after a time. The objects to be tinned are 

 placed in a proper vessel with a sheet of pure 

 tin perforated with many small holes. The 

 alkaline solution is poured over them, and then 

 heat is applied while they are occasionally 

 moved about with a rod of zinc. The tinning 

 is effected very rapidly, a few minutes being 

 sufficient for a deposition of a bright coating 

 of the metal. 



Plating Steel, etc., with Nickel. There 

 were recently exhibited before the Polytechnic 

 Association of the American Institute several 

 specimens of iron and steel, upon which nickel 

 had been deposited by the battery by a process 

 devised by Dr. Isaac Adams, of Boston. It 

 was claimed for this process that, while nickel 

 is a much cheaper metal than silver, it is much 

 harder, and is not affected by atmospheric in- 

 fluences, while, at the same time, the color is 

 nearly equal to that of silver. Nickel is ad- 

 mirably adapted to the engraver's purposes, 

 as, from its extreme hardness, a plate of nickel 

 will outwear several plates of copper. Hither- 

 to it has been found impossible to deposit 

 nickel to a greater thickness than a mere film. 

 The mere deposition of nickel on steel is noth- 

 ing new. Directions for the process will be 

 found in Smee's work, published many years 

 ago. But thus far it has been found impossi- 

 ble to deposit nickel in thick plates, for, as soon 

 as a film has been thrown down, the nickel is 

 deposited in the form known as the "black 

 deposit," which is friable and worthless. Hith- 

 erto it has been thought necessary to use pure 

 nickel for the pole or anode that is to be dis- 

 solved, but Dr. Adams has succeeded, even 

 when the metal employed did not contain 

 more than 75 per cent, of nickel. The solu- 

 tion employed is the double sulphate of nickel 

 and ammonia ; but it must be prepared in a 

 special manner, in order to insure success. 

 Van NostrancPs Magazine. 



Alloys of Copper and Tin. In a note to 

 the French Academy, M. Riche submits the 

 following facts concerning the alloys of copper 

 and tin: He first considers the question of 

 density. Some determinations were made 

 upon bars of the two metals, weighing from 

 fifty to sixty grms., but the results obtained 

 were unimportant, owing to the great differ- 

 ence which exists in the alloys. The same 

 metals reduced to fine powder were afterward 

 operated upon, when it was observed that the 

 contraction increases very regularly, from the 

 very rich alloy in tin to the mixture SnCu 2 , 



