STRENGTH IN SPECIALTY MIXTURES.
the rough round and the turned bar enables us to perceive the difference that may exist between the strength of the iron with its surface affected by the walls of a green sand mould and that of iron having its rough surface turned off.
It was first planned to have all these test bars cast on end, so as to afford the most favorable conditions to insure solid bars, etc., but in starting with car wheel mixtures, difficulty was found in getting the half-inch square test bars to "run," and. as there were other strong irons I desired tests from, I had, on account of the one-half bars, to change the plan of casting and had all bars cast flat. The three test bars from each of the four sizes were cast all in one flask, poured from the same gate, and out of the same ladle.
These test bars were cast by some of the most prominent foundry specialists in this country. They are not a crucible melt of estimated mixtures or of a special heat, but are taken from ct regular heats" " run " for making castings in the specialties herein mentioned, therefore represent the strength of the actual metal used in actual practice for the manufacture of the castings outlined as far as is practical with bars cast flat.* A. complete chemical analysis of the various mixtures obtained in the tests shown in this Chapter can be seen on page 299. The analyses were all taken from the rough bars shown in the respective Tables.
The micrometer measurements given in the following tables are the average of dimensions taken from the four sides of the square and round bars and hence give the size of the test specimen in the thousandth part of an inch. The common rule measurements givr thr si'/r as closely as it is practical to roughly
* Views of the fractures of these various irons arc seen in Figs. 05 to 102, iit the? close- of this chapter.of six-inch ^»*as pipe to mould it in, leaving both ends Ij