The Scientific American cyclopedia of formulas : partly based upon the twenty-eighth edition of Scientific American cyclopedia of receipts, notes and queries 15,000 formulas / edited by Albert A. Hopkins.

Albert A. Hopkins

Date:: 1910

Credit: The Scientific American cyclopedia of formulas : partly based upon the twenty-eighth edition of Scientific American cyclopedia of receipts, notes and queries 15,000 formulas / edited by Albert A. Hopkins. Source: Wellcome Collection.

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$(Properties of Alloys) (Properties of Alloys) should be constantly agitated by stirring, or otherwise, and poured into the molds at the lowest temperature consistent with the requisite fluidity, and cooled as rap¬ idly as the nature of the alloy and the purpose for which it is designed will ad¬ mit. With regard to the melting point of an alloy, it should be borne in mind that it fuses at a lower temperature than that at which the most refractory con¬ stituent melts, and sometimes below that of either, which knowledge should guide the operator in so regulating the tempera¬ ture as not to make the charge unneces¬ sarily hot. It is a well-known fact that the char¬ acter of many alloys is altered by repeat¬ ed remelting, and that the scrap obtained in working cannot be used again without the addition of a certain quantity of new metal. A given mixture may be employed for the formation of an alloy, which is highly malleable, ductile, and tenacious, and the scrap from the same alloy, when remelted, may be brittle and unworkable; but when af suitable quantity of new metal is added, the combination may form an alloy even superior to the original one with regard to its good working proper¬ ties. It is to the advantage of the man¬ ufacturer, as regards economy, to use as much scrap as possible in alloying, and the quantity thus employed varies from one-third to two-thirds of the weight of the charge. Of course, in using old metal, many more impurities are liable to be in¬ troduced than with new metal, and al¬ though the same impurities may exist in the new metal, the quantities may be in¬ sufficient to produce a deteriorating ef¬ fect, but when augmented from old metal may then rise to such proportions as to entirely alter the physical properties of the alloy. The presence of notable quan¬ tities of foreign matter is generally ex¬ hibited by increased hardness and a mod¬ ification of the structure, as seen on a freshly fractured surface. The difficulty of maintaining uniformity in an alloy after repeated remelting is least when only two metals are mixed together, and increases when the combi¬ nation requires the presence of three or more metals. Thus German silver re¬ quires much greater care in this respect than brass •; and soft solder, containing only lead and tin, requires less care than fusible alloy, containing bismuth or cad¬ mium in addition to lead and tin. Those alloys which contain as an essential con¬ stituent a volatile metal, such as zinc or antimony, are generally altered most by remelting, and it is requisite to know, at [< any rate approximately, what the furnace loss is, so that the defection may be coun¬ terbalanced by the addition of the quan¬ tity of fresh metal requisite to maintain the right composition. Many errors arise from this cause, as well as from overdo¬ ing what is required. Where possible, a chemical analysis is the best means of solving the problem, but as this is out of the question in most cases, a few sim¬ ple trials with weighed quantities, and careful observation of the results obtained, by testing its malleability, color and frac¬ ture, will generally afford sufficient evi¬ dence of the required amount to be added. In making experimental tests, a small melting furnace, such as that used in a metallurgical laboratory, a strong pair of hand rolls, and an anvil, would be very useful adjuncts to every casting shop. The quantity of metal operated upon need not exceed one pound in weight, and as this could be cast in a long strip, its suit¬ ability for stamping or rolling could be readily tested. Such test pieces, if care¬ fully labeled and preserved, would be most valuable for future reference, and there can be no doubt that both employers and employed would thus gain a vast amount of information which would prove of great benefit both as a standard of workman¬ ship and of economy of production. It is a great annoyance to find, after a quan¬ tity of metal has been mixed, and the castings made, that the alloy is unsuit¬ able for the work required of it, either from unsuitable constituents, improper mixing, or impure materials; which an¬ noyance could be avoided by a few pre¬ liminary trials on a small scale. The casting of such trial tests could be made in an iron or sand mold, and the time of cooling made to approximate to that of a large mass by judicious treatment. An¬ other advantage of such an experimental plant would be that new combinations could be readily tried, and the effect of certain impurities on well-known alloys ascertained, by purposely adding these bodies in definite amounts to a weighed quantity of the alloy. It has been observed that cold work¬ ing of metals often produces an augmen¬ tation of strength. Le Chatelier finds that there is a limit to the increase of strength obtained by the cold working of pure metals or of those containing less than 1 to 2% of impurities. For all met¬ als examined, excepting silver, the maxi¬ mum strength after cold working is double that of the perfectly annealed specimens. In the case of alloys, some follow the same law as pure metals; others, such ]$