Electrotype Manipulation - neues Buch

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: from defect. A few weeks' experience among medals will be of more avail, in guiding the judgment, than pages of written instructions. 31. To Copy Plaister Casts.?Foursome boiling water into a plate; stand the cast face upwards in this water: the water must not be deep enough to reach the face of the cast. In about two minutes, the cast will be filled with water. In this condition, it will be advisable to stand it on the stove by the fire-side, for another two minutes, in order to drive off by evaporation any superabundance of water that may be on the surface. Then, without loss of time, wrap round it a ribbon of pasteboard as before, ( 28.) and immediately pour in the melted wax. After the wax is solid, let it remain for two or three hours, and the mould may be lifted off from the plaister, without further trouble. 32. To render wax moulds conductible.?They, whose knowledge of electricity is the most elementary, are aware that wax is a non-conductor; and as such will not be of any service to convey the voltaic current. In order to render its surface conducteous, many plans have been devised. There is one which combines the three advantages of simplicity, certainty, and economy: and this alone will be described. It is to cover the surface with black-lead; the application of this substance is due to Mr. Murray. 33. This article is known in commerce under the several names of plumbago, graphite, and black lead. The latter might naturally enough induce those unacquainted with the subject, to conclude that lead held a prominent place in its composition. This, however, is not the case; it contains no lead at all; it consists of carbon and iron; the principal portion being carbon. This substance has been already mentioned; ( 5.) it is a very good conductor. Plumbago is ...