THE AMERICAN HISTORICAL RECORD fusion ; or when the proportion of zinc added does not require ting; and not with an iron rod which has a tendency to pro duce dry alloys and may modify the nature of the com pounds by adding some iron to the alloy—a small proportion it is true but nevertheless appreciable. 8. To carefully clean the crucible after each operation in order to maintain the accuracy of the mixture and facilitate the fusion. operation. If alloys thus prepared give some trouble in ob taining good results they are very economical and present the advantage of keeping as strictly as is allowed by the fusion the proportions of the mixture. Moreover in practice it is generally- acknowledged that a small proportion of an old alloy added to a new one improves it by giving it the homogeneousness which otherwise would be imparted only by a second fusion. In ternary or quarternary alloys made of copper zinc tin and lead it will always be well in order to obtain more ho mogeneousness in the final mixture to alloy beforehand the more fusible metals such as zinc tin and lead ; and to com bine this first alloy with the copper under the best conditions possible. In this way the last combination will possess bet ter qualities than an alloy made in one operation. However we repeat it alloys made by the first direct me thod although much more simple and economical do not an swer all the wants of the arts and do not present the same guarantees as those which have been remelted. For instance runners from bronze or brass castings of a first fusion when more easily worked than another alloy made directly by one operation. we always mean those in which copper is a component part made from old metal ; but on the other hand the surfaces are not so clean and the grain is not so close and easily produce sharp casts. These defects are more to be guarded when pieces of machinery are to be produced. As a rule the oftener a metal is melted the more it loses its previous qualities. lying
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